Research On The Impact Force Induced By Piston Slap And Vibration Of Internal Combustion Engine Block

The impact force induced by piston slap is one of most important excitingsources of mechanical vibration and noise of diesel engine. It is difficult to measureaccurately the impact force because the piston slap happens in the inner of engine.Then, building right theoretical model and calculating the impact force is a simple andfeasible approach. With more strict law of vibration and noise of I.C. engine, theprediction technology of vibration and noise of I.C. engine grows up gradually.However, in the high frequency domain there is not a good method to predictvibration and noise of I.C. engine. And as a powerful tool for predicting vibration inhigh frequency domain,Statistical Energy Analysis(SEA) is used in some engineeringfields, but seldom apply in the vibration of I.C. Engine. Thus, this paper attempts toresearch the surface vibration of the cylinder block induced by piston slap.This paper obtains point mobility of piston and cylinder inner wall by thecombination of experiment and theoretical analysis to get the equivalent mass,equivalent spring constant and equivalent damping constant. Considering the cylinderpressure, the force induced by the connecting rod, and the frictions between the pistonand the liner, a good model of piston slap is produced. Then, this paper calculates theimpact forces induced by piston slap by MATLAB and researches the piston'ssecondary motion. And the calculated impact forces are consistent with those in theactual operation.To ZH1110 diesel, this paper recognizes advisable subsystems: the liner and theblock. And by experiment and SEA this paper obtains all SEA parameters, includingmodal density, equivalent mass, internal loss factors and coupling loss factors. Then,with these parameters we predict the surface vibration of the cylinder block inducedby piston slap and draw the velocity curves. In addition, this paper also analyzes theavailability of these parameters in different frequency domains and chooses properfrequency bands to research. Furthermore, this is validated by experiment.At last, by experiment about testing surface vibration of the cylinder block ofZH1110 diesel, this paper compares the results measured and the results predicted bySEA. The rationality of the piston slap model is validated by using coherence analysismethods. And the results of analysis in both timing domain and frequency domainproved that the SEA models built in this paper can properly predict the vibrationresponse in some special frequency bands.