Abstract:
A fuel shut-off system for a carburetor substantially reduces or prevents the delivery of fuel to an engine when the engine is turned off and as it coasts to a stop. The fuel shut-off system preferably reduces or eliminates the pressure differential across a nozzle through which fuel is delivered from a fuel chamber through a fuel-and-air mixing passage of the carburetor and into the engine. In this manner, the flow of fuel through the nozzle is reduced and preferably eliminated immediately upon engine turn-off to prevent the after-fire and associated problems within a residually hot exhaust system. The system incorporates an actuator, preferably a solenoid valve, having a first position which obstructs a vacuum bypass passage communicating between the fuel chamber and the fuel-and-air mixing passage, and a second position which enables communication between the vacuum bypass passage and a fuel chamber passage which otherwise communicates with a near atmospheric pressure source.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to carburetors and more particularly to a carburetor with a fuel shut-off system. 
     BACKGROUND OF THE INVENTION 
     It is known to use a carburetor to provide a fuel-and-air mixture to an engine to support combustion in and operation of the engine. If a hot or warmed-up engine is turned off under high speed conditions, such as for example, 3,600 r.p.m. or higher, an engine governor moves a carburetor throttle valve to its wide-open position permitting air flow through the carburetor; and the engine coasts to a stop. As the engine slows down, air is pulled into the engine and the carburetor continues to deliver fuel to the engine. With the ignition system turned off, the unburned fuel-and-air pass without being ignited through the engine and into the hot exhaust system downstream of the engine. Under certain conditions, the fuel-and-air may then ignite within hot regions in the exhaust system resulting in a loud boom or “after-fire”. Beyond the unsettling noise of the after-fire, the expanding gases from the ignited fuel-and-air mixture in the exhaust system can create sufficient pressure to damage the engine and exhaust components. 
     U.S. Pat. No. 4,111,176 discloses a float feed carburetor having a fuel bowl or chamber vent passage, a vacuum bypass passage and a solenoid valve operable to close the bowl vent passage when the vehicle ignition system is turned off to shut down the engine. Undesirably, the vacuum bypass passage remains open to the bowl vent passage in all positions of the solenoid valve and throughout the operation of the carburetor and engine. With this construction, an enlarged diameter bowl vent passage is required to prevent undue interference with the fluid flow through the fuel-and-air mixing passage of the carburetor due to the interaction between the vacuum bypass passage and fuel bowl vent passage. 
     Some carburetors have a solenoid valve attached to the bottom of the fuel bowls of the carburetor and operable to close the inlet of the fuel nozzle when the engine is shut-off. This requires a liquid tight seal between the fuel bowl and the solenoid valve, a specialized arrangement of the fuel nozzle and seat area for the solenoid valve, and heat from the solenoid valve can be transferred to the fuel in the fuel bowl. 
     SUMMARY OF THE INVENTION 
     A fuel shut-off system for a carburetor substantially reduces or prevents the delivery of fuel to an engine after the engine is turned off. The fuel shut-off system preferably reduces or eliminates the pressure differential across a nozzle through which fuel is delivered from a fuel chamber through the carburetor and into the engine. In this manner, the flow of fuel through the nozzle is reduced and preferably eliminated to prevent the after-fire and associated problems within a residually hot exhaust system. 
     An actuator, preferably a three-way electric solenoid valve, is operable to control the opening and closing of one or more carburetor vent passages to control the pressure differential across the nozzle. Desirably, the carburetor is a float feed carburetor having a fuel chamber in communication through the nozzle with a fuel-and-air mixing passage formed in the carburetor. When the combustion engine is running, the fuel chamber is vented to the atmosphere through a fuel chamber passage, and when the engine is not running or initially shut-down, the fuel chamber is communicated with the fuel-and-air mixing passage through a vacuum bypass passage. 
