## 3 Results--HiL-Based Calibration and Validation of TWC and HEGO Diagnoses
### Phase #3--Emission Verification  
Due to the active adjustment of the air-fuel mixture and the subsequent loading and unloading of the oxygen storage of the TWC, there is a risk that the parallelization event negatively affects the tailpipe emissions during drive cycle operation, especially when considering aged components. Therefore, it is imperative that a final OBD calibration is evaluated in terms of its emission impact, both for an OK and a nOK system. The emission verification of a final OBD calibration is the scope of \"Phase #3--Emission Verification\" (Figure 2). In order to ensure that the work from Phase #3 can also be supported by the HiL test bench, this chapter validates the performance of all real-time models in compound in closed loops with regard to the emission behavior at the tailpipe. In Figures 11-14, HiL-simulations of the virtual vehicle are compared to the ones of a vehicle measurement on the chassis dynamometer during WLTC operation. Figure 11 shows the absolute cumulative results of gaseous tailpipe emissions, relevant for EU6d legislation, for the HiL simulation compared to the real measurements on the chassis dynamometer for an OK system. In order to make a meaningful statement about the simulation quality, both the emission  
Figure 10: HiL-based failure path validation (MILing/Healing). values from the HiL simulation and those from the chassis dyno are displayed with regards to their respective legislative limits (Figure 14). From Figure 14, a maximum deviation of 7%-points (NO\({}_{\rm x}\)) between HiL simulation and chassis dyno measurement can be observed. Figure 11 also shows that both cold start emissions and the emission behavior during the parallelization event are well represented both quantitatively and qualitatively. The large relative difference in NO\({}_{\rm x}\) emissions between the simulation and vehicle measurement can mainly be attributed to one event. The second parallelization attempt during the HiL simulation completes directly, while the second event in the vehicle measurement is interrupted and runs through completely in a third attempt. This event is causing one additional NO\({}_{\rm x}\) breakthrough (Figure 12, 868 s-873 s) in the vehicle measurement, significantly influencing the overall NO\({}_{\rm x}\) result. Figure 12 gives a detailed insight into the transient emission results in the range of 760 s to 880 s of the WLTC (Figure 11) where the parallelization event occurs. Slight deviations between the simulated and the measured signals can be observed. These are due to minor differences in the operating points caused by slightly different driving behaviors. Due to the behavior of the constant volume flow sampling (CVS) emission measurement system at the chassis dynamometer, a lag and mostly a slightly different profile of the simulated emission signal is observed compared to the chassis dynamometer measurement. Another reason for a slightly different emission behavior is that the parallelization in the HiL simulation starts at second 835 and fully completes. In the vehicle measurement, the parallelization starts but stops after approx. 10 s and starts again at second 850 and then successfully runs through. Despite these minor differences, overall, it can be stated that the emission behavior during the parallelization event (and other emission events such as TWC  
Figure 11: Comparison of WLTC HiL and chassis dynamometer measurement for an OK system—Tailpipe emissions NO\({}_{\rm x}\), CO and HC (cumulated). purge events) is reproduced with sufficient accuracy for all gaseous emission components, both qualitatively and quantitatively, considering an OK system. Figure 13 shows the absolute cumulative results of gaseous tailpipe emissions, relevant for EU6d legislation, for the HiL simulation compared to the real measurements on the chassis dynamometer for a nOK system, a latent HEGO sensor.