Technical field of the invention

The present invention concerns a bearing housing for a cooling liquid pump of an internal combustion engine, as defined in the preamble of claim 1. The invention also concerns a cooling liquid pump for a cooling system of an internal combustion engine, as defined in the preamble of another independent claim. The invention further concerns a cooling system for an internal combustion engine, as defined in a further claim.

Background of the invention

Large internal combustion engines, such as ship or power plant engines, are provided with liquid cooling systems. A typical cooling system comprises a high temperature (HT) circuit and a low temperature (LT) circuit. The two circuits may be separated from each other or part of the cooling liquid flowing in one of the cooling circuits may be introduced into the other circuit to control the temperatures in the HT circuit and the LT circuit.

The HT circuit is typically used for controlling the temperature of the cylinder liners and the cylinder heads. Depending on the application, the HT circuit may also be connected to a high -temperature part of a double-stage charge air cooler. The LT circuit typically serves at least part of one or more charge air coolers and a lube oil cooler

Temperature in the HT circuit is, depending on the engine type, typically around 70-102 °C and in the LT circuit 38-60 °C. A relatively high temperature in the HT circuit is desirable for ensuring safe ignition and combustion of low- quality heavy fuels also at low loads, for minimizing temperature fluctuations in the components of the cylinders and for preventing corrosion that can be caused by excessive cooling. Therefore, there is a need to control the temperature in the HT circuit.

Summary of the invention

An object of the present invention is to provide a bearing housing for a cooling liquid pump of the bearing housing. The characterizing features of the bearing housing according to the invention are given in the characterizing part of claim 1. Another object of the invention is to provide an improved cooling liquid pump for a cooling system of an internal combustion engine. The characterizing features of the cooling liquid pump according to the invention are given in the characterizing part of another independent claim. A further object of the invention is to provide a cooling system for an internal combustion engine, as defined in a further claim.

The bearing housing according to the invention is configured to receive a first bearing and a second bearing for supporting a shaft of the cooling liquid pump, the bearing housing comprising a first inlet for receiving cooling liquid to be pressurized and for supplying the cooling liquid further to an impeller of the cooling liquid pump. The bearing housing further comprises a second inlet, and the first inlet and the second inlet merge into a common inlet chamber for supplying the cooling liquid received via the first and second inlets to said impeller of the pump.

The bearing housing according to the invention allows mixing two fluid flows in the bearing housing. This allows efficient utilization of space and reduces the number of components in a cooling system. The bearing housing can be utilized for mixing two cooling liquid flows that are at different temperatures. This allows controlling the temperature of the cooling liquid flow leaving a cooling liquid pump. The construction also allows axial feeding of cooling liquid to an impeller of the pump.

According to an embodiment of the invention, the first inlet and the second inlet open from the bearing housing radially outwards.

According to an embodiment of the invention, the first inlet and the second inlet open onto an outer surface of the bearing housing at locations that are located in the circumferential direction of the bearing housing at least 60 degrees from each other. This ensures sufficient space around the inlets for connecting incoming fluid channels to the bearing housing.

According to an embodiment of the invention, the common inlet chamber is configured to supply the cooling liquid to said impeller in the axial direction of the shaft of the cooling liquid pump. According to an embodiment of the invention, the bearing housing comprises a partition wall that is configured to divide the internal volume of the bearing housing into a space for accommodating said bearings of the cooling liquid pump and a space for receiving the cooling liquid.

According to an embodiment of the invention, the partition wall is configured to support one end of a mechanical seal that is configured to be arranged around the shaft of the cooling liquid pump.

According to an embodiment of the invention, the bearing housing is configured to be connected to an impeller housing accommodating said impeller.

According to an embodiment of the invention, the bearing housing is configured to be connected to the impeller housing by means of a V-band clamp. The use of a V-band clamp ensures serviceability of the cooling liquid pump and also allows different mutual angular positions of the bearing housing and the impeller housing. The V-band clamp also allows a compact size of the cooling liquid pump. The V-band clamp further allows using same components for assembling pumps with different rotation directions.

