US3456929A

US3456929A - Carburetters

Info

Publication number: US3456929A
Application number: US658778A
Authority: US
Inventors: Geoffrey Lloyd Lawrence
Original assignee: Zenith Carburetter Co Ltd
Current assignee: Zenith Carburetter Co Ltd
Priority date: 1966-08-12
Filing date: 1967-08-07
Publication date: 1969-07-22
Anticipated expiration: 1986-07-22
Also published as: DE1576646A1; DE1973194U; ES344321A1

Description

July 22, 1969 G. L. LAWRENCE 3,456,929

. CARBURETTERS Filed Aug. 7, 1967 2 Sheets-Sheet l Figi.

July 22 1969 G. l.. LAWRENCE y 3,456,929

CARBURETTERS Filed Aug. 7, 1967 v 2 Sheets-Sheet 2 FLgZ i I0 22 36 I2 l] figg-l 1'1"' I United States Patent O 3,456,929 CARBURETTERS Geoffrey Lloyd lLawr-enee, Stanmore, England, assigner to The Zenith Carhnretter Company Limited, Honeypot Lane, Stanmore, lEngland Filed Aug. 7, 1967, Ser. No. 658,778 Ciaims priority, application Great Britain, Aug. 12, 1966, 36,237/66; Apr. 20, 1967, 18,270/57 int. Ci. FtiZm 23/04 US. Cl. 261--44 6 Claims ABSTRACT F THE DESCLQSURE To enable the air valves of air valve carburetters to be set to provide a consistent lift of the air valve for a given total weight of air ow, there is provided, in a 'bypass passage past the air valve, an adjustable valve so that the total leakage, i.e. that due to manufacturing tolerances and that through the adjustable valve, can be set to a standard. Separate control of the total leakage flow to a limited extent may be provided for idling adjustment.

This invention relates to carburetters of the air valve type in which the air valve is a slide valve movable transversely across the mixture passage in the carburetter body so as to vary the cross-sectional area of a gap between the inner end of the said slide valve and a fixed surface in the said passage, which gap is hereinafter referred to as the throat, the slide valve being movable to vary the said area by differential air pressure acting on the two sides of a diaphragm or piston coupled to the slide valve.

The slide valve passes through an opening in the wall of the mixture passage on the side of the latter opposite to the fixed surface, into a housing which is divided into two chambers by the diaphragm or piston on which the differential air pressure acts, the rst chamber on the side of the diaphragm or piston nearest to the mixture passage being connected to the ambient atmosphere or to a source of sub-atmospheric pressure. The second chamber, on the other side of the piston or diaphragm is in communication With the mixing chamber of the carburetter, which is the part of the mixture passage downstream of the air valve and upstream of a throttle valve in the mixture passage, and a spring acts on the slide valve to urge it towards the fixed surface in the mixture passage. The throat is considered as being situated downstream of the air valve, since the depression created by the air valve prevails in the throat. The pressure prevailing in the first chamber thus tends to lift the slide valve against the spring, the degree of lifting increasing as the air ow inspired `by the engine through the mixing chamber increases.

For a number of reasons, it is desirable to be able to alter the effective flow capacity of the passage means into the mixing chamber to some extent independently of the movement of the slide valve and the general object of the present invention is to provide for such alterations to be carried out.

Whilst the iiow of air past the slide valve will take place mainly through the gap between the said slide valve and the fixed surface some leakage flow will take place around the sides of the said valve and through clearance between the said slide valve and the opening in the body through which it extends into the chamber on the side of the diaphragm nearest to the mixture passage, and in carburetters of the same construction and size the leakage tiow will Vary from one to another due to working tolerances in the manufacture of the parts and resulting differences in the clearance.

3,456,929 Patented July 22, 1969 ice Theoretically, the setting of the throttle valves of a number of nominally identical carburetters to cause an identical weight of air to iiow through all of them for idling purposes should result in equal flow rates of air through the gap between the slide valve and the fixed surface. In practice, due to variations in the leak path, the air valve adjusts itself according to the leakage and takes up a position which varies from one carburetter to another. As a result, the quantity of fuel delivered into the air stream, as will be described hereinafter, depends on the actual position of the slide valve, and the idling mixture will vary from one carburetter to another.

It has been found that provision for small adjustments in the size of the passage means providing air flow other than through the gap between the slide valve and the fixed surface may be advantageous in the setting of the carburetter for idling.

The movement of the slide valve controls the position of a needle in a jet orifice through which fuel is admitted to the gap between the said slide valve and the fixed surface, so that the quantity of fuel drawn into the mixture passage, for a given depression acting on the jet, varies with the position of the said slide valve.

To avoid or reduce to a minimum the inclusion in the exhaust emission of an internal combustion engine of toxic elements such as carbon monoxide and unburnt hydrocarbons it is essential that the fuel/air ratio of the mixture supplied to the engine cylinders shall be closely controlled, and the present invention, by enabling a constant air valve position for a given weight of total air flow through the carburetter to be obtained, makes readily possible the achievement of a correct ratio.

According to the present invention, in an air valve carburetter for internal combustion engines comprising an induction passage, a housing adjacent to said induction passage and divided into a first chamber and a second chamber by a movable wall, a slide valve connected to said movable wall and slidably movable with clearance through an opening in the wall of the induction passage, said opening connecting said induction passage and said first chamber, the said slide valve co-operating with a part of the wall of the induction passage to provide a variable gap, biasing means acting on said slide valve to urge it towards said -wall part, a mixing chamber formed in the induction passage between the slide valve and a throttle valve downstream of said slide valve, the said second chamber being connected to the mixing chamber whereas the said first chamber is arranged to receive air at a pressure greater than that existing in the mixing chamber, air ow into the mixing chamber additional to ow through the said gap is adjustable by means of at least one valve in passage means through which a part of said additional ow passes.

Two valves may be provided, each of which is adapted to alter the ow capacity of said passage means, and the said passage two means may comprise two separate passages controlled respectively by one and the other of the said two valves. One of the two valves may provide for a relatively large range of adjustment whereas the other of said valves provides for a relatively small range of adjustment.

Means may be provided for sealing one of the said valves so that it cannot be adjusted except by removal of the seal, and the said sealing means may be provided for the valve providing the larger range of adjustment.

The said passage means may provide a connection between the mixing chamber of the carburetter and the said first chamber, the valve in said passage being adjustable to a fixed setting.

The invention is hereinafter described with reference to the accompanying drawings, in which:

FIGURE 1 is a sectional elevation of one form of air valve carburetter embodying the invention; and

FIGURE 2 is a section of the carburetter taken on the line 2--2 of FIGURE 1.

In the illustrated embodiment of the invention there is shown two valves both of which are independently operable to vary the flow of air into the mixing chamber of the carburetter, but it will be understood that one of these valves may be omitted if adjustment of the air flow for one of the purposes hereinbefore set forth is not required.

Referring to the drawings, the carburetter comprises a body through which extends a mixture passage 11 of circular cross section. An air valve in the form of a slide valve 12, slidable transversely of the passage 11, extends through an opening 13 at one side of the mixture passage, the said slide valve 12 having a flat surface 14 which co-operates with a flat fixed surface 15 in the mixture passage, lying on a chord to the circumference of the said passage, to provide a throat 16 the area of which varies with the position of the slide valve 12. The surface 15 is formed on a bridge 17 having sloping side surfaces at 18 and 19 so that the area of the throat decreases and increases progressively on opposite sides of the surface 15.

A buttery throttle valve 21 is provided in the mixture passage 11 downstream of the slide valve 12, the space 22 between the said throttle valve 21 and slide valve 12 forming a mixing chamber.

The slide valve 12 extends into a housing, formed partly in the carburetter body 10 and partly by a separate cap member 23. A flexible annular diaphragm 24, clamped at its inner edge to the slide valve 12 and at its outer edge between the carburetter body 10 and the cap member 23, divides the housing into two

chambers

25 and 26, the chamber 25, on the side of the diaphragm 24 remote from the mixture passage 11, being connected to the mixing chamber 22 by an opening 27 in the slide valve 12. The chamber 26 is connected at 28 to the atmosphere. The carburetter is normally mounted with the housing uppermost, so that the weight of the slide valve 12 tends to urge it towards the surface 15, and a light spring 29 is provided to further bias it in the same direction. A dashpot device 31 is provided to damp the movements of the slide valve 12. The diaphragm 24 may be replaced by a piston sliding in a cylinder.

A fuel supply chamber 32 is provided below the bridge 17, in which liquid fuel supplied by a pump from a fuel tank in the conventional manner is maintained at a desired level by an inlet valve (not shown) controlled by a pivoted oat 33. A fuel jet 34 mounted in the bridge 17 enables fuel from the chamber 32 to be drawn'into the mixture passage 11 by air flow across the said jet 34, a tapered needle 35 carried by the slide valve 12 being provided to vary the effective area of the jet in accordance with the position of the said slide valve.

Th carburetter as so far described is substantially of conventional form, and it will be understood that, when air is being drawn through the mixture passage by the suction in the cylinders of an internal combustion engine to which the carburetter is connected, depression created in the mixing chamber will also act in the chamber 2S, so that atmospheric air pressure acting in the chamber 26 will tend to lift the slide valve 12 and increase the area of the throat 16, thus varying the air flow to keep the depression substantially constant. Since the depression will tend to increase as the throttle valve opens, the slide valve 12 will lift as the throttle valve opens, to increase the ow of air into the mixing chamber, and at the same time increase the flow of fuel from the jet 34.

It has already been stated that some leakage flow of air into the mixing chamber 22 will take place through clearance around the sides of the slide valve 12 (at 36 in FIGURE 2), and through the opening 13, and that such leakage flow will aect the flow rate of air through the throat 16 when a given weight of air flows through the carburetter. Since the quantity of fuel delivered into 4. the air stream depends on the lift of the slide valve, the idling mixture will vary from one to another of nominally identical carburetters.

To enable a standard flow rate to be achieved, it is necessary to provide for the adjustment of the total flow of air additional to that which passes through the throat, and to enable such adjustment to be provided, a passage is formed in the carburetter body 10 connecting the mixing chamber 22 to the chamber 26, and a valve is provided to control the air flow through this passage. Referring to FIGURE 1, a bore 37 is formed, extending from the exterior of the carburetter body into the mixing chamber 22, the outer part of the bore 37 being screw-threaded at 38, and a step being formed at 39 adjacent the inner end of the bore. A counterbore 41 is provided at the outer end of the screwthreaded part 38. A second bore 42 extends from the chamber 26 so as to intersect the bore 37 between the screwthreaded part 38 and the step 39. A screw-threaded plug 43 engaging the screw-threaded part 38 of the bore 37 has integral with it a tapered needle 44 extending past the step 39 so that, by screwing the plug 43 in or out, the effective area of the passage formed by the

hores

37 and 42 can be varied. The plug 43 has a screw-driver slot 45 to enable it to be manipulated, and is of such a length that it lies wholly within the body 10, enabling the bore 37 to be sealed by a sealing disc 46 pressed into the counterbore 41.

Since the chamber 26 is in communication with the atmosphere, the passage constituted by the

bores

37 and 42 is, in effect, in parallel with the leakage paths, and adjustment of the valve needle 44 will vary the total leakage flow and enable all of a number of nominally identical carburetters to be set to provide a standard air flow rate through the throats thereof.

It will be understood that the valve controlled passage, instead of leading from the chamber 26 into the mixing chamber 22 may lead from any other point at which air at or near atmospheric pressure is available, and the valve may be of any suitable type. A needle valve is preferred since it is capable of fine adjustment.

In order to compensate for a relatively wide range of differences of air leakage in the carburetters, the needle valve 44 is provided with a relatively long tapered needle.

It is desirable that, once the needle valve 44 has been set, it shall not be disturbed, and consequently, if adjustment of air flow past the slide valve 12 is required for purposes other than to set the carburetter to a standard by compensating for differences of leakage due to varying clearances, separate provision for such other purposes should be provided.

Referring to FIGURE 2 of the drawings, a passage 47 is provided in the carburetter body 1t) alongside the mixture passage 11, leading from the end of the body at which the air enters. The other end of the passage 47 is closed, and it is intersected adjacent the closed end by a transverse passage 48 leading from the exterior of the body 10 into the mixing chamber 22. The transverse passage 48 is screwthreaded at its outer end, at 49, and is stepped at 51 between its inner end and its intersection with the passage 47. A needle valve to control the How of air in the

passages

47, 48 is provided by a screw plug 52 carrying a tapered needle 53 at its inner end to co-operate with the step 51. The screw plug 52 is screwed into the transverse passage 48 and is provided with a locknut 52a to enable it to be locked in any position to which it is set. The tapered needle 53 has a relatively short tapered portion and a relatively small included angle, so that the range of adjustment provided is considerably less than that provided by the needle valve 44, and is extended, at its smaller end, by a cylindrical portion 54 of a length such that it extends past the step 51 so long as the screw thread on the plug 52 engages with the screw thread in the passage 48, thus ensuring that the effective area of the passage cannot exceed a predetermined maximum. Thus, by adjusting the plug 52 a small change in the air flow through the passage 48 and consequently in the total air ow past the air valve piston or slide 12 can be made without altering the position of the plug 43, to provide fine adjustment of the fuel/air mixture at idling speeds of the engine. Such variation is required to compensate for engine stiffness and other characteristics. The range of adjustment is limited to ensure that adjustment of the plug 52 cannot alter the fuel/air ratio suiciently to increase the content of toxic elements such as carbon dioxide and hydrocarbons in the exhaust emission.

I claim:

1. In an air valve carburetter for internal combustion engines comprising an induction passage, a housing adjacent to said induction passage and divided into a first chamber and a second chamber by a movable wall, a slide valve connected to said movable wall and slidably movable with clearance through an opening in the wall of the induction passage, said opening connecting said induction passage and said first chamber, said slide valve co-operating with a part of the wall of the induction passage to provide a variable gap, biasing means acting on said slide valve to urge it towards said wall part, a mixing chamber formed in the induction passage between the slide valve and a throttle valve downstream of said slide valve, said second chamber being connected to the mixing chamber whereas said first chamber is arranged to receive air at a pressure greater than that existing in the mixing chamber, the improvement comprising passage means for the ow of air into the mixing chamber additional to the flow through said gap, a first valve in said passage means adjustable to vary the air ow in said passage means over a relatively large range and a second valve in said passage means adjustable to vary the air flow in said passage means over a considerably smaller range, wherein air flow into the mixing chamber additional to fiow through said gap is adjustable by means of at least one valve in passage means through which a part of said additional flow passes.

2. An air valve carburetter according to claim 1 wherein the passage means comprises two separate passages, the first valve being provided in one of said passages and the second valve being provided in the other of said passages.

3. An air valve carburetter according to claim 1, wherein sealing means are provided for said first valve, having the larger range of adjustment, so that it cannot be adjusted except by removal of the seal.

4. An air valve carburetter according to claim 1 wherein said first and second valves are needle valves.

5. An air valve carburetter according to claim 1 wherein said passage means provide a connection between the mixing chamber of the carburetter and the first chamber, said first valve, having the larger range of adjustment, being in said passage and adjustable to a fixed setting.

6. An air valve carburetter according to claim 5 wherein said first valve is a needle valve carried by a screw plug mounted in a bore extending to the exterior of the carbureter.

References Cited UNITED STATES PATENTS 3,078,079 2/ 1963 Mick.

3,147,320 9/ 1964 Tubb 261-44 X 3,198,498 8/ 1965 Mennesson.

3,243,167 3/1966 Winkler 261-44 3,321,195 5/1967 Korte.

3,342,463 9/ 1967 Date et al 261--44 3,351,327 11/1967 Simonet et al.

. FOREIGN PATENTS 1,429,365 1/ 1966 France.

TIM R. MILES, Primary Examiner U.S. Cl. X.R.