ALL-WHEEL DRIVE VEHICLE

Description

[0001] The invention relates to an all-wheel-drive, two-track vehicle according to the preamble of claim 1.

[0002] In an all-wheel-drive vehicle, the all-wheel drive can be implemented with a total of four electric motors, each of which is a wheel hub motor assigned to one of the vehicle's wheels. In this case, the vehicle does not require differentials. Alternatively, an all-wheel-drive system can be implemented with one electric motor assigned to the front axle and one to the rear axle, each driving power to the vehicle's wheels via a front and rear differential, respectively. Furthermore, there are concepts with one electric motor and a locking differential on the front axle and two electric motors on the rear axle, each driving one rear wheel. Drive systems with an internal combustion engine and torque distribution via three locking differentials are also known from off-road vehicles.

[0003] A vehicle of this type with all-wheel drive features a selectable all-wheel drive system in which the drivetrain includes an electric motor. In front-wheel drive mode, the electric motor drives only the front axle of the vehicle. The electric motor can be coupled to a driveshaft via a center differential and a center clutch. The driveshaft is connected to the rear wheels of the vehicle via a rear axle differential and drive shafts. When the center clutch is disengaged, the rear axle is decoupled from the drivetrain, while when the center clutch is engaged, the rear axle can be engaged with the drivetrain.

[0004] An electrically powered off-road vehicle with two or more electric motors presents the following problem: While multiple electric motors can be effectively controlled independently in terms of torque and speed without requiring a mechanical connection between the front and rear axles, this means that each electric motor must meet the torque and power requirements of the connected wheel(s). Since one wheel or axle is often unable to deliver torque during off-road operation, the other drive must provide its full power. This places high demands on each electric motor. In this case, the combined power output of all electric motors frequently exceeds the requirements of the entire vehicle. Furthermore, there is a risk of individual electric motors becoming overloaded during off-road operation, resulting in reduced torque and power output.Each electric motor must also have its own control unit (positive inverter). Therefore, multi-motor drives are very expensive and heavy. US Patent 5,373,912 A discloses a vehicle drivetrain with an internal combustion engine that drives a center differential to distribute power to the front and rear axle differentials. DE 103 04 806 A1 discloses an all-wheel-drive vehicle with an internal combustion engine that drives a center differential via a transmission. EP 248 582 B1 discloses an all-wheel-drive vehicle with a center differential that drives the front and rear axle differentials to drive the vehicle wheels via cardan shafts. WO2019197336A1 discloses an all-wheel-drive vehicle whose drivetrain includes exactly one electric motor.

[0005] The object of the invention is to provide an all-wheel-drive, two-track vehicle whose functionality is increased compared to the prior art and which, in particular, can drive efficiently in front-wheel drive mode and / or switch to all-wheel drive mode while driving under load.

[0006] The problem is solved by the features of claim 1. Preferred embodiments of the invention are disclosed in the dependent claims.

[0007] The invention relates to an all-wheel-drive vehicle with selectable all-wheel drive. According to the invention, the vehicle's drivetrain comprises exactly one electric motor, which, in front-wheel drive mode, drives only the vehicle's front axle. The electric motor can be coupled to a driveshaft via a center differential or intermediate axle differential and a center clutch. The driveshaft can be connected to the vehicle's rear wheels via a rear axle differential and drive shafts. When the center clutch is disengaged, the rear axle is decoupled from the drivetrain. When the center clutch is engaged, the rear axle can be engaged with the drivetrain. According to the invention, a rear axle disconnect clutch is installed in one of the rear axle's drive shafts. In front-wheel drive mode, i.e., when the center clutch is disengaged, the rear axle disconnect clutch is open.In this way, a section of the drivetrain between the center clutch and the rear axle differential is deactivated, specifically the driveshaft and the differential housing of the rear axle differential. The differential gears of the rear axle differential, however, rotate without load.

