JP2005112241A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To develop an intrincic damping performance by stabilizing backlash. <P>SOLUTION: This electric power steering device is formed such that the molybdenum disulfide particles of a solid lubricating material are driven, by shot peening, on at least one of the sliding surfaces of the outer peripheral surfaces of the support parts 22a and 22b of a rotating shaft 20 with the inner peripheral surfaces of the inner rings 34a and 34b of bearings 26a and 26b so that a film treatment of approximately several μ in thickness can be performed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus of a type that reduces a rattling sound by moving a rotating shaft by deforming an elastic body when tooth surfaces of a worm and a worm wheel come into contact with each other.

  A conventional example substantially the same as the electric power steering device described in Patent Document 1 is shown in FIGS.

  FIG. 3 is a longitudinal sectional view of an electric power steering apparatus according to a conventional example. 4 is a cross-sectional view of the electric power steering apparatus shown in FIG. FIG. 5A is a cross-sectional view showing the main parts of the rotating shaft and the bearing shown in FIG. 3 before the torque transmission direction is switched, and FIG. 5B is the main part of the rotating shaft and the bearing. It is sectional drawing which shows, Comprising: A torque transmission direction switches and the state which the rotating shaft moved is shown.

  In the column assist type electric power steering apparatus shown in FIG. 3, a steering shaft 2 (input shaft) is rotatably supported on the steering column 1.

  An output shaft 3 is connected to the vehicle front side of the steering shaft 2 (input shaft). A steering gear (not shown) or the like is connected to the front side of the output shaft 3 via a universal joint (not shown) or the like.

  The base end of the torsion bar 4 is press-fitted and fixed to the front side of the steering shaft 2 (input shaft). The torsion bar 4 extends inside the hollow output shaft 3 and has a distal end. Is fixed to the end of the output shaft 3 by a fixing pin 5.

  A plurality of grooves 6 for detecting a torque sensor are formed on the vehicle rear side of the output shaft 3, and a torque sensor sleeve 7 is disposed outside the grooves 6 in the radial direction. The sleeve 7 has a vehicle rear side end fixed to a vehicle front side end of the steering shaft 2 (input shaft) by caulking or the like. A coil 8 and a substrate are provided outside the sleeve 7 in the radial direction.

  As will be described later, a worm wheel 12 meshed with a worm 11 driven by an electric motor 10 is attached to the output shaft 3.

  Therefore, the steering force generated when the driver steers the steering wheel (not shown) is transmitted to the steered wheels (not shown) via the input shaft 1, the torsion bar 4, the output shaft 3, and the rack and pinion type steering device. Is done. Further, the rotational force of the electric motor 10 is transmitted to the output shaft 3 via the worm 11 and the worm wheel 12, and the output is obtained by appropriately controlling the rotational force and the rotational direction of the electric motor 10. An appropriate steering assist torque can be applied to the shaft 3.

  As shown in FIG. 4, a motor side end 21 of the rotating shaft 20 is connected to the rotor 10a of the electric motor 10 so as to be movable in the axial direction by serration fitting or spline fitting.

  As shown in FIGS. 4 and 5, the rotary shaft 20 is connected to the motor side end portion 21, support portions 22 a and 22 b rotatably supported by bearings 26 a and 26 b described later, and support portions 22 a and 22 b. Adjacent large diameter portions 23a and 23b, flange portions 24a and 24b adjacent to the large diameter portions 23a and 23b, and a worm 11 formed between the flange portions 24a and 24b.

  The support portions 22a and 22b are provided with bearings 26a and 26b, respectively, so that the rotary shaft 20 is rotatably supported with respect to the housing 27.

  Elastic members 30a and 30b interposed between the bearings 26a and 26a and the flange portions 24a and 24b of the rotary shaft 20 are small-diameter hole disc portions 31a and 31b disposed on the support portions 22a and 22b of the rotary shaft 20, respectively. 31b and large-diameter hole disk portions 32a and 32b arranged on the outer periphery of the large-diameter portions 23a and 23b, and both are connected by elastic portions 33a and 33b.

  In the assembled state, the elastic members 30a and 30b make the large-diameter hole disk portions 32a and 32b abut on the flange portions 24a and 24b of the rotary shaft 20, and are U-shaped on the inner rings 34a and 34b of the bearings 26a and 26b. The small-diameter hole disk portions 31 and 31b are brought into contact with each other through the bent bushes 35a and 35b, and a predetermined preload is applied to the elastic portions 33a and 33b.

  Therefore, after the rotary shaft 20 is supported by the bearings 26a and 26b via the bushes 35a and 35b and moved in the axial direction, the impact force generated between the tooth surfaces of the worm 11 and the worm wheel 12 is applied to the elastic members 30a and 30b. 30b can be bent, and the rotating shaft 20 can be relaxed by moving it in the axial direction, thereby reducing the hitting sound.

  As described above, in the conventional example, in order to smoothly move the rotating shaft 20 and the bearings 26a and 26b in the axial direction, the bushes 35a and 35b having good slidability are fixed to the bearing inner rings 34a and 34b. .

As the bushes 35a and 35b, the surface of the back metal is coated with a Teflon layer, and as shown in Patent Document 1, it is bent and fixed to the bearing inner ring in a U shape.
Japanese Patent No. 3253578

  However, the fit between the bearings 26a and 26b and the rotary shaft 20 has a large variation due to the thickness tolerance of the bushes 35a and 35b, and the backlash between the worm 11 and the worm wheel 12 is increased. There was a problem that the performance of relaxing the hitting sound with the tooth surface could not be exhibited sufficiently.

  As shown in FIG. 5, the inner ring 34b of the bearing 26b and the flange 24b of the rotary shaft 20 are in contact with the small-diameter hole disk portion 31b of the elastic member 30b by being pressed by the elastic portion 33b.

  A bush 35b fixed in a U-shape is interposed between the small-diameter hole disk portion 31b and the inner ring 34b.

  Since the friction coefficient between the bush 35b and the small diameter hole disk portion 31b is smaller than the friction coefficient between the flange 24b and the large diameter hole disk portion 32b, the rotary shaft 20 and the bearing inner ring 34b can only move smoothly in the axial direction. There is also a difference in speed in the rotational direction.

  Further, as shown in FIGS. 5A and 5B, when the torque transmission direction between the worm 11 and the worm wheel 12 is switched, the direction of the axial force of the worm 11 is reversed, and the worm 11 is in the axial direction. When moving until it comes into contact with the opposite bearing, the small-diameter hole disk portion 31b and the bearing inner ring 34b, which have a speed difference, are abruptly pressed, forcing the flange-like portion of the bush 35b to break down over a long period of use. There was a problem of doing.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an electric power steering apparatus that can stabilize backlash and exhibit original buffer performance.

In order to achieve the above object, an electric power steering apparatus according to claim 1 of the present invention includes a worm formed on a rotating shaft and a bearing that rotatably supports the rotating shaft, and the rotating shaft and the An electric power steering device in which an elastic body is provided between the bearing and the rotating shaft is moved relative to the housing by deforming the elastic body when the tooth surfaces of the worm and the worm wheel come into contact with each other. In
Shot peening is performed on at least one of sliding surfaces between the outer peripheral surface of the rotating shaft and the inner peripheral surface of the inner ring of the bearing.

  The electric power steering apparatus according to a second aspect of the present invention is characterized in that a solid lubricant is driven into at least one of the sliding surfaces by the shot peening and is subjected to a film treatment.

  The electric power steering apparatus according to claim 3 of the present invention is characterized in that the solid lubricant is molybdenum disulfide.

  As described above, according to the present invention, at least one of the sliding surfaces of the outer peripheral surface of the support portion of the rotating shaft and the inner peripheral surface of the inner ring of the bearing is subjected to shot peening to form molybdenum disulfide that is a solid lubricant. Bushing can be abolished because the particles are driven and the film is processed. Therefore, it is not necessary to estimate the clearance by the thickness tolerance of the bushing between the support portion of the rotating shaft and the inner ring of the bearing, the backlash can be stabilized, and the original buffer performance can be exhibited. . Also, the friction coefficient between the flange part of the rotating shaft and the large-diameter hole disk part and the friction coefficient between the small-diameter hole disk part and the bearing inner ring are substantially equal, and there is no speed difference in the rotation direction. It is also possible to prevent damage to the disk part.

  Hereinafter, an electric power steering apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of an electric power steering apparatus according to an embodiment of the present invention.

  FIG. 2 is a cross-sectional view of the bearing shown in FIG.

  As shown in FIG. 1, a motor side end 21 of a rotating shaft 20 is connected to a rotor 10a of an electric motor 10 so as to be movable in the axial direction by serration fitting or spline fitting.

  The rotary shaft 20 includes a motor-side end portion 21, support portions 22 a and 22 b that are rotatably supported by bearings 26 a and 26 b described later, and large-diameter portions 23 a and 23 b adjacent to the support portions 22 a and 22 b, The flange parts 24a and 24b adjacent to the large diameter parts 23a and 23b and the worm 11 formed between the flange parts 24a and 24b are provided.

  The support portions 22a and 22b are provided with bearings 26a and 26b, respectively, so that the rotary shaft 20 is rotatably supported with respect to the housing 27.

  Elastic members 30a and 30b interposed between the bearings 26a and 26a and the flange portions 24a and 24b of the rotary shaft 20 are small-diameter hole disc portions 31a and 31b disposed on the support portions 22a and 22b of the rotary shaft 20, respectively. 31b and large-diameter hole disk portions 32a and 32b arranged on the outer periphery of the large-diameter portions 23a and 23b, and both are connected by elastic portions 33a and 33b.

  In the assembled state, the elastic members 30a and 30b have the large-diameter hole disk portions 32a and 32b in contact with the flange portions 24a and 24b of the rotary shaft 20, and the small-diameter hole disk portions on the inner rings 34a and 34b of the bearings 26a and 26b. 31 and 31b are in contact with each other, and a predetermined preload is applied to the elastic portions 33a and 33b.

  Therefore, after the rotating shaft 20 is supported by the bearings 26a and 26b and moved in the axial direction, the impact force generated between the tooth surfaces of the worm 11 and the worm wheel 12 is deflected by the elastic members 30a and 30b. The shaft 20 can be relaxed by moving it in the axial direction, thereby reducing the hitting sound.

  In the present embodiment, at least one of the sliding surfaces of the outer peripheral surfaces of the support portions 22a and 22b of the rotating shaft 20 and the inner peripheral surfaces of the inner rings 34a and 34b of the bearings 26a and 26b is solidified by shot peening. Lubricating molybdenum disulfide particles are implanted to perform coating treatment with a thickness of about several microns. That is, in FIG. 1 and FIG. 2, film processing is performed on the cross hatched portion.

  For shot peening, WPC processing (registered trademark) is optimal, and this WPC processing is performed with a shot particle size of 40 to 200 μm and an injection speed of 100 m / sec or more, and the surface temperature is overheated and rapidly cooled to the A3 transformation point or higher. It is a method to make it.

  For the thickness tolerances of about 40 to 50 μm of the bushes 35a and 35b having a Teflon layer coated on the surface of the back metal (iron plate), the dimensional change due to the processing according to this embodiment can be canceled by correcting before the processing. Therefore, the outer peripheral surfaces of the support portions 22a and 22b of the rotary shaft 20 and the inner peripheral surfaces of the inner rings 34a and 34b of the bearings 26a and 26b are fitted by a solid lubricant coating process, and the bush is eliminated. Therefore, it becomes possible to pack only the thickness tolerance of the bush, the backlash can be stabilized, and the original buffer performance can be exhibited.

  In addition, since the bushes 35a and 35b do not have the flanges, the damage is not caused. However, the friction coefficient between the flanges 24a and 24b of the rotary shaft 20 and the large-diameter hole disk portions 32a and 32b, and the small diameters. The friction coefficients between the hole disk portions 31a and 31b and the bearing inner rings 34a and 34b are substantially equal and there is no speed difference in the rotation direction, so that the large and small diameter disk portions 31a to 32b can be prevented from being damaged.

  In addition, this invention is not limited to embodiment mentioned above, A various deformation | transformation is possible.

1 is a cross-sectional view of an electric power steering device according to an embodiment of the present invention. It is sectional drawing of the bearing shown in FIG. It is a longitudinal cross-sectional view of the electric power steering apparatus which concerns on a prior art example. FIG. 4 is a cross-sectional view of the electric power steering device shown in FIG. 3. (A) is sectional drawing which shows principal parts, such as a rotating shaft and a bearing shown in FIG. 3, Comprising: Before torque transmission direction switches, (b) shows the principal parts, such as a rotating shaft and a bearing. It is sectional drawing, Comprising: A torque transmission direction switches and the state which the rotating shaft moved is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering column 2 Steering shaft 3 Output shaft 4 Torsion bar 5 Fixing pin 6 Groove 7 Sleeve 8 Coil 10 Electric motor 10a Rotor 11 Worm 12 Worm wheel 20 Rotating shaft 21 Motor side edge part 22a, 22b Support part 23a, 23b Large diameter Part 24a, 24b flange part 26a, 26b bearing 27 housing 30a, 30b elastic member 31a, 31b small diameter hole disk part 32a, 32b large diameter hole disk part 33a, 33b elastic part 34a, 34b inner ring 35a, 35b bush

Claims (3)

A worm formed on the rotating shaft and a bearing that rotatably supports the rotating shaft are provided, and an elastic body is provided between the rotating shaft and the bearing, and the tooth surfaces of the worm and the worm wheel are in contact with each other. In the electric power steering apparatus that moves the rotating shaft with respect to the housing by deforming the elastic body when in contact with the housing,
An electric power steering apparatus characterized in that shot peening is performed on at least one of sliding surfaces between an outer peripheral surface of the rotating shaft and an inner peripheral surface of an inner ring of the bearing.   2. The electric power steering apparatus according to claim 1, wherein a solid lubricant is applied to at least one of the sliding surfaces by the shot peening to perform a film treatment.   The electric power steering apparatus according to claim 2, wherein the solid lubricant is molybdenum disulfide.

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