JP5321565B2 - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device, which can suppress the rattling noise of a spline engaging part and suppress the delay of torque transmission or damage. <P>SOLUTION: A power transmission member 51 is made of the same metal as those of an output shaft 292 and a worm shaft 23, and a small-diameter column part is formed in the center in its axial direction. An elastic member 53, having its outer diameter dimension larger than the small diameters of a female spline 232 and a female spline 293 and smaller than the large diameters of the female spline 232 and the female spline 293, is fitted around the small-diameter column part. The elastic member 53 is hollow and cylindrical, is made of a material such as rubber, a synthetic resin, or elastomer, and is wound on the outer peripheral surface of the small-diameter column part by press-molding or injection molding. Thus, the outer peripheral surface of the elastic member 53 is fastened and fitted in the small-diameter inner peripheral surfaces of the female spline 232 and the female spline 293. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention eliminates the backlash of an electric power steering device, in particular, a worm gear reducer that transmits auxiliary steering force, and generates a rattling sound of the worm gear reducer even if a large impact or vibration is transmitted from the wheel to the worm wheel. The present invention relates to an electric power steering device that is suppressed.

  The steering torque of the steering wheel is detected, and the rotation of the worm driven by the actuator is transmitted to the steering shaft via the worm wheel, assisting the steering force applied to the steering wheel to facilitate the operation of the steering wheel. There is an electric power steering device having a steering force assisting device.

  In such an electric power steering apparatus, if there is a large backlash between the worm and the worm wheel due to a manufacturing error or assembly error of a single component, the tooth surfaces of the worm and the worm wheel are not aligned. There is a problem that an awkward rattling sound is generated by colliding with each other, and the sound is recognized as an abnormal sound by the driver of the vehicle.

  For this reason, the bearing for supporting the worm shaft is configured to be movable in the meshing direction of the worm and the worm wheel, and a means for pressing the worm in the worm wheel direction is provided, and the backlash amount of the meshing portion of the worm and the worm wheel is provided. Some have been proposed to reduce

  However, in order to press the worm in the worm wheel direction, a structure that allows the inclination of the worm shaft relative to the inner ring or the outer ring of the bearing that holds the worm shaft is required. However, if the worm shaft is allowed to tilt, the shaft center of the worm shaft and the shaft center of the actuator output shaft may be tilted without being coaxially arranged (declination), or the two shaft centers may be relatively displaced. Axis misalignment (eccentricity) occurs.

  For this reason, there has been proposed a structure in which a worm shaft and an actuator output shaft, each of which is firmly supported by a bearing, are coupled with an allowance for declination and eccentricity (Patent Documents 1 and 2). In the electric power steering device of Patent Document 1, a power transmission member having male splines formed at both ends is interposed between a female spline of a worm shaft and a female spline of a motor output shaft, and a gap between the spline tooth surfaces is provided. The worm shaft and the motor output shaft are coupled to increase the worm shaft, and the declination and eccentricity between the worm shaft axis and the motor output shaft axis are allowed.

  However, the electric power steering device of Patent Document 1 can suppress the occurrence of rattling noise at the spline engaging portion because the gap between the spline tooth surfaces becomes small when the amount of declination or eccentricity is large. However, when the amount of declination or eccentricity is small (that is, when the axis of the worm shaft is coincident with the axis of the motor output shaft), the gap between the spline tooth surfaces becomes large. There was a risk of rattling noise.

  In the electric power steering device of Patent Document 2, a torsion bar is inserted into a through-hole formed in the shaft center of the worm shaft, and one end of the torsion bar is connected to a motor output shaft through a joint. Due to the elastic deformation of the bar, the deflection angle and eccentricity between the axis of the worm shaft and the axis of the motor output shaft are allowed.

  However, since the electric power steering device of Patent Document 2 transmits torque through the torsion bar, there is a risk of delay in torque transmission due to elastic deformation of the torsion bar and damage of the torsion bar.

JP 2004-237755 A JP 2006-56296 A

  The present invention engages the spline between the worm shaft and the female spline of the motor output shaft by interposing a power transmission member that allows declination and eccentricity, and suppresses the occurrence of rattling noise at the spline engaging portion. It is another object of the present invention to provide an electric power steering device capable of suppressing torque transmission delay and damage.

