JP2007050844A - Power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power steering device capable of suppressing noise emission associated with changes in the backlash between a worm shaft and a worm wheel. <P>SOLUTION: Vibration due to meshing of the worm shaft 18 with the worm wheel 19 is sensed by a vibration sensor 43 and monitored at all times. When the backlash is increased by a change with time to result in an increase in the vibration sensed by the vibration sensor 43, the input value to an ECU 14 from the vibration sensor exceeds the prescribed value. This causes the ECU 14 to drive the movable part 46 of an electromagnetic actuator 38 for a prescribed rotating angle. In association with rotation of the movable part 46, a locating member 39 is driven for the same rotating angle, and as a result, the locating member 39 makes displacement in the second axial direction X2 for a prescribed amount owing to the action of a screw coupling mechanism as a motion transforming mechanism 40. The worm shaft 18 moves in the second axial direction X2 for the prescribed amount, and the backlash is reduced by a prescribed amount. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that generates a steering assist force by an electric motor.

  A reduction gear is used in an electric power steering system (EPS) for a vehicle. For example, an electric power steering device that amplifies the output of the electric motor and transmits it to the steering mechanism by decelerating the rotation of the output shaft of the electric motor via a worm shaft and worm wheel, and torque assists the steering operation has been proposed. (For example, refer to Patent Document 1).

An appropriate backlash is required for the meshing between the worm shaft and the worm wheel, but the backlash increases due to wear of the tooth portion due to a change over time, and there is a possibility that abnormal noise is generated.
JP 2002-166838 A

  The present invention has been made in view of the above problems, and provides an electric power steering apparatus capable of suppressing the generation of noise accompanying a change in backlash between a worm shaft and a worm wheel.

  In order to achieve the above object, the present invention includes a steering assisting electric motor having an output shaft, and a transmission mechanism for transmitting the rotation of the output shaft of the electric motor to a steering mechanism. A multi-lead type worm shaft and a worm wheel meshing with the worm shaft are provided, and a drive mechanism for moving the worm shaft in the axial direction is provided, and the drive mechanism includes an electromagnetic actuator. .

  In the multi-lead type worm, the tooth thickness decreases as it advances in one axial direction, and the tooth thickness increases as it advances in the other axial direction. Therefore, if the worm shaft is moved in the one axial direction by the drive mechanism including the electromagnetic actuator, the backlash between the worm shaft and the worm wheel is reduced, and conversely, the worm shaft is moved to the other axis by the drive mechanism. If it is moved in the direction, the backlash increases. As described above, by adjusting the backlash, it is possible to suppress the generation of noise accompanying the backlash change. As an electromagnetic actuator, a rotary solenoid, a step motor, etc. can be illustrated.

  The electromagnetic actuator includes a fixed portion and a rotating movable portion, and the drive mechanism includes a motion conversion mechanism for converting a rotational motion by the movable portion of the electromagnetic actuator into a linear motion and transmitting the linear motion to the worm shaft. There is a case (Claim 2). In this case, the rotation of the movable part of the electromagnetic actuator is converted into axial movement, and the worm shaft is moved in the axial direction. As the motion conversion mechanism, for example, a screw coupling mechanism may be used. In that case, the structure is simple and the operation is reliable.

  A bearing that rotatably supports the end of the worm shaft and positions the worm shaft in the axial direction; and a positioning member that positions the outer ring of the bearing in the axial direction. The drive mechanism includes the positioning member In some cases, the worm shaft may be moved in the axial direction via the bearing. In this case, since the positioning member is used, there is an advantage that the motion conversion mechanism can be easily laid out. For example, the inner peripheral surface of the housing hole for housing the worm shaft and the outer peripheral surface of the positioning member may be coupled by a screw coupling mechanism as a motion conversion mechanism. Further, a positioning member is supported in the housing hole for housing the worm shaft so as to be axially movable and non-rotatable, and the movable part of the electromagnetic actuator and the positioning member are coupled by a screw coupling mechanism as a motion conversion mechanism You may make it do.

  Further, there may be provided vibration detection means for detecting vibration caused by meshing of the worm shaft and worm wheel, and control means for controlling the operation of the electromagnetic actuator in accordance with a signal from the vibration detection means. . In this case, the occurrence of noise can be reliably suppressed by adjusting the backlash by moving the worm shaft in the axial direction in response to the detection of the occurrence of vibration accompanying the increase in backlash.

  Here, the amount of movement in the axial direction of the worm shaft by the drive mechanism is preferably set so that the backlash between the worm shaft and the worm wheel is not smaller than the appropriate backlash. The means may control the operation of the electromagnetic actuator so that the worm shaft is displaced by a predetermined amount in the axial direction when the value detected by the vibration detecting means exceeds a predetermined value.

Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus according to an embodiment of the present invention. Referring to FIG. 1, an electric power steering apparatus 1 includes a steering shaft 3 connected to a steering member 2 such as a steering wheel, an intermediate shaft 5 connected to the steering shaft 3 via a universal joint 4, and an intermediate As a steered shaft extending in the left-right direction of an automobile, having a pinion shaft 7 connected to the shaft 5 via a universal joint 6 and rack teeth 8a meshing with pinion teeth 7a provided in the vicinity of the end of the pinion shaft 7 Rack bar 8. The pinion shaft 7 and the rack bar 8 constitute a rack and pinion mechanism as the steering mechanism A.

The rack bar 8 is supported in a housing 9 fixed to the vehicle body so as to be capable of linear reciprocation through a plurality of bearings (not shown). Both end portions of the rack bar 8 protrude to both sides of the housing 9, and tie rods 10 are coupled to the respective end portions. Each tie rod 10 is connected to a corresponding steering wheel 11 via a corresponding knuckle arm (not shown).
When the steering member 2 is operated and the steering shaft 3 is rotated, this rotation is converted into a linear motion of the rack bar 8 along the left-right direction of the automobile by the pinion teeth 7a and the rack teeth 8a. Thereby, steering of the steered wheel 11 is achieved.

The steering shaft 3 is divided into an input shaft 3a connected to the steering member 2 and an output shaft 3b connected to the pinion shaft 7. These input and output shafts 3a and 3b are on the same axis line via a torsion bar 12. They are connected to each other so as to be relatively rotatable.
A torque sensor 13 is provided for detecting a steering torque based on a relative rotational displacement amount between the input and output shafts 3a and 3b via the torsion bar 12, and the torque detection result of the torque sensor 13 is an ECU (Electronic Control Unit: electronic). Control unit) 14. The ECU 14 drives and controls the steering assisting electric motor 16 via the drive circuit 15 based on a torque detection result or a vehicle speed detection result given from a vehicle speed sensor (not shown). The output rotation of the electric motor 16 is decelerated through a speed reducer 17 as a transmission device, transmitted to the output shaft 3b of the steering shaft 3, and further converted into a linear motion of the rack bar 8 through the pinion shaft 7, for steering. Is assisted.

The speed reducer 17 is a worm shaft 18 as a drive gear that is rotationally driven by the electric motor 16, and a worm wheel as a driven gear that meshes with the worm shaft 18 and is connected to the output shaft 3 b of the steering shaft 3 so as to be integrally rotatable. 19 is provided.
With reference to FIG. 2, the worm shaft 18 is arranged coaxially with the output shaft 20 of the electric motor 16. The worm shaft 18 has first and second end portions 18a and 18b that are separated from each other in the axial length direction, and has a tooth portion at an intermediate portion 18c between the first and second end portions 18a and 18b.