     When the engine ignition system is on and the engine is operating, the solenoid-controlled valve is in a running position closing the vacuum bypass passage and preferably opening an atmosphere passage which only then communicates with the fuel chamber passage. When the ignition system is turned off, to shut-off the engine, the solenoid-controlled valve is moved to a non-running position so that the vacuum bypass passage communicates with the fuel chamber passage and preferably the atmosphere passage is closed. This results in substantially equal pressure at an outlet of the nozzle in the area of the fuel-and-air mixing passage and at an inlet of the nozzle in the area of the fuel chamber. With the pressure being substantially equal across the fuel nozzle, fuel flow through the nozzle stops. Desirably, because the solenoid-controlled valve closes the vacuum bypass passage during normal operation of the engine and carburetor, the fuel chamber passage can be made smaller in size than in prior systems which left the vacuum bypass passage open at all times. 
     Objects, features and advantages of this invention include providing a carburetor with a fuel shut-off which prevents fuel flow to the engine after the engine is shut down, prevents after-fire, reduces engine exhaust emissions, enables use of a solenoid valve of reduced size, does not require a liquid tight seal between the solenoid valve and carburetor, eliminates the need for specially formed fuel jets and nozzles, avoids problems associated with solenoid heat transferred to the fuel bowl of a float feed carburetor, enables use of a smaller fuel bowl vent passage, is of relatively simple design and economical manufactured and assembly, and in use has a long service life. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects, features and advantages of this 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 cross sectional view of a carburetor having a fuel shut-off system in accordance with the present invention; 
     FIG. 2 is a top plan view of the carburetor; 
     FIG. 3 is an end view of the carburetor showing an inlet with an open choke plate; 
     FIG. 4 is a sectional view of the carburetor taken generally along line  4 — 4  of FIG. 2; 
     FIG. 5 is a partial and fragmentary sectional view of the carburetor taken generally along line  5 — 5  of FIG. 3; 
     FIG. 6 is a perspective view of a seat insert of the carburetor illustrating an upper surface thereof; 
     FIG. 7 is a perspective view of the seat insert illustrating a under surface thereof; 
     FIG. 8 is an enlarged fragmentary cross sectional view of the carburetor taken from circle  8  of FIG. 5; 
     FIG. 9 is a sectional view similar to FIG. 5 but of a second embodiment of a carburetor; and 
     FIG. 10 is an enlarged fragmentary cross sectional view of the carburetor taken from circle  10  of FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring in more detail to the drawings, FIG. 1 illustrates a carburetor  10  embodying this invention for a combustion engine, not shown. In operation air enters an inlet  12  of a fuel-and-air mixing passage  14  defined by a carburetor body  16  of the carburetor  10 . Fuel enters the fuel-and-air mixing passage  14  via a main fuel feed passage  18  having a nozzle  20  disposed in the region of a venturi  22  within the passage  14 . The fuel mixes with the air and exists the carburetor  10  at an outlet  24  of the fuel-and-air mixing passage  14  where the mixture then flows into a combustion chamber, not shown, of the engine. Fuel enters the main fuel feed passage  18  from a fuel chamber  26  of the carburetor  10  defined by a fuel bowl  28  engaged sealably to the underside of the carburetor body  16 , and preferably with a sealing gasket therebetween. The fuel chamber  26  is preferably of a float type having a float  30  which opens and closes a fuel inlet valve to replenish fuel in the bowl as it is delivered to and consumed by the operating engine. 
     During normal running conditions of the combustion engine, liquid fuel flows from the lower fuel chamber  26  to the fuel-and-air mixing passage  14  disposed above, because the fuel-and-air mixing passage  14  is at sub-astmospheric pressure and the fuel chamber or float type chamber  26  is near atmospheric pressure. Fuel thus flows upward through the nozzle  20  of the main fuel feed passage  18  and into the fuel-and-air mixing passage  14 . The vacuum within the fuel-and-air mixing passage  14  is greatest at the nozzle and venturi  22  region where air flow velocity is relatively high. The vacuum produced by the combustion chamber of a running engine and exposed to the mixing passage  14  is controlled or limited by a throttle plate  36  supported rotatably within the passage  14  between the outlet  24  and venturi  22  by the body  16 . A choke plate  38 , supported rotatably within the mixing passage  14  between the venturi  22  and the inlet  12  is advantageous for starting a cold engine. As best illustrated in FIGS. 3 and 5, to maintain the fuel chamber  26  at atmospheric pressure, a fuel chamber passage  32  is carried by the carburetor body  16  and communicates between the fuel chamber  26  and an atmosphere port  34  located near the inlet  12  of the fuel-and-air mixing passage  14 . However, port  34  can communicate with any near atmospheric pressure source preferably located downstream of the air cleaner unit, not shown. 
