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Dynamic characteristics of a line regulator and ratio control valve for an electronic controlled metal belt CVT are investigated by considering the CVT shift dynamics. Based on the dynamic models of the variable force solenoid valve, line regular valve and ratio control valve, simulations are performed and compared with the test results. It is seen that the ratio control valve has a on-off characteristics, which may result in a pressure pulsation in the primary actuator. In addition, the effects of the orifice size at the ratio control valve exhaust port are investigated. It is found that as the orifice size is decreased, magnitude of the residual pressure increases, which ensures the belt clamping force to transmit a large torque during the downshift at the cost of slow shifting. It is expected that the dynamic models of the CVT hydraulic system obtained in this study can be used in design of a prototype CVT

A fuzzy logic ratio control algorithm for a metal belt CVT is suggested considering the on-off characteristics of the ratio control valve and the nonlinear characteristics of the CVT shift dynamics. In the fuzzy logic, variable computation time for the error of the ratio and the rate of the error is suggested depending on the velocity of the rate of the CVT ratio. Experimental results show that a desired speed ratio can be achieved at a steady state by the fuzzy logic in spite of the fluctuating primary pressure. In addition, it was found that a faster response and better robustness can be obtained when compared with those of the PID control. It is expected that the ratio control algorithm suggested in this study can be implemented in a prototype CVT.