Brakes – Elements – Shoes
Reexamination Certificate
1998-10-22
2001-01-09
Graham, Matthew C. (Department: 3613)
Brakes
Elements
Shoes
C188S073370
Reexamination Certificate
active
06170620
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a disc brake, and more particularly to an anti-squeal shim structure therein for eliminating “brake squeal” and for heat insulation.
2. Related art
A disc brake generally includes a disc rotor rotating with a wheel of an automotive vehicle, a pair of friction pads each having a backing plate and a friction member secured to the disc rotor side of the backing plate, a caliper secured to a support member of the vehicle and supporting the friction pads movably toward and away from opposite friction surfaces of the disc rotor, and hydraulic actuating means such as a hydraulic cylinder urging the friction pads through forcing members such as a brake piston and a finger of the caliper against the friction surfaces of the disc rotor to restrain a rotation of the disc rotor.
With such a construction, a disc brake may under some conditions emit squealing noise in operation. This brake squeal noise is considered to be caused by relative displacements between the backing plates of the friction pads and the forcing members and by vibrations due to interactions between the friction pads and the disc rotor when the friction pads are urged against the disc rotor.
To reduce or eliminate such brake squeal noise, generally anti-squeal shims each made of a steel plate with damping material layers applied to both faces thereof have been interposed between the friction pads and the forcing members. In most cases, each damping material layer of the anti-squeal shims is formed of a layer consisting solely of a synthetic rubber of about 100 microns thick, the surface of which layer further being coated with a graphite layer to decrease the coefficient of friction.
However, the conventional anti-squeal shim with the rubber only layer suffers from the following shortcomings. Satisfactory vibration damping properties cannot be obtained, and thereby the brake squeal cannot be prevented satisfactorily. When the anti-squeal shim is urged against the caliper, a lateral flow is occurred in the rubber layer thereof and the layer is apt to come off. Since the heat resisting temperature of the rubber layer is low, usually about 150° C., the frictional heat produced between the friction pad and the disc rotor and transmitted to the anti-squeal shim through the friction pad ages and rags the rubber layer in a relatively short period of time. Therefore, the conventional anti-squeal shim is not durable, and thereby the effect of reducing the brake squeal is further deteriorated in a relatively short period of time.
The present inventor has disclosed another type of anti-squeal shim, in Japanese Patent Laying-open Publication No. Showa 63-101530, wherein the damping material layers applied to the both sides of a metal plate are formed of a compound including a heat resistant nonmetal fiber other than asbestos, an elastomer and a filler. According to this anti-squeal shim, the effect of reducing the brake squeal can be heightened, there is little danger of a lateral flow occurring in the damping material layers, or the compound layers, and the heat resisting temperature of the compound layers is high, thus the anti-squeal shim is durable and can keep the effect of reducing the brake squeal stably in a long period of time. In addition, the anti-squeal shim has a good heat insulation property and reduces the heat transfer from the friction pad to the brake fluid in the hydraulic system therethrough, improving the reliability of the hydraulic system of the brake apparatus.
However, the anti-squeal shim with the compound layers presents problems discussed hereinafter. The greater the percentage of the heat resisting nonmetal fiber and the filler in the compound is, the higher become the effect of reducing the brake squeal and the heat insulation property of the anti-squeal shim. The reason for it appears to be that the greater the percentage of the nonmetal fiber and the filler in the compound is, the more the compound has voids therein. However, as the percentage of the nonmetal fiber and the filler is increased in the compound to improve the effect of reducing the brake squeal noise and the heat insulation property, the percentage of the elastomer is inversely decreased, causing the bonding strength between the nonmetal fiber and the elastomer in the compound to be decreased. As a result, separations between the elastomer and the nonmetal fiber are apt to occur in the compound layer during a punching process or the like in the manufacturing process of the anti-squeal shim.
On the other hand, in a disc brake, generally, the contact area between the anti-squeal shim and the forcing member such as a brake piston or a finger of the caliper is relatively small. For example, generally the brake piston is hollow with a thin wall shell with the open end thereof opposed to the anti-squeal shim, and thereby the contact area between the anti-squeal shim and the piston forms a ring shape. Accordingly, in case of the conventional anti-squeal shim wherein both faces thereof are coated with the damping material layers, if the anti-squeal shim and the forcing member are directly opposed to each other, an extremely high pressure will be partially applied to the damping material layer on the side of the forcing member. To obviate the above-mentioned disadvantage, another shim, so-called “backing-up shim”, has heretofore been interposed between the anti-squeal shim and the forcing member.
However, the disc brake apparatus equipped with the backing-up shim has the following deficiencies.
(a) Numbers of parts as well as manufacturing costs are increased.
(b) Even if the anti-squeal shim is provided with holes therethrough or recesses at the periphery thereof to improve the heat insulating effect, the desired effect cannot be produced because the backing-up shim covers the holes or recesses.
SUMMARY OF THE INVENTION
It is accordingly a principal object of the present invention to provide a disc brake and anti-squeal shim therefor which can improve the effect of reducing the brake squeal and the heat insulation property.
It is another object of the present invention to provide a disc brake and anti-squeal shim therefor which can obviate the separations between the elastomer and the nonmetal fiber in the damping material layer, or compound layer.
It is a further object of the present invention to provide a disc brake and anti-squeal shim therefor which can dispense with a backing-up shim.
An anti-squeal shim in accordance with the present invention comprises a metal plate and a compound layer applied at least to one side of the metal plate. The compound includes a nonmetal fiber other than asbestos, an elastomer, a filler and small pieces, or grains or particles, of cork. The compound may be applied either only to one side of the metal plate or the both sides of the metal plate.
Cork has numerous closed cells disposed throughout its mass. Each of the cells contains air, which generally occupies 50% of the total volume of cork. Accordingly, in the present invention, voids in the compound can be increased by addition of the small pieces of cork to the compound without increasing the percentage of the fiber and the filler. As a result, the effect of reducing the brake squeal and the heat insulation property can be considerably improved and yet separations between the elastomer and the nonmetal fiber in the compound layer can be obviated.
In a particular aspect of the present invention, the compound layer is applied only to one side of the metal plate.
According to a disc brake provided by the present invention, a pair of friction pads are positioned on opposite sides of a disc rotor rotating with a wheel of an automotive vehicle so as to be movable toward and away from the opposite sides of the disc rotor. Each of the friction pads has a backing plate and a friction member secured to the disc rotor side of the backing plate. A hydraulic actuating means is provided to urge the friction pads through forcing members against the opposite sides of the disc rotor to restr
Akita Hiroaki
Fukawa Toyotaka
Birch & Stewart Kolasch & Birch, LLP
Graham Matthew C.
Nguyen Xuan Lan
U-Sun Gasket Corporation
LandOfFree
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