JP2010143527A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device for reducing manhours for manufacturing, and improving ease of attachment work. <P>SOLUTION: A pre-load mechanism part 40 pressing a worm shaft 7 in a worm wheel 9 direction comprises a holder 25, a pad 29, and a torsion spring 27. A second rolling bearing 32 disposed on an electric motor 3 side of the pre-load mechanism part 40 is elastically supported to a housing 5 by an annular retainer 35 disposed on the electric motor 3 side of the second rolling bearing 32, and an elastic part 35b applying pre-load in a bottom face 5c direction of the housing to the second rolling bearing 32 is provided at an end part of the second rolling bearing 32 side of the retainer 35. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus having an improved speed reduction mechanism.

  In an electric power steering apparatus using an electric motor as a power source, auxiliary steering torque generated from the electric motor in response to the steering torque applied to the steering wheel is transmitted to the output shaft of the steering mechanism via a power transmission mechanism including a speed reduction mechanism. To communicate.

  In an electric power steering apparatus using a worm reduction gear as the power transmission mechanism, a worm wheel meshes with a worm connected to a drive shaft of an electric motor, and the worm wheel is connected to an output shaft connected to a steering mechanism. It is fitted.

  In an electric power steering apparatus using such a worm reducer, an appropriate backlash is provided between gear tooth surfaces where the worm and the worm wheel mesh. However, due to the backlash, the gear tooth surfaces of the worm and the worm wheel generate a hitting sound due to vibrations input from the road surface through the tires when the vehicle is running, and the driver feels uncomfortable. There was a problem. In order to eliminate this hitting sound, a mechanism for eliminating a backlash by providing a preload mechanism for urging the worm in the worm wheel direction is conventionally known.

  FIG. 3 is a cross-sectional view showing a part of the speed reduction mechanism in the electric power steering apparatus according to the conventional example, and FIG. 4 is an enlarged view of a portion C in FIG.

  An electric motor 103 (only a part of which is shown in the figure) that is an auxiliary power source of the electric power steering apparatus is fixed to the housing 105. In the housing 105, a worm shaft 107 and a worm wheel 109 constituting a worm reduction mechanism are provided. The worm wheel 109 is fitted on the output shaft 111.

  A worm shaft 107 is coupled to the drive shaft 110 of the electric motor 103 so as to be movable in the axial direction and not to be relatively rotatable. A worm 107 b is formed at the center in the axial direction of the worm shaft 107. The worm shaft 107 is rotatably supported by the housing 105 by first and second rolling bearings 117 and 132 interposed between a base 115 on the side of the electric motor 103 and an end near the end far from the electric motor 103, respectively. Yes.

  Ring-shaped elastic members 122 and 123 are disposed on both sides in the axial direction of the first rolling bearing 117 on the electric motor 103 side. These two elastic members are respectively held in the axial direction by a pair of ring-shaped holding members 122a, 122b, 123a, 123b.

  Both ends of the inner ring 117b of the first rolling bearing 117 are in contact with ring-shaped holding members 122a and 123a. The ring-shaped holding members 122a and 123a in contact with the inner ring 117b are connected to the worm shaft 107. Is not fixed. The ring-shaped holding members 122b and 123b on the side not in contact with the inner ring 117b are fitted and fixed to the worm shaft 107, respectively. For this reason, the two elastic members 122 and 123 allow the worm shaft 107 to move in the axial direction within the elastic limit.

  A holder 125 is fitted in a bottom portion 105 b that is farther from the electric motor 103 inside the housing 105.

  On the inner peripheral side of the holder 125, a second rolling bearing 132 is rotatably fitted to the housing 105 via the holder 125 so that the worm shaft 107 is rotatably supported at the tip, and is fixed to the holder 125 by caulking ( D part circled in FIG. 4). A bush 130 is fitted on the inner peripheral surface of the second rolling bearing 132. The bush 130 supports the worm shaft 107 so as to be slidable in the axial direction.

