Abstract:
A drive train ( 1 ) of a purely electrically all-wheel drivable motor vehicle has a first axle ( 2 ) with axle halves ( 7, 8 ) and a differential ( 9 ) connecting them, a second axle ( 3 ) with axle halves ( 4, 5 ) and a differential connecting them, and first and second electric machines ( 19, 20 ) for driving the axles ( 2, 3 ). The first electric machine ( 19 ) is connected via a first transmission ( 24 ) to one axle half ( 7 ) of the the first axle ( 2 ) and the second electric machine ( 20 ) is connected via a second transmission ( 25 ) to the other axle half ( 8 ) of the first axle ( 2 ). The two differentials ( 6, 9 ) are connected to each other via a shaft ( 13 ). The drive train provides an all-wheel drive with simple construction, and standardization.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a drive train of a purely electrically all-wheel drivable motor vehicle, with a first axle which has axle halves and a differential connecting the latter, with a second axle which has axle halves and a differential connecting the latter, and with two electric machines for driving the two axles. 
         [0003]    2. Description of the Related Art 
         [0004]    Such a drive train, which is usable for an electrically drivable earth-moving vehicle or for an agricultural vehicle with four-wheel drive, is known from DE 600 13 340 T2. In said drive train, the two electric machines are arranged longitudinally with respect to the direction of travel above the one, rear axle, and interact with a gearing which is arranged in front of the rear axle. The gearing is connected via one shaft or two shafts to the differentials which are assigned to the two axles, therefore the rear axle and the front axle. 
         [0005]    It is the object of the present invention to provide a drive train of a purely electrically all-wheel drivable motor vehicle, which, with an arrangement of two electric machines in the region of an axle of the drive train, permits all-wheel drive, and therefore drive also of the other axle, with structurally simple, in particular standardized means. 
       SUMMARY OF THE INVENTION 
       [0006]    The drive train of the purely electrically all-wheel drivable motor vehicle therefore has a first axle and a second axle. The first axle and the second axle are both divided. The first axle has the axle halves and a differential connecting the latter. The respective electric machine has, in particular, the function of an electric motor and of a generator, and therefore the electric machine as an electric motor serves for driving the respective axle and, in the function thereof as a generator, is driven via the respective axle. 
         [0007]    It is essential in the case of the drive train according to the invention for one of the two electric machines, referred to as the first electric machine, to be directed via a first gearing to the one axle half of the first axle and for the other electric machine, referred to below as the second electric machine, to be connected via a second gearing to the other axle half of the first axle. Since the one electric machine is connected via the gearing assigned thereto to the one axle half of the first axle, and the other electric machine is connected via the gearing assigned thereto to the other axle half of the first axle, individual wheel drives of the first axle and therefore torque vectoring are possible. 
         [0008]    In order now also to drive the second axle of the drive train, according to the invention the two halves of the first axle, which bear the left and right wheel of the motor vehicle, are connected to each other via the differential. Both this differential of the first axle and the differential of the second axle are connected via a shaft. 
         [0009]    Owing to the connection of the two electric machines via the gearings assigned thereto to the axle halves of the first axle and via the differential assigned to said first axle, the torque introduced into the first axle via the electric machines is, as it were, mixed in the region of said differential and a portion of torque from said differential is introduced via the shaft into the differential assigned to the second axle. 
         [0010]    The drive train is preferably used in a motor vehicle which is in the form of a passenger vehicle. Said passenger vehicle is in particular a sports car. Said motor vehicle, in particular the passenger vehicle or the sports car, is preferably in the form of rear drive. The two electric machines are therefore arranged in the rear region of the motor vehicle or of the drive train. In the force flux in the path of the two electric machines arranged in the rear region of the drive train, first of all the first, rear axle is driven and, from there via the shaft, the second, front axle is driven. 
         [0011]    It is considered to be particularly advantageous if the two electric machines are arranged behind the rear axle, and therefore behind the first axle. 
         [0012]    In principle, however, the motor vehicle may be in the form of front drive. 
