JPH11115776A - Motor-driven power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor-driven power steering device which can prevent the damage of a torque transmission course in spite of a simple formation. SOLUTION: In this motor-driven power steering device, since a power transmission means having a friction face and a pressing means pressed against the friction face is provided between the rotary shaft 102a of a motor 10 and the input shaft of a speed reduction mechanism, a power transmission is planned to be carried out by utilizing a relatively small frictional force generated between a friction plate 131 and a receiving member before the output torque of the motor 102 is increased by the speed reduction mechanism. Thus, since it is unnecessay to increase the pressing power of the pressing means and to enlarge the area of the friction face, the formation of the power transmission means can be made simple and compact.

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.

[0002]

2. Description of the Related Art As an electric power steering device for a vehicle, a rotational output of an electric motor, which is an auxiliary steering torque, is reduced by a gear device to transmit an appropriate torque and speed to an output shaft of a steering mechanism. Things are known. When such an electric power steering device is operated, a sudden force received by a wheel from a road surface may oppose the output of the electric motor and generate an impact force. Such an impact force may cause damage to the electric motor and the power transmission mechanism.

In order to reduce or eliminate this impact force,
In the prior art, an example in which a slip mechanism utilizing frictional force is provided on the output shaft of a steering mechanism to act as a torque limiter that causes slip when excessive torque is applied (Japanese Utility Model Application No. 4-75506).
No.) or measures such as placing an electromagnetic clutch acting as a torque limiter on the rotating shaft were taken.

[0004]

However, in the above-mentioned conventional electric power steering apparatus, the output of the electric motor is usually transmitted to the output shaft via a deceleration (torque increase) mechanism in the above-mentioned example. In order to transmit the increased torque, the frictional force used in the sliding mechanism needs to be considerably increased. Therefore, there is a problem that strict load management is required to obtain a constant frictional force. Further, in the example of (1), it is necessary to always supply the necessary power to the electromagnetic clutch, which is not preferable from the viewpoint of energy saving. There is a problem that must be.

An object of the present invention is to provide an electric power steering apparatus which has a simple structure and can prevent damage to an electric motor and a power transmission system.

[0006]

In order to achieve the above object, an electric power steering apparatus according to the present invention comprises a housing,
A motor having a rotating shaft mounted on the housing, an output shaft connected to a steering mechanism for steering wheels, and an input shaft connected to the output shaft and decelerating from the input shaft to the output shaft; And a power transmission means provided between the rotating shaft of the motor and the input shaft of the speed reducing mechanism for transmitting power. A friction plate which is non-rotatable relative to one of the input shafts but is movably mounted in the axial direction; and a receiving member which is non-rotatably mounted to the other of the rotary shaft and the input shaft A pressing member for pressing the friction plate against the receiving member, and power is transmitted by utilizing a frictional force generated between the friction plate and the receiving member. , The frictional force is greater than the power normally transmitted from the motor, It is smaller than the impact force generated between the over motor and wheels.

[0007]

According to the electric power steering apparatus of the present invention, the power transmission means having the friction surface and the pressing means pressed against the friction surface is provided between the rotation shaft of the motor and the input shaft of the speed reduction mechanism. Before the output torque of the motor is increased by the speed reduction mechanism, power transmission is performed using a relatively small friction force generated between the friction plate and the receiving member. Has become. Therefore, there is no need to increase the pressing force of the pressing means, and it is not necessary to increase the area of the friction surface, so that the configuration of the power transmission means can be made simple and compact.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is an axial partial cross-sectional view of an electric power steering apparatus 100 according to an embodiment of the present invention.

Referring to FIG. 1, an electric power steering apparatus 100 includes a housing 101 and a tube 110 extending therefrom. Housing 101
Is fixed to a vehicle body (not shown) by a bracket 114 and the tube 110 is fixed by a bracket 115. An input shaft 111 having one end connected to a steering wheel (not shown) extends inside the tube 110 and is rotatably supported with respect to the tube 110. The other end of the input shaft 111 is the torque detector 1
12.

The torque detecting device 112 is also provided in the housing 1
Transmission shaft 11 which extends inside 01 and is rotatably supported
3 is connected. The transmission shaft 113 is connected to a steering device (not shown), and transmits torque for steering the wheels. The torque detector 112 is provided to detect the relative torque between the input shaft 111 and the transmission shaft 113 and thereby appropriately control the auxiliary steering force. The configuration is well known, and is described below. Details are not described.

The worm wheel 104 is coaxially mounted on the transmission shaft 113 near the torque detecting device 112. The worm wheel 104 meshes with a worm gear 103a (see FIG. 2) of the speed reducer input shaft 103 extending in a direction perpendicular to the plane of FIG. The speed reducer input shaft 103 is connected to a rotation shaft of the motor 102 (see FIG. 2).