  A small diameter portion 125 a protruding in the direction of the bottom surface 105 c is formed on the end surface of the holder 125 on the bottom surface 105 c side of the housing 105. A part of the inner peripheral surface of the small-diameter portion 125a is open to communicate with the outer peripheral side, and an axial cross-sectional shape is formed in a substantially U shape. The holder 125 is fitted in the housing 105 so that the substantially U-shaped opening side is opposite to the worm wheel 109.

  A pad 129 is attached to the small diameter portion 125a from the substantially U-shaped opening side, and a torsion spring 127 is wound around the outer peripheral side of the small diameter portion 125a and the outer peripheral surface 129a on the opening side of the pad 129. ing.

  The holder 125, the pad 129, the torsion spring 127, the second rolling bearing 132, and the bush 130 fitted in the second rolling bearing 132 constitute a preload mechanism 140. As described above, the preload mechanism 140 is fixed by press-fitting the holder 125 into the inner peripheral surface of the bottom 105b of the housing 105.

  The pad 129 is biased in the direction of the worm wheel 109 by the force of the torsion spring 127 wound around the small-diameter portion of the holder 125 to rewind, thereby generating a pre-pressure on the worm shaft 107. Due to this preload, the worm shaft 107 is urged in the direction of the meshing portion with the worm wheel 109 to reduce backlash at the meshing portion between the worm 107b and the worm wheel 109, and hit the tooth surface caused by backlash. Sound can be reduced.

Further, in Patent Document 1, the shafts of two rolling bearings provided at the base portion of the worm shaft on the electric motor side and the end portion far from the electric motor are connected to the drive shaft of the electric motor and the worm connected thereto. Both rolling bearings are arranged slightly eccentric to the worm wheel side from the shaft center, and an elastic member is provided between the worm shaft and each bearing to constitute a preload mechanism. An electric power steering device for removing lashes is disclosed.
Table 2003-047948

  In the configuration of the conventional preload mechanism described above, a rolling bearing is assembled on the inner peripheral side of the holder and fixed by caulking, so that it takes a number of manufacturing processes, and the preload is applied to the bottom of the bag-shaped housing. Since it is necessary to fix the mechanism portion by press-fitting, it is difficult to visually confirm the assembly. Therefore, there is a problem that the workability of assembly is poor.

  The present invention has been made in view of such a situation, and an object thereof is to provide an electric power steering device capable of reducing the number of manufacturing steps and improving workability at the time of assembly.

  In order to achieve the above object, an electric power steering apparatus according to the present invention transmits auxiliary steering torque generated from an electric motor to an output shaft through a reduction mechanism. A housing for housing the speed reduction mechanism, comprising: a worm shaft coupled to a drive shaft; a worm integrally provided on the worm shaft; and a worm wheel meshed with the worm and externally fitted to the output shaft. And a first rolling bearing and a second rolling bearing that rotatably support the worm shaft on the housing by a base portion on the electric motor side of the worm shaft and an end portion opposite to the base portion in the axial direction. And an electric power steering provided at the end of the worm shaft with a preload mechanism for applying a preload toward the worm shaft in a meshing direction with the worm wheel. The second rolling bearing is provided adjacent to the electric motor side in the axial direction of the second rolling bearing, and the end direction of the worm shaft in the axial direction with respect to the second rolling bearing. It is characterized in that it is elastically supported by a holding member having an elastic part for applying a preload.

  ADVANTAGE OF THE INVENTION According to this invention, the electric power steering apparatus which can aim at reduction of the number of manufacturing processes and improvement of workability | operativity at the time of an assembly | attachment can be provided.

  Hereinafter, an electric power steering apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of a power auxiliary part of an electric power steering apparatus according to an embodiment of the present invention, and FIG. 2 is an enlarged cross-sectional view showing a component part of FIG. is there.

  An electric motor 3 (only a part of which is shown in the figure), which is an auxiliary power source of the electric power steering device, is fixed to the housing 5. In the housing 5, a worm shaft 7 and a worm wheel 9 constituting a worm reduction mechanism are provided.

  A spline fitting portion 10 a is provided on the drive shaft 10 of the electric motor 3, and is coupled to a spline fitting portion 7 a provided on the worm shaft 7. As a result, the worm shaft 7 is connected to the drive shaft 10 of the electric motor 3 so as to be movable in the axial direction and is not relatively rotatable, and the tilt of the drive shaft 10 of the electric motor 3 and the worm shaft 7 is allowed. Can do.

