To provide an electric power steering device equipped with an enhanced power transmitting efficiency in its reduction gear mechanism and an excellent durable lifetime.
The electric power steering device includes the reduction gear mechanism composed of a driving gear made of metal and a follower gear structured so that a resin part made of a resin compound and furnished at the peripheral surface with teeth is formed rigidly on the periphery of a core pipe of metal, the driving gear being supported by ball bearings, wherein the ratio of the radius of curvature of an inner ring raceway groove of the ball bearing to the ball diameter is between 50.5-56.5%, including the limits, while the ratio of the radius of curvature of the outer ring raceway groove to the ball diameter is between 52.5-59.0%, including the limits, and a grease compound prepared by including metallic soap as a thickening agent in a base metal whose dynamic viscosity at 40°C is 12-55 mm2/s, is encapsulated in the ball bearing.
Hironori Honda
Toshimitsu Ichikawa
Takeshi Takamatsu
Yuriko Hamada
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