electric actuator

Abstract

An electric actuator includes an electric motor capable of forward and reverse rotation, and a motion conversion mechanism that converts rotation of the electric motor into reciprocating linear motion of a threaded shaft. The motion conversion mechanism includes a nut that is rotated by the electric motor, and the threaded shaft that is screwed into the nut in a manner that allows the threaded shaft to advance and retreat. A lubricant retaining portion that is capable of retaining a lubricant is formed on an inner periphery of an axial end of the nut, and has an outer diameter that is larger than a diameter of a threaded hole of the nut. A cover member is provided that covers an axial opening end of the lubricant retaining portion. Wear of a screwing portion of the nut and the threaded shaft is inhibited by sufficiently lubricating the screwing portion, thereby improving durability of the nut and the threaded shaft.

Description

TECHNICAL FIELD

[0001] The present application relates to an electric actuator provided with a motion conversion mechanism that converts rotation of an electric motor capable of forward and reverse rotation into reciprocating linear motion of a threaded shaft. BACKGROUND

[0002] The electric actuator is provided with an electric motor capable of forward and reverse rotation and a motion conversion mechanism that converts rotation of the electric motor into reciprocating linear motion of a threaded shaft, and if the nut of the motion conversion mechanism is caused to rotate forward and reverse by the electric motor, the threaded shaft that is screwed into the nut in a manner that is capable of advancing and retreating performs reciprocating linear motion. Such an electric actuator is used in, for example, an electric parking brake device of a vehicle (see, for example, Patent Literature 1).

[0003] In an electric parking brake device provided with this electric actuator, if a parking brake lever inside a drum brake is moved from a release position to a working position by the reciprocating linear motion of the threaded shaft of the electric actuator, the brake shoe is pressed against the inner peripheral surface of the brake drum that rotates together with the wheel, and by the frictional resistance that is generated between the two, the rotation of the wheel is braked and the vehicle becomes in a parked brake state. Also, if the electric motor of the electric actuator is caused to reverse from the parked brake state, the parking lever is moved from the working position to the release position and the brake shoe is separated from the inner peripheral surface of the brake drum, and the parked brake state of the vehicle is released.

[0004] In the motion conversion mechanism of the electric actuator, since the threaded shaft that is screwed into the rotating nut performs reciprocating linear motion with respect to the nut, there is a problem in that sliding friction occurs at the screwing portion of the threaded shaft and the nut, and wear occurs at the screwing portion of the two.

[0005] Therefore, in Patent Literature 2, a structure is proposed in which an oil groove is formed on the inner thread portion of the nut that is screwed with the outer thread portion of the threaded shaft, and lubricating oil is stored in the oil groove. According to this structure, the lubricating oil that is stored in the oil groove is drawn out from the oil groove by the relative rotation of the threaded shaft and the nut, and the lubricating oil is supplied to the entire screwing portion of the outer thread portion of the threaded shaft and the inner thread portion of the nut and is used for lubrication of the screwing portion.

[0006] In addition, in Patent Literature 3, a structure is proposed in which a solid lubricant is embedded in a screw sleeve (nut) that is screwed with a screw rod (threaded shaft), and a solid lubricant baffle is provided at the upper and lower ends of the screw sleeve. According to this structure, the solid lubricant that is embedded in the screw sleeve does not come out of the screw sleeve due to the solid lubricant baffle, and thus lubrication of the screwing portion of the screw rod and the screw sleeve is stably performed by the solid lubricant.

[0007] PRIOR ART DOCUMENTS

[0008] PATENT LITERATURE

[0009] Patent Literature 1: Japanese Patent Application Laid-Open No. 2019-006223

[0010] Patent Literature 2: Japanese Patent Application Laid-Open No. 2001-132813

[0011] Patent Literature 3: Japanese Patent Application Laid-Open No. Hei 53-014413 SUMMARY

[0012] PROBLEMS TO BE SOLVED BY THE INVENTION

[0013] In the electric actuator proposed in Patent Literature 1, if a lubricant such as grease is applied to the threaded shaft in order to lubricate the screwing portion of the nut and the threaded shaft, the lubricant enters the inside of the nut by rotation of the nut and is used for lubrication of the screwing portion of the nut and the threaded shaft, but the following problems arise.

