Abstract:
The invention relates to a drive unit for motor vehicles, comprising an internal combustion engine, a transmission which is mounted downstream therefrom and is provided with an integrated differential, and a separating clutch that is disposed between the internal combustion engine and the transmission. The differential is driven via a bevel wheel and a bevel-gear drive comprising a drive pinion on an output shaft of the transmission. In order to create a drive unit that is advantageous regarding structure and efficiency, the bevel wheel ( 48 ) of the differential ( 16 ) is placed laterally from the separating clutch ( 26 ) from a vertical perspective and partly protrudes (A) therefrom in an axial direction.

Description:
This application is a 371 application of PCT/EP2004/000603, which claims priority from DE 10318742.1, filed Apr. 25, 2003. 
   The invention relates to a drive unit for motor vehicles according to the preamble of claim  1 . 
   BACKGROUND 
   Such a drive unit which is installed lengthwise, with a front axle differential which is integrated into the change speed gearbox, is disclosed by EP 1 120 587 A1 for example. Here the differential of conventional design is positioned in the axial direction behind the separating clutch which is located on the crankshaft of the internal combustion engine, yielding a specific overhang of the internal combustion engine which is defined by way of the axes of rotation of the driven front wheels of the motor vehicle and yielding a corresponding weight distribution. It is within the scope of structural conditions to try to dimension the indicated overhang as small as possible. 
   DE 34 18 557 C2 furthermore discloses a drive unit in which the differential is located in front of the separating clutch in the axial direction; however this solution entails considerable structural complexity, due for example to the significant lateral offset of the output shaft of the change speed gearbox which drives the differential, and by one axle shaft of the differential having to be routed through the oil pan of the internal combustion engine. 
   The object of the invention is to propose a drive unit of the generic type which with only little additional construction effort permits shortening of the drive unit, particularly of the distance between the engine/gearbox flange and the axle differential, or makes possible an additional installation space for clutch-side powertrain parts. 
   SUMMARY OF THE INVENTION 
   This object is achieved in the invention. The solution can be used both for front-wheel drive and also for rear-wheel drive. Advantageous developments of the invention are described by the other claims. 
   The ring gear of the differential of the invention as viewed from a vertical perspective is mounted laterally from the separating clutch and projects partly over it in the axial direction. With the proposal as claimed in the invention the drive unit is significantly shortened and the differential with the outgoing axle shafts is advantageously displaced forward, by which the indicated overhang is reduced and a more uniform weight distribution of the motor vehicle is achieved. Alternatively the installation space gained in the axial direction can be used for example for additional installation of a starter-generator device. 
   In one advantageous development of the invention the differential case comprising the axle bevel gears and planet gears can also be positioned laterally next to the separating clutch. This results in that at the minimally necessary lateral offset of the output shaft of the change speed gearbox the separating clutch and the ring gear with differential case can be positioned next to one another and can be operated without adversely affecting their function. 
   The separating clutch can advantageously be a multidisk friction clutch of conventional design which is small in radial extent. The multidisk friction clutch can be a wet or dry friction clutch, a two-disk dry clutch, for example, with a diameter reduced proportionally to the increased friction surface. 
   Furthermore, the differential housing of the differential of the change speed gearbox can be built partly around the separating clutch, the flywheel of the internal combustion engine which bears the separating clutch projecting radially over the ring gear. Thus an especially advantageous “internested” design is produced in which the flywheel of the internal combustion engine with the starter gear rim for the starter can remain essentially unchanged structurally, while the separating clutch is modified accordingly. 
   Furthermore, the differential housing can be designed especially advantageously in part by the adjoining housing of the internal combustion engine and/or the integral housing cover which laterally covers the differential can also partly cover the housing of the internal combustion engine. In addition to a structure which is especially well-suited to casting, this results in additional stiffening of the drive unit in the area of the screw connection between the internal combustion engine and the adjoining differential which is integrated into the housing of the change speed gearbox. 
   An embodiment is also possible in which the integral housing cover roughly overlaps the engine flange and the housing cover in the longitudinal direction of the gearbox is braced by means of bolts relative to the engine flange (by means of bolting). 
   The change speed gearbox can furthermore have a shaft configuration with an input shaft and an output shaft which bears the drive pinion for driving the differential. This yields an especially advantageous gearbox design of simple structure with favorable transmission efficiency due to reduced engagement of teeth; a third shaft, for example a countershaft, can be omitted accordingly. The drive pinion is dimensioned so that an exactly defined, predetermined distance between the input shaft and the output shaft can be set. 
   Here the input shaft and the output shaft can be aligned for example so as to be axially parallel. In one alternative embodiment the input shaft and the output shaft can run obliquely to one another at least in individual areas, so that the drive pinion and the ring gear of the differential are designed for example as beveloid gears so that the output shaft runs in the direction toward the input shaft. Thus the distance between the input shaft and the output shaft can be reduced, and this measure can additionally lead to keeping the length of the gearbox short. That is, depending on the desired distance between the input shaft and the output shaft, either the diameter of the drive pinion is chosen to that effect, the drive pinion and the ring gear can be made as beveloid gears, or a combination of the two in the change speed gearbox can be implemented. 
   In particular, for an axially parallel execution of the input shaft and the output shaft, the axial distances between the input shaft and the output shaft can be advantageously increased proportionally to produce a large lateral offset. Moreover radial enlargement of the corresponding gear sets optionally makes possible a further reduction in the overall length of the change speed gearbox, even if it does not affect the indicated reduction of the overhang. On the other hand, by reducing the axial distance by for example a “longer” bevel gear, for example a larger drive pinion, and the concomitant reduction of the distance between the input shaft and the output shaft however a shorter speed-transforming transmission can be achieved, if this is desirable. 
   Furthermore, one axle shaft of the differential can advantageously extend below the input shaft of the change speed gearbox and to the other output side of the differential in the axial direction closely following the separating clutch. Furthermore, the output shaft can be pivot mounted laterally in relation to the input shaft so that the indicated axle shaft intersects the input shaft closely below or above it. These measures contribute both to an optimum shortening of the drive unit which is possible within the scope of structural conditions and also to improved ground clearance of the motor vehicle. 
   One embodiment of the invention is described below with further details. 
   The attached drawings are in diagrammatic form wherein 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a front drive unit for motor vehicles with an internal combustion engine which is only suggested, a partially illustrated change speed gearbox with an integrated differential and a multi-disk friction clutch in a top view; 
       FIG. 2  shows a side view of the housing cover of the differential in the area of the separating plane between the internal combustion engine and the change speed gearbox; 
       FIG. 2   a  shows a side view of the housing cover of the differential in the area of the engine flange between the internal combustion engine and the change speed gearbox; 
       FIG. 3  shows the configuration of the differential, the gearbox shafts and the multidisk friction clutch as shown in  FIG. 1 , but without the illustrated housing sections; 
       FIG. 4  shows the configuration as shown in  FIG. 3  in a view corresponding to the arrow X. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows in highly schematic form a front drive unit  10  which can be installed lengthwise in a motor vehicle, with an internal combustion engine  12  which is only suggested, and a downstream change speed gearbox  14  with an integrated differential  16 . The indicated components are described only to the extent that this is necessary for this invention; otherwise the components can be of the design known to one skilled in the art or can correspond to the prior art. 
   A flywheel  20  with a flywheel sprocket  22  shrink-fitted onto the circumferential side is attached to the crankshaft  18  of the internal combustion engine  12 . The crankshaft  18  is pivot mounted in the housing  24  of the internal combustion engine  12  in a manner which is not shown. 
   On the flywheel  20  of the internal combustion engine  12  there is a multidisk friction clutch  26  as a separating clutch, which in this exemplary embodiment is a double dry friction clutch of conventional design with two friction disks  28 . The clutch actuation is not the subject matter of the invention and therefore is not shown. As a result of the two friction disks  28  the separating clutch  26  can be made smaller or with a smaller outside circumference in the radial direction, with an identical or even larger drive transmission output compared for example to a single-disk dry friction clutch. 
   The housing  30  of the change speed gearbox  14  in the illustrated vertical separating plane  32  is flanged to the housing  24  of the internal combustion engine  12 , the housing section  30   a  of the differential  16  integrated into the housing  30  being made in a manner yet to be described. 
   The change speed gearbox  14  is a conventional transmission with several gears, for the sake of simplified representation only the gear sets with the gears  34 ,  35 , and  38 ,  40  being shown for the first and second forward gear of the change speed gearbox  14 . For the sake of form it should be emphasized that an axle or shaft of the change speed gearbox for accommodating a reverse gear wheel for the reverse gear of the change speed gearbox  14  is not included in the shaft configuration to be described. 
   The gears  34 ,  38  (and others) sit on the input shaft  42  and the gears  36 ,  40  (and others) sit on the output shaft  44  of the change speed gearbox  14 . The gear sets  34 ,  36  and  38 ,  40  can be activated by way of synchronizer clutches (not shown) for shifting the transmission ratios or gears of the change speed gearbox  14 . 
