Research On The Clamping Force Control For V-belt CVT Based On Slip Ratio

For metal V-belt continuously variable transmission (CVT), if the clamping force is too large, the transmission efficiency will decrease, or if the clamping force is too little, the belt will slip, and the belt and the belt pulley will be abraded. Based on the project "The research on the principle of transmission and control of metal V-belt continuously variable transmission", which is supported by National Natural Science Foundation of China (NSFC), and from the angle of transmission mechanisms, the clamping force control method based on slip feedback is put forward.First, the mechanical structure and transmission principle of metal V-belt CVT is analyzed, and the computing method of the force between belt and pulley is provided. Due to the relative movement at cornerite between blocks and bands, the force analysis is done, and the distribution of the thrust between blocks and the tension on bands in the operating zone is derived. To begin with the friction between bands and blocks and between blocks and pulleys, the principle of slip transmission is elaborated.Then, according to the demands of the project, the slip test bench of metal V-belt CVT is designed and built. Variable frequency motor is chosen to be speed and load control device, and the energy feedback is realized by common DC bus, and also the CVT case is rebuilt to measure the axial displacement of movable pulley precisely. The feedforward-feedback complex control method is used, which increased the accuracy and stability of loading torque and pulley clamping force control.The CVT slip characteristics are studied on the test bench under different speed ratios, different clamping forces of secondary pulley, and different primary pulley speeds. The results show that the effect of clamping force and pulley speed on friction coefficient can be ignored, however the speed ratio has great influence on the friction coefficient. Under the same slip ratio condition, the coefficient is large when ratio is low. Based on the result, the target slip zone which has large friction coefficient is defined, and based on slip feedback, the clamping force control model with slip model as feedforward and with real slip ratio as feedback is built. The simulation result indicates that the clamping force control based on slip feedback increases the friction coefficient between belt and pulley, and reduces the clamping force between primary and secondary pulleys.At last, the model of clamping force control based on slip feedback is verified by speed ration tracking test, the transmission efficiencies of slip controlled CVT are tested under different speed ratio conditions. Compared to the transmission efficiency with traditional clamping force control, the one with clamping force control based on slip feedback can improve transmission efficiency of CVT.