JPH08105472A - Drum brake with automatic shoe gap adjusting mechanism - Google Patents

Abstract

PURPOSE: To provide a drum brake which is constituted to stably block operation of an automatic shoe gap adjusting mechanism when the press force of a brake shoe is increased to an excessive value. CONSTITUTION: An engagement releasing device 64 releases the pawl part 56 of an adjusting member 52 and a star wheel 36 from an engagement state therebetween through deformation when the increase of a drum brake temperature occurs. Since the engagement release device 64 is attached to a first engaging member 38, when the increase of a drum brake temperature occurs simultaneously with the increase of the inside diameter of a rotary drum as a result of the press force of a brake shoe being increased to an excessive value, operation of an automatic shoe gap adjusting mechanism is reliably blocked. In this case, since a slide protrusion surface 66 is deformed in such a manner that it is positioned closer to the outer peripheral side than a cylinder surface along the cylinder surface pressing the outer peripheral surface thereof, the pawl part 56 is reliably separated through small deformation. This constitution decreases a deformation amount of the adjusting member 52 and suitably suppresses the generation of an excessive load and performs stable blocking of automatic shoe gap adjustment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drum brake having an automatic shoe clearance adjusting mechanism, and more particularly to a technique for preventing the shoe clearance from becoming too small.

[0002]

2. Description of the Related Art A strut having a star wheel in an intermediate portion, which is engaged with one and the other of a pair of expandable brake shoes and has engaging teeth on its outer peripheral surface, and one of the brake shoes. An adjusting member rotatably attached to the shoe web and having a claw portion that engages with the engaging teeth of the star wheel, and the adjusting member rotates when the brake shoe is expanded. There is known a drum brake with an automatic shoe gap adjusting mechanism of a type that is moved and the star wheel is rotated in a predetermined direction by the claw portion to extend the struts to automatically adjust the shoe gap. There is.

The above-mentioned strut has, for example, a pair of first engaging members and second engaging members which are respectively engaged with shoe webs of a pair of brake shoes, and has a columnar shape as a whole, and a star wheel in an intermediate portion. And a connecting member having. In this strut, the first engaging member is fitted into one of the cylindrical portions of the connecting member in the fitting hole, and the second engaging member is screwed into the other of the cylindrical portion of the connecting member in the female screw hole. When the connecting member is rotated in a predetermined direction via the star wheel, the connecting member is pulled out from the second engaging member and the entire length is extended.

In the above-mentioned drum brake, the amount of expansion of the brake shoe when the brake is applied is predetermined because the shoe gap between the rotating drum and the brake shoe becomes large due to wear of the brake shoe, for example. When the adjusting member is rotated in the one direction in response to a braking operation in which the brake shoes are expanded, the star wheel is rotated in a predetermined direction by the claw portion when the amount exceeds the predetermined amount. . As a result, the overall length of the strut is extended, the approaching positions of the brake shoes are separated when the brake is not operated, and the shoe gap is automatically adjusted to a preset substantially constant value.

By the way, when the drum brake is actuated, particularly when the wheel cylinder is actuated, the brake shoe is pressed against the rotary drum with a relatively large pressing force, but the pressing force is excessive during sudden braking or the like. Then, the rotary drum is elastically deformed by the pressing force and the inner diameter thereof is enlarged. Therefore, in such a case, even if the brake shoe is not worn, the expansion amount thereof may exceed the predetermined constant amount and the shoe clearance may be automatically adjusted. However, if the shoe clearance is automatically adjusted in such a case, then the shoe clearance becomes smaller when the drum brake is deactivated, and further, there is a problem that the brake may rub. there were.

