JPH0639665U - Electric power steering device - Google Patents

Abstract

(57) [Summary] (Correction) [Purpose] To provide an electric power steering device that has a simple structure and can prevent damage to a torque transmission path. [Structure] Biasing members 119 and 120 for biasing the bearing means of the output shaft 103 in the axial direction of the output shaft are provided.
The urging force of the urging member is larger than the force received by the worm gear 103a from the worm wheel 104 in normal operation, and the axial direction generated in the worm gear by the rotation of the output shaft when the worm wheel is forcibly stopped. Since the force is set to be smaller than the thrust, the axial movement of the output shaft can be prevented during normal operation, and the force can be transmitted from the output shaft to the worm wheel without any trouble. However, when an overload occurs due to, for example, the worm wheel suddenly stopping, the thrust of the output shaft that continues to rotate with respect to the worm wheel is absorbed by moving the output shaft itself in the axial direction. be able to.

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 system for a vehicle, which is configured to reduce the rotational output of an electric motor, which serves as an auxiliary steering torque, by means of a gear system and transmit appropriate torque and speed to the output shaft of the steering system. Is known (for example, Japanese Patent Laid-Open No. 3-128565).

[0003]

【Problems to be solved】

 By the way, in the above-mentioned electric power steering apparatus of the prior art, the output shaft and the rotary shaft of the electric motor are directly connected. Therefore, for example, if the steering is turned off, the steering stops suddenly when the steering limit angle is reached due to the action of the steering stopper, but even in such a case, the electric motor tries to continue to rotate due to inertia. Therefore, an unreasonable force may be applied between the output shaft and the electric motor. Such an unreasonable force may cause damage in any of the torque transmission paths.

To solve such a problem, Japanese Patent Laid-Open No. 2-175381 discloses a planetary gear mechanism provided between an electric motor and an output shaft so that a ring gear of the planetary gear mechanism, which is normally fixed, is A configuration is disclosed in which power transmission is blocked by rotating it when a load occurs. However, the planetary gear mechanism has a complicated structure, is heavy, and is expensive to manufacture.

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

[0006]

[Means for solving the problem]

 In order to achieve the above object, an electric power steering apparatus according to the present invention comprises a housing, a motor, an output shaft connected to the motor and having a worm gear formed on an outer periphery thereof, a worm wheel meshing with the worm gear, and the output. It comprises a bearing means for rotatably holding the shaft and a holding means for attaching the bearing means to the housing, and the holding means has a biasing member for biasing the bearing means in the axial direction of the output shaft. The urging force of the urging member is larger than the force that the worm wheel receives from the worm wheel in normal operation, and is generated in the worm gear by the rotation of the output shaft when the worm wheel is forcibly stopped. It is set smaller than the axial thrust.

[0007]

[Action]

 According to the electric power steering device of the present invention, a biasing member for biasing the bearing means of the output shaft in the axial direction of the output shaft is provided, and the biasing force of the biasing member in normal operation is It is set to be larger than the force received by the worm gear from the worm wheel and smaller than the axial thrust generated in the worm gear by the rotation of the output shaft when the worm wheel is forcibly stopped. The movement of the output shaft in the axial direction can be prevented, and the force can be transmitted from the output shaft to the worm wheel without any trouble. However, when an overload occurs, for example, when the worm wheel suddenly stops, the thrust of the output shaft that continues to rotate with respect to the worm wheel is absorbed by moving the output shaft itself in the axial direction. be able to.

[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 output shaft 103 extending in the direction perpendicular to the paper surface in FIG. The output shaft 103 is connected to the rotary shaft of the motor 102, only a part of which is visible in FIG.

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 output 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.

FIG. 2 is a view of the device cut along the II-II section of FIG. 1 and viewed in the axial direction. In FIG. 2, the electric motor 102 is attached to the left end of the housing 101. A rotating shaft (not shown) of the electric motor 102 is connected to the output shaft 103 via the clutch mechanism 102a. The clutch mechanism 102a and the output shaft 103 are connected by the engagement of the female serration 102b provided on the clutch mechanism 102 and the male serration 103b provided on the outer periphery of the left end of the output shaft 103. A worm gear 103a is formed on a part of the outer periphery of the output shaft 103 and meshes with the worm wheel 104.

The blind hole-shaped perforated portion 101 c provided in the housing 101 is provided with a sliding bearing (bush) 107 in the inner portion thereof and ball bearings 105 and 106 on the motor 102 side. The vicinity of both ends of 103 is rotatably supported. The outer rings of the ball bearings 105 and 106 are attached to the housing 101 in a loose-fitting manner, so that they can be moved with a slight force in the axial direction. The punched portion 101c is formed by unidirectionally cutting with a drill or the like from the side to which the motor 102 is attached when the housing 101 is processed. The outer diameter of the sliding bearing 107 is smaller than the outer diameters of the bearings 105 and 106, so that the output shaft 103 and the sliding bearing 107 can be incorporated from the motor side.

A flange portion 103b is formed in the center of the output shaft 103, and a step portion 101d is formed at a position radially outward of the flange portion 103b in the housing 101. In the normal operating state, the collar portion 103b is in contact with the inner ring of the ball bearing 106, and the step portion 101d is in contact with the outer ring thereof. The step portion 101d limits the movement of the ball bearing 106 relative to the housing 101 in the right axial direction. Two disc springs 119 and 120 are mounted between the ball bearings 105 and 106 via two spacers 117 and 118 so as to face each other. The lock nut 121, which is in contact with the inner ring of the ball bearing 105, applies a predetermined preload to the disc springs 119 and 120 via the ball bearings 105 and 106 and the spacers 117 and 118. Further, a tubular screw 122 is provided so as to come into contact with the outer ring of the ball bearing 105. The tubular screw 122 restricts the ball bearing 105 from moving to the left in the axial direction. The ball bearings 105 and 106, the spacers 117 and 118, and the disc springs 119 and 120 form a holding means, and the disc springs 119 and 120 form an urging member.

Next, the operation of the holding means according to the present invention will be described below. In normal operation, the rotational torque generated by the motor 102 is transmitted to the worm wheel 104 via the output shaft 103. At this time, a reaction force is generated between the worm gear 103a of the output shaft 103 and the worm wheel 104. However, since the preload applied by the lock nut 121 is larger than the reaction force, the ball bearings 105, 10 6 move in the axial direction. Never move to. Therefore, in such a state, the output shaft 103 is rigidly fixed to the housing 101 in the axial direction, and therefore the rotational torque of the motor 102 is directly transmitted to the worm wheel 104. .

However, at a large steering angle, a steering stopper (not shown) may prevent further rotation of the steering shaft, that is, the worm wheel 104. In this case, the supply of electric power to the motor 102 is cut off at the same time as the rotation is stopped, but the output shaft 103 tries to continue to rotate due to the inertial force of the motor 102. However, since the worm wheel 104 has already stopped, an excessive axial thrust of the output shaft 103 is generated.

In such a case, in the electric power steering device according to the present invention, the thrust force of the output shaft 103 overcomes the biasing force of the disc springs 119, 120 pressing the ball bearings 105, 106, so that the output shaft Reference numeral 103 denotes an element that moves in the axial direction together with the ball bearing 105 or 106 while rotating and absorbs this force to prevent damage to the transmission system. The output shaft 103 once moved returns to the original position by turning the steering in the opposite direction.

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 are possible. . For example, coil springs may be used instead of the disc springs 119 and 120.

[0018]

[Effect of device]

 As described above, according to the electric power steering apparatus of the present invention, the biasing member that biases the bearing means of the output shaft in the axial direction of the output shaft is provided, and the biasing force of the biasing member is provided. Is set to be larger than the force that the worm gear receives from the worm wheel in normal operation, and smaller than the axial thrust generated in the worm gear by the rotation of the output shaft when the worm wheel is forcibly stopped. During the normal operation, the movement of the output shaft in the axial direction can be prevented, and the force can be transmitted from the output shaft to the worm wheel without any trouble. However, when an overload occurs due to a sudden stop of the worm wheel, for example, the thrust of the output shaft that continues to rotate with respect to the worm wheel is moved by moving the output shaft itself in the axial direction. Can be absorbed.

[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 ... Output shaft 104 ... Worm wheel

Claims (1)

[Scope of utility model registration request] 1. A housing, a motor, an output shaft connected to the motor and having a worm gear formed on the outer periphery thereof, a worm wheel meshing with the worm gear, and bearing means for rotatably holding the output shaft. And a holding means for attaching the bearing means to the housing, wherein the holding means has a biasing member for biasing the bearing means in the axial direction of the output shaft, and the biasing force of the biasing member is Electric power steering that is set to be larger than the force that the worm gear receives from the worm wheel in normal operation and smaller than the axial thrust generated in the worm gear by the rotation of the output shaft when the worm wheel is forcibly stopped. apparatus.