According to an embodiment of the invention, the bearing housing is configured to be connectable to the impeller housing in two or more different angular positions. According to an embodiment of the invention, the bearing housing is configured to be connectable to the impeller housing in any angular position. The possibility to connect the bearing housing and the impeller housing in different angular positions allow adapting the cooling liquid pump to different applications.

The cooling liquid pump according to the invention comprises a rotatable shaft, a first impeller attached to the shaft to be driven by the shaft to pressurize cooling liquid introduced into the pump, a first inlet for receiving cooling liquid and supplying it further to said first impeller, and an outlet for receiving pressurized cooling liquid from said first impeller and discharging it from the pump. The cooling liquid pump further comprises a second inlet, and the first inlet and the second inlet merge into a common inlet chamber for supplying the cooling liquid received via the first and second inlet to said first impeller of the pump.

According to an embodiment of the invention, the first inlet and the second inlet open from the cooling liquid pump radially outwards. According to an embodiment of the invention, the first inlet and the second inlet open onto an outer surface of the cooling liquid pump at locations that are located in the circumferential direction of the cooling liquid pump at least 60 degrees from each other.

According to an embodiment of the invention, the common inlet chamber is configured to supply the cooling liquid to said first impeller in the axial direction of the shaft of the cooling liquid pump.

According to an embodiment of the invention, the cooling liquid pump comprises a mechanical seal arranged around the shaft to prevent leakages from the common inlet chamber.

According to an embodiment of the invention, the cooling liquid pump comprises a bearing housing defined above.

According to an embodiment of the invention, the cooling liquid pump comprises a first impeller housing connected to the bearing housing and accommodating said first impeller.

According to an embodiment of the invention, first impeller housing is connected to the bearing housing by means of a V-band clamp.

According to an embodiment of the invention, the mutual angle of the bearing housing and the first impeller housing about the axial direction of the shaft is adjustable.

According to an embodiment of the invention, the cooling liquid pump comprises a third inlet, a second impeller attached to the shaft of the cooling liquid pump for pressurizing cooling liquid received through the third inlet, and a second outlet for discharging cooling liquid pressurized by the second impeller. The second impeller allows using the same cooling liquid pump for pressurizing the cooling liquid for both a high-temperature cooling circuit and a low- temperature cooling circuit. That allows a very compact arrangement for cooling systems that are provided with two cooling circuits and reduces the number of components in the cooling system.

According to an embodiment of the invention, the cooling liquid pump comprises a second impeller housing and the second impeller is arranged within the second impeller housing. By providing the cooling liquid pump with a separate impeller housing for the second impeller, the serviceability of the cooling liquid pump is improved. The second impeller housing could be identical to the first impeller housing, thus reducing the number of different components in the pump.

According to an embodiment of the invention, the second impeller housing is connected to an adjacent part of the cooling liquid pump such that the mutual angular position of the second impeller housing and the adjacent part is adjustable. This allows adapting the construction to the needs of different cooling systems, for instance by changing the positions of the inlets and outlets of the pump.

According to an embodiment of the invention, the cooling liquid pump comprises a leakage chamber arranged between the first impeller and the second impeller and configured to collect possibly leaking cooling liquid from the first impeller and/or the second impeller. This allows easy detection of leakages and ensures that the cooling liquids from different cooling circuits are not mixed within the pump unnoticed.

According to an embodiment of the invention, the cooling liquid pump comprises a mechanical seal arranged around the shaft between the first impeller and the leakage chamber and a mechanical seal arranged around the shaft between the leakage chamber and the second impeller. The mechanical seals prevent mixing of cooling liquids of different cooling circuits within the pump. In case of a failure of any of the mechanical seals, a leakage can be detected from the leakage chamber.

The cooling system according to the invention comprises a high-temperature cooling circuit for circulating cooling liquid and a low-temperature cooling circuit for circulating cooling liquid, wherein cooling liquid is circulated in the high- temperature cooling circuit at a higher temperature than in the low-temperature cooling circuit. The cooling system comprises a cooling liquid pump defined above for circulating cooling liquid pressurized by the first impeller in the high- temperature cooling circuit. Because of the cooling liquid pump according to the invention, cooling liquid flows at different temperatures can be mixed within the pump to keep the temperature in the high-temperature cooling circuit at a suitable level. According to an embodiment of the invention, the high-temperature cooling circuit is arranged to cool down at least cylinder liners of the engine.

