JP2013071681A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably bias a bearing of a driving gear in a predetermined preload direction in an electric power steering device including a preload means for removing backlash of a driving gear and a driven gear.SOLUTION: The electric power steering device 10 includes the preload means 30 for biasing the bearing 23A of a worm gear 21 in the predetermined preload direction. In the preload means 30, a guided part 101 is provided in the outer periphery of a bearing case 40 holding the bearing 23A of the worm gear 21, a guiding surface 102, which is contacted with the guided part 101 of the bearing case 40 to guide the movement of the bearing case 40 in the predetermined preload direction of the bearing 23A, is provided on a gear housing 11 side, and two planar guiding surfaces 102 parallel to each other are included on the gear housing 11 side. Each guided part 101 of the bearing case 40 contacted with each guiding surface 102 comprises two projected parts 101A adjacent to each other along the preload direction.

Description

  The present invention relates to an electric power steering apparatus.

  In an electric power steering device, a pinion shaft connected to a steering shaft via a torsion bar is pivotally supported by a gear housing, and a rack shaft that meshes with the pinion shaft is supported by the gear housing so as to be linearly movable. A worm gear coupled to the gear housing is pivotally supported by the gear housing, and a worm wheel fixed to the intermediate portion of the pinion shaft and meshing with the worm gear is pivotally supported by the gear housing. The electric motor applies a steering assist torque corresponding to the steering torque applied by the driver to the steering shaft to the rack shaft through the engagement of the worm gear and the worm wheel and the engagement of the pinion shaft and the rack shaft.

  In such an electric power steering device, the distance between the worm gear and the worm wheel can be easily set without being affected by the dimensional error of parts such as the worm gear at the time of assembly, and the worm gear and the worm wheel are engaged after the assembly. As these change over time, it is necessary to easily adjust their interaxial distances to eliminate their backlash.

  The electric power steering device described in Patent Document 1 has preload means for urging a bearing supporting the tip shaft portion of the worm gear in a predetermined preload direction so as to apply preload to the meshing portion of the worm gear and the worm wheel. doing. The distance between the shafts of the worm gear and the worm wheel is adjusted by the urging force of the preload means, and their backlash is removed.

  The preload means described in Patent Document 1 is for fitting a guide case having a guide surface that accommodates a bearing and guides the bearing so as to move in a predetermined preload direction into a fitting hole of the gear housing. . On the other hand, an adjustment screw is screwed into a holding hole provided in the gear housing, and a coil spring backed up by the adjustment screw is inserted. A pressing body pressed by the coil spring is inserted into a hole provided in the guide case, and biases the bearing in the guide case in a predetermined preload direction. The adjustment screw is screwed with a lock nut for preventing loosening.

Patent 3646205

  The electric power steering device described in Patent Literature 1 includes two planar guide surfaces that are parallel to the inner periphery of the bearing housing hole of the guide case, and the outer circumferential arc surface of the outer ring of the bearing is used as the planar guide. The bearing is brought into direct contact with the surface to guide the bearing in a predetermined preload direction.

  However, in the electric power steering device described in Patent Document 1, only one point composed of each of the outer peripheral circular arc surfaces on both sides of the outer ring of the bearing is guided in contact with the planar guide surfaces on both sides of the guide case. . Therefore, the outer ring of the bearing can rotate about its own axis with respect to the guide case, causing the bearing to run around and abnormal noise, and the bearing cannot be urged stably in a predetermined preload direction.

  In addition, when trying to suppress the generation of noise by reducing the gap between the outer peripheral arc surface of the outer ring of the bearing and the guide surface, the surface pressure between one outer peripheral arc surface of the outer ring of the bearing and the guide surface is excessive. become. As a result, the friction between the outer circumferential arc surface of the outer ring of the bearing and the guide surface becomes excessive, and the bearing cannot be moved and guided with respect to the guide case by the spring force of the spring.

  An object of the present invention is to stably bias a drive gear bearing in a predetermined preload direction in an electric power steering apparatus having a preload means for removing backlash of a drive gear and a driven gear. is there.