  A worm 7 b is formed at the center in the axial direction of the worm shaft 7. A worm wheel 9 is engaged with the worm 7b. The worm wheel 9 is composed of a core metal 9a fitted on the output shaft 11 and resin gear teeth 9b formed on the outer diameter side of the core metal, and the gear teeth 9b mesh with the worm 7b.

  The output shaft 11 is connected to a steering shaft (not shown) provided with a steering wheel (not shown) at the rear end of the vehicle via a torsion bar (not shown). Is provided with a torque sensor mechanism (not shown) for detecting the steering torque applied thereto. An intermediate shaft (not shown) is connected to the front side of the output shaft 11 via a universal joint (not shown).

  Thus, the steering torque generated when the driver steers the steering wheel (not shown) is the steering shaft (not shown), the torsion bar (not shown), the output shaft 11, the universal joint (not shown), the intermediate shaft (not shown). It is transmitted to a steered wheel (not shown) via a steering mechanism (not shown) such as a rack and pinion type steering device. The auxiliary steering torque generated from the electric motor 3 in response to the detected steering torque is transmitted to the output shaft 11 via the worm 7b and the worm wheel 9, and the rotational force of the electric motor 3 and Appropriate steering assist torque can be applied to the output shaft 11 by appropriately controlling the rotation direction.

  In the electric power steering apparatus according to the present embodiment, a first bearing support portion 15 a is formed on the base portion 15 of the worm shaft 7 on the electric motor 3 side. An enlarged diameter portion 15b having a diameter larger than that of the first bearing support portion 15a is formed adjacent to the worm 7b side in the axial direction of the first bearing support portion 15a, and is electrically driven in the axial direction of the first bearing support portion 15a. On the motor 3 side, a reduced diameter portion 15c having a diameter smaller than that of the first bearing support portion 15a is formed adjacently.

  The first bearing support portion 15a is provided with a first rolling bearing 17 that rotatably supports the worm shaft 7 on the housing 5 on the electric motor 3 side. The outer ring 17 a of the first rolling bearing 17 has an end surface on the worm 7 b side fitted in a step portion 18 formed on the inner peripheral surface of the housing 5, and an end surface on the electric motor 3 side is locked by a retaining ring 19. This is fixed to the housing 5. The inner ring 17b of the first rolling bearing 17 is externally fitted with a slight gap on the outer peripheral surface of the first bearing support portion 15a, and the inner diameter side of the end surface on the worm 7b side is the first bearing support portion of the worm shaft 7. It is formed by a step between 15a and the enlarged diameter portion 15b, and faces the surface facing the electric motor 3 in the axial direction in the axial direction.

  On the other hand, a cylindrical holding member 20 is fitted on the reduced diameter portion 15c adjacent to the electric motor 3 side of the first bearing support portion 15a. An elastic member 23 to be described later is disposed on the outer peripheral surface of the holding member 20. The inner diameter side of the end surface on the worm 7b side in the axial direction of the holding member 20 is formed by a step between the first bearing support portion 15a and the reduced diameter portion 15c of the worm shaft 7 and faces the electric motor 3 in the axial direction. Touching. The outer diameter side of the end surface on the worm 7 b side in the axial direction of the holding member 20 faces the inner diameter side of the end surface on the electric motor 3 side in the axial direction of the inner ring 17 b of the first rolling bearing 17. That is, the inner ring 17 b of the first rolling bearing 17 is formed by a step between the first bearing support portion 15 a and the diameter-enlarged portion 15 b of the worm shaft 7, the surface facing the electric motor 3 in the axial direction, and the holding member 20. It is disposed between the end surface on the worm 7b side in the axial direction, and the axial dimension of the inner ring 17b is formed by a step between the first bearing support portion 15a and the enlarged diameter portion 15b. The dimension is slightly shorter than the dimension in the axial direction between the opposing surface and the end surface on the worm 7b side in the axial direction of the cylindrical holding member 20. In other words, the dimension of the inner ring 17b in the axial direction is shorter than the dimension of the first bearing support portion 15a formed on the worm shaft 7 in the axial direction.