The above problem is solved by the following means. That is, the first invention is a gear housing, an actuator that is provided in the gear housing and generates auxiliary steering torque corresponding to the steering torque applied to the steering wheel, an output shaft that outputs rotation of the actuator, and the output A worm connected to a shaft, a worm wheel meshing with the worm, decelerating the rotation of the worm and transmitting it to the steering shaft, an output shaft side female spline formed on the shaft of the output shaft, and a shaft of the worm the formed warm side female spline includes a power transmission member male spline is formed at both ends of the axially splined with clearance in the spline tooth surfaces of the output shaft side female spline and the worm side female spline, the power transmission member, the male spline formed at both ends in the axial direction The small-diameter cylindrical portion formed in the central portion in the axial direction between an outer diameter dimension greater than the diameter of the output shaft side female spline and the worm side female spline, the output shaft-side female spline and worm-side female An electric power steering apparatus including a hollow cylindrical elastic member smaller than a large diameter of a spline.

  According to a second aspect of the present invention, in the electric power steering apparatus according to the first aspect, the outer peripheral surface of the elastic member is fitted with a small-diameter inner peripheral surface of the output shaft side female spline and the worm side female spline. This is an electric power steering device.

  A third invention is the electric power steering device according to the first invention, wherein the power transmission member is made of metal.

  According to a fourth aspect of the present invention, there is provided an electric power steering apparatus according to the first aspect, further comprising a preload imparting mechanism that is provided in the gear housing and biases the worm toward the worm wheel. It is a power steering device.

  A fifth aspect of the invention is the electric power steering apparatus according to the first aspect of the invention, further comprising a torque limiter that is provided in the gear housing and restricts the torque transmitted from the actuator to the steering shaft from exceeding a predetermined value. This is an electric power steering device.

  An electric power steering apparatus according to the present invention includes an output shaft-side female spline formed at the shaft center of the output shaft, a worm-side female spline formed at the shaft center of the worm, an output shaft-side female spline, and a worm-side female spline. A male spline that engages the spline with a gap in the spline tooth surface is formed at both ends in the axial direction, and is formed at the central portion in the axial direction of the power transmission member. The elastic member is larger than the small diameter of the side female spline and the worm side female spline and smaller than the large diameter of the output shaft side female spline and the worm side female spline.

  Therefore, even if the shaft center between the worm and the output shaft is decentered or declined, the clearance between the spline engaging portions allows the decentering or declination, and the rotation of the actuator can be smoothly transmitted to the worm. In addition, even if the amount of declination or eccentricity is small and the gap between the spline tooth surfaces is large, the elastic member of the power transmission member is elastically deformed to suppress the occurrence of rattling noise at the spline engaging portion. it can.

BRIEF DESCRIPTION OF THE DRAWINGS It is the front view which showed the whole electric power steering device of this invention, and cut | disconnected a part. FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. It is an expanded sectional view of the meshing part of the worm and worm wheel of FIG. FIG. 3 is an enlarged cross-sectional view showing the vicinity of a coupling portion between a motor output shaft and a worm shaft in FIG. 2. (A) is an expanded sectional view showing a motor output shaft and a worm shaft in a state where the power transmission member is removed, and (b) is an enlarged sectional view showing the power transmission member. FIG. 5 is an enlarged cross-sectional view showing the vicinity of a shaft support at the left end of the worm shaft in FIG. 4. It is BB sectional drawing of FIG. It is a perspective view which takes out from the gear housing and shows the preload provision mechanism which assembled | attached the holder, the preload pad, and the torsion coil spring. FIG. 9 is an exploded perspective view of FIG. 8.

  Embodiments of the present invention will be described below with reference to the drawings. 1 is a front view of the electric power steering apparatus according to the present invention, partly cut away, FIG. 2 is a cross-sectional view taken along line AA of FIG. 1, and FIG. 3 is a view of the worm and worm wheel of FIG. It is an expanded sectional view of a meshing part. 4 is an enlarged cross-sectional view showing the vicinity of the coupling portion between the motor output shaft and the worm shaft of FIG.

  FIG. 5A is an enlarged sectional view showing the motor output shaft and the worm shaft with the power transmission member removed, and FIG. 5B is an enlarged sectional view showing the power transmission member. 6 is an enlarged cross-sectional view showing the vicinity of the shaft support portion at the left end of the worm shaft in FIG. 4, and FIG. 7 is a cross-sectional view along BB in FIG. FIG. 8 is a perspective view showing a preload applying mechanism in which a holder, a preload pad, and a torsion coil spring are assembled, taken out from the gear housing, and FIG. 9 is an exploded perspective view of FIG.

