Strategy for EOBD Compliant Plausibility Check of Air Mass Flow Sensor in Absence of Boost Pressure Sensor 2008-01-1296
In the move towards cleaner diesel emissions, the European On Board Diagnostics (EOBD) legislation mandates monitoring of drift of air mass flow sensor. Drift of a sensor is defined as the phenomenon in which output signal slowly deviates independent of the measured property. Long term drift usually indicates a slow degradation of sensor properties over a long period of time. Drift monitoring of the air mass flow sensor involves comparing the signal from the sensor with a reference signal under special operating conditions. Boost pressure sensor, which measures absolute intake manifold pressure and intake air temperature, is used to calculate the reference signal.
For engines with constant geometry turbo charger, boost pressure sensor is solely used for drift monitoring. Therefore, it was a challenge to come up with a means of finding the drift in air flow mass sensor without boost pressure sensor.
This paper investigates one method to predict boost pressure during those modes of operation when drift monitoring is active. We investigate the effects of approximating the boost pressure and intake air temperature and estimate the error involved in drift monitoring. Finally it is demonstrated that air mass flow sensor can be consistently and reliably checked for drift by the methods described in the paper.