A sensor control apparatus for controlling a gas sensor which includes a measurement chamber into which a target gas is introduced, an oxygen concentration detection cell, and a pump cell,
- the oxygen concentration detection cell having a first solid electrolyte body and paired first electrodes which are formed on the first solid electrolyte body, one of which is disposed to face the measurement chamber, and the other of which is disposed in a reference oxygen chamber set to a reference oxygen partial pressure atmosphere, and being configured to generate an electromotive force cell voltage corresponding to an oxygen partial pressure difference between the measurement chamber and the reference oxygen chamber,
- the pump cell having a second solid electrolyte body and paired second electrodes which are formed on the second solid electrolyte body and one of which is disposed to face the measurement chamber, and being configured to pump out oxygen contained in the target gas introduced into the measurement chamber or pump oxygen into the measurement chamber in accordance with pump current flowing between the second electrodes,
- the sensor control apparatus comprising:
- a current control section configured to control the pump current such that the electromotive force cell voltage becomes equal to a previously set control target voltage;
- a first condition judgment section configured to judge whether or not a first deterioration detection condition is satisfied, said first detection condition being previously set and indicating that the current control section is controlling the pump current;
- a second condition judgment section configured to judge, when the first condition judgment section judges that the first deterioration detection condition is satisfied whether or not a previously set second deterioration detection condition is satisfied when the first condition judgment section judges that the first deterioration detection condition is satisfied;
- a deterioration detection energization section configured to supply deterioration detection current having a predetermined constant current value to the oxygen concentration detection cell when the second condition judgment section judges that the second deterioration detection condition is satisfied;
- and
- a deterioration voltage detection section configured to detect deterioration detection voltage after a predetermined deterioration detection time following the supply of the deterioration detection current by the deterioration detection energization section to the oxygen concentration detection cell, the deterioration detection voltage being generated in the oxygen concentration detection cell as a result of the deterioration detection current flowing to the oxygen concentration detection cell, wherein
- the control target voltage is set to a stoichi-time voltage which is the electromotive force cell voltage in the case where the oxygen concentration of the target gas is equal to the oxygen concentration of gas discharged from an internal combustion engine as a result of combustion in the internal combustion engine of an air-fuel mixture having a stoichiometric air-fuel ratio,
- the first deterioration detection condition is that the electromotive force cell voltage falls within a first voltage range set to include the stoichi-time voltage, and
- the second deterioration detection condition is that the electromotive force cell voltage falls within a second voltage range that is set to include the stoichi-time voltage, is narrower than the first voltage range, and is included within the first voltage range.