Carburettors Operating Under A Constant Reduced Pressure

Abstract

A carburettor operating under a constant reduced pressure comprising a mixing chamber formed in the intake manifold between the main and an auxiliary throttle valve, and fed with air and fuel by an emulsifying chamber, the input of air in which as required for idling and reduced load conditions, is controlled by a valve controlled in its turn by a vacuum chamber which is selectively connected with the atmosphere and with the intake manifold so as to make said valve close the corresponding input whenever the rotary speed of the engine is above a predetermined value and the main throttle valve is simultaneously closed or substantially so or else whenever the temperature of the engine cooling medium sinks underneath a predetermined value.

Description

Our invention has for its object improvements in carburattors operating under a constant reduced pressure. Carburettors of such a type are generally provided with a main throughput adjusting flap controlled by the accelerator pedal and with a transversely shifted auxiliary flap or piston, adapted to move under the action of the reduced pressure prevailing in the mixing chamber located between two closing members whereby a substantial constant reduced pressure is obtained in said mixing chamber. The auxiliary flap or piston is connected in this case with a needle valve adapted to move inside the opening of a jet so as to release the latter to an extent varying with the position of the needle valve and consequently of the auxiliary flap or piston. The jet and its needle valve are fitted inside an emulsion-forming chamber, connected on the one hand with the mixing chamber through suitable channels and on the other hand with the external atmosphere through one or more ports which may be opened and closed to a varying extent in accordance with the actual operative conditions of the engine, in order to obtain a predetermined reduction in pressure in the emulsion-forming chamber and thereby in the amount of fuel to be injected.

Such carburettors are generally satisfactory within a large range of operative conditions for the engines incorporating said carburettors. There are however two operative conditions for which problems arise as concerns both pollution of the atmosphere by the exhaust gases and acceleration. In fact, when idling, the engine produces unburnt residuary components and carbonic gas to an increasing extent by reason of the air flowing then at a slow rate and the atomization of the fuel being poor. Furthermore, when the engine decelerates, the main flap is closed while the engine is still running at a high speed and therefore difficulties arise which are ascribable to the considerable reduction in pressure prevailing in the admission manifold. It has already been attempted to remove this last drawback by cutting off completely or partly the admission of fuel during the deceleration stage. It has been found however, in the case of certain engines that the contents of unburnt components and carbonic gas do not then decrease in the exhaust gases and that in contradistinction, they increase and, generally speaking, greater difficulties arise in such a case when accelerating after such a deceleration stage.

Our invention has for its object to cut out such difficulties and provides the following improvements in the carburettors of the type referred to:

the air input port or ports of the emulsion-forming chamber are provided with a cross-sectional passage area such that all or almost all the air required for burning passes through said ports when the engine is not subjected to any load and runs under idling conditions and possibly under initiating acceleration conditions, the auxiliary flap being then completely closed; on the other hand the emulsion-forming chamber is connected with the mixing chamber through one or more horizontal smalldiameter mixture-conveying tubes starting from the bottom of the emulsion-forming chamber and opening into an emulsion-forming tube of a larger diameter opening in its turn into the mixing chamber while a passageway for air is provided, starting from the upper end of the emulsion-forming chamber and opening into the emulsion-forming tube in a direction oblique with reference to the fuel-conveying tubes, which latter are provided in registry therewith with radial bores furthering the formation of the emulsion;

a conical valve adapted to move axially of one of the air input ports in the emulsion chamber is connected with a control member, the position of which depends on the rotary speed of the engine and on the position of the main flap whereby the cross-sectional area of said port is reduced and consequently the mixture becomes richer when the main flap is closed or substantially so and the engine revolves at a speed above a predetermined value;

as a further development of the invention, the last-mentioned conical valve is connected with the diaphragm of a casing or vacuum box the inside of which is subjected to a reduced pressure and is connected through a pipe with the engine input manifold on the downstream side of the main flap through the agency of a three-way electrically controlled valve controlled by a tachometric relay and a switch controlled by the main flap so as to connect the inside of the casing subjected to a reduced pressure with the admission manifold when the main flap is closed or substantially so and the rotary speed of the engine is above a predetermined value, said connection being cut off when the main flap opens or when the engine speed drops underneath said value, so as to set the inside of the casing under atmospheric pressure through the third way of the electromagnetically controlled valve;

the electromagnetically controlled valve may also be actuated by a thermosensitive switch operated by the temperature of the engine-cooling fluid, so as to connect the inside of the casing subjected to a reduced pressure with the admission manifold when said temperature lies under a predetermined value whereby the conical valve reduces the cross-sectional area of the port controlled by it and consequently ensures the production of a richer carburetted mixture;

a conical member engaging one of the air input ports in the emulsion chamber may also be connected with a hand-operable member adapted to close said port when the engine is to be started under low temperature conditions.

By way of example and with a view to further the understanding of the invention, the single figure of the accompanying drawing is a diagrammatic cross-section of an embodiment of our improved carburettor.

In said figure, it is apparent that the body 1 of the carburettor is provided with the main throughput-controlling flap 2, the pivot 2a of which is connected through suitable means which are not illustrated with the accelerator pedal. The extensions 3 of the body 1 is provided with an auxiliary flap 4 the transversely shifted pivot 4a of which is connected with the needle valve 5 through means which are not illustrated. The mixing chamber 1d extends between the two flaps 2 and 4. The float chamber 1c is fed with gasoline through the connection 21 secured to the cover, incorporated with the extension 3, by the screw 20. The float 23 defines the level through the agency of the needle valve 24 cooperating with the connection 22 opening into the connection 21.

The emulsion-forming chamber 1e communicates with the mixing chamber 1d through the emulsion-forming tube 9 into which the air-feeding channel 8 and the gasoline-feeding duct or ducts 10 fed by the emulsion-forming chamber open. The air feeding channel 8 is directed obliquely with reference to the cooperating end of the duct or ducts 10 which are provided with radial bores 10a adapted to perfect the emulsion. The emulsion-forming tube 9 opens into the venturi-shaped section 1a of the mixing chamber 1d. The gasoline enters the emulsion-forming chamber 1e through the jet 7 the opening port of which is controlled by the conical end 5a of the needle valve 5 in accordance with the position assumed by the auxiliary flap 4. The needle valve 5 slides inside a guiding member 6.

The amount of fuel passing out of the jet 7 depends furthermore on the reduced pressure prevailing in the emulsion-forming chamber 1e, which pressure depends in its turn on the constant cross-sectional passageway area afforded by the channel 8 and on the cross-sectional passageway area afforded by the air input ports of the emulsion-forming chamber 1e. Said chamber 1e may be provided with a plurality of air input ports controlled by suitably actuated flaps so as to make the mixture richer upon acceleration and power for other circumstances, so as to prevent the presence of unburnt components and of carbonic gas in the exhaust gases or a modification in the input of air with modifications of the atmospheric pressure and the like.

In the case illustrated, two correcting flaps are provided of which that referenced as 16 is carried by a diaphragm 17 and is adapted to control an auxiliary air input through the channel 1f so as to open the latter whenever the pressure in the admission manifold sinks underneath a predetermined value. Said pressure is tapped off a point located with reference to the flap 2 in a manner such that the reduction in pressure can act only if the flap 2 begins opening. This causes the mixture to become poorer whereby the consumption of fuel is reduced under partial loads. To this end, the chamber 19 extending between the diaphragm 17 and the cover 15 is connected with the admission manifold the reduced pressure in which shifts the diaphragm against the pressure exerted by the spring 18.

The conical valve 12 cooperates with the opening 11a in the washer 11 urged against its seat by the spring 37. Said frustoconical valve 12 is rigidly secured to the barometric bellows 14 by the screw 13, said bellows being secured furthermore to the rod 14a projecting out of a vacuum box 25 screwed onto the body 1 by the nut 26 fitted over the elastic washers 27. Air being admitted into the emulsion-forming chamber 1e through the opening 1b, the vacuum box 25 may be shifted by the starter rod 28 while its output pipe 29 is connected with the admission manifold through the electromagnetically controlled three-way valve 30, the output 32 of which opens into said manifold and the output 31 of which opens into the atmosphere.

The electromagnetically controlled valve 30 is controlled by a tachometric relay 35 energized by a switch 36 provided underneath the pivot 2a of the main flap 2 and also independently thereof by a heat sensitive switch 34 controlled by the temperature of the cooling fluid of the engine.

It should be remarked that the input port or ports of the emulsion-forming chamber 1e are designed in a manner such that when the engine is idling, the fuel-burning air passes entirely or substantially so through said ports, the auxiliary flap 4 being closed so that the emulsified carburetted mixture passes out of the emulsion-forming tube 9 under excellent fuel-atomizing conditions even if the air input is very small. It should also be remarked that the conical valve 12 forms a means for very simply adjusting the fuel contents in the mixture through its conventional connection with the barometric bellows 14, so as to be shifted bodily therewith under the influence of the reduced pressure in the admission manifold. The corrections thus obtained depend on the one hand on the temperature of the fluid cooling the engine upon opening of the communication between the connections 29 and 32 as provided by heat-controlled switch 34 when the temperature of the cooling fluid sinks underneath a predetermined value. When such a communication is obtained, vacuum is established in the vacuum box 25 whereupon the conical valve 12 is drawn downwardly. Consequently, the cross-sectional operative area of the port 11 a decreases, which results in an increase in the reduction in pressure in the emulsion-forming chamber 1e and in an increased richness of the fuel and air mixture. On the other hand, the electromagnetically controlled valve 30 is energized by the tachometric relay 35 controlled by the switch 36. This has for its result a communication between the connections 29 and 32 when the engine is decelerated while the main flap 2 is closed and the engine continues running at a high speed. The reduced pressure acts on the vacuum box 25 and there is obtained a further downward shifting of the conical valve 12 and consequently an increased richness for the mixture. It should be remarked that this modus operandi leads to a substantial reduction in the contents of unburnt residuals and carbonic gas in the exhaust gases, although such a modus operandi is in strict contradiction with all prior practice attempting to reach a similar result during a deceleration stage. The provision of a nozzle in the connection 32 allows furthermore an adjustment of the more or less considerable delay in the operation of the mixture-enriching means.

