JP2011136652A - Electric power steering system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized electric power steering system capable of attaining constantly smooth and axial transmission of a steering auxiliary force. <P>SOLUTION: The steering auxiliary force of an electric motor 18 is transmitted through a worm shaft 20 and a worm wheel 21. The worm wheel 21 has a tooth-shaped body 55 made of synthetic resin and a core metal 56. The core metal 56 has an outer cylinder 58 and an inner cylinder 59 extending from the outer edges 57a and 57b of a conical tapered annular body 57 toward the axial same side of an output shaft 13. The outer cylinder 58 is connected with the tooth-shaped body 55 to rotate with each other and the inner cylinder 59 is rotatably fitted onto the outer periphery of an output shaft 13 to rotate with each other. The front end 60 of the inner cylinder 59 abuts on or approaches the end face 61 of the inner ring 50 of a bearing 27. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus.

In the electric power steering apparatus, the output rotation of the electric motor for assisting steering is decelerated through the decelerating mechanism and transmitted to the steering mechanism. For example, the speed reduction mechanism includes a worm shaft connected to the rotating shaft of the electric motor and a worm wheel connected to the output shaft of the steering shaft.
In order to ensure the support rigidity of the worm wheel, there is known a structure in which the output shaft is rotatably supported by a pair of bearings arranged close to both sides sandwiching the worm wheel in the axial direction of the output shaft.

  On the other hand, the pair of bearings is replaced with a single bearing disposed on the radial extension line of the meshing center of the worm and the worm wheel. It has been proposed that the distance between the two gears is kept constant to prevent shifting of the meshing positions of both gears and rattling between the meshing tooth surfaces, and as a result, it is possible to always transmit the steering assist force smoothly. (For example, refer to Patent Document 1).

JP 2003-327142 A

  When using a pair of bearings arranged close to both sides sandwiching the worm wheel in the axial direction of the output shaft, there is a demand for downsizing the electric power steering device in the axial direction of the steering shaft, and an impact absorbing mechanism on the steering shaft. However, it is impossible to meet the demand for ensuring a sufficient contraction stroke (shock absorbing stroke) of the steering shaft.

  In Patent Document 1, as shown in FIG. 5, a worm wheel 80 includes a main body portion 82 having a cup-shaped recess structure 81, and an annular portion 83 having teeth on the outer periphery and connected to the outer periphery of the main body portion 82. It has. The main body portion 82 is provided on the annular plate 85 extending in the radial direction of the output shaft 84, the outer peripheral flange 86 provided on the outer periphery of the annular plate 85 and connected to the inner periphery of the annular portion 83, and the inner periphery of the annular plate 85. And an inner peripheral flange 87 as an attachment flange that extends in the opposite direction to the outer peripheral flange 86 and is rotatably attached to the outer periphery of the output shaft 84. The outer peripheral flange 86, the annular plate 85, and the inner peripheral flange 87 of the main body 82 have a crank shape in cross section.

A meshing center 91 between the worm shaft 92 and the worm wheel 80 is disposed on a radially extending line 90 passing through a support center 89 of a single bearing 88 that rotatably supports the upper end of the output shaft 84.
In order to avoid contact between the annular plate 85 of the main body 82 of the worm wheel 80 and the outer ring 93 of the bearing 88, it is necessary to provide a gap 94 having a predetermined gap amount S1 between the annular plate 85 and the end surface of the outer ring 93. There is. Further, in order to ensure the connection strength between the main body portion 82 and the output shaft 84 and to ensure the coaxiality between the worm wheel 80 and the output shaft 84, the inner peripheral flange 87 and the output shaft 84 are fitted to each other with a predetermined fit. It is necessary to fit with the length S2.

For this reason, the worm wheel 80 takes an axial space of S1 + S2 from the end surface of the inner ring 95 of the bearing 88 on the outer periphery of the output shaft 84. As a result, the electric power steering with respect to the axial direction of the steering shaft. The size of the device was not enough.
The present invention has been made based on such a background, and an object of the present invention is to provide an electric power steering device that can always transmit a steering assist force smoothly and that is small in the axial direction.

