Drive device for a vehicle axle

Abstract

The invention relates to a drive device for a vehicle axle of a two-track vehicle. According to the invention, precisely one central multiple disk brake (57), which acts as the vehicle wheel brake and by means of which the vehicle can be braked, is assigned to the vehicle axle instead of conventional vehicle wheel brakes.

Description

[0001] Drive device for a vehicle axle

[0002] DESCRIPTION:

[0003] The invention relates to a drive device for a vehicle axle according to the preamble of claim 1.

[0004] To increase efficiency and range, braking of an electrified vehicle is carried out by an electric drive in generator mode (hereinafter referred to as recuperation mode), provided certain boundary conditions are met.

[0005] A generic drive device for a vehicle axle has an axle differential that allows for a 50 / 50 distribution. Its input side is connected to an electric motor, while its output sides drive on flanged shafts leading to the two vehicle wheels.

[0006] In the above-mentioned state of the art, different braking torques cannot be set at the vehicle wheels during recuperation mode. Therefore, braking torque redistribution is not available during recuperation mode. For safety reasons, the recuperation range is restricted. If this range is exceeded, recuperation is deactivated and the conventional vehicle braking system takes over. In this case, the state of the art implements vehicle dynamics control using the conventional vehicle braking system, in which a control unit specifically controls the vehicle wheel brakes with different braking torques in order to influence the driving behavior. Therefore, no recuperation takes place while braking torque redistribution is being implemented. Accordingly, the recuperation performance and thus the fuel consumption and electric range are limited due to driving safety aspects.

[0007] Sports cars, in particular, usually feature a torque vectoring system on the rear axle. This directs drive torque bypassing the differential directly to the vehicle wheels. This allows the drive torque to be distributed freely on each axle. In addition to the conventional drive with a differential, such a torque vectoring system also features two superposition gears, two frictionally controlled clutches, two actuators, a control unit, and usually its own hydraulic system.

[0008] DE 10 2009 013 293 A1 discloses a differential gear with torque vectoring functionality. DE 10 2015 112 924 A1 discloses a device for controlling a differential with slip limitation. DE 10 2018 133 223 A1 discloses a vehicle axle with electric drive motors.

[0009] The object of the invention is to provide a drive device for a vehicle axle of a two-track vehicle in which, compared to the prior art, the recuperation power during ferry operation is increased and / or the drive device is designed in a space-saving manner.

[0010] The object is solved by the features of claim 1. Preferred developments of the invention are disclosed in the subclaims.

[0011] The invention is based on a drive device for a vehicle axle of a two-track vehicle having an axle differential. Its input side is drivingly connected to an electric motor, while its output sides drive on flanged shafts leading to the two vehicle wheels. The vehicle axle has a superposition gear with a multi-plate clutch for each vehicle wheel. With the aid of the superposition gear, the electric motor can be connected directly to the vehicle wheel flanged shaft, bypassing the axle differential. The generic electric motor can be operated in a motor mode during vehicle acceleration and in a recuperation mode during vehicle deceleration.

[0012] According to the invention, not only a drive torque redistribution but also a braking torque redistribution between the two vehicle wheels is possible during recuperation mode. During braking torque redistribution, a braking torque path running between the vehicle wheel and the electric motor can be divided by controlling the respective multi-plate clutch. This can be done by activating a differential braking torque path, which carries a differential braking torque from the vehicle wheel via the axle differential to the electric motor, and by a superposition braking torque path, which carries a superposition braking torque from the vehicle wheel past the axle differential via the superposition gear to the electric motor. In this way, the vehicle wheels can be subjected to different braking torques in recuperation mode, so that the vehicle wheels can brake with different intensity.

[0013] If the vehicle axle is designed without wheel brakes, recuperation must function sufficiently at all times. This means that emergency braking or hill descent must be guaranteed safely, even with a fully charged battery. The braking function is subject to a high safety rating. The drive system must be developed according to these requirements.

[0014] Against this background, according to the characterizing part of claim 1, the vehicle axle is equipped with precisely one central multi-disk brake acting as a wheel brake, allowing vehicle braking to be carried out evenly on both sides of the vehicle. The central multi-disk brake can be used to perform vehicle braking as an alternative to or in addition to the multi-disk clutch. Therefore, if the electric motor is not or only partially capable of recuperation, the multi-disk brake can take over the braking task at least partially or completely. The multi-disk brake can, for example, cause vehicle braking depending on the current recuperation capacity.

