In order to reflect the essential characteristics of heavy tractor electro-hydraulic hitch proportional raising valves more accurately, the internal structure and working mechanism of each hydraulic component in the proportional raising valves are analyzed based on the field operation environment and operation requirements of heavy tractor electro-hydraulic hitches in this paper, a proportional raising valve load-sensitive hydraulic system circuit is designed, and an electro-hydraulic hitch cartridge proportional raising valve based on the plate valve design concept is developed. Besides, a nonlinear mathematical simulation model of proportional raising valves based on boundary conditions is established based on the state space method of modern control theory. The simulation model is built with MATLAB/Simulink. The dynamic and static performances are simulated and analyzed using the fourth-order Runge-Kutta algorithm, and the movement patterns of its internal spool is revealed. The simulation results showed that for static performance, the output flow of the proportional raising valve fluctuates briefly near the driving voltage of 3.9 V due to the influence of uniform-pressure-drop valve pressure regulation. As the pressure difference between the oil inlet and outlet of the two-position three-way proportional directional valve is basically maintained at about 1.5 MPa, the maximum flow rate is about 62 L/min under the action of uniform-pressure-drop valve, which is close to the product performance of the two-position three-way proportional directional valve, and the proportional raising valve has good load pressure compensation and steady-state speed regulation characteristics. In terms of dynamic performance, when the load pressure changes step by step, the output flow fluctuation of the proportional raising valve system is small, the adjustment time is short, and the influence of the load change is small. When the driving voltage changes step by step, the proportional raising valve has good dynamic speed regulation performance. Then, based on the indoor test platform of load-sensitive hydraulic system, the plug-in proportional raising valve of electro-hydraulic hitch is tested and studied. The test results show that the steady flow output of proportional raising valve has experienced 3 successive stages: dead zone, slow increase in flow and rapid increase in flow. Over the 3 stages, the maximum flow rate can reach about 60 L/min and return stroke error is less than 5%. At the same time, the test data of the valve is in good agreement with the steady flow simulation data, and the maximum flow error is about 3.33%. When the load pressure changes step by step, the proportional raising valve compensation pressure in real time is about 1.5MPa, the hydraulic shock is small, the static flow output of the proportional raising valve is stable, and the system flow is maintained at about 30 L/min when the load pressure changes step by step, which is basically consistent with the simulation data. When the driving voltage changes step by step, the flow rate of the system changes from 15 L/min to 27 L/min, which is basically consistent with the simulation data, and the flow rate error is only 3.57%, the proportional raising valve has good dynamic speed regulation and good steady-state speed regulation, meeting the field operation requirements of heavy tractor electro-hydraulic hitch. This study provides good reference for modeling, simulation and experimental analysis of key components of tractor hydraulic system. © 2019, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.
