JP2012101638A - Electric power steering system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering system capable of suppressing generation of teeth cracking sound for a long period and preventing a reduction in responsiveness.SOLUTION: The EPS is provided with: a reduction mechanism 24 composed of a worm shaft 26 meshed with a worm wheel 25; a motor 21 driven and coupled to a steering shaft 3 via the reduction mechanism 24; a shaft coupling 41 which couples a base end 26a of the worm shaft 26 so as to be tilted with respect to an output shaft 36 of the motor 21; and a curved plate spring 51 which biases the distal end 26b of the worm shaft 26 toward the worm wheel 25. The shaft coupling 41 is composed of a ball-type constant-speed joint of a fixed type.

Description

  The present invention relates to an electric power steering apparatus.

  2. Description of the Related Art Conventionally, some electric power steering apparatuses (EPS) give an assist force for assisting a steering operation to a steering system by rotationally driving a steering shaft using a motor as a drive source. As such an EPS, there is known an EPS provided with a speed reduction mechanism formed by meshing a worm shaft rotated by a motor and a worm wheel connected to a steering shaft.

  By the way, in the case of EPS using the deceleration mechanism as described above, rattling noise may occur due to the backlash when switching the steering direction or applying reverse input. Therefore, in such an EPS, in many cases, one end of the worm shaft is tiltably connected to the output shaft of the motor, and the other end of the worm shaft is pressed against the worm wheel by using an urging means. A so-called anti-backlash system that removes backlash by adjusting the distance between the axes is incorporated (for example, see Patent Document 1). In general, a shaft joint for connecting such a worm shaft to a motor output shaft so as to be tiltable is composed of a pair of joints (yokes) and an elastic body interposed therebetween. (See Patent Document 1 and FIG. 3).

Japanese Patent Laid-Open No. 2004-203154

  However, in the shaft joint used in the EPS of Patent Document 1, since the worm shaft tilts when the elastic body is compressed between the pair of yokes, the repulsive force (elastic force) of the elastic body accompanies the tilt of the worm shaft. ) Increases. As a result, when wear of each tooth portion of the worm shaft and the worm wheel progresses due to long-term use, the worm shaft cannot be tilted sufficiently, and there is a possibility that rattling noise is likely to occur.

  Therefore, it can be considered that the elastic body is made of a material having a low elastic coefficient so that the worm shaft can be tilted sufficiently even when the wear of each tooth portion progresses. However, in this case, since the elastic body is easily deformed, even when the motor torque is transmitted, the elastic body is greatly deformed, resulting in a delay in torque transmission and a response of assist force application. The problem that it falls is caused.

  The present invention has been made to solve the above-described problems, and the object thereof is to suppress the generation of rattling noise over a long period of time and to prevent a decrease in responsiveness. An object is to provide an electric power steering apparatus.

  In order to achieve the above object, a first aspect of the present invention is directed to a speed reduction mechanism formed by meshing a worm shaft and a worm wheel, a motor connected to a steering shaft via the speed reduction mechanism, and an output of the motor. In the electric power steering apparatus comprising: a shaft coupling that connects the one end portion of the worm shaft with respect to the shaft so as to be tiltable; and an urging means that urges the other end portion of the worm shaft toward the worm wheel. The gist of the shaft joint is a constant velocity joint.

  According to the above configuration, since the shaft coupling is constituted by a constant velocity joint, unlike the conventional case where the worm shaft tilts by compressing the elastic body, a repulsive force is generated as the worm shaft tilts. Therefore, the worm shaft can be sufficiently tilted even when the wear of each tooth portion progresses. Thereby, generation | occurrence | production of a rattling sound can be suppressed over a long term. In addition, the constant velocity joint can transmit torque smoothly at a constant speed even when the worm shaft is inclined with respect to the output shaft of the motor, thus preventing a delay in torque transmission and reducing responsiveness. Can be prevented.

  The invention according to claim 2 is the electric power steering apparatus according to claim 1, characterized in that the worm shaft is provided so as to be axially movable with respect to a housing accommodating the speed reduction mechanism.

