Electric braking device

Abstract

In this electric braking device, a screw shaft 51 of a linear motion conversion mechanism 50 rotates in response to rotational motion of an electric motor, and the rotational motion of the screw shaft 51 is converted into linear motion of a nut 60 of the linear motion conversion mechanism 50. The linear motion of the nut 60 in a forward direction X1 causes a piston 70 to move linearly, thereby increasing a braking force. A portion of the nut 60 that receives a force from the screw shaft 51 is disposed in the forward direction X1 relative to a rotation center PA of the nut 60 such that, when the nut 60 linearly moves in the forward direction X1 in a state in which a screw axis Zv of the screw shaft 51 is inclined with respect to a nut axis Zn of the nut 60, the nut 60 is caused to rotate in a direction in which the screw axis Zv is along the nut axis Zn by a force that the screw shaft 51 receives from the nut 60 and a force that the nut 60 receives from the piston 70.

Description

electric braking device

[0001] The present invention relates to an electric braking device mounted on a vehicle.

[0002] Patent Document 1 discloses an electric braking device that adjusts the braking force applied to a wheel by controlling the rotation angle of an electric motor. In the electric braking device, the rotational motion of the electric motor is converted into linear motion by a linear motion conversion mechanism. The linear motion conversion mechanism has a rotating part to which the rotational motion of the electric motor is input and a linear motion part having a part that engages with the rotating part. The rotational motion is converted into linear motion at the engagement part between the rotating part and the linear motion part, and the linear motion is output from the linear motion part.

[0003] The electric braking device includes a pressing element interposed between the linear motion part of the linear motion conversion mechanism and the bottom wall of the piston. A surface of the pressing element facing the bottom wall of the piston is defined as a first surface, and a surface of the bottom wall of the piston that contacts the first surface is defined as a second surface. One of the first surface and the second surface is configured to be arc-shaped in side view.

[0004] Japanese Patent Application Laid-Open No. 2020-193641

[0005] In the electric braking device described above, when the rotational motion of the electric motor is input to the rotating part of the linear motion conversion mechanism, the rotational motion is converted into linear motion at the engagement point between the rotating part and the linear motion part, causing the linear motion part to move linearly forward. As the linear motion part moves linearly forward, the pressing element pushes the piston, and the piston presses the friction material against the rotating body that rotates integrally with the wheel. As a result, a braking force is applied to the wheel.

[0006] The linear motion conversion mechanism is configured so that the linear motion part is disposed coaxially with the rotating part. However, when the linear motion part moves linearly forward, it may tilt relative to the rotating part so that the angle between the axis of the linear motion part and the axis of the rotating part becomes larger. In this case, if the linear motion of the linear motion part continues in a state where the angle between the two axes deviates from 0 (zero), excessive load is applied to the engagement part between the rotating part and the linear motion part. As a result, wear of the engagement part is likely to progress.

[0007] An electric braking device that solves the above problem is a device in which a rotating part of a linear motion conversion mechanism rotates in response to the rotational motion of an electric motor, the rotational motion of the rotating part is converted into linear motion in a forward or backward direction of a linear motion part of the linear motion conversion mechanism, the linear motion of the linear motion part in the forward direction causes linear motion of a piston, thereby increasing the braking force applied to the wheels of a vehicle, and the linear motion part rotates about a predetermined imaginary point when the direction of the force received from the rotating part and the direction of the force received from the piston are excessively different. In this electric braking device, when the linear motion part moves linearly in the forward direction with its axis tilted with respect to the axis of the rotating part, a portion of the linear motion part that receives the force from the rotating part is positioned in the forward direction relative to the rotation center of the linear motion part so that the axis of the linear motion part rotates in a direction along the axis of the rotating part due to the force received from the rotating part and the force received from the piston.

[0008] The electric braking device has an effect of extending the life of the linear motion conversion mechanism.

[0009] FIG. 1 is a cross-sectional view showing an outline of an electric braking device according to an embodiment. FIG. 2 is a schematic diagram showing a linear motion conversion mechanism of a comparative example. FIG. 3 is an operational diagram showing the linear motion conversion mechanism of the comparative example in a state where the caliper body is deflected. FIG. 4 is a schematic diagram showing the linear motion conversion mechanism of the electric braking device according to an embodiment in a state where the caliper body is not deflected. FIG. 5 is an operational diagram showing the linear motion conversion mechanism of the electric braking device according to an embodiment in a state where the caliper body is deflected. FIG. 6 is an operational diagram showing the linear motion conversion mechanism when the braking force is increased in a state where the caliper body is deflected in the electric braking device according to an embodiment. FIG. 7 is a schematic diagram showing the linear motion conversion mechanism provided in an electric braking device according to a modified example. FIG. 8 is a cross-sectional view showing an outline of an electric braking device according to another modified example.

[0010] An embodiment of an electric braking device mounted on a vehicle will be described below with reference to Figures 1 to 6. <Overall Configuration of Electric Brake Device> As shown in Figure 1, the electric braking device 20 is a caliper-type disc brake device. The electric braking device 20 includes a disc rotor 21 that rotates integrally with the wheel 10, and two brake pads 22A, 22B. Each of the two brake pads 22A, 22B includes a backing plate 23 and a friction material 24 supported by the backing plate 23. The disc rotor 21 is disposed between the two brake pads 22A, 22B. A braking force is applied to the wheel 10 by sandwiching the disc rotor 21 between the friction materials 24 of the two brake pads 22A, 22B.

[0011] The electric braking device 20 includes a caliper body 30. The caliper body 30 has a cylinder body 31, a bridge portion 32, and a claw portion 33. The cylinder body 31 and the claw portion 33 are disposed so as to sandwich the disc rotor 21 therebetween. The bridge portion 32 is a portion of the caliper body 30 that connects the cylinder body 31 and the claw portion 33. The bridge portion 32 is disposed radially outward of the disc rotor 21. Of the two brake pads 22A, 22B, the brake pad 22A is assembled to the claw portion 33, and the brake pad 22B is assembled to the cylinder body 31. The cylinder body 31 is also provided with a cylinder 35. The cylinder 35 is a cylindrical hole with a bottom that opens on the side of the cylinder body 31 where the disc rotor 21 is located.

[0012] The electric braking device 20 includes an electric motor 41, a reduction gear mechanism 43, a linear motion conversion mechanism 50, and a piston 70. In the electric braking device 20, the rotational motion of the electric motor 41 causes the linear motion of the piston 70, thereby adjusting the braking force applied to the wheel 10. In other words, the electric braking device 20 can adjust the braking force applied to the wheel 10 by controlling the rotation angle of the electric motor 41.

[0013] The direction of linear motion of the piston 70 when increasing the braking force is referred to as the "forward direction X1." The direction of linear motion of the piston 70 when decreasing the braking force is referred to as the "reverse direction X2." The reverse direction X2 is the opposite direction to the forward direction X1. Furthermore, the direction of rotational motion of the electric motor 41 for linearly moving the piston 70 in the forward direction X1 is referred to as the "forward direction." The direction of rotational motion of the electric motor 41 for linearly moving the piston 70 in the reverse direction X2 is referred to as the "reverse direction." The reverse direction is the opposite direction to the forward direction.

[0014] The electric motor 41 is mounted to the cylinder body 31. The reduction mechanism 43 is housed inside a gear case 44 mounted to the cylinder body 31. The linear motion conversion mechanism 50 and the piston 70 are each housed inside the cylinder 35 of the cylinder body 31.

[0015] <Reduction Mechanism> The reduction mechanism 43 is a mechanism that reduces the speed of the rotational motion of the electric motor 41 and transmits the reduced speed to the linear motion conversion mechanism 50. The reduction mechanism 43 is composed of, for example, a plurality of gears. Of the plurality of gears, the gear that outputs to the linear motion conversion mechanism 50 is referred to as an output gear 45.

[0016] <Linear Motion Conversion Mechanism> The linear motion conversion mechanism 50 is a mechanism that converts the rotational motion transmitted from the reduction mechanism 43 into linear motion and outputs it to the piston 70. The linear motion conversion mechanism 50 includes a screw shaft 51 to which the rotational motion is input from the reduction mechanism 43, a nut 60 arranged coaxially with the screw shaft 51, and a rotation restriction unit (not shown) that restricts rotation of the nut 60. In this embodiment, the screw shaft 51 functions as the "rotating unit of the linear motion conversion mechanism," and the nut 60 functions as the "linear motion unit of the linear motion conversion mechanism." In this case, the nut axis Zn, which is the axis of the nut 60, corresponds to the "axis of the linear motion unit," and the screw axis Zv, which is the axis of the screw shaft 51, corresponds to the "axis of the rotating unit" (see FIG. 4).

[0017] The end of the screw shaft 51 on the backward direction X2 side is defined as a first end 52. The first end 52 is fixed to the output gear 45 so as to rotate integrally with the output gear 45. The screw shaft 51 extends from the first end 52 in the forward direction X1. That is, the screw shaft 51 penetrates the bottom wall 35A of the cylinder 35, and the end of the screw shaft 51 on the forward direction X1 side is located inside the cylinder 35. The screw shaft 51 is rotatably supported by the cylinder 35. A flange 53 is provided at a midpoint in the longitudinal direction of the screw shaft 51. The flange 53 is located inside the cylinder 35. A thrust bearing 101 and a load sensor 103 are arranged between the flange 53 and the bottom wall 35A of the cylinder 35.

[0018] A portion of the screw shaft 51 that is further forward in the X1 direction than the flange 53 is formed as a male threaded portion 54. The nut 60 is located in the cylinder 35 further forward in the X1 direction than the flange 53. The nut 60 is located radially outward from the male threaded portion 54. An annular engaging portion 61 that protrudes radially inward is provided on the inner circumferential surface of the nut 60 at a midpoint in the longitudinal direction of the nut 60. The engaging portion 61 engages with the male threaded portion 54 of the screw shaft 51. In other words, the circumferential surface of the engaging portion 61 is formed as a female thread, and therefore the engaging portion 61 is threadedly engaged with the male threaded portion 54. Note that neither a portion of the inner circumferential surface of the nut 60 that is further forward in the X1 direction than the engaging portion 61 nor a portion of the inner circumferential surface of the nut 60 that is further backward in the X2 direction than the engaging portion 61 is formed as a female thread.

[0019] In this embodiment, the rotational motion is converted into linear motion by the engagement portion between the male thread portion 54 and the engagement portion 61. Therefore, when the electric motor 41 rotates in the forward direction, the nut 60 moves linearly in the forward direction X1. On the other hand, when the electric motor 41 rotates in the reverse direction, the nut 60 moves linearly in the backward direction X2. Hereinafter, the engagement portion between the male thread portion 54 and the engagement portion 61 will be referred to as a "conversion portion CP," which is a portion that converts the rotational motion of the screw shaft 51 into linear motion of the nut 60. In other words, it can be said that the linear motion conversion mechanism 50 includes the conversion portion CP.

[0020] The nut 60 includes a transmission portion 63 that transmits linear motion to the piston 70. The transmission portion 63 is located further in the backward direction X2 than the end of the engagement portion 61 in the forward direction X1. Preferably, the transmission portion 63 is located further in the backward direction X2 than the center of the engagement portion 61 in the longitudinal direction. In this embodiment, the transmission portion 63 is located further in the backward direction X2 than the end of the engagement portion 61 in the backward direction X2.

[0021] The transmission portion 63 is configured so that its thickness gradually increases as it moves in the backward direction X2. When the surface of the transmission portion 63 that transmits force to the piston 70 is defined as a first surface 63a, the first surface 63a is configured so that it is positioned radially outward as it moves in the backward direction X2. For example, the first surface 63a is a spherical surface that is convex toward a second surface 75a of a receiving portion 75 of the piston 70, which will be described later.

[0022] <Piston> The piston 70 is installed in the cylinder 35 so as to be able to move linearly in the forward direction X1 and the backward direction X2. The piston 70 has a disk-shaped bottom wall 71 and a cylindrical peripheral wall 73 extending in the backward direction X2 from the periphery of the bottom wall 71. The nut 60 is housed in the space inside the peripheral wall 73.

[0023] The piston 70 includes a receiving portion 75 that contacts the transmission portion 63 of the nut 60 and receives force from the transmission portion 63. The receiving portion 75 may be integrally formed with the piston 70 or may be a component fixed to the piston 70. The receiving portion 75 is provided at the end of the peripheral wall 73 on the backward direction X2 side. The receiving portion 75 has an annular shape and protrudes radially inward from the peripheral wall 73. The surface of the receiving portion 75 that contacts the first surface 63a of the transmission portion 63 is referred to as a second surface 75a. The second surface 75a is configured to be gradually positioned radially inward as it moves in the forward direction X1. For example, the second surface 75a is tapered. The second surface 75a makes line contact with the transmission portion 63 of the nut 60. Furthermore, the contact position between the transmission part 63 and the receiving part 75, i.e., the contact position between the first surface 63a and the second surface 75a, is located in the backward direction X2 further than the conversion part CP of the linear motion conversion mechanism 50. When the nut 60 moves linearly in the forward direction X1, the reception part 75 is pressed by the transmission part 63 of the nut 60, causing the piston 70 to move linearly in the forward direction X1.

[0024] <Operations and Effects of the Present Embodiment> When a braking force is applied to the wheel 10, the electric motor 41 rotates in the forward direction. This rotational motion of the electric motor 41 is transmitted to the linear motion conversion mechanism 50 via the reduction gear mechanism 43. Specifically, when rotational motion is input to the screw shaft 51, the rotational motion is converted into linear motion by the conversion portion CP of the linear motion conversion mechanism 50. As a result, the nut 60 moves linearly in the forward direction X1. At this time, the transmission portion 63 of the nut 60 pushes the receiving portion 75 of the piston 70 in the forward direction X1. As a result, the piston 70 moves linearly in the forward direction X1, and the two brake pads 22A, 22B sandwich the disc rotor 21. As a result, a braking force is applied to the wheel 10.

[0025] When the electric braking device 20 applies a braking force to the wheel 10 in this manner, a reaction force against the pressure of the two brake pads 22A, 22B is applied to the claw portion 33 and the cylinder body 31. Meanwhile, the claw portion 33 and the cylinder body 31 are connected by a bridge portion 32 located radially outward of the disc rotor 21. Therefore, when a reaction force against the pressure from the brake pads 22A, 22B is applied, the caliper body 30 is deflected.

[0026] The operation of the linear motion conversion mechanism 50 when the caliper body 30 is deflected as described above will now be described. First, a linear motion conversion mechanism 50A of a comparative example will be described with reference to Figures 2 and 3. Figure 2 schematically shows the linear motion conversion mechanism 50A of the comparative example when the caliper body 30 is not deflected. Figure 3 schematically shows the linear motion conversion mechanism 50A of the comparative example when the caliper body 30 is deflected as described above.

[0027] As shown in FIG. 2, in the linear motion conversion mechanism 50A of the comparative example, the transmission portion 63A of the nut 60A is provided at the end in the forward direction X1. Therefore, a receiving portion 75A is provided on the bottom wall 71A of the piston 70A. In FIGS. 2 and 3, a first point P1 is the portion where the nut receives force from the piston when a braking force is applied. A second point P2 is the portion where the nut receives force from the screw shaft. Furthermore, if the direction of the force received from the screw shaft 51 and the direction of the force received from the piston 70A deviate excessively, the nut 60A rotates around a predetermined imaginary point. The rotation center PA shown in FIG. 2 corresponds to the "predetermined imaginary point" described above.

[0028] The screw shaft 51 is supported by the caliper body 30. The third point P3 is a portion where the caliper body 30 receives force from the screw shaft 51. Therefore, when the caliper body 30 bends as shown in Figure 3, the screw axis Zv of the screw shaft 51 tilts. In other words, the angle between the nut axis Zn of the nut 60A and the screw axis Zv increases.

