Abstract:
An air intake hydrocarbon vapor trap system for an internal combustion engine comprising a hydrocarbon-adsorptive medium, such as activated carbon, disposed in a gravitationally low point in the intake air flow passageway between the entrance to the system and the engine. The intake duct itself is configured to provide the low region for disposition of the medium. The medium is thereby fully exposed to the flow of gases through the duct and is not confined to a separate walled pit as in the prior art. The medium, for example, activated carbon, may be provided in any of several forms, such as in a pelletized bed, a rigid formed structure, or as a “sheet” or “paper.” Preferably, the medium is disposed in the engine compartment to optimally transfer heat away from it during engine shut-down.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to internal combustion engines; more particularly, to devices for preventing escape of hydrocarbon vapors from internal combustion engines; and most particularly, to a hydrocarbon vapor trap disposed in the air intake portions of such an engine for adsorbing vapors when the engine is shut down.  
       BACKGROUND OF THE INVENTION  
       [0002]     Gasoline-fueled motor vehicles have numerous sites from which gasoline hydrocarbons (HC) can evaporate into the atmosphere. Atmospheric HC is a major contributor to smog formation; thus, there is great interest in providing means for reducing or preventing inadvertent escape of HC vapors from vehicles and their internal combustion engines.  
         [0003]     The control of HC vapors escaping into the atmosphere is also the subject of substantial state and federal regulations. For example, The California Air Resources Board (CARB) has adopted stringent vapor emissions regulations, known generally as Low Emission Vehicle II (LEV II) and Partial Zero Emission Vehicle (PZEV). 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).  
         [0004]     Vapor traps are well known. For example, present-day vehicles are commonly equipped with an adsorptive canister system for preventing the escape of hydrocarbon vapors displaced from a vehicle&#39;s fuel tank during refueling of the vehicle.  
         [0005]     Fuel vapors can also escape from an engine via the air intake system after the engine is shut down. Residual fuel in the air intake manifold, whether from fuel injection or carburetion, or from ventilation of the crankcase, is readily vaporized by residual engine heat and can migrate out of the engine through the air intake opening.  
         [0006]     Various approaches are known in the art for preventing such migration. For one example, the throttle valve may be closed, thus trapping vapors within the manifold. A disadvantage of this approach is that it requires an electronic throttle control, which may also eliminate a “limp home” mode of engine operation if there is a problem with the electronics. For another example, carbon grids may be added between the air cleaner and the throttle plate. A disadvantage of this approach is that the carbon grids obscure a significant portion of the cross-sectional area of the air flow path service to reduce engine power and, if not closely-spaced, can be relatively inefficient.  
         [0007]     Yet another approach is disclosed by U.S. Pat. No. 6,505,610 (&#39;610), the relevant disclosure of which is incorporated herein by reference, comprising an engine intake system through which ambient air enters a combustion engine to be combusted with hydrocarbon fuel in combustion chamber space of the engine for running the engine. A walled main intake passageway has an upstream end communicated to ambient atmosphere and a downstream end communicated to the engine combustion chamber space. An imperforate walled pit encloses an interior space disposed at an elevation vertically below an imperforate wall of the main intake passageway and includes an imperforate wall separating the pit interior space from the main passageway. The pit has a first entrance communicating the interior space to ambient atmosphere and a second entrance communicating the interior space to the main intake passageway through the imperforate wall of the main passageway for enabling gaseous hydrocarbon that is heavier than air to fall into the interior space upon encountering the second entrance of the pit when migrating upstream within the main intake passageway toward the second entrance of the pit from the downstream end of the main passageway. A medium disposed within the interior space collects gaseous hydrocarbon that has fallen through the entrance opening into the pit. The air flow is reversed when the engine is restarted, and the collected hydrocarbon is stripped from the medium and returned to the main passageway to be conveyed to the combustion space.  
         [0008]     A significant drawback of the disclosed hydrocarbon trap is the bulk and added cost of providing a walled pit separate from and below the main air passageway. It is well known in the automotive arts that underhood space is very limited and is not readily available for an additional walled pit. In addition, not all vapors will fall into the pit; some may pass by the entrance and thereby be lost to the atmosphere.  
         [0009]     What is needed in the art is a hydrocarbon trap for an engine air intake system which does not significantly impede the flow of air; which does not consume significant additional underhood space; which does not require a separate walled pit; and which is exposed to all the air flowing through the system to optimize adsorption and subsequent desorption of hydrocarbons.  
         [0010]     It is a principal object of the present invention to minimize the escape of hydrocarbon vapors from an engine air intake system after the engine is turned off.  
       SUMMARY OF THE INVENTION  
       [0011]     Briefly described, an air intake hydrocarbon vapor trap in accordance with the invention comprises a hydrocarbon-adsorptive medium, such as activated carbon, disposed in a gravitationally low point in the intake air flow path between the entrance to the system and the intake manifold. Preferably, the intake duct itself is configured to accentuate a low region for disposition of the medium. The medium is fully exposed to the flow of gases through the duct and is not confined to a separate walled pit as in the prior art. The medium, as activated carbon, may be provided in any of several forms, such as in a pelletized bed, a rigid formed structure, or as a “sheet” or “paper.” 
         [0012]     Hydrocarbon adsorption by the activated carbon medium is inversely proportional to the temperature at the adsorption site. That is, lowering the temperature at the adsorption site has the effect of increasing adsorption. In a preferred embodiment in accordance with the invention, The intake duct supporting the medium is located so as to conduct the heat of combustion contained in the intake duct away from the medium to lower the temperature of the medium thereby optimizing hydrocarbon adsorption. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0014]      FIG. 1  is a prior art hydrocarbon vapor trap substantially as disclosed in the &#39;610 incorporated reference;  
         [0015]      FIG. 2  is a schematic view of a hydrocarbon vapor trap and associated internal combustion engine, in accordance with the invention;  
         [0016]      FIG. 3  is a longitudinal cross-sectional view of a first embodiment of the trap shown in  FIG. 2 ;  
         [0017]      FIG. 4  is a longitudinal cross-sectional view of a second embodiment;  
         [0018]      FIG. 5  is a longitudinal cross-sectional view of a third embodiment;  
         [0019]      FIG. 6  is a transverse cross-sectional view, taken along line A-A in  FIG. 4 , showing a first adsorptive medium configuration;  
         [0020]      FIG. 7  is a transverse cross-sectional view, taken along line A-A in  FIG. 4 , showing a second adsorptive medium configuration;  
         [0021]      FIG. 8  is a transverse cross-sectional view, taken along line A-A in  FIG. 4 , showing a third adsorptive medium configuration;  
         [0022]      FIG. 9  is the view shown in  FIG. 8  with finned heat sink projections added.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     The advantages conferred by the present invention may be better appreciated by first considering a prior art hydrocarbon trap system for an engine air intake, substantially as disclosed in U.S. Pat. No. 6,505,610.  
         [0024]     Referring to  FIG. 1 , in a prior art hydrocarbon trap system  01 , an internal combustion engine  16  comprises an intake system  18  through which ambient air enters the engine for combustion with hydrocarbon fuel for running the engine. The fuel may be introduced by a fuel injection system that together with the intake system may be embodied as air-fuel module  20 . When engine  16  is naturally aspirated, the module acts as an induction system wherein engine vacuum inducts air and fuel into the individual engine cylinders.  
         [0025]     Module  20  comprises a walled main intake passageway  22  that has an upstream end  24  communicated to ambient atmosphere  25  and a downstream end  26  communicated to the engine combustion chamber space, typically through intake valves (not shown) that operate in suitably timed relation to engine operation. An imperforate walled pit  28 , that may be integrally formed with module  20 , encloses an interior space  30  disposed at an elevation vertically below an imperforate bottom wall  32  of main passageway  22 . Pit  28  has a first entrance  34  communicating interior space  30  to ambient atmosphere  25  and a second entrance  36  communicating interior space  30  to main intake passageway  22  through imperforate wall  32 .  
         [0026]     Entrance  34  comprises a separate hydrocarbon cleaning line, or conduit,  37  that runs from wall  32  to the bottom wall of pit  28 . Conduit  37  is separate from walled main intake passageway  22  and runs parallel to passageway  22 . A suitable medium  38  for collecting hydrocarbon is disposed within interior space  30 . An example of a suitable medium is activated carbon.  
         [0027]     When engine  16  is running, atmospheric air is drawn through passageway  22  and into engine  16  wherein it forms, with injected fuel, a combustible mixture that is ignited to power the engine. The parallel path through line  37  and pit  28  imposes no significant restriction to the intake airflow.  
