Effects of control structure on performance for an automotive powertrain with a continuously variable transmission

摘要

The wheel speed control problem of an automotive powertrain equipped with a conventional spark-ignition engine directly connected to a continuously variable transmission (CVT) and an electronic throttle is considered. We revisit the seminal work by Guzzella & Schmid, 1995 and show that the control structure that dedicates the throttle actuator to maintaining engine operation at the maximum fuel efficient operating points results in a single-input, two-output (SITO) system that presents a fundamental limitation in the achievable wheel speed response. The limitation arises from the nonminimum phase (NMP) zero in the transfer function from the CVT ratio rate to the vehicle wheel speed. We, then relax the requirements on the fuel efficient operation and employ the electronic throttle as a second actuator for the wheel speed regulation problem. The resulting two-input, two-output (TITO) control structure is then analyzed to determine how to mitigate the limitations associated with the NMP zero. Our results substantiate the trade-off between fuel economy and performance that is widely recognized in practice and in the literature.