JP2007270943A - Worm reducer and electric power steering device inc0rporating the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the occurrence of slapping sounds in a worm reducer 6a and suppress colliding noise due to collision of an elastic force applying means 29 made of a metal plate for applying elastic force to a worm shaft 8 in the direction toward a worm wheel. <P>SOLUTION: The worm reducer is provided with an outer ring 22 fitted on the outside of a second ball bearing 11b and supporting it on a part toward the tip end of the worm shaft 8 and structuring the second ball bearing 11b, and the elastic force applying means 29 between an outer ring 22 composing the second ball bearing 11b and an inner peripheral face of a recessed hole 45 provided to a gear housing 10. The elastic force applying means 29 is composed by covering an elastic material 51 such as an elastomer like synthetic rubber having a larger elastic deforming amount than that of a synthetic resin on the surface of a plate spring 65 made of a metal plate. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The worm speed reducer according to the present invention and the electric power steering apparatus incorporating the worm reducer are incorporated in a steering apparatus of an automobile and use an electric motor as auxiliary power, so that a driver can operate with a force required to operate the steering wheel. Used for mitigation.

  A power steering device is widely used as a device to reduce the force required for the driver to operate the steering wheel when giving a steering angle to the steered wheels (usually the front wheels except for special vehicles such as forklifts) Has been. In addition, an electric power steering apparatus that uses an electric motor as an auxiliary power source in such a power steering apparatus has begun to spread in recent years. The electric power steering device can be made smaller and lighter than the hydraulic power steering device, has advantages such as easy control of the magnitude (torque) of auxiliary power and less power loss of the engine.

  In addition, a worm speed reducer including a worm shaft and a worm wheel is also widely provided in the middle of a power transmission path for transmitting power from the rotating shaft of the electric motor to the steering shaft. However, such a worm reducer has an inevitable backlash. The backlash increases as the dimensional error and assembly error of each component of the worm reducer such as the worm shaft, the worm wheel, and the bearings supporting these members increase. When such a large backlash exists, the tooth surfaces of the worm wheel and the worm partly collide with each other, and an irritating rattling sound may be generated.

  In view of such circumstances, Patent Document 1 describes a worm speed reducer for an electric power steering device in consideration of reducing the backlash and an electric power steering device incorporating the same. . 9 to 12 show an electric power steering device having a conventional structure described in Patent Document 1. FIG. In the case of the conventional structure shown in FIGS. 9 to 12, a first steering shaft 2 in which the steering wheel 1 is fixed to the rear end portion (left end portion in FIG. 9), and the front end portion of the first steering shaft 2. A cylindrical member 3 coupled to (the right end portion of FIG. 9) and a torsion bar 4 inserted inside the cylindrical member 3, and a rear end portion (left end portion of FIG. 9) of the torsion bar 4 And the front end of the first steering shaft 2 are coupled. Further, the portion near the front end of the torsion bar 4 (the portion near the right end in FIG. 9) is inserted inside the second steering shaft 5, and the front end portions of the torsion bar 4 and the second steering shaft 5 are joined to each other. Yes. The front end portion of the second steering shaft 5 is connected to a rack and pinion type steering mechanism (not shown) through a universal joint (not shown).

  A worm wheel 7 constituting the worm speed reducer 6 is externally fitted and fixed to a part of the second steering shaft 5. Further, the worm 9 of the worm shaft 8 is engaged with the worm wheel 7. Both end portions of the worm shaft 8 are rotatably supported inside the gear housing 10 by first and second ball bearings 11a and 11b (FIGS. 10 and 11). An electric motor 12 is coupled to the gear housing 10.

  Of the worm shaft 8, a base end portion (left end portion in FIG. 10) on the electric motor 12 side and one end portion (right end portion in FIG. 10) of the rotating shaft 13 of the electric motor 12 are connected by a power transmission mechanism 14. It is coupled to allow power transmission. The power transmission mechanism 14 includes first and second meshing elements 17 and 18 provided with first and second meshing teeth 15 and 16 respectively at three positions in the circumferential direction on one axial surface, and both And an elastic element 19 provided between the meshing elements 17 and 18. The elastic element 19 is provided with meshing teeth 20 and 20 at six positions in the circumferential direction on the outer peripheral surface. And the 1st meshing tooth 15 provided in the said 1st meshing element 17 is made to mesh | engage in every other 3 positions among the several parts between the side surfaces of each of these meshing teeth 20 and 20. The second meshing teeth 16, 16 provided on the second meshing element 18 are meshed from the opposite side at the remaining three positions.

  Of the first and second ball bearings 11a and 11b, the first ball bearing 11a on the electric motor 12 side (left side in FIG. 10) is externally fitted to a portion near the base end of the worm shaft 8, The worm shaft 8 is rotatably supported with respect to the gear housing 10 by the first ball bearing 11a. On the other hand, the second ball bearing 11b on the opposite side (right side in FIG. 10) from the electric motor 12 is externally supported on the tip of the worm shaft 8 and around the second ball bearing 11b. 11 and 12 are provided with elasticity applying means 21 as shown in detail. This elastic force imparting means 21 is formed by curving a belt-shaped spring steel plate whose overall length is longer than the overall circumferential length of the outer peripheral surface of the outer ring 22 constituting the second ball bearing 11b in a substantially circular shape, A U-shaped notch 23 is formed at the center in the width direction at one circumferential edge, and a narrow projecting piece 24 is formed at the center in the width direction at the other circumferential edge. Then, the projecting piece 24 is protruded from the inside of the notch 23 to the outside in the radial direction of the portion near the one end in the circumferential direction of the elasticity applying means 21, and the width sandwiching the notch 23 near the one end in the circumferential direction Both side portions in the direction are engaged with the outer peripheral edge of the other end in the circumferential direction of the elasticity applying means 21.

  In addition, spring pieces 26 and 26 are provided at a plurality of circumferential positions on one side edge in the width direction (right side edge in FIG. 12) of the curved portion 25 that is curved in a circular shape in the middle portion in the circumferential direction of the elasticity applying means 21. Protrusively formed. Each of the spring pieces 26, 26 is inclined in a direction away from the bending portion 25 with respect to the width direction of the bending portion 25 as it goes radially inward. Then, the second ball bearing 11 b is fitted inside the curved portion 25, and the elasticity applying means 21 is inserted into a concave hole 27 provided in a part of the gear housing 10 on the side opposite to the electric motor 12. And the second ball bearing 11b, the outer ring 22 of the second ball bearing 11b is elastically pressed toward the electric motor 12 by the spring pieces 26 and 26. As a result, the worm shaft 8 having the second ball bearing 11b fitted on the tip thereof is elastically pressed toward the electric motor 12 by the spring pieces 26, 26.

A concave portion 28 is formed in a part of the inner peripheral surface of the concave hole 27 provided in the gear housing 10 on the opposite side of the worm wheel 7 (the lower end portion of FIGS. 10 and 11) in the circumferential direction. 28, both end edges in the circumferential direction of the elasticity applying means 21 are made to enter. Both circumferential edges of the circumferential direction are elastically pressed against the bottom surface of the recess 28, and are portions on both sides in the circumferential direction that are opposite to the worm wheel 7 of the elasticity applying means 21 (near the lower end in FIG. 11). The portion) elastically presses the second ball bearing 11b in the direction toward the worm wheel 7. As a result, a portion where the second ball bearing 11 b is fitted on the tip of the worm shaft 8 is elastically displaced in a direction toward the worm wheel 7.
According to the conventional structure described in Patent Document 1 shown in FIGS. 9 to 12, a preload is applied to the meshing portion between the worm 9 of the worm shaft 8 and the worm wheel 7 by the elastic force applying means 21. There is a possibility that generation of an annoying rattling noise at the meshing portion can be suppressed to some extent.

