JP2543629Y2 - Drum brake - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drum brake capable of automatically adjusting the clearance between a brake shoe and a brake drum.

[0002]

2. Description of the Related Art As a conventional drum brake, a pair of brake shoes, a shoe return spring member for urging the pair of brake shoes toward each other, and a biasing force of the shoe return spring member are provided. An actuator that presses the pair of brake shoes in a direction away from each other, a first engagement member that engages one of the brake shoes, and a second engagement member that engages the other of the brake shoes. A strut provided with an abutting member that can move in the length direction by being screwed to the first engaging member and rotated in contact with the second engaging member, and a brake shoe when the brake is operated; When the clearance between the brake drum and the brake drum is larger than a predetermined amount, a mechanism having an adjustment mechanism for automatically adjusting the length of the strut by rotating the contact member of the strut is usually adopted. It has been.

[0003]

However, in the drum brake having the above structure, when the abutment member of the strut is rotated by the adjustment mechanism, there is a possibility that the abutment member may be caused to rotate by the adjustment mechanism. It may not be possible to adjust the shoe clearance (clearance between the brake drum and the brake shoe).

On the other hand, since the drum brake generates thermal expansion due to heat generated during the operation of the brake on the brake drum, a bimetal strip bent with a member having a large coefficient of thermal expansion inside by a predetermined amount is engaged with the first engagement of the strut. A structure that is provided between the contact member provided on the member and the second engagement member, and that when the heat is generated, the bimetal strip is expanded to prevent the contact member from moving much by the thermal expansion of the brake drum. Drum brake has been proposed (Japanese Patent Publication No. 58
However, in this bimetal strip, since the springback at the time of molding is generated to a considerable extent, the bent ends do not adhere to each other even at room temperature, and the contact member of the strut is reduced accordingly. There is a problem that the shoe clearance becomes excessive due to insufficient movement. Further, when the rotational resistance of the contact member changes due to aging or individual differences, the expansion characteristic of the bimetal strip changes, and there is a problem that proper shoe clearance cannot be adjusted. Further, in order to keep the rotation resistance of the contact member constant, the expanding force of the bimetal strip is increased (the biasing force is applied by the bimetal strip to maintain the rotation resistance of the contact member constant). In addition, the biasing force of the shoe return spring member, that is, the shoe return spring member itself must be relatively large, and there are restrictions on space, and an increase in the biasing force of the shoe return spring member increases loss of brake operation. It is not preferable because it leads.

Therefore, a first object of the present invention is to stabilize the shoe clearance without causing the abutment member to rotate with the adjusting mechanism when the abutting member of the strut is rotated by the adjusting mechanism. It is to provide a drum brake.

Further, a second object of the present invention is to achieve the first object described above, and to produce a considerable amount of springback at the time of forming the bimetal strip, or to change the rotational resistance of the contact member over time or An object of the present invention is to provide a drum brake that can stabilize shoe clearance without increasing the urging force of a shoe return spring member, even if it changes due to individual differences or the like.

[0007]

According to the first aspect of the present invention, there is provided a drum brake according to the present invention.
A pair of brake shoes, a shoe return spring member for urging the pair of brake shoes in a direction approaching each other, and a direction for separating the pair of brake shoes from each other against the urging force of the shoe return spring member An actuator that presses the brake shoe, a first engagement member that engages with one of the brake shoes, and a second engagement member that engages with the other of the brake shoes. A strut provided with an abutting member that can move in the longitudinal direction by being screwed to the first engaging member and rotated while being in contact with the engaging member, and a clearance between the brake shoe and the brake drum when a brake is actuated. An adjusting mechanism for automatically adjusting the length of the strut by rotating a contact member provided on the strut when the strut length is larger than a predetermined amount. DOO is characterized by comprising a biasing member that biases said first engagement member in a direction and the second engagement member to reduce the length.