[0008] In a preferred embodiment, the invention describes a single-motor drive with a total of three differentials and five clutches. This arrangement allows the vehicle to operate efficiently in front-wheel drive mode, with the driveshaft and rear bevel gear completely decoupled. Switching to all-wheel drive can occur fully automatically while driving under load (and vice versa). Furthermore, the drive torque at the wheels can be controlled by selectively engaging the differential locks (off-road operation). In contrast, in a vehicle with multiple electric motors, each electric motor must meet the requirements (torque and power) of the driven wheel(s). The total power output is obtained by adding up all the installed electric motors. This would result in system power outputs that are far too high.

[0009] The concept according to the invention provides exactly one electric motor, which is designed to meet the requirements of the entire vehicle. The power requirement in off-road operation is generally lower. The drive concept is capable of continuously distributing the required drive power to individual wheels. There is no risk of the electric motor overheating.

[0010] In front-wheel drive, the center locking clutch is engaged, and all other clutches are disengaged. The right rear wheel (shown in the figures) drives the differential gears of the rear axle differential; however, since there is no connection to the left rear wheel, no power is transmitted between the rear bevel gear and the rear wheels. Therefore, the differential housing (i.e., the differential carrier), the rear bevel gear, the driveshaft, and the rear half of the center clutch do not rotate.

[0011] According to the invention, the drivetrain is designed such that a change from front-wheel drive to all-wheel drive can be performed without interrupting traction during driving. When switching from front-wheel drive to all-wheel drive, the rear axle locking clutch is engaged. This accelerates the rear angle gearbox, the driveshaft, and the rear clutch half of the center clutch to a speed corresponding to the vehicle speed. The rear axle disconnect clutch is then engaged, followed by the rear axle locking clutch opening, and immediately thereafter the center clutch engaging (this is just one possibility; the shift sequence can be modified as desired). According to the invention, the rear axle locking clutch is designed as a multi-plate clutch because it must perform the synchronization. The center clutch and the rear axle disconnect clutch are dog clutches, as they are engaged without load and at a minimal differential speed.A positive connection to the rear axle has now been established.

[0012] To compensate for speed differences between the front and rear axles, the center differential lock opens. This process may need to occur under load. Therefore, the center differential lock is preferably designed as a multi-plate clutch. A dog clutch would also be possible, but would result in reduced comfort. In on-road all-wheel-drive operation, it makes sense to engage the center differential lock and rear differential lock (preferably designed as multi-plate clutches) using slip control. The center differential lock and the rear differential disconnect clutch, however, remain permanently engaged, while the front differential lock remains permanently disengaged.

[0013] The switch from all-wheel drive to front-wheel drive occurs when the drive torque is low. The front and rear axle locking clutches are open, while the center locking clutch is closed; immediately afterwards, the center clutch and rear axle disconnect clutch open.

[0014] Off-road all-wheel drive engages from on-road all-wheel drive. Front-wheel drive is not intended for off-road use. To variably distribute drive torque to the desired wheel, the front axle locking clutch, the center locking clutch, and the rear axle locking clutch are fully or partially engaged. It is advantageous that, for the reasons mentioned above, the center locking clutch and the rear axle locking clutch are preferably designed as multi-plate clutches, thus enabling controlled off-road operation.

[0015] The front axle locking clutch is preferably designed as a dog clutch for the following reasons: Firstly, the front axle locking clutch is only engaged in extreme driving situations. In these situations, comfort plays only a minor role. Many off-road vehicles forgo this clutch entirely. Secondly, the front axle locking clutch – unlike the center and rear axle locking clutches – does not have a dual function.

[0016] The key features are highlighted in detail below: In one technical implementation, the rear axle differential can be locked via a rear axle locking clutch. The rear axle locking clutch is preferably implemented as a load-shiftable multi-plate clutch. When the locking clutch is engaged, a differential housing of the rear axle differential is coupled to one of the drive shafts, thus forming a rear axle differential lock.

[0017] As mentioned above, the center clutch is open in front-wheel drive mode. According to the invention, the center clutch is closed for switching from front-wheel drive to all-wheel drive with the rear axle engaged. The center clutch can preferably be a non-load-engageable dog clutch. Therefore, the two clutch halves of the center clutch must operate at approximately the same speed to enable load-free shifting. For this purpose, the rear axle locking clutch acts in a dual function as a synchronizing clutch, by means of which a synchronization process takes place before the center clutch is closed. During the synchronization process, the driveshaft (which is stationary in front-wheel drive mode) is accelerated to the vehicle speed. In this way, the clutch half of the center clutch connected to the driveshaft can be synchronized to the speed of the clutch half connected to the center differential.

