中文摘要：

为了实现对拖拉机多段液压机械无级变速传动（hydro-mechanical continuously variable transmission,HMCVT）在任意稳定行驶速度和许可牵引负载下经济性最佳的控制,该文对拖拉机经济性最佳的无级变速规律进行了研究。根据拖拉机能量传递的特点,考虑HMCVT在不同传动比下存在效率差异的特征,把研究拖拉机的经济性最佳转化为对整车效率最大的研究。在分析整机传动系统效率特性的基础上,针对效率最大的目标函数和约束条件,求解了整车效率数值,结果表明在任意目标车速和牵引负载下,优化后拖拉机整车效率在35%-40%之间,并得出了效率最大时HMCVT最佳传动比、发动机转速和转矩,确定了基于整车效率最大的拖拉机HMCVT传动变速原理。研究表明：基于整车效率最大化原则能够实现拖拉机在任意车速和牵引负载下的整车经济性最佳,根据整车效率最大化确定的拖拉机多段HMCVT经济性最佳无级变速规律,为下一步制定装备多段HMCVT的拖拉机的经济性最佳控制策略提供参考。

英文摘要：

To realize the optimal economic control of a tractor with the multi-range hydro-mechanical continuously variable transmission（HMCVT） under any steady running speed and allowable traction load, the speed changing law of the best economy for tractors was studied in this paper. In the conventional economy research of tractors equipped with multi-range hydro-mechanical CVT, to realize the best economy of the tractor and the optimal matching of the transmission with the engine, the main method is that the engine is kept on the optimal economic work range by adjusting the throttle of engine and the transmission ratio of multi-range hydro-mechanical CVT. This method lacks considering the efficiency influence of multi-range hydro-mechanical CVT. Really, the efficiency of multi-range hydro-mechanical CVT has large difference in different transmission ratio. This feature influences the economy and efficiency of tractors. It was considered in this paper that the economy of tractor was decreased due to the losing of power passing through the transmission when the power is transmitted from engine to load by transmission. If the total efficiency of tractors was largest, the power losing in the transmission train was least on finishing a unit of production task. The best economy of tractors could be denoted by the maximum efficiency of tractors. According to the energy transmission characteristics of tractors, considering the difference of efficiency of multi-range hydro-mechanical CVT under different transmission ratio, the study of the best economy for tractors was transformed into the research of maximum efficiency for tractors. It was presented that the speed change law of multi-range hydro-mechanical CVT based on the maximum efficiency of tractors. Based on the analysis of the efficiency characteristics of the whole transmission system, the total vehicle efficiency was optimized for the objective function of maximum efficiency and constraint conditions. Using the circularly optimizing method of 4 parameters which were