JP2005212559A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce preload force, suppress friction, and keep good steering performance at the time of steering of a steering wheel, while effectively suppressing gear noise by increasing the preload force when a worm wheel rotates and oscillates by oscillation transmitted from a tire. <P>SOLUTION: A preload mechanism provided in the vicinity of an opposite motor side bearing 10 comprises an energizing member 13 fitted in a worm shaft 3, a ring-shaped elastic body 14 such as rubber integrally molded on the energizing member 13, and a metallic ring 15 covering the elastic body 14. The elastic body 14 changes its rigidity so that the rigidity is improved correspondingly when a frequency input in the worm shaft 3 becomes high, and so that the rigidity is lowered correspondingly when the frequency input in the worn shaft 3 becomes low. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus that generates an auxiliary steering torque from an electric motor in response to a steering torque applied to a steering wheel, decelerates the torque by a reduction gear, and transmits it to an output shaft of a steering mechanism.

  As an electric power steering device for a vehicle, the rotation output of an electric motor serving as an auxiliary steering torque is decelerated by a gear device and transmitted to the output shaft of the steering mechanism, and the steering force applied to the steering wheel is assisted to steer the wheel. What is comprised so that it may perform is known. In such an electric power steering apparatus, power is transmitted to the output shaft while reducing the rotation of the electric motor using a power transmission mechanism provided in the housing.

  In an electric power steering apparatus using a worm gear mechanism as the power transmission mechanism, backlash occurs between the tooth surfaces of the worm and the worm wheel, and thus a continuous gear hitting sound is generated from the meshing portion. There is such a thing.

  Conventionally, when a worm shaft and a worm wheel are assembled, backlash occurs at a relatively large rate after assembly due to dimensional errors of the worm, the worm shaft, a bearing portion that supports the worm shaft, a worm wheel, and a steering shaft that supports the worm shaft. Will occur. Therefore, it is necessary to assemble each component separately for each accuracy.

  In addition, when the output of the steering assist force is advanced as in recent years, the wear of both tooth surfaces of the worm and the worm wheel is increased, and the occurrence of backlash is unavoidable. In this case, rotational vibration is generated in the worm wheel due to vibration transmitted from the tire, and gear hitting sound due to backlash may leak into the vehicle compartment.

For this reason, in Patent Document 1, in order to prevent gear hitting sound, there is a method of urging the worm in the worm wheel direction (meshing direction) and preloading it by appropriate urging means to eliminate backlash. Are known.
JP 2000-43739 A

  However, applying preload to the meshing tooth surface may increase the friction and affect the steering performance such as the return of the steering wheel.

  In addition, if the preload is set small to reduce friction, the worm wheel is easily displaced by the rotational vibration of the worm wheel caused by the vibration transmitted from the tire, and the gap between the tooth surfaces becomes large. As a result, there is a possibility that the effect of reducing gear hitting sound may be reduced.

  The present invention has been made in view of the circumstances as described above, and when the worm wheel rotates and vibrates due to vibration transmitted from the tire, the preload is increased to effectively suppress the gear hitting sound. In the case of steering wheel steering or the like, an object is to provide an electric power steering device capable of maintaining good steering performance by reducing preload and suppressing friction.

In order to achieve the above object, an electric power steering apparatus according to claim 1 of the present invention generates auxiliary steering torque from an electric motor in response to a steering torque applied to a steering wheel, and decelerates by a reduction gear. In the electric power steering device that transmits to the output shaft of the steering mechanism
The drive gear shaft in the speed reducer is rotatably supported at substantially both ends by a motor side bearing on the side close to the electric motor and an anti-motor side bearing on the side away from the electric motor,
The drive gear shaft is supported by the motor-side bearing so as to be substantially swingable, and is supported by the anti-motor-side bearing so as to be displaceable in a substantially radial direction.
The anti-motor side bearing or the vicinity thereof includes elastic means for elastically biasing and preloading the drive gear shaft in the meshing direction of the driven gear,
The elastic means is characterized in that its rigidity changes corresponding to the frequency input to the drive gear shaft.

  In the electric power steering apparatus according to claim 2 of the present invention, the elastic means changes correspondingly to increase in rigidity when the frequency input to the drive gear shaft increases, while the drive means When the frequency input to the gear shaft is lowered, the rigidity changes correspondingly.

