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This paper describes a technique which uses Energy Dispersive X-ray Spectroscopy (EDX) to track progressive changes in wet friction material surface chemistry as the material is cycled under various energy and temperature conditions. Using this technique, elements can be identified on the surface and compared with the base friction material and fluid chemistries to obtain a quantitative measure of chemistry changes at the interface. Performance effect of surface chemistry change can be obtained by corresponding measurement of the coefficient of friction. Additionally, surface chemistry changes can be compared with progressive changes in friction material degradation as measured by Thermogravimetric Analysis (TGA) after identical conditions of use. Surface chemistry change and mating surface temperatures have been measured versus cycles at several energy loadings. Separate tests have been performed to follow friction material degradation changes during cycling.

The study of energy losses in disengaged wet clutches is important to efforts to maximize the efficiency of automatic transmissions. This paper describes a simple, accurate method of investigating clutch drag using the SAE #2 machine. By recording coast down speed versus time with known inertia, average and instantaneous torques can be calculated. Bearing and component losses can also be identified by running empty and partially built clutches. Many individual variables can be studied under laboratory controlled conditions. Friction plate geometry, surface finish, groove design, and plate flatness are evaluated at various levels of pack clearance, oil flow, oil level, and temperature. The influence of clutch speed on the magnitude of power loss is also shown. Results are analyzed to demonstrate the relative contribution of each factor. Conclusions are drawn to maximize effectiveness of effort to reduce power loss.

This paper presents results of an SAE #2 Machine study of several factors influencing wet friction material operation. By adjusting test condition, it is shown how plate deflection, spacer roughness, power loading, energy loading, etc. can produce mechanical and/or thermal distress of the friction material. In comparative testing, it is also shown how these problems can be reduced or eliminated by proper selection of friction material, groove, assembly and spacer plate geometries, oil type and flow, etc. The purpose of this work is to contribute to understanding of wet friction couples to permit identification of the mode of failure (1) to provide corrective action in present designs and (2) to optimize future design.

The fact that temperature can affect the performance of friction material has long been recognized, and many studies of the phenomena have been made. For the most part, results have been contradictory and indicate a complex relationship between temperature and other variables that constitute the conditions of use. This paper offers a report on the continuing effort to establish the extent of change produced and the mechanism by which such change is effected. Data are presented on SAE #2 machine test of three friction materials in three oils controlled at varying temperature level. How the temperature effects can be further modified by pressure or power loadings are also demonstrated. In addition, study of friction hysteresis with temperature-performance at temperature as affected by previous history - is included. Theories are proposed to explain trends noted in the data.

The literature provides considerable evidence confirming interaction of oil and friction material on performance characteristics obtained in a wet friction unit. Both elements can be modified to meet a wide range of requirements. Furthermore, it is well established that the performance obtained with any specific oil-material combination can be modified with usage. In this report, additional evidence of interaction is offered from test of five friction materials and five oil types. How the interactions are affected by conditions of use is also explored. Data on variable energy loading, power loading, oil sump temperature, oil flow, and sump volume factors are included, not only as a design guide on methods of eliminating or minimizing performance fluctuations resulting from such interactions, but also to demonstrate the kind of variable that can produce the chemical and/or physical change of sufficient magnitude to modify results.

Paper type friction materials can be used to provide higher dynamic coefficient and better engagement characteristics in wet application, but the softer structure of these products necessitates care for the surface condition of the mating spacer plate if optimum durability is to be obtained. This report covers methods of studying surfaces and relating the observed finish to durability obtained under special dynamometer test conditions. A variety of surface preparations have been investigated including rolled, tumbled, ground, and sanded finishes. Friction material durability was studied as a function of mating plate preparation, roughness, surface profile, and hardness. Relative sensitivity to mating surface of various paper friction formulations is provided. Acknowledging the limitations of the present state-of-the-art, an attempt is made to define spacer requirements for use with these types of friction materials.