[0015] For safety reasons, the central multi-disk brake can preferably be used primarily for braking in the case of uniform braking on both sides of the vehicle. In contrast, in the case of uneven braking on both sides of the vehicle, it is preferable for the multi-disk clutch to be used primarily for braking.

[0016] In one technical implementation, the multi-disk brake is constructed from an inner disc carrier, an outer disc carrier, and an intermediate disc pack. The electric motor can be connected directly or indirectly to the input side of the axle differential via its rotor shaft. According to a first design variant, the multi-disk brake can act directly on the rotor shaft. In this case, the inner disc carrier can be connected in a rotationally fixed manner to the rotor shaft, while the outer disc carrier is connected in a rotationally fixed manner to a transmission housing wall.

[0017] In a specific embodiment, the rotor shaft of the electric machine can be connected to an intermediate shaft via a countershaft stage. The intermediate shaft can be aligned axially parallel to the rotor shaft. With regard to an axially short transmission housing, the intermediate shaft can extend on one side from the countershaft stage back towards the front of the electric machine in the opposite direction to the rotor shaft. The electric machine can be installed transversely in the vehicle axle so that the rotor shaft of the electric machine is aligned axially parallel to the flange shafts. With regard to space-saving positioning, it is advantageous if an installation space can be provided between the front of the electric machine, the countershaft stage, the intermediate shaft and the rotor shaft, in which space-saving installation space the multi-disk brake can be positioned.Preferably, the countershaft stage can be realized as an axially short countershaft spur gear stage, which is constructed from a fixed gear arranged on the rotor shaft and an input gear meshing therewith, which is connected in a rotationally fixed manner to the differential housing of the axle differential.

[0018] In a second design variant, the multi-disk brake can act directly on the differential housing of the axle differential. In this case, the inner disc carrier can be non-rotatably connected to the differential housing, while the outer disc carrier is non-rotatably connected to a transmission housing wall.

[0019] The provision of multi-disk brakes eliminates the need for conventional vehicle wheel brakes, which consist of a brake disc positioned on the vehicle wheel drive shaft and a cooperating brake caliper. This prevents brake wear, which is otherwise emitted into the environment by conventional vehicle brakes.

[0020] Two embodiments of the invention are described below with reference to the attached figures.

[0021] They show:

[0022] Fig. 1 to 5 different representations of a vehicle axle with integrated central multi-disk brake.

[0023] Fig. 1 shows an electrified vehicle axle, in particular a rear axle, with a drive unit 1 consisting of an electric motor EM and a transmission 3. The electric motor EM is connected to a high-voltage battery 2. As can also be seen from Fig. 1, conventional vehicle wheel brakes have been omitted from the vehicle axle. Instead of such conventional vehicle wheel brakes, the vehicle axle has a central multi-disk brake 57, described later, and multi-disk clutches 33. The central multi-disk brake 57 effects vehicle braking alternatively or in addition to the multi-disk clutches 33. The vehicle axle has a drive unit 1 comprising an electric motor EM and a transmission 3, via which the electric motor EM drives the rear wheels HR, HL. The electric motor EM is connected via its rotor shaft 5 with the interposition of a countershaft stage 7 to the input side 8 of an axle differential 9.Its output sides are connected to the vehicle's rear wheels (HR, HL). In Figure 1, the electric motor EM is mounted transversely in the vehicle axle. Accordingly, the rotor shaft 5 and the flange shafts 27 are axially parallel to each other, leading from the output sides of the axle differential 3 to the vehicle's rear wheels (HL, HR). Likewise, the multi-disk clutches 33 and the multi-disk brake 57 installed in the vehicle axle are axially parallel to each other in the vehicle's transverse direction y.

[0024] The vehicle axle, viewed in the vehicle's transverse direction y, has a superposition gear 11 on each side of the vehicle, by means of which the electric motor EM can be directly connected to one of the flange shafts 27, bypassing the axle differential 9. With the aid of the two superposition gears 11, the electric motor EM can therefore drive directly onto the vehicle wheels HR, HL via the load paths L1, L2 indicated by dashed lines, bypassing the axle differential 9.

[0025] Figure 2 shows a specific transmission structure of the transmission 3 of the vehicle axle. Accordingly, the countershaft stage 7 consists of two spur gear stages 19, 20. The rotor shaft 5 of the electric motor EM is connected to an intermediate shaft 13 via a first spur gear stage 19. The first spur gear stage 19 is constructed from a fixed gear 15 arranged on the rotor shaft 5 and a meshing fixed gear 17 arranged on the intermediate shaft 13. The intermediate shaft 13 is connected to the input side 8 of the axle differential 9 via a second spur gear stage 20. The second spur gear stage 20 is constructed from a fixed gear 21 arranged on the intermediate shaft 13 and an input-side axle differential gear 23. The axle differential gear 23 is connected in a rotationally fixed manner to a rotating differential housing 25.According to Figure 2, the axle differential 9 drives in the vehicle transverse direction y in a 50 / 50 distribution on both sides to the two flange shafts 27 leading to the vehicle wheels HL, HR.

[0026] The two superposition gears 11 are mirror-inverted with respect to a vehicle center longitudinal plane passing through the axle differential 9. Thus, each of the two superposition gears 11 has a gear ratio stage 28 designed in the manner of a planetary gear (but without an external ring gear) having a sun gear 47 on the outside of the vehicle, viewed in the vehicle transverse direction y, which is non-rotatably mounted on the flange shaft 27, and a sun gear 29 on the inside of the vehicle, which is rotatably arranged as an idler gear on the flange shaft 27. The sun gear 29 on the inside of the vehicle meshes with planet gears 41 on the inside of the vehicle, each of which is non-rotatably mounted on a carrier shaft 43. Each carrier shaft 43 has a planet gear 45 on the outside of the vehicle, which meshes with the sun gear 47 on the outside of the vehicle. The vehicle-inner sun gear 29, the vehicle-outer sun gear 47 and the planet gears 41, 45 have the number of teeth zi to Z4 indicated in Figures 3 and 4.

[0027] The vehicle's internal sun gear 29 (i.e., the idler gear) sits together with an inner disk carrier 31 of a multi-disk clutch 33 on a hollow shaft through which the flange shaft 27 extends. The inner disk carrier 31 interacts via a disk pack with an outer disk carrier 39, which is non-rotatably connected to the differential housing 25. The disk pack located between the outer disk carrier 39 and the inner disk carrier 31 can be pressurized via an annular piston (not shown), which is adjustable by a horizontal stroke by a hydraulic cylinder in order to actuate the multi-disk clutch 33 to a predetermined degree of clutch engagement. The multi-disk clutch 33 is powershiftable and controllable with slip.

[0028] A core of the invention lies in the axially short geometry of the transmission 3 in the vehicle transverse direction y. Accordingly, the countershaft stage 7 is formed from the two axially short spur gear stages 19, 20. The intermediate shaft 31 extends in Figure 2 in the vehicle transverse direction y on one side from the countershaft spur gear stage 19 - opposite to the rotor shaft 5 - in the direction of the electric machine end face 51, specifically forming an installation space 53 which is axially delimited between the electric machine end face 51 and the countershaft spur gear stage 19 and radially delimited between the intermediate shaft 13 and an outer transmission housing wall 55. Positioned in the installation space 53 is a multi-disk brake 57 which is constructed from an inner disk carrier 59 and an outer disk carrier 61 with a disk pack arranged between them.The inner disk carrier 59 is arranged in a rotationally fixed manner on the rotor shaft 5, while the outer disk carrier 61 is connected in a rotationally fixed manner to the gearbox housing wall 55.

[0029] Figure 3 shows the vehicle axle in an operating situation in drive mode when driving straight ahead, in which there is a torque requirement in which the drive torque MR delivered to the right vehicle wheel HR is greater than the drive torque ML delivered to the left vehicle wheel HL.

[0030] To meet this torque requirement, in Figure 3, a total drive torque Man is introduced into the input gear 23 of the axle differential 9 from the electric motor EM via the countershaft stage 7. In the operating situation indicated in Figure 3, the right-hand multi-plate clutch 33 is closed to a degree that permits slippage. The left-hand multi-plate clutch 33, in contrast, is fully open. As a result, the total drive torque Man at the input gear 23 is divided into a differential torque MD leading to the axle differential 9 and a superimposed torque Mu, which is transmitted to the right-hand flange shaft 27 via the right-hand multi-plate clutch 33 and the right-hand transmission stage 28.In order to ensure a drive torque flow via the right-hand multi-plate clutch 33 to the right-hand vehicle wheel HR, it is relevant that there is a speed difference between the input gear 23 of the axle differential 9 and the inner disk carrier 31, at which the speed no of the input gear 23 is greater than the speed niR of the inner disk carrier 31. It is also relevant that the speed niR of the inner disk carrier 31 is greater than the speed AR of the right-hand vehicle wheel HR. This is achieved, for example, under the conditions shown in Figure 3, namely.

