JP2006027321A - Electric power-steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power-steering device which surely suppresses increase in backlash or generation of noise accompanying it. <P>SOLUTION: A bearing unit 31 comprises a second bearing 23 supporting a second end part 18b of a worm shaft 18 and a bearing housing 29 holding the second bearing 23. A bearing unit 31 is supported so as to be biased in a support hole 32 of a housing 17a in the directions X1, X2 where a distance D1 between the center of the worm shaft 18 and the center of a worm wheel 19 is lengthened or shortened. Energizing force generated by an energizing member 33 is provided to a bearing unit 31 through a driving member 34. A component force in the direction X2 where the distance D1 is shortened and a component force in the first axial direction Y1 of the worm shaft 18 are obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus that generates a steering assist force by an electric motor.

A reduction gear is used in an electric power steering system (EPS) for automobiles. For example, in the column type EPS, the rotation of the output shaft of the electric motor is decelerated through the worm shaft and the worm wheel, so that the output of the electric motor is amplified and transmitted to the steering mechanism, and the steering operation is torque-assisted. Yes.
A moderate backlash is necessary for the meshing of the worm shaft and the worm wheel, but for example, when driving on a rough road, a rattling sound due to the backlash is generated due to reverse input from the road surface. There is.

  In order to prevent the occurrence of rattling noise, it is necessary to strictly adjust the amount of backlash generated between the worm shaft and the worm wheel within the range of machining accuracy of each component. Conventionally, when assembling the worm shaft and the worm wheel, each part is selected according to the degree of variation in dimensional accuracy, and the components with the appropriate combination accuracy are combined (so-called matching assembly). The work was very laborious and the manufacturing cost was high.

Even if the backlash is initially set to an appropriate range by matching assembly, the backlash may increase due to wear of the tooth portion due to a change over time, and noise may be generated.
Therefore, the worm shaft can be biased toward the worm wheel, and the biasing member extending along the radial direction of the worm shaft biases the worm shaft in the radial direction that is the biasing direction, thereby increasing backlash. There has been proposed an electric power steering device that suppresses (for example, see Patent Document 1).

However, there is a problem that the apparatus becomes large because the biasing means must be arranged along the radial direction of the worm shaft.
Therefore, an electric power steering device has been proposed that includes a cam mechanism that converts a part of the urging force of the urging member that urges the worm shaft in the axial direction into a force that urges the worm shaft toward the worm wheel. (For example, patent document 2).
JP 2000-43739 A JP 2002-145082 A

However, there is a possibility that a new play occurs in the cam mechanism and causes noise, or a smooth operation for suppressing backlash cannot be performed.
The present invention has been made in view of the above problems, and it is an object of the present invention to provide an electric power steering device that can reliably suppress an increase in backlash and noise accompanying the backlash.

  In order to achieve the above object, the present invention provides an electric power steering apparatus that transmits the power of an electric motor for assisting steering to a steering mechanism via a transmission including a worm shaft and a worm wheel. A bearing member that is rotatably supported and can be biased in a direction that increases or decreases the distance between the centers of the worm shaft and the worm wheel, a drive member that is held by a housing so as to be movable in a direction parallel to the axial direction of the worm shaft, and a drive An engagement means for engaging the member and the bearing member with each other; and an urging member for urging the worm shaft in the axial direction via the drive member and the bearing member. The engagement means is provided on the drive member and the bearing member. Each of the protrusions and recesses includes a protrusion and a recess having a V-shaped cross section that are provided to engage with each other and restrict rotation of the bearing member, and the protrusion and the recess are biasing forces of the biasing member. The worm shaft part is characterized in that each include a cam surface engaging each other to convert a force that urges in a direction to shorten the distance between the centers.

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, and as a result, backlash. The noise can be reduced by suppressing the increase.
Further, since the urging force is also applied in the axial direction of the worm shaft, the axial preload can also be applied to the bearing supporting the worm shaft, and the generation of operating noise due to the bearing gap can also be suppressed. .

