Electric power steering apparatus

Abstract

An electric power steering apparatus comprises a transmission mechanism having a drive gear and a driven gear. One end of the drive gear is supported by a bearing hole in a housing through a bearing and a curved plate spring. The curved plate spring comprises a main body surrounding the bearing and at least one crank-shaped elastic tongue supported by at least one of ends of the main body. A recess formed on an inner peripheral surface of the bearing hole has a bottom and a pair of inner wall surfaces opposed to each other in the circumferential direction of the bearing hole. A relief portion for avoiding contact with a connection portion of the elastic tongue is formed between at least one of the inner wall surfaces and the inner peripheral surface of the bearing hole. A boundary between the relief portion and the inner peripheral surface of the bearing hole is engaged with the main body of the curved plate spring, to restrict the movement of the main body in the circumferential direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the schematic configuration of an electric power steering apparatus according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view showing the configuration of a reduction gear mechanism serving as a transmission mechanism provided in the electric power steering apparatus shown in FIG. 1 and its vicinity:

FIG. 3 is a perspective view of a curved plate spring;

FIG. 4 is a cross-sectional view taken along a line IV-IV shown in FIG. 2;

FIG. 5 is a cross-sectional view taken along a line V-V shown in FIG. 2;

FIG. 6 is an exploded perspective view of a power transmission joint;

FIG. 7 is a cross-sectional view of a principal part of an electric power steering apparatus according to another embodiment of the present invention;

FIG. 8 is a cross-sectional view taken along a line VIII-VIII shown in FIG. 7; and

FIG. 9 is a perspective view of a curved plate spring in still another embodiment of the present invention.

Claims

1. An electric power steering apparatus comprising: a transmission mechanism for transmitting power of an electric motor for steering assist to a steering mechanism, the transmission mechanism comprising a drive gear and a driven gear meshed with the drive gear;a bearing for rotatably supporting one end in an axial direction of the drive gear;a housing accommodating the transmission mechanism, the housing having a bearing hole formed therein for supporting the bearing so that the bearing can be biased in a direction in which a center-to-center distance between the drive gear and the driven gear is changed; anda curved plate spring for elastically urging the drive gear through the bearing in a direction in which the center-to-center distance is shortened,wherein a recess is formed on an inner peripheral surface of the bearing hole in the housing,the recess has a bottom and a pair of inner wall surfaces opposed to each other in a circumferential direction of the bearing hole,the curved plate spring comprises an annular main body surrounding the bearing and having a pair of ends in a circumferential direction thereof and at least one elastic tongue supported in a cantilevered shape by at least one of the pair of ends of the main body,the elastic tongue has a base end connected to the main body, a pressing portion for elastically pressing the bottom of the recess, and a connection portion for connecting the base end and the pressing portion to each other, to have a crank shape,a relief section for avoiding contact with the connection portion of the elastic tongue is formed between at least one of the inner wall surfaces of the recess and the inner peripheral surface of the bearing hole, anda boundary between the relief portion and the inner peripheral surface of the bearing hole is engaged with the main body of the curved plate spring, to restrict the movement of the main body in a circumferential direction thereof.

2. The electric power steering apparatus according to claim 1, wherein the base end of the elastic tongue generally extends in the circumferential direction of the main body, anda width of the base end of the elastic tongue is smaller than a width of the main body in an axial direction of the main body.

3. The electric power steering apparatus according to claim 1, wherein the relief portion includes a chamfer.

4. The elastic power steering apparatus according to claim 1, wherein an annular elastic member having a pair of ends in a circumferential direction thereof is interposed between an outer periphery of the main body of the curved plate spring and the inner peripheral surface of the bearing hole.

5. The electric power steering apparatus according to claim 4, wherein the elastic tongue of the curved plate spring is arranged between the pair of ends of the elastic member.

6. The electric power steering apparatus according to claim 4, wherein a groove extending in a circumferential direction of the bearing hole and accommodating a part of the elastic member is formed on the inner peripheral surface of the bearing hole.

7. The electric power steering apparatus according to claim 6, wherein the inner peripheral surface of the bearing hole includes a first half on a side of the driven gear and a second half on the opposite side of the driven gear in the circumferential direction of the bearing hole,a portion, corresponding to the first half, of the elastic member is accommodated in the groove so as not to project inward in a radial direction of the bearing hole, anda portion, corresponding to the second half, of the elastic member is accommodated in the groove so as to partially project inward in the radial direction of the bearing hole.

8. The electric power steering apparatus according to claim 1, wherein the drive gear comprises a worm shaft, and the driven gear comprises a worm wheel.