  Here, in the EPS provided with a speed reduction mechanism formed by meshing the worm shaft and the worm wheel, when the steering shaft is rotated by the steering operation, the worm shaft needs to be rotated by the worm wheel connected to the steering shaft. . Further, when the worm shaft and the worm wheel rotate, their respective tooth portions slide with each other. Therefore, at the start of steering, a steering force that exceeds the frictional force (static frictional force) acting between the teeth of the worm shaft and the worm wheel is required. In the EPS incorporating the anti-backlash system, the worm shaft is pressed against the worm wheel, so that the frictional force acting between these teeth is increased. There is a risk of ring degradation.

  In this respect, according to the above configuration, since the worm shaft is movable in the axial direction, the worm shaft is axially moved without sliding between the tooth portion of the worm wheel and the tooth portion of the worm shaft at the start of steering. The worm wheel can be rotated within the movable range. Thereby, a feeling of catching can be reduced.

  According to a third aspect of the present invention, in the electric power steering apparatus according to the second aspect of the present invention, the axial movement of the worm shaft is caused between the worm shaft and a fixed member fixed to the housing. The gist is that an elastic member to be compressed is provided.

  According to the above configuration, when the worm shaft moves in the axial direction, the elastic member is compressed between the fixed member and the worm shaft is in direct contact with the fixed member, so that the movement is restricted. , It becomes possible to suppress the generation of abnormal noise. In addition, since the repulsive force of the elastic member gradually increases as the compression amount of the elastic member increases, the steering force necessary for the steering operation gradually increases, thereby realizing a better steering feeling. Can do.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to suppress generation | occurrence | production of a rattling sound over a long term, the electric power steering apparatus which can prevent the fall of responsiveness can be provided.

The schematic block diagram of an electric power steering device (EPS). Sectional drawing which shows schematic structure of an EPS actuator. AA sectional drawing of FIG. The exploded perspective view of a shaft coupling. The expanded sectional view which shows a shaft coupling vicinity. BB sectional drawing of FIG.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
As shown in FIG. 1, in an electric power steering apparatus (EPS) 1, a steering shaft 3 to which a steering 2 is fixed is connected to a rack shaft 5 via a rack and pinion mechanism 4. Thereby, the rotation of the steering shaft 3 accompanying the steering operation is converted into a reciprocating linear motion of the rack shaft 5 by the rack and pinion mechanism 4. The steering shaft 3 is formed by connecting a column shaft 8, an intermediate shaft 9, and a pinion shaft 10. The reciprocating linear motion of the rack shaft 5 accompanying the rotation of the steering shaft 3 is transmitted to a knuckle (not shown) via tie rods 11 connected to both ends of the rack shaft 5, whereby the steered angle of the steered wheels 12. That is, the traveling direction of the vehicle is changed.

  The EPS 1 also includes an EPS actuator 22 that applies an assist force for assisting the steering operation to the steering system using the motor 21 as a drive source. The EPS actuator 22 of the present embodiment is configured as a so-called column-type EPS actuator, and the motor 21 is drivingly connected to the column shaft 8 via a speed reduction mechanism 24. The speed reduction mechanism 24 is configured by meshing a worm wheel 25 connected to the column shaft 8 and a worm shaft 26 connected to the motor 21. The rotation of the motor 21 is decelerated by the deceleration mechanism 24 and transmitted to the column shaft 8 so that the motor torque is applied to the steering system as an assist force.

Next, the configuration of the EPS actuator in the present embodiment will be described.
As shown in FIG. 2, the EPS actuator 22 includes a housing 31 that houses the speed reduction mechanism 24. The housing 31 includes a worm shaft housing portion 32 in which the worm shaft 26 is housed, and a worm wheel housing portion 33 that is formed continuously with the worm shaft housing portion 32 and in which the worm wheel 25 is housed. . The worm shaft housing portion 32 is a cylindrical space extending in the axial direction (left and right direction in FIG. 2) of the worm shaft 26, and one end side (right side in FIG. 2) is a motor fixing hole 34 to which the motor 21 is fixed. Communicating with Further, the other end side (the left side in FIG. 2) of the worm shaft housing portion 32 is opened to the outside, and the opening end is closed by an end cover 35 fixed to the opening end.

