Method for operating a drive device for a motor vehicle and corresponding drive device

Abstract

A method for operating a drive device for a motor vehicle includes: during a coasting operation of the motor vehicle in which a shifting clutch is open and the internal combustion engine stands still starting the internal combustion engine in a first operating mode with the electric machine and in a second operating mode by at least partially closing the shifting clutch with a coupling torque set at the shifting clutch, thereby operatively connecting the internal combustion engine with at least one wheel, wherein the internal combustion engine is started in the first operating mode when a predictively determined wheel slip predictive value exceeds a wheel slip setpoint value, and wherein when the internal combustion engine is started in the second operating mode the electric machine is used for starting the internal combustion engine and for driving the at least one wheel when a wheel slip actual value exceeds the wheel slip setpoint value.

Claims

1. A method for operating a drive device for a motor vehicle, said method comprising: during a coasting operation of the motor vehicle in which a shifting clutch is open and the internal combustion engine stands still starting the internal combustion engine in a first operating mode with the electric machine and in a second operating mode by at least partially closing the shifting clutch with a coupling torque set at the shifting clutch, thereby operatively connecting the internal combustion engine with at least one wheel, wherein the internal combustion engine is started in the first operating mode when a predictively determined wheel slip predictive value exceeds a wheel slip setpoint value, and wherein when the internal combustion engine is started in the second operating mode the electric machine is used for starting the internal combustion engine and for driving the at least one wheel when a wheel slip actual value exceeds the wheel slip setpoint value.

2. The method of claim 1, wherein the wheel slip setpoint value is one of an absolute value, a relative value with respect to a starting value and a differential value.

3. The method of claim 1, further comprising after starting the internal combustion engine in the first operating mode at least partially closing the shifting clutch, to drive the at least one wheel.

4. The method of claim 3, wherein after starting the internal combustion engine in the first operating mode the shifting clutch is closed completely to drive the at least one wheel.

5. The method of claim 1, further comprising determining the coupling torque by taking a wheel slip actual value into account, said wheel slip actual value being determined based on at least one of the measured wheel slip of the at least one wheel and the calculated wheel slip of the at least one wheel.

6. The method of claim 1, wherein the wheel slip actual value is determined from a wheel slip of multiple wheels of the motor vehicle.

7. The method of claim 6, wherein the wheel slip actual value is determined from the wheel slip of the multiple wheels of the motor vehicle by one of weighted average formation, differential formation, sum formation and ratio formation.

8. The method of claim 5, wherein the wheel slip is determined while a coupling torque, which is different from zero is transmitted via the shifting clutch.

9. The method of claim 1, further comprising increasing the coupling torque increased when the wheel slip actual value is greater than the wheel slip setpoint value to drive the wheel by means of the electric machine.

10. The method of claim 1, further comprising controlling the wheel slip actual value by open loop or closed loop control to the wheel slip setpoint value or in the direction of the wheel slip setpoint value by adjusting the coupling torque.

11. The method of claim 1, wherein a torque provided by the electric machine in the second operating mode is selected so that said torque provided by the electric machine is greater than the coupling torque and a starting torque required for starting the internal combustion engine.

12. A drive device for a motor vehicle, comprising: an internal combustion engine; a shifting clutch adapted for operatively connecting the internal combustion engine with at least one wheel of the motor vehicle, and an electric machine for starting the internal combustion engine, wherein the drive device is configured to start the internal combustion engine during a coasting operation of the motor vehicle in which a shifting clutch is open and the internal combustion engine stands still, in a first operating mode with the electric machine and in a second operating mode by at least partially closing the shifting clutch with a coupling torque set at the shifting clutch, thereby operatively connecting the internal combustion engine with at least one wheel, to start the internal combustion engine in the first operating mode when a predictively determined wheel slip predictive value exceeds a wheel slip setpoint value, and when the internal combustion engine is started in the second operating mode to operate the electric machine for starting the internal combustion engine and for driving the at least one wheel when a wheel slip actual value exceeds the wheel slip setpoint value.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which the sole FIGURE shows a schematic representation of a chassis of a motor vehicle

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(2) Throughout all the Figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.

