JP2002362387A - Power steering - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem of noise resulting from rattling sound caused by the backlash of a reduction gear when amplifying the output of a motor through the reduction gear to torque-assist steering operation. SOLUTION: A worm wheel 12 is fixed to a second steering shaft 3 connected to a steering mechanism. A first and a second rolling bearings 13, 14 support the second steering shaft 3 rotatably on both sides with the worm wheel 12 held in between. An outer ring 15 of the first rolling bearing 13 is held to an upper housing 6 accommodating a torque sensor 9, and an inner ring 18 abuts on the worm wheel 12. The second rolling bearing 14 is held to a lower housing 7 accommodating the worm wheel 12. When the upper and lower housings 6, 7 are connected, the first rolling bearing 13 pushed by the upper housing 6 applies axial pre-load to the worm wheel 12 to reduce the backlash of a worm shaft 11 and the worm wheel 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering apparatus for assisting a driver in steering.

[0002]

2. Description of the Related Art For example, in a column assist type EPS, the rotational force of a motor is transmitted to a worm and further transmitted to a worm wheel to reduce the speed and amplify the output of the motor, thereby assisting the steering operation with torque. A proper backlash is necessary for the engagement of the worm and the worm wheel.
A rattling sound (rattling sound) due to backlash may occur.

[0003] In the column assist type EPS, since the reduction gear and the steering wheel are close to each other, the noise generated in the reduction gear is transmitted to the driver and gives a feeling of discomfort.
Conventionally, when assembling a worm and a worm wheel, adjustment is performed so that an appropriate backlash exists between the worm and the worm wheel within the range of machining accuracy. However, this operation is very troublesome. This is because each component is selected according to the degree of variation in dimensional accuracy, and components whose combination accuracy is appropriate are combined (so-called matching assembly).

Therefore, for example, Japanese Patent Application Laid-Open No. 2000-43939
As disclosed in Japanese Patent Application Laid-Open Publication No. H11-163, it has been proposed that the worm shaft can be biased toward the worm wheel, and the worm shaft is biased by a biasing means in a radial direction that is the bias direction.

[0005]

However, in the above-mentioned matching assembly, the number of steps is increased, and the above-mentioned Japanese Patent Laid-Open Publication
Japanese Patent No. 43739 has a problem that the structure becomes complicated and the manufacturing cost increases. The present invention has been made in view of the above problems, and an object of the present invention is to provide a power steering device capable of preventing noise with a simple structure at low cost.

[0006]

Means for Solving the Problems and Effects of the Invention In order to achieve the above object, the invention according to claim 1 comprises an input shaft connected to a steering wheel, an output shaft connected to a steering mechanism, and fixed to the output shaft. A driven gear that moves integrally in the axial direction and the rotation direction of the output shaft, a torque detection unit that detects a torque applied to the input shaft, and a steering assist force applying unit that applies a steering assist force to the driven gear via a drive gear. A first housing mainly housing the input shaft and the torque detecting means;
A second housing that mainly houses the output shaft and the driven gear and is connected to the first housing; and a preload that is pressed by one of the housings in a state where the two housings are connected to apply a preload in the axial direction to the driven gear. And providing means.

According to the present invention, when the two housings are connected to each other, the preload applying means applies an axial preload to the driven gear by being pushed, for example, by the first housing, so that the backlash between the driven gear and the driven gear is reduced. Can be suppressed, and generation of noise due to rattle noise can be prevented. The conventional matching assembly can be dispensed with, and there is no need to employ a complicated structure for biasing one end of the worm shaft in the radial direction, so that noise can be prevented at low cost.

According to a second aspect of the present invention, in the first aspect, in the preload applying means, the outer ring is held in one of the housings so as to rotatably support the output shaft, and the inner ring contacts the driven gear. It is characterized by including a bearing. In the present invention, since the driven gear is urged while killing the internal clearance of the bearing, a great effect can be exhibited in preventing rattle noise. According to a third aspect of the present invention, in the second aspect, the preload applying means includes an elastic body that urges an outer ring of the bearing in an axial direction. In the present invention, since the elastic body is interposed in the preload application, the dimensional accuracy of each component does not have to be so strict.

According to a fourth aspect of the present invention, in the first, second or third aspect, the steering assisting force applying means includes a motor for generating a steering assisting force in accordance with a detection result of the torque detecting means. Things. In a so-called electric power steering device that obtains a steering assist force using a motor, rattle noise once generated between gears is hardly contained by an input from a tire when traveling on a rough road, and this may cause noise. ,
According to the present invention, noise can be suppressed by suppressing the generation of rattle noise itself.