     When the running engine is shut down, if fuel does not cease to flow through the nozzle  20  and into the combustion chamber, the vacuum produced from the coast-down and any dieseling of the engine could potentially pull an unburned fuel-and-air mixture into the-still hot exhaust of the engine. Under certain conditions, this fuel-and-air mixture may ignite within the hot regions of the exhaust producing a potentially damaging “after-fire.” This “after-fire” is eliminated by stopping fuel flow through the nozzle  20 . Fuel flow is stopped by instantaneously equalizing pressure between the float chamber  26  and the venturi  22  region of the fuel-and-air mixing passage  14 . To equalize the pressure, when the engine is coasting down, a vacuum bypass passage  40  communicates between the fuel chamber  26  and the venturi  22  region of the fuel-and-air mixing passage  14  at a bypass port  41 , as best shown in FIGS. 1,  4  and  5 . 
     A fuel shut-off system  42  equalizes the pressure across the main fuel feed passage  18  when the engine is initially shut-down or coasting down, and assures a differential pressure to promote fuel flow into the fuel-and-air mixing passage  14  when the engine is running. The fuel chamber passage  32  and the vacuum bypass passage  40  (as best shown in FIG. 4) are part of the fuel shut-off system  42  which also includes an atmosphere passage  44 . The fuel chamber passage  32 , the atmosphere passage  44  and the vacuum bypass passage  40  all communicate independently to a common valve chamber  46  of a three-way electrical solenoid valve  48  of the fuel shut-off system  42 . 
     As best illustrated in FIGS. 4,  5  and  8 , when the engine is running, the three-way solenoid valve  48  of the first embodiment is in an energized obstructing or closing the vacuum bypass passage  40  while the atmosphere passage  44  communicates with the fuel chamber passage  32  via the valve chamber  46 . When the engine is not running the solenoid valve  48  of the first embodiment is de-energized obstructing or closing the atmosphere passage  44  while the vacuum bypass passage  40  communicates with the fuel chamber passage  32  via the valve chamber  46 . An elongated actuator  50  of the solenoid valve  48  is retracted partially out of the valve chamber  46  when the solenoid valve  48  is energized to an atmospheere or retracted position  49 . The actuator  50  has an enlarged head  52  fixed to a distal end of an armature  54  disposed concentrically along an axis  56 . The enlarged head  52  retracts along the axis  56  and seals against a vacuum bypass seat  58  via a first mating surface  60  of the enlarged head  52  which is generally annular in shape and is defined radially between an outer perimeter  62  of the enlarged head  52  and the outer cylindrical surface of the armature  54 . When the engine is coasting down or not-running the solenoid valve  48  is deenergized and the actuator  50  extends into the valve chamber  46  to vacuum bypass or extended position  51 , shown in phantom in FIG.  8 . The solenoid valve  48  remains in the extended position  51  even after the engine comes to a complete stop. A substantially conical second surface  64  of the enlarged head  52  which is opposite that of the first mating surface  60  engages an atmosphere seat  66  within the valve chamber  46  and opposing the vacuum bypass seat  58 . The atmosphere vent passage  44  extends between the atmosphere port  34  and the atmosphere seat  66 . When the second mating surface  64  and the atmosphere seat  66  are engaged sealably, the vacuum bypass passage  40  and the fuel chamber passage  32  are in communication with one another via the valve chamber  46  and through a passage port  68  connecting valve chamber  46  with fuel chamber passage  32 . 