(3) The FIGURE shows a region of a motor vehicle 1, in particular a region of a chassis of the motor vehicle 1. The motor vehicle 1 has a drive device 2 for providing a drive torque for at least one wheel axle 3 at which in the here shown exemplary embodiment two wheels 4 are provided. The wheels 4 are each operatively connected with a differential transmission 6 via a subaxle 5, in particular an axle differential transmission. The subaxles 5 thus represent output shafts of the differential transmission 6. An input shaft 7 of the differential transmission 6 is connected to a switching transmission 8. By means of the switching transmission 8 different transmission ratios between the drive device 2 and the differential transmission 6 or its input shaft 7 can be set.

(4) The drive device 2 has an internal combustion engine 9 and an electric machine 10. The electric machine 10 is for example configured as a starter or a starter generator. It can be or is operatively connected with the internal combustion engine 9 permanently or via a clutch. The internal combustion engine 9 can be operatively connected with the shifting transmission 8 and thus with the wheels 4 via a shifting clutch 11 of the drive device 2. The wheels are insofar drivable or driven wheels or are provided on a drivable axle. Beside the wheels 4 of course at least another wheel, in particular multiple wheels that are assigned to a further axle can be present. These wheels can be configured as non-driven wheels or the further axle can be configured as a non-driven axle. As an alternative of course a drive aggregate for example an electric machine can be assigned to the at least one further wheel.

(5) When the internal combustion engine 9 is at standstill, for example during a coasting operation of the motor vehicle 1, the shifting clutch 11 is open, in particular completely open, so that an operative connection between the internal combustion engine 9 and the wheels is completely interrupted. In order to switch from the coasting operation into a normal operation in which the internal combustion engine 9 is in operation and hereby has a rotational speed, which at least corresponds to the idling speed of the internal combustion engine 9, the internal combustion engine 9 has to be dragged out of the standstill to a defined rotational speed.

(6) This can be provided by means of the electric machine 10. As an alternative the shifting clutch 1 can be at least partially closed in order to transmit a coupling torque from the wheels 4 via the shifting clutch 11 to the internal combustion engine 9. The latter is preferred because the energy required for starting the internal combustion engine 9 is withdrawn from the kinetic energy of the driving motor vehicle 1. On the other hand an operation of the electric machine 10 while withdrawing electrical energy for example from the energy storage of the motor vehicle 1 is not required, may however be performed optionally. On the shifting clutch 11 a coupling torque for starting the internal combustion engine 9 is set which is to be transmitted via the shifting clutch 11. Correspondingly the shifting clutch 11 is at least partially closed in order to start the internal combustion engine 9.

(7) It is provided to perform a first operating mode when a predictively determined wheel slip predictive value exceeds a wheel slip setpoint value. When this is not the case a second operating mode can be performed. In the first operating mode the internal combustion engine 9 is started by means of the electric machine 10, in particular solely by means of the electric machine 10, wherein the shifting clutch 11 is completely open. In the second operating mode on the other hand the internal combustion engine 9 is driven by partially closing the shifting clutch 11 and is thus started. The wheel slip setpoint value is hereby a threshold value for a wheel slip actual value, which is present between at least one of the wheels 4 or both wheels 4 and aground of the motor vehicle 1. The wheel slip setpoint value is for example different for different motor vehicle state variables. The motor vehicle state variables may for example include an actual yaw rate of the motor vehicle 1, a setpoint yaw rate, a yaw rate difference between the actual yaw rate and the setpoint yaw rate, a rolling speed, an acceleration, in particular a longitudinal acceleration or a transverse acceleration or a trailer coupling state.

(8) In the second operating mode the electric machine 10 is first deactivated, i.e., it does not generate a torque for driving the internal combustion engine 9. However when during the stating of the internal combustion engine 9 by means of the electric machine 10 in the second operating mode it is determined that a wheel slip exceeds the wheel slip setpoint value the electric machine 10 is additionally operated in order to start the internal combustion engine 9 and to drive the wheels 4 or at least one of the wheels 4. This allows supporting the driving operation of the motor vehicle 1 also when the shifting clutch 11 is at least partially closed during the second operating mode.

(9) With the described configuration of the drive device 2 or the motor vehicle 1 and the explained approach an energy efficient starting of the internal combustion engine 9 can be achieved, while at the same time ensuring a safe driving of the motor vehicle 1. The driving operation is also not adversely influenced when the motor vehicle 1 or its wheels 4 are on a ground with low friction value.

(10) What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: