Electric actuator and drum brake for vehicle equipped with the same

Abstract

An electric actuator has an electric motor capable of forward and reverse rotation, a motion conversion mechanism that converts rotation of the electric motor into reciprocating linear motion of a threaded shaft, an actuator housing that houses the electric motor and the motion conversion mechanism, and a protective cover that covers a portion of the threaded shaft that extends outward from the actuator housing. A ventilation hole is formed in the actuator housing to ventilate a sealed space inside the actuator housing and inside the protective cover. A moisture-permeable waterproof member that allows air to pass in and out and prevents water from passing in and out is provided at the ventilation hole. A cover member that can cover the ventilation hole in communication with the outside air is provided. This does not result in an increase in the number of parts, a complication of the structure, and a rise in cost. The internal pressure of the actuator can be controlled by a simple structure to improve the durability of the protective cover.

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, and a drum brake for a vehicle provided with the electric actuator. BACKGROUND

[0002] The electric actuator is configured 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. If the nut of the motion conversion mechanism is rotated forward and reverse by the electric motor, the threaded shaft that is inserted through the nut is screwed in and out in a manner that enables reciprocating linear motion. Such an electric actuator is used, for example, in an electric parking brake device of a drum brake for a vehicle (see, for example, Patent Literature 1).

[0003] In the electric parking brake device provided with the electric actuator, if the parking brake lever inside the drum brake is moved from the release position to the working position by the reciprocating linear motion of the threaded shaft of the electric actuator via a traction mechanism, 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 generated therebetween, the rotation of the wheel is braked and the vehicle becomes in a parking brake state. Also, if the electric motor of the electric actuator is reversed from the parking 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 parking brake state of the vehicle is released.

[0004] However, in the electric actuator, although the electric motor and the motion conversion mechanism are housed in a sealed space inside the actuator housing, the portion of the threaded shaft of the motion conversion mechanism that extends outside the actuator housing is covered by a stretchable bellows-shaped protective cover.

[0005] Also, in the electric actuator, if the threaded shaft of the motion conversion mechanism performs reciprocating linear motion as described above, the volume of the sealed space inside the actuator housing changes and a pressure difference is generated. That is, if the threaded shaft advances from the operating position to the release position and the protective cover elongates, the volume of the sealed space increases and a negative pressure is generated in the sealed space, and due to this negative pressure, the protective cover is concave. On the other hand, if the threaded shaft retreats from the release position to the operating position and the protective cover contracts, the volume of the sealed space decreases and a positive pressure is generated in the sealed space, and due to this positive pressure, the protective cover is convex. If such concave and convex of the protective cover repeats, the protective cover is subjected to an overload and a problem of reduced durability occurs. Note that the concave and convex of the protective cover occurs not only due to the increase and decrease of the volume of the sealed space caused by the reciprocating linear motion of the threaded shaft as described above, but also due to changes in the altitude (air pressure) and air temperature at which the electric actuator is disposed.

[0006] Therefore, in Patent Literature 2, a mechanism (ventilation mechanism) is proposed in which a ventilation unit is installed to a gear housing that defines a sealed space together with a motor housing, and the sealed space is communicated with the atmosphere by the ventilation unit and an air flow path formed between the motor housing and the gear housing and a ventilation hole formed through a partition wall of the motor housing, whereby the internal pressure of the sealed space is regulated.

[0007] Prior Art Documents

[0008] Patent Literature

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

[0010] Patent Literature 2: Japanese Patent Application Laid-Open (JP A) No. 2020-003034 SUMMARY

[0011] PROBLEMS TO BE SOLVED BY THE INVENTION

[0012] However, in the structure proposed in Patent Literature 2, the ventilation hole needs to be formed in the partition wall of the motor housing, and the air flow path needs to be formed between the motor housing and the gear housing, and in addition, the extra ventilation unit needs to be installed to the gear housing, and therefore, there is a problem that the number of parts increases, the structure is complicated, and the cost rises.

[0013] The present application has been made in view of the above problems, and it is an object to provide an electric actuator in which the number of parts does not increase, the structure is not complicated, and the cost does not rise, and in which the durability of a protective cover is improved by suppressing the change in the internal pressure of the actuator by a simple structure, and a drum brake for vehicle provided with the electric actuator.

