Due to the increase in emission requirements for non-road vehicles in many countries and the reduction of agricultural personnel, tractors are developing towards high horsepower and electrification. According to the working conditions of high-horsepower tractors, a hydromechanical continuously variable transmission (HMCVT) is designed for hybrid tractors. Taking a tractor equipped with this transmission as the research object, an equivalent factor global optimization model was established and a genetic algorithm was used to optimize the equivalent factor S offline to obtain the optimal equivalent factor of the tractor under different operating mileage and the initial state of charge (SOC) of battery. By using the optimized equivalent factor, the tractor can be in the charge depleting (CD) mode for a longer time on the premise of making full use of the energy in the battery, so as to improve the auxiliary ability of the motor in the whole operation cycle to reduce the fuel consumption of the tractor. The effectiveness of the control strategy is verified by MATLAB/Simulink and hardware in the loop (HIL) tests, and the fuel economy of tractors is improved by 2.939% and 3.909% respectively in the two tests.

The design parameters of the transmission directly affect the vehicle’s dynamics and fuel economy, due to the complexity of the tractor’s working conditions and operating modes, the optimization of the transmission design parameters is more difficult. In this paper, an independently designed hydro-mechanical CVT transmission is taken as the research object, and the transmission design parameters are optimized based on the tractor’s whole life-cycle speed usage rate, and the Multi-Objective Genetic Algorithm(MOGA) is used for optimization and solution. In this paper, the fuel consumption rate and hill climbing degree are taken as the optimization objective function, the parameters that have a greater influence on the optimization objectives are selected as the design variables, and the constraints are determined. A multi-objective genetic algorithm based on the Pareto optimality principle combined with experimental design is used to establish a multi-objective optimization model of the transmission device based on modeFrontier, and a global search for optimality is carried out, and a Pareto optimal solution is finally obtained. The results of the study find the optimal solution under the constraints, reflecting the conflicting characteristics between power and fuel economy. The design variables of the Pareto optimal solution obtained through optimization iterations based on the whole life cycle speed usage rate satisfy the matching requirements of the transmission well.

The design parameters of the transmission directly affect the vehicle's dynamics and fuel economy, due to the complexity of the tractor's working conditions and operating modes, the optimization of the transmission design parameters is more difficult. In this paper, an independently designed hydro-mechanical CVT transmission is taken as the research object, and the transmission design parameters are optimized based on the tractor's whole life-cycle speed usage rate, and the multi-objective genetic algorithm is used for optimization and solution. In this paper, the fuel consumption rate and hill climbing degree are taken as the optimization objective function, the parameters that have a greater influence on the optimization objectives are selected as the design variables, and the constraints are determined. A multi-objective genetic algorithm based on the Pareto optimality principle combined with experimental design is used to establish a multi-objective optimization model of the transmission device based on modeFrontier, and a global search for optimality is carried out, and a Pareto optimal solution is finally obtained. The results of the study find the optimal solution under the constraints, reflecting the conflicting characteristics between power and fuel economy. The design variables of the Pareto optimal solution obtained through optimization iterations based on the whole life cycle speed usage rate satisfy the matching requirements of the transmission well.

According to the working condition of high-horsepower tractors, a hydraulic mechanical continuously variable transmission (HMCVT) suitable for plug-in hybrid tractors is designed. Taking the tractor with this transmission as the research object, a global optimization model of equivalent factor is established to improve the control effect of the Equivalent consumption minimization strategy (ECMS); and then used genetic algorithm to optimize the equivalent factor S off-line to obtain the best correction coefficient MAP of different operating mileage and the initial value of battery State of Charge (SOC). Then based on the optimal correction coefficient map, the ECMS strategy based on equivalent factor optimization is established. Considering the efficiency of the power battery, motor and other components, the power distribution between the diesel engine and the motor under the optimal equivalent factor is obtained. The effectiveness of the control strategy is verified by MATLAB/Simulink and hardware-in-the-loop tests, and the fuel economy of tractors is improved by 2.939% and 3.909% respectively in the two tests.

During the mode switching process of a hybrid tractor equipped with a mechanical-hydraulic compound transmission (HMCVT) device, the separation and combination of the clutch will cause transient shocks, affecting the smoothness and driving comfort of the entire vehicle. This article establishes a system dynamics model in SimulationX simulation software and builds a hardware-in-the-loop (HIL) test platform for testing to study the simulation and testing when switching from pure electric drive mode to hybrid speed coupling mode. In order to solve the problem of slow dynamic response of the engine, this study proposes a control strategy of "clutch oil pressure fuzzy control + motor torque compensation” and uses the orthogonal test range analysis method and variance analysis method to optimize the vehicle mode switching quality. Taking the switching timing of the six clutches C0, C2, C3, C4, C6 and C7 involved in this article as the factors A, B, C, D, E and F of the orthogonal test range analysis, the clutch switches 0.5s ahead of time. On-time switching and delayed switching of 0.5s are used as three levels. L27(36) orthogonal table is selected for simulation test. Range method analysis shows that scheme A3B1C3D3E1F2 is the optimal switching scheme, that is, clutches C2 and C6 switch 0.5s in advance, and clutch C7 is on time. Switching, clutches C0, C3 and C4 are switched with a delay of 0.5s, the output shaft speed drop is reduced from 21.875% to 1.63%, the dynamic load coefficient is reduced from 8.473 to 2.72, and the impact degree is reduced from 26.181m/s3 to 7.08m/ s3, the switching time is reduced from 1.345s to 0.35s. A hardware-in-the-loop test platform was built for testing. The hardware-in-the-loop (HIL) test results were consistent with the overall trend of the simulation results, verifying the effectiveness of the proposed control strategy and method.