Electric actuator

Abstract

To provide an electric actuator which is easy to assemble.SOLUTION: An electric actuator includes: a motor having an output shaft; a planetary gear mechanism which changes a speed of rotational power output from the output shaft; a ball screw mechanism to which the rotational power with the speed changed by the planetary gear mechanism is transmitted; and a housing that accommodates at least the planetary gear mechanism. The planetary gear mechanism includes: a sun gear connected to the output shaft; a ring gear attached to the housing and arranged concentrically on a radially outer side of the sun gear; a plurality of planetary gears arranged between the sun gear and the ring gear in a radial direction and that engage with the sun gear and the ring gear; a plurality of support shafts connected to each of the planetary gears on one axial end side; a carrier to which the other axial end side of the plurality of support shafts is connected; and a rolling bearing having an outer ring formed integrally with the ring gear and attached to the housing, and supporting the carrier in a rotational manner.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention 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 has a motor, a planetary gear mechanism that reduces the rotational power of the motor, and a ball screw mechanism that operates by the reduced rotational power. The planetary gear mechanism includes a sun gear that is driven to rotate by the motor, a ring gear that is arranged concentrically with the sun gear and fixed to a housing of the electric actuator, a plurality of planetary gears that mesh with the sun gear and the ring gear, a plurality of support shafts to which the planetary gears are rotatably attached, and a rolling bearing that includes an inner ring to which the plurality of support shafts are fixed and is attached to the housing. The ball screw mechanism includes a screw shaft that is fixed to the inner ring of the rolling bearing, and a nut that is screwed to the screw shaft via a plurality of balls and moves in the axial direction by the rotation of the screw shaft. The brake caliper presses the brake pad against the brake disc by a piston that moves in conjunction with the nut, thereby performing a braking operation. [Prior art documents] [Patent documents]

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

[0004] In the electric actuator described in Patent Document 1, if the concentricity between the ring gear supported by the housing and the outer ring of the rolling bearing deteriorates, abnormal noise may occur at the gear meshing area and power transmission efficiency may decrease, so high-precision assembly is required. SUMMARY OF THE PRESENT EMBODIMENT In view of the above circumstances, an object of the present invention is to provide an electric actuator that is easy to assemble. [Means for solving the problem]

[0005] The electric actuator of the present invention includes a motor having an output shaft, a planetary gear mechanism that changes the speed of rotational power output from the output shaft, a ball screw mechanism to which the rotational power changed in speed by the planetary gear mechanism is transmitted, and a housing that accommodates at least the planetary gear mechanism, The planetary gear mechanism includes: A sun gear connected to the output shaft; a ring gear attached to the housing and 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 plurality of support shafts, each of which has an axial end connected to each of the planetary gears; a carrier to which the other axial ends of the plurality of support shafts are connected; a rolling bearing including an outer ring formed integrally with the ring gear and attached to the housing, the rolling bearing supporting the carrier for rotation. Effect of the Invention

[0006] According to the present invention, the assembly of the electric actuator can be simplified. [Brief description of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view of an electric actuator according to a first embodiment of the present invention. [Diagram 2] 2 is a cross-sectional view taken along line AA in FIG. 1. [Diagram 3] FIG. 4 is a cross-sectional view of an electric actuator according to a second embodiment of the present invention. [Figure 4] FIG. 11 is a cross-sectional view of an electric actuator according to a third embodiment of the present invention. [Diagram 5]FIG. 2 is an enlarged cross-sectional view showing the periphery of a planetary gear. [Figure 6A] FIG. 11 is an enlarged cross-sectional view showing the periphery of a planetary gear according to a modified example. [Figure 6B] FIG. 11 is an enlarged cross-sectional view showing the periphery of a planetary gear according to a modified example. [Figure 6C] FIG. 11 is an enlarged cross-sectional view showing the periphery of a planetary gear according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] <Overview of the embodiment of the present disclosure> Below, an overview of the embodiments of the present disclosure will be listed and described. (1) An electric actuator according to an embodiment includes a motor having an output shaft, a planetary gear mechanism that changes the speed of rotational power output from the output shaft, a ball screw mechanism to which the rotational power changed in speed by the planetary gear mechanism is transmitted, and a housing that accommodates at least the planetary gear mechanism, The planetary gear mechanism includes: A sun gear connected to the output shaft; a ring gear attached to the housing and 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 plurality of support shafts, each of which has an axial end connected to each of the planetary gears; a carrier to which the other axial ends of the plurality of support shafts are connected; a rolling bearing including an outer ring formed integrally with the ring gear and attached to the housing, the rolling bearing supporting the carrier for rotation.

