JP2005161894A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent occurrence of backlash and prevent increase of torque loss even when fluctuation of distance between the centers of both gears is large. <P>SOLUTION: In an electric power steering device equipped with a small gear and a large gear that are shiftably supported, a first end 29 of a worm shaft 26 and a first bearing 32 for supporting this are supported elastically shiftably in the axial direction S and first and second radial directions R1 and R2 using a cylindrical member 47, an annular elastic element 50, and an elastic element 61, and the worm shaft 26 is energized to a worm wheel side (the first radial direction R1). The cylindrical member 47 has a slit 53 and can elastically deform in the first and second radial directions R1 and R2. The shifts of the first end 29 and the first bearing 32 with respect to a first holding hole 40 are received by the elastic deformation of the cylindrical member 47, the annular elastic element 50, and the elastic element 61. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to support of gears used in an electric power steering apparatus.

  Generally, a reduction mechanism including a small gear and a large gear meshing with the small gear is used in the electric power steering apparatus (EPS). For example, in the column type EPS, the rotational force of the motor shaft is transmitted to the worm shaft as a small gear and further transmitted to the worm wheel as a large gear, so that the output of the motor is amplified and transmitted to the steering mechanism, and the steering operation is torque-assisted. doing.

A moderate backlash is required for meshing between the worm shaft and the worm wheel. For example, when driving on a rough road and receiving a reaction force (reverse input) from the tire, the rattling noise (rattle sound) caused by the backlash ) May occur.
In order to prevent the occurrence of the rattling noise, it is necessary to strictly adjust the backlash amount within the range of processing accuracy. Specifically, when assembling the worm shaft and worm wheel, each part is selected according to the degree of variation in dimensional accuracy, and the components that have the appropriate combination accuracy are combined (so-called matching operation). ).

However, 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 deterioration over time, and abnormal noise may be generated. Further, when the worm wheel contains a synthetic resin, there is a possibility that the backlash may be clogged due to temperature expansion or moisture absorption swelling during use, resulting in an increase in torque loss.
Therefore, the worm shaft is supported so as to be deflectable in the radial direction, and the worm shaft is elastically biased toward the worm wheel, thereby eliminating backlash of the meshing between both gears and preventing the generation of abnormal noise. It has been proposed to prevent the increase (see, for example, Patent Document 1). Specifically, a recess is formed in a part of the inner peripheral surface of the holding hole of the housing that holds the bearing for supporting the worm shaft, and an elastic O-ring is wound around the outer ring of the bearing, and the O-ring is held in the holding hole. The worm shaft is urged toward the worm wheel by an urging force generated by an elastic repulsion force generated by compression between the worm shaft and the bearing.
JP-A-10-281235.

  In Patent Document 1, when the tooth portion of the worm wheel is worn, the worm shaft is biased toward the worm wheel, that is, the distance between the worm shaft axis and the worm wheel axis (center distance) is reduced. Therefore, backlash is not generated. However, if the amount of deviation of the worm shaft toward the worm wheel increases and the inter-center distance decreases beyond a predetermined amount, the compression of the O-ring by the holding hole and the bearing is released, and the worm shaft moves toward the worm wheel. It becomes impossible to energize. As a result, backlash occurs between the worm shaft and the worm wheel, and noise is generated.

  On the other hand, when temperature expansion or hygroscopic swelling occurs in the worm wheel, the increase in the meshing resistance is prevented by biasing the worm shaft away from the worm wheel, that is, by increasing the distance between the cores. This prevents an increase in torque cross. However, when the amount of deviation of the worm shaft away from the worm wheel increases and the inter-center distance increases beyond a predetermined amount, the O-ring is excessively crushed between the holding hole and the bearing, and the bearing and worm Shaft bias is regulated. As a result, the meshing resistance increases and the torque cross increases.

A similar problem exists in an electric power steering apparatus having a general gear other than the worm shaft and the worm wheel.
The present invention has been made in view of such a background, and even when the variation in the distance between the center of the small gear and the large gear supported to be deflectable is large, the occurrence of backlash can be prevented and the increase in torque cross can be prevented. An object of the present invention is to provide an electric power steering device that can be used.

  In order to achieve the above object, the present invention provides an electric power steering apparatus that transmits output rotation of an electric motor for assisting steering to a steering mechanism via a small gear and a large gear meshing with the small gear. A pair of bearings rotatably supporting the second end and the second end, and a radial direction having a slit extending in the axial direction of the bearing while being fitted to an outer ring of at least one bearing and holding the bearing Between the outer peripheral surface of the cylindrical member and the inner peripheral surface of the holding hole. And an annular elastic member that crosses the slit.

