Method for controlling the level of oxygen stored by a catalyst within a catalytic converter

A method for controlling the oxygen storage level of a catalyst within a catalytic converter coupled to an engine comprising the steps of:

• monitoring a mass air flow rate into the engine and a first air/fuel ratio signal from a first gas sensor positioned upstream from the catalytic converter and a second air/fuel ratio signal from a second gas sensor positioned downstream from the catalytic converter;
• generating an estimate of the oxygen storage level of the catalyst by:
• continuously calculating an oxygen storage level, a rich adaptation parameter, and a lean adaptation parameter in a series of iterations,
• wherein values for the oxygen storage level, and the rich and the lean adaptation parameters calculated in a previous iteration are stored in a memory:
• providing an expression for the mass of oxygen flowing into the catalytic converter,
• wherein the expression includes the term (.lambda..sub.inlet -1)/.lambda..sub.inlet where .lambda..sub.inlet is equal to a normalized air/fuel ratio:
• providing a rate modifier;
• multiplying the expression by the rate modifier:
• and
• integrating the expression over a predetermined time interval to produce an estimate of the oxygen storage level of the catalyst;
• and
• comparing the estimate with a desired oxygen storage level and generating an oxygen error value;
• analyzing the oxygen error value to produce an offset value;
• comparing the first air/fuel ratio signal with a desired air/fuel ratio and generating an air/fuel ratio error value;
• applying the offset value to the air/fuel error value and generating a compensation value;
• and
• adjusting the mass fuel flow rate into the engine by the compensation value.

A method for controlling the oxygen storage level of a catalyst within a catalytic converter coupled to an engine comprising the steps of:

• receiving signals from an MAP sensor, a first gas sensor positioned upstream from the catalytic converter, and a second gas sensor positioned downstream from the catalytic converter;
• using the signals to compute values for a pumping delay time and for an exhaust system transport delay;
• determining a computed oxygen storage level of the catalyst using an expression for the mass of oxygen flowing into the catalytic converter,
• wherein the expression includes the term (.lambda..sub.inlet -1)/.lambda..sub.inlet where .lambda..sub.inlet is equal to a normalized air/fuel ratio, and
• wherein the stored values for the pumping delay time and the exhaust system transport delay are applied to the expression and
• wherein a rate modifier is applied to the expression;
• comparing the computed oxygen storage level to a predetermined threshold value, which provides positive and negative oxygen deviation values;
• and
• responding to a positive oxygen deviation value by decreasing an air/fuel ratio into the engine, and
• responding to a negative oxygen deviation value by increasing the air/fuel ratio into the engine.