Patent Publication Number: US-2010126477-A1

Title: Evaporative emissions control system

Description:
TECHNICAL FIELD 
     This disclosure is related to evaporative emissions control systems. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Evaporative emissions control systems are used to capture and contain fuel vapors generated in fuel tanks of vehicles and stationary storage systems. Known systems include vapor storage devices connected via vapor lines to a fuel tank. Known systems include vapor storage devices having a vent line connectable to atmospheric air and a purge line connectable to a vacuum source, e.g., an intake manifold of an internal combustion engine. 
     Fuel vapor can be generated in the fuel storage tank and stored in the vapor storage device ongoingly, including fuel vapor generated due to variations in ambient temperature over time, referred to as diurnal fuel vapor. Stored fuel vapor can be purged from the vapor storage device by air flow through the vapor storage device, e.g., when low pressure is introduced to the purge line and air is drawn through the vapor storage device through the vent line. In some applications, e.g., a hybrid vehicle using a plug-in electric charging system, a fuel tank may generate diurnal fuel vapors for storage in the vapor storage device, and purging of the fuel vapor stored in the vapor storage device may not occur for an extended time period. If the vapor storage device is not purged, the vapor storage device may saturate and release any subsequently produced fuel vapor into the atmosphere. 
     SUMMARY 
     A sealable fuel vapor storage and recovery system includes a fuel tank and a vapor storage device. The vapor storage device includes a chamber containing fuel vapor adsorbent material and has a first end including first and second openings and a second end including a third opening. The first end and the chamber and the second end define a linear flow path therebetween. The first opening of the vapor storage device is fluidly connected to a vent opening in the fuel storage tank. The second opening of the vapor storage device is fluidly connected to a purge line fluidly connectable to an induction system via a purge valve. The third opening is fluidly connected to a vent valve in fluid communication with atmospheric air. The vent valve is selectively controllable to one of an open position and a closed position. The vent valve seals the third opening of the vapor storage device when controlled in the closed position and has a cross-sectional area equal to a cross-sectional area of the third opening of the vapor storage device when controlled in the open position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       One or more embodiments will now be described, by way of example, with reference to the accompanying FIGURE which is a schematic diagram of a sealable fuel vapor storage and recovery system in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the FIGURE, wherein the showing is for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same, an embodiment of a sealable fuel vapor storage and recovery system  10  is shown. The illustration is schematic and the components are not drawn to scale. The sealable fuel vapor storage and recovery system  10  is depicted as an element of a system that includes an internal combustion engine  12  and a control module  14  in the embodiment. The sealable fuel vapor storage and recovery system  10  can be applied to a motor vehicle employing multiple propulsion technologies, e.g., a hybrid vehicle, although the disclosure is not so limited. 
     The internal combustion engine  12  can include a multi-cylinder internal combustion engine that generates mechanical power by combusting fuel comprising gasoline and other combustible liquids in combustion chambers (not shown). The engine  12  is operatively controlled by the control module  14 . The control module  14  preferably comprises a digital programmable device include a microprocessor that monitors input signals from sensors (not shown) and generates output signals to control actuators (not shown) to operate the engine  12  and the sealable fuel vapor storage and recovery system  10 . Line  16  between the engine  12  and the control module  14  schematically depicts the flow of input signals and output signals therebetween. 
     The sealable fuel vapor storage and recovery system  10  includes a fuel tank  18  and a fuel vapor adsorption canister  50 . During operation of the engine  12 , fuel is delivered from the fuel tank  18  by a fuel pump (not shown, but often located in the fuel tank) through a fuel line (not shown) to a fuel rail and fuel injectors (not shown) that preferably supplies fuel to each cylinder of the engine  12 . Operation of the fuel pump and fuel injectors is preferably managed by the control module  14 . 
     In one embodiment, the fuel tank  18  is a blow-molded device formed using high density polyethylene having one or more interior layers that are impermeable to fuel including gasoline. A fill tube  22  is connected to the fuel tank  18 , having a fill end  26  through which fuel can be poured and an outlet end  28  emptying into the fuel tank  18 . A one-way valve  30  prevents liquid fuel from splashing out the fill tube  22 . There is a removable fuel cap  24  that can sealably close the fill end  26 . An on-board refueling vapor recovery system (hereafter ‘ORVR’) includes an ORVR signal line  35  that communicates to the control module  14  an operator request to pour fuel into the fuel tank  18  through the fill tube  22 . A volume of fuel  32  is indicated with upper surface  34 . A float-type fuel level indicator  36  provides a fuel level signal through line  38  to the control module  14 . In one embodiment, a fuel tank pressure sensor  40  and a temperature sensor  42  generate signals transmitted to the control module  14  via lines  44  and  46 , respectively. The fuel tank  18  is provided with a vent line  20  that leads through seal  48  from the top of the fuel tank  18  to the fuel vapor adsorption canister  50 . A float valve  52  within the fuel tank  18  prevents liquid fuel from entering the vent line  20 . Fuel vapor mixed with air can flow through the vent line  20  to a first opening  54  of the fuel vapor adsorption canister  50 . Preferably, fuel vapor flows through the vent line to the fuel vapor adsorption canister  50  when fuel is poured into the fuel tank  18  through the fill tube  22  as part of on-board refueling vapor recovery. 
     The fuel vapor adsorption canister  50  preferably includes a body  53  comprising a closed structure molded of a fuel-impermeable thermoplastic polymer, e.g., nylon. The closed structure of the fuel vapor adsorption canister  50  includes a first end  51  including the first opening  54  and a second opening  68 , and a second end  62  including a third opening  66 . The first end  51 , the body  53 , and the second end preferably form a single chamber  56  for containing a mass of an adsorbent material  58 . The fuel vapor adsorption canister  50  includes one or more granule retaining elements (not shown) to facilitate retention of the adsorbent material  58  in the single chamber  56  of the body  53 . The fuel vapor adsorption canister  50  includes one or more diffusers (not shown) to diffuse vapor and airflow across a cross-section of the single chamber  56  of the body  53 . The adsorbent material  58  preferably comprises an activated carbon material, e.g., activated carbon granules operative to adsorb hydrocarbon vapors passing from the fuel tank  18  and ORVR system through the vent line  20  to the first opening  54 . Preferably, a first dimension of the body  53  defines a longitudinal axis  55 . Preferably, the first end  51 , the single chamber  56  of the body  53 , and the second end  62  of the fuel vapor adsorption canister  50  are linearly arranged parallel to the longitudinal axis  55 . Thus, a linear flow path is defined through the fuel vapor adsorption canister  50  between the first end  51 , the single chamber  56  of the body  53 , and the second end  62  substantially parallel to the longitudinal axis  55 . 
     A first end of a vent tube  70  connects to the third opening  66  of the fuel vapor adsorption canister  50  in one embodiment. A second end  78  of the vent tube  70  connects to a vent valve  72 , referred to as a diurnal control valve (hereafter ‘DCV’). The DCV  72  preferably comprises a single-stage high-flow sealable valve  76  operatively connected to a normally closed solenoid  74  that is operatively connected to the control module  14  via a control line  80 . When the DCV  72  is in the closed position, the sealable valve  76  sealably closes the second end  78  of the vent tube  70 . When the DCV  72  is in the open position (as shown), the second end  78  of the vent tube  70  fluidly connects to atmospheric air, including connecting to atmospheric air via a second tube  70 ′ in one embodiment. Preferably there is no orifice or other flow restriction device in the vent tube  70  or the second tube  70 ′. Preferably, inner diameters of the vent tube  70 , the DCV  72  when opened, and the second tube  70 ′ are such that they impose minimal or substantially no restrictions to flow of air into or out of the third opening  66  of the fuel vapor adsorption canister  50  when the DCV  72  is controlled in the open position relative to any anticipated system pressure drop and associated vapor flow rate. In one embodiment, the tube  70 ′, the DCV  72 , and the vent tube  70  each have cross-sectional flow areas that are equal to a cross-sectional flow area of the third opening  66  of the fuel vapor adsorption canister  50  when controlled in the open position to minimize flow restriction between the third opening  66  of the fuel vapor adsorption canister  50  and atmospheric air. In one embodiment (not shown) the tube  70 ′ is omitted, and the DCV  72  and the vent tube  70  each have cross-sectional flow areas that are equal to or larger than a cross-sectional flow area of the third opening  66  of the fuel vapor adsorption canister  50 . In one embodiment (not shown) the tube  70 ′ and the vent tube  70  are omitted, and the DCV  72  directly fluidly connects to the third opening  66  of the fuel vapor adsorption canister  50  and has a cross-sectional flow area that defines a cross-sectional flow area of the third opening  66 . 
     Preferably a pressure relief valve  96  is configured to provide flow around the DCV  72  via tube  94  in either an overpressure condition or an over-vacuum (or underpressure) condition. The pressure relief valve  96  protects the sealable fuel vapor storage and recovery system  10  from damage due to overpressure and over-vacuum events. In one embodiment, the pressure relief valve  96  has a positive pressure threshold at or near 25 kPa-gage, and a negative pressure threshold at or near 10 kPa-gage. The DCV  72  is normally closed (not shown), including during vehicle shutdown and during vehicle operation when the engine  12  is not operating. The DCV  72  is energized to open during refueling events and during purging events during operation of the engine  12 . 
     The second opening  68  of the first end  51  of the fuel vapor adsorption canister  50  fluidly connects to an induction system via a purge line  82 , a solenoid-actuated purge valve  84 , and a second purge line  82 ′. The induction system comprises an intake manifold (not shown) of the engine  12  in one embodiment. The purge valve  84  includes a sealable valve  88  and a normally-closed solenoid  86  operatively connected to the control module  14  via a control line  92 . 
