Linear motion actuator and electric brake device
Patent Information
- Application Number
- JP2022151384
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2022-09-22
- Publication Date
- 2025-09-03
Smart Images
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Abstract
Description
[Technical field]
[0001] The present invention relates to a linear actuator and an electric brake device, and to a technique that employs a linear motion mechanism that converts the rotational motion of a rotational drive source into linear motion to linearly drive a driven member such as a brake pad. [Background technology]
[0002] 2. Description of the Related Art There has been proposed an electric linear motion actuator that converts the rotational motion of an electric motor into linear motion to linearly drive a driven member that is supported so as to be freely movable in the axial direction (Patent Document 1). In the electric linear actuator of Patent Document 1, as shown in Fig. 7 of Patent Document 1, an outer ring member 21 supported by a housing 20 slides in the axial direction to press an inner brake pad 14 against a disc rotor 10. A reaction force from the pressing force of the inner brake pad 14 causes the caliper 11 to move in the opposite direction to the outer ring member 21 and press the outer pad 13 against the disc rotor 10, thereby braking the disc rotor 10.
[0003] A lubricant that lubricates the sliding guideway is provided on the outer peripheral surface of the outer ring member 21. When the outer ring member 21 slides in the cylinder chamber 20a inside the housing 20, the lubricant reduces sliding resistance and suppresses friction. [Prior art documents] [Patent documents]
[0004] [Patent Document 1] Patent No. 6478571 Summary of the Invention [Problem to be solved by the invention]
[0005] However, the caliper 11 has a bridge structure that straddles the disc rotor 10 as shown in Figure 8 of the present application, and when a force that brakes the disc rotor 10 is supported, the caliper 11 elastically deforms at the bridge structure portion so that the center side of the disc rotor 10 opens more.
[0006] At this time, the outer race member 21 slides inside the cylinder chamber 20a, while at the same time, the outer race member 21 vertically contacts the surface of the disc rotor 10 via the pad holder 18 and the inner pad 14. Due to the elastic deformation of the caliper 11, the outer race member 21 receives an unbalanced load so as to tilt with respect to the cylinder chamber 20a. As shown in FIG. 9, the components constituting the linear motion mechanism undergo elastic deformation in response to the unbalanced load of the outer race member 21, so that the gap between the outer race member 21 and the cylinder chamber 20a becomes partially zero (contact state) at the contact portion A1, and wear occurs due to sliding while in contact. This impedes the sliding of the outer race member 21. That is, in order for the outer race member 21 to slide in the cylinder chamber 20a without being hindered by tilt caused by elastic deformation of the caliper 11, it is necessary to suppress wear between the outer race member 21 and the cylinder chamber 20a.
[0007] It is generally known that when two metal parts having a hardness difference slide against each other with a large sliding resistance such that one metal part scratches the other metal part, a severe form of wear called abrasive wear occurs. The outer ring member 21 must transmit force without plastic deformation, and is made of, for example, carbon steel that can achieve high hardness through heat treatment. On the other hand, a casting is used for the caliper 11 in consideration of mass production. Castings have a lower hardness than heat-treated carbon steel. In addition, since the outer ring member 21 receives an unbalanced load and contacts the cylinder chamber 20a in an inclined position, the contact surface slides in a scratching manner, which is likely to cause abrasive wear. If the outer ring member 21 continues to slide while abrasive wear is occurring, the wear will be further accelerated, and there is a risk that the sliding surfaces will stick to each other.
[0008] An object of the present invention is to provide a linear actuator and an electric brake device capable of preventing abrasive wear of sliding surfaces or adhesion between sliding surfaces. [Means for solving the problem]
[0009] A linear motion actuator of the present invention is a linear motion actuator including a rotary drive source, a linear motion mechanism that converts a rotary motion of the rotary drive source into a linear motion of a linear motion part, and a housing that slidably holds the linear motion part of the linear motion mechanism, The actuator includes a contact pressure reducing means for reducing the contact pressure between at least the housing and the linear motion portion. The term "reducing the contact pressure" means that the contact pressure of the linear actuator of the present invention is reduced in a predetermined operating state, compared to the contact pressure of a linear actuator of a conventional structure not provided with a contact pressure reducing means. The predetermined operating state refers to, for example, a state in which the housing is elastically deformed, or a state in which the linear actuator is tilted due to an unbalanced load.
[0010] According to this configuration, since the contact pressure reducing means for reducing the contact pressure between the housing and the linear moving part is provided, when the housing is elastically deformed or when the linear moving part is tilted due to an unbalanced load, the contact pressure between the housing and the linear moving part can be avoided, or even if the housing and the linear moving part come into contact, the contact pressure can be reduced, thereby preventing abrasive wear of the sliding surfaces or adhesion between the sliding surfaces.
[0011] The rotary drive device includes a speed reducing mechanism that reduces the speed of rotation of the rotary drive source, and the linear motion mechanism converts the rotary motion output by the speed reducing mechanism into linear motion.
[0012] The linear motion part may be provided in a cylindrical shape, and supported in a cylinder chamber formed in the housing so as to be slidable along the axial direction of the linear motion part, and the contact surface pressure reducing means may include a tapered part that tapered radially inwardly toward the end face of the linear motion part at least at the axial base end of the outer circumferential surface of the linear motion part toward the base end side of the linear motion part. In this case, the contact surface pressure can be easily reduced by the tapered part of the linear motion part, and therefore manufacturing costs can be reduced more than by taking measures such as increasing the rigidity of the housing.
[0013] The contact pressure reducing means may include a tapered portion at an axial tip of the outer peripheral surface of the linear moving part, the diameter of which is tapered radially inward toward the end face of the linear moving part on the tip side of the linear moving part. The contact pressure can be more reliably reduced by the tapered portion at the axial tip of the linear moving part and the tapered portion at the axial base end.
[0014] The contact surface pressure reducing means may include an expanded diameter portion that expands radially outwardly at an axial tip end of the cylinder chamber toward the open end of the cylinder chamber. The expanded diameter portion and the reduced diameter portion of the linear motion portion can more reliably reduce the contact surface pressure.
[0015] The contact surface pressure reducing means may include an elastic body provided at an axial tip of the cylinder chamber. The elastic body guides the linear moving part, thereby reducing the deflection angle between the housing and the linear moving part, thereby making it possible to avoid contact between the housing and the linear moving part or to reduce the contact surface pressure even if the housing and the linear moving part come into contact with each other.
[0016] The elastic body may be made of rubber, resin, or metal having a lower hardness than the outer circumferential surface of the linear motion portion, in which case various materials can be used as the elastic body, increasing the degree of freedom in design.
[0017] The reduced diameter portion may have a tapered or crowned shape that reduces in diameter toward the end face. When the reduced diameter portion has a tapered shape, the structure can be simplified and the manufacturing cost can be reduced compared to when the reduced diameter portion has a crowned shape. When the reduced diameter portion has a crowned shape, the contact surface pressure can be reduced with high accuracy.
[0018] The rotary drive source may be an electric motor.
