DRIVE DEVICE FOR A VEHICLE AXLE

Description

[0001] The invention relates to a drive device for a vehicle axle of a two-track vehicle according to the preamble of claim 1.

[0002] 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.

[0003] A drive device of this type for a vehicle axle has an axle differential by means of which a 50 / 50 distribution can be achieved. Its input side is driven by an electric motor, while its output sides drive to flange shafts leading to the two vehicle wheels.

[0004] In the prior art described above, different braking torques cannot be set at the vehicle wheels during recuperation. Therefore, brake torque redistribution is not available during recuperation. For safety reasons, the recuperation range is limited. If this range is exceeded, recuperation is deactivated and the conventional vehicle braking system takes over. Accordingly, in the prior art, vehicle dynamics control is implemented using a conventional vehicle braking system, in which a control unit selectively applies different braking torques to the vehicle's wheel brakes to influence driving behavior.

[0005] No recuperation takes place during the brake torque redistribution process. Consequently, the recuperation power, and therefore the consumption or electric range, is limited for driving safety reasons.

[0006] Especially in sports cars, a torque vectoring system is usually found on the rear axle. This system directs drive torque past the differential directly to the wheels. This allows for free distribution of drive torque on each axle. In addition to the conventional drive with differential, such a torque vectoring system also includes two superimposed gears, two positive-locking clutches, two actuators, a control unit, and typically its own hydraulic system.

[0007] A differential gear with torque vectoring functionality is known from DE 10 2009 013 293 A1. A device for controlling a differential with slip limitation is known from DE 10 2015 112 924 A1. A vehicle axle with electric drive motors is known from DE 10 2018 133 223 A1. A differential gear with torque vectoring function and internal multi-plate brakes is known from US 2010240485A1.

[0008] 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 performance during driving operation is increased.

[0009] The problem is solved by the features of claim 1. Preferred embodiments of the invention are disclosed in the dependent claims.

[0010] The invention relates to a drive device for a vehicle axle of a two-track vehicle, which has an axle differential. The input side of the differential is driven by an electric motor, while its output sides drive to flange shafts leading to the two vehicle wheels. The vehicle axle has a superimposed transmission with a multi-plate clutch for each vehicle wheel. The electric motor can be directly connected to the wheel flange shaft by means of the superimposed transmission, bypassing the axle differential. The electric motor according to this invention can be operated in motor mode during vehicle acceleration and in recuperation mode during vehicle deceleration.

[0011] The invention enables a redistribution of braking torque between the two vehicle wheels during recuperation mode. During this redistribution, the braking torque path running between the vehicle wheel and the electric motor can be divided by controlling the respective multi-plate clutch. This division is achieved into a differential braking torque path, which transmits a differential braking torque from the vehicle wheel via the axle differential to the electric motor, and a superimposed braking torque path, which transmits a superimposed braking torque from the vehicle wheel past the axle differential via the superimposed transmission to the electric motor. In this way, the vehicle wheels can be subjected to different braking torques during recuperation mode, allowing them to brake with varying degrees of intensity.

[0012] In a vehicle axle design without wheel brakes, it is essential that recuperation functions reliably and consistently. This means that even with a fully charged battery, emergency braking or downhill driving must be reliably ensured. The braking function is subject to a high safety rating. The drive system must be developed according to these requirements.

[0013] Against this background, according to the characterizing part of claim 1, a multi-plate brake acting as a vehicle wheel brake is assigned to each side of the multi-plate clutch on each side of the vehicle. Vehicle braking can be carried out by means of the multi-plate brake as an alternative or in addition to the multi-plate clutch. Therefore, if the electric motor is unable to recuperate energy, or is only partially able to do so, the multi-plate brake can take over the braking task at least partially or completely.

[0014] The braking effect of the multi-plate clutch depends on the current operating state of the electric motor. For example, the multi-plate brake can initiate braking depending on the current recuperation capacity.

[0015] In a control-engineered and component-reduced design variant, both the multi-plate clutch and the multi-plate brake on each side of the vehicle can be actuated via a common hydraulic cylinder. This common hydraulic cylinder is connected to the control unit via a single hydraulic line. When the control unit applies brake pressure to the hydraulic cylinder, hydraulic pressure builds up within the cylinder, which then pushes a ring piston against both a multi-plate clutch pack and a multi-plate brake pack.

[0016] Starting from the unactuated state, the ring piston presses the multi-plate clutch pack against an axial stop via a clutch release clearance until the kiss point is reached. This clutch release clearance is preferably independent of the current braking situation, meaning it remains constant regardless of whether braking is applied evenly or unevenly on each side of the vehicle.

[0017] Similarly, starting from the unactuated state, the ring piston presses the multi-plate clutch of the multi-plate brake against an axial stop via a disc brake release clearance until the kiss point is reached. Unlike a multi-plate clutch, the disc brake release clearance can be varied depending on the current braking situation. This variation of the disc brake release clearance is achieved in a structurally simple manner, preferably by axially adjusting the disc brake stop.

