EP0093750A1

EP0093750A1 - Idle mixture adjusting device with fuel cut-off during deceleration

Info

Publication number: EP0093750A1
Application number: EP82903334A
Authority: EP
Inventors: John Eastman Barnes
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-11-16
Filing date: 1982-11-11
Publication date: 1983-11-16
Also published as: EP0079763A1; WO1983001813A1; ZA828411B

Abstract

Pour économiser du carburant pendant la décélération d'un moteur, il a été proposé de couper l'alimentation de carburant. De telles propositions ont entraîné des modifications substantielles de la conception du carburateur. Le carburateur décrit comprend un papillon-valve (14), un orifice de ralenti (26) au travers duquel un mélange carburant/air est envoyé côté aval du papillon-valve (14) lorsque ce dernier se trouve dans une position fermée, un canal (16) menant à l'orifice de ralenti et le long duquel le mélange carburant/air est aspiré, un dispositif de réglage du mélange de ralenti réglable longitudinalement (27) ayant une pointe conique (38) se projetant dans le canal (16) et mobile manuellement pour déplacer la pointe (38) vers et en retrait de l'orifice (26) pour régler le mélange de ralenti du moteur, et des moyens actionnables par l'intermédiaire du dispositif de réglage du mélange de ralenti (27) pour empêcher l'alimentation en carburant au travers de l'orifice de ralenti pendant la décélération du moteur. L'alimentation en carburant peut être empêchée en bloquant l'orifice de ralenti (26) et/ou en mettant à l'évent la région adjacente à cet orifice (26). Un tel dispositif (27) est simple à monter et ne demande aucune modification importante de la conception d'un carburateur.To save fuel during deceleration of an engine, it has been proposed to cut off the fuel supply. Such proposals resulted in substantial modifications to the design of the carburetor. The carburetor described comprises a throttle valve (14), an idle orifice (26) through which a fuel / air mixture is sent to the downstream side of the throttle valve (14) when the latter is in a closed position, a channel (16) leading to the idle port and along which the fuel / air mixture is drawn in, a longitudinally adjustable idle mixture adjuster (27) having a conical tip (38) projecting into the channel (16) and manually movable to move the tip (38) to and away from the orifice (26) for adjusting the engine idle mixture, and means operable through the idle mixture adjuster (27) for prevent fuel from being fed through the idle port during engine deceleration. Fuel supply can be prevented by blocking the idle port (26) and / or by venting the region adjacent to this port (26). Such a device (27) is simple to assemble and does not require any significant modification to the design of a carburetor.

Description

IDLEMIXTUREADJUSTINGDEVICEWITHFUELCUT-OFFDURINGDECELERATION

This invention relates to internal combustion engines which are provided with their fuel/air mixture by a carburettor, and in particular to an improved carburettor therefor. There are very stringent regulations governing th exhaust emission of internal combustion engines of vehicles and many arrangements have been adopted with a view to meeting these regulations. One particular area where emission from the exhaust has to be controlled is during deceleration; for example, when a vehicle is running downhi using its engine as a brake, the engine continues to run at relatively high speed even though the throttle is closed bu small amount of fuel is drawn through the idle jet. Althou this amount of fuel is small, the resulting mixture of fuel and air will be relatively rich in view of the lack of air supply. Undesirable and possibly illegal emissions can then occur from the exhaust system because of incomplete or incorrect combustion and there is also the risk of an over-rich surge when the throttle is opened. To avoid this problem, internal combustion engine manufacturers have usually made arrangements to supply extra air during these conditions so as to prevent the mixture fro becoming overly rich. This can be achieved, for example, by slightly opening the throttle butterfly valve during periods of engine braking or by providing an air bypass which is opened under the control of a valve so as to allow extra air

SUBSTITUTE SHEET into the engine manifold to prevent an over-rich mixture. either case, the result is a reduction in the braking abil of the engine because of the extra quantity of air passing the engine. There have also been proposals to cut off the fu supply during decelaration but all such proposals have^' involved a substantial redesign or change of the carburett This may be possible for fitting to a new vehicle but is undesirable or impossible for an existing vehicle. It is therefore an object of this invention to provide a simple way of dealing with this situation.

According to the invention there is provided a carburettor for an internal combustion engine comprising a throttle valve, an idling port through which a fuel/air mixture is supplied on the downstream side of the valve wh the latter is in a closed position, a channel leading to t idling port and along which the fuel/air mixture is drawn, longitudinally adjustable idle mixture adjusting device ha tapered tip projecting into the channel and manually movab to move the tip towards and away from the port to set the idling mixture of the engine, and means operable through t idle mixture adjusting device for preventing the supply of through the idling port during engine deceleration, i.e. w the throttle valve is closed and the engine is still turni over at a rate above idling, or in other words, during periods when the "vacuum" downstream of the throttle valv exceeds a certain figure.

By adopting the invention, it will be seen that contrast with prior solutions which add more air to preve the fuel/air mixture from becoming overly rich, the prese invention aims to eliminate fuel in the mixture passing t the combustion chambers of an engine during deceleration an engine or engine braking. Therefore use of the invent can avoid potential pollution problems under deceleration conditions and also gives the added advantage of reducing fuel consumption; this can represent a significant saving hilly regions or in heavy traffic. Also by adopting the invention, better engine braking can be achieved since les air is admitted to the engine and also less fuel is being burnt during deceleration conditions.

The device replaces the idle mixture adjustment Thus a conventional idle mixture adjustment screw can be r and replaced with a device which can then act both to cut the supply of fuel during deceleration and as the conventional idle mixture adjustment screw during normal operation of the engine. This has the advantage that a carburettor does not need any modification apart from this change and in addition there is the advantage that existin carburettors in internal combustion engines can be modifie according to the invention in a relatively simple fashion.

The replacement of the idle mixture adjusting screw is a s

-ξT3RE_C∑

O PI Z- , V. lrO change which can be effected by a moderately skilled car user.

The term "vacuum" is used herein on occasion and this term should be construed in the sense used in the automotive engineering field. Thus "vacuum" is not to be understood as meaning a straight scientific vacuum or zero pressure but instead a pressure reduced below atmospheric pressure which exists in the manifold. In practice "vacuu is usually referred to in inches or centimetres of mercury and again a reference to a certain number of inches of mercury does not mean an absolute pressure above zero pressure but instead a pressure reduction by that much bel the existing atmospheric pressure. References herein to vacuum are therefore to be construed in this sense. According to one embodiment of the invention the fuel is prevented from passing through the idling port by directly sensing the pressure in the manifold and, when a sufficiently reduced pressure is noted, the fuel supply is prevented. The idle mixture adjusting device can have a p running from or near its tip to a pressure sensing device a separate conduit from a tap on the manifold can be provi to the pressure sensing device.

Many modern vehicles have dual diaphragm dis¬ tributors with which to retard the spark under idling conditions. This is done to achieve more complete com¬ bustion. In addition the butterfly valve is kept slightly

o____. - 5 -

open when idling. The result is that manifold pressure u idling is often higher than normal, e.g. 12 inches (30.5 of mercury but as the throttle is opened slightly, the manifold pressure actually reduces to 18 to 20 inches (46 51 cm) of mercury whilst during engine braking and deceleration the manifold pressure is often not as low as with engines without these combustion control techniques. purely pneumatic sensing is used to actuate the device of invention under these circumstances, hunting may occur because it is not always easy to distinguish on the basis manifold pressure engine deceleration and engine running w the throttle slightly open and the engine under light load As a result in these cases it is important to sense the deceleration condition of the engine in a manner indirectl related to the manifold pressure, i.e. throttle closed and fast engine speed.

Therefore, at least in such a situation, means a provided to sense engine speed electrically or electronica using for example a centrifugal speed switch or by measuri the rate of ignition pulses and the throttle position, i.e closed or not closed, and those means are arranged to activate the means for preventing the fuel flow during eng braking or deceleration corresponding to periods when the "vacuum" downstream of the throttle valve exceeds or shoul exceed a certain figure. The use of this technique is not however, limited to such situations since the sensing of

OM engine speed electrically is a simple technique which can avoid the use of moving parts as required in, say, a pressure-operated switch.

According to one embodiment of the invention the fuel is prevented from passing through the idling port by physically blocking that port. This can be achieved by moving the tip of the device towards the said idling port close it during periods of engine deceleration, e.g. movin the tip by means of an electrically-operated solenoid or b means of a differential pressure sensing device.

According to one such embodiment the idle mixtur adjusting device comprises operating means forming part of the idle mixture adjusting device for moving the tip towar said idling port to close it during periods when the "vacu downstream of the throttle valve exceeds a certain figure, and a port runs from or near the tip of the idle mixture adjusting device through the body of the device to respons means for sensing the pressure at the tip, the said operat means being responsive to move the said tip according to t pressure sensed through the said port.

