JPH0525705B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to an improvement in a tandem master cylinder that generates two hydraulic pressures for braking that are hydraulically independent from each other in a braking device for an automobile or the like.

(Background of the invention) In some conventional tandem master cylinders, the mounting load of the first return spring behind the floating piston is made larger than the mounting load of the second return spring in front of the floating piston. The piston and the floating piston are moved forward at the same time, and the two return ports are closed at the same time to reduce the ineffective pedal stroke during braking. A pressure equalizing plunger is installed to receive the respective hydraulic pressures of the second hydraulic pressure chamber in front of the floating piston from the front and back, and while the main piston and the floating piston are moving forward together, the pressure generated in the second hydraulic pressure chamber is The floating piston passes through the return port by causing the pressure equalizing plunger to retreat relative to the forward movement of the floating piston by hydraulic pressure and suppressing a sudden rise in hydraulic pressure in the second hydraulic pressure chamber. It also prevents the piston seal from galling, and further reduces the amount of brake fluid lost, which would otherwise be buffled into the reservoir from the return port and become ineffective for braking action, further reducing the ineffective petal stroke. The conventional tandem master cylinder as described above is already known from Japanese Patent Publication No. 60-21098 by the applicant of the present patent.

However, in the conventional type described above, since the pressure equalizing plunger is retracted with respect to the floating piston by the hydraulic pressure in the second hydraulic pressure chamber, the rising of the first hydraulic pressure chamber and the second hydraulic pressure chamber is If the initial hydraulic pressure difference is small, it has been reported that the pressure equalizing plunger does not move back, which causes a problem in that the effectiveness of preventing galling of the piston seal is reduced. This problem arises because when the difference in the mounting load between the first return spring and the second return spring is small, the sliding resistance of the pressure equalizing plunger and the spring force of the spring that urges the pressure equalizing plunger forward are large. This occurs when the braking operation is carried out slowly so that the hydraulic pressure in the first and second hydraulic pressure chambers rises slowly.

(Object of the Invention) An object of the present invention is to solve the above-mentioned problems, and even when the difference in mounting load between the first and second return springs is small, the sliding resistance of the small-diameter piston in the floating piston and the small-diameter piston spring To provide a tandem master cylinder capable of preventing galling of a piston seal of a floating piston even when the spring force of the cylinder takes a large value or when a braking operation is performed slowly.

(Characteristics of the Invention) In order to achieve the above object, the present invention provides a floating piston with a cylinder hole formed coaxially with a first
A small-diameter cylinder communicating with the hydraulic pressure chamber and the second hydraulic pressure chamber is provided, and a small-diameter piston is loaded into the small-diameter cylinder to partition the first hydraulic pressure chamber and the second hydraulic pressure chamber,
A rod member is disposed between the small diameter piston and the front end wall of the cylinder to define the most advanced position of the small diameter piston with respect to the floating piston, thereby determining the relative position of the small diameter piston with respect to the moving floating piston at the start of braking. It is characterized in that it is mechanically moved back by a rod member to moderate the degree of volume reduction of the second hydraulic chamber.

(Embodiment of the invention) FIG. 1 is a sectional view showing an embodiment of the invention.

A cylinder hole 3 is formed inside the body 2 of the tandem master cylinder 1, and a main piston 4 and a floating piston 5 are movably loaded therein. A reservoir 6 is attached to the upper part of the body 2, and a predetermined amount of brake fluid is filled inside the reservoir 6. 7 is a mounting flange, and 8 is a push rod that is pushed by a servo motor or a brake pedal (both not shown).

In the cylinder hole 3, a first hydraulic pressure chamber 9 is formed between the main piston 4 and the floating piston 5, and a second hydraulic pressure chamber 11 is formed between the floating piston 5 and the cylinder front end wall 10. . 12, 13, 1
4 and 15 are annular piston seals that are attached to the main piston 4 and the floating piston 5, respectively, and slide on the inner wall of the cylinder hole 3.

