Patent Application
20060048752
The present invention relates generally to fuel delivery systems, and more particularly to a low evaporative emission fuel system depressurization via solenoid valve.
The United States Environmental Protection Agency (EPA) and California Air Resources Board (CARB) emissions standards are becoming increasingly stringent with a phase-in of the California Level II and Federal Tier II standards. The California level II standard focuses on fleet average NMOG (Non-Methane Organic Gas) for car manufacturers, and Tier II standard focuses on NOx (Nitrogen Oxide) emissions. Both the Level II and Tier II evaporation standards are designed to substantially lower emissions from the prior standard levels. Thus, these and future standards would affect every automotive vehicle and every major auto manufacturer, effectively the entire auto industry. As such, improvements in the fuel system to reduce tailpipe and evaporation emissions are desired. In general, emissions categories include evaporative, tailpipe, incidental, and re-fueling emissions. Further, the evaporative emissions typically encompass engine-off diurnal losses and running losses.
In general, vehicle fuel systems re-pressurize during diurnal (i.e. daytime) heating. Because fuel pressure is then high for long periods during the engine-off condition, any fuel leaks are exacerbated. A primary and problematic leak source is the fuel injectors. If fuel injectors leak during the engine off condition, fuel leaks into the intake manifold that then can evaporate into the atmosphere through the air inlet or exhaust pipe. In many cases, the evaporative emissions through the Air Inlet System (AIS) constitute the majority of the allowed emissions (regulated by CARB and EPA).
Fuel leakage typically occurs because the fuel delivery system remains pressurized after the automotive vehicle is turned off. Maintaining fuel pressure in the fuel delivery system after a vehicle is turned off is a common practice of automotive manufacturers in order to keep the fuel system ready to quickly restart the engine. There are several desirable reasons for keeping the fuel system filled with fuel during periods of non-operation. Those reasons include minimizing emissions during restart and avoiding annoying delays in restarting. However, because the fuel remains pressurized, fuel may leak from various components in the fuel delivery system. One common source of leakage is through the fuel injectors, which are used in most automotive fuel systems. Fuel can also leak by permeation through various joints in the fuel delivery system.
Restoring fuel rail (a.k.a. fuel manifold) pressure quickly at or before key-on is essential for a fast restart, but high fuel pressure during key-off causes injector leakage and emission issues as mentioned above. Typical fuel rail pressure remains high after key-off and is also high during diurnal heating of the vehicle.
Upon engine key-off, the vehicle fuel delivery system (fuel rail, line, and filter) may increase in temperature due to “soaking” in its hot engine compartment, but then it cools toward ambient temperature and a vacuum may be created therein. As the vacuum is created within the fuel delivery system, vapor and/or liquid fuel may be drawn into the fuel system's volume. With the added volume (mass) in the system and upon diurnal warming, the fuel delivery system re-pressurizes. The re-pressurization causes engine-off fuel injector leakage into an intake manifold, which exacerbates evaporative emissions.
As stated above, fuel leakage is particularly exacerbated by diurnal temperature cycles. During a typical day, the temperature rises to a peak during the middle of the day. In conjunction with this temperature rise, the pressure in the fuel delivery system also increases, which results in leakage through the fuel injectors and other components. This temperature cycle repeats itself each day, thus resulting in a repeated cycle of fuel leakage and evaporative emissions.
When the engine is off, the fuel rail should remain full of fuel to be ready for the next engine restart, which minimizes fuel rail re-pressurization time. However, for practical reasons, the fuel rail may not remain entirely full and a vapor space may fill the remaining volume. Typically, a fuel pump flow rate compensates adequately for the vapor space so that the re-pressurization time may be minimally increased.