  The worm wheel 19 is connected to an intermediate portion in the axial direction of the output shaft 3b of the steering shaft 3 so as to be integrally rotatable and immovable in the axial direction. The worm wheel 19 includes an annular cored bar 19a coupled to the output shaft 3b so as to be integrally rotatable, and a synthetic resin member 19b surrounding the cored bar 19a and having teeth 19c formed on the outer periphery. The core metal 19a is inserted into the mold when the synthetic resin member 19b is molded with resin, for example.

  The worm shaft 18 is accommodated in an accommodation hole 21 a formed in the housing 21 of the speed reducer 17. A region including the meshing portions of the worm shaft 18 and the worm wheel 19 is filled with a lubricant such as grease. The first end portion 18a of the worm shaft 18 and the output shaft 20 of the electric motor 16 are connected to each other coaxially via a cylindrical joint 22 so that power can be transmitted.

The first and second end portions 18a and 18b of the worm shaft 18 are rotatably supported by the housing 21 of the speed reducer 17 via corresponding first and second bearings 23 and 24, respectively. The first and second bearings 23 and 24 are, for example, ball bearings.
Inner rings 25 and 26 of the first and second bearings 23 and 24 are fitted to the first and second end portions 18a and 18b of the worm shaft 18 so as to be integrally rotatable. Each inner ring 25, 26 faces the corresponding first and second step portions 27, 28 formed on the outer peripheral surface of the worm shaft 18. The first and second step portions 27 and 28 have an annular shape and are opposite to each other.

  The inner ring 26 of the second bearing 24 and the second step portion 28 of the worm shaft 18 are in contact with each other. The inner ring 25 of the first bearing 23 and the first step portion 27 of the worm shaft 18 are opposed to each other with a predetermined interval. An elastic member 29 as an urging member is interposed between the end surface of the inner ring 25 of the first bearing 23 and the first step portion 27 of the worm shaft 18, and the elastic member 29 attaches the worm shaft 18 to the worm shaft 18. It is urged in the first axial direction X1. As the elastic member 29, for example, a disc spring as shown in FIG. 2 can be used. A compression coil spring can also be used.

  Further, the outer ring 30 of the first bearing 23 is held in a non-rotatable manner by a bearing holding portion 31 formed in the housing hole 21 a of the housing 21. A screw member 33 is screwed into a screw portion 32 formed continuously with the bearing holding portion 31. The first bearing 23 is positioned in the axial direction of the worm shaft 18 by the screw member 33 coming into contact with the end face of the outer ring 30 of the first bearing 23. The screw member 33 that positions the first bearing 23 is fixed by the lock member 34.

  The first end 18 a of the worm shaft 18 and the output shaft 20 of the electric motor 16 are fitted from the corresponding ends of the joint 22 and coupled to the joint 22. Specifically, a spline portion 18d provided at the first end portion 18a of the worm shaft 18 is splined to the joint 22 so as to be movable in the axial direction, while the output shaft 20 of the electric motor 16 is jointed by, for example, press fitting. 22.

The outer ring 35 of the second bearing 24 is held in a non-rotatable manner by a bearing holding portion 36 formed in the accommodation hole 21 a of the housing 21. In the accommodation hole 21a, a drive mechanism 37 for moving the worm shaft 18 in the axial direction is accommodated in a portion connected to the bearing holding portion 36 when necessary.
The drive mechanism 37 includes a rotary electromagnetic actuator 38, a positioning member 39 that is driven by the electromagnetic actuator 38 to position the outer ring 35 of the second bearing 24 in the axial direction, and the rotational motion output from the electromagnetic actuator 38 is linear. And a motion conversion mechanism 40 for converting into motion. The motion conversion mechanism 40 is a screw connection mechanism including a female screw portion 41 formed on the inner peripheral surface of the housing hole 21 a of the housing 21 and a male screw portion 42 provided on the positioning member 39 and screwed into the female screw portion 41. It is configured.

  A vibration sensor 43 as vibration detection means is attached to the housing 21 of the speed reducer 17, and a signal from the vibration sensor 43 is given to the ECU 14. The ECU 14 controls the operation of the electromagnetic actuator 38 via the drive circuit 44. Specifically, when the input value from the vibration sensor 43 exceeds a predetermined value, the ECU 14 drives and controls the electromagnetic actuator 38 so that the worm shaft 18 is displaced by a predetermined amount in the axial direction. As the vibration sensor, for example, a piezoelectric type acceleration sensor or the like can be used.

  Referring to FIG. 3, the worm shaft 18 is a multiple lead type. Therefore, as the worm shaft 18 advances (moves) in the first axial direction X1, the tooth thickness of the portion of the worm shaft 18 that meshes with the worm wheel 19 decreases, and the worm shaft 18 advances in the second axial direction X2 ( The tooth thickness of the portion of the worm shaft 18 that meshes with the worm wheel 19 increases. That is, the pitch P2 of the worm shaft 18 is smaller than the pitch P1.

  Next, referring to FIG. 4 which is an enlarged view, the electromagnetic actuator 38 includes a fixed portion 45 fixed to the housing 21 and a rotatable cylindrical movable portion 46. As the electromagnetic actuator 38, a rotary solenoid, a step motor, or the like can be used. When the electromagnetic actuator 38 is composed of a rotary solenoid, for example, the fixed portion 45 is constituted by a yoke holding a coil, and the movable portion 46 is constituted by a rotor in which a plurality of permanent magnets are arranged on the circumference around the rotation center. Will be configured.

  On the inner peripheral surface of the housing hole 21 a of the housing 21, the female screw portion 41 is formed so as to continue to the bearing holding portion 36. The positioning member 39 includes an annular main body 47 and a shaft 48 that extends in the axial direction from the center of the main body 47 and can rotate integrally with the main body 47. The shaft portion 48 is fitted to the cylindrical movable portion 46 of the electromagnetic actuator 38 so as to be integrally rotatable. On the outer periphery of the main portion 47, the male screw portion 42 that is screwed with the female screw portion 41 of the accommodation hole 21a is formed.

  According to the present embodiment, since the multi-lead type worm shaft 18 having different pitches P1 and P2 depending on the moving direction is used, for example, if the worm shaft 18 is moved in the first axial direction X1. The backlash between the worm shaft 18 and the worm wheel 19 can be increased, and the backlash can be decreased by moving the worm shaft 18 in the second axial direction X2. As described above, by adjusting the backlash, it is possible to suppress the generation of noise accompanying the backlash change.

  More specifically, the vibration sensor 43 detects vibration caused by the meshing between the worm shaft 18 and the worm wheel 19 and is constantly monitored. When the backlash increases due to the change over time and, as a result, the vibration detected by the vibration sensor 43 increases, the input value from the vibration sensor to the ECU 14 exceeds a predetermined value. Then, the ECU 14 drives the movable part 46 of the electromagnetic actuator 38 by a predetermined rotation angle. As the movable portion 46 rotates, the positioning member 39 is driven by the same rotation angle. As a result, the positioning member 39 is moved by a predetermined amount in the second axial direction X2 by the action of the screw coupling mechanism as the motion conversion mechanism 40. Displace. As a result, the worm shaft 18 moves by a predetermined amount in the second axial direction X2, and the backlash is reduced by a predetermined amount.

In this way, since the occurrence of vibration due to the increase in backlash is detected and the backlash is reduced, the generation of noise can be reliably suppressed.
In addition, since a screw coupling mechanism is used as the motion conversion mechanism 40, the structure is simple and the operation is reliable.
Further, since the worm shaft 18 is moved in the axial direction by using the positioning member 39 for positioning the outer ring 35 of the second bearing 24 in the axial direction, there is an advantage that the motion conversion mechanism 40 can be easily laid out. In the present embodiment, the screw connection mechanism as the motion conversion mechanism 40 is provided between the accommodation hole 21 a of the housing 21 and the positioning member 39. Specifically, the screw coupling mechanism as the motion conversion mechanism 40 includes an internal thread portion 41 on the inner circumferential surface of the housing hole 21 a of the housing 21 for housing the worm shaft 18 and an outer circumferential surface of the main portion 47 of the positioning member 39. And a male screw portion 42.

The amount of movement of the worm shaft 18 in the axial direction (the above-mentioned predetermined amount) every time the input value from the vibration sensor 43 exceeds a predetermined value is the backlash between the worm shaft 18 and the worm wheel 19. It is preferably set so as not to be smaller than the appropriate backlash.
The present invention is not limited to the above-described embodiment. For example, as shown in FIG. 5, the housing hole 21a of the housing 21 is axially movable and non-rotatable, for example, using spline coupling. Thus, the positioning member 39A may be supported, and the motion conversion mechanism 40A may be provided between the rotation shaft as the movable portion 46A of the electromagnetic actuator and the positioning member 39A. Specifically, the motion converting mechanism 40A is configured by the male screw portion 49 provided on the outer peripheral surface of the movable portion 46A and the female screw portion 50 of the screw hole formed in the positioning member 39A.

  In addition, various modifications can be made within the scope of the claims of the present invention.

It is a mimetic diagram showing a schematic structure of an electric power steering device of one embodiment of the present invention. It is sectional drawing of the principal part of an electric power steering device. It is a schematic diagram of a worm shaft. It is an expanded sectional view of the important section of an electric power steering device. It is a general | schematic expanded sectional view of the principal part of the electric power steering apparatus of another embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, A ... Steering mechanism, 14 ... ECU (control part), 16 ... Electric motor, 17 ... Reduction gear (transmission mechanism), 18 ... Worm shaft, 18b ... Second end (Warm shaft End), X1... First axial direction (axial direction of worm shaft), X2... Second axial direction (axial direction of worm shaft), 19... Worm wheel, 24. ... outer ring (outer ring of second bearing), 38 ... electromagnetic actuator, 39, 39A ... positioning member, 40, 40A ... motion conversion mechanism, 41 ... female screw portion (motion conversion mechanism), 42 ... male screw portion (motion conversion mechanism) 43, vibration sensor (vibration detecting means), 45, fixed portion, 46, 46A, movable portion, 49, male screw portion (motion conversion mechanism), 50 ... female screw portion (motion conversion mechanism).

Claims (5)

An electric motor for steering assistance having an output shaft;
A transmission mechanism for transmitting the rotation of the output shaft of the electric motor to the steering mechanism, the transmission mechanism including a multi-lead type worm shaft and a worm wheel meshing with the worm shaft,
An electric power steering apparatus comprising a drive mechanism for moving a worm shaft in the axial direction, the drive mechanism including an electromagnetic actuator.   The electromagnetic actuator according to claim 1, wherein the electromagnetic actuator includes a fixed portion and a movable portion that rotates, and the drive mechanism converts the rotational motion by the movable portion of the electromagnetic actuator into a linear motion and transmits the linear motion to the worm shaft. An electric power steering apparatus including a mechanism.   The drive mechanism according to claim 2, comprising a bearing that rotatably supports an end portion of the worm shaft and positions the worm shaft in the axial direction, and a positioning member that positions an outer ring of the bearing in the axial direction. An electric power steering apparatus, wherein a worm shaft is moved in an axial direction via the positioning member and the bearing.   4. The vibration detecting means according to claim 1, wherein the vibration detecting means detects vibration caused by meshing of the worm shaft and the worm wheel, and the control means controls the operation of the electromagnetic actuator in accordance with a signal from the vibration detecting means. An electric power steering apparatus comprising:   5. The electric power according to claim 4, wherein the control means controls the operation of the electromagnetic actuator so that the worm shaft is displaced by a predetermined amount in the axial direction when the detection value by the vibration detecting means exceeds a predetermined value. Steering device.

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