Control device for oxygen concentration sensor

A control device for controlling an oxygen concentration sensor comprising:

• a voltage sweeping unit for applying a voltage to the oxygen concentration sensor for a predetermined time interval during an impedance detection process, in which information about an exhaust gas air and fuel ratio is obtained according to an output voltage of the oxygen concentration sensor;
• a pre-sweeping voltage memory for storing a terminal voltage of the oxygen concentration sensor, which is referred as an initial terminal voltage, just before the voltage sweeping unit applies the voltage to the oxygen concentration sensor;
• an impedance detection unit for detecting an element impedance in accordance with the voltage applied by the voltage sweeping unit;
• a voltage returning unit for returning the terminal voltage of the oxygen concentration sensor to the initial terminal voltage after a predetermined time interval has elapsed since the voltage sweeping unit applies the voltage to the oxygen concentration sensor;
• a monitoring unit for monitoring the terminal voltage of the oxygen concentration sensor after the voltage returning unit starts returning the terminal voltage of the oxygen concentration sensor to the initial terminal voltage;
• a determination unit for determining whether a monitored terminal voltage of the oxygen concentration sensor reaches a certain voltage, which is calculated by adding an offset voltage to a stored terminal voltage in the pre-sweeping voltage memory, or by subtracting the offset voltage from the stored terminal voltage;
• and
• a stop unit for stopping a returning operation of the voltage returning unit when the determination unit determines that the monitored terminal voltage reaches the certain terminal voltage.