Claims
- 1. An electric heater assemblage for attachment to the air intake opening of a fuel vapor recovery canister of the type containing material adapted to alternately adsorb and store, or release fuel vapor, comprising in combination:
- (a) a wafer of electric resistance heating material, and means for making electrical connection thereto for effecting energization of the same,
- (b) said wafer having opposite expansive surfaces,
- (c) a first wall located at one side of said wafer and having an expansive surface coextensive with one wafer surface,
- (d) a second wall located at the opposite side of said wafer and having an expansive surface coextensive with the other wafer surface,
- (e) said first wall and wafer defining a first chamber and said second wall and wafer defining a second chamber in communication with the first chamber at the periphery of the wafer, and
- (f) means for directing air from the exterior of the canister into the first chamber, past one side of said wafer and the periphery of the wafer into the second chamber, past the opposite side of said wafer and thereafter to the interior of the canister, for imparting heat to the said material contained in the canister.
- 2. The invention as defined in claim 1, and further including:
- (a) a canister fcr holding a quantity of said vapor adsorbing and releasing material,
- (b) said air-directing means comprising a molded plastic heater housing having an air inlet port and having mounting means for supporting the said walls and wafer in a fixed position with respect to the canister.
- 3. The invention as defined in claim 2, wherein:
- (a) said heater housing carries means for releasably securing the heater housing to the canister.
- 4. The invention as defined in claim 2, wherein:
- (a) said electrical connection means comprises a pair of ring contacts disposed on opposite faces respectively of said wafer, and
- (b) a pair of electrical leads respectively connected with said ring contacts and extending from the heater housing.
- 5. The invention as set forth in claim 1, wherein:
- (a) said first wall comprises an apertured metal plate.
- 6. The invention as set forth in claim 1, wherein:
- (a) said second wall comprises an apertured metal plate.
- 7. The invention as set forth in claim 1, wherein:
- (a) said first wall comprises a metal-clad insulating circuit board.
- 8. The invention as set forth in claim 7, wherein:
- (a) the metal portion of said circuit board faces the wafer.
- 9. The invention as set forth in claim 1, wherein:
- (a) said second wall comprises a metal-clad insulating circuit board.
- 10. The invention as set forth in claim 9 wherein:
- (a) the metal portion of said circuit board faces the wafer.
- 11. The invention as defined in claim 1, and further including:
- (a) a cansiter for holding a quantity of said vapor adsorbing and releasing material, and
- (b) an enclosure having inlet and outlet passages, said enclosure surrounding the wafer and walls and being carried by said canister.
- 12. The invention as defined in claim 1, and further including:
- (a) spacer means disposed between said walls and the wafer so as to retain the walls and wafer in spaced relation with respect to one another.
- 13. The invention as defined in claim 12, wherein:
- (a) said spacer means comprises a pair of wave washers.
- 14. The invention as defined in claim 1, wherein:
- (a) said wafer comprises a disk of PTC ceramic material.
- 15. The invention as defined in claim 14, wherein:
- (a) said disk is imperforate.
CROSS RFFERENCES TO RELATED APPLICATIONS
U.S. Application for Patent in the names of Peter J. Lupoli, Donald J. Mattis and Robert S. Miller entitled FUEL VAPOR RECOVERY SYSTEM FOR AUTOMOTIVE VEHICLES, U.S. Ser. No. 717,515 filed Mar. 28, 1985.
Research and development of the present invention and application have not been Federally-sponsored, and no rights are given under any Federal program.
1. Field of the Invention
This invention relates to fuel vapor recovery canisters for automotive vehicles, and more particularly to canisters of the type containing adsorptive material and which are intended to trap and store vapors from the vehicle's fuel tank and carburetor, and to purge stored vapor and condensate during initial operation of the vehicle's engine.
