GB2142384A - Carburettor idling fuel control device - Google Patents

Abstract

A main body (11) has a diaphragm (16) separating the body into two chambers (17, 18) one of which is exposed to the atmosphere through a passage (39) and the other of which is connectible to the carburettor via a coupling (41) to transmit the manifold depression to this chamber. A needle (30) rigidly connected to the diaphragm may control the flow of fuel through the carburettor idling system and acts to close the idling system when the manifold depression experienced in the chamber (18) exceeds a predetermined threshold. In alternative embodiments the carburettor idling fuel supply is closed by a solenoid valve controlled by an electrical switch (85) operated by the diaphragm (16), the valve acting directly on the fuel supply or connecting the carburettor float chamber vent to manifold depression. <IMAGE>

Description

SPECIFICATION An auxiliary carburettor control device The present invention relates to an auxiliary control device for a carburettor, and particularly to a control device acting on the idling fuel supply to inhibit the fuel supply to the carburettor idling system during certain running conditions.

It has long been known that the manifold depression in a carburettor of an internal combustion engine reaches its maximum when the engine is decelerating with the throttle closed since, in these conditions, the greatest ratio between the engine speed and the throttle opening is achieved. The manifold depression in such circumstances can be several orders of magnitude greater than the manifold depression acting when the throttle is open and the engine is accelerating. In such circumstances the fuel supply is subjected to a greater induction force whilst the requirement for fuel by the engine is at its minimum so that large quantities of fuel are drawn into the engine and passed through it only partially burnt leading to substantial fuel wastage and considerable excess pollution due to the presence of noxious gases in the incompletely combusted fuel in the engine exhaust.Such incompletely combusted fuel sometimes ignites in the exhaust system of the engine causing a characteristic popping or backfiring due to the rapid expansion of the gases. This is extremely detrimental to the exhaust system.

In an attempt to reduce the pollution occurring in such conditions modern carburettors are made in such a way that the main running jet is entirely isolated from the manifold depression when the throttle is closed so that excess fuel is not drawn through the main jet in such operating conditions. This relates particularly to the so-called fixed jet carburettors which are provided with a secondary idling fuel supply system to provide the engine with fuel when the throttle is closed since, otherwise, the engine would stop running due to the fuel starvation caused by closure of the throttle.Such a by-pass system, however, is now again subject to the excess maniffold depression on overrun and although the metering passages are extremely small whereby to limit the amount of fuel passing therethrough in normal conditions, during overrun conditions when the manifold depression is extremely high the amount of fuel exscaping through the idling system can be not inconsiderable.

The present invention seeks, therefore, to provide a device which will deal with this problem by detecting the manifold pressure and acting in one of a number of different ways (depending on the particular type of carburettor involved) to restrict or inhibit fuel flow through the carburettor idling system.

In its broadest aspect, therefore, the present invention provides an auxiliary control device for a carburettor, which is sensitive to the carburettor manifold depression and operative when the manifold depression exceeds a certain threshold value to inhibit fuel supply to the carburettor idling system.

In a preferred embodiment of the invention the device has a body including a diaphragm which when fitted to the carburettor can be exposed on one side to the manifold depression and on the other to atmospheric pressure, whereby to be flexed against resilient biasing means when the manifold depression exceeds the said threshold value, the device including means link ed to the diaphragm to effect inhibition of the fuel supply when the diaphragm is so flexed.

The means linked to the diaphragm may act directly by mechanical action to restrict the fuel supply, or may act via an electrical switching arrangement to inhibit the fuel supply or, in a further arrangement, may cause a change in the pressure balance between the float chamber of the carburettor and the manifold in order to negate the effect of the high manifold depression.

The device according to the present invention, includes in one embodiment, a body portion housing a needle movable axially therein, the body portion being adapted to be screwed into the carburettor in place of the idling adjustment screw normally provided therein, with the needle acting as the volume control needle; the body having a diaphragm exposed on one side to the manifold depression and linked to the needle so that when the manifold depression exceeds the said threshold value the diaphragm flexes and the needle is moved to close the fuel metering orifice of the carburettor idling system. In another embodiment a direct solenoid valve may replace the needle valve.

