Drum brakes

Abstract

Provided is a drum brake comprising a shoe hold mechanism that improves tracking of the movement of brake shoes. A shoe hold pin of the shoe hold mechanism provided to the drum brake has: a base part that is locked to a back plate; a shaft part that is provided continuous from the base part, and a distal-end head part that is provided continuous at an axial end part of the shaft part, an engaging part provided to a shoe hold spring being engaged with the distal-end head part. A protruding part (contact part) with which the engaging part is brought into contact is provided at a position spaced from the distal-end head part toward the shaft-part side. The shoe hold mechanism makes it possible to improve the tracking of the movement of first and second brake shoes.

Description

Technical Field

[0001] The present invention relates to a drum brake used for braking a vehicle.

Background Art

[0002] The brake shoe of the vehicle drum brake described in Patent Document 1 includes a web arranged in parallel with the back plate, and the web is elastically supported on the back plate via a shoe holding mechanism, such as a shoe holding pin and a shoe holding spring, respectively.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the shoe holding mechanism described in Patent Document 1 mentioned above, since the short-side opening edge of the vertically long opening of the shoe holding spring formed by bending a metal leaf spring into a U shape is simply hooked on the left and right flange surfaces of the arrowhead-shaped head of the shoe holding pin for fixing, when following the movement of the brake shoe accompanying brake operation, the Compression amount increases, and as a result, the biasing force of the shoe holding spring increases, so that the followability of the shoe holding pin with respect to the movement of the brake shoe deteriorates. In particular, there is room for improvement for a type of brake in which the movement of the brake shoe during brake operation is large.

[0005] One of the objects of the present invention is to provide a drum brake provided with a shoe holding mechanism that improves the followability with respect to the movement of the brake shoe.

Means for Solving the Problems

[0006] As a means to solve the above problems, the drum brake of the present invention comprises a back plate fixed to a vehicle, a brake shoe placed on the back plate, a shoe hold spring positioned on the side of the shoe web of the brake shoe opposite to the back plate side, and a shoe hold pin that holds the shoe hold spring so as to be able to swing so as to bias the brake shoe toward the back plate side, wherein the shoe hold pin has a base that is locked to the back plate, a shaft portion provided continuously from the base portion and the shaft portion is inserted into through holes formed in the back plate, the shoe web, and the shoe hold spring, respectively, and a tip head provided continuously from the axial end of the shaft portion and the tip head to which a latch provided on the shoe hold spring is latched, and a contact portion is provided at a position spaced apart from the tip head toward the shaft portion to which the latch contacts A pair of curved concave surfaces are formed at the boundary between the tip head and the shaft portion, and a projection is formed on the shaft portion side of each curved concave surface, projecting radially outward from the outer circumferential surface of the shaft portion, and this projection acts as a step between the outer circumferential surface of the shaft portion and the curved concave surface, and the step is the contact portion. It is characterized by the following:

[0007] According to a drum brake according to one embodiment of the present invention, the ability to follow the movement of the brake shoe by the shoe holding mechanism can be improved. [Brief explanation of the drawing]

[0008] [Figure 1] A front view of the drum brake according to this embodiment. [Figure 2] A front view of the shoe-holding mechanism used in the drum brake according to this embodiment. [Figure 3] This is a cross-sectional view along line AA in Figure 1, showing only the essential parts. [Figure 4] (a) is a cross-sectional view of the retainer of the shoe-holding mechanism used in the drum brake according to this embodiment, and (b) is a view of (a) in the direction of arrow B. [Figure 5] A side view of the shoe hold pin of the shoe hold mechanism used in the drum brake according to this embodiment. [Figure 6]A perspective view of the area near the tip of the shoe hold pin of the shoe hold mechanism used in the drum brake according to this embodiment. [Figure 7] This figure shows a shoe-holding mechanism used in a drum brake according to this embodiment, in which the retainer's latching portion is latched onto each projection of the shoe-holding pin. [Figure 8] This figure shows how the retainer swings relative to the shoe hold pin, starting from the state in Figure 7. [Modes for carrying out the invention]

[0009] This embodiment will be described in detail below with reference to Figures 1 to 8. In the drum brake 1 according to an embodiment of the present invention, referring to Figure 1, a pair of arched first and second brake shoes 3 and 4 are arranged on the inner surface of a back plate 2 fixed to the non-rotating portion of the vehicle's axle. One end of the first and second brake shoes 3 and 4 abuts against the piston of the wheel cylinder 7, and the other end abuts against the piston of the spreader device 8. The drum brake 1 according to this embodiment employs a leading-trailing type. Specifically, when the drum brake 1 according to this embodiment operates as a normal hydraulic brake, the wheel cylinder 7 operates to expand the first and second brake shoes 3 and 4 radially outward from the back plate 2, causing the outer circumference first and second linings 27 and 28 to slide against the brake drum (not shown) and provide braking. On the other hand, when acting as a parking brake, which is one example of an action to maintain the vehicle in a stopped state, the electric actuator including the spreader device 8 expands the first and second brake shoes 3 and 4 radially outward from the back plate 2, causing the first and second linings 27 and 28 on the outer circumference to slide against the brake drum (not shown) and apply braking force.

[0010] Referring to Figure 1, first and second shoe return springs 10 and 11 are tensioned between the first brake shoe 3 and the second brake shoe 4, respectively, on the inside of the wheel cylinder 7 and the inside of the spreader device 8. These first and second shoe return springs 10 and 11 constantly bias the first and second brake shoes 3 and 4 in the diameter-reducing direction. An automatic braking gap adjustment device 14 is positioned on the center side of the back plate 2 of the first shoe return spring 10 on the wheel cylinder 7 side, which regulates the diameter-reduced position of the first and second brake shoes 3 and 4 and automatically adjusts the braking gap. An axle insertion hole 17 is formed approximately in the center of the back plate 2. The back plate 2 has an insertion hole 19 (see Figure 3) through which the shoe hold pin 33 of each shoe hold mechanism 30, more specifically the shaft portion 64 of the shoe hold pin 33, is inserted. The insertion hole 19 is formed in a circular shape.

[0011] Referring to Figures 1 and 3, the first and second brake shoes 3 and 4 are formed of the same shape and used by reversing them. The first and second brake shoes 3 and 4 each comprise first and second shoe webs 21 and 22 arranged parallel to the back plate 2, arc-shaped first and second rims 24 and 25 arranged on the outer edges of the first and second shoe webs 21 and 22 in a direction perpendicular to the first and second shoe webs 21 and 22, and first and second linings 27 and 28 attached to the outer circumferential surfaces of these first and second rims 24 and 25.

[0012] The first and second shoe webs 21 and 22 (the first shoe web 21 is shown in Figure 3) have through holes 29 through which the shoe hold pins 33 of each shoe hold mechanism 30, more specifically the shaft portion 64 of the shoe hold pins 33, are inserted. The through holes 29 are formed in a circular shape. The portions of these first and second shoe webs 21 and 22 between the first and second shoe return springs 10 and 11 are elastically supported by the back plate 2 by multiple shoe hold mechanisms 30. In this embodiment, two shoe hold mechanisms 30 are provided for each of the first and second shoe webs 21 and 22.

[0013] As described above, each shoe-holding mechanism 30 elastically supports the first and second shoe webs 21 and 22 with respect to the back plate 2, and has the same structure for the first and second shoe webs 21 and 22. Therefore, only the structure of the shoe-holding mechanism 30 that elastically supports the first shoe web 21 with respect to the back plate 2 will be described below.