[0018] For safety reasons, when braking is even on both sides of the vehicle, it is preferable for the multi-plate brake to primarily engage the brakes. Conversely, when braking is uneven on both sides, it is preferable for the multi-plate clutch to primarily engage the brakes to enable energy recuperation. Against this background, the multi-plate brake clearance can be varied as follows: when braking is even on both sides, the multi-plate brake clearance can be smaller than the multi-plate clutch clearance. This ensures that during the closing stroke of the ring piston, the multi-plate brake engages first, and only later does the multi-plate clutch engage.

[0019] In contrast, with uneven braking on both sides of the vehicle, the multi-plate brake clearance is greater than the multi-plate clutch clearance. As a result, during the closing stroke of the ring piston, the multi-plate clutch on the side of the vehicle controlled by the control unit with higher brake pressure engages first. Only later does the multi-plate brake engage.

[0020] The multi-disc brake clearance or the brake characteristic curve of the multi-disc brake can preferably be varied as follows: The axially adjustable stop of the multi-disc brake can be designed as a pushrod. The pushrod acts as an axially adjustable axial stop on both sides of the vehicle. For this purpose, the pushrod is axially adjustable between movement stops by a pushrod axial travel.

[0021] When using the pushrod, the following situation arises during uneven braking: On the side of the vehicle subjected to higher brake pressure, the closing stroke of the ring piston shifts the multi-plate clutch and, consequently, the pushrod by the pushrod's axial travel towards the opposite side of the vehicle. Therefore, on the side of the vehicle subjected to higher brake pressure, the available multi-plate brake release clearance increases by the pushrod's axial travel compared to braking with even pressure. Preferably, the multi-plate brake release clearance is dimensioned to be a bit larger than the multi-plate clutch release clearance. This ensures that, during braking, the multi-plate clutch engages first, and only then does the multi-plate brake engage.

[0022] On the side of the vehicle subjected to higher brake pressure, the following situation arises during uneven braking: The multi-plate brake release clearance is reduced due to the pushrod adjustment. Preferably, the reduced multi-plate brake release clearance is dimensioned to be smaller than the multi-plate clutch release clearance, such that actuation of the multi-plate clutch on the side subjected to higher brake pressure is prevented.

[0023] The vehicle axle can also have a disconnect clutch on each side of the vehicle. When the disconnect clutch is open, the wheel on one side of the vehicle can rotate freely. Its rotational speed correlates with the current vehicle speed, which forms a reference value on the basis of which a control unit performs a vehicle dynamics control function, such as an ABS function. With the invention, the recuperation mode can be maintained during the execution of the vehicle dynamics control function, so that recuperation energy can be recovered even during the execution of the vehicle dynamics control function.

[0024] In one technical implementation, during the execution of the vehicle dynamics control function (i.e., during the detection of the rotational speed of the freely rotating vehicle wheel), the vehicle wheel on the opposite side of the vehicle can transmit a braking torque to the electric motor via the superimposed transmission. This allows the vehicle dynamics control function to be performed simultaneously with the recuperation mode.

[0025] The disconnect clutch can divide the flange shaft on each side of the vehicle into a differential-side subshaft and a wheel-side subshaft. The superimposed transmission is preferably completely decoupled from the differential-side subshaft, but can be coupled to the wheel-side subshaft via the multi-plate clutch. With the disconnect clutch open, the axle differential is thus de-loaded, interrupting the differential braking torque path and enabling braking torque transmission from the vehicle wheel to the electric motor only via the superimposed transmission.

[0026] A simple design is achieved when the disconnect coupling is implemented as a jaw coupling with a sliding sleeve. This sleeve can be axially adjustable between an open and a closed position. In the closed position, the internal teeth of the sliding sleeve can mesh with the external teeth of both the differential-side and wheel-side partial shafts. Conversely, in the open position, the teeth are disengaged, preventing torque transmission. The sliding sleeve can be equipped with a spring that allows it to be preloaded towards the closed position.

[0027] With a view to simple control engineering and a reduced number of components, the multi-plate clutch, the multi-plate brake, and the disconnect clutch on each side of the vehicle can be controlled by the control unit via a common hydraulic line. Preferably, the hydraulic cylinder that actuates the multi-plate clutch and the multi-plate brake can also actuate the disconnect clutch.

[0028] In normal operation, meaning without ABS intervention, both dog clutches of the vehicle axle are closed. When braking torque is transmitted via the respective closed dog clutch, the facing tooth flanks of the sliding sleeve's internal teeth and the external teeth of the differential-side partial shaft are in contact. To ensure the closed position, it is preferred that the tooth flanks have angled supports. With the aid of these supports, an axial force component builds up under braking torque, which pushes the sliding sleeve towards the closed position. The magnitude of the axial force component acting on the sliding sleeve correlates with the magnitude of the braking torque flowing through the disengaging clutch. This means that as the braking torque decreases, the axial force component also decreases, while as the braking torque increases, the axial force component also increases.

