Vehicle and method of controlling a vehicle

1. A vehicle comprising:

a prime mover;

a first group of one or more wheels;

a second group of two or more wheels; and

a driveline to connect the prime mover via a transmission to the first and second groups of wheels such that the first group of one or more wheels may be driven by the prime mover when the driveline is in a first mode of operation and the second group of wheels may additionally be driven by the prime mover when the driveline is in a second mode of operation,

the driveline including an auxiliary driveline comprising an auxiliary driveshaft and drive means between the auxiliary driveshaft and the second group of wheels,

wherein the drive means comprises:

a ring gear arranged to be driven by the auxiliary driveshaft;

an input portion;

a plurality of output portions each operable to drive a respective different wheel of the second group of wheels;

a differential arranged to enable the respective output portions of the drive means to rotate at different respective speeds;

a first releasable torque transmitting means operable releasably to connect the input portion of the drive means to the output portions of the drive means thereby to allow the input portion of the drive means to drive the output portions of the drive means, wherein the first releasable torque transmitting means is operable to enable slippage of the input portion of the drive means with respect to the output portions of the drive means thereby to vary an amount of torque that is transmitted from the input portion of the drive means to the output portions of the drive means; and

wherein the first releasable torque transmitting means is operable to enable the output portions of the drive means to rotate independent of the rotation of the ring gear thereby to enable the ring gear to be brought to rest when the driveline is in the first mode of operation; and

a locking clutch operable releasably to connect a cage of the differential to an output portion of the drive means thereby to couple rotation of the cage of the differential to rotation of the output portion of the drive means,

wherein the locking clutch and the first releasable torque transmitting means are respectively provided on opposite sides of the ring gear.

2. The vehicle of claim 1 wherein the first releasable torque transmitting means comprises friction clutch means.

3. The vehicle of claim 1 wherein the output portions of the drive means are arranged to provide torque to each one of a pair of side shafts of the vehicle, the side shafts being arranged to provide torque to respective different wheels of the second group of wheels.

4. The vehicle of claim 1 wherein the input portion of the locking clutch is coupled to the cage of the differential.

5. The vehicle of claim 4 wherein the output portion of the locking clutch is coupled to an output of the differential.

6. The vehicle of claim 1 wherein the locking clutch comprises friction clutch means.

7. The vehicle of claim 1 wherein the driveline includes a power transfer unit (PTU) operable releasably to connect the prime mover to the auxiliary drive shaft, the driveline being operable when in the first mode to allow the auxiliary drive shaft to come to rest when the prime mover is driving the first group of wheels.

8. The vehicle of claim 7 wherein at least a portion of the PTU is integrated into a housing of the transmission of the vehicle.

9. The vehicle of claim 7 wherein the PTU is arranged to be actuated by actuator means powered by a power supply of the transmission, optionally the power supply being arranged to provide one selected from amongst pressurised hydraulic fluid and electrical current.

10. The vehicle of claim 1 wherein the prime mover comprises first and second prime movers.

11. A method of controlling a driveline of a motor vehicle comprising the steps of:

driving a first group of one or more wheels of the driveline in a first mode of operation of the driveline; and

coupling an auxiliary portion of the driveline to a second group of two or more wheels and driving the second group of two or more wheels in addition to the first group in a second mode of operation of the driveline,

the step of coupling the auxiliary portion to the second group of wheels comprising:

coupling an auxiliary driveshaft of the auxiliary portion of the driveline to the second group of wheels by means of a first releasable torque transmitting means and a differential, the first releasable torque transmitting means being arranged to releasably couple a ring gear to a plurality of output portions of a drive means of the auxiliary driveline each arranged to drive different respective wheels of the second group of two or more wheels, the differential being arranged to allow at least two wheels of the second group of wheels to rotate at different respective speeds, and whereby coupling the auxiliary driveshaft to the second wheel group causes the ring gear to be driven by the auxiliary driveshaft;

the method comprising applying torque to an input portion of the first releasable torque transmitting means via the auxiliary driveshaft and the ring gear and controlling the first releasable torque transmitting means to vary the proportion of the torque applied to the portion of the first releasable torque transmitting means that is transmitted across the first releasable torque transmitting means to the output portions of the drive means,

the method further comprising controlling a locking clutch, disposed on the opposite side of the ring gear to the first releasable torque transmitting means, to releasably couple rotation of a cage of the differential to rotation of the output portions of the drive means.

12. The method of claim 11 comprising the step of varying the proportion of torque transmitted by the first releasable torque transmitting means to be one of a substantially continuous range of values between first and second values.

13. The method of claim 12 wherein the first value corresponds to substantially no torque transmitted between the input portion of the first releasable torque transmitting means and the output portions of the drive means and the second value corresponds to substantially 100% torque transfer between the input portion of the first releasable torque transmitting means and the output portions of the drive means.

14. The method of claim 11 wherein the first releasable torque transmitting means comprises a single wet clutch or a single multi-plate wet clutch.

15. A vehicle comprising:

a first prime mover and a second prime mover wherein at least one of the first and second prime movers is an electric machine;

a first group of one or more wheels;

a second group of two or more wheels; and

a driveline to selectively connect each of the first and second prime movers via a transmission to the first and second groups of wheels such that the first group of one or more wheels may be driven by the connected one of the first and second prime movers when the driveline is in a first mode of operation and the second group of wheels may additionally be driven by the connected one of the first and second prime movers when the driveline is in a second mode of operation,

the driveline including an auxiliary driveline comprising an auxiliary driveshaft and drive means between the auxiliary driveshaft and the second group of wheels,

wherein the drive means comprises:

an input portion;

a plurality of output portions each operable to drive a respective different wheel of the second group of wheels;

a differential arranged to enable the respective output portions of the drive means to rotate at different respective speeds;

a first releasable torque transmitting means operable releasably to connect the input portion of the drive means to the output portions of the drive means thereby to allow the input portion of the drive means to drive the output portions of the drive means, wherein the first releasable torque transmitting means is operable to enable slippage of the input portion of the drive means with respect to the output portions of the drive means thereby to vary an amount of torque that is transmitted from the input portion of the drive means to the output portions of the drive means; and

wherein the drive means comprises a ring gear arranged to be driven by the auxiliary driveshaft, the ring gear being coupled to an input portion of the first releasable torque transmitting means, an output of the first releasable torque transmitting means being operable to drive a cage of the differential,

wherein the first releasable torque transmitting means is operable to enable the output portions of the drive means to rotate independent of the rotation of the ring gear thereby to enable the ring gear to be brought to rest when the driveline is in the first mode of operation; and

a locking clutch operable releasably to connect a cage of the differential to an output portion of the drive means thereby to couple rotation of the cage of the differential to rotation of the output portion of the drive means.