Abstract:
A torque-transmitting device is connected to a prime mover unit and a speed-changing transmission and includes a hydrodynamic torque-converter or fluid coupling with a pump wheel, a turbine wheel and in some cases a stator wheel. The torque-transmitting device has a disconnecting clutch to uncouple it from the prime mover unit.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a torque-transmitting device, particularly for motor vehicles, with a prime mover unit such as a combustion engine with a driving shaft, a speed-changing transmission with a transmission input shaft, and a hydraulic coupling device between the prime mover unit and the transmission, i.e., a fluid coupling such as a Föttinger coupling, or a hydrodynamic torque converter, consisting of at least a pump wheel connected to the torque-input side and a turbine wheel connected to the torque-output side, as well as in some cases a stator wheel interposed between the pump wheel and the turbine wheel, and at least one housing solidly connected to the pump wheel and containing the turbine wheel. 
     Devices of this kind have been known for a long time and have been optimized for a great variety of diverse tasks and requirements. In order to completely disengage the torque-transmitting unit from the prime mover unit, DE-OS 40 07 424 proposes the use of a mechanical clutch arranged outside of the housing between the prime mover unit and the torque-transmitting unit, where the mechanical clutch either comprises a separate piston housing for the hydraulic control of the clutch or requires the axial displacement of a housing shell for disengaging the clutch. Thus, the proposed solution requires more space in the axial direction and is expensive to implement. 
     OBJECT OF THE INVENTION 
     Therefore, the object of the present invention is to provide a torque-transmitting device that comprises a disconnecting clutch between the hydraulic coupling device (i.e., a fluid coupling or hydrodynamic torque converter) and the prime mover unit but requires neither appreciably more axial space nor additional external actuator means for the disconnecting clutch while at the same time offering the advantage of a simple and cost-effective design. 
     SUMMARY OF THE INVENTION 
     The invention is embodied in a torque-transmitting device comprising a prime mover unit such as a combustion engine with a driving shaft, a speed-changing transmission with a transmission input shaft, and a hydraulic coupling device between the prime mover unit and the transmission, i.e., a fluid coupling such as a Föttinger coupling, or a hydrodynamic torque converter, comprising at least a pump wheel connected to the torque-input side and a turbine wheel connected to the torque-output side, as well as in some cases a stator wheel interposed between the pump wheel and the turbine wheel, at least one housing solidly connected to the pump wheel and enclosing the turbine wheel, and also comprising at least one disconnecting clutch that is arranged inside the housing and serves to uncouple the housing from the prime mover unit. 
     Accordingly, the disconnecting clutch can be arranged in a space-saving manner immediately inside the housing and without the need for additional housing parts. 
     It is particularly advantageous to use the disconnecting clutch to uncouple the prime mover unit from the fluid coupling or torque converter with the speed-changing transmission because the two aggregates can be operated independently of each other. Thus, for example, an electric machine driving the torque converter can power the motor vehicle when the prime mover unit is uncoupled, or the prime mover unit can power only additional auxiliary aggregates without driving the torque-transmitting device. 
     In advantageous arrangements, the electric machine is rotationally locked to the housing, for example by means of toothed profiles, friction wheels, belt drives or chains; or the electric machine may be arranged immediately around the housing with the rotor being solidly attached to the housing so that it rotates together with the latter. Thus, the “stator” is mounted on and rotates with the housing of the electric machine i.e. has a non-rotatable connection to a component, e.g., to the housing or a supporting holder mounted on the housing, of either the prime mover unit or the speed-changing transmission. The latter may be, for example, an automatic step-shifting transmission, continuously variable transmission or the like. 
     The housing of the torque-transmitting device, particularly in combination with an attached rotor, represents the inertial mass for the prime mover unit. To increase the moment of inertia, the rotor can be equipped with an additional inertial mass that is preferably arranged between the prime mover unit and the torque-transmitting unit and preferably has a shape that conforms, but leaves a clearance, to the contour of the one half of the housing that faces towards the prime mover unit, to make optimum use of the available space. 
     An inventive embodiment of the disconnecting clutch may consist, e.g., of an axially movable piston with preferably at least one friction lining arranged near the outer perimeter by which the piston engages a corresponding friction surface on the housing or on a component connected to the housing; or the piston may comprise a pressure surface by which it acts against laminar clutch disks that are attached to the housing to form a frictional coupling. In an advantageous arrangement, the at least one friction lining can be mounted on a conically sloped, ring-shaped exterior part of the piston conforming to the conical shape of the one half of the housing facing towards the side of the prime mover unit. This allows the centrifugal effect of the rotating housing to generate greater amounts of contact pressure and to thereby increase the amount of torque that can be transmitted. 
