Abstract
Binary pump control on the pulley system of a Continuously Variable Transmission (CVT) could produce a line pressure drop during full mode to half mode transition. If the pressure drops, the belt will slip. Currently there is no tool/method available to evaluate the pressure drop variation with respect to variation in the design variables or boundary conditions in the binary pump control circuit. The current work is about developing a simulation model that can calculate the pressure drop for mode transitions in CVT binary pump control circuit and optimizing the model for minimizing the pressure drop. The virtual model of the binary pump system was built in AMESim using the hydraulic and hydraulic component design libraries. Sensitivity studies were conducted for various parameters in the model that affect the pressure dip during mode transition. Based on the sensitivity studies, the most significant parameters affecting the pressure drop were identified and the parameter values were optimized for reducing the pressure drop. Results show that in the baseline design, reverse flow between the line and the suction, when the pump-line and pump-suction orifices of the binary switching valve were both open, was causing the significant dip in the line pressure when transitioning from full flow to half flow mode. The presence of notch significantly decreases the overlap between the pump-suction and pump-line orifices’ opening, thereby leading to lesser reverse flow between the line and the suction and lesser dip in line pressure. Further, decreasing the underlap of the pump-suction portion of the spool, leads to lesser line pressure dip as this would also reduce the overlap between the pump-suction and the pump-line orifices. By optimizing the design, the pressure drop can be decreased from about 16 bar in the original circuit to about 0.8 bar.