Brakes – Wheel – Axially movable brake element or housing therefor
Reexamination Certificate
1998-11-17
2001-02-27
Oberleitner, Robert J. (Department: 3613)
Brakes
Wheel
Axially movable brake element or housing therefor
C188S25000B, C188S25100R
Reexamination Certificate
active
06193025
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pad used for disk brakes that control the revolution of revolving parts of vehicles and machines.
2. Description of Background Information
Disk-brake pads are used for friction members in disk brakes that control the speed of automobiles, railway vehicles, and machines. The friction member comprises a backing plate that contacts a piston and a friction material that rubs against a disk. An underlayer material is sometimes provided between the backing plate and the friction material when the load for the friction material is severe or when the improvement of the performance of the friction material is required.
The underlayer material has three major functions. The first is to prevent the heat generated by friction from conducting to the brake piston. The second is to prevent the deterioration of the bonding between the friction material and the backing plate when the performance of the friction material is improved at the cost of bonding strength. The third is to reduce noises generated by the vibration of the friction material.
Therefore, it is desirable that the material used for the underlayer material not only be suitable for a friction material but also have a heat insulation effect, a good bonding with the backing plate, and an ability to compensate the performance weakness of a standard friction material.
A friction material particularly for heavy loads, known as a semimetallic pad, includes a substantial amount of steel fiber or steel particles. Because this pad has high thermal conductivity owing to its constituents and conducts the heat generated by friction to the backing plate readily, it is common to employ an underlayer material as a thermal insulator to prevent the heat conduction when this semimetallic pad is used.
In this case, the heat generated at the friction surface diffuses to both the disk and pad. When the pad has high thermal conductivity, it undesirably absorbs the heat. When the pad has low thermal conductivity, most of the heat is conducted to the disk and dissipated by the revolution of the disk. In other words, an underlayer material reduces the thermal conductivity of the pad and directs the generated heat to the revolving disk to be dissipated there.
An underlayer material should also have a strong bonding with the backing plate. In order to maintain the strong bonding in withstanding repetitive temperature variations, the underlayer material should have a composition similar to that of the friction material and thus have good compatibility with the friction material.
An underlayer material principally consists of fibrous materials, binders, and powder and/or granular fillers. Particularly, when a semimetallic material is used as the friction material, it is desirable that steel fiber be used as the fibrous material because the same has good compatibility with the friction material.
As the constituents thereof, some underlayer materials have the same phenolic resin-based binder as the friction material has and include a material having a cushion effect such as cashew dust or rubber powders to absorb vibration caused by friction. Because these organic substances have low thermal conductivity, small specific gravity, and small specific heat, they reduce the thermal conductivity of the underlayer material. A fibrous material is used to resist the shearing force generated between the disk rubbing surface and the backing plate when frictional force is applied. Inorganic fillers are used to reinforce heat-resisting properties.
As mentioned above, an underlayer material has various purposes, and to fulfill these purposes suitable materials are incorporated. However, under heavy load conditions, particularly when a car descends a long downhill with increased frequency of brake application, for instance, if the heat dissipation is insufficient from the brake, the heat generated by friction will accumulate in the disk and pad, raising the temperature thereof considerably. If this condition continues for a prolonged period of time or recurs many times, the organic materials used in the underlayer material will deteriorate and even carbonize in an extreme case, resulting in increased thermal conductivity and loss of the vibration absorption effect thereof.
SUMMARY OF THE INVENTION
The principal object of the present invention is to improve the heat-resisting property of an underlayer material and offer a reliable pad applicable to heavy-duty disk brakes.
The feature of the invention is that the underlayer material includes powders or granules of linear or branched plastic having a melting temperature of 200° C. or higher at normal pressure.
The heat-resisting property of the linear or branched plastic used affects the thermal decomposition property thereof. It is desirable that the heating loss thereof be 50% or less when measured by a thermobalance at 450° C. on a specimen 10 to 15 mg in weight when the temperature is raised by a rate of 10° C./min in the atmosphere. On the other hand, three-dimensionally cross-linked polymers lack sufficient elasticity to exert a cushion effect, although they have a superior heat-resisting property.
It is desirable that such linear or branched plastic be at least one kind of plastic selected from the group consisting of polyallylenesulfone, polyallylenesulfide, a liquid crystal polymer (LCP), and amorphous polyallylate or be a polymer alloy including any of these polymers. These plastic materials are used not only to utilize the heat of fusion when they melt but also to prevent gas generation due to decomposition thereof and of other materials. To exploit the advantages of the plastic, it is desirable that the underlayer material include steel fiber and at least one kind of fiber selected from the group consisting of copper or copper alloy fiber, organic fiber, and inorganic fiber. It is preferable that the underlayer material in the brake pad of the invention be used in combination with a friction material containing steel fiber to maximize the performance of the pad.
Yet, it is especially effective for heavy-duty application that a plurality of layers of underlayer material is provided and the layer close to the friction material and the layer close to the backing plate have different compositions so that the cushion effect thereof is increased.
It is usual practice to improve the heat-resisting property of constituent plastic in order to improve the property of the underlayer material as a whole. The adoption of linear or branched plastic as the constituent plastic is a feature of the invention. Linear or branched plastic has a discernible melting point as is seen in polyethylene, polyvinyl chloride, and nylon and will melt before decomposing, absorbing heat of fusion from the environment. The melting causes the plastic to adhere closely to the neighboring fiber and fillers, forming a stronger matrix. It is desirable that linear or branched plastic be selected from a superengineering plastic group or superheat-resistive plastics, with amorphous plastics being accepted.
As for the plastic to be included in the underlayer material, pulverized plastic is desirable, because it is easily dispersed at the time of blending. Granular plastic is also dispersible by means of mixing. Proper selection of a mixing means even allows the use of fibrous or pelletized plastic.
The group of linear plastics having a melting point of 200° C. or higher at normal pressure is called engineering plastics, which includes a nylon group (nylon 6 and nylon 66), polyvinyl chloride (PVC), polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) both belonging to a polyester group, and polytetrafluoroethylene (PTFE) and polychlorotrifluoroethylene (PCTF) both belonging to a fluorocarbon group. There also is another kind of plastic called superengineering plastics, which includes polyphenylenesulfide (PPS), polysulfone (PSF), polyethersulfone (PES), polyetherimide (PEI), polyetheretherketone (PEEK), and aromatic polyester (brand names of Unitika Ltd
Greenblum & Bernstein P.L.C.
Oberleitner Robert J.
Sumitomo Electric Industries Ltd.
Williams Thomas J.
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