  According to the first aspect of the present invention, the drive gear driven by the electric motor is pivotally supported on the gear housing, the driven gear meshing with the drive gear is fixed to the steering shaft, and the meshing portion between the drive gear and the driven gear is fixed. In an electric power steering apparatus that includes a spring for applying a preload and has a preload means for urging a drive gear bearing in a predetermined preload direction, the preload means covers the outer periphery of a bearing case that holds the drive gear bearing. A guide portion is provided on the side of the gear housing to contact the guided portion of the bearing case and guide the movement of the bearing case in a predetermined preload direction of the bearing. Two planar guide surfaces are provided on the gear housing side, and each guided portion of the bearing case in contact with each guide surface is formed of two convex portions adjacent to each other along the preload direction. It is intended.

  According to a second aspect of the present invention, in the first aspect of the invention, the preload means further includes a bearing case that includes a bearing accommodating hole that accommodates a bearing of the drive gear, and a guided portion is provided on the outer periphery. A guide hole for housing the bearing case, and a guide surface that contacts the guided portion of the bearing case and guides the bearing case so as to move in a predetermined preload direction of the bearing. Two planar guide surfaces having a guide case and housing the bearing case are attached to a mounting portion provided in the gear housing and are parallel to the inner periphery of the guide hole of the guide case. And each guided portion of the bearing case in contact with each guide surface of the guide case is composed of two convex portions adjacent to each other along the preload direction of the bearing.

  The invention according to claim 3 is the invention according to claim 2, wherein the bearing case is made of plastic and the guide case is made of metal.

  The invention according to a fourth aspect is the invention according to any one of the first to third aspects, wherein the convex portion has a cylindrical surface shape.

  The invention according to a fifth aspect is the invention according to any one of the first to third aspects, wherein the convex portion has a spherical shape.

(Claim 1)
(a) The preload means is provided with a guided portion on the outer periphery of the bearing case that holds the bearing of the drive gear, and contacts the guided portion of the bearing case to guide the movement of the bearing case in a predetermined preload direction of the bearing. The guide surface is provided on the side of the gear housing, and two planar guide surfaces that are parallel to each other are provided on the side of the gear housing. It consists of two convex parts adjacent to each other along the preload direction.

  Since two points consisting of two convex portions (each guided portion) on both sides of the bearing case are guided in contact with the respective planar guide surfaces on both sides of the gear housing, the bearing case is attached to the gear housing. On the other hand, it is prevented from rotating around its own axis, and the bearing of the drive gear is stably urged in a predetermined preload direction without swinging or abnormal noise.

  In addition, the projection (guided portion) of the bearing case is brought into contact with a planar guide surface provided on the gear housing side, and the guide portion is guided, and the gap between the guided portion and the guide surface is reduced to reduce noise. Reduce the occurrence. At the same time, there are two projections on one side of the bearing case, and the friction between the guided portion and the guide surface is reduced by suppressing the surface pressure between the guided portion and the guide surface from becoming excessive. The bearing case is lightly moved by the spring force of the spring so that it can be moved and guided with respect to the gear housing.

(Claim 2)
(b) The preload means includes a bearing housing hole for housing the bearing of the drive gear, and has a bearing case having a guided portion on the outer periphery, and a guide hole for housing the bearing case. A guide case having a guide surface on the inner periphery of the guide hole for guiding the bearing case so as to move in a predetermined preload direction of the bearing in contact with the guided portion, and the guide case containing the bearing case The bearing case includes two planar guide surfaces that are parallel to each other on the inner periphery of the guide hole of the guide case, and are in contact with the guide surfaces of the guide case. Each guided portion is composed of two convex portions adjacent to each other along the preload direction of the bearing.

  Since two points consisting of two convex portions (each guided portion) on both sides of the bearing case are guided in contact with the respective planar guide surfaces on both sides of the guide case, the bearing case has its own axis relative to the guide case. Thus, the bearing of the driving gear is stably urged in a predetermined preload direction without swinging or abnormal noise.

  In addition, the convex portion (guided portion) of the bearing case is brought into contact with the planar guide surface of the guide case and guided, and the gap between the guided portion and the guide surface is reduced to suppress the generation of noise. At the same time, there are two projections on one side of the bearing case, and the friction between the guided portion and the guide surface is reduced by suppressing the surface pressure between the guided portion and the guide surface from becoming excessive. The bearing case is made small and can be moved and guided with respect to the guide case by the spring force of the spring.