Completely eliminating known leak elements is not a viable option, so current AIS evaporative emission strategies include two typical options, among others, to reduce evaporative emissions due to injector leaks at key-off engine conditions. In a first option, vehicle manufacturers attempt to equip the AIS system with hydrocarbon traps. The hydrocarbon traps are mounted in the engine air inlet duct to prevent escape of hydrocarbons through an engine induction system. However, this first option is relatively expensive and is counter productive from a power loss or a packaging perspective. In a second option, vehicle manufacturers attempt to equip vehicles with low leak injectors to minimize loss and evaporation through the air induction system. This second option has been met with limited success because “low leak” is unfortunately not necessarily equivalent to “no leak”.
Another recent emission control strategy introduced a fuel delivery system that is depressurized during diurnals by opening the fuel delivery system via a 2.5 to 10 psi pressure relief valve after the fuel system pressure has been reduced through a normal cooling process. While this depressurization strategy is completely passive, it may not provide a high engine-off pressure to ensure a good, fast hot restart. Still another recent emission control strategy introduced a fuel delivery system that prevents a creation of a vacuum that would cause a refill of fuel, fuel vapor or air in the fuel delivery system. However, this vacuum limiting strategy may be workable only if the fuel delivery system does not refill itself upon thermal contraction of the fuel; the fuel pressure may not rise again upon subsequent thermal expansion because an average fuel temperature during diurnal is typically less than an average fuel temperature at engine shut-off.
Via experimentation using various volatile gasoline compositions, the following fuel temperature and fuel pressure correlations were found to be applicable. If the maximum fuel system temperature attained during the diurnal (which excludes the period elapsed while the engine was cooling down shortly after running) is about 135° F., a 10.0 psi (pounds per square inch) fuel pressure value enables the fuel delivery system to retain the gasoline, i.e. the fuel push out does not occur. If the maximum fuel system temperature is attained during the diurnal is about 125° F., a 7.5 psi fuel pressure value retains the gasoline. If the maximum fuel system temperature attained during the diurnal is 115° F., a 5.0 psi fuel pressure value retains the gasoline. If the maximum fuel system temperature attained during the diurnal is 105° F., a 2.5 psi fuel pressure value retains the gasoline. Thus, if 125° F. is the highest temperature expected due to diurnal heating alone, then a 7.5 psi or greater pressure regulator may prevent fuel vapor from pushing out the liquid fuel from the rail, line, and filter. This pressure regulator may also release fuel from the line into the tank to keep the pressure at or below 7.5 psi. Otherwise, the fuel pressure may increase further until another system element relieves the fuel pressure at a higher pressure setting. In the figures and text to follow, the pressure regulator setting is stated to be set to 2.5 psi. This pressure setting is intended to be an example and another pressure setting may be used.
Although high engine-off fuel rail pressure is essential for a fast restart, high engine-off fuel rail pressure may also cause injector leakage and emission issues due the leakage. As such, a solution that keeps the fuel delivery system with high engine-off pressure to ensure a good, fast hot restart and keeps the fuel rail with low or no pressure when cool to minimize the injector leakage and leakage related emissions is desirable.
In view of the above discussed problems, it would be advantageous to provide a fuel delivery system that minimizes fuel pressure rise due to diurnal heating by opening a solenoid-actuated valve, thus reducing high engine-off fuel rail pressures which can cause injector leakage, and consequently evaporative emissions.
The present invention is defined by the appended claims. This description summarizes some aspects of the present embodiments and should not be used to limit the claims.
A fuel solenoid valve is provided in a fuel delivery system to minimize fuel leakage and evaporative emissions during diurnal cycles by preventing pressure buildup as the temperature of the fuel system rises. The fuel solenoid valve is provided between a pressurized side of the delivery system and the fuel tank. In one embodiment, the fuel solenoid valve is closed when the engine is running or when the engine is off and the rail is hot. When the fuel rail cools down, the solenoid valve opens to bleed a desired amount of fuel thereby creating a fuel vapor space. Thereafter, during hot soak conditions of the diurnal cycles when the fuel rail is hot again while the engine is off, the pressure will rise due to the thermal expansion of the fuel and the created fuel vapor space minimizes further rising of the fuel pressure. Further, by adjusting the solenoid valve opening time, the pressure rising limit may be set at a desired pressure to minimize injector leakage. One advantage of the fuel pressure relief valve is that it can be employed as an inexpensive passive valve without the need for electronics or a controller.
In another aspect of the invention, the solenoid valve is opened once a pressure drops below a desired pressure value indicating that cool-off has occurred.
In still another aspect of the invention, the solenoid valve is opened after a desirable lapse of time from key-off, inferring that a cool-off has occurred.
In yet another aspect of the invention, the solenoid valve is opened when the fuel delivery system senses a desired fuel temperature, inferring that a fuel's vapor pressure has dropped below atmospheric pressure.
In another aspect, the fuel delivery system waits for a cool-down before the solenoid valve is opened when the fuel pressure is above 2.5 psi or below −0.5 psi.
In another aspect, the present invention provides a method for minimizing fuel leakage and evaporative emissions during diurnal cycles in a fuel delivery system by preventing pressure buildup as a temperature of the fuel system rises. The method provides a fuel solenoid valve between a pressurized side of the delivery system side and a fuel tank. The fuel solenoid valve is closed when the engine is running or when the engine is off and the rail is hot. When the fuel rail cools down, the solenoid valve is opened to bleed a desired amount of fuel thereby creating a fuel vapor space. Thereafter, during hot soak conditions of the diurnal cycles when the fuel rail is hot again and while the engine is off, the pressure will rise due to the thermal expansion of the fuel and the created fuel vapor space minimizes further rising of the fuel pressure. Further, by adjusting the solenoid valve opening time, the pressure rising limit may be set at a desired pressure to minimize injector leakage.
Further aspects and advantages of the invention are described below in conjunction with the present embodiments
The invention, together with the advantages thereof, may be understood by reference to the following description in conjunction with the accompanying figures, which illustrate some embodiments of the invention
a-6b are flow charts illustrating embodiments of another method for opening the solenoid valve of
a-7b are flow charts illustrating embodiments of another method for opening the solenoid valve of
While the present invention may be embodied in various forms, there is shown in the drawings and will hereinafter be described some exemplary and non-limiting embodiments, with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiments illustrated.
In this application, the use of the disjunctive is intended to include the conjunctive. The use of definite or indefinite articles is not intended to indicate cardinality. In particular, a reference to “the” object or “a” object is intended to denote also one of a possible plurality of such objects.
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After engine key-off, the volume of the fuel begins to contract while cooling down. Additional fuel may be drawn up or retrieved toward the fuel rail 20 to compensate for the contracting fuel, from either the fuel pump 12, via the check valve 16, or a fuel line 28 which terminates at the bottom of the fuel tank 11 and below the fuel level. However, if the fuel line 28 terminates above the bottom of the fuel tank 11 and above the fuel level, fuel vapor (or air) may be drawn up into the fuel rail 20 instead. When the diurnal cycle is at a minimum temperature during the night (46), the fuel rail temperature reaches a minimum value (typically 65° F.). Consequently, the fuel rail pressure reaches a corresponding minimum pressure (typically limited to −2.5 psi by the check valve in the parallel pressure relief valve 16) (46).
As part of the diurnal cycle, the fuel rail temperature begins to increase again during daytime warming, after having reached the minimum value during the night (46). Thus, the pressure in the fuel rail 20 increases as the temperature of the fuel rail 20 increases, until the temperature and pressure reach a maximum (typically 105° F.), which usually occurs in the middle of the day (48). The pressure increase that occurs during the diurnal cycle causes conventional fuel delivery systems to leak fuel through the fuel injectors 22, thereby contributing to evaporative emissions. This fuel leak is repeated during each diurnal cycle until the automotive vehicle is restarted. One would recognize that separate diurnal events may not necessarily exhibit substantially equal maximum fuel pressures.