[0018] After the synchronization process has been completed, the center clutch and the rear axle disconnect clutch are engaged in any sequence during the subsequent process. With both the center clutch and the rear axle disconnect clutch engaged, the rear axle locking clutch and / or the center locking clutch are disengaged.

[0019] In a specific embodiment, the center differential can have an intermediate shaft leading to the center clutch at the rear of the vehicle and a pinion shaft leading to a front axle differential at each of its two output sides. The pinion shaft leading to the front axle differential can be connected to the front wheels of the front axle via the front axle differential and via drive shafts. The center differential can also be locked via a center locking clutch. The center locking clutch can preferably be implemented as a load-shiftable multi-plate clutch. When the locking function is activated, a differential carrier of the center differential can be coupled to the drive shaft leading to the front axle differential, thus forming a center differential lock in all-wheel-drive mode.

[0020] The center locking clutch can function in a dual capacity, not only as a differential lock. Additionally, when engaged (i.e., in front-wheel drive mode), it can transmit drive torque from the center differential to the front axle differential.

[0021] Preferably, the electric motor is directly or indirectly connected to the center differential in a drive-related manner. In this case, the electric motor drives, for example, a gear train and / or a reduction gear via an interposed transmission and / or a reduction stage, onto a gear mounted on the differential housing of the center differential.

[0022] The front axle differential can also be locked via a front axle locking clutch. Unlike the center and rear axle locking clutches, the front axle locking clutch can be implemented as a non-load-shifting dog clutch. When the locking function is activated, a differential housing of the front axle differential can be coupled to a driveshaft, thus forming a front axle differential lock.

[0023] With the drivetrain according to the invention, the vehicle can drive efficiently in front-wheel drive mode, while the driveshaft and, optionally, an angle gear interposed between the driveshaft and the rear axle differential are completely decoupled from the drivetrain. The switch from front-wheel drive to all-wheel drive can occur fully automatically while driving and under load. The same applies to the switch from all-wheel drive to front-wheel drive. Furthermore, the drive torque at the wheels can be controlled by selectively engaging the three differential locks. Overall, the invention therefore relates to an electric motor drive with three differentials, namely the front axle differential, the rear axle differential, and the center differential, as well as a total of five clutches, namely the rear axle disconnect clutch, the rear axle locking clutch, the center clutch, the center locking clutch, and the front axle locking clutch.

[0024] Front-wheel drive can be activated in an energy-saving efficiency mode of the vehicle. In contrast, all-wheel drive can be divided into on-road and off-road modes, meaning off-road driving or on-road driving.

[0025] In on-road operation, the rear axle locking clutch (designed as a multi-plate clutch) and / or the center locking clutch (designed as a multi-plate clutch) can be opened and closed in a slip-controlled manner to adjust driving dynamics. In contrast, in on-road operation, the center clutch and the rear axle disconnect clutch are permanently closed, while the front axle locking clutch is open.

[0026] Off-road operation is identical to on-road operation, with the exception that the front axle locking clutch is engaged. The front axle locking clutch (preferably a non-load-shiftable dog clutch) can be engaged by the driver before starting off-road driving (i.e., when the vehicle is unloaded).

[0027] Exemplary embodiments of the invention are described below with reference to the accompanying figures.

[0028] They show: Fig. 1 shows a schematic representation of the drive train of a two-track motor vehicle with a longitudinally mounted electric motor; Fig. 2 shows a view corresponding to the Figure 1 a drive train with a transversely mounted electric motor.