  According to the present invention, in addition to the elastic deformation (change in wire diameter) of the annular elastic member, the corresponding first and second ends of the small gear are elastically sufficiently elastic in the radial direction by the elastic deformation of the cylindrical member. Can be greatly biased. Therefore, for example, the tooth portion of the large gear is worn, the small gear is biased toward the large gear, and the distance (inter-center distance) between the small gear axis and the large gear axis greatly exceeds a predetermined amount. Even in this case, the small gear can be urged toward the large gear. As a result, it is possible to prevent occurrence of abnormal noise by preventing backlash between the small gear and the large gear. Furthermore, for example, when the large gear is made of a synthetic resin and temperature expansion or hygroscopic swelling occurs, the small gear can be sufficiently biased away from the large gear, thus preventing an increase in meshing resistance. Thus, an increase in torque loss can be prevented.

  In the present invention, the slit includes a plurality of first slits extending from one end of the tubular member toward the other end and second slits extending from the other end of the tubular member toward the one end. In some cases, the first and second slits are alternately arranged in the circumferential direction of the cylindrical member. In this case, both the one end portion and the other end portion of the cylindrical member can be sufficiently expanded and contracted in the radial direction, and a larger amount of deviation of the corresponding first and second end portions of the small gear can be secured. it can.

In the present invention, a circumferential groove for holding the annular elastic member may be provided on at least one of the outer peripheral surface of the cylindrical member and the inner peripheral surface of the holding hole. In this case, it can be easily assembled only by fitting the annular elastic member into the circumferential groove.
In the present invention, an elastic member may be interposed between at least one end surface of the cylindrical member and a facing member facing the end surface. In this case, the cylindrical member can be elastically biased also in the axial direction, and a larger amount of bias can be secured at the corresponding first and second end portions of the bearing and the small gear.

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 1 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, A pinion shaft 7 connected to the intermediate shaft 5 via a universal joint 6 and a rack shaft 10 that forms a rack 9 that meshes with a pinion 8 provided at the tip of the pinion shaft 7 and extends in the left-right direction of the vehicle are provided. doing.

  Tie rods 11 are connected to both ends of the rack shaft 10, and each tie rod 11 is connected to a corresponding wheel 12 via a corresponding knuckle arm (not shown). When the steering member 2 is operated and the steering shaft 3 is rotated, this rotation is transmitted to the pinion 8 via the intermediate shaft 5 and the like, and the straight line of the rack shaft 10 along the left-right direction of the vehicle is driven by the pinion 8 and the rack 9. Converted into movement. Thereby, the steering of the wheel 12 is achieved.

The steering shaft 3 has a first steering shaft 13 as a cylindrical input shaft connected to the steering member 2 and a second steering shaft 14 as an output shaft connected to the pinion shaft 7 via the intermediate shaft 5 or the like. doing. The first and second steering shafts 13 and 14 are coaxially connected to each other via a torsion bar 15.
A torque sensor 16 that detects the amount of relative rotational displacement between the first steering shaft 13 and the second steering shaft 14 via the torsion bar 15 is provided. The detection signal of the torque sensor 16 is given to the control unit 17. The control unit 17 calculates the steering torque applied to the steering member 2 based on the detection signal from the torque sensor 16, and passes the driver 18 based on the calculated steering torque, the vehicle speed detection signal from the vehicle speed sensor 22, and the like. Thus, the voltage applied to the steering assisting electric motor 19 is controlled. As a result, the electric motor 19 is driven, and the output rotation of the electric motor 19 is transmitted to the second steering shaft 14 via a speed reduction mechanism 20 formed of, for example, a worm gear mechanism, and further, the intermediate motor 5 and the like are This is transmitted to the steering mechanism 21 including the rack shaft 10, the tie rod 11, the knuckle arm and the like to assist the driver's steering.

  FIG. 2 is a cross-sectional view of a main part of the electric power steering apparatus 1. Referring to FIG. 2, a housing 23 that houses the speed reduction mechanism 20 is provided. The speed reduction mechanism 20 includes a worm shaft 26 as a small gear coupled to an output shaft 24 of an electric motor 19 fixed to a housing 23 via a joint 25 such as a spline joint, and a worm shaft 26. And a worm wheel 27 as a large gear coupled to the second steering shaft 14 so as to be integrally rotatable and immovable in the axial direction.

