JP2002284023A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate play in the axial direction of a rotary shaft of an electric motor and suppress deflection of rotary shaft axis simultaneously by a simple support configuration in an electric power steering device. SOLUTION: In this electric power steering device 10, one end part of the rotary shaft 32 of the electric motor 30 is supported on a motor case 31 by a bearing 71, and the rotary shaft 32 is supported in two ways in the axial direction for the bearing 71 so as to be immobile.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an electric power steering apparatus.

[0002]

2. Description of the Related Art An electric power steering apparatus is disclosed in
As described in 11-342856, the electric motor is fixed to the housing, the housing supports the assist shaft of the steering device,
An assist shaft is connected to a rotating shaft of the electric motor, and torque of the electric motor is transmitted to a steering device to assist steering.

[0003]

In the prior art, when the rotating shaft of the electric motor is supported by the motor case, if the rotating shaft has a backlash in the axial direction, the backlash will be a source of hitting noise. In addition, a complicated configuration is required such that the rotating shaft is supported at two points by bearings provided at both ends so as not to move in the axial direction to suppress the axial runout during rotation.

SUMMARY OF THE INVENTION An object of the present invention is to provide a power steering apparatus which, with a simple supporting structure, eliminates backlash in the axial direction of the rotating shaft of an electric motor and suppresses runout of the rotating shaft.

[0005]

According to a first aspect of the present invention, there is provided an electric motor in which an electric motor is fixed to a housing, an assist shaft of a steering device is supported on the housing, and an assist shaft is connected to a rotating shaft of the electric motor. In a power steering apparatus, only one end of a rotating shaft of an electric motor is axially immovably supported on a motor case by a bearing, and the other end is connected to an assist shaft.

According to a second aspect of the present invention, in the first aspect of the present invention, there is further provided an outer race in which the bearing is fixed to a motor case;
An inner ring rotatably supported via a rolling element with respect to the outer ring, one end of the rotating shaft being a small-diameter portion that is inserted into and supported by the inner ring, and a step portion at the root of the small-diameter portion is defined as an inner ring. A stopper that is applied to one end face and is engaged at the tip of the small diameter portion is applied to the other end face of the inner ring, and the inner ring is sandwiched between the step portion of the small diameter portion and the stopper.

According to a third aspect of the present invention, in the first aspect of the present invention, there is further provided an outer ring in which the bearing is fixed to a motor case;
An inner ring rotatably supported via a rolling element with respect to the outer ring, one end of the rotating shaft being a small-diameter portion that is inserted into and supported by the inner ring, and a step portion at the root of the small-diameter portion is defined as an inner ring. A nut screwed to the end of the small diameter portion is applied to one end surface of the inner ring, and the inner ring is sandwiched between the step portion of the small diameter portion and the nut.

According to a fourth aspect of the present invention, in the first aspect of the present invention, there is further provided an outer ring in which the bearing is fixed to a motor case;
An inner ring rotatably supported via a rolling element with respect to the outer ring, one end of the rotating shaft being a small-diameter portion that is inserted into and supported by the inner ring, and a step portion at the root of the small-diameter portion is defined as an inner ring. The tip of the small diameter portion is pressed into the inner race against one end face.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the rotary shaft and the assist shaft of the electric motor are spigot-coupled.

[0010]

According to the first aspect of the present invention, the following operations are provided. Since only one end of the rotating shaft of the electric motor is immovably supported on the bearing of the motor case in both directions in the axial direction, it is possible to eliminate the backlash in the axial direction and to prevent the occurrence of a tapping sound. At the same time, the rotational runout of the rotating shaft can be minimized, and cantilever support becomes possible.

According to the second aspect of the present invention, the following operations are provided. By inserting the small-diameter part of the rotating shaft into the inner ring of the bearing, and holding the inner ring between the step part of the small-diameter part and the stopper fixed to the tip of the small-diameter part, the rotating shaft can be easily connected to the bearing with a simple configuration. Can be immovably supported in both directions.

According to the third aspect of the invention, the following effects are obtained. By inserting the small-diameter part of the rotating shaft into the inner ring of the bearing, and holding the inner ring between the stepped part of the small-diameter part and the nut screwed to the tip of the small-diameter part, the rotating shaft is positioned in the axial direction with respect to the bearing with a simple configuration. Can be immovably supported in both directions.

