JP3812990B2 - Duo servo 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

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a duo servo drum brake mounted on a vehicle or the like, and more particularly to a technique for stabilizing the braking force of a duo servo drum brake.
[0002]
[Prior art]
Conventionally, various types of drum brakes have been used to brake the running of the vehicle. These drum brakes are of a leading trailing type, depending on the arrangement of brake shoes pressed against the inner peripheral surface of the brake drum. It is classified into two-reading type or duo servo type.
[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.
In the primary shoe, the front side in the forward rotation direction of the brake drum is used as an input unit, and the front side in the forward rotation direction of the brake drum 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.
[0004]
As a result, when the primary shoe and the secondary shoe are expanded and pressed against the inner peripheral surface of the brake drum, the braking reaction force acting on the primary shoe is input to the front side of the secondary shoe and presses the secondary shoe against the brake drum. 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]
[Problems to be solved by the invention]
The duo-servo type drum brake described above can not only obtain a very high braking force, but also it can be easily downsized and a parking brake can be easily incorporated, compared to a leading trailing type or two leading type drum brake. It has many advantages.
However, such a duo-servo drum brake is sensitive to changes in the friction coefficient of the brake shoe lining, and thus tends to be difficult to stabilize the braking force.
[0006]
The duo-servo drum brake can obtain the same braking force regardless of whether the brake drum rotates forward or backward. Therefore, the mechanism that stabilizes the braking force also rotates the brake drum. It is preferred that they operate equally regardless of direction.
[0007]
Accordingly, an object of the present invention is to provide a duo-servo type drum brake capable of obtaining a stable braking force regardless of forward rotation and backward rotation of the brake drum.
[0008]
[Means for Solving the Problems]
The duo-servo type drum brake of the present invention includes a primary shoe and a secondary shoe arranged to face the inside of the brake drum, and uses the braking reaction force acting on the primary shoe to attach the secondary shoe to the brake drum. A duo-servo type drum brake that presses and receives a braking reaction force by an anchor disposed on the front side in the forward rotation direction of the brake drum from the secondary shoe,
Pressing means for pressing 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 on the front side in the forward rotation direction of the brake drum from the secondary shoe;
A first swing is supported by the first anchor so as to be swingable and swings when a braking reaction force acting on the first anchor from the secondary shoe is received at the base end when the brake drum rotates forward. 1 control lever,
A second anchor disposed closer to the front side in the forward rotation direction of the brake drum than the primary shoe;
The second anchor is supported by the second anchor so as to be capable of swinging, and when the braking drum receives a braking reaction force acting on the second anchor from the primary shoe when the brake drum rotates backward, the second anchor swings. and a second control lever.
The first and second control levers are connected to each other by a connecting link to operate the control means, and the pressing means controls a pressing force that presses the primary shoe and the secondary shoe against the brake drum.
[0009]
In the duo servo drum brake configured as described above, when the brake drum that rotates forward is braked, the first control lever is moved around the first anchor by the braking reaction force that acts on the first anchor from the secondary shoe. Rocks.
When the brake drum that rotates backward is braked, the second control lever swings around the second anchor due to the braking reaction force that acts on the second anchor from the primary shoe.
The first and second control levers are connected to each other by a connecting link to operate the control means, and the pressing means controls the pressing force that presses the primary shoe and the secondary shoe against the brake drum.
[0010]
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, respectively, regardless of whether the brake drum rotates forward or backward. The control means is operated by swinging the second control lever, and the pressing force for pressing the primary shoe and the secondary shoe against the brake drum is controlled by controlling the operation of the pressing means.
Therefore, according to the present invention, when the braking force exceeds a predetermined value, the pressing force 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 again applied. Since it is possible to perform control to increase the braking force and increase the braking force, it is possible to provide a duo-servo drum brake capable of obtaining a stable braking force.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a duo servo drum brake according to the present invention will be described in detail with reference to FIGS.
Here, FIG. 1 is a front view showing an outline of the overall structure of a duo-servo type drum brake according to an embodiment of the present invention, FIG. 2 is a front view showing an enlarged main part of FIG. 1, and FIG. FIG. 4 is an enlarged front view of the main part for explaining the operation of the parking lever shown in FIG. 2, and FIG. 5 is FIG. FIG. 6 is a principal enlarged front view for explaining the operation of the first control lever shown in FIG. 2, and FIG. 6 is a principal enlarged front view for explaining the operation of the second control lever and the connecting link shown in FIG.
