Modeling and control simulation for farm tractors with hydro-mechanical CVT

To develop the control system of hydro-mechanical continuously variable transmission (HMCVT), a tractor power train model is built by using the principle of dynamics and modular method, which includes the engine, HMCVT, running system and driven implement. According to the characteristic of power split, HMCVT is separated as axes set, variable displacement pump-motor system, clutch set and control system. The control logic model of range shift process is developed by using the theory of finite state machine. It is realized that TCU continuously controls the process of speed change and range shift. The dynamic characteristic of automatic speed changing and ranges shifting is simulated. The result indicates that it is an effective method to improve the dynamic performances of HMCVT by using the variable parameters PID control method which use engine speed and throttle values as control parameters and the feedforward control method which use throttle change rate as control parameters. The model can be used conveniently for the analysis of tractor dynamic performance and the research of HMCVT control method.