  Furthermore, since the cross section of the ridge and the ridge for engaging the drive member and the bearing member is V-shaped, no gap is generated between the cam surfaces, and the generation of rattling noise can be suppressed. In addition, the drive member and the bearing member can be smoothly moved relative to each other, and the backlash can be reliably suppressed.

Preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram of an electric power steering apparatus according to an embodiment of the present invention.
Referring to FIG. 1, an electric power steering device 1 includes a steering shaft 3 connected to a steering member 2 such as a steering wheel, an intermediate shaft 5 connected to the steering shaft 3 via a universal joint 4, As a steered shaft extending in the left-right direction of an automobile, having a pinion shaft 7 connected to the shaft 5 via a universal joint 6 and rack teeth 8a meshing with pinion teeth 7a provided in the vicinity of the end of the pinion shaft 7 Rack bar 8. The pinion shaft 7 and the rack bar 8 constitute a steering mechanism A including a rack and pinion mechanism.

The rack bar 8 is supported in a housing 9 fixed to the vehicle body so as to be capable of linear reciprocation through a plurality of bearings (not shown). Both end portions of the rack bar 8 protrude to both sides of the housing 9, and tie rods 10 are coupled to the respective end portions. Each tie rod 10 is connected to a corresponding steering wheel 11 via a corresponding knuckle arm (not shown).
When the steering member 2 is operated and the steering shaft 3 is rotated, this rotation is converted into a linear motion of the rack bar 8 along the left-right direction of the automobile by the pinion teeth 7a and the rack teeth 8a. Thereby, steering of the steered wheel 11 is achieved.

The steering shaft 3 is divided into an input-side upper shaft 3 a that is continuous with the steering member 2 and an output-side lower shaft 3 b that is continuous with the pinion shaft 7. These upper and lower shafts 3 a and 3 b are connected via a torsion bar 12. Are connected to each other so as to be relatively rotatable on the same axis.
A torque sensor 13 is provided for detecting a steering torque based on the amount of relative rotational displacement between the upper and lower shafts 3a, 3b via the torsion bar 12, and the torque detection result of the torque sensor 13 is obtained from an ECU (Electronic Control Unit: electronic Control unit) 14. The ECU 14 drives and controls the steering assisting electric motor 16 via the drive circuit 15 based on a torque detection result or a vehicle speed detection result given from a vehicle speed sensor (not shown). The output rotation of the electric motor 16 is decelerated via a speed reducer 17 as a transmission device and transmitted to the pinion shaft 7 and converted into a linear motion of the rack bar 8 to assist steering.

The speed reducer 17 is a worm shaft 18 as a drive gear that is rotationally driven by an electric motor 16, and meshes with the worm shaft 18 and is connected to the lower shaft 3 b of the steering shaft 3 so as to be integrally rotatable. A worm wheel 19 is provided.
Referring to FIG. 2, worm shaft 18 is arranged coaxially with output shaft 20 of electric motor 16. The worm shaft 18 has first and second end portions 18a and 18b that are separated from each other in the axial length direction, and has a tooth portion 18c at an intermediate portion between the first and second end portions 18a and 18b.

  The worm wheel 19 is coupled to an intermediate portion in the axial direction of the lower shaft 3b of the steering shaft 3 so as to be integrally rotatable and immovable in the axial direction. The worm wheel 19 includes an annular cored bar 19a coupled to the lower shaft 3b so as to be integrally rotatable, and a synthetic resin member 19b surrounding the cored bar 19a and having teeth 19c formed on the outer periphery. The core metal 19a is inserted into the mold when the synthetic resin member 19b is molded with resin, for example.

The first end portion 18 a of the worm shaft 18 and the opposite end portion of the output shaft 20 of the electric motor 16 are connected to each other via a power transmission joint 21 so as to be able to transmit power.
The first and second end portions 18a and 18b of the worm shaft 18 are rotatably supported by the housing 17a of the speed reducer 17 via corresponding first and second bearings 22 and 23, respectively. The first and second bearings 22 and 23 are, for example, ball bearings having inner rings 24 and 25 and outer rings 26 and 27, respectively.

