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The noise in hydraulic machines presents itself as fluid-borne noise (FBN), structure-borne noise (SBN) and air-borne noise (ABN). FBN is caused by the unsteady flow produced by pumps and motors or the operation of digital hydraulics, and propagates through the system causing SBN, which in turn causes ABN. This article reports on a novel integrated FBN attenuation approach, which employs a hybrid control system by integrating an active feedforward noise attenuator with passive tuned flexible hoses. The passive hoses are tuned to cancel the high-frequency pressure pulsations, whilst the active controller is designed to attenuate the dominant harmonic ripples. Adaptive notch filters with a variable step-size filtered-X Least Mean Square algorithm were applied in the new designed active piezoelectric actuator with high preload and operating forces, a wide bandwidth and very good linear dynamics. A time-domain hose model considering coupling of longitudinal wall and fluid waves was used to model and tune the flexible hose. Very good FBN cancellation was achieved by using the proposed integrated control approach, which was validated by comparing with numerical simulation and experiments. It can be concluded that the active attenuator with passive flexible hoses can form an effective, cost-efficient and practical solution for FBN attenuation. As the problem of high noise levels generated by hydraulically powered machines has risen significantly in awareness amongst industry and the general public, this work constitutes an important contribution to the sustainable development of low noise hydraulic fluid power machines.

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Fluid-borne noise (FBN) is a major contributor to structure-borne noise (SBN) and air-borne noise (ABN) in hydraulic fluid power systems and could lead to increased fatigue in system components. FBN is caused by the unsteady flow generated by pumps and motors and propagates through the system resulting in SBN and ABN. New hydraulic technologies such as digital switched hydraulic converters also generate unavoidable FBN. This article reports on a novel integrated FBN attenuation approach, which employs a hybrid control system by integrating an active feed forward noise attenuator with passive tuned flexible hoses. The active system which consists of adaptive notch filters using a variable step-size filtered-X Least Mean Squares algorithm is used to control a newly designed high-force high-bandwidth piezoelectric actuator in order to attenuate the dominant narrowband pressure ripples. The passive hose is tuned in the frequency domain and used to cancel the high-frequency pressure ripples. A time-domain hose model considering coupling of longitudinal wall and fluid waves was used to model the flexible hose in the integrated control system. Very good FBN cancellation was achieved by using the integrated control approach in simulation and experiments. It is an effective, cost-efficient and practical solution for FBN attenuation. The problem of high noise levels generated by hydraulically powered machines has risen significantly in awareness within industry and amongst the general public, and this work constitutes an important contribution to the sustainable development of low noise hydraulic fluid power machines.

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