Exhaust emission control for engine

A method of controlling an air-fuel ratio of an engine having a catalytic converter disposed in an exhaust gas passage connected to the engine, the catalytic converter storing and releasing oxygen and having an oxygen saturated condition and a completely oxygen depleted condition, comprising steps of:

• estimating a first storage capacity of the catalytic converter by integrating an excessive oxygen flow rate entering the catalytic converter over a first time period from the completely oxygen depleted condition to the oxygen saturated condition;
• estimating a second storage capacity by integrating an oxygen desorption flow rate over a second time period from the oxygen saturated condition to the completely oxygen depleted condition;
• determining a target value for an oxygen storage level within the catalytic converter based on a mathematical result derived using the first storage capacity and the second storage capacity;
• and
• controlling an air-fuel ratio of an exhaust gas supplied to the catalytic converter to maintain the oxygen storage level within the catalytic converter at the determined target value.

A method of controlling the air-fuel ratio of an atmosphere in a catalytic converter which is operatively connected with an internal combustion engine, comprising steps of:

• storing oxygen on a first material in the catalytic converter which adsorbs and releases oxygen rapidly;
• storing oxygen on a second material in the catalytic converter which adsorbs and releases oxygen more slowly than the first material;
• and
• controlling the air-fuel ratio of the exhaust gas entering the catalytic converter to control the amount of oxygen which is adsorbed on the first material to a predicted predetermined amount which is less than the maximum amount of oxygen which can be adsorbed onto the first material;
• checking the predicted predetermined amount by controlling the air-fuel ratio of the exhaust gas supplied into the catalytic converter so that the first material becomes saturated with oxygen;
• controlling the amount of oxygen in the exhaust gas supplied to the catalytic converter so that oxygen is released from the first material;
• detecting a first period required for the oxygen storage status of the first material to go from full saturation to total depletion;
• controlling the amount of oxygen in the exhaust gas supplied to the catalytic converter so that oxygen is adsorbed onto the first material;
• detecting a second period required for the oxygen storage status to go from total depletion to full saturation;
• detecting the respective mass flow amount of oxygen during the first and second periods and determining a first amount of oxygen released and a second amount of oxygen adsorbed;
• comparing the first and second amounts;
• and
• determining a target oxygen storage value based on the comparison of the first and second amounts.

An apparatus for controlling an air-fuel ratio of an engine having a catalytic converter disposed in an exhaust gas passage connected to the engine, the catalytic converter storing and releasing oxygen and having an oxygen saturated condition and a completely oxygen depleted condition, comprising:

• means for estimating a first storage capacity of the catalytic converter by integrating an excessive oxygen flow rate entering the catalytic converter over a first time period from the completely oxygen depleted condition to the oxygen saturated condition;
• means for estimating a second storage capacity by integrating an oxygen desorption flow rate over a second time period from the oxygen saturated condition to the completely oxygen depleted condition;
• means for determining a target value for an oxygen storage level within the catalytic converter based on a mathematical result derived using the first storage capacity and the second storage capacity;
• and
• means for controlling an air-fuel ratio of an exhaust gas supplied to the catalytic converter to maintain the oxygen storage level within the catalytic converter at the determined target value.

An apparatus for controlling the air-fuel ratio of an atmosphere in a catalytic converter which is operatively connected with an internal combustion engine, comprising:

• means for storing oxygen on a first material in the catalytic converter which adsorbs and releases oxygen rapidly;
• means for storing oxygen on a second material in the catalytic converter which adsorbs and releases oxygen more slowly than the first material;
• and
• means for controlling the air-fuel ratio of the exhaust gas entering the catalytic converter to control the amount of oxygen which is adsorbed on the first material to a predicted predetermined amount which is less than the maximum amount of oxygen which can be adsorbed onto the first material;
• means for checking the predicted predetermined amount by controlling the air-fuel ratio of the exhaust gas supplied into the catalytic converter so that the first material becomes saturated with oxygen;
• means for controlling the amount of oxygen in the exhaust gas supplied to the catalytic converter so that oxygen is released from the first material;
• means for detecting a first period required for the oxygen storage status of the first material to go from full saturation to total depletion;
• means for controlling the amount of oxygen in the exhaust gas supplied to the catalytic converter so that oxygen is adsorbed onto the first material;
• means for detecting a second period required for the oxygen storage status to go from total depletion to full saturation;
• means for detecting the respective mass flow amount of oxygen during the first and second periods and determining a first amount of oxygen released and a second amount of oxygen adsorbed;
• means for comparing the first and second amounts;
• and
• means for determining a target oxygen storage value based on the comparison of the first and second amounts.

An exhaust emission control arrangement for an internal combustion engine having a fuel supply mechanism and an exhaust passage, comprising:

