JPH1122756A - Duo-servo type drum brake - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a duo-servo type drum brake to provide a stable brake force even when a brake drum effects advance rotation or reverse rotation. SOLUTION: By using a brake reaction force inputted from a secondary shoe 3 or a primary shoe 2 to first or second anchor pins 11 and 12, first and second control levers 40 and 50 are oscillated to operate a control rod 23. By controlling operation of a wheel cylinder 20, a press force by which the primary shoe 2 and a secondary shoe 3 are pressed against a brake drum is controlled. Thus, when a brake force exceeds a given value, a pressure force by which the primary shoe 2 and the secondary shoe 3 are pressed against a brake drum is decreased. When a brake force is decreased to a value lower than a given value, a press force is increased again and the brake force is restored.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a duo-servo type drum brake mounted on a vehicle or the like, and more particularly, to a technique for stabilizing a braking force of a duo-servo type drum brake.

[0002]

2. Description of the Related Art Conventionally, various types of drum brakes have been used to brake the running of a vehicle, and these drum brakes are arranged according to the arrangement of brake shoes pressed against the inner peripheral surface of a brake drum. It is classified into a leading trailing type, a two-leading type, a duo servo type, and the like.

[0003] A duo-servo type drum brake generally includes two brake shoes, a primary shoe and a secondary shoe, which are arranged to face each other. The input side of the primary shoe in the forward rotation direction of the brake drum serves as an input portion, and the forward side of the brake drum in the forward rotation direction is connected to the front side of the secondary shoe via an adjuster, for example. On the other hand, the front side of the secondary shoe abuts on an anchor attached to the backing plate, and the braking reaction force acting on the primary shoe and the secondary shoe is received by the anchor.

Thus, when the primary shoe and the secondary shoe are expanded and pressed against the inner peripheral surface of the brake drum, a braking reaction force acting on the primary shoe is input to the near side of the secondary shoe, and the secondary shoe is applied to the brake drum. Since the pressing is performed, both the primary shoe and the secondary shoe act as a leading shoe, and a braking force with a very high gain can be obtained.

[0005]

The above-described duo-servo type drum brake not only can obtain an extremely high braking force but also can be easily miniaturized as compared with a leading trailing type or two-leading type drum brake. And has many advantages such as easy installation of a parking brake. However, such a duo-servo type drum brake tends to be difficult to stabilize the braking force because it is sensitive to a change in the friction coefficient of the lining of the brake shoe.

The duo servo type drum brake is
Since the same braking force is obtained regardless of whether the brake drum rotates forward or backward, the mechanism for stabilizing the braking force also operates equally regardless of the rotation direction of the brake drum. Preferably, there is.

SUMMARY OF THE INVENTION An object of the present invention is to provide a duo-servo type drum brake capable of obtaining a stable braking force regardless of the forward rotation and backward rotation of the brake drum.

[0008]

SUMMARY OF THE INVENTION A duo-servo type drum brake according to the present invention comprises a primary shoe and a secondary shoe which are arranged inside a brake drum so as to face each other, and uses a braking reaction force acting on the primary shoe. The secondary shoe is pressed against the brake drum, and a braking reaction force is received by an anchor disposed forward of the secondary shoe in the forward rotation direction of the brake drum. The primary shoe and the secondary shoe Pressing means for pressing the brake drum against the brake drum; control means for controlling the operation of the pressing means; a first anchor disposed forward of the secondary shoe in the forward rotation direction of the brake drum; Rockably supported by the anchor of A first control lever that swings when receiving a braking reaction force acting on the first anchor from the cantilever shoe at a base end thereof, and a first control lever that is disposed closer to the forward rotation direction of the brake drum than the primary shoe. And the second anchor is swingably supported by the second anchor and receives at its base end a braking reaction force acting on the second anchor from the primary shoe when the brake drum rotates backward. The second rocking
Equipped with a control lever. And the first and second control levers operate the control means,
The pressing means controls a pressing force for pressing the primary shoe and the secondary shoe against the brake drum.

