GB2248663A - Valve for controlling brake fluid pressure - Google Patents

Abstract

A valve for controlling the hydraulic pressure created by brake fluid is mounted in the brake fluid passage formed between the master cylinder of a four-wheeled vehicle and the wheel cylinders at the rear wheels. Flow of brake fluid around the ball 7 of the valve is not hindered whatever position the ball assumes. During hard braking, the valve permits the brakes to produce stable braking action. The valve has ball guide portions shifted circumferentially from holes 14 formed in a flow plate 12. A spring 22 is mounted between a bleeding disk 19 and a piston 6. <IMAGE>

Description

VALVE FOR CONTROLLINC BRAKE FLUID PRESSURE FIELD OF THE INVENTION The present invention relates to a valve used on a fourwheeled vehicle such as an automobile to control the hydraulic pressure created by brake fluid.

BACKGROUND OF THE INVENTION All the wheels of a four-wheeled vehicle such as an automobile are equipped with a brake system. When the vehicle is moving, the brake system is affected by the force of inertia.

Therefore, when the brake system is operated, it is necessary to make the brake fluid pressure applied to the front wheels different from the brake fluid pressure applied to the rear wheels. In particular, immediately after the brakes are applied. the same pressure is applied to all four wheels. As the braking force acts on the wheels. the inertia of the automobile body acts on the front wheels and so the pressure applied to the rear wheels is reduced; otherwise the rear wheels would lock. Therefore, a brake fluid pressure control valve is provided so that the hydraulic pressure may act on the rear wheels differently than on the front wheels in relation to the inertia acting on the automobile body.

The brake fluid pressure control valve on which the invention is based is shown in Fig. 1, where the control valve has a housing 1. When the housing is mounted on the body of an automobile, it is tilted by an appropriate angle of fi (Fig. 11) such that the left end as viewed in Fig. 1 is higher than the right end. The front end of the housing 1 has a connection port 2 for connection with the wheel cylinders (not shown). A cap 3 is mounted at the rear end and has a connection port 4 for connection with the master cylinder (not shown). A stepped piston 6 is fitted in the housing 1 so as to be slidable. The piston 6 is centrally provided with a hole 5. A ball 7 is movably received in the housing 1 to open or close the hole 5 formed in the center of the piston 6. The ball 7 is located closer to the connection port 5 than the piston 6.

More specifically,.a cylinder 8 and a tubing 11 are inserted into the housing 1 from the right as viewed in the figure.

The piston 6 is held by the cylinder 8 so as to be slidable. The tubing 11 has a portion 9 in which the ball 7 is received. Neither the cylinder 8 nor the tubing 11 extends entirely through the housing 1. A flow plate 12 is held between the tubing 11 and the cap 3 via an 0 ring 13 which provides seal. The flow plate 12 is provided with five holes 14 (see Figs. 6 and 7) to pass brake fluid.

One of the holes 14 is located in the center, while the others are disposed in a symmetrical manner near the outer periphery. The central hole 14 is disposed opposite to a hole 15 formed in the center of the connection port 4 in the cap 3.

The portion 9 of the tubing 11 which receives the ball 7 has ball guide portions 10 (see Fig. 2) around the axis of the tubing 11 and opposite to the holes 14. Each ball guide portion 10 has plural grooves 16. A seal member 17 is mounted on the central portion of the piston 6 at the side of the ball 7 and around the hole 5. When the ball 7 moves to the left and comes into contact with the seal member 17, the seal member makes intimate contact with the ball to close up the hole 5. A chamber 18 is formed inside the housing 1 to the left of the piston 6, and a bleeding disk 19 is mounted in the chamber 18. The bleeding disk 19 has protrusions 19a to permit brake fluid to flow when the disk 19 has been moved to the connection port 2.

In the brake fluid pressure control valve built as described above, the housing 1 is mounted to the automotive body in such a way that the housing 1 is tilted upwardly to the left by the given angle S (Fig. 11) as described previously. The wheel cylinders at the rear wheels are connected to the connection port 2.

The master cylinder is connected to the connection port 4. The wheel cylinders at the front wheels are directly connected to the master cylinder without via this brake fluid pressure control valve.

