Method and system for operating a drive train of a motor vehicle

1. A method for operating a drive train of a motor vehicle, comprising the steps of:

detecting at least one variable quantifying or influencing a movement of the motor vehicle;

estimating based on the at least one variable whether or not a relevant driving situation is imminent, wherein a relevant driving situation is to be understood as a driving situation where a deviation between an actual driving behavior of the motor vehicle and a driving behavior predetermined by a driver can be expected, or as every situation where a different driving behavior between single-axle operation and all-wheel drive operation discernible by the driver exists;

detecting with environmental sensors of the motor vehicle or with a navigation device of the motor vehicle a roadway section located in the direction of travel in front of the motor vehicle;

checking whether the roadway section has a curve with a radius of curvature that is smaller than a predetermined radius of curvature, and

switching on an all-wheel drive of the motor vehicle as a function of the at least one variable prior to an occurrence of the relevant driving situation and before passing the roadway section.

2. The method of claim 1 , further comprising

for estimating whether the relevant driving situation is imminent, checking whether a torque available on a permanently driven primary axle of the motor vehicle is greater than a maximum torque transferable at the primary axle to the road surface, and

when this is the case, estimating whether a driver is expected to request a portion of the available torque greater than the transferable torque, and

when the driver is expected to request such greater portion, switching the all-wheel drive on.

3. The method of claim 2 , wherein the maximum torque transferable at the primary axle to the road surface is determined based on a coefficient of friction, a wheel load acting on wheels of the primary axle and a lateral force acting on the wheels of the primary axle.

4. The method of claim 1 , wherein the at least one variable comprises a variable selected from a lateral acceleration, a target yaw rate and a velocity of the motor vehicle, the method further comprising

checking based on the at least one selected variable in combination with an estimated driving behavior of the driver, whether a relevant driving situation can be expected, and

when this is the case, switching the all-wheel drive on.

5. The method of claim 4 , wherein the driving behavior of the driver is estimated by taking into account an activated mode of operation of the motor vehicle that influences a driving dynamics of the motor vehicle.

6. The method of claim 4 , wherein the estimated driving behavior of the driver and an actual driving behavior of the driver is continuously compared and used to estimate an overall driving behavior of the driver.

7. The method of claim 5 , further comprising

determining whether a predetermined threshold value for a slip at one of the wheels of the permanently driven primary axle of the motor vehicle is exceeded as a function of the activated mode of operation of the motor vehicle, and

when this is the case, switching the all-wheel drive on.

8. The method of claim 5 , further comprising

determining whether a predetermined threshold value for an oversteer and understeer of the motor vehicle that depends on the activated mode of operation of the motor vehicle is exceeded, and

when this is the case, switching the all-wheel drive on.

9. The method of claim 1 , further comprising

after the all-wheel drive is switched on, determining based on the least one variable or additional variables quantifying or influencing the movement of the motor vehicle whether switching off the all-wheel drive would cause a relevant driving situation, and

when this is not the case, switching the all-wheel drive off after a predetermined holding period.

10. The method of claim 9 , wherein the holding period is predetermined as a function of an activated mode of operation that influences the driving dynamics of the motor vehicle or as a function of an estimated driving behavior of the driver, or both.

11. The method of claim 1 , further comprising

monitoring a roadway section located below or in front of the motor vehicle with a detection device of the motor vehicle, and

determining therefrom a coefficient of friction of the roadway section.

12. The method of claim 11 , wherein the detection device is a multi-level laser scanner.

13. A method for operating a drive train of a motor vehicle, comprising the steps of:

detecting at least one variable quantifying or influencing a movement of the motor vehicle;

providing with one or more driver assistance systems of the motor vehicle a future acceleration or a future target radius of the motor vehicle,

estimating based on the at least one variable and the future acceleration or the future target radius whether or not a relevant driving situation is imminent, wherein a relevant driving situation is to be understood as a driving situation where a deviation between an actual driving behavior of the motor vehicle and a driving behavior predetermined by a driver can be expected, or as every situation where a different driving behavior between single-axle operation and all-wheel drive operation discernible by the driver exists, and

switching on an all-wheel drive of the motor vehicle prior to an occurrence of the relevant driving situation.

