JP3770310B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus using an electric motor as a generation source of steering assist force.
[0002]
[Prior art]
As an electric steering apparatus for an automobile, there is an apparatus provided with a first steering shaft connected to a steering wheel, and a second steering shaft connected to the first steering shaft via a torsion bar and connected to a steering mechanism. . In this apparatus, the relative displacement amount in the rotation direction of the first and second steering shafts is detected by a torque sensor, and the rotation of the electric motor is controlled by the second steering shaft via the speed reduction mechanism based on the detection result of the torque sensor. Thus, the operation of the steering mechanism according to the rotation of the steering wheel is assisted by the rotation of the electric motor, so that the burden on the driver for steering is reduced.
[0003]
As the speed reduction mechanism, a mechanism having a worm and a worm wheel is provided. The worm shaft provided with the worm and the second steering shaft provided with the worm wheel are supported at both ends in the axial length direction by bearings to prevent movement in the radial direction and the axial length direction.
When the worm shaft and worm wheel are assembled, adjustment is made so that an appropriate backlash exists between the worm and the worm wheel within the range of machining accuracy. If this increases, the backlash increases and becomes excessive, which causes noise.
[0004]
Therefore, for example, as disclosed in Japanese Patent Application Laid-Open No. 2000-43739, the worm shaft can be biased toward the worm wheel, and the worm shaft is biased in the radial direction that is the biasing direction by the biasing means, thereby increasing backlash. It has been proposed to suppress this.
[0005]
[Problems to be solved by the invention]
However, there is a problem that the apparatus becomes large because the biasing means and the member for adjusting the biasing force of the biasing means must be arranged along the radial direction of the worm shaft.
The present invention has been made in view of the above problems, and an object of the present invention is to provide an electric power steering apparatus that is small in size and can suppress an increase in backlash and generation of noise associated therewith.
[0006]
[Means for Solving the Problems]
To achieve the above objective,
The invention according to claim 1 is an electric power steering apparatus that transmits rotation of a steering assisting electric motor driven according to torque applied to a steering shaft to a steering mechanism via a worm shaft and a worm wheel. An urging member that urges the worm shaft in the axial direction; and a cam mechanism that converts at least a part of the urging force of the urging member into a force that urges the worm shaft toward the radial worm wheel, The worm shaft is held by the housing via a cam mechanism so as to be biased toward the radial worm wheel.
[0007]
In the present invention, even if a dimensional error between the parts increases due to wear of the teeth of the worm shaft and the worm wheel, this can be absorbed by biasing the worm shaft toward the worm wheel. Therefore, an increase in backlash can be suppressed. Moreover, since the urging member can be laid out along the axial direction of the worm shaft, the electric power steering apparatus can be reduced in size.
The invention described in claim 2 is characterized in that in claim 1, an adjusting member for adjusting the biasing force of the biasing member is further provided. In the present invention, when the urging member is incorporated for assembling the electric power steering apparatus, the urging force of the urging member is adjusted by the adjusting member without being affected by the dimensional error of each component. The backlash can be adjusted. After the adjustment and incorporation, the function of automatically suppressing the increase in backlash is ensured, so that it is not particularly necessary to operate the adjustment member.
[0008]
According to a third aspect of the present invention, in the first or second aspect, the cam mechanism includes first and second cam members each having a cam surface engaged with each other, and the first cam member is interposed via a bearing. the worm shaft is capable biased to rotatably support and radial worm wheel side of the worm shaft along with且one bearings Te, the second cam member is allowed displacement of only axial worm shaft into the supporting hole of the housing It is characterized by being supported in a state where In the present invention, for example, if the backlash between the worm wheel and the worm shaft is increased due to a change over time such as the occurrence of wear, the first cam member is displaced toward the worm shaft, so that the second cam member is Displacement toward the worm wheel side along with the worm shaft can prevent the increase in the backlash.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus according to an embodiment of the present invention. Referring to FIG. 1, an electric power steering apparatus 1 includes a steering shaft (steering shaft) 3 connected to a steering wheel (steering wheel) 2, and a pinion gear 4 provided at the tip of the steering shaft 3. The rack gear 5 meshes with the pinion gear 4 and the rack shaft 6 extends in the left-right direction of the vehicle.
[0010]
Tie rods 7 are coupled to both ends of the rack shaft 6, and each tie rod 7 is connected to a corresponding wheel 8 via a corresponding knuckle arm. When the steering wheel 2 is operated and the steering shaft 3 is rotated, this rotation is converted by the pinion gear 4 and the rack gear 5 into a linear motion of the rack shaft 6 along the left-right direction of the vehicle. Thereby, steering of the wheel 8 is achieved.
The steering shaft 3 is divided into a cylindrical first steering shaft 9 connected to the steering wheel 2 and a second steering shaft 10 connected to the pinion gear 4. These first and second steering shafts 10 are torsional. The bars 11 are connected to each other on the same axis.
