JP2003095119A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the transmission torque capacity of a worm wheel by using a simple fitting structure. SOLUTION: A worm wheel 42 meshed with a worm 41 driven by the rotation of a steering assistant motor is fitted onto a rotating shaft 23, rolling bearings 7 and 8 supporting the rotating shaft 23 are disposed on both sides of the worm wheel 42, and a tube part 43 allowed to abut on the rolling bearings 8 is integrally formed on the side face of the worm wheel 42. The transmission torque capacity of the worm wheel is increased by a component force applied to the worm wheel 42 in tooth lateral direction and a frictional resistance force provided when the worm wheel 42 is pressed against the rolling bearings 7 and 8 by the component force.

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 steering assist force.

[0002]

2. Description of the Related Art The steering of an automobile is arranged outside a vehicle compartment for steering a steering wheel (generally a front wheel) for rotating a steering wheel arranged inside the vehicle compartment. It is performed by telling the steering mechanism.

FIG. 6 is a sectional view showing the structure of a conventional electric power steering apparatus. BACKGROUND ART As a power steering device for automobiles, a hydraulic type and an electric type are known. Generally, the hydraulic type is mounted on a vehicle larger than a standard vehicle, and the electric type is mounted on a light vehicle, but recently, the electric type is being mounted on a vehicle larger than a standard vehicle.

As an electric power steering device,
As shown in FIG. 6, for example, transmission means 101 for transmitting the rotation of the steering wheel 100 for steering to a steering mechanism (not shown) connected to the wheels, a motor 102 for steering assistance, and a rotational force of the motor 102 And a reduction gear mechanism 103 which increases and transmits to a part of the transmission means 101. The operation of the steering mechanism according to the rotation of the steered wheels 100 is assisted by the rotation of the motor 102, and the operation of the driver for steering is performed. It is configured to reduce the labor burden.

The transmission means 101 includes a first steering shaft 104 connected to the steered wheels 100 and a second steering shaft 106 connected to the first steering shaft 104 via a torsion bar 105.
And a connecting shaft 1 such as a universal joint connecting the second steering shaft 106 and the rack and pinion type steering mechanism.
07 and. The first steering shaft 104 is rotatably supported in the housing 109 via a needle bearing 108, and the second steering shaft 106 is rotatably supported in the housing 109 via two rolling bearings 110 and 111. Has been done.

In the housing 109, a torque sensor 112 for detecting the torque applied to the first steering shaft 104 by rotating the steered wheels 100 by the twist generated in the torsion bar 105, and the reduction gear mechanism 103. Is housed.

The motor 102 is mounted outside the housing 109. The reduction gear mechanism 103 includes a worm wheel 113 connected to the output shaft of the motor 102 and a worm wheel 1 press-fitted in the middle of the second steering shaft 106.
And the rotation of the motor 102 from the worm 113 and the worm wheel 114 to the second steering shaft 10.
6 is transmitted.

[0008]

The conventional electric power steering apparatus constructed as described above is generally mounted on a passenger vehicle of a class of about 1500 cc from a light vehicle, and the steering rudder assist force by the motor 102 is 1500 cc.
Since the size may be smaller than that of a normal class vehicle of a super class or more, even in the structure in which the worm wheel 114 is press-fitted and fixed to the second steering shaft 106, the worm wheel 11
4 was able to sufficiently transmit the required torque to the second steering shaft 106.

However, when the electric power steering apparatus is mounted on, for example, a vehicle of the above 1500 cc class or more, it is necessary to use a high output motor to increase the steering assist force. In the structure in which the worm wheel 114 is press-fitted and fixed, the worm wheel 114 may slip with respect to the second steering shaft 106, resulting in insufficient required torque transmission.

Therefore, in order to sufficiently transmit the required torque even when a high output motor is used, for example, the worm wheel 114 may be key-fitted, spline-fitted, or serrated-fitted to the second steering shaft 106. Conceivable. However, in the case of key fitting, there is a problem that it is difficult to process the key groove and to incorporate the worm wheel 114 into the second steering shaft 106, and in the case of spline fitting and serration fitting, the spline Serration is difficult to process, and a gap is generated in the fitting portion of the worm wheel 114, which causes the worm wheel 114 to rattle in the circumferential direction during steering, resulting in abnormal noise.

