JP2002234451A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent increase in a size due to worm shaft radial directional arrangement of an energizing member deflecting a worm shaft to the worm wheel side and serving as a mechanism regulating backlash. SOLUTION: A second rolling bearing 14 supporting a first steering column 2 connected to a steering wheel 1 is provided with an outer ring 16 fastened and fixed around a lower housing 7 and an inner ring 17 fastened and fixed in the first steering column 2. An O-ring 18 housed in a circumference groove of the first steering column 2 is held between the first steering column 2 and the second rolling bearing 14. When a center distance between the worm shaft 11 and the worm wheel 12 is changed because of thermal expansion and the like in the worm wheel 12 including a synthetic resin, the O-ring 18 is elastically deformed to absorb this change for keeping the backlash constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus using an electric motor as a source of a steering assist force.

[0002]

2. Description of the Related Art As an electric steering device for an automobile, a first steering shaft connected to a steered wheel, a second steering shaft connected to the first steering shaft via a torsion bar and connected to a steering mechanism are provided. There are devices provided with: In this device, the relative displacement of the first and second steering shafts in the rotation direction is detected by a torque sensor, and the rotation of the electric motor is reduced via a speed reduction mechanism to the second steering shaft based on the detection result of the torque sensor. The operation of the steering mechanism according to the rotation of the steered wheels is assisted by the rotation of the electric motor, thereby reducing the driver's labor for steering.

[0003] As the above-mentioned speed reduction mechanism, one having a worm and a worm wheel is provided. The worm shaft provided with the worm and the second steering shaft provided with the worm wheel have both ends in the axial direction supported by bearings. When assembling the worm shaft and the worm wheel, adjustment is made so that an appropriate backlash exists between the worm and the worm wheel within the range of machining accuracy.

On the other hand, in order to prevent noise caused by backlash, a worm wheel made of a synthetic resin is generally used. However, a worm wheel made of a synthetic resin has a large dimensional change due to a rise in temperature, and a dimensional change due to water absorption, as compared with, for example, an aluminum alloy or the like constituting a housing of an electric power steering apparatus. For this reason, the center distance between the worm shaft and the worm wheel changes, and as a result, the amount of backlash changes, which may cause noise or increase the operating resistance and deteriorate the steering feeling. There is.

Therefore, for example, Japanese Patent Application Laid-Open No. 2000-43939
As disclosed in Japanese Patent Application Laid-Open Publication No. H10-209, it has been proposed to maintain the backlash constant by allowing the worm shaft to be biased toward the worm wheel and biasing the worm shaft in the radial direction which is the bias direction thereof by biasing means. I have.

[0006]

However, since the urging means and a member for adjusting the urging force of the urging means must be arranged along the radial direction of the worm shaft, the size of the apparatus is increased. There's a problem. The present invention has been made in view of the above problems, and an object of the present invention is to provide an electric power steering apparatus capable of maintaining a constant backlash with a small and simple structure.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for controlling the rotation of an electric motor, which is mounted on a housing and generates a steering assist force, via a worm shaft and a worm wheel. In a motor-driven power steering device for transmitting to a shaft, a bearing interposed between a housing and the steering shaft to rotatably support the steering shaft, and an elastic member sandwiched between an inner ring of the bearing and the steering shaft. With
The inner ring of the bearing and the output shaft are loosely fitted to each other, and the elastic member absorbs a change in the center distance between the worm wheel and the worm shaft.

According to the present invention, even if the worm wheel expands due to heat or water absorption and the center distance between the worm wheel and the worm shaft changes, the expansion is absorbed by the elastic member. In the position, a constant backlash can be maintained. In addition, this can be realized with a small and simple structure in which an elastic member is interposed between the inner ring of the bearing and the steering shaft. The above steering shaft may be any shaft as long as the worm wheel is integrally connected. Therefore, it may be the first steering shaft to which the steering wheel is connected, and the second steering shaft to which the steering mechanism such as the rack and pinion mechanism is connected.
May be used.

Also, if the elastic member is an O-ring,
The use of general-purpose parts is preferable in that the manufacturing cost can be reduced. However, it is necessary to form a circumferential groove in the steering shaft or the inner ring of the bearing to accommodate the O-ring. Further, the elastic member may be an annular plate made of rubber or synthetic resin. In this case, it is not necessary to form a groove or the like for accommodating the elastic member in the steering shaft and the inner ring of the bearing.

