JPH0735248U - Electric power steering device - Google Patents

Abstract

(57) [Summary] (Correction) [Purpose] To provide an electric power steering device having a simple structure and capable of preventing damage to a torque transmission path. A power transmission means having a friction surface and a pressing means pressed by the friction surface is a rotary shaft 102a of the motor 102.
Between the friction plate 131 and the receiving member before the output torque of the motor increases due to the reduction mechanism. Power is transmitted using frictional force. Therefore, it is not necessary 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 structure of the power transmission means can be made simple and compact.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an electric power steering device.

[0002]

[Prior art]

 An electric power steering device for a vehicle is configured to reduce the rotational output of an electric motor, which is an auxiliary steering torque, by means of a gear device and transmit appropriate torque and speed to the output shaft of the steering mechanism. Are known. During operation of such an electric power steering device, a sudden force received by the wheels from the road surface may oppose the output of the electric motor to generate an impact force. Such impact force may cause damage to the electric motor and the power transmission mechanism.

In order to alleviate or eliminate this impact force, in the prior art, a sliding mechanism that uses frictional force is provided on the output shaft of the steering mechanism, and as a torque limiter that causes sliding when excessive torque is applied. Measures have been taken such as an example (actual application No. 4-75506) or an example in which an electromagnetic clutch acting as a torque limiter is arranged on the rotating shaft.

[0004]

【Problems to be solved】

 However, in the above-mentioned electric power steering apparatus of the prior art, in the example, since the output of the electric motor is normally transmitted to the output shaft through the deceleration (torque increase) mechanism, the output shaft is provided with the sliding mechanism. As a result, the frictional force used in the sliding mechanism must be considerably increased so that the increased torque can be transmitted. Therefore, there is a problem that strict load management is required to obtain a constant frictional force. In addition, in the above example, the power required for the electromagnetic clutch must always be supplied, which is not preferable from the viewpoint of energy saving, and if the rated output of the electric motor increases, the coil of the electromagnetic clutch, etc. There is a problem that it has to be considerably large.

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

[0006]

[Means for solving the problem]

 In order to achieve the above object, an electric power steering apparatus of the present invention comprises a housing, a motor attached to the housing, having a rotating shaft, an output shaft connected to a steering mechanism for steering wheels, and the output shaft. Is provided between the rotation shaft of the motor and the input shaft of the reduction mechanism, the reduction mechanism being coupled to the input shaft, the reduction mechanism transmitting decelerating power from the input shaft to the output shaft, And a friction plate that is not rotatable relative to one of the rotation shaft and the input shaft but is movably mounted in the axial direction. The friction plate and the receiving member, the receiving member being attached to the other of the rotating shaft and the input shaft so as not to rotate relative to each other, and the pressing member for pressing the friction plate against the receiving member. Power is transmitted by using the frictional force generated between Has become earthenware pots by being, the frictional force is greater than the power that would normally be transmitted from the motor is set smaller than the impact force generated between the motor and the drive wheels.

[0007]

[Action]

 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 reduction mechanism. Therefore, before the output torque of the motor is increased by the reduction mechanism, relatively small frictional force generated between the friction plate and the receiving member is used to transmit power. ing. Therefore, it is not necessary 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 structure of the power transmission means can be made simple and compact.

[0008]

【Example】

 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a partial sectional view in the axial direction of an electric power steering apparatus 100 according to an embodiment of the present invention.

In FIG. 1, an electric power steering device 100 is composed of a housing 101 and a tube 110 extending from the housing 101. The housing 101 is fixed to a vehicle body (not shown) by a bracket 114, and the tube 110 is fixed to a vehicle body (not shown). An input shaft 111 whose one end is connected to a steering wheel (not shown) extends inside the tube 110 and is rotatably supported by the tube 110. The other end of the input shaft 111 is connected to the torque detection device 112.

The torque detection device 112 also extends inside the housing 101 and is connected to a transmission shaft 113 which is rotatably supported. The transmission shaft 113 is connected to a steering device (not shown) and transmits torque for steering the wheels. The torque detection device 112 is provided so as to detect the relative torque between the input shaft 111 and the transmission shaft 113 and appropriately control the assisting steering force by using the torque, and its configuration is well known. Details are not described in.

A worm wheel 104 is coaxially attached to the transmission shaft 113 in the vicinity of the torque detection device 112. The worm wheel 104 meshes with the worm gear 103a (see FIG. 2) of the speed reducer input shaft 103 extending in the direction perpendicular to the paper surface in FIG. The decelerator input shaft 103 is connected to the rotating shaft of the motor 102 (see FIG. 2).

The operation of the electric power steering device 100 shown in FIG. 1 will be described below. The input shaft 111 is rotated by the input of steering torque from a steering wheel (not shown), 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 torque value detected by the rotation torque detection device 112 is sent to a judgment circuit (not shown) and compared with a predetermined value. When the torque exceeds the predetermined value, it is a case where the auxiliary steering force is required, and therefore a drive command is issued to drive the motor 102. The motor 102 driven by the drive command rotates the decelerator input shaft 103, and 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 detecting device 112 is lower than the predetermined value, the auxiliary steering force is unnecessary and the motor 102 is not driven. The speed reducer input shaft 103 and the worm wheel 104 form a speed reducer.

FIG. 2 is an axial view of the device cut along the line II-II in FIG. In FIG. 2, the electric motor 102 is attached to the right end of the housing 101. A male spline 102b is formed on the outer end of a rotary shaft 102a that is rotatably supported by the bearing 102b with respect to the electric motor 102. Two annular friction plates 131 are attached around the male spline 102b of the rotating shaft 102a. The friction plate 131 has a female spline groove 131a at the center opening, and by fitting the female spline groove 131a to the male spline groove 102b of the rotary shaft, the friction plate 131 cannot rotate relative to the rotary shaft 102, but the axis line. It can move in any direction.

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 has a configuration in which a large diameter portion 133a and a small diameter portion 133b are connected by a conical portion 133c. The inner diameter of the large diameter portion 133a is formed to be slightly larger than the outer shape of the friction plate 131, so that the movement of the friction plate 131 in the axial direction is not hindered.

Two coned disc springs 132 are placed back to back around the rotary shaft 102 so as to be sandwiched between the two friction plates 131 and contact them. A circumferential groove 133d is formed on the inner circumference of the friction plate housing 133 and near the outer circumference of the friction plate 131 on the electric motor side. A restraining plate 134 is provided in the circumferential groove 133c, and is attached thereto by crimping the end portion of the friction plate housing. It should be noted that the friction plate 131 is sandwiched between the pressing plate 134 and the conical portion 133c and the distance between them is set to a predetermined value so that the biasing force of the disc spring 132 does not drop below the reference value. is doing. The friction plate housing 133 and the pressing plate 134 form a receiving member, and the disc spring 132 forms a pressing member.

A speed reducer input shaft 103 coaxial with a rotary shaft 102 a of the electric motor 102 is rotatably supported by bearings 105 and 106 in the vicinity of both ends of the housing 101. A male spline 103e is formed at the end of the decelerator input shaft 103 on the electric motor side, and a female spline 133e is formed on the inner circumference of the small diameter portion 133b of the friction plate housing 133. The housing 133 is mounted such that it cannot rotate relative to the decelerator input shaft 103 but can move in the axial direction. The tip of the small diameter portion 133b of the friction housing 133 contacts the spacer 137 and is prevented from further moving in the axial direction. The bearings 105 and 106 have outer rings 105a and 106a, inner rings 105b and 106b, respectively, and a plurality of balls 105c and 106c held between the two rings. A spacer 135 is provided on the side of the bearing 106 opposite to the electric motor (on the worm gear side) so as to be sandwiched between the step portion of the housing 101 and the outer ring 106 a of the bearing 106. Further, on the electric motor side of the bearing 106, a snap ring 136 is inserted in the circumferential groove of the housing, and the bearing 106 is sandwiched between the spacer 135 and the snap ring 136 so that it cannot move in the axial direction.

The decelerator input shaft 103 has a flange portion 103c formed adjacent to the inside of the bearing 105, a flange portion 103b formed adjacent to the bearing 106, and a worm wheel 104 formed between the flange portions. The worm gear 103a which meshes is formed. A male spline 103d engaged with the nut 107 is formed on the end of the decelerator input shaft 103 opposite to the motor, and the inner ring 105b of the bearing 105 is held between the flange 103c and the nut 107. ing. The worm wheel 104 and the worm gear 103a form a reduction mechanism.

Next, the operation of the pressing means according to the present invention will be described below. In normal operation, the rotating torque generated by the motor 102 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 separate them from each other in the direction of pressing the pressing plate 134 and the friction plate housing 133. Therefore, the friction plate 131 is compressed between the disc spring 132 and the retaining plate 134 and the friction plate housing 133, and generates a friction force in response to the pressed force. The distance between the urging force of the disc spring 132 and the friction plate 131 is set so that this frictional force is larger than the torque generated by the motor 102 in normal operation. It rotates integrally with the plate housing 133. 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, and is transmitted to a steering device (not shown) for steering operation.

By the way, the wheels may receive an impact force due to the unevenness of the road surface. In such a case, the impact force may be transmitted backward to the motor 102 via the power transmission system and may face the output of the motor. Due to this facing, excessive stress is generated in the power transmission system, possibly damaging the parts.

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 pressing plate 134 and the friction plate housing 133 may be smaller than the impact force. Since the urging force of the disc spring 132 is set, slippage occurs between the friction plate 131 and the pressing plate 134 or the friction plate housing 133 in response to the generation of the impact force. Most of the impact force is absorbed by this slip, so damage to the power transmission system can be prevented.

Further, in the electric power steering apparatus according to the present invention, the urging force applied from the disc spring 132 to the friction plate 131 is entirely received by the friction plate housing 133. For example, in the structure in which the friction plate is biased against the housing, a thrust force is generated in the speed reducer input shaft to increase the rolling resistance of the bearing, but this embodiment has the above structure. Therefore, the thrust force due to the urging of the friction plate is not applied to the bearing 102b that supports the rotating shaft 102a of the electric motor 102 and the bearings 105 and 106 that support the decelerator input shaft 103. Therefore, in this embodiment, the rolling resistance around the shaft is reduced, and the returning property of the handle is improved. Further, in this embodiment, by providing the two friction plates 131, the transmission capacity can be improved or the diameter thereof can be reduced as compared with the case of one friction plate. Furthermore, since two friction plates are used, even if the torque transmission capability of the spline of one friction plate is small, sufficient torque can be transmitted by combining the two.

Although the present invention has been described with reference to the embodiments, the present invention should not be construed as being limited to the above embodiments, and it goes without saying that appropriate modifications and improvements can be made. . For example, the number of friction plates may be one. Further, the friction housing 133 is axially movable with respect to the decelerator input shaft 103, but the friction housing 133 and the friction housing 133 may be coupled to each other by using, for example, a radial penetrating pin.

[0023]

[Effect of device]

 As described above, according to the electric power steering device of the present invention, the power transmission means having the friction surface and the pressing means pressed by the friction surface is the rotation shaft of the motor and the input shaft of the reduction mechanism. Is provided between the friction plate and the receiving member before the output torque of the motor is increased by the speed reduction mechanism, the power transmission is performed by using the comparatively small frictional force generated between the friction plate and the receiving member. I am supposed to do it. Therefore, it is not necessary 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 structure of the power transmission means can be made simple and compact.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view in the axial direction of an electric power steering device 100 that is an embodiment of the present invention.

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

[Explanation of symbols]

 101 ... Housing 102 ... Motor 103 ... Reduction gear input shaft 104 ... Worm wheel 131 ... Friction plate 132 ... Disc spring 133 ... Friction plate housing 134 ... Presser plate

Claims (1)

[Scope of utility model registration request] 1. A housing, a motor attached to 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 the input shaft. And a power transmission means that is provided between the rotation shaft of the motor and the input shaft of the reduction mechanism and that transmits power from the shaft to the output shaft. The transmission means includes a friction plate that is not rotatable relative to one of the rotation shaft and the input shaft but is movable in the axial direction, and a relative rotation relative to the other of the rotation shaft and the input shaft. And a pressing member that presses the friction plate against the receiving member, and the friction force generated between the friction plate and the receiving member is used to generate power. The frictional force is normally transmitted from the motor. An electric power steering device, which is larger than the power to be reached but smaller than the impact force generated between the motor and the wheels.