The frictional behavior of wet clutches for applications such as automatic transmissions have a controlling influence over the function of the entire system during operation. This encompasses everything from fuel economy to harshness, vibration, noise and comfort. The wear characteristics, including velocity dependence of the coefficient of friction (COF) and also the friction curve of the clutch material used, determine the functional lifetime of the clutch. There are now increasing demands for higher torque capacity at reduced sizes. These can only be met by development of new friction materials and lubricants, with the consequent need for intensive, rapid and cost effective testing [1,2]. The development of new materials is costly and time consuming; and the need is currently for standardized short time test procedures that can be recognized by both suppliers and OEMs.
Full-scale clutch tests, such as the JASO M348 carried out on the SAE No. 2 Friction Test Machine (Figure 1), are usually used to acquire friction data, but these tests have the disadvantage in being expensive, inflexible, time consuming and linked to one special test rig. SAE tests mix up friction and endurance/durability as they are run to failure and so are not ideal for specific friction data. To evaluate each new friction material recipe or process change it is necessary to fabricate and assemble full-scale clutch components for each test scenario. It has been recognized by developers that in order to make significant savings of development time and cost a simple benchtop screening test could be used to rank friction materials in the laboratory prior to full-scale clutch tests. The paradigm of benchtop testing is simple and effective [3,4]. The researcher is aware that modelling to a great extent makes use of friction data and that many parameters affect friction behavior including: