Carburetor with fuel vapor control

Information

  • Patent Grant
  • 6439546
  • Patent Number
    6,439,546
  • Date Filed
    Tuesday, August 29, 2000
    24 years ago
  • Date Issued
    Tuesday, August 27, 2002
    22 years ago
Abstract
A carburetor having a plurality of restricted fluid flow paths upstream of a fuel and air mixing passage to inhibit the passage of large fuel vapor bubbles through the fuel paths and to the fuel and air mixing passage. Desirably, the restricted flow paths constrain large volume vapor bubbles and clusters of bubbles from passing therethrough undistributed in the fuel to prevent an inconsistent or overly lean fuel and air mixture from being delivered to the engine. At least two restrictive flow paths diffuse, separate, and/or break up the large vapor bubbles and clusters into a plurality of smaller vapor bubbles which are more uniformly distributed within the liquid fuel flowing through the carburetor to provide a more consistent flow of fuel to the engine.
Description




FIELD OF THE INVENTION




This invention relates generally to carburetors and more particularly to diaphragm type carburetors.




BACKGROUND OF THE INVENTION




Carburetors are currently used to supply liquid hydrocarbon volatile fuels to a wide range of two-cycle and four-cycle internal combustion engines including hand held engines such as engines for chainsaws and weed trimmers as well as a wide range of marine engine applications. Diaphragm type carburetors are particularly useful for hand held and other engine applications wherein the engine may be operated in substantially any orientation including up side down. Typically, diaphragm carburetors have been used with two-cycle engines and there is a continuing struggle to reduce the exhaust emissions of these engines to prevent escape to the atmosphere of hazardous hydrocarbon vapors and to comply with increasingly strict governmental regulations regarding the same. Still further, engine manufacturers are continually seeking carburetors which are easy to calibrate and of low cost to manufacture and assemble.




A typical diaphragm type carburetor has a diaphragm fuel pump which draws liquid fuel from a fuel tank and delivers that fuel under pressure to a fuel metering system which provides a metered quantity of fuel into a stream of air flowing through the carburetor for delivery to the engine. Undesirably, a significant amount of fuel vapor may exist within the fuel system, such as within the fuel tank and/or fuel lines leading to the carburetor. Fuel may also tend to vaporize within the carburetor to provide still further fuel vapor within the fuel system. This fuel vapor tends to collect in various portions of cavities and passages within the carburetor to form large vapor bubbles and large clusters of vapor bubbles. When the large vapor bubbles, clusters or portions thereof are drawn along with the liquid fuel supply and delivered to the engine, the fuel supply to the engine can become inconsistent or undesirably lean resulting in unstable engine operation, especially for engines equipped with fuel injection apparatus. To combat this, the carburetor may be set to provide a somewhat richer than required fuel and air mixture to ensure adequate fuel is supplied to the engine. However, this may increase the hydrocarbon content of the engine emissions. These problems are exasperated with engine operation at ambient temperatures above 80° F. which causes the rate of fuel vapor generation to increase significantly.




SUMMARY OF THE INVENTION




A carburetor having a plurality of restricted fluid flow paths upstream of a fuel and air mixing passage to inhibit the passage of large fuel vapor bubbles through the fuel paths and to the fuel and air mixing passage. Desirably, the restricted flow paths constrain large volume vapor bubbles and clusters from passing therethrough undistributed to prevent an inconsistent or overly lean fuel and air mixture from being delivered to the engine. At least two restrictive flow paths diffuse, separate, disperse and/or break up the large vapor bubbles and clusters into a plurality of smaller vapor bubbles which are more uniformly separated and distributed within the liquid fuel flowing through the carburetor to provide a more consistent flow of fuel to the engine.




In one form, the restrictive flow paths comprise a plurality of small openings in the carburetor body which define an outlet of a fuel metering chamber from which the fuel is supplied to the fuel and air mixing passage. In another form, the restrictive flow paths are defined through a porous material disposed between a fuel pump and the fuel metering chamber of the carburetor downstream of the fuel pump. Both the porous material between the fuel pump and fuel metering chamber and the plurality of holes defining the outlet of the fuel metering chamber may be used in the same carburetor, if desired.




