Exhaust gas purification system for engine

1. An exhaust gas purification system for an engine that includes a diesel particulate filter (DPF) for collecting particulate matter (PM) in an exhaust gas exhausted from the engine to an exhaust passage, the exhaust gas purification system comprising:

a central processing unit (CPU) and a memory storing instructions that causes the CPU to:

classify a PM accumulation state of the DPF into multiple evaluation stages based on a plurality of evaluation indices,

said PM accumulation state classifying step includes:

determining a current evaluation stage; and

determining whether to move up the current evaluation stage to an evaluation stage of a next rank when a value of each of a prescribed number of the evaluation indices is greater than each threshold value;

repeatedly performing determination of the current evaluation stage and determination of whether to move up the current evaluation stage to the evaluation stage of the next rank; and

said instructions further cause the CPU to:

detect a defect of different types of sensors used for calculating each of the plurality of evaluation indices; and

redetermine the current evaluation stage without using, among the different types of sensors, a sensor of which a defect is detected by the defect detection step; and

newly redetermine the current evaluation stage as a substitute for the current evaluation stage upon detection of a defect of the sensor, by using an evaluation index other than an evaluation index based on an output value of the sensor of which a defect is detected,

wherein a regeneration treatment of the PDF is executed based on the newly determined current evaluation stage when the defect of the sensor is detected.

2. The exhaust gas purification system for an engine according to claim 1 , wherein said instructions further cause the CPU to:

upon detection of a defect of a supply air flow meter as one of the sensors by the defect detecting step, an alternative evaluation index is calculated based on a supply air flow rate as a substitute for a supply air flow rate measured by the supply air flow meter of which a defect is detected, and the current evaluation stage is newly redetermined by using the alternative evaluation index and at least one of the other evaluation indices.

3. The exhaust gas purification system for an engine according to claim 2 , wherein said instructions further cause the CPU to:

upon detection of a defect of the supply air flow meter as one of the sensors by the defect detecting step, the evaluation index is calculated based on the supply air flow rate calculated by the alternative evaluation index calculating step as a substitute for the supply air flow rate measured by the supply air flow meter of which a defect is detected, and determination of whether to move up the current evaluation stage to the evaluation stage of the next rank is performed by the moving up step by using the alternative evaluation index and at least one of the other evaluation indices.

4. The exhaust gas purification system for an engine according to claim 2 , further comprising:

a pressure sensor that measures a pressure at an intake manifold part connected to the engine on the upstream side; and

a temperature sensor that measures a temperature at the intake manifold part,

wherein the supply air flow rate is calculated from the measured pressure and temperature.

5. The exhaust gas purification system for an engine according to claim 2 ,

wherein the supply air flow rate is calculated from a map indicating a relationship between an engine rotational speed and a fuel injection amount of the engine calculated based on outputs from a crank sensor, a cam sensor, an accelerator sensor, and a throttle sensor.

6. The exhaust gas purification system for an engine according to claim 1 , wherein said instructions further cause the CPU to:

upon detection of a defect of the sensor by the defect detecting step, determination of whether to move up the current evaluation stage to the evaluation stage of the next rank is performed by the moving up step by using the evaluation index other than the evaluation index based on the output value of the sensor of which a defect is detected.

7. The exhaust gas purification system for an engine according to claim 1 ,

wherein the plurality of evaluation indices includes at least a PM accumulation amount which is obtained such that the difference between a PM emission amount contained in the exhaust gas from the engine and a PM regeneration amount in the DPF is temporally cumulated,

wherein the different types of sensors include a plurality of sensors used for calculating the PM accumulation amount, the plurality of sensors includes a sensor used for calculating the PM emission amount and a sensor used for calculating the PM regeneration amount, and

wherein the PM accumulation amount is invalidated upon a defect of the sensor used for calculating the PM regeneration amount being detected by the defect detection part.

8. The exhaust gas purification system for an engine according to claim 1 ,

wherein said instructions further cause the CPU to:

upon newly redetermining the current evaluation stage, reset the previous evaluation stage and redetermine the current evaluation stage by using the lowest evaluation stage as a default.

