Active control of fluid-bome noise in hydraulic systems using in-series and by-pass structures

The nature of digital hydraulic systems may cause severe fluid-borne noise problems because of the pulsed nature of the flow. An effective method to reduce the noise that does not impair the system performance and efficiency is needed. This article reports on initial investigations of an active valve for pressure pulsation attenuation in switched inertance hydraulic systems (SIHS) based on in-series and by-pass structures. The in-series structure represents a valve arranged in line between the SIHS and the load providing a controlled pulsating pressure drop, whilst for the by-pass structure the valve was arranged in parallel with the load providing a controlled pulsating bleed-off flow. A high-performance piezoelectric valve was used as the active controller. Adaptive notch filters with the filtered-X least mean square algorithm were applied for pressure pulsation attenuation, while a frequency-domain least mean square filter was used for secondary path identification. Simulated and experimental results show that excellent cancellation was achieved using the proposed methods, which have several advantages over passive noise control systems. Comparison of the in-series and by-pass structures is discussed in terms of system performance, robustness and advantages. The proposed control structures are very promising for fluid-borne noise cancellation in fluid power systems or other fluid systems with severe noise or vibration problems.