Structure Vibration Analysis and Sound Quality Improvement for a Four-Cylinder Engine 2023-01-1153

In this paper, taking an inline four-cylinder engine with a second-order balance shaft as the research object, a method for modeling and analyzing the vibration of the engine structure is proposed, and the sound quality of the engine is evaluated by the Moore–Glasberg loudness. First, the finite element model of the engine was established, and the experimental mode of the engine casing, crankshaft and balance shaft were measured. The natural frequencies and modal shapes obtained by calculation and experiment were compared and analyzed, which validate the established finite element model. Second, in order to obtain the accurate torsional vibration of crankshaft nose, a flexible multi-body dynamic model of the engine was established, and the inertia and torsional stiffness of the drive shaft at crankshaft nose was taken into consideration in the developed model. The calculated and measured torsion angle at crankshaft nose were compared and analyzed. The results showed that the maximum relative error between the calculated value and the measured value of the torsion angle at crankshaft nose is less than 15%,and the average relative error is less than 10% . The vibration acceleration of the nodes on the block surface was calculated and analyzed with the established flexible multi-body dynamic model, and the calculated data was compared with the measured data, which validate the flexible multi-body dynamic model. Thirdly, taking the vibration velocity from engine block surface as the boundary condition, the radiated sound power level and the field point sound pressure level of the engine block were calculated using the Wave Based Techniques . The calculated results showed that acoustic power levels of the engine existed in the frequency band of 1000-1800 Hz is large. In order to improve the sound quality of the engine, the Moore–Glasberg method was used to calculate the loudness characteristics of the engine field points, and an engine structure re-design method to enhance sound quality is proposed.