METHOD AND SYSTEM FOR FUEL VAPOR CONTROL

• US 20140074385A1
• Filed: 09/12/2012
• Published: 03/13/2014
• Est. Priority Date: 09/12/2012
• 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., Jentz, Robert Roy, Bohr, Scott A., Kragh, Niels Christopher
• Granted Patent: US 9,026,345 B2
• Time in Patent Office: Days
• US Class Current: 701/113
• CPC Class Codes: F02M 25/0818 having means for pressurising the evaporative emission space

Abstract

Methods and systems are provided for performing a vehicle-off fuel system leak test. A vehicle controller may be woken up after a vehicle has been in a key-off condition for a sufficient amount of time to monitor a fuel tank for pressure and temperature stabilization. If the pressure and temperature of the fuel tank is stable, a fuel pump may be operated to raise a fuel tank vapor pressure, and fuel system leaks are identified based on a rate of pressure decay from the fuel tank.

Claims

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

during a vehicle-off condition, and while a fuel tank temperature stays within a threshold range,

operating a fuel pump to raise a fuel tank vapor pressure to identify leaks in the fuel system.

2. The method of claim 1, wherein operating the fuel pump to raise a fuel vapor pressure includes operating the fuel pump for a duration to raise the vapor pressure above a threshold pressure.

3. The method of claim 2, wherein the duration of operating the fuel pump is based on a fill level of fuel in the fuel tank.

4. The method of claim 2, further comprising, indicating a fuel system leak based on a change in fuel tank pressure after the duration and while the fuel tank temperature stays within the range.

5. The method of claim 4, wherein the indicating includes indicating a fuel system leak in response to a change in fuel tank pressure after the duration being above a threshold, the threshold adjusted based on a fuel tank temperature.

6. The method of claim 5, wherein a vehicle controller is set to a sleep mode in response to an onset of the vehicle-off condition, and wherein operating the fuel pump during the vehicle-off condition further includes waking up the fuel system controller from the sleep mode upon elapse of a first duration since the onset of the vehicle-off condition, sealing the fuel tank, and monitoring the fuel tank temperature for a second duration since the waking up, the first duration longer than the second duration.

7. The method of claim 6, further comprising, in response to the fuel tank temperature going outside the threshold range, not operating the fuel pump to identify leaks in the fuel system.

8. The method of claim 7, further comprising, in response to an automatic engine-on event during the vehicle-off condition, operating the fuel pump and aborting the identifying of leaks in the fuel system.

9. The method of claim 8, wherein the automatic engine-on event includes the engine being turned on automatically, and without input from a vehicle operator.

10. The method of claim 9, wherein the automatic engine-on event includes an automatic engine restart from idle-stop.

11. The method of claim 1, wherein the vehicle-off condition includes a key-off condition where the vehicle includes an active key, a stop button actuated condition where the vehicle includes an ignition start/stop button, and a passive key being outside a threshold distance of the vehicle where the vehicle includes a passive key.

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

monitoring a fuel tank pressure after a vehicle-off event; and

in response to a change in fuel tank pressure during the monitoring being less than a threshold,

sealing the fuel system and operating a fuel pump to raise fuel tank pressure to a threshold pressure; and

indicating fuel system leaks based on a rate of bleed-down from the threshold pressure.

13. The method of claim 12, wherein the indicating includes indicating a fuel system leak based on the rate of bleed-down from the threshold pressure being faster than a threshold rate, the threshold rate based on one or more of a fuel tank temperature, a fuel level in the fuel tank, altitude, and fuel type.

14. The method of claim 13, wherein the fuel system includes a fuel tank coupled to a canister, the canister coupled to an engine intake via a canister purge valve and further coupled to atmosphere via a canister vent valve, and wherein sealing the fuel system includes closing each of the canister vent valve and canister purge valve.

15. The method of claim 14, wherein the threshold pressure is based on one or more of a vapor pressure of fuel vapors in a vapor space of the fuel tank and a fill level of the fuel tank.

16. The method of claim 15, wherein the vehicle fuel system includes a controller that is shifted to a sleep mode in response to the vehicle-off event, and wherein monitoring a fuel tank pressure after a vehicle-off event includes, waking up the controller from the sleep mode after a first duration since the vehicle-off event and monitoring the fuel tank pressure for a second duration after the waking, the second duration being shorter than the first duration.

17. The method of claim 16, further comprising,

in response to the change in fuel tank pressure being more than the threshold, re-monitoring the fuel tank pressure for the second duration, and in response to the change on fuel tank pressure during the re-monitoring being less than the threshold, sealing the fuel system and operating the fuel pump to identify fuel system leaks.

18. A vehicle system, comprising:

an engine including an intake;

a fuel system including a fuel tank, a canister, a first valve coupling the canister to the engine intake, a second valve coupling the canister to atmosphere, and a fuel pump coupled to the fuel tank;

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

a control system with computer readable instructions for;

waking up from a sleep mode following a duration since a vehicle-off event;

monitoring a fuel tank pressure after the waking up; and

if the fuel tank pressure stays within a threshold range during the monitoring,

closing the first and second valves to seal the fuel tank;

operating the fuel pump to raise a fuel tank pressure;

discontinuing fuel pump operation when fuel tank pressure is at a threshold pressure; and

indicating fuel system leaks based on a rate of pressure bleed-down from the threshold pressure.

19. The system of claim 18, wherein the controller includes further instructions for not operating the fuel pump and not indicating fuel system leaks in response to one of the fuel tank pressure not staying within the threshold range during the monitoring and the engine being turned on automatically, and without input from a vehicle operator, during the monitoring.

20. The system of claim 18, wherein the indicating includes indicating a fuel system leak based on the rate of pressure bleed-down from the threshold pressure being faster than a threshold rate, one or more of the threshold pressure and the threshold rate based on a fuel tank temperature.