SAE International Aggressive Torque Converter Clutch Slip Control and Driveline Torsional Velocity Measurements 2008-01-1584

In automatic transmissions, an open torque converter transmits torque from the engine to the transmission using fluid coupling. Although torque converters are ideal launch devices for automatic transmissions, they are inefficient in steady-state operations. An electronically controlled capacity clutch (ECCC) is implemented to control the slip between the pump and turbine of the torque converter, thereby increasing its energy transfer efficiency and increasing vehicle fuel economy. Even though reducing torque converter slip minimizes losses due to fluid coupling, it also decreases the damping provided by a slipping torque converter and as a result increases the sensitivity of the driveline to engine excitations. This investigation uses driveline torsional velocity response measurements to evaluate the effects of using slip feedback closed-loop control with a very aggressive torque converter ECCC slip schedule in automatic transmissions. Experimental results for a General Motors Sport Utility Vehicle equipped with a 6-speed Rear-Wheel-Drive automatic transmission with and without all-wheel-drive, and different torque converter isolator configurations are presented. The effects of the very aggressive ECCC slip strategy on vehicle drivability are also discussed.