VEHICLE AND METHOD OF CONTROLIING A VEHICLE

Embodiments of the invention provide a vehicle comprising: prime mover means; at least first and second groups of one or more wheels; and a driveline to connect the prime mover means to the first and second groups of one or more wheels such that the first group of one or more wheels is driven by the prime mover means when the driveline is in a first mode of operation and the second group of one or more wheels is additionally driven by the prime mover means 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 one or more wheels, the drive means being operable to connect the second group of one or more wheels to the auxiliary driveshaft when the driveline transitions between the first mode and the second mode, the drive means having an input portion, an output portion and first and second releasable torque transmitting means coupled in series therebetween, the first releasable torque transmitting means having an input portion and an output portion, the first releasable torque transmitting means being operable to allow slip between the respective portions thereby to modulate an amount of torque transmitted from the input to the output portion, the second releasable torque transmitting means also having an input portion and an output portion, the second releasable torque transmitting means being operable between a first condition in which the input portion is isolated from the output portion and a second condition in which the input and output portions are directly coupled such that torque applied to the input portion is transmitted substantially directly to the output portion. Dans des modes de réalisation, l'invention concerne un véhicule comprenant : des moyens de moteur principal ; au moins des premier et second groupes d'une ou de plusieurs roues ; et une transmission servant à connecter les moyens de moteur principal aux premier et second groupes d'une ou de plusieurs roues, de telle sorte que le premier groupe d'une ou de plusieurs roues est entraîné par les moyens de moteur principal lorsque la transmission se trouve dans un premier mode de fonctionnement et le second groupe d'une ou de plusieurs roues étant également entraîné par les moyens de moteur principal lorsque la transmission se trouve dans un second mode de fonctionnement. La transmission comprend une transmission auxiliaire dotée d'un arbr