[0014] That is, as shown in (a) and (b), if the threaded shaft 103 is subjected to reciprocating linear motion in the arrow direction, the lubricant applied to the threaded shaft 103 is swept by the nut 108 and remains at both axial end portions (near the movement limit) of the threaded shaft 103. Also, if the lubricant remains on the end surface of the nut 108, the lubricant is scattered to the surroundings due to centrifugal force based on rotation of the nut 108. Thus, the problem arises that the central portion in the axial direction (portion A shown in the figure) of the threaded shaft 103 is insufficiently lubricated and oil film shortage occurs, promoting wear in this portion. Figure 8

[0015] Also, in the lubrication structure proposed in Patent Literature 2, since the oil groove is formed on the upper end of the internal thread portion of the nut, there is a problem that the range of application is limited to the structure in which the nut and the threaded shaft are arranged in the longitudinal direction.

[0016] Further, in the lubrication structure proposed in Patent Literature 3, since the lubricant is limited to a solid lubricant, there is a problem that the range of application is narrow.

[0017] The present application has been made in view of the above problems, and has an object to provide an electric actuator capable of suppressing wear of the screwing portion of the nut and the threaded shaft by sufficiently lubricating the screwing portion and thereby improving the durability of the nut and the threaded shaft.

[0018] MEANS FOR SOLVING THE PROBLEMS

[0019] ​To achieve the above object, a first feature of the present application is that an electric actuator is provided with an electric motor capable of forward and reverse rotation, and a motion conversion mechanism that converts rotation of the electric motor into reciprocating linear motion of a threaded shaft, the motion conversion mechanism being provided with a nut that is rotated by the electric motor, and the threaded shaft that is screwed into the nut in a manner that allows it to advance and retreat, in the electric actuator, a lubricant holding portion that is capable of holding a lubricant having a larger outer diameter than the diameter of the threaded hole of the nut is formed in the inner periphery of the axial end of the nut, and a cover member that covers the axially open end of the lubricant holding portion is provided.

[0020] A second feature of the present application is based on the first feature, and is that the cover member is integrally provided with a cover portion and a cylindrical portion that is coaxial with the nut, and the cover member is mounted to the nut by fitting a convex portion formed in the inner periphery of the cylindrical portion with a concave portion formed in the outer periphery of the nut, or fitting a convex portion formed in the outer periphery of the nut with a concave portion formed in the inner periphery of the cylindrical portion.

[0021] A third feature of the present application is based on the second feature, and is that a cylindrical scraper portion is formed in the inner periphery of the cover portion, and the inner diameter of the scraper portion is set to be slightly larger than the outer diameter of the threaded shaft, thereby forming a slight radial gap between the scraper portion and the threaded shaft.

[0022] A fourth feature of the present application is based on the second or third feature, and is that the outer diameter of the cylindrical portion is equal to or smaller than the outer diameter of the nut.

[0023] A fifth feature of the present application is based on any one of the first to fourth features, and is that the cover member is composed of a rubber material.

[0024] Effects of the Invention

[0025] According to the first feature of the present application, even if the threaded shaft enters the nut due to rotation of the nut, the lubricant applied to the threaded shaft is held in the lubricant holding portion of the nut, so that excess lubricant is not left on the end surface of the nut, and the left lubricant is not scattered around due to centrifugal force based on rotation of the nut. Furthermore, the lubricant held in the lubricant holding portion of the nut is applied to the threaded shaft when the threaded shaft comes out of the nut, but the amount of application of the lubricant is limited by the cover member, so that a necessary and sufficient amount of lubricant is applied over a wide range of the threaded shaft. As a result, local shortage of lubricant (oil film shortage) of the threaded shaft does not occur, lubrication of the screwing portion of the nut and the threaded shaft is sufficiently performed, and wear of the screwing portion is suppressed, so that durability of the nut and the threaded shaft is improved.

[0026] According to the second feature of the present application, the cover member can be simply mounted to the outer periphery of the nut in one-touch by fitting the convex portion and the concave portion.

[0027] According to a third feature of the invention, since the inner diameter of the scraper portion formed on the inner circumference of the cover portion of the cover member is set to be slightly larger than the outer diameter of the threaded shaft, forming a small radial gap between them, the lubricant remaining in the lubricant holding portion of the nut is scraped off by the scraper portion and uniformly applied to the threaded shaft with a predetermined thickness. In this case, since the scraper portion does not contact the threaded shaft, no frictional resistance is generated between them, and the threaded shaft can slide smoothly without resistance. In addition, since the scraper portion is not subjected to external force from the threaded shaft, damage to the scraper portion can be prevented, thereby improving the durability of the cover member.

[0028] According to a fourth feature of the invention, by making the outer diameter of the cylindrical portion of the cover member less than or equal to the outer diameter of the nut, when assembling the cover member and fitting the nut to the radial bearing, the cover member can be assembled in a manner that does not interfere with the radial bearing.

[0029] According to a fifth feature of the invention, since the cover component is made of a soft and elastic rubber material, damage to the cover component can be prevented even if the cover component comes into contact with the threaded shaft, thereby improving its durability. Attached Figure Description

[0030] Figure 1 This is a perspective view of the electric actuator of the present invention.

[0031] Figure 2 This is a plan view of the electric actuator of the present invention.

[0032] Figure 3 This is a plan sectional view of the nut and threaded shaft portion of the electric actuator of the present invention.

[0033] Figure 4 yes Figure 3 Four enlarged detail images.

[0034] Figure 5 yes Figure 4 5-5 line section view.

[0035] Figure 6 yes Figure 4 A 6-6 line sectional view.

[0036] Figure 7 (a) and (b) are schematic cross-sectional views showing the application state of lubricant to the threaded shaft in the electric actuator of the present invention.

[0037] Figure 8 (a) and (b) are schematic cross-sectional views showing the application of lubricant to the threaded shaft in an existing electric actuator.

[0038] Explanation of reference numerals in the attached figures

[0039] 1. Electric actuator;

[0040] 2. Electric motor;

[0041] 2a Output shaft of electric motor;

[0042] 3. Threaded shaft;

[0043] 3b External thread of the threaded shaft;

[0044] 4. Motion conversion mechanism;

[0045] 5. Transmission mechanism;

[0046] 6. Drive gear;

[0047] 8 nuts;

[0048] 8A Nut's sleeve portion;

[0049] The cylindrical part of 8B nut;

[0050] 8a Internal thread of nut;

[0051] 8b The recess of the nut;

[0052] 10. Actuator housing;

[0053] 19. Intermediate gear;

[0054] 20 Driven gear;

[0055] 21. Lubricant holding section;

[0056] 22. Cover components;

[0057] 22A Cover portion of cover component;

[0058] 22B The cylindrical portion of the cover component;

[0059] 22a Scraper section of cover component;

[0060] 22b The protrusion of the cover component;

[0061] Inner diameter of the scraper section;

[0062] The outer diameter of the threaded shaft;

[0063] δ represents a tiny gap. Detailed Implementation

[0064] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0065] Figure 1 This is a perspective view of the electric actuator of the present invention. Figure 2is a plan view of the electric actuator.

[0066] The electric actuator 1 of the present embodiment is provided in an electric parking brake device not shown, and Figure 2 as shown, has an electric motor 2 capable of forward and reverse rotation as a drive source, a motion conversion mechanism 4 that converts the rotation of the electric motor 2 to reciprocating linear motion of a threaded shaft 3, and a transmission mechanism (gear mechanism) 5 for transmitting the rotation of the electric motor 2 to the motion conversion mechanism 4, and these electric motor 2, motion conversion mechanism 4, and transmission mechanism 5 are housed in an actuator housing 10. Note that, in the following description, the arrow direction shown in Figure 1 and Figure 2 is set as the "front-rear direction".

[0067] The above-described actuator housing 10 is composed of a housing main body 11 that integrally has a first housing 11A and a second housing 11B that are cylindrical, a motor cover 12 that covers and is attached to the open end of the first housing 11A of the housing main body 11, and a gear cover 13 that covers and is attached to the open end of the housing main body 11 from the side (right side of Figure 2 ) opposite the motor cover 12.

[0068] And, as shown in Figure 2 , the electric motor 2 is housed in the first housing 11A of the housing main body 11, and a small-diameter drive gear 6 is attached to the end portion (rear end portion) of an output shaft (motor shaft) 2a that faces inside the gear cover 13, extending out from the electric motor 2 toward the rear (right side of Figure 2 ). Here, the axial one end (front end) of the electric motor 2 is fitted and held in a recessed portion 12a formed in the motor cover 12, and the axial other end (rear end) of the electric motor 2 is fitted and held in a circular hole 11b formed in an end wall 11a of the first housing 11A. Note that the output shaft (motor shaft) 2a of the electric motor 2 is rotatably supported to the first housing 11A via a bearing 7.

[0069] In addition, the second housing 11B of the housing main body 11 is disposed to the side of the first housing 11A, and the motion conversion mechanism 4 is housed in this second housing 11B. This motion conversion mechanism 4 has a rotatable nut 8 and the threaded shaft 3 that is screwed into the nut 8 in a linearly movable manner.

[0070] The above-described nut 8 integrally has a sleeve portion 8A and a barrel portion 8B that is larger in diameter than the sleeve portion 8A, and is rotatably supported to the second housing 11B by a radial bearing (ball bearing) 9 assembled to the outer periphery of the sleeve portion 8A. Here, an internal thread 8a is spirally engraved in the inner periphery of the sleeve portion 8A.

[0071] The threaded shaft 3 is a cylindrical sliding member that extends in the front-rear direction. A brake cable (not shown) is connected to a circular hole 3a formed at its front end. The other end of the brake cable is connected to the parking brake lever of an electric parking brake device (not shown). Furthermore, a flange 3A is integrally formed at the rear end of the threaded shaft 3. The outer periphery of the flange 3A engages with a pair of guide grooves 14a formed axially along the inner periphery of a cylindrical guide member 14 housed within the gear cover 13. Therefore, rotation of the threaded shaft 3 is prevented by the guide member 14, and the threaded shaft 3 performs reciprocating linear motion in the front-rear direction without rotation.

[0072] Furthermore, an external thread 3b is spirally engraved on the outer periphery of the threaded shaft 3 within a specified range, and the threaded shaft 3 is screwed into the sleeve portion 8A of the nut 8. Therefore, during the insertion of the threaded shaft 3 into the nut 8, the external thread 3b engraved on the outer periphery of the threaded shaft 3 and the internal thread 8a engraved on the inner periphery of the sleeve portion 8A of the nut 8 are screwed into each other.

[0073] Furthermore, the portion of the threaded shaft 3 extending outward toward the actuator housing 10 is covered by a stretchable corrugated protective cover 15 made of a soft and elastic rubber material or the like. One end (front end) of the protective cover 15 is fitted into the outer periphery of the front end of the threaded shaft 3, and the other end (rear end) of the protective cover 15 is fitted into the outer periphery of the cylindrical portion 11c protruding from the second housing 11B of the actuator housing 10.

[0074] like Figure 2 As shown, an axial space is formed within the cylindrical portion 8B of the nut 8 between the cylindrical portion 8B and the flange portion 3A of the threaded shaft 3. Multiple disc springs 16 are housed in a stacked manner in the axial direction, and the axial position of these disc springs 16 is restricted by a retaining ring 17 that abuts against the driven gear 20. It should be noted that these disc springs 16 constitute a force-applying unit that applies force in the direction (rearward) that causes the threaded shaft 3 to move away from the nut 8.

[0075] Here, below, based on Figure 2 The structure of transmission mechanism 5 will be described.

[0076] The transmission mechanism 5 transmits the rotation of the output shaft 2a of the electric motor 2 to the nut 8 of the motion conversion mechanism 4, and includes the drive gear 6 mounted on the output shaft 2a of the electric motor 2, the intermediate gear 19 rotatably supported on the support shaft 18, and the driven gear 20 mounted on the outer periphery of the cylindrical portion 8B of the nut 8.

[0077] The aforementioned intermediate gear 19 is rotatably supported by a support shaft 18 mounted between the housing body 11 of the actuator housing 10 and the guide member 14, and integrally comprises a large-diameter intermediate gear 19a and a small-diameter intermediate gear 19b with different diameters. Here, the large-diameter intermediate gear 19a meshes with the drive gear 6, and the diameter of the large-diameter intermediate gear 19a is set to be larger than the diameter of the drive gear 6. In addition, the small-diameter intermediate gear 19b meshes with a driven gear 20 with a larger diameter than itself, and the driven gear 20 is fitted into the outer periphery of the cylindrical portion 8B of the nut 8.

[0078] Next, the following is based on Figures 3 to 6 The characteristic structure of the present invention will be described.

[0079] Figure 3 This is a plan sectional view of the nut and threaded shaft portion of the electric actuator of the present invention. Figure 4 yes Figure 3 Four enlarged detail images, Figure 5 yes Figure 4 5-5 line section view, Figure 6 yes Figure 4 A 6-6 line sectional view.

[0080] In this embodiment, such as Figures 3 to 5 As shown, a lubricant holding portion 21 with an outer diameter larger than the diameter of the threaded hole of the nut 8 is formed on the inner circumference of one axial end (front end) 8A1 of the sleeve portion 8A of the nut 8. This lubricant holding portion 21 can hold lubricant such as grease. Furthermore, a cover member 22 covering the axial opening end of the lubricant holding portion 21 is installed on the outer circumference of one axial end (front end) 8A1 of the sleeve portion 8A of the nut 8.

[0081] The aforementioned cover component 22 is integrally formed from rubber material, such as... Figure 4 As shown, it integrally comprises an annular cover portion 22A that axially covers the axially open end of the lubricant holding portion 21 and a cylindrical portion 22B coaxial with the nut 8. Here, as Figure 4 As shown, an annular protrusion 22b is integrally formed around the inner periphery of the end of the cylindrical portion 22B of the cover member 22, and an annular groove-shaped recess 8b is integrally formed around the outer periphery of the end of the sleeve portion 8A of the nut 8.

[0082] Further, the cover member 22 is simply installed to the end outer periphery of the sleeve portion 8A of the nut 8 in one-touch by fitting the protrusion 22b formed in the end inner periphery of the cylindrical portion 22B of the cover member 22 into the recess 8b formed in the end outer periphery of the sleeve portion 8A of the nut 8. Note that, in the present embodiment, the protrusion 22b is formed in the cylindrical portion 22B of the cover member 22 and the recess 8b is formed in the sleeve portion 8A of the nut 8, but the cover member 22 can also be simply installed to the end outer periphery of the sleeve portion 8A of the nut 8 in one-touch by forming a recess in the cylindrical portion 22B of the cover member 22 and a protrusion in the sleeve portion 8A of the nut 8 and fitting these recess and protrusion into each other.

[0083] In the present embodiment, as shown in FIG. 2, the outer diameter of the cylindrical portion 22B of the cover member 22 is the same as the outer diameter of the sleeve portion 8A of the nut 8. Further, a cylindrical scraper portion (scraping portion) 22a that protrudes integrally toward the front (left) is formed in the inner periphery of the cover portion 22A of the cover member 22, and a tapered surface 22bl that expands in diameter toward the front (left) is formed in the inner periphery of the front end of the scraper portion 22a. Here, as shown in FIG. 2, the inner diameter of the scraper portion 22a is set to be slightly larger than the outer diameter of the threaded shaft 3. Figure 4 Figure 4 Figure 4 Figure 6 Therefore, a radial annular minute gap δ (= (D - d) / 2) is formed between the scraper portion 22a and the threaded shaft 3.

[0084] Further, the electric actuator 1 configured as above is used as an actuator of an electric parking brake device not shown, and the operation of the electric actuator 1 will be described below with reference to FIG. 1. Figure 7 Figure 1 Figure 2

[0085] Figure 2 As shown in FIG. 1, the state in which the threaded shaft 3 is advanced and in which the electric parking brake device is in a state in which the parking brake is released is a state in which the brake cable not shown installed to the top end of the threaded shaft 3 is relaxed, and in this state, the brake shoes of the drum brake are separated from the inner peripheral surface of the brake drum. Thus, no frictional resistance is generated between the brake shoes and the brake drum, the electric parking brake device is in a state in which the parking brake is released, and the brake drum and the wheel are freely rotatable, so that the running of the vehicle can be achieved.

[0086] ​​​​​​​​​If the parking brake switch (not shown) is operated from the above state and is in the ON state, the electric motor 2 of the electric actuator 1 is energized and the electric motor 2 is started. Then, the rotation of the output shaft 2a of the electric motor 2 is slowed down by the transmission mechanism 5 and transmitted to the motion conversion mechanism 4, and the rotation of the output shaft 2a of the electric motor 2 is converted into linear motion (reverse motion) of the threaded shaft 3.

[0087] That is, the rotation of the output shaft 2a of the electric motor 2 is decelerated and transmitted from the drive gear 6 to the intermediate gear 19, which rotates at a predetermined speed. Furthermore, the rotation of the intermediate gear 19 is decelerated and transmitted to the nut 8 of the motion conversion mechanism 4 through the meshing small-diameter intermediate gear 19b and the driven gear 20, which rotates at a predetermined speed.

[0088] As described above, if nut 8 rotates, the threaded shaft 3 connected to nut 8 will engage as follows: Figure 7 As shown in (a), the vehicle moves linearly backward, and a brake cable (not shown) mounted on the top of the threaded shaft 3 is pulled. This actuates the parking brake lever of the electric parking brake device, causing the brake shoes to expand and press against the inner circumferential surface of the brake drum, thus generating frictional resistance between them. This frictional resistance then brakes the rotation of the brake drum and the wheel, bringing the vehicle into a parking brake state.

[0089] If the parking brake switch (not shown) is operated and placed in the open state to release the aforementioned parking brake state, the electric motor 2 reverses, and the rotation of its output shaft 2a is transmitted to the nut 8 of the motion conversion mechanism 4 via the same transmission path as described above, thus causing the nut 8 to reverse. If the nut 8 reverses in this way, the threaded shaft 3 screwed into the nut 8... Figure 7 (b) The arrow moves forward in a straight line, and the electric actuator 1 returns to its original position. Figure 2 The state shown indicates that the electric parking brake has been released.

[0090] However, in this embodiment, a lubricant holding portion 21 with an outer diameter larger than the diameter of the threaded hole of the nut 8 and capable of holding lubricant is formed on the inner circumference of one axial end of the nut 8, and a cover member 22 is provided to cover the axial opening end of the lubricant holding portion 21. Therefore, even if the threaded shaft 3 enters the nut 8 due to the rotation of the nut 8, the lubricant applied to the threaded shaft 3 will be retained in the lubricant holding portion 21 of the nut 8. Thus, as Figure 7 As shown in (a) and (b), no excess lubricant will remain on the end face of nut 8, and the remaining lubricant will not be scattered around due to the centrifugal force based on the rotation of nut 8.

[0091] In addition, the lubricant remaining in the lubricant holding portion 21 of the nut 8 is applied to the threaded shaft 3 when the threaded shaft 3 comes out of the nut 8, but the amount of application of the lubricant is limited by the cover member 22, and thus a necessary and sufficient amount of lubricant is applied over a wide range of the threaded shaft 3. As a result, local shortage of lubricant (oil film shortage) of the threaded shaft 3 does not occur, lubrication of the threaded engagement portion of the nut 8 and the threaded shaft 3 is sufficiently performed, and wear of the threaded engagement portion is suppressed, thereby improving the durability of the nut 8 and the threaded shaft 3.

[0092] In addition, in the present embodiment, the inner diameter of the scraper portion 22a formed in the inner periphery of the cover portion 22A of the cover member 22 is set to be slightly larger than the outer diameter of the threaded shaft 3, and a slight radial gap δ is formed therebetween, and thus the lubricant remaining in the lubricant holding portion 21 of the nut 8 is scraped off by the scraper portion 22a, and as shown in (a) and (b), the lubricant is uniformly applied to the threaded shaft 3 at a predetermined thickness δ. In this case, since the scraper portion 22a does not come into contact with the threaded shaft 3, frictional resistance does not occur therebetween, and the threaded shaft 3 can smoothly slide without resistance. In addition, since the scraper portion 22a is not subjected to external force from the threaded shaft 3, damage of the scraper portion 22a can be prevented, and the durability of the cover member 22 can be improved. The outer diameter of the cylindrical portion 22B of the cover member 22 is set to be slightly larger than the outer diameter of the sleeve portion 8A of the nut 8, and a slight radial gap δ is formed therebetween, and thus the lubricant remaining in the lubricant holding portion 21 of the nut 8 is scraped off by the scraper portion 22a, and as shown in (a) and (b), the lubricant is uniformly applied to the threaded shaft 3 at a predetermined thickness δ. In this case, since the scraper portion 22a does not come into contact with the threaded shaft 3, frictional resistance does not occur therebetween, and the threaded shaft 3 can smoothly slide without resistance. In addition, since the scraper portion 22a is not subjected to external force from the threaded shaft 3, damage of the scraper portion 22a can be prevented, and the durability of the cover member 22 can be improved. Figure 7 The outer diameter of the cylindrical portion 22B of the cover member 22 is set to be slightly larger than the outer diameter of the sleeve portion 8A of the nut 8, and a slight radial gap δ is formed therebetween, and thus the lubricant remaining in the lubricant holding portion 21 of the nut 8 is scraped off by the scraper portion 22a, and as shown in (a) and (b), the lubricant is uniformly applied to the threaded shaft 3 at a predetermined thickness δ. In this case, since the scraper portion 22a does not come into contact with the threaded shaft 3, frictional resistance does not occur therebetween, and the threaded shaft 3 can smoothly slide without resistance. In addition, since the scraper portion 22a is not subjected to external force from the threaded shaft 3, damage of the scraper portion 22a can be prevented, and the durability of the cover member 22 can be improved.

[0093] The nut 8 is inserted into the radial bearing 9 and assembled, but since the outer diameter of the cylindrical portion 22B of the cover member 22 is equal to or smaller than the outer diameter of the sleeve portion 8A of the nut 8, even after the cover member 22 is fitted to the nut 8, the nut 8 can be assembled to the radial bearing 9 without interference of the cover member 22 with the radial bearing 9.

[0094] In addition, in the present embodiment, since the cover member 22 is made of a soft and elastic rubber material, damage of the cover member 22 can be prevented even when the cover member 22 comes into contact with the threaded shaft 3, and the durability of the cover member 22 can be improved.

[0095] Note that the above describes a case where the present application is applied to the electric actuator of the electric parking brake device of the drum brake for a vehicle, but the present application can also be applied to an electric actuator used in any other device.

[0096] In addition to the above, the application of the present application is not limited to the above-described embodiments, and it is obvious that various modifications can be made within the scope of the technical idea recited in the claims, the specification, and the drawings.​​

Claims

1. An electric actuator (1) provided with an electric motor (2) capable of forward and reverse rotation and a motion conversion mechanism (4) that converts rotation of the electric motor (2) into reciprocating linear motion of a threaded shaft (3), the motion conversion mechanism (4) is provided with a nut (8) that is rotated by the electric motor (2) and the threaded shaft (3) that is screwed into the nut (8) in a manner capable of advancing and retreating, the electric actuator (1) is characterized in that a lubricant holding portion (21) that has an outer diameter larger than the diameter of the threaded hole of the nut (8) and is capable of accommodating a lubricant is formed in the inner periphery of an axial end of the nut (8), a cover member (22) that covers the axial open end of the lubricant holding portion (21) is provided, the cover member (22) integrally has a cover portion (22A) and a cylindrical portion (22B) that is coaxial with the nut (8), the cover member (22) is attached to the nut (8) by fitting a protrusion (22b) formed in the inner periphery of the cylindrical portion (22B) into a recess (8b) formed in the outer periphery of the nut (8) or fitting a protrusion formed in the outer periphery of the nut (8) into a recess formed in the inner periphery of the cylindrical portion (22B).

2. The electric actuator according to claim 1, characterized in that a cylindrical scraper portion (22a) is formed in the inner periphery of the cover portion (22A), the inner diameter (φD) of the scraper portion (22a) is set to be slightly larger than the outer diameter (φd) of the threaded shaft (3) to form a slight radial gap (δ) between the scraper portion (22a) and the threaded shaft (3).

3. The electric actuator according to claim 1 or 2, characterized in that the outer diameter of the cylindrical portion (22B) is equal to or smaller than the outer diameter of the nut (8).

4. The electric actuator according to claim 1 or 2, characterized in that the cover member (22) is made of a rubber material.

Images