JPH1151094A - Duo-servo type drum brake - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a duo-servo type drum brake capable of yielding high stable braking force. SOLUTION: When braking reaction force D acting on the anchor pin 10 of a secondary shoe 3 is increased to exceed a given braking reaction force, a control lever 40 is fluctuated at a given angle or more. Then, the fluctuating end 42 of the control lever 40 is engaged with the tip 62 of a reaction lever 60 to push and move the reaction lever 60 to the secondary shoe 3 side. The result decreases pressing force evolved by pressing a primary shoe 2 to a brake drum 100 by means of an input lever 30 and braking force. Placing the input lever 30 at the primary shoe 2 side than a wheel cylinder 20 easily places each link in a limited space.

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] The duo-servo type drum brake is
Generally, it has two brake shoes, a primary shoe and a secondary shoe, arranged opposite to each other. The primary shoe has an input portion on the front side in the forward rotation direction of the brake drum and the forward side in the forward rotation direction on the brake drum is connected to the near side on the front side of the secondary shoe via an adjuster, for example, a link member.
The front side of the secondary shoe abuts on an anchor attached to the backing plate, so that 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, the duo-servo type drum brake has a problem that it is difficult to stabilize the braking force because it is sensitive to a change in the friction coefficient of the lining of the brake shoe.

In the conventional duo-servo drum brake, a primary shoe and a secondary shoe are expanded by a pair of hydraulic pistons projecting from a wheel cylinder disposed on an anchor side to a primary shoe side and a secondary shoe side. The structure is such that it is pressed against the brake drum, and advanced hydraulic control is required to stabilize the braking force, and the overall mechanism could not be simplified.

SUMMARY OF THE INVENTION An object of the present invention is to provide a duo-servo type drum brake which can solve the above-mentioned problems of the prior art and can stabilize the braking force while facilitating the installation of a parking brake. is there.

[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 opposed to each other inside the drum and have their ends linked to each other, and which act on the primary shoe. A duo-servo-type drum brake for receiving braking reaction force from an anchor pin fixed to a backing plate via a secondary shoe and pressing each shoe against a drum: fixed to the backing plate near the anchor pin and fixed to the primary shoe. Operating means for applying an urging force to the inner surface of the drum; struts having both ends fixedly provided near the anchor pin between the primary shoe and the secondary shoe; and the secondary shoe and the anchor pin around the anchor pin. And the braking reaction force A control bar swinging in the direction of the secondary shoe; a control bar pivotally supported by the secondary shoe, one end of the control bar being in contact with a swing end of the control bar, and the other end being in contact with the strut; A balance link that pushes the strut toward the primary shoe by swinging the strut; one end of which is held by the primary shoe so as to maintain a relative position with respect to the strut; When the control lever further receives a predetermined braking reaction force from the secondary shoe after the control lever comes into contact with the balance link, the control lever is engaged with the swing end of the control lever and the strut is engaged with the strut. A reaction lever acting on the primary shoe to reduce the pressing force. It is.

In the duo-servo type drum brake of the present invention, the base end of the duo-servo-type drum brake is pivotally supported so as to be swingable, and when swung by a parking brake operation, pushes the strut toward the primary shoe. In addition, a parking brake lever that presses the secondary shoe against the brake drum by the reaction force can be further provided.

Further, an input lever is provided which is pivotally supported in the vicinity of the center by a lever pin provided on the primary shoe, and one end of the input lever is engaged with the operating means and has the other end when receiving an urging force. The reaction force against the urging force is returned to the lever pin by abutting on the strut, the urging force from the operating means is transmitted to the primary shoe, and the reaction lever is pivotally supported by the reper pin and is opposed to the strut. It is also possible to adopt a configuration in which the target position is maintained and the input to the primary shoe is made one point of the lever pin.

Further, an input lever is provided which is pivotally supported near the center by a lever pin provided on the reaction lever, and one end of the input lever is engaged with the actuating means and the other end thereof receives an urging force. The reaction force against the urging force is returned to the lever pin in contact with the strut, and the urging force from the operating means is transmitted to the primary shoe via the reaction lever, and the reaction lever is moved relative to the strut. The position can be maintained, and the input to the primary shoe can be used as one point of the reaction lever holding portion.

In the duo-servo-type drum brake of the present invention having the above-described structure, when the operating means applies a biasing force to the primary shoe by the normal brake operation, the input lever presses the secondary shoe via the strut against the brake drum. At the same time, the primary shoe is pressed against the brake drum by the reaction force. On the other hand, the control lever swings when its base end receives a braking reaction force acting on the anchor from the secondary shoe, and the swing end is displaced toward the secondary shoe to push one end of the balance link. The balance link swings when pushed by the control lever, and the other end pushes the primary shoe against the brake drum via the strut, and the secondary shoe is pushed against the brake drum by the reaction force. That is, the duo servo type drum brake of the present invention also performs the operation of pressing the primary shoe and the secondary shoe against the brake drum by the strut using the braking reaction force acting on the anchor from the secondary shoe.

On the other hand, when the braking reaction force acting on the anchor from the secondary shoe increases, and exceeds a predetermined braking reaction force set by the distance between the members, that is, when the swing amount of the control lever increases, the control lever Swinging end engages the tip of the reaction lever, and pushes the reaction lever toward the secondary shoe. As a result, the pressing force of the input lever pressing the primary shoe against the brake drum decreases, so that the braking force of the primary shoe decreases and the braking reaction force acting on the primary shoe also decreases. As a result, the pressing force for pressing the front side of the secondary shoe against the brake drum decreases, and the braking force by the secondary shoe also decreases, so that the braking reaction force acting on the anchor from the secondary shoe decreases.

When the braking reaction force acting on the anchor from the secondary shoe falls below the above-mentioned set value, the swing angle of the control lever becomes small, and the engagement between the control lever and the reaction lever is released. Then, since the pressing force for pressing the primary shoe against the brake drum increases again, the braking force increases again. That is,
The duo-servo type drum brake of the present invention also has an automatic adjustment function for reducing the braking force when the braking force exceeds a predetermined value.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment and a second embodiment of a duo-servo type drum brake according to the present invention will be described in detail with reference to FIGS. here,
FIG. 1 is a front view schematically showing an overall structure of a duo-servo type drum brake according to a first embodiment of the present invention, FIG. 2 is an enlarged front view showing a main part of FIG. 1, and FIG. FIG. 4 is an enlarged front view of the main part illustrating the operation of the parking lever shown in FIG. 2, and FIG. 5 is an enlarged front view of the main part illustrating the operation of the parking lever shown in FIG. Main part enlarged front view for explaining the operation of the control lever, balance link and strut shown in FIG. 6,
FIG. 7 is an enlarged front view of a main part for explaining the operation of the control lever and the reaction lever shown in FIG. 2, FIG. 7 is a front view schematically showing the entire structure of a duo-servo type drum brake according to a second embodiment of the present invention, FIG. 8 is an enlarged front view showing a main part of FIG. 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.

First Embodiment First, a duo-servo type drum brake according to a first embodiment of the present invention will be described with reference to FIGS.

The duo-servo type drum brake 100 of the first embodiment is provided with a brake drum (not shown) that rotates forward in a counterclockwise direction as shown by an arrow R in FIG. The primary shoe 2 and the secondary shoe 3 supported on the backing plate 1 so as to be able to expand are arranged so as to face each other in the brake drum.

Between the front end 4 of the primary shoe 2 and the front end 5 of the secondary shoe 3, a link member for these brake shoes and a sliding surface of a brake drum are provided. An adjuster 6 is interposed as a means for adjusting the clearance therebetween. 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.

On the other hand, between the engaging portion 7 provided on the primary shoe 2 and the engaging portion 8 provided on the secondary shoe 3, a strut 9 formed of a highly rigid material (for example, a metal plate) is provided. Both ends are fixedly interposed.
Thus, when the strut 9 is pushed toward the primary shoe 2, the primary shoe 2 can be pushed against the brake drum. When the strut 9 is pushed toward the secondary shoe 3, the secondary shoe 3 can be pushed against the brake drum.

