US3684257A

US3684257A - Carburetters

Info

Publication number: US3684257A
Application number: US55836A
Authority: US
Inventors: Geoffrey Lloyd Lawrence
Original assignee: Zenith Carburetter Co Ltd
Current assignee: Zenith Carburetter Co Ltd
Priority date: 1969-07-22
Filing date: 1970-07-17
Publication date: 1972-08-15
Anticipated expiration: 1989-08-15
Also published as: DE2035772A1; GB1300577A; DE7027378U; FR2055391A5; DE2035772C3; SE354320B; NL7010774A; DE2035772B2

Abstract

A carburetter of the constant depression type, in which fuel enters the throat of the induction passage through a jet orifice controlled by a profiled needle moving with the air valve slide, is arranged to have air supplied to the jet orifice to mix with the fuel, so that an air/fuel emulsion or mixture, instead of fuel alone, is delivered to the induction passage. Provision is also made for controlling the temperature of the air supplied to the induction passage of the carburetter.

Description

[ 51 Aug. 15,1972

5w: States Patent Lawrence Date et a1.

[54] CARBURETTERS [72] Inventor:

3,342,463 9/ l 967 .261/44 3,016,889 9/1967 Sweeney..................261/50 A 1,919,793 ..261/121 A Geoffrey Lloyd Lawrence, Stanmore, England [73] Assignee: The Zenith Carburetter Company 7/1933 Linga................... 3,207,491 9/1965 Kingsleyetal.............

4 M mm Wm WT. A mm m MP n M mS ST W WP WN m n m0 F 7 2 Limited, Stanmore, England July 17, 1970 Great Britain [22] Filed:

171,328 Austria........................26l/44 Germany.....................261/44 [21] Appl. No.: 55,836

[] Foreign Application Priority Data July 22, 1969 M & a m s mm D mm V m ms i, We mm MM Great Britain..........36,844/69 March 24, 1970 Great Britain..........14,302/

[57] ABSTRACT A carburetter of the constant depression type, in which fuel enters the throat of the induction passage [52] US. Cl.............26l/39 B, 261/44 R, 261/121 A,

261/ .F02m 9/06 .261/44 R, 121 A, 50 A, 39 B,

through a jet orifice controlled by a profiled needle moving with the air valve slide, is arranged to have air [58] Field of Search...

supplied to the jet orifice to mix with the fuel, so that an air/fuel emulsion or mixture, instead of fuel alone, is delivered to the induction passage. Provision is also [56] References Cited UNITED STATES PATENTS made for controlling the temperature of the air supplied to the induction passage of the carburetter.

8 Claims, 4 Drawing Figures 2/1957 Sebok et "Emmi ra PATENTEDAUSIS |s12 3.684.257

sum 1 BF 3 PATENTEDAUQS sum 3 or 3 3.584257 FIG. 4.

II ll.

CARBURE'I'IERS This invention relates to carburetters of the constant depression type, which carburretters are provided, in the induction passage thereof, with a throttle valve to control the admission of fuel air mixture to the cylinders of an internal combustion engine to which the carburetter is connected, and upstream of the throttle valve, with an air valve operated automatically in accordance with the depression existing in the chamber defined by the part of the induction passage between i said throttle valve and air valve so as to control the flow of air into the said chamber and maintain a substantially constant depression therein.

In such carburetters liquid fuel is supplied through a jet opening into the induction passage at a position where the effective area of the said passage is controlled by the air valve and thus varies with the degree of opening of the latter, the effective area of the jet being controlled by a profiled needle which is moved with opening of the air valve to increase the effective area of the jet.

' It has been found that, in carburetters of the constant depression type, the fuel/air ratio of the mixture supplied for idling, at a given position of the air valve, varies with the temperature conditions, the proportion of fuel in the mixture increasing with the fuel and air temperatures.

So far as the effect of fuel temperature on the fuel/air ratio is concerned, this is believed to be due to changes in fuel viscosity with temperature, it being the usual practice to supply only fuel unmixed with air, through the fuel jet, and it is found that, under low fuel flow conditions, when the engine is idling, the fuel flow for a given position of the needle varies with temperature. The said variation is believed to be due to the fact that the fuel flow through the annular space between the jet wall and the needle is largely laminar, laminar flow being particularly subject to variation with viscosity.

So far as the effect of air temperature on the fuel/air ratio is concerned, the variation in fuel/air ratio is believed to be due to the fact that the mass flow of air at a given throttle valve setting increases with the air density, which density varies with the air temperature, the proportion of fuel to air in the mixture therefore increasing as the air temperature increases. Thus, if the fuel supply is adequate for idling under cold engine conditions, the mixture is too rich under hot engine conditions, leading to incomplete combustion and an undesirable proportion of CO in the exhaust gases.

It is the object of the present invention to provide an improved arrangement of a carburetter of the type referred to, in which the fuel flow under idling conditions is less affected by temperature, so that consistent idling of an engine can be obtained under both hot and cold conditions particularly in regard to the emission of the CO and hydrocarbon constituents of the exhaust gases.

According to the invention there is provided a carburetter of the constant depression type having, in the induction passage thereof, a throttle valve to control the admission of fuel air mixture to the cylinders of an internal combustion engine to which the carburetter is connected, an air valve in the said induction passage, upstream of the said throttle valve and operated automatically in accordance with the depression existing when the carburetter is in operation, in the chamber defined by the part of the induction passage between said throttle valve and air valve so as to define a throat of variable area to control the flow of air into the said chamber and maintain a substantially constant depression therein, and a fuel supply jet opening into said throat, the effective area of the jet being controlled by a profiled needle which is moved with opening of the air valve to increase the effective area of the said jet, wherein one or more passages are provided to admit air to the space between the jet wall and the needle to create turbulence in said space and form an emulsion with the fuel.

Preferably, the needle is biased transversely of the jet so as to engage the jet wall at one side thereof, and the air is admitted to the said space on the opposite side of the jet.

The needle is preferably biassed towards the side of the jet wall which is downstream in relation to the direction of air flow through the induction passage.

The passage or passages provided to admit air to the space between the jet wall and the needle may be radial to the jet orifice and may lead from an air inlet in the carburetter induction passage upstream of the air valve.

Means may be provided for controlling the temperature of air supplied to the induction passage of the carburetter so as to maintain the temperature of said air substantially constant, and the control of the temperature of the air may be provided by drawing air from both relatively hot and relatively cold air sources, temperature controlled valve means being provided to determine the proportions of the total air supply drawn from said two sources.

There will now be described, by way of example and with reference to the accompanying drawings, one form of carburetter of the constant depression type embodying the present invention, and one arrangement for controlling the temperature of the air supplied to the said carburetter.

In the drawings;

FIG. 1 is a view in elevation, partly in longitudinal section, of a constant depression type carburetter embodying the invention;

FIG. 2 is a sectional elevation, on a larger scale, corresponding to part of FIG. 1;

FIG. 3 is a section on the line 3 3 of FIG. 2; and

FIG. 4 is a diagrammatic view showing one arrangement for controlling the temperature of the air supplied to the carburetter.

Referring to FIG. 1, the carburetter comprises a body 10 in which is formed a through passage 11 constituting an induction passage adapted to be supplied with atmospheric air at its inlet end 12 and to be connected at its other end 13 to the induction manifold (not shown) of an internal combustion engine. A butterfly-type throttle valve 14 is provided in the passage 11 adjacent the end 13 thereof, and an air valve slide 15, of known type, co-operates with a bridge 16 in the induction passage to define a throat of variable cross sectional area, the position of the air valve slide being controlled, in the known manner, by the difference between air pressures acting above and below a diaphragm mounted in a housing 17 carried by the carburetter body and coupled to the air valve slide 15, so

that depression in the part of the induction passage between the air valve slide and the throttle valve 14 tends to lift the air valve and increase the throat area, thereby tending to keep the said depression substantially constant.

The air valve slide 15 carries a profiled needle extending across the throat into a fuel supply jet 18 connected in the usual manner to a fuel supply chamber in which fuel is maintained at a constant level by a float valve.

Referring now to FIG. 2 of the drawings, which shows the parts immediately surrounding the throat of the carburetter, and in particular the fuel supply system, the fuel supply jet 18, which has its axis aligned with the axis of the air valve slide 15, is located in an opening in the bridge 16. The fuel supply jet 18 is located centrally in the opening in the bridge 16 by two

bushes

19, 21 pressed into the said opening, flow of fuel along the outside surface of the jet 18 being prevented by two

packing rings

22 and 23, which are conveniently O-rings. The lower O-ring 23 is supported by a collar 24 locked axially in position by a screw-threaded retaining sleeve 25.

A spring 26 taking its abutment on a shoulder 27 on the collar 24 acts downwardly on the jet 18 to urge it against an adjusting screw 28 mounted in the retaining sleeve and providing an adjustable abutment by means of which the axial position of the jet 18 can be adjusted. Fuel reaches the jet 18 through radial apertures in the retaining sleeve 25 and adjusting screw 28, from the float chamber through which the retaining sleeve 25 extends downwardly, a packing ring 29 being provided to prevent leakage of fuel from the float chamber around the sleeve 25.

- The jet 18 is located in the rotational sense by a radial pin 31 thereon engaging in a radial hole in the collar 24, and by an eccentn'cally positioned longitudinally extending pin 32 on the collar 24 engaging in a hole in the carburetter body.

The jet 18 has an intermediate bore portion 33 defining the jet orifice, between upper and

lower end portions

34 and 35, both of larger diameter than the orifice 33.

