JP3909254B2 - Drum brake device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent generation of a dragging due to an imperfect return of a brake shoe upon releasing a brake in a drum brake device having a shoe driving cam capable of controlling a braking force in accordance with the force of the brake. <P>SOLUTION: The drum brake device has the shoe driving cam for mechanically controlling the braking force in accordance with the force of the brake acting on an anchor pin from the brake shoe. A cam pin provided on a cam plate and pressing the brake shoe in accordance with rotation of the cam plate freely rotates on the cam plate. Contact surface of the cam pin and the brake shoe is set on a flat surface. <P>COPYRIGHT: (C)2003,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a drum brake device that can control the pressing force of the brake shoe to the drum according to the braking force to ensure high effectiveness and stability of the brake, and is also suitable for electrification of the brake device. Specifically, the present invention relates to an improvement for preventing dragging due to a return failure of a pair of brake shoes when releasing the brake.
[0002]
[Prior art]
Conventionally, various types of drum brake devices have been used to brake the running of the vehicle, but these drum brake devices are arranged according to the arrangement of brake shoes pressed against the inner peripheral surface of a substantially cylindrical drum. It is classified as a reading trailing type, a two reading type, or a duo servo type.
[0003]
A duo-servo type drum brake device generally includes a pair of brake shoes of a primary shoe and a secondary shoe disposed in a cylindrical drum so as to face each other.
In the primary shoe, the forward rotation direction inlet side of the drum serves as an input portion, and the forward rotation direction outlet side of the drum is connected to the inlet side of the secondary shoe via an adjuster, for example. On the other hand, the outlet side of the secondary shoe is brought into contact with an anchor portion mounted on the backing plate, and the brake force (braking torque) acting on the primary shoe and the secondary shoe is received by the anchor portion.
[0004]
As a result, when the primary shoe and the secondary shoe are expanded and pressed against the inner peripheral surface of the drum, the braking force acting on the primary shoe is input to the inlet side of the secondary shoe so that the secondary shoe is pressed against the inner peripheral surface of the drum. Therefore, the self-servo action acts on both the primary shoe and the secondary shoe, and a braking force with a very high gain can be obtained.
[0005]
The above-mentioned duo-servo type drum brake device not only can obtain extremely high braking force, but also is easy to miniaturize and incorporates a parking brake as compared with a leading trailing type or two-leading type drum brake device. It has many advantages such as being easy.
However, such a duo-servo drum brake device is sensitive to changes in the friction coefficient of the brake shoe lining, and therefore tends to be difficult to stabilize the braking force, and a device for stabilizing the braking force is required. .
[0006]
Also, recent brake devices for vehicles are equipped with an anti-lock brake system to make the brake function intelligent and to deal with electric vehicles (EV vehicles) suitable for reducing environmental pollution. Electrification is also an important issue.
[0007]
Against this background, the applicant of the present application has expanded the pair of brake shoes according to the shoe operating force transmitted from the operating force generating means to the input lever during service braking as a shoe drive mechanism for expanding the brake shoes during braking. A link mechanism that opens and presses against the drum, and applies a braking limiting force to the input lever in a direction that reduces the action of the shoe operating force when the braking force acting on the anchor pin during braking reaches a predetermined magnification with respect to the shoe operating force. Have already proposed.
By using such a link mechanism, it is possible to stabilize the braking force in the duo-servo type drum brake device, and in addition to the conventional hydraulic wheel cylinder as an operation force generating means, an electric motor, etc. The brake device could be easily electrified simply by adopting the electric operating force generating means utilizing the power.
[0008]
[Problems to be solved by the invention]
By the way, in the drum brake device, in general, each brake shoe is returned when the brake is released by a tensile force by a shoe return spring. In the conventional case, the shoe return spring is stretched between the anchor pin and a position away from the anchor pin on the brake shoe web by a predetermined distance.
[0009]
However, at the time of braking, the anchor pin end of the brake shoe on the input side is displaced to the outer drum side from the anchor pin mounting position due to the diameter expanding operation, and from the line of action of the return force of the shoe return spring. It will come off.
Therefore, when the brake is released, in order to accurately return the end of the brake shoe on the input side to the anchor pin, a rotational force that directs the end of the brake shoe toward the anchor pin is required, and a linear tensile force by the shoe return spring is required. Therefore, it is difficult to accurately return to the anchor pin, and there is a possibility that the brake shoe may be dragged due to a return failure or the like.
