Brake device

Abstract

To obtain, as one example, a brake device which can suppress an increase of a friction force between screws which are screwed with each other, and the lowering of the mechanical rigidity and durability of a screw.SOLUTION: A brake device according to the present embodiment comprises a rotating member and a linear motion member at which male screws and female screws are arranged, and one of the rotating member and the linear motion member has a first region and a second region in which a first screw is arranged, and which are aligned in a direction along a rotating shaft. The first region has a first end and a second end which are connected to the second region, a first groove is formed at the first region, a range in which the first screw in the second region is arranged is larger than a range in which the first screw in the first region is arranged in a peripheral direction, the second screw is engaged with the first screw in the second region, the linear motion member moves in a first direction, and the second screw thereby approaches the second end.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] Embodiments of the present invention relate to a braking device.

Background Art

[0002] Conventionally, a braking device is known that converts the rotation of a rotating member driven by a motor into the linear motion of a linear member, and presses a brake pad against a brake rotor via the piston by the linear member. For example, a groove is provided in the screw of the rotating member. The groove supplies lubricating oil to the male screw and the female screw that mesh with each other, and reduces the friction between the male screw and the female screw (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the conventional configuration, the contact area between the male screw and the female screw is reduced by the groove, so that the vertical resistance per unit contact area increases. The increase in the vertical resistance may increase the frictional force between the male screw and the female screw and accelerate the wear of the screw. The dust generated by the wear may increase the coefficient of friction in the friction between the male screw and the female screw and may cause abnormal noise. Further, for the groove, for example, if the circumferential width is ensured to be large over the entire length of the screw, it is advantageous from the viewpoint of ensuring the supply amount of lubricating oil. On the other hand, there is room for improvement in terms of the increase in the frictional force between the two screws described above and the influence on the mechanical strength and durability of the screw due to the provision of the groove.

[0005] Therefore, the present invention has been made in view of the above, and provides a braking device capable of suppressing an increase in the frictional force between screws that mesh with each other and a decrease in the mechanical strength and durability of the screws.

Means for Solving the Problem

[0006] The braking device according to an embodiment of the present invention includes, as an example, a male screw and a female screw that meshes with the male screw. One of them is provided on a rotating member that is rotatable around a rotating shaft. The other of the male screw and the female screw is provided. When the rotating member rotates in a first rotation direction around the rotating shaft, it moves in a first direction along the rotating shaft. When the rotating member rotates in a second rotation direction opposite to the first rotation direction, it moves in a second direction opposite to the first direction. A linear motion member, and a piston that is pushed in the first direction by the linear motion member moving in the first direction and presses a braking member against a brake rotor by moving in the first direction. One of the rotating member and the linear motion member is provided with a first screw, which is one of the male screw and the female screw provided on the member, and has a first region and a second region arranged in a direction along the rotating shaft. The first region has a first end that is one end of the first region in the direction along the rotating shaft and is connected to the second region, and a second end that is the other end of the first region in the direction along the rotating shaft. A first groove that divides the first screw in the circumferential direction around the rotating shaft is provided in the first region. In the circumferential direction, the range where the first screw is provided in the second region is larger than the range where the first screw is provided in the first region. At least a part of the second screw, which is the other of the male screw and the female screw, in the direction along the rotating shaft meshes with the first screw in the second region. When the linear motion member moves in the first direction, the second screw approaches the second end. Therefore, as an example, when the braking member wears due to repeated braking, the position of the linear motion member moves in the first direction. When the position of the linear motion member moves in the first direction, a portion of the second screw that was located, for example, closer to the first end than the second end approaches the second end, and a portion of the second screw that was located, for example, on the side opposite to the second end than the first end meshes with the first screw in the first region. In the first region, dust generated by wear can be discharged into the first groove.Furthermore, in the second region, the contact area between the first screw and the second screw (the contact area per turn of one thread of the screw) is larger than the contact area between the first screw and the second screw in the first region (the same as above). Therefore, when at least a part of the second screw meshes with the first screw in the second region, the vertical resistance per unit contact area between the first screw and the second screw is reduced, and consequently, the frictional force between the first screw and the second screw is reduced. By reducing the frictional force between the first screw and the second screw, the wear of the first screw and the second screw is reduced. As a result, the braking device of the present embodiment can suppress an increase in the frictional force between the first screw and the second screw. In addition, as an example, in the circumferential direction, the braking device according to the embodiment of the present invention is configured such that the range in which the first screw is provided in the second region is larger than the range in which the first screw is provided in the first region. Therefore, for example, compared with a mode in which the first groove is provided in the first screw so that the first groove extends over the entire first region and the second region and the ranges in which the first screw is provided in the first region and the second region are equal in the circumferential direction, the strength and durability of the first screw can be improved by the amount by which the range in which the first screw is provided in the second region is larger than that in the first region.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

[0008] (First Embodiment) Hereinafter, the first embodiment will be described with reference to FIGS. 1 to 7. In the present specification, the components according to the embodiment and the description of the components may be described in a plurality of expressions. The components and the description thereof are merely examples and are not limited by the expressions in the present specification. The components may be specified by different names from those in the present specification. Further, the components may be described by expressions different from those in the present specification.

[0009] FIG. 1 is a cross-sectional view schematically showing a braking device 10 according to the first embodiment. As shown in FIG. 1, the braking device 10 includes a caliper 11, a brake rotor 12, a rotary-linear motion conversion mechanism 13, a rotary transmission mechanism 14, a motor 15, and an ECU 16. The rotary-linear motion conversion mechanism 13 and the rotary transmission mechanism 14 are incorporated in the caliper 11.

[0010] The braking device 10 can operate as a hydraulic brake and can also operate as an electric brake. For example, the caliper 11 constitutes a hydraulic brake, and the caliper 11, the rotary-linear motion conversion mechanism 13, the rotary transmission mechanism 14, and the motor 15 constitute an electric brake. Note that the braking device 10 may simply be an electric brake.

[0011] The electric brake is a so-called electric parking brake (EPB). That is, the braking device 10 is configured such that the braking state by the electric brake function is maintained during parking. Note that the electric brake may be activated during driving or temporary stop.

[0012] The caliper 11 has a body 21, a piston 22, two brake pads 23, and a piston seal 24. The brake pad 23 is an example of a braking member. A cylinder 25 is provided in the body 21.

[0013] The cylinder 25 is a substantially cylindrical hole extending along the central axis Ax. The central axis Ax is an example of a rotation axis. The central axis Ax in the present embodiment is the center of the cylinder 25. Note that the rotation axis is not limited to the central axis Ax of the cylinder 25.

[0014] Hereinafter, the direction along the central axis Ax is referred to as the axial direction, the direction orthogonal to the central axis Ax is referred to as the radial direction, and the direction of rotation about the central axis Ax is referred to as the circumferential direction. Further, one direction (the left direction in FIG. 1) in the axial direction of the central axis Ax is referred to as the lock direction D1, and the other direction (the right direction in FIG. 1) in the axial direction of the central axis Ax is referred to as the release direction D2. The lock direction D1 is an example of the first direction. The release direction D2 is an example of the second direction. The release direction D2 is the opposite direction of the lock direction D1.

[0015] The cylinder 25 is a bottomed cylindrical hole opened in the lock direction D1. The piston 22 is accommodated in the cylinder 25 so as to be reciprocable along the central axis Ax. A hydraulic chamber R is provided in the cylinder 25.

[0016] By the increase in the hydraulic pressure in the hydraulic chamber R, the piston 22 moves in the lock direction D1 and presses the back plate 27 of the brake pad 23, thereby pressing the lining 28 of the brake pad 23 against the brake rotor 12. Thereby, the wheel of the vehicle that rotates integrally with the brake rotor 12 is braked, and a braking state by the hydraulic brake is obtained.

