Electric actuator and method of assembling electric actuator

Abstract

To reduce the manufacturing cost of an electric actuator.SOLUTION: An electric actuator comprises: a rolling bearing which has an inner ring and rolling elements; a motor which has an output shaft; a ball screw mechanism which has a screw shaft and in which an outer peripheral surface of the screw shaft is fitted to an inner peripheral surface of the inner ring; a planetary gear mechanism which has a sun gear coupled to the output shaft; a fitting shaft in which an outer peripheral surface is fitted to the inner peripheral surface of the inner ring and which has a first circular hole; and a sphere which has an outer diameter larger than an inner diameter of the first circular hole. The first circular hole is formed so as to be arranged concentrically with the screw shaft in a state where the respective outer peripheral surfaces of the screw shaft and the fitting shaft are fitted to the inner peripheral surface of the inner ring. A second circular hole which is arranged concentrically with the output shaft and has an inner diameter smaller than the outer diameter of the sphere is formed in an end surface of the output shaft or the sun gear. A peripheral edge of one circular hole out of the first circular hole arranged concentrically with the screw shaft and the second circular hole arranged concentrically with the output shaft abuts on the other part of an outer peripheral surface of the sphere in a state where a part of the outer peripheral surface of the sphere abuts on a peripheral edge of the other circular hole.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present disclosure relates to an electric actuator and a method for assembling an electric actuator. [Background technology]

[0002] Patent Document 1 discloses an electric actuator used in a brake caliper of a disc brake device. This electric actuator includes a motor, a planetary gear mechanism that reduces the rotational power of the motor, a rolling bearing with an inner ring to which the reduced rotational power is transmitted, and a ball screw mechanism with a screw shaft connected to the inner ring. The planetary gear mechanism includes a sun gear that is rotationally driven by the motor, a ring gear arranged concentrically with the sun gear, multiple planet gears that mesh with the sun gear and the ring gear, and multiple support shafts that are fixed to the inner ring of the rolling bearing and rotatably support each planet gear. The ball screw mechanism includes a nut that is threadedly engaged with a screw shaft via multiple balls and moves axially as the screw shaft rotates. The brake caliper performs braking by pressing brake pads against a brake disc using a piston that moves in conjunction with the nut. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2022-532228 Summary of the Invention [Problem to be solved by the invention]

[0004] When assembling the electric actuator, high positional accuracy is required for each gear and support shaft in order to ensure precision in meshing of each gear of the planetary gear mechanism, which increases manufacturing costs. The present disclosure aims to reduce the manufacturing costs of electric actuators. [Means for solving the problem]

[0005] The electric actuator of the present disclosure includes a rolling bearing having an inner ring with a raceway formed on its outer peripheral surface and rolling elements that roll on the raceway, a motor having an output shaft arranged on one axial side of the inner ring, a ball screw mechanism having a screw shaft arranged on the other axial side of the inner ring, the outer peripheral surface of the screw shaft being fitted onto the other axial side of the inner peripheral surface of the inner ring, a planetary gear mechanism having a sun gear connected to the output shaft, which changes the speed of the rotational power output from the output shaft and transmits it to the inner ring, and a fitted shaft having an outer peripheral surface fitted onto the one axial side of the inner peripheral surface of the inner ring and having a first circular hole formed in an end face on the one axial side, and an outer diameter larger than the inner diameter of the first circular hole. and a sphere having a first circular hole formed therein, the first circular hole of the fitting shaft being formed so as to be concentric with the screw shaft when the outer peripheral surfaces of the screw shaft and the fitting shaft are fitted onto the inner peripheral surface of the inner ring, and a second circular hole being concentric with the output shaft and having an inner diameter smaller than the outer diameter of the sphere being formed on the end face on the other axial side of the output shaft or the sun gear when the sun gear is connected to the output shaft, and when a portion of the outer peripheral surface of the sphere abuts against the periphery of one of the first circular hole arranged concentrically with the screw shaft and the second circular hole arranged concentrically with the output shaft, the periphery of the other circular hole abuts against the other portion of the outer peripheral surface of the sphere.

[0006] The method of assembling the electric actuator disclosed herein includes the steps of fitting the outer peripheral surface of the screw shaft to the other axial side of the inner peripheral surface of the inner ring, fitting the outer peripheral surface of the fitting shaft to the one axial side of the inner peripheral surface of the inner ring, and arranging the first circular hole concentrically with the screw shaft; connecting the sun gear to the output shaft and arranging the second circular hole concentrically with the output shaft; and abutting a portion of the outer peripheral surface of the sphere against the periphery of one of the first circular hole arranged concentrically with the screw shaft and the second circular hole arranged concentrically with the output shaft, while abutting the periphery of the other circular hole against another portion of the outer peripheral surface of the sphere.

