Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Noninterengaged fiber-containing paper-free web or sheet...
Reexamination Certificate
1999-06-30
2001-02-20
Weisberger, Richard (Department: 1774)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Noninterengaged fiber-containing paper-free web or sheet...
C428S295100, C428S299100, C428S299700, C428S301100, C428S301400
Reexamination Certificate
active
06190761
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a friction material for use in vehicle. More particularly, the present invention relates to a friction material for vehicle brakes which generate less brake noise, particularly less creep noise when an automatic car starts to run.
2. Description of the Related Art
As a friction material mainly for vehicle brakes or the like, there has been recently used one having a porosity from 10% to 30% for the purpose of improving fade resistance and enhancing effect at high velocity.
When a vehicle is operated in rainy weather or runs over puddles, the friction material gets wet with water. Further, when a vehicle is parked outside at night, the friction material can easily absorb water.
The friction material thus moistened generates a low frequency noise when the vehicle is braked and runs at velocity of not more than 5 km/h shortly before stopping while it is being dried. The friction material thus moistened also generates such a low frequency noise when an automatic car starts to run at a very low velocity, i.e., during the full release of the brake pedal which has been stepped after switching to D range, causing the brake to drag due to creep force. Such a low frequency noise is also called “creep noise”. This noise offends the operator and thus makes a nuisance of the operator.
The greater the porosity of the friction material is, the more is the water absorption of the friction material and the greater is such a low frequency noise. Further, when the friction material is moistened, squeal is generated, or the friction coefficient is excessively raised, causing the generation of abnormal effect.
Claiming that a friction material which has been impregnated with a water repellent material so that is rendered water repellent can be prevented from forming an extremely thin water film thereon to inhibit a phenomenon called jada during clutch meet in respect to clutch facing, a dry friction material obtained by impregnating a friction material matrix made of organic fiber, inorganic fiber, metal wire, filler and binder with a water repellent material has been proposed (Japanese patent published unexamined application Hei. 4-234479).
According to the above cited application, the water repellent material to be used for this purpose is preferably a material which exhibits water repellency but doesn't impair friction characteristics, such as silicone oil and fluororesin.
The friction material which has thus been rendered water repellent can exert its desired effect on troubles as occurring when a vehicle is parked at night to cause the friction pad to get moistened. However, such a friction material generates greater creep noise when the vehicle starts to run with the rotor and friction pad being directly wet with water due to car washing or the like than friction materials which have not been rendered water repellent, bringing about a contrary effect.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a friction material which generates less brake noise, particularly less creep noise when an automatic car starts to run.
The foregoing object of the present invention is accomplished with the following constitutions:
(1) A friction material made of a fibrous reinforcement, a friction modifier, a lubricant and a binder, comprising a water-repellent fluoropolymer incorporated therein.
(2) The friction material as defined in Clause (1), further comprising an alkaline metal salt incorporated therein.
(3) The friction material as defined in Clause (1) or (2), wherein said fluoropolymer is one selected from the group consisting of ethylene tetrafluoride polymer, tetrafluoroethylene-hexafluoropropylene copolymer and polyvinylidene fluoride or a combination thereof.
In accordance with the present invention, the use of the friction material having the foregoing structure makes it possible to effectively reduce creep noise not only when the friction pad is moistened after a prolonged parking at night (hereinafter simply referred to as “during moistening”) but also when the friction pad gets wet with water during car washing (hereinafter simply referred to as “during wetting with water”).
In the present invention, it was found that the scattering of a water-repellent fluoropolymer in a well known hydrophilic matrix makes it possible to exert an effect of reducing creep noise and the provision of the matrix with a better hydrophilicity developed by an alkaline metal salt makes it possible to further reduce creep noise.
Since the foregoing alkaline metal salt acts to render a friction material matrix hydrophilic, it may be added in powder form if added at the first stage of the procedure. Alternatively, since the alkaline metal salt is water-soluble, the friction material thermoformed may be impregnated with the alkaline metal salt in the form of aqueous solution.
REFERENCES:
patent: 5534169 (1996-07-01), Vicki
patent: 4-234479 (1992-08-01), None
Sasaki Yosuke
Yanagi Michinori
Akebono Brake Industry Co. Ltd.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Weisberger Richard
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