In the following description, the front side of the brake drum forward rotation direction is simply referred to as the front side, and the front side of 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 radially inner side, and a direction toward the outer side of the backing plate is referred to as a radially outer side.
[0012]
As shown in FIGS. 1 and 2, the duo-servo drum brake 100 of this embodiment includes a brake drum (not shown) that rotates forward in the counterclockwise direction as shown by an arrow R. The primary shoe 2 and the secondary shoe 3 that are supported by the backing plate 1 so as to be expandable are disposed so as to face each other in the brake drum.
[0013]
An adjuster 6 for adjusting the clearance between the brake shoe and the sliding surface of the brake drum is provided between the front end 4 of the primary shoe 2 and the front end 5 of the secondary shoe 3. Is intervening. Thereby, 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 drum brake 100 of the present embodiment, both the primary shoe 2 and the secondary shoe 3 function as leading shoes.
[0014]
A strut 9 formed of a thick metal plate is interposed between the engaging portion 7 provided on the primary shoe 2 and the engaging portion 8 provided on the secondary shoe 3. Accordingly, when the strut 9 is pushed toward the secondary shoe 3, the secondary shoe 3 can be pressed against the brake drum. Further, when the strut 9 is pushed toward the primary shoe 2, the primary shoe 2 can be pressed against the brake drum.
[0015]
On the other hand, an anchor block 10 is implanted in the backing plate 1 between the front end portion of the primary shoe 2 and the front end portion of the secondary shoe 3.
At the end of the anchor block 10 on the secondary shoe 3 side, there is a first anchor pin 11 that receives the braking reaction force acting on the secondary shoe 3 when the brake drum rotates in the forward direction (counterclockwise in the figure). Projected.
Further, a second anchor pin 12 that receives a braking reaction force acting on the primary shoe 2 when the brake drum rotates in the backward direction (clockwise in the figure) protrudes from the end of the anchor block 10 on the primary shoe 2 side. Has been.
[0016]
Furthermore, the tip of the parking lever 13 that operates the duo-servo drum brake 100 of the present embodiment as a parking brake is swingably supported on the web 3 a of the secondary shoe 3 by the support shaft 14.
[0017]
In addition, a wheel cylinder 20 (pressing means) is implanted in a portion on the inner side in the radial direction from the anchor block 10 of the backing plate 1. The piston 21 of the wheel cylinder 20 is pressed according to the hydraulic pressure generated according to the stepping operation force when the driver of the vehicle equipped with the duo servo drum brake 100 of the present embodiment performs the stepping operation of the brake pedal. It protrudes to the primary shoe 2 side with pressure.
[0018]
Further, a controller 22 (control means) for controlling the operation of the wheel cylinder 20 is connected to the end of the wheel cylinder 20 on the secondary shoe 3 side. And if the control rod 23 which protrudes from the control part 22 to the secondary shoe 3 side is pushed to the primary shoe 2 side, the hydraulic pressure applied to the piston 21 decreases. The control rod 23 is urged so as to protrude toward the primary shoe 3 by an urging spring (not shown).
[0019]
An input lever 30 formed from a thick metal plate is pivotally supported on the web 2 a of the primary shoe 2 by a support shaft 31, and can swing within a plane parallel to the surface of the backing plate 1. . The input lever 30 has a radially outer end 32 in contact with the tip of the piston 21 and a radially inner end 33 in contact with the end of the strut 9.
As a result, when the piston 21 of the wheel cylinder 20 protrudes toward the primary shoe 2, the input lever 30 swings around the support shaft 31 counterclockwise in the figure, and the radially inner end 33 is formed on the secondary shoe 3. Displace to the side.
[0020]
Further, a first control lever 40 machined from a metal block material is assembled to the first anchor pin 11 so as to be swingable 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 secondary shoe 3 is pressed against the brake drum while the brake drum is rotating forward, the first control lever 40 is moved by the braking reaction force acting on the first anchor pin 11 from the secondary shoe 3. The proximal end 41 is pressed and swings around the first anchor pin 11 in the clockwise direction in the figure, and the radially inner swing end 42 pushes the control rod 23 toward the primary shoe 2.
[0021]
Similarly, a second control lever 50 formed from a thick metal plate is assembled to the second anchor pin 12 so as to be swingable 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.