According to the fourth aspect of the invention, the following effects are obtained. By inserting the small-diameter part of the rotating shaft into the inner ring of the bearing, applying the step of the small-diameter part to one end surface of the inner ring, and press-fitting the tip of the small-diameter part into the inner ring, the rotating shaft can be connected to the bearing with a simple configuration. On the other hand, it can be immovably supported in both axial directions.

According to the fifth aspect of the invention, the following effects are obtained. Since the rotary shaft of the electric motor and the assist shaft are made coaxial by inlay connection, only one end of the rotary shaft is supported by the bearing, and the end near the assist shaft is not supported. The number of bearings used can be reduced.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a front view showing an electric power steering apparatus partially cut away, FIG. 2 is a sectional view taken along the line II-II of FIG. 1, and FIG. 3 is a sectional view taken along the line III-III of FIG. 4 is a perspective view showing a magnet holder, FIG. 5 shows a brush holder, (A) is a front view, (B) is a side view, FIG. 6 shows a grommet, (A) is a front view, (B) is a side view,
(C) is a plan view, FIG. 7 is a side view showing a main part of FIG. 3, and FIG.
FIG. 9 is a cross-sectional view showing a rotary shaft support structure of the first embodiment, FIG. 9 is a cross-sectional view showing a rotary shaft support structure of the second embodiment, and FIG. 10 is a cross-sectional view showing a rotary shaft support structure of the third embodiment. .

As shown in FIGS. 1 and 2, the electric power steering apparatus 10 includes a gear housing 1 made of an aluminum alloy and fixed to a vehicle body frame or the like by a bracket (not shown).
1 (first to third gear housings 11A to 11C). A pinion shaft 14 is connected to a steering shaft 12 to which a steering wheel is coupled via a torsion bar 13. It is supported by the first gear housing 11A so as to be movable left and right. Steering shaft 12 and pinion shaft 14
Between them, a steering torque detecting device 17 is provided. still,
The steering shaft 12 and the pinion shaft 14 have bearings 12A, 1
It is supported by the gear housing 11 via 4A and 14B.

As shown in FIG. 2, the steering torque detecting device 17 includes two detection coils 17A surrounding a cylindrical core 17C engaged with the steering shaft 12 and the pinion shaft 14,
17B is provided in the third gear housing 11C. The core 17C is provided with a vertical groove 17E that engages with the guide pin 17D of the pinion shaft 14 so as to be movable only in the axial direction, and has a spiral groove 17G that engages with the slider pin 17F of the steering shaft 12. As a result, the steering torque applied to the steering wheel is applied to the steering shaft 12, and when a relative displacement in the rotational direction occurs between the steering shaft 12 and the pinion shaft 14 due to the elastic torsional deformation of the torsion bar 13, the steering shaft 12 The displacement of the pinion shaft 14 in the rotation direction causes the core 17C to be displaced in the axial direction, and the displacement of the core 17C changes the inductance of the detection coils 17A and 17B due to magnetic changes around the detection coils 17A and 17B. . That is, when the core 17C moves toward the steering shaft 12, the inductance of the detection coil 17A closer to the core 17C increases, and the inductance of the detection coil 17B closer to the core 17C decreases. Can be detected.

The rack shaft 1 in the first gear housing 11A
As shown in FIG. 2, a rack guide 19 is built in a cylinder portion 18 provided at a portion opposed to the pinion 15 with one end of the bush 6 interposed therebetween.
9A) is repelled toward the rack shaft 16 by a spring 21 supported on the back surface by a cap 20 attached to the cylinder portion 18 to press the rack 16A of the rack shaft 16 against the pinion 15 and to connect one end of the rack shaft 16 to the pinion 15. It is slidably supported. The other end of the rack shaft 16 is supported by a bearing 22. In the middle part of the rack shaft 16, left and right tie rods 23A, 23 are connected by connecting bolts 22A, 22B.
B is connected.

As shown in FIG. 3, a motor case 31 of the electric motor 30 is fixed to the second gear housing 11B, and an assist shaft 33 is connected to a rotating shaft 32 of the electric motor 30 via a connector 80. The assist shaft 33 is supported at both ends of the second gear housing 11B by bearings 34 and 35 such as ball bearings. The inner ring of the bearing 34 is held by a stopper ring 36A, and the outer ring is held by a lock nut 36B. A worm gear 37 is integrally provided at an intermediate portion of the assist shaft 33, and a worm wheel 38 meshing with the worm gear 37 is fixed to an intermediate portion of the pinion shaft 14. The torque generated by the electric motor 30 is applied to the rack shaft 16 as a steering assist force via the engagement between the worm gear 37 and the worm wheel 38 and the engagement between the pinion 15 and the rack 16A. To assist the steering force.