     When the clutch is engaged, to transmit the torque from the driving shaft to the housing and thus to the pump wheel that is solidly attached to it, the piston according to the invention can be arranged around and rotationally locked to a connecting part of the driving shaft that extends into the housing. The connecting part is, e.g., centered on or in the driving shaft and non-rotatably connected to the latter through an axially flexible and rotationally stiff torque-transmitting sheet-metal plate, the connecting part being attached to the torque-transmitting sheet-metal plate through a radially oriented flange-like part. The connecting part can also be formed by the driving shaft itself. 
     It is further advantageous to actuate the piston by means of the pressure supplied by the existing oil pump that is used to run the transmission. A chamber is formed for this purpose between the housing wall on the prime mover side and the piston, which can be supplied with oil, e.g., via a bore through the transmission input shaft, thereby creating a positive pressure differential relative to the pressure in the housing. The pressure differential causes the piston to move axially in the direction towards the turbine wheel and thereby retracts the friction layers from the housing wall or opens a set of laminar disks, so that the clutch is disengaged. The axial travel of the piston can be induced, e.g., by means of a toothed profile on the connecting part, or the piston can be solidly attached to the connecting part via a ring-shaped intermediate part, the latter being axially movable. The axial travel can also be made to work against the force generated by leaf springs that are distributed over the perimeter and are connected to the piston at the ends facing towards the perimeter and at their opposite ends to a driving part, e.g., to the housing or the connecting part, or else to a part that has a force-transmitting relationship to the housing or the connecting part. The axial travel is compensated for by the intermediate part, which for this purpose may have a wave-shaped cross-section. The peaks and valleys of the waves can advantageously be arranged transverse to the radial direction of the ring. 
     It may furthermore be advantageous to provide the torque-transmitting device with a lockup clutch of an essentially known design in order to bypass the torque converter when the rpm of the prime mover unit exceeds a set, pre-determined rpm value and to conduct the torque flow directly from the housing to the transmission input shaft. In an advantageous configuration, the lockup clutch, likewise, is shaped as a piston that may be of a design corresponding to that of the piston of the disconnecting clutch. The piston has a rotationally locked and axially movable mounting connection to the driven side, e.g., on the turbine hub. 
     In an embodiment according to the invention, the disconnecting clutch piston may have a friction surface on the reverse side of where the friction lining is attached, and the lockup clutch piston may have at least one friction lining at the same radial location, so that a frictional engagement occurs on the disconnecting clutch piston. A second chamber is being formed by the two pistons, which can be kept open by establishing a pressure in excess of the interior pressure of the torque converter and is closed by reducing the pressure. The pressure build-up occurs by adding pressure medium, preferably a converter medium such as oil or automatic transmission fluid (ATF), which may be introduced, e.g., through an opening from the space between the rotationally locked seat of the stator wheel and the transmission input shaft. 
     In accordance with a further concept of the invention, a flange may be provided, preferably extending radially from the exterior perimeter towards the inside, that can comprise friction surfaces for both pistons, so that a discrete piston acts with its friction linings against each side, whereby a mutually independent operation of the two clutches can be provided. In an advantageous configuration, the flange that is fastened at its exterior perimeter and extends towards the inside conforms to the contour of the one half of the enclosure on the output side, whereby a space-saving configuration is achieved. 
     As a further advantageous design possibility, the two clutches may be arranged at a radial distance from each other, so that the friction linings of one clutch make frictional contact with the housing or a part connected to it at a smaller diameter and the friction linings of the other clutch make contact at a larger diameter. As an advantageous arrangement, the disconnecting clutch can be located at a smaller diameter in a bay of the housing towards the prime mover unit, and the lockup clutch can be arranged radially outside of the disconnecting clutch. Both pistons may have a conical shape to enhance the compressive force, so that the friction linings that contact the housing wall follow the contour of the latter and enclose an angle α between 90° and 180°, but preferably between 120° and 170°, with the direction perpendicular to the driving shaft or the direction perpendicular to the transmission input shaft. It can further be advantageous in view of the amounts of torque to be transmitted from the prime mover unit if a larger angle α is selected for the disconnecting clutch than for the lockup clutch. 
