Patent Application
20080308074
The present invention relates to a fuel system for an internal combustion engine; particularly, to a method and an evaporation emissions system for preventing or reducing the emission of hydrocarbon pollutants into the atmosphere; and most particularly, to an advanced evaporative emissions canister having a device containing a membrane which acts as a filter media to prevent or reduce the permeation of hydrocarbon fuel to the atmosphere. The device containing the membrane is external with respect to the evaporative emissions canister.
Evaporative emissions result from any one of several events which includes venting of fuel vapors from the fuel tank due to diurnal changes in ambient pressure and/or temperatures (known in the art as “diurnal” emissions or “bleed” emissions), by refueling of the vehicle (known in the art as “refueling” emissions) or by vaporization of fuel by a hot engine and/or exhaust. Generally, the venting of fuel vapor from the fuel tank due to diurnal pressure and/or temperature (diurnal emission), and the escape of fuel vapor during refueling (refueling emissions) are responsible for a majority of the emissions.
Environmental regulations imposed on the automotive industry, by the environmental Protection Agency require that automotive vehicles such as gasoline and diesel powered passenger cars and trucks have on board hydrocarbon emissions controls to prevent or limit the amount of hydrocarbon pollutants expelled into the atmosphere. Such hydrocarbon pollutants are a major contributor to smog formations and contribute to the depletion of the ozone layer in our atmosphere. As a result of government mandates, automotive manufacturers are constantly being challenged to find better and more efficient ways to prevent or reduce the emissions of hydrocarbon fuel vapors and other pollutants into the atmosphere. Such emissions can be controlled by canister systems that employ carbon, preferably activated carbon, to adsorb and hold the hydrocarbon vapors. The adsorbed hydrocarbon vapor is periodically desorbed from the carbon by drawing fresh air into the carbon bed to displace the hydrocarbon fuel vapor. The displaced fuel vapor is then passed to the engine where it is consumed. The renewed carbon can then adsorb additional hydrocarbon fuel vapor from the fuel system by withdrawing the air back out through the vent side of the canister.
Currently, fuel systems employed in the automotive industry employ evaporative emissions canister having an inlet port for receiving fuel vapor from the fuel tank where the fuel vapor is adsorbed on an adsorbent material and stored until such time the stored fuel vapor is returned to the fuel tank or, preferably, directed to the engine where it is consumed. Examples of evaporative emissions canisters are described in a number of U.S. patents and patent applications such as U.S. Pat. Nos. 4,203,401 to Kingsley et al.; 4,658,796 To Yoshida et al.; 4,683,862 to Formuto et al.; 5,119,791 to Gifford, et al.; 5,408,977 to Cotton; 5,924,410 to Dumas et al.; 5,957,114 to Johnson et al.; 6,136,075 to Bragg et al.; 6,237,574 to Jamrog et al.; 6,540,815 to Hiltzik et al.; and RE38, 844 to Hiltzik et al., and U.S. Pat. Appln. Nos. Nos. 2005/0061301 to Meiller; 2005/0123458 to Meiller; and 2006/0065252 to Meiller.
In prior art evaporative emission canisters, the amount of fuel vapor that can be contained in the canister is finite and dependent upon the amount and adsorbent capability characteristics of the adsorbent material contained in the canister. Some prior art canisters employ auxiliary canisters to increase the adsorbent material capacity. The use of additional canisters not only increase the complexity and cost of the evaporative emissions system, but also requires additional space considerations due to the limited space available in the region of the vehicle wherein a canister is installed. Therefore, there is a need in the industry for an evaporative emissions canister which provides increased adsorbent capacity without seriously increasing the complexity, cost and spatial requirements associated with the use of additional canisters and/or filters to achieve the mandated reduction of fuel vapor emissions.
It has been found that the emission of hydrocarbon fuel pollutants into the atmosphere during fueling of an automotive vehicle, during diurnal changes in the fuel system, and in the operation of such vehicle, can be substantially reduced or eliminated by integrally incorporating a membrane into a device in the fresh air line of the evaporative emissions canister. The device containing the membrane is installed outside the evaporative emissions canister, which allows significant freedom in determining the most efficient configuration and location of the device in the emissions system.
The membrane useful in the present invention is characterized as a cellular fibular material having physical properties such as pore size, nominal flow path, membrane area and thickness favorable for the separation and trapping of fuel vapor molecules while allowing any air molecules present to flow freely therethrough. Membranes found to be effective in the present invention are available from Amersham Biosciences Membrane Separations Group, W. L. Gore & Associates. The membrane of the present invention not only increases the efficiency of the adsorbent material, but also restricts most of the hydrocarbon molecules associated with fuel vapor from permeating the membrane and escaping into the atmosphere, while allowing clean air molecules to pass through the membrane. Typically, the membrane is effective to prevent substantially all of the fuel vapor from passing therethrough while allowing substantially all of the air molecules to pass therethrough. More typically, the membrane prevents greater than about 80% of the fuel vapor molecules from passing through the membrane while allowing greater than about 95% of the air molecules to pass therethrough. Most typically, the membrane prevents greater than about 95% of the fuel vapor molecules from passing through the membrane while allowing greater than about 99% of the air molecules to pass therethrough and be expelled to the atmosphere.
Accordingly, it is a primary object of this invention to provide an improved evaporative emissions system, which incorporates a membrane in a housing separate from the evaporative emissions canister wherein the full capacity of the adsorbent material can be effectively utilized.
It is another object of the invention to provide an evaporative emissions canister that provides reduced fuel emissions to the atmosphere.
It is still another object of the invention to optimize the overall packaging of the evaporative emissions system by allowing the membrane housing to be more efficiently configured and located in the emissions system.
It is yet another object of the invention to provide all of the above objects of the invention without complexity and economic considerations.
These objects as well as other objects, features and advantages of the present invention will be apparent to those skilled in the art from the following detailed description, appended claims and accompanying drawings.
According to the invention, an evaporative emissions canister such as that described in commonly assigned U.S. patent application Ser. No. 11/592,973, filed Nov. 3, 2006, the contents of which are incorporated herein by reference thereto, can be effectively employed to not only reduce the amount of fuel vapor pollutants such as nitrogen oxides, sulfur oxides, etc. into the atmosphere, but to substantially improve the efficiency of the adsorbent material in the evaporative emissions canister by installing a separate housing member containing a membrane wherein the separate housing is installed outside the evaporative emissions canister. In a typical installation, the device is placed in the fresh air line where the membrane permits the free flow of air without obstruction from the atmosphere to the evaporative emissions canister during a purge step, and from the evaporative emissions canister to the atmosphere during a regeneration step, while preventing the emission of hydrocarbon fuel vapors and pollutants into the atmosphere.
In addition to the afore-mentioned physical properties necessary for the sufficient separation of fuel vapor molecules from fresh air molecules in the evaporative emissions system, there are other properties that affect mass transfer during gas separation through a membrane. Such additional properties include:
The membrane employed in the present invention effectively prevents or reduces the permeation of fuel vapor molecules through the membrane while allowing air molecules to pass freely therethrough. More specifically, the evaporative emissions canister of the present invention incorporates the membrane externally with respect to the canister and more specifically externally on the vent or fresh air side of the evaporative emissions canister at the vent or fresh air inlet/outlet port. By installing the membrane externally at the vent or fresh air inlet/outlet port, the membrane prevents the permeation of the hydrocarbon fuel vapor through the membrane, thereby allowing the entire adsorbent bed to be utilized for adsorbing fuel vapor as opposed to prior canisters which effectively utilize only a fraction of the adsorbent material contained in the canister for the adsorption of the fuel vapor. A considerable amount of the adsorbent material is used as a buffer on the vent side of the canister. Accordingly, prior devices effectively utilize only about one-half to two-thirds of the capacity of the adsorbent bed. As more fully described below, the evaporative emissions canister of the present invention which utilizes a membrane on the vent or fresh air side of the canister provides a more effective and more efficient device for preventing or reducing the emission of fuel vapor into the atmosphere.
The canister device of the present invention may be of any physical configuration and dimension employed in the art for the prevention or reduction of hydrocarbon emissions into the atmosphere. However, for the purpose of illustration, the automotive evaporative emissions canister comprises:
a first housing having a circumferential side member having an inner surface and an outer surface, a top member having an inner surface and an outer surface and a bottom member having an inner surface and an outer surface, wherein the inner surface of said circumferential side member, the inner surface of the top member and the inner surface of the bottom member form a first chamber for receiving fuel vapor from a fuel tank and a second chamber containing a fuel vapor-adsorbent material for adsorbing the fuel vapor from the fuel tank;
a partition extending vertically downwardly from the inner surface of the top member, wherein the partition divides the second chamber containing the fuel vapor-adsorbent material into a first compartment and a second compartment;
a first tubular member extending upwardly from the housing and in operable communication with the fuel vapor-receiving chamber, the first tubular member providing a passage through which the fuel vapor flows into the fuel vapor-receiving chamber;
a first port in the housing, the first port providing open communication between the housing and the first tubular member;
a second tubular member extending upwardly from the housing and in operable communication with the fuel-receiving chamber, the second tubular member providing a passage through which fuel vapor flows from the evaporative emissions canister to an automotive engine where the fuel vapor is consumed;
a second port in the housing, the second port providing open communication between the fuel vapor receiving chamber and said second tubular member;
a third tubular member extending upwardly from the housing, the third tubular member providing a passage through which fresh air is admitted to the second chamber during a purging step, and through which air from an air/fuel mixture is vented to the atmosphere in a venting step; and
a third port in the housing, the third port providing open communication between the fuel vapor adsorbent chamber and the third tubular member, and
an auxiliary housing containing a membrane, wherein the auxiliary housing containing the membrane is disposed in the fresh air line outside the confines of the evaporative emissions canister.
As described in the aforementioned copending U.S. patent application Ser. No. 11/572,973, the fuel vapor from the fuel tank may contain a small amount of liquid fuel entrained along with the fuel vapor. If such liquid fuel is allowed to contact the adsorbent material in the evaporative emissions canister, the effectiveness of the adsorbent material may be severely diminished. Therefore, the canister of the aforementioned copending application contains provisions for a liquid-fuel trap to be integrally incorporated into the canister directly above the adsorbent chamber. Such canister would find similar utility in the present application.
Turning now to the drawings,
When the adsorbent material 14 becomes saturated with the fuel vapor, engine controller 28 commands fuel vapor valve 30 to close the fuel vapor load line 18 and the fuel vapor is desorbed from the adsorbent material 14 and drawn by vacuum through an engine vacuum controller 28 connecting engine vacuum line 26 to the engine 24 where the desorbed fuel vapor is consumed. A vacuum is created by opening the fresh air valve 34 causing fresh air from the atmosphere to be drawn into the canister 12 through a membrane 36 (
As shown in
In order to keep the adsorbent material 14 inside the adsorbent chamber 50, a barrier member 56 may be disposed between the fuel vapor-receiving chamber 48 and the adsorbent chamber 50 to keep the adsorbent material 14 from inadvertently escaping the adsorbent chamber 50 and entering the fuel vapor-retaining chamber 48. Typically the barrier member 56 is a porous material such as a foamed polymeric material, a fibrous material, or the like. Typically, a relatively rigid support member having one or more apertures therein to allow the fuel vapor to flow therethrough is disposed between the fuel vapor receiving chamber and the adsorbent chamber. The bottom surface of the support member includes a plurality of finger elements extending downwardly from the bottom surface of the barrier member. The finger elements interconnect with the barrier member to provide the barrier member with a relatively flat surface having increased surface area. A barrier layer and a support member similar to that discussed above may be place between the adsorbent material in compartment 54a and the fresh air port 40.
As described in the aforementioned copending U.S. patent application Ser. No. 11/572,973, the fuel vapor from the fuel tank may contain a small amount of liquid fuel entrained along with the fuel vapor. If such liquid fuel is allowed to contact the adsorbent material in the evaporative emissions canister, the effectiveness of the adsorbent material may be severely diminished. Therefore, the canister of the aforementioned copending application contains provisions for a liquid-fuel trap to be integrally incorporated into the canister directly above the adsorbent chamber. Such canister would find similar utility in the present application. In those instances where liquid fuel is entrained with the fuel vapor into the evaporative emissions canister, such liquid fuel may be separated from the fuel vapor by a liquid-fuel trap where such liquid fuel remains until it is evaporated and passed on the engine along with the desorbed fuel vapor from the adsorbent material where it is consumed. A more detailed description of a liquid fuel trap is set forth in the aforementioned copending U.S. patent application Ser. No. 11/572,973.
The evaporative emissions canister of the present invention is manufactured from any material possessing the desirable properties and characteristics, such as flexibility, fuel resistance, heat resistance, pressure resistance, weatherability, dimensional stability, and high impact strength. Typically, such material is a polymeric material, more preferably, a polyamide material such as nylon, an aromatic polyamide such as aramid or a polyolefin such as polyethylene.
Typically, the evaporative emissions canister, including the various parts thereof, is molded in one piece to provide a continuous unitary structure thereby preventing the need for any assembly steps.
The adsorbent material useful in the invention may be any of the conventional materials effective to adsorb hydrocarbon materials such as fuel vapor. Preferable, the adsorbent material is carbon and most preferably activated carbon. The carbon can be in any desired form having an effective particle size sufficient to maximize the absorbance of the fuel vapor in the canister.
Typically, the evaporative emissions canister will include a volume compensator, as is well known in the art, located at the bottom of the canister housing to limit shifting of the adsorbent material during operation of the automotive vehicle.
While the present invention has been fully illustrated and described in detail, other designs, modifications and improvements will become apparent to those skilled in the art. Such designs, modifications and improvements are considered to be within the spirit of the present invention, the scope of which is determined only by the scope of the appended claims.
