Modeling and Experimental Validation of the Time Delay in a Pilot Operated Proportional Directional Valve

The pilot-operated proportional directional valve is a crucial component in the airplane landing gear retraction system. The time delay of the proportional valve directly affects the retraction behavior even the flight safety and needs to be analyzed. Therefore, the modeling and analysis of a typical pilot-operated proportional directional valve are presented in this paper. Substantially, the nonlinear valve system is composed of four subsystems: mechanical, electronic, electromagnetic, and fluid dynamic subsystems. The subsystems are modeled based on a lumped parameter approach. The coupling among the subsystems is analyzed. The nonlinearity is implemented using a specific set of equations in the model. Especially, the nonlinearity observed in practical application is considered in modeling the effect of the electronic anti-unloading power drive circuit on the pulse-width modulation signal. The analytical results of the model show good agreement with the experimental ones. The investigation shows that the delay of the valve results from multiple subsystems' dynamic performances which act sequentially on the main spool. The effect of the electronic part and the structural part is analyzed, and the proportion of each part is given based on the simulation results. The analysis shows that the model can provide a direct suggestion in choosing the valve part to optimize and the optimization effect limit.