Field of the Invention [0001] The present invention relates to a bearing unit for turbochargers and a method for manufacturing a bearing unit.

Background Information [0002] Increasingly more vehicles of the more recent generation are equipped with turbochargers. In order to achieve the target demands and the legal requirements, it is imperative to promote development in the complete drive train and also to optimize the individual components as well as the system as a whole with respect to their reliability and efficiency.

[0003] Known turbochargers have a turbine housing, a compressor housing, and a bearing housing which is conventionally connected to the turbine housing on the turbine side and to the compressor housing on the compressor side. A shaft, which supports the turbine wheel and the compressor wheel, is mounted in the bearing housing. The shaft in combination with the turbine wheel is also referred to as a turbocharger stator and is radially and axially mounted in the bearing housing. In current turbochargers, a central radial bearing and an axial bearing located on the compressor side are often provided. This structure has the disadvantage that, due to the axial bearing located on the compressor side, a lot of oil is supplied to this point. Due to this and to the disadvantageous drainage situation in this area, the risk of oil leaks and power losses due to oil churning are increased. During assembly, the individual parts of the so-called shaft aggregate must be individually threaded onto the stator, which was previously inserted into the bearing housing, which complicates automation. Each part located in the shaft aggregate has a large influence on the journal stroke due to its plane parallelism tolerances and its flatness tolerances. Likewise, each part located in the shaft aggregate affects the contour gap in the compressor and turbine, which consequently influences the efficiency of the turbine and compressor. [0004] The object of the present invention is to provide a bearing unit for a turbocharger that reduces or alleviates the previously described disadvantages.

Brief Summary of the Invention

[0005] The present invention relates to a bearing unit according to Claim 1 and a method for producing a bearing unit according to Claim 13.

[0006] The bearing unit according to the invention has a two-part, cylindrical bearing cartridge which is suitable for arrangement in a bearing housing and comprises one first component, one second component, and a bearing element, wherein the bearing element has at least one axial bearing surface. The bearing element is surrounded at least partially by the bearing cartridge both radially and also axially. It is advantageous in this type of bearing unit that it has few components and is very compactly structured. In addition, it provides an improved oil drainage behavior and reduces the risk of oil leaks because the sealing parts are unloaded. Because the bearing cartridge may be pre-assembled, the assembly is faster and automatable. Additional advantages include: a wider radial bearing spacing and short overhangs, reduction of friction losses and churning losses in the bearing housing, reduction of the journal stroke, and a variable spacing between turbine-side and compressor-side axial bearing points.

[0007] In embodiments, the bearing unit may additionally comprise a bearing housing in which the bearing cartridge is arranged.

[0008] In embodiments which are combinable with all previously described embodiments, the bearing cartridge may have functional surfaces for both the radial bearing and for the axial bearing. In particular, the bearing cartridge may comprise first and second axial bearing surfaces and first and second radial bearing surfaces.

[0009] In embodiments which are combinable with all previously described embodiments, the bearing unit is designed in such a way that the bearing cartridge, with the bearing element, may be inserted into a bearing housing as a pre-assembled unit.

[0010] In embodiments which are combinable with all previously described embodiments, the first component of the bearing cartridge may have one first radial bearing surface and one first axial bearing surface, and the second component of the bearing cartridge may have one second radial bearing surface and one second axial bearing surface. The first and second components may have respective channels which discharge in the area of the respective axial bearing surface and/or in the area of the respective radial bearing surface. The channels may be arranged in the first and second components of the cartridge in such a way that they may transport a fluid from radially and/or axially outside of the bearing cartridge to the radial bearing surfaces and/or to the axial bearing surfaces. [0011] In embodiments which are combinable with all previously described embodiments, the bearing element may have a central through passage to accommodate the turbocharger stator.

[0012] In embodiments, which are combinable with all previously described embodiments, the first component or the second component may have a collar. In particular, the collar may at least partially surround the respectively other of the first and second components in the radial direction. The collar may at least partially radially surround the bearing element. [0013] In embodiments which are combinable with all previously described embodiments, bearing pads may be arranged on the first axial bearing surface of the first component and/or on the second axial bearing surface of the second component. [0014] In embodiments which are combinable with all previously described embodiments, the bearing element may have one third and one fourth axial bearing surface on correspondingly oppositely aligned lateral surfaces of the bearing element. Bearing pads may be arranged on at least one of the third and fourth axial bearing surfaces of the bearing element. The third axial bearing surface may be arranged opposite the first axial bearing surface of the first component, and the fourth axial bearing surface may be arranged opposite the second axial bearing surface of the second component.

