Research On Economic Control Of Tractor Hydro-mechanical Continuously Variable Transmission

Hydro-mechanical continuously variable transmission(HMCVT)has the characteristics of hydraulic and mechanical double flow transmission,which is an ideal transmission form.It has the stability of hydraulic transmission and high efficiency of mechanical transmission.In order to realize the optimal fuel economy of tractors equipped with HMCVT,the speed changing control strategy of tractors was studied based on the analysis of the influence of the engine and HMCVT on the tractor’s fuel economy.For the tractors binary adjusted by engine and HMCVT,the characteristics of brake specific fuel consumption and HMCVT transmission efficiency were analyzed.Based on the characteristics,a kind of control strategy of optimal fuel economy which took the ratio of brake specific fuel consumption g_e to HMCVT transmission efficiencyη_b as the index was proposed.A load feedback control principle of tractors was designed to ensure stable driving of tractors under any target speed and improve operational quality.The optimal engine speed,torque and HMCVT speed ratio of tractors at any working point in the load characteristic field were calculated by using the parameter cycle algorithm,which ensured the engineering realization of the optimal fuel economic control strategy of tractors under the dual coordinated regulation.The results showed that the distribution of the optimal speed ratio appeared in the form of terraced field.The optimal speed ratio of the platform part corresponded to the working state of the pure mechanical drive of HMCVT.At this time,HMCVT was at the highest efficiency point.The distribution percentage of optimal speed ratio reached 72.84%when HMCVT worded in the state of high transmission efficiency.This meant that HMCVT mainly worked at high-efficiency area under the control strategy of optimal fuel economy.Compared with unary regulation which took g_e or g_e/η_b as the index and the binary regulation which took g_e as the index,the tractor fuel consumption was obviously reduced.Under the control of the optimal strategy of fuel economy,tractor was more likely to work in lower fuel consumption state,when it worked stably at a certain target speed.The fuel consumption of tractor was simulated by Simulink software.The simulation results showed that the optimal economic speed changing control strategy could reduce the fuel consumption of tractor by 5.29%and 2.42%respectively under the conditions of ploughing and field transportation,compared with the binary regulation which took g_eas the index.The research suggested that the optimal fuel economic speed changing control strategy of tractors with g_e/η_bas the index could improved the fuel economy of tractors under any working condition.