JPH112260A - Drum brake device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve stability of the effect of a brake, in a duo-servo type drum brake device. SOLUTION: A wheel cylinder to spread a distance between the opposed ends of one of a pair of brake shoes comprises a pressure chamber for driving a drive piston abutted the end part of each brake shoe, by a fed liquid pressure, a control piston 22 in which a flow passage 18 communicated with the pressure chamber is formed, a valve element 20 to close the flow passage 18 and bring the pressure chamber into a sealed state when an anchor reaction force reaches a given magnification and the control piston 22 is pushed back in a control chamber 16 and a seal member 52 being arranged in a gap provided at the periphery of the control piston 22 and escaping hydraulic fluid in the pressure chamber to the control chamber 16 when a hydraulic pressure in the control chamber 16 is reduced to a value lower than a hydraulic pressure in the pressure chamber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drum brake device mounted on a vehicle or the like, and more particularly, to an improvement of a duo-servo type drum brake device.

[0002]

2. Description of the Related Art A drum brake device used for a vehicle or the like generally includes an input portion (wheel cylinder), a brake shoe that expands in a drum by a force from the input portion to generate a braking force, and a brake shoe. And an anchor portion for supporting the above. And the input part is the entrance side and the anchor part is the exit side with respect to the forward direction of the drum.
The one whose input section is on the exit side is called a trailing shoe.

[0003] As the conventional drum brake device, there are used types such as a leading trailing type, a two-leading type, and a duo-servo type. In the leading trailing type, a wheel cylinder for expanding the shoe is arranged between one opposed end of a pair of opposed shoes, and an anchor portion is arranged at each other shoe end, so that the leading shoe and the trailing shoe are arranged. And is incorporated.

The two-leading type has a structure in which two leading shoes are incorporated. Among them, the single-acting type (TP1W) has a high gain when moving forward and becomes a two-trailing type when moving backward so as to be relatively driven. The gain is lower than when moving forward. Two-leading double-acting type (T
P2W) has a high gain with the same effect in forward and backward movement. The duo-servo system is a high-gain brake that links two shoes and uses the braking force generated in the primary shoe as an input to the secondary shoe, and has the same effect in forward and backward traveling.

[0005]

However, the above-mentioned two-leading type has a problem in that it requires two wheel cylinders, so that it is expensive and the mechanism of the parking brake becomes complicated. On the other hand, the duo-servo type has many advantages over the leading trailing type and the two-leading type in that extremely high braking efficiency is obtained, it is easy to miniaturize, and it is easy to incorporate a parking brake. On the other hand, on the other hand, there is a serious drawback in that, for example, the lining friction coefficient of the brake shoe and the contact state of the rotating drum are sensitive to the change of the braking effect, and a stable braking characteristic cannot be obtained.

On the other hand, the above-mentioned leading trailing type is superior in stability to the former two, and is easy to incorporate a parking brake. Therefore, in recent years, drum brake devices have become mainstream. But,
In the leading trailing type, the braking effect is low, and in order to compensate for it, it was necessary to enlarge the booster of the master cylinder or increase the drum diameter, making it difficult to downsize the drum brake device .

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a drum brake device having a high braking effect, excellent stability of the braking effect, and easy to incorporate a parking brake. Another object of the present invention is to reduce the size and cost of the brake system by realizing the miniaturization of the booster and the like of the master cylinder.

[0008]

A drum brake device according to the present invention for achieving the above object has a pair of brake shoes, a primary shoe and a secondary shoe, which are disposed opposite to each other in a cylindrical drum space. And a wheel cylinder disposed between one opposed ends of the pair of brake shoes, wherein the wheel cylinders move the brake shoes to a drum by hydraulic pressure supplied to a pressure chamber. A drive piston that presses and a cylindrical shape with the axis lined in the drum axis direction,
An anchor pin sandwiched between the drive piston and an end of the brake shoe to function as a pressing force transmitting means between the drive piston and the end of the brake shoe; and a master cylinder spaced from the pressure chamber. A control chamber communicating with the control chamber, and a base end side is arranged facing the control chamber so as to be arranged in parallel with the drive piston, and the control chamber and the pressure chamber are provided on a base end face facing the control chamber. A control piston in which a flow path for communicating with the control piston is provided, and a reaction force receiving portion which is provided at one end side and which is located at the tip end side of the drive piston and receives an anchor reaction force from the brake shoe via an anchor pin is provided. On the other end side, a reaction force output portion is provided which is in contact with the tip of the control piston, and reduces the anchor reaction force transmitted from the brake shoe to the drive piston at a predetermined ratio to reduce the reaction force. A lever member that acts on the distal end of the control piston, and a pressure passage that is pressed into contact with a flow path that is opened at the base end surface of the control piston when the control piston is pushed into the control chamber by the pressing force of the lever member. A valve body elastically supported in the control chamber, the control piston, and an inner wall of a cylinder body that slidably holds the control piston, so as to block the flow of the hydraulic fluid into the pressure chamber by closing the valve. When the hydraulic pressure in the control chamber acting on the other end side is lower than the hydraulic pressure on the pressure chamber side acting on one end side, the hydraulic fluid on the pressure chamber side is sent to the control chamber side. And a seal member to escape.

According to the above configuration, when not in operation, the valve body elastically supported in the control chamber opens the flow passage formed in the control piston, and the pressure chamber and the control chamber communicate with each other. In this state, when the hydraulic pressure is supplied from the master cylinder by the brake operation, the hydraulic pressure is immediately supplied to the pressure chamber. When the hydraulic pressure from the master cylinder is supplied to the pressure chamber via the control chamber and the flow path on the control piston by the brake operation, the drive piston is pushed out of the pressure chamber, and the primary shoe and the secondary shoe are moved. The end is pressed through the anchor pin.

Each of the brake shoes, the ends of which are pressed by the drive piston, expands and is pressed against the drum to generate a braking force. At the time of braking, an anchor reaction force having a magnitude corresponding to the braking effect is transmitted from the secondary shoe to the drive piston via the anchor pin. Then, when the braking effect increases and the anchor pin is pushed back by a certain amount or more due to the anchor reaction force, the anchor pin presses not only the driving piston but also one end of the lever member.

The anchor reaction force transmitted to the lever member acts as a force for pushing back the advanced control piston by the hydraulic pressure of the master cylinder, and acts on the control piston. Therefore, when the anchor reaction force reaches a predetermined magnification with respect to the input from the master cylinder, the control piston is pushed back into the control chamber by the anchor reaction force acting on the control piston via the lever member.

The control piston pushed back into the control chamber by the anchor reaction force closes the flow path communicating with the pressure chamber by the valve body elastically contacting the flow path opened at the base end thereof. Is kept in a closed state, and the hydraulic pressure in the pressure chamber acting on the drive piston is kept constant. When the braking efficiency is reduced under the braking condition in which the pressure chamber is sealed as described above, the anchor reaction force acting on the control piston via the lever member is weakened, and the control piston is controlled by the hydraulic pressure from the master cylinder. Is again pushed out in the advance direction, the blockage of the flow path by the valve body is released, and the supply of the hydraulic pressure from the control chamber to the pressure chamber via the flow path on the control piston is resumed. As described above, since the control piston controls the supply of the hydraulic pressure to the pressure chamber in accordance with the anchor reaction force, the wheel cylinder must stably receive the anchor reaction force of a fixed magnification with respect to the input from the master cylinder. Becomes possible.

Further, when the flow path of the control piston is closed by the valve body and the pressure chamber is in a closed hydraulic pressure holding state,
If the hydraulic pressure in the pressure chamber rises due to some factor (for example, drum runout), and the driving piston presses the brake shoe more, the effect of the brake increases, and the so-called fluctuation of the effect of the brake increases. Occur. However, in the wheel cylinder of the present invention, when the flow path of the control piston is closed by the valve body and the pressure chamber is in a closed hydraulic pressure holding state, the hydraulic pressure in the pressure chamber increases due to some factors, When the hydraulic pressure of the control chamber becomes higher than the hydraulic pressure of the control chamber, the seal member provided in the gap around the control piston allows the hydraulic fluid in the pressure chamber to escape to the control chamber side and suppresses the rise in the hydraulic pressure in the pressure chamber. To reduce fluctuations in brake effectiveness.

Further, when the flow path of the control piston is closed by the valve body and the pressure chamber is in a closed hydraulic pressure state,
Even when the brake operation is released and the supply of hydraulic pressure from the master cylinder to the control chamber is released, the hydraulic pressure in the pressure chamber becomes relatively higher than the hydraulic pressure in the control chamber. The seal member provided in the gap of (2) allows the hydraulic fluid in the pressure chamber to escape to the control chamber side, and lowers the hydraulic pressure in the pressure chamber. That is, if the pressure in the control chamber is reduced by the release of the brake operation, even if the flow path of the control piston is closed by the valve element, the pressure in the pressure chamber is quickly increased by the seal member provided around the control piston. The hydraulic pressure drops, and the pushing of the pair of drive pistons by the hydraulic pressure can be released.

In other words, the wheel cylinder of the present invention has a function of supplying and discharging the hydraulic fluid to and from the pressure chamber during the braking operation by closing the flow passage formed in the control piston. Sharing the valve body that restricts the inflow to maintain the anchor reaction force at a constant magnification, and the seal member that functions as a check valve that lowers the hydraulic pressure in the pressure chamber according to the operating pressure on the master cylinder side It is intended to be.

By sharing the functions in this manner, the spring member that urges the valve body to press the valve body against the flow path of the control piston can be used without considering the response at the time of opening the flow path. Emphasis is placed on improving sealing and stability when the road is closed, and the biasing force can be set large.
By setting the urging force of the spring material for urging the valve body to be strong as described above, the adhesion force of the valve body to the flow path of the control piston is increased, and the sealed state in which the flow path is closed by the valve body is more stable. And hold it. Further, since the close contact force with the flow path is increased by the strong urging force of the spring material, it is not necessary to form the valve body with a rubber material in order to enhance the close contact. Therefore, by forming the valve body from a metal material or the like having high mechanical strength, good sealing performance can be ensured, durability can be improved, and operation reliability as a wheel cylinder can be improved.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a drum brake device according to the present invention will be described below in detail with reference to the drawings. 1 to 5 show one embodiment of a drum brake device according to the present invention. FIG. 1 is a sectional view of a main part showing a state where the drum brake device is not operated, and FIG. FIG. 3 is a perspective view showing a schematic configuration, FIG. 3 is a cross-sectional view of a principal part showing an operation when an anchor reaction force is equal to or less than a predetermined magnification in the drum brake device, and FIG. 4 is an explanatory view of a lever operation by the lever member shown in FIG. FIG. 5 is a sectional view showing the operation of the drum brake device when the anchor reaction force exceeds a predetermined magnification.

The drum brake device 1 is of a so-called duo-servo type. As shown in FIG. 2, the drum brake device 1 includes a primary shoe 3 and a secondary shoe 4 which are disposed opposite to each other in a space inside a cylindrical drum. A pair of brake shoes 3, 4; a wheel cylinder 5 disposed between one opposing ends of the pair of brake shoes 3, 4 for expanding the respective brake shoes 3, 4; The primary and
An adjuster (link mechanism) 6 for inputting the output of the shoe 3 to the secondary shoe 4 and a backing plate 7 for supporting these components are provided.

As shown in FIG. 1, a pair of brake shoes 3, 4 are provided with an arc-shaped rim 3a along the inner peripheral surface of the drum.
4a, webs 3b, 4b projecting from the rims 3a, 4a to the inner diameter side, and linings 3c, 4c adhered to the outer periphery of the rims 3a, 4a. Each of the brake shoes 3, 4 is attached to the backing plate 7 so as to be able to advance and retreat toward the inner peripheral surface of the drum. The opposite ends of the pair of brake shoes 3 and 4 on the backing plate 7 are urged by return springs 8a, 8b and 9 in a direction approaching each other (that is, a direction away from the drum). ing.

A strut constituting a parking brake and a parking lever are also incorporated on the backing plate 7, and the pair of brake shoes 3, 4 can be pressed against the drum by operating the parking lever.

The adjuster 6 is adapted to move according to the progress of wear of the linings 3c, 4c of the brake shoes 3, 4,
The distance between the ends of the brake shoes 3, 4 is adjusted. The gap between the ends of the brake shoes 3 and 4 is automatically adjusted by the operation of the adjuster lever 11b whose tip abuts on the adjustment gear on the adjuster 6 by the adjuster spring 11a.

The wheel cylinder 5 has been devised in order to solve the difficulty of the conventional duo-servo type drum brake device in that the stability of the braking effect is low.

Specifically, the wheel cylinder 5
A pair of drive pistons 12 and 13 which are arranged to face the pressure chamber 10 and are driven forward and backward toward the ends of the brake shoes 3 and 4 by the hydraulic pressure supplied to the pressure chamber 10;
The tip surfaces 12a, 1a, 1b of these drive pistons 12, 13
The drive piston 1 is held between the end portions of the brake shoes 3 and 4 facing the upper end 3a and the front end surfaces 12a and 13a.
An anchor pin 15 functioning as a pressing force transmission means between the end portions of the brake shoes 3 and 4 and the anchor pin 15 is provided at a position closer to the center of the drum than the pressure chamber 10 and is used for brake operation. A control chamber 16 that receives a hydraulic pressure from a master cylinder (M / C) that generates a corresponding hydraulic pressure from a supply port 16a, and is provided in the control chamber 16 to allow the pressure chamber 10 and the control chamber 16 to communicate with each other. Valve element 2 that opens and closes flow path 18
0, and a pair of opposingly arranged opposing units with the base end facing the control chamber 16 so as to be arranged in parallel with the driving pistons 12 and 13 on the center side of the drum with respect to the pair of driving pistons 12 and 13. The control pistons 22 and 23 and the pair of control pistons 22 and 23 and the pair of drive pistons 12 and 1
3, a cylinder body 24 slidably supporting the pressure chamber 10 and the control chamber 16, and one end is located at the tip end side of the driving pistons 12, 13 and the other end is the control piston. Lever members 25 that are located at the distal ends of the control pistons 22 and 23 and transmit the anchor reaction force acting on the drive pistons 12 and 13 from the brake shoes to the control pistons 22 and 23.

Each of the driving pistons 12 and 13 is slidable in a liquid-tight manner on the cylinder body 24 by an annular sealing member 27 provided in a sealing groove on the outer periphery thereof.
The tip surfaces of the drive pistons 12 and 13 projecting from the cylinder body 24 are finished flat. In addition, the base ends of the drive pistons 12 and 13 are opposed to each other so that the distal ends of the drive pistons 12 and 13 are kept in contact with the brake shoes 3 and 4 via the anchor pins 15. Each driving piston 1 is provided in the pressure chamber 10.
A spring (compression coil spring) 29 that urges the second and the third 13 away from each other is provided. The pressure chamber 10 is provided with a bleeder screw 30 for air release.

Each of the anchor pins 15 has a columnar shape with its axis directed in the drum axis direction. One side of the outer periphery is in contact with the flat tip surfaces 12a, 13a of the drive pistons 12, 13, and the other side is the other side. The brake shoes 3 and 4 are fitted to the arcuate surfaces 3d and 4d formed at the ends of the brake shoes 3 and 4 facing the tip surfaces 12a and 13a. That is, the anchor pin 15
Are the tip surfaces 12a, 13a of the drive pistons 12, 13.
And concave arcuate surfaces 3d, 4 at the ends of the respective brake shoes 3, 4.
and d.

The control pistons 22 and 23 are slidable in a liquid-tight manner on the cylinder body 24 by annular seal members 51, 52 and 53 provided in seal grooves on the outer peripheral portion of the respective pistons. I have. The base ends of the control pistons 22 and 23 are urged in a direction away from each other by a spring (compression coil spring) 32 provided in the control chamber 16, and a step 22 a formed on the distal end side is provided. The protrusion amount is regulated by abutting the anchor 23a on the anchor plates 34 and 35 which are connected and fixed to the cylinder body 24. Each control piston 2 described above
2,23, when the pressing force F ₂ acting on the distal end side through the lever member 25 described above is greater than the fluid pressure acting on the proximal side, is pushed back to the control room 16 side by the valve body 20 The channel 18 is closed.

One end of the lever member 25 has a forked shape extending to both sides of the tip of the drive pistons 12 and 13. One side of the bifurcated end of the lever member 25 is attached to the drive pistons 12 and 1 by an anchor reaction force.
A reaction force receiving portion 36 having a concave arcuate surface (in this embodiment, a cylindrical surface having an axis in the axial direction of the drum) in contact with the outer peripheral surface of the anchor pin 15 pressed and displaced to the third side is formed. ing. Further, the other side of the bifurcated one end of the lever member 25 is rotatable on the cylindrical curved surfaces 34a, 35a on the anchor plates 34, 35 at a position radially outside the drum with respect to the reaction force receiving portion 36. (In the case of this embodiment, a cylindrical surface having an axis in the axial direction of the drum) 37 which serves as a swing fulcrum by contacting the swinging fulcrum.

The anchor plates 34 and 35 are made of a metal material having higher wear resistance than the cylinder body 24. The surfaces of the anchor plates 34 and 35 are finished smoothly so that the frictional resistance with the convex curved surface portion 37 is reduced. I have. The anchor plates 34 and 35 are for preventing the cylinder body 24 from being worn due to contact friction with the end of the lever member 25.

On the other end of the lever member 25, a convexly curved surface (in this embodiment, a cylindrical surface having an axis in the axial direction of the drum) is in contact with the distal end surfaces of the control pistons 22 and 23. Is provided. With the above configuration, each lever member 25 is connected to the contact point C between the anchor pin 15 and the contact point between the convex curved surface portion 37 and the anchor plates 34 and 35 as a swing fulcrum P as shown in FIGS. operating swung by the anchor reaction force F ₁ acting.
The lever member 25 includes an anchor reaction force F ₁ acting on the contact point C.
Is reduced to a predetermined ratio, and is output to a contact point O between the control pistons 22 and 23 and the reaction force output unit 38. Ratio to reduce the anchor reaction force F ₁ acting on the contact C, from the rocking fulcrum P, which was according to the distance L _1, L ₂ of the respective action point C, to O, the control from the lever member 25 the piston 22, anchor reaction force F ₂ acting on the 23 becomes _{(L 1 / L 2) F} 1.

The valve body 20 has a spherical shape. A flow path for communicating the control chamber 16 with the pressure chamber 10 includes a flow path 18 formed in one control piston 22,
A communication channel 19 is formed in the cylinder body 24 so as to be continuous with the channel 18. The flow path 18 formed in the control piston 22 is provided with the control piston 2.
2, a mortar-shaped valve seat 41 on which the valve body 20 sits is formed in this opening.

