Turbochargers are used within internal combustion engine systems to increase the pressure of the intake air entering the internal combustion engine to a pressure above atmospheric pressure. This is known as a “boost pressure”. By increasing the pressure of the intake air entering the internal combustion engine, more oxygen is available within the internal combustion engine to support the combustion of a larger amount of fuel, and therefore increases the amount of power produced by the engine.

Turbochargers comprise a compressor and a turbine. The compressor comprises a compressor wheel configured to impart energy to an incident fluid stream, and the turbine comprises a turbine wheel configured to extract energy from an incident fluid stream. The compressor wheel and the turbine wheel are attached to opposite ends of a turbocharger shaft, such that the two rotate in unison. The compressor receives intake air from the atmosphere and delivers the intake air to an intake manifold of the internal combustion engine. The turbine receives exhaust gas from an exhaust manifold of the internal combustion engine and delivers the exhaust gas to an aftertreatment system. During use, exhaust gas leaving the internal combustion engine passes through the turbine, causing the turbine wheel to rotate. The rotation of the turbine wheel drives the compressor wheel, which acts to compress the intake air as it is delivered to the intake manifold.

Exhaust gases from internal combustion engines contain substances that are harmful to the environment. Most countries have vehicle emission standards which limit the amount of such substances that an internal combustion engine system is permitted to emit. Consequently, modern internal combustion engine systems comprise exhaust gas aftertreatment systems designed to remove harmful substances from the exhaust gas.

Typically, an exhaust gas aftertreatment system will comprise a particulate filter and one or more catalytic reducers. The particulate filter removes heavy combustion products, e.g. soot, from the exhaust gas. The catalytic reducers remove harmful substances such as Nitrogen Oxides (NOx) from the exhaust gas. Catalytic reducers generally comprise a large number of narrow channels made from a material selected to support a chemical reaction that removes NOx from the exhaust gas. The narrow channels provide a large surface area for the catalytic reaction to take place. Several kinds of catalytic reducers are available on the market, such as two-way catalytic reducers, three-way catalytic reducers, diesel oxidation catalytic reducers (DOCs), and selective catalytic reducers (SCRs). DOCs and SCRs are typically employed in diesel engine systems. For the SCRs specifically, in order for the SCR reaction to work, it is necessary to mix an exhaust gas aftertreatment fluid with the exhaust gas before it enters the catalytic reducer. The exhaust gas aftertreatment fluid is usually a mixture of around 30% to 35% by volume urea (CO(NH2)2) to about 65% to 70% by volume deionised water (H2O). The exhaust gas aftertreatment fluid is often referred to as Diesel Exhaust Fluid (DEF) and is commonly available under the registered trademark AdBlue.

Conventionally, the DEF is mixed with the exhaust gas in a decomposition chamber. The DEF is injected into the decomposition chamber using a dosing module. In the decomposition chamber, heat is exchanged from the exhaust gas to the DEF which causes the water within the DEF to evaporate and the urea to thermally decompose into the reductants ammonia (NH3) and Isocyanic Acid (HNCO) which are required to support the SCR reaction.

A typical decomposition chamber comprises a relatively large cross-sectional area in comparison to the width of standard exhaust gas ducting. Exhaust gas entering the decomposition chamber expands, causing the velocity of the exhaust gas to reduce and the pressure of the exhaust gas to increase. This rapid expansion of the exhaust gas causes the formation of turbulent vortices. DEF is then injected into the decomposition chamber, whereupon the turbulent vortices encourage mixing of the DEF with the exhaust gas. The heat exchange between the exhaust gas and the DEF causes the urea in the DEF to decompose into the reductants, and the mixture of reductants and exhaust gas is then passed to the SCR.

If the exhaust gas and DEF are not mixed well enough, the heat exchange between the DEF and the exhaust gas will not be sufficient to decompose the DEF into the required reductants. Furthermore, poor mixing means that the reductants are not evenly distributed within the flow, and therefore some channels of the catalytic reducer will not receive enough reductant to support the SCR reaction. To ensure adequate mixing, it is common for the decomposition chamber to comprise a mixing plate configured to generate additional turbulence. However, the additional turbulence caused by the mixing plate and the fluidic friction exerted by the mixing plate on the exhaust gas creates a back-pressure on the exhaust gas in the decomposition chamber. This back pressure is passed upstream and acts to increase the pumping work of the internal combustion engine, and accordingly reduces the overall efficiency of the engine system.

In turbocharged engine systems, the narrow geometry of the turbine outlet passage means that any aftertreatment fluid injected in the vicinity of the turbine outlet is likely to impinge on the surfaces defining the turbine outlet, where it is at risk of solidifying. Typically, the decomposition chamber and the dosing module are positioned at a distance significantly downstream of the turbine outlet passage and away from the turbine itself so that more space is available to accommodate larger mixing structures that will support mixing of the aftertreatment fluid with the exhaust gas and reduce the risk of impingement of aftertreatment fluid on the walls of the mixing structures. However, this requires a large amount of space and therefore makes the engine bulkier. Furthermore, as the exhaust gas travels from the turbine wheel, it loses energy to pipe friction and transient heat dissipation. Accordingly, when the decomposition chamber is placed away from the turbine less heat is available to cause decomposition of the DEF.

It is an object of the invention to obviate or mitigate one or more disadvantages of the prior art, whether described herein or elsewhere.

According to a first aspect of the invention, there is provided a turbine for a turbocharger, comprising: a turbine inlet passage configured to receive exhaust gas from an internal combustion engine; a turbine wheel chamber configured to receive exhaust gas from the turbine inlet passage, the turbine wheel chamber configured to contain a turbine wheel supported for rotation about a turbine axis; a turbine outlet passage configured to receive exhaust gas from the turbine wheel chamber; and an auxiliary passage comprising: an auxiliary passage inlet configured to receive exhaust gas from the turbine outlet passage; and an auxiliary passage outlet configured to deliver exhaust gas to the turbine outlet passage from the auxiliary passage. The exhaust gas that is received by the turbine outlet passage may have, in particular, passed through a turbine wheel contained within the turbine wheel chamber. As used herein, the term “auxiliary passage” encompasses any fluid-carrying structure which is able to route exhaust gas from the auxiliary passage inlet to the auxiliary passage outlet. The terms “auxiliary passage inlet” and “auxiliary passage outlet” encompass openings of the auxiliary passage defining respective fluidic interfaces with the turbine outlet passage. The “auxiliary passage inlet” and “auxiliary passage outlet” may be defined by the turbine outlet passage, and in particular may be openings formed in a wall defining the turbine outlet passage. The term “turbine outlet passage” encompasses a structure configured to receive exhaust gas that has passed through a turbine wheel at a position immediately downstream of the turbine wheel.

The exhaust gas flow in the auxiliary passage, otherwise known as the auxiliary flow, is separate to the flow through the turbine outlet passage, otherwise known as the turbine bulk flow. The auxiliary passage enables the auxiliary flow to be conditioned so that it has different properties to the turbine bulk flow. For example, the auxiliary passage may be configured to change the direction, speed, pressure, turbulence or the like of the exhaust gas flowing therethrough.

Under normal conditions, the flow regime in the turbine outlet passage is generally an unsuitable location for the injection of aftertreatment fluid. However, the re-conditioned exhaust gas flow through the auxiliary passage can be used in one or more fluidic applications in the auxiliary passage outlet to support improved decomposition where aftertreatment fluid is injected. For example, by using an auxiliary passage, a dosing module may be provided to inject after treatment fluid into the turbine outlet passage, and the auxiliary passage may direct exhaust gas flow into the aftertreatment fluid to cause turbulence and improve mixing. Additionally or alternatively, the auxiliary passage can direct flow over the nozzle of the dosing module to clean it. Additionally or alternatively, the momentum of the auxiliary flow may be used to increase the momentum of the aftertreatment fluid as it is injected, so that the aftertreatment fluid is able to dissipate across substantially the entire cross-sectional area of the turbine outlet passage, thereby providing increased uniformity of the after treatment fluid across the flow in the turbine outlet passage. In yet further alternative or additional embodiments, the auxiliary passage may be used to create a narrow layer of fast moving fluid over a surface of the turbine outlet passage where impingement of aftertreatment fluid is likely to take place, so as to avoid deposit build up on the surfaces of the turbine outlet. Other applications of the auxiliary flow will be apparent from the description.

It will be appreciated that in order for the auxiliary passage to condition the auxiliary flow to provide the beneficial functionality described above, it must be supplied with exhaust gas. It is advantageous to position the auxiliary passage inlet within the turbine outlet passage so that it is supplied with exhaust gas that has passed through the turbine wheel. As such, the turbine bulk flow is not divided before the turbine wheel, and therefore the turbine wheel is able to extract the maximum possible amount of work from the turbine bulk flow. By contrast, if the auxiliary passage inlet was positioned before the turbine wheel, then the mass flow to the turbine wheel would be reduced and less work would be extracted from the exhaust gas, thus reducing the efficiency of the turbine. It has also been found that positioning the auxiliary passage inlet within the turbine outlet passage leads to a simpler and more compact arrangement, as it is not necessary to cast or machine conduits bypassing the turbine wheel. Further still, because the auxiliary passage inlet is positioned within the turbine outlet passage, this ensures that the auxiliary flow is sourced from a position close to the turbine wheel. Accordingly, less energy is lost to friction compared to locations downstream of the turbine outlet passage.

The auxiliary passage inlet may be located at a position of the turbine outlet passage that is fluidly upstream of the auxiliary passage outlet relative to the flow through the turbine outlet passage. For example, the auxiliary passage inlet may define a centroid, the auxiliary passage outlet may define a centroid, and the centroid of the auxiliary passage inlet may be upstream of the auxiliary passage outlet in relation to the exhaust gas flow through the turbine outlet passage. The term “centroid” encompasses the geometric centre of an inlet or outlet, including for example the geometric centres of the openings forming the auxiliary inlet and the auxiliary outlets.

Because the auxiliary passage inlet is upstream of the auxiliary passage outlet, the auxiliary passage inlet is positioned closer to the turbine wheel than the auxiliary passage outlet. The exhaust in the turbine outlet passage in the vicinity of the auxiliary at the auxiliary passage inlet is therefore subject to fewer losses to pipe friction or transient energy losses than the exhaust gas at the auxiliary passage outlet. Accordingly, the fluid entering the auxiliary passage has a relatively high energy and is more suitable for conditioning by the auxiliary passage.

The turbine wheel may comprise an exducer defining an exducer diameter, the turbine outlet passage may define a centreline; and the auxiliary passage inlet may be spaced apart from the exducer of the turbine wheel by a distance of at most around 5 exducer diameters along the centreline of the turbine outlet passage. As used herein the term “centreline” encompasses a line prescribed by the centroid of a cross-section of the turbine outlet passage along the direction of flow of exhaust gas. That is to say, the centreline of the turbine outlet passage is an imaginary line drawn along the turbine outlet passage which is always positioned at the geometric centre of the exhaust gas flowing therethrough. Typically, although not always, the centreline will be an extension of the turbine axis, which may diverge from the turbine axis in dependence upon the geometry of the turbine outlet passage.

As used herein, the term “exducer” encompasses the part of the turbine wheel configured to discharge exhaust gas to the turbine outlet passage. The spacing of the auxiliary passage inlet from the exducer of the turbine wheel may be measured from the most downstream part of the tips of the blades of the turbine wheel to the most upstream part of the auxiliary passage inlet viewed from the perspective of the centreline.

Because the auxiliary passage inlet is within around 5 exducer diameters of the turbine wheel, the auxiliary passage inlet is positioned relatively close to the turbine wheel. This ensures that the exhaust gas entering the auxiliary passage is relatively high energy, as it has not lost any energy to pipe friction, transient heat loss or the like. Furthermore, this promotes a compact arrangement. In general, the auxiliary passage inlet should be positioned as close as possible to the turbine wheel, whilst remaining downstream of the turbine wheel. This may be dictated by factors such as manufacturing tolerances. Preferably, the auxiliary passage inlet it spaced apart from the exducer by at most 3 exducer diameters or at most 1 exducer diameter.

The auxiliary passage outlet may be spaced apart from the exducer of the turbine wheel by a distance of at most around 10 exducer diameters along the geometric centreline of the turbine outlet passage. Because the auxiliary passage outlet is within around 10 exducer diameters of the turbine wheel, the auxiliary passage inlet is positioned relatively close to the turbine wheel. Accordingly, the application for which the auxiliary flow is used can be positioned close to the turbine wheel. This is particularly advantageous where the turbine outlet also functions as a decomposition chamber for exhaust gas aftertreatment fluid, since the exhaust gas flow through the auxiliary passage can be used to mitigate one or more problems associated with aftertreatment fluid injection close to the turbine wheel. For example, as discussed above, the auxiliary passage can be used to clean the nozzle of a dosing module, to improve reductant decomposition, to prevent deposit formation on the walls of the turbine outlet or the like. Preferably, the auxiliary passage outlet is positioned closer to the turbine wheel to provide a compact arrangement. For example, within around 1 , 3 or 5 exducer diameters.

The turbine may comprise a turbine housing at least in part defining the turbine inlet, the turbine wheel chamber and the turbine outlet passage, and the auxiliary passage may be defined at least in part by the turbine housing. That is to say, the turbine housing may comprise at least part of the auxiliary passage. As used herein, the term “turbine housing” encompasses a structure configured to contain and guide exhaust gas flow into and out of the turbine wheel. The turbine housing may, for example, define a radial inlet volute and an axial outlet. The turbine housing may define the entire geometry of the auxiliary passage, from the auxiliary passage inlet to the auxiliary passage outlet. Alternatively, the turbine housing may define only part of the auxiliary passage, for example one or more surfaces defining a portion of the auxiliary passage. In such embodiments, the remaining geometry of the auxiliary passage may be defined one or more by additional components separate to the turbine housing, for example a connection adapter, an insert, a baffle or the like.

Because the auxiliary passage is at least partially defined by the turbine housing, the turbine housing and auxiliary passage can be manufactured as a single integral component, and thus the ease of manufacturing and assembly is increased.

The turbine may comprise a turbine housing defining the turbine inlet and the turbine wheel chamber, and a connection adapter which may at least partially define the turbine outlet passage, and the auxiliary passage may be defined at least in part by the connection adapter. That is to say, the connection adapter may define at least a portion of the turbine outlet passage. The remainder of the turbine outlet passage may be defined by the turbine housing. Alternatively, the connection adapter may define substantially all of the turbine outlet passage. The connection adapter may be joined to the turbine housing, for example using fasters, clips, v-bands or the like. The connection adapter may comprise at least part or all of the auxiliary passage. That is to say, the connection adapter may comprise one or more surfaces defining the geometry of the auxiliary passage.

