Electric actuator

Abstract

To provide an electric actuator that can inhibit a reduction in service life of a rolling bearing and an increase in weight of the rolling bearing, which are caused by press-fitting of a part of a carrier of a planetary gear mechanism into an inner ring.SOLUTION: A planetary gear mechanism of an electric actuator comprises: a sun gear connected to an output shaft of a motor; a ring gear arranged concentrically radially outside the sun gear; a plurality of planetary gears that are arranged radially between the sun gear and the ring gear and mesh with the sun gear and the ring gear; and a carrier fixed to the inner ring of a rolling bearing. The carrier has: a plurality of support shafts that rotatably support respective planetary gears; an annular carrier body with the plurality of support shafts fixed to its side on one axial side; and a cylindrical portion fixed to the side on the other axial side of the carrier body. An annular groove into which the cylindrical portion is inserted is formed in the side on one axial side of the inner ring, the inner peripheral surface of the cylindrical portion is pressed into the inner peripheral surface of the annular groove, and the outer diameter of the annular groove is larger than the outer diameter of the cylindrical portion.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to 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 planetary gears that mesh with the sun gear and the ring gear, and a carrier with multiple support shafts that rotatably support each planetary 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] In the electric actuator, the support shaft of the carrier is press-fitted axially into the inner ring of the rolling bearing and fixed thereto. Therefore, press-fitting the support shaft into the inner ring may deform the raceway along which the rolling elements roll on the outer circumferential surface of the inner ring, potentially shortening the life of the rolling bearing. Furthermore, since it is necessary to secure space in the inner ring for the support shaft to be press-fitted, the radial thickness of the inner ring increases, increasing the weight of the rolling bearing. The present disclosure aims to provide an electric actuator that can suppress a reduction in the lifespan of a rolling bearing and an increase in the weight of the rolling bearing caused by a portion of the carrier of a planetary gear mechanism being pressed into an inner ring. [Means for solving the problem]

[0005] The electric actuator of the present disclosure includes a ball screw mechanism having a screw shaft, an inner ring having an inner peripheral surface to which the screw shaft is fixed and an outer peripheral surface to which a raceway is formed, and a rolling bearing having rolling elements that roll on the raceway, a motor having an output shaft, and a planetary gear mechanism that changes the speed of the rotational power output from the output shaft and transmits it to the inner ring, and the planetary gear mechanism includes a sun gear connected to the output shaft, a ring gear that is arranged concentrically on the radial outside of the sun gear, and a planetary gear that is arranged radially between the sun gear and the ring gear and that rotates the sun gear and the front The gearbox comprises a plurality of planetary gears that mesh with the ring gear and a carrier fixed to the inner ring, the carrier having a plurality of support shafts that rotatably support each of the planetary gears, a ring-shaped carrier body having the plurality of support shafts fixed to a side surface on one axial side, and a cylindrical portion fixed to a side surface on the other axial side of the carrier body, and an annular groove into which the cylindrical portion is inserted is formed on the side surface on one axial side of the inner ring, the inner surface of the cylindrical portion is pressed into the inner surface of the annular groove, and the outer diameter of the annular groove is larger than the outer diameter of the cylindrical portion. [Effects of the Invention]

[0006] According to the present disclosure, it is possible to suppress a reduction in the life of the rolling bearing and an increase in the weight of the rolling bearing, which are caused by a portion of the carrier of the planetary gear mechanism being press-fitted into the inner ring. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view of an electric actuator according to an 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 a carrier of the planetary gear mechanism. [Figure 4] 5A to 5C are explanatory views showing a manufacturing method of the inner ring of the rolling bearing. DETAILED DESCRIPTION OF THE INVENTION

[0008] 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 ball screw mechanism having a screw shaft, an inner ring having an inner peripheral surface to which the screw shaft is fixed and an outer peripheral surface to which a raceway is formed, and a rolling bearing having rolling elements that roll on the raceway, a motor having an output shaft, and a planetary gear mechanism that changes the speed of the rotational power output from the output shaft and transmits it to the inner ring, and the planetary gear mechanism includes a sun gear connected to the output shaft, a ring gear that is arranged concentrically on the radial outside of the sun gear, and a planetary gear that is arranged radially between the sun gear and the ring gear, and The gearbox comprises a plurality of planetary gears that mesh with the ring gear and a carrier fixed to the inner ring, the carrier having a plurality of support shafts that rotatably support each of the planetary gears, a ring-shaped carrier body having the plurality of support shafts fixed to its side surface on one axial side, and a cylindrical portion fixed to the side surface on the other axial side of the carrier body, and an annular groove into which the cylindrical portion is inserted is formed on the side surface on the one axial side of the inner ring, the inner surface of the cylindrical portion is pressed into the inner surface of the annular groove, and the outer diameter of the annular groove is larger than the outer diameter of the cylindrical portion.

[0009] According to the electric actuator, the outer diameter of the annular groove formed in the inner ring of the rolling bearing is larger than the outer diameter of the cylindrical portion of the carrier. Therefore, when the inner peripheral surface of the cylindrical portion is press-fitted into the inner peripheral surface of the annular groove, the outer peripheral surface of the cylindrical portion does not contact the outer peripheral surface of the annular groove. This prevents deformation of the raceway formed on the outer peripheral surface of the inner ring, even when the cylindrical portion is press-fitted into the annular groove. As a result, a reduction in the life of the rolling bearing can be prevented. Furthermore, an annular gap is formed between the outer peripheral surface of the annular groove and the outer peripheral surface of the cylindrical portion, and this gap acts as a thinning of the inner ring. Therefore, even if the radial thickness of the inner ring increases to form the annular groove in the inner ring, an increase in the weight of the rolling bearing can be prevented.

[0010] (2) In the electric actuator described in (1) above, it is preferable that the plurality of support shafts, the carrier body, and the cylindrical portion are integrally formed. In this case, high accuracy of positioning of the carrier body and the plurality of support shafts can be easily ensured simply by press-fitting the cylindrical portion into the annular groove of the inner ring.

[0011] <Details of the embodiment> Preferred embodiments will now be described with reference to the drawings. [Overall configuration] 1 is a cross-sectional view of an electric actuator 10 according to an 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.

[0012] 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. 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. The motor 11 is fixed to a housing 15.

[0013] The housing 15 includes a first member 151 and a second member 152. The first member 151 has a cylindrical outer peripheral wall 15a and a side wall 15b that closes the end of the outer peripheral wall 15a on one axial side (the right side in FIG. 1; the same applies below). The second member 152 has a cylindrical outer peripheral wall 15c and a side wall 15d that closes the end of the outer peripheral wall 15c on the other axial side (the left side in FIG. 1; the same applies below).

[0014] One axial end of outer peripheral wall 15c of second member 152 abuts against the other axial end of outer peripheral wall 15a of first member 151. In this state, first member 151 and second member 152 are connected by fasteners 17 such as bolts. A circumferential groove 15e is formed on the inner periphery of outer peripheral walls 15a, 15c of housing 15, spanning these outer peripheral walls 15a, 15c in the axial direction. The specific structure of housing 15 is not particularly limited, and the design can be modified as appropriate.

[0015] 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, and a carrier 24. The sun gear 21 is disposed concentrically with the output shaft 11a of the motor 11 and is coupled to the output shaft 11a so as to be rotatable integrally therewith. The sun gear 21 has a large number of teeth 21a formed on its outer circumferential surface.

[0016] The ring gear 22 is formed in an annular shape. The ring gear 22 is an internal gear with many teeth 22a formed on its inner peripheral surface. The ring gear 22 is disposed concentrically with the sun gear 21, radially outward of the sun gear 21. The outer peripheral surface of the ring gear 22 is fitted into and fixed in a circumferential groove 15e of the housing 15.

[0017] 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. The carrier 24 is fixed to the inner ring 42 of the rolling bearing 14 and supports each planetary gear 23 rotatably (on its own axis). Details of the carrier 24 will be described later.

[0018] 1 and 2, 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.

[0019] 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 a circumferential groove 15e of the housing 15. The ring gear 22, or the ring gear 22 and the outer ring 41, are fixed to the housing 15 with fasteners 16 such as bolts.

[0020] 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, and a pair of shoulders 42b (see FIG. 3) are formed on both axial sides of the raceway 42a. The inner ring 42 is disposed radially inward of the outer ring 41 and concentric with the outer ring 41.

[0021] 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.

[0022] 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 disposed concentrically with the inner ring 42 of the rolling bearing 14. One axial end of the screw shaft 32 is fitted into and fixed to the inner peripheral surface 42c of the inner ring 42. The screw shaft 32 is rotatably supported relative 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.

[0023] 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.

[0024] 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.

[0025] 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 15d1 formed in the side wall 15d on the other axial side of the housing 15. A seal 18 seals the gap between the outer peripheral surface of the piston 37 and the inner peripheral surface of the opening 15d1.

[0026] [Career] 3 is an enlarged cross-sectional view showing the periphery of the carrier 24 of the planetary gear mechanism 12. The planetary gears 23 and the screw shaft 32 are not shown in FIG. 1 and FIG. 3. As shown in FIGS. 1 and 3, the carrier 24 has a carrier main body 25, a plurality of support shafts 26, and a cylindrical portion 27.

[0027] The carrier body 25 is formed in an annular shape (see FIG. 2). The carrier body 25 is disposed between the inner ring 42 of the rolling bearing 14 and the plurality of planetary gears 23. The carrier body 25 is disposed concentrically with the sun gear 21 and the inner ring 42. In this embodiment, the inner diameter of the carrier body 25 is larger than the inner diameter of the inner ring 42, and the outer diameter of the carrier body 25 is smaller than the outer diameter of the inner ring 42.

[0028] The multiple support shafts 26 are fixed to a side surface 25a on one axial side of the carrier body 25. The multiple support shafts 26 are arranged at equal intervals in the circumferential direction of the carrier body 25. The number of support shafts 26 is the same as the number of planetary gears 23 (three in this embodiment). The support shafts 26 are formed in a cylindrical shape. The support shafts 26 are inserted into the inner peripheries of the planetary gears 23. The planetary gears 23 are supported rotatably (on their axes) relative to the support shafts 26.

[0029] The cylindrical portion 27 is formed in a cylindrical shape. The cylindrical portion 27 is arranged concentrically with the carrier body 25. The cylindrical portion 27 is fixed to a side surface 25b on the other axial side of the carrier body 25. In this embodiment, the carrier body 25, the plurality of support shafts 26, and the cylindrical portion 27 are integrally formed.

[0030] Annular Groove An annular groove 45 is formed in a side surface 42d on one axial side of the inner ring 42. The annular groove 45 is formed in a circular ring shape around the entire circumference of the side surface 42d of the inner ring 42. The annular groove 45 is formed concentrically with the inner ring 42. The annular groove 45 is formed so that the cylindrical portion 27 of the carrier 24 is inserted into it.

[0031] In this embodiment, the axial length of the annular groove 45 is greater than the axial length of the cylindrical portion 27. The inner circumferential surface 27a of the cylindrical portion 27 is press-fitted into the inner circumferential surface 45a of the annular groove 45. This fixes the cylindrical portion 27 of the carrier 24 to the inner ring 42. The outer diameter D1 of the annular groove 45 is greater than the outer diameter D2 of the cylindrical portion 27. An annular gap S is formed between the outer circumferential surface 45b of the annular groove 45 and the outer circumferential surface 27b of the cylindrical portion 27. As described above, when the inner circumferential surface 27a of the cylindrical portion 27 is press-fitted into the inner circumferential surface 45a of the annular groove 45, the outer circumferential surface 27b of the cylindrical portion 27 does not come into contact with the outer circumferential surface 45b of the annular groove 45.

[0032] When the plurality of planetary gears 23 revolve around the axis C in accordance with the rotation of the sun gear 21, the carrier 24 is decelerated and rotates around the axis C. The inner ring 42 rotates around the axis C together with the cylindrical portion 27 of the carrier 24. 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 moves back and forth in the axial direction together with the nut 33.

[0033] [Manufacturing method of inner ring] Figure 4 is an explanatory diagram showing a manufacturing method for the inner ring 42 of the rolling bearing 14. When manufacturing the inner ring 42, first, an inner ring blank 50 is subjected to a carburizing heat treatment, and then the outer peripheral surface of the inner ring blank 50 is subjected to turning and grinding. Note that in Figure 4, the machined parts are indicated by cross-hatching. As a result, a raceway 42a and a shoulder 42b with final dimensions are formed on the outer peripheral surface of the inner ring blank 50, as shown in the upper diagram of Figure 4.

[0034] Next, with the shoulder 42b of the inner ring blank 50 held by a chuck (not shown), as shown in the lower drawing of Figure 4, the inner peripheral surface of the inner ring blank 50 is turned, and then the radial thickness portion of the inner ring blank 50 is turned to form the annular groove 45. At this time, the shoulder 42b in its final dimension serves as the turning reference, so that concentricity between the inner peripheral surface of the inner ring blank 50 and the annular groove 45 is ensured when the turning is completed.

