Patent ID: 7278938

Claim:
A power transmission device comprising: a pulley to which a rotational power is transmitted via a belt; a motor having a rotor; a shaft to which a rotational power of the pulley and a rotational power of the rotor are transmitted; a first one-way clutch including an inner ring, an outer ring, and engagement members disposed between the inner ring and the outer ring, the first one-way clutch transmitting the rotational power of the pulley to the shaft when a rotational speed of the pulley is relatively higher than that of the rotating shaft; and a second one-way clutch including an inner ring, an outer ring, and engagement members disposed between the inner ring and the outer ring, the second one-way clutch transmitting the rotational power of the rotor to the shaft when the rotational speed of the rotor is relatively higher than that of the shaft; wherein, in the second one-way clutch, the inner ring has an engagement cylindrical surface in an outer periphery thereof and is rotatable together with the shaft; the outer ring has an engagement cam-surface in an inner periphery thereof and is rotatable together with the rotor; and the engagement members are engagement rollers disposed between the engagement cylindrical surface of the inner ring and the engagement cam-surface of the outer ring; wherein,in the first one-way clutch, the inner ring has an engagement cam-surface in an outer periphery thereof and is rotatable together with a shaft; the outer ring has an engagement cylindrical surface in an inner periphery thereof and is rotatable together with the pulley; and the engagement members are engagement rollers disposed between the engagement cam-surface of the inner ring and the engagement cylindrical surface of the outer ring.