[0017] The piston 22 has an outer peripheral surface 22a and an end surface 22b. The outer peripheral surface 22a is formed in a substantially cylindrical shape facing outward in the radial direction of the central axis Ax. The end surface 22b is the end surface of the piston 22 in the locking direction D1.

[0018] A recess 22c is provided in the piston 22. The recess 22c is a bottomed cylindrical hole opened in the release direction D2. That is, the recess 22c is provided on the side opposite to the outer peripheral surface 22a and the end surface 22b. The recess 22c forms a part of the hydraulic chamber R.

[0019] The outer peripheral surface 22a of the piston 22 faces the inner peripheral surface 25a of the cylinder 25. The inner peripheral surface 25a of the cylinder 25 is the inner peripheral surface of the body 21 formed in a substantially cylindrical shape facing inward in the radial direction of the central axis Ax.

[0020] A minute gap (clearance) is provided between the outer peripheral surface 22a of the piston 22 and the inner peripheral surface 25a of the cylinder 25. The outer peripheral surface 22a slides on the inner peripheral surface 25a in a state lubricated by the working fluid existing in the gap.

[0021] The piston seal 24 is interposed between the outer peripheral surface 22a of the piston 22 and the inner peripheral surface 25a of the cylinder 25, and seals the gap between the outer peripheral surface 22a and the inner peripheral surface 25a. Thereby, the piston seal 24 suppresses the leakage of the working fluid from the hydraulic chamber R through the gap.

[0022] The piston seal 24 is attached to the inner peripheral surface 25a of the cylinder 25 and is restricted from moving with respect to the body 21. Note that the piston seal 24 may be attached to the outer peripheral surface 22a of the piston 22.

[0023] The piston seal 24 has a retraction function that, as the hydraulic pressure in the hydraulic chamber R decreases, pulls the piston 22 in the release direction D2 toward the hydraulic chamber R by an elastic force, separating the end face 22b of the piston 22 from the brake pad 23. That is, as the hydraulic pressure in the hydraulic chamber R decreases and the pressing force on the back plate 27 of the piston 22 is released, the pressing of the lining 28 against the brake rotor 12 by the piston 22 is released. Thereby, a braking release state by the hydraulic brake is obtained. Thus, the caliper 11 can operate as a hydraulic brake.

[0024] The rotary-linear motion conversion mechanism 13 is provided inside the caliper 11. The rotary-linear motion conversion mechanism 13 has a rotating member 31 and a linear motion member 32. The rotating member 31 is an example of a rotating member and a member.

[0025] The rotating member 31 is supported by the body 21 so as to be rotatable about the central axis Ax. The linear motion member 32 is attached to the rotating member 31 so as to be linearly movable in the axial direction in response to the rotation of the rotating member 31.

[0026] The rotation transmission mechanism 14 is, for example, a speed reducer having a plurality of rotating elements such as gears. The rotation transmission mechanism 14 transmits the rotation of the output shaft of the motor 15 to the rotating member 31. The rotating member 31 rotates about the central axis Ax by the torque input from the rotation transmission mechanism 14.

[0027] The rotating member 31 has a coupling portion 41, a flange 42, and a shaft 43. The coupling portion 41 rotates integrally with the output shaft of the rotation transmission mechanism 14. The flange 42 is located between the coupling portion 41 and the shaft 43 and is formed in a substantially disk shape that projects radially from the coupling portion 41 and the shaft 43 in the direction of the central axis Ax.

[0028] The shaft 43 projects in the locking direction D1 from the flange 42. The shaft 43 is formed in a substantially cylindrical shape that extends axially along the central axis Ax. In the present embodiment, the central axis Ax is also the central axis of the flange 42 and the shaft 43.

[0029] A thrust bearing 44 is provided between the flange 42 and the body 21 of the caliper 11. The body 21 axially supports the rotating member 31 via the thrust bearing 44.

[0030] FIG. 2 is a cross-sectional view schematically showing the rotary-linear motion conversion mechanism 13 of the first embodiment. As shown in FIG. 2, the shaft 43 has an outer peripheral surface 43a. The outer peripheral surface 43a is a substantially cylindrical curved surface that extends in the axial direction and faces radially outward. A male screw 45 is provided on the outer peripheral surface 43a. The male screw 45 is an example of a male screw and a first screw.

[0031] The linear motion member 32 has a cylindrical portion 51 and two protrusions 52. The cylindrical portion 51 is formed in a substantially cylindrical shape that extends in the axial direction and surrounds the central axis Ax. The cylindrical portion 51 has an inner peripheral surface 51a.

[0032] The inner peripheral surface 51a is a substantially cylindrical curved surface that extends in the axial direction and faces radially inward. A female screw 53 is provided on the inner peripheral surface 51a. The female screw 53 is an example of a female screw and a second screw.

[0033] The female screw 53 meshes with the male screw 45 of the rotating member 31. In the present embodiment, in the axial direction, the length of the female screw 53 is shorter than the length of the male screw 45. The female screw 53 is closer to the end of the linear motion member 32 in the release direction D2 than to the end of the linear motion member 32 in the lock direction D1. Note that the position of the female screw 53 is not limited to this example.

[0034] The protrusions 52 protrude radially outward from the cylindrical portion 51. The two protrusions 52 protrude from the cylindrical portion 51 in opposite directions (the upward and downward directions in each figure). Note that the number and direction of the protrusions 52 are not limited to this example.

[0035] As shown in FIG. 1, a part of the rotary-linear motion conversion mechanism 13 is accommodated in the recess 22c of the piston 22. A part of the shaft 43 of the rotating member 31 is located in the recess 22c of the piston 22. Further, the linear motion member 32 is provided so as to be axially movable within the recess 22c.

[0036] Two guide grooves 22d are provided in the recess 22c of the piston 22. The two guide grooves 22d are recessed on the outer side in the radial direction and in opposite directions (upward and downward in each figure), and extend in the axial direction.

[0037] The protrusion 52 of the linear motion member 32 is accommodated in the guide groove 22d so as to be movable along the guide groove 22d. For example, by the side surface of the guide groove 22d facing in the circumferential direction abutting against the side surface of the protrusion 52 facing in the circumferential direction, the rotation of the linear motion member 32 about the central axis Ax is restricted.

[0038] As described above, the male screw 45 of the rotating member 31 meshes with the female screw 53 of the linear motion member 32, and the rotation of the protrusion 52 of the linear motion member 32 is restricted by the guide groove 22d of the piston 22. Thereby, the linear motion member 32 can linearly move in the axial direction according to the rotation of the rotating member 31. In other words, the linear motion member 32 can move in a substantially parallel translation in the axial direction.

[0039] The motor 15 is driven by driving power based on a control signal. The motor 15 rotates the output shaft of the motor 15 to rotationally drive the rotating member 31 about the central axis Ax via the rotation transmission mechanism 14.

[0040] FIG. 3 is a front view showing the rotating member 31 of the first embodiment. When the output shaft of the motor 15 rotates in one direction, the rotating member 31 rotates in the normal rotation direction Dn about the central axis Ax shown in FIG. 3. The normal rotation direction Dn is an example of the first rotation direction. When the rotating member 31 rotates in the normal rotation direction Dn, the linear motion member 32 moves straight (moves) in the lock direction D1.

[0041] The linear motion member 32 that moves in the lock direction D1 pushes the piston 22 in the lock direction D1. The piston 22 pushed by the linear motion member 32 moves in the lock direction D1, thereby pressing the lining 28 against the brake rotor 12 via the back plate 27. As a result, a braking state by the electric brake function in which the wheel of the vehicle that rotates integrally with the brake rotor 12 is braked is obtained.