The needle 20 is biased, for example by means such as are described in our British Pat. specification No. 1,444,405 so as to engage the wall of the jet orifice 33 on the side thereof which is downstream with respect to the direction of air flow in the carburetter induction passage 11, and, as shown in FIG. 3, two radial passages 36 in the jet wall open into the said jet orifice 33 on the side thereof opposite to the point of engagement of the needle 20 therewith. A single radial passage 36, or more than two such passages, may be provided instead of the two passages described. The outer ends of the passages 36 open into a slot 37 in the lower bush 21, and a channel 38 in the carburetter body, leading into the said slot, has mounted in it an impact tube 39 positioned upstream of the bridge 16. The impact tube 39 has a restricted passage 41 at its end which opens into the passage 39, and the passages 36 provide a further restriction of flow of air into the jet orifice 33. The impact tube 39 may be replaced by a static head pick-up.

During operation of the carburetter, the restriction of air flow by the throat in the induction passage 11 produces a pressure differential which acts on the diaphragm associated with the air valve slide 15, lifting said slide, and with it the needle 20, to a position at which equilibrium is established. The resultant depression at the throat creates a pres-sure difference between the jet discharge and the float chamber and between the jet orifices 33 and the inlet end of the impact tube 39 or static head pick-up, so that fuel is drawn from the float chamber through the jet, and air is drawn through the impact tube or pick-up into the jet orifice 33, the air mixing with the fuel to produce an emulsion which is discharged into the air stream in the induction passage.

The quantity of air fed into the jet orifice, and consequently the proportion of air to fuel, is controlled by the restricted passage 41 and the passages 36, while the rate at which fuel is supplied to the engine is controlled in the normal manner by the needle 20.

It has been found that the fuel supply arrangement according to the invention is insensitive to fuel viscosity, and therefore to fuel temperature, and this is believed to be due to two considerations, namely 1. that the introduction of air into the fuel metering orifice creates turbulent flow conditions in the orifice, and turbulent flow is affected by fuel viscosity to a far smaller extent that is laminar flow.

2. Because the introduction of air into the fuel metering orifice reduces the depression acting on the fuel, the passage between the wall of the jet orifice and the needle must have a greater cross-sectional area to permit the flow of a given quantity of fuel than would be required if only fuel were present in the orifice. Under operating conditions, this has the effect of reducing the proportion of boundary layer to total passage area, which results in improved flow stability.

The temperature of the air supplied to the induction passage 11 of the carburetter may be controlled by means such as are shown diagrammatically in FIG. 4, in which part of an internal combustion engine is shown at 44, the induction manifold of the said engine is shown at 45, and the exhaust manifold at 46. The carburetter, which is of the constant depression type, and embodies the arrangement shown in FIGS. 2 and 3, is shown at 47, and the throttle valve at 48. Air is supplied to the carburetter inlet through an air cleaner 49 to which air is supplied through a duct 51. The duct 51 has an inlet end at 52 open to the atmosphere at a point where the air is at the ambient atmospheric temperature, and has connected to it at 53 a branch duct 54 the inlet end of which is so positioned with relation to the exhaust manifold 46 that air entering the duct 54 receives heat from the said exhaust manifold. It will be evident that, if desired, the duct 54 may be connected to an air heating chamber receiving heat from the said exhaust manifold. A flat valve 55 is provided at the junction 53 of the

ducts

51 and 54, the position of the said flap valve 55 being controlled by a bi-metallic coil 56 subjected to the temperature of the ambient air and exerting a variable bias tending to move the flap valve 55 to a position in which it closes the duct 51 and opens the duct 54. The arrangement is such that the bias acting on the flap valve 55 decreases with rise of temperature, so that, with low air flows, such as occur with small throttle opening and low temperature, the flap valve tends to take up a position in which a relatively large proportion of the air is received from the duct 54,

either increase of air flow, due to larger throttle opening or increase of temperature, moving the flap valve to increase the proportion of air received from the duct 51.

Thus a relatively constant temperature of the air supplied to the carburetter is maintained under idling conditions when the air flow is relatively low, but mainly cold air is supplied under high flow conditions regardless of engine temperature.

The air supplied through the duct 54 may be heated by means other than by heat derived from the exhaust manifold, and the valve acting to vary the proportions of cold and warm air may be of any suitable form other than that specifically described herein.