According to an embodiment of the invention, the low-temperature cooling circuit is arranged to cool down intake air of the engine in at least one charge air cooler.

According to an embodiment of the invention, the cooling liquid pump is connected in the cooling system such that the first inlet receives cooling liquid in a first temperature range and the second inlet receives cooling liquid in a second temperature range, the second temperature range being higher than the first temperature range.

According to an embodiment of the invention, the first inlet is arranged to receive cooling liquid from a heat exchanger that is configured to cool down the cooling liquid or from the low-temperature cooling circuit.

According to an embodiment of the invention, the second inlet is arranged to receive cooling liquid from the high-temperature cooling circuit.

According to an embodiment of the invention, the second inlet is arranged to receive cooling liquid from a by-pass valve that is configured to allow supplying the cooling liquid of the high-temperature cooling circuit selectively to the second inlet of the cooling liquid pump or to a heat exchanger that is configured to cool down the cooling liquid.

According to an embodiment of the invention, the cooling liquid pump comprises a third inlet, a second impeller attached to the shaft of the cooling liquid pump for pressurizing cooling liquid received through the third inlet, and a second outlet for discharging cooling liquid pressurized by the second impeller, and the second impeller is arranged to pressurize cooling liquid circulated in the low-temperature cooling circuit. The same pump can thus be used for circulating the cooling liquid both in the high-temperature cooling circuit and the low-temperature cooling circuit.

Brief description of the drawings

Embodiments of the invention are described below in more detail with reference to the accompanying drawings, in which Fig. 1 shows a cooling system according to an embodiment of the invention,

Fig. 2 shows a perspective view of a cooling liquid pump according to an embodiment of the invention,

Fig. 3 shows a cross-sectional view of the cooling liquid pump of Fig. 2, and

Fig. 4 shows a partial cross-sectional view of the cooling liquid pump of Fig. 2.

Detailed description of embodiments of the invention

In figure 1 is shown schematically a cooling system of an internal combustion engine 40. The engine 40 is a large internal combustion engine, such as a main or an auxiliary engine of a ship or an engine that is used at a power plant for producing electricity. The cylinder bore of the engine 40 is at least 150 mm. Figure 1 shows an in-line engine, but the engine could also be a V-engine.

In the embodiment of figure 1 , the engine 40 is provided with two turbochargers

45, 46. A first turbocharger 45 is a low-pressure turbocharger and a second turbocharger 46 is a high-pressure turbocharger. The turbochargers 45, 46 are connected in series. The pressure of the intake air of the engine 40 is raised in the low-pressure turbocharger 45 from the ambient pressure to a first pressure level and then in the high-pressure turbocharger 46 from the first pressure level to a second pressure level, which is higher than the first pressure level.

The intake air of the engine 40 could be pressurized also by a single turbocharger. A V-engine could be provided with separate turbochargers for each bank of the engine. A V-engine could thus be provided with two turbochargers arranged in parallel, or two low-pressure turbocharger arranged in parallel and two high-pressure turbochargers arranged in parallel.

The intake air of the engine 40 is cooled down between the low-pressure turbocharger 45 and the high-pressure turbocharger 46 and after the high-pressure turbocharger 46. A low-pressure charge air cooler 47, 48 is arranged between the low-pressure turbocharger 45 and the high-pressure turbocharger

46. The low-pressure charge air cooler 47, 48 comprises a first stage 47 and a second stage 48. A high-pressure charge air cooler 49, 50 is arranged after the high-pressure turbocharger 46. The high-pressure charge air cooler 49, 50 comprises a first stage 49 and a second stage 50. The intake air is thus cooled down in two stages both between the turbochargers 45, 46 and downstream from the high-pressure turbocharger 46. The two stages of the charge air coolers could also be separate charge air coolers. The cooling system could also be provided with single stage cooling between the turbochargers 45, 46 and/or between the high-pressure turbocharger 46 and the engine 40.

