JP2012071815A - Electric power steering system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering system that achieves an improvement in durability of a worm and a worm wheel even if having a structure in which a worm shaft with the worm is pressed by using a biasing means so as to reduce the distance between the rotation centers of the worm and the worm wheel.SOLUTION: The electric power steering system includes: an elastic body 11b that is arranged so as to be in contact with the inner periphery of an inner ring 6a of a rolling bearing 6 on the side of a motor 1 and is expandable in the axial-length direction by force in the axial-length direction applied to a worm 3; and circular rings 11a, 11c that are held by the worm or the inner ring so as to be in contact with both ends of the inner ring and restrict the radial movement of the worm.

Description

  The present invention relates to an electric power steering apparatus using a motor as a generation source of steering assist force.

  The electric power steering apparatus for a vehicle includes a motor for assisting steering and a reduction gear mechanism that transmits a rotational force of the motor to the steering means, and the operation of the steering means according to the rotation of the steering means is performed by the rotation of the motor. It is configured to assist and reduce the labor burden of the driver for steering.

The reduction gear mechanism includes a worm as a worm interlocking with the rotation of the motor and a worm wheel as a worm wheel meshing with the worm.
In the electric power steering apparatus using the reduction gear mechanism in this way, in order to reduce the backlash amount of the meshing portion of the worm and the worm wheel, and eliminate the rattling noise caused by the backlash at the time of turning, The worm, the worm wheel, the bearing, the housing, and the like are selected and assembled so that the distance between the rotation centers of the worm wheel is within an allowable range, but this assembly takes a lot of time. Therefore, a structure incorporating an adjustment mechanism is used. (Patent Document 1)

  As an adjustment mechanism, a certain amount of internal clearance is provided in the motor side bearing of the worm shaft, and the non-motor side bearing is pressed against the worm wheel side by a spring as a movable center. In order to move the worm shaft, it is necessary to provide a certain amount of internal backlash in the motor-side bearing. If the backlash is too small, the rigidity becomes high and the spring load of the non-motor-side bearing is overcome and the worm cannot be operated. If the backlash is too large, noise inside the bearing will be generated. Therefore, the internal clearance of the motor side bearing is produced under extremely strict dimensional control.

Japanese Patent No. 39951913

However, in the conventional electric power steering device configured to reduce the amount of backlash by using the adjustment mechanism as described above, the use condition becomes severe due to weight reduction and miniaturization, and practical use in large vehicles. In this case, since the load becomes large, a large load and rotational torque are applied to the adjustment mechanism in the radial direction every time the vehicle is steered. Therefore, there is a problem that the worm wheel tooth surface is liable to deteriorate such as sag and wear. . Further, it is necessary to set an increase in the preload by this pressing, but this degree of freedom is relatively low.
The present invention has been made in view of such circumstances, and a main object of the present invention is to provide a worm provided with a worm using an urging means so that the distance between the rotation centers of the worm and the worm wheel is shortened in order to reduce the amount of backlash. An object of the present invention is to provide an electric power steering device capable of improving the durability of a worm and a worm wheel even when the shaft is pressed.

  In order to solve the above-mentioned problems, the invention according to claim 1 is directed to a worm coupled to the output shaft of a motor, a rolling bearing that rotatably supports the worm, meshed with the worm, and used as a steering means. The connected worm wheel, a bearing that supports the worm on the non-motor side so that the distance between the rotation centers of the worm and the worm wheel is long and short, and the bearing is biased in the direction that the distance between the rotation centers is short Means for assisting steering by rotation of the motor, and arranged in contact with the inner periphery of the inner ring of the motor-side rolling bearing, the axial force applied to the worm An elastic body that can be extended in the axial length direction by the worm, and the worm or the inner ring held in the radial direction so as to contact both ends of the inner ring. Is summarized in that that a ring for limiting the movement of the.

  That is, according to the electric power steering device of the first aspect, when the tooth surfaces of the worm and the worm wheel are in contact with each other, the elastic body is deformed, so that the rotation shaft is made to the housing. Since it is designed to move in at least one of the axial direction and the radial direction, it can cope with a large backlash than before, and the elastic body is also resistant to vibrations transmitted from the wheels and from the motor. It is possible to alleviate the collision between tooth surfaces against the transmitted vibration, thereby reducing the tapping sound of the tooth surfaces.

  The gist of the invention described in claim 2 is that the elastic body and the ring are integrally formed. In other words, since the elastic body is integrally formed with the annular ring, it has strength against the load applied to the bearing, and it is easy to assemble with high precision to the bearing, and it is difficult to cause axial displacement and protrusion, and has long-term performance. Can be maintained.