[0014] Referring to Figures 2 and 3, the shoe hold mechanism 30 includes a shoe hold spring 32 positioned on the side of the first shoe web 21 of the first brake shoe 3 that is opposite to the back plate 2 side, and a shoe hold pin 33 that holds the shoe hold spring 32 so as to be able to swing in order to bias the first brake shoe 3 toward the back plate 2 side. The shoe hold spring 32 includes a compression coil spring 36 positioned to surround the shaft portion 64 of the shoe hold pin 33, and a retainer 37 that abuts against one axial end of the compression coil spring 36 and has a hook portion 48 that hooks onto the tip head 65 of the shoe hold pin 33. The other axial end of the compression coil spring 36 abuts against the side of the first shoe web 21 that is opposite to the back plate 2 side, around the insertion hole 29, via a spring hold member 40. The spring hold member 40 holds the other axial end of the compression coil spring 36.

[0015] Referring to Figure 3, the spring holding member 40 comprises an annular plate portion 43 that abuts the side of the first shoe web 21 opposite to the back plate 2 side, a small-diameter cylindrical portion 44 that protrudes from the inner circumference of the annular plate portion 43 toward the insertion hole 29 of the first shoe web 21 and fits into the insertion hole 29, and a large-diameter cylindrical portion 45 that protrudes from the outer circumference of the annular plate portion 43 toward the side opposite to the back plate 2 side. The other axial end of the compression coil spring 36 is held within the large-diameter cylindrical portion 45 of the spring holding member 40. The compression coil spring 36 corresponds to the spring portion. Referring to Figures 3 and 4, the retainer 37 is formed as a whole in a cup shape, in other words, in a bottomed inverted frustoconical shape with an internal space (a shape in which the peripheral wall portion bulges slightly radially outward). More specifically, the retainer 37 includes a hooking portion 48 that is hooked onto the tip head 65 of the shoe hold pin 33 (described later), a body portion 49 that is integrally continuous with the hooking portion 48 and expands in diameter as it moves away from the back plate 2, and a flange portion 50 that is integrally provided radially outward from the axial end of the body portion 49.

[0016] The latching portion 48 includes a roughly rectangular, elongated vertical opening 53 that penetrates through it, and elongated vertical recesses 54 that extend on both sides of the elongated vertical opening 53 and are formed as roughly rectangular recesses. The elongated vertical opening 53 is formed by press working from the body portion 49 side, and a curved convex surface 56 is formed on the opening edge of the elongated vertical opening 53 on the body portion 49 side. The curved convex surface 56 corresponds to the curved surface. The elongated vertical opening 53 and the elongated vertical recesses 54 are perpendicular to each other. In the elongated vertical opening 53, a pair of opposing arc-shaped opening wall surfaces 58, 58 are formed at the midpoint in the longitudinal direction of a pair of opposing longitudinal opening wall surfaces along the longitudinal direction. The inner diameters of the pair of arc-shaped opening wall surfaces 58, 58 are roughly the same as the outer diameter of the shaft portion 64 of the shoe hold pin 33, which will be described later. The width of the opposing openings on the shorter side of the vertically elongated opening 53 is set to be slightly larger than the thickness of the arrowhead-shaped tip head 65 of the shoe hold pin 33 (distance between the pair of flat sections 73, 73), smaller than the maximum width of the arrowhead-shaped tip head 65 (maximum distance between the pair of curved sections 72, 72), and smaller than the outer diameter of the shaft portion 64 of the shoe hold pin 33.

[0017] On the one hand, the opposing opening widths on the longitudinal side of the vertically long opening 53 are set to be slightly larger than the maximum width of the arrow-shaped tip head 65 of the shoe hold pin 33 described later. The width on the short side of the vertically long recess 54 is set to be slightly larger than the thickness of the arrow-shaped tip head 65 of the shoe hold pin 33 described later. The width on the longitudinal side of the vertically long recess 54 is set to be slightly larger than the maximum width of the arrow-shaped tip head 65 of the shoe hold pin 33 described later. The body portion 49 extends with its peripheral wall portion gradually expanding in diameter while being slightly curved outward in the radial direction. The flange portion 50 has a predetermined thickness and is formed in an annular shape. A pair of linear notch portions 60, 60 are provided on the outer peripheral surface of the flange portion 50 so as to face each other. The outer diameter of the flange portion 50 coincides with the outer diameter of the compression coil spring 36. And one axial end of the compression coil spring 36 abuts against the surface of the flange portion 50 on the side of the back plate 2.

