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The conventional wet friction material, derived from mixing paper and friction material ingredients using paper making technology, has certain restraints in which it can work. When these restrictions are respected during the transmission design, the result can be an excellently performing transmission. These constraints restrict the designer in the endeavor to achieve higher performance from the same transmission size, or smaller and cost effective designs. The main restriction is the temperature stability, when more energy has to be dissipated in a smaller area. In this case, better cooling and/or a lining with higher heat resistance has to be used. Carbon fiber is considered as a friction material for its high heat / abuse resistance and a consistent coefficient of friction. This paper describes and summarizes some of the most important results obtained during the development of a carbon fiber material, with a similar cost to that of a conventional paper lining.

Since porosity is known to have a very significant influence on the coefficient of friction of wet friction material, a new technique was developed to determine porosity. To measure porosity, “Laserthermographie” uses the fact, that thermal properties of any friction material are specifically influenced by pores. Any increase or decrease of the pore volume will lead to a change in heat capacity, heat conductivity and apparent density of the friction material: Using a modulated energy source (laser) thermal waves are generated on a friction material surface. The “thermal response” of this surface is then detected by an infrared radiation detector.