GB2514347A

GB2514347A - A Rotating Barrel Carburettor

Info

Publication number: GB2514347A
Application number: GB201309026A
Authority: GB
Inventors: Keith Lawes
Original assignee: VEPEC Ltd
Current assignee: VEPEC Ltd
Priority date: 2013-05-20
Filing date: 2013-05-20
Publication date: 2014-11-26
Also published as: WO2014188150A1; GB201309026D0

Abstract

Disclosed is a carburettor incorporating an air passage 5, and a fuel passage 3. A rotating barrel 4 is arranged between the air passage 5 and the fuel passage 3 so that a first portion of its surface is exposed to the air passage 5, and a second portion of its surface is exposed to the fuel passage 3. The rotation of the barrel 4 transfers fuel from fuel passage 3 to the air passage 5 via an indent feature 6, the proportion of that indent feature 6 that is exposed to the air or fuel passage being varied to meter the amount of fuel transferred. A moving means is provided causing the fuel to flow over the indent so that air brought back into the fuel passage in the indent is stripped from the indent feature and the resulting air bubbles are then carried away by the fuel flow.

Description

A Rotating Barrel Carburettor The present invention relates to a carburettor for internal combustion engines.

At present fuel is typically metered into an engine either by a carburettor or a fuel injection system.

Carburettors are normally simple mechanical devices with no electronic control. They have the advantage of being low cost. Carburettors generally meter fuel by utilising the low pressure that occurs in the inlet manifold of the engine during the inlet stroke to draw the fuel through small precisely sized jets or orifices.

It can be seen that the amount of fuel delivered is empirical and will be determined by several variables, the primary determinants being the magnitude and duration of the pressure differential across the jet, the diameter of the jet, and the viscosity of the fuel.

The jet diameter is particularly crucial, with small differences in diameter producing significant changes in fuel flow. The very small holes required for small engines present a particular challenge to achieve accurately and repeatedly. This leads to considerable production variability between individual carbureftors. Small jets also are prone to blockage due to contaminants in the fuel, or to gumming up during periods of inactivity as may occur when a piece of equipment is laid up over the winter.

Fuel injection systems generally utihse a fuel rail pressurised to a known pressure dispensing fuel through a known sized orifice controlled by a solenoid activated valve.

Again the amount of fuel delivered is empirical and controlled by the pressure differential across the orifice, fuel viscosity, orifice dimension, and the time the solenoid valve is held open for.

Fuel injection systems are generally electronically controlled and have the advantage of flexible programmable operation to cope with a wide range of operating conditions. Their main disadvantage is cost and complexity. The injectors, fuel pressurisafion system and associated high pressure plumbing together with the electronics is a significant additional cost for an engine, in particular for smaller installations. They also require an electrical supply which is again inconvenient on a lower cost installation.

The present invention seeks to provide a ow cost fuelling system that has significant advantages over both conventional carburettors and fuel injection systems in particular for smafl engine appHcations.

According to a first aspect of the invention there is provided a carburettor for an internal combustion engine, the carburettor incorporating an air passage adapted to be connected to an inlet tract of an engine, and a fuel passage, and a rotatable barrel, the rotatable barrel being arranged between the air passage and the fuel passage so that a first portion of its surface is exposed to the air passage) and a second portion of its surface is exposed to the fuel passage, the rotation of the barrel transferring fuel from the fuel passage to the air passage via an indent feature on the surface of the barrel to provide an air/fuel mix for the engine1 characterised by fuel moving means by which the fuel within the fuel passage is caused to flow along the fuel passage and over the indent feature on the barrel, so that air brought back into the fuel passage in the indented feature is stripped from the indent feature and replaced by fresh fuel, and that the resulting air bubbles are then carried away from the region of the indent feature by the fuel flow.

Preferably the amount of both the air and the fuel that is entering the air passage is primarily controlled by a single sliding throttle, said sliding throttle masking both a portion of the air passage and a portion of the fuel carrying indent, as it is opened said throttle progressively exposing a greater proportion of the air passage and a greater proportion of the fuel carrying indent, thereby maintaining the correct fuel air ratio over the operating range of the engine.

Preferably the amount of fu& that is conveyed from the fuel passage to the air passage is primarily determined by the volumetric size of the portion of the fuel carrying indent that is exposed by the sliding throttle, said volumetric size being set such that the amount of fuel delivered will provide the correct amount of fuel for the amount of air being allowed into the engine by the sliding throttle, thereby maintaining the correct air fuel ratio over the operating range of the engine.