[0029] The following describes an operating situation that occurs during recuperation mode, in which the multi-plate clutch is open on one side of the vehicle (not actuated) and engaged on the other, actuated side. In this case, increased braking torque flows from the vehicle wheel to the electric motor on the actuated side, while only reduced braking torque flows from the vehicle wheel to the electric motor on the non-actuated side. Therefore, there is a risk that the vehicle wheel on the non-actuated side will lock if the reduced braking torque flowing through the closed dog clutch falls below a certain braking torque limit. In this case, a vehicle dynamics control function, such as ABS, must be activated, which, for safety reasons, opens one of the dog clutches. This disengages the load on the axle differential.This allows the vehicle wheel on the non-actuated side of the vehicle to rotate freely, its rotational speed correlating with the current vehicle speed, which forms a reference value on the basis of which the control unit performs the vehicle dynamics control function (ABS function).

[0030] The opening of the claw clutch in the case of ABS can be carried out simply and automatically from a control engineering perspective as follows: Accordingly, the forces acting on the sliding sleeve, i.e. spring preload force, actuator force and axial force component, are designed such that a resulting force moves the sliding sleeve into the open position if the axial force component falls below an axial force limit value that correlates with the brake torque limit value due to decreasing braking torque.

[0031] The invention allows conventional, hydraulically operated wheel brakes to be omitted from the vehicle axle. In this case, braking of the vehicle wheels can be carried out solely by actuating the two multi-plate clutches.

[0032] Preferably, each of the two superimposed gear units can have a loose gear rotatably mounted on the flange shaft. The loose gear can be driven by the electric motor. Furthermore, the loose gear can be coupled to the flange shaft via the multi-plate clutch. The gear ratio between the electric motor and the loose gear can preferably be slightly shorter than the gear ratio between the electric motor and the differential input side. This ensures that the loose gear rotates somewhat slower than the flange shaft. This guarantees a braking torque flow from the flange shaft via the multi-plate clutch towards the electric motor.

[0033] Furthermore, the input-side axle differential gear can mesh with a fixed gear mounted on an intermediate shaft. In this case, the superimposed gear unit can have a fixed gear mounted on the intermediate shaft that meshes with the loose gear.

[0034] In the transmission structure outlined above, the multi-plate clutch can be actuated on one side of the vehicle. In this case, a brake torque split can occur, whereby the brake torque coming from the vehicle wheel is divided into the reduced differential brake torque and the superimposed brake torque. As the torque path continues towards the electric motor, the superimposed brake torque is introduced into the intermediate shaft via the intermediate shaft's fixed gear. The intermediate shaft therefore acts as a summing shaft, where the superimposed brake torque and the differential brake torque are added together. Conversely, on the non-actuated side of the vehicle, the vehicle wheel receives the differential brake torque from the actuated side via the axle differential, which is then transmitted to the intermediate shaft and added together.

[0035] The multi-plate clutches of the two superimposed transmissions can preferably be integrated into a vehicle dynamics control system. In this case, during recuperation mode, a control unit can actuate one or both of the multi-plate clutches depending on current driving parameters to support driving behavior through brake torque redistribution.

[0036] An embodiment of the invention is described below with reference to the accompanying figures. These show: Figs. 1 to 4 each show views of a first comparative example of a drive device for a vehicle axle not encompassed by the invention; Figs. 5 to 9 each show views of a second comparative example not encompassed by the invention; Fig. 10 in a view corresponding to the Fig. 6An embodiment of the invention; Fig. 11 Brake characteristics of the multi-plate clutch and the multi-plate brake on both sides of the vehicle during uniform braking; and Fig. 12 Brake characteristics of the multi-plate clutch and the multi-plate brake on both sides of the vehicle during uneven braking.

[0037] For the sake of a simpler understanding of the invention, the following will be used: Figs. 1 to 4 First, a comparative example not covered by the invention is described. In the Fig. 1 The diagram roughly schematically depicts a drive system for a two-track vehicle with an electrified rear axle. The drive system is located in the Fig. 1The illustration is shown only to the extent necessary for understanding the invention. Accordingly, both the front wheels VR, VL and the rear wheels HR, HL of the vehicle each have a wheel brake 1. Each wheel brake 1 consists of a brake caliper 3, actuated by a hydraulic cylinder (not shown), and a brake disc 5. The hydraulic cylinders of the wheel brakes 1 are each connected to a control unit 8 via hydraulic lines 7. The control unit 8 can apply brake pressure to the hydraulic cylinder of a wheel brake 1 via a corresponding hydraulic line 7, thereby bringing the brake caliper 3 and its brake pads into contact with the brake disc 5. Fig. 1The two hydraulic lines 7, which run to the rear of the vehicle, are routed to a hydraulic valve 9. The hydraulic valve 9 forms a branch point. At the hydraulic valve 9, the hydraulic line 7 from the left side of the vehicle branches into a partial line 11 to the left rear vehicle brake 1 and into a partial line 13, which leads to a drive unit 12 of the vehicle's rear axle. Similarly, at the hydraulic valve 9, the hydraulic line 7 from the right side of the vehicle branches into a partial line 11 to the right rear vehicle brake 1 and into a partial line 13, which also leads to the drive unit 12 of the vehicle's rear axle. The drive unit 12 has, according to the Fig. 2 an electric motor EM which drives the rear wheels HR, HL via a gearbox 14.

[0038] Each of the two partial lines 13 leads from the hydraulic valve 9 to a multi-plate clutch actuator 15 designed as a hydraulic cylinder 15 ( Fig. 2) a multi-plate clutch 19. The two multi-plate clutches 19 are part of the transmission 14 of the vehicle's rear axle, the transmission structure of which is described later. According to the Fig. 1 The hydraulic valve 9 can be switched in two positions. In the position shown, the hydraulic lines 7 are fluidically connected to the partial lines 11 leading to the respective rear wheel brakes 1, while the hydraulic cylinders 15 of the two multi-plate clutches 19 are fluidically decoupled from the control unit 8. In contrast, in the second switching position (not shown), the two hydraulic lines 7 are each fluidly connected to the partial lines 13, via which the hydraulic cylinders 15 of the multi-plate clutches 19 can be controlled by the control unit 8.

[0039] As from the Fig. 2As can be seen, the electric motor EM of the electrified rear axle of the vehicle is installed in a transverse configuration, so that the electric motor EM is arranged parallel to the axle to the flange shafts 23 which lead to the vehicle wheels HR, HL.

[0040] The electric motor shaft 27 is connected via a reduction gear spur gear stage 29 to an intermediate shaft 31, which consists of a fixed gear 33 arranged on the electric motor shaft 27 and a meshing fixed gear 35 arranged on the intermediate shaft 31. The intermediate shaft 31 is connected to the input side of an axle differential 39 via a further spur gear stage 37, which consists of a fixed gear 41 arranged on the intermediate shaft 31 and an input-side axle differential gear 43. The axle differential 39 drives in the transverse direction y of the vehicle to the two flange shafts 23 leading to the vehicle wheels HL and HR on both sides.

[0041] As from the Fig. 2As further shown, the rear axle has a superimposed transmission 45 on each side of the vehicle, by means of which the electric motor EM can be directly connected to the respective flange shaft 23 by bypassing the axle differential 39. The two superimposed transmissions 45 are mirror images of each other with respect to a longitudinal longitudinal plane of the vehicle. Each of the two superimposed transmissions 45 has a loose gear 49 rotatably mounted on the flange shaft 23, which meshes with the intermediate shaft fixed gear 51. An outer plate carrier 53 of the multi-plate clutch 19 is formed on the respective loose gear 49, which interacts with an inner plate carrier 55 formed on the flange shaft 23.The lamellar pack located between the outer lamellar carrier 53 and the inner lamellar carrier 55 can be compressed by a ring piston 57, which is adjustable by means of the hydraulic cylinder 15 by a horizontal stroke in order to actuate the lamellar clutch 19 up to a predetermined degree of engagement. The two lamellar clutches 19 are load-shiftable and can be controlled with slip.

[0042] During recuperation mode, the electric machine EM operates in generator mode, in which the two vehicle wheels HL, HR transmit a braking torque ML and MB via the flange shafts 22, 25 towards the axle differential 39. In the axle differential 39, the two braking torques ML and MB are summed to form a total braking torque, which is then transmitted to the electric machine EM, which is operating as a generator.

[0043] Brake torque redistribution during recuperation mode is carried out as follows: The control unit 8 switches the hydraulic valve 9 to its second switching position (not shown). This connects the control unit 8, via the partial line 13 on the right side of the vehicle, to the hydraulic cylinder 15 of the multi-plate clutch 19 located on the right side of the vehicle. It also connects the control unit 8, via the partial line 13 on the left side of the vehicle, to the hydraulic cylinder 15 of the multi-plate clutch 19 located on the left side of the vehicle. In contrast, the rear vehicle brakes 1 are not actuated and are therefore deactivated.By hydraulically actuating one of the multi-plate clutches 19, a brake torque path is divided into a differential brake torque path, which carries a differential brake torque M 2 from the respective vehicle wheel via the axle differential 39 to the electric machine EM, and into a superimposed brake torque path, which carries a superimposed brake torque M 1 from the respective vehicle wheel past the axle differential 39 via the superimposed transmission 45 to the electric machine EM.

[0044] For example, in the Fig. 3 The electric machine EM is in recuperation mode, while simultaneously a brake torque redistribution takes place, in which the right multi-plate clutch 19 is not completely engaged, but only to a certain degree of engagement, allowing slippage. The left multi-plate clutch 19, on the other hand, is fully open. According to the Fig. 3The braking torque MR applied to the right rear wheel HR is split at the right multi-plate clutch 19 into a differential torque M 2, which leads to the axle differential 39, and a superimposed torque M 1, which is transmitted via the multi-plate clutch 19 to the intermediate shaft 31. The left rear wheel HL receives the differential torque M 2 from the right side of the vehicle via the axle differential 39. Therefore, the differential torque M 2 from the left rear wheel HL and the differential torque M 2 from the right rear wheel HL are transmitted via the axle differential 39 to the intermediate shaft 31. Additionally, the superimposed torque M 1 from the right rear wheel HR is transmitted via the superimposed gear 45 on the right, actuated side of the vehicle to the intermediate shaft 31. The intermediate shaft 31 acts as a summing shaft, at which all braking torques are added up to a total braking torque, which is directed via the reduction stage 29 to the electric machine EM and recuperated there.

