Powertrain for an electric vehicle

Abstract

The invention relates to a drive train (1) for an electric vehicle comprising an electric motor (2) with a rotor shaft (3) arranged on a drive axle (d(an)) and an output axle (d(ab)) arranged parallel to it, with a differential (5) and two cardan shafts connected to the differential (5), each with drive wheels and externally actuated service brakes (10, 11), as well as a transmission (4) arranged between the drive axle (d(an)) and the output axle (d(ab)). To better protect the service brakes (10, 11) from external influences, the service brakes (10, 11) are arranged directly on the differential (5).

Description

The invention relates to a drive train for an electric vehicle with an electric machine having a rotor shaft arranged on a drive shaft and an output shaft arranged parallel to it with a differential, two cardan shafts connected to the differential, drive wheels with externally switchable service brakes and a gearbox arranged between the rotor shaft and the differential. Powertrains for multi-track electric vehicles include at least one electric motor. In the case of an electric motor driving multiple wheels on a drive axle, a differential is required to compensate for different wheel speeds when cornering and similar situations. For space reasons, this differential is arranged parallel to and spaced apart from the drive axle, with the electric motor's rotor shaft on an output axle. Preferably, the differential incorporates drive shafts to compensate for vibrations between the vehicle body containing the electric motor and the drive wheels. These drive shafts drive the drive wheels. Service brakes, which can be actuated automatically from the outside and / or manually by the driver, are located on the drive wheels. The service brakes are exposed to the external environmental conditions at the drive wheels. For example, the following are considered state of the art: AT 520 430 B1, DE 10 2022 103 839 B3, DE 38 13 528 A1 and CN 1 11 878 528 A. The object of the invention is the further development of a drive train for an electric vehicle. In particular, the object of the invention is to protect the service brakes against environmental influences while adhering to specified installation spaces. The problem is solved by the subject matter of claim 1. The dependent claims describe advantageous embodiments of the subject matter of claim 1. The proposed powertrain is designed for a multi-track electric vehicle with at least one electric motor. One of the at least one electric motor drives the drive wheels of an axle and, if necessary, recuperates kinetic energy in generator mode. To compensate for speed differences between the drive wheels, a drive axle containing a differential is provided parallel to the drive axle of the electric motor with its rotor shaft. Cardan shafts are arranged on both sides of the differential, for example, bolted to flanges machined onto the differential's bevel gear shafts. At their other end, these cardan shafts are rotationally connected to a drive wheel, meaning they drive it or, in recuperation mode, drive it. It should be understood that in simple cases, the term "cardan shafts" may refer to rigid drive shafts. Torque transmission between the rotor shaft and the differential is achieved by means of a gearbox that compensates for the radial misalignment. The gearbox can be single-stage, for example using spur gears, or multi-stage, for example as a speed-changing gearbox with several selectable stages or as a continuously variable transmission, friction drive, or the like, and preferably automated and / or manually operated at the driver's request. Several described electric machines can be provided, for example, in an all-wheel drive vehicle, each drive axle is equipped with an electric machine with a rotor shaft arranged on a drive axle and an output shaft arranged parallel to it with a differential and two cardan shafts connected to the differential. The electric vehicle has a service brake on at least one drive axle, on each drive side with one or more drive wheels. This service brake can be actuated externally. This means that the service brake can be actuated by the driver, for example, via a brake pedal, and / or automatically in hazardous or detected braking situations. To protect the service brakes from environmental influences such as dirt, water, salt, abrasion, and the like, at least one service brake assigned to each drive wheel is located directly on the differential, for example, on the bevel gear shaft. The position, set back from the drive wheels, protects the service brakes from dirt, water, and other contaminants simply by virtue of the distance, thus improving their function and service life and reducing wear. Additionally, the service brakes can be encapsulated.Additionally, the installation space and degrees of freedom at the drive wheels increase, allowing for optimization of track width, rim design, and tire width on the drive axle. To improve the utilization of the installation space at the electric motor, a first service brake can be arranged on the same side of the differential as the electric motor. This places the service brake in the same axial position as the electric motor on the output shaft. The outer diameter of this first service brake is selected such that, with respect to the output shaft, it lies radially within the installation space defined by the electric motor, allowing it to be accommodated without requiring additional installation space and without altering the geometry of the electric motor. This means that the first service brake at least partially overlaps the electric motor in the axial direction but does not overlap it radially. The second service brake can be arranged on the other side of the differential, axially spaced from the electric motor.This service brake can radially overlap the installation space of the electric motor, as there is generally no corresponding radial space restriction on the motor's radial installation space. Essentially, the friction surfaces of both service brakes are the same size to ensure consistent braking performance. For dry service brakes with different diameters, the annular friction ring surfaces can be adapted to each other. According to the invention, it has been found that the service brakes can be designed as multi-disc brakes with alternatingly layered, rotationally fixed first discs and second discs rotating at the wheel speed of the drive wheels. These second discs can be axially preloaded against each other by means of an axially acting and displaceable actuating element. The actuating element can be designed as a mechanically, electrically, and / or hydraulically displaceable actuating lever or pot, which axially preloads a disc, such as an end disc, to achieve a braking effect of the service brake by means of frictional engagement of the discs. Preferably, the service brakes are encapsulated and wet-operated.For example, the service brakes share a common fluid volume, such as oil volume, with the differential, the gearbox and, if applicable, the electric motor, whereby corresponding housing parts are connected to each other and sealed at corresponding interfaces between rotationally fixed and rotating components, and through appropriate measures, such as bores, scoop tubes and / or the like, the return of the fluid to a pressureless reservoir, for example in the gearbox, is ensured. The clutch plates are, for example, non-rotatably mounted in clutch plate carriers, with an outer clutch plate carrier being part of or rigidly connected to the housing of the corresponding service brakes. The inner clutch plate carrier is non-rotatably connected to the corresponding part of the differential. Preferably, for example to reduce rotating mass, the first clutch plates can be designed as counter-plates and non-rotatably mounted in the outer clutch plate carrier. The second clutch plates, so-called friction plates, accordingly have friction linings on both sides and are non-rotatably mounted in the inner clutch plate carrier. It is understood that the arrangement of the counter-plates and friction plates can also be reversed. Furthermore, all clutch plates except for one end plate can have friction linings on one side.The friction surfaces of the friction plates form a friction engagement with the smooth areas of the opposing plates - counter plates or one-sided smooth friction surface of a friction plate with only one-sided friction lining - under axial preload and thus provide the required braking torque in total, depending on the actuating force of the actuating means. In the case of service brakes with unequal diameters, the uniformity of the friction surface, and thus the same braking torque at the drive wheels for a given braking force, is achieved according to the invention by means of a different number of friction plates. For example, the first service brake has at least one more friction plate with a corresponding counter-friction surface (either a counter plate or an end plate) than the second service brake. It is advantageous to keep the number of plates as low as possible, corresponding to the requirements for maximum braking torque, in order to ensure short service brake actuation times. Therefore, it is advantageous to select the largest possible diameter within the available installation space and to compensate for the diameter of the first service brake with the smallest possible number of friction plates.In an advantageous embodiment, for example, the first service brake can have six and the second service brake five friction plates and a corresponding number of plates provided with counter-friction surfaces - counter plate and each end plate provided with only one counter-friction surface. Each of the service brakes is actuated, for example, by means of an axial preload on the friction plates by means of a rotationally fixed actuating piston, lever, or the like, which can be axially displaced hydraulically, electrically, and / or mechanically against the action of a return spring, against a rotationally fixed axial stop. Preferably, the actuating means, for example, a hydraulically actuated ring piston or individual pistons distributed around the circumference, an electrical and / or mechanical actuating mechanism, the actuating lever or piston, the end plate axially actuated by it, the end plate connected to the axial stop, and the axial stop itself are arranged in a housing-fixed and rotationally fixed manner, so that only the friction plates with the corresponding components of the differential rotate. The invention is explained in more detail with reference to the embodiment shown in the single figure. This figure shows a cross-sectional view of an electric drive train with service brakes. The drive train 1 includes the electric machine 2 with the rotor shaft 3 arranged on the drive shaft d(an). In motor mode, the rotor shaft 3 drives the drive wheels (not shown). In generator mode, it captures kinetic energy from the drive wheels, converts it into electrical energy, and supplies it to consumers and / or a vehicle battery. The rotor shaft 3 is connected to the gearbox 4, which compensates for the distance between the drive shaft d(an) and the output shaft d(ab) and optionally provides a fixed or selectable gear ratio. The differential 5 is arranged on the output shaft d(ab). It comprises the two bevel gear shafts 6 and 7 with flanges 8 and 9 for attaching cardan shafts (not shown), each of which carries one or more fixed or steerable drive wheels.The bevel gear shafts 6, 7 each accommodate one of the service brakes 10, 11, so that these are encapsulated and located away from the drive wheels, protecting them from environmental influences such as dirt, water, and the like. In the illustrated embodiment, a common, two-part housing 12 with the two housing parts 13, 14 is provided, which accommodates the electric motor 2, the gearbox 4, the differential 5, and the two service brakes 10, 11 in a fluid and oil chamber and seals the bevel gear shafts 6, 7 to the outside by means of the dynamic seals 15, 16. The service brakes 10, 11 are designed as wet-operated, cooled multi-disc brakes 17, 18 and contain the alternately layered discs, which are designed as counter discs 19, 20 and as friction discs 21, 22 with friction linings arranged on both sides. The counter-lamellae 19, 20 are non-rotatably suspended in the respective housing-fixed outer lamella carriers 23, 24, and the friction lamellae 21, 22 are non-rotatably suspended in the inner lamella carriers 25, 26 which are connected to the bevel gear shafts 6, 7. The lamellae, stacked alternately in this manner, are each pressed against the axial stops 29, 30 by means of the end lamellae 27, 28 and are axially actuated at the opposite end lamellae 31, 32 by the actuating means 33, 34. In the case of the multi-disc brake 17, the actuating element 33 contains the hydraulic piston 37, which directly actuates the end plate 31 against the action of the spring(s) 39. In the case of the multi-disc brake 18, the actuating pot 36 is loaded by the hydraulic piston 38, which is axially displaced against the action of the spring(s) 40 when braking is required, thus preloading the end plates 32 against the axial stop 30. The multi-disc brakes 17, 18 are released by pressure reduction at the pistons 37, 38, thereby relaxing the springs 39, 40. To optimize the installation space of the service brakes 10, 11, the service brake 10 is radially located within the installation space defined by the electric machine 2 and therefore has a smaller diameter D1 compared to the diameter D2 of the service brake 11. By designing the service brakes 10, 11 as multi-disc brakes 17, 18, any difference in friction and braking torques due to the differences in diameters D1, D2 can be compensated for by matching the friction surfaces of the multi-disc brakes 17, 18 with respect to an adapted number of friction discs 21, 22 and the corresponding number of counter discs 19, 20, including end discs 27, 28, 31, 32. In the illustrated embodiment, the friction surfaces of the friction plates 21, 22 are essentially identical by means of seven friction plates 21 of the lamellar brake 17 and six friction plates 22 of the lamellar brake 18. Reference symbol list 1 Drive train 2 Electric machine 3 Rotor shaft 4 Gearbox 5 Differential 6 Bevel gear shaft 7 Bevel gear shaft 8 Flange 9 Flange 10 Service brake 11 Service brake 12 Housing 13 Housing part 14 Housing part 15 Seal 16 Seal 17 Multi-disc brake 18 Multi-disc brake 19 Counter disc 20 Counter disc 21 Friction disc 22 Friction disc 23 Outer disc carrier 24 Outer disc carrier 25 Inner disc carrier 26 Inner disc carrier 27 End disc 28 End disc 29 Axial stop 30 Axial stop 31 End disc 32 End disc 33 Actuating means 34 Actuating means 36 Actuating pot 37 Piston 38 Piston 39 Spring 40 Spring D1 Diameter D2 Diameter d(in) Drive shaft d(ab) Output shaft

Claims

Drive train (1) for an electric vehicle with an electric machine (2) with a rotor shaft (3) arranged on a drive shaft (d(an)) and an output shaft (d(ab)) arranged parallel to it, with a differential (5) and two cardan shafts connected to the differential (5) with drive wheels and externally switchable service brakes (10, 11), as well as a transmission (4) arranged between the rotor shaft (3) and the differential (5), wherein the service brakes (10, 11) are arranged directly on the differential (5), wherein the service brakes (10, 11) are designed as multi-disc brakes (17, 18) with alternately layered, rotationally fixed first discs and second discs rotating at the wheel speeds of the drive wheels, and the discs can be preloaded against each other by means of an axially displaceable actuating means (33, 34), wherein, in the case of unequal diameters (D1, D2) of the Service brakes (10,11) the uniformity of the friction surface is achieved by means of a different number of friction plates (21, 22). Drive train (1) according to claim 1 , characterized in that a first service brake (10) is located on the same side of the differential as the electric machine and is arranged radially within the installation space defined by the electric machine (2) with respect to the output axis (d(ab)). Drive train (1) according to claim 1 or 2, characterized in that a second service brake (11) is arranged axially spaced from the electric machine (2) and the installation spaces overlap radially with respect to the output axis (d(ab)). Drive train (1) according to one of claims 1 to 3, characterized in that the friction surfaces of the two service brakes (10, 11) are of the same size. Drive train (1) according to one of the preceding claims, characterized in that the first lamellae are designed as counter lamellae (19, 20) and the second lamellae are designed as friction lamellae (21, 22) which can be brought into frictional engagement with the counter lamellae (19, 20) under axial preload and have friction linings arranged on both sides. Drive train (1) according to one of the preceding claims, characterized in that the first multi-plate brake (17) has at least one more friction plate (21) than the second multi-plate brake (18). Drive train (1) according to claim 6, characterized in that the first multi-plate brake (17) has six friction plates and the second multi-plate brake (18) has five friction plates. Drive train (1) according to one of claims 1 to 7, characterized in that the lamellae can each be preloaded by means of a rotationally fixed, hydraulically arranged axial stop (29, 30) against the action of a spring (39, 40) against a rotationally fixed axial stop.

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