Abstract:
A clutch unit for use in the drive train of a motor vehicle between a drive unit and a transmission including at least one transmission input shaft. The clutch unit includes at least one wet clutch device that is provided with a plurality of clutch elements, in particular clutch discs, that are at least partially wetted by a coolant such as oil. The coolant carries away frictional heat that is generated by slippage between adjacent clutch discs during certain vehicle operating conditions. The heat absorbed by the clutch coolant is cooled by heat transfer from the coolant to a cooler that surrounds the clutch unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of International Application Serial No. PCT/DE2007/000295, having an international filing date of Feb. 15, 2007, and designating the United States, the entire contents of which is hereby incorporated by reference to the same extent as if fully rewritten. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a clutch unit that includes at least one wet clutch that is cooled by a cooling fluid like, e.g., oil, that flows over the friction surfaces. The present invention particularly relates to a clutch unit that includes at least one multidisc clutch having input discs and output discs that are disposed behind one another in an axial direction, wherein a coolant flows between the discs at least when the multidisc clutch is open. The present invention furthermore relates to a clutch unit that includes at least two clutches, in particular multidisc clutches. 
     2. Description of the Related Art 
     Multidisc clutch units are disclosed in German published patent application Nos. DE 10 2004 061 020 A1, DE 10 2004 029 145 A1, and DE 10 2004 016 061 A1. 
     In such clutch units, typically the heat generated through friction at the discs has to be removed by a coolant. For that purpose, the clutches are cooled by oil in most applications. The oil has to be introduced into the clutches and has to be pumped out from the clutches again after the cooling process, in order to be cooled itself, in turn, in a cooler. Thereafter, it can be fed back into the coolant loop. 
     The quantity of cooling oil supplied to the clutches can be controlled according to the driving condition of the vehicle. While driving, a minimum coolant volume flow can be provided, in order to remove the heat generated by the slippage control of at least one of the clutches. During clutch operation, a large volume flow can be provided, since a rather large amount of heat is thus generated. During synchronization, the volume flow of cooling oil can be reduced to zero, in order to avoid a residual drag moment at the clutch discs. The largest volume flow is required during so-called stall. Thus, the entire engine power is dissipated by the clutch as heat. 
     Systems that use a separate oil cooler are state of the art. The hot oil is pumped out of the clutch and run into an oil container, or into the transmission sump. From there, the oil is pumped out by a separate pump and fed back to the clutch through an oil cooler. 
     It is an object of the present invention to provide a cooling device, which facilitates improved cooling of wet clutches. The clutch device in accordance with the present invention should furthermore only require little installation space, and it should preferably be possible to integrate it into the clutch unit. Furthermore, the clutch device in accordance with the present invention should have high efficiency and should be producible in a cost effective manner. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, the heat generated through the slippage of the friction discs of a wet clutch is removed by a coolant fluid that is in a coolant loop, and that is fed back to the clutch over and over again for heat removal. Within the coolant loop the liquid is cooled in order to again remove heat when it is run through the clutch the next time. The liquid is cooled by contacting a radially outward fluid cooled surface after leaving the friction discs, and by being run along that surface. The surface required for cooling is disposed in the radial direction around the outer clutch. That arrangement is shown in  FIGS. 1 and 2 . 
       FIGS. 1 and 2  illustrate the basic principle of an oil cooling system including an annular cooler  3 ′ that is integrated into the bell-shaped clutch housing. The functional principle and the configuration of the annular cooler will be described below in more detail. 
       FIG. 3  shows the cooling oil flow path in the illustrated double clutch. 
     The cooling oil is supplied close to the center of the clutch. Subsequently, it flows through the cooling oil grooves of the discs of the inner and of the outer clutch. The oil rotating with the clutch, which has heated up in both clutches, exits from the disc carrier of the outer clutch due to centrifugal force and impacts the wall of the cooler. 
