JP2005319922A - Power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the occurrence of noises and the deterioration of steering feeling over the long term in a power steering device. <P>SOLUTION: The contact surface of a member swingably supporting a worm shaft 18 of a speed reducing gear 17 reducing the output rotation of an electric motor 16 and transmitting it to a steering mechanism so as to be deviated to the worm wheel 19 side, which contacts other members is formed of an elastic layer made of an elastic material. More specifically, a power transmitting surface 46 of a transmitting member 43 interposed between first and second engagement members 41, 42 of a power transmitting joint 21 connecting the output shaft 20 of the electric motor 16 and the first end 18a of the worm shaft 18 is formed of the elastic layer 48. Furthermore, the contact surface of a sleeve 60 oscillatorily supporting the second end 18b of the worm shaft 18 so as to be deviated to the worm wheel 19 side, which is contacted with a housing 17a, is formed of the elastic layer 65. <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 for an electric power steering system (EPS) for automobiles. For example, in column-type EPS, the rotation of the output shaft of the electric motor is decelerated via the worm shaft and the worm wheel, so that the output of the electric motor is amplified and transmitted to the steering mechanism to assist the steering operation with torque. ing.
Appropriate backlash is required for meshing between the small gear and the large gear as a reduction mechanism. However, rattling noise may occur due to backlash, for example, when the gear rotates forward or reverse, or when a reaction force from a tire is input while traveling on a rough road such as a stone pavement. If it is transmitted as noise in the passenger compartment, the driver is uncomfortable.

For this reason, conventionally, the reduction gears are assembled by selecting the combination of the small gears and the large gears so as to achieve an appropriate backlash, so-called layered assembly, but this method has a problem that productivity is extremely low. is there. Further, even if the assembly is performed by layer, there is another problem that unevenness of steering torque occurs due to eccentricity of the shaft of the worm wheel.
Thus, it has been studied to eliminate backlash by providing a biasing member such as a spring body that biases the worm shaft toward the worm wheel and biases the worm shaft in the biasing direction. At that time, the cylindrical joint that connects the output shaft of the electric motor and the worm shaft is usually spline-fitted at the end of the worm shaft. In order to achieve this, it is necessary to provide some backlash. However, there is a problem that an abnormal noise accompanying the rattling noise is generated due to the looseness.

Therefore, the output shaft of the electric motor and the worm shaft are allowed to move between the output shaft of the electric motor and the worm shaft through a joint including an elastic member (transmission member) formed entirely of an elastic material such as rubber or soft resin, while allowing the worm shaft to be biased. There is provided an electric power steering device that is connected so as to be able to transmit (for example, Patent Document 1).
The end of the worm shaft opposite to the side connected to the output shaft of the electric motor is usually slidably disposed with respect to the housing so that the bearing can be biased toward the large gear side, The bearing is urged in the direction of the large gear by an urging member (for example, Patent Document 2).
JP 2002-145083 A JP 2002-67992 A

  However, in the joint that connects the motor output shaft and the worm shaft, a large sag or plastic deformation occurs in the transmission member that has been repeatedly subjected to a load after long-term use. There may be a gap between the members. Due to this gap, there is a problem that play occurs in the rotation direction of the joint, the steering feeling is deteriorated, and noise is generated.

  Further, at the end of the worm shaft opposite to the side connected to the output shaft of the electric motor, there is a problem that noise is generated due to collision between the bearing and the housing when the worm shaft rotates. Therefore, it has been studied to reduce noise at the time of collision by holding the bearing with a sleeve made of hard resin or the like and providing an O-ring on the outer peripheral surface of the sleeve. However, when the load is applied to the worm shaft, the O-ring is crushed and the sleeve exposed outside the O-ring cannot be prevented from colliding with the housing. There is a problem that you can not.

  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 can suppress generation of noise and deterioration of steering feeling.