[0014] TECHNICAL SOLUTION FOR SOLVING THE PROBLEMS

[0015] To achieve the above object, a first feature of the present application is an electric actuator provided with an electric motor capable of forward and reverse rotation, a motion conversion mechanism that converts the rotation of the electric motor into reciprocating linear motion of a threaded shaft, an actuator housing that houses the electric motor and the motion conversion mechanism, and a protective cover that covers the portion of the threaded shaft that extends outside the actuator housing, wherein a ventilation hole that ventilates the sealed space inside the actuator housing and the protective cover is formed in the actuator housing, a moisture-permeable and water-resistant member that allows the entry and exit of air and prevents the entry of water is provided to the ventilation hole, and a cover member that can ventilate the ventilation hole with the outside air is provided.

[0016] On the basis of the first feature, a second feature of the present application is that the actuator housing has a first housing that houses the electric motor and a second housing that houses the motion conversion mechanism, and the vent hole is formed in the vicinity of the threaded shaft of the second housing.

[0017] On the basis of the first or second feature, a third feature of the present application is that the moisture-permeable waterproof member is provided on the side of the closed space of the vent hole, and a filter is provided on the side of the cover member of the vent hole.

[0018] On the basis of the third feature, a fourth feature of the present application is that at least one of the moisture-permeable waterproof member and the filter is fixed to the vent hole by heat welding.

[0019] A fifth feature of the present application is that the electric actuator described in any one of the first to fourth features is used to expand / contract a brake shoe provided on a base plate, so that the brake shoe presses / releases the inner periphery of a brake drum that rotates together with a wheel, thereby generating / releasing a required braking force, and the cover member is a mounting cylinder portion for fixing the electric actuator to the base plate.

[0020] On the basis of the fifth feature, a sixth feature of the present application is that the mounting cylinder portion is integrally formed in the base plate, and the portion of the threaded shaft that extends outside the actuator housing is inserted into the mounting cylinder portion, thereby fixing the electric actuator to the base plate.

[0021] On the basis of the fifth feature, a seventh feature of the present application is that the mounting cylinder portion is mounted to the base plate via a mounting member that is fixed to the base plate, and the portion of the threaded shaft that extends outside the actuator housing is inserted into the mounting cylinder portion, thereby fixing the electric actuator to the base plate.

[0022] On the basis of the seventh feature, an eighth feature of the present application is that the mounting cylinder portion is a cylindrical member, and a discharge port is formed in the vicinity of the lowermost portion thereof.

[0023] Effects of the Invention

[0024] According to the first feature of the present application, the closed space in the actuator housing and the protective cover is communicated with the atmosphere only by a simple structure of forming a vent hole in the actuator housing, so that the internal pressure change of the closed space due to the sliding, elevation, and temperature change of the threaded shaft is suppressed. Therefore, the increase in the number of parts, the complication of the structure, and the cost increase accompanying the same are not caused, and the depression and expansion of the protective cover can be suppressed by a simple structure to achieve the improvement in the durability thereof. Further, by the moisture-permeable waterproof member provided in the vent hole, the intrusion of water from the vent hole into the closed space can be reliably prevented, and the high operation stability of the electric actuator is ensured. In addition, by the cover member covering the vent hole, the vent hole is not exposed to the atmosphere, so that the intrusion of foreign matter from the outside can be suppressed.

[0025] According to the second feature of the present application, since the vent hole is formed in the vicinity of the threaded shaft of the first housing of the actuator, the pressure change in the protective cover accompanying the sliding of the threaded shaft can be effectively suppressed, and the improvement in the durability and the sealing property of the protective cover can be achieved.

[0026] According to the third feature of the present application, since the moisture-permeable waterproof member is provided on the closed space side of the vent hole, and the filter is provided on the cover member side of the vent hole, the foreign matter contained in the outside air is removed by the filter, and the clogging of the moisture-permeable waterproof member due to the foreign matter can be prevented. Therefore, the function of the moisture-permeable waterproof member is not impaired, and the high performance thereof can be stably maintained.

[0027] According to the fourth feature of the present application, at least one of the moisture-permeable waterproof member and the filter can be easily fixed by heat fusion.

