DETERIORATION DETECTING DEVICE FOR LIMIT CURRENT TYPE OXYGEN DENSITY SENSOR

摘要

PURPOSE:To detect deteriorating condition the captioned sensor by detecting a period when an internal-combustion engine is controlled by fuel supply interruption and by comparing an output current obtained by applying a predetermined voltage with the reference value of the voltage, only when the period is over a predetermined value. CONSTITUTION:Deterioration detecting routine is made by interruption of every predetermined time or every predetermined revolution number of an internal- combustion engine. When the internal-combustion engine 1 is in fuel supply interruption and the gas in an exhaust manifold 4 is replaced from exhaust gas to the atmosphere, high voltage VM is applied to an oxygen density sensor 5. And oxygen density of the atmosphere is measured correctly without breaking the density sensor 5 by making interruption control for more than a predetermined time TM and considering the time when the gas in the manifold 4 becomes completely the same as the atmosphere. Then the current IM of this time is compared with the reference current IB of the oxygen density sensor 5 of the atmosphere before deterioration to detect presence of deterioration.