Active vibration isolation system for a diesel engine

An active two-stage vibration isolation rig for a diesel engine, on which four servo-hydraulic actuators are used as secondary vibration sources, is described in this paper. The upper mass of the rig consists of a marine diesel engine and an electrical eddy current dynamometer, weighting approximately 1100 kg in total. The intermediate mass is not a single mass in the traditional sense but composed of four small rigid plates to which the rods of hydraulic actuator and resilient rubber isolators are attached. The intermediate mass weighs about 68 kg in total with each plate weighting 17 kg. Two control methods based on adaptive multi-notch filtered algorithm were applied to isolate the engine vibration transmission through four isolating mounts. One was a one-input one-output system, another was a 4-input 4-output decentralized control system. The experimental results demonstrate that good attenuation was obtained in the effective range for phase compensation of secondary path but acceleration increase occurred in a higher frequency region because of nonlinearity caused by the hydraulic system. The acceleration increases may cause higher total vibration level than uncontrolled vibration responses. A pre-compensator and a digital compensator, which were placed in series with the adaptive multi-notch filter, were designed to eliminate undesirable influences of hydraulic actuator nonlinearity on the active vibration isolation performance. The experimental investigation shows that the improved method attenuates the unwanted vibration increases effectively. The features of the active system, the development activities carried out on the system and experimental results of the system are discussed in the paper.