JP2005088820A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve reduction of a number of parts and miniaturization of a device capable of applying a pre-load along the axial and radial directions to a bearing body 8 and a worm shaft 6. <P>SOLUTION: This device is equipped with a worm wheel 12 provided on a steering shaft, and the worm shaft 6 rotated and driven by an electric motor 2. A coil spring 9 is interposed between the bearing body 8 attached on one end of the worm shaft 6 and a lid 11 of a housing 1 in a state of being compressed along the axial direction. An end of the coil spring 9 on a side separated from the worm wheel 12 is assembled in a tilted posture offset toward the worm wheel 12 with respect to a reference axis L0 of the worm shaft 6 only by a predetermined amount ΔD. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus using an electric motor as a power source, and more particularly to an improvement of an electric power steering apparatus using a worm shaft and a worm wheel.

  As a power steering device that applies steering assist torque, an electric power steering device that uses an electric motor as a power source has less energy loss because it only needs to be operated at the time of steering assist, compared to a device that uses a hydraulic pump as a power source. In addition, it has advantages such as easy electronic control and excellent responsiveness, and is particularly suitable for small cars. A worm shaft that is rotationally driven by an electric motor and a worm wheel provided on the steering shaft are typically used as a speed reduction mechanism that transmits the output of the electric motor to the steering shaft at a reduced speed. Both ends of the worm shaft are rotatably supported by a bearing body such as a ball bearing.

In Patent Document 1 and Patent Document 2, the worm shaft can be displaced in the axial direction and the radial direction so as to reduce or eliminate the backlash between the worm tooth surfaces, and an axial preload is applied to the worm shaft. Discloses a technique for applying a radial preload toward the worm wheel. For example, in Patent Literature 1, an axial preload is applied by a coil spring as an elastic body, and a radial preload is applied by a leaf spring or the like. In Patent Document 2, a cam mechanism is provided between a coil spring that applies axial preload and a bearing body, and this cam mechanism allows a part of the axial biasing force of the coil spring to be radially directed toward the worm wheel. It is converted to preload.
Special table 2002-518242 gazette JP 2002-145082 A

  In Patent Document 1 and Patent Document 2 described above, a leaf spring, a cam mechanism, and the like are used in order to apply a radial preload to the worm shaft, and accordingly, the number of parts, the size of the device, and the cost are increased. Further improvements were desired due to an increase. The present invention has been made in view of such a problem, and an electric power steering device that can effectively reduce and avoid backlash and shakiness of a bearing body by applying a preload in an axial direction and a radial direction to a worm shaft. However, the main purpose is to reduce the number of parts, reduce the size, and reduce the cost.

  A worm wheel provided on the steering shaft and rotatable around an axis; a worm shaft having a worm meshing with the worm wheel and driven to rotate by an electric motor; and a bearing body attached to one axial end of the worm shaft; And an elastic body such as a coil spring interposed between the bearing body and the housing in a state compressed in the axial direction of the worm shaft. This elastic body is assembled in an inclined posture in which an end portion far from the worm wheel is offset in a radial direction toward the worm wheel as compared with an end portion close to the worm wheel.

  Since the elastic body is assembled while being compressed in the axial direction, a preload along the axial direction of the worm shaft is applied from the elastic body to the bearing body and the worm shaft, and the posture in which the elastic body is inclined. Therefore, a preload in the radial direction toward the worm wheel is given to the bearing body and the worm shaft by the self-restoring force of the elastic body. Thus, since both axial and radial preload can be applied to the bearing body and the worm shaft, backlash between tooth surfaces and rattling of the bearing body can be effectively reduced or eliminated. . In addition, it is possible to apply preload in both the axial direction and the radial direction substantially only by the elastic body, and since there is no need for a leaf spring or a cam mechanism for applying the radial preload, the number of parts can be reduced. , Great effects such as downsizing and cost reduction can be obtained.

  Preferably, the holder has a holder interposed between the bearing body and the elastic body, and the holder has a non-rotating body shape in which a portion fitted to the bearing body and a portion fitted to the elastic body are eccentric from each other. I am doing. With this holder, the elastic body can be inclined, and it is not necessary to change the shape of the housing or the like, and it can be easily applied to an existing power steering apparatus.