Because the connection adapter defines the auxiliary passage and the turbine outlet passage separately to the turbine housing, it is possible for the auxiliary passage and the turbine outlet passage to include complex geometry that would be impossible or prohibitively expensive to manufacture if the auxiliary passage and the turbine outlet passage were part of the turbine housing.

The turbine may further comprise a dosing module comprising a nozzle configured to deliver an aftertreatment fluid to the turbine outlet passage. The nozzle may be an atomising nozzle. As used herein, the term “dosing module” encompasses any device configured to introduce aftertreatment fluid to the turbine outlet structure. The aftertreatment fluid may be a fluid required to support a chemical reaction in an exhaust gas aftertreatment process. For example, the aftertreatment fluid may be DEF for use in an SCR process. The term “nozzle” encompasses the part of the dosing module from which the aftertreatment fluid leaves the dosing module. That is to say, the part of the dosing module from which aftertreatment fluid emanates. The doing module may be a self-atomising dosing module configured to create a fine spray or mist of aftertreatment fluid emanating from a nozzle of the dosing module. Where the dosing module is self-atomising, it does not require any additional components to be present to cause the aftertreatment fluid to atomise. As such, the aftertreatment fluid can be mixed with the exhaust gas immediately upon its exit from the nozzle of the dosing module. This improves the speed of atomisation and increases the rate of decomposition of the urea in the aftertreatment fluid.

The nozzle of the dosing module may be substantially aligned with a surface defining the auxiliary passage or a surface of the turbine outlet passage. That is to say, the nozzle of the dosing module does not protrude into the auxiliary passage or the turbine outlet passage. It is an inherent property of the auxiliary passage and the turbine outlet passage that these passages will be defined by the surfaces of a housing component, such as for example a turbine housing, a connection adapter, a diffuser or the like. A surface defining the auxiliary passage or the turbine outlet passage therefore encompasses any surface which acts to contain exhaust gas within the auxiliary passage or the turbine outlet passage. In other words, the surface is a surface delineating the outermost geometry of the fluid-carrying parts of the auxiliary passage or the turbine outlet passage. The term “aligned” encompasses the fluid-injecting part of the nozzle lying substantially flush with the surface. As the skilled person would understand, such alignment does not need to be absolute, and small amounts of misalignment may be tolerated provided that the nozzle of the dosing module does not protrude into the auxiliary passage or the turbine outlet passage in an manner which would cause a significant obstruction to flow. Because the nozzle is substantially aligned with the surface, the auxiliary passage or turbine outlet passage are generally free of obstructions which would impede exhaust gas flow therethrough.

The nozzle of the dosing module may be positioned within the auxiliary passage such that the dosing module may be configured to deliver aftertreatment fluid to the turbine outlet passage via the auxiliary passage. That is to say, during use the dosing module delivers aftertreatment fluid to the auxiliary passage and the aftertreatment fluid passes through at least a portion of the auxiliary passage before entering the turbine outlet passage. Because the aftertreatment fluid is injected into the auxiliary passage before entering the turbine outlet passage, the aftertreatment fluid is able to exchange momentum with the exhaust gas flowing through the auxiliary passage before entering the turbine outlet passage. This momentum exchange may be used to provide a beneficial effect such as cleaning the nozzle of the dosing module, or to ensure the aftertreatment fluid is carried across a greater lateral extent of the turbine outlet passage.

The auxiliary passage may comprise an outlet portion extending from the nozzle to the auxiliary passage outlet, the outlet portion may define an outlet axis, and wherein the outlet axis may be inclined relative to a centreline of the turbine outlet passage by an angle up to around 70°. In alternative embodiments, the outlet axis may be inclined relative to the centreline by an angle between around 20° to around 70°, around 30° to around 60°, around 40° to around 50°, or around 45°. The relative angle between the outlet axis and the centreline may be measured at the centroid of the auxiliary passage outlet.

Due to the momentum carried by the mixture of the auxiliary flow and aftertreatment fluid passing through the outlet portion of the auxiliary passage, as the angle between the outlet axis and the centreline increases, the likelihood of impingement of aftertreatment fluid on the wall of the turbine outlet passage opposite to the auxiliary passage outlet also increases. Aftertreatment fluid which impinges on the wall of the turbine outlet may not be hot enough to evaporate, and my lead to deposit formation. Whilst this can be mitigated by reducing the angle between the outlet axis and the centreline, if the angle is too small the length of the auxiliary passage must be increased and so the auxiliary passage outlet must be placed further downstream (and potentially outside of the preferred distance from the turbine wheel exducer as discussed previously). It has been found that when the angle between the outlet axis and centreline is in the ranges above, this reduces the risk of aftertreatment fluid impingement on the wall of the turbine outlet passage whilst keeping the auxiliary passage compact.

The auxiliary passage may comprise an inlet portion extending from auxiliary passage inlet to the nozzle, the inlet portion may define an inlet axis, and the inlet axis may be inclined relative to a centreline of the turbine outlet passage by an angle between around 20° to around 70°. In alternative embodiments, the inlet axis may be inclined relative to the centreline by an angle between around 30° to around 60°, around 40° to around 50°, or around 45° to around 70°, or around 45°. The relative angle between the inlet axis and the centreline may be measured at the centroid of the auxiliary passage inlet.

As the angle of the inlet axis of the auxiliary passage increases, the momentum change required for exhaust gas to pass into the auxiliary passage increases, thus causing resistance to flow. However, if the angle of the inlet axis is too small, the auxiliary passage must be made longer. It has been found that when the angle between the inlet axis and the centreline is in the ranges above, this reduces the amount of momentum change required for the exhaust gas to enter the auxiliary passage whilst keeping the overall length of the auxiliary passage compact. The cross-sectional area of the outlet portion of the auxiliary passage may increase along the outlet axis from the nozzle of the dosing module to the auxiliary passage outlet. That is to say, the second portion of the auxiliary passage comprises diverging sides which diverge outwards in the direction of the auxiliary passage outlet.

The dosing module will produce a fine spray of atomised aftertreatment fluid which emanates in the shape of a cone from the tip of the dosing module. In some embodiments, the outlet portion of the auxiliary passage diverges at an angle that is around equal to or greater than the spray cone angle of the nozzle. For example, the spray cone angle may be around 45° to around 50°, and the outlet portion may diverge at an angle of around 60°. In such embodiments, because the outlet portion of the auxiliary passage diverges at the same or a higher rate than the spray cone, this reduces the risk of impingement of aftertreatment fluid on the walls of the auxiliary passage. However, if the outlet portion diverges at too steep of an angle, the auxiliary flow will decelerate such that it loses the potential to influence flow in the turbine outlet passage. Therefore, in alternative embodiments the spray cone angle may be the same as set out above, whilst the outlet portion of the auxiliary passage diverges at a shallower angle, such as a round 5° to 10°. Although the aftertreatment fluid will be likely to impinge on the walls of the outlet portion, the velocity of the auxiliary flow will remain high such that shearing forces will clean any impinged aftertreatment fluid from the walls to avoid deposit formation.

The turbine outlet passage may define a diffuser. That is to say the turbine outlet passage may comprise a diffuser. As used herein the term “diffuser” encompasses a divergent passage, where the cross sectional area of the passage increases along a length of the passage. As the cross sectional area of the diffuser increases (i.e. as the walls which define the outlet passage diverge) the velocity of the turbine bulk flow decreases and the pressure increases. The increase in pressure may be used to increase the efficiency of the turbine and/or an associated exhaust gas aftertreatment system. For example, where the turbine comprises a dosing module, reducing the velocity of the turbine bulk flow through the turbine outlet passage may allow injected aftertreatment fluid to more readily penetrate the turbine bulk flow in the turbine outlet passage. The diffuser may be aligned with and extend symmetrically about the turbine axis. That is to say, the diffuser may be an axial diffuser. The diffuser, may comprise a generally circular cross-section, defined by conically shaped walls of the turbine outlet passage. However, in alternative embodiments substantially any diffuser shape may be used, including asymmetric diffusers etc.

The auxiliary passage inlet may comprise a scoop extending into the turbine outlet passage and the scoop may be configured to direct exhaust gas flow into the auxiliary passage. As used herein, the term “scoop” encompasses any type of obstruction to the flow in the turbine outlet passage which is configured to deflect or guide fluid into the auxiliary passage. The turbine outlet passage may in part be defined by a ducting. The scoop may at least in part be defined by the ducting, for example, by one or more punched sections protruding into the turbine outlet passage. “Extending into the turbine outlet” encompasses extending at least in part in a radial direction towards the centreline of the turbine outlet passage. A scoop may take the form of a dome shaped structure, a slat, or any other suitable type of protruding feature configured to deflect or guide fluid into the auxiliary passage.

The scoop may present an obstruction to the bulk exhaust gas flow travelling through the diffuser and may be configured to promote the passing of exhaust gas into the auxiliary inlet and hence to the auxiliary outlet. Providing an increased flow of exhaust gas through the auxiliary passage ensures there is enough exhaust gas available to support the specific beneficial effect provided by conditioned flow of the auxiliary passage.

The auxiliary passage may comprise a plurality of auxiliary passage inlets. That is to say, the auxiliary passage comprises at least two auxiliary inlets, and the auxiliary passage is configured to route exhaust gas from the at least two auxiliary inlets to the auxiliary outlet. For example, the auxiliary passage may comprise a manifold portion connecting the plurality of auxiliary passage inlets to the auxiliary passage outlet. Providing a plurality of auxiliary inlets may increase the mass flow rate of exhaust gas received by the auxiliary passage from the turbine outlet passage. This may increase the volume of the auxiliary flow that can be supplied to support the downstream application. At least one or all of the plurality of auxiliary passage inlets may comprise a scoop to further increase the volume of the auxiliary flow. Furthermore, the auxiliary passage inlets may disturb the turbine bulk flow in the turbine passage, leading to localised regions of turbulence which restrict flow through the turbine outlet passage. Providing multiple auxiliary passage inlets means that each inlet can be made smaller and thus induce less turbulence.

The auxiliary passage inlets may be substantially axially aligned relative to a centreline of the turbine outlet passage. That is to say, the plurality of auxiliary inlets share a common axial position relative to the centreline. Because the plurality of auxiliary inlets are axially aligned, the inlets receive exhaust gas from a common axial location of the turbine outlet passage which is closer to the turbine wheel than the auxiliary passage outlet.

The auxiliary passage may be generally equally spaced about the centreline. The plurality of auxiliary passage inlets may be defined by openings in the surface of the turbine outlet passage and the auxiliary passage inlets may be provided around a circumference of the surface. Spacing the auxiliary passage inlets equally reduces the overall disturbance to the turbine bulk flow in the turbine outlet passage.

The turbine outlet passage may define a perimeter, and the auxiliary passage may extend around the perimeter so as to provide fluid communication between the plurality of auxiliary passage inlets. The term “perimeter” encompasses the outermost part of the turbine outlet passage relative to the centreline of the outlet passage. The auxiliary passage may extend around a portion of the perimeter or around the entire perimeter. For example, if the turbine outlet passage has a circular cross section, the portion of the auxiliary passage may extend in an arc around part or all of the turbine outlet passage. As another example, the portion of the auxiliary passage extending around the perimeter may be a substantially toroidal conduit.

The turbine may further comprise a wastegate arrangement comprising: a wastegate passage configured to provide fluid communication from the turbine inlet passage to the turbine outlet passage such that exhaust gas travelling through the wastegate passage does not pass through the turbine wheel chamber; and a moveable valve member configured to selectively permit or prevent fluid flow through the wastegate passage by blocking the wastegate passage. That is to say, the turbine may be a wastegated turbine. The wastegate passage receives a portion of the turbine bulk flow, the received portion of the turbine bulk flow defining a wastegate flow. The wastegate passage differs the auxiliary passage in that the wastegate passage receives the wastegate flow from a location upstream of the turbine wheel chamber, whereas the auxiliary passage inlet receives he auxiliary flow from a location downstream of the turbine wheel chamber.

The moveable valve member may be any suitable type of body or assembly which is configured to permit and prevent fluid flow through the wastegate passage. By way of example, the valve member may be a flap type valve member or a rotary type valve member. A flap type valve member, may comprise a flap and an actuator, the actuator being configured to move the flap between a fully open configuration and a closed configuration; the actuator may be manually controlled, pneumatically controlled and/or electronically controlled actuator. A rotary type valve member, may be a valve member that is configured to rotate about a central axis, and where rotation of the member regulates the flow of fluid through the passage.

As exhaust gas passes through the turbine wheel chamber, the turbine wheel is rotated by the force of the exhaust gas impinging upon the turbine blades, thereby extracting mechanical work from the exhaust gas. The mechanical work extracted from the exhaust gas results in a corresponding loss of energy in the exhaust gas flow. This may be observed as a decrease in pressure, temperature and/or velocity, for example, between the exhaust gas in the turbine inlet and the exhaust gas in the turbine outlet passage.

The wastegate passage may be configured to deliver fluid to the turbine outlet passage via the auxiliary passage. That is to say, the auxiliary passage may be fluidly interposed between the turbine outlet passage and the wastegate passage such that, during use when the wastegate valve is open, the wastegate flow passes through at least a portion of the auxiliary passage before entering the turbine outlet passage. Because the wastegate flow is received by the auxiliary passage, the wastegate flow may be used to support the same application as the auxiliary flow (e.g. dosing module nozzle cleaning etc.). Furthermore, because the wastegate flow has not passed through the turbine wheel, it will have higher internal energy than the auxiliary flow and therefore provides increased energy to support the application of the auxiliary flow. The moveable valve member may be further configured to selectively prevent fluid communication from the auxiliary passage inlet to the auxiliary passage outlet via the auxiliary passage. Because the wastegate flow passes through the auxiliary passage, the wastegate flow is able to support the same application as the auxiliary flow (e.g. dosing module nozzle cleaning etc.) in place of the auxiliary flow. When the wastegate is open, it may be preferable for all of the exhaust gas after exiting the turbine wheel chamber to pass through the turbine outlet passage, rather than a portion of the gas being diverted away from the turbine outlet passage along the auxiliary passage. Preventing flow passing through the auxiliary inlet to the auxiliary outlet, when not required, may reduce the disturbance to the turbine bulk flow of fluid in the turbine outlet passage, thereby reducing energy losses in the turbine bulk flow as it flows through the turbine outlet passage.

In a first configuration of the wastegate arrangement, the valve member may be positioned such that fluid flow from the auxiliary inlet to the auxiliary outlet via the auxiliary passageway is permitted, and fluid flow from the turbine inlet passage to the turbine outlet passage via the wastegate passage is permitted. That is to say in the first configuration both the wastegate passage and the auxiliary passage are open for fluid flow therethrough. In the first configuration, both the wastegate flow and the auxiliary flow can be used in the same manner to provide a benefit in the turbine outlet passage.