  However, when the metal outer ring 22 of the second ball bearing 11b is pressed by the elastic force imparting means 21 made of a spring steel plate as in the conventional structure described in Patent Document 1 described above, the metal portion on the surface thereof is When exposed, the metal portion comes into contact with the outer ring 22 made of metal such as bearing steel, and further, the metal portion comes into contact with the inner surface of the metal gear housing 10. In this case, an irritating metal sound is generated at the contact portion between the elasticity applying means 21 and the outer ring 22 and the gear housing 10. On the other hand, in the case of the conventional structure described in Patent Document 1, a buffer material such as synthetic resin is coated on the entire surface or the inner peripheral side portion of the elasticity applying means 21. However, when the worm speed reducer 6 is used, the torque applied to the worm shaft 8 increases, and the gear reaction force applied to the worm shaft 8 from the worm wheel 7 increases, so that the tip of the worm shaft 8 moves from the worm wheel 7. When it tends to be greatly displaced in the direction of leaving, there is a possibility that a part of the elastic force imparting means 21 strongly collides with the outer ring 22 of the second ball bearing 11b or the inner surface of the gear housing 10. When the cushioning material is a synthetic resin, the amount of elastic deformation of the synthetic resin is small, so that it is difficult to reduce the impact force between the elasticity applying means 21 and the outer ring 22 or the gear housing 10. For this reason, there is a possibility that a large annoying collision sound may be generated at the contact portion between the elasticity applying means 21 and the outer ring 22 or the gear housing 10.

  In addition to the conventional structure described above, only between a part in the circumferential direction of the outer peripheral surface of the outer ring 22 of the second ball bearing 11b and a part in the circumferential direction of the concave hole 27 provided in the gear housing 10, It is also conceivable to provide elastic force imparting means configured by bending the metal plate into an annular shape, and elastically displace the second ball bearing 11b in the direction approaching the worm wheel 7 by the elastic force imparting means. However, in this case, the inner surfaces of the metal elasticity applying means strongly collide with each other, and there is a possibility that a loud and harsh collision sound may be generated.

Japanese Patent Laid-Open No. 2004-203154

  In view of the circumstances as described above, the present invention has a structure capable of suppressing the occurrence of rattling noise in the worm speed reducer, and a resilient force applying means made of a metal plate that displaces the worm shaft in a direction approaching the worm wheel; The invention was invented in order to effectively suppress the occurrence of a collision sound due to a collision with another member or a collision between a part of the elasticity applying means.

The worm speed reducer according to the present invention includes a worm wheel, a worm shaft, and elasticity applying means.
Of these, the worm wheel is fixed to any member of a shaft, a pinion provided on the front end side of the shaft, and a sub-pinion that meshes with the rack at a position away from the pinion.
The worm shaft is rotatably supported at both ends by a pair of bearings on the inner side of the gear housing, and a worm provided at an intermediate portion meshes with the worm wheel.
The elasticity applying means is made of a metal plate, applies elasticity to the worm shaft, and applies elasticity in the direction toward the worm wheel to the worm shaft.

  In particular, in the worm speed reducer according to the first aspect of the present invention, the elastic force imparting means is formed on the surface of a plate spring made of a metal plate, such as an elastomer such as rubber having a larger elastic deformation amount than a synthetic resin. It is configured by covering an elastic material.

  According to a second aspect of the present invention, there is provided an electric power steering apparatus according to the present invention, a steering shaft having a steering wheel provided at a rear end portion, a pinion provided at a front end side of the steering shaft, and the pinion or the pinion. The rack meshed with the supported member, the worm speed reducer according to claim 1, the electric motor for rotationally driving the worm shaft constituting the worm speed reducer, and the direction of torque applied to the steering shaft or pinion And a torque sensor for detecting the magnitude and a controller for controlling the driving state of the electric motor based on a signal input from the torque sensor. The steering shaft is the shaft according to claim 1.

In the case of the worm speed reducer of the present invention and the electric power steering apparatus incorporating the same as described above, the elasticity in the direction toward the worm wheel is applied to the worm shaft by the elasticity applying means. For this reason, a preload can be applied to the meshing portion between the worm wheel and the worm shaft, and generation of an annoying rattling noise at the meshing portion can be suppressed.
In particular, in the case of the present invention, the elasticity applying means is configured by covering the surface of a plate spring made of a metal plate with an elastic material having a larger elastic deformation amount than the synthetic resin. For this reason, the torque applied to the worm shaft during use of the worm reducer increases, and the gear reaction force applied to the worm shaft from the worm wheel increases, so that the worm shaft tends to be greatly displaced away from the worm wheel. Even when a part of the elasticity applying means collides with another member, or when the elastic force applying means collides with each other, the elastic force in which the surface of the leaf spring is coated is applied. Can be fully absorbed by the material. Since this elastic material has a larger amount of elastic deformation than synthetic resin, it is easy to reduce the impact force. As a result, even if a part of the elasticity applying means collides with another member or a part of the elasticity applying means collides with each other, it is possible to sufficiently suppress generation of an unpleasant loud collision sound. .