  The motor 21 is fixed to the motor fixing hole 34 of the housing 31 so that the axial direction of the output shaft 36 is orthogonal to the axial direction of the steering shaft 3 (column shaft 8) penetrating the housing 31. Yes. The worm shaft 26 connected to the output shaft 36 is rotatably supported at both ends by first and second rolling bearings 37 and 38 provided in the housing 31 and connected to the steering shaft 3. Is engaged with the worm wheel 25. In the present embodiment, ball bearings are employed as the first and second rolling bearings 37 and 38.

  Here, the EPS actuator 22 of the present embodiment has a so-called anti-backlash for removing the backlash by adjusting the inter-axis distance between the worm wheel 25 and the worm shaft 26 constituting the speed reduction mechanism 24.・ The system is installed.

  More specifically, one end portion of the worm shaft 26 (the right end portion in FIG. 2, hereinafter referred to as a base end portion 26a) is connected to the output shaft 36 of the motor 21 via a shaft coupling 41 so as to be tiltable. Further, the base end portion 26 a of the worm shaft 26 is rotatably supported by a first rolling bearing 37. The first rolling bearing 37 is provided in a fixed portion 42 having a larger diameter than the worm shaft housing portion 32 formed on one end side of the worm shaft housing portion 32. The first rolling bearing 37 is provided in a state in which movement in the axial direction is restricted with respect to the housing 31 by a fixed plug 43 in which an outer ring 37 a is fixed to one end of the worm shaft housing portion 32.

  On the other hand, the other end portion of the worm shaft 26 (the left end portion in FIG. 2, hereinafter referred to as the front end portion 26 b) is rotatably supported by a second rolling bearing 38. The second rolling bearing 38 is provided so as to be movable in a direction in which the second rolling bearing 38 comes in contact with and separates from the worm wheel 25 (vertical direction in FIG. 2), and is a curved plate as a biasing means curved so as to surround the outer periphery thereof. The spring 51 is biased toward the worm wheel 25 side. The tip end portion 26b is press-fitted into the inner ring 38b of the second rolling bearing 38.

  Specifically, a support portion 52 for accommodating and supporting the second rolling bearing 38 and the curved leaf spring 51 is formed on the other end side (left side in FIG. 2) of the worm shaft accommodating portion 32. The inner diameter of the support portion 52 is formed larger than the outer diameter of the second rolling bearing 38. Accordingly, the second rolling bearing 38 is provided in the support portion 52 so as to be movable in a direction in which the second rolling bearing 38 is in contact with or separated from the worm wheel 25. The second rolling bearing 38 is provided with a space in the axial direction of the worm shaft 26 between the end cover 35 and the tip end portion 26 b of the worm shaft 26 is integrated with the second rolling bearing 38. It is provided so as to be movable in the axial direction. The support portion 52 is made of an elastic material and has an arcuate elastic ring 53 interposed between the curved leaf spring 51 and the support portion 52 and between the end cover 35 and the second rolling bearing 38. Is provided.

  As shown in FIG. 3, the curved leaf spring 51 includes an arcuate arc portion 54 that comes into contact with the outer ring 38 a of the second rolling bearing 38, and a spring portion 55 that is disposed radially outward from the arc portion 54. The spring portions 55 and the arc portions 54 are connected to both ends of the connection portions 56. A housing recess 57 for housing the spring portion 55 of the curved leaf spring 51 is formed on the peripheral wall of the support portion 52 on the side opposite to the worm wheel 25 (upper side in FIG. 3). The second rolling bearing 38 is biased toward the worm wheel 25 side (lower side in FIG. 3) by the spring portion 55 coming into contact with the bottom surface 57a of the housing recess 57 and pressing the bottom surface 57a. Has been. As a result, as shown in FIG. 2, the worm shaft 26 tilts about one end thereof, the distance between the worm shaft 26 and the worm wheel 25 is adjusted, and backlash is removed. .

(Connection structure between worm shaft and output shaft)
Next, a connection structure between the worm shaft and the motor output shaft in the EPS of the present embodiment will be described.