[0019] The electric brake device of the present invention comprises any one of the linear actuators of the present invention, a brake rotor, and a friction pad that contacts the brake rotor to generate a braking force, and the friction pad is brought into contact with and separated from the brake rotor by the linear portion of the linear actuator. Effect of the Invention
[0020] The linear actuator of the present invention is provided with a contact pressure reducing means for reducing the contact pressure between the housing and the linear moving part, thereby making it possible to prevent abrasive wear of the sliding surfaces or adhesion between the sliding surfaces. [Brief description of the drawings]
[0021] [Figure 1] 1 is a vertical sectional view of an electric brake device according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3A] 2 is a vertical sectional view of a main part of a linear actuator of the electric brake device. FIG. [Figure 3B] 4 is a vertical cross-sectional view of the linear actuator in a state where a linear motion portion of the linear motion actuator is advanced. FIG. [Figure 4A] FIG. 6 is a vertical sectional view of a main portion of a linear actuator of an electric brake device according to a second embodiment of the present invention. [Figure 4B] 4 is a vertical cross-sectional view of the linear actuator in a state where a linear motion portion of the linear motion actuator is advanced. FIG. [Diagram 5] FIG. 11 is a vertical sectional view of a main part of a linear actuator of an electric brake device according to a third embodiment of the present invention. [Figure 6] FIG. 11 is a vertical sectional view of a main part of a linear actuator of an electric brake device according to a fourth embodiment of the present invention. [Figure 7] FIG. 2 is a vertical cross-sectional view of a main part of a linear actuator of an electric brake device according to a reference proposal example. [Figure 8] FIG. 13 is a schematic diagram of a caliper of an electric brake device according to a conventional example when the caliper is deformed. [Figure 9] 2 is a vertical sectional view of a main part of a linear actuator of the electric brake device. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] [First embodiment] An embodiment of the present invention will be described in conjunction with FIGS. 1 through 3B. As shown in Fig. 1, the electric brake device according to the embodiment is a so-called floating type brake, which has a bridge structure. Fig. 1 is a cross-sectional view taken along line II in Fig. 2. <Outline of the structure of the electric brake device> The electric brake device includes a caliper 11, a linear actuator 1, a brake rotor 10, and friction pads 13, 14. The friction pads 13, 14 are brought into contact with and separated from the brake rotor 10 by a linear portion 21 of the linear actuator 1, which will be described later.
[0023] A caliper 11 is provided on the vehicle so as to surround an outer circumferential portion of each brake rotor 10. A claw portion 12 is provided at an end of the outboard side OS of the caliper 11. The claw portion 12 faces a side surface of the outboard side OS of the brake rotor 10 in the axial direction. A friction pad 13 of the outboard side OS is supported by the claw portion 12. In this specification, when the brake device is mounted on the vehicle, the outer side in the vehicle width direction is referred to as the outboard side OS, and the central side in the vehicle width direction is referred to as the inboard side IS.
[0024] An inboard side IS friction pad 14 is supported on the outboard end of the linear actuator 1 of the caliper 11. This friction pad 14 faces a side surface of the inboard side IS of the brake rotor 10 in the axial direction. The linear actuator 1 drives the friction pads 13, 14 to contact and separate from the brake rotor 10. Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. A mount 15 shown in Fig. 2 is supported on a knuckle (not shown) of a vehicle. Pin support pieces 16, 16 are provided on both longitudinal ends of the mount 15. Slide pins 17, 17 extending parallel to each other in the axial direction are provided on the respective ends of these pin support pieces 16, 16. The caliper 11 is supported by the slide pins 17, 17 so as to be slidable in the axial direction.
[0025] As shown in Figure 1, during braking, the friction pad 14 on the inboard side IS comes into contact with the brake rotor 10 by driving the linear actuator 1, pressing the brake rotor 10 in the axial direction. The reaction force of this pressing force causes the caliper 11 to slide to the inboard side. As a result, the friction pad 13 on the outboard side supported by the claw portion 12 of the caliper 11 comes into contact with the brake rotor 10. The friction pads 13, 14 on the outboard side OS and inboard side IS tightly hold the brake rotor 10 from both axial sides, so that a braking force is applied to the brake rotor 10.
[0026] The linear motion actuator 1 includes a housing 20, an electric motor 24 (FIG. 2) which is a rotational drive source, a speed reduction mechanism 30 which reduces the rotation of the electric motor 24 (FIG. 2), and a linear motion mechanism 2 which converts the rotational motion output by the speed reduction mechanism 30 into linear motion. The tubular housing 20 is integrally provided with the caliper 11, and the electric motor 24 (FIG. 2) is supported by the housing 20. A cylinder chamber 20a in the form of a cylindrical hole is formed in the housing 20, and the linear motion mechanism 2 is incorporated in the cylinder chamber 20a. The open end of the housing 20 on the inboard side IS is covered by a cover 23.
