Patent ID: 6309536
Filing Date: 2001-10-30
Classification: B01D,F01N,F02D,G01N,Y02T

Abstract:
An apparatus for detecting a functional condition of an NOx occlusion catalyst, comprising an NOx sensor disposed in an exhaust pipe of an internal combustion engine at a location downstream of the NOx occlusion catalyst, said NOx sensor including a first measurement space having a first oxygen-pumping cell and an oxygen-concentration-measuring cell and communicating with a measurement gas via a first diffusion-controlling layer; a second measurement space having a second oxygen-pumping cell and communicating with the first measurement space via a second diffusion-controlling layer; and a heater for heating said cells to a predetermined active temperature,said apparatus further comprising:first pumping-current control means for controlling the concentration of oxygen in said first measurement space to a constant level by applying a first pumping current to said first oxygen-pumping cell such that an output voltage from said oxygen-concentration-measuring cell is maintained at a constant value;constant-voltage application means for applying a constant voltage to said second oxygen-pumping cell in a direction such that oxygen is pumped out from said second measurement space;second pumping-current detection means for detecting a second pumping current which flows through said second oxygen-pumping cell according to the concentration of NOx in the measurement gas;minimum value detection means for detecting during operation control of the internal combustion engine at a lean air-fuel ratio a minimum value of the second pumping current during a predetermined waiting time after start of operation control of the internal combustion engine at a lean air-fuel ratio; andfunctional condition judgment means for judging a functional condition of said NOx occlusion catalyst based on a relative value calculated as the difference between a value of the second pumping current detected by said second pumping-current detection means after elapse of the waiting time and the minimum value of the second pumping current detected by said minimum value detection means.