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Air/fuel ratio feedback control system for lean combustion engine

  • US 5,009,210 A
  • Filed: 01/07/1987
  • Issued: 04/23/1991
  • Est. Priority Date: 01/10/1986
  • Status: Expired due to Fees
First Claim
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1. A control system for feedback control of the air/fuel ratio of an air-fuel mixture supplied to an internal combustion engine which uses a three-way catalyst for purifying the exhaust gas, the control system comprising:

  • air/fuel ratio detection means for detecting actual values of air/fuel ratio in the engine;

    load detection means for detecting the load under which the engine is operating;

    transient condition detection means for detecting any of predetermined transient operating conditions of the engine; and

    control means for performing feedback control of the feed of fuel or air to the engine based on the detected actual values of air/fuel ratio, the control means comprising target value setting means for determining the target value of the air/fuel ratio according to information obtained by said load detection means and said transient condition detection means such that the target value becomes a first value which is higher than the stoichiometric air/fuel ratio at least during predetermined steady-state operation of the engine and shifts to a second value which is optimum for the activities of the three-way catalyst when any of said predetermined transient operating conditions is detected and modulation means for regulating the feed of fuel or air to the engine at the start of the shift of the target value such that the air/fuel ratio deviates from said second value in the direction reverse to the target value immediately before the shift only for a predetermined period of time.

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