  The shaft coupling 41 is constituted by a fixed ball-type constant velocity joint in which axial displacement between two axes is restricted. Specifically, as shown in FIG. 4, the shaft coupling 41 includes a bottomed cylindrical (cup-shaped) outer race 61, an annular inner race 62 disposed inside the outer race 61, and the outer race 61. A plurality of balls 63 that transmit torque to and from the inner race 62 and a cage 64 that holds the position of each ball 63 are provided.

  More specifically, as shown in FIGS. 4 and 5, the inner peripheral surface of the outer race 61 is formed in a concave spherical shape. A plurality (six in this embodiment) of ball grooves 65 extending in the axial direction of the outer race 61 (in the left-right direction in FIG. 5) are formed on the inner peripheral surface of the outer race 61. The ball grooves 65 are formed in a circular arc shape in cross section perpendicular to the axial direction of the outer race 61, and are formed at equiangular intervals in the circumferential direction.

  The outer peripheral surface of the inner race 62 is formed in a convex spherical shape. A plurality of (six in this embodiment) ball grooves 66 extending in the axial direction of the inner race 62 (the left-right direction in FIG. 5) are formed on the outer peripheral surface of the inner race 62. The ball groove 66 has a cross-sectional shape orthogonal to the axial direction of the inner race 62 formed in an arc shape and is formed at equal angular intervals in the circumferential direction, and faces the ball groove 65 of the outer race 61.

  The ball 63 is disposed so as to be able to roll between the ball groove 65 of the outer race 61 and the ball groove 66 of the inner race 62 facing the ball groove 65. Each ball 63 transmits torque between the outer race 61 and the inner race 62 by engaging with the ball grooves 65 and 66 in the circumferential direction.

  The cage 64 is formed in an annular shape and is disposed between the outer race 61 and the inner race 62. The retainer 64 is formed with a plurality (six in this embodiment) of retaining holes 67 penetrating in the radial direction. The holding holes 67 are formed in a substantially square shape and are formed at equiangular intervals in the circumferential direction. Each holding hole 67 contains one ball 63.

  As shown in FIG. 5, a base end portion 26 a of the worm shaft 26 is connected to the inner race 62 of the shaft coupling 41 so as to be relatively movable in the axial direction with respect to the inner race 62 and to be integrally rotatable. Yes. Specifically, serration teeth 71 extending in the axial direction of the worm shaft 26 are formed on the outer peripheral surface of the base end portion 26 a, and the inner peripheral surface of the inner race 62 is formed in the axial direction of the inner race 62. Extending serration teeth 72 are formed. The base end portion 26 a of the worm shaft 26 is connected to the inner race 62 so as to be relatively movable in the axial direction and integrally rotatable with the inner race 62 by serration fitting.

  Further, the base end portion 26 a of the worm shaft 26 is fitted in a gap fitting state in which a slight gap is provided between the inner end 37 b of the first rolling bearing 37 and the first rolling bearing 37. On the other hand, it is provided so as to be movable in the axial direction. Further, in the present embodiment, an elastic ring 73 made of an elastic material is sandwiched between the main body portion 26 c where the tooth portion of the worm shaft 26 is formed and the inner ring 37 b of the first rolling bearing 37. Here, as described above, the tip 26b of the worm shaft 26 is accompanied by elastic deformation of the elastic ring 53 interposed between the end cover 35 and the second rolling bearing 38 shown in FIG. The second rolling bearing 38 is provided integrally with the second rolling bearing 38 so as to be movable in the axial direction. Accordingly, the worm shaft 26 can move in the axial direction within the housing 31 by elastic deformation of the elastic rings 53 and 73.

  On the other hand, as shown in FIG. 5, the output shaft 36 of the motor 21 is connected to the outer race 61 of the shaft coupling 41 so as to be integrally rotatable. In the present embodiment, the outer race 61 is connected to the output shaft 36 via a disk-shaped yoke 74 and a spacer 75 interposed between the outer race 61 and the yoke 74.

