Speed changing control strategy for improving tractor fuel economy

In order to realize the optimal fuel economy of tractors equipped with hydro-mechanical continuously variable transmission (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, brake specific fuel consumption and HMCVT transmission efficiency have great changes at different work points. Based on the characteristic, the paper put forward a kind of control strategy of optimal fuel economy which take the ratio of brake specific fuel consumption ge to HMCVT transmission efficiency ηb as the index. 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 transmission efficiency of HMCVT was higher than 0.92, and reached 54.16% when transmission efficiency was higher than 0.94. This meant that HMCVT mainly worked at high-efficiency area under the control strategy of optimal fuel economy. Compared with unary regulation which took ge or ge/ηb as the index and the binary regulation which take ge as the index, the tractor fuel consumption was obviously reduced. The surface of ge/ηb was smoother, which was more suitable for the complex working environment of tractors. Under the control of the optimal strategy of fuel economy, the working point proportion of the low fuel consumption area in the whole load characteristic field was 3.03, 1.27 and 1.20 times as great as the other three speed changing control strategies; while the proportion of high fuel consumption area was 0.183, 0.299 and 0.439 times as few as the other three control strategies. It showed that tractor was more likely to work in lower fuel consumption state, when it worked stably at a certain target speed. The research suggested that the optimal fuel economic speed changing control strategy of tractors with ge/ηb as the index can improve the fuel economy of tractors under any working condition. The results lay a foundation for the realization of the control strategy of the follow-up engineering and the test verification.