Such an embodiment is particularly adapted for use with the so-called "fixed jet" carburettors. Engines fitted with such carburettors sometimes also includes a solenoid or otherwise electrically operated valve in the fuel supply linked to the ignition circuit to cut off the fuel supply when the ignition circuit is broken. The purpose of such a valve is to prevent the engine "running on" when the ignition circuit is switched off.. This can happen in certain circumstances, particularly where pollution control systems are involved.

Such emission control systems have the effect of causing the engine to run hotter than hithertofore so that "dieseling", that is ignition of the fuel simply upon compression, can take place with the effect that switching off the electrical ignition circuit does not certainly stop the engine. By providing a valve in the fuel supply circuit, it can be ensured that the fuel supply to the engine is cut off at the same time as the electrical supply to the ignition circuit so that the engine will stop without fail when the electrical circuit is broken. This solenoid valve can be employed according to the principles of the present invention by electrically connecting a switch sensitive to the diaphragm movement into the circuit so that operation of this switch also causes closure of the fuel supply valve even when the ignition circuit is otherwise unbroken.In this way, when the engine is in overrun conditions and an excessively high manifold depression exists the diaphragm in the body of the device is flexed to cause actuation of an electrical switch sensitive to diaphragm movements and thereby turn off the fuel supply until the manifold depression has fallen to a value below the predetermined threshold allowing the switch to be turned back on and the valve to open allowing fuel to flow through to the carburettor again.

The body of the device may comprise a main body portion carrying the diaphragm and a body stem portion which is adjustable longitudinally of its length with respect to the main body portion whereby to vary the biasing force of resilient biasing means compressed between the diaphragm and the stem.

There may further be provided adjustment means on the main body portion for adjusting the position of diaphragm and consequently position of the needle with respect to the stem in embodiments where a needle replacing the normal idling jet needle is employed. Such a needle is preferably sealed in the stem by means of a seal which frictionally engages the needle and the stem and flexes upon relative movement between the two in such a way that no relative sliding movement takes place between the seal and either the needle or the bore in the stem.This ensures that the chamber within the body which is exposed to the manifold depression is securely isolated from the annular space between the needle and the bore in the stem so that any tendency for fuel to be drawn along this space in operation of the device, particularly in the periods when the manifold depression has exceeded the threshold value causing closure of the idling jet, can be avoided.

In another embodiment of the invention the manifold depression is used to trigger valve control means for communicating the manifold depression to a carburettor vent. Such carburettor vents are provided in the float chamber in order to ensure that the atmospheric pressure prevails within the float chamber during normal operation.By connecting a duct or tube into the vent line, however, with a suitable valve controlled by the device sensitive to manifold pressure, it is possible to interconnect the float chamber vent with the manifold when the manifold depression exceeds the threshold value so that the pressure differential at the fuel outlet of the carburettor, which pressure differential would normally urge excess fuel through the restricted orifice, is now removed once the threshold manifold depression has been exceeded so that no resultant driving force exists during such conditions. Such valve means preferably a three port valve body having a valve slide therein displaced by a solenoid actuated by the solenoid switch controlled by the diaphragm of the carburettor control device or actuated directly by the diaphragm.Alternatively, however, the valve means may be a shutter valve the position of the shutter of which is controlled in dependence on the energisation of a coil connected to receive electrical supply under the control of the switch controlled by the diaphragm.

Thus, by means of a simple auxiliary control device sensitive to the manifold depression, the excess fuel drawn into the engine during overrun conditions can be prevented either by mechanically closing the fuel outlet with a needle displaced by the diaphragm, or by electrically closing a valve in the fuel outlet by means of a switch actuated by movement of the diaphragm, or finally by negating the pressure differential between the float chamber of the carburettor, sometimes within the air cleaner, and the carburettor venturi. These various different systems are applicable to the various different kinds of carburettor currently utilised in motor vehicles driven by internal combustion engines.

