Abstract:
A drive arrangement for an electric vehicle has an axle drive device of a portal design with two electric machines for driving the wheels of an axle of the electric vehicle, and at least one electric energy store that can be discharged when an electric machine is operated as a motor and/or can be charged when an electric machine is operated as a generator. The drive arranged is characterized in that the two electric machines ( 11 ) of the axle drive device ( 10 ) are combined with a respectively assigned transmission ( 12 ) in an electric axle to drive the individually suspended wheels ( 2 ) of the axle by means of, in each case, one articulated shaft flange ( 13 ) via a respective articulated shaft. Frequency converters assigned respectively to the two electric machines are combined in a converter unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 USC 119 to German Patent Application No. 10 2010 007 642.2, filed on Feb. 5, 2010, the entire disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a drive arrangement for an electric vehicle. 
     2. Description of the Related Art 
     DE 296 11 867 U1 discloses a chassis for a utility vehicle with a portal axle and a wheel rotatably mounted at each of the two ends of the portal axle. Each wheel is driven by an electric traction motor installed in the portal axle. This portal axle is a rigid axle that is relatively heavy and provides only a low level of comfort. 
     The object of the invention is to improve the generic portal axle and to increase the level of comfort. 
     SUMMARY OF THE INVENTION 
     The invention relates to a drive arrangement for an electric vehicle. The drive arrangement is an axle drive device that has two electric machines combined with a respectively assigned transmission in an electric axle to drive individually suspended wheels of the axle by means of, in each case, one articulated shaft flange via a respective articulated shaft. Additionally, two frequency converters are assigned to the respective electric machines and are combined in a converter unit. Thus, a drive unit for an electric vehicle is formed in an easy way by integrating the two electric machines and the respectively assigned transmissions in a common unit that defines the electric axle. The guidance of the wheel is not influenced by the weight of the drive unit due to the separation of the drive unit from a wheel-guiding unit. The chassis, in particular the individual wheel suspension of the wheels therefore can be adopted from a conventional vehicle. Frequency converters are necessary for operating the respective electric machine. However, in accordance with the invention, the frequency converters are combined in a converter unit. This minimizes the number of necessary components and permits a reduction in the high voltage lines used. 
     The invention will now be presented in more detail on the basis of a drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic top perspective view of a drive arrangement according to the invention. 
         FIG. 2  is a schematic plan view of the drive arrangement of  FIG. 1 . 
         FIG. 3  is a schematic side view of the drive arrangement of  FIGS. 1 and 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A vehicle  1  in accordance with the invention includes an electric axle  10 , a converter unit  20  and an electric energy store  30 , as illustrated in  FIGS. 1 to 3 . The electric axle  10  illustrated in this embodiment is a rear axle of an electric vehicle. The electric axle  10  comprises two electric machines  11  that are arranged coaxially in a common housing. The electric machines  11  preferably are permanently excited synchronous machines to ensure that they can be actuated effectively. Each electric machine  11  drives a respective articulated shaft flange  13  via an associated transmission  12 , which comprises a spur gear stage. The articulated shaft flange  13  is provided for connection to an individually suspended wheel  2  via an articulated shaft  13   a . A wheel-guiding unit of the individually suspended wheel  2  comprises, for example, conventional front-axle crossmembers, front-axle crosslinks and vibration-damped McPherson strut axles. This produces an electric portal axle with a high level of comfort in an electric vehicle. 
     The electric axle  10  also comprises a cooling device so that a coolant, such as water, is fed in via a feed line  15   a , and the heated coolant is discharged again via a discharge line  15   b.    
     The electric axle  10  with the two coaxially arranged electric machines  11  is integrated directly into the rear axle of the electric vehicle in this embodiment. The housing of the electric axle  10  is screwed, for example, to longitudinal members or crossmembers of the electric vehicle. The low center of gravity as a result of the installation position, i.e. the portal arrangement owing to the spur gear stage around which the respective transmission  12  engages, is highly advantageous for the movement dynamics. Each electric machine  11  drives an associated wheel  2 . In this embodiment, the electric power of an electric machine  11  is 60 kilowatts and gives rise to a maximum drive torque of 80 Newton meters. Each electric machine  11  also has a position sensor that determines the precise position of the rotor for optimum operation. Each electric machine  11  is supplied with a suitable alternating current via terminals  14  on the electric axle  10 . 
