Abstract:
An evaporative emissions canister includes a housing containing a hydrocarbon adsorbing material, such as carbon. The canister may be configured to such that a portion acts as a buffer canister of such that the entire canister is used to adsorb hydrocarbon emissions. The canister housing is generally cylindrical with a reduced cross-sectional area portion and is configured in a manner to allow flow along a relatively straight line; with both features acting to increase purge efficiency and reduce restriction, respectively.

Description:
FIELD OF THE INVENTION 
     This invention relates to evaporative emission systems for automotive vehicles, and more particularly to, evaporative emissions canisters. 
     BACKGROUND OF THE INVENTION 
     Conventional automotive evaporative systems include a carbon canister communicating with a fuel tank to adsorb fuel vapors from the fuel tank. The carbon canister adsorbs the fuel vapor until it is saturated, at which time, the fuel vapor is desorbed from the carbon canister by drawing fresh air therethrough. Such a system is shown in FIG. 1. System 10 includes fuel tank 12 coupled to carbon canister 14 and engine 16 via vapor purge lines 17 and 24, respectively. Fuel vapor from tank 12 flows through line 17 into canister 14, where the fuel is adsorbed onto the carbon. Fresh air is then emitted through vent port 18 to atmosphere. When the canister becomes saturated with fuel, engine controller 19 commands valve 20 to open so that the fuel may be desorbed from the carbon and flow to engine 16 via purge line 24. 
     Occasionally, it may be necessary to purge the canister when both the canister is full and a large vapor volume exists in the fuel tank. Thus, upon purging, in the system described with reference to FIG. 1, vapor is drawn from both the canister and the engine. As a result, the large vapor volume flowing directly from the tank to the engine may cause the engine to temporary run in an undesirably rich condition. To prevent this, a relatively small carbon canister 26, typically termed a buffer canister, is disposed between the fuel tank and the engine. This buffer canister 26, due to its relatively small size, quickly saturates such that the vapors flowing to the engine may break through the carbon bed to be consumed by the engine. The effect of the buffer canister is to reduce any large hydrocarbon or fuel vapor spikes going to the engine to prevent the over rich condition. In other words, the buffer canister acts to dampen any fuel vapor spikes typically flowing directly from the fuel tank to the engine. 
     The disadvantage with this approach is primarily due to the fact that a secondary canister must be utilized in the system. This creates added expense due to couplings, vapor lines, associated hardware and general system complexity. To overcome these disadvantages, some systems utilize a vapor purge line flowing directly from the tank to the primary carbon canister, with the purge line being embedded deep into the carbon bed. Such a system is depicted in FIG. 2. In this system, when fuel vapor from the fuel tank 12 is to be purged directly into engine 16, the fuel vapor must at least go through a portion of the primary carbon canister, shown at bracket 28. Thus, a portion of the canister acts to buffer any hydrocarbon spikes from the fuel tank. 
     The inventors of the present invention have found certain disadvantages with the system described in FIG. 2. For example, in order to utilize a portion of the primary canister as a buffer, fuel vapor line 17 must necessarily penetrate into the carbon bed. Because of this, manufacturing issues arise in that the vapor purge line must be sealed in a manner so as to prevent leakage between the line and the atmosphere at the intersection with the primary canister. In addition, the purge line must contain a screen or filter to prevent the carbon from dislodging from the canister. Furthermore, the amount of penetration is determined on a vehicle line basis. Thus, a relatively small engine may require a certain volume for the buffer whereas a relatively large engine may require a different volume. This fact requires unique manufacturing tooling to precisely locate the depth of the fuel tank purge line within the carbon canister. 
