Patent ID: 7736256

Claim:
An electric power steering device for vehicles comprising a tie rod connecting bar supported to make a linear motion, a rotary member rotatable around the tie rod connecting bar, a rotation conversion device for converting a rotation of a steering shaft to a rotation of the rotary member, a rotation/linear motion conversion device for converting a rotation of the rotary member to a linear motion of the tie rod connecting bar, and a power assist electric motor to give a rotational force to the rotary member, wherein the rotation/linear motion conversion device is a planetary gear device including a ring gear, a sun gear, a planetary pinion and a carrier supporting the planetary pinion, and in the correspondence between pitch diameters and thread numbers of the ring gear, the sun gear and the planetary pinion the thread number of either the ring gear or the sun gear is increased or decreased so that thereby an axial displacement is generated between the ring gear and the sun gear when the ring gear rotates around the sun gear with a planetary motion of the planetary pinion.