JP6414665B2 - Power transmission joint, worm reducer, and electric power steering device - Google Patents

Description

  The present invention relates to a power transmission joint, a worm reducer, and an electric power steering device.

  In general, an electric power steering apparatus employs a structure in which a worm shaft is urged toward the worm wheel in order to reduce backlash of the worm speed reducer. Therefore, since the worm shaft tilts around the bearing provided on the electric motor side, an axial deviation occurs in the connecting portion between the worm shaft and the output shaft of the electric motor. A joint is required to allow this axial deviation and transmit the rotational torque of the electric motor to the worm shaft.

  As the joint, there has been proposed a joint including a motor side joint, a worm side joint, and a cap that is interposed between the joints and is individually fitted to the protruding portion of each joint (see, for example, Patent Document 1). ). The cap has a three-layer structure in which an elastic member such as rubber is sandwiched between a pair of resin members. The cap includes a power transmission surface that faces the protruding portion of each joint, and on each power transmission surface, the elastic member projects slightly from the resin member.

JP2013-173440A

When the torque of the electric motor is abruptly applied, after the protruding portion of the elastic member is rapidly compressed on the power transmission surface, the resin member collides with the protruding portion of each joint made of steel material vigorously. There is a risk that abnormal noise will occur due to the hitting sound.
In addition, since the resin member and the elastic member slide relative to each other, the surface of the elastic member and the surface of the resin member form a flush power transmission surface between the power transmission surface and the protrusion of the joint. In addition, a gap may occur. When the joint is vibrated with such a gap, the resin member comes into contact with the protruding portion of the joint without being buffered by the elastic member on the power transmission surface. For this reason, there is a possibility that an abnormal noise due to the hitting sound may occur.

  An object of the present invention is to provide a power transmission joint, a worm speed reducer, and an electric power steering device that can suppress the generation of abnormal noise caused by contact hitting sound on a power transmission surface.

The invention of claim 1 is a power transmission joint that transmits torque between the first shaft (14a) and the second shaft (18) facing each other in the axial direction (X), and is connected to the first shaft. The first rotating element (23), the second rotating element (24) connected to the second shaft, and the first rotating element and the second rotating element are interposed between both the rotating elements to transmit torque. An intermediate element (25) operatively coupled, the first rotating element and the second rotating element each including a plurality of axially extending engaging protrusions (29, 30), each engaging protrusion Are arranged alternately in the rotational direction (Z), each engaging projection includes a power transmission surface (29a, 30a), and the intermediate element is interposed between the corresponding engaging projections of both rotating elements, respectively. A plurality of power transmission sections (32) that The portion includes a pair of power transmission surfaces (32a, 32b) that respectively engage with the power transmission surfaces of the corresponding engaging protrusions of both rotating elements, and the intermediate element has a pair of end layers (a pair of end layers (a) facing in the axial direction ( 41) and an elastic layer (42) interposed between the pair of end layers, and the pair of power transmission surfaces of each of the power transmission units are formed by a part of the elastic layer. And the elastic layer is bonded to the pair of end layers, and in the power transmission unit, the elastic layer includes a main portion (42c) interposed between the pair of end layers, and Provided is a power transmission joint (20) including a pair of flanges (42d, 42e) coupled to both ends of the main body and each having a power transmission surface .

In addition, although the alphanumeric character in a parenthesis represents the corresponding component etc. in embodiment mentioned later, this does not mean that this invention should be limited to those embodiment as a matter of course. The same applies hereinafter .
According to a second aspect of the present invention, the elastic layer may be rubber vulcanized and bonded to the pair of end layers.

According to a third aspect of the present invention, the resin layer as the pair of end layers and the rubber layer as the elastic layer may be integrally formed by two-color molding .

According to a fourth aspect of the present invention, there is provided a worm shaft (18) as the second shaft disposed coaxially with the output shaft (14a) of the electric motor as the first shaft, and a worm wheel meshing with the worm of the worm shaft. A worm speed reducer (15) comprising: (19) and the power transmission joint (20) according to any one of claims 1 to 5, wherein the output shaft and the worm shaft are coupled so as to transmit torque.

As in claim 5, the worm shaft includes a first end (18a) connected to the power transmission joint, and a second end (18b) opposite to the first end, A housing (17) that houses the worm shaft and the worm wheel, and is supported by the housing so as to be displaceable in a direction that increases or decreases a center distance (D1) between the worm shaft and the worm wheel. A bearing (34) that rotatably supports the second end portion and a biasing member (60) that biases the bearing in a direction in which the distance between the centers decreases may be further provided.

