Abstract: A method for a plug-in hybrid electric vehicle, comprising: during a first condition, including an engine-off condition and the plug-in hybrid electric vehicle coupled to an external power source; heating a fuel vapor canister based on a fuel tank vacuum; and opening a fuel tank isolation valve to draw heated vapors into a fuel tank. In this way, a passive purge operation may be executed, thereby purging the fuel vapor canister without forcing the engine to turn on. Thus, the vehicle may be operated at peak fuel economy without increasing emissions.

Abstract: A method for a vehicle fuel system, comprising: during an engine-off condition, including an ambient temperature within a threshold range, operating a cooling fan to increase a fuel tank vacuum; and indicating leaks in the vehicle fuel system based on the increased vacuum. In this way, an EONV test may be run at mild ambient temperatures which would not otherwise result in the development of adequate fuel tank vacuum to pass the EONV test.

Abstract: Systems and methods for improving fuel vapor purging for a vehicle are presented. In one example, a fuel vapor storage canister vent valve is housed in a fuel vapor storage canister for the purposes of heating contents of the fuel vapor storage canister and venting the fuel vapor storage canister to atmosphere.

Abstract: A method for operating a vehicle system is provided. The method includes monitoring a change in a temperature of the fuel vapor canister coupled to a fuel tank via a canister temperature sensor and adjusting operation of a fuel tank isolation valve based on the change in temperature of the fuel vapor canister.

Abstract: Methods and systems for fuel system leak detection are disclosed. In one example approach, a method comprises, during an engine-on condition, delivering fuel from a fuel tank to one or more cylinders of the engine while the fuel tank is sealed off from atmosphere, and indicating a leak based on pressure in the fuel tank. For example, a leak may be indicated in response to a pressure decrease in the fuel tank greater than an expected pressure decrease, where the expected pressure decrease is based on a fuel level in the fuel tank.

Abstract: Embodiments for monitoring fuel system degradation are provided. In one example, a method for a vehicle comprises evacuating fuel from a first fuel tank to a second fuel tank, and indicating fuel system degradation in response to a change in fuel system pressure following the evacuation of fuel. In this way, fuel system degradation may be indicated without use of a separate pressure building device.

Abstract: A method, comprising: indicating a leak of a first diameter on a canister side of a fuel system following applying a vacuum to the fuel system with a fuel tank isolation valve closed; and indicating a leak of a second diameter on a fuel tank side of the fuel system, based on a vacuum decay in an isolated fuel tank following applying a vacuum to the fuel system with the fuel tank isolation valve open. In this way, an evaporative leak check module with a single reference orifice may be used to determine leaks of multiple sizes in multiple sectors of a fuel system. This may allow current production models to meet more stringent emissions regulations in the future.

Abstract: A method, comprising: indicating leakage on a canister side of a fuel system based on a first fuel system pressure following applying a vacuum to the fuel system with a fuel tank isolation valve closed; and indicating leakage on a fuel tank side of the fuel system based on the first fuel system pressure and a second fuel system pressure following applying a vacuum to the fuel system with the fuel tank isolation valve open. In this way, an ELCM with a single reference orifice may be used to perform a leak test with two different thresholds for leak detection. This may allow vehicles currently in production to meet future emissions standards without costly upgrades to the ELCM.

Abstract: A method for a plug-in hybrid electric vehicle, comprising: during a first condition, including an engine-off condition and the plug-in hybrid electric vehicle coupled to an external power source; heating a fuel vapor canister based on a fuel tank vacuum; and opening a fuel tank isolation valve to draw heated vapors into a fuel tank. In this way, a passive purge operation may be executed, thereby purging the fuel vapor canister without forcing the engine to turn on. Thus, the vehicle may be operated at peak fuel economy without increasing emissions.

Abstract: A method for a plug-in hybrid electric vehicle, comprising: during a first condition, including an engine-off condition and the plug-in hybrid electric vehicle coupled to an external power source, cooling a vapor canister based on an ambient temperature. In this way, bleed emissions may be reduced in PHEVs during conditions when the vehicle is parked and recharging at a high ambient temperature.

Abstract: A method for a plug-in hybrid electric vehicle, comprising: during a first condition, including an engine-off condition and the plug-in hybrid electric vehicle coupled to an external power source, cooling a vapor canister based on an ambient temperature. In this way, bleed emissions may be reduced in PHEVs during conditions when the vehicle is parked and recharging at a high ambient temperature.

Abstract: A method for localizing restrictions in a fuel system during refueling, comprising: monitoring fuel tank pressure, fuel vapor canister temperature, and evaporative leak check module pressure during a refueling event; and responsive to a premature shutoff event, indicating a location of a restriction among a plurality of locations based on whether monitored pressure and temperature changes during the refueling event are greater than respective thresholds. In this way, the cause of a premature shutoff event may be diagnosed without requiring additional sensors within the fuel system.

Abstract: A method for a vehicle fuel system, comprising: during an engine-off condition, including an ambient temperature within a threshold range, operating a cooling fan to increase a fuel tank vacuum; and indicating leaks in the vehicle fuel system based on the increased vacuum. In this way, an EONV test may be run at mild ambient temperatures which would not otherwise result in the development of adequate fuel tank vacuum to pass the EONV test.

Abstract: A method for purging fuel vapors, comprising: purging fuel tank vapors directly from a fuel tank to an engine intake, bypassing a canister, via a venturi, while drawing canister vapors via the venturi into the purged fuel tank vapors en route to the engine intake. In this way, fuel tank vapors may be used to enable purging of a fuel vapor canister, even under conditions where there is insufficient manifold vacuum to enable a canister purge routine. By increasing the frequency of purge opportunities, bleed emissions from a saturated canister may be reduced.

Abstract: A method for operating a fuel system is disclosed. The method includes sequentially purging fuel vapors from each of a plurality of regions of a canister. Purging a region includes opening an air inlet valve associated with that region and maintaining air inlet valves associated with each other region closed to direct fuel vapors to at least one purge outlet.

Abstract: A method and system for testing an evaporative emission control system for leaks. The method includes opening a canister purge valve by an amount sufficient to provide a flow equivalent to a predetermined orifice diameter. Then, a vacuum pump evacuates a reference volume consisting of the portion of the evaporative emission control system extending from the canister purge valve to an evacuation level control monitor. The system determines the pressure in the reference volume at the end of a specified evacuation time, and that value is stored as the threshold test value. Then, the system closes the canister purge valve and proceeds to evacuate the entire evaporative emission control system for a predetermined time. At the end of that time, the system identifies the absence of a leak if the system pressure falls at least to the threshold test value. A powertrain control module controls the canister purge valve.

Abstract: A method for detecting leaks in an evaporative emission control system. The method begins by activating a PCM at a selected interval, for a selected period. During the selected period, the PCM monitors system pressure and temperature. The PCM then determines a relationship between changes in system temperature and changes in system pressure, and it identifies a leak based on predetermined criteria related to the relationship. The relationship can be the ideal gas law, which allows the calculation of an expected pressure, based upon differences in temperature. If the actual pressure is considerably below the expected pressure, then one can infer the presence of a leak.

Abstract: Embodiments for controlling fuel vapors are disclosed. In one example, a method comprises during a purge of a fuel vapor canister, adjusting a heater of the fuel vapor canister based on a rate of a purge flow exiting the fuel vapor canister and a concentration of hydrocarbons released from the fuel vapor canister. In this way, a fuel vapor canister purge efficiency may be increased.

Abstract: A method and system for testing an evaporative emission control system for leaks. The method begins by setting a variable reference orifice to a preselected diameter. Then, a vacuum pump evacuates a reference volume in the vicinity of the variable reference orifice. The reference volume is defined by the vacuum pump, and the reference orifice. Then, after a specified evacuation time, the method determines a pressure in the reference volume. That pressure is stored as the threshold test value. The method continues by evacuating the entire EVAP system for a predetermined time. A leak can then be identified if after the evacuation, the system pressure falls at least to the threshold test value. Switching the vacuum pump between the first and second positions is accomplished with a changeover valve having parallel airways configured for evacuating a small volume to the reference orifice and also evacuating the entire EVAP system.

Abstract: Systems and methods to control fuel tank pressure to reduce fuel oxidation in plug-in hybrid electric vehicles are disclosed. A method comprises routing vapors from a fuel system canister to the fuel tank to maintain the fuel tank pressure at a desired pressure. In this way, the engine may be maintained off for greater durations while still retaining fuel quality of fuel stored on-board the vehicle.