  Inner rings 24, 25 of the first and second bearings 22, 23 are fitted to the first and second end portions 18a, 18b of the worm shaft 18 so as to be integrally rotatable. The inner rings 24 and 25 are in contact with corresponding positioning step portions 18d and 18e of the worm shaft 18 which are opposite to each other. The outer ring 26 of the first bearing 22 is non-rotatably held in the bearing holding hole 28 of the housing 17a of the speed reducer 17.

On the other hand, the outer ring 27 of the second bearing 23 is held in a bearing holding hole 30 provided in the bearing housing 29 so that it cannot rotate relative to the shaft and cannot move in the axial direction. The second bearing 23 and the bearing housing 29 constitute a bearing unit 31 as a bearing member.
A bearing unit 31 as a bearing member is held in a support hole 32 provided in the housing 17a. This support hole 32 causes the bearing unit 31 to move in a direction X1 in which the distance D1 between the centers of the worm shaft 18 and the worm wheel 19 (corresponding to the distance between the rotation center C1 of the worm shaft 18 and the rotation center C2 of the worm wheel) is longer or shorter. It is formed in a biasing hole that can be held biased to X2.

Further, the bearing unit 31 receives an urging force from an urging member 33 made of, for example, a compression coil spring via the driving member 34, and the first axial direction Y1 (on the electric motor 16 side) of the worm shaft 18 and between the centers. It is biased in the direction X2 in which the distance D1 is shortened.
Referring to FIG. 3, which is a cross-sectional view taken along the line III-III in FIG. 2, a recess 35 is provided in a part of the inner periphery of the support hole 32 that supports the bearing unit 31. A drive member 34 is accommodated. Further, a protrusion 36 is formed on a part of the outer periphery of the bearing housing 29 of the bearing unit 31 and extends into the recess 35 so as to face the drive member 34.

With reference to FIG. 3 and FIG. 4 which is an exploded sectional view of the backlash adjusting mechanism, the drive member 34 faces the first surface 34 a facing the bottom surface 35 a of the recess 35 and the protrusion 36 of the bearing housing 29. And a second surface 34b.
On the first surface 34a of the drive member 34, a ridge 37 having a V-shaped cross section is formed so as to extend in parallel with the axial directions Y1 and Y2 of the worm shaft 18, and is formed on the bottom surface 35a of the recess 35. Is formed such that a concave strip 38 having a V-shaped cross section engaging with the convex strip 37 extends in parallel with the axial directions Y1 and Y2. The drive member 34 is allowed to move only in the direction parallel to the axial directions Y1 and Y2 of the worm shaft 18 by the engagement of the protrusions 37 and the recesses 38.

The recess 38 may be provided on the drive member 34 and the protrusion 37 may be provided on the bottom surface 35 a of the recess 35. Further, a plurality of ridges 37 and a plurality of ridges 38 may be provided to form a comb shape.
As shown in FIG. 4, the biasing member 33 is interposed between the end wall 17b of the housing 17a and the end surface 34c of the drive member 34 opposed thereto, and the drive member 34 is disposed in the axial direction Y1, Y1 of the worm shaft 18. Energize in a direction parallel to Y2.

The second surface 34b of the drive member 34 is an inclined surface that is inclined with respect to the axial directions Y1 and Y2 of the worm shaft 18, while the protrusion 36 of the bearing housing 29 is an inclined surface that faces the second surface 34b. 36a.
3 and 4, the inclined surface 36a of the protrusion 36 is formed with a ridge 39 having a V-shaped cross section, and the inclined second surface 34b of the drive member 34 has A concave line 40 having a V-shaped cross section is formed to slidably engage with the convex line 39. The rotation of the bearing unit 31 in the circumferential direction is restricted by the engagement of the ridges 39 and the ridges 40. A concave line 40 may be provided on the inclined surface 36 a of the protrusion 36, and a convex line 39 may be provided on the second surface 34 b of the drive member 34.