[0031] Z2 > Z3

[0032] Z4 > Z1 ni_ = np = no niR = riR ■ (zi ■ Z3) / (Z2 ■ Z4) niR < no.

[0033] The differential torque MD, which is transmitted from the input gear 23 to the differential housing 25 in Figure 3, is distributed 50 / 50 between the two flange shafts 27 in the axle differential 9. Accordingly, a partial torque MDL is transmitted via the left flange shaft 27 to the left vehicle wheel HL, while an equally large partial torque MDR is transmitted via the right flange shaft 27 to the right vehicle wheel HR. At the vehicle's outer sun gear 47, a torque addition occurs, in which the partial torque MDR and the superimposed torque Mu are added to form a drive torque MR, which is transmitted to the right vehicle wheel HR.

[0034] Figure 4 shows an operating situation when driving straight ahead in braking mode and with vehicle dynamics control, in which a braking torque request exists in which the braking torque MR applied to the right vehicle wheel HR is greater than the braking torque ML applied to the left vehicle wheel HL.

[0035] To meet this braking torque requirement, in Figure 4 the left multi-plate clutch 33 is closed to a degree that permits slippage. The right multi-plate clutch 33, in contrast, remains fully open. In this way the following is achieved: The braking torque MR that can be applied to the right vehicle wheel HR is fully introduced into the axle differential 9 (i.e. up to the axle bevel gear 67 of the right flange shaft 27). In addition, the partial load paths L1, L2 are formed: The differential housing 25, the left multi-plate clutch 33 and the left transmission stage 28 are integrated in the partial load path L1. A superposition torque Mu is guided via the partial load path L1 to the vehicle-outer sun gear 47 of the left transmission stage 28.There, a torque addition occurs, in which the braking torque ML delivered by the left vehicle wheel HL is added to the superimposed torque Mu to form a total torque Ms, which is fed into the axle differential 9 (i.e., to the axle bevel gear 65 of the left flange shaft 27). A braking torque Mßr is fed to the electric motor EM via the partial load path L2 and recuperated there.

[0036] The total torque Ms fed from the left flange shaft 27 into the axle differential 3 and the right braking torque MR fed from the right flange shaft 27 into the axle differential 3 are equal due to the 50 / 50 distribution in the axle differential 9. Accordingly, the braking torque MR applied on the right side of the vehicle is larger than the braking torque ML applied on the left side of the vehicle by the superimposed torque Mu generated at the left multi-plate clutch 33.

[0037] In order to ensure a torque flow in the load path L1 from the differential housing 25 via the left multi-plate clutch 33 and the left gear ratio 28 to the left flange shaft 27, it is relevant that there is a speed difference between the differential housing 25 and the inner disk carrier 31, at which the speed no of the differential housing 25 is greater than the speed niL of the inner disk carrier 31. It is also relevant that the speed niL of the inner disk carrier 31 is greater than the speed nL of the left flange shaft 27. This is achieved, for example, under the conditions shown in Figure 4, namely

[0038] Z2 > Z3

[0039] Z4 > Z1 nL = nR = no niL = nR ' (Z1 ' Z3) / (Z2 ■ Z4) niR < no.

[0040] Figure 5 shows a second embodiment of the invention in a view corresponding to Figure 2. In contrast to Figure 2, in Figure 5 the multi-disk brake 57 acts directly on the differential housing 25 of the axle differential 9. The inner disc carrier 59 of the multi-disk brake 57 is connected in a rotationally fixed manner to the differential housing 25 in Figure 5, while the outer disc carrier 61 is connected in a rotationally fixed manner to a transmission housing wall 55. Otherwise, the further transmission structure and the function achieved with the transmission 3 are identical to those described with reference to Figures 2, 3, and 4.