The invention of claim 6 provides an electric power steering device (1) including the worm reduction gear.

  According to the invention of claim 1, the pair of power transmission surfaces of the power transmission portion of the intermediate element is formed by a part of the elastic layer. Therefore, even when the first shaft and the second shaft are inclined with respect to each other, in the power transmission portion of the intermediate element, the pair of end layers do not come into contact with the power transmission surfaces of the engaging protrusions of both rotation elements. Therefore, generation | occurrence | production of the noise resulting from the contact sound with respect to the power transmission surface of the engaging protrusion of both rotation elements can be suppressed.

In addition, since the elastic layer is bonded to the pair of end layers, it is possible to suppress the generation of abnormal noise due to backlash between the pair of end layers and the elastic layer interposed between the both end layers. The elastic layer includes a main body interposed between the pair of end layers and a pair of flanges connected to both ends of the main body and each having a power transmission surface, so that the pair of end layers and the elastic layer It is possible to reliably suppress the generation of abnormal noise due to the rattling noise.
According to the invention of claim 2 , since the rubber as the elastic layer is integrated with the pair of end layers by vulcanization adhesion, it is possible to reduce the assembling process for assembling separate parts to each other. be able to.

According to the invention of claim 3 , by using two-color molding, the intermediate element can be easily and reliably integrally molded .
According to the invention of claim 4 , it is possible to realize a quiet worm speed reducer by suppressing the generation of abnormal noise even when the axis of the worm shaft is inclined with respect to the axis of the output shaft of the electric motor. it can.

According to the fifth aspect of the present invention, in order to suppress backlash between the worm shaft and the worm wheel, the second end portion of the worm shaft is displaced in a direction that reduces the center-to-center distance between the worm shaft and the worm wheel. Even if the axis of the worm shaft is inclined with respect to the axis of the output shaft of the electric motor, the end layer does not come into contact with the power transmission surfaces of the engaging protrusions of both rotating elements in the power transmission joint. Therefore, it is possible to realize a quiet worm speed reducer by suppressing the generation of abnormal noise due to contact sound.

According to the invention of claim 6 , a quiet electric power steering device can be realized.

1 is a schematic diagram of an electric power steering apparatus to which a worm reduction gear including a power transmission joint according to an embodiment of the present invention is applied. It is sectional drawing of the principal part of an electric power steering device. It is a disassembled perspective view of a power transmission coupling. It is a disassembled perspective view of the principal part of the intermediate element of a power transmission coupling. It is sectional drawing of the power transmission part of an intermediate element. It is the schematic sectional drawing cut | disconnected along the VI-VI line of FIG. 2, and has shown the structure which supports the 2nd end part of a worm shaft. It is a schematic perspective view of the leaf | plate spring as an urging member for removing the backlash of a worm reduction gear.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus including a power transmission joint according to an embodiment of the present invention. As shown in FIG. 1, an electric power steering apparatus 1 includes a steering mechanism 4 for turning a steered wheel 3 based on an operation of a driver's steering wheel 2 (steering member), and an assist mechanism for assisting the driver's steering operation. 5 is provided.

  The steering mechanism 4 includes a steering shaft 6 that serves as a rotating shaft of the steering wheel 2. The steering shaft 6 includes a column shaft 7 connected to the center of the steering wheel 2, an intermediate shaft 9 connected to one end (lower end in the axial direction) of the column shaft 7 via a universal joint 8, and an intermediate shaft 9 And a pinion shaft 11 connected to one end (lower end in the axial direction) via a universal joint 10.

The column shaft 7 includes an input shaft 7a connected to the steering wheel 2, an output shaft 7b connected to the intermediate shaft 9, and a torsion bar 7c that coaxially connects the input shaft 7a and the output shaft 7b. Yes.
A pinion 11 a is provided at the lower end in the axial direction of the pinion shaft 11. The steering mechanism 4 includes a rack shaft 12 that forms a rack 12a that meshes with the pinion 11a. The pinion 11a and the rack 12a form a rack and pinion mechanism A that is a motion conversion mechanism.

  When the steering shaft 6 rotates in accordance with the steering operation by the driver, the rotational motion is converted into the axial reciprocating linear motion of the rack shaft 12 via the rack and pinion mechanism A. The reciprocating linear motion of the rack shaft 12 is transmitted to the steered wheels 3 through tie rods 13 connected to both ends of the rack shaft 12. Thereby, the turning angle of the steered wheels 3 is changed, and the traveling direction of the vehicle is changed.

