Method and system for fuel system control

• US 9,027,533 B2
• Filed: 07/26/2012
• Issued: 05/12/2015
• Est. Priority Date: 07/26/2012
• Status: Active Grant

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Pifher, Kenneth L., Peters, Mark W.
• Primary Examiner(s): Gimie, Mahmoud
• Application Number:
  US13/559,455
• Publication Number:
  US 20140026866A1
• Time in Patent Office: 1,020 Days
• Field of Search: 123/520, 123/519, 123/518, 123/516, 123/521, 123/198.D
• US Class Current: 123/520
• CPC Class Codes: B60K 15/01 Arrangement of fuel conduits chassis frame forming fluid conduit means B62D21/17
• CPC Class Codes: B60K 15/035 characterised by venting means
• CPC Class Codes: B60W 20/00 Control systems specially adapted for hybrid vehicles hybrid vehicle design, B60K6/00; electric vehicles B60L
• CPC Class Codes: B60Y 2200/92 Hybrid vehicles
• CPC Class Codes: F02D 41/0032 Controlling the purging of the canister as a function of the engine operating conditions
• CPC Class Codes: F02D 41/0035 to achieve a special effect, e.g. to warm up the catalyst
• CPC Class Codes: F02D 41/004 Control of the valve or purge actuator, e.g. duty cycle, closed loop control of position
• 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 33/02 for collecting and returning condensed fuel apparatus for re-atomising condensed fuel F02M29/00
• CPC Class Codes: Y10T 137/0396 Involving pressure control

Abstract

Methods and systems are provided for controlling a fuel system in a hybrid vehicle. Before canister purging is stopped by closing a purge valve, a canister vent valve is closed to hold fuel tank vacuum. Then, during a subsequent canister purge, the purge valve is opened before opening the vent valve, allowing canister purge to initiate under fuel tank vacuum conditions.

Claims

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

purging hydrocarbons from a canister to an engine intake with a vent valve and a purge valve open; and

selectively closing the vent valve while the purge valve remains open and before purge is triggered to stop responsive to fuel tank pressure being lower than a threshold pressure during engine operation.

2. The method of claim 1, wherein selectively closing the vent valve responsive to fuel tank pressure includes fully closing the vent valve responsive to the fuel tank pressure being below the threshold pressure.

3. The method of claim 2, further comprising, maintaining the vent valve closed until purge conditions are met.

4. The method of claim 3, wherein maintaining the vent valve closed until purge conditions are met includes maintaining the vent valve fully closed until a canister load is higher than a threshold load, and then sequentially opening the purge valve followed by the vent valve.

5. The method of claim 4, further comprising, while maintaining the vent valve closed, indicating a fuel system leak based on a change in the fuel tank pressure.

6. The method of claim 5, wherein indicating a leak based on a change in fuel tank pressure includes indicating a leak in the fuel system responsive to the change in fuel tank pressure being faster than a threshold rate.

7. The method of claim 4, wherein the fuel system further includes a vapor blocking valve coupled between the fuel tank and the canister, and wherein the vapor blocking valve is opened responsive to purge valve opening, and closed responsive to vent valve closing.

8. The method of claim 1, wherein the vehicle is a hybrid electric vehicle.

9. A method for a hybrid vehicle fuel system, comprising:

responsive to canister load being above a first threshold, opening a purge valve followed by a vent valve to purge hydrocarbons stored in a canister to an engine intake; and

responsive to canister load falling below the first threshold before purge is triggered to stop, closing the vent valve while maintaining the purge valve open to hold vacuum in a fuel tank.

10. The method of claim 9, further comprising, responsive to canister load falling below a second threshold lower than the first threshold, triggering the purge to stop by closing the purge valve.

11. The method of claim 10, wherein closing the vent valve includes fully closing the vent valve and wherein closing the purge valve includes fully closing the purge valve.

12. The method of claim 11, further comprising, maintaining the purge valve and the vent valve closed until purging conditions are met, and then sequentially opening the purge valve followed by the vent valve.

13. The method of claim 12, further comprising, while maintaining the purge valve and the vent valve closed, indicating fuel system degradation based on a rate of change in fuel tank vacuum.

14. The method of claim 13, wherein the indication includes indicating fuel system degradation based on the rate of bleed-up in fuel tank vacuum to barometric pressure being faster than a threshold rate.

15. The method of claim 12, wherein the fuel system further includes a vapor blocking valve coupled between the fuel tank and the canister, further comprising, responsive to canister load being above the first threshold, opening the vapor blocking valve after opening the purge valve, and responsive to canister load falling below the first threshold, closing the vapor blocking valve after closing the vent valve.

16. A vehicle fuel system, comprising:

an engine including an intake;

a fuel tank coupled to the engine intake via a canister, a vent valve, and a purge valve;

a pressure sensor coupled to the fuel tank for estimating a fuel tank vacuum; and

a control system with computer readable instructions for,

in response to purge conditions being met,

opening the purge valve followed by the vent valve to purge canister hydrocarbons to the engine intake while drawing vacuum into the fuel tank; and

during purging,

selectively closing the vent valve responsive to fuel tank vacuum being higher than a threshold to hold vacuum in the fuel tank.

17. The fuel system of claim 16, wherein the control system includes further instructions for, after selectively closing the vent valve, selectively closing the purge valve responsive to a canister load being lower than a threshold.

18. The fuel system of claim 17, wherein the control system includes further instructions for maintaining the vent valve and the purge valve closed until purge conditions are met again.

19. The fuel system of claim 18, wherein the control system includes further instructions for, while maintaining the vent valve and the purge valve closed, monitoring a rate of change in fuel tank vacuum, and indicating fuel system degradation in response to the rate of change in fuel tank vacuum being higher than a threshold rate.

20. The fuel system of claim 18, further comprising a vapor blocking valve coupled between the fuel tank and the canister, wherein the control system includes further instructions for, opening the vapor blocking valve after opening the purge valve and the vent valve when purge conditions are met, and closing the vapor blocking valve after closing the purge valve and the vent valve when canister load is lower than the threshold.