  As shown in FIG. 1, an electric power steering apparatus according to the present invention includes a steering shaft 12 having a steering wheel 11 fixed to the rear side of the vehicle body (the right side in FIG. 1), a steering column 13 having the steering shaft 12 inserted therein, An assist device 20 for applying auxiliary torque to the steering shaft 12 and a steering gear 30 connected to the front side of the vehicle body of the steering shaft 12 (left side in FIG. 1) via a rack / pinion mechanism (not shown). .

  The steering shaft 12 is formed by combining an outer shaft 12A and an inner shaft 12B by spline engagement so that rotational force can be transmitted and relative displacement in the axial direction can be achieved. Further, the vehicle body front side of the outer shaft 12A and the vehicle body rear side of the inner shaft 12B are spline-engaged and joined via a synthetic resin. Accordingly, the outer shaft 12A and the inner shaft 12B can shorten the total length by breaking the synthetic resin at the time of collision.

  The cylindrical steering column 13 inserted through the steering shaft 12 is formed by combining the outer column 13A and the inner column 13B so as to be telescopically movable. When an axial impact is applied, the cylindrical steering column 13 absorbs energy from the impact. However, it has a so-called collapsible structure in which the overall length is reduced. The vehicle body front side end portion of the inner column 13B is coupled and fixed to the vehicle body rear side end surface of the gear housing 21. Further, the vehicle body front side end portion of the inner shaft 12B is passed through the inside of the gear housing 21 and connected to a worm wheel described later.

  The steering column 13 is supported by a support bracket 14 at a middle portion thereof on a part of the vehicle body 18 such as a lower surface of the dashboard. Further, a locking portion (not shown) is provided between the support bracket 14 and the vehicle body 18, and when an impact in a direction toward the front side of the vehicle body is applied to the support bracket 14, the support bracket 14 is locked to the locking bracket 14. It moves away from the vehicle and moves to the front side of the vehicle.

  The upper end portion of the gear housing 21 is also supported on a part of the vehicle body 18. In the case of the present embodiment, a tilt mechanism and a telescopic mechanism are provided, so that the position of the steering wheel 11 in the longitudinal direction and the height position can be freely adjusted. Such a tilt mechanism and a telescopic mechanism are well known in the art and are not characteristic features of the present invention, and thus detailed description thereof is omitted.

  Further, the output shaft 19 protruding from the vehicle body front side end surface of the gear housing 21 at the vehicle body front side end portion of the inner shaft 12B is connected to the rear end portion of the intermediate shaft 16 via the universal joint 15. . Further, the input shaft 31 of the steering gear 30 is connected to the front end portion of the intermediate shaft 16 via another universal joint 17. A pinion (not shown) is coupled to the input shaft 31. A rack (not shown) fitted in the steering gear 30 so as to be reciprocally slidable meshes with the pinion, and the rotation of the steering wheel 11 moves the tie rod 32 to steer a wheel (not shown).

  Each of the universal joints 15 and 17 can be provided with a vibration absorbing device for preventing vibration applied to the intermediate shaft 16 from the ground via the wheels to the steering wheel 11.

  As shown in FIGS. 2 to 9, the assist device 20 includes a worm wheel 22, a worm shaft 23, and a preload applying mechanism 24 that are externally fitted and fixed to the output shaft 19. Among these, the preload applying mechanism 24 includes a torsion coil spring 25 that is an elastic body and a preload pad 26 that is a single member. Further, the assist device 20 includes ball bearings 27 and 28.

  Further, a torque sensor (not shown) is provided around the middle portion of the inner shaft 12B to detect the direction and magnitude of torque applied to the inner shaft 12B from the steering wheel 11, and in accordance with the detection signal, The electric motor (actuator) 29 is driven to generate auxiliary torque with a predetermined magnitude in a predetermined direction.

  The worm wheel 22 and the worm shaft 23 are provided inside the gear housing 21 and mesh with a worm 231 formed at an intermediate portion of the worm wheel 22 and the worm shaft 23. The electric motor 29 includes a case 291 fixed to the gear housing 21, a permanent magnet stator (not shown) provided on the inner peripheral surface of the case 291, an output shaft 292 provided inside the case 291, A rotor (not shown) provided at a middle portion of the output shaft 292 so as to face the stator is provided.

