Research on Hierarchical Collaborative Control of Dual-Axis Drive Hybrid Electric Tractor for Hill and Mountain Terrain Considering Traction Efficiency and Energy Consumption Economy

Hybrid tractors operating in hilly terrain often suffer from reduced overall performance due to unregulated slip rate variations. To address this issue, this paper proposes a hierarchical cooperative control strategy that jointly optimizes traction efficiency and energy consumption. First, a traction force–slip rate coupling model is developed, and an adaptive slip rate control method is designed to determine the optimal traction force distribution range, thereby improving traction efficiency. Next, an equivalent consumption minimization strategy (ECMS) is formulated to minimize equivalent fuel consumption, using the torque coupler ratio and torque distribution ratio as optimization variables. These two methods are then integrated through slip rate and traction force as transfer variables, forming a hierarchical cooperative control framework that simultaneously considers both objectives. The proposed method is validated under plowing conditions through MATLAB simulations and Hardware-in-the-Loop (HIL) tests, using a fixed coordinated traction force allocation method as a benchmark. Results show that, compared to the benchmark, the proposed method reduces slip rate loss by 29.6%, increases traction efficiency by 8.7%, and decreases equivalent fuel consumption by 14.4%. This study provides new insights into improving the energy efficiency of hybrid tractors in complex terrains.