     There may further be an advantage in an embodiment with only one clutch that is capable of performing both the function of the disconnecting clutch and of the lockup clutch. For this purpose, the clutch can be connected through an axially movable control flange with a form-locking engagement to the driving shaft or its connecting part that extends into the housing, or it may be connected to the turbine wheel or its hub or similar element that is arranged on the transmission input shaft. The axially movable control flange may, e.g., consist of a U-shaped flange that is open towards the driving shaft and whose radially inner U-leg can be supported without rotational constraint on the transmission input shaft. At the outside circumference, the radially outer U-leg can have an external tooth profile for a form-locking engagement with an internal tooth profile oriented axially in the direction of the driving shaft, and the radially outer U-leg can also have an internal tooth profile to engage an external profile on a shoulder of the driving shaft or on its connecting part. The axial movement is effected by the application of pressure to the control flange. For example, a pressure channel may be provided in the transmission shaft that is directed towards the end face of the U-shaped control flange and moves the latter against the pressure of the medium in the converter. The reverse movement occurs when the pressure channel is opened, in which case the control flange can be moved backwards by the pressurized medium in the converter. When the clutch is used as a lockup clutch, the torque supplied by the prime mover unit can be transmitted by a free-wheeling element arranged between the driving shaft and the housing. The free-wheeling element is overrun when an electric machine arranged around the housing sets the latter into rotary motion. 
     Other advantageous embodiments of the invention may involve the use of a damper device that may work between the driving shaft and the housing and/or between the turbine wheel or the lockup clutch and the transmission input shaft. These kinds of damper devices can be based on an essentially known design that comprises an input member and an output member that are rotatable relative to each other as they work against the force of at least one energy-storage device such as a compressive helix spring, an arcuate spring, a rubber element and/or a similar device. 
     With the torque-transmitting device according to the invention it is possible for the prime mover unit and the torque-transmitting unit for a speed-changing transmission to function independently of each other, so that a method can be proposed in accordance with the invention whereby the motor vehicle may be powered alternatively by an engine and an electric machine. In an arrangement of this kind, the electric machine has a rotationally locked connection to the housing of the torque-transmitting unit, for example by means of toothed profiles or belt drives, or the electric machine is directly attached to the housing. Preferably, the rotor is arranged so that it surrounds the torque converter or fluid coupling. The disconnecting clutch is disengaged in the alternative power mode. The electric machine drives the housing as well as a transmission oil pump, whereby the torque converter is filled with fluid, so that the turbine wheel and thus the transmission input shaft are entrained by the rotating housing. 
     As a further advantageous mode of operation according to the invention, a method is proposed for starting the prime mover unit with the electric machine. In a first step, with the disconnecting clutch disengaged, the rotor and/or an inertial mass of the converter unit, e.g., the inertial mass of the torque-converter itself and/or an additional inertial mass that is attached to the rotor, is put into rotation and brought up to speed. In a second step, the disconnecting clutch is engaged, so that the rotation is imparted to the driving shaft and the prime mover unit is started. It is advantageous to actuate the clutch by using the pressure that is provided by the oil pump as soon as the electric machine starts to turn. As a further concept, an accelerated starting process can be proposed in which the disconnecting clutch is engaged as soon as there is sufficient pressure to perform the engagement. The resulting mixed mode between inertial start and direct start offers the possibility of using a lower rpm of the electric machine. When an external pump is used that is independent of the rpm of the electric machine, e.g., an electric pump, the disconnecting clutch can be engaged immediately and a direct start can be performed. 
     As is essentially known, after the prime mover unit has been started, an electric machine of this kind may be used as an electric power generator. The electric machine can be of the synchronous, asynchronous, or reluctance type or the like. 
     The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be explained on the basis of FIGS. 1 through 4, all of which represent partial views of torque-transmitting devices in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 represents an embodiment of a torque-transmitting device  1  with a driving shaft  2  belonging to a prime mover unit (not shown) and a connecting flange  3  that is received and centered in a recess  2   a  of the driving shaft  2 . The flexible torque-transmitting sheet-metal plate  4  is bolted to the driving shaft  2  and to a sheet-metal connector plate  5  that is centered on and welded to the connecting flange  3 . To eliminate axial vibrations of the prime mover unit, one of the sheet-metal plates  4 ,  5  in this arrangement may have resilience in the axial direction. Angular and axial misalignments between the driving shaft  2  and the connecting flange  3  can be compensated for through the flexible torque-transmitting sheet-metal plate  4 . 
     To seat the connecting flange  3  on the transmission input shaft  6 , the connecting flange  3  has a recess  3   a  where the transmission input shaft  6  is axially received with an interposed slide bushing  7  and the transmission input shaft  6  is sealed against the connecting flange  3  by means of a seal  6   a.  The housing part  8  at the prime mover side of the housing  9 , e.g., a sheet-metal stamping, has an axially extending portion  8   a  serving as support flange where the housing part  8  is rotatably supported on the outside circumference of the connecting flange  3  with a slide bushing  10  and sealed by means of the seal  11 . The housing part on the opposite side from the prime mover unit is welded to the pump wheel  12  whereby the converter housing  9  is formed. Through the converter medium, e.g., oil or automatic transmission fluid (ATF), the pump wheel  12  drives the turbine wheel  13  that is mounted on a hub  14 . 
