Failure detecting device for a fuel supply system of an internal combustion engine

A failure detecting device for a fuel supply system of an internal combustion engine, comprising:

• a fuel vapor supply device for supplying and stopping fuel vapor from a fuel supply system to an intake air passage of an engine;
• an air-fuel ratio sensor disposed in an exhaust gas passage of the engine for detecting air-fuel ratio of an exhaust gas from the engine;
• an electronic control unit receiving an output signal from the air-fuel ratio sensor, and performing the functions of:
• a) calculating an air-fuel ratio feedback correction factor in accordance with the output signal from the air-fuel ratio sensor in such a manner that the output signal from the air-fuel ratio sensor becomes an output corresponding to a stoichiometric air-fuel ratio;
• b) calculating a feedback learning correction factor when the fuel vapor supply device is not supplying fuel vapor to the intake air passage in such a manner that the center value of the fluctuation of the air-fuel ratio feedback correction factor agrees with a predetermined reference value;
• c) calculating a fuel vapor learning correction factor when the fuel vapor supply device is supplying fuel vapor to the intake air passage in such a manner that the center value of the fluctuation of the air-fuel ratio feedback correction factor agrees with said reference value;
• d) calculating a first air-fuel ratio correction factor in accordance with the air-fuel ratio feedback correction factor and the feedback learning correction factor;
• e) calculating a second air-fuel ratio correction factor in accordance with the air-fuel ratio feedback correction factor and the feedback learning correction factor and the fuel vapor learning correction factor;
• f) controlling the amount of fuel supplied to the engine in accordance with the first air-fuel ratio correction factor when the fuel vapor supply device is not supplying fuel vapor to the intake air passage, and in accordance with the second air-fuel ratio correction factor when the fuel vapor supply device is supplying fuel vapor to the intake air passage;
• g) determining whether the value of the first air-fuel ratio correction factor is within a predetermined range when the fuel vapor supply device is supplying fuel vapor to the intake air passage;
• and
• h) stopping the fuel vapor supply device from supplying fuel vapor to the intake air passage when it is determined that the value of the air-fuel ratio correction factor is larger than or smaller than said predetermined range, and determining that the fuel supply system has failed if the value of the air-fuel ratio correction factor is larger than a predetermined upper limit value or lower than a predetermined lower limit value after the fuel vapor supply has been stopped.

A method for detecting failure in a fuel supply system of an internal combustion engine comprising steps of;

• a) supplying and stopping fuel vapor from a fuel supply system to an intake air passage of an internal combustion engine;
• b) detecting an air-fuel ratio of an exhaust gas from the engine;
• c) setting an air-fuel ratio feedback correction factor in accordance with the air-fuel ratio of the exhaust gas in such a manner that the air-fuel ratio of the exhaust gas becomes a stoichiometric air-fuel ratio;
• d) setting a feedback learning correction factor when the fuel vapor is not supplied to the intake air passage in such a manner that the center value of the fluctuation of the air-fuel ratio feedback correction factor agrees with a predetermined reference value;
• e) setting a fuel vapor learning correction factor when the fuel vapor is supplied to the intake air passage in such a manner that the center value of the fluctuation of the air-fuel ratio feedback correction factor agrees with said reference value;
• f) setting a first air-fuel ratio correction factor in accordance with the air-fuel ratio feedback correction factor and the feedback learning correction factor;
• g) setting a second air-fuel ratio correction factor in accordance with the air-fuel ratio feedback correction factor and the feedback learning correction factor and the fuel vapor learning correction factor;
• h) controlling the amount of fuel supplied to the engine in accordance with the first air-fuel ratio correction factor when the fuel vapor is not supplied to the intake air passage, and in accordance with the second air-fuel ratio correction factor when the fuel vapor is supplied to the intake air passage;
• i) determining whether the value of the first air-fuel ratio correction factor is within a predetermined range when the fuel vapor is supplied to the intake air passage;
• and
• j) stopping the fuel vapor supply to the intake air passage when it is determined that the value of the air-fuel ratio correction factor is larger than or smaller than said predetermined range, and determining that the fuel supply system has failed if the value of the air-fuel ratio correction factor is larger than a predetermined upper limit value or lower than a predetermined lower limit value after the fuel vapor supply has been stopped.