Patent ID: 6374596
Filing Date: 2002-04-23
Classification: F01N,F02B,Y02A,Y02T

Abstract:
An exhaust-gas cleaning device for an engine, said exhaust-gas cleaning device comprising:a NOx-absorbing material provided in an exhaust passage to absorb NOx under oxygen-rich conditions where the oxygen concentration is high and release absorbed NOx as the oxygen concentration decreases; an oxygen-absorbing material provided in the exhaust passage to absorb oxygen under oxygen-rich conditions where the oxygen concentration is high and release absorbed oxygen as the oxygen concentration decreases; an oxygen concentration controlling means for controlling the oxygen concentration in the exhaust passage; an oxygen concentration detecting means provided downstream of the NOx-absorbing material and the oxygen-absorbing material; an absorption quantity detecting means which determines a first amount of absorption of NOx and oxygen absorbed by the NOx-absorbing material and the oxygen-absorbing material based on a sensing signal fed from the oxygen concentration detecting means at a time when the oxygen concentration upstream of the NOx-absorbing material and the oxygen-absorbing material is just transferred from a high concentration state maintained for a preset first reference time to a low concentration state by controlling the oxygen concentration with the oxygen concentration controlling means, and determines a second amount of absorption of NOx and oxygen absorbed by the NOx-absorbing material and the oxygen-absorbing material based on a sensing signal fed from the oxygen concentration detecting means at a time when the oxygen concentration upstream of the NOx-absorbing material and the oxygen-absorbing material is just transferred from the high concentration state maintained for a preset second reference time which is longer than the first reference time to the low concentration state by controlling the oxygen concentration with the oxygen concentration controlling means; a NOx quantity estimating means which obtains a first estimated value of the amount of NOx absorbed by the NOx-absorbing material during the first reference time and a second estimated value of the amount of NOx absorbed by the NOx-absorbing material during the second reference time in accordance with engine operating condition; and a deterioration detecting means which makes a judgment on deterioration of the NOx-absorbing material based on the first amount of absorption and the second amount of absorption of NOx and oxygen determined by the absorption quantity detecting means and the first estimated value and the second estimated value of the amount of absorbed NOx obtained by the NOx quantity estimating means.