In a second configuration of the wastegate arrangement, the valve member may be positioned such that fluid flow from the auxiliary inlet to the auxiliary outlet via the auxiliary passage is permitted, and fluid flow from the turbine inlet to the turbine outlet passage via the wastegate passage is prevented. That is to say, in the second configuration the wastegate is closed and the auxiliary passage is open.

In a third configuration of the wastegate arrangement, the valve member may be positioned such that fluid flow from the auxiliary inlet to the auxiliary outlet via the auxiliary passage is prevented; and fluid flow from the turbine inlet to the turbine outlet passage via the wastegate passage is permitted. That is to say, in the third configuration the wastegate passage is open whilst the auxiliary passage is closed. In such a configuration, the wastegate flow may be used to support the application that the auxiliary flow is otherwise used for. In a fourth configuration of the wastegate arrangement, the valve member may be positioned such that fluid flow from the auxiliary inlet to the auxiliary outlet via the auxiliary passage is prevented, and fluid flow from the turbine inlet to the turbine outlet passage via the wastegate passage is prevented. That is to say, in the fourth configuration both the wastegate passage and the auxiliary passage may be closed. Closing both the wastegate passage and the auxiliary passage ensures maximum power output of the turbine and minimum flow disruption in the turbine outlet passage.

The term wastegate assembly and wastegate arrangement may be used interchangeably.

The turbine outlet passage may further comprise: a first portion upstream of the auxiliary passage inlet, the first portion may define a first flow area; and a second portion downstream of the auxiliary passage inlet and upstream of the auxiliary passage outlet, the second portion may define a second flow area that may be smaller than the first flow area. The term “flow area” encompasses the area of the turbine outlet passage perpendicular to the direction of flow of exhaust gas. Because the second flow area is smaller than the first flow area, the second portion of the turbine outlet passage exerts a back pressure on the first portion of the turbine outlet passage, thus encouraging turbine bulk flow to enter the auxiliary passage inlet. The second portion of the turbine outlet passage may be defined by a restriction of the turbine outlet passage which may include, for example, the turbine outlet passage having a narrower diameter downstream of the auxiliary passage inlet, and/or the presence of one or more protrusions, baffles or scoops extending into the turbine outlet passage from a wall of the turbine outlet passage. In such embodiments, the turbine outlet passage may be a generally a straight outlet passage, may comprise a diverging diffuser, or may have any other suitable geometry.

The second flow area may be between around 5 % to around 15 %, and may be preferably around 10 % smaller than the first flow area.

In general, as the second flow area decreases in size the back pressure exerted by the second portion of the turbine outlet passage on the turbine bulk flow increases, which causes the turbine bulk flow to enter the auxiliary passage inlet. It has been found that when the second flow area is smaller than the first flow area by around 5 %, this encourages sufficient intake of turbine bulk flow by the auxiliary passage inlet. However, if the second flow area is too small, too much back pressure is created. This increases the pumping work of the engine, and therefore reduces the overall efficiency of the engine system. It has been found that when the second flow area is no more than around 15 % smaller than the first flow area the amount of back pressure produced by the second portion of the turbine outlet passage is large enough to increase the flow rate through the auxiliary passage, but not so large as to significantly impact the overall efficiency of the engine system.

The auxiliary passage may be external to the turbine outlet passage. The term ‘external’ may encompass embodiments in which the turbine outlet passage comprises an inner surface delimiting an extremity of the turbine outlet passage, and in which at least part or all of the auxiliary passage lies outside of the inner surface relative to a central axis of the turbine outlet passage. Accordingly, in such embodiments, the auxiliary passage does not present an impediment to flow through the turbine outlet passage. In such embodiments, the auxiliary passage inlet and the auxiliary passage outlet may be defined by openings in the side wall of the turbine outlet passage.

According to a second aspect of the invention there is provided a method of operating a turbine for a turbocharger, comprising: receiving exhaust gas from an internal combustion engine into a turbine inlet passage; receiving exhaust gas from the turbine inlet passage into a turbine wheel chamber, the turbine wheel chamber being configured to contain a turbine wheel supported for rotation about a turbine axis; receiving exhaust gas from the turbine wheel chamber into a turbine outlet passage; and receiving a portion of the exhaust gas form the turbine outlet passage into and auxiliary passage via an auxiliary passage inlet; and delivering exhaust gas from the auxiliary passage to the turbine outlet passage via an auxiliary passage outlet.

The auxiliary passage inlet may be located at a position of the turbine outlet passage that is fluidly upstream of the auxiliary passage outlet relative to the flow through the turbine outlet passage.

The turbine wheel may comprise an exducer defining an exducer diameter, the turbine outlet passage may define a centreline; and the auxiliary passage inlet may be spaced apart from the exducer of the turbine wheel by a distance of at most around 5 exducer diameters along the centreline of the turbine outlet passage.

The auxiliary passage outlet may be spaced apart from the exducer of the turbine wheel by a distance of at most around 10 exducer diameters along the geometric centreline of the turbine outlet passage.

The turbine may comprise a turbine housing at least in part defining the turbine inlet, the turbine wheel chamber and the turbine outlet passage, and the auxiliary passage may be defined at least in part by the turbine housing.

The turbine may comprise a turbine housing defining the turbine inlet and the turbine wheel chamber, and a connection adapter at least partially defining the turbine outlet passage, and the auxiliary passage may be defined at least in part by the connection adapter.

The method may further comprise delivering aftertreatment fluid to the turbine outlet passage using a dosing module having a nozzle, e.g. an atomising nozzle.

The nozzle of the dosing module may be substantially aligned with a surface defining the auxiliary passage or a surface of the turbine outlet passage.

The nozzle of the dosing module may be positioned within the auxiliary passage such that the dosing module is configured to deliver aftertreatment fluid to the turbine outlet passage via the auxiliary passage.

The auxiliary passage may comprise an outlet portion extending from the nozzle to the auxiliary passage outlet, the outlet portion may define an outlet axis, and the outlet axis may be inclined relative to a centreline of the turbine outlet passage by an angle up to around 70°.

The auxiliary passage may comprise an inlet portion extending from auxiliary passage inlet to the nozzle, the inlet portion may define an inlet axis, and the inlet axis may be inclined relative to a centreline of the turbine outlet passage by an angle between around 20° to around 70°.

The cross-sectional area of the outlet portion of the auxiliary passage may increase along the outlet axis from the nozzle of the dosing module to the auxiliary passage outlet.

The turbine outlet passage may define a diffuser.

The diffuser may be aligned with and may extend symmetrically about the turbine axis.

The auxiliary passage inlet may comprise a scoop extending into the turbine outlet passage and the scoop may be configured to direct exhaust gas flow into the auxiliary passage.

The auxiliary passage may comprise a plurality of auxiliary passage inlets.

The auxiliary passage inlets are substantially axially aligned relative to a centreline of the turbine outlet passage.

The auxiliary passage may be generally equally spaced about the centreline.

The turbine outlet passage may define a perimeter, and the auxiliary passage may extend around the perimeter so as to provide fluid communication between the plurality of auxiliary passage inlets.

The turbine may further comprise a wastegate arrangement comprising: a wastegate passage configured to provide fluid communication from the turbine inlet passage to the turbine outlet passage such that exhaust gas travelling through the wastegate passage does not pass through the turbine wheel chamber; and a moveable valve member configured to selectively permit or prevent fluid flow through the wastegate passage by blocking the wastegate passage.

The wastegate passage may be configured to deliver fluid to the turbine outlet passage via the auxiliary passage. The moveable valve member may be further configured to selectively prevent fluid communication from the auxiliary passage inlet to the auxiliary passage outlet via the auxiliary passage.

In a first configuration of the wastegate arrangement, the valve member may be positioned such that fluid flow from the auxiliary inlet to the auxiliary outlet via the auxiliary passageway is permitted, and fluid flow from the turbine inlet passage to the turbine outlet passage via the wastegate passage is permitted.

In a second configuration of the wastegate arrangement, the valve member may be positioned such that fluid flow from the auxiliary inlet to the auxiliary outlet via the auxiliary passage is permitted, and fluid flow from the turbine inlet to the turbine outlet passage via the wastegate passage is prevented.

In a third configuration of the wastegate arrangement, the valve member may be positioned such that fluid flow from the auxiliary inlet to the auxiliary outlet via the auxiliary passage is prevented; and fluid flow from the turbine inlet to the turbine outlet passage via the wastegate passage is permitted.

In a fourth configuration of the wastegate arrangement, the valve member may be positioned such that fluid flow from the auxiliary inlet to the auxiliary outlet via the auxiliary passage is prevented, and fluid flow from the turbine inlet to the turbine outlet passage via the wastegate passage is prevented.

The term wastegate assembly and wastegate arrangement may be used interchangeably.

The turbine outlet passage may further comprise: a first portion upstream of the auxiliary passage inlet, the first portion may define a first flow area; and a second portion downstream of the auxiliary passage inlet and upstream of the auxiliary passage outlet, the second portion may define a second flow area smaller than the first flow area. The second flow area may be between around 5 % to around 15 %, and preferably around 10 % smaller than the first flow area.

The auxiliary passage may be external to the turbine outlet passage. In such embodiments, the auxiliary passage inlet and the auxiliary passage outlet may be defined by openings in the side wall of the turbine outlet passage.

According to a third aspect of the invention there is provided, a turbine for a turbocharger, the turbine comprising: a turbine inlet passage configured to receive exhaust gas from an internal combustion engine, the exhaust gas received by the turbine inlet passage defining a turbine bulk flow; a turbine wheel chamber configured to receive the turbine bulk flow from the turbine inlet passage, the turbine wheel chamber configured to contain a turbine wheel supported for rotation about a turbine axis; a turbine outlet passage configured to receive the turbine bulk flow from the turbine wheel chamber; and an auxiliary passage configured to receive a portion of the turbine bulk flow from a first position of the turbine upstream of the turbine outlet passage, the portion of the turbine bulk flow received by the auxiliary passage defining an auxiliary flow, the auxiliary passage further configured to deliver the auxiliary flow to the turbine bulk flow at a second position of the turbine downstream of the turbine wheel chamber; wherein the turbine is configured such that the auxiliary flow is always permitted to flow from the first position of the turbine to the second position of the turbine.

The term “auxiliary passage” encompasses any fluid carrying passage configured to carry fluid separately to the turbine inlet passage, turbine wheel chamber and turbine outlet passage. This many include the use of conduits, passages, cut-outs, perforations, grooves, notches, channels or the like. The “first position of the turbine upstream of the turbine outlet passage” encompasses, for example, a position within the turbine wheel chamber or the turbine inlet passage. The “second position of the turbine downstream of the turbine wheel chamber” encompasses, for example, a position within the turbine outlet passage. The auxiliary passage being arranged “such that the auxiliary flow bypasses at least a portion of the turbine wheel chamber” encompasses an arrangement in which the auxiliary passage contains the auxiliary flow so that it does not pass through at least part of the turbine wheel or turbine wheel chamber. Because the auxiliary passage is configured to receive the auxiliary flow from a first position of the turbine upstream of the turbine outlet passage and to deliver the auxiliary flow to the turbine bulk flow at a second position of the turbine downstream of the turbine wheel chamber, in use the auxiliary flow bypasses at least a portion of the turbine wheel.

The turbine being “configured such that the auxiliary flow is always permitted to flow from the first position of the turbine to the second position of the turbine” encompasses the auxiliary passage being arranged such that exhaust gas is allowed to pass from an inlet of the auxiliary passage, which receives exhaust gas from the turbine wheel chamber or the turbine inlet passage, to an outlet of the auxiliary passage, which delivers fluid to the turbine outlet passage, across all operating conditions of the turbine. That is to say, the auxiliary passage is arranged so that at least some flow through the auxiliary passage is always permitted regardless of the operating condition of the turbine (e.g. regardless of the actuation state of a variable geometry mechanism or a wastegate). This may include, for example, the auxiliary passage being substantially free from valves or closures that are configured to prevent flow through the auxiliary passage.

Under normal conditions, the flow regime in the turbine outlet passage is generally an unsuitable location for the injection of aftertreatment fluid. However, the re-conditioned exhaust gas flow through the auxiliary passage can be used in one or more fluidic applications in the auxiliary passage outlet to support improved decomposition where aftertreatment fluid is injected. For example, by using an auxiliary passage, a dosing module may be provided to inject after treatment fluid into the turbine outlet passage, and the auxiliary passage may direct exhaust gas flow into the aftertreatment fluid to cause turbulence and improve mixing. Additionally or alternatively, the auxiliary passage can direct flow over the nozzle of the dosing module to clean it. Additionally or alternatively, the momentum of the auxiliary flow may be used to increase the momentum of the aftertreatment fluid as it is injected, so that the aftertreatment fluid is able to dissipate across substantially the entire cross-sectional area of the turbine outlet passage, thereby providing increased uniformity of the after treatment fluid across the flow in the turbine outlet passage. In yet further alternative or additional embodiments, the auxiliary passage may be used to create a narrow layer of fast moving fluid over a surface of the turbine outlet passage where impingement of aftertreatment fluid is likely to take place, so as to avoid deposit build up on the surfaces of the turbine outlet. Other applications of the auxiliary flow will be apparent from the description.

It will be appreciated that in order for the auxiliary passage to condition the auxiliary flow to provide the beneficial functionality described above, it must be supplied with exhaust gas. When the turbine bulk flow passes through the turbine wheel chamber, the turbine wheel is rotated by the force of the exhaust gas impinging upon the turbine blades, thereby extracting mechanical work from the turbine bulk flow. The mechanical work results in a corresponding loss of energy in the turbine bulk flow. As such, the turbine bulk flow upstream of the turbine outlet passage has a higher energy than the turbine bulk flow downstream of the turbine wheel chamber. The higher energy of the turbine bulk flow at the first position of the turbine can be applied to influence the exhaust gas flow at the second position of the turbine as described above.

Furthermore, because the auxiliary passage always allows fluid to flow therethrough, there are no operating conditions of the turbine in which flow is prevented from flowing through the auxiliary passage. This means that the auxiliary passage is always operable to deliver flow to the second position of the turbine. Consequently, whichever application above is being supported by the auxiliary flow will be maintained across all operating conditions of the turbine.

The auxiliary passage may receive at least around 0.1 % of the turbine bulk flow received by the turbine inlet passage. That is to say, the geometry of the auxiliary passage is chosen so that at least around 0.1 % of the turbine bulk flow received by the turbine inlet may pass through the auxiliary passage regardless of the operating condition of the turbine. This can be measured, for example, by comparing the mass flow rate of the turbine bulk flow received by the turbine inlet to the mass flow rate of the auxiliary flow. The turbine bulk flow received by the turbine inlet is the total amount of incident exhaust gas delivered to the turbine from the internal combustion engine. This is achievable by controlling the cross-sectional area of the auxiliary passage.

Even a relatively small amount of auxiliary flow can be used to support a beneficial effect in the turbine outlet. For example, an auxiliary flow of around 0.1 % of the turbine bulk flow is sufficient to support cleaning of the nozzle of a dosing module. In other embodiments, the auxiliary flow may be at least around 0.2 %, 0.3%, 0.4%, 0.5%, 1 %, 1.5 %, 2 %, 2.5%, 3 %, 4 %, or 5 % of the turbine bulk flow. In general, the larger the auxiliary flow is in proportion to the turbine bulk flow, the more energy there is available to support the specific application of the auxiliary flow in the second position of the turbine.

The auxiliary passage may receive at most around 10 % of the turbine bulk flow received by the turbine inlet passage. That is to say, the geometry of the auxiliary passage is chosen so that at most around 10 % of the turbine bulk flow may pass through the auxiliary passage.

If the mass flow rate of the auxiliary flow as a proportion of the turbine bulk flow is increased, less work is extracted from the turbine bulk flow from the turbine wheel. Consequently, increasing the auxiliary flow results in a corresponding decrease in the efficiency of the turbine wheel, and lower power output of the internal combustion engine. It has been found that is the auxiliary flow is more than around 10 % of the turbine bulk flow the corresponding drop in efficiency of the turbine is generally too high to be tolerated. Preferably, the flow through the auxiliary passage should be kept as small as possible to support the beneficial effect and no higher. It has been found that when the mass flow rate of the auxiliary flow is at most around 0.2 %, 0.3 %, 0.4 %, 0.5 %, 1 %, 1.5 %, 2 %, 2.5% of the mass flow rate of the turbine bulk flow nozzle cleaning of the dosing module can be adequately supported without having a significantly negative impact on the efficiency of the turbine. In particular, the efficiency of the turbine at 1 % to 2 % leakage may only decrease by around 1% to 2 %. In most applications, such a small decrease in efficiency can be tolerated. However, in other embodiments the auxiliary flow may be at most around 3 %, 4 %, or 5 % of the turbine bulk flow.

The first position may be the turbine inlet passage, and wherein the auxiliary passage may define an auxiliary passage inlet in direct fluid communication with the turbine inlet passage. That is to say, the auxiliary passage inlet is positioned so that exhaust gas may flow directly from the turbine inlet passage to the auxiliary passage. Because the exhaust gas contained in the turbine inlet passage has not passed through the turbine wheel, the exhaust gas in the turbine inlet passage is high energy compared to the exhaust gas at any position further downstream. By joining the auxiliary passage to the turbine inlet passage, this ensures that more energy is available for supporting the beneficial effect at the downstream position to which the exhaust gas is routed.

The turbine may comprise a housing having an internal surface at least partially defining the turbine inlet passage, the internal surface may comprise an opening defining the auxiliary passage inlet. That is to say, the auxiliary passage inlet is an opening formed in a wall of the turbine housing defining the turbine inlet passage. For example, the auxiliary passage inlet may be an opening in a wall defining an inlet volute.

The opening ensures that the auxiliary passage is in direct fluid communication with the turbine inlet passage.

The first position may be the turbine wheel chamber, and the auxiliary passage may define an auxiliary passage inlet in direct fluid communication with the turbine wheel chamber. That is to say, the auxiliary passage inlet is positioned so that exhaust gas may flow directly from the turbine wheel chamber to the auxiliary passage.

To enable the turbine wheel to rotate, a clearance must be present between the tips of the blades of the turbine wheel and the surface of the turbine housing defining the turbine wheel chamber. During use, some of the turbine bulk flow will spill over the tips of the blades. The turbine wheel cannot extract energy from the spilled exhaust gas, and consequently the spilled exhaust gas has higher internal energy. Because the auxiliary passage inlet is in direct fluid communication with the turbine wheel chamber, the auxiliary passage may receive the spilled portion of the turbine bulk flow, and thus make use of the energy of this fluid which would otherwise be wasted.

The turbine may comprise a housing having an internal surface at least partially defining the turbine wheel chamber, the internal surface may comprise an opening defining the auxiliary passage inlet. That is to say, the auxiliary passage inlet is an opening formed in a wall of the turbine housing defining the turbine wheel chamber. The opening ensures that the auxiliary passage is in direct fluid communication with the turbine wheel chamber.

The turbine may comprise a turbine wheel, the turbine wheel may be a radial or a mixed flow turbine wheel comprising an inducer and an exducer, the internal surface may be correspondingly shaped to the turbine wheel such that the internal surface may define an inducer surface portion conforming to the inducer and an exducer surface portion conforming to the exducer, and the inducer surface portion may comprise the opening defining the auxiliary passage inlet. The term “radial turbine wheel” encompasses a turbine wheel configured to receive incident exhaust gas in a radial direction in relation to the turbine axis. The term “mixed flow turbine wheel” encompasses a turbine wheel configured to receive incident exhaust gas at an angle having a radial component relative to the turbine axis. The “inducer” encompasses the portion of the turbine wheel which receives the exhaust gas, and the “exducer” encompasses the portion of the turbine wheel which discharges exhaust gas.

It has been found that the pressure of spilled fluid over the blade tips is greatest at the inducer of the turbine wheel. Accordingly, a greater amount of spilled exhaust gas can be collected by placing the opening within the corresponding portion of the internal surface of the turbine wheel chamber. However, in alternative embodiments the exducer surface portion may comprise the opening defining the auxiliary passage inlet, or both the inducer and exducer portions may comprise openings defining auxiliary passage inlets (of an auxiliary passage having multiple inlets).

The first position of the turbine may be the turbine inlet passage and the second position of the turbine may be the turbine outlet passage; and the auxiliary passage may comprise a valve assembly configured to control the flow rate of the auxiliary flow through the auxiliary passage. That is to say, the auxiliary passage functions as a wastegate passage which extends between the turbine inlet passage and the turbine outlet passage.

The valve is able to substantially act as a wastegate valve by permitting a large amount of the turbine bulk flow to bypass the turbine wheel. However, because the turbine is configured such that the auxiliary flow is always permitted to flow from the first position of the turbine (the turbine inlet passage) to the second position of the turbine (the turbine outlet passage), there is always sufficient flow through the auxiliary passage to support the downstream application of the auxiliary flow (e.g. nozzle cleaning etc.). For example, when the valve is in a fully open configuration it may permit around 20 % to around 40 % or around 50 %, or preferably around 25 % of the turbine bulk flow to bypass the turbine wheel, whereas when the valve is in its most restricted position it may still permit at least around 0.1 % (or more) of the turbine bulk flow to bypass the turbine wheel through the auxiliary passage.

The valve assembly may be configured such that the auxiliary flow is always permitted to flow from the turbine inlet passage to the turbine outlet passage via the valve assembly. That is to say, when the valve assembly is in its most restricted configuration it still permits at least some auxiliary flow to pass from the turbine inlet to the turbine outlet. For example, the valve assembly may be configured so that it cannot be fully closed or so that, if it is closed, it still permits a small amount of fluid flow therethrough.

Accordingly, the there is always sufficient flow through the auxiliary passage to support the downstream application of the auxiliary flow (e.g. nozzle cleaning etc.).

The valve assembly may comprise: a valve member supported for movement between an open configuration and a closed configuration; and a valve seat defined by the auxiliary passage, the valve member may be configured to engage the valve seat in the closed configuration, and a leakage passage configured to permit the auxiliary flow to flow from the turbine inlet passage to the turbine outlet passage when the valve member is in the closed configuration. The leakage passage may be considered to define a portion of the auxiliary passage when the valve member is in the closed configuration. The leakage passage encompasses any structure of the valve member and/or the valve seat which is configured to permit auxiliary flow to travel around the valve member from the turbine inlet passage to the turbine outlet passage when the valve is in the closed configuration.

The valve member may comprise a through hole extending from a first side of the valve member to a second side of the valve member opposite the first side, the through hole may define the leakage passage. For example, the valve member may be a flap-type valve member of a conventional wastegate, and the through hole may be a hole formed in the body of the valve member. The use of a through hole is a very simple geometry that can permit the auxiliary flow to pass through the valve member when it is in a closed configuration. The valve member may comprise more than one such through hole.

The valve member may comprise a groove facing the valve seat, the groove may be configured to permit fluid flow around the valve member when the valve member is in the closed configuration, and the groove and the valve seat may define the leakage passage. The groove of the valve member may be, for example, formed in an outer surface of the valve member. The use of a groove is another very simple geometry that can permit the auxiliary flow to pass through the valve member when it is in a closed configuration. The valve member may comprise more than one such groove.

The valve seat may comprise a groove facing the valve member, the groove may be configured to permit fluid flow around the valve member when the valve member is in the closed configuration, and the groove and the valve seat may define the leakage passage. The groove of the valve seat may be for example, formed in an outer surface of the valve seat. Again, the use of a groove is a simple geometry that can permit the auxiliary flow to pass through the valve member when it is in a closed configuration. The valve seat may comprise more than one such groove.

The auxiliary passage may comprise: a first branch configured to permit fluid communication from the turbine inlet passage to the turbine outlet passage; and a second branch configured to permit fluid communication from the turbine inlet passage to the turbine outlet passage; and the valve assembly may be configured to selectively permit or prevent flow through the first branch; and the second branch may be configured such that flow therethrough is always permitted. That is to say, in such arrangements the auxiliary passage is bifurcated into two sub-passages (or “branches”). The first branch comprises the valve, and the valve is configured to selectively block flow through the first branch, for example in the manner of a conventional wastegate.

The second branch is separate to the first branch, and the valve cannot be used to block or restrict flow through the second branch. Accordingly, the second branch remains open across all operating conditions of the turbine. The second branch can be easily manufactured as a simple conduit, for example in the manner of a pin hole in a wastegate assembly.

The turbine housing may comprise an internal surface at least partially defining the turbine inlet passage, the internal surface may comprise a first opening defining an inlet of the first branch and a second opening defining an inlet of the second branch. That is to say, the first and second branches are directly connected to the turbine inlet passage via openings defined in the wall of the turbine housing. The two branches may subsequently merge after the valve assembly of the first branch. This is a simple configuration that can be easily manufactured by introducing a leakage through-hole which connects the turbine inlet passage to a wastegate plenum separately to a wastegate valve passage. In such arrangements, the wastegate valve passage defines the first branch of the auxiliary passage, and the leakage through hole defines the second branch of the auxiliary passage.

The turbine may comprise: a turbine housing at least partially defining the turbine inlet passage, the turbine wheel chamber and the turbine outlet passage; and a valve housing comprising the valve assembly and at least partially defining the auxiliary passage; the valve housing may be formed separately to and may be engageable with the turbine housing. That is to say, the valve housing and the turbine housing are not integrally formed. Because the valve housing and the turbine housing are separate to one another, it is possible to manufacture complex geometries that would not be possible if the turbine housing and valve housing were integrally formed.

The turbine may comprise a variable geometry arrangement comprising: a nozzle ring having at least one nozzle vane, a shroud plate having at least one aperture configured to receive the at least one nozzle vane, the nozzle ring and the shroud plate may define an annular inlet passage therebetween, the annular inlet passage may fluidly connect the turbine inlet passage to the turbine wheel chamber, the annular inlet passage may define a width measured along the turbine axis, and at least one of the nozzle ring and the shroud plate may be movable along the turbine axis to vary the width of the annular inlet passage. That is to say, the variable geometry arrangement may be a sliding vane type variable geometry arrangement. The turbine may comprise a recess configured to receive the at least one nozzle vane when the at least one nozzle vane is received by the at least one aperture; and the first position of the turbine may be the recess. That is to say, the auxiliary passage receives fluid from recess. Due to the clearance between the nozzle vane and the aperture, during use exhaust gas passing through the annular inlet passage has a tendency to leak into the recess. The leaked fluid loses some of its internal energy as it leaks and therefore reduces the efficiency of the turbine. However, the leaked fluid has not passed through the turbine wheel and therefore has a high energy relative to the turbine bulk flow in the turbine outlet passage. Because the auxiliary passage is connected to the recess, the higher energy of this leaked fluid can be harnessed and used to support one of applications in the turbine outlet passage discussed above.

The turbine may comprise a turbine housing defining the recess, the recess may comprise an opening defining an inlet of the auxiliary passage. That is to say, the inlet of the auxiliary passage is positioned in the recess.

The shroud plate may comprise at least one pocket configured to receive the at least one nozzle vane, and the first position of the turbine may be the pocket. That is to say, the shroud plate may be a so-called “multiple cavity” shroud plate comprising a separate pocket for the receipt of each individual nozzle vane. In such arrangements, the auxiliary passage may be connected to one or more of the pockets to receive fluid that has leaked into the pockets.

The pocket may comprise an opening defining an inlet of the auxiliary passage.

According to a fourth aspect of the invention, there is provided a method of operating a turbine for a turbocharger, comprising: receiving exhaust gas from an internal combustion engine into a turbine inlet passage, the exhaust gas received by the turbine inlet passage defining a turbine bulk flow; receiving the turbine bulk flow from the turbine inlet passage into a turbine wheel chamber, the turbine wheel chamber configured to contain a turbine wheel supported for rotation about a turbine axis; receiving the turbine bulk flow from the turbine wheel chamber into a turbine outlet passage; receiving a portion of the turbine bulk flow from a first position upstream of the turbine outlet passage into an auxiliary passage, the portion of the turbine bulk flow received by the auxiliary passage defining an auxiliary flow, delivering the auxiliary flow to the turbine bulk flow at a second position of the turbine downstream of the turbine wheel chamber; and permitting the auxiliary flow to flow from the first position of the turbine to the second position of the turbine across all operating conditions of the turbine.

The method may further comprise receiving into the auxiliary passage at least around 0.1 % of the turbine bulk flow received by the turbine inlet passage.

The method may further comprise receiving into the auxiliary passage at most around 10 % of the turbine bulk flow received by the turbine inlet passage.

The first position may be the turbine inlet passage, and the auxiliary passage may define an auxiliary passage inlet in direct fluid communication with the turbine inlet passage.

The turbine may comprise a housing having an internal surface at least partially defining the turbine inlet passage, the internal surface may comprise an opening defining the auxiliary passage inlet.

The first position may be the turbine wheel chamber, and the auxiliary passage may define an auxiliary passage inlet in direct fluid communication with the turbine wheel chamber.

The turbine may comprise a housing having an internal surface at least partially defining the turbine wheel chamber, the internal surface may comprise an opening defining the auxiliary passage inlet.

The turbine may comprise a turbine wheel, the turbine wheel may be a radial or a mixed flow turbine wheel comprising an inducer and an exducer, the internal surface may be correspondingly shaped to the turbine wheel such that the internal surface may define an inducer surface portion conforming to the inducer and an exducer surface portion conforming to the exducer, and the exducer surface portion may comprise the opening defining the auxiliary passage inlet. The first position of the turbine may be the turbine inlet passage and the second position of the turbine may be the turbine outlet passage; and the method may further comprise: controlling the flow rate of the auxiliary flow through the auxiliary passage using a valve assembly.

