Cylinder-to-cylinder variation abnormality detecting device

1. A cylinder-to-cylinder variation abnormality detecting device, comprising:

a rotational fluctuation detecting module that detects a rotational fluctuation among cylinders of an engine having at least two or more cylinders;

a rotational fluctuation type abnormality determining module that determines whether or not a cylinder-to-cylinder variation abnormality is occurring, based on the rotational fluctuation detected by the rotational fluctuation detecting module;

an air-fuel ratio detecting module that detects an air-fuel ratio of an air-fuel mixture, from oxygen content and unburned fuel content in an exhaust gas from the engine;

an air-fuel ratio fluctuation type abnormality determining module that determines whether or not the cylinder-to-cylinder variation abnormality is occurring, based on a fluctuation in the air-fuel ratio detected by the air-fuel ratio detecting module;

a frequency component extracting module that extracts a particular frequency component corresponding to an engine combustion cycle, included in the rotational fluctuation detected by the rotational fluctuation detecting module;

a frequency component type abnormality determining module that determines whether or not the cylinder-to-cylinder variation abnormality is occurring, based on the particular frequency component extracted by the frequency component extracting module; and

a cylinder-to-cylinder variation abnormality determination finalizing module that finalizes a determination that the cylinder-to-cylinder variation abnormality is occurring, in the case where the rotational fluctuation type abnormality determining module determines that the cylinder-to-cylinder variation abnormality is there, and also the air-fuel ratio fluctuation type abnormality determining module determines that the cylinder-to-cylinder variation abnormality is there,

wherein, in the case where the rotational fluctuation type abnormality determining module determines that the cylinder-to-cylinder variation abnormality is there but the air-fuel ratio fluctuation type abnormality determining module determines that there is no abnormality, if the frequency component type abnormality determining module determines that the cylinder-to-cylinder variation abnormality is there, the cylinder-to-cylinder variation abnormality determination finalizing module finalizes the determination that the cylinder-to-cylinder variation abnormality is occurring.

2. The cylinder-to-cylinder variation abnormality detecting device according to claim 1 ,

wherein, in the case where the rotational fluctuation type abnormality determining module determines that there is no abnormality, the cylinder-to-cylinder variation abnormality determination finalizing module finalizes a determination that the cylinder-to-cylinder variation abnormality is not occurring, and

wherein, in the case where the rotational fluctuation type abnormality determining module determines that the cylinder-to-cylinder variation abnormality is there but the air-fuel ratio fluctuation type abnormality determining module determines that there is no abnormality, if the frequency component type abnormality determining module determines that there is no abnormality, the cylinder-to-cylinder variation abnormality determination finalizing module finalizes determination that no cylinder-to-cylinder variation abnormality is occurring.

3. The cylinder-to-cylinder variation abnormality detecting device according to claim 2 , wherein the rotational fluctuation detecting module calculates a rotational angle speed between crank angles of

720°/(number of cylinders/2)

for each of the two or more of the engine, and detects rotational fluctuation from respective differences between the respective rotational angle speeds of at least some of the two or more cylinders.

4. The cylinder-to-cylinder variation abnormality detecting device according to claim 3 , wherein the frequency component extracting module has a band-pass filter that selectively passes a frequency component equivalent to one combustion cycle of the engine, and extracts the frequency component equivalent to the one combustion cycle of the engine using the band-pass filter.

5. The cylinder-to-cylinder variation abnormality detecting device according to claim 4 , wherein the frequency component extracting module extracts the frequency component equivalent to the one combustion cycle of the engine when the engine is in an idling state.

6. The cylinder-to-cylinder variation abnormality detecting device according to claim 3 , wherein, in the case where a value obtained by accumulating the square of the frequency component for a predetermined period of time exceeds a predetermined threshold value, the frequency component type abnormality determining module determines that the cylinder-to-cylinder variation abnormality is there.

7. The cylinder-to-cylinder variation abnormality detecting device according to claim 2 , wherein the frequency component extracting module has a band-pass filter that selectively passes a frequency component equivalent to one combustion cycle of the engine, and extracts the frequency component equivalent to the one combustion cycle of the engine using the band-pass filter.

8. The cylinder-to-cylinder variation abnormality detecting device according to claim 7 , wherein the frequency component extracting module extracts the frequency component equivalent to the one combustion cycle of the engine when the engine is in an idling state.

9. The cylinder-to-cylinder variation abnormality detecting device according to claim 2 , wherein, in the case where a value obtained by accumulating the square of the frequency component for a predetermined period of time exceeds a predetermined threshold value, the frequency component type abnormality determining module determines that the cylinder-to-cylinder variation abnormality is there.

10. The cylinder-to-cylinder variation abnormality detecting device according to claim 1 , wherein the rotational fluctuation detecting module calculates a rotational angle speed between crank angles of

720°/(number of cylinders/2)

for each of the two or more of the engine, and detects rotational fluctuation from respective differences between the respective rotational angle speeds of at least some of the two or more cylinders.

11. The cylinder-to-cylinder variation abnormality detecting device according to claim 10 , wherein the frequency component extracting module has a band-pass filter that selectively passes a frequency component equivalent to one combustion cycle of the engine, and extracts the frequency component equivalent to the one combustion cycle of the engine using the band-pass filter.

12. The cylinder-to-cylinder variation abnormality detecting device according to claim 11 , wherein the frequency component extracting module extracts the frequency component equivalent to the one combustion cycle of the engine when the engine is in an idling state.

13. The cylinder-to-cylinder variation abnormality detecting device according to claim 10 , wherein, in the case where a value obtained by accumulating the square of the frequency component for a predetermined period of time exceeds a predetermined threshold value, the frequency component type abnormality determining module determines that the cylinder-to-cylinder variation abnormality is there.

14. The cylinder-to-cylinder variation abnormality detecting device according to claim 1 , wherein the frequency component extracting module has a band-pass filter that selectively passes a frequency component equivalent to one combustion cycle of the engine, and extracts the frequency component equivalent to the one combustion cycle of the engine using the band-pass filter.

15. The cylinder-to-cylinder variation abnormality detecting device according to claim 14 , wherein the frequency component extracting module extracts the frequency component equivalent to the one combustion cycle of the engine when the engine is in an idling state.

16. The cylinder-to-cylinder variation abnormality detecting device according to claim 1 , wherein, in the case where a value obtained by accumulating the square of the frequency component for a predetermined period of time exceeds a predetermined threshold value, the frequency component type abnormality determining module determines that the cylinder-to-cylinder variation abnormality is there.