In the duo-servo type drum brake constructed as described above, when the brake drum rotating forward is braked, the first control lever is moved to the first control lever by the braking reaction force acting on the first anchor from the secondary shoe.
Rocks around the anchor. When the brake drum that rotates backward is braked, the second control lever swings around the second anchor due to a braking reaction force acting on the second anchor from the primary shoe. The first and second control levers operate the control unit, and the pressing unit controls the pressing force of pressing the primary shoe and the secondary shoe against the brake drum.

That is, the duo-servo type drum brake of the present invention uses the braking reaction force input from the secondary shoe or the primary shoe to the first or second anchor, regardless of whether the brake drum rotates forward or backward, respectively. The control means is operated by swinging the first and second control levers, and the operation of the pressing means is controlled to control the pressing force for pressing the primary shoe and the secondary shoe against the brake drum. Therefore, according to the present invention, when the braking force exceeds a predetermined value, the pressing force for pressing the primary shoe and the secondary shoe against the brake drum is reduced,
When the braking force falls below a predetermined value, it is possible to perform control to increase the pressing force again to recover the braking force, so that it is possible to provide a duo servo type drum brake capable of obtaining a stable braking force. .

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a duo-servo type drum brake according to the present invention will be described below in detail with reference to FIGS. Here, FIG. 1 is a front view schematically showing the entire structure of a duo-servo type drum brake according to one embodiment of the present invention, FIG. 2 is an enlarged front view showing a main part of FIG. 1, and FIG. Main part enlarged front view illustrating the operation of the wheel cylinder and input lever and strut shown therein,
FIG. 4 is an enlarged front view of a main part illustrating the operation of the parking lever shown in FIG. 2, FIG. 5 is an enlarged front view of a main part explaining the operation of the first control lever shown in FIG. 2, and FIG. FIG. 4 is an enlarged front view of a main part for explaining operation of a second control lever and a connection link shown in FIG. 2. In the following description, the front side in the brake drum forward rotation direction is simply referred to as the front side, and the front side in the brake drum forward rotation direction is simply referred to as the front side. Further, a direction toward the center of the backing plate is referred to as a radial inside, and a direction toward the outside of the backing plate is referred to as a radial outside.

As shown in FIGS. 1 and 2, the duo-servo-type drum brake 100 of the present embodiment includes a brake drum (not shown) which rotates forward in a counterclockwise direction as shown by an arrow R. The primary shoe 2 and the secondary shoe 3 supported in a floating anchor manner on the backing plate 1 are arranged to face each other in the brake drum.

Further, between the front end 4 of the primary shoe 2 and the front end 5 of the secondary shoe 3,
An adjuster 6 for adjusting the clearance between the brake shoes and the sliding surface of the brake drum is provided. Accordingly, the braking reaction force acting on the primary shoe 2 is input to the front side of the secondary shoe 3 via the adjuster 6, and presses the secondary shoe 3 against the brake drum. That is, in the duo-servo type drum brake 100 of the present embodiment, both the primary shoe 2 and the secondary shoe 3 function as leading shoes.

A strut 9 made of a thick metal plate is interposed between an engaging portion 7 provided on the primary shoe 2 and an engaging portion 8 provided on the secondary shoe 3. Thus, when the strut 9 is pushed toward the secondary shoe 3, the secondary shoe 3 can be pushed against the brake drum. When the strut 9 is pushed toward the primary shoe 2, the primary shoe 2 can be pushed against the brake drum.

On the other hand, an anchor block 10 is planted on the backing plate 1 between the front end of the primary shoe 2 and the front end of the secondary shoe 3. At the end of the anchor block 10 on the secondary shoe 3 side, a first anchor pin 11 for receiving a braking reaction force acting on the secondary shoe 3 when the brake drum rotates in the forward direction (counterclockwise in the drawing). It is protruding. A second anchor pin 12 protrudes from an end of the anchor block 10 on the primary shoe 2 side to receive a braking reaction force acting on the primary shoe 2 when the brake drum rotates in a retreating direction (clockwise in the drawing). Have been.

Further, the tip of a parking lever 13 for operating the duo-servo type drum brake 100 of this embodiment as a parking brake is swingably supported on a web 3a of the secondary shoe 3 by a support shaft 14.

