METHOD FOR OPERATING A DRIVETRAIN OF A MOTOR VEHICLE, AND DRIVETRAIN FOR A MOTOR VEHICLE

Abstract

A method for operating a drivetrain of a motor vehicle comprising an engageable and disengageable four-wheel drive and at least two intermeshing gears, in which the four-wheel drive is switched off by the opening of at least one clutch of the drivetrain, wherein a change of engagement of the gears resulting from the switching off is actively braked by an electric machine of the drivetrain.

Claims

1-6. (canceled)

7. A method for operating a drivetrain of a motor vehicle comprising: an engageable and disengageable four-wheel drive and at least two intermeshing gears, in which the four-wheel drive is switched off by the opening of at least one clutch of the drivetrain, wherein a change of engagement of the gears resulting from the switching off is actively braked by means of an electric machine of the drivetrain.

8. The method according to claim 7, wherein the drivetrain comprises at least one drive motor different from the electric machine, a first axle drivable by the drive motor and a second axle drivable by the drive motor across the clutch, which is decoupled upon switching off the four-wheel drive from the drive motor.

9. The method according to claim 8, wherein the drivetrain comprises at least one transmission, across which the axles are drivable by the drive motor.

10. The method according to claim 9, wherein a traction operation of the transmission is carried out for the braking of the change of engagement by means of the electric machine.

11. The method according to claim 10, wherein the electric machine provides at least one torque to bring about the traction operation of the transmission, which is introduced into the transmission by the electric machine.

12. A drivetrain for a motor vehicle comprising: an engageable and disengageable four-wheel drive, with at least two intermeshing gears and with at least one clutch, which can be switched from a closed state to an opened state in order to switch off the four-wheel drive, wherein the drivetrain comprises at least one electric machine, which is adapted to actively brake a change of engagement of the gears resulting from the switching off.

Description

[0025] The drawing shows in the single FIGURE a schematic representation of a drivetrain according to the invention for a motor vehicle, the drivetrain being designed to carry out the method according to the invention.

[0026] The single FIGURE shows in a schematic representation a drivetrain for a motor vehicle designed as a passenger car, for example, being denoted overall by reference number 10. The drivetrain 10 comprises a clutch 12, for example one designed as a frictional clutch, especially a multi-plate clutch, which is also known as an all-wheel clutch. Furthermore, the drivetrain 10 comprises at least two intermeshing gears 14 and 16, shown in particular schematically in the FIGURE. The gears 14 and 16 have respective toothings which engage with each other. In this way, the gears 14 and 16 interact by form fitting, so that for examples torques can be transmitted from one of the gears 14 and 16 to the other respective gear 16 or 14 and vice versa. The drivetrain 10 moreover comprises an engageable and disengageable four-wheel drive 18. In order to switch on and thus activate the at first switched off and thus deactivated four-wheel drive 18, for example, the clutch 12 is shifted for example from an opened to a closed state. In order to switch off and thus activate the at first switched on and thus activated four-wheel drive 18, for example, the clutch 12 is shifted for example from its closed state to its opened state. The shifting of the clutch 12 from the opened state to the closed state is also known as a closing of the clutch 12, while the shifting of the clutch 12 from the closed state to the opened state is also known as an opening of the clutch 12.

[0027] In the following, a method for operating the drivetrain 10 will be explained with the aid of the FIGURE. In the method, the at first switched on four-wheel drive 18 is switched off by opening at least the clutch 12, also known as the all-wheel clutch.

[0028] Now, in order to realize an especially comfortable operation of the drivetrain 10 and thus of the motor vehicle as a whole, it is proposed in the method that a change of engagement of the gears 14 and 16 resulting from the switching off of the four-wheel drive 18 is actively braked and thus dampened by means of an electric machine 20 of the drivetrain 10. In this way, excessive noise resulting from the change of engagement can be avoided, so that an especially good ride comfort can be achieved.

[0029] It can be seen from the FIGURE that the drivetrain 10 comprises at least one additionally provided drive motor 22, different from the electric machine, which in the present instance is designed as an internal combustion engine or a combustion engine. Alternatively, it is conceivable for the drive motor 22 to be designed as a further electric machine. The drive motor 22 designed in the present case as a combustion engine comprises a cylinder housing 24, by which multiple combustion chambers in the form of cylinders 26 are formed. The drive motor 22 comprises an output shaft 28, which is designed for example as a crankshaft. The drive motor 22 may provide torques for the driving of the motor vehicle across the output shaft, especially in a traction operation of the drive motor 22, these torques being known as driving torques or driving moments for the driving of the motor vehicle.