Here, the electric motor 30 is configured as follows. That is, the electric motor 30 includes a cylindrical yoke 52 formed of a magnetic material such as iron, and a cylindrical yoke 52 formed of an insulating resin material forming magnet housing sections 53 </ b> B at a plurality of circumferential positions on the inner periphery of the yoke 52. A magnet holder 53 (FIG. 4) composed of a shaped body 53A, a magnet 54 housed and positioned and held in a magnet housing section 53B of the magnet holder 53, and pressed into the magnet 54 positioned and held by the magnet holder 53. The stator 51 includes a magnet cover 55 (not shown) formed of an extremely thin plate of a non-magnetic material.

The electric motor 30 has a rotor 56 inserted inside the stator 51 and fixed to the rotating shaft 32. The rotor 56 includes an amateur core 57 and a commutator 58 provided on the outer periphery of the rotating shaft 32.

The electric motor 30 has a brush 61 (FIG. 5) which is brought into contact with the commutator 58 of the rotor 56.
And a brush holding portion 62B for positioning and holding the brush 61
Cylindrical body 6 made of an insulating resin material forming
It has a brush holder 62 (FIG. 5) made of 2A. In addition, the electric motor 30 is connected to the brush 61 positioned and held by the brush holder 62 via the pigtail through the connection terminal 63.
A, and a power supply connector 63 integrally formed with the brush holder 62 with an insulating resin material containing the connection terminal 63A.

When electric power is supplied from the brush 61 to the armature core 57 through the commutator 58 of the rotor 56, the magnetic lines of force of the armature core 57 are
By cutting off the magnetic field generated by the magnet 54, the rotor 56 rotates.

However, the electric motor 30 has the following characteristic configuration. (1) In the electric motor 30, the yoke 52 is a cylindrical body with one end opened and the other end closed, and the yoke 52 is used as the motor case 31. The yoke 52 is, as shown in FIG.
It has one end flange portion 52A fixed to 1B and the other end closed portion 52B, and is provided with a closing cap 52D that is attached to the other end closed portion 52B via an O-ring 52C.

(2) As shown in FIG. 4, the magnet holder 53 has a cylindrical body 53A having a magnet accommodating section 53B.
The outer periphery of the tubular body 53A is spigot-coupled to the yoke 52, and the engaging portion 53C that engages with the engaging portion 62C of the brush holder 62 is connected to the outer periphery of the tubular body 53A so that the circumferential specific position And the outer periphery of the engaging portion 53C can be spigot-coupled to the housing 11B.

(3) As shown in FIG. 5, the brush holder 62 forms a short cylinder 62A having a brush holder 62B, and the brush holder 62B is formed at a plurality of circumferential positions on the inner periphery of the short cylinder 62A. The spring 6 is attached to the brush holding portion 62B.
4. The brush 61 is inserted, and the brush 61 is pressed against the commutator 58 of the rotor 56 by the spring force of the spring 64. In the brush holder 62, one end of the outer periphery of the short cylinder 62A is spigot-coupled to the yoke 52 constituting the motor case 31, and the other end of the outer periphery of the short cylinder 62A is spigot-coupled to the housing 11B.

The brush holder 62 has an engaging portion 62C formed in a specific position in the circumferential direction on one end side and a locking portion 62D formed in a specific position in the circumferential direction on the other end side. By engaging the engaging portion 53C of the magnet holder 53 with the engaging portion 62C of the brush holder 62, the brush 61 held by the brush holder 62 with respect to the magnet 54 of the stator 51 positioned by the magnet holder 53.
Eliminating the phase shift, rotation performance of the electric motor 30 is prevented from becoming different things in the forward direction and reverse direction, to avoid performance degradation. Further, the locking portion 6 of the brush holder 62
By locking the 2D to a locking portion 65A formed concavely at a specific circumferential position on the inner side of the spigot coupling portion 65 of the housing 11B, the circumferential mounting position of the brush holder 62 can be easily and reliably positioned. .

(4) The grommet 66 is provided in the brush holder 62.
There is assembled is deposited. The grommet 66 is a connection portion between the housing 11B and the motor case 31 (yoke 52), and is a connector seal portion 6 which is mounted on a connector insertion portion 68 formed by cutting out a flange portion 67 of the housing 11B.
6A and an O-ring 66B that is loaded into a ring groove 69 formed in the flange 67 of the housing 11B. The brush holder 62 includes a connector seal portion 66A of the grommet 66 on the power supply connector 63 and an O-ring 6 of the grommet 66 on the short cylindrical body 62A of the brush holder 62.
6B, the housing 11B and the motor case 3
1 (yoke 52) is assembled in a liquid-tight manner at the connection portion.

