JP2010089625A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent sound hitting and torque fluctuation of a ball and a rack shaft screw groove or nut without using a high-precision bearing in an electric power steering device.
In an electric power steering apparatus 10, a bearing device 30 includes first and second ball bearings 31 and 32 arranged in the axial direction of a nut 22, and each ball bearing 31 and 32 has an outer ring 31A, 32A and / or inner rings 31B and 32B are movable in the axial direction of the nut 22 with respect to the balls 31C and 32C, and the inner rings 31B and 32B of the first ball bearing 31 and the second ball bearing 32 are moved to the outer periphery of the nut 22. Are slidably loaded and the elastic body 34 is sandwiched between the inner rings 31B and 32B.
[Selection] Figure 2

Description

  The present invention relates to an electric power steering apparatus.

  As an electric power steering device, as described in Patent Document 1, a nut having a rack shaft that is linearly moved by applying a manual steering force and is screwed into a thread groove provided on the rack shaft via a ball is attached to the housing. Some have an assist motor which is supported by a bearing device and assists a manual steering force by applying a rotational force to a nut.

  The bearing device described in Patent Document 1 is composed of a double-row angular ball bearing, the inner ring is fixed to the outer periphery of the nut, the outer ring is slidably loaded on the inner periphery of the housing, and both end portions of the outer ring are provided. An elastic body is sandwiched between the housing and the housing.

A bearing device provided on the outer periphery of the nut can be displaced in the axial direction with compression deformation of the elastic body with respect to the housing. Accordingly, (i) the ball and the thread groove or nut of the rack shaft can absorb the shock that rattles in the axial direction by small input of the road surface unevenness by the deformation of the elastic body, or (ii) the ball and Torque fluctuations at the time of nut rotation caused by poor machining accuracy of the rack shaft thread groove and nut are absorbed by the elastic body.
JP2002-145080

The electric power steering device described in Patent Document 1 has the following problems.
(1) The elastic bodies provided at both ends of the outer ring of the double row angular ball bearing do not preload two balls forming the double row, and do not contribute to eliminating the rattling of the bearing itself. In order to eliminate the rattling of the bearing itself, it is necessary to increase the machining accuracy of each part of the bearing, which increases the cost.

  (2) The bearing device that supports the nut is a double-row angular ball bearing, in which a single outer ring is slidably loaded on the inner periphery of the housing, and the axial contact length of the outer ring that contacts the housing is double-row. A long length of minutes. Therefore, the bearing provided on the outer periphery of the nut is not easily displaced in the axial direction due to the large sliding resistance of the outer ring, and sufficiently obtains the above-mentioned (i) impact prevention effect and (ii) torque fluctuation prevention effect. I can't.

  SUMMARY OF THE INVENTION An object of the present invention is to prevent the hitting noise and torque fluctuation of the ball and rack shaft screw grooves or nuts without using a high-precision bearing in the electric power steering apparatus.

  The invention according to claim 1 has a rack shaft that is linearly moved by applying a manual steering force, a nut that is screwed into a screw groove provided on the rack shaft via a ball is supported by a bearing device on the housing, and the nut In the electric power steering apparatus having an assist motor for assisting a manual steering force by applying a rotational force to the bearing, the bearing device is composed of first and second ball bearings arranged in the axial direction of the nut, and each ball bearing is These outer rings and / or inner rings are movable in the axial direction of the nut relative to the balls, and the inner rings of the first ball bearing and the second ball bearing are slidably loaded on the outer periphery of the nut, and the inner rings The outer ring of the first ball bearing and the second ball bearing is slidably loaded on the inner periphery of the housing, and the elastic body is clamped between the outer rings. It is what I did.

  According to a second aspect of the present invention, in the first aspect of the invention, an annular spacer is interposed between the outer rings of the first ball bearing and the second ball bearing, and an axially central portion of the inner periphery of the spacer. Provided with a narrow annular stopper portion, an elastic body interposed between the inner rings of the first ball bearing and the second ball bearing, and a spacer that is constantly clamped by the inner rings, and a spacer A thin ball portion that is sandwiched between the inner ring and the annular stopper portion when the amount of compressive deformation of the thick wall portion exceeds a certain value, or a first ball bearing. An annular spacer is interposed between the inner rings of the first and second ball bearings, and a narrow annular stopper is provided at the axial center of the outer periphery of the spacer, so that the first ball bearing and the second ball bearing An elastic body interposed between the outer rings has a thick wall part that is always pinched by the outer rings, and an annular stopper for the spacer. Is obtained so as to have a thin portion pinched by their outer ring and the annular stopper portion when compressive deformation of the thick portion is additionally provided exceeds a predetermined value.

