Dynamic simulation on shift process of tractor hydraulic power split continuously variable transmission during acceleration

Abstract: The effect of the design parameters of the hydraulic power split continuously variable transmission on the shift process during tractor acceleration was investigated. First, the model of the power train was developed with the software of Simulation X, including the engine, the transmission, the load and the clutch control system, and 8 groups of the experiments were used to validate the correctness of the model. Considering the effect of the rotational inertia on the shift process during acceleration, a complete model of the tractor with the rear axle was built. Then, based on the evaluating index of the tractor peak acceleration and the clutch friction work, five groups of design parameters were simulated and analyzed. According to the simulation results, the trend of the shift process according to the different shift starting time is not monotonous, the shift impact could be reduced by shifting before the designed shift points (about ?0.65 s in this study); the maximum slipping time is a function of the flow and pressure of oil, in order to shorten the period of the slipping time and improve the shift quality, long overlap time (0.2 s in this study) and large charge flow (6 L/min in this study) should be used; the large tractor weight can reduce the speed impact of tractor and the friction work of clutch but lead to bad impact on dynamic load, therefore the determination of the tractor weight should fully consider the impact of both the traveling speed and dynamic load of tractor. In addition, the shift impact could also be reduced by using Integrated Hydraulic Pump-Motor and reducing the engine speed during shift, but the effect of the swash plate axial piston units and engine on shift process was not so significant. This study can provide references for the study in continuously variable tractor transmissions and the control system.