Monitoring Structure

Monitoring Structure







Monitoring Cycle

Data acquisition
The duration of the crankshaft segments is measured continuously for every combustion cycle.

Sensor wheel adaptation
Within a defined engine speed range and during fuel cut-off, the adaptation of the sensor wheel tolerances, instead of misfire detection, is carried out. With progressing adaptation the sensitivity of the misfire detection is increasing. The adaptation values are stored in a non-volatile memory and are taken into consideration for the calculation of the engine roughness.

Misfire detection
The following operating steps are performed for each measured segment corrected by the sensor wheel adaptation.

Calculation of the engine roughness
The engine roughness is derived from the differences of the segment durations. Different statistical methods are used to distinguish between normal changes of the segment duration and the changes due to misfiring.

Detecting of multiple misfiring
If several cylinders are misfiring (e.g. alternating one combustion/one misfire event) the calculated engine roughness values may be so low, that the threshold is not exceeded during misfiring and therefore misfiring would not be detected.

Based on this fact, the periodicity of the engine roughness value is used as additional information during multiple misfiring. The engine roughness value is filtered and a new multiple filter value is created. If this filter value increases due to multiple misfiring, the roughness threshold is decreased. By applying this strategy, multiple misfiring is detected reliably.

Calculation of the engine roughness threshold value
The engine roughness threshold value consists of the base value, which is determined by a load/speed dependent map.

During warm-up an engine coolant temperature dependent correction value is added. In case of multiple misfiring the threshold is reduced by an adjustable factor. Without sufficient sensor wheel adaptation the engine roughness threshold is limited to a speed dependent minimum value. A change of the threshold towards a smaller value is limited by a variation constant.

Determination of misfiring
Misfire detection is performed by comparing the engine roughness threshold value with the engine roughness value.

If a misfire event is detected in a cylinder, the misfire detection of the next cylinder in firing order is deactivated to prevent a faulty diagnosis.

Statistics, fault processing
Within an interval of 1000 crankshaft revolutions the detected misfiring events are added for each cylinder. If the sum of all cylinder misfire incidents exceeds a predetermined value, the fault code for emission relevant misfiring is preliminarily stored. If only one cylinder is misfiring, a cylinder selective fault code is stored. If more than one cylinder is misfiring, the fault code for multiple misfiring is also stored.

Within an interval of 200 crankshaft revolutions the detected number of misfiring events is weighted and calculated for each cylinder. The weighting factor is determined by a load/speed dependent map.

If the sum of cylinder misfire incidents exceeds a predetermined value, the fault code for indicating catalyst damage relevant misfiring is stored and the MIL is illuminated at once (blinking).

If the cylinder selective count exceeds the predetermined threshold, the following measures take place:
- the oxygen sensor closed loop system is switched to open loop
- the cylinder selective fault code is stored. If more than one cylinder is misfiring, the fault code for multiple misfire is also stored
- the fuel supply to the respective cylinder is cut-off

All misfire counters are reset after each interval.