Abstract:
A drive unit, for an electric vehicle, comprising an electric machine that can be arranged in the area of an end of a vehicle axle of the electric vehicle and also a transmission unit, which co-operates with the electric machine, for driving a wheel of the electric vehicle. The electric machine and the transmission unit can be arranged adjacent to the wheel. The electric machine is designed so that the electric machine can be arranged adjacent to a wheel at either of the two ends of the vehicle axle in the drive unit for driving the wheel concerned. The invention also concerns a vehicle axle incorporating the drive unit.

Description:
[0001]    This application is a national stage completion of PCT/EP2012/062402 filed Jun. 27, 2012 which claims priority from German Application Serial No. 10 2011 080 038.7 filed Jul. 28, 2011. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention concerns a drive unit for an electric vehicle comprising an electric machine, in particular an electric motor that can be arranged in an area at an end of a vehicle axle of the electric vehicle, and also a transmission unit which co-operates with the electric motor in order to drive an adjacent wheel of the electric vehicle. 
         [0003]    The invention also concerns a vehicle axle for an electric vehicle comprising, in each case, a drive unit at opposite ends of the vehicle axle for the respective wheel-adjacent driving of a wheel. 
       BACKGROUND FIELD OF THE INVENTION 
       [0004]    Electric vehicles are understood to be vehicles operated by electrical energy. Electric vehicles include electric automobiles, in particular, which in recent years have increasingly gained attention because of their possible reduction of traffic-originating CO2 emissions and a desired reduction of dependence on petroleum as the basis of gasoline, diesel fuel, etc. 
         [0005]    Instead of the internal combustion engine used in conventional vehicles, an electric motor, whose electrical energy is supplied by, for example, accumulators carried in the electric vehicle, is used in electric vehicles. 
         [0006]    Wheel-hub electric motors can be used, as the electric motor, for driving an electric automobile. In that case, the wheel-hub electric motor is built directly into a wheel of the electric automobile and, at the same time, supports the wheel hub so that part of the wheel-hub electric motor rotates together with the wheel as an external rotor. 
         [0007]    However, wheel-hub electric motors have the disadvantage that the chassis of the electric automobile reacts less comfortably, since the use of wheel-hub motors increases the unsprung masses of the electric vehicle. Moreover, wheel-hub motors are directly exposed to environmental influences, impact loads and the possibly high temperatures of the brakes, which reduce their useful life and their reliability. 
       SUMMARY OF THE INVENTION 
       [0008]    Thus, an objective of the present invention is to provide a drive unit and a vehicle axle which, on the one hand, reduces unsprung masses and, at the same time, can be produced extremely inexpensively. This simplifies its maintenance. 
         [0009]    With a drive unit for an electric vehicle comprising an electric machine, in particular an electric motor that can be arranged in an area at an end of a vehicle axle of the electric vehicle, and also a transmission unit which co-operates with the electric machine in order to drive an adjacent wheel of the electric vehicle, the said objective is achieved if the electric machine and the transmission unit can be arranged, adjacent to the wheel, and the electric machine is designed such that it can be arranged in the drive unit, adjacent to the wheel, at either of the two ends of the vehicle axle in order to drive the wheel concerned. 
         [0010]    The invention also achieves the objective by virtue of a vehicle axle comprising in each case a drive unit on respective opposite parts of the vehicle axle for the wheel-adjacent driving of a wheel. 
         [0011]    Thus, the drive unit can be used both on the left and/or the right side and also on a front or a rear axle for driving a front wheel or rear wheel. In this way, the production costs for a drive unit can be substantially reduced since no design changes of the drive unit are needed, in particular for its arrangement on the left or the right side of the vehicle and for its wheel-adjacent arrangement on a front or rear axle. In all, therefore, a total of four identical electric machines are used with a four-wheel electric vehicle. Furthermore, by virtue of the wheel-adjacent arrangement, for example on a rear axle of the electric vehicle, the unsprung masses as a whole are reduced since the drive unit is not used in the wheel itself, i.e., as a wheel-hub motor. If the drive unit is arranged adjacent to the wheel, on a trailing arm of a torsion beam axle, the drive unit does not undergo the complete stroke of a jouncing movement of the wheel but, in essence, only a pivoting movement about a connection point of the torsion beam axle to the body of the electric vehicle. 
         [0012]    Expediently, the electric machine and in particular its housing is made symmetrical. This ensures that the electric machine and the drive unit can be particularly simply exchanged. At the same time, the drive unit can be simply fixed to a vehicle axle since a symmetrical housing structure simplifies the fixing of the drive units for a mechanic. Likewise, during robot-assisted assembly a substantial time saving is possible since the drive unit does not first have to be turned to a predetermined position; thanks to its symmetrical structure the drive unit can be fixed on the vehicle axle in several positions without restricting its function. 