According to the present invention, fuel leakage and evaporative emissions can be minimized by adding a solenoid fuel valve 22 to the fuel delivery system 10. As shown in
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When the engine is running, the solenoid valve 22 is closed. After engine key-off, and while the fuel rail 20 is hot, typically the PPRV 16 of the ERFS 10 is designed to keep the fuel rail 20 at a desired fuel pressure for hot restart by bleeding a relatively small amount of fuel back to the fuel tank 11. The PPRV 16 typically bleeds only after the fuel pressure has risen to a pressure level, due to the fact that the cooling system (not shown) are off, that automatically opens or unseals the pressure relief valve 13 of the PPRV 16. However, for this embodiment, the solenoid valve 22 is opened to drain fuel for a short time substantially immediately after key-off. The solenoid valve 22 is thus open to bleed down a desired amount of the pressure side fuel to form a fuel vapor space, typically only a few centiliters (cc) of fuel. Subsequently while the engine is still off and during hot soak conditions, as the fuel rail 20 heats up the fuel pressure will rise due to thermal expansion of the fuel, and the formed fuel vapor space will reduce or minimize the rise of the fuel pressure. As such, by adjusting the opening time of the solenoid valve 22, one may set a pressure rising limit to a desired pressure, such as 1.45 to 2.90 psi (i.e. 10 to 20 kpa) to minimize injector leakage.
The opening of the solenoid valve 16 can be accomplished by powering a control module or modules 23 for a short period following the key-off event. The power control module (PCM) 23 may also control the fuel pump 12 via a pump control unit 24, as shown in
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Preferably, one may want to reduce fuel pressure to substantially zero pressure so that no fuel may leak out or be drawn in (intentionally or unintentionally). Because it is also desirable to have the fuel system fully liquid to minimize re-pressurization time, it is another goal to prevent a fuel release or push out. The fuel push out occurs where a sum of the fuel's vapor pressure and the pressure of the dissolved gasses push the liquid fuel out of the fuel system back into the tank. Thus, a combined goal becomes to control the fuel pressure to a value just above fuel vapor pressure (plus the pressure of the dissolved gasses).
The combined goal has three steps. A first step is to know the fuel composition. In the absence of a fuel composition sensor, one may choose the most volatile fuel expected. A second step is to know a temperature of the hottest fuel in the system, which is typically found at the fuel rail skin. In the absence of a fuel rail temperature sensor, one can use a worst case temperature. For example, a temperature value of 175° F. shortly after engine key-off and another temperature value between 105° F. to 135° F. during a maximum diurnal heating. Based on fuel composition and fuel temperature, the fuel vapor pressure can be computed from
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Another method's flow chart 800 shown in
Still referring to the flow chart 800, after a method initialization, at step 802, a recurring status check as to whether the operator of the vehicle has turned the ignition key to the “off” position is performed at step 804. In the negative, the status check of step 804 is repeated after a first desirable time. Otherwise, a recurring check as to whether the ignition key has been off for a relatively long duration, say three (3) hours for example, to insure that the fuel in the fuel rail has cooled off, is performed at step 806. In the affirmative, another check as to whether the fuel pressure has risen above or exceeded another threshold pressure level, say 3 psig (18 psia), for example, is performed at step 808. Otherwise, the step 806 check is repeated after a second desirable wait time. If the previous step 808 check is answered positively, the solenoid valve 22 is opened for a relatively short duration to bleed off excess fuel volume in the delivery system 10, at step 810. In the negative, a further check as to whether the fuel pressure has dropped to below a desirable pressure level, for example to below 0 psig, is performed at step 812. In the affirmative, the solenoid valve 22 is opened for a preset duration to allow the fuel delivery system 10 to ingest additional fuel volume, at step 814. Otherwise, the step 808 check is repeated after a third desirable wait time. Thus, this control method may be locked into repeating the last two fuel pressure checks, namely 808 and 812, as long as the engine key has been off for at least 3 hours.