14. The method of claim 13 , further comprising

for estimating whether the relevant driving situation is imminent, checking whether a torque available on a permanently driven primary axle of the motor vehicle is greater than a maximum torque transferable at the primary axle to the road surface, and

when this is the case, estimating whether a driver is expected to request a portion of the available torque greater than the transferable torque, and

when the driver is expected to request such greater portion, switching the all-wheel drive on.

15. The method of claim 14 , wherein the maximum torque transferable at the primary axle to the road surface is determined based on a coefficient of friction, a wheel load acting on wheels of the primary axle and a lateral force acting on the wheels of the primary axle.

16. The method of claim 13 , wherein the at least one variable comprises a variable selected from a lateral acceleration, a target yaw rate and a velocity of the motor vehicle, the method further comprising

checking based on the at least one selected variable in combination with an estimated driving behavior of the driver, whether a relevant driving situation can be expected, and

when this is the case, switching the all-wheel drive on.

17. The method of claim 16 , wherein the driving behavior of the driver is estimated by taking into account an activated mode of operation of the motor vehicle that influences a driving dynamics of the motor vehicle.

18. The method of claim 16 , wherein the estimated driving behavior of the driver and an actual driving behavior of the driver is continuously compared and used to estimate an overall driving behavior of the driver.

19. The method of claim 17 , further comprising

determining whether a predetermined threshold value for a slip at one of the wheels of the permanently driven primary axle of the motor vehicle is exceeded as a function of the activated mode of operation of the motor vehicle, and

when this is the case, switching the all-wheel drive on.

20. The method of claim 17 , further comprising

determining whether a predetermined threshold value for an oversteer and understeer of the motor vehicle that depends on the activated mode of operation of the motor vehicle is exceeded, and

when this is the case, switching the all-wheel drive on.

21. The method of claim 13 , further comprising

after the all-wheel drive is switched on, determining based on the least one variable or additional variables quantifying and/or influencing the movement of the motor vehicle whether switching off the all-wheel drive would cause a relevant driving situation, and

when this is not the case, switching the all-wheel drive off after a predetermined holding period.

22. The method of claim 21 , wherein the holding period is predetermined as a function of an activated mode of operation that influences the driving dynamics of the motor vehicle or as a function of an estimated driving behavior of the driver, or both.

23. The method of claim 13 , further comprising

monitoring a roadway section located below or in front of the motor vehicle with a detection device of the motor vehicle, and

determining therefrom a coefficient of friction of the roadway section.

24. The method of claim 23 , wherein the detection device is a multi-level laser scanner.

25. A system for operating a drive train of a motor vehicle, comprising

a detection device configured to detect at least one variable quantifying or influencing a movement of the motor vehicle;

environmental sensors or a navigation device, or both, wherein the environmental sensors and the navigation device are configured to determine a roadway section located in the direction of travel in front of the motor vehicle, with the roadway section having a curve with a radius of curvature that is smaller than a predetermined radius of curvature; and

a controller configured to

estimate, based on the at least one variable whether a relevant driving situation is imminent, wherein a relevant driving situation is to be understood as a driving situation where a deviation between an actual driving behavior of the motor vehicle and a driving behavior predetermined by a driver can be expected, or as every situation where a different driving behavior between single-axle operation and all-wheel drive operation discernible by the driver exists, and to

switch on an all-wheel drive prior to an occurrence of the relevant driving situation and before passing the roadway section.

26. A system for operating a drive train of a motor vehicle, comprising

a detection device configured to detect at least one variable quantifying or influencing a movement of the motor vehicle;

a controller configured to

estimate, based on the at least one variable and by considering a future acceleration or a future target radius of the motor vehicle provided by one or more driver assistance systems of the motor vehicle, with which a semi-autonomous or an autonomous operation of the motor vehicle is enabled, whether a relevant driving situation is imminent, wherein a relevant driving situation is to be understood as a driving situation where a deviation between an actual driving behavior of the motor vehicle and a driving behavior predetermined by a driver can be expected, or as every situation where a different driving behavior between single-axle operation and all-wheel drive operation discernible by the driver exists, and to

switch on an all-wheel drive of the motor vehicle as a function of the at least one variable and only prior to an occurrence of the relevant driving situation.