The valve body 20 is slidably housed and held in a substantially cylindrical holder 43. The holder 43 has a reduced diameter at the distal end so that the valve body 20 does not come off, and is provided with a flange 43a at the proximal end. The holder 43 is fixed to the control piston 22 side by a guide cylinder 45 that is in contact with the base end surface of the control piston 23 by a spring 32 that biases the pair of control pistons 22 and 23 away from each other. It is held so that it can advance and retreat by a distance.

The holder 43 is provided with a valve spring 42 for elastically supporting the valve body 20.
The valve spring 42 is mounted in the holder 43 in a compressed state, and urges the valve body 20 and the holder 43 so as to protrude toward the control piston 22 as much as possible. When the anchor reaction force is equal to or less than a predetermined value, the valve body 20
The dimensions of each part of the holder 43 and the guide tube 45 are set such that the state of the holder 43 and the guide tube 45 is maintained.
That is, when the control piston 22 is pushed into the control chamber 16 by the pressing force of the lever member 25, the valve body 20 is pressed against the valve seat 41 opened on the base end surface of the control piston 22. , The pressure chamber 1
6 so as to prevent the hydraulic fluid from flowing into the control chamber 16.
It is elastically supported inside.

On the outer periphery of the control piston 22,
An auxiliary liquid chamber 47 communicating with the pressure chamber 10 is defined between an inner wall 24a of the cylinder that slidably supports the control piston 22 and an outer periphery of the control piston 22. A step portion 49 for increasing the volume of the auxiliary liquid chamber 47 when displaced toward the chamber 16 is provided.

Further, seal members 51 and 52 provided so as to close a gap between the control piston 22 and a cylinder inner wall 24a for slidably holding the control piston 22.
3, the seal member 52 located between the control chamber 16 and the communication flow path 19 has, as shown in FIG. 3, an outer peripheral lip portion 52a that contacts the cylinder inner wall 24a and an outer peripheral lip portion 52a. A so-called cup seal having a structure having a recess 52b formed on one side to provide a predetermined elasticity is used. The seal member 52 is mounted on the control piston 22 with the depression 52b facing the control chamber 16 and acts on one end side of the pressure chamber 10 acting on the other end side. When the fluid pressure in the chamber 16 becomes low, it functions as a check valve for releasing the hydraulic fluid in the pressure chamber 10 to the control chamber 16.

In the wheel cylinder 5 described above, when the vehicle is moving forward, the drum is driven to rotate in the direction of the arrow (a) in FIG. 1, and the lever member 25 on the brake shoe 4 functioning as a secondary shoe is attached to the anchor. The reaction force is transmitted to the control piston 23. During backward travel, the brake shoe 3 functions as a secondary shoe, and the lever member 25 on the brake shoe 3 transmits an anchor reaction force to the control piston 22.

At the time of non-operation, as shown in FIG. 1, a valve body 20 elastically supported in the control chamber 16 opens a flow passage 18 formed in the control piston 22 to open the pressure chamber 10 and the control chamber 16. When the hydraulic pressure is supplied from the master cylinder by the brake operation in a state where they are in communication with each other, the hydraulic pressure is immediately supplied to the pressure chamber 10. The brake operation causes the hydraulic pressure from the master cylinder to rise in the control chamber 16.
And the pressure chamber 1 via the flow path 18 on the control piston 22
When supplied to zero, the pair of drive pistons 12 and 13 are pushed out of the pressure chamber 10 and press the ends of the primary shoe and the secondary shoe via the anchor pin 15.

Each brake shoe whose end is pressed by the drive pistons 12 and 13 expands and is pressed against the drum to generate a braking force. At the time of this braking, an anchor reaction force of a magnitude corresponding to the braking effect is transmitted from the secondary shoe to the driving pistons 12 and 13 via the anchor pins 15. When the braking effect increases and the anchor pin 15 is pushed back by a certain amount or more due to the anchor reaction force, the anchor pin 15 presses not only the driving pistons 12 and 13 but also one end of the lever member 25.

The anchor reaction force F ₁ transmitted to the lever member 25 becomes a force for pushing back the control piston 22 in the advanced state by the hydraulic pressure of the master cylinder.
Acts on the control piston 22. Therefore, when the anchor reaction force reaches a predetermined magnification with respect to the input from the master cylinder, the control piston 22 by the pressing force F ₂ acting on the control piston 22 via the lever member 25 is pushed back into the control chamber 16.

The control piston 22 pushed back into the control chamber 16 by the anchor reaction force causes the valve body 20 to resiliently contact the flow path 18 opened at the base end thereof, so that the pressure chamber 10
Is closed to keep the pressure chamber 10 in a sealed state, and the hydraulic pressure of the pressure chamber 10 acting on the drive pistons 12 and 13 is kept constant. As described above, when the braking effect is reduced under the braking condition in which the pressure chamber 10 is closed, the anchor reaction force acting on the control piston 22 via the lever member 25 is weakened, and the hydraulic pressure from the master cylinder is reduced. As a result, the control piston 22 is pushed again in the advance direction, so that the closing of the flow path 18 by the valve body 20 is released, and the supply of the hydraulic pressure from the control chamber 16 to the pressure chamber 10 via the flow path 18 on the control piston 22 is restarted. Is done. As described above, since the control piston 22 controls the supply of the hydraulic pressure to the pressure chamber 10 according to the anchor reaction force, the wheel cylinder 5 stabilizes the anchor reaction force at a fixed magnification with respect to the input from the master cylinder. And receive it.

That is, since the drum brake device 1 of the above-described embodiment is basically a duo-servo type drum brake device, it has a high braking effect characterized by the duo-servo type and incorporates a parking brake. The advantage of being easy is retained.

Further, the wheel cylinder 5 is devised so that when the anchor reaction force of the secondary shoe 4 reaches a predetermined magnification with respect to the input from the master cylinder,
The control piston 22 receiving the anchor reaction force at its tip via the lever member 25 is displaced toward the control chamber 16, and closes the valve body 20 that opens and closes the flow path 18 from the master cylinder to the pressure chamber 10, The hydraulic pressure acting on the pair of drive pistons 12 and 13 pressing the primary shoe 3 and the secondary shoe 4 is kept constant. Therefore, it is possible to stably obtain an anchor reaction force of a constant magnification with respect to the input, and it is possible to solve a serious problem that the stability of the brake effect that the conventional duo servo type has is low. .

The control piston 22 controls the pressure chamber 1
When 0 is in the closed hydraulic pressure holding state, the hydraulic pressure in the pressure chamber 10 rises due to some factor (for example, the swing of the drum), whereby the pressing of the brake shoes by the drive pistons 12 and 13 is prevented. When the braking force is increased, the braking effect is increased, which causes a so-called fluctuation of the braking effect. However, in the wheel cylinder 5 of the present invention,
When the flow path 18 of the control piston 22 is closed by the valve body 20 and the pressure chamber 10 is in a closed hydraulic pressure holding state, the hydraulic pressure in the pressure chamber 10 increases due to some factors, and When the hydraulic pressure becomes higher than the hydraulic pressure in the control chamber 16, the seal member 52 provided in the gap around the control piston 22 allows the hydraulic fluid in the pressure chamber 10 to escape to the control chamber 16 side, and the pressure chamber 10 Suppresses the rise in hydraulic pressure inside the vehicle and suppresses fluctuations in brake effectiveness.

Furthermore, if the pressure chamber 10 is in a closed hydraulic pressure holding state, the pressure chamber 10
Even if the hydraulic pressure in the inside rises and the pressing of the brake shoe 3 by the driving piston 12 increases, at the same time, the pressing force acting on the control piston 22 via the lever member 25 increases, and the control piston 22 is the control room 16
As a result, the volume of the auxiliary liquid chamber 47 connected to the pressure chamber 10 increases due to the behavior of the control piston 22 as shown in FIG. The increase in the volume of the auxiliary liquid chamber 47 increases the substantial volume of the pressure chamber 10, suppresses an increase in the hydraulic pressure of the pressure chamber 10, and suppresses fluctuations in the effectiveness of the brake.

Therefore, when the hydraulic pressure is maintained, even if the hydraulic pressure in the pressure chamber 10 increases due to the swing of the drum or the like, the increase in the hydraulic pressure is reduced by the pressure reducing operation by the seal member 52 or the response of the control piston 22. At the same time, the inconvenience of the so-called fluctuation of the braking effect does not occur,
A stable braking effect can be maintained. Therefore, the braking effect is high, the stability of the braking effect is high, the parking brake is easily incorporated, and the size and cost of the brake system are reduced by downsizing the booster of the master cylinder. be able to.

The control piston 22 controls the pressure chamber 1
When the brake operation is released and the supply of the hydraulic pressure from the master cylinder to the control chamber 16 is released when the hydraulic pressure 0 is in the closed hydraulic pressure holding state, the hydraulic pressure in the pressure chamber 10 relatively increases even if the hydraulic pressure in the control chamber 16 is released. Since the pressure becomes higher than the hydraulic pressure in the control piston 16, the sealing member 52
However, the hydraulic fluid in the pressure chamber 10 escapes to the control chamber 16 side,
The fluid pressure in the pressure chamber 10 is reduced. That is, if the pressure in the control chamber 16 decreases due to the release of the brake operation, the valve body 20
Therefore, even if the flow path 18 of the control piston 22 is closed, the hydraulic pressure in the pressure chamber 10 is quickly reduced by the seal member 52 provided around the control piston 22, and the pair of drive pistons 12 , 13 by hydraulic pressure can be released.