The assist mechanism 5 includes an electric motor 14 that applies assist torque to the column shaft 7, a worm speed reducer 15 that transmits the rotation of the electric motor 14 to the column shaft 7, and an ECU (Electronic Control Unit) that controls the operation of the electric motor 14. ) 16.
The worm reducer 15 transmits torque to the housing 17, the worm shaft 18, the worm wheel 19 that meshes with the worm shaft 18, the output shaft 14 a (first shaft) and the worm shaft 18 (second shaft) of the electric motor 14. And a power transmission joint 20 that can be connected. The worm shaft 18, the worm wheel 19 and the power transmission joint 20 are accommodated in the housing 17.

The rotation of the electric motor 14 is transmitted to the column shaft 7 via the worm speed reducer 15, whereby a motor torque is applied to the steering shaft 6 and the steering operation is assisted.
The electric power steering apparatus 1 also detects a steering torque T, which is a torque applied to the steering shaft 6 when the driver performs a steering operation, based on the relative rotation between the input shaft 7a and the output shaft 7b of the column shaft 7. A torque sensor 21 is provided. On the other hand, the vehicle is provided with a vehicle speed sensor 22 that detects a vehicle speed V (vehicle traveling speed).

The ECU 16 sets a target assist force based on the detected steering torque T and the detected vehicle speed V, and the electric motor 14 so that the assist torque applied from the electric motor 14 to the column shaft 7 becomes the target assist torque. Feedback control of the current supplied to.
In the present embodiment, the electric power steering apparatus 1 will be described based on an example of a so-called column assist type in which the electric motor 14 applies power to the column shaft 7, but the present invention is not limited thereto, and the present invention The present invention can be applied to a so-called pinion assist type electric power steering device in which a motor applies power to a pinio shaft.

As shown in FIG. 2, the worm shaft 18 is disposed coaxially with the output shaft 14 a of the electric motor 14. The output shaft 14a (first shaft) and the worm shaft 18 (second shaft) face each other in the axial direction X. That is, the output shaft 14 a and the worm shaft 18 are opposed to each other in the axial direction X.
The worm shaft 18 has a first end portion 18a and a second end portion 18b that are separated in the axial length direction, and an intermediate tooth portion 18c between the first end portion 18a and the second end portion 18b.

  The worm wheel 19 is connected to an intermediate portion in the axial direction of the output shaft 7 b of the column shaft 7 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 output shaft 7b so as to be integrally rotatable, and a resin member 19b surrounding the cored bar 19a and having teeth 19c formed on the outer periphery. The cored bar 19a is inserted into the mold when the resin member 19b is molded, for example.

The first end portion 18a of the worm shaft 18 and the end portion of the output shaft 14a of the electric motor 14 opposed to the first end portion 18a are connected to each other through a power transmission joint 20 so as to be able to transmit torque and swing with each other.
Specifically, the power transmission joint 20 is fixed to the first rotating element 23 fixed to the first end 18a of the worm shaft 18 so as to be integrally rotatable, and to the output shaft 14a of the electric motor 14 so as to be integrally rotatable. A second rotating element 24 and an intermediate element 25 that is interposed between the first rotating element 23 and the second rotating element 24 and transmits torque between the rotating elements 23 and 24 are provided.

As shown in FIG. 3, the first rotating element 23 includes a boss 26 formed with a fitting hole 26 a into which the first end portion 18 a (see FIG. 2) of the worm shaft 18 is press-fitted, and a boss 26 radially outward. And an annular flange 27 extending in the direction. The boss 26 is fitted to the first end portion 18a of the worm shaft 18 so as to be integrally rotatable and immovable in the axial direction.
The second rotating element 24 is formed with a fitting hole 28a into which the output shaft 14a (see FIG. 2) of the electric motor 14 is press-fitted, and the annular body facing the flange 27 of the first rotating element 23 in the axial direction X. 28.

The flange 27 of the first rotating element 23 is configured to equally spaced a plurality of engaging protrusions 29 protruding in the axial direction Y toward the main body 28 of the second rotating element 24 in the rotating direction Z (corresponding to the circumferential direction). Provided.
Further, the main body 28 of the second rotating element 24 equally spaced apart the plurality of engaging protrusions 30 protruding in the axial direction Y toward the flange 27 of the first rotating element 23 in the rotating direction Z (corresponding to the circumferential direction). It is provided as follows. The engagement protrusions 29 and the engagement protrusions 30 are alternately arranged in the rotation direction Z (circumferential direction).

