Patent ID: 6099717
Filing Date: 2000-08-08
Classification: F02D

Abstract:
A method of detecting a deteriorated condition of a wide range air-fuel ratio sensor, wherein the air-fuel ratio sensor includes two cells each having an oxygen ion conductive solid electrolytic body heated by a heater and two porous electrodes disposed on opposite sides of the oxygen ion conductive solid electrolytic body, respectively, the two cells being disposed so as to oppose each other with a gap therebetween, one of the cells being used as a pump cell for pumping oxygen out of or into the gap, and the other cell of the cells being used as an electromotive force cell for generating a voltage according to a difference in oxygen concentration between an oxygen reference chamber and the gap, the method comprising:a first step of applying a current to the electromotive force cell;a second step of detecting a voltage Vs0 across the electrodes on opposite side surfaces of the electromotive force cell;a third step of suspending said applying of the current to the electromotive force cell;a fourth step of detecting a voltage Vs1 across the electrodes on the opposite side surfaces of the electromotive force cell after a lapse of a time ranging from 10 .mu.s to 1 ms after said third step;a fifth step of detecting a voltage Vs2 across the electrodes on the opposite sides of the electromotive force cell after a lapse of a time ranging from 10 ms to 50 ms after said third step; anda sixth step of detecting the deteriorated condition of the wide range air-fuel ratio sensor based on said voltages Vs0, Vs1, and Vs2;wherein said third step is executed after a lapse of a predetermined time from the start of energizing of the heater for allowing said voltage Vs0 detected at said second step to become equal to or lower than a predetermined value.