  In order to achieve the above object, the present invention includes a driven member (21) having a driven member (20) and a driven portion (53) to which a driving force is transmitted directly or indirectly from the driving member. A transmission mechanism (19) for transmitting the output rotation of the electric motor (18) to the steering mechanism (A), an output shaft (13) that can be rotated together with the driven member, and a bearing provided in the housing (25). A bearing (27) having an outer ring (49) held by a holding cylinder and an inner ring (50) fitted to the outer periphery of the output shaft, and a support center (C2) of the bearing is provided on the driven member. The driven member is disposed radially inward of the transmission center (for example, the engagement center C1) of the driven part in the axial direction, and the driven member includes a driven part forming body (55) having an outer periphery provided with the driven part, and the driven part. Rotating along with the formation The cored bar includes an annular main body (57) and an outer edge (57a) and an inner edge (57b) of the annular main body in the axial direction (X1) of the output shaft. An outer cylinder (58) and an inner cylinder (59) extending on the same side, and the outer cylinder is connected to the driven portion forming body so as to be able to rotate together with the outer cylinder (58), and the inner cylinder is connected to an outer periphery of the output shaft. Provided is an electric power steering device that is fitted so as to be able to rotate together and the tip (60) of the inner cylinder is in contact with or close to the end surface (61) of the inner ring of the bearing.

  In the present invention, the operating point of torque fluctuation at the time of meshing of, for example, a worm shaft as a driving member and, for example, a worm wheel as a driven member coincides with the support center of the bearing. By being able to be suppressed, it is possible to reliably prevent the shift of the meshing position and the abnormal rattling. As a result, an appropriate backlash is always maintained and a smooth steering assist force can be transmitted.

  Moreover, for example, the outer cylinder and inner cylinder of the core metal of the worm wheel as the driven member extend from the main body of the core metal to the same side in the axial direction of the output shaft, and the tip of the inner cylinder is fitted to the output shaft. It was made to contact or be close to the end face of the inner ring of the bearing. Therefore, the axial space occupied by, for example, the worm wheel as the driven member on the outer periphery of the output shaft is an amount obtained by adding the gap amount S1 and the fitting length S2 from the end face of the inner ring in Patent Document 1. On the other hand, in the present invention, the length corresponding to the fitting length of the inner cylinder of the core metal is sufficient on the output shaft, and the electric power steering device can be downsized in the axial direction.

  The transmission mechanism may be a worm gear mechanism including a worm shaft as a driving member and a worm wheel as a driven member having teeth as a driven portion. The transmission mechanism may be a parallel shaft gear mechanism such as a spur gear or a helical gear, in addition to the staggered shaft gear mechanism such as the worm gear mechanism. Further, the transmission mechanism may be a belt / pulley mechanism including a driving pulley as a driving member and a driven pulley as a driven member to which a driving force is transmitted from the driving pulley via a belt as a transmission member.

Further, since the outer cylinder and the inner cylinder of the core metal extend from the core metal body to the same side in the axial direction of the output shaft, the inner cylinder and the outer cylinder have a double cylinder shape, and the strength of the core metal is significantly improved. . For example, when compared with a cored bar having a cross-sectional crank shape of Patent Document 1, it is possible to ensure about twice the strength of the double cylinder as in the present invention.
In some cases, the annular main body is formed in a conical taper shape. In this case, it is possible to secure a space for accommodating a part of other parts between the annular main body having a conical taper shape and the housing, for example, which can contribute to downsizing.

  In the above description, the alphanumeric characters in parentheses represent reference numerals of corresponding components in the embodiments described later, but the scope of the claims is not limited by these reference numerals.

1 is a partial cross-sectional schematic diagram showing a schematic configuration of an electric power steering apparatus according to an embodiment of the present invention. It is a perspective view of the attachment structure of a steering column. It is sectional drawing to which a part of FIG. 1 was expanded. It is the schematic which shows the positional relationship of the bearing holding part and eccentric fitting part of the 2nd housing as an eccentric housing. It is a schematic sectional drawing of the principal part of the conventional electric power steering device.

Embodiments of the present invention will be specifically described below with reference to the drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus 1 as a vehicle steering apparatus 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, an intermediate A pinion shaft 7 connected to the shaft 5 via a universal joint 6 and a rack 8a that meshes with the pinion 7a provided in the vicinity of the end of the pinion shaft 7 so as to extend in the axial direction as the left-right direction of the automobile. It has a rack shaft 8 as a shaft. The pinion shaft 7 and the rack shaft 8 constitute a steering mechanism A composed of a rack and pinion mechanism.