[0042] When the output shaft of the motor 15 rotates in the reverse direction, the rotating member 31 rotates in the reverse rotation direction Dr around the central axis Ax shown in FIG. 3. The reverse rotation direction Dr is the direction opposite to the normal rotation direction Dn. The normal rotation direction Dn and the reverse rotation direction Dr are included in the circumferential direction.

[0043] When the rotating member 31 rotates in the reverse rotation direction Dr, the linear motion member 32 moves straight (moves) in the release direction D2, which is the direction away from the piston 22. Due to the movement of the linear motion member 32 in the release direction D2, the pressing force of the piston 22 on the back plate 27 is reduced, and the pressing of the lining 28 against the brake rotor 12 by the piston 22 is released. As a result, a released state (non-braking state) of braking by the electric brake function is obtained. Thus, the caliper 11, the rotary-linear conversion mechanism 13, the rotary transmission mechanism 14, and the motor 15 can operate as an electric brake.

[0044] In the present embodiment, the ECU 16 in FIG. 1 controls the motor 15 of the braking device 10. The ECU 16 may also be referred to as an electronic control unit. The ECU 16 may be partially configured by hardware such as a CPU or a controller that executes software, or may be entirely configured by hardware. Note that the motor 15 is not limited to the ECU 16, and may be controlled by, for example, a dedicated controller of the braking device 10.

[0045] When the ECU 16 receives an instruction signal to shift to the braking state from, for example, an operation switch (SW) of the electric brake function, the ECU 16 controls the motor 15 so that the rotating member 31 rotates in the forward rotation direction Dn. On the other hand, when the ECU 16 receives an instruction signal to release the braking state from the operation switch, the ECU 16 controls the motor 15 so that the rotating member 31 rotates in the reverse rotation direction Dr.

[0046] FIG. 4 is a partial cross-sectional view showing the rotating member 31 of the first embodiment. FIG. 4 shows a cross-section of a part of the rotating member 31 along the line F4-F4 in FIG. 3. As shown in FIG. 4, the shaft 43 of the rotating member 31 has a first region 61 and a second region 62.

[0047] Each of the first region 61 and the second region 62 is a part of the shaft 43. The first region 61 and the second region 62 are arranged in the axial direction. The male screw 45 is provided in each of the first region 61 and the second region 62.

[0048] Hereinafter, a part of the male screw 45 provided in the first region 61 may be referred to as the male screw 45A, and a part of the male screw 45 provided in the second region 62 may be referred to as the male screw 45B. In the present embodiment, the male screws 45A and 45B have substantially the same cross-sectional shape and are continuous with each other.

[0049] The cross-sectional shapes of the male screws 45A and 45B may be different from each other or may be divided. However, the male screws 45A and 45B form one male screw 45 that can mesh with one female screw 53. That is, the female screw 53 can move between a position meshing with the male screw 45A and a position meshing with the male screw 45B across the boundary between the male screw 45A and the male screw 45B.

[0050] The first region 61 extends in the axial direction. The first region 61 has a first inner end 61a and a first outer end 61b. The first inner end 61a is an example of the first end. The first outer end 61b is an example of the second end.

[0051] The first inner end 61a is one end of the first region 61 in the axial direction, connected to the second region 62. In the present embodiment, the first inner end 61a is the end of the first region 61 in the release direction D2.

[0052] The first outer end 61b is the other end of the first region 61 in the axial direction. In the present embodiment, the first outer end 61b is the end of the first region 61 in the lock direction D1 and also the end of the shaft 43 in the lock direction D1.

[0053] The second region 62 is continuous with the first region 61 and extends in the axial direction. The second region 62 has a second inner end 62a and a second outer end 62b.

[0054] The second inner end 62a is one end of the second region 62 in the axial direction, connected to the first region 61. In the present embodiment, the second inner end 62a is the end of the second region 62 in the lock direction D1.

[0055] The first inner end 61a and the second inner end 62a are provided at the same position in the axial direction. The first inner end 61a and the second inner end 62a are the boundary between the first region 61 and the second region 62.

[0056] The second outer end 62b is the other end of the second region 62 in the axial direction. In the present embodiment, the second outer end 62b is the end of the second region 62 in the release direction D2 and also the end of the shaft 43 in the release direction D2. The second outer end 62b is connected to the flange 42. Note that the second outer end 62b is not limited to this example.

[0057] Two first grooves 65 are provided in the first region 61. Note that the number of the first grooves 65 is not limited to this example. One first groove 65 may be provided in the first region 61, or three or more first grooves 65 may be provided.

[0058] The first groove 65 opens to the outer peripheral surface 43a of the shaft 43 and divides the male screw 45A in the circumferential direction. That is, the male screw 45A has a plurality of portions spaced apart from each other in the circumferential direction via the first groove 65. When the number of the first grooves 65 is one, the plurality of portions are connected to each other at positions separated from the first groove 65. In other words, the first groove 65 extends so as to cross the thread of the male screw 45A.

[0059] The first groove 65 extends in the axial direction between the first inner end 61a and the first outer end 61b. Note that the first groove 65 may extend in other directions. For example, the first groove 65 may extend spirally around the central axis Ax. The two first grooves 65 are spaced apart from each other at equal intervals in the circumferential direction.

[0060] The lengths of the two first grooves 65 in the axial direction are substantially equal. The widths of the two first grooves 65 in the circumferential direction are also substantially equal. Also, the depths of the two first grooves 65 in the radial direction are substantially equal. Note that the shapes of the two first grooves 65 may be different from each other.

[0061] The depth of the first groove 65 in the radial direction is the distance between the apex of the male screw 45A in the radial direction and the bottom of the first groove 65. In the present embodiment, the depth of the first groove 65 is longer (deeper) than the height of the male screw 45A. Note that the depth of the first groove 65 may be the same as or shorter (shallower) than the height of the male screw 45A.

[0062] No groove for dividing the male screw 45B in the circumferential direction is provided in the second region 62. Therefore, in the axial direction, the position where the end of the first groove 65 in the release direction D2 is provided can be defined as the first inner end 61a of the first region 61 and the second inner end 62a of the second region 62.

[0063] The male screw 45A is divided in the circumferential direction by the first groove 65. In other words, in the first groove 65, the male screw 45A is missing. On the other hand, the male screw 45B is not divided by a groove. Therefore, the male screw 45B is provided over the entire area (entire circumference) of the second region 62 in the circumferential direction. Note that the male screw 45B may be missing.

[0064] In the circumferential direction, the range where the male screw 45B is provided in the second region 62 is larger than the range where the male screw 45A is provided in the first region 61. The range where the male screw 45 is provided is at least one of the length in the circumferential direction and the angle around the central axis Ax.

[0065] FIG. 5 is a cross-sectional view schematically showing the male screw 45 and the female screw 53 of the first embodiment. As shown in FIG. 5, the male screw 45 has a plurality of threads 71. Each of the plurality of threads 71 has two side surfaces 71a, 71b. Further, the female screw 53 has a plurality of threads 72. Each of the plurality of threads 72 has two side surfaces 72a, 72b. One of the side surfaces 71b, 72b faces in the substantially locking direction D1. The other side surfaces 71a, 72a face in the substantially releasing direction D2.

[0066] The male screw 45 and the female screw 53 of the present embodiment are so-called saw blade screws. The side surfaces 71b, 72a extend substantially in the radial direction. The side surfaces 71a, 72b are inclined obliquely with respect to the radial direction. Note that the male screw 45 and the female screw 53 may be other screws such as a triangular screw, a trapezoidal screw, and each screw.