[0035] Next, with the shoulder 42b of the inner ring blank 50 held by the chuck, the inner peripheral surface of the inner ring blank 50 is ground to its final dimensions. In this process, the shoulder 42b in its final dimensions serves as the machining reference, ensuring concentricity between the inner peripheral surface 42c in its final dimensions and the annular groove 45 after the turning process. Therefore, by press-fitting the cylindrical portion 27 of the carrier 24 into the annular groove 45 of the inner ring 42, the positional accuracy of the carrier body 25 and each support shaft 26 is ensured.

[0036] [Effects of the embodiment] According to the electric actuator 10 of this embodiment, the outer diameter D1 of the annular groove 45 formed in the inner ring 42 of the rolling bearing 14 is larger than the outer diameter D2 of the cylindrical portion 27 of the carrier 24. Therefore, when the inner circumferential surface 27a of the cylindrical portion 27 is press-fitted into the inner circumferential surface 45a of the annular groove 45, the outer circumferential surface 27b of the cylindrical portion 27 does not come into contact with the outer circumferential surface 45b of the annular groove 45. Therefore, even when the cylindrical portion 27 is press-fitted into the annular groove 45, deformation of the raceway 42a formed on the outer circumferential surface of the inner ring 42 can be suppressed. As a result, a decrease in the life of the rolling bearing 14 can be suppressed.

[0037] Furthermore, an annular gap S is formed between the outer peripheral surface 45b of the annular groove 45 and the outer peripheral surface 27b of the cylindrical portion 27, and this gap S serves as a thinning area of the inner ring 42. Therefore, even if the radial thickness of the inner ring 42 increases in order to form the annular groove 45 in the inner ring 42, an increase in the weight of the rolling bearing 14 can be suppressed.

[0038] The carrier body 25, the plurality of support shafts 26, and the cylindrical portion 27 of the carrier 24 are integrally formed. As a result, high-precision positional accuracy of the carrier body 25 and the plurality of support shafts 26 can be easily ensured by simply press-fitting the cylindrical portion 27 into the annular groove 45 of the inner ring 42.

[0039] [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, the electric actuator 10 of this embodiment is used in a vehicle disc brake device, but may also be used in other devices. Furthermore, in the carrier 24 of the planetary gear mechanism 12, the carrier body 25 and the multiple support shafts 26 may be formed from different parts, and the carrier body 25 and the cylindrical portion 27 may be formed from different parts. [Explanation of symbols]

[0040] 10 Electric Actuators 11 Motor 11a Output shaft 12 Planetary gear mechanism 13 Ball screw mechanism 14 Rolling bearings 21 Sun gear 22 Ring gear 23 Planetary gear 24 Career 25 Carrier body 25a side 25b side 26 Support shaft 27 Cylindrical part 27a Inner surface 27b Outer surface 32 Screw shaft 42 Inner circle 42a orbit 42c Inner surface 43 Rolling elements 45 Annular groove 45a Inner surface 45b Outer surface D1 Annular groove outer diameter D2 Outer diameter of cylindrical part

Claims

1. a ball screw mechanism having a screw shaft; a rolling bearing including an inner ring having an inner peripheral surface to which the screw shaft is fixed and an outer peripheral surface to which a raceway is formed, and rolling elements that roll on the raceway; a motor having an output shaft; a planetary gear mechanism that changes the speed of the rotational power output from the output shaft and transmits the rotational power to the inner ring, The planetary gear mechanism includes: a sun gear connected to the output shaft; a ring gear arranged concentrically on the radially outer side of the sun gear; a plurality of planetary gears disposed radially between the sun gear and the ring gear and meshing with the sun gear and the ring gear; a carrier fixed to the inner ring, The carrier is a plurality of support shafts that rotatably support the planetary gears; a ring-shaped carrier body having a plurality of the support shafts fixed to a side surface on one axial side; a cylindrical portion fixed to a side surface on the other axial side of the carrier body, an annular groove into which the cylindrical portion is inserted is formed on a side surface of the inner ring on one axial side; an inner circumferential surface of the cylindrical portion is press-fitted into an inner circumferential surface of the annular groove; An electric actuator, wherein the outer diameter of the annular groove is larger than the outer diameter of the cylindrical portion.

2. The electric actuator according to claim 1 , wherein the plurality of support shafts, the carrier body, and the cylindrical portion are integrally formed.

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