The worm wheel 27 includes an annular core metal 27a coupled to the second steering shaft 14, and a synthetic resin member 27b that surrounds the periphery of the core metal 27a and forms a tooth portion 28 on the outer peripheral surface. The cored bar 27a is inserted into the mold when the resin of the synthetic resin member 27b is formed, for example.
The joint 25 is coupled to the distal end portion of the first end portion 29 having a small diameter of the worm shaft 26. A worm tooth portion 31 having a diameter larger than that of the first and second end portions 29 and 30 and meshing with the tooth portion 28 of the worm wheel 27 is formed at an intermediate portion in the axial direction of the worm shaft 26.

The first and second end portions 29 and 30 of the worm shaft 26 are rotatably supported by first and second bearings 32 and 33 as a pair of corresponding bearings, respectively. The first and second bearings 32 and 33 are, for example, ball bearings.
The inner rings 34, 35 of the first and second bearings 32, 33 are fitted to the base end portion and the second end portion 30 of the corresponding first end portion 29 of the worm shaft 26, respectively. The inner ring 34 of the first bearing 32 is in contact with the positioning step portion 36 of the worm shaft 26 and is restricted from moving toward the second end portion 30. The inner ring 35 of the second bearing 33 is in contact with the positioning step portion 37 of the worm shaft 26 and is restricted from moving toward the first end portion 29.

The outer ring 38 of the first bearing 32 is held in the first holding hole 40 of the housing 23 via the holding member 39. The outer ring 41 of the second bearing 33 is held in the second holding hole 42 of the housing 23 and positioned in contact with the positioning step 43 of the housing 23.
The outer ring 38 of the first bearing 32 is urged to the second bearing 33 side via the holding member 39 by a screw member 44 for preload adjustment. The screw member 44 applies a preload to the first and second bearings 32 and 33 by being screwed into a screw hole 45 formed adjacent to the first holding hole 40 of the housing 23. After the screw member 45 is screwed into the screw hole 45 and the pressure adjustment is performed, the screw member 44 is engaged with the lock nut 46 and fixed so as not to rotate.

  FIG. 3 is an enlarged cross-sectional view around the holding member 39, and FIG. 4 is a partial perspective view of the holding member 39. With reference to FIGS. 3 and 4, the feature of the present embodiment is that the first end portion 29 of the worm shaft 26 is connected to the first end 29 via the holding member 39 and the first bearing 32. The worm shaft 26 is elastically biased and supported in the radial direction R1 (radial worm wheel side) and the second radial direction R2 opposite thereto, and the worm shaft 26 is biased toward the worm wheel 27 side (first radial direction R1). Therefore, the backlash is not generated.

Specifically, the holding member 39 is fitted to the outer ring 38 of the first bearing 32 to hold the first bearing 32, the outer peripheral surface 48 of the cylindrical member 47, and the first member 32. An annular elastic member 50 interposed between the inner peripheral surface 49 of the holding hole 40 and an elastic member 61 are included.
The cylindrical member 47 is formed of a synthetic resin such as engineering plastic or a metal such as spring steel (engineering plastic in the present embodiment), and has elasticity. The outer ring 38 of the first bearing 32 is fitted on the inner peripheral surface 51 of the cylindrical member 47. An annular step 52 is formed at one end of the inner peripheral surface 51 of the tubular member 47, and the outer ring 38 of the first bearing 32 is in contact with the annular step 52.

  The cylindrical member 47 has a slit 53 extending in the axial direction S of the worm shaft 26 and can be expanded and contracted in the first and second radial directions R1 and R2. The slit 53 includes a first slit 56 that extends from one end 54 of the cylindrical member 47 toward the other end 55, and a second slit 57 that extends from the other end 55 of the cylindrical member 47 toward the one end 54. Are included (three in this embodiment). The first and second slits 56 and 57 are alternately arranged at equal intervals in the circumferential direction of the tubular member 47. Each of the first slits 56 is provided on the cylindrical member 47 so as to have a uniform circumference, and is open to one end surface 58 of the cylindrical member 47.

The second slits 57 are respectively provided on the cylindrical member 47 so as to have a uniform circumference, and are open to the other end surface 59 of the cylindrical member 47. Each of the first and second slits 56 and 57 has a predetermined length in the axial direction S, and includes portions facing each other in the circumferential direction.
A circumferential groove 60 for holding the annular elastic member 50 is formed on the outer peripheral surface 48 of the cylindrical member 47 over the entire circumference. The circumferential groove 60 is disposed, for example, at two locations on the outer circumferential surface 48 of the cylindrical member 47. Each circumferential groove 60 intersects both the first and second slits 56 and 57.

  As the annular elastic member 50, for example, an O-ring can be used. The annular elastic members 50 are respectively fitted in the corresponding circumferential grooves 60 and tightly bind the cylindrical member 47 across the first and second slits 56 and 57 in the circumferential direction. Each annular elastic member 50 protrudes radially outward from the outer peripheral surface 48 of the cylindrical member 47 and is fitted to the inner peripheral surface 49 of the first holding hole 40 of the housing 23.