  1 to 5 show a first example of an embodiment of the present invention. The feature of the worm speed reducer for the electric power steering apparatus of this example is that the elasticity applying means 29 provided around the tip of the worm shaft 8 is provided around the tip of the worm shaft 8 in order to apply elasticity in the direction toward the worm wheel 7. The structure is devised. The other basic structure itself is substantially the same as the structure widely known in the past, such as the conventional structure shown in FIGS. 9 to 12 described above, so that it is equivalent to the conventional structure shown in FIGS. Are denoted by the same reference numerals, and redundant description is omitted or simplified. The following description will focus on features of this example and parts different from the conventional structure.

  In the case of the worm speed reducer 6a of this example, both end portions of the worm shaft 8 are rotatably supported with respect to the gear housing 10 by the first and second ball bearings 11a and 11b. Among these ball bearings 11a and 11b, the inner ring 30 constituting the first ball bearing 11a is fitted on a cylindrical portion 31 provided at the base end portion (left end portion in FIGS. 1 and 2) of the worm shaft 8. ing. In addition, a cylindrical holding member 32 is fitted and fixed to a portion of the cylindrical portion 31 (left end portion in FIGS. 1 and 2) that is distant from the inner ring 30 toward the distal end side. Between the outward flange 33 provided on the outer peripheral surface of the holding member 32 and the inner ring 30, and between the inner ring 30 and a shoulder 34 provided on the outer peripheral surface of the worm shaft 8 near the proximal end, A pair of locking rings 35, 35 and a cylindrical member 36 made of an elastic material provided between the locking rings 35, 35 are provided. A small radial gap is provided between the outer peripheral surface of the worm shaft 8 and the inner peripheral surface of the inner ring 30 of the first ball bearing 11a. The outer ring 37 constituting the first ball bearing 11 a is sandwiched between a step surface 38 formed on the inner surface of the gear housing 10 and a retaining ring 39 locked to the inner surface of the gear housing 10. The axial displacement of the outer ring 37 is restricted.

  A female spline portion 40 is provided on the inner peripheral surface of the cylindrical portion 31 provided at the base end portion of the worm shaft 8, and a male spline portion is provided on the outer peripheral surface of one end portion (the right end portion in FIGS. 1 and 2) of the rotating shaft 13 of the electric motor 12. 41 is formed, and the spline engagement portion 42 formed by spline engagement of both the male and female spline portions 40 and 41 transmits power between the ends of the rotary shaft 13 and the worm shaft 8. Combined as possible.

  Further, a second ball bearing 11b is externally fitted to a small-diameter shaft portion 43 provided at the tip portion (the right end portion in FIGS. 1 and 3) of the worm shaft 8. That is, the inner ring 44 constituting the second ball bearing 11b is externally fitted and fixed to the small diameter shaft portion 43. And the said small diameter shaft part 43 and the 2nd ball bearing 11b are inserted in the concave hole 45 provided in a part of said gear housing 10. FIG. As shown in FIG. 4, the inner peripheral surface of the concave hole 45 has a substantially oval cross section, and a pair of parallel flat portions 46, 46 provided on both sides in the width direction (left and right direction in FIG. 4). And a pair of partial cylindrical surface portions 47a, 47b in which both edge portions of the flat portions 46, 46 are connected to each other.

Each said plane part 46 and 46 is located on the virtual plane orthogonal to the central axis of the worm wheel 7 (FIGS. 1-3). Further, a pair of locking grooves 48, 48 are formed at the end portions (lower end portions in FIG. 4) of the flat portions 46, 46 opposite to the worm wheel 7. The distance d ₁ between the flat portions 46 and 46 is slightly larger than the outer diameter D of the outer ring 22 constituting the second ball bearing 11b. On the other hand, the distance d ₂ in the direction parallel to the plane portions 46 and 46 between the center portions in the width direction (left and right direction in FIG. 4) of the partial cylindrical surface portions 47a and 47b is set to the second length. It is made sufficiently larger than the outer diameter D of the outer ring 22 of the ball bearing 11b. Then, the second ball bearing 11 b can move in the recess 45 with respect to the worm wheel 7. Further, the perspective movement of the second ball bearing 11 b with respect to the worm wheel 7 is smoothly performed because the outer ring 22 is guided to the flat portions 46 and 46.