9. An engine system, comprising:

an engine;

an exhaust passage which an exhaust gas exhausted from the engine is passed through;

a diesel particulate filter (DPF) provided on the exhaust passage, the DPF collecting particulate matter (PM) in the exhaust gas passing through the exhaust passage;

a central processing unit (CPU); and

a memory storing instructions that cause the CPU to:

classify a PM accumulation state of the DPF into multiple evaluation stages based on a plurality of evaluation indices;

said PM accumulation state classifying step includes:

determining a current evaluation state; and

determining whether to move up the current evaluation stage to an evaluation stage of a next rank when a value of each of a prescribed number of the evaluation indices is greater than each threshold value;

repeatedly performing determination of the current evaluation stage and determination of whether to move up the current evaluation stage to the evaluation stage of the next rank; and

said instructions further cause the CPU to:

detect a defect of different types of sensors used for calculating each of the plurality of evaluation indices; and

redetermine the current evaluation stage without using, among the different types of sensors, a sensor of which a defect is detected by the defect detection step; and

newly redetermine the current evaluation stage as a substitute for the current evaluation stage upon detection of a defect of the sensor, by using an evaluation index other than an evaluation index based on an output value of the sensor of which a defect is detected,

wherein a regeneration treatment of the DPF is executed based on the newly determined current stage when the defect of the sensor is detected.

10. The engine system according to claim 9 ,

wherein said instructions further cause the CPU to:

upon detection of a defect of a supply air flow meter as one of the sensors by the defect detecting step, an alternative evaluation index is calculated based on a supply air flow rate as a substitute for a supply air flow rate measured by the supply air flow meter of which a defect is detected, and the current evaluation stage is newly redetermined by using the alternative evaluation index and at least one of the other evaluation indices.

11. The engine system according to claim 10 ,

wherein said instructions further cause the CPU to:

upon detection of a defect of the supply air flow meter as one of the sensors by the defect detecting step, the evaluation index is calculated based on the supply air flow rate calculated by the alternative evaluation index calculating step as a substitute for the supply air flow rate measured by the supply air flow meter of which a defect is detected, and determination of whether to move up the current evaluation stage to the evaluation stage of the next rank is performed by the moving up step by using the alternative evaluation index and at least one of the other evaluation indices.

12. The engine system according to claim 10 , further comprising:

a pressure sensor that measures a pressure at an intake manifold part connected to the engine on the upstream side; and

a temperature sensor that measures a temperature at the intake manifold part,

wherein the supply air flow rate is calculated from the measured pressure and temperature.

13. The engine system according to claim 10 ,

wherein the supply air flow rate is calculated from a map indicating a relationship between an engine rotational speed and a fuel injection amount of the engine calculated based on outputs from a crank sensor, a cam sensor, an accelerator sensor, and a throttle sensor.

14. The engine system according to claim 9 ,

wherein said instructions further cause the CPU to:

upon detection of a defect of the sensor by the defect detecting step, determination of whether to move up the current evaluation stage to the evaluation stage of the next rank is performed by the moving up step by using the evaluation index other than the evaluation index based on the output value of the sensor of which a defect is detected.

15. The engine system according to claim 9 ,

wherein the plurality of evaluation indices includes at least a PM accumulation amount which is obtained such that the difference between a PM emission amount contained in the exhaust gas from the engine and a PM regeneration amount in the DPF is temporally cumulated

wherein the different types of sensors include a plurality of sensors used for calculating the PM accumulation amount, the plurality of sensors include a sensor used for calculating the PM emission amount and a sensor used for calculating the PM regeneration amount, and

wherein the PM accumulation amount is invalidated upon a defect of the sensor used for calculating the PM regeneration amount being detected by the defect detection part.

16. The engine system according to claim 9 ,

wherein said instructions further cause the CPU to:

upon newly redetermining the current evaluation stage, reset the previous evaluation stage and redetermine the current evaluation stage by using the lowest evaluation stage as a default.