Study On Power Re-circulation In Hydro-mechanical Composite Transmission

Hydro-mechanical variable transmission(HMCVT for short) is a new hydraulic power and mechanical power flow parallel transmission, the transmission speed regulating characteristics, and can significantly increase the power vehicle fuel economy and dynamic performance. It’s now widely used in sanitation trucks, agricultural vehicles, construction vehicles, special vehicles for military, so it is important to study the social and practical value. The power re-circulation is the most important phenomenon in the hydro-mechanical variable transmission system, so the research on it is becoming more and more important.First, the paper presents the current research achievements in HMCVT at home and abroad, and conducted a comprehensive analysis of it’s basic characteristics, introduced the stepless speed regulation characteristic, power split ratio characteristics and efficiency in output-coupled HMCVT or input-coupled HMCVT.Secondly, the paper analysis the power flow of the important component: differential gear train in Hydro-mechanical variable transmission and the system, summed up when power re-circulation happened, the influence of power re-circulation on the overall efficiency of the system. On this basis, proposed 36 kinds of scheme of compound HMCVT, and how power re-circulation influence on the efficiency of compound HMCVT when system under five different power flow state. And it compared the power split characteristic and efficiency characteristic between input-coupled HMCVT, output-coupled HMCVT and compound HMCVT.Then, the paper using power bond graph modeling theory modeled compound hydro-mechanical composite transmission subsystems, on the basis of the entire hydro-mechanical composite transmission power bond graph modeling. Using 20-SIM simulation software, carry on the simulation analysis to the system model. It showed the stepless speed regulation characteristic, the relationship between hydraulic power and power split ratio, the relationship between total efficiency and power split ratio. The simulation results verify the research in re-circulation and efficiency of the system.Finally, the paper designed the test scheme of compound HMCVT, which can verify the correctness of the theoretical analysis through speed characteristics test, power split ratio and efficiency test. And it also gives the guidance to the later design.