To shift the rotation speed of an electric motor at the generation of resonance from the rotation speed region by intentionally providing a parallel- shaft type gear drive (front-stage reduction gear) in the input side of an eccentric swing type planetary gear (rear-stage reduction gear).
A front-stage reduction gear 20 is a parallel-shaft type gear drive. A rear-stage reduction gear 21 is composed of an eccentric swing type planetary gear having a fixed internal gear 28, an external gear 29 engaged with the internal gear 28, and an input crankshaft 30 as an eccentric input shaft which is engaged with the external gear 29 and swingingly rotates the external gear 29. A value obtained by multiplying the reduction ratio of the front-stage reduction gear 20 by the maximum rotation speed per second of the electric motor in an ordinary control rotation speed region and a substantial torque fluctuation amount of the rear-stage reduction gear 21 per a rotation of the crankshaft 30 becomes smaller than natural vibration of a drive system formed by containing the electric motor, the reduction gear, and the second member.
HASHIMOTO MASATAKA
IWATA MITSUYOSHI