[0029] In Figure 1Figure 1 shows a drivetrain in a two-track vehicle. The drivetrain comprises an electric motor 1 mounted longitudinally in the vehicle. A gearbox 3 and a spur gear stage 5 for torque conversion are connected downstream of the electric motor 1. The spur gear stage 5 consists of a gear 7 mounted on the gearbox output shaft 16 and an input gear 9 of a differential carrier 11 of a center differential 13. The center differential 13 has an intermediate shaft 17 leading to a center clutch 15 at the rear of the vehicle and a pinion shaft 21 leading to a front axle differential 19 at the front of the vehicle. Figure 1 The pinion shaft 21 leading towards the front of the vehicle is connected via a bevel gear 23 to a ring gear 25 of a differential basket of the front axle differential 19.

[0030] The two shafts 17, 21 are in the differential basket 13 of the center differential 13 with their axle bevel gears 29 in tooth engagement with compensating gears 31, which are rotatably mounted on the differential basket 11.

[0031] The front axle differential 19 is in the Figure 1 The center differential 13 is designed in approximately the same way. Accordingly, from the output sides of the front axle differential 19, drive shafts 33 are led on both sides in the transverse direction of the vehicle to the front wheels 35.

[0032] The intermediate shaft 17, which leads to the rear of the vehicle, is in the Figure 1The center coupling 15, implemented as a dog coupling, can be connected to a cardan shaft 39, which drives via a bevel gear 41 onto an input-side ring gear 43 of a differential basket 45 of a rear axle differential 47, the construction of which is essentially identical to that of the center differential 13. The two output sides of the rear axle differential 47 are connected to the rear wheels 51 via drive shafts 49.

[0033] In addition to the aforementioned center clutch 15, the drivetrain has four further clutches, which are described below. The front axle differential 19 can be locked via a front axle locking clutch 53. The front axle locking clutch 53 is implemented as a non-load-shiftable dog clutch. When the locking function is activated, the differential carrier 27 of the front axle differential 19 is coupled to the left driveshaft 33, forming a front axle differential lock. Similarly, the center differential 13 can also be locked via a center locking clutch 55. The center locking clutch 55 is implemented as a load-shiftable multi-plate clutch. When the locking function is activated, the center locking clutch 55 couples the differential basket 11 of the center differential 13 with the pinion shaft 21 leading to the front of the vehicle. In the same way, the rear axle differential 47 can also be locked via a rear axle locking clutch 57.The rear axle locking clutch 57 is also implemented as a non-load-shiftable dog clutch. When the locking function is activated, the rear axle locking clutch 57 couples the differential carrier 27 of the front axle differential 19 with the right driveshaft 49, thus forming a rear axle differential lock. Additionally, a rear axle disconnect clutch 59 is installed in the left driveshaft 49.

[0034] The front axle differential 19, the angle drive 23, the front axle locking clutch 53, the center locking clutch 55, the center differential 13, the center clutch 15, the spur gear stage 5, and the transmission 3 are compactly combined in a common transmission housing to form a front axle transmission unit 10, as shown in Figure 1. The clutches 53, 55, 15, and optionally the transmission 3, can be actuated centrally by a shift system (not shown). Similarly, at the rear axle, the rear axle differential 47, the rear axle disconnect clutch 49, the rear axle locking clutch 57, and the angle drive 41 are combined to form a rear axle transmission unit 50.

[0035] The vehicle can be operated in the following operating modes: The front-wheel drive is activated in an energy-saving efficiency mode. In this mode, only the center locking clutch 55 is engaged, while all other clutches are disengaged. In this way, the drive torque generated in the electric motor 1 is transmitted via the transmission 16, the spur gear stage 5, and the differential housing 11 of the center differential 13 to the pinion shaft 21 leading to the front axle differential 19. Due to the disengaged center clutch 15 and the disengaged rear axle disconnect clutch 59, a section of the drive train between the center clutch 15 and the rear axle differential 47 is deactivated in the front-wheel drive mode. This includes, in particular, the driveshaft 39, the angle drive 41, and the differential housing 45 of the rear axle differential 47, while the differential gears in the rear axle differential 47 rotate without load.

[0036] The center locking clutch 55 therefore acts in a dual function in front-wheel drive, on the one hand for torque transmission, and on the other hand as a differential lock during all-wheel drive.

