JPH08105471A - Drum brake with shoe gap automatic adjusting mechanism - Google Patents

Abstract

PURPOSE: To provide a drum brake with a shoe gap automatic adjusting mechanism which is constituted to suitably stop operation of a shoe gap automatic adjusting mechanism during the increase of a drum brake temperature. CONSTITUTION: An adjusting member 52 is provided with a rotation blocking member 50 to block clockwise rotation during brake operation as a result of an energizing force in a counterclockwise rotation direction being increased to a value higher than that in a clockwise rotation direction through the force of a spring 70 at a given temperature. Thereby, even when a press force exerted on a rotary drum 76 is increased to an excessive value, when the temperature of the rotation block member 50 attains a given value as a result of the temperature of a drum brake being increased, an energizing force is increased to block rotation of the adjusting member 52, and operation of a shoe gap automatic adjusting mechanism is blocked. In this case, since the friction heat of the rotary drum 76 is transmitted to the rotation block member 50 through press of an end part 72 against a shoe rim 22 and temperature is increased at a similar speed, operation of the shoe gap automatic adjusting mechanism is blocked without a delay.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drum brake provided with a shoe clearance automatic adjusting mechanism, and more particularly to a technique for improving temperature characteristics of the shoe clearance automatic adjusting mechanism.

[0002]

2. Description of the Related Art Struts which are respectively engaged with one and the other of a pair of expandable brake shoes and have a star wheel in an intermediate portion, and a shoe web of the one brake shoe, on which a rotating shaft of the brake shoe is attached. An adjusting member having a claw portion that is attached so as to be rotatable about an axis parallel to and that rotates the star wheel by being rotated in one direction around the axis, and the adjusting member in the one direction. A biasing spring, and the adjusting member is rotated in the one direction according to the biasing force of the spring in response to a braking operation in which the brake shoes are opened, and the star wheel causes the star wheel to move in a predetermined direction. With the shoe gap automatic adjustment mechanism, the struts are extended to automatically adjust the shoe gap by being rotated in the same direction. Lamb brake is known.

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.

[0005]

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 by a relatively large pressing force, but during sudden braking or the like. When the pressing force becomes excessive, the rotating 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 value 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.

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 along with the temperature rise. For example, Japanese Laid-Open Patent Publication No. 55-159342 and Japanese Utility Model Publication No. 5
That is the technique disclosed in Japanese Patent Publication No. 9-133842. 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. Because the entire length can be extended,
The expansion of the shoe drum during expansion of the rotary drum is suppressed, and the shoe gap is not automatically adjusted.

Similarly, the technique of utilizing the shape change of the bimetal is disclosed in Japanese Patent Laid-Open No. 55-159343 and Japanese Utility Model Laid-Open No. 61-160336 previously filed by the present applicant. . The former is to prevent the action of the adjusting member by attaching a bimetal to the adjusting member and separating the claw portion of the adjusting member from the star wheel when the temperature rises. The latter is a state in which one end of a ring-shaped bimetal is attached to one of the connecting member and the first engaging member in a non-rotatable manner, and the outer peripheral surface of the cylindrical portion of the connecting member is fitted to the first engaging member. By being provided between the inner peripheral surface of the hole and the inner peripheral surface of the other member when the temperature rises, the outer peripheral surface of the other member is wound or inscribed in the inner peripheral surface to prevent the connecting member from rotating in the predetermined direction. It gives a rotation resistance.

However, in the above-mentioned conventional techniques, since the bimetal is provided in the strut or the like provided at a position relatively distant from the rotary drum,
A delay in temperature rise occurs with respect to the rotary drum whose temperature is directly raised by frictional heat or the like. Therefore, if the adjusting member is rotated in accordance with the operation of expanding the brake before the temperature at which the bimetal is made to function is reached, the shoe clearance can be automatically adjusted. That is,
Due to the delay in the temperature rise of the bimetal, there was a problem that the automatic adjustment blocking function did not work sufficiently.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an automatic shoe clearance adjusting mechanism capable of suitably blocking the action of the shoe clearance automatic adjusting mechanism when the temperature of the drum brake rises. To provide drum brakes.

[0010]

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, one end of which is the shoe rim of the brake shoe. Is attached to the adjusting member in a state of being in contact with the brake shoe, and the urging force for urging the adjusting member in the rotation direction opposite to the one direction is increased as the temperature of the brake shoe rises. A rotation blocking member for blocking the rotation of the adjusting member in the one direction.

