Abstract:
A valve is disposed between a fuel tank and an engine intake manifold in a small engine fuel system equipped to recapture running loss evaporative emissions. The valve includes a resilient diaphragm that blocks the flow path When vapor pressure in the fuel tank reaches a predetermined level, the diaphragm opens and allows the vacuum forces in the manifold to purge the vapors in the fuel tank by drawing the vapors into the manifold to be burned in the engine. The diaphragm isolates the fuel tank vapor dome from the vacuum pressure generated in the manifold, thereby preventing the engine from being starved of fuel. The valve may be integrated with a liquid discriminating valve to form a valve assembly.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/703,184, filed Jul. 28, 2005 entitled “Vapor Control System For Small Engines”, which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to vapor control systems and more particularly to a fuel vapor control system for applications requiring vapor control, such as small engine applications.  
       BACKGROUND OF THE INVENTION  
       [0003]     Recent pending regulations for controlling the emission of fuel vapors have required installation of fuel vapor emission control devices to limit escape of fuel vapors through the engine air inlet during periods when the engine is not operating and provide a purging mechanism that operates when the engine is running. This recently imposed requirement on small engine manufacturers has created problems in installing the engines in the equipment in which they are to be used inasmuch as the equipment manufacturer commonly purchases the engine and fuel tank for installation as a subassembly during final assembly of the engine operated equipment. Thus, the burden of providing fuel vapor emission control for these applications has been imposed upon the small engine manufacturer and has created problems in the design and installation of the tank and fuel system for the small engines.  
         [0004]     Recapturing running loss evaporative emissions is one way to meet these pending regulations. During purging, vacuum forces pull vapor in the fuel tank into the manifold so that the vapors can be burned in the engine. However, the vacuum forces may be so great that it creates a high vacuum pressure state in the fuel tank, starving the engine of fuel.  
         [0005]     There is a desire for a vapor control system that can recapture running loss evaporative emissions without causing the engine to stall because of insufficient fuel.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention is directed to a valve for use in a small engine fuel system equipped to recapture running loss evaporative emissions. The valve structure allows purging of fuel vapors in a fuel tank via vacuum forces in an engine intake manifold. In one embodiment, the valve is disposed in a vapor flow path connecting the small engine fuel tank and the engine intake manifold. The valve includes a resilient diaphragm that blocks the flow path. When vapor pressure in the fuel tank reaches a predetermined level, the diaphragm opens and allows the vacuum forces in the manifold to purge the vapors in the fuel tank by drawing the vapors into the manifold. These vapors are then burned in the engine. The diaphragm prevents the engine from being fuel-starved by isolating the fuel tank vapor dome from the vacuum pressure generated in the manifold. The valve may include a check valve to allow fresh air to enter the fuel tank as fuel is consumed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a representative view of a fuel system incorporating the invention;  
         [0008]      FIG. 2  is a perspective view of one embodiment of the invention;  
         [0009]      FIG. 3  is a representative section view of one embodiment of the invention in a first operating position;  
         [0010]      FIG. 4  is a representative section view of the embodiment shown in  FIG. 3  in a second operating position; and  
         [0011]      FIG. 5  is a representative section view of another embodiment of the invention.  
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0012]      FIGS. 1 through 4  are representative diagrams of a vapor system, such as a small engine fuel system  10 , incorporating a valve  12  according to one embodiment the present invention. The system  10  is designed to recapture running loss evaporative emissions to meet more stringent emission requirements for small engine devices, such as lawn mowers and portable generators.  
         [0013]     Referring to  FIGS. 1 and 2 , the valve  12  includes a housing  14 , an optional fuel tank port  16  and an engine manifold port  18 . As will be described in greater detail below, the ports  16 ,  18  may be eliminated without departing from the scope of the invention.  
         [0014]     The valve  12  is attachable to a fuel tank  20  so that the fuel tank port  16  communicates with a vapor dome  22  in the tank  20 . The manifold port  18  communicates with an engine manifold  24  so that vapor can flow through the manifold port  18  to send fuel vapor to the engine  24 . In one embodiment, the tank port  16  is attached to a liquid/vapor discriminator  26  with overfill protection that prevents liquid fuel from entering the valve  12 .  
         [0015]      FIG. 3  is a section view of the valve  12  taken along line  3 - 3  in  FIG. 1 . The tank port  16  and the manifold port  18  open up into a cavity  30  via a tank passage  32  and a manifold passage  34 , respectively, within the housing  14 . In the illustrated embodiment, the passages  32 ,  34  are coupled with the tank port  16  and the manifold port  18 , respectively, to connect with the fuel tank  20  and the engine manifold  24 . However, the passages  32 ,  34  may also be openings in the valve housing  14  that communicate directly with the fuel tank  20  and/or the manifold  14  without any port in between. For example, the valve  12  may be placed inside a fuel tank and attached so that vapor can flow from the tank  20  directly to the fuel tank passage  32 .  
         [0016]     A diaphragm  36  disposed within the cavity  30  over the passages  32 ,  34  open and close the passages  32 ,  34  to selectively create a vapor flow path. In one embodiment, the diaphragm  36  has a bead  38  that engages with a groove  40  in the cavity  30  to form a leak-free seal holding the diaphragm  36  in place. A vent opening  42  may be formed in the housing  14  to vent the cavity  30  to the atmosphere to prevent a pressure-locked condition, which would prevent the diaphragm  36  from actuating. The vent opening  42  may also act as an atmospheric pressure reference for the diaphragm  36  by keeping the pressure in the cavity  30  at atmospheric pressure.  
         [0017]     In  FIG. 3 , the diaphragm  36  is in an open position, forming a flow path indicated by arrow A. The diaphragm  36  is arranged so that it will be normally closed when vacuum forces in the manifold port  34  pull vapor from the tank port  32  through the passages  32 ,  34  and the cavity  30  along the flow path A so that the vapor can be burned in the small engine. The diaphragm  36  actuates to the open position shown in  FIG. 3  when the pressure in the fuel tank vapor dome  22  reaches a predetermined level (e.g., greater than atmospheric pressure), allowing vapor to flow from the tank port passage  32  to the manifold port passage  34 . At this point, excess vapors from the fuel tank  20  are purged by the engine manifold  24  until the system  10  reaches equilibrium, causing the diaphragm  36  to reseat back to its normally closed position. In one embodiment, the system  10  reaches equilibrium when the pressure underneath the diaphragm  36  is at atmospheric pressure.  
         [0018]     In one embodiment, the valve  12  also includes a normally-closed check valve  44  and at least one orifice  46  that allows make-up air into the fuel tank  20 . In the illustrated embodiment, the check valve  44  is an umbrella seal valve, but any other valve may be used as the check valve  44  without departing from the scope of the invention. The valve  12  may also include an optional resilient member  48 , such as a coil spring, that biases the diaphragm  36  to a closed position and creates a head valve function to protect the fuel tank  20  from an overfill condition during refueling. The resilient member  48  holds the diaphragm  36  in a closed position during refueling until the fuel tank pressure, and therefore the pressure in the tank port  16 , reaches a predetermined level high enough (e.g., higher than atmospheric pressure) to overcome the biasing force of the resilient member  48  and push the diaphragm  36  open. Note, however, that the resilient member  48  may be eliminated from the valve  12  without departing from the scope of the invention.  
         [0019]      FIG. 4  shows the valve  12  when the diaphragm  36  is in its normally closed position. This occurs when the vacuum pressure in the manifold port  18  is high enough to pull the diaphragm  36  shut and seal off the passages  32 ,  34 . As a result, the valve  12  isolates the vacuum pressure in the manifold port  18  and prevents the vacuum pressure in the engine manifold  24  from creating a vacuum pressure in the vapor dome  22  that in turn stops the flow of fuel to the engine carburetor (not shown) via a gravity feed or fuel pump (not shown). As fuel is consumed by the engine (not shown), the check valve  44  opens to allow fresh atmospheric make-up air from the make-up air orifices  46  to relieve potential vacuum pressure in the vapor dome  22 , increasing the vapor pressure in the tank  20 . Once the vacuum pressure in the fuel tank  20  has been dissipated, the check valve  44  returns to its closed position.  
         [0020]      FIG. 5  is a representative section view of a valve assembly according to one embodiment of the invention. In this embodiment, the inventive valve  12  described above is integrated with the liquid discriminator (LD) valve  26  to form a valve assembly  51 . The LD valve  26  can be any type of valve that can discriminate between liquid fuel and fuel vapor. Possible LD valves that could be incorporated into the valve assembly  51  include, but are not limited to, rollover valves, variable orifice valves, grade vent valves, or grade vent valves with reverse flow capability. The LD valve portion  50  of the valve assembly  51  has an LD passage  54  that is opened and closed by an LD float  56 . A portion of the liquid discriminating valve  50  portion of the assembly  51  is disposed in the fuel tank  20  when the fuel system is assembled.  
         [0021]     As shown in the figure, fuel vapor enters the inventive valve  12  portion of the assembly  51  through the liquid discriminating valve portion  50  rather than through a tank port. More particularly, the housing  14  of the valve  12  includes an opening  58  that fluidically couples the tank port passage  32  of the valve  12  with the LD passage  54  of the LD valve  50 . When the LD passage  54  is open, fuel vapor in the fuel tank  20  flows through holes  58  formed in the LD housing  52  and up through the LD passage  54  into the tank port passage  32 . The combined valve  12  and liquid discriminating valve  50  portions may share a common housing  59  so that the entire assembly  51  can be connected to the tank  20  as a single unit in a single manufacturing step. The assembly  51  may be connected to the tank  20  via any appropriate method, such as welding, a grommet, interference fit, etc. By integrating the valve  12  with the liquid discriminating valve  50  into a single unit, this embodiment eliminates the need for a separate tank port  16  to direct fuel vapor into the valve  12  and provides a simple way to assemble a small engine vapor management system.  
         [0022]     The description above focuses on using the inventive valve in a small engine fuel system. However, the valve may be used in any application requiring vapor pressure control without departing from the scope of the invention.  
         [0023]     Although the invention has hereinabove been described with respect to the illustrated embodiments, it will be understood that the invention is capable of modification and variation and is limited only by the following claims.