JPH09196091A - Duo-servo type parking brake device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perfectly prevent the generation of brake judder. SOLUTION: Since a shoe-to-shoe spring 54 is stretched under a parking brake, link 42 of both brake shoes 20, 26, the angular moment in the direction for separating from the inner peripheral surface of a brake drum 12 can be generated in an upper end of the brake shoe 26. Since centering springs 60, 62 are respectively stretched between a lower end of each brake shoe 20, 26 and a backing plate 14, a distance of the brake shoe 20 from an anchor pin 34 can be reduced. Consequently, generation of brake judder can be perfectly prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a duoservo type parking brake device.

[0002]

2. Description of the Related Art As a vehicle brake device, a main brake device for decelerating or stopping a running vehicle, a parking brake device for maintaining a stopped state,
There is. As the latter parking brake device, a duo-servo type parking brake device that can obtain a large braking force with a small operating force is suitable. An example of this type of Duo servo type parking brake device is
No. 72325, which will be described below.

As shown in FIG. 4, the brake body of the parking brake device 100 is incorporated in a duo-servo type drum brake device 102. The drum brake device 102 includes a disc-shaped backing plate 104 which is arranged on the opening end side of a brake drum (not shown). A pair of brake shoes 108 and 110 are arranged on both sides of a through hole 106 provided at the axial center of the backing plate 104. Each of the brake shoes 108, 110 has a curved shoe body 108A, 110A and the shoe body 108A,
It is composed of linings 108B and 110B fixed to 110A. Also, the brake shoes 108,
The shoe main bodies 108A and 110A of 110 are movably supported by shoe holddowns 112 arranged in the respective intermediate portions.

An anchor pin 114 is arranged between the upper ends of the brake shoes 108 and 110. Further, one ends of return springs 116 and 118 are locked near the upper ends of the brake shoes 108 and 110, respectively, and the other ends of the return springs 116 and 118 are locked to the anchor pin 114. Therefore, the upper ends of the brake shoes 108 and 110 are provided with the return spring 11
6, 118 are respectively urged toward the anchor pin 114 side and held in contact with the anchor pin 114. A link 120 connects the lower ends of the brake shoes 108 and 110.

The one brake shoe 10 described above is also used.
A parking brake lever 122 having a substantially arc plate shape is arranged on the back surface side of 8. The upper end of the parking brake lever 122 is swingably connected to the upper end of one brake shoe 108 by a pin 124.
Further, between the vicinity of the upper end of the parking brake lever 122 and the vicinity of the upper end of the other brake shoe 110,
A flat strut 126 is suspended. Further, one end of a parking brake cable 128 is fixed to the lower end of the parking brake lever 122.

Next, referring to the schematic operation diagrams shown in FIGS. 5 (A) to 5 (C), the structure up to this point (that is, the shoe-to-shoe spring 132 and the drag prevention spring 134, which will be described later, are omitted. The operation of the parking brake device 100 according to the configuration will be described.

First, when the parking brake device 100 is not operated, as shown in FIG. 5A, since the parking brake lever 122 is not swinging, both brake shoes 108 are urged by the urging force of the return springs 116 and 118. , 110 are engaged with anchor pins 114 at their upper ends and are also separated from the brake drum.

Next, when the parking brake device 100 is operated from this state, the parking brake cable 128 is pulled to the left side in the state shown in FIG. Therefore, the parking brake lever 122 has the pin 12
It swings to the other brake shoe 110 side around four times. Therefore, in the state where the parking brake starts to be pulled (begins to work), as shown in FIG. 5B, the upper end portion of one brake shoe 108 receives the pressing force B ′ in the expansion direction and is separated from the anchor pin 114. Then it is pressed against the brake drum. Along with this, a pressing force C ′ in the anti-drum rotation direction (the direction opposite to the arrow A ′ direction) acts from the lower end of one brake shoe 108 to the lower end of the other brake shoe 110 via the adjuster device 130. . As a result, the upper end of the other brake shoe 110 contacts the anchor pin 114.