  The gist of the invention described in claim 3 is that the elastic body has a cylindrical portion and an annular convex portion that protrudes in the radial direction of the worm on the outer periphery of the cylindrical portion. That is, since an extreme deformation is not caused when an excessive load is applied to the bearing, the elastic body and the bearing are hardly damaged.

  The gist of the invention described in claim 4 is that an annular body is provided between the inner periphery of the elastic body and the worm. That is, since the elastic body is integrally formed with the worm side ring, it can be assembled to the worm with high accuracy, and it is difficult to cause axial displacement and protrusion, and the performance can be maintained for a long time.

  According to these inventions, the durability of the worm and the worm wheel can be improved even when the worm is pressed using the urging means so that the distance between the rotation centers of the worm and the worm wheel is shortened.

The expanded sectional view which shows the structure of the reduction gear mechanism part of the electric power steering apparatus which concerns on this invention. 1 is a cross-sectional view showing an overall configuration of an electric power steering apparatus according to the present invention. The expanded sectional view of the movement control object of the electric power steering device concerning the present invention. The perspective view which shows the structure of the curved leaf | plate spring of the electric power steering apparatus which concerns on this invention. Sectional drawing of the main components of the electric power steering apparatus which concerns on this invention.

Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof.
FIG. 1 is an enlarged cross-sectional view showing a configuration of a reduction gear mechanism portion of an electric power steering device according to the present invention, and FIG. 2 is a cross-sectional view showing an overall configuration of the electric power steering device.

  The electric power steering apparatus includes a steering assist motor 1, a worm 3 as a worm joined to an output shaft 1 a of the motor 1 via a shaft joint 2, and a worm wheel as a worm wheel meshing with the worm 3. 4 and a steering means 5 connected to the reduction gear mechanism A.

  The steering means 5 has one end connected to the steering wheel B for steering and a first steering shaft 51 having a cylindrical portion 51a at the other end, and is inserted into the cylindrical portion 51a, and one end thereof is the first. A torsion bar 52 that is twisted by the action of a steering torque applied to the steered wheel B, and the other end of the torsion bar 52 are connected to the other end of the torsion bar 52. The second steering shaft 53 is connected to, for example, a rack and pinion type steering mechanism (not shown) via a universal joint.

  The worm 3 of the reduction gear mechanism A has shaft portions 3 a and 3 b at both ends, and the shaft portion 3 a at one end is rotatably supported by an aluminum support member 7 via a first rolling bearing 6. Thus, the output shaft 1 a of the motor 1 is joined, and the shaft portion 3 b at the other end is supported by the support member 7 via the second rolling bearing 8. The shaft portions 3a, 3b are press-fitted with rolling bearings 6, 8 in 6a, 8a. The worm wheel 4 includes an annular tooth body 41 made of synthetic resin and a metal core member 42 coupled to the inside of the annular tooth body 41, and the core member 42 is fitted in the middle of the second steering shaft 53. It is fixed.

  The support member 7 accommodates the worm 3, the first accommodating portion 7 a that rotatably supports the shaft portions 3 a and 3 b of the worm 3 via the rolling bearings 6 and 8, and the worm wheel 4. It has the 2nd accommodating part 7b which supported the wheel 4 via the 2nd steering shaft 53 and the two rolling bearings 9 and 10 fitted by this 2nd steering shaft 53. As shown in FIG.

  The first accommodating portion 7a is elongated in the axial length direction of the worm 3, and at one end portion in the longitudinal direction, a support hole 71 for supporting the rolling bearing 6 by loose fitting, an annular groove 72 connected to the support hole 71, and a motor. A mounting portion 73 is provided, and a retaining ring 14 for restricting movement of the rolling bearing 6 in the axial length direction by contacting the outer ring 6 b of the rolling bearing 6 is fitted in the annular groove 72.

  The rolling bearing 6 that supports the shaft 3a at one end includes an inner ring 6a and an outer ring 6b, and a plurality of rolling elements 6c interposed between the inner ring 6a and the outer ring 6b.

  A movement restraining body 11 as a ring of the present invention that restrains the movement of the worm 3 in the axial length direction is fitted and held on the shaft portion 3b of the worm 3 rotatably supported by the rolling bearings 6 and 8. ing. The movement restraining body 11 has an outer peripheral surface of a metal inner ring 11a fitted to the outer peripheral surface of the worm shaft and a larger diameter than the inner annular ring 11a, and is fitted to the inner ring 6a of the rolling bearing 6. The elastic body 11b is integrally provided on the inner peripheral surface of the metal outer ring 11c to be joined by a coupling means such as vulcanization adhesion.