[0018] Referring to FIGS. 3, 5, and 6, the shoe hold pin 33 has a base portion 63 locked to the back plate 2, a shaft portion 64 continuously extending from the base portion 63 and inserted into the insertion hole 19 of the back plate 2, the insertion hole 29 of the first shoe web 21, and the inside of the compression coil spring 36 respectively, and an arrow-shaped tip head 65 continuously provided at the axial end of the shaft portion 64 and engaged with the engaging portion 48 of the retainer 37. Note that the internal space of the compression coil spring 36 corresponds to the insertion hole. The base portion 63 is formed with a circular planar surface 68 on the side opposite to the back plate 2 side, and the side contacting the back plate 2 is formed with a curved convex surface 69 protruding from the circular planar surface 68 toward the back plate 2 side and gradually reducing in diameter. In short, the curved convex surface 69 of the base portion 63 of the shoe hold pin 33 abuts against the opening edge of the insertion hole 19 of the back plate 2, and as a result, the shoe hold pin 33 is locked to the back plate 2 so as to be swingable about the base portion 63. The shaft portion 64 extends from the radial center of the curved convex surface 69 of the base portion 63. The shaft portion 64 is inserted into the inside of the small-diameter cylindrical portion 44 of the spring hold member 40 including the insertion hole 19 of the back plate 2 and the insertion hole 29 of the first shoe web 21 and the inside of the compression coil spring 36 respectively.

[0019] The tip head 65 is formed in a tapered arrowhead shape. Specifically, the tip head 65 includes a pair of curved surface portions 72, 72 whose distance from each other gradually decreases toward the tip, and a pair of flat surface portions 73, 73 whose distance from each other is the same along the axial direction. The top surface 75 of the tip head 65 is formed flat. Naturally, the maximum width of the tip head 65 (the maximum distance between the pair of curved surface portions 72, 72) is set to be considerably larger than the thickness of the tip head 65 (the distance between the pair of flat surface portions 73, 73). The thickness of the tip head 65 is set to be smaller than the outer diameter of the shaft portion 64. The maximum width of the tip head 65 is set to be smaller than the inner diameter of the small-diameter cylindrical portion 44 of the spring holding member 40 including the insertion hole 19 of the back plate 2 and the insertion hole 29 of the first shoe web 21, and also smaller than the inner diameter of the compression coil spring 36. As described above, the maximum width of the tip head 65 is set to be slightly smaller than the longitudinal width of the vertically long concave portion 54 as the latching portion 48 of the retainer 37.

[0020] Referring to FIGS. 5 and 6, at the boundary between the tip head 65 and the shaft portion 64, a pair of curved concave surfaces 78, 78 are respectively formed on the side of the pair of curved surface portions 72, 72. A plurality of protrusions 80 that protrude radially outward from the outer peripheral surface of the shaft portion 64 are formed on the side of the shaft portion 64 from the pair of curved concave surfaces 78, 78. In the present embodiment, the protrusion 80 is formed as a stepped portion between the outer peripheral surface of the shaft portion 64 and the curved concave surface 78. Note that the protrusion 80 does not protrude outward from the flat surface portion 73 of the tip head 65. In short, the protrusion 80 is disposed inside the flat surface portion 73. The protrusion 80 is formed on the curved concave surface 82, and the apex is formed in a substantially spherical shape with a rounded shape. Note that the portion from the curved concave surface 82 to the apex of the protrusion 80 corresponds to a curved surface. The protrusions 80 are formed at two positions respectively at both ends in the width direction of a single curved surface portion 72 of the tip head 65, and a total of four positions are formed for the pair of curved surface portions 72, 72.

