CN113227700B

CN113227700B - Heat exchanger with integrated bypass

Info

Publication number: CN113227700B
Application number: CN201980085332.5A
Authority: CN
Inventors: N·施密特
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 2018-12-20
Filing date: 2019-12-13
Publication date: 2023-03-28
Anticipated expiration: 2039-12-13
Also published as: WO2020126889A1; CN113227700A; DE102018222568A1

Abstract

The invention relates to a heat exchanger (1) of the multi-circuit type, comprising at least one first region (14) for cooling a working medium of a transmission and a second region (15) for cooling a working medium of a hydraulic retarder (23), and an attachment (16) for distributing the working medium into different regions (14, 15) of the heat exchanger (1). It is proposed that the heat exchanger (1) has at least one bypass (18, 20), by means of which the first region (14) of the heat exchanger (1) and the second region (15) of the heat exchanger (1) are connected to one another.

Description

Heat exchanger with integrated bypass

The present invention relates to a heat exchanger of the multi-flow path type according to the preamble of claim 1. The invention also relates to a cooling system having at least two working medium circuits and to a transmission comprising a heat exchanger according to the invention or a cooling system according to the invention.

In a liquid working medium in a vehicle, for example, a temperature rise due to energy conversion into heat is transferred in a heat exchanger to a cooling medium in order to maintain the availability of the working medium and to make the working medium available for further energy absorption.

Such a working medium may be a lubricating medium in a motor or transmission, which becomes hot due to the movement of existing components; alternatively, the working medium can also be oil or water of a hydrodynamic braking device which converts the kinetic energy of the vehicle into heat by means of the blade assembly, which heat is transferred to the working medium.

Heat exchangers are usually implemented in a plate or shell type construction, in which a plurality of similar plates or shells are fastened (e.g. welded) on top of one another and alongside one another, and then form passages through which the cooling medium and the working medium to be cooled, respectively, are guided past one another.

If several working media are to be cooled in a vehicle, several heat exchangers can be provided for this purpose, each of which cools the working media by means of a cooling medium. If a plurality of heat exchangers is used for cooling a plurality of working media, these heat exchangers can be optimally adapted corresponding to the working medium circuit to be cooled and can have, for example, different geometries. However, the use of a plurality of heat exchangers is relatively expensive and requires a correspondingly large installation or installation space for arranging the heat exchangers.

It is known that in vehicles, it is also possible to cool a plurality of working media in a common heat exchanger, wherein the heat exchanger then has a plurality of regions which can each be brought into contact with a cooling medium in order to dissipate heat. Such heat exchangers are also referred to as multi-flow heat exchangers. For example, one cooling medium circuit and two working medium circuits can be coupled to a 3-pass heat exchanger. The working medium circuit can be designed, for example, as a working medium circuit of the transmission and as a working medium circuit of the retarder.

Such a multi-channel heat exchanger is known, for example, from DE 197 12 599a1, in which a plurality of oil feed elements are provided, which are each led to a fixedly associated channel in order to come into contact there with a cooling medium which is likewise supplied to the heat exchanger for heat transfer.

Such multi-flow heat exchangers are geometrically constrained in terms of their construction and can therefore only be designed conditionally for the working medium circuit to be cooled. In connection with the design of such a multi-flow heat exchanger, pressure losses may occur in the working medium circuit during the flow through the passages of the heat exchanger, which pressure losses may have a negative effect on the working medium circuit.

Against this background, the object on which the invention is based is to provide a new heat exchanger and an improved cooling system with a heat exchanger of the multi-flow path type.

This object is achieved by a heat exchanger according to patent claim 1 and a cooling system according to patent claim 8. Advantageous developments are the subject matter of the dependent claims and of the following description and the drawings.

According to the invention, a heat exchanger of the multi-circuit type is proposed, which comprises at least one first region for cooling a working medium of the transmission and a second region for cooling a working medium of the hydraulic retarder. The heat exchanger comprises accessories for distributing the working medium into different zones of the heat exchanger. According to a design of the heat exchanger, the heat exchanger has a corresponding flow resistance in the region in which the working medium is guided. The flow resistance of the heat exchanger makes it possible to achieve a pressure increase in the working medium circuit in a defined working region.

