Electric braking device

Abstract

An electric braking device (1) comprises: a second flange part (15) that protrudes in a rotation radial direction of a rotating member (12) outside a cylinder (20); and an elastic body (16) that is provided between a bottom part (21) of the cylinder (20) and the second flange part (15), and that separates the cylinder (20) and the second flange part (15) by elastic force during non-braking.

Description

electric braking device

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

[0002] Generally, electric braking devices have bearings that allow the rotary-to-linear motion conversion mechanism to rotate relative to the caliper housing. For example, Patent Document 1 discloses a disc brake that includes a thrust bearing that allows the rotary-to-linear motion conversion mechanism to rotate relative to a cylinder that houses a piston.

[0003] Japanese Patent Application Laid-Open No. 2020-100368

[0004] However, since the amount of warpage of the bearing ring of the thrust bearing is subject to manufacturing errors and changes over time, when the axial force applied to the thrust bearing is small, the displacement of the screw shaft relative to the axial force may become unstable. One aspect of the present disclosure aims to realize an electric braking device in which the displacement of the screw shaft relative to the axial force applied to the thrust bearing is stable.

[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 that transmits rotational motion generated by an electric motor to a linear motion conversion mechanism, converts the rotational motion of a rotating member of the linear motion conversion mechanism into linear motion of a linear motion member of the linear motion conversion mechanism that drives a piston provided in a cylindrical cylinder having a bottom, and generates a braking force on a wheel by pressing a friction portion attached to the linear motion member against a friction-bearing portion that rotates together with the wheel of a vehicle, wherein the rotating member is equipped with: a first flange portion that penetrates the bottom of the cylinder and is provided on the rotating member and protrudes radially from inside the cylinder in the direction of rotation of the rotating member; a thrust bearing that is provided between the first flange portion and the bottom of the cylinder and allows relative rotation between the rotating member and the cylinder; a second flange portion that is provided on the rotating member and protrudes radially from outside the cylinder in the direction of rotation of the rotating member; and an elastic body that is provided between the bottom of the cylinder and the second flange portion and uses elastic force to separate the cylinder and the second flange portion when not braking.

[0006] According to one aspect of the present disclosure, it is possible to stabilize the displacement of the screw shaft in response to the axial force applied to the thrust bearing.

[0007] It is a sectional view of the electric braking device according to the first embodiment of the present disclosure. It is a diagram for explaining the displacement of the screw shaft with respect to the axial force. It is a sectional view of the electric braking device according to the second embodiment of the present disclosure.

[0008] [Embodiment 1] Fig. 1 is a cross-sectional view of an electric braking device according to embodiment 1 of the present disclosure. The electric braking device 1 shown in Fig. 1 includes a linear motion conversion mechanism 10, a cylinder 20, a piston 30, a friction portion 40, and a piston seal 50, and is used, for example, in an electric caliper disposed on a wheel of a vehicle. Hereinafter, a forward direction and a reverse direction will be defined as shown by the arrows in Fig. 1.

[0009] The linear motion conversion mechanism 10 has a linear motion member 11 and a screw shaft 12. The linear motion member 11 is, for example, a nut and has a cylindrical shape. The outer circumferential surface of the linear motion member 11 faces the inner circumferential surface of the piston 30. The screw shaft 12 is an example of a rotating member and is screwed with the linear motion member 11.

[0010] The cylinder 20 has a cylindrical shape with a bottom 21. The screw shaft 12 passes through the bottom 21 of the cylinder 20. A first flange 13 is provided on the screw shaft 12 inside the cylinder 20. The first flange 13 protrudes from the inside of the cylinder 20 in the direction of the rotational diameter of the screw shaft 12.

[0011] A thrust bearing 14 is provided between the first flange portion 13 and the bottom portion 21 of the cylinder 20. The screw shaft 12 is inserted through the thrust bearing 14. The thrust bearing 14 allows the screw shaft 12 to rotate relative to the cylinder 20.

[0012] A gear 15 is provided on the outside of the cylinder 20. Rotational motion generated by an electric motor is transmitted to the gear 15. The gear 15 is connected to the screw shaft 12 by a key member 15A. The gear 15 connected to the screw shaft 12 by the key member 15A is an example of a second flange portion. The rotational motion of the gear 15 is transmitted to a linear motion member 11 that threads onto the screw shaft 12. The linear motion member 11 converts the rotational motion of the screw shaft 12 into linear motion. When the gear 15 rotates in a predetermined forward direction, the linear motion member 11 moves linearly forward, and when the gear 15 rotates in the reverse direction, the linear motion member 11 moves linearly backward. A piston 30 is connected to the linear motion member 11 by a key member 31. The piston 30 moves linearly inside the cylinder 20 together with the linear motion member 11.

