Brakes – Wheel – Axially movable brake element or housing therefor
Utility Patent
1998-07-14
2001-01-02
Butler, Douglas C. (Department: 3613)
Brakes
Wheel
Axially movable brake element or housing therefor
C188S071100, C188S25100R, C188S25000B
Utility Patent
active
06167992
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates generally to braking elements and more particularly to an abrasive coating disposed on the surface of a brake pad in a pattern designed to reduce the amount of noise generated during the initial breaking in period of the brake pad with the rotor.
2. Discussion
Brake assemblies in automobiles or other motor vehicles generally include a friction material and a counter-friction material that selectively cooperate with one another to either partially or completely decelerate the automobile. In disc brake systems, the counter-friction material is a rotor; whereas in a drum brake systems, the counter-friction material is a drum.
With respect to disc brake systems, the rotor is generally comprised of cast iron or other metallic material having a surface thereon adapted for contact with a friction material, such as that typically disposed on a surface of a brake pad. The brake pad is usually comprised of a steel or other substrate (i.e., a support surface) having a friction material thereon, wherein the surface of the friction material is adapted for contact with the friction surface of the rotor. When the brake pad is urged up against the rotor, a sufficient amount of friction is generated between the two objects so as to cause the automobile to decelerate, either partially or completely.
The friction material, which is resistant to heat generated by friction during contact with the surface of the rotor, usually comprises a mixture of a cured organic or inorganic binder and a filler material. Natural and synthetic resins and rubber compounds are frequently used as binders, the filler typically consisting of metal chips, metal oxides, asbestos, mineral wool, or other abrading materials dispersed in the binder.
One problem with metal rotors is that they are susceptible to oxidation or corrosion. If the brakes are used often, this problem is not too severe as the friction between the rotor and the brake pad is usually sufficient to remove any thin film of oxidation or corrosion. However, if the brakes are not used for a substantial period of time, such as on a new vehicle kept in a manufacturer's or merchant's lot, the resulting buildup of oxidation or corrosion on the rotor's friction surface can adversely affect the performance of the brake. The corrosion can become so severe that it results in pitting or scarring of the rotor surface, which can render the rotor unsuitable for achieving the desired braking performance. In some instances, the corrosion can cause the rotor to bond to the friction material of the brake pad, which can result in cohesive failure of the friction material or separation of the friction material from its substrate or support surface.
One solution to this problem is to use rotors that have been coated or otherwise surface treated to inhibit corrosion of the rotor. Such treatments include oil or grease or the like; electro deposition coatings such as cathodic electrodeposition of amine-salted epoxy resins curable with isocyanate crosslinkers; other curable coatings such as melamine-cured OH-functional acrylic coatings; thermoplastic coatings such as high-molecular weight acrylic or polyurethane latexes or oil-based alkyd coatings; metal oxide coatings where a thin film of oxidation is allowed to form without pitting; and inorganic coatings such as zinc particles dispersed in a potassium silicate solution.
A problem with treated rotors is that although they are resistant to corrosion, the treated surface often does not provide adequate braking performance, especially when matched with a friction material on the brake pad that is itself designed for use with the underlying metal out of which the rotor is made.
It has been proposed to provide an abrasive coating on the brake pad that would have the effect of removing the protective coating on the rotor during the initial breaking in period of the brakes (e.g., during the first 200 brake applications).
For example, it has been proposed to use a coating of abrasive carborundum particles on the brake pad for this purpose. Such a coating, however, can produce an undesired increase in the new or ‘green’ friction of the brakes, resulting in unpredictable, noisy, or ‘sticky’ braking action. Also, with such coatings containing high levels of aggressive abrasive particles, enough particles can embed in the surface of the pad so as to prolong the undesirable performance characteristics.
Another problem arises with rotors that have been resurfaced after being in service for a particular length of time. Occasionally, the resurfacing procedure is improperly executed and results in a rotor surface that is uneven. This uneven rotor surface does not mate well with the brake pad, thus leading to poor braking performance.
Again, it was proposed to provide an abrasive coating on the friction material to remedy any surface irregularities of the rotor after an improper resurfacing procedure. It was thought that the abrasive coating would essentially polish the rotor to remove the surface irregularities therefrom. To accomplish this, an abrasive coating was placed on the entire surface of the friction material of the brake pad. However, this configuration lead to accumulation of the abrasive coating at the trailing edge of the friction material, thus leading to unacceptable levels of noise during braking operations.
Therefore, there is considerable industry interest in the elimination or abatement of noise generated during the initial breaking in period of the brake pad with the rotor; that is, the period leading up to the establishment of a burnish relationship between the brake pad and the rotor. This interest extends to newly manufactured rotors, as well as resurfaced rotors. This noise problem is of special concern to manufacturers and retailers of replacement brake pads. The generation of unacceptable levels of noise generated during the initial braking in period of the brake pad with the rotor will result in consumer dissatisfaction.
Therefore, there exist a need for a brake pad that is capable of removing a corrosion-resistant coating from a rotor during the initial breaking in period of the brake pad with the rotor. Also, there exists a need for a brake pad that is capable of polishing away the surface irregularities of an improperly resurfaced rotor. Additionally, there exists a need for a brake pad that does not generate unacceptable levels of noise during this initial breaking in period with the rotor. Furthermore, there exists a need for a brake pad that maintains good braking performance both during and after this breaking in period with the rotor.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the present invention, a braking element for use with a rotatable counter-friction material comprises a friction surface, the friction surface having first and second spaced apart lateral edges substantially perpendicular to the direction of rotation of the counter-friction material, the friction surface having third and fourth spaced apart lateral edges substantially parallel to the direction of rotation of the counter-friction material, the friction surface having an abrasive coating disposed on at least a portion thereof, wherein at least one of the first and second lateral edges are free of the abrasive coating.
A more complete appreciation of the present invention and its scope can be obtained from understanding the accompanying drawings, which are briefly summarized below, the following detailed description of the invention, and the appended claims.
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p
Ancheta Lionel
Stonecipher Michael
Torpey Michael
Allied-Signal Inc.
Butler Douglas C.
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