In order to achieve the object set forth, the invention therefore proposes that the heat exchanger has at least one bypass, by means of which the first region of the heat exchanger and the second region of the heat exchanger are connected to one another. Since the two regions of the multi-flow heat exchanger conducting the working medium are connected to each other by a bypass, the flow resistance of the heat exchanger can be reduced in a certain region.

In the design of the heat exchanger of the multi-circuit type, the bypass is integrated in the connection plate of the heat exchanger. The connection plate has a connection end for connection to the working medium circuit and a connection end for connection of the cooling medium circuit to the heat exchanger. The connection plate may be connected (e.g., welded) to an end plate of the heat exchanger.

In a further embodiment of the heat exchanger, the bypass is embodied as a channel formed in a connecting plate of the heat exchanger, which channel is closed and sealed by a connecting element provided for this purpose or the transmission housing or the retarder housing itself when the heat exchanger is mounted on the transmission housing or the retarder housing.

If the heat exchanger has a connecting element by means of which the heat exchanger can be fastened to the transmission housing or the retarder housing, it can be provided in a further embodiment that the bypass is integrated in this connecting element of the heat exchanger.

In an advantageous development, it can be provided that the throughput of the bypass is controllable or adjustable. For this purpose, a valve can be provided in the bypass. The valve can be designed, for example, as a pressure valve, a flow valve, a seat valve, a directional control valve or a throttle valve or orifice valve. The seat valve can be designed, for example, as a check valve which allows the working medium flowing through to flow in only one direction.

The cooling system according to the invention comprises a cooling medium circuit, a working medium circuit of the transmission, a working medium circuit of the hydraulic retarder and a multi-flow heat exchanger. The first region of the heat exchanger is designed for cooling the working medium of the transmission and the second region of the heat exchanger is designed for cooling the working medium of the hydraulic retarder. It proposes: the supply line to the first region of the heat exchanger is connected by a bypass to the supply line to the second region of the heat exchanger. Alternatively or in addition, the return line from the first zone of the heat exchanger may be connected by a bypass to the return line from the second zone of the heat exchanger. In this embodiment, the bypass is not directly integrated in the heat exchanger, whereby a conventional multi-flow heat exchanger may be used in the cooling system. Since the two supply lines or the two return lines are connected to each other by a bypass, the flow resistance of the heat exchanger can be reduced in a certain working region, and thus a pressure rise in the working medium circuit to which the multi-flow heat exchanger is applied can be avoided.

In this embodiment of the bypass, it can also be provided that the throughput of the bypass is controllable or adjustable. The bypass flow can be expediently controlled or regulated as a function of the pressure prevailing in the working medium circuit and/or the temperature of the working medium. In order to control or regulate the flow through the bypass, a valve may be arranged in the bypass. The valve can be designed, for example, as a pressure valve, a flow valve, a seat valve, a directional control valve or a throttle valve or orifice valve. The seat valve can be designed, for example, as a check valve which allows the working medium flowing through to flow in only one direction.

The multi-flow heat exchanger is connected to the working medium circuit of the transmission and the working medium circuit of the hydraulic retarder in such a way that, in an operating state in which the hydraulic retarder is not activated, the working medium of the transmission is also guided through a region of the heat exchanger that is provided for cooling the working medium of the retarder and is cooled. The region provided for cooling the operating medium of the retarder and the region provided for cooling the operating medium of the transmission are then connected in series, and the operating medium of the transmission is guided through both regions of the heat exchanger and is cooled.

The series connection of the two regions of the heat exchanger provided for cooling the working medium results in: the heat exchanger has a high flow resistance, whereby a corresponding pressure loss occurs at the heat exchanger. The pressure loss at the heat exchanger can be correspondingly reduced by the provision of the bypass.

A transmission of a motor vehicle comprising a heat exchanger of the multiple flow path type according to the invention and/or a cooling system according to the invention is the subject of patent claim 13.

The invention is further elucidated below by way of example with the aid of the drawing, which allows a plurality of embodiments. In the drawings:

figure 1 shows part of a cooling system with two working medium circuits in a first operating state,

figure 2 shows part of a cooling system with two working medium circuits in a second operating state,

figure 3 shows a view of a multi-flow heat exchanger,

fig. 4 shows a cross-sectional illustration of the multi-flow heat exchanger illustrated in fig. 3, with a bypass arrangement according to the first embodiment,

fig. 5 shows a cross-sectional illustration of the multi-flow heat exchanger illustrated in fig. 3, with a bypass arrangement according to a second embodiment,

fig. 6 shows a sectional illustration of the multi-flow heat exchanger illustrated in fig. 3, with a bypass arrangement according to a third embodiment.