The present invention relates to an electric power steering device that transmits the output rotation of an electric motor for assisting steering to a steering mechanism by decelerating the output rotation through a reduction gear provided with a small gear and a large gear. A member that is swingably supported so as to be biased toward the gear side is provided, and a contact surface with the other member of this member is formed by an elastic layer made of an elastic material.
The electric power steering apparatus of the present invention includes a power transmission joint that connects the output shaft of the electric motor and the input shaft of the speed reducer, which is the first end of the small gear, so that power can be transmitted. The joint is interposed between the first and second engaging members connected to the output shaft and the input shaft so as to be integrally rotatable, and the first and second engaging members are not rotatable relative to each other. And a transmission member that oscillates between the two members and supports the small gear so that it can be biased toward the large gear. The transmission member includes first and second engagement members. A plurality of power transmission surfaces serving as contact surfaces that are elastically engaged with the combined member, and the transmission member supports an elastic layer made of an elastic material that forms the power transmission surface, and the elastic layer It is preferable to have a composite structure with a hard core material There.

  The electric power steering apparatus according to the present invention is configured such that the second end of the small gear opposite to the first end connected to the output shaft of the electric motor is connected to the large gear via a bearing. An elastic layer made of an elastic material, which includes a sleeve that is swingably supported so as to be biased, and a biasing member that biases the sleeve in the direction of the large gear, and the sleeve forms a contact surface with the housing. And a sleeve structure made of a hard material that supports the elastic layer and holds the bearing.

According to the present invention, the back gear is eliminated by supporting the small gear so as to be swingable so as to be biased toward the large gear, and the contact surface of the member for supporting the other member is made of an elastic material. Since it is formed of an elastic layer, it is possible to suppress the generation of noise and deterioration of steering feeling caused by backlash, backlash of members, collision, and the like.
In particular, among the power transmission joints in which the above-described member connects the output shaft of the electric motor and the first end of the small gear so as to be able to transmit power, the transmission interposed between the first and second engaging members. When the transmission member is a member, the transmission member has a composite structure of the elastic layer and the core material, thereby maintaining the effect of suppressing the generation of abnormal noise caused by the rattling noise by the elastic layer, and the elastic layer by the core material. Thus, it is possible to reduce the amount of sag and plastic deformation when subjected to repeated loads over a long period of use compared to a transmission member formed entirely of an elastic material. Therefore, it is possible to suppress a gap between the transmission member and the engaging member that engages with the transmission member, and due to the gap, a backlash occurs in the rotation direction of the joint, and the steering feeling is deteriorated. Generation of noise or noise can be better suppressed over a long period of time.

  When the member is a sleeve that supports the second end portion of the small gear on the opposite side so as to be able to be biased to the large gear side via a bearing, the sleeve is provided with the elastic layer. As a composite structure of the sleeve body and the entire surface of the contact surface is formed of an elastic layer, it is possible to more reliably prevent noise associated with the collision between the sleeve and the housing as compared with the O-ring.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of an electric power steering apparatus including a power transmission joint according to an embodiment of the present invention.
Referring to FIG. 1, an electric power steering apparatus 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, and an intermediate 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 rack and pinion mechanism A as a steering 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 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 connected to the steering member 2 and an output-side lower shaft 3 b connected to the pinion shaft 7, and these upper and lower shafts 3 a, 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 a relative rotational displacement amount between the upper and lower shafts 3a and 3b via the torsion bar 12, and a torque detection result of the torque sensor 13 is obtained from an ECU (Electric 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 the speed reducer 17 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 (small gear) 18 as an input shaft that is rotationally driven by the electric motor 16, and a worm wheel that 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. (Large gear) 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 direction thereof, 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 connected 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 that surrounds the cored bar 19a and has 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 18a of the worm shaft 18 and the opposite end portion of the output shaft 20 of the electric motor 16 are connected so as to be able to transmit power coaxially via a power transmission joint 21 which is a feature of the present embodiment. Has been.
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 ball bearings, for example.

  Inner rings 24 and 25 of the first and second bearings 22 and 23 are fitted to the first and second end portions 18a and 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 corresponding bearing holding hole 28 of the housing 17a of the speed reducer 17. Further, the outer ring 27 of the second bearing 23 is held by the sleeve 60 in a non-rotatable manner in a corresponding bearing holding hole 29 of the housing 17 a while being held by the sleeve 60.

  The power transmission joint 21 will be described in detail with reference to FIG. 3 which is a cross-sectional view taken along the line III-III in FIG. 2 and FIG. 2 and FIG. 4 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 a transmission member 43 for transmitting torque. The first and second engaging members 41 and 42 are made of, for example, metal.

  Next, referring to FIGS. 3, 4, and 5 </ b> A, the transmission member 43 includes an annular main body 44 and a plurality of engagement arms 45 extending radially from the main body 44. The plurality of engaging arms 45 are arranged at equal intervals in the circumferential direction X of the main body 44. Each engagement arm 45 has a pair of power transmission surfaces (contact surfaces) 46 facing each other in the circumferential direction X, as shown in FIG. 5B, which is a cross-sectional view taken along line 5B-5B in FIGS. In addition, each power transmission surface 46 has a mountain shape so that the central portion in the axial direction swells. 5A, the power transmission surface 46 has a mountain shape so that the central portion in the radial direction (the direction in which the engagement arm 45 extends from the main body 44) swells.

Referring to FIG. 4, 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 projections 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. 3, the first and second engagement protrusions 55, 56 of the first and second engagement members 41, 42 are alternately arranged in the circumferential direction, The corresponding engagement protrusion 45 of the transmission 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 transmission member 43 sandwiched in the circumferential direction.

Further, as shown in FIGS. 3 and 4, the first and second engagement protrusions 55 and 56 are power transmission surfaces 57 and 58 that contact the power transmission surface 46 of the corresponding engagement arm 45 of the transmission member 43. Respectively.
According to the present embodiment, the transmission member 43 is made of a hard material, and surrounds the core member 47 whose shape is smaller than that of the transmission member 43 and the entire outer peripheral surface of the core member 47. It has a composite structure with an elastic layer 48 forming a power transmission surface 46 on the side surface on the circumferential direction X side.

As the hard material that forms the core material 47, various hard materials that support the elastic layer 48 and do not cause sag or plastic deformation can be used. For example, a hard resin such as glass fiber reinforced polyamide, polybutylene terephthalate, polyacetal, Metal, ceramic and the like are preferable.
On the other hand, the elastic material forming the elastic layer 48 preferably has a Shore A hardness of 30 to 90 (or Shore D hardness of 20 to 70). If the hardness is less than this range, the elastic layer 48 is too soft, and the effect of suppressing the sag and plastic deformation when subjected to repeated loads over a long period of use becomes insufficient. There is a possibility that it is impossible to reliably prevent the gap from being generated. Conversely, when this range is exceeded, the elastic layer 48 is too hard and the effect of suppressing the generation of abnormal noise due to the rattling noise cannot be sufficiently obtained. There is a fear.

  Preferred examples of the elastic material include rubber and soft resin. Examples of the rubber include ethylene-propylene copolymer rubber (EPM), ethylene-propylene-diene copolymer rubber (EPDM), silicone rubber, urethane rubber (U), and the like. Can be mentioned. Examples of the soft resin include polyolefin resin, polyamide resin, polyester resin, polyurethane resin, polyacetal resin, polyphenylene oxide resin, polyimide resin, fluorine resin, and thermosetting urethane resin. Further, for example, olefin-based, urethane-based, polyester-based, polyamide-based, fluorine-based and other oil-resistant thermoplastic elastomers can be used.

  The transmission member 43 having a composite structure is manufactured by various manufacturing methods such as an insert molding method and a coating method. In the insert molding method, a mold provided with a holding portion for holding the core material 47 in a cavity corresponding to the outer shape of the transmission member 43 is prepared, and the core material 47 previously formed in a predetermined shape is held in the holding portion. In this state, an elastic material heated and melted is injected into the cavity and then cooled and solidified. If the elastic material is rubber, the elastic layer 48 is formed by vulcanization. Also, in the coating method, a solution that becomes the basis of the elastic material is applied to the outer peripheral surface of the formed core material 47 by dipping method, spray coating method, or other coating method, and dried to solidify or a melt is applied. Then, the elastic layer 48 is formed by cooling and solidifying, and further vulcanizing when the elastic material is rubber.

In the embodiment, the elastic layer 48 is formed on the entire outer peripheral surface of the core material 47, but the elastic layer may be formed only on the power transmission surface 46. However, it is preferable to form the elastic layer 48 on the entire outer peripheral surface of the core material 47 as in the embodiment, thereby improving the adhesion of the elastic layer 48 to the core material 47 and improving the durability of the transmission member 43. Can be improved.
By using the transmission member 43 having the above-described composite structure, the elastic layer 48 is supported by the core material 47 while maintaining the effect of suppressing the generation of noise caused by the rattling noise by the elastic layer 48, It is possible to reduce the amount of sag and the amount of plastic deformation when subjected to repeated loads over a long period of use compared to a conventional transmission member formed entirely of an elastic material. Therefore, the generation of a gap between the transmission member 43 and the first and second engaging members 41 and 42 engaged with the transmission member 43 is suppressed, and the rotation of the power transmission joint 21 is caused by the gap. It is possible to better prevent the steering feeling from deteriorating and the generation of noise due to backlash in the direction over a long period of time.

  Next, referring to FIGS. 2, 6, and 7, the sleeve 60 has an annular shape and is fitted to the outer peripheral surface of the outer ring 27 to hold the second bearing 23, and one end of the main body 61. A composite of a sleeve main body 64 in which an end plate portion 62 that closes the opening, a columnar protrusion 63 that protrudes outward from the center of the outer end surface of the end plate portion 62 is integrally formed of a hard material, and an elastic layer 65 made of an elastic material. It has a structure. An annular concave groove 66 is formed on the outer peripheral side surface of the end plate portion 62, and the elastic layer 65 includes an outer peripheral side surface of the end plate portion 62 including the inside of the concave groove 66 and an outer peripheral side surface of the main body portion 61 that is continuous therewith. Is formed so as to surround.

The columnar protrusion 63 and the main body portion 61 are arranged coaxially. Therefore, the columnar protrusion 63 is arranged coaxially with the worm shaft 18 supported by the second bearing 23.
2 and 6, one end portion of a tension coil spring 68 as a biasing member that biases the sleeve 60 toward the worm wheel 19 is hooked and connected to the outer peripheral surface near the tip of the columnar protrusion 63. A concave groove 67 is formed.

Referring to FIG. 7, the columnar protrusions 63 are formed in a substantially flat cross-section with opposite flat surfaces 69 provided at positions opposite to each other across the center line of the cylinder on the outer peripheral surface of the cylinder. The columnar protrusion 63 is disposed with the flat surface 69 facing in parallel with the swinging direction Y of the worm shaft 18.
As the hard material forming the sleeve body 64, various hard materials can be used. For example, hard resin such as glass fiber reinforced polyamide, polybutylene terephthalate, polyacetal, metal, ceramic and the like are preferable.

  On the other hand, the elastic material forming the elastic layer 65 preferably has a Shore A hardness of 30 to 80 (or Shore D hardness of 20 to 40). If the hardness is less than this range, the elastic layer 65 is too soft and easily breaks when a load is applied to the worm shaft, and the sleeve body 64 exposed by the breakage may collide with the housing 17a to generate noise. On the other hand, if it exceeds this range, the elastic layer 65 is too hard and may itself collide with the housing 17a to generate noise.

  Preferred examples of the elastic material include rubber and soft resin. Examples of the rubber include ethylene-propylene copolymer rubber (EPM), ethylene-propylene-diene copolymer rubber (EPDM), silicone rubber, urethane rubber (U) and the like. Can be mentioned. Examples of the soft resin include polyolefin resin, polyamide resin, polyester resin, polyurethane resin, polyacetal resin, polyphenylene oxide resin, polyimide resin, fluorine resin, and thermosetting urethane resin. Further, for example, olefin-based, urethane-based, polyester-based, polyamide-based, fluorine-based and other oil-resistant thermoplastic elastomers can be used.

The sleeve 60 having the composite structure is manufactured by an insert molding method, a coating method, or the like, similarly to the transmission member 43.
Referring to FIG. 2, the housing 17a has a bearing holding hole 29 for holding the sleeve 60, and a columnar protrusion 63 of the sleeve 60 held by the bearing holding hole 29 so that the housing 17a protrudes outside the housing 17a. It has a through hole 17c provided in the end wall 17b, and the bearing holding hole 29 is formed as a biasing hole capable of biasingly holding the second bearing 23 on the radial worm wheel side. Referring to FIG. 7, the through-hole 17 c is formed in a substantially flat shape that is substantially similar to the cross-sectional shape of the columnar protrusion 63, and the clearance in the swing direction Y is set larger than the columnar protrusion 63. In addition, the clearance with respect to the width between the flat portions 69 of the columnar protrusion 63 that is orthogonal to the swinging direction Y is set small. As a result, the sleeve 60 is restricted from swinging in the direction orthogonal to the swing direction Y and the rotation of the worm shaft 18 in the rotational direction, and is allowed to swing in the swing direction Y. , Is held by the housing 17a.

  Referring to FIG. 2, one end portion of a tension coil spring 68 as an urging member is hooked on a concave groove 67 and connected to a tip end portion of a columnar protrusion 63 that protrudes to the outside of the housing 17 a through the through hole 17 c. ing. The other end of the tension coil spring 68 is connected to the housing 17a (not shown). The urging force (tensile force) of the tension coil spring 68 urges the second end portion 18 b of the worm shaft 18 toward the worm wheel 19 via the sleeve 60 and the second bearing 23. Thereby, the backlash between the worm shaft 18 and the worm wheel 19 is removed.

Further, in this state, the elastic layer 65 forming the outer peripheral side surface of the sleeve 60 is compressed in the thickness direction and is in contact with the inner peripheral surface of the bearing holding hole 29, whereby the sleeve is rotated when the worm shaft 18 is rotated. It can be prevented that 60 collides with the bearing holding hole 29 to generate noise.
Referring to FIG. 2, the outer ring 26 of the first bearing 22 is positioned in the axial direction by a preload adjusting and backlash adjusting screw member 36 screwed into a screw hole 35 connected to the corresponding bearing holding hole 28. ing. Thus, a preload is collectively applied to the first and second bearings 22 and 23, and the worm shaft 18 is positioned to contribute to the removal of backlash with the worm wheel 19.

In the above-described embodiment, both the transmission member 43 of the power transmission joint 21 and the sleeve 60 have a composite structure, thereby suppressing the generation of noise and the deterioration of steering feeling most effectively. Only one of them may have a composite structure.
In addition, various modifications can be made within the scope of the claims, such as application of the present invention to an electric power steering apparatus including another reduction mechanism such as a helical gear mechanism.

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 a disassembled perspective view of a power transmission coupling. 5A is a partially cutaway front view of the transmission member, and FIG. 5B is a cross-sectional view taken along line 5B-5B in FIG. 5A. It is a partially cutaway side view of a sleeve. It is a front view of a sleeve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering device 16 Electric motor 17 Reduction gear 18 Small gear (worm shaft)
18a First end (input shaft of reduction gear)
18b Second end 19 Large gear (worm wheel)
20 Output shaft 21 Power transmission joint 23 Second bearing 41 First engagement member 42 Second engagement member 43 Transmission member 46 Contact surface (power transmission surface)
47 Core material 48 Elastic layer 60 Sleeve 64 Sleeve body 65 Elastic layer 68 Biasing member (tensile coil spring)
A Steering mechanism (rack and pinion mechanism)

Claims (3)

  In an electric power steering apparatus that decelerates the output rotation of an electric motor for assisting steering through a reduction gear including a small gear and a large gear and transmits the reduced rotation to the steering mechanism, the small gear is biased toward the large gear. An electric power steering apparatus comprising: a member that is swingably supported so that a contact surface with another member of the member is formed by an elastic layer made of an elastic material. In Claim 1, the power transmission coupling which connects the output shaft of the above-mentioned electric motor, and the input shaft of the reduction gear which is the 1st end of a small gear so that power transmission is possible,
The power transmission joint includes first and second engaging members coupled to the output shaft and the input shaft, respectively, so as to be integrally rotatable,
It is interposed between the first and second engaging members and is connected to both members so as not to rotate relative to each other so as to transmit torque between the two members and swing so that the small gear can be biased toward the large gear. A transmission member that supports it,
The transmission member has a plurality of power transmission surfaces as contact surfaces that elastically engage with the first and second engagement members, respectively.
The electric power steering device according to claim 1, wherein the transmission member has a composite structure of an elastic layer made of an elastic material that forms a power transmission surface and a core material made of a hard material that supports the elastic layer. 3. The second end of the small gear, which is opposite to the first end connected to the output shaft of the electric motor, can be biased toward the large gear via a bearing. A sleeve that is swingably supported;
A biasing member for biasing the sleeve in the direction of the large gear,
The sleeve has a composite structure of an elastic layer made of an elastic material that forms a contact surface with the housing and a sleeve main body made of a hard material that supports the elastic layer and holds a bearing. Electric power steering device.

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