JP2014193638A - Power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power steering device capable of stably reducing backlash.SOLUTION: A power steering device includes: a worm shaft 2 which rotates in conjunction with driving of an electric motor 7; a worm wheel which engages with the worm shaft 2 and is used for transmitting a rotation force of the electric motor 7 to a rack shaft 7 for steering wheels; a gear case 3 which houses the worm shaft 2; a first bearing 10 which rotatably supports a tip side of the worm shaft 2; a second bearing 20 which is supported by the gear case 3 and has a center axis arranged parallel with a center axis of the first bearing 10; a connection member 30 which connects the first bearing 10 with the second bearing 20; and a biasing member which biases the worm shaft 2 to the worm wheel. The first bearing 10 may move on a circular arc track where the center axis of the second bearing 20 is the center.

Description

  The present invention relates to a power steering apparatus.

  As a conventional power steering device, a device that reduces backlash of teeth between the worm wheel and the worm shaft by urging a bearing that supports the worm shaft meshing with the worm wheel by a spring is known (for example, Patent Document 1).

  In this type of power steering device, the inner peripheral surface of the gear case that accommodates the bearing is formed into an elongated hole shape having a two-sided width so that the bearing supporting the worm shaft can be moved by the biasing force of the spring. (For example, refer to Patent Document 2).

Japanese Patent Laid-Open No. 3-112784 JP 2000-43739 A

  In the configuration in which the bearing slides along the two-surface width, the movement of the bearing is hindered by friction, and there is a possibility that the backlash cannot be stably reduced.

  The present invention has been made in view of the above problems, and an object thereof is to provide a power steering device that can stably reduce backlash.

  The present invention is a power steering device for assisting a steering force applied to a steering handle by a driver, the worm shaft rotating as the electric motor is driven, and the rack shaft meshing with the worm shaft and turning a wheel. A worm wheel for transmitting the rotational force of the electric motor, a gear case that accommodates the worm shaft, a first bearing that rotatably supports the distal end side of the worm shaft, and a center shaft that is supported by the gear case. A second bearing parallel to the central axis of the first bearing; a connecting member that connects the first bearing and the second bearing; and a biasing member that biases the worm shaft toward the worm wheel. The first bearing moves on a circular arc track around the central axis of the second bearing.

  According to the present invention, since the first bearing moves on the circular arc track centering on the central axis of the second bearing, the first bearing moves smoothly without generating friction with the gear case. Therefore, backlash can be stably reduced.

It is sectional drawing which shows the power steering apparatus which concerns on 1st Embodiment of this invention. It is sectional drawing which follows the AA line in FIG. It is sectional drawing which shows the power steering apparatus which concerns on 2nd Embodiment of this invention. It is sectional drawing which follows the AA line in FIG. It is sectional drawing which follows the BB line in FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment>
A power steering apparatus 100 according to a first embodiment of the present invention will be described with reference to FIGS. 1 and 2.

  The power steering device 100 is a device that is mounted on a vehicle and assists a steering force applied by a driver to a steering wheel.

  As shown in FIG. 1, a power steering device 100 is connected to an output shaft 7 a of an electric motor 7 and rotates as the electric motor 7 is driven. The power steering device 100 meshes with the worm shaft 2 and is linked to a steering handle. And a worm wheel 1 (see FIG. 2) for transmitting the rotational force of the electric motor 7 to a rack shaft that steers the wheel. The worm shaft 2 rotates as the electric motor 7 is driven, and the rotation of the worm shaft 2 is decelerated and transmitted to the worm wheel 1. The worm wheel 1 and the worm shaft 2 constitute a worm speed reducer.

  The electric motor 7 outputs a torque corresponding to the steering torque calculated based on the torsion amount of the torsion bar that is twisted by the relative rotation of the input shaft and the output shaft constituting the steering shaft. Torque output from the electric motor 7 is transmitted from the worm shaft 2 to the worm wheel 1 and applied to the steering shaft as assist torque.

  The worm shaft 2 is accommodated in a metal gear case 3. A part of the worm shaft 2 is formed with a tooth part 2a that meshes with a tooth part 1a of the worm wheel 1 (see FIG. 2).