         [0013]    Advantageously, the electric machine has fixing means which are arranged symmetrically, in particular radially symmetrically, relative to a respective drive axis of the electric machine. This enables reliable fixing of the electric machine even more simply by means of the fixing means onto a vehicle axle in the area near the wheel. 
         [0014]    Expediently, at least one coolant inlet and a coolant outlet are provided for cooling the electric machine, these being arranged symmetrically relative to the fixing means and/or a distance away from one another and one behind the other parallel to a drive axis of the electric machine. This ensures easy accessibility for the connection of hoses for the coolant circuit for cooling the electric machine, in particular the electric motor. Moreover, if the coolant inlet and coolant outlet are a spaced apart, maintenance is further simplified. 
         [0015]    Advantageously, the electric machine has a holding device for fixing at least one transmission component, in particular a planetary gear system of the transmission unit. The advantage achieved thereby is that it enables reliable fixing of the transmission unit to the electric machine and so also a more simple fixing of the drive unit onto a vehicle axle. 
         [0016]    Expediently, the holding device comprises at least one holding projection which is in particular U-shaped. In particular, the open side of the U-shaped holding projection can be orientated, in the radial direction, starting from a drive axis of the electric machine. Likewise, a plurality of holding projections can be arranged peripherally around the drive axis of the electric machine and spaced apart. The U-shaped design enables a particularly simple positioning of a transmission unit on the electric machine by means of the holding device. 
         [0017]    Advantageously, the transmission unit comprises a planetary gear system with a ring gear, wherein the ring gear can be fixed to the holding device, in the axial direction, onto the electric machine. In this way, a transmission unit with a planetary gear system can be driven by means of a sun shaft which, in particular, corresponds to the drive axis of the electric machine, and the drive output takes place via a web of the satellite gear system; in this case, the ring gear is arranged in a rotationally fixed manner on the holding device so enabling a reliable transmission of the drive torque of the electric machine by way of the planetary gear system, for example to a spur gear stage as a further transmission component of the transmission unit. 
         [0018]    Expediently, the ring gear is attached to the holding device, in particular rotationally fixed thereto, by means of a locking ring. The advantage of this is that it enables a soft coupling of the ring gear to the electric machine and thus an acoustic decoupling of the ring gear from the surroundings. It is then also possible to attach the drive unit, on a vehicle axle, and to fix the ring gear by means of further fastening means to a trailing arm of the vehicle axle. 
         [0019]    Advantageously, the ring gear has at least one axial and/or radial all-round groove. By means of an axial groove, which preferably corresponds with the holding device of the electric machine, the ring gear can be brought into engagement with and fixed to the electric machine. This ensures a firm connection and rotationally fixed arrangement in the circumferential direction of the ring gear. If the ring gear has a radial all-round groove, a locking ring can be fitted into this groove so that the locking ring engages both in the radial all-round groove and also in the U-shaped holding projections, thereby fixing the ring gear on the electric motor in the axial direction. 
         [0020]    Expediently, a rotation speed sensor is designed as an ABS sensor for the speed of either the transmission unit and/or the electric machine. The advantage of this is that the ABS sensor does not have to be arranged directly on the wheels themselves, where it would be exposed to weathering influences, but instead the ABS sensor can be arranged directly in the transmission unit so increasing the reliability of the ABS sensor. At the same time, there is no need for an additional ABS sensor, besides a rotation speed sensor for the electric machine, which reduces manufacturing costs for the transmission unit. 
         [0021]    Advantageously, a ring magnet is arranged on the shaft of the transmission unit so that the rotation speed of the shaft can be detected by the ABS sensor. This has the advantage of enabling the speed of the shaft to be detected with very little wear, which increases the reliability of the ABS sensor. Moreover, the ABS sensor can also detect the rotation speed of the shaft either radially or axially by virtue of the teeth of gearwheels of the transmission unit. Likewise, the sensor can be arranged on any drive input gearwheel, in particular, a spur gear and/or pinion and/or web and/or planetary shaft and/or sun shaft. 
         [0022]    Expediently, the ring gear is made of steel and/or the housing of the electric machine is made of aluminum. If the housing of the electric machine is made of aluminum heat can be effectively dissipated by way of the outer surface of the housing of the electric machine. In that case, the outer surface of the housing of the electric machine can be provided with a spiral all-round groove for cooling. Making the ring gear of steel ensures that the connection between the transmission unit and the electric machine is sufficiently strong. 
         [0023]    Other important characteristics and advantages of the invention emerge from the drawings and the associated figure descriptions that refer to the drawings. 
         [0024]    It is understood that the characteristics mentioned above and those still to be explained below can be used not only in the combination indicated in each case, but also in other combinations or in isolation, without going outside the scope of the present invention. 