[0041] LIST OF REFERENCE SYMBOLS:

[0042] I Drive unit

[0043] 3 gearboxes

[0044] 5 Rotor shaft

[0045] 7 Countershaft stage

[0046] 8 Entrance page

[0047] 9 axle differential

[0048] II Superposition gear

[0049] 13 Intermediate shaft

[0050] 15, 17 fixed gears

[0051] 19, 20 Spur gear stage

[0052] 21 Fixed gear

[0053] 23 Input gear

[0054] 25 differential housing

[0055] 27 flange shafts

[0056] 31 inner disc carrier

[0057] 33 multi-plate clutch

[0058] 39 outer disc carrier

[0059] 41 vehicle-internal planetary gears

[0060] 29 vehicle-internal sun gear

[0061] 43 Support shaft

[0062] 45 outer planetary gears

[0063] 47 vehicle outer sun gear

[0064] 51 Electrical machine front side

[0065] 53 installation space

[0066] 55 Gearbox housing wall

[0067] 57 multi-disk brake

[0068] 59 inner disc carrier

[0069] 61 outer disc carrier

[0070] 65 left axle bevel gear

[0071] 67 left axle bevel gear ni_, np vehicle wheel speeds no speed of the differential housing DIR, riiL speed of the inner disk carrier 31 of the multi-disk clutch

[0072] Man total drive torque

[0073] MR on the right vehicle wheel detachable

[0074] Output torque / braking torque ML on the left vehicle wheel

[0075] Output torque / braking torque

[0076] MD differential torque

[0077] Mu superposition moment

[0078] MDL, MDR Partial moments Ms Total moment zi to Z4 Number of teeth

Claims

PATENT CLAIMS:

1. Drive device for a vehicle axle of a two-track vehicle, which has an axle differential (9), the input side (8) of which is drivingly connected to an electric machine (EM) and the output sides of which drive on flange shafts (27) leading to the two vehicle wheels (HL, HR), wherein each flange shaft (27) is assigned a superposition gear (11) by means of which the electric machine (EM) can be connected directly to the flange shaft (27) while bridging the axle differential (9), wherein the superposition gears (11) can be controlled by a control unit for torque redistribution between the vehicle wheels (HL, HR), in particular braking torque redistribution during recuperation operation of the electric machine (EM), characterized in that the vehicle axle is assigned exactly one central multi-disk brake (57) acting as a vehicle wheel brake, by means of which vehicle braking can be carried out.

2. Drive device according to claim 1, characterized in that the multi-disk brake (57) is constructed from an inner disk carrier (59), an outer disk carrier (61) and an intermediate disk pack.

3. Drive device according to claim 1 or 2, characterized in that the electric machine (EM) with its rotor shaft (5) is indirectly or directly drivingly connected to the input side (8) of the axle differential (9), and that in particular the multi-disk brake (57) acts directly on the rotor shaft (5).

4. Drive device according to claim 3, characterized in that the inner disk carrier (59) is connected in a rotationally fixed manner to the rotor shaft (5), while the outer disk carrier (61) is connected in a rotationally fixed manner to a gearbox housing wall (55).

5. Drive device according to one of the preceding claims, characterized in that the rotor shaft (5) is connected to an intermediate shaft (13) via a countershaft stage (7), in particular a countershaft spur gear stage, that the intermediate shaft (13) is aligned axially parallel to the rotor shaft (5), and / or that the intermediate shaft (13) extends on one side from the countershaft stage (7) in the direction of the electric machine end face (51), in particular while forming a multi-disk brake installation space (53) between the electric machine end face (51), the countershaft stage (7) and the intermediate shaft (13) and the rotor shaft (5).

6. Drive device according to one of the preceding claims, characterized in that the electric machine (EM) is installed transversely in the vehicle axle, so that the rotor shaft (5) is aligned axially parallel to the flange shafts (27).

7. Drive device according to one of the preceding claims, characterized in that the input side (8) of the axle differential (9) has an input gear (23) which is connected in a rotationally fixed manner to a differential housing (25), and in particular that the intermediate shaft (13) is peacefully connected to the differential housing (25) via a spur gear stage (20), which preferably consists of a fixed gear (21) formed on the intermediate shaft (13) and the input gear (23) of the differential housing (25) meshing therewith.

8. Drive device according to one of the preceding claims, characterized in that the multi-disk brake (57) acts directly on the differential housing (25) of the axle differential (9).

9. Drive device according to claim 8, characterized in that the inner disk carrier (59) is connected in a rotationally fixed manner to the differential housing (25) and the outer disk carrier (61) is connected in a rotationally fixed manner to a transmission housing wall (55).

10. Drive device according to one of the preceding claims, characterized in that the multi-disk brake (57) serves as a replacement for conventional vehicle wheel brakes on the vehicle axle.

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