Experiments on the transmission paths and dynamic behavior of engine structure vibration. II. Motoring tests

Abstract

In order to gain a better understanding of the transmission behavior of the excitation forces in the engine structure, such as the gas forces, the inertia forces, the piston slap forces, and the valve seating impact forces, a series of motoring tests was carried out on a four-cylinder (bore: 86 mm, stroke: 84 mm), in-line, water-cooled high-speed diesel engine. The motoring tests were carried out by changing the combinations of the excitation forces, and at different engine speeds. Under the motoring tests, it could be seen that even the cylinder block bottom sides could be steadily excited by the valve seating impact forces. The transmission behavior of each of the excitation forces can be identified distinctly by the particular frequency components in the power spectral density diagrams of the engine structure responses. Finally, new types of transfer functions were proposed in order to identify the relationship between the kinetc energy of the impulsive excitation forces (such as the piston slap forces and the valve seating impact forces) and the induced engine structure responses. These new transfer functions could be determined under motoring conditions and can greatly overcome the difficulties in estimating the engine structure responses.