[0013] The friction portion 40 is, for example, a brake pad. When the piston 30 moves linearly forward, the axial force of the screw shaft 12 is applied to the friction portion 40, and the friction portion 40 is pressed against a friction target portion, such as a disc rotor, that rotates together with the wheel, generating a braking force on the wheel. The piston seal 50 is provided between the cylinder 20 and the piston 30 and prevents foreign matter from entering the inside of the cylinder 20.

[0014] The screw shaft 12 is inserted through a disc spring 16 and a radial bearing 17, which are provided between the thrust bearing 14 and the gear 15. The radial bearing 17 has an outer ring 17A and an inner ring 17B as raceways. The outer ring 17A of the radial bearing 17 is fixed to the cylinder 20, and the inner ring 17B of the raceway is fitted onto the outer periphery of the screw shaft 12. The inner ring 17B of the raceway may be fitted onto the outer periphery of the screw shaft 12 by a clearance fit or an interference fit. The radial bearing 17 may be a ball bearing that uses balls as rolling elements, or a roller bearing that uses rollers that are shaped like truncated cones or the like as rolling elements.

[0015] The disc spring 16 is an example of an elastic body. The disc spring 16 abuts against the inner ring 17B of the radial bearing 17 and the gear 15 (the second flange portion according to the first embodiment). The disc spring 16 does not abut against the outer ring 17A of the radial bearing 17. The disc spring 16 separates the inner ring 17B of the radial bearing 17 and the gear 15 by its elastic force. Because the disc spring 16 rotates integrally with the gear 15 and the inner ring 17B of the radial bearing 17, no sliding resistance occurs between the gear 15 and the inner ring 17B of the radial bearing 17. Because the disc spring 16 does not abut against the outer ring 17A of the radial bearing 17, which is fixed to the cylinder 20, no sliding resistance occurs between the disc spring 16 and the outer ring 17A of the radial bearing 17.

[0016] FIG. 2 is a diagram illustrating the displacement of the screw shaft relative to the axial force. The axial force is the force with which the piston presses the friction portion. The raceway of the thrust bearing 14 may be warped. The warp of the raceway of the thrust bearing 14 is flattened when a predetermined axial load is applied to the raceway. As shown by the solid line in FIG. 2, ideally, the displacement of the screw shaft 12 increases steadily as the axial force of the screw shaft 12 increases. However, if the thrust bearing 14 is warped, the displacement of the screw shaft 12 relative to the axial force of the screw shaft 12 will not be as ideal until the axial force of the screw shaft 12 reaches F1 and the raceway of the thrust bearing 14 is flattened, as shown by the dashed line in FIG. 2.

[0017] Furthermore, since the warping of the raceway of the thrust bearing 14 changes due to manufacturing errors and changes over time such as wear, the axial force F1 at which the raceway of the thrust bearing 14 becomes flat may change, and in the range where the axial force of the screw shaft 12 is less than F1, the displacement of the screw shaft 12 relative to the axial force of the screw shaft 12 may not be stable.

[0018] In the electric braking device 1 of the first embodiment, the elastic force of the disc spring 16 urges the gear 15 in the backward direction so as to move away from the radial bearing 17. Because the gear 15 is connected to the screw shaft 12, the elastic force of the disc spring 16 urges the screw shaft 12 in the backward direction, and the first flange portion 13 provided on the screw shaft 12 is urged toward the thrust bearing 14. The disc spring 16 is configured so that the elastic force of the disc spring 16 causes the first flange portion 13 to press the raceway of the thrust bearing 14 with a force of F1 or more. By flattening the raceway of the thrust bearing 14 in advance using the elastic force of the disc spring 16, the displacement of the screw shaft 12 relative to the axial force of the screw shaft 12 can be made closer to the relationship shown by the solid line in Figure 2.

[0019] [Embodiment 2] Another 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 above embodiment, and the description thereof will not be repeated.

[0020] 3 is a cross-sectional view of an electric braking device according to a second embodiment of the present disclosure. In the electric braking device 1 according to the second embodiment, the disc spring 16 abuts against the cylinder 20 and the outer ring 17A of the radial bearing 17. The outer ring 17A of the radial bearing 17 is not fixed to the cylinder 20. The radial bearing 17 can move linearly in the forward and backward directions together with the gear 15 and the screw shaft 12. The inner ring 17B of the radial bearing 17 is connected to the gear 15.

