FUEL SYSTEM LEAK CHECK BASED ON FUEL REID VAPOR PRESSURE

• US 20150114089A1
• Filed: 10/31/2013
• Published: 04/30/2015
• Est. Priority Date: 10/31/2013
• Status: Active Grant

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Dudar, Aed M., Yang, Dennis Seung-Man, Ognjanovski, Rob Jr.
• Granted Patent: US 9,458,801 B2
• Time in Patent Office: Days
• US Class Current: 73/40
• CPC Class Codes: F02D 2200/0611 Fuel type, fuel composition or fuel quality
• CPC Class Codes: F02D 41/0045 Estimating, calculating or determining the purging rate, amount, flow or concentration
• CPC Class Codes: F02M 25/0809 Judging failure of purge control system

Abstract

A method for an evaporative emissions leak test, comprising: adjusting a pressure threshold based on a fuel volatility of a fuel contained in a fuel tank; and performing the evaporative emissions leak test based on the adjusted pressure threshold. By determining fuel volatility and adjusting a pressure threshold based on the fuel volatility, a more robust and accurate evaporative emissions leak test may be employed without adding additional components to a fuel system.

Claims

1. A method for an evaporative emissions leak test, comprising:

adjusting a pressure threshold based on a fuel volatility of a fuel contained in a fuel tank; and

performing the evaporative emissions leak test based on the adjusted pressure threshold.

2. The method of claim 1, where the fuel volatility is determined by:

venting fuel vapor from the fuel tank to a fuel vapor canister; and

determining a hydrocarbon percentage of the vented fuel vapor with a hydrocarbon sensor coupled between the fuel tank and the fuel vapor canister.

3. The method of claim 2, further comprising:

determining a fuel Reid Vapor Pressure based on the determined hydrocarbon percentage of the vented fuel vapor.

4. The method of claim 1, where the evaporative emissions leak test is an engine-off natural vacuum test, and where performing the evaporative emissions leak test further includes indicating degradation based on comparing a fuel tank pressure to the adjusted pressure threshold.

5. The method of claim 4, where the adjusted pressure threshold is a threshold for a fuel tank pressure rise portion of the engine-off natural vacuum test.

6. The method of claim 5, further comprising:

responsive to the fuel tank pressure being less than the adjusted pressure threshold following the fuel tank pressure rise portion of the engine-off natural vacuum test, performing a vacuum portion of the engine-off natural vacuum test.

7. The method of claim 6, further comprising:

responsive to a fuel tank vacuum being less than a vacuum threshold following the vacuum portion of the engine-off natural vacuum test, indicating an evaporative emissions system leak.

8. The method of claim 1, where the evaporative emissions leak test is an evaporative leak check module based test.

9. The method of claim 8, further comprising:

isolating an evaporative leak check module from the fuel tank;

activating a vacuum pump comprising the evaporative leak check module;

drawing a vacuum across a reference orifice; and

setting a pressure threshold based on the vacuum drawn across the reference orifice.

10. The method of claim 9, further comprising:

coupling the evaporative leak check module to the fuel tank;

activating the vacuum pump; and

drawing a vacuum on the fuel tank.

11. The method of claim 10, further comprising:

responsive to a fuel tank pressure being greater than the adjusted pressure threshold, indicating an evaporative emissions system leak.

12. A method for an evaporative emissions system leak test, comprising:

determining a reference vacuum threshold;

venting fuel vapor from a fuel tank;

determining a fuel Reid Vapor Pressure of the fuel vapor;

adjusting the reference vacuum threshold based on the fuel Reid Vapor Pressure;

drawing a vacuum on a fuel tank with an evaporative leak check module; and

indicating degradation of the evaporative emissions system based on the adjusted reference vacuum threshold.

13. The method of claim 12, where determining the reference vacuum threshold further comprises:

isolating an evaporative leak check module from the fuel tank;

activating a vacuum pump comprising the evaporative leak check module;

drawing a vacuum across a reference orifice; and

determining a reference vacuum in the evaporative leak check module.

14. The method of claim 13, where determining a fuel Reid Vapor Pressure of the fuel vapor further comprises:

venting fuel vapor from the fuel tank to a fuel vapor canister;

determining a hydrocarbon percentage of the fuel vapor with a hydrocarbon sensor coupled between the fuel tank and the fuel vapor canister; and

determining a fuel Reid Vapor Pressure based on the hydrocarbon percentage of the fuel vapor.

15. The method of claim 14, where indicating degradation of the evaporative emissions system based on the adjusted reference vacuum threshold further comprises:

coupling the evaporative leak check module to the fuel tank;

activating the vacuum pump; and

determining a resulting vacuum in the fuel tank.

16. The method of claim 15, further comprising:

indicating degradation of the evaporative emissions system if the resulting vacuum in the fuel tank is less than the adjusted reference vacuum threshold.

17. A method for an evaporative emissions system leak test, comprising:

responsive to an engine off condition, closing a canister vent valve;

determining a resulting pressure of a fuel tank;

determining a Reid Vapor Pressure of a fuel in the fuel tank;

determining a threshold pressure based on the fuel Reid Vapor Pressure; and

comparing the resulting pressure of the fuel tank to the threshold pressure.

18. The method of claim 17, where determining a Reid Vapor Pressure of a fuel in the fuel tank further comprises:

opening the canister vent valve;

determining a hydrocarbon percentage of a fuel vapor in the fuel tank; and

determining the Reid Vapor Pressure of the fuel in the fuel tank based on the hydrocarbon percentage of the fuel vapor.

19. The method of claim 17, further comprising:

responsive to the resulting pressure of the fuel tank being greater than the threshold pressure, indicating no degradation of the fuel tank.

20. The method of claim 19, further comprising:

responsive to the resulting pressure of the fuel tank being less than the threshold pressure, closing the canister vent valve; and

comparing a resulting fuel tank vacuum to a vacuum threshold.