JP2024046159A - Linear motion actuator and electric brake device - Google Patents

Abstract

To provide a linear motion actuator and an electric brake device capable of preventing occurrence of abrasive wear of a sliding surface and fastening of the sliding surfaces to each other.SOLUTION: A linear motion actuator 1 includes: an electric motor; a linear motion mechanism converting rotary motion of the electric motor to linear motion of a linear motion portion 21; and a housing 20 slidably holding the linear motion portion 21. The linear motion actuator further includes contact surface pressure reduction means 6 for reducing contact surface pressure between the housing 20 and the linear motion portion 21. The linear motion portion 21 has a cylindrical shape, and the linear motion portion 21 is supported by a cylinder chamber 20a of the housing 20 slidably along an axial direction C1. The contact surface pressure reduction means 6 includes: a first diameter reduced portion 6A of which a diameter is gradually reduced radially inward as proceeding toward a base end-side end face 21a at an axial base end portion on an outer peripheral surface of the linear motion portion 21; and a second diameter reduced portion 6B of which a diameter is gradually reduced radially inward as proceeding toward a tip-side end face 21b at an axial tip portion on the outer peripheral surface of the linear motion portion 21.SELECTED DRAWING: Figure 3A

Description

The present invention relates to a linear motion actuator and an electric brake device, and more particularly to a technology that employs a linear motion mechanism that linearly drives a driven member such as a brake pad by converting the rotational motion of a rotational drive source into linear motion.

2. Description of the Related Art There has been proposed an electric linear 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.

The outer peripheral surface of the outer ring member 21 is provided with lubricating oil for lubricating the sliding guide surface. When the outer ring member 21 slides in the cylinder chamber 20a inside the housing 20, the lubricating oil reduces sliding resistance and suppresses friction.

Patent No. 6478571

However, the caliper 11 has a bridge structure that straddles the disc rotor 10 as shown in FIG. 8 of the present application, and when it supports a force that brakes the disc rotor 10, the caliper 11 elastically deforms at the bridge structure portion so that the center side of the disc rotor 10 opens more.

At this time, the outer race member 21 slides in 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 hinders the sliding of the outer race member 21.
In other words, in order for the outer race member 21 to slide in the cylinder chamber 20a without being hindered by the tilt caused by the elastic deformation of the caliper 11, it is necessary to suppress wear between the outer race member 21 and the cylinder chamber 20a.

It is generally known that when two metal parts with different hardnesses slide with large sliding resistance, such as one metal part scratching the other, abrasive wear, which is a severe form of wear, occurs. It is being
The outer ring member 21 needs to transmit force without being plastically deformed, and is made of, for example, carbon steel that can achieve high hardness through heat treatment. On the other hand, the caliper 11 is made of cast metal in consideration of mass production. Cast iron is less hard than heat-treated carbon steel.
Further, since the outer ring member 21 subjected to an uneven load contacts the cylinder chamber 20a in an inclined position, the contact surface slides as if scratching, which tends to cause abrasive wear. If the outer ring member 21 continues to slide while abrasive wear has occurred, the wear will be further accelerated and there is a risk that the sliding surfaces may become stuck to each other.

An object of the present invention is to provide a linear actuator and an electric brake device that can prevent abrasive wear of sliding surfaces or sticking of sliding surfaces to each other.

The linear actuator of the present invention includes a rotational drive source, a linear motion mechanism that converts the rotational motion of the rotational drive source into a linear motion of a linear motion part, and a linear motion mechanism that slidably holds the linear motion part of the linear motion mechanism. A linear actuator comprising: a housing;
The apparatus further includes a contact surface pressure reducing means for reducing a contact surface pressure between at least the housing and the linear motion part.
The above-mentioned "reducing the contact surface pressure" means that the present invention reduces the contact surface pressure when the linear motion part is in a predetermined operating state for a linear motion actuator with a conventional structure that is not equipped with a contact surface pressure reduction means. This means that the contact surface pressure is reduced when the linear motion part is in the same operating state. The predetermined operating state refers to, for example, a state in which the housing is elastically deformed or a state in which the linear motion part is tilted due to an uneven load.