Various embodiments of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a sectional view of a first embodiment of the invention; Figure 1 a is an enlarged sectional view of a detail of the embodiment of Figure 1; Figure 2 is a sectional view of an embodiment similar to Figure 1, but modified to accommodate a different mode of operation; Figure 3 is a schematic sectional view of a third embodiment of the invention adapted for carburettors not having a separate idling system; and Figure 4 is a schematic view of a further embodiment of the invention.

Referring now to the embodiment of Figure 1, the device comprises a main body generally indicated 11 in the form of two half-shell parts 12, 1 3 secured around the rim by screws 14 (which may be replaced by any other suitable fixing means) and having a diaphragm 1 6 separating the interior chamber defined by the two half-shells 12, 1 3 into two compartments 17, 18. The diaphragm 1 6 is clamped at its rim between the two half-shell parts 12, 1 3 of the main body 11.

A metal reinforcement plate 1 9 is carried by the central portion of the diaphragm 1 6 and resilience of the diaphragm is ensured by an annular corrugation or series of corrugations 20 in the diaphragm between its clampd rim and the reinforcing plate 19.

The lower body half-shell 12 has a boss 21 with a threaded aperture 22 receiving a hollow stem 23 which projects through the aperture 22 into the lower compartment 18. Over the end of the stem 23 is fitted a cap 24 having a central aperture 25 through which passes a needle 26 attached at one end to the reinforcing plate 1 9 of the diaphragm 1 6. A seal 27 having a radially inwardly directed lip 28 is located at the uppermost end of the stem 23 and contacts the cap 24 with the mouth defined by the lip 28 extended by contact with the needle 26. This is illustrated in particular in Figure 1 a. The purpose of the seal 27 will be described in greater detail below.

The needle 26 passes through an interior passage 29 within the stem 23 and has a tapered tip 30 projecting from a threaded end 31 of the stem 23. A lock nut 32 threaded onto the upper part of the stem 23 which is itself screwed into the threaded opening 22 in the boss 21 enables the amount by which the stem 23 projects into the chamber 1 8 to be adjusted and locked to set the precompression of a compression spring 33 which surrounds the upper end of the needle 26 and is compressed between the cap 24 and the reinfforcing plate 1 9 of the diaphragm 16 thereby biasing the diaphragm 1 9 upwardly.

Normal mixture setting can be adjusted by means of an adjustment screw 34 threaded in an opening 35 in an enlarged boss 36 of the upper half-shell 13. The adjustment screw 34 has a hexagonal end 37 and a spring 38 surrounds the exposed portion to inhibit vibrations from displacing the screw. The halfshell 1 3 further has a bleed hole 39 allowing the interior compartment 1 7 to communicate with the atmosphere whilst the half-shell 12 has an outlet hole 40 with a connector spigot 41 allowing a flexible tube or other duct to be connected thereto.

The embodiment of Figure 1 is adapted for use with carburettors of the type having a separate idling jet system and the threaded end 31 of the stem 33 has dimensions such as to allow the device to be fitted into a threaded opening in the carburettor body which normally receives the idling volume control screw. The normal idling volume control screw is thus removed and the device of the present invention fitted in its place, and it will be appreciated that the length of the stem 23 is such as to allow such mounting without the main body portion 11 fouling existing parts of the carburettor. The spigot 41 is then connected to a flexible duct or tube which leads to the carburettor manifold at a point where it experiences the manifold depression.

By turning the whole of the body 11, which is clamped to the stem 23 by the lock nut 32, the stem 23 can be screwed into the carburettor body. The axial position of the tip 30 of the needle 26 is adjusted by turning the screw 34 with respect to the body 11 by acting on the hexagon end 37. In normal oprating conditions the carburettor behaves entirely normally, but when on over-run conditions the manifold depression increases to its maximum, this generates a vacuum in the compartment 18 and causes the diaphragm 1 6 to be deflected to urge the needle 26 downwardly (as viewed in Figure 1) with respect to the stem 23 thereby closing the flow path for the idling system and preventing any fuel from being drawn into the carburettor through this path.On over-run conditions the main jet is, of course, already closed so that no fuel would normally be drawn this way into the engine, but because of the extremely high manifold depression the fuel lost through the idling jet can be substantial. The precise pressure at which the diaphragm 1 6 moves is determined by adjustment of the degree of projection of the stem 23 into the compartment 18, which is effected by slackening the nut 32 and turning the body 11 with respect to the stem 23, and subsequently retightening the nut 32.

Because the needle 26 is immersed at its tip 30 in the fuel in the idling flow path, and because the compartment 1 8 is under vacuum in many operating conditions there would be a tendency for fuel to be drawn up the annular space between the needle 26 and the bore 29 in the stem 23. Ingress of fuel into the compartment 18 is prevented by the seal 27 which, having a resilient lip 28, seals tightly around the needle 26 and prevents fuel passage. No wear of the seal 27 will take place since the movements of the needle 26 are sufficiently small to result only in flexure of the lips 28 without causing sliding movement between the needle 26 and the contacting portion of the seal lip 28.

Turning now to the embodiment illustrated in Figure 2, many of the component parts are the same or fulfil a similar function to the components in the embodiment of Figure 1 and these have been assigned the same reference numerals. The embodiment of Figure 2 differs from that of Figure 1, however, in that it is adapted for use with carburettors having an idling fuel outlet solenoid valve. Such solenoid valves are usually fitted in the carburettor for the purpose of being certain to avoid "running on" when the ignition is switched off and are particularly provided for engines having exhaust emission control systems one side result of the operation of which is a tendency for the engine to run hot and to continue running after the ignition has been switched off..This is avoided by the solenoid valve which is only open when the ignition circuit is complete and which closes when the ignition circuit is broken, whereby to close the idling fuel outlet and prevent any further fuel from being drawn through the idling system, in this way ensuring that the engine will stop reliably when switched off.. The embodiment of Figure 2 makes use of such a solenoid valve to de-energise the valve thereby preventing fuel from being supplied to the carburettor during overrun conditions by sensing the maniffold depression and switching off the solenoid when a manifold depression above a predetermined or selected threshold is detected.For this purpose the stem 23 which is screwed into the boss 21 in the same way as the stem 23 in the embodiment of Figure 1, is provided with a bore 29 passing right through, but instead of being provided with a needle 26 the stem 23 has a coupling 43 at its free end for connection to a suitable duct leading to the manifold to transffer the manifold depression to the interior of the compartment 1 8 through the bore 29 in the stem 23.

For this purpose the bore 29 is in fact not sealed as in the embodiment of Figure 1 but has a transverse passage 44 allowing the bore 29 to communicate with the compartment 1 8 despite the fact that the end of the bore 29 is not closed by the cap 24. This prevents closure of bore 29 when the diaphragm 1 9 is displaced downwards increasing the pressure on the cap 24 and possibly closing the aperture in it by contact with the diaphragm or a spigot carried thereby.The reinforcement plate 1 9 of the diaphragm 1 6 is attached by a rod 45 to a switch 46 secured to the boss 36 of the half-shell 1 3. Now, in normal use the diaphragm 1 6 will flex with changes in the manifold depression, but only after the manifold depression has exceeded a certain threshold will the switch 46 be actuated to deenergise the solenoid holding open the fuel path. This then prevents fuel from being delivered from the idling system during overrun conditions.

The above two embodiments of the invention are adapted for use with carburettors having a fixed jet and a separate idling system. Other types of carburettor will need the additional devices illustrated in Figures 3 and 4. These devices are adapted for use in cooperation with the embodiment of Figure 2 and to be connected in a duct leading from the manifold to the float chamber vent. The basic principle of this device is to interconnect the manifold and float chamber upon deceleration thereby balancing the pressures in the manifold and the float chamber and preventing the generation of the pressure differential driving in excess fuel. This is achieved by the use of a latching solenoid connected to the solenoid switch 46 in the embodiment of Figure 2.

Upon the occurrence of a high vacuum in the manifold the switch 46 operates to activate the solenoid which latches in to operate the valve illustrated in Figure 3 to interconnect the manifold and the float chamber in a manner which will be described in greater detail below.

The valve illustrated in Figure 3 comprises a T-coupling body 50 having three branches 51, 52 and 53 each of which has an external threaded portion receiving a cap nut 54, 55, 56 respectively. Each cap nut 54, 55, 56 traps a respective conically ended union 57, 58, 59 against a conically flared mouth 60, 61, 62 of a T-shape internal passage comprising a main bore 63 and a transverse bore 64.