[0006]

On the other hand, at the time of sudden braking as described above, since the rotary drum slides on the lining of the brake shoe, frictional heat is generated and the temperature of the drum brake rises. Therefore, paying attention to this temperature rise,
The useless change of the shoe clearance is suppressed by utilizing the shape change of the bimetal accompanying the temperature rise. For example, the techniques disclosed in Japanese Patent Laid-Open No. 55-159342 and Japanese Utility Model Laid-Open No. 59-133842 are such techniques. According to these techniques, since the bimetal is inserted between the first engaging member and the connecting member, which are fitted to each other, they are axially separated from each other when the temperature rises and the strut of the strut is separated. Since the entire length is extended, the shoe gap is prevented from increasing when the rotary drum is expanded, and the shoe gap is not automatically adjusted. However, in these techniques, since the connecting member and the first engaging member are axially separated from each other by the shape change of the bimetal against the spring of the adjusting member that rotates the star wheel, the bimetal used is deformed. It was difficult to set force, amount of change, etc., and it was difficult to obtain a stable action.

The present invention has been made in view of the above circumstances, and its object is to stably prevent the operation of the automatic shoe clearance adjusting mechanism when the pressing force of the brake shoe becomes excessive. (EN) A drum brake with an automatic shoe clearance adjusting mechanism.

[0008]

In order to achieve such an object, the gist of the present invention is a drum brake with a shoe clearance automatic adjusting mechanism of the type described above, which runs along the outer peripheral surface of the star wheel. A tip end having a sliding convex surface and a base end portion fixed to the strut, and the sliding convex surface is positioned on the outer peripheral side of the star wheel by deformation due to temperature rise, and the claw of the adjusting member is provided. A disengagement device is provided that separates the part from the engagement teeth of the star wheel.

[0009]

With this configuration, in the drum brake, the sliding convex surface is located on the outer peripheral side of the star wheel due to the deformation caused by the temperature rise, and the claw portion of the adjusting member is engaged with the engaging tooth of the star wheel. A disengagement device is provided that separates the device from. Therefore, when the inner diameter of the rotating drum is increased due to the excessive pressing force of the brake shoe and the temperature of the drum brake is increased at the same time, the disengagement device is deformed and the claw portion of the adjusting member is deformed. Is separated from the outer peripheral surface of the star wheel, and the automatic adjustment of the shoe clearance is reliably prevented.

At this time, at the tip of the disengagement device, there is provided a sliding convex surface that slides with the claw portion of the adjusting member along the outer peripheral surface of the star wheel, and the sliding convex surface is used as the star wheel. Since it is deformed so as to be positioned on the outer peripheral side, the claw portion can be reliably separated with a small deformation as compared with the case where the sliding surface is flat. For this reason,
The rigidity required for the disengagement device is relatively low, and
The amount of deformation of the adjusting member is reduced, and the occurrence of excessive load is suitably suppressed. Moreover, the claw portion of the adjusting member is pressed by the engaging teeth of the star wheel, but the pressing force is relatively small, for example, about 100 to 500 g,
No significant force is required to separate the pawl from the outer teeth of the star wheel. Therefore, these prevent stable adjustment of the shoe clearance automatically.

Preferably, the disengagement device is
A U-shaped holding portion having a pair of protrusions facing each other at both ends is provided at the base end portion, and is parallel to each other on the outer circumferential surface of the non-rotating portion of the strut at positions opposite to each other in the circumferential direction. Further, it is fixed at the holding portion to a fixing portion composed of a pair of slit grooves formed at a distance smaller than the distance between the pair of protrusions. By doing this, the disengagement device is inserted into the slit groove provided in the strut from both ends of the sandwiching portion, so that the sandwiching portion is the slit groove, and the pair of protrusions is the outer peripheral surface of the strut. Each is elastically engaged and fixed. Therefore, the disengagement device can be easily attached and detached, and the disengagement device can be attached to the conventional struts not provided with the disengagement device by simply forming a pair of slit grooves. It becomes possible.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, a pair of arcuate brake shoes 12 and 14 are provided on a backing plate 10 so that they can be expanded by shoe hold down devices 16 and 18. The brake shoes 12, 14 are fixed to the outer peripheral surface of the shoe rim 22, the shoe web 20 positioned substantially parallel to the plate surface of the backing plate 10, the shoe rim 22 fixed to the outer peripheral side end surface of the shoe web 20. And a lining 24, respectively. One end of the brake shoes 12, 14 has a wheel cylinder 26 fixed on the backing plate 10.
Of the brake shoes 12, 14 at positions near the wheel cylinder 26 and on the inner peripheral side of the backing plate 10 while being engaged with both ends of the brake shoe 12, 14.
The return springs 28 are interposed between the brake shoes 12 and 14, and the other ends of the brake shoes 12 and 14 are respectively brought into contact with the anchors 30 fixed on the backing plate 10. There is.