[0009] According to the above configuration, the ring gear of the planetary gear mechanism and the outer ring of the rolling bearing are formed as a single unit, so that the concentricity of the ring gear and the outer ring is ensured at the component manufacturing stage, making it easy to assemble the electric actuator.

[0010] (2) In the electric actuator of (1) above, a flange connected to the housing is formed integrally with the ring gear and the outer ring. With this configuration, the planetary gear mechanism can be easily attached to the housing, making it even easier to assemble the electric actuator.

[0011] (3) In the electric actuator according to the above (1) or (2), the rolling bearing has an inner ring having a raceway formed on its outer circumferential surface and integrally formed with the carrier, and rolling elements that roll on the raceway, The ball screw mechanism includes a screw shaft formed integrally with the carrier, The support shaft is rotatably connected to the carrier by a clearance fit.

[0012] According to this configuration, the inner ring of the planetary gear mechanism, the carrier, and the screw shaft of the ball screw mechanism are integrally formed, so that the concentricity of the inner ring, the carrier, and the screw shaft is ensured at the manufacturing stage of the parts, and the assembly of the electric actuator can be made easier. Since the inner ring, the carrier, and the screw shaft are integrally formed, the radial dimensions can be made smaller than when they are provided separately, and the electric actuator can be made smaller in the radial direction. When the radial dimensions of the inner ring, the carrier, and the screw shaft are reduced, the radial distance between the raceway of the inner ring and the support shaft is naturally reduced. If the support shaft were press-fitted and fixed to the carrier, the raceway of the inner ring would be easily deformed by the press-fit of the support shaft, and the rotational accuracy of the inner ring may deteriorate. However, in the embodiment, the support shaft is rotatably connected to the carrier by a clearance fit, so that the deformation of the raceway is suppressed and the rotational accuracy can be ensured. Furthermore, since the outer ring and the ring gear are formed integrally and the concentricity of the two is ensured, the fitting precision requirements between the support shaft and the inner ring can be relaxed accordingly, making production easier.

[0013] <Details of the embodiment of the present disclosure> Hereinafter, details of the embodiments of the present disclosure will be described with reference to the drawings. [First embodiment] FIG. 1 is a cross-sectional view of an electric actuator according to a first embodiment of the present invention. 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 disc brake device of a vehicle.

[0014] The electric actuator 10 includes a motor 11, a planetary gear mechanism 12, a ball screw mechanism 13, and a housing 14. 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 for the motor 11. The motor 11 is fixed to a housing 14. The housing 14 has a cylindrical outer peripheral wall 14a and a pair of side walls 14b, 14c that close both axial ends of the outer peripheral wall 14a. In this embodiment, the main body 11b of the motor 11 is fixed to one of the side walls 14b.

[0015] FIG. 2 is a cross-sectional view taken along line AA in FIG. As shown in FIGS. 1 and 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, a carrier 35, and a rolling bearing 25. The sun gear 21 is disposed concentrically with the output shaft 11a of the motor 11 and is connected to the output shaft 11a so as to be rotatable together with the output shaft 11a. 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, and a large number of teeth 22a are formed on the inner peripheral surface. The outer peripheral surface of the ring gear 22 is fixed to the inside of the outer peripheral wall 14a of the housing 14. The ring gear 22 is disposed concentrically with the sun gear 21.

[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. Each planetary gear 23 has a large number of teeth 23a formed on its outer circumferential surface. Each planetary gear 23 meshes with the sun gear 21 and the ring gear 22. The number of planetary gears 23 is not limited and can be changed as appropriate.

[0018] The support shaft 24 is formed in a cylindrical shape. One axial end side (the right side in FIG. 1) of the support shaft 24 is relatively rotatably connected to the planetary gear 23. The other axial end side (the left side in FIG. 1) of the support shaft 24 is fixed to the carrier 35.

[0019] The carrier 35 is formed in a disk shape. The carrier 35 is disposed concentrically with the sun gear 21 and the ring gear 22. The carrier 35 is rotatably supported by the housing 14 via a rolling bearing 25. The carrier 35 rotates about the axis C as the plurality of planetary gears 23 revolve about the axis C in conjunction with the rotation of the sun gear 21.