[0011]

In this way, the adjusting member is urged by the urging force of the spring in the rotational direction opposite to the one direction as the temperature of the brake shoe rises. By increasing the urging force that is applied, a rotation blocking member that blocks rotation in one direction during braking operation is attached. Therefore, when the biasing force of the rotation blocking member becomes larger than the biasing force of the spring as the temperature of the drum brake increases, the rotation of the adjusting member is blocked and the action of the shoe gap automatic adjusting mechanism is blocked. At this time, since the rotation preventing member is attached to the adjusting member with one end thereof being in contact with the shoe rim which comes into contact with the rotating drum through the lining during the action of the drum brake, it is sensitive to the temperature rise of the rotating drum. Then the temperature is raised. Therefore, when the inner diameter of the rotating drum is expanded by the pressing force and the temperature of the drum brake is increased at the same time, the action of the shoe clearance automatic adjusting mechanism is prevented without delay.

Here, preferably, the rotation preventing member is
A shoe rim that is a U-shaped bent bimetal plate that deforms in a direction in which both ends are separated when the temperature rises, and that has a normal line in a reaction force direction that generates a rotational moment opposite to the one direction at the one end. The other end is fixed to the adjusting member while being in contact with one surface. With this structure, the both ends of the rotation preventing member are separated due to the temperature rise, and the biasing force for biasing the adjusting member in the rotation direction opposite to the rotation direction by the biasing force of the spring is increased. To be made.

[0013]

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, 14 are provided on a backing plate 10 so as to be able to expand each other by shoe hold down devices 16, 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 the surface of one of the brake shoes 14 on the side of the backing plate 10 of the shoe web 20 so as to be rotatable about one axis in the portion located on the side of the wheel cylinder 26. 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 disk-shaped star wheel 36 having outer peripheral teeth on the circumferential surface at the longitudinal intermediate portion thereof, and is configured to be extended with the rotation of the star wheel 36 in one direction. Has been done.

The strut 34 is shown in FIGS. 2 (a) and 2 (b).
As shown in the cross section of the main part, the first engaging member 40 engaging with the shoe web 20 of the brake shoe 12 and provided with the fitting hole 38, the shoe web 20 of the brake shoe 14, and the parking lever 32 are engaged. A second engaging member 44 that is fitted with a female screw hole 42 and a connecting member 48 in which the star wheel 36 is integrally formed at an intermediate portion of a cylindrical shaft portion 46 are provided. Connecting member 4
A male screw is formed on one end side of the shaft portion 46 divided into two by the star wheel 36 of No. 8, and this connecting member 48 is screwed to the second engaging member 44 on the one end side, and Struts 34 are configured by being fitted to the first engaging member 40 on the other end side.

Returning to FIG. 1, in the vicinity of the engaging portion of the shoe web 20 of the brake shoe 12 with the first engaging member 38,
On the surface opposite to the backing plate 10, U
The rotation preventing member 50 having a character shape is attached to the end surface 49 on the shoe rim 22 side.
An adjustment member 52 attached to the is provided so as to be rotatable by a pin 54.

The adjusting member 52 has a base 58 having a hole 56 into which the pin 54 is fitted, as shown in a perspective view in FIG.
An engaging projection 60 formed continuously from the base 58 and engaging with one end of the first engaging member 40, and the base 58.
Is formed by being bent at a substantially right angle in a direction away from the base portion 58 from a bent portion 62 that is bent at a substantially right angle to one direction, and is elastically pressed by the outer peripheral teeth of the star wheel 36 at the tip portion. Bending part that is bent at a substantially right angle in the same direction as the bending part 62 at a position opposite to the rotating arm 66 having the claw part 64 and the rotating arm 66 sandwiching the hole 56 of the base part 58. And 68. The adjusting member 52 is biased in the clockwise direction in FIG. 1 by a spring 70 stretched between the brake shoe 12 and the shoe web 20.

