Detection of cylinder bore non-cleanup using modeling of piston ring dynamics

A study was undertaken to develop a method of detecting an automotive engine manufacturing defect known as cylinder bore non-cleanup. This defect is best described as a rough surface finish inside any cylinder bore of an engine. This defect causes increased piston ring wear and engine noise and vibration. Recently published literature on engine vibration analysis and defect detection is presented. Special emphasis was placed on engine dynamic modeling.; This study examines the effects of cylinder bore non-cleanup on the motion of the piston rings. This is accomplished by modeling the dynamics of the piston and piston rings using a mass-spring-damper model. The equations of motion are derived and the model is presented in state-space form. The input to the model is the force exerted on the piston rings by the cylinder bore surface. The outputs of the model are the piston ring accelerations or vibrations. These vibrations were analyzed in the frequency domain to determine the dominant frequency components. A bank of bandpass filters was designed to filter the measured vibration data from engines with the non-cleanup condition. This was done to increase the signal to noise ratio in narrow bands corresponding to frequency components predicted by the model.; Data collection was carried out using an engine test stand that was capable of measuring cylinder block vibration while the crankshaft is being driven by a motor. Three engines with increasing levels of the non-cleanup defect are tested. The measured vibration signals were filtered through the bandpass filters. The RMS value of the filtered measured vibration signals were calculated. A threshold level of detection was set based on the comparison of the RMS value for good engines and for engines with the non-cleanup defect.