The rack shaft 8 is supported in a housing 9 fixed to the vehicle body through a plurality of bearings (not shown) so as to be capable of linear reciprocation in the axial direction. Both end portions of the rack shaft 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 steered 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 a linear motion in the axial direction of the rack shaft 8 by the pinion 7a and the rack 8a. Thereby, the turning of the steered wheel 11 is achieved.

  The steering shaft 3 includes an input shaft 12 connected to the steering member 2 and an output shaft 13 connected to the intermediate shaft 5. The input shaft 12 and the output shaft 13 are connected via a torsion bar 14 so as to be relatively rotatable on the same axis. That is, when a steering torque of a predetermined value or more is input to the steering member 2, the input shaft 12 and the output shaft 13 rotate in the same direction while rotating relative to each other.

  A torque sensor 15 arranged around the steering shaft 3 detects the steering torque input to the steering member 2 based on the relative rotational displacement amounts of the input shaft 12 and the output shaft 13. The torque detection result of the torque sensor 15 and the vehicle speed detection result from the vehicle speed sensor 16 are input to an ECU 17 (Electronic Control Unit) as a control device.

The electric power steering apparatus 1 includes a steering assist mechanism B. The steering assist mechanism B includes an electric motor 18 for assisting steering, and a transmission mechanism 19 for transmitting the output torque of the electric motor 18 to the steering mechanism A. For example, a three-phase brushless motor is used as the electric motor 18.
The transmission mechanism 19 includes a worm gear mechanism having a worm shaft 20 as a driving member and a worm wheel 21 as a driven member that meshes with the worm 20c of the worm shaft 20. The worm shaft 20 is connected to the rotating shaft of the electric motor 18 through a joint so that torque can be transmitted. The worm wheel 21 is connected to the output shaft 13 of the steering shaft 3 so as to be able to rotate together and not to move in the axial direction.

  When the electric motor 18 rotationally drives the worm shaft 20, the worm wheel 21 is rotationally driven by the worm shaft 20, and the worm wheel 21 and the output shaft 13 rotate together. The rotation of the output shaft 13 is transmitted to the pinion shaft 7 through the intermediate shaft 5. The rotation of the pinion shaft 7 is converted into the movement of the rack shaft 8 in the axial direction. Thereby, the steered wheel 11 is steered. That is, when the worm shaft 20 is rotationally driven by the electric motor 18, the steered wheels 11 are steered, and the driver's steering is assisted.

The electric motor 18 is controlled by the ECU 17. The ECU 17 drives and controls the electric motor 18 based on the torque detection result from the torque sensor 15 and the vehicle speed detection result from the vehicle speed sensor 16.
A steering column 22 that rotatably supports the steering shaft 3 is fitted to the tube housing 23, a first housing 24 as an eccentric housing fitted to the lower end of the tube housing 23, and the first housing 24. The second housing 25 is provided.

  The tube housing 23 rotatably supports the input shaft 12 via a bearing 26 at the upper end thereof. A bearing 27 having a support center C2 (bearing center) is disposed radially inward of the engagement center C1 as a transmission center between the worm shaft 20 and the worm wheel 21 (transmission center in the axial direction of the worm wheel 21). The bearing 27 is held by the second housing 25 and rotatably supports the output shaft 13.

  The first housing 24 rotatably supports both ends of the worm shaft 20 via a bearing (not shown). The second housing 25 includes a bearing holding portion 28 that is a cylindrical surface that holds the bearing 27, and an eccentric fitting portion 30 that is a cylindrical surface that is fitted to the fitting portion 29 of the first housing 24. . The eccentric fitting portion 30 is eccentric with respect to the bearing holding portion 28. That is, as shown in FIG. 4, the center E <b> 2 of the eccentric fitting portion 30 is offset from the center E <b> 1 of the bearing holding portion 28 by a predetermined amount. The direction in which the center E2 of the eccentric fitting portion 30 is offset is preferably a direction that is orthogonal to the direction of the center distance between the worm shaft 20 and the worm wheel 21.

On the other hand, the fitting portion 29 of the first housing 24 is eccentric with respect to the torque sensor holding portion 42. The direction in which the fitting portion 29 is eccentric with respect to the torque sensor holding portion 42 is the same direction as the direction in which the eccentric fitting portion 30 is eccentric with respect to the bearing holding portion 28.
Accordingly, in FIG. 1, the second housing 25 is rotationally displaced with respect to the first housing 24 to adjust the rotational position of the second housing 25 with respect to the first housing 24. The distance between the centers of the wheels 21 can be adjusted, and as a result, the backlash between the tooth surfaces of both gears can be adjusted appropriately.

  Referring to FIG. 1 and FIG. 2, which is a perspective view of steering column mounting structure D, first and second housings 24 and 25 after backlash adjustment are connected to each other by first screw 31 and second screw 32. Fixed. As shown in FIG. 2, the second housing 25 has a pair of screw insertion holes 33 having an arc shape concentric with the bearing holding portion 28. The first screw 31 and the second screw inserted into each screw insertion hole 33 are screwed into screw holes (not shown) of bosses 34 and 35 formed in the first housing 24.

On the other hand, as shown in FIG. 1, the second housing 25 is fixed to the vehicle body side member 37 via the mounting bracket 36. Specifically, one end 36 a of the mounting bracket 36 is fixed to the vehicle body side member 37 using a screw 38.
As shown in FIG. 2, the first screw 31 is inserted into a screw insertion hole (not shown) made of a circular hole formed in the other end 36 b of the mounting bracket 36 and the screw insertion hole 33 of the second housing 25. It is inserted and fixed by screwing into the screw hole of the boss 34 of the first housing 24. That is, the first screw 31 fastens the first housing 24 and the second housing 25 together with the mounting bracket 36. On the other hand, the second screw 32 is inserted through the screw insertion hole 33 of the second housing 24 and screwed into the screw hole of the boss 35 of the first housing 24.

The pair of screw insertion holes 33 are arranged at asymmetric positions that are not point-symmetric with respect to the output shaft 13, and prevent erroneous assembly of the second housing 25 (the second housing 25 being mounted upside down). ing. Furthermore, although not shown, a misassembly prevention protrusion may be extended from a part of the periphery of the second housing 25.
1 and FIG. 3 which is an enlarged view of FIG. 1, the first housing 24 includes a cylindrical portion 39 coaxially fitted to the lower end of the tube housing 23, and the cylindrical portion 39. And a gear housing portion 40 connected to the lower end of the gear.

  As shown in FIG. 3, on the inner periphery of the cylindrical portion 39 of the first housing 24, there is a fitting portion 41 fitted to the outer periphery of the lower end of the tube housing 23, and the torque sensor 15 below the fitting portion 41. Is provided with a torque sensor holding part 42. Further, the fitting portion 29 that fits into the eccentric fitting portion of the second housing 25 is provided at the lower end of the gear housing portion 40 of the first housing 24. The fitting portion 41 and the torque sensor holding portion 42 are configured by concentric cylindrical surfaces, and the fitting portion 29 is formed on a cylindrical surface that is eccentric with respect to the concentric cylindrical surface.

  2 and 3, the second housing 25 includes an annular bottom wall 44 that defines the bottom of the gear housing space, and a bearing holding that extends from the inner periphery of the bottom wall 44 in the axial direction of the output shaft 13. A cylinder 45, an eccentric cylinder 46 extending axially downward from the outer periphery of the bottom wall 44, and an annular flange 47 extending radially outward from the lower end of the eccentric cylinder 46 are provided. The annular flange 47 is formed with the arc-shaped screw insertion hole 33 described above.

  The bearing holding portion 28 is provided on the inner periphery of the bearing holding tube 45, and the eccentric fitting portion 30 is provided on the outer periphery of the eccentric tube 46. The bearing 27 is constituted by a rolling bearing having an outer ring 49 and an inner ring 50, for example, a ball bearing. The outer periphery of the outer ring 49 of the bearing 27 is fitted and fixed to the bearing holding portion 28, and the inner periphery of the inner ring 50 of the bearing 27 is fitted to the outer periphery of the output shaft 13 so as to be able to rotate together.

The inner ring 50 is sandwiched between a stepped portion 51 formed on the outer periphery of the output shaft 13 and a nut 52 locked in the outer peripheral groove of the output shaft 13, whereby the shaft between the output shaft 13 and the bearing 27. Directional relative movement is restricted.
An annular flange 48 extending inward in the radial direction from the upper end of the bearing holding cylinder 45 is provided. The outer ring 49 of the bearing 27 is sandwiched between the annular flange 48 and a retaining ring 43 locked to the inner peripheral groove of the bearing holding cylinder 45, whereby the axial direction between the second housing 25 and the bearing 27 is achieved. Movement is restricted. As a result, the axial movement of the output shaft 13 is restricted by the second housing 25 via the bearing 27.

The worm wheel 21 has a tooth forming body 55 as an annular driven portion forming body made of synthetic resin and having an outer periphery 54 on which teeth 53 as driven portions are formed, and a core connected to the tooth forming body 55 so as to be able to rotate together. Gold 56 is provided.
The cored bar 56 has an annular main body 57 having a conical taper shape, and the same side in the axial direction of the output shaft 13 from the outer edge 57a and the inner edge 57b of the annular main body 57 (in this embodiment, the axial direction of the output shaft 13). An outer cylinder 58 and an inner cylinder 59 extending downward). The outer cylinder 58 is connected to the tooth forming body 55 so as to be able to rotate together. The inner cylinder 59 is fitted to the outer periphery of the output shaft 13 so as to be able to rotate together, and the front end 60 (lower end) of the inner cylinder 59 is in contact with the end surface 61 of the inner ring 50 of the bearing 27 or a minute gap is provided. It is close.

An annular flange 62 extending radially outward from the lower end of the outer cylinder 58 of the core metal 56 is formed, and the annular flange 62 is inserted into a mold for resin molding of the tooth forming body 55.
As described above, because the support center C2 (bearing center) of the bearing 27 that supports the output shaft 13 is disposed radially inward of the engagement center C1 of the worm shaft 20 and the worm wheel 21, the second housing The bearing holding cylinder 45 is formed to have a smaller diameter than the outer cylinder 58 of the core metal 56 of the worm wheel 21, and a part of the bearing holding cylinder 45 is inserted into the outer cylinder 58.

  According to the present embodiment, the support center C2 (bearing center) of the single bearing 27 that supports the output shaft 13 is disposed radially inward of the engagement center C1 of the worm shaft 20 and the worm wheel 21. The operating point of torque fluctuation when the worm shaft 20 and the worm wheel 21 are engaged with each other coincides with the support center C <b> 2 of the bearing 27. Accordingly, since the swinging of the output shaft 13 can be completely suppressed, it is possible to surely prevent the meshing position from being shifted and abnormal rattling. As a result, an appropriate backlash is always maintained and a smooth steering assist force can be transmitted.

  Moreover, as shown in FIG. 3, the outer cylinder 58 and the inner cylinder 59 of the cored bar 56 of the worm wheel 21 extend from the annular main body 57 of the cored bar 56 to the same side in the axial direction X1 of the output shaft 13. The tip 60 of the inner cylinder 59 is brought into contact with or close to the end surface 61 of the inner ring 50 of the bearing 27 fitted to the output shaft 13. Therefore, in Patent Document 1, the axial space occupied by the worm wheel 21 on the outer periphery of the output shaft 13 is an amount obtained by adding the gap amount S1 and the fitting length S2 from the end face of the inner ring as shown in FIG. On the other hand, in the present embodiment, the length corresponding to the fitting length of the inner tube 59 of the cored bar 56 with respect to the output shaft 13 is sufficient, and the electric power steering device 1 can be downsized in the axial direction.

Further, the cored bar 56 has a double cylinder shape having the outer cylinder 58 and the inner cylinder 59, and the strength of the cored bar 56 is remarkably improved. For example, when compared with a cored bar having a cross-sectional crank shape of Patent Document 1, it is possible to ensure about twice the strength of the double cylinder as in the present embodiment.
Further, since the annular main body 57 of the cored bar 56 is formed in a conical taper shape, other parts are provided between the annular main body 57 forming the conical taper shape and the cylindrical portion 39 of the first housing 24. It is possible to secure a space P for accommodating a part of the cap, for example, a cap fixing leg or the like (not shown) for fixing the torque sensor 15, which contributes to downsizing.