It should be remarked that the arrangement described which is highly advantageous in certain cases may not be suitable in other cases and in fact it may be reversed so as to reduce the richness of the mixture during deceleration without widening thereby the scope of the invention as defined in the accompanying claims.

The elastic fitting of the vacuum box 25 on the body 1 through the agency of the elastic washers 27 and the control of said vacuum box by a starter rod 28 ensures the formation of a richer mixture for starting under cold temperature conditions conditions in a particularly simple manner since the drawing of the starter rod 28 shifts the vacuum box system bodily downward so as to close the port 11a.

Claims

What I claim is:

1. In a carburettor fitted in the intake manifold of an internal combustion engine, operating under constant reduced pressure conditions, and comprising a main accelerator controlled throttle-valve in the manifold, an auxiliary throttling member subjected to the reduced pressure in the manifold on the upstream side of the main throttle valve and defining with the latter a fuel-and-air mixing chamber, an emulsion-forming chamber, a fuel-fed jet opening into said emulsion-forming chamber and a needle valve controlling said jet and controlled by the auxiliary throttling member, the provision of at least one input port feeding air into the emulsion-forming chamber in amounts corresponding substantially to the complete burning of the fuel under idling and reduced load conditions, for which the auxiliary member is closed and of a connection between the emulsion-forming chamber and the mixing chamber including at least one horizontal small diameter tube provided with radial perforations, starting from the bottom of the emulsion-forming chamber, a large-diameter channel opening into the mixing chamber and fed by said small diameter tube, and an air feeding channel starting from the upper end of the emulsion-forming chamber and opening obliquely into said large diameter channel above the end of the small-diameter tube feeding the large diameter channel.

2. A carburettor as claimed in claim 1, comprising a conical valve controlling one of the input ports and a member controlled by the rotary speed of the engine and by the position assumed by the main throttle valve and controlling said conical valve to thereby modify the cross-sectional area of the port and consequently the richness of the fuel-and-air mixture when the main throttle valve is substantially closed and the rotary speed of the engine is above a predetermined value.

3. A carburettor as claimed in claim 1, comprising a conical valve controlling one of the input ports, a vacuum chamber including a diaphragm controlling said conical valve, a three-way electrically controlled valve adapted to connect selectively the inside of the vacuum chamber with the external atmosphere and with a point of the engine intake manifold on the downstream side of the main throttle valve, a circuit energizing said valve, a tachometric relay controlled by the rotary speed of the engine, and a switch inserted in series with said relay in the valve energizing circuit to make said valve connect the vacuum box with the manifold whenever the main throttle valve is substantially closed and simultaneously the rotary speed of the engine is above a predetermined value, and connect the vacuum box with the atmosphere in all other cases.

4. A carburettor as claimed in claim 1, comprising a conical valve controlling one of the input ports, a vacuum chamber including a diaphragm controlling said conical valve, a three-way electrically controlled valve adapted to connect selectively the inside of the vacuum chamber with the external atmosphere and with a point of the engine intake manifold on the downstream side of the main throttle valve, a circuit energizing said valve, a tachometric relay controlled by the rotary speed of the engine, and a switch inserted in series with said relay in the valve energizing circuit to make the valve connect the vacuum box with the manifold whenever the main throttle valve is substantially closed and simultaneously the rotary speed of the engine is above a predetermined value, and connect the vacuum box with the atmosphere in all other cases, and a further switch controlled by the temperature of the engine-cooling medium and controlling the valve energizing circuit to make the valve connect the inside of the vacuum box with the manifold whenever said temperature sinks underneath a predetermined value.

5. a carburettor as claimed in claim 1, comprising a conical valve controlling one of the input ports, a vacuum chamber including a diaphragm controlling said conical valve, a three-way electrically controlled valve adapted to connect selectively the inside of the vacuum chamber with the external atmosphere and with a point of the engine intake manifold on the downstream side of the main throttle valve, a circuit energizing said valve, a tachometric relay controlled by the rotary speed of the engine, a switch inserted in series with said relay in the valve energizing circuit to make the valve connect the vacuum box with the manifold whenever the main throttle valve is substantially closed and simultaneously the rotary speed of the engine is above a predetermined value, and connect the vacuum box with the atmosphere in all other cases, a further switch controlled by the temperature of the engine-cooling medium and controlling the valve energizing circuit to make the valve connect the vacuum box with the manifold whenever said temperature sinks underneath a predetermined value and hand-operable means controlling the conical valve to make the latter close the corresponding port when starting the engine under low temperature conditions.

6. A carburettor as claimed in claim 1, comprising a conical valve controlling one of the input ports and hand-operable means controlling the conical valve to make the latter close the corresponding port when starting the engine under low temperature conditions.