Abstract:
A drive unit for motor vehicles with hybrid drive and a drive train in a longitudinal arrangement, between the internal combustion engine and the first axle, comprising a housing piece, a through driveshaft, an electric motor, surrounding the through driveshaft with a first clutch before the electric motor and a second clutch thereafter, whereby a second axle is also to be driven with minimal space requirement. A first electric motor is thus physically combined with the first clutch, surrounding a second electric motor and the through driveshaft and is connected to the second axle by means of a third clutch, an offset gear and a shaft.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a drive unit for a motor vehicle with a hybrid drive and a drive train in a longitudinal arrangement, which drive train also comprises an internal combustion engine, a longitudinal shaft for driving a first axle, and a gear mechanism, and which drive unit is arranged between the internal combustion engine and the first axle and comprises a housing part, a through-drive shaft, an electrical machine surrounding the through-drive shaft and a first clutch upstream of and a second clutch downstream of the electrical machine. With the longitudinal arrangement, the permanently driven, in this case the first, axle is generally the rear axle. 
         [0002]    Such a drive train is known from DE 29 43 554 C2, but is only illustrated schematically. The rotation speed ratios and structural features are now shown. In any case the electrical machine is used both as a drive or an additional drive and as a starter and generator. A few more details, if only for a drive train having a transverse design, are given in EP 775 607 B1. Therein, the electrical machine has a relatively high rotation speed and is connected to the axle drive via a planetary gear mechanism, as is the internal combustion engine. The planetary gear mechanism is a superposition gear mechanism, in which the two drive torques are added to one another. This has the disadvantage that if only one of the two drives is working, the other needs to be blocked in order to provide a supporting torque. Furthermore, a purely electromotive drive for the second axle is added there. In order to accommodate such an additional drive on a rear axle, there is too little space there without altering the design. If, in the case of a drive train with a longitudinal design, the second driven axle is intended to be the front axle, it is not possible to solve this problem of space and it is also necessary to extensively alter the entire vehicle. 
       SUMMARY OF THE INVENTION 
       [0003]    It is therefore the object of the invention, in the case of a vehicle with a drive train in a longitudinal arrangement, to provide an additional electrical drive for the second (generally the front) axle, incurring as few costs as possible and with as few changes as possible to the vehicle. The drive unit should also be capable of being used in modular fashion (i.e. in various configurations) and should manage with the space which, in conventional all-wheel drive vehicles, is available for a transfer case. It should therefore also not be any longer. 
         [0004]    According to the invention, this is achieved by virtue of the fact that a first electrical machine is structurally combined with the first clutch, and that, for driving a second axle, the drive unit comprises a second electrical machine, which surrounds the through-drive shaft, and is drive-connected to a shaft leading to the second driven axle via a third clutch and an offset drive. The installation length is therefore only determined by the two directly adjacent electrical machines, especially if the second electrical machine is also structurally combined with the third clutch, with the result that, together with the offset drive, the contour of a transfer case can be seen. Furthermore, no changes to the vehicle are required, since the drive train connected to the drive unit is conventional. 
         [0005]    It is advantageous if the clutch is arranged within the electrical machine, since the electrical machines can thus be designed to have a rotation speed which is appropriate for the engine rotation speed and, owing to the larger radius of the rotor, can be designed to be very narrow. 
         [0006]    In one development of the invention, the first electrical machine and the second electrical machine are each accommodated by a housing comprising a cylindrical casing and an axially normal wall, and the cylindrical casings are screwed to one another. The preconditions for a modular use are therefore provided, and the assembly of the two coaxial modules is simplified and the installation length further shortened. 
         [0007]    If the electrical machine comprises a stator fixed in the housing and a rotor, and if the clutch in each case is a multi-plate clutch comprising an inner part and an outer part, in a further continuation of the concept of the invention, both the first and the second rotor are mounted in a bearing on the axially normal wall of the housing and have a replaceable coupling disk, which is connected to the clutch outer part such that it is fixed against rotation, the clutch being arranged between the bearing and the coupling disk. The replaceable coupling disk makes it possible to use identical rotors for both electrical machines; they are matched to their installation situation by fitting the respectively suitable coupling disk. 