In order to achieve the first and second objects, the drum brake according to the second aspect of the present invention comprises:
In addition to that of claim 1, the strut comprises:
The contact member provided on the first engagement member and the second engagement member may be provided with a bimetal strip bent with the member having a large thermal expansion coefficient by a predetermined amount inside. Features.

[0009]

According to the drum brake of the present invention, the urging member urges the first engaging member and the second engaging member of the strut in a direction in which the length is reduced. Since a constant urging force, that is, a rotation resistance is applied to the contact member, the contact member does not rotate with the adjustment mechanism.

According to the second aspect of the present invention, in addition to the function of the first aspect, the urging member includes a first engaging member and a second engaging member of the strut. Since the biasing force is also applied to the bimetal strip provided between them, even if the bimetal strip has a springback during molding, it does not expand at room temperature. Further, even if the rotational resistance of the contact member may change due to aging or individual differences, the urging member applies a constant urging force, that is, rotational resistance to the contact member. The expansion characteristics of the bimetal strip according to the temperature are stabilized without increasing the urging force.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A drum brake according to an embodiment of the present invention will be described below with reference to the drawings. The directions of up, down, left, right, and rotation used in the following description are the same as those in the drawings for convenience.

FIGS. 1 and 2 show a drum brake according to this embodiment. In each of the drawings, the brake drum is omitted. In the drawing, reference numeral 1 denotes a substantially disk-shaped backing plate mounted on a non-rotating portion of a vehicle or the like. The backing plate 1 includes a pair of left and right brake shoes 2a and 2b (one brake shoe 2b).
a, the other brake shoe 2b) is movably supported in a direction away from each other. Here, linings 3a, 3b that generate frictional force by contacting a brake drum (not shown) are fixed to the arcuate outer surfaces of the brake shoes 2a, 2b, respectively. The other brake shoe 2b is connected to a lever 5 via a fulcrum 4 on the upper portion thereof.
A parking brake wire (not shown) is provided below the lever 5 to swing the lever 5 clockwise.

A return spring (shoe return) for urging the brake shoes 2a and 2b in opposing directions (between the fulcrum 4 in the other brake shoe 2b). Spring member)
A brake fluid pressure generated by depressing a brake pedal (not shown) increases the urging force of the return spring 6 by a predetermined amount (above the fulcrum 4 in the other brake shoe 2b). An actuator 7 is provided for pressing the upper ends of the brake shoes 2a and 2b facing each other in a direction away from each other, and a strut 8 is provided below the return spring 6 by a predetermined amount. ing.

The strut 8 has a shape extending in the left-right direction, and has one brake shoe 2a at the left end.
Engaging portion 9 having a substantially U-shaped cross section that is engaged with and abuts on the right side of
a of the first engaging member 10a having a and a right end portion thereof, while being in contact with and engaging with the left side of the other brake shoe 2b.
A second engaging member 10b having a U-shaped engaging portion 9b. The lever 5 is further provided on the engaging portion 9b of the second engaging member 10b such that the lever 5 is in contact with the left side thereof. Have been.

The first engaging member 10a has a screw portion 11 formed on the outer peripheral surface on the right side of the engaging portion 9a, and a screw portion 11 is provided between the engaging portion 9a and the screw portion 11. An annular convex portion 12 having a predetermined diameter larger than the outer diameter of the annular protrusion 12 is provided. Here, a locking hole 14 for locking one end of a spring (biasing member) 13 to be described later is formed on the projection 12 side of the engagement portion 9a.
a is provided. Then, the first engagement member 10a
The screw member 11 has a first engaging member 10a formed by the rotation of a contact member 16 having a screw hole 15 formed on the inner periphery thereof.
(The protrusion 12 serves as a stopper for the leftward movement of the contact member 16). A plurality of claws 17 are provided on the outer peripheral portion of the contact member 16 at a predetermined pitch in a circumferential direction, and the claws 17 constitute a ratchet mechanism together with an adjusting mechanism 18 described later.