With the aid of fig. 1 and 2, the cooling system 24 according to the invention shall be explained in detail in the following. Fig. 1 and 2 show a part of a cooling system 24 of a motor vehicle. The cooling system 24 comprises a cooling medium circuit 28, a working medium circuit 26 of the transmission and a working medium circuit 25 of the hydraulic retarder 23.

In order to supply the transmission with pressurized oil, an oil pump 33, which is advantageously arranged inside the transmission, is provided, which is coupled to the input shaft of the transmission and can therefore be driven by the drive assembly. A volumetric flow of oil of the working medium circuit 26 of the transmission is thus produced as a function of the rotational speed of the drive assembly. The oil pump 33 is fed via a suction line from an oil sump 34, wherein a suction filter 35 is connected upstream of the oil pump 2 and an oil filter 36 is connected downstream of the oil pump in order to ensure that no dirt enters the working medium circuit 26. First, the primary pressure circuit 37 and the secondary pressure circuit 38 of the working medium circuit 26 can be supplied from the suction line.

A plurality of

valves

29, 30, 31, 32 are provided in the working medium circuit 26 of the transmission. The valve 29 is designed as a main pressure valve which can be actuated by a pressure regulating valve which is not shown here.

The converter relief valve 30 protects the converter 22 against an inadmissibly high overpressure in that it limits the inlet pressure p0 upstream of the converter 22. The inlet pressure p0 upstream of the torque converter 22 is set by the converter relief valve 30, wherein the converter relief valve 30 opens when a certain pressure value is reached or exceeded, so that oil can flow out by backflow in the direction of the suction side of the oil pump 33, to be precise into the oil sump 34, until the desired inlet pressure p0 is reached again.

Behind the torque converter 22, a torque converter backpressure valve 31 is arranged in the torque converter exhaust line, by means of which a pressure p1 behind the torque converter 22 is set. If the pressure p1 downstream of the torque converter 22 exceeds a predetermined pressure value, the torque converter backpressure valve 31 opens, so that the working medium of the transmission can flow out in the direction of the cooling or lubrication circuit until the pressure p1 downstream of the torque converter 22 is generated again.

In the cooling system 24, a heat exchanger 1 of the multi-circuit design is provided, which comprises two

regions

14, 15 for cooling the working medium. The first region 14 of the heat exchanger 1 is designed for cooling oil as a working medium of the transmission, and the second region 15 of the heat exchanger 1 is designed for cooling oil as a working medium of the hydraulic retarder 23. In addition to the retarder oil circuit 25 and the transmission oil circuit 26, a cooling medium circuit 28, for example of a motor vehicle, is connected to the heat exchanger 1, which cooling medium circuit comprises a vehicle heat exchanger 27. The heat exchanger 1 is therefore designed here as a so-called 3-pass heat exchanger.

The valve 32 is controlled in dependence of the retarder operation. As illustrated in fig. 1, in the first operating state the retarder 23 is not activated and the remaining working medium remaining in the retarder 23 is conducted out of the oil sump 34 via the line 39 via the valve 32. The supply of working medium to the retarder 23 via the line 40 is prevented by the valve 32. The first operating state is exemplary a towing operation of the motor vehicle. During the first operating state, the working medium of the transmission to be cooled is guided through both the first region 14 and the second region 15 of the heat exchanger 1 and is therefore cooled by both

regions

14, 15 of the heat exchanger 1. The thus cooled working medium is supplied to the transmission for further use via the valve 32 and the line 44.

In the second operating state illustrated in fig. 2, the retarder 23 is activated manually or by the control arrangement and the working medium is conveyed into the working chamber of the retarder 23 via the line 41. The valve 32 is then adjusted to its second position. Thereby, the working medium warmed up in the retarder 23 can be transferred via the line 39 into the line 42 and then cooled by the second area 15 of the heat exchanger 1. The now cooled working medium from the second region 15 of the heat exchanger 1 is supplied to the retarder 23 via the valve 32 and the line 40 for further use. The working medium of the transmission to be cooled during operation of the retarder is supplied to the first region 14 of the heat exchanger 1 through the valve 32 and the line 43 and is cooled through this first region. In the second operating state, the working medium of the retarder 23 and the working medium of the transmission are therefore cooled in two mutually separate cooling medium circuits. The second operating state is, for example, a coasting operation of the motor vehicle.

