JPS5928930Y2 - Wheel cylinder device for drum brakes - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a wheel cylinder device for a drum brake that prevents the rear wheels of a vehicle from locking.

If a sudden and excessive braking force is applied to the drum brake, the rotation of the wheels will stop and the wheels will slide on the road surface.

In such a sliding state, the braking force is actually smaller than the braking force generated by the wheels when the wheels are rotating, and the vehicle body skids.

In order to prevent such wheel locking and to obtain the maximum braking force for the wheels, the present invention is designed to prevent the locking of the wheels and to obtain the maximum braking force for the wheels. A wheel cylinder device is proposed in which when the applied force exceeds a certain value that causes the wheels to lock, a control valve is closed in accordance with the movement of the piston, cutting off the hydraulic pressure from the mask cylinder. It is something to do.

The structure of the present invention will be explained based on the illustrated embodiment. As shown in FIG.
The pistons 9 and 3 each protrude from the main body 2 due to the pressure fluid introduced into these cylinders from the inlet passage 10, and press the brake shoes against the inner circumferential surface of the brake drum. There is.

Seal rings 22 and 23 are attached to the circumferential surfaces of each piston 9 and 30, respectively, to ensure liquid tightness of the sliding parts.

In practice, the cylinder 17 is arranged inside the closure body 1;
This closure body 1 is screwed into a cylindrical portion 19 provided on the left end side of the main body 2, and a seal ring 25 is supported on the outer periphery of the closure body 1.
The cylindrical portion 19 is sealed.

A disc-shaped valve seat 6 is abutted against the inner end wall of the cylindrical portion 19 via a seal ring 20, and is fixed by the closing body 1.

A protruding rod 16, which will be described later, is loosely inserted through the center of the valve seat 6, and a passage connecting the passage 10 with the cylindrical portion 19 is formed.

A ball I is pressed against the protruding rod 16 by the force of a spring 8, and the ball 7 and the valve seat 6 constitute a control valve that opens and closes the passage 10.

The cylindrical portion 19 and the cylinder 18 are connected by a passage 13.

The inner end of the cylinder 17 has a large diameter starting from the stepped portion 21, into which the plunger 5 fitted with a cup-shaped seal ring 14 is fitted.

The right end surface of the plunger 5 is provided with a groove 11 extending in the radial direction and a protruding rod 16, and is pressed against the valve seat 6 by the force of a spring 4 interposed between the stepped portion 21 and the plunger 5. ing.

The plunger 5 also has a passage 12 passing therethrough, which allows the hydraulic pressure in the groove 11 or cylindrical portion 19 to act on a recess 15 formed in the end face of the piston 3.

The piston 3 supports a seal ring 24 on the end surface that abuts against the plunger 5.

Next, the operation of the device of the present invention having the above configuration will be explained.

When the brake is released, the force of the return spring that is passed between the pair of left and right brake shoes causes the piston 3 to
is pressed against the plunger 5, and the large diameter portion of the outer end of the piston 9 is pressed against the end wall of the main body 2.

Further, the plunger 5 is pressed against the valve seat 6 by the spring 21, and the protruding rod 16 pushes the ball 7 against the spring 8 to open the passage 10.

When the brake is applied, the pressure fluid enters the cylindrical portion 19 through the passage 10, enters the cylinder 18 through the passage 13, and pushes the piston 9, while the pressure fluid in the cylindrical portion 19 passes through the passage 12 of the plunger 5 into the piston 3. Enter the recess 15 and press the piston 3.

In this way, the pair of brake shoes are pushed apart by the pair of pistons 9 and 3, and are frictionally engaged with the inner peripheral surface of the brake drum to generate braking force.

The piston 9 engages at the beginning of the brake shoe (rearward with respect to the direction of rotation of the brake drum), while the piston 3 engages at the end of the brake shoe.

That is, the piston 3 acts as an anchor for the brake shoe.

As the piston 3 protrudes leftward, the piston 3 separates from the plunger 5, and the pressure receiving area of the piston 3 becomes larger than that of the cylinder 17.
is equal to the cross-sectional area of

When the force that piston 3 receives as an anchor increases,
The piston 3 moves back and collides with the plunger 5 again.

