Constant Negative-pressure Carburettors

Abstract

Constant negative-pressure carburettor to minimize exhaust pollution of internal combustion engines comprising a main conduit having a main valve and an auxiliary conduit having a main valve actuated from the exterior and an additional valve, the proportional fuel flowing between the two valves, an additional complementary valve being provided so as to cap the main conduit and the auxiliary conduit, the valve being connected to the fuel-proportioning needle.

Description

The invention relates to improvements to constant negative-pressure carburettors. Carburettors of the aforementioned kind usually comprise a main valve for adjusting the flow rate and actuated by the accelerator pedal, and an eccentric flap or piston, the additional valve moving under the action of the negative pressure in the mixture chamber disposed between the two valve elements, thus producing a substantially constant negative pressure in the mixture chamber. The additional flap or piston is then connected to a needle moving in the orifice of a jet and uncovering it to a varying extent, depending on the position of the needle and consequently of the additional element. The jet and needle are disposed in a fuel-air mixture chamber and are connected to the mixture chamber by suitable passages and may also be connected to air by one or more orifices which can be opened or closed to an extent varying with the operating conditions of the engine so as to obtain a certain negative pressure in the mixture chamber which, together with the position of the needle in the jet, determines the proportion of fuel.

The aforementioned kind of carburettor is usually satisfactory over a wide operating range of an engine equipped therewith, but two operating conditions still cause problems with regard to air pollution by exhaust gases and engine pick-up. During idling and starting, i.e. at low speeds and loads, the content of unburned fuel and carbon monoxide in the exhaust gases tends to increase because the air speed is low and ; the fuel atomization is incomplete. Pick-ups are defective for the same reason, so that it is impossible to have low contents of carbon monoxide in the exhaust gases simultaneously with a smooth start. Either the adjustment is suitable for a perfect start, in which case the carbon monoxide content during idling is excessively high, or the carbon monoxide content during idling is correct but the start is defective. Furthermore, when the engine decelerates, the main flap is closed and the engine is still rotating at high speed, resulting in difficulties because of the very large negative pressure in the inlet pipe. Attempts have been made to obviate the last-mentioned disadvantage by totally or partly cutting off the fuel supply during deceleration, but it has been found that in some engines, the content of unburned fuel and carbon monoxide in the exhaust gases increases instead of decreasing, and more general difficulties have also been encountered in starting up the engine after deceleration. To obviate these disadvantages in a manner similar to that used in venturi carburettors, attempts have been made to obtain good atomization under all conditions by providing a relatively high negative pressure between the main flap and the additional flap, but this clearly reduces the maximum power obtainable with an engine provided with a carburettor of the aforementioned kind.

The invention, which aims to obviate the aforementioned difficulties, relates to improvements to constant negative-pressure carburettors characterized in that the carburettor comprises a large-diameter main conduit and a small-diameter auxiliary conduit, each conduit comprising a main valve, the main valve of the auxiliary conduit being directly actuated by an external control whereas the main valve of the main conduit is indirectly actuated by a means sensitive to the negative pressure upstream of the main valve, an additional, eccentric valve being provided in the auxiliary conduit upstream of the main valve and moved into its closing position by a return element, the passage or the passages towards the fuel-air chamber terminating between the main and additional valves of the auxiliary conduit, the eccentric, additional valve connected to the fuel-proportioning needle being disposed upstream of the main and auxiliary conduits and capping them.

The main feature of the invention can be developed in the following ways

a. The return elements for the additional valve in the auxiliary conduit and for the additional valve connected to the proportioning needle are calibrated differently, so as to produce a negative pressure upstream of the main valve of the auxiliary conduit which is greater than the negative pressure upstream of the main valve of the main conduit.

b. The return element for the additional valve in the auxiliary conduit comprises manual and automatic adjusting means for varying the calibration of the return element so as to vary the idling richness, and for adapting the richness to the atmospheric pressure and ambient temperature.

c. The return element for the additional valve in the auxiliary conduit is connected to an adjusting means comprising a rod, one end of which is articulated to a lever secured to the pivot of the additional valve connected to the fuel-proportioning needle, the other end of the rod being connected to the movement of a lever secured to the pivot of the main valve in the main conduit, the movements of the aforementioned ends being connected so that when the main and additional valves move in parallel, the seat of the return element on the rod does not vary, whereas when the main valve moves in advance of the additional valve, the seat moves and so varies the calibration of the return element so as to enrich the mixture.

