Wet type friction material

Details Wet type friction material Wet type friction material

1999-06-09

2001-11-13

Hess, Bruce H. (Department: 1774)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C428S293400, C428S297400, C428S688000

Reexamination Certificate

active

06316083

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wet type friction material which is used in a clutch facing of a power transmission system of an automobile, an industrial machine, a railroad vehicle, etc., and which is used in an oil.
2. Description of the Related Art
Concerning friction materials for wet type clutch facings, a variety of chartaceous friction materials have been used widely. A chartaceous friction material comprises a substrate and a binder which is impregnated into and cured in the substrate. The substrate is formed of organic fibers and a several types of friction conditioners admixed with the organic fibers. The binder is composed of a thermosetting resin, such as a phenolic resin, etc.
However, the aforementioned friction material has a problem in that it exhibits not only a low heat resistance but also a low friction coefficient. Accordingly, a variety of countermeasures are taken to solve the problem.
Regarding one of the countermeasures, a number of friction plates is increased to enlarge the contact area with respect to a mating member, for instance, in a field of clutch facings. However, the construction of the wet type clutch is not only complicated but also large-sized by adopting such a countermeasure. Accordingly, the counter measure results in a large energy loss and a high cost.
Moreover, a trial has been carried out in which a copper-based sintered friction material is applied to a wet type clutch. If such a sintered friction material can be utilized, even when the number of friction plates is less and the contact area is small, the wet type clutch can satisfy the heat resistance and the strength against pressure. Consequently, the aforementioned problem can be solved. However, many of the sintered-metal-based friction materials exhibit a friction coefficient lower than organic friction materials in most of the cases. Hence, as a wet type clutch for a recent high-performance automobile, the sintered-metal-based friction materials cannot necessarily exhibit satisfactory friction characteristics.
Japanese Examined Patent Publication (KOKOKU) No. 7-021,298 discloses a two-layered wet type friction material which comprises a friction-surface side and a fixed-surface side. The friction-surface side includes a chartaceous substrate into which a thermosetting resin is impregnated. The chartaceous substrate is prepared by a papermaking machine with fibrous components, inorganic fillers and friction conditioners in a wet manner. The fixed-surface side includes a chartaceous substrate into which a thermosetting resin is impregnated. The chartaceous substrate is prepared by a papermaking machine with fibrous components in a wet manner. However, in the friction material, the fixed-surface side contributes only to improving the cooling ability and the mechanical strength, but little affects the friction characteristics. The friction characteristics depend on the friction-surface side itself. The friction-surface side exhibits a friction coefficient which is equivalent to those general wet type friction materials.
SUMMARY OF THE INVENTION
The present invention has been developed in view of the aforementioned circumstances. It is therefore an object of the present invention to provide a novel chartaceous friction material which can securely exhibit a much higher friction coefficient and an upgraded heat resistance.
A wet type friction material according to the present invention carries out the aforementioned object. A first aspect of the present friction material is a wet type friction material of a layered construction, in which at least two layers are laminated, one of the two layers being a friction-surface layer disposed on a friction-surface side, the other one thereof being a base layer disposed on a fixed side, wherein the entire friction material exhibiting a Young's modulus of Et, the base layer exhibiting a Young's modulus of Eb, and the Et and the Eb satisfying a relationship of Eb/Et<1 (i.e., a ratio of Eb with respect to Et is less than 1).
A second aspect of the present wet type friction material is characterized in that each of the friction-surface layer and the base-surface layer of the first aspect of the present wet type friction material includes an organic-and-inorganic composite binder which is prepared by drying and burning a sol solution, the sol solution being prepared by hydrolyzing at least one member selected from the group consisting of a metallic alkoxide and a metallic alkoxide substituted by an organic group.
A third aspect of the present wet type friction material is characterized in that the friction-surface layer of the first aspect of the present wet type friction material includes a composite filler which is made by entangling a fibrous material around a filler powder.
A fourth aspect of the present wet type friction material is characterized in that the friction-surface layer of the first aspect of the present wet type friction material includes a porous filler which is composed of a porous inorganic compound.
A fifth aspect of the present wet type friction material is characterized in that the friction-surface layer of the first aspect of the present wet type friction material includes a composite filler which is prepared by entangling a fibrous material around a porous filler being composed of a porous inorganic compound.
A sixth aspect of the present wet type friction material is characterized in that the friction-surface layer of the second aspect of the present wet type friction material includes diatomaceous earth.
A seventh aspect of the present wet type friction material is characterized in that the friction-surface layer of the second aspect of the present wet type friction material includes graphite.
In the first aspect of the present wet type friction material, the Young's modulus Et of the entire friction material and the Young's modulus Eb of the base layer satisfies the relationship of Eb/Et<1. Accordingly, the Young's modulus Eb of the base layer is lower than the Young's modulus Et of the entire friction material. Thus, when the present friction material slides on the mating member, it is good in the ability of following the mating member because the base layer exhibits the low Young's modulus Eb. As a result, it is possible to secure a large contact area with respect to the mating member.
Moreover, since the friction-surface layer exhibits a high Young's modulus, it is possible to secure a high friction coefficient. Thus, in accordance with the present wet type friction material, it is possible to secure a remarkably high friction coefficient by the synergetic effect of the action of the base layer and the action of the friction-surface layer. When the Eb/Et is 1 or more, the base layer is too hard to exhibit the high ability of following the mating member. Consequently, the contact area decreases so that the friction coefficient decreases. It is especially preferred that the Eb/Et satisfies the relationship of Eb/Et<0.7. If such is the case, the base layer exhibits the ability of following the mating member extremely well.
The lower limit of the Eb/Et is not limited in particular. However, the Eb/Et preferably satisfies the inequality, 0.01 <Eb/Et (i.e., a ratio of Eb with respect to Et is less than 0.01), further preferably, the inequality, 0.1 <Eb/Et. When the Eb/Et is 0.01 or less, the friction-surface layer is too hard to exhibit an ability of following the mating member. Consequently, the contact area decreases so that the friction coefficient decreases.
Concerning the characteristics of friction materials, it is preferred that they maintain a high friction coefficient over a wide range of sliding speeds. For example, when the ratio between a first friction coefficient which is exhibited by a friction material at a sliding speed of 0.5 m/s and a second friction coefficient which is exhibited by the same at a sliding speed of 0.05 m/s is as close as 1, it is said that the friction material is superb. Moreo

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