A wheel cylinder 20 (pressing means) is implanted in a portion of the backing plate 1 radially inside the anchor block 10. When the driver of the vehicle equipped with the duo-servo drum brake 100 of the present embodiment steps on the brake pedal, for example, the piston 21 of the wheel cylinder 20 presses the piston 21 in accordance with the hydraulic pressure generated in accordance with the stepping operation force. It projects to the primary shoe 2 side by pressure.

A control section 22 (control means) for controlling the operation of the wheel cylinder 20 is connected to an end of the wheel cylinder 20 on the secondary shoe 3 side. When the control rod 23 protruding from the control unit 22 toward the secondary shoe 3 is pushed toward the primary shoe 2, the hydraulic pressure applied to the piston 21 is reduced. The control rod 23 is biased by a biasing spring (not shown) so as to protrude toward the primary shoe 3.

An input lever 30 formed of a thick metal plate is provided on the support shaft 3 on the web 2a of the primary shoe 2.
1 and is swingable in a plane parallel to the surface of the backing plate 1. The input lever 30 has a radially outer end 32 abutting on the tip of the piston 21 and a radially inner end 33 abutting on the end of the strut 9. Thereby, the piston 21 of the wheel cylinder 20
Is projected toward the primary shoe 2, the input lever 30 swings around the support shaft 31 in the counterclockwise direction in the figure, and its radially inner end 33 is displaced toward the secondary shoe 3.

A first control lever 40 machined from a block material of a metal material is mounted on the first anchor pin 11 so as to swing in a plane parallel to the surface of the backing plate 1. . The front end of the secondary shoe 3 is in contact with the base end 41 of the control lever 40. Thus, when the brake drum is rotating forward, the secondary shoe 3
When the first control lever 40 is pressed by the brake drum, the base end 41 of the first control lever 40 is pressed by the braking reaction force acting on the first anchor pin 11 from the secondary shoe 3, and is shown around the first anchor pin 11. The control rod 23 swings clockwise, and the swing end 42 on the inner side in the radial direction is
To the primary shoe 2 side.

Similarly, a second control lever 50 formed of a thick metal plate is mounted on the second anchor pin 12 so as to swing in a plane parallel to the surface of the backing plate 1. The proximal end 51 of the control lever 50 is in contact with the front end of the primary shoe 2. Thereby, when the primary shoe 2 is pressed by the brake drum while the brake drum is rotating backward, the second control lever 50
The base end 51 is pressed by the braking reaction force acting on the second anchor pin 12 from the primary shoe 3, and swings around the second anchor pin 12 in the clockwise direction in the drawing. It is displaced to the primary shoe 2 side.

Further, the first control lever 40 and the second control lever 50 are connected by a band-shaped connecting link 60. That is, the link 6
The zero main body portion 61 extends into the gap between the anchor block 10 and the wheel cylinder 20. The end 62 on the primary shoe 2 side is pivotally supported by the swing end 52 of the second control lever 50. The end 63 on the side of the secondary shoe 2 is pivotally supported at the center of the first control lever 40 in the longitudinal direction. Thus, when the second control lever 50 swings around the second anchor pin 12, the first control lever 40 swings around the first anchor pin 11 in the same direction.

Next, the operation of the duo-servo type drum brake 100 of the present embodiment configured as described above will be described with reference to FIGS.

When the driver of the vehicle equipped with the duo-servo-type drum brake 100 of this embodiment steps on the brake pedal, hydraulic pressure corresponding to the driver's brake operating force acts on the wheel cylinder 20. Then, as shown in FIG. 3, the piston 2 of the wheel cylinder 20
1 is a pressing force A corresponding to the hydraulic pressure acting on the input lever 30
Is pushed toward the primary shoe 2 side. As a result, the input lever 30 swings around the support shaft 31 in the counterclockwise direction in the figure, and the inner end 3
3 pushes the strut 9 toward the secondary shoe 3 with a pressing force B obtained by multiplying the pressing force A by the lever ratio of the input lever 30, so that the secondary shoe 3 is pressed by the brake drum. At the same time, a reaction force C that pushes the strut 9 with the pressing force B acts on the support shaft 31 of the input lever 30.
The support shaft 31, that is, the primary shoe 2 is also pressed by the brake drum. Thus, the primary shoe 2
When both and the secondary shoe 3 are pressed against the brake drum, the rotation of the brake drum is braked. When the braking reaction force acting on the primary shoe 2 is input to the near side of the secondary shoe 3 via the adjuster 6, the braking force by the secondary shoe 3 is further increased, and the braking force is further increased.

