Abstract:
In a drive arrangement for wheels of a motor vehicle which are driven by means of an electric machine via a differential, the electric machine includes a rotor and a stator and drives a drive element of the differential whose output shafts output to the wheels of the motor vehicle. In order to achieve a structurally compact construction which enables favorable transmission ratios the rotor outputs to the drive element of the differential and that by interposing a gear mechanism, the drive element and/or the output shafts are supported offset to the rotation axis of the rotor.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the priority of German Patent Application, Serial No. 10 2011 100 817.2, filed May 6, 2011, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a drive arrangement for wheels of a motor vehicle. 
     The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention. 
     In electrically driven motor vehicles or hybrid drives, it is know to drive an axle of the motor vehicle by means of an electromotor or an electric machine (also shiftable to function as generator during braking) via a customary differential. If the electric machine is to have a high torque or respectively a high driving power, the accommodation in the motor vehicle can pose problems. 
     It would be desirable and advantageous to provide an improved drive arrangement with which relatively large size electric motors or electric machines can be built in a structurally favorable manner and with higher constructive degrees of freedom 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention a drive arrangement for wheels of a motor vehicle can include a differential having a drive element and output shafts, wherein the output shafts are operably connected to the wheels of the motor vehicle, an electric machine having a rotor defining a rotation axis and connected in driving relationship with the drive element of the differential, and a gear mechanism, wherein the drive element and/or the output shafts are supported at an offset relative to the rotation axis of the rotor through interposition of the gear mechanism. Shifting of the rotation axis of the electric machine relative to the rotation axis of the differential allows building the electric machine large in size without for example impairing the ground clearance in the region of the differential; the electric machine can, however, also be arranged toward the front or the rear or combined obliquely. Further, the gear mechanism allows to favorably influence the overall transmission ratio electric machine : differential output (flange shafts) at structurally favorable dimensions. 
     According to another advantageous feature of the invention, the hollow drive shaft of the rotor can carry a pinion, which meshes with an internally toothed internal gear and is connected to the drive element of the differential, wherein at least one of the output shafts or respectively, flange shafts of the differential extends through the hollow shaft. This results in a compact and with regard to manufacturing favorable arrangement. 
     The differential with the drive element and the internally toothed internal gear can advantageously be mounted on a side of the electric machine, wherein one of the output shafts or respectively flange shafts in the reverse drive is guided through the hollow drive shaft of the electric machine. In contrast to this, the differential can also be arranged on one side of the electric machine and the drive pinion with the internal gear on the other side of the electric machine, wherein the shaft which connects the internal gear to the drive element of the differential is then to be configured as hollow shaft, which would have to be arranged axially parallel to the output shaft. 
     According to another advantageous feature of the invention, the differential can be supported coaxial to the rotor of the electric machine and output to the offset supported flange shafts via intermediate shafts and two gear mechanisms. Instead of the one gear mechanism two gear mechanisms can be provided which are arranged downstream of the differential with regard to the force flux, and which then output to the output shafts or respectively the flange shafts. 
     In a particularly advantageous and with respect to installation space favorable layout, the differential can be arranged inside the hollow shaft of the rotor, while the two gear mechanisms are positioned on both sides outside of the electric machine. The two gear mechanisms can in turn be formed by pinions on the intermediate shafts and by internally toothed internal gears on the output shafts or respectively, flange shafts. 
     In a further advantageous embodiment of the invention, the rotor of the electric machine can output to the drive element of the differential via a first gear mechanism and the output elements of the differential can output to the offset output shafts or respectively flange shafts via intermediate shafts and second gear mechanisms. This achieves to further increase the overall transmission ratio between the electric machine and output to the output shafts or respectively, flange shafts or respectively the driven wheels of the motor vehicle at a structurally particularly compact construction which allows realizing high drive torques at adequate dimensions of the electric machine. 
     Advantageously, the first gear mechanism can be shiftable via a shifting device into a driveless neutral position or into at least one transmission stage. This enables further degrees of freedom in the transmission layout of the drive arrangement at a small additional effort and a simple transmission-technical shut down of the electric machine in the neutral position of the switching device. 