[0010]

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. Referring 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 a vehicle body (not shown). The gear housing 5 includes an upper housing 6 and a lower housing 7 that are fitted together. Specifically, the lower housing 7 has a cylindrical shape, and an upper end 7 a of the lower housing 7 is fitted to an annular step 6 a on the outer periphery of the lower end of the upper housing 6. The lower housing 7 houses a worm gear mechanism 8 as a reduction gear mechanism, and the upper housing 6 houses a torque sensor 9, a control board 10, and the like.

The worm gear mechanism 8 includes a worm shaft 11 connected to a rotating shaft of a motor (not shown) through a joint mechanism such as a spline, and meshes with the worm shaft 11 and is arranged in the axial direction of the second steering shaft 3. Worm wheel 1 that can rotate integrally with the middle part and is restricted from moving in the axial direction
2 is provided. Although not shown, the worm shaft 11 is rotatably supported in the lower housing 7 via a pair of bearings. The worm wheel 12 includes an annular core 12 a that is integrally rotatably coupled to the second steering shaft 3, and a core 12.
A synthetic resin member 12b surrounding the periphery of a
And The core metal 12a is made of, for example, the synthetic resin member 12.
It is inserted into a mold at the time of resin molding of b.

The second steering shaft 3 includes a worm wheel 12
Are rotatably supported by first and second rolling bearings 13 and 14 which are arranged vertically above and below in the axial direction. The outer ring 15 of the first rolling bearing 13 is fitted and held in a bearing holding hole 16 in a cylindrical projection 6b at the lower end of the upper housing 6. The upper end surface of the outer ring 15 is in contact with an annular step 17 serving as the bottom of the bearing holding hole 16, and the upward movement of the outer ring 15 with respect to the upper housing 6 is restricted. On the other hand, the inner race 18 of the first rolling bearing 13 is connected to the second steering shaft 3.
Are fitted by an interference fit. The lower end surface of the inner ring 18 is in contact with the upper end surface of the cored bar 12 a of the worm wheel 12.

The outer race 19 of the second rolling bearing 14 is fitted and held in a bearing holding hole 20 of the lower housing 7. The lower end surface of the outer ring 19 abuts on the annular step portion 21 at the lower end of the lower housing 7, and the movement of the outer ring 19 with respect to the lower housing 7 in the axial downward direction is restricted. The inner ring 22 of the second rolling bearing 14 is attached to the second steering shaft 3 so as to be integrally rotatable and restricted in relative axial movement. The inner wheel 22 includes a step portion 23 of the second steering shaft 3 and the second steering shaft 3.
And a nut 24 to be screwed into the threaded portion of the screw.

The torsion bar 4 passes through the first and second steering shafts 2, 3. Upper end 4a of torsion bar 4
Is connected to the first steering shaft 2 by a connecting pin 25 so as to be able to rotate integrally with the first steering shaft 2, and the lower end 4 b of the torsion bar 4 is connected to the second steering shaft 3 by a connecting pin 26 so as to be able to rotate integrally with the second steering shaft 3. The lower end of the second steering shaft 3 is connected to a steering mechanism such as a rack and pinion mechanism via an intermediate shaft (not shown). The connection pin 25 connects the third steering shaft 27 arranged coaxially with the first steering shaft 2 so as to be integrally rotatable with the first steering shaft 2. The third steering shaft 27 passes through a tube 28 constituting a steering column.

The upper portion of the first steering shaft 2 is rotatably supported by the upper housing 6 via a third rolling bearing 29 composed of, for example, a needle roller bearing. The reduced diameter portion 30 at the lower part of the first steering shaft 2 and the hole 31 at the upper part of the second steering shaft 3
The first and second steering shafts 2 and 3 are 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. In the present embodiment, referring to FIG. 1, when upper and lower housings 6 and 7 are connected, both housings 6 and 7 are relatively brought close to each other. At this time, the first housing 6 held by upper housing 6 Is urged downward in the figure, and the worm shaft 11 held by the lower housing 7 is urged upward in the figure.

Specifically, the step 17 of the upper housing 6 urges the outer ring 15 of the first rolling bearing 13 downward. This urging force makes the internal clearance of the first rolling bearing 13 zero, and urges the worm wheel 12 downward in the drawing via the inner ring 18 of the first rolling bearing 13 to be urged downward. Worm wheel 12 is mounted on the lower housing 7
Through the worm shaft 11 urged upward. As a result, the worm wheel 12
Since the backlash of the meshing portion between the gear and the worm shaft 11 can be suppressed, it is possible to prevent the generation of noise due to the rattling noise (rattling) of the meshing portion.