2. Description of the Related Art Including Information Disclosed Under 37 CFR .sctn..sctn.1.97-1.99
Within the past several years a number of attempts have been made to limit the escape into the atmosphere of gasoline vapors from automotive fuel systems, especially those due to evaporation which occurs while the vehicles are idle. Special fuel tank caps have been employed in order to reduce or eliminate fumes that would otherwise be released into the surroundings. In addition, there have been proposed evaporative emission control systems that involve the use of charcoal-filled canisters which are connected, through vapor lines, to the fuel tanks such that gasoline vapors from the tanks are channelled into the canisters, and adsorbed or partially condensed in the charcoal. The vapor line in such a system is connected to an inlet port located at the top of the canister. A second port on the canister is also provided, known as a "purge" port, from which a line extends to the intake manifold or carburetor of the vehicle's engine. When the vehicle is started, condensed fuel and vapor that is stored in the charcoal is released and sucked into the engine, to be burned.
Both open- and closed-bottom canisters have been proposed. In the open-bottom canister, there is typically one or more relatively large air-intake passages that can admit fresh air from the engine compartment during operation of the engine. This fresh air flow picks up much of the stored fuel from the charcoal and carries it to either the carburetor or else to the intake manifold. Additional fumes which enter the canister during engine operation are purged continuously, leaving the charcoal in a relatively "dry" condition, ready to adsorb fuel after the engine is shut down. Usually there is some type of filter material, such as fiberglass wadding, at the fresh air intake area so as to eliminate any tendency for dirt or dust to be drawn into the canister.
Some canisters have been designed to draw vapors from both the fuel tank and the carburetor float bowl during engine shutdown, and to purge such fuel vapors or their condensate during vehicle operation. Other arrangements, such as that described above, involve recovery of fumes from only the vehicle's fuel tank.
Where it is desired to draw vapors from both the fuel tank and the carburetor float bowl, there are usually required control valves in order to enable the float bowl to vent into the canister when the engine is not running, while still not interfering with the normal operation thereof. In addition, fuel tank pressure valves have been incorporated in certain vehicles, these functioning to restrict venting of the tank during idle periods, and to increase the capability of venting into the canister during engine operation. Various other arrangements have also been proposed and produced.
The major problem with evaporative emission control systems of the type employing activated carbon or activated charcoal as adsorptive materials housed in a vapor canister, is that under conditions of low ambient temperature the fuel that has been adsorbed exhibits a reluctance to be released and purged from the canister. It has been determined that with adsorptive substances currently being employed, satisfactory release of the stored fuel will occur at room temperatures and above; however, when the temperatures fall much below these values, the efficiency of the system suffers significantly. The ability of the carbon to release the fuel is poor until the canister temperature rises.
Such canister units are therefore generally located in the engine compartment of the vehicle, and with the exception of extremely cold weather, eventually the desired, elevated canister temperatures are reached. However, until this occurs the fuel occupying the canister tends to remain there, as opposed to being promptly drawn into the intake manifold so as to be burned off.
U.S. Pat. Nos. 3,221,724 and 3,757,753 disclose charcoal-containing canisters that are intended to be heated directly from heat generated by the engine when the latter is operating. In the device of patent '724, a charcoal-filled container is incorporated in the vehicle's air-strainer; heat is provided to the charcoal by air that has been heated by the engine block and exhaust manifold, and which is drawn through the air-intake port of the air-strainer compartment. In patent No. '753, heat for the canister is obtained from an open jacket formed around the exhaust pipe leading from the engine. The jacket is connected with a conduit that in turn extends to the bottom of the canister in order to permit a flow of heated air to enter the same. The upper portion of the canister has an outlet that is connected to the air-strainer for the carburetor. Both devices operate in a similar manner in that they rely upon engine heat to provide the desired vapor-purging activity in the canister.
U.S. Pat. Nos. 3,191,587 and 3,675,634 both involve charcoal-containing fuel vapor recovery canisters connected to receive and store vapors from a vehicle's fuel tank.
U.S. Pat. No. 3,927,300 relates to the use of PTC ceramic material as a self-regulating heater in a number of different applications. U.S. Pat. Nos. 4,108,125; 4,279,234; 4,387,690; 4,448,173 and 4,450,823 all disclose the use of PTC material for heating fuel as it enters the carburetor of an internal combustion engine.
The major problem with almost all fuel vapor recovery canister systems heretofore proposed is that the response is too slow as regards purging of the stored/condensed fuel. In cold weather the temperatures in the engine compartment are low until after a prolonged period of operation. In the device noted above, which incorporates the jacket that surrounds the exhaust pipe, the actual heat transferred to the canister has been found to be inadequate, and again, largely dependent on the ambient temperatures existing in the engine compartment.