[0067] The angle θ1 of the thread 71 of the male screw 45 and the angle θ2 of the thread 72 of the female screw 53 are different from each other. For this reason, the male screw 45 and the female screw 53 can contact each other by line contact. The angle θ1 is the angle between the two side surfaces 71a, 71b of the thread 71. The angle θ2 is the angle between the two side surfaces 72a, 72b of the thread 72.

[0068] In the present embodiment, the angle θ1 is larger than the angle θ2. For this reason, the position P where the side surface 71b of the thread 71 and the side surface 72a of the thread 72 contact each other is closer to the valley 71d of the thread 71 than to the apex 71c of the thread 71. In other words, the position P is farther from the valley 72d of the thread 72 than from the apex 72c of the thread 72. For this reason, the distance between the central axis Ax and the position P becomes relatively short, and the rotation load of the rotating member 31 is reduced.

[0069] A gap G is formed between the male screw 45 and the female screw 53. For example, a gap G is formed between the crest 71c of the thread 71 and the valley 72d of the thread 72. Also, a gap G is formed between the valley 71d of the thread 71 and the crest 72c of the thread 72.

[0070] When the braking device 10 is first manufactured or when the brake pad 23 is replaced with a new one, the lining 28 of the brake pad 23 has a predetermined thickness. On the other hand, when the braking device 10 repeats braking, the thickness of the lining 28 decreases due to wear. Therefore, when the braking device 10 repeats braking, the position of the back plate 27 moves in the locking direction D1.

[0071] When the braking device 10 performs braking by the electric brake function, the linear motion member 32 moves to a position where the piston 22 abuts against the back plate 27 and the lining 28 abuts against the brake rotor 12. Therefore, the position where the linear motion member 32 pushes the piston 22 also moves in the locking direction D1 as the lining 28 wears.

[0072] When the braking by the electric brake function is released, an electric current is passed through the motor 15, and the rotating member 31 rotates in the reverse rotation direction Dr. At this time, the ECU 16 measures the load acting on the motor 15, for example, by measuring the value of the electric current flowing through the motor 15. When the piston 22 separates from the brake pad 23, the load and the electric current value acting on the motor 15 decrease. The ECU 16 stops the motor 15 when a predetermined time has elapsed after the electric current value falls below the threshold value. Therefore, the position of the linear motion member 32 during non-braking also moves in the locking direction D1 as the lining 28 wears.

[0073] When the braking device 10 is first manufactured, at least a part of the female screw 53 meshes with the male screw 45B in the second region 62. In the present embodiment, when the braking device 10 is first manufactured, the entire female screw 53 meshes with the male screw 45B in the second region 62. At this time, the female screw 53 is separated from the male screw 45A in the first region 61.

[0074] FIG. 2 shows the rotary-linear motion conversion mechanism 13 when the braking device 10 of the present embodiment was first manufactured. Also, in FIG. 2, the linear motion member 32 in the non-braking state is shown by a solid line, and the linear motion member 32 in the braking state is shown by a two-dot chain line.

[0075] As shown by the two-dot chain line in FIG. 2, when the braking device 10 of the present embodiment was first manufactured, the linear motion member 32 in the braking state that pushes the piston 22 is separated from the male screw 45A in the first region 61. That is, when the braking device 10 was first manufactured, the entire area of the female screw 53 meshes with the male screw 45B regardless of whether the linear motion member 32 is in the braking state or the non-braking state. Note that a part of the female screw 53 in the linear motion member 32 in the braking state may mesh with the male screw 45A. Also, a part of the female screw 53 in the linear motion member 32 in the non-braking state may mesh with the male screw 45A.

[0076] FIG. 6 is a cross-sectional view schematically showing the rotary-linear motion conversion mechanism 13 in the saturation state of the first embodiment. As the linear motion member 32 moves in the locking direction D1, the female screw 53 approaches the first outer end 61b of the first region 61. For example, due to the movement of the linear motion member 32 accompanying the wear of the lining 28 described above, the female screw 53 approaches the first outer end 61b. Also, at this time, at least in the linear motion member 32 in the braking state, the entire area of the female screw 53 meshes with the male screw 45A. Note that the female screw 53 also approaches the first outer end 61b due to the movement of the linear motion member 32 caused by the rotation of the rotating member 31 in the normal rotation direction Dn.

[0077] When the braking device 10 repeatedly performs braking by the electric brake function, at least one of the male screw 45 and the female screw 53 wears. The male screw 45 and the female screw 53 generate dust due to wear. The dust is a part of the male screw 45 or the female screw 53 that has fallen off from the male screw 45 and the female screw 53.

[0078] When dust exists between the male screw 45 and the female screw 53, it functions, for example, like an abrasive material. That is, as the relative rotation between the rotating member 31 and the linear moving member 32 occurs, the thread 71 of the male screw 45 and the thread 72 of the female screw 53 are worn. Further, this wear may, as it progresses, bring the angle θ1 of the thread 71 and the angle θ2 of the thread 72 closer to each other.

[0079] When the angle θ1 of the thread 71 and the angle θ2 of the thread 72 approach each other, the male screw 45 and the female screw 53 come into contact with each other by surface contact. For this reason, the friction coefficient of the friction between the male screw 45 and the female screw 53 increases.

[0080] Dust can be discharged (stored) into the gap G between the male screw 45 and the female screw 53. The male screw 45 and the female screw 53 can suppress an increase in the friction coefficient of the friction between the male screw 45 and the female screw 53 due to wear by forming the gap G.

[0081] FIG. 7 is a graph schematically showing an example of the change in the friction coefficient of the friction between the male screw 45 and the female screw 53 of the first embodiment. The solid-line graph in FIG. 7 shows an example of the change in the friction coefficient in this embodiment.

[0082] The vertical axis of FIG. 7 indicates the friction coefficient of the friction between the male screw 45 and the female screw 53. The horizontal axis of FIG. 7 indicates the wear amount of the brake pad 23. The wear amount is the decrease in thickness from the initial thickness of the brake pad 23.

[0083] The wear amount of the brake pad 23 is approximately proportional to the number of brakings in the braking device 10. Also, the wear amounts of the male screw 45 and the female screw 53 are approximately proportional to the number of brakings in the braking device 10. For this reason, the wear amounts of the male screw 45 and the female screw 53 are approximately proportional to the wear amount of the brake pad 23. Therefore, the horizontal axis of FIG. 7 simultaneously indicates the wear amount of the brake pad 23, the number of brakings in the braking device 10, and the wear amounts of the male screw 45 and the female screw 53.

[0084] As shown in FIG. 7, when the number of braking operations in the braking device 10 increases and the wear amounts of the brake pad 23, the male screw 45, and the female screw 53 increase, the friction coefficient of the friction between the male screw 45 and the female screw 53 increases due to the generated dust. From the time when the braking device 10 is manufactured, at least until the wear amount of at least the brake pad 23 reaches the saturation point Ps in FIG. 7, at least one of the male screw 45 and the female screw 53 increases the friction coefficient of the friction between the male screw 45 and the female screw 53 due to wear.

[0085] Hereinafter, a state in which at least one of the male screw 45 and the female screw 53 increases the friction coefficient of the friction between the male screw 45 and the female screw 53 due to wear is referred to as a non-saturation state. The non-saturation state is an example of the first state. As shown in FIG. 2, in the non-saturation state, at least a part of the female screw 53 meshes with the male screw 45B in the second region 62.

