GB2074657A - Hot restart valve for diaphragm carburetor - Google Patents

Abstract

A hot restart valve 64, (120) Fig. 2 (not shown) generally for use with a diaphragm carburetor 10 has a control chamber 68 and a vapor discharge chamber 66 separated by a spring biased diaphragm. The vapor discharge chamber communicates with the fuel chamber 26 of the carburetor and a vapor venting port 76 has a movable, normally-open vent valve 78. The control chamber 68 monitors air flow through the carburetor induction passage via a signal port 94, and activates the diaphragm 70 to which the vent valve is connected in responsive to the air flow. During engine operation the vent valve 78 is drawn in to seal the vapor venting port 76, and at engine shutdown the valve 78 opens to allow evacuation of vapor from the fuel chamber of the carburetor. <IMAGE>

Description

SPECIFICATION Hot restart valve for diaphragm carburetor This invention relates to a diaphragm carburetor which can be evacuated of fuel vapors to promote restarting after a "hot soak" period.

More particularly this invention relates to a diaphragm carburetor in cooperation with a pneumatically operated valve for rapid vapor evacuation from a carburetor fuel chamber, thereby promoting liquid fuel transfer to the fuel chamber, fuel metering to the induction passage and subsequently fuel delivery to the engine.

The diaphragm carburetor has been widely used in conjunction with the liquid fuel fired internal combustion engine. More particularly the diaphragm carburetor has found considerable application on small internal combustion enginepowered appliances such as lawn mowers, weed cutters, snow blowers and chain saws. A primary concern of the manufacturer of these appliances is a lightweight, compact engine assembly to minimize the total weight of their appliances. To accommodate these equipment manufacturers, the engine suppliers have developed light, compact and cfficient engine assemblies.

The internal combustion engine operates at temperatures well above ambient temperatures.

The engine is generally a compact assembly, as described above, and consequently the heat from the engine tends to heat all of the elements in or near it, including the carburetor. During engine operation the fuel pump and associated channels provide fuel to the carburetor fuel chamber.

Diaphragm carburetors generally utilize a diaphragm to operate a valve which regulates fuel flow to a fuel chamber. This fuel chamber has an arrangement of main and idle fuel nozzles, and channels connecting the fuel chamber to a carburetor induction passage for fuel-air mixing and induction to the engine.

As the engine heats up, the carburetor functions continuously with fuel being transferred to and through the carburetor. This continuous fuel flow helps to maintain the carburetor at a temperature cooler than that of the engine.

However, upon shutdown the engine is at an elevated temperature, to which the carburetor is exposed without the benefit of any continuously cooling fluid flow. Consequently, the carburetor temperature also rises. This period of engine shutdown at an elevated temperature is known as the "hot soak" period.

At an elevated temperature the fuel in the carburetor fuel chamber vaporizes, and is trapped in the fuel chamber; the vapor is then slowly evacuated through the fuel nozzles communicating to the induction passage. Such vaporization and subsequent loss of fuel from the fuel chamber diminishes the liquid fuel available in the fuel chamber for restarting the engine. This lack of fuel has been found to inhibit the restarting of an internal combustion engine with a diaphragm carburetor. The fuel chamber for most applications is relatively small, that is, on the order of only a few cubic centimeters. It is well known that a temperature of only 1 500 F. is sufficient to vaporize the most volatile fraction of a normal, consumer-grade gasoline mixture.Therefore, after a "hot soak" period most of the fuel delivered to this fuel chamber for restarting is rapidly vaporized leaving virtually no fuel for starting. In addition, the pressure in the fuel chamber increases, inhibiting proper functioning of the diaphragm operator for fuel delivery and correspondingly impairing fuel metering for engine restart.

The present invention overcomes this problem by providing a vent for vapor pressure relief and vapor evacuation from the fuel chamber, thus allowing further liquid fuel to be transferred to the fuel chamber. The fuel transfer can thus be viewed as again serving the function of a coolant.

A diaphragm carburetor for an internal combustion engine in accordance with this invention has a body defining an induction passage wherein a throttle plate is pivotally mounted. Associated with the carburetor is a fuel chamber, a signal port to monitor air flow through the induction passage, and a vapor exhaust port communicating between the fuel chamber and a vapor discharge chamber of a hot restart vent valve assembly. The vent valve assembly has a body defining a cavity which has a diaphragm positioned in the cavity dividing the cavity into a control chamber and a vapor discharge chamber.

The vent valve assembly body defines a vent valve port wherein a normally open vent valve, responsive to a bias spring and to the diaphragm, is movably positioned in the valve port. The vent valve is affixed to the diaphragm at one end to move to a closed position in response to air flow through the induction passage. The valve provides egress for vapor from the fuel chamber at engine shutdown but prevents air ingress to the fuel chamber during engine operation.

One way of carrying out the invention is described in detail below with reference to drawings which illustrate only one specific embodiment, in which: FIGURE 1 is a cross-sectional view of a carburetor incorporating an exhaust valve within the principles of this invention wherein a valve and carburetor are combined in a unitary structure; and FIGURE 2 is a cross-sectional view of an alternative embodiment of this invention.

In FIGURE 1 a carburetor 10 has several major components, including a body portion 12 which has a central portion defining an air induction passage 14 with a sidewall 1 6. Body portion 12 encloses a fuel pump 20 and defines a main fuel line 18, which has a coupling means 22, shown as a fitting, connecting main fuel line 1 8 to a fuel source (not sown). The body 1 2 defines a passage 24 which communicates fuel pump 20 with a fuel chamber 26, defined by body 12 and an assembly 28 composed of a cover plate 30 and a diaphragm operator 32 secured to body 12 by a bolt 34 and similar bolts (not shown). The diaphragm operator 32 has a centrally located rivet 36. A lever 38 is pivotally mounted on a pin 40 and one arm of the lever abuts the head of rivet 36.A bias spring 42 extends between the just described lever arm and the carburetor body, when the diaphragm is in the reference position shown in FIGURE 1. Affixed to the other arm of the lever 38 is a needle valve 44 seated in an aperture 46 of body 12 at the junction of passage 24 and fuel chamber 26, for controlling fuel flow from passage 24 into fuel chamber 26. Body portion 12 and wall 16 define a main fuel nozzle 48 and idle fuel nozzles 50 and 52. Body 12 defines a fuel well 54 and a port 56 ahead of main fuel nozzle 48, and port 56 communicates fuel nozzle 48 with fuel chamber 26. Idle fuel nozzles 50 and 52 communicate with an idle fuel chamber 51 by passages 53 and 55, respectively, all three elements are defined by body 12. The idle fuel chamber 51 communicates with fuel chamber 26 by a passage 57 defined by body 12.An adjustable needle valve 58 is positioned in port 56 to control fuel flow from fuel chamber 26; needle valve 48 is controlled by a screw shaft 60. A throttle plate 62 is pivotally mounted in induction passage 14 between the main fuel nozzle 48 and an internal combustion engine (not shown).

Body 12 of carburetor 10 also defines a vent valve assembly 64, having a vapor chamber 66 and an air flow monitoring chamber 68. A pneumatic operator 70 is mounted between chambers 66 and 68. A wall 72 defines the upper surface of chamber 66. Wall 72 also defines a recess 74 and a vent valve port 76 within said recess 74 to receive a valve member 78 affixed to a valve stem 80. Affixed to pneumatic operator 70 in vapor chamber 66 is a mounting member 82 to which valve stem 80 is attached. On the surface of operator 70 obverse to that to which valve stem 80 is attached is a mounting plate 84, which is in chamber 68. A wall 86 of chamber 68 is defined by wall 16 of induction passage 14, which wall 86 has a knob 88 projecting from it inwardly to chamber 68. A bias spring 90, attached to knob 88, extends through chamber 68 and is attached to mounting plate 84.A pneumatic signal port 92, a passage 93 and a port 94, all defined by body 12, communicate the flow in induction passage 14 with air flow monitoring chamber 68. A vapor exhaust port 95, a passage 96 and a vapor chamber port 97, all defined by carburetor body 12, communicate between chamber 66 of valve assembly 64 and a fuel chamber 26. A passage 98 of valve assembly 64 and an opening 99 defined by wall 1 6 of induction passage 14 communicate between recess 74 and induction passage 14 downstream of throttle plate 62.

Carburetor 10 is a diaphragm carburetor of a type known in the art. Fuel is transferred from a source (not shown) through main fuel line 1 8 to fuel pump 20, and thence to passage 24 communicating with fuel chamber 26. Fuel is pumped to chamber 26 based upon a demand function dependent upon a pressure differential between chamber 26 and atmospheric pressure, to actuate diaphragm operator 32. This in turn displaces lever 38 against bias spring 42, and lever 38 pivots about pin 40 to open needle valve 44, allowing the fuel to fill chamber 26. Fuel is then passed through port 56 past needle valve 58 and then through main fuel nozzle 48. At idle speeds fuel is fed downstream of an effectively closed throttle plate 62, through idle nozzles 50 and 52 from idle fuel chamber 51, in response to a reduced demand.The fuel demand is that demand caused by the rapid induction of air in induction passage 14 past the fuel nozzle 48. Fuel is metered from nozzle 48 causing an air-fuel mixture to flow through the induction passage 14, past the throttle plate 62, and thus to the internal combustion engine.

During the normal functioning of the engine and carburetor the engine temperature increases well above ambient. However, in large part due to the continued flow of liquid fuel to and through carburetor 10, the temperature of fuel chamber 26 is maintained at a temperature below that of the engine. When the engine is turned off the fuel stops flowing, and carburetor 10 is now subject to an increase in temperature from the elevated engine temperature. This period of non-operating time is referred to as the "hot soak" and causes an increase in carburetor temperature. It has been found that the most volatile fraction of most gasoline fuels has a fractional distillation temperature of 1500 F. In the present case it was found that the fuel in fuel chamber 26 was all volatilized after about 10 minutes of the hot soak period.The volume of this fuel chamber of the test carburetor and in most small engine carburetors is on the order of a few cubic centimeters. The carburetor 10 thus can be at an elevated temperature for a considerable length of time thereby evacuating the fuel chamber. Restarting the engine again requires fuel. However, as fuel is pumped into the hot fuel chamber 26 is is almost immediately converted to a vapor and is unavailable for metering through the fuel nozzle 48, thereby resulting in the hot restart problem.

In the present invention vent valve assembly 64 includes valve member 78 that is normally open during engine shutdown. Therefore, as fuel is drawn into fuel chamber 26 when the engine is being restarted it will be vaporized and allowed to escape through vent valve assembly 64. Vent valve assembly 64 is a normally open valve, of which chamber 66 communicates with fuel chamber 26 through passage 96 and ports 95 and 97. Chamber 66 also communicates with induction passage 14 downstream of throttle plate 62 through port 76, recess 74, passage 98 and port 99 when valve member 78 is in the open position. Valve member 78 is biased in this open or venting position by bias spring 90 acting on pneumatic operator 70 through mounting plate 84. During periods of engine operation there is a rapid flow of air through induction passage 1 4.

This rapid rush of air creates a vacuum or reduced pressure condition in chamber 68 of valve assembly 64. Chamber 68 communicates with induction passage 14 through passage 93 and ports 92 and 94. As air or the air-fuel mixture rushes past port 94 of induction passage 14, a pressure below atmospheric pressure is achieved in chamber 68. When the pressure in chamber 68 is about 3 inches of water below that pressure in chamber 66, pneumatic operator 70 retracts against the force of bias spring 90, thereby pulling valve member 78 to close port 76 against further fuel vapor exhaust and likewise to seal fuel chamber 26 from exposure to air entry during engine operation.

As noted, therefore, valve member 78 is closed during air flow through induction passage 1 4 at a level sufficient to create a reduced differential pressure of at least three inches of water between chambers 66 and 68. Valve member 78 is open at all other times. After a "hot soak" time carburetor 10 and fuel chamber 26 are well above 1500 F. As fresh fuel is pumped into this chamber 26 to restart the engine it is almost immediately vaporized, and this vapor must be evacuated before more fuel can be pumped into this chamber 26. The vapor in chamber 26 inhibits diaphragm operator 32 from properly functioning and thereby inhibits the introduction of more fuel for engine restart. This evaporation of the liquid fuel in chamber 26 acts as a cooling step.

Unfortunately the volume of fuel is not adequate to completely cool the carburetor 10 or, more particularly, the fuel chamber 26 and, therefore, fresh fuel must repeatedly be introduced. This requires rapid evacuation of the fuel vapor from chamber 36 through vent valve assembly 64.

When the engine is restarted air flows through the induction passage 14, thereby causing valve member 78 to close port 76 and the carburetor 10 functions in its normal mode. In a similar fashion recess 74 could as well be vented to atmosphere, but as a matter of convenience and to maintain arelatively clean and closed system it is illustrated and preferred to be vented to the induction passage 14.

FIGURE 2 depicts an alternative embodiment of the invention wherein carburetor 10 and a vent valve assembly 120 are shown as separate entities. In FIGURE 2 vent valve assembly 1 20 inciudes a body 122 which encloses a vapor chamber 66 and an air flow monitoring chamber 68. Body 122 defines passages 124 and 125 in which fittings 126 and 127, respectively, are inserted as a coupling means. Similarly inserted in passages 93 and 96 of carburetor 10 are fittings 128 and 130, respectively. A conduit 1 32 connecting fittings 1 26 and 1 28 thereby communicates chamber 68 with conduction passage 14. A conduit 1 34 connecting fittings 127 and 130 communicates chamber 66 of valve 120 with fuel chamber 26 of carburetor 10.In the present case chamber 66 is vented to atmosphere through port 76 and recess 74 of valve assembly 120 when valve member 78 is in the open position. The valve assembly 120 of FIGURE 2 functions to evacuate the vapor formed in chamber 26 and thereafter vent the vapor through port 76 and recess 74 of valve assembly 1 20 when valve member 78 is in the open position; in the same manner as provided in the valve assembly 64 of FIGURE 1. In the embodiment of FIGURE 2 this vapor is evacuated to the atmosphere, rather than the induction passage 14 as shown in FIGURE 1.

Those skilled in the art will recognize that certain variations can be made in the illustrated embodiments without forsaking the principles of the invention. It is, therefore, the intention in the appended claims to cover all such modifications and alterations as may fall within the true scope and spirit of the invention.

Claims (7)

1. A diaphragm carburetor for an internal combustion engine having a body defining an induction passage with a throttle plate pivotally mounted in said induction passage and having a fuel chamber, in combination with a vent valve assembly including a body with a cavity wherein said body defines a vent valve port, a normally open valve member positioned in the vent port and movable between open and closed positions, said body also defining a vapor chamber communicating with said fuel chamber and an air flow monitoring chamber, a bias spring positioned to maintain the valve member in the normally open position, a pneumatic operator connected to said valve member, and said body further defining a pneumatic signal port in communication with said induction passage, said pneumatic operator being arranged and disposed for moving said valve member from said normally open position to said closed position in response to flow through said induction passage.

2. A diaphragm carburetor as claimed in Claim 1, wherein the pneumatic operator is operable to close said normally open valve member at a predetermined differential pressure between the chambers of the valve assembly.

3. A diaphragm carburetor as claimed in Claim 2, wherein the differential pressure is substantially three inches or less of water pressure.

4. A diaphragm carburetor as claimed in Claim 1, wherein the signal port communicates with the induction passage downstream of the throttle plate.

5. In combination with a diaphragm carburetor for an internal combustion engine, which carburetor comprises a body defining an induction passage, a throttle plate pivotally mounted in said induction passage, a fuel chamber, a signal port for providing a control signal responsive to air flow through the induction passage, and an exhaust port for venting fuel vapor, the improvement which comprises a hot restart vent valve assembly, having a body with a cavity, a pneumatic operator positioned in the cavity to define a vapor discharge chamber and an air flow monitoring chamber, a vent valve port defined by the assembly body communicating with the vapor discharge chamber, a bias spring positioned in one of said chambers to apply a bias force to hold a vent valve member in the vent valve port open when the pneumatic operator is in a reference position, means coupling the vapor discharge chamber to the carburetor exhaust port to allow venting of fuel vapor through the vapor discharge chamber and the vent valve port when the pneumatic operator is in said reference position, and means coupling the control chamber to the carburetor signal port, for effecting displacement of said pneumatic operator out of the reference position in a direction to overcome the bias force responsive to presence of said control signal, thus closing the vent valve member and preventing venting of any fuel vapor when air is flowing through the carburetor induction passage.

6. The combination defined in Claim 5, wherein said hot restart valve assembly vents the vapor to the carburetor induction passage.

7. A diaphragm carburetor and vent valve assembly substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.