     A first operating state of the sealable fuel vapor storage and recovery system  10  includes the purge valve  84  sealingly closed (as shown) and the DCV  72  sealingly closed (not shown). With the fuel cap  24  sealingly closed, the sealable fuel vapor storage and recovery system  10  is a closed system, and can experience variations in pressure caused by expansion and contraction of gases caused by temperature changes, e.g., due to diurnal temperature variations. When the DCV  72  is closed, there is no pressure differential across, and therefore no flow through, the fuel vapor adsorption canister  50 . Therefore, minimal loading of the fuel vapor adsorption canister  50  occurs. The first operating state is commanded by the control module  14  under conditions including when the engine  12  is turned off and when the vehicle is commanded off. 
     A second operating state of the sealable fuel vapor storage and recovery system  10  includes a signal from the ORVR signal line  35  to the control module  14  indicating a refueling event, and preferably preceding opening the fuel cap  24 . When the refueling signal is received across the ORVR signal line  35 , the DCV  72  is commanded open by the control module  14  to facilitate flow of fuel vapor and air through the fuel vapor adsorption canister  50  during refueling and ORVR operation due to a pressure drop across the fuel vapor adsorption canister  50 . The purge valve  84  remains sealingly closed during this operating state. The DCV  72  can be opened when the fuel tank  18  is pressurized, causing tank vapors to vent into the fuel vapor adsorption canister  50 . The volume of vented vapor into the fuel vapor adsorption canister  50  is directly proportional to tank vapor space volume. A nearly empty fuel tank generates and vents a larger volume of vapor compared to a nearly full fuel tank. The adsorption status of the fuel vapor adsorption canister  50 , i.e., one of being purged or being loaded with refueling vapors, is a function of fuel level in the fuel tank. A nearly empty fuel tank  18  indicates a fully purged fuel vapor adsorption canister  50  because the engine  12  has previously operated for a period of time sufficient to consume fuel, including purging fuel vapor stored therein. Subsequently, the purged fuel vapor adsorption canister  50  has a vapor storage capacity sufficient to adsorb fuel vapor vented from the pressurized fuel tank. 
     A third operating state of the sealable fuel vapor storage and recovery system  10  includes purging the fuel vapor adsorption canister  50 , in one embodiment by operating the engine  12 . During purging, e.g., during engine operation, the DCV  72  is controlled to the open position, and the purge valve  84  is opened (not shown), creating a flow path between the tube  70 ′, through the DCV  72  and the fuel vapor adsorption canister  50  through the second opening  68  to purge line  82  through the solenoid-actuated purge valve  84 . In one embodiment, the flow path to the intake manifold of the engine  12  is due to a pressure drop caused by engine operation. Flow of air through the fuel vapor adsorption canister  50  purges the adsorbed fuel which can be ingested and burned in the engine  12  during engine operation. The DCV  72  seals the third opening  66  of the fuel vapor adsorption canister  50  when controlled in the closed position. 
     A sealable fuel vapor storage and recovery system was constructed in accordance with an embodiment of the disclosure to simulate operation of the sealable fuel vapor storage and recovery system  10  including operating in the second operating state described herein. Evaporative emissions tests were conducted using a rectangularly-shaped steel fuel tank having a total volume of 108 liters (29 gal.) filled with 54 liters (14 gal.) of fuel having a Reid Vapor Pressure (‘RVP’) of 50 kPa (7 psi) fuel at 24° C. (75° F.). The fuel tank was pressurized to 15 kPa-gage pressure by pumping air into the tank. The pressure was released into the first end  51  of the fuel vapor adsorption canister  50  constructed as described herein having a linear flow path, with the DCV  72  controlled in the open position. Breakthrough emissions were measured in a test cell referred to as a SHED (‘Sealed Housing for Evaporative Determination) enclosure. The second tube  70 ′ connected to the DCV  72  was fitted with flow restriction orifices having various diameters. Table 1 shows results of the emissions tests, comprising breakthrough emissions, in mg HC, corresponding to a diameter of the flow restriction orifice. A corresponding elapsed period of time for pressure to bleed down from 15 kPa to 1.5 kPa is shown for each flow restriction orifice. The results indicate that breakthrough emissions increased with decrease in orifice diameter size, which is opposite of what was expected. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Breakthrough 
                 Time for Pressure Bleed 
               
               
                   
                 Emissions, 
                 Down to 1.5 kPa, 
               
               
                 Orifice, mm 
                 mg 
                 Sec 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 9 
                 331 
                 1.6 
               
               
                 6.7 
                 361 
                 2.8 
               
               
                 4 
                 424 
                 7.7 
               
               
                 0.5 
                 945 
                 500 
               
               
                   
               
            
           
         
       
     
     The larger diameter orifices result in higher vapor flow rates through the fuel vapor adsorption canister  50  during an on-board refueling event causing increased fluid turbulence and improved surface contact between the fuel vapors and carbon particles of the adsorbent material  58 . There is increased hydrocarbon adsorption and lower breakthrough emissions with increased orifice size, i.e., decreased flow restriction between the third opening  66  to the vapor storage device  50  and atmospheric air when operating in the second operating state during on-board refueling. 
     The disclosure has described certain preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.