(5) According to the above (2) to (4), the electric motor 30
Is fixed to the housing 11B as follows.

The grommet 66 is attached to the brush holder 62. The cylindrical body 53A of the magnet holder 53 is spigot-coupled to the motor case 31 (yoke 52) of the electric motor 30. Subsequently, one end side of the short cylindrical body 62A of the brush holder 62 is spliced to the motor case 31 (yoke 52). At this time, the engaging portion 62C of the brush holder 62 is engaged with the engaging portion 53C of the magnet holder 53.

The engaging portion 53C of the magnet holder 53 is spigot-coupled to the spigot coupling portion 65 of the housing 11B (FIG. 3). At the same time, the short cylindrical body 6 of the brush holder 62
The other end of 2A is connected to the spigot joint 65 of the housing 11B.
To the spigot. At this time, the locking portion 62D of the brush holder 62 is locked to the locking portion 65A of the housing 11B.

At the same time as the above, the connector seal portion 66A of the grommet 66 is connected to the flange portion 6 of the housing 11B.
The O-ring 66 </ b> B of the grommet 66 is sealed to the connector
B is loaded into the ring groove 69 provided in the flange 67 and is sealed between the flange 67 and the flange 52 </ b> A of the yoke 52.

The motor case 31 (yoke 52) of the electric motor 30 includes the motor case 31 (yoke 52) utilizing the above-described magnet holder 53 and the housing 1.
The flange portion 52 of the yoke 52 is centered on the housing 11B by the spigot connection with the housing 11B by the spigot connection with the housing 11B and the spigot connection between the motor case 31 (yoke 52) and the housing 11B using the brush holder 62.
A is fastened and fixed to the flange 67 of the housing 11B.

Next, the rotating shaft 32 of the electric motor 30 is supported by the motor case 31 as follows.

(1) The rotary shaft 32 and the assist shaft 33 of the electric motor 30 are spliced and connected to the cylindrical connector 80,
Only one end of the rotating shaft 32 is connected to the motor case 31 (yoke 5
The other end of 2) is supported by a bearing 71 such as a ball bearing provided at the center of the closed portion 52B, and the other end of the rotating shaft 32 has an unsupported structure.

More specifically, as shown in FIG. 7, a fitting shaft (or fitting hole) 32A provided at the tip of the rotating shaft 32 of the electric motor 30 is pressed into a hole 81 of the connecting body 80. Fixed,
It is connected so as to be able to rotate integrally without any play Also, on the same axis as the rotating shaft 32, a fitting shaft (or fitting hole) 33 </ b> A provided at the tip of the assist shaft 33 is spliced into the hole 81 of the connecting body 80, and the fitting of the assist shaft 33 is performed. Coaxial part 33A
Of the fitting shaft (or fitting hole) 33B on the side of
Is splined (serrated).

Accordingly, the rotary shaft 32 and the assist shaft 33 of the electric motor 30 are coaxially connected by being spigot-coupled to the same hole 81 of the connecting body 80. As a result, the rotary shaft 3
2, the end on the side to which the connecting body 80 is coupled has an unsupported structure with no bearing interposed in the motor case 31, and both ends of the assist shaft 33 are connected to the housing 11B via the bearings 34 and 35 as described above. Supported, and only one end of the rotating shaft 32 is connected to the motor case 31 via the bearing 71 as described above.
Points were to be supported.

(2) When the base end (one end) of the rotating shaft 32 of the electric motor 30 is supported on the motor case 31 (yoke 52) by the bearing 71 provided on the motor case 31, the rotating shaft 32 is attached to the bearing 71. On the other hand, it was immovably supported in both axial directions.

Specifically, as shown in FIG. 8, the bearing 71 has an outer ring 71A which is caulked and fixed (or press-fitted) to the motor case 31 (yoke 52), and a rolling element 71C such as a ball with respect to the outer ring 71A. Inner ring 7 supported rotatably
1B. And one end of the rotating shaft 32 is a small-diameter portion 91 that is inserted into and supported by the inner race 71B,
A stepped portion 91A at the base of the small diameter portion 91 is applied to one end face of the inner ring 71B, and a stopper 92 such as a circlip or a tapered circlip engaged with a stop groove 91B provided at the tip of the small diameter portion 91 is connected to the other of the inner ring 71B. The inner ring 71B is sandwiched between the stepped portion 91A of the small diameter portion 91 and the stopper 92.

