JP2002255048A - Motor-driven power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor-driven power steering device as an improvement of a conventional arrangement in which a biasing member to bias a worm shaft toward a worm wheel is installed in the radial arrangement of the worm shaft as a mechanism to adjust backlash, involving the problem as enlarged dimensions. SOLUTION: In a bearing holding hole 41 formed in a lower housing 7, a second rolling bearing 14 supporting rotatably a first steering shaft 2 continued to a steering wheel 1 is held in such a way as capable of biasing in the direction going apart from the worm shaft 11. The inner ring 17 of the second rolling bearing 14 is tightly fitted on the first steering shaft 2. A moisture absorbing member 43 is interposed between a semi-circumference of the hole 41 on the worm shaft 11 side and the outer ring 16 of the second rolling bearing 14. The moisture absorbing member 43 is made of a synthetic resin having approximately an equal expansion amount by moisture absorption to a synthetic resin member 12b of the worn wheel 12, and biases the first steering shaft 2 through the second rolling bearing 14.

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, the dimensions of a synthetic resin worm wheel change due to moisture absorption. The worm wheel made of a synthetic resin has a large dimensional change due to a temperature rise as compared with, for example, an aluminum alloy or the like that forms the housing of the 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, causing noise or increasing the operating resistance, resulting in a poor steering feeling. Or Therefore, as described in Japanese Patent Application Laid-Open No. 2000-43939, for example, the worm shaft can be biased toward the worm wheel, and the backlash is kept constant by biasing the worm shaft in the radial direction, which is the bias direction, by biasing means. It has been proposed to maintain.

[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 of controlling the rotation of an electric motor mounted on a housing and generating a steering assist force via a worm shaft and a worm wheel. In an electric power steering device for transmitting power to a shaft, a bearing that rotatably supports the steering shaft and a bearing holding hole that is formed in a housing and holds the bearing so as to be biased in a radial direction and away from the worm shaft. And a moisture-absorbing member interposed between the bearing and at least half of the worm shaft side and the bearing.

In the present invention, the moisture absorbing member expands due to moisture absorption in the same manner as the worm wheel expands due to moisture absorption.
The moisture absorbing member biases the steering shaft away from the worm shaft via the bearing. Thus, the backlash can be maintained constant regardless of the expansion of the worm wheel. In addition, this can be realized with a small and simple structure in which a moisture absorbing member is interposed between the bearing and the bearing holding hole. In particular, since the bearing can be displaced following a change in the center distance between the worm wheel and the worm shaft, the steering shaft can be stably held without causing backlash or the like regardless of the dimensional change of the worm wheel.

The steering shaft described above 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, or the second steering shaft to which a steering mechanism such as a rack and pinion mechanism is connected. Further, if the moisture absorbing member and the worm wheel include a synthetic resin whose dimensional change due to moisture absorption is substantially equal, the influence of moisture absorption can be reliably avoided, and the backlash can be kept constant.

Further, if the moisture absorbing member and the worm wheel include a synthetic resin whose dimensional changes due to thermal expansion are substantially equal, the effects of temperature and moisture absorption can be reliably avoided, and the backlash can be maintained constant. . The above-described moisture absorbing member and the worm wheel may use the same kind of synthetic resin,
Different kinds of synthetic resins may be used. In addition, it is preferable that the worm wheel includes a cored bar and a synthetic resin held by the cored bar in the following point. First, it is possible to prevent generation of noise such as rattling noise while securing the strength of the worm wheel. Moreover, since the synthetic resin can be made thin, even if a thin-walled hygroscopic member is used, an expansion amount commensurate with the dimensional change of the worm wheel can be obtained. Thus, a small electric power steering device can be provided.

[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 which meshes with the worm shaft 11 and is rotatably attached to an axially intermediate portion of the first steering shaft 2 as shown in FIG. The worm wheel 12 includes an annular metal core 12a that is integrally rotatably coupled to the first steering shaft 2, and a synthetic resin member 12a that surrounds the metal core 12a to form teeth.
The cored bar 12a is inserted into a mold at the time of resin molding of the synthetic resin member 12b, for example.

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 FIGS. 1 and 2, the outer race 16 of the second rolling bearing 14 is fitted and held in a bearing holding hole 41 in a cylindrical projection 7b at the upper end of the lower housing 7. The inner race 17 of the second rolling bearing 14 is mounted on the first steering shaft 2.
Are fitted by an interference fit. Referring to FIG. 2, bearing holding hole 41 has an accommodating recess 42 that is recessed in a stepped shape at most in semi-circumferential portion 41 a on the worm shaft 11 side. The accommodation recess 42, the moisture absorbing member 43 made of a cross-section semicircular plate is accommodated, the moisture absorbing member 43
Is in contact with the outer peripheral surface of the outer ring 16 of the second rolling bearing 14. The moisture absorbing member 43 is made of the same or different synthetic resin as the synthetic resin member 12b of the worm wheel 12.

On the other hand, the worm shaft 11 of the bearing holding hole 41
The semi-circumferential portion 41b on the opposite side forms an elliptical semi-circular arc surface, and a minute gap S (for example, 10 to 20 μm) is provided between the semi-circular portion 41b and the outer peripheral surface of the outer ring 16 opposed thereto. Thus, the second rolling bearing 14 can be deflected in the radial direction away from the worm shaft 11. Referring to FIG. 1, the torsion bar 4 includes first and second torsion bars.
Through the steering shafts 2 and 3 of the vehicle. The upper end 4a of the torsion bar 4 is connected to the first steering shaft 2 by a connecting pin 20 so as to be integrally rotatable, and the lower end 4b of the torsion bar 4 is connected to the second steering shaft 3 by a connecting pin 21 so as to be integrally rotatable. Have been.

