Patent ID: 8825324

Claim:
A four-wheel-drive vehicle comprising: a drive source to generate torque forming a driving force of the vehicle; a driving force transmission system to transmit the torque of the drive source to main driven wheels and auxiliary driven wheels; a dog clutch provided in the driving force transmission system and capable of transmitting the torque to an auxiliary driven wheel side by engagement of a recess portion and a protruding portion; a determination unit to determine whether a friction coefficient of a road surface is lower than a predetermined value based on an index value relating to the friction coefficient of the road surface; a control clutch provided on an upstream side or a downstream side of the dog clutch in the driving force transmission system as viewed in a torque transmitting direction and capable of controlling the torque transmitted to the auxiliary driven wheel side; and a control unit configured to generate a first control signal to engage the dog clutch before the vehicle starts when the determination unit determines that the friction coefficient of the road surface is lower than the predetermined value, and configured to generate a second control signal to instruct the control clutch to increase the torque transmitted to the auxiliary driven wheel side when the main driven wheels slips at the start of the vehicle, wherein when the four-wheel drive vehicle is shifted from a two-wheel drive to a four-wheel drive, a propeller shaft is rotated by the control clutch, and thereafter the dog clutch is engaged.