A parking lever 32 is provided on a surface of the shoe web 20 of one of the brake shoes 14 on the backing plate 10 side so as to be rotatable about a single axis at a portion located on the wheel cylinder 26 side. Shoe web 20 of brake shoe 12 and brake shoe 14
Struts 34 are laid between the shoe web 20 and the parking lever 32, and the brake shoes 12 and 14 are supported by the struts 34 from the inside. The strut 34 has a disc-shaped star wheel 36 having outer peripheral teeth on its peripheral surface at the middle portion in the longitudinal direction, and is extended with rotation of the star wheel 36 in one direction. A first engaging member 38 that engages with the shoe web 20 on the brake shoe 12 side, a second engaging member 40 that engages with the shoe web 20 on the brake shoe 14 side, and the star wheel 36 in the middle portion. And a connecting member 42 which is rotatably fitted to the first engaging member 38 and is screwed to the second engaging member 40.

In the vicinity of the engaging portion of the shoe web 20 of the brake shoe 12 with the first engaging member 38, the adjusting member 52 is provided on the surface opposite to the backing plate 10.
Is rotatably provided by a pin 54. The adjusting member 52 is provided with a claw portion 56 that is elastically pressed against the outer peripheral teeth of the star wheel 36 and an engaging protrusion 58 that engages with one end of the first engaging member 38. This adjusting member 52 is used for the shoe web 2 of the brake shoe 12.
The spring 60 stretched between 0 and the
Is urged clockwise in the
In the same figure, when the wheel cylinder 26 is actuated, the strut 34 is rotated clockwise while the strut 34 is moved rightward as the brake shoes 12 and 14 are expanded. Also, the wheel cylinder 2
When 6 is inactive, the strut 34 is moved leftward until the brake shoe 12 and the first engaging member 38 come into contact with each other according to the urging force of the return spring 28, and the urging force of the spring 60 is resisted. The pin 54 rotates counterclockwise.

Then, with the rotational movement of the adjusting member 52, the claw portion 56 is slidably contacted with the outer peripheral teeth of the star wheel 36 and is reciprocated as shown by an arrow in FIG. 2B. When the amount of movement exceeds a predetermined amount, the claw portion 56 engages with the outer peripheral teeth of the star wheel 36 to rotate it in the clockwise direction in FIG.
The screwing amount of No. 2 is made shallow so as to be extracted from the second engaging member 40 by a predetermined amount, and the overall length of the strut 34 is increased.
As a result, the approach positions of the brake shoes 12 and 14 are separated by a predetermined distance when the wheel cylinder 26 is inactive, and the rotation indicated by the two-dot chain line in FIG. 1 is achieved regardless of wear of the brake shoes 12 and 14. The shoe gap with the drum 62 is automatically adjusted to be substantially constant. A predetermined rotation resistance is imparted to the star wheel 36, for example, by pressing the return spring 28, and when the star wheel 36 is engaged with the claw portion 56, it is rotated with the rotation of the adjusting member 52 as described above. However, their rotation is blocked when they come into sliding contact with each other.

A disengagement device 64 is attached to the first engagement member 38 of the strut 34 as shown in an enlarged view in FIG. 2 (a). As shown in FIGS. 2 (b) and 3, the disengagement device 64 has the star wheel 36 at the tip.
The elongated deformed portion 68 having the sliding convex surface 66 along the outer peripheral surface of the deformed portion 68 and the U-shaped deformed portion 68 are continuously connected to the proximal end side of the deformed portion 68 to form a substantially right angle with the deformed portion 68. A pair of protrusions 7 that are formed by being bent into two and that face each other at both ends.
And a holding portion 72 having 0 and 70, and the sliding convex surface 66 is attached so as to be located between the outer peripheral surface of the first engaging member 38 and the claw portion 56 of the adjusting member 52. .
The disengagement device 64 is made of, for example, a material that deforms according to the temperature such as bimetal, and when the temperature rises, as shown by the broken line in FIG. 2B, the sliding convex surface 66 thereof is located on the outer peripheral side of the star wheel 36, whereby the claw portion 56 of the adjusting member 52 is moved to the star wheel 36. And the engagement is released.