  Further, when the second housing 25 as the eccentric housing is rotated with respect to the first housing 24 in a state where the first screw 31 and the second screw 32 are loosened, the eccentric fitting of the second housing 25 is performed. As the portion 30 rotates, the axis of the worm shaft 20 supported by the first housing 24 and the axis of the worm wheel 21 supported by the second housing 25 via the bearing 27 move relative to each other. Thus, the distance between the centers of the worm shaft 20 and the worm wheel 21 can be adjusted, and the backlash between the tooth surfaces of both gears can be adjusted appropriately. After adjusting the backlash, the first screw 31 and the second screw 32 are tightened to restrict relative rotation between the housings 24 and 25.

Further, since the bearing 27 that directly supports the output shaft 13 is the only bearing 27, it is possible to prevent the output shaft 13 from being twisted when the inter-center distance is adjusted.
Further, the positional relationship between the torque sensor 15 held by the torque sensor holding portion 42 and the output shaft 13 slightly changes with the adjustment of the inter-center distance, but as the torque sensor 15, for example, a Hall IC or other non-contact type By using this sensor, it is possible to make the torque sensor 15 less susceptible to the influence of eccentricity, and as a result, it is possible to obtain a favorable steering feeling through obtaining stable assist performance.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, the worm wheel 21 is an electric power steering device (a so-called column assist type electric power steering device) in which the worm wheel 21 is connected to the output shaft 13 of the steering shaft 3 so as to be able to rotate together. However, the present invention is not limited to this, and may be applied to an electric power steering device (so-called pinion assist type electric power steering device) of a type in which a worm wheel is connected to a pinion shaft so as to be able to rotate together.

  In the above embodiment, the transmission mechanism 19 is a worm gear mechanism including the worm shaft 20 as a driving member and the worm wheel 21 as a driven member having a tooth 53 as a driven portion. In addition to a staggered shaft gear mechanism such as a worm gear mechanism, a parallel shaft gear mechanism such as a spur gear or a helical gear may be used. Further, the transmission mechanism may be a belt / pulley mechanism including a driving pulley as a driving member and a driven pulley as a driven member to which a driving force is transmitted from the driving pulley via a belt as a transmission member. In addition, various modifications are possible within the scope of the claims of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Steering member, 3 ... Steering shaft, 12 ... Input shaft, 13 ... Output shaft, 14 ... Torsion bar, 15 ... Torque sensor, 18 ... Electric motor, 19 ... Transmission mechanism, 20 ... Worm Shaft (drive member), 21 ... worm wheel (driven member), 22 ... steering column, 24 ... first housing, 25 ... second housing, 27 ... bearing, 28 ... bearing holding portion, 29 ... fitting portion, DESCRIPTION OF SYMBOLS 30 ... Eccentric fitting part, 42 ... Torque sensor holding | maintenance part, 49 ... Outer ring, 50 ... Inner ring, 53 ... Teeth (driven part), 54 ... Outer circumference of tooth forming body, 55 ... Tooth forming body (driven part forming body) ), 56 ... Metal core, 57 ... Ring body, 57a ... Outer edge, 57b ... Inner edge, 58 ... Outer cylinder, 59 ... Inner cylinder, 60 ... End, 61 ... End face (inner ring), A ... Steering mechanism, B ... steering assist mechanism, C1 ... meshing Center (transfer center), C2 ... support center, X1 ... axial direction, D ... of the steering column mounting structure

Claims (2)

A transmission mechanism including a driving member and a driven member having a driven part to which driving force is transmitted directly or indirectly from the driving member, and transmitting the output rotation of the steering assist electric motor to the steering mechanism;
An output shaft capable of rotating together with the driven member;
An outer ring held by a bearing holding cylinder provided in the housing and a bearing having an inner ring fitted to the outer periphery of the output shaft,
The support center of the bearing is disposed radially inward of the transmission center of the driven part with respect to the axial direction of the driven member,
The driven member includes a driven part forming body having an outer periphery provided with the driven part, and a core bar coupled to the driven part forming body so as to be able to rotate together with the driven part forming body,
The core metal has an annular main body, and an outer cylinder and an inner cylinder extending from the outer edge and the inner edge of the annular main body to the same side in the axial direction of the output shaft,
The outer cylinder is connected to the driven part forming body so as to be able to rotate together with the driven part forming body,
The inner cylinder is fitted to the outer periphery of the output shaft so as to be able to rotate together.
An electric power steering device in which a tip of the inner cylinder is in contact with or close to an end face of the inner ring of the bearing.   The electric power steering apparatus according to claim 1, wherein the annular main body is formed in a conical taper shape.

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