Patent ID: 8602154

Claim:
An electric power steering device comprising: a steering assist electric motor having an output shaft; a speed reduction mechanism including an input shaft disposed coaxially with the output shaft of the electric motor; and a power transmission joint which couples the output shaft of the electric motor to the input shaft of the speed reduction mechanism for power transmission, the power transmission joint including an annular first engagement member co-rotatably connected to the output shaft of the electric motor, an annular second engagement member co-rotatably connected to the input shaft of the speed reduction mechanism, and an elastic member disposed between the first and second engagement members for transmitting a torque between the first and second engagement members, wherein: the elastic member includes an annular main body, and a plurality of engagement arms provided at predetermined intervals circumferentially along the main body and extending radially from the main body, the first and second engagement members each includes a plurality of engagement projections engaged with respective ones of the engagement arms of the elastic member circumferentially along the main body, each of the engagement arms of the elastic member includes a pair of power transmission faces, which are engaged with power transmission faces of corresponding engagement projections of the first and second engagement members with interference fits, the power transmission faces of the engagement arms include first power transmission faces each having a first interference fit and second power transmission faces each having a second interference fit, the first interference fit being larger than the second interference fit and each of the first power transmission faces being bulged into a first chevron shape, and each of the second power transmission faces being bulged into a second chevron shape different from the first chevron shape, each of the first and second engagement members including a respective engagement projection that engages a respective first power transmission face of an engagement atm, and another respective engagement projection that engages a respective second power transmission face of an engagement arm, and the first power transmission faces are disposed radially symmetrically with respect to a center of the annular main body of the elastic member.