Model Based Control for a Pressure Control Type CVT

A model based control algorithm for the pressure control type CVT has been developed. First, a P-line is proposed from the steady state relationship between the primary and secondary pressure for the given speed ratio to predict the shift performance. The P-line shows the pressure difference from the steady state primary pressure to the maximum(or minimum) pressure available for the given secondary pressure. It is found from the P-line that the bigger the pressure difference, the faster the shift speed. Based on the steady state characteristics of the pressure control type ratio control valve(RCV), the model based control algorithm is proposed. In the model based control, ratio control solenoid valve(RCSV) control duty is supplied in the feedforward loop. The following findings are obtained from the experiments; (1) linear control algorithm such as PID type controller can be used for the pressure control type CVT while nonlinear or adaptive control logic should be applied for the flow control type CVT, (2) the model based control is able to provide improved tracking performance and robustness compared to those by the linear controller owing to the RCSV control duty input in the feedforward loop.