A stop ring 17 is fixed to the left open end 16 of the cylinder bore 3, and the stop ring 17 sets the maximum retracted position, ie, the return position, of the main piston 4. One end of a locking rod 18 is screwed into the front end of the main piston 4, and a head portion 19 is formed at the other end of the locking rod 18. Head part 19
is arranged so as to be engageable inside the cup-shaped spring receiver 20. A first return spring 21 is compressably loaded between the main piston 4 and the cup-shaped spring receiver 20 and has an installation load set by the engagement between the head portion 19 and the cup-shaped spring receiver 20. Ru. 22 is a return port that releases the pressure in the first hydraulic chamber 9 to the atmospheric pressure in the reservoir 6;
When the pressure in the first hydraulic chamber 9 becomes negative than the atmospheric pressure in the reservoir 6 during a brake return operation, etc., air is released between the outer periphery of the main piston 4 and the piston seal 13 and the inner wall of the cylinder hole 3. , a supply hole for sucking the brake fluid from the reservoir 6 into the first hydraulic pressure chamber 9, and 24 an output hole for connecting the first hydraulic pressure chamber 9 to one brake system (not shown). Also, a chamber 25 surrounded by a cup-shaped spring receiver 20
is in constant communication with the first hydraulic chamber 9 through a small hole 26.

The rear part of the floating piston 5 is always in contact with the collar part 27 formed at the front part of the cup-shaped spring receiver 20, and when the main piston 4 is in the illustrated return position,
The floating piston 5 is given a maximum separation position from the main piston 4, ie, the return position shown in FIG. 1, by the mounting load of the first return spring 21. Reference numeral 28 denotes a stop bolt that limits the maximum retracted position of the floating piston 5, and is provided as necessary. A second return spring 29 having a smaller installation load than the first return spring 21 is loaded between the front part of the floating piston 5 and the front end wall 10 of the cylinder. 5 is biased in the return direction. 30 is a return port for releasing the pressure in the second hydraulic pressure chamber 11 to the atmospheric pressure in the reservoir 6;
When the pressure in the second hydraulic chamber 11 becomes negative than the atmospheric pressure in the reservoir 6 during a brake return operation or the like, the floating piston 5 and the piston seal 1
A supply hole 32 allows the brake fluid in the reservoir 6 to be sucked into the second hydraulic pressure chamber 11 from between the outer circumference of the cylinder hole 5 and the inner wall of the cylinder hole 3. This is the output hole that connects the

A small diameter cylinder 33 is formed inside the floating piston 5 coaxially with the cylinder hole 3, and a small diameter piston 34 is loaded into the small diameter cylinder 33 so as to be movable back and forth. 35 and 36 are respectively attached to the small diameter piston 34 and are connected to the small diameter cylinder 33.
This is a small diameter piston seal that slides on the inner wall of the piston. The small diameter piston seal 35 transfers the hydraulic pressure of the chamber 25 which is communicated with the first hydraulic pressure chamber 9 through the small hole 26 to the chamber 38 which is communicated with the second hydraulic pressure chamber 11 through the small hole 37.
The small-diameter piston seal 36 is installed to prevent leakage from the side of the chamber 3.
It is installed so that the hydraulic pressure on the 8 side will not leak to the chamber 25 side.

The small-diameter piston 34 has a boss 39 formed at its rear portion that faces the head portion 19 of the locking rod 18 so as to be able to come into contact with it, and a rod member 4 formed at its front portion.
The rear end of 0 is screwed together. The rod member 40
is inserted through a through hole 42 provided at the front end 41 of the floating piston 5, and a head portion 43 is formed at the front end. The small-diameter piston 34 and the rod member 40 are urged forward by a small-diameter piston spring 44 loaded in the chamber 25, and the head portion 43 and the recess 45 formed in the front end wall 10 come into contact with each other. . Due to the abutment between the head portion 43 and the recess 45, the maximum forward position of the small diameter piston 34 relative to the floating piston 5 is defined by the length of the rod member 40.

The operation of the embodiment shown in FIG. 1 will be explained below.

The push rod 8 is not pushed and the main piston 4
When both the floating piston 5 and the floating piston 5 are in the illustrated return position, the first hydraulic chamber 9 and the second hydraulic chamber 11 are connected to the reservoir 6 via the return ports 22 and 30, respectively.
and is open to atmospheric pressure.

When the push rod 8 is pushed to the right by the driver, the second return spring 29 is compressed first by the action of the first return spring 21 which has a larger mounting load than the second return spring 29.
The main piston 4 and the idle piston 5 are simultaneously advanced while maintaining the illustrated spacing. Therefore, one return port 22 is simultaneously closed by the piston seal 13 and the other return port 30 is simultaneously closed by the piston seal 15, and the second hydraulic chamber 11 is compressed.

When the floating piston 5 is advanced as described above, the relative position of the small diameter piston 34 whose most advanced position is defined by the rod member 40 and the floating piston 5 is moved, and the volume of the chamber 25 is increased. The volume of chamber 38 increases. The volume increase/decrease of the chamber 38 and the chamber 25 described above is performed by retracting the small diameter piston 34 relative to the floating piston 5 due to the hydraulic pressure difference between the first hydraulic pressure chamber 9 and the second hydraulic pressure chamber 11. will also be carried out with certainty.

Therefore, the forward stroke of the floating piston 5 is:
It corresponds to the sum of the amount discharged from the output hole 32 and the volume increase of the chamber 38, and is larger than that without the small diameter piston 34. 2
The rise in hydraulic pressure in the hydraulic pressure chamber 11 is alleviated, and galling of the piston seal 15 by the return port 30 is prevented.

On the other hand, due to the reduction in the volume of the chamber 25, hydraulic pressure is generated in the first hydraulic pressure chamber 9 even if the relative separation position between the main piston 4 and the floating piston 5 does not change. However, this hydraulic pressure is due to the product of the effective area of the small diameter piston 34 and the relative retraction amount of the small diameter piston 34 with respect to the floating piston 5, and does not act so that the piston seal 13 is squeezed by the return port 22. , is mostly consumed as the amount discharged from the output hole 24.

As described above, when the main piston 4 and the floating piston 5 move forward and the piston seals 13 and 15 pass through the return ports 22 and 30, respectively,
Compression of the second return spring 29 reduces the load difference between the first return spring 21 and the second return spring 29. This first return spring 2
1 and the second return spring 29, the floating piston 5 is moved back and forth by the hydraulic pressure, so that the hydraulic pressure in the first hydraulic pressure chamber 9 and the second hydraulic pressure chamber 1
1 is balanced, and the output hole 2
The hydraulic pressures outputted from brakes 4 and 32 have the same pressure and are discharged to their respective brake systems.

When the push rod 8 is pushed when the brake system connected to the first hydraulic pressure chamber 9 fails, the main piston 4 and the floating piston 5 move forward as one, and the second hydraulic pressure Hydraulic pressure is generated in chamber 11 . When the hydraulic pressure becomes larger than the mounting load of the first return spring 21, the first return spring 21 is compressed, and the pushing force of the push rod 8 is
This is directly transmitted to the floating piston 5 via the main piston 4 and the cup-shaped spring receiver 20, and the hydraulic pressure in the second hydraulic pressure chamber 11 increases, and the brake system connected to the output hole 32 is operated. At this time, small diameter piston 3
4 is moved in the backward direction against the small-diameter piston spring 44 by the hydraulic pressure of the second hydraulic pressure chamber 11, but as the first return spring 21 is compressed, it protrudes into the interior of the chamber 25. When the head portion 19 of the locking rod 18 and the boss 39 come into contact with each other, the small-diameter piston 34 is prevented from retreating beyond a predetermined value. Further, in the early stage of the rise of the hydraulic pressure in the second hydraulic pressure chamber 11, if a hydraulic pressure that causes the small diameter piston 34 to retreat is generated before the first return spring 21 is sufficiently compressed, the rod member 40
The head portion 43 of the floating piston 5 comes into contact with the front end portion 41 of the floating piston 5, thereby preventing the piston from retreating more than a predetermined amount.

When the push rod 8 is pushed when the brake system connected to the second hydraulic pressure chamber 11 fails,
First, the main piston 4 and the floating piston 5 move forward together, the second return spring 29 is compressed, and the front end 41 of the floating piston 5 comes into contact with the cylinder front end wall 10. During the above operation, the chamber 25, which is moved forward together with the floating piston 5, is compressed by the small diameter piston 34, and the hydraulic pressure in the chamber 25 reaches the first
It is discharged from the hydraulic pressure chamber 9 through the output hole 24. Next, after the floating piston 5 comes into contact with the cylinder front end wall 10, the hydraulic pressure in the first hydraulic chamber 9 further increases due to the compression of the first return spring 21, and the output hole 2
The brake system connected to 4 is operated.

