To provide the large torque while restricting the looseness due to the back lash by providing a friction reduction gear and a worm reduction gear arranged in series to each other between an output shaft and a driven shaft.
An intermediate part of a steering shaft 2 to be rotated by the operation of a steering wheel is supported inside of a housing 15 freely to be rotated. One side of the housing 15 is provided with an electric motor 5 as an auxiliary power source and a reduction gear 4a for reducing the rotary driving force and for transmitting the reduced rotary driving force to the steering shaft 2. The reduction gear 4a is formed of a friction reduction gear 42 and a worm reduction gear 43 arranged in series to each other from a side of the electric motor 5. Since a wedge roller type friction reduction gear 2 is used for a front stage part of the reduction gear 4a, generation of noise and vibration at the time of operation is prevented, and a back lash at a degree for giving the influence to the operation is eliminated so as to prevent the generation of uncomfortableness of occupants, and lowering of operability of the steering wheel is prevented.
SAKAI KOICHI
ITO HIROYUKI
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