US3690307A

US3690307A - Vapor venting and purging system for engines

Info

Publication number: US3690307A
Application number: US63463A
Authority: US
Inventors: Cormac G O'neill
Original assignee: Physics International Co
Current assignee: Physics International Co
Priority date: 1970-08-13
Filing date: 1970-08-13
Publication date: 1972-09-12
Anticipated expiration: 1989-09-12

Abstract

Apparatus for use with an internal combustion engine wherein a fuel float bowl and gasoline tank are connected through a vapor trap to the ambient atmosphere to prevent pollution by hydrocarbon vapors. The vapor trap is purged at high engine loads by an air flow through the vapor trap and into the engine, the air flow being controlled by the use of a sensor stationed along the path of the fuel or air components prior to their entering the cylinders. In a fuel injection engine of the type wherein fuel pressure varies with engine load, the vapor trap is coupled to a venturi through a valve that is opened only when the fuel pressure exceeds a predetermined value. The valve has a variable opening so that only small amounts of purge air flow through the vapor trap to the engine at moderate engine loads and large amounts of purge air flow only at very high engine loads, to provide a minimal change in the fuel-to-air ratio.

Description

United States Patent ONeill Sept. 12, 1972 [54] VAPOR VENTING AND PURGING SYSTEM FOR ENGINES [72] Inventor: Cormac G. ONeill, Lafayette, Calif.

[73] Assignee: Physics International Company,

San Leandro, Calif.

22 Filed: Aug. 13, 1910 211 Appl. No.2 63,463

[52] US. Cl ..l23/l36, 123/121 [51] Int. Cl ..F02m 59/00 [58] Field oiSearch..l23/l19, 136, 139 AW, 140 M, 123/121 [56] References Cited UNITED STATES PATENTS 2,443,120 6/1948 Saucier 123/121 3,370,578 2/ 1968 Spelts ..123/136 X 3,456,635 7/1969 Hervert ..123/1 36 3,540,423 11/1970 Tolles ..123/1 36 3,221,724 12/ 1965 Wentworth ..123/ 136 OTHER PUBLICATIONS SAE Journal, Dec. 1956, pg. 24- 29.

Primary Examiner-Laurence M. Goodridge Attorney-Lindenberg, Freilich & Wasserman [57] ABSTRACT Apparatus for use with an internal combustion engine wherein a fuel float bowl and gasoline tank are connected through a vapor trap to the ambient atmosphere to prevent pollution by hydrocarbon vapors. The vapor trap is purged at high engine loads by an air flow through the vapor trap and into the engine, the air flow being controlled by the use of a sensor stationed along the path of the fuel or air components prior to their entering the cylinders. In a fuel injection engine of the type wherein fuel pressure varies with engine load, the vapor trap is coupled to a venturi through a valve that is opened only when the fuel pressure exceeds a predetermined value. The valve has a variable opening so that only small amounts of purge air flow through the vapor trap to the engine at moderate engine loads and large amounts of purge air flow only at very high engine loads, to provide a minimal change in the fuel-to-air ratio.

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SHEET 2 0F 2 VAPoQ p TRA H INVEIQTOR. COQMAC G. OME/LL 24,4 M WW VAPOR VENTING AND PURGING SYSTEM FOR ENGINES BACKGROUND OF THE INVENTION 1. Field of the Invention I This invention relates to engines of the type which employ vapor traps to reduce pollution from fuel-holding bowls and gasoline tanks, and more particularly, to a novel system for purging the vapor traps.

2. Description of the Prior Art One source of atmospheric pollution is the evaporation of fuel from the float bowl which holds fuel prior to entering the cylinders. Such pollution can be greatly reduced when the engine is at rest by disconnecting the bowl from the air intake and venting the bowl through a carbon or other type of vapor trap which absorbs the vapors. The vapor trap also may be connected to the fuel tank vent to absorb vapors from it. Such vapor traps should be purged while the engine is running to rid them of trapped vapors. It is known that such purging may be accomplished by coupling the inlet of the vapor trap to the throat of an air inlet nozzle or venturi where air is drawn into the engine. However, the extra fuel vapor admitted into the cylinder during such purging can change the fuel-to-air ratio and increase the exhaust emissions. Accordingly, it is desirable to purge the vapor trap only at high engine loads, where the added vapor constitutes only a small percentage of the total mixture being fed to the engine.

One method which has been proposed for controlling purging of the vapor trap involves the use of a valve coupled to the exhaust of the engine for sensing exhaust back pressure. Exhaust back pressure varies approximately as the square of engine load, but typically, the exhaust back pressure is very low, measuring only a few inches of water on a water pressure gauge at maximum power output. Consequently, to enable purging to begin at intermediate power levels, a large cylinder is needed to convert the change in back pressure to a force sufficient to operate the valve. In addition, the exhaust contains corrosive materials at a high temperature, so that mechanisms which can operate reliably in such an environment over long periods of time are expensive.

OBJECTS AND SUMMARY OF THE INVENTION An object of the present invention is to provide an economical and reliable system for purging the vapor trap of an engine.

Another object is to provide apparatus for purging the vapor trap of an engine, in a manner that results in a minimum effect on the fuel-to-air ratio of the engine.

In accordance with one embodiment of the present invention, an economical and reliable system is provided for purging the vapor trap which captures fuel vapors from the float bowl and the gasoline tank of an engine. The system includes a valve for coupling the inlet of the vapor trap to the venturi of the engine to draw air in reverse through the vapor trap. In a fuel injection engine wherein fuel pressure to the injectors is dependent upon engine load, the valve is operated by the fuel pressure so that the vapor trap is purged only above a predetermined engine load. The fact that purging occurs only above a predetermined engine load minimizes the change in fuel-to-air ratio resulting from the added purge air or vapor. While it would be desirable to purge often at very high engine loads, many engines are operated at only moderate loads for long periods, as in vehicles driven on side streets. Thus, it is desirable to employ a small purge flow even at moderate engine loads, that will eliminate trapped hydrocarbons over an extended period of engine operation, and yet will not add them to the engine intake at a rate that would substantially affect the fuel-to-air ratio. The system reliably assures that the purge valve will open only at a predetermined load because fuel pressure increases as the square of engine load, and because high fuel pressures such as 60 to 200 psi are created at high loads. The high pressure of the pumped fuel allows a small and reliable valve to be used, while the fact that the fuel is not at a high temperature and is not highly corrosive eliminates temperature and corrosion problems, thereby avoiding the need for expensive valve materials.

The valve which connects the inlet of the vapor trap to the venturi of the engine for purging, is a variable opening valve for allowing a greater rate of purge air to flow at higher engine loads. The valve first begins to open at a moderately low engine load, and opens to a greater extent as the load increases further. This assures purging of the vapor trap even if the engine is not operated at high loads, while taking advantage of high load conditions to obtain rapid purge. Yet, at all loads there is only a minimal effect on the fuel-to-air ratio.

The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially diagrammatic view of an engine constructed in accordance with the present invention;

FIG. 2 illustrates details of the purge valve of the engine of FIG. 1; and

FIG. 3 is a partially diagrammatic view of an engine constructed in accordance with another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, the engine includes a cylinder block 10 which has several cylinders that burn fuel and air to provide power. Air is fed to the cylinders through an air inlet assembly 12 which includes an air cleaner and silencer 14, a constricted portion or venturi l6, and a manifold 18 that distributes air to the several cylinders. Fuel is held in a float bowl 20 that receives fuel from a gasoline tank (not shown). Fuel in the bowl is pumped by a high pressure pump 22 through a conduit or pipeline 24 to several fuel injectors 26 that inject fuel into the cylinders. A section 28 of the pipeline leads pumped fuel to a spill valve unit 30 that discharges it back into the float bowl. The spill valve unit 30 can block the return of pumped fuel so as to maintain a high fuel pressure in the pipeline 24. The spill valve unit is designed to maintain progressively higher pressures in the pipeline 24 at progressively higher engine loads, so that the fuel injectors 26 can inject fuel at a greater rate. This type of engine is described in greater detail in my copending application entitled, MASS FLOW METERED FUEL INJECTION SYSTEM, Ser. No. 33,376, filed Apr. 30, 1970.

The upper region of the float bowl must be vented to permit the escape of fuel vapors, particularly when the engine is operating and considerable amounts of vapor are generated by engine heat. Such venting is accomplished through a vent line 56 that leads to a valve assembly 42. When the engine is operating the valve assembly 42 vents the float bowl through a vent line 32 that leads to the air cleaner 14, so that fuel vapors are drawn into the engine where they are burned. The vent line 32 cannot be used when the engine is stopped, since the vapors would not be drawn into the engine, but would escape into the atmosphere. Venting of the float bowl 20 is required even when the engine is stopped, since the high temperature existing for a period after the engine is turned off results in the generation of considerable vapor. If this vapor were not vented, the pressure could damage a metering diaphragm 78 of the spill valve unit 30 or collapse a float 90 in the float bowl. In order to prevent the escape of hydrocarbon vapor to the atmosphere, a carbon vapor trap 34 is provided which has an outlet 36 leading to the ambient atmosphere and an inlet 38 which can be coupled through the valve assembly 42 to the upper regions of the float bowl when the engine is stopped. The vapor trap 34 is also connected at all times to a line 39 that leads to the vent outlet of the fuel tank, to trap vapors escaping from the tank. Thus, vapor from the two fuel containers (the float bowl and the fuel tank) are trapped to prevent fuel vapor pollution.

Although the carbon vapor trap 34 may have a considerable capacity to absorb fuel vapors, it must be purged periodically to avoid saturation and breakthrough. Such purging is accomplished by coupling the inlet 38 of the vapor trap through the valve assembly 42 and through a purge line 40 that leads to the venturi 16 of the air inlet, when the engine is running at moderate and high loads. It would be possible to purge the vapor trap-even'when the engine is running at a low load. However, at low'loads only an extremely low flow rate of purge air (which initially contains a high proportion of fuel vapors) could be permitted to enter the engine, in order to avoid a large change in fuel-to-air ratio in the cylinders. Such a large change in fuel-to-air ratio would causev the engine to emit additional toxic constituents from its exhaust. At high loads, when the air and fuel flow into the engine at a high rate, even a high purge flow will have only a relatively small effect upon the fuelto-air ratio. It should be understood that high load" is not synonomous with high speed, since an engine that is rapidly accelerating from a low speed has a high load and low speed, while an engine that is decelerating from a high speed may have a low load and high speed.

The control of venting of the float bowl through either the air inlet or vapor trap, and the purging of the vapor trap, are controlled by the position of a valve member 46 in a cylinder 44 of the valve assembly 42, which is also shown in FIG. 2. A spring 48 urges the valve member 46 to slide forward, or to the left, while fluid at an inlet 50 urges the valve member backward, or to the right (through a diaphragm 51, to prevent leakage). The inlet 50 is coupled through a line 52 to the outlet of the fuel pump 22, so the pressure of fuel at the outlet of the pump determines the position of the valve member. The valve cylinder 44 has a vent inlet 54 that is coupled through the line 56 to the float bowl 20, and has an outlet 58 that is coupled through the vent line 32 to the air cleaner of the engine. A vent outlet 64 connects the valve to the vapor trap 34.

When the engine is stationary, valve member 46 is urged by spring 48 to the left end of the cylinder, and the float bowl 20 is connected via vent inlet 54 and vent outlet 64 to the vapor trap 34. When the engine is started, the fuel pressure quickly rises to 20 psi, and does not fall below this level even at a very low load.

Application of this minimum pressure to the inlet 50- urges valve member 46 to move to the right, so that a valve portion 62 disconnects the float bowl inlet 54 from vent outlet 64, and the inlet 54 is instead connected to outlet 58 which leads to the air cleaner. This occurs whenever the engine is running. Thus, the float bowl is always vented to the air cleaner when the engine is running even if the engine is running slowly. When the engine is turned off, the valve member 46 is urged to an extreme left position. A valve portion 60 then blocks venting of the float bowl inlet 54 through the air cleaner, and the float bowl inlet 54 is automatically vented only through the outlet 64 which leads to the carbon vapor trap 34.

As mentioned above, the carbon vapor trap 34 should be purged when the engine runs. To accomplish this, the inlet 38 of the vapor trap is coupled through a line 66 to a purge inlet 68 of the valve cylinder. When the engine is operated at increasing loads, the pressure of pumped fuel, which is applied at the cylinder inlet 50, increases. The valve member 46 moves to the right against the force of the spring 48, by a distance that is proportional to the power output. A valve portion 70 is then in a position to allow the purge inlet 68 to be coupled to a purge outlet 72 that is connected to the purge line 40. The purge line 40 leads to the throat of the venturi 16, where a vacuum is created when the engine is operating. This vacuum draws air through the carbon vapor trap 34, purging it of hydrocarbons which are then drawn through the venturi 16 to the engine cylinders.

When the vapor trap 34 is purged for the first time after the engine is started, the purge air delivered to the cylinders of the engine contains a high proportion of fuel vapors. However, subsequent purging results in substantially only extra air being drawn into the engine. In order to minimize changes in the fuel-to-air ratio in the cylinders of the engine, purging is begun only at a moderate flow rate so as to produce the minimum change in fuelto-air ratio. It may be noted that the valve portion 70 which controls purging includes a cylindrical portion 74 and a tapered portion 76. At idling and light loads, the cylindrical portion 74 covers the purge outlet 72 so that no purging occurs. At a predetermined engine load, the tapered portion 76 begins to pass over the outlet 72, progressively opening a passage for purge air from the purge inlet68 to the outlet 72. As the engine load increases, increasingly greater amounts of purge air can be drawn through the vapor trap and into the engine.

The reason for providing the variable opening valve action is to provide the best compromise between adequate purging and alteration in fuel-to-air ratio, for an engine operated under a variety ofconditions. An engine is typically operated in a manner that produces short random periods of very high load, as when an automobile driver accelerates to enter a highway, and longer random periods of moderately high load, as when the driver accelerates from a stop in ordinary traffic or cruises at high speed. The variable purging design takes advantage of any period of high load operation to effect a proportionate increase in purging, while maintaining variation in fuel-to-air ratio below a predetermined maximum value.

The control of the valve 42 by fuel pressure enables a sensitive and economical valve to be used to control venting and purging in accordance with engine load.

The fuel pump 22 may be driven by the engine or it may be driven by a motor connected to the alternator. The spill valve 30, which regulates fuel pressure, includes a diaphragm 78 that can lift and lower a stem 80 that moves a valve closing member 82. The valve closing member 82 is urged upwardly by a spring 84 so that a substantial fuel pressure acting against the upper face of the valve closing member 82 is required to open the valve. Thus, a relatively high pressure such as psi is maintained at the outlet of the pump 22 and up to the spill valve, to prevent the formation of vapor bubbles in the line. Pressures exceeding the approximately 20 psi initial pressure can be maintained in the line 24 by additional upward force on the spill valve closing member 82, when the diaphragm 78 is urged upwardly. The greater fuel pressure increases the amount of fuel injected into the cylinders at high engine loads. An upward force on the diaphragm 78 is provided by a line 86 leading from the upper side of the diaphragm to taps 88 at the venturi 16 of the air inlet assembly. At greater loads, a greater vacuum is provided at the taps 88, to draw up the valve diaphragm 78.

