CN113623343A

CN113623343A - Drum brake

Info

Publication number: CN113623343A
Application number: CN202110302887.XA
Authority: CN
Inventors: 饭室智启; 鸭川延明; 乔海超
Original assignee: TBK Co Ltd
Current assignee: TBK Co Ltd
Priority date: 2020-05-08
Filing date: 2021-03-22
Publication date: 2021-11-09
Also published as: JP7407064B2; JP2021177092A

Abstract

A drum brake (B) is provided with a cylindrical brake drum (31), brake shoes (40, 40), and an expansion device (5). The expanding device has: a pressing force generating member that applies a pressing force in an axial direction in accordance with a braking operation; a transmission member; a pressing member that is screwed to the transmission member in an axial direction and is connected to the brake shoe so as not to rotate in the axial direction; and a clearance adjustment mechanism that adjusts a clearance between the brake lining and the inner circumferential surface of the brake drum. The clearance adjustment mechanism adjusts the clearance between the brake lining and the inner circumferential surface of the brake drum by rotating the transmission member about the axial direction and withdrawing the pressing member in the axial direction. The pressing member includes a stopper that restricts the pressing member from being pulled out by a predetermined amount in the axial direction with respect to the transmission member.

Description

Drum brake

Technical Field

The present invention relates to a drum brake, and more particularly, to a drum brake provided with a clearance adjustment mechanism.

Background

A drum brake is provided with: a cylindrical brake drum attached to be rotatable integrally with an axle; and a pair of brake shoes which are swingably held by the anchor bracket and arranged along the inner peripheral surface of the brake drum, and a brake lining provided on the brake shoes so as to face the brake drum is pressed against the inner peripheral surface of the brake drum, so that the rotation of the brake drum (a wheel provided on the axle) is braked by friction generated between the brake lining and the brake drum.

The drum brake has the following structure: an expansion device that performs an outward extending operation in accordance with a brake operation is attached to a tip end of the brake shoe, and the brake shoe is swung based on the extending operation of the expansion device to press the brake lining against an inner circumferential surface of the brake drum. The expanding device of the drum brake comprises: a tappet; a sleeve coaxially mounted to the tappet; and a screw rod screwed with the sleeve and having an outer end connected to the brake lining, wherein the tappet is inserted into the accommodating space formed in the housing. Here, the tappet and the sleeve are connected by a circlip, and the relative movement in the axial direction is restricted. Further, a one-way clutch (one-way clutch) is disposed between the tappet and the sleeve so as to allow the sleeve to rotate in one direction about the axis with respect to the tappet and restrict the sleeve from rotating in the other direction about the axis with respect to the tappet. The brake lining wears due to friction with the brake drum, and this wear causes a gap (hereinafter, also referred to as a shoe gap) between the brake lining and the brake drum to become large, which may also cause deterioration in the brake performance. Therefore, the drum brake is provided with a clearance adjustment mechanism that reduces the shoe clearance in accordance with the wear of the brake lining and automatically adjusts the clearance between the brake lining and the brake drum so as to be always constant (see, for example, japanese patent application laid-open No. 2006-242238). The clearance adjustment mechanism rotates the sleeve independently (in the one direction) with respect to the screw rod, so that the screw rod screwed with the sleeve is drawn out to thereby swing the brake lining to reduce the shoe clearance.

Disclosure of Invention

Problems to be solved by the invention

However, in the conventional drum brake described above, when the shoe clearance is adjusted after the wear of the brake lining has progressed to reach a certain wear limit (use limit), there is a problem as follows: the screw is excessively drawn out to interfere with (bite into) the brake drum, and there is a problem that the gap adjustment mechanism and the brake drum may be damaged.

The present invention has been made in view of the above problems, and an object thereof is to provide a drum brake capable of preventing damage to a gap adjustment mechanism and a brake drum due to an excessive adjustment of a shoe gap.

Means for solving the problems

In order to achieve the above object, a drum brake according to the present invention includes: a cylindrical brake drum provided to a rotating member and rotatable integrally with the rotating member; a brake shoe which is provided to a fixed member so as to be swingable and has a brake lining disposed along an inner circumferential surface of the brake drum; and an expansion device that swings the brake shoe in accordance with a brake operation to press the brake lining against an inner circumferential surface of the brake drum, the expansion device including: a pressing force generating member that applies a pressing force in an axial direction in accordance with a braking operation; a transmission member provided to the pressing force generation member so as to be rotatable in the axial direction; a pressing member that is screwed into the transmission member in the axial direction, is connected to the brake shoe so as to be non-rotatable in the axial direction, and presses the brake lining against the inner circumferential surface of the brake drum by swinging the brake shoe by the pressing force transmitted from the transmission member; and a clearance adjustment mechanism that rotates the transmission member in the axial direction and extracts the pressing member in the axial direction, thereby displacing a relative position of the pressing member with respect to the axial direction of the transmission member and adjusting a clearance between the brake lining and an inner circumferential surface of the brake drum, wherein the pressing member includes a stopper that restricts the pressing member from being extracted by a predetermined amount in the axial direction with respect to the transmission member.

