Systems and methods for engine-off natural vacuum leak testing

• US 10,273,907 B2
• Filed: 04/15/2015
• Issued: 04/30/2019
• Est. Priority Date: 12/30/2014
• 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., Liu, Chingpo, Yang, Dennis Seung-Man, Jentz, Robert Roy, Tseng, Fling Finn, Makki, Imad Hassan, Pearce, Russell Randall
• Primary Examiner(s): Le, Son T
• Assistant Examiner(s): Devito, Alex T
• Application Number:
  US14/687,792
• Publication Number:
  US 20160186695A1
• Time in Patent Office: 1,476 Days
• Field of Search: 73 40, 73 492, 73 497
• CPC Class Codes: F02M 25/0809 Judging failure of purge control system

Abstract

A method is provided, comprising terminating a pressure rise portion of an engine-off natural vacuum test based on an initial rate of change of a fuel system pressure upon sealing a fuel system; and initiating a vacuum portion of the engine-off natural vacuum test responsive to suspending the pressure rise portion. The initial rate of change may indicate a likelihood of the pressure rise portion reaching a pressure rise threshold. In this way, the vacuum portion of the test may be initiated earlier, increasing the likelihood of a conclusive result being obtained during a test time limit.

Claims

1. A method, comprising:

measuring a rate of change of fuel system pressure during an initial pressure rise of an engine-off natural vacuum test, wherein an initial pressure rise is a duration between a sealing of a fuel system and a pressure rise curve reaching an inflection point;

terminating a pressure rise portion of the engine-off natural vacuum test based on a positive initial rate of change of the fuel system pressure being less than a threshold; and

initiating a vacuum portion of the engine-off natural vacuum test responsive to terminating the pressure rise portion.

2. The method of claim 1, further comprising:

maintaining closed a valve coupled between a fuel tank and atmosphere for a duration of the vacuum portion of the engine-off natural vacuum test; and

following the duration of the vacuum portion of the engine-off natural vacuum test, indicating degradation of the fuel system based on a comparison of a fuel tank vacuum and a threshold.

3. The method of claim 2, wherein the threshold is adjusted based on a heat rejection index, the heat rejection index indicative of an amount of heat transferred to the fuel system during a previous drive cycle.

4. The method of claim 3, wherein the heat rejection index is based on a time-weighted driving aggressiveness index.

5. The method of claim 3, wherein the heat rejection index is based on a resistance of a heating element of a heated exhaust gas oxygen sensor coupled within an exhaust conduit proximal to one or more portions of the fuel system.

6. The method of claim 1, wherein the positive initial rate of change of the fuel system pressure is determined based on a fuel system pressure change that occurs between sealing of the fuel system by closing a valve coupled between a fuel tank and atmosphere, and a subsequent inflection point in a fuel system pressure profile as determined via a pressure sensor coupled between the fuel tank and a fuel vapor canister.

7. The method of claim 6, further comprising:

fitting the fuel system pressure profile to a polynomial;

determining a likelihood of the fuel system pressure reaching a pressure threshold within a predetermined duration; and

terminating the pressure rise portion of the engine-off natural vacuum test by coupling the fuel system to atmosphere responsive to the likelihood being less than a threshold.

8. The method of claim 7, further comprising:

continuing the pressure rise portion of the engine-off natural vacuum test by maintaining the fuel system sealed from atmosphere responsive to the likelihood being greater than the threshold.

9. A method, comprising:

adjusting an evaporative emissions leak test parameter based on a time-weighted driving aggressiveness index for an immediately previous drive cycle;

sealing a fuel system from atmosphere;

responsive to a fuel system pressure profile reaching an inflection point while fuel tank pressure is still increasing, determining a likelihood of a fuel system pressure reaching a pressure threshold;

terminating a pressure rise portion of an evaporative emissions leak test responsive to the likelihood being less than a threshold; and

indicating degradation based on the adjusted evaporative emissions leak test parameter.

10. The method of claim 9, wherein the time-weighted driving aggressiveness index is based on an engine heat rejection inference during a vehicle run time duration.

11. The method of claim 10, wherein the vehicle run time duration is a total vehicle run time between a most recent vehicle-off event and a previous vehicle-on event.

12. The method of claim 11, wherein the engine heat rejection inference is based on an engine load between the most recent vehicle-off event and the previous vehicle-on event.

13. The method of claim 12, wherein the time-weighted driving aggressiveness index weights time periods closer to the most recent vehicle-off event more than time periods closer to the previous vehicle-on event.

14. The method of claim 9, wherein the evaporative emissions leak test is an engine-off natural vacuum test.

15. The method of claim 14, wherein the evaporative emissions leak test parameter is a pressure rise threshold for the engine-off natural vacuum test.

16. The method of claim 14, wherein the evaporative emissions leak test parameter is a vacuum threshold for the engine-off natural vacuum test.

17. The method of claim 9, further comprising:

initiating the evaporative emissions leak test only when the time-weighted driving aggressiveness index is greater than a threshold and wherein the time-weighted driving aggressiveness index is based on a heat transfer model between an engine exhaust system and a fuel tank.

18. The method of claim 9, wherein the evaporative emissions leak test parameter is further adjusted based on a resistance of a heating element of a heated exhaust gas oxygen sensor coupled within an exhaust conduit, and not based on a dedicated exhaust temperature sensor.

19. A vehicle system, comprising:

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

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

adjust one or more thresholds for an engine-off natural vacuum test based on a time-weighted driving aggressiveness index;

following a vehicle-off event, isolate the fuel system from atmosphere;

based on an initial rate of change of fuel system pressure being less than a threshold, but not based on an absolute fuel system pressure, and responsive to a pressure rise curve inflection point,

terminate a pressure rise portion of the engine-off natural vacuum test; and

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

20. The vehicle system of claim 19, where the controller is configured with instructions stored in non-transitory memory, that when executed, cause the controller to:

initiate a vacuum portion of the engine-off natural vacuum test responsive to terminating the pressure rise portion of the engine-off natural vacuum test;

indicate a failing test result based on the one or more adjusted thresholds;

couple the fuel system to atmosphere;

at a subsequent vehicle-on event, confirm whether a vehicle soak greater than a threshold occurred, the vehicle soak determined based on a resistance of a heated exhaust gas oxygen sensor; and

indicate degradation of the fuel system responsive to the vehicle soak being less than the threshold.