The valve assembly may be configured such that the auxiliary flow is always permitted to flow from the turbine inlet passage to the turbine outlet passage via the valve assembly.

The valve assembly may comprise: a valve member supported for movement between an open configuration and a closed configuration; and a valve seat which may be defined by the auxiliary passage, the valve member may be configured to engage the valve seat in the closed configuration, and a leakage passage which may be configured to permit the auxiliary flow to flow from the turbine inlet passage to the turbine outlet passage when the valve member is in the closed configuration.

The valve member may comprise a through hole extending from a first side of the valve member to a second side of the valve member opposite the first side, the through hole may define the leakage passage.

The valve member may comprise a groove facing the valve seat, the groove may be configured to permit fluid flow around the valve member when the valve member is in the closed configuration, and the groove and the valve seat may define the leakage passage.

The valve seat may comprise a groove facing the valve member, the groove may be configured to permit fluid flow around the valve member when the valve member is in the closed configuration, and the groove and the valve seat may define the leakage passage.

The auxiliary passage may comprise: a first branch configured to permit fluid communication from the turbine inlet passage to the turbine outlet passage; and a second branch configured to permit fluid communication from the turbine inlet passage to the turbine outlet passage; and the valve assembly may be configured to selectively permit or prevent flow through the first branch; and the second branch may be configured such that flow therethrough is always permitted.

The turbine housing may comprise an internal surface at least partially defining the turbine inlet passage, the internal surface may comprise a first opening defining an inlet of the first branch and a second opening defining an inlet of the second branch.

The turbine may comprise: a turbine housing at least partially defining the turbine inlet passage, the turbine wheel chamber and the turbine outlet passage; and a valve housing comprising the valve assembly and at least partially defining the auxiliary passage; the valve housing may be formed separately to and may be engageable with the turbine housing.

The turbine may comprise a variable geometry arrangement comprising: a nozzle ring which may have at least one nozzle vane, a shroud plate which may have at least one aperture configured to receive the at least one nozzle vane, the nozzle ring and the shroud plate may define an annular inlet passage therebetween, the annular inlet passage may fluidly connect the turbine inlet passage to the turbine wheel chamber, the annular inlet passage may define a width measured along the turbine axis, and at least one of the nozzle ring and the shroud plate may be movable along the turbine axis to vary the width of the annular inlet passage.

The turbine may comprise a recess configured to receive the at least one nozzle vane when the at least one nozzle vane is received by the at least one aperture; and the first position of the turbine may be the recess.

The turbine may comprise a turbine housing, the turbine housing may define the recess, the recess may comprise an opening defining an inlet of the auxiliary passage.

The shroud plate may comprise at least one pocket configured to receive the at least one nozzle vane, and the first position of the turbine may be the pocket.

The pocket may comprise an opening defining an inlet of the auxiliary passage. A detailed description of the invention will now be provided with reference to the accompanying drawings in which:

Figure 1 is a schematic illustration of an internal combustion engine system according to the prior art;

Figure 2 is a schematic cross-sectional side view of a turbine according to an embodiment of the first aspect of the invention;

Figure 3 is a schematic cross-sectional side view of a turbine according to a second embodiment of the first aspect of the invention;

Figures 4A to 4D are schematic cross-sectional views of a control valve according to an embodiment of the first aspect of the invention;

Figure 5 is a cross-sectional side view of a turbine according to a third embodiment of the first aspect of the invention;

Figure 6 is a cross-sectional front view of the turbine of Figure 5;

Figure 7 is a schematic cross-sectional side view of a fourth embodiment of a turbine according to the first aspect of the invention;

Figure 8 is a schematic cross-sectional side view of a first embodiment of a turbine according to the third aspect of the invention;

Figure 9 is a schematic cross-sectional side view of a second embodiment of a turbine according to the third aspect of the invention;

Figure 10 is a schematic cross-sectional side view of a third embodiment of a turbine according to the second aspect of the invention;

Figure 11 is an enlarged schematic cross-sectional side view of a wastegate arrangement of the turbine of Figure 10; Figure 12 is an enlarged cross-sectional view of a further embodiment of a wastegate arrangement of a turbine according to the third aspect of the invention;

Figure 13 is an enlarged cross-sectional view of a further embodiment of a wastegate arrangement of a turbine according to the third aspect of the invention;

Figure 14 is an enlarged cross-sectional view of a further embodiment of a wastegate arrangement of a turbine according to the third aspect of the invention;

Figure 15 is a schematic perspective view of a removable wastegate assembly according to the third aspect of the invention; and

Figure 16 is a schematic cross-sectional side view of a fourth embodiment of a turbine according to the third aspect of the invention.

Figure 1 shows a schematic view of a turbocharged diesel engine system 2 according to the prior art. The system 2 comprises a diesel internal combustion engine 4, a turbocharger 6 and an exhaust gas aftertreatment system 8. The turbocharger 6 comprises a compressor 10 and a turbine 12 mounted to a common turbocharger shaft 14 so that the two rotate in unison. The compressor 10 receives intake air from a low pressure intake duct 16 connected to atmosphere. The low pressure intake duct 16 may comprise a particulate filter to clean the intake air. The compressor 10 compresses the intake air using power provided by the turbocharger shaft 14 and supplies the compressed intake air to the engine 4 via a high pressure intake duct 18 and an intake manifold 20. Although not shown, the high pressure intake duct 18 may comprise an intercooler configured to cool the intake air before it reaches the engine 4. Inside the engine 4, an internal combustion process takes place and useful work is produced. As a result of the internal combustion process, exhaust gases are created by the engine 4. The engine 4 is fluidly connected to an exhaust manifold 22 which is in turn connected to the turbine 12 via a high pressure exhaust gas duct 24. The turbine 12 extracts energy from the exhaust gas to drive the turbocharger shaft 14 and thereby power the compressor 10. Exhaust gas leaving the turbocharger 12 is supplied to the exhaust gas aftertreatment system 8 via a downpipe 26. The downpipe 26 is relatively long in extent, for example at least 2 metres in length, as indicated by the broken line in Figure 1. The exhaust gas aftertreatment system 8 comprises a decomposition chamber 28 having a diameter larger than that of the downpipe 26. The decomposition chamber 28 comprises a mixing element 30 disposed therein. The mixing element 30 typically comprises a number of baffles configured to deflect the flow through the decomposition chamber 28 to cause turbulence within the decomposition chamber 28. The exhaust gas aftertreatment system 8 comprises a dosing module 32 configured to inject an exhaust gas aftertreatment fluid, and specifically Diesel Exhaust Fluid (DEF), into the decomposition chamber 28 downstream of the mixing element 30 in the region where the exhaust gas is most turbulent. Heat exchange between the DEF and the exhaust gas within the decomposition chamber 28 causes the urea contained within the DEF to decompose into the reductants ammonia (NH3) and Isocyanic Acid (HNCO). The mixture of reductants and exhaust gas is then passed to a selective catalytic reducer (SCR) 34 and a diesel oxidation catalyst (DOC) 36. Finally, the exhaust gas is passed to an outlet duct 38 and onwards to a muffler (not shown) before being discharged to atmosphere.

Figure 2 shows a schematic cross sectional view of a turbine 100 according to an embodiment of the present invention. The turbine 100 comprises a turbine housing 102 and a turbine wheel 104 supported by a turbocharger shaft 106 and configured to rotate about turbine axis 108. The turbine housing 102 defines a turbine inlet passage 110, a turbine wheel chamber 112 and a turbine outlet passage 114. The turbine inlet passage 110 defines a volute configured to receive exhaust gas from an internal combustion engine (not shown) and is configured to encourage swirling of the exhaust gas about the turbine axis 108. The exhaust gas received by the turbine inlet passage defines a turbine bulk flow 111. The turbine outlet passage 114 comprises a side wall 116 that is generally co-axial with the turbine axis 108. The side wall 116 is generally tapered so as to define a diffuser configured to cause expansion of the exhaust gas in the turbine outlet passage 114 and thereby increase the efficiency of the turbine 100. The diffuser is aligned with and symmetrical about the turbine axis 108. However, it will be appreciated that in alternative embodiments of the invention the diffuser may be asymmetrical, or the turbine outlet passage 114 may be straight-sided such that it does not define a diffuser. The turbine 100 further comprises an auxiliary passage 118 comprising an auxiliary passage inlet 120 and an auxiliary passage outlet 122. The auxiliary passage inlet 120 receives a portion of the turbine bulk flow 111 from the turbine outlet passage 114. The auxiliary passage 118 runs externally to the turbine outlet passage 114 such that it lies radially outwards of the side wall 116. The portion of the turbine bulk flow 111 received by the auxiliary passage 118 defines an auxiliary flow 123. The auxiliary passage inlet 120 and the auxiliary passage outlet 122 are defined by openings in the side wall 116 of the turbine outlet passage 114. The auxiliary passage inlet 120 is upstream of the auxiliary passage outlet 122 with respect to the turbine bulk flow 111 , such that the auxiliary passage inlet 120 is closer to the turbine wheel 104 than the auxiliary passage outlet 122.

The turbine further comprises a dosing module 130, which is held by a mount defined by the turbine housing 102 (not shown). The dosing module 130 comprises a nozzle 132 configured to generate a substantially atomized spray of exhaust gas aftertreatment fluid, in particular DEF. The nozzle 132 is received within a corresponding hole of the turbine housing 102 so that the nozzle 132 is exposed to the auxiliary flow 123. In particular, the hole is located in a portion of the turbine housing 102 which in part defines the auxiliary passage 118. The nozzle 132 is further aligned with the auxiliary passage outlet 122, at the position where the auxiliary flow 123 merges with the turbine bulk flow 111. The nozzle 132 is aligned with the wall of the auxiliary passage 118 so that it does not protrude into the auxiliary passage 118 or the turbine outlet passage 114. As such, the nozzle 132 does not present an obstruction to the auxiliary flow 123 or the turbine bulk flow 111. Nevertheless, small amounts of misalignment may be accommodated with little detriment to performance.

The nozzle 132 generates a substantially conical spray of aftertreatment fluid, shown by dashed lines, which permeates through the turbine outlet passage 118 and across the turbine outlet passage 114. As such, the aftertreatment fluid mixes with the turbine bulk flow 111 and decomposes in the turbine outlet passage 114. Because the dosing module 132 injects aftertreatment fluid into the turbine outlet passage 114, a separate decomposition chamber downstream of the turbine 100 does not need to be provided.

During use, the turbine inlet passage 110 delivers the turbine bulk flow to the turbine wheel chamber 112. In the turbine wheel chamber 112, the turbine bulk flow 111 passes through the turbine wheel 104. The turbine wheel 104 is a so-called radial turbine wheel which comprises blades configured to receive the turbine bulk flow in a radial direction relative to the turbine axis 108 and to re-direct the turbine bulk flow axially relative to the turbine axis 108. During this re-direction, the turbine bulk flow 111 imparts a force on the blades causing the turbine wheel 104 to rotate, thereby driving rotation of a compressor wheel (not shown) via the shaft 106. The turbine bulk flow 111 then passes to the turbine outlet passage 114 where, due to the tapered side wall 116 it is expanded and decelerated. The turbine bulk flow 111 is subsequently transferred via downstream ducting to one or more further components of an exhaust gas aftertreatment system (not shown).

The geometry of the auxiliary passage 118 may change the speed and/or direction of the auxiliary flow 123 relative to the turbine bulk flow 111. For example, the auxiliary passage 118 may narrow or widen to accelerate or decelerate the auxiliary flow 123 so that it has a faster or slower velocity than the turbine bulk flow 111, to angle the auxiliary flow 123 with or against the direction of swirl through the turbine outlet passage 114, or to angle the auxiliary flow 123 inwardly towards the turbine axis 108. When the auxiliary flow 123 is re-introduced to the turbine bulk flow 111 , the difference in velocity and/or direction can be used to influence the spray of aftertreatment fluid from the dosing module 130 to improve the mixing of the aftertreatment fluid with turbine bulk flow 111 (and thereby improve reductant decomposition), or to prevent impingement of aftertreatment fluid on one or more surfaces of the turbine outlet passage 114 (and thereby reduce the risk of deposit formation on the walls of the turbine outlet passage 114).

For example, in the embodiment shown in Figure 2, the auxiliary flow 123 is directed over the nozzle 132 of the dosing module 130 by the auxiliary passage 118. The auxiliary flow 123 therefore exerts a shearing action over the nozzle 132, which helps to prevent aftertreatment fluid pooling in the vicinity of the nozzle 132. This reduces the chance that aftertreatment fluid will cool and solidify in front of the nozzle 132, which could block the nozzle 132 or obstruct flow through the auxiliary passage 118 and/or turbine outlet passage 114. In an embodiment, the auxiliary passage 118 may narrow so as to accelerate the auxiliary flow so that it passes over the nozzle 132 with higher velocity than the turbine bulk flow 111. Nevertheless, it will be appreciated that in alternative embodiments the auxiliary passage outlet 122 and the dosing module 132 may have a different relative configuration, so as to promote improved mixing, or to prevent impingement or the like as discussed above as may be desired.

The turbine wheel 104 comprises an exducer 140 defining an exducer diameter. The auxiliary passage inlet 120 is preferably positioned as close as possible to the turbine wheel 104 downstream of the exducer 140. Since the auxiliary passage inlet 120 is upstream of the auxiliary passage outlet 122 which is aligned with the dosing module 130, positioning the auxiliary passage inlet 120 close to the exducer 140 ensures that there is sufficient space within the turbine outlet passage 114 to position the dosing module 130 close to the turbine wheel 104. This enables the dosing module 130 to inject DEF in a region with high temperature so as to improve decomposition. Furthermore, sourcing the auxiliary flow 123 from a position close to the turbine wheel 104 ensures that the auxiliary flow 123 has more energy, since less energy is lost to pipe friction compared to positions further downstream.

In the embodiment shown, the auxiliary passage inlet 120 is spaced apart from the exducer 140 by around 0.5 exducer diameters along the turbine axis 108. In other embodiments, the auxiliary passage inlet 120 may be spaced apart from the exducer 140 by around 1 , 2, 3, 4 or 5 exducer diameters along the turbine axis 108. The auxiliary passage outlet 122 is preferably positioned downstream of the auxiliary passage inlet 120 whilst remaining close to the turbine wheel 104. In the embodiment shown, the auxiliary passage outlet 122 is positioned around 2 exducer diameters from the turbine wheel 104 along the turbine axis 108. However, the auxiliary passage outlet 122 may be positioned up to around 5 or 10 exducer diameters from the turbine wheel 104.