  Further, a part of the outer peripheral surface of the outer ring 22 in the circumferential direction opposite to the worm wheel 7 (the lower end portion in FIGS. 1, 3, and 4) and a part of the inner peripheral surface of the concave hole 45 in the circumferential direction In the meantime, the elasticity giving means 29 is provided. The elasticity applying means 29 is constituted by a plate spring 65 made of a metal plate such as a spring steel plate. The leaf spring 65 includes a partial cylindrical pressing portion 49 provided at an intermediate portion, and a pair of locking plate portions 50 that are provided at both ends of the pressing portion 49 and are bent outward in the radial direction of the outer ring 22. 50.

  In particular, in the case of this example, the elasticity applying means 29 is bonded to the entire surface of the leaf spring 65 with a thin elastic material 51 such as an elastomer such as synthetic rubber having a larger elastic deformation amount than that of synthetic resin. It is configured by coating by baking or the like. The elastic material 51 can be covered only on a part of the surface of the leaf spring 65. For example, only the portions that engage with the entire front and back side surfaces of the pressing portion 49 of the leaf spring 65 and the locking grooves 48, 48 provided on the inner surface of the concave hole 45 of the locking plate portions 50, 50. In addition, the elastic material 51 can be covered.

  Such elasticity applying means 29 is provided between a part of the outer peripheral surface of the outer ring 22 in the circumferential direction opposite to the worm wheel 7 and a part of the inner peripheral surface of the concave hole 45 in the circumferential direction. At the same time, the leading edges of the locking plate portions 50 and 50 are locked in the locking grooves 48 and 48. In this state, one of the convex curved surface (the lower surface in FIGS. 3 and 4) of the pressing portion 49 and the pair of partial cylindrical surface portions 47a and 47b of the concave hole 45 (below in FIGS. 3 and 4). A gap is provided between the inner surface of the partial cylindrical surface portion 47a.

  Such elasticity applying means 29 presses the concave curved surface side of the pressing portion 49 against the outer peripheral surface of the outer ring 22 of the second ball bearing 11b, thereby causing the outer ring 22 to move toward the worm wheel 7 (FIG. 3, (4 above) is given elasticity. Accordingly, the tip of the worm shaft 8 is given elasticity in the direction toward the worm wheel 7 by the elasticity applying means 29 via the second ball bearing 11b. As a result, the worm shaft 8 tends to be inclined with respect to the rotating shaft 13 (FIG. 1) of the electric motor 12, and the distance between the central axes of the worm shaft 8 and the worm wheel 7 tends to be reduced. The tooth surfaces of the worm 9 and the worm wheel 7 of the shaft 8 are pressed against each other with the preload applied. In the case of this example, the locking plate portions 50, 50 formed at both ends of the elasticity applying means 29 are locked to the locking grooves 48, 48, so that the second ball bearing 11b is stable. Can give elasticity. On the other hand, in the case of the conventional structure described in Patent Document 1 shown in FIGS. 9 to 12 described above, the notch 23 and the projecting piece 24 are engaged. May not be given elasticity.

  Moreover, the electric power steering apparatus of this example incorporates the worm speed reducer 6a provided with the worm wheel 7, the worm shaft 8, and the leaf spring 29 as described above. That is, the electric power steering apparatus of this example includes the worm speed reducer 6a, a steering shaft provided with a steering wheel 1 (see FIG. 9) at the rear end, a universal joint and an intermediate shaft on the front end side of the steering shaft. An input shaft coupled via the input shaft, a pinion coupled to the end of the input shaft, a rack meshed with the pinion, and an electric motor 12 that rotationally drives the worm shaft 8 constituting the worm speed reducer 6a. A torque sensor provided around the steering shaft for detecting the direction and magnitude of torque applied from the steering wheel 1 to the steering shaft; and a driving state of the electric motor 12 based on a signal input from the torque sensor And a controller for controlling.

  In the case of the electric power steering apparatus incorporating the worm speed reducer for the electric power steering apparatus of the present example configured as described above, the worm shaft 8 is directed toward the worm wheel 7 by the elasticity applying means 29 made of a metal plate. Is elastically pressed. For this reason, preload can be applied to the meshing portion of the worm wheel 7 and the worm 9 of the worm shaft 8 with an inexpensive structure, and the occurrence of rattling noise at this meshing portion can be suppressed at a low cost, The assembly work of the worm speed reducer 6a can be easily performed.