(Claim 3)
(c) The bearing case is made of plastic, and the guide case is made of metal. Thereby, the slidability of the guided portion of the bearing case with respect to the guide surface of the guide case can be improved.

(Claim 4)
(d) The convex portions of (a) and (b) described above can be cylindrical.

(Claim 5)
(e) The convex portions of (a) and (b) described above may be spherical.

FIG. 1 is a longitudinal sectional view showing an electric power steering apparatus. FIG. 2 is a sectional view taken along line II-II in FIG. FIG. 3 is a cross-sectional view showing the support structure of the worm gear. 4A and 4B show a joint structure of a worm gear, where FIG. 4A is a perspective view showing a small assembly state, and FIG. 4B is a perspective view showing components. FIG. 5 is a perspective view showing the gear housing and the preload means. 6A and 6B show a preload means, FIG. 6A is a front view showing a small assembly state, and FIG. 6B is a perspective view showing components. FIG. 7 is a cross-sectional view showing an assembled state of the preload means. FIG. 8 shows a bearing case, (A) is a perspective view, (B) is a front view, and (C) is a side view. FIG. 9 shows a bearing case, and (A) to (C) are perspective views showing modifications thereof.

  As shown in FIGS. 1 and 2, the electric power steering apparatus 10 includes a gear housing 11 that is fixed to a vehicle body by a bracket (not shown). An output shaft 14 (steering shaft) is coupled to an input shaft 12 to which a steering wheel (not shown) is coupled via a torsion bar 13. In the gear housing 11, a torque sensor 15 for detecting the steering torque applied to the steering wheel by the driver based on the relative rotational displacement amount of the input shaft 12 and the output shaft 14 according to the twist of the torsion bar 13 is incorporated. The input shaft 12 and the output shaft 14 are pivotally supported by the gear housing 11 through bearings 12A, 14A, and 14B.

  A rack shaft 16 having a rack that meshes with the pinion of the output shaft 14 is supported on the gear housing 11 so as to be movable in the left-right direction. A rack guide 19 that is pressed against the rack shaft 16 by a spring 18 supported on the back by a cap 17 is built in a portion of the gear housing 11 facing the pinion of the output shaft 14 with one end of the rack shaft 16 in between. ing.

  The electric motor 20 is fixed to the gear housing 11. As shown in FIG. 3, the bearings 22 and 23 at the opposite ends of the worm gear 21 (drive gear) connected to the electric motor 20 intersect the axis of the output shaft 14 and are orthogonal to each other in this embodiment. It is pivotally supported by the gear housing 11 via 22A and 23A. A coupling 24 is press-fitted into the drive shaft 20A of the electric motor 20, and as shown in FIG. 4, a coupling 25 is press-fitted into the shaft portion 22 of the worm gear 21, and the coupling 24 and the coupling 25 are made of ethylene propylene rubber or the like. It connects with the rubber joint 26 which becomes. The rubber joint 26 has rubber elasticity and is provided with radial protrusions 26B on the outer periphery of the annular hollow core 26A. The blade portion 24A of the coupling 24 and the blade portion 25A of the coupling 25 are sequentially fitted in the opposing gaps of the protruding portions 26B adjacent to each other in the circumferential direction of the rubber joint 26, and the rotational force of the electric motor 20 causes the rubber joint 26 to Is transmitted to the worm gear 21.

  At this time, as shown in FIG. 3, the outer ring of the bearing 22A for the shaft portion 22 of the worm gear 21 is fixed to the step hole of the gear housing 11 by the bearing nut 27 screwed to the gear housing 11, and the inner ring of the bearing 22A is The worm gear 21 is sandwiched between a flange 22F provided on the shaft portion 22 of the worm gear 21 and a coupling 25 press-fitted into the shaft portion 22. Thereby, the worm gear 21 is supported by the gear housing 11 without backlash in the axial direction. Further, the worm gear 21 can be slightly swung around the position near the center in the width direction of the bearing 22A due to the elasticity of the rubber joint 26. This swing of the worm gear 21 is absorbed by the elastic deformation of the rubber joint 26. Further, a spring loaded in the hollow portion of the hollow core 26A of the rubber joint 26, in this embodiment, a compression coil spring 28 is loaded in a compressed state between the end surface of the coupling 24 and the end surface of the shaft portion 22 of the worm gear 21. The vibration that may occur in the axial direction of the worm gear 21 is absorbed.

