Electric axle arrangement for a motor vehicle

Abstract

Electric axle arrangement for a motor vehicle with two electric machines (4, 6) which are operatively connected to a first and a second drive wheel (10, 12) via a drive train arrangement (8), wherein each electric machine (4, 6) is operatively connected to the respective drive wheel (10, 12) via an input shaft (16, 18), an output shaft (78, 80) and a transmission arrangement (36, 37) comprising at least one transmission stage, wherein the first and second input shafts (16, 18) are arranged coaxially along an input axis (14) and the first and second output shafts (78, 80) are arranged coaxially along an output axis (82), and wherein the transmission stages (38, 40, 42, 44) are designed such that, in the case of identical actual torques at the drive wheels (10, 12), axial force compensation of the transmission stages (38, 40, 42, 44) takes place, characterized in that at least in the area at the wave ends facing away from each other (94, 96; 110, 112;118, 120) of two shafts (16, 18; 50, 56; 78, 80) extending coaxially to an axis (14; 58; 82) a force sensor element (102, 104) is provided, wherein a control unit is provided which is connected to the force sensor elements (102, 104) in terms of control technology and determines a differential torque of the two drive wheels (10, 12).

Description

[0001] The invention relates to an electric axle arrangement for a motor vehicle with two electric machines which are operatively connected to a first and a second drive wheel via a drive train arrangement, wherein each electric machine is operatively connected to the respective drive wheel via an input shaft, output shaft and a transmission arrangement which has at least one transmission stage, wherein the first and the second input shaft are arranged coaxially along an input axis and the first and second output shaft are arranged coaxially along an output axis, and wherein the transmission stages are designed such that axial force compensation of the transmission stages takes place when the actual torques at the drive wheels are equal.

[0002] Such an electric axle arrangement is known, for example, from German patent DE 10 2009 006 523 B4. This makes it possible to control the drive wheels of a motor vehicle individually and independently of one another in a simple manner. A special design of the gear stages ensures that, with the same actual torque at the drive wheels, the axial forces acting on the respective output shafts compensate each other. However, the target torque of the respective electric motors is processed in a control unit. In practice, dealing with the torque accuracy of electric motors, especially the deviation between target and actual torque, presents a significant challenge. Furthermore, the deviation between target and actual torque can depend on a large number of other parameters, such as manufacturing tolerances, temperature dependence, and sensor tolerances for voltage, current, and rotor position detection.These tolerance zones can overlap in an extremely unfavorable way, so that, for example, the actual torques deviate so greatly from each other that the vehicle unintentionally deviates from its intended trajectory, such as straight-line driving. Furthermore, with such an axle arrangement, it is not possible to selectively improve the vehicle's color dynamics, for example, when cornering, by intentionally distributing uneven torque.

[0003] The object of the invention is therefore to avoid the aforementioned disadvantages in a simple and cost-effective manner.

[0004] This problem is solved according to the invention by providing a force sensor element at least in the region of the shaft ends facing away from each other of two shafts running coaxially to an axis, wherein a control unit is provided which is connected to the force sensors and determines a differential torque of the two drive wheels. This makes it possible in a particularly simple way to precisely adjust the actual torques present at the drive wheels to the desired driving dynamics or vehicle position. In addition, the actual torques acting on the respective drive wheels can also be calculated in this way.

[0005] As secondary prior art in this context, German patent application DE 10 2006 027 090 A1 should be mentioned, which discloses the provision of force sensor elements at the shaft ends of an output shaft in a motor vehicle with a drive engine and a differential gear in order to determine the respective applied torque based on the measured axial forces, thereby influencing the torque distribution. German patent application DE 10 2015 221 745 A1 also discloses the measurement of the axial force of a shaft in a drive unit in order to calculate a torque.

[0006] In a particularly advantageous manner, the respective transmission arrangement features an intermediate shaft, wherein the first and second intermediate shafts are arranged coaxially along an intermediate axis. It is especially advantageous if the force sensors are provided at least in the area at the ends of the intermediate shafts facing away from each other. In this area, the force sensors are particularly easy and cost-effective to install, whereas their placement in the area of ​​the input or output shafts is more difficult due to space constraints.