The inner ring 11a is press-fitted into the shaft portion 3a and is fixed to the coupling 22 fixed to the shaft portion 3a with screws in the axial direction.
At the same time, the outer ring 11c has a gap in the axial direction with the shaft 3c and the coupling end surface 22a together with the end face of the bearing inner ring 6a, and restricts the movement of the worm shaft 3 in the axial direction.

  A radially projecting portion 11d is provided at the center of the inner diameter portion of the outer annular ring 11c to restrict radial movement with respect to the inner annular ring 11a. The protrusion 11d limits the movement in the radial direction and protects the elastic body from a large load, thereby making the elastic body 11b durable.

  A support hole 74 that supports the second rolling bearing 8 and the curved leaf spring 12 that is externally fitted to the rolling bearing 8 is provided at the other end of the first housing portion 7a. The support hole 74 has a radial dimension of the first side portion 74a in which the distance H between the rotation centers of the worm 3 and the worm wheel 4 is longer than a center thereof than a radial dimension of the second side portion 74b in which the distance H between the rotation centers is reduced. The curved leaf spring 12 can be bent between the circumferential surface of the first side portion 74a and the rolling bearing 8, and the distance H between the rotation centers is long and short. There is a gap that can be moved in this direction. Further, a recess 74c for receiving the end portions 12a, 12b of the curved leaf spring 12 is provided in the circumferential center portion of the circumferential surface of the first side portion 74a.

  3 is an enlarged cross-sectional view taken along the line II of FIG. 1, and FIG. 4 is a perspective view showing the configuration of the curved leaf spring. The curved leaf spring 12 is made of a belt-shaped spring steel that is curved in a substantially circular shape along the outer peripheral surface of the rolling bearing 8 in the middle of its longitudinal direction and has a length longer than the circumferential length of the rolling bearing 8. One end 12a has a notch recess 12c at the center in the width direction, and the other end 12b has notch recesses 12d and 12d on both sides in the width direction. The end portions 12a and 12b are intersected without being widened by inserting the end portion 12a or 12b on the side, and the end portions 12a and 12b cross the outer peripheral surface of the rolling bearing 8, in other words, the curved portion 12e. I try to isolate it. Ends 12a and 12b of the curved leaf spring 12 are inserted into the recess 74c and bent in the recess 74c, thereby biasing the worm 3 via the rolling bearing 8 in a direction in which the distance H between the rotation centers is shortened. is doing.

  A plurality of springs that abut against the side surface 74d of the support hole 74 and press the second rolling bearing 8 toward the motor 1 at a position separated in the longitudinal direction on one side in the width direction of the curved portion 12e of the curved leaf spring 12. The piece 12f is integrally formed. The spring piece 12f is provided so as to incline inward with respect to the peripheral surface of the curved portion 12e. The spring piece 12f is bent by contacting the side surface 74d of the support hole 74, and the reaction force of the elastic restoring force is the second force. In addition to the outer ring 8b of the rolling bearing 8, the worm 3 is pressed toward the motor 1 from the outer ring 8b through the rolling elements and the inner ring 8a.

  In addition, a torque sensor 13 for detecting a steering torque applied to the steered wheels B by a relative rotational displacement amount of the steering shafts 51 and 53 according to the twist of the torsion bar 52 is built in the support member 7. The motor 1 is configured to be driven and controlled based on the torque detected by 13.

  In the electric power steering apparatus configured as described above, when the worm 3 is assembled, the curved leaf spring 12 is inserted into the support hole 74 of the support member 7, and the end portions 12a and 12b of the curved leaf spring 12 are inserted into the recess 74c. To set the position of the curved leaf spring 12, in other words, the urging direction of the rolling bearing 8 by the ends 12a, 12b. Then, the worm 3 in which the rolling bearings 6 and 8 are press-fitted into the shaft portions 3a and 3b is inserted into the first housing portion 7a, the second rolling bearing 8 is inserted inside the curved leaf spring 12, and the first rolling is performed. The bearing 6 is loosely fitted into the support hole 71 and the retaining ring 14 is fitted into the annular groove 72 to restrict the movement of the worm 3 in the axial length direction.

  End portions 12a and 12b of the curved leaf spring 12 for urging the incorporated worm 3 are inserted into the recesses 74c of the support member 7, and the rolling bearing 8 and the rolling bearing 8 are formed by bending of the end portions 12a and 12b. Since the supported worm 3 is urged in the direction in which the distance H between the rotation centers becomes shorter (the direction of the worm wheel), the backlash amount of the meshing portion of the worm 3 and the worm wheel 4 can be reduced, Even when the wear amount of the teeth of the worm 3 and the worm wheel 4 increases, the backlash amount of the meshing portion can be reduced.

