| 摘要 |
PROBLEM TO BE SOLVED: To suppress the effects of unburned hydrocarbons to output voltage in the case where it is arranged behind the exhaust gas purifying catalyst of an internal combustion engine. SOLUTION: In a sensor element 1, a detecting electrode 4 is provided on the outer surface of zirconia ceramics 2, a reference electrode 3 is provided on the inside surface, and a spinel protective layer I is provided on the outer surface of the detecting electrode 4. The tip of the sensor element 1 is covered with a protective cover 10 formed of an outside partition wall 11 with a through hole 11a and an inside partition wall 12 with a through hole 12a. If we let a pressure difference between the inside and outside of the protective cover 10 at the time of passing the air of a volume flow rate Q (l/min) from the outside of the protective cover 10 to the inside be ΔP(atm), a ratio ΔP/Q<2> is 3.2×10<-5> (atm.min<2> .l<-2> ). As a reverse period (high output maintaining time + flow output maintaining time) is approximately constant at the time of changing the surface temperature of the sensor element 1 in a sensor active temperature region in this oxygen sensor, it is possible to detect the degradation of catalysts with accuracy. |
