High torque capacity wet paper friction member

Abstract

[Problems]To provide a wet paper friction member which has high torque capacity and excellent thermal stability simultaneously. [Solution Means]A wet paper friction member is produced by impregnating thermosetting resin into a paper body; curing it with heat; and then forming it with pressure. A fiber base material comprises 20-80 wt % of the paper body and comprises cellulose pulp, aramid pulp, and homopolymer acrylic pulp the drainability of which is adjusted to 120-280 ml, and thermosetting resin such as straight phenol resin, alkyl modified phenol resin, epoxy modified phenol resin, tung oil modified phenol resin, cashew oil modified phenol resin, tung oil/cashew modified phenol resin is impregnated at 20-40 wt %, and thereby, high torque capacity and heat resistance, and mechanical strength are realized simultaneously.

Description

DETAILED DESCRIPTION OF THE INVENTION

1. Technical Field to Which the Invention Belongs

The present invention relates to a wet or wet-tpype paper friction member used in a clutch and brake component of an automatic transmission of a vehicle.

2. Prior Art

A wet paper friction member is produced by dispersing a mixture of a fiber base material such as pulp and a friction modifier in water and forming a paper body; making it dry and thereafter, impregnating it with thermosetting resin; heating and curing it; and then forming it with pressure. The functions of a wet paper friction member are influenced by a blend of the fiber base material, a filler and the friction modifier etc. which are main components of the paper body, and impregnated thermosetting resin. Therefore, choice and blending amount of materials have been researched for improvement of a wet paper friction member according to its use.

It has been known that a friction modifier has an important role in influencing porosity and surface configuration of a friction member; and fiber ingredient affects porosity and flexibility of the friction member and thus, has an influence on friction property and heat resistance, and mechanical strength.

Phenol resin which is used mainly as a binder has an influence not only on mechanical strength of a friction member but also on frictional coefficient as well as velocity dependence of the frictional coefficient. Particularly, since frictional coefficient in the low velocity range which is referred to as ‘torque capacity’ is highly influenced by resin, the research has been made using various oil-based materials or modified materials.

For example, Patent Document 1 discloses a wet paper friction member which is produced by blending pulp which is fibrillated poly-acrylonitrile-based copolymer acrylic fiber (hereinafter referred to as the ‘copolymer acrylic pulp’) and filler, and thus, forming a paper body; and impregnating it with thermosetting resin and then curing it.

[Patent Document 1]

Japanese Patent Publication No. 45808/1993

PROBLEMS TO BE SOLVED BY THE INVENTION

In a clutch and brake component of an automatic transmission, the ability to transmit torque in the state where it is stopped or slightly slides is the most fundamental function and referred to as the torque capacity. If torque capacity is high, for example, a diameter of a clutch can be reduced or the number of friction members can be reduced and thus, a clutch component can be miniaturized. On the other hand, calorific value per unit area of a brake and a clutch during operation increases due to high frictional coefficient. This tends to lower the heat resistance and mechanical strength of the friction member; and therefore, a wet paper friction member which is excellent in torque capacity, heat resistance and mechanical strength could not be easily produced.

As for the wet paper friction member of Patent Document 1, copolymer acrylic pulp is particularly low in heat resistance and chemical resistance, and therefore, contraction of dimension is caused during processing step of a wet paper friction member. Therefore, accurate processing has been difficult, or there have been other problems such that large strength degradation of the friction member is occurred during operation due to frictional heat or chemicals in automatic transmission fluid.

In view of the above problems, it is an object of the present invention to provide a wet paper friction member which is used mainly in a clutch and a brake of an automatic transmission and has high torque capacity and excellent thermal stability simultaneously. Improvement was made by focusing attention on a fiber base material and resin in a friction modifier forming a paper body among compositions of a conventional wet paper friction member. This realized successful development of a high torque capacity wet paper friction member which has friction property, heat resistance and mechanical strength simultaneously, and has high versatility without limitation to its application.

MEANS TO SOLVE THE PROBLEM

The present invention solved the above-mentioned problems by providing a wet paper friction member which is produced by impregnating thermosetting resin into a paper body, curing it by heat, and forming it with pressure, wherein said paper body comprises fiber base material and filler, characterized in that said fiber base material comprises 20-80 wt % of the total weight of said paper body, and comprises cellulose pulp, aramid pulp, and homopolymer acrylic pulp the drainability of which is 120-280 ml.