[0029] When the braking force is increased and the angle between the nut axis Zn and the screw axis Zv becomes larger, the nut 60A moves linearly in the forward direction X1. A reaction force F1 is input to the first point P1 from the receiving portion 75A of the piston 70A. The reaction force F1 acts in the backward direction X2. Meanwhile, a forward force F2 that tries to linearly move the nut 60A in the forward direction X1 acts on the second point P2, which is the conversion portion CP of the linear motion conversion mechanism 50A.

[0030] In the nut 60A, the first point P1 to which the reaction force F1 is input is located further in the forward direction X1 than the second point P2 to which the forward force F2 is input. Furthermore, as shown in FIG. 3 , the screw shaft 51 is tilted. Therefore, the difference between the direction of the reaction force F1 acting on the first point P1 and the direction of the forward force F2 acting on the second point P2 is not 180°. Therefore, the load applied from the nut 60A to the piston 70A is uneven. On the page in FIG. 3 , of the contact portion of the nut 60A with the piston 70A, the load F1b applied to the portion below the screw shaft 51 is small, while the load F1a applied to the portion above the screw shaft 51 is large.

[0031] Also, on the paper surface of Figure 3, of the contact portion of the screw shaft 51 with the nut 60A, the load F2a applied to the portion above the screw shaft 51 is large, while the load F2b applied to the portion below the screw shaft 51 is large.

[0032] Here, the reaction force F1 is equal to the forward force F2, and the sum of the loads F1a and F1b is equal to the sum of the loads F2a and F2b. Furthermore, the load F1a becomes greater than the load F1b, and the load F2b becomes greater than the load F2a. This causes an excessive misalignment between the direction of the force the nut 60A receives from the screw shaft 51 and the direction of the force the piston 70A receives, generating a force that rotates the nut 60A clockwise relative to the rotation center PA. As a result, as indicated by arrow Y1 in FIG. 3 , the nut 60A tilts in a direction that increases the angle between the nut axis Zn and the screw axis Zv. A large angle between the nut axis Zn and the screw axis Zv increases wear between the nut 60A and the screw shaft 51.

[0033] Next, the linear motion conversion mechanism 50 provided in the electric braking device 20 of this embodiment will be described with reference to Figures 4 to 6. Figure 4 schematically shows the linear motion conversion mechanism 50 when the caliper body 30 is not deflected. Figure 5 schematically shows the linear motion conversion mechanism 50 when the caliper body 30 is deflected as described above. Figure 6 schematically shows the linear motion conversion mechanism 50 when increasing braking force even when the caliper body 30 is deflected.

[0034] 5, when the caliper body 30 is bent, the screw axis Zv of the screw shaft 51 supported by the caliper body 30 tilts. In other words, the angle between the nut axis Zn and the screw axis Zv increases.

[0035] When the braking force is increased and the angle between the nut axis Zn and the screw axis Zv becomes larger, and the nut 60 moves linearly in the forward direction X1, a reaction force F1 is input to the first point P1 from the receiving portion 75 of the piston 70. Meanwhile, a forward force F2 that tries to move the nut 60 linearly in the forward direction X1 acts on the second point P2, which is the conversion portion CP of the linear motion conversion mechanism 50. The reaction force F1 corresponds to the force that the nut 60 receives from the piston 70, and the forward force F2 corresponds to the force that the nut 60 receives from the screw shaft 51.

[0036] In this embodiment, the first point P1 is located in the backward direction X2 relative to the second point P2. Therefore, the nut 60 is pulled by a reaction force F1 acting on the first point P1 and a forward force F2 acting on the second point P2. This pulling force causes the nut 60 to rotate about the rotation center PA in a direction Y2 that causes the angle between the nut axis Zn and the screw axis Zv to approach 0 (zero), as shown in FIG. 6 , i.e., in a direction in which the axis of the linear motion part is aligned with the axis of the rotating part. As a result, the nut 60 is maintained coaxially disposed with respect to the screw shaft 51. Therefore, compared to the comparative example, the angle between the nut axis Zn and the screw axis Zv can be brought closer to 0 (zero), thereby suppressing wear between the nut 60 and the screw shaft 51 during linear motion of the nut 60.