Preferably the fuel carrying indent has variable volume along its length, the variation in volume being used to map the amount of fuel that is carried between the fuel passage and the air passage for a given throttle position.

Alternatively the fuel carrying indent consists of a plurality of spaced indentations in the form of selectively exposable slots, the total volume of the slots that are exposed by the sliding throttle determining the amount of fuel that is transferred between the two passages, the slots being of variying volume along the length of the rotor, the variation in volume being used to map the amount of fuel that is carried between the fuel passage and the air passage for a given throttle position.

Preferably the sliding throttle is substantially cylindrical, consisting of a cylindrical barrel with an offset coaxial cylindrical recess, the offset cylindrical recess having a diameter substantially identical to the diameter of the rotating barrel, the main outer diameter of the sliding throttle sifting within a bore in the body of the carburettor coaxial to the rotating barrel, the offset cylindrical recess enveloping the surface of the rotatable barrel that is exposed to the air passage, the main body of the sliding throttle being adapted to block off a portion of the air passage into the engine to control the air flow in the engine, the offset cylindrical recess masking off a proportion of the fuel carrying indent to control the flow of fuel into the engine.

Preferably the sliding throttle has resilient means acting upon it to cause the edge of the cylindrical cut nearest to the engine to be urged down onto the surface of the rotatable barrel, thereby limiting any fuel leakage from the masked portion of the fuel carrying indent under this edge.

Preferably the sliding throttle has resilient means acting upon it to causes the end of the sliding throttle nearest to the air passage to be forced down onto the surface of the rotatable barrel, thereby limiting any fuel leakage from the masked portion of the fuel carrying indents under the end of the throttle barrel.

According to a second aspect of the invention there is provided a damper plate that limits the rate of increase of air flow into the engine when the throttle is opened rapidly, this preventing the engine from stalling when the throttle is opened rapidly, said damper plate being opened by the action of the vacuum in the engine manifold upon the damper plate, the rate of opening of the damper plate being limited by a mechanical damper.

Preferably the damper plate comprises a plate rotationally fast on an axle, the axle being linked to a rotary damper.

Preferably when the throttle is dosed the damper plate is forced to its closed position by the skiing throttle pressing directly upon the damper plate.

Preferably the air passage forms part of the inlet tract to an internal combustion engine.

Alternatively the air passage forms part of the transfer tract within a 2 stroke internal combustion engine.

Preferably the rotatable barrel is rotated synchronously with the engine. Preferably the rotatable barrel is rotated by a belt driven by the engine.

Preferably the rotation of the barrel is timed so that the fuel carrying indent is exposed to the air passage during the period when the air in the air passage is flowing at its maximum velocity, so the movement of the air in the air passage will strip the fuel from the fuel carrying indent in the rotor, displacing the fuel with air which the fuel carrying indent will then carry back to the fuel passage.

Preferred embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which Figures 1 a, lb1 and 1 c show cross sectional views of a rotating barrel carburettor at idle.

Figure Id shows a general sectional view of a rotating barrel carburettor.

Figures 2a and 2b show cross sectional views of a rotating barrel carburettor at full throttle.

Figure 2c shows a cross sectional end view of a fuel supply pump Figures 3a and 3b show general external views of the rotating barrel Figures 4a 4b and 4c show general external views of the throttle slider.

Referring now to all figures there is shown a rotating barrel carburettor.

The rotating barrel carburettor I consists of a carburettor body 2 incorporating a fuel passage 3, a rotatable barrel 4 and an air passage 5. The rotating barrel 4 has one side exposed to the fuel passage 3 and one side exposed to the air passage 5. The rotating barrel 4 is tightly toleranced within the carburettor body 2 to prevent fuel leaking up the sides of the rotating barrel 4.

The rotating barr& 4 is shown in greater detail in Figures 3a and Sb. The rotating barrel 4 has a fuel carrying indent 6. This fuel carrying indent 6 comprises a pluraty of spaced parallel slots 30 machined into the surface of the rotating barrel 4 extending along the barrel in the direction of movement of the throttle. The use of multiple slots minimises fluid communication between the air passage 5 and the masked portion of the fuel carrying indent 6.The rotating barrel 4 has a drive shaft 14 extending from the main barrel The first fuel slot 36 nearest the drive shaft 14 is the slot that suppltes fuel to the engine at idle. As the engine takes proportionally more fuel at low throttle the slots at the low (closed) throttle end of the ident 34 are larger than the slots at the full throttle end of the ident 35.

