Electric braking device

Abstract

This electric braking device (1) has a first curved surface on at least one of a pressing surface (14) of a linear motion part (11) and a pressed surface (32) of a piston (30), and has a second curved surface in a range in which a connection member (50) engaged with the first engagement part (31) and the second engagement part (13) engages with the first engagement part (31) so as to swing so that the linear motion axis of the piston (30) is inclined.

Description

electric braking device

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

[0002] Generally, an electric braking device that uses a screw mechanism to move a piston in the axial direction of a cylinder requires a rotation prevention mechanism that restricts relative rotation of the linearly moving part and the piston with respect to the cylinder. Patent Document 1 discloses a ball screw device that includes a rotation prevention member that prevents relative rotation of the nut with respect to the housing, and a retaining ring that is engaged so as to span between the nut with a first retaining ring groove and the piston with a second retaining ring groove.

[0003] JP 2023-82214 A

[0004] However, in the ball screw device disclosed in Patent Document 1, when a retaining ring is used to prevent relative displacement of the nut with respect to the piston, an offset load is generated on the nut due to the axial tilt of the piston with respect to the axial direction of the cylinder, which may reduce the life of the screw mechanism. One aspect of the present disclosure aims to suppress the offset load generated in the linear motion part of the linear motion conversion part due to the axial tilt of the piston with respect to the axial direction of the cylinder.

[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 converts the rotational motion of an electric motor into linear motion of a linear motion part of a linear motion conversion mechanism, drives a piston that is in contact with the inner periphery of a cylinder using the linear motion, and presses a friction material against a rotating body that rotates together with the wheel of a vehicle, thereby applying a braking force to the wheel, wherein the piston has a first engagement part with which a connecting member engages on its inner circumferential surface, and has a second engagement part that engages with the connecting member on its outer circumferential surface of the linear motion part that faces the inner circumferential surface of the piston, the connecting member engages with both the first engagement part and the second engagement part, a pressing surface of the linear motion part that presses the piston and a pressed surface of the piston that is pressed by the linear motion part are in contact, at least one of the pressing surface and the pressed surface has a first curved surface, and the connecting member has a second curved surface in a range engaged with the first engagement part so that the piston swings so that the linear motion axis of the linear motion is tilted.

[0006] 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 converts the rotational motion of an electric motor into linear motion of a linear motion part of a linear motion conversion mechanism, drives a piston, and applies a braking force to a vehicle wheel by pressing a friction material against a rotating body that rotates together with the wheel, wherein the piston has a cylindrical shape with a bottom, is engaged with the friction material, and has an outer peripheral surface abutting a cylinder, the linear motion part has a cylindrical shape, an outer peripheral surface facing the inner peripheral surface of the piston, and has a pressing surface that abuts a predetermined pressed surface of the piston when the linear motion part moves linearly in accordance with the rotational motion of the electric motor, and is provided with a connecting member that connects the piston to the linear motion part by engaging with the inner peripheral surface of the piston and the outer peripheral surface of the linear motion part, and at least one of the pressing surface and the pressed surface has a first curved surface so that the axial direction of the piston is inclined with respect to the axial direction of the cylinder, and a second curved surface is provided on the surface of the connecting member in a range that engages with the inner peripheral surface of the piston.

[0007] According to one aspect of the present disclosure, it is possible to suppress an unbalanced load that occurs in a linear moving part due to an inclination of the axial direction of the piston with respect to the axial direction of the cylinder.

[0008] 1 is a cross-sectional view of an electric braking device according to an embodiment of the present disclosure; FIG. 2 is a diagram showing an example of a method for connecting a piston of an electric braking device according to an embodiment of the present disclosure to a linear moving part;

[0009] Fig. 1 is a cross-sectional view of an electric braking device according to an embodiment 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, brake pads 40, and a connecting member 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 arrows in Fig. 1. In Fig. 1, the forward direction and the reverse direction are parallel to an axis A along which the cylinder 20 extends.

[0010] The linear motion conversion mechanism 10 has a linear motion part 11 and a rotating part 12. The linear motion part 11 is, for example, a nut and has a cylindrical shape. The rotating part 12 is a threaded shaft that is rotatable about a rotation axis that overlaps with the axis A of the cylinder 20. The linear motion part 11 has an outer circumferential surface that faces the inner circumferential surface of the piston 30, and the inner circumferential surface is threadedly engaged with the rotating part 12.

