SYSTEMS AND METHODS FOR ENGINE-OFF NATURAL VACUUM LEAK TESTING WITH FUEL ENABLEMENT COMPENSATION

• US 20170016795A1
• Filed: 07/15/2015
• Published: 01/19/2017
• Est. Priority Date: 07/15/2015
• 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., Mullins, John
• Granted Patent: US 10,190,934 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: F02M 25/0818 having means for pressurising the evaporative emission space
• CPC Class Codes: G01M 3/025 Details with respect to the testing of engines or engine parts
• CPC Class Codes: G01M 3/3272 for verifying the internal pressure of closed containers

Abstract

Methods and systems are provided for increasing the robustness of engine off natural vacuum testing. In one example, following an engine-off event, a heat rejection inference is determined, and further adjusted based on a fuel level and ambient temperature. In this way, an evaporative emissions system leak test may be enabled under conditions where the leak test may otherwise not be executed, thus increasing opportunities for evaporative emissions system leak detection and correspondingly reducing bleed emissions.

Claims

1. A method for an evaporative emissions system, comprising:

adjusting a threshold for an evaporative emissions leak test entry condition based on at least a fuel level;

responsive to the evaporative emissions leak test entry condition being greater than the adjusted threshold, adjusting a parameter of the evaporative emissions leak test based on the evaporative emissions leak test entry condition; and

indicating degradation based on the adjusted parameter.

2. The method of claim 1, further comprising:

adjusting the threshold for the evaporative emissions leak test entry condition based on an ambient temperature.

3. The method of claim 1, wherein the evaporative emissions leak test entry condition comprises an engine heat rejection inference during an engine run time duration.

4. The method of claim 3, wherein the engine run time duration is a total engine run time between a most recent vehicle-off event and a previous vehicle-on event.

5. The method of claim 4, where the engine heat rejection inference is based on at least an engine intake mass air flow summation between the most recent vehicle-off event and the previous vehicle-on event.

6. The method of claim 4, wherein the engine heat rejection inference is based on at least a number of miles driven between the most recent vehicle-off event and the previous vehicle-on event.

7. The method of claim 3, further comprising:

initiating the evaporative emissions leak test only when the engine heat rejection inference is greater than the adjusted threshold.

8. The method of claim 1, wherein the evaporative emissions leak test is an engine-off natural vacuum test.

9. The method of claim 8, wherein the evaporative emissions leak test parameter is a pressure rise threshold for the engine-off natural vacuum test.

10. The method of claim 8, wherein the evaporative emissions leak test parameter is a vacuum threshold for the engine-off natural vacuum test.

11. The method of claim 1, further comprising:

adjusting one or more evaporative emissions system operating parameters responsive to an indication of degradation.

12. The method of claim 10, wherein the one or more evaporative emissions system operating parameters comprise a fuel vapor canister purge schedule.

13. A method for an evaporative emissions system, comprising:

following a vehicle-off event, determining an engine heat rejection inference for an engine run time duration;

adjusting an engine heat rejection inference entry threshold based on a current fuel level and a current ambient temperature;

responsive to the engine heat rejection inference being greater than the adjusted entry threshold, adjusting one or more pressure thresholds for an engine-off natural vacuum test based on the engine heat rejection inference;

isolating the evaporative emissions system from atmosphere; and

indicating degradation of the evaporative emissions system based on the one or more adjusted pressure thresholds.

14. The method of claim 13, wherein the engine heat rejection inference is based on at least an engine intake mass air flow summation, and wherein the engine run time duration comprises an engine run time between the vehicle-off event and a previous vehicle-on event.

15. The method of claim 13, wherein adjusting an engine heat rejection inference entry threshold based on a current fuel level and current ambient temperature comprises:

decreasing the engine heat rejection inference entry threshold as fuel level decreases; and

increasing the engine heat rejection inference entry threshold as ambient temperature decreases.

16. The method of claim 13, wherein adjusting an engine heat rejection inference entry threshold comprises retrieving a 3D lookup table stored in a powertrain control module.

17. The method of claim 13, wherein adjusting one or more pressure thresholds for an engine-off natural vacuum test based on the engine heat rejection inference comprises:

indicating a difference between a measured engine heat rejection inference and an adjusted engine heat rejection inference entry threshold; and

adjusting the one or more pressure thresholds based on a magnitude of the indicated difference.

18. A vehicle system, comprising:

a fuel system isolatable from atmosphere via one or more valves;

a fuel level indicator; and

a controller configured with instructions stored in non-transitory memory, that when executed, cause the controller to;

adjust an entry threshold for an engine heat rejection inference based at least in part on a fuel level;

following a vehicle-off event, responsive to an engine heat rejection inference for a vehicle run time duration between the vehicle-off event and a previous vehicle-on event being greater than the adjusted entry threshold, adjust one or more pressure thresholds for an engine-off natural vacuum test based on the engine heat rejection inference;

isolate the fuel system from atmosphere; and

indicate degradation of the fuel system based on the one or more adjusted pressure thresholds.

19. The vehicle system of claim 18, wherein the entry threshold for the engine heat rejection inference is based at least in part on an ambient temperature.

20. The vehicle system of claim 18, wherein the controller is further configured with instructions stored in non-transitory memory, that when executed, cause the controller to:

initiate the engine-off natural vacuum test only when the engine heat rejection inference is greater than the adjusted threshold.