The cooling system of the engine 40 comprises a high-temperature cooling circuit and a low-temperature cooling circuit. In the low-temperature cooling circuit, the temperature of the cooling liquid is lower than in the high-temperature cooling circuit. Temperature in the high -temperature cooling circuit is typically around 70-105 °C and in the low-temperature cooling circuit 35-55 °C. The cooling liquid in the cooling circuits can be, for instance, water. The cooling liquid can also contain additives, for example for preventing corrosion.

The cooling system comprises a cooling liquid pump 1 for circulating the cooling liquid in the cooling system. In the embodiment of figure 1 , the cooling system comprises a single cooling liquid pump 1. The cooling liquid pump 1 comprises a high-temperature portion 2 for pressurizing the cooling liquid circulated in the high-temperature cooling circuit and a low-temperature portion 3 for pressurizing the cooling liquid circulated in the low-temperature cooling circuit. The cooling liquid pump 1 is provided with a common shaft 10 for driving both the high -temperature portion 2 and the low-temperature portion 3. The cooling liquid pump 1 is mechanically coupled to the engine 40 to be driven by the engine. Instead of a single cooling liquid pump 1 circulating cooling liquid both in the low-temperature cooling circuit and the high-temperature cooling circuit, the cooling system could be provided with separate low-temperature and high-temperature pumps.

The cooling liquid pump 1 comprises a first inlet 13, a second inlet 14 and a third inlet 17. The first 13 and the second inlet 14 are inlets of the high-temper- ature portion 2 and the third inlet 17 is an inlet of the low-temperature portion 3. The cooling liquid pump 1 further comprises a first outlet 16, which is an outlet of the high-temperature portion 2, and a second outlet 18, which is an outlet of the low-temperature portion 3.

The high-temperature cooling circuit is arranged to cool down at least the cylinder liners and the cylinder heads of the engine 40. In the high-temperature cooling circuit, the cooling liquid flows from the high-temperature portion 2 of the cooling liquid pump 1 to the engine 40, where heat is transferred from the cylinder liners and the cylinder heads of the engine 40 to the cooling liquid. A check valve 51 is arranged on the downstream side of the high-temperature portion 2 of the cooling liquid pump 1 to prevent backflow to the cooling liquid pump 1 .

From the engine 40, the cooling liquid flows to a first by-pass valve 41. The first by-pass valve 41 allows conducting the cooling liquid selectively either to the second inlet 14 of the high-temperature portion 2 of the cooling liquid pump 1 or to a first heat exchanger 42. The first heat exchanger 42 is configured to cool down the cooling liquid received from the high-temperature cooling circuit. From the first heat exchanger 42, the cooled down cooling liquid is conducted to the third inlet 17 of the cooling liquid pump 1 , i.e. the inlet 17 of the low- temperature portion 3. The first by-pass valve 41 can be used for controlling the temperature of the cooling liquid in the high-temperature cooling circuit. If the temperature is too low, hot cooling liquid can be conducted from the end of the high -temperature cooling circuit to the second inlet 14 of the high-tem- perature portion 2 of the cooling liquid pump 1 to increase the temperature in the high-temperature cooling circuit. If the temperature is too high, the cooling liquid from the high-temperature cooling circuit can be conducted to the first heat exchanger 42.

The cooling system further comprises a second by-pass valve 43. The second by-pass valve 43 allows by-passing the first heat exchanger 42 to conduct cooling liquid from the high-temperature cooling circuit to the inlet 17 of the low-temperature portion 3 of the cooling liquid pump 1 .

