JP2013208933A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of eliminating a backlash by applying a proper pre-load to an engaging portion between a worm gear and a worm wheel and improving engagement strength between the worm gear and the worm wheel.SOLUTION: An electric power steering device is structured so that a pre-load direction P in which pre-load means 30 energizes a bearing 23A on the other end side is set to a radial direction passing through the central axis of the worm gear within a range of a minor angle interposed between: a direction of a radial component FL of a driving reaction which a worm gear receives from a worm wheel when the worm gear rotates in a left turn steering direction within a cross section perpendicular to an axis of the worm gear; and a direction of a radial component FR of a driving reaction which the worm gear receives from the worm wheel, when the worm gear rotates in a right turn steering 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 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.

  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 Document 1 has the following problems.
(1) Based on the specifications of the teeth of the worm gear and worm wheel, when the steering assist torque of the electric motor is transmitted by meshing between the worm gear and the worm wheel, the direction of the driving reaction force that the worm gear receives from the worm wheel depends on the preloading means. It differs from the preload direction applied to the worm gear bearing. For this reason, an appropriate preload cannot be applied to the meshing portion of the worm gear and the worm wheel.

  (2) No consideration is given to the effect of the preload applied to the meshing part of the worm gear and worm wheel on the meshing strength of the worm gear and worm wheel.

  An object of the present invention is to remove the backlash by applying an appropriate preload to the meshing portion of the worm gear and the worm wheel in the electric power steering apparatus, and to improve the meshing strength of the worm gear and the worm wheel.

  According to the first aspect of the present invention, both ends of the worm gear driven by the electric motor are pivotally supported by bearings provided in the gear housing, and the worm wheel meshing with the worm gear is fixed to the steering shaft so that the worm gear and the worm wheel mesh with each other. In an electric power steering apparatus having a preload means for biasing a worm gear bearing in a predetermined preload direction so as to apply a preload to a large portion, the worm gear is supported to be swingable around a bearing on one end side. In addition, the bearing on the other end side is biased in a predetermined preload direction by the preloading means, and the preloading direction in which the preloading means biases the bearing on the other end side is within the cross section perpendicular to the axis of the worm gear, and the worm gear is steered to the left. Direction of the radial component FL of the driving reaction force that the worm gear receives from the worm wheel when the worm gear rotates in the direction, and the worm gear turns right The worm gear is set in the radial direction passing through the central axis of the worm gear within the range of the minor angle between the worm gear and the radial component FR of the driving reaction force received from the worm wheel. Is.

  According to a second aspect of the present invention, in the first aspect of the present invention, the preload direction in which the preloading means biases the bearing on the other end side of the worm gear is directed to the center of the worm wheel in the cross section perpendicular to the axis of the worm gear. It is set in a direction oblique to the radial direction.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the preload means further includes a bearing case attached to the gear housing, and the bearing case includes a bearing housing hole for housing the bearing of the worm gear. A guide surface that contacts the outer periphery of the bearing and guides the bearing so as to move in the preload direction is provided on the inner periphery of the bearing receiving hole.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, the preload means further comprises a bearing accommodating hole for accommodating a worm gear bearing, and a spring insertion hole into which a spring for biasing the bearing is inserted. The bearing case has a bearing case that intersects with the bearing accommodation hole, and a cylindrical seat rubber is brought into contact with the opening end surface of the spring insertion hole of the bearing case, so that the spring can be accommodated in the inner diameter portion of the seat rubber. The bearing case containing the bearing is attached to the case mounting portion provided in the gear housing, the hole direction of the spring insertion hole of the bearing case is set in the preload direction of the bearing, and the seat rubber containing the spring is provided in the gear housing. And the seat rubber is brought into contact with the opening end surface of the spring insertion hole of the bearing case, and the cover around the opening of the rubber loading hole of the gear housing is removed. The inner surface of the lid to be fixed to a surface is obtained by the so by close contact with the outer end face of the sheet rubber.

  According to a fifth aspect of the present invention, in the fourth aspect of the invention, the bearing case further includes a cylindrical projecting portion having an inner periphery of the annular body as a bearing receiving hole and projecting radially outward of the annular body. The cylindrical projection is loaded into a rubber loading hole provided in the gear housing, and the spring insertion hole is formed through the axial direction of the cylindrical projection.

(Claim 1)
(a) When the preload direction P by the preload means is within the cross section perpendicular to the axis of the worm gear and the worm gear rotates in the left steering direction, the direction of the radial component FL of the driving reaction force that the worm gear receives from the worm wheel, and the worm gear Is set in the radial direction passing through the central axis of the worm gear within the range of the minor angle sandwiched by the direction of the radial component FR of the driving reaction force received from the worm wheel when the worm gear rotates to the right. The Therefore, with a simple configuration, the worm gear urges the worm gear in a direction generally opposite to the direction of the driving reaction force received from the worm wheel during both left and right turning, so that the worm gear and the worm gear are A generally appropriate preload can be applied to the meshing portion of the wheel, and backlash between the two can be eliminated.

