Dynamic Effect of the Intermediate Block in a Hydraulic Control System

The intermediate block is a basic element in an hydraulic control system, and is usually used to install all hydraulic components and guides the fluid flows. However, the effect of this block is usually neglected, but it has to be taken into consideration when high performance applications, especially at high frequencies, have to be achieved. This paper focuses on this component and shows how it can influence the hydraulic system dynamics. The main contributions of this work are the implementation of a Bond Graph model of this component, which can easily be integrated in the whole system model, and a complete analysis of the effects (pressure drop, compressibility, inertia) induced by the intermediate block on the whole system performances. The relationship between flow rates and pressure drops along with the energy losses in the block are obtained according to a method based on the decomposition of the circuit in parts for which the local losses can be obtained from abacuses. The Computational Fluid Dynamics (CFD) is used for the validation of the results. Besides, the compressibility and inertial effects are carefully studied since they have a great influence on the hydraulic frequency. Finally, simulations and experiments are implemented for demonstrating the importance of the effect of the intermediate block in the hydraulic system modeling. By introducing compressibility and inertial effects of the intermediate block, the simulation result shows better agreement with experimental results at high frequencies. This comparison demonstrates that the control design can reach better performance when considering the dynamic model of the intermediate block.