On the other hand, when operating the duo-servo type drum brake 100 of this embodiment as a parking brake, the swing end 15 of the parking lever 13 shown in FIG. Then, as shown in FIG. 4, the parking lever 13 swings clockwise in the drawing with the end of the strut 9 on the side of the secondary shoe 3 serving as a fulcrum, and moves the support shaft 14, that is, the secondary shoe 3 in the direction of arrow D
Press on the brake drum as indicated by. At the same time, the parking lever 13 pushes the strut 9 toward the primary shoe 2 as shown by the arrow E, and pushes the primary shoe 2 against the brake drum. As a result, the rotation of the brake drum is braked, and the parking brake functions.

When the driver of the vehicle equipped with the duo-servo-type drum brake 100 of this embodiment steps on the brake pedal to push the secondary shoe 2 against the brake drum, as shown in FIG. Then, a braking reaction force F acts on the first anchor pin 11 from the secondary shoe 3 via the base end 41 of the first control lever 40. Then, the first control lever 40 swings around the first anchor pin 11 clockwise in the drawing. As a result, the swing end 42 of the first control lever 40 is displaced toward the primary shoe 2 and is not shown by the pressing force G obtained by multiplying the braking reaction force F by the lever ratio of the first control lever 40. The control rod 23 is pushed toward the primary shoe 2 against the urging force of the urging spring.

When the control rod 23 is pushed, the control unit 2
2 reduces the hydraulic pressure acting on the wheel cylinder 20 by the hydraulic control circuit provided therein, and reduces the pressing force applied to the input lever 30 by the piston 21. Then, the pressing force of the wheel cylinder 20 pressing the primary shoe 2 and the secondary shoe 3 against the brake drum decreases, and the braking force by the duo-servo type drum brake 100 of the present embodiment decreases. Along with this,
When the braking reaction force F acting on the secondary shoe 3 decreases, the pressing force G by which the swing end 42 of the first control lever 40 pushes the control rod 23 also decreases, so that the control rod 23 is biased (not shown). The oil pressure that is pushed back by the spring and acts on the wheel cylinder 20 is restored.
That is, the duo-servo-type drum brake 100 of this embodiment automatically reduces the braking force when the braking force by the primary shoe 2 and the secondary shoe 3 exceeds a predetermined value, and when the braking force falls below a predetermined value. It has an automatic adjustment function to increase the braking force again.

On the other hand, when the vehicle equipped with the duo-servo type drum brake 100 of the present embodiment runs backward, FIG.
As shown by an arrow S therein, the brake drum rotates backward in the illustrated clockwise direction. At this time, when the driver of the vehicle steps on the brake pedal, the braking reaction force acting on the primary shoe 2 pressed by the brake drum becomes H,
Acts on the second anchor pin 12 via the proximal end 51 of the control lever 50. As a result, the second control lever 50 swings clockwise in the figure around the second anchor pin 12, and the pressing force I obtained by multiplying the braking reaction force H by the lever ratio of the second control lever 50. Then, the link 60 is pushed toward the primary shoe 2.

When the connecting link 60 is displaced toward the primary shoe 2, the first control lever 4 connected to the second control lever 50 by the connecting link 60.
0 swings clockwise around the first anchor pin 11 to push the control rod 23 toward the primary shoe 2. That is, the duo-servo drum brake 100 of the present embodiment automatically reduces the braking force when the braking force by the primary shoe 2 and the secondary shoe 3 exceeds a predetermined value even when the brake drum rotates backward. And it has an automatic adjustment function for increasing the braking force again when the braking force falls below a predetermined value. In addition, the lever ratio of the second control lever 50 and the position at which the end 63 of the connection link 60 on the secondary shoe 3 side is connected to the first control lever 40 are appropriately set, so that the second
The control characteristic of controlling the control unit 22 by the swing of the control lever 50 can be optimized.