[0028] According to the fifth feature of the present application, since the mounting cylinder portion for fixing the electric actuator to the floor panel of the drum brake of a vehicle is used as the cover member, the number of parts can be reduced to achieve the weight reduction and the cost reduction.

[0029] According to the sixth feature of the present application, the electric actuator can be simply mounted to the drum brake of a vehicle by the mounting cylinder portion formed integrally with the floor panel. Further, since the portion of the threaded shaft extending outward of the actuator housing is inserted into the mounting cylinder portion, the protective cover covering the portion of the threaded shaft extending outward of the actuator housing is protected by the mounting cylinder portion, and the damage of the protective cover due to external force can be prevented to improve the durability thereof.

[0030] According to a seventh feature of the present application, the electric actuator is attached to the floor panel by the attachment cylinder portion which is formed separately from the floor panel, so that the attachment position of the electric actuator can be easily changed. Also, since the portion of the threaded shaft which extends outward of the actuator housing is inserted into the attachment cylinder portion, the protective cover which covers the portion of the threaded shaft which extends outward of the actuator housing is protected by the attachment cylinder portion, so that the durability of the protective cover can be improved by preventing damage to the protective cover caused by external forces.

[0031] According to an eighth feature of the present application, since the discharge port is formed near the lowermost portion of the cylindrical member, i.e., the attachment cylinder portion, the ventilation of the attachment portion can be performed well via the discharge port, and water or the like which has penetrated into the attachment portion can be discharged to the outside from the discharge port. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a front view of a key portion of a drum brake for a vehicle according to the present application. Figure 2 is a perspective view of a key portion of a drum brake for a vehicle according to the present application. Figure 3 is a front view of a key portion of a drum brake for a vehicle according to the present application. Figure 1 is a sectional view taken along line 3-3 of Figure 4 is a sectional view of a drum brake for a vehicle according to another aspect of the present application. Figure 5 is a perspective view of an electric actuator according to the present application. Figure 6 is a horizontal sectional view showing a state when a threaded shaft of an electric actuator according to the present application is advanced. Figure 7 is a horizontal sectional view showing a state when a threaded shaft of an electric actuator according to the present application is retracted. Figure 6 is an enlarged view of a detail of Figure 8 is a horizontal sectional view showing a state when a threaded shaft of an electric actuator according to the present application is retracted.

[0033] REFERENCE NUMERALS

[0034] 1 electric actuator;

[0035] 2 electric motor;

[0036] 2a output shaft of the electric motor;

[0037] 3 threaded shaft;

[0038] 4 motion conversion mechanism;

[0039] 5 transmission mechanism;

[0040] 8 nut;

[0041] 10 actuator housing;

[0042] 11 housing body;

[0043] 11A first housing of the housing body;

[0044] 11B The second shell of the shell body;

[0045] 15. Protective shield;

[0046] 22. Install the cylinder section (cover component);

[0047] 22a The discharge port of the installed cylinder;

[0048] 29. Vent holes;

[0049] 30. Drum brakes for vehicles;

[0050] 31. Base plate;

[0051] 32 Mounting brackets (mounting components);

[0052] 40 moisture-permeable and waterproof components;

[0053] 41. Filter. Detailed Implementation

[0054] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0055] [Drum Brakes for Vehicles] First, based on Figures 1 to 3 The general configuration of the vehicle drum brake of the present invention will be described. Figure 1 This is a front view of a key component of the vehicle drum brake of the present invention. Figure 2 This is a 3D view of key components of the drum brake system used in this vehicle. Figure 3 yes Figure 1 3-3 line section view.

[0056] The vehicle drum brake 30 of the present invention is provided on each wheel of a vehicle, and includes an electric parking brake device for electrically locking the rotation of the wheels when the vehicle is parked.

[0057] The vehicle drum brake 30 has a disc-shaped base plate 31 fixed to the side of the vehicle body, and a circular hole 31a (not shown) is formed in the center of the base plate 31 for an axle to pass through. Furthermore, although not shown, on the back side of the base plate 31... Figure 1 The device comprises, on the inner side of the paper (vertical direction), a pair of arc-shaped (bow-shaped) brake shoes that can contact and separate from the inner circumferential surface of the brake drum, which rotates together with the wheel; a rotatable parking brake lever that expands these brake shoes and presses them against the inner circumferential surface of the brake drum by the action of the electric actuator 1 of the present invention; a return spring that forces the pair of brake shoes toward the closing direction (the direction away from the inner circumferential surface of the brake drum); a wheel cylinder that presses the pair of brake shoes against the inner circumferential surface of the brake drum by hydraulic pressure generated in the master cylinder when the brake pedal is operated; and an automatic adjuster for automatically adjusting the radial clearance between the brake shoes and the brake drum.

[0058] However, the electric actuator 1 used to drive the electric parking brake is mounted at an angle to the upper front of the base plate 31 via a mounting sleeve 22 that engages with the mounting bracket 32. Specifically, the electric actuator 1 is mounted on a threaded shaft 3 (see reference 3). Figure 3 The extension end (front end) of the actuator is installed in a downward inclined state. It should be noted that the mounting cylinder 22 also functions as a cover component that covers the vent hole 29 of the electric actuator 1.

[0059] Here, the mounting bracket 32 ​​is a sheet metal component that is separate from the base plate 31, such as Figure 1 and Figure 2 As shown, it is mounted on the surface of the base plate 31 at three points by double-ended bolts 33 and nuts 34 that engage with the double-ended bolts. It should be noted that the retaining ring 21 of the electric actuator 1, which is rolled around the outer periphery of its actuator housing 10, engages with the mounting cylinder 22, and the mounting cylinder 22 is mounted and supported in a state of accurate positioning on the mounting bracket 32.

[0060] like Figure 3 As shown, although the portion of the threaded shaft 3 of the electric actuator 1 extending outwards from the actuator housing 10 is covered by a retractable, serpentine protective cover 15 made of a soft and elastic rubber material, this protective cover 15 is covered by a mounting cylinder 22 that is welded to the mounting bracket 32. Therefore, a portion of the threaded shaft 3 and the protective cover 15 are inserted into the interior of the mounting cylinder 22. Here, one end of the mounting cylinder 22 in the longitudinal direction is mounted to the end of the actuator housing 10 and extends along the threaded shaft 3, while a cylindrical plug 23 is installed at the opening at the other end in the longitudinal direction. Furthermore, when the electric actuator 1 is mounted on the base plate 31, as... Figure 2 As shown, a circular outlet 22a is formed near the lowermost end of the mounting cylinder 22.

[0061] It should be noted that in this embodiment, since the mounting cylinder 22 and the mounting bracket 32 ​​are separately constructed from the base plate 31, and the mounting bracket 32 ​​is mounted on the front of the base plate 31 by multiple (three of each in this embodiment) double-ended bolts 33 and nuts 34, although the mounting position of the electric actuator 1 on the base plate 31 can be easily changed, if... Figure 4 As shown, the mounting cylinder 22 can also be integrally formed with the base plate 31. This structure reduces the number of parts and assembly time, thereby reducing the cost of the electric parking brake device.

[0062] However, as Figure 3 As shown, a flexible tube 24 is inserted into and fixed at one end of the plug 23. The tube 24 extends obliquely downward from the plug 23 and then bends in a U-shape. The other end is as shown... Figure 1 and Figure 2As shown, connector 25 is inserted into and fixed to the lower front of base plate 31. Here, as... Figure 1 and Figure 2 As shown, the connector 25 is mounted on the lower front of the base plate 31 by two double-ended bolts 37 and two nuts 38 that engage with the double-ended bolts.

[0063] In addition, such as Figure 3 As shown, one end of a brake cable 26 is mounted on the front end of the threaded shaft 3 of the electric actuator 1 via a connector 27. Specifically, the connector 27 is secured by a pin 28 inserted into a through-hole 3a at the front end of the threaded shaft 3, and one end of the brake cable 26 is inserted into and secured to this connector 27. Here, the brake cable 26 is inserted into and passes through a tube 24, and its other end is connected to one end of a parking brake lever (not shown) assembled on the rear side of the base plate 31.

[0064] [Electric Actuator]

[0065] Next, based on Figures 5 to 8 The details of the structure and function of the vehicle drum brake 1 of the present invention will be described.

[0066] Figure 5 This is a perspective view of the electric actuator of the present invention. Figure 6 This is a horizontal sectional view showing the state of the threaded shaft of the electric actuator as it advances. Figure 7 yes Figure 6 7 detailed enlarged images, Figure 8 This is a horizontal sectional view showing the state of the threaded shaft of the electric actuator of the present invention when it is retracted. It should be noted that in the following description, [the following will be used to describe the state of the threaded shaft]. Figure 5 , Figure 6 as well as Figure 8 The arrows shown indicate the "front and back" direction.

[0067] The electric actuator 1 in this embodiment is as follows: Figure 1 and Figure 2 The actuator of the electric parking brake device provided with the vehicle drum brake 30 shown is used, such as... Figure 6 As shown, the actuator housing 10 includes an electric motor 2, a motion conversion mechanism 4 that converts the rotation of the electric motor 2 into the reciprocating linear motion of the threaded shaft 3, and a transmission mechanism 5 for transmitting the rotational motion of the electric motor 2 to the conversion mechanism 4. The electric motor 2, the motion conversion mechanism 4, and the transmission mechanism 5 are housed within the actuator housing 10.

[0068] The aforementioned actuator housing 10 comprises a housing body 11 integrally having a cylindrical first housing 11A and a second housing 11B, a motor cover 12 covering the open end of the first housing 11A of the housing body 11, and a side opposite to the motor cover 12 (Figure 6 The gear cover 13 (located on the rear side) covers the opening end of the housing body 11.

[0069] Moreover, such as Figure 6 As shown, an electric motor 2 is housed in the first housing 11A of the housing body 11, and an electric motor 2 is located at the rear of the electric motor 2. Figure 6 A small-diameter drive gear 6 is mounted on the end (rear end) of the output shaft (motor shaft) 2a extending from the rear of the motor 2 and facing the inside of the gear cover 13. Here, one axial end (front end) of the electric motor 2 is fitted and held in the recess 12a formed in the motor cover 12, and the other axial end (rear end) of the electric motor 2 is fitted and held in the circular hole 11b formed in the end wall 11a of the first housing 11A. It should be noted that the output shaft (motor shaft) 2a of the electric motor 2 is rotatably supported in the first housing 11A via a bearing 7.

[0070] Furthermore, the second housing 11B of the housing body 11 is integrally disposed on the side of the first housing 11A, and a motion conversion mechanism 4 is housed in the second housing 11B. The motion conversion mechanism 4 has a rotatable nut 8 and a threaded shaft 3 that is screwed into the nut 8 and capable of reciprocating linear movement.

[0071] The nut 8 integrally comprises a sleeve portion 8A and a cylindrical portion 8B with a larger diameter than the sleeve portion 8A. It is rotatably supported on the second housing 11B by a radial bearing (ball bearing) 9 assembled on the outer periphery of the sleeve portion 8A. Here, an internal thread 8a is helically engraved on the inner periphery of the sleeve portion 8A.

[0072] The threaded shaft 3 is a long, cylindrical sliding component, such as... Figure 3 As shown, one end of the brake cable 26 is connected to its front end via connector 27. Additionally, 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, which is 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.

[0073] Furthermore, an external thread 3b is spirally engraved on the outer periphery of the threaded shaft 3 within a specified range. The threaded shaft 3 can be screwed into the sleeve portion 8A of the nut 8 in an advancing and retracting manner. In the insertion portion 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.

[0074] In addition, the portion of the threaded shaft 3 extending outward toward the actuator housing 10 is covered by a serpentine protective cover 15 as described above. 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) is fitted into the outer periphery of the cylindrical portion 11c integrally protruding from the second housing 11B of the actuator housing 10.

[0075] However, in this embodiment, such as Figure 5 and Figure 6 As shown, a vent hole 29, serving as a ventilation mechanism, is formed near the threaded shaft 3 of the second housing 11B of the actuator housing 10 to allow ventilation of the sealed space within the actuator housing 10 and the protective cover 15. More specifically, although the second housing 11B has an end wall 11d through which the threaded shaft 3 passes, a circular vent hole 29 is formed near the threaded shaft 3 in this end wall 11d. Furthermore, as... Figure 7 As shown in detail, on the inner space side of the vent 29 ( Figure 7 A breathable and waterproof component 40 is installed on the right side of the vent 29, in the external space side. Figure 7 A filter 41 is installed on the left side. Here, the breathable and waterproof component 40 has the function of allowing air while preventing water from entering or leaving the sealed space inside the actuator housing 10 and the protective cover 15. In this embodiment, the breathable and waterproof component 40 and the filter 41 are fixed to the vent hole 29 of the end wall 11d of the second housing 11B by heat fusion. It should be noted that although both the breathable and waterproof component 40 and the filter 41 are fixed by heat fusion in this embodiment, either one can be fixed by heat fusion, and it is not limited to this embodiment. Moreover, in this embodiment, a structure is adopted in which the mounting cylinder 22 covers the vent hole 29 formed in the actuator housing 11B.

[0076] In addition, such as Figure 6 As shown, multiple disc springs 16 are stacked in the axial space between the cylindrical portion 8B of the nut 8 and the flange portion 3A of the threaded shaft 3. 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 to the threaded shaft 3 in the direction away from the nut 8 (rearward).

[0077] Here, based on Figure 6 The structure of transmission mechanism 5 will be described.

[0078] 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.

[0079] The aforementioned intermediate gear 19 is rotatably supported on a support shaft 18 erected 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, but 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.

[0080] Furthermore, the electric actuator 1 configured as described above is used as the actuator of the electric parking brake device as previously stated, and the function of the electric actuator 1 will be explained below.

[0081] Figure 6 The indicated state is that the threaded shaft 3 is advancing and the brake cable 26 installed at the front end of the threaded shaft 3 (see reference) Figure 3 The relaxed state, in this state Figure 1 and Figure 2 The brake shoes of the drum brake 30 shown are separated from the inner circumferential surface of the brake drum. Therefore, no frictional resistance is generated between the brake shoes and the brake drum, and the electric parking brake device is in the parking brake released state.

[0082] 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 starts. 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.

[0083] 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. Then, 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.

[0084] As described above, if nut 8 rotates, the threaded shaft 3 connected to nut 8 will engage as follows: Figure 8 As shown, it moves in a straight line and then backwards, with the brake cable 26 (see reference) mounted on the top of the threaded shaft 3. Figure 3 The brake lever of the electric parking brake is pulled. The brake cable 26 pulls the brake shoe, causing it to open 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, thus putting the vehicle in a parking brake state.

[0085] As described above, if the threaded shaft 3 retreats as shown in FIG. 6, the threaded shaft 3 intrudes into the closed space within the actuator housing 10 and the protective cover 15. Here, in the case where the end wall lid of the second housing 1 IB is not formed with the vent hole 29, the volume of the closed space decreases by an amount corresponding to the volume of the intrusion of the threaded shaft 3, and thus the air within the closed space is compressed and the internal pressure of the closed space becomes positive, and as described above, due to this positive pressure, the protective cover 15 expands and various malfunctions occur. Figure 8

[0086] However, in the present embodiment, since the vent hole 29 as the vent mechanism is formed in the end wall lid of the second housing 1 IB, the air (internal air) within the closed space is discharged to the outside from the vent hole 29 as shown by the solid arrows in FIG. 7. As a result, the internal pressure of the closed space is maintained to be approximately atmospheric pressure, and the protective cover 15 does not malfunction by expanding, etc. Note that the change in the internal pressure due to changes in altitude, air temperature, etc. can be suppressed regardless of the reciprocating linear motion of the threaded shaft 3. Figure 7

[0087] Next, if the not-shown parking brake switch is operated to be in the off state in order to release the above-described parking lock state, the electric motor 2 is reversed, the rotation of the output shaft 2a thereof is transmitted to the nut 8 of the motion conversion mechanism 4 via the same transmission path as described above, and thus the nut 8 is reversed. If the nut 8 is reversed in this way, the threaded shaft 3 screwed into the nut 8 moves linearly and advances, and the electric actuator 1 returns to the state shown in FIG. 5, and thus the parking brake of the electric parking brake device is released. Figure 6

[0088] As described above, if the threaded shaft 3 advances as shown in FIG. 5, since the threaded shaft 3 exits from the closed space within the actuator housing 10 and the protective cover 15, the internal pressure of the closed space decreases by an amount corresponding to the volume of the exit of the threaded shaft 3. Here, in the case where the end wall lid of the second housing 1 IB is not formed with the vent hole 29, the volume of the closed space increases by an amount corresponding to the volume of the exit of the threaded shaft 3, and thus the air within the closed space expands and the internal pressure of the closed space becomes negative, and as described above, due to this negative pressure, the protective cover 15 is depressed and various malfunctions occur. Figure 6

[0089] However, in the present embodiment, since the vent hole 29 is formed in the end wall lid of the second housing 1 IB, the external air expands as shown by the dashed arrows in FIG. 6, and thus the internal pressure of the closed space is maintained to be approximately atmospheric pressure, and the protective cover 15 does not malfunction by being depressed, etc. Note that the change in the internal pressure due to changes in altitude, air temperature, etc. can be suppressed regardless of the reciprocating linear motion of the threaded shaft 3. Figure 7 ​​​​The outside air flows into the closed space from the vent hole 29 as indicated by the dotted arrows. As a result, the internal pressure of the closed space is maintained at approximately atmospheric pressure, and the boot 15 does not malfunction, such as being dented. Note that in this case, the outside air flows into the closed space through the filter 41 and the moisture-permeable waterproof member 40, so foreign matter contained in the outside air is removed by the filter 41, and the moisture-permeable waterproof member 40 is not clogged by foreign matter, and the function of the moisture-permeable waterproof member 40 is not impaired. Also, since the infiltration of moisture contained in the outside air into the closed space is prevented by the moisture-permeable waterproof member 40, the function of the electric motor 2, the motion conversion mechanism 4, the transmission mechanism 5, and the like housed in the closed space is not impaired by moisture, and the motion stability is improved. Also, by providing the cover member, i.e., the cylindrical mounting cylinder portion 22, which covers the vent hole 29, the vent hole 29 is not exposed to the atmosphere, and the intrusion of foreign matter from the outside can be suppressed.

[0090] As described above, in the present embodiment, the closed space inside the actuator housing 20 and the boot 15 is communicated with the atmosphere by a simple structure in which the vent hole 29 is formed in the second housing 1 IB of the actuator housing 10, so the internal pressure change of the closed space caused by the sliding of the threaded shaft 3 can be suppressed. Thus, the increase in the number of parts, the complication of the structure, and the cost increase accompanying the same are not caused, and the expansion and contraction of the boot 15 can be suppressed by a simple structure, so the improvement in the durability of the boot 15 can be achieved. In particular, in the present embodiment, since the vent hole 29 is formed in the vicinity of the threaded shaft 3 of the second housing 1 IB, the pressure change in the boot 15 accompanying the sliding of the threaded shaft 3 can be effectively suppressed, and the improvement in the durability and the sealing property of the boot 15 can be achieved. In this way, the structure simplification, the cost reduction, and the improvement in the durability of the electric actuator 1 can be achieved, and as a result, the structure simplification, the cost reduction, the improvement in the durability, and the motion stability of the drum brake 30 for a vehicle provided with the electric actuator 1 can be achieved.

[0091] Also, since the infiltration of water into the closed space from the vent hole 29 can be reliably prevented by the moisture-permeable waterproof member 40 provided at the vent hole 29, the electric actuator 1 can be ensured to have high motion stability. Also, in the present embodiment, since the moisture-permeable waterproof member 40 is provided on the inside space side of the vent hole 29, and the filter 41 is provided on the outside space side of the vent hole, foreign matter contained in the outside air is removed by the filter 41, and the moisture-permeable waterproof member 40 can be prevented from being clogged by foreign matter. Also, in the present embodiment, the moisture-permeable waterproof member 40 and the filter 41 can be easily fixed by heat fusion.

[0092] Also, in the present embodiment, as described above, Figure 2As shown, since the discharge port 22a is formed near the lowermost portion of the mounting cylinder portion 22, the ventilation in the mounting cylinder portion 22 can be performed well via the discharge port 22a, and water or the like immersed in the mounting cylinder portion 22 can be discharged to the outside from the discharge port 22a.

[0093] In addition, since the portion of the threaded shaft 3 extending outside the actuator housing 10 is inserted into the mounting cylinder portion 22, the protective cover 15 covering the portion of the threaded shaft 3 extending outside the actuator housing 10 is protected by the mounting cylinder portion 22, and damage of the protective cover 15 caused by external force can be prevented, thereby improving the durability thereof.