         [0013]    The wheels assigned to the drive train are connected thereto in particular individually via propeller shafts. The drive train therefore does not have a rigid axle. 
         [0014]    It is considered to be particularly advantageous if the two electric machines are arranged transversely with respect to the direction of travel of the motor vehicle. Under the aspect of a structurally particularly simple design of the drive train, it is advantageous here if the axes of rotation of the rotors of the electric machines are identical. The electric machines are therefore arranged next to each other with respect to the direction of travel of the motor vehicle. In particular, the electric machines are arranged symmetrically to a longitudinal center axis relating to the two axles. This substantially permits a symmetrical distribution of weight of the individual components of the drive train with respect to the central longitudinal plane of the drive train. 
         [0015]    According to a preferred embodiment of the invention, provision is made for the respective electric machine to be connected via a spur gear toothing to the associated axle half of the first axle in order to drive the latter. This design makes it possible to form the respective gearing with structurally simple, in particular standardized means. Furthermore, it is considered to be advantageous if the differential of the first axle and/or of the differential of the second axle have/has a crown wheel. In an embodiment with two crown wheels, the latter are connected to each other in particular via the shaft. The shaft has, in the region of the averted ends, pinions which interact with the crown wheels. Since a respective pinion engages in a respective crown wheel, a torque mixed in the differential of the first axle is therefore transmitted from the two halves of the first axle, by means of the shaft, to the second shaft. The pinions assigned to the shaft and/or the corresponding crown wheels can differ in size, and therefore different transmission ratios are brought about in conjunction with the associated crown wheels. 
         [0016]    This results in the simple possibility of electrically fitting a purely electrically driven vehicle with only one drive axle with all-wheel without an additional electric machine for the other axle. In particular, the possibility arises of using, for essentially partial regions of the drive train according to the invention, technology which is already known from conventional all-wheel vehicles, thus technology which is used in known all-wheel vehicle wheels driven by means of internal combustion engines. This relates in particular to the transmission of torque by the first axle to the second axle. For example, it is known that the shaft additionally has a controllable clutch, in particular a hang-on clutch. The shaft can also be designed in a known manner as a propeller/cardan shaft. There is in particular the possibility of using a combination, which is already known for conventional all-wheel vehicles, of propeller/cardan shaft with hang-on clutch and connected vehicle axle, in the drive train according to the invention, without further modifications. 
         [0017]    According to a particularly preferred design, provision is made for the two gearings, in particular the spur gear toothings of the two gearings, and the differential of the first axle to have a common housing. In particular, the housing is of two-part design and, in particular, has two housing shells. Said housing requires bearings which are separate in each case for the respective left and right bearings of the shafts of the two gearings of the two spur gear stages, i.e. a total in each case of four coaxially arranged bearing points per shaft. In order nevertheless to permit a simply constructed housing, with only two housing shells together with respective bearings on the two outer sides of the housing shells, it is proposed, instead of the in each case two central bearings of the shafts, now to provide needle bearings for the respective two shafts, said needle bearings then being mounted one in the other. By use of the needle bearings, the central bearings can be omitted, and therefore two simply constructed housing halves can be used. 
         [0018]    Further features of the invention emerge from the dependent claims, the attached drawing and the description of the preferred exemplary embodiments, which are reproduced in the drawing, without being limited thereto. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  shows a schematic diagram of a first embodiment of the drive train according to the invention. 
           [0020]      FIG. 2  shows a schematic diagram of a second embodiment of the drive train according to the invention. 
           [0021]      FIG. 3  shows, in an enlarged illustration, a partial region of the drive train illustrated in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    The exemplary embodiment according to  FIG. 1  illustrates a drive train  1  for a purely electrically all-wheel drivable motor vehicle, which is, in particular, a passenger vehicle, specifically a sports car. 
