A Misfire Detection Index for Four-Stroke Single-Cylinder Motorcycle Engines—Part II: Gap Distance and Gap Slope

Two new misfire detection indexes for single-cylinder motorcycle engines—dubbed gap distance (GD) and gap slope (GS)—are proposed in this study. GD and GS quantify the change in engine angular acceleration using the tooth time measured by the crankshaft position sensor (CKPS). GD is defined as the product of the spacing distance I (the distance from the top dead center at the explosion stroke [TDC2] to the engine speed trend line parallel to the engine speed axis) and spacing distance II (the distance from the bottom dead center at the expansion stroke [BDC2] to the engine speed trend line parallel to the engine speed axis). GS is defined as the difference between the two slopes between the engine speed inclination line and the engine speed trend line. Here the engine speed trend line connects two engine speeds at the top dead center at the intake stroke (TDC1) of the current and subsequent cycles. The GD and GS indexes can detect misfires using the engine speeds at only four teeth. The location of these four teeth could be changed to best simulate the change in engine angular acceleration for engines. The threshold range for GD and GS lies between the point where the misfire detection rate reaches 100% and the point where both the ratio of misfire detection to misfire signal (Mdtn/Msig) and the ratio of misfire signal to misfire detection (Msig/Mdtn) begin to deviate from 100%. Both GD and GS show a good misfire detection rate of approximately 99% and a perfect detection fault rate of 0% for an engine speed range of 3,000-8,000 under 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%.