Torque Converter Clutch Low Slip Speed Detection and Control

A torque converter clutch (TCC) is an important element of automatic transmissions because it affects fuel economy and driveability. Although torque converters are ideal launch devices for transmissions, they are inefficient in steady-state operations. For that reason, a TCC is used to control and minimize the slip between the torque converter pump and turbine, thereby increasing the efficiency of the driveline and improving fuel economy. However, low TCC slip speeds increase the likelihood that disturbances cause the TCC to have zero slip or crash. In the absence of TCC slip, it is essential to quickly restore slip and regain driveline isolation to maintain driveability. To recover TCC slip, pressure to the TCC must be reduced significantly to overcome the effects of clutch material nonlinearities and hydraulic hysteresis. Unfortunately, large pressure reductions can also result in undesirable slip overshoot. In this investigation, the truncated sequential probability ratio test is used to achieve fast and robust detection at the low signal-to-noise ratios caused by the low TCC slip speeds. In the event of a crash, two unique TCC pressure command sequences are presented which maximize the response of the system hydraulics while also minimizing clutch slip overshoot. The effectiveness of the proposed methods are evaluated using experimental results from small and large vehicles equipped with automatic front and rear-wheel drive transmissions.