JP2002067991A - Motor-driven power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce rotational torque applied to a meshing part, to improve restoring ability of a steering wheel after it is assisted by a motor, and to reduce an increase of a backlash amount even when a large meshing reaction force is applied to a worm. SOLUTION: By providing an elastic body 14a such as a coil spring energizing the worm 71 rotated by the motor 6 for steering assistance toward a worm wheel 72 and a hydraulic attenuating mechanism 20 damping meshing reaction force applied to the worm 71 when assisting steering, a preload of the meshing part by the elastic body 14a can be reduced and the increase of the backlash amount can be reduced even when a large meshing reaction force is applied to the worm 71.

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 a motor as a source of a steering assist force.

[0002]

2. Description of the Related Art In the steering of a motor vehicle, the steering operation of a steering wheel disposed inside a vehicle compartment is performed by turning the steering wheel (generally, a front wheel) outside the vehicle compartment for steering. This is done by telling the steering mechanism.

FIG. 3 is a sectional view of a conventional electric power steering apparatus, and FIG. 4 is a sectional view of a speed reduction mechanism.
As an electric power steering device for an automobile, for example, as shown in FIGS.
0, a first steering shaft 101 having an upper end connected thereto, and a lower end coaxially connected to a lower end of the steering shaft 101 via a torsion bar 102, and a lower end connected to a steering mechanism connected to wheels. A second steering shaft 103, a torque sensor 104 for detecting a torque applied to the first steering shaft 101 by rotating the steered wheels 100 by torsion generated in the torsion bar 102, and a detection result of the torque sensor 104. Assisted driving motor 105
And a speed reduction mechanism having a worm 106 and a worm wheel 107 connected to the output shaft of the motor 105 to reduce the rotation of the output shaft and transmit the reduced speed to the second steering shaft 103. The operation of the corresponding steering mechanism is assisted by the rotation of the motor 105, so that the burden on the driver for steering is reduced.

A worm 106 constituting a speed reduction mechanism is disposed so as to intersect with the axis of the second steering shaft 103, is supported in a housing 110 via a pair of rolling bearings 108, 108, and has a worm wheel 107. Is provided with a pair of rolling bearings 10.
It is supported in the housing 110 via 9, 109.

When the speed reduction mechanism is used as described above, the worm 106 and the worm wheel 107 are used in order to reduce the amount of backlash at the meshing portion between the worm 106 and the worm wheel 107 and eliminate the rattling noise caused by the backlash during steering. The worm 10 processed so that the distance between the centers of rotation of 107 and the distance between the centers of the fitting holes in which the rolling bearings 108 and 109 are fitted within an allowable range.
6, worm wheel 107, rolling bearings 108, 10
9. The second steering shaft 103 and the housing 110 are selected and assembled, but this assembly requires a lot of time, and an improvement measure has been demanded.

FIG. 5 is a sectional view of a main part of an electric power steering apparatus proposed by the applicant of the present invention. The applicant of the present invention has a bearing member 111 in which the end of the worm 106 rotated by the steering assist motor 105 is fitted on the opposite side to the motor, thereby enabling the worm 106 to move in the radial direction. Worm wheel 1
07 so as to apply a preload to a portion engaged with the bearing member 111.
An electric power steering apparatus comprising: a coil spring 112 for biasing the coil spring in a radial direction; and an adjusting screw 113 for adjusting the amount of deflection of the coil spring 112, and reducing the amount of backlash by applying a preload to the meshing portion. Proposed earlier.

[0007]

However, when the worm gear or the like of the speed reduction mechanism has its tooth trace twisted in the rotational direction with respect to the rotation center line, when a rotational torque is applied from the worm 106 to the worm wheel 107, in other words, When the steering is assisted by the rotation of the motor 105, the worm 10
6 moves radially along the tooth traces of the worm wheel 107, a component force (hereinafter referred to as meshing reaction force) is generated, and the meshing reaction force causes the worm 106 to move in the radial direction. In the case where the preload due to the contact force 112 is relatively small, the worm 10
6 is relatively large, the amount of backlash at the meshing portion is increased, and the effect of reducing the rattling noise due to the preload is reduced. When the preload by the coil spring 112 is relatively large, the rotational torque applied to the meshing portion increases, and the return of the steered wheels after the motor 105 assists the steering decreases.

An object of the present invention is to provide an electric power steering device that can solve the above-mentioned problems.

[0009]

An electric power steering apparatus according to a first aspect of the present invention includes a driving gear rotated by a steering assist motor and a driven gear meshed with the driving gear and connected to a steering mechanism. In the electric power steering apparatus which assists the steering by rotation of the motor, an urging means for urging the drive gear toward the driven gear, and a meshing reaction force applied to the drive gear when assisting the steering. And a damping means for damping.