         [0025]    Preferred example embodiments of the invention are illustrated in the drawings and are explained in more detail in the description that follows, wherein the same indexes are used for the same, or similar, or functionally equivalent components or elements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The figures show, in each case schematically: 
           [0027]      FIG. 1   a:  A structure of a vehicle axle of a vehicle; 
           [0028]      FIG. 1   b:  The left-hand area of the vehicle axle in  FIG. 1 , shown in a detailed three-dimensional view; 
           [0029]      FIG. 2   a:  An electric motor of a drive unit, shown in cross-section, according to a first embodiment of the present invention; 
           [0030]      FIG. 2   b:  A three dimensional view of an electric motor in  FIG. 2   a;    
           [0031]      FIG. 2   c:  An electric motor, as in  FIG. 2   a,  with a ring gear; 
           [0032]      FIG. 2   d:  An electric motor, as in  FIG. 2   a,  with a ring gear to be attached; 
           [0033]      FIG. 3   a:  An electric motor of a drive unit with a ring gear attached, as in  FIG. 2   c;    
           [0034]      FIG. 3   b:  An electric motor, as in  FIG. 3   a,  viewed along the direction of the drive axis of the electric motor; and 
           [0035]      FIG. 4 : A cross-section through a transmission unit of a drive unit, according to a second embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0036]      FIG. 1   a  shows a structure of a vehicle axle of a vehicle. 
         [0037]    In  FIG. 1   a,  indexed  1  is a vehicle axle, for example a rear axle of a motor vehicle. The vehicle axle  1  has a transverse profile  1   a  that extends over the width of the vehicle, perpendicularly to the vehicle axle  1 . Trailing arms  1   b  are arranged at each end of the transverse profile  1  a. Corresponding mountings  2  are arranged, at the ends of the transverse profile  1   a,  to attach the vehicle axle  1  to the vehicle. In addition, a damper  3  and a spring  4  are provided which enable a wheel  5  of the vehicle to be damped during the operation of the vehicle. In this case, a drive unit is arranged adjacent to the wheel, for example, in the area of the trailing arm  1   b,  designed in particular as the trailing arm  1   b.    
         [0038]      FIG. 1   b  shows, in detail, the three-dimensional structure of the left-hand side of the vehicle axle  1  in  FIG. 1   a.  On the transverse profile  1   a,  the trailing arm  1   b  is arranged on which, in turn, are arranged a damper  3  and a spring  4 , both connected to the body of the vehicle. The wheel  5  is connected to the trailing arm  1   b  and is mounted to rotate by means of a wheel bearing  5   a.    
         [0039]      FIG. 2   a  shows an electric motor of a drive unit, shown in cross-section, according to a first embodiment of the present invention. 
         [0040]    In  FIG. 2   a,  indexed  10  is an electric motor for a wheel-adjacent drive unit. 
         [0041]    The electric motor  10  comprises a drive spindle  13 , at the open end, on which drive teeth  14 , for example a sun gear of a planetary gear system, are arranged. On the side of the drive spindle  13 , opposite to the drive teeth  14 , a rotation speed sensor  15  is arranged to detect the rotation speed of the electric motor  10 . As a whole, in the normal manner, the electric motor  10  comprises a stator  11  inside the housing  16   a  of the electric motor  10  and a rotor  12  inside the stator  11  for driving the drive spindle  13 . The housing  16   a  of the electric motor  10  is closed in an airtight and fluid-tight manner by a cover  16   b,  on the side where the speed sensor  15  is located. On the outer side of the housing  16   a,  in the area of the stator, all-round cooling fins  17  are arranged in order to dissipate, as effectively as possible, the heat of the electric motor  10  into the surroundings. 
         [0042]      FIG. 2   b  shows a three-dimensional view of the electric motor as in  FIG. 2   a,    
         [0043]      FIG. 2   b  shows the electric motor  10  according to  FIG. 2   a.  In this case, as also in  FIG. 2   a,  the electric motor  10  is designed symmetrically and in cartridge form so that the electric motor  10 , for repair purposes, can be exchanged easily without having to dismantle completely a transmission unit. At the drive-teeth end  14 , the holding end  24 , the electric motor has holding projections  23  which are U-shaped with their openings facing outward from the drive spindle  13  in the radial direction. In addition, projecting fixing eyes  22  are provided, around the area of the opposite end, which are positioned to enable the electric motor  10  to be bolted onto a transmission unit and/or onto a vehicle axle. As shown in  FIG. 2   b,  on the upper side a coolant inlet  21   a  and a coolant outlet  21   b  are provided, which are a spaced apart from one another, in the axial direction, and which serve to carry coolant to and from a cooling circuit of the electric motor. 
