Misfire Detection in a Dynamic Skip Fire Engine 2015-01-0210

Misfire detection and monitoring on US passenger vehicles are required to comply with detailed and specific requirements contained in the OBD-II regulations. Numerous technical papers and patents discuss various methods and metrics for detecting misfire in conventional all-cylinder firing engines. However, the current methods are generally not suitable for detecting misfires in a dynamic skip fire engine. For example, a detection approach based on peak crankshaft angular acceleration may work well in conventional, all-cylinder firing engine operation, since it is expected that crankshaft acceleration will remain generally consistent for a given operating condition. In a skip fire engine, any cylinder or cycle may be skipped. As a result, the crankshaft acceleration peaks and profiles may change abruptly as the firing sequence changes. This paper presents two approaches for detecting misfires in a dynamic skip fire engine.

The first method utilizes crankshaft angular acceleration with the addition of cylinder skip or fire status, which is used to recognize a firing sequence in order to ignore skips and apply a separate threshold to various sequences. For the second approach, a torque model based on multi-cylinder pressure modeling is employed. The paper describes the details in modeling cylinder pressure, indicated torque and crankshaft angular acceleration, and proposes a new metric for misfire detection. Validation tests are carried out both on an engine dynamometer and a vehicle under steady state and transient conditions. The results indicate a very promising approach for detecting misfires in a dynamic skip fire engine.