Method for sensing exhaust gas for OBD

Abstract

All of NO x , PM, HC and CO concentrations necessary for realization of OBD are determined by utilization of an in-vehicle existing NO x sensor. A NO x sensor arranged in an exhaust pipe detects the NO x concentration in the exhaust gas. On the basis of O 2 concentration detected in a course of detection of the NO x concentration, PM, HC and CO concentrations are determined in conversion through mutual correspondences of the concentrations.

1 . A method for sensing exhaust gas for OBD which comprises detecting a NO x  concentration in the exhaust gas by a NO x  sensor arranged in an exhaust pipe, PM, HC and CO concentrations being determined in conversion, on the basis of an O 2  concentration sensed in the course of detection of said NO x  concentration, from mutual correspondences of the concentrations.  
   
   
       2 . The method according to  claim 1  wherein an oxidation catalyst is arranged in the exhaust pipe and downstream of the NO x  sensor, a temperature sensor being arranged on an inlet side of said oxidation catalyst to detect an exhaust temperature, purified ratios of the PM, HC and CO concentrations being determined depending upon catalytic activity of the oxidation catalyst at a current exhaust temperature, the PM, HC and CO concentrations being compensated on the basis of the purified ratios.