In the first invention, the urging means urges the driving gear toward the driven gear, and the damping means attenuates the meshing reaction force applied to the driving gear. Even when the preload is relatively small, the movement of the driving gear due to the meshing reaction force can be suppressed by the damping means, the backlash amount of the meshing portion can be reduced, and the toothing due to the increased backlash amount can be reduced. The effect of reducing sound can be enhanced. In addition, since the preload applied to the meshing portion can be made relatively small, the rotational torque applied to the meshing portion can be reduced, and the return of the steered wheels after the motor assists the steering can be improved.

An electric power steering apparatus according to a second aspect of the present invention includes a housing accommodating the drive gear, wherein the damping means is filled with a liquid, and a liquid chamber provided in the housing; The liquid chamber is formed into two variable chambers, and is provided with a piston that moves by the meshing reaction force and a communication path that allows the two variable chambers to communicate with each other.

In the second aspect of the invention, the movement of the drive gear due to the meshing reaction force is transmitted to the piston in the liquid chamber, and the incompressible liquid in one of the variable chambers communicates with the piston while moving in the liquid chamber. Flow into the other variable chamber, and the volume of the variable chamber changes little by little, so when the meshing reaction force is applied relatively quickly due to unevenness of the road surface, etc., the sudden movement of the drive gear due to the meshing reaction force is immediately suppressed. It is possible to reduce an increase in the backlash amount. In addition, when the meshing state changes over time due to a dimensional change of the driven gear or the like, the piston can be moved without generating a damping force, and the damping force can be set according to the size of the communication passage. Therefore, the force for damping can be stabilized.

[0013] In the electric power steering apparatus according to a third aspect of the present invention, the urging means is an elastic body, and the elastic body is housed in the variable chamber to urge the drive gear through the piston. It is characterized by.

According to the third aspect of the present invention, since the elastic body of the urging means is housed in the variable chamber filled with the liquid of the damping means, the urging is performed without providing a separate member for protecting the urging means. The means can be reliably protected.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. FIG. 1 is a sectional view of an electric power steering device according to the present invention. The electric power steering device has a first steering shaft 2 having one end connected to a steered wheel 1 for steering and a cylindrical portion at the other end, and one end inserted into the cylindrical portion and having one end connected to the other end of the steering shaft 2. A torsion bar 3 coaxially connected to the torsion bar 3 and twisted by the action of a steering torque applied to the steering wheel 1, and a second steering shaft 4 coaxially connected at the other end to the other end of the torsion bar 3.
And a first and a second corresponding to the torsion of the torsion bar 3.
The steering wheel 1 is determined by the relative rotational displacement of the steering shafts 2 and 4.
A torque sensor 5 for detecting a steering torque applied to the motor, a steering assist motor 6 driven based on the torque detected by the torque sensor 5, and a rotation speed of the motor 6 A speed reduction mechanism 7 having a drive gear (hereinafter, referred to as a worm) 71 and a driven gear (hereinafter, referred to as a worm wheel) 72 for transmitting to the two steering shafts 4, and a housing 8 in which the torque sensor 5 and the speed reduction mechanism 7 are accommodated.
The motor 6 is attached to the housing 8.

The housing 8 has a first housing portion 8a for housing the torque sensor 5, and a second housing portion 8b continuous with the housing portion 8a and housing the worm wheel 72.
And a third accommodating portion 8c which is continuous with the accommodating portion 8b and accommodates the worm 71.

FIG. 2 is a sectional view of the speed reduction mechanism. The accommodating portion 8c is elongated in the axial direction of the worm 71, and is connected to one end of the worm 71 at one longitudinal end thereof with the concave portion 81 into which the shaft portion 71a provided at one end of the worm 71 is inserted, and the concave portion 81, A cylindrical guide hole 82 is formed in the shaft portion 71a in the radial direction. Further, a fitting hole 83 and a screw hole 84 continuous with the fitting hole 83 are provided at the other end of the housing portion 8c. Further, the motor 6 having a case communicating with the third housing portion 8c is attached to the housing 8.

The speed reduction mechanism 7 includes an output shaft 60 of the motor 6.
And a worm wheel 72 fitted and fixed in the middle of the second steering shaft 4 and connected to a steering mechanism.
Worm 71 and worm wheel 7
2, the rotation of the output shaft 60 is decelerated and transmitted to the second steering shaft 4, and from the second steering shaft 4 via a universal joint to, for example, a rack and pinion type steering mechanism (not shown). I try to communicate.

The worm 71 is disposed so as to intersect with the axis of the second steering shaft 4.
71b are provided. The shaft portion 71a at one end is inserted into the concave hole 81, and is rotatably supported by a bearing member 9 movably housed in the guide hole 82. The shaft portion 71b at the other end is rotatably supported in the fitting hole 83 via the rolling bearing 11, and the screw hole 84
The position of the worm 71 in the axial direction can be adjusted by a screw ring 12 screwed into the worm 71. A lock nut 13 is screwed onto the screw ring 12.