  In particular, in the case of this example, the elasticity applying means 29 is configured by covering the surface of a plate spring 65 made of a metal plate with an elastic material 51 having an elastic deformation amount larger than that of synthetic resin. For this reason, the torque applied to the worm shaft 8 when the worm reduction gear 6a is used increases, and the gear reaction force applied to the worm shaft 8 from the worm wheel 7 increases, so that the worm shaft 8 moves away from the worm wheel 7. Even when the displacement tends to be greatly displaced, the impact force generated when a part of the elastic force imparting means 29 abuts against the inner surface of the concave hole 45 of the gear housing 10 or the outer ring 22 of the fourth ball bearing 11b. The elastic material 51 coated on the surface of the leaf spring 65 can be sufficiently absorbed. Since the elastic material 51 has a larger elastic deformation amount than that of the synthetic resin, it is easy to reduce the impact force. As a result, even when a part of the elasticity applying means 29 collides with the gear housing 10 or the outer ring 22, it is possible to sufficiently suppress the generation of an unpleasant loud collision sound.

  Next, FIG. 5 shows a second example of the embodiment of the present invention. In the case of this example, a part in the circumferential direction of the outer peripheral surface of the outer ring 22 constituting the second ball bearing 11b, which is externally fitted to the small-diameter shaft portion 43 provided at the tip portion of the worm shaft 8, and the gear housing 10 Elasticity imparting means 29a is provided between a part of the inner circumferential surface of the recessed hole 45 provided in the circumferential direction and a part in the circumferential direction. The elastic force imparting means 29a is formed by bending a metal plate such as a spring steel plate in an annular shape, and the two positions opposite to each other in the diametrical direction are sufficiently close to each other and deformed so as to have an arcuate shape as a whole. A leaf spring 66 is provided. The elastic force applying means 29a is configured by covering the entire inner peripheral surface and outer peripheral surface of the leaf spring 66 with elastic materials 51, 51 such as an elastomer such as synthetic rubber by bonding, baking, or the like. ing.

  Further, both end portions in the longitudinal direction of the leaf spring 66 constituting the elasticity applying means 29a are opposed to each other through the gap 52. Further, in a state where the gap 52 is positioned at the center of the elastic force applying means 29a in the width direction (left and right direction in FIG. 5), it is opposite to the worm wheel 7 (see FIGS. 1 to 3) on the outer peripheral surface of the outer ring 22. The elasticity applying means 29a is installed between a part in the circumferential direction on the side (the lower end in FIG. 5) and a part in the circumferential direction of the inner peripheral surface of the concave hole 45. In this state, a portion on the worm wheel 7 side (upper side in FIG. 5) of the outer peripheral surface of the elasticity applying means 29a contacts the outer peripheral surface of the outer ring 22 of the second ball bearing 11b. The part on the opposite side (lower side in FIG. 5) contacts one (lower side in FIG. 5) partial cylindrical surface part 47a of the pair of partial cylindrical surface parts 47a and 47b of the concave hole 45. A pair of step portions 53, 53 are formed at the end opposite to the worm wheel 7 of the pair of flat portions 46, 46 constituting the concave hole 45, and inside these step portions 53, 53. Both ends of the elastic force applying means 29a are inserted in the arc direction (left and right direction in FIG. 5).

  The portion on the worm wheel 7 side of the outer peripheral surface of the elastic force imparting means 29a is pressed against the outer peripheral surface of the outer ring 22 of the second ball bearing 11b to apply elasticity to the outer ring 22 in the direction toward the worm wheel 7. Yes. As a result, the worm shaft 8 tends to be inclined with respect to the rotating shaft 13 (see FIG. 1) of the electric motor 12, and the distance between the central axes of the worm shaft 8 and the worm wheel 7 tends to be reduced. The tooth surfaces of the worm 9 and the worm wheel 7 of the shaft 8 are pressed against each other with the preload applied.