[0020] The rolling bearing 25 includes an outer ring 26, an inner ring 28, and a plurality of rolling elements 27. The rolling bearing 25 in this embodiment is a deep groove ball bearing. The rolling bearing 25 is disposed concentrically with the sun gear 21, the ring gear 22, and the carrier 35 of the planetary gear mechanism 12. The rolling bearing 25 may be another type of rolling bearing, such as a cylindrical roller bearing.

[0021] The outer ring 26 is formed in an annular shape. A raceway 26a is formed on the inner peripheral surface of the outer ring 26. The outer peripheral surface of the outer ring 26 is fixed to the inside of the outer peripheral wall 14a of the housing 14. The outer ring 26 and the ring gear 22 are arranged side by side in the axial direction and are fitted into a circumferential groove 14a3 formed on the inner peripheral surface of the outer peripheral wall 14a. The outer ring 26 and the ring gear 22 of this embodiment are formed integrally. That is, the planetary gear mechanism 12 of this embodiment includes an annular member 30 having a portion that functions as the ring gear 22 and a portion that functions as the outer ring 26 of the rolling bearing 25. The annular member 30 is fixed to the housing 14 by a fastener 16 such as a bolt.

[0022] The housing 14 of this embodiment includes a first member 14A including one side wall 14b and an axial part 14a1 of the outer peripheral wall 14a, and a second member 14B including the other side wall 14c and another axial part 14a2 of the outer peripheral wall 14a, and is configured by connecting the first member 14A and the second member 14B with a fastener 17 such as a bolt. The first member 14A and the second member 14B are separated in the middle of the axial direction of the circumferential groove 14a3. Therefore, the circumferential groove 14a3 can be opened in a state where the first member 14A and the second member 14B are not connected. The specific structure of the housing 14 is not particularly limited, and the design can be changed as appropriate.

[0023] The inner ring 28 in this embodiment is formed in an annular shape. A raceway 28a is formed on the outer peripheral surface of the inner ring 28. The inner ring 28 is disposed radially inside the outer ring 26. The inner ring 28 is disposed concentrically with the outer ring 26. The inner peripheral surface of the inner ring 28 is fixed to the outer peripheral surface of the carrier 35.

[0024] The multiple rolling elements 27 are disposed radially between the outer ring 26 and the inner ring 28. The rolling elements 27 in this embodiment are balls. The rolling elements 27 roll on the raceway 26a of the outer ring 26 and the raceway 28a of the inner ring 28. Although not shown, the rolling bearing 25 includes a cage that maintains the circumferential spacing of the multiple rolling elements 27.

[0025] 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 a carrier 35 of the planetary gear mechanism 12. The screw shaft 32 is fixed to the carrier 35.

[0026] The nut 33 is formed in a cylindrical shape. The nut 33 is disposed radially outward of the screw shaft 32. The nut 33 is disposed concentrically with the screw shaft 32. An inner peripheral raceway surface 33a is formed on the inner peripheral surface of the nut 33. The inner peripheral raceway surface 33a is disposed facing the radially outward side of the outer peripheral raceway surface 32a.

[0027] A plurality of balls 34 are disposed between the outer peripheral raceway surface 32a and the inner peripheral raceway surface 33a, and roll on the outer peripheral raceway surface 32a and the inner peripheral 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. A piston (pressing member) 37 is fixed to the nut 33. This piston 37 moves in the axial direction together with the nut 33, and presses the brake pad (not shown) against the brake disc. The piston 37 is inserted into an opening 14c1 formed in the side wall 14c of the housing 14. A seal 18 seals between the outer peripheral surface of the piston 37 and the inner peripheral surface of the opening 14c1.

[0028] In the electric actuator 10 of the above embodiment, the rotational power output from the motor 11 is decelerated by the planetary gear mechanism 12 and transmitted to the ball screw mechanism 13, causing the piston 37 to reciprocate in the axial direction. The ring gear 22 and the outer ring 26 of the rolling bearing 25 in the planetary gear mechanism 12 of this embodiment are integrally formed. Therefore, the concentricity between the ring gear 22 and the outer ring 26 can be ensured at the manufacturing stage. Therefore, the assembly precision required when assembling the electric actuator 10 can be relaxed, making the assembly work easier.

[0029] <Second embodiment> FIG. 3 is a cross-sectional view of an electric actuator according to a second embodiment of the present invention. In the electric actuator 10 of this embodiment, a flange 22b protruding radially outward is integrally formed on the ring gear 22 of the planetary gear mechanism 12. The other configurations are the same as those of the first embodiment, so detailed description will be omitted.

[0030] The flange 22b is used to fix the ring gear 22 and the outer ring 26 to the housing 14. The housing 14 in this embodiment has a first member 14A formed by one side wall 14b, and a second member 14B formed by the outer circumferential wall 14a and the other side wall 14c. The flange 22b is sandwiched between the first member 14A and the second member 14B and fixed to the first and second members 14A and 14B with fasteners 19 such as bolts.

[0031] In this embodiment, since the flange 22b is formed integrally with the ring gear 22, the planetary gear mechanism 12 can be easily attached to the housing 14, and the assembly of the electric actuator 10 can be made even easier.

[0032] <Third embodiment> Fig. 4 is a cross-sectional view of an electric actuator according to a third embodiment of the present invention, Fig. 5 is an enlarged cross-sectional view showing the periphery of a planetary gear. In the electric actuator 10 of this embodiment, the inner ring 28 of the rolling bearing 25, the carrier 35, and the screw shaft 32 are integrally formed. That is, the planetary gear mechanism 12 of this embodiment includes a rotating member 31 having a portion that functions as the inner ring 28, a portion that functions as the carrier 35, and a portion that functions as the screw shaft 32.

[0033] In this embodiment, the support shaft 24 is fixed to the planetary gear 23 so as to be rotatable together with the planetary gear 23. The support shaft 24 is connected to the carrier 35 so as to be rotatable relative to the carrier 35. As shown in FIG. 5, a support hole 36 extending in the axial direction is formed in one axial end face of the carrier 35. The support shaft 24 is fitted into the support hole 36. The inner diameter of the support hole 36 is slightly larger than the outer diameter of the support shaft 24. Therefore, the support shaft 24 is fitted into the support hole 36 by a clearance fit. Therefore, the support shaft 24 is connected to the carrier 35 so as to be rotatable. A lubricant 40 such as grease is filled in the gap generated between the support shaft 24 and the support hole 36. This lubricant 40 enables the support shaft 24 to rotate smoothly and suppresses wear of the support shaft 24 and the carrier 35.

[0034] One axial end face 24a of the support shaft 24 and one axial end face 23b of the planetary gear 23 can abut against one side wall 14b of the housing 14. The support shaft 24 is loosely fitted into the support hole 36 and can move in the axial direction, but the one end face 24a of the support shaft 24 and one end face 23b of the planetary gear 23 abut against the side wall 14c, thereby restricting the axial movement of the support shaft 24 and preventing the support shaft 24 from coming off the support hole 36.

[0035] In the electric actuator 10 of this embodiment, the inner ring 28 of the rolling bearing 25, the carrier 35, and the screw shaft 32 of the ball screw mechanism 13 are integrally formed. Therefore, the concentricity of the inner ring 28, the carrier 35, and the screw shaft 32 is ensured at the component manufacturing stage. Therefore, when assembling the electric actuator 10, it is no longer necessary to connect and fix the inner ring 28, the carrier 35, and the screw shaft 32 while aligning their axial centers C, and the precision required for assembling the electric actuator 10 is relaxed, making the assembly work easier.

[0036] In the electric actuator 10 of this embodiment, the inner ring 28, the carrier 35, and the screw shaft 32 are integrally formed, so that the radial dimension can be made smaller than when the inner ring 28, the carrier 35, and the screw shaft 32 are provided separately. Therefore, it is possible to make the electric actuator 10 smaller in the radial direction. On the other hand, when the radial dimensions of the inner ring 28, the carrier 35, and the screw shaft 32 are reduced, the radial distance between the raceway 28a of the inner ring 28 and the support shaft 24 is reduced. In this case, if the support shaft 24 is press-fitted and fixed to the carrier 35, the raceway 28a of the inner ring 28 is easily deformed by the press-fitting of the support shaft 24, and the rotation accuracy of the inner ring 28 may deteriorate. In this embodiment, the support shaft 24 is rotatably connected to the carrier 35 by a clearance fit. Therefore, the deformation of the raceway 28a is suppressed, and the rotation accuracy of the inner ring 28 can be ensured.