The co-pending application above identified discloses a number of arrangements that have been devised for heating air that is drawn in through the open bottom of a canister, all employing self-regulating PTC ceramic heating elements. In several embodiments a number of individual slabs are employed with zinc die-castings that form a grid, in order to provide the desired heat transfer to the air stream. In other embodiments, there is shown a single PTC element in the form of an apertured slab having a generally "honeycomb" configuration. While tests performed on these earlier designs have indicated that they perform well, efforts have since been made to simplify the various structures, as well as to effect modifications which provide a heating assembly that is less expensive while performing in a manner essentially equivalent to that of the previously constructed units.
The above disadvantages and drawbacks of prior evaporative emission control systems of the charcoal-canister type are largely obviated by the present invention which has for one object the provision of a novel and improved charcoal-type pollution control system which is especially simple in construction and reliable in operation, and which provides significant reduction in the undesirable release of fuel vapors into the atmosphere from the engine's fuel system, over a wide range of ambient temperatures.
Another object of the invention is to provide an improved pollution control system as outlined above wherein heat transfer from a single slab-like PTC element is established along an air flow path that extends through co-extensive heater chambers formed on opposite faces of the slab, and wherein there occurs maximum heat transfer to such air due to prolonged contact with both the heated opposite faces of the PTC element itself and with the opposite walls of such chambers.
Yet another object of the invention is to provide an improved pollution control system in accordance with the foregoing, wherein the heating of air entering the canister takes place along a serpentine path, resulting in an efficient transfer of heat from the PTC element.
A still further object of the invention is to provide an improved pollution control system of the kind indicated wherein the bottom of the canister is essentially completely closed, so as to eliminate the possibility of water entering through its bottom, thereby maintaining the canister interior relatively moisture free.
A related object of the invention is to provide an improved pollution control system as above characterized wherein a controlled purging of stored/condensed fuel vapors from the charcoal can be effected with a single, relatively simple slab-like heating element constituted of PTC ceramic material, the element being especially inexpensive, and economical to fabricate.
Yet another object of the invention is to provide an improved pollution control system of the kind indicated wherein the recovery of fuel vapors and condensate that have accumulated during periods when the vehicle is idle, begins substantially at the time that the vehicle engine is started, such stored fuel products being quickly and effectively drawn into the engine cylinders and immediately burned.
A still further object of the invention is to provide an improved pollution control system as outlined above, wherein the parts are simple in structure, being essentially in the form of molded plastic components and simple metal stampings, and wherein the system is adaptable for use with a variety of vehicle types, with little or no modifications being required.
The above objects are accomplished by an electric heater assemblage for attachment to the air intake opening of a fuel vapor recovery canister of the type containing material adapted to alternately adsorb and store, or release fuel vapor. The heater comprises a wafer of electric resistance heating material, and electrical connections for effecting energization of the wafer. The wafer has opposite expansive surfaces. There is a first wall which is located at one side of the wafer and has an expansive surface coextensive with one wafer surface, and a second wall located at the opposite side of the wafer and having an expansive surface coextensive with the other wafer surface. The first wall and wafer define a first chamber and the second wall and wafer define a second chamber in communication with the first chamber at the periphery of the wafer. Means are provided for directing air from the exterior of the canister into the first chamber, past one side of the wafer and the periphery of the wafer into the second chamber, and past the opposite side of the wafer and thereafter to the interior of the canister, for imparting heat to the said material contained in the canister.
The wafer is preferably constituted as a single relatively simple slab or disk of positive temperature coefficient ceramic material that exhibits a self-regulating effect by presenting increased resistance to current flow when there occurs a rise in temperature. The arrangement is such that the initial power applied to the PTC material is relatively high, to produce rapid heating, and gradually is automatically reduced as the temperatures rise. Maximum heat transfer to the air stream is achieved by virtue of a serpentine flow path that is established past both of the opposite faces of the PTC material, prior to the air entering the interior of the canister. High efficiency is thus achieved without resorting to relatively more expensive or intricate shapes of PTC material, such as multiple slabs and mountings therefor, honeycomb structures, etc.
Other features and advantages will hereinafter appear.
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Patent Grant
4721846
