JP2013210005A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device in which a driving gear can be largely rocked without enlarging an internal space of a bearing on one end side.SOLUTION: An electric power steering device 10 is configured such that: a raceway groove 111A of an outer ring 111 of a bearing 22A on one end side comprises one circular arc r having a curvature radius of 110 to 124% of a curvature radius of a ball 113 and a one-point-contact sectional shape having the curvature center (a) of the circular arc r set at the width-direction center L of the raceway groove 111A; and a raceway groove 112A of an inner ring 112 comprises two circular arcs r1 and r2 each having curvature radiuses exceeding 100% of the curvature radius of the ball 113, and has a two-point-contact sectional shape having curvature centers b and c of the circular arcs r1 and r2 set on both sides of the width-direction center L of the raceway groove 112A.

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 during assembly, and the mesh between the worm gear and the worm wheel after 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.

  At this time, in the electric power steering device described in Patent Document 1, an annular convex portion provided on the proximal end shaft portion of the worm gear is supported by the bearing. As a result, the worm gear is supported so as to be able to swing around the base end side bearing, and the front end side bearing can be displaced in a predetermined preload direction, thereby eliminating backlash of the worm gear and the worm wheel. Is.

JP2002-21943

  In the electric power steering device described in Patent Document 1, it is necessary to provide an annular convex portion on the base end shaft portion of the worm gear, which increases the cost.

  In order to swingably support the worm gear on the bearing on the base end side, it is conceivable that the bearing is a ball bearing and the internal clearance between the raceway groove and the ball of the inner and outer rings is increased.

  However, for example, the above-mentioned internal clearance necessary for swinging the worm gear by 0.45 degrees is 0.029 mm. This is due to the vibration and noise of the inner ring in which the base end shaft portion of the worm gear is loaded, and thus the vibration and noise of the worm gear. Cause. In order to further increase the swing angle of this worm gear, the inner ring can be displaced in the axial direction of the outer ring, which also causes vibration and noise, The shoulder riding rate and the surface pressure that ride on the groove shoulders of the inner and outer rings are increased, and the durability is significantly reduced.

  An object of the present invention is that a drive gear driven by an electric motor is supported so as to be swingable around a bearing on one end side, and the bearing on the other end side is urged in a predetermined preload direction by preload means. In the electric power steering apparatus as described above, the drive gear can be greatly swung without increasing the internal clearance of the bearing on one end side.

  According to the first aspect of the present invention, both ends of the drive gear driven by the electric motor are pivotally supported by bearings provided in the gear housing, and the driven gear meshing with the drive gear is fixed to the steering shaft. And a preload means for urging the bearing of the driven gear in a predetermined preload direction so that the preload is applied to the meshing portion with the engagement portion, and the drive gear is supported to be swingable about the bearing on one end side. In addition, in the electric power steering apparatus in which the bearing on the other end side is urged in a predetermined preload direction by the preloading means, the bearing on the one end side is a ball bearing, and the raceway groove of the outer ring is a radius of curvature of the ball. It has a one-point contact cross-sectional shape in which the center of curvature is provided at the center in the width direction of the raceway groove, and the raceway groove of the inner ring is the radius of curvature of the ball. Each with a radius of curvature exceeding 100% One of consists arc is obtained by their centers of curvature such that a two-point contact of the cross section which is provided on both sides of the widthwise center of said track groove.

(Claim 1)
(a) In a bearing capable of swinging one end side of the drive gear, the raceway groove of the outer ring is composed of one circular arc having a curvature radius of 110 to 124% of the curvature radius of the ball, and the center of the curvature is the raceway groove. The cross-sectional shape of a one-point contact provided in the center in the width direction is used. Since the ball is in contact with the raceway groove of the outer ring at one point, this reduces the internal clearance between the raceway groove of the inner and outer races and the ball, and the one end shaft of the drive gear with respect to the outer ring fixed to the gear housing. The inner ring on which the part is supported can be swung greatly.

  (b) Since the radius of curvature of the raceway groove of the outer ring is set to 110 to 124% of the radius of curvature of the ball, even if the inner ring swings greatly with respect to the outer ring, the shoulder riding rate at which the ball rides on the groove shoulder of the inner and outer rings The increase in surface pressure can be suppressed, and the durability is not adversely affected.

