An Evaluation of Transient System Optimization Used for Spark Calibration Over the FTP Urban Schedule

Transient System Optimization (T.S.O.) was developed as a systematic means to optimize the calibrations of up to three engine control variables -- air-fuel ratio, spark advance and exhaust gas recirculation, to provide the minimum fuel penalty while meeting specified levels of exhaust emissions: HC, CO and NOx. In this study we evaluated the performance of T.S.O. in optimizing the spark advance calibration on the hot FTP urban schedule.

The process was applied to each of the following cases: a mature spark calibration supplied with the vehicle, that calibration retarded by 10 degrees and an MBT calibration. This provided different initial conditions under which to evaluate T.S.O.. The results of the study showed that the final calibrations achieved the same fuel economy as the mature calibration with equivalent or lower emissions: however, the resulting spark advance calibrations were markedly different from each other. We have concluded that no unique optimum spark advance calibration exists because tradeoffs among spark table cells permit equivalent fuel economy and emissions for different calibrations.