[0094] Note that the above describes the application of the electric actuator of the present application to the electric parking brake device for the drum brake of the vehicle, but the electric actuator of the present application can also be applied to electric actuators used in other arbitrary devices.

[0095] In addition, the application of the present application is not limited to the above-described embodiments, and it is obvious that various modifications can be implemented within the scope of the technical idea recited in the claims, the specification, and the drawings.

Claims

1. An electric actuator (1) having an electric motor (2) capable of forward and reverse rotation, a motion conversion mechanism (4) that converts rotation of the electric motor (2) into reciprocating linear motion of a threaded shaft (3), an actuator housing (10) that houses the electric motor (2) and the motion conversion mechanism (4), and a protective cover (15) that covers a portion of the threaded shaft (3) that extends outside the actuator housing (10), characterized in that, a vent hole (29) that performs ventilation of a sealed space inside the actuator housing (10) and inside the protective cover (15) is formed in the actuator housing (10), a moisture-permeable waterproof member (40) that allows the passage of air and prevents the passage of water is provided in the vent hole (29), and a cover member (22) that covers the vent hole (29) in a manner that allows ventilation with outside air is provided.

2. The electric actuator according to claim 1, characterized in that, the actuator housing (10) has a first housing (11A) that houses the electric motor (2) and a second housing (11B) that houses the motion conversion mechanism (4), the vent hole (29) is formed in the vicinity of the threaded shaft (3) of the second housing (11B).

3. The electric actuator according to claim 1 or 2, characterized in that, at least one of the moisture-permeable waterproof member (40) and the filter (41) is fixed to the vent hole (29) by heat welding.

4. A drum brake (30) for a vehicle having an electric actuator (1) having an electric motor (2) capable of forward and reverse rotation, a motion conversion mechanism (4) that converts rotation of the electric motor (2) into reciprocating linear motion of a threaded shaft (3), an actuator housing (10) that houses the electric motor (2) and the motion conversion mechanism (4), and a protective cover (15) that covers a portion of the threaded shaft (3) that extends outside the actuator housing (10), a vent hole (29) that performs ventilation of a sealed space inside the actuator housing (10) and inside the protective cover (15) is formed in the actuator housing (10), a moisture-permeable waterproof member (40) that allows the passage of air and prevents the passage of water is provided in the vent hole (29), and a cover member (22) that covers the vent hole (29) in a manner that allows ventilation with outside air is provided, by expanding / contracting a brake shoe provided to a base plate (31) using the electric actuator, the brake shoe is pressed against / relieved from pressing against an inner periphery of a brake drum that rotates together with a wheel, thereby generating / releasing a required braking force, the cover member (22) is a mounting cylinder portion for fixing the electric actuator (1) to the base plate (31).

5. The drum brake for a vehicle according to claim 4, characterized in that, ​ ​ ​ ​ The mounting cylinder portion (22) is formed integrally with the base plate (31), and the portion of the threaded shaft (3) extending outward of the actuator housing (10) is inserted into the mounting cylinder portion (22), thereby fixing the electric actuator (1) to the base plate (31).

6. The drum brake for a vehicle according to claim 4, characterized in that The mounting cylinder portion (22) is mounted to the base plate (31) via a mounting member (32) fixed to the base plate (31), and the portion of the threaded shaft (3) extending outward of the actuator housing (10) is inserted into the mounting cylinder portion (22), thereby fixing the electric actuator (1) to the base plate (31).

7. The drum brake for a vehicle according to claim 6, characterized in that The mounting cylinder portion (22) is a cylindrical member, and a discharge port (22a) is formed near the lowermost portion thereof.

8. The electric actuator according to claim 4, characterized in that The actuator housing (10) includes a first housing (11A) housing the electric motor (2) and a second housing (11B) housing the motion conversion mechanism (4), The vent hole (29) is formed near the threaded shaft (3) of the second housing (11B).

9. The electric actuator according to claim 4 or 8, characterized in that The moisture-permeable waterproof member (40) is provided on the side of the vent hole (29) of the sealed space, and a filter (41) is provided on the side of the vent hole (29) of the cover member (22).

10. The electric actuator according to claim 9, characterized in that At least one of the moisture-permeable waterproof member (40) and the filter (41) is fixed to the vent hole (29) by heat welding.

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