However, since the direction of rotation of the brake drum is in the direction of arrow A ', one brake shoe 108 and the other brake shoe 110 both rotate in the drum rotation direction due to this rotation, and one brake shoe. The upper end of 108 abuts the anchor pin 114 (the abutting force at this time is indicated by arrow D ′). Along with this, a rotational force E ′ in the expansion direction acts on the lower end portion of the other brake shoe 110 with the adjuster device 130 as a fulcrum, and the rotational force E ′ also causes the other brake shoe 110 to press the brake drum. To be done. As a result, one brake shoe 108 and the other brake shoe 11
Zero acts as a leading shoe when torque is generated, and servo force is obtained.

However, with only the above-mentioned structure, there is a problem that the brake shoes 108 and 110 come into contact with the brake drum and are dragged, thereby causing brake judder.

That is, when the parking brake starts to be pulled (begins to work), it is expanded from one brake shoe 108 side as described above.
Since the distance a'from 14 is large, the swing amount b'of the parking brake lever 122 at the time of shifting from the state shown in FIG. 5B to the state shown in FIG. 5C also becomes large. Therefore, the contact force D ′ when the upper end of one brake shoe 108 contacts the anchor pin 114 becomes large, which causes a relatively large peak torque (arrow P in FIG. 6).
See). Due to this peak torque, one brake shoe 108 comes into contact with the brake drum and dragging occurs, causing brake judder.

Further, when the parking brake is returned, that is, when the cable pulling force is weakened in order to release the parking brake torque, the biasing force of the return spring 116 is applied to the upper end of the other brake shoe 110, as shown in FIG. Since F ₁ 'is acting toward the anchor pin 114 side and the reaction force F ₂ ' from the strut 126 is acting, the moment M _{1 in the} clockwise direction in the figure is applied to the upper end portion of the other brake shoe 110. 'Acts. Therefore, the pressing force G'on the brake drum still acts on the lower end portion of the other brake shoe 110, and this pressing force G'is larger than the normal pressing force H'on the brake drum. The lower end of the shoe 110 is pressed against the brake drum. Therefore, the adjuster device 1
A relatively large pressing force I ′ acts from the lower end of the other brake shoe 110 to the lower end of the one brake shoe 108 via 30. As a result, the parking brake torque is less likely to be released on the side of one brake shoe 108, dragging occurs, and brake judder occurs.

Therefore, in the case of the above construction, at the beginning of braking (actuation of the parking brake), a relatively large peak torque (F) is generated, and a brake judder is generated on one brake shoe 108 side. At the time of returning the parking brake, both brake shoes 108 and 110 (particularly one brake shoe 108 side) are caused by the action of the rotational moment (M ₁ ') to the brake drum pressure contact side. Brake judder occurs.

In view of this point, in the parking brake device 100 disclosed in the above-mentioned publication, regarding the former problem, a drag preventing spring (centering spring) is provided between the backing plate 104 and the intermediate portion of the other brake shoe 110. ) 134 is installed to cope with this. That is, the drag prevention spring 13
By restraining the movement of the lower ends of the brake shoes 108, 110 to some extent by the urging force of No. 4, a and b are made smaller. The latter problem is dealt with by arranging shoe-to-shoe springs 132 near the lower ends of the brake shoes 108 and 110 to pull and urge the lower ends of the brake shoes 108 radially inward.
That is, the biasing force of the shoe-to-shoe spring 132 cancels the clockwise moment M ₁ ′ acting on the other brake shoe 110.

[0015]

However, in the case of the above structure, there is no problem if the biasing force of the drag prevention spring 134 is such that the brake shoe 110 is centered when the brake is not applied. When the biasing force is such that the centering action is to be caused when the parking brake starts to be pulled (when it starts to work), the biasing force of the drag prevention spring 134 must be necessarily increased. In this case, that is, when the urging force of the drag prevention spring 134 is increased, the urging force is too large, so the brake shoe 10
8 comes into contact with the brake drum to generate brake judder.

In consideration of the above facts, an object of the present invention is to obtain a duoservo type parking brake device capable of completely preventing the occurrence of brake judder.

[0017]

According to the present invention, there is provided a backing plate fixed to a non-rotating portion of a vehicle, and a backing plate movably held by the backing plate and arranged to face an inner peripheral surface of a brake drum. A pair of brake shoes, an anchor means arranged between the one ends of these brake shoes and engageable with the one end, a connecting means for connecting the other ends of these brake shoes, and one end A lever body that is swingably connected to the other brake shoe and has a parking brake cable fixed to the other end, and a strut that connects one end of this lever body and one end of the other brake shoe. A configured duo-servo type parking brake device, one end of which is locked to the anchor means side with respect to the connecting portion of the brake shoe with the strut. And the other end is locked to the anchor means to urge one end of each brake shoe to the anchor means side, and one end is locked to one brake shoe and the other end is A second urging means that is locked to the other end side of the other brake shoe with respect to the connection part with the strut in the other brake shoe and urges the both brake shoes toward each other, and one end The other end of each brake shoe is locked to the axial center side of the backing plate, and the other end of the brake shoe is locked to the axial center side of the backing plate. And a third urging means for urging.

According to the above structure, when the parking brake cable is pulled, the lever body swings around the connecting portion with one brake shoe. Therefore, one brake shoe moves in the direction in which one end thereof is separated from the anchor means. At this time, since the other brake shoe is connected to the one brake shoe via the connecting means, one end of the other brake shoe engages with the anchor means. Then, as the brake drum rotates, both brake shoes integrally move in the drum rotation direction, and one end of one brake shoe abuts and engages with the anchor means. As a result, both brake shoes act as leading shoes, and function as a duoservo type parking brake device.

Here, in the above-described process, the abutting force when one end of one brake shoe abuts on the anchor means is separated from the anchor means by one end of the one brake shoe when the parking brake cable starts to be pulled. It depends on the distance. In this case, according to the present invention, the third urging means for urging the other end of the brake shoe toward the axial center of the backing plate is provided for each brake shoe. Therefore, each brake shoe has an initial position with respect to the backing plate. The centering action on each of them is working. Therefore, the movement of each brake shoe is restricted by the third biasing means, and the distance between the one end portion of the one brake shoe and the anchor means is shortened. Therefore, the contact load (peak load) when the one end contacts the anchor means is reduced. Therefore, at the start of pulling the parking brake cable, one brake shoe does not come into contact with the brake drum and be dragged.

In addition, as a supplementary note, if an attempt is made to cause a centering action at the initial stage of braking (when the parking brake starts to be pulled), the biasing force of the centering spring becomes too large in the conventional structure, and the brake shoe may come into contact with the brake drum. However, in the present invention, since the respective brake shoes are centered by the third urging means, the brake shoes do not come into contact with the brake drum.

Further, one end of the first urging means for urging one end portion of each brake shoe toward the anchor means side is locked to the anchor means side with respect to the connecting portion with the strut, and Since the reaction force acts on the other brake shoe via the strut, a rotational moment in the direction of being pressed against the brake drum tends to act on one end of the other brake shoe. However, in the present invention, since the other end of the second urging means is locked to the other end side of the other brake shoe with respect to the connecting portion with the strut, one end of the other brake shoe is concerned. A rotational moment acts to separate the one end from the brake drum. Therefore, when the parking brake lever is returned, the parking brake torque on one brake shoe side is easily released, and the one brake shoe is prevented from coming into contact with the brake drum and being dragged.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows the overall structure of a center brake type duo-servo type parking brake device 10. As shown in this figure, a parking brake device 10 includes a brake drum 12 having a hat-shaped cross section, which is attached to a propeller shaft (a part is shown by a chain double-dashed line).
And a backing plate 14 arranged on the opening side of the brake drum 12 and having a substantially disc shape. Through holes 16 for passing through the shaft are formed at the axial center of the backing plate 14, and mounting holes 18 are formed at four locations around the through holes 16. Backing plate 1
4 is fixed to the housing, which is a non-rotating portion, by bolting through these mounting holes 18.

On both sides of the backing plate 14 with the through hole 16 interposed therebetween, a pair of brake shoes 20, 26 are arranged so as to face each other. One of the brake shoes 20 includes a curved strip plate-shaped web 22A and the web 2A.
A curved strip-shaped rim 2 which is arranged perpendicular to the outer surface of 2A.
2B, and a lining 24 fixed to the outer surface of the rim 22B of the shoe body 22 and arranged to face the inner peripheral surface of the brake drum 12. Similarly, the other brake shoe 26
Shoe body 2 including a web 28A and a rim 28B
8 and a lining 30. The brake shoes 20, 26 are elastically and movably supported by the backing plate 14 by a well-known shoe holddown 32 at substantially the center thereof.

An anchor pin 34 as an anchor means standing upright from the backing plate 14 is arranged between the upper ends (one ends) of the brake shoes 20, 26. Further, the lower end portions (the other end portions) of the brake shoes 20, 26 are connected to each other by the adjuster device 3 as a connecting means.
6 are connected. The adjuster device 36
The axial length thereof is adjusted by rotating the adjusting wheel 36A at a predetermined timing, whereby the clearance between the linings 24, 30 and the inner peripheral surface of the brake drum 12 is adjusted. It has become so.

A parking brake lever 38 as a lever body is arranged on the back side of the web 22A of the one brake shoe 20. The parking brake lever 38 has a substantially arc surface shape, and the upper end portion of the parking brake lever 38 is pinned by the pin 40 to the web 2 of the one brake shoe 20.
It is pivotally supported by 2A. The upper end of the parking brake lever 38 and the upper end of the other brake shoe 26 are connected to each other by a parking brake link 42 as a strut.
Are linked by Further, one end of a parking brake cable 44 is connected to the lower end of the parking brake lever 38.

Further, near the upper ends (one ends) of the webs 22A, 28A of the brake shoes 20, 26, one ends of return springs 46, 48 as first biasing means, which are tension coil springs, are locked. Has been.
In addition, the locking position of one end of the return springs 46 and 48 is located above the engagement position of the brake shoes 20 and 26 with the parking brake link 42 (on the anchor pin 34 side). In addition, the return spring 4
The other ends of 6, 48 are locked to the anchor pins 34 described above, respectively. As a result, the pair of brake shoes 2
The upper ends of 0 and 26 are engageable with the anchor pin 34 by receiving a biasing force toward the anchor pin 34 side.

Further, spring engaging holes 50 and 52, which are circular holes, are formed in the upper ends of the webs 22A and 28A of the pair of brake shoes 20 and 26, respectively. The positions where the spring locking holes 50 and 52 are formed are on the lower side (adjuster device 36 side) of the position where the brake shoes 20 and 26 engage with the parking brake link 42. One spring locking hole 5
The other end of a shoe-to-shoe spring 54 as a second urging means, which is a tension coil spring, is locked to 0, and one end of the shoe-to-shoe spring 54 is engaged to the other spring locking hole 52. It has been stopped. As a result, the upper ends of the pair of brake shoes 20, 26 are
They are tension-biased toward each other.

Further, a pair of brake shoes 20, 26
Bottoms of webs 22A, 28A (rims 22B, 28B
Spring engaging portions 56 and 58 that are bent in a triangular shape in a front view are formed on the side (contacting with). The third spring locking portion 56 is a third coil spring, which is a tension coil spring.
One end of a centering spring 60 as an urging means is locked, and one end of a centering spring 62 as a third urging means, which is also a tension coil spring, is locked at the other spring locking portion 58. Has been done. The other ends of the centering springs 60 and 62 are respectively locked by spring locking walls 64 provided upright below the through holes 16 of the backing plate 14. As a result, the lower ends of the pair of brake shoes 20, 26 are tension-biased (centered) to the axial center side of the backing plate 14 (the initial position side before braking).

Next, the operation and effect of this embodiment will be described with reference to the schematic operation diagrams shown in FIGS. 2 (A) to 2 (C).

First, when the parking brake device 10 is not in operation, the parking brake lever 38 is not swinging as shown in FIG. 2A, so that the brake shoes 20 of both brake springs 20 are urged by the return springs 46 and 48. , 26 are engaged with anchor pins 34 at their upper ends. Therefore, in this state, the brake shoes 20, 26
Are separated from the inner peripheral surface of the brake drum 12.

Next, when the parking brake device 10 is operated from this state, the parking brake cable 4 is
4 is pulled to the left in the state shown in FIG. Therefore, the parking brake lever 38 swings around the pin 40 toward the other brake shoe 26 side. Therefore, when the parking brake is applied (beginning of operation),
As shown in FIG. 2B, one brake shoe 20
The upper end of the anchor pin 3 receives the pressing force B in the expansion direction and the anchor pin 3
4 and is pressed against the inner peripheral surface of the brake drum 12. Along with this, from the lower end portion of one brake shoe 20 via the adjuster device 36 to the other brake shoe 2
A pressing force C in the direction opposite to the drum rotation direction (the direction opposite to the arrow A direction) acts on the lower end of 6. As a result, the upper end of the other brake shoe 26 contacts the anchor pin 34.