  The base end side which is the electric motor 7 side of the worm shaft 2 is rotatably supported by the bearing 4. The bearing 4 has a ball interposed between an annular inner ring and an outer ring. The outer ring of the bearing 4 is sandwiched between a step portion 3 a formed in the gear case 3 and a lock nut 5 fastened in the gear case 3. The inner ring of the bearing 4 is sandwiched between the step 2 b of the worm shaft 2 and the joint 9 that is press-fitted into the end of the worm shaft 2. Thereby, the movement to the axial direction of the worm shaft 2 is controlled.

  The power steering device 100 has a non-backlash structure for reducing backlash between the tooth portion 1a of the worm wheel 1 and the tooth portion 2a of the worm shaft 2. Hereinafter, the non-backlash structure will be described with reference to FIGS. 1 and 2.

  A protruding portion 3 c that protrudes in the radial direction of the worm shaft 2 is formed on the distal end side of the gear case 3. An elongated hole-shaped opening 3 b is formed at the tip of the gear case 3. The gear case 3 has a lid 6 that seals the opening 3b. The lid 6 is fastened to the gear case 3 with bolts. An O-ring 8 that seals between the gear case 3 and the lid 6 is interposed. A space 3 d extending in a direction perpendicular to the axial direction of the worm shaft 2 is formed inside the gear case 3.

  The front end side of the worm shaft 2 is rotatably supported by the first bearing 10. The first bearing 10 includes an annular inner ring 10a and an outer ring 10b, and a ball 10c as a rolling element interposed between the inner ring 10a and the outer ring 10b so as to roll freely. The inner ring 10 a of the first bearing 10 is provided by being fitted to the outer peripheral surface of the tip portion of the worm shaft 2.

  The second bearing 20 connected to the first bearing 10 via the connecting member 30 is accommodated in the space 3 d of the gear case 3. The second bearing 20 includes an annular inner ring 20a and an outer ring 20b, and a ball 20c as a rolling element interposed between the inner ring 20a and the outer ring 20b so as to freely roll. The inner ring 20 a of the second bearing 20 is provided by being fitted to the outer peripheral surface of the rod 40 supported by the gear case 3.

  The rod 40 is a cylindrical member, and both end portions thereof are inserted into concave portions 6b and 3e formed coaxially on inner surfaces 6a and 3f facing each other of the lid 6 and the protruding portion 3c. The rod 40 is supported by the gear case 3 in parallel with the central axis of the first bearing 10, that is, the central axis of the worm shaft 2.

  The rod 40 is formed with an annular portion 40a that protrudes annularly in the radial direction from the outer peripheral surface. The annular portion 40a is sandwiched between the inner ring 20a of the second bearing 20 and the inner surface 3f of the protruding portion 3c. Thereby, rotation of the rod 40 is controlled. On the inner surface 6a of the lid 6, an annular portion 6c that protrudes in an annular shape is formed. The annular portion 6c is formed to have an inner peripheral surface that is continuous with the inner peripheral surface of the recess 6b. The inner ring 20 a of the second bearing 20 is sandwiched and fixed between the annular portion 40 a of the rod 40 and the annular portion 6 c of the lid 6. Thus, the second bearing 20 is supported by the gear case 3, and the central axis thereof is parallel to the central axis of the first bearing 10.

  The connecting member 30 connects the first annular portion 31 in which the first bearing 10 is accommodated, the second annular portion 32 in which the second bearing 20 is accommodated, and the first annular portion 31 and the second annular portion 32. And a connecting portion 33. The connecting member 30 is disposed in the gear case 3 with a gap between the outer peripheral surface thereof and the inner surface of the gear case 3.

  The outer ring 10 b of the first bearing 10 is fitted and provided on the inner peripheral surface of the first annular portion 31. The outer ring 20 b of the second bearing 20 is fitted and provided on the inner peripheral surface of the second annular portion 32. As described above, the connecting member 30 connects the outer ring 10b of the first bearing 10 and the outer ring 20b of the second bearing 20. Therefore, the connecting member 30 can rotate about the rod 40 as a central axis by the action of the second bearing 20. That is, the first bearing 10 held by the connecting member 30 can rotate around the rod 40 that is the central axis of the second bearing 20.

