Patent ID: 8371977

Claim:
A transmission ratio variable mechanism capable of changing a transmission ratio of a steered angle of steered wheels to a steering angle of a steering member, comprising: an input member and an output member capable of rotation about a first axis; a first bearing ring, having first and second end surfaces, for differentially rotatably coupling the input member and the output member to each other; a second bearing ring for rotatably supporting the first bearing ring via a rolling element; and an actuator capable of rotation-driving the second bearing ring, wherein a second axis being a center line of the first bearing ring and the second bearing ring is inclined to the first axis, wherein the input member and the output member respectively have power transmission surfaces respectively opposite the first and the second end surfaces of the first bearing ring, wherein a first concave-convex engaging section for power-transmittably engaging the first end surface of the first bearing ring and the power transmission surface of the input member corresponding to the first end surface is arranged, wherein the first concave-convex engaging section includes a first convex portion arranged on one of the first end surface and the power transmission surface corresponding to the first end surface, and a first concave portion that is arranged on an alternate surface and that is engaged with the first convex portion, wherein a second concave-convex engaging section for power-transmittably engaging the second end surface of the first bearing ring and the power transmission surface of the output member corresponding to the second end surface is arranged, and wherein the second concave-convex engaging section includes a second convex portion arranged on one of the second end surface and the power transmission surface corresponding to the second end surface, and a second concave portion that is arranged on an alternate surface and that is engaged with the second convex portion.