According to this configuration, since a contact pressure reducing means is provided for reducing the contact pressure between the housing and the linear moving part, when the housing is elastically deformed or when the linear moving part is tilted due to an unbalanced load, contact between the housing and the linear moving part can be avoided, or the contact pressure can be reduced even if the housing and the linear moving part come into contact. This makes it possible to prevent abrasive wear of the sliding surfaces or adhesion between the sliding surfaces.

The apparatus includes a deceleration mechanism that decelerates the rotation of the rotary drive source, and the linear motion mechanism converts the rotational motion output from the deceleration mechanism into linear motion.

The linear motion part is provided in a cylindrical shape, and is supported in a cylinder chamber formed in the housing so that the linear motion part can slide freely along the axial direction of the linear motion part, and the contact surface pressure reducing means may include a reduced diameter part at least at the axial base end of the outer circumferential surface of the linear motion part, the diameter of which is reduced radially inward as it approaches the end face on the base end side of the linear motion part. In this case, since the contact surface pressure can be easily reduced by the reduced diameter part of the linear motion part, it is possible to reduce manufacturing costs more than, for example, taking measures such as increasing the rigidity of the housing.

The contact surface pressure reducing means may include a diameter-reducing portion that decreases in diameter inward in the radial direction toward an end face on the distal end side of the linear motion portion at an axially distal end portion of the outer circumferential surface of the linear motion portion. The contact surface pressure can be more reliably reduced by the diameter-reduced portion at the axially distal end and the diameter-reduced portion at the axially proximal end of the linear motion portion.

The contact surface pressure reducing means may include an expanded diameter portion at the axial end of the cylinder chamber, which expands radially outward toward the open end of the cylinder chamber. This expanded diameter portion and the reduced diameter portion of the linear motion portion can more reliably reduce the contact surface pressure.

The contact surface pressure reducing means may include an elastic body provided at the axial tip of the cylinder chamber. The elastic body guides the linear motion part, thereby reducing the deflection angle between the housing and the linear motion part, thereby avoiding contact between the housing and the linear motion part, or reducing the contact surface pressure even if the housing and the linear motion part come into contact.

The elastic body may be made of rubber, resin, or a metal whose hardness is lower than that of the outer peripheral surface of the linear motion part. In this case, various materials can be used as the elastic body, which increases the degree of freedom in design.

The diameter-reducing portion may have a tapered shape or a crowning shape that decreases in diameter toward the end face. When the reduced diameter portion has a tapered shape, the structure can be simplified and manufacturing costs can be lowered than when the reduced diameter portion has a crowned shape. When the reduced diameter portion has a crowning shape, the contact surface pressure can be reduced with high accuracy.

The rotational drive source may be an electric motor.

The electric brake device of the present invention includes the linear motion actuator according to any one of the present invention, a brake rotor, and a friction pad that comes into contact with the brake rotor to generate a braking force, the linear motion portion of the linear motion actuator. This brings the friction pad into contact with and away from the brake rotor.

The linear actuator of the present invention is equipped with a contact pressure reduction means for reducing the contact pressure between the housing and the linear motion part, thereby preventing abrasive wear of the sliding surfaces or adhesion between the sliding surfaces.

FIG. 1 is a longitudinal cross-sectional view of an electric brake device according to a first embodiment of the present invention. 2 is a sectional view taken along line II-II in FIG. 1. FIG. 2 is a vertical sectional view of a main part of a linear actuator of the electric brake device. FIG. It is a longitudinal cross-sectional view of the same linear motion actuator in a state where the linear motion part moves forward. It is a longitudinal cross-sectional view of the main part of the direct-acting actuator of the electric brake device concerning the 2nd embodiment of the present invention. 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. FIG. 11 is a longitudinal sectional view of a main portion of a linear actuator of an electric brake device according to a third embodiment of the present invention. It is a longitudinal cross-sectional view of the principal part of the direct-acting actuator of the electric brake device concerning the 4th embodiment of the present invention. FIG. 2 is a longitudinal sectional view of a main part of a linear actuator of an electric brake device according to a reference proposal example. FIG. 13 is a schematic diagram of a caliper of an electric brake device according to a conventional example when the caliper is deformed. It is a longitudinal cross-sectional view of the main part of the linear actuator of the same electric brake device.

[First embodiment]
Embodiments of the present invention will be described in conjunction with FIGS. 1 to 3B.
As shown in FIG. 1, the electric brake device according to the embodiment is a bridge structure electric brake device that is a so-called floating type brake. FIG. 1 is a sectional view taken along line II in FIG. 2.
<Schematic structure of electric brake device>
The electric brake device includes a caliper 11, a linear actuator 1, a brake rotor 10, and friction pads 13, 14. Abut against and separate from.

A caliper 11 is provided in the vehicle so as to surround the outer peripheral side of each brake rotor 10. A claw portion 12 is provided at the end of the outboard side OS of the caliper 11. The claw portion 12 faces the 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 this claw portion 12. In this specification, when a brake device is mounted on a vehicle, the outer side of the vehicle in the vehicle width direction is referred to as an outboard side OS, and the center side of the vehicle in the vehicle width direction is referred to as an inboard side IS.

In the caliper 11, an inboard side IS friction pad 14 is supported at the outboard side end of the linear actuator 1. This friction pad 14 faces the 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 and 14 to bring them into contact with and away from the brake rotor 10.
FIG. 2 is a sectional view taken along the line II-II in FIG. 1. A mount 15 shown in FIG. 2 is supported on a knuckle (not shown) of the vehicle. Pin support pieces 16, 16 are provided at both ends of the mount 15 in the longitudinal direction. Slide pins 17, 17 extending parallel to each other in the axial direction are provided at respective ends of these pin support pieces 16, 16. The caliper 11 is supported by the slide pins 17, 17 so as to be freely slidable in the axial direction.

As shown in FIG. 1, during braking, the friction pad 14 of the inboard side IS comes into contact with the brake rotor 10 due to the drive of the linear actuator 1, and presses the brake rotor 10 in the axial direction. The caliper 11 slides inboard due to the reaction force of the pressing force. As a result, the outboard side friction pad 13 supported by the claw portion 12 of the caliper 11 comes into contact with the brake rotor 10. Braking force is applied to the brake rotor 10 by strongly sandwiching the brake rotor 10 from both sides in the axial direction between the friction pads 13 and 14 of the outboard side OS and the inboard side IS.

The linear actuator 1 includes a housing 20, an electric motor 24 (FIG. 2) that is a rotational drive source, a deceleration mechanism 30 that decelerates the rotation of the electric motor 24 (FIG. 2), and a rotation output from the deceleration mechanism 30. It includes a linear motion mechanism 2 that converts motion into linear motion. A cylindrical housing 20 is integrally provided with the caliper 11, and an electric motor 24 (FIG. 2) is supported by the housing 20. A cylinder chamber 20a having a cylindrical hole shape is formed in the housing 20, and the linear motion mechanism 2 is incorporated in this cylinder chamber 20a. The open end of the inboard side IS of the housing 20 is covered by a cover 23.

<Electric motor>
2 is, for example, a permanent magnet type synchronous motor, but may also be, for example, a DC motor using brushes, a reluctance motor not using permanent magnets, or an induction motor.

<Deceleration mechanism>
As shown in FIG. 1, a speed reduction mechanism 30 covered with a cover 23 is provided on the inboard side IS of the housing 20. This deceleration mechanism 30 is a mechanism that decelerates and transmits the rotation of the electric motor 24 (FIG. 2) to an output gear 33 fixed to a rotating shaft 34. As shown in FIG. 2, the speed reduction mechanism 30 includes a plurality of gear trains. In this example, the speed reduction mechanism 30 can reduce the rotation of an input gear 31 attached to the rotor shaft 25 of the electric motor 24 using an intermediate gear 32, and transmit the speed reduction to the output gear 33.

<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 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.

The cylindrical linear motion part 21 is supported in the 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. The outer peripheral surface of the linear motion part 21 is coated with a lubricating oil for lubricating the sliding guide surface. A boot 61 is provided between the housing 20 and the outboard end of the linear motion part 21. The inner peripheral surface of the linear motion part 21 is provided with a helical projection that protrudes a predetermined distance radially inward and is formed in a helical shape. A number of planetary rollers 49 mesh with this helical projection.

A support member 35 is provided at one axial end 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 surface of the inner ring of these rolling bearings 36. The rotating shaft 34 is rotatably supported by the support member 35 via the plurality of rolling bearings 36.

A carrier 40 that can rotate around the rotation axis 34 is provided on the inner circumference of the linear motion section 21. The carrier 40 has a pair of disks that are arranged facing each other in the axial direction. Of these disks, the disk closest to the support member 35 is called the inner disk, and the other disk is called the outer disk. On the side of the outer disk facing the inner disk, multiple pillar members are provided 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 multiple pillar members.

The inner disk is rotatably supported on the rotating shaft 34 by a plain bearing 44b fitted between the inner disk and the rotating shaft 34. The outer disk has a shaft insertion hole formed in the center, into which a plain bearing 44a is fitted. The outer disk is rotatably supported on the rotating shaft 34 by the plain bearing 44a. Restraint sections 4 and 5 are provided on both axial ends of the rotating shaft 34 to restrain the axial position of the rotating shaft 34 and carrier 40 relative to the support member 35.

A plurality of roller shafts 47 are provided on the carrier 40 at intervals in the circumferential direction. Both ends of each roller shaft 47 in the axial direction are supported across the inner disk and the outer disk. Both disks each have a plurality of shaft insertion holes formed therein. Each shaft insertion hole consists of a long 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 movable in the radial direction within the range of each shaft insertion hole. Elastic rings 50 that bias the roller shafts 47 inward in the radial direction are stretched between both ends of the plurality of roller shafts 47 in the axial direction.

Planetary rollers 49 are supported rotatably 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.

<Means for reducing contact surface pressure>
3A, the linear actuator 1 is provided with a contact pressure reducing means 6 that reduces 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 from coming into contact with the linear moving part 21. The contact pressure reducing means 6 includes first and second reduced diameter parts 6A and 6B.

The first diameter-reducing portion 6A has a tapered shape that decreases in diameter in the radial direction toward the proximal end surface 21a of the linear motion portion 21 at the base end in the axial direction on the outer peripheral surface of the linear motion portion 21. and extends a predetermined length L1 in the axial direction. The second diameter-reducing portion 6B is a tapered portion whose diameter decreases inward in the radial direction toward the end surface 21b on the distal end side of the linear motion portion 21 at the axially distal end portion of the outer circumferential surface of the linear motion portion 21. It extends a predetermined length L2 in the axial direction. The degree of taper and axial dimension of each reduced diameter portion 6A, 6B are determined by, for example, a test or simulation.

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 housed in the cylinder chamber 20a and is not braking the brake rotor 10 (Figure 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 reduced diameter portion 6A, 6B are smoothly connected to each other without any steps.

As shown in FIG. 3B, when the linear motion part 21 is advanced to the outboard side OS to brake the brake rotor 10 (FIG. 1) and the caliper 11 (FIG. 1) is elastically deformed by the reaction force, the first and second reduced diameter parts 6A and 6B can prevent contact between the cylinder inner diameter and the linear motion part 21 or reduce the contact surface pressure even if contact occurs at the contact part A1.

<Effect>
According to the electric brake device described above, since the contact surface pressure reduction means 6 is provided, when the housing 20 is elastically deformed or when the linear motion section 21 is tilted due to an uneven load, the housing 20 and the linear motion section 21 come into contact with each other. It is possible to avoid this, or to reduce the contact surface pressure even when the housing 20 and the linear motion part 21 come into contact with each other. This can prevent abrasive wear of the sliding surfaces or sticking of the sliding surfaces to each other.

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.

<About other embodiments>
In the following description, parts corresponding to those previously described in each embodiment are given the same reference numerals, and redundant description will be omitted. When only a part of the configuration is described, other parts of the configuration are the same as those of the previously described embodiment unless otherwise specified. Identical configurations produce the same effects. It is not only possible to combine the parts specifically described in each embodiment, but also to partially combine the embodiments, as long as the combination does not cause any problems.

[Second embodiment: FIG. 4A, FIG. 4B]
As shown in FIGS. 4A and 4B, the first and second reduced diameter portions 6A and 6B may have a crowned shape that reduces in diameter toward the corresponding end surfaces 21a and 21b. The crowning shape may be a single circular arc or a crowning connecting multiple circular arcs, or may be a logarithmic crowning. When the reduced diameter portions 6A and 6B have a crowning shape, the contact surface pressure can be reduced more accurately than when they have a tapered shape. Other effects similar to those of the above-described embodiment are achieved.