[0086] In the non-saturation state, until the wear amount of the brake pad 23 reaches the crossing point Pb in FIG. 7 from the time when the braking device 10 is manufactured, the entire area of the female screw 53 meshes with the male screw 45B in the second region 62. Until the wear amount of the brake pad 23 reaches the crossing point Pb from the time when the braking device 10 is manufactured, the wear amount of the brake pad 23 and the friction coefficient are approximately proportional.

[0087] When the wear amount of the brake pad 23 exceeds the crossing point Pb, a part of the female screw 53 meshes with the male screw 45A in the first region 61. For this reason, in the first region 61, the first groove 65 faces the female screw 53. The dust generated by the male screw 45 and the female screw 53 can be discharged into the first groove 65. Further, through the first groove 65, the working fluid is supplied between the male screw 45 and the female screw 53. The working fluid can lubricate the male screw 45 and the female screw 53.

[0088] Dust is discharged into the first groove 65, and the working fluid lubricates the male screw 45 and the female screw 53, so that an increase (gradient) in the friction coefficient of the friction between the male screw 45 and the female screw 53 is reduced. However, in the non-saturation state, the increase in the friction coefficient continues.

[0089] When the wear amount of the brake pad 23 reaches the saturation point Ps, the angle θ1 of a part of the thread crest 71 of the male screw 45 and the angle θ2 of a part of the thread crest 72 of the female screw 53 become approximately equal. For this reason, the male screw 45 and the female screw 53 do not increase the friction coefficient due to wear.

[0090] Hereinafter, a state in which the male screw 45 and the female screw 53 do not increase the friction coefficient of the friction between the male screw 45 and the female screw 53 due to wear is referred to as a saturation state. The saturation state is an example of the second state. Note that in the saturation state, the angle θ1 and the angle θ2 may remain different.

[0091] In the saturation state, the friction coefficient of the friction between the male screw 45 and the female screw 53 may change temporarily. However, in the saturation state, the friction coefficient is maintained substantially constant for at least a predetermined period.

[0092] As shown in FIG. 6, in the saturation state, at least a part of the female screw 53 meshes with the male screw 45A in the first region 61. In the saturation state of the present embodiment, the entire female screw 53 meshes with the male screw 45A in the first region 61. Note that in the saturation state, for example, a part of the female screw 53 in the linear movement member 32 in the non-braking state may mesh with the male screw 45B in the second region 62.

[0093] As described above, when transitioning from the non-saturation state to the saturation state, at least a part of the female screw 53 meshes with the male screw 45A in the first region 61. Also, in the present embodiment, when transitioning from the non-saturation state to the saturation state, the range in which the female screw 53 and the male screw 45A mesh increases.

[0094] The graph of the dashed-two-dot line in FIG. 7 shows the change in the friction coefficient in a comparative example where the first groove 65 is not provided in the shaft 43. Even when the first groove 65 is not provided in the shaft 43, when the wear amount of the brake pad 23 reaches the saturation point Ps, the male screw 45 and the female screw 53 no longer increase the friction coefficient due to wear. The saturation point Ps in the present embodiment is substantially equal to the saturation point Ps in the comparative example.

[0095] The length of the first groove 65 is set such that when the wear amount of the brake pad 23 reaches the saturation point Ps, the entire area of the female screw 53 meshes with the male screw 45A. Note that the length of the first groove 65 is not limited to this example.

[0096] The friction coefficient in the saturation state of the present embodiment is lower than the friction coefficient in the saturation state of the comparative example where the first groove 65 is not provided. Further, the friction coefficient in the saturation state of the present embodiment is lower than the friction coefficient at which abnormal noise may be generated due to the friction between the male screw 45 and the female screw 53. Therefore, the braking device 10 of the present embodiment can suppress the generation of abnormal noise due to friction in the saturation state.

[0097] In the braking device 10 according to the first embodiment described above, the rotating member 31 has a first region 61 and a second region 62 arranged in the direction along the central axis Ax. Male threads 45 are provided in each of the first region 61 and the second region 62. The first region 61 has a first inner end 61a and a first outer end 61b. The first inner end 61a is one end of the first region 61 in the direction along the central axis Ax and is connected to the second region 62. The first outer end 61b is the other end of the first region 61 in the direction along the central axis Ax. A first groove 65 that divides the male thread 45 in the circumferential direction around the central axis Ax is provided in the first region 61. In the circumferential direction, the range in which the male thread 45B is provided in the second region 62 is larger than the range in which the male thread 45A is provided in the first region 61. At least a part of the female thread 53 meshes with the male thread 45B in the second region 62, at least at the initial stage of manufacturing the braking device 10. When the linear movement member 32 moves in the locking direction D1, the female thread 53 approaches the first outer end 61b. For example, due to repeated braking, at least one of the male thread 45 and the female thread 53 wears. The dust generated by the wear accumulates between the male thread 45 and the female thread 53, increasing the friction coefficient of the friction between the male thread 45 and the female thread 53. On the other hand, when the brake pad 23 wears due to repeated braking, the position of the linear movement member 32 moves in the locking direction D1. When the position of the linear movement member 32 moves in the locking direction D1, the female thread 53 (the portion located closer to the first inner end 61a than the first outer end 61b) approaches the first outer end 61b, and the female thread 53 (the portion located on the side opposite to the first outer end 61b with respect to the first inner end 61a. The portion located between the first inner end 61a and the second outer end 62b) comes to mesh with the male thread 45A in the first region 61. In the first region 61, the dust generated by wear can be discharged into the first groove 65. Further, in the circumferential direction, the contact area (the contact area per one turn of one thread) between the male thread 45B and the female thread 53 in the second region 62 is larger than the contact area (the same as above) between the male thread 45A and the female thread 53 in the first region 61.Therefore, when at least a part of the female screw 53 meshes with the male screw 45B in the second region 62, the vertical resistance per unit contact area between the male screw 45B and the female screw 53 is reduced, and as a result, the frictional force between the male screw 45B and the female screw 53 is reduced. By reducing the frictional force between the male screw 45B and the female screw 53, the wear of the male screw 45B and the female screw 53 is reduced. At the initial stage of manufacturing the braking device 10, since the wear of the male screw 45B and the female screw 53 is not relatively advanced, there is sufficient room to store dust between the male screw 45B and the female screw 53, and an increase in the friction coefficient due to wear is particularly suppressed. Thereby, the braking device 10 of the present embodiment can suppress an increase in the frictional force between the male screw 45 and the female screw 53, and can suppress the generation of abnormal noise due to the friction between the male screw 45 and the female screw 53. Further, in the present embodiment, in the circumferential direction, the first groove 65 is provided in the male screw 45 such that the range in which the male screw 45B in the second region 62 is provided is larger than the range in which the male screw 45A in the first region 61 is provided. For example, compared with a mode in which the first groove is provided over the entire first region and the second region, and in the circumferential direction, the ranges in which the male screws are provided in the first region and the second region are of the same size, the strength and durability of the male screw 45 can be improved by the amount by which the range in which the male screw 45B in the second region 62 is provided is larger than that in the first region 61.

