AIR FUEL RATIO DETECTOR

摘要

PURPOSE:To detect an air fuel ratio correctly from an excessive fuel region to a thin region by flowing a sufficiently large current to an oxygen pump element and cuasing the voltage across an oxygen concentration cell element to vary steeply at an ideal air fuel ratio point. CONSTITUTION:An air fuel ratio detector 2 is arranged in an exhaust pipe 1. The air fuel ratio detector 2 is constituted by providing a solid-state electrolyte oxygen concentration cell element 10 having porous electrodes 8 and 9 on both flanks of an oxygen ion conductive solid-state electrolyte 7 and a solid-state elctrolyte pump element 6 then forming an air chamber communicating with the outside air at the opposite side of where the oxygen concentration cell element of an oxygen pump element 6 is arranged. The electromotive force (e) of the oxygen concentration cell element 10 is inputted to an electronic controller 17 to control the pump current Ip of the oxygen pump element 6. A changeover switch 19 is provided to an input/output terminal of the oxygen pump element 6 and constant current sources E1-E6 are connected to respective switch points. Then, the constant current sources are selected to vary the suction current of the oxygen pump element, causing a shift in the steep change point of the electromotive force of the oxygen concentration cell element.