In the case of the use of a 3-pass heat exchanger 1, in which the first region 14 and the second region 15 are produced in a component, the design of the two

regions

14, 15 is subject to corresponding constraints. The 3-circuit heat exchanger 1 can thus be produced, for example, in a plate-type construction, wherein the size and number of the plates used for the two

regions

14, 15 cannot be selected at will. The design of the heat exchanger 1 results in a corresponding flow resistance of the heat exchanger 1. This flow resistance leads to a corresponding pressure loss in the heat exchanger 1, which can have a negative effect at least on the working medium circuit 26 of the transmission. For example, the function of the converter backpressure valve 31 may be deactivated, so that the converter internal pressure and thus also the pressure p1 downstream of the converter 22 is no longer determined by the converter backpressure valve 31 but by the losses of the working medium circuit 26 arranged downstream and therefore increases. This pressure increase has a negative effect on the service life of the torque converter 22 and the shift quality of the transmission and also leads to an earlier switching (ultrafilten) of the converter relief valve 30, as a result of which the working medium required for the torque converter 22 and for the cooling or lubrication of the transmission is drawn off into the oil sump 34 and is no longer available for the cooling or lubrication of the transmission and for the torque converter 22.

According to the invention, therefore, at least one

bypass

18, 20 is provided in the cooling system 24, as a result of which the pressure loss at the heat exchanger 1 can be reduced.

According to fig. 1, the heat exchanger 1 has a bypass 18 arranged on the input side and a bypass 20 arranged on the output side. A bypass 18 arranged on the input side connects the supply line of the first region 14 of the heat exchanger 1 with the supply line of the second region 15 of the heat exchanger 1. A bypass 20 arranged on the output side connects the return line of the first region 14 of the heat exchanger 1 with the return line of the second region 15 of the heat exchanger 1.

During the towing operation of the motor vehicle, the working medium of the transmission to be cooled is guided through both the first region 14 and the second region 15 of the heat exchanger 1 and is thus cooled by both

regions

14, 15 of the heat exchanger 1. This is achieved by the series connection of the two

regions

14, 15 of the heat exchanger 1: the heat exchanger 1 has a high flow resistance, as a result of which a corresponding pressure loss occurs at the heat exchanger 1. By means of the provided bypasses 18, 20, the pressure losses at the heat exchanger 1 can be reduced, which in turn leads to a limitation of the internal torque converter pressure or the pressure p1 downstream of the torque converter 22 in the working medium circuit 26 and avoids the disadvantages mentioned above. A valve 19 is arranged in the bypass 18, which valve is designed here as a check valve 19. A valve 21 is arranged in the bypass 20, which valve is likewise designed here as a check valve 21.

According to fig. 1, the pressure in the retarder circuit 25 is low, because the retarder is not activated. The valve 19 therefore opens the bypass 18 when a defined pressure is present at the connection 7 of the heat exchanger 1 and a portion of the transmission oil is guided directly through the second region 15 of the heat exchanger 1, bypassing the first region 14 of the heat exchanger 1. The valve 21 opens the bypass 20 when a defined pressure is present at the connection 8 of the heat exchanger 1, as a result of which a portion of the transmission oil bypasses the second region 15 of the heat exchanger 1 and is cooled only by the first region 14 of the heat exchanger 1.

In the arrangement according to fig. 2, only a bypass 18 with a check valve 19 is provided, which serves to reduce the pressure loss at the heat exchanger 1. According to fig. 2, a coasting operation of the motor vehicle is illustrated, in which the retarder 23 is activated and thus a higher pressure level prevails in the retarder circuit 25. Thereby, the balls of the check valve 19 are pressed against the seat of the check valve 19, thereby closing the bypass 18. Thus, the working medium of the transmission is cooled in the first region 14 of the heat exchanger 1 and the working medium of the retarder 32 is cooled in the second region 15 of the heat exchanger 1. If the motor vehicle is operated in coasting mode with the retarder 23 activated, the working medium of the transmission to be cooled is only conducted through the second region 15 of the heat exchanger 1, whereby a lower flow resistance prevails in the working medium circuit 26.

