Engine exhaust purification arrangement

An exhaust purification arrangement for an engine (1), comprising:

• a catalyst (3) provided in an exhaust passage (2) of the engine (1);
• a front sensor (4) which detects an air-fuel ratio of exhaust flowing into the catalyst (3);
• and
• a processor (6) programmed to:
• estimate a first amount of oxygen stored in the catalyst, the first amount being estimated to change at a first rate;
• estimate a second amount of oxygen stored in the catalyst;
• estimate the first rate based on an excess oxygen concentration and a relationship between the first amount and the second amount;
• and
• compute a target air-fuel ratio to be supplied to the engine (1) so that the amount of oxygen in the exhaust gas maintains the first amount of oxygen in the material at a predetermined target value.

An exhaust purification arrangement for an engine (1), comprising:

• a catalyst (3) provided in an exhaust passage (2) of the engine (1), said catalyst including a material which stores oxygen in the form of a high speed component which is rapidly adsorbed and released from the material and which stores oxygen in the form of a low speed component which is slowly adsorbed and released from the material;
• means for detecting an air-fuel ratio of exhaust flowing into the catalyst (3);
• means for computing an oxygen storage amount of the catalyst (3) based on the detected exhaust air-fuel ratio;
• means for computing a target air-fuel ratio of the engine (1) so that the high speed component of oxygen storage amount is maintained at-a predetermined target value;
• means for limiting the target air-fuel ratio to a lower limiter when the computed target air-fuel ratio is less than the lower limiter;
• means for lowering the lower limiter to the rich side after the engine (1) has run under a predetermined lean air-fuel ratio;
• and
• means for controlling the air-fuel ratio of the engine (1) based on the target air-fuel ratio.

A method of controlling an air-fuel ratio of an engine having a catalytic converter within an exhaust passage connected to the engine, comprising the steps of:

• determining, based on a sensed engine operating parameter, the mass flow rate of oxygen flowing into the catalytic converter;
• estimating an oxygen storage amount stored on a first material which adsorbs and releases oxygen quickly and a second material which stores and releases oxygen more slowly than the first material, by integrating the mass flow rate over a predetermined period of time;
• computing a difference between the estimated oxygen storage amount stored on the first material and target oxygen storage level for the first material;
• determining a change in an air-fuel ratio value of exhaust gas which is supplied to the catalytic converter which will adjust the amount of oxygen stored on the first material to the target oxygen storage level of the first material;
• determining a maximum value for the air-fuel ratio change;
• limiting the change in air-fuel ratio to a value less than the maximum value.

A method of controlling the air-fuel ratio of an atmosphere in an catalytic converter which is operatively connected with an internal combustion engine, comprising the 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 predetermined target amount which is less than the maximum amount of oxygen which can be adsorbed onto the first material.

A method of controlling the air-fuel ratio of an atmosphere in an catalytic converter, wherein said step of controlling the air-fuel ratio of the exhaust gases includes:

• controlling the air-fuel ratio of the exhaust gases to within upper and lower air-fuel ratio limits;
• determining if the first material is saturated with oxygen;
• and
• temporarily reducing the lower air-fuel ratio limit to enrich the air-fuel mixture to rapidly lower the amount of oxygen stored in the first material toward the target value.

An exhaust purification arrangement for an engine (1), comprising:

• a catalyst (3) provided in an exhaust passage (2) of the engine (1),the catalyst storing a first amount of oxygen by a first material and a second amount of oxygen by a second material,
• a front sensor (4) which detects an air-fuel ratio of exhaust flowing into the catalyst (3);
• and
• compute the first amount of oxygen stored in the catalyst, based on the detected exhaust air-fuel ratio;
• and
• compute a target air-fuel ratio to be supplied to the engine (1) so that the amount of oxygen in the exhaust gas maintains the first amount of oxygen at a predetermined target value.