[0007] Advantageously, the force sensor elements can be arranged on a stationary housing part, with an axial bearing element being arranged at the respective shaft end, which interacts with the respective force sensor element.

[0008] The respective gear stage is advantageously designed using helical spur gear pairs. This allows axial force compensation to be achieved in a particularly simple and cost-effective manner.

[0009] To ensure optimal force measurement and avoid any associated noise, it is advantageous for the force sensor to be axially pre-tensioned by a spring. To implement a simple parking lock with this electrical axle arrangement, a parking lock wheel is advantageously arranged on each input shaft.

[0010] The invention is explained in more detail with reference to a drawing, which shows: Fig. 1 a schematic representation of a first embodiment of an electrical axle arrangement according to the invention in train operation, Fig. 2 the electrical axle arrangement from Fig. 1 in push mode, Fig. 3 a first alternative embodiment of the inventive electrical axle arrangement in train operation and Fig. 4 a second alternative embodiment of the electric axle drive according to the invention in train operation.

[0011] Fig. Figure 1 shows a schematic view of a first embodiment of an electric axle arrangement 2 according to the invention for a motor vehicle (not shown). Two electric motors 4 and 6 are provided, which are operatively connected via a drive train arrangement 8 to a first drive wheel 10 and a second drive wheel 12 to drive them. The drive train arrangement 8 essentially consists of two input shafts 16 and 18, which are nested within each other and extend coaxially along an input axis 14. Reference numerals 20, 22, 24, and 26 denote known axial and radial bearings, respectively, which support the first and second input shafts 16 and 18 relative to each other. Reference numerals 28 and 30 denote rolling bearings that support the input shafts 16 and 18 relative to a housing part (not shown) in a known manner.Furthermore, the input shafts 16, 18 have parking lock wheels 32, 34 which ensure a parking lock of the electric machines 4, 6 in a known manner.

[0012] As a further part of the drive train arrangement 8, a gear arrangement 36, 37 is assigned to each electric machine 4, 6, wherein each gear arrangement 36, 37 is composed of two gear stages 38, 40 and 42, 44. In the present embodiment, all gear stages 38, 40, 42, 44 are designed as helical spur gear pairs. The input shaft 16 is coupled to a first intermediate shaft 50 via gear stage 38, formed by gears 46, 48, and the second input shaft 18 is coupled to a second intermediate shaft 56 via gear stage 42, consisting of gears 52, 54. These intermediate shafts 50, 56 are also arranged coaxially along an intermediate axis 58 and mesh with each other in a known manner, being supported relative to each other by radial and axial bearings 60, 62, 64.For the sake of completeness, it should be noted that the intermediate shafts 50, 56 are also supported by means of rolling bearings 66, 68 relative to a housing part which is not shown further.

[0013] The gear stages 40, 44, consisting of gears 70, 72 and 74, 76, then couple the first intermediate shaft 50 to a first output shaft 78 and the second intermediate shaft 56 to a second output shaft 80, to which the drive gears 10, 12 are articulated in a known manner. The output shafts 78, 80 are also arranged coaxially along an output axis 82 and are mutually supported by radial and axial bearings 84, 86, 88. Here, too, rolling bearings 90, 92 are used to support the output shafts 78, 80 against housing parts not shown.

[0014] The powertrain assembly 8 is in the Fig. Figure 1 shows the train in operation, as indicated by the arrows. Here, the torque acting on drive wheel 10 is significantly greater than the torque acting on drive wheel 12. To determine the exact differential torque and thus optimally adjust the torques acting on drive wheels 10 and 12, axial bearing elements 98 and 100 are provided at the shaft ends 94 and 96 of the intermediate shafts 50 and 56 in this embodiment. Under load, these bearing elements act on force sensors 102 and 104. The force sensors 102 and 104 are, in turn, arranged on stationary housing parts 106 and 108. In this embodiment, an axial force acts on the force sensor 104 due to the different torques in the gear stages 38 and 40 and 42 and 44.The force sensor elements 102, 104 are in turn connected to a control unit (not shown) which, in the simplest case, calculates the differential torque and can derive the actual torques at the drive wheels 10, 12 from it.