When the brake pedal (not shown) is pushed down to produce hydraulic pressure in the master cylinder, the pressure is transmitted to the wheel cylinders at the front wheels directly and to the wheel cylinder at the rear wheels via the brake fluid pressure control valve. Therefore, the braking force acting on the front wheels varies linearly with the amount of movement made by the brake pedal, while the braking force acting on the rear wheels is moderated by the control valve. When the brake pedal is pushed down only a little and a large braking force is not yet developed, the brake fluid forced out of the master cylinder flows through the connection port 4, the hole 15, the holes 14 in the flow plate 12, the grooves 16 in the tubing 11, and passes across the surface of the ball 7 as indicated by the arrows in Fig. 1.Then, the fluid enters the hole 5 in the piston 6, flows through the chamber 18, comes out of the connection port 2, and goes to the wheel cylinders at the rear wheels. The relation of the hydraulic pressure P: sent to the wheel cylinders at the rear wheels to the hydraulic pressure P1 produced by the master cylinder is shown in Fig. 3. That is, this relation is given by a straight line a. The rear wheels are braked by the pressure transmitted in this way.

At this time, the ball 7 is placed to the right as viewed in Fig. 1 by its own weight. Accordingly, the hole 5 in the piston 6 is not closed and operates as described above. When the brake pedal is further pushed down to increase the braking force, the ball 7 is moved upward on the inclined surface inside the tubing 11 and comes into intimate contact with the seal member 17 on the piston 6, thus closing up the hole 5. Then, the brake fluid pressure acting on the wheel cylinders at the rear wheels is confined to the portion located on the downstream side of the hole 5 in the piston 6. As a result, the pressure is maintained constant as indicated by a straight line b in Fig. 3 independent of increases in the hydraulic pressure created by the master cylinder.

If the driver further pushes down on the brace pedal, then the hydraulic pressure in the wheel cylinders increases. This pressure acts on the pressure-receiving surface of the piston 6 which is on the side of the ball 7. Then, the piston 6 is moved to the left while the hole 5 is maintained closed up by the baIl T.

The brake fluid existing in the pipe extending from the hole 5 in the piston 6 to the chamber 18 and into the wheel cylinders is subjected to the pressure. As a result, the hydraulic pressure in the wheel cylinders increases as indicated by a straight line c as shown in Fig. 3. This brake fluid pressure control valve operates in the manner described thus far, and controls the hydraulic pressure acting on the rear wheels to prevent the rear wheels from locking.

Unfortunately, this conventional control valve has a disadvantage. As shown in Fig. 2, the holes 14 in the flow plate 12 are disposed opposite to the ball guide portions 10. Since brake fluid collides against the ball guide portions 10 after flowing through the hole 14 and reaching the surroundings of the ball 7, it does not smoothly flow through the hole 5 in the piston 6. Rather, it acts on the ball 7, pushing it to the left as viewed in Fig. 1.

Consequently, the condition indicated by the straight line b shown in Fig. 3 is reached earlier than the instant of time at which the hole 5 in the piston 6 should be closed up. Also, the operating points indicated by the turning points in the graph of Fig. 3 vary among brake fluid pressure control valves.

The brake fluid pressure control valve of this structure has another disadvantage. In particular, the bleeding disk 19 disposed in the chamber 18 is normally inclined. When brake fluid pours into the chamber 18 from the hole 5 in the piston 6 and the bleeding disk 19 moves to close up the connection port 2, the disk 19 forces the brake fluid existing in front of the disk 19 into the wheel cylinders, or brake fluid flows in the wheel cylinders before the connection port 2 is closed, thus increasing the pressure inside the wheel cylinders.

Another problem arises from the fact that the piston 6 is moved according to the difference in area between the pressurereceiving surface of the portion 9 receiving the ball 7 and the pressure-receiving surface of the chamber 18. Therefore, when the brake pedal is released, it gradually returns to its original position according to the reduction in the hydraulic pressure. For this reason, if the brake pedal is pushed down immediately after the control valve is opened, the gap between the ball 7 and the piston 6 is not constant. Thus, the hydraulic pressure is not controlled regularly. This makes the performance unstable.

SUMMARY OF THE INVENTION It is an object of the invention to provide a brake fluid pressure control valve which does not vary in operating points from r S one product to another and shows stable performance.

lt is another object of the invention to provide a brake fluid pressure control valve which controls brake fluid regularly.

The first-mentioned object is achieved in accordance with the teachings of the invention by a brake fluid pressure control valve which is of the same type as the aforementioned conventional valve and has ball guide portions in the form of stripes formed radially on the side of a piston inside a housing and a flow plate disposed inside the housing on the side of a connection port for connection with a master cylinder, the flow plate being provided with holes for permitting passage of brake fluid. The holes are shifted from the ball guide portions circumferentially inside the housing. When brake fluid flows, it is not affected by the ball guide portions, because these guide portions are not opposite to the holes in the flow plate. Hence, the operating points do not vary among products.

