Method and apparatus for diagnosing fault in continuous variable valve duration system

1. A method of diagnosing a fault in a continuous variable valve duration (CVVD) system, the method comprising:

an information collection step of collecting information necessary to determine whether a fault diagnosis mode entry condition of the CVVD system is satisfied;

a determination step of determining whether the fault diagnosis mode entry condition is satisfied based on the information collected in the information collection step;

a manifold pressure-based prediction duration calculation step of calculating prediction duration corresponding to a current engine RPM and manifold pressure when the fault diagnosis mode entry condition is satisfied;

a sensor output-based duration calculation step of calculating current duration based on an output value of a motor sensor for detecting an RPM of a duration control motor of the CVVD system;

a duration comparison step of comparing the manifold pressure-based prediction duration D1 with the sensor output-based duration D2; and

a determination step of determining an error of the motor sensor or whether the CVVD system has failed by comparing a duration difference cumulative value, which is a cumulative value of difference values between the D1 and the D2, with a threshold previously stored in a recording device.

2. The method of claim 1 , wherein:

the information necessary to determine whether the fault diagnosis mode entry condition is satisfied, which is collected in the information collection step, comprises information about whether an MAP sensor positioned in an air-intake line and a crank sensor positioned in the air-intake line to detect the engine RPM are normal and fuel cut information, and

in the determination step, the fault diagnosis mode entry condition is determined to have been satisfied when the MAP sensor and the crank sensor are a normal state and fuel cut operates.

3. The method of claim 1 , wherein in the manifold pressure-based prediction duration calculation step, the prediction duration corresponding to the current engine RPM and manifold pressure is calculated using a duration map in which a manifold pressure change according to a valve duration change has been stored.

4. The method of claim 1 , wherein in the sensor output-based duration calculation step, the current duration is calculated based on a duration position value according to an accumulation of the RPM of the motor capable of being aware based on the output of the motor sensor.

5. The method of claim 1 , wherein the determination step comprises:

a first determination step of diagnosing an error of the motor sensor by comparing the duration difference cumulative value (cumulative Diff) with a first threshold previously stored in the recording device; and

a second determination step of diagnosing a fault in the CVVD system by comparing the duration difference cumulative value (cumulative Diff) with a second threshold which is a different threshold previously stored in the recording device when the duration difference cumulative value (cumulative Diff) exceeds the first threshold.

6. The method of claim 5 , wherein if, as a result of the determination of the comparison in the determination step, the duration difference cumulative value (cumulative Diff) is greater than the first threshold and equal to or smaller than the second threshold, an error of the motor sensor is determined and a mode switches to a limp-home mode which is an emergency driving mode.

7. The method of claim 5 , wherein if, as a result of the determination of the comparison in the determination step, the duration difference cumulative value (cumulative Diff is greater than the first threshold and greater than the second threshold, a system failure is determined and failure information is displayed through a sound signal or visual display means in such a way as to be recognizable by a driver.

8. An apparatus for diagnosing a fault in a continuous variable valve duration (CVVD) system, the apparatus comprising:

an ECU; and

a CVVD controller configured to determine a control value in cooperation with the ECU and control a shaft for variable duration by controlling a duration control motor based on the determined control value,

wherein the CVVD controller comprises a sensor output-based duration calculation unit configured to calculate current duration based on an output value of a motor sensor for detecting an RPM of the duration control motor of the CVVD system,

wherein the ECU comprises:

an information collection unit configured to collect information necessary to determine whether a fault diagnosis mode entry condition of the CVVD system is satisfied,

a determination unit configured to determine whether the fault diagnosis mode entry condition is satisfied based on the information collected by the information collection unit,

a manifold pressure-based prediction duration calculation unit configured to calculate prediction duration corresponding to a current engine RPM and manifold pressure when the fault diagnosis mode entry condition is satisfied; and

a determination unit configured to compare the manifold pressure-based prediction duration D1 with the sensor output-based duration D2 and to determine an error of the motor sensor or whether the CVVD system has failed by comparing a duration difference cumulative value, which is a cumulative value of difference values between the D1 and the D2, with a threshold previously stored in a recording device.

9. The apparatus of claim 8 , wherein:

the information necessary to determine whether the fault diagnosis mode entry condition is satisfied, which is collected in the information collection step, comprises information about whether an MAP sensor positioned in an air-intake line and a crank sensor positioned in the air-intake line to detect the engine RPM are normal and fuel cut information, and

the determination unit determines that the fault diagnosis mode entry condition is satisfied when the MAP sensor and the crank sensor are a normal state and fuel cut operates.

10. The apparatus of claim 8 , wherein the manifold pressure-based prediction duration calculation unit calculates the prediction duration corresponding to the current engine RPM and manifold pressure using a duration map in which a manifold pressure change according to a valve duration change has been stored.

11. The apparatus of claim 8 , wherein the sensor output-based duration calculation unit calculates the current duration based on a duration position value according to an accumulation of the RPM of the motor capable of being aware based on the output of the motor sensor.

12. The apparatus of claim 8 , wherein the determination unit diagnoses an error of the motor sensor by comparing the duration difference cumulative value (cumulative Diff) with a first threshold previously stored in the recording device and diagnoses a fault in the CVVD system by comparing the duration difference cumulative value (cumulative Diff) with a second threshold which is a different threshold previously stored in the recording device when the duration difference cumulative value (cumulative Diff) exceeds the first threshold.

13. The apparatus of claim 12 , wherein:

when the duration difference cumulative value (cumulative Diff) is greater than the first threshold and equal to or smaller than the second threshold, an error of the motor sensor is determined and a mode switches to a limp-home mode which is an emergency driving mode, and

when the duration difference cumulative value (cumulative Diff is greater than the first threshold and greater than the second threshold, a system failure is determined and failure information is displayed through a sound signal or visual display means in such a way as to be recognizable by a driver.