[0027] <Electric motor> 2 is, for example, a permanent magnet type synchronous motor, but the electric motor 24 may also be, for example, a DC motor using brushes, a reluctance motor not using permanent magnets, or an induction motor.
[0028] <Deceleration mechanism> As shown in Fig. 1, a reduction gear mechanism 30 covered by a cover 23 is provided on the inboard side IS of the housing 20. This reduction gear mechanism 30 is a mechanism that reduces the rotation of the electric motor 24 (Fig. 2) and transmits it to an output gear 33 fixed to a rotating shaft 34. As shown in Fig. 2, the reduction gear mechanism 30 includes a plurality of gear trains. In this example, the reduction gear mechanism 30 reduces the rotation of an input gear 31 attached to a rotor shaft 25 of the electric motor 24 by an intermediate gear 32, and can transmit the rotation to the output gear 33.
[0029] <Linear motion mechanism> The linear motion mechanism 2 in this example is a planetary roller screw type linear motion mechanism. The linear motion mechanism 2 converts the rotational motion output by the reduction gear mechanism 30 into linear motion, and causes the friction pads 13, 14 to contact and separate from the brake rotor 10. The linear motion mechanism 2 has a rotating shaft 34 that is rotated by an electric motor 24 (FIG. 2), a conversion mechanism unit 3 that converts the rotational motion of the rotating shaft 34 into linear motion, and restraint units 4, 5. The conversion mechanism unit 3 has a linear motion unit 21 that is a piston (also called an "outer ring member"), a support member 35, a backup plate 57 that is an annular thrust plate, a thrust bearing 58, a rolling bearing 36, a carrier 40, slide bearings 44a, 44b, and a plurality of planetary rollers 49.
[0030] A cylindrical linear motion part 21 is supported in a cylinder chamber 20a of the housing 20 so as to be prevented from rotating and to be movable along the axial direction of the linear motion part 21. A lubricant for lubricating the sliding guide surface is applied to the outer circumferential surface of the linear motion part 21. A boot 61 is provided between the housing 20 and the outboard end of the linear motion part 21. A helical projection is provided on the inner circumferential surface of the linear motion part 21, protruding a predetermined distance radially inward and formed in a helical shape. A plurality of planetary rollers 49 mesh with this helical projection.
[0031] A support member 35 is provided on one axial end side of the linear motion portion 21 within the housing 20. This support member 35 has a boss portion and a flange portion extending radially outward from the boss portion. A plurality of rolling bearings 36 are fitted into the boss portion, and a rotating shaft 34 is fitted into the inner diameter surfaces of the inner rings of these rolling bearings 36. The rotating shaft 34 is rotatably supported by the support member 35 via the plurality of rolling bearings 36.
[0032] A carrier 40 that is rotatable around a rotation axis 34 is provided on the inner periphery of the linear motion portion 21. The carrier 40 has a pair of disks that are arranged facing each other in the axial direction. Of these disks, the disk closer to the support member 35 is called the inner disk, and the other disk is called the outer disk. Of the outer disk, a plurality of pillar members are provided on the side facing the inner disk so as to protrude in the axial direction (inboard side) from the outer peripheral edge of this side. The outer disk and the inner disk are integrally provided by these plurality of pillar members.
[0033] The inner disc is rotatably supported on the rotating shaft 34 by a plain bearing 44b fitted between the inner disc and the rotating shaft 34. A shaft insertion hole is formed in the center of the outer disc, and a plain bearing 44a is fitted into this shaft insertion hole. The outer disc is rotatably supported on the rotating shaft 34 by the plain bearing 44a. Restraint portions 4 and 5 that restrain the axial positions of the rotating shaft 34 and carrier 40 relative to the support member 35 are provided on both axial ends of the rotating shaft 34.
[0034] A plurality of roller shafts 47 are provided on the carrier 40 at intervals in the circumferential direction. Both axial ends of each roller shaft 47 are supported across the inner disc and the outer disc. A plurality of shaft insertion holes are formed in each of the discs. Each shaft insertion hole is an elongated hole extending a predetermined distance in the radial direction. Both axial ends of each roller shaft 47 are inserted into each shaft insertion hole, and these roller shafts 47 are supported so as to be freely movable in the radial direction within the range of each shaft insertion hole. Elastic rings 50 that bias the roller shafts 47 radially inward are hung across both axial ends of the plurality of roller shafts 47.
[0035] A planetary roller 49 is rotatably supported on each roller shaft 47. A circumferential groove or a spiral groove that meshes with the spiral protrusion of the linear motion part 21 is formed on the outer peripheral surface of each planetary roller 49. Each planetary roller 49 is interposed between the outer peripheral surface of the rotating shaft 34 and the inner peripheral surface of the linear motion part 21. Each planetary roller 49 is pressed against the outer peripheral surface of the rotating shaft 34 by the biasing force of the elastic ring 50. When the rotating shaft 34 rotates, each planetary roller 49 that contacts the outer peripheral surface of the rotating shaft 34 rotates due to contact friction. Therefore, when the rotating shaft 34 rotates, each planetary roller 49 revolves while rotating on its own axis. As a result, the linear motion part 21 moves in the axial direction, and the linear motion actuator 1 is driven.
[0036] <Methods for reducing contact pressure> 3A, the linear actuator 1 is provided with a contact pressure reducing means 6 for reducing the contact pressure between at least the housing 20 and the linear moving part 21. The contact pressure reducing means 6 may be configured to prevent the housing 20 and the linear moving part 21 from coming into contact with each other. The contact pressure reducing means 6 includes first and second reduced diameter parts 6A and 6B.
[0037] The first reduced diameter portion 6A is a tapered portion at the axial base end of the outer circumferential surface of the linear moving portion 21, the diameter of which is reduced radially inward toward the end face 21a on the base end side of the linear moving portion 21, and extends a predetermined length L1 in the axial direction. The second reduced diameter portion 6B is a tapered portion at the axial tip end of the outer circumferential surface of the linear moving portion 21, the diameter of which is reduced radially inward toward the end face 21b on the tip side of the linear moving portion 21, and extends a predetermined length L2 in the axial direction. The taper degree and axial dimension of each reduced diameter portion 6A, 6B are determined, for example, by testing or simulation.
[0038] The axial center portion 21c of the linear motion portion 21 forms a cylindrical surface parallel to the axial direction C1 of the linear motion portion 21. When the linear motion portion 21 is accommodated in the cylinder chamber 20a and is not braking the brake rotor 10 (FIG. 1), the cylindrical surface 21c, which is not reduced in diameter, of the outer circumferential surface of the linear motion portion 21 faces the cylinder chamber 20a, and an initial radial gap δ is secured with respect to the cylinder chamber 20a. The cylindrical surface 21c and each of the reduced diameter portions 6A, 6B are smoothly connected to each other without any steps.
[0039] As shown in FIG. 3B, when the linear motion part 21 is advanced toward the outboard side OS to brake the brake rotor 10 (FIG. 1) and the caliper 11 (FIG. 1) is elastically deformed due to the reaction force, the first and second reduced diameter parts 6A, 6B can prevent contact between the cylinder inner diameter and the linear motion part 21 or can reduce the contact surface pressure even if contact occurs at the contact part A1.
[0040] <Action and effect> According to the electric brake device described above, since the contact surface pressure reducing means 6 is provided, when the housing 20 is elastically deformed or when the linear motion part 21 is tilted due to an unbalanced load, contact between the housing 20 and the linear motion part 21 can be avoided, or the contact surface pressure can be reduced even if the housing 20 and the linear motion part 21 come into contact with each other. This makes it possible to prevent abrasive wear of the sliding surfaces or adhesion between the sliding surfaces.
[0041] The contact surface pressure reducing means 6 includes first and second reduced diameter portions 6A, 6B in the linear motion portion 21. In this way, the contact surface pressure can be easily reduced by the reduced diameter portions 6A, 6B of the linear motion portion 21, and therefore manufacturing costs can be reduced more than by taking measures such as increasing the rigidity of the housing. In addition, the contact surface pressure can be more reliably reduced by the first reduced diameter portion 6A at the axial base end and the second reduced diameter portion 6B at the axial tip end.
[0042] <Other embodiments> In the following description, parts corresponding to matters previously described in each embodiment are given the same reference numerals, and duplicated description is omitted. When only a part of the configuration is described, the other parts of the configuration are the same as the previously described embodiment unless otherwise specified. The same configuration has the same action and effect. It is possible to combine not only the parts specifically described in each embodiment, but also partially combine embodiments together, provided that there is no particular problem with the combination.
[0043] [Second embodiment: Figs. 4A and 4B] As shown in Figures 4A and 4B, the first and second reduced diameter portions 6A, 6B may have a crowning shape that reduces in diameter toward the corresponding end faces 21a, 21b. The crowning shape may be a crowning formed by connecting a single arc or multiple arcs, or may be a logarithmic crowning. When the reduced diameter portions 6A, 6B have a crowning shape, the contact surface pressure can be reduced more accurately than when they have a tapered shape. Other effects are the same as those of the above-mentioned embodiment.
[0044] [Third embodiment: FIG. 5] As shown in Fig. 5, the contact surface pressure reducing means 6 may have a first reduced diameter portion 6A at the axial base end of the linear motion portion 21 and an expanded diameter portion 20aa formed in the cylinder chamber 20a of the housing 20. The expanded diameter portion 20aa expands radially outward at the axial tip end of the cylinder chamber 20a toward the open end of the cylinder chamber 20a. The expanded diameter portion 20aa in this example has a tapered shape that expands toward the open end, but may have the crowning shape described above. The expanded diameter portion 20aa and the first reduced diameter portion 6A of the linear motion portion 21 can reduce the contact surface pressure more reliably.
[0045] [Fourth embodiment: FIG. 6] As shown in Fig. 6, the contact surface pressure reducing means 6 may have a first reduced diameter portion 6A on the base end side of the linear motion portion 21 and an elastic body Db provided in the cylinder chamber 20a of the housing 20. The elastic body Db is an annular body with a rectangular cross section provided at the axial tip of the cylinder chamber 20a, and is made of rubber, resin, or a metal with a lower hardness than the outer circumferential surface of the linear motion portion. With the elastic body Db attached to the annular groove 20ab formed in the cylinder chamber 20a, the inner circumferential surface of the elastic body Db comes into sliding contact with the axial tip of the outer circumferential surface of the linear motion portion 21. This axial tip is cylindrical.
[0046] The elastic body Db guides the linear motion part 21, thereby reducing the deflection angle between the housing 20 and the linear motion part 21, and thus it is possible to avoid contact between the housing 20 and the linear motion part 21, or to reduce the contact surface pressure even if the housing 20 and the linear motion part 21 come into contact with each other. In addition, the contact surface pressure between the elastic body Db and the first reduced diameter part 6A of the linear motion part 20 can be more reliably reduced.
[0047] [Reference proposal example: Figure 7] As shown in Fig. 7, the contact surface pressure reducing means 6 may be composed of only an elastic body Db provided in the cylinder chamber 20a. This elastic body Db has the same configuration as the elastic body Db in the fourth embodiment (Fig. 6). In this case, the elastic body Db guides the linear motion part 21, so that the deflection angle between the housing 20 and the linear motion part 21 is reduced, and contact between the housing 20 and the linear motion part 21 can be avoided, or even if the housing 20 and the linear motion part 21 come into contact, the contact surface pressure can be reduced. In addition, since the reduced diameter part of the linear motion part 21 can be omitted, the structure can be simplified and the cost can be reduced compared to the fourth embodiment.
[0048] The linear motion mechanism is not limited to a planetary roller screw type linear motion mechanism, and for example, a ball screw mechanism or the like may be adopted. A so-called direct motor type linear actuator may be used in which the reduction mechanism is omitted and the rotational motion of the rotary drive source is directly transmitted to the linear mechanism. The electric brake device is not limited to a floating type brake, but may be an opposed piston type electric brake device. The first and second reduced diameter portions may be formed in a combination of a crowning shape and a tapered shape. At least one of the reduced diameter portions and the enlarged diameter portion of the cylinder chamber may be formed in a combination of a crowning shape and a tapered shape.
[0049] Although the embodiment of the present invention has been described above, the disclosed embodiment is illustrative in all respects and is not restrictive. The scope of the present invention is indicated by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]
[0050] Reference Signs List 1... linear actuator, 2... linear mechanism, 6... contact surface pressure reducing means, 6A... first reduced diameter portion, 6B... second reduced diameter portion, 10... brake rotor, 13, 14... friction pad, 20... housing, 20a... cylinder chamber, 20aa... enlarged diameter portion, 21... linear portion, 24... electric motor (rotary drive source), 30... reduction mechanism, Db... elastic body
Claims
1. A linear motion actuator including: a rotary drive source; a linear motion mechanism that converts the rotary motion of the rotary drive source into the linear motion of a linear motion part; and a housing that slidably holds the linear motion part of the linear motion mechanism, A linear motion actuator comprising a contact surface pressure reducing means for reducing the contact surface pressure between at least the housing and the linear motion portion.
2. 2. The linear motion actuator according to claim 1, further comprising a speed reduction mechanism that reduces the rotation of the rotary drive source, wherein the linear motion mechanism converts the rotational motion output by the speed reduction mechanism into linear motion.
3. 3. The linear actuator according to claim 1 or 2, wherein the linear moving part is provided in a cylindrical shape, the linear moving part is supported in a cylinder chamber formed in the housing so as to be slidable along the axial direction of the linear moving part, and the contact surface pressure reducing means includes a tapered part that tapered radially inward at least at a base end in the axial direction on the outer peripheral surface of the linear moving part toward an end face on the base end side of the linear moving part.
4. 4. The linear actuator according to claim 3, wherein the contact surface pressure reducing means includes a tapered portion at an axial tip end portion of the outer peripheral surface of the linear moving portion, the diameter of which tapers radially inward toward an end face on the tip side of the linear moving portion.
5. 4. The linear actuator according to claim 3, wherein the contact surface pressure reducing means includes an expanded diameter portion that expands radially outward at an axial tip end of the cylinder chamber toward an open end of the cylinder chamber.
6. 4. The linear actuator according to claim 3, wherein the contact surface pressure reducing means includes an elastic body provided at the axial tip of the cylinder chamber.
7. 4. The linear motion actuator according to claim 3, wherein the elastic body is made of rubber, resin, or metal having a lower hardness than the outer peripheral surface of the linear motion portion.
8. 4. The linear actuator according to claim 3, wherein the reduced diameter portion has a tapered or crowned shape that reduces in diameter toward the end face.
9. 3. The linear actuator according to claim 1, wherein the rotary drive source is an electric motor.
10. 10. An electric brake device comprising: the linear motion actuator according to claim 9; a brake rotor; and a friction pad that comes into contact with the brake rotor to generate a braking force, wherein the friction pad is brought into contact with and separated from the brake rotor by the linear motion part of the linear motion actuator.