At the front side of the secondary shoe 3, an anchor pin 10 suspended from the surface of the backing plate 1 is provided.
Are arranged to receive a braking reaction force acting on the secondary shoe 3. A wheel cylinder 20 as an actuating means is implanted at a position on the backing plate 1 radially inside the anchor pin 10. The piston 21 of the wheel cylinder 20 projects toward the primary shoe 2 with a pressing force corresponding to, for example, a brake pedal operating force by a driver of a vehicle equipped with the duo-servo type drum brake 100 of the first embodiment. It has been like that.

In the gap between the web 2a of the primary shoe 2 and the backing plate 1, an input lever 30 formed of a highly rigid material (for example, a metal plate) is provided.
It is arranged so as to face the strut 9 and the wheel cylinder 20. The input lever 30 includes a support shaft 31
As a result, it is pivotally supported by the web 2a and is swingable in a plane parallel to the surface of the backing plate 1. The input lever 30 has one end 32 in contact with the tip of the piston 21 and the other end 33 with the end of the strut 9 on the primary shoe 2 side. As a result, when the piston 21 of the wheel cylinder 20 protrudes toward the primary shoe 2, the input lever 30 swings counterclockwise around the lever pin 31, which is a support shaft, and pushes the strut 9 to move the secondary shoe. 3 is pressed against the brake drum, and the primary shoe 2 is pressed against the brake drum via the support lever pin 31 by the reaction force.

Further, the control lever 40 machined from a block material of a metal material is provided with the anchor pin 10.
Thereby, it is swingably supported 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 radially outer base end 41 of the control lever 40. Thus, when the base end 41 is pressed by the braking reaction force acting on the anchor pin 10 from the secondary shoe 3, the control lever 40 swings around the anchor pin 10 in the counterclockwise direction in the drawing, and the control lever 40 radially inwards. Is displaced toward the secondary shoe 3.

On the upper surface of the web 3a of the secondary shoe 3, a balance link 50 formed in a substantially L shape from a thick metal plate is supported by a support shaft 51, and is parallel to the surface of the backing plate 1. It is swingable inside. The tip 52 of the longer side abuts on the swinging end 42 of the control lever 40, and the tip 53 of the shorter side abuts on the end of the strut 9 on the secondary shoe 3 side. Thus, when the balance link 50 is pushed by the control lever 40, the balance link 50 swings around the support shaft 51 by a slight angle in the clockwise direction in the drawing, and pushes the strut 9 toward the primary shoe 2.

The strut 9 and the wheel cylinder 2
A reaction lever 60 is formed between the primary shoe 2 and the secondary shoe 3 and press-formed from a thick metal plate. A base end 61 of the reaction lever 60 is pivotally supported on the web 2a by a lever pin 31 that supports the input lever 30 on the web 2a of the primary shoe 2. The tip 62 is bent in an L-shape, and faces the swing end 42 of the control lever 40 with a slight gap. Thereby, the control lever 40
Is pushed by the secondary shoe 3 and the anchor pin 10
, The reaction lever 60 engages with the swing end 42 of the control lever 40 and is pushed toward the secondary shoe 3.

