Driveline and method of controlling a driveline

1. A motor vehicle driveline having:

at least first and second groups of one or more wheels; and

control means,

the driveline being operable by means of the control means to connect a torque transmission path from prime mover means to the first and second groups of one or more wheels such that the first group of one or more wheels and not the second group is coupled to the torque transmission path when the driveline is in a first mode of operation and both the first and second groups of one or more wheels are coupled to the torque transmission path when the driveline is in a second mode of operation,

the driveline being operable to connect the second group to the torque transmission path by an auxiliary portion comprising first and second releasable torque transmitting means and a prop shaft, the first releasable torque transmitting means being operable to connect a first end of the prop shaft to the torque transmission path from the prime mover means, the second releasable torque transmitting means being operable to connect a second end of the prop shaft to the second group of one or more wheels,

when the driveline is in the first mode the control means being configured to cause the driveline to transition to the second mode when one or more of a plurality of trigger conditions is met, each of the trigger conditions being met when an instant value of a vehicle operating parameter exceeds a respective threshold value, each respective threshold value being determined by the control means at least in part in dependence on a speed value corresponding to vehicle speed.

2. A driveline according to claim 1 , wherein each trigger condition has a respective identity, the control means being configured to control the driveline to transition from the first mode to the second mode at a prescribed connect rate.

3. A driveline according to claim 2 , wherein the connect rate is determined in dependence at least in part on the identity of the trigger condition that is met.

4. A driveline according to claim 2 , wherein the connect rate is determined at least in part in dependence on the speed value.

5. A driveline according to claim 1 , wherein the one or more trigger conditions include a condition wherein an instantaneous amount of torque being delivered to one or more of the wheels is above a prescribed instantaneous torque threshold, the prescribed instantaneous torque threshold being determined at least in part in dependence on the speed value.

6. A driveline according to claim 1 , wherein the one or more trigger conditions include a condition wherein an instantaneous amount of torque developed by the prime mover means is above a prescribed instantaneous prime mover torque threshold, the prescribed instantaneous prime mover torque threshold being determined at least in part in dependence on the speed value.

7. A driveline according to claim 1 , wherein the one or more trigger conditions include a condition wherein a steering angle is above a prescribed steering angle threshold, the prescribed steering angle threshold being determined at least in part in dependence on the speed value.

8. A driveline according to claim 7 , wherein the one or more trigger conditions include a condition wherein a rate of change of steering angle exceeds a steering angle rate threshold, the steering angle rate threshold being determined at least in part in dependence on the speed value.

9. A driveline according to claim 8 , wherein the one or more trigger conditions include a condition wherein steering angle and rate of change of steering angle exceed respective threshold values.

10. A driveline according to claim 1 , wherein the one or more trigger conditions includes a condition wherein an amount of slip of one or more wheels exceeds a prescribed slip threshold, the prescribed slip threshold being determined at least in part in dependence on the speed value.

11. A driveline according to claim 1 , wherein the one or more trigger conditions include a condition wherein an instantaneous amount of lateral acceleration is above a prescribed instantaneous lateral acceleration threshold, the prescribed instantaneous lateral acceleration threshold being determined at least in part in dependence on the speed value.

12. A driveline according to claim 1 , wherein the one or more trigger conditions include a condition wherein a throttle or accelerator pedal position value is above a prescribed pedal position threshold, the prescribed pedal position threshold being determined at least in part in dependence on the speed value.

13. A driveline according to claim 1 , wherein the control means is configured to cause the prop shaft to be disconnected from both the torque transmission path from the prime mover means and said second group of one or more wheels when the driveline is in the first mode.

14. A driveline according to claim 1 , wherein the prime mover means comprises at least one of an engine and an electric machine.

15. A driveline according to claim 1 , wherein the prime mover means comprises an engine and an electric machine.

16. A vehicle comprising a driveline according to claim 1 .

17. A vehicle according to claim 16 , wherein the control means is configured to control the vehicle to operate in a selected one of a plurality of driving modes in each of which one or more vehicle sub-systems are operated in a prescribed one of a plurality of respective configurations.

18. A vehicle according to claim 17 , wherein the one or more trigger conditions are determined at least in part in dependence on the selected driving mode.

19. A method of operating a motor vehicle driveline comprising:

causing by means of control means a torque transmission path from prime mover means to be connected to first and second groups of one or more wheels such that the first group of one or more wheels and not the second group is coupled to the torque transmission path when the driveline is in a first mode of operation and both the first and second groups of one or more wheels are coupled to the torque transmission path when the driveline is in a second mode of operation;

connecting the second group to the torque transmission path by means of an auxiliary portion of the driveline, the auxiliary portion comprising first and second releasable torque transmitting means and a prop shaft, the first releasable torque transmitting means being operable to connect a first end of the prop shaft to the torque transmission path from the prime mover means, the second releasable torque transmitting means being operable to connect a second end of the prop shaft to the second group of one or more wheels; and

when the driveline is in the first mode, causing the driveline to transition to the second mode when one or more of a plurality of trigger conditions is met, each of the trigger conditions being met when an instant value of a vehicle operating parameter exceeds a respective threshold value, each respective threshold value being determined by the control means at least in part in dependence on a speed value corresponding to vehicle speed.

20. A motor vehicle driveline having:

at least first and second groups of one or more wheels; and

control means,

the driveline being operable by means of the control means to connect a torque transmission path from prime mover means to the first and second groups of one or more wheels such that the first group of one or more wheels and not the second group is coupled to the torque transmission path when the driveline is in a first mode of operation and both the first and second groups of one or more wheels are coupled to the torque transmission path when the driveline is in a second mode of operation,

the driveline being operable to connect the second group to the torque transmission path by means of an auxiliary portion comprising first and second releasable torque transmitting means and a prop shaft, the first releasable torque transmitting means being operable to connect a first end of the prop shaft to the torque transmission path from the prime mover means, the second releasable torque transmitting means being operable to connect a second end of the prop shaft to the second group of one or more wheels,

when the driveline is in the first mode the control means being operable to cause the driveline to transition to the second mode when one or more of a plurality of trigger conditions is met, each of the trigger conditions being met when an instant value of a vehicle operating parameter exceeds a respective threshold value, each respective threshold value being determined by the control means at least in part in dependence on a vehicle speed or a speed of the driveline.

21. A method of operating a motor vehicle driveline comprising:

causing by means of control means a torque transmission path from prime mover means to be connected to first and second groups of one or more wheels such that the first group of one or more wheels and not the second group is coupled to the torque transmission path when the driveline is in a first mode of operation and both the first and second groups of one or more wheels are coupled to the torque transmission path when the driveline is in a second mode of operation;

connecting the second group to the torque transmission path by means of an auxiliary portion of the driveline, the auxiliary portion comprising first and second releasable torque transmitting means and a prop shaft, the first releasable torque transmitting means being operable to connect a first end of the prop shaft to the torque transmission path from the prime mover means, the second releasable torque transmitting means being operable to connect a second end of the prop shaft to the second group of one or more wheels; and

when the driveline is in the first mode causing the driveline to transition to the second mode when one or more of a plurality of trigger conditions is met, each of the trigger conditions being met when an instant value of a vehicle operating parameter exceeds a respective threshold value, each respective threshold value being determined by the control means at least in part in dependence on a vehicle speed or a speed of the driveline.