JP5161318B2 - Fuel vapor storage and recovery system - Google Patents

Description

  The present invention relates to a fuel vapor storage and recovery device for reducing vaporous emissions from automobiles.

  Fuel vapor storage and recovery devices having fuel vapor storage canisters have been widely known in the art for many years. Gasoline fuel used in many internal combustion engines is very volatile. Vaporous emissions of fuel vapor from a vehicle having an internal combustion engine are generated primarily by ventilation of the fuel tank of the vehicle. When the vehicle is parked, the air will carry hydrocarbons escaped from the fuel tank due to changes in temperature and pressure. Some fuel will necessarily evaporate against the air in the tank and take the form of steam for this purpose. If the air released from the fuel tank can flow out and flow untreated around, it will definitely carry this fuel vapor. There is government regulation on how much fuel vapor is emitted from the vehicle fuel system.

  Normally, to prevent fuel vapor loss to the surroundings, the vehicle fuel tank is vented through a passage to a canister containing a suitable fuel adsorbent such as activated carbon. Fine particles of activated carbon with a large surface area are widely used to temporarily adsorb the fuel vapor.

  A fuel vapor storage and recovery system having a fuel vapor storage canister (so-called carbon canister) is stopped during an extended period of time when the vehicle is refueled and the steamed air is discharged from the fuel tank (refueling discharge: refueling) emissions), it is necessary to deal with fuel vapor emissions.

  Fuel recovery systems for the European market usually do not play an important role because these refueling emissions are not generally discharged via carbon canisters. However, in an integrated fuel vapor storage and recovery system for the North American market, refueling emissions are emitted via carbon canisters.

  Obviously, due to the nature of the adsorbent in the carbon canister, the carbon canister has a limited packing capacity. While it is desirable to use a carbon canister with a high carbon operating capacity, it is desirable to use a relatively small volume carbon canister for design purposes. In order to ensure sufficient carbon operating capacity of the carbon canister at all times during typical operation of the internal combustion engine, a certain negative pressure is applied to the interior of the canister via the fuel vapor discharge port of the carbon canister from the intake system of the engine. As a result, the atmosphere is guided to the canister and reaches the atmospheric intake port, and the captured fuel vapor is captured and conveyed to the intake manifold of the intake system of the engine via the fuel vapor discharge port. During the canister purge mode, the fuel vapor stored in the carbon canister is combusted in the internal combustion engine.

  Modern fuel vapor storage and recovery systems are very efficient, but they still release hydrocarbons that remain in the atmosphere. These so-called "bleed emissions" (diurnal breathing loss / DBL) are caused by diffusion, especially when there is a high concentration gradient of hydrocarbons between the carbon canister air vent port and the adsorbent. Brought about. When the hydrocarbon concentration gradient can be reduced, bleed emission can be significantly reduced. Obviously, this can be achieved by increasing the operating capacity of the carbon canister.

  However, only some percentage of the hydrocarbons stored in the carbon canister is effectively swept away or released during the purge mode. This is a problem for a car that has a limited time for purging. For example, in an electric hybrid car, the operation mode of the internal combustion engine is relatively short.

  Another problem is associated with the use of so-called flexi fuels with large amounts of ethanol. Ethanol is a highly volatile fuel with a relatively high vapor pressure. For example, so-called E10 fuel (10% ethanol) is currently the most easily vaporized on the market. This means that the carbon canister fuel vapor uptake from the fuel tank is extremely high. On the other hand, in the normal purging mode of conventional carbon canisters, only some percent of the fuel vapor wicking is released. As a result, the fuel vapor capacity of a typical carbon canister is used up relatively early. The bleed emission of a full carbon canister then increases to a degree that usually exceeds the emission values given by law.

  In order to improve the purge removal rate during the purging mode, a few steam storage and recovery devices using so-called purge heaters have been proposed. By heating the air introduced into the canister via the air intake port, the efficiency of removing hydrocarbons trapped in the fine pores of the adsorbent is significantly improved.

  For example, U.S. Pat.No. 6,230,693 (B1) describes a fuel evaporative gas control system that reduces the amount of fuel vapor discharged from a vehicle by using an auxiliary canister that operates with a storage canister of the fuel evaporative gas control system. Disclose. The storage canister includes a first adsorbent and has a vent port in communication therewith. The auxiliary canister has a main body portion, first and second passages, a heater, and a connector. Inside the main body, the second adsorbent contacts the heater all over. In the regeneration phase of operation of the control system, the heater heats the purge air passing through the second adsorbent. This can more easily release the fuel vapor adsorbed during the previous storage phase in operation by the second and first adsorbents, and the fuel vapor will burn during combustion.

  Further, according to US Pat. No. 6,230,693, the storage canister of the fuel evaporative gas control system has two adjacent compartments for storing fuel vapors connected by a flow path. In particular, partitioning the canisters actually means flow suppression. Since the driving pressure of the flow through the canister is very low, minimizing flow suppression is an important design consideration.

  It is an object of the present invention to provide a fuel vapor storage and recovery apparatus having a fuel vapor storage canister having a further improved so-called bleed emission, that is, an improved radial breathing loss efficiency. Another object of the present invention is to provide a fuel vapor storage and recovery device including a fuel vapor storage canister having a high operating capacity even with a relatively small design and a low carbon content.

  These and other objects are achieved by a fuel vapor storage and recovery device having a fuel vapor storage canister, the fuel vapor canister having at least first and second vapor storage partitions having adsorbents; At least a steam suction port, an air vent port, and a purge port, and the fuel vapor storage canister has an air flow between the steam suction port and the air vent port and between the air vent port and the purge port. A path is formed, and the first and second vapor storage partitions are separated from each other by an air gap diffusion barrier in the flow direction.

  In particular, by providing an air gap insulation between several steam storage partitions and several steam storage beds, the lower concentration of hydrocarbons, i.e., diffusion of hydrocarbons towards the atmosphere is very slow, This significantly reduces the dialing breathing loss.

  In one embodiment of the fuel vapor storage device according to the present invention, at least the first and second vapor storage partitions are arranged in a coaxial relationship.

  In the present application, the term “coaxial” does not mean that the fuel vapor storage partition necessarily has a circular cross section. These partition portions may have a rectangular cross section. In one embodiment of the present invention, the fuel vapor storage device may have at least some adjacent vapor storage partitions.

  The fuel vapor storage device according to a preferred embodiment of the present invention is characterized in that a third vapor storage partition is disposed in a coaxial relationship with the first and second vapor storage partitions. To do. The third vapor storage partition may have porous monolithic carbon as an adsorbent. As will be apparent to those skilled in the art, the third steam storage partition and the first and second steam storage partitions are similarly filled or included with fine granular activated carbon.

  In a preferred embodiment of the fuel vapor storage device according to the present invention, the vapor storage partition is integrated into a common canister housing and meets the need for a compact design that requires little space.

  In order to eliminate a non-use area in the steam storage bed, each of the steam storage partitions has a circular cross-sectional area, and the downstream partition of the air flow from the atmospheric vent port toward the purge port. Has a larger cross-sectional area than that of the upstream steam storage partition. Due to the design of the vapor storage partition, the purging gas effectively flows through all the carbon beds, improving the purge removal rate during the purge mode and greatly reducing bleed emissions.

  In this regard, each of the vapor storage partitions has a cross-sectional area at the downstream end thereof that is greater than or equal to the cross-sectional area of the upstream end with respect to the air flow from the atmospheric vent port toward the purge port. Sometimes this device has advantages.

  In one embodiment of the fuel vapor storage device according to the present invention, at least one flow diverter is provided that forms an expanded air gap diffusion barrier. Due to the presence of such a flow diverter, the length of the diffusion barrier air path can be many times, or at least twice as long.

  The flow diverter has the shape of a cup-like insert that is at least partially arranged around one steam storage bed.

  One embodiment of the fuel vapor storage device according to the present invention has a purge heater that operates during purging, thereby greatly improving the purge removal rate during operation of the internal combustion engine.

  The purge heater is located, for example, in a purge heater partition that directly communicates with the purge port.