[0045] To ensure a braking torque flow from the flange shaft 23 via the engaged multi-plate clutch 19 towards the electric motor EM, it is important that there is a speed difference between the flange shaft 23 and the loose gear 49, such that the loose gear 49 rotates slightly slower than the flange shaft 23. The gear ratio between the electric motor EM and the loose gear 49 is therefore designed to be slightly shorter than the gear ratio between the electric motor EM and the differential input side.

[0046] As soon as the control unit 8 detects an emergency situation and / or ABS / 8 intervention is required during recuperation mode, the control unit 8 ends the recuperation mode. In this case, the control unit 8 adjusts the hydraulic valve 9 to the position in which Fig. 1shown switching position, whereby the driving dynamics control is carried out during further driving operation solely by means of the rear vehicle wheel brakes 1, while the multi-plate clutches 19 can no longer be controlled.

[0047] In the Fig. 4 Another operating situation during recuperation mode is indicated. Accordingly, the right multi-plate clutch 19 is completely closed. The left multi-plate clutch 19, on the other hand, is fully open. Thus, in the Fig. 4 The braking torque MR applied to the right rear wheel HR is transmitted completely via the multi-plate clutch 19 to the intermediate shaft 31. From there, the braking torque is transmitted via the reduction gear 29 to the electric motor EM, where recuperation takes place. The left rear wheel HL, on the other hand, rotates without load at a speed determined by the axle differential 31.

[0048] In the above comparative example, the following condition must be met for the ABS function to function on the vehicle axle: At least one vehicle wheel HL, HR of the vehicle axle must rotate freely so that a sensor-detectable reference rotational speed n ref can be established, which correlates with the current vehicle speed. This reference speed forms a reference value for the control unit 8, on the basis of which the control unit 8 controls the ABS function. When the ABS function is activated, the control unit 8 adjusts the braking torques acting on the remaining three vehicle wheels. The drive device according to the comparative example ( Figs. 1 to 4) is not ABS-compatible during recuperation mode, as no freely rotating vehicle wheel HL, HR can be positioned on the vehicle axle during recuperation mode. Although, with the multi-plate clutch 19 fully closed (i.e., without slippage) on the actuated side of the vehicle, the vehicle wheel on the other, non-actuated side of the vehicle can be shifted without load (see the operating state according to the Fig. 4However, during recuperation mode, the unloaded vehicle wheel is subjected to a rotational speed via the axle differential 39 that does not correlate with the current vehicle speed and is therefore unsuitable as a reference value for the ABS function. To achieve free rotation of a vehicle wheel in the comparative example, the recuperation mode of the electric motor EM would have to be deactivated so that the electric motor EM rotates freely, thus disengaging the axle differential 39. In this case, however, no recuperation energy can be recovered during the execution of the ABS function.

[0049] In contrast, in the Figures 5 to 9A second comparative example, not covered by the invention, is shown, which is designed in such a way that the recuperation mode can be maintained even during the execution of the ABS function, so that recuperation energy can be recovered even during the execution of the ABS function.

[0050] For this purpose, the vehicle axle has a disconnect coupling implemented as a jaw coupling 58 on each side of the vehicle. The jaw coupling 58 divides the flange shaft 23 on each side of the vehicle into a differential-side partial shaft 59 and a wheel-side partial shaft 61. The inner plate carrier 55 of the respective multi-plate coupling 19 is rotationally fixed on the wheel-side partial shaft 61. Accordingly, the superimposed transmission 45 can be coupled to the wheel-side partial shaft 61 via the multi-plate coupling 19, while the differential-side partial shaft 59 is not connected to the superimposed transmission 45. If one of the two jaw couplings 57 is open, the axle differential 39 is disengaged, thus interrupting the differential brake torque path and enabling brake torque transmission from the vehicle wheel to the electric motor EM only via the superimposed transmission 45.

[0051] The claw coupling 58 has a sliding sleeve 63 which is axially adjustable between an open position and a closed position. In the Fig. 7 The jaw coupling 58 is schematically shown in a developed view in both the open ("open") and closed ("closed") positions. In the closed position, a sliding sleeve internal toothing 65 engages with the external toothing 66, 67 of the differential-side partial shaft 59 and the wheel-side partial shaft 61. In contrast, in the open position, the tooth engagement is disengaged, so that no torque transmission occurs via the jaw coupling 58. A preload spring 69 is associated with the sliding sleeve 63 of the jaw coupling 58, by means of which the sliding sleeve 63 is held in place by a spring preload force Fv ( Fig. 7 ) has advanced towards the closed position.

[0052] According to the Fig. 6Both the multi-plate clutch actuator 15 and the sliding sleeve actuator 73 are implemented as hydraulic cylinders, which are connected to the control unit 8 on each side of the vehicle via a common hydraulic line 7, as shown in the Fig. 5The common hydraulic line 7 is directly connected to the multi-plate clutch actuator 15, transmitting pressure. The multi-plate clutch actuator 15 is in turn connected to the sliding sleeve actuator 73 via a connecting line 75, also transmitting pressure. When actuated by the control unit 8, hydraulic pressure is built up in the multi-plate clutch actuator 15, which pushes the annular piston 57 against a multi-plate pack of the multi-plate clutch 19 to close the multi-plate clutch 19 to a predetermined degree of engagement. The annular piston 57 also pushes against the multi-plate pack of the multi-plate brake 81. In the same way, hydraulic pressure is also built up in the sliding sleeve actuator 73, which applies an actuator force FA to the sliding sleeve 63 in the open position.