[0015] In embodiments which are combinable with all previously described embodiments, the cartridge may comprise a geometric element which connects the cartridge rotationally fixed to a bearing housing. The geometric element may be provided as an anti-rotation means to connect the bearing cartridge rotationally fixed to the bearing housing and to position it axially. In particular, the collar may have at least one recess which, together with a pin, is suited for connecting the bearing cartridge rotationally fixed to the bearing housing and to position it axially. Alternatively, for example, a holding plate may be provided as an anti- rotational means. These types of elements have the advantage that they are used simultaneously as anti-rotation means and for an axial positioning of the cartridge in the bearing housing.

[0016] In embodiments which are combinable with all previously described embodiments, the bearing element may be designed to be connected rotationally fixed to the turbocharger stator.

[0017] In embodiments which are combinable with all previously described embodiments, the bearing element may have a shoulder on an inner through passage, the shoulder being designed to interact with a shoulder of a turbocharger stator so that the axial positioning of the bearing element on the turbocharger stator is fixed. Alternatively, a radial lateral surface of the bearing element, in particular one of the surfaces which is also used at least partially as an axial bearing surface, may be designed to abut against a shoulder of a turbocharger stator, by which means an axial position of the bearing element on the turbocharger stator may be fixed.

[0018] In embodiments which are combinable with all previously described embodiments, an inner diameter of one axial end of the collar of the second component may be designed as step-shaped in order to interact with a correspondingly step-shaped circumferential surface of the first component in order to form a centering and a stop. [0019] In embodiments which are combinable with all previously described embodiments, the bearing element may be designed as ring-shaped. In particular, the bearing element may be designed as a double ring shape. The bearing element may be arranged completely within the bearing cartridge. Alternatively, the bearing element may be designed in the form of a cylindrical bush. The bearing element may have at least one first annular extension extending radially outward on which at least one of the third and fourth axial bearing surfaces is arranged. The third and the fourth axial bearing surfaces may be provided on opposite lateral surfaces of the first annular extension. Alternatively, the bearing element may have one second annular extension extending radially outward and the third axial bearing surface may then be provided on the first annular extension and the fourth axial bearing surface may be arranged on the second annular extension. The two annular extensions may be arranged spaced apart from one another with respect to a longitudinal axis of the cylindrical bush. The third and fourth axial bearing surfaces may be arranged on radial surfaces facing away from one another of the annular extensions of the bearing element. The third axial bearing surface may be arranged opposite the first axial bearing surface of the first component, and the fourth axial bearing surface may be arranged opposite the second axial bearing surface of the second component. [0020] The bearing element in cylindrical shape may have third and fourth radial bearing surfaces on its circumferential surface, wherein in each case on of the third and fourth radial bearing surfaces is arranged respectively opposite one of the first and second radial bearing surfaces of the first and second components. This type of embodiment is advantageous because the bearing element, together with the cartridge, combines both the axial bearing and also the radial bearing in a compact way. [0021] In a cylindrical embodiment of the bearing element, at least one oil slinger may be arranged on the circumference of the bearing element. The oil slinger may be arranged axially outside of the bearing cartridge, in particular on the compressor side axially in front of the bearing cartridge. The bearing element may additionally have a compressor-side core assembly seal, in particular in the form of at least one annular piston groove. The cylindrical bearing element may be designed as one piece.

[0022] The invention further comprises a method for producing a bearing unit for a turbocharger. The method comprises the following steps: producing one first component and one second component of a two-part cylindrical bearing cartridge which is suitable for arrangement in a bearing housing; introducing at least one part of a bearing element having at least one axial bearing surface between the first component and the second component, and assembling the first and second components so that the part of the bearing element with the axial bearing surface is surrounded both radially and axially by the bearing cartridge.

[0023] In embodiments, the first and second components may be coherently connected to one another during the assembly by means of a fitting connection, fitting dowel, clamping pin, fitting bolt, screw connection, clamping connection, or weld connection.

[0024] In embodiments of the method which are combinable with all previously described embodiments, the first component may be arranged in a bearing housing prior to the introduction of the bearing element, then a turbocharger stator may be pushed through the first component, and subsequently the bearing element may be mounted on the turbocharger stator, before the second component is assembled with the first component. Alternatively, the method may comprise: inserting the assembled bearing cartridge into a bearing housing and pushing a turbocharger stator through a central through passage of the bearing element into the assembled bearing cartridge. In embodiments, the bearing element may be fixed on the turbocharger stator by means of press-fitting or screwing. A compressor wheel may be arranged on the turbocharger stator and the compressor wheel, together with the bearing element, may be fastened rotationally fixed on the turbocharger stator by means of a shaft nut. The bearing element is thus clamped between the compressor wheel, and, for example, a shoulder on the stator.

