SOx concentration acquiring apparatus of internal combustion engine

A SOx concentration acquiring apparatus of an internal combustion engine, comprising:

• a sensor cell formed by a solid electrolyte layer, a first sensor electrode provided on one of opposite surfaces of the solid electrolyte layer such that the first sensor electrode is exposed to an exhaust gas discharged from the internal combustion engine, and a second sensor electrode provided on the other surface of the opposite surfaces of the solid electrolyte layer;
• and
• an electronic control unit for controlling a sensor voltage which is a voltage applied to the sensor cell and acquiring a sensor current which is a current flowing through the sensor cell,
• wherein the electronic control unit is configured to:
• execute a decomposition voltage increasing control for increasing the sensor voltage from a first voltage lower than an oxygen increasing voltage to a second voltage equal to or higher than the oxygen increasing voltage, the oxygen increasing voltage being a voltage at which an amount of oxygen component produced by SOx decomposing to sulfur component and the oxygen component is larger than the amount of the oxygen component consumed by the sulfur component being oxidized by the oxygen component to the SOx;
• execute a reoxidation voltage decreasing control for decreasing the sensor voltage from the second voltage to a third voltage lower than an oxygen decreasing voltage after the electronic control unit executes the decomposition voltage increasing control, the oxygen decreasing voltage being a voltage at which the amount of the oxygen component consumed by the sulfur component being oxidized by the oxygen component to the SOx is larger than the amount of the oxygen component produced by the SOx decomposing to the sulfur component and the oxygen component;
• acquire the sensor currents as SOx concentration currents, respectively after the sensor voltage reaches the oxygen decreasing voltage while the electronic control unit executes the reoxidation voltage decreasing control, wherein the sensor voltage is continuously decreased while acquiring the SOx concentration currents during the reoxidation voltage decreasing control;
• acquire the sensor current as a high-voltage current when the sensor voltage decreases to a fourth voltage equal to or lower than the oxygen decreasing voltage;
• acquire the sensor current as a low-voltage current when the sensor voltage decreases to a fifth voltage lower than the fourth voltage;
• acquire a change rate of the sensor current as a sensor current change rate while the sensor current changes from the high-voltage current to the low-voltage current;
• acquire currents which change from the high-voltage current at the sensor current change rate and correspond to the sensor voltages, at which the electronic control unit acquires the SOx concentration currents, as base currents, respectively;
• acquire an integration value of differences between each of the base currents and each of the SOx concentration currents;
• and
• acquire a SOx concentration of the exhaust gas on the basis of the integration value.