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In the competitive market of the car industry today, companies need to continuously strive to optimize the performance, price and environmental properties of their products in order to survive. Wet clutches, as parts of transmission components of passenger cars are no exception. An understanding of how the wet clutch system functions and fails is necessary to optimize price and service life. The friction characteristics of the wet clutch system are determined by lubricant-surface interactions in the contact between the friction discs. Wet clutch failure can often be associated with the deterioration of friction characteristics which eventually leads to stick-slip or shudder. Consequently, knowledge of why and of how friction characteristics change over time is of the outermost significance to enable the understanding and prediction of wet clutch performance. As the lubricant is an essential component of the wet clutch system, lubricant ageing is a factor of importance.

Wet clutches operating under low velocity and continuous sliding are increasingly important in vehicle transmissions. This presents new challenges in improving anti-shudder properties of the clutch system. In order to determine anti-shudder properties the friction-velocity relationship is generally examined. The friction-velocity characteristics are however influenced by the way they are measured, and the measurement methods differ between different standards and OEM approvals, thus making direct comparisons of the anti-shudder requirements difficult. This study investigates how different parameters influence anti-shudder properties. Results show how the obtained friction-velocity characteristics are influenced by the choice of different test procedures and parameters. Methods for presenting the anti-shudder properties are compared for the different cases and a method for evaluation of the properties is suggested.