Referring now to figure la, lb and lc it can be seen that a pulley 13 is mounted on the rotor drive shaft 14. This is coupled to the engine (not shown) by a toothed belt (not shown) so as to rotate at half engine speed.

A fuel supply pump 19 is also driven by the drive shaft 14. The fuel supply pump in this embodiment is a conventional twin gear pump. Figure 2c shows a sectional end view of the pump 19 along the line B-B of Figure 2b. This pump consists of a pump driven gear 21 coupled to the drive shaft 14, and a pump idler gear 20. The fuel supply pump 19 draws fuel from the tank through the fuel inlet 22 then through a fuel input passage 25 and then pushes it out through an internal passage 26 which is coupled to the fuel passage 3. The fuel is pushed through the fuel passage 3 and exits via the fuel outlet 23 and returns back to the fuel tank. It can be seen that the requirement for the pump is to supply a reasonable fuel flow at low pressures, therefore a wide variety of low cost pumps or impellers or even gravity could be employed to achieve the required flow along the fuel passage 3.

As the rotating barrel 4 rotates within the carburettor body 2 the fuel carrying indent 6 picks up fuel from the fuel passage 3 and transfers it to the air passage 5.

Normally the rotation of the rotating barrel 4 is timed such that the fuel carrying indent 6 is exposed to the inlet flow in the air passage 5 during the inlet stroke such that the air flow during the inlet stroke strips the fuel from the fuel carrying indent 6. The fuel carrying indent 6 will then carry air back to the fuel passage 3. The fuel flow in the fuel passage 3 generated by the fuel supply pump 19 will then displace this air from the fuei carrying indent 6 and replace it with a fresh packet of fuel. The air will then be carried back to the fuel tank via the fuel outlet 23.

A cylindrical sflding throttle 8 is used to control both the amount of air and the amount of fuel entering the engine. The sliding throttle is shown in greater detail in figures 4a, 4b and 4a The shding throttle has a main diameter 9 and an offset cyUndrical recess 10. The main diameter 9 of the sliding throttle slides within the throttle bore 11 in the carburettor body: and blocks off a variable portion of the air passage 5 into the engine. The offset cylindrical recess 10 covers the surface of the rotating barrel 4 where it is exposed to the air passage 5, thereby masking a variable portion of the fuel carrying indent 6. The diameter and radial offset of the offset cylindrical recess 10 are a close match to the diameter and offset of the rotating barrel 4 to minimise clearance between the offset cylindrical recesslO and the surface of the rotating barrel 4, minimising fluid communication between the masked part of the fuel carrying indent 6 and the air passage 5.

The cylindrical sliding throttle 8 is biassed into its closed position by a throttle spring 12.

The throttle is opened by means of a cable or other linkage (not shown) in the conventional manner.

As can be seen the primary determinant of the amount of air and fuel entering the engine will be the position of the cylindrical sliding throttle 8 The air flow will be determined by how much of the air passage is blocked by the main body of the cylindrical sliding throttle 8. The fuel flow will be determined by the volume of the fuel indent 6 that the offset cylindrical recess 10 leaves exposed to the air passage 5. The air fuel ratio can therefore be set by at any throttle opening by adjusting the volume of the fuel carrying indent 6 that is exposed to the air passage 5 at that throttle opening.

in practice if there are small gaps between the cylindrical sliding throttle 8 and the rotating barrel 4 at part load extra fuel may be drawn from the masked indents 6 into the air passage 5. To reduce this flow, which will cause part load mixture to be richer than intended, the cylindrical sliding throttle can be sprung against the rotating barrel 4. it has been found that the most beneficial spring loadings are to apply a slight rotational torque to the cylindrical sliding throttle S such that the edge ba of the offset cylindrical recess 10 in the cylindrical sliding throttle 8 bears down against the surface of the rotating barrel 4. This can be facilitated by tabs on the end of the throttle return spring 12 which apply the necessary torque to the cylindrical sliding throttle 8. It has also been found that providing a separate spring (not shown) to gently force the end face 37 of the cylindrical sliding throttle 8 nearest to the air passage 5 against the rotating barrel 4 reduces any fuel leakage past the end face 37 of the cyUndrical sliding throttle 8.