(Claim 2)
(b) The preload direction P by the preload means is set in a direction oblique to the radial direction A of the worm gear toward the center of the worm wheel at an angle α in the cross section perpendicular to the axis of the worm gear. At this time, due to the specifications of the teeth of the worm gear and the worm wheel, the teeth of the worm gear have a certain advance angle γ, and the thickness of the teeth of the worm wheel is thin at the center in the tooth width direction and gradually increases toward both ends. Therefore, when the bearing on the other end side of the worm gear is preloaded in the oblique direction at the angle α described above, and when the worm gear swings at the angle θ about the bearing on the one end side as the center C, the teeth of the worm gear are It is displaced along the tooth gap, and meshes at the portion where the worm wheel has a thicker tooth. Thereby, the meshing strength with respect to the impact of the worm gear and the worm wheel is improved.

(Claim 3)
(c) the preload means has a bearing case attached to the gear housing, the bearing case has a bearing housing hole for housing the bearing of the worm gear, and moves the bearing in the preload direction in contact with the outer periphery of the bearing. A guide surface for guiding is provided on the inner periphery of the bearing receiving hole. Therefore, the bearing on the other end side of the worm gear can be guided by the guide surface of the worm wheel so as to move stably in the preload direction.

(Claim 4)
(d) A bearing case in which the preload means includes a bearing housing hole for housing a worm gear bearing, and a spring insertion hole through which a spring for biasing the bearing is inserted intersects the bearing housing hole. A case in which a cylindrical seat rubber is brought into contact with the opening end face of the spring insertion hole of the bearing case and the spring can be accommodated in the inner diameter portion of the seat rubber, and the bearing case housing the bearing is provided in the gear housing. The seat rubber is attached to the attachment portion, the hole direction of the spring insertion hole of the bearing case is set to the preload direction of the bearing, the seat rubber containing the spring is loaded into the rubber loading hole provided in the gear housing, and the seat rubber is The inner surface of the lid that is in contact with the opening end surface of the spring insertion hole of the bearing case and is fixed to the lid mounting surface around the opening of the rubber loading hole of the gear housing is closely attached to the outer end surface of the seat rubber. Make. Therefore, when the bearing case is attached to the gear housing, the guide surface of the bearing case is defined in a direction for guiding the bearing in a predetermined preload direction. Accordingly, the single spring inserted into the spring insertion hole of the bearing case can guide the bearing on the other end side of the worm gear so as to stably move in the preload direction.

(Claim 5)
(e) The bearing case includes a cylindrical projecting portion that has an inner periphery of the annular body as a bearing receiving hole and projects outward in the radial direction of the annular body, and the cylindrical projecting portion is provided in a rubber housing. The spring insertion hole was formed in the axial direction of the cylindrical protrusion. Therefore, by loading the cylindrical protrusion of the bearing case into a rubber loading hole provided in the gear housing, the guide surface of the bearing case is easily and reliably defined in a direction for guiding the bearing in a predetermined preload direction.

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 an exploded perspective view showing the electric power steering apparatus. FIG. 7 is an exploded perspective view showing the gear housing and the preload means. FIG. 8 is a perspective view showing the bearing case. FIG. 9 is a schematic diagram showing the force acting on the bearing of the worm gear. FIG. 10 shows the meshed state of the worm gear and the worm wheel, (A) is a front view showing a state where the worm gear is swung, (B) is a plan view of (A), and (C) is a state where the worm gear is swung. It is a top view which shows a state without. FIG. 11 is a schematic view showing a meshed state of teeth of the worm gear and the worm wheel.

  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 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, 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 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 FIG. 5, the seat rubber 50 includes a cylindrical body 51 that is loaded into the rubber loading hole 82 of the gear housing 11 </ b> B, and a flange 51 </ b> F that protrudes outward from the proximal end portion of the cylindrical body 51. And a small-diameter portion 51 </ b> A having a stepped portion 51 </ b> S on the outer periphery 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, an appropriate preload is applied to the meshing portion between the worm gear 21 and the worm wheel 29 to remove backlash, and the meshing strength between the worm gear 21 and the worm wheel 29 is improved. The following configuration is provided.

  A direction P in which the preload means 30 biases the bearing 23A of the shaft portion 23 of the worm gear 21 is determined as follows. That is, the preload direction P by the preload means 30 is the driving reaction force that the worm gear 21 receives from the worm wheel 29 when the worm gear 21 rotates in the left-turning direction within the cross section perpendicular to the axis of the worm gear 21 as shown in FIG. Of the radial component FL of the worm gear 21 and the radial component FR of the driving reaction force received by the worm gear 21 from the worm wheel 29 when the worm gear 21 rotates in the right steering direction. Thus, it is set in the radial direction passing through the central axis of the worm gear 21.

  Further, the preload direction P in which the preload means 30 urges the bearing 23 </ b> A is obliquely crossed at an angle α with the radial direction A of the worm gear 21 toward the center of the worm wheel 29 in the cross section perpendicular to the axis of the worm gear 21. Is set.

Therefore, according to the present embodiment, the following operational effects can be obtained.
(a) When the preload direction P by the preload means 30 is within the cross section perpendicular to the axis of the worm gear 21 and the worm gear 21 rotates in the left-turning direction, the radial component FL of the driving reaction force received by the worm gear 21 from the worm wheel 29 When the worm gear 21 is rotated in the right-turning direction, the worm gear 21 is within the range of the minor angle sandwiched between the worm gear 21 and the direction of the radial component FR of the driving reaction force received from the worm wheel 29. It is set in the radial direction passing through the central axis. Therefore, the worm gear 21 is urged in a direction substantially opposite to the direction of the driving reaction force received by the worm gear 29 from the worm wheel 29 in the case of left steering and right steering with a simple configuration. A generally appropriate preload can be applied to the meshing portion of the worm gear 21 and the worm wheel 29, and the backlash of both can be removed.

  (b) The preload direction P by the preload means 30 is set in a direction that is oblique with an angle α with respect to the radial direction A of the worm gear 21 toward the center of the worm wheel 29 in the cross section perpendicular to the axis of the worm gear 21. . At this time, due to the specifications of the teeth of the worm gear 21 and the worm wheel 29, the teeth of the worm gear 21 have a certain advance angle γ, and the tooth thickness t of the worm wheel 29 is thin at the center in the tooth width direction and is directed toward both ends. It becomes thicker gradually. Accordingly, the bearing 23A on the other end side of the worm gear 21 is preloaded in a direction obliquely intersecting with the angle α described above, whereby the worm gear 21 is centered on the bearing 22A on one end side as shown in FIGS. 10A and 10B. (FIG. 10C shows a state of not swinging), the teeth of the worm gear 21 are displaced along the tooth groove 29A of the worm wheel 29 as shown in FIG. The tooth 29 of the wheel 29 is engaged at a thicker portion. Thereby, the meshing strength with respect to the impact of the worm gear 21 and the worm wheel 29 is improved.

  (c) The preload means 30 has a bearing case 40 attached to the gear housing 11B. The bearing case 40 is provided with a bearing receiving hole 43 for receiving the bearing 23A of the worm gear 21, and is in contact with the outer periphery of the bearing 23A. Is provided on the inner periphery of the bearing housing hole 43 so as to guide the bearing to move in the preload direction P. Therefore, the bearing 23A on the other end side of the worm gear 21 can be guided by the guide surface 101 of the worm wheel 29 so as to move stably in the preload direction.

  (d) The preload means 30 includes a bearing housing hole 43 for housing the bearing 23A of the worm gear 21, and the spring insertion hole 44 through which the spring 60 for biasing the bearing 23A is inserted intersects the bearing housing hole 43. The cylindrical seat rubber 50 is brought into contact with the opening end surface of the spring insertion hole 44 of the bearing case 40 so that the spring 60 can be accommodated in the inner diameter portion of the seat rubber 50. The bearing case 40 containing the bearing 23A is attached to the case attaching portion 81 provided in the gear housing 11B, the hole direction of the spring insertion hole 44 of the bearing case 40 is set to the preload direction of the bearing 23A, and the spring 60 is accommodated. The seat rubber 50 is loaded into a rubber loading hole 82 provided in the gear housing 11B, and the seat rubber 50 is inserted into the spring insertion hole of the bearing case 40. Is 4 abuts against the opening end face of, brought into close contact with the inner surface of the lid 70 which is fixed to the lid mounting surface 71 around the opening of the rubber loading hole 82 of the gear housing 11B on the outer end face of the sheet rubber 50. Therefore, when the bearing case 40 is attached to the gear housing 11B, the guide surface 101 of the bearing case 40 is defined in a direction for guiding the bearing 23A in a predetermined preload direction. Thus, the single spring 60 inserted through the spring insertion hole 44 of the bearing case 40 can guide the bearing 23A on the other end side of the worm gear 21 so as to move stably in the preload direction.

  (e) The bearing case 40 includes a cylindrical protrusion 42 that has an inner periphery of the annular body 41 as a bearing receiving hole 43 and protrudes radially outward of the annular body 41, and the cylindrical protrusion 42 is a gear housing. It was loaded in a rubber loading hole 82 provided in 11B, and the spring insertion hole 44 was formed in the axial direction of the cylindrical projection 42. Therefore, by loading the cylindrical projecting portion 42 of the bearing case 40 into the rubber loading hole 82 provided in the gear housing 11B, the guide surface 101 of the bearing case 40 can be easily and reliably provided in a direction to guide the bearing 23A in a predetermined preload direction. Stipulated in

  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.

  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 worm gear driven by an electric motor are pivotally supported by bearings provided in a gear housing, a worm wheel meshing with the worm gear is fixed to a steering shaft, and a preload is applied to a meshing portion between the worm gear and the worm wheel. In the electric power steering apparatus having preload means for biasing the worm gear bearing in a predetermined preload direction, the worm gear is supported so as to be swingable around the bearing on one end side, and the other The end bearing is biased by the preloading means in a predetermined preloading direction, and the preloading direction in which the preloading means biases the other end bearing is within the cross section perpendicular to the axis of the worm gear, and the worm gear is rotated in the left steering direction. Sometimes the worm gear rotates in the direction of the radial component FL of the driving reaction force received from the worm wheel, and the worm gear rotates in the right steering direction. When the worm gear is within the scope of the minor angle sandwiched between the direction of the radial component FR a driving reaction force received from the worm wheel is set to a radial direction passing through the center axis of the worm gear. Thus, in the electric power steering apparatus, it is possible to remove the backlash by applying an appropriate preload to the meshing portion between the worm gear and the worm wheel, and to improve the meshing strength between the worm gear and the worm wheel.

DESCRIPTION OF SYMBOLS 10 Electric power steering apparatus 11A, 11B Gear housing 12 Input shaft 14 Output shaft 20 Electric motor 21 Worm gear 22A One end side bearing 23A The other end side bearing 29 29 Worm wheel 30 Preload means 40 Bearing case 41 Annular body 42 Cylindrical protrusion 43 Bearing Housing hole 44 Spring insertion hole 50 Sheet rubber 51 Tubular body 60 Spring 70 Lid 71 Lid mounting surface 81 Case mounting part 82 Rubber loading hole 101 Guide surface

Claims (5)

Both ends of the worm gear driven by the electric motor are pivotally supported by bearings provided in the gear housing, the worm wheel meshing with the worm gear is fixed to the steering shaft, and preload is applied to the meshing portion between the worm gear and the worm wheel. In the electric power steering apparatus having preload means for urging the worm gear bearing in a predetermined preload direction,
The worm gear is supported so as to be swingable around a bearing on one end side, and the bearing on the other end side is biased in a predetermined preload direction by a preload means,
The preload direction in which the preload means urges the bearing on the other end is within the cross section perpendicular to the axis of the worm gear, and the radial component FL of the driving reaction force that the worm gear receives from the worm wheel when the worm gear rotates in the left-turning direction. When the worm gear rotates in the right-turning direction, the worm gear passes through the central axis of the worm gear within a range of an inferior angle between the worm gear and the direction of the radial component FR of the driving reaction force received from the worm wheel. An electric power steering apparatus characterized by being set in a radial direction.   2. The preload direction in which the preload means biases the bearing on the other end side is set in a direction oblique to the radial direction of the worm gear toward the center of the worm wheel in a cross section perpendicular to the axis of the worm gear. Electric power steering device.   The preload means has a bearing case attached to the gear housing, the bearing case has a bearing housing hole for housing the bearing of the worm gear, and guides the bearing so as to move in the preload direction in contact with the outer periphery of the bearing. The electric power steering apparatus according to claim 1 or 2, wherein a surface is provided on an inner periphery of the bearing receiving hole. The preload means comprises:
A bearing housing hole for housing the bearing of the worm gear, and having a bearing case comprising a spring insertion hole through which the spring for biasing the bearing is inserted intersecting the bearing housing hole,
A cylindrical seat rubber is brought into contact with the opening end surface of the spring insertion hole of the bearing case, and the spring can be accommodated in the inner diameter portion of the seat rubber.
A bearing case containing a bearing is attached to a case mounting portion provided in the gear housing, a hole direction of a spring insertion hole of the bearing case is set to a preload direction of the bearing, and a seat rubber containing a spring is provided in the gear housing. The seat rubber is loaded into the rubber loading hole, the seat rubber is brought into contact with the opening end surface of the spring insertion hole of the bearing case, and the inner surface of the lid fixed to the lid mounting surface around the opening of the rubber loading hole of the gear housing is seat rubber. The electric power steering apparatus according to claim 3, wherein the electric power steering apparatus is in close contact with the outer end surface of the electric power steering apparatus.   The bearing case includes a cylindrical projection that has an inner periphery of the annular body as a bearing receiving hole and projects radially outward of the annular body, and the cylindrical projection is loaded into a rubber loading hole provided in the gear housing. The electric power steering apparatus according to claim 4, wherein the spring insertion hole is formed so as to penetrate in an axial direction of the cylindrical protrusion.

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