Electric braking device

Abstract

To improve durability of an electric braking device.SOLUTION: A connection mechanism (31) of an electric braking device (1) connects a transmission unit (17) that transmits rotation of an electric motor (15) to a rotation unit (29), and includes a slid portion (31B) fixed to the transmission unit (17) and a sliding portion (31A) fixed to the rotation unit (29), and the sliding portion (31A) slides on the slid portion (31B) at a predetermined dynamic friction coefficient along with rotation of the rotation unit (29) in a braking force decreasing direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an electric braking system. [Background technology]

[0002] Patent Document 1 discloses a technology for addressing the problem of the durability of an electric braking device being compromised when a power failure occurs while braking force is being generated, by providing an elastic part that is positioned so as to be included within the movable range of the linear moving part or piston. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-049155 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the prior art, there is room for improvement in terms of reducing the axial size of the electric braking device. One aspect of the present disclosure aims to improve the durability of an electric braking device. [Means for solving the problem]

[0005] In order to solve the above problems, an electric braking device according to one aspect of the present disclosure is an electric braking device in which a rotating part of a linear motion conversion mechanism rotates in conjunction with the rotation of an electric motor, and the linear motion part of the linear motion conversion mechanism moves linearly, thereby generating a braking force on a wheel of a vehicle.The electric braking device comprises: a transmission part that transmits the rotation of the electric motor to the rotating part; and a connection mechanism that connects the transmission part to the rotating part, the connection mechanism having a slidable part fixed to the transmission part and a sliding part fixed to the rotating part, and configured so that as the rotating part rotates in the direction of decreasing the braking force, the sliding part slides against the slidable part with a predetermined dynamic friction coefficient. [Effects of the Invention]

[0006] According to one aspect of the present disclosure, the durability of the electric braking device can be improved. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic cross-sectional view of an electric braking device according to a first embodiment of the present disclosure. [Figure 2] FIG. 10 is a schematic diagram illustrating the configuration of a connection mechanism in an electric braking device according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Embodiment 1] FIG. 1 is a schematic cross-sectional view of an electric braking device according to a first embodiment of the present disclosure. The electric braking device 1 shown in Fig. 1 is mounted on a vehicle and generates a braking force on wheels 13 of the vehicle. As shown in Fig. 1, the electric braking device 1 is connected to a reservoir tank 11 that stores brake fluid and a wheel cylinder 12 provided on the wheel 13. The electric braking device 1 presses a friction member 12A against a rotating member 12B in accordance with the hydraulic pressure in the wheel cylinder 12, thereby generating a braking force on the wheel 13.

[0009] The electric braking device 1 includes a cylinder mechanism 14 , an electric motor 15 , a linear motion conversion mechanism 16 , a transmission unit 17 , a connection mechanism 31 , and a locking unit 32 . The cylinder mechanism 14 has a cylinder 18 and a piston 19 that is arranged within the cylinder 18 and is capable of linear movement. Within the cylinder 18, a fluid chamber 20 into which brake fluid is introduced is defined by the piston 19. The fluid chamber 20 is connected to the reservoir tank 11 and the wheel cylinder 12. A piston seal 21 is provided between the cylinder 18 and the piston 19 to prevent brake fluid from leaking from the fluid chamber 20 into the inside of the cylinder 18. The linear motion conversion mechanism 16 is a ball screw mechanism having a screw shaft 29 and a nut 30 connected to the piston 19 . The screw shaft 29 is an example of a rotating part, and has a male thread formed on the side surface. The nut 30 is an example of a linear motion part, and its inner peripheral surface faces the side of the screw shaft 29, and a female thread is formed on the inner peripheral surface. The nut 30 is fixed to the piston 19. The nut 30 converts the rotation of the screw shaft 29 into linear motion. The piston 19 moves linearly together with the nut 30. When the piston 19 moves in a direction that reduces the volume of the liquid chamber 20, the braking force generated on the wheel 13 increases. When the piston 19 moves in a direction that expands the volume of the liquid chamber 20, the braking force generated on the wheel 13 decreases. Hereinafter, the rotation direction of the screw shaft 29 when the braking force generated on the wheel 13 increases will be referred to as the braking force increasing direction, and the rotation direction of the screw shaft 29 when the braking force generated on the wheel 13 decreases will be referred to as the braking force decreasing direction.