[0010] The elastic member may be a rubber or synthetic resin coating layer coated on one of the outer peripheral surface of the steering shaft and the inner peripheral surface of the inner race of the bearing. This case is preferable in that the thickness of the elastic member can be extremely reduced. The change in the center distance between the worm wheel and the worm shaft is, for example, 10 to 2
The elastic deformation amount is about 0 μm, and a sufficient elastic deformation can be achieved even with a thin rubber or synthetic resin coating layer.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic sectional view of an electric power steering apparatus according to an embodiment of the present invention. With reference to FIG. 1, in the present electric power steering device (hereinafter simply referred to as a power steering device), a first steering shaft 2 as an input shaft to which a steering wheel 1 is attached, a rack and pinion mechanism, and the like. A second steering shaft 3 as an output shaft connected to a steering mechanism (not shown) is coaxially connected via a torsion bar 4.

The gear housing 5 supporting the first and second steering shafts 2 and 3 is made of, for example, an aluminum alloy.
It is attached to the vehicle body (not shown). The gear housing 5 includes an upper housing 6 and a lower housing 7 that are fitted together. Specifically, the upper housing 6 has a cylindrical shape, and a lower end 6 a thereof is fitted to an annular step 7 a on the outer periphery of the upper end of the lower housing 7. The upper housing 6 houses a worm gear mechanism 8 as a reduction gear mechanism, and the lower housing 7 houses a torque sensor 9, a control board 10, and the like.

As shown in FIG. 2, the worm gear mechanism 8 includes a worm shaft 11 connected to a rotating shaft 32 of an electric motor 31 via a joint mechanism such as a spline 33, for example.
And a worm wheel 12 made of a synthetic resin (for example, a polyamide resin), which meshes with the worm shaft 11 and is integrally rotatably attached to an axially intermediate portion of the first steering shaft 2 as shown in FIG. Worm wheel 12
May be composed entirely of a synthetic resin or may include a reinforcing core.

Referring to FIG. 2, both ends of worm shaft 11 are provided with a pair of rolling bearings 3 held by upper housing 6.
4 and 35 respectively support rotatably. The inner rings of the two rolling bearings 34 and 35 are arranged in corresponding constrictions of the worm shaft 11, the outer ring of the rolling bearing 34 at one end of the worm shaft 11 is positioned on the upper housing 6, and the other end of the worm 11 (motor side). The outer ring of the rolling bearing 35) is urged toward the rolling bearing 34 by a preload adjusting member 36.

The preload adjusting member 36 is made of, for example, a screw.
By being screwed into a screw hole formed in the upper housing 6, a preload is applied to the pair of rolling bearings 34 and 35, and the worm shaft 11 is positioned in the axial direction.
A lock nut 37 stops the preload adjusting member 36. With reference to FIG. 1, the first steering shaft 2 is rotatably supported by first and second rolling bearings 13 and 14 which are arranged so as to sandwich the worm wheel 12 vertically in the axial direction. The outer race 15 of the first rolling bearing 13 is supported by the upper housing 6.

Referring to FIG. 1, the outer race 16 of the second rolling bearing 14 is fitted into a cylindrical projection 7b at the upper end of the lower housing 7, and is fixed by an interference fit (close fit). . Referring to FIG. 1 and FIG. 3 which is an enlarged view of a main part of FIG. 1, the inner race 17 of the second rolling bearing 14 and the first
The steering shaft 2 has a predetermined radial gap S (for example, 10 to 2).
0 μm), and an O-ring 18 as an elastic member is sandwiched between the inner race 17 and the first steering shaft 2. The O-ring 18 is accommodated in, for example, a circumferential groove 19 formed on the outer periphery of the first steering shaft 2, and is elastically deformed by an amount corresponding to the gap S. The peripheral groove 19 may be formed on the inner peripheral surface of the inner race 17 of the second rolling bearing 14.

Referring to FIG. 1, the torsion bar 4 is a first torsion bar.
And the second steering shafts 2 and 3. The upper end 4a of the torsion bar 4 is connected to the first steering shaft 2 by a connecting pin 20.
And the lower end 4 of the torsion bar 4
b is connected to the second steering shaft 3 by a connecting pin 21 so as to be integrally rotatable. The connection pin 21 connects a third steering shaft 22 disposed coaxially with the second steering shaft 3 so as to be integrally rotatable with the second steering shaft 3. A pinion (not shown) is integrally formed at the lower end of the third steering shaft 22, and this pinion meshes with a rack shaft (not shown) extending in the left-right direction of the vehicle to form a steering mechanism. Third
The periphery of the steering shaft 22 penetrates the inside of a tube 23 constituting a steering column.

The lower portion of the second steering shaft 3 is rotatably supported by the lower housing 10 via a third rolling bearing 24 formed of, for example, a needle roller bearing. The reduced diameter portion 25 on the upper part of the second steering shaft 3 and the hole 26 on the lower part of the first steering shaft 2 regulate the relative rotation of the first and second steering shafts 2 and 3 within a predetermined range. Are provided with a predetermined play in the rotation direction. According to the present embodiment, it is assumed that the worm wheel 12 made of a synthetic resin thermally expands or expands due to moisture absorption, and the center distance D (see FIG. 2) between the worm wheel 12 and the worm shaft 11 changes. The O-ring 18 as an elastic member
Can be absorbed.