     After the clutch disc cooling process, the oil arrives at a rotary feed gap  8 ′ within which the oil is kept in rotation by blades  4 ′ that are disposed on the disc carrier  14 ′. Through the kinetic energy of the oil, and due to the centrifugal force pressure due to the rotation, the oil is guided out of the clutch housing by an oil outlet guide mechanism  6 ′. The oil outlet guide mechanism is preferably provided in the lower portion of the clutch housing or of the clutch bell. Subsequently, the oil preferably flows through a jet pump  5 ′, which only operates under correspondingly high volume flows. By virtue of the jet pump, the cooling system is capable of increasing the volume flow very quickly when large volume flows of cooling oil are required. As already described, the oil exiting from the jet pump is supplied to the clutch in the center. Furthermore, the cooling system includes an overflow opening  7 ′, which prevents the clutch from filling up with oil and which can be used for oil exchange with the transmission, if so desired. 
     Through the system illustrated in  FIG. 3 , the following driving conditions of a motor vehicle can be implemented: 
     Driving: 
     The outlet guide mechanism  6 ′ or a regulating element  13 ′ is adjusted so that a small volume flow is diverted from the rotating ring of oil  2 ′. At that small volume flow, the jet pump  5 ′ does not operate. Thus, no oil is withdrawn from the storage cavity and/or transmission sump. The oil conveyed by the outlet guide mechanism  6 ′ flows back into the clutch. There, the heat is absorbed, which is generated by the slipping discs when the clutch is at least partially disengaged. Thereafter, the oil impacts the fluid cooled surface of the cooler  3 ′, which surrounds the clutches, and subsequently returns into the rotary feed gap  8 ′. Through the oil exchange pipe  10 ′, a preferably constant small volume flow can flow from the transmission sump  9 ′ into the rotary feed gap  8 ′. The volume flow equilibrium within the clutch, which is upset by that small volume flow, is balanced again by the overflow edge  12 ′. The oil that does not exit from the clutch through the outlet guide mechanism, runs over the overflow edge  12 ′ back directly into the transmission sump. 
     Shifting/Cooling: 
     The outlet guide mechanism  6 ′, or a regulating element  13 ′, is adjusted so that a volume flow that is as large as possible is drawn from the rotating ring of oil  2 ′. At that large oil volume flow, the jet pump operates and increases the volume flow accordingly. The entire volume flow is supplied to the clutch. In the clutch, that volume flow absorbs the heat generated by friction during the shifting process, uphill creep, or stall. Subsequently, the oil is cooled at the fluid cooled surface of the cooler  3 ′ and returns into the rotary feed gap  8 ′ again. The oil exchange pipe  10 ′ feeds a small volume flow from the transmission sump  9 ′ into the rotary feed gap  8 ′. The total volume flow balance is upset by the oil exchange pipe  10 ′ and by the jet pump  5 ′. The difference in volume flow between oil withdrawn from the rotary feed gap  8 ′ and the oil that is supplied to the clutch and to the rotary feed gap, is balanced by the overflow edge  12 ′. 
     Synchronizing 
     During synchronizing, no oil must flow through the discs of the clutch, since oil that is disposed in the clutch transmits moments through the slippage to the transmission input shaft, which are undesirable during synchronizing. 
     The outlet guide mechanism  6 ′, or an adjustment element  13 ′, is adjusted so that no oil is drawn from the rotating oil ring  2 ′. No oil is supplied to the clutch. The oil exchange pipe  10 ′ operates the same way as in the shifting and driving conditions. The oil supplied by the oil exchange pipe does not flow through the clutch. Therefore, that oil does not create any drag moments at the respective transmission input shaft. The oil volume flow coming from the oil exchange pipe  10 ′ flows over the overflow edge  12 ′ back into the transmission sump  9 ′. 
     System Initialization 
     When the engine is stopped, the oil in the oil ring  2 ′ collects in the lower portion of the clutch or of the clutch housing. When the engine starts, the blades  4 ′ paddle through the oil and make it rotate. At a certain speed of rotation, the oil ring is fully configured, and the oil cycle can be started by opening the outlet guide mechanism  6 ′ or the regulating element  13 ′. 
     System with Heat Sink 
     Depending upon the cooling power of the annular oil cooler, a suitable heat sink has to be used in order to intermediately store the amount of heat that was generated during stall. That arrangement serves to provide that the system also remains in thermal equilibrium under conditions that release large amounts of heat (e.g. stall). Either the transmission sump or a separate oil tank for the clutch can be used as an active heat sink. The transmission housing and the clutch bell form an additional passive heat sink. 
     System without Heat Sink 
     When the amount of heat generated during stall can be directly cooled off by the oil cooler, no heat sink is required. Here, it must be assured that the cooler has the same capacity as the capacity dissipated into heat during stall. 
     The cooled oil that is removed from the clutch by the oil outlet guide mechanism  6 ′ can be directly fed back to the clutch. The entire available oil volume includes the oil volume in the conduits, in the clutch, and in the rotary feed gap  8 ′. 
     Embodiments of the Particular Components 
     Rotary Feed Gap 
     In order to use the kinetic energy of the oil for feeding it, the oil must be kept in rotation by the rotating feed blades  4 ′. Thus, mechanical energy is imparted to the oil in order to be able to compensate for the friction losses at the wall of the gap, which oppose the direction of movement. 
     The rotary feed gap  8 ′ is bounded by the wall of the cooler, or by the clutch housing, and by the partition plate  1 ′. The overflow edge  12 ′ limits the height of the rotary feed gap, and thus the maximum height of the rotating oil ring. 
     Rotating Feed Blades 
     It is the object of the rotating feed blades  4 ′ to keep in rotation the oil that is found in the rotary feed gap  8 ′. Thus, the blades compensate for the velocity loss resulting from friction between the wall and the oil. Several rotating feed blades can be used; however, at least one blade has to be used. 
     The rotating feed blades are disposed at the outer disc carrier  14 ′. They can either be bolted to the disc carrier, welded, or soldered. Furthermore, the blades can be directly integrated into the disc carrier. 
     The shape of the blades can either be straight across the direction of movement, concave, or convex. Additionally, the blade can be twisted in order to achieve an axial feed component. 
     The blades can be made of metal and also of plastic. 
     Partition Plate 
     The partition plate  1 ′, which is visible in  FIGS. 3 and 4 , has the object to separate from the clutches the storage cavity and/or the transmission sump  9 ′ having a fluid storage level  23 ′. When the engine is running, the height of upper edge  24 ′ of the partition plate prevents oil from the transmission sump  9 ′ to flow into the clutches, since due to the rotating oil ring  2 ′, the oil level in the clutch is below the oil level  22 ′ in the transmission sump. When the engine is turned off, the oil level in the clutch rises above the oil level in the transmission sump. In that state, the partition plate prevents oil from the clutch to flow into the transmission sump, since the oil in the clutch is required for the initialization process when the engine is started again. 
     The overflow opening and the oil exchange mechanism are integrated into the partition plate. 
     Oil Exchange Mechanism 
     The oil exchange pipe  10 ′ shown in  FIGS. 3 and 5  uses the elevation difference of the rotating oil ring  2 ′ relative to the oil level  22 ′ in the transmission sump  9 ′ to facilitate a constant oil flow from the transmission sump into the clutch. The oil exchange mechanism operates according to the principle of communicating pipes. 
     When the vehicle is disposed in horizontal position, enough oil is available in order to form an oil ring when the engine is started. When the vehicle stands on an incline, there is the risk that oil within in the clutch flows into the transmission sump  9 ′ through the oil exchange pipe  10 ′. As a consequence, the oil remaining in the clutch is not sufficient to form an oil ring  2 ′ by means of the kinetic energy of which the oil cycle is put in motion. For that reason, the oil exchange mechanism is provided with a check valve  11 ′, which avoids a backflow of oil from the clutch into the transmission sump  9 ′. Check valve  11 ′ can be a flap, a ball check valve, or a similar mechanism. 
     The oil exchange components can be made of plastic and also of metallic materials. 
     Overflow Opening 
     As can be seen in  FIG. 6 , overflow opening  7 ′ is above the upper portion of the partition plate  1 ′. The overflow opening can either be configured as a slotted hole whose overflow edge extends at a predetermined radius, or it can be provided as several bore holes with the same diameter disposed next to one another, or it can be configured as an approximate semi-circular opening. 
     The overflow edge  12 ′ of the slotted opening determines the maximum filling level of the rotary feed gap  8 ′. When the oil level reaches the overflow edge  12 ′, superfluous oil flows through the opening and flows into the oil reservoir (separate clutch oil tank or transmission sump). The size of the overflow opening is determined by the maximum volume flow difference between the volume flow supplied to the clutch and the volume flow from the outlet guide mechanism. 
     The overflow opening  7 ′ shown in  FIG. 6  prevents a filling up of the rotary feed gap  8 ′, which would cause the clutch to fill with oil and would cause the discs of the outer clutch  25 ′ to run in an oil bath. This would cause splashing losses, and when the clutch is open, it would cause an undesired torque transmission. Additionally, the overflow opening  7 ′ contributes to the oil exchange between the clutch and the transmission sump/clutch oil tank, which is necessary to avoid a partially excessive oil attrition. 
     Outlet Guide Mechanism 
     It is the object of the outlet guide mechanism  6 ′ to divert oil from the rotating oil ring and to use its kinetic energy to create an oil loop and to operate the subsequently connected jet pump  5 ′. 
     In the conduit downstream of the jet pump  5 ′, it is necessary that the fluid that runs in the conduits only partially fills them, since the friction losses in filled tubular conduits creates a pressure drop. The pressure within the conduits must not exceed the ambient atmospheric pressure. In order to avoid that, an opening is made in the conduit at a suitable location in order to allow air to be sucked in. 
     The oil can be fed out of the rotary feed gap  8 ′ in radial and in axial directions. The following variants can be realized: 
     Outlet Guide in the Radial Direction According to  FIG. 7   
     Here the oil is fed out of the rotary feed gap  8 ′ in the radial direction. The branch-off from oil outlet guide mechanism  6 ′ is performed in a tangential direction relative to the rotating flow direction. A volume flow regulating element  13 ′ connects to the branch-off, by which the volume flow in the branch-off can be adjusted. 
     Outlet Guide in the Axial Direction According to  FIGS. 8 and 9   
     During outfeed in the axial direction, a flap  15 ′, which pivots about a rotation axis  16 ′, is submerged in the rotating oil ring. When the flow engages the flap, oil is diverted through the flap  15 ′ having an approximately U-shaped recess. Flap  15 ′ has a curvature in the direction of the outfeed pipe  17 ′, and thus diverts and branches the fed fluid off into the outfeed pipe  17 ′ and supplies it to the downstream jet pump  5 ′. 
     When the drive means for the rotation axis is located on the outside, it extends through a bore in the housing and is sealed with a seal element. An O-ring  18 ′ or other seal elements can be used as a seal element. 
     In an embodiment with an outfeed in the axial direction, shown in  FIGS. 10 and 11 , a slide  20 ′ is provided, which is movably supported in the axial direction. The slide has an approximately U-shaped recess, which has a curvature in the direction of the outfeed pipe, and thus redirects the fed fluid and supplies it to the outfeed pipe  17 ′. The slide is moved by a regulating element through the slide linkage  19 ′ into the respective required position. 
     Options to Actuate the Oil Outlet Guide Mechanisms 
     Flap Electromagnetically Actuated 
     The outfeed flap  15 ′, the slide  20 ′, and the volume flow regulating element  13 ′ can be driven by a solenoid. The volume flow regulating element  13 ′ and the slide  20 ′ can be moved directly by the plunger of a solenoid. The outfeed flap  15 ′ can be connected for rotation about rotation axis  16 ′ by an additional lever in order to facilitate its rotation. 
     Oil Outlet Guide Mechanism Actuated by an Electric Motor 
     The outfeed flap  15 ′, the slide  20 ′, and the volume flow regulating element  131  can be driven by an electric motor (with or without a transmission). The outfeed flap  15 ′ can be directly driven by the shaft of the electric motor or by the output shaft of a transmission. The slide  20 ′ and the volume flow regulating element  13 ′ can be moved by a lever mounted to the motor- or transmission shaft and a connecting rod, in order to produce linear movement. The slide  20 ′ and the volume flow regulating element  13 ′ can also be driven by an electric motor with a linear unit. 
     Flap Actuated by a Shape Memory Alloy 
     It is conceivable to move the outfeed flap  15 ′ and/or the slide  20 ′ and/or the volume flow regulating element  13 ′ by a shape memory wire, which becomes, e.g., shorter or longer when heated. When hot oil exits from the clutch, the wire becomes shorter and moves the respective outfeed mechanism into the position in which more oil is fed, and thus more oil is fed to the clutch. When colder oil exits from the clutch again, the wire becomes longer again, which causes a reset of the outfeed mechanisms. For resetting the outfeed mechanisms, they have to be provided with a respective reset spring. 
     The described actuation variant is a system that controls itself. 