Next, the operation of the duo-servo type drum brake 100 of the first 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 the first embodiment steps on the brake pedal, a hydraulic pressure corresponding to the driver's brake operating force acts on the wheel cylinder 20. . Then, as shown in FIG. 3, the piston 21 of the wheel cylinder 20 pushes one end 32 of the input lever 30 toward the primary shoe 2 with a pressing force A corresponding to the applied oil pressure.
Thereby, the input lever 30 swings around the lever pin 31 in the counterclockwise direction in the drawing, and the other end 33 of the strut 9 is moved to the secondary shoe by the pressing force B obtained by multiplying the pressing force A by the lever ratio of the input lever 30. Because it is pushed to the 3 side,
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 lever pin 31 of the input lever 30, so that the lever pin 31, ie, the primary shoe 2, is pressed by the brake drum. When the primary shoe 2 and the secondary shoe 3 are both pressed against the brake drum in this manner, 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 the duo-servo type drum brake 100 of the first embodiment is operated as a parking brake, the swinging end of the parking lever 12 is displaced toward the primary shoe 2 as shown in FIG. . Then, the parking lever 12 swings clockwise in the figure with the end of the strut 9 on the side of the secondary shoe 3 serving as a fulcrum, and
1, that is, the secondary shoe 3 is pressed against the brake drum. At the same time, the parking lever 12 pushes the strut 9 toward the primary shoe 2 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 secondary shoe 3 is pressed against the brake drum as described above with reference to FIG.
As shown in (2), a braking reaction force D acts on the secondary shoe 3. The braking reaction force D is applied to the control lever 4
When input is made to the base end 41 of 0, the control lever 40 swings around the anchor pin 10 in the counterclockwise direction in the figure. Then, the swing end 42 of the control lever 40 is displaced toward the secondary shoe 3, and the pressing force E obtained by multiplying the braking reaction force D by the lever ratio (L1 / L2) of the control lever 40 causes the balance link 50 to move. The tip 52 is pushed toward the secondary shoe 3. Thus, the other end 53 of the balance link 50 pushes the strut 9 toward the primary shoe 2 by the pressing force F obtained by multiplying the pressing force E by the lever ratio (L3 / L4) of the balance link 50.

Then, since the primary shoe 2 is pressed against the brake drum by the pressing force A of the wheel cylinder 20 and the pressing force F of the strut 9, the braking force of the primary shoe 2 is further increased. Further, since a larger braking reaction force acting on the primary shoe 2 is input to the front side of the secondary shoe 3 and presses the secondary shoe 3 against the brake drum, the braking force by the secondary shoe 3 is further increased.

The gain of the braking force can be set to an appropriate value by appropriately adjusting the lever ratio (L1 / L2) of the control lever 40 and the lever ratio (L3 / L4) of the balance link 50.

On the other hand, when the braking force by the primary shoe 2 and the secondary shoe 3 increases, the braking reaction D acting on the anchor pin 10 from the secondary shoe 3 also increases. And the base end 4 of the control lever 40
When the braking reaction force D input to 1 exceeds a braking reaction force determined by a preset interval and ratio between the members, the control lever 40 swings by a predetermined angle or more. Then, the swing end 42 of the control lever 40 is engaged with the tip 63 of the reaction lever 60, and pushes the reaction lever 60 toward the secondary shoe with the pressing force E. As a result, the pressing force of the input lever 30 pressing the primary shoe 2 against the brake drum decreases, so that the braking force by the primary shoe 2 decreases and the braking reaction force acting on the primary shoe 2 also decreases. Then, the pressing force for pressing the front side of the secondary shoe 3 against the brake drum decreases, and the braking force by the secondary shoe 3 also decreases.
The braking reaction force D acting on the anchor pin 10 from the secondary shoe 3 decreases. When the braking reaction force D acting on the anchor pin 10 from the secondary shoe 3 becomes smaller than the braking reaction force determined by a predetermined interval and ratio between the members, the swing angle of the control lever 40 decreases. ,
The engagement between the control lever 40 and the reaction lever 60 is released. As a result, the pressing force for pressing the primary shoe 2 against the brake drum increases again, and the braking force increases again. That is, the duo-servo type drum brake 100 of the first embodiment also has an automatic adjustment function of reducing the braking force when the braking force exceeds a predetermined value.

That is, the duo-servo type drum brake 100 of the first embodiment brakes the primary shoe 2 and the secondary shoe 3 with a stronger pressing force by using the braking reaction force D acting on the anchor pin 10 from the secondary shoe 3. Not only does it have a self-multiplying function of the braking force that presses the drum to obtain a greater braking force, but also has an automatic adjustment function that reduces the braking force when the braking force exceeds a predetermined value. Therefore, according to the present invention, it is possible to provide a duo-servo type drum brake capable of obtaining a large and stable braking force.

Since the wheel cylinder 20 has a structure in which the piston 21 protrudes only toward the primary shoe 2, the input lever 30 is moved to the wheel cylinder 2.
0 can be arranged on the primary shoe 2 side. Also, the control lever 40 and the balance link 5
Since the parking lever 12 and the parking lever 12 can be arranged on the secondary shoe 3 side with respect to the wheel cylinder 20, each link can be easily arranged in a limited space.

Second Embodiment A duo-servo drum brake according to the second embodiment is a duo-servo drum brake 1 according to the first embodiment.
The input lever, strut, and reaction lever have different shapes and mutual assembling relations from those of 00.

That is, as shown in FIGS. 7 and 8, the duo-servo drum brake 2 of the second embodiment is used.
00, the piston 21 of the wheel cylinder 20
Input lever 70 which is swung by the lever pin 71
Accordingly, the primary shoe 2 is pivotally supported not by the web 2a but by the reaction lever 80.

The end portion 81 of the reaction lever 80 on the primary shoe 2 side engages with the engaging portion 7 of the web 2a, and can transmit a pressing force in a direction of pressing the primary shoe 2 against the brake drum. It has been. A body portion 82 of the reaction lever 80 extends between the wheel cylinder 20 and the strut 90 toward the secondary shoe 3, and a tip 83 thereof is bent into an L-shape, and a swing end 42 of the control lever 40 is formed.
And can be engaged.

The strut 90 has an end 91 on the side of the secondary shoe 3 connected to the web 3 a of the secondary shoe 3 and the other end 53 of the balance link 50, similarly to the duo-servo drum brake 100 of the first embodiment. I agree. On the other hand, the end 92 on the primary shoe 2 side is engaged with the other end 73 of the input lever 70 and the engaging portion 84 of the reaction lever 80, and the duo servo type drum brake 100 of the first embodiment is engaged. Is not directly engaged with the web 2a of the primary shoe 2.

When the piston 21 of the wheel cylinder 20 pushes one end 72 of the input lever 70 toward the primary shoe 2, the input lever 70 is moved to the lever pin 71.
, The other end 73 pushes the strut 90 toward the primary shoe 2 and presses the secondary shoe 3 against the brake drum. The reaction force is applied to the reaction lever 80 via the lever pin 71.
The reaction lever 80 presses the primary shoe 2 against the brake drum.

On the other hand, the swing end 4 of the control lever 40
When the second lever 2 engages the tip 83 of the reaction lever 80 and pushes the reaction lever 80 toward the secondary shoe 3, the pressing force of the reaction lever 80 pressing the primary shoe 2 against the brake drum decreases.

The pressing force by which the parking lever 12 pushes the strut 90 toward the primary shoe 2 is transmitted from the end 92 of the strut 90 on the primary shoe 2 side to the engaging portion 84 of the reaction lever 80. As a result, the primary shoe 2 has the reaction lever 80
To the brake drum.

The operation of the duo-servo drum brake 200 of the second embodiment other than the above-described parts is the same as that of the duo-servo drum brake 100 of the first embodiment.

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 above-described embodiment, the primary shoe 2 and the secondary shoe 3 are configured to be pressed against the brake drum using the wheel cylinder 20 that is operated by hydraulic pressure. Alternatively, a link mechanism operated by a wire cable can be used.

[0043]

As is apparent from the above description, the duo-servo type drum brake of the present invention brakes the primary shoe and the secondary shoe with a stronger pressing force by using the braking reaction force acting on the anchor from the secondary shoe. It has a self-multiplication function for pressing the drum to obtain a larger braking force, and an automatic adjustment function for reducing the braking force when the braking force exceeds a predetermined value. Therefore, according to the present invention, it is possible to provide a duo-servo type drum brake capable of obtaining a large and stable braking force. Further, since the operating member of the operating means is configured to be displaced only to the primary shoe side, the input lever can be arranged on the primary shoe side with respect to the wheel cylinder. Further, since the control lever, the balance link, the parking lever and the like can be arranged on the secondary shoe side with respect to the wheel cylinder, each link can be easily arranged in a limited space.

