Experiments on the transmission paths and dynamic behavior of engine structure vibrations. I. Background and static tests

In order to establish a method of estimating the engine structure surface responses, a series of experiments was made on a four-cylinder (bore: 86 mm, stroke: 84 mm), in-line, water-cooled high-speed diesel engine. The results obtained in static conditions are summarized with the necessary background. The propagation behavior of excitation forces in the engine structure, the vibration behavior of the vibration transmission paths, and the transfer functions of the transmission paths were examined in static conditions. The distribution of the damping in the engine structure, the influence of cooling water, the lubrication oil, the oil pressure, and the crank position on the transfer functions were also examined. After the experiments, we found that (a) a different excitation force induces different responses on the engine structure surfaces because of its different transmission paths and their transmission behavior; (b) the forces applied on the cylinder head can be transmitted along the cylinder head bolts, and the engine structure can be excited by this force just as strongly as by the identical force applied on the piston top; and (c) most of the damping in the engine structure is induced by the oil film existing around the main moving parts such as the pistons, the connecting rods, and the crankshaft.