Thus, when the primary shoe 2 is pressed against the brake drum while the brake drum is rotating backward, the second control lever 50 is moved by the braking reaction force acting on the second anchor pin 12 from the primary shoe 3. The proximal end 51 is pressed and swings around the second anchor pin 12 in the clockwise direction in the figure, and the radially inner swing end 52 is displaced toward the primary shoe 2 side.
[0022]
The first control lever 40 and the second control lever 50 are connected by a band-plate-like connection link 60. That is, the main body portion 61 of the connection link 60 extends into the gap between the anchor block 10 and the wheel cylinder 20. Further, the end portion 62 on the primary shoe 2 side is pivotally supported by the swing end 52 of the second control lever 50. Further, the end portion 63 on the secondary shoe 2 side is pivotally supported at the longitudinal center portion of the first control lever 40. 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.
[0023]
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.
[0024]
When a driver of a vehicle equipped with the duo-servo drum brake 100 of the present embodiment depresses the brake pedal, a hydraulic pressure corresponding to the driver's brake operating force is applied to the wheel cylinder 20. Then, as shown in FIG. 3, the piston 21 of the wheel cylinder 20 pushes the radially outer end 32 of the input lever 30 toward the primary shoe 2 with a pressing force A corresponding to the acting hydraulic pressure.
As a result, the input lever 30 swings around the support shaft 31 in the counterclockwise direction shown in the drawing, and the end portion 33 on the radially inner side has a pressing force B obtained by multiplying the pressing force A by the lever ratio of the input lever 30. Since the strut 9 is pushed toward the secondary shoe 3, the secondary shoe 3 is pressed by the brake drum.
At the same time, the reaction force C obtained by pushing the strut 9 with the pressing force B acts on the support shaft 31 of the input lever 30, so that the support shaft 31, that is, the primary shoe 2 is also pressed by the brake drum.
When the primary shoe 2 and the secondary shoe 3 are both pressed against the brake drum in this way, the rotation of the brake drum is braked. When 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, the braking force by the secondary shoe 3 is further increased and the braking force is further increased.
[0025]
On the other hand, when the duo servo drum brake 100 of this embodiment is operated as a parking brake, the swing end 15 of the parking lever 13 shown in FIG. 1 is displaced toward the primary shoe 2 side. Then, as shown in FIG. 4, the parking lever 13 swings in the clockwise direction in the drawing with the end of the strut 9 on the secondary shoe 3 side as a fulcrum, and the support shaft 14, that is, the secondary shoe 3 is indicated by an arrow D. Press against the brake drum. At the same time, the parking lever 13 pushes the strut 9 toward the primary shoe 2 as indicated by the arrow E, and presses the primary shoe 2 against the brake drum. As a result, the rotation of the brake drum is braked and the parking brake functions.
[0026]
By the way, when the driver of the vehicle equipped with the duo servo drum brake 100 of the present embodiment depresses the brake pedal and the secondary shoe 2 is pressed against the brake drum, as shown in FIG. A braking reaction force F acts on the first anchor pin 11 from the shoe 3 through the base end 41 of the first control lever 40. Then, the first control lever 40 swings around the first anchor pin 11 in the clockwise direction in the drawing.
As a result, the swinging end 42 of the first control lever 40 is displaced toward the primary shoe 2 and is not shown due to 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.
[0027]
When the control rod 23 is pushed, the control unit 22 reduces the hydraulic pressure applied to 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 with which the wheel cylinder 20 presses the primary shoe 2 and the secondary shoe 3 against the brake drum decreases, and the braking force by the duo servo 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 that the swinging end 42 of the first control lever 40 pushes the control rod 23 also decreases. The hydraulic pressure acting on the wheel cylinder 20 is restored by being pushed back by a biasing spring (not shown).
That is, the duo servo 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 the predetermined value. It has an automatic adjustment function that increases the braking force again.
[0028]
On the other hand, when the vehicle equipped with the duo servo drum brake 100 of the present embodiment travels backward, the brake drum rotates backward in the clockwise direction as shown by an arrow S in FIG. At this time, when the driver of the vehicle depresses the brake pedal, the braking reaction force acting on the primary shoe 2 pressed by the brake drum is increased by the second reaction force H via the base end 51 of the second control lever 50. Acts on anchor pin 12. As a result, the second control lever 50 swings around the second anchor pin 12 in the clockwise direction in the figure, and is applied by the pressing force I obtained by multiplying the braking reaction force H by the lever ratio of the second control lever 50. Then, the connecting link 60 is pushed to the primary shoe 2 side.
