Systems and methods for fuel tank grade vent valve diagnostics

1. A method comprising:

predicting an upcoming fuel slosh event in a fuel tank positioned in a fuel system of a vehicle;

sealing the fuel system within a threshold duration of the upcoming fuel slosh event; and

diagnosing a first or a second grade vent valve coupled to the fuel tank as a function of a fuel level in the fuel tank and a pressure monitored in the fuel system during the fuel slosh event.

2. The method of claim 1 , further comprising diagnosing the first grade vent valve under conditions where the fuel level in the fuel tank is lower than a first fuel level threshold but greater than a second fuel level threshold; and

diagnosing the second grade vent valve under conditions where the fuel level in the fuel tank is greater than or equal to the first fuel level threshold.

3. The method of claim 1 , wherein the fuel slosh event results in a fuel wave traveling first in a direction towards the second grade vent valve and away from the first grade vent valve, and subsequently in a direction away from the second grade vent valve and towards the first grade vent valve.

4. The method of claim 1 , wherein the fuel tank is of a non-uniform height; and

wherein the first grade vent valve is at a lower height and wherein the second grade vent valve is at a greater height with respect to a maximal height of the fuel tank; and

wherein a fuel limit vent valve is positioned at an intermediate height with respect to the first grade vent valve and the second grade vent valve.

5. The method of claim 1 , further comprising:

indicating the second grade vent valve is stuck closed in response to the pressure remaining substantially constant during the fuel slosh event;

indicating the second grade vent valve is functioning as desired or expected in response to the pressure increasing and then decreasing with an absence of a zero pressure reading during the fuel slosh event; and

indicating the second grade vent valve is stuck open in response to the zero pressure reading during the fuel slosh event.

6. The method of claim 1 , further comprising:

indicating the first grade vent valve is stuck closed in response to the pressure increasing and then decreasing during the fuel slosh event; and

indicating the first grade vent valve is functioning as desired or expected in response to the pressure remaining substantially constant during the fuel slosh event.

7. The method of claim 1 , wherein the first grade vent valve is submerged in fuel throughout the fuel slosh event when diagnosing the second grade vent valve; and

wherein the first grade vent valve becomes transiently unsubmerged and then resubmerged in fuel during the fuel slosh event when diagnosing the first grade vent valve.

8. The method of claim 1 , wherein the second grade vent valve becomes transiently submerged in liquid fuel during the fuel slosh event when diagnosing the first grade vent valve and the second grade vent valve.

9. The method of claim 1 , wherein predicting the upcoming fuel slosh event is a function of an orientation of the fuel tank with respect to the vehicle.

10. The method of claim 1 , wherein predicting the upcoming fuel slosh event is based on one or more of information retrieved from an onboard navigation system, information provided as a result of route-learning methodology, information retrieved from a smart traffic system, and information related to driving patterns of nearby vehicles as retrieved via vehicle-to-vehicle communications.

11. The method of claim 1 , wherein sealing the fuel system within the threshold duration of the upcoming fuel slosh event further comprises:

establishing a predetermined negative pressure with respect to atmospheric pressure in the fuel system.

12. The method of claim 1 , further comprising:

in response to an indication of degradation of either the first grade vent valve or the second grade vent valve, taking mitigating action that includes providing requests to either a vehicle operator or an autonomous control system of the vehicle to avoid specified parking situations which may lead to one or more of undesirable pressure increases in the fuel system and/or liquid fuel entering into one or more lines that couple the fuel system to an evaporative emissions control system.

13. A method comprising:

predicting in advance a fuel slosh event in a fuel tank positioned in a fuel system of a vehicle, the fuel slosh event inferred to result in a fuel wave traveling towards a second, higher elevation grade vent valve with respect to a maximal height of the fuel tank and away from a first, lower elevation grade vent valve, and then traveling away from the second grade vent valve and towards the first grade vent valve;

trapping a predetermined negative pressure with respect to atmospheric pressure in the fuel system within a threshold duration of the fuel slosh event occurring;

monitoring a pressure in the fuel system during the fuel slosh event; and

indicating, based on the pressure monitored in the fuel system during the fuel slosh event, whether the second grade vent valve is degraded when a fuel level in the fuel tank is greater than or equal to a first fuel level threshold, or whether the first grade vent valve is degraded when the fuel level in the fuel tank is less than the first fuel level threshold but greater than a second fuel level threshold.

14. The method of claim 13 , wherein under conditions where the fuel level in the fuel tank is greater than or equal to the first fuel level threshold, the first grade vent valve remains submerged in fuel throughout the fuel slosh event; and

wherein under conditions where the fuel level in the fuel tank is less than the first fuel level threshold but greater than the second fuel level threshold, the first grade vent valve becomes transiently unsubmerged in fuel during the fuel slosh event.

15. The method of claim 13 , wherein indicating degradation of the second grade vent valve includes indicating the second grade vent valve is stuck closed in response to the pressure remaining substantially constant during the fuel slosh event, or indicating the second grade vent valve is stuck open in response to a zero pressure reading during the fuel slosh event.

16. The method of claim 13 , wherein indicating degradation of the first grade vent valve includes indicating the first grade vent valve is stuck closed in response to the pressure increasing and then decreasing during the fuel slosh event.

17. The method of claim 13 , further comprising:

in response to an indication of degradation of either the first grade vent valve or the second grade vent valve, monitoring one or more of a vehicle pitch angle, vehicle yaw angle, and vehicle roll angle during a parking condition or driving condition of the vehicle; and

providing a request to avoid situations where fuel tank pressure relief is compromised due to the degraded first grade vent valve or the second grade vent valve or that there is a likelihood of liquid fuel entering into one or more lines that couple the fuel system to an evaporative emissions control system of the vehicle.

18. A system for a vehicle, comprising:

a fuel tank positioned in a fuel system of the vehicle, the fuel tank including a first grade vent valve positioned at a lower height with respect to a maximal height of the fuel tank than a second grade vent valve, and further including a fuel level sensor for monitoring a fuel level in the fuel tank and a fuel tank pressure transducer; and

a controller with computer readable instructions stored on non-transitory memory that when executed, cause the controller to:

receive an indication of a predicted upcoming fuel slosh event inferred to result in a fuel wave traveling in a direction towards the second grade vent valve and then away from the second grade vent valve and towards the first grade vent valve;

establish a predetermined negative pressure with respect to atmospheric pressure in the fuel system within a threshold duration of the fuel slosh event occurring; and

diagnose the first grade vent valve in response to the fuel level in the fuel tank being below a first fuel level threshold but greater than a second fuel level threshold and diagnose the second grade vent valve in response to the fuel level in the fuel tank being greater than or equal to the first fuel level threshold, where diagnosing either the first grade vent valve or the second grade vent valve is based on a pressure in the fuel system monitored via the fuel tank pressure transducer during the fuel slosh event.

19. The system of claim 18 , further comprising:

an onboard navigation system; and

wherein the controller receives the prediction of the upcoming fuel slosh event based on information retrieved from the onboard navigation system related to a vehicle maneuver inferred to result in the fuel wave traveling in the direction towards the second grade vent valve and then away from the second grade vent valve and towards the first grade vent valve.

20. The system of claim 18 , further comprising:

a device for wireless communication between the controller of the vehicle and one or more smart traffic lights; and

wherein the controller receives the prediction of the upcoming fuel slosh event based on information retrieved from the one or more smart traffic lights.