Shift quality of tractors fitted with hydrostatic power split CVT during starting

The matching of the control parameters of clutch hydraulic systems was studied in order to improve the shift quality of the tractors fitted with hydrostatic power split continuously variable transmission (CVT) during starting. Firstly, mathematical models of the clutch hydraulic system, CVT and tractor were constructed, and the models of the key components were tested and validated. Secondly, an evaluation indicator of the shift quality was determined, and 6 parameters which may affect shift quality were defined including instruction time and the instruction voltage for clutch pressure control. Thirdly, through single-factor simulation, the influence mechanism of parameters on tractor shift quality was determined. Finally, a solutions map was proposed, and a matching law of the control parameters was obtained accordingly. The results showed that the tractor shift quality improves with increasing of the initial instruction voltage at the first voltage rise and increasing instruction time consumed at the second voltage rise but decreases with the increasing of the terminal instruction voltage. If the interaction among various parameters is considered, the terminal instruction voltage should be taken as a low value, the pressure relief time of brake relative to shift start node should not be too long.