     Flap Actuated by Bi-Metal 
     It is also possible to drive the outfeed flap  15 ′ and/or the slide  20 ′ and/or the volume flow regulating element  13 ′ by a bimetallic mechanism. The control principle is identical with the one including a shape memory wire. The reset spring for the regulation elements, however, would not be used in that application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following description of the figures, among others, embodiments for the cooler  3 ′, schematically illustrated in the  FIGS. 1 to 3  are described in more detail. In conjunction with the figure description further advantages, features, and details of a torque transfer device configured in accordance with the present invention or of a clutch unit configured in accordance with the present invention are described in more detail. 
       The figures show the following: 
         FIGS. 1 and 2  show a basic oil cooling arrangement for a double clutch; 
         FIG. 3  shows a coolant loop for the double clutch shown in  FIGS. 1 and 2 ; 
         FIG. 4  shows partition plate conditions with an engine off and on; 
         FIG. 5  is an enlarged view of the oil exchange mechanism; 
         FIG. 6  shows the partition plate and overflow opening; 
         FIG. 7  is an enlarged, fragmentary view of the radial outfeed arrangement; 
         FIG. 8  is an enlarged, fragmentary view of the axial outfeed arrangement with a flow control flap; 
         FIG. 9  is a view taken along the line A-A of  FIG. 8 ; 
         FIG. 10  is an enlarged, fragmentary view of the axial outfeed arrangement with a slide for flow control; 
         FIG. 11  is a view taken along the line B-B of  FIG. 10 ; 
         FIG. 12  is a fragmentary cross-sectional view of a first embodiment of a torque transmitting device; 
         FIG. 13  is a simplified schematic illustration of a torque transmitting device with a cooler in a semi sectional view; 
         FIG. 14  is a view taken along the line III-III of  FIG. 13 ; 
         FIG. 15  is an enlarged, fragmentary view of a cooler of a torque transmitting device in accordance with an embodiment of the present invention; 
         FIG. 16  is an enlarged detail of  FIG. 15 ; 
         FIG. 17  is a cross-sectional view of a torque transmitting device with cooler in accordance with another embodiment of the present invention; 
         FIG. 18  is an enlarged detail of a portion of  FIG. 17  in accordance with another embodiment of the present invention; 
         FIG. 19  is an enlarged detail of a portion of  FIG. 17  in accordance with another embodiment of the present invention; 
         FIG. 20  shows a cross-sectional view of a cooler for a torque transmitting device in accordance with another embodiment of the present invention; 
         FIG. 21  shows a cross-sectional view of a cooler for a torque transmitting device in accordance with another embodiment of the present invention; 
         FIG. 22  is a simplified fragmentary cross-sectional view of a torque transmitting device in accordance with another embodiment of the present invention; 
         FIG. 23  is a simplified fragmentary cross-sectional view of a torque transmitting device in accordance with another embodiment of the present invention; 
         FIG. 24  is a simplified fragmentary cross-sectional view of a torque transmitting device in accordance with another embodiment of the present invention; 
         FIG. 25  is a cross-sectional view of a torque transmitting device in accordance with another embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 12  shows a fragmentary cross-sectional view of a portion of a torque transmitting device  1  that is included as part of a drive train of a motor vehicle. A wet double clutch  6  in multidisc construction is disposed between a drive unit  3 , in particular an internal combustion engine from which a crankshaft extends, and a transmission  5 . Between the drive unit  3  and the double clutch  6 , a vibration damper  8  is connected, which is only indicated by its reference numeral in  FIG. 12 . The vibration damper  8  is preferably a dual mass flywheel. 
     The crankshaft of the internal combustion engine  3  is connected, e.g. through threaded connections, with an input component of the vibration damper  8 . The input component of the vibration damper  8  is coupled by energy storage elements in a known manner to an output component of the vibration damper. The output component of the vibration damper  8  is non-rotatably connected through a hub component  22  with an input component  24  of the double clutch  6 . The clutch input component  24  is integrally connected with an outer disc carrier  26  of a first multidisc clutch assembly  27 . Radially within the outer disc carrier  26 , an inner disc carrier  28  of the first multidisc clutch assembly  27  is disposed. The inner disc carrier  28  is mounted at the radial inner portion of a hub component  30 , which is non-rotatably connected to a first transmission input shaft. 
     The clutch input component  24 , or the outer disc carrier  26 , of the first multidisc clutch assembly  27  is non-rotatably connected through a coupling component to an outer disc carrier  36  of a second multidisc clutch assembly  38 . Radially within the outer disc carrier  36 , an inner disc carrier  40  of the second multidisc assembly  38  is disposed, which is connected to the radially inner portion of a hub component  41 . The hub component  41  is non-rotatably connected through a spline connection with a second transmission input shaft  42 , which is configured as a hollow shaft. The first transmission input shaft is rotatably disposed within the second transmission input shaft  42 . 
     The two multidisc clutch assemblies  27  and  38  are actuated by respective actuation levers  45  and  44 , whose radial inner ends are supported at actuation supports. Between the vibration damper  8  and the outer disc carrier  26  of the first multidisc clutch assembly  27 , a clutch cover  55  is disposed, which is mounted to a radially outer portion of a transmission housing section  58 . The clutch cover  55  separates a wet cavity  56 , in which the two multidisc clutch assemblies  27  and  38  are disposed, from a dry receiver cavity  57 , in which the vibration damper  8  is received. Radially inwardly between the clutch cover  55  and the clutch input component  24 , a bearing means  70  is disposed. 
     During the operation of the twin clutch  6 , heat is generated through friction at the discs. In order to remove the heat, cooling oil is supplied to the clutch  6 , wherein the cooling oil is cooled in a cooling loop. The cooling oil volume supplied to the clutch has to be controlled according to the driving condition of the vehicle. While driving, a minimum cooling volume flow is required, in order to remove the heat generated by the slippage control of the clutch. During clutch operation, a large volume flow has to be supplied, since a rather large amount of heat is generated. During synchronization, the cooling volume flow has to be reduced to zero, in order to avoid a residual drag moment at the clutch discs. The largest volume flow is required at rotational speeds that could cause stalling of the engine. During a stall, the drive unit rotates and the driven unit is stopped. The entire engine power is dissipated through the clutch in the form of heat. 
     Radially outwardly of the outer disc carrier  26  of the first multidisc clutch assembly  27 , an annular chamber  81  is provided that is used for receiving a cooler  84 . The annular chamber  81  is bounded radially outwardly by the transmission housing section  58 . In the axial direction, the annular chamber  81  is bounded on the drive side by the clutch cover  55 . Towards the transmission side, the annular chamber  81  is bounded by a wall  85  of wet cavity  56 . 
     In  FIGS. 13 and 14 , the basic principle of a torque transmitting device with a cooling system in accordance with the present invention is illustrated in a schematically simplified manner in different views. A crankshaft  88  of an internal combustion engine can be coupled by a first multidisc clutch  91  or by a second multidisc clutch  92  to a first transmission input shaft  101  or to a second transmission input shaft  102 . The multidisc clutch assemblies  91 ,  92  include outer multidisc carriers  94 ,  95  and inner multidisc carriers  97 ,  104 , respectively. An annular cooler  106  is disposed radially outwardly of the multidisc clutches  91 ,  92 . The flow direction of the cooling oil is indicated by a dotted arrow  108  in  FIG. 14 . 
     The cooling oil is cooled by contacting the radial inner wall of the annular cooler  106 , and by being guided along that wall immediately after leaving the cooling oil channels in the friction discs of the clutches  91 ,  92 . The surface necessary for cooling is disposed radially about the outer clutch  91  according to one aspect of the present invention. The cooling oil that is heated up by the slippage occurring in the clutches directly contacts the surface of the annular cooler  106  after leaving the outer disc carrier  94 . 
     In  FIG. 15  a portion of a clutch disc facing  121  is shown in a side view. Arrow  122  indicates that the clutch disc facing rotates clockwise during operation. The clutch disc facing  121  has radially outwardly-extending external teeth  124  that engage with radially inwardly extending recesses  125  between teeth provided on a disc carrier  128 . The disc carrier  128  includes radially outwardly-extending outer teeth  130 . At a radial distance from the disc carrier  128 , a cooler  136  with a cooler wall  138  is disposed. The cooler  136  is of annular form. 
