Method and system for estimating fuel vapor pressure

• US 5,878,727 A
• Filed: 06/02/1997
• Issued: 03/09/1999
• Est. Priority Date: 06/02/1997
• Status: Expired due to Fees

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Huls, Thomas Allan
• Primary Examiner(s): Moulis, Thomas N.
• Application Number:
  US08/867,313
• Time in Patent Office: 645 Days
• Field of Search: 123/516, 123/518, 123/519, 123/520, 123/198 D, 73/117.3, 73/118.1, 73/119 A
• US Class Current: 123/520
• CPC Class Codes: F02D 41/003 Adding fuel vapours, e.g. drawn from engine fuel reservoir
• CPC Class Codes: F02D 41/28 Interface circuits
• CPC Class Codes: F02M 25/0809 Judging failure of purge control system

Abstract

A method for estimating fuel vapor pressure includes determining (102) an amount of fuel present in a fuel tank, pumping (104) a vapor mixture from the fuel tank until a predetermined gauge pressure is obtained, and measuring (108) the time necessary to reach the predetermined gauge pressure. Fuel vapor pressure is than directly quantified (108) based on the measured time and the detected fill level. Thus, an estimate of the fuel vapor pressure can be obtained without requiring information regarding fuel temperature, or addition of any dedicated sensor circuitry to a conventional on-board vapor management/leak detection system.

Claims

1. A method for estimating fuel vapor pressure comprising the steps of:

determining an amount of liquid fuel present in a fuel tank;

applying a vacuum to the fuel tank;

measuring a length of time necessary to reach a predetermined pressure within the fuel tank; and

determining fuel vapor pressure based on the measured length of time and the detected amount of liquid fuel.

2. The method of claim 1 further comprising the steps of detecting a temperature of the fuel, and estimating effective fuel volatility based on the detected temperature and the determined fuel vapor pressure.

3. The method of claim 1 further comprising the steps of comparing the measured length of time to a time threshold value, and validating results of a fuel vapor system leak testing procedure if the time threshold is not exceeded.

4. The method of claim 3 further comprising the steps of comparing the amount of fuel present in the fuel tank to a fill level threshold value, and validating the results of the vapor leak testing procedure if the fill level threshold value is exceeded.

5. The method of claim 1 further comprising the steps of comparing the estimated fuel vapor pressure to a vapor pressure threshold value, and validating results of a fuel vapor system leak testing procedure if the vapor pressure threshold is not exceeded.

6. The method of claim 5 further comprising the steps of comparing the amount of fuel present in the fuel tank to a fill level threshold value, and validating the results of the vapor leak testing procedure if the fill level threshold value is exceeded.

7. The method of claim 1 wherein said step of applying a vacuum is performed during an evacuation phase of an on-board fuel vapor leak testing process.

8. A system for estimating fuel vapor pressure comprises:

a first sensor connected to a fuel tank for providing an output indicative of an amount of liquid fuel present in the tank;

means for applying a vacuum to the fuel tank;

a second sensor connected to the tank for providing an output indicative of pressure within the tank;

a processor connected to said first and second sensor, said processor including means for comparing the output of said second sensor to a predetermined pressure value; and

a timer connected to said processor for measuring a length of time necessary for the output of said second sensor to reach the predetermined pressure value, wherein said processor determines fuel vapor pressure based on the measured length of time and the amount of liquid fuel present in the tank.

9. The system of claim 8 further comprising a third sensor connected to the tank for providing an output indicative of liquid fuel temperature, wherein said processor is responsive to the output of said third sensor for estimating effective fuel volatility based on fuel temperature and the determined fuel vapor pressure.

10. The system of claim 8 further comprising means for comparing the measured length of time to a time threshold value, wherein said processor validates results of a fuel vapor system leak testing procedure if the time threshold is not exceeded.

11. The system of claim 10 further comprising means for comparing the amount of liquid fuel to a fill level threshold value, wherein said processor validates the results of the vapor leak testing procedure if the fill level threshold value is exceeded.

12. The system of claim 8 further comprising means for comparing the estimated fuel vapor pressure to a vapor pressure threshold value, wherein said processor validates results of a fuel vapor system leak testing procedure if the vapor pressure threshold is not exceeded.

13. The system of claim 12 further comprising means for comparing the amount of liquid fuel to a fill level threshold value, wherein said processor validates the results of the vapor leak testing procedure if the fill level threshold value is exceeded.

14. A method for validating test results of a vapor leak test procedure comprises the steps of:

determining an amount of liquid fuel present in a fuel tank;

applying a vacuum to the fuel tank;

measuring a length of time necessary to reach a predetermined pressure within the fuel tank;

comparing the measured length of time to a time threshold value; and

validating the fuel vapor system leak testing procedure results if the time threshold value is not exceeded.

15. The method of claim 14 further comprising the steps of comparing the amount of fuel present in the fuel tank to a fill level threshold value, and validating the results of the vapor leak testing procedure if the fill level threshold value is exceeded.

16. The method of claim 14 wherein said step of applying a vacuum is performed during an evacuation phase of the fuel vapor leak testing process.