In other words, the wheel cylinder 5 of the present invention
The function of supplying / discharging the hydraulic fluid to / from the pressure chamber 10 during the braking operation is controlled by closing the flow path 18 formed in the control piston 22 so as to restrict the flow of the hydraulic fluid into the pressure chamber 10 and to provide an anchor reaction force. And a seal member 52 having a function as a check valve for lowering the fluid pressure in the pressure chamber 10 in accordance with the operating pressure on the master cylinder side.
And to share.

By sharing the functions in this manner, the spring member that urges the valve body 20 to press the valve body 20 against the flow path 18 of the control piston 22 does not consider the responsiveness when the flow path 18 is opened. In addition, the urging force can be set to be large, with emphasis placed on the improvement of the sealing performance and the stability when the flow path 18 is closed, and the urging force of the spring material for urging the valve body 20 can be set as described above. The control piston 22
The contact force of the valve body 20 with respect to the flow path 18 is increased, and the hermetically closed state in which the flow path 18 is closed by the valve body 20 can be more stably maintained. Further, as the valve element 20, the contact force with the flow path 18 is increased by the strong urging force of the spring material, so that it is not necessary to form the valve element 20 with a rubber material in order to enhance the adhesion. Therefore, the valve element 2
0 is formed of a metal material or the like having high mechanical strength so that good sealing performance can be ensured, durability can be improved, and operation reliability of the wheel cylinder 5 can be improved.

In the above-described configuration, the servo ratio at which the valve element 20 operates is controlled by the control piston 22 facing the control chamber 16,
23 can be set to an arbitrary value by changing the leverage ratio of the lever member 25 that transmits the anchor reaction force to the control pistons 22 and 23 and the design change of the braking characteristic according to the vehicle type. Can be easily handled.

The lever member 25 can significantly reduce the anchor reaction force input from the brake shoe and input the control force to the control pistons 22 and 23. In other words,
By appropriately setting the lever ratio by the lever member 25, the pressure receiving areas of the control pistons 22 and 23 facing the control chamber 16 can be made extremely small.
Due to the compactness of 2, 23, the size of the wheel cylinder 5 and the size of the brake device can be more easily reduced.

Drive pistons 12 and 13 for pressing the ends of the brake shoes 3 and 4 via the anchor pin 15
Are flat surfaces, and the contact between the anchor pin 15 and the driving pistons 12 and 13 is a combination of a circumferential surface and a flat surface.
No prying force is generated between the end faces 2 and 13, and the operation reliability is improved.

[0051]

The drum brake device of the present invention is basically a duo-servo type drum brake device, and therefore has a high braking effect, which is characterized by a duo-servo type, and can easily incorporate a parking brake. The advantage is that it is retained. In addition, the wheel cylinder that expands between the opposing ends of the pair of brake shoes during braking operation is devised, and the secondary shoe anchor reaction force reaches a predetermined magnification with respect to the input from the master cylinder. Then, the control piston receiving the anchor reaction force at the distal end via the anchor pin and the lever member is displaced to the control chamber side, and the flow path for supplying the hydraulic fluid from the master cylinder to the pressure chamber is closed by the valve body. Thus, the hydraulic pressure acting on the pair of drive pistons pressing the primary shoe and the secondary shoe is kept constant. Therefore, it is possible to stably obtain an anchor reaction force of a constant magnification with respect to the input, and it is possible to solve a serious problem that the stability of the brake effect that the conventional duo servo type has is low. .

Also, when the flow path to the pressure chamber is closed by the valve body and the pressure chamber is in a closed hydraulic pressure holding state, the hydraulic pressure in the pressure chamber is increased due to some factor (for example, swing of the drum). When the brake piston is lifted and thereby the pressing force of the brake shoe by the driving piston is increased, the braking effect is increased, which causes a problem of so-called fluctuation of the braking effect. However, in the wheel cylinder of the present invention, when the flow path to the pressure chamber is closed by the valve body and the pressure chamber is in a closed hydraulic pressure holding state, the hydraulic pressure in the pressure chamber increases due to some factors, and the pressure is increased. When the hydraulic pressure in the chamber becomes higher than the hydraulic pressure in the control chamber, the seal member provided in the gap around the control piston releases the hydraulic fluid in the pressure chamber to the control chamber side,
It is possible to suppress a rise in the hydraulic pressure in the pressure chamber and suppress a fluctuation in the effectiveness of the brake.

Further, when the flow path of the control piston is closed by the valve body and the pressure chamber is in a closed hydraulic pressure holding state,
Even when the brake operation is released and the supply of hydraulic pressure from the master cylinder to the control chamber is released, the hydraulic pressure in the pressure chamber becomes relatively higher than the hydraulic pressure in the control chamber. The seal member provided in the gap allows the hydraulic fluid in the pressure chamber to escape to the control chamber side, and quickly reduces the hydraulic pressure in the pressure chamber even when the flow path of the control piston is closed by the valve element. Can be done.

