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Exhaust emission control system

  • US 10,443,474 B2
  • Filed: 01/08/2018
  • Issued: 10/15/2019
  • Est. Priority Date: 01/23/2017
  • Status: Active Grant
First Claim
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1. An exhaust emission control system, comprising:

  • a fuel injector;

    a NOx storage catalyst provided in an exhaust passage of an engine and configured to store NOx;

    a urea selective catalytic reduction (SCR) catalyst provided in the exhaust passage downstream of the NOx storage catalyst; and

    a processor operatively coupled to the fuel injector and configured to execute a NOx reduction controlling module to set a NOx reduction condition and, when the processor determines that the NOx reduction condition is satisfied, control the fuel injector to perform NOx reduction processing in which an air-fuel ratio of exhaust gas is set to be one of near a stoichiometric air-fuel ratio and rich, and the NOx stored in the NOx storage catalyst is reduced, whereinthe NOx reduction condition includes a condition in which a NOx stored amount in the NOx storage catalyst is larger than a given reference stored amount and the engine operates within a given reduction-allowed operating range determined based on an engine speed and an engine load,the NOx reduction controlling module sets a first operating range that is a reduction-allowed operating range for performing the NOx reduction processing a first time after the engine is started, to be larger than a second operating range that is a reduction-allowed operating range for performing the NOx reduction processing a second and subsequent times after the engine is started, andthe NOx reduction controlling module sets the first operating range by expanding the second operating range toward at least one of a higher engine speed side and a higher engine load side.

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