         [0028]     When engine  16  stops running, certain hydrocarbons may be present in passageway  22  proximate engine  16 , and they may tend to migrate upstream through passageway  22  along wall  32  toward upstream end  24 . Upon encountering entrance  36 , however heavier-than-air hydrocarbons  10  will fall through into interior space  30 . When they come in contact with medium  38 , the molecules will be adsorbed by the medium. In this way, those molecules are collected and prevented from escaping to atmosphere, thereby preventing their emission to the environment.  
         [0029]     When engine  16  is again run, a small amount of intake air may pass through cleaning line  37  to purge molecules from medium  38 . As air passes across the medium, collected hydrocarbon molecules entrain with the air, and the mixture exits pit  28  through entrance  36  to re-enter the intake airflow through main passageway  22  and pass into engine  16 .  
         [0030]     As noted above, a problem with the prior art apparatus is its bulk and the fact that not all the air and hydrocarbon migrating upstream after engine shutdown is shunted past the adsorption medium, the medium being confined to a separate chamber in pit  28 . The prior art apparatus, therefore, is believed to be relatively inefficient. While performing the same function as the prior art apparatus in much the same way, the present invention overcomes these two disadvantages (bulk and inefficiency).  
         [0031]     Referring to  FIG. 2 , in an improved hydrocarbon trap system  01 ′ in accordance with the invention, an internal combustion engine  16  comprises an intake system  18 ′ through which ambient air enters the engine for combustion with hydrocarbon fuel for running the engine, preferably including air cleaner  19 . The fuel may be introduced by a fuel injection system that together with the intake system may be embodied as air-fuel module  20 ′. When engine  16  is naturally aspirated, the module acts as an induction system wherein engine vacuum inducts air and fuel into the individual engine cylinders.  
         [0032]     Module  20 ′ comprises a walled main intake passageway  22 ′ that has an upstream end  24 ′ communicated to ambient atmosphere  25  and a downstream end  26 ′ communicated to the engine combustion chamber space, typically through a throttle valve  27  and intake valves (not shown) that operate in suitably timed relation to engine operation in known fashion.  
         [0033]     Main intake passageway  22 ′ includes, as an integrated part to form a continuous passageway, passageway portion  23 . That is, passageway portion  23  runs in series with main intake passageway  22 ′ and is not running as a separate line parallel to main intake passageway  22 ′ as in the case of main intake passageway  22  to conduit  37  shown in prior art trap system  01  ( FIG. 1 ).  
         [0034]     Main intake passageway  22 ′ is preferably configured such that a bottom wall  31  of passageway portion  23  preferably is disposed at an elevation vertically below bottom wall  32 ′ of main intake passageway  22 ′, as shown in detail in  FIG. 3 . Preferably, bottom wall  31  is the lowest point within portion  23  and main intake passageway  22 ′. Preferably, upper wall  29  of portion  23  is disposed at an elevation vertically below bottom wall  32 ′ of main intake passageway  22 ′.  
         [0035]     A suitable medium  38 ′ for collecting hydrocarbon is disposed within portion  23 , for example, along the bottom wall  31  thereof. An example of a suitable medium is activated carbon, as may be formed into any of various shapes, some exemplary forms of which are shown in  FIGS. 6 through 8 , as discussed hereinbelow.  
         [0036]     When engine  16  is running, atmospheric air is drawn through main intake passageway  22 ′ and into engine  16  wherein it forms, with injected fuel, a combustible mixture that is ignited to power the engine. The path through portion  23  and past medium  38 ′ imposes no significant restriction to the intake airflow.  
         [0037]     When engine  16  stops running, certain hydrocarbons may be present in main intake passageway  22 ′ proximate engine  16 , and they may tend to migrate upstream through passageway  22 ′ along bottom wall  32 ′ toward upstream end  24 ′. Upon encountering portion  23 , however heavier-than-air hydrocarbons will fall to the lowest portions of main intake passageway  22 ′ in portion  23 . When the hydrocarbon molecules come into contact with medium  38 ′, the molecules are adsorbed by medium  38 ′. In this way, those molecules are collected and prevented from escaping to atmosphere, thereby preventing their emission to the environment.  
         [0038]     When engine  16  is again run, intake air passes through portion  23  and thereby purges the HC molecules from medium  38 ′ which re-enter the intake airflow through main intake passageway  22 ′ and pass into engine  16 .  