[0098] According to another explanation, at least a part of the female screw 53 meshes with the male screw 45B in the second region 62 in a non-saturation state where at least one of the male screw 45 and the female screw 53 increases the friction coefficient of the friction between the male screw 45 and the female screw 53 due to wear. Also, at least a part of the female screw 53 meshes with the male screw 45A in the first region 61 when transitioning from the non-saturation state to a saturation state where the male screw 45 and the female screw 53 do not increase the friction coefficient due to wear. In particular, in the present embodiment, when the female screw 53 transitions from the non-saturation state to a saturation state where the male screw 45 and the female screw 53 do not increase the friction coefficient due to wear, the entire area of the female screw 53 in the braking state where the brake pad 23 is pressed against the brake rotor 12 meshes with the male screw 45A in the first region 61. In the non-saturation state, for example, due to repeated braking, at least one of the male screw 45 and the female screw 53 wears. The dust generated by this wear increases the friction coefficient of the friction between the male screw 45 and the female screw 53. On the other hand, when the brake pad 23 wears due to repeated braking, the position of the linear movement member 32 moves in the locking direction D1. When the position of the linear movement member 32 moves in the locking direction D1, the female screw 53 (the portion located on the side opposite to the first outer end 61b rather than the first inner end 61a) meshes with the male screw 45A in the first region 61. That is, the meshing length between the female screw 53 and the male screw 45A in the first region 61 increases. In the first region 61, the dust generated by wear can be discharged into the first groove 65. For this reason, when at least a part of the female screw 53 meshes with the male screw 45A in the first region 61, the increase (gradient) of the friction coefficient due to wear is reduced, and finally the increase of the friction coefficient stops at a relatively low value. That is, when at least a part of the female screw 53 meshes with the male screw 45A in the first region 61, the friction coefficient when transitioning from the non-saturation state to the saturation state is reduced. Thereby, the braking device 10 of the present embodiment can suppress the increase in the frictional force between the male screw 45 and the female screw 53, and can suppress the generation of abnormal noise due to the friction between the male screw 45 and the female screw 53.

[0099] The angle θ1 of the thread 71 of the male screw 45 and the angle θ2 of the thread 72 of the female screw 53 are different from each other. Thereby, the contact area between the male screw 45 and the female screw 53 is reduced, and the frictional force between the male screw 45 and the female screw 53 is reduced. Also, a gap G is formed between the male screw 45 and the female screw 53. Dust generated by wear between the male screw 45 and the female screw 53 can be discharged into the gap G. Therefore, the braking device 10 of the present embodiment can suppress an increase in the frictional force between the male screw 45 and the female screw 53, and can suppress the generation of abnormal noise due to friction between the male screw 45 and the female screw 53.

[0100] In the second region 62, a groove that circumferentially divides the male screw 45 is not provided. Thereby, when at least a part of the female screw 53 meshes with the male screw 45B in the second region 62, the vertical resistance per contact area between the male screw 45B and the female screw 53 is reduced, and thus the frictional force between the male screw 45B and the female screw 53 is reduced. Thereby, the braking device 10 of the present embodiment can suppress an increase in the frictional force between the male screw 45 and the female screw 53, and can suppress the generation of abnormal noise due to friction between the male screw 45 and the female screw 53. Further, when the first groove 65 is provided in the rotating member 31 by processing, the second region 62 can be held, for example, by a chuck. Therefore, the braking device 10 of the present embodiment can easily provide the first groove 65 in the rotating member 31.

[0101] (Second Embodiment) Hereinafter, the second embodiment will be described with reference to FIG. 8. In the description of the following plurality of embodiments, components having the same functions as those already described components may be given the same reference numerals as those of the already described components, and the description may be further omitted. Also, a plurality of components given the same reference numeral do not necessarily have all functions and properties in common, and may have different functions and properties according to each embodiment.

[0102] FIG. 8 is a cross-sectional view schematically showing the rotary-linear conversion mechanism 13 according to the second embodiment. In the second embodiment, two second grooves 81 are provided in the second region 62. FIG. 8 shows one of the two second grooves 81.

[0103] The second groove 81 opens to the outer peripheral surface 43a of the shaft 43 and divides the male screw 45B in the circumferential direction. When one second groove 81 is provided in the second region 62, the plurality of portions are connected to each other at positions separated from the second groove 81. In other words, the second groove 81 extends so as to cross the thread ridge 72 of the male screw 45B.

[0104] The second groove 81 extends in the axial direction between the second inner end 62a and the second outer end 62b. Note that the second groove 81 may extend in other directions. For example, the second groove 81 may extend in a spiral shape. The two second grooves 81 are circumferentially spaced apart at equal intervals.

[0105] The lengths of the two second grooves 81 in the axial direction are substantially equal. The widths of the two second grooves 81 in the circumferential direction are also substantially equal. Also, the depths of the two second grooves 81 in the radial direction are substantially equal. Note that the shapes of the two second grooves 81 may be different from each other.

[0106] In the present embodiment, the depth of the second groove 81 is longer (deeper) than the height of the male screw 45B. Note that the depth of the second groove 81 may be the same as or shorter (shallower) than the height of the male screw 45B.

[0107] The width of the second groove 81 in the circumferential direction is shorter than the width of the first groove 65 in the circumferential direction. Therefore, in the circumferential direction, the range where the male screw 45A is provided in the first region 61 is larger than the range where the male screw 45B is provided in the second region 62.

[0108] The second groove 81 is connected to the end in the release direction D2 of the corresponding first groove 65. In the axial direction, the position where the first groove 65 and the second groove 81 are connected can be defined as the first inner end 61a of the first region 61 and the second inner end 62a of the second region 62.

[0109] The first region 61 and the second region 62 may be provided with grooves that taper toward the release direction D2. In this case, a part of the groove in the axial direction is the first groove 65, and the other part of the groove in the axial direction is the second groove 81.

[0110] The width of the first groove 65 in the circumferential direction and the width of the second groove 81 in the circumferential direction may be the same. In this case, the number of the first grooves 65 provided in the first region 61 is larger than the number of the second grooves 81 provided in the second region 62. For this reason, in the circumferential direction, the range where the male screw 45A is provided in the first region 61 is larger than the range where the male screw 45B is provided in the second region 62.

[0111] In the brake device 10 of the second embodiment described above, the second region 62 is provided with the second groove 81 that divides the male screw 45 in the circumferential direction around the central axis Ax. Thereby, when at least a part of the female screw 53 meshes with the male screw 45B in the second region 62, the dust generated by the wear of the male screw 45 and the female screw 53 can be discharged into the second groove 81. Further, the first groove 65 and the second groove 81 can supply the working fluid to the male screw 45 and the female screw 53. Therefore, the brake device 10 of the present embodiment can suppress an increase in the frictional force between the male screw 45 and the female screw 53, and can suppress the generation of abnormal noise due to the friction between the male screw 45 and the female screw 53.

[0112] Also, in the present embodiment, in the circumferential direction, since the first groove 65 and the second groove 81 are provided in the male screw 45 such that the range where the male screw 45B is provided in the second region 62 is larger than the range where the male screw 45A is provided in the first region 61, for example, the first groove is provided across the entire first region and the second region, and in the circumferential direction, compared with a mode in which the range where the male screw is provided in the first region and the range where the male screw is provided in the second region are of the same size, the strength and durability of the male screw 45 can be improved by the amount by which the range where the male screw 45B is provided in the second region 62 is larger than that in the first region 61.

[0113] (Third Embodiment) Hereinafter, the third embodiment will be described with reference to FIG. 9. FIG. 9 is a cross-sectional view schematically showing the rotary-linear motion conversion mechanism 13 according to the third embodiment. In FIG. 9, the linear motion member 32 at the initial stage when the braking device 10 is manufactured is shown by a two-dot chain line, and the linear motion member 32 in the saturation state is shown by a solid line.

[0114] As shown in FIG. 9, a male screw 145 is provided on the rotary member 31 of the third embodiment instead of the male screw 45. The male screw 145 is an example of a male screw and a second screw. The male screw 145 is equal to the male screw 45 of the first embodiment except for the points described below.

[0115] The male screw 145 is provided on the outer peripheral surface 43a of the shaft 43 at a position separated from the flange 42 in the locking direction D1. The male screw 145 is not divided in the circumferential direction by a groove. Note that the male screw 145 may be divided in the circumferential direction by a groove.

[0116] A female screw 153 is provided on the linear motion member 32 of the third embodiment instead of the female screw 53. The female screw 153 is an example of a female screw and a first screw. The female screw 153 is equal to the female screw 53 of the first embodiment except for the points described below.

[0117] In the axial direction, the length of the female screw 153 is longer than the length of the male screw 145. The female screw 153 is closer to the end of the linear motion member 32 in the locking direction D1 than the end of the linear motion member 32 in the release direction D2. Note that the position of the female screw 153 is not limited to this example.

[0118] The linear motion member 32 of the third embodiment has a first region 161 and a second region 162. The first region 161 and the second region 162 are arranged side by side in the axial direction. The female screw 153 is provided in each of the first region 161 and the second region 162.

[0119] Hereinafter, a part of the female screw 153 provided in the first region 161 may be referred to as the female screw 153A, and a part of the female screw 153 provided in the second region 162 may be referred to as the female screw 153B.

[0120] The first region 161 extends in the axial direction and has a first inner end 161a and a first outer end 161b. The first inner end 161a is an example of the first end. The first outer end 161b is an example of the second end.

[0121] The first inner end 161a is one end of the first region 161 in the axial direction connected to the second region 162. In the present embodiment, the first inner end 161a is the end of the first region 161 in the locking direction D1. The first outer end 161b is the other end of the first region 161 in the axial direction.

[0122] The second region 162 is continuous with the first region 161 and extends in the axial direction. The second region 162 has a second inner end 162a and a second outer end 162b. The second inner end 162a is one end of the second region 162 in the axial direction connected to the first region 161. The first inner end 161a and the second inner end 162a are provided at the same position in the axial direction. The second outer end 162b is the other end of the second region 162 in the axial direction.

[0123] Two first grooves 165 are provided in the first region 161. The first groove 165 opens to the inner peripheral surface 51a of the cylindrical portion 51 and divides the female screw 153A in the circumferential direction. The first groove 165 extends in the axial direction between the first inner end 161a and the first outer end 161b. Note that the first groove 165 may extend in other directions.

[0124] No groove is provided in the second region 162 to divide the female screw 153B in the circumferential direction. Therefore, in the circumferential direction, the range where the female screw 153B is provided in the second region 162 is larger than the range where the female screw 153A is provided in the first region 161. Note that a groove may be provided in the second region 162.

[0125] As shown by the two-dot chain line in Fig. 9, in the non-saturated state including the initial stage when the braking device 10 was manufactured, at least a part of the male screw 145 meshes with the female screw 153B in the second region 162. In the non-saturated state, at least one of the male screw 145 and the female screw 153 increases the friction coefficient of the friction between the male screw 145 and the female screw 153 due to wear.

[0126] When the linear movement member 32 moves in the locking direction D1, the male screw 145 (the part located closer to the first inner end 161a than the first outer end 161b) approaches the first outer end 161b of the first region 161. When the male screw 145 (the part located on the side opposite to the first outer end 161b with respect to the first inner end 161a) meshes with the female screw 153A in the first region 161, the dust generated between the male screw 145 and the female screw 153 can be discharged into the first groove 165. Also, through the first groove 165, the working fluid is supplied between the male screw 145 and the female screw 153.

[0127] When transitioning from the non-saturated state to the saturated state, at least a part of the male screw 145 meshes with the female screw 153A in the first region 161. In the saturated state, the male screw 145 and the female screw 153 no longer increase the friction coefficient due to wear.

[0128] As in the first embodiment and the third embodiment described above, the first grooves 65, 165 may be provided on the rotating member 31 or may be provided on the linear movement member 32. Note that a female screw may be provided on the rotating member 31 and a male screw may be provided on the linear movement member 32.

[0129] The braking device according to at least one of the embodiments described above includes, as an example, a male screw, a female screw that meshes with the male screw, one of which is provided, a rotating member that is rotatable about a rotation axis, and the other of the male screw and the female screw is provided. When the rotating member rotates in a first rotation direction about the rotation axis, it moves in a first direction along the rotation axis. When the rotating member rotates in a second rotation direction opposite to the first rotation direction, it moves in a second direction opposite to the first direction. A linear motion member, and a piston that is pushed in the first direction by the linear motion member moving in the first direction and presses a braking member against a brake rotor by moving in the first direction. One of the rotating member and the linear motion member is provided with a first screw, which is one of the male screw and the female screw provided on the member, and has a first region and a second region arranged in a direction along the rotation axis. The first region has a first end that is one end of the first region in the direction along the rotation axis and is connected to the second region, and a second end that is the other end of the first region in the direction along the rotation axis. A first groove that divides the first screw in the circumferential direction around the rotation axis is provided in the first region. In the circumferential direction, the range where the first screw is provided in the second region is larger than the range where the first screw is provided in the first region. At least a part of the second screw, which is the other of the male screw and the female screw, in the direction along the rotation axis meshes with the first screw in the second region. When the linear motion member moves in the first direction, the second screw approaches the second end. Therefore, as an example, when the braking member wears due to repeated braking, the position of the linear motion member moves in the first direction. When the position of the linear motion member moves in the first direction, a portion of the second screw that was located, for example, on the side of the first end rather than the second end approaches the second end, and a portion of the second screw that was located, for example, on the side opposite to the second end rather than the first end meshes with the first screw in the first region. In the first region, dust generated due to wear can be discharged into the first groove.Furthermore, in the second region, the contact area between the first screw and the second screw (the contact area per turn of one thread of the screw) is larger than the contact area between the first screw and the second screw in the first region (the same as above). Therefore, when at least a part of the second screw meshes with the first screw in the second region, the vertical resistance per unit contact area between the first screw and the second screw is reduced, and consequently, the frictional force between the first screw and the second screw is reduced. By reducing the frictional force between the first screw and the second screw, the wear of the first screw and the second screw is reduced. As a result, the braking device of the present embodiment can suppress an increase in the frictional force between the first screw and the second screw, and can suppress the generation of abnormal noise due to the friction between the first screw and the second screw. Further, as an example, in the circumferential direction, the first groove is provided in the first screw such that the range in which the first screw is provided in the second region is larger than the range in which the first screw is provided in the first region. For example, the first groove is provided across the entire first region and the second region, and in the circumferential direction, compared with a mode in which the range in which the first screw is provided in the first region and the range in which the first screw is provided in the second region are of the same size, the strength and durability of the first screw can be improved by the amount by which the range in which the first screw is provided in the second region is larger than that in the first region.