     The inventors of the present invention have found further disadvantages with both prior art systems. For example, because the relatively constant cross-sectional area of the canister, vapor may inadvertently break through the vent port. In addition, these canisters are generally laid out such that the vapor flows through the canister in a serpentine manner. This may cause an increase in the flow restriction, which may have the effect of premature shutting off of the fuel fill nozzle, for example. Also, to accommodate various vehicle line applications, each system may require a plurality of different size canisters located in a variety of positions throughout the system, making packaging on a vehicle a concern. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an easily manufacturable, multiple application carbon canister which overcomes the disadvantages of prior art canisters. This object is achieved, and disadvantages of prior art are overcome, by providing a novel evaporative emission canister for an evaporative emission system. The system includes a fuel tank coupled to an engine via a vapor purge line. The canister, in turn, is coupled to the fuel tank and the engine. In one particular aspect of the invention, the canister includes a generally cylindrical housing defining a circumference. The housing has a first, relatively larger cross-sectional area portion, a second, relatively smaller cross-sectional area portion, and a tapered section therebetween. A first hydrocarbon adsorbing zone is entirely disposed in a portion of the first area to define a first plenum adjacent a first end of the housing. A second hydrocarbon adsorbing zone is disposed in a portion of the first area, the tapered section, and a portion of the second area to define a second plenum between the first the second hydrocarbon adsorbing zones and a third plenum adjacent a second end of the housing. A vent port is formed on the second portion for venting air to atmosphere upon adsorption of hydrocarbons and for admitting air upon desorption of hydrocarbons during a purging operation of the canister. The vent port communicates directly with the third plenum and is coupled thereto in a tangential orientation relative to the circumference of the housing so as to create a swirling flow as fluid enters the third plenum upon a purging operation. A purge port is formed on the first portion and is adapted for connection to the engine to allow desorbed hydrocarbon to flow thereto. The purge port communicates directly with the first plenum and is coupled thereto in a tangential orientation relative to the circumference of the housing so as to create a swirling flow as fluid enters the first plenum upon loading the canister. An intermediate port is formed on the first portion and is disposed between the vent port and the purge port. The intermediate port communicates directly with the second plenum and is coupled thereto in a tangential orientation relative to the circumference of the housing so as to create a swirling flow as fluid enters the second plenum upon loading the canister. The intermediate port is selectively coupled to the fuel tank. When fuel vapor from the tank is directly purged into the intermediate port, the first hydrocarbon adsorbing zone acts as a hydrocarbon buffer. When fuel vapor from the tank is directly purged into the purge port and when the intermediate port is closed, the first hydrocarbon adsorbing zone cooperates with the second hydrocarbon adsorbing zone such that both zones adsorb hydrocarbons. 
     The second plenum is adapted to receive at least one standoff. The standoff separates the first and second hydrocarbon adsorbing zones. The standoff is sufficiently sized so as to accommodate a plurality of sizes of the first hydrocarbon adsorbing zone, respectively. The canister may also include a biasing means to bias the first and the second hydrocarbon adsorbing zones in a compressed manner. 
     Accordingly, an advantage of the present invention is ease of manufacturability and reduced manufacturing costs. 
     Another advantage of the present invention is that a multiple application canister may be produced and slightly adapted for a particular vehicle line. 
     Another, more specific, advantage of the present invention is that the canister may be quickly configured to provide maximum vapor storage capacity. 
     Another, more specific, advantage of the present invention is that the canister may be quickly configured with different buffering zone volumes. 
     Yet another advantage of the present invention is that a single unit may be easily packaged on a particular vehicle line. 
     Still another advantage of the present invention is reduced flow restriction through the canister. 
     Yet another advantage of the present invention is reduced potential for hydrocarbon breakthrough. 
     Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIGS. 1 and 2 are schematic representations of prior art evaporative emissions systems for automotive vehicles; 
     FIG. 3 is a schematic representation of an evaporative emission system for an automotive vehicle according to one aspect of the present invention; 
     FIG. 4 is a schematic representation of an evaporative emission system for an automotive vehicle according to another aspect of the present invention; 
     FIG. 5 is a perspective view of an evaporative emissions canister used in the system of FIGS. 3 and 4; and, 
     FIGS. 6a and 6b are side views of alternative configurations of the canister taken along line 6-6 of FIG. 5 and as shown in FIGS. 3 and 4, respectively. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning first to FIGS. 3, 5, 6a and 6b, evaporative emissions system 50 includes fuel tank 52 connected to tank vapor purge line 54. Tank vapor purge line 54 is connected to evaporative emissions canister 56 via intermediate port 57. Canister 56, in this example, includes a bed of activated carbon to adsorb hydrocarbon emissions from fuel tank 52. Engine purge line 60 is connected to canister 56 via purge port 61 and communicates between canister 56 and engine 62. Vent line 63 is connected to canister 56, via vent port 68, to vent air to atmosphere. Vapor management valve 64, which is a conventional solenoid actuated valve, is disposed within line 60 and is controlled by engine controller 69. Canister vent valve 66, which may also be a solenoid actuated valve connected to controller 69, is normally open. Valve 66 is closed upon conduction of on-board diagnostic testing (OBD), as is well known to those skilled in the art. 
     As the volume of vapor increases in fuel tank 52, the vapor flows through line 54 into port 57 to canister 56 where the hydrocarbons are adsorbed and air passes through vent line 63 to the atmosphere. Thus, as is well known to those skilled in the art, canister 56 acts to store hydrocarbons while preventing their release to the atmosphere. Upon purging canister 56, valve 64 is opened and the engine&#39;s vacuum serves to draw fresh air through vent port 68 so as to desorb the hydrocarbons stored in canister 56. The hydrocarbons thus released are then routed, via line 60, to engine 62 to be consumed therein. 