[0010] The transmission unit 17 is for transmitting the rotation of the electric motor 15 to the screw shaft 29. The transmission unit 17 shown in Fig. 1 includes, for example, a first gear 26, a second gear 27, a third gear 28, and a bearing 28A. The first gear 26 is fixed to the motor shaft 25 of the electric motor 15 . The second gear 27 is in mesh with the first gear 26 . The third gear 28 is in mesh with the second gear 27 and is rotatably supported by a bearing 28A.

[0011] The connection mechanism 31 connects the third gear 28 of the transmission part 17 to the screw shaft 29. The connection mechanism 31 has a sliding part 31A and a slidable part 31B. The sliding part 31A has a columnar shape coaxial with the screw shaft 29, and has a male thread formed on the side surface. The sliding part 31A is connected to the screw shaft 29 so as not to rotate relative to the screw shaft 29, or is formed integrally with the screw shaft 29. In other words, the sliding part 31A is fixed to the screw shaft 29, which is the rotating part. The sliding portion 31B is provided in the hollow portion 28B of the third gear 28, and is formed with a female thread that screws together with the male thread of the sliding portion 31A. The sliding portion 31B may be connected to the hollow portion 28B of the third gear 28 so as to be unable to rotate relative to the third gear 28. As described above, the sliding portion 31B is fixed to the third gear 28 of the transmission part 17. The locking portion 32 is coaxial with the screw shaft 29, and its diameter is larger than the opening of the hollow portion 28B.

[0012] The male thread formed on the sliding part 31A has a thread direction opposite to that of the male thread formed on the screw shaft 29. When the screw shaft 29 rotates in a direction to decrease the braking force, a torque is applied to the sliding part 31A in a direction to loosen the screw engagement with the slidable part 31B. The sliding part 31A is configured so that a torque is applied to the sliding part 31A in a direction to loosen the screw engagement with the slidable part 31B, and the screw engagement with the slidable part 31B loosens when the absolute value of the torque applied to the sliding part 31A becomes equal to or greater than a first predetermined torque. The magnitude of the first predetermined torque is equal to or less than the maximum torque that can be generated by the electric motor 15. The magnitude of the first predetermined torque can be adjusted by the lead angle of the male thread of the sliding part 31A. When the screw shaft 29 rotates in a direction to increase the braking force, a torque is applied to the sliding part 31A in a direction to tighten the screw engagement with the slidable part 31B.

[0013] If the power supply to the electric motor 15 is lost while a large braking force is being generated on the wheels 13, the brake fluid that flows back into the fluid chamber 20 applies a force to the piston 19 that tries to push it back toward the third gear 28. The force pushing the piston 19 back is converted into rotational motion that rotates the screw shaft 29 in the direction of decreasing the braking force. The sliding part 31A slides against the slidable part 31B with a predetermined coefficient of kinetic friction, and converts the kinetic energy that rotates the screw shaft 29 in the direction of decreasing the braking force into heat energy or the like and consumes it.

[0014] If the power supply to the electric motor 15 is lost while a large braking force is being generated on the wheels 13, torque equal to or greater than the first predetermined torque may be applied to the sliding part 31A in a direction that loosens the screw engagement with the sliding target part 31B as the threaded shaft 29 rotates in the direction that reduces the braking force. This torque loosens the screw engagement between the sliding part 31A and the sliding target part 31B. At this time, the kinetic energy of the threaded shaft 29 is consumed by loss due to the sliding between the sliding part 31A and the sliding target part 31B, so that transmission of excessive torque to the threaded shaft 29 can be suppressed.

[0015] When the threaded engagement between sliding part 31A and slidable part 31B loosens, locking part 32 abuts against the opening of hollow part 28B of third gear 28, thereby locking sliding part 31A so that sliding part 31A does not come off from slidable part 31B. Because sliding part 31A does not come off completely from slidable part 31B, when power supply to electric motor 15 is restored and screw shaft 29 rotates in the direction increasing the braking force, the threaded engagement between sliding part 31A and slidable part 31B tightens, allowing for quick return.

[0016] [Embodiment 2] A second embodiment of the present disclosure will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the first embodiment, and the description thereof will not be repeated.

[0017] 2 is a schematic diagram showing the configuration of a connection mechanism in an electric braking device according to embodiment 2 of the present disclosure. As shown in Fig. 2, in connection mechanism 31 according to embodiment 2, the method of fitting sliding portion 31A and slidable portion 31B is different from that of embodiment 1.