  While it has been found advantageous to locate the purge heater divider at the upstream end of the air flow during the purge cycle, alternatively the purge heater divider is located in one fuel storage bed. May be.

  In order to facilitate the transfer of heat from the purge heater to the carbon bed, it is effective when the purge heater partition is concentrically surrounded by the vapor storage bed at least in a non-insulated form, thereby surrounding the Heat can be released to the steam storage bed. As described at the beginning of this application, higher temperatures allow full purging of hydrocarbons from the carbon bed, increasing volume capacity and preventing fuel vapor breakthrough during the fuel vapor storage cycle. . In this respect, the purge results are also significantly improved by the same temperature distribution through the carbon bed.

  “Non-insulated” does not mean that the purge heater or purge heater element is in direct contact with the carbon bed, but the purge heater is not shielded against the surrounding carbon bed. For example, the purge heater partition has a basket-like structure and allows heat to be released to the surrounding carbon bed.

  The purge heater has one or more electric heating elements, which are connected to an electrical energy source, such as a car battery.

  The purge heater has, for example, an electrically conductive ceramic as the heating element.

  Alternatively, the purge heater comprises electrically conductive carbon, preferably porous monolithic carbon. Such porous monolithic carbon is disclosed in, for example, US Application Publication No. 2007-0056954 (A1). These monolithic carbon heating elements have a channel structure that allows air flow from the heating elements and can facilitate heat release directly through purging air absorbed from the atmosphere.

  The present invention will now be described by way of example with reference to the accompanying drawings.

1 shows a cross-sectional view of a carbon canister according to the present invention. It is a decomposition | disassembly schematic diagram of the partition part of the said carbon canister.

  A fuel vapor storage and recovery apparatus 1 is shown in FIG. The illustration is schematic, and the components are not drawn to scale.

  The fuel vapor storage and recovery apparatus 1 has a steam intake port 3 connected to a fuel tank (not shown), a vent port 4 leading to the atmosphere, and a purge port 5 connected to an internal combustion engine of an automobile (not shown). ing. The carbon canister 2 is packed with an adsorbent in the form of finely divided activated carbon.

  During the period when the automobile engine is stopped, the carbon canister 2 is connected to the fuel tank of the automobile via the steam intake port 3 and is connected to the atmosphere via the ventilation port 4.

  As described at the beginning of the present application, the fuel in the fuel tank evaporates into the air space above the full liquid level of the fuel tank during the vehicle stop period. The steam carried by the air flows to the carbon canister 2 through the steam intake port 3. When the vehicle is refueled, the internal combustion engine is usually also stopped. In the integrated system, the air flow through the steam intake port 3 is assumed to have a flow rate corresponding to the refueling flow rate by the fuel supplied to the fuel tank. Accordingly, the hydrocarbons carried by the air are pumped into the carbon bed of the carbon canister at a flow rate of up to 60 liters per minute. The activated carbon in the carbon canister adsorbs hydrocarbons, and the hydrocarbon molecules are trapped in the carbon internal pore structure. More or less purified air is released from the vent port 4.

  In the vehicle engine operation cycle, a flow path between the vent port 4 and the purge port 5 is established. The internal combustion engine sucks a predetermined amount of air from the atmosphere through the ventilation port 4, across the carbon canister 2, and into the purge port 5 for burning in the cylinder of the internal combustion engine, thereby purging the adsorbent of the carbon canister 2. Is done.

  In the figure, arrow 6 indicates the air flow during purging of the carbon canister. Hereinafter, the terms “downstream” and “upstream” always refer to the air flow during purging of the carbon canister 2.

  The carbon canister 2 has first, second, and third steam storage partitions 7, 8, 9. The first steam storage partition section 7 is the steam storage partition section adjacent to the steam intake port 3 and the largest steam storage partition section with respect to the air flow at the time of introduction of hydrocarbons into the carbon canister 2.

  As is clear from FIG. 1, the vapor storage partitions 7, 8, 9 have a circular cross-sectional area and are arranged in a coaxial relationship. The first steam storage partition 7 surrounds the steam storage partitions 8 and 9. A purge heater partition 10 is provided next to the vent port 4 on the upstream side of the third steam storage partition 9, which is also cylindrical and has a circular cross section. The purge heater partition 10 includes four electric heating elements 11, which are electrically connected in series to an electric energy source, for example a vehicle battery. The heating element can be, for example, a PTC thyristor or an NTC thyristor, or can be, for example, an electrically conductive carbon heating element.

  The heating element may have a cylindrical shape, and an electrically conductive porous carbon monolith such as a synthetic carbon monolith generally disclosed in US Patent Application Publication No. 2007-0056954 may be used. Each heating element 11 forms a continuous longitudinal channel (not shown), allowing air flow in the longitudinal direction at each heating element. The heating element 11 is activated only during the purging operation of the fuel vapor storage and recovery device 1.

  The purge heater partition 10 has two suction openings 12 on the upstream end face for introducing the atmosphere into the purge heater partition 10. The purge heater partition 10 has a relatively thin peripheral wall 13 that releases heat from the heating element 11 of the resistor to the carbon bed around the first vapor storage partition 7. Designed to be transmitted.

  However, first, the heating element 11 directly transfers heat to the atmosphere introduced into the purge heater partition 10. The purge heater partition 10 is aligned with the third steam storage partition 9 at its downstream end, and the third steam storage partition 9 is connected to the second steam storage partition 8 at its downstream end. The purge heater partition 10 and the third and second steam storage partitions 9 and 8 are coaxially surrounded by the first steam storage partition 7.

  The first and second vapor storage partitions 7 and 8 are packed or filled with fine activated carbon, and the third vapor storage partition 9 can include a porous monolithic carbon element. .

  Between the third steam storage partition part 9 and the second steam storage partition part 8, and similarly between the second steam storage partition part 8 and the first steam storage partition part 7, the first and Second air gaps 14a and 14b are provided.

  The air gap 14a that forms the transition from the third steam storage partition part 9 to the second steam storage partition part 8 is the difference in diameter between the third steam storage partition part 9 and the second steam storage partition part 8. According to funnel shape. The first steam storage partition 7 has a constant diameter over the entire length and is smaller than the diameter of the second steam storage partition 8. Moreover, the 2nd vapor | steam storage partition part 8 also has a fixed diameter over the full length.

  The carbon bed in the second steam storage partition 8 is partially contained and supported by a cup-shaped insert 15 that forms a U-turn flow path for purge air as shown by the arrow in FIG. To do. With this design, the length of the air passage is twice the length of the second steam storage partition 8. The insert 15 functions as a flow diverter for purging air.

  The size of each partition of the carbon canister 2 is best obtained from the exploded view of FIG.

  Referring again to FIG. 1, it can be seen that the insulating element 17 is disposed between the bottom cover 16 and the insert 15 of the carbon canister 2.

  Furthermore, a ring-shaped channel 18 forms a transition to the first vapor storage partition 7 at the downstream end of the air gap 14. In the ring-shaped channel 18, a flow opening 19 is formed, and the flow opening 19 is configured so that the air flow of the purge air is easily directed to the upstream end of the first vapor storage partition 7. .

  In the operation cycle of the internal combustion engine of the vehicle, the fuel vapor storage and recovery apparatus 1 of the present invention is set to the purge mode. Air from the internal combustion engine of the vehicle is guided to the purge partition 10 via the ventilation port 4 and the suction opening 12. The heating element 11 is electrically connected to the vehicle battery during purging. The air flow through or around the heating element 11 is thereby heated to a temperature below 150 degrees Celsius. At the same time, the heat radiation emitted from the heating element 11 heats the carbon bed around the first vapor storage partition 7. The heated air is transferred to the bottom grid 20 at the downstream end of the carbon bed in the steam storage partition 8 and the second steam storage partition 8 through the third steam storage partition 9 and the air gap 14a. It flows in and is redirected upward by the cup-shaped insert 15 in the extended and routed air gap 14b. On the way, the atmosphere is filled with hydrocarbons stored in the carbon bed. As shown by the arrows in FIG. 1, this air flow makes a U-turn inside the extended air gap 14b and flows into the carbon bed of the first steam storage partition 7 at the end of the air gap 14b. Eventually, a purging line is introduced into the purge port 5 and connected to the internal combustion engine.

  When the internal combustion engine is shut down, the discharge of fuel vapor entering the carbon canister from the vapor intake port 3 will be directed in the opposite direction toward the vent port 4, whereby the air gaps 14a, 14b provide an effective diffusion barrier. Therefore, bleed emission can be effectively reduced.

DESCRIPTION OF SYMBOLS 1 Fuel vapor storage and recovery apparatus 2 Carbon canister 3 Steam intake port 4 Ventilation port 5 Purge port 6 Arrow 7 First steam storage partition 8 Second steam storage partition 9 Third steam storage partition 10 Purge heater partition 11 Heating element 12 Suction opening 13 Walls 14a, 14b Air gap 15 Insert 16 Bottom lid 17 Insulating element 18 Ring-shaped channel 19 Flow opening 20 Bottom grid

Claims (13)

A fuel vapor storage and recovery device having a fuel vapor storage canister, wherein the fuel vapor storage canister includes at least first and second vapor storage partitions filled with an adsorbent to form a vapor storage bed, and a fuel Having at least one vapor inlet port connected to the tank, an air vent port, and a purge port;
The fuel vapor storage canister forms an air flow path between the at least one vapor intake port and the atmospheric vent port and between the atmospheric vent port and the purge port;
The first steam storage partition is closer to the steam intake port than the second steam storage partition, the first steam storage partition accepts steam from the fuel tank,
It said first and second vapor storage partition section in the flow direction, Ri Contact are separated from each other by an air gap diffusion barrier,
Before Symbol first and the second vapor storage partition portion is disposed in coaxial relationship, a third steam disposed in the first and the coaxial relationship with said second vapor storage partition part A fuel vapor storage and recovery device , comprising a storage partition, wherein the second and third steam storage partitions are located in the first steam storage partition . 2. The fuel vapor storage and recovery apparatus according to claim 1, wherein the third vapor storage partition portion has porous monolithic carbon as an adsorbent. 3. 3. The fuel vapor storage and recovery apparatus according to claim 1, wherein the vapor storage partition is integrated in a common canister housing. 4. 4. The fuel vapor storage and recovery device according to claim 1, wherein each of the vapor storage partition portions has a circular cross-sectional area and extends from the atmospheric vent port toward the purge port. The fuel vapor storage and recovery apparatus according to claim 1, wherein the air flow has a cross-sectional area of the downstream partition portion larger than that of the upstream steam storage partition portion. 5. The fuel vapor storage and recovery apparatus according to claim 1, wherein each of the vapor storage partition portions has an air flow from the atmospheric vent port toward the purge port at a downstream end portion thereof. A fuel vapor storage and recovery device having a cross-sectional area greater than or equal to the cross-sectional area of the upstream end with respect to the flow. 6. The fuel vapor storage and recovery apparatus according to claim 1, further comprising at least one flow diverter forming an extended air gap diffusion barrier. . 7. The fuel vapor storage and recovery device of claim 6, wherein the flow diverter has the shape of a cup-shaped insert disposed at least partially around one vapor storage bed. Steam storage and recovery equipment. The fuel vapor storage and recovery apparatus according to any one of claims 1 to 7, further comprising a purge heater that operates during purging. 9. The fuel vapor storage and recovery apparatus according to claim 8, wherein the purge heater is located in a purge heater partition that directly communicates with the purge port. 10. The fuel vapor storage and recovery device according to claim 8 or 9, wherein the purge heater partition is at least in a non-insulated form and is coaxially surrounded by the vapor storage bed, so that heat is released to the surrounding vapor storage bed. A fuel vapor storage and recovery device characterized by that. 11. The fuel vapor storage and recovery apparatus according to claim 8, wherein the purge heater has one or more electric heating elements, and the electric heating elements are connected to an electric energy source. A fuel vapor storage and recovery device. 12. The fuel vapor storage and recovery device according to claim 8, wherein the purge heater has an electrically conductive ceramic as the heating element. 13. The fuel vapor storage and recovery apparatus according to claim 8, wherein the purge heater includes electrically conductive carbon, preferably porous monolithic carbon.