The spill valve 30 provides a fuel pressure in the line 24 which increases more than proportionately to an increase in engine load; in fact, the increase is generally greater than the square of the increase in engine load. Accordingly, the valve assembly 42 which controls venting and purging is closely regulated by engine load, and it can begin purging at close to a predetermined desired engine load level. The liquid fuel at the outlet of the pump 22 experiences a large change in pressure, measured in many pounds per square inch. Accordingly, only a relatively small chamber at the left side of the valve 42 is required to move the valve member 46 with sufficient force so that the various pressures at the other inlets and outlets of the valve cylinder have a negligible effect on valve operation. Not only is the initial engine load level at which purging begins accurately controlled, but the levels at which increasingly greater rates of purge air are allowed to flow is also accurately controlled.

The fluid inlet 50 of the valve and the pipe 52 that couples it to the pump outlet serve as a sensor for controlling the variable opening valve. The fact that this sensor apparatus contacts the fuel which is at only a moderate temperature, allows relatively inexpensive materials to be used for the valve. This may be compared to systems which measure exhaust back pressure, wherein the sensing apparatus for controlling a valve must withstand hot corrosive vapors, and where a large cylinder is required to convert the relatively small change in exhaust back pressure into a large enough force to reliably operate a purge control valve.

FIG. 3 illustrates apparatus constructed in accordance with another embodiment of the invention, wherein a valve 42A is utilized which is operated by a transducer that senses the degree of vacuum in the venturi 16. The transducer 90 moves a valve member 46 which is identical to the valve member described in the embodiment of FIG. 1 and 2, in accordance with the sensed flow of air into the engine. This, of course, is a substitute for the apparatus that moves the valve member 46 in accordance with the pressure of fuel in the fuel line 24. As in the engine described above, the purge portion of the valve 42A includes a tapered valve portion 76 that couples the inlet of the vapor trap 34 to the venturi 16 in an amount that depends upon the rate at which air is being drawn into the engine. By using a transducer 90 that senses air prior to its entering the engine, no very hot or corrosive gases are dealt with by the transducer, and special materials are not required. However, by utilizing a separate transducer 90, the engine is made somewhat more expensive and complex than the engine of FIG. 1 which utilizes fuel pressure. The transducer 90 can employ a pressure gauge that measures the degree of vacuum at the venturi, and whose output drives a linear motor or solenoid to move the valve member 46.

Thus, the invention provides systems for use with an engine that has a vapor trap to prevent air pollution, wherein sensing apparatus is utilized which senses the fuel or air component at a point along its path prior to entering the cylinder of the engine where it is burned. In the apparatus of FIG. 1, the fuel component is sensed at a point near the outlet of the pump, although the pressure could be sensed at a point near the spill valve. In any case, the fuel should be sensed prior to its entering the cylinder (i.e., not after it is burned and becomes an exhaust gas), so that only moderate temperatures are dealt with. As previously mentioned, the sensing of fuel pressure which rises very fast with increasing load, enables a sensitive determination of when a predetermined load is reached. In the apparatus of FIG. 3, the air component is sensed prior to its entering the cylinder of the engine, rather than the fuel component. In either case, however, relatively non-corrosive and low temperature components are sensed. The apparatus also provides a variable opening valve which begins purging of the vapor trap at a predetermined engine load, and which progressively increases the amount of purge air which can enter the engine at progressively higher loads. This assures purging of the vapor trap for a variety of operating routines, while producing a minimal change in the fuel-to-air ratio.

Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art and, consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.