     Particularly preferably, the first gear mechanism can be a planet gear train with a housing-fixed element, a driven element and a driving element, wherein via the shifting device, the housing-fixed element can be shifted to be housing-fixed, shifted to be freely rotatable, or coupled to the outputting element. With this, the neutral position and two transmission stages are shiftable in a structurally simple and compact construction. 
     In a preferred constructive layout, the element which can be shifted to be housing-fixed can be the sun gear of the planet gear train, which carries a shifting gear system which interacts with a control sleeve which is actuated via an actuator, wherein the control sleeve is further coupleable to a housing-fixed gear system on one hand and a gear system which is formed on the outputting element on the other hand. Further, the driving element of the planet gear train can be the internal gear which is connected to the hollow shaft of the electric machine and the outputting element of the planet carrier. 
     In an alternative, constructively simpler embodiment, the first gear mechanism between the electric machine and the drive element of the differential can be a non shiftable planet gear train with housing-fixed elements and an outputting element. Such planet gear trains have a particularly short axial dimension and allow transmission of high torques at a manufacturing-wise small effort. 
     The internal gear of the planet gear train or the sun gear can be connected to the rotor of the electric machine in a rotationally fixed manner at different definable transmission ratios, the sun gear or the internal gear can be arranged housing-fixed and finally the planet carrier can be drivingly coupled to the drive element of the differential. 
     The second gear mechanisms between the intermediate shafts of the differential and the output shafts can be formed by spur gears which mesh with one another or by pinions which are provided on the intermediate shafts and by internal gears which are arranged on the output shafts which are arranged offset to the pinions. 
     Finally, in order to achieve a structurally compact and mounting wise favorable construction the electric machine and the differential can be mounted in a common axle housing together with the output shafts and optionally with the intermediate shafts and the at least one gear mechanism. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which: 
         FIG. 1  shows a schematic illustration of a first drive arrangement with an electric machine, which outputs to a laterally mounted differential via a gear mechanism, wherein the rotation axis of the electric machine is offset to the rotation axis of the differential; 
         FIG. 2  shows a schematic illustration of a second drive arrangement with an electric machine and a differential which is integrated in the rotor of the electric machine, which differential outputs to radially offset flange shafts via coaxial intermediate shafts and lateral gear mechanisms. 
         FIG. 3  shows a schematic illustration of a third drive arrangement with a first gear mechanism between the rotor of the electric machine and the differential and second gear mechanisms between the intermediate shafts and the radially offset flange shafts; and 
         FIG. 4  shows a schematic illustration of a modification of the drive arrangement of  FIG. 3  in which the first gear mechanism between the rotor of the electric machine and the differential is shiftable into a neutral position and into two transmission stages via a shifting device. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. 
     Turning now to the drawing, and in particular to  FIG. 1 , there is shown a schematic illustration of a first drive arrangement for an electrically driven axle (for example a front axle or rear axle) of a motor vehicle designated  10 , which is substantially formed by an electric machine  12  and a differential  14 . 
     The driving electric machine  12 , which can be operated during braking or coasting of the motor vehicle as a generator, has a ring-shaped stator  16  and a ring shaped rotor  18  which is arranged on a hollow drive shaft  20 . The hollow drive shaft  20  is mounted in housing walls  24   a ,  24   b  of an axle housing  24  for rotation about a first rotation axis via rolling bearings  22 , which rotation axis thus defines the “center” of the electric machine  12 . 
     Further, the hollow drive shaft  20  carries a pinion  28  which together with an internally toothed pot shaped internal gear  30  forms a gear mechanism  32  which increases the torque of the electric machine  12 . 
     The hub  30   a  of the internal gear  30  is rotatably supported via a rolling bearing  3  in the housing cover  24   c  which is flanged to the housing  24  or to the housing wall  24   a  thereof, wherein the internal gear  30  defines a rotation axis  36  which is offset to the rotation axis  26  of the rotor  20 , for example in construction position downward. 