     The clutch disc facing  121  includes cooling oil grooves  141 ,  142 . The cooling grooves  141 ,  142  have openings near throughbores  144 ,  145  that are provided in the disc carrier  128 . The medium to be cooled is indicated by small circles  148 . Arrow  151  represents a radial velocity component of the medium to be cooled. Arrow  152  represents a circumferential velocity component of the medium to be cooled. In the cooler  136 , a cooling medium, preferably water, is included, which is indicated by larger circles  155 . Arrow  158  indicates that the cooling medium  155  flows through the annular cooler  136  in a counterclockwise direction. 
     Due to the rotation of the disc carrier  128  and of the clutch disc facing  121 , the cooling oil, when leaving the clutch disc, has a an initial radial velocity component  151  produced by the centrifugal force, and also has an initial circumferential velocity component  152  produced by the circumferential pulling effect of the cooling oil grooves  141 ,  142 . The outer teeth  130  of the outer disc carrier  128  act as a circumferential guide mechanism and thus maintains the final circumferential velocity component  153  of the oil almost constant. As a result of the circumferential pulling effect, the time of exposure of the hot oil at the surface of the cooler wall  138  is increased, which facilitates the discharge of an accordingly large amount of heat to the cooler  136 . 
     As shown in  FIG. 16 , by virtue of the rather large peripheral speed of the disc carrier  128 , during the operation of the clutch, and by virtue of the relatively small distance between the cooler wall  138  and the outer teeth  130  of the disc carrier  128 , an oil drag flow with a high level of turbulence is produced. The greater the turbulence of the flow, the better the heat transfer from the cooling oil to the cooler. Through the strong swirling of the oil molecules, which do not only move in the circumferential direction, but also transversely to the flow direction, the result is that each oil molecule reaches the surface of the cooler at least once and can discharge the stored heat. 
     A steel disc  241  is shown in  FIG. 17  and is engaged with an outer disc carrier  242 . An oil cooler  244  is disposed radially outwardly of the outer disc carrier  242 . The cooler  244  has an inlet  245  and an outlet  246  for the cooling medium. The arrows shown in  FIG. 17  indicate the cooling medium flowing through the cooler  244 . 
     The cooler  244  is annular and is disposed so that cooling oil leaving the outer disc carrier  242  directly impacts the surface of the cooler inner wall  249 . The flow direction of the cooling medium is always against the direction of rotation of the engine and thus of the clutch. That causes small energy losses due to the low average temperature difference between the fluids. The principle of operation of the present invention is similar to the principle of operation of a counterflow heat exchanger. The difference, however, is that hot cooling oil from the clutch is provided to the cooler over the entire cooler circumference, which means the oil inflow temperature is almost constant. The cooling medium temperature in the cooler, however, increases from the cooler inlet  245  to the cooler outlet  246 . 
     The distance between the outer teeth of the outer disc carrier  242  and the cooler inner wall  249  of the cooler  244  is determined by the diameter of the cooler. That distance is preferably selected so that the cooling power due to the high turbulence of the cooling oil, and thus a large heat-transfer coefficient, becomes as large as possible, and the drag moment due to the Newtonian shear stress of the cooling oil becomes as low as possible. The effect of the distance on the cooling power and on the heat-transfer coefficient is indirectly proportional, which means that when the distance is large, the drag moment is small and the cooling power is low. At a distance as small as possible, cooling power and drag moment are inversely affected. 
     In order to improve heat transfer, the heat transfer surface between the cooler inner wall  249  and the cooling medium can be enlarged. For that purpose, several possibilities can be considered. 
       FIG. 18  shows that the cooler  244  can be filled with a plurality of balls  251 - 253  having an open porous metal foam structure. The balls  251 - 253  are preferably made of a material that corresponds to the material of the cooler housing. The cooler can also be filled with a material present in the form of loose material, e.g., with metal chips. The filling is preferably performed so that the material is in contact with the cooler wall, so that the contact surface between the cooler wall and the cooling medium is highly increased, while only slightly increasing the flow-through resistance of the cooler to the cooling medium. 
       FIG. 19  shows that the cooler  244  can also include installed annular turbulence plates  256  for surface area increase, and which are beaded or perforated, or beaded and perforated. The plates  256  are preferably disposed so that they are in contact with the heat absorbing cooler inner wall, and can thus conduct the heat into the center of the cooler  244  in order to be able to transfer it to the cooling medium there. Through the perforation and/or corrugation of the plates  256 , the flowing cooling medium is deflected with respect to its flow direction. The molecules of the cooling medium are thereby increasingly deflected with respect to the main flow direction, and thus facilitate a higher heat-transfer coefficient, and consequently a greater cooling power through an increased contact with the turbulence plates  256  and the cooler walls. Additionally, the cooling power is increased by the increased surface area. 
