JPH0972355A - Shoe driving mechanism of drum brake - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lighten the labor for a gap adjusting work and the like, and simultaneously reduce the manufacturing cost of a drum brake. SOLUTION: Pressing operation of a pair of brake shoes 3, 4 against the inner face of a drum 2 is performed by means of a link mechanism constituted of first and second levers 15, 18, a strut 21, an energization member 19 mutually energizing a first lever and a second lever, and the like, and the link mechanism restrains increase of lever stroke accompanying wear of lining by increasing the lever ratio between the mutual levers due to relative rotation of the levers 15, 18 at operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pair of brake shoes arranged opposite to each other in a cylindrical inner space of a drum to advance and retreat toward the inner surface of the drum to press the lining on the outer periphery of the brake shoe against the inner surface of the drum. The present invention relates to a shoe drive mechanism of a drum brake which is brought into a braking state or a non-braking state in which it is separated from the inner surface of the drum.

[0002]

2. Description of the Related Art Generally, a drum brake device used in a vehicle or the like is capable of advancing and retracting a pair of brake shoes arranged opposite to each other in a cylindrical drum inner space and the pair of brake shoes toward the inner surface of the drum. A back plate supported on the back plate and the respective brake shoes on the back plate are moved back and forth toward the inner surface of the drum so that the lining of the outer periphery of the brake shoe is pressed against the inner surface of the drum or in a non-braking state in which it is separated from the inner surface of the drum. And a adjuster for adjusting a clearance between the drum and the brake shoe.

The adjuster is for avoiding an excessive stroke of the operation lever of the brake pedal or the parking brake due to the abrasion of the lining attached to the brake shoe. , Various automatic adjustment types have been developed.

As a manual type adjuster, a screw type one which is arranged between one ends of a pair of brake shoes arranged so as to face each other is widely used.

[0005]

However, the manual adjuster has a problem that maintenance work is time-consuming because the clearance adjustment work must be performed in a timely manner according to the progress of lining wear. Further, the automatic adjustment type has a problem that the maintenance work can be reduced, but the structure becomes complicated and the manufacturing cost of the drum brake increases.

The present invention has been made in view of the above circumstances. An object of the present invention is to provide a shoe drive mechanism for a drum brake, which can reduce the labor for the clearance adjustment work and at the same time reduce the manufacturing cost of the drum brake. The configuration suppresses an increase in lever stroke due to lining wear.

[0007]

In order to achieve the above object, a shoe drive mechanism for a drum brake according to the present invention, and a pair of brake shoes arranged opposite to each other in a cylindrical inner space of a drum are provided to face an inner surface of the drum. A shoe drive mechanism of a drum brake, which is moved forward and backward to press the outer lining of the brake shoe against the inner surface of the drum or into a non-braking state separated from the inner surface of the drum. Lever supporting pivot that is erected on the back plate that is supported so that it can move forward and backward, and the middle part is rotatably supported by the pivot and the brake operation cable end is connected to one end for brake operation. A lever-shaped first lever that rotates in response to the lever, and one brake that is rotatably supported at the one end and the other end at the other end. A second lever shoe pressing portion abutting on-menu is formed, said second lever is the first
Urging member for urging the one end of the first lever and the one end of the second lever toward each other so as to interlock with the first lever, and the one end is freely rotatable to the other end of the first lever. And a strut connected to the other brake shoe and having the other end connected to the other brake shoe to limit the return movement of the brake shoe, by the relative rotation of the first lever and the second lever. It is characterized in that the lever ratio between these levers is increased to suppress an increase in the lever stroke due to the liner wear.

Alternatively, a pair of brake shoes arranged opposite to each other in a cylindrical inner space of the drum are moved toward and away from the inner surface of the drum to press a lining of an outer periphery of the brake shoe against the inner surface of the drum, or a drum inner surface. A shoe driving mechanism for a drum brake in a non-braking state separated from the lever, and a lever-supporting pivot that is erected on a back plate that supports the brake shoe so as to be capable of advancing and retracting toward the inner surface of the drum, An intermediate portion is rotatably supported by the pivot, a brake operation cable end is connected to one end, and a lever-shaped first lever that rotates in response to a brake operation, and one end rotatably attached to the pivot A second lever that is supported and has a shoe pressing portion that is in contact with one brake shoe at the other end, and the second lever A biasing member that biases one end of the first lever and one end of the second lever toward each other so as to interlock with the first lever, and is formed on the other end of the first lever. One end is connected to a pin that passes through the elongated hole formed in the second lever and the elongated hole formed in the intermediate portion of the second lever, and the other end is connected to the other brake shoe to perform the returning operation of the brake shoe. The lever ratio of these levers is determined by the relative rotation amount of the first lever and the second lever and the movement amount of the pin in the elongated hole of the lever. It is characterized by increasing and suppressing the increase of the lever stroke accompanying the liner wear.

A link mechanism is composed of limited parts such as first and second levers, struts, and biasing members for biasing the first and second levers together. Due to the relative rotation with the second lever, the lever ratio between these levers increases, and an increase in the lever stroke due to the liner wear can be suppressed.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of a shoe drive mechanism for a drum brake according to the present invention will be described below in detail with reference to the drawings. 1 and 2 show an embodiment of a shoe drive mechanism for a drum brake according to the present invention. FIG. 1 is a front view of the shoe drive mechanism 1 for a drum brake, and FIG. 2 is a view as seen from an arrow A in FIG. Is.

The shoe drive mechanism 1 includes a pair of brake shoes 3 and 4 arranged to face each other in the inner space of a cylindrical drum 2.
A braking state in which the outer linings 5, 6 of the brake shoes 3, 4 are pressed against the inner surface of the drum 2 by advancing and retreating toward the inner surface of the drum 2, or the outer linings 5, 6 of the brake shoes 3, 4 are set on the inner surface of the drum 2. It is a link mechanism which is separated from the non-braking state.

The pair of brake shoes 3 and 4 is the drum 2
Arc-plate-shaped rims 3a, 4a along the inner peripheral surface of the web, and webs 3b, 4 protruding from the rims 3a, 4a toward the inner diameter side.
b and linings 5 and 6 attached to the outer circumferences of the rims 3a and 4a. Then, the respective brake shoes 3, 4 are moved back and forth toward the inner surface of the drum 2 by a holding device 8 (see FIG. 2).
Attached to. Further, as shown in FIG. 2, the end portions of the pair of brake shoes 3 and 4 on the back plate 9 that face each other are approached by the tension springs 10 and 11 (that is, the direction away from the drum 2). ).

The shoe drive mechanism 1 is provided between one ends of the brake shoes 3 and 4 facing each other, and as shown in FIG. 1, a pivot shaft for supporting a lever which is erected on a back plate 9. 13, a lever-shaped first lever 15 having an intermediate portion rotatably supported by the pivot shaft 13 and an end portion of a brake operating cable 14 connected to one end thereof to rotate in response to a brake operation. One end is rotatably supported by the pivot shaft 13 and the other end is in contact with the web 4b of the brake shoe 4 on one side.
Second lever 18 formed with 7 and one end of first lever 15 and one end of second lever 18 approach each other so that second lever 18 operates in conjunction with first lever 15. An urging member (tensile spring) 19 for urging in the direction,
A strut whose one end is rotatably connected to the other end of the first lever 15 by a pin 20 and the other end is connected to the web 3b of the other brake shoe 3 to limit the returning movement of the brake shoes 3, 4. And 21.

For example, the other end of the brake operating cable 14 is connected to a parking brake lever or a brake pedal, and is pulled in the direction of arrow (a) in FIG. 1 by pulling the parking lever.
The first lever 15 is rotated clockwise around the pivot 13.

Further, the urging member 19 moves to the second position until the brake shoe 4 comes into contact with the drum 2 and a reaction force (resistive force) of a certain degree or more acts on the shoe pressing portion 17 of the second lever 18. The elastic coefficient is set so that the lever 18 and the first lever 15 rotate integrally. Further, when the second lever 18 and the first lever 15 relatively rotate against the urging force of the urging member 19, the relative rotation amount of the first lever 15 reaches a specified amount. Then, there is provided a stopper 23 that comes into contact with the side surface of the second lever 18 and restrains the rotation of the first lever 15 with respect to the second lever 18. The first lever 15 shown by the chain double-dashed line in FIG. 1 shows the state in which the stopper 23 is in contact with the second lever 18.

In the shoe drive mechanism 1 described above, when the brake operating cable 14 is pulled in the direction of arrow (a) in FIG. 1 by the brake operation, the brake shoe 4 is moving toward the drum 2 and hits the drum 2. Previously,
Reaction force F acting on the shoe pressing portion 17 of the second lever 18
_{Since 1} is a sliding resistance mainly acting on the brake shoe 4 and a relatively small force, the urging member 19 does not extend, and the second lever 18 rotates integrally with the first lever 15.
In this way, when the second lever 18 and the first lever 15 rotate integrally, the lever ratio between these levers is small, and the second lever 18 moves with respect to the movement amount on the other end side. The movement amount (lever stroke) of the one end of the first lever 15 is small.

When the brake shoe 4 hits the drum 2 and the reaction force F ₁ acting on the shoe pressing portion 17 of the second lever 18 increases, the urging member 19 extends and the first lever 15 extends. Until the upper stopper 23 comes into contact with the side surface of the second lever 18, the first lever 15 moves to the second
After rotating with respect to the lever 18, the brake shoe 4 is pressed against the drum 2 with a pressing force corresponding to the force pulling the brake operation cable 14, and a desired braking force is exerted. In this way, when the first lever 15 is rotated with respect to the second lever 18, the lever ratio between these levers increases due to the movement of the action point where the tensile force is applied by the brake operation cable 14. The first lever 15 in comparison with the movement amount of the second lever 18 on the other end side.
The amount of movement (lever stroke) at one end of
Therefore, the brake shoes 3, 4 can be pressed against the drum 2 with a large force.

As described above, when the brake shoes 3 and 4 hit the drum 2, the levers 15 and 18
As the lever ratio as the lever mechanism increases, the relationship between the clearance between the brake shoe and the drum and the stroke of the first lever 15 becomes as shown by the curve f in FIG. The stroke of the first lever 15 is slightly longer when the lining wear is small compared to the characteristic g of the conventional mechanism that does not change, but when the lining wear is large (that is, the clear run between the brake shoe and the drum is On the contrary, the stroke of the first lever 15 becomes smaller and the increase in the lever stroke due to the lining wear can be suppressed, resulting in a reduction in the time for clearance adjustment work and the like. can do. Further, by using the shoe drive mechanism 1 having the above-described configuration, the conventional adjuster can be eliminated, and the configuration is much simpler than that of the conventional self-adjusting adjuster. Manufacturing costs can also be reduced.

In FIG. 3, the initial stroke s of the curve f is the relative rotation of the levers until the stopper 23 of the first lever 15 contacts the second lever 18.

FIG. 4 is a front view showing another embodiment of the shoe drive mechanism of the drum brake according to the present invention. The shoe drive mechanism 25 of the other embodiment includes a pair of brake shoes 3, 4 arranged to face each other in a cylindrical drum inner space.
In a braking state in which the linings 5 and 6 on the outer periphery of the brake shoes 3 and 4 are pressed against the inner surface of the drum by advancing and retracting toward the inner surface of the drum, or in a non-braking state in which the linings 5 and 6 are separated from the inner surface of the drum 2. In the same manner as in the above-described embodiment, the link mechanism is provided between one ends of the brake shoes 3, 4 facing each other. In addition,
Although not shown, the back plate that supports the brake shoes 3 and 4 and the drum may have the same configuration as in the previous embodiment.

The shoe drive mechanism 25 has a lever support pivot 13 provided upright on a back plate, an intermediate portion rotatably supported by the pivot axle 13, and one end of which is connected to an end of a brake operation cable 14. And a lever-shaped first lever 15 that rotates in response to a brake operation, and a shoe pressing member that has one end rotatably supported by the pivot shaft 13 and the other end that abuts the web 4b of one brake shoe 4. A second lever 18 having a portion 17 is formed, and one end of the first lever 15 and one end of the second lever 18 are close to each other so that the second lever 18 operates in conjunction with the first lever 15. Urging member 19 for urging the first lever 15 in the other direction, and an elongated hole 26 formed in the other end of the first lever 15 and a second
One end is connected to a pin 28 that is inserted through an elongated hole 27 formed in the intermediate portion of the lever 18, and the other end is connected to the web 3b of the other brake shoe 3 to limit the return movement of the brake shoe. And a strut 21.

Also in the case of the shoe drive mechanism 25, when the brake operation cable 14 is pulled in the direction of the arrow (b) in FIG. 1 by the brake operation, the brake shoe 4 is moving toward the drum and before hitting the drum. Then the second
Since the reaction force F ₂ acting on the shoe pressing portion 17 of the lever 18 is a relatively small force mainly due to the sliding resistance acting on the brake shoe 4, the biasing member 19 does not extend and the second lever 18 rotates integrally with the first lever 15. In this way, when the second lever 18 and the first lever 15 rotate integrally, the lever ratio between these levers is small, and the second lever 18 moves with respect to the movement amount on the other end side. , Amount of movement of one end of the first lever 15 (lever stroke)
Is small.

When the brake shoe 4 hits the drum and the reaction force F ₂ acting on the shoe pressing portion 17 of the second lever 18 increases, the urging member 19 extends and the first lever 15 moves. At the same time as rotating with respect to the second lever 18, the component force of the reaction force received by the strut 21 and the brake operating cable 1 acting on the first lever 15
The pin 28 moves in the slots 26, 27 by the moment about the pivot 13 due to the pulling force of 4, and as a result,
The lever ratio between the levers increases, and the movement amount (lever stroke) of one end portion of the first lever 15 increases as compared with the movement amount of the second lever 18 on the other end side. The force allows the brake shoes 3, 4 to be pressed against the drum.

As described above, when the brake shoes 3 and 4 hit the drum, the lever ratio between the levers 15 and 18 increases as a lever mechanism, so that the clearance (clearance) between the brake shoe and the drum is increased. And the stroke of the first lever 15 is shown by the curve f in FIG.
₂ , the stroke of the first lever 15 when the lining wear is small becomes slightly larger than the characteristic g ₂ by the conventional mechanism in which the lever ratio does not change, but when the lining wear becomes large ( That is, when the clear run between the brake shoe and the drum becomes large), the stroke of the first lever 15 becomes smaller, and the increase in the lever stroke due to the lining wear can be suppressed, resulting in a decrease in the stroke. Moreover, as in the case of the first embodiment, it is possible to reduce the time and labor required for the clearance adjustment work and the like. Further, by using the shoe drive mechanism 25 having the above-described configuration, the conventional adjuster can be eliminated, and the configuration is much simpler than that of the conventional automatic adjustment type adjuster. Manufacturing costs can also be reduced.

In FIG. 5, the initial stroke s ₂ of the curve f is the relative rotation between the levers 15 and 18.

[0026]

According to the shoe drive mechanism of the drum brake of the present invention, the limited parts such as the first and second levers, the struts, and the biasing members for biasing the first and second levers together are limited. A link mechanism is configured, and the relative rotation between the first lever and the second lever increases the lever ratio between these levers, and it is possible to suppress an increase in lever stroke due to liner wear. As a result, it is possible to reduce the time and effort required for adjusting the clearance. In addition, by using the shoe drive mechanism with the above configuration, it is possible to eliminate the need for a conventional adjuster, and since the configuration is much simpler than that of a conventional self-adjusting adjuster, it is possible to manufacture a drum brake. The cost can also be reduced.

[Brief description of drawings]

FIG. 1 is a front view of an embodiment of a shoe drive mechanism for a drum brake according to the present invention.

FIG. 2 is a view on arrow A in FIG.

FIG. 3 is a characteristic curve diagram showing the relationship between the clearance between the shoe and the drum and the lever stroke in the embodiment of the present invention.

FIG. 4 is a front view of essential parts of another embodiment of the shoe drive mechanism of the drum brake according to the present invention.

FIG. 5 is a characteristic curve diagram showing the relationship between the clearance between the shoe and the drum and the lever stroke in another embodiment of the present invention.

[Explanation of symbols]

 1 Shoe Drive Mechanism 2 Drums 3, 4 Brake Shoe 5, 6 Lining 9 Back Plate 13 Axis 14 Brake Operation Cable 15 First Lever 17 Shoe Pressing Part 18 Second Lever 19 Biasing Member 21 Strut 23 Stopper 25 Shoe Drive Mechanism 26, 27 oblong hole 28 pins

Claims (2)

[Claims] 1. A braking state or a drum inner surface in which a pair of brake shoes arranged opposite to each other in a cylindrical drum inner space are advanced and retracted toward the inner surface of the drum to press the outer lining of the brake shoe against the inner surface of the drum. A shoe drive mechanism for a drum brake which is separated from the non-braking state, wherein a lever-supporting pivot that is erected on a back plate that supports the brake shoe so as to be capable of advancing and retracting toward the inner surface of the drum, An intermediate portion is rotatably supported by the pivot shaft, a brake operation cable end is connected to one end of the lever, and a lever-like first lever that rotates in response to a brake operation is provided. One end is rotatably attached to the pivot shaft. A second lever that is supported and has a shoe pressing portion that is in contact with one of the brake shoes at the other end, and the second lever is the first lever. And a biasing member that biases one end of the first lever and one end of the second lever toward each other so as to interlock with the lever of the first lever, and one end of which is rotatable to the other end of the first lever. And a strut that is connected to the other brake shoe and has the other end connected to the other brake shoe to limit the return movement of the brake shoe, by means of relative rotation between the first lever and the second lever. A shoe drive mechanism for a drum brake, wherein the lever ratio between these levers is increased to suppress an increase in lever stroke due to lining wear. 2. A braking state or a drum inner surface in which a pair of brake shoes arranged so as to be opposed to a cylindrical drum inner space are advanced and retracted toward the inner surface of the drum to press the outer lining of the brake shoe against the inner surface of the drum. A shoe drive mechanism for a drum brake which is separated from the non-braking state, wherein a lever-supporting pivot that is erected on a back plate that supports the brake shoe so as to be capable of advancing and retracting toward the inner surface of the drum, An intermediate portion is rotatably supported by the pivot shaft, a brake operation cable end is connected to one end of the lever, and a lever-like first lever that rotates in response to a brake operation is provided. One end is rotatably attached to the pivot shaft. A second lever that is supported and has a shoe pressing portion that is in contact with one of the brake shoes at the other end, and the second lever is the first lever. A biasing member that biases one end of the first lever and one end of the second lever toward each other so as to interlock with the lever of the first lever, and a length formed at the other end of the first lever. A strut that has one end connected to a pin that passes through the hole and the elongated hole formed in the intermediate portion of the second lever, and the other end is connected to the other brake shoe to limit the returning operation of the brake shoe. And a relative rotation amount between the first lever and the second lever and a movement amount of each of the pins in the elongated hole of the lever increases a lever ratio between these levers, A shoe drive mechanism for a drum brake, which suppresses an increase in lever stroke due to lining wear.