[0015] The following only refers to the opposite. Fig. 1. Differences occurring in the electrical axle arrangement 2.

[0016] Fig. Figure 2 now shows a schematic view of the axle drive 2. Fig. 1 in overrun mode. The electric motors 4, 6 of the vehicle are towed and can be operated in generator mode (recuperation). The arrows appearing in the drivetrain arrangement 8 are opposite Fig. 1. Conversely, the forces in the intermediate shafts 50, 56 are equal in magnitude, but they do not cancel each other out because they act in opposite directions. However, forces can also be measured here by the respective force sensor elements 102, 104, and actual torques per drive wheel 10, 12 can be derived from them. In the present embodiment, however, the torques acting on the drive wheels 10, 12 are equal.

[0017] Fig. Figure 3 shows the electric axle drive 2, wherein the axle bearing elements 98, 100 are arranged at opposite shaft ends 110, 112 of the output shafts 78, 80. Here, too, the force sensor elements 102, 104 are arranged on a stationary housing part 114, 116 in the area of ​​the drive wheels 10, 12. The drive train assembly 8 is shown here in traction operation, wherein the axial forces in the output shafts 78, 80 act in the direction of the housing parts 114 and 116, respectively, and can be detected by the force sensor elements 102 and 104, respectively. The torques acting on the drive wheels 10, 12 are equal in this embodiment.

[0018] Fig.Figure 4 shows a further embodiment of the electric axle drive 2 according to the invention, in which the axial bearing elements 98 are arranged at the shaft ends 118, 120 of the input shafts 16, 18. As can be seen from this example, the input shafts 16, 18, as well as the intermediate shafts 50, 56, and the output shafts 78, 80, can be designed in multiple parts. Here, the force sensor elements 102, 104 are arranged on stationary housing parts 126, 128 via spring elements 122, 124.

Claims

[1] Electric axle arrangement for a motor vehicle with two electric machines (4, 6) which are operatively connected to a first and a second drive wheel (10, 12) via a drive train arrangement (8), wherein each electric machine (4, 6) is operatively connected to the respective drive wheel (10, 12) via an input shaft (16, 18), an output shaft (78, 80) and a transmission arrangement (36, 37) comprising at least one transmission stage, wherein the first and second input shafts (16, 18) are arranged coaxially along an input axis (14) and the first and second output shafts (78, 80) are arranged coaxially along an output axis (82), and wherein the transmission stages (38, 40, 42, 44) are designed such that, in the case of identical actual torques at the drive wheels (10, 12), axial force compensation of the transmission stages (38, 40, 42, 44) takes place, characterized by, that at least in the area at the opposite ends (94, 96; 110, 112; 118, 120) of two shafts (16, 18; 50, 56; 78, 80) running coaxially to an axis (14; 58; 82) a force sensor element (102, 104) is provided, wherein a control unit is provided which is connected to the force sensor elements (102, 104) in terms of control technology and determines a differential torque of the two drive wheels (10, 12). [2] Electrical axle arrangement according to claim 1, characterized by , that the respective gear arrangement (36, 37) has an intermediate shaft (50, 56), wherein the first and second intermediate shafts (50, 56) are arranged coaxially along an intermediate axis (58). [3] Electrical axle arrangement according to claim 2, characterized by , that the force sensor elements (102, 104) are provided at least in the area at the intermediate shaft ends (94, 96) facing away from each other. [4] Electrical axle arrangement according to one of claims 1-3, characterized by, that the force sensor elements (102, 104) are arranged on a stationary housing part (106, 108; 114, 116; 126, 128), wherein an axial bearing element (98, 100) is arranged at the respective shaft end (94, 96; 110, 112; 118, 120) which cooperates with the respective force sensor element (102, 104). [5] Electrical axle arrangement according to one of the preceding claims, characterized by , that each gear stage (38, 40, 42, 44) is formed by helical spur gear pairs. [6] Electrical axle arrangement according to one of the preceding claims, characterized by , that the force sensor element (102, 104) is pre-tensioned in the axial direction by a spring element (122, 124). [7] Electrical axle arrangement according to one of the preceding claims, characterized by , that a parking lock wheel (32, 34) is arranged on each of the input shafts (16, 18).

Images