Abstract:
An emissions control canister including an insert having an elongate well and flange. The insert extends into a chamber such that a carbon adsorption column is a hollow cylinder around the insert. After vapors flow through the column of adsorbent, flow is directed through holes in the flange and out through an atmosphere port. The flow path through the hollow cylinder has an increased L/D ratio and improves emission performance. In a second embodiment, a cylindrical tube surrounds the exit port and extends into the insert, forcing vapor flow along a tortuous path between the cylindrical wall and the insert. In a third embodiment, a final scrubber is added inside the tube.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a device for controlling evaporative emissions from vehicles; more particularly, to a device for controlling hydrocarbon emissions during refueling and shutdown; and most particularly, to a carbon-filled canister having a cap-shaped internal insert resulting in an improved emissions flow path through the canister in both fill and purge modes.  
       BACKGROUND OF THE INVENTION  
       [0002]     Canisters for controlling evaporative emissions from vehicles are well known. Such emissions are created at two particular times: first, while a vehicle is being refueled, and vapor-laden air is being displaced from the fuel tank (known in the art as “refueling emissions”); and second, while a vehicle is shut down for an extended period, and fuel-laden adsorber in a canister spontaneously degases to the atmosphere (known in the art as “diurnal emissions” or “bleed” emissions).  
         [0003]     In the prior art, refueling emissions are collected typically by a canister disposed between a port in the vehicle fuel tank and outside atmosphere. The canister has two side-by-side chambers filled with an adsorptive carbon composition and connected at one end such that gases follow a U-shaped flow path through the canister. Valving is provided such that the canister can be degassed of fuel by engine vacuum when the vehicle&#39;s engine is restarted. In desorption mode, outside air is drawn into the canister in reverse flow through the adsorption mode exhaust port and sweeps adsorbed fuel from the carbon beds into the engine intake manifold.  
         [0004]     The California Air Resources Board (CARB) has published more stringent emissions regulations, known generally as Low Emission Vehicle II (LEV II) and Partial Zero Emission Vehicle (PZEV). PZEV is more stringent than LEV II.  
         [0005]     The CARB first adopted LEV standards in 1990. These first LEV standards ran from 1994 through 2003. LEV II regulations, running from 2004 through 2010, represent continuing progress in emission reductions. As the state&#39;s passenger vehicle fleet continues to grow and more sport utility vehicles and pickup trucks are used as passenger cars rather than work vehicles, the new, more stringent LEV II standards are necessary for California to meet federally-mandated clean air goals outlined in the 1994 State Implementation Plan (SIP). When LEV II is fully implemented in 2010, it is estimated that smog-forming emissions in the Los Angeles area will be reduced by 57 tons per day, while the statewide reduction will be 155 tons per day.  
         [0006]     PZEV-conforming vehicles are those that have achieved the CARB&#39;s cleanest tailpipe emission standard—the Super Ultra Low Emission Vehicle (SULEV) standard. In addition, they have nearly zero evaporative emissions and their emission control equipment is warranted for 15 years/150,000 miles.  
         [0007]     Prior art canisters as described above have been capable of meeting the original LEV standards, and with the addition of a downstream carbon “scrubber” can meet the PZEV standards. For both LEV II and PZEV applications, the canister&#39;s diurnal emission performance can be greatly improved by increased flow path length and partitioning of the carbon bed. These features allow the carbon closest to the fresh air source to be very well purged, and keep migrating hydrocarbon vapors away from the atmospheric port.  
         [0008]     One means known in the art for partitioning a canister is to provide a horizontal plate in the carbon bed, breaking the bed into two shorter chambers. An opening in the plate allows flow between chambers. The opening must be large enough to allow for acceptable flow restriction performance. Because the driving pressure for flow through a canister is very low, it is an important design consideration that flow restriction be kept to a minimum. This configuration requires two separate filings and settlings of loose carbon into the canister and thus increases manufacturing cost.  