The second-mentioned object is achieved by a brake fluid control valve comprising a housing, a first connection port for connection with wheel cylinders. a chamber formed on the side of the first connection port, a bleeding disk taking the form of a sheet and mounted in the chamber, a spring mounted between the bleeding disk and the larger portion of the piston to bias the disk toward the first connection port and to bias the piston in the opposite direction. and a liquid passage between the disk and the front end of the housing. When the bleeding disk closes up the first connection port, no adverse effects are produced.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view of a conventional brake fluid pressure control valve; Fig. 2 is a cross-sectional view taken on line Il-Il of Fig. 1, for showing the positional relation of holes in a flow plate to ball guide portions of a tubing:: Fig. 3 is a graph.for illustrating the operation of the valve shown in Fig. 1; Fig. 4 is a cross-sectional view of a brake fluid pressure control valve according to the invention; Fig. 5 is a cross-sectional view taken on line V-V of Fig. 4; Fig. 6 is a front elevation of the valve shown in Fig. 4, corresponding to Fig. 5; Fig. 7 is a cross-sectional view of the flow plate and the protrusion shown in Fig. 6; Fig. 8 is a cross-sectional view of another brake fluid pressure control valve according to the invention; Fig. 9 is a front elevation of the bleeding disk shown in Fig. 4; Fig. 10 is a cross-sectional view of the bleeding disk shown in Fig. 9; Figs. 11-13 are views similar to Fig. 8, but showing different conditions; and Fig. 14 is a graph for illustrating the operation of the valve shown in Fig. 8.

DETAILED DESCRIPTION OF THE INVENTION It is to be noted that like components are indicated by like reference numerals in various figures. Figs. 4-7 show brake fluid pressure control valve according to the invention. This valve is similar to the conventional valve shown in Figs. 1 and 2 except that the holes 14 in the flow plate 12 are shifted from the ball guide portions 10 by 45 as shown in Fig. 5. To accomplish this shift, an arcshaped protrusion 20 is formed on the plate 12 by press working, as shown in Figs. 6 and 7. When the flow plate 12 is mounted between the tubing 11 and the cap 3, the plate 12 is placed in position as shown in Fig. 2, using the protrusion 20 as a mark.

In this example, the protrusion 20 is formed on the flow plate 12 and employed as a mark during assembly operation to place the flow plate 12 in position. Marks other than a protrusion, such as a notch, an impression, and a symbol, can also be utilized.

Since the above-described brake fluid control valve is constructed in this way, the holes 14 in the flow plate 12 are shifted from the ball guide portions 10. Therefore. it is unlikely that the ball 7 is pushed violently by the pressure created by the brake fluid. This eliminates variations of the turning points of the brake fluid pressure characteristic. Consequently, the performance of the pressure control valve is stable.

Figs. 8-13 show another brake fluid pressure control valve according to the invention. This valve is similar to the conventional valve shown in Figs. 1 and 2 except for the following.

The piston 6 has a recess 21 at its front end. The base of a coiled spring 22 is fitted in the recess 21. The front end of the spring 22 is pressed against the inner surface of the bleeding disk 19.

This disk 19 is biased toward the connection port 2 for connection to wheel cylinders by the spring 22 inside the housing 1. Also, the disk 19 is pressed against the piston 6. When the bleeding disk 19 is urged into the connection port 2, it follows that the port 2 is closed, but the disk 19 has a plurality of protrusions 19a (see Figs. 9 and 10) to form a gap that forms a liquid passage 23 (Fig.

8) through which the brake fluid flows. In this manner, circulation of the brake fluid is not hindered. Instead of forming the protrusions 19a on the bleeding disk 19, protrusions can be formed at the front end of the housing 1 to form the liquid passage 23.

The operation of the brake fluid pressure control valve constructed as described above is next described by referring to Figs. 11-13. This control valve is mounted to an automotive body (not shown) such that the rear side is tilted downward by t (Fig.

11) as described already. Therefore, the ball 7 bears against the rear flow plate 12 by its own weight as shown in Fig. 11. When the brake pedal (not shown) is pressed down, hydraulic pressure is supplied from the master cylinder (not shown). The ball 7 does not move until the vehicle velocity decreases down to a given velocity and so a certain gap is secured between the ball 7 and the seal member 17 on the piston 6. The hydraulic pressure passes around the ball 7 from the connection port 4, goes through the hole 5 in the piston 6, and reaches the connection port 2. Then, it is sent to the wheel cylinders. Under this condition. the braking forces applied to the front and rear wheels increase in proportion to the hydraulic pressure in the master cylinder.