     The differential  14  is for example configured as a planet gear train which is known per se and is therefore not further described. The differential  14  is arranged in a further housing cover  24   d  which is bolted to the housing cover  24   c . The drive element of the differential  14  is the planet carrier (not shown) which is drivingly connected to the hub  30   a  of the internal gear  30 . 
     The outer gear  38  as the one output element is drivingly connected to a first flange shaft  40  and the sun gear  42  as second output element is drivingly connected to the flange shaft  44  of the differential  14 . The flange shaft which is rotatably supported in the hub  30   a  and via a rolling bearing  46  in the housing wall  24   b  extends in the reverse drive through the hollow drive shaft  20  of the rotor  18 . 
     The flange shafts  40 ,  44  are connected to the driven wheels of the motor vehicle via cardan shafts in a manner which is not shown. 
     The offset of the rotation axes  26  of the electric machine  12  and the differential  14  with the flange shafts  40 ,  42  is here determined by the inner diameter of the hollow drive shaft  20  and the outer diameter of the backward guided flange shaft  44  which should run freely. 
     The transmission ratio between the electric machine  12  and the differential  14  can be defined by the configuration of the gear mechanism  32 . Via the differential  14  an adjustment of the rotational speed of the driven wheels of the motor vehicle is realized for example when negotiating curves. 
       FIG. 2  shows a second alternative drive device  10 ′, which however is only described insofar as it significantly differs from the drive device  10  according to  FIG. 1 . Functionally equivalent parts are provided with same reference signs. The housing  24  is only shown partially, however it can be configured essentially similar to  FIG. 3  which is explained below. 
     Different to  FIG. 1 , the differential  48  is configured as bevel gear differential, whose differential case  50  is integrated with coaxial rotation axis in the hollow drive shaft  20  of the electric machine  12 . The hollow drive shaft  20  is provided with an internal spline  20 , which in circumferential direction form fittingly interacts with a corresponding outer spline on the differential case  50 . 
     The axle bevel gears (not visible, compare  FIG. 3 ) of the differential  48  output to intermediate shafts  52 , which are rotatably supported in the housing walls  24   a ,  24   b  which are only shown as outline and which carry pinions  54  on both sides, which pinions  54  in connection with pot-shaped internal gears  56  form two laterally arranged gear mechanisms  58 . 
     The internal gears  56  are drivingly and fixedly connected to the flange shafts  40 ,  44  which are supported in outer housing covers  24   e  and define a rotation axis  36  which extends offset (here for example downward) to the rotation axis  26 . 
     As can be readily seen from  FIG. 2 , the gear mechanism according to  FIG. 1  is here divided into two gear mechanisms  58 , which are positioned downstream of the differential  48  with regard to the force flux and on both sides of the electric machine  12 . Since the flange shaft  44  of  FIG. 1  does thus not have to be guided through the hollow drive shaft  20  of the rotor  18 , the offset between the rotation axes  26 ,  36  can be chosen larger than in the embodiment according to  FIG. 1  if needed. 
       FIG. 3  shows a third alternative embodiment of the drive arrangement  10 ″ in more detail. Functionally equivalent parts are again provided with same reference signs. 
     Again, the bevel gear differential  48  is integrated coaxial relative to the rotor in the hollow drive shaft  20  of the latter wherein the hollow drive shaft  20  is rotatably supported on bearing necks  50   a  of the differential case via rolling bearings  60 , and the bearing necks  50   a  are rotatably supported on bearing collars of the head side housing walls  24   a ,  24   b  via further rolling bearings  62 . With regard to the housing wall  24   a  it is noted that in the shown example, the latter transitions into a hub section  74   a , which is further explained below. 
     The rotor  18  or respectively, its hollow drive shaft  20  drives the drive element or respectively, the differential case  50  of the differential  48  via a first gear mechanism  64 . 
     The gear mechanism  64  has a internal gear  66 , which has an internal toothing and is fixedly connected to the hollow drive shaft  20 , a planet gear wheel carrier  68  integrated into the differential case and having planet gears  72  which are supported on axes  70  (only one planet gear is visible), and finally a sun gear  74  which is fixedly connected to the housing wall  24   a.    
