Model Simplification And Shifting Analysis Of Hydro-mechanical Continuously Variable Transmission

Hydro-mechanical continuously variable transmission(HMT) is a kind of infinitely variable transmission with the advantages of high efficiency, high power density and continuous speed ratio. As the function of the hydraulic components in the closed hydraulic circuit reverse, there are several problems in the power-shift process, for example, a sudden change of the fixed displacement hydraulic components’ speed, the fluctuation of the output torque and the speed ratio in the driveline, the power interruption and the shift shock. All of these will cause a bad feeling on riding. Therefore, establishing a simplified model of the transmission for shifting control based on the model, analyzing the reason and studying the control strategy of power shifting are the key to improve the shifting quality and the comprehensive performances.In this paper, the two range arithmetic HMT was regarded as the research object. The influences of the hydro-mechanical key parameters on power shifting were taken into account. Model simplification and shifting analysis of the HMT were carried out. Which included the following:(1) the model of the closed hydraulic circuit was built. Based on the mathematical models of hydraulic oil bulk modulus, volumetric efficiency and load, the relations between the inputs and the hydro-mechanical key parameters were analyzed and the models were simplified.(2) The structure and principle of multi-plate wet clutches hydraulic control system were introduced. The simplified models of the clutches and digital proportional relief valve were established.(3) By lever analogy, the speed and torque models of multiple planetary transmission(a mechanical branch and a split-flow mechanism), which were bulit. Moreover, based on the MATLAB/Simulink software, the total simulation model was established, including the closed hydraulic circuit system, the clutches hydraulic control system and multiple planetary transmission. The verification experiments were carried out and the comparative results showed that the hydraulic oil bulk modulus simplified model, the digital proportional relief valve simplified model and the total simulation model were nearly correct. Finally, the power-shift method of the simplified HMT model was researched, including the clutches method and regulating the variable displacement hydraulic component method. The simulation results showed that the shift shock could be reduced relatively by controlling good oil pressures of the clutches and making a little displacement in the power-shift process.