Oxygen storage control of engine exhaust gas purification catalyst

An air/fuel ratio control device for an engine, the engine provided with an exhaust gas purification catalyst storing and releasing oxygen in response to the oxygen concentration of exhaust gas of the engine, comprising:

• means for injecting fuel in the engine to generate an air/fuel mixture;
• means for detecting an air/fuel ratio of the air/fuel mixture;
• means for detecting a flowrate of the exhaust gas;
• means for calculating an oxygen concentration of the exhaust gas based on the air/fuel ratio;
• means for calculating an oxygen amount in the exhaust gas based on the oxygen concentration and the flowrate of the exhaust gas;
• means for repeatedly calculating a variation rate of an oxygen storage amount of the catalyst based on the oxygen amount in the exhaust gas and an oxygen storage amount of the catalyst on an immediately preceding occasion when the calculation of the variation rate was performed;
• means for calculating the oxygen storage amount of the catalyst by accumulating the variation rate;
• means for calculating a target oxygen amount in the exhaust gas which reduces the difference between the oxygen storage amount and the predetermined target oxygen storage amount;
• means for calculating a target air/fuel ratio based on the target oxygen amount and the flowrate of the exhaust gas;
• and
• means for controlling a fuel injection amount of the fuel injecting means to a fuel injection amount corresponding to the target air/fuel ratio.

An air/fuel ratio control method for an engine, the engine provided with an exhaust gas purification catalyst storing and releasing oxygen in response to the oxygen concentration of exhaust gas of the engine and a fuel injector which injects fuel in the engine to generate an air/fuel mixture;

• the method comprising:
• detecting an air/fuel ratio of the air/fuel mixture;
• detecting a flowrate of the exhaust gas;
• calculating an oxygen concentration of the exhaust gas based on the air/fuel ratio;
• calculating an oxygen amount in the exhaust gas based on the oxygen concentration and the flowrate of the exhaust gas;
• calculating repeatedly a variation rate of an oxygen storage amount of the catalyst based on the oxygen amount in the exhaust gas and an oxygen storage amount of the catalyst on an immediately preceding occasion when the calculation of the variation rate was performed;
• calculating the oxygen storage amount of the catalyst by accumulating the variation rate;
• calculating a target oxygen amount in the exhaust gas which reduces the difference between the oxygen storage amount and the predetermined target oxygen storage amount;
• calculating a target air/fuel ratio based on the target oxygen amount and the flowrate of the exhaust gas;
• and
• controlling a fuel injection amount of the fuel injector to a fuel injection amount corresponding to the target air/fuel ratio.