The intermediate element 25 includes an annular support portion 31 and a plurality of arm-shaped power transmission portions 32 extending radially from the support portion 31. Each power transmission part 32 is interposed between the corresponding engaging protrusions 29 and 30 of the first rotating element 23 and the second rotating element 24, respectively.
Each power transmission portion 32 includes a pair of power transmission surfaces 32a and 32b that engage with the power transmission surfaces 29a and 30a of the corresponding engagement protrusions 29 and 30 of the first rotation element 23 and the second rotation element 24, respectively.

As shown in FIG. 4 which is an exploded perspective view and FIG. 5 which is a cross-sectional view of the power transmission unit 32, the intermediate element 25 includes a resin layer 41 as a pair of end layers facing in the axial direction Y, and a pair of resins. The unit is configured as a unit having a three-layer structure (sandwich structure) in which a rubber layer 42 as an elastic layer interposed between the layers 41 is overlapped.
As the resin layer 41, a resin such as polyacetal (POM), polypropylene (PP), polyamito (PA), polybutylene terephthalate (PBT), or the like can be used. As the rubber layer 42, rubbers such as silicone rubber, urethane rubber, nitrile rubber, hydrogenated nitrile rubber, and thermoplastic elastomer (TPE) can be used.

The front shape of the resin layer 41 and the front shape of the rubber layer 42 are substantially the same. The resin layer 41 includes an annular first portion 41 a that forms part of the support portion 31, and a plurality of second portions 41 b that extend radially from the first portion 41 a and form part of the power transmission portion 32.
The rubber layer 42 includes an annular first portion 42 a that forms a part of the support portion 31, and a plurality of second portions 42 b that extend radially from the first portion 42 a and form a portion of the power transmission portion 32.

The second portion 42b of the rubber layer 42 includes a main portion 42c interposed between the second portions 41b of the pair of resin layers 41, and a pair of flanges 42d and 42e connected to both ends of the main portion 42c. The cross section is substantially I-shaped.
As shown in FIG. 5, the flanges 42 d and 42 e of the second portion 42 b of the rubber layer 42 cover the end faces in the circumferential direction of the second portions 41 b of both resin layers 41. End faces in the circumferential direction of the flanges 42d and 42e of the second portion 42b of the rubber layer 42 constitute power transmission surfaces 32a and 32b. That is, the pair of power transmission surfaces 32 a and 32 b of each power transmission unit 32 is formed by a part of the rubber layer 42.

The rubber layer 42 is bonded to the pair of resin layers 41. Specifically, the rubber layer 42 are a pair of the resin layer 4 1 and the vulcanized rubber. A resin layer 41 as a pair of end layers and a rubber layer 42 as an elastic layer are integrally formed by two-color molding.
Referring again to FIG. 2, the first end 18 a of the worm shaft 18 is rotatably supported by the housing 17 via the first bearing 33. The second end portion 18 b of the worm shaft 18 is rotatably supported by the housing 17 via the second bearing 34.

The elastic deformation of the rubber layer 42 of the intermediate element 25 of the power transmission joint 20 allows the worm shaft 18 to swing relative to the output shaft 14 a of the electric motor 14 around the bearing center of the first bearing 33.
The first bearing 33 and the second bearing 34 are constituted by ball bearings, for example.
The first bearing 33 includes an inner ring 35 that is fitted to the first end 18 a of the worm shaft 18 so as to be integrally rotatable, and an outer ring 37 that is fixed to a bearing hole 36 provided in the housing 17.

An outer ring 37 is sandwiched in the axial direction between a positioning step portion 38 provided at an end portion of the bearing hole 36 and a fixing member 39 screwed to a screw portion provided in the bearing hole 36. . Thereby, the axial movement of the outer ring 37 is restricted.
The inner ring 50 of the second bearing 34 is fitted in a fitting recess 51 provided on the outer periphery of the second end 18b of the worm shaft 18 so as to be integrally rotatable. One end surface of the inner ring 50 is in contact with a positioning step portion 52 provided on the outer periphery of the second end portion 18b, whereby the axial movement of the inner ring 50 relative to the worm shaft 18 is restricted.

  The housing 17 is provided with a bearing hole 53 for holding the second bearing 34. The bearing hole 53 has a direction Y1 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 19) increases or decreases. , Y2 (increasing direction Y1 and decreasing direction Y2) are formed in a biasing hole that can be held biasably.

An urging member 60 made of, for example, an annular leaf spring is interposed between the inner periphery of the bearing hole 53 and the outer ring 54 of the second bearing 34. The urging member 60 urges the second bearing 34 in the direction Y2 in which the center distance D1 decreases. The urging member 60 is a thin plate member formed of, for example, a sheet metal.
Referring to FIG. 6, which is a cross-sectional view taken along line VI-VI in FIG. 2, and FIG. 7, which is a perspective view, the biasing member 60 has an end ring shape surrounding the outer periphery 54 a of the outer ring 54 of the second bearing 34. A main body portion 61, a pair of rotation restriction portions 62 extending in a bent shape from the first end portion 61a and the second end portion 61b, which are circumferential ends of the main body portion 61, and each rotation restriction portion 62; And a pair of cantilevered elastic tongue pieces 63 each extending in a bent shape.

The width of each rotation restricting portion 62 is narrower than the width of the main portion 61. The main body 61 is held on the inner periphery of the bearing hole 53 of the housing 17 by friction engagement. As shown in FIG. 7, one of the pair of elastic tongues 63 is disposed on the first side edge 61c side, and the other elastic tongue piece 63 is disposed on the second side edge 61d side and is staggered.
Referring to FIG. 6 again, the bearing hole 53 of the housing 17 is formed in a part of the inner periphery thereof in a direction opposite to the second bearing 34 on the worm wheel 19 side (direction Y2 in which the center-to-center distance decreases). A receiving recess 64 that is recessed in the direction Y1 in which the distance between the centers increases is formed. The tip of each elastic tongue 63 of the urging member 60 is received by the bottom 64 c of the receiving recess 64 of the bearing hole 53, and the urging force of each elastic tongue 63 passes through the second bearing 34 and the first of the worm shaft 18. The two end portions 18b are biased in the direction Y2 in which the center distance D1 decreases.

The receiving recess 64 has a pair of inner walls 64a and 64b that face each other in the rotation direction Z (circumferential direction) of the bearing hole 53, and each rotation restricting portion 62 of the urging member 60 is formed on the corresponding inner walls 64a and 64b. By contacting, the rotation of the urging member 60 in the rotation direction Z (circumferential direction) of the bearing hole 53 is regulated.
According to the present embodiment, as shown in FIG. 5, the pair of power transmission surfaces 32 a and 32 b of the power transmission portion 32 of the intermediate element 25 is formed by a part of the elastic layer (rubber layer 42). Therefore, even when the second shaft (worm shaft 18) is inclined with respect to the first shaft (output shaft 14a), the pair of end layers (the second layer of the resin layer 41 in the power transmission portion 32 of the intermediate element 25). The portion 41 b) does not come into contact with the power transmission surfaces 29 a and 30 a of the engagement protrusions 29 and 30 of the first rotating element 23 and the second rotating element 24. Therefore, it is possible to suppress the generation of abnormal noise due to the contact hitting sound with respect to the power transmission surfaces 29 a and 30 a of the engaging protrusions 29 and 30 of both the rotating elements 23 and 24.

In addition, since the elastic layer (rubber layer 42) is bonded to the pair of end layers (resin layer 41), it is possible to suppress the generation of noise caused by rattling between the end layers and the elastic layer. Can do.
In addition, since the rubber layer 42 as an elastic layer is integrated with the pair of end layers (resin layer 41) by vulcanization adhesion, it is possible to reduce an assembling process for assembling separate parts to each other. be able to.

Also, a resin layer 41 as a pair of end layers and a rubber layer 42 as an elastic layer are integrally formed by two-color molding. By using the two-color molding, the intermediate element 25 can be easily and reliably integrally molded.
In the power transmission unit 32, the elastic layer 42 bonded to the pair of end layers (resin layer 41) includes a main portion 42c interposed between the pair of end layers (resin layer 41), and a power transmission surface. 32a, 42d pair of flanges with 32b, is formed in a substantially I-shaped configuration including a 42e. Therefore, it is possible to reliably suppress the generation of abnormal noise due to rattling noise between the pair of end layers and the elastic layer.