[0030] The drivetrain 10 moreover comprises a transmission 30, known as the main transmission, comprising for example the gears 14 and 16. The transmission 30 here comprises a transmission input shaft 32, which is drivable for example across a starting element 35 by the output shaft 28 and thus by the drive motor 22. The starting element 35 is designed for example as a friction-locking clutch and thus as a friction clutch or separating clutch. Moreover, the transmission 30 comprises a transmission output shaft 34, by which the transmission 30 can provide torques for the driving of the motor vehicle. The transmission output shaft 34 is thus drivable by the transmission input shaft 32 and across this and across the starting element 35 by the output shaft 28. For example, the clutch 12 is drivable by the transmission output shaft 34, so that the clutch 12 is itself drivable across the transmission output shaft 34, the transmission input shaft 32 and the starting element 35 by the output shaft 28 and thus by the drive motor 22. In other words, the driving torques provided by the drive motor 22 across the output shaft 28 are channeled across the output shaft 28, the starting element 35, the transmission input shaft 32 and the transmission output shaft 34 into the clutch 12.

[0031] The drivetrain 10 moreover comprises a first axle, designed as a front axle 36, which is also known as the primary axle, and having first wheels in the form of front wheels 38 and 40. The front wheels 38 and 40 are drivable across the transmission 30 by the drive motor 22, especially bypassing the clutch 12. The front axle 36 comprises an axle transmission 42, in addition to and different from the transmission 30, which is also known as the front axle transmission and is designed as a differential, especially a bevel gear differential transmission.

[0032] Furthermore, the drivetrain 10 comprises a second axle in the form of a rear axle 44, having second wheels in the form of rear wheels 46 and 48. The rear axle 44 comprises a second axle transmission 50, in addition to and different from the transmission 30 and the axle transmission 42, which is also known as the rear axle transmission and is designed for example as a differential, especially a bevel gear differential transmission.

[0033] The front wheels 38 and 40 are drivable across the axle transmission 42 and the main transmission by the drive motor 22. The rear wheels 46 and 48 are drivable across the axle transmission 50, the clutch 12 and the main transmission by the drive motor 22. If the four-wheel drive 18 is switched off by opening the clutch 12, the rear axle 44 and hence the rear wheels 46 and 48 are decoupled from the drive motor 22, while the front axle 36 and hence the front wheels 38 and 40 are coupled to the drive motor 22. In this way, when the drive motor 22 is providing driving torques, only the front wheels 38 and 40 but not the rear wheels 46 and 48 of the four wheels are driven, so that the drivetrain 10 is operated in a two-wheel mode. But if the four-wheel drive 18 is switched on by closing the clutch 12, then when the drive motor 22 is providing driving torques both the front wheels 38 and 40 and the rear wheels 46 and 48 are driven, so that the drivetrain 10 is operated in a four-wheel operation. Since the drivetrain 10 in the exemplary embodiment shown in the FIGURE has only the four wheels, the four-wheel drive 18 is an all-wheel drive, so that the four-wheel operation is an all-wheel operation.

[0034] Hence, if the clutch 12 is opened, the rear wheels 46 and 48 will be decoupled from the drive motor 22. Hence, the clutch 12 is utilized to create a first separation point T1.

[0035] In order to realize a second, rear separation point T2 with respect to the first separation point T1, a form-fitting coupling device is used, designed in the present case as a claw clutch 52. The claw clutch 52 is optionally provided and could be omitted. The claw clutch 52 can be moved between at least one decoupling position and at least one coupling position. In the decoupling position, a flow of force in the drivetrain 10 is interrupted at the second separation point T2. In the coupling position, the flow of force in the drivetrain 10 is closed in form-fitting manner by means of the claw clutch 52 at the second separation point T2. In the coupling position, the rear wheels 46 and 48 are coupled by the claw clutch 52 in form fitting manner with a shaft of the drivetrain 10, designed as a Cardan shaft 54, while the Cardan shaft 54 is or can be driven by the drive motor 22 across the clutch 12 and the transmission 30 when the clutch 12 is closed and the drive motor 22 is providing driving torques. Hence, if the claw clutch 52 is closed, the rear wheels 46 and 48 can be driven in form fitting by the Cardan shaft 54, especially when the Cardan shaft 54 is driven. In the decoupling position, however, the rear wheels 46 and 48 are decoupled from the Cardan shaft 54, by which is meant that in the decoupling position of the claw clutch 52 the rear wheels 46 and 48 are not coupled across the claw clutch 52 with the Cardan shaft 54. Hence, in the decoupling position of the claw clutch 52 the rear wheels 46 and 48 are not driven across the claw clutch 52 by the Cardan shaft 54 and vice versa.