[0011]
A torque sensor 12 is provided for detecting a steering torque based on a relative rotational displacement amount between the first steering shaft 9 and the second steering shaft 10 via the torsion bar 11, and the torque detection result of the torque sensor 12 is a control unit. 13 is given. The control unit 13 controls the voltage applied to the steering assisting electric motor 15 via the driver 14 based on the torque detection result. The rotation of the motor shaft 16 (see FIG. 2) of the electric motor 15 is transmitted to the second steering shaft 10 via a speed reduction mechanism 17 including a worm mechanism, and steering is assisted.
[0012]
Referring to FIG. 2, the speed reduction mechanism 17 includes a worm shaft 18 and a worm wheel 19 that mesh with each other. The worm shaft 18 is connected to the motor shaft 16 of the electric motor 15, and worm teeth 20 are integrally formed in the middle in the axial direction. The worm wheel 19 is engaged with the second steering shaft 10 so as to be integrally rotatable.
The worm shaft 18 is disposed so as to intersect the axis of the second steering shaft 10. The worm shaft 18 has first and second ends 21 and 22 that face each other in the axial direction. The first end 21 is rotatably supported in a bearing hole 25 of the gear housing 24 via a first bearing 23 using a ball bearing.
[0013]
One end of the outer ring 26 of the first bearing 23 is abutted against the positioning step 27 of the gear housing 24 and positioned. On the other hand, an elastic member 29 made of, for example, a rubber plate is interposed between the other end portion (end portion on the motor shaft side) of the outer ring 26 and the end surface of the positioning screw 28. Reference numeral 49 denotes a lock nut for fixing the positioning screw 28. The outer ring 26 is normally pressed against the positioning step portion 27 by the relatively strong elastic repulsive force of the elastic member 29. One end of the inner ring 30 of the first bearing 23 is engaged with the positioning step 31 of the worm shaft 18. The first end 21 of the worm shaft 18 is connected to the end of the motor shaft 16 via a power transmission joint 32.
[0014]
The worm shaft 18 can be biased toward the worm wheel 19, and a backlash adjusting mechanism 33 is provided so that an increase in backlash between the worm shaft 18 and the worm wheel 19 can be suppressed.
Specifically, the second bearing 34 that supports the second end 22 of the worm shaft 18 can be biased toward the worm wheel 19. A space 35 that accommodates the worm shaft 18 in the gear housing 24 is open to the outside through a housing hole 36 that extends along the extending direction of the second end 22 of the worm shaft 18. Most of the backlash adjusting mechanism 33 is accommodated in the accommodation hole 36.
[0015]
The backlash adjustment mechanism 33 includes a cam mechanism 39 including first and second cam members 37, 38, an adjustment screw 41 as an adjustment member screwed into a screw portion 40 formed at the inlet of the accommodation hole 36, and an adjustment screw 41, and a biasing member 42 made of, for example, a compression coil spring, which is interposed between the second cam member 38 and elastically biases the second cam member 38 in the axial direction of the worm shaft 18. . Reference numeral 43 denotes a lock nut for fixing the adjustment screw 41.
[0016]
Referring to FIG. 2 and FIG. 3 which is an enlarged view, the first and second cam members 37 and 38 are cams inclined at a predetermined angle (for example, 45 °) with respect to the axial length direction of the worm shaft 18. Surfaces 44 and 45 are formed, and these cam surfaces 44 and 45 are slidably engaged with each other. The cam surfaces 44 and 45 are provided with an engagement structure 50 for stopping mutual relative rotation and ensuring mutual sliding. As the engagement structure, a structure in which a protrusion formed on one of the cam surfaces 44 and 45 is fitted to a recess formed on the other is conceivable.
[0017]
The first cam member 37 rotatably supports the second end portion 22 of the worm shaft 18 via the second bearing 34 and moves together with the second bearing 34 in the radial direction of the worm shaft 18, that is, toward the worm wheel side. It can be biased. In order to realize this, a predetermined amount of gap is secured between the first cam member 37 and the inner surface of the space 35 that accommodates the first cam member 37. Referring to FIG. 3, the first cam member 37 is in contact with the outer peripheral surface of the outer ring 51 of the second bearing 34 and the end surface of the outer ring 51 on the adjustment screw 41 side, and holds the outer ring 51. The end face of the inner ring 52 of the second bearing 34 on the counter adjustment screw 41 side is in contact with the step formed on the second end 22 of the worm shaft 18 and positioned.
[0018]
On the other hand, the second cam member 38 accommodated in the accommodation hole 36 is prevented from rotating around the axis of the worm shaft 18 and is only allowed to move in the axial length direction of the worm shaft 18. In order to realize this, an engagement structure 46 is provided between the outer peripheral surface of the second cam member 38 and the inner peripheral surface of the accommodation hole 36. The engaging structure 46 is formed on one of the outer peripheral surface of the second cam member 38 and the inner peripheral surface of the accommodation hole 36, and is formed on the other side with a ridge extending parallel to the axial direction of the worm shaft 18. And a concave line that engages with the convex line. A plurality of ridges and ridges may be provided to form a comb shape, for example, a spline structure.