  Further, the curved leaf spring 12 is curved along the outer peripheral surface of the rolling bearing 8, and the gap between the curved leaf spring 12 and the rolling bearing 8 and the second side portion 74 b of the support hole 74 may be eliminated. Therefore, it is possible to limit the movement of the worm 3 in the direction intersecting with the direction in which the distance H between the rotation centers becomes longer or shorter. That is, when the worm 3 to the worm wheel 4 are twisted in the rotation direction with respect to the rotation center line, and when a rotational torque is applied from the worm 3 to the worm wheel 4, in other words, when the steering assist is performed by the rotation of the motor 1. A component force (hereinafter referred to as a meshing reaction force) is generated so that the worm 3 moves in the radial direction along the teeth of the worm wheel 4. The worm 3 is pressed in the radial direction by the meshing reaction force, and the second rolling bearing 8 is pressed in a direction intersecting with the direction in which the distance between the rotation centers becomes longer or shorter by the pressing force. It is a structure that can restrict the movement of the rolling bearing 8 due to this pressing, and consequently the movement of the worm 3.

  As described above, the worm 3 biased by the curved leaf spring 12 swings in the direction in which the distance H between the rotation centers becomes longer or shorter around the support portion to the first rolling bearing 6. Since the first rolling bearing 6 is fitted to the movement suppressing body 14 and loosely fitted to the support hole 71, the worm 3 can be swung together with the second rolling bearing 8, and the worm 3 is elastic. Since it is joined to the output shaft 1a via the shaft coupling 2 having the tooth bodies 23, the swing allowable amount of the worm 3 can be increased. Therefore, even when the temperature rise of the worm wheel 4 having the synthetic resin annular tooth body 41 and the amount of expansion due to moisture absorption increase, the increase in the meshing resistance of the meshing portion can be suppressed, and the worm 3 and the worm wheel 4 can be made smooth. Can be rotated.

  The worm 3 is pressed toward the non-motor side by the shaft coupling 2 having the first and second joints 21 and 22 and the elastic tooth body 23 interposed between the joints 21 and 22. Since it is pressed to the motor 1 side by the spring piece 12f of the curved leaf spring 12, the axial force applied to the worm 3 can be balanced, and the rotation of the worm 3 can be improved.

Further, since the worm 3 is coupled to the output shaft 1 a by the shaft coupling 2 having the elastic tooth body 23, the propagation of the sound generated on the motor 1 side to the worm 3 can be blocked by the elastic tooth body 23. At the same time, it is possible to eliminate noise from the shaft joint.
Further, since the rolling bearing 6 is fixed to the housing by the elastic body 11b and the retaining ring 14 of the movement suppressing body 11, the component force that moves in the radial direction and the axial direction of the worm 3 can be absorbed. The collision between the tooth surfaces of the wheel 4 can be mitigated, thereby reducing the tapping sound of the tooth surfaces. For this reason, the workability of assembling the rolling bearing can be improved as compared with the case where the rolling bearing is fixed using a screw ring.

  DESCRIPTION OF SYMBOLS 1 Motor, 1a Output shaft, 2 shaft coupling (pressing means pressure), 3 worm, 4 worm wheel, 5 steering means, 7 support member, 6, 8 rolling bearing (bearing) 12 curved leaf spring (biasing means), 12f Spring piece, 12g Contact part, 12h Bend part, 11 Movement suppression body, 11a Inner ring, 11b Elastic body, 11c Outer ring, H Distance between rotation centers

Claims (4)

  A worm that is interlocked with the output shaft of the motor, a rolling bearing that rotatably supports the worm, a worm wheel that meshes with the worm and that is connected to the steering means, and the worm and the worm wheel on the side opposite to the motor. A bearing that is movably supported in a direction in which the distance between the rotation centers becomes longer and shorter, and an urging means for the bearing in a direction in which the distance between the rotation centers becomes shorter, and assists steering by the rotation of the motor. In the electric power steering apparatus, an elastic body disposed so as to be in contact with an inner circumference of the inner ring of the motor side rolling bearing and capable of extending in an axial length direction by a force in an axial length direction applied to the worm, and both ends of the inner ring And an annular ring that is held by the worm or the inner ring so as to be in contact with the worm and restricts the movement of the worm in the radial direction. That the electric power steering system.   2. The electric power steering apparatus according to claim 1, wherein the elastic body and the annular ring are integrally formed.   3. The electric power steering apparatus according to claim 1, wherein the elastic body has a cylindrical portion and an annular convex portion that protrudes in a radial direction of the worm on an outer periphery of the cylindrical portion.   The electric power steering apparatus according to any one of claims 1 to 3, further comprising a ring body between an inner periphery of the elastic body and the worm.