  Ring-shaped elastic members 22 and 23 are provided on both sides in the axial direction of the first rolling bearing 17, that is, on the enlarged diameter portion 15 b on the worm 7 b side and the reduced diameter portion 15 c on the electric motor 3 side. The two elastic members 22 and 23 are sandwiched in the axial direction by a pair of ring-shaped holding members 22a and 22b and 23a and 23b, respectively.

  Of the pair of ring-shaped holding members 22a and 22b holding the elastic member 22 on the worm 7b side, the holding member 22a on the first rolling bearing 17 side is wormed in the axial direction of the inner ring 17b of the first rolling bearing 17. It contacts the outer diameter side of the end surface on the 7b side, and its inner peripheral surface is not fixed to the worm shaft 7. Further, the holding member 22b on the worm 7b side is in contact with the step portion 15d formed on the worm 7b side in the axial direction of the diameter-enlarged portion 15b, and the surface on the worm 7b side is in contact with the inner peripheral surface. The part 15b is externally fitted and fixed. Due to such a configuration, the elastic member 22 on the worm 7b side can be elastically deformed in the axial direction when the ring-shaped holding member 22a on the first rolling bearing 17 side moves in the axial direction.

  The elastic member 23 on the electric motor 3 side is fitted on the outer periphery of the cylindrical holding member 20 fitted on the reduced diameter portion 15 c of the worm shaft 7. Of the pair of ring-shaped holding members 23 a and 23 b holding the elastic member 23 on the electric motor 3 side, the holding member 23 a on the first rolling bearing 17 side is electrically driven in the axial direction of the inner ring 17 b of the first rolling bearing 17. It contacts the outer diameter side of the end surface on the motor 3 side, and its inner peripheral surface is not fixed to the cylindrical holding member 20. Further, the holding member 23b on the electric motor 3 side is in contact with the enlarged diameter portion 20a formed on the electric motor side in the axial direction of the outer peripheral surface of the cylindrical holding member 20, and the inner peripheral surface thereof. Is externally fixed to the outer peripheral surface of the cylindrical holding member 20. Due to such a configuration, the elastic member 23 on the electric motor 3 side can be elastically deformed in the axial direction when the ring-shaped holding member 23a on the first rolling bearing 17 side moves in the axial direction.

  Since the elastic members 22 and 23 as described above are provided on both sides of the first rolling bearing 17 disposed on the electric motor 3 side, the worm shaft 7 includes the first bearing support portion 15a and the first rolling bearing 17. It is possible to move in the axial direction as much as the dimensional difference in the axial direction. Further, since the first rolling bearing 17 is externally fitted to the first bearing support portion 15 a with a gap, the first rolling bearing 17 can be inclined with respect to the drive shaft 10 of the electric motor 3.

  An annular holder 25 is fitted and fixed to the bottom 5 b of the housing 5 that is farther from the electric motor 3 inside the housing 5. The annular holder 25 constitutes a preload mechanism portion 40 together with a pad 29 and a torsion spring 27 described later.

  A small-diameter portion 25a protruding in the direction of the bottom surface 5c is formed on the end surface of the holder 25 on the bottom surface 5c side of the housing 5. A part of the inner diameter side of the small diameter portion 25a is open to communicate with the outer circumference side.

  The inner peripheral surface of the small-diameter portion 25a is formed in a substantially U-shaped cross section in the axial direction with the communicating portion with the outer peripheral surface as the opening side (upper side in FIG. 2). That is, the inner peripheral surface of the small-diameter portion 25a includes an inner peripheral surface 25b on the side facing the radial direction across the opening and the axial center, and both ends in the circumferential direction of the inner peripheral surface 25b from both circumferential edges of the opening. It extends in parallel to the edge and is formed with opposing planes (not shown). The inner peripheral surface of the small diameter portion 25a forms a pad attachment portion P with an inner peripheral surface 25b on the side facing the opening and a plane (not shown) facing each other. The holder 25 is fitted in the housing 5 so that the opening side of the small diameter portion 25a is opposite to the worm wheel 9 (lower side in FIG. 2).

  A pad 29 is attached to the pad attachment portion P in the direction of the opposed inner peripheral surface 25b from the opening side. The pad 29 is slidably attached in the radial direction to the above-described opposing plane (not shown) forming the pad attachment portion P, and the outer diameter on the opening side is smaller than the outer diameter of the small diameter portion 25a. Is also set larger. The tip of the worm shaft 7 is pivotally supported by a pad 29.

  A torsion spring 27, which is an elastic body, is wound around the outer peripheral side of the small diameter portion 25 a of the holder 25 and the outer peripheral surface 29 a on the opening side of the pad 29. Both ends of the torsion spring 27 are locked by a locking portion (not shown) formed on the outer peripheral surface of the small diameter portion 25a.

  As described above, the outer peripheral surface 29a on the opening side of the pad 29 is set to have an outer diameter larger than that of the small diameter portion 25a. For this reason, by winding the torsion spring 27 around the outer peripheral surface 29a on the outer peripheral side of the small diameter portion 25a and the opening portion side of the pad 29, the pad 29 is opposite to the opening portion side due to the force that the torsion spring 27 tries to unwind. Preload is applied in the lateral direction (downward in FIG. 2). That is, the pad 29 is biased toward the worm wheel 9 by this preload. The axial center of the pad 29 in a state where the pad 29 is biased in this way is slightly eccentric to the side opposite to the opening, that is, the worm wheel 9 side than the axial center of the worm shaft 7. For this reason, the worm shaft 7 pivotally supported by the pad 29 is urged toward the worm wheel 9 by the preload by the torsion spring 27.

  Thus, the worm shaft 7 is biased in the direction of the meshing portion with the worm wheel 9 to reduce backlash of the meshing portion between the worm 7b and the worm wheel 9 and to strike the tooth surface caused by the backlash. Sound can be reduced.

  In the present embodiment, a second rolling bearing 32 is disposed on the side of the electric motor 3 in the axial direction of the holder 25. An end surface on the bottom surface 5 c side of the housing 5 in the axial direction of the outer ring 32 a of the second rolling bearing 32 is in contact with an end surface on the electric motor 3 side in the axial direction of the holder 25. A bush 30 that supports the worm shaft 7 so as to be slidable in the axial direction is fitted in the inner ring 32b of the second rolling bearing.

  The bush 30 includes a cylindrical portion 30a that is fitted in the inner ring 32b of the second rolling bearing 32, and a radially outwardly extending flange portion 30b that is formed at an end portion on the electric motor 3 side in the axial direction of the cylindrical portion 30a. Are integrally formed. The collar portion 30b extends in the radial direction to the vicinity of the outer peripheral surface of the inner ring 32b, and the end surface on the bottom surface 5c side of the housing 5 in the axial direction of the collar portion 30b contacts the end surface on the electric motor 3 side of the inner ring 32b. is doing. A second bearing support portion 34 formed near the tip of the worm shaft 7 is slidable in the axial direction on the inner peripheral surface of the cylindrical portion 30a of the bush 30 and has a slight radial gap. It is fitted. Due to this gap, the worm shaft 7 can swing. Thus, the second rolling bearing 32 supports the worm shaft 7 on the housing 5 via the bush 30 so as to be rotatable.

  In the present embodiment, an annular retainer 35 is disposed on the electric motor 3 side in the axial direction of the second rolling bearing 32, and the second rolling bearing 32 is elastically supported by the housing 5 by the retainer 35. Has been. The retainer 35 includes a cylindrical portion 35a formed in a truncated conical shape having one end tapered, and an elastic portion 35b formed integrally with an end portion on the tapered side of the cylindrical portion 35a (in FIG. 2). Part B).

  The elastic portion 35b is in contact with the end surface on the electric motor 3 side in the axial direction of the annular portion 35c extending inward in the radial direction and the outer ring 32a of the second rolling bearing 32 from the tapered edge of the cylindrical portion 35a. An annular bearing contact portion 35d, and a bent portion 35e that elastically urges the annular portion 35c and the bearing contact portion 35d in a direction away from each other in the axial direction. The bent portion 35e has a bent shape in which a cross section connecting the inner diameter side of the annular portion 35c and the inner diameter side of the bearing contact portion 35d is substantially U-shaped and bent into a substantially arc shape. The bent portion 35e can be elastically biased so that the annular portion 35c and the bearing contact portion 35d are separated from each other in the axial direction.

  The retainer 35 is fitted into the inner periphery of the housing 5 such that the large diameter side of the cylindrical portion 35a is in the axial direction and the taper side where the elastic portion 35b is formed is the second rolling bearing 32 side in the axial direction. Has been. The bearing contact portion 35d of the elastic portion 35b is in contact with the end surface on the side of the electric motor 3 in the axial direction of the outer ring 32a of the second rolling bearing 32 by applying an elastic preload in the direction of the bottom surface 5c of the housing 5. By providing the retainer 35 in this manner, the second rolling bearing 32 is sandwiched between the retainer 35 and the holder 25 by applying an elastic preload in the direction of the bottom surface 5c of the housing 5 by the elastic portion 35b of the retainer 35. The housing 5 is elastically supported.

  As described above, according to the electric power steering apparatus of the present invention, the second rolling bearing that rotatably supports the worm shaft is elastically supported by the housing by the retainer having the elastic portion. There is no need to assemble and fix the second rolling bearing to the holder, and the swaging process can be reduced. Furthermore, since it is not necessary to press-fit the holder assembled with the second rolling bearing, it is also easy to visually confirm the assembled state when assembling each component of the second rolling bearing and the preload mechanism. It can contribute to the improvement of workability.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible.

It is sectional drawing of the power auxiliary | assistance part of the electric power steering apparatus which concerns on embodiment of this invention. It is sectional drawing which expands and shows the A member of FIG. 1, and disassembles a structural member. It is sectional drawing of the power auxiliary | assistance part of the electric power steering apparatus which concerns on a prior art example. It is sectional drawing which expands and shows the B section of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 Electric motor 5 Housing 5a Shaft support hole 5b Bottom part 5c Bottom face 7 Worm shaft 7a Spline fitting part 7b Worm 9 Worm wheel 9a Core metal 9b Gear tooth 10 Drive shaft 10a Spline fitting part 11 Output shaft 15 Base 15a 1st bearing support Part 15b Expanded part 15c Reduced part 17 First rolling bearing 17a Outer ring 17b Inner ring 18 Step part 19 Retaining ring 20 Cylindrical holding member 20a Expanded part 22, 23 Elastic member 22a, 22b, 23a, 24b Ring-shaped holding member 25 Holder 25a Small diameter portion 25b Inner peripheral surface 27 Torsion spring 29 Pad 29a Opening side outer peripheral surface 30 Bush 30a Tube portion 30b Brim portion 32 Second rolling bearing 32a Outer ring 32b Inner ring 34 Second bearing support portion 35 Retainer 35a Tubular portion 35b Elasticity Part 35c annular part 35d shaft Contact portion 35e bent part 40 preload mechanism

Claims (1)

In order to transmit the auxiliary steering torque generated from the electric motor to the output shaft through the speed reduction mechanism,
The speed reduction mechanism includes a worm shaft coupled to a drive shaft of the electric motor, a worm integrally provided on the worm shaft, and a worm wheel meshed with the worm and externally fitted to the output shaft. Become
A housing that houses the speed reduction mechanism;
First and second rolling bearings that rotatably support the worm shaft on the housing by a base portion of the worm shaft on the electric motor side and an end portion opposite to the base portion in the axial direction;
In the electric power steering apparatus provided with a preload mechanism that applies a preload to the end portion of the worm shaft toward the meshing direction of the worm shaft with the worm wheel,
The second rolling bearing is provided adjacent to the electric motor side in the axial direction of the second rolling bearing, and preloads the second rolling bearing in the axial direction toward the end portion of the worm shaft. An electric power steering apparatus, wherein the electric power steering apparatus is elastically supported by a holding member having an elastic part.

Images