[0019]
Since the rotation of the first cam member 37 is stopped by the engagement structure 46, the second cam member 38 and the engagement structure 50, the first cam member 37 has moved in the axial direction of the worm shaft 18. Sometimes, the worm shaft 18 is displaced in the radial worm wheel side and in the opposite direction.
Opposing end portions of, for example, a compression coil spring as the urging member 42 are fitted into guide protrusions 47 and 48 formed on the opposing end surfaces of the adjusting screw 41 and the second cam member 38, respectively.
[0020]
When the backlash adjusting mechanism 33 is incorporated in the electric power steering apparatus 1, the amount of deflection of, for example, the compression coil spring as the biasing member 42 is adjusted by operating the adjusting screw 41 in a state where the lock nut 43 is loosened. A part of this urging force is converted into an urging force that biases the worm shaft 18 toward the worm wheel 19 and is adjusted to reduce backlash. The amount of deviation of the second end 22 of the worm shaft 18 toward the worm wheel 19 is, for example, about 30 microns.
[0021]
Since the elastic repulsive force of the elastic member 29 is set to be much larger than the urging force of the urging member 42, the first bearing 23 is normally in contact with the positioning step portion 27. Therefore, the elastic member 29 does not work to contribute to backlash adjustment. However, when a very large power fluctuation or the like occurs and the worm shaft 18 vibrates in the axial direction, the elastic member 29 works to suppress this vibration.
In the present embodiment, even if a dimensional error between parts increases due to wear of teeth of the worm shaft 18 and the worm wheel 19, this is automatically absorbed by biasing the worm shaft 18 toward the worm wheel 19. As a result, the backlash does not increase excessively. In addition, since the backlash adjusting mechanism 33 including the urging member 42 can be laid out along the axial direction of the worm shaft 18, the electric power steering apparatus 1 can be reduced in size.
[0022]
In particular, when the worm shaft 18 is made of iron and the worm wheel 19 is made of a synthetic resin, a remarkable effect can be exhibited in solving the problems associated with increase / decrease in backlash. That is, the worm wheel 19 made of synthetic resin has the advantage that the rattling noise itself is less likely to occur and the advantage that it can easily rotate even if wear powder enters the gear meshing portion. When combined, it is expected that the size will decrease in the direction of increasing backlash due to wear and temperature shrinkage. However, the backlash adjustment mechanism 33 can suppress an increase in backlash.
[0023]
Conversely, the size of the worm wheel 19 made of synthetic resin increases due to temperature expansion and swelling, the backlash is extremely reduced, the rotational resistance of the worm wheel 19 is increased, and the torque transmission efficiency is also expected to deteriorate. However, since the backlash adjustment mechanism 33 can prevent an extreme decrease in backlash, it is possible to prevent an increase in resistance torque.
Further, once the urging force of the urging member 42 is adjusted once by the adjusting screw 41 when the backlash adjusting mechanism 33 is assembled, the function of automatically adjusting the backlash is ensured thereafter. There is no need to operate.
[0024]
In addition, this invention is not limited to the said embodiment, For example, you may abolish the elastic member 29. FIG. In addition, various modifications can be made within the scope of the claims of the present invention.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a main part of an electric power steering apparatus including a backlash adjustment mechanism.
FIG. 3 is an enlarged view of a main part of FIG. 2;
[Explanation of symbols]
1 Electric power steering device 3 Steering shaft (steering shaft)
15 Electric motor 16 Motor shaft 17 Deceleration mechanism 18 Worm shaft 19 Worm wheel 22 Second end 33 Backlash adjustment mechanism 34 Second bearing 36 Housing hole 37 First cam member 38 Second cam member 39 Cam mechanism 41 Adjustment Screw 42 Biasing members 44, 45 Cam surface 46 Engagement structure 50 Engagement structure

Claims (3)

In the electric power steering apparatus that transmits the rotation of the steering assisting electric motor driven according to the torque applied to the steering shaft to the steering mechanism via the worm shaft and the worm wheel,
A biasing member for biasing the worm shaft in the axial direction;
A cam mechanism that converts at least a part of the urging force of the urging member into a force that urges the worm shaft toward the radial worm wheel;
The electric power steering apparatus according to claim 1, wherein the worm shaft is held in a housing via a cam mechanism so as to be biased toward the radial worm wheel. The electric power steering apparatus according to claim 1, further comprising an adjustment member that adjusts an urging force of the urging member. In claim 1 or 2,
The cam mechanism includes first and second cam members each having a cam surface engaged with each other,
The first cam member, is capable biased radially worm wheel side of the worm shaft along with rotatably supporting且one bearings of the worm shaft via a bearing,
The electric power steering apparatus, wherein the second cam member is supported by the support hole of the housing in a state in which only displacement in the axial direction of the worm shaft is allowed.

Images