Oxygen concentration sensor for an internal combustion engine

Claim 1

An oxygen concentration sensor, comprising: an oxygen ion conductive solid electrolyte member forming a gas diffusion restricted region into which a measuring gas is introduced; a pair of electrodes sandwiching said solid electrolyte member; pump current supply means applying a pump voltage to said pair of electrodes through a current detection element to generate a pump current; and a heater element connected to said solid electrolyte member for heating said solid electrolyte member when a heater current is supplied from a heater current source; wherein said oxygen concentration sensor detects an oxygen concentration in said measuring gas in terms of a current value of said pump current supplied through said current detection element and controls oxygen concentration in said gas diffusion restricted region by conducting oxygen ions through said solid electrolyte member in accordance to the flow of said pump current; and wherein said current detection element is connected to the electrode of said pair of electrodes facing said gas diffusion restricted region for insuring that said current value is representative of said pump current and possible leakage current from said heater current.