[0021] From the apex of each projection 80 toward the curved concave surface 82, the curved convex surfaces 56, 56 (sloping surfaces) of the opening edges of the pair of arc-shaped opening wall surfaces 58, 58, which are the retainer's latching portion 48, come into contact with the short-side opening edge of the vertically elongated opening 53. In short, the portion from the apex of the projection 80, which is located at a distance from the tip head 65 toward the shaft portion 64, that is, at a position with the curved concave surface 78 in between, toward the curved concave surface 82, acts as a contact portion that comes into contact with the retainer's latching portion 48, that is, the short-side opening edge of the vertically elongated opening 53 (the curved convex surfaces 56, 56 of the opening edges of the pair of arc-shaped opening wall surfaces 58, 58).

[0022] Next, to briefly explain how to assemble the shoe hold mechanism 30, referring to Figure 3, the arrowhead-shaped tip 65 of the shoe hold pin 33 is inserted into the insertion hole 19 of the back plate 2 from the side opposite to the first shoe web 21, and the shaft portion 64 of the shoe hold pin 33 is inserted into the small diameter cylindrical portion 44 of the spring hold member 40, which includes the insertion hole 19 of the back plate 2 and the insertion hole 29 of the first shoe web 21. Next, the vertically elongated opening 53 of the retainer 37's latching portion 48, against which one axial end of the compression coil spring 36 abuts, is aligned with the arrowhead-shaped tip 65 of the shoe hold pin 33. The arrowhead-shaped tip 65, including each projection 80, is then inserted into the vertically elongated opening 53 of the retainer 37's latching portion 48, while the other axial end of the compression coil spring 36 is brought into contact with the surface of the first shoe web 21 around the insertion hole 29, on the side opposite to the back plate 2, via the annular plate portion 43 of the spring hold member 40.

[0023] Next, the shoe hold pin 33 is rotated approximately 90° around its axis relative to the retainer 37, so that the arrowhead-shaped tip 65 of the shoe hold pin 33 fits into the elongated recess 54 of the retainer 37's latching portion 48. As a result, the compression coil spring 36 is held between the flange portion 50 of the retainer 37 and the first shoe web 21 by the spring hold member 40 with a predetermined set load. Also, referring to Figure 7, the curved convex surfaces 56, 56 (sagging surfaces) of the short-side opening edge of the elongated opening 53, which is the latching portion 48 of the retainer 37, i.e., the opening edges of the pair of arc-shaped opening wall surfaces 58, 58, abut against the curved concave surface 82 side from the apex of each projection 80 of the shoe hold pin 33. Furthermore, a gap is created between the arrowhead-shaped tip 65 of the shoe hold pin 33 and the bottom surface of the elongated recess 54, which is the latching portion 48 of the retainer 37. Furthermore, the shoe-holding mechanism 30 allows the first brake shoe 3 to be elastically supported relative to the back plate 2 so that it can swing toward the back plate 2.

[0024] Furthermore, in the shoe-holding mechanism 30 of the drum brake 1 according to this embodiment, the curved convex surfaces 56, 56 (sloping surfaces) of the short-side opening edge of the vertically elongated opening 53, which is the latching portion 48 of the retainer 37, that is, the opening edges of the pair of arc-shaped opening wall surfaces 58, 58, abut against the curved concave surface 82 side from the apex of each projection 80 of the shoe-holding pin 33. Therefore, as shown in Figure 8, even if a tilting force is applied to the corresponding shoe-holding pin 33 to follow the torque load due to brake operation and the movement of the first and second brake shoes 3, 4 due to lining wear, the shoe-holding pin 33 and the retainer 37 can swing relatively easily. In other words, even if the shoe-holding pin 33 tilts, the retainer 37 is less likely to tilt. Therefore, the compression coil spring 36 is less flexible than in the conventional (described in Patent Document 1). Compression amount The increase in biasing force is suppressed. As a result, the increase in biasing force transmitted to the shoe hold pin 33 via the retainer 37 by the compression coil spring 36 can be suppressed compared to the conventional method (described in Patent Document 1), and the ability to follow the movement of the first brake shoe 3 can be improved.

[0025] Moreover, when the shoe hold pin 33 is tilted, each projection 80 of the shoe hold pin 33 is the short side opening edge of the vertically elongated opening 53, which is the hooking portion 48 of the retainer 37, that is, the curved convex surface 56, 56 of the opening edge of the pair of arc-shaped opening wall surfaces 58, 58 Opening side By moving in this direction, it is possible to further suppress the increase in biasing force transmitted to the shoe hold pin 33 via the retainer 37 by the compression coil spring 36, thereby further improving the responsiveness to the movement of the first brake shoe 3.

[0026] In the drum brake 1 according to the embodiment described above, the shoe hold pin 33 of the shoe hold mechanism 30 has a base portion 63 that is locked to the back plate 2, a shaft portion 64 that is continuously provided from the base portion 63 and is inserted into the insertion hole 19 of the back plate 2, the insertion hole 29 of the first or second shoe web 21 or 22 and the inside of the compression coil spring 36, respectively, and a tip portion 65 that is continuously provided from the axial end of the shaft portion 64 and is engaged with a hooking portion 48 (short side opening edge of the vertically elongated opening 53) provided on the retainer 37 of the shoe hold spring 32, and a contact portion (projection 80) that the hooking portion 48 (short side opening edge of the vertically elongated opening 53) abuts against is provided at a position spaced apart from the tip portion 65 toward the shaft portion 64 and inside the flat portion 73 of the tip portion 65.

[0027] As a result, even if the corresponding shoe hold pin 33 tilts to follow the movement of the first and second brake shoes 3 and 4 due to brake operation, the retainer 37 is less likely to tilt, thus reducing the compression coil spring 36 compared to the conventional one (described in Patent Document 1). Compression amount The increase in the compression coil spring 36 is suppressed. As a result, the increase in the biasing force transmitted to the shoe hold pin 33 via the retainer 37 by the compression coil spring 36 can be suppressed compared to the conventional method (described in Patent Document 1), and the ability to follow the movement of the first and second brake shoes 3 and 4 can be improved. Furthermore, even if the shoe hold pin 33 of the shoe hold mechanism 30 follows the movement of the first and second brake shoes 3 and 4, the compression coil spring 36 Compression amount Because it becomes more stable, controllability improves when electrifying the system.

[0028] Furthermore, in the shoe-holding mechanism 30 of the drum brake 1 according to this embodiment, a projection 80 that protrudes radially outward from the outer circumferential surface of the shaft portion 64 is used as the contact portion, so that the latching portion 48 (short side opening edge of the vertically elongated opening 53) provided on the retainer 37 can be easily latched.

[0029] Furthermore, in the shoe-holding mechanism 30 provided in the drum brake 1 according to this embodiment, the contact portion is formed as a curved concave surface 82 including the approximately spherical, rounded apex of each projection 80, while the short-side opening edge of the vertically elongated opening 53, which is the latching portion 48 of the retainer 37, that is, the opening edges of the pair of arc-shaped opening wall surfaces 58, 58, are also formed as curved convex surfaces 56, 56 (sloping surfaces). Therefore, when following the movement of the first and second brake shoes 3, 4 accompanying brake operation, the approximately spherical, rounded apex of these projections 80 towards the curved concave surface 82 and the curved convex surfaces 56, 56 of the short-side opening edge of the vertically elongated opening 53 (the opening edges of the pair of arc-shaped opening wall surfaces 58, 58) slide smoothly, thereby suppressing the generation of abnormal noises and the like.

[0030] Furthermore, as mentioned above, the shoe hold spring described in Patent Document 1 employs a metal leaf spring that has been bent into a U-shape. However, in small-diameter drum brakes where there is insufficient space between the axle and the drum, the placement of this shoe hold spring becomes difficult, which presents a problem.

[0031] In contrast, the shoe-holding spring 32 of the shoe-holding mechanism 30 in the drum brake 1 according to this embodiment comprises a compression coil spring 36 arranged to surround the shaft portion 64 of the shoe-holding pin 33, and a retainer 37 having a hooking portion 48 that abuts against one axial end of the compression coil spring 36 and hooks onto the tip head 65 of the shoe-holding pin 33. As a result, the space occupied by the shoe-holding mechanism 30 can be reduced compared to conventional shoe-holding springs made by bending a metal leaf spring into a U shape, and it can be used without problems even in small-diameter drum brakes where there is insufficient space between the axle and the drum.

