Suganuma N., Yoshizumi K., Honda I., Ohta K.

This paper presents the theoretical procedure to predict the acoustic and vibratory response of the crankcase and piston slap impact force considering the dynamic behavior of piston and cylinder liner. Piston slap in internal combustion engines, which causes engine noise and liner cavitation, is an impact phenomenon between the piston and cylinder liner when the side force acting on the reciprocating piston changes its direction. With a view to predicting engine noise or liner cavitation caused by piston slap and reducing their levels, it is important to achieve an accurate estimation of the impact force and the vibratory response of each engine components, such as cylinder liner. Piston slap is a complex transient collision phenomenon, on which the vibratory characteristics of the liner have a large influence. This paper presents an analytical model of the impact force and the vibratory response of cylinder liner induced by the piston slap in internal combustion engines. In this method, the equation of motion for the coupled system of piston and cylinder liner is derived, taking account of several resonant modes of the cylinder liner to simulate accurately time histories of the impact force and the vibratory response. This method consists of the following three steps: (1) Simulation analysis of the mechanical impact force of piston slap that is induced by the combustion pressure and inertia forces. (2) Estimation of vibration transmission and noise radiation properties of the crank case using FEM, BEM and modal analysis technique. (3) A combination of excitation force and vibro-acoustic characteristics of the structure gives the engine noise spectrum. This method was applied to an actual diesel engine and the calculated noise spectrum agreed well with the measure one. The low-noise structural design of a piston was also examined using this method.