   Furthermore, the output shaft  44  bears a drive pinion  46  which meshes with a ring gear  48  of the bevel gear differential  16 . The differential  16  in the conventional manner drives two axle half shafts  52 ,  54  which are pivot mounted in the differential housing  30   a  by way of axle bevel gears and planet gears (not shown) which are supported in the differential case  50 . While the axle half shaft  52  which is shown on the left in the drawings is routed only through the large housing cover  56  of the differential  16 , the right half axle shaft  54 , crossing the input shaft  42  of the change speed gearbox  14 , extends as far as the opposing housing section of the differential housing  30   a . In the conventional manner the drive shafts (not shown) which drive the front wheels of the motor vehicle are connected to the axle half shafts  52 ,  54 . 
   The input shaft  42  and the output shaft  44  can run so as to be axially parallel, as shown in  FIGS. 1 and 3 . If a shorter distance (section C,  FIG. 3 ) is required between the input shaft  42  and the output shaft  44  for a certain gearbox design, on the one hand the pinion diameter of the drive pinion  46  can be increased and/or on the other hand the drive pinion  46  and the ring gear  48  of the differential  16  can each be made for example as beveloid gears. The latter measure results in that then the output shaft  44 ′ runs obliquely in the direction to the input shaft  42 ; this is shown schematically by the broken line in  FIG. 1 . With known joint pieces (not shown) the output shaft  44 ′ can be moved again into an axially parallel alignment of the input shaft  42  when the desired distance between the input shaft  42  and the output shaft  44 ′ is reached. 
   As is to be seen in the drawings in  FIGS. 1 and 2 , the large housing cover  56  of the differential  16  can extend forward beyond the indicated separating plane  32  between the engine housing  24  and the housing  30  of the change speed gearbox  14  so that the integral housing cover  56  projects over the engine housing  24  in sections and is screwed to the latter and to the housing section  30   a  of the differential  16  (compare  FIG. 2 , generally with screws designated as  58 ). 
   According to another embodiment, the housing cover  56 ′ of the differential  16 ′ can overlap the flange  240  of the drive unit  24 . In doing so, connecting means  560 ,  561  which are inserted lengthwise into the housing cover  56 ′, for example long screws, can be connected (screwed) to the flange  240  of the drive unit  24  ( FIG. 2   a ). 
   As  FIGS. 1 ,  3 , and  4  show, the differential case  50  which holds the axle bevel gears and planet gears (not shown) and the ring gear  48  of the differential  16  are positioned laterally next to the separating clutch  26 , and the lateral offset of the differential which is necessary for this purpose can be kept smaller by the reduced outside circumference of the separating clutch  26 . Due to the lateral offset in turn the differential  16  can be shifted forward to a greater extent (to the left in  FIG. 1 ), the ring gear  48  projecting in the axial direction over the separating clutch  26  by the section A which is shown in  FIG. 3 . 
   Furthermore, as shown in  FIG. 1 , the differential housing  30   a  of the differential  16  of the change speed gearbox  14  is built partly around the separating clutch  26 , the flywheel  20  which bears the separating clutch  26  with the sprocket ring  22  of the internal combustion engine  12  projecting radially over the ring gear  48  by the amount B which is shown in  FIG. 3 . 
   Due to the above described, not overly large lateral offset of the differential  16 , furthermore the change speed gearbox  14  can be made with only two axially parallel shaft configurations or with only the input shaft  42  and the output shaft  44  which bears the pinion  46  for driving the differential  16 . This means that a third shaft, for example a countershaft, for achieving the required axial distance between the input shaft  42  and the output shaft  44  can be omitted. 
   Here the gears  34 ,  36  and  38 ,  40  (and other gears) are enlarged in diameter for the transmission ratios of the change speed gearbox  14  for achieving the require lateral offset of the differential  16  and the axial distance between the input shaft  42  and the output shaft  44 , optionally with the stipulated transmission ratios unchanged. Optionally the gears  34 ,  36  and  38 ,  40  and other speed gears can be reduced in width by the increase of the diameter so that an increase of the rotating masses of the change speed gearbox  14  can be avoided and its overall length can be reduced. 
   The longer axle shaft  54  of the differential  16 , as is especially apparent in  FIG. 4 , extends at a short distance s 1  below the input shaft  42  of the change speed gearbox  14  and closely following the separating clutch  26  (compare distance s 2  in  FIG. 3 ) to the other output side of the differential  16 . 
   Finally, the output shaft  44  of the change speed gearbox  14 , as can be seen especially in  FIG. 4 , is pivot mounted laterally in relation to the input shaft  42  so that the indicated axle shaft  54  as described above intersects the input shaft  42  closely below the latter (distance s 1 ). 
   The invention is not limited to the described embodiment. Thus, instead of shifting the differential  16  forward, the acquired installation space can also be used for additional installation of a starter-generator device by means of which the internal combustion engine  12  is started in the conventional manner and optionally the motor vehicle can be electrically driven by way of the change speed gearbox  14  and/or the vehicle electrical system can be supplied with current in generator operation.