[0029]
When the connecting link 60 is displaced to the primary shoe 2 side, the first control lever 40 connected to the second control lever 50 by the connecting link 60 swings around the first anchor pin 11 in the clockwise direction in the drawing, and is controlled. The rod 23 is pushed toward the primary shoe 2 side.
That is, even when the brake drum rotates backward, 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, In addition, it has an automatic adjustment function for increasing the braking force again when the braking force falls below a predetermined value.
In addition, by appropriately setting the lever ratio of the second control lever 50 and the position at which the end 63 on the secondary shoe 3 side of the connecting link 60 is connected to the first control lever 40, the second control lever 50 The control characteristic for controlling the control unit 22 by swinging can be optimized.
[0030]
That is, according to the duo-servo type drum brake 100 of the present embodiment, the secondary drum 2 or the primary shoe 3 inputs the first or second anchor pins 11 and 12 respectively, regardless of whether the brake drum rotates forward or backward. Using the braking reaction force, the first and second control levers 40 and 50 are swung to push the control rod 23 to control the pressing force for pressing the primary shoe 2 and the secondary shoe 3 against the brake drum. Therefore, the braking force can be stabilized by controlling so that the braking force does not increase beyond a predetermined value.
[0031]
As mentioned above, although each embodiment of the duo-servo type drum brake according to the present invention was described in detail, it goes without saying that the present invention is not limited to the above-described embodiment, and various modifications are possible.
For example, in the above-described embodiment, the primary shoe 2 and the secondary shoe 3 are pressed against the brake drum using the wheel cylinder 20 that is operated by hydraulic pressure. It can also be used.
In the above-described embodiment, by using the connecting link 60, the first control lever 40 is swung by the swing of the second control lever 50, and the control rod 23 is pushed. However, it is also possible to change the shape of the second control lever 50 and push the control rod 23 directly.
[0032]
【The invention's effect】
As is apparent from the above description, the duo-servo type drum brake of the present invention has a braking reaction input from the secondary shoe or primary shoe to the first or second anchor, respectively, regardless of whether the brake drum rotates forward or backward. Using force, the control means is operated by swinging the first and second control levers, and the pressing force for pressing the primary shoe and the secondary shoe against the brake drum is controlled by controlling the operation of the pressing means. .
Therefore, according to the present invention, when the braking force exceeds a predetermined value, the pressing force 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 again applied. Since it is possible to perform control to increase the braking force and increase the braking force, it is possible to provide a duo-servo drum brake capable of obtaining a stable braking force.
[Brief description of the drawings]
FIG. 1 is a front view showing an outline of the overall structure of a duo servo drum brake according to an embodiment of the present invention.
FIG. 2 is an enlarged front view showing the main part of FIG.
3 is an enlarged front view of a main part for explaining the operation of the wheel cylinder, the input lever, and the strut shown in FIG. 2. FIG.
4 is an enlarged front view of a main part for explaining the operation of the parking lever shown in FIG. 2;
FIG. 5 is an enlarged front view of a main part for explaining the operation of the first control lever shown in FIG. 2;
6 is an enlarged front view of a main part for explaining the operation of the second control lever and the connecting link shown in FIG. 2. FIG.
[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 5 of primary shoe Front end 6 of secondary shoe Adjuster 7, 8 Engaging portion 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 Connecting Link 100 One Implementation According to the Present Invention Form of duo servo drum brake

Claims (1)

A primary shoe and a secondary shoe arranged to face the inside of the brake drum, and the secondary shoe is pressed against the brake drum by using a braking reaction force acting on the primary shoe, and more than the secondary shoe. A duo-servo type drum brake that receives a braking reaction force by an anchor arranged on the front side in the forward rotation direction of the brake drum,
Pressing means for pressing 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 on the front side in the forward rotation direction of the brake drum from the secondary shoe;
A first swing is supported by the first anchor so as to be swingable and swings when a braking reaction force acting on the first anchor from the secondary shoe is received at the base end when the brake drum rotates forward. 1 control lever,
A second anchor disposed closer to the front side in the forward rotation direction of the brake drum than the primary shoe;
The second anchor is supported by the second anchor so as to be capable of swinging, and when the braking drum receives a braking reaction force acting on the second anchor from the primary shoe when the brake drum rotates backward, the second anchor swings. and a second control lever,
The first and second control levers are connected to each other by a connecting link to operate the control means, and the pressing means controls a pressing force that presses the primary shoe and the secondary shoe against the brake drum. Duo servo drum brake.

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