Further, the ridges 39 and the ridges 40 are provided so as to extend along the plane P including the rotation center C <b> 1 of the worm shaft 18 and to be inclined obliquely with respect to the axial direction of the worm shaft 18.
In addition, referring to FIG. 3, a cam surface 39a is constituted by a pair of inclined surfaces of convex ridges 39 having a V-shaped cross section, and a cam surface 40a is formed by a pair of inclined surfaces of concave ridges 40 also having a V-shaped cross section. Is configured. The cam surface 39a and the cam surface 40a are engaged with each other, thereby converting a part of the urging force of the urging member 33 into a force that urges the worm shaft 18 in the direction X2 that shortens the distance D1 between the centers.

That is, referring to FIG. 4, the urging force F acts on the bearing housing 29 from the drive member 34 in a direction inclined with respect to the axial directions Y1 and Y2 of the worm shaft 18, and the component force F1 causes the worm shaft 18 to move. This corresponds to a force that urges the center distance D1 in the direction X2 and the component force F2 corresponds to a force that urges the worm shaft 18 in the first axial direction Y1.
On the other hand, the outer ring 26 of the first bearing 22 is pressed against the positioning step 17c of the housing 17a by the preload adjusting and backlash adjusting screw members 48 screwed into the screw holes 47 connected to the corresponding bearing holding holes 28. And is positioned in the axial direction.

  Next, the power transmission joint 21 will be described in detail with reference to FIG. 5 which is a cross-sectional view taken along the line VV in FIG. 2 and FIG. 2 and FIG. 6 which is an exploded perspective view. First, referring to FIG. 2, the power transmission joint 21 includes a first engagement member 41 coupled to the output shaft 20 of the electric motor 16 so as to be integrally rotatable, and a worm shaft 18 as an input shaft of the speed reducer 17. Between the first and second engagement members 41 and 42, and a second engagement member 42 connected to the first end 18a of the first end portion 18a so as to be integrally rotatable. And an elastic member 43 for transmitting torque.

The first and second engaging members 41 and 42 are made of, for example, metal. The elastic member 43 is made of, for example, synthetic rubber or synthetic resin such as polyurethane.
Next, referring to FIGS. 5 and 6, the elastic member 43 includes an annular main body 44 and a plurality of engagement arms 45 extending in the radial direction from the main body 44. The plurality of engagement arms 45 are arranged at equal intervals in the circumferential direction Z of the main body 44. Each engagement arm 45 has a pair of power transmission surfaces 46 that face each other in the circumferential direction Z.

Referring to FIG. 6, the first and second engaging members 41, 42 are annular main portions 51, which form fitting holes 49, 50 for fitting the output shaft 20 and the worm shaft 18, respectively. 52 and a plurality of first and second engaging protrusions 55 and 56 formed to project from the opposing surfaces 53 and 54 of the main body portions 51 and 52, respectively.
The first and second engagement protrusions 55 and 56 of the first and second engagement members 41 and 42 are arranged at equal intervals in the circumferential direction of the corresponding main body portions 51 and 52, respectively.

  In the assembled state of the power transmission joint 21, as shown in FIG. 5, the first and second engagement protrusions 55 and 56 of the first and second engagement members 41 and 42 are alternately arranged in the circumferential direction, A corresponding engagement arm 45 of the elastic member 43 is sandwiched between the first and second engagement protrusions 55 and 56 adjacent to each other in the circumferential direction. In other words, the first and second engaging protrusions 55 and 56 adjacent in the circumferential direction are engaged with each other with the corresponding engaging arm 45 of the elastic member 43 sandwiched in the circumferential direction.