From the low-temperature portion 3 of the cooling liquid pump 1 , the cooling liquid is conducted to a second heat exchanger 44, where the cooling liquid is heated. A check valve 52 is arranged between the low-temperature portion 3 of the cooling liquid pump 1 and the second heat exchanger 44 to prevent backflow to the cooling liquid pump 1. From the second heat exchanger 44, the cooling liquid is conducted to the second stage 48 of the low-pressure charge air cooler, where heat is transferred from the intake air of the engine 40 to the cooling liquid. From the second stage 48 of the low-pressure charge air cooler, the cooling liquid is conducted to the second stage 50 of the high- pressure charge air cooler, where heat is transferred from the intake air to the cooling liquid. From the second stage 50 of the high-pressure charge air cooler, the cooling liquid is conducted to the first stage 49 of the high-pressure charge air cooler. In the first stage 49 of the high-pressure charge air cooler, further heat is transferred from the intake air to the cooling liquid. From the first stage 49 of the high-pressure charge air cooler, the cooling liquid is conducted to the first stage 47 of the low-pressure charge air cooler. Although the cooling liquid has been heated in the other cooling stages, the temperature of the cooling liquid is still lower than the temperature of the intake air after the low-pressure turbocharger 45, and heat is transferred from the intake air to the cooling liquid.

After the first stage 47 of the low-pressure charge air cooler, the temperature of the cooling liquid in the low-temperature cooling circuit is at its highest. The cooling liquid is conducted to the first inlet 13 of the high-temperature portion 2 of the cooling liquid pump 1. In the cooling liquid pump 1 , the cooling liquid is mixed with the cooling liquid that is introduced into the high-temperature portion 2 through the second inlet 14.

Part of the cooling liquid from the low-temperature cooling circuit can flow to the first heat exchanger 42, where it is cooled down before being conducted through the second by-pass valve 43 to the inlet 17 of the low-temperature portion 3 of the cooling liquid pump 1 .

The low-temperature cooling circuit can be arranged to cool down also the lube oil of the engine. A lube oil cooler could be arranged in the low-temperature cooling circuit, for instance, between the first stage 49 of the high-pressure charge air cooler and the first stage 47 of the low-pressure charge air cooler.

Depending on the engine 40, the cooling system could be configured also in many alternative ways. For instance, the first stage 47 of the low-pressure charge air cooler could be arranged in the high-temperature cooling circuit. The cooling circuits could also comprise by-pass ducts for one or more stages 47, 48, 49, 50 of the charge air coolers.

Figure 1 shows a simplified illustration of a cooling system, and the cooling system can comprise many additional components. For instance, the cooling system can comprise a low-temperature stand-by pump and a high-temperature stand-by pump. The stand-by pumps can be driven for circulating cooling liquid in the cooling system when the engine 40 is not running. Figures 2-4 show different views of a cooling liquid pump 1 according to an embodiment of the invention. The cooling liquid pump 1 can be used in the cooling system of figure 1. The cooling liquid pump 1 comprises a high-tem- perature portion 2 and a low-temperature portion 3. The high -temperature portion 2 is configured to pressurize cooling liquid that is circulated in a high-tem- perature cooling circuit of a cooling system and the low-temperature portion 3 is configured to pressurize cooling liquid that is circulated in a low-temperature cooling circuit of a cooling system. Some components of the cooling liquid pump 1 are common to the high-temperature portion 2 and the low-temperature portion 3 of the cooling liquid pump 1 .

The cooling liquid pump 1 comprises a rotatable shaft 10. The shaft 10 is configured to be driven by the engine that is cooled down by the cooling system in which the cooling liquid pump 1 is used. A gearwheel 33 can be attached to one end of the shaft 10 for driving the shaft 10.

The cooling liquid pump 1 is an impeller pump 1. The cooling liquid pump 1 comprises a first impeller 11 attached to the shaft 10 and a second impeller 12 attached to the shaft 10. The first impeller 11 is configured to pressurize cooling liquid in the high-temperature portion 2 of the pump 1 and the second impeller 12 is configured to pressurize cooling liquid in the low-temperature portion 3 of the pump 1 .

The shaft 10 is supported by a first bearing 8 and a second bearing 9. The cooling liquid pump 1 comprises a bearing housing 4, which is configured to receive the first bearing 8 and the second bearing 9. The first bearing 8 is arranged at a first end of the cooling liquid pump 1 and the second bearing 9 is arranged at a distance from the first bearing 8 towards a second end of the cooling liquid pump 1. In the embodiment of the figures, the shaft 10 is supported solely by the first bearing 8 and the second bearing 9. All the bearings of the pump 1 are thus arranged in the bearing housing 4. Both impellers 11 , 12 of the pump 1 are arranged on the same side of the bearings 8, 9.