[0025] In embodiments of the method which are combinable with all previously described embodiments, the method may additionally comprise: after producing the first and second components of the bearing cartridge and before introducing the bearing elements between the first component and the second component: provisionally assembling the first and second components of the bearing cartridge; post-processing of the inner and/or the outer diameter of the bearing cartridge; and disassembling the first and the second components. Alternatively, the method in embodiments may comprise: post-processing of the inner and/or the outer diameter of the bearing cartridge after the assembly of the first and second components and prior to the insertion into a bearing housing.

[0026] Additional details and features of the invention are described by way of the following figures.

Brief Description of the Drawings

Figure 1 shows a sectional view of the bearing unit according to the invention according to one first embodiment;

Figure 2 shows perspective views of the components of the bearing unit from the embodiment from Figure 1;

Figure 3 shows a sectional view of the bearing unit according to the invention according to one second embodiment; Figure 4 shows perspective views of the components of the bearing unit from the embodiment from Figure 3. Detailed Description of the Invention

[0027] Embodiments of the bearing unit according to the invention for a turbocharger stator will subsequently be described based on the figures. In addition, the method according to the invention for producing a bearing unit for a turbocharger will be described in greater detail.

[0028] Figure 1 through Figure 4 show two embodiments of the bearing unit according to the invention. The generally common elements of the two embodiments are described together. Differences between the two embodiments are contrasted and described directly by way of the figures.

[0029] In Figure 1 through Figure 4, the two exemplary embodiments of bearing unit 10 or 20 are depicted, which have a two-part, cylindrical bearing cartridge 110, 210, which is suitable for arrangement in a bearing housing, and comprises one first component 112, 212 and one second component 114, 214 respectively. Bearing unit 10, 20 additionally comprises a bearing element 120, 220, wherein bearing element 120, 220 has at least one axial bearing surface. Bearing element 120, 220 is completely surrounded, in the embodiment from Figure 1 and Figure 2, and at least partially surrounded, in the embodiment from Figure 3 and Figure 4, both radially and also axially by bearing cartridge 110, 210. In particular, the part of bearing element 120, 220 that has the axial bearing surface is surrounded in the two embodiments both radially and also axially by bearing cartridge 110, 210. It is advantageous in this type of bearing unit 10, 20 that it has few components and is very compactly structured. The few components also contribute to a reduction of changes due to imbalance caused by, for example, the skewed position of individual elements. In addition, bearing unit 10, 20 according to the invention provides an improved oil drainage behavior and reduces the risk of oil leakage because the sealing parts are unloaded. This is achieved because the lubricating oil may be uniformly distributed to all bearing points and may be subsequently centrally discharged via an oil drain in the bearing housing. Due to suitable geometries in the bearing housing and in the bearing cartridge, the rotational energy of the shaft may displace the draining oil into a vortex to convey it into the oil drain in a targeted way. A build up of oil, and the risk of oil leakage connected thereto, may thus be counteracted.

[0030] The assembly is faster and automatable because the bearing cartridge may be pre-assembled. Additional advantages include, for example, a wider radial bearing spacing and short overhangs (stabilizing effect), reduction of friction losses and churning losses in the bearing housing, reduction of the journal stroke, and a variable spacing between turbine-side and compressor-side axial bearing points. Furthermore, the gap which is formed between bearing unit 10, 20 or stationary cartridge 110, 210 of bearing unit 10, 20 and the bearing housing, may be designed such that this functions as a squeeze oil damping.

[0031] Bearing element 120, 220 has a central through passage to accommodate turbocharger stator 130, 230, see for example Figure 1 and Figure 3, in which bearing unit 10, 20 is depicted with turbocharger stator 130, 230 arranged therein. The components of bearing cartridge 110, 210 have functional surfaces both for radial bearing and also for axial bearing. In particular, bearing cartridges 1 10, 210 have first and second axial bearing surfaces and first and second radial bearing surfaces. Cartridge 110, 220 of bearing unit 10, 20 is arranged in a bearing housing (not shown in the figures). In particular, bearing unit 10, 20 is designed in such a way that bearing cartridge 110, 210, with bearing element 120, 220, may be inserted into a bearing housing as a pre-assembled unit.

