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Exhaust purification device of an engine

  • US 5,715,679 A
  • Filed: 03/22/1996
  • Issued: 02/10/1998
  • Est. Priority Date: 03/24/1995
  • Status: Expired due to Term
First Claim
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1. An exhaust purification device of an engine having an exhaust passage, comprising:

  • an NOx absorbent arranged in the exhaust passage, said NOx absorbent absorbing NOx therein when an air-fuel ratio of exhaust gas flowing into the NOx absorbent is lean and releasing absorbed NOx therefrom when the air-fuel ratio of the exhaust gas flowing into the NOx absorbent becomes rich;

    estimating means for estimating an amount of NOx absorbed in the NOx absorbent to obtain an estimated amount of NOx stored in the NOx absorbent;

    air-fuel ratio detecting means arranged in the exhaust passage downstream of the NOx absorbent for generating an output signal indicating an air-fuel ratio of exhaust gas which flows out from the NOx absorbent;

    NOx amount calculating means for calculating an entire amount of NOx stored in the NOx absorbent on the basis of the output signal of said air-fuel ratio detecting means when the air-fuel ratio of exhaust gas flowing into the NOx absorbent is changed from lean to rich so as to release NOx from the NOx absorbent;

    correction value calculating means for calculating a correction value for said estimated amount of NOx, which correction value is a value by which said estimated amount of NOx corrected by said correction value when the air-fuel ratio of exhaust gas flowing into the NOx absorbent is changed from lean to rich so as to release NOx from the NOx absorbent indicates said entire amount of NOx calculated by said NOx amount calculating means; and

    control means for controlling the air-fuel ratio of exhaust gas flowing into the NOx absorbent to change the air-fuel ratio of exhaust gas flowing into the NOx absorbent from lean to rich to release NOx from the NOx absorbent when said estimated amount of NOx corrected by said correction value exceeds a predetermined amount.

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