Fig. 3 shows the heat exchanger 1 of the multi-flow path type in a plan view. The connections for connecting the working

medium circuits

25, 26 and the cooling medium circuit 28 to the heat exchanger 1 are located on the end plate 2 of the heat exchanger 1. In this embodiment, the heat exchanger 1 has two

connection plates

3,4 for this purpose. In the connection plate 3, a connection 7 for supplying the operating medium of the transmission to be cooled, a connection 9 for supplying the operating medium of the retarder 23 to be cooled and a connection 5 for returning the heated cooling medium are provided. Correspondingly, a connection 8 for the cooled working medium of the reflux transmission, a connection 10 for the cooled working medium of the reflux retarder 23 and a connection 6 for the supply of the cooling medium are provided in the connection plate 4. The

connection plates

3,4 are connected (e.g. welded) to the end plates 2 of the heat exchanger.

It follows from the connection distribution that the plate heat exchanger shown here functions according to the so-called convection principle, in which the flow directions of the working medium flow to be cooled and the cooling medium flow are opposite. Since the working medium flow and the cooling medium flow towards each other and finally flow through each other, a large heat transfer can be achieved. The connection distribution can naturally also be formed such that the plate heat exchanger functions according to the so-called direct flow principle, in which the working medium flow to be cooled and the cooling medium flow through the heat exchanger flow in the same direction.

Fig. 4 to 6 show a heat exchanger 1 of the multi-circuit type in a sectional illustration, which is designed in a known manner as a plate heat exchanger. A plurality of plates arranged one above the other is arranged between two end plates and forms a plate pack through which the working medium to be cooled and the cooling medium flow. The channel 11, through which the cooling medium is guided, is in heat-transferring contact with the

channel

12 or 13, through which the working medium flows. The transmission oil as a working medium of the transmission flows through the connection 7 into the passage 12 of the first region 14 of the heat exchanger 1. This is illustrated by the corresponding arrows. The retarder oil, which is the working medium of the retarder 23, reaches the passage 13 of the second region 15 of the heat exchanger 1 through the connection 9, which is likewise illustrated by corresponding arrows. In the connection plate 3, a connection 7 for supplying transmission oil to be cooled, a connection 9 for supplying retarder oil to be cooled and a connection 5 for returning the heated cooling medium are provided. Furthermore, in the connection plate 3 and the heat exchanger 1, fittings 16 for distributing the working medium to

different regions

14, 15 of the heat exchanger 1 are introduced in the connection end 9.

According to the invention, it is now proposed that the heat exchanger 1 has at least one bypass 18, by means of which the first region 14 of the heat exchanger 1 and the second region 15 of the heat exchanger 1 are connected to one another.

According to fig. 4, the bypass 18 is arranged in a connecting element 17 by means of which the heat exchanger 1 can be mounted on the transmission housing or the retarder housing. The bypass 18 is preferably integrated directly in the connecting element 17. For example, the bypass 18 may be molded into the connecting element 17 or otherwise embedded in the connecting element 17. In an alternative embodiment, the bypass 18 can be arranged in the transmission housing or the retarder housing. This may be advantageous, for example, in that the heat exchanger 1 may be mounted to the transmission housing or the retarder housing without an intermediate connecting element 17. A valve 19, which is designed here as a check valve, is arranged in the bypass 18. If the pressure in the working medium circuit 25 of the retarder 23 is low because the retarder 23 is not activated, the check valve 19 can open due to the pressure in the working medium circuit 26 of the transmission, whereby a part of the transmission oil bypasses the first region 14 of the heat exchanger 1 and is led into the second region 15 of the heat exchanger 1.

According to fig. 5, an alternative way for arranging the bypass 18 is shown. The bypass 18 is integrated directly in the connection plate 3. For example, the bypass 18 may be molded into the web 3 or otherwise embedded in the web 3. A valve 19, which is also designed here as a check valve, is arranged in the bypass 18. Reference is made to fig. 4 with regard to the working mode.

