노크센서를 이용한 비정상 엔진진동 측정 연구

Abstract

Accelerometers have been used to measure engine vibrations. However, this is costly, and it is difficult to set the measuring location. Therefore, a method using the knock sensor was studied. This has advantages based on its economic feasibility, along with the level of convenience and speed. However, the voltage output frequency range of the knock sensor is low, and it requires the use of the analytic method with time domain. Moreover, the simulation-engine and shaker are used for the test rather than for application to an actual vehicle. Additionally, most of the research methods were used for measuring the vibrations based on the RPM change under the normal engine vibration condition, and analyzing the input frequency order at the combustion chamber, which varies according to the crank axis angle. Consequently, there is a lack of research focusing on abnormal vibrations in the actual vehicle. Thus, this study aims to measure and analyze the abnormal vibrations due to defective power balance per cylinder, which has the highest frequency of failure in the actual vehicle engine, via the circuit designed with the knock sensor. Thus, an amplifier and filter circuit was designed, which can extend the low voltage output frequency of the knock sensor, and has an adequate filtering capacity. To create the defective power balance conditions, misfire circumstances were formed by sequentially blocking the fuel supplied to each cylinder of the quadruple cylinder engine. The vibration signals from the knock sensor passing through the designed circuit were measured using an oscilloscope. The values were saved and then subjected to fast Fourier transform, and the power spectral density was obtained. Finally, the results were studied via comparative analysis using normal vibration trends.