[0036] Preferably, if the four-wheel drive 18 is switched off, both the clutch 12 and the claw clutch 52 are opened, so that the Cardan shaft 54 is stationary and driven neither by the rear wheels 46 and 48 nor by the drive motor 22. In this way, an especially efficient two-wheel operation can be achieved.

[0037] The electric machine 20, especially its rotor, is coupled for example with the transmission output shaft 34, especially across an optionally provided spur gear state 56. The electric machine 20 for example can be operated in a motor mode and thus as an electric motor and/or in a generator mode and thus as a generator. In the motor mode, the electric machine 20 can provide torques, for example, by means of which the wheels can be driven, especially depending on whether the four-wheel drive 18 is switched on or switched off. When the four-wheel drive 18 is switched on, the electric machine 20 can drive the front wheels 38 and 40 and the rear wheels 46 and 48, while the electric machine 20 when the four-wheel drive 18 is switched off can only drive the front wheels 38 and 40. The electric machine 20 is thus a drive motor provided in addition to the drive motor 22, for example, by means of which the wheels can be electrically driven. Hence, the motor vehicle is designed for example as a hybrid vehicle.

[0038] Furthermore, respective rotational speed sensors are provided, by means of which respective rotational speeds of the front wheels 38 and 40, the output shaft 28, the electric machine 20, especially the rotor of the electric machine 20, the Cardan shaft 54, the rear wheels 46 and 48 and for example a rotational speed of a side shaft or a ring gear of the axle transmission 50 can be detected. Moreover, a rotational speed sensor is provided for example for detecting a rotational speed of the transmission 30, the rotational speed of the transmission 30 being a rotational speed of the transmission input shaft 32 or the transmission output shaft 34. The notations in the FIGURE are: [0039] n.sub.VL the rotational speed of the front wheel 38 [0040] n.sub.M the rotational speed of the output shaft 28 [0041] n.sub.VR the rotational speed of the front wheel 40 [0042] n.sub.G the rotational speed of the transmission 30 [0043] n.sub.E the rotational speed of the electric machine 20, especially its rotor [0044] n.sub.K the rotational speed of the Cardan shaft 54 [0045] n.sub.HL the rotational speed of the rear wheel 46 [0046] n.sub.HR the rotational speed of the rear wheel 48 [0047] n.sub.HW the rotational speed of the side shaft or ring gear

[0048] In the process of switching off the four-wheel drive 18, the rear axle 44 is decoupled from the drive motor 22 by opening the clutch 12 and optionally the claw clutch 52. For example, a traction operation of the transmission 30 is produced for the braking of the change of engagement of the gears 14 and 16 by means of the electric machine 20, especially by operating the electric machine 20 as an electric motor and thus providing at least one torque, which is channeled from the electric machine 20, especially from its rotor, into the transmission 30. In particular, the change of engagement is braked in dependence on at least one of the mentioned rotational speeds so that the electric machine 20 is operated and in particular controlled or regulated for the braking of the change of engagement in dependence on the at least one rotational speed.

[0049] Since the electric machine 20 is utilized to brake the change of engagement, additional and separate components such as dampening and frictional elements for the dampening of the change of engagement can be avoided, so that the number of parts, the weight, and the costs of the drivetrain 10 can be kept within an especially low range. Furthermore, the costs, the weight, and the design space requirement of the drivetrain 10 can be kept especially low, since the electric machine 20 takes on a dual function. On the one hand, the electric machine 20 is utilized for the electrical driving of the wheels. On the one hand, the electric machine 20 is utilized for the specific and hence active braking of the change of engagement, so that an especially good ride comfort can be achieved.