  A worm wheel 29 (driven gear) that meshes with a worm gear 21 driven by the electric motor 20 is fixed to an intermediate portion of the output shaft 14. The electric motor 20 is driven according to the steering torque detected by the torque sensor 15, and the torque of the electric motor 20 is transmitted to the output shaft 14 via the meshing portion of the worm gear 21 and the worm wheel 29, and eventually to the rack shaft 16. The steering assist force is applied and assists the steering torque applied to the steering wheel by the driver.

  However, the electric power steering apparatus 10 includes preload means 30 that applies preload to the meshing portion of the worm gear 21 and the worm wheel 29 in order to remove backlash at the meshing portion of the worm gear 21 and the worm wheel 29. The preload means 30 biases a bearing 23A provided on the shaft portion 23 of the worm gear 21 in a predetermined preload direction.

  As shown in FIGS. 5 and 6, the preload means 30 has a bearing case 40, a guide case 50, and a spring 60. In this embodiment, the preload means 30 further has a bump stopper rubber 70.

  As shown in FIGS. 6 and 7, the bearing case 40 is generally composed of a cylindrical body 41, and a short cylindrical protrusion 42 protrudes radially outward from one circumferential position on the outer periphery of the cylindrical body 41. Yes. The bearing case 40 includes a round hole-shaped bearing housing hole 43 in the inner periphery of the cylindrical body 41 for housing the bearing 23 </ b> A for the shaft portion 23 of the worm gear 21 in a press-fitted state. The bearing case 40 has a spring for energizing the bearing 23 </ b> A, in this embodiment, a round hole-shaped spring accommodating hole 44 for accommodating the coil spring 60, intersecting one place in the circumferential direction of the bearing accommodating hole 43. Thus, the protrusion 42 is provided. The bearing receiving hole 43 is formed so as to penetrate in the axial direction of the cylindrical body 41, and the spring accommodating hole 44 is formed so as to penetrate in the axial direction of the protrusion 42 that matches the radial direction of the cylindrical body 41.

  The bearing housing hole 43 of the bearing case 40 includes an annular step portion 45 having a small inner diameter on the side far from the meshing portion between the worm gear 21 and the worm wheel 29 in the axial direction, and a large inner diameter side without the annular step portion 45. Is loaded with the outer ring of the bearing 23A. One end of the outer ring of the bearing 23 </ b> A contacts the step end surface of the annular step portion 45. The inner ring of the bearing 23 </ b> A is clamped between a step end surface provided at the small diameter end of the shaft portion 23 of the worm gear 21 and a retaining ring 81 engaged with the small diameter end portion of the shaft portion 23.

  In this embodiment, the spring accommodation hole 44 provided in the protrusion 42 of the bearing case 40 is loaded with the bump stopper rubber 70 together with the spring 60. That is, a small outer diameter portion, which is a portion directly below the flange 71 in the cylindrical bump stopper rubber 70, is loaded into the spring accommodation hole 44. The front end surface of the small outer diameter portion of the bump stopper rubber 70 is in contact with the outer peripheral surface of the outer ring of the bearing 23 </ b> A, and the end surface of the bump stopper rubber 70 around the spring accommodation hole 44 provided in the protrusion 42 of the bearing case 40 is It can be held between the receiving surface 46 to be formed and the receiving surface 55 provided in the concave portion 54 on the inner periphery of the guide hole 53 described later of the guide case 50. As a result, the bump stopper rubber 70 is pinched between the outer peripheral surface of the outer ring of the bearing 23A and the receiving surface 55 of the inner periphery of the guide case 50, and can absorb impact reverse input from the wheel side elastically. To do.

