Abstract:
An electrical axle ( 200, 300, 400 ) for a four wheeled road vehicle is provided, comprising an electrical propulsion motor ( 210, 310, 410 ) arranged coaxially on said axle ( 200, 300, 400 ), a first planetary gear ( 222   a,    322   a,    422   a ) connected to said electrical propulsion motor ( 210, 310, 410 ) and to a first side of said axle ( 200, 300, 400 ), and a second planetary gear ( 222   b,    322   b,    422   b ) connected to said electrical propulsion motor ( 210, 310, 410 ) and to a second side of said axle ( 200, 300, 400 ), said first and second planetary gears ( 222, 322, 422 ) is forming a differential mechanism ( 220, 320, 420 ), and a torque vectoring unit ( 240, 340, 440 ) comprising an electrical motor ( 242, 342, 442 ) arranged coaxially on said axle ( 200, 300, 400 ) for providing a change in torque distribution between said first side and said second side of said axle ( 200, 300, 400 ), wherein said electrical motor ( 242, 342, 442 ) of said torque vectoring unit ( 240, 340, 440 ) is connected to the first and second planetary gears ( 222, 322, 422 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an electrical axle of a four wheeled vehicle. More particularly, the present invention relates to an electrical axle having a torque vectoring unit for providing a torque difference between a right wheel and a left wheel of said axle. 
       BACKGROUND 
       [0002]    For road vehicles it is desirable to be able to distribute different drive torque to different wheels for improving the vehicle stability and/or performance. Torque vectoring units for road vehicles are thus known which purpose is to cause the drive torque distribution of a vehicle to change. 
         [0003]    Such torque vectoring devices are arranged to shuffle drive torque laterally on a driven axle, or longitudinally between a driven axle and a non-driven axle. 
         [0004]    In order to obtain the desired result with regard to the driving dynamics, it may in certain situations be advantageous to provide a drive wheel with a positive torque in relation to the other drive wheel on the driving axle. Such a positive torque may be obtained in a way known per se by a mechanical gear device for gearing-up or increasing the rotational speed of the drive shaft for the wheel in question by for example 10%. 
         [0005]    Many examples of such mechanical gear devices are known. In such arrangements being both heavy and expensive, torque vectoring devices are arranged at either side of the central differential for the two drive shafts. 
         [0006]    Hence, when a differential rotational speed between two wheels is requested the prior art devices are affecting the rotational speed relative the absolute rotational speed, leading to heavy devices having a relatively high power consumption. 
         [0007]    In view of this, the applicant has previously presented a torque vectoring unit which overcomes the above mentioned drawbacks. Such unit, fully disclosed in WO2010101506, includes an electrical motor coupled to a driven axle of a road vehicle such that, upon activation, it provides a positive torque to one wheel and an opposite torque to another wheel, each wheels being disposed on the same axle. 
         [0008]    The torque vectoring unit is arranged on a driven axle of the vehicle. The propulsion force may be provided by means of an electrical motor, such that the torque vectoring unit is operating on an electrical axle of the vehicle. Such electrical axles are highly attractive for providing four-wheeled drive in e.g. a hybrid car, i.e. a vehicle being equipped with a first transmission for providing propulsion torque to the front axle, and a second transmission for providing propulsion torque to the rear axle. 
         [0009]    Although the previously presented unit is highly attractive, the increasing demands of the industry require improvements relating to performance, simplicity, space requirements, cost etc. Therefore, there is a need for an electrical axle with a torque vectoring unit, said electrical axle being more compact and more cost effective. 
       SUMMARY 
       [0010]    Accordingly, the present invention preferably seeks to mitigate, alleviate or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination and solves at least the above-mentioned problems by providing a device according to the appended claims. 
         [0011]    It is thus an object of the invention to provide an electrical axle with a torque vectoring unit, which overcomes the above mentioned problems. 
         [0012]    A further object of the present invention is to provide an electrical axle with a torque vectoring unit which provides a higher gear ratio. 
         [0013]    Moreover, an object of the present invention is to provide an electrical axle with a torque vectoring device which has a significantly reduced size. 
         [0014]    According to a first aspect, an electrical axle for a four wheeled road vehicle is provided. The electrical axle comprises an electrical propulsion motor arranged coaxially on said axle, a first planetary gear connected to said electrical propulsion motor and to a first side of said axle, and a second planetary gear connected to said electrical propulsion motor and to a second side of said axle, said first and second planetary gears is forming a differential mechanism, and a torque vectoring unit comprising an electrical motor arranged coaxially on said axle for providing a change in torque distribution between said first side and said second side of said axle, wherein said electrical motor of said torque vectoring unit is connected to the first and second planetary gears. 
