Patent ID: 7959778

Claim:
A sensor control apparatus comprising: an air/fuel ratio sensor having a sensor cell with a pair of electrodes on opposite sides of a solid electrolyte and capable of detecting a concentration of a particular gas component of an exhaust gas emitted from an internal combustion engine; a current source capable of supplying a predetermined current between the pair of electrodes; and a control unit comprising: a current control section that turns on/off the current source at a predetermined cycle; a voltage detecting section that detects voltages generated between the pair of electrodes at respective times when the current source is turned on and off; a differential voltage detecting section that calculates a differential voltage between the voltages that are generated at the respective times when the current source is turned on and off and detected by the voltage detecting section; a first voltage comparing section that compares the differential voltage with a first threshold voltage; a half-activated state determining section that determines that the sensor cell has reached a half-activated state that enables the air/fuel ratio sensor to measure whether an air/fuel ratio of the exhaust gas is rich or lean on the basis of an output of the sensor cell, when the differential voltage is lower than the first threshold voltage; a second voltage comparing section that compares, when it is determined by the half-activated state determining section that the sensor cell has reached the half-activated state, a voltage between the pair of electrodes, which is detected by the voltage detecting section when the current source is on or off, with a second threshold voltage that is different than the first threshold voltage; a rich/lean measurement result output section that outputs a signal indicative of the air/fuel ratio of the exhaust gas being rich or lean on the basis of the result of comparison by the second voltage comparing section; a full-activated state determining section that determines whether the sensor cell has reached a full-activated state on the basis of information that is different from the differential voltage after it is determined by the half-activated state determining section that the sensor cell has reached the half-activated state; wherein the full-activated state determining section uses an internal resistance value of the sensor cell as said information; and a resistance value detecting section that detects the internal resistance value of the sensor cell, wherein the full-activated state determining section compares the internal resistance value of the sensor cell with a threshold value and determines that the sensor cell has reached the full-activated state when the internal resistance value is lower than the threshold value.