JPS636391B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a master cylinder for operating a brake or the like.

In hydraulic brakes, which are widely used in automobiles, when the brake pedal is depressed, the master cylinder's push rod is pushed, which moves the master cylinder's piston and pumps out oil. . This oil then operates the wheel cylinder, causing the brake shoe to move and press the lining against the brake drum. In order to increase the braking force of such brakes, the wheel cylinders and servo cylinders may be made larger. However, increasing the size of the wheel cylinder requires a large amount of oil to close the gap between the lining and the drum. In addition, the amount of oil consumed to operate the booster such as the vacuum servo increases considerably, and moreover, this must be supplied from the master cylinder. Therefore, if the braking force of the brake is increased, the amount of oil consumed from the moment the brake pedal starts to be depressed until the brake actually exerts the braking force increases. As a result, the pedal stroke required before the brakes are activated increases, resulting in a poor feeling when applying the brakes.

In order to improve this situation, for example,
As seen in Publication No. 64567, a small diameter piston is integrally installed in a large diameter cylinder into which a large diameter piston is fitted, which is operated by a push rod, and this small diameter piston is fitted into the small diameter cylinder. By communicating a large-diameter liquid chamber formed by a large-diameter piston and cylinder with a small-diameter liquid chamber formed by a small-diameter piston and cylinder through a through hole provided in the small-diameter piston. During the initial stroke, the movement of the large-diameter piston sends the oil in the large-diameter liquid chamber through the communication hole and the small-diameter liquid chamber, and the volume of the large-diameter liquid chamber becomes sufficiently small (becomes zero). After that, there is a type that moves a small diameter piston together with a large diameter piston to send out oil from a small diameter fluid chamber, thereby reducing the brake pedal stroke required for the brake to generate braking force. .

However, in the case of such a conventional example, it is necessary to provide two cylinders, and
It is necessary to provide a check valve to prevent oil from flowing backwards from the small-diameter liquid chamber to the large-diameter liquid chamber, which complicates the configuration and also reduces oil flow resistance. The problem is that it increases.

Furthermore, as seen in Japanese Patent Application Laid-Open No. 57-41245, it is possible to reduce the number of parts by using an oddly shaped cylinder and an oddly shaped piston, but even in this case it is possible to reduce the number of parts in a limited space. Since it is necessary to provide a valve, there are still problems in that the structure cannot be simplified and the oil flow resistance cannot be reduced.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a master cylinder that is simple in structure and has excellent operability and reliability.

In order to achieve such an object, the present invention provides a cylinder whose front end has a smaller inner diameter than other parts, a first piston that fits into the large diameter part of this cylinder, and a small diameter part of the cylinder. and a second piston having a small diameter portion that fits into the large diameter portion of the cylinder and a large diameter portion that fits into the large diameter portion of the cylinder. Also,
A large-diameter liquid chamber formed by sandwiching the second piston and a small-diameter liquid chamber are communicated through a through hole provided in the second piston, and are opposed to the rear end opening of the through hole. A valve is attached to the front end surface of the first piston. A return spring is provided that slides and biases the first piston rearward to form a predetermined gap between both pistons, while pushing the first piston forward against the return spring. and a return spring that slides and urges the second piston backward, and
Only when the first piston is located near the rear end of the cylinder, the first piston and the second piston
The cylinder is provided with a return port that connects a large diameter liquid chamber formed between the cylinder and the piston to a reservoir, thereby forming a master cylinder.

Therefore, in the initial stroke due to the pressing action of the plunger, only the first piston moves forward to reduce the volume of the large-diameter liquid chamber, so that the oil in the large-diameter liquid chamber is The gap is gradually reduced as the first piston approaches the second piston. In addition, in such an initial stroke, since the amount of decrease in volume per unit stroke is large, the amount of oil delivered is large.

Further, after the gap disappears, the through hole is closed and the second piston moves forward together with the first piston, so that the oil in the small diameter liquid chamber is sent out. Note that in such a second stage stroke, the volume reduction per unit stroke is small, so the amount of oil delivered is reduced, but the oil pressure is high.

On the other hand, when the pressing action by the plunger is released, the first piston and the second piston slide back almost simultaneously to the rear due to the tension of the return spring, and the first piston returns to the second piston at the same time.
The structure includes an on-off valve that closes the through hole only when it is in contact with the piston and opens it in other situations, so the resistance of the through hole can be reduced and the oil movement is prevented. The associated pressure loss can be reduced, and the operating force can be reduced.

The present invention will be explained below with reference to an illustrated embodiment.
FIG. 1 shows a master cylinder 1 according to this embodiment. This master cylinder 1 has a cylindrical shape, and a small diameter portion 2 is formed at the front end thereof. A first piston 3 and a second piston 4 having a smaller diameter than the first piston are housed in the master cylinder 1, respectively. A push rod 6 is inserted into a recess 5 formed on the back side of the first piston 3.
This push rod 6 is connected to a brake pedal (not shown). A primary cup 7 and a secondary cup 8 are provided on the outer circumferential side of the first piston 3.
are attached to each. A recess 9 is formed between the pair of cups 7 and 8. The liquid chamber formed by the recess 9 is connected to the port 1.
0 communicates with the reservoir 11. Further, the distal end side of the primary cup 7 of the piston 3 is communicated with a reservoir 11 via a return port 12. Furthermore, a rubber valve 13 is attached to the front end side of the piston 3.

Next, the second piston 4 has a through hole 14 formed in the center thereof in the axial direction. This piston 4 also has a primary cup 15 and a secondary cup 16 on its front end side and rear end side, respectively.
are installed in pairs. The primary cup 15 is in contact with the small diameter portion 2 of the cylinder 1. In addition, a recess 17 is provided on the outer circumferential side of the piston 4.
A liquid chamber formed by this recess 17 is communicated with the reservoir 11 through a port 18. A return spring 19 is attached to the front end of the piston 4, and a return spring 20 is also attached between the pistons 3 and 4.

Note that the master cylinder 1 is connected to, for example, a vacuum servo cylinder 21. This vacuum servo cylinder 21 is further connected to four wheel cylinders 22 that constitute wheel brakes.

In the above configuration, when the brake pedal is not depressed and the two pistons 3 and 4 are both in the backward movement position, the tip of the piston 3 and the piston are connected as shown in FIG. There is a constant gap S between the rear end of 4 and the rear end of 4.
The length of this gap S corresponds to the stroke required from when the brake pedal is first depressed until the brake generates a braking force. That is, the amount of oil delivered until this stroke S becomes zero is approximately equal to the amount of oil consumed until the brake lining moved by the wheel cylinder 22 comes into contact with the drum.

Therefore, when the brake pedal is depressed, the first piston 3 is moved to the right in FIG. 1 via the rod 6. Since the primary cup 7 of the piston 3 closes the return port 12, the oil on the front side is pressurized by the movement of the piston 3, and as a result, the oil passes through the through hole 14 of the second piston 4. Then, it is supplied to the vacuum servo cylinder 21. Oil is further supplied from this cylinder 21 to the wheel cylinder 22, and the wheel cylinder 2
2, the brake shoe is moved so that its lining comes into contact with the brake drum. This causes the brake to exert braking force. During the first stage stroke of the master cylinder 1, the primary cup 7 of the piston 3 is in contact with the larger diameter portion of the master cylinder 1, so the amount of oil delivered per unit stroke increases. There is.

Next, when the front end side of this piston 3 comes into contact with the rear end side of the second piston 4, the rubber valve 13 closes the through hole 14 of the second piston 4.
Therefore, after this, the first piston 3 and the second piston 4 will move together. and the second
Since the primary cup 15 of the piston 4 is in contact with the small diameter portion 2 of the master cylinder 1, the amount of oil delivered per subsequent unit stroke becomes smaller. In other words, in the second stage of stroke of the master cylinder 1, the amount of oil delivered per unit stroke decreases, but conversely the pressure of the oil increases.

