JPS599773B2 - Disc brake piston - Google Patents

Abstract

PURPOSE:Proposed is a piston used for a disc brake which is operated by liquid pressure, the total composition of which is made of synthetic resin material so as to minimize its weight.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piston for a hydraulically actuated device for a disc brake.

Since disc brakes have lower gain than drum brakes, the mechanical gain leading to the pre-Niki pedal cylinder is increased #,:7,-:
,,W.

For this reason, the pressure receiving area of the piston in the disc brake hydraulically actuated device is made larger than that of the drum brake, but this increases the weight of the entire hydraulically actuated device including the piston.

In order to reduce the weight of the piston, the piston of a conventional hydraulic actuator for a disc brake is formed into a hollow or cup shape by cutting or forging, as illustrated in FIG.

This piston 5 is fitted into the cylinder 4, its open end abuts against the back plate 8, and the friction pad 1o coupled thereto is pressed against the brake disc 2, while the hydraulic reaction force causes the cylinder 4 to The integral caliber 3 is moved relative to the fixed member 1, the reaction force piece 6 collides with the back plate 7, and the friction pad 9 coupled thereto is pressed against the brake disc 2, thereby applying a braking force to the brake disc 2. Grant.

The outer periphery of the piston 5 is cut off at the open end to form a small-diameter portion 13 . One end of a cylindrical flexible dust-proof boot 12 is tightly fitted and supported by the small-diameter portion 13 , and the other end is attached to the cylinder 4 . It is adapted to be locked in an annular groove.

Since such a conventional piston 5 has a part to which the dustproof boot 12 is attached, it would be difficult to reduce the weight by making the thickness of other parts sufficiently thin and uniform, which would complicate the process and be disadvantageous in terms of cost. .

SUMMARY OF THE INVENTION An object of the present invention is to provide a piston for a hydraulic actuation device for a disc brake that is easy to manufacture and can be significantly reduced in weight by bonding a synthetic resin layer to a cup-shaped core metal.

For this reason, the configuration of the present invention includes a core bar 19 that integrally has a working piece 21 that expands radially outward at the open end of the cup-shaped body, at least a closed end wall 26 of the core bar and the working piece 21.
1, and a synthetic resin layer covering both the inner and outer walls of the outer circumferential wall surface of the core metal and the closed end wall and filling the inside of the through holes, and forming a piston body. A hard metal coating is formed on the entire surface.

According to the present invention, it is possible to achieve weight reduction that far exceeds the weight reduction limit of conventional steel pistons, and moreover, it exhibits functions comparable to those of steel pistons.

If the thickness of the metal coating provided on the surface of the piston is 5 μm or more, the wear conditions during contact with the cylinder will be the same as those of conventional steel pistons, and there will be no problem.

Furthermore, since the synthetic resin layer that makes up the piston body does not come into contact with brake fluid, there is no change in material quality or strength.

The present invention will be explained based on specific examples.

As shown in FIG. 2, a synthetic resin layer 18 is bonded around a cup-shaped core metal 19 which is preferably press-molded to form a piston body 15, and a metal coating 17 is provided on the entire surface of the piston body 15. It is formed.

The cup-shaped core bar 19 is integrally formed with a closed end wall 26 and a working piece 21 formed by expanding the open end radially outward. Through holes 23, 22, and 29 are formed so as to tightly bond to the synthetic resin layer 18.

The through holes 23 and 22 are provided so that the synthetic resin layer 18 is joined at both the inner and outer end surfaces of the closed end wall 26 during molding of the piston.

Further, the through hole 29 is provided to exhaust the reaction gas generated from the synthetic resin layer 18 to the outside.

If there is no through hole 29, reaction gas will easily get trapped in the corner of the core metal 19 at the open end, and if the gas does not escape, the synthetic resin layer 18
Holes are formed inside the material, which reduces its strength.

As the synthetic resin material constituting the piston body 15, polyethylene terephthalate, ABS resin, nylon, acetate plastic, polycarbonate, acetal homopolymer, acetal copolymer, noryl resin, polyimide resin, polyphenylene sulfide resin, etc. can be used.

Among these, especially when using nylon, it is effective to mix about 30% by weight of glass fiber as a reinforcing material.

Furthermore, when using Noryl resin, it is appropriate to mix steel or other metal fibers, thereby further increasing the strength.

For other synthetic resins, it is also effective to mix metal fibers or metal powder instead of glass fibers to improve the strength.

When using steel as the metal fiber, if there is a problem such as rusting in relation to the synthetic resin, the synthetic resin should be mixed with a material that has been previously subjected to surface treatment, such as plating or coating.

Next, regarding the metal coating 17, it is effective to apply industrial hard chrome plating.

This thickness needs to be at least 5 μm.

In addition to chrome plating, lead plating can also be applied to practical use, which is advantageous in terms of cost.

The frictional heat generated during braking is transferred to the friction butt 10 and the back plate 8.
It is transmitted to the piston 5 through the diameter, and its temperature can reach 400°C or more.

Under such high temperatures, the synthetic resin layer 18 tends to undergo thermal decomposition when exposed to oxygen in the air.

However, by providing the metal coating 17 by plating, thermal decomposition of the synthetic resin layer 18 can be prevented.

Furthermore, if the synthetic resin layer 18 comes into direct contact with the brake fluid, a reaction may occur during long-term use and contaminate the brake fluid, but this can also be prevented by the metal coating 17 formed by plating.

To actually manufacture a piston, glass fiber or metal powder is mixed as a reinforcing material into the synthetic resin material mentioned above, this material is filled into a mold, and the core metal 19 is embedded inside the material. Then heat and press to shape.

During this heating and pressing process, an annular groove 16 for attaching the dustproof boot is simultaneously formed.

Next, the entire surface of the piston body 15 obtained by molding is plated with chrome to complete the piston body 15.

The outer shape of the action piece 21 may be circular, but if it is made into a rectangular or other suitable shape in accordance with the shape of the back plate of the friction pad, a more uniform hydraulic pressure can be transmitted to the friction pad.

By using a synthetic resin material, the piston of the hydraulic actuator according to the present invention can be significantly lighter than conventional steel pistons.

By using the core bar 19, the annular groove 16 for attaching the dustproof boot and the action piece 21 for transmitting hydraulic pressure to the friction pad can be integrally and easily formed at the open end.

Since the hard metal coating 17 is applied to the entire surface of the piston, the material of the synthetic resin layer 18 is prevented from changing due to brake fluid or from changing over time due to contact with the outside air, and the fitting part with the cylinder is prevented. Sufficient strength against wear.

If a reinforcing material such as glass fiber or metal fiber is mixed into the synthetic resin layer 18 constituting the piston body, the compressive strength can be improved.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view illustrating a conventional disc brake equipped with a piston, FIG. 2 is a longitudinal sectional view of a piston of a hydraulically actuated device according to the present invention, and FIG. 3 is a left side view of the same piston. 15... Piston, 17... Metal coating, 18... Gosho resin layer, 19... Core metal, 21... Working piece , 22 , 23, 29...
...through hole.

Claims (1)

[Claims] 1. A core metal 19 that integrally has a working piece 21 that expands radially outward at the open end of the cup-shaped body, and a through hole provided in at least the closed end wall 26 of the core metal and the working piece 21, respectively; A piston body is formed by a synthetic resin layer that covers the outer peripheral wall surface of the core metal and both the inner and outer wall surfaces of the closed end wall and is filled inside the through hole, and a hard metal coating is formed on the entire surface of the piston body. A piston for a hydraulic actuation device for a disc brake, characterized by: