US2167892A - Liquid fuel feeding device for internal combustion engines - Google Patents

Description

Patented Aug. 1,1939

LIQUID FUEL FEEDING MEYICE FOR INTER- NAL COMBUSTION ENGINES .Raymond Leslie Kent,

minrham,

Marston Green, near Birand Murray Duncan Scott, Bury Green, Oheshunt, England Application November a, 1936, serial No.

In Great Britain November 8, 1935 3 Claims.

This invention relates to fuel lift carburettors for use wherein the main fuel supply reservoir is normally located at a level below that of the carburettor, and the carburettor is designed to produce a depression capable of raising the fuel groin the reservoir level to that of the carburet- There have been numerous attempts to produce a carburettor of this type by utilizing a venturi to step up or multiply the engine suction so that the depression created within the carburettor is sufficient at all times to raise fuel from the low level reservoir to the carburettor.

The dimculty has, however, been to select a venturi or venturis which is or are capable both of meeting the condition that the engine cylinders must be adequately filled at low engine speeds with full throttle opening and that still gives a sufficient multiplication factor to raise fuel. Or, in other words, if the size of the venturi is sufiicient to provide the least possible resistance to the flow of mixture at all speeds under full throttle opening conditions, it will not at all speeds be found capable of creating sufiicient depression to lift the fuel thereto, 0n the other hand, when employing a venturi of comparatively smaller size which is capable of raising fuel at all engine speeds, it will be found that when the throttle is fully opened at high engine speeds the demand upon the venturi is too great to enable it to maintain a suillcient supply of mixture to the engine.

We have found in accordance with this invention that by employing a venturi whose cross sectional area is capable of variation that it is possible so to arrange for a substantially constant relationship to be obtained between the depression existing on the engine side of the carburettor and that existing at some predetermined point or section in the axis of the venturi, the depression obtained at this point or section being used to raise fuel from a reservoir situated below the level of the carburettor, and furthermore remaining substantially at the minimum value sumcient for this purpose.

According to this invention therefore a fuel lift carburettor device for internal combustion engines comprises the combination of a low level fuel supply reservoir and a carburetting apparatus having a fuel intake chamber at alevel above the reservoir, a jet orifice or orifices, to which fuel is supplied from the intake chamber, a jet needle or other means for controlling the amount of fuel passing the jet orifice or orifices,

a ventur the r flec ive t ess section l area of which is so capable .of variation as to give a normal Venturi action in all its positions of adjust-' ment and a pressure responsive member responsive to the depression produced in the venturi, which depression is also transmitted to the intake chamber to raise fuel from the low level reservoir, and means actuated by the pressure responsive member for causing adjustments in the cross sectional area of theventuri and for controlling the position of the jet needle or other jet control means.

Thus the resultant cross sectional area of the venturi with reference to axial length will, in our invention, give a variation similar to that of a normal venturi of adjustment, there will be an unbroken streamline flow through the venturi without turbulent effect. Preferably, the venturi is composed of two relatively moving male and female parts of such configurations that in any relative position of thertwo parts, the resultant cross sectional area will, as just stated, give a normal Venturi action, 1. e.. an unbroken streamline flow.

The variable venturi may consist of a station ary member of conventional Venturi design, fitted with an axially movable tapered member, movable by the pressure responsive member, the members being so arranged and designed that at all times the depression at some predetermined section is at a maximum in relation to the depression existing between this composite venturi and the induction ports of the engine.

The tapered member may be formed integrally with a piston constituting the pressure responsive member, the piston being mounted ,in a cylinder to which the depression created by the venturi is transmitted.

One embodiment of the invention is illustrated in the accompanying drawing which is a sectional lay-out of a fuel feeding device embodying a venturi whose cross-section is capable of variation, the moving parts being shown in their slow running or at rest position withthe entrance to the venturi closed or substantially closed.

Referring to the drawing, l indicates part of the throttle or intake pipe to the engine in whichis the usual throttle valve 2. In the intake pipe I is a venturi I, the depression at the front of which is transmitted to a needle controlled jet 3 and to a fuel intake or float chamber 4 and also to a pressure responsive member 5, which controls the size of the jet opening through a needle valve 28 and also oper-'- ates a choke member i.

so that whatever the position r The choke piece 8 is movable under the control of the member I in relation to the venturi I, so as in effect to constitute a venturi of variable cross-section as herein described.

The parts just described are shown in their slow running or at rest position with the entrance to the venturi throat closed or substantially closed. It is an essential feature of the invention that the pressure responsive member is so constructed and arranged that it will only operate to permit the opening of the choke when the depression created in the system is sufflcient to raise fuel under all conditions.

In operation, when the engine crank shaft is rotated for the purpose oi. starting, and the throttle valve 2 partly opened, the depression produced will be communicated through the venturi to the jet 8 and to the float chamber and the depression created therein will be suflicient to raise fuel from the supply tank.

As previously stated the pressure responsive member is so loaded that until the depression created is sufllcient to raise fuel into the fuel chamber, it will not operate to raise the choke member 8 and thus permit the opening of the choke.

Fuel on entering the intake chamber will flow to the jet where it is mixed with a small quantity of air, the emulsion so formed passing into the venturi throat whence it is drawn into the engine as an explosive mixture.

To describe the embodiment of the invention illustrated, in detail it comprises a two part casting, the lower half of which is indicated at 8 and the upper part at 8. In the lower part 8 is a bore III, which is a continuation of the throttle pipe. A bore ll of the same size is provided in the upper portion 8 of the casting, but which is provided also with an enlarged bore l2 con-- stituting a cylinder, in which is slidably mounted the pressure responsive member in the form of apiston I8. The piston I8 is not a perfectly air tight flt in its cylinder.

A sleeve ll inserted in the bores III, II serves to spigot together the two parts of the casting, which are bolted together along their meeting faces in which as is hereinafter described are provided the feed passages to the venturi throat. v

The interior of the sleeve II is shaped to constitute the venturi I and it will be observed that part of the wall of the cylinder I 2 is cut away as at ii to enable the admission of air to the downstream end of the venturi, when the choke piece 8, which is tapered, has been moved upwardly by the pressure responsive member against the action of a spring IS.

The spring I8 is held in position against a detachable cover plate I! for the cylinder l2.

The employment of a return spring, while not essential has the advantage that it enables a reduction in the mass of the piston so that there is a smaller tendency for the position of the piston to vary on rough roads.

The float chamber 4 is incorporated in the lower part 8 of the casting and is provided with an inlet pipe l8 from the feed tank (not shown). I! is a float controllinga cut-off valve indicated generally at so that when the chamber is full the admission of liquid fuel is pre vented.

Petrol from the chamber 8 passes through a feed passage 2|, to a jet chamber 22, which is formed as an enlargement of a bore 28 extending through both parts of the c sti g, In the bore 28 is mounted the needle valve of which is provided with a flanged head 24 for engagement with an annular groove 25 in, the piston II. It will be observed that suction induced by the engine draws the fuel upwardly past the jet 8 from the jet chamber 22, the jet discharge mixing with air drawn down the bore 8|, the emulsion so formed being drawn up the annular'space between the needle 28 and the bore 28 and passing thence to the venturi.

It will be appreciated therefore that as the piston l8 rises and falls the needle valve 28 will move with it and so increase or decrease the size of the (main) jet opening. The jet 8 may be held in position by means of a spring (not shown), one end of which bears against the screw plug 22' closing the jet chamber 22.

In the throat of the venturi are a number of holes 21 giving access to an outer-groove 28 which isfed through two diametrically opposed ducts 28 extending into an annular groove 88 formed in the meeting face of the casting 8 and into one side of which groove the bore 28 merges.

The depression in the system is transmitted to the cylinder l2 containing the piston il8 through a bore 8| which at one end opens into the bore 28 and at its other end communicates through a port 82 with the cylinder top.

The flt of the piston l8 within the cylinder is such as to provide a certain leakage but in order to reduce the eilect of variation in the piston clearance which would vary the amount oi air bleed, an additional bleed hole 88 tothe atmosphere is provided.

In some cases it may be desirable to provide a damping action to delay the initial movement of the piston and for this purpose an annular groove 84 is cut in the cylinder wall for communication with the bore 8| the effect of which is to create an air seal round the piston;

When the piston is damped in this manner it may also be desirable to provide for a rapid movement oi! the piston through a small portion of its travel from its lower or rest position. This may be efl'ected by means of a port 88 communicating with the interior of the cylinder at a point immediately above the rim of the piston l8. The port 88 will also operate to prevent the piston from being sucked downwards when the throttle is flrst opened owing to the depression acting immediately on the nose of the piston before it has a chance of acting on the top as it would if the full damping were in action.

A turn cock 88 may be provided for controlling the strength of the mixture and starting when the engine is cold. It will be obvious that by turning the cook 88' to the position shown it will restrict the e 8| and so cause a pressure drop resulting in a difference in depression between the choke and the float chamber thereby increasing the amolmt oi suction on the jet.

Since it may not always be convenient to adjust the main jet opening a subsidiary jet 8! is provided by-passing the main jet, the size of the subsidiary vjet being adjustable by means of a needle valve 88 actuated bya screw 88 having a milled head.

The float chamber 8 may be connected to the cylinder l2 by means of a passage 88 in order that any lag in the movement of the piston during acceleration will result in a temporary increase in the pressure drop across the jet.

As previously stated the fuel intake to the venturi through the holes 21 is located at a p nt p e m of the point of minimum cross- 28, one end tion factor of the venturi will be of flow will correspond of the depression section of the female member and thus nearer the entrance end of the venturi, since by so positioning the intake it simplifiesv the design of the venturi and choke member 6 which will give a true Venturi action at all speeds and thus secure a multiplication of the depression, which is substantially constant for all positions of the choke member.

.An essential feature of this invention is to provide a venturi of variable cross section which at all speeds will produce sufficient depression to lift fuel under the most adverse conditions normally encountered without imposing sumcient restriction on the inflowing mixture to cause appreciable loss of power.

Previously, self-feeding carburettor constructions have been proposed with a large Venturi area having some form of controllable obstruc tion below the throat, but with this arrangementthe venturi is not properly effective unless the obstruction is removed out of the way; so that at low engine speeds, the depression created by the venturi will not be sumcient to maintain the requisite supply of fuel or mixture to the engine, the reason being that the multiplying efi'ect of a venturi varies with its shape, thus, if the intake is obstructed, the pressure drop or depression set up in the systelnwill be mainly due to the obstruction, and only in a minor degree due to the drop across the Venturi throat. In other words, by simply obstructing the intake the depression in due to the obstruction plus the multiplied depression produced by the drop across the Venturi throat. If the former is relatively large, the combined multiplication factor of the whole system will be considerably less than that obtainable with a simple venturi.

It instead a small venturi is employed, the de pression, provided the venturi is small enough, would always be multiplied to an extent such as to ensure afisufiicient supply of fuel to the engine. It will be found, however, that the amount of fuel that has to be passed through it in order to satisfy the engine requirements will have the eflect of drowning it and so decreasing the suc-: tion effect, with the result that the multiplicaconsiderably reduced. Therefore, since th'e'unmultiplied vacuum in the engine manifold is inadequate to raise fuel under all conditions unless it is made high enough to affect the power of the engine adversely, it is the object of this invention to provide a venturi which, under all conditions of operation, is ofthe correct size according to existing conditions to pass the amount of air and fuel required by the engine at full load. We have, therefore, found that by employing a venturi having two relatively moving parts 6 and 'l, of such cross sectional outline that in any relative position of the two parts their difference in. cross sectional area in the direction of the axis to the cross sectional area of a normal venturi for that particular set oi conditions. Since the multiplying effect of a venturi is governed by the rate of change oi cross sectional area along its axis, the respective members forming the venturi should be so shaped that the difference between the squares of their diameters at various axial positions should in any of the positions of the parts diminish progressively towards the point of minimum cross sectional area of the resultant passage and increase thereafter towards the engine at a small or preferably smaller rate.

the system will be the result We have alsdfound that this set of conditions can more easily be secured by arranging for the fuel and/or depression intake of the venturi to be not at the point of smallest cross section of the female member but at a point upstream thereof and thus nearer to the entrance. As hereinafter described, therefore, we thus arrange the fuel intake through holes located at a point upstream of the. point of minimum diameter of the female member.

As previously stated, the fuel intake to the venturi through the holes 2! is located at a point upstream of the point of minimum cross section of the female member and thus nearer the entrance end of the venturi, since by so positioning the intake it simplifies the design 01 the ven: turi and choke member 6 which will give a true Venturi action at all speeds, and thus secure a multiplication of the depression, which is substantially constant for all positions of the choke member.

The operation of the foregoing description, but to recapitulate, when the engine is at rest the piston H which is at its lowest position in the cylinder it is so arranged that the choke member 6 integral therewith almost completely closes the venturi i. At this time the needle valve 26 lowest position so as to afl'ord the maximum 0bstruction to the let nozzle. @n starting up the engine, when the throttle is partly opened, the suction caused thereby will through the Venturi throat and feed passages and via the bores 23 and Ml to the float chamber when fuel will be drawn in from the supply It.

Fuel upon entering the chamber will flow down the passage it into the chamber 2i and thence be transmitted the device will be clear 1mm will also be at its be drawn through the jet twhere it will mix with air drawn in from the bleed hole 3t and past the piston. The emulsion of fuel and air will now pass up the feed passages into the venturi where it will it with further air and be drawn into the engine as an explosive mixture. Dn further opening of the throttle the depression originally created in the system will be built up until it is sumcient to raise the piston it against its spring it choke member 6 and increasing the eifective cross-sectional area of the venturi increasing the opening of and simultaneously opening the jet orifice ii.

For convenience it may be assumed that a float chamber depression equal to 2 lbs. per square inch will be needed to aspirate fuel into the float chamber under the most arduous conditions.

Under these circumstances, the weight of the piston should be such that a depression oi d pounds per square inch acting upon its upper surface would just fall to raise it so as to ensure that under all conditions fuel will be aspirated into the float chamber.

By the provision of the venturi of variable cross section, we ensure the building up of a depression of sufllcient magnitude in the various passages described and in the float chamber so as to raise fuel, notwithstanding the position which the piston may occupy in response to any particular throttle opening, this state oi aflairs being maintained with a depression at the base of the venturi or the induction pipe oi such a small magnitude as to have no appreciable adverse effect upon the power output of an engine.

What we claim is:

till) til . l. A fuel raising and carburetting device for a fuel chamber, mixture passage including a Venturi tube, a pressure responsive member, means placing said member and the fuel chamber in communication with the throat of the venturi, a fuel Jet including a jet opening and a needle valve for controlling the effective area thereof, means connecting the Jet opening on one side thereof to the venturi and on the other side to the fuel chamber, and a choke piece movable into and out of the Venturi throat to vary the choke opening, both the needle valve and choke piece being actuated by the pressureresponsive member which is so restrained that it will cause a depression in the system sufllcient to raise fuel to the fuel chamber before it increases the jet and choke openings.

2. In a fuel raising and carburetting device for use in internal combustion engines, the combination of a fuel chamber, a fluid pressure responsive member, a fuel Jet including a movable element shaped to vary the area of opening thereof according to its position, a variable choke comprising a venturi having a throat and a choke member carried by the pressure responsive member and movable into and out of a position within the Venturi throat to vary the choke ber, said pressure responsive member being ac tiveiy responsive to pressure in the Venturi throat to move said jet movable element to increase the extent of opening of the fuel jet and to move said choke member to increase the extent of the opening of the throat only when the pressure in the fuel chamber has been lowered to a point at which it is capable of raising fuel to said chamber under normal conditions, conduit means between the fuel chamber and the pressure responsive member, and an adjustable control valve in said conduit.

3. A device as claimed in claim 1 in which the first means has its orifice at a point upstream of the narrowest section of said venturi.

RAYMOND LESLIE KENT. MURRAY DUNCAN soon.

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