[0037] In this embodiment, the outer ring 26 and the ring gear 22 are formed integrally and their concentricity is ensured. This makes it possible to relax the precision of the fit between the support shaft 24 of the planetary gear mechanism 12 and the carrier 35, making their manufacture easier.

[0038] Other configurations in the third embodiment are similar to those in the first embodiment, so detailed description will be omitted.

[0039] <Modification> 6A to 6C are enlarged cross-sectional views showing the periphery of a planetary gear according to a modified example. 6A, a groove 24b is formed on the outer circumferential surface of the support shaft 24 inserted into the support hole 36. The groove 24b extends in the circumferential direction of the support shaft 24 and is formed on the entire outer circumferential surface of the support shaft 24.

[0040] 6B, a plurality of recesses 24c are formed on the outer circumferential surface of the support shaft 24 inserted into the support hole 36. The recesses 24c are formed randomly and dispersed in the circumferential and axial directions of the support shaft 24.

[0041] 6A and 6B, the lubricant 40 filled in the gap between the outer circumferential surface of the support shaft 24 and the inner circumferential surface of the support hole 36 can be held in the groove 24b or the recess 24c. Therefore, the frictional resistance of the support shaft 24 against the carrier 35 can be reduced for a long period of time.

[0042] In the modification shown in Fig. 6C, a low-friction coating 24d is provided on the outer peripheral surface of the support shaft 24 inserted into the support hole 36. By providing such a low-friction coating 24d, it is possible to reduce the frictional resistance of the support shaft 24 with respect to the carrier 35. As the low-friction coating, a known composition such as DLC (diamond-like carbon) that can exhibit high lubricity and abrasion resistance can be used. As a method for applying the low-friction coating, known methods such as deposition such as CVD and PVD, sputtering, plating, and thermal spraying can be used.

[0043] Although the embodiments have been described above, it will be understood that various changes in form and details are possible without departing from the spirit and scope of the claims. 6A to 6C, the groove 24b, the recess 24c, and the low-friction coating 24d formed in the support shaft 24 may be provided on the inner circumferential surface of the support hole 36 of the carrier 35. The groove 24b may extend in the axial direction instead of the circumferential direction.

[0044] 5, one end surface 24a, 23b of one of the support shaft 24 and the planetary gear 23 may abut against the side wall 14b of the housing 14. At least one end surface 24a, 23b of the support shaft 24 and the planetary gear 23 may abut against the main body 11b of the motor 11 instead of the side wall 14b of the housing 14.

[0045] The housing 14 is required to accommodate at least the planetary gear mechanism 12. The housing 14 may accommodate the motor 11 and the ball screw mechanism 13 in their entirety. [Explanation of symbols]

[0046] 10: Electric actuator 11: Motor 12: Planetary gear mechanism 13: Ball screw mechanism 14: Housing 21: Sun gear 22: Ring gear 22b: Flange 23: Planetary gear 24: Support shaft 25: Rolling bearings 26: Outer ring 27: Rolling element 28: Insider 28a:orbital 32: Screw shaft 34: Ball 35: Career

Claims

1. a motor having an output shaft, a planetary gear mechanism that changes the speed of the rotational power output from the output shaft, a ball screw mechanism to which the rotational power changed in speed by the planetary gear mechanism is transmitted, and a housing that accommodates at least the planetary gear mechanism; The planetary gear mechanism includes: A sun gear connected to the output shaft; a ring gear attached to the housing and 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 plurality of support shafts, each of which has an axial end connected to each of the planetary gears; a carrier to which the other axial ends of the plurality of support shafts are connected; a rolling bearing including an outer ring formed integrally with the ring gear and attached to the housing, the rolling bearing rotatably supporting the carrier.

2. The electric actuator according to claim 1 , wherein a flange connected to the housing is integrally formed with the ring gear and the outer ring.

3. The rolling bearing has an inner ring having a raceway formed on its outer circumferential surface and integrally formed with the carrier, and rolling elements that roll on the raceway, The ball screw mechanism includes a screw shaft formed integrally with the carrier, The electric actuator according to claim 1 or 2, wherein the support shaft is rotatably connected to the carrier by a clearance fit.

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