     According to one aspect of the present invention, as best shown in FIGS. 5, 6a and 6b, canister 56 includes a generally cylindrical housing 70 defining circumference 72 and longitudinal axis 73. In a preferred embodiment, housing 70 is formed of a plastic material. A circumferential housing 70 is desirable to create a more even flow distribution through the canister for better carbon bed utilization as well as increased mechanical strength, less housing material per unit volume and reduced flow restriction. Housing 70 has a first, relatively larger cross-sectional area portion 74, a second, relatively smaller cross-sectional area portion 76, and a tapered section 78 therebetween. A first hydrocarbon adsorbing zone 80 is entirely disposed in a portion of first area 74 to define first plenum 82 adjacent first end 84 of housing 70. A second hydrocarbon adsorbing zone 86, axially aligned with first hydrocarbon adsorbing zone 80, is disposed in a portion of first area 74, tapered section 78, and a portion of second area 76 to define second plenum 88 between first hydrocarbon adsorbing zone 80 and second hydrocarbon adsorbing zone 86 and third plenum 90 adjacent second end 92 of housing 70. Second hydrocarbon adsorbing zone 86 has a smaller cross-sectional area that first hydrocarbon adsorbing zone 80 so that, upon a purging operation, a more complete and efficient purge of the carbon may occur at the location of vent port 68. This is desirable to reduce the potential for hydrocarbon breakthrough to atmosphere upon re-loading of the canister. First hydrocarbon adsorbing zone 80 and second hydrocarbon adsorbing zone 86 are axially aligned so that the flow restriction through the canister is minimized. First hydrocarbon adsorbing zone 80 and second hydrocarbon adsorbing zone 86 are biased with bias spring 93 in a compressed manner. This reduces the potential for a direct leak path through the adsorbing zones. In addition, screens 96, 98, 100 and 102 are positioned at the ends of the zones 80, 86 to contain the carbon. 
     Vent port 68 is formed on second portion 76 for venting air to atmosphere upon adsorption of hydrocarbons and for admitting air upon desorption of hydrocarbons during a purging operation of the canister. In a preferred embodiment, vent port 68 communicates directly with third plenum 90 and is coupled thereto in a tangential orientation relative to circumference 72 of housing 70 so as to create a swirling flow as fluid enters third plenum 92 upon a purging operation. The swirling flow causes a better desorption of the carbon because a more even flow distribution may be provided across the face of second zone 86. 
     Purge port 61 is formed on first portion 74 and is adapted for connection to engine 62 to allow desorbed hydrocarbon to flow thereto. In a preferred embodiment, Purge port 61 communicates directly with first plenum 82 and is coupled thereto in a tangential orientation relative to circumference 72 of housing 70 so as to create a swirling flow as fluid enters first plenum 82 upon loading the canister. 
     Intermediate port 57 is formed on first portion 74 and is disposed between vent port 68 and purge port 61. Intermediate port 57 communicates directly with second plenum 88 and is coupled thereto in a tangential orientation relative to circumference 72 of housing 70 so as to create a swirling flow as fluid enters second plenum 88 upon loading the canister. 
     According to the present invention, intermediate port 57 is selectively coupled to fuel tank 52. When fuel vapor from tank 52 is directly purged into intermediate port 57, first hydrocarbon adsorbing zone 80 acts as a hydrocarbon buffer. This buffer zone acts to dampen any vapor spikes when purging from the tank directly to the engine, as is shown in the configuration of FIG. 3. 
     Alternatively, system 50 may be configured as shown in FIG. 4. In this configuration, intermediate port 57 is plugged with cap 93 and line 54 is directly connected to line 60 via &#34;T&#34; connector 94. Thus, when fuel vapor from tank 52 is directly purged into purge port 61 and when intermediate port 57 is closed, first hydrocarbon adsorbing zone 80 cooperates with second hydrocarbon adsorbing zone 86 such that both zones adsorb hydrocarbons. In this configuration, when no buffer zone is required for the particular vehicle line, the entire carbon available may be utilized to store the hydrocarbons. 
     In a preferred embodiment, second plenum 88 is adapted to receive standoffs 110, 112. Standoffs 110, 112 separate first hydrocarbon adsorbing zone 80 and second hydrocarbon adsorbing zone 86. The standoffs are sufficiently sized in length so as to accommodate a plurality of sizes of first hydrocarbon adsorbing zone 80. That is, when a relatively large buffer zone is required, standoffs 110, 112 are relatively small, as shown in FIG. 6b. On the other hand, when a relatively small buffer zone is required, standoffs 110, 112 are relatievely large, as shown in FIG. 6a. In addition, when no buffer zone is required such that port 57 is plugged and zone 80 cooperates with zone 86 to create a relatively high capacity canister, standoffs 110, 112 are made relatively small, as shown in FIG. 6b. 
     While the best mode for carrying out the invention has been described in detail, those skilled in the art in which this invention relates will recognize various alternative designs and embodiments, including those mentioned above, in practicing the invention that has been defined by the following claims.