[0021] The gear 15 and the radial bearing 17 connected to the gear 15 in the electric braking device 1 according to the second embodiment of the present disclosure are an example of a second flange portion. The elastic force of the disc spring 16 urges the gear 15 and the radial bearing 17 (the second flange portion according to the second embodiment) to move away from the cylinder 20. Because the gear 15 is connected to the screw shaft 12, the elastic force of the disc spring 16 urges the screw shaft 12 in the backward direction, and the first flange portion 13 provided on the screw shaft 12 is urged toward the thrust bearing 14. The elastic force of the disc spring 16 flattens the raceway ring of the thrust bearing 14 in advance, thereby enabling the displacement of the screw shaft 12 relative to the axial force of the screw shaft 12 to approach the relationship shown by the solid line in FIG. 2 .

[0022] [Modifications] In the above-described first and second embodiments, the disc spring 16 is provided between the second flange portion according to each embodiment and the cylinder 20, but the second flange portion according to each embodiment may be biased in the retracting direction by an elastic body other than the disc spring 16. For example, instead of the disc spring 16, an elastic body such as a wave washer or an O-ring may be used to bias the second flange portion according to each embodiment in the retracting direction.

[0023] [Summary] An electric braking device according to one aspect of the present disclosure is an electric braking device that transmits rotational motion generated by an electric motor to a linear motion conversion mechanism, converts the rotational motion of a rotating member of the linear motion conversion mechanism into linear motion of a linear motion member of the linear motion conversion mechanism that drives a piston provided in a cylindrical cylinder having a bottom, and generates a braking force on a wheel of a vehicle by pressing a friction portion attached to the linear motion member against a frictioned portion that rotates together with the wheel of the vehicle, wherein the rotating member comprises: a first flange portion that penetrates the bottom of the cylinder and is provided on the rotating member and protrudes radially from inside the cylinder in the direction of rotation of the rotating member; a thrust bearing that is provided between the first flange portion and the bottom of the cylinder and allows relative rotation between the rotating member and the cylinder; a second flange portion that is provided on the rotating member and protrudes radially from outside the cylinder in the direction of rotation of the rotating member; and an elastic body that is provided between the bottom of the cylinder and the second flange portion and uses elastic force to separate the cylinder and the second flange portion when not braking. In the present disclosure, an elastic body is provided between a second flange portion provided on the rotating member and the cylinder. The elastic force of the elastic body separates the second flange portion from the cylinder, and a thrust bearing provided between a first flange portion provided on the rotating member and the cylinder is pressed by the first flange portion. Therefore, by pressing the thrust bearing with the elastic force of the elastic body, the displacement of the screw shaft is stabilized even for small axial forces, which previously caused unstable displacement of the screw shaft in response to axial forces.

[0024] In one aspect of the electric braking device of the present disclosure, the electric braking device has a radial bearing that allows relative rotation between the rotating member and the cylinder and is fitted around the outer periphery of the rotating member, and the elastic body is in contact with the inner ring of the radial bearing and the second flange portion, but is not in contact with the outer ring of the radial bearing. The elastic body is in contact with the inner ring of the radial bearing and the second flange portion, but is not in contact with the outer ring of the radial bearing. The inner ring of the radial bearing is fitted around the outer periphery of the rotating member and rotates together with the rotating member. The elastic body is in contact with the inner ring of the radial bearing, and therefore rotates together with the rotating member. Because the elastic body is not in contact with the outer ring of the radial bearing, no sliding resistance is generated between the elastic body and the outer ring of the radial bearing.

[0025] In the electric braking device according to the aspect of the present disclosure, relative rotation of the outer ring of the radial bearing with respect to the cylinder is restricted.

[0026] [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.

Claims

1. An electric braking device that transmits rotational motion generated by an electric motor to a linear motion conversion mechanism, converts the rotational motion of a rotating member of the linear motion conversion mechanism into linear motion of a linear motion member of the linear motion conversion mechanism that drives a piston located within a cylindrical cylinder with a bottom, and generates braking force on a vehicle wheel by pressing a friction part attached to the linear motion member against a frictioned part that rotates together with the wheel, wherein the rotating member penetrates the bottom of the cylinder and comprises: a first flange part that is attached to the rotating member and protrudes radially inside the cylinder in the direction of rotation of the rotating member; a thrust bearing that is attached between the first flange part and the bottom of the cylinder and allows relative rotation between the rotating member and the cylinder; a second flange part that is attached to the rotating member and protrudes radially outside the cylinder in the direction of rotation of the rotating member; and an elastic body that is attached between the bottom of the cylinder and the second flange part and uses elastic force to separate the cylinder and the second flange part when not braking.

2. An electric braking device as described in claim 1, characterized in that it has a radial bearing that allows relative rotation between the rotating member and the cylinder and is fitted onto the outer periphery of the rotating member, and the elastic body contacts the inner ring of the radial bearing and the second flange portion, but does not contact the outer ring of the radial bearing.

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