     At the end that faces towards the turbine wheel  13 , the connecting flange  3  spreads out into a radially extending flange portion  15  which, by means of rivets  16  distributed along its circumference, holds a ring-shaped intermediate part  17  of undulating cross-section. The undulating shape provides resilience to allow axial movement. At its outer radius, the intermediate part  17 , again by means of rivets  18  distributed along its circumference, holds a piston  19  for a disconnecting clutch  20 . The radially outer portion  21  of the piston  19  is cone-shaped to conform to the corresponding contour of the housing part  8  and carries a friction lining  22  that engages the friction surface  23  of the housing part  8  when the clutch  20  is engaged. Due to the conical shape of the outer portion  21  of piston  19 , the contact force, being dependent on the rpm of the housing  9 , becomes greater with the increase in the centrifugal forces. 
     The disconnecting clutch  20  is controlled by the pressure of a medium in the chamber  24  that is formed by the piston  19  and the housing part  8 . To accomplish this purpose, a pressure-generating device (not shown) supplying the torque-converter  28  and the transmission (which follows the converter in the torque-flow path) pumps converter medium through a bore  25  in the transmission input shaft  6 , a feeder hole  26 , and a connector opening (not shown) of the slide bushing  10  or the connecting flange  3  into the chamber  24 , building up the pressure in chamber  24  to the point where it exceeds the pressure in the converter chamber  27 . The resulting axial movement of the piston  19  causes the friction lining  22  to exhibit an increasing amount of slippage until it is completely retracted so that separation of the driving shaft  2  from the housing  9  occurs and the torque converter  28  is put out of operation. The friction lining  22  may also consist of a plurality of individual friction linings and/or of friction linings with various surface configuration that ensure the passage of a minimum amount of converter medium for cooling. 
     Among other applications, the use of a disconnecting clutch  20  is advantageous in embodiments comprising an electric machine (as shown). In the drawing, only the rotor  29  of the electric machine is indicated, being arranged around the housing  9  on a support  32  that is welded to the housing. The stator (not shown) is attached to a stationary, non-rotating part of the prime mover unit and/or of the transmission. To increase its moment of inertia, the rotor  29  is equipped with an additional inertial mass  30  that conforms to the contour of the cone-shaped portion  21  of the housing part  8  and is bolted to the rotor by means of screws  31  passing all the way through the support  32 . When the electric machine is activated, the housing  9  rotates with the disconnecting clutch in an undefined state, i.e., not yet locked into frictional contact, and drives the oil pump that is connected to the housing, preferably to the neck  33  of the converter. The oil pump now supplies an increased amount of fluid to the chamber  24 , which causes the disconnecting clutch  20  to disengage. When the housing  9  has attained enough momentum to start the prime mover unit, the pressure in the chamber  24  is reduced and the clutch  20  is engaged so that a frictional locking contact is made with the housing  9 , whereby the rotation is transmitted to the driving shaft  2  and the prime mover unit is started. Once the prime mover unit is running, the electric machine is used as a power generator. If the electric machine is to be used as the only power source for the motor vehicle, the disconnecting clutch  20  remains permanently disengaged. 
     A lockup clutch  34  is provided for bypassing the converter  28 . The lockup clutch  34  comprises a piston  35  with at least one friction lining  37  that may have a surface finish or configuration designed to assure the passage of a minimum amount of converter medium for cooling. The piston  35 , too, has a conical shape in its radially outer portion that carries the friction lining  37 . To perform its function, the piston  35 , by means of an axially formed neck  38  extending towards the turbine wheel, is supported and centered on the turbine hub  14  with axial and rotational mobility, limited by a stop in the form of a radially stepped-up shoulder  39  of the turbine hub. The converter medium to supply the chamber  52  for disengaging the lockup clutch  34  is fed through the gap  53  between the transmission input shaft  6  and the hollow stator shaft  54 . The pressure for engaging the lockup clutch  34  is built up by introducing converter medium into the converter chamber  27  through the annular gap  55  between the stator shaft  54  and the converter neck  33 . To engage the disconnecting clutch  20 , the pressure in the chambers  27 ,  52  is increased in relation to that in the chamber  24 . A controlled amount of slippage is obtained in the lockup clutch  34  by varying the pressure in chambers  52 ,  27  but keeping the overall pressure in the two chambers  52 ,  27  sufficiently high for the disconnecting clutch  20  to remain engaged. Examples of reference values for the pressure ranges in the chambers  24 ,  27 ,  52  for controlling the clutches  20  and  34  are shown in Table 1. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Pressure in 
                 Pressure in 
                 Pressure in 
               