[0037] A change from front-wheel drive to all-wheel drive with the rear axle engaged is performed as follows: First, the rear axle locking clutch 57 is engaged. This initiates a synchronization process in which the driveshaft 39 is accelerated to a speed corresponding to the vehicle speed. This synchronizes the clutch half of the center clutch 15 connected to the driveshaft 39 with the speed of the clutch half connected to the input shaft 17. After the synchronization process is complete, the center clutch 15 is engaged and the rear axle disconnect clutch 59 is engaged in any desired sequence. With both the center clutch 15 and the rear axle disconnect clutch 59 engaged, the rear axle locking clutch 57 is disengaged.To compensate for subsequent differences in rotational speed between the front and rear axles, the center locking clutch 55 is also opened. Since this process may occur under load, the center locking clutch 55 is implemented as a multi-plate clutch. Implementing the center locking clutch 55 as a dog clutch would, on the other hand, result in a loss of comfort.

[0038] The all-wheel drive system can be divided into on-road and off-road modes. In on-road mode, the rear axle locking clutch 57 and the center locking clutch 55 can be opened and closed with slip control for a driving dynamics setting, while the center clutch 15 and the rear axle disconnect clutch 59 are permanently closed, and the front axle locking clutch 53 is permanently open.

[0039] Off-road operation is identical to on-road operation, except that the front axle locking clutch 53 is engaged without load before starting off-road operation. The front axle locking clutch 53 is only required in the engaged position in extreme off-road driving situations.

[0040] Therefore, the three locking clutches 53, 55, 57 provide off-road functionality in which all differentials 13, 19 and 47 can be bridged.

[0041] In on-road operation, the differential locks are not required. In this case, from a driving dynamics perspective, it is advantageous if the center locking clutch 55 and the rear axle locking clutch 57 are opened and / or closed in a slip-controlled manner, thus allowing for a small degree of control over torque transmission.

[0042] The switch from all-wheel drive to front-wheel drive is carried out as follows: First, the center locking clutch 55 is engaged to transmit torque from the electric motor 1 to the front axle by bypassing the center differential 13. Then, the center clutch 15 and the rear axle disconnect clutch 59 are disengaged to deactivate the section of the drive train between the center clutch 15 and the rear axle differential 47.

[0043] In Figure 2 In a further embodiment, a drive train in a two-track vehicle is shown. The design and functionality of the drive train are essentially identical to the design and functionality of the one in the Figure 1 shown powertrain. In contrast to the Figure 1 is in the Figure 2The electric motor 1 and the front axle transmission unit 10 are not mounted longitudinally, but transversely in the vehicle direction. A further angle drive 61 is engaged between the center clutch 15 and the cardan shaft 39. In addition, the drive shaft 21 leading to the front axle drives – unlike the Figure 1 - not via a bevel gear, but via a spur gear stage 61 to the front axle differential 19. REFERENCE MARK LIST:

[0044] 1 Electric motor 3 Manual transmission 5 Spur gear stage 7, 9 Gears 10 Transmission housing 11 Differential basket 13 Center differential 15 Center clutch 17 Intermediate shaft 19 Front axle differential 21 Pinion shaft 23 Bevel gear 25 Ring gear - front axle differential 27 Differential basket - front axle 29 Axle bevel gears 31 Differential gears 33 Front axle drive shafts 35 Front wheels 39 Cardan shaft 41 Bevel gear 43 Ring gear - rear axle differential 45 Differential basket 47 Rear axle differential 49 Rear axle drive shafts 50 Rear axle transmission unit 51 Rear wheels 53 Front axle limited-slip clutch 55 Center limited-slip clutch 57 Rear axle limited-slip clutch 59 Rear axle disconnect clutch 60 Angle drive 61 Spur gear stage FR Direction of travel