     The forces are transmitted from each electric machine  11  to a respective wheel  2  via, in each case, a hydraulic multi-disk clutch (not illustrated) that permits precise transmission of force. The multi-disk clutches are closed permanently and are controlled automatically. For safety reasons a multi-disk clutch has to be opened by the driver by means of an operator control to decouple a respective electric machine  11  from a respective wheel  2 . A fixed transmission reduction of the respective transmission  12  reduces the high output rotational speed of the respective electric machine  11  and transmits the torques to a wheel  2  via the respective articulated shaft flanges  13  and the articulated shafts  13   a.    
     The converter unit  20  comprises an electronic power unit that comprises frequency converters (AC/DC transformers) for the two respective electric machines  11  of the portal axle  10  to regulate the currents for the respective electric machines  11 . The frequency converters convert the alternating current of the electric machine  11  into the direct current of the electric energy store  30 . The electric energy store  30  preferably is a high voltage battery, such as a lithium ion battery. 
     The portal axle  10  and the converter unit  20  have a low-temperature water cooling circuit. Cooling ducts for the cooling circuit are accommodated in the housing of the portal axle and have a feed line  15   a  and a discharge line  15   b.    
     The electric currents are conducted via special high-voltage cables between the electric axle  10 , the converter unit  20  and the electric store  30 . 
     The essential components of the drive arrangement, specifically the electric axle  10 , the converter unit  20  and the electric energy store  30 , are arranged in an optimum way in the electric vehicle. In this context, to make available a necessary quantity of energy for the electric vehicle, a relatively large and relatively heavy electric energy store  30  is necessary, for example 350 kg. In view of this weight, the electric energy store  30  is arranged near the center of gravity of the electric vehicle. It is therefore located in the central region of the electric vehicle, between the two axles. In view of the large volume, the electric energy store  30  is arranged in the rear part of the central region of the electric vehicle and specifically behind the driver&#39;s space or the driver&#39;s cab. In particular in sports vehicles, corresponding installation space is available in this region in sports cars. 
     The electric energy store  30  is arranged in front of the rear axle when viewed in the direction of travel. Thus, good protection is provided in the case of a rear-end crash of the electric vehicle. The greater part of the crash energy is absorbed by the chassis or the crossmember of the rear axle and the electric energy store  30  therefore is protected effectively against damage. The electric energy store  30  is not wider than the distance between the longitudinal carriers of the electric vehicle. Hence, the electric energy store  30  also is protected well in the event of a side impact of the electric vehicle. In this case, the longitudinal carriers absorb the corresponding forces. The front part of the electric vehicle, with the crossmember of the front axle, forms a reliable protection of the electric energy store  30  against damage in the event of a head-on crash. 
     A high-performance electric vehicle is obtained due to the above-described optimization of the weight distribution. The electric energy store  30  is by far the heaviest component of the drive arrangement, and is arranged near the center of gravity of the electric vehicle. Thus, agile handling and good freedom of the electric vehicle from twisting are obtained. Furthermore, the arrangement permits the use of an individual compact electric energy store  30 . This provides advantages in terms of cooling and cabling. 
     The converter unit  20  also is arranged in the rear region of the electric vehicle. Thus, the necessary cabling between the converter unit  20 , the portal axle  10  and the electric energy store  30  is minimized. The converter unit  20  is arranged as low as possible for further optimizing weight distribution. Such a space preferably is behind the electric axle  10  when viewed in the direction of travel. The converter unit  20  comprises both frequency converters. Thus, just a single high-voltage cable is necessary between the electric energy store  30 , arranged in front of the electric axle  10 , and the converter unit  20 . This high-voltage cable permits direct current to flow between the converter unit  20  and the electric energy store  30 . The converter unit  20  then converts the direct current into two alternating currents that are suitable for the respective electric machines  11 . The converter unit  20  is positioned so that its electrical terminals for the alternating current which is made available by a respective frequency converter are positioned near to the terminals  14  of the electric axle to reduce the required cables even more. 
     The arrangement of the components therefore permits an ideal combination between crash safety and performance. All components are positioned precisely in a way so that the center of gravity is as low as possible and the required high-voltage cabling is as short as possible. Minimizing the high-voltage cabling results in a further reduction in weight and improved efficiency of the drive arrangement. 
     The electric energy store  30  is accessed in the region of the underfloor of the electric vehicle. This permits improved integration of the components of the drive arrangement into the electric vehicle, for example underneath the vehicle body components, as well as a more pleasing design. 
     A further improvement through increased use of identical components is obtained if the second axle of the electric vehicle also is provided as an electric axle  11 . In particular, two identical electric portal axles, each with an assigned identical converter unit  20 , can then be installed as identical components. This results in an electric vehicle whose four wheels can be driven separately by a respective electric machine. This electric vehicle also has a high level of comfort by virtue of the fact that the conventional chassis of a vehicle can be used for the individual suspension of the wheels.