  With the above configuration, the cylindrical member 47 is held in the first holding hole 40 via the annular elastic member 50. Further, the first holding hole 40 is formed in a circular hole having a larger diameter than the cylindrical member 47, and the cylindrical member 47 can be biased in the first and second radial directions R1 and R2. ing. That is, the cylindrical member 47 can be biased with respect to the first holding hole 40 with a simple configuration in which the first holding hole 40 is formed as a simple circular hole. The first holding hole 40 is formed as a long hole extending in the first and second radial directions R1 and R2 instead of the circular hole, and the length in the short direction is set to the diameter of the annular elastic member 50. A corresponding length may be set. In this case, the cylindrical member 47 can be reliably prevented from being biased in directions other than the first and second radial directions R1 and R2 with respect to the first holding hole 40.

The elastic member 61 is interposed between the one end face 58 and the other end face 59 of the cylindrical member 47 and the screw member 44 and the housing 23 as opposed members facing the both end faces 58 and 59, respectively. 47 deviation in the axial direction S is allowed. As the elastic member 61, for example, an O-ring can be used.
One end surface 62 of the screw member 44 is opposed to the one end surface 58 of the cylindrical member 47 in the axial direction S, and the annular step portion 63 of the housing 23 is relative to the other end surface 59 of the cylindrical member 47 in the axial direction S. It is suitable. One elastic member 61 is sandwiched between one end surface 58 of the cylindrical member 47 and one end surface 62 of the screw member 44, and the other elastic member 61 is the other end surface 59 of the cylindrical member 47 and the annular stepped portion of the housing 23. 63.

With reference to FIGS. 2 and 3, the urging force by the screw member 44 is transmitted to the first bearing 32 via the elastic member 61 and the cylindrical member 47, and further to the second bearing 33 via the worm shaft 26. To be told.
In the assembled state (initial state), the first end portion 29 of the worm shaft 26 is biased in the direction away from the worm wheel 27 with respect to the first holding hole 40 of the housing 23 (second radial direction R2). ing. Accordingly, the cylindrical member 47 and the annular elastic member 50 are compressed between the first holding hole 40 and the first bearing 32 to generate an elastic repulsive force, and the worm shaft 26 is interposed via the first bearing 32. An urging force to the worm wheel 27 side (first radial direction R1) is applied to the first end portion 29.

  According to the present embodiment, in addition to the elastic deformation (change in wire diameter) of the annular elastic member 50, the first deformation of the worm shaft 26 is caused by the elastic deformation of the tubular member 47 in the first and second radial directions R1, R2. The end portion 29 can be elastically biased sufficiently large in the first and second radial directions R1, R2. Accordingly, the tooth portion 28 of the synthetic resin member 27b of the worm wheel 27 is worn, and the worm shaft 26 is biased toward the worm wheel 27 side (first radial direction R1), so that the axis of the worm shaft 26 and the axis of the worm wheel 27 Even when the distance (the distance between the cores) greatly decreases beyond a predetermined amount, the worm shaft 26 can be biased toward the worm wheel 27 (first radial direction R1). As a result, it is possible to prevent backlash from occurring between the worm shaft 26 and the worm wheel 27, thereby preventing the generation of abnormal noise.

  Further, when temperature expansion or hygroscopic swelling occurs in the synthetic resin member 27b of the worm wheel 27, the tubular member 47 and the annular elastic member 50 are deformed to move the worm shaft 26 away from the worm wheel 27 (second Since it can be sufficiently biased in the radial direction R2), it is possible to prevent an increase in meshing resistance and an increase in torque cross. Furthermore, since the cylindrical member 47 has a predetermined thickness and has sufficient strength, it is prevented from being excessively crushed even if a very large load is applied due to reverse input from the wheel 12 or the like. Thus, the first end portion 29 of the worm shaft 26 can be supported elastically.

Further, since the first and second slits 56 and 57 are formed in the cylindrical member 47, both the one end portion 54 and the other end portion 55 of the cylindrical member 47 are connected to the first and second radial directions R1 and R2. It is possible to sufficiently expand and contract, and it is possible to secure a larger amount of deviation of the first end portion 29 of the worm shaft 26.
Further, by providing the circumferential groove 60 on the outer peripheral surface 48 of the cylindrical member 47, the annular elastic member 50 can be easily assembled to the cylindrical member 47 only by fitting the annular elastic member 50 to the corresponding circumferential groove 60. Can do.