[0011] The piston 30 has, for example, a cylindrical shape with a bottom. The bottom surface of the piston 30 abuts against the brake pad 40. The inner circumferential surface of the piston 30 faces the outer circumferential surface of the linear motion part 11. The outer circumferential surface of the piston 30 faces the inner circumferential surface of the cylinder 20. The brake pad 40 is an example of a friction material. The piston 30 has a first engagement portion 31 on a part of its inner circumferential surface. The piston 30 shown in FIG. 1 has two first engagement portions 31 on its inner circumferential surface. The first engagement portions 31 are, for example, through holes that penetrate between the inner circumferential surface and the outer circumferential surface of the piston 30. The opening shape of the first engagement portion 31 is, for example, a perfect circle.

[0012] The linear motion part 11 has a second engagement part 13 on a part of its outer circumferential surface. The second engagement part 13 is disposed at a position facing the first engagement part 31 of the piston 30. The linear motion part 11 shown in FIG. 1 has two second engagement parts 13 on its outer circumferential surface. The second engagement parts 13 are, for example, recesses recessed in the radial direction from the outer circumferential surface of the linear motion part 11. The bottom surface of the second engagement parts 13 shown in FIG. 1 is a curved surface, and the opening shape of the second engagement parts 13 is a perfect circle.

[0013] The forward direction end of the outer peripheral surface of the linear moving part 11 has a first curved surface 14 that is curved toward the axis A of the cylinder 20 and is narrowed. The inner peripheral surface of the piston 30 has a tapered surface 32 at a position facing the first curved surface 14. When the first engaging part 31 of the piston 30 is at a position facing the second engaging part 13 of the linear moving part 11, the first curved surface 14 of the linear moving part 11 abuts against the tapered surface 32 of the piston 30.

[0014] The connecting member 50 connects the linear moving part 11 and the piston 30 by engaging with the first engagement portion 31 of the piston 30 and the second engagement portion 13 of the linear moving part 11. The connecting member 50 is, for example, a steel ball. The electric braking device 1 shown in FIG. 1 has two connecting members 50. A portion of the connecting member 50 engages with the second engagement portion 13 of the linear moving part 11, and another portion of the connecting member 50 engages with the first engagement portion 31 of the piston 30. The spherical surface of the portion of the surface of the connecting member 50 that engages with the first engagement portion 31 of the piston 30 is an example of a second curved surface. The diameter of the spherical connecting member 50 is smaller than the hole diameter of the first engagement portion 31 of the piston 30 and larger than the depth of the second engagement portion 13 of the linear moving part 11. Furthermore, the difference between the diameter of the connecting member 50 and the sum of the depths of the first engagement portion 31 and the second engagement portion 13 is smaller than the depth of the second engagement portion 13.

[0015] 2 is a diagram illustrating an example of a method for connecting a piston of an electric braking device according to an embodiment of the present disclosure to a linear motion part. As shown in FIG. 2 , the connecting member 50 is inserted from the opening of the first engagement part 31 on the outer circumferential surface side of the piston 30, and a portion of the connecting member 50 protrudes from the opening of the first engagement part 31 on the inner circumferential surface side of the piston 30 toward the second engagement part 13 of the linear motion part 11, thereby engaging with the second engagement part 13. Because the diameter of the connecting member 50 is larger than the depth of the second engagement part 13, the connecting member 50 can engage with the first engagement part 31 even when engaged with the second engagement part 13. The opening of the first engagement part 31 on the outer circumferential surface side of the piston 30 is covered by the inner circumferential surface of the cylinder 20, so that the connecting member 50 is housed in a space formed by the first engagement part 31 of the piston 30 and the second engagement part 13 of the linear motion part 11.

[0016] Because the difference between the diameter of the connecting member 50 and the sum of the depths of the first engaging portion 31 and the second engaging portion 13 is smaller than the depth of the second engaging portion 13, the connecting member 50 will not come off the second engaging portion 13 even when it abuts against the inner circumferential surface of the cylinder 20. Furthermore, because the diameter of the connecting member 50 is larger than the depth of the second engaging portion 13 of the linear moving portion 11, the connecting member 50 will not come off the first engaging portion 31 even when it abuts against the bottom surface of the second engaging portion 13. Therefore, the piston 30 is connected to the linear moving portion 11, and the linear movement of the piston 30 relative to the linear moving portion 11 is restricted.

[0017] As shown in FIG. 1 , in the linear motion conversion mechanism 10, the rotating unit 12 rotates when rotational motion is transmitted from an electric motor (not shown). The rotation of the rotating unit 12 is transmitted to the linear motion unit 11, the inner circumferential surface of which is threadedly engaged with the rotating unit 12. The relative rotation of the linear motion unit 11 with respect to the cylinder 20 is restricted by frictional force. For example, the brake pad 40 may be engaged with the piston 30 by frictional force generated at a contact portion where the brake pad 40 and the bottom surface of the piston 30 come into contact, thereby restricting the relative rotation of the linear motion unit 11 and the piston 30 with respect to the cylinder 20. This allows the linear motion unit 11 to efficiently convert the rotation of the rotating unit 12 into linear motion. The relative rotation of the linear motion unit 11 with respect to the cylinder 20 is also restricted by frictional force generated at a contact portion between the tapered surface 32 of the piston 30 and the first curved surface 14 of the linear motion unit 11.

[0018] If a waterproof and dustproof mechanism using an O-ring or the like is provided between the inner surface of the cylinder 20 and the outer surface of the piston 30, the relative rotation of the linear moving part 11 with respect to the cylinder 20 is also regulated by the frictional force between the outer surface of the piston 30 and the waterproof and dustproof mechanism.

[0019] When the linearly moving part 11 moves linearly in the forward direction, the first curved surface 14 of the linearly moving part 11 serves as a pressing surface that presses the piston 30, and the tapered surface 32 of the piston 30 serves as a pressed surface. The piston 30 moves in the forward direction in accordance with the linear movement of the linearly moving part 11 in the forward direction. The movement of the piston 30 in the forward direction presses the brake pads 40, and the brake pads 40 are pressed against a rotating body such as a disc rotor that rotates together with the wheel, thereby applying a braking force to the wheel.

[0020] The position at which the connecting member 50 contacts the first engagement portion 31 and the second engagement portion 13 changes depending on the rotation direction of the rotating portion 12. The linear axis of the piston 30 tilts with respect to the axis A of the cylinder 20 depending on the position at which the connecting member 50 contacts the inner wall surface of the first engagement portion 31. The axial direction of the piston 30 can oscillate, for example, within a range R shown in FIG. 1. The range R passes through the contact point where the first curved surface 14 of the linear motion portion 11 and the tapered surface 32 of the piston 30 contact each other, and has a spherical crown shape that is convex in the forward movement direction. In the cross-sectional view of FIG. 1, the range R is illustrated as a circular arc.

[0021] The load applied in a direction that tilts the linear axis of the piston 30 relative to the axis A of the cylinder 20 is absorbed by the spherical surface (second curved surface) in the range where the connecting member 50 engages with the first engagement portion 31, and is transmitted to the inner surface of the cylinder 20.

[0022] [Modifications] In the above embodiment, the connecting member 50 is a steel ball, but this is not limiting. The connecting member 50 may be formed of a material other than steel as long as it has sufficient rigidity to avoid deformation due to the load applied in accordance with the rotational movement of the electric motor. Furthermore, the connecting member 50 may have a surface that becomes the second curved surface at least in the area where it engages with the first engagement portion 31, and may have a shape other than a sphere as long as the shape does not impair the function of connecting the piston 30 to the linear motion portion 11. For example, the connecting member 50 may be hemispherical, oval, or semi-oval.

[0023] In the above embodiment, the first engagement portion 31 has a circular opening and is a through-hole that penetrates between the inner and outer circumferential surfaces of the piston 30. However, this is not limited thereto. The first engagement portion 31 may have any shape as long as it has an opening at least on the inner circumferential surface side of the piston 30 and is capable of engaging with the connecting member 50. For example, the first engagement portion 31 may be a recess or a hole that does not penetrate between the inner and outer circumferential surfaces of the piston 30. The opening shape of the first engagement portion 31 may be, for example, an elongated hole extending in the direction of the linear axis of the piston 30. By forming the first engagement portion 31 as an elongated hole extending in the direction of the linear axis of the piston 30, it is possible to prevent the piston 30 from colliding with the connecting member 50 due to swinging in a direction that tilts the linear axis.

[0024] In the above embodiment, the first engagement portion 31 is illustrated on the forward direction side of the piston 30. However, the first engagement portion 31 may be disposed at a position on the rearward direction side of the piston 30. By disposing the first engagement portion 31 at a position on the rearward direction side of the piston 30, contact with a seal member (not shown) provided between the piston 30 and the cylinder 20 can be prevented.

[0025] In the above embodiment, the second engagement portion 13 has a recessed portion with a curved bottom surface, but this is not limited thereto. The second engagement portion 13 may have any shape as long as it is recessed from the outer circumferential surface of the linear motion portion 11 and can engage with the connecting member 50. For example, the bottom surface of the second engagement portion 13 may be flat, and the opening shape of the second engagement portion 13 may be polygonal. The bottom surface of the second engagement portion 13 may also be a curved surface, for example, an arc shape having a center identical to the range R. By having the bottom surface of the second engagement portion 13 have an arc shape having a center identical to the range R, it is possible to suppress an unbalanced load generated in the linear motion portion 11 due to the pivoting of the connecting member 50 in a direction that tilts the linear motion axis of the piston 30.

[0026] In the above embodiment, the electric braking device 1 is illustrated with two each of the connecting members 50, the first engaging portions 31, and the second engaging portions 13. However, it is sufficient for the electric braking device 1 to include at least one each of the connecting members 50, the first engaging portions 31, and the second engaging portions 13.

[0027] In the above embodiment, the pressing surface of the linear moving part 11 that presses the piston 30 is the first curved surface 14, and the pressed surface of the piston 30 that is pressed by the linear moving part 11 is the tapered surface 32. However, it is sufficient if at least one of the pressing surface of the linear moving part 11 and the pressed surface of the piston 30 forms the first curved surface. When the pressed surface of the piston 30 is a curved surface, the pressing surface of the linear moving part 11 may be a tapered surface.

[0028] In the above embodiment, the piston 30 is engaged by frictional force generated at the contact portion where the brake pad 40 and the bottom surface of the piston 30 come into contact. However, engagement between the brake pad 40 and the bottom surface of the piston 30 is not limited to frictional force generated at these contact portions. For example, the piston 30 and the brake pad 40 may be provided with mating portions that fit together, and the piston 30 may be mated with the brake pad 40, thereby engaging the brake pad 40 with the bottom surface of the piston 30. The relative rotation of the linearly moving portion 11 and the piston 30 with respect to the cylinder 20 can be restricted without relying on the force with which the piston 30 presses against the brake pad 40.

[0029] In the above embodiment, the piston 30 has a cylindrical shape with a bottom, but is not limited to this. For example, the bottom shape of the piston 30 may be a regular polygon. The piston 30 only needs to be restricted from rotating relative to the cylinder 20, and the piston 30 may have a fitting portion on its side that fits with the cylinder 20 or the brake pad 40. Furthermore, the bottom shape of the piston 30 may be annular, and may have a fitting portion that fits with the bottom of the piston 30 and the brake pad.

[0030] The dimensions of the linear motion conversion mechanism 10, the cylinder 20, the piston 30, and the connecting member 50 are not limited to those shown in Figures 1 and 2, but are determined according to the required strength determined at the design stage of the electric braking device 1.

[0031] [Summary] An electric braking device according to one aspect of the present disclosure is an electric braking device that converts the rotational motion of an electric motor into linear motion of a linear motion part of a linear motion conversion mechanism, drives a piston that is in contact with the inner periphery of a cylinder with the linear motion, and applies a braking force to the wheel by pressing a friction material against a rotating body that rotates together with the wheel, wherein the piston has a first engagement part with which a connecting member engages on its inner circumferential surface, and has a second engagement part that engages with the connecting member on its outer circumferential surface that faces the inner circumferential surface of the piston, the connecting member engages with both the first engagement part and the second engagement part, a pressing surface of the linear motion part that presses the piston and a pressed surface of the piston that is pressed by the linear motion part are in contact, at least one of the pressing surface and the pressed surface has a first curved surface, and the connecting member has a second curved surface in a range engaged with the first engagement part so that the piston swings so that the linear motion axis of the linear motion is tilted. When the piston rotates so that the linear axis of the linear moving part is tilted relative to the axial direction of the cylinder, the piston may come into contact with the linear moving part, potentially generating an unbalanced load on the linear moving part. In the present disclosure, the pressing surface where the linear moving part presses the piston and the pressed surface where the piston is pressed by the linear moving part are in swingable contact, thereby reducing the force applied to the linear moving part when the piston rotates so that the linear moving axis is tilted, and suppressing the unbalanced load generated between the pressing surface and the pressed surface. Furthermore, by having the second curved surface in the range where the connecting member engages with the first engaging part, the force generated when the piston rotates so that the linear moving axis is tilted is not transmitted to the linear moving part via the connecting member, but is transmitted to the contact portion between the piston and the inner peripheral surface of the cylinder. This reduces the force applied to the linear moving part, thereby suppressing the unbalanced load generated between the first engaging part and the connecting member.

[0032] In an electric braking device according to one aspect of the present disclosure, the first engagement portion has a through hole that penetrates between the inner and outer circumferential surfaces of the piston, and the first engagement portion has a through hole that penetrates between the inner and outer circumferential surfaces of the piston, thereby facilitating assembly by inserting a connecting member through the through hole.

[0033] In an electric braking device according to one aspect of the present disclosure, the connecting member is a sphere. If the connecting member has a complex shape, the processing, manufacturing, and assembly costs for shaping and assembling the connecting member increase. For example, if the connecting member is processed so that it makes surface contact with the second engagement portion of the linear motion portion, the processing costs increase. In the present disclosure, by forming the connecting member into a spherical shape, material that has been pre-processed into a spherical shape can be used as is without additional processing, allowing for inexpensive processing, manufacturing, and assembly.

[0034] In an electric braking device according to one aspect of the present disclosure, the relative rotation of the piston and the linear moving part with respect to the cylinder is restricted by a frictional force generated at a contact point between the piston and the frictional part. By restricting the relative rotation of the piston and the linear moving part with respect to the cylinder by a frictional force generated at a contact point between the piston and the frictional part, it is possible to reduce the costs of processing, manufacturing, and assembling a rotation prevention member for restricting the relative rotation and a groove into which the rotation prevention member is inserted, thereby reducing the manufacturing cost of the electric braking device.

[0035] An electric braking device according to one aspect of the present disclosure converts the rotational motion of an electric motor into linear motion of a linear-motion part of a linear motion conversion mechanism, drives a piston, and applies a braking force to a vehicle wheel by pressing a friction material against a rotating body that rotates together with the wheel, wherein the piston has a cylindrical shape with a bottom, is engaged with the friction material, and has an outer peripheral surface abutting a cylinder, the linear-motion part has a cylindrical shape, an outer peripheral surface facing the inner peripheral surface of the piston, and has a pressing surface that abuts a predetermined pressed surface of the piston when the linear-motion part moves linearly in accordance with the rotational motion of the electric motor, and a connecting member that connects the piston to the linear-motion part by engaging with the inner peripheral surface of the piston and the outer peripheral surface of the linear-motion part, and at least one of the pressing surface and the pressed surface has a first curved surface so that the axial direction of the piston is inclined with respect to the axial direction of the cylinder, and a second curved surface is provided on the surface of the connecting member in a range that engages with the inner peripheral surface of the piston.

[0036] [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 converts the rotational motion of an electric motor into linear motion of a linear motion conversion mechanism, drives a piston that is in contact with the inner circumference of a cylinder using that linear motion, and applies a braking force to a vehicle wheel by pressing a friction material against a rotating body that rotates together with the wheel, wherein the piston has a first engagement portion with which a connecting member engages on its inner peripheral surface, and a second engagement portion that engages with the connecting member on the outer peripheral surface of the linear motion part that faces the inner peripheral surface of the piston, the connecting member engages with both the first engagement portion and the second engagement portion, the pressing surface of the linear motion part that presses the piston comes into contact with the pressed surface of the piston that is pressed by the linear motion part, and at least one of the pressing surface and the pressed surface has a first curved surface, and the connecting member has a second curved surface in the area that is engaged with the first engagement portion so that the piston can swing so that the linear motion axis of the linear motion is tilted.

2. The electric braking device according to claim 1, wherein the first engaging portion has a through hole that penetrates between the inner and outer peripheral surfaces of the piston.

3. An electric braking device according to claim 1 or 2, wherein the connecting member is a ball.

4. An electric braking device that converts the rotational motion of an electric motor into the linear motion of a linear motion part of a linear motion conversion mechanism, drives a piston, and applies a braking force to a vehicle wheel by pressing a friction material against a rotating body that rotates together with the wheel, wherein the piston has a cylindrical shape with a bottom, is engaged with the friction material, and its outer surface abuts against a cylinder, the linear motion part has a cylindrical shape, its outer surface faces the inner peripheral surface of the piston, and has a pressing surface that abuts against a predetermined pressed surface of the piston when it moves linearly in accordance with the rotational motion of the electric motor, and comprises a connecting member that connects the piston to the linear motion part by engaging with the inner peripheral surface of the piston and the outer peripheral surface of the linear motion part, and at least one of the pressing surface and the pressed surface has a first curved surface so that the axial direction of the piston can tilt with respect to the axial direction of the cylinder, and the connecting member has a second curved surface in the area of ​​its surface that engages with the inner peripheral surface of the piston.

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