In the drum brake according to the present invention, it is preferable that the transmission member includes a housing portion that houses the pressing member in the axial direction, and the housing portion is provided with a stopper receiving portion, and when the pressing member is extracted by the predetermined amount in the axial direction, the stopper comes into contact with the stopper receiving portion to restrict the pressing member from being extracted by more than the predetermined amount in the axial direction.

In the drum brake according to the present invention, it is preferable that the pressing member includes a first pressing member that is screwed to the transmission member and is accommodated in the accommodating portion, and a second pressing member that is provided on a distal end side of the first pressing member and is connected to the brake shoe, and the first pressing member and the second pressing member are detachably coupled to each other.

In the drum brake according to the present invention, it is preferable that a torsion spring that allows relative rotation of the transmission member in one direction around the axial direction with respect to the pressing force generating member and restricts relative rotation of the transmission member in the other direction around the axial direction is disposed between the transmission member and the pressing force generating member, and the stopper has an outer diameter smaller than an inner diameter of the torsion spring and is configured to be insertable in the axial direction through the torsion spring.

Effects of the invention

According to the drum brake of the present invention, since the stopper function is activated when the amount of withdrawal of the pressing member reaches the predetermined amount to prevent the pressing member from being excessively withdrawn, even if the drum brake is continuously used beyond the limit of use of the brake lining, the pressing member can be prevented from interfering with the brake drum during the braking operation, and therefore, the backlash adjustment mechanism, the brake drum can be effectively prevented from being damaged, and the wheel can be effectively prevented from being locked.

In the drum brake according to the present invention, the pressing member is divided into the first pressing member and the second pressing member, and the first pressing member and the second pressing member are detachably coupled to each other, whereby when the dust-proof cover is attached to the drum brake across the pressing member and the brake housing, the cover can be attached to the brake housing in a state where the first pressing member and the second pressing member are separated from each other, and therefore, the work of replacing the cover can be facilitated.

Further, in the drum brake according to the present invention, since the stopper is formed so as to have an outer diameter smaller than the inner diameter of the torsion spring and so as to be axially insertable into the torsion spring, a stroke in the withdrawal direction (axial direction) of the pressing member can be ensured to be large while the entire drum brake is made compact.

Drawings

Fig. 1 is a front view showing a drum brake according to the present embodiment.

Fig. 2 is a cross-sectional view taken along an arrow a-a in fig. 1, and shows a state in which the drum brake is not operated.

Fig. 3 is a cross-sectional view taken along an arrow a-a in fig. 1, and shows a state when the drum brake is operated.

Fig. 4 is a sectional view showing an exploded state of the sleeve assembly of the drum brake.

Fig. 5 is a sectional view showing an assembled state of the screw of the drum brake.

Fig. 6 is a sectional view showing an exploded state of the screw of the drum brake.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. First, an overall structure of a drum brake according to an embodiment of the present invention will be described with reference to fig. 1 to 6. In fig. 2, 3, and the like, hatching of a part of the cross-sectional portion is omitted for ease of viewing the drawings.

As shown in fig. 1, the drum brake B is mainly composed of: an anchor bracket 2 fixed to the vehicle body together with a dust cover 29; a drum unit 3 provided with a brake drum 31 provided on the axle 1 and rotating integrally with the axle 1; a brake shoe unit 4 including a pair of

brake shoes

40, 40 provided swingably on the anchor bracket 2 and arranged along the inner circumferential surface of the brake drum 31; and an expanding device 5 that swings the

brake shoes

40, 40 to press against the inner peripheral surface of the brake drum 31 in accordance with a braking operation. In fig. 1, the drum unit 3 (brake drum 31) is indicated by a two-dot chain line, and detailed illustration thereof is omitted.

The anchor bracket 2 has a circular opening 21 at the center, and the anchor bracket 2 is fixed to an axle housing (not shown) of a vehicle body via bolts (not shown) inserted into bolt holes 22 provided around the opening 21. Further, a brake shoe support portion 25 is formed at a lower portion of the anchor bracket 2, the brake shoe support portion 25 is branched into two in a thickness direction of the anchor bracket 2 (a direction orthogonal to the paper surface in fig. 1), and a pair of pin insertion openings 24 are opened in the brake shoe support portion 25 along left and right sides in a front view.

The drum unit 3 is configured such that a rim (not shown) is mounted on a hub (not shown) rotatably mounted on the axle 1 projecting outward from the opening 21 of the anchor bracket 2 via a bearing, and a brake drum 31 is incorporated. Further, the wheel is attached to the rim, and the brake drum 31 and the wheel rotate integrally via the hub.

The brake shoe unit 4 has two

brake shoes

40, 40 arranged on the left and right in front view with the anchor bracket 2 interposed therebetween. Each brake shoe 40 includes: a web portion 41 extending in an arc shape; a rim (rim) portion 42 attached to the outer peripheral end of the web portion 41; and a brake lining (hereinafter referred to as "lining") 43 fixed to the rim portion 42 by a rivet or the like. The brake shoe 40 is disposed along the inner circumferential surface of the brake drum 31 with the lining 43 facing the inner circumferential surface of the brake drum 31.

Since the base end portion of the brake shoe 40 is pivotally connected to the anchor bracket 2 via the anchor pin 44 inserted into the pin insertion hole 24 of the brake shoe support portion 25, the brake shoe 40 can swing in the left-right direction in fig. 1 about the anchor pin 44. Between the front end portions of the pair of brake shoes 40, a return spring 45 is provided so as to connect them to each other. When the brake operation is not performed (when the brake is not operated), each brake shoe 40 is biased by the return spring 45 and is held at a position swung inward (i.e., a position separated from the brake drum 31).

The expansion device 5 fixed to the anchor bracket 2 is disposed between the front end portions of the pair of

brake shoes

40, 40. As will be described later, when the braking operation (braking action) is performed, the expanding device 5 presses the leading end portions of the brake shoes 40 outward against the urging force of the return springs 45 by the extending action (withdrawing action) of the screw rods 57. The brake shoes 40 are swung outward about the anchor pins 44 so that the linings 43 are pressed against the inner circumferential surface of the brake drum 31, thereby generating frictional force between the linings 43 and the inner circumferential surface of the brake drum 31 to brake the rotation of the brake drum 31. Therefore, a predetermined braking action is performed on the wheel that rotates integrally with the brake drum 31.

As shown in fig. 2 and 3, the expanding device 5 includes: a housing 51 having a space formed at the center thereof as a wedge accommodating portion 51a, and formed with a pair of

cylindrical portions

51b, 51b communicating with the wedge accommodating portion 51a from both side portions; a wedge 52 that is insertably mounted to the wedge accommodating portion 51 a; a sleeve assembly 53 inserted into each of the cylindrical portions 51b and slidably disposed in a direction along the axis X (hereinafter, also referred to as an "axial direction"); and a screw 57 screwed with the sleeve assembly 53 in the axial direction and extending outward toward the side of the housing 51. A cover 59 for preventing dust from entering the cylindrical portion 51b is detachably attached to the opening end of the cylindrical portion 51b of the housing 51.

In fig. 2 and 3, the expansion device 5 is configured to be bilaterally symmetrical, and hereinafter, based on the arrangement posture of the expansion device 5 shown in fig. 2 and 3, the inner side (the wedge housing portion 51a side) in the axial direction of the housing 51 is referred to as "one end side", and the outer side (the brake shoe 40 side) in the axial direction of the housing 51 is referred to as "the other end side". Fig. 2 shows a state of the expansion device 5 when the brake is not operated, and fig. 3 shows a state of the expansion device 5 when the brake is operated.

The wedge 52 is formed in a shaft shape, and is attached to the housing 51 in a direction orthogonal to the axial direction (hereinafter, referred to as "axial orthogonal direction") so as to be insertable and removable by the action of the partition plate in the cavity 9. As shown in fig. 2, when the brake is not operated (when the brake is released), the wedge 52 is pulled outward from the wedge accommodating portion 51a by the biasing force of the wedge spring 52 a. On the other hand, as shown in fig. 3, at the time of braking operation, the wedge 52 moves in the axis orthogonal direction (downward in fig. 3) in the wedge accommodating portion 51a against the urging force of the wedge spring 52a, and is thus in a state of being inserted into the wedge accommodating portion 51 a. The insertion end portion 52b, which is the end portion on the side inserted into the wedge accommodating portion 51a, has a wedge shape formed to taper toward the front end, and has inclined surfaces 52c on both sides in the axial direction. Further, a roller holding member 52e that supports the pair of rollers 52f is provided on the tip end side (insertion end 52b side) of the wedge 52. The pair of rollers 52f are provided rotatably with respect to the roller holding member 52e and movable in directions (axial directions) toward and away from each other. The roller holding member 52e is provided so as to be capable of reciprocating in the direction orthogonal to the axis, and is constantly urged toward the outside (upward in fig. 3) of the housing 51 in the direction orthogonal to the axis by the wedge spring 52a together with the wedge 52. The roller holding member 52e operates together with the wedge 52 to convert the linear motion in the direction orthogonal to the axis of the wedge 52 into the linear motion in the direction of the axis of the sleeve assembly 53.

As shown in fig. 4, the sleeve assembly 53 is configured to have: a tappet 54 having a body portion 54a and a cylindrical portion 54b, the body portion 54a being formed on one end side in the axial direction and having an outer diameter slightly smaller than the inner diameter of the cylindrical portion 51b, the cylindrical portion 54b being provided on the other end side in the axial direction and having an outer diameter smaller than the outer diameter of the body portion 54 a; a sleeve 55 formed in a cylindrical shape having the same outer diameter as the body portion 54a of the tappet 54 and fitted outside the cylindrical portion 54b of the tappet 54 at one end side in the axial direction; a C-shaped circlip 56 that is provided on the fitting surface of the tappet 54 and the sleeve 55 to connect the two and restricts relative movement in the axial direction of the two; and a torsion spring 61 supported between the tappet 54 and the sleeve 55.

The tappet 54 is formed in a stepped cylindrical shape by a main body portion 54a and a cylindrical portion 54b having different outer diameters from each other. An inclined surface 54c substantially parallel to the inclined surface 52c of the wedge 52 is formed on one end side of the body portion 54 a. The cylindrical portion 54b is formed with a spring attachment hole 54s that supports one end side of the torsion spring 61. In addition, a ring attachment groove 54r is formed in the cylindrical portion 54b over the entire outer circumferential surface. The tappet 54 is fitted to the innermost side of the tube 51b, and the inclined surface 54c is brought into contact with the circumferential surface of the roller 52f, so that the tappet can slide in the axial direction in the tube 51b via the roller 52f by the insertion and extraction operation of the wedge 52.

The sleeve 55 is formed in a hollow substantially cylindrical shape having a through hole 55a extending in the axial direction. The through-hole 55a is formed with the following structures disposed in order from one end side in the axial direction and communicating coaxially with each other: a cylindrical hole 55b into which the cylindrical portion 54b of the tappet 54 is fitted; a spring mounting hole 55s that supports the other end side of the torsion spring 61 in the axial direction; a stopper insertion hole 55c through which a stopper 57d formed on one end side in the axial direction of the screw 57 is inserted; and a female screw 55d screwed with the male screw 57c of the screw 57. An annular ring attachment groove 55r is formed in the cylindrical hole 55b of the sleeve 55 over the entire inner circumferential surface. The stopper insertion hole 55c is formed to have an inner diameter larger than an outer diameter of the stopper 57 d. An annular stopper receiving portion 55e extending in a direction orthogonal to the axial direction is formed at a step portion between the stopper insertion hole 55c and the female screw portion 55 d.

When the cylindrical portion 54b of the tappet 54 is fitted into the cylindrical hole 55b of the sleeve 55, the ring mounting groove 54r engraved along the outer circumferential surface of the cylindrical portion 54b is matched with the ring mounting groove 55r engraved along the inner circumferential surface of the cylindrical hole 55b, so that an integral clearance for fitting the circlip 56 is formed between the fitting surfaces of the tappet 54 and the sleeve 55. When the cylindrical portion 54b of the tappet 54 is fitted in the cylindrical hole 55b of the sleeve 55, the spring attachment hole 54s opened on the other end side of the cylindrical portion 54b is matched with the spring attachment hole 55s opened on the one end side of the sleeve 55, so that an integral clearance in which the torsion spring 61 is disposed is formed in the tappet 54 and the sleeve 55.

The circlip 56 is formed of a steel wire rod to which a heat treatment such as quenching, tempering, or austempering is applied, and can be elastically deformed in the diameter reduction direction by partially cutting out the ring to have a C shape (front ring shape). The circlip 56 is disposed in

ring mounting grooves

54r and 55r formed integrally with each other between the fitting surfaces of the tappet 54 and the sleeve 55 so as to couple the tappet 54 and the sleeve 55 so as not to be disengaged in the axial direction.

The torsion spring 61 is, for example, a compression coil spring obtained by winding a raw material wire having a circular cross section and processing the wound raw material wire into a spiral shape, and cutting the spiral material into a predetermined length. The torsion spring 61 is attached in a state of being elastically compressed and deformed in the axial direction, with an outer peripheral surface on one end side thereof engaging with an inner peripheral surface of the spring attachment hole 54s of the tappet 54 and an outer peripheral surface on the other end side thereof engaging with an inner peripheral surface of the spring attachment hole 55 s. The torsion spring 61 has a function of a one-way clutch, which allows relative rotation of the sleeve 55 around the axis with respect to the tappet 54 in a diameter reducing direction (for example, rightward rotation in the case where the spring winding direction is rightward) in which the spring outer diameter is reduced, and integrally prevents relative rotation of the sleeve 55 with respect to the tappet 54 in a diameter expanding direction (for example, leftward rotation in the case where the spring winding direction is leftward) in which the spring outer diameter is increased, in the case where the tappet 54 and the sleeve 55 are engaged with each other on the outer peripheral surface. As shown in fig. 2, the inner diameter of the torsion spring 61 is formed larger than the outer diameter of the stopper 57d, and the stopper 57d can be inserted through the torsion spring 61 in the axial direction. Therefore, the drum brake B can be made compact as a whole, and a large stroke in the withdrawal direction (axial direction) of the screw 57 can be ensured.

As shown in fig. 5, 6, and the like, the screw 57 includes a threaded shaft portion 57a and an adjustment dial portion 57b, the threaded shaft portion 57a is accommodated in the through hole 55a of the sleeve 55, and the adjustment dial portion 57b is detachably fastened to the threaded shaft portion 57a by a countersunk bolt 57 j.

The threaded shaft portion 57a is formed in a rod shape extending in the axial direction, and has an external threaded portion 57c on the outer peripheral surface thereof. The male screw portion 57c is screwed to the female screw portion 55d of the sleeve 55. A flange-shaped stopper 57d having an outer diameter larger than that of the male screw portion 57c is integrally formed on one end side in the axial direction of the threaded shaft portion 57 a. The stopper 57d is inserted into the through hole 55a of the sleeve 55 and is configured to be able to abut against the stopper receiving portion 55 e. Thereby, the screw 57 is attached to the through hole 55a of the sleeve 55 in a non-detached state. Further, a fitting portion 57e that is convex toward the adjustment dial portion 57b is formed on the other end side of the threaded shaft portion 57a in the axial direction. A threaded hole 57f into which a countersunk bolt 57j is screwed is formed in the axial direction in the axial center of the fitting portion 57 e.

The adjustment dial portion 57b is detachably attached to the other end side in the axial direction of the threaded shaft portion 57 a. The clamp 58 is rotatably locked to the adjustment dial portion 57b around a screw axis of the screw 57. The clip 58 engages with the web 41 of the brake shoe 40. The screw 57 is connected to the brake shoe 40 via a clamp 58 that clamps the adjustment dial portion 57 b. Further, a center hole 57g through which the countersunk bolt 57j is inserted is formed in the adjustment dial portion 57b so as to penetrate in the axial direction. Further, a fitting hole 57h formed so as to be capable of fitting with a fitting portion 57e of the threaded shaft portion 57a is recessed in the adjustment dial portion 57 b. Further, a cover attachment groove 57i is formed in the circumferential direction in the outer peripheral portion of the adjustment dial portion 57 b.

The screw 57 having the above-described structure is integrally assembled by fitting the fitting portion 57e of the threaded shaft portion 57a into the fitting hole 57h of the adjustment dial portion 57b, and then screwing the countersunk bolt 57j into the threaded hole 57f of the threaded shaft portion 57a through the center hole 57g of the adjustment dial portion 57 b. The screw 57 is attached to the sleeve 55 by screwing the male screw portion 57c of the threaded shaft portion 57a into the female screw portion 55d of the sleeve 55. A cover 59 for preventing dust from entering the cylindrical portion 51b is detachably attached between the screw 57 and the housing 51. As a method of attaching the cover 59, first, the threaded shaft portion 57a is attached to the through hole 55a of the sleeve 55 in a non-detached state, and then one end side of the cover 59 is pressed into the cover attachment hole 51d of the housing 51. Then, when the adjustment dial portion 57b is fastened to the threaded shaft portion 57a by the countersunk bolt 57j and the other end side of the cover 59 is engaged with the cover attachment groove 57i of the adjustment dial portion 57b, the cover 59 is attached to the housing 51 so as to straddle between the screw 57 and the housing 51. By dividing the screw 57 into the threaded shaft portion 57a and the adjustment dial portion 57b in this way, the cover 59 can be attached to the housing 51 with the threaded shaft portion 57a and the adjustment dial portion 57b separated from each other, and therefore, the work of replacing the cover 59 can be facilitated. As a fastening member (fastening means) for the threaded shaft portion 57a and the adjustment dial portion 57b, for example, other fastening members (fastening means) such as a positioning pin and a stopper ring may be applied.

A helical spline 55f is engraved on the outer peripheral surface of the sleeve 55, and the drive ring 62 meshes with the helical spline 55f at a predetermined wobbling degree (for example, 3 mm). The drive ring 62 has a conical surface 62a that abuts against an inclined surface 51c formed at an outer end of the tube portion 51b, and is configured to provide a predetermined frictional resistance between the inclined surface 51c and the conical surface 62a by a drive spring 63 that biases the drive ring 62 toward one end side in the axial direction.

The expanding device 5 having the above-described configuration includes the clearance adjusting mechanism 6, and when the lining 43 is worn, the clearance adjusting mechanism 6 automatically reduces the clearance (shoe clearance) between the lining 43 and the brake drum 31 to adjust the clearance to a predetermined clearance. The gap adjustment mechanism 6 includes a sleeve unit 53, a screw 57, a drive ring 62, a drive spring 63, and the like.

Next, the operation of the drum brake B having the above-described configuration at the time of braking operation or at the time of non-operation will be described.

When a braking operation is performed, compressed air is supplied into the chamber 9 in accordance with the braking operation, and the wedge 52 is pressed in a direction (downward direction in fig. 2 and 3) of being inserted into the wedge accommodating portion 51a by the wedge 52 against the biasing force of the wedge spring 52a based on the operation of the partition plate in the chamber 9. Due to the wedge action of the inclined surface 52c of the wedge member 52 and the inclined surface 54c of the tappet 54 extending parallel to each other, the pressing force is converted into a pressing force in the axial direction via the roller 52f, and is transmitted to the sleeve assembly 53. The tappet 54 and the sleeve 55 are subjected to the pressing force and integrally move in the cylindrical portion 51b from one end side to the other end side in the axial direction.

The helical spline 55f of the sleeve 55 meshes with the drive ring 62 in the axial direction with a prescribed degree of wobbling. When the amount of movement of the sleeve 55 based on the above-described braking action is within the range of the degree of rattling, the sleeve 55 moves linearly in the axial direction in the tube portion 51b without rotating the drive ring 62. At this time, the drive ring 62 is held in a state in which the conical surface 62a is in contact with the inclined surface 51c of the housing 51 by the biasing force of the drive spring 63.

The screw 57 engaged with the sleeve 55 is locked to the brake shoe 40 by the clamp 58, and operates together with the sleeve 55 to move linearly in the axial direction by the frictional resistance of the clamp 58 and the frictional resistance on the thread surface without causing relative rotation of the screw 57 with respect to the sleeve 55. Further, due to the extension of the screw 57 in the axial direction, the brake shoe 40 swings outward around the anchor pin 44, and the lining 43 is pressed against the inner circumferential surface of the brake drum 31, thereby generating friction therebetween to brake the rotation of the brake drum 31.

When the braking operation is released, the wedge 52 is moved in a direction of being pulled out from the wedge accommodating portion 51a (upward direction in fig. 2 and 3) by the urging force of the wedge spring 52 a. The screw 57 and the sleeve assembly 53 are moved from the other end side to the one end side in the axial direction within the cylinder portion 51b by the action of the return spring 45 provided astride between the two

brake shoes

40, 40 to be accommodated inside in the axial direction. When the amount of movement of the sleeve 55 is within the range of the degree of shaking, the sleeve 55 moves linearly in the axial direction within the tube portion 51b without rotating, as in the case of the extension.

On the other hand, if the linings 43 are worn continuously, the amount of movement in the axial direction of the screw 57 and the sleeve assembly 53 is increased to obtain the same braking effect when the braking operation is performed. At this time, when the amount of movement of the sleeve 55 at the time of performing the braking action exceeds the amount corresponding to the degree of rattling, the meshing surface of the helical spline 55f abuts against the meshing surface of the drive ring 62, whereby the drive ring 62 receives a pressing force toward the other end side in the axial direction. The frictional force between the inclined surface 51c and the conical surface 62a is reduced by the pressing force, and the drive ring 62 rotates along the meshing surface of the helical spline 55 f. Further, the sleeve 55 is linearly moved in the axial direction within the cylindrical portion 51b by the relative rotation of the sleeve 55 with respect to the tappet 54 being prevented by the one-way clutch function of the torsion spring 61.

When the brake operation is released, the screw 57 and the sleeve assembly 53 are returned to one end side in the axial direction by the biasing force of the return spring 45, and the contact between the drive ring 62 and the helical spline 55f is released. Therefore, the drive ring 62 is pressed toward one end side in the axial direction by the urging force of the drive spring 63, and the conical surface 62a abuts against the inclined surface 51c of the housing 51. Thus, the drive ring 62 is restricted from rotating by frictional resistance at the abutment surfaces. In contrast, the sleeve 55 moves toward one end side in the axial direction within the tube portion 51b without resistance for an amount corresponding to the degree of rattling between the helical spline 55f and the drive ring 62. On the other hand, when the amount of movement of the sleeve 55 exceeds the amount corresponding to the degree of rattling, the helical spline 55f abuts against the engagement surface on the other end side of the drive ring 62, so that the movement in the axial direction is prevented.