• a catalytic converter disposed in the exhaust gas passage, the catalytic converter housing a three-way catalyst including a first material which adsorbs oxygen quickly and a second material which stores oxygen at a rate slower than the first material;
• a first oxygen sensor which detects an oxygen concentration of exhaust gas upstream of the catalyst;
• a second oxygen sensor which detects an oxygen concentration of exhaust gas downstream of the catalyst;
• and
• a microprocessor programmed to:
• calculate, using the upstream oxygen concentration, an excess/deficiency oxygen concentration in exhaust gas upstream of the catalyst with respect to a stoichiometric oxygen concentration;
• calculate an oxygen storage amount of at least the first material of the catalyst based on the excess/deficiency oxygen concentration;
• calculate a specific period oxygen storage amount of the catalyst during a period in which the upstream oxygen concentration is higher than the stoichiometric concentration while the downstream oxygen concentration is in a predetermined concentration range including the stoichiometric oxygen concentration;
• calculate a specific period oxygen release amount of the first material during a period in which the upstream oxygen concentration is lower than the stoichiometric concentration while the downstream oxygen concentration is in the predetermined concentration range;
• sample a specific period oxygen storage amount as a maximum oxygen storage amount at a time at which the downstream oxygen concentration becomes greater than the predetermined concentration range;
• sample a specific period oxygen release amount as a maximum oxygen release amount at a time at which the downstream oxygen concentration becomes smaller than the predetermined concentration range;
• calculate an average value of the maximum oxygen storage amount and the maximum oxygen release amount;
• determine a target value of the oxygen storage amount which has a predetermined relationship with the average value;
• and
• control a fuel supply amount of the fuel supply mechanism to maintain the oxygen storage amount of the first material at the target value.

An exhaust emission control arrangement for an engine, the engine comprising a fuel supply mechanism and an exhaust passage, the controller comprising;

• a catalytic converter disposed in the exhaust gas passage, the catalytic converter storing a three-way catalyst;
• means for detecting an oxygen concentration of exhaust gas upstream of the catalyst as an upstream oxygen concentration;
• means for detecting an oxygen concentration of exhaust gas downstream of the catalyst as a downstream oxygen concentration;
• means for calculating, from the upstream oxygen concentration, an excess/deficiency oxygen concentration in exhaust gas upstream of the catalyst with respect to a stoichiometric oxygen concentration which corresponds to a stoichiometric air-fuel ratio of a fuel mixture provided to the engine;
• means for calculating an oxygen storage amount of the catalyst based on the excess/deficiency oxygen concentration;
• means for calculating a specific period oxygen storage amount of the catalyst during a period in which the upstream oxygen concentration is higher than the stoichiometric concentration while the downstream oxygen concentration is in a predetermined concentration range including the stoichiometric oxygen concentration;
• means for calculating a specific period oxygen release amount of the catalyst during a period in which the upstream oxygen concentration is lower than the stoichiometric concentration while the downstream oxygen concentration is in the predetermined concentration range;
• means for sampling a specific period oxygen storage amount as a maximum oxygen storage amount at a time at which the downstream oxygen concentration becomes greater than the predetermined concentration range;
• means for sampling a specific period oxygen release amount as a maximum oxygen release amount at a time at which the downstream oxygen concentration becomes smaller than the predetermined concentration range;
• means for calculating an average value of the maximum oxygen storage amount and the maximum oxygen release amount;
• means for determining a target value of the oxygen storage amount based on the average value;
• and
• means for controlling a fuel supply amount of the fuel supply mechanism to cause the oxygen storage amount of the catalyst to coincide with the target value.

A method for controlling an exhaust emission of an engine, the engine comprising a fuel supply mechanism, an exhaust passage and a catalytic converter disposed in the exhaust gas passage, the catalytic converter storing a three-way catalyst, the method comprising;

• detecting an oxygen concentration of exhaust gas upstream of the catalyst as an upstream oxygen concentration;
• detecting an oxygen concentration of exhaust gas downstream of the catalyst as a downstream oxygen concentration;
• calculating, from the upstream oxygen concentration, an excess/deficiency oxygen concentration in exhaust gas upstream of the catalyst with respect to a stoichiometric oxygen concentration which corresponds to a stoichiometric air-fuel ratio of a fuel mixture provided to the engine;
• calculating an oxygen storage amount of the catalyst based on the excess/deficiency oxygen concentration;
• calculating a specific period oxygen storage amount of the catalyst during a period in which the upstream oxygen concentration is higher than the stoichiometric concentration while the downstream oxygen concentration is in a predetermined concentration range including the stoichiometric oxygen concentration;
• calculating a specific period oxygen release amount of the catalyst during a period in which the upstream oxygen concentration is lower than the stoichiometric concentration while the downstream oxygen concentration is in the predetermined concentration range;
• sampling a specific period oxygen storage amount as a maximum oxygen storage amount at a time at which the downstream oxygen concentration becomes greater than the predetermined concentration range;
• sampling a specific period oxygen release amount as a maximum oxygen release amount at a time at which the downstream oxygen concentration becomes smaller than the predetermined concentration range;
• calculating an average value of the maximum oxygen storage amount and the maximum oxygen release amount;
• determining a target value of the oxygen storage amount based on the average value;
• and
• controlling a fuel supply amount of the fuel supply mechanism to cause the oxygen storage amount of the catalyst to coincide with the target value.

A method of determining a target oxygen content of a catalyst forming part of an exhaust emission control for an internal combustion engine comprising the steps of:

• determining a first maximum amount of oxygen that a catalyst material can rapidly adsorb;
• determining a second maximum amount of oxygen that the catalyst material can rapidly release;
• and
• averaging the first and second maximum amounts and setting the target oxygen content on a predetermined percentage of the average.

An arrangement for determining a target oxygen content of a catalyst forming part of an exhaust emission control for an internal combustion engine, comprising:

• an apparatus including an air-fuel sensor and a gas flow sensing arrangement for:
• determining a first maximum amount of oxygen that a catalyst material can rapidly adsorb;
• determining a second maximum amount of oxygen that the catalyst material can rapidly release;
• and
• averaging the first and second maximum amounts and setting the target oxygen content on a predetermined percentage of the average.