d. A calibrated valve is provided in the additional valve connected to the proportioning needle so as to admit air through the additional valve when the latter is completely closed.

e. The downstream passage of the main valve of the auxiliary conduit terminates in the neck of a venturi tube disposed downstream of the main valve of the main conduit.

f. The downstream passage of the main valve of the auxiliary conduit is divided into a number of channels terminating in the inlet pipe near cylinder distribution means.

g. The upstream passage of the main valve of the auxiliary conduit terminates axially in a cylindrical cavity having tangentially disposed outlet ducts, the cavity forming a housing for a centrifugal wheel having an axial inlet for fuel-air mixture coming from the auxiliary conduit and a radial outlet towards the tangential outlets of the cylindrical cavity.

h. Driving means are provided for driving the centrifugal wheel in rotation.

i. Undirectional connecting means are provided between the main valve of the auxiliary conduit and the main valve of the main conduit so as to close the main valve of the main conduit with the closure of the main valve in the auxiliary conduit, the closure of the main valve in the main conduit being more rapid than the closure of the main valve in the auxiliary conduit.

The following description will be more easily understood with reference to the accompanying drawings, which are given by way of example and in which:

FIG. 1 is a view in section of a constant negative-pressure carburettor according to the invention.

FIG. 2 shows an elevation of a constant negative-pressure carburettor according to the invention, showing the means for actuating the various elements thereof,

FIG. 3 is a diagrammatic cross-section of a detail of another embodiment of the carburettor, and

FIG. 4 shows a cross-section along line 3--3 of FIG. 3.