FIG. 2 is a partial sectional view showing another embodiment of the invention. Note that the same parts as in the embodiment shown in FIG. 1 are designated by the same reference numerals.

The difference from the embodiment shown in FIG. 1 is that the head 43 of the rod member 40 is engaged with a spring retainer 46 that is pressed against the cylinder front end wall 10 by the second return spring 29. By configuring this, the small diameter piston spring 44 (FIG. 1) can be omitted.

FIG. 3 is a partial cross-sectional view showing another embodiment of the invention. Like the embodiment shown in FIG. 2, the same parts as in the embodiment shown in FIG. 1 are designated by the same reference numerals.

The embodiment shown in FIGS. 1 and 2 has a screw hole 48 formed in the front end wall 47 of the cylinder.
The difference is that a rod member 49 inserted from the outside is fixed. By configuring as described above, the most forward position of the small diameter piston 34 can be defined from the outside of the body 2, and the most forward position of the small diameter piston 34 can be easily changed as necessary by replacing the rod member 49. can do.

(Modification) The rod member 40 in the embodiment shown in FIG.
Although it is configured to be screwed together with the small diameter piston 34, it may be formed integrally with the small diameter piston 34.

(Effects of the Invention) As explained above, according to the present invention, the floating piston is formed coaxially with the cylinder hole, and the first
A small-diameter cylinder passing through the hydraulic pressure chamber and the second hydraulic pressure chamber is provided, and a small-diameter piston that partitions the first hydraulic pressure chamber and the second hydraulic pressure chamber is loaded into the small-diameter cylinder,
Since a rod member is arranged between the small diameter piston and the front end wall of the cylinder to define the most advanced position of the small diameter piston relative to the floating piston, even if the difference in the mounting loads between the first and second return springs is small, the small diameter Even if the sliding resistance of the piston or the spring force of the small diameter piston spring takes on a large value,
Alternatively, even if the braking operation is performed slowly, galling of the piston seal of the floating piston can be prevented.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, and FIG.
The figure is a partial sectional view showing another embodiment of the present invention.
The figure is a partial sectional view showing another embodiment of the invention. 1... Tandem master cylinder, 2... Body, 3... Cylinder hole, 4... Main piston, 5...
...Floating piston, 6...Reservoir, 8...Push rod, 9...First hydraulic pressure chamber, 10, 47...Cylinder front end wall, 11...Second hydraulic pressure chamber, 12-15
... Piston seal, 18 ... Locking rod, 19
...Head part, 20...Cup-shaped spring holder,
21...First return spring, 22...Return port, 25...Chamber, 26...Small hole, 29...Second return spring, 30...Return port, 3
3...Small diameter cylinder, 34...Small diameter piston, 3
5, 36...Small diameter piston seal, 37...Small hole, 38...Chamber, 39...Boss, 40.49...
Rod member, 41...front end, 42...through hole,
43...Head portion, 44...Small diameter piston spring, 45...Concave portion, 46...Spring retainer, 48...Threaded hole.

Claims (1)

[Claims] 1. A main piston is placed at the end of the cylinder hole, and a floating piston is placed between the main piston and the front end wall of the cylinder.
A first hydraulic pressure chamber is formed between the main piston and the floating piston, a second hydraulic pressure chamber is formed between the floating piston and the front end wall of the cylinder, and a first hydraulic pressure chamber is formed at the rear of the floating piston. The mounting load of the return spring is made larger than the mounting load of the second return spring in front of the floating piston, and the mounting load of the first return spring is reduced by the locking rod connected to the main piston and the locking rod receiving member connected to the floating piston. In the tandem master cylinder, the cylinder hole is provided with a return port that forms a regulating locking means and is opened and closed by piston seals attached to the front ends of the main piston and the floating piston. A small-diameter cylinder is provided coaxially with the first hydraulic pressure chamber and the second hydraulic pressure chamber, and the small-diameter cylinder includes:
A rod is loaded with a small-diameter piston that partitions the first hydraulic pressure chamber and the second hydraulic pressure chamber, and is provided between the small-diameter piston and the front end wall of the cylinder and defines the most advanced position of the small-diameter piston with respect to the floating piston. A tandem master cylinder characterized by the arrangement of parts.