[0037] That is, in the electric braking device 20, in order to rotate the nut 60 so that the screw axis Zv is aligned with the nut axis Zn by the forward force F2 that the nut 60 receives from the screw shaft 51 and the reaction force F1 that the nut 60 receives from the piston 70, the portion of the nut 60 that receives the force from the screw shaft 51 is positioned further in the forward direction X1 than the rotation center PA of the screw shaft 51. Therefore, the electric braking device 20 can extend the life of the linear motion conversion mechanism 50.

[0038] This embodiment can further achieve the following effects: (1) Even if the transmission part 63 is positioned further forward in the X1 direction than the engagement part 61, the contact position between the transmission part 63 and the receiving part 75 of the piston 70 can be positioned further backward in the X2 direction than the conversion part CP of the linear motion conversion mechanism 50. However, in this case, it is necessary to increase the radial size of the transmission part 63, which in turn increases the size of the electric braking device.

[0039] In this regard, in the electric braking device 20 of this embodiment, the transmission part 63 is disposed further in the backward direction X2 than the end of the engagement part 61 in the forward direction X1. This prevents the transmission part 63 from becoming too large in the radial direction, thereby preventing the electric braking device 20 from becoming too large.

[0040] <Modifications> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

[0041] One of the first surface of the transmitting portion 63 and the second surface of the receiving portion 75 may be a spherical surface that is convex toward the other surface. For example, as shown in Fig. 7, the second surface 75b of the receiving portion 75 may be a spherical surface, and the first surface 63b of the transmitting portion 63 may be a tapered surface.

[0042] The first surface of the transmission portion 63 and the second surface of the receiving portion 75 may be configured to allow relative rotation of the nut 60 with respect to the piston 70. The rotation axis of the screw shaft 51 when the caliper body 30 is deflected is defined as the predetermined axis. In this case, the first surface of the transmission portion 63 may be a curved surface extending in the circumferential direction around the predetermined axis.

[0043] - As long as the contact position between the transmission part 63 and the reception part 75 is located in the backward direction X2 from the second point P2, the transmission part 63 and the reception part 75 may be positioned so that the contact position is located at any position.

[0044] The linear motion conversion mechanism may be a mechanism in which the nut functions as the rotating part and the screw shaft functions as the linear motion part. Fig. 8 shows an electric braking device 120 equipped with such a linear motion conversion mechanism 150. The linear motion conversion mechanism 150 includes a nut 160 that functions as the rotating part and a screw shaft 151 that functions as the linear motion part.

[0045] The nut 160 has a nut body 161, a flange 163 connected to the end of the nut body 161 in the backward direction X2, and a connecting shaft 165 extending from the flange 163 in the backward direction X2. The connecting shaft 165 is fixed to the output gear 45 of the reduction mechanism 43. The nut body 161 has a cylindrical shape, and an engaging portion 162 is provided on the inner circumferential surface of the nut body 161. The engaging portion 162 is a portion of the inner circumferential surface of the nut body 161 that is internally threaded.

[0046] The screw shaft 151 has a cylindrical shaft body 152, a cylindrical portion 154 arranged coaxially with the shaft body 152, and a connecting portion 157 connecting the shaft body 152 and the cylindrical portion 154. The shaft body 152 is located inside the nut body 161. The circumferential surface of the shaft body 152 is provided with a male threaded portion 153 that is externally threaded. The male threaded portion 153 is threadedly engaged with an engaging portion 162 of the nut body 161.

[0047] Connecting portion 157 connects the end of shaft body 152 in forward direction X1 to the end of cylindrical portion 154 in forward direction X1. Cylindrical portion 154 is disposed so as to surround nut body 161 from the radial outside. In the example shown in FIG. 8 , cylindrical portion 154 is provided with a transmission portion 155 that transmits linear motion to piston 70. Of transmission portion 155, a first surface 155a facing piston 70 is preferably a spherical surface that is convex toward piston 70.

[0048] The transmission part 155 is disposed further in the backward direction X2 than the end of the conversion part CP of the linear motion conversion mechanism 150 in the forward direction X1. Preferably, the transmission part 155 is disposed further in the backward direction X2 than the center in the longitudinal direction of the conversion part CP. In the example shown in FIG. 8 , the transmission part 155 is disposed further in the backward direction X2 than the conversion part CP.