That is, according to the duo-servo drum brake 100 of the present embodiment, regardless of whether the brake drum rotates forward or backward, the secondary shoe 2
Alternatively, using the braking reaction force input from the primary shoe 3 to the first or second anchor pins 11 and 12, respectively, the first and second control levers 40 and 50 are swung to push the control rod 23, and Since the pressing force for pressing the shoe 2 and the secondary shoe 3 against the brake drum can be controlled, the braking force can be controlled so as not to increase to a predetermined value or more, and the braking force can be stabilized.

Although the embodiments of the duo-servo type drum brake according to the present invention have been described in detail, the present invention is not limited to the above-described embodiments.
It goes without saying that various changes are possible. For example, in the embodiment described above, the primary shoe 2 and the secondary shoe 3 are pressed against the brake drum by using the wheel cylinder 20 that is operated by hydraulic pressure. However, for example, an actuator or an electric actuator that is operated by air pressure is used. It can also be used. In the above-described embodiment, the link 6
0, the second control lever 50
Swings the first control lever 40 to push the control rod 23. However, the shape of the second control lever 50 is changed so that the control rod 23 is pushed directly. You can also

[0032]

As is apparent from the above description, the duo-servo-type drum brake of the present invention is capable of rotating the brake drum forward or backward and rotating the secondary or primary shoe from the first or second anchor, respectively. The first and second control levers are swung to operate the control means using the braking reaction force input to the control unit to control the operation of the pressing means to reduce the pressing force for pressing the primary shoe and the secondary shoe against the brake drum. To control. Therefore, according to the present invention, when the braking force exceeds a predetermined value, the pressing force for pressing the primary shoe and the secondary shoe against the brake drum is reduced, and when the braking force falls below the predetermined value, the pressing force is reduced again. Since the control for increasing the braking force to recover the braking force can be performed, it is possible to provide a duo-servo type drum brake capable of obtaining a stable braking force.

[Brief description of the drawings]

FIG. 1 is a front view schematically showing the entire structure of a duo-servo type drum brake according to an embodiment of the present invention.

FIG. 2 is an enlarged front view showing a main part of FIG. 1;

FIG. 3 is an enlarged front view of a main part for explaining operations of a wheel cylinder, an input lever, and struts shown in FIG. 2;

FIG. 4 is an enlarged front view of an essential part for explaining the operation of the parking lever shown in FIG. 2;

FIG. 5 is an enlarged front view of an essential part for explaining the operation of a first control lever shown in FIG. 2;

FIG. 6 is an enlarged front view of an essential part for explaining operations of a second control lever and a connecting link shown in FIG. 2;

[Explanation of symbols]

R Forward rotation direction of brake drum S Reverse rotation direction of brake drum 1 Backing plate 2 Primary shoe 3 Secondary shoe 4 Front end of primary shoe 5 Front end of secondary shoe 6 Adjuster 7, 8 Engagement part 9 Strut 10 Anchor block 11 First anchor pin 12 Second anchor pin 13 Parking lever 20 Wheel cylinder 21 Piston 22 Control unit 23 Control rod 30 Input lever 40 First control lever 50 Second control lever 60 Connection link 100 One embodiment according to the present invention Duo servo type drum brake of form

Claims (1)

[Claims] A primary shoe and a secondary shoe which are disposed inside the brake drum so as to face each other, wherein the secondary shoe is pressed against the brake drum by using a braking reaction force acting on the primary shoe; A duo-servo-type drum brake that receives a braking reaction force by an anchor disposed forward of the brake drum in the forward rotation direction of the brake drum, and a pressing unit that presses the primary shoe and the secondary shoe against the brake drum. Control means for controlling the operation of the pressing means; a first anchor disposed forward of the secondary shoe in the forward rotation direction of the brake drum; and a first anchor that is swingably supported by the first anchor. And the brake drum has rotated forward A first control lever that swings when receiving a braking reaction force acting on the first anchor from the secondary shoe at its base end; and a first control lever that is disposed closer to the forward rotation direction of the brake drum than the primary shoe. A second anchor, which is swingably supported by the second anchor, and transmits a braking reaction force acting on the second anchor from the primary shoe when the brake drum rotates backward. A second control lever that swings when it is received by the first and second control levers. The first and second control levers operate the control unit, and the pressing unit presses the primary shoe and the secondary shoe against the brake drum. A duo-servo type drum brake that controls pressure.