  In the electric power steering apparatus according to claim 3 of the present invention, the frequency input to the drive gear shaft is low with respect to the rigidity (α) of the elastic means when the frequency input to the drive gear shaft is high. The rigidity (β) ratio (α / β) of the elastic means is set to about 2 or more.

  The electric power steering apparatus according to a fourth aspect of the present invention is characterized in that the elastic means has a plurality of holes for adjusting the rigidity of the elastic means to be different depending on the radial direction.

  The electric power steering apparatus according to claim 5 of the present invention is characterized in that the elastic means has its cross-sectional shape changed along the axial direction in order to adjust the rigidity of the elastic means to be different depending on the radial direction.

  The electric power steering apparatus according to a sixth aspect of the present invention is characterized in that the elastic means changes its section modulus in order to adjust its rigidity so as to vary depending on the radial direction.

  As described above, according to the present invention, the anti-motor side bearing or its vicinity includes elastic means for elastically biasing and preloading the drive gear shaft in the meshing direction of the driven gear, The rigidity of the elastic means changes in accordance with the frequency input to the drive gear shaft. For example, the elastic means changes so that its rigidity increases correspondingly when the frequency input to the drive gear shaft increases, and correspondingly when the frequency input to the drive gear shaft decreases. , The stiffness has changed to be low. Therefore, when the worm wheel rotates and vibrates due to vibration transmitted from the tire, the preload is increased to effectively suppress the gear hitting sound, while in the case of steering wheel turning, the preload is decreased. The friction can be suppressed and the steering performance can be maintained well.

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

(Embodiment)
FIG. 1 is a longitudinal sectional view of an electric power steering apparatus according to an embodiment of the present invention. FIG. 2A is a cross-sectional view of the preload mechanism, and FIG. 2B is a vertical cross-sectional view of the preload mechanism. FIG. 3 is a graph showing the relationship between frequency and rigidity in the elastic body of the preload mechanism.

  As shown in FIG. 1, an output shaft 1 is connected to an input shaft (not shown) connected to a steering wheel (not shown) via a torsion bar (not shown) and the like, and a worm gear speed reduction is connected to the output shaft 1. The worm wheel 2 of the mechanism is fixed.

  The worm wheel 2 is engaged with a worm 3a, and the worm shaft 3 for the worm 3a has an opposite motor side bearing 10 on the side away from the electric motor 5 at both ends thereof, and the electric motor. The motor-side bearing 20 on the side close to 5 is rotatably supported.

  The housing 4 for the worm gear speed reduction mechanism is configured integrally with the electric motor 5, and the worm shaft 3 is spline-fitted with the drive shaft 6 of the electric motor 5. More specifically, the worm shaft 3 is provided with a female spline on the inner diameter of the end thereof, and at least one of the splines within the width of the motor-side bearing 20 and the male spline at the end of the drive shaft 6 of the electric motor 5. The inclination of the drive shaft 6 and the worm shaft 3 of the electric motor 5 can be allowed by the play between them.

  The non-motor side bearing 10 is fixed to the housing 4 via a holder 11, and a bush 12 is provided on the inner ring side thereof. The inner diameter of the bush 12 has a gap with the worm shaft 3. Thereby, the worm shaft 3 can be displaced in a substantially radial direction.

  The motor-side bearing 20 is compressed between its both end surfaces and a flange 22 integrally provided in the middle of the worm shaft 3 and a nut 23 fixed to the end of the worm shaft 3 with screws and caulking or a ring stopper. The worm shaft 3 is elastically supported through the pair of rubber dampers 21 and 21 so as to be concentric. As a result, the worm shaft 3 can move in the axial direction with respect to the motor-side bearing 20 within the elastic range of the rubber damper 21.

  Further, a minute gap is formed between the worm shaft 3 and the inner peripheral surface of the inner ring 20a of the motor side bearing 20 so that the worm shaft 3 can be tilted with respect to the inner ring 20a of the motor side bearing 20. As a result, the worm shaft 3 can reliably swing with respect to the inner ring 20 a of the motor-side bearing 20.