[0010]
In addition, when a link mechanism is used as a shoe drive mechanism, depending on the form of the contact portion between the brake mechanism and the mechanism member on the link mechanism side that expands the brake shoe, the end of the brake shoe may be biased during braking operation. There is a risk that the load will act, preventing the brake shoe from returning when the brake is released, and dragging the brake shoe in the same manner.
[0011]
The present invention has been made in view of the above circumstances, and its object is to control the braking force according to the braking force, to ensure a stable effect of the brake, and to ensure the return of the brake shoe when the brake is released. An object of the present invention is to provide a highly reliable drum brake device that does not cause dragging of the brake shoe due to a return failure.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a drum brake device according to the present invention includes a pair of brake shoes disposed opposite to each other in a drum, and an anchor pin provided upright on a backing plate at one opposed end side of the pair of brake shoes. And an operation force generating means for generating a shoe operation force in response to a braking operation, a cam plate rotatable around the anchor pin, and a cam pin supported by the cam plate and abutting against an end of each brake shoe. A shoe drive cam, the cam plate rotates around the anchor pin in response to the shoe operating force of the operating force generating means, and the brake shoe is expanded via the cam pin. Direction in which the cam plate reduces the action of the shoe operating force according to the braking force acting on the cam plate via the cam pin In a drum brake device which rotates to control the braking force,
Each cam pin is rotatably mounted on the cam plate, and the contact surface of each cam pin with each brake shoe is set to a flat surface that allows sliding displacement in the radial direction of the drum at the end of each brake shoe. It is characterized by that.
[0013]
In the drum brake device configured as described above, at the time of braking operation, the cam plate of the shoe drive cam that receives the shoe operating force output from the operating force generating means rotates around the anchor pin, and with the rotation of this cam plate, Each cam pin on the cam plate expands each brake shoe to generate a braking force. During braking, the cam plate rotates in a direction that reduces the action of the shoe operating force according to the braking force acting on the cam pin from the brake shoe on the output side, thereby limiting the braking force.
[0014]
Each cam pin on the shoe drive cam that presses the end of each brake shoe to the drum side during braking has a flat contact surface with the end of the brake shoe and is rotatably mounted on the cam plate. Therefore, the end portion of the brake shoe can freely slide and displace in the diameter increasing direction or the diameter decreasing direction during the diameter increasing operation or the diameter reducing operation of the brake shoe.
Therefore, during braking, the anchor pin end of the brake shoe on the input side is displaced to the drum side outward from the anchor pin mounting position due to the diameter expanding operation, and is disengaged from the line of return force of the shoe return spring. However, the eccentric load that hinders the movement of the brake shoe does not act between the cam pin that presses the brake shoe against the drum and the end of the brake shoe. Only by force, the end of the brake shoe can be quickly returned to the initial position by following the movement of the cam pin.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of a drum brake device according to the invention will be described in detail with reference to the drawings.
FIG. 1 is a front view showing a first embodiment of a drum brake device according to the present invention.
The drum brake device 1 according to the first embodiment is a so-called duo-servo type drum brake device, and is a pair of a primary shoe 3 and a secondary shoe 4 that are arranged opposite to each other in a substantially cylindrical drum inner space (not shown). Brake shoes 3, 4 and a pair of brake shoes 3, 4 are arranged on opposite sides of the pair of brake shoes 3, 4 to generate a shoe operating force for pressing the brake shoes 3, 4 against the drum when operating the service brake Operating force generating means 6 for transmitting the shoe, and a shoe driving cam 7 which is a shoe driving mechanism for transmitting the shoe operating force generated by the operating force generating means 6 to each of the brake shoes 3 and 4 to expand the brake shoes 3 and 4 And an adjuster which is disposed between the other opposing ends of the brake shoes 3 and 4 and also serves as a link function for inputting the output of the primary shoe 3 to the secondary shoe 4 Knit 8, and a anchor pin 10 provided upright on a backing plate for supporting these components.
[0016]
In FIG. 1, illustration of the backing plate and the drum is omitted. Also, a shoe return spring that urges the ends of the brake shoes 3 and 4 toward each other, a mechanism that drives the adjuster unit 8, and the like are not shown.
A drum (not shown) is concentric with the backing plate and rotates in the direction of arrow R in FIG. 1 when the vehicle moves forward.
[0017]
The brake shoes 3 and 4 are attached to the backing plate by a shoe hold-down device (not shown) so as to be movable toward the inner periphery of the drum. The end portions of the brake shoes 3 and 4 on the side of the operating force generating means 6 are biased in directions toward each other (that is, directions away from the drum) via shoe return springs.