  At this time, the spring 60 is inserted into the hollow portion of the bump stopper rubber 70 accommodated in the spring accommodating hole 44 of the bearing case 40, and the spring 60 is the outer peripheral surface of the outer ring of the bearing 23 </ b> A and the receiving surface 55 of the inner periphery of the guide case 50. The bearing 23A can be biased in a predetermined preload direction.

  In the bearing case 40, the portion of the bearing housing hole 43 where the spring housing hole 44 opens is a missing portion of the annular step portion 45, and the annular step portion 45 is formed on the outer periphery of the spring 60 and the bump stopper rubber 70 and the outer ring of the bearing 23A. This avoids obstruction of contact with the surface.

  The bearing case 40 is provided with a guided portion 101 on the outer periphery on both sides across the diameter line of the cylindrical body 41 that coincides with the central axis of the protrusion 42 and the spring accommodating hole 44. The specific shape of the guided portion 101 will be described later.

  As shown in FIG. 6, the guide case 50 is generally composed of a cylindrical body 51, and an overhanging protrusion 52 is provided at one circumferential position on the outer periphery of the cylindrical body 51. The guide case 50 includes a guide hole 53 that accommodates the bearing case 40 on the inner periphery of the cylindrical body 51. In the guide case 50, the guide hole 53 is formed into a substantially square hole shape, and the guide surface 102 is formed on two opposing surfaces on the inner periphery of the guide hole 53. The guide surface 102 of the guide case 50 is in contact with the guided portion 101 of the bearing case 40, and guides the bearing case 40 so that the bearing case 40 moves in a predetermined preload direction of the bearing 23A.

  The guide case 50 is on the inner surface side of the protrusion 52, and a recess 54 is formed on one of the other two surfaces where the guide surface 102 on the inner periphery of the guide hole 53 is not formed, and the protrusion 42 of the bearing case 40. And the flange 71 of the bump stopper rubber 70 is loaded in the recess 54. The recess 54 includes a receiving surface 55 that supports the spring 60 and the bump stopper rubber 70.

  In the preload means 30, the bearing case 40 is an oil-free bush made of plastic such as oil-impregnated polyacetal resin, and the guide case 50 is made of metal such as iron-based sintered alloy.

  In the preload means 30, the guide surfaces 102 provided in the guide holes 53 of the guide case 50 are two planar guide surfaces 102 that are parallel to each other. Then, each guided portion 101 of the bearing case 40 that is intermediately fitted to each guide surface 102 of the guide case 50 is brought into contact with the two convex portions 101A adjacent to each other along the preload direction to be applied to the bearing 23A of the worm gear 21. To be. As shown in FIGS. 8 and 9A, the convex portion 101A of the present embodiment extends over the entire width of the cylindrical body 41 along the axial direction of the cylindrical body 41 on the outer periphery of the cylindrical body 41 in the bearing case 40. Forms a cylindrical surface that extends. The convex portion 101 </ b> A may be formed by embedding a part of the arc of a Teflon (registered trademark) pin in a recess provided on the outer periphery of the cylindrical body 41, and forming the remaining arc of the Teflon (registered trademark) pin.

  The convex portions 101A, which are the guided portions 101 provided on the outer circumferences on both sides of the bearing case 40, may have a short cylindrical surface provided only at the center in the width direction of the cylindrical body 41 as shown in FIG. As shown in FIG. 9C, a spherical shape provided at the center in the width direction of the cylindrical body 41 may be used.

  The preload means 30 includes a bearing case 40 in which the spring 60 and the bump stopper rubber 70 are accommodated as described above and accommodated in the guide case 50 as a small assembly 31 as shown in FIGS. Then, the guide case 50 in the state of the small assembly 31 is loaded into the hole-shaped mounting portion 90 provided in the gear housing 11. The mounting portion 90 of the gear housing 11 is provided with a concave positioning portion 91 for the guide case 50 in a part of the hole surface in the circumferential direction. On the other hand, the above-described protrusion 52 of the guide case 50 is a positioned portion that engages with the concave positioning portion 91 of the gear housing 11. By engaging the protrusion 52 of the guide case 50 with the concave positioning portion 91 of the gear housing 11 and positioning the mounting position of the guide case 50 with respect to the mounting portion 90 of the gear housing 11, the bearing by the guide surface 102 of the guide case 50. The guide direction of the guided portion 101 of the case 40 is set to a predetermined preload direction of the bearing 23A of the worm gear 21.