         [0039]     Referring to  FIG. 3 , upstream flow of HC vapors  10  from engine  16  is directed downwards into portion  23  by the gravitational relationship of portion  23  to main intake passageway  22 ′. This flow direction urges the HC vapors toward medium  38 ′ which is distributed along a region of bottom wall  31 . In contrast to prior art embodiment  01 , the entire flow of air and HC vapors in passageway  22 ′ is made available to the medium. Preferably the cross-sectional area of portion  23  is sized to accommodate the thickness of medium  38 ′ such that portion  23  presents no significant restriction to the flow of air to the engine during operation thereof.  
         [0040]     Referring to  FIG. 4 , the upper wall  29 ′ of portion  23 ′ is continuous with the upper wall of main intake passageway  22 ′; this configuration provides a straighter path for intake air while also providing a low region for accumulation of HC vapors but at a cost of less direction for the vapors when the engine is off. This configuration is applicable to an engine requiring lesser improvement in evaporative emissions.  
         [0041]     Referring to  FIG. 5 , portion  23 ″ is similar to portion  23 ′ but includes a spoiler  40  extending downwards from the upper wall of passageway  22 ′, providing strong direction to vapors migrating along passageway  22 ′ from engine  16 .  
         [0042]     In any of portions  23 , 23 ′, 23 ″, medium  38 ′ may extend along bottom wall  31 , both laterally and longitudinally, as shown in  FIGS. 3 and 4 , including along the inclined entrance to the portion, to present a relatively large surface area for vapor adsorption.  
         [0043]     Referring to  FIG. 6 , a first embodiment  38 - 1  of medium  38 ′ is disposed in portion  23 ′ on bottom wall  31  and between sidewalls  42  thereof and is retained in place by, for example, tabs  44  extending from sidewalls  42 . Medium  38 - 1  comprises a layer of granulated or pelletized carbon  46  overlain by a sheet  48  of open cell foam and a rigid grid element  50 . These forms of activated carbon have the advantages of being readily available and inexpensive.  
         [0044]     Referring to  FIG. 7 , a rigid carbon form  38 - 2  comprises a surface pattern of longitudinal grooves  52  to increase surface area. The surface topography may include any shapes to increase surface area, or may be flat to minimize flow restriction. Methods for making rigid carbon forms are well known in the art.  
         [0045]     Referring to  FIG. 8 , a carbon “sheet” or “paper”  54  comprising carbon form  38 - 3  is disposed along bottom wall  31  and may also be extended along walls  42  as desired. An exemplary material is an Activated Carbon Sheet, Stock Number ACS-135/270, available from MeadWestvaco Corporation, Stamford, Conn., USA. Sheet  54  may be retained in portion  23 ′ as by tabs  44  ( FIG. 6 ), by adhesives, or by any other convenient means of attachment.  
         [0046]     The medium configurations  38 - 1 , 38 - 2 , 38 - 3  are shown for simplicity in respect to embodiment  23 ′ shown in  FIG. 4  but of course these medium configurations are equally applicable to all configurations of trap portions  23 ,  23 ′,  23 ″.  
         [0047]     Referring again to  FIG. 2 , preferably passageway  23  and medium  38 ′ are located in an area  56  of the engine compartment  58  to conduct the hotter temperatures of the gases contained in downstream end  26 ′ of intake passageway  22 ′ away from medium  38 ′ during periods of engine shutdown such that temperature  60  of medium  38 ′ is lower than temperature  62  of the gases within passageway  22 ′ to thereby improve the efficiency of hydrocarbon adsorption.  FIG. 9  shows embodiment  38 - 3 ′ wherein finned heat sink projections  64  extend from bottom wall  31  and/or side walls  42  to transfer heat away from sheet  54  and toward lower temperature  64  in area  56 . It is understood that the use of finned heat sink projections  64  for improving the efficiency of cooling is equally applicable to all configurations of trap portions  23 ,  23 ′,  23 ″ and embodiments  38 - 1 ,  38 - 2  and  38 - 3 , respectively.  
         [0048]     What has been disclosed is an improved hydrocarbon trap system for collecting hydrocarbon emissions from an engine intake system during periods of engine shutdown, wherein the trap is formed as a low region within the intake air passageway itself, rather than as a separate pit adjacent to and communicating with the intake air passageway but separated therefrom by an imperforate wall, as in the prior art. 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.