Further, the ends of the brake shoes 3 and 4 on the side of the adjuster unit 8 are also urged so as to be maintained in contact with the ends of the adjuster unit 8 by the urging force of a shoe-to-shoe spring (not shown). Has been.
[0018]
In the case of the present embodiment, as shown in FIG. 4, the operating force generating means 6 causes the output rod 6a to advance in the direction of the arrow (A) in response to a brake operation such as a brake pedal for service brakes, thereby operating the shoe. It is a wheel cylinder that outputs a pressing force with a force W.
[0019]
The adjuster unit 8 originally adjusts the distance between the ends of the brake shoes 3 and 4 according to the progress of the lining wear of the brake shoes 3 and 4. The adjustment gear 8a is rotated by rotation of an adjuster lever that rotates in accordance with the amount of displacement of 4, and the interval between the ends of the brake shoes 3 and 4 is automatically adjusted.
[0020]
As shown in FIGS. 2 to 4, the shoe drive cam 7 of the present embodiment is brought into contact with the end of the primary shoe 3 on a cam plate 76 that is rotatably supported by the anchor pin 10 by a pin fitting hole 76a. Primary cam pin 21 as a shoe engaging cam portion that contacts, secondary cam pin 23 as a shoe engagement cam portion that contacts the end of secondary shoe 4, and an input receiving portion that receives shoe operating force W from operating force generating means 6 The input pin 25 is provided.
[0021]
The primary cam pin 21 and the secondary cam pin 23 are disposed at a position radially outside the drum, and a secondary cam pin 23 is positioned radially inside the drum, with the anchor pin 10 interposed therebetween.
As shown in FIG. 4, the input pin 25 is arranged at an end position that is further away from the secondary cam pin 23 toward the radially inner side.
[0022]
The shoe drive cam 7 receives the shoe operating force W of the operating force generating means 6 at the input pin 25, thereby causing the cam plate 76 to rotate counterclockwise in the figure, and the cam pins 21, 23 on the cam plate 76. The brake shoes 3 and 4 are expanded via the brakes to generate a braking force. At the time of braking, the brake force Fa acting on the cam plate 76 from the output side brake shoe (secondary shoe 4 at the time of forward braking, primary shoe 3 at the time of reverse braking) via the cam pin is used, The braking force is controlled by applying a rotational moment M ₃ in the direction in which the action of the shoe operating force is reduced (ie, clockwise) to the cam plate 76.
[0023]
In the shoe drive cam 7, when the distance between the input pin 25 and the anchor pin 10 is L ₁ and the shoe operating force input from the operating force generating means 6 is W, the counterclockwise working on the cam plate 76 by the shoe operating force W is applied. The rotational moment M _{1 in the} direction is
M ₁ = W × L ₁ (1)
It is.
Further, when the force with which the primary cam pin 21 presses the primary shoe 3 against the drum is F ₀ and the separation distance between the anchor pin 10 and the primary cam pin 21 is L ₂ , the reaction force from the primary shoe 3 acts on the cam plate 76. Rotational moment M ₂
M ₂ = F ₀ × L ₂ (2)
It is.
[0024]
Further, in the forward braking shown in FIG. 4, when the braking force acting on the cam plate 76 from the secondary shoe 4 via the secondary cam pin 23 is Fa, and the separation distance between the secondary cam pin 23 and the anchor pin 10 is s, The clockwise rotational moment M ₃ acting on the cam plate 76 by the braking force Fa acting on the plate 76 is M ₃ = Fa × s (3)
It is.
The shoe drive cam 7 controls the braking force so that the rotational moments shown in (1) to (3) are balanced.
[0025]
Shoe drive cam 7 of the present embodiment, FIG. 3 and FIG. 4, each cam pin 21, 23 of the well as equipped rotatably cam plate 76, the brake shoes 3 of the cam pins 21, 23 , 4 are set to flat surfaces 21a, 23a that allow sliding displacement in the radial direction of the drum at the ends of the brake shoes 3, 4 respectively.