[0032] In order to combine both the axial bearing and the radial bearing into a compact bearing unit 10, 20, the first components 112, 212 of bearing cartridge 110, 210 respectively have one first radial bearing surface and one first axial bearing surface, and the second components 114, 214 of bearing cartridge 110, 210 respectively have one second radial bearing surface and one second axial bearing surface. The first and second radial bearing surfaces of the bearing cartridge components are inner radial bearing surfaces which are arranged opposite the corresponding rotating radial bearing surfaces. The bearing cartridge components may additionally also have an outer radial bearing surface. During operation of the turbocharger, an oil coating forms between bearing cartridge 110, 220 and the bearing housing in the area of the outer radial bearing surfaces, by which means the squeeze oil damping mentioned at the outset occurs between bearing cartridge 110, 210 and the bearing housing. [0033] First and second components 112, 114, 212, 214 respectively have channels which discharge in the area of the respective axial bearing surface and/or in the area of the respective radial bearing surface. The channels are arranged in first and second components 112, 114, 212, 214 of bearing cartridge 110, 210 in such a way that they may transport a fluid from radially and/or axially outside of bearing cartridge 110, 210 to the radial bearing surfaces and/or the axial bearing surfaces to ensure a sufficient lubrication of the axial and radial bearings.

[0034] In the embodiment from Figure 3 and Figure 4, first component 212 has a collar 216, and in the embodiment from Figure 1 and Figure 2, second component 114 has a collar 116. Collar 116, 216 surrounds the respective other of the components (thus, in the first case second component 214, and in the second case first component 112) at least partially in the radial direction. In the embodiment from Figure 3 and Figure 4, collar 216 virtually completely surrounds component 214 radially. Collar 216 also radially surrounds at least the part of bearing element 220 on which the axial bearing surfaces are arranged. In the embodiment from Figure 1 and Figure 2, collar 116 surrounds only one part of component 112. In this case, collar 116 additionally completely surrounds bearing element 220.

[0035] To improve the performance of the axial bearings, so-called bearing pads 122 may be provided on the bearing surfaces. These are depicted, for example, in Figure 2 on the axial bearing surfaces of bearing element 120. According to the embodiment of the combination made from bearing element and bearing cartridge, bearing pads 122 may be arranged on the first axial bearing surface of first component 112, 212 and/or on the second axial bearing surface of second component 114, 214. Bearing pads are then correspondingly provided on the bearing elements. All combinations may be considered here, so that bearing pads 122 are always arranged on one of two oppositely arranged axial bearing surfaces. Thus, bearing element 120, 220 has one third and one fourth axial bearing surface which are arranged on correspondingly oppositely aligned lateral surfaces of bearing element 120, 220. The two axial bearing surfaces of bearing element 120, 220 interact with the two axial bearing surfaces of bearing cartridge 110, 210 and thus form the axial bearing for the turbocharger stator. In Figure 1 through Figure 4, the third axial bearing surface is arranged opposite the first axial bearing surface of first component 112, 212, and the fourth axial bearing surface is arranged opposite the second axial bearing surface of second component 114, 214. The bearing pads may thus be arranged either on the two axial bearing surfaces of the first and second components of bearing cartridge 110, 210, or on the two axial bearing surfaces of the bearing element, or respectively on one axial bearing surface of one of the components and on the corresponding axial bearing surface of bearing element 120, 220. The bearing pads are preferably arranged on the non- rotating components, thus the axial bearing surfaces of the first and second components of bearing cartridge 110, 210, and therefore no bearing pads are provided on bearing element 120, 220.

[0036] To connect cartridge 110, 210 rotationally fixed to the bearing housing, cartridge 110, 210 may comprise a geometric element. The geometric element may be configured as an anti -rotational means. In Figure 2 and Figure 4, embodiments are shown in which collar 116, 216 has at least one recess which, together with a pin, is suited for connecting bearing cartridge 110, 210 rotationally fixed to the bearing housing. Alternatively, for example, a holding plate may also be provided as an anti -rotational means. These types of elements, regardless of whether a recess-pin combination or holding plate, have the advantage that they are used not only as an anti -rotational means, but also simultaneously for an axial positioning of the cartridge in the bearing housing.

[0037] Bearing element 120, 220 may be designed to be connected rotationally fixed to the turbocharger stator. For example, the bearing element may be pressed on, clamped on, or screwed on. Thus, bearing element 120 from Figure 1 and Figure 2 is screwed onto the stator via a corresponding thread. In the embodiment from Figure 3 and Figure 4, the bearing element may be clamped on the turbocharger stator, for example, as an aggregate with a compressor wheel and by means of a shaft nut (neither is shown in the figures).

