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For the evaluation of environment load from vehicles under road driving condition, on-board measurement system with the ability to measure emission concentration, engine conditions and vehicle conditions is necessary. These days, with the advancement of measurement technology, on-board exhaust gas analyzers have been developed, and it is now possible to measure the volume emission of exhaust gas using these analyzers. However, it is important to evaluate the mass emission from vehicles. For the conversion from the volume emission to the mass emission, the value of exhaust flow rate is required. However, the measurement method of exhaust flow rate with high accuracy has not been established. In this study, the measurement method of exhaust gas flow rate, the Map Method, was investigated for gasoline vehicles.

The object of this study is to investigate an on-board diagnostic method to detect the deterioration of a three-way catalyst (TWC) under actual vehicle operating conditions, including the acceleration state. The signal data of two oxygen sensors were processed by the fast Fourier transformation (FFT) method. As a result, we found that the power spectrum of the signal waves can be the index of catalyst deterioration degree. Furthermore, it was confirmed that the difference between the power spectrum of the upstream oxygen sensor signal and one of the downstream oxygen sensor signal named ΔPower is effective index for detection of deteriorated catalyst under acceleration conditions.