In addition, even when the axis of the worm shaft 18 is inclined with respect to the axis of the output shaft 14a of the electric motor 14, it is possible to suppress the generation of abnormal noise and realize a quiet worm speed reducer 15.
In order to suppress backlash between the worm shaft 18 and the worm wheel 19, the second end portion 18b of the worm shaft 18 is displaced in the direction Y2 in which the center distance D1 between the worm shaft 18 and the worm wheel 19 is reduced. Te, even the axis of the worm shaft 18 is inclined relative to the axis of the output shaft 14a of the electric motor 14, the power transmission coupling 2 0, power transmission surface 29a of the engaging projections 29, 30 of the two rotary elements 23, 24 , 30a does not contact the end layer (resin layer 41). Therefore, it is possible to realize a quiet worm speed reducer 15 by suppressing the generation of abnormal noise caused by the contact sound with respect to the power transmission surfaces 29a and 30a.

In addition, a quiet electric power steering device 1 can be realized.
The present invention is not limited to the above-described embodiment. For example, a pair of end layers and an elastic layer may be bonded to each other using an adhesive in the intermediate element. In addition, the present invention can be variously modified within the scope of the claims.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 2 ... Steering wheel, 3 ... Steering wheel, 4 ... Steering mechanism, 5 ... Assist mechanism, 6 ... Steering shaft, 7 ... Column shaft, 14 ... Electric motor, 14a ... Output shaft (1st shaft) ), 15 ... Worm reducer, 16 ... ECU, 17 ... Housing, 18 ... Worm shaft, 18a ... First end, 18b ... Second end, 18c ... Teeth, 19 ... Worm wheel, 20 ... Power transmission joint , 23 ... 1st rotation element, 24 ... 2nd rotation element, 25 ... Intermediate element, 26 ... Boss, 27 ... Flange, 28 ... Main body, 29, 30 ... Engagement protrusion, 29a, 30a ... Power transmission surface, 31 ... Support part, 32 ... Power transmission part, 32a, 32b ... Power transmission surface, 34 ... Second bearing, 41 ... Resin layer (end part layer), 41a ... First part, 41b ... Second part, 42 ... Go Layer (elastic layer), 42a ... first part, 42b ... second part, 42c ... main part, 42d, 42e ... flange, 60 ... biasing member, C1, C2 ... center of rotation, D1 ... center distance, X ... Axial direction, Y1 ... direction in which the center distance increases, Y2 ... direction in which the center distance decreases, Z ... direction of rotation

Claims (6)

A power transmission joint that transmits torque between a first shaft and a second shaft opposed in the axial direction,
A first rotating element connected to the first shaft;
A second rotating element connected to the second shaft;
An intermediate element interposed between the first rotating element and the second rotating element and connecting the rotating elements so as to transmit torque;
The first rotating element and the second rotating element each include a plurality of engaging protrusions extending in the axial direction, and the engaging protrusions are arranged alternately in the rotating direction, and each engaging protrusion is a power Including the transmission surface,
The intermediate element includes a plurality of power transmission portions respectively interposed between corresponding engagement protrusions of the two rotation elements, and each of the power transmission portions is respectively engaged with a power transmission surface of the corresponding engagement protrusion of the two rotation elements. Including a pair of mating power transmission surfaces,
The intermediate element is configured as a unit in which a pair of end layers facing in the axial direction and an elastic layer interposed between the pair of end layers are overlapped,
The pair of power transmission surfaces of each of the power transmission units is formed by a part of the elastic layer ,
The elastic layer is bonded to the pair of end layers,
In the power transmission section, the elastic layer includes a main body interposed between the pair of end layers, and a pair of flanges connected to both ends of the main body and each having a power transmission surface. 2. The power transmission joint according to claim 1 , wherein the elastic layer is rubber vulcanized and bonded to the pair of end layers. The power transmission joint according to claim 2 , wherein the resin layer as the pair of end layers and the rubber layer as the elastic layer are integrally formed by two-color molding. A worm shaft as the second shaft disposed coaxially with an output shaft of the electric motor as the first shaft;
A worm wheel meshing with the worm of the worm shaft;
Worm reduction gear and a power transmission coupling according to any one of claim 1 to 3 for connecting the worm shaft and the output shaft to transmit the torque. The worm shaft according to claim 4 , comprising a first end connected to the power transmission joint, and a second end opposite to the first end.
A housing for housing the worm shaft and the worm wheel;
A bearing that is supported by the housing so as to be displaceable in a direction that increases or decreases the distance between the centers of the worm shaft and the worm wheel, and that rotatably supports the second end of the worm shaft;
A worm reduction device further comprising a biasing member that biases the bearing in a direction in which the distance between the centers decreases. An electric power steering apparatus comprising the worm reducer according to claim 4 or 5 .

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