         [0008]    In one particularly advantageous embodiment, the inner part of the first clutch rests on a first shaft, which is drive-connected to the internal combustion engine, and the outer part of the first clutch is connected to a second shaft (which represents the through-drive shaft) such that it is fixed against rotation, which shaft passes through the second electrical machine and leads to the second clutch; and the inner part of the second clutch is connected to a primary wheel of the offset drive such that it is fixed against rotation via a hollow shaft, and the outer part of the second clutch is connected to the coupling disk of the second electrical machine such that it is fixed against rotation. The drive unit is therefore completely modularized; the unit with the first electrical machine is the first module and the unit with the second electrical machine is the second module. It is thus possible, for example, for the first module to be used on its own if a hybrid vehicle is to be equipped with only one driven axle. 
         [0009]    Advantageous developments consist in the fact that an actuator cylinder, which contains an annular piston, for the clutch is fixed to the axially normal wall, and the annular piston interacts with a contact-pressure plate of the clutch via a thrust bearing and that the first and/or the second electrical machine each have a rotation speed sensor, which is fixed to the axially normal wall, and a rotation speed transmitter collar is fitted to the rotor. The former makes it possible to actuate the clutches without a rotary input to a rotating part, and the latter makes control possible in which the meshing of a clutch is dependent on the rotation speed ratios. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    In the text which follows, the invention will be described and explained with reference to drawings, in which: 
           [0011]      FIG. 1  shows a schematic of a drive train with the drive unit according to the invention, 
           [0012]      FIG. 2  shows the drive unit according to the invention in longitudinal section, and 
           [0013]      FIG. 3  shows a detail from  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    In  FIG. 1 , the internal combustion engine of a motor vehicle is denoted by  1 . It is connected to a through-drive shaft  4  via an oscillation damper  2 , possibly on a flywheel, and a first clutch  3 . This through-drive shaft  4  drives a first driven axle  7 *, in this case its axle gear mechanism  7  and therefore, in the exemplary embodiment shown, the rear wheels  8 , via a second clutch  5  and a shift transmission  6 . 
         [0015]    The drive unit according to the invention comprises a first module  10  and a second module  12  directly adjacent thereto. A first electrical machine  11  is located in the first module  10 , and a second electrical machine  13  is located in the second module  12 . The second electrical machine  13  drives a propeller shaft  16  via a third clutch  14  and an offset drive  15 , which propeller shaft  16  leads to the second driven axle  17 *, and therefore to the front wheels  18  via an axle gear mechanism  17 . In order to control the two electrical machines  11 ,  13 , power electronics  19  are provided which are connected to an energy store  20 , for example a rechargeable battery. 
         [0016]    In  FIG. 2 , the drive unit comprises the two modules  10 ,  12 . The housing of the first module comprises a cylindrical casing  21  and an axially normal wall  22 , and the housing of the second module  12  comprises a cylindrical casing  23  and an axially normal wall  24 . A first stator winding  25  of the first electrical machine  11  is fixed in the casing  21 , and a second stator winding  26  of the second electrical machine  13  is fixed in the casing  23 . The rotors of these machines are denoted by  27  and  28 . The two casings  21 ,  23  of the two modules  10 ,  12  are screwed to one another to form a common housing by means of a number of bolts  29 . 
         [0017]    The casing  23  of the second module  12  is adjoined by a housing cover  31 , which contains the offset drive  15 . This offset drive  15  comprises a primary gear wheel  32 , which can be driven by the second rotor  28  via the third clutch  14 , and a secondary gear wheel  36 , which is driven in this case via a toothed chain  35 . Instead of the toothed chain, other traction mechanisms or intermediate gear wheels could also be provided. Bearings  33 ,  34  are provided on both sides of the primary gear wheel  32 . The secondary gear wheel  37  is guided in bearings  37  and is connected to a flange  38  such that it is fixed against rotation, to which flange  38  the propeller shaft  16  is connected. An output drive flange  39 , which is adjoined by the second clutch  5  ( FIG. 1 ), is also provided coaxially with the primary gear wheel  32 . 
         [0018]    With reference to  FIG. 3 , the content of the two modules  10 ,  12  will now be described in more detail. The first shaft  40 , which is driven via the oscillation damper  2 , is mounted firstly by means of a bearing  41  in the wall  22  of the housing. It is connected to an inner part  42  of the first clutch  3  such that it is fixed against rotation. Its outer part  43  is connected to a coupling piece  45  such that it is fixed against rotation, which coupling piece  45  contains a needle bearing  62 , in which the other end of the first shaft  40  is mounted. A coupling disk  46  is likewise connected, in this case welded, to the coupling piece  45  such that it is fixed against rotation. The outer part  43  of the clutch, the coupling piece  45  and the coupling disk  46  therefore form a welded unit. The coupling disk  46  is fixedly connected to the first rotor  27  by means of bolts  47 . As is yet to be shown, the two rotors  27 ,  28  have an identical design. They differ from one another only in terms of the shape of the coupling disks  46  which, because they are screwed on by means of the bolts  47 , can be selected depending on the future use. 
         [0019]    The first clutch  3  contains, in a known manner, a set of plates  44 , on which and on whose plate springs  49  a pressure plate  48  acts. This pressure plate  48  is acted on by an actuator, which comprises an annular cylinder  52 , which is fixed to the housing, and an annular piston  51 , via a thrust bearing  50 . Furthermore, an oil-feed hole  53  to the cylinder  52  and a needle bearing  54 , in which a rotor disk  55  is mounted, are provided in the wall  22  of the housing. The first clutch  3  is therefore accommodated within the first rotor  27  and between the coupling disk  46  and the rotor disk  55 . A rotation speed transmitter collar  57  with suitable teeth is fixed to the rotor disk  55  and interacts with a rotation speed sensor  58 , which is fixed to the housing. The output signal of the rotation speed sensor  58  can be used by the control system in order to influence the meshing of the clutch as a function of the rotation speed difference present. 
         [0020]    The second module  12  contains a second shaft  60 , which is connected to the coupling piece  45  of the first module such that it is fixed against rotation and is mounted in various needle bearings  69 , some in the housing and some in the second clutch  14 . The third clutch  14  in the second module  12  again comprises an outer part  63  and an inner part  67  with a set of plates  64  therebetween. The outer part  63  is welded to a bearing ring  65 , as is a coupling disk  66 . Owing to the fact that the bearing ring  65  has a larger diameter than the coupling piece  45  of the first module  10 , a different coupling disk  66  is used here, and the inner diameter of the outer part  63  of the clutch  3  is larger. The rotor  28  of the second electrical machine  13  differs from that of the first electrical machine  11  merely by the other coupling disk  66  which has been screwed on. The inner part  67  of the second clutch  14  is mounted on the second shaft  60  in needle bearings  69  and extends into a hollow shaft  68  on which (see  FIG. 2 ) the primary gear wheel  32  of the offset drive  15  rests such that it is fixed against rotation. 
         [0021]    A more detailed description of the second module  12  is not required since the two modules are constructed with as large a number as possible of identical parts. Thus, for example, the needle bearing  74  of the second rotor  28  is identical to the needle bearing  54  of the first rotor  27 . The differences merely consist in the various shafts and shaft connections of the inner parts  42 ,  67  and outer parts  43 ,  63  of the clutches and of the coupling piece  45  and of the bearing ring  65 . Thanks to the modular design, it is also possible to use only the first module  10  on its own (for a vehicle with only one driven axle) or only the second module  12  on its own (for a vehicle with a conventional drive for one axle and an additional electrical drive for the second axle). Overall, the silhouette of the drive unit described is not any larger than that of a conventional transfer case.