What is claimed is:

1. In an engine which has a fuel container, an air intake assembly that includes a constricted portion for drawing in air, and a cylinder for confining a combination of fuel and air while it is burned, the improvement comprising:

vapor trap means coupled to the ambient atmosphere for trapping fuel vapors;

vapor trap means;

end of said cylinder with a force that increases as the rate of fuel delivery to said engine cylinder increases.

second, and third ports respectively coupled to said fuel container, said inlet of said vapor trap means, and said cylinder means, said valve also including a valve member moveable in said valve a variable opening valve having a valve cylinder with body and having forward and rearward ends, and forward and rearward ends, a valve member spring means for urging said valve member in a mounted in said cylinder and having a tapered porpredetermined forward direction, tion which narrows towards said forward end of said valve member having portions that block comsaid cylinder, and a spring for urging said valve munication between said first and third ports of member towards said forward end of said cylinder, I Said hOllOW Valve y n y until Said. Valve said cylinder having a pair of openings respectively member is moved rearwardly a first distance, that coupled to said vapor trap means d t id block communication between said second and stricted portion of said air intake means, at least third Ports y until Said valve e e i moved (me f id openings l d b hi d h i i i l rearwardly a second distance greater than said first i i of h id part of id tapered portion distance, and that permit communication between of said valve member; and said first and second ports only while said valve means responsive to the rate of fuel delivered to said member lies forward of a predetermined distance cylinder and coupled to one end f i valve which is substantially no more than said first cylinder for producing a pressure therein that dlslance; a urges said valve member towards said rearward valve operating means responsive to engine load for moving said valve member progressively rearwardly within said valve housing at progressively higher engine loads, including moving said valve member rearwardly by at least said first distance whenever the engine is on, whereby to vent said container to said cylinder only when the engine is on, to purge said vapor trap only at high engine a hydrocarbon vapor trap having an outlet coupled loads, and to vent said container to said vapor trap to the ambient atmosphere and an inlet; when the engme a valve including a hollow valve body with first,

2. In an engine which has at least one fuel container for holding fuel and cylinder means for burning a fuel 25 component and air component to provide power, the

improvement comprising:

Claims

1. In an engine which has a fuel container, an air intake assembly that includes a constricted portion for drawing in air, and a cylinder for confining a combination of fuel and air while it is burned, the improvement comprising: vapor trap means coupled to the ambient atmosphere for trapping fuel vapors; first means for coupling said fuel container to said vapor trap means; a variable opening valve having a valve cylinder with forward and rearward ends, a valve member mounted in said cylinder and having a tapered portion which narrows towards said forward end of said cylinder, and a spring for urging said valve member towards said forward end of said cylinder, said cylinder having a pair of openings respectively coupled to said vapor trap means and to said constricted portion of said air intake means, at least one of said openings located behind the initial position of the widest part of said tapered portion of said valve member; and means responsive to the rate of fuel delivered to said cylinder and coupled to one end of said valve cylinder for producing a pressure therein that urges said valve member towards said rearward end of said cylinder with a force that increases as the rate of fuel delivery to said engine cylinder increases.

2. In an engine which has at least one fuel container for holding fuel and cylinder means for burning a fuel component and air component to provide power, the improvement comprising: a hydrocarbon vapor trap having an outlet coupled to the ambient atmosphere and an inlet; a valve including a hollow valve body with first, second, and third ports respectively coupled to said fuel container, said inlet of said vapor trap means, and said cylinder means, said valve also including a valve member moveable in said valve body and having forward and rearward ends, and spring means for urging said valve member in a predetermined forward direction, said valve member having portions that block communication between said first and third ports of said hollow valve body only until said valve member is moved rearwardly a first distance, that block communication between said second and third ports only until said valve member is moved rearwardly a second distance greater than said first distance, and that permit communication between said first and second ports only while said valve member lies forward of a predetermined distance which is substantially no moRe than said first distance; and valve operating means responsive to engine load for moving said valve member progressively rearwardly within said valve housing at progressively higher engine loads, including moving said valve member rearwardly by at least said first distance whenever the engine is on, whereby to vent said container to said cylinder only when the engine is on, to purge said vapor trap only at high engine loads, and to vent said container to said vapor trap when the engine is off.