METHOD AND SYSTEM FOR FUEL VAPOR CONTROL

• US 20130112176A1
• Filed: 11/08/2011
• Published: 05/09/2013
• Est. Priority Date: 11/08/2011
• Status: Active Grant

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Peters, Mark W., Jentz, Robert Roy, Butler, Darrell Erick, Dudar, Aed Mohammad
• Granted Patent: US 9,027,532 B2
• Time in Patent Office: Days
• US Class Current: 123/521
• CPC Class Codes: F02M 25/0809 Judging failure of purge control system
• CPC Class Codes: F02M 25/089 Layout of the fuel vapour installation

Abstract

Methods and systems are provided for generating sufficient vacuum to enable a leak detection routine. While a fuel tank pressure is within mechanical limits, fuel vapors are purged from a canister to an engine with an isolation valve open to generate a desired level of vacuum in the fuel tank. Thereafter, the fuel tank is isolated and leak detection is performed concurrent to the purging.

Claims

1. A method of operating a fuel system including a fuel tank coupled to a fuel vapor canister via an isolation valve, comprising,

purging fuel vapors from the canister to an engine intake for a duration with the isolation valve open until a threshold level of fuel tank vacuum is generated.

2. The method of claim 1, wherein the duration is based on a purge flow rate and a fuel tank vacuum level.

3. The method of claim 2, wherein the threshold level includes a fuel tank vacuum level required to enable a fuel system leak detection routine.

4. The method of claim 1, wherein during the purging, a vacuum generation potential of the purging is higher than a threshold, the vacuum generation potential based at least on a purge flow rate.

5. The method of claim 1, wherein the purging includes increasing a purge flow rate independent of a canister fuel vapor load until the threshold level of fuel tank vacuum is generated.

6. The method of claim 1, further comprising, after the duration, purging fuel vapors from the canister to the engine intake with the isolation valve closed while simultaneously applying the generated fuel tank vacuum to the fuel system to identify a fuel system leak.

7. The method of claim 5, wherein identifying the fuel system leak includes, when a rate of vacuum decay from the isolated fuel tank is higher than a threshold rate, indicating a fuel system leak.

8. The method of claim 1, wherein during the purging with the isolation valve open, a fuel tank pressure is lower than a mechanical pressure limit of the fuel tank.

9. The method of claim 1, further comprising, after the threshold level of fuel tank vacuum is generated, ending the purging and applying the generated fuel tank vacuum to the fuel system to identify a fuel system leak.

10. A method of operating a fuel system including a fuel tank coupled to a canister via an isolation valve, comprising:

during a first purging condition, purging fuel vapors from the canister to an engine intake with the isolation valve open; and

during a second purging condition, purging fuel vapors from the canister to the engine intake, with the isolation valve closed,

wherein during each of the first and second purging conditions, a fuel tank pressure is within a mechanical pressure limit of the fuel tank.

11. The method of claim 10, wherein during the first condition, a fuel tank vacuum level is lower than a threshold level, and wherein during the second condition, the fuel tank vacuum level is higher than the threshold level.

12. The method of claim 10, wherein during the first condition, the purging is at a first, higher purge flow rate, and wherein during the second condition, the purging is at a second, lower purge flow rate.

13. The method of claim 11, wherein the second purge flow rate is based on a canister fuel vapor load, and wherein the first purge flow rate is independent of the canister fuel vapor load.

14. The method of claim 10, wherein during the first condition, the purging is for a first duration based on canister load, engine load, and fuel tank vacuum level, and wherein during the second condition, the purging is for a second duration based on canister load and engine load, the first duration being longer than the second duration.

15. The method of claim 13, wherein the first duration increases as a difference between the fuel tank vacuum level and a threshold vacuum level for enabling a leak detection routine increases.

16. The method of claim 10, further comprising, during the first condition, after the first duration has elapsed, purging fuel vapors from the canister to the engine intake with the isolation valve closed while simultaneously detecting a leak in the fuel tank.

17. The method of claim 16, wherein the detecting is based on a rate of vacuum decay from the fuel tank with the isolation valve closed.

18. A fuel system for a vehicle comprising:

a fuel tank;

a canister coupled to the fuel tank via a valve;

an engine including an intake;

a pressure sensor coupled to the fuel tank and configured to estimate a fuel tank vacuum level; and

a control system with computer readable instructions for;

purging fuel vapors from the canister to the engine intake with the isolation valve open for a duration until the fuel tank vacuum level is higher than a threshold vacuum level; and

after the duration, purging fuel vapors from the canister to the engine intake with the isolation valve closed while simultaneously detecting a leak in the fuel system.

19. The system of claim 18, wherein detecting a leak in the fuel system includes indicating a fuel tank leak when a rate of decrease in the fuel tank vacuum level is higher than a threshold rate.

20. The system of claim 18, wherein the control system includes further instructions for,

determining an initial purge flow rate of the purging with the isolation valve open based on engine speed, engine load, and canister load;

and

increasing the purge flow rate of the purging with the isolation valve open in response to the estimated fuel tank vacuum level being lower than the threshold level.