Patent ID: 7972488

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 in which the gas to be measured is introduced through a second diffusion resistor portion after being 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 wherein the third electrode is arranged in the second measurement chamber so that a current corresponding to a concentration of the gas to be measured 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 so that 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: an oxygen partial pressure changing unit for changing an oxygen partial pressure in the second measurement chamber by changing an oxygen partial pressure in the first measurement chamber; a first pump current detecting unit for detecting a current flowing through the second oxygen ion pump cell before the oxygen pressure changing unit changes the oxygen partial pressure; a second pump current detecting unit for detecting a current flowing through the second oxygen ion pump cell after the oxygen pressure changing unit changes the oxygen partial pressure; and a deterioration judging unit for judging that the second oxygen ion pump cell is in a deteriorated state when a ratio between the currents detected by the first and second current detecting unit is out of a preset range; the oxygen partial pressure of the gas to be measured in the first measurement chamber, which is measured based on the current flowing in the first oxygen ion pump cell, is determined whether or not the oxygen partial pressure is a predetermined value, and wherein the oxygen partial pressure changing unit changes the oxygen partial pressure in the first measurement chamber when the oxygen partial pressure is determined as the predetermined value.