Test Groups WBMXV02.8M52 & WBMXV02.8Z35
General Description - Method of engine misfire detection is based on monitoring crankshaft acceleration. Engine roughness is derived from differences from segment periods (120 degree crank angle) durations which are corrected and compared to a load and engine-speed dependent thresholds. Different statistical methods are used to distinguish between normal changes of segment duration and changes due to misfire. Segment periods are measured through an angular range of 120 degree crank angle. Segment starts 78 degrees before TDC. Beginning and end of segments are located at same angle. Duration of crankshaft segments is measured continuously. See Figure and Fig 1-Fig 2 .
Sensor Wheel Adaptation - To eliminate manufacturing tolerances and off-center installation, adaptation of sensor wheel tolerances is carried out during fuel cut-off. Segment periods are corrected by adaptation values. With progressing adaptation, sensitivity of misfire detection is increasing.
Calculation Of Engine Roughness Threshold Value - Engine roughness threshold value consists of base value, which is determined by a load/speed dependent map. During warm-up, base value is multiplied by a coolant temperature defendant correction value. Without sufficient sensor wheel adaptation, engine roughness threshold is limited depending on wheel tolerances expected.
Error Window - Within an interval of 200 and 1000 crankshaft revolutions, "error windows" to check for similar engine conditions are determined. Upon detection of misfire, window is extended if current operating point is not within window.
Engine Operating Point Window - Engine operating window is updated with each segment without misfire.
Misfire Detection - Within an interval of 1000 crankshaft revolutions (3000 segments), detected misfire events are added for each cylinder. If sum of all cylinder misfire incidents exceeds a predetermined value, a fault code is stored. If more than one cylinder is misfiring, all misfiring cylinders will be specified and individual fault codes for all misfiring cylinders will be stored. Within an interval of 200 crankshaft revolutions, detected number of misfiring events is weighted and calculated for each cylinder. Weighting factor is determined by a load/speed dependent map. If sum of cylinder misfire incidents exceeds a predetermined value, a fault code is stored and MIL is illuminated at once. If cylinder selective count exceeds predetermined threshold, following measures take place:
- Lambda closed loop system is switched to open-loop.
- Cylinder selective fault code is stored.
- If more than one cylinder is misfiring, fault codes for all individual cylinders will be stored.
- Fuel supply to respective cylinder is cut-off.