However, since the direction of rotation of the brake drum 12 is in the direction of arrow A, both brake shoes 20 and the other brake shoe 26 are dragged by this rotation and both rotate in the direction of drum rotation, and one brake shoe is rotated. The upper end of 20 contacts the anchor pin 34 (the contact force at this time is shown by arrow D). Along with this, with the adjuster device 36 as a fulcrum, the other brake shoe 26
A rotational force E in the expansion direction acts on the lower end portion of 0, and the other brake shoe 26 is also pressed against the inner peripheral surface of the brake drum 12 by this rotational force E. As a result, the one brake shoe 20 and the other brake shoe 26 both act as leading shoes when torque is generated, and a servo force is obtained, thus functioning as a duo-servo type parking brake device 10.

The contact force D when the upper end of one brake shoe 20 contacts the anchor pin 34 in the above-mentioned process is determined by the anchor pin of the upper end of the one brake shoe 20 when the parking brake cable 44 starts to be pulled. Separation distance a from 34 (and swing distance b of the parking brake lever 38 depending on the separation distance a)
Depends on In this case, in this embodiment, the lower ends of the brake shoes 20 and 26 are attached to the backing plate 1.
Centering springs 60, 6 that urge the shaft 4 toward the axis
2 is provided for each brake shoe 20, 26, the backing plate 14 is attached to each brake shoe 20, 26.
The centering action to the initial position of is working respectively. Therefore, the movements of the brake shoes 20 and 26 are restricted even when the parking brake device 10 is operated by the centering springs 60 and 62, and the movement from the anchor pin 34 at the upper end portion of the one brake shoe 20 described above is restricted. The separation distance a (and the swing distance b of the parking brake lever 38) becomes shorter. Therefore, the contact load D (peak load) when the upper end of one brake shoe 20 contacts the anchor pin 34 is reduced. Therefore, when the parking brake cable 44 starts to be pulled, the lining 24 of the one brake shoe 20 does not come into contact with the inner peripheral surface of the brake drum 12 and be dragged.

Further, as shown in FIG. 3, one end of the return springs 46 and 48 (in particular, the return spring 46) for urging the upper ends of the brake shoes 20 and 26 toward the anchor pin 34 has a parking brake. It is locked to the anchor pin 34 side rather than the connection part with the link 42, and the urging force F ₁ acts toward the anchor pin 34 side, and the parking brake link 42 is provided to the other brake shoe 26. Since the reaction force F ₂ acts on the other brake shoe 26, a rotational moment (clockwise moment in FIG. 3) in the direction in which it is pressed against the brake drum 12 tends to act on the upper end portion of the other brake shoe 26. However, in the present embodiment, one end of the shoe toe spring 54 is locked to a lower side (adjuster device 36 side) of the other brake shoe 26 with respect to the connection portion with the parking brake link 42, and one brake shoe 26 is locked. The urging force F ₃ is acting toward the 20 side, and this shoe toe spring 5
The urging force F _{3 of} 4 is the urging force F _{1 of the} return spring 46.
Therefore, a counterclockwise rotational moment M ₁ in the direction of separating the upper end of the other brake shoe 26 from the inner peripheral surface of the brake drum 12 acts on the upper end of the other brake shoe 26. For this reason, when the parking brake lever 38 is returned, the other brake shoe 2 that has been operated by the conventional structure.
The pressing force G (see FIG. 7) that tries to press the lower end of 6 to the inner peripheral surface of the brake drum 12 is not generated. Therefore, the pressing force I input from the lower end of the other brake shoe 26 to the lower end of the one brake shoe 20 via the adjuster device 36 is small, and the parking brake torque in the one brake shoe 20 is easily released. . As a result, the one brake shoe 20 and the other brake shoe 26 (in particular, the one brake shoe 20) do not come into contact with the inner peripheral surface of the brake drum 12 and are dragged.