[0032] Furthermore, in the shoe-holding mechanism 30 of the drum brake 1 according to this embodiment, it is not necessary to form the insertion hole 19 of the back plate 2 in an elongated shape (a shape adopted in a configuration in which the base of the shoe-holding pin is arrowhead-shaped and inserted from the brake shoe side), as the insertion hole 19 is formed in a circular shape. This results in improved waterproofing, eliminates the need for waterproofing structures such as waterproofing covers, and also improves processability, offering cost advantages.

[0033] In this embodiment, the shoe-holding mechanism 30 of the drum brake 1 employs a compression coil spring 36 and a retainer 37 as the shoe-holding spring 32. However, although there are concerns regarding the space occupied, a metal leaf spring bent into a U-shape can also be used. Furthermore, while the drum brake 1 in this embodiment employs a leading-trailing type, the shoe-holding mechanism 30 in this embodiment can also be applied to other types of drum brakes such as duo-servo or two-leading, and the automatic braking gap adjustment device 14 is not required.

[0034] Furthermore, the present invention is not limited to the embodiments described above, and various modifications are included. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. Also, it is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations.

[0035] This application claims priority under Japanese Patent Application No. 2023-83149, filed on 19 May 2023. The entire disclosure of Japanese Patent Application No. 2023-83149, filed on 19 May 2023, including the specification, claims, drawings, and abstract, is incorporated into this application by reference. [Explanation of Symbols]

[0036] 1 Drum brake, 2 Back plate, 3 First brake shoe, 4 Second brake shoe, 19 Through hole, 21 First shoe web, 22 Second shoe web, 29 Through hole, 32 Shoe hold spring, 33 Shoe hold pin, 36 Compression coil spring (spring part), 37 Retainer, 48 Locking part, 56 Curved convex surface (curved surface), 63 Base, 64 Shaft part, 65 Tip head, 72 Curved surface part, 73 Flat part, 80 Protrusion (contact part), 82 Curved concave surface (curved surface)

Claims

1. It is a drum brake, and the drum brake is, A back plate that is fixed to the vehicle, The brake shoe placed on the back plate, A shoe hold spring is positioned on the side of the shoe web of the brake shoe that is opposite to the back plate side, The system includes a shoe hold pin that holds the shoe hold spring so as to be pivotable in such a way that it biases the brake shoe toward the back plate, The aforementioned shoehold pin is A base that is locked to the back plate, A shaft portion provided continuously from the base portion, the shaft portion being inserted into the insertion holes formed in the back plate, the shoe web, and the shoe hold spring, respectively, A tip portion provided continuously with the axial end of the shaft portion, the tip portion having a latch portion provided on the shoe hold spring that latches to it, A contact portion is provided at a distance from the tip end toward the shaft portion, against which the locking portion abuts. A pair of curved concave surfaces are formed at the boundary between the tip portion and the shaft portion, and a projection is formed on the shaft portion side of each curved concave surface, projecting radially outward from the outer circumferential surface of the shaft portion, and this projection acts as a step between the outer circumferential surface of the shaft portion and the curved concave surface. A drum brake characterized in that the stepped portion is the contact portion.

2. A drum brake according to claim 1, The aforementioned tip is formed in the shape of an arrowhead, having a pair of flat surfaces and a pair of curved surfaces. The drum brake is characterized in that the contact portion is positioned inward from the flat portion.

3. A drum brake according to claim 1 or 2, The drum brake is characterized in that the contact portion is formed on a curved surface.

4. A drum brake according to claim 1, The drum brake is characterized in that the latching portion has a curved surface, and the curved surface contacts the contact portion.

5. In the drum brake described in claim 1, The aforementioned shoe-hold spring comprises a spring portion and A retainer having the aforementioned latching portion and contacting the spring portion, A drum brake characterized by having the following features.

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