The anchor force received by the piston 3 is received by the hydraulic pressure of the cylindrical portion 19 acting on the plunger 5, and as the anchor reaction force increases, the plunger 5 and the piston 3 are integrally moved against the spring 21. Push back outwards.

At this time, the liquid in the chamber housing the spring 4 returns to the cylindrical portion 19 side while compressing the cup-shaped seal ring 14 inwardly.

When the hydraulic pressure applied to the inlet passage 10 also increases and the braking force increases, the force applied from the brake shoe to the piston 3 as an anchor also increases, and the wheel becomes locked.

When the force applied to the piston 3 reaches such a limit value,
The hydraulic pressure acting on the plunger 5 greatly deflects the spring 4 and moves the plunger 5 to the left, the protruding rod 16 also retires, the ball 7 engages the valve seat 6, and the passage 10 is moved to the cylindrical portion 19.
It may also be blocked.

Therefore, the hydraulic pressure applied to plunger 5 and piston 9 does not increase any further.

As is clear from the above explanation, the pe plunger 5 is designed so that the hydraulic pressure applied to the piston as an anchor is equal to the hydraulic pressure applied to the plunger when the braking force reaches a limit value that causes the wheels to lock. By setting the cross-sectional area of , even if excessive brake fluid pressure is applied, that fluid pressure is cut by the action of the control valve constituted by the ball 7, and locking of the wheels is prevented.

In other words, the maximum torque generated by the brake is generally determined by the friction coefficient of the road surface, so when the torque stops increasing or decreases due to wheel locking, the hydraulic pressure that pushes the plunger 5 to the left overcomes the anchor reaction force. , the plunger 5 moves to the left while compressing the spring 4, and the control valve closes the passage 10, cutting off the increase in hydraulic pressure applied to each piston.

The coefficient of friction between the road surface and the tires changes depending on the speed of the vehicle, and as the speed of the vehicle decreases, the frictional engagement force between the wheels and the road surface increases, causing the wheels to rotate again and exert effective braking force.

The cylinder device according to the present invention is attached to each left and right wheel, so even if the wheel load is unbalanced due to the loading condition of the vehicle, the cylinder device is installed to the maximum extent according to the frictional engagement force between each wheel and the road surface. You can get braking power.

As explained above, the present invention is a drum brake wheel cylinder device that includes a first cylinder that engages a piston on both ends of the main body for pushing the starting end of the brake shoe, and a terminal end that serves as an anchor for the brake shoe. A second cylinder into which a piston supporting the piston is fitted is provided separately, the diameter of the inner end of the second cylinder is enlarged, a plunger 5 which engages with the piston is fitted into this, and the plunger is provided with a control valve that opens and closes a passage that guides hydraulic pressure to the second cylinder, and is configured such that hydraulic pressure acts separately on the second piston and the plunger, and that the second cylinder and the first cylinder are connected to each other by a passage, so if the anchor reaction force of the brake shoe acting on the second piston increases enough to cause the wheels to lock, the hydraulic pressure that was acting directly on the second piston will increase When this plunger is moved by hydraulic pressure, the control valve closes and cuts off the hydraulic pressure from the mask cylinder, thereby locking the wheels. It is possible to shorten the duration of the wheel or prevent the wheels from locking.

Therefore, an excellent effect can be obtained in that the maximum braking force corresponding to the load on each wheel can be effectively obtained.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a drum brake wheel cylinder device according to the present invention. 3.9...Piston, 5...Plunger, 6...Valve seat, 7...Ball, 10
...Entrance passage, 16...Protrusion rod, 17,
18...Cylinder.

Claims (1)

[Scope of utility model registration request] The first one is located at both ends of the main body. The first piston is fitted with a second piston, respectively. a second cylinder, a passage that opens in the center of the main body and is connected to the second cylinder, a control valve including a ball provided in the middle of the passage, and a large diameter at the inner end of the second cylinder. a plunger that fits into the cylinder and can abut against the second piston; a passage that passes through the plunger and allows hydraulic pressure in the passage to act on the second piston; and a passage that is attached to the plunger and can abut against the ball. a protrusion rod that normally opens the control valve and closes the control valve as the plunger moves; the second cylinder and the first cylinder;
Drum brake wheel cylinder device consisting of a passage connecting the cylinder○