On the other hand, on the outer peripheral surface of the first engaging member 38, as shown in FIG. 4, are formed in parallel to each other at positions opposite to each other in the circumferential direction and at intervals smaller than the interval between the pair of projections 70, 70. A pair of slit grooves 74, 74 (only one shown)
Is provided. The engagement releasing device 64 is inserted into the slit grooves 74, 74 from both end sides of the U-shaped holding portion 72 so that the holding portion 72 has the slit grooves 74, 74.
The pair of protrusions 70, 70 are elastically engaged with the outer peripheral surface of the first engaging member 38 and fixed to the first engaging member 38. That is, the disengagement device 64 is fixed to the outer peripheral surface of the non-rotating portion of the strut 34 at the sandwiching portion 72.

By the way, when the drum brake is actuated, particularly when the wheel cylinder 26 is actuated, the brake shoes 12, 14 are pressed against the rotary drum 62 by a relatively large pressing force, but the brake shoes 12, 14 are pressed by the sudden braking or the like. If the pressure becomes excessive, the inner diameter of the rotary drum 62 will increase. Therefore, in such a case, the movement amount of the claw portion 56 of the adjusting member 52 may exceed the predetermined value, and the shoe gap may be automatically adjusted. However, during such sudden braking, the rotating drum 62 slides on the linings 24 of the brake shoes 12 and 14, so frictional heat is generated and the temperature of the drum brake rises. As a result, as shown by the broken lines in FIGS. 2 (a) and 2 (b), the deforming portion 68 of the disengagement device 64 deforms according to its temperature, and the sliding convex surface 66 moves upward in FIG. The claw portion 56 of the adjusting member 52 is moved upward in the figure, the elastically pressed state of the claw portion 56 against the star wheel 36 is released, and the action of the shoe gap automatic adjusting mechanism is blocked.

That is, in the present embodiment, the disengagement device 64 for separating the claw portion 56 of the adjusting member 52 from the star wheel 36 by deforming when the temperature of the drum brake rises is the disengagement device 64 of the strut 34. The brake shoe 1 is attached to the engaging member 38.
When the pressing force of 2, 14 becomes excessive and the inner diameter of the rotary drum 62 increases, and the temperature of the drum brake rises at the same time, the action of the shoe clearance automatic adjusting mechanism is reliably prevented, Subsequent reduction of the shoe gap during the non-actuation of the drum brake is suitably suppressed.

At this time, in the disengagement device 64, a sliding convex surface 66 for sliding with the claw portion 56 of the adjusting member 52 is provided along the outer peripheral surface of the star wheel 36, and the sliding convex surface 66 is provided. Since it deforms so as to be located on the outer peripheral side of the star wheel 36, it is possible to reliably separate the claw portion 56 with a small deformation as compared with the case where the sliding convex surface 66 is flat. Therefore, the rigidity required for the disengagement device 64 is relatively low, and the amount of deformation of the adjusting member 52 is small, so that the generation of an excessive load is suitably suppressed. Moreover, the claw portion 56 of the adjusting member 52 is pressed by the engaging teeth of the star wheel 36, but since the pressing force is relatively small, for example, about 100 to 500, the claw portion 56 is pressed by the star wheel 36. It does not require a large force to separate it from the outer peripheral surface. Therefore, these prevent stable adjustment of the shoe clearance automatically.

Further, according to the present embodiment, the disengagement device 6
4 is a U-shaped holding portion 7 having a pair of protrusions 70, 70.
2 are provided, and the U-shaped end portions of the holding groove 72 are inserted into the pair of slit grooves 74, 74 provided in the first engaging member 38, so that the holding portion 72 forms the slit grooves 74, 74.
The protrusions 70, 70 are elastically engaged with and fixed to the outer peripheral surface of the first engagement member 38, respectively. Therefore, the disengagement device 64 can be easily attached and detached, and a pair of slit grooves 74, 74 are formed in the first engagement member 38 even in a conventional strut having no such disengagement device 64. The disengagement device 64 can be attached only by forming

Next, another embodiment of the present invention will be described. It should be noted that in the following description, the description of the portions common to the above-described embodiment will be omitted.

