Abstract
As tailpipe emissions regulations for automobiles are made stricter, high power and the reduction of harmful substances in tailpipe emissions, as well as reductions in the precious metal content of the catalyst, are required in the development of exhaust systems. A low precious metal two-bed large-diameter close-coupled catalytic converter has been developed for the new 1.8L i-VTEC engine to achieve low tailpipe emissions, high power, and a low precious metal content.
Previously, compliance with tailpipe emissions regulations has been achieved with the close-coupled and underfloor positioning of the catalyst. However, since the warm-up speed for an underfloor catalyst is slow, it is difficult to reduce the amount of precious metal used. In this exhaust system, a two-bed catalyst is close-coupled to a cylinder head integrated with a low heat mass exhaust manifold, which shortens the catalyst warm-up time. In addition to reducing tailpipe emissions immediately after starting the engine, this also achieves low pressure loss and high power through the large-diameter catalyst. The shape of the bell mouth cone has been optimized using CAE to equalize the gas feed to the end of the catalyst inlet, and the positioning of the exhaust sensors has been optimized. This achieves an improvement in the catalyst purification properties and high-precision air-fuel ratio control, attaining low precious metal content and achieving low tailpipe emissions that comply with LEVII-ULEV and EURO4 standards and are 75% lower than 2005 Japan emission standards.
Previously, substrate retention was difficult in a high-vibration environment because the retention area of a large-diameter substrate is small. However, optimization of the positioning of a converter stay and rigidity has reduced vibration and enabled the retention of a large-diameter substrate.
Keywords:Emissions, close-coupled catalytic converter, precious metals, catalyst gas flow, pressure loss