FUEL SYSTEM DIAGNOSTICS

• US 20160290286A1
• Filed: 03/30/2015
• Published: 10/06/2016
• Est. Priority Date: 03/30/2015
• 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, Robert Jr.
• Granted Patent: US 9,771,899 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: F02M 25/0809 Judging failure of purge control system
• CPC Class Codes: F02M 25/0836 Arrangement of valves controlling the admission of fuel vapour to an engine, e.g. valve being disposed between fuel tank or absorption canister and intake manifold
• CPC Class Codes: F02M 25/089 Layout of the fuel vapour installation

Abstract

Methods and systems are provided for detecting a fuel tank oil-canning event during conditions when a vacuum is applied to the fuel tank, such as during a fuel system leak test or during purging of a fuel system canister. In one example, a method may include comparing the fuel tank pressure changes during a leak test to changes in fuel tank temperature or fill level and indicating fuel tank oil-canning in response to a higher than threshold rise in fuel tank pressure during or following application of vacuum to the fuel tank while each of a fuel temperature and fill level remain unchanged. By detecting fuel tank oil-canning accurately, appropriate countermeasures can be taken.

Claims

1. A method for a fuel system, comprising:

indicating fuel tank oil-canning responsive to a higher than threshold rise in fuel tank pressure during or following application of vacuum to a fuel tank while each of a fuel temperature and fill level remain within a range.

2. The method of claim 1, further comprising, in response to the indication of fuel tank oil-canning, discontinuing the application of vacuum and immediately venting the fuel tank to atmosphere.

3. The method of claim 2, further comprising, in response to no indication of fuel tank oil-canning, maintaining the fuel tank sealed.

4. The method of claim 2, wherein during application of vacuum to the fuel tank includes during purging of fuel vapors from a fuel system canister to an engine intake manifold using engine intake vacuum.

5. The method of claim 4, wherein the purging includes opening a canister purge valve coupled between the fuel system canister and the engine intake manifold, and wherein the threshold is based on a degree of opening of the canister purge valve.

6. The method of claim 2, wherein during or following application of vacuum to the fuel tank includes during a fuel system leak detection routine wherein engine intake vacuum is applied to the fuel tank until a target fuel tank vacuum is reached.

7. The method of claim 6, wherein the threshold is based on the target fuel tank vacuum.

8. The method of claim 1, further comprising, indicating the fuel temperature is within a range based on output from a temperature sensor coupled to the fuel tank.

9. The method of claim 8, further comprising, indicating the fill level is within a range based on an estimation of fuel slosh, the estimation based on output from one or more of a fill level sensor and a vehicle motion sensor.

10. The method of claim 1, wherein the indicating includes setting a diagnostic code.

11. A method for an engine, comprising:

sealing a fuel tank after pulling down fuel tank pressure to a threshold vacuum; and

responsive to one or more of a drop in fuel tank pressure below the threshold vacuum and a higher than threshold rise in fuel tank pressure after the sealing, while each of a fuel temperature and fill level remain within a range, unsealing the fuel tank.

12. The method of claim 11, further comprising, setting a diagnostic code to indicate that the one or more of the drop in fuel tank pressure below the threshold vacuum and the higher than threshold rise in fuel tank pressure is due to fuel tank oil-canning.

13. The method of claim 11, wherein the sealing the fuel tank is responsive to fuel system leak detection conditions being met, and wherein unsealing the fuel tank includes discontinuing fuel system leak detection.

14. The method of claim 11, wherein the fuel tank is coupled to a fuel system canister, and wherein sealing the fuel tank includes closing one or more of a canister vent valve coupled between the fuel system canister and atmosphere, and a fuel tank isolation valve coupled between the fuel system canister and the fuel tank, and wherein unsealing the fuel tank includes opening the canister vent valve and the fuel tank isolation valve.

15. The method of claim 11, further comprising, responsive to neither of a drop in fuel tank pressure below the threshold vacuum and the higher than threshold rise in fuel tank pressure after the sealing, maintaining the fuel tank sealed and estimating a fuel system leak based on a rate of vacuum decay.

16. A fuel system, comprising:

an engine receiving fuel from a fuel tank;

a canister for storing fuel tank fuel vapors;

a canister vent valve (CVV) in a vent line coupling the canister to atmosphere;

a canister purge valve (CPV) in a purge line coupling the canister to the engine;

a vehicle motion sensor;

a fuel level sensor coupled to the fuel tank for estimating a fill level of the tank;

a temperature sensor coupled to the fuel tank for estimating a temperature of the tank; and

a controller with computer readable instructions stored on non-transitory memory for;

pulling down fuel tank pressure to a threshold pressure by opening the CPV and applying engine vacuum to the fuel tank;

after vacuum pull-down, sealing the fuel system; and

responsive to a higher than threshold rise in fuel tank pressure while each of a temperature and fill level of the fuel tank remain within a range, unsealing the fuel system and aborting a fuel system leak test.

17. The system of claim 16, wherein the controller includes further instructions for:

indicating fuel tank oil-canning responsive to the higher than threshold rise in fuel tank pressure while one or more of the temperature and fill level of the fuel tank remain within the range.

18. The system of claim 16, wherein the controller includes further instructions for:

responsive to the higher than threshold rise in fuel tank pressure while one or more of the temperature and fill level of the fuel tank fall outside the range, indicating no fuel tank oil-canning, unsealing the fuel system and aborting the fuel system leak test.

19. The system of claim 16, wherein the controller includes further instructions for:

responsive to a lower than threshold rise in fuel tank pressure, maintaining the fuel system sealed and indicating a fuel system leak based on a rate of vacuum decay being higher than a threshold rate.

20. The system of claim 16, wherein sealing the fuel system includes closing one or more of a canister vent valve coupled between the canister and atmosphere, and a fuel tank isolation valve coupled between the fuel system canister and the fuel tank, and wherein unsealing the fuel system responsive to the higher than threshold rise in fuel tank pressure includes opening the canister vent valve and the fuel tank isolation valve to vent the fuel tank.