         [0044]      FIG. 2   c  now shows a ring gear  25  arranged at the end of the electric motor  10 , on the holding projections  23 . The ring gear  25  has grooves  27 , distributed around its circumference, which correspond with the holding projections  23 , on the holding side  24  of the electric motor  10 . As shown in  FIGS. 2   c  and  2   d,  the ring gear  25  is pushed into the respective axial grooves  27  in the holding projections  23 . An all-round groove  25   a,  arranged on the ring gear, is formed in such manner that when the ring gear is in interlocked contact with the grooves  27  in the corresponding holding projections  23  of the electric motor  10 , in particular by virtue of the U-shape of the holding projections  23  and the circumferential groove  25   a,  interrupted by the grooves  27 , an all-round recess is formed. A locking ring  26 , which then fixes the ring gear  25  to the electric motor  10  in the axial direction, is fitted into the said recess. When the grooves  27  of the ring gear  25  are engaged with the holding projections  23 , the ring gear  25  is also attached to the electric motor  10  in a rotationally fixed manner. 
         [0045]      FIG. 3   a  shows an electric motor of a drive unit with a ring gear fixed in place in accordance with  FIG. 2   c.    
         [0046]      FIG. 3   a  shows the electric motor  10  with the ring gear  25  fitted on it, as in 
         [0047]      FIG. 2   c,  viewed in cross-section. The ring gear  25  is attached, in a rotationally fixed manner, by the engagement of the grooves  27  in the holding projections  23  and is axially fixed by means of the locking ring  26 . This is again made clear by  FIG. 3   b,  which shows a section along the section axis A-A in  FIG. 3   a.  The holding projections  23 , in which the grooves  27  of the ring gear  25  engage, can be seen clearly. Visible on the inside is the drive spindle  13  of the electric motor  10 , which has drive teeth  14  in the area of the ring gear. 
         [0048]      FIG. 4  shows a cross-section through a transmission unit of a drive unit, according to a second embodiment of the present invention. 
         [0049]      FIG. 4  shows a transmission unit  33  for the wheel-adjacent driving of an electric vehicle, which is arranged essentially in the area of the trailing arm  1   b  of a vehicle axle. A spur gear  32  of a pinion-spur gear arrangement is also visible. A spur shaft is indirectly connected to an electric motor  10  in order to drive a wheel (not shown). On the side of the spur gear  32 , opposite to the wheel bearing  5   a,  a ring magnet  31  is arranged on the drive spindle  32   a.  An ABS sensor  30  is positioned, in the area of the ring magnet  31 , in order to determine the rotation speed of the drive spindle  32   a.  Besides this, further ABS sensors can also be arranged on other drive gearwheels or their shafts, in particular a spur gear shaft, pinion shaft, web shaft, planetary shaft or sun shaft. The ABS sensor  30  can determine radially or axially a rotation speed of the shaft concerned by way of the spline teeth of the gearwheel. 
         [0050]    In summary, among other things, the invention has the advantages that in a simple and reliable manner a ring gear can be coupled to an electric machine so that the ring gear is acoustically decoupled from the surroundings. Furthermore the drive unit can be made conveniently since it can be fitted on both the front and the rear axle and on the left and/or the right side, without any additional design measures for the wheel-adjacent driving of a wheel of an electric vehicle. By means of the holding projections and corresponding grooves, the ring gear can indeed be very reliably attached rotationally fixed to the electric motor. Moreover there is no need for an additional ABS sensor on a wheel of the motor vehicle, and the ABS sensor is integrated in the transmission unit of the drive unit, so reducing production costs and increasing the reliability of the ABS sensor. 
         [0051]    Although the present invention has been described above with reference to preferred example embodiments, it is not limited to these but can be modified in many ways. 
       INDEXES 
       [0052]      1  Vehicle axle 
         [0053]      1   a  Transverse profile 
         [0054]      1   b  Trailing arm 
         [0055]      2  Mounting 
         [0056]      3  Damper 
         [0057]      4  Spring 
         [0058]      5  Wheel 
         [0059]      5   a  Wheel bearing 
         [0060]      10  Electric motor 
         [0061]      11  Stator 
         [0062]      12  Rotor 
         [0063]      13  Drive spindle 
         [0064]      14  Drive teeth 
         [0065]      15  Rotation speed sensor 
         [0066]      16   a  Housing of the electric motor 
         [0067]      16   b  Cover 
         [0068]      17  Cooling fin 
         [0069]      21   a  Coolant inlet 
         [0070]      21   b  Coolant outlet 
         [0071]      22  Fixing eye 
         [0072]      23  Holding projection 
         [0073]      24  Holding side 
         [0074]      25  Ring gear 
         [0075]      25   a  All-round groove 
         [0076]      26  Locking ring 
         [0077]      27  Groove 
         [0078]      30  ABS sensor 
         [0079]      31  Ring magnet 
         [0080]      32  Spur gear 
         [0081]      32   a  Drive spindle 
         [0082]      33  Drive unit