JP2007050845A - Power steering system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power steering system capable of adjusting the backlash between a worm shaft and a worm wheel simply by a simple construction. <P>SOLUTION: The first end 18a of a double lead type worm shaft 18 is supported by the output shaft 20 of a motor 16 through a joint 22. It is not required to use any bearing for supporting the first end 18a of the worm shaft 18. The second end 18b of the worm shaft 18 is supported by a duplex type angular ball bearing 23 movable in a single piece with the worm shaft 18 in the axial direction. Through the duplex type angular ball bearing 23, the position of the worm shaft 18 about the axial direction can be adjusted by operating a screw member 24 as an adjusting member driven into an accommodation hole 21a in a housing 21. Thereby the backlash is adjusted simply. A preload is given to the bearing 23 by fastening together the two inner rings of the bearing 23. <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. ing.

A moderate backlash is required between the worm shaft and the worm wheel, but excessive backlash causes noise. In order to adjust the backlash, it has been proposed to use a multi-lead type worm shaft (see, for example, Patent Document 1). In this case, the backlash is adjusted by moving the worm shaft in the axial direction.
On the other hand, for the purpose of facilitating the setting of the preload of the pair of bearings that respectively support the pair of end portions of the worm shaft, two angular bearings are provided on one of the pair of bearings, and their thrust surfaces are There has been proposed an electric power steering apparatus that is arranged side by side so as to form a combination on the back (see, for example, Patent Document 2).
JP 2001-341656 A JP 2001-278078 A

  The electric power steering apparatus of Patent Document 1 employs a structure in which a pair of end portions of the worm shaft are fixed by bearings, and each bearing is supported in the axial direction by a stopper such as a corresponding plug. Therefore, in order to adjust the backlash, it is necessary to adjust the stoppers together, and there is a problem that the adjustment takes time. There is also a problem that the number of parts increases.

  The present invention has been made in view of the above problems, and it is an object of the present invention to provide an electric power steering apparatus that can easily adjust the backlash with a simple structure.

  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 worm shaft having first and second ends, and a worm wheel meshing with the worm shaft, the first end of the worm shaft being connected via a joint by the output shaft of the electric motor The second end of the worm shaft is supported by a combination angular bearing that can move integrally with the worm shaft in the axial direction, and the position of the worm shaft in the axial direction is adjusted via the combination angular bearing. It is characterized by providing the adjustment member for doing.

  In the present invention, since the first end portion of the worm shaft is supported by the output shaft of the electric motor via the joint, a bearing that supports the first end portion of the worm shaft is unnecessary. Therefore, the structure can be simplified and the size can be reduced. Further, the backlash can be easily adjusted only by adjusting the position of the multi-lead type worm shaft in the axial direction via the combination angular bearing that supports the second end portion of the worm shaft.

  In the case of a combined angular bearing, for example, the preload adjustment can be performed only by tightening two inner rings. Specifically, two of the combination angular bearings are provided between a nut screwed into a male screw portion provided at the second end portion of the worm shaft and a step portion provided on the worm shaft so as to face the nut. In some cases, the preload of the combined angular bearing is adjusted by sandwiching the inner ring in the axial direction (claim 2).

  And an urging member that urges the worm shaft in any axial direction and a housing that forms an accommodation hole for accommodating the worm shaft, and an internal thread portion is formed on an inner peripheral surface of the accommodation hole. The adjusting member includes a screw member that is screwed into the female screw portion of the accommodation hole, and the screw member may move the worm shaft in the axial direction via the combination angular bearing against the biasing member. (Claim 3). In this case, the backlash adjustment can be easily performed only by the operation of rotating the screw member.

  The screw member as the adjusting member has a cylindrical shape, and is interposed between the inner peripheral surface of the housing housing hole and the outer peripheral surfaces of the two outer rings of the combined angular bearing, and supports the two outer rings. In some cases, a male screw portion that is engaged with the female screw portion of the inner peripheral surface of the accommodation hole is formed on the outer peripheral surface of the peripheral side wall. In this case, since the screw (male thread) is formed in the member itself that supports the combined angular bearing, the structure can be simplified, and the worm shaft can be securely axially connected through the combined angular bearing. Can be moved to.