               
                   
                 chamber 24 
                 chamber 52 
                 chamber 27 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Clutch 20 disengaged 
                 5 bar 
                   4 bar 
                   3 bar 
               
               
                 Clutch 34 disengaged 
               
               
                 Clutch 20 engaged 
                 0 bar 
                  11 bar 
                  10 bar 
               
               
                 Clutch 34 disengaged 
               
               
                 Clutch 20 engaged 
                 0 bar 
                 0-10 bar 
                 0-10 bar 
               
               
                 Clutch 34 slipping 
               
               
                   
               
             
          
         
       
     
     The radial contour of piston  35  roughly follows the shape of the turbine wheel  13 . At a radius that lies inside of the greatest axial overhang of the piston  35  towards piston  19 , pockets  40  are formed in the piston  35  to accommodate and take up the thrust of energy-storing elements  42  belonging to the damper device  41 . In this manner, the piston  35  with pockets  40  in combination with a ring-shaped disk-like part  43  (to which the piston  35  is connected by spacer bolts that are not shown) with pockets  44  for the energy-storing elements  42  functions as an input member of the damper device  41 . The output member is constituted by an axially interposed flange  45  with cutouts  46  for the energy-storing elements  42 . At its inside circumference, the flange  45  has an internal tooth profile  47  that engages an external tooth profile  48  of the turbine hub  14  with rotational play. This provides a limited extent of relative rotation between the piston  35  and the turbine hub  14  in opposition to the force of the energy-storing elements  42  that can be distributed around the circumference. In combination with the friction device  49 , this arrangement provides damping in case of rotational oscillations. 
     The turbine hub  14  is rotationally locked to the transmission input shaft  6  by means of the tooth profile  50 , axially spaced apart from the connecting flange  3  by means of the stop contact  51  and sealed against the stator shaft by means of the seal  56 . At a radius outside of the seal  56 , the turbine hub  14  is provided with a radially outward-directed flange-like part  57  to receive the turbine wheel  13 . The latter is attached to the circumference of the flange-like part  57 , e.g., by pulsed resistance welding with the addition of a reinforcing ring  58  on the side of the turbine wheel  13  that faces away from the flange-like part  57 . At its inside, the turbine wheel bears axially against the stator wheel  59  by means of the bearing  60 , while the stator wheel  59 , in turn, bears axially against the pump wheel by means of the bearing  61 . The stator wheel is mounted on a free-wheeling hub  62  surrounding a flange-like part  63  with an internal tooth profile  64  providing a non-rotatable connection to the stator shaft. 
     FIG. 2 represents an embodiment of a torque-transmitting device  101  that is similar to the embodiment of the torque-transmitting device  1  in FIG. 1 except that the following features are different: 
     The element that carries the friction surfaces  123 ,  165  of the disconnecting clutch  120  and the lockup clutch  134  is provided in the form of a flange  166  that is non-rotatably connected to the housing  109  of the torque converter  128  and comprises on its two sides the friction surfaces  123 ,  165  for the friction linings  122 ,  137  of the two clutches  120 ,  134 . The flange  166  has a conical shape and slopes away from the turbine wheel  113 . The pistons  119 ,  134  conform to this contour, and the axially movable piston  119  now becomes disengaged by feeding converter medium at a requisite pressure to the chamber  124  not shown in FIG.  2 . This embodiment allows separate control and operation of the two clutches  120 ,  134 , so that the lockup clutch  134  may be engaged or operated with slip while the disconnecting clutch  120  is disengaged. It is further possible to also operate the disconnecting clutch  120  in a slipping mode. 