  FIG. 1 is a cross-sectional view showing a schematic configuration of an electric power steering apparatus to which an embodiment described later is applied. This electric power steering apparatus has a worm wheel 12 rotatable around an axis, a worm 13 meshing with the worm wheel 12, and a worm shaft 6 rotated by a motor 2 as an electric motor, and the worm shaft. 6 and a pair of bearing bodies 7 and 8 that rotatably support both ends of the bearing 6.

  The worm wheel 12 is provided on the steering shaft of the vehicle, and rotates around the axis together with the steering shaft. Although not shown, the steering shaft rotates with the steering wheel and is linked to a pair of steering wheels via a well-known rack and pinion.

  The motor 2 is driven and controlled based on a steering input torque detected by a known torque sensor, and generates a predetermined steering assist torque. The motor 2 is attached to the housing 1 that houses and holds the worm shaft 6, the worm wheel 12, and the like. It is fixed. The output shaft 2a of the motor 2 and the worm shaft 6 are coaxially connected via flexible joints 3-5. The flexible joints 3 to 5 include a first flange 3 fixed to the output shaft 2a, a second flange 4 fixed to the worm shaft 6, and a rubber filled in a gap between fitting portions of both flanges 3 and 4. The elastic body 5 is capable of transmitting the rotations of both the shafts 2a and 6 while allowing slight shaft misalignment and inclination of the shafts 2a and 6.

  The first bearing body 7 near the motor 2 rotatably supports the worm shaft 6 while allowing the worm shaft 6 to be inclined, as in a well-known universal bearing, and the outer ring side is fitted to the housing 1. Yes. A coil spring (compression coil spring) 9 as an elastic body is interposed in a compressed state between the second bearing body 8 on the distal end side far from the motor 2 and the lid portion 11 which is a part of the housing 1. Has been. The lid portion 11 is fixed to the housing 1 here, but may be formed integrally with the housing 11.

  A predetermined gap 21 is secured between the outer periphery of the second bearing body 8 and the worm shaft 6 and the inner periphery of the housing 1. Moreover, the bending of the worm shaft 6 with respect to the output shaft 2a is allowed by the above-described flexible joints 3 to 5. Therefore, the second bearing body 8 and the worm shaft 6 are moved in the direction (radial direction) approaching / separating from the worm wheel 12 with respect to the first bearing body 7 which is a universal bearing, that is, the direction inclined with respect to the output shaft 2a. And can be moved slightly in the axial direction of the worm shaft 6.

  As shown in FIG. 2, the second bearing body 8 includes an inner ring 8b and an outer ring 8c that sandwich the rolling element 8a, and a thrust bearing that can withstand a thrust load is preferably used. The inner ring 8b is fixed to the tip of the worm shaft 6. A holder 14 (or 14A) is interposed between the outer ring 8c and the coil spring 9. The holder 14 is formed with a first step portion 15 that holds one first axial end 9 a of the coil spring 9. The first step portion 15 is formed with a first bottom surface 16 that is in pressure contact with the axial end surface of the coil spring 9 and a first cylindrical surface 17 that is fitted to the inner peripheral surface of the coil spring 9 substantially without any gap. Has been. A second step 18 that holds the other second axial end 9 b of the coil spring 9 is formed in the lid 11 that forms a part of the housing 1. The second stepped portion 18 is formed with a second bottom surface 19 that is pressed against the axial end surface of the coil spring 9 and a second cylindrical surface 20 that fits into the inner peripheral surface of the coil spring 9 substantially without any gap. Has been.

  The coil spring 9 is interposed between the bottom surfaces 16 and 19 in a state of being compressed in the axial direction along the reference axis L0, and the radial direction of the coil spring 9 (except for the axial direction) by the cylindrical surfaces 17 and 20 Direction) is restricted or prohibited. That is, both ends of the coil spring 9 are fixedly held by the step portions 15 and 18. The cylindrical surfaces 17 and 20 are formed in a conical shape that tapers inwardly of the coil spring 9. The reference axis L0 is coincident with the axis of the motor output shaft 2a, and is substantially equal to the axes of the worm shaft 6 and the first and second bearing bodies 7 and 8 in the initial state assembled to the housing 1. I'm doing it.

  The coil spring 9 has a radial direction in which the second axial end 9b far from the worm wheel 12 faces the worm wheel 12 as compared to the first axial end 9a near the worm wheel 12 (upward direction in FIG. 2). Are assembled in an inclined posture offset by a predetermined amount ΔD. In other words, the axis L1 of the coil spring 9 that forms an eccentric cylindrical shape in the assembled and compressed state is inclined with respect to the reference axis L0 so as to move away from the worm wheel in the radial direction as it approaches the worm wheel in the axial direction. . That is, the coil spring 9 is assembled in a state of being biased in the direction perpendicular to the axis so that a preload in the radial direction (upward in FIG. 2) toward the meshing portion with the worm wheel 12 acts. However, the compression direction of the coil spring 9 (the direction in which the compression force acts) coincides with the reference axis L0.

  Since the coil spring 9 is assembled in a state compressed in the axial direction in this way, in addition to the axial preload being applied to the second bearing body 8 and the worm shaft 6 including the holder 14, the coil Since the spring 9 is assembled in an inclined posture with respect to the reference axis L0, the self-restoring force of the coil spring 9 causes the second bearing body 8 including the holder 14 and the worm shaft 6 to engage with the worm wheel 12. A radial preload is applied. That is, the radial preload can be applied using the coil spring 9 for applying the axial preload. Accordingly, the backlash between the tooth surfaces of the worm 6a and the worm wheel 12 can be effectively reduced and eliminated, and an appropriate preload is applied to the bearing bodies 7 and 8 to suppress the generation of sound vibration due to the bearing gap or the like.・ It can be avoided. In addition, since a leaf spring, a cam mechanism, and the like for applying the radial preload are not required, great effects such as reduction in the number of parts, miniaturization, space saving, and cost reduction can be obtained.

  The center of the worm wheel may deviate from the center of rotation due to manufacturing errors or the like. In this case, the distance (radius) from the rotation center of the worm wheel to the outer peripheral surface of the worm wheel varies depending on the circumferential position, and in particular, at the maximum radius with the largest radius, the engagement with the worm shaft becomes stronger and the smallest with the smallest radius At the radius, the engagement with the worm shaft is reduced. Therefore, the bias amount ΔD of the coil spring is preferably set larger than the difference between the maximum radius and the minimum radius of the worm wheel 12. As a result, the worm shaft can be urged to the worm wheel side without excess or shortage even in the situation of the minimum radius regardless of manufacturing errors of the worm wheel, and a sufficient meshing height can be ensured while avoiding backlash. .

  A ring-shaped cushioning material 10 is provided on the outer peripheral surface of the holder 14 so as to be opposed to each other with a predetermined gap. The cushioning material 10 is made of a suitable cushioning material such as rubber or resin so as to suppress or avoid the generation of sound vibration at the time of collision with the holder 14, and except for a third embodiment described later. The housing 1 and the lid 11 are fixed. The cushioning material 10 regulates the amount of radial displacement of the second bearing body 8 while allowing the second bearing body 8 including the holder 14 to swing and displace in the radial direction. Generation of sound vibration at the time of collision can be sufficiently reduced and avoided.

  Hereinafter, characteristic configurations and operational effects of the individual embodiments will be described in detail.

  In the first embodiment shown in FIG. 2, the lid portion 11 has a complete rotating body shape with respect to the reference axis L0, and the axis L2 of the lid portion 11 is offset by a predetermined amount ΔD toward the worm wheel 12 side. That is, the axis L2 of the lid assembly portion in the housing 1 is eccentric with respect to the reference axis L0. In this case, the holder 14 and the cover part 11 can be made into a complete rotating body shape, and the manufacture thereof is easy. On the other hand, the axis L2 of the lid assembly part of the housing 1 is decentered with respect to the reference axis L0 of the worm shaft housing part, making the housing 1 relatively difficult to manufacture.

  In the second embodiment shown in FIG. 3, the lid portion 11A has a non-rotating body shape, and the axis L3 of the second cylindrical surface 20A of the lid portion 11 is made while matching the axis of the outer peripheral surface of the lid portion 11A with the reference axis L0. Is decentered by a predetermined amount ΔD toward the worm wheel 12 with respect to the reference axis L0. In this case, the holder 14 can be formed into a complete rotating body shape, and the housing 1 can be formed along one reference axis L0. On the other hand, the lid portion 11 has a non-rotating body shape, and it is necessary to perform circumferential positioning when the lid portion 11 is assembled to the housing 1.

