Systems are employed in electronic engine controls for detecting a misfire of a combustion event. If a cylinder repeatedly misfires, fuel is typically shut off to that cylinder on the next engine cycle. This prevents the passage of a large amount of unburned fuel to an exhaust catalyst. This is done to prevent degradation of the catalyst's performance and useful life, and thereby minimize emissions.
Some misfire detection schemes use a rotational speed sensor mounted on an engine's crankshaft for converting engine rotation into an electrical signal. Some of these schemes monitor average angular velocity and attempt to predict misfiring based on signature analysis of this average engine crankshaft velocity. Other schemes rely on measuring average engine crankshaft acceleration. Both of these schemes suffer from inaccuracy because they rely on multi-combustion cycle averaging. This is problematic because these schemes are inaccurate and unreliable during transient operating conditions and other conditions related to combustion instability including engine crankshaft variability from cylinder to cylinder firings.
Additionally, the misfire component of the sensed signal varies considerably in magnitude and frequency over the full operating range of the engine. Since averaging schemes rely on predicting a change from a steady state condition they inherently loose accuracy under these transient operating conditions. Also, non-combustion related effects are substantial. These effects are typically attributable to variations in engine load torque, friction torque, and inertia torque.
Other schemes, embedded in ignition systems, can only detect ignition related misfiring conditions which are a subset of the possible misfiring conditions and therefore lack the full function necessary to accurately determine misfire.
What is needed is an improved system for detecting misfire in internal combustion engines that is more reliable, accurate, requires minimum calibration, and can be easily applied to different engine families.