  (c) The inner ring raceway groove is composed of two arcs each having a radius of curvature exceeding 100% of the radius of curvature of the ball, and the center of curvature is provided on both sides of the center in the width direction of the raceway groove. It had a cross-sectional shape. Since the ball is in contact with the raceway groove of the inner ring at two points, the displacement of the inner ring in the axial direction of the outer ring can be suppressed.

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 perspective view showing the worm gear support structure in a cutaway manner. 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 cross-sectional view taken along line V-V in FIG. FIG. 6 is a schematic view showing a three-point contact ball bearing of the present invention.

  As shown in FIGS. 1 and 2, the electric power steering apparatus 10 includes gear housings 11 </ b> A and 11 </ b> B that are 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 11B, 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 in accordance with the twist of the torsion bar 13 is incorporated. The input shaft 12 and the output shaft 14 are pivotally supported on the gear housings 11A and 11B via 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 11A so as to be movable in the left-right direction. Note that the rack of the rack shaft 16 is pressed against the pinion of the output shaft 14 by a spring 18 supported on the back by a cap 17 at a portion of the gear housing 11 </ b> A opposite to the pinion of the output shaft 14 across one end of the rack shaft 16. A rack guide 19 is built in.

  The electric motor 20 is fixed to the gear housing 11B. As shown in FIGS. 2 and 3, shafts 22 and 23 at both ends of a worm gear 21 (drive gear) connected to and driven by the electric motor 20 intersect with the axis of the output shaft 14, and are orthogonal in this embodiment. Further, it is pivotally supported by the gear housing 11B via the bearings 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 (not shown) of the coupling 24 and the blade portion 25A of the coupling 25 are sequentially fitted in the opposing gaps of the protrusions 26B adjacent to each other in the circumferential direction of the rubber joint 26, and the rotational force of the electric motor 20 is increased. It is transmitted to the worm gear 21 via the rubber joint 26.

  At this time, as shown in FIG. 3, the outer ring 111 of the bearing 22A for the shaft portion 22 of the worm gear 21 is fixed to the step hole of the gear housing 11B by a bearing nut 27 screwed to the gear housing 11B. 112 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 11B without play 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.

  The electric power steering apparatus 10 has preloading means 30 for applying preload to the meshing portion between the worm gear 21 and the worm wheel 29 in order to remove backlash at the meshing portion between 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 to 7, the preload means 30 has a bearing case 40, a seat rubber 50, and a spring 60.

  As shown in FIG. 8, the bearing case 40 is made of an annular body 41 (C-shaped annular body to be described later), and has a short cylindrical shape radially outward from one circumferential position on the outer periphery of the annular body 41. The cylindrical protrusion 42 is protruded. The bearing case 40 includes a bearing housing hole 43 for housing the bearing 23 </ b> A for the shaft portion 23 of the worm gear 21 on the inner periphery of the annular body 41. Further, the bearing case 40 has a spring for energizing the bearing 23 </ b> A, in this embodiment, a round hole-shaped spring insertion hole 44 through which the coil spring 60 is inserted, intersecting one place in the circumferential direction of the bearing housing hole 43. As shown in FIG. The bearing receiving hole 43 is formed so as to penetrate in the axial direction of the annular body 41, and the spring insertion hole 44 is formed so as to penetrate in the axial direction of the cylindrical protrusion 42 that matches the radial direction of the annular body 41.

  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 gear housing 11B is made of metal.

  Here, as shown in FIG. 8, the bearing case 40 includes a C-shaped annular body 41 that is separated from one place in the circumferential direction. The annular body 41 of the bearing case 40 in which the bearing 23A is accommodated in the bearing accommodation hole 43 is attached to a hole-like case attachment portion 81 provided in the gear housing 11B in a reduced diameter state. That is, the bearing case 40 forms a bearing receiving hole 43 for holding the bearing 23A for the shaft portion 23 of the worm gear 21 in a reduced diameter state of the annular body 41 attached to the case attaching portion 81, and A guide surface 101 that guides the bearing 23 </ b> A so as to move in a predetermined preload direction in contact with the outer periphery is provided on the inner periphery of the bearing receiving hole 43. The guide surface 101 provided in the bearing case 40 includes two planar guide surfaces 101 and 101 that are parallel to each other in the reduced diameter state of the annular body 41. The inner ring of the bearing 23 </ b> A accommodated in the bearing accommodation hole 43 of the bearing case 40 abuts on a step end surface 23 </ b> B provided at the small diameter end of the shaft portion 23 of the worm gear 21.

