Misfire Detection Index for Four-Stroke Single-Cylinder Motorcycle Engines—Part I: Detrended Engine rpm Amplitude

This article presents a misfire detection index for motorcycles with a single-cylinder engine. Compared with automobiles with multicylinder engines, attempts to diagnose single-cylinder motorcycle engine misfires have been rare. Therefore, a new index, detrended engine rpm amplitude (DERA), is proposed to detect misfires using tooth time measured by the crankshaft position sensor; thus, there is no additional cost for the DERA index. This index is defined as the difference between the squares of the maximum and minimum values of engine speed (rpm) detrended by the engine speed trend line, instead of the linear regression method. Thus calculating the DERA index becomes simple and fast, and it is advantageous to reduce the computation time. Here the engine speed trend line is a line connecting the engine speeds at the first teeth of the current and subsequent cycles. The analysis of the optimal threshold for detecting misfires reveals that DERA yields a good misfire detection rate of more than 98% for an engine speed range of 3,000-8,000 rpm in load conditions of over 50%. If the lower boundary limit for the load over which misfires can be accurately detected is clearly defined, a good detection rate can be achieved even under load conditions below 50%. If only two teeth among the entire teeth can be specified optimally that best demonstrate the changes of the detrended engine speed (DRPM) due to misfire, the DERA index could be used to diagnose misfires even for motorcycles with a small number of teeth on the target wheel.