Objects, features and advantages of this invention include providing a carburetor which provides a more stable supply of fuel to an engine, reduces the hydrocarbon exhaust emissions from the engine, facilitates calibrating the carburetor for a particular engine or engine family, prevents large volumes of undispersed fuel vapor from being delivered to the engine all at once, improves engine operation especially at ambient temperatures above 80° F., provides a pressure restriction between the fuel pump and fuel metering chamber to improve pressure regulation and fuel flow through the carburetor, is of relatively simple design and economical manufacture and assembly, reliable, durable, and in service has a long useful 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 sectional view of a carburetor embodying the present invention;





FIG. 2

is a perspective view of the body of the carburetor of

FIG. 1

with an end cap and fuel metering diaphragm removed;





FIG. 3

is a perspective view of a body of another carburetor embodying the present invention; and





FIG. 4

is a perspective view of a body of another carburetor embodying the present invention.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS




Referring in more detail to the drawings,

FIGS. 1 and 2

illustrate a diaphragm type carburetor


10


embodying the present invention and having a main body


12


with a fuel and air mixing passage


14


therethrough, a fuel pump


16


, and a fuel metering assembly


18


communicating with the outlet of the fuel pump


16


through a diaphragm controlled valve


20


. The fuel pump


16


draws fuel from a fuel source such as a fuel tank and delivers it to a fuel metering chamber


22


which communicates with the fuel and air mixing passage


14


through one or more adjustable needle valves, low speed fuel nozzles


26


and a high speed fuel nozzle


28


downstream of the needle valves. A throttle valve


30


in the fuel and air mixing passage


14


controls the flow of air therethrough and thus varies the magnitude of the pressure drop across the low speed fuel nozzles


26


and the high speed fuel nozzle


28


to control the flow of fuel through the nozzles


26


,


28


and the delivery of a fuel and air mixture to the engine.




As shown in

FIG. 1

, the fuel pump


16


is defined between an end plate


32


and the carburetor body


12


and has a diaphragm


34


defining a fuel chamber


36


on one side and a crankcase pressure pulse chamber


38


on its other side communicating with the engine crankcase through a passage


40


. Negative pressure pulses from the engine crankcase displace the diaphragm


34


in a direction tending to increase the volume of the fuel chamber


36


to draw fuel from a fuel tank through an inlet passage


42


in the body


12


. A fuel inlet valve


44


which is preferably a flap type check valve integral with the fuel pump diaphragm


34


is opened by the decreased pressure within the fuel chamber


36


to permit fuel flow therethrough and into the fuel chamber


36


. A subsequently provided positive pressure pulse from the engine crankcase to the pressure pulse chamber


38


displaces the fuel pump diaphragm


34


in a direction tending to decrease the volume of the fuel chamber


36


to thereby increase the pressure of the fuel therein and to discharge it through an outlet valve


46


. The outlet valve


46


is also preferably flap type check valve integral with the fuel pump diaphragm


34


and is opened by the increase in pressure in the fuel chamber


36


.




Fuel discharged from the fuel pump outlet is delivered under pressure to the fuel metering assembly


18


of the carburetor


10


through a porous member


51


received in a counterbore


53


in the body


12


and a fuel metering inlet passage


52


. The porous member


51


preferably serves as a fuel filter to remove contaminants from the fuel. In accordance with this invention, the porous member


51


provides a diffuser which breaks up large vapor bubbles and large clusters of bubbles into separate smaller vapor bubbles and may absorb or restrict the flow of these smaller vapor bubbles through the member


51


. The smaller vapor bubbles are more evenly dispersed or distributed in the liquid fuel flowing through the member


51


as compared to the large vapor bubbles and clusters to provide a more uniform and consistent supply of liquid fuel to the fuel metering assembly


18


. The porous member


51


is preferably relatively thick axially or in the direction of fuel flow to inhibit the recombination or coalescence of fuel vapor into large bubbles or clusters downstream of the member


51


such as occurs with a relatively thin filter or screen at the outlet of the fuel pump


16


. The member


51


may be a felt material, open or closed cell foam, sintered bronze, a synthetic compound, or other permeable substance or material which defines, in essence, a plurality of flow paths and permits a sufficient flow rate of fuel therethrough while preventing the passing of large vapor bubbles and large clusters of bubbles. The porous member


51


preferably has an average pore size of about 20 μm to 500 μm, a height or axial length of about 1 mm to 12 mm, a diameter of about 1.5 mm to 6 mm and a nominal size or volume of about 0.0018 cc to 0.340 cc.




The fuel metering assembly


18


functions as a vacuum actuated pressure regulator receiving pressurized fuel from the fuel pump


16


and regulating its pressure to a predetermined pressure, usually subatmospheric, to control the delivery of fuel from the fuel metering assembly


18


. The assembly


18


has an inlet valve


20


with a needle shaped head


56


and a shank


58


which is actuated by a lever arm


60


connected at one end to the valve, fulcrumed between its ends on a pin


62


and having a control arm


64


actuated at its free end by a fuel metering diaphragm


66


. The inlet valve


20


is yieldably biased to its closed position bearing on a valve seat


68


by a coil spring


70


received in a pocket


72


of the carburetor body


12


and bearing on the arm


64


of the lever arm


60


. As the pressure changes within the fuel metering chamber


22


defined on one side of the fuel metering diaphragm, the fuel metering diaphragm is displaced to bear on the arm


64


and hence rotate the lever arm


60


to cause a corresponding movement of the inlet valve


20


between its open and closed positions to selectively permit fuel to enter the metering chamber


22


through the inlet valve


20


.




In use, as fuel is drawn from the metering chamber


22


, the quantity of fuel therein will decrease and the differential pressure on the metering diaphragm


66


will move the lever arm


60


against the bias of the spring


70


in a clockwise direction (as viewed in FIG.


1


), to open the valve


20


and allow fuel to enter the metering chamber


22


. As the metering chamber


22


fills with additional fuel, the diaphragm


66


will tend to move the lever arm


60


clockwise and close the valve


20


to thereby regulate the pressure of the fuel within the metering chamber


22


.




Desirably, the porous member


51


also acts as a buffer between the fuel pump outlet and the inlet valve


20


and attenuates fluctuations in and reduces the magnitude of pulses in the fuel pressure produced by the fuel pump. The porous member


51


also increases the resistance to fuel flow which causes the valve


20


to be opened further to obtain the required fuel flow through the valve


20


which provides a smoother or improved pressure regulation of fuel supplied to the nozzles


26


,


28


and lower velocity fuel flow across the valve


20


to reduce the generation of fuel vapor and improve carburetor performance.




The carburetor body


12


has a fuel and air mixing passage


14


formed therethrough with the throttle valve


30


disposed in a downstream portion of the fuel and air mixing passage


14


. An upstream or choke valve bore portion


80


of the fuel and air mixing passage


14


preferably contains or cooperates with a choke valve (not shown) and leads to a venturi


82


. The venturi


82


has a converging upstream portion


84


, a throat


86


and a diverging downstream portion


88


leading to a throttle valve portion


90


of the passage


14


containing the throttle valve


30


.




In accordance with this invention, fuel in the metering chamber


22


is supplied preferably to both the high speed fuel nozzle


28


and idle or low speed fuel nozzles


26


through at least two holes


92


which collectively define a fuel outlet of the metering chamber


22


. The holes


92


each extend essentially perpendicular to and open into a fuel feed passage


94


which leads to a check valve


96


and both a low speed needle valve


98


and a high speed needle valve


100


, which adjust fuel flow to the low speed fuel nozzles


26


and the high speed fuel nozzle


28


, respectively. The check valve


96


prevents the back bleeding of air from the fuel and air mixing passage


14


to the fuel metering chamber


22


during purging of the carburetor or otherwise when the metering chamber


22


is at a vacuum or negative pressure (relative to the air mixing passage


14


).




The low speed needle valve


98


has a valve head or conical tip


102


on a shank


104


threaded into the body


12


and axially displaceable relative to a valve seat


106


to control the size of the annular gap or orifice


108


between them and leading to a fuel passage


109


to provide a restriction under at least some fuel flow conditions and thereby control the flow of fuel from the fuel metering chamber


22


to the low speed fuel nozzles


26


. Similarly, the high speed needle valve


100


has a valve head or conical tip


110


on a shank


112


threaded into the body


12


and axially displaceable relative to a valve seat


114


to control the size of the annular gap or orifice


116


between them and leading to a fuel passage


117


to provide a restriction under at least some fuel flow conditions and thereby control the flow of fuel from the fuel metering chamber


22


to the high speed fuel nozzle


28


.




The holes


92


define the metering chamber outlet and a plurality of essentially separate fuel flow paths and are sized to inhibit and preferably prevent the passage of large vapor bubbles and clusters therethrough. In contrast, conventional carburetors have a fuel metering chamber outlet defined by a single opening generally of the same diameter as a passage immediately downstream thereof which permits large vapor bubbles and clusters to flow therethrough thereby reducing the volume of liquid fuel supplied to the engine at a given time, by including the large vapor bubbles and clusters, providing a leaner, and thereby inconsistent fuel supply to the engine. As any large vapor bubbles or clusters are drawn into the holes


92


, they are broken up into a plurality of separate, smaller vapor bubbles and are dispersed within the liquid fuel flowing through the holes


92


to provide a more uniform distribution of fuel vapor within the liquid fuel which exits the metering chamber


22


. Desirably, the flow of fuel and/or fuel vapor through each hole


92


causes the flow velocity to increase resulting in turbulent flow which aids in the breakdown into small fuel vapor bubbles and the emulsion and dispersion of the smaller fuel vapor bubbles within the liquid fuel and inhibits or prevents the smaller bubbles from coalescing into large bubbles or clusters downstream of the holes


92


. Desirably, this provides a more consistent and stable supply of liquid fuel to the fuel and air mixing passage and hence, a more consistent and stable fuel and air mixture delivered to the engine. Therefore, the temporary supply of an undesirably lean fuel and air mixture to the engine due to the presence of large vapor bubbles and clusters in the liquid fuel is avoided. As a result, the carburetor does not have to be calibrated to provide a richer than required fuel and air mixture to the engine and the hydrocarbon emissions of the engine are reduced.




Preferably, the holes


92


are formed in a location where fuel vapor normally collects within the metering chamber


22


to assist in the scavenging of fuel vapor and to prevent the collection of an excessive amount of fuel vapor within the carburetor which might affect pressure regulation and consistent fuel delivery. Desirably, the holes


92


are formed in or near the highest location of the metering chamber relative to the standard or normal operating position (indicated by arrow


120


in

FIG. 1

) of the carburetor


10


in use, as fuel vapor will tend to rise to this location. For clarity, the standard or normal operating position


120


of the carburetor is rotated slightly clockwise relative to its orientation as drawn in

FIG. 1

until the axis


122


of the mixing passage


14


is perpendicular to a line containing arrow


120


. The holes


92


may be of generally any size depending on the number of holes as long as they are small enough to effectively break-up, separate, diffuse and/or disperse the large bubbles and clusters into suitably smaller bubbles. This will be dependent on the carburetor size and design and the type and size of the engine. If the holes


92


are positioned in a desired area of the metering chamber


22


where vapor bubbles tend to gather and collect, the holes


92


may be larger in size as the bubbles will be drawn through on a more consistent basis and before excessively large bubbles or clusters are permitted to form in the metering chamber


22


. If the holes


92


cannot be formed in an ideal location such that the fuel vapor is not consistently drawn out of the metering chamber


22


and undesirably large vapor bubbles and clusters may form in the metering chamber


22


, then the holes


92


should be made smaller to ensure the large bubbles and clusters are adequately broken-up and dispersed. In any event, the holes


92


must have a combined area large enough to avoid causing an undue restriction to fuel flow from the metering chamber


22


and to permit a sufficient fuel flow therethrough so that the carburetor can supply enough fuel to meet the maximum fuel demand of the engine.




