Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
Reexamination Certificate
1999-12-13
2001-08-28
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
Having fuel vapor recovery and storage system
C123S557000, C123S519000
Reexamination Certificate
active
06279548
ABSTRACT:
TECHNICAL FIELD
This invention pertains to evaporative fuel vapor emissions from automotive vehicles. More specifically, this invention pertains to an improved fuel vapor adsorption canister system and method of operation that reduces the breakthrough of fuel vapor to the atmosphere.
BACKGROUND OF THE INVENTION
Fuel evaporative emission control systems have been in use on automotive vehicles for over 30 years. The gasoline fuel used in many internal combustion engines is quite volatile. The fuel typically consists of a hydrocarbon mixture ranging from high volatility butane (C-4) to lower volatility C-8 to C-10 hydrocarbons. When a vehicle is parked in a warm environment during the daytime heating (i.e., diurnal heating), the temperature in the fuel tank increases. The return of hot fuel from the engine also heats the contents of the fuel tank. The vapor pressure of the heated gasoline increases and fuel vapor will flow from any opening in the fuel tank. Normally, to prevent fuel vapor loss into the atmosphere, the tank is vented through a conduit to a canister containing suitable fuel adsorbent material. High surface area activated carbon granules are widely used to temporarily adsorb the fuel vapor.
The fuel vapor enters the canister through a top inlet of the canister and diffuses downwardly under its own pressure and gravity into the bed of carbon granules where it is adsorbed in temporary storage. The total volume of adsorbent is specified so as to be suitable to retain a quantity of fuel vapor expected to evaporate from the fuel tank during normal or representative usage of the vehicle.
The canister is molded of a thermoplastic material and shaped so that ambient air can be drawn through the carbon granule bed during engine operation to purge adsorbed fuel from the surfaces of the carbon particles and carry the removed fuel vapor into the air induction system of the vehicle. Typically, a partition is formed in the canister to lengthen the flow path of vapor and air through the volume of carbon particles. Thus, the fuel vapor enters at one end of the flow path and escapes to the atmosphere at the opposite end, the vent end, if the quantity of fuel exceeds the adsorption capacity of the carbon volume. Ambient air, induced to flow through the activated carbon bed under engine intake vacuum, enters the canister at the “vent” end of the flow path. The air traverses the full length of the flow path and exits the canister with desorbed, i.e., purged fuel at the vapor inlet end of the carbon volume. Typically, neither the canister nor the purge air experience heating other than ambient heating.
The described emission control system obviously works in a repeating cyclical mode. When the engine is not running, fuel vapor generated by diurnal heating, or the like, flows to the canister and is adsorbed up to the capacity of the adsorbent volume. The vehicle may remain idle for several days and fuel vapor will accumulate in the canister. The initial loading will be at the inlet end of the adsorbent volume but the fuel gradually becomes distributed along the entire adsorbent bed pathway. When the vehicle engine is started and can accommodate a secondary fuel-air mixture, a purge valve is opened and purge air is drawn through the adsorbent volume. Purging can continue as long as the engine is running and the air can cause the removal of a substantial portion of the stored fuel vapor. But a portion of the adsorbed hydrocarbons remain adsorbed on the carbon. That portion is called the “heel” and it significantly limits the capacity of the carbon to adsorb additional fuel.
Environmental regulators are proposing lower limits on the amount of fuel vapor that can escape the evaporative emission system during a prescribed test of the system in a closed space called SHED (Sealed Housing for Evaporative Determination). For example, the California Air Resources Board (CARB) has proposed “near zero” and “zero” evaporative emission standards for automotive vehicles for year 2004. The proposed standards require near-zero fuel vapor emissions from all the sources: permeation losses through plastic fuel system parts; leaks through the fittings and joints; and canister breakthrough emissions. Reducing the emissions through the leaks involves the selection of better sealing joints and connectors or eliminating some of joints, and reducing permeation losses involves the selection of low permeability or no permeability materials, whereas reducing canister breakthrough emissions to near-zero requires new technologies in the canister design. An object of this invention is to provide a canister system, and method of operating the system, that will limit canister breakthrough emissions to less than 0.02 grams fuel loss per test.
SUMMARY OF THE INVENTION
In one aspect, this invention provides a method of increasing the adsorption capacity of an evaporative emission control system by selectively heating a small portion of the adsorption material before air purging of the canister. Granular activated carbon is a preferred adsorbent material. The adsorbent portion that is heated is located at the purge air inlet region of the canister system. Generally, only about 1% to 5%, and preferably less than 3%, by volume of the total adsorbent is heated prior to purging. But that portion is heated to a temperature at which the normal flow of ambient purge air will remove substantially all of the adsorbed fuel, including the hydrocarbon heel, during a purge cycle. When high surface area carbon granules are employed, the upstream secondary carbon volume is preferably heated to about 350° F. (177° C.).
A volume of carbon granules heated to 350° F. is readily stripped of gasoline vapor with a flow of ambient air of suitable duration. No hydrocarbon heel remains in the heated volume, and during the subsequent vapor loading cycle, vapor breaking through the main carbon volume is readily adsorbed in the “green,” or hydrocarbon-free, secondary volume.
Preferably, the relatively small secondary volume of adsorbent is thus heated prior to each purge cycle. Heating may be initiated by the engine control computer module and accomplished using vehicle battery-powered, embedded electrical heating elements, or the like. When a temperature sensor in the secondary adsorbent volume indicates that a suitable purge temperature has been reached, the engine control computer causes the heater to be shut off and the purge valve to be opened. Engine induction system vacuum induces the flow of purge air from the engine compartment, through the secondary and primary adsorbent volumes and into the operating engine. The air flow both strips the volume of hydrocarbons and cools the granules to restore their full adsorptive capacity before the next vapor load cycle.
The secondary volume of adsorbent may be located in the canister adjacent the air purge inlet. In this embodiment, the secondary volume is closely adjacent the main adsorbent volume and it may be preferable to provide some thermal insulation between them. In a second embodiment, the small heated volume is located in a smaller, secondary molded canister in the air inlet line with the vent valve.
Other objects and advantages of the invention will become more apparent from a detailed description of preferred embodiments that follows. The description will refer to the drawings that are described in the next section of this specification.
REFERENCES:
patent: 4598686 (1986-07-01), Lupoli et al.
patent: 4732588 (1988-03-01), Covert et al.
patent: 4778495 (1988-10-01), Bishop et al.
patent: 4864103 (1989-09-01), Bishop et al.
patent: 5355861 (1994-10-01), Arai
patent: 5377644 (1995-01-01), Krohm
patent: 5456236 (1995-10-01), Wakashiro et al.
patent: 5482023 (1996-01-01), Hunt et al.
patent: 5687697 (1997-11-01), Ishikawa et al.
patent: 6098601 (2000-08-01), Reddy
General Motors Corporation
Grove George A.
Moulis Thomas N.
LandOfFree
Evaporative emission control canister system for reducing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Evaporative emission control canister system for reducing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Evaporative emission control canister system for reducing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2448487