(Claim 1)
(a) The bearing device that supports the nut includes two ball bearings, and each bearing can move the outer ring and / or the inner ring with respect to the ball in the axial direction of the nut. Therefore, the elastic body sandwiched between the inner rings or the outer rings of the two ball bearings applies a preload to the balls of each bearing, and contributes to eliminating rattling of the bearing itself. The backlash of the bearing itself can be eliminated and the cost can be reduced without increasing the processing accuracy of each part of the bearing.

  (b) The bearing device supporting the nut is composed of two ball bearings, and each bearing can move the outer ring and / or the inner ring with respect to the ball in the axial direction of the nut. Therefore, when an impact load directed in one axial direction is input to the rack shaft and the nut is displaced in both directions, only the outer ring and / or the inner ring of one of the two bearings is affected by the inner circumference and / or the housing. It will slide on the outer periphery of the nut. When an impact load directed to the other axial direction is input to the rack shaft, only the inner ring of the other of the two bearings slides on the outer periphery of the nut. At this time, the axial contact length of the outer ring in contact with the housing of each bearing and the axial contact length of the inner ring in contact with the nut are as short as half of the two bearings. Accordingly, each bearing has a smaller sliding resistance of the outer ring and / or inner ring, so that it can be easily displaced in the axial direction to easily deform the elastic body, and (i) the thread and nut of the ball and the rack shaft, However, due to the small input of the road surface irregularities, the shock that rattles in the axial direction can be absorbed smoothly by the deformation of the elastic body to sufficiently prevent hitting sound, or (ii) the processing accuracy of the thread groove and nut of the ball and rack shaft is poor. The resulting torque fluctuation during nut rotation is smoothly absorbed by the elastic body.

(Claim 2)
(c) The elastic body sandwiched between the inner rings or the outer rings of the two ball bearings has a constant thickness and the amount of compressive deformation of the thick section is always clamped by the inner ring or the outer ring. And a thin-walled portion that is pinched when exceeding. Therefore, when the load (load F (thrust) in FIG. 3) input in the axial direction of the rack shaft corresponding to the high-speed traveling of the vehicle is in the small and medium load range, the thick portion of the elastic body is compressed (in FIG. 3). The small spring constant (load F / deformation amount L) of which the thick portion is developed is flexibly absorbed by the small and medium loads. On the other hand, when the load input in the axial direction of the rack shaft is in a large load range corresponding to low-speed traveling or extremely low-speed traveling (stationary operation) of the vehicle, the thin portion of the elastic body is compressed and the thin portion appears. The large spring constant that reliably resists the impact caused by the large load. The maximum impact force is reliably supported by abutting against the stopper portion of the spacer via the thin portion of the elastic body.

  FIG. 1 is a cross-sectional view showing a main part of an electric power steering apparatus, FIG. 2 is a schematic view showing an impact absorbing operation by an elastic body clamped between two ball bearings, and FIG. 3 is a schematic showing a spring constant of the elastic body. FIG.

  FIG. 1 shows a main part of an electric power steering device 10 mounted on a vehicle or the like, in which 11 is a housing, 12 is a rack shaft, 20 is a ball nut device, 30 is a bearing device, and 40 is an electric assist motor.

  A rack shaft 12 provided so as to penetrate the inside of the housing 11 is engaged with a pinion attached to a steering shaft (not shown), and a manual steering force applied to the steering shaft by a steering operator is linearly moved left and right in the housing 11. To do.

  The ball nut device 20 supports a nut 22 that is screwed into a screw groove 12 </ b> A provided in the rack shaft 12 via a ball 21 within the housing 11, with a bearing device 30.

  The assist motor 40 is fixedly provided around the rack shaft 12 in the housing 11 and applies a rotational force to the nut 22 of the ball nut device 20. In the assist motor 40, the stator 41 is fixed to the inner periphery of the housing 11, and the rotor 42 is coaxially disposed outside the rack shaft 12. The inner peripheral portion of one end of the nut 22 is splined to the outer peripheral portion of the rotor 42 at one end.

  In the electric power steering apparatus 10, when the assist motor 40 is driven and controlled according to the steering direction and the steering torque of the manual steering force applied by the steering operator to the steering shaft, the nut 42 is spline-coupled. The nut 22 of the ball nut device 20 is rotated, and the rotation of the nut 22 causes the rack shaft 12 to move linearly in the axial direction. Thereby, the wheel connected with the rack shaft 12 via the tie rod is steered. The assist motor 40 assists the manual steering force of the steering person.

  Hereinafter, the bearing device 30 will be described in detail. The bearing device 30 includes first and second ball bearings 31 and 32 arranged in the axial direction of the nut 22 of the ball nut device 20, and each of the bearings 31 and 32 has an outer ring 31A, 32A and / or an inner ring 31B. , 32B is movable in the axial direction of the nut 22 with respect to the balls 31C, 32C. In the bearings 31 and 32 of this embodiment, the inner diameters of the inner rings 31B and 32B on the side without the shoulders are cylindrical surfaces from the groove bottoms of the inner rings 31B and 32B, and the shouldered sides of the inner rings 31B and 32B are mutually connected. As a result, the inner rings 31B and 32B can be moved in the axial direction of the nut 22 with respect to the balls 31C and 32C.

  In the bearing device 30, the outer rings 31A and 32A of the first ball bearing 31 and the second ball bearing 32 are fixedly loaded on the inner periphery of the housing 11, and an annular spacer 33 is provided between the outer rings 31A and 32A. It is intervening. Further, the inner rings 31B and 32B of the first ball bearing 31 and the second ball bearing 32 are loaded so as to be slidable at least in the axial direction on the outer periphery of the nut 22, and the elastic body 34 is interposed between the inner rings 31B and 32B. Is pinching. That is, in the first ball bearing 31 and the second ball bearing 32, the outer ring 31 </ b> A, the spacer 33, and the outer ring 32 </ b> A are loaded on the inner periphery of the housing 11, and the support portion 11 </ b> A provided on the inner periphery of the housing 11 and the housing 11. The outer ring 31A, the spacer 33, and the outer ring 32A are held by a stopper 35 screwed to the inner periphery of the outer ring 31A. In addition, the first ball bearing 31 and the second ball bearing 32 are loaded with an inner ring 31B, an elastic body 34, and an inner ring 32B on the outer periphery of the nut 22, and the flange 22A provided on the outer periphery of the nut 22 and the nut 22 The inner ring 31B, the elastic body 34, and the inner ring 32B are held by a stopper 36 screwed to the outer periphery.

  The bearing device 30 has a wide portion 33A of the spacer 33 interposed between the outer ring 31A of the first ball bearing 31 and the second ball bearing 32A, and has a narrow width at the axially central portion of the inner periphery of the wide portion 33A. An annular stopper portion 33B is provided. Then, the elastic body 34 interposed between the inner ring 31B of the first ball bearing 31 and the inner ring 32B of the second ball bearing 32 has a thick portion 34A that is always pinched by the inner rings 31B and 32B. The thin portion 34B is attached to the stopper portion 33B of the spacer 33 and is sandwiched between the inner rings 31B and 32B and the stopper portion 33B when the amount of compressive deformation of the thick portion 34A exceeds a certain value. In this embodiment, the elastic body 34 can be bonded and integrated around the stopper portion 33B of the spacer 33 by baking or the like.

  Therefore, in the electric power steering apparatus 10, the shock absorbing operation by the elastic body 34 sandwiched between the two ball bearings 31 and 32 is as follows.

  (1) When the rack shaft 12 receives a small to medium load in one of the axial directions when the vehicle is traveling at a high speed or the like, the nut 22 and the inner ring 31B of the first ball receiver 31 together with the rack shaft 12 are shown in FIG. -Move slightly as shown in FIG. At this time, the inner ring 32 </ b> B of the second ball bearing 32 is supported by the stopper 35 on the housing 11 side through the balls 32 </ b> C and the outer ring 32 </ b> A and does not move, but slides on the outer periphery of the nut 22. As a result, the portion closer to the first ball bearing 31 of the thick part 34A of the elastic body 34 is elastically compressed and deformed, and flexibly absorbs the impact caused by the small to medium load.

  (2) When the rack shaft 12 receives a heavy load in one of the axial directions, such as during low-speed traveling or extremely low-speed traveling (stationary operation), the nut 22 and the inner ring 31B of the first ball bearing 31 are 12 and a large movement as shown in FIG. At this time, the inner ring 32B of the second ball bearing 32 is supported by the stopper 35 on the housing 11 side via the ball 32C and the outer ring 32A and does not move, but slides on the outer periphery of the nut 22. . As a result, after the portion closer to the first ball bearing 31 of the thick portion 34A of the elastic body 34 is elastically compressed and deformed to the maximum extent, the thin portion 34B closer to the first ball bearing 31 of the elastic body 34 becomes the spacer. It is pinched between the 33 stopper portions 33B and reliably resists an impact caused by the large load. The maximum impact force resulting from the maximum load received by the rack shaft 12 abuts against the stopper portion 33B of the spacer 33 via the thin portion 34B of the elastic body 34 and is reliably supported.

  Spring characteristics corresponding to the above-described shock absorbing operations (1) and (2) of the elastic body 34, in other words, the compression deformation amount L and the spring constant F / which is the ratio of the spring load F expressed by the deformation amount L. L is as shown in FIG.

According to the present invention, the following operational effects can be obtained.
(a) The bearing device 30 that supports the nut 22 includes two ball bearings 31, 32, and the bearings 31, 32 can move their inner rings 31B, 32B in the axial direction of the nut 22 with respect to the balls 31C, 32C. Accordingly, the elastic body 34 sandwiched between the inner rings 31B and 32B of the two ball bearings 31 and 32 preloads the balls 31C and 32C of the bearings 31 and 32, and the bearings 31 and 32 themselves Contributes to eliminating rattling. The backlash of the bearings 31 and 32 themselves can be eliminated and the cost can be reduced without increasing the processing accuracy of each part of the bearings 31 and 32.

  (b) The bearing device 30 that supports the nut 22 includes two ball bearings 31 and 32, and the bearings 31 and 32 can move their inner rings 31B and 32B in the axial direction of the nut 22 with respect to the balls 31C and 32C. Therefore, when an impact load directed to one side in the axial direction is input to the rack shaft 12 and the nut 22 is displaced in both directions, only the inner ring 32B of one of the two bearings 31 and 32 has an outer periphery of the nut 22. It will slide on. When an impact load directed to the other axial direction is input to the rack shaft 12, only the inner ring 31 </ b> B of the other bearing 31 of the two bearings 31 and 32 slides on the outer periphery of the nut 22. At this time, the axial contact lengths of the inner rings 31B and 32B in contact with the nuts 22 of the bearings 31 and 32 are as short as half of the two bearings 31 and 32, respectively. Accordingly, the bearings 31 and 32 are easily displaced in the axial direction and the elastic body 34 is easily deformed as the sliding resistance of the inner rings 31B and 32B decreases, and (i) the ball 21 and the rack shaft 12 are deformed. Due to the small input of the road surface unevenness between the thread groove 12A or the nut 22 and the impact that rattles in the axial direction is smoothly absorbed by the deformation of the elastic body 34 to sufficiently prevent sound hitting, or (ii) the ball 21 and the rack shaft 12 Torque fluctuations during rotation of the nut 22 due to poor machining accuracy of the thread groove 12A and the nut 22 are smoothly absorbed by the elastic body 34.

  (c) The elastic body 34 sandwiched between the inner rings 31B and 32B of the two ball bearings 31 and 32 has a thick portion 34A that is always sandwiched by the inner rings 31B and 32B, and a thick portion 34A. A thin portion 34B that is pinched when the amount of compressive deformation exceeds a certain value. Therefore, when the load (load F (thrust) in FIG. 3) input in the axial direction of the rack shaft 12 corresponding to the high-speed traveling of the vehicle is in the small and medium load region, the thick portion 34A of the elastic body 34 is compressed ( The small spring constant (load F / deformation amount L) expressed by the thick portion 34A is flexibly absorbed by the small and medium loads. On the other hand, when the load input in the axial direction of the rack shaft 12 is in a large load range corresponding to low speed travel or extremely low speed travel (stationary operation) of the vehicle, the thin portion 34B of the elastic body 34 is compressed, and the thin wall The large spring constant developed by the portion 34B reliably resists the impact caused by the large load. Then, the maximum impact force strikes against the stopper portion 33B of the spacer 33 via the thin portion 34B of the elastic body 34 and is reliably supported.

  In the above embodiment, the elastic body 34 is sandwiched between the inner rings 31B and 32B of the first ball bearing 31 and the second ball bearing 32. However, in the present invention, the first ball bearing 31 is used. The elastic body 34 may be sandwiched between the outer rings 31A and 32A of the second ball bearing 32. An elastic body may be sandwiched between the outer rings 31A and 32A of the first ball bearing 31 and the second ball bearing 32, and an elastic body may be sandwiched between the inner rings 31B and 32B.

  Moreover, in the said Example, although the 1st ball bearing 31 and the 2nd ball bearing 32 shall be a magneto bearing, in this invention, the 1st ball bearing 31 and the 2nd ball bearing 32 are single row. An angular ball bearing may be used. At this time, an elastic body is sandwiched between the front-aligned inner rings of the two single-row angular ball bearings, and an elastic body is sandwiched between the rear-aligned outer rings of the two single-row angular ball bearings.

  Further, in the present invention, the first ball bearing 31 and the second ball bearing 32 are not limited to adopting a magnetic bearing or a single-row angular contact ball bearing, and the outer ring and / or the inner ring is a nut shaft relative to the ball. Anything that can move in the direction can be widely adopted.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration of the present invention is not limited to this embodiment, and even if there is a design change or the like without departing from the gist of the present invention. It is included in the present invention.

FIG. 1 is a cross-sectional view showing a main part of the electric power steering apparatus. FIG. 2 is a schematic diagram showing an impact absorbing operation by an elastic body sandwiched between two ball bearings. FIG. 3 is a schematic diagram showing the spring constant of the elastic body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electric power steering apparatus 11 Housing 12 Rack shaft 12A Thread groove 20 Ball nut apparatus 21 Ball 22 Nut 30 Bearing apparatus 31 First ball bearing 31A, 32A Outer ring 31B, 32B Inner ring 31C, 32C Ball 32 Second ball bearing 33 Annular Spacer 33A Wide width portion 33B Annular stopper portion 34 Elastic body 34A Thick portion 34B Thin portion 40 Electric assist motor

Claims (2)

A rack shaft that linearly moves with manual steering force applied. A nut that is screwed into a thread groove provided on the rack shaft via a ball is supported by a bearing device on the housing, and rotational force is applied to the nut. In an electric power steering apparatus having an assist motor for assisting manual steering force,
The bearing device is composed of first and second ball bearings arranged in the axial direction of the nut, each ball bearing allowing the outer ring and / or the inner ring to move in the axial direction of the nut with respect to the ball,
Each inner ring of the first ball bearing and the second ball bearing is slidably loaded on the outer periphery of the nut, and an elastic body is sandwiched between the inner rings, or
An electric power steering device characterized in that the outer rings of the first ball bearing and the second ball bearing are slidably loaded on the inner periphery of the housing, and an elastic body is sandwiched between the outer rings. An annular spacer is interposed between the outer rings of the first ball bearing and the second ball bearing, and a narrow annular stopper portion is provided at the axially central portion of the inner periphery of the spacer. And an elastic body interposed between the inner rings of each of the second ball bearings, and a thick part that is always clamped by the inner rings, and an annular stopper part of the spacer so that the thick part is compressed and deformed. Having an inner ring and a thin-walled portion that is pinched by the annular stopper when the amount exceeds a certain value, or
An annular spacer is interposed between the inner rings of the first ball bearing and the second ball bearing, and a narrow annular stopper is provided at the axially central portion of the outer periphery of the spacer. The elastic body interposed between the outer rings of the ball bearings of No. 2 is attached to the annular stopper portion of the spacer and the thick portion that is always clamped by the outer rings, and the amount of compressive deformation of the thick portion is increased. The electric power steering apparatus according to claim 1, further comprising a thin portion that is clamped by the outer ring and the annular stopper portion when a predetermined value is exceeded.

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