Desirably, the combined flow area of all of the holes


92


is equal to or greater than the flow area of the fuel feed passage


94


downstream thereof. Preferably, the holes


92


have a combined flow area at least as large and preferably greater than the flow area of either needle valve


98


,


100


so that the needle valves


98


,


100


provide a restriction which may be adjusted to control fuel flow to the nozzles


26


,


28


. If the holes


92


are very small the drag or resistance to flow therethrough may increase requiring additional holes to provide a sufficient fuel flow from the metering chamber


22


. Additionally, with very small holes


92


on the order of about 0.13 mm to 0.20 mm in diameter, clogging of the holes can be a problem requiring very fine filtering upstream of the holes


92


. For carburetors for most small displacement engines, generally less than 50 cc's, the holes


92


are each preferably less than 1.0 mm in diameter. Further, the holes


92


preferably have a short length so that fuel vapor which flows into a hole is quickly combined with fuel flowing through the other holes and within the fuel feed passage. The length of each hole is preferably between about 0.25 mm to 0.76 mm.




In one embodiment, for a carburetor with a fuel feed passage


94


having a diameter of 1 mm, an effective implementation of the present invention comprised providing four holes


92


in the body


12


with each hole


92


about 0.56 mm in diameter to provide a combined flow area of the holes


92


slightly larger than the flow area of the fuel feed passage


94


. In a conventional carburetor, the metering chamber outlet would simply be defined by a single opening defined by the drilling forming the fuel feed passage and of the same diameter as this passage. Although in this example the combined flow area of the holes


92


is greater than the flow area of the fuel feed passage


94


, as previously mentioned, this does not have to be true. The combined flow areas of the holes


92


may be less than or equal to the flow area of the fuel feed passage


94


but is preferably always greater than the effective flow area through each needle valve


98


,


100


.





FIGS. 3 and 4

, illustrate alternate embodiments of carburetors


10


′ and


10


″, with bodies having holes


92


′ and


92


″, respectively, formed in different locations relative to the metering chamber


22


. In each embodiment


10


′,


10


″ the holes


92


′,


92


″ define the outlet of the metering chamber


22


as in the first embodiment carburetor


10


. In

FIG. 4

, the holes are formed about a portion of the perimeter of the fuel metering chamber


22


and lead to a pair of branch passages which communicate with each other to direct all of the fuel and/or vapor to the downstream needle valves and associated fuel nozzles


26


,


28


. The holes


92


,


92


′,


92


″ may be moved as desired and are preferably disposed in the uppermost or highest location in the fuel metering chamber relative to the standard or usual operating position of the carburetor when assembled on a particular engine, because this is where the fuel vapor is likely to collect. Thus, this position helps to more consistently remove the fuel vapor from the metering chamber as it collects to prevent excessively large bubbles or large clusters of bubbles from gathering in the fuel metering chamber.




Each of the carburetors


10


,


10


′,


10


″ has a fuel supply circuit


120


defined at least in part in the main body


12


and comprising the fuel pump


16


, the fuel metering inlet passage


52


, the fuel metering chamber


22


, the fuel feed passage


94


, and the fuel passages


109


,


117


and nozzles


26


,


28


leading to the fuel and air mixing passage


14


. Desirably, the porous member


51


and the holes


92


,


92


′,


92


″ are also provided in the fuel supply circuit


120


and each provide a plurality of essentially separate fuel flow paths through which the fuel flows to break up large fuel vapor bubbles and clusters and provide a more consistent and stable supply of fuel to the engine. The combined flow of the fuel flow paths is sufficient to meet the maximum engine fuel demand and preferably, no single fuel flow path is sufficient to meet the maximum engine fuel demand. If desired, only one of the porous member


51


or the holes


92


,


92


′,


92


″ may be provided in a carburetor.




While the holes


92


,


92


′,


92


″ have been described with reference to defining an outlet of the fuel metering chamber


22


, the invention can be applied elsewhere in the carburetor to limit the passage of large vapor bubbles and clusters through the carburetor. For example, a plurality of small holes could be formed downstream of the fuel pump outlet and leading to the fuel metering inlet passage


52


. Similarly, the porous member


51


can be disposed in areas or passages of the carburetor other than the counterbore


53


downstream of the fuel pump


16


. Still other modifications within the spirit and scope of the appended claims will be apparent to those skilled in the art.