         [0009]     A downstream carbon scrubber to meet PZEV diurnal emission levels is known to be installed either in line at the atmospheric port of a canister or in an added dedicated chamber molded onto the canister housing itself. Either configuration increases the overall size of a canister, which is undesirable because of space considerations in the region of a vehicle wherein a canister is installed. Thus what is needed in the art is means for incorporating a scrubber within the existing volume of a prior art canister while still meeting PZEV emission standards.  
         [0010]     Another means for improving the efficiency of a canister is to increase the L/D ratio wherein L is the length of the flow path and D is its average diameter. Therefore, what is further needed in the art is an improved canister having an increased L/D ratio.  
         [0011]     It is a principal object of the present invention to provide improved emissions adsorption means for meeting both the LEV II and PZEV standards at lower is manufacturing cost, greater simplicity of assembly, and low footprint in a vehicle.  
       SUMMARY OF THE INVENTION  
       [0012]     Briefly described, an emissions control canister in accordance with the invention includes improvements within the second of two parallel carbon bed chambers arranged for sequential flow of emissions from a fuel tank to atmosphere. An insert shaped roughly like an inverted top hat having an elongate bowl and a brim (flange) is disposed at the outlet end of the second chamber, the elongated bowl portion extending into the chamber. When the chamber is charged with carbon, the carbon column thus takes the form of a hollow cylinder around the insert rather than a solid cylinder as in the prior art.  
         [0013]     In a first embodiment in accordance with the invention, after the vapors flow through the hollow cylinder column of carbon adsorbent, the flow is directed through holes in the flange and out through the atmosphere port. The path for fuel vapors to flow along the hollow cylinder has a much increased L/D ratio as compared to the ratio for a solid cylinder of comparable length. This arrangement also reduces the total volume of carbon required for the canister.  
         [0014]     In a second embodiment, the chamber is provided with a thin cylindrical tube surrounding the atmosphere port and extending into the insert. Flow through the flange cannot escape directly to the atmosphere port as in the first embodiment but rather is forced along a tortuous path between the cylindrical tube and the insert wall, makes a 180° turn at the end of the tube, and then again flows the length of the tube before reaching the atmosphere port. The tortuous path reduces flow of hydrocarbons from the carbon beds to atmosphere, especially diurnal emissions which are driven only by diffusion and therefore are path-length sensitive.  
         [0015]     In a third embodiment, for meeting PZEV standards a cylindrically-shaped scrubber is added inside the cylindrical tube so that the flow, after making the second 180°, is directed through the scrubber which is formed, preferably, as a pressed carbon monolith having a plurality of longitudinal passageways. The scrubber preferably is secured and centered in the tube via a porous, compressible strap that extends around the end and along the sides of the scrubber.  
         [0016]     The disclosed canister design allows a single canister to be used for both LEV II needs (second embodiment) and PZEV needs (third embodiment) simply by installing a scrubber in the insert to meet PZEV requirements. Where neither PZEV nor LEV II standards is required, the cylindrical wall may be omitted, and the insert still provides emissions control superior to that provided by the prior art solid-cylinder carbon fill. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0018]      FIG. 1  is an elevational cross-sectional view of a prior art two-chamber emissions adsorption canister, configured for meeting LEV II requirements;  
         [0019]      FIG. 2  is an elevational view of a first prior art canister, showing a molded receptacle in the housing for incorporating a scrubber to meet PZEV requirements;  
         [0020]      FIG. 3  is an elevational view of a second prior art canister, showing a separate scrubber housing attached downstream of the atmosphere port in the canister to meet PZEV requirements;  
         [0021]      FIG. 4  is an elevational cross-sectional view of a first embodiment of an improved two-chamber emissions adsorption canister in accordance with the invention;  
         [0022]      FIG. 5  is an isometric view from beneath of an insert for use in an improved canister in accordance with the invention;  
         [0023]      FIG. 6  is an isometric view from above of the insert shown in  FIG. 5 ;  
         [0024]      FIG. 7  is an elevational cross-sectional view of a second embodiment of an improved two-chamber emissions adsorption canister in accordance with the invention;  
         [0025]      FIG. 8  is an isometric side view of a scrubber monolith for use in the tube shown in  FIGS. 7, 11 , and  12 ;  
         [0026]      FIG. 9  is a plan view of a flexible sling for holding and centering the scrubber shown in  FIG. 8 ;  
         [0027]      FIG. 10  is an isometric view from above showing the sling shown in  FIG. 9  installed onto the scrubber shown in  FIG. 8  to form a sub-assembly in preparation for insertion into the tube shown in  FIGS. 7, 11 , and  12 ;  
         [0028]      FIG. 11  is an elevational cross-sectional view of a third embodiment of an improved two-chamber emissions adsorption canister in accordance with the invention, showing the scrubber installed to meet PZEV requirements; and  
         [0029]      FIG. 12  is an elevational cross-sectional view showing the sling and scrubber shown in  FIG. 10  installed as an alternative form of the third embodiment shown in  FIG. 11 .  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]     The benefits of an improved emissions adsorption canister in accordance with the invention may be better appreciated by first considering exemplary prior art canisters.  
         [0031]     Referring to  FIG. 1 , a first prior art emissions adsorption canister  10  comprises a housing  12  including a first chamber  14  separated from a second chamber  16  by a septum  18 .  
         [0032]     Housing  12  includes a first molded end cap  20  formed on first chamber  14  for receiving and distributing vapors  22  entering from a fuel tank  24  via an entrance port  26 . Cap  20  includes a second port  28  selectively connectable to an internal combustion engine  30  for vacuum purge of adsorbed emissions  32  in reverse flow through canister  10 . Typically, fuel tank  24  and engine  30  are components of a vehicle  31 . The adsorption and purge modes are separated and regulated by valving and logical control means (not shown).  
         [0033]     Housing  12  includes a second end cap  34  formed on second chamber  16  for connecting second chamber  16  to atmosphere  36  via atmosphere port  38 .  
         [0034]     Housing  12  is molded such that first and second chambers  14 , 16  may be filled with emissions adsorbent, typically activated carbon  15 , from open end  40  by inverting housing  12 . Open end  40  is closed by a third end cap  42  having a crossover space  44  formed therein for allowing vapor flow  46  between chambers  14 , 16  in either direction. Perforated plates  48  keep the carbon from migrating within and out of the canister while permitting flow therethrough at low pressure resistance. An additional plate  50  is disposed across second chamber  16  and defines a final chamber  16   a  which may be filled with special adsorption material  17  having better bleed emissions performance.  
         [0035]     In adsorption mode of prior art canister  10 , vapors  22  flow through cap  20  and are partially adsorbed in chamber  14 . Additional vapors  52  flow through chamber  14 , crossover space  44  (vapors  46 ), and are additionally adsorbed  54  in chambers  16 , 16   a.  Air initially in canister  10  is expelled via atmosphere port  38 .  
         [0036]     In desorption mode, flow through the canister is reversed. First, a connection is opened between port  28  and engine  30 . Then, vapors  32  are stripped from carbon in chambers  14 , 16 , 16   a  by atmospheric air drawn in through port  38  and are conveyed to engine  30  where they are combusted.  
         [0037]     As noted above, a shortcoming of prior art canister  10  is the relatively low L/D ratio in chamber  16   a  making it less efficient. Further, chamber  16   a  must be filled with carbon and settled and plate  50  installed in separate steps prior to the main filling step for chambers  14 , 16 , at additional manufacturing complexity and cost.  
         [0038]     Referring to  FIG. 2 , a second embodiment  10 ′ of a prior art canister includes a housing  12 ′ having an integrally molded receptacle  12   a  for receiving a hydrocarbon scrubber (not visible) to meet PZEV standards.  
         [0039]     Referring to  FIG. 3 , a third embodiment  10 ″ of a prior art canister includes a housing  12 ″ and a separate scrubber housing  12   b  connected to the atmosphere port  38 ′ of housing  12 ″.  
         [0040]     Turning now to improved canisters in accordance with the invention, referring to  FIGS. 4 through 6 , a first embodiment  110  of an improved canister comprises a housing  112  including a first chamber  114  separated from a second chamber  116  by a septum  118 .  
         [0041]     Housing  112  includes a first molded end cap  120  on first chamber  114  for receiving and distributing vapors  22  entering from a fuel tank  24  via an entrance port  126 . Cap  120  includes a second port  128  connectable to an internal combustion engine  30  for vacuum purge of adsorbed emissions  32  in reverse flow through canister  110 . The adsorption and purge modes are separated and regulated by conventional valving and logical control means (not shown).  
         [0042]     Housing  112  includes an integral second end cap  134  on second chamber  116  for connecting second chamber  116  to atmosphere  36  via atmosphere port  138 .  
         [0043]     Housing  112  is molded such that first and second chambers  114 , 116  may be filled with emissions adsorbent, typically activated carbon, from open end  140  by inverting housing  112 . Open end  140  is closed after such filling by a third end cap  142  having a crossover space  144  formed therein for allowing vapor flow  46  between chambers  114 , 116  in either direction. Perforated plates  148  keep the carbon from migrating within and out of the canister while permitting flow therethrough at low pressure resistance.  
         [0044]     Prior art additional plate  50  is replaced by a generally “hat-shaped” insert  170  having a central well  172  formed by a cylindrical wall  174  and a flanged rim  176  surrounding the opening to well  172 . Flanged rim  176  is provided with a plurality of perforations  178  for low-resistance passage of vapors therethrough, and is further provided with a plurality of flexible peripheral wipers  180  and spacer posts  182  extending axially of insert  170 . During assembly of canister  110 , insert  170  is inserted, open end forward, into second chamber  116  through end  140  and is advanced until stopped by posts  182  engaging cap  134 . Wipers  180  are resiliently compressed against the walls of chamber  116 , centering the insert and retaining the insert against cap  134  while carbon adsorbent is filled around insert  170 , creating a hollow cylinder  184  of adsorbent between insert  170  and wall  171  of chamber  116 . Of course, carbon is further added to fill both chambers  114 , 116 .  
         [0045]     In adsorption mode of improved canister  110 , vapors  22  flow through end cap  120  and are partially adsorbed in chamber  114 . Additional vapors  52  flow through chamber  114 , crossover space  144  (vapors  46 ), and are additionally adsorbed  54  in chamber  116 . Vapor flow  56  in the hollow cylinder-shaped carbon region  184  around insert  170  is especially efficient in removing emissions because of an increased L/D ratio. Air initially in canister  110  is expelled via atmosphere port  138 .  
         [0046]     In desorption mode, flow is reversed through the canister. First, a connection is opened between port  128  and engine  30 . Then, vapors  32  are stripped from carbon in chambers  114 , 116  by atmospheric air drawn in through port  138  and are conveyed to engine  30  where they are combusted.  
         [0047]     As noted above, a benefit of improved canister  110  is the increased L/D ratio in second chamber  116 , making the unit significantly more efficient. Because chamber  116  is filled with carbon and settled along with chamber  114 , manufacturing complexity and cost are reduced over the prior art.  
         [0048]     Referring to  FIG. 7 , a second embodiment  210  of an improved emissions adsorption canister is substantially identical with first embodiment  110 , and numbering of most of the identical elements is omitted for clarity. The novel feature of embodiment  210  is the addition of a cylindrical tubular member (“tube”)  286  formed integrally with second chamber cap  234 , surrounding atmosphere port  238 , and extending axially into second chamber  216 , forming thereby a tortuous pathway for flow of vapor. The diameter of tube  286  is selected such that the tube extends into insert  170  and is slightly offspaced therefrom, creating an annular flow space  288  between tube  286  and insert wall  174 . The result is that vapor flow  56  passing through hollow cylinder-shaped region  184  and perforated rim  176  cannot exit second chamber  216  immediately. Instead, the vapor is directed through a first 180° turn into annular space  288 , travels the length of tube  286  into the bowl end  287  of central well  172 , makes a second 180° turn, and again travels the length of tube  286  before exiting at port  238 . The extended diffusion pathway-afforded by tube  286  in insert  170  greatly reduces diurnal bleed of vapors adsorbed onto carbon in the canister. Second embodiment  210  is intended to meet LEV II standards when the volume and carbon loading of chambers  214 , 216  is sized properly for a specific emissions load, the determination of which is well known in the art of engine emissions adsorption.  
         [0049]     Referring to  FIG. 11 , a third embodiment  310  of an improved emissions adsorption canister is identical with second embodiment  210  in all respects save one, and numbering of most elements is omitted for clarity. The novel feature of embodiment  310  is the addition of a high-efficiency vapor scrubber  390  disposed within cylindrical tube  286 . Scrubber  390  is preferably a cylindrical pressed carbon monolith having a plurality of longitudinal passageways  392  providing thereby a large surface area for adsorption of hydrocarbon emissions. Carbon monolith scrubber  390  may be formed from a special adsorbent material such as, for example, a rolled felted carbon coated material, such as Kynol™, available from American Kynol, Inc. of Pleasantville, N.Y. Vapor flowing into insert end  287  as in embodiment  210  must then pass through scrubber  390  before exiting at atmosphere port  338 .  
         [0050]     As noted above and shown in  FIGS. 2 and 3 , inclusion of such a scrubber at the end of the vapor flowpath is known in the art. Third embodiment  310  is intended to meet PZEV standards when the carbon volume of chambers  314 , 316  is sized properly for a specific emissions load, similar to the requirement for LEV II in embodiment  210 .  
         [0051]     An important manufacturing advantage of canister embodiment  210  is that it provides a common platform for either LEV II or PZEV applications simply by adding or omitting scrubber  390 . No other changes are required and the footprint within a vehicle is identical.  
         [0052]     Scrubber  390  is inserted into cylindrical tube  286  during assembly of embodiment  310  and must be retained in place during the working lifetime of the canister. First and second retaining seals  394  may be installed at the periphery of each end of scrubber  390 , seals  394  having flexible wipers  396  similar to insert wipers  180  for centering the scrubber within the canister. Alternatively, the scrubber may be retained by annular polymeric gaskets (not shown), which may be formed in known fashion from a cross-linkable elastomeric composition such as a silicone and may be installed with the scrubber in liquid form prior to becoming cross-linked.  
         [0053]     Because a scrubber formed as a carbon monolith is relatively fragile and easily damaged, such a scrubber is vulnerable to shock and vibration. In addition, silicone elastomers such as Viton are known to exhibit relatively high coefficients of thermal expansion. Under cold start conditions, for example, in the arctic, a scrubber could become loose in its mountings and be damaged. Referring to  FIGS. 9, 10 , and  12 , in a currently preferred configuration  310 ′ of embodiment  310 , a flexible, porous, resilient sling  400  is provided for installing and retaining scrubber  390  within cylindrical tube  286  in lieu of either seals  394  ( FIG. 11 ) or elastomeric gaskets. In installation, an end  402  of scrubber  390  is placed on a center portion  404  of sling  400 , and strap ends  406  are folded alongside the cylindrical surface of scrubber  390  to form a sub-assembly  408 , as shown in  FIG. 10 . Prior to insertion of insert  170  into the canister as described above, sub-assembly  408  is inserted into tube  286 , followed by insertion of insert  170 , as shown in  FIG. 12 . Preferably, sling  400  is die-cut from planar stock of either a loose, thick, woven polyester fabric or an open-cell resilient foam.  
         [0054]     Advantages of sling  400  over an annular resilient elastomeric gasket are a) cost, b) much greater ease of assembly of embodiment  310 ′ over embodiment  310 , and c) the outer surface of scrubber  390  is made available as additional vapor adsorption area.  
         [0055]     While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.