The connecting pin 21 connects the third steering shaft 22 arranged coaxially with the second steering shaft 3 to the second steering shaft 3.
It is connected so as to be able to rotate integrally with it. At the lower end of the third steering shaft 22, a pinion (not shown) is integrally formed.
The pinion meshes with a rack shaft (not shown) extending in the left-right direction of the vehicle to form a steering mechanism. The periphery of the third steering shaft 22 is a tube 2 constituting a steering column.
3. 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 first
The lower shaft 26 of the steering shaft 2 is fitted with a predetermined play in the rotation direction so as to regulate the relative rotation of the first and second steering shafts 2 and 3 within a predetermined range. According to the present embodiment, the moisture absorbing member 12 expands due to moisture absorption in the same manner as the worm wheel 12 expands due to moisture absorption.
The first steering shaft 2 is deviated in a direction away from the worm shaft 11 via. Thus, regardless of the expansion of the worm wheel 12, the backlash of the meshing portion between the worm shaft 11 and the worm wheel 12 can be kept constant. As a result, generation of noise can be prevented, and deterioration of the steering feeling due to an increase in rotational resistance can be prevented. In addition, this is used as the second rolling bearing 14.
It can be realized with a small and simple structure in which a moisture absorbing member 43 is interposed between the bearing member 41 and the bearing holding hole 41.

In particular, since the second rolling bearing 14 is displaced following the change in the center distance D between the worm wheel 12 and the worm shaft 11, the first steering shaft 2 is disregarded regardless of the dimensional change of the worm wheel 12. Can be stably held without causing backlash or the like. The synthetic resin (for example, polyamide resin) used for the moisture absorbing member 43 and the synthetic resin member 12b of the worm wheel 12 may be the same or different, but a synthetic resin whose dimensional change due to moisture absorption is substantially equal is employed. You.

The moisture absorbing member 43 and the synthetic resin member 12
When a synthetic resin having substantially the same dimensional change due to thermal expansion is used as the synthetic resin used for b, the influence of temperature and humidity can be reliably avoided, and the backlash can be kept constant. Further, since the worm wheel 12 is constituted by the metal core 12a and the synthetic resin member 12b, there are the following advantages.
That is, the worm wheel 1 is strengthened by the core 12a.
2 can prevent the generation of noise such as rattling noise by the synthetic resin member 12b while ensuring high strength. Moreover, since the thickness of the synthetic resin member 12b can be reduced, it is possible to use a thin-walled moisture absorbing member for realizing an expansion amount balanced with the expansion amount of the synthetic resin member 12b. As a result, it is possible to provide a small electric power steering apparatus as a whole by reducing the thickness of the moisture absorbing member 43.

In the above-described embodiment, 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 1 supporting the first steering shaft 2 is provided.
Although the moisture absorbing member 43 is provided along the line 4, if the worm wheel 12 is provided on the second steering shaft 3, the second
The hygroscopic member is provided along the rolling bearing that supports the steering shaft 3. That is, the bearing provided with the moisture absorbing member may be a shaft to which the worm wheel 12 is integrally connected.

In the above embodiment, the moisture absorbing member 4
Although the reference numeral 3 is along the substantially half circumference of the outer ring 16 on the worm shaft 11 side, if the range of １ ／ rotation to を rotation including the center of the substantially half circumference, the second rolling bearing is attached to the moisture absorbing member 43. 14 can be exerted. 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.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electric power steering device 2 1st steering shaft 3 2nd steering shaft 4 Torsion bar 5 Gear housing 6 Upper housing 7 Lower housing 8 Worm gear mechanism 11 Worm shaft 12 Worm wheel 12a Core metal 12b Synthetic resin member 14 Second Rolling bearing 16 Outer ring 17 Inner ring 41 Bearing holding holes 41a, 41b Half-peripheral portion 42 Containing recess 43 Hygroscopic member D Center distance S Gap

Continued on the front page (72) Inventor Etsuro Kitami 3-5-8 Minamisenba, Chuo-ku, Osaka-shi F-term in Koyo Seiko Co., Ltd. 3D033 CA04 3J017 AA03 CA06 DA02

Claims (4)

[Claims] 1. An electric power steering device mounted on a housing and transmitting rotation of an electric motor for generating a steering assist force to a steering shaft via a worm shaft and a worm wheel, wherein the steering shaft is rotatably supported. A bearing formed in the housing, the bearing holding hole diametrically holding the bearing so as to be biased in a direction away from the worm shaft, and at most the bearing holding hole between the semi-peripheral portion on the worm shaft side and the bearing. An electric power steering device comprising: a moisture absorbing member interposed in the power steering device. 2. The electric power steering apparatus according to claim 1, wherein the moisture absorbing member and the worm wheel include a synthetic resin whose dimensional change due to moisture absorption is substantially equal. 3. The electric power steering apparatus according to claim 1, wherein the moisture absorbing member and the worm wheel include a synthetic resin whose dimensional changes due to thermal expansion are substantially equal. 4. An electric power steering apparatus according to claim 1, wherein said worm wheel includes a metal core and a synthetic resin member which is held by said metal core and forms teeth.