[0049] In this case, a receiving portion 175 is provided on the peripheral wall 73 of the piston 70 at a portion facing the transmission portion 155. The receiving portion 175 has a second surface 175a with which the first surface 155a comes into contact. The second surface 175a is configured to allow rotation of the screw shaft 151 relative to the piston 70. In the example shown in Fig. 8, the second surface 175a is a tapered surface.

[0050] The electric braking device does not have to be a caliper-type disc brake device as long as it is equipped with a linear motion conversion mechanism having a nut and a screw shaft. <Other Technical Ideas> Next, technical ideas that can be understood from the above embodiment and modified examples will be described.

[0051] [Supplementary Note 1] The transmission part is preferably located further in the retreat direction than the conversion part. [Supplementary Note 2] The contact position between the transmission part and the reception part is preferably located further in the advance direction than the rotation center of the linear motion part.

[0052] [Note 3] It is preferable that the transmission part has a first surface facing the receiving part, and the receiving part has a second surface with which the first surface comes into contact, and that the first surface and the second surface are configured so that the linear moving part can rotate relative to the piston around a predetermined axis that is perpendicular to the axis of the linear moving part and passes through the center of rotation.

[0053] [Supplementary Note 4] The first surface is preferably a spherical surface convex toward the second surface, or a surface extending in a circumferential direction about an orthogonal axis perpendicular to the axis of the linear motion part. [Supplementary Note 5] The second surface is preferably a spherical surface convex toward the first surface, or a surface extending in a circumferential direction about an orthogonal axis perpendicular to the axis of the rotating part.

[0054] [Note 6] Preferably, the rotating part is a threaded shaft rotatably supported by the caliper body, and the linear motion part is a nut arranged coaxially with the rotating part and radially outward of the rotating part.

[0055] [Appendix 7] An electric braking device in which a rotating part of a linear motion conversion mechanism rotates in response to the rotational motion of an electric motor, the rotational motion of the rotating part is converted into linear motion in a forward or backward direction of a linear motion part of the linear motion conversion mechanism, and the linear motion of the linear motion part in the forward direction causes linear motion of a piston, thereby increasing the braking force applied to the wheels of a vehicle, wherein: between the rotating part and the linear motion part, a conversion part is provided that converts the rotational motion into linear motion, and the rotating part engages with the linear motion part; the linear motion part includes a transmission part that transmits the linear motion to the piston, and the piston includes a receiving part that contacts the transmission part and receives force from the transmission part; and the contact position of the transmission part and the receiving part is located further in the backward direction than the forward direction end of the conversion part.

Claims

1. An electric braking device in which a rotating part of a linear motion conversion mechanism rotates in response to the rotational motion of an electric motor, the rotational motion of the rotating part is converted into linear motion in a forward or backward direction of a linear motion part of the linear motion conversion mechanism, and the linear motion of the linear motion part in the forward direction causes linear motion of a piston, thereby increasing the braking force applied to the wheels of a vehicle, and the linear motion part rotates about a predetermined imaginary point when the direction of the force it receives from the rotating part and the direction of the force it receives from the piston deviate excessively, wherein when the axis of the linear motion part moves linearly in the forward direction with the axis of the linear motion part tilted relative to the axis of the rotating part, the part of the linear motion part that receives force from the rotating part is positioned in the forward direction relative to the rotation center of the linear motion part so that the axis of the linear motion part rotates in a direction along the axis of the rotating part due to the force that the linear motion part receives from the rotating part and the force that the linear motion part receives from the piston.

2. The electric braking device described in claim 1, wherein the linear motion conversion mechanism includes a conversion part that converts the rotational motion of the rotating part into linear motion of the linear motion part, the linear motion part includes a transmission part that transmits linear motion to the piston, and the piston includes a receiving part that contacts the transmission part and receives a force from the transmission part, and the contact position between the transmission part and the receiving part is located in the backward direction relative to the conversion part.

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