Anomaly diagnosing apparatus and method for addition valve

An anomaly diagnosing method for an addition valve, wherein

• the addition valve is arranged in an exhaust passage of an internal combustion engine and adds fuel to exhaust gas,
• the engine includes an air flowmeter, which is arranged in an intake passage and detects an air amount, and a catalyst, which is arranged in the exhaust passage and has an oxidizing function,
• the addition valve is arranged upstream of the catalyst in the exhaust passage, and
• the engine also includes an air-fuel ratio sensor, which is arranged downstream of the addition valve in the exhaust passage, an exhaust temperature sensor, which is arranged downstream of the catalyst in the exhaust passage, and a fuel injection valve, which supplies fuel into a combustion chamber,
• the anomaly diagnosing method comprising:
• calculating an estimated air-fuel ration, which is an estimated value of an air-fuel ratio based on an intake air amount detected by the air flowmeter and the sum of a fuel amount injected by the fuel injection valve and a fuel amount added by the addition valve;
• and
• determining that there is a stuck-closed anomaly in the addition valve if a logical conjunction is true of a condition that a detected value of the air-fuel ratio sensor is greater than the estimated air fuel-ratio by a margin greater than or equal to a specified amount and a condition that a detected value of the exhaust temperature sensor in a period in which the addition valve adds fuel is smaller than a reference value in that period by a margin greater than or equal to a predetermined amount.

A non-transitory computer readable memory medium storing a program that causes a processor to perform an anomaly diagnosing process for an addition valve, wherein

• the addition valve is arranged in an exhaust passage of an internal combustion engine and adds fuel to exhaust gas,
• the engine includes an air flowmeter, which is arranged in an intake passage and detects an air amount, and a catalyst, which is arranged in the exhaust passage and has an oxidizing function,
• the addition valve is arranged upstream of the catalyst in the exhaust passage,
• the engine also includes an air-fuel ratio sensor, which is arranged downstream of the addition valve in the exhaust passage, an exhaust temperature sensor, which is arranged downstream of the catalyst in the exhaust passage, and a fuel injection valve, which supplies fuel into a combustion chamber, and
• the anomaly diagnosing process includes
• calculating an estimated air-fuel ration, which is an estimated value of an air-fuel ratio based on an intake air amount detected by the air flowmeter and the sum of a fuel amount injected by the fuel injection valve and a fuel amount added by the addition valve, and
• determining that there is a stuck-closed anomaly in the addition valve if a logical conjunction is true of a condition that a detected value of the air-fuel ratio sensor is greater than the estimated air fuel-ratio by a margin greater than or equal to a specified amount and a condition that a detected value of the exhaust temperature sensor in a period in which the addition valve adds fuel is smaller than a reference value in that period by a margin greater than or equal to a predetermined amount.