Engine exhaust purification device

An engine exhaust purification device comprising:

• a catalyst (3) provided in an engine exhaust passage (2),
• a first sensor (4) which detects an exhaust characteristic of flowing into the catalyst (3),
• a second sensor (5) which detects an air-fuel ratio of exhaust flowing out of the catalyst (3), and
• a microprocessor (6) programmed to:
• compute the oxygen storage amount of the catalyst (3) using the detected exhaust characteristic,
• perform reset processing which initializes the oxygen storage amount to a maximum value when the air-fuel ratio of the exhaust from the catalyst (3) detected via the second sensor (5) exceeds a lean determining value, and initializes the oxygen storage amount to a minimum value when the air-fuel ratio of the exhaust from the catalyst (3) detected via the second sensor (5) exceeds a rich determining value,
• compute a target air-fuel ratio of an engine (1) so that the oxygen storage amount of the catalyst (3) is a predetermined target value based on the computed oxygen storage amount, and
• compare a reset processing frequency with a determining value, and determine that the catalyst (3) has deteriorated when the reset processing frequency exceeds the determining value.

An engine exhaust purification device comprising:

• a catalyst (3) provided in an engine exhaust passage (2),
• means (4) for detecting an exhaust characteristic flowing into the catalyst (3),
• means for computing an oxygen storage amount of the catalyst (3) using the detected exhaust characteristic,
• means for computing a target air-fuel ratio of the engine (1) based on the computed oxygen storage amount such that the oxygen storage amount of the catalyst is a predetermined target value, and
• means for determining a deterioration of the catalyst (3) based on an integrated value of the oxygen storage amount for a predetermined time.

An engine exhaust purification device comprising:

• a catalyst (3) provided in an engine exhaust passage (2),
• means (4) for detecting an exhaust characteristic of flowing into the catalyst (3),
• means (5) for detecting an air-fuel ratio of exhaust flowing out of the catalyst (3),
• means (6) for computing the oxygen storage amount of the catalyst (3) using the detected exhaust characteristic,
• means (6) for performing reset processing which initializes the oxygen storage amount to a maximum value when the air-fuel ratio of the exhaust from the catalyst (3) detected via the second sensor (5) exceeds a lean determining value, and initializes the oxygen storage amount to a minimum value when the air-fuel ratio of the exhaust from the catalyst (3) detected via the second sensor (5) exceeds a rich determining value,
• means (6) for computing a target air-fuel ratio of an engine (1) so that the oxygen storage amount of the catalyst (3) is a predetermined target value based on the computed oxygen storage amount, and
• means (6) for comparing a reset processing frequency with a determining value, and
• means (6) for determining that the catalyst (3) has deteriorated when the reset processing frequency exceeds the determining value.

A method for determining a deterioration of the catalyst, comprising:

• computing the oxygen storage amount of the catalyst (3) using the detected exhaust characteristic,
• performing reset processing which initializes the oxygen storage amount to a maximum value when the air-fuel ratio of the exhaust from the catalyst (3) detected via the second sensor (5) exceeds a lean determining value, and initializes the oxygen storage amount to a minimum value when the air-fuel ratio of the exhaust from the catalyst (3) detected via the second sensor (5) exceeds a rich determining value,
• computing a target air-fuel ratio of an engine (1) so that the oxygen storage amount of the catalyst (3) is a predetermined target value based on the computed oxygen storage amount, and
• comparing a reset processing frequency with a determining value, and
• determining that the catalyst (3) has deteriorated when the reset processing frequency exceeds the determining value.