Three-way catalyst diagnostics for advanced emissions control systems

Automotive emissions are stringently regulated. Since 1980, a three-way catalyst (TWC) has been used to convert harmful emissions of hydrocarbons, carbon monoxide, and oxides of nitrogen into less harmful gases in order to meet these regulations. The TWC's efficiency of conversion of these gases is primarily dependent on the mass ratio of air to fuel (A./F) in the mixture leaving the exhaust manifold and entering the catalyst. This paper develops a method by which a dynamic TWC model can be used for diagnostic purposes. This diagnostic method is analyzed in the context of a hypothesis test that is based on the oxygen storage capacity of the TWC. The Neyman-Pearson criterion is used as the basis for this hypothesis test. It is initially applied in the case of a single sample where the variance of the data is assumed to be known. This is then expanded to a multiple-sample case through the use of Student's t test. The improved fidelity of the t test is demonstrated, and it is shown that larger sample sizes provide further improvement in the quality of the hypothesis test.