[0018] The sliding portion 31A according to the second embodiment is a cylindrical protrusion 31C protruding from the side surface of the pillar-shaped portion. The sliding portion 31B according to the second embodiment is a recess 31D provided in the side wall of the hollow portion 28B. The recess 31D is, for example, a groove or hole provided in the side wall of the hollow portion 28B, and has a width and depth sufficient to accommodate the protrusion 31C therein.

[0019] The recess 31D has a tapered portion 31E on the side of the opening of the sliding portion 31B facing the screw shaft 29. When the sliding portion 31A is rotating in the direction of increasing the braking force, the protrusion 31C comes into contact with the tapered portion 31E and is guided along the tapered portion 31E to the back of the recess 31D. When the protrusion 31C reaches the inside of the recess 31D, the sliding portion 31A fits into the sliding portion 31B, and the rotation of the third gear 28 is transmitted to the screw shaft 29.

[0020] 2, when the screw shaft 29 is rotating in the braking force decreasing direction and torque equal to or greater than a first predetermined torque is applied to the sliding portion 31A, the protrusion 31C slides from the position indicated by the dashed line along the recess 31D. At this time, the kinetic energy of the screw shaft 29 is consumed by loss due to the sliding between the sliding portion 31A and the slid portion 31B, so that excessive torque can be prevented from being transmitted to the screw shaft 29. Furthermore, in the second embodiment, the contact surface between the sliding portion 31A and the slid portion 31B is smaller than in the first embodiment. This makes it easier for the sliding portion 31A and the slid portion 31B to slide when torque is applied in a direction that reduces the braking force of the rotating portion. By making it easier for the sliding portion 31A and the slidable portion 31B to slide, the sliding portion 31A can come off the slidable portion 31B, thereby releasing the connection between the sliding portion 31A and the nut 30 and the electric motor 15, which has a large mass. As a result, it is possible to further prevent excessive torque from being transmitted to the screw shaft 29. Furthermore, by providing the tapered portion 31E in the recessed portion 31D, even if the sliding portion 31A comes off the slidable portion 31B, it is possible to easily re-engage the convex portion 31C with the recessed portion 31D.

[0021] [Modification] In the first and second embodiments described above, the electric braking device 1 is configured such that the piston 19 moves linearly in a direction that reduces the fluid chamber 20 in response to the rotation of the electric motor 15, and the friction member 12A is pressed against the rotating member 12B by the hydraulic pressure of the brake fluid, thereby generating a braking force on the wheel 13. However, the electric braking device 1 may be configured to generate a braking force on the wheel 13 by a method other than pressing the friction member 12A against the rotating member 12B by the hydraulic pressure of the brake fluid. For example, the electric braking device 1 may be configured, like an electric caliper, to abut the piston 19 against the friction member 12A without using brake fluid, and the linear movement of the piston 19 presses the friction member 12A against the rotating member 12B, thereby generating a braking force on the wheel 13.

[0022] In the first embodiment, one end of the sliding portion 31A is connected to the threaded shaft 29, and the other end is provided with the locking portion 32. However, the other end of the sliding portion 31A according to the first embodiment does not necessarily have to be provided with the locking portion 32. This allows the axial size of the electric braking device 1 to be further reduced. In the second embodiment, the other end of the sliding portion 31A is not connected to the locking portion 32. However, the other end of the sliding portion 31A according to the second embodiment may be connected to the locking portion 32. This can prevent the sliding portion 31A from coming off the slidable portion 31B.

[0023] In the second embodiment, the sliding portion 31A is a cylindrical convex portion and the sliding target portion 31B is a concave portion, but the sliding target portion 31B may be provided with a cylindrical convex portion and the sliding portion 31A may be provided with a concave portion. The concave portion does not have to have the tapered portion 31E.

[0024] The transmission unit 17 is not limited to the configurations of the above-described Embodiments 1 and 2. For example, the transmission unit 17 may transmit the rotation of the electric motor 15 to the screw shaft 29 using a planetary gear mechanism. The rotating part may be a nut and the linear part may be a screw shaft.

[0025] 〔summary〕 An electric braking device according to one aspect of the present disclosure is an electric braking device in which a rotating part of a linear motion conversion mechanism rotates in conjunction with the rotation of an electric motor, and the linear motion part of the linear motion conversion mechanism moves linearly, thereby generating a braking force on a wheel of a vehicle.The electric braking device comprises: a transmission part that transmits the rotation of the electric motor to the rotating part; and a connection mechanism that connects the transmission part to the rotating part, the connection mechanism having a slidable part fixed to the transmission part and a sliding part fixed to the rotating part, and configured so that as the rotating part rotates in the direction of reducing the braking force, the sliding part slides against the slidable part with a predetermined dynamic friction coefficient. The connection mechanism is configured so that the sliding part and the slidable part slide with a predetermined dynamic friction coefficient as the rotating part rotates in the braking force decreasing direction. As a result, the kinetic energy of the rotating part in the braking force decreasing direction is used to slide the sliding part and the slidable part of the connection mechanism. In this way, by consuming the kinetic energy of the rotating part, the kinetic energy with which the linear part of the linear motion conversion mechanism collides with the electric braking device can be reduced, and the durability of the electric braking device can be improved. In addition, the connection mechanism that connects the transmission part to the rotating part can reduce the kinetic energy with which the linear part of the linear motion conversion mechanism collides with the electric braking device, thereby making it possible to reduce the axial size of the electric braking device compared to when a member for reducing kinetic energy is inserted in the axial direction of the electric braking device.

[0026] In one aspect of the electric braking device of the present disclosure, the connection mechanism is configured with a screw, and the connection mechanism is configured so that the screw loosens when the absolute value of the torque becomes equal to or greater than a first predetermined torque that is equal to or less than the maximum torque generated by the electric motor. In the electric braking device, when the braking force is reduced, a reaction force of the braking force applied by the electric braking device is applied to the electric braking device, so the absolute value of the torque of the electric motor required to rotate the rotating part in the direction of reducing the braking force can be made smaller than the first predetermined torque. For this reason, by configuring the screws of the connection mechanism to loosen when the torque reaches or exceeds the first predetermined torque, which is less than the maximum value of the torque generated by the electric motor, it is possible to both satisfy the functionality of the electric braking device and improve the durability of the electric braking device.

[0027] In one aspect of the electric braking device of the present disclosure, in the connection mechanism, one of the sliding portion and the slidable portion has a cylindrical convex portion, and the other of the sliding portion and the slidable portion has a concave portion that is a groove or a hole, and the connection mechanism is connected by fitting the convex portion and the concave portion together. By having one of the sliding part and the slidable part be a cylindrical convex part and the other be a groove or hole concave part, the contact area between the sliding part and the slidable part can be made smaller than with other structures (e.g., screws), which makes it easier for the sliding part and the slidable part to slide when torque is applied in the direction that reduces the braking force of the rotating part.

[0028] [Additional Notes] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure. [Explanation of symbols]

[0029] 1 Electric braking device 13 wheels 15 Electric motor 16. Linear motion conversion mechanism 17 Transmission section 18 cylinders 19 Piston 29 Screw shaft (rotating part) 30 nuts 31 Connection mechanism 31A Sliding part 31B Sliding part 31C convex part 31D Recess 31E tapered section 32 Locking part

Claims

1. An electric braking device in which a rotating part of a linear motion conversion mechanism rotates in conjunction with rotation of an electric motor, and a linear motion part of the linear motion conversion mechanism moves linearly, thereby generating a braking force on a wheel of a vehicle, a transmission unit that transmits rotation of the electric motor to the rotating unit; an electric braking device comprising: a connection mechanism that connects the transmission part to the rotating part, the connection mechanism having a slidable part fixed to the transmission part and a sliding part fixed to the rotating part, and configured so that the sliding part slides against the slidable part with a predetermined dynamic friction coefficient as the rotating part rotates in a direction that reduces the braking force.

2. 2. The electric braking device according to claim 1, wherein the connection mechanism is configured with a screw, and the connection mechanism is configured so that the screw loosens when the absolute value of the torque reaches or exceeds a first predetermined torque that is less than or equal to a maximum value of the torque generated by the electric motor.

3. In the connection mechanism, one of the sliding part and the slidable part has a cylindrical convex part, and the other of the sliding part and the slidable part has a concave part which is a groove or a hole, The electric braking device according to claim 1 , wherein the connection mechanism is connected by fitting the protrusion into the recess.

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