  In the present embodiment, as shown in FIGS. 1 and 2, the worm shaft 3 is biased in the vicinity of the non-motor side bearing 10 in the direction of meshing with the worm wheel 2 by the preload mechanism. is there.

  The preload mechanism includes an urging member 13 fitted to the end of the worm shaft 3, a ring-shaped elastic body 14 such as rubber integrally formed on the outer peripheral surface of the urging member 13, and the ring-shaped The metal ring 15 is integrally formed on the outer peripheral surface of the elastic body 14. The metal ring 15 is press-fitted into the housing 4.

  The urging member 13 on the inner diameter side is assembled eccentrically to the worm wheel 2 side with respect to the shaft center of the non-motor side bearing 10. Thereby, when the worm shaft 3 is assembled, the ring-shaped elastic body 14 is deformed to generate a pre-pressure (elastic urging force) that urges the worm wheel 2 in a direction of meshing with the worm wheel 2. it can.

  In the present embodiment, the rigidity of the ring-shaped elastic body 14 changes in accordance with the frequency input to the worm shaft 3.

  As shown in FIG. 3, the ring-shaped elastic body 14 changes so that its rigidity increases correspondingly when the frequency input to the worm shaft 3 is increased, while being input to the worm shaft 3. As the frequency decreases, the rigidity changes correspondingly. In addition, the two-dot chain line of FIG. 3 has shown the characteristic of the coil spring.

  When the worm wheel 2 rotates and vibrates due to vibration transmitted from the tire, the frequency input to the worm shaft 3 is relatively high, for example, 10 to 20 Hz. In this case, in the conventional case, the worm shaft 3 repeatedly repeats a slight displacement due to the reaction force from the worm wheel 2, and there is a possibility that gear hitting sound between the tooth surfaces is generated due to backlash.

  On the other hand, in the present embodiment, the elastic body 14 changes so as to increase the rigidity correspondingly when the frequency input to the worm shaft 3 is increased, so that the worm wheel 2 is rotationally vibrated. In this case, the elastic urging force can be increased, the preload can be increased, the backlash can be suppressed, and the gear hitting sound can be effectively and reliably suppressed.

  On the other hand, in the case of steering wheel steering or the like, if the preload is set to be large as in the prior art, there is a risk that friction will increase and affect steering performance such as return of the steering wheel.

  On the other hand, in the present embodiment, the elastic body 14 changes so as to have a correspondingly low rigidity when the frequency input to the worm shaft 3 is low. In this case, the elastic biasing force can be reduced, the preload can be reduced, the friction can be suppressed, and the steering performance can be maintained well.

  From the above, when the worm wheel 2 is rotationally vibrated by vibration transmitted from the tire, the preload is increased to effectively suppress the gear hitting sound, while in the case of steering wheel turning, the preload is reduced. The steering performance can be favorably maintained by reducing the friction and suppressing the friction.

  Preferably, as shown in FIG. 3, the elastic body 14 when the frequency input to the worm shaft 3 is low relative to the rigidity (α) of the elastic body 14 when the frequency input to the worm shaft 3 is high. The ratio (α / β) of the rigidity (β) is set to about 2. In addition, the dashed-two dotted line of FIG. 3 has shown the characteristic of the coil spring as mentioned above.

(Modification group of embodiment)
FIG. 4A is a cross-sectional view of a portion of the preload mechanism according to the first modification of the present embodiment, and FIG. 4B is a vertical cross-sectional view of the portion of the preload mechanism.

  FIG.4 (c) is related with the 2nd modification of this Embodiment, and is a cross-sectional view of the location of a preload mechanism, (d) is a longitudinal cross-sectional view of the location of the preload mechanism.

  FIG. 4E is a cross-sectional view of a portion of the preload mechanism according to a third modification of the present embodiment, and FIG. 4F is a vertical cross-sectional view of the portion of the preload mechanism.

  As is apparent from the drawings, these modified examples have basically the same structure as the above-described embodiment, and only different points will be described.

  4 (a) and 4 (b), the elastic body 14 has a plurality of holes 16 for adjusting the rigidity of the elastic body 14 to be different depending on the radial direction. These holes 16 may be collected, for example, on the substantially upper side and the substantially lower side of the worm shaft 3 (the biasing member 13) as shown in the figure. Thus, by changing the diameter and layout of the holes 16 as appropriate, the rigidity can be variously adjusted depending on the direction.