Therefore, according to the master cylinder 1 according to this embodiment, the oil pressure in the master cylinder 1 with respect to the brake pedal depression force is as shown in FIG.
From point A, where the brakes begin to apply, the oil pressure generated by the master cylinder 1 increases rapidly. That is, as shown by the solid line in FIG. 2, the slope becomes large at point A. Incidentally, in a conventional master cylinder, the oil pressure changes linearly with respect to the pedal force, as shown by the chain line in the figure. Further, when the master cylinder 1 according to this embodiment is used, the relationship between the pedal force and the pedal stroke is as shown in FIG. 3, and the pedal stroke required to reach the point A where the brake exerts braking force is The stroke becomes. This value is clearly smaller than the conventional pedal stroke value L shown by the chain line in the figure, and therefore the pedal stroke required until the brake is activated is smaller.

As is clear from the above description, according to the present invention, during the initial stroke due to the pressing action of the plunger, only the first piston moves forward, reducing the volume of the large-diameter liquid chamber, while the second piston moves forward. In order to move close to the second piston, the oil in the large diameter liquid chamber is sent out through a through hole provided in the second piston and the small diameter liquid chamber, and the first piston approaches the second piston. As a result, the gap gradually decreases.

In addition, in the second stage of stroke where the gap disappears, the valve attached to the front end of the first piston comes into contact with the rear end opening of the through hole formed in the second piston and closes it. Since the second piston is moved forward by the first piston, the oil in the small diameter liquid chamber is now sent out.

Therefore, a large amount of low-pressure oil can be delivered during the initial stroke before the brake shoe is closed, and high-pressure oil can be delivered with a small operating force (pedal force) after the brake is activated. This improves the operability of the master cylinder.

In addition, since the through-hole is closed only when the first piston is in contact with the second piston and is provided with an on-off valve that opens the through-hole in other conditions, the liquid chamber has a large diameter. Since the resistance of the through hole that communicates with the small-diameter liquid chamber can be reduced, the pressure loss caused by the movement of oil can be reduced, and the first and second pistons can move smoothly. , the operating force of the master cylinder can be further reduced.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a master cylinder according to an embodiment of the present invention, Fig. 2 is a graph showing changes in oil pressure generated by the master cylinder with respect to brake pedal depression force, and Fig. 3 is a graph showing changes in oil pressure generated by the master cylinder according to the brake pedal depression force. 3 is a graph showing the relationship between brake pedal depression force and brake stroke when the brake pedal is pressed. In addition, in the reference numerals used in the drawings, 1...master cylinder, 2...small diameter portion, 3...first piston, 4...second piston, 14...through hole.

Claims (1)

[Claims] 1. A cylinder whose front end has a smaller inner diameter than other parts, a first piston that fits into the large diameter part of the cylinder, a small diameter part that fits into the small diameter part of the cylinder, and a large diameter part of the cylinder. A second piston is provided with a large-diameter portion that fits into the second piston, and a large-diameter liquid chamber and a small-diameter liquid chamber formed by sandwiching the second piston are provided in communication with each other. a through hole;
a valve mounted on the front end surface of the first piston facing the rear end opening of the through hole, and sliding the first piston rearward to form a predetermined gap between the two pistons; a return spring that urges the first piston; a push rod that pushes the first piston forward against the return spring; and a return spring that slides and urges the second piston backward; The cylinder is provided with a return port that communicates the large diameter liquid chamber formed between the first piston and the second piston with the reservoir only when the piston is located near the rear end of the cylinder. By this, in the initial stroke, the oil in the large diameter liquid chamber is sent out through the through hole provided in the second piston and the small diameter liquid chamber by the movement of the first piston, and the gap is closed.
A master cylinder characterized in that, after the gap disappears, the second piston is moved forward together with the first piston to send out the oil in the small diameter liquid chamber.