  Specifically, as shown in FIGS. 4 and 5, a plurality (four in this embodiment) of engaging claws 76 projecting toward the yoke 74 are formed on the bottom surface 61 a of the outer race 61 on the output shaft 36 side. Has been. On the other hand, a plurality of (four in this embodiment) engaging claws 77 projecting toward the outer race 61 are formed on one end surface 74a of the yoke 74 on the outer race 61 side. As shown in FIG. 6, the outer race 61 and the yoke 74 are connected so that the engaging claws 76 and 77 are alternately arranged in the circumferential direction. On the other hand, the spacer 75 is made of a resin material and is formed in an annular shape. The spacer 75 is formed with an engagement piece 78 that extends radially outward and is sandwiched between adjacent engagement claws 76 and 77. The connecting end portion 36 a of the output shaft 36 is press-fitted into a fitting hole 79 opened in the other end surface 74 b of the yoke 74, and is connected to the yoke 74 so as to be integrally rotatable.

  In the shaft coupling 41 configured as described above, each ball 63 rolls in the ball grooves 65 and 66, and the inner race 62 swings with respect to the outer race 61, so that the worm shaft 26 outputs the output of the motor 21. It can be tilted with respect to the shaft 36. At the start of steering, the base end portion 26a of the worm shaft 26 moves relative to the inner race 62 of the shaft coupling 41 in the axial direction of the worm shaft 26, and the tip end portion 26b of the worm shaft 26 is second rolled. By moving integrally with the bearing 38 in the axial direction, it moves in the axial direction. When the worm shaft 26 moves to one end side, the elastic ring 73 provided between the main body portion 26c of the worm shaft 26 and the first rolling bearing 37 is compressed in the axial direction, so that the worm shaft 26 is When moving to the other end side, an elastic ring 53 provided between the end cover 35 and the second rolling bearing 38 is compressed in the axial direction. That is, in this embodiment, the end cover 35 and the first rolling bearing 37 correspond to a fixing member fixed to the housing 31, and the elastic rings 53 and 73 correspond to elastic members.

As described above, according to the present embodiment, the following operational effects can be achieved.
(1) The shaft coupling 41 for connecting the base end portion 26a of the worm shaft 26 to the output shaft 36 of the motor 21 so as to be tiltable is constituted by a fixed ball type constant velocity joint.

  According to the above configuration, since the shaft coupling 41 is constituted by a constant velocity joint, unlike the conventional case where the worm shaft 26 is tilted by compressing the elastic body, the repulsion occurs as the worm shaft 26 tilts. The worm shaft 26 can be tilted sufficiently even if no force is generated and the wear of each tooth portion progresses. Thereby, generation | occurrence | production of a rattling sound can be suppressed over a long term. In addition, the constant velocity joint can transmit torque smoothly at a constant speed even when the worm shaft 26 is inclined with respect to the output shaft 36 of the motor 21, thereby preventing a delay in torque transmission and responding. The fall of property can be prevented.

(2) The worm shaft 26 is provided so as to be movable in the axial direction with respect to the housing 31 in which the speed reduction mechanism 24 is accommodated.
Here, at the start of steering as described above, a steering force exceeding the frictional force (static frictional force) acting between each tooth portion of the worm shaft 26 and the worm wheel 25 is required, which is a feeling of catching. As a result, the steering feeling may be reduced. In this regard, according to the above configuration, since the worm shaft 26 is movable in the axial direction, the tooth portion of the worm wheel 25 and the tooth portion of the worm shaft 26 do not slide at the start of steering, so that the worm shaft The worm wheel 25 can be rotated within a range in which 26 can move in the axial direction. As a result, the feeling of catching can be reduced, and delicate steering with a small steering amount can be easily performed without causing a decrease in steering feeling.

  (3) Elastic rings 53 and 73 are provided between the worm shaft 26 and the end cover 35 and the first rolling bearing 37 fixed to the housing 31 to be compressed as the worm shaft 26 moves in the axial direction. It was. According to the above configuration, it is possible to suppress the generation of noise compared to the case where the worm shaft 26 is in direct contact with the end cover 35 or the first rolling bearing 37 and its movement is restricted. Further, as the amount of compression of the elastic rings 53 and 73 increases, the repulsive force of the elastic rings 53 and 73 gradually increases, so that the steering force necessary for the steering operation gradually increases. Feeling can be realized.

