Solid anti-friction devices – materials therefor – lubricant or se – Solid anti-friction device – article or material therefor – Animal or plant matter
Reexamination Certificate
1998-12-09
2002-07-23
Toomer, Cephia D. (Department: 1714)
Solid anti-friction devices, materials therefor, lubricant or se
Solid anti-friction device, article or material therefor
Animal or plant matter
C508S107000, C508S108000, C106S036000, C523S149000, C523S155000
Reexamination Certificate
active
06423668
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a friction material to be used as a clutch facing or the like in a power transmission system of a motor vehicle, industrial machine, railway vehicle, etc., and the method of producing such a friction material. The friction material of the present invention is especially useful as a wet friction material to be used in oil.
2. Description of Related Art
Examples of a friction material for use in a facing of a wet clutch include a paper-like friction material, as disclosed in Japanese Patent publication Sho 58-47345, etc., which is composed of organic fiber as a paper like substrate and various friction modifiers, and is further impregnated with a binder of a thermosetting resin such as phenol resin for hardening purposes.
Such a friction material is, however, low in heat resistance and small in coefficient of friction, because the paper-like substrate and binder are both organic substances. To overcome this problem, various measures have been taken.
Examples of such various measures include increasing the number of friction discs and enlarging the area thereof in a clutch facing, for example. These measures, however, make the wet clutch construction complex and large, resulting in energy loss enlarging and costs increasing, too.
A copper-based sintered friction material, for example, has been tried to be applied to a wet clutch, too. Such a sintered friction material exhibits satisfactory heat resisance and pressure resistance even with a small number of friction discs and small area thereof to overcome the above-described problems. However, the coefficients of friction of many kinds of sintered metal-based friction material are frequently less than that of organic friction material. Consequently, the friction characteristics thereof is not good enough to be applied to a wet clutch of a recent motor vehicle with an increased performance.
SUMMARY OF THE INVENTION
It is an object of the present invention to ensure a large coefficient of friction when an organic paper-like substrate is used.
With a first aspect of the friction material of the present invention, a paper-like substrate composed of a fibrous material, and an inorganic binder with which the substrate is impregnated.
With a second aspect of the friction material of the present invention, the inorganic binder in the friction material of the first aspect contains two or more kinds of metal elements, inclusive of at least quadrivalent metal elements.
With a third aspect of the friction material of the present invention, the two or more kinds of metal elements in the friction material of the second aspect have different valences from each other.
With a fourth aspect of the present invention, the method of producing a friction material includes a first step of hydrolyzing at least one of metal alkoxide and organic group-replaced metal alkoxide to prepare a sol solution, a second step of impregnating a paper-like substrate of a fibrous material with the sol solution to prepare an impregnated substrate, and a third step of drying and firing the impregnated substrate. The first, second and third steps are performed in order.
It is preferable that silicone resin which is composed of a siloxane framework containing organic groups is further mixed with the sol solution.
The preferred weight ratio between metal alkoxide and organic group-replaced metal alkoxide ranges from 3:7 to 0:10.
It is preferable to perform the third step in an atmosphere containing ammonia. Furthermore, it is preferable to perform the third step under the supercritical conditions.
In addition, it is preferable that the paper-like substrate used in the second step is subjected to a hydroxyl group-introducing treatment previously.
With the friction material of the present invention, the fibrous material composing the paper-like substrate is bonded with the inorganic binder, resulting in the inorganic binder appearing in a surface of the substrate. Consequently, when friction is generated, the inorganic binder exhibits friction characteristics to increase the coefficient of bounding friction, resulting in a large coefficient of friction being obtained, as compared to the cases organic binder such as phenol resin is used.
The fibrous material adapted to compose the paper-like substrate is at least one of inorganic fiber such as glass fiber, rock wool, pottasium titanate fiber, ceramic fiber, silica fiber, silica-alumina fiber, kaolin fiber, bauxite fiber, boron fiber, magnesia fiber or metal fiber, and organic fiber such as linter pulp, wood pulp, synthetic pulp, polyester-based fiber, polyamide-based fiber, polyimide-based fiber, polyvinyl alcohol denatured fiber, polyvinylchloride fiber, polypropylene fiber, polybenzoimidazol fiber, acryl fiber, carbon fiber, phenol fiber, nylon fiber or cellulose fiber.
Examples of the inorganic binder include metal oxide such as silica, alumina, titania, zirconia or silica-alumina, and organic functional group-composite metal oxide containing groups such as methyl group or phenyl group. It is preferable that the binder contains silicone resin, too. Soft silicone resin enables both improvement of the flexibility and increase of the contacting area, resulting in further increase of the coefficient of friction. The preferred amount of silicone resin ranges from 5 to 70 parts by weight per 100 parts by weight of the total amount of the inorganic binder and silicone resin. If the amount of silicone resin is greater than the above range, the coefficient of friction decreases while the amount of silicone resin is less than theabove range, the effect resulting from the addition of silicone resin is difficult to be exhibited.
In addition, at least one or more various friction modifiers and fillers such as barium sulfide, calcium carbonate, magnesium carbonate, silicon carbide, boron carbide, titan carbide, silicon nitride, boron nitride, alumina, silica, zirconia, cashew dust, rubber dust, diatomaceous earth, talc, kaoline, magneisum oxide, molybdenum disulfide, nitrile rubber, acrylonitrile-butadiene rubber, styren butadiene rubber, silicon rubber or fluoro rubber, can be added by a proper amount.
The preferred composition ratio of these components is such that the amount of the inorganic binder ranges from 10 to 70 volume % per 100% of the total amount of the fibrous material, friction modifiers, etc. If the amount of the inorganic binder is less than the above range, the bonding strength of fibers in the paper-like substrate decreases to reduce the durability, whereas if the amount of the inorganic binder is greater than the above range, the friction characteristics decrease.
It is preferable that the inorganic binder as one component of the friction material of the present invention contains two or more kinds of metal elements, inclusive of at least quadrivalent metal elements. With this arrangement, greater coefficients of friction and higher abrasion resistance are ensured.
The reason for this effect has not been clarified. However, it can be considered that into the space defined mainly by one kind of metal elements, the other kind of metal elements are introduced to produce a proper twisting in molecules, and consequently, internal stress is generated to increase the strength of the binder framework.
It is preferable that the metal elements including at least quadrivalent metal elements have different valences. More specifically, it is preferable to include quadrivalent metal elements and tervalent metal elements, or include quadrivalent metal elements and bivalent metal elements, for example. With this arrangement, the coefficients of friction further increase and the abrasion resistance is further improved.
Examples of the quadrivalent metal elements include silicon (Si) and titanium (Ti). Examples of the tervalent metal elements include aluminum (Al), gallium (Ga) and iron (Fe), and examples of the bivalent metal elements include magnesium (Mg), calcium (Ca) and barium (Ba). In some cases, univalent metal elements such as potassium (K)
Kawabata Masataka
Nakanishi Masatsugu
Shirasawa Atsushi
Suzuki Atsushi
Burns Doane , Swecker, Mathis LLP
Toomer Cephia D.
Toyota Jidosha & Kabushiki Kaisha
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