Moreover, the HEGO sensor has been simulated by interpolating the linear lambda signal (low-pass filter response) through the 1-D table shown in Figure 5.
Since the target of this work is to develop a controller based on the standard sensors installed onboard the vehicle, even the HEGO response has been modeled and analyzed.
Obviously, the same logic can be used with a HEGO signal by inverting [mathematical expression not reproducible] and [mathematical expression not reproducible].
The top plot shows the simulated response of an HEGO sensor installed at the TWC inlet, the only information used by the AFR unbalance estimator, together with the crankshaft position.
After the development and validation phases were successfully carried out in the simulation environment, the algorithm was tested on the HEGO signal acquired from the real vehicle during several experimental tests.
A high-pass filtering stage (fc = 4 Hz) was added to the estimation algorithm to process the HEGO experimental signal in case the closed-loop oscillation was active, as in the operating conditions shown in Figure 20.