At this time, the drive ring 62 is restricted from rotating by the abutment with the inclined surface 51c of the housing 51 as described above, and the drive ring 62 is not allowed to rotate freely. In contrast, the torsion spring 61 accommodated in the sleeve assembly 53 restricts the rotation of the sleeve 55 in a direction (e.g., left rotation) in which it rotates along the meshing surface of the one end side of the drive ring 62, and allows the rotation of the sleeve 55 in a direction (e.g., right rotation) in which it rotates along the meshing surface of the other end side of the drive ring 62. Thus, the sleeve 55 is thus rotated along the meshing surface on the other end side of the drive ring 62. Further, the circlip 56 applies frictional resistance to the relative rotation of the sleeve 55 with respect to the tappet 54, and the return spring 45 exerts an urging force that rotates the sleeve 55 just against the frictional resistance.

Here, the screw 57 receives frictional resistance from the clamp 58 locked to the brake shoe 40 and whose rotation is restricted. This frictional resistance is greater than the frictional resistance of the thread surface between the screw 57 and the sleeve 55, and therefore the screw 57 and the sleeve 55 do not rotate integrally. Thus, the sleeve 55 rotates independently with respect to the tappet 54 and the screw 57. And, by the rotation of the sleeve, the screw 57 is drawn out in the axial direction by a drawing amount corresponding to the amount of rotation of the sleeve 55.

Therefore, in the clearance adjustment mechanism 6, when the lining 43 is worn, the sleeve 55 is moved by an amount exceeding a predetermined amount (an amount corresponding to the degree of rattling) during the braking operation, and on the other hand, the sleeve 55 is rotated by a rotation amount corresponding to the excess amount during the braking release, and the screw 57 is pulled out by a pull-out amount corresponding to the rotation amount along the outer side in the axial direction, whereby the clearance (shoe clearance) between the lining 43 and the brake drum 31 is automatically adjusted to a constant value.

Here, the amount of extraction of the screw 57 is in proportional relation to the amount of wear of the lining 43. In the present embodiment, the wear amount of the lining 43 and the withdrawal amount of the screw 57 are designed to be 1: in relation to 2, the amount of screw 57 drawn out is designed to be 2 times the amount of wear of lining 43. Therefore, when the wear amount of the lining 43 up to the use limit is 10mm, the extraction amount of the screw 57 extracted in accordance with the wear amount (use limit) is 20 mm. The amount of the screw 57 drawn out is obtained by multiplying the number of revolutions (cumulative number of revolutions) of the sleeve 55 by the pitch between the two

threads

55c and 57 a. In the present embodiment, the pitch of the screw is set to 1mm, and the screw 57 is withdrawn by an amount of 1 pitch of the screw (1mm) every 1 rotation of the sleeve 55. Therefore, in the present embodiment, when the sleeve 55 rotates 20 revolutions, the amount of withdrawal of the screw 57 is 20mm, and the amount of wear of the lining 43 reaches 10mm (limit of use).

In the present embodiment, in order to limit excessive extraction of the screw 57, when the wear amount of the bush 43 reaches the use limit (10mm), the stopper 57d of the screw 57 abuts against the stopper receiving portion 55e of the sleeve 55, and the stopper function is activated. Specifically, when the amount of withdrawal of the screw 57 reaches a predetermined withdrawal amount (20mm) set in advance by the long-term use of the drum brake B, the stopper 57d abuts against the stopper receiving portion 55e, thereby restricting the movement of the screw 57 in the axial direction. By preventing the screw 57 from being excessively drawn out beyond the predetermined drawing amount (by preventing the shoe clearance from being excessively adjusted) in this way, it is possible to prevent the screw 57 from interfering with the brake drum 31 (biting into the brake drum 31) during the operation of the brake.

As described above, according to the drum brake B of the present embodiment, by activating the stopper function when the amount of withdrawal of the screw 57 reaches the predetermined withdrawal amount and preventing the screw 57 from being excessively withdrawn, even if the drum brake B is continuously used beyond the limit of use of the lining 43, the screw 57 and the brake drum 31 can be prevented from interfering with each other during braking operation, and therefore, the occurrence of damage to the slack adjustment mechanism 6 and the brake drum 31 and the occurrence of wheel lock can be effectively suppressed.

In the drum brake B according to the present embodiment, the screw 57 is divided into the threaded shaft portion 57a and the adjustment dial portion 57B, and the threaded shaft portion 57a and the adjustment dial portion 57B are detachably fastened by the countersunk bolt 57j, whereby when the dust-proof cover 59 is attached across the screw 57 and the housing 51, the cover 59 can be attached to the housing 51 in a state where the threaded shaft portion 57a and the adjustment dial portion 57B are separated from each other, and therefore, the replacement work of the cover 59 can be facilitated.

Further, in the drum brake B according to the present embodiment, since the outer diameter of the stopper 57d is formed smaller than the inner diameter of the torsion spring 61 and the stopper 57d is configured to be insertable in the axial direction with respect to the torsion spring 61, a large stroke in the withdrawal direction (axial direction) of the screw 57 can be ensured while the overall size of the drum brake B is reduced.

The present invention is not limited to the above embodiments, and can be modified as appropriate within a range not departing from the gist of the present invention.

In the above embodiment, the predetermined withdrawal amount of the screw 57 is set to 20mm corresponding to the use limit (the limit wear amount) of the lining 43, but the present invention is not limited to this configuration, and the predetermined withdrawal amount of the screw 57 may be appropriately set in accordance with the required specifications of the vehicle or the like, and for example, the predetermined withdrawal amount of the screw 57 may be set to less than 20mm, and the stopper function may be activated before the wear amount of the lining 43 reaches the use limit.

In the above embodiment, the screw 57 is divided into the threaded shaft portion 57a and the adjustment dial portion 57b, but the configuration is not limited to this, and for example, the stopper 57d may be divided from another portion of the screw 57 and may be detachably attached to the stopper.

In the above embodiment, the threaded shaft portion 57a and the adjustment dial portion 57b are configured to be attachable and detachable by a threaded fastening structure, but the present invention is not limited to this structure, and the threaded shaft portion 57a and the adjustment dial portion 57b may be configured to be attachable and detachable by a fitting structure (recess-projection fitting structure) having a rotation stopper that restricts relative rotation of both. As the rotation stopper of the threaded shaft portion 57a and the adjustment dial portion 57b, for example, two-side width fitting, D-cut (D-cut) fitting, spline fitting, key fitting, or the like can be adopted.

In the above embodiment, the leading shoe brake is exemplified as the drum brake B, but the present invention is not limited to this configuration, and for example, a one-way servo drum brake, a double servo drum brake, or a double leading shoe drum brake may be applied.

Claims

1. A drum brake, comprising:

a cylindrical brake drum provided to a rotating member and rotatable integrally with the rotating member;

a brake shoe which is provided to a fixed member so as to be swingable and has a brake lining disposed along an inner circumferential surface of the brake drum; and

an expansion device that swings the brake shoe in accordance with a brake operation to press the brake lining against an inner circumferential surface of the brake drum,

the expanding device has:

a pressing force generating member that applies a pressing force in an axial direction in accordance with a braking operation;

a transmission member provided to the pressing force generation member so as to be rotatable in the axial direction;

a pressing member that is screwed into the transmission member in the axial direction, is connected to the brake shoe so as to be non-rotatable in the axial direction, and presses the brake lining against the inner circumferential surface of the brake drum by swinging the brake shoe by the pressing force transmitted from the transmission member; and

a clearance adjustment mechanism that adjusts a clearance between the brake lining and an inner circumferential surface of the brake drum by rotating the transmission member in the axial direction and extracting the pressing member in the axial direction, thereby displacing a relative position of the pressing member with respect to the transmission member in the axial direction,

the pressing member includes a stopper that restricts the pressing member from being pulled out by a predetermined amount in the axial direction with respect to the transmission member.

2. A drum brake according to claim 1,

the transmission member has a housing portion that houses the pressing member in the axial direction,

a stopper receiving portion is provided in the accommodating portion,

when the pressing member is extracted by the predetermined amount in the axial direction, the stopper abuts against the stopper receiving portion to restrict the pressing member from being extracted by more than the predetermined amount in the axial direction.

3. A drum brake according to claim 2,

the pressing member has a first pressing member screwed with the transmission member and accommodated in the accommodating portion, and a second pressing member provided on a leading end side of the first pressing member and connected to the brake shoe,

the first pressing member and the second pressing member are coupled to be separable from each other.

4. A drum brake according to any one of claims 1 to 3,

a torsion spring that allows relative rotation of the transmission member in one direction about the axial direction with respect to the pressing force generating member and restricts relative rotation of the transmission member in the other direction about the axial direction is disposed between the transmission member and the pressing force generating member,

the stopper has an outer diameter smaller than an inner diameter of the torsion spring, and is configured to be insertable into the torsion spring in the axial direction.