Dynamic Characterization of Wet Friction Component under Realistic Transmission Shift Conditions

A wet friction component continues to play a critical role in a step-ratio automatic transmission (AT) system. It is hydraulically actuated to alter planetary gear configurations for automatic shifting. During a shift event, its engagement torque is transmitted to AT output shaft, directly affecting vehicle shift quality. The friction component behaviors vary widely under different conditions. In a vehicle development process, unanticipated behaviors often lead to an inefficient trial-and-error approach for adjusting shift feel. Thus, a shift improvement process can benefit from upfront characterization of friction component behaviors. The so-called SAE#2 test system has served as the industry-standard since 1960's for evaluating friction components. It provides a useful means for evaluating friction component design variables. However, its standardized test conditions do not adequately capture dynamic effects of AT shift control variables. As a result, SAE#2 test data often fail to correlate with vehicle shift quality, limiting its utility during AT shift improvement processes. A new friction component test system, reported at 2005 IPC-13 conference [1], is designed to significantly enhance the capabilities of the conventional SAE#2 system. It enables accurate replication of AT shift control variables, specifically pressure and slip without complete AT hardware. This paper presents an example of plate clutch characterization conducted on the new test system. Engagement torque is measured under dynamically changing conditions that closely follow pressure and slip speed profiles observed in a test vehicle. The test data from the new test system are compared against a static torque map constructed from the standard SAE#2 conditions. It is shown that pressure and speed profiles make a measurable impact on clutch behavior. Analysis results illustrate the importance of correctly representing AT shift control variables in order to successfully support shift improvement efforts through friction component testing.