  As shown in FIG. 2, a flange portion 17 having a planar end surface 17 a is formed to protrude from the outer peripheral surface on the distal end side of the gear case 3. A through hole 13 is formed in the flange portion 17. The opening of the through hole 13 that opens to the inner peripheral surface of the gear case 3 is formed facing the outer peripheral surface 31 a of the first annular portion 31. A coil spring 12 as an urging member is accommodated in the through hole 13. The opening of the through hole 13 that opens to the end surface 17 a of the flange portion 17 is sealed with a bolt 14.

  The coil spring 12 is accommodated in the through hole 13 in a compressed state between the front end surface of the bolt 14 and the flat surface portion 31 b formed in a flat shape on the outer peripheral surface 31 a of the first annular portion 31. The biasing force of the coil spring 12 acts on the connecting member 30 via the first annular portion 31 and acts to rotate the connecting member 30 about the rod 40. Therefore, the first bearing 10 held by the connecting member 30 can move on the circular arc track centering on the rod 40 (on the two-dot chain line shown in FIG. 2). Accordingly, the worm shaft 2 is urged by the urging force of the coil spring 12 in a direction in which the gap between the tooth portion 2a and the tooth portion 1a of the worm wheel 1 is reduced, that is, in a direction in which backlash is reduced. Thus, the coil spring 12 biases the worm shaft 2 toward the worm wheel 1 by applying a biasing force to the first annular portion 31.

  The portion of the outer peripheral surface 31a of the first annular portion 31 that contacts the coil spring 12 is the flat portion 31b, so that the urging force of the coil spring 12 can be stably applied to the first annular portion 31.

  As shown in FIG. 1, the first annular portion 31 of the connecting member 30 is formed with an annular extending portion 34 that extends in the axial direction of the worm shaft 2. The extending part 34 has the same outer diameter as the outer diameter of the first annular part 31, and the inner diameter is smaller than the inner diameter of the first annular part 31. It is desirable to form a stepped portion 35 to which the first bearing 10 is locked at the boundary between the inner peripheral surfaces of the first annular portion 31 and the extending portion 34.

  An annular groove 34a is formed on the outer peripheral surface of the extending portion 34, and an O-ring 36 as an elastic member is accommodated in the annular groove 34a. When a load exceeding the biasing force of the coil spring 12 is input from the wheel side, the first bearing 10 moves on the circular arc track centering on the rod 40 with a strong force against the biasing force of the coil spring 12. At this time, since the O-ring 36 abuts against the inner surface of the gear case 3 and is compressed between the extending portion 34 and the inner surface of the gear case 3, the outer peripheral surface 31 a of the first annular portion 31 is urged against the inner surface of the gear case 3. It is prevented from hitting. Therefore, it is possible to reduce the occurrence of metal touch sound due to the contact between the first annular portion 31 and the inner surface of the gear case 3. The compression amount of the O-ring 36 is adjusted by the depth of the annular groove 34a. Instead of being accommodated in the annular groove 34a of the extended portion 34, the O-ring 36 may be formed in an annular groove on the outer peripheral surface of the first annular portion 31, and accommodated in the annular groove, or a gear case. You may make it fix to the inner peripheral surface of 3 with an adhesive material etc.

  As shown in FIG. 2, a convex portion 31 c is provided on the outer peripheral surface 31 a of the first annular portion 31. The convex portion 31 c is brought into contact with the inner surface of the gear case 3 when a load exceeding the urging force of the coil spring 12 is input from the wheel side and the first bearing 10 moves against the urging force of the coil spring 12. It is formed. Thus, the convex part 31c functions as a stopper that restricts the movement of the first bearing 10 beyond a predetermined distance. The moving distance of the first bearing 10 is set by the height of the convex portion 31c in the radial direction. The moving distance of the first bearing 10 is set so that transmission of power between the worm shaft 2 and the worm wheel 1 is maintained. Thus, when the first bearing 10 moves against the urging force of the coil spring 12, the convex portion 31c has a gap (backlash amount) between the tooth portion 1a of the worm wheel 1 and the tooth portion 2a of the worm shaft 2. ) Is properly maintained.

