ENGINE OFF NATURAL VACUUM LEAKAGE CHECK FOR ONBOARD DIAGNOSTICS

• US 20030061864A1
• Filed: 10/01/2001
• Published: 04/03/2003
• Est. Priority Date: 10/01/2001
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: General Motors Corporation (General Motors Company)
• Inventors: Wong, Kevin C., Western, William
• Granted Patent: US 6,550,316 B1
• Time in Patent Office: Days
• US Class Current: 73/40
• CPC Class Codes: F02M 25/0809 Judging failure of purge control system
• CPC Class Codes: F02M 25/0818 having means for pressurising the evaporative emission space

Abstract

A diagnostic method and system detects leaks in a vapor handling system of a vehicle that includes a fuel tank and a pressure/vacuum sensor that senses pressure and vacuum in the fuel tank. A canister recovers vapor from the fuel tank. A canister vent solenoid selectively provides atmospheric air to the canister. A controller connected to the canister vent solenoid and the pressure/vacuum sensor executes a leakage detection test that is capable of detecting leaks in the vapor handling system that have a diameter on the order of 0.020 inch. The leakage detection test includes a volatility test phase, a pressure phase, a vacuum phase, an analysis phase and a results phase. In other features, the leakage detection algorithm generates data sets having greater than 25 standard deviations between leakage and no-leakage data sets.

Claims

1. A diagnostic system for detecting leaks in a vapor handling system of a vehicle, comprising:

a fuel tank;

a pressure/vacuum sensor that senses pressure and vacuum in said fuel tank;

a canister for recovering vapor from said fuel tank;

a canister vent solenoid for selectively providing atmospheric air to said canister; and

a controller connected to said canister vent solenoid and said pressure/vacuum sensor that executes a leakage detection test that detects leaks in said vapor handling system that have a minimum diameter on the order of 0.020 inch.

2. The diagnostic system of claim 1 wherein said leakage detection algorithm generates data sets having greater than 25 standard deviations between leakage and no-leakage data sets.

3. The diagnostic system of claim 1 wherein said leakage detection test includes a volatility test phase.

4. The diagnostic system of claim 3 wherein said volatility test phase classifies a volatility of said vapor in said fuel tank into low, medium and high volatility, and wherein said leakage diagnostic test is aborted if said volatility is high.

5. The diagnostic system of claim 3 wherein said leakage diagnostic test includes a pressure phase that is performed after said volatility test phase.

6. The diagnostic system of claim 5 wherein, during said pressure phase, said controller closes said canister vent solenoid and measures a pressure change in said fuel tank.

7. The diagnostic system of claim 6 wherein, during said pressure phase, if said pressure is increasing and said pressure change exceeds a pressure target value, said controller initiates an analysis phase.

8. The diagnostic system of claim 7 wherein, during said pressure phase, if said pressure is not increasing, said controller checks for a vacuum and performs a vacuum phase if said vacuum is present.

9. The diagnostic system of claim 8 wherein, during said pressure phase, if said pressure is not increasing and said vacuum is not present, said controller initiates said vacuum phase if said pressure remains zero for a first predetermined period.

10. The diagnostic system of claim 9 wherein, during said analysis phase, said controller opens said canister vent solenoid, sums an absolute value of a pressure change and an absolute value of a vacuum change and initiates a reporting phase.

11. The diagnostic system of claim 10 wherein, during said reporting phase, said controller inputs said sum to an exponentially-weighted moving average, compares said exponentially-weighted moving average to a threshold and declares a leak if said exponentially-weighted moving average exceeds said threshold.

12. The diagnostic system of claim 11 wherein, during said vacuum phase, said controller opens said canister vent solenoid for a second predetermined period so that said vacuum phase begins at atmospheric pressure.

13. The diagnostic system of claim 12 wherein, during said vacuum phase, said controller sets a vacuum target equal to a total target minus said pressure change measured in said pressure phase.

14. The diagnostic system of claim 13 wherein, during said vacuum phase, said controller closes said canister vent solenoid and measures a vacuum change.

15. The diagnostic system of claim 14 wherein, during said vacuum phase, if said vacuum is increasing and said vacuum change exceeds said target value, said controller initiates said analysis phase.

16. The diagnostic system of claim 15 wherein, during said vacuum phase, if said vacuum is decreasing said controller initiates said analysis phase.

17. The diagnostic system of claim 17 wherein, during said vacuum phase, if said vacuum is zero for a second predetermined period said controller initiates said analysis phase.

18. A diagnostic method for detecting leaks in a vapor handling system of a vehicle, comprising the steps of:

sensing pressure and vacuum in a fuel tank of said vehicle;

recovering vapor from said fuel tank using a canister;

selectively providing atmospheric air to said canister using a canister vent; and

executing a leakage detection test using a controller, wherein said leakage detection test detects leaks in said vapor handling system that have a minimum diameter on the order of 0.020 inch.

19. The diagnostic method of claim 18 further comprising the step of generating data sets having greater than 25 standard deviations between leakage and no-leakage data sets.

20. The diagnostic method of claim 18 further comprising the step of performing a volatility test phase during said leakage detection test.

21. The diagnostic method of claim 20 further comprising the step of classifying a volatility of said vapor in said fuel tank into low, medium and high volatility during said volatility test, wherein said leakage diagnostic test is aborted if said volatility is high.

22. The diagnostic method of claim 21 wherein said leakage diagnostic test includes a pressure phase that is performed after said volatility test phase.

23. The diagnostic method of claim 22 further comprising the step of closing said canister vent and measuring a pressure change in said fuel tank during said pressure phase.

24. The diagnostic method of claim 23 further comprising the step of initiating an analysis phase during said pressure phase if said pressure is increasing and said pressure change exceeds a pressure target value.

25. The diagnostic method of claim 24 further comprising the step of during said pressure phase, if said pressure is not increasing, checking for a vacuum and performing a vacuum phase if said vacuum is present.

26. The diagnostic method of claim 25 further comprising the step of during said pressure phase, if said pressure is not increasing and a vacuum is not present, initiating said vacuum phase if said pressure remains zero for a first predetermined period.

27. The diagnostic method of claim 26 further comprising the steps of:

during said analysis phase, opening said canister vent;

summing an absolute value of a pressure change and an absolute value of a vacuum change; and

initiating a reporting phase.

28. The diagnostic method of claim 27 further comprising the steps of:

during said reporting phase, inputting said sum to an exponentially-weighted moving average;

comparing said exponentially-weighted moving average to a threshold; and

declaring a leak if said exponentially-weighted moving average exceeds said threshold.

29. The diagnostic method of claim 28 further comprising the step of during said vacuum phase, opening said canister vent for a second predetermined period so that said vacuum phase begins at atmospheric pressure.

30. The diagnostic method of claim 29 further comprising the step of during said vacuum phase, setting a vacuum target equal to a total target minus said pressure change measured in said pressure phase.

31. The diagnostic method of claim 30 further comprising the step of during said vacuum phase, closing said canister vent and measuring a vacuum change.

32. The diagnostic method of claim 31 further comprising the step of during said vacuum phase, if said vacuum is increasing and said vacuum change exceeds said target value, initiating said analysis phase.

33. The diagnostic method of claim 32 further comprising the step of initiating said analysis phase if said vacuum is decreasing during said vacuum phase.

34. The diagnostic method of claim 33 further comprising the step of initiating said analysis phase during said vacuum phase if said vacuum is zero for a second predetermined period.