Four wheel drive system

A four wheel drive system of a vehicle comprising:

• a power plant for producing a driving force,
• a front wheel driving mechanism for transmitting the driving force to drive right and left front wheels,
• a rear wheel driving mechanism for transmitting the driving force to drive the right and left rear wheels,
• right and left wheel clutches provided in one of the driving mechanisms for controlling the amount of the driving force transmitted to wheels driven through the one of the driving mechanisms,
• a cut-off clutch for controlling the driving force transmitted to the wheels driven through the one of the driving mechanisms,
• control means for engaging the cut-off clutch before the right and left wheel clutches are engaged,
• a speed reduction mechanism connected with an input shaft of the one of the driving mechanisms for reducing a rotation speed of an input shaft transmitted to the wheels driven through the one of the driving mechanisms, the speed reduction mechanism comprising a ring gear case in which the right and left wheel clutches are disposed,
• a pair of control valves controlled by the control means for controlling a hydraulic pressure introduced into the right and left wheel clutches so that engaging forces of the right and left wheel clutches are changed, respectively, and an oil pump connected with and driven by an input shaft of the one of the driving mechanisms for producing the hydraulic pressure for the right and left wheel clutches, and
• a casing in which the ring gear case and the oil pump are disposed.

A four wheel drive system for a vehicle comprising:

• a power plant for producing a driving force,
• a front wheel driving mechanism for transmitting the driving force to drive right and left front wheels,
• a rear wheel driving mechanism for transmitting the driving force to drive right and left rear wheels,
• right and left wheel clutches provided in one of the front and rear wheel driving mechanisms for controlling an amount of the driving force transmitted to wheels driven through the one of the front and rear wheel driving mechanisms,
• a cut-off clutch interposed between the power plant and the right and left wheel clutches for controlling the driving force transmitted to the wheels driven through the one of the front and rear wheel driving mechanisms, and
• control means for engaging the cut-off clutch before the right and left wheel clutches are engaged.