[Function]

The present invention can provide a wet paper friction member having excellence in torque capacity, heat resistance and mechanical strength since the fiber base material comprises 20-80 wt % of the total weight of the paper body, and comprises cellulose pulp, aramid pulp, and homopolymer acrylic pulp the drainability of which is 120-280 ml.

[Embodiments]

A wet paper friction member according to the present invention is produced by blending specified fiber base material and filler etc. and thus, producing a paper body; impregnating the paper body with thermosetting resin; curing it by heating; and forming it with pressure. The fiber base material comprises cellulose pulp, aramid pulp, homopolymer acrylic pulp and other fibers at 20-80 wt % of the total weight of the paper body. Drainability of the homopolymer acrylic pulp is adjusted to 120-280 ml. Thermosetting resin such as straight phenol resin, alkyl modified phenol resin, epoxy modified phenol resin, tung oil modified phenol resin, cashew oil modified phenol resin and tung oil/cashew oil modified phenol resin is impregnated into said paper body at 20-40 wt %. Thus, high torque capacity, heat resistance and mechanical strength are realized simultaneously.

The fiber base material comprises cellulose pulp, aramid pulp, homopolymer acrylic pulp and other fiber at 20-80 wt % of the total weight of the paper body.

While aramid pulp has excellent thermal stability and paper-making property, it is expensive in comparison with cellulose pulp, and also has inferior compatibility with thermosetting resin such as phenol resin. In addition, while cellulose pulp has better compatibility with resin and is cheaper in comparison with aramid pulp, it is inferior in thermal stability and mechanical strength. On the other hand, homopolymer acrylic pulp has excellent compatibility with thermosetting resin such as phenol resin and has a characteristic that it does not thermofuse. Therefore, when it is used with aramid pulp and cellulose pulp, excellent thermal stability and mechanical strength can be achieved at low cost. When the amount of the fiber base material is above 80 wt % of the total weight of the paper body, smooth member surface can not be obtained. When it is below 20 wt %, mechanical strength is lowered.

Drainability of homopolymer acrylic pulp forming a paper body is adjusted to 120-280 ml.

Drainability is a degree of beating of fiber, and the smaller drainability is, the larger the degree of beating of fiber is, resulting in increase of splitting degree of each fiber. When splitting degree of acrylic pulp is increased, intertwist between fibers increases, and sufficient mechanical strength can be obtained after phenol resin is impregnated and cured.

When homopolymer acrylic pulp the drainability of which is smaller than 120 ml is used for the one forming a paper body, the amount of split fiber is too large and the size of holes becomes too small, and therefore, clogging tends to be caused during frictional sliding, and heat resistance is lowered.

When aramid pulp the drainability of which is above 280 ml is used for the one forming a paper body, intertwist between fibers becomes small and therefore, sufficient mechanical strength can not be obtained.

As thermosetting resin, any one or some of resins among straight phenol resin, alkyl modified phenol resin, epoxy modified phenol resin, tung oil modified phenol resin, cashew oil modified phenol resin and tung oil/cashew oil modified phenol resin can be used to be impregnated into said paper body at 20-40 wt %.

In general, tung oil modified phenol resin, cashew oil modified phenol resin and tung oil/cashew oil modified phenol resin etc. are known to be effective in increasing frictional coefficient in the low velocity range. On the other hand, when such oil modified materials are used, there are problems such that heat resistance and mechanical strength are lowered. In the meantime, straight phenol is not so effective in increasing frictional coefficient in the low velocity range, but, it has sufficient heat resistance and mechanical strength. Therefore, when it is used with the above-mentioned modified materials, high frictional coefficient and heat resistance, as well as mechanical strength can be achieved simultaneously. When the amount of these resins impregnated with a paper body was under 20 wt % of the total weight of the friction member, sufficient mechanical strength can not be obtained, and when it is 40 wt % or more, heat resistance is lowered.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] A graph showing the results of torque capacity evaluation;

[FIG. 2] A graph showing the results of durability evaluation;

[FIG. 3] A graph showing the results of durability evaluation; and

[FIG. 4] A graph showing the results of compressive strength evaluation.

EXAMPLES

Examples will be explained concretely below.

Example

A clutch disk was produced by impregnating oil modified straight phenol resin into a paper body comprising 10 wt % of cellulose pulp, 10 wt % of aramid pulp, 30 wt % of homopolymer acrylic pulp, and 50% of filler such as diatomaceous earth, at 30 wt % of a friction member; curing it by heating, and then bonding it to a core plate.

Comparative Example

As Comparative Example, a clutch disk was produced by impregnating straight phenol resin into a paper body comprising 30 wt % of cellulose pulp, 30 wt % of aramid pulp, 30 wt % of diatomaceous earth, and 10 wt % of carbon-based filler, at 35 wt % of a friction member; curing it by heating; and then bonding it to a core plate.

Torque capacity, heat resistance and mechanical strength of a wet friction clutch disc produced by the above-mentioned processes were evaluated by the following testing methods:

<Conditions for Torque Capacity Evaluation>

• Testing device: SAE No. 2 friction testing apparatus
• Condition for achieving performance: number of friction surfaces: 6
• Oil temperature: 80 degrees Celsius
• Surface pressure: 0.5 MPa, 1.0 MPa, 2.0 MPa
• Rotational speed: 0.72, 1, 5, 10, 25, 50, 75, 100 rpm

As a result of the above tests, a wet paper friction member of Example had high frictional coefficient at low speed, that is, high torque capacity, and also had excellent velocity property of the frictional coefficient.

<Condition for High-Speed Durability Evaluation>

• Testing device: SAE No. 2 friction testing apparatus
• Condition for achieving performance: number of friction surfaces: 6
• Oil temperature: 100 degrees Celsius
• Surface pressure: 0.785 MPa
• Rotational speed: 7100 rpm
• Inertial mass: 0.01 Kg·m/s²
• Amount of lubricating oil: 360 ml/min

As a result of the above tests, a wet paper friction member of Example had small deterioration of frictional coefficient, that is, high heat resistance, and also had relatively small abrasion loss after the test in comparison with Comparative Example as shown in FIGS. 2 and 3.

<Condition for Compressive Strength Evaluation>

• Testing device: repetitive compressive strength testing apparatus
• Condition for evaluation: number of friction surfaces: 2
• Oil temperature: 120 degrees Celsius
• Surface pressure: 10.0 MPa
• Cycle: loading 2 sec, unloading 4 sec

As a result of the above tests, a wet paper friction member of Example had relatively excellent mechanical strength in comparison with Comparative Example as shown in FIG. 4.

It is known from FIGS. 1-4 that a friction member of Example had high torque capacity along with sufficient heat resistance and mechanical strength in comparison with a friction member of Comparative Example

It is known from the above results that when a fiber base body comprises cellulose pulp, aramid pulp, homopolymer acrylic pulp and other fibers at 20-80 wt % of the total weight of a paper body; drainability of homopolymer acrylic pulp is adjusted to 120-280 ml; and moreover, thermosetting resin such as straight phenol resin, alkyl modified phenol resin, epoxy modified phenol resin, tung oil modified phenol resin, cashew oil modified phenol resin, tung oil/cashew oil modified phenol resin, is impregnated into said papermaking body at 20-40 wt % of a friction member, high torque capacity, heat resistance and mechanical strength are achieved simultaneously. This high torque wet paper friction member can be used for many wet friction applications.

ADVANTAGES OF THE INVENTION

According to the present invention, a fiber base material comprises 20-80 wt % of the total weight of a papermaking body, and comprises cellulose pulp, aramid pulp, and homopolymer acrylic pulp the drainability of which is 120-280 ml, and thereby, the effects of improving torque capacity, heat resistance and mechanical strength of a wet paper friction member are achieved.

Claims

1. A wet paper friction member which is produced by impregnating thermosetting resin into a paper body; curing it by heating; and forming it with pressure,

wherein said paper body comprises fiber base material and filler,

characterized in that said fiber base material comprises 20-80 wt % of said paper body and comprises cellulose pulp, aramid pulp, and homopolymer acrylic pulp the drainability of which is 120-280 ml.

2. A wet paper friction member as claimed in claim 1, wherein said thermosetting resin comprises any one of some of resins among straight phenol resin, alkyl modified phenol resin, epoxy modified phenol resin, tung oil modified phenol resin, cashew oil modified phenol resin, tung oil/cashew oil modified phenol resin.

3. Cancelled

4. A wet paper friction member as claimed in claim 1, wherein said thermosetting resin comprises 20-40 wt % of said friction member.

5. A wet paper friction member as claimed in claim 2, wherein said thermosetting resin comprises 20-40 wt % of said friction member.