The bearing housing 4 forms part of a pump housing. Further parts of the pump housing are a first impeller housing 5, a second impeller housing 6 and an end portion 7. The pump housing could comprise even further parts and/or some of the parts could be integrated to each other. The first impeller housing 5 is configured to accommodate the first impeller 11 and the second impeller housing 6 is configured to accommodate the second impeller 12.

The bearing housing 4 has a first end. The shaft 10 protrudes out of the first end of the bearing housing 4. A first end of the first impeller housing 5 is connected to a second end of the bearing housing 4. A first end of the second impeller housing 6 is connected to a second end of the first impeller housing 5. The end portion 7 is connected to a second end of the second impeller housing 6.

The bearing housing 4 comprises a partition wall 4A. The partition wall 4A divides the internal volume of the bearing housing 4 into a space 4B for accommodating the first 8 and second bearing 9 of the cooling liquid pump 1 and a space 4C for receiving the cooling liquid. The partition wall 4A is configured to support one end of a first mechanical seal 28 that is arranged around the shaft 10 of the cooling liquid pump 1 . Another end of the first mechanical seal 28 is arranged against the first impeller 11 . The purpose of the first mechanical seal 28 is to prevent leakages to the bearings 8, 9 of the cooling liquid pump 1 and out of the bearing housing 4.

The term “mechanical seal” means here a seal comprising a static seal face arranged in a static portion of the seal and a rotary seal face arranged in a rotatory portion of the seal. At least one of the portions is spring loaded and pushed towards the other portion, and a fluid film between the seal faces forms the seal.

In the embodiment of the figures, the second end of the bearing housing 4 is provided with a flange 19. The first end of the first impeller housing 5 is provided with a flange 20 that can be arranged against the flange 19 of the bearing housing 4. A V-band clamp 21 fastens the bearing housing 4 and the first impeller housing 5 to each other. The second end of the first impeller housing 5 is provided with a flange 22. The first end of the second impeller housing 6 is provided with a flange 23 that can be arranged against the flange 22 at the second end of the first impeller housing 6. A V-band clamp 24 fastens the second impeller housing 6 to the first impeller housing 5. The second end of the second impeller housing 6 is provided with a flange 25. The end portion 7 is provided with a flange 26 that can be arranged against the flange 25 at the second end of the second impeller housing 6. A V-band clamp 27 fastens the end portion 7 to the second end of the second impeller housing 6. In the embodiment of the figures, the first impeller housing 5 and the second impeller housing 6 are identical parts. This reduces the number of different parts needed for the pump 1 . However, the impeller housings 5, 6 could also be different parts.

The two separate impeller housings 5, 6 improve serviceability of the cooling liquid pump 1 . The mutual angles between the bearing housing 4 and the first impeller housing 5, the first impeller housing 5 and the second impeller housing 6, and the second impeller housing 6 and the end portion 7 about the axial direction of the cooling liquid pump 1 can be adjusted. This allows arranging the inlets and outlets of the cooling liquid pump 1 in different position in respect of each other. This allows the cooling liquid pump 1 to be easily adapted to different cooling systems.

The cooling liquid pump 1 comprises a first inlet 13, a second inlet 14 and a third inlet 17. The first 13 and the second inlet 14 are for the high-temperature portion 2 of the cooling liquid pump 1 and the third inlet 17 is for the low-temperature portion 3. The cooling liquid pump 1 is configured such that the third inlet 17 is not in fluid communication with the first inlet 13 and the second inlet 14. Cooling liquid introduced into the pump 1 through the inlet 17 of the low- temperature portion 3 does thus not mix with the cooling liquid introduced into the pump through the inlets 13, 14 of the high-temperature portion 2.

The cooling liquid pump 1 comprises a first outlet 16 and a second outlet 18. The first outlet 16 is for the high-temperature portion 2 and the second outlet 18 is for the low-temperature portion 3.