[0130] Also, as an example, the braking device according to at least one of the embodiments described above includes a male screw and a female screw that meshes with the male screw. One of them is provided on a rotating member that is rotatable around a rotation axis, and the other of the male screw and the female screw is provided. When the rotating member rotates in a first rotation direction around the rotation axis, it moves in a first direction along the rotation axis, and when the rotating member rotates in a second rotation direction opposite to the first rotation direction, it moves in a second direction opposite to the first direction. A linear motion member, and a piston that is pushed in the first direction by the linear motion member moving in the first direction and presses the braking member against the brake rotor by moving in the first direction. One of the rotating member and the linear motion member is provided with a first screw, which is one of the male screw and the female screw provided on the member, and has a first region and a second region arranged in a direction along the rotation axis. In the first region, a first groove that divides the first screw in the circumferential direction around the rotation axis is provided. In the circumferential direction, the range where the first screw is provided in the second region is larger than the range where the first screw is provided in the first region. The second screw, which is the other of the male screw and the female screw, has at least a part in the direction along the rotation axis meshing with the first screw in the second region in a first state where at least one of the first screw and the second screw increases the friction coefficient between the first screw and the second screw due to wear. When transitioning from the first state to a second state where the first screw and the second screw do not increase the friction coefficient due to wear, all of the second screw in the direction along the rotation axis in the state where the braking member is pressed against the brake rotor meshes with the first screw in the first region. Therefore, as an example, when the braking member wears due to repeated braking, the position of the linear motion member moves in the first direction. When the position of the linear motion member moves in the first direction, a portion that was located, for example, on the side opposite to the second end rather than the first end in the second screw meshes with the first screw in the first region. That is, the meshing length between the second screw and the first screw in the first region increases.In the first region, the dust generated by wear can be discharged into the first groove. Therefore, when at least a part of the second screw meshes with the first screw in the first region, the increase (gradient) in the friction coefficient due to wear is reduced, and ultimately the increase in the friction coefficient stops at a relatively low value. That is, when at least a part of the second screw meshes with the first screw in the first region, the friction coefficient when transitioning from the first state to the second state is reduced. Further, the contact area between the first screw and the second screw in the second region (the contact area per turn of one thread of the screw) is larger than the contact area between the first screw and the second screw in the first region (the same as above). For this reason, in the first state, the vertical resistance per contact area between the first screw and the second screw is reduced, and consequently the frictional force between the first screw and the second screw is reduced. By reducing the frictional force between the first screw and the second screw, the wear of the first screw and the second screw is reduced. Thereby, the braking device of the present embodiment can suppress an increase in the frictional force between the first screw and the second screw, and can suppress the generation of abnormal noise due to the friction between the first screw and the second screw.

[0131] In the above braking device, as an example, the angle of the thread of the male screw and the angle of the thread of the female screw are different from each other. Therefore, as an example, the contact area between the male screw and the female screw is reduced, and the frictional force between the male screw and the female screw is reduced. Also, a gap is formed between the male screw and the female screw. The dust generated by the wear of the first screw and the second screw can be discharged into the gap. Therefore, the braking device of the present embodiment can suppress an increase in the frictional force between the first screw and the second screw, and can suppress the generation of abnormal noise due to the friction between the first screw and the second screw.

[0132] In the above braking device, as an example, in the second region, a groove for dividing the first screw in the circumferential direction is not provided. Therefore, as an example, when at least a part of the second screw meshes with the first screw in the second region, the vertical resistance per contact area between the first screw and the second screw is reduced, and consequently, the frictional force between the first screw and the second screw is reduced. Thereby, the braking device of the present embodiment can suppress an increase in the frictional force between the first screw and the second screw, and can suppress the generation of abnormal noise due to the friction between the first screw and the second screw. Further, the second region can be held, for example, by a chuck when the first groove is provided in the member. Therefore, the braking device of the present embodiment can easily provide the first groove in the member.

[0133] In the above braking device, as an example, in the second region, a second groove for dividing the first screw in the circumferential direction around the rotation axis is provided. Therefore, as an example, when at least a part of the second screw meshes with the first screw in the second region, the dust generated by the wear of the first screw and the second screw can be discharged into the second groove. Further, the first groove and the second groove can supply lubricating oil to the first screw and the second screw. Therefore, the braking device of the present embodiment can suppress an increase in the frictional force between the first screw and the second screw, and can suppress the generation of abnormal noise due to the friction between the first screw and the second screw.

[0134] In the above description, suppression is defined as, for example, preventing the occurrence of an event, action, or influence, or reducing the degree of an event, action, or influence. Also, in the above description, limitation is defined as, for example, preventing movement or rotation, or allowing movement or rotation within a predetermined range and preventing movement or rotation exceeding the predetermined range.

[0135] The embodiments of the present invention have been illustrated above. However, the above embodiments and modifications are merely examples and are not intended to limit the scope of the invention. The above embodiments and modifications can be implemented in various other forms, and various omissions, replacements, combinations, and changes can be made without departing from the gist of the invention. Also, the configurations and shapes of each embodiment and each modification can be partially interchanged and implemented.

Explanation of Reference Numerals

[0136] 10…Brake device, 12…Brake rotor, 22…Piston, 23…Brake pad (braking member), 31…Rotating member, 32…Linear motion member, 45, 45A, 45B…Male screw (first screw), 53…Female screw (second screw), 61, 161…First region, 61a…First inner end (first end), 61b…First outer end (second end), 62, 162…Second region, 65, 165…First groove, 71, 72…Thread, 81…Second groove, 145…Male screw (second screw), 153, 153A, 153B…Female screw (first screw), Ax…Central axis (rotation axis), D1…Locking direction (first direction), D2…Release direction (second direction), Dn…Forward rotation direction (first rotation direction), Dr…Reverse rotation direction (second rotation direction), θ1, θ2…Angles.

Claims

1. One of a male screw and a female screw that meshes with the male screw is provided, and a rotating member that is rotatable about a rotation axis, The other of the male screw and the female screw is provided, and when the rotating member rotates in a first rotation direction about the rotation axis, it moves in a first direction along the rotation axis, and when the rotating member rotates in a second rotation direction opposite to the first rotation direction, it moves in a second direction opposite to the first direction, a linear motion member, A piston that is pushed in the first direction by the linear motion member moving in the first direction and presses a braking member against a brake rotor by moving in the first direction, comprising One of the rotating member and the linear motion member is provided with a first screw, which is one of the male screw and the female screw provided on the member, and has a first region and a second region arranged in a direction along the rotation axis, The first region has a first end that is one end of the first region in the direction along the rotation axis and is connected to the second region, and a second end that is the other end of the first region in the direction along the rotation axis, A first groove that divides the first screw in the circumferential direction about the rotation axis is provided in the first region, In the circumferential direction, the range in which the first screw is provided in the second region is larger than the range in which the first screw is provided in the first region, At least a part of the second screw, which is the other of the male screw and the female screw, in the direction along the rotation axis meshes with the first screw in the second region, When the linear motion member moves in the first direction, the second screw approaches the second end, A braking device.

2. One of a male screw and a female screw that meshes with the male screw is provided, and a rotating member that is rotatable about a rotation axis, The other of the male screw and the female screw is provided, and when the rotating member rotates in a first rotation direction around the rotation axis, it moves in a first direction along the rotation axis, and when the rotating member rotates in a second rotation direction opposite to the first rotation direction, it moves in a second direction opposite to the first direction, a linear motion member, Pushed in the first direction by the linear motion member moving in the first direction, and pressing the braking member against the brake rotor by moving in the first direction, a piston, Comprising, One of the rotating member and the linear motion member is provided with a first screw, which is one of the male screw and the female screw provided on the member, and has a first region and a second region arranged in a direction along the rotation axis, A first groove that divides the first screw in the circumferential direction around the rotation axis is provided in the first region, In the circumferential direction, the range where the first screw is provided in the second region is larger than the range where the first screw is provided in the first region, At least a part of the second screw, which is the other of the male screw and the female screw, meshes with the first screw in the second region in a first state where at least one of the first screw and the second screw increases the friction coefficient between the first screw and the second screw due to wear, When transitioning from the first state to a second state where the first screw and the second screw do not increase the friction coefficient due to wear, all of the second screw in the direction along the rotation axis in the state where the braking member is pressed against the brake rotor meshes with the first screw in the first region, A braking device.

3. The angle of the thread of the male screw and the angle of the thread of the female screw are different from each other. The braking device according to claim 1 or claim 2.

4. The braking device according to any one of claims 1 to 3, wherein a groove for dividing the first screw in the circumferential direction is not provided in the second region.

5. The braking device according to any one of claims 1 to 3, wherein a second groove for dividing the first screw in the circumferential direction around the rotation axis is provided in the second region.

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