     FIG. 3 represents an embodiment of a torque-transmitting device  201  similar to the preceding embodiments, comprising two independently controllable clutches  220 ,  234 , that are equipped with friction linings  222 ,  237 , respectively, to engage corresponding friction surfaces  223 ,  265  of the housing part  208  on the prime-mover side of the housing  209 . The friction surface  223  for the disconnecting clutch  220  is arranged at a radius inside the friction surface  265  for the lockup clutch  234 . Both friction surfaces have a conical shape, where the angle α between the direction perpendicular to the rotational axis  270  and the conical slope of the frictional surface  223  lies in the range 100°&lt;α&lt;110°. The corresponding angle α′ for the lockup clutch lies in the range 130°&lt;α′&lt;140°. The choice of the angles α, α′ is a determining factor for the magnitude of the increased contact pressure of the friction linings  222 ,  237  against the friction surfaces  223 ,  265  as a result of the centrifugal force. 
     A further embodiment of a torque-transmitting device  301  according to the invention is shown in FIG.  4 . It has a single clutch  320  that is used both as lockup clutch and disconnecting clutch. This is accomplished by arranging the piston  319  of the clutch  320  on an axially movable control flange  367  of U-shaped cross-section. The radially inner leg  369  of the control flange  367  is centered in a cylindrical recess  371  of the turbine hub  314  that opens towards the side of the prime mover. By means of the seals  370   a,    370   b,  the control flange  367  forms a chamber  368  that is supplied through a supply bore  372  with converter medium from the hollow transmission input shaft  373 . When the fluid in the chamber  368  is pressurized, the control flange  367  is moved axially against the pressure of fluid in the chamber  324  that is formed by the piston  319  and the housing part  308 ; or, if the pressure in chamber  324  is greater than in chamber  368 , the control flange  367  is pushed in the reverse direction. Through this axial displacement of the control flange  367 , an axially protruding internal tooth profile  374  of the radially outer leg  375  is brought into form-locking engagement with an exterior tooth profile  376  of the connecting flange  303  whereby a torque-transmitting connection with the driving shaft  302  is established. At the opposite end stop of the displacement range, an external tooth profile  377  is brought into form-locking engagement with the internal tooth profile  378  of the turbine hub  314 . The external tooth profile  377  also engages the output member  345  of the damper device  3412  so that the latter is effective in both the separator and the lockup mode of the clutch. 
     To start the prime mover unit, the rotor  329  of the electric machine turns the housing  309  and, together with the housing  309 , also drives the pump wheel  312  and an oil pump downstream in the torque-flow. The oil pump supplies pressure to the chambers  324 ,  368 , thereby disengaging the clutch  320  and moving the control flange  367  axially towards the side of the prime mover unit so that the control flange is brought into form-locking engagement with the connecting flange  303 . When the rotational momentum is sufficient to start the prime mover unit, the clutch  320  is engaged by pressurizing the fluid in the chamber  327  and the prime mover unit is started. The free-wheeling hub  379  that is interposed between the housing part  308  and the connecting flange  379  is overrun in this starting process. After the prime mover unit has been started, the pressure in chamber  368  is lowered, and at the same time the pressure is lowered in chamber  327  or raised in chamber  324 , so that the resulting axial movement brings the control flange  367  into form-locking engagement with the turbine hub  314  and the clutch  320  is disengaged. Now, if the torque converter  328  is to be bypassed, the clutch  320  is engaged by pressurizing the fluid in the chamber  327 , or a slipping mode of operation is obtained through a controlled amount of pressurizing. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic and specific aspects of the aforedescribed contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the appended claims.