The present invention has been made in view of such circumstances, and provides an electric power steering apparatus capable of sufficiently transmitting a required torque with a simple fitting structure even when a high-output motor is used. The purpose is to do.

[0012]

According to a first aspect of the present invention, there is provided an electric power steering apparatus, wherein a worm rotated by a motor for steering assistance, a worm wheel meshing with the worm, and a rotation of the worm wheel are steered. In an electric power steering device that includes a rotary shaft that transmits to a mechanism and a bearing that supports the rotary shaft, and is configured to assist steering by rotation of the motor, the worm wheel is press-fitted into the rotary shaft, One side of the worm wheel has a first movement restricting portion that restricts movement of the worm wheel in one axial direction, and the other side of the worm wheel is in contact with the bearing to contact the worm wheel. It is characterized by having a second movement restricting portion for restricting movement in the other axial direction.

According to the first aspect of the invention, the teeth of the worm and the worm wheel forming the reduction gear mechanism are twisted in the rotational direction with respect to the center line of rotation, and the tooth surface of the worm causes torque in the rotational direction of the worm wheel. When is added,
A component force is generated in the tooth width direction (axial length direction) of the worm wheel, but the movement of the worm wheel in the axial length direction is restricted by the first and second movement restriction portions, so When steering assist is performed by rotation,
The worm wheel will be pressed by the first movement limiting portion or the second movement limiting portion by the component force,
The transfer torque capacity can be increased by the frictional resistance force due to this pressing.

Since the transmission torque capacity can be increased by the component force in the tooth width direction applied to the worm wheel as described above, in addition to the friction resistance force at the press-fitting portion of the worm wheel press-fitted to the rotary shaft, the pressing force is applied. It is possible to obtain a frictional resistance force due to, and it is possible to increase the transmission torque capacity by a simple fitting structure.

In the electric power steering apparatus according to the second aspect of the present invention, the first movement restricting portion is formed by a bearing press-fitted into the rotary shaft to support the rotary shaft.

In the second aspect of the invention, since the bearing for supporting the rotary shaft constitutes the first movement restricting portion, the transmission torque capacity can be increased without increasing the number of parts.

In the electric power steering apparatus according to the third aspect of the present invention, the second movement restricting portion is composed of a tubular portion provided integrally with the worm wheel.

According to the third aspect of the present invention, since the tubular portion integrated with the worm wheel constitutes the second movement limiting portion, the transmission torque capacity can be increased without increasing the number of parts. Further, the axial direction position of the bearing with respect to the rotary shaft can be determined by the tubular portion, and since it is not necessary to provide this positioning means on the rotary shaft, the structure of the rotary shaft can be simplified and the cost can be reduced. Can be achieved.

The electric power steering apparatus according to the fourth aspect of the invention is characterized in that the second movement restricting portion is an annulus interposed between the bearing and the worm wheel.

According to the fourth aspect of the present invention, the transmission torque capacity can be increased by adding the ring body to the existing structure.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the drawings showing the embodiments thereof. Embodiment 1 FIG. 1 is a sectional view showing the structure of an electric power steering apparatus according to the present invention, and FIG. 2 is an enlarged sectional view showing the structures of a reduction gear mechanism and a motor portion. As shown in FIGS. 1 and 2, the electric power steering device includes a transmission unit 2 for transmitting a rotation of a steering wheel 1 for steering to a steering mechanism (not shown) connected to the wheels, and a motor for steering assistance. 3 and a reduction gear mechanism 4 that increases the rotational force of the motor 3 and transmits it to a part of the transmission means 2.

The transmission means 2 is a first wheel connected to the steered wheels 1.
The steering shaft 21 and the torsion bar 22 on the first steering shaft 21.
A second steering shaft 23 that is coaxially connected via
The steering shaft 23 and a connecting shaft 24 such as a universal joint that connects the rack and pinion type steering mechanism are provided.

The first steering shaft 21 is rotatably supported in the housing 6 via the needle bearing 5, and the second steering shaft 23 is supported via the first rolling bearing 7 and the second rolling bearing 8 in the above-mentioned manner. It is rotatably supported in the housing 6.

In the housing 6, a torque sensor 9 for detecting the torque applied to the first steering shaft 21 by rotating the steered wheels 1 by the twist generated in the torsion bar 22, and the reduction gear mechanism 4. Is housed.