As described above, in this embodiment, the centering springs 60, 62 for reducing the distance a (the swing distance b of the parking brake lever 38) from the anchor pin 34 at the upper end of the one brake shoe 20 are braked. While tensioning each shoe 20, 26,
Connect the upper end of the other brake shoe 26 to the brake drum 1
Since the shoe-to-shoe spring 54 that generates the rotation moment M ₁ in the direction away from the inner peripheral surface of 2 is stretched, both when the parking brake cable is pulled and when the parking brake lever is returned.
It is possible to prevent the brake shoes 20 and 26 from being dragged, and thus to completely prevent the occurrence of brake judder.

In the parking brake device 10 of this embodiment, the parking brake lever 38 is configured to expand first from the side of the brake shoe 20 on which the parking brake lever 38 is pivotally supported, as in the conventional case. The problem of loosening of the device 10 also does not occur. That is, when the rotation direction of the brake drum 12 is the arrow A direction, the parking brake cable 44 is tightened by expanding the parking brake lever 38 first from the side of the brake shoe 20 on which the parking brake lever 38 is pivotally supported. This will prevent loosening.

Further, although the center brake type parking brake device 10 has been described as an example in the present embodiment,
The present invention is not limited to this, and the present invention may be applied to a wheel-type parking brake device.

[0039]

As described above, in the duoservo type parking brake device according to the present invention, one end of the parking brake device is locked to one brake shoe and the other end is connected to the strut of the other brake shoe. Second urging means that is locked to the other end side of the other brake shoe and urges both brake shoes toward each other, and one end of the second shoe is more than the connecting portion of the brake shoe with the strut. A third biasing means that locks the other end of each of the brake shoes toward the axial center of the backing plate and locks the other end of the brake shoe toward the axial center of the backing plate. Since it has, the brake shoe contacts the brake drum both when the parking brake cable is pulled and when the parking brake lever is returned. It can be prevented, thereby having an excellent effect of the generation of the brake judder can be completely prevented.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing a center brake type and duo servo type parking brake device according to an embodiment.

FIG. 2 is a schematic operation diagram for explaining an operation of the parking brake device shown in FIG. 1 in relation to a centering spring.

FIG. 3 is a schematic operation diagram for explaining an operation of the parking brake device shown in FIG. 1 in relation to shoe-to-shoe springs.

FIG. 4 is an overall configuration diagram of a parking brake device according to a conventional example.

FIG. 5 is a schematic operation diagram corresponding to FIG. 2 for explaining a mechanism in which a brake judder occurs.

FIG. 6 is a graph showing that a relatively large peak torque is generated at the beginning of the parking brake.

FIG. 7 is a schematic operation diagram corresponding to FIG. 3 for explaining a mechanism in which a brake judder occurs.

[Explanation of symbols]

10 parking brake device 12 brake drum 20 brake shoe (one brake shoe) 26 brake shoe (other brake shoe) 34 anchor pin (anchor means) 36 adjuster device (coupling means) 38 parking brake lever (lever body) 42 parking brake link (Strut) 44 Parking brake cable 46 Return spring (first biasing means) 48 Return spring (first biasing means) 54 Shu-to-shoe spring (second biasing means) 60 Centering spring (third biasing) 62) Centering spring (third urging means)

Claims (1)

[Claims] 1. A backing plate fixed to a non-rotating portion of a vehicle, and a pair of brake shoes movably held by the backing plate and arranged to face an inner peripheral surface of a brake drum. Anchor means arranged between the one ends of the brake shoes and engageable with the one ends, a connecting means for connecting the other ends of these brake shoes, and one end swingable to one brake shoe. Connected,
A duo-servo type parking brake device including a lever body having a parking brake cable fixed to the other end, and a strut connecting one end of this lever body and one end of the other brake shoe. One end of the brake shoe is locked to the anchor means side of the connecting part with the strut and the other end of the brake shoe is locked to the anchor means. One biasing means and one end is locked to one brake shoe, and the other end is locked to the other end side of the other brake shoe with respect to the connecting part of the other brake shoe with the strut. Second urging means for urging the brake shoes of the brake shoe toward each other and one end of the brake shoe is connected to the strut. The other end with locked to the other end side is locked to the shaft center side of the backing plate, the third to urge respective other ends of the brake shoes on the shaft center side of the backing plate
A duo-servo type parking brake device, comprising: