An RC filter for hydraulic switching control with a transmission line between valves and actuator

Abstract

Hydraulic switching control with fast switching valves may excite unacceptable hydraulic and mechanical oscillations. Particularly if transmission lines are used, which have many oscillation modes, the avoidance of resonances by a proper timing of the switching pulses is hardly feasible. Then, passive filters may be a good solution. A simple RC filter applied to a cylinder drive with a transmission line to the switching valves is investigated by a transfer function analysis, numerical methods, and experiments. Properties of the dynamic behaviour are elucidated by approximate relations derived from the transfer function by asymptotic methods. A simple dimensioning rule recommends sizing the filter resistance close to the hydraulic impedance of the transmission line. The capacitance’s sizing is a trade off between a potential reduction of the resonance peak due to the cylinder natural frequency and a softness of the hydraulic drive system.