The operation of the electric power steering apparatus 100 shown in FIG. 1 will be described below. Input of a steering torque from a steering wheel (not shown) rotates the input shaft 111, and the rotation torque is transmitted to the transmission shaft 113 via the rotation torque detection device 112. The transmission shaft is connected to the steering device (not shown) as described above, and transmits the torque for steering. In this case, the value of the torque detected by the rotation torque detecting device 112 is sent to a not-shown determination circuit, where it is compared with a predetermined value. If the torque exceeds a predetermined value,
Since the auxiliary steering force is required, the motor 102
A drive command is issued to drive. The motor 102 driven by the drive command rotates the speed reducer input shaft 103,
Further, the rotational torque is transmitted to the transmission shaft 113 via the worm wheel 104. When the value of the torque detected by the rotation torque detection device 112 is lower than a predetermined value, the auxiliary steering force is unnecessary, and the motor 102 is not driven.
Note that the speed reducer input shaft 103 and the worm wheel 10
4 together with deceleration means.

FIG. 2 is a view of the apparatus cut along the II-II section of FIG. 1 and viewed in the axial direction. In FIG. 2, an electric motor 102 is attached to a right end of a housing 101. A male spline 102c is formed at the outer end of a rotating shaft 102a rotatably supported by the electric motor 102 by a bearing 102b. Rotating shaft 102a
Around the male spline 102c, two annular friction plates 131 are attached. The friction plate 131 has a female spline groove 131a in the center opening, and the female spline groove 131a is fitted into the male spline groove 102c of the rotating shaft, so that the friction plate 131 cannot rotate relative to the rotating shaft 102a but is in the axial direction. It is movable.

A friction plate housing 133 is provided so as to surround the outer periphery of the friction plate 131. The hollow friction plate housing 133 includes a large diameter portion 133a and a small diameter portion 13a.
3b is connected by a conical part 133c. The inner diameter of the large-diameter portion 133a is formed slightly larger than the outer shape of the friction plate 131, and does not hinder the movement of the friction plate 131 in the axial direction.

Two disc springs 132 are back-to-back around the rotary shaft 102a, and are in contact with them so as to be sandwiched between two friction plates 131. The inner periphery of the friction plate housing 133 and the friction plate 13 on the electric motor side
A peripheral groove 133d is formed in the vicinity of the outer periphery of 1. A holding plate 134 is provided in the circumferential groove 133c, and is attached thereto by caulking an end of the friction plate housing. In addition, by holding the friction plate 131 between the pressing plate 134 and the conical portion 133c and setting the distance between them to a predetermined value, the urging force of the disc spring 132 does not decrease below the reference value. . The friction plate housing 133 and the holding plate 134 constitute a receiving member, and the disc spring 132 constitutes a pressing member.

A reducer input shaft 103 coaxial with a rotating shaft 102a of the electric motor 102 is rotatably supported by bearings 105 and 106 near both ends of the housing 101. A male spline 103e is formed at the end of the reducer input shaft 103 on the side of the electric motor, and a female spline 133e is formed at the inner periphery of the small diameter portion 133b of the friction plate housing 133. 133 is attached so that it cannot rotate relative to the speed reducer input shaft 103 but can move in the axial direction. The distal end of the small diameter portion 133b of the friction housing 133 abuts on the spacer 137 to prevent further movement in the axial direction. The bearings 105 and 106 are respectively provided with outer rings 105a,
106a, inner rings 105b and 106b, and a plurality of balls 105c and 106c held between the two wheels. On the opposite side (worm gear side) of the bearing 106 from the electric motor, the step of the housing 101 and the outer race 10 of the bearing 106
6a, a spacer 135 is provided. Further, on the electric motor side of the bearing 106, a snap ring 136 is inserted into a circumferential groove of the housing, and the bearing 106 is sandwiched between the spacer 135 and the snap ring 136 and cannot be moved in the axial direction.

The speed reducer input shaft 103 forms a flange 103c adjacent to the inside of the bearing 105, forms a flange 103b adjacent to the bearing 106, and meshes with the worm wheel 104 between the flanges. Worm gear 103a is formed. A male spline 103d engaged with a nut 107 is provided at an end of the speed reducer input shaft 103 opposite to the motor.
Are formed, and the flange portion 103c and the nut 107
The inner ring 105b of the bearing 105 is sandwiched. Note that the worm wheel 104 and the worm gear 103a constitute a speed reduction mechanism.

Next, the operation of the pressing means according to the present invention will be described below. In normal operation, the motor 10
2 is transmitted to the friction plate 131 via the rotating shaft 102a. As described above, the two friction plates 131 are urged by the disc spring 132 so as to be separated from each other in the direction in which the pressing plate 134 and the friction plate housing 133 are pressed. Therefore, the friction plate 131 is
2 is compressed between the holding plate 134 and the friction plate housing 133, and generates a frictional force according to the pressed force.
The urging force of the disc spring 132 and the distance between the friction plates 131 are set so that the friction force becomes larger than the torque generated by the motor 102 in a normal operation. Housing 13
3 rotates integrally. The torque transmitted to the friction plate housing 133 rotates the worm wheel 104 via the worm gear 103a of the speed reducer input shaft 103,
This is transmitted to a steering device (not shown) to perform a steering operation.

Incidentally, the wheels may receive an impact force due to unevenness of the road surface. In such a case, the impact force is
In some cases, the power is transmitted in a reverse direction to the motor 102 via the power transmission system, and the power is opposed to the output of the motor. Due to this opposition, excessive stress is generated in the power transmission system, and in some cases, there is a possibility that components may be damaged.

In such a case, in the electric power steering apparatus according to the present invention, the frictional force generated between the friction plate 131, the holding plate 134, and the friction plate housing 133 is smaller than the above-mentioned impact force. Since the biasing force of the disc spring 132 is set, a slip occurs between the friction plate 131 and the holding plate 134 or the friction plate housing 133 in response to the generation of the impact force. Since the impact force is almost completely absorbed by the slip, it is possible to prevent the power transmission system from being damaged.

Further, in the electric power steering device according to the present invention, the disc spring 132 moves the friction plate 131.
Of the friction plate housing 133
Has been received by For example, in the configuration in which the friction plate is urged against the housing, a problem arises in that a thrust force is generated on the reduction gear input shaft and the rolling resistance of the bearing increases, but this embodiment has the above-described configuration. Therefore, a bearing 102b that supports the rotating shaft 102a of the electric motor 102 and a bearing 10 that supports the reduction gear input shaft 103
No thrust force due to the urging of the friction plate is applied to 5, 106. Therefore, in this embodiment, the rolling resistance around the axis is reduced, and the return of the handle is improved. In this embodiment, the friction plate 13
By providing two sheets, the transmission capacity can be improved or the diameter can be reduced as compared with the case of one sheet. Further, since two friction plates are used, even if the torque transmission capacity of the spline of one friction plate is small,
By combining them, sufficient torque can be transmitted.

Although the present invention has been described with reference to the exemplary embodiments, the present invention should not be construed as being limited to the above-described exemplary embodiments, but can be modified and improved as appropriate. For example, one friction plate may be used. Further, the friction housing 133 is movable in the axial direction with respect to the speed reducer input shaft 103. However, the friction housing 133 may be connected to each other using, for example, a radial through pin.

[0023]

As described above, according to the electric power steering apparatus of the present invention, the power transmission means having the friction surface and the pressing means pressed against the friction surface is provided by the power transmission means having the rotating shaft of the motor and the power transmission means. Since it is provided between the input shaft of the speed reduction mechanism and the output torque of the motor is increased by the speed reduction mechanism, a relatively small friction force generated between the friction plate and the receiving member is used. To perform power transmission. Therefore, there is no need to increase the pressing force of the pressing means, and it is not necessary to increase the area of the friction surface, so that the configuration of the power transmission means can be made simple and compact.

[Brief description of the drawings]

FIG. 1 is an axial partial cross-sectional view of an electric power steering apparatus 100 according to an embodiment of the present invention.

FIG. 2 is a view of the device cut along the II-II plane of FIG. 1 and viewed in the axial direction.

[Explanation of symbols]

 101 housing 102 motor 103 reduction gear input shaft 104 worm wheel 131 friction plate 132 disk spring 133 friction plate housing 134 holding plate

Claims (1)

[Claims] A motor mounted on the housing and having a rotating shaft; an output shaft connected to a steering mechanism for steering wheels; an input shaft connected to the output shaft and having an input shaft; A speed reduction mechanism for transmitting power at a reduced speed from the shaft to the output shaft; and a power transmission means provided between the rotation shaft of the motor and the input shaft of the speed reduction mechanism for transmitting power. The transmission means includes a friction plate which is non-rotatable with respect to one of the rotation shaft and the input shaft but is movably mounted in the axial direction, and a relative rotation with respect to the other of the rotation shaft and the input shaft. A receiving member that is immovably mounted, and a pressing member that presses the friction plate against the receiving member, and power is generated by utilizing a frictional force generated between the friction plate and the receiving member. The frictional force is normally transmitted from the motor. Greater than the power to be reached, but electric power steering apparatus that is smaller than the impact force generated between the motor and the wheels.