[0007] The method for assembling the electric actuator disclosed herein includes the steps of fitting the outer peripheral surface of the screw shaft to the other axial side of the inner peripheral surface of the inner ring, fitting the outer peripheral surface of the fitting shaft to the one axial side of the inner peripheral surface of the inner ring, and arranging the first circular hole concentrically with the screw shaft; connecting the sun gear to the output shaft and arranging the second circular hole concentrically with the output shaft; abutting a part of the outer peripheral surface of the sphere against the periphery of one of the first circular hole arranged concentrically with the screw shaft and the second circular hole arranged concentrically with the output shaft, and abutting the periphery of the other circular hole against another part of the outer peripheral surface of the sphere; and pushing the sphere abutting against the peripheries of the first circular hole and the second circular hole toward the other axial side to accommodate it in the accommodation space of the fitting shaft. [Effects of the Invention]

[0008] According to the present disclosure, the manufacturing costs of electric actuators can be reduced. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of an electric actuator according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view taken along line AA in FIG. [Figure 3] FIG. 2 is an enlarged cross-sectional view showing the periphery of the inner ring of the rolling bearing. [Figure 4] FIG. 10 is a cross-sectional view showing the electric actuator in the middle of assembly. [Figure 5] FIG. 10 is a cross-sectional view showing the electric actuator in the middle of assembly. [Figure 6] FIG. 10 is a cross-sectional view showing the electric actuator in the middle of assembly. [Figure 7] FIG. 10 is a cross-sectional view showing the electric actuator in the middle of assembly. [Figure 8] FIG. 10 is a cross-sectional view showing the electric actuator in the middle of assembly. [Figure 9] FIG. 10 is a cross-sectional view showing the electric actuator in the middle of assembly. [Figure 10] FIG. 10 is a cross-sectional view showing a main part of an electric actuator according to a second embodiment of the present disclosure. [Figure 11] FIG. 10 is a cross-sectional view showing a main part of an electric actuator according to a third embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] First, the contents of the embodiment will be listed and explained. <Outline of the embodiment> (1) The electric actuator of the present disclosure includes a rolling bearing having an inner ring with a raceway formed on its outer peripheral surface and rolling elements that roll on the raceway; a motor having an output shaft arranged on one axial side of the inner ring; a ball screw mechanism having a screw shaft arranged on the other axial side of the inner ring, the outer peripheral surface of the screw shaft being fitted onto the other axial side of the inner peripheral surface of the inner ring; a planetary gear mechanism having a sun gear connected to the output shaft, which speed-changes the rotational power output from the output shaft and transmits it to the inner ring; a fitted shaft whose outer peripheral surface is fitted onto the one axial side of the inner peripheral surface of the inner ring and has a first circular hole formed in an end face on the one axial side; and a sphere having the following structure: the first circular hole of the fitting shaft is formed so as to be concentrically arranged with the screw shaft when the outer peripheral surfaces of the screw shaft and the fitting shaft are fitted with the inner peripheral surface of the inner ring; a second circular hole is formed on the end face on the other axial side of the output shaft or the sun gear when the sun gear is connected to the output shaft, the second circular hole being concentric with the output shaft and having an inner diameter smaller than the outer diameter of the sphere; and when a part of the outer peripheral surface of the sphere abuts against the periphery of one of the first circular hole arranged concentrically with the screw shaft and the second circular hole arranged concentrically with the output shaft, the periphery of the other circular hole abuts against the other part of the outer peripheral surface of the sphere.

[0011] According to the electric actuator, the outer peripheral surfaces of the screw shaft and the mating shaft of the ball screw mechanism are fitted to the inner peripheral surface of the inner ring of the rolling bearing, so that the first circular hole formed in one axial end face of the mating shaft is concentric with the screw shaft. Furthermore, the sun gear of the planetary gear mechanism is connected to the output shaft of the motor, so that the second circular hole formed in the other axial end face of the output shaft or the sun gear is concentric with the output shaft. The edges of the first and second circular holes thus arranged abut against the outer peripheral surfaces of spheres, so that the screw shaft of the ball screw mechanism and the output shaft of the motor are concentrically arranged. This allows the axis of the screw shaft to easily align with the axis of the output shaft. As a result, the positional accuracy requirements for the gears of the planetary gear mechanism can be relaxed, thereby reducing the manufacturing cost of the electric actuator.

[0012] (2) In the electric actuator of (1), it is preferable that an accommodation space is formed inside the mating shaft, which is connected to the first circular hole and into which the sphere abutting against each periphery of the first circular hole and the second circular hole is pushed toward the other axial direction and accommodated. In this case, after the axis of the screw shaft and the axis of the output shaft are aligned, the spheres abutting against the peripheries of the first circular hole and the second circular hole are pushed to the other axial direction, thereby accommodating the spheres in the accommodation space inside the mating shaft. This allows the electric actuator to be configured compactly in the axial direction. Furthermore, since the periphery of the second circular hole can be prevented from abutting against the spheres while the output shaft is rotating, torque loss can be reduced.

[0013] (3) In the electric actuator of (2), it is preferable that the fitting shaft has a deformation promoting portion that promotes radially outward deformation of the portion pressed against the outer peripheral surface of the sphere when the sphere is pushed into the accommodating space. In this case, when the sphere is pushed axially in the other direction, the portion of the fitting shaft that is pressed against the outer circumferential surface of the sphere is easily deformed radially outward by the deformation promoting portion, thereby making it easier to accommodate the sphere in the accommodation space of the fitting shaft.

[0014] (4) In the electric actuator of any one of (1) to (3), the second circular hole is preferably a center hole formed in the end face of the output shaft on the other axial side as a machining reference for the output shaft. In this case, the center hole formed as a machining reference for the output shaft also serves as the second circular hole with which the sphere abuts, thereby further reducing the manufacturing costs of the electric actuator.

[0015] (5) The method of assembling the electric actuator of (1) includes the steps of fitting the outer peripheral surface of the screw shaft to the other axial side of the inner peripheral surface of the inner ring, fitting the outer peripheral surface of the fitting shaft to the one axial side of the inner peripheral surface of the inner ring, and arranging the first circular hole concentrically with the screw shaft; connecting the sun gear to the output shaft and arranging the second circular hole concentrically with the output shaft; and abutting a part of the outer peripheral surface of the sphere against the periphery of one of the first circular hole arranged concentrically with the screw shaft and the second circular hole arranged concentrically with the output shaft, while abutting the periphery of the other circular hole against the other part of the outer peripheral surface of the sphere. According to the above-described method for assembling an electric actuator, the same effects as those of the electric actuator described in (1) above can be achieved.

[0016] (6) The method of assembling the electric actuator of (2) includes the steps of fitting the outer peripheral surface of the screw shaft to the other axial side of the inner peripheral surface of the inner ring, fitting the outer peripheral surface of the fitting shaft to the one axial side of the inner peripheral surface of the inner ring, and arranging the first circular hole concentrically with the screw shaft; connecting the sun gear to the output shaft and arranging the second circular hole concentrically with the output shaft; abutting a part of the outer peripheral surface of the sphere against the periphery of one of the first circular hole arranged concentrically with the screw shaft and the second circular hole arranged concentrically with the output shaft, and abutting the periphery of the other circular hole against another part of the outer peripheral surface of the sphere; and pushing the sphere abutting against the peripheries of the first circular hole and the second circular hole toward the other axial side to accommodate it in the accommodation space of the fitting shaft. According to the above method for assembling an electric actuator, the same effects as those of the electric actuator described in (2) above can be achieved.

[0017] <Details of the embodiment> Preferred embodiments will now be described with reference to the drawings. [First embodiment] 1 is a cross-sectional view of an electric actuator 10 according to a first embodiment of the present disclosure. The electric actuator 10 is a device that converts the rotational power of a motor 11 into linear motion of a piston 37 and outputs the motion. The electric actuator 10 of this embodiment is used as a drive device for a brake caliper that presses brake pads against a brake disc in a vehicle disc brake device.

[0018] The electric actuator 10 includes a motor 11 , a planetary gear mechanism 12 , a ball screw mechanism 13 , a rolling bearing 14 , and a housing 15 . The motor 11 has a main body 11b incorporating a rotor and a stator, and an output shaft 11a protruding from the main body 11b and outputting rotational power. The output shaft 11a is disposed on one axial side (the right side in FIG. 1; the same applies below) of the inner ring 42 of the rolling bearing 14. In FIG. 1, the axis of the output shaft 11a is indicated by the symbol C. A known electric motor is used as the motor 11.

[0019] The housing 15 includes a first housing 151 and a second housing 152 . The first housing 151 accommodates the ball screw mechanism 13 and the rolling bearing 14. The first housing 151 has a cylindrical outer peripheral wall 15a and an annular side wall 15b that closes the end of the outer peripheral wall 15a on the other axial side (the left side in FIG. 1; the same applies below). A circumferential groove 15c is formed in the inner periphery on one axial side of the outer peripheral wall 15a. A threaded hole 15d is formed in the end face on one axial side of the outer peripheral wall 15a. A plurality of threaded holes 15d are formed at equal intervals around the circumferential direction of the outer peripheral wall 15a.

[0020] The second housing 152 accommodates the motor 11. The second housing 152 has an annular side wall 15e and a cylindrical outer peripheral wall 15f. The side wall 15e is positioned axially to one side of the first housing 151. A through-hole 15e1 is formed on the outer peripheral side of the side wall 15e, penetrating the side wall 15e in the axial direction. A plurality of through-holes 15e1 are formed at equal intervals around the circumferential direction of the side wall 15e. The outer peripheral wall 15f protrudes from a radially intermediate portion of the side wall 15e to one side in the axial direction. The main body 11b of the motor 11 is fixed to the inner periphery of the outer peripheral wall 15f. The specific structure of the housing 15 is not particularly limited, and the design can be modified as appropriate.

[0021] Fig. 2 is a cross-sectional view taken along line AA in Fig. 1. As shown in Fig. 1 and Fig. 2, the planetary gear mechanism 12 includes a sun gear 21, a ring gear 22, a plurality of planetary gears 23, a plurality of support shafts 24, and a carrier 25. The sun gear 21 is disposed concentrically with the output shaft 11a of the motor 11. The sun gear 21 in this embodiment is formed in a cylindrical shape. A large number of teeth 21a are formed on the outer peripheral surface of the sun gear 21. A press-fit groove 21b is formed in the center of one axial end face of the sun gear 21. The output shaft 11a of the motor 11 is press-fitted into the press-fit groove 21b. Therefore, the sun gear 21 is connected to the output shaft 11a of the motor 11 so as to be rotatable together with it.

[0022] The ring gear 22 has an annular gear body 22a and an annular flange 22b. The gear body 22a is an internal gear with a large number of teeth 22c formed on its inner circumferential surface. The gear body 22a is disposed concentrically with the sun gear 21, radially outward from the sun gear 21. The outer circumferential surface of the gear body 22a is fitted into and fixed to a circumferential groove 15c of the first housing 151.

[0023] The flange 22b protrudes radially outward from the outer peripheral surface on one axial side of the gear body 22a. A through-hole 22d is formed in the flange 22b, penetrating the flange 22b in the axial direction. A plurality of through-holes 22d are formed at equal intervals around the circumference of the flange 22b. The flange 22b is disposed between the outer peripheral wall 15a of the first housing 151 and the side wall 15e of the second housing 152, and is fixed to the housing 15 by a plurality of bolts 17. Each bolt 17 passes through the through-hole 15e1 in the side wall 15e and the through-hole 22d in the flange 22b, and is fastened to the screw hole 15d in the outer peripheral wall 15a.

[0024] The multiple planetary gears 23 are disposed radially between the sun gear 21 and the ring gear 22. The planetary gear mechanism 12 of this embodiment includes three planetary gears 23. A large number of teeth 23a are formed on the outer peripheral surface of each planetary gear 23. Each planetary gear 23 meshes with the sun gear 21 and the ring gear 22. Each planetary gear 23 revolves around the axis C as the sun gear 21 rotates. The number of planetary gears 23 is not limited and can be changed as appropriate.

[0025] The support shaft 24 is formed in a cylindrical shape. One axial side of the support shaft 24 is inserted into the inner periphery of the planetary gear 23. The planetary gear 23 is supported rotatably (on its axis) relative to the support shaft 24. The other axial side of the support shaft 24 is press-fitted and fixed into an inner ring 42 of the rolling bearing 14. The inner ring 42 rotates about the axis C as the multiple planetary gears 23 revolve around the axis C in conjunction with the rotation of the sun gear 21. Therefore, the inner ring 42 also functions as the carrier 25 of the planetary gear mechanism 12.

[0026] The rolling bearing 14 has an outer ring 41, an inner ring 42, and a plurality of rolling elements 43. The rolling bearing 14 in this embodiment is a deep groove ball bearing. The rolling bearing 14 is disposed concentrically with the sun gear 21 and the ring gear 22 of the planetary gear mechanism 12. The rolling bearing 14 may be another type of rolling bearing, such as a cylindrical roller bearing.

[0027] The outer ring 41 is formed in an annular shape. A raceway 41a is formed on the inner peripheral surface of the outer ring 41. The outer ring 41 is arranged next to the other axial side of the ring gear 22. The outer peripheral surface of the outer ring 41 is fitted into and fixed to the circumferential groove 15c of the first housing 151. The inner ring 42 is formed in an annular shape. A raceway 42a is formed on the outer peripheral surface of the inner ring 42. The inner ring 42 is arranged concentrically with the outer ring 41, radially inward of the outer ring 41.

[0028] The plurality of rolling elements 43 are disposed radially between the outer ring 41 and the inner ring 42. In this embodiment, the rolling elements 43 are balls. The rolling elements 43 roll on raceways 41 a of the outer ring 41 and raceways 42 a of the inner ring 42. Although not shown, the rolling bearing 14 includes a cage that maintains the circumferential spacing of the plurality of rolling elements 43.

[0029] The ball screw mechanism 13 includes a screw shaft 32, a nut 33, and a plurality of balls . The screw shaft 32 is formed in a cylindrical shape. The screw shaft 32 is arranged concentrically with the inner ring 42 of the rolling bearing 14 on the other axial side of the inner ring 42. The outer peripheral surface at one axial end of the screw shaft 32 is fitted into and fixed to the other axial side of the inner peripheral surface 42b of the inner ring 42. The screw shaft 32 is rotatably supported with respect to the housing 15 by the rolling bearing 14. An outer peripheral raceway surface 32a is formed on the outer peripheral surface of the screw shaft 32.

[0030] The nut 33 is formed in a cylindrical shape. The nut 33 is disposed concentrically with the screw shaft 32 on the radially outer side of the screw shaft 32. An inner circumferential raceway surface 33a is formed on the inner circumferential surface of the nut 33. The inner circumferential raceway surface 33a is disposed facing the radially outer side of the outer circumferential raceway surface 32a.

[0031] A plurality of balls 34 are disposed between the outer circumferential raceway surface 32a and the inner circumferential raceway surface 33a, and roll on the outer circumferential raceway surface 32a and the inner circumferential raceway surface 33a. The screw shaft 32 and the nut 33 are screwed together via the plurality of balls 34. Therefore, the nut 33 moves in the axial direction as the screw shaft 32 rotates.

[0032] A piston (pressing member) 37 is fixed to the nut 33. This piston 37 moves axially together with the nut 33, and presses a brake pad (not shown) against a brake disc. The piston 37 is inserted into an opening 15b1 formed in the side wall 15b on the other axial side of the first housing 151. A seal 18 seals the gap between the outer peripheral surface of the piston 37 and the inner peripheral surface of the opening 15b1.

[0033] When the plurality of planetary gears 23 revolve around the axis C in accordance with the rotation of the sun gear 21, the inner ring 42 is decelerated and rotates around the axis C. Therefore, the rotational power output from the output shaft 11a of the motor 11 is decelerated (changed in speed) by the planetary gear mechanism 12 and transmitted to the inner ring 42 of the rolling bearing 14. The rotational power transmitted to the inner ring 42 is transmitted to the screw shaft 32 of the ball screw mechanism 13, and as the screw shaft 32 rotates, the piston 37 together with the nut 33 reciprocates in the axial direction.

[0034] 3 is an enlarged cross-sectional view showing the periphery of the inner ring 42 of the rolling bearing 14. As shown in FIGS. 1 and 3, the electric actuator 10 further includes a fitting shaft 51 and a spherical body 52 that are used during assembly. The fitting shaft 51 is formed in a cylindrical shape. The outer peripheral surface of the fitting shaft 51 is fitted and fixed to one axial side of the inner peripheral surface 42b of the inner ring 42. An end face 51a on one axial side of the fitting shaft 51 is disposed substantially flush with an end face on one axial side of the inner ring 42. The fitting shaft 51 is disposed concentrically with the inner ring 42 and the screw shaft 32.

[0035] A first circular hole 51b is formed in the end face 51a of the fitting shaft 51. The first circular hole 51b is formed so as to be concentric with the screw shaft 32 in a state in which the outer circumferential surfaces of the screw shaft 32 and the fitting shaft 51 are fitted into the inner circumferential surface 42b of the inner ring 42. The first circular hole 51b in this embodiment is formed by a part of the space on the inner circumferential side of the fitting shaft 51. The first circular hole 51b is formed so that its inner diameter gradually decreases from an opening edge on one axial side to a terminal edge on the other axial side. The shape of the first circular hole 51b is not limited to that of this embodiment.

[0036] An accommodation space 51c for accommodating the sphere 52 is formed inside the fitting shaft 51. The accommodation space 51c is formed concentrically with the fitting shaft 51. In this embodiment, the accommodation space 51c is formed by another portion of the space on the inner periphery side of the fitting shaft 51. The accommodation space 51c communicates with the first circular hole 51b and opens at the end face of the fitting shaft 51 on the other axial side.

[0037] The axial length of the accommodation space 51c is greater than the axial length of the first circular hole 51b. The accommodation space 51c is formed so that its inner diameter gradually decreases from the opening edge on the other axial side to the terminal edge on one axial side. The innermost diameter position on one axial side of the accommodation space 51c coincides with the innermost diameter position P on the other axial side of the first circular hole 51b. The shape of the accommodation space 51c is not limited to that of this embodiment.

[0038] The outer diameter of the sphere 52 is larger than the inner diameter of the first circular hole 51b. The outer diameter of the sphere 52 in this embodiment is larger than the innermost diameter of the first circular hole 51b (accommodation space 51c). When assembling the electric actuator 10, the sphere 52 is pushed into the sun gear 21 from one axial side of the fitting shaft 51, passing through the first circular hole 51b and being accommodated in the accommodation space 51c. The electric actuator 10 in this embodiment is completed in the state shown in FIG. 3 where the sphere 52 is accommodated in the accommodation space 51c.

[0039] An annular groove 51d that opens at the end face 51a is formed in the fitting shaft 51. The annular groove 51d is formed from the end face 51a of the fitting shaft 51 to a position that corresponds to the middle of the axial direction of the accommodation space 51c. As a result, when the sphere 52 is pressed into the accommodation space 51c as described above, the portion of the fitting shaft 51 that is pressed against the outer peripheral surface of the sphere 52, i.e., the peripheral portion of the first circular hole 51b at the innermost diameter position P, can be easily deformed (elastically deformed) radially outward (see FIG. 9). Therefore, the annular groove 51d functions as a deformation promoting portion that promotes radially outward deformation of the peripheral portion that is pressed against the outer peripheral surface of the sphere 52.

[0040] A second circular hole 21d is formed in the center of the end face 21c on the other axial side of the sun gear 21. The second circular hole 21d is formed so as to be concentric with the output shaft 11a when the sun gear 21 is coupled to the output shaft 11a. The second circular hole 21d of this embodiment is formed so that its inner diameter gradually decreases from the opening edge on the other axial side to partway along on one axial side. The inner diameter of the second circular hole 21d is smaller than the outer diameter of the sphere 52. In other words, the outer diameter of the sphere 52 is larger than the inner diameter of the second circular hole 21d. In this embodiment, the outer diameter of the sphere 52 is larger than the innermost diameter of the second circular hole 21d. The shape of the second circular hole 21d is not limited to that of this embodiment.

[0041] 4 to 9 are cross-sectional views showing a state in the middle of assembly of the electric actuator 10. As shown in FIG. 4, once the ball screw mechanism 13 is assembled into the first housing 151, the rolling bearing 14 and the fitting shaft 51 are assembled from one axial side of the first housing 151. Specifically, as shown in FIG. 5, the outer peripheral surface of the outer ring 41 is fitted into the circumferential groove 15c of the first housing 151. At the same time, the outer peripheral surface of one axial end of the screw shaft 32 is fitted into the other axial side of the inner peripheral surface of the inner ring 42. In this state, the outer peripheral surface of the fitting shaft 51 is fitted into one axial side of the inner peripheral surface of the inner ring 42. As a result, the first circular hole 51b of the fitting shaft 51 is arranged concentrically with the screw shaft 32.

[0042] Next, the ring gear 22, the plurality of planetary gears 23, and the support shaft 24 of the planetary gear mechanism 12 are assembled to the first housing 151. As shown in FIG. 5, the support shaft 24 is press-fitted into the inner ring 42 in advance, but it may also be press-fitted into the inner ring 42 after the rolling bearing 14 is assembled. As shown in FIG. 6, the ring gear 22 is fitted into the circumferential groove 15c of the first housing 151. Each planetary gear 23 is attached to the support shaft 24.

[0043] The sun gear 21 of the planetary gear mechanism 12 is assembled to the second housing 152 side. Specifically, the output shaft 11a of the motor 11 is press-fitted into the press-fit groove 21b of the sun gear 21, and the sun gear 21 is connected to the output shaft 11a. As a result, the second circular hole 21d of the sun gear 21 is arranged concentrically with the output shaft 11a of the motor 11.

[0044] Next, as shown in FIG. 7, the sphere 52 is brought into contact with the first circular hole 51b of the fitting shaft 51. In this embodiment, a portion of the outer circumferential surface of the sphere 52 (the left portion in FIG. 7) is brought into contact with the periphery of the first circular hole 51b (here, the periphery of the innermost diameter position P). At this time, although not shown, the sphere 52 is placed in the first circular hole 51b of the fitting shaft 51 with one axial side of the first housing 151 facing upward. This causes the sphere 52 to be held in contact with the first circular hole 51b. The sphere 52 may be brought into contact with the first circular hole 51b before the gears 22, 23 and the support shaft 24 of the planetary gear mechanism 12 are assembled to the first housing 151.

[0045] Next, as shown in FIG. 8, the second housing 152 is brought close to one axial side of the first housing 151, and the second circular hole 21d of the sun gear 21 is brought into contact with the sphere 52 that is in contact with the first circular hole 51b. In this embodiment, the periphery (here, the opening edge) of the second circular hole 21d of the sun gear 21 is brought into contact with another part (the right part in FIG. 8) of the outer circumferential surface of the sphere 52. This operation is also performed with one axial side of the first housing 151 facing upward, that is, with the first circular hole 51b and the sphere 52 maintained in contact. When the second circular hole 21d is in contact with the sphere 52, the axis C of the output shaft 11a of the motor 11 and the axis of the screw shaft 32 of the ball screw mechanism 13 are aligned.

[0046] Next, the second housing 152 is fixed to the first housing 151 by the bolts 17. Specifically, the bolts 17 pass through the through holes 15e1 of the side wall 15e and the through holes 22d of the flange 22b, and are tightened into the threaded holes 15d of the outer peripheral wall 15a. As the bolts 17 are tightened, the spheres 52 abutting against the peripheries of the first circular hole 51b and the second circular hole 21d are pushed toward the other axial direction by the sun gear 21.

[0047] When the sphere 52 is pressed into the other axial direction, the peripheral edge portion of the first circular hole 51b in the fitting shaft 51 at the innermost diameter position P is pressed radially outward by the outer peripheral surface of the sphere 52. The peripheral edge portion pressed radially outward is elastically deformed so as to expand in diameter radially outward, as shown in Fig. 9. At this time, because an annular groove (deformation promoting portion) 51c is formed radially outward from the peripheral edge portion in the fitting shaft 51, the peripheral edge portion is easily elastically deformed radially outward.

[0048] When the peripheral edge portion elastically deforms radially outward, the sphere 52 passes through the innermost diameter position P of the first circular hole 51b and is accommodated in the accommodation space 51c (see FIG. 3). When the sphere 52 is accommodated in the accommodation space 51c, the peripheral edge portion returns to its original state due to an elastic restoring force. As a result, movement of the sphere 52 in the accommodation space 51c to one side in the axial direction is restricted. The opening on the other axial side of the accommodation space 51c is blocked by the end face on one axial side of the screw shaft 32. Therefore, movement of the sphere 52 in the accommodation space 51c to the other side in the axial direction is also restricted. Therefore, the sphere 52 is held in a state accommodated in the accommodation space 51c.

[0049] According to the electric actuator 10 of the first embodiment, the outer peripheral surfaces of the screw shaft 32 and the mating shaft 51 of the ball screw mechanism 13 are fitted into the inner peripheral surface 42b of the inner ring 42 of the rolling bearing 14, so that the first circular hole 51b of the mating shaft 51 is arranged concentrically with the screw shaft 32. Furthermore, the sun gear 21 of the planetary gear mechanism 12 is connected to the output shaft 11a of the motor 11, so that the second circular hole 21d of the sun gear 21 is arranged concentrically with the output shaft 11a. The peripheries of the first circular hole 51b and the second circular hole 21d arranged in this manner abut against the outer peripheral surfaces of the spheres 52, so that the screw shaft 32 of the ball screw mechanism 13 and the output shaft 11a of the motor 11 are arranged concentrically. This makes it possible to easily align the axis of the screw shaft 32 with the axis C of the output shaft 11a. As a result, the positional accuracy requirements for the planetary gear 23, the support shaft 24, etc. of the planetary gear mechanism 12 can be relaxed, and the manufacturing cost of the electric actuator 10 can be reduced.

[0050] Furthermore, with the peripheries of the first circular hole 51b and the second circular hole 21d in contact with the sphere 52, the bolt 17 is tightened and the sun gear 21 presses the sphere 52 to the other axial direction, thereby accommodating the sphere 52 in the accommodation space 51c inside the fitting shaft 51. This allows the assembled electric actuator 10 to be compact in the axial direction. Furthermore, since the periphery of the second circular hole 21d can be prevented from abutting against the sphere 52 while the output shaft 11a is rotating, torque loss can be reduced.

[0051] Furthermore, the fitting shaft 51 has an annular groove (deformation promoting portion) 51d that promotes radially outward deformation of the portion pressed against the outer circumferential surface of the sphere 52 when the sphere 52 is pressed into the accommodation space 51c. This makes it easier for the pressed portion of the fitting shaft 51 to deform radially outward, making it possible to easily accommodate the sphere 52 in the accommodation space 51c of the fitting shaft 51.

[0052] [Second embodiment] 10 is a cross-sectional view showing a main portion of an electric actuator 10 according to a second embodiment of the present disclosure. In this embodiment, the deformation promoting portion of the fitting shaft 51 differs from that of the first embodiment. A stepped portion 51e recessed radially inward is formed over the entire circumferential direction on the outer peripheral surface of the fitting shaft 51. The stepped portion 51e is formed on the fitting shaft 51 from a position corresponding to the middle of the axial direction of the accommodation space 51c to the end face 51a on one axial side.

[0053] By forming the step portion 51e as described above, the radial thickness of the portion of the fitting shaft 51 that is pressed against the outer peripheral surface of the sphere 52, i.e., the peripheral portion of the first circular hole 51b at the innermost diameter position P, is reduced. This allows the peripheral portion to easily deform (elastically deform) radially outward when the sphere 52 is pressed into the accommodation space 51c. Therefore, the step portion 51e functions as a deformation promoting portion that promotes radially outward deformation of the peripheral portion that is pressed against the outer peripheral surface of the sphere 52.

[0054] Other configurations of this embodiment are the same as those of the first embodiment, so the same reference numerals are used and the description thereof will be omitted. Note that the peripheral edge portion of the fitting shaft 51 in this embodiment may be composed of a plurality of arc pieces divided in the circumferential direction. In this case, the peripheral edge portion can be more easily deformed radially outward.

[0055] In the electric actuator 10 of the second embodiment, too, the axis of the screw shaft 32 can be easily aligned with the axis C of the output shaft 11a. As a result, the positional accuracy requirements for the planetary gears 23 and the support shafts 24 of the planetary gear mechanism 12 can be relaxed, thereby reducing the manufacturing cost of the electric actuator 10. Furthermore, by accommodating the spherical body 52 in the accommodation space 51c of the fitting shaft 51, it is possible to prevent the periphery of the second circular hole 21d from coming into contact with the spherical body 52 during rotation of the output shaft 11a, thereby reducing torque loss.

[0056] Furthermore, the fitting shaft 51 has a step portion (deformation promoting portion) 51e that promotes radially outward deformation of the portion pressed against the outer circumferential surface of the sphere 52 when the sphere 52 is pressed into the accommodation space 51c. This makes it easier for the pressed portion of the fitting shaft 51 to deform radially outward, so that the sphere 52 can be easily accommodated in the accommodation space 51c of the fitting shaft 51.

[0057] [Third embodiment] 11 is a cross-sectional view showing a main part of an electric actuator 10 according to a third embodiment of the present disclosure. In this embodiment, the configurations of the output shaft 11a of the motor 11 and the sun gear 21 differ from those of the first embodiment. The sun gear 21 in this embodiment is formed in a cylindrical shape. The output shaft 11a of the motor 11 is fitted and fixed to the inner periphery of the sun gear 21. In this way, the sun gear 21 is connected to the output shaft 11a.

[0058] An end face 11c on the other axial side of the output shaft 11a protrudes further toward the other axial side than the sun gear 21. A second circular hole 11d is formed in the center of the end face 11c of the output shaft 11a. The second circular hole 11d is formed concentrically with the output shaft 11a. Therefore, when the sun gear 21 is connected to the output shaft 11a, the second circular hole 11d is arranged concentrically with the output shaft 11a. The shape of the second circular hole 11d is similar to the shape of the second circular hole 21d in the first embodiment, and therefore description thereof will be omitted.

[0059] The second circular hole 11d is a center hole formed in the end face 11c of the output shaft 11a as a machining reference when the outer peripheral surface of the output shaft 11a is turned. Since other configurations of this embodiment are similar to those of the first embodiment, the same reference numerals are used and their description will be omitted. Note that the fitting shaft 51 in this embodiment may be formed with the stepped portion 51e of the second embodiment as a deformation promoting portion instead of the annular groove 51d.

[0060] According to the electric actuator 10 of the third embodiment, the outer peripheral surfaces of the screw shaft 32 and the mating shaft 51 of the ball screw mechanism 13 are fitted onto the inner peripheral surface 42b of the inner ring 42 of the rolling bearing 14, thereby arranging the first circular hole 51b of the mating shaft 51 concentrically with the screw shaft 32. Furthermore, the output shaft 11a of the motor 11 is formed with a second circular hole 11d concentric with the output shaft 11a. The peripheries of the first circular hole 51b and the second circular hole 11d abut against the outer peripheral surfaces of the spheres 52, respectively, thereby arranging the screw shaft 32 of the ball screw mechanism 13 and the output shaft 11a of the motor 11 concentrically. This allows the axis of the screw shaft 32 to easily align with the axis C of the output shaft 11a. As a result, the positional accuracy requirements for the planetary gears 23 and the support shaft 24 of the planetary gear mechanism 12 can be relaxed, thereby reducing the manufacturing cost of the electric actuator 10.

[0061] Furthermore, with the sphere 52 abutting against the peripheries of the first circular hole 51b and the second circular hole 11d, the bolt 17 is tightened and the output shaft 11a pushes the sphere 52 toward the other axial direction, thereby accommodating the sphere 52 in the accommodation space 51c of the fitting shaft 51. This allows the assembled electric actuator 10 to be configured compactly in the axial direction. Furthermore, since the periphery of the second circular hole 11d can be prevented from abutting against the sphere 52 while the output shaft 11a is rotating, torque loss can be reduced.

[0062] Furthermore, the fitting shaft 51 has an annular groove (deformation promoting portion) 51d that promotes radially outward deformation of the portion pressed against the outer circumferential surface of the sphere 52 when the sphere 52 is pressed into the accommodation space 51c. This makes it easier for the pressed portion of the fitting shaft 51 to deform radially outward, making it possible to easily accommodate the sphere 52 in the accommodation space 51c of the fitting shaft 51.

[0063] [others] Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims. For example, although the electric actuator 10 of the above embodiment is used in a disc brake device of a vehicle, it may also be used in other devices.

[0064] In the above embodiment, the second circular hole 21d (11d) is brought into contact with the sphere 52 while the first circular hole 51b is in contact with the sphere 52. However, the first circular hole 51b may be brought into contact with the sphere 52 while the second circular hole 21d (11d) is in contact with the sphere 52. In this case, the sphere 52 may be placed in contact with the second circular hole 21d (11d) while the other axial side of the second housing 152 is facing upward.

[0065] The accommodation space 51c is open at the end face on the other axial side of the fitting shaft 51, but it does not have to be open at that end face. The deformation promoting portion of the fitting shaft 51 may have a shape other than the annular groove 51d of the first embodiment and the stepped portion 51e of the second embodiment. In addition, the fitting shaft 51 does not have to have a deformation promoting portion formed thereon.

[0066] The electric actuator 10 in the above embodiment is completed in a state where the sphere 52 is accommodated in the accommodation space 51c of the fitting shaft 51 (see FIG. 3), but it may also be completed in a state where the sphere 52 abuts against the first circular hole 51b and the second circular hole 21d (11d) as shown in FIG. 8. Hereinafter, this completed product will be referred to as the completed product of FIG. 8.

[0067] In the finished product of FIG. 8, the bolts 17 that secure the second housing 152 to the first housing 151 should have an axial length that allows them to be completely tightened into the threaded holes 15d in the state shown in FIG. 8. Furthermore, once the bolts 17 have been completely tightened, the axial position of the sun gear 21 should be aligned with the axial positions of the planetary gears 23, as shown in FIG. 3. During use of the finished product of FIG. 8, the output shaft 11a rotates with the periphery of the second circular hole 21d (11d) constantly abutting against the sphere 52, resulting in significant torque loss. Therefore, the finished product of FIG. 8 can be used when significant torque loss does not cause any problems. [Explanation of symbols]

[0068] 10 Electric Actuators 11 Motor 11a Output shaft 11c End face 11d Second circular hole (center hole) 12 Planetary gear mechanism 13 Ball screw mechanism 14 Rolling bearings 21 Sun gear 21c end face 21d Second circular hole 32 Screw shaft 42 Inner circle 42a orbit 42c Inner surface 43 Rolling elements 51 Mating shaft 51a End face 51b 1st circular hole 51c Containment Space 51d Annular groove (deformation promotion part) 51e Step section (deformation promotion section) 52 sphere

Claims

1. a rolling bearing having an inner ring having a raceway formed on its outer peripheral surface and rolling elements that roll on the raceway; a motor having an output shaft disposed on one axial side of the inner ring; a ball screw mechanism including a screw shaft arranged on the other axial side of the inner ring, wherein an outer peripheral surface of the screw shaft is fitted onto the other axial side of an inner peripheral surface of the inner ring; a planetary gear mechanism having a sun gear connected to the output shaft, which changes the speed of the rotational power output from the output shaft and transmits it to the inner ring; a fitting shaft having an outer peripheral surface fitted to the one axial side of the inner peripheral surface of the inner ring and having a first circular hole formed in an end surface on the one axial side; a sphere having an outer diameter larger than an inner diameter of the first circular hole, the first circular hole of the fitting shaft is formed so as to be concentric with the screw shaft in a state in which the outer peripheral surfaces of the screw shaft and the fitting shaft are fitted onto the inner peripheral surface of the inner ring, a second circular hole, which is arranged concentrically with the output shaft and has an inner diameter smaller than the outer diameter of the sphere, formed on the other axial end surface of the output shaft or the sun gear when the sun gear is connected to the output shaft; An electric actuator in which a portion of the outer surface of the sphere abuts against the periphery of one of the first circular hole arranged concentrically with the screw shaft and the second circular hole arranged concentrically with the output shaft, and the periphery of the other circular hole abuts against another portion of the outer surface of the sphere.

2. 2. The electric actuator according to claim 1, wherein an accommodation space is formed inside the fitting shaft, the accommodation space being connected to the first circular hole and into which the sphere abutting against each peripheral edge of the first circular hole and the second circular hole is pushed toward the other axial direction and accommodated.

3. 3. The electric actuator according to claim 2, wherein the fitting shaft has a deformation promoting portion that promotes radially outward deformation of a portion that is pressed against an outer peripheral surface of the sphere when the sphere is pushed into the accommodating space.

4. 4. The electric actuator according to claim 1, wherein the second circular hole is a center hole formed in the end face of the output shaft on the other axial side as a machining reference for the output shaft.

5. 2. A method for assembling the electric actuator according to claim 1, comprising the steps of: a step of fitting an outer peripheral surface of the screw shaft to the other axial side of the inner peripheral surface of the inner ring, and fitting an outer peripheral surface of the fitting shaft to the one axial side of the inner peripheral surface of the inner ring, so as to dispose the first circular hole concentrically with the screw shaft; connecting the sun gear to the output shaft and arranging the second circular hole concentrically with the output shaft; a step of abutting a portion of the outer surface of the sphere against the periphery of one of the first circular hole arranged concentrically with the screw shaft and the second circular hole arranged concentrically with the output shaft, and abutting the periphery of the other circular hole against another portion of the outer surface of the sphere.

6. 3. A method for assembling the electric actuator according to claim 2, comprising the steps of: a step of fitting an outer peripheral surface of the screw shaft to the other axial side of the inner peripheral surface of the inner ring, and fitting an outer peripheral surface of the fitting shaft to the one axial side of the inner peripheral surface of the inner ring, so as to dispose the first circular hole concentrically with the screw shaft; connecting the sun gear to the output shaft and arranging the second circular hole concentrically with the output shaft; a step of abutting a portion of an outer peripheral surface of the sphere against a peripheral edge of one of the first circular hole arranged concentrically with the screw shaft and the second circular hole arranged concentrically with the output shaft, and abutting a peripheral edge of the other circular hole against a second portion of the outer peripheral surface of the sphere; a step of pushing the spheres abutting against the peripheries of the first circular hole and the second circular hole toward the other axial direction to accommodate them in the accommodation space of the mating shaft.

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