Search Results

A metal support has a potential to improve an engine output and the conversion efficiency. In order to satisfy both requirements, the back pressure drop should be reduced and the high-temperature use of the catalyst converter has to be a must. To develop such a metal support, a manifold converter without a retainer is the best choice. Removing a retainer resulted in joining the metal honeycomb-core to the jacket. Brazing was selected. Installing as a manifold converter led a metal support to the severe environment in which the high mechanical durability was required. The back pressure drop, the adhesion of the washcoat and the conversion performance have been investigated for the high-temperature use. To develop the brazed structure to meet the high mechanical durability, analyzing the temperature distribution and the fracture modes in a metal support has been conducted through the endurance engine-bench test.

To realize the high performance of the three-way catalyst, this development focused on the heat resistance of the CeO2-ZrO2 solid solution (CZ) that possesses the oxygen storage capacity (OSC). A new concept of the OSC compound with high durability is proposed. We devised a new method of inhibiting the coagulation of the primary CZ particles by placing diffusion barrier layers made of alumina among the primary CZ particles. This material is called “ACZ”. The specific surface area of ACZ was larger than that of the conventional CZ after durability test. The sintering of Pt on the ACZ-added catalyst is inhibited and the crystal size of CZ in the ACZ-added catalyst is smaller than that in the CZ-added catalyst. The OSC and the light off temperature of the ACZ-added catalyst are improved.

Catalyst specifications and converter layouts were studied to identify the high conversion performance under various in-use driving conditions, high mileage intervals and extended life cycle. The effects of volumes, configuration, selection and loading distribution of precious metals, additive components and substrate type for catalyst were studied on engine dynamometers and vehicle tests to optimize a catalyst converter system. Moreover, model gas experiments were conducted to analyze deterioration mechanisms and conversion characteristics of catalysts. As a result, the concept of a divided catalyst converter system, which provides separate functions for a close-coupled and an under-floor catalyst, was found to be effective for the future exhaust system. For reducing HC emissions, the close-coupled catalyst should warm up quickly and resist a high temperature. The under-floor catalyst, located at a rather low temperature position, is durable and maintains high NOx conversion.