JP3828989B2 - Duo-servo drum brake device - Google Patents

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 that operates mechanically.
[0002]
[Prior art]
Conventionally, various types of drum brakes are used to brake the running of the vehicle. These drum brakes are arranged according to the leading-trailing type or the two-tool type depending on the arrangement of the brake shoes pressed against the inner peripheral surface of the drum. It is classified as a reading type or a duo servo type.
[0003]
Of these, 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. The front side of the secondary shoe abuts on an anchor pin attached to the backing plate, and the braking reaction force acting on the primary shoe and the secondary shoe is received by the anchor pin.
[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]
Here, the duo-servo drum brake described above can not only obtain extremely high braking force compared to leading trailing and two-leading drum brakes, but also is easy to miniaturize and incorporates a parking brake. It has many advantages such as being easy. On the other hand, it is sensitive to changes in the friction coefficient of the lining of the brake shoe and has a problem that it is difficult to stabilize the braking force.
[0006]
SUMMARY OF THE INVENTION An object of the present invention is to provide a mechanically operated duo-servo drum brake that solves the above-described problems of the prior art and is improved so that the braking force can be stabilized with a simple configuration. It is in.
[0007]
[Means for Solving the Problems]
With respect to the above object, the present invention includes a primary shoe and a secondary shoe arranged to face the inside of the brake drum, and presses the secondary shoe against the brake drum using a braking reaction force acting on the primary shoe. And a duo-servo type drum brake that receives a braking reaction force by an anchor pin disposed forward of the secondary shoe in the forward rotation direction of the brake drum from the secondary shoe:
A strut that presses the primary shoe against the brake drum by rotation of an operation lever, and can swing around the anchor pin, and one end abuts the secondary shoe and the other end is the strut. An engaging control lever;
When one end of the control lever receives a predetermined braking reaction force from the secondary shoe, the other end of the control lever cooperates with the anchor pin and is in a direction opposite to the primary shoe pressing direction of the strut. Further, the strut is biased.
[0008]
That is, in the duo-servo type drum brake of the present invention, a part of the braking reaction force acting on the secondary shoe presses the primary shoe against the brake drum at a ratio corresponding to the lever ratio centering on the anchor pin of the control lever. Input to the strut in the reverse direction. As a result, when the braking force increases to the vicinity of a predetermined value due to the boosting action, the pressing force with which the struts press the primary shoe against the brake drum is greatly reduced, and the braking force is reduced. On the other hand, when the braking force decreases, the pressing force with which the struts press the primary shoe against the brake drum is reduced to a small extent, so that the braking force is recovered.
Therefore, since the braking force can be automatically suppressed to a desired braking force, a duo-servo type drum brake having a stable braking force that operates mechanically can be obtained.
[0009]
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 FIG. 1 and FIG.
Here, FIG. 1 is a schematic front view showing the overall structure of a duo-servo type drum brake according to an embodiment of the present invention, and FIG. 2 is a schematic front view for explaining the operation of each member 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.
[0010]
First, an outline of the entire structure of the duo servo drum brake of this embodiment will be described with reference to FIG.
The duo-servo drum brake 1 of this embodiment includes a brake drum (not shown) that rotates forward in the counterclockwise direction as indicated by an arrow R in FIG. In the brake drum, a primary shoe 2 and a secondary shoe 3 are arranged so as to face each other.
An adjuster 6 that adjusts 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 1 of the present embodiment, both the primary shoe 2 and the secondary shoe 3 act as leading brake shoes.
[0011]
On the other hand, an operating lever 7 that expands the primary shoe 2 and the secondary shoe 3 outward in the radial direction and presses them against the brake drum is swingably supported by a support shaft 8 attached to the front side of the secondary shoe 3. Yes.
In addition, the engaging portion 9 provided on the support shaft 8 side of the operating lever 7 and the engaging portion 10 provided on the front side of the primary shoe 2 are connected to the primary shoe 2 by the rotation of the operating lever 7. Both end portions of the struts 11 that are pressed against each other are engaged with each other.
The basic configuration of the operation lever 7 and the strut 11 is the same as that of a conventional parking brake.
[0012]
An anchor pin 13 is suspended from the backing plate 12 to which the primary shoe 2 and the secondary shoe 3 are attached in such a manner that the primary shoe 2 and the secondary shoe 3 can be expanded. A control lever 14 is attached to the anchor pin 13 so as to be swingable in a plane parallel to the backing plate 12.
Further, the control lever 14 is a thick plate-like member extending in parallel with the surface of the backing plate 12, and the front end of the secondary shoe 3 is connected to a radially outer end 15 via a braking reaction force transmission pin 16. The end on the side is in contact. The end 17 on the radially inner side of the control lever 14 is inserted through a through hole 11a formed in the central portion of the strut 11 in the longitudinal direction, and is engaged with the strut 11 in the longitudinal direction.
[0013]
Next, the operation of the duo servo drum brake 1 of the present embodiment configured as described above will be described with reference to FIG.
In order to operate the duo-servo type drum brake 1 of this embodiment, the swing end 7a of the operation lever 7 is pulled by, for example, a brake cable or the like, and displaced inward in the radial direction of the brake drum.
