Deterioration determination apparatus for ammonia sensor

A deterioration determination apparatus for an ammonia sensor, the deterioration determination apparatus being configured to be usable with an ammonia sensor that includes

• an ammonia element portion that includes
• a solid electrolyte that has oxygen ion conductivity,
• an ammonia electrode that is provided on a first surface of the solid electrolyte that is exposed to a measured gas that contains oxygen and ammonia, and
• a reference electrode that is provided on a second surface of the solid electrolyte on a side opposite the first surface,
• a potential difference detecting unit that detects a potential difference between the ammonia electrode and the reference electrode, and
• an ammonia concentration calculating unit that calculates an ammonia concentration in the measured gas based on the potential difference detected by the potential difference detecting unit,
• the deterioration determination apparatus comprising:
• a voltage applying unit that applies a DC voltage between the ammonia electrode and the reference electrode;
• a current detecting unit that detects a DC current that flows between the ammonia electrode and the reference electrode;
• a deterioration determining unit that compares a first evaluation value and a second evaluation value, and determines whether deterioration has occurred in the ammonia element portion at an evaluation time or subsequent to the evaluation time,
• the first evaluation value being based on a first sensor current that is a DC current that is detected by the current detecting unit obtained when the voltage applying unit applies a DC voltage between the ammonia electrode and the reference electrode at an initial time that is during an initial use period of the ammonia sensor, and
• the second evaluation value being based on a second sensor current that is a DC current that is detected by the current detecting unit obtained when the voltage applying unit applies a DC voltage of a same magnitude as that at the initial time between the ammonia electrode and the reference electrode at the evaluation time that is subsequent to the initial usage period of the ammonia sensor;
• and
• a map unit in which a relationship between the potential difference or the ammonia concentration, and the first evaluation value is determined as a relationship map, based on the first evaluation values at a plurality of instances in which the potential difference detected by the potential difference detecting unit or the ammonia concentration calculated by the ammonia concentration calculating unit differs, at the initial time and, wherein
• the deterioration determining unit is configured to
• collate the potential difference detected by the potential difference detecting unit or the ammonia concentration calculated by the ammonia concentration calculating unit with the relationship map, and read the first evaluation value at the potential difference or the ammonia concentration from the relationship map, before the voltage applying unit applies the DC voltage at the evaluation time, and
• compare the first evaluation value and the second evaluation value that is based on the second sensor current.

A deterioration determination apparatus for an ammonia sensor, the deterioration determination apparatus being configured to be usable with an ammonia sensor that includes

• an ammonia element portion that includes
• a solid electrolyte that has oxygen ion conductivity,
• an ammonia electrode that is provided on a first surface of the solid electrolyte that is exposed to a measured gas that contains oxygen and ammonia, and
• a reference electrode that is provided on a second surface of the solid electrolyte on a side opposite the first surface,
• a potential difference detecting unit that detects a potential difference between the ammonia electrode and the reference electrode, and
• an ammonia concentration calculating unit that calculates an ammonia concentration in the measured gas based on the potential difference detected by the potential difference detecting unit,
• the deterioration determination apparatus comprising:
• a voltage applying unit that applies a DC voltage between the ammonia electrode and the reference electrode;
• a current detecting unit that detects a DC current that flows between the ammonia electrode and the reference electrode;
• and
• a deterioration determining unit that compares a first evaluation value and a second evaluation value, and determines whether deterioration has occurred in the ammonia element portion at an evaluation time or subsequent to the evaluation time,
• the first evaluation value being based on a first sensor current that is a DC current that is detected by the current detecting unit obtained when the voltage applying unit applies a DC voltage between the ammonia electrode and the reference electrode at an initial time that is during an initial use period of the ammonia sensor, and
• the second evaluation value being based on a second sensor current that is a DC current that is detected by the current detecting unit obtained when the voltage applying unit applies a DC voltage of a same magnitude as that at the initial time between the ammonia electrode and the reference electrode at the evaluation time that is subsequent to the initial usage period of the ammonia sensor, wherein
• the deterioration determining unit is configured to
• determine the first evaluation value based on a first difference and the first sensor current, the first difference being obtained by a detected voltage value that is the potential difference detected by the potential difference detecting unit before the voltage applying unit applies the DC voltage at the initial time being subtracted from an applied voltage value that is the DC voltage applied by the voltage applying unit at the initial time, and
• determine the second evaluation value based on a second difference and the second sensor current, the second sensor current being obtained by a detected voltage value that is the potential difference detected by the potential difference detecting unit before the voltage applying unit applies the DC voltage at the evaluation time being subtracted from an applied voltage value that is the DC voltage applied by the voltage applying unit at the evaluation time.

