An electrically heated catalytic converter for an engine

摘要

The electrically heated catalytic converter of the present invention has a substrate, for a catalyst, which is formed as a scroll-like cylindrical laminated assembly. The scroll-like cylindrical laminated assembly is formed by laminating a thin corrugated metal sheet and a thin plain metal sheet and winding the laminated metal sheets together around a center electrode. The outermost layer of the laminated assembly is connected to an outer electrode. The corrugated metal sheet has an insulating coating made of an alumina Al2O3, and the plain metal sheet has no insulating coating. Local conductive connections are formed between the thin metal sheets by soldering the thin metal sheets using strips of zirconium solder foils interposed between the layers of the thin metal sheets. Since zirconium has larger reducing capability than aluminum, the alumina in the insulating coating is reduced by zirconium and precipitates at the local conductive connections. Therefore, the plain metal sheet and the corrugated metal sheet are electrically connected at the local conductive connections. The solder foils in the respective layers are arranged in such a manner that a strip of solder foil in one layer overlaps with strips of solder foils in adjoining layers only at its ends, and does not overlap with strips of solder foils in the layers next to the adjoining layers when viewed from the radial direction. Since the solder foils in two adjoining layers overlap only by a small area, electric current flows between the local conductive connections concentrates in the overlapped area when electricity is fed to the electrodes. Therefore, hot spots are formed. The resistances of overall electric paths can be easily adjusted by changing the lengths of the solder strips, i.e., distances between the hot spots. Therefore, the amount of electric current flowing through electric paths can be kept at appropriate level. $$