         [0023]    The drive train  1  with individual wheel suspension has a first, rear axle  2  and a second, front axle  3 . The rear axle  2  has two axle halves  7  and  8  having propeller shafts. A differential  9  connects said axle halves. The front axle  3  has two axle halves  4  and  5  having propeller shafts. A differential  6  connects said axle halves. Front wheels  10  are connected to the two axle halves  4  and  5 , and rear wheels  11  are connected to the axle halves  7  and  8 . 
         [0024]    The forward direction of travel, referred to in short below as direction of travel, is illustrated by the arrow  12 . 
         [0025]    The two differentials  6  and  9  are connected by means of a shaft  13 , which is designed in particular as a propeller shaft or cardan shaft. The shaft has a controllable clutch, in particular in the manner of a hang-on clutch  14 , in order, in particular, to couple or to decouple the two axles  2  and  3 . The shaft  13  is mounted with the clutch  14  in bearings  15  arranged on both sides of the clutch  14 . The bearings of the axle halves  4  and  5  of the front axle  3  and the bearings of the axle halves  7  and  8  of the rear axle  2  are denoted by the reference number  16 . In the region of the ends averted from the wheels  10 ,  11 , the axle halves  4  to  8  are mounted in the differentials  6  and  7 , respectively. 
         [0026]    The respective differential  6  or  9  has a crown wheel  17 . The crown wheels  17  interact with pinions  18  which are arranged at averted ends of the shaft  13  and are connected to the shaft  13 . The crown wheels  17  and/or the pinions  18  can differ in size. 
         [0027]    The drive train  1  has two electric machines  19 ,  20  which are arranged transversely with respect to the direction of travel  12  of the motor vehicle. The axes of rotation of the two electric machines  19  and  20  illustrated by the respective driven shafts  21  of said electric machines, are identical. The stator of the respective electric machine  20  is denoted by the reference number  22 , and the rotor of the respective electric machine  20 , to which rotor the driven shaft  21  is connected, is denoted by the reference number  23 . The respective rotor  23  and the respective driven shaft  21  are mounted in, for example, two bearings  43 . The one, first electric machine  19  is connected via a first gearing  24  to the axle half  7  of the rear axle  2 , and the other, second electric machine  20  is connected via a second gearing  25  to the other axle half  8  of the rear axle  2 . Each gearing  24  or  25  is designed as a spur gearing and therefore has a spur gear toothing. Specifically, the respective gearing  24  or  25  has a pinion  26  which is connected to the driven shaft  21  for rotation therewith, and a spur gear  27  meshing with said pinion, wherein said spur gear is mounted in an intermediate shaft  28  and is connected thereto for rotation therewith. A pinion  29  which interacts with a spur gear  30  is connected to the respective intermediate shaft  28 , on that side of said intermediate shaft  28  which faces the rear wheel  11 . The respective spur gear  30  is mounted in the axle half  7  or  8  and is connected thereto for rotation therewith. Each of the two intermediate shafts  28  is mounted in the region of the averted ends thereof in bearings  31 . The axes of rotation of the two intermediate shafts  28  are identical. 
         [0028]    The two gearings  24  and  25  and the differential  9  of the rear axle  2  are arranged in a common housing. Since the two electric machines  19 ,  20  and gearings  24 ,  25  and spur gear toothings are formed separately from one another, an individual wheel drive of the wheels  11  of the rear axle  2 , and therefore torque vectoring, is possible. In order also to drive the front axle  3 , the two axle halves  7  and  8  of the rear axle  2  are connected to each other via the differential  9 . The torque mixed in said differential  9  is therefore transmitted by the axle halves  7  and  8  of the rear axle  2  to the front axle  3  by means of the shaft  13 . This produces the possibility of using a combination of propeller/cardan shaft  13  with hang-on clutch  14  and connected vehicle axle, which combination is already known from conventional all-wheel vehicles, and therefore from all-wheel vehicles driven by means of an internal combustion engine, in a purely electrically drivable vehicle, without further modifications. 
         [0029]    The possibility of torque vectoring is illustrated in the figure by the indication ΔT. By this means, different torques can be introduced into the axle halves  7 ,  8 . 
