Drive system for four-wheel drive vehicle, four-wheel drive vehicle, and control method for four-wheel drive vehicle

A drive system for a four-wheel drive vehicle, the drive system being mounted in a four-wheel drive vehicle that includes front wheels serving as main drive wheels and rear wheels serving as auxiliary drive wheels, includes: a propeller shaft that transmits the driving force from the engine side to the rear wheels side; a dog clutch that is able to interrupt torque transmission between the engine and the propeller shaft; a torque coupling that is able to interrupt torque transmission between the propeller shaft and the rear wheels; and an ECU that interrupts both torque transmissions by the dog clutch and the torque coupling when the vehicle speed is higher than or equal to a predetermined speed.