When the throttle of an internal combustion engine is opened rapidly there is a tendency for the engine to stafl because the mixture becomes temporarily lean. This is primarily because the initial increase in fuel delivery is used up wetting the walls of the inlet. To prevent this happening with the rotating barrel carburettor a damper mechanism is fitted.

This consists of a damper flap 15, which is pivoted on a damper shaft 16. This damper shaft is connected to a rotary damper 17.

When the throttle is dosed a flat 35 on the cylindrical sliding throttle 8 presses on the end 18 of the damper flap 15 forcing it into its closed position. In this position it provides a partial restriction on the air flow into the engine. When the throttle is opened the damper flap 15 is then free to move. The vacuum in the air passage 5 will then act on the inner face of the damper flap 15 and it will start to open. However the damping action of the rotary damper 17 will restrict the rate at which the damper flap wUl open, limiting the rate of increase of the air flow into the engine and preventing the engine from stalling.

Figure la and lb shows the engine at idle. The cylindrical sliding throttle 8 is bearing against the throttle stop screw 33. Only the first slot 36 of the indent is exposed metering the required amount of fuel into the engine. The small diagonal cutout 32 in the cylindrical sliding throtfle 8 is the primary control over the amount of air entering the engine at idle.

The throttle stop screw 33 can be used as a secondary control to adjust the idle speed. A flat 35 on the cylindrical sliding throttle S bears upon the end 18 of the damper flap 15 forcing it closed.

Figures 2a and 2b show the engine at full throttle. The cylindrical sliding throttle S is fully withdrawn to allow the maximum amount of air into the engine. All the slots 30 of the fuel indent 6 are exposed to the air passage to allow the maximum amount of fuel into the engine. The vacuum in the air passage 5 has fuily opened the damper flap 15.An important advantage of the device shown is that it has volumetric metering of the fuel being transferred to the inlet tract. The amount of fuel is determined primarily by the dimensions of the exposed part of the fuel carrying indent. Inlet pressure, fuel viscosity, temperature and fuel supply pressure will have only secondary effects on the amount of fuel delivered. This should lead to more accurate and repeatable fuel metering.

S

An important advantage of the device shown is that the fuel preparation is very good. The air flow in the manifold is very high v&ocity and strips the fuel from the fuel carrying indent in a violent and rapid manner causing good atomisation of the fuel.

An important advantage of the device shown is repeatability between devices. The actual dimensions of the fuel carrying indent, even for a sma engine, are comparatively large.

The volumetric capacity of the indent is typically greater than 5 cubic millimetres. This means that it can be machined accurately and at low cost. This should lead to repeatable and more accurate fuel metering between different devices.

An important advantage of the device shown is that is resistance to blockage.

Conventional carburettors, in particular for small engines, have very small jets which are prone to blocking, in particular after a winter layup. The current device has no small jets, and has the mechanical rotation of the rotor to displace any contamination or gumming within the device.

An important advantage of the device shown compared to float bowl carburettors is that it has mu!ti position operation. It is not affected by the orientation at which it is used.

An important advantage of the device shown is simplicity and robustness. Small carburettors, in particular diaphragm carburettors which are used for multi position operation, have many small parts which are vulnerable to damage, in particular plastic or rubber diaphragms and smafi pump mechanisms. The current device has simple and robust construction and no small vulnerable plastic or rubber parts.

Although described as a carburettor, it will be appreciated that the device could equally well be used as a variable displacement pump to transfer variable amounts of fluid between a fluid passage and a gas passage.

Claims

A carburettor for an internal combustion engine, the carburettor incorporating an inlet air passage adapted to be connected to an inlet tract of an engine, and a fuel passage, and a rotatable barrel, the rotatable barrel being arranged between the air passage and the fuel passage so that a first portion of its surface is exposed to the air passage, and a second portion of its surface is exposed to the fuel passage, the rotation of the barrel transferring fuel from the fuel passage to the air passage via an indent feature on the surface of the barrel to provide an airlfuel mix for the engine, characterised by fuel moving means by which the fuel within the fuel passage is caused to flow along the fuel passage and over the indent feature on the barrel, so that air brought back into the fuel passage in the indented feature is stripped from the indent feature and replaced by fresh fuel, and that the resulting air bubbles are then carried away from the region of the indent feature by the fuel flow
2. A carburettor as claimed in claim 1, wherein the amount of both the air and the fuel that is entering the air passage is primarily controlled by a single sliding throttle, said sliding throttle masking both a portion of the air passage and a portion of the fuel carrying indent, as it is opened said throttle progressively exposing a greater proportion of the air passage and a greater proportion of the fuel carrying indent, thereby maintaining the correct fuel air ratio over the operating range of the engine.
3. A carburettor as claimed in claim I or 2, wherein the amount of fuel that is conveyed from the fuel passage to the air passage is primarily determined by the volumetric size of the portion of the fuel carrying indent that is exposed by the sliding throttle, said volumetric size being set such that the amount of fuel deuvered will provide the correct amount of fuel for the amount of air being allowed into the engine by the sliding throttle, thereby maintaining the correct air fuel ratio over the operating range of the engine.
4. A carburettor as claimed in claim 1, 2 or 3, wherein the fuel carrying indent has variable volume along its length, the variation in volume being used to map the amount of fuel that is carried between the fuel passage and the air passage far a given throttle position.
5. A carburettor as claimed in any one of the preceding claims, wherein the fuel carrying indent consists of a plurality of spaced indentations in the form of selectively exposable slots, the total volume of the slots that are exposed by the sliding throttle determining the amount of fuel that is transferred between the two passages, the slots being of variable depth, width and/or circumferential length along the length of the rotor, the variation in depth, width and/or circumferential length being used to map the amount of fuel that is carried between the fuel passage and the air passage for a given throttle position.
6. A carburettor as claimed in any one of the preceding claims, wherein the sliding throttle is substantially cylindrical, consisting of a cylindrical slide with an offset coaxial cyhndrical recess, the offset cylindrical recess having a diameter substantially identical to the diameter of the rotating barrel, the main outer diameter oF the sliding throttle sitting within a bore in the body of the carburettor coaxial to the rotating barrel, the offset cylindrical recess enveloping the surface of the rotatable barrel that is exposed to the air passage, the main body of the sliding throttle being adapted to block off a selected portion of the air passage into the engine to control the air flow in the engine, the offset cylindrical recess masking off a proportion of the fuel carrying indent to control the flow of fuel into the engine.
7. A carburettor as claimed in any one of the preceding claims, wherein the sliding throttle has a resilient means acting upon it to cause the edge of the cylindrical recess nearest to the engine to be urged onto the surface of the rotatable barrel, thereby limiting any fuel leakage from the masked portion of the fuel carrying indent under this edga
8. A carburettor as claimed in any one of the preceding claims, wherein the sliding throttle has a resilient means acting upon it to cause the end of the sliding throttle nearest to the air passage to be urged onto the surface of the rotatable barrel, thereby limiting any fuel leakage from the masked portion of the fuel carrying indents under the end of the throttle.
9. A carburettor as claimed in any one of the preceding claims, wherein a damper plate that limits the rate of increase of air flow into the engine when the throttle is opened rapidly, to prevent the engine from stalling when the throttle is opened rapidly, said damper plate being opened by the action of the vacuum downstream of the carburettor upon the damper plate, the rate of opening of the damper plate being limited by a mechanical damper.
10. A carburettor as claimed in 9, wherein the damper plate comprises a plate rotationay fast on an axle, the axle being inked to a rotary damper.
11. A carburettor as claimed in claim 9 or 10, wherein when the throttle is closed the damper plate is urged to its closed position by the sliding throttle pressing directly upon the damper plate.
12. A carburettor as claimed in any one of the preceding claims, wherein the air passage forms part of the inlet tract to an internal combustion engine.
13. A carburettor as claimed in any one of the claims ito 11, wherein the air passage forms part of a transfer tract of a two stroke internal combustion engine.
14. A carburettor as claimed in any one of the preceding claims, wherein the rotatable barrel is rotated synchronously with the engine.
15. A carburettor as claimed in claim 14 wherein the rotatable barrel is rotated at half engine speed.
16. A carburettor as claimed in claim 14 or 15! wherein the rotatable barrel is rotated by a belt driven by the engine.
17. A carburettor as claimed in any one of the preceding claims, wherein the rotation of the barrel is timed so that the fuel carrying indent is exposed to the air passage during the inlet stroke of the engine so the movement of the air in the air passage will strip the fuel from the fuel carrying indent in the rotor, displacing the fuel with air which the fuel carrying indent will then carry back to the fuel passage.
18. A carburettor substantially as described herein with reference to, and as illustrated in, the accompanying drawings