Gas sensor and gas sensor operation control method

A limiting-current type gas sensor measuring concentration of NOx in a measurement gas, said gas sensor comprising:

• a sensor element having a base part made of an oxygen-ion conductive solid electrolyte, said sensor element including:
• a gas inlet through which said measurement gas is introduced from an external space;
• a first internal space communicating with said gas inlet under predetermined diffusion resistance;
• a main pump cell as an electrochemical pump cell including an inner pump electrode located to face said first internal space, an out-of-space pump electrode located to face a space other than said first internal space, and said solid electrolyte located between said inner pump electrode and said out-of-space pump electrode;
• a measurement electrode located inside said sensor element, at least one diffusion control part being located between said measurement electrode and said first internal space;
• a measurement pump cell as an electrochemical pump cell including said measurement electrode, said out-of-space pump electrode, and said solid electrolyte located between said measurement electrode and said out-of-space pump electrode;
• a reference electrode located inside said sensor element and capable of being in contact with a reference gas;
• and
• a heater part buried in said sensor element and heating said sensor element;
• and
• a controller controlling operation of said gas sensor, said controller including:
• a determination element configured to perform condition determination processing of determining whether said gas sensor satisfies a predetermined diagnostic condition when said gas sensor is in an operation state capable of measuring a NOx concentration;
• a diagnostic element configured to perform diagnostic processing of diagnosing a situation of control to said gas sensor in a case that said gas sensor is determined to satisfy said diagnostic condition;
• and
• an adjustment element configured to perform adjustment processing of adjusting a condition under which said gas sensor is controlled in accordance with a result of diagnosis in said diagnostic processing, wherein
• said gas sensor is put into said operation state capable of measuring said NOx concentration at least when:
• said heater part heats said sensor element to a predetermined element driving temperature;
• a main pump voltage is applied to said main pump cell so that an oxygen concentration in said first internal space is constant;
• and
• a measurement pump voltage is applied to said measurement pump cell so that oxygen generated through decomposition of NOx in said measurement electrode is pumped out,
• in said diagnostic processing, said diagnostic element compares said main pump voltage and a diagnostic threshold set in advance as a value of a voltage not causing decomposition of NOx in said main pump cell,
• said adjustment element includes a temperature adjustment element performing temperature adjustment processing as said adjustment processing, and
• said temperature adjustment processing is processing to cause, in a case that said main pump voltage is diagnosed to be equal to said diagnostic threshold or more in said diagnostic processing, said main pump voltage to be less than said diagnostic threshold, at least in a way that said heater part increases said element driving temperature in said operation state by a predetermined increase amount.