         [0015]    According to a second aspect, a four wheeled road vehicle is provided, comprising an electrical axle according to the first aspect. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]    Hereinafter, the invention will be described with reference to the appended drawings, wherein: 
           [0017]      FIG. 1  is a schematic view of a vehicle according to an embodiment; 
           [0018]      FIG. 2  is a schematic view of a vehicle according to another embodiment; 
           [0019]      FIG. 3  is a schematic view of a vehicle according to a further embodiment; 
           [0020]      FIG. 4  is a schematic view of a vehicle according to a yet further embodiment; 
           [0021]      FIG. 5  is a schematic view of a vehicle according to another embodiment; 
           [0022]      FIG. 6  is a schematic view of a torque vectoring device according to an embodiment; 
           [0023]      FIG. 7  is a cross sectional view of an electrical axle of a vehicle including a torque vectoring device according to an embodiment; 
           [0024]      FIG. 8  is a cross sectional view of an electrical axle of a vehicle including a torque vectoring device according to another embodiment; 
           [0025]      FIG. 9  is an isometric view of the gear change device shown in  FIG. 8 ; 
           [0026]      FIG. 10  is a cross sectional view of a torque vectoring device according to a further embodiment; and 
           [0027]      FIG. 11  is an isometric view of the gear change device shown in  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    Several embodiments of the present invention will be described in more detail below with reference to the accompanying drawings in order for those skilled in the art to be able to carry out the invention. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The embodiments do not limit the invention, but the invention is only limited by the appended claims. Furthermore, the terminology used in the detailed description of the particular embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. 
         [0029]    Examples of drive line configurations of a vehicle are shown in  FIGS. 1 to 6 . In these embodiments, the vehicle  10  has a front axle  12  being connected to a rear axle  14 , and a torque vectoring device  16 . 
         [0030]    In  FIG. 1 , the front axle  12  is driven by means of a transmission  18 , and the rear axle  14  is driven by means of an electrical motor  20 . The torque vectoring device  16  is arranged at the electrical rear axle  14 . 
         [0031]    In  FIG. 2 , a similar configuration is shown but here the rear axle is driven by means of a transmission  18 , and the front axle is driven by means of an electrical motor  20 . Consequently, the torque vectoring device  16  is arranged at the electrical front axle. 
         [0032]      FIGS. 3 and 4  show configurations where the front axle  12  or the rear axle  14  is driven by an electrical motor  20 , wherein the torque vectoring device  16  is arranged at the driven electrical axle  12 ,  14 . 
         [0033]    As a further example,  FIG. 5  shows a configuration in which the front axle  12  and the rear axle  14  are driven by electrical motors  20 . Torque vectoring devices  16  are arranged at each electrical axle  12 ,  14 . 
         [0034]    With reference to  FIG. 6 , a basic setup of an electrical axle  100  including a torque vectoring device  110  is shown. A driving axle  100  of a vehicle is driven by means of a propulsion unit  120  and has two wheels  102   a,    102   b  connected to opposite ends of the axle  100 . The propulsion unit  120 , provided as an electrical motor, is coupled to a differential mechanism  130  for allowing the wheels  102   a,    102   b  to rotate at different velocities. An electrical motor  140  is connected to the differential mechanism  130 , for providing a torque difference to opposite ends of the axle  100 . A control means  150  is further connected to the electrical motor  140 , and configured to calculate and transmit control signals to the electrical motor  140  of the torque vectoring device  110 . 
         [0035]    When the vehicle is travelling on a straight course, both wheels  102   a,    102   b  will rotate at the same speed. In this situation, the electrical motor  140  will stand still. When the vehicle passes a surface having inhomogeneous friction, the torque vectoring device  110  may be used to enhance the traction potential of the driving axle  100 . In such cases, the control means  150  sends a signal to the electrical motor  140  of the torque vectoring device  110  that will activate and apply a torque. Upon this, an increase of torque will be provided to one of the ends of the axle  100 , and a corresponding torque decrease will be provided to the opposite end of the axle  100 . 
         [0036]    An embodiment of an electrical axle  200  of a vehicle including a torque vectoring device is shown in greater detail in  FIG. 7 . The electrical axle  200 , which includes an electrical propulsion motor  210 , a differential mechanism  220 , and a torque vectoring device  240 , is configured to be connected to a left wheel shaft and a right wheel shaft (not shown). The electrical propulsion motor  210  is arranged coaxially on the axle  200 , and is connected on each lateral side to a differential mechanism  220  consisting of two coaxially aligned planetary gears  222   a,    222   b,  of which the electrical propulsion motor  210  is driving the sun gears  224   a,    224   b.  The left and right wheel shafts are connected to the planetary carriers  226   a,    226   b  of the respective planetary gears  222   a,    222   b.  The ring gear  228   a,    228   b  of the respective planetary gear  222   a,    222   b  has an outer surface which is connectable, e.g. by means of teeth, to the torque vectoring device  240 . 
         [0037]    The torque vectoring device  240  includes an electrical motor  242  arranged coaxially on the axle  200 , such that the rotational axis of the motor  242  is aligned with the rotational axis of the electrical propulsion motor  210 . The electrical motor  242  is further arranged distally of the differential mechanism  220 , i.e. between one of the planetary gears  220   a,    200   b  and the adjacent wheel shaft. 