[0026]
In the case of the present embodiment, the contact surfaces 3d and 4d of the brake shoes 3 and 4 that contact the flat surfaces 21a and 23a of the cam pins 21 and 23 are also finished to be flat surfaces. The drum brake device 1 according to the present embodiment mainly stabilizes the braking force at the time of forward braking, and increases the diameter of the primary shoe 3 (ie, displacement toward the inner surface of the drum) during forward braking. ), The contact surface 3e of the primary shoe 3 with respect to the anchor pin 10 is set to an arc surface circumscribing the anchor pin 10 on the circumference centered on the primary cam pin 21. This is to increase the degree of freedom of displacement toward the inner surface of the drum when the primary shoe 3 is expanded in diameter so that it can be easily detached from the anchor pin 10.
[0027]
Furthermore, in the present embodiment, a spring 27 that sets an initial position between the secondary shoe 4 and the secondary cam pin 23 is provided at the end of the secondary shoe 4.
This spring 27 biases the secondary cam pin 23 that is in contact with the flat contact surface 4d of the secondary shoe 4 toward the bulging portion 4f provided at one end of the contact surface 4d, thereby causing unnecessary slipping in the initial stage. This prevents this and stabilizes the behavior of the brake shoe 4 during braking.
[0028]
In the drum brake device 1 described above, during the braking operation, the cam plate 76 of the shoe drive cam 7 that receives the shoe operating force W output from the operating force generating means 6 rotates around the anchor pin 10, and the cam plate 76 With rotation, the cam pins 21 and 23 on the cam plate 76 expand the brake shoes 3 and 4 to generate a braking force. During braking, the braking force Fa acting on the cam pin 23 from the brake shoe 4 on the output side generates a rotational moment M ₃ in a direction that reduces the rotation of the cam plate 76 due to the shoe operating force W, thereby limiting the braking force. Therefore, stable braking effectiveness can be ensured.
[0029]
The shoe drive cam 7 is disposed between the operating force generating means 6 and the brake shoes 3 and 4 and mechanically controls the braking force. Therefore, the operating force generating means 6 is a conventional hydraulic type. Not only hydraulic actuators such as wheel cylinders but also electric actuators such as electric motors can be used, and it is possible to easily perform electrification for the purpose of intelligent brake functions and hybrid vehicles.
[0030]
Further, the cam pins 21 and 23 on the shoe drive cam 7 that press the end portions of the brake shoes 3 and 4 to the drum side during braking are set on the flat surfaces 21a and 23a so that the cam pins 21 and 23 are in contact with the brake shoe end portions. At the same time, since the cam plate 76 is rotatably mounted, the end portions of the brake shoes 3 and 4 can be freely expanded or reduced when the brake shoes 3 and 4 are expanded or contracted. Slip displacement is possible.
Therefore, at the time of braking, the end portion on the anchor pin 10 side of the brake shoe 3 on the input side is displaced to the drum side outside the mounting position of the anchor pin 10 by the diameter expanding operation, and the return force of the shoe return spring is applied. Even if the brake shoe 3 deviates from the line, an unbalanced load that hinders the movement operation of the brake shoe 3 does not act between the cam pin 21 pressing the brake shoe 3 against the drum and the end of the brake shoe 3. Thus, it becomes possible to quickly return the end of the brake shoe 3 to the initial position by following the movement of the cam pin 21 only with the return force of the conventional shoe return spring, and the drag caused by the return failure of the brake shoe 3 can be prevented. Occurrence can be eliminated.
[0031]
FIG. 5 is an enlarged front view of the main part of the second embodiment of the drum brake device according to the present invention.
The shoe drive cam 70 of the drum brake device 100 shown here uses a spring 29 instead of the spring 27 shown in the first embodiment, and the other configuration is the same as that of the first embodiment. It is the same. About the structure similar to 1st Embodiment, description is abbreviate | omitted by attaching | subjecting the same number.
The spring 29 used in the drum brake device 100 of the second embodiment includes a first urging portion 29a for setting an initial position of the secondary cam pin 23 on the contact surface 4d of the secondary shoe 4, and a primary The leaf spring integrally formed with the second urging portion 29b for urging the shoe 3 to set the initial position of the primary cam pin 21 on the contact surface 3d. The cam pins 21 and 23 can be positioned with respect to the brake shoes 3 and 4.
[0032]
FIG. 6 is a front view of the main part of the third embodiment of the drum brake device according to the present invention.
The shoe drive cam 71 of the drum brake device 200 shown here is an improvement on a part of the first embodiment, and a flat surface 11a is formed on the outer periphery instead of the anchor pin 10 shown in the first embodiment. The anchor pin 11 is used, and the primary shoe 3 is formed with a flat anchor engaging portion 3g that slidably contacts the flat surface 11a.
