Abstract:
A torque transmission device for a motor vehicle having a locking mechanism for locking at least one wheel of the motor vehicle, which wheel is connected to an output shaft of the torque transmission device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a National Stage Application of PCT International Application No. PCT/EP2011/063585 (filed on Aug. 8, 2011), under 35 U.S.C. §371, which claims priority to German Patent Application No. 10 2010 034691.8 (filed on Aug. 18, 2010), which are each hereby incorporated by reference in their respective entireties. 
     
    
     TECHNICAL FIELD 
       [0002]    Embodiments relate to a torque transmission device for a motor vehicle having a locking mechanism for locking at least one wheel of the motor vehicle, which wheel is connected to an output shaft of the torque transmission device. 
       BACKGROUND 
       [0003]    Torque transmission devices of this type having a locking mechanism are used in a multiplicity of motor vehicle types, in particular in the case of electric or hybrid vehicles. The locking mechanism can serve, for example, as a parking lock, in order to prevent the vehicle from rolling away in a parked state. It is of particular significance here that the locking takes place reliably, with the result that securing of the vehicle is always ensured, even in the case of high loads which act on the locking mechanism, for example when the vehicle is parked on a slope. In addition, locking mechanisms of this type have to be designed in such a way that they can be engaged even if a vehicle is still rolling slowly. This requires a very robust design of the locking mechanism, which is associated with corresponding production costs. 
       SUMMARY 
       [0004]    It is, therefore, an object of the invention to provide a torque transmission device which can be produced inexpensively and which makes reliable locking possible at the same time. 
         [0005]    The abovementioned object and others are achieved by a torque transmission device having the features of a locking mechanism configured to lock at least one wheel of the motor vehicle; an output shaft configured for connection to the at least one wheel; a differential gear mechanism configured for connection to the output shaft; and a drive unit; a clutch unit configured to drive-connect the output shaft, the differential gear mechanism and the drive unit are drive-connected to one another; and a rotatable component operationally arranged between the wheel and the clutch unit and which is configured for engagement with the locking mechanism. 
         [0006]    The torque transmission device in accordance with embodiments comprises a differential gear mechanism, which is connected to the output shaft, and a drive unit which are drive-connected to one another via a clutch unit. The locking mechanism of the torque transmission device can be brought into engagement with a rotatable component of the torque transmission device which is arranged functionally between the wheel of the vehicle and the clutch unit. 
         [0007]    In other words, the locking mechanism is not provided in functional terms between the drive unit and the clutch unit, but rather lies “behind” the clutch unit as viewed from the drive unit. At least partial decoupling of the drive unit from the at least one wheel is achieved in the locked state as a result of the positioning of the clutch unit between the drive unit and the locking mechanism, without the forces which act on the torque transmission device in the case of a load (for example, if the vehicle is parked on a slope) having to be absorbed by the clutch unit. The locking mechanism which is arranged functionally between the wheel and the clutch unit is therefore arranged “in front of” the clutch unit and in every case ensures reliable locking independently of a design of the clutch unit. 
         [0008]    A further advantage of the above-described arrangement of the components of the torque transmission device consists in that the components which are arranged between the wheel and the locking mechanism and the components which are arranged between the locking mechanism and the drive unit are braked in a temporally offset manner if the locking mechanism is not activated during a rest state of all the components. In order to dimension the locking mechanism in such a way that reliable locking of the at least one wheel is ensured even in situations of this type, the sum of the forces which are produced by the braking of the components which lie “in front of” the locking mechanism and those which lie “behind” the locking mechanism usually has to be taken into consideration as the maximum loading which occurs. Since the rigidities of the involved components between the wheel and the locking mechanism are relatively low, it takes approximately half a second in the case of a slowly rolling vehicle from the latching of the locking mechanism until the first loading peak is reached. 
         [0009]    In contrast, there are as a rule substantially higher rigidities between the locking mechanism and the drive unit, with the result that the loads which occur there in conjunction with latching of the locking mechanism are associated with higher-frequency oscillations. As a result of a suitable design of the clutch unit, the latter acts as a damping means which dissipates the oscillations which act between the locking mechanism and the drive unit within the abovementioned time period of approximately 0.5 second or at least modulates them temporally in such a way that the loading peaks which are produced by the components which lie “in front of” and “behind” the locking mechanism do not act at the same time on the locking mechanism. It is therefore not the sum of the two loads which has to be used for dimensioning of the locking mechanism, but rather merely the higher of the two loads. 
         [0010]    Although the advantages of the torque transmission device in accordance with embodiments have been described only by way of example using a motor vehicle, it goes without saying that the discussed torque transmission device can in principle also be used in other fields. 
         [0011]    In accordance with one advantageous embodiment of the present invention, the locking mechanism comprises a detent which can be brought into engagement in a positively locking manner with a detent gear which is connected fixedly to the rotatable component so as to rotate with it. A locking mechanism of this type can be implemented in a structurally simple manner and at the same time ensures reliable locking of the rotatable component relative to the locking mechanism. In particular, the detent is fastened pivotably to a housing of the torque transmission device and is configured in such a way that locking and releasing can be realized by a pivoting movement of the detent. 
         [0012]    The rotatable component can be a component of the differential gear mechanism, in particular a cage of the differential gear mechanism. 
         [0013]    In accordance with a further advantageous refinement of the torque transmission device according to the invention, the clutch unit comprises a slipping clutch. The slipping clutch can be, for example, a multiple disk clutch. Clutch units of this type are inexpensive and reliable and are available in a very wide variety of different embodiments. The above-described adaptation of the damping characteristic in the region between the locking mechanism and the drive unit is therefore possible in a simple way by the selection of a clutch unit with suitable performance parameters. 
         [0014]    It can be provided that the torque transmission device comprises a step-up or step-down gear mechanism which is drive-connected on the input side to the drive unit and which is connected on the output side to the differential gear mechanism, the step-up or step-down gear mechanism being configured, in particular, as a planetary gear mechanism. In particular, the clutch unit is arranged functionally between the step-up or step-down gear mechanism and the drive unit. 
         [0015]    Furthermore, it can be provided that the clutch unit comprises an input shaft and an output shaft, the input shaft being connected to a rotor of the drive unit which is configured as an electric motor, and the output shaft being drive-connected directly or indirectly to an input member of the differential gear mechanism. As a result, a compact and reliable overall design can be realized. 
         [0016]    Further embodiments of the invention are specified in the description, the drawing and the subclaims. 
     