As FIGS. 1 and 2 show, the carburettor is made up of three main elements, a central element 1 comprising the main conduit 1b, the auxiliary conduit 1a and the constant-level tank 1c; an upper element 2 formed with a passage 2a common to the main conduit 1b and the auxiliary conduit 1a and the lid 2b of the constant-level tank 1c. Finally, a bottom element 3 is provided for securing to the engine inlet pipe. A main valve 4b pivotally mounted on a shaft 5b in the main conduit 1b is connected by a rod 6b to a capsule 33 comprising a diaphragm (not shown) bounding two separate chambers, the outer chamber being connected by pipe 32 to the space upstream of valve 4b. A main valve 4a is pivotally mounted on a shaft 5a in the auxiliary conduit 1a and is connected by a rod 6a e.g. to the accelerator pedal. A unidirectional link 6c is provided between the main valve 4a of the auxiliary conduit and the main valve 4b of the main conduit. Fuel is fed to the auxiliary conduit 1a only through a pipe 20 having apertures 20a for improving the mixture. The fuel is drawn into a mixture chamber 1d connected to the constant-level tank by a jet 19 having a calibrated orifice 19a. A constant level of fuel is maintained in tank 1c by a float 18 controlling a needle valve 17 disposed in a needle-valve holder 16. If required, chamber 1d can have an air inlet 22 connected to a duct whose input is controlled by means adapted to regulate the amount of air entering the mixture chamber in dependence upon the various engine operating parameters. The aforementioned regulation of the air arriving through apertures 20a in connection with the movement of needle 11 and consequently of its conical head 11a in orifice 19a of jet 19 determines the mixture of the fuel with air. Needle 11 is slidably mounted in sealing-tight manner in a bushing 21 fitted into the lid 2b of the constant-level tank. The fuel arrives through a connecting pipe 15 secured by a screw 14 to cover 2b. The motion of needle 11 is controlled by an additional flap 7 pivotally mounted on an eccentric shaft 8, the upper element of needle 11 being connected to valve 7 via a rod 10 of a crank arm 9 and rod 8a. Valve 7 is moved into its closure position by a return means, so that valve 7 opens to an extent depending on the increase in the air flow through the carburettor, thus producing a corresponding movement of needle 11 and its conical head 11a into the orifice 19a of jet 19. An additional valve 12 is also mounted on shaft 13, which is eccentrically mounted in the input of auxiliary member 1a. Valve 12 is moved into its closure position by return means. In the example shown in FIGS. 1 and 2, the auxiliary member 1a is prolonged by a duct 3b terminating in the neck of venturi tube 26 disposed in pipe 3a upstream of valve 4b. Consequently, the fuel-air mixture leaving tube 20 is conveyed in the stream of gas downstream of the main valves 4a and 4b and is also accelerated in the venturi tube 26. Consequently, excellent atomization is obtained under all operating conditions, thus ensuring excellent operation from idling up to full power. If an opening 22 is provided in the mixture chamber 1d, idling may still present a problem in that the additional valve 7 is in theory completely closed during idling and the idling air enters through opening 22. When it is desired to adjust the idling speed, it is found that the richness is not constant under all idling conditions. This is because, when air enters through aperture 22, the negative pressure increases with the speed of rotation, but since the air flow increases less quickly than the flow of fuel through jet 19, the fuel-air ratio varies with the idling rotation speed. In order to avoid this difficulty and to obtain a substantially constant negative pressure for all idling rotation speeds between 500 r.p.m. and nearly 1,000 r.p.m, a valve 23 is provided in an orifice 7a of the additional valve 7. Valve 23 is pressed upon its seat by a calibrated spring 24 secured to valve 7 e.g. by a rivet 25. Valve 23 is shaped so as to uncover an opening of varying size depending upon its position, so that an additional air supply travels through orifice 7a such that the richness of the mixture in the carburettor is substantially constant for all idling speeds between 500 r.p.m. and 1,000 r.p.m. As FIG. 2 shows, rod 6a, which is connected e.g. to the accelerator pedal of a passenger car, is directly connected to shaft 5a of main valve 4a in the auxiliary member by a lever 5c, rod 6a being extended by an element 6c ending in an elongated opening 6d and mounted on a spindle 5e secured to lever 5d which is secured to shaft 5b of the main valve 4b in the main conduit. Accordingly, when rod 6a moves to the right and tends to open the main valve 4a in the auxiliary conduit, element 6c has no effect on the main valve 4b in the main conduit. On the other hand, when rod 6a moves to the left and tends to close valve 4a, valve 4b is closed by the action of valve 4a. Consequently, the main valve 4a in the auxiliary conduit is directly controlled by the car driver both when opening and closing, whereas the main valve 4b in the main member is controlled by the driver only when closing, its opening being controlled by capsule 35 in dependence on the pressure upstream of the main valve 4b in the main conduit. Of course, a device for closing the main valve 4b can be provided in the main conduit so as to close valve 4b more rapidly than valve 4a by moving valve 4b through a larger angle, e.g. twice the closure angle of valve 4a.

The shaft 13 of the additional valve 12 for the auxiliary conduit comprises a lever 13b connected by a spring 29 to an adjusting screw 31 mounted in an element 30 having additional inlets (not shown) for adjusting the calibration of spring 29 with respect to atmospheric pressure and to the surrounding air temperature.

Screw 31 can be used for manually adjusting the calibration of spring 29 in order to obtain a desired richness during idling. Since the opening of the additional valve 12 with respect to the opening of the main valve 4a determines the negative pressure between the two valves, and since the negative pressure determines the flow rate of fuel through jet 19, any variation in the tension on spring 29 and consequently any variation in the opening of valve 12 can be used to influence the supply of fuel and consequently the richness of the mixture.