Therefore, a constant backlash can be maintained at the position where the worm shaft 11 and the worm wheel 12 mesh with each other. As a result, generation of noise can be prevented, and the steering feeling deteriorates due to an increase in rotational resistance. Can be prevented. Moreover, this is simply called the second
And a small and simple structure in which an O-ring 18 is interposed between the inner ring 17 of the rolling bearing 14 and the first steering shaft 2. Since the O-ring 18 is a general-purpose component, the manufacturing cost can be reduced.

FIG. 4 shows another embodiment of the present invention. Referring to FIG. 4, the present embodiment is different from the embodiment of FIG. 1 in that an annular plate 27 made of rubber or synthetic resin is used as an elastic member instead of an O-ring, Between the inner wheel 17 and the first steering shaft 2,
It is at the pinched point. In the present embodiment, there is an advantage that the peripheral groove 19 required in the embodiment of FIG. 1 can be eliminated. Also, instead of the elastic member of FIG. 1, as shown in FIG. 5A or 5B, the outer peripheral surface 2a of the first steering shaft 2 and the inner peripheral surface 17a of the inner ring 17 of the second rolling bearing 14 are provided. May be a rubber or synthetic resin coating layer 28 or 29 coated on either one of them. This is preferable in that the thickness of the coating layers 28 and 29 as elastic members can be extremely reduced.
Even if the thickness of the coating layers 28 and 29 is reduced in this way, it is sufficient to absorb the above-described change in the inter-core distance D. This is because the change in the center distance D is, for example, 1
This is because the elastic deformation amount is about 0 to 20 μm, and the elastic deformation amount of this degree can sufficiently be achieved even with the thin rubber or synthetic resin coating layers 28 and 29.

In each of the above embodiments, the description has been given of the case where the worm wheel 12 is provided on the first steering shaft 2. Therefore, the second rolling bearing 14 supporting the first steering shaft 2 has elasticity. Although the members are provided, if the worm wheel 12 is provided on the second steering shaft 3, the second steering shaft 3
The elastic member is provided on the rolling bearing that supports.
That is, the bearing provided with the elastic member may be a shaft to which the worm wheel 12 is integrally connected.

In addition, various changes can be made within the scope of the claims of the present invention.

[Brief description of the drawings]

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

FIG. 2 is a sectional view taken along the line II-II in FIG.

FIG. 3 is an enlarged view of a main part of FIG. 1;

FIG. 4 is a schematic sectional view of an electric power steering apparatus according to another embodiment of the present invention.

FIGS. 5A and 5B are schematic cross-sectional views of a second steering shaft and an inner race of a rolling bearing according to still another embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 electric power steering device 2 first steering shaft 3 second steering shaft 4 torsion bar 5 gear housing 6 upper housing 7 lower housing 8 worm gear mechanism 11 worm shaft 12 worm wheel 14 second rolling bearing 16 outer ring 17 inner ring 18 O-ring (elastic member) 19 circumferential groove 27 annular plate (elastic member) 28, 29 coating layer (elastic member)

Continued on the front page (72) Inventor Kitami Etsuro 3-5-8 Minamisenba, Chuo-ku, Osaka-shi Inside Koyo Seiko Co., Ltd. (72) Inventor Teruo Tsutsui 3-58-8 Minamisenba, Chuo-ku, Osaka-shi Koyo Seiko Co., Ltd. F term (reference) 3D033 CA00 CA02 CA04 3J009 DA04 DA05 EA06 EA19 EA23 EA32 EC05 FA08 FA14 3J030 AB04 BA03 CA10

Claims (4)

[Claims] An electric power steering device mounted on a housing for transmitting rotation of an electric motor for generating a steering assist force to a steering shaft via a worm shaft and a worm wheel. A bearing interposed therebetween and rotatably supporting the steering shaft; and an elastic member sandwiched between the inner ring of the bearing and the steering shaft. The inner ring of the bearing and the output shaft are loosely fitted to each other, and the elastic member A motor-driven power steering device characterized by absorbing a change in a distance between a worm wheel and a center of a worm shaft. 2. An electric power steering apparatus according to claim 1, wherein said elastic member is an O-ring. 3. An electric power steering apparatus according to claim 1, wherein said elastic member is an annular plate made of rubber or synthetic resin. 4. The elastic member according to claim 1, wherein the elastic member is a rubber or synthetic resin coating layer coated on one of the outer peripheral surface of the steering shaft and the inner peripheral surface of the inner ring of the bearing. Electric power steering device.