Patent ID: 8187436

Claim:
A sensor deterioration judging apparatus for judging whether a gas sensor is in a deteriorated state, the gas sensor including: a first measurement chamber into which a gas to be measured is introduced through a first diffusion resistor portion; a first oxygen ion pump cell having a first oxygen ion conductor and first and second electrodes provided on the first oxygen ion conductor wherein the first electrode is arranged in the first measurement chamber which pumps oxygen into or out of the gas that has been introduced into the first measurement chamber to be measured; a second measurement chamber into which the gas to be measured is introduced through a second diffusion resistor portion after having been subjected to oxygen pumping in the first measurement chamber; a second oxygen ion pump cell having a second oxygen ion conductor and third and fourth electrodes provided on the second oxygen ion conductor so that the third electrode is provided in the second measurement chamber, wherein a current corresponding to a concentration of a particular gas in the second measurement chamber flows in the second oxygen ion pump cell; a reference oxygen chamber set to have a reference oxygen partial pressure atmosphere; and an oxygen partial pressure detection cell having a third oxygen ion conductor and fifth and sixth electrodes provided on the third oxygen ion conductor wherein the fifth electrode is provided in the first measurement chamber and the sixth electrode is provided in the reference oxygen chamber, the sensor deterioration judging apparatus comprising: a first pump current detecting unit, a status judging unit, a pump stopping unit, a second pump current detecting unit, a deterioration judging unit, and having a processor configured to detect a first pump current flowing through the first oxygen ion pump cell; to determine an oxygen partial pressure of the gas to be measured on the basis of the first pump current, and to judge whether the determined oxygen partial pressure of the gas to be measured is equal to a preset status judgment reference value; to stop the pumping in or out of oxygen that is being performed by the first oxygen ion pump cell when the status judging unit judges that the oxygen partial pressure of the gas to be measured is equal to the status judgment reference value which is equivalent to the oxygen partial pressure in the atmosphere; to detect a second pump current flowing through the second oxygen ion pump cell after the pump stopping unit stops the pumping operation of the first oxygen ion pump cell; and to judge that the second oxygen ion pump cell is in a deteriorated state when an oxygen partial pressure in the second measurement chamber calculated on the basis of the second pump current differs from a deterioration judgment reference value that is set in advance on the basis of the status judgment reference value.