         [0038]    The electrical motor  242  of the torque vectoring device  240  is connected directly to the ring wheel  228   b  of the second planetary gear  222   b,  and connected to the ring wheel  228   a  of the first planetary gear  222   a  via a rotatable balancing shaft  244  extending parallel with the axle  200 , and provided with gears for engagement with the ring gear  228   a  of the planetary gear  222   a.  The gears of the balancing shaft  244  are configured for transmitting torque to the planetary gear  222   a  upon rotation of the balancing shaft  244 , wherein the torque transmitted to the planetary gear  222   a  has an opposite direction compared to the torque transmitted to the other planetary gear  222   b  directly. 
         [0039]    The ring wheels  228   a,    228   b  are coupled to the electrical motor via a cycloidal drive  250  for creating a gear reduction between the electrical motor  242  and the differential mechanism  220 . The cycloidal drive  250  includes an eccentric input shaft  252  which is directly driven by the electrical motor  242 . A cycloidal disc is directly connected to the input shaft  252  and free to rotate within a stationary ring wheel. Upon rotation, the disc is driving an output shaft including a disc with a plurality of rollers, which rollers are allowed to rotate within corresponding recesses in the disc. 
         [0040]    Preferably, the gear reduction may be in the range of a factor 30 to 50, although other factors may also be applicable. Typical gear reduction requirements may be dependent on the desire for a low performance motor, which thus requires a high reduction, as well as on a desired low reduction in order to reduce the maximum speed of the motor. 
         [0041]    In another embodiment, the output shaft of the cycloidal drive is the ring wheel, while the roller disc is held stationary. 
         [0042]    Now turning to  FIG. 8 , another embodiment of an electrical axle  300  is shown. The electrical axle  300  includes an electrical propulsion motor  310  and a differential mechanism  320  identical with what has previously been described with reference to  FIG. 7 . The torque vectoring device  340  differs from the previous embodiment in the choice of reduction gear  350 , which in this case is a differential planetary gear. Such differential planetary gear is very compact and provides a greater gear reduction between the electrical motor  342  and the differential mechanism  320  than a regular planetary gear. 
         [0043]    For example, if a gear reduction of a factor  50  is desired, it would normally require  3  or  4  planetary gears arranged in series. Hence, the choice of a differential planetary gear is highly advantageous. 
         [0044]    The differential planetary gear  350 , which is also shown in  FIG. 9 , includes planets  352  having two different gears of which one is connected to the ring wheels of the planetary gears  322   a,    322   b  of the differential mechanism, and the other is connected to stationary ring wheel  354 . The second gear of the planets  352  is also connected to a sun wheel  356  which in turn is connected to the electrical motor  342 . The planet carrier  358  is thus not connected to any of the axles. 
         [0045]    In  FIG. 10  a third embodiment of an electrical axle  400  is shown. The electrical axle  400  includes an electrical propulsion motor  410  and a differential mechanism  420  identical with what has previously been described with reference to  FIGS. 7 and 9 . The torque vectoring device  440  differs from the previous embodiment in the choice of reduction gear  450 , which in this case is a double cycloidal drive. Such double cycloidal drive is very compact and provides a greater gear reduction between the electrical motor  442  and the differential mechanism  420  than a regular planetary gear. Further, the use of a double cycloidal drive provides a balancing effect of radial reaction forces and balancing of weight, which means that the reduction gear allows a higher rotational speed. 
         [0046]    A double cycloidal drive may e.g. operate up to 16.500 rpm, which is far more than a regular cycloidal drive as described above with reference to  FIG. 7 . 
         [0047]    The double cycloidal drive, which is also shown in  FIG. 11 , comprises two discs  452 ,  454  which are arranged eccentric on the rotational shaft of the electrical motor  442 . A plurality of rollers  456  are provided on a roller support  458  which is locked with respect to rotational movement. The eccentric movement of the discs  452 ,  454  provides a stepwise movement relative the ring wheel  459  of the cycloidal drive  450 , whereby a gear reduction is achieved. 
         [0048]    In a further embodiment the double cycloidal drive  450  is replaced by a multi-cycloidal drive comprising three or more discs which are arranged on the rotational shaft of the electrical motor. 
         [0049]    In a yet further embodiment the gear reduction  250 ,  350 ,  450  is omitted, such that the electrical motor of the torque vectoring unit is connected directly the ring wheel of the second planetary gear of the differential mechanism, and to the ring wheel of the second planetary gear of the differential mechanism via the balancing shaft. Such embodiment is advantageous in that less components are used, although it requires extreme performance of the electrical motor. 
         [0050]    It will be appreciated that the embodiments described in the foregoing may be combined without departing from the scope as defined by the appended patent claims. Although the present invention has been described above with reference to specific embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the invention is limited only by the accompanying claims and, other embodiments than the specific above are equally possible within the scope of these appended claims. 
         [0051]    In the claims, the term “comprises/comprising” does not exclude the presence of other elements or steps. Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly advantageously be combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. The terms “a”, “an”, “first”, “second” etc do not preclude a plurality. Reference signs in the claims are provided merely as a clarifying example and shall not be construed as limiting the scope of the claims in any way.