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A high performance catalyzed hydrocarbon (HC) trap, consisting of a Ag-impregnated zeolite and a three-way catalyst (TWC), was developed to achieve the stringent exhaust regulations such as SULEV. To improve the HC retention ability and durability of Ag-zeolite, the effects of wash-coat loading, HCs species, space velocities (SV) etc. on HC desorption profiles upon heating-up were examined in detail. In the present study, a simulated durability test using a cyclic lean-stoichiometric aging, was developed and applied for durability evaluation. An ultraviolet visible near-infrared spectrophotometer (UV-Vis) showed that specific chemical species of Ag were responsible for the delay of HC desorption. After the cyclic aging, the retention effect of Ag was only seen with aromatic compounds. It was revealed that the HC retention effect on aromatic compounds was maintained at high SV values, which was confirmed by actual vehicle tests.

A catalyzed hydrocarbon (HC) trap aiming at the super-ultra low emission vehicle (SULEV) regulation was developed using a metal-impregnated zeolite. To enhance the adsorption and to raise the desorption temperature for a wide range of HC species, the modification of zeolite with certain metals was needed and Ag was found to be the most promising. Using a Ag impregnated zeolite, a three way catalyst was prepared, and its HC purification ability for a model gas simulating cold-start HCs was studied. Its heat resistance was also examined. A vehicle test for a fresh catalyzed HC trap showed that the cold-start HC after the newly developed trap almost reached the SULEV regulation level.

A new diagnosis method for an air-fuel ratio cylinder imbalance has been developed. The developed diagnosis method is composed of two parts. The first part detects an occurrence of an air-fuel ratio cylinder imbalance by using a two revolution frequency component of an EGO sensor output signal or an UEGO sensor output signal upstream from a catalyst. The two revolution frequency component is from a cycle where an engine rotates twice. The second part of the diagnosis method detects an increase of emissions by using a low frequency component which is calculated from the output of an EGO sensor downstream from the catalyst. When the two revolution frequency component calculated using the upstream sensor output is larger than a certain level and the low frequency component calculated using the downstream sensor output is shifted to a leaner range, the diagnosis judges that the emissions increase is due to an air-fuel ratio cylinder imbalance.