Each of the unions 57, 68 59 has a respective tubular portion 65, 66, 67 with a respective axial passage 68, 69, 70.

The main bore 63 in the T-shape body 50 houses a slide valve or plunger 71 which is a sliding fit within the bore 63. The right hand end of the plunger 71 (as viewed in Figure 3) has a section 72 of reduced diameter surrounded by a compression spring 73 which presses between the annular shoulder separating the portion 72 of reduced diameter from the main body 71 and the facing end of the union 58 thereby urging the plunger 71 to the left as viewed in Figure 3. The plunger has a central passage 74 passing through it from end to end, this passage having cranked end portions 78, 79 leading into conical end faces 80, 87 respectively of the plunger 71.

Finally, the plunger 71 has an annular recess 82 at a mid portion thereof, and this annular recess 82 communicates with the interior bore 74 via a radial passage 83. iThe tubular portion 65 of the union 57 has a central bore 68 housing a plunger 84 of a solenoid 85 which is screwed into an enlarged end portion 86 of the union itself. The solenoid 85 has terminals 86 for connection to electrical leads leading from the solenoid switch 46 of the pressure sensor device illustrated in Figure 2.

The interior bore 68 of the union 57 has a transverse passage 87 communicating with a coupling union 88.

In use of the device illustrated in Figure 3 the coupling union 88 is connected to receive the manifold depression, whilst the union 66 is connected to the atmosphere and the union 67 is connected in the carburettor vent line.

During operation the solenoid 85 is energised and the plunger 84 is drawn in allowing the spring 73 to urge the plunger 71 to the left as illustrated in Figure 3 so that the carburettor vent is open to the atmosphere through the bore 70, the annular channel 82, the radial passage 83, the bore 74 in the plunger 71, the inclined passage 79 and the bore 69 in the union 66. When a large manifold depression is sensed by the device of Figure 2 the solenoid 85 is switched off and the solenoid plunger 84 therefore moves to the right displacing the conical end 80 of the valve plunger 71 from the conical seat in the union 57 opening communication with the passage 87 and the bore 68 through the inclined end passage 78 to the main bore 74 in the valve plunger 71.The balancing force of the spring 73 is overcome so that the conical tip 81 of the valve plunger 71 is pressed against the inner end of the union 58 thereby closing off communication to the atmosphere. The carburettor vent and manifold depression now communicate with one another balancing the pressures in each so that there is no pressure differential to drive fuel into the engine. The valve may also be oprated by a depression sensing diaphragm device, such as that illustrated in Figures 1 and 2.

A similar control valve is illustrated in Figure 4. This is in the form of a shutter valve having a disc shutter 90 cooperating with the open ends 91, 92 of facing tubular bosses 93, 94 within a housing 95.

The valve shutter disc 90 has a plurality of openings or apertures 96 in a circular array at a greater diameter than the outer diameter of either of the bosses 93, 94 and a compression coil spring 97 urges the valve shutter into contact with the mouth 92 of the boss 94. A coil 98 surrounds an axial extension of the boss 91, indicated with the reference numeral 99 which is formed as a coupling leading to the atmosphere. The boss 94 communicates with a coupling 100 which in use is connected to the maniffold.

The body 95 has a further coupling 101 the interior of which communicates with the interior chamber 102 of the body 95 and which is in use connected to the carburettor vent. The disc shutter 90 is made from a suitable ferromagnetic material so that when the coil 98 is energised it will be drawn towards the coil against the action of the spring 97, and when the coil 98 is deenergised the coil 97 can urge the shutter 90 in the opposite direction to close the mouth 92 of the boss 94. Thins, when the coil is deenergised the carburettor vent is connected by the valve to the atmosphere, whilst when the coil 98 is energised the connection to the atmosphere is cut off and the manifold and carburettor vent are interconnected.

The valve may also be operated by direct mechanical connection of its operating number to a depression sensing diaphragm device such as that illustrated in Figure 1 or Figure 2.