Claims

1. All-wheel drive vehicle, the drivetrain of which has precisely one electric machine (1) which, in a front-wheel drive, only drives the front axle of the vehicle, wherein the electric machine (1) is couplable via a centre differential (13) and a centre clutch (15) to a cardan shaft (39), which is connectable in terms of drive to rear wheels (51) of the vehicle via a rear axle differential (47) and via propeller shafts (49), and wherein the rear axle is decoupled from the drivetrain when the centre clutch (15) is open and the rear axle is connected to the drivetrain when the centre clutch (15) is closed, wherein a rear axle separating clutch (59) is installed in one of the propeller shafts (49) of the rear axle, wherein, in the front-wheel drive, that is, with the centre clutch (15) open, the rear axle separating clutch (59) is opened, as a result of which a train section between the centre clutch (15) and the rear axle differential (47) is immobilized, wherein a change from the front-wheel drive to the all-wheel drive during the driving mode can be carried out without interruption of tractive force, and wherein, for the change from the front-wheel drive to the all-wheel drive, the centre clutch (15) can be closed, characterized in that the rear axle differential (47) is lockable via a rear axle locking clutch (57) as a powershiftable multi-plate clutch, and in that the rear axle locking clutch (57) acts in dual function as a synchronizing clutch, by means of which, before the centre clutch (15) is closed, a synchronizing operation takes place in which the cardan shaft (39) is accelerated to a rotational speed correlating with the vehicle speed such that the coupling half of the centre clutch (15) connected to the cardan shaft (39) can be synchronized with the rotational speed of the coupling half of the centre clutch (15) connected to the centre differential (13).

2. Vehicle according to Claim 1, characterized in that, when the locking function is activated, a differential cage (45) of the rear axle differential (47) is coupled to one of the rear axle propeller shafts (49) to form a rear axle differential lock.

3. Vehicle according to Claim 1 or 2, characterized in that, after the synchronizing operation has been carried out, in an arbitrary shift sequence the centre clutch (15) closes and the rear axle separating clutch (59) closes, and in that, in particular when the centre clutch (15) is closed and the rear axle separating clutch (59) is closed, the rear axle locking clutch (57) opens and / or the centre locking clutch (55) opens.

4. Vehicle according to any one of the preceding claims, characterized in that the centre differential (13) on its output sides has an intermediate shaft (17) leading to the rear of the vehicle to the centre clutch (15) and a pinion shaft (21) leading to the front of the vehicle to a front axle differential (19), and in that, in particular, the pinion shaft (21) is connected in terms of drive via the front axle differential (19) and via front axle propeller shafts (33) to front wheels (35) of the front axle, and in that, in particular, the centre differential (13) is lockable via a centre locking clutch (55), in particular a powershiftable multi-plate clutch, and in that, in particular when the locking function is activated, a differential cage (11) of the centre differential (13) is coupled to the drive shaft (21) leading to the front axle differential (19) to form a centre differential lock.

5. Vehicle according to Claim 4, characterized in that the centre locking clutch (55) acts in dual function not only as a differential lock, but, in the closed state, that is, in the front-wheel drive, ensures transmission of driving torque from the centre differential (13) to the front axle differential (19).

6. Vehicle according to any one of the preceding claims, characterized in that the electric machine (1) indirectly or directly drives a gearwheel (9) formed on the differential cage (11) of the centre differential (13), in particular by interconnecting a manual transmission (3) and / or a countershaft stage (5) for torque conversion, such as a spur gear stage.

7. Vehicle according to Claim 4, 5 or 6, characterized in that the front axle differential (19) is lockable via a front axle locking clutch (53), in particular a non-powershiftable dog clutch, and in that, when the locking function is activated, a differential cage (27) of the front axle differential (19) is coupled to a front axle propeller shaft (33) to form a front axle differential lock.

8. Vehicle according to any one of the preceding claims, characterized in that the front-wheel drive is activated in an energy-saving efficiency mode of the vehicle, and / or in that the all-wheel mode can be divided into an on-road mode and into an off-road mode.

9. Vehicle according to Claim 8, characterized in that, in the on-road mode, the rear axle locking clutch (57), which is in the form of a multi-plate clutch, and / or the centre locking clutch (55), which is in the form of a multi-plate clutch, are openable and closable in a slip-controlled manner for adjustment of the driving dynamics, while the centre clutch (15) and the rear axle separating clutch (59) are continuously closed and the front axle locking clutch (53) is open, and / or in that, in particular, the off-road mode is identical to the on-road mode, except that the front axle locking clutch (53) is closed.