Further, it is possible to eliminate the need for the matching assembly conventionally required, and it is also possible to eliminate the need for a complicated structure as in the conventional system for biasing one end of the worm shaft in the radial direction. When the housings 6 and 7 are assembled, the first
Noise can be reduced at a low cost with a simple structure in which a preload is applied to the rolling bearing 13. By the way, EPS
In this case, the rattle sound once generated by the input from the tire when traveling on a rough road is difficult to stop, and this may be noise.However, in the present embodiment, since the rattle sound generation itself can be suppressed, the noise is reduced. It can be suppressed effectively.

In particular, when the first rolling bearing 13 urges the worm wheel 12, whose axial movement is restricted by the second steering shaft 3, downward, the urging force is applied to the worm wheel 12 via the second steering shaft 3. Since it is also provided to the second rolling bearing 14, the internal clearance between the first and second rolling bearings 13, 14 can also be reduced. Therefore, the play in the axial direction of the second steering shaft 3 can be remarkably reduced, and a great effect can be exhibited in preventing rattle noise. In addition, the first and second rolling bearings 1
Instead of using expensive angular contact bearings, inexpensive radial contact bearings may be used as 3 and 14.

FIG. 2 shows another embodiment of the present invention. Referring to FIG. 2, the present embodiment is different from the embodiment of FIG. 1 in that outer ring 1 of first rolling bearing 13 is provided.
The point is that an elastic body 32 made of, for example, a disk spring is interposed between the step 5 and the step 17 of the bearing holding hole 16. In this embodiment, since the elastic body 32 is interposed for applying the preload, there is an advantage that the dimensional accuracy of each component does not have to be so strict. Note that the present invention is not limited to the above embodiment, and various changes can be made within the scope of the claims of the present invention. Test The noise level was measured using the electric power steering apparatus shown in FIG. 1 while variously changing the rotational torque of the steering shaft. The results shown in FIG. 1 were obtained. Although we did not directly measure the axial preload on the worm wheel,
Since the rotational torque is considered to increase, the result of FIG. 1 indirectly proves that the noise level decreases with an increase in the preload.

When the rotational torque is 2 Nm, the backlash is considered to be almost zero. In addition, the noise level in the range of the rotation torque of 0.9 to 1 Nm is about 45 dΒ, and high quietness is achieved. When the rotational torque is in the range of 0.9 to 1 Nm, it is considered that there is a level of backlash that does not deteriorate the return of the steering wheel. Therefore, it has been found that application of an appropriate preload is very effective in reducing noise in practical use.

[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 schematic sectional view of an electric power steering apparatus according to another embodiment of the present invention.

FIG. 3 is a graph showing a correlation between a rotational torque of a steering shaft and a noise level.

[Explanation of symbols]

 Reference Signs List 1 steering wheel 2 first steering shaft 3 second steering shaft 4 torsion bar 5 gear housing 6 upper housing (first housing) 7 lower housing (second housing) 8 worm gear mechanism 11 worm shaft 12 worm wheel 12a core Gold 12b Synthetic resin member 13 First rolling bearing 14 Second rolling bearing 15 Outer ring 16 Bearing holding hole 17 Step 18 Inner ring 32 Elastic body

Claims (4)

[Claims] An input shaft connected to a steering wheel, an output shaft connected to a steering mechanism, a driven gear fixed to the output shaft and integrally moving in an axial direction and a rotational direction of the output shaft, and a torque applied to the input shaft. , A steering assisting force applying means for applying a steering assisting force to a driven gear via a driving gear, a first housing mainly housing the input shaft and the torque detecting means, an output shaft and a driven gear. A second housing mainly accommodated in the first housing, and a preload applying means for applying a preload in the axial direction to the driven gear by being pushed by one of the housings in a state where the two housings are connected to each other. A power steering device, characterized in that: 2. The preloading means according to claim 1, wherein
A power steering device comprising a bearing in which an outer ring is held in one of housings so as to rotatably support an output shaft, and an inner ring abuts on a driven gear. 3. The preload applying means according to claim 2, wherein
A power steering device comprising an elastic body for urging an outer ring of the bearing in an axial direction. 4. A power steering apparatus according to claim 1, wherein said steering assisting force applying means includes a motor for generating a steering assisting force in accordance with a detection result of said torque detecting means.