  In a state where the guide case 50 of the small assembly 31 is loaded in the mounting portion 90 of the gear housing 11, the cover plate 92 closes the opening of the mounting portion 90 with the bolt 93. At this time, between the mounting portion 90 of the gear housing 11 and the guide case 50, radial pressing means 94 that presses the guide case 50 in the radial direction to determine the radial position of the guide case 50 with respect to the gear housing 11; An axial pressing means 95 that presses the guide case 50 in the axial direction and determines an axial position of the guide case 50 with respect to the gear housing 11 is provided.

  In this embodiment, the radial pressing means 94 and the axial pressing means 95 are made of O-rings. As shown in FIG. 7, the radial pressing means 94 is loaded into a small-diameter stepped portion provided on the outer periphery on one end side of the cylindrical body 51 of the guide case 50, and a small-diameter hole portion on the back side of the mounting portion 90 of the gear housing 11. It is inserted into the inner periphery in a radially compressed state. As shown in FIG. 7, the axial pressing means 95 is sandwiched between the end face on the other end side of the cylindrical body 51 of the guide case 50 and the lid plate 92 and is inserted in an axially compressed state.

  Therefore, when the worm gear 21 is assembled in the electric power steering apparatus 10, the small assembly 31 of the preload means 30 is loaded into the mounting portion 90 of the gear housing 11. At this time, the protrusion 52 included in the guide case 50 of the small assembly 31 is engaged with the concave positioning portion 91 of the mounting portion 90 of the gear housing 11, and the guided portion 101 of the bearing case 40 is guided by the guide surface 102 of the guide case 50. The guide direction is set to a predetermined preload direction of the bearing 23A of the worm gear 21. Further, the radial mounting position of the guide case 50 with respect to the gear housing 11 is defined by the radial pressing means 94.

  The worm gear 21 having the bearing 22A and the coupling 25 inserted into the shaft portion 22 is inserted into the gear housing 11, and the shaft portion 23 of the worm gear 21 is inserted into the bearing 23A that is already assembled into the small assembly 31 of the preload means 30. Then, the above-described retaining ring 81 is engaged with the small diameter end portion of the shaft portion 23. Further, the bearing 22 </ b> A inserted into the shaft portion 22 of the worm gear 21 is fixed to the step hole of the gear housing 11 by the bearing nut 27 that is screwed into the gear housing 11. The worm gear 21 can slightly swing around a position near the center in the axial direction of the bearing 22A. The opening of the mounting portion 90 of the gear housing 11 is closed by the lid plate 92, and the axial mounting position of the guide case 50 with respect to the gear housing 11 is defined by the axial pressing means 95.

  Thus, the spring 60 accommodated in the small assembly 31 of the preload means 30 biases the bearing 23A of the worm gear 21 in a predetermined preload direction, and the worm gear 21 is positioned near the center in the axial direction of the bearing 22A by the spring force of the spring 60. It swings about the center and can apply a preload to the meshing part of the worm gear 21 and the worm wheel 29, thereby eliminating backlash of the meshing part. In addition, the preload means 30 correctly moves the bearing 23A of the worm gear 21 in the predetermined preload direction due to the presence of the guided portion 101 (convex portion 101A) of the bearing case 40 and the guide surface 102 of the guide case 50. An appropriate meshing position can be maintained in the axial length direction of the worm wheel 29, and the worm gear 21 can be smoothly moved in the radial direction due to variation in the meshing reaction force.

Therefore, according to the electric power steering apparatus 10, the following operational effects are obtained.
(a) The preload means 30 has a bearing case 40 and a guide case 50. The bearing case 40 includes a bearing accommodating hole 43 that accommodates the bearing 23A of the worm gear 21, and includes a spring accommodating hole 44 that accommodates a spring 60 for biasing the bearing 23A so as to intersect the bearing accommodating hole 43. A guided portion 101 is provided in the first. The guide case 50 includes a guide hole 53 that accommodates the bearing case 40, and guides the bearing case 40 so as to move in a predetermined preload direction of the bearing 23A in contact with the guided portion 101 of the bearing case 40. 102 is provided on the inner periphery of the guide hole 53. The guide case 50 that houses the bearing case 40 in which the bearing 23 </ b> A and the spring 60 are housed is attached to the attachment portion 90 provided in the gear housing 11.

  That is, the preload means 30 is preliminarily assembled into the state of the small assembly 31 in which the bearing case 40 in which the bearing 23A and the spring 60 are accommodated is accommodated in the guide case 50, and the guide case 50 in the state of the small assembly 31 is assembled into the gear housing 11. Assembling is completed by attaching to the mounting portion 90, and assemblability can be improved.

  Further, by accommodating the spring 60 in the spring accommodating hole 44 of the bearing case 40, it is possible to form the small assembly 31 in which the spring 60 is stably assembled without fear of dropping off. Further, since the spring 60 directly urges the bearing 23 </ b> A to urge the bearing 23 </ b> A, the large structure of the preload means 30 can be accommodated while the overall structure of the preload means 30 is reduced in size and size. Thus, the bearing case 40 can be prevented from being deformed by the amount that the bearing 23A is not pressed via the bearing, and the durability thereof can be improved.

  (b) The bearing case 40 is made of plastic, and the guide case 50 is made of metal. Thereby, the slidability of the guided portion 101 of the bearing case 40 with respect to the guide surface 102 of the guide case 50 can be improved.

  (c) A concave positioning portion 91 for the guide case 50 is provided on the mounting portion 90 of the gear housing 11, and a protrusion 52 (positioned portion) provided on the guide case 50 is engaged with the concave positioning portion 91. By positioning the mounting position of the guide case 50 with respect to the mounting portion 90 of the gear housing 11, the guide direction of the bearing case 40 by the guide case 50 is set to a predetermined preload direction of the bearing 23A. Thereby, the bearing 23A of the worm gear 21 can be urged in a predetermined preload direction while simply setting the assembly direction of the preload means 30 with respect to the gear housing 11.

  (d) Two guided guide surfaces 102 that are parallel to each other are provided on the inner periphery of the guide hole 53 of the guide case 50, and each guided portion of the bearing case 40 that is in contact with each guide surface 102 of the guide case 50. 101 is composed of two convex portions 101A adjacent to each other along the preload direction of the bearing 23A. Since the two points of the two convex portions 101A (each guided portion 101) on both sides of the bearing case 40 are guided in contact with the planar guide surfaces 102 on both sides of the guide case 50, the bearing case 40 is guided. It is prevented from rotating about its own axis with respect to the case 50, and is stably urged in a predetermined preload direction without swinging or abnormal noise on the bearing 23A of the worm gear 21.

  Further, the convex portion 101A (guided portion 101) of the bearing case 40 is brought into contact with the planar guide surface 102 of the guide case 50 for guidance, and the gap between the guided portion 101 and the guide surface 102 is reduced. Suppresses abnormal noise. At the same time, there are two convex portions 101A to be the guided portion 101 of the bearing case 40 on one side so as to prevent the surface pressure between the guided portion 101 and the guide surface 102 from becoming excessive, thereby guiding the guided portion 101. The friction of the guide surface 102 is reduced, and the bearing case 40 can be easily moved and guided with respect to the guide case 50 by the spring force of the spring 60.

  (e) A cylindrical bump stopper rubber 70 is loaded into the spring housing hole 44 of the bearing case 40, and the bump stopper rubber 70 is formed in the receiving surface 46 provided around the spring housing hole 44 of the bearing case 40 and the guide case 50. It can be held between the receiving surface 55 provided on the periphery. When a steering reaction force, which is a reverse input caused by a wheel curb collision or the like, impacts the worm wheel 29 and attempts to displace the worm gear 21 meshing with the worm wheel 29 in the radial direction, the displacement is detected as a bump stopper rubber. 70 absorbs elastically and can relieve shock.

  At this time, by accommodating the spring 60 in the inner diameter portion of the bump stopper rubber 70, the entire structure of the preload means 30 can be reduced in size and size.

  (f) When the spring 60 accommodated in the inner diameter portion of the bump stopper rubber 70 of the above (e) is a coil spring, the overall structure of the preload means 30 using the coil spring can be reduced in size and size.

  (g) A radial pressing means 94 for pressing the guide case 50 in the radial direction between the mounting portion 90 of the gear housing 11 and the guide case 50 to determine the radial position of the guide case 50; And an axial pressing means 95 for determining the axial position of the guide case 50 by pressing the guide case 50 in the axial direction. Thereby, the guide case 50 can be easily attached to the attachment portion 90 of the gear housing 11 without backlash.

  (h) Since the radial pressing means 94 and the axial pressing means 95 of (g) described above are made of O-rings, the mounting structure of the guide case 50 can be further simplified.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration of the present invention is not limited to this embodiment, and even if there is a design change or the like without departing from the gist of the present invention. It is included in the present invention. For example, the drive gear (worm gear) bearing is not limited to a rolling bearing, but may be a sliding bearing.

  The drive gear is not limited to a worm gear and the driven gear is a worm wheel, but the drive gear may be a hypoid pinion and the driven gear may be a hypoid wheel. Further, bevel gears may be used for the drive gear and the driven gear.

  The present invention pivots a drive gear driven by an electric motor to a gear housing, fixes a driven gear meshing with the drive gear to a steering shaft, and applies a preload to a meshing portion of the drive gear and the driven gear. In the electric power steering apparatus having a preload means for biasing the drive gear bearing in a predetermined preload direction, the preload means has a guided portion on the outer periphery of the bearing case that holds the drive gear bearing. A guide surface is provided on the gear housing side to contact the guided portion of the bearing case and guide the movement of the bearing case in a predetermined preload direction of the bearing. A surface is provided on the gear housing side, and each guided portion of the bearing case in contact with each guide surface is composed of two convex portions adjacent to each other along the preload direction. Thereby, in the electric power steering apparatus having preload means for removing backlash between the drive gear and the driven gear, the bearing of the drive gear can be stably urged in a predetermined preload direction.

DESCRIPTION OF SYMBOLS 10 Electric power steering apparatus 11 Gear housing 12 Input shaft 14 Output shaft (steering shaft)
20 Electric motor 21 Worm gear (drive gear)
23A Bearing 29 Worm wheel (driven gear)
30 Preload means 40 Bearing case 43 Bearing housing hole 50 Guide case 53 Guide hole 60 Spring 90 Mounting portion 101 Guided portion 101A Protruding portion 102 Guide surface

Claims (5)

A drive gear driven by an electric motor is pivotally supported on the gear housing, a driven gear meshing with the drive gear is fixed to the steering shaft, and a spring is provided to apply a preload to the meshing portion of the drive gear and the driven gear. In the electric power steering apparatus having preload means for urging the gear bearing in a predetermined preload direction,
The preload means
A guided portion is provided on the outer periphery of the bearing case that holds the bearing of the drive gear, and a guide surface that contacts the guided portion of the bearing case and guides the movement of the bearing case in a predetermined preload direction of the bearing is provided on the gear housing. On the side,
Two projecting portions provided with two planar guide surfaces which are parallel to each other on the gear housing side, and each guided portion of the bearing case in contact with each of the guide surfaces is adjacent to each other along the preload direction. An electric power steering apparatus comprising: The preload means comprises:
A bearing housing hole for housing the bearing of the drive gear, and having a bearing case in which a guided portion is provided on the outer periphery,
A guide having a guide hole for accommodating the bearing case, and a guide surface that contacts the guided portion of the bearing case and guides the bearing case so as to move in a predetermined preload direction of the bearing. Have a case,
A guide case containing the bearing case is attached to a mounting portion provided in the gear housing,
On the inner periphery of the guide hole of the guide case, it has two planar guide surfaces that are parallel to each other,
2. The electric power steering apparatus according to claim 1, wherein each guided portion of the bearing case in contact with each guide surface of the guide case includes two convex portions adjacent to each other along the preload direction of the bearing.   The electric power steering apparatus according to claim 2, wherein the bearing case is made of plastic and the guide case is made of metal.   The electric power steering apparatus according to claim 1, wherein the convex portion has a cylindrical surface shape.   The electric power steering apparatus according to claim 1, wherein the convex portion has a spherical shape.

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