Claims
  • 1. A carburetor for an engine, comprising:a body having a fuel and air mixing passage therethrough at least one nozzle opening into the air mixing passage and configured to discharge fuel into the air mixing passage, a metering chamber defined at least in part in the body, having an inlet in communication with a supply of fuel, and an outlet defined by a plurality of separate holes in the body upstream of all of the nozzles and through the nozzles in communication with the fuel and air mixing passage and positioned within the body at a location to which fuel vapor normally collects at least when the body is in its normal operating position so that fuel vapor and liquid fuel in the metering chamber are drawn from the metering chamber through at least one of said plurality of holes for delivery through at least one nozzle to the fuel and air mixing passage, and the plurality of holes have a combined flow area sufficient to enable the carburetor to satisfy the maximum fuel demand of the engine and no single one of the plurality of holes has an area sufficient to enable the carburetor to satisfy the maximum fuel demand of the engine and each hole has an area small enough to inhibit the passage of large vapor bubbles and clusters of bubbles downstream thereof and to break them into smaller bubbles which pass through the hole and are discharged with liquid fuel through at least one of the nozzles into the fuel and air mixing passage of the carburetor.
  • 2. The carburetor of claim 1 which also comprises a porous member carried by the body, having a plurality of pores through which fuel flows to reduce the size of large vapor bubbles and clusters of bubbles.
  • 3. The carburetor of claim 2 wherein the porous member has an average pore size of between 20 μm and 500 μm.
  • 4. The carburetor of claim 2 wherein the porous member has an axial length between 1 mm and 12 mm.
  • 5. The carburetor of claim 2 wherein the porous member has a volume of between 0.0018 cc to 0.340 cc.
  • 6. The carburetor of claim 2 wherein the porous member has an average pore size of between 20μ and 500 μm.
  • 7. The carburetor of claim 6 wherein the porous member has an axial length between 1 mm and 12 mm.
  • 8. The carburetor of claim 6 wherein the porous member has a volume of between 0.0018 cc to 0.340 cc.
  • 9. The carburetor of claim 1 which also comprises a diaphragm fuel pump carried by the body and having an inlet in communication with a source of fuel and an outlet through which fuel is discharged under pressure, a fuel passage downstream of and in communication with the outlet and a porous member disposed within the fuel passage and defining a plurality of fuel flow paths through which fuel discharged from the fuel pump flows.
  • 10. The carburetor of claim 9 wherein the porous member has an average pore size of between 20 μm and 500 μm.
  • 11. The carburetor of claim 1 wherein each hole of said plurality of holes has a diameter of between about 0.13 mm and 1.0 mm.
  • 12. The carburetor of claim 1 which also comprises a restriction downstream of the plurality of holes constructed to control in part fuel flow to the fuel and air mixing passage and wherein the combined flow area of the fuel flow paths is at least equal to the flow area of the restriction.
  • 13. The carburetor of claim 12 which also comprises a needle valve carried by the body and defining the restriction.
  • 14. The carburetor of claim 12 wherein the combined flow area of the plurality of holes is greater than the flow area of the restriction.
  • 15. The carburetor of claim 12 wherein the restriction is disposed between the outlet of the metering chamber and the fuel and air mixing passage.
  • 16. The carburetor of claim 1 wherein the plurality of holes are positioned in the area of the highest portion of the fuel metering chamber relative to the normal operating position of the carburetor.
  • 17. The carburetor of claim 1 which also comprises a fuel feed passage communicating the metering chamber outlet with the fuel and air mixing passage and having a flow area greater than any one of said plurality of holes.
  • 18. The carburetor of claim 17 wherein the combined flow area of the plurality of holes is at least equal to the flow area of the fuel feed passage.
  • 19. The carburetor of claim 17 wherein each of the plurality of holes extends essentially perpendicularly to the fuel feed passage.
  • 20. The carburetor claim 1 wherein each hole has a length between 0.25 mm and 0.76 mm.
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Number Name Date Kind
3085791 Phillips Apr 1963 A
3272485 Newman Sep 1966 A
3275306 Phillips Sep 1966 A
3454265 Phillips Jul 1969 A
4104994 Phillips Aug 1978 A
4770822 Sejimo Sep 1988 A
5775300 Sugii Jul 1998 A
5891369 Tuggle et al. Apr 1999 A
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Number Date Country
60-88857 May 1985 JP
10131807 May 1998 JP