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In addition, the pressure relief valve 13 is also connected on the filtered side of the fuel delivery system 10. The fuel solenoid valve 22 is closed when the engine is running or when the engine is off and the rail is hot. When the fuel rail 20 has cooled down, the solenoid valve 22 opens to bleed a desired amount of fuel to create the fuel vapor space. Thereafter, during hot soak conditions of the diurnal cycles when the fuel rail 20 is hot again while the engine is off, the pressure will rise due to the thermal expansion of the fuel and the created fuel vapor space minimizes further rising of the fuel pressure. Further, by adjusting the opening time of the solenoid valve 22, the pressure rising limit may be set at a desired pressure to minimize injector leakage. Alternately, the fuel solenoid valve 22 may be connected (or “Teed”) to the fuel delivery system 10 on an unfiltered side of the fuel delivery system 10.
The recurring features of the MRFS 900 are similar to the prior embodiment and accordingly bear like reference numbers. In one aspect of the MFRS 900, a corresponding control method opens the solenoid valve 22 for a short duration time substantially immediately after key-off. This control method is substantially similar to the control method depicted in
In another aspect of the MFRS 900, another corresponding control method opens the solenoid valve 22 once a pressure drops below a desired pressure value indicating that cool-off has occurred. This other control method is substantially similar to the control method depicted in
In another aspect of the MFRS embodiment 900, another corresponding control method opens the solenoid valve 22 after a given lapse of time from key-off, inferring that a cool-off has occurred. This other control method is substantially similar to the control method depicted in
In another aspect of the MFRS 900, another corresponding control method opens the solenoid valve 22 when the fuel delivery system 10 senses a desired fuel temperature, inferring that a fuel's vapor pressure has dropped below atmospheric temperature. This other control method is substantially similar to the control method depicted in
In another aspect of the MFRS 900, another corresponding control method allows or waits for the fuel delivery system 10 to cool-down before the solenoid valve 22 is opened when the fuel pressure is either above 2.5 psi or below −0.5 psi. This other control method is substantially similar to the control method depicted in
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Alternately, the ERFS 1000 is provided with the solenoid valve 22 normally closed. Correspondingly, further aspects of this ERFS 1000 may be provided with alternate control methods of the solenoid valve 22 that are substantially similar to the control methods described in conjunction with the alternate aspects of the previously discussed fuel delivery system embodiment 10. Thereafter, this method ends at step 1110.
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Alternately, when an injector flow is substantially zero but the pump 12 is on (key-on, engine-off before engine start), and if the rail pressure exceeds a target rail pressure, one can reduce the rail pressure. In prior ERFS designs, one could not reduce rail pressure when the injectors were not yet operating. The fuel injectors 21 typically open shortly after the engine begins to turn via the starter motor. Typically, the fuel injectors 21 open shortly after the engine begins to turn via a starter motor. In the event that the fuel injector flow suddenly increases, the fuel pump 12 may need to be spinning in a fast ready mode to meet the pressure needed for the now-open fuel injectors 21. Accordingly, an ability of an ERFS or an MRFS system to respond to increases in injector flow is substantially improved. In addition, one may be able to enjoy electrical power savings associated with the ERFS 1300 with substantially no degradation in pressure control response.
Further, when functioning as a diurnal depressurization device, the ERFS 1300 may operate in a similar manner to previously discussed embodiments 10 and 1000. However, the solenoid valve control module 23 is also active during key-on and engine off.
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In another aspect, the electronic pressure regulator can be operated at anytime after engine key-off. As such, the fuel rail pressure is controlled to the minimum required pressure during the entire engine key-off period, which results in the minimum injector leak. Accordingly
While a preferred embodiment of the invention has been described, it should be understood that the invention is not so limited, and modifications may be made without departing from the invention. The scope of the invention is defined by the appended claims, and all devices that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein.