The characteristics obtained at this time are indicated by line A1 (unloaded) and line At (loaded) in Fig. 14. In the graph of Fig. 14, the hydraulic pressure PM in the master cylinder, or the hydraulic pressure PF applied to the front wheels, is plotted on the horizontal axis, and the hydraulic pressure PR applied to the rear wheels is plotted on the vertical axis. In the graph, I, is an ideal partitioning curve in unloaded condition, and It is an ideal partitioning curve in loaded condition. Subsequently, the hydraulic pressure in the master cylinder increases, lowering the vehicle velocity greatly. In this state, the ball 7 rolls toward the piston 6 by inertia and is seated on the seal member 17, thus closing up the hole 5 in the piston 6 as shown in Fig. 12.Therefore, the hydraulic pressure is no longer sent to the wheel cylinders. The pressure in each wheel cylinder is kept constant. If the master cylinder supplies hydraulic pressure to increase the pressure in the chamber where the ball 7 is received, the piston 6 is not moved until a certain valve is reached, because of the difference in area of pressure-receiving surface between the opposite sides of the piston 6 and because of the biasing force of the spring 22.

Specifically, let A and B be the area of the larger portion of the piston 6 and the area of the smaller portion, respectively.

Also, let P, and Pb be the hydraulic pressure in each wheel cylinder and the hydraulic pressure in the master cylinder, respectively.

Since A > B, the piston 6 is not moved unless the pressure Pb increases to satisfy the relation P, x A + W *= Pb X B where E is the biasing force of the spring 22. The characteristics derived at this time are indicated by line B, (unloaded) and line B2 (loaded) in Fig. 14.

Under this condition, the braking force applied to the rear wheels does not increase if the braking force applied to the front wheels increases. Then, if the hydraulic pressure inside the master cylinder increases and the pressure on the entrance side increases so that the pressure Pb satisfies the aforementioned equation, the piston 6 advances. According to this, brake fluid in the chamber 18 flows into the wheel cylinders to increase the hydraulic pressure in each wheel cylinder. From the above equation, the pressure at this time is given by P, = B/A x Pb - W/A That is, the hydraulic pressure in each wheel cylinder increases at a rate which is B/A times as high as the rate at which the hydraulic pressure in the master cylinder increases. The characteristic obtained at this time is indicated by line C in Fig. 14, whether the vehicle is loaded or unloaded.In this way, the brake fluid pressure control valve permits appropriate hydraulic pressure to be supplied to the wheel cylinders. Hence, stable braking effort is derived.

If the hydraulic pressure in the master cylinder increases rapidly by hard braking or for other reason, then brake fluid flows into the chamber 18 through the hole 5 in the piston 6, increasing the hydraulic pressure inside the chamber 18 quickly. Since the bleeding disk 2 closes the connection port 2 for connection with the wheel cylinders, hydraulic pressure is supplied to the wheel cylinders only through the liquid passage 23. Thus, it is unlikely that the hydraulic pressure in each wheel cylinder increases rapidly. If a very large increase in the pressure takes place, the outer periphery of the bleeding disk 19 deflects, further narrowing the fluid passage 23. This certainly prevents hydraulic pressure inside each wheel cylinder from increasing. When the brakes are released, the spring 22 returns the piston 6 to its initial position. Therefore. if the brakes are applied immediately thereafter, the performance does not become unstable.

Claims (3)

WHAT IS CLAIMED IS:

1. A valve for controlling the pressure created by brake fluid, said valve comprising: a housing having a connection port for ccnnection with wheel cylinders, the connection port being formed at the front end of the housing; a second connection port for connection with a master cylinder, the second connection port being formed at the rear end of the housing; a piston fitted in the housing so as to be slidable, the piston having a-)tele in its center: a ball movably placed between the piston and the second connection port to open or close the hole in the center of the piston; radially arranged ball guide portions formed on the side of ths piston inside the housing: and a flow plate disposed on the sideof the second connection port inside the housing and provided with holes for permitting passage of brake fluid, the holes in the flow rate being shifted circuferentially of the housing fro the ball guide portions.

f. A valve for controlling the pressure created by brake fluids said valve comprising: a housing having a connection port for connection with wheel cylinders, the connection port being formed at the front end of the housing; a second connection port for connection with a master cylinder, the second connection port being formed at the rear end of the housing; a piston fitted in the housing so as to be slidable, the piston having a hole sn its center; a ball movably placed between the piston and the second connection port to open or close the hole in the center of the piston; a bleeding disk mounted between the piston in the housing and the second connection port; a spring mounted between the bleeding disk and the piston to bias the disk toward the front end of the housing and to bias the piston toward the rear end of the housing; ; and a passage through which brake fluid flows and which is formed between the bleeding disk and the front end of the housing.

3. A valve for controlling the pressure created by brake fluid substantially as hereinbefore described with reference to the accomtanying drawings.