The second engaging member 10b is provided with a cylindrical tubular portion 19 on the left side of the engaging portion 9b, and the inner diameter of the tubular portion 19 is the first engaging member. 10
a larger than the outer diameter of the threaded portion 11 by a predetermined amount and the contact member 1
6 is smaller than the outer diameter by a predetermined amount. A locking hole 14b for locking the other end of the spring 13 described later is provided on the cylindrical portion 19 side of the engaging portion 9b of the second engaging member 10b.

In a state where the contact member 16 is screwed to the first engagement member 10a, the screw portion 1 protruding to the right side thereof is provided.
1 is inserted into the cylindrical portion 19 of the second engaging member 10b. At this time, the bimetal strip 20 is sandwiched between the right side surface of the contact member 16 and the left side surface of the cylindrical portion 19. . The bimetal strip 20 is formed by bending a rectangular member in which members having different coefficients of thermal expansion are overlapped with each other by a predetermined amount with the member having the larger coefficient of thermal expansion on the inside, and forming an arc portion on one side of the bent portion. And the other end is formed into a shape having a flat plate portion, and at room temperature, both members are in contact with each other and overlap each other. When the heat is absorbed, the two flat portions are separated from each other and expanded by a predetermined amount in accordance with the amount of heat. In addition, both flat portions of the bimetal strip are provided with holes for inserting the first engagement members 10a. Then, the contact member 16 is arranged at a predetermined position on the first engagement member 10a, and the bimetal strip 20 is
While holding the cylindrical portion 19 of the second engagement member 10b,
Coil portion 21 and locking portions 22a, 2 provided on both sides thereof
2b, and is inserted into the coil portion 21 of a spring (biasing member) 13 having a predetermined biasing force, and the ends of the locking portions 22a and 22b on both sides of the spring 13 are respectively engaged with the first engagement member 10a. Locking hole 14a and second engagement member 1
0b, the strut 8 is locked.
Will be assembled.

A fulcrum 23 is provided below the strut 8 of the one brake shoe 2a by a predetermined amount.
The fulcrum 23 is provided with a claw lever 24 that can swing about the fulcrum 23. This claw lever 24 is provided at the fulcrum 2
3 and a fulcrum 2
And a laterally extending portion 26 extending rightward from the right side of the strut 8. A left side surface of the engaging portion 9 a of the first engaging member 10 a of the strut 8 is provided on a right side surface of the upwardly extending portion 25. Abuts. An operating claw 27 that can be engaged between the claw 17 on the backing plate 1 side of the contact member 16 is provided at a distal end portion of the side extending portion 26.
7 is such that when the pawl lever 24 swings clockwise by a predetermined angle, the pawl lever 17 gets over the engaged pawl 17 and the next pawl 1
The contact member 16 is rotated to a predetermined angle by moving the contact member 16 to the side of the pawl 17 or further to the claw 17 thereof (a ratchet mechanism), and the contact member 16 is moved rightward by a predetermined amount (first engagement member). The screw portion 11 of 10a and the screw hole 15 of the contact member 16 are cut in a direction that satisfies the above operation.) One end of a claw spring 28 having a predetermined urging force is locked to the laterally extending portion 26 of the claw lever 24, and the other end of the claw spring 28 is connected to one of the brake shoes 2.
It is locked by the lower hole 29 provided in a. The pawl lever 24 and the pawl spring 28 constitute the adjusting mechanism 18.

Next, the operation of the drum brake of the present embodiment having the above configuration will be described. First, when a brake pedal (not shown) is depressed, brake fluid pressure
, The actuator 7 pushes the brake shoes 2a, 2b in a direction away from each other against the urging force of the return spring 6 to move them. Then, the brake shoes 2a, 2b bring the respective linings 3a, 3b into contact with the inner peripheral surface of a brake drum (not shown), and generate a frictional force therebetween to brake the rotation of the brake drum or to reduce the brake drum rotation. The non-rotation state will be maintained. When the depression of the brake pedal is released or released, the brake shoes 2a, 2
b, the pressure on the brake shoes 2a, 2b
Is moved in a direction approaching each other by the urging force of the return spring 6 to release the contact with the brake drum.

