Bush bearing

1. A bush bearing for rotatably supporting a rotating shaft portion of an end portion of a driving gear which meshes via a meshing portion with a driven gear of a transmission for transmitting the power of an electric motor for steering assistance to a steering mechanism in an electric power steering system, comprising:

a bearing body having an inner peripheral surface which is brought into rotatable contact with a cylindrical outer peripheral surface of said rotating shaft portion; at least one first groove and at least one second groove provided on an outer peripheral surface of said bearing body so as to extend in a first direction about an axis of said rotating shaft portion; a first elastic ring member fitted in said at least one first groove and having a first projecting portion partially projecting radially outward from the outer peripheral surface of said bearing body on a meshing portion side in a second direction which is perpendicular to the axis of said rotating shaft portion and is toward the meshing portion and a first portion not projecting radially outward from the outer peripheral surface of said bearing body on an opposite side to the meshing portion side in the second direction; and a second elastic ring member fitted in said at least one second groove and having a second projecting portion partially projecting radially outward from the outer peripheral surface of said bearing body on the opposite side and a second portion not projecting radially outward from the outer peripheral surface of said bearing body on the meshing portion side.

2. The bush bearing according to claim 1 , wherein said at least one first groove is constituted by an annular groove having a center offset from the axis of said rotating shaft portion toward the meshing portion side, and said at least one second groove is constituted by an annular groove having a center offset from the axis of said rotating shaft portion toward the opposite side.

3. The bush bearing according to claim 1 , wherein said at least one first groove is constituted by a first groove portion disposed on the meshing portion side and a second groove portion disposed on the opposite side and having a first depth which is deeper than that of the first groove portion, and said at least one second groove is constituted by a third groove portion disposed on the meshing portion side and a fourth groove portion disposed on the opposite side and having a second depth which is shallower than that of the third groove portion.

4. The bush bearing according to claim 1 , wherein said bearing body includes a bearing main body having at least one slit which is open at an axial one end face thereof and extends toward an axial other end face thereof.

5. The bush bearing according to claim 4 , wherein said at least one slit is closed at a side of the axial other end face or extends to the axial other end face and is open at the axial other end face.

6. The bush bearing according to claim 4 , wherein said bearing main body has at least another slit which is open at the axial other end face and extends toward the axial one end face.

7. The bush bearing according to claim 6 , wherein said at least another slit is closed at a side of the axial one end face or extends to the axial one end face and is open at the axial one end face.

8. The bush bearing according to claim 1 , wherein said bearing body is made of a synthetic resin and said inner peripheral surface is rotatably brought into direct contact with the cylindrical outer peripheral surface of said rotating shaft portion.

9. The bush bearing according to claim 1 , wherein said bearing body includes a bearing main body made of a synthetic resin or aluminum, and a bush member constituted by a multilayered sliding member which is fitted to an inner peripheral surface of said bearing main body and has a sliding inner peripheral surface which is rotatably brought into direct contact with the cylindrical outer peripheral surface of said rotating shaft portion.