FIG. 5 is a view showing another disengagement device 76. The disengagement device 76 is made of, for example, a bimetal, and has a longitudinal deformable member 78 having a sliding convex surface 66 similar to that of the disengagement device 64 at the tip portion. And a sandwiching member 80, and the sandwiching member 80 is pinned to the base end portion of the deformable member 78. The inner diameter of the holding member 80 is smaller than the outer diameter of the first engaging member 38. When the disengagement device 76 is attached to the first engagement member 38, for example, a shallow peripheral groove having the same width as the holding member 80 is provided on the outer peripheral surface of the attachment position of the first engagement member 38. The engagement releasing device 76 is inserted into the circumferential groove from the opening side of the nipping member 80, whereby the nipping member 80 is elastically engaged with the circumferential groove and fixed to the first engaging member 38. That is, the disengagement device 76 composed of two members in this way may be used, and in that case, the first engagement member 3 is used.
It is preferable that the nipping portion for fixing to 8 does not use bimetal or the like.

Although one embodiment of the present invention has been described in detail above, the present invention can be implemented in still another mode.

For example, in the above embodiment, the so-called L
An example in which the present invention is applied to a T-type drum brake has been shown.・ Reading type drum brakes,
It is also applied to duo servo type drum brakes.

In the above embodiment, the case where the present invention is applied to the drum brake of the type in which the shoe clearance is automatically adjusted when the brake shoes 12 and 14 are expanded by the wheel cylinder 26 has been described. The present invention can be similarly applied to a drum brake in which the shoe clearance is automatically adjusted when the parking brake lever 32 is rotated.

Although the disengagement devices 64 and 76 are made of bimetal, any material can be used so long as the sliding convex surface 66 is deformed so as to move upward in FIG. Instead of this, another material such as a shape memory alloy may be used.

The disengagement devices 64 and 76 may be attached to the first engaging member 38 by elastically fixing them to the first engaging member 38 by the sandwiching portion 72, the sandwiching member 80 and the like. To
For example, the deformable member 78 of the disengagement device 76 may be directly fixed by a pin or the like.

Although not illustrated one by one, the present invention can be variously modified without departing from the spirit thereof.

[Brief description of drawings]

FIG. 1 is a diagram showing a main part of a drum brake according to an embodiment of the present invention.

FIG. 2 is an enlarged view of the main part of FIG. 1, where (a) is
In FIG. 1, the state viewed from the bottom is shown, and (b) shows the bb section in (a).

3 is a perspective view showing an engagement release member used in the drum brake of FIG. 1. FIG.

FIG. 4 is a diagram illustrating a slit groove of a first engagement member.

FIG. 5 is a view showing an engagement releasing device used in another embodiment of the present invention.

[Explanation of symbols]

 12, 14: Brake shoe 22: Shoe rim 34: Strut 36: Star wheel 52: Adjusting member 56: Claw portion 64, 76: Disengagement device 66: Sliding convex surface

Claims (1)

[Claims] 1. A strut having a star wheel at an intermediate portion, which is engaged with one and the other of a pair of expandable brake shoes and has engaging teeth on an outer peripheral surface thereof, and one of the brake shoes. An adjusting member that is rotatably attached to the shoe web and that has a claw portion that engages with the engaging teeth of the star wheel, and the adjusting member rotates when the brake shoe is opened. Is moved and the star wheel is rotated in a predetermined direction by the claw portion,
In a drum brake with a shoe gap automatic adjusting mechanism of a type in which the strut is extended to automatically adjust the shoe gap, a tip having a sliding convex surface along the outer peripheral surface of the star wheel and fixed to the strut. A base end portion, and disengagement for locating the sliding convex surface on the outer peripheral side of the star wheel by deformation due to temperature rise and separating the claw portion of the adjusting member from the engaging tooth of the star wheel. A drum brake with an automatic shoe clearance adjustment mechanism that is equipped with a device.