  4C and 4D, in the elastic body 14, the position of the urging member 13 and the position of the metal ring 15 press-fitted into the housing 4 are shifted in the axial direction. That is, an elastic biasing force is generated by the shearing and bending stress of the elastic body 14. That is, in order to adjust the rigidity of the elastic body 14 so as to vary depending on the radial direction, the cross-sectional shape is changed along the axial direction. The metal ring 15 is press-fitted into the housing 4 while the elastic body 14 is formed with a small diameter on the side opposite to the motor. Thus, by appropriately changing the cross-sectional shape along the axial direction, the rigidity can be variously adjusted depending on the direction.

  In the third modification example of FIGS. 4E and 4F, the elastic body 14 has its section modulus changed depending on the direction in order to adjust the rigidity of the elastic body 14 to be different depending on the radial direction. That is, the elastic body 14 has, for example, a pair of small diameter portions and a pair of large diameter portions as illustrated. In this way, by appropriately changing the section modulus, the rigidity can be variously adjusted depending on the direction.

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

1 is a longitudinal sectional view of an electric power steering device according to an embodiment of the present invention. (A) is a cross-sectional view of the preload mechanism, and (b) is a vertical cross-sectional view of the preload mechanism. It is a graph which shows the relationship between the frequency and rigidity in the elastic body of a preload mechanism. (A) is related with the 1st modification of this Embodiment, and is a cross-sectional view of the location of a preload mechanism, (b) is a longitudinal cross-sectional view of the location of the preload mechanism. (C) is a cross-sectional view of a portion of the preload mechanism according to the second modification of the present embodiment, and (d) is a vertical cross-sectional view of the portion of the preload mechanism. (E) is a cross-sectional view of a portion of the preload mechanism according to the third modification of the present embodiment, and (f) is a vertical cross-sectional view of the portion of the preload mechanism.

Explanation of symbols

1 Output shaft 2 Worm wheel (driven gear)
3 Worm shaft (drive gear shaft)
3a Worm (drive gear)
DESCRIPTION OF SYMBOLS 4 Housing 5 Electric motor 6 Drive shaft 10 Anti-motor side bearing 11 Holder 12 Bush 13 Energizing member 14 Elastic body 15 Metal ring 16 Hole 20 Motor side bearing 20a Inner ring 21 Rubber damper 22 Flange 23 Nut

Claims (6)

In the electric power steering device that generates auxiliary steering torque from the electric motor in response to the steering torque applied to the steering wheel, decelerates by the reducer, and transmits it to the output shaft of the steering mechanism.
The drive gear shaft in the speed reducer is rotatably supported at substantially both ends by a motor side bearing on the side close to the electric motor and an anti-motor side bearing on the side away from the electric motor,
The drive gear shaft is supported by the motor side bearing so as to be substantially swingable, and is supported by the anti-motor side bearing so as to be displaceable in a substantially radial direction.
The anti-motor side bearing or the vicinity thereof includes elastic means for elastically biasing and preloading the drive gear shaft in the meshing direction of the driven gear,
The electric power steering apparatus according to claim 1, wherein the elasticity of the elastic means changes in accordance with a frequency input to the drive gear shaft.   The elastic means changes correspondingly when the frequency input to the drive gear shaft increases, and the rigidity changes correspondingly when the frequency input to the drive gear shaft decreases. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus changes so as to reduce its rigidity.   Ratio (α / β) of the rigidity (β) of the elastic means when the frequency input to the drive gear shaft is low to the rigidity (α) of the elastic means when the frequency input to the drive gear shaft is high The electric power steering apparatus according to claim 2, wherein the electric power steering apparatus is set to about 2 or more.   The electric power steering apparatus according to any one of claims 1 to 3, wherein the elastic means has a plurality of holes for adjusting the rigidity thereof to be different depending on the radial direction.   The electric power according to any one of claims 1 to 3, wherein the elastic means has a cross-sectional shape changed along the axial direction in order to adjust the rigidity of the elastic means so as to vary depending on the radial direction. Steering device.   The electric power steering apparatus according to any one of claims 1 to 3, wherein the elastic means changes its section modulus in order to adjust its rigidity so as to vary depending on a radial direction.

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