The distances from the turbine exducer 140 to the auxiliary passage inlet 120 and the auxiliary passage outlet 122 may be measured from the tips of the blades of the turbine wheel 104 to the centroids of the auxiliary passage inlet 120 and the auxiliary passage outlet 122. In some embodiments, the turbine outlet passage 114 may define a nonlinear path comprising bends. In such instances, the distances from the turbine exducer 140 to the auxiliary passage inlet 120 and the auxiliary passage outlet 122 may be measured along a centerline of the turbine outlet passage 114. The centerline is the line prescribed by the centroid of the turbine outlet passage 114 along the direction of the turbine bulk flow 111. The turbine housing 102 is made from metal, for example cast iron or the like. In some embodiments, the housing 102 may be made from stainless steel, for example types 304, 403 or 904 stainless steel. The use of stainless steel is advantageous as it resists corrosion which may be cause by the impingement of DEF on the surfaces of the turbine housing 102, in particular the turbine outlet passage 114. In the present embodiment, the turbine housing 102 is a single integral component. However, in alternative embodiments the turbine may comprise a turbine housing assembly having multiple housing components. In particular, the turbine housing assembly may comprise a turbine housing defining the turbine inlet passage 110 and the turbine wheel chamber 112, and a connection adapter defining the turbine outlet passage 314. The turbine housing may interface with the connection adapter for example at the position shown by the line 103 in Figure 2. In such embodiments, the connection adapter may be made from stainless steel and the turbine housing may be made from cast iron. This provides the advantage that stainless steel is only used in the regions where DEF impingement is likely to occur.

Although not shown, the auxiliary passage inlet 120 may further comprise a scoop which extends radially into the turbine outlet passage 112 towards the turbine axis 108. The scoop acts as a baffle which re-directs the bulk turbine flow 111 into the auxiliary passage 118. The scoop therefore helps to increase the amount of the turbine bulk flow 11 that is received by the auxiliary passage 118.

Figure 3 shows a cross-sectional perspective side view of a part of a turbine 200 according to another embodiment of the present invention. The turbine 200 is the same as the turbine 100 of the previous embodiment aside from the differences described below. Like reference numerals have therefore been used to denote equivalent features to the previous embodiment discussed above. The turbine wheel and shaft have been omitted from Figure 3 for clarity.

The turbine 200 of the present embodiment differs from the previous embodiment in two principal ways. First, the turbine housing 202 defines a plenum 242 downstream of the turbine wheel chamber 212. The plenum 242 is a generally hollow portion of the turbine housing 202 which partially defines both the turbine outlet passage 214 and the auxiliary passage. A conically shaped insert 244 is received within the plenum 242 and acts to divide the plenum 242 into the turbine outlet passage 214 and the auxiliary passage 218. In particular, the auxiliary passage 218 is defined by the portion of the plenum 242 radially outward of the insert 244 with respect to the turbine axis 208. The insert 244 is made from stainless steel so as to prevent corrosion caused by any aftertreatment fluid that impinges upon it. Because the insert 244 is made from stainless steel, the turbine housing 202 can be made from cast iron. The insert 244 comprises a first aperture located at a proximal end relative to the turbine wheel chamber 212 which defines the auxiliary passage inlet 220, and a second aperture located at a distal end relative to the turbine wheel chamber 212 which defines the auxiliary passage outlet 222.

Secondly, the turbine 200 of the present embodiment differs from the previous embodiment in that it comprises a wastegate arrangement 246. The wastegate arrangement 246 comprises a wastegate passage 248 and a movable valve member 250. The wastegate passage 248 provides fluid communication between the turbine inlet passage 210 and the turbine outlet passage 214 via the auxiliary passage 218. In particular, the wastegate passage 248 receives a portion of the turbine bulk flow 211 from the turbine inlet passage 210 and delivers this to the auxiliary passage 218. The portion of the turbine bulk flow 211 received by the wastegate passage defines a wastegate flow 251. In turn, the auxiliary passage delivers the wastegate flow to the turbine outlet passage 214 via the auxiliary passage outlet 222. Accordingly, the wastegate flow 251 bypasses the turbine wheel and turbine wheel chamber 212 before re-joining the turbine bulk flow 211.

The wastegate passage 248 comprises a wastegate passage inlet 252 and a wastegate passage outlet 254. The wastegate passage inlet 252 is defined by an opening in a surface defining the turbine inlet passage 210 so as to provide flow communication from the turbine inlet passage 210 to the wastegate passage 248. The wastegate passage outlet 254 is defined by an opening in a surface of the housing 242 defining the auxiliary passage 218 so as to provide flow communication from the wastegate passage 248 to the auxiliary passage 218.

The valve member 250 is a so-called flap-type wastegate valve configured to control flow through the wastegate passage 248 and the auxiliary passage 218 by blocking one or other of the wastegate passage outlet 254 or the auxiliary passage inlet 220. In particular, the valve member 250 comprises a first valve portion 256 on a first side of the valve member 250 which is configured to engage a valve seat surrounding the wastegate passage outlet 254 so as to substantially block the wastegate passage outlet 254. This thereby prevents the wastegate flow 251 passing through the wastegate passage 248. The valve member 250 further comprises a second valve portion 258 on a second side of the valve member 250 configured to engage the insert 244 to substantially block the auxiliary passage inlet 220. This thereby prevents the auxiliary flow 223 from entering the auxiliary passage 118. The valve member 205 is supported by an actuation rod (not shown) that is rotatable about an axis generally perpendicular to the turbine axis 208 so that it may rotate between a number of configurations.

In a first configuration, the valve member 250 is rotated to a position in which it blocks neither the wastegate passage outlet 254 nor the auxiliary passage inlet 220. Therefore, in the first configuration both the wastegate passage 248 and the auxiliary passage 218 are open. As such, in the first configuration, both the auxiliary flow 223 and the wastegate flow 251 can be used to clean the nozzle 232 of the dosing module 230. Since the wastegate flow 251 has not passed through the turbine wheel, it has a higher energy than the auxiliary flow 223, and therefore can provide more energy to the downstream application of the auxiliary flow (e.g. nozzle 232 cleaning or the like).

In a second configuration the valve member 250 is rotated to a position in which it blocks the wastegate passage outlet 254 whilst the auxiliary passage inlet 220 remains open. This is the configuration shown in Figure 3. In the second configuration, only the auxiliary flow 218 is used for the downstream application (in the present embodiment, cleaning the nozzle 232). Because the wastegate passage outlet 254 is blocked, wastegate flow 251 cannot bypass the turbine wheel and therefore all of the turbine bulk flow 211 passes through the turbine wheel, thus maximising the amount of power produced by the turbine 200.

In a third configuration the valve member 250 is rotated to a position in which the auxiliary passage inlet 220 is blocked and the wastegate passage outlet 254 is open. In the third configuration, the wastegate flow 251 is used to provide cleaning of the nozzle 232. As previously mentioned, the wastegate flow 251 has not passed through the turbine wheel and is therefore able to provide more energy to support the downstream application (e.g. nozzle 232 cleaning).

Although the disclosed embodiment uses the auxiliary flow 218 and wastegate flow 251 to clean the nozzle 132 of the dosing module 130, it will be appreciated that in other embodiments the auxiliary flow 218 and wastegate flow 251 may be used to support a different application which influences flow in the turbine outlet passage 214, for example those described in relation to the first embodiment.

Although the wastegate arrangement 246 of the present embodiment is a flap type valve positioned within the auxiliary passage 118, it will be appreciated that in alternative embodiments substantially any suitable wastegate arrangement may be used. For example, the wastegate arrangement 246 may comprise an external wastegate which receives the wastegate flow 251 via one or more conduits external to the turbine housing.

Additionally or alternatively, the wastegate arrangement 246 may comprise a rotary barrel-type control valve. An example of such a barrel-type control valve 260 is shown in Figures 4A to 4D. The control valve 260 comprises a generally hollow tubular housing 262 defining a valve cavity 263 and a valve member 264. The valve member 264 is supported for rotation about a valve axis 266. The valve cavity 263 receives auxiliary flow 223 from a first portion of the auxiliary passage 218a and receives wastegate flow 251 from the wastegate passage 248. The auxiliary flow 223 and the wastegate flow 251 merge in the valve cavity 263 and exit the valve cavity via a second portion of the auxiliary passage 218b, whereupon the two flows 223, 261 are delivered back into the turbine outlet passage 214. As shown in Figure 4A, the valve member 264 is movable to a first configuration in which both the first portion of the auxiliary passage 218a and the wastegate passage 248 are open. As shown in Figure 4B, the valve member 264 is movable to a second configuration in which it blocks the wastegate passage 248 whilst the first portion of the auxiliary passage 218a remains open. As shown in Figure 4C, the valve member 264 is movable to a third configuration in which it blocks the first portion of the auxiliary passage 218a whilst the wastegate passage 248 remains open. Finally, with reference to Figure 4D the rotary control valve 260 also defines a fourth configuration in which the valve member 264 is movable to a position in which it blocks both the first portion of the auxiliary passage 218a and the wastegate passage 248. In the fourth configuration, no auxiliary flow 223 or wastegate flow 251 is provided to supply the downstream application (i.e. no nozzle cleaning or the like takes place).

Figures 5 and 6 show a turbine 300 according to a further embodiment of the present invention. The turbine 300 of the present embodiment is the same as the turbines of the previous embodiments aside from the differences described below. Like reference numerals have therefore been used to denote equivalent features to the previous embodiments discussed above.

The turbine 300 of the present embodiment differs from the previous embodiments in that the auxiliary passage 318 comprises a plurality of auxiliary passage inlets 320. The auxiliary passage inlets 320 are each defined by a respective opening in the side wall 316 of the turbine outlet passage 314. Although not shown, in further embodiments the auxiliary passage inlets may comprise scoops to increase the amount of turbine bulk flow 311 received. The auxiliary passage inlets 320 are axially aligned relative to the turbine axis 308. As best shown in Figure 6, the auxiliary passage 318 comprises a generally toroidal passage 319 which extends around the perimeter of the turbine outlet passage 314 and provides fluid communication between all of the plurality of auxiliary passage inlets 320 (for clarity, only some of the inlets 320 have been labelled in Figure 6). In this sense, the toroidal passage 319 therefore functions as a manifold. The auxiliary passage 318 further comprises an axial passage 317 which provides fluid communication between the toroidal passage 319 and the auxiliary passage outlet 322. The axial passage 317 extends generally axially relative to the turbine axis 308 from the toroidal passage 319 in downstream direction relative to the turbine bulk flow 311. The auxiliary passage outlet 322 is aligned with and positioned slightly upstream of the nozzle 332 of the dosing module 330 so as to direct the auxiliary flow 323 over the nozzle 332 to thereby keep the nozzle free of deposits.

The auxiliary passage inlets 320 will create a disturbance to the turbine bulk flow 311 as it passes over the inlets 320. In general, the increasing the size of the inlets 320 increases the amount of turbine bulk flow 311 that can be received, however this also increases the disturbance to the turbine bulk flow 311. This disturbance could lead to unwanted turbulence which exerts a back pressure on the turbine 300. In the present embodiment, because the auxiliary passage 318 comprises multiple auxiliary passage inlets 320 effective inlet area from which the auxiliary passage 318 can receive turbine bulk flow 311 is increased whilst the size of each inlet 320 remains relatively small. As such, each individual inlet presents a relatively small disturbance. In the present embodiment, the auxiliary passage 318 comprises 12 auxiliary passage inlets 320. However, in alternative embodiments substantially any number of auxiliary passage inlets 320 may be used according to requirements.

Preferably, the auxiliary passage inlets 320 are generally equally spaced about the turbine axis 308. Spacing the auxiliary passage inlets 320 equally ensures that the disturbances to flow caused by the inlets 320 are the maximum distance apart from one another, so that the overall disturbance is spread out. However, in alternative embodiments uneven spacing may be used.

In contrast to the previous embodiments, in the present embodiment the nozzle 332 of the dosing module 330 is positioned in the turbine outlet passage 314 and is not positioned in the auxiliary passage 318. Nevertheless, it will be appreciated that the nozzle 332 could be positioned in the auxiliary passage 318, or that the nozzle of the previous embodiments could be positioned in their respective turbine outlet passages. In the present embodiment, the auxiliary passage comprises a stepped portion 370 formed by two sequentially arranged generally right-angled bends. The stepped portion 370 protrudes into the turbine outlet passage 314 in an inwardly radial direction. The stepped portion 370 ensures that the auxiliary passage outlet 322 is radially aligned with the nozzle 332 so that the auxiliary flow 323 is correctly aligned to clean the nozzle 332.

With reference to both Figures 5 and 6 in conjunction, the turbine 300 further comprises a wastegate arrangement 346 having a wastegate passage 348 which terminates in a wastegate passage outlet 354. In contrast to the previous embodiment, the wastegate passage outlet 354 is defined by an opening of the side wall 316 of the turbine outlet passage 314. As such, the wastegate passage outlet 354 communicates directly with the turbine passage outlet 314. However, with reference to Figure 6, the auxiliary passage 318 further comprises a communication passage 372 which provides fluid flow communication between the wastegate passage 348 and the auxiliary passage 318. During use, when the wastegate is closed, auxiliary flow 323 may enter the wastegate passage 348 from the auxiliary passage 318. The communication passage 372 is relatively narrow and therefore when the wastegate is open the majority of the wastegate flow will travel through the wastegate passage 348 to the wastegate passage outlet 354. However, a small portion of the wastegate flow may travel through the communication passage 372 to the auxiliary passage 318 and onwards to the auxiliary passage outlet 322 where it may be used to clean the nozzle 332. Furthermore, some of the wastegate flow may exit the auxiliary passage 318 via the auxiliary passage inlets 320. This flow may cause a disturbance to the turbine bulk flow 311 in the turbine outlet passage 314, however the effect of such disturbance on the turbine bulk flow is negligible.

Nevertheless, it will be appreciated that in alternative embodiments the turbine 300 may not include the communication passage 372, such that the auxiliary passage 318 and wastegate passage 348 are fluidly separate from one another. Further still, in alternative embodiments the turbine 300 may not comprise a wastegate at all.

Figure 7 shows a turbine 400 according to a further embodiment of the present invention. The turbine 400 of the present embodiment is substantially the same as the turbines of the previous embodiments aside from the differences described below. Like reference numerals have therefore been used to denote equivalent features to the previous embodiments discussed above.

The present embodiment differs from the previous embodiment in that the nozzle 432 of the dosing module 430 is positioned approximately half way along the auxiliary passage 418 and in that the nozzle 432 is configured to inject the aftertreatment fluid at an angle relative to the turbine axis 408. In particular, the auxiliary passage 418 defines an inlet portion 474 extending from the auxiliary passage inlet 420 to the nozzle 432 of the dosing module 430, and an outlet portion 476 extending from the nozzle 432 of the dosing module 430 to the auxiliary passage outlet 422.

The inlet portion 474 defines an inlet axis 478 extending longitudinally along the inlet portion 474. The inlet axis 478 is inclined relative to the turbine axis 408 (or a centreline) by around 45°. However, in alternative embodiments the inlet axis 478 may be inclined relative to the turbine axis 408 by up to around 70°, around 20° to around 70°, around 30° to around 60°, or around 40° to around 50°. In general, a shallower angle between the inlet axis 478 and the turbine axis 408 is preferable so that the axial momentum of the exhaust gas entering the auxiliary passage is not lost.

The outlet portion 476 defines an outlet axis 480 extending longitudinally along the outlet portion 480. The outlet axis 480 is inclined relative to the turbine axis 408 (or centreline) by around 45°. However, in alternative embodiments the inlet axis 478 may be inclined relative to the turbine axis 408 by around 20° to around 70°, around 30° to around 60°, around 40° to around 50°, or around 45° to around 70°. Again, in general, a shallower angle between the outlet axis 480 and the turbine axis 408 is preferable to conserve axial momentum, and also to reduce the risk of DEF impingement on the wall of the turbine outlet passage 411 opposite the dosing module 430. However, if the angles of the inlet axis 478 or the outlet axis 476 are too shallow, then the axial distance between the auxiliary passage inlet 420 and the auxiliary passage outlet 422 will increase. This makes the arrangement less compact and could potentially cause the auxiliary outlet passage to lie outside the preferred range of around 10 exducer diameters from the turbine wheel 404.

In alternative embodiments the inlet portion 474 and the outlet portion 476 may not extend longitudinally, but instead may comprise complex geometry including bends, twists or the like. In such cases, the inlet axis 478 and the outlet axis 476 may be centrelines extending along the inlet portion 474 and the outlet portion 476 respectively. The relevant angle between these centrelines and the turbine axis 408 (or a centreline of the turbine outlet passage 414) may be measured as the angle between a tangent to the centreline at the centroid of the auxiliary passage inlet 420 or the auxiliary passage outlet 422 to the turbine axis 408.

The inlet portion 474 defines a generally constant cross-sectional area, whilst the outlet portion 476 diverges along the outlet axis 480 in the direction from the nozzle 432 of the dosing module 430 to the auxiliary passage outlet 422. During use, the nozzle 432 generates a generally conical spray pattern of atomised DEF, shown by dotted lines in Figure 7. Preferably, the outlet portion 476 diverges at an angle that is equal to or greater than the angle of the spray cone generated by the nozzle 321. For example, the spray cone angle may be around 45° to around 50°, and the outlet portion may diverge at an angle of around 60°. Because the outlet portion 476 diverges at such an angle, this ensures that DEF does not impinge on the sides of the auxiliary passage 418 and therefore deposit formation in the auxiliary passage is avoided. However, if the outlet portion 476 diverges at too steep of an angle, the auxiliary flow will decelerate such that it loses the potential to influence flow in the turbine outlet passage 414. Therefore, in alternative embodiments the spray cone angle may be around 45° to around 50°, whilst the outlet portion 476 of the auxiliary passage 418 diverges at a shallower angle, such as a round 5° to 10°. Although the aftertreatment fluid will be likely to impinge on the walls of the outlet portion 476, the velocity of the auxiliary flow will remain high such that shearing forces will clean any impinged aftertreatment fluid from the walls to avoid deposit formation.

The turbine outlet passage 414 of the present embodiment comprises a straight portion 482 which is a generally cylindrical extension of the outlet of the turbine wheel chamber 412 leading up to the auxiliary passage inlet 420. The straight portion 482 defines a first portion of the turbine outlet passage 414 having a first flow area measured in a plane perpendicular to the turbine axis 408. The turbine outlet passage 414 further comprises a diffuser portion 483 which begins immediately downstream of the auxiliary passage inlet 420 at a vertex 484 defined between the auxiliary passage inlet 420 and the side wall 416. The vertex 484 defines a second portion of the turbine outlet passage 414 having a second flow area measured in a plane perpendicular to the turbine axis 408. In order to encourage a greater portion of the turbine bulk flow 411 to enter the auxiliary passage 418, the second flow area is smaller than the first flow area. In general, the smaller the second flow area is in comparison to the first flow area, the greater the proportion of the turbine bulk flow that is forced into the auxiliary passage inlet. However, if the second flow area is too small, a high back pressure will be exerted on the engine which will increase pumping work. Therefore, preferably the second flow area is smaller than the first flow area by between around 5% to around 15%, and preferably by around 10%.

Although the turbine 400 shown comprises a diffuser portion 483, it will be appreciated that in alternative embodiments the diffuser 400 may not comprise a diffuser. Furthermore, the second flow area may be defined by a second portion of the turbine outlet passage 414 having any suitable shape. For example, the second portion could be defined by an inwardly extending protrusion, baffle or generally any other suitable restriction which would create a back pressure with the result of forcing more exhaust gas into the auxiliary passage inlet 420. Due to the similarities between the constructions of the first to fourth embodiments of the invention, all of which comprise an auxiliary passage outlet configured to receive exhaust gas from the turbine outlet passage, it will be appreciated that the optional or subordinate features of any one of the four embodiments may be combined with the features of another embodiment. For example, any embodiment may have any number of auxiliary passage inlets, any type of wastegate arrangement (or no wastegate arrangement), any type of diffuser (or no diffuser), any number of auxiliary passage outlets, any configuration of auxiliary passage or the like.

Figure 8 shows a schematic cross-sectional view of a turbine 500 according to an embodiment of the present invention. The turbine 500 comprises a turbine housing 502 and a turbine wheel 504 supported by a turbocharger shaft 506 and configured to rotate about turbine axis 508. The turbine housing 502 defines a turbine inlet passage

510, a turbine wheel chamber 512 and a turbine outlet passage 514. The turbine inlet passage 510 is configured to receive exhaust gas from the internal combustion engine. The exhaust gas received by the turbine inlet passage 510 defines a turbine bulk flow

511. The turbine inlet passage 510 defines a volute configured to encourage swirling of the exhaust gas circumferentially around and radially towards the turbine axis 510. The turbine wheel chamber 512 receives the turbine bulk flow 511 from the turbine inlet passage 510 in a radial direction, and redirects the turbine bulk flow 511 axially along the turbine axis 508. The turbine outlet passage 514 receives the turbine bulk flow 511 from the turbine wheel chamber 512. The turbine outlet passage 514 comprises a generally tapered side wall 516 defining a diffuser configured to cause expansion of the exhaust gas in the turbine outlet passage 514.

The turbine 500 further comprises a dosing module 518 configured to inject exhaust gas aftertreatment fluid, otherwise known as DEF, into the turbine outlet passage 514. Consequently, the turbine 500 does not need to be provided with a decomposition chamber separate to and downstream of the turbine (such as in the prior art). The dosing module 518 is a self-atomising dosing module comprising a nozzle 520 configured to substantially atomise the DEF into a fine spray that permeates in a conical pattern across the turbine outlet passage 514, as shown by the dashed lines in Figure 8. The dosing module 518 is generally aligned with the side walls 516 of the turbine outlet passage 514 and does not protrude into the turbine outlet passage 514. The nozzle 520 of the dosing module 518 is exposed to exhaust gas passing through the turbine outlet passage 514. During use, DEF injected into the turbine outlet passage 514 by the dosing module 518 may pool at the nozzle 520 of the dosing module. The temperature of the nozzle 520 is not as high as the temperature of the exhaust gas passing thorough the turbine outlet passage 514. Consequently, when the urea in the DEF decomposes into the reductant ammonia, the ammonia is not hot enough to evaporate and will solidify in the region of the nozzle 520. This could prevent the nozzle 520 from functioning correctly, exert back pressure on the engine, and reduce the amount of harmful substances removed by the exhaust gas aftertreatment system.

In order to mitigate deposit formation near the nozzle 520, the turbine 500 comprises an auxiliary passage 522. The auxiliary passage 522 connects the turbine inlet passage 510 to the turbine outlet passage 514. The turbine inlet passage 510 is upstream of the turbine wheel chamber 512 and turbine outlet passage 514, and may be considered to define a first position of the turbine 500. The turbine outlet passage 514 is downstream of the turbine wheel chamber 512 and may be considered to define a second position of the turbine 500. The auxiliary passage 522 is defined by a conduit 524 of the turbine housing 502 extending between the turbine inlet passage 510 and the turbine outlet passage 514. The auxiliary passage 522 defines an auxiliary passage inlet 526 in the form of an opening formed in a surface 528 of a part of the turbine housing 502 defining the turbine inlet passage 510 upstream of the turbine wheel chamber 512. The auxiliary passage 522 receives a portion of the turbine bulk flow 511 which defines an auxiliary flow 525.

Because the exhaust gas in the turbine inlet passage 510 has not passed through the turbine wheel 504, the temperature and pressure of the exhaust gas in the turbine inlet passage 510 is higher than the temperature and pressure of the exhaust gas in the turbine outlet passage 514. As such, during use exhaust gas will naturally travel from the turbine inlet passage 510 to the turbine outlet passage 514 via the auxiliary passage 522. As shown in Figure 2, the auxiliary passage 522 joins the turbine outlet passage 514 at the doser nozzle 520 and directs the auxiliary flow 525 over the nozzle 520. The auxiliary flow 525 exerts a high shearing force on the nozzle 520 which acts to keep the nozzle 520 clean so that reductant does not collect in this region. Furthermore, due to the higher temperature of the auxiliary flow 525 passing over the nozzle 520, more energy is available to cause evaporation of any collected reductant. Consequently reductant deposition at the nozzle 520 is mitigated.

The above notwithstanding, it will be appreciated that in alternative embodiments the auxiliary flow 525 may be employed in any suitable application downstream of the turbine wheel 504 other than cleaning the nozzle 520 of the dosing module 518. For example, the auxiliary flow 525 could be used to provide heat to a structure upon which DEF impinges, so as to encourage evaporation of reductants and thus reduce deposit formation. Additionally or alternatively, the auxiliary flow 525 could be used to provide high velocity flow over a particular part of the side wall 516 to mitigate DEF impingement on that part of the side wall 516. Generally speaking, the auxiliary flow may be used in substantially any suitable application which influences one of more operating parameters of the turbine outlet passage 514.

The auxiliary passage 512 is substantially free from any valves or closures which would otherwise prevent flow from the turbine inlet passage 510 to the turbine outlet passage 514. Accordingly, the auxiliary passage 522 is configured such that flow from the turbine inlet passage 510 to the turbine outlet passage 514 is always permitted across all operating conditions of the turbine 500.

The amount of auxiliary flow 525 can be measured as a proportion of the turbine bulk flow delivered to the turbine inlet passage 510 by the engine. In this context, the measurement of the “amount” may encompass a mass or volumetric flow rate, and the “proportion” may encompass a fraction numerated by the mass or volumetric flow rate through the auxiliary passage 522 and denominated by the corresponding mass or volumetric flow rate of exhaust gas delivered to the turbine inlet passage 510 (i.e. the turbine bulk flow 511). In general, increasing the size of the auxiliary flow 525 in relation to the turbine bulk flow 511 provides more energy to support the particular application of the auxiliary flow (e.g. nozzle 520 cleaning) but decreases the efficiency of the turbine 500. Preferably, auxiliary flow 525 is between at least around 0.1 % and at most around 10 % of the turbine bulk flow 511. It has been found that by limiting the proportion of the auxiliary flow 525 to at least around 0.1 % of the turbine bulk flow 511 , a sufficient amount of fluid is available to support the downstream application of the auxiliary flow 525 (e.g. nozzle 520 cleaning). Furthermore, by limiting the proportion of the auxiliary flow 525 to at most around 10 % of turbine bulk flow 511 the corresponding drop in turbine efficiency is acceptable. Preferably the auxiliary flow 525 is around 1 % to around 2 % of the turbine bulk flow 511, which has been found to result in a relatively small drop in the efficiency of the turbine of around 1 % to 2 %.

It will be appreciated that flow rate of the auxiliary flow 525 will be a function of the geometry of the auxiliary passage 522. This may depend, amongst other things, upon the cross-sectional area of the auxiliary passage 522 and any resistance to flow through the auxiliary passage 522 caused for example by pipe friction due to the length of the auxiliary passage 522 and the presence of bends, elbows, or the like in the auxiliary passage 522.

The energy extracted from the turbine bulk flow 511 by the turbine wheel 504 is used to drive a compressor. Where the auxiliary flow 525 is around 2 % of the turbine bulk flow the fluid leakage through the auxiliary passage 522 is not sufficiently large to provide a wastegating effect that can be used to control the speed of rotation of the turbine wheel 504 prevent over-speed events. Therefore, it will be appreciated that in further embodiments the turbine 500 may additionally comprise a wastegate arrangement, discussed further below.

Figure 9 shows a schematic cross-sectional view of a turbine 600 according to an embodiment of the present invention. The turbine 600 is substantially identical to the turbine 500 of Figure 8 aside from the aspects described below. Like reference numerals have been used to refer to features common to the embodiment of Figure 8 described above.

In the embodiment of Figure 9, the auxiliary passage 622 is defined by a conduit 624 extending from the turbine wheel cavity 612 to the turbine outlet passage 614. The turbine wheel cavity 612 may be considered to define a first position of the turbine 600 and the turbine outlet passage 614 may be considered to define a second position of the turbine 600. The auxiliary passage 622 comprises an auxiliary passage inlet 626 which is defined by a surface 628 of the housing 602 at least partially defining the turbine wheel chamber 612. The turbine wheel 604 is a so-called radial turbine wheel. Although not shown in Figure 9, it will be appreciated that the turbine wheel 604 comprises a plurality of turbine blades defining blade tips. The turbine wheel 604 comprises an inducer 630 configured to receive the turbine bulk flow 611 in a radial direction relative to the turbine axis 608 from the inlet volute 610 and an exducer 632 configured to discharge the turbine bulk flow 611 along the turbine axis 608 in the direction of the turbine outlet passage 614. Accordingly, the turbine blades are shaped so that they comprise a component of curvature in a plane in which the turbine axis 608 lies (i.e. the plane of Figure 9) between the inducer 630 and the exducer 632. The surface 628 of the housing 602 defining auxiliary passage inlet 626 is a surface of the turbine housing 602 facing the blades of the turbine wheel 604 and having a corresponding curvature in the plane in which the turbine axis 608 lies to that of the blades of the turbine wheel 604. The surface 628 comprises an inducer portion 634 defining the part of the turbine wheel cavity 612 containing the inducer 630 of the turbine wheel 604 and an exducer portion 636 containing the exducer 632 of the turbine wheel 604. The auxiliary passage inlet 626 is positioned in the exducer portion of the surface 628 of the turbine housing 602.

During use the turbine wheel 604 will rotate at high rotational velocity about the turbine axis 608. In order to permit the free rotation of the turbine wheel 604 within the turbine wheel cavity 612 the surface 628 of the turbine housing 602 is spaced apart from the blades of the turbine wheel 604 to define a clearance therebetween. During use, the rotation of the turbine wheel 604 imparts a centrifugal force on the exhaust gas in the turbine wheel chamber 612 causing it to be flung radially outwards relative to the turbine axis 608. Unavoidably, due to the clearance some of the exhaust gas will spill over the tips of the blades. The spilled exhaust gas does not impart any force to the turbine blades, and therefore little useful work is extracted from this spilled exhaust gas. Because little energy is extracted from the spilled exhaust gas by the turbine wheel, the spilled exhaust gas is relatively high in energy compared to the exhaust gas which has not spilled over the tips of the blades. Because the auxiliary passage inlet 626 is positioned within the turbine wheel chamber 612, the auxiliary passage 622 is able to harness the energy of the spilled exhaust gas, which would otherwise be wasted, and use this to support a particular application in the turbine outlet passage 614. In the embodiment shown the application is to provide cleaning of the nozzle 620 of the dosing module 618, however other applications of the auxiliary flow 625 may alternatively or additionally be provided as described previously. The pressure of the exhaust gas that is spilled over the tips of the blades is higher at the inducer 630 than at the exducer 632. By locating the auxiliary passage inlet 626 in the inducer portion of the surface 628 of the turbine housing 602, a relatively large amount of fluid can be extracted. However, in alternative embodiments the auxiliary passage inlet 626 may be positioned at substantially any location of the surface 628 of the housing 602 where it is able to capture exhaust gas that has spilled over the tips of the turbine blades, such as for example at the exducer portion 632 as shown in Figure 9. As set out above in relation to Figure 8, preferably the auxiliary flow 625 is around 1 % to around 2 % of the turbine bulk flow 611. However, because energy losses are experienced due to exhaust gas spilling over the tips of the blades, the corresponding drop in efficiency caused by the auxiliary passage 622 is generally less than that of the embodiment of Figure 8. The loss in efficiency can be calculated by the product of the turbine efficiency coefficient and the amount of auxiliary flow. In particular, for an 80 % efficient turbine (having an efficiency coefficient of 0.8) where the auxiliary flow 625 is around 1 % to around 2 % of the turbine bulk flow 611 , the corresponding drop in efficiency will be around 0.8 % to 1.6 %.

Figure 10 shows a cross-sectional view of a turbine 700 according to a further embodiment of the present invention. The turbine 700 is substantially identical to the turbine 500 of Figure 8 aside from the aspects described below. Like reference numerals have been used to refer to features common to the embodiment of Figure 8 described above. The turbine 700 is a so-called “twin volute” turbine having a pair of inlet volutes 710. However, the principles of the invention are not impacted by the number of turbine inlet passage volutes 710, and in alternative embodiments a single inlet volute may be used.

The turbine 700 comprises a wastegate arrangement 726 for controlling the amount of exhaust gas delivered to the turbine wheel 704. The wastegate arrangement 726 comprises a wastegate passage 728 fluidly connecting one of the turbine inlet passage volutes 710 and the turbine outlet passage 714. The wastegate passage 728 may be considered to define an auxiliary passage within the nomenclature of the present invention. The wastegate passage 728 comprises an upstream portion 730, a plenum 732, and a downstream portion 734. The upstream portion 730 fluidly connects one of the turbine inlet passage volutes 710 to the plenum 732, and the downstream portion 734 connects the plenum 732 to the turbine outlet passage 714. The wastegate passage 728 comprises a wastegate passage outlet 735 defined by a side wall 716 of the turbine outlet passage 714. The dosing module 718 is aligned with the wastegate passage outlet 735 such that flow through the wastegate passage 728 passes over the nozzle 720 of the dosing module 718 to clean the nozzle 720 and thereby mitigate deposit formation.

The wastegate arrangement 726 further comprises a wastegate valve assembly 736 positioned within the wastegate plenum 732. A close-up view of the wastegate valve assembly 736 is shown in Figure 11. The wastegate valve assembly 736 comprises a valve member 738 supported for rotation by an actuation rod 740. The valve member 738 comprises a valve plate 742 and a valve plate support 744. The valve plate 742 is connected to the valve plate support 744, and the valve plate support 744 is connected to the actuation rod 740.

The turbine housing 702 defines a valve seat 746 which circumferentially surrounds the upstream portion 730 of the wastegate passage 728 at the interface between the plenum 732 and the upstream portion 730. In the configuration shown in Figure 11 , the valve plate 742 bears against the valve seat 746 to substantially form a seal against the valve seat 746. In this configuration, the valve plate 742 substantially restricts flow from the upstream portion 730 of the wastegate passage 728 to the plenum 732 or the downstream portion 734. During use, rotation of the actuation rod 740 causes a corresponding rotation of the valve plate support 744 and the valve plate 742. This rotation lifts the valve plate 742 out of contact with the valve seat 746 to thereby permit fluid to flow from the upstream portion 730 of the wastegate passage 728 to the plenum 732 and the downstream portion 734. Accordingly, the wastegate valve assembly 736 is configured to selectively open and close the upstream portion 730 of the wastegate passage 728 to thereby permit or substantially restrict flow through the wastegate passage 728.

The valve plate 742 comprises a pair of leakage passages 724. The leakage passages 724 are formed as through holes which extend from a first side of the valve plate 742 to a second side of the valve plate 742 opposite the first side. The first side of the valve plate 742 is in fluid communication with the upstream portion 730 of the wastegate passage 728 and the second side of the valve plate 742 in fluid communication with the plenum 732 of the wastegate passage 728. Accordingly the leakage passages 724 permit fluid flow to flow from the turbine inlet passage 710 to the turbine outlet passage 714 via the wastegate passage 728 even when the wastegate assembly 736 is in the closed configuration shown in Figures 4 and 5. It will be appreciated that the leakage passages 724 therefore define part of the auxiliary passage in the context of the present invention.

The presence of the leakage passages 724 ensures that even when the wastegate assembly 736 is in the closed configuration, some auxiliary flow 735 is permitted to pass through the wastegate passage 728 to support cleaning of the nozzle 720 of the dosing module 718. In alternative embodiments, the auxiliary flow 735 may be used to support an application aside from nozzle cleaning, as previously discussed. The leakage passages 724 are sized so that the proportion of exhaust gas which bleeds through the leakage passages 724 is between at least around 0.1 % and at most around 10 % of the total exhaust gas delivered to the turbine inlet passage by the internal combustion engine, as previously discussed. The turbine inlet passage 710 defines a reference flow area in a plane bisecting the wastegate passage 728 and normal to the direction of the turbine bulk flow in the turbine inlet passage (i.e. in the plane of Figure 10). Preferably, the reference flow area of the turbine inlet passage 710 is approximately at least around 10 to 200 times larger than the combined flow area of the leakage passages 724, and is preferably at least 50 times larger or at least 100 times larger. Accordingly, the difference in size between the reference flow area and the leakage passages 724 ensures that there is always sufficient flow through the wastegate passage 728 to support nozzle cleaning (or another application), whilst also ensuring that in the closed configuration the quantity of auxiliary flow 735 is sufficiently small that the turbine 700 is still able to produce sufficient power to drive the compressor.

In alternative embodiments, the auxiliary passage may be formed by any suitable features of the wastegate valve assembly 736 configured permit a small amount of fluid to bleed through the wastegate passage 728 when the wastegate valve assembly 736 is in the closed configuration. For example, the valve member 742 may comprise a single leakage passage 724 or may comprise three or more leakage passages 724. Additionally or alternatively, with reference to the embodiment of Figure 12, the valve plate support 744 may comprise one or more leakage passages 724’ formed as through holes extending through the valve plate support 744.

Additionally or alternatively, with reference to the embodiment of Figure 13, the valve plate 742 may comprise one or more grooves 748 facing the valve seat 746. The grooves 748 permit fluid to pass from the upstream portion 730 of the wastegate passage 728 to the plenum 732 around the valve plate 742. The grooves may at least partially define leakage passages. Further still, the valve seat 746 may comprise grooves in addition or alternatively to the grooves 748 of the valve plate 742, defining further leakage passages.

With reference to Figure 14, in yet further embodiments, the turbine housing 702 may comprise a through hole 727 extending from the turbine inlet passage 710 to the plenum 732 of the wastegate passage 728 separately to the upstream portion 730 (i.e. the wastegate aperture) of the wastegate passage 728. In this case, the upstream portion 730 of the wastegate aperture 728 may be considered to define a first branch of the auxiliary passage, and the through hole 727 may be considered to define a second branch of the auxiliary passage. The through hole 727 cannot be shut by the wastegate valve member 742, and therefore auxiliary flow 725 is permitted to flow through the auxiliary passage across all operating conditions of the turbine 700.

In further alternatives, the through hole 727 may be a passage that extends from the turbine inlet passage 710 to the turbine outlet passage 714 entirely separately to the wastegate passage 728 (i.e. such that it does not merge with the wastegate passage 728). In such arrangements, the wastegate arrangement 726 may be a conventional wastegate which does not comprise any leak passages, and the passage extending from the turbine inlet passage 710 to the turbine outlet passage 714 separately to the wastegate passage 728 may be considered to define an auxiliary passage according to the present invention.

With reference to Figures 10 and 11, the wastegate arrangement 726 may be incorporated as an integral part of the turbine housing 702. That is to say, the turbine housing 702 may define substantially all of the wastegate passage 728, including the upstream portion 730, plenum 732 and downstream portion 734. It is possible to manufacture such an arrangement for example by using investment casting. However, depending upon the complexity of the wastegate geometry, such arrangements may be complex or expensive to manufacture.

With reference to Figure 15, in a further embodiment the wastegate arrangement 726 may define a wastegate housing 750 which is received within a correspondingly shaped recess 752 of the turbine housing 702. The wastegate housing 750 may be considered to define a valve housing in the nomenclature of the present invention. In such embodiments, the wastegate housing 750 may define, at least in part, the upstream portion 730, plenum 732 and downstream portion 734 of the wastegate passage 728. The wastegate valve assembly 736 may be supported by the wastegate housing 750.

Because the wastegate housing 750 and the turbine housing 702 are separate components, this permits the wastegate housing 750 to be manufactured using different processes to the turbine housing 702. Typically, the turbine housing 702 is cast as a single piece. Given that the size of the required leakage passages are relatively small, it may be difficult or prohibitively expensive to include the leakage passage as cast features within a single integral turbine housing. Furthermore, depending upon the position and configuration of the auxiliary passage, it may be difficult or prohibitively expensive to machine the auxiliary passage into the turbine housing after casting. However, by forming the wastegate housing 750 separately to the turbine housing 702, it is easy machine additional features onto the wastegate housing 750.

Figure 16 shows a cross-sectional view of a turbine 800 according to a further embodiment of the present invention. The turbine 800 is substantially identical to the turbine 500 of Figure 8 aside from the aspects described below. Like reference numerals have been used to refer to features common to the embodiment of Figure 8 described above.

The turbine 800 is a variable geometry turbine and comprises a variable geometry arrangement 828. The variable geometry arrangement 828 is of a so-called “sliding vane” type and comprises a nozzle ring 830 and a shroud plate 832 defining an annular inlet passage 834 therebetween which fluidly connects the turbine inlet passage 810 to the turbine wheel chamber 812. The nozzle ring 830 comprises a plurality of nozzle vanes 836 circumferentially distributed around the turbine axis 808. The shroud plate 832 comprises a plurality of correspondingly shaped apertures 838 configured to receive the nozzle vanes 836. The turbine housing 802 defines an annularly shaped recess 840 within which the shroud plate 832 is received so that the shroud plate does not move relative to the turbine housing 802. The nozzle ring 830 is supported for linear movement parallel to the turbine axis 808. During use, movement of the nozzle ring 830 toward the shroud plate 832 causes the nozzle vanes 836 to be received within the annular recess 840 and the axial width of the annular inlet passage 834 to reduce. In this manner, the velocity and pressure of the exhaust gas delivered to the turbine wheel 804 can be controlled to vary the speed of rotation of the turbine wheel 804 and thus avoid choke and surge events in the compressor.

The turbine housing 802 further comprises an auxiliary passage 822 defined by a conduit 824 which is fluidly connected to the annular recess 840 at an auxiliary passage opening 826 positioned within the recess 840. The annular recess 840 may therefore be considered to define a first position of the turbine 800. The auxiliary passage 822 is fluidly connected to the turbine outlet passage 814. The turbine outlet passage 814 may be considered to define a second location of the turbine downstream of the turbine wheel chamber 812. The dosing module 818 is positioned at the point at which the auxiliary passage 822 joins the turbine outlet passage 814 so that flow through the auxiliary passage 822 passes over the nozzle of the dosing module 818.

During use, high pressure fluid in the turbine inlet passage 810 has a tendency to leak into the annular recess 840 between the sides of the shroud plate 832 and the sides of the annular recess 840. This is due to the presence of a clearance between the recess 840 and the shroud plate 832 to allow the shroud plate 832 to be received by the recess. High pressure fluid is also able to leak into the recess 840 between the nozzle vanes 834 and the apertures 838. Again, this is due to the presence of a clearance between the nozzle vanes 836 and the apertures 838 which is required to enable the nozzle vanes 836 to be received within the apertures 838. The nozzle vanes 836 are typically aerofoil-shaped, and comprise a pressure side and a suction side. During use, due to the presence of the clearances above, exhaust gas passing through the annular inlet passage 834 leaks into the recess 840 on the pressure side of the nozzle vanes 836 and out of the recess 840 on the suction side. The leaked fluid loses some of its internal energy as it leaks, thus meaning that less energy is available for extraction by the turbine.

However, because the auxiliary passage 822 is connected to the recess 840, the leaked fluid can be employed to support a particular application in the turbine outlet passage, such as cleaning the nozzle 820 of the dosing module 818, or substantially any other application as discussed previously above in relation to earlier embodiments.

In alternative embodiments, instead of allowing the nozzle vanes 836 to pass into the recess 840, the shroud plate 832 may comprise a series of pockets having closed ends and configured to receive the nozzle vanes 836 therein. In such embodiments, auxiliary passage may fluidly connect one or more of the shroud plate 832 pockets so as to enable fluid which leaks into the shroud plate 832 pockets to provide cleaning of the nozzle 820 of the dosing module.

Although the turbine wheels 104, 304, 404, 504, 604, 704, 804 disclosed above are radial turbine wheels, it will be appreciated that in alternative embodiments substantially any type of turbine wheel may be used, including axial turbine wheels or mixed-flow turbine wheels.