     The hub section  74   a  of the sun gear  74  forms the bearing collar for the mentioned rolling bearing  62  and at the same time the sliding bearing of the one intermediate shaft  52 , here on the left. 
     The intermediate shafts  52  are fixedly bolted to the axle bevel gears  78  of the differential  48  and rotatably supported in the housing walls  24   a ,  24   b  or respectively, the hub section  74   a  of the housing-fixed sun gear  74  via rolling bearings  80 . The axle bevel gears  78  mesh with the planet bevel gears  82 , which are rotatably supported on engagement pin  84 . 
     As previously described in  FIG. 2 , the intermediate shafts  52  further carry pinions  54  which together with the internal gears  56  on the flange shafts  40 ,  44  form the gear mechanisms  58  on both sides. 
     The flange shafts  40 ,  44  are rotatably supported in bearing collars of the housing walls  24   a ,  24   b  and in the housing covers  24   e  via rolling bearings  86 ,  88 , wherein the rotation axis of the flange shafts is again correspondingly offset downwards. 
     Through the gear mechanism  64  which is situated upstream of the differential  48  with regard to the force flux and the two gear mechanisms  58  which are situated downstream of the differential with regard to the force flux, an overall transmission ratio of for example 5 between the rotor  18  of the driving electric machine  12  and the outputting flange shafts  40 ,  44  can be designed at a structurally and constructively favorable layout. 
     A further transmission layout is achieved with the drive arrangement  10 ′″ according to  FIG. 4 , in which the first gear mechanism  64 ′ is configured shiftable. The drive arrangement  10 ′″ is only described insofar as it significantly differs from  FIG. 3 . Functionally similar parts are provided with same reference signs. 
     In contrast to  FIG. 3 , the sun gear  74 ′ of the planet gear train  64 ′ which is shiftable via a shifting device  90  is not supported fixed to the housing but rotatably on the left intermediate shaft  52 . 
     The sun gear  74 ′ further carries a shifting gear  96  with an outer shifting tooth system  94   a , on which a control sleeve  98  with a corresponding internal tooth system is shiftably arranged. 
     The control sleeve  98  interacts with a housing-fixed shifting gear system  110  and with a shifting gear system  102  on the internal gear  66  of the hollow shaft  20  which carries the planet gear train  64 . 
     The control sleeve  98  is shiftable via a shift fork  106  from the drawn neutral position—in which the sun gear  74 ′ is freely rotatable—towards the left onto the shifting gear system  100  which is fixed to the housing or to the right onto the shifting gear system  102  of the hollow shaft  20 . 
     In the neutral position of the shifting device  90 , the sun gear  74 ′ is freely rotatable and with this the electric machine  12  decoupled from the differential  64 ′ or respectively from the entire output. 
     When the sun gear  74 ′ is shifted to be fixed to the housing according to  FIG. 3  a defined first transmission stage is established. 
     In the right shifting position of the shifting device  90 , the sun gear  74 ′ is coupled to the hollow shaft  20  or respectively the internal gear  66 , whereby the planet gear train  64 ′ is blocked in itself or respectively a second transmission stage 1:1 is established. The remaining function of the drive arrangement  10 ′″ corresponds to the drive arrangement  10 ″ of  FIG. 3 . 
     The differential  14  according to  FIG. 1  can also be a bevel gear differential as in  FIGS. 2 ,  3  and  4  and contrariwise the bevel gear differential can be a differential of a different design. 
     For achieving a different transmission ration, the gear mechanism  64  can also be configured such the rotor  18  or respectively its hollow drive shaft  20  outputs to the sun gear  74  which in this instant is rotatably supported, while the internally toothed internal gear  66  is arranged fixed to the housing 
     Instead of the gear mechanisms  58  with an internal gear  56  the latter can also be configured as spur gear drives, wherein then the pinion  54  would mesh with a further spur gear on the flange shafts  40 ,  44 . Likewise, the switching device can be configured in a different manner. 
     While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.