Exciting forces and their relationship to turbocharged diesel engine vibration
The work presented here quantifies the forces applied to the main bearings of three six-cylinder turbocharged diesel engines and reviews their exciting properties in both time and frequency domains. The engine structure response at the bearing supports and the outer surfaces are correlated. Vibration acceleration was measured, in the three different directions, at the engine main bearings and the outer surface. The liner vibrations were also measured. A theoretical model for calculating the bearing forces and estimating the bearing moment characteristics is proposed. The calculated bearing forces are investigated in both time and frequency domains. The characteristics of the forces driving the piston across the cylinder clearance are calculated. The characteristics of the forces acting on the liner by the piston are also calculated. Combining the results of the measurements with the theoretical model for force calculation, a technique for estimating the actual running clearance of the piston is presented. A technique for deriving the displacement from the measured acceleration is developed. By representing the engine response in terms of displacement it is possible to recognise the applied force time history and thus the identification of the specific parts of the engine structure primarily excited by moments and by direct force. It is shown that the engine structure response is a transient phenomenon and is maximum in the vicinity of the applied force. The displacement technique for quantifying engine response provides detailed information of the distortion of the running engine enabling the prediction of mechanical inputs which control the turbocharged engine noise.