[0053] As can be seen from the Fig. 7As can be seen from the diagram, in the closed position the opposing tooth flanks 77 of the sliding sleeve's internal teeth 65 and the external teeth 66 of the differential-side partial shaft 59 are in contact with each other. The tooth flanks 77 have inclined backings, so that under braking torque, the sliding sleeve 63 is subjected to an axial force component Fax acting in the direction of the closed position. The magnitude of the axial force component Fax correlates with the magnitude of the braking torque to be transmitted, as can be seen from the two diagrams. Figs. 8 and 9 This means that as the braking torque decreases, the axial force component Fax decreases, while as the braking torque increases, the axial force component Fax increases. In the Fig. 7The directions of action of the forces acting on the sliding sleeve 63 are shown, namely the axial force component F ax , the preload force Fv of the preload spring 69 and the actuator force FA of the sliding sleeve actuator 73. In the lower half of the development ( Fig. 7 ) the sum of the axial force component F ax and the preload force Fv is greater than the actuator force FA, so that the jaw coupling 58 remains closed. In contrast, in the upper half of the development ( Fig. 7 ) the sum of the axial force component F ax and the preload force Fv is less than the actuator force FA , so that the jaw coupling 58 is closed.

[0054] The following will be based on the Figs. 8 and 9 An operating situation during recuperation mode is described in the diagram. Fig. 8 The braking torques generated during this operating situation are shown in the diagram. Fig. 9The forces acting on the sliding sleeve 63 are shown. Up to time t1, the dog clutches 58 on both sides of the vehicle are closed and the multi-plate clutches 19 are open. Therefore, a uniform braking torque distribution occurs, in which the braking torques ML and MR applicable to both sides of the vehicle are equal. The two braking torques ML and MR are combined at the axle differential 39 to form a total torque, which is then directed towards the electric motor EM.

[0055] From time t 1 onwards, according to the Fig. 8A brake torque redistribution occurs, in which the multi-plate clutch 19 on the right side of the vehicle is actuated, while the multi-plate clutch 19 on the left side remains open. The two dog clutches 58 remain closed. This increases the brake torque MR available on the right side of the vehicle, which consists of a differential brake torque M 2 transmitted via the axle differential 39 and a superimposed brake torque M 1 transmitted via the right superimposed gear 45. The brake torque ML available on the left side of the vehicle assumes the value of the reduced differential brake torque M 2 on the right side of the vehicle.

[0056] Upon reaching time t 3, the situation approaches in the Fig. 8The braking torque ML, which can be applied to the left side of the vehicle, is at the zero mark. In this case, there is a risk that the vehicle wheel HL on the left side of the vehicle will lock. Therefore, for safety reasons, the vehicle dynamics control function (ABS function) is activated to prevent such a wheel lock-up. To activate the vehicle dynamics control function, one of the dog clutches 58 must be opened so that the rotational speed n ref ( Fig. 6 ) of a freely rotating vehicle wheel as a reference value for the vehicle dynamics control function.

[0057] Such an opening of the jaw coupling 58 is achieved simply and automatically from a control engineering perspective as follows: The opening process of the right jaw coupling 58 takes place using the forces acting on the sliding sleeve 63, namely axial force component F ax, spring preload force Fv and actuator force FA. These are designed such that a resultant force FR ( Fig. 9The sliding sleeve 63 is only moved into the open position when the axial force component F ax falls below a certain axial force limit value due to the decreasing braking torque M 2. This occurs in the Fig. 9 at time t 2, at which there is hardly any braking torque ML that can be transferred from the left vehicle wheel HL and therefore there is a risk of vehicle wheel locking up.

[0058] In the Fig. 6The ABS function is activated on the left, non-actuated side of the vehicle as an example. The resulting braking torques are shown. Accordingly, the braking torque MR, which can be applied on the right side of the vehicle, is transmitted to the electric motor EM via the closed multi-plate clutch 19. The left dog clutch 58 is closed, while the left multi-plate clutch 19 is open. The right dog clutch 58 is open due to the force ratio acting on the sliding sleeve 63. This disengages the right output side of the axle differential 39. The vehicle wheel HL on the left side of the vehicle therefore rotates freely, establishing a reference rotational speed n ref that correlates with the actual vehicle speed.

[0059] In Figure 10An embodiment of the invention is shown, the basic structure and function of which are essentially identical to those in the preceding comparative example. In contrast to the comparative example of Figures 5 to 9 is in the exemplary embodiment of the Figure 10 An additional multi-disc brake 81, acting as a vehicle wheel brake, is arranged on each side of the vehicle. The inner disc carrier 83 of the multi-disc brake 81 is rigidly connected to the flange shaft 23 via a radial connecting flange 82.