In the electric motor 30, the small diameter portion 91 of the rotary shaft 32 is inserted into the inner ring 71B of the bearing 71 provided on the other end closed portion 52B of the motor case 31 (yoke 52).
Stop groove 91 at the tip of small diameter portion 91 protruding from inner ring 71B
B, after the stopper 92 is engaged, the other end occluded portion 52B
The closure cap 52D is sealed via the ring 52C.

Therefore, according to the present embodiment, the following operations are provided. Only the base end (one end) side of the rotating shaft 32 of the electric motor 30 is immovably supported on the bearing 71 of the motor case 31 in both directions in the axial direction. it can. At the same time, the rotational runout of the rotating shaft 32 can be minimized, and cantilever support is possible.

The small diameter portion 91 of the rotating shaft 32 is inserted into the inner ring 71B of the bearing 71, and the inner ring 71B is sandwiched between the stepped portion 91A of the small diameter portion 91 and the stopper 92 engaged with the tip of the small diameter portion 91. With a simple configuration, the rotating shaft 32 is
Can be immovably supported in both directions in the axial direction.

Since the rotary shaft 32 of the electric motor 30 and the assist shaft 33 are coaxially formed by spigot-coupling, only one end of the rotary shaft 32 is supported by the bearing 71, and the end of the rotary shaft 32 near the assist shaft 33 is provided. Are not supported, and the number of bearings used for the rotating shaft 32 can be reduced.

(Second Embodiment) (FIG. 9) In the second embodiment, the motor case 31 (yoke 52) is also provided by a bearing 71 provided at the base end (one end) of the rotating shaft 32 of the electric motor 30 in the motor case 31. ), The rotating shaft 32 is immovably supported on the bearing 71 in both axial directions.

More specifically, as shown in FIG. 9, the bearing 71 includes an outer ring 71A that is caulked and fixed (or press-fitted and fixed) to the motor case 31 (yoke 52) and a rolling element 71C such as a ball with respect to the outer ring 71A. Inner ring 7 supported rotatably
1B. One end of the rotating shaft 32 is a small-diameter portion 101 that is inserted into and supported by the inner ring 71B, and a step portion 101A at the base of the small-diameter portion 101 is used as the inner ring 71B.
The nut 102 screwed to the tip of the small diameter portion 101 is applied to the other end surface of the inner ring 71B, and the small diameter portion 1
The inner ring 71B is sandwiched between the step portion 101A and the nut 102 of FIG.

In the electric motor 30, the small diameter portion 101 of the rotary shaft 32 is inserted into the inner ring 71B of the bearing 71 provided on the other end closed portion 52B of the motor case 31 (yoke 52) and protrudes from the inner ring 71B. After the nut 102 is screwed onto the tip of the small diameter portion 101, the closing cap 52D is sealed to the other end closed portion 52B via the O-ring 52C.

According to this embodiment, the small diameter portion 101 of the rotating shaft 32 is inserted into the inner race 71B of the bearing 71, and the small diameter portion 101
By sandwiching the inner race 71B between the stepped portion 101A of the small diameter portion 101 and the nut 102 screwed to the tip of the small diameter portion 101, the rotating shaft 32 can be immovably supported on the bearing 71 in both directions in the axial direction with a simple configuration.

(Third Embodiment) (FIG. 10) Also in the third embodiment, the motor case 31 (yoke 52) is provided by a bearing 71 provided at the base end (one end) of the rotating shaft 32 of the electric motor 30 in the motor case 31. ), The rotating shaft 32 is immovably supported on the bearing 71 in both axial directions.

Specifically, as shown in FIG.
Has an outer ring 71A caulked and fixed (or press-fitted and fixed) to the motor case 31 (yoke 52), and an inner ring 71B rotatably supported on the outer ring 71A via a rolling element 71C such as a ball. One end of the rotary shaft 32 is a small-diameter portion 111 that is inserted into and supported by the inner race 71B, and a step 111A at the base of the small-diameter portion 111 is formed as the inner race 71B.
Of the small-diameter portion 111 to the inner ring 71B.
Into the press.

According to the present embodiment, the small diameter portion 111 of the rotating shaft 32 is inserted into the inner ring 71B of the bearing, the step 111A of the small diameter portion 111 is applied to one end surface of the inner ring 71B, and the tip of the small diameter portion 111 is attached. By press-fitting the inner ring 71B, the rotating shaft 32 can be immovably supported on the bearing in both axial directions with a simple configuration.