Although the auxiliary control device of the present invention has been described hereinabove with particular reference to its production as an auxiliary unit for mounting on a carburettor, it is within the scope of the present invention for the system to be incorporated directly in the body of the carburettor and the present invention therefore comprehends a carburettor incorporating an auxiliary control device operating on the principles described herein above.

Claims (14)

1. An auxiliary control device for a carburettor, which is sensitive to the carburettor manifold depression and operative when the manifold depression exceeds a certain threshold value to inhibit the fuel supply to the carburettor idling system.

2. An auxiliary control device as claimed in Claim 1, in which the device has a body including a diaphragm which, when fitted to the carburettor, can be exposed on one side to the manifold depression and on the other to atmospheric pressure, whereby to be flexed against resilient biasing means when the manifold depression exceeds the said threshold value, the device including means linked to the diaphragm to effect inhibition of the fuel supply when the diaphragm is so flexed.

3. An auxiliary control device as claimed in Claim 2, in which the means linked to the diaphragm act directly by mechanical action to restrict the fuel supply.

4. An auxiliary control device as claimed in Claim 2, in which the means linked to the diaphragm act via an electrical switching arrangement to inhibit the fuel supply.

5. An auxiliary control device as claimed in Claim 2, in which the means linked to the diaphragm act to cause a change in the pressure balance between the float chamber of the carburettor and the manifold in order to negate the effect of the manifold depression.

6. An auxiliary control deVice, as claimed in Claim 2 or Claim 3, in which the device includes a body portion housing a needle movable axially therein, the body portion being adapted to be screwed into the carburettor in place of the idling adjustment screw normally provided therein, with the needle acting as the volume control needle; the body having a diaphragm exposed on one side to the manifold depression and linked to the needle so that when the manifold depression exceeds the said threshold value the diaphragm flexes and the needle is moved to close the fuel metering orifice of the carburettor idling system.

7. An auxiliary control device as claimed in Claim 6, in which the said needle valve is replaced by a solenoid valve.

8. An auxiliary control device as claimed in Claim 7, in which the solenoid valve is so arranged that when a high manifold depression, above a certain threshold value, exists the diaphragm in the body of the device is flexed to cause actuation of an electrical switch sensitive to diaphragm movements and thereby turn off the fuel supply until the manifold depression has fallen to a value below the predetermined threshold allowing the switch to be turned back on and the valve to open allowing fuel to flow through to the carburettor again.

9.An auxiliary control device as clamed in any preceding Clam, in which the body of the device comprises a main body portion carrying the diaphragm and a body stem portion which is adjustable longitidunally of its length with respect to the main body portion whereby to vary the biasing force of resilient biasing means compressed between the diaphragm and the stem.

10. An auxiliary control device as claimed in Claim 9, in which there are further provided adjustment means on the body portion for adjusting the position of the diaphragm and consequently the position of the needle with respect to the stem.

11. An auxiliary control device as clamed in Claim 10, in which the said needle is sealed in the stem by means of a seal which frictionally engages the needle and the stem and flexes upon relative movement between the two in such a way that no relative sliding movement takes place between the seal and either the needle or the bore in the stem.

1 2. An auxiliary control device as claimed in Claim 1, in which the manifold depression is used to trigger valve control means for communicating the manifold depression to a carburettor vent so as to interconnect the float chamber vent with the manifold when the maniffold depression exceeds the threshold value so that the pressure differential at the fuel outlet of the carburettor, which would normally urge excess fuel through the restricted orifice, is inhibited.

1 3. An auxiliary control device as claimed in Claim 12, in which the said valve means comprise a three port valve body having a valve slide therein displaced by a solenoid actuated by a solenoid switch controlled by the diaphragm of the carburettor control device.

14. An auxiliary control device as claimed in Claim 13, in which the said solenoid switch is actuated directly by the diaphragm.

1 5. An auxiliary control device as clamed in Claim 1 2 or Claim 13, in which the valve means comprise a shutter valve the position of the shutter of which is controlled in dependence on the energisation of a coil connected to receive electrical supply under the control of the switch ccntrolled by the diaphragm.

1 6. An auxiliary control device substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.