The housing 6 is connected to the first housing body 61 having a substantially cylindrical first housing portion 6a in which the lower end of the first steering shaft 21 and the torque sensor 9 are housed, and the first housing portion 6a. , A substantially cylindrical second accommodating portion 6b accommodating the second steering shaft 23 and the worm wheel 42 of the reduction gear mechanism 4, and communicating with one side of the second accommodating portion 6b,
A second housing body 62 having a substantially cylindrical third accommodating portion 6c for accommodating the worm 41 of the reduction gear mechanism 4, and a case 31 communicating with the third accommodating portion 6c at one end of the third accommodating portion 6c. Is attached to the motor 3.

In the second accommodating portion 6b, the worm wheel 42
First and second support holes 63 and 64 for rotatably supporting the second steering shaft 23 via the rolling bearings 7 and 8 are provided on both sides of the accommodation area. Further, the first housing body 61 and the second housing body 62 are detachably connected by a connecting means such as a bolt. The first supporting hole 63 is provided in the boundary portion between the first accommodating portion 6a and the second accommodating portion 6b, and the first accommodating portion 6b has the first supporting hole 63.
The second support hole 64 is provided on the side opposite to the housing portion 6a.

In the first rolling bearing 7, the inner ring 7a is press-fitted into the second steering shaft 23, and the outer ring 7b is fitted in the first support hole 63. The inner ring 8a of the second rolling bearing 8 is the second
The outer ring 8b is press-fitted into the steering shaft 23 and fitted into the second support hole 64. By fitting the outer ring 7b into the support hole 63 and the outer ring 8b into the support hole 64, the rolling bearing 7,
The position of 8 in the housing 6 is determined.

FIG. 3 is an enlarged sectional view of the reduction gear mechanism portion. The reduction gear mechanism 4 includes a worm 41 connected to the output shaft 32 of the motor 3, and a worm wheel 42 meshed with the worm 41 and fitted in the middle of the second steering shaft 23.
It has and.

The worm 41 and the worm wheel 42 are arranged so that their rotation center lines intersect (specifically, orthogonal). Further, the tooth traces of the worm 41 and the worm wheel 42 are twisted in the rotation direction with respect to the rotation center line, and when torque is applied in the rotation direction of the worm wheel 42 by the tooth surface of the worm 41 by the rotation of the motor 3, the worm wheel 42 is rotated. A component force is generated in the tooth width direction of 42.

The worm wheel 42 is composed of a metal wheel body 42b having a fitting hole 42a that is press-fitted into the second steering shaft 23, and an outer periphery of the wheel body 42b. Resin ring tooth 4
2c and on both sides of this worm wheel 42,
First and second movement restricting portions 1 for restricting movement of the worm wheel 42 to one and the other in the axial direction by the component force.
0 and 11 are provided.

The first movement limiting portion 10 is composed of the first rolling bearing 7, and one end of the inner ring 7a of the first rolling bearing 7 is brought into contact with one side surface of the worm wheel 42 so that the worm wheel 42 moves. Movement in one axial direction is restricted.

The second movement restricting portion 11 is composed of a cylindrical portion 43 integrally provided on the other side surface of the worm wheel 42 so as to be concentric with the fitting hole 42a. This tube 43
Is formed in such a length as to come into contact with one end of the inner ring 8a of the second rolling bearing 8, and the tubular portion 43 comes into contact with one end of the inner ring 8a to move the worm wheel 42 in the other axial direction. I am trying to limit it. The tubular portion 43 is integrally formed with the wheel body 42b by press molding or the like.

The worm 41 has a shaft portion 41 at both ends thereof.
a and 41b are rotatably supported in the third accommodating portion 6c via rolling bearings 44 and 45. In FIG. 3, reference numeral 12 is an adjusting nut screwed in the middle of the second steering shaft 23 to adjust the axial position of the inner ring 8a of the second rolling bearing 8 in the axial direction. The position of the inner ring 8a in the axial direction is determined with the portion 43.

In the electric power steering apparatus having the above-described structure, the second steering shaft 2 in which the first rolling bearing 7, the worm wheel 42 and the second rolling bearing 8 are fitted
3 is inserted into the second housing portion 6b of the second housing body 62, and the first housing body 61, which supports the first steering shaft 21 and the torque sensor 9, is connected to the second housing body 62 by a connecting means such as a bolt. By doing so, the reduction gear mechanism 4 part is assembled.