When the parking brake is operated, the lever 5 swings clockwise about the fulcrum 4 by pulling a parking brake wire (not shown). The strut 8 that is in contact with the inside moves to the left and the brake shoe 2
The lining 3a of a is brought into contact with the inner peripheral surface of a brake drum (not shown). Then, the lever 5 swings around the contact portion of the strut 8 which has hardly moved to the second engagement member 10b, thereby moving the position of the fulcrum 4 rightward, and the other brake. The lining 3b of the shoe 2b is brought into contact with the inner peripheral surface of a brake drum (not shown). The two brake shoes 2a and 2b balance the pressing force against the respective brake drums, and
a and 3b are pressed against the brake drum.

Here, the shoe clearance (the clearance between the lining 3a of one brake shoe 2a and a brake drum not shown) and the other brake shoe 2b
(The sum of the clearance between the lining 3b and the brake drum, not shown) becomes larger than a predetermined amount, the contact portions of the struts 8 and the respective brake shoes 2a, 2b when the actuator 7 performs the braking operation. , The total amount of clearance that occurs is increased. Then, the pawl lever 24 abutting on the engaging portion 9a of the first engaging member 10a pivots clockwise by the urging force of the pawl spring 28, and the strut 8 moves rightward by the pressing force due to this pivoting. Then, it comes into contact with the other brake shoe 2b. When the amount of movement of the strut 8 (that is, the shoe clearance) exceeds a predetermined amount, the swing angle of the claw lever 24 exceeds a predetermined value, and the operating claw 27 provided on the claw lever 24 moves downward. It moves over the claw 17 on the side where the contact member 16 is engaged and moves to the next claw 17 side or further to the further claw 17 side, and rotates the corresponding contact member 16 by a predetermined angle. Thereby, the contact member 16 moves rightward on the first engagement member 10a, and the strut 8 is extended.

As described above, the shoe clearance can be reduced to an appropriate amount, but the brake shoes 2a, 2
If the amount of heat generated by the friction between b and the brake drum increases, the diameter of the brake drum increases, and if the shoe clearance is adjusted in this state, when the temperature of the brake drum drops, the shoe clearance becomes too clogged. State, and in the worst case, dragging will occur. The bimetal strip 20 is provided to avoid this. When the amount of heat generated by the friction increases, the heat is transmitted to the bimetal strip 20, so that the temperature of the bimetal strip 20 itself increases in accordance with the heat generation, and the bimetal strip 20 expands in accordance with the increased temperature. become. Then, in a state where the bimetal strip 20 is expanded by a predetermined amount, the length of the strut 8 is adjusted so that the shoe clearance is adjusted to an appropriate state. Even if it becomes smaller, the temperature of the bimetal strip 20 itself drops and the length of the strut 8 is reduced, so that the shoe clearance is maintained in an appropriate state.

The amount of expansion of the bimetal strip 20 is determined by the rotational resistance of the contact member 16, the urging force of the return spring 6, the urging force of the spring 13, and the pawl lever 24, in addition to the above-mentioned heat generation (temperature). The pressing force (that is, the claw spring 28
The influence of temperature on all elements other than the temperature can be ignored, and the rotational resistance of the contact member 16, which may change due to aging or individual differences, is also fixed by the spring 13. (Since the urging force, that is, the rotational resistance is always applied), the relationship between the amount of expansion of the bimetal strip 20 and the temperature is always kept constant, and a stable shoe clearance is maintained. Can be obtained.

Further, the spring 13 urges the first engaging member 10a and the second engaging member 10b of the strut 8 in the direction of shortening the length, and the contact member 16 is also fixed. Since the force, that is, the rotation resistance is applied, the abutting member 16 is caused to rotate along with the adjusting mechanism 18 (the abutting member 16 is rotated in a direction to move to the left due to the rise of the claw lever 24). And stable shoe clearance can be obtained.

Further, since the spring 13 also applies the biasing force to the bimetal strip 20 provided between the first engaging member 10a and the second engaging member 10b of the strut 8, Even if the bimetal strip 20 has a springback during molding, it does not expand at normal temperature (a temperature range in which the diameter expansion of the brake drum can be ignored, the same applies hereinafter). Also, as mentioned above,
Even if the rotational resistance of the contact member 16 may change due to aging or individual differences, a constant urging force, that is, rotational resistance is also applied to the contact member 16 by the spring 13. Even if the urging force is not increased, the spreading characteristics of the bimetal strip 20 are constant (that is, determined only by the temperature). Therefore, the shoe clearance can be further stabilized.

Naturally, the biasing force of the spring 13 is larger than the expanding force of the bimetal strip 20 at the normal temperature, and at a temperature higher than the normal temperature, the spring 13 expands the bimetal strip 20 at the temperature. It is set appropriately so as not to disturb the relationship with the quantity.

Further, in the drum brake of this embodiment, the spring 13 is arranged coaxially with the strut 8, so that the arrangement space does not increase, and the strut 8 is assembled by the spring 13 as described above. Therefore, there is also an advantage that the struts 8 do not fall apart at the time of assembling the drum brake or the like.

[0028]

[Effect of the Invention] As described in detail above, claim 1 of the present invention
According to the drum brake described above, the urging member urges the first engagement member and the second engagement member of the strut in the direction of reducing the length, and the contact member has a constant urging force. That is, since rotation resistance is given, the contact member does not rotate with the adjustment mechanism. Therefore,
A stable shoe clearance can be obtained.

According to the drum brake of the second aspect of the present invention, in addition to the effect of the first aspect, in addition to the effect of the first aspect, the urging member comprises a first engaging member and a second engaging member of the strut. Since the biasing force is also applied to the bimetal strip provided between them, even if the bimetal strip has a springback during molding, it does not expand at room temperature. Further, even if the rotational resistance of the contact member may change due to aging or individual differences, the urging member applies a constant urging force, that is, rotational resistance to the contact member. The expansion characteristics of the bimetal strip according to the temperature are stabilized without increasing the urging force. Therefore, the shoe clearance can be further stabilized.

[Brief description of the drawings]

FIG. 1 is a front view showing a drum brake according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line XX shown in FIG.

[Explanation of symbols]

 2a One brake shoe 2b The other brake shoe 6 Return spring (shoe return spring) 7 Actuator 8 Strut 10a First engaging member 10b Second engaging member 13 Spring (biasing member) 16 Contact member 18 Adjusting mechanism 20 Bimetal Strip

Claims (2)

(57) [Scope of request for utility model registration] 1. A pair of brake shoes, a shoe return spring member for urging the pair of brake shoes in a direction approaching each other, and a pair of brake shoes against the urging force of the shoe return spring member. An actuator that presses in a direction away from each other, a first engagement member that engages with one of the brake shoes, and a second engagement member that engages with the other of the brake shoes, wherein the first engagement member A strut provided with an abutment member that can move in the longitudinal direction by being screwed to the first engagement member and rotated while being in contact with the second engagement member; and the brake shoe and the brake when the brake is operated. An adjusting mechanism for automatically adjusting the length of the strut by rotating a contact member provided on the strut when a clearance between the strut and the drum is larger than a predetermined amount. In a rk, the struts, drum brake, characterized in that it comprises a biasing member that biases said first engagement member in a direction and the second engagement member to reduce the length. 2. The strut is bent between a contact member provided on the first engagement member and the second engagement member with a member having a large thermal expansion coefficient by a predetermined amount inside. 2. A bimetal strip is provided.
Drum brake as described.