The flat surface 11a functions as a positioning surface for determining the initial position of the primary shoe 3, and at the same time, when the primary shoe 3 is expanded or contracted, the primary shoe 3 can slide on the flat surface 11a to obtain a smooth behavior. I am doing so.
[0033]
In the present invention, the specific form of the spring for setting the initial contact position between the cam pin and the brake shoe is not limited to that of each of the above embodiments. When the brake shoe is enlarged or reduced in diameter, the end of the brake shoe can be smoothly rotated around the cam pin to prevent a return failure or the like, so that the design can be changed as appropriate.
[0034]
【The invention's effect】
As described above, according to the drum brake device of the present invention described in claim 1, the cam plate of the shoe drive cam that receives the shoe operating force output from the operating force generating means moves around the anchor pin during the braking operation. As the cam plate rotates, each cam pin on the cam plate expands each brake shoe to generate a braking force. During braking, the braking force that acts on the cam pin from the brake shoe on the output side generates a rotational moment in a direction that reduces the rotation of the cam plate due to the shoe operating force, thereby limiting the braking force. Can be secured.
[0035]
Further, since the shoe drive cam is disposed between the operating force generating means and each brake shoe and mechanically controls the braking force, the operating force generating means is a hydraulic type such as a conventional hydraulic wheel cylinder. In addition to this actuator, an electric actuator such as an electric motor can be used, and it is possible to easily perform electrification for making the brake function intelligent or making the vehicle hybrid.
[0036]
In addition, each cam pin on the shoe drive cam that presses the end of each brake shoe toward the drum side during braking has a flat contact surface with the brake shoe end and is rotatably mounted on the cam plate. Therefore, the end portion of the brake shoe can freely slide and displace in the diameter increasing direction or the diameter decreasing direction during the diameter increasing operation or the diameter reducing operation of the brake shoe.
Therefore, during braking, the anchor pin end of the brake shoe on the input side is displaced to the drum side having a larger diameter than the anchor pin mounting position due to the diameter expanding operation, so that it deviates from the line of action of the return force of the shoe return spring. Even when the brake shoe is released, an unbalanced load that hinders the movement of the brake shoe does not act between the cam pin that presses the brake shoe against the drum and the end of the brake shoe. Even with the return force alone, the end of the brake shoe can be quickly returned to the initial position by following the movement of the cam pin, and the occurrence of drag due to the return failure of the brake shoe can be eliminated.
[Brief description of the drawings]
FIG. 1 is a front view of a main part of a first embodiment of a drum brake device according to the present invention.
FIG. 2 is a front view of the shoe drive cam shown in FIG.
3 is a perspective view of the shoe drive cam shown in FIG. 1. FIG. FIG.
4 is an enlarged front view showing an acting force during forward braking of the shoe drive cam shown in FIG. 1. FIG.
FIG. 5 is an enlarged front view of a main part of a second embodiment of the drum brake device according to the present invention.
FIG. 6 is a front view of an essential part of a third embodiment of a drum brake device according to the present invention.
[Explanation of symbols]
1 Drum brake device 3 Primary shoe (brake shoe)
3d Contact surface 4 Secondary shoe (brake shoe)
4d Contact surface 6 Operating force generating means (wheel cylinder)
7 Shoe drive cam (Shoe drive mechanism)
8 Adjuster unit 10 Anchor pin 11 Anchor pin 11a Flat surface 21 Primary cam pin (cam pin)
21a Flat surface 23 Secondary cam pin (cam pin)
23a flat surface 25 input pin 27 spring 29 spring 29a first biasing portion 29b second biasing portion 70, 71 shoe drive cam 76 cam plate 100 drum brake device 200 drum brake device

Claims (1)

A pair of brake shoes arranged opposite to each other in the drum, an anchor pin erected on the backing plate on one opposite end side of the pair of brake shoes, and an operation force generation that generates a shoe operation force according to the braking operation And a shoe drive cam having a cam plate rotatable around the anchor pin and a cam pin supported by the cam plate and abutting against an end portion of each brake shoe. The cam plate rotates around the anchor pin to expand the brake shoe via the cam pin, and at the time of braking according to the braking force acting on the cam plate from the brake shoe via the cam pin In the drum brake device in which the cam plate rotates in a direction to reduce the action of the shoe operating force to control the braking force,
Each cam pin is rotatably mounted on the cam plate, and the contact surface of each cam pin with each brake shoe is set to a flat surface that allows sliding displacement in the radial direction of the drum at the end of each brake shoe. A drum brake device characterized by that.

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