  Next, the operation of the non-backlash structure will be described.

  In a normal state, the first bearing 10 held by the connecting member 30 is urged toward the worm wheel 1 by the urging force of the coil spring 12, whereby the tooth portions 1 a of the worm shaft 2 and the worm wheel 1, There is no backlash of 2a.

  As the power steering device 100 is driven, wear of the worm shaft 2 and the tooth portions 1a and 2a of the worm wheel 1 proceeds. In this case, the first bearing 10 held by the connecting member 30 moves on the circular arc track (on the two-dot chain line shown in FIG. 2) centered on the rod 40 by the urging force of the coil spring 12. The backlash of the teeth 1a and 2a between the shaft 2 and the worm wheel 1 is reduced.

  According to the above embodiment, there exist the effects shown below.

  (1) Since the first bearing 10 moves on the circular arc track centering on the rod 40 that is the central axis of the second bearing 20, the first bearing 10 moves smoothly without generating friction with the gear case 3. Therefore, the backlash can be stably reduced by the biasing force of the coil spring 12.

  (2) Since there is no sliding surface that guides the movement of the first bearing 10 inside the gear case 3, the impact sound is caused by an increase in the clearance between the first bearing 10 and the sliding surface due to wear of the sliding surface. There is no possibility that the first bearing 10 will malfunction or that the first bearing 10 will malfunction due to stepped wear on the sliding surface.

  (3) Since there is no sliding surface inside the gear case 3, there is no possibility that abrasion powder is generated. Therefore, there is no possibility that rotation failure due to wear powder entering the inside of the first bearing 10 or abnormal wear due to wear powder entering the worm reduction gear.

  (4) Since the first bearing 10 moves on the circular arc track centering on the rod 40 that is the central axis of the second bearing 20, the tip side of the worm shaft 2 has a small inter-axis distance with respect to the worm wheel 1. The worm wheel 1 also moves in the axial direction while moving in this direction. Therefore, the advance angle of the worm shaft 2 with respect to the advance angle of the worm wheel 1 is increased, and the reduction gear efficiency is improved. Therefore, it is possible to reduce the backlash and improve the speed reducer efficiency.

Second Embodiment
A power steering apparatus 200 according to a second embodiment of the present invention will be described with reference to FIGS. Below, it demonstrates centering on a different point from the said 1st Embodiment. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The power steering apparatus 200 is different from that of the power steering apparatus 100 according to the first embodiment in the non-backlash structure. Hereinafter, a non-backlash structure in the power steering apparatus 200 will be described.

  A protruding portion 3 c that protrudes in the radial direction of the worm shaft 2 is formed on the distal end side of the gear case 3. A circular opening 3 b is formed at the tip of the gear case 3. The gear case 3 has a lid 6 that seals the opening 3b. The lid 6 is fastened to the gear case 3 with bolts. An O-ring 8 that seals between the gear case 3 and the lid 6 is interposed. A space 3 d extending in a direction perpendicular to the axial direction of the worm shaft 2 is formed inside the gear case 3.

  The front end side of the worm shaft 2 is rotatably supported by the first bearing 10. The first bearing 10 includes an annular inner ring 10a and an outer ring 10b, and a ball 10c as a rolling element interposed between the inner ring 10a and the outer ring 10b so as to roll freely. The inner ring 10 a of the first bearing 10 is provided by being fitted to the outer peripheral surface of the tip portion of the worm shaft 2.

  The second bearing 20 connected to the first bearing 10 via the connecting member 50 is accommodated in the space 3 d of the gear case 3. The second bearing 20 includes an annular inner ring 20a and an outer ring 20b, and a ball 20c as a rolling element interposed between the inner ring 20a and the outer ring 20b so as to freely roll. The outer ring 20b of the second bearing 20 is fitted between the inner peripheral surface of the gear case 3 and between the step 3g formed in the opening 3b of the gear case 3 and the step 6d formed in the opening of the lid 6. It is clamped by and fixed. As described above, the second bearing 20 is supported by the gear case 3, and the central axis X (see FIG. 4) thereof is parallel to the central axis of the first bearing 10.

  The connecting member 50 is a disk-shaped member and has a circular through hole 50 a that houses the first bearing 10. The through hole 50a is not concentric with the central axis X of the second bearing 20, but is formed eccentrically from the central axis X.

  An inner ring 20 a of the second bearing 20 is fitted and provided on the outer peripheral surface of the connecting member 50. Therefore, the connecting member 50 can rotate around the central axis X in the second bearing 20. It is desirable to form an annular protrusion 50b on the outer peripheral surface of the connecting member 50, with which the inner ring 20a of the second bearing 20 is locked.

  The outer ring 20b of the first bearing 10 is fitted and provided on the inner peripheral surface of the through hole 50a. Thus, the first bearing 10 is disposed inside the inner ring 20a of the second bearing 20, and the connecting member 50 connects the outer ring 10b of the first bearing 10 and the inner ring 20a of the second bearing 20. Therefore, the connecting member 50 can rotate about the central axis X of the second bearing 20 by the action of the second bearing 20. That is, the first bearing 10 held by the connecting member 50 can rotate about the central axis X of the second bearing 20.

  The connecting member 50 is formed with a plate-like protrusion 51 that protrudes in the axial direction of the worm shaft 2. As shown in FIG. 5, the coil spring 12 is accommodated in the through hole 13 in a compressed state between the tip surface of the bolt 14 and the protruding portion 51. The urging force of the coil spring 12 acts on the connecting member 50 via the protrusion 51 and acts to rotate the connecting member 50 about the central axis X. Therefore, the first bearing 10 held by the connecting member 50 can move on the circular arc track (on the two-dot chain line shown in FIGS. 4 and 5) centered on the central axis X of the second bearing 20. Thereby, the worm shaft 2 is moved in a direction in which the gap between the tooth portion 2a and the tooth portion 1a of the worm wheel 1 is reduced by the urging force of the coil spring 12, that is, in a direction in which backlash is reduced. As described above, the coil spring 12 biases the worm shaft 2 toward the worm wheel 1 by applying a biasing force to the protruding portion 51 of the connecting member 50.

  As shown in FIG. 5, the inner surface of the gear case 3 is provided with a rubber 55 as an elastic member at a position facing the protruding portion 51. The rubber 55 is fixed with an adhesive or the like. When a load exceeding the urging force of the coil spring 12 is input from the wheel side, the first bearing 10 vigorously resists the urging force of the coil spring 12 and has an arc centered on the central axis X of the second bearing 20. Move in orbit. At this time, the protruding portion 51 of the connecting member 50 abuts against the rubber 55 and the rubber 55 is compressed between the protruding portion 51 and the inner surface of the gear case 3, so that the protruding portion 51 strikes the inner surface of the gear case 3 vigorously. Is prevented. Therefore, it is possible to reduce the occurrence of a metal touch sound due to the contact between the protruding portion 51 and the inner surface of the gear case 3. The rubber 55 may be provided not on the inner surface of the gear case 3 but on the protruding portion 51.

  Next, the operation of the non-backlash structure will be described.

  In a normal state, the protrusion 51 of the connecting member 50 is biased by the biasing force of the coil spring 12, and the first bearing 10 held by the connecting member 50 is biased toward the worm wheel 1 side. There is no backlash between the teeth 1a, 2a of the worm shaft 2 and the worm wheel 1.

  As the power steering device 100 is driven, wear of the worm shaft 2 and the tooth portions 1a and 2a of the worm wheel 1 proceeds. In that case, the first bearing 10 held by the connecting member 50 is on an arcuate track centering on the central axis X of the second bearing 20 by the urging force of the coil spring 12 (two-dot chain shown in FIGS. 4 and 5). Therefore, the backlash of the tooth portions 1a and 2a between the worm shaft 2 and the worm wheel 1 is reduced.

  The second embodiment described above also has the same effect as the first embodiment.

  The embodiment of the present invention has been described above. However, the above embodiment only shows a part of application examples of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. Absent.

  For example, in the above embodiment, it has been described that the worm wheel 1 is provided on the steering shaft linked to the steering handle. However, instead of this configuration, the worm wheel 1 may be provided on a pinion shaft that is provided separately from the steering shaft and meshes with the rack shaft.

DESCRIPTION OF SYMBOLS 100 Power steering apparatus 1 Worm wheel 1a Tooth part 2 Worm shaft 2a Tooth part 3 Gear case 7 Electric motor 10 1st bearing 10a Inner ring 10b Outer ring 12 Coil spring (biasing member)
20 second bearing 20a inner ring 20b outer ring 30 connecting member 31 first annular part 32 second annular part 33 connecting part 34 extending part 36 O-ring (elastic member)
40 Rod 50 Connecting member 50a Through hole 51 Protruding portion 55 Rubber (elastic member)

Claims (9)

A power steering device for assisting a steering force applied to a steering wheel by a driver,
A worm shaft that rotates as the electric motor is driven;
A worm wheel that meshes with the worm shaft and transmits the rotational force of the electric motor to a rack shaft that steers the wheel;
A gear case that houses the worm shaft;
A first bearing that rotatably supports the tip side of the worm shaft;
A second bearing supported by the gear case and having a central axis parallel to the central axis of the first bearing;
A connecting member for connecting the first bearing and the second bearing;
A biasing member that biases the worm shaft toward the worm wheel,
The power steering device according to claim 1, wherein the first bearing is movable on a circular arc track centering on the central axis of the second bearing. A rod supported by the gear case;
Each of the first bearing and the second bearing includes an annular inner ring and an outer ring, and rolling elements interposed between the inner ring and the outer ring so as to freely roll.
The inner ring of the first bearing is provided to be fitted to the outer peripheral surface of the tip portion of the worm shaft,
The inner ring of the second bearing is provided to be fitted to the outer peripheral surface of the rod,
The connecting member connects the outer ring of the first bearing and the outer ring of the second bearing;
2. The power steering apparatus according to claim 1, wherein the first bearing is movable on a circular arc track centered on the rod. The connecting member includes an annular first annular portion in which the first bearing is accommodated, a second annular portion in which the second bearing is accommodated, and a coupling that connects the first annular portion and the second annular portion. And comprising
The outer ring of the first bearing is fitted to the inner circumferential surface of the first annular portion, and the outer ring of the second bearing is fitted to the inner circumferential surface of the second annular portion. The power steering device according to claim 2, wherein the power steering device is provided.   The power steering apparatus according to claim 3, wherein a biasing force of the biasing member acts on the first annular portion. The connecting member is formed with an extending portion extending in the axial direction of the worm shaft,
The outer surface of the extension portion or the inner surface of the gear case has an elasticity that is compressed between the extension portion and the gear case when the first bearing moves against the biasing force of the biasing member. The power steering apparatus according to claim 1, wherein a member is provided. Each of the first bearing and the second bearing includes an annular inner ring and an outer ring, and rolling elements interposed between the inner ring and the outer ring so as to freely roll.
The first bearing is disposed inside the inner ring of the second bearing,
The inner ring of the first bearing is provided to be fitted to the tip of the worm shaft,
The outer ring of the second bearing is provided to be fitted to the inner peripheral surface of the gear case,
The power steering apparatus according to claim 1, wherein the connecting member connects the outer ring of the first bearing and the inner ring of the second bearing. The connecting member is a disk-shaped member having a circular through hole that houses the first bearing,
On the outer peripheral surface of the connecting member, the inner ring of the second bearing is fitted and provided,
On the inner peripheral surface of the through hole, the outer ring of the first bearing is fitted and provided,
The power steering apparatus according to claim 6, wherein the through hole is formed eccentrically from a central axis of the second bearing. The connecting member is formed with a protruding portion protruding in the axial direction of the worm shaft,
The power steering apparatus according to claim 6 or 7, wherein the urging force of the urging member acts on the protruding portion.   An elastic member that is compressed between the protrusion and the gear case when the first bearing moves against the urging force of the urging member is provided on the inner surface of the protrusion or the gear case. The power steering apparatus according to claim 8.

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