In this assembled state, the worm wheel 4
One side surface of the second rolling bearing 7 contacts the inner ring 7a of the first rolling bearing 7,
Further, the tubular portion 43 integrally provided on the other side surface of the worm wheel 42 abuts on the inner ring 8a of the second rolling bearing 8, and the movement of the worm wheel 42 to one side and the other side in the axial direction is restricted. . During this assembly, the position of the inner ring 8a in the second rolling bearing 8 in the axial direction can be adjusted by rotating the adjusting nut 12, so that even if there is a dimensional error in the axial direction. The tubular portion 43 can be brought into contact with the inner ring 8a.

The electric power steering apparatus assembled in this way is operated by the rotation of the motor 3 to assist steering, in other words, when the worm 41 is rotated by the rotation of the motor 3, the second steering of the worm wheel 42 is performed. A frictional resistance force can be obtained at the fitting portion to the shaft 23, and the worm wheel 42 is caused to move the inner ring 7a of the first rolling bearing 7 by the component force applied to the worm wheel 42.
Or the inner ring 8a of the second rolling bearing 8 is pressed through the tubular portion 43 to obtain a frictional resistance force due to this pressure, and the frictional resistance force due to this pressure causes the worm wheel 42 to move. The transmission torque capacity to the second steering shaft 23 can be increased.

In addition to the simple fitting structure in which the worm wheel 42 is fitted to the second steering shaft 23, the increase of the transmission torque capacity is made possible by the existing two bearings 7 and 8 supporting the second steering shaft 23. This can be achieved by the worm wheel 42 and the tubular portion 43 formed integrally with the worm wheel 42, and the cost can be reduced as compared with the case where the transmission torque capacity of the worm wheel 42 is increased by key fitting, spline fitting, or the like.

Further, since the position of the inner ring 8a of the second rolling bearing 8 in the axial direction can be determined by the tubular portion 43, the positioning step portion which determines the axial position of the inner ring 8a in the second steering shaft 23 can be determined. It is not necessary to provide the above, the structure of the second steering shaft 23 can be simplified, and the cost can be reduced.

Embodiment 2 FIGS. 4 and 5 are sectional views showing the structure of the essential parts of Embodiment 2 of the electric power steering apparatus. The electric power steering apparatus according to the second embodiment includes a tubular ring body 13 between the second rolling bearing 8 and the worm wheel 42 instead of providing the tubular portion 43 integrally with the worm wheel 42. The second movement restriction unit 11 is provided.

The ring body 13 uses a collapsible spacer for absorbing an assembling error in the axial direction at the time of assembling, or a coil spring which can be bent by a force exceeding the steering assist force of the motor 3. To use.

In the second embodiment, when the ring body 13 is a collapsible spacer, the ring body 13 has one side surface of the worm wheel 42 in contact with the inner ring 7a of the first rolling bearing 7 and the worm wheel. The other side surface of the second rolling bearing 8 and the inner ring 8a of the second rolling bearing 8 are interposed so that no gap is formed. When the ring body 13 is a coil spring,
Both ends of the ring body 13 are in contact with the other side surface of the worm wheel 42 and the inner ring 8a of the second rolling bearing 8 while one side surface of the worm wheel 42 is in contact with the inner ring 7a of the first rolling bearing 7. To be intervened.

In the second embodiment, when the steering assist is performed by the rotation of the motor 3, the worm wheel 4 is used.
It is possible to obtain a frictional resistance force in the fitting portion of the second steering shaft 23 to the second steering shaft 23, and further, the component force applied to the worm wheel 42 causes the worm wheel 42 to move to the first rolling bearing 7
The inner ring 7a of the second rolling bearing 8 is pressed against the inner ring 7a of the second rolling bearing 8 and the inner ring 8a of the second rolling bearing 8 is pressed against the inner ring 7a of the second rolling bearing 8 to obtain a frictional resistance force. The transmission torque capacity of the wheel 42 to the second steering shaft 23 can be increased.

Further, when the vehicle rides on a curb, a reverse input is applied to the worm wheel 42 from the steering wheel side through the steering mechanism, the connecting shaft 24 and the second steering shaft 23, and the reverse input causes the worm wheel 42 to rotate. When a component force is applied to the other side of the tooth width direction of 42, the worm wheel 42 is pressed by the inner ring 8a of the second rolling bearing 8 via the ring body 13, so when the ring body 13 is a coil spring. By the pressing, the coil spring can be bent in the axial direction. As a result, the frictional resistance force due to the pressing can be reduced,
The worm wheel 42 and the second steering shaft 23 can be relatively rotated, and damage to the teeth of the worm wheel 42 due to reverse input can be reduced.

When a collapsible spacer or a coil spring is used as the ring body 13, for example, when the reduction gear mechanism 4 part is assembled by connecting the first housing body 61 to the second housing body 62 with bolts. Since a part of the collapsible spacer can be plastically deformed or the coil spring can be bent by the tightening force of the bolt, the assembling property of the reduction gear mechanism 4 part can be improved and the reduction gear mechanism 4 part can be easily assembled. The dimensional tolerance in the axial direction can be increased, and the workability can be improved.

The ring 13 may have a plate shape such as a disc spring or a wave spring, as well as a cylindrical shape. The wheel body 42b of the worm wheel 42 has a fitting cylinder 42d whose inside is press-fitted into the second steering shaft 23 as shown in FIGS.
In addition to the structure having, the fitting cylinder 42d may be eliminated and the thickness may be close to the tooth width dimension.

The other configurations and effects are the same as those of the first embodiment.
Since they are the same as the above, the same reference numerals are given to the same parts, and the detailed description and action and effect thereof will be omitted.

In the embodiment described above, the first rolling bearing 7 is used as the first movement limiting portion 10. However, in addition to this, the first movement limiting portion 10 is provided on the second steering shaft 23. It may be a step 25 in the direction (Fig.
(See FIG. 5).

[0048]

According to the first aspect of the present invention, the worm wheel press-fitted into the rotary shaft by the component force applied to the worm wheel in the tooth width direction and the frictional resistance force caused by the component force. The transmission torque capacity can be increased and the bearing for supporting the rotating shaft prohibits the movement of the worm wheel in the other axial direction. Therefore, the transmission torque of the worm wheel can be increased by key fitting, spline fitting, etc. The structure is simple compared to the case of increasing the capacity,
Cost can be reduced.

According to the second and third inventions, the transmission torque capacity can be increased without increasing the number of parts. Moreover, according to the third aspect of the invention, since it is not necessary to provide a positioning means for determining the position of the bearing with respect to the rotating shaft in the axial direction, it is possible to simplify the structure of the rotating shaft and reduce the cost. Can be planned.

According to the fourth invention, the transmission torque capacity can be increased by adding the ring body to the existing structure.

[Brief description of drawings]

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

FIG. 2 is an enlarged cross-sectional view showing a configuration of a reduction gear mechanism and a motor portion of the electric power steering device according to the present invention.

FIG. 3 is an enlarged cross-sectional view of a reduction gear mechanism portion of the electric power steering device according to the present invention.

FIG. 4 is a sectional view showing a configuration of a main part of a second embodiment of an electric power steering apparatus according to the present invention.

FIG. 5 is a cross-sectional view showing a configuration of a main part of a second embodiment of an electric power steering device according to the present invention.

FIG. 6 is a cross-sectional view showing a configuration of a conventional electric power steering device.

[Explanation of symbols]

3 motor 7 First rolling bearing 8 Second rolling bearing 10 First movement restriction unit 11 Second movement restriction unit 13 ring 23 Second steering shaft (rotating shaft) 41 Warm 42 worm wheel 43 Tube

Claims (4)

[Claims] 1. A worm that is rotated by a motor for steering assistance, a worm wheel that meshes with the worm, a rotary shaft that transmits the rotation of the worm wheel to a steering mechanism, and a bearing that supports the rotary shaft. In the electric power steering device, which is configured to assist steering by rotation of the motor, the worm wheel is press-fitted into the rotary shaft, and one side of the worm wheel is provided in one of the worm wheel axial direction. Has a first movement limiting portion that limits movement of the worm wheel, and a second movement limiting portion that abuts on the bearing and limits movement of the worm wheel in the other axial direction on the other side of the worm wheel. An electric power steering device comprising: 2. The electric power steering apparatus according to claim 1, wherein the first movement restricting portion is a bearing that is press-fitted into the rotary shaft and supports the rotary shaft. 3. The first movement limiting portion is a tubular portion integrally provided with the worm wheel.
The electric power steering device described. 4. The electric power steering apparatus according to claim 1, wherein the second movement restricting portion is an annular body interposed between the bearing and the worm wheel.