[0060] The multi-disc brake 81 has a disc pack arranged between an inner disc carrier 83 and an outer disc carrier 85. The disc pack of the multi-disc brake 81 and the disc pack of the multi-disc clutch 19 can be actuated on each side of the vehicle via the hydraulic cylinder 15 (i.e., the multi-disc clutch actuator). During vehicle braking, the control unit 8 applies brake pressure to one or both hydraulic cylinders 15. This builds up hydraulic pressure in the respective hydraulic cylinder 15, which moves the annular piston 57 by one closing stroke, pressing against both the disc pack of the multi-disc clutch 19 and the disc pack of the multi-disc brake 81.

[0061] Starting from the unactuated state, the ring piston 57 presses the multi-plate clutch pack 19 over a multi-plate clutch clearance s K until the kiss point is reached against an axial stop 87 ( Fig. 10), which is axially fixed to the inner plate carrier 55 of the multi-plate clutch 19. Simultaneously, the ring piston 57 presses the plate pack of the multi-plate brake 81 against a pressure rod 89 via a multi-plate brake clearance s B until the kiss point is reached. This acts on both sides of the vehicle as an axially adjustable axial stop against which the plate pack of the respective multi-plate brake 81 is pressed. The pressure rod 89 is movable between movement stops 91 by a pressure rod axial travel Δs ( Fig. 10 ) axially adjustable.

[0062] The following will be based on the Figure 11 A uniform braking process is described in which the control unit 8 applies the same brake pressure to the hydraulic cylinders 15 on both sides of the vehicle. In this case, the pressure rod 89 remains centered, that is, stationary without shifting to the left or right. According to the Figure 11On both sides of the vehicle, the brake disc clearance s B is smaller than the clutch disc clearance s K. Therefore, during the closing stroke of the ring piston 57, the brake disc 81 engages first, and only later does the clutch disc 19 engage.

[0063] Based on the Figure 12An uneven braking process is described in which the control unit 8 applies brake pressure to the hydraulic cylinder 15 on the right side of the vehicle, while the left side of the vehicle is not subjected to brake pressure. During the closing stroke of the right ring piston 57, both the multi-plate pack of the right multi-plate clutch 19 is pressed against the axial stop 87 and the multi-plate pack of the right multi-plate brake 81 is pressed against the pressure rod 89, which acts as an axial stop. This causes the pressure rod 89 to be moved towards the left side of the vehicle by the pressure rod axial travel Δs. Therefore, the braking characteristic curve of the multi-plate brake 81 is shifted, as indicated by double arrows in the right-hand diagram of Figure 12. This results in a multi-plate brake clearance s B on the right side of the vehicle that is increased by the pressure rod axial travel Δs compared to the braking case with uniform braking ( Fig. 11The multi-plate brake release clearance sB is dimensioned larger by an additional dimension a than the multi-plate clutch release clearance sK. This ensures that the braking torque MR, which can be applied on the right side of the vehicle, is first transmitted via the right-hand superimposed transmission 45 to the electric motor EM and recuperated there. If, during further braking, the right-hand multi-plate brake release clearance sB is exhausted, the multi-plate brake 81 also engages. In the right-hand diagram of the Figure 12 A braking torque M TV is entered. The braking torque M TV is transmitted via the right superimposed gear 45 towards the electric motor EM when the kiss point of the right multi-disc brake 81 is reached, i.e. when the right multi-disc brake clearance s B is exhausted.

[0064] On the opposite left side of the vehicle, which is not subjected to brake pressure, the left diagram shows the following: Figure 12The following situation exists: The available brake disc clearance s B is reduced due to the pressure rod adjustment to the left. The brake disc clearance s B is smaller than the clutch disc clearance s K, thus preventing actuation of the clutch disc 19 on the side of the vehicle not subjected to brake pressure.

[0065] It should be emphasized that the invention does not apply to the embodiment of the Figs. 10 to 12 is limited. Rather, the multi-disc brakes 81, whose design and function are based on the Figs. 10 to 12 This is explained, also in the comparative example of the Figs. 1 to 4 as well as in the comparative example of the Figs. 5 to 9 installable. REFERENCE MARK LIST:

[0066] 1 Vehicle wheel brakes 3 Brake caliper 5 Brake disc 7 Hydraulic lines 9 Hydraulic valve 11 Partial line 12 Drive unit 13 Partial line 14 Transmission 15 Hydraulic cylinder of the multi-plate clutches 19 19 Multi-plate clutches 23 Flange shafts 27 Electric motor shaft 29 Countershaft spur gear stage 31 Intermediate shaft 33 Fixed gear 35 Fixed gear 37 Further spur gear stage 39 Axle differential 41 Fixed gear 43 Axle differential gear 45 Superimposed gear 45 Left-hand superimposed gear 45 Right-hand superimposed gear 49 Loose gear 51 Intermediate shaft fixed gear 53 Outer plate carrier 55 Inner plate carrier 57 Ring piston 58 Disconnect clutch 58 Right-hand disconnect clutch 58 Left-hand disconnect clutch 59 Differential-side partial shaft 61 Wheel-side partial shaft 63 Sliding sleeve 65 Sliding sleeve internal teeth 66 External teeth of the differential-side partial shaft 67 External teeth of the wheel-side partial shaft 69 Preload spring 73 Sliding sleeve actuator 75 Connecting line 77 Tooth flank 81 Multi-plate brake 82 RadialConnecting flange 83 Inner plate carrier 85 Outer plate carrier 87 Axial stop of the multi-plate clutch 89 Pushrod 91 Movement stops HL, HR Vehicle wheels 8 Control unit EM Electric machine ML at left rear wheel HL Deployable braking torque MR at right rear wheel HR Deployable braking torque M 1 Superposition torque M 2 Differential torque FV Preload spring force FA Actuator force F ax Axial force component FR Resultant force n ref Reference speed s B Multi-plate brake release clearance s K Multi-plate clutch release clearance Δs Pushrod axial travel a Additional dimension Left side of vehicle Right side of vehicle

Claims

1. Drive device for a vehicle axle of a two-track vehicle, which has an axle differential (39) whose input side is connected in terms of drive to an electric machine (EM) and whose output sides output drive to flange shafts (23) leading to the two vehicle wheels (HL, HR), wherein the vehicle axle has on each vehicle side a respective superposition gearing (45) with a multiplate clutch (19), by means of which superposition gearing the electric machine (EM) is able to be connected directly to the vehicle-wheel flange shaft (23) while bypassing the axle differential (39), wherein the multiplate clutches (19) are able to be controlled by a control unit (8), specifically in particular for a redistribution of braking torque between the vehicle sides in the recuperation mode of the electric machine (EM), characterized in that, on each vehicle side, the multiplate clutch (19) is assigned a multiplate brake (81) acting as a vehicle-wheel brake, by means of which vehicle braking operations are able to be carried out as an alternative or in addition to the multiplate clutch (19).

2. Drive device according to Claim 1, characterized in that, on each vehicle side, both the multiplate clutch (19) and the multiplate brake (81) are able to be actuated via a common hydraulic cylinder (15) which is connected via exactly one hydraulic line (7) to the control unit (8), and in that in particular the hydraulic cylinder (15), when controlled by the control unit (8), builds up a hydraulic pressure by way of which a pressure element, in particular an annular piston (57), presses against both a plate pack of the multiplate clutch (19) and a plate pack of the multiplate brake (81).

3. Drive device according to Claim 1 or 2, characterized in that the pressure element (57), starting from the non-actuated state, presses the plate pack of the multiplate clutch (19) against an axial stop (87) over a clearance (sK) until the kiss point is reached, and in that in particular the clearance (sK) does not vary according to the braking situation, that is to say with uniform braking or with non-uniform braking on each vehicle side.

4. Drive device according to Claim 3, characterized in that the pressure element (57), starting from the non-actuated state, presses the plate pack of the multiplate brake (81) against an axial stop (89) over a clearance (ss) until the kiss point is reached, and in that in particular the clearance (ss) varies according to the braking situation, specifically in particular by way of axial adjustment of the axial stop (89).

5. Drive device according to Claim 4, characterized in that, with uniform braking on both vehicle sides, the multiplate-brake clearance (ss) is smaller in size than the multiplate-clutch clearance (sK), so that, in particular during the closing stroke of the pressure element (57), firstly the multiplate brake (81) enters into braking engagement and only over the further course the multiplate clutch (19) enters into braking engagement.

6. Drive device according to Claim 4 or 5, characterized in that, with non-uniform braking on both vehicle sides, the multiplate-brake clearance (ss) is larger in size than the multiplate-clutch clearance (sK), so that, during the closing stroke of the pressure element (57), firstly the multiplate clutch (19) of the vehicle side controlled with a higher braking pressure by the control unit (8) enters into braking engagement and only over the further course the multiplate brake (81) enters into braking engagement.

7. Drive device according to one of Claims 4 to 6, characterized in that the axially adjustable axial stop of the multiplate brake (81) is a pressure bar (89), and in that the pressure bar (89) acts as an axially adjustable axial stop on both vehicle sides, this being axially adjustable between movement stops (91) by a pressure-bar axial travel (Δs).

8. Drive device according to Claim 7, characterized in that, with non-uniform braking, on the vehicle side to which a higher braking pressure is applied, during the closing stroke of the pressure element (57), the plate pack of the multiplate brake (81) adjusts the pressure bar (89) by the pressure-bar axial travel (Δs) towards the counterpressure vehicle side, so that the available multiplate-brake clearance (sB) is increased by the pressure-bar axial travel (Δs), specifically in comparison with the braking situation of uniform braking, and in that in particular the multiplate-brake clearance (ss) is larger in size than the multiplate-clutch clearance (sK) by an additional dimension (a), so that, in particular during the closing stroke of the pressure element (57), firstly the multiplate clutch (19) enters into braking engagement and only over the further course the multiplate brake (81) enters into braking engagement.

9. Drive device according to Claim 8, characterized in that, with non-uniform braking, on the counterpressure vehicle side, the multiplate-brake clearance (ss) is reduced due to the pressure-bar adjustment, and that in particular the multiplate-brake clearance (ss) is smaller in size than the multiplate-clutch clearance (sK), so that actuation of the multiplate clutch (19) on the opposite vehicle side is ruled out.