    
     
       DRAWING 
         [0017]    In the following text, the invention will be described purely by way of example using one advantageous embodiment with reference to the appended drawing. 
           [0018]      FIG. 1  illustrates a torque transmission device in accordance with embodiments. 
       
    
    
     DESCRIPTION 
       [0019]      FIG. 1  illustrates a motor/gear mechanism unit  10  which comprises an electric motor  12  which is drive-connected via a step-down gear mechanism  14  to a cage  16  of a differential gear mechanism  18 . A drive of the differential gear mechanism  18  makes it possible to deliver the torque which is generated by the electric motor  12  to half shafts  20   a,    20   b  which are connected to wheels (not shown) of a motor vehicle. The electric motor  12  has a rotor which is connected fixedly to a hollow shaft  22  so as to rotate with it. The hollow shaft  22  is connected to a slipping clutch  24  which is arranged functionally between the electric motor  12  and the step-down gear mechanism  14 . The slipping clutch  24  is configured as a multiple disk clutch and comprises outer disks  26   a  and inner disks  26   b  which are arranged in an alternating manner and form a multiple disk assembly. A disk spring  28  presses the disks  26   a,    26   b  against one another with a predefined force, in order to provide well defined coupling between the hollow shaft  22 , which surrounds the half shaft  20   b  coaxially, and an input shaft  30  of the step-down gear mechanism  14 . 
         [0020]    The step-down gear mechanism  14  is configured as a two-stage planetary gear mechanism. The input shaft  30  is connected fixedly to a sun gear  32  so as to rotate with it, which sun gear  32  in turn meshes with a first planetary gear set  34 . Gearwheels  34   a  of the first planetary gear set  34  are in each case connected fixedly to a gearwheel  36   a  of a second planetary gear set  36  so as to rotate with it, the gearwheels  34   a  having a greater diameter than the gearwheels  36   a.  The gearwheels  36   a  of the second planetary gear set  36  mesh with an internal gear  38  which is fastened to a housing  40  which surrounds the step-down gear mechanism  14  at least partially. 
         [0021]    During operation of the electric motor  12 , a torque is transmitted via the clutch  24  and the gear mechanism  14  to the differential gear mechanism  18 , since the gearwheels  36   a  which are mounted together with the gearwheels  34   a  on a planetary carrier (not shown) roll on the internal gear  38 , and therefore, at the same time drive the differential cage  16  to produce a rotational movement. 
         [0022]    If the vehicle having the motor/gear mechanism unit  10  is parked on a slope, it would roll backward, since, in a powerless state, the electric motor  12  does not produce a relevant resistance which would decisively inhibit a rotational movement of the above-described components. In order to prevent the vehicle from rolling backward, a parking lock  42  is provided which comprises a detent  44 . The detent  44  has at least one detent tooth  46  which can be brought into a positively locking engagement with a toothing system of complementary configuration of a detent gear  48 . The detent gear  48  is in turn arranged fixedly on the differential cage  16  so as to rotate with it. 
         [0023]    If the parking position of the vehicle is to be secured, the parking lock  42  is activated and the detent  44  is brought into engagement with the detent gear  48  by way of a suitable actuation mechanism, said detent gear therefore being secured in a rotationally fixed manner. As a result, a rotation of the differential cage  16 , and therefore, of the half shafts  20   a,    20   b,  is also impeded. In other words, the vehicle can no longer be moved, since the parking lock  42  blocks the differential gear mechanism  18  directly. The locking is very reliable, since it is independent of the properties of the slipping clutch  24  which is arranged functionally “behind” the parking lock  42  when a parked state of the vehicle is considered. 
         [0024]    The above-described position of the slipping clutch  24  relative to the other components of the motor/gear mechanism unit  10  is associated with the further advantage that the parking lock  42  has to be designed for lower loads than in the case of conventional motor/gear mechanism units. If namely the vehicle is still moving a little upon activation of the parking lock  42 , loads which, coming from the wheels, are transmitted via the differential gear mechanism  18  to the parking lock  42 , therefore, act on the components of the parking lock  42 . Said loads are added to by loads which are generated by the components between the parking lock  42  and the electric motor  12 , since said components also have to be braked. If the peaks of the two loads overlap temporally, the two loads are added together. As a result, the parking lock  42  has to be of correspondingly robust design. 
         [0025]    By way of the functional position of the slipping clutch  24  between the electric motor  12  and the parking lock  42 , the rigidity of this “part” of the motor/gear mechanism unit  10  can be influenced. That is to say, the loads which are associated with the braking of the components which are arranged in this region and the resulting oscillations are damped by the slipping clutch  24  in such a way that they have already substantially decayed when the load peaks act on the parking lock  42 , which load peaks occur only after approximately half a second on account of the lower rigidity of the system between the wheels and the parking lock  42 . The load peaks are therefore not added together and the maximum loading to be absorbed by the parking lock  42  is substantially lower than in conventional systems. Accordingly, the parking lock  42  can be of simpler configuration, which leads to savings of installation space and cost advantages. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
           10  Motor/gear mechanism unit 
           12  Electric motor 
           14  Step-down gear mechanism 
           16  Differential cage 
           18  Differential gear mechanism 
           20   a,    20   b  Half shaft 
           22  Hollow shaft 
           24  Slipping clutch 
           26   a  Outer disk 
           26   b  Inner disk 
           28  Disk spring 
           30  Input shaft 
           32  Sun gear 
           34  First planetary gear set 
           36  Second planetary gear set 
           34   a,    36   a  Gearwheel 
           38  Internal gear 
           40  Housing 
           42  Parking lock 
           44  Detent 
           46  Detent tooth