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A CVT ratio control algorithm is proposed to improve the engine performance by considering the powertrain response lag. In the CVT powertrain, there exists a response lag, which results from the throttle response, engine torque dynamics, CVT filling time, CVT shift dynamics, and the drive shaft dynamics including the tire. This response lag causes the deviation of the engine operation from the optimal operation line for the minimum fuel consumption. In the CVT ratio control algorithm suggested in this paper, the desired CVT speed ratio is modified from the vehicle velocity, which is estimated after the time delay due to the powertrain response lag. In addition, the acceleration map is constructed to estimate the vehicle acceleration from the throttle pedal position and the CVT ratio. Using the CVT ratio control algorithm and the acceleration map, vehicle performance simulations and experiments are performed to evaluate the engine performance and fuel economy.

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

In this paper, a new formula for calculating primary and secondary thrusts for metal belt CVT's will be proposed considering variation of band tension, block compression and active arc for each of the primary and secondary pulleys. For the secondary thrust, an effective friction coefficient is introduced considering the effect of flange deflection. Nondimensional primary and secondary thrust of the metal belt CVT by the new formula agree well with the experimental results except for low torque range, 0 <λ< 0.2 at a speed ratio i=1.0. The new formula can be used in design of the primary and secondary thrusts control system with sufficient accuracy.