  (4) A fixed ball-type constant velocity joint is adopted as the shaft coupling 41, and the base end portion 26a of the worm shaft 26 is serrated to the inner race 62 of the shaft coupling 41 so that the base end portion 26a becomes the inner joint. It was connected to the race 62 so as to be axially movable and integrally rotatable. According to the above configuration, the worm shaft 26 can be largely tilted as compared with the case where a sliding ball type constant velocity joint is used. Further, since the serration is fitted, the motor torque can be efficiently transmitted from the inner race 62 of the shaft coupling 41 to the worm shaft 26.

  (5) A plurality of engaging claws 76 projecting toward the output shaft 36 are formed on the outer race 61 of the shaft coupling 41, and alternately arranged in the circumferential direction between the engaging claws 76 of the outer race 61 on the output shaft 36. A yoke 74 having a plurality of engaging claws 77 is provided. Further, a resin material in which a plurality of engagement pieces 78 are formed between the outer race 61 and the yoke 74 in the circumferential direction by the engagement claw 76 of the adjacent outer race 61 and the engagement claw 77 of the yoke 74 is formed. A spacer 75 is provided. According to the above configuration, since the spacer 75 is interposed between the engaging claw 76 of the outer race 61 and the engaging claw 77 of the yoke 74, even if the outer race 61 and the yoke 74 have a dimensional variation, The occurrence of rattling in the circumferential direction between the claws 76 and 77 can be suppressed. Thereby, the dimensional accuracy requested | required of the outer race 61 and the yoke 74 can be eased, and the increase in manufacturing cost can be suppressed.

In addition, the said embodiment can also be implemented in the following aspects which changed this suitably.
In the above embodiment, the spacer 75 is interposed between the outer race 61 and the yoke 74 of the shaft coupling 41. The claw 77 may be directly engaged. Further, the yoke 74 and the spacer 75 may be eliminated, and the connection end portion 36a of the output shaft 36 of the motor 21 may be directly coupled to the outer race 61 so as to be integrally rotatable.

  In the above embodiment, the tip end portion 26b of the worm shaft 26 and the second rolling bearing 38 are integrally configured to be movable in the axial direction with respect to the housing 31. However, the present invention is not limited to this. For example, the front end portion 26b is fitted into the inner ring 38b of the second rolling bearing 38 with a gap, and is sandwiched in the axial direction between the inner ring 38b and the main body portion 26c of the worm shaft 26. By providing an elastic ring, the distal end portion 26 b may be movable in the axial direction with respect to the housing 31.

  In the above embodiment, the elastic rings 53, between the main body portion 26c of the worm shaft 26 and the inner ring 37b of the first rolling bearing 37 and between the outer ring 38a of the second rolling bearing 38 and the end cover 35, respectively. However, the present invention is not limited to this, and the elastic rings 53 and 73 need not be provided. In this case, the worm shaft 26 is disposed with a space in the axial direction between the main body portion 26 c of the worm shaft 26 and the inner ring of the first rolling bearing 37.

  In the above embodiment, the base end portion 26a of the worm shaft 26 is serrated to the inner race 62 of the shaft coupling 41, so that the base end portion 26a can move in the axial direction with respect to the inner race 62 and can rotate integrally. Connected. However, the present invention is not limited to this, for example, by forming the cross-sectional shapes orthogonal to the axial direction of the outer peripheral surface of the base end portion 26 a and the inner peripheral surface of the inner race 62 in polygonal shapes, They may be coupled so as to be axially movable and integrally rotatable.

  In the above embodiment, the worm shaft 26 is provided so as to be movable in the axial direction with respect to the housing 31. However, the present invention is not limited thereto, and the worm shaft 26 may be provided so as not to move in the axial direction relative to the housing 31.

  In the above embodiment, the worm shaft 26 is connected to the inner race 62 of the shaft coupling 41 and the output shaft 36 of the motor 21 is connected to the outer race 61. However, the present invention is not limited thereto, and the output shaft 36 is connected to the inner race 62. In addition, the worm shaft 26 of the motor 21 may be coupled to the outer race 61.

  In the above embodiment, the urging means is configured by the curved leaf spring 51 that is curved in an arc shape so as to surround the outer periphery of the second rolling bearing 38. However, the biasing means is not limited to this, and the second rolling bearing 38 The biasing means may be configured by another member such as a coil spring as long as it can be biased so as to be close to the wheel 25.

  In the above embodiment, a fixed ball type constant velocity joint is adopted as the shaft coupling 41, but the present invention is not limited to this, and a cross groove type constant velocity joint (see, for example, Japanese Patent Application Laid-Open No. 2008-89014), a tripod type, etc. A sliding type (sliding type) constant velocity joint such as a high speed joint (for example, see Japanese Patent Application Laid-Open No. 2010-14259) may be adopted. In such a sliding constant velocity joint, axial displacement between the two axes is allowed. For example, the base end of the worm shaft is not connected to the inner race so as to be axially movable by being serrated. Therefore, these shapes can be simplified.

  In the above-described embodiment, the present invention is embodied in a so-called column type EPS 1, but is not limited thereto, and may be applied to a so-called pinion type EPS that applies an assist force to the pinion shaft 10, for example.

Next, technical ideas that can be understood from the above embodiments and other examples will be described below together with their effects.
(A) In the electric power steering apparatus according to claim 2 or 3, the shaft coupling is a fixed ball-type constant velocity joint, and one end portion of the worm shaft is serrated into an inner race of the shaft coupling. An electric power steering apparatus characterized by being coupled to the inner race so as to be axially movable and integrally rotatable. According to the above configuration, the worm shaft can be largely tilted as compared with the case where a sliding ball type constant velocity joint is used. Further, since the serration is engaged, the motor torque can be efficiently transmitted from the inner race of the shaft coupling to the worm shaft.

  (B) In the electric power steering apparatus according to any one of claims 1 to 3 and (A), the outer race of the shaft coupling is formed with a plurality of engaging claws protruding toward the output shaft. The output shaft is provided with a yoke having a plurality of engaging claws arranged alternately in the circumferential direction between the engaging claws of the outer race, and is adjacent to the outer race and the yoke. An electric power steering apparatus comprising a spacer made of a resin material in which an engaging portion is formed to be held in a circumferential direction by the engaging claw of the outer race and the engaging claw of the yoke. According to the above configuration, since the spacer is interposed between the engaging claw of the outer race and the engaging claw of the yoke, even if the outer race and the yoke have a dimensional variation, there is a backlash in the circumferential direction between the engaging claws. The occurrence of sticking can be suppressed. Thereby, the dimensional accuracy requested | required of an outer race and a yoke can be eased, and the increase in manufacturing cost can be suppressed.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus (EPS), 3 ... Steering shaft, 21 ... Motor, 24 ... Deceleration mechanism, 25 ... Worm wheel, 26 ... Worm shaft, 26a ... Base end part, 26b ... Tip part, 26c ... Main-body part, DESCRIPTION OF SYMBOLS 31 ... Housing, 35 ... End cover, 36 ... Output shaft, 37 ... 1st rolling bearing, 38 ... 2nd rolling bearing, 41 ... Shaft coupling, 51 ... Curve leaf spring, 53, 73 ... Elastic ring, 61 ... Outer race, 62 ... inner race, 63 ... ball, 64 ... cage, 71, 72 ... serration teeth, 74 ... yoke, 75 ... spacer, 76, 77 ... engagement claw, 78 ... engagement piece.

Claims (3)

A speed reduction mechanism that engages a worm shaft and a worm wheel, a motor that is drivingly connected to the steering shaft via the speed reduction mechanism, and one end portion of the worm shaft that is tiltably connected to the output shaft of the motor In the electric power steering apparatus comprising a shaft coupling and an urging means for urging the other end portion of the worm shaft toward the worm wheel,
The electric power steering apparatus, wherein the shaft coupling is a constant velocity joint. The electric power steering apparatus according to claim 1, wherein
The electric power steering apparatus, wherein the worm shaft is provided so as to be movable in an axial direction with respect to a housing that houses the speed reduction mechanism. The electric power steering apparatus according to claim 2,
An electric power steering apparatus characterized in that an elastic member that is compressed as the worm shaft moves in the axial direction is provided between the worm shaft and a fixed member fixed to the housing.

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