| 초록 |
This paper deals with the methodology for detecting misfired cycles by using the discrete Fourier transform-based frequency analysis. This methodology discriminates single or dual cylinder misfires at first, and then it identifies misfired cylinders for misfired cycles. In general, the highest amplitude of DFT exists at lower harmonic modes than the number of cylinders during misfires. However, because it is located at the same harmonic mode with the number of cylinders at high speed conditions even though misfires take place, origin shift should be introduced in order to identify the misfired cycles even at a high speed operating condition. New origin can be located at the averaged real and imaginary values of the transformed engine rpm on the complex plane during normal combustion cycles. Based on this new origin of the complex plane, the circle of threshold can be derived as a boundary for detecting misfires at each harmonic mode. Single cylinder misfires can be detected when transformed engine rpms are located outside this circle of threshold at both the first and second harmonic modes. In case of opposing dual cylinder misfires, misfires can be detected when transformed engine rpms are located outside this circle of threshold at the first harmonic mode and inside it at the second harmonic mode. On the contrary, the transformed engine rpms of the non-opposing dual cylinder misfires are inside it at the first harmonic mode and outside it at the second harmonic mode. In other words, the misfire detection criteria of a non-opposing dual cylinder misfire are vice versa of the opposing dual cylinder misfire. The misfired cylinders of single cylinder and opposing dual cylinder misfires can be identified by their phases at the first harmonic mode, and those of the non-opposing dual cylinder misfire can be done by them at the second harmonic mode. |