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 3b 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 coupled to each other coaxially via a cylindrical joint 22 so that power can be transmitted. The first end 18 a of the worm shaft 18 and the output shaft 20 of the electric motor 16 are respectively 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 first axial direction X1 and the second axial direction X2. On the other hand, the output shaft 20 of the electric motor 16 is coupled to the joint 22 by press fitting, for example. Thus, the first end portion 18 a of the worm shaft 18 is supported by the output shaft 20 of the electric motor 16 through the joint 22. The first axial direction X1 of the worm shaft 18 is a direction toward the joint 22, and the second axial direction X2 is a direction opposite to the first axial direction X1.

  On the other hand, the second end 18b of the worm shaft 18 is rotatably supported by a combination angular ball bearing 23 as a combination angular bearing. The combined angular contact ball bearing 23 adjusts the backlash between the worm shaft 18 and the worm wheel 19 by moving the worm shaft 18 in the first or second axial direction X1, X2 via the combined angular contact ball bearing 23. It is supported by a screw member 24 as an adjustment member.

  The screw member 24 has a bottomed cylindrical shape, and has a peripheral side wall 25 and an end wall 26. A male screw portion 25 a is formed on the outer periphery of the peripheral side wall 25, and the male screw portion 25 a is screwed into a female screw portion 21 b formed in the accommodation hole 21 a of the housing 21. Further, a lock nut 27 that fixes the screw member 24 is screwed into the male screw portion 25a. A tool engaging hole 26 a for rotating the screw member 24 is formed in the end wall 26.

  The worm shaft 18 is biased in the first axial direction X1 by a biasing member 28 made of an elastic member such as a compression coil spring. The biasing member 28 is interposed between the end wall 26 of the screw member 24 and a nut 37 (see FIG. 4) for fixing the combined angular ball bearing 23 to the worm shaft 18. As the urging member 28, for example, a compression coil spring as shown in FIG. 2 can be used, but not limited to this, a disc spring can be used. The urging member 28 is not limited to a metal member, and a rubber body, a resin body, or the like can be used.

Referring to FIG. 3, the worm shaft 18 is a multiple lead type. Therefore, the tooth thickness of the worm shaft 18 increases as it proceeds in the first axial direction X1, and the tooth thickness decreases as it proceeds in the second axial direction X2. That is, the pitch P1 of the worm shaft 18 is smaller than the pitch P2.
Therefore, 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 reduced, and the worm shaft 18 can be moved in the second axial direction X2. As a result, the backlash can be increased. In this way, the backlash can be adjusted.

  Next, referring to FIG. 4, the combination angular ball bearing 23 includes an angular ball bearing 32 including an inner ring 29, an outer ring 30 and a rolling element 31, and an angular ball bearing 36 including an inner ring 33, an outer ring 34 and a rolling element 35. Two bearings are combined. The angular width of the angular ball bearing 32 and the angular ball bearing 36 is adjusted so that a predetermined preload is applied when used in the back combination.

  A male screw portion 18e is formed on the outer periphery of the second end portion 18b of the worm shaft 18, and a nut 37 is screwed into the male screw portion 18e. Two inner rings 29 and 33 of the combined angular ball bearing 23 are sandwiched in the axial direction between the nut 37 and a step portion 18f provided on the worm shaft 18 so as to face the nut 37. As a result, the rear combined angular An appropriate preload is applied to the ball bearing 23.

  The outer rings 30 and 34 of the angular ball bearings 32 and 36 are supported by the inner peripheral surface of the peripheral side wall 25 of the screw member 24 so as not to rotate. Further, the peripheral side wall 25 of the screw member 24 is formed with an engagement protrusion 38 that protrudes inward in the radial direction at the end opposite to the end wall 26. The engagement protrusion 38 is engaged with the end face 30a of the outer ring 30 of the angular ball bearing 32, and the combined angular ball bearing 23 can be moved in the second axial direction X2 in a lump.

The engagement protrusion 38 may be provided on the entire circumference of the peripheral side wall 25 or may be provided on a part of the circumferential direction.
According to the present embodiment, the first end portion 18a of the worm shaft 18 is supported by the output shaft 20 of the electric motor 16 via the joint 22, and thus the first end portion 18a of the worm shaft 18 is supported. No bearing is required. Therefore, the structure can be simplified and the size can be reduced. Further, the backlash can be easily adjusted only by adjusting the axial position of the multi-lead type worm shaft 18 via the combination angular ball bearing 23 that supports the second end portion 18b of the worm shaft 18. .

Further, in the case of the combined angular contact ball bearing 23, only the two inner rings 29 and 33 are clamped and tightened between the step portion 18f of the worm shaft 18 and the nut 37, and the appropriate combination angular contact ball bearing 23 is obtained. A preload can be applied.
Further, since the position of the worm shaft 18 that is urged in the first axial direction X1 by the urging member 28 can be adjusted only by rotating the screw member 24, the backlash can be adjusted very easily. can do.