A deterioration determination apparatus for an ammonia sensor, the deterioration determination apparatus being configured to be usable with an ammonia sensor that includes

• an ammonia element portion that includes
• a solid electrolyte that has oxygen ion conductivity,
• an ammonia electrode that is provided on a first surface of the solid electrolyte that is exposed to a measured gas that contains oxygen and ammonia, and
• a reference electrode that is provided on a second surface of the solid electrolyte on a side opposite the first surface,
• a potential difference detecting unit that detects a potential difference between the ammonia electrode and the reference electrode, and
• an ammonia concentration calculating unit that calculates an ammonia concentration in the measured gas based on the potential difference detected by the potential difference detecting unit,
• the deterioration determination apparatus comprising:
• a voltage applying unit that applies a DC voltage between the ammonia electrode and the reference electrode;
• a current detecting unit that detects a DC current that flows between the ammonia electrode and the reference electrode;
• and
• a deterioration determining unit that compares a first evaluation value and a second evaluation value, and determines whether deterioration has occurred in the ammonia element portion at an evaluation time or subsequent to the evaluation time,
• the first evaluation value being based on a first sensor current that is a DC current that is detected by the current detecting unit obtained when the voltage applying unit applies a DC voltage between the ammonia electrode and the reference electrode at an initial time that is during an initial use period of the ammonia sensor, and
• the second evaluation value being based on a second sensor current that is a DC current that is detected by the current detecting unit obtained when the voltage applying unit applies a DC voltage of a same magnitude as that at the initial time between the ammonia electrode and the reference electrode at the evaluation time that is subsequent to the initial usage period of the ammonia sensor, wherein:
• in an exhaust pipe of an internal combustion engine in which a catalyst that reduces NOX and a reducing agent supply apparatus that supplies a reducing agent that contains ammonia to the catalyst are arranged, the ammonia sensor detects a concentration of ammonia that flows out from the catalyst;
• and
• the deterioration determining unit determines the initial time and the evaluation time in a period during which a fuel-cut operation is performed by the internal combustion engine and the reducing agent is supplied to the catalyst by the reducing agent supply apparatus.

A deterioration determination apparatus for an ammonia sensor, the deterioration determination apparatus being configured to be usable with an ammonia sensor that includes

• an ammonia element portion that includes
• a solid electrolyte that has oxygen ion conductivity,
• an ammonia electrode that is provided on a first surface of the solid electrolyte that is exposed to a measured gas that contains oxygen and ammonia, and
• a reference electrode that is provided on a second surface of the solid electrolyte on a side opposite the first surface,
• a potential difference detecting unit that detects a potential difference between the ammonia electrode and the reference electrode, and
• an ammonia concentration calculating unit that calculates an ammonia concentration in the measured gas based on the potential difference detected by the potential difference detecting unit,
• the deterioration determination apparatus comprising:
• a voltage applying unit that applies a DC voltage between the ammonia electrode and the reference electrode;
• a current detecting unit that detects a DC current that flows between the ammonia electrode and the reference electrode;
• and
• a deterioration determining unit that compares a first evaluation value and a second evaluation value, and determines whether deterioration has occurred in the ammonia element portion at an evaluation time or subsequent to the evaluation time,
• the first evaluation value being based on a first sensor current that is a DC current that is detected by the current detecting unit obtained when the voltage applying unit applies a DC voltage between the ammonia electrode and the reference electrode at an initial time that is during an initial use period of the ammonia sensor, and
• the second evaluation value being based on a second sensor current that is a DC current that is detected by the current detecting unit obtained when the voltage applying unit applies a DC voltage of a same magnitude as that at the initial time between the ammonia electrode and the reference electrode at the evaluation time that is subsequent to the initial usage period of the ammonia sensor, wherein:
• the potential difference detecting unit is configured to detect the potential difference between the ammonia electrode and the reference electrode that is generated when a reduction reaction of oxygen and an oxidation reaction of ammonia in the ammonia electrode become equal;
• the ammonia sensor further includes
• a NOX element portion that includes a second solid electrolyte that has oxygen ion conductivity and is arranged so as to oppose the solid electrolyte, a measured gas chamber that is formed so as to be in contact with a third surface of the second solid electrolyte, a diffusion resistance portion that introduces the measured gas to the measured gas chamber while limiting a diffusion speed, a pump electrode that is provided in a position inside the measured gas chamber on the third surface, a NOX electrode that is provided in a position inside the measured gas chamber on the third surface, and one or a plurality of second reference electrodes that are provided on a fourth surface of the second solid electrolyte on a side opposite the third surface,
• a pump unit that applies a DC voltage between the pump electrode and the other reference electrode with the second reference electrode as a positive side, and pumps out oxygen in the measured gas inside the measured gas chamber,
• a pump current detecting unit that detects a DC current that flows between the pump electrode and the other reference electrode,
• an oxygen concentration calculating unit that calculates an oxygen concentration in the measured gas based on the DC current detected by the pump current detecting unit,
• a NOX detecting unit that applies a DC voltage between the NOX electrode and the other reference electrode with the other reference electrode as the positive side, and detects the DC current that flows between the NOX electrode and the other reference electrode, and
• a NOX concentration calculating unit that calculates a NOX concentration in the measured gas based on the DC current detected by the NOX detecting unit, and
• the ammonia concentration calculating unit is configured to correct the ammonia concentration based on at least either of the oxygen concentration calculated by the oxygen concentration calculating unit and the NOX concentration calculated by the NOX concentration calculating unit.