The first inlet 13 and the second inlet 14 are arranged in the bearing housing 4. The first inlet 13 and the second inlet 14 merge into a common inlet chamber 15 for supplying the cooling liquid received via the first 13 and second inlets 14 to the first impeller 11 of the pump 1 . The cooling liquid introduced into the high-temperature portion 2 through the first 13 and second inlets 14 is thus mixed in the inlet chamber 15 and while flowing through the high-temperature portion 2 to the outlet 16 of the high-temperature portion 2. The two inlets 13, 14 allow mixing of cooling liquid flows having different temperatures in the cooling liquid pump 1 and provide thus a compact construction. Together with the two impellers 11 , 12, which allow using the same cooling liquid pump 1 in both the high-temperature and low-temperature cooling circuits, a very space-efficient solution for a cooling system of an internal combustion engine 40 is achieved.

The first inlet 13 and the second inlet 14 open from the bearing housing 4 radially outwards. In the embodiment of the figures, the first inlet 13 and the second inlet open onto an outer surface of the bearing housing 4 at locations that are located in the circumferential direction of the bearing housing 4 approximately 135 degrees from each other. Preferably, the angle is at least 60 degrees to provide sufficient space for connections of cooling liquid pipes.

The common inlet chamber 15 is configured to supply the cooling liquid to the first impeller 11 in the axial direction of the shaft 10 of the cooling liquid pump 1.

The third inlet 17 is arranged in the end portion 7 of the pump housing. From the third inlet 17, the cooling liquid is supplied in axial direction of the shaft 10 to the second impeller 12. From the second impeller 12, the pressurized cooling liquid flows to the second outlet 18 of the cooling liquid pump 1 .

In the embodiment of the figures, the cooling liquid pump 1 comprises a leakage chamber 32 that is arranged between the first impeller 11 and the second impeller 12. The leakage chamber 32 is configured to collect possibly leaking cooling liquid from both the first impeller 11 and the second impeller 12. The leakage chamber 32 is provided with an outlet opening outside of the pump housing. The leakage chamber 32 and the outlet allow detecting internal leakage of the cooling liquid pump 1 . In the embodiment of the figures, the cooling liquid pump 1 comprises a partition wall element 34. The partition wall element 34 separates the high-temperature portion 2 from the low-temperature portion 3. The shaft 10 protrudes through the partition wall element 34. The partition wall element 34 comprises an annular groove. The leakage chamber 32 is delimited by the annular groove and an inner surface of the pump housing.

A second mechanical sealing 29 is arranged around the shaft 10 between the first impeller 11 and the partition wall element 34. The purpose of the second mechanical seal 29 is to prevent leakages from the high-temperature portion 2 to the low-temperature portion 3. A third mechanical seal 30 is arranged around the shaft 10 between the partition wall element 34 and the second impeller 12. The purpose of the third mechanical seal 30 is to prevent leakages from the low-temperature portion 3 to the high-temperature portion 2.

The partition wall element 34 comprises at least one hole 35 for allowing fluid flow from the shaft 10 to the leakage chamber 32. In case of a failure of the second 29 or third mechanical seal 30, the leaking cooling liquid is thus collected into the leakage chamber 32.

Instead of a separate partition wall element, the leakage chamber 32 could be formed by integral walls of the first impeller housing 5 and the second impeller housing 6.

The second impeller 12 is attached to an end of the shaft 10. The end of the shaft 10 is provided with a conical surface, and the second impeller 12 is tightened against the conical surface by means of a bolt 36.

The first impeller 11 is attached to the shaft 10 by means of a key piece 37, which prevents rotation of the first impeller 11 relative to the shaft 10, and by means of a circle clip 38, which prevents moving of the first impeller 11 relative to the shaft 10 in the axial direction. The fastening arrangements of both the first impeller 11 and the second impeller 12 are not susceptible to mounting faults and thus provide a reliable construction.

It will be appreciated by a person skilled in the art that the invention is not limited to the embodiments described above, but may vary within the scope of the appended claims.