       FIG. 20  shows a cross-sectional view of a cooler  260  in the form of a bent tube  261 . The tube  261  is closed by a cover  263 ,  264 , respectively, at each of its open ends, wherein the covers are welded to the tube  261 . The cooler  260  thus has the shape of a ring provided with an opening  266 . In order to avoid escape of the oil drag flow during operation, the opening  266  is closed by a bridge plate, which is not shown. 
       FIG. 21  shows a cross-sectional view of a cooler  270  that can be produced by milling from a solid ring  271 . The cavity receiving the cooling medium is thus fabricated by milling. Subsequently, the cooler  270  is closed by a suitable cover. The cooler  270  includes an inlet  276  and an outlet  277  that open radially outwardly for the cooling medium. 
       FIG. 22  shows a crankshaft  281  of an internal combustion engine that can be coupled to the transmission shafts  286 ,  287  through multidisc clutches  284 ,  285 . A clutch cover  288  is supported at a transmission housing section  289 , which is also designated as a clutch bell. The clutch cover  288  includes a U-shaped cross section  291  radially between the multidisc clutch  284  and the clutch bell  289 . The U-shaped cross section  291  of the clutch cover  288  defines an annular cavity  292 , which is closed on the drive side by a circular annular disc  293 . The clutch cover  288  among other things is used for supporting the clutch engagement forces of the multidisc clutches  284 ,  285  through a bearing, which is not shown. By virtue of the U-shaped cross section  291 , it is possible to integrate the cooler into the clutch cover  288 . 
       FIG. 23  shows that the clutch bell  289  can also be provided as a cast component. Then, it is advantageous to cast an annular cavity  295  into the clutch bell  289 . The annular cavity  295  can be used as a cooler and can be closed by cover  296 . When the cooler does not have to be filled with additional swirl plates, it is possible to integrally cast the closed cavity  295  with respective connections. The clutch bell  289  with the cavity  295  can be connected directly to the engine by a flange and a suitable seal. 
       FIG. 24  shows a clutch bell  300  that is radially inwardly contacted by a cooler  302 . The cooler  302  is disposed in the radial direction between the multidisc clutch  284  and the clutch bell  300 . A radially extending water inflow bore  304  is provided in clutch bell  300 . The water inflow bore  304  is connected to the inner cavity of the cooler  302  through a connection spout  305 . The connection spout  305  extends parallel to the transmission input shafts  286 ,  287 . The free end of the connection spout  305  is received in an axial bore  307  in the clutch bell  300  and is sealed by an O-ring  308 . During installation, the cooler  302  is inserted from the drive side into the clutch bell  300 . Thus, the connection spout  305  and an additional connection spout are inserted into respective bores in the clutch bell  300 . In the region outside the clutch bell  300 , connection conduits for the input and the output of cooling medium are mounted, which are not shown. 
       FIG. 25  shows a cross-sectional view of a cooler  310  that is disposed radially between a clutch bell  312  and an outer disc carrier  242  that includes a steel disc  241 . The cooler  310  includes an inlet bore  314  and an outlet bore  315  for the cooling medium. The inlet bore  314  is aligned with an inlet bore  316  provided in the clutch bell  312 . The outlet bore  315  of the cooler  310  is aligned with an outlet bore  317  provided in the clutch bell  312 . The inlet bores  314 ,  316  and the outlet bores  315 ,  317  extend parallel to one another in a vertically downward direction. The cooler connections are sealed respectively by an O-ring  318 ,  319  with respect to the clutch bell  312 . Connection conduits, which are not shown, are then connected to the inlet and outlet bores  316 ,  317 , respectively, of the clutch bell  312 . 
     The disclosed embodiments do not constitute any restrictions of the invention. To the contrary, numerous variations and modifications are possible within the scope of the present disclosure, in particular those that can be formed by combination or variation of particular features, or elements, or method steps, in conjunction with those included in the general description, and in the description of the figures, and in the claims, and in the drawings.