According to fig. 6, another alternative way for arranging the bypass 18 is shown. The bypass 18 is formed by the connecting plate 3 and the connecting element 17. In order to connect the first region 14 of the heat exchanger 1 to the second region 15 of the heat exchanger 1, a channel is inserted into the connecting plate 3, which channel is closed and sealed by a connecting element 17 when this connecting element is fitted. A valve 19, which is also designed here as a check valve, can be arranged in the bypass 18. In case the heat exchanger is fitted on the transmission housing or retarder housing without an intermediate connecting element 17, the passage embedded in the connection plate 3 may also be closed and sealed by the transmission housing or retarder housing. Reference is further made to fig. 4 with regard to the mode of operation.

Since the transmission oil flowing through the bypass is still cooled by the part of the heat exchanger 1 and is not directly conducted to the oil pan, an inadmissibly high oil pan temperature rise can be avoided.

List of reference numerals

1. Heat exchanger

2. End plate

3. Connecting plate

4. Connecting plate

5. Connecting end for cooling medium

6. Connecting end for cooling medium

7. Connecting end of a working medium circuit of a transmission

8. Connecting end of a working medium circuit of a transmission

9. Connecting end of working medium loop of retarder

10. Connecting end of working medium loop of retarder

11. Channel for guiding cooling medium

12. Channel for guiding working medium

13. Channel for guiding working medium

14. First region

15. Second region

16. Accessories

17. Connecting element

18. Bypass path

19. Valve with a valve body

20. Bypass path

21. Valve with a valve body

22. Torque converter

23. Main retarder

24. Cooling system

25. Working medium loop of retarder

26. Working medium circuit of transmission

27. Heat exchanger

28. Cooling medium circuit

29. Valve with a valve body

30. Valve with a valve body

31. Valve with a valve body

32. Valve with a valve body

33. Oil pump

34. Oil pan

35. Suction filter

36. Oil filter

37. Main pressure circuit

38. Secondary pressure circuit

39. Pipeline

40. Pipeline

41. Pipeline

42. Pipeline

43. Pipeline

44. Pipeline

Claims

1. A cooling system (24) comprising a cooling medium circuit (28), a working medium circuit (26) of a transmission, a working medium circuit (25) of a hydraulic retarder (23) and a heat exchanger (1) of the multi-circuit type, wherein a first region (14) of the heat exchanger (1) is designed for cooling the working medium of the transmission and a second region (15) of the heat exchanger (1) is designed for cooling the working medium of the hydraulic retarder (23), wherein the heat exchanger (1) is connected to the working medium circuit (26) of the transmission and to the working medium circuit (25) of the hydraulic retarder (23) in such a way that, in an operating state in which the hydraulic retarder (23) is deactivated, the first region (14) is connected in series with the second region (15), wherein a supply line to the first region (14) of the heat exchanger (1) is connected by a bypass (18) to a supply line to the second region (15) of the heat exchanger (1) and/or a return line from the first region (14) of the heat exchanger (1) is connected by a bypass line (20), wherein the amount of the return line from the heat exchanger (20) is adjustable, wherein the return line is connected to the bypass (20 or the return line of the bypass (20), so that the flow resistance of the heat exchanger can be reduced in the first region (14) and/or the second region (15).

2. A cooling system (24) according to claim 1, characterized in that for controlling or regulating the flow through the bypass (18, 20) a valve (19, 21) is arranged in the bypass (18, 20).

3. A cooling system (24) according to claim 2, characterized in that the valves (19, 21) are designed as pressure valves, flow valves, seat valves, directional control valves or throttle valves or orifice valves.

4. The cooling system (24) according to any one of claims 1 to 3, characterized in that the bypass (18, 20) is integrated in a connection plate (3, 4) of the heat exchanger (1).

5. A cooling system (24) according to any of claims 1-3, characterized in that the bypass (18, 20) is implemented as a channel formed in a connection plate (3, 4) of the heat exchanger (1), which channel is closed by a connection element (17), a transmission housing or a retarder housing.

6. The cooling system (24) according to any one of claims 1 to 3, characterised in that the bypass (18, 20) is integrated in a connecting element (17) of the heat exchanger (1), by means of which the heat exchanger (1) can be fastened on a transmission housing or a retarder housing.

7. A cooling system (24) according to any of claims 1-3, characterized in that in case the hydraulic retarder (23) is not activated, the working medium of the transmission is also led through a second area (15) of the heat exchanger (1) provided for cooling the working medium of the hydraulic retarder (23) and cooled.

8. Transmission of a motor vehicle, comprising a cooling system (24) according to at least one of claims 1 to 7.