The rotation preventing member 50 is a bimetal plate which is bent in a U shape so that both ends thereof are separated from each other as the temperature rises, and one end 72 of the brake shoe 12 is formed. It is pressed by the shoe rim 22 and is fixed by rivets or the like to the end surface 49 of the other end portion 74, which is located on the side opposite to the rotating arm 66 of the bent portion 68. As shown in FIG. 1, the pressing position of the one end portion 72 against the shoe rim 22 is such that the reaction force direction of the normal line A (that is, the inner circumferential direction) at the pressing position and the rotation center of the adjusting member 52 are The straight line B passing through the pressing position is positioned toward the rear side in the rotation direction (clockwise direction) by the urging force of the spring 70. That is, the one end portion 72 is pressed against one surface of the shoe rim having a normal line in the reaction force direction that produces a rotational moment opposite to the rotational direction due to the biasing force of the spring 70. For this reason,
The rotation preventing member 50 applies to the adjusting member 52 an urging force in a direction opposite to the rotation direction of the urging force of the spring 70, that is, in the counterclockwise direction in FIG.

The operation of the adjusting member 52 will be described below. In the normal operating state, the biasing force applied by the spring 70 is sufficiently larger than that of the rotation blocking member 50, so that the adjustment member 52 is biased in the clockwise rotation direction based on the difference. As a result, the adjusting member 52 urges the strut 34 to the right in FIG. 1 by the engagement projection 60, and when the wheel cylinder 26 is in operation, the strut 34 is expanded along with the expansion of the brake shoes 12, 14. The pin 54 is rotated clockwise while being moved rightward. Further, when the wheel cylinder 26 is not operating,
As the strut 34 is moved leftward until the brake shoe 12 and the first engaging member 40 come into contact with each other according to the urging force of the return spring 28, the spring 7
The pin 54 rotates counterclockwise against the biasing force of zero.

With the rotational movement of the adjusting member 52, the claw portion 64 is slidably contacted with the outer peripheral teeth of the star wheel 36 and reciprocated as shown by an arrow in FIG. 2B. When the amount of movement exceeds a predetermined amount,
The claw portion 64 engages with the outer peripheral teeth of the star wheel 36 and rotates it clockwise in FIG.
The amount of screwing in is reduced to make the female screw hole 4 of the second engaging member 44
A predetermined amount is extracted from No. 2, and the overall length of the strut 34 is increased. As a result, the approach positions of the brake shoes 12, 14 are separated by a predetermined distance when the wheel cylinder 26 is inactive, and the brake shoes 1 and 14 are separated from each other.
Despite the wear of Nos. 2 and 14, the shoe gap between the rotary drum 76 and the two-dot chain line in FIG. 1 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 64, 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.

By the way, when the drum brake is actuated, particularly when the wheel cylinder 26 is actuated, the brake shoes 12 and 14 are pressed against the rotary drum 76 by a relatively large pressing force, but during sudden braking or the like. When the pressing force becomes excessive, the rotating drum 76 is elastically deformed by the pressing force and the inner diameter thereof is enlarged. For this reason, the shoe gap between the inner diameter of the rotating drum 76 and the outer diameter of the shoe is large even though the brake shoes 12 and 14 are not worn.

On the other hand, at the time of sudden braking as described above, the rotary drum 76 causes the lining 2 of the brake shoes 12, 14 to rotate.
4 is slid, frictional heat is generated to raise the temperature of the drum brake, but the frictional heat at that time is transmitted to the shoe rim 22 via the lining 24. Therefore, the temperature of the shoe rim 22 is raised at the same speed as the rotating drum 76. At this time, the rotation blocking member 50
Since the one end portion 72 thereof is brought into contact with the shoe rim 22, the frictional heat is transmitted from the shoe rim 22 and the temperature is raised at a similar speed. Due to this temperature rise, the rotation preventing member 50 tries to deform in a direction in which the one end portion 72 and the other end portion 74 are separated from each other, but the one end portion 72 is attached to the adjusting member 52 while being pressed by the shoe rim 22. Therefore, the adjusting member 5
The counterclockwise urging force acting on 2 increases as the temperature rises.

When the temperature of the drum brake is raised to a temperature determined in advance by the shape of the rotation preventing member 50, the initial pressing force on the shoe rim 22, the characteristics of the bimetal, etc., the above rotation preventing member. The counterclockwise biasing force of the spring 50 is sufficiently larger than the clockwise biasing force of the spring 70, and when the wheel cylinder 26 is acted on as described above, the adjusting member 52 rotates clockwise. Will not occur. Therefore, when such a temperature rise occurs, the brake shoe 1
Even when the expansion amounts of 2 and 14 are larger than a predetermined amount, the shoe gap is not automatically adjusted.

That is, according to this embodiment, the adjusting member 5
In the second example, as the temperature of the brake shoe 12 increases, the urging force that urges the adjusting member 52 in the rotation direction opposite to the clockwise rotation direction by the urging force of the spring 70 increases. A rotation blocking member 50 that blocks rotation in the clockwise direction during braking operation is attached.
Therefore, when the biasing force of the rotation blocking member 50 becomes larger than the biasing force of the spring 70 as the temperature of the drum brake increases, the rotation of the adjusting member 52 is blocked and the action of the shoe gap automatic adjusting mechanism is blocked. . At this time,
Since the one end portion 72 of the rotation preventing member 50 is pressed against the shoe rim 22, the frictional heat of the rotating drum 76 is transmitted through the lining 24 and the shoe rim 22 to raise the temperature at a similar speed. The action of the shoe clearance automatic adjusting mechanism is prevented without delay.

Therefore, the rotary drum 7 is subjected to sudden braking or the like.
When the pressing force applied to 6 becomes excessively large and the shoe gap increases due to the enlargement of the inner diameter of the shoe 6, when the temperature rises at the same time, the rotation blocking member 50 immediately acts on the adjusting member 52. Rotation is blocked and the shoe clearance is not automatically adjusted. Accordingly, in such a case, the shoe gap is preferably prevented from becoming too small, and as a result, the friction of the brake is appropriately prevented.

Although one embodiment of the present invention has been described in detail above, the present invention can be implemented in other modes.

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.

Further, in the above-described embodiment, the rotation preventing member 50 is formed in a U shape, and both ends thereof are separated when the temperature rises, so that the rotation preventing member 50 is biased in the direction opposite to the rotation direction by the biasing force of the spring 70. The power was increased, but its shape is changed appropriately. For example, it may be V-shaped or S-shaped, or may be formed in a substantially linear shape at room temperature,
The adjusting member 52 may be biased by bending in a predetermined direction when the temperature rises. Further, the attachment position to the adjusting member 52 is appropriately changed, for example, the other end portion 74 of the rotation blocking member 50 is bent to the side opposite to the one end portion 72, and the engaging protrusion 60 of the base portion 58 of the adjusting member 52 is provided. A bent portion may be provided on the side opposite to and may be attached to the lower portion in FIG.

Also, in the embodiment, the rotation preventing member 5
Although 0 is made of bimetal, a shape memory alloy or the like may be used as long as it is deformable as the temperature of the brake shoe rises.

Although not specifically exemplified, the present invention can be variously modified without departing from the gist thereof.

[Brief description of drawings]

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

2A and 2B are sectional views showing the structure of the strut of FIG. 1, wherein FIG. 2A is a sectional view taken along the axial direction, and FIG. 2B is a sectional view taken along line bb in FIG. 2A.

3 is an enlarged perspective view of the adjusting member of FIG. 1. FIG.

[Explanation of symbols]

 12, 14: Brake shoe 22: Shoe rim 34: Strut 36: Star wheel 50: Rotation blocking member 52: Adjusting member 64: Claw 70: Spring

Claims (1)

[Claims] 1. A strut that is engaged with one and the other of a pair of expandable brake shoes and has a star wheel in the middle, and a pivot shaft of the brake shoe on the shoe web of the one brake shoe. An adjusting member having a claw portion that is attached so as to be rotatable about an axis parallel to and that rotates the star wheel by being rotated in one direction around the axis, and the adjusting member in the one direction. A biasing spring, and the adjusting member is rotated in the one direction in accordance with the biasing force of the spring in response to a braking operation in which the brake shoe is opened, and the claw portion causes the star wheel to move in a predetermined direction. Drum brace with an automatic shoe gap adjustment mechanism of the type in which the struts are extended to automatically adjust the shoe gap by being rotated in the direction. And one end of the brake shoe is attached to the adjusting member in contact with the shoe rim of the brake shoe, and the adjusting member is urged in a rotation direction opposite to the one direction as the temperature of the brake shoe rises. A drum brake with an automatic shoe gap adjusting mechanism, comprising a rotation blocking member for blocking the rotation of the adjusting member in the one direction by increasing the biasing force.