The bearing member 9 is formed in a cylindrical shape by a metal material. The shaft portion 71a rotates at an intermediate position in the axial direction of the bearing member, in other words, at an intermediate position in the moving direction of moving along the guide hole 82. A fitting hole 91 is provided so as to be fitted so as to contact the guide hole 82 on both sides of the fitting hole 91 in the moving direction to prevent the fitting hole 91 from moving in a direction intersecting the moving direction. The movement preventing portions 9a, 9a are provided, and the shaft portion 71a is supported at both ends of the guide hole 82 by the movement preventing portions 9a, 9a. Further, a concave portion 92 is provided at one end of the bearing member 9.

A cylindrical sliding bearing 93 made of synthetic resin and having a through hole formed with a smaller diameter than the inner diameter of the fitting hole 91 is fitted and fixed to the fitting hole 91. 93 allows the shaft portion 71a to slide in the axial direction. It should be noted that the sliding bearing 93 may be eliminated, and the shaft portion 71a may be directly fitted into the fitting hole 91.

The bearing member 9 is urged by the urging means 14 in the moving direction so as to apply a preload to the mesh portion of the worm 71 with the worm wheel 72, and is further applied to the bearing member 9 via the worm 71. A damping means 20 for damping the meshing reaction force is provided.

The urging means 14 is an elastic body 14 such as a coil spring.
a. The damping means 20 is provided in a cylindrical container 21 having a sealed structure, and a liquid chamber 22 filled with a liquid such as oil.
And a piston 23 that is accommodated in the liquid chamber 22 to form the two variable chambers 22a and 22b, and that moves by the meshing reaction force.
A communication passage 24 having a relatively small diameter for communicating the communication passages 2a and 22b.
The elastic member 14a is accommodated in one of the variable chambers 22a opposite to the bearing member 9, and the elastic member 14a urges the piston 23 toward the bearing member 9. I have.

The piston 23 has a disk portion 23a corresponding to the inner diameter of the liquid chamber 22, and a rod portion 23b projecting from the center of one surface of the disk portion 23a.
Is extended outside through a sealing member 25 provided at one end of the cylindrical container 21, and the rod portion 23 b contacts the bottom surface of the concave portion 92 of the bearing member 9.

The cylindrical container 21 is detachably screwed to the open edge of the guide hole 82, and is prevented from loosening by the lock nut 26 screwed to the cylindrical container 21.

In the electric power steering apparatus constructed as described above, when the worm 71 is incorporated, the cylindrical container 2
By moving the bearing member 9 through the piston 23 by the operation of 1, the worm 71 is brought into contact with the worm wheel 72, and the worm 71 and the worm wheel 72 are checked by rotating the worm wheel 72 to confirm that no backlash has occurred. The amount of backlash at the meshing portion can be eliminated. At this time, the elastic body 14a urges the worm 71 toward the worm wheel 72 via the piston 23 and the bearing member 9, and applies a preload to the meshing portion of the worm 71 with the worm wheel 72.

When the worm 71 is incorporated as described above,
The shaft portion 71a of the worm 71 is fitted in a fitting hole 91 provided in the middle of the bearing member 9 in the axial direction, and further provided on both sides of the fitting hole 91 in the moving direction of the bearing member 9. The movement inhibition portions 9a, 9a contact the guide holes 82,
The bearing member 9 is prevented from moving in a direction intersecting the moving direction, and the shaft portion 71 a is supported at both ends with respect to the guide hole 82.

The worm 71 is radially pressed along the tooth traces of the worm wheel 72 by the steering assist, and this pressing force, in other words, the above-mentioned radially engaging reaction force is applied to the bearing member 9 from the shaft portion 71a. When it is applied, the elastic body 14a that urges the piston 23 can suppress the movement of the bearing member 9 due to the meshing reaction force, and can reduce an increase in the amount of backlash.

Further, when the vehicle is traveling on a rough road, when the meshing reaction force is relatively quickly applied to the worm 71 and the bearing member 9 due to the unevenness of the road surface, the piston 23 abutting on the bearing member 9 moves inside the liquid chamber 22. While moving one of the variable chambers 22
a of the incompressible liquid from the communication passage 24 to the other variable chamber 22.
b, the volume of the variable chamber 22a changes little by little, so that a rapid movement of the worm 71 due to the meshing reaction force can be suppressed, and an increase in the amount of backlash can be reduced. Moreover, since the movement of the worm 71 due to the meshing reaction force can be suppressed by the damping means 20, the urging force of the urging means 14 can be made relatively small, and the preload applied to the meshing portion can be made relatively small. Therefore, the rotational torque applied to the meshing portion can be reduced, and the return of the steered wheels 1 after the motor 6 assists the steering can be improved.

Further, the dimensions of the worm 71 and the worm wheel 72 change slowly due to an increase in the amount of wear of the teeth of the worm 71 and the worm wheel 72, and thermal expansion or water absorption of the worm wheel 72 made of synthetic resin. When the meshing state changes over time due to the dimensional change over time, the worm 71 can be moved without operating the damping means 20, in other words, overcoming the force of the elastic body 14a without applying pressure to the liquid.

Further, if the variation in the assembling accuracy is within the movable range of the worm 71 by the urging means 14 and the damping means 20, it is not necessary to select and assemble the worm 71 and the like, and the assembling property can be improved.

In the embodiment described above, the liquid of the damping means 20 may be water instead of oil.
Instead of using a liquid, a gas or an elastic member such as a spring that does not apply a preload to the meshing portion may be used. Also,
As a means for moving the piston 23 by the meshing reaction force, the rod portion 23b provided integrally with the disc portion 23a is used. In addition, the rod portion 23b is formed integrally with the bearing member 9 separately from the disc-shaped piston 23. The rod may be used, or a rod interposed between the disc-shaped piston 23 and the bearing member 9 may be used, and the means is not particularly limited.

The liquid chamber 22 of the damping means 20 is provided in the housing 8 via the cylindrical container 21 and the housing 8
May be provided directly.

In the embodiment described above, the bearing member 9 for supporting one end of the worm 71 is provided, and the worm 71 is urged through the bearing member 9.
In addition, the bearing member 9 is eliminated, for example, the piston 23
The rod portion 23b may directly contact the shaft portion 71a.

The speed reducing mechanism 7 according to the embodiment described above is a worm gear including a drive gear 71 as a worm 71 and a driven gear 72 as a worm wheel, and a drive gear and a hypoid wheel as a hypoid pinion. May be a hypoid gear provided with a driven gear. Further, the reduction mechanism may be a bevel gear.

[Brief description of the drawings]

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

FIG. 2 is a sectional view of a speed reduction mechanism of the electric power steering device according to the present invention.

FIG. 3 is a sectional view of a conventional electric power steering device.

FIG. 4 is a cross-sectional view of a speed reduction mechanism portion of a conventional electric power steering device.

FIG. 5 is a cross-sectional view of a main part of the electric power steering device previously proposed by the applicant of the present invention.

[Explanation of symbols]

 Reference Signs List 6 motor 14 urging means 14a elastic body 20 damping means 22 liquid chamber 22a, 22b variable chamber 23 piston 24 communication hole (communication passage) 71 drive gear (worm) 72 driven gear (worm wheel)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tatsuo Otsuka 3-5-8 Minamisenba, Chuo-ku, Osaka-shi, Osaka Inside Koyo Seiko Co., Ltd. (72) Inventor Kenichiro Aoto 3-5-minamisenba, Chuo-ku, Osaka-shi, Osaka No. 8 Inside Koyo Seiko Co., Ltd. (72) Inventor Tetsuya Murakami 3-5-8 Minamisenba, Chuo-ku, Osaka City, Osaka Prefecture Inside (72) Inventor Shigetaka Kinme 3-chome, Minamisenba, Chuo-ku, Osaka City, Osaka Prefecture No. 8 Inside Koyo Seiko Co., Ltd. (72) Inventor Takeo Iino 3-8-5 Minamisenba, Chuo-ku, Osaka-shi, Osaka Prefecture Inside (72) Inventor Tomoyuki Takei 3--5 Minamisenba, Chuo-ku, Osaka-shi, Osaka No. 8 Koyo Seiko Co., Ltd. (72) Kunihiro Oka 3-8, Minamisenba, Chuo-ku, Osaka-shi, Osaka F-ter (Reference) 3D033 CA04 CA16 3J009 DA03 DA11 EA06 EA19 EA23 EA32 FA08

Claims (3)

[Claims] 1. An electric power steering apparatus comprising: a driving gear rotated by a steering assist motor; and a driven gear meshing with the driving gear and connected to a steering mechanism, and assisting the steering by rotation of the motor. An electric power steering apparatus comprising: urging means for urging the drive gear toward a driven gear; and damping means for attenuating a meshing reaction force applied to the drive gear when assisting steering. 2. A housing for accommodating the driving gear, wherein the damping means is filled with a liquid and a liquid chamber provided in the housing, and a liquid chamber accommodated in the liquid chamber and having two liquid chambers. The electric power steering apparatus according to claim 1, further comprising: a piston that moves by the meshing reaction force; and a communication path that allows the two variable chambers to communicate with each other. 3. The electric power steering apparatus according to claim 2, wherein the urging means is an elastic body, and the elastic body is housed in the variable chamber to urge the drive gear via the piston.