Economic control strategy of HMT tractor considering transmission efficiency

The transmission efficiency of hydro-mechanical continuously variable transmission (HMT) plays an important role in determining the integral economic performance of tractors equipped with HMT, because its efficiency will fluctuate greatly with the change of input and output conditions. These fluctuations will greatly affect the fuel consumption and power output of tractors, and ultimately affect the operating cost of tractors, which is of great significance to the agricultural machinery industry with fuel consumption as the key factor. The research focus of this paper is to optimize the engine and HMT operating point through two different control strategies, and put forward two economic control strategies: the engine efficiency optimization control strategy (EOCS) with the highest engine efficiency as the objective function and the integral efficiency optimization control strategy (IOCS) with the highest engine and HMT integral efficiency as the objective function. The main purpose is to study how different control strategies affect the performance and economy of tractors by paying attention to engine efficiency and integral system efficiency. At first, the efficiency model including engine and HMT are established, so as to better understand how to optimize them cooperatively and achieve the highest operating efficiency. The efficiency model provides a basis for optimizing control parameters (engine speed and HMT speed ratio), and control parameters play a vital role in the economy of HMT tractors. The improved fish swarm algorithm is used in the optimization process, which is very suitable for dealing with complex optimization problems. The algorithm is helpful to determine the optimal engine speed and HMT speed ratio of the two control strategies, and to ensure the best economic matching of engine speed and HMT speed ratio under various conditions. In this study, the simulation model of HMT tractor is established based on Matlab/Simulink, and the real tractor data is included in the model to simulate the performance of tractor under typical working conditions more accurately. To simulate real conditions, a cyclic working condition model is constructed that treats vehicle speed and working resistance as the key parameters. According to the road/operation test data of real vehicles, the data segments of common working conditions are extracted, these working conditions mimic typical operational scenarios that tractors face, such as plowing or hauling loads, and are used to compare the effectiveness of the two control strategies. The simulation results show that the fuel consumption of the two control strategies is obviously different. Under the cyclic working condition, the fuel consumption of IOCS is 1.356 liters, while that of EOCS is 1.381 liters. The fuel consumption of IOCS is 1.81% lower than that of EOCS. With the decrease of fuel consumption of IOCS, it shows that it can optimize the integral system efficiency of engine and HMT more effectively and provide better economy. But the results also show that there are differences in acceleration performance between the two strategies. Although the IOCS strategy has lower fuel consumption, it will lead to more drastic changes in the engine operating point with the change of load. The acceleration performance may be unstable, especially in the environment where the speed needs to be changed quickly and smoothly. In contrast, EOCS has a higher fuel consumption, but the engine operating point changes more smoothly than IOCS in the process of load change, and its acceleration performance is better than IOCS because its reserve torque is higher than IOCS. This smoother acceleration response is especially beneficial in the operating environment with high requirements for rapid acceleration and stable power output. Overall, the research in this paper shows the importance of selecting appropriate control strategies according to specific operational requirements. While IOCS strategy is more economical, EOCS strategy may be more suitable for tractor operation when acceleration performance is more important. The research results can lay a research foundation for HMT tractors to formulate control strategies that meet the requirements of engineering applications.