[Brief description of the drawings]

FIG. 1 is a front view schematically showing an overall structure of a duo-servo type drum brake according to a first 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 operations of a control lever, a balance link and struts shown in FIG. 2;

FIG. 6 is an enlarged front view of an essential part for explaining operation of a control lever and a reaction lever shown in FIG. 2;

FIG. 7 is a front view schematically showing the overall structure of a duo-servo type drum brake according to a second embodiment of the present invention.

FIG. 8 is an enlarged front view showing a main part of FIG. 7;

[Explanation of symbols]

A Servo force B Primary shoe pressing force C Secondary shoe pressing force D Braking reaction force E Control force F Primary shoe pressing force G Primary shoe returning force R Forward rotation direction of brake drum 1 Backing plate 2 Primary shoe 3 Secondary shoe 4 Primary shoe Front end 5 Front end of secondary shoe 6 Adjuster 7,8 Engagement part 9 Strut 10 Anchor pin 11 Support shaft 12 Parking lever 13 Operating end 20 Wheel cylinder 21 Piston 30 Input lever 31 Lever pin 40 Control lever 50 Balance link 51 Support shaft 60 Reaction lever 70 Input lever 71 Lever pin 80 Reaction lever 90 Strut 100 Duo servo type drum brake according to the first embodiment of the present invention 200 A second embodiment of the duo-servo drum brake according to Akira

Claims (4)

[Claims] 1. A primary shoe and a secondary shoe, which are opposed to each other on the inside of a drum and have their ends linked to each other, are provided. A braking reaction force from the drum acting on the primary shoe is applied to the backing plate via the secondary shoe. A duo-servo type drum brake that receives with a fixed anchor pin and presses each shoe against a drum, and is an operating unit that is fixed to the backing plate near the anchor pin and applies an urging force to the inner surface of the drum to the primary shoe. A strut whose both ends are fixedly passed in the vicinity of the anchor pin between the primary shoe and the secondary shoe, and which is clamped between the secondary shoe and the anchor pin around the anchor pin, and the braking reaction force causes the secondary shoe direction Swinging control bar And the other end is in contact with the swinging end of the control bar, and the other end is in contact with the strut. A balance link that pushes toward the side, one end of which is held by the primary shoe so as to maintain the relative position to the strut, and the other end of which extends toward the secondary shoe engages with the swing end of the control lever. When the control lever further receives a predetermined braking reaction force from the secondary shoe after the control lever comes into contact with the balance link, a force for engaging with the swinging end and reducing the primary shoe pressing force on the strut. And a reaction lever acting on the drum. 2. A base end of the secondary shoe is swingably supported by the secondary shoe. When the base shoe is swung by a parking brake operation, the strut is pushed toward the primary shoe, and a reaction force of the strut causes the strut to rotate. 2. The duo-servo type drum brake according to claim 1, further comprising a parking brake lever that presses the brake drum against the brake drum. 3. An input lever pivotally supported near the center by a lever pin provided on the primary shoe,
When one end of the input lever is engaged with the operating means and receives an urging force, the other end contacts the strut and returns a reaction force to the lever pin to the lever pin, and the urging force from the operating means 2. The reaction shoe is transmitted to the primary shoe, and the reaction lever is pivotally supported by the reper pin to maintain a relative position with the strut, and an input to the primary shoe is made at one point of the lever pin.
Or the duo-servo type drum brake according to 2. 4. An input lever, which is pivotally supported near the center by a lever pin provided on the reaction lever, the other end of which is engaged when one end of the input lever is engaged with the operating means and receives an urging force. The reaction force against the urging force is returned to the lever pin in contact with the strut, and the urging force from the operating means is transmitted to the primary shoe via the reaction lever, and the reaction lever is moved relative to the strut. 3. The duo-servo type drum brake according to claim 1, wherein the position is maintained, and the input to the primary shoe is made to be one point of the reaction lever holding portion.