Vehicle front and rear wheels drive system and clutch changeover method

A vehicle front and rear wheels drive system having a speed-changeable change-speed apparatus disposed along a power transmission path extending from primary drive wheels to secondary drive wheels, said change-speed apparatus having a composite planetary gear device provided in a casing fixed to a vehicle body, comprising:

• changeover clutch discs for, respectively, a direct coupling clutch and a change-speed clutch disposed on a movable element provided concentrically with an input shaft or an output shaft of said change-speed apparatus to which power is transmitted from said primary drive wheels, said movable element being adapted to move along an axial direction of said input shaft or said output shaft and meshing with a carrier of said composite planetary gear device in such a manner as not to rotate relative to said carrier;
• and
• an elastic body and an actuator both for changing over a state between engagement and disengagement of said direct coupling clutch or said change-speed clutch, said elastic body and said actuator being disposed such that operating directions of said elastic body and, said actuator are opposed to each other in the axial direction;
• wherein said elastic body brings one of said direct coupling clutch and said change-speed clutch into engagement by moving said movable element by virtue of a biasing force thereof, and
• said actuator changes over the engagement of said clutches from the engagement of said one clutch to the engagement of the other clutch by moving said movable element against the biasing force of said elastic body by virtue of a thrust of the actuator.