A carburettor of the aforementioned kind can be used for adjusting the richness over most of the engine utilization curve corresponding to the minimum emission of unburned fuel and carbon monoxide. During acceleration, however, the engine should be supplied with a mixture appropriate for maximum power. The enrichment should decrease in proportion as the engine operating conditions approach equilibrium. To this end, a kinematic connection is provided between the motion of the additional valve 7 and of the main valve 4b. The kinematic connection consists of a lever 8c secured to the shaft 8 of the additional valve 7, of a rod 27, one end 27a of which is articulated on lever 8c, whereas the other end of rod 27 can slide freely in an orifice in spindle 5e. Consequently, when the main valve 4b and the additional valve 7 move simultaneously and in parallel, the center of rod 27 does not move, because rod 27 pivots round point 27a, articulation 27a moving the same distance to the left as spindle 5e and the other end of rod 27 move to the right. On the other hand, during sudden acceleration the main valve 4b opens more rapidly than the additional valve 7, so that articulation 27a moves a smaller distance towards the left than the other end of rod 27 and spindle 5e move towards the right, and the center moves towards the right and thus tensions spring 28 connected via lever 13a to shaft 13 of the additional valve 12. Since an increase in the tension on the return elements for valve 12 tend to close it to a greater extent for a given negative pressure upstream of valve 4b, the richness of the mixture is increased since the negative pressure increases in the space between valve 4a and valve 12, the increase in richness disappearing in proportion as valve 7 catches up with valve 4b. The cases shown in FIGS. 1 and 2 describe an embodiment in which the mixture produced in auxiliary conduit 1a is mixed with the air travelling through main conduit 1b and subsequently reaches the engine inlet pipe and the cylinders. Alternatively, only the main conduit 1b may be connected to the engine inlet pipe, so that the inlet pipe is filled with air only. In the latter case, the downstream outlet of the main valve 4a of the auxiliary conduit 1a is subdivided into a number of ducts connected by pipes to the inlet pipe inlets in the cylinder head and opening immediately upstream of the cylinder distribution means, i.e. immediately upstream of the inlet valves. In order to ensure that the mixture leaving the auxiliary conduit 1a is uniformly distributed in the various ducts, a cylindrical cavity 35 is formed downstream of duct 3b. Cavity 35 has tangential outlets 35a, 35b, 35c, 35d in the case, for example, of a four-cylinder engine. In such cases, a centrifugal wheel 32 is disposed in the axis of cavity 33 and has an axial inlet facing duct 3b and radial outlets facing the periphery of cavity 35. Depending upon individual cases and assembly requirements, wheel 32 can be mounted so as to rotate freely under the effect of the stream of gas flowing through it, or can be driven in rotation e.g. by an electric motor 34. The last-mentioned feature ensures that the mixture is homogenized but that the distribution to ducts 35a, 35b, 35c and 35d is uniform, and also ensures that the pulsation of the inlet pipe is reduced and does not reach the valve in the auxiliary conduit 1a.

Claims

We claim:

1. In a constant negative-pressure carburettor for internal combustion engines including a main conduit,, a smaller diameter auxiliary conduit, main valve means in each conduit, said main valve of said auxiliary conduit being actuated directly by external control means and said main valve of said main conduit being actuated indirectly by means sensitive to negative pressure upstream of said latter main valve,

the improvement which comprises first additional valve means in said auxiliary conduit upstream of the main valve means in said conduit,

second additional valve means mounted above both of said main and auxiliary conduits,

means connecting said second additional valve means to a fuel-proportioning means,

and return element means for both of said first and second additional valve means and being calibrated differently in order to produce a negative-pressure upstream of the main valve of said auxiliary conduit which is greater than the negative pressure upstream of the main valve of the main conduit.

2. A constant negative-pressure carburettor according to claim 1, in which the return element for said first additional valve means comprises adjusting means for varying the calibration of said return element means in order to vary the idling richness and for adjusting the richness in response to atmospheric pressure and ambient temperature.

3. A constant negative-pressure carburettor according to claim 1, in which the return element means for said first additional valve means is connected to adjusting means including a rod, one end of which is articulated to a lever secured to said second additional valve means, the other end of said rod being connected to said main valve in said main conduit, the movements of the rod ends being such that when said second additional valve means and said main valve means move in parallel, the seat of the return element on the rod does not vary, whereas when said main valve means moves in advance in said second additional valve means, the seat moves and so varies the calibration of the return element means in order to enrich the mixture.

4. A constant negative-pressure carburettor according to claim 1 including calibrated valve means in said second additional valve means in order to admit air through said second additional valve means when the latter is completely closed.

5. A constant negative-pressure carburettor according to claim 1 in which the downstream passage of said auxiliary conduit terminates in the neck of venturi means positioned downstream of said main valve in said main conduit.

6. A constant negative-pressure carburettor according to claim 1 in which the downstream passage of the main valve means in said auxiliary conduit terminates axially in a cylindrical cavity having tangential outlet ducts and including centrifugal wheel means in said cavity having an axial inlet for fuel-air mixture coming from said auxiliary conduit and a radial outlet towards the tangential outlet of said cylindrical cavity.