  In particular, the screw member 24 has a cylindrical shape and is interposed between the inner peripheral surface of the housing hole 21 a of the housing 21 and the outer peripheral surfaces of the two outer rings 30, 34 of the combined angular ball bearing 23. The peripheral side wall 25 which supports is included. Accordingly, since the screw (male thread portion 25 a) is formed on the member itself that supports the combined angular ball bearing 23, the structure can be simplified, and the worm shaft 18 can be connected via the combined angular ball bearing 23. It can be reliably moved in the axial direction.

Next, FIG. 5 shows another embodiment of the present invention. This embodiment is different from the embodiment of FIG. 2 in that a biasing member 28A for biasing the worm shaft 18 in the second axial direction X2 is provided, and the combined angular ball is opposed to this biasing member 28A. The screw member 24A that can move the bearing 23 in the first axial direction X1 is provided.
As the urging member 28 </ b> A, an elastic member that is accommodated in the joint 22 and interposed between the first end portion 18 a of the worm shaft 18 and the output shaft 20 of the electric motor 16 can be used. As the elastic member, in addition to a metal compression coil spring and disc spring, a rubber body or a synthetic resin body can be used.

  Further, the engagement protrusion 38A of the screw member 24A is provided at the axial intermediate portion of the peripheral side wall 25, and pushes the end face of the outer ring 34 of the angular ball bearing 36 of the combined angular ball bearing 23 in the first axial direction X1. become. Since other configurations are the same as those of the embodiment of FIG. 2, the same reference numerals are given to the drawings, and description thereof is omitted. Also in the present embodiment, the same operational effects as in the embodiment of FIG. 2 can be obtained.

  In addition, the present invention is not limited to the above embodiments, and 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 sectional drawing 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 device, A ... Steering mechanism, 16 ... Electric motor, 17 ... Reduction gear (transmission mechanism), 18 ... Worm shaft, 18a ... First end, 18b ... Second end, 18d ... Spline Part, 18e ... male screw part, 18f ... step part, X1 ... first axial direction (axial direction of worm axis), X2 ... second axial direction (axial direction of worm axis), 19 ... worm wheel, 20 ... output Shaft, 21 ... Housing, 21a ... Accommodating hole, 21b ... Female thread, 22 ... Joint, 23 ... Combined angular ball bearing (combined angular bearing), 24, 24A ... Screw member (adjusting member), 25 ... Peripheral side wall, 25a ... Male thread portion, 26 ... end wall, 28, 28A ... biasing member, 29, 33 ... inner ring, 30, 34 ... outer ring, 31, 35 ... rolling element, 32, 36 ... angular ball bearing, 37 ... nut, 38, 38A ... engagement Cause.

Claims (4)

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 includes a multi-lead worm shaft having first and second ends, and a worm wheel meshing with the worm shaft,
The first end portion of the worm shaft is supported by the output shaft of the electric motor so as to be axially movable through a joint,
The second end of the worm shaft is supported by a combination angular bearing that can move integrally with the worm shaft in the axial direction,
An electric power steering apparatus comprising an adjustment member for adjusting the position of the worm shaft in the axial direction via a combined angular bearing.   2. The combination angular bearings according to claim 1, wherein two of the combination angular bearings are provided between a nut screwed into a male screw portion provided at a second end portion of the worm shaft and a step portion provided on the worm shaft so as to face the nut. An electric power steering device in which the preload of the combined angular bearing is adjusted by sandwiching the inner ring in the axial direction. In Claim 1 or 2, it comprises a biasing member that biases the worm shaft in any axial direction, and a housing that forms a housing hole that houses the worm shaft,
A female screw part is formed on the inner peripheral surface of the accommodation hole,
The adjustment member includes a screw member that is screwed into the female screw portion of the accommodation hole,
The screw member moves the worm shaft in the axial direction through a combination angular bearing against the urging member. 4. The screw member as the adjustment member according to claim 3, wherein the screw member has a cylindrical shape and is interposed between the inner peripheral surface of the housing receiving hole and the outer peripheral surfaces of the two outer rings of the combined angular bearing. Including a peripheral side wall supporting the outer ring,
An electric power steering device characterized in that a male screw portion that is screwed into a female screw portion of an inner peripheral surface of the accommodation hole is formed on the outer peripheral surface of the peripheral side wall.

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