In the case of this example configured as described above, the entire inner peripheral surface and outer peripheral surface of the leaf spring 66 formed in an annular shape are covered with elastic materials 51 and 51 having a larger elastic deformation amount than the synthetic resin. The elasticity applying means 29a is configured. Therefore, the torque applied to the worm shaft 8 when the worm reduction gear 6a is used increases, and the gear reaction force applied to the worm shaft 8 from the worm wheel 7 increases, so that the worm shaft 8 moves away from the worm wheel 7. Even if it tends to be greatly displaced, a part of the elasticity applying means 29a collides with the inner surface of the concave hole 45 of the gear housing 10, the outer ring 22 of the fourth ball bearing 11b, or the elasticity applying means. The impact force generated when a part of the inner peripheral surface of 29a abuts can be sufficiently absorbed by the elastic members 51, 51 covering the surface of the leaf spring 66. As a result, even if a part of the elasticity applying means 29a collides with the gear housing 10 or the outer ring 22 or a part of the elasticity applying means 29a collides with each other, it is possible to sufficiently generate an unpleasant loud collision sound. Can be kept small.
Since other configurations and operations are the same as in the case of the first example of the above-described embodiment, the same parts are denoted by the same reference numerals, and overlapping illustrations and descriptions are omitted.

  The basic structure of the leaf springs 29 and 29a constituting the elasticity applying means for applying elasticity to the worm shaft 8 in order to apply elasticity in the direction toward the worm wheel 7 to the worm shaft 8 is the same as that of each example described above. It is not limited to the structure. For example, in the present invention, a synthetic rubber having a larger elastic deformation amount than that of a synthetic resin is formed on the surface of a metal plate leaf spring constituting the elasticity applying means 21 incorporated in the conventional structure shown in FIGS. An elastic material such as an elastomer may be coated, and the elastic force applying means 21 may apply a elastic force to the tip of the worm shaft 8 via the second ball bearing 11b.

  Further, as the basic structure of the electric power steering apparatus of the present invention, for example, various structures shown in FIGS. In the structure shown in FIG. 6, the electric motor 12 and the worm speed reducer 6 a are provided around the intermediate portion of the steering shaft 54 as in the case of the above-described examples. That is, the electric power steering apparatus shown in FIG. 6 includes a steering shaft 54 in which the steering wheel 1 is fixed to the rear end portion (right end portion in FIG. 6), and the front end side (left end side in FIG. 6) of the steering shaft 54. ) And the pinion 58 coupled to the lower end of the input shaft 57, and the pinion 58 or a member supported by the pinion 58. A rack (not shown), a torque sensor and a controller (not shown) are provided. And the gear housing 10 which comprises the worm reduction gear 6a is being fixed to the front-end part (left end part of FIG. 6) of the steering column 59 which penetrated the said steering shaft 54. As shown in FIG. A case 60 constituting the electric motor 12 is fixed to the gear housing 10. The worm wheel 7 (see FIGS. 1 to 3) constituting the worm speed reducer 6a is externally fixed to an intermediate portion of the inner shaft 61 constituting the front end side portion of the steering shaft 54. The torque sensor is provided around an intermediate portion of the steering shaft 54.

  The rotation of the steering shaft 54 is transmitted to the input shaft 57 of the steering gear via the universal joints 55 and 55 and the intermediate shaft 56. The input shaft 57 rotates the pinion 58 constituting the steering gear, pushes and pulls the tie rods 62 and 62 through the rack, and gives a desired steering angle to a steered wheel (not shown).

  In the structure shown in FIG. 7, the electric motor 12 and the worm speed reducer are provided in the peripheral portion of the pinion 58 (see FIG. 6) to be engaged with the rack. The worm wheel 7 (see FIGS. 1 to 3) is fixed to the pinion 58 or a part of the member supported by the pinion 58. In the case of the structure shown in FIG. 7, the torque sensor can be provided not on the periphery of the steering shaft 54 but on the periphery of the pinion 58.

Further, as shown in FIG. 8, the electric motor 12 and the worm speed reducer 6a are provided in the peripheral part of the sub-pinion 64 that is engaged with the position disengaged from the engaging part with the pinion 58 at a part of the rack 63. You can also. In the case of the structure shown in FIG. 8, the worm wheel fixed to the sub-pinion 64 and the worm shaft 8 are engaged with each other. Also in the case of the structure shown in FIG. 8, a torque sensor can be provided in the peripheral portion of the pinion 58.
The electric power steering apparatus of the present invention can be applied to any of the structures shown in FIGS.

