FUEL SYSTEM DIAGNOSTICS

• US 20140069394A1
• Filed: 09/11/2012
• Published: 03/13/2014
• Est. Priority Date: 09/11/2012
• Status: Active Grant

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Jentz, Robert Roy, Peters, Mark W., Casedy, Michael, Dudar, Aed M.
• Granted Patent: US 9,243,591 B2
• Time in Patent Office: Days
• US Class Current: 123/520
• CPC Class Codes: F02M 25/0809 Judging failure of purge control system

Abstract

Methods and system are provided for identifying unintended closing (or corking) of a mechanical valve coupled to a fuel tank. If tank vent valve corking is identified during a leak test, fuel tank pressure data collected during the leak test is disregarded and not used to determine a fuel system leak. Instead, a fuel system leak test is repeated to improve reliability of test results.

Claims

1. A method for a vehicle fuel system, comprising:

during a fuel system leak test, and in response to unintended temporary closing of a mechanical valve coupled to a fuel tank, not completing the fuel system leak test.

2. The method of claim 1, wherein the fuel system leak test includes,

closing a vent valve coupled between the fuel system canister and atmosphere;

opening a purge valve coupled between a fuel system canister and an engine intake;

applying engine intake vacuum to the fuel tank with the mechanical valve open; and

following the applying, isolating the fuel tank by closing the purge valve with the mechanical valve still open, monitoring a vacuum bleed-up in the fuel tank, and indicating a fuel system leak based on a rate of vacuum bleed-up.

3. The method of claim 2, wherein an identification of unintended temporary closing of the mechanical valve is based on one or more inflections in fuel tank pressure during the applying of vacuum to the fuel tank, or one or more inflections in fuel tank pressure during the vacuum bleed-up.

4. The method of claim 3, wherein the identification is further based on a rate of vacuum pull-down during the applying of vacuum to the fuel tank and a rate of vacuum bleed-up during the isolating the fuel tank.

5. The method of claim 4, wherein the identification includes indicating unintended temporary closing of the mechanical valve during the applying of vacuum to the fuel tank based on the rate of vacuum pull-down in the fuel tank being higher than a first threshold rate, and indicating unintended temporary closing of the mechanical valve during the isolating the fuel tank based on the rate of vacuum bleed-up in the fuel tank being higher than a second, different threshold rate.

6. The method of claim 5, wherein the identification further includes, indicating re-opening of the temporarily closed mechanical valve during the applying of vacuum based on a change in the rate of vacuum pull-down, and indicating re-opening of the temporarily closed mechanical valve during the isolating the fuel tank based on a change in the rate of vacuum bleed-up.

7. The method of claim 2, wherein not completing the fuel system leak test includes closing the purge valve, opening the vent valve;

and resuming fuel system settings from before the leak test was initiated, and not indicating a fuel system leak based on the rate of vacuum bleed-up during the monitoring.

8. The method of claim 7, further comprising, after resuming fuel system settings, re-opening the purge valve, re-closing the canister vent valve, re-applying engine intake vacuum to the fuel tank with the mechanical valve open, following the re-application, re-isolating the fuel tank by closing the purge valve with the mechanical valve still open, re-monitoring the vacuum bleed-up, and in response to no unintended temporary closing of the mechanical valve, indicating a fuel system leak based on the rate of vacuum bleed-up during the re-monitoring.

9. The method of claim 1, wherein the fuel system leak test is performed while the vehicle is moving, and the unintended temporary closing of the mechanical valve is caused by sources external to the fuel system including vehicle maneuvers performed while the vehicle is moving.

10. The method of claim 9, wherein the vehicle maneuvers include vehicle turns at vehicle speeds higher than a threshold speed, vehicle turns at higher than a threshold turn speed, vehicle travel along an incline that is higher than a threshold grade, and vehicle travel along a track having a lower than threshold smoothness.

11. A method for a vehicle fuel system, comprising:

opening a purge valve use engine intake vacuum to pull down fuel tank;

in response to a pressure inflection during a first vacuum pull-down, closing the purge valve, releasing vacuum from the fuel tank, and not identifying fuel system leaks based on a first fuel tank vacuum bleed-up immediately following the first vacuum pull-down; and

in response to no pressure inflection during a second vacuum pull-down, closing the purge valve to isolate the fuel tank, and identifying fuel system leaks based on a second fuel tank vacuum bleed-up immediately following the second vacuum pull-down.

12. The method of claim 11, further comprising, in response to the pressure inflection during the first vacuum pull-down, and after the first fuel tank vacuum bleed-up, opening the purge valve to apply engine intake vacuum to the fuel tank during a third vacuum pull-down, and after the third vacuum pull-down, closing the purge valve to isolate the fuel tank, and in response to no pressure inflection during any discrete number of vacuum pull down, identifying fuel system leaks based on vacuum bleed-up immediately following the variable number of vacuum pull-down.

13. The method of claim 12, further comprising, in response to the pressure inflection during the first vacuum pull-down, indicating unintended temporary closing of a mechanical vent valve coupled to the fuel tank.

14. A method for a fuel system coupled to a vehicle engine, comprising:

opening a purge valve to pull down engine intake vacuum in a fuel tank;

after applying the vacuum, closing the purge valve to isolate the fuel tank and release vacuum;

in response to a pressure inflection during a first vacuum bleed-up, not identifying fuel system leaks based on the first vacuum bleed-up; and

in response to no pressure inflection during a second vacuum bleed-up, identifying fuel system leaks based on the second vacuum bleed-up.

15. The method of claim 14, further comprising, in response to the pressure inflection during the first vacuum bleed-up, and after releasing the vacuum, re-opening the purge valve to pull down engine intake vacuum in the fuel tank, after the vacuum pull-down, closing the purge valve to re-isolate the fuel tank, and in response to no pressure inflection during the vacuum pull-down, identifying fuel system leaks based on a third vacuum bleed-up immediately following the vacuum pull-down.

16. The method of claim 15, further comprising, in response to the pressure inflection during the first vacuum bleed-up, indicating unintended temporary closing of a mechanical vent valve coupled to the fuel tank.

17. A vehicle fuel system, comprising:

an engine including an intake manifold;

a fuel tank coupled to the intake manifold via a canister, the fuel tank including a mechanical vent valve;

a purge valve coupled between the intake manifold and the canister and configured to enable an intake manifold vacuum to be applied on the fuel tank via the canister;

a canister vent valve coupled to the canister and configured to isolate the fuel system from atmosphere; and

a controller with computer readable instructions for,

closing the canister vent valve;

opening the purge valve with the mechanical vent valve assumed open to pull down a threshold amount of intake manifold vacuum on the fuel tank;

after vacuum pull-down, closing the purge valve to bleed-up vacuum from the fuel tank;

in response to a pressure inflection during the vacuum pull-down, indicating unintended temporary closing of the mechanical vent valve and not identifying a fuel system leak based on the vacuum bleed-up; and

in response to no pressure inflection during the vacuum pull-down, identifying a fuel system leak based on the vacuum bleed-up.

18. The system of claim 17, wherein not identifying a fuel system leak based on the vacuum bleed-up includes disregarding data from the vacuum bleed-up, closing the purge valve, and resuming fuel system settings from before the vacuum pull-down.

19. The system of claim 18, further comprising, after resuming fuel system settings, re-opening the purge valve to reapply the threshold amount of intake manifold vacuum on the fuel tank, re-closing the canister vent valve and in response to no pressure inflection during the vacuum reapplication, closing the purge valve to bleed-up vacuum from the fuel tank, and identifying a fuel system leak based on the vacuum bleed-up following the vacuum reapplication.

20. The system of claim 19, wherein indicating unintended temporary closing of the mechanical vent valve includes indicating temporary closing of the vent valve due to a vehicle maneuver.