Control Device and Diagnostic Method for Internal Combustion Engine

1 . A control device for an internal combustion engine provided with a first fuel injection valve and a second fuel injection valve for a cylinder, the control device comprising:

a diagnosing unit configured such that, when there is an abnormality that makes an air-fuel ratio of the internal combustion engine richer than a specified value, the diagnosing unit determines whether the first fuel injection valve or the second fuel injection valve has the abnormality, based on

change of the air-fuel ratio occurring as a result of first injection control for performing fuel injection while changing a distribution ratio of a fuel injection amount distributed to the first fuel injection valve to a fuel injection amount distributed to the second fuel injection valve, and

a value of the air-fuel ratio obtained as a result of second injection control for performing fuel injection while maintaining the distribution ratio at a predetermined ratio.

2 . The control device for the internal combustion engine according to claim 1 ,

wherein the second injection control is carried out by causing either the first fuel injection valve or the second fuel injection valve to inject fuel, and

wherein, based on the change of the air-fuel ratio occurring as a result of the first injection control, the diagnosing unit selects whether the first fuel injection valve or the second fuel injection valve is to inject fuel in the second injection control.

3 . The control device for the internal combustion engine according to claim 2 ,

wherein the first injection control is carried out while increasing the distribution ratio of the fuel injection amount distributed to the first fuel injection valve to the fuel injection amount distributed to the second fuel injection valve, and

wherein

when the air-fuel ratio becomes still richer as a result of the first injection control, the diagnosing unit causes the second fuel injection valve to inject fuel in the second injection control, and

when the air-fuel ratio approaches the specified value as a result of the first injection control, the diagnosing unit causes the first fuel injection valve to inject fuel in the second injection control.

4 . The control device for the internal combustion engine according to claim 3 ,

wherein as a result of the second injection control carried out by causing the second fuel injection valve to inject fuel,

when the air-fuel ratio does not deviate from the specified value or deviates from the specified value by an amount less than a first threshold, the diagnosing unit determines that the first fuel injection valve has the abnormality, and

when the air-fuel ratio deviates from the specified value by an amount more than the first threshold, the diagnosing unit determines that the second fuel injection valve has the abnormality, and

wherein as a result of the second injection control carried out by causing the first fuel injection valve to inject fuel,

when the air-fuel ratio does not deviate from the specified value or deviates from the specified value by an amount less than the first threshold, the diagnosing unit determines that the second fuel injection valve has the abnormality, and

when the air-fuel ratio deviates from the specified value by an amount more than the first threshold, the diagnosing unit determines that the first fuel injection valve has the abnormality.

5 . The control device for the internal combustion engine according to claim 3 ,

wherein as a result of the second injection control carried out by causing the second fuel injection valve to inject fuel,

when the air-fuel ratio does not deviate from the specified value or deviates from the specified value by an amount less than a first threshold, the diagnosing unit determines that the first fuel injection valve has a measurement abnormality, and

when the air-fuel ratio deviates from the specified value by an amount more than the first threshold, the diagnosing unit determines that the second fuel injection valve is stuck open, and

wherein as a result of the second injection control carried out by causing the first fuel injection valve to inject fuel,

when the air-fuel ratio does not deviate from the specified value or deviates from the specified value by an amount less than the first threshold, the diagnosing unit determines that the second fuel injection valve has a measurement abnormality, and

when the air-fuel ratio deviates from the specified value by an amount more than the first threshold, the diagnosing unit determines that the first fuel injection valve is stuck open.

6 . The control device for the internal combustion engine according to claim 1 ,

wherein the first injection control is carried out while increasing the distribution ratio of the fuel injection amount distributed to the first fuel injection valve to the fuel injection amount distributed to the second fuel injection valve,

wherein the second injection control is carried out by causing both the first fuel injection valve and the second fuel injection valve to inject a reduced amount of fuel while maintaining the distribution ratio at a predetermined ratio,

wherein when the air-fuel ratio becomes still richer as a result of the first injection control,

when the air-fuel ratio deviates from the specified value by an amount more than a second threshold as a result of the second injection control, the diagnosing unit determines that the second fuel injection valve is stuck open, and

when the air-fuel ratio does not deviate from the specified value or deviates from the specified value by an amount less than the second threshold as a result of the second injection control, the diagnosing unit determines that the first fuel injection valve has a measurement abnormality, and

wherein when the air-fuel ratio approaches the specified value as a result of the first injection control,

when the air-fuel ratio deviates from the specified value by an amount more than a second threshold as a result of the second injection control, the diagnosing unit determines that the first fuel injection valve is stuck open, and

when the air-fuel ratio does not deviate from the specified value or deviates from the specified value by an amount less than the second threshold as a result of the second injection control, the diagnosing unit determines that the second fuel injection valve has a measurement abnormality.

7 . The control device for the internal combustion engine according to claim 1 ,

wherein the first injection control is carried out while increasing the distribution ratio of the fuel injection amount distributed to the first fuel injection valve to the fuel injection amount distributed to the second fuel injection valve,

wherein the second injection control is carried out by causing both the first fuel injection valve and the second fuel injection valve to inject fuel while

maintaining the distribution ratio at a predetermined ratio,

supplying fuel to the first fuel injection valve and the second fuel injection valve at a reduced pressure, and

correcting an injection pulse width of the first fuel injection valve and an injection pulse width of the second fuel injection valve upward in accordance with reduction of the pressure of the fuel,

wherein when the air-fuel ratio becomes still richer as a result of the first injection control,

when the air-fuel ratio approaches the specified value as a result of the second injection control, the diagnosing unit determines that the second fuel injection valve is stuck open, and

when the air-fuel ratio does not approach the specified value as a result of the second injection control, the diagnosing unit determines that the first fuel injection valve has a measurement abnormality, and

wherein when approaches the specified value as a result of the first injection control,

when the air-fuel ratio approaches the specified value as a result of the second injection control, the diagnosing unit determines that the first fuel injection valve is stuck open, and

when the air-fuel ratio does not approach the specified value as a result of the second injection control, the diagnosing unit determines that the second fuel injection valve has a measurement abnormality.

8 . The control device for the internal combustion engine according to claim 5 , the control device further comprising

an abnormality-addressing processing unit configured to perform abnormality-addressing processing in accordance with a diagnosis provided by the diagnosing unit,

wherein when the diagnosing unit determines that the first fuel injection valve has a measurement abnormality, the abnormality-addressing processing unit stops fuel injection from the first fuel injection valve and maintains fuel injection from the second fuel injection valve so as to operate the internal combustion engine,

wherein when the diagnosing unit determines that the second fuel injection valve is stuck open, the abnormality-addressing processing unit stops fuel injection from the first fuel injection valve and maintains fuel injection from the second fuel injection valve so as to operate the internal combustion engine,

wherein when the diagnosing unit determines that the second fuel injection valve has a measurement abnormality, the abnormality-addressing processing unit stops fuel injection from the second fuel injection valve and maintains fuel injection from the first fuel injection valve so as to operate the internal combustion engine, and

wherein when the diagnosing unit determines that the first fuel injection valve is stuck open, the abnormality-addressing processing unit stops fuel injection from the second fuel injection valve and maintains fuel injection from the first fuel injection valve so as to operate the internal combustion engine.

9 . A diagnostic method for an internal combustion engine provided with a first fuel injection valve and a second fuel injection valve for a cylinder, the diagnostic method comprising:

carrying out first injection control for performing fuel injection while changing a distribution ratio of a fuel injection amount distributed to the first fuel injection valve to a fuel injection amount distributed to the second fuel injection valve, when there is an abnormality that makes an air-fuel ratio of the internal combustion engine richer than a specified value;

determining change of the air-fuel ratio occurring as a result of the first injection control;

carrying out second injection control for performing fuel injection while maintaining the distribution ratio at a predetermined ratio;

determining a deviation, from the specified value, of the air-fuel ratio obtained as a result of the second injection control; and

determining whether the first fuel injection valve or the second fuel injection valve has the abnormality, based on the change of the air-fuel ratio occurring as a result of the first injection control and the deviation of the air-fuel ratio obtained as a result of the second injection control.

10 . The diagnostic method for the internal combustion engine according to claim 9 ,

wherein the second injection control is carried out by causing either the first fuel injection valve or the second fuel injection valve to inject fuel, and

wherein, based on the change of the air-fuel ratio occurring as a result of the first injection control, it is selected whether the first fuel injection valve or the second fuel injection valve is to inject fuel in the second injection control.

11 . The diagnostic method for the internal combustion engine according to claim 10 ,

wherein the first injection control is carried out while increasing the distribution ratio of the fuel injection amount distributed to the first fuel injection valve to the fuel injection amount distributed to the second fuel injection valve, and

wherein

when the air-fuel ratio becomes still richer as a result of the first injection control, the second fuel injection valve injects fuel in the second injection control, and

when the air-fuel ratio approaches the specified value as a result of the first injection control, the first fuel injection valve injects fuel in the second injection control.

12 . The diagnostic method for the internal combustion engine according to claim 11 ,

wherein as a result of the second injection control carried out by causing the second fuel injection valve to inject fuel,

when the air-fuel ratio does not deviate from the specified value or deviates from the specified value by an amount less than a first threshold, it is determined that the first fuel injection valve has the abnormality, and

when the air-fuel ratio deviates from the specified value by an amount more than the first threshold, it is determined that the second fuel injection valve has the abnormality, and

wherein as a result of the second injection control carried out by causing the first fuel injection valve to inject fuel,

when the air-fuel ratio does not deviate from the specified value or deviates from the specified value by an amount less than the first threshold, it is determined that the second fuel injection valve has the abnormality, and

when the air-fuel ratio deviates from the specified value by an amount more than the first threshold, it is determined that the first fuel injection valve has the abnormality.