[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.

[Fourth embodiment: FIG. 6]
As shown in FIG. 6, the contact surface pressure reducing means 6 includes 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. It may be. The elastic body Db is an annular body with a rectangular cross section provided at the tip end in the axial direction of the cylinder chamber 20a, and is made of rubber, resin, or metal having a lower hardness than the outer peripheral surface of the linear motion part. In a state where the elastic body Db is 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 axially distal end of the outer circumferential surface of the linear motion part 21. This axial end portion is cylindrical.

By guiding the linear motion part 21 by the elastic body Db, 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, the contact surface pressure can be more reliably reduced between the elastic body Db and the first reduced diameter part 6A of the linear motion part 20.

[Reference proposal example: Figure 7]
As shown in FIG. 7, the contact surface pressure reducing means 6 may consist only of an elastic body Db provided in the cylinder chamber 20a. This elastic body Db has the same configuration as the elastic body Db (FIG. 6) in the fourth embodiment. Also in this case, since the linear motion part 21 is guided by the elastic body Db, 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 is avoided. Alternatively, even if the housing 20 and the linear motion part 21 come into contact, the contact surface pressure can be reduced. Further, since the diameter-reduced portion of the linear motion portion 21 can be omitted, the structure can be simplified and costs can be reduced compared to the fourth embodiment.

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 crowning shape and a tapered shape, and at least one of the reduced diameter portions and the enlarged diameter portion of the cylinder chamber may be formed in a crowning shape and a tapered shape.

Although the embodiments of the present invention have been described above, the embodiments disclosed herein are illustrative in all respects and are not restrictive. The scope of the present invention is indicated by the claims rather than the above description, and is intended to include all modifications within the meaning and scope of the claims.

DESCRIPTION OF SYMBOLS 1... Direct-acting actuator, 2... Direct-acting mechanism, 6... Contact surface pressure reduction means, 6A... First reduced diameter part, 6B... Second reduced diameter part, 10... Brake rotor, 13, 14... Friction pad, 20... Housing, 20a... Cylinder chamber, 20aa... Expanded diameter part, 21... Linear motion part, 24... Electric motor (rotary drive source), 30... Reduction mechanism, Db... Elastic body

Claims (10)

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,
A linear 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. The linear actuator according to claim 1, further comprising a deceleration mechanism that decelerates the rotation of the rotary drive source, wherein the linear motion mechanism converts rotational motion output from the deceleration mechanism into linear motion. The linear motion actuator according to claim 1 or 2, wherein the linear motion section is provided in a cylindrical shape, and the linear motion section is arranged in a cylinder chamber formed in the housing in an axial direction of the linear motion section. The contact surface pressure reducing means is slidably supported along the outer peripheral surface of the linear motion section at least at the proximal end in the axial direction and radially inwardly toward the proximal end surface of the translation section. A direct-acting actuator that includes a diameter-reducing section that reduces its diameter. In the linear actuator according to claim 3, the contact surface pressure reducing means includes a tapered portion that reduces inwardly in diameter at the axial tip of the outer peripheral surface of the linear part as it approaches the end face on the tip side of the linear part. In the linear actuator according to claim 3 or 4, the contact surface pressure reducing means includes an expanding portion that expands radially outward at the axial end of the cylinder chamber toward the open end of the cylinder chamber. The linear actuator according to any one of claims 3 to 5, wherein the contact surface pressure reducing means includes an elastic body provided at an axial end portion of the cylinder chamber. 7. The linear actuator according to claim 6, wherein the elastic body is made of rubber, resin, or metal having a lower hardness than the outer peripheral surface of the linear moving part. The linear actuator according to any one of claims 3 to 7, wherein the diameter reducing portion has a tapered shape or a crowning shape whose diameter decreases toward the end face. The linear actuator according to any one of claims 1 to 8, wherein the rotary drive source is an electric motor. An electric brake device comprising the linear actuator according to claim 9, a brake rotor, and a friction pad that contacts the brake rotor to generate a braking force, and in which the linear part of the linear actuator brings the friction pad into contact with and separates it from the brake rotor.

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