Method for controlling the level of oxygen stored by a catalyst within a catalytic converter
First Claim
1. A method for controlling the oxygen storage level of a catalyst within a catalytic converter coupled to an engine comprising the steps of:
- obtaining an expression for the mass of oxygen flowing into the catalytic converter,wherein the expression includes the term (λ
inlet -1)/λ
inlet where λ
inlet is equal to a normalized air/fuel ratio;
applying a rate modifier to the expression to obtain an oxygen storage rate to continuously calculate the oxygen storage level of the catalyst;
comparing the 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, andresponding to a negative oxygen deviation value by increasing the air/fuel ratio into the engine.
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Abstract
The catalyst control method of the invention continuously estimates a level of oxygen stored by a catalyst within a catalytic converter. The estimated oxygen stored by the catalyst is compared to a predetermined threshold and positive or negative deviations in the oxygen amount from the threshold is determined. When a positive deviation from the threshold amount is detected, the air/fuel ratio flowing into an engine (16) is decreased. Correspondingly, when a negative deviation is detected, the air/fuel ratio flowing into the engine (16) is increased. The amount of oxygen stored by the catalyst is determined by analyzing signals from a first gas sensor (28) positioned upstream from a catalytic converter (34) and a second gas sensor (30) positioned downstream from the catalytic converter (34). An engine control unit (10) integrates an expression for the mass flow rate of excess oxygen into the catalytic converter (34). Engine control unit (10) applies a change in air/fuel ratio to maintain the oxygen level on the catalyst within the catalytic converter (34) at a desired level.
215 Citations
14 Claims
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1. A method for controlling the oxygen storage level of a catalyst within a catalytic converter coupled to an engine comprising the steps of:
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obtaining an expression for the mass of oxygen flowing into the catalytic converter, wherein the expression includes the term (λ
inlet -1)/λ
inlet where λ
inlet is equal to a normalized air/fuel ratio;applying a rate modifier to the expression to obtain an oxygen storage rate to continuously calculate the oxygen storage level of the catalyst; comparing the 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. - View Dependent Claims (2, 3, 4)
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5. A method for controlling the oxygen storage level of a catalyst within a catalytic converter coupled to an engine comprising the steps of:
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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 (λ
inlet -1)/λ
inlet where λ
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. - View Dependent Claims (6, 7, 8)
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9. A method for controlling the oxygen storage level of a catalyst within a catalytic converter coupled to an engine comprising the steps of:
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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 (λ
inlet -1)/λ
inlet where λ
inlet is equal to a normalized air/fuel ratio, andwherein 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. - View Dependent Claims (10, 11, 12, 13, 14)
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Specification