ESTIMATING VEHICLE FUEL REID VAPOR PRESSURE

• US 20140297071A1
• Filed: 03/29/2013
• Published: 10/02/2014
• Est. Priority Date: 03/29/2013
• 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
• Granted Patent: US 9,850,853 B2
• Time in Patent Office: Days
• US Class Current: 701/22
• CPC Class Codes: F02D 19/084 Blends of gasoline and alcohols, e.g. E85
• CPC Class Codes: F02D 19/085 Control based on the fuel type or composition
• CPC Class Codes: F02D 2041/225 Leakage detection
• CPC Class Codes: F02D 2200/0606 Fuel temperature
• CPC Class Codes: F02D 2200/0612 determined by estimation
• CPC Class Codes: F02D 2200/703 Atmospheric pressure
• CPC Class Codes: F02D 41/0025 Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
• CPC Class Codes: F02D 41/042 for stopping the engine
• CPC Class Codes: F02D 41/22 Safety or indicating devices for abnormal conditions in air/fuel ratio feedback systems F02D41/1495, in electric control linkage F02D11/107, in purge control systems F02M25/0809
• CPC Class Codes: F02M 25/0809 Judging failure of purge control system
• CPC Class Codes: Y02T 10/30 Use of alternative fuels, e.g. biofuels
• CPC Class Codes: Y10S 903/93 Conjoint control of different elements

Abstract

Methods and systems are provided for estimating fuel volatility. During a vehicle-off condition following a refueling event, fuel volatility may be estimated. Based on estimated fuel volatility, fuel injection amount and leak test thresholds may be adjusted.

Claims

1. A method for an engine, comprising:

adjusting a leak test threshold for a fuel system leak test based on fuel volatility, the fuel volatility estimated during a vehicle-off condition after a refueling event while a fuel tank temperature is stable; and

indicating fuel system degradation based on the leak test.

2. The method of claim 1, wherein adjusting the leak test threshold includes increasing the threshold as the estimated fuel volatility increases.

3. The method of claim 2, wherein the vehicle-off condition after a refueling event while a fuel tank temperature is stable includes a vehicle-off condition immediately following a refueling event, wherein a change in fuel tank temperature for a first duration of the vehicle-off is within a threshold amount.

4. The method of claim 3, wherein the fuel volatility estimated during the vehicle-off condition includes, isolating a fuel tank of the fuel system, the fuel tank coupled to the engine, operating a fuel pump of the fuel system for a second duration to raise fuel tank pressure, and estimating the fuel volatility based on a peak fuel tank pressure.

5. The method of claim 4, wherein the estimated fuel volatility is further adjusted based on barometric pressure.

6. The method of claim 5, further comprising, during a vehicle-on condition following the vehicle-off condition, adjusting an engine fuel injection amount based on the estimated fuel volatility.

7. A method for an engine fuel system, comprising:

during a first vehicle-off condition following a refueling event, wherein a fuel tank temperature stays within a threshold range,

isolating a fuel tank; and

operating a fuel pump to estimate a fuel volatility.

8. The method of claim 7, wherein the first vehicle-off condition includes a vehicle key-off event immediately following the refueling event where the fuel tank temperature stays within the threshold range.

9. The method of claim 8, wherein operating the fuel pump to estimate a fuel volatility includes operating the fuel pump without operating the engine for a duration of the first vehicle-off condition to raise a fuel tank pressure above a threshold pressure, and estimating the fuel volatility based on peak pressure of the isolated fuel tank, a duration of operating the fuel pump based on one or more of a fill level of the fuel tank and the fuel tank temperature.

10. The method of claim 9, wherein the fuel system includes a fuel vapor canister coupled between the fuel tank and the engine, and wherein isolating the fuel tank includes closing a canister vent valve coupled between the canister and atmosphere, and closing a canister purge valve coupled between the canister and an engine intake.

11. The method of claim 10, wherein the estimated fuel volatility is further adjusted based on barometric pressure.

12. The method of claim 11, further comprising, during a second vehicle-off condition following the first vehicle-off condition, performing a leak test to identify fuel system degradation, a threshold of the leak test based on the estimated fuel volatility, the leak detection threshold increased as the estimated fuel volatility increases.

13. The method of claim 7, further comprising, during an engine-on condition following the first vehicle-off condition, adjusting a fuel injection amount based on the estimated fuel volatility, the injection amount decreased as the estimated fuel volatility increases.

14. The method of claim 7, wherein the engine fuel system is coupled in a hybrid vehicle system.

15. The method of claim 7, wherein the estimated fuel volatility includes an estimated fuel Reid Vapor Pressure (RVP).

16. A hybrid vehicle system, comprising:

an engine including an intake;

an electric motor;

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

a pressure sensor coupled to the fuel tank;

a temperature sensor coupled to the fuel tank; and

a controller with computer readable instructions for;

shifting to a sleep mode at a first vehicle-off event following a tank refueling event;

waking up from the sleep mode upon elapse of a duration since the first 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 without operating the engine;

estimating a fuel volatility based on a peak tank pressure; and

adjusting a leak detection threshold based on the estimated fuel volatility.

17. The system of claim 16, wherein the controller includes further instructions for,

during a second vehicle-off event following the first vehicle-off event,

in response to leak test conditions being met,

applying pressure on the fuel system to provide a threshold fuel tank pressure;

isolating the fuel system; and

indicating a fuel system leak based on a rate of pressure change from the threshold fuel tank pressure being higher than the leak detection threshold.

18. The system of claim 17, wherein applying pressure on the fuel system includes applying a negative pressure on the fuel system, and wherein indicating a fuel system leak based on the rate of pressure change includes indicating a fuel system leak based on a rate of pressure bleed-up from the threshold fuel tank pressure to barometric pressure.

19. The system of claim 17, wherein leak test conditions being met include fuel tank pressure staying within the threshold range for a duration since the second vehicle-off event, and wherein applying pressure on the fuel system includes operating the fuel pump to apply a positive pressure on the fuel system, and wherein indicating a fuel system leak based on the rate of pressure change includes indicating a fuel system leak based on a rate of pressure bleed-down from the threshold fuel tank pressure to barometric pressure.

20. The system of claim 17, wherein the controller includes further instructions for, during an engine-on condition following the first vehicle-off event, adjusting a fuel injection amount based on the estimated fuel volatility.