An Electro-Hydraulic Hitch System Based on Digital Hydraulic Valves with Adaptive Control for High-Horsepower Tractors

Conventional tractor hitch systems employing mechanically controlled multi-way valves suffer from low control precision and sluggish dynamic response, which render them inadequate for field operations characterized by highly variable soil resistance. To address these limitations, this paper proposes an electro-hydraulic hitch control system based on digital hydraulic valves for high-horsepower tractors. The proposed system integrates a load-sensing pump with pressure-compensated proportional valves to achieve supply-demand flow matching for the hitch cylinder, improving the smoothness of implement attitude regulation. Furthermore, an adaptive fuzzy Proportional-Integral-Derivative (PID) control strategy is developed for simultaneous tillage depth and traction force control, enhancing the accuracy of both controlled variables. A tractor simulation model and an experimental test rig are established to evaluate the hitch control performance under various operating modes. Experimental results demonstrate that the proposed digital-valve-based hitch system exhibits favorable control performance. Compared with conventional PID control, the proposed approach improves the depth stability coefficient and the load stability coefficient by 7.5% and 7.4%, respectively, under depth and traction control modes. Under force-position combined control, the depth and load stability coefficients reach 92.1% and 89.1%, respectively, confirming that the proposed method maintains both tillage depth consistency and load regulation effectiveness.