[0038] Bearing unit 10, 20 additionally has a device for the axial positioning of bearing element 120, 220. Thus, a radial lateral surface of bearing element 120, 220, in particular one of the surfaces which is also used at least partially as an axial bearing surface in the embodiment from Figure 1 and Figure 2, is designed to abut against a shoulder of a turbocharger stator 130, 230, by which means an axial position of bearing element 120, 220 on turbocharger stator 130, 230 may be fixed. In the case of an axial positioning of the bearing element, as this is shown for the embodiment from Figure 1, if bearing pads are provided on the bearing element, then these would not extend across the entire lateral surface, as shown in Figure 2, but instead only over the part which functions as the axial bearing surface, and a radially inward part of the lateral surfaces would remain free in order to function as a contact surface for the axial positioning. Alternatively, it may also be provided that the bearing element has a shoulder on the inner through passage, the shoulder being designed to interact with a shoulder of the turbocharger stator so that the axial positioning of the bearing element on the turbocharger stator is fixed.

[0039] In the embodiment from Figure 1 and Figure 2, an inner diameter of one axial end of collar 116 of second component 114 is configured as step-shaped in order to interact with a correspondingly step-shaped circumferential surface of first component 112. In addition, a centering and a stop are formed for the assembly of two cartridge components 112, 114. The step-shaped part has a smaller shoulder which functions as the centering. The larger shoulder functions for fixing first and second components 112, 114 on one another, for example, by means of screwing, shrinking, gluing, or other known fixing methods. A larger radial shoulder functions as a stop, which in turn is used for the axial positioning and via which the torque may also be transmitted. [0040] In the embodiment from Figure 3 and Figure 4, a radial shoulder for axial positioning of the bush and an axial shoulder for radial centering of the two bearing cartridge components to one another are provided. [0041] In the embodiment from Figure 1 and Figure 2, bearing element 120 is configured as ring shaped. In particular, bearing element 120 is configured as double ring shaped, with one area with a smaller diameter between two annular sections with larger diameters (see Figure 2). Alternatively, however, an annular bearing element with a constant diameter may be provided. The form of bearing element 120 depicted in Figure 2 is advantageous because a targeted flexibility or pliability of the lateral walls with the axial bearing surfaces may be generated by the section with the reduced diameter. This increases the load capacity. As already mentioned above, bearing element 120 of the embodiment from Figure 1 and Figure 2 is arranged completely within bearing cartridge 110, which means that bearing element 120 is completely surrounded by bearing cartridge 110 in both the radial direction and also in the axial direction.

[0042] Figure 3 and Figure 4 show an alternative embodiment for bearing element 220 in the form of a cylindrical bush. Bearing element 220 then has at least one first annular extension extending radially outward on which at least one of the third and fourth axial bearing surfaces is arranged. In the embodiment from Figure 3 and Figure 4, bearing element 220 has first and second annular extensions 222, 224. Two annular extensions 222, 224 are arranged spaced apart from one another with respect to a longitudinal axis of the cylindrical bush. The third and fourth axial bearing surfaces are provided on radial surfaces facing away from one another of annular extensions 222, 224 of bearing element 220. The third axial bearing surface is provided on first annular extension 222 and the fourth axial bearing surface is arranged on second annular extension 224. In the assembled state of bearing unit 20, the third axial bearing surface is arranged opposite the first axial bearing surface of first component 212, and the fourth axial bearing surface is arranged opposite the second axial bearing surface of second component 214. In an alternative embodiment with only one annular extension, the third and the fourth axial bearing surfaces are provided on opposite lateral surfaces of the one annular extension.

[0043] With further reference to Figure 3 and Figure 4, bearing element 220 in cylindrical shape has third and fourth radial bearing surfaces 226, 228 on its circumferential surface. Each of third and fourth radial bearing surfaces 226, 228 is arranged opposite one of the first and second radial bearing surfaces of first and second components 212, 214. This type of embodiment is advantageous because the bearing element, together with the cartridge, combines both the axial bearing and also the radial bearing in a compact way. Therefore, in bearing unit 20, bearing element 220 is guided within cartridge 210 by annular extension(s) 222, 224 with the axial bearing surfaces, by which means the axial bearing of turbocharger stator 230 is realized. At the same time, cartridge 210, together with bearing element 220, also realizes the radial bearing for turbocharger stator 230 in this case. In the embodiment from Figure 1 and Figure 2, the radial bearing surfaces of cartridge 110 for the radial bearing interact directly with corresponding radial bearing surfaces on turbocharger stator 130.