That is, in the wheel cylinder of the present invention, the spring member for urging the valve body so as to press the valve body against the flow path of the control piston does not need to consider the response at the time of opening the flow path. With an emphasis on the improvement of sealing performance and stability when closed, the biasing force can be set large, and by setting the biasing force of the spring material for biasing the valve body to be strong in this way, The tightness of the valve body with respect to the flow path of the control piston is increased, and the closed state in which the flow path is closed by the valve body can be more stably maintained. Further, since the close contact force with the flow path is increased by the strong urging force of the spring material, it is not necessary to form the valve body with a rubber material in order to enhance the close contact. Therefore, by forming the valve body from a metal material or the like having high mechanical strength, good sealing performance can be ensured, durability can be improved, and operation reliability as a wheel cylinder can be improved.

Further, in the drum brake device of the present invention, the servo ratio at which the valve element operates is determined by changing the pressure receiving area of the control piston facing the control chamber and the lever ratio of the lever member transmitting the anchor reaction force to these control pistons. Can be set to an arbitrary value, and it is possible to easily cope with a change in the design of the braking characteristic according to the vehicle type or the like. Also, by using the lever member, the anchor reaction force input from the brake shoe can be greatly reduced and input to each control piston, and by appropriately setting the lever ratio by the lever member, it is possible to face the control chamber. The pressure receiving area of the control piston can be extremely small, and the downsizing of the control piston makes it easier to downsize the wheel cylinder and the brake device. In addition, the end surface of the drive piston that presses the end of the brake shoe via the anchor pin is a flat surface, and the contact between the anchor pin and the drive piston is a combination of the circumferential surface and the flat surface. No prying force is generated between the drive piston and the end face, and the operation reliability is improved.

[0056]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a main part showing a non-operating state of an embodiment of a drum brake device according to the present invention.

FIG. 2 is a perspective view showing a schematic configuration of an embodiment of a drum brake device according to the present invention.

FIG. 3 is an essential part cross-sectional view showing an operation when an anchor reaction force is equal to or smaller than a predetermined magnification in one embodiment of the drum brake device according to the present invention.

FIG. 4 is an explanatory view of a lever operation by a lever member provided in one embodiment of the drum brake device according to the present invention.

FIG. 5 is an essential part cross-sectional view showing an operation when an anchor reaction force exceeds a predetermined magnification in one embodiment of the drum brake device according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 drum brake device 3 primary shoe (brake shoe) 4 secondary shoe (brake shoe) 5 wheel cylinder 7 backing plate 10 pressure chamber 12, 13 drive piston 15 anchor pin 16 control room 16a supply port 18 flow path 20 valve body 22 , 23 Control piston 24 Cylinder body 24a Cylinder inner wall 25 Lever member 29, 32, 42 Spring (spring material) 34, 35 Anchor plate 36 Reaction force receiving part 37 Convex surface part 38 Reaction force output part 41 Valve seat 43 Holder 45 Guide cylinder 47 auxiliary liquid chamber 49 step 52 seal member (cup seal)

Claims (1)

[Claims] 1. A pair of brake shoes, a primary shoe and a secondary shoe, disposed opposite to each other in a cylindrical inner space of a drum, and a wheel cylinder disposed between one opposing ends of the pair of brake shoes. And a drive piston that presses the brake shoe against the drum by hydraulic pressure supplied to a pressure chamber; and a cylinder having an axis oriented in the drum axis direction. An anchor pin sandwiched between the drive piston and an end of the brake shoe and functioning as a pressing force transmitting means between the drive piston and the end of the brake shoe; and a master spaced from the pressure chamber. A control chamber communicating with the cylinder; and A control piston provided with a flow path for communicating the control chamber with the pressure chamber at a base end surface facing the control chamber; and a brake located at one end side at a distal end side of the drive piston via an anchor pin. A reaction force receiving portion is provided for receiving an anchor reaction force from the shoe, and a reaction force output portion is provided at the other end to abut on the tip of the control piston, so that the anchor is transmitted from the brake shoe to the drive piston. A lever member for reducing the reaction force at a predetermined ratio to act on the distal end of the control piston; and an opening at the base end face of the control piston when the control piston is pushed into the control chamber by the pressing force of the lever member. A valve body elastically supported in the control chamber so as to be in pressure contact with the flow path to block the flow path and to prevent inflow of the hydraulic fluid into the pressure chamber; Hydraulic pressure in the control chamber, which acts on the other end than hydraulic pressure on the pressure chamber, which is installed to close the gap between the inner wall of the cylinder body and slidably holds the control piston. And a seal member for allowing the hydraulic fluid in the pressure chamber to escape to the control chamber when the pressure becomes low.