Further, the elastic member 61 is interposed between the both end surfaces 58 and 59 of the cylindrical member 47 and the corresponding one end surface 62 of the screw member 44 and the annular stepped portion 63 of the housing 23, so that the cylindrical member 47 is The axial direction S can also be biased elastically, and a larger amount of bias can be secured in the first bearing 32 and the first end portion 29 of the worm shaft 26.
The present invention is not limited to the contents of the above-described embodiments, and various modifications can be made within the scope of the claims. For example, as shown in FIG. 5, the circumferential groove 60 may be provided on the inner circumferential surface 49 of the first holding hole 40 of the housing 23 in addition to the outer circumferential surface 48 of the tubular member 47. Further, as shown in FIG. 6, the circumferential groove 60 of the tubular member 47 may be eliminated, and the circumferential groove 60 may be provided on the inner circumferential surface 49 of the first holding hole 40 of the housing 23.

  Furthermore, the number of the annular elastic members 50 may be one, or three or more. In this case, the circumferential groove 60 is formed in a number corresponding to the number of the annular elastic members 50. The number of the first and second slits 56 and 57 may be one or two, or four or more. Further, the number of the first and second slits 56 and 57 may be different from each other. When the number of slits formed in the cylindrical member 47 is only one, the slits may be formed over the entire length of the cylindrical member 47.

  Further, the elastic member 61 may be provided only on one of the one end surface 58 and the other end surface 59 of the cylindrical member 47. Further, the second holding hole 42 of the housing 23 is formed as a long hole extending in the first and second radial directions R1, R2, and the second end 30 of the worm shaft 26 is formed in the first and second radial directions. R1 and R2 may be biased. Alternatively, the second end 30 may be swingably supported by using a spherical bearing for the second bearing 33 that supports the second end 30 of the worm shaft 26.

  Furthermore, as shown in FIG. 7, the second bearing 33 may be held in the second holding hole 42 of the housing 23 via the holding member 39. In this case, the second holding hole 42 is formed in the same manner as the first holding hole 40 in the embodiment shown in FIGS. The elastic member 61 is disposed between, for example, the one end surface 58 of the cylindrical member 47 and the positioning step portion 43 of the housing 23. Further, a spur gear, a helical gear, or the like may be used as the small gear and the large gear.

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 an expanded sectional view around a holding member. It is a partial perspective view of a holding member. It is sectional drawing of the principal part of other embodiment of this invention. It is sectional drawing of the principal part of other embodiment of this invention. It is sectional drawing of the principal part of other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 19 Electric motor 21 Steering mechanism 23 Housing (opposing member)
26 Worm shaft (small gear)
27 Worm wheel (large gear)
29 1st edge part 30 2nd edge part 32 1st bearing (a pair of bearing)
33 Second bearing (a pair of bearings)
38 Outer ring 41 Outer ring 40 First holding hole (holding hole)
42 Second holding hole (holding hole)
44 Screw member (opposing member)
47 cylindrical member 48 outer peripheral surface 49 inner peripheral surface 50 annular elastic member 53 slit 54 one end 55 other end 56 first slit 57 second slit 58 one end surface 59 other end surface 60 circumferential groove 61 elastic member S axial direction R1 First radial direction (radial worm wheel side, small gear radial large gear side)
R2 Second radial direction

Claims (4)

In the electric power steering device that transmits the output rotation of the electric motor for assisting steering to the steering mechanism via the small gear and the large gear meshing with the small gear,
A pair of bearings rotatably supporting each of the first and second ends of the small gear;
A cylindrical member that is fitted to the outer ring of at least one bearing and holds the bearing, and has a slit extending in the axial direction of the bearing and can be expanded and contracted in the radial direction;
A housing including a holding hole for holding the cylindrical member on the radial large gear side of the small gear so as to be able to be biased;
An electric power steering apparatus comprising: an annular elastic member that is interposed between an outer peripheral surface of the cylindrical member and an inner peripheral surface of the holding hole and crosses the slit.   In Claim 1, the said slit is a 1st slit extended toward the other end part from the one end part of a cylindrical member, and a 2nd slit extended toward the one end part from the other end part of a cylindrical member, respectively. An electric power steering apparatus comprising a plurality of first and second slits arranged alternately in a circumferential direction of the cylindrical member.   3. The electric power steering apparatus according to claim 1, wherein a circumferential groove for holding the annular elastic member is provided on at least one of the outer peripheral surface of the cylindrical member and the inner peripheral surface of the holding hole.   4. The electric power steering apparatus according to claim 1, wherein an elastic member is interposed between at least one end face of the cylindrical member and a facing member facing the end face.

Images