When DFSO conditions are established and UEGO
sensor measurement settles at constant lean reading, the fuel induction process will start by commanding fuel to one cylinder only and firing the spark plugs at the appropriate timing to complete the combustion.
The top plot shows the measured HEGO signal, the middle plot the measured lambda values in the two exhaust runners (two UEGO sensors had been installed for the purpose), and the lower plot the estimator performance in terms of Coherence Index robustness, together with the actual lambda difference (i.
Figures 24 through 28 present some simulations result of the UEGO-based control system, showing in the top plot the fuel quantity (expressed in mg/stroke) injected in each cylinder, in the center plot the UEGO signal, and in the bottom plot the closed-loop correction factors.
For a clearer evaluation of the controller's performance, also the simulated UEGO signal (in green) is shown.
It can be based both on HEGO and UEGO sensors, and it takes advantage of the unevenly spaced firing order of the engine for recognizing which is the richer and which is the leaner cylinder.
Better results would be obtained using a UEGO sensor.
Closed-loop individual cylinder air-fuel ratio control via UEGO signal spectral analysis", Control Engineering Practice, Volume 18, Issue 11, November2010, Pages 1295-1306, ISSN 0967-0661, http://dx.
STATISTICS BASED DETECTION AND ISOLATION OF UEGO SENSOR FAULTS
In fact, it has been observed that for asymmetrical faults, the inducing mechanism is scheduled to work based on the local variations of the UEGO signal and not based on the commanded AFR reference signal, which becomes very challenging in the presence of noise and disturbances.
In order to characterize the distribution of [DELTA][lambda] for a given operation of the UEGO sensor, it is necessary to consider a density function that fits the data distribution ([DELTA][lambda](k)) regardless of the type of operation (symmetrical/asymmetrical).
the estimation of the statistical parameters of the measured data from the UEGO sensor can be performed.
The switch model approach in  was proposed to diagnose the operation of the UEGO sensor.