  In the third embodiment shown in FIG. 4, the cushioning material 10 </ b> A is fixed to the inner peripheral surface of the lid portion 11. In this case, like the case without the cushioning material 10A, the lid portion 11 can be directly fixed to the housing 1, and the shape of the lid portion 11 can be changed little, which is advantageous in terms of cost.

  In the fourth embodiment shown in FIGS. 5 and 6, the holder 14 </ b> A has a non-rotating body shape, and the axis of the inner peripheral surface 22 of the holder 14 </ b> A fitted to the second bearing body 8 is made to coincide with the reference axis L <b> 0. The axis L4 of the first cylindrical surface 17A of the holder 14A fitted to the spring 9 is eccentric by a predetermined amount ΔD in the direction away from the worm wheel 12 with respect to the reference axis L0. In this case, since the coil spring 9 can be decentered / inclined by the holder 14A, it is not necessary to decenter the housing 1 and the lid portion 11, and the housing 1 and the lid portion 11 are formed and assembled along one reference axis L0. be able to. For this reason, it can be easily applied to an existing power steering apparatus. Further, the eccentric amount ΔD of the coil spring 9 can be easily changed / adjusted by changing / changing the holder 14A.

  As described above, the present invention has been described based on the specific embodiments. However, the present invention is not limited to the above-described embodiments, and includes various modifications and changes without departing from the spirit of the present invention. . For example, in the above embodiment, the coil spring according to the present invention is applied only to one second bearing body, but the coil spring according to the present invention is applied to both of a pair of bearing bodies provided at both ends of the worm shaft. You can also

  Further, as shown in FIG. 1, the holder may be omitted, and a stepped portion for receiving the coil spring 9 may be formed in the bearing body 8. In this case, since the holder is omitted, the number of parts is reduced, and the entire length of the coil spring can be utilized to the maximum. Further, rubber may be used instead of the coil spring.

  Technical ideas other than the above claims that can be understood from the above description are listed.

  (1) The amount of eccentricity of the coil spring is set larger than the difference between the maximum radius and the minimum radius of the worm wheel. In this case, even if the worm wheel radius varies due to manufacturing errors of the worm wheel, the worm shaft is pushed toward the worm wheel side even at the portion where the worm wheel is engaged with the minimum radius portion to reduce backlash. Sufficient meshing height can be ensured while suppressing.

  (2) A holder interposed between the bearing body and the coil spring is provided, and a step portion for holding one axial end of the coil spring is formed in the holder. In this case, there is no need to form a stepped portion for holding the coil spring in the bearing body, and an existing bearing body can be used, which is advantageous in terms of cost.

  (3) A step portion for holding one axial end of the coil spring is formed in the bearing body. In this case, the holder as described above can be omitted, and the entire length of the coil spring can be utilized to the maximum.

  (4) It has a ring-shaped cushioning material facing the outer peripheral surface of the bearing body or holder with a predetermined gap. With this cushioning material, the amount of displacement in the radial direction of the bearing body can be regulated, and the generation of sound vibration at the time of collision with the bearing body (holder) can be sufficiently reduced and avoided.

The sectional view showing the electric power steering device for vehicles to which the present invention is applied. Sectional drawing of the coil spring vicinity which concerns on 1st Example. Sectional drawing of the coil spring vicinity which concerns on 2nd Example. Sectional drawing of the coil spring vicinity which concerns on 3rd Example. Sectional drawing of the coil spring vicinity which concerns on 4th Example. The front view which shows the holder of FIG. 5 alone.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Housing 2 ... Motor (electric motor)
6 ... Worm shaft 8 ... Second bearing body 9 ... Coil spring 10 ... Buffer material 11 ... Lid (housing)
12 ... Worm wheel 14 ... Holder

Claims (2)

A worm wheel provided on the steering shaft and rotatable around the axis;
A worm shaft having a worm meshing with the worm wheel and driven to rotate by an electric motor;
A bearing body attached to one axial end of the worm shaft;
An elastic body interposed between the bearing body and the housing in a state compressed in the axial direction of the worm shaft,
This electric power steering apparatus is characterized in that the elastic body is assembled in an inclined posture in which an end portion far from the worm wheel is offset in a radial direction toward the worm wheel as compared with an end portion close to the worm wheel. The holder has a holder interposed between the bearing body and the elastic body, and the holder has a non-rotating body shape in which a portion fitted to the bearing body and a portion fitted to the elastic body are eccentric from each other. The electric power steering apparatus according to claim 1, wherein

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