I claim:

1. A carburetter of the constant depression type, comprising: a body defining an induction passage which extends therethrough; the body carrying a throttle valve in the induction passage, the throttle valve being arranged to control the admission of fuel air mixture to the cylinders of an internal combustion engine to which the carburetter may be connected; and an air valve in the induction passage upstream of the throttle valve, the air valve defining a throat of variable area through which, during operation of the carburetter, air flows into a chamber defined by the part of the induction passage between the air valve and the throttle valve, the air valve being operated automatically to vary the area of said throat in accordance with the depression existing in said chamber so at to maintain a substantially constant depression in said chamber; the body also defining an opening which extends transversely of the induction passage and opens into the throat; a fuel supply jet located in said opening and arranged to control the supply of fuel into the throat, the effective area of the jet being controlled by a profiled needle which is movable with opening of the air valve to increase the effective area of the jet, said fuel supply jet having a through bore which opens into the throat, said through bore comprising a bore portion defining a jet orifice, and a larger diameter portion on the side of said jet orifice remote from the throat; and means for supplying air to the through bore to form an air-fuel mixture;

wherein said fuel supply jet comprises two axially spaced parts, the radial outer surfaces of which cooperate in a fluid tight manner with adjacent wall portions of the opening in which the jet is located; and the means for supplying air includes radial passages in the fuel supply jet and an air supply passage defined in said body; said radial passages comprising at least two r'adial passages each of which opens in the radial outer surface of the fuel supply jet between the two axially spaced parts thereof, and which extend through the wall of the fuel supply jet to open at their other ends in the jet orifice, said air supply passage having one end in communication with a source of air and the other end opening into the space between the adjacent wall portions to communicate with said jet orifice via said radial passages, so that all the air fed through said air supply passage towards said other end is fed directly into the jet orifice via said radial passages to mix with the fuel within the jet orifice for creating turbulence in said jet for forming an 'rfuel mixture therein. 2. car uretter according to claim 1, wherein the end of the air supply passage in communication with a source of air includes an impact tube which necks down from its inlet end to a restricted passage.

3. A carburetter according to claim 1, wherein the said passages lead from an air inlet in the carburetter induction passage upstream of the air valve.

4. A carburetter according to claim 1, wherein the needle is biased transversely of the jet so as to engage the jet wall at one side thereof, and the air is admitted to the space on the opposite side of the jet from said needle.

5. A carburetter according to claim 2, wherein the needle is biased towards the side of the jet wall which is downstream in relation to the direction of air flow through the induction passage.

6. A carburetter according to claim 1, wherein means are provided for controlling the temperature of air supplied to the induction passage of the carburetter so as to maintain the temperature of said air substantially constant.

7. A carburetter according to claim 6, wherein the control of the temperature of the air is provided by means for drawing air from both relatively hot and relatively cold air sources, and temperature controlled valve means being provided to determine the proportions of the total air supply drawn from said two sources.

8. A carburetter according to claim 7, wherein the temperature controlled valve means comprises a flap valve at the junction of air ducts leading respectively from said relatively hot and relatively cold air sources, and bi-metallic spring means exerting a force on said flap valve urging it towards a position in which it closes the duct leading from the source of relatively cold air, which bias is reduced by the action of increasing temperature on the bi-metallic spring.

Claims

1. A carburetter of the constant depression type, comprising: a body defining an induction passage which extends therethrough; the body carrying a throttle valve in the induction passage, the throttle valve being arranged to control the admission of fuel air mixture to the cylinders of an internal combustion engine to which the carburetter may be connected; and an air valve in the induction passage upstream of the throttle valve, the air valve defining a throat of variable area through which, during operation of the carburetter, air flows into a chamber defined by the part of the induction passage between the air valve and the throttle valve, the air valve being operated automatically to vary the area of said throat in accordance with the depression existing in said chamber so at to maintain a substantially constant depression in said chamber; the body also defining an opening which extends transversely of the induction passage and opens into the throat; a fuel supply jet located in said opening and arranged to control the supply of fuel into the throat, the effective area of the jet being controlled by a profiled needle which is movable with opening of the air valve to increase the effective area of the jet, said fuel supply jet having a through bore which opens into the throat, said through bore comprising a bore portion defining a jet orifice, and a larger diameter portion on the side of said jet orifice remote from the throat; and means for supplying air to the through bore to form an airfuel mixture; wherein said fuel supply jet comprises two axially spaced parts, the radial outer surfaces of which cooperate in a fluid tight manner with adjacent wall portions of the opening in which the jet is located; and the means for supplying air includes radial passages in the fuel supply jet and an air supply passage defined in said body; said radial passages comprising at least two radial passages each of which opens in the radial outer surface of the fuel supply jet between the two axially spaced parts thereof, and which extend through the wall of the fuel supply jet to open at their other ends in the jet orifice, said air supply passage having one end in communication with a source of air and the other end opening into the space between the adjacent wall portions to communicate with said jet orifice via said radial passages, so that all the air fed through said air supply passage towards said other end is fed directly into the jet orifice via said radial passages to mix with the fuel within the jet orifice for creating turbulence in said jet for forming an air-fuel mixture therein.

2. A carburetter according to claim 1, wherein the end of the air supply passage in communication with a source of air includes an impact tube which necks down from its inlet end to a restricted passage.