     Referring to FIGS. 6-8, the valve chamber  46  is defined between the carburetor body  16  and a seat insert  70  of the solenoid valve  48 . The seat insert  70  is sealably engaged between an exterior surface of carburetor body  16  and a solenoid housing  72  of the solenoid valve  48 . The seat insert  70  has an under-surface  74  which is exposed within the valve chamber  46  and carries the vacuum bypass seat  58 . An upper surface  76  of the seat insert  70  has a recess defining a secondary chamber  78  disposed beneath the solenoid housing  72 . A hole  79  extends through the insert  70  between the under and upper surfaces  74 ,  76  thereby communicating between the secondary chamber  78  and valve chamber  46 . The vacuum bypass seat  58  encircles the hole  79 . The armature  54  of the actuator  50  of the solenoid valve  48  extends and retracts through the hole  79 . The hole  79  is defined by an inner perimeter  80  of the vacuum bypass seat  58 . The perimeter  80  is somewhat star shaped wherein the hole  79  has a circular portion  82  and a series of grooves or slots  84 . Each one of the grooves  84  extend lengthwise axially and have a depth which extends radially outward from the circle portion  82  of the hole  79 . Furthermore, the grooves  84  are spaced circumferentially around the circular portion  82 . The circular portion  82  is intermittedly defined by curved portions  86  of the inner perimeter  80  disposed between the alternating grooves  84 . The curved portions  86  of the inner perimeter  80  are in close proximity to, or engaged slidably with the armature  54  of the actuator  50  thereby aligning and stabilizing the actuator  50  of the solenoid valve  48  as it extends and retracts into and out of the valve chamber  46 . Disposed radially outward from the hole  79  is an aperture  88  which extends through the seat insert  70  between the under and upper surfaces  74 ,  76  and communicates between the secondary chamber  78  and the vacuum bypass passage  40  with which it is preferably aligned. The plurality of the circumferentially spaced grooves  84  provide the portal between the valve and secondary chambers  46 ,  78  and the respective fuel chamber passage port  68  and vacuum bypass aperture  88 . 
     The armature  54  of the solenoid is made of a ferro-magnetic material such as iron and is slidably received in a coil of electric wire disposed in the housing. Applying an electric current to the coil causes the armature to move the valve head  52  to the position shown in solid line in FIGS. 5 and 8, and when the coil is deenergized, the armature is yieldably biased by a spring in the housing  72  to move the valve head  52  to the position shown in phantom line in FIG.  8 . 
     With the carburetor  10  installed on an engine, the solenoid coil is manually energized during starting and operation of the engine and is deenergized during stopping or turning off the engine to terminate the delivery of fuel to the engine while it coasts to a stop or ceases to rotate. Typically, the solenoid coil is connected electrically to an ignition “kill switch” or other device which disconnects the solenoid coil from an energizing current. 
     Referring to FIGS. 9 and 10, a second embodiment of a carburetor  10 ′ is shown having a fuel shut-off system  42 ′. Unlike the first embodiment wherein the solenoid valve  48  is energized to an atmospheric or retracted position  49  when the engine is running and thereby exposing the float chamber  26  to atmospheric pressure, a solenoid valve  48 ′ of the second embodiment is de-energized when in an atmospheric or retracted position  49 ′ regardless of whether the engine is running or after coast down. The solenoid valve  48 ′ is temporarily energized to a vacuum bypass or extended position  51 ′ only during coast down of the engine immediately following engine shut down. 
     Fuel shut-off system  42 ′ is designed such that an armature  54 ′ of the solenoid valve  48 ′ is biased by a springing (not shown) in the solenoid housing to the retracted position  49 ′ of the valve head  52 ′. applying an electric current to the solenoid coil causes the armature to move the valve head  52 ′ to the extended position  51 ′ shown in phantom line in FIG.  10 . This can be accomplished by discharging a capacitor  90 , at key off, causing a temporary electric current to flow through the solenoid during engine coast down. When the capacitor  90  is fully discharged, after the engine has come to a complete stop, the bias spring returns the valve head  52 ′ to the retracted position  49 ′ and the system  42 ′is in the engine start mode of venting atmosphere to a channel  32 ′ and to the float chamber  26 ′. Although this mode of operation requires the addition of the capacitor  90 , it has the advantage that in the event of a solenoid failure the engine would start and run normally, with the exception of shut down (coast down) fuel flow interruption. 
     While the form of the invention herein disclosed constitutes the presently preferred embodiment, many others are possible. For instance, the solenoid valve can take the form of a rotary valve with passages extending laterally through the armature. It is not intended herein to mention all the possible equivalent forms or ramifications of the invention. It is understood that the terms used herein are merely descriptive rather than limiting and that various changes may be made without departing from the spirit or scope of the invention.