  Further, the electric power steering apparatus of the present invention is not limited to a structure in which the pinion 58 fixed to the end of the input shaft 57 and the rack 63 (see FIG. 8) are directly meshed with each other. For example, a pin provided at the lower end portion of the input shaft 57 is engaged with a long hole of a pinion gear provided separately from the input shaft 57 so that the long hole can be displaced in the length direction. And a rack 63, and a structure incorporating a so-called vehicle speed responsive variable gear ratio mechanism (VGS) that changes the ratio of the displacement amount of the rack 63 to the rotation angle of the steering shaft 54 according to the vehicle speed, and each of the examples described above. Can be combined with structure.

The figure which cut | disconnects and shows the worm reducer part of the electric power steering apparatus of the 1st example of embodiment of this invention. The A section expanded sectional view of FIG. The B section expanded sectional view. CC sectional drawing of FIG. The figure similar to FIG. 4 which shows the electric power steering apparatus of the 2nd example of embodiment of this invention. The figure which cut | disconnects and shows the structure of the 1st example which provided the worm reduction gear and the electric motor around the steering shaft among the basic structures of an electric power steering device. The figure which cuts a part and shows the structure of the 2nd example which similarly provided the worm reduction gear and the electric motor in the peripheral part of the pinion. The figure which cuts off a part of 3rd example structure which similarly provided the worm reduction gear and the electric motor in the peripheral part of a subpinion. The fragmentary sectional view showing the electric power steering device of one example of the conventional structure. DD enlarged sectional view of FIG. EE expanded sectional view of FIG. The perspective view which takes out and shows only the elasticity provision means integrated in the structure of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 1st steering shaft 3 Cylindrical member 4 Torsion bar 5 2nd steering shaft 6, 6a Worm reducer 7 Worm wheel 8 Worm shaft 9 Worm 10 Gear housing 11a First ball bearing 11b Second Ball bearing 12 electric motor 13 rotating shaft 14 power transmission mechanism 15 first meshing tooth 16 second meshing tooth 17 first meshing element 18 second meshing element 19 elastic element 20 meshing tooth 21 elasticity applying means 22 outer ring 23 Notch 24 Projection piece portion 25 Curved portion 26 Spring piece 27 Recess hole 28 Recess portion 29, 29a Elasticity imparting means 30 Inner ring 31 Cylindrical portion 32 Holding member 33 Outward flange portion 34 Shoulder portion 35 Locking ring 36 Cylindrical member 37 Outer ring 38 Step Surface 39 Retaining ring 40 Female spline part 41 Male spline part 42 Spline Engagement part 43 Small diameter shaft part 44 Inner ring 45 Recessed hole 46 Plane part 47a, 47b Partial cylindrical surface part 48 Engagement groove 49 Press part 50 Engagement plate part 51 Elastic material 52 Gap 53 Step part 54 Steering shaft 55 Universal joint 56 Intermediate shaft 57 Input shaft 58 Pinion 59 Steering column 60 Case 61 Inner shaft 62 Tie rod 63 Rack 64 Sub pinion 65 Leaf spring 66 Leaf spring

Claims (2)

The worm wheel includes a worm wheel, a worm shaft, and an elastic force imparting means. The worm wheel includes a shaft, a pinion provided on the front end side of the shaft, and a sub-pinion that meshes with the rack at a position away from the pinion. The worm shaft is rotatably supported by a pair of bearings on the inner side of the gear housing at both end portions, and a worm provided at an intermediate portion is connected to the worm wheel. In the worm speed reducer, the elasticity applying means is made of a metal plate, gives elasticity to the worm shaft, and gives elasticity in the direction toward the worm wheel to the worm shaft. ,
A worm speed reducer characterized in that the elasticity applying means is configured by covering the surface of a plate spring made of a metal plate with an elastic material having a larger elastic deformation amount than that of synthetic resin.   The worm deceleration according to claim 1, a steering shaft provided with a steering wheel at a rear end portion, a pinion provided on a front end side of the steering shaft, a rack meshed with the pinion or a member supported by the pinion, A torque sensor for detecting the direction and magnitude of torque applied to the steering shaft or pinion, a signal input from the torque sensor, and an electric motor for rotationally driving a worm shaft constituting the worm speed reducer. An electric power steering apparatus comprising: a controller for controlling a driving state of the electric motor, wherein the steering shaft is the shaft according to claim 1.

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