  As shown in FIG. 2, a hollow cylindrical slip ring (torque limiter) 221 is inserted between the inner peripheral surface of the worm wheel 22 and the outer peripheral surface of the output shaft 19. When the torque transmitted from the electric motor 29 to the output shaft 19 exceeds a predetermined value, the slip ring 221 slips between the inner peripheral surface of the worm wheel 22 and the outer peripheral surface of the output shaft 19, and the output shaft 19 from the electric motor 29. The torque transmitted to the worm wheel 22 is limited to prevent the tooth surfaces of the worm wheel 22 and the worm 231 from being damaged. Instead of the slip ring 221, a torque limiter may be provided inside the electric motor 29 to limit the torque transmitted from the electric motor 29 to the output shaft 19.

  A female spline (worm side female spline) 232 is formed at the shaft center of the base end portion (left end portion in FIGS. 2 to 6) of the worm shaft 23, and the tip end portion (right end in FIGS. 2 to 6) of the output shaft 292 is formed. Is formed with a female spline (output shaft side female spline) 293. The female spline 232 and the female spline 293 are formed with the same nominal diameter.

  Male splines 511 and 512 are formed at both ends of the cylindrical power transmission member 51, the left male spline 511 is spline-engaged with the female spline 293 of the output shaft 292, and the right male spline 512 is connected to the worm shaft 23. The female spline 232 is engaged with the spline. The male splines 511 and 512 are formed in a dimension that allows spline engagement with a clearance between the spline tooth surfaces of the female spline 293 and the female spline 232. Therefore, the power transmission member 51 connects the end portions of the worm shaft 23 and the output shaft 292 by spline engagement, and the worm shaft 23 rotates together with the output shaft 292.

  The power transmission member 51 is made of the same metal as the output shaft 292 and the worm shaft 23, and as shown in detail in FIG. 5, a small-diameter cylindrical portion 52 is formed at the center in the axial direction. The small-diameter cylindrical portion 52 has an elastic member 53 whose outer diameter d is larger than the small diameters WD2 and OD2 of the female spline 232 and female spline 293 and smaller than the large diameters WD1 and OD1 of the female spline 232 and female spline 293. Is fitted. The elastic member 53 has a hollow cylindrical shape and is made of a material such as rubber, synthetic resin, or elastomer, and the outer peripheral surface of the small-diameter cylindrical portion 52 is covered by press molding or injection molding. Therefore, the outer peripheral surface 531 of the elastic member 53 is tightly fitted to the small-diameter inner peripheral surfaces of the female spline 232 and the female spline 293.

  As shown in detail in FIG. 6, the ball bearing 27 rotatably supports the base end portion of the worm shaft 23 inside the gear housing 21. The ball bearing 27 is a single row deep groove type, and includes a rolling surface of each ball 271, an outer ring raceway provided on the inner peripheral surface of the outer ring 272, and an inner ring raceway provided on the outer peripheral surface of the inner ring 273 for each ball 271. , Each one point is in contact.

  Further, the inner ring 273 is externally fitted on the outer peripheral surface near the base end of the worm shaft 23 in a portion coinciding with the spline engaging portion (spline engaging portion of the female spline 232 and the male spline 512) in the axial direction. . The axial center position of the spline engaging portion and the axial center position of the ball bearing 27 are substantially matched. Further, by providing a minute gap between the inner peripheral surface of the inner ring 273 and the outer peripheral surface of the worm shaft 23, the inclination of the worm shaft 23 with respect to the ball bearing 27 in a predetermined range can be freely made.

  An O-ring 47 as an elastic body is incorporated in an annular groove 46 formed on the outer peripheral surface of the worm shaft 23 and radially inside the inner ring 273 of the ball bearing 27. The O-ring 47 is compressed between the inner ring 273 of the ball bearing 27 and the worm shaft 23, and generates a uniform repulsive force over the entire circumference against the radial displacement of the worm shaft 23.

  Accordingly, when a light load from the road surface or the like is applied to the worm shaft 23, a radial load is generated and the worm shaft 23 is displaced. However, since the load is received by the O-ring 47, the worm shaft 23 and the ball The inner ring 273 of the bearing 27 is not in direct contact with each other, and neither metal hitting sound is generated.

  Further, when a heavy load generated by the assist of the electric motor 29 is applied to the worm shaft 23, the worm shaft 23 and the inner ring 273 of the ball bearing 27 come into contact with each other to receive the load, but the speed is attenuated by the O-ring 47. Therefore, the contact sound does not become a problem. Further, since the worm shaft 23 receives a uniform load from the ball bearing 27, the worm shaft 23 can be favorably held with respect to the ball bearing 27.

  The outer peripheral surface of the base end portion (left end portion in FIG. 6) of the worm shaft 23 is a cylindrical surface that does not form a male screw portion. A restraining member 43 is externally fitted to a portion near the base end of the cylindrical portion 238 having the cylindrical surface on the outer peripheral surface. The holding member 43 is formed in a cylindrical shape as a whole, and has an outward flange portion 431 on the outer peripheral surface of the base end portion. In addition, a thin cylindrical portion 432 protruding in the axial direction (left side in FIG. 6) is formed on the base end surface (left end portion in FIG. 6) of the holding member 43.

  Then, with the restraining member 43 fitted on the outer peripheral surface of the cylindrical portion 238, the tip edge of the cylindrical portion 432 provided on the restraining member 43 is formed on the outer peripheral surface of the cylindrical portion 238 of the worm shaft 23 over the entire circumference. The holding member 43 is coupled and fixed to the cylindrical portion 238 by caulking in the locking groove 239.

  Then, both end surfaces in the axial direction of the inner ring 273 constituting the ball bearing 27, one side (right side surface in FIG. 6) of the outward flange 431 formed on the outer peripheral surface of the holding member 43, and the base end of the worm shaft 23 ( A pair of locking rings 45 are provided between the side surface of the flange 233 provided on the outer peripheral surface near the left end in FIG. In addition, cylindrical members 44 and 44 made of an elastic material are provided between the locking rings 45 and 45. An inner ring 273 is provided between one side of the outward flange portion 431 of the holding member 43 and the side surface of the flange portion 233 of the worm shaft 23, and the locking rings 45, 45 provided on both sides of the inner ring 273 and the cylindrical member 44, 44 and is elastically sandwiched between them.

  The worm shaft 23 can be freely displaced in a predetermined range in the axial direction with respect to the ball bearing 27. The cylindrical members 44 and 44 can be made of rubber, synthetic resin, or metal such as a disc spring. In the present embodiment, a radial gap of about C2 or C3 is provided inside the ball bearing 27.

  Further, an outer ring 272 constituting the ball bearing 27 is fitted on the inner peripheral surface of a support hole 211 provided in a part of the gear housing 21. Further, one end surface in the axial direction of the outer ring 272 (the right end surface in FIG. 6) abuts against a step portion 212 provided on the inner peripheral surface of the support hole 211, and the other end surface in the axial direction of the outer ring 272 (the left end in FIG. 6). Surface) is held down by a locking ring 213 locked to the inner peripheral surface.

  Further, the ball bearing 28 rotatably supports the tip end portion (the right end portion in FIGS. 2 and 3) of the worm shaft 23 inside the gear housing 21. This ball bearing 28 is a single-row deep structure, and includes a rolling surface of each ball 281, an outer ring raceway provided on the inner peripheral surface of the outer ring 282, and an inner ring raceway provided on the outer peripheral surface of the inner ring 283 for each ball 281. Are touched by one point each. The outer ring 282 constituting the ball bearing 28 is fixed to a holder 41 fixed to the inside of the gear housing 21.

  The holder 41 has an L-shaped cross section and is formed in an annular shape as a whole. An outer ring 282 is provided on a large-diameter portion 411 provided on the inner peripheral surface of one half of the holder 41 (the left half in FIGS. 2 and 3). The inner fitting is fixed. Further, an elastic bushing 42 is externally fitted to a large-diameter portion 234 provided at a portion outside the worm 231 on the outer peripheral surface near the tip of the worm shaft 23. The bush 42 is formed in a cylindrical shape as a whole.

  Further, an outward flange portion 421 is formed on the outer peripheral surface of the left end of the bush 42 for fitting the large diameter portion 234 therein. The inner side surface of the outward flange 421 is abutted against one end surface in the axial direction of the inner ring 283 constituting the ball bearing 28 (the left end surface in FIGS. 2 and 3). In the case of the present embodiment, the inner peripheral surface of the bush 42 is a simple cylindrical surface that does not form an inward flange portion.

  The large-diameter portion 234 of the worm shaft 23 is loosely inserted inside the bush 42 and the tip end portion of the worm shaft 23 protrudes from one axial end portion (the right end portion in FIGS. 2 and 3) of the bush 42. I am letting. Further, an inner ring 283 constituting the ball bearing 28 is externally fitted to the intermediate portion of the bush 42 in the axial direction.

  Further, by providing a minute gap between the inner peripheral surface of the bush 42 and the outer peripheral surface of the large-diameter portion 234, the worm shaft 23 can be tilted in a predetermined range with respect to the bush 42.

  Further, the large diameter portion 234 provided on the worm shaft 23 and the small diameter portion 235 provided on the tip side of the large diameter portion 234 are continuous by a tapered surface 236. Further, a tapered surface 237 is provided at a connection portion between the right end surface of the worm shaft 23 and the small diameter portion 235.

  On the other hand, the small diameter portion 235 is inserted into the preload pad 26. The preload pad 26 is formed of a synthetic resin mixed with a solid lubricant. A preload pad 26 is provided between the other end surface of the holder 41 (the right end surface in FIGS. 2 and 3) and the bottom surface of the recessed hole 214 provided in a part of the gear housing 21.

In addition, a through hole 261 penetrating in the axial direction is formed in the central portion of the preload pad 26, and the small diameter portion 235 of the worm shaft 23 can be inserted inside the through hole 261. The inner peripheral surface of the through-hole 261 has a function as a sliding bearing that supports the small diameter portion 235 of the worm shaft 23.

  Moreover, the inner peripheral surface by the side of the electric motor 29 among the said through-holes 261 is made into the taper surface 262 where the diameter became large as it went to the opening end. The diameter of the opening of the tapered surface 262 is larger than the diameter of the small diameter portion 235 provided at the tip of the worm shaft 23 by 0.5 mm or more. The preload pad 26 is supported inside the concave hole 214 so as to be freely displaced within a predetermined range.

  In the case of the present embodiment, a holder 41 for fixing to a part of the gear housing 21, a preload pad 26, and a torsion coil spring 25 are combined as shown in detail in FIGS. 3 and 7 to 9. ing. Of these, as shown in detail in FIG. 9, the holder 41 has a through-hole 412 having a rectangular cross section at the center. In addition, two first protrusions 413, 413, and two first protrusions 413, 413, respectively, at four positions located on the periphery of the opening of the through hole 412 on one side surface (front side surface in FIG. 9) of the holder 41. Second protrusions 414 and 414 are formed.

  Among these, the first protrusions 413 and 413 are present on the worm wheel 22 side (the −Y side on the upper side of FIGS. 7 to 9) across the central axis 230 of the worm shaft 23, and the second protrusions 414, 414 exists on the + Y side (the lower side of FIGS. 7 to 9) opposite to the first protrusions 413 and 413 across the central axis 230 of the worm shaft 23. Moreover, concentric partial cylindrical surface portions 415a, 415a, 415b, and 415b are provided on the outer diameter side surfaces of the first and second protrusions 413, 413, 414, and 414, respectively. Further, locking projections 416 and 416 projecting on the side opposite to the worm wheel 22 are provided on the side surface on the opposite side to the worm wheel 22 at a portion near the tip of each of the second projections 414 and 414.

  On the other hand, on the outer peripheral surface of the preload pad 26, a narrow projecting portion 264 is provided at an intermediate portion in the arc direction of the first partial cylindrical surface portion 263 provided on the portion opposite to the worm wheel 22, and the tip of the projecting portion 264 is provided. The surface is a third partial cylindrical surface portion 265 concentric with the first partial cylindrical surface portion 263. In addition, plane portions 266 and 266 are provided at two positions on the outer circumferential surface of the preload pad 26 on the opposite side in the radial direction.

  Further, the contact portion between the outer peripheral surface of the preload pad 26 and the inner peripheral edge of the torsion coil spring 25 has an arc shape, and the length of the contact portion in the arc direction is the length of one turn of the torsion coil spring 25. Is small enough. Further, the radius of curvature of the second partial cylindrical surface 269 provided on the worm wheel 22 side (the upper side in FIGS. 7 to 9) of the outer peripheral surface of the preload pad 26 is made smaller than the radius of curvature of the first partial cylindrical surface 263. ing.

  Further, of these flat portions 266 and 266, at one end portion on the opposite side to the worm wheel 22 (lower end portion in FIGS. 7 to 9), an axial half portion on the holder 41 side (rear side half portion in FIGS. 7 to 9). ), A pair of arm portions 267 and 267 are formed. In addition, the outer surface of the preload pad 26 projects to the outer diameter side at one end in the axial direction opposite to the holder 41 (front end in FIGS. 7 to 9) on the opposite side of the worm wheel 22. A stop projection 268 is provided.

  Then, the preload pad 26 is combined with the holder 41, and the holder 41 and the preload pad 26 provided with the torsion coil spring 25 are assembled inside the gear housing 21. Subsequently, by inserting the tip of the worm shaft 23 inside a through hole 261 provided in the central portion of the preload pad 26, the worm shaft 23 is given elasticity in the direction toward the worm wheel 22. .

  The holder 41, the preload pad 26, and the torsion coil spring 25 are combined as follows. First, one side of each of the second protrusions 414 and 414 of the holder 41 (the lower side surface of FIGS. 7 to 9) and one side of the locking protrusions 416 and 416 provided on each of the second protrusions 414 and 414 ( The side surfaces of the arm portions 267 and 267 provided on the preload pad 26 are opposed to the back side surfaces of FIGS. In this state, the holder 41 and the preload pad 26 are combined. When the holder 41 and the preload pad 26 are combined in this way, displacement in the axial direction of the preload pad 26 with respect to the holder 41 is prevented.

  Next, the locking portions 251 and 251 provided at both end portions of the torsion coil spring 25 are arranged between the first and second protrusions 413, 413, 414 and 414 adjacent to each other. In this state, the torsion coil spring 25 is externally fitted to the outer diameter side surface of each of the first and second protrusions 413, 413, 414, and 414 and the outer peripheral surface of the preload pad 26. In a state where the third partial cylindrical surface portion 265 provided in the preload pad 26 does not contact the inner peripheral edge of the torsion coil spring 25, the central axis of the through hole 261 provided in the preload pad 26 is relative to the central axis of the holder 41. , One side (upper side of FIGS. 7 to 9) is offset.

  In a state where the preload pad 26 and the torsion coil spring 25 are combined with the holder 41, the holder 41 is fixed to a predetermined portion of the gear housing 21, and the tip of the worm shaft 23 is inserted into the through hole 261 provided in the preload pad 26. The small diameter part 235 of the part is inserted. Then, the diameter of the torsion coil spring 25 is elastically expanded by the third partial cylindrical surface portion 265 provided on the preload pad 26. Then, the torsion coil spring 25 tends to elastically return in the direction of rewinding (reducing its diameter), whereby elasticity in the direction toward the worm wheel 22 is applied from the torsion coil spring 25 to the preload pad 26.

  As described above, there is a minute gap between the inner circumferential surface of the inner ring 273 and the outer circumferential surface of the worm shaft 23, and the inclination of the worm shaft 23 with respect to the ball bearing 27 in a predetermined range is free. Therefore, by applying elasticity in the direction toward the worm wheel 22 to the preload pad 26, the worm shaft 23 tilts in the direction toward the worm wheel 22 with the axial center position of the ball bearing 27 as a fulcrum. Then, the worm 231 of the worm shaft 23 and the tooth surfaces of the worm wheel 22 are brought into contact with each other with a preload applied, and the amount of backlash at the meshing portion of the worm 231 and the worm wheel 22 is reduced.

  In the embodiment of the present invention, the male splines 511 and 512 at both ends of the power transmission member 51 are spline-engaged with a clearance between the spline teeth of the female spline 293 of the output shaft 292 and the female spline 232 of the worm shaft 23. ing. Accordingly, even if the shaft centers of the worm shaft 23 and the output shaft 292 are decentered, or the shaft centers of the worm shaft 23 and the output shaft 292 are decentered as a result of tilting the worm shaft 23 in the direction toward the worm wheel 22. The clearance of the spline engaging portion allows for eccentricity and declination, and the rotation of the electric motor 29 can be smoothly transmitted to the worm shaft 23. Further, since the power transmission member 51 is made of metal, it has high rigidity, and there is no possibility of delay in torque transmission or damage to the power transmission member 51.

  Further, in the embodiment of the present invention, the elastic member 53 on the outer periphery of the power transmission member 51 is fitted into the small-diameter inner peripheral surfaces of the female spline 232 and the female spline 293. Therefore, even when the amount of declination or eccentricity is small (that is, the axial center of the worm shaft 23 and the axial center of the output shaft 292 substantially coincide), even if the clearance between the spline tooth surfaces becomes large, the elastic member 53. Can be elastically deformed to suppress the occurrence of rattling noise of the spline engaging portion. In addition, the elastic member 53 on the outer periphery of the power transmission member 51 can also suppress the occurrence of rattling noise at the spline engaging portion due to torque reversal or vibration of the vehicle body.

DESCRIPTION OF SYMBOLS 11 Steering wheel 12 Steering shaft 12A Outer shaft 12B Inner shaft 13 Steering column 13A Outer column 13B Inner column 14 Support bracket 15 Universal joint 16 Intermediate shaft 17 Universal joint 18 Car body 19 Output shaft 20 Assist device 21 Gear housing 211 Support hole 212 Step part 213 Locking ring 214 Concave hole 22 Worm wheel 221 Slip ring (torque limiter)
23 Worm shaft 230 Central axis 231 Worm 232 Female spline (Worm female spline)
233 Hook portion 234 Large diameter portion 235 Small diameter portion 236 Tapered surface 237 Tapered surface 238 Tube portion 239 Locking structure 24 Preloading mechanism 25 Torsion coil spring 251 Locking portion 26 Preload pad 261 Through hole 262 Tapered surface 263 First part cylindrical surface portion 264 Projection 265 Third portion cylindrical surface portion 266 Planar portion 267 Arm portion 268 Locking projection portion 269 Second portion cylindrical surface portion 27 Ball bearing 271 Ball 272 Outer ring 273 Inner ring 28 Ball bearing 281 Ball 282 Outer ring 283 Inner ring 29 Electric motor (actuator)
291 Case 292 Output shaft 293 Female spline (Output shaft side female spline)
DESCRIPTION OF SYMBOLS 30 Steering gear 31 Input shaft 32 Tie rod 41 Holder 411 Large diameter part 412 Through-hole 413 1st protrusion 414 2nd protrusion 415a, 415b Partial cylindrical surface part 416 Locking protrusion 42 Bush 421 Outward flange part 43 Holding member 431 Outward flange part 432 Cylindrical part 44 Cylindrical member 45 Locking ring 46 Annular groove 47 O-ring 51 Power transmission member 511, 512 Male spline 52 Small diameter cylindrical part 53 Elastic member 531 Outer peripheral surface

Claims (5)

Gear housing,
An actuator provided in the gear housing for generating an auxiliary steering torque corresponding to the steering torque applied to the steering wheel;
An output shaft for outputting the rotation of the actuator,
A worm coupled to the output shaft,
A worm wheel that meshes with the worm, decelerates the rotation of the worm, and transmits it to the steering shaft;
An output shaft-side female spline formed in the shaft center of the output shaft,
A worm side female spline formed on the shaft center of the worm,
A male spline that engages the spline with a gap in the spline tooth surface of the output shaft side female spline and the worm side female spline is provided with a power transmission member formed at both ends in the axial direction,
The power transmission member is formed between the male splines formed at both ends in the axial direction.
Of the small-diameter cylindrical portion formed in the central portion in the axial direction, its outer diameter is larger than the diameter of the output shaft side female spline and the worm side female spline, the output shaft-side female spline and the worm-side female spline An electric power steering apparatus comprising a hollow cylindrical elastic member having a diameter smaller than that of a large diameter. In the electric power steering apparatus according to claim 1,
The electric power steering apparatus according to claim 1, wherein an outer peripheral surface of the elastic member is fitted into a small-diameter inner peripheral surface of the output shaft side female spline and the worm side female spline. In the electric power steering apparatus according to claim 1,
The electric power steering device, wherein the power transmission member is made of metal. In the electric power steering apparatus according to claim 1,
An electric power steering apparatus comprising a preload applying mechanism provided in the gear housing and biasing the worm toward the worm wheel. In the electric power steering apparatus according to claim 1,
An electric power steering apparatus comprising a torque limiter provided in the gear housing and configured to limit a torque transmitted from the actuator to a steering shaft from becoming a predetermined value or more.

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