Nonlinear control of a continuously variable transmission (CVT) for hybrid vehicle powertrains

Automotive engineers are continuously exploring various engine, transmission, and chassis technologies to increase overall vehicle performance, fuel economy, and safety. One promising powertrain concept is the continuously variable transmission (CVT) which offers a continuum of infinitely variable gear ratios between established minimum and maximum limits. This continuous gear ratio spectrum can increase the overall powertrain efficiency and eliminate the unwanted jerks associated with manual and automatic transmissions. Although basic CVT designs may have difficulty with high torque/low speed requirements, a hybrid power split continuously variable transmission configuration offers both fixed gearing and adjustable pulleys to satisfy driving demands. The effective control of the variable radius pulleys allows the designation of engine torque/speed to improve overall system performance for a given operating condition. In the paper, the fundamental components, configuration, and kinematics of a power split CVT are discussed. A suite of mathematical models is presented which includes the internal combustion spark ignition engine, clutch, transmission differential, and chassis dynamics. The problem of wheel speed control of a CVT equipped vehicle is considered. An adaptive nonlinear controller is designed to ensure asymptotic tracking of the desired wheel speed.