Patent Publication Number: US-7210466-B1

Title: Purge valve and vapor control system

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to fuel systems and more particularly to a purge valve and vapor control system for use in a fuel system. 
     BACKGROUND OF THE INVENTION 
     Increasingly strict environmental regulations are being promulgated by governmental agencies, including regulations restricting the emission to atmosphere of hazardous hydrocarbon fuel vapors. Such regulations are becoming increasingly common with respect to machines having small engines including both handheld and ground supported machines such as lawnmowers, leaf blowers, weed trimmers, power washers and the like. 
     To facilitate compliance with these regulations, various fuel vapor control systems and methodologies have been employed. For example, a carbon canister may be employed to receive fuel vapor from a fuel system, such as from a fuel tank, and to collect and hold the fuel vapor prior to it being purged to an intake manifold of the engine for combustion in the engine. During hot soak conditions, such as when a hot engine is shut off or a vehicle engine is exposed to hot ambient conditions for an extended period of time, fuel vapor generation may be sufficient to saturate or overload the fuel vapor canister. Once saturated or overloaded, the vapor canister is no longer effective. Passively purged vapor canisters may vent to the atmosphere excess fuel vapor which results in unacceptably high hydrocarbon fuel vapor emission to the atmosphere. 
     SUMMARY OF THE INVENTION 
     A vapor control system includes a vapor receiver having an inlet through which vapor is received, an outlet through which vapor is discharged, and a control valve having a first inlet in communication with the outlet of the vapor receiver, a second inlet in communication with a pressure source and an outlet. The control valve also includes a valve having a closure moveable between a first position preventing communication between the first inlet and the outlet, and a second position permitting communication between the first inlet and the outlet in response to a pressure signal over a threshold pressure provided from the pressure source through the second inlet. Movement of the closure to its second position permits routing of vapor from the vapor receiver, through the first inlet and out of the outlet of the control valve. 
     Desirably, in one presently preferred implementation, the pressure source is an intake manifold of an engine and the outlet of the control valve is also communicated with the intake manifold so that when the valve head is moved towards its second position, fuel vapor can be purged from the vapor receiver and delivered to the intake manifold of the engine for combustion therein. The closure preferably is carried by a flexible diaphragm actuated by change in pressure in the intake manifold which is communicated to the diaphragm through the second inlet. In this manner, the threshold pressure at which the closure and diaphragm are moved may be a function of the surface areas of the diaphragm exposed to the intake manifold pressure on opposed sides of the diaphragm. 
     Some of the objects, features and advantages that may be achieved by at least some embodiments of the present invention include providing a vapor control system that reduces emission to atmosphere of hydrocarbon fuel vapor, actively purges a vapor canister, provides a mechanical actuation and initiation of the canister purge cycle, does not require electricity, does not interfere with steady operation or acceleration of the engine, preferably operates only during deceleration of the engine when the vacuum in the inlet manifold is highest, operates during the frequent excursions of the throttle during normal governor operation, is of relatively simple design and economical manufacture and assembly, and has a long, useful life in service. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments and best mode, appended claims and accompanying drawings in which: 
         FIG. 1  is a schematic view of a vapor control system according to one presently preferred embodiment of the invention; 
         FIG. 2  is an enlarged sectional view of a mechanical purge valve according to one aspect of the present invention illustrated in a first or closed position; 
         FIG. 3  is a sectional view of the purge valve of  FIG. 2  illustrated in a second or open position and with a modified closure; and 
         FIG. 4  is an enlarged fragmentary sectional view illustrating a portion of an outlet of the purge valve. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring in more detail to the drawings,  FIG. 1  illustrates a fuel system  10  including a vapor control system  12  and vapor purge valve  14  according to one presently preferred embodiment of the present invention. The fuel system  10  includes a fuel tank  16  that contains a supply of liquid fuel to support operation of an engine  18 . Gaseous phase fluids, including fuel vapors, are also contained within the fuel tank  16 , and may be vented through an appropriate valve or outlet  20  to, for example, a vapor receiver such as a vapor canister  22 . The vapor canister has a passage  23  through which vapor is received, and through which vapor may also be purged or discharged from the vapor canister  22 . So in this embodiment, the passage  23  acts as an inlet and an outlet. If desired, the vapor canister  22  may include a separate outlet so that the passage  23  acts as an inlet and vapor would then be purged through the separate outlet. The vapor canister  22  usually includes a filter, or filter material like activated carbon to “hold” the vapor (hydrocarbon) thus allowing only the hydrocarbon-free product to the atmosphere through a vent  70  in the vapor canister  22 . The hydrocarbons are purged from the vapor canister  22  through the valve  14  to an intake manifold  24  of the engine  18  for combustion in the engine. 
     As best shown in  FIGS. 2 and 3 , the purge valve  14  is preferably interposed between the fuel tank  16  and the vapor canister  22  to control venting or purging of the vapor canister  22 . The purge valve  14  includes a body  26 , a pressure responsive member  28  carried by the body  26 , first and second inlets  30 ,  32 , and an outlet  34 . The pressure responsive member is preferably a flexible diaphragm  28  trapped about its periphery between two portions  36 ,  38  of the valve body  26 . On one side, the diaphragm  28  defines part of a pressure signal chamber  40  with one of the valve body portions  38 , and on its other side defines part of a chamber  42  into which the first inlet  30  and outlet  34  extend. A valve seat  44  is provided in the chamber  42  preferably adjacent to the outlet  34  and defines part of a passage  46  of the outlet  34 . 
     To close the outlet  34  and prevent purging or venting of the vapor canister  22  therethrough, the diaphragm  28 , or a valve head or closure  50  carried by the diaphragm  28 , preferably engages the valve seat  44  to at least substantially inhibit fluid flow therethrough. The closure  50  may be separate from, connected to or carried by (as shown in  FIG. 3 ), or part of or integral with the diaphragm  28 . When the closure  50  is engaged with the valve seat  44 , the valve  14  is in its first or closed position and communication between the first inlet  30  and the outlet  34  is at least substantially prevented. Preferably, to yieldably bias the diaphragm  28  to its first position, a biasing member, such as a spring  52 , is disposed in the pressure signal chamber  40  and acting on the diaphragm  28 . The diaphragm  28  may have one or more convolutions  53  to increase the flexibility and range of movement of the diaphragm  28  in use. 
     As best shown in  FIG. 3 , the diaphragm  28  is moveable away from the valve seat  44  to a second or open position wherein the first inlet  30  is communicated with the outlet  34 . In this position, the vapor canister  22  is communicated with the outlet  34  to permit venting or purging of the vapor canister  22 . As best shown in  FIG. 4 , a jet or orifice  54  may be disposed in the outlet  34  to control the fluid flow rate therethrough. 
     Desirably, the second inlet  32  is communicated with the intake manifold  24 , to provide a pressure signal in the pressure signal chamber  40  that acts on an effective surface area of the diaphragm  28  exposed to the pressure signal chamber. The effective surface may include areas of the diaphragm directly exposed to the chamber  40  and, for example, the exposed area of a retainer  56  disposed between the diaphragm  28  and the spring  52 . The outlet  34  preferably also is communicated with the intake manifold  24  of the engine  18  such as through a suitable conduit  60  providing a pressure signal through the orifice  54  and outlet passage  46  acting on the diaphragm  28  in an area bounded by the valve seat  44 . In this embodiment, the effective surface area of the diaphragm  28  exposed in the pressure signal chamber  40  preferably is greater than the surface area bounded by the valve seat  44 . Accordingly, the intake manifold pressure signal as applied to the opposed sides of the diaphragm  28  provides a net force tending to displace the diaphragm  28  away from the valve seat  44 . The valve  14  can be calibrated to move between its first and second positions by, for example, communicating the pressure signal chamber  40  and chamber  42  with different locations in the intake manifold that have different pressure values or ranges, and based on the size of the orifice  54  and the force of the spring  52  provided on the diaphragm  28 . In one implementation, the chamber  40  is communicated with a high-pressure differential area of the intake manifold and the chamber  42  is communicated with a lower pressure differential area of the intake manifold. 
     Preferably, the purge valve  14  is used with a speed controlled or governed vehicle that varies its throttle position in an effort to maintain a desired or preset engine speed. As the engine  18  decelerates, an at least momentary increase in vacuum pressure in the intake manifold  24  is communicated to the purge valve  14  through the outlet  34  and the second inlet  32 . When the pressure signal is above a threshold value, the diaphragm  28  is moved to its second position with the closure  50  removed from the valve seat  44  permitting communication between the first inlet  30  and the outlet  34 . Therefore, the vapor canister  22  can be purged of fuel vapor through the first inlet  30 , and discharged from the purge valve  14  through the outlet  34  to the intake manifold  24  for combustion in the engine  18 . During this activity, fresh air is vented into the vapor canister  22  through the atmospheric vent  70 . 
     The flow rate of fluid from the vapor canister  22  and to the engine  18  through the purge valve  14  is controlled by the size of the orifice  54  in the outlet passage  46 . Desirably, this avoids undo engine instability due to the varied ratio of air and fuel delivered to the engine  18  while purging or venting the vapor canister  22 . Also, by purging the vapor canister  22  as the engine  18  decelerates or a throttle valve (not shown) is closed in a governed or speed controlled engine, the instability due to the varied air to fuel ratio can be minimized since variation in the air to fuel ratio is most tolerable during engine deceleration or throttle closing wherein the engine fuel demand is less than, for example, during engine acceleration. 
     Desirably, the purging of the vapor canister  22  occurs mechanically, without electricity, and is automatic in response to a suitable pressure signal from the intake manifold  24 . The purge valve  14  itself could be mounted on the vapor canister  22 , the engine  18 , fuel tank  16 , or any other suitable location. 
     While certain preferred embodiments have been shown and described, persons of ordinary skill in this art will readily recognize that the preceding description has been set forth in terms of description rather than limitation, and that various modifications and substitutions can be made without departing from the spirit and scope of the invention. By way of example without limitation, the closure  50  may be integral with the diaphragm  28 , or coupled to, carried by or otherwise responsive to diaphragm movement to move the closure  50  relative to the valve seat  44  as desired. Also, the vapor canister may have a separate inlet and outlet, the inlet and outlet may be combined in one passage with in-flow and out-flow at different times, or the flow and passages in the vapor canister may be otherwise arranged as desired. Of course, still other modifications and substitutions can be made. The invention is defined by the following claims.