  The annular body 41 of the bearing case 40 is provided with one projecting piece 41A that is cut off in a C-shape and is opposed in the circumferential direction on the one end surface side in the axial direction of the annular body 41, and the other projecting piece 41B is provided. The annular body 41 is provided on the other end surface side in the axial direction. In the above-described reduced diameter state of the annular body 41, the protruding piece 41A and the protruding piece 41B are set so as to be aligned in a certain range in the circumferential direction.

  As shown in FIG. 5, the preload means 30 abuts the cylindrical sheet rubber 50 on the opening end surface of the spring insertion hole 44 provided in the cylindrical projection 42 of the bearing case 40 (end surface 42 </ b> A of the cylindrical projection 42). A spring 60 can be loaded on the inner diameter portion of the rubber 50. That is, the annular body 41 of the bearing case 40 containing the bearing 23A is attached to the case attachment portion 81 provided in the gear housing 11B, and the cylindrical protrusion 42 of the bearing case 40 is loaded into the rubber loading hole 82 provided in the gear housing 11B. When the seat rubber 50 containing the spring 60 is loaded into the rubber loading hole 82, the seat rubber 50 contacts the opening end face of the spring insertion hole 44 of the bearing case 40 (end face 42A of the cylindrical protrusion 42). Touched. Further, the inner surface of the lid 70 fixed to the lid mounting surface 71 around the opening of the rubber loading hole 82 of the gear housing 11B is brought into close contact with the outer end surface of the seat rubber 50. The lid 70 is fixed to the lid mounting surface 71 of the gear housing 11B by a bolt 72.

  Here, as shown in FIGS. 5 and 7, the seat rubber 50 is formed of a cylindrical body that is loaded into the rubber loading hole 82 of the gear housing 11 </ b> B, and a flange that protrudes outward from the proximal end portion of the cylindrical body 51. 51F is provided, and a small-diameter portion 51A having a stepped portion 51S on the outer periphery is provided at the tip of the cylindrical body 51. The flange 51F of the seat rubber 50 is fitted into an annular recess 82A provided in the opening of the rubber insertion hole 82 of the gear housing 11B, and the lid 70 fixed to the lid mounting surface 71 around the opening of the rubber loading hole 82. It is pinched by the inner surface. The small diameter portion 51A of the seat rubber 50 is inserted into the spring insertion hole 44 provided in the cylindrical protrusion 42 of the bearing case 40, and the stepped portion 51S on the outer periphery of the small diameter portion 51A is the opening end surface of the spring insertion hole 44 of the bearing case 40. It abuts on (end surface 42A of the cylindrical protrusion 42).

  The preload means 30 is provided with a positioning portion 91 for the bearing case 40 in the gear housing 11B, and a positioned portion 92 provided in the bearing case 40 is engaged with the positioning portion 91 so that the preload means 30 is connected to the case mounting portion 81 of the gear housing 11B. The mounting position of the bearing case 40 is positioned. The positioning portion 91 of the gear housing 11B includes a rubber loading hole 82 provided in the gear housing 11B. The positioned portion 92 of the bearing case 40 is composed of a cylindrical protrusion 42 protruding outward in the radial direction of the annular body 41. As described above, the cylindrical protrusion 42 of the bearing case 40 is loaded into the rubber loading hole 82 of the gear housing 11B, and the mounting position of the bearing case 40 with respect to the case mounting portion 81 of the gear housing 11B is positioned.

  Therefore, when the worm gear 21 is assembled in the electric power steering apparatus 10, the worm gear 21 in which the bearing 23A held by the annular body 41 of the bearing case 40 is inserted into the shaft portion 23 is connected to the electric motor 20 in the gear housing 11B. Inserted from the mounting side. The annular body 41 of the bearing case 40 is inserted into the case mounting portion 81 of the gear housing 11B while being reduced in diameter, and the cylindrical protrusion 42 of the bearing case 40 is inserted into the rubber loading hole 82 from the case mounting portion 81 side of the gear housing 11B. Is inserted from the oblique direction. After the annular body 41 and the cylindrical projecting portion 42 of the bearing case 40 are inserted into the case mounting portion 81 and the rubber loading hole 82 of the gear housing 11B, the annular body 41 is slightly reduced in diameter in the case mounting portion 81. It is relaxed and the installation is completed. When the annular body 41 of the bearing case 40 is completely attached, the two guide surfaces 101, 101 of the bearing case 40 are parallel to each other.

  Further, the seat rubber 50 and the spring 60 are loaded into the rubber loading hole 82 of the gear housing 11B from the outside. The seat rubber 50 is brought into contact with the opening end surface of the spring insertion hole 44 of the bearing case 40 (end surface 42A of the cylindrical projection 42), and the spring 60 is loaded on the inner diameter portion of the seat rubber 50. Then, the lid 70 is fixed to the lid mounting surface 71 around the opening of the rubber loading hole 82 of the gear housing 11B. The inner surface of the lid 70 comes into pressure contact with the outer end surface of the sheet rubber 50 and the spring 60 from above, and comes into close contact with the end surface of the sheet rubber 50.

  Next, the bearing 22A inserted into the shaft portion 22 of the worm gear 21 is fixed to the step hole of the gear housing 11B by the bearing nut 27 screwed into the gear housing 11B. The worm gear 21 can slightly swing around a position near the center in the axial direction of the bearing 22A.

  Thus, the spring 60 of the preload means 30 urges the bearing 23A of the worm gear 21 in a predetermined preload direction, and the worm gear 21 swings around the position in the vicinity of the center in the axial direction of the bearing 22A by the spring force of the spring 60. Thus, preload can be applied to the meshing portion of the worm wheel 29, and backlash of the meshing portion is eliminated. Moreover, since the preload means 30 moves the bearing 23A of the worm gear 21 in the predetermined preload direction correctly due to the presence of the guide surface 101 of the bearing case 40, the worm gear 21 maintains an appropriate meshing position in the axial length direction of the worm wheel 29. In addition, the worm gear 21 can be moved smoothly in the radial direction due to fluctuations in the meshing reaction force.

  However, in the electric power steering apparatus 10, in order to allow the worm gear 21 to swing greatly without increasing the internal clearance of the bearing 22 </ b> A for the one end shaft portion 22 of the worm gear 21, the following (i) to ( It has the configuration of iii).

(i) The bearing 22A is a three-point contact ball bearing.
As shown in FIG. 6, the three-point contact ball bearing 22A includes an outer ring 111 and an inner ring 112, a large number of balls 113 arranged in a freely rolling manner between the raceway grooves 111A and 112A of these inner and outer rings, A cage and a seal plate (not shown) for sealing an annular opening between the inner and outer rings are provided.

  (ii) The raceway groove 111A of the outer ring 111 is composed of one arc r having a curvature radius of 110 to 124% of the curvature radius of the ball 113, and the center of curvature a is the center L in the width direction of the raceway groove 111A (the inner and outer rings 111). , 112 in the width direction center point and the surface passing through the center o of the ball 113). The ball 113 is in contact with the point A of the arc r of the raceway groove 111A.

  (iii) The raceway groove 112A of the inner ring 112 is composed of two arcs r1 and r2 each having a radius of curvature exceeding 100% of the curvature radius of the ball 113, and the centers of curvature b and c thereof are the center in the width direction of the raceway groove 112A. It has a two-point contact cross-sectional shape provided on both sides of L. The ball 113 is in contact with the point B of the arc r1 and the point C of the arc r2 of the raceway groove 112A. The center of curvature b is on the line connecting point B and the center o of the ball 113, and the center of curvature c is on the line connecting point C and the center o of the ball 113.

Therefore, according to the present embodiment, the following operational effects can be obtained.
(a) In the bearing 22A that can swing one end side of the worm gear 21, the raceway groove 111A of the outer ring 111 is composed of one arc r having a curvature radius of 110 to 124% of the curvature radius of the ball 113, and its curvature. The center o has a one-point contact cross-sectional shape provided at the center L in the width direction of the track groove 111A. Since the ball 113 comes into contact with the raceway groove 111A of the outer ring 111 at one point, the ball 113 is fixed to the gear housing 11B while reducing the internal gap between the raceway grooves 111A, 112A of the inner and outer rings 111, 112 and the ball 113. The inner ring 112 on which the one end shaft portion of the worm gear 21 is supported can be largely swung with respect to the outer ring 111 that is formed.

  (b) Since the radius of curvature of the raceway groove 111A of the outer ring 111 is set to 110 to 124% of the radius of curvature of the ball 113, even if the inner ring 112 swings greatly with respect to the outer ring 111, the ball 113 is moved into the inner and outer rings 111, 112. As a result, it is possible to suppress an increase in the shoulder riding rate and the contact pressure that rides on the shoulder of the groove, and the durability is not adversely affected.

  (c) The raceway groove 112A of the inner ring 112 is composed of two arcs r1 and r2 each having a radius of curvature exceeding 100% of the radius of curvature of the ball 113, and the centers of curvature b and c are defined in the width direction of the raceway groove 112A. The cross-sectional shape was a two-point contact provided on both sides of the center L. Since the balls 113 are in contact with the raceway groove 112A of the inner ring 112 at two points, the displacement of the inner ring 112 in the axial direction of the outer ring 111 can be suppressed.

  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.

  Further, the bearing case is not limited to a C-shaped annular body that is partially cut off in the circumferential direction, and may be composed of an annular body that is continuous in the circumferential direction.

  In the present invention, both ends of a driving gear driven by an electric motor are pivotally supported by bearings provided in a gear housing, and a driven gear meshing with the driving gear is fixed to a steering shaft, and the meshing between the driving gear and the driven gear is performed. Preload means for urging the bearing of the driven gear in a predetermined preload direction so as to apply preload to the part, and the drive gear is supported so as to be swingable around the bearing on one end side. In the electric power steering apparatus in which the end-side bearing is urged in a predetermined preload direction by the preload means, the one end-side bearing is a ball bearing, and the raceway groove of the outer ring has a radius of curvature of the ball of 110 to 124. It has a one-point contact cross-sectional shape with a center of curvature provided in the center in the width direction of the raceway groove, and the raceway groove of the inner ring provides 100% of the radius of curvature of the ball. Two arcs with different radii of curvature? It was in that their center of curvature having a two-point contact of the cross section which is provided on both sides of the widthwise center of said track groove. As a result, the drive gear driven by the electric motor is supported so as to be able to swing around the bearing on one end side, and the electric power generated by urging the bearing on the other end side in a predetermined preload direction by the preloading means. In the steering device, the driving gear can be greatly swung without increasing the internal clearance of the bearing on one end side.

10 Electric power steering apparatus 11A, 11B Gear housing 14 Output shaft (steering shaft)
20 Electric motor 21 Worm gear (drive gear)
22A One end side bearing 23A The other end side bearing 29 Warm wheel (driven gear)
30 Preload means 111 Outer ring 111A Track groove 112 Inner ring 112A Track groove 113 Ball

Claims (1)

Both ends of the drive gear driven by the electric motor are pivotally supported by bearings provided in the gear housing, the driven gear meshing with the drive gear is fixed to the steering shaft, and preload is applied to the meshing portion between the drive gear and the driven gear. In addition, it has a preload means for urging the bearing of the driven gear in a predetermined preload direction,
In the electric power steering device, the drive gear is supported so as to be swingable around a bearing on one end side, and the bearing on the other end side is urged in a predetermined preload direction by a preload means.
The bearing on the one end side is a ball bearing;
The outer ring raceway groove is composed of one circular arc having a curvature radius of 110 to 124% of the curvature radius of the ball, and has a one-point contact cross-sectional shape with the center of curvature provided in the center in the width direction of the raceway groove,
The inner ring raceway groove is composed of two circular arcs each having a radius of curvature exceeding 100% of the radius of curvature of the ball, and has a two-point contact cross-sectional shape with the centers of curvature provided on both sides of the center in the width direction of the raceway groove. An electric power steering apparatus comprising:

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