Further, as shown in FIGS. 5 and 6, the first and second engagement protrusions 55 and 56 include power transmission surfaces 57 and 58 to the corresponding engagement arms 45 b of the elastic member 43, respectively. The engagement arm 45 is sandwiched between the first and second engagement members 41 and 42 with an interference in the axial direction, and the elastic repulsive force causes the worm shaft 18 to elastically move in the second axial direction Y2. Is energized.
According to the present embodiment, even if a dimensional error between the parts increases due to wear of the teeth of the worm shaft 18 and the worm wheel 19, the worm shaft 18 is automatically biased toward the worm wheel 19 side. Therefore, an increase in backlash can be suppressed and noise can be reduced.

Further, since the urging force is also applied to the first axial direction Y1 of the worm shaft 18, the axial preload can be applied to the first bearing 22 supporting the worm shaft 18, and the operation caused by the bearing gap is performed. Generation of sound can also be suppressed.
Further, since the cross sections of the ridges 39 and the ridges 40 for engaging the drive member 34 and the bearing housing 29 of the bearing unit 31 are V-shaped, there is no gap between the cam surfaces 39a and 40a. , Generation of rattling noise can be suppressed. In addition, the drive member 34 and the bearing unit 31 can be smoothly moved relative to each other, and the backlash can be reliably suppressed.

Further, since the urging member 33 can be laid out along the axial direction of the worm shaft 18, the electric power steering device 1 can be reduced in size.
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, in the present embodiment, it is possible to suppress an increase in backlash regardless of the dimensional change of the worm wheel.

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, in this embodiment, since an extreme decrease in backlash can be prevented, an increase in resistance torque can be prevented.
In addition, this invention is not limited to the said embodiment, For example, it replaces with the urging | biasing by the elastic member 43 of the power transmission coupling 21, and the worm shaft 18 is made into the 2nd axis | shaft using a compression coil spring and other elastic bodies. You may make it urge in the direction Y2. A tension coil spring may be used as the urging member 33.

It is a mimetic diagram showing a schematic structure of an electric power steering device of one embodiment of the present invention. It is sectional drawing of the principal part of an electric power steering device. It is sectional drawing which follows the III-III line of FIG. It is an exploded sectional view of the mechanism which adjusts backlash. It is sectional drawing which follows the VV line of FIG. It is a disassembled perspective view of a power transmission coupling.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 2 Steering member 3 Steering shaft 5 Intermediate shaft 7 Pinion shaft 8 Rack bar A Rack and pinion mechanism (steering mechanism)
16 Electric motor 17 Reducer (transmission device)
17a housing 18 worm shaft 18b second end (one end)
19 Worm wheels C1, C2 Center of rotation D1 Center-to-center distance X2 Direction in which center-to-center distance is shortened F1 Component force F2 Component force 20 Output shaft 21 Power transmission joint 23 Second bearing 27 Outer ring 29 Bearing housing 30 Bearing holding hole 31 Bearing unit (Bearing member)
32 Support hole 33 Biasing member 34 Drive member 34a First surface 34b Second surface 34c End surface 35 Recess 35a Bottom surface 36 Projection 36a Inclined surface 37 Convex strip 38 Concave strip 39 Convex strip (engaging means)
40 Concave (engagement means)
39a, 40a Cam surface 41 First engagement member 42 Second engagement member 43 Elastic member 45 Engagement arm

Claims (1)

In the electric power steering device that transmits the power of the steering assisting electric motor to the steering mechanism via the transmission device including the worm shaft and the worm wheel,
A bearing member that rotatably supports one end of the worm shaft and is capable of being biased in a direction of increasing or decreasing the distance between the centers of the worm shaft and the worm wheel;
A drive member held by a housing so as to be movable in a direction parallel to the axial direction of the worm shaft;
Engagement means for engaging the drive member and the bearing member with each other;
A biasing member that biases the worm shaft in the axial direction via the drive member and the bearing member;
The engagement means includes a protrusion and a recess having a V-shaped cross section that are provided on the drive member and the bearing member, respectively, engage with each other and restrict rotation of the bearing member,
Each of the ridges and the ridges includes cam surfaces that are engaged with each other to convert a part of the urging force of the urging member into a force that urges the worm shaft in a direction that shortens the distance between the centers. Electric power steering device.

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