Then, the operation lever 7 swings around the support shaft 8 as a fulcrum, and the strut 11 is displaced toward the primary shoe 2 side. As a result, the primary shoe 2 is displaced radially outward by the strut 11 and pressed against the brake drum. At the same time, since the operating lever 7 swings with the engaging portion 9 as a fulcrum, the support shaft 8 is displaced radially outward. As a result, the front end of the secondary shoe 3 is displaced radially outward by the support shaft 8 and is pressed against the brake drum.
As a result, both the primary shoe 2 and the secondary shoe 3 are expanded and pressed against the brake drum, and the rotation of the brake drum is braked.
[0014]
At this time, the reaction force of the braking force with which the primary shoe 2 brakes the rotation of the brake drum is input to the front side of the secondary shoe 3 via the adjuster 6. Thereby, the higher the braking force of the primary shoe 2 is, the stronger the secondary shoe 3 is pressed against the brake drum, and the braking force of the secondary shoe 3 is also increased.
[0015]
On the other hand, the control lever 14 is swung around the anchor pin 13 counterclockwise by the braking reaction force B acting on the secondary shoe 3.
When the radially inner end 17 of the control lever 14 swings to a position where it engages with the through hole 11a of the strut 11, the strut 11 has a braking reaction force B to the lever ratio (L1 / L2) of the control lever 14. ) Is applied to the side opposite to the direction in which the strut 11 presses the primary shoe 2.
[0016]
Therefore, even if the operating force for operating the operating lever 7 is kept constant, if the braking force by the primary shoe 2 and the secondary shoe 3 changes in the increasing direction, the braking reaction force B acting on the control lever 14 also increases. Therefore, the control force C applied to the strut 11 by the control lever 14 also increases.
As a result, the pressing force A by which the strut 11 presses the primary shoe 2 against the brake drum is greatly reduced, so that the braking force of the primary shoe 2 is reduced. Then, since the braking reaction force acting on the primary shoe 2 is reduced, the pressing force for pressing the secondary shoe 3 against the brake drum is also reduced, and the braking force by the secondary shoe 3 is also reduced.
On the other hand, when the braking force by the primary shoe 2 and the secondary shoe 3 changes in the decreasing direction, the braking reaction force B acting on the control lever 14 decreases, so that the control force C applied to the strut 11 by the control lever 14 also increases. It also decreases.
As a result, the pressing force A by which the strut 11 presses the primary shoe 2 against the brake drum is reduced, and the braking force of the primary shoe 2 increases. Then, since the braking reaction force acting on the primary shoe 2 also increases, the pressing force for pressing the secondary shoe 3 against the brake drum also increases, and the braking force by the secondary shoe 3 also increases.
[0017]
That is, in the duo-servo type drum brake 1 of the present embodiment, it is possible to automatically increase or decrease the braking force by the primary shoe 2 and the secondary shoe 3 even when the brake operation force for operating the operation lever 7 is kept constant. Since it can be controlled in the vicinity of the value, it is possible to prevent an excessive effect and obtain a stable braking force.
[0018]
The magnitude of the control force C that the control lever 14 acts on the strut 11, that is, the suppression gain of the increase / decrease change in braking force by the primary shoe 2 and the secondary shoe 3 is the braking reaction that the secondary shoe 3 acts on the control lever 14. It can be adjusted by appropriately changing the value of the dimension L1 between the force application point and the center of the anchor pin 13.
[0019]
As mentioned above, although one 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 distal end 17 of the control lever 14 is inserted into an insertion hole penetrating through the central portion of the strut 11 in the longitudinal direction. It is also possible to engage both of them by interposing the end of the control lever 14 between the strut 11 and the primary shoe 2.
[0020]
【The invention's effect】
As is clear from the above description, the present invention is a case where a part of the braking reaction force acting on the secondary shoe is taken out and applied in the reverse direction to the strut that presses the primary shoe against the brake drum, and the braking force increases. Since the strut greatly reduces the pressing force with which the strut presses the primary shoe and when the braking force decreases, the strut has a structure that decreases the pressing force with which the primary shoe presses the primary shoe. A duo-servo type drum brake with stable power can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic front view showing an overall structure of a duo servo drum brake according to an embodiment of the present invention.
FIG. 2 is a schematic front view for explaining the operation of each member shown in FIG.
[Explanation of symbols]
A Primary shoe pressing force B Braking reaction force C Strut control force R Brake drum forward rotation direction 1 Duo servo drum brake 2 of the present invention 2 Primary shoe 3 Secondary shoe 4 Front end of primary shoe 5 Front end of secondary shoe Part 6 Adjuster 7 Operation lever 8 Support shafts 9 and 10 Engagement part 11 Strut 12 Backing plate 13 Anchor pin 14 Control lever 15 End of control lever 16 Brake reaction force transmission pin 17 End of control lever

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 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 pin arranged on the front side in the forward rotation direction of the brake drum,
A strut that presses the primary shoe against the brake drum by rotating an operation lever;
A control lever that is swingable around the anchor pin and has one end abutting the secondary shoe and the other end engaging the strut;
When one end of the control lever receives a predetermined braking reaction force from the secondary shoe, the other end of the control lever cooperates with the anchor pin and is in a direction opposite to the primary shoe pressing direction of the strut. The duo-servo drum brake device is characterized in that the strut is urged on the drum.

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