| The hydro-mechanical transmission(HMT)is a new type of transmission that combines mechanical transmission and hydraulic transmission.It not only has high transmission efficiency,but also can realize a large range of infinitely variable rotation speed.It can match well with the engine,and also adapt to the needs of vehicles in different working environments.According to the working principle of HMT and the analysis of its working characteristics,this paper explores the influencing factors of the HMT mode switching process,and studies the HMT mode switching strategy with the goal of improving the mode switching quality.The structure and working principle of the hydraulic mechanical transmission device are expounded.According to the structural form of the hydro-mechanical transmission,the speed regulation characteristics、torque characteristics and power split characteristics of HMT in different modes are analyzed;the dynamic model of HMT in different modes and the mathematical model of each component are established.According to the working characteristics of HMT,the relationship between the displacement change of the hydraulic speed control system and the mode switching is analyzed,and the optimal displacement of the hydraulic components when the HMT mode is switched is determined;the inherent work of the hydraulic speed control system is analyzed.The influence law of characteristics and mode switching mechanism on the mode switching process of HMT;combined with the analysis of HMT working principle and mode switching process.According to the analysis of the mode shifting process,and taking the output torque loss coefficient,impact degree and mode switching time as the evaluation indicators,a coordinated control strategy of the hydraulic speed control system and the mode switching mechanism in the HMT mode switching process is proposed.Based on the flow balance equation of the hydraulic speed control system and referring to the stable output speed before switching,the displacement of the hydraulic components is predicted and adjusted;based on the model predictive control theory,the clutch torque during the mode switching process is coordinated and controlled,thereby inhibiting the clutch engagement(separation)process and the influence of the displacement adjustment of the hydraulic speed control system on the torque during the HMT mode switching process.AMEsim and simulink software are used to establish the simulation model of the hydraulic mechanical transmission,and the simulation analysis of the mode switching process is carried out.The results show that the mode switching strategy formulated in this paper can reduce the output torque loss during the mode switching process under different working conditions.The switching time is shortened,and the switching quality of the HMT mode is better improved. |
