Internal combustion engine diagnostic method and internal combustion engine diagnostic device

A diagnostic method for an internal combustion engine that includes a first fuel injection valve structured to inject fuel directly into a cylinder of the internal combustion engine and includes a second fuel injection valve structured to inject fuel into an intake passage connected to the cylinder, the diagnostic method comprising:

• defining a first region in which feedback control of air-fuel ratio is implemented;
• injecting fuel from only the first fuel injection valve during each combustion cycle in the first region;
• defining a high-revolution high-load region outside of the first region, wherein in the high-revolution high-load region, open loop control of air-fuel ratio is implemented, and a fuel injection quantity required per combustion cycle exceeds a maximum fuel injection quantity that the first fuel injection valve is capable of injecting per combustion cycle;
• in the high-revolution high-load region, setting the first fuel injection valve to inject fuel at the maximum fuel injection quantity, and setting the second fuel injection valve to inject fuel supplementarily to the fuel injection quantity from the first fuel injection valve;
• defining a second region within the first region;
• during each combustion cycle in the second region, injecting fuel from the first fuel injection valve and the second fuel injection valve;
• during each combustion cycle in the second region, setting a ratio between a quantity of fuel injection from the first fuel injection valve and a quantity of fuel injection from the second fuel injection valve to a predetermined ratio constant independently of operating status;
• calculating a mock learning value for the second fuel injection valve from a first air-fuel ratio learning value learned in the first region and a second air-fuel ratio learning value learned in the second region;
• and
• implementing a diagnosis on the second fuel injection valve, based on the mock learning value.

A diagnostic device for an internal combustion engine, the diagnostic device comprising:

• a first fuel injection valve structured to inject fuel directly into a cylinder of the internal combustion engine;
• a second fuel injection valve structured to inject fuel into an intake passage connected to the cylinder;
• a fuel injection controller configured to:
• inject fuel from only the first fuel injection valve during each combustion cycle in a predetermined first region defined in a predetermined air-fuel ratio feedback control region in which feedback control of air-fuel ratio is implemented;
• inject fuel from the first fuel injection valve and the second fuel injection valve during each combustion cycle in a predetermined second region defined in the air-fuel ratio feedback control region;
• and
• set a ratio between a fuel injection quantity from the first fuel injection valve and a fuel injection quantity from the second fuel injection valve in the second region, to a predetermined ratio constant independently of operating status;
• and
• a diagnoser configured to implement a diagnosis on at least one of the first fuel injection valve and the second fuel injection valve, based on at least one of a first air-fuel ratio learning value learned in the first region and a second air-fuel ratio learning value learned in the second region.

A diagnostic device for an internal combustion engine, the diagnostic device comprising:

• a first fuel injection valve structured to inject fuel directly into a cylinder of the internal combustion engine;
• a second fuel injection valve structured to inject fuel into an intake passage connected to the cylinder;
• a first region controller configured to inject fuel from only the first fuel injection valve during each combustion cycle in a first region in which feedback control of air-fuel ratio is implemented;
• a high-revolution high-load region controller configured to:
• in a high-revolution high-load region defined outside of the first region wherein in the high-revolution high-load region, a fuel injection quantity required per combustion cycle exceeds a maximum fuel injection quantity that the first fuel injection valve is capable of injecting per combustion cycle;
• set the first fuel injection valve to inject fuel at the maximum fuel injection quantity;
• and
• set the second fuel injection valve to inject fuel supplementarily to the fuel injection quantity from the first fuel injection valve;
• and
• implement open loop control of air-fuel ratio;
• a second region controller configured to:
• during each combustion cycle in a second region defined within the first region,
• inject fuel from the first fuel injection valve and the second fuel injection valve;
• set a ratio between a fuel injection quantity from the first fuel injection valve and a fuel injection quantity from the second fuel injection valve to a predetermined ratio constant independently of operating status;
• and
• control the fuel injection quantities from the first fuel injection valve and the second fuel injection valve to be at the predetermined ratio;
• a mock learning value calculator configured to calculate a mock learning value for the second fuel injection valve from a first air-fuel ratio learning value learned in the first region and a second air-fuel ratio learning value learned in the second region;
• and
• a diagnoser configured to implement a diagnosis on the second fuel injection valve, based on the mock learning value.