[0044] Oil slinger 240, shown in Figure 3, represents an optional feature, and is arranged on the circumference of bearing element 220 in the cylindrical embodiment of bearing element 220. Oil slinger 240 is arranged axially outside of bearing cartridge 210, in the example shown, in particular on the compressor side axially in front of bearing cartridge 210. Bearing element 220 additionally has a optional compressor-side core assembly seal 250 (see Figure 3 or Figure 4), in particular in the form of at least one annular piston groove. For example, two annular piston grooves may be provided as shown in Figure 3 and Figure 4. Cylindrical bearing element 220 may be designed as one piece. This is likewise shown in Figure 3 and Figure 4. A one-piece bearing element 220 is advantageous for the axial positioning of the components on turbocharger stator 230, for example, the axial positioning of the compressor wheel on turbocharger stator 230. [0045] In the following, methods will be described as to how bearing unit 10, 20 according to the invention may be produced. Initially, in general, first components 112, 212 and second components 114, 214 must be produced for two-part, cylindrical bearing cartridge 110, 210 which is suitable for arrangement in a bearing housing. In one first potential for production, first component 112, 212 is arranged in a bearing housing, then a turbocharger stator 130, 230 is pushed through first component 112, 212, and subsequently bearing element 120, 220 is mounted on turbocharger stator 130, 230. Bearing element 120, 220 may be, for example, screwed onto turbocharger stator 130, 230. However, any other fixing type, which enables a rotationally fixed fastening, may be provided, for example, press fitting or clamping (see above with reference to Figure 3 and Figure 4). Subsequently, first component 112, 212 and second component 114, 214 are assembled in the bearing housing. Afterwards, at least the part of bearing element 120, 220 with the axial bearing surfaces is arranged between first component 112, 212 and second component 114, 214 and surrounded radially and also axially by bearing cartridge 110, 210. As was already described above, in the embodiment from Figure 1 and Figure 2, the complete bearing element 120 is surrounded radially and axially by bearing cartridge 110, thus is arranged completely within the interior of bearing cartridge 110.

[0046] First and second components 112, 212, 114, 214 of bearing cartridge 110, 210 may be coherently connected to one another during the assembly by means of a fitting connection, fitting dowel, clamping pin, fitting bolt, screw connection, clamping connection, or weld connection.

[0047] In one alternative potential assembly, bearing element 120, 220 is arranged (at least partially with regard to the embodiment from Figure 3 and Figure 4) between two components 112, 212, 114, 214 and then the cartridge components are assembled. Subsequently, the assembled bearing cartridge 110, 210 is inserted into the bearing housing, and turbocharger stator 130, 230 is pushed through the central through passage of bearing element 210, 220 into assembled bearing cartridge 110, 210. [0048] A compressor wheel may additionally be arranged on turbocharger stator 130, 230 so that the compressor wheel, together with bearing element 220, may be fastened rotationally fixed to turbocharger stator 230 by means of a shaft nut. Bearing element 220 is thereby clamped on turbocharger stator 230 between the compressor wheel and, for example, a shoulder (see Figure 3).

[0049] In embodiments, the method may additionally comprise the following steps: after producing first and second components 112, 212, 114, 214 of bearing cartridge 110, 210 and prior to introducing bearing element 120, 220 between first components 112, 212 and second components 114, 214, first and second components 112, 212, 114, 214 of bearing cartridge 110, 210 may be provisionally assembled. Then, a post-processing of the inner and/or outer diameter of bearing cartridge 110, 210 is carried out and the subsequent disassembly of the first and second components. Alternatively, the method may also provide a post-processing of the inner and/or outer diameter of bearing cartridge 110, 210 after the assembly of first and second components 112, 212, 114, 214 with bearing element 120, 220 arranged (at least partially) therebetween and prior to the insertion of assembled bearing cartridge 110, 210 into a bearing housing. Due to this potential for additional processing of the cartridge, the maintenance of low tolerances and the centering may be optimized.

[0050] Although the present invention has been described above and is defined in the attached claims, it should be understood that the invention may also be alternatively defined according to the following embodiments:

A bearing unit (10; 20) for a turbocharger stator (130; 230) comprising a two-part, cylindrical bearing cartridge (110; 210), which is suitable for arrangement in a bearing housing and has one first component (112; 212) and one second component (114; 214); and

a bearing element (120; 220), wherein the bearing element (120; 220) has at least one axial bearing surface,

characterized in that the bearing element (120; 220) is at least partially surrounded both radially and also axially by the bearing cartridge (110; 210).

The bearing unit according to Embodiment 1, characterized in that the bearing unit (10; 20) additionally comprises a bearing housing in which the bearing cartridge (110; 210) is arranged.

The bearing unit according to Embodiment 1 or Embodiment 2, characterized in that the bearing cartridge (110; 210) has functional surfaces both for radial bearing and also for axial bearing, in particular wherein the bearing cartridge (110; 210) comprises first and second axial bearing surfaces and first and second radial bearing surfaces.

The bearing unit according to any one of the preceding embodiments, characterized in that the bearing unit (10; 20) is configured in such a way that the bearing cartridge (110; 210), with the bearing element (120; 220), can be introduced into a bearing housing as a pre-assembled unit.

The bearing unit according to any one of the preceding embodiments, characterized in that the first component (112; 212) of the bearing cartridge (110; 210) has one first radial bearing surface and one first axial bearing surface, and the second component (1 14; 214) of the bearing cartridge (110; 210) has one second radial bearing surface and one second axial bearing surface.

The bearing unit according to Embodiment 5, characterized in that the first and second components (112, 114; 212, 214) each have channels that discharge in the area of the respective axial bearing surface and/or in the area of the respective radial bearing surface.

The bearing unit according to Embodiment 6, characterized in that the channels in the first and second components (112, 114; 212, 214) of the bearing cartridge (110; 210) are arranged in such a way that they can transport a fluid from radially and/or axially outside of the bearing cartridge (110; 210) to the radial bearing surfaces and/or to the axial bearing surfaces.

The bearing unit according to any one of the preceding embodiments, characterized in that the cartridge (110; 210) comprises a geometric element which connects the cartridge (110; 210) rotationally fixed to a bearing housing.

The bearing unit according to any one of the preceding embodiments, characterized in that the first component or the second component (114; 212) has a collar (116; 216), in particular wherein the collar (116; 216) at least partially surrounds the respectively other of the first and second components (112; 214) in the radial direction.

The bearing unit according to Embodiment 9, characterized in that the collar (116; 216) at least partially surrounds the bearing element (120; 220) in the radial direction.

The bearing unit according to any one of Embodiments 5 through 10, characterized in that bearing pads (122) are arranged on the first axial bearing surface of the first component (112; 212) and/or on the second axial bearing surface of the second component (114; 214).

The bearing unit according to any one of the preceding embodiments, characterized in that the bearing element (120; 220) has one third and one fourth axial bearing surface on correspondingly oppositely oriented lateral surfaces of the bearing element (120; 220).

The bearing unit according to Embodiment 12, characterized in that bearing pads (122) are arranged on at least one of the third and fourth axial bearing surfaces of the bearing element (120; 220).

The bearing unit according to Embodiment 12 or Embodiment 13, characterized in that the third axial bearing surface is arranged opposite the first axial bearing surface of the first component (112; 212), and the fourth axial bearing surface is arranged opposite the second axial bearing surface of the second component (114; 214).

The bearing unit according to any one of Embodiments 9 through 14, characterized in that at least one anti-rotation means is provided to connect the bearing cartridge (110; 210) rotationally fixed to a bearing housing and to axially position the bearing cartridge, in particular wherein the collar (116; 216) has at least one recess which, together with a pin, is suitable for connecting the bearing cartridge (110; 210) rotationally fixed to a bearing housing and axially positioning the bearing cartridge, or wherein a holding plate is provided as an anti -rotational means.

The bearing unit according to any one of the preceding embodiments, characterized in that the bearing element is designed to be connected rotationally fixed to the turbocharger stator (130; 230).

The bearing unit according to any one of the preceding embodiments, characterized in that the bearing element (120; 220) has a shoulder on an inner through passage which is designed to interact with a shoulder of a turbocharger stator (130; 230).

The bearing unit according to any one of the preceding embodiments, characterized in that a radial lateral surface of the bearing element (120; 220), in particular one of the axial bearing surfaces, is designed to abut a shoulder of a turbocharger stator (130; 230), by which means an axial position of the bearing element (120; 220) on the turbocharger stator (130; 230) can be fixed.

The bearing unit according to any one of Embodiments 9 through 18, characterized in that an inner diameter of one axial end of the collar (116) of the second component (114) is configured as step-shaped to interact with a correspondingly step-shaped circumferential surface of the first component (112) to form a centering and a stop.

The bearing unit according to any one of the preceding embodiments, characterized in that the bearing element (120) is configured to be ring shaped, in particular wherein the bearing element (120) is configured to be double ring shaped.

The bearing unit according to Embodiment 20, characterized in that the bearing element is arranged completely inside of the bearing cartridge (110).

The bearing unit according to any one of Embodiments 1 through 19, characterized in that the bearing element (220) is configured in the form of a cylindrical bush.

The bearing unit according to Embodiment 22, characterized in that the bearing element (220) has at least one first annular extension (222, 224) extending radially outward on which at least one of the third and fourth axial bearing surfaces is arranged. The bearing unit according to Embodiment 23, characterized in that the third and the fourth axial bearing surface are provided on the opposite lateral surfaces of the first annular extension, or

that the bearing element (220) has one second annular extension (224) extending radially outward and the third axial bearing surface is provided on the first annular extension (222) and the fourth axial bearing surface is arranged on the second annular extension (224).

The bearing unit according to Embodiment 24, characterized in that the two annular extensions (222, 224) are arranged spaced apart from one another with respect to a longitudinal axis of the cylindrical bush, and wherein the third and fourth axial bearing surfaces are arranged on radial surfaces facing away from one another of the annular extensions (222, 224) of the bearing element (220).

The bearing unit according to Embodiment 25, characterized in that the third axial bearing surface is arranged opposite the first axial bearing surface of the first component (212), and the fourth axial bearing surface is arranged opposite the second axial bearing surface of the second component (214).

The bearing unit according to any one of Embodiments 22 through 26, characterized in that the bearing element (220) has third and fourth radial bearing surfaces (226, 228) on its circumferential surface, wherein one of the third and fourth radial bearing surfaces respectively is arranged opposite one of the first and second radial bearing surfaces respectively of the first and second components (212, 214). 28. The bearing unit according to any one of the preceding embodiments, characterized in that the bearing element (220) has a central through passage to accommodate the turbocharger stator (230). The bearing unit according to any one of Embodiments 22 through 28, characterized in that at least one oil slinger (240) is arranged on the circumference of the bearing element (220), in particular wherein the oil slinger is arranged axially outside of the bearing cartridge (210), in particular on the compressor side axially in front of the bearing cartridge (210).

The bearing unit according to any one of Embodiments 22 through 29, characterized in that the bearing element (220) additionally has a compressor side core assembly seal (250), in particular in the form of at least one annular piston groove.

The bearing unit according to any one of Embodiments 22 through 30, characterized in that the bearing element (220) is formed as one piece.

A method for producing a bearing unit for a turbocharger comprising: producing one first component (112; 212) and one second component (114; 214) of a two-part, cylindrical bearing cartridge (110; 210) which is suitable for arrangement in a bearing housing;

introducing at least one part of a bearing element (120; 220) with at least one axial bearing surface between the first component (112; 212) and the second component (114; 214);

assembling the first and second components (112, 114; 212, 214) so that the part of the bearing element (120, 220) with the axial bearing surface is surrounded both radially and also axially by the bearing cartridge (110; 210).

The method according to Embodiment 32, characterized in that the first and second components (112, 212; 114, 214) may be coherently connected to one another during the assembly by means of a fitting connection, fitting dowel, clamping pin, fitting bolt, screw connection, clamping connection, or weld connection. The method according to Embodiment 32 or Embodiment 33, characterized in that, prior to the introduction of the bearing element (120; 220), the first component (112; 212) is arranged in a bearing housing, then a turbocharger stator (130; 230) is pushed through the first component (112; 212), and subsequently the bearing element (120; 220) is mounted on the turbocharger stator (130; 230), before the second component (114; 214) is assembled with the first component (112; 212).

The method according to Embodiment 32 or Embodiment 33, characterized in that the method additionally comprises:

inserting the bearing cartridge (110; 210) into a bearing housing; and pushing a turbocharger stator (130; 230) through a central through passage of the bearing element (120; 220) into the assembled bearing cartridge (110; 210).

The method according to Embodiment 34 or Embodiment 35, characterized in that the bearing element (120) is fixed on the turbocharger stator (130) by means of press-fitting or screwing.

The method according to any one of Embodiments 34 through 36, characterized in that a compressor wheel is arranged on the turbocharger stator (230) and the compressor wheel is fixed, together with the bearing element (220), on the turbocharger stator (230) by means of a shaft nut.

The method according to any one of Embodiments 32 through 37, additionally comprising:

after the production of the first and second components (112, 212; 114, 214) of the bearing cartridge (110; 210) and prior to the introduction of the bearing element (120; 220) between the first component (112; 212) and the second component (114; 214):

provisionally assembling the first and second components (112, 212; 114, 214) of the bearing cartridge (110; 210); post-processing of the inner and/or outer diameter of the bearing cartridge (110; 210); and

disassembling the first and second components.

The method according to any one of Embodiments 32 through 37, additionally comprising:

post-processing the inner and/or the outer diameter of the bearing cartridge (110; 210) after the assembly of the first and second components (112, 114; 212, 214) and prior to the insertion into a bearing housing.