DETERIORATION DETECTING DEVICE FOR LIMIT CURRENT TYPE OXYGEN DENSITY SENSOR

摘要

PURPOSE:To detect deterioration of the captioned sensor without break with a proper applying voltage by increasing sensor applying voltage at a predetermined speed while an internal-combustion engine is interrupt in fuel supply and comparing output current when increase amount of the sensor output current of each time becomes almost zero with a reference value. CONSTITUTION:Deterioration detection is performed every predetermined time or every predetermined revolution number of an engine. Fuel supply to internal-combustion engine 1 is interrupted by utilizing a property in which output current of a density sensor 5 becomes almost constant regardless of the change in applying voltage at a certain current value in proportion to the oxygen density to apply optimum applying voltage while replacing the gas in an exhaust manifold 4 from exhaust gas to the atmosphere, and to obtain output current In in the atmosphere. The changing ratio of the In to a reference output current IB at the time of detecting oxygen density before deterioration is obtained to detect deterioration. Even if change of temperature is generated in the density sensor 5, or applying voltage is changed, output current value does not almost change. The only thing to do is to reduce applying voltage proportionally with density.