The embodiment of the present invention has been described with reference to the drawings. However, the specific configuration of the present invention is not limited to this embodiment, and changes in design and the like can be made without departing from the gist of the present invention. The present invention is also included in the present invention. For example, when the electric power steering device 10 is driven in reverse or when the tire runs on a curb, the impact force generated on the tooth surface of the worm gear 37 provided in the assist shaft 33 is reduced to reduce the beating sound between the tooth surfaces, or In order to avoid damaging the torque transmission path due to the inertial thrust of the shaft 33, even when the assist shaft 33 is elastically supported via an elastic deformation tool or the like so as to be able to move in the axial direction on the bearings 34, 35, the rotation shaft 32 is As shown in FIGS. 8 to 10, one end of the rotating shaft supporting structure of the present invention which eliminates backlash in the axial direction can be employed by supporting one end of the bearing 71 in both directions in the axial direction as shown in FIGS.

[0052]

As described above, according to the present invention, in an electric power steering apparatus, a simple support structure
It is possible to eliminate the backlash in the axial direction of the rotating shaft of the electric motor, and at the same time, to suppress the runout of the rotating shaft.

[Brief description of the drawings]

FIG. 1 is a front view showing an electric power steering apparatus partially cut away.

FIG. 2 is a sectional view taken along the line II-II in FIG.

FIG. 3 is a sectional view taken along the line III-III of FIG. 2;

FIG. 4 is a perspective view showing a magnet holder.

FIG. 5 shows a brush holder, (A) is a front view,
(B) is a side view.

FIG. 6 shows a grommet, (A) is a front view,
(B) is a side view, and (C) is a plan view.

FIG. 7 is a side view showing a main part of FIG. 3;

FIG. 8 is a cross-sectional view illustrating a rotation shaft support structure according to the first embodiment.

FIG. 9 is a cross-sectional view illustrating a rotation shaft support structure according to a second embodiment.

FIG. 10 is a sectional view showing a rotation shaft support structure according to a third embodiment.

[Explanation of symbols]

 Reference Signs List 10 electric power steering device 11B housing 30 electric motor 31 motor case 32 rotating shaft 33 assist shaft 71 bearing 71A outer ring 71B inner ring 71C rolling element 91, 101, 111 small diameter portion 91A, 101A, 111A step portion 92 stopper 102 nut

Continued on the front page F term (reference) 3D033 CA02 CA03 5H607 AA04 BB01 BB04 BB14 CC01 CC03 DD07 DD19 EE32 EE36 GG08 HH02 HH06 JJ00 KK03 KK07

Claims (5)

[Claims] 1. An electric power steering device comprising an electric motor fixed to a housing, an assist shaft of a steering device supported on the housing, and an assist shaft connected to a rotation shaft of the electric motor. An electric power steering apparatus characterized in that only one end is axially immovably supported on a motor case by a bearing and the other end is connected to an assist shaft. 2. An outer ring in which the bearing is fixed to a motor case, and an inner ring rotatably supported on the outer ring via a rolling element, wherein one end of the rotating shaft is inserted into the inner ring. A small-diameter portion to be supported, a step portion at the base of the small-diameter portion is applied to one end surface of the inner ring, and a stopper fixed to the tip of the small-diameter portion is applied to the other end surface of the inner ring, and the step portion of the small-diameter portion and the stopper are provided. 2. The electric power steering apparatus according to claim 1, wherein the inner ring is held between the two. 3. An outer ring in which the bearing is fixed to a motor case, and an inner ring rotatably supported by the outer ring via a rolling element, wherein one end of the rotating shaft is inserted into the inner ring. The small-diameter portion is supported, and the step at the base of the small-diameter portion is applied to one end surface of the inner ring, and the nut screwed to the tip of the small-diameter portion is applied to the other end surface of the inner ring. The electric power steering device according to claim 1, wherein the electric power steering device is held. 4. An outer ring in which the bearing is fixed to a motor case, and an inner ring rotatably supported by the outer ring via a rolling element, wherein one end of the rotating shaft is inserted into the inner ring. 2. The electric power steering apparatus according to claim 1, wherein the small diameter portion is supported, a step at the base of the small diameter portion is applied to one end surface of the inner ring, and a tip of the small diameter portion is press-fitted into the inner ring. 5. The electric power steering apparatus according to claim 1, wherein a rotary shaft and an assist shaft of the electric motor are spigot-coupled.