         [0030]    The drive train of the embodiment according to  FIG. 1  requires separate bearings in each case for the left and right bearing points in each case of the axles of the two spur gear stages and the axle halves of the rear axle, i.e. a total of four coaxially arranged bearing points per axle. 
         [0031]    The exemplary embodiment of a drive train according to the illustration of  FIGS. 2 and 3  illustrates a modified mounting of the axles. This makes it possible to use a simply constructed housing with only two housing shells together with respective bearings on the two outer sides of the housing shells. In this case, instead of the in each case two central bearings of the axles as per the embodiment according to  FIG. 1 , needle bearings are provided in the embodiment according to  FIGS. 2 and 3 . By use of the needle bearings, the central bearings can be omitted and therefore two simply constructed housing halves can be used. 
         [0032]    In the embodiment of  FIGS. 2 and 3 , drive train parts corresponding to the embodiment according to  FIG. 1  have been denoted by reference numbers which correspond to reference numbers in  FIG. 1 . The modification of the embodiment of  FIGS. 2 and 3  in relation to the embodiment according to  FIG. 1  is discussed in detail below. 
         [0033]      FIG. 2  basically illustrates that only two outer bearings  31 , which are mounted in the housing, are necessary for the mounting of the two intermediate shafts  32 ,  33 , while the and the intermediate shaft  32  is mounted in the intermediate shaft  33  by means of two needle bearings  34 . The intermediate shaft  33  has a tubular section  35  for receiving the undulating section  36  of the intermediate shaft  32 , said section  36  passing through the section  35 . That region of the section  36  which is arranged within the section  35  is mounted radially in the section  35  by means of the two needle bearings  34 . A flange section  37  extends perpendicularly to the section  35  of the intermediate shaft  33 , and a flange section  38  extends perpendicularly to the section  36  of the intermediate shaft  22 . A further needle bearing  39  which serves for the axial mounting of the intermediate shaft  32  and of the intermediate shaft  33  is arranged between the two flange sections  37  and  38 . On the sides thereof which face the rear wheels  11 , the section  36  of the intermediate shaft  32  and the section  35  of the intermediate shaft  33  are mounted in the bearings  31 . 
         [0034]    The mounting of the axle halves  7  and  8  takes place in a manner corresponding to the plugged-together mounting of the intermediate shafts  32 ,  33 , with the needle bearings  34  and  39  provided in this connection. This detail is illustrated in enlarged form in  FIG. 3 , with a certain modification taking place there because of the planetary differential which is present. 
         [0035]    A torque is introduced by the two spur gears  33  into the axle halves  7  and  8  independently because of the action of the two electric machines  19  and  20 . Said axle halves  7  and  8  are mounted on the side thereof facing the rear wheels  11  in the bearings  16 . Said bearings, in precisely the same manner as the bearings  31  according to this embodiment, are housing-side bearings, wherein the bearings  16  and  31  which are assigned to the one rear wheel  11  are mounted in the one housing half, while the bearings  16  and  31  which are assigned to the other rear wheel  11 , are mounted in the other housing half of the housing. The housing itself is not illustrated. 
         [0036]    The axle half  7  is inserted with a section  40  into a tubular section  41  of the axle half  8 , and two needle bearings  42  are provided for the radial mounting of the sections  40  and  41 . With this mounting of the two axle halves  7  and  8 , the two central bearings provided in the embodiment according to  FIG. 1  can therefore be omitted and replaced by needle bearings. The differential  9  which is in the form of a planetary differential and likewise has needle-bearing bearing components is arranged in the torque flux between the section  40  of the axle half  7  and the section  41  of the axle half  8 . 
         [0037]    Therefore, as per the embodiment according to  FIGS. 2 and 3 , a drive train  1  is proposed, in which a common housing is provided for the gearings  24  and  25  and the differential  9 , with two housing shells, wherein the respective shafts of the gearing and of the lower axle  2  are not mounted centrally in the housing, but rather, instead, the shafts assigned to the respective axle have a needle mounting one inside the other.