Anomaly diagnosing apparatus and method for air flowmeter

An anomaly diagnosing method for an air flowmeter, wherein

• the air flowmeter is arranged in an intake passage of an internal combustion engine and detects an air amount,
• the engine includes a catalyst, which is arranged in an exhaust passage and has an oxidizing function, an addition valve, which is arranged upstream of the catalyst in the exhaust passage and adds fuel to exhaust gas, 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 amount, which is an estimated value of an air amount, based on an air-fuel ratio detected by the air-fuel ratio sensor and an injection amount injected by the fuel injection valve;
• and
• determining that there is an anomaly in which a detected value of the air flowmeter is greater than an actual value if a logical conjunction is true of the condition that the detected value of the air flowmeter is greater than the estimated air amount by a margin greater than or equal to a specified amount and the condition that an amount by which a detected value of the exhaust temperature sensor exceeds a reference value is smaller than or equal to a predetermined amount.

A non-transitory computer readable medium that stores a program for causing a processor to execute an anomaly diagnosing process for an air flowmeter, wherein

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