Test Group 1BMXV04.9S62
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- Catalyst Monitoring Based On Monitoring Oxygen Storage Capability - Engine closed loop feedback control generates lambda (air/fuel ratio) oscillations in exhaust gas. These oscillations are dampened by oxygen storage activity of catalyst. Amplitude of remaining lambda oscillations downstream of catalyst indicates storage capability. To determine catalyst efficiency, oscillation of upstream sensor is needed to calculate oxygen in and output (catalyst) by engine air mass and lambda-deviation. Downstream sensor signal for a threshold catalyst then is derived from this basic value. Anytime real sensor signal oscillation (downstream) corresponds to the model, a defective catalyst is recognized. See Fig 1.
- Monitoring Cycle -
Monitoring cycle is represented by the following:
- Computation Of Efficiency Of Catalyst - Alternating current component of voltage of oxygen sensors before and after catalyst is determined, rectified and averaged. Actual quotient of oxygen sensor voltage before catalyst and voltage of oxygen sensor after catalyst is determined. Simultaneously, theoretical quotient of this voltage of oxygen sensors is computed in relation to operating point of engine. Respective operating point is determined using parameters load and engine speed.
- Fault Evaluation - At end of diagnostic period, number of stored values in adaptation matrix exceeding a limit is determined. If this number of stored values itself exceeds a threshold, a defective catalyst is evaluated.
- Check Of Monitoring Conditions - Monitoring principle is based on detection of relevant oscillations of downstream sensor signal during regular lambda control. It is necessary to check driving conditions for exceptions where no regular lambda control is possible. During such periods, and for a certain time afterward, computations of amplitude values and the following processing is interrupted, avoiding a distortion of monitoring information.