In this embodiment the device can comprise a sle having on its outer surface a screw thread to enable it to threaded into the bore of the idle mixture adjustment scre the carburettor, a central plunger εlidably mounted within the sleeve, the plunger having a nose or tip which is arranged to close the idling port when the plunger moves t closed position, a diaphragm attached to the rear of the plunger and exposed to the pressure existing between the plunger and sleeve on its inner side, and a bore from the nose or tip of the plunger through the body of the plunge and into communication with the region between the plunge and sleeve and therefore the inner side of the diaphragm. The other side of the diaphragm can be subject to atmosph pressure, a spring being provided around the plunger to u it away from the closed position or the other side of the diaphragm can be subject to a constant reduced pressure.

In an alternative embodiment, the bore through t plunger can be in communication with one side of a diaphra For example, the other side of the diaphragm can be subjec to atmospheric pressure, and the plunger is then movable towards the closed position against the action of a spring The other side of the diaphragm could alternatively be subject to a constant reduced pressure. This pressure can calibrated to ensure movement of the plunger at a precise "vacuum" in the manifold and this arrangement can be made more sensitive and precise than the use of a spring and atmospheric pressure.

In these embodiments during periods of high suct in the engine manifold corresponding to engine braking or deceleration, the region adjacent the said one side of the diaphragm is reduced by being in communication with the hi suction through the bore from the tip of the plunger and t

O PI plunger is moved to the closed position by the diaphragm, plunger being returned to the open position when the press in the engine manifold and so the pressure in the region adjacent the said one side of the diaphragm thereafter increases once engine deceleration or braking finishes.

There are, however, other ways according to the invention in which the plunger can be operated. Thus, for example, the plunger could be movable under the effect of solenoid between the open and closed positions and the hig suction existing in the manifold during engine braking or deceleration can be detected by means of a pressure sensit electrical switch which then controls the actuation of the solenoid to move the plunger to its closed position or alternatively the solenoid could be actuated according to RPM of the engine and the position of the throttle or butterfly valve.

Some carburettors have one or more auxiliary idl ports or the last of their progression ports, sometimes otherwise called "off-idle ports" or "transfer ports", positioned downstream or alongside the throttle valve in i closed idle position. Therefore even when a device is use to close the idling port, it is still possible for fuel/ai mixture to be sucked through this additional port or ports from downstream of the throttle valve. Accordingly an alternative manner of prevent fue flow is to vent the region at the lower end of the passage

-gt$RE

OMP IP to normal atmospheric pressure so reducing or avoiding an suction of fuel along the idle port passageway.

According to this embodiment the idle mixture adjusting device includes means for venting to the atmosp the region of the channel leading to the idling port near idling port.

In another embodiment of the invention, the dev may both block the idling port and vent to the atmosphere region of the channel leading to the idling port. It is also known to provide some form of solenoi operated plunger to close the idling port when the igniti of a petrol engine is switched off so preventing the engin from continuing to work by dieεel operation which can sometimes occur particularly when traces of carbon are present in the combustion chamber. Such an arrangement ca readily be incorporated with a device according to the invention so that the tip of the device closes the idling and/or the device vents that region, either way preventing the supply of fuel both during engine braking or decelerat and when the ignition is switched off.

According to another aspect of the invention, th invention also extends to the idle mixture adjusting devic se for use as a replacement of the idle mixture adjustment Therefore according to this aspect of the invention there provided an idle mixture adjusting device for a carburetto an internal combustion engine comprising a body having an

Jt 7 .___wOMϊpP

^^VA outer screwthread to enable it to be screwed to the idle m adjusting screw hole of a carburettor, a pointed/tapered t projecting into the channel and manually movable to move t tip towards and away from the port to set the idling mixtu of the engine, and operating means forming part of the idl mixture adjusting device for moving the tip towards the sa idling port to close it and/or venting to the atmosphere ^"t region of the tip during periods of engine deceleration.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagram of a carburettor in accor¬ dance with the invention;

Figure 2 is an enlarged view of a portion of tha carburettor in the region of the idle mixture adjustment screw but showing a device according the invention in position during normal operatio of the engine;

Figure 3 is a diagram similar to Figure 2 showin the device during engine braking or deceleration

Figure 4 is a view of a modified device accordin to the invention;"

Figure 5 is a diagram of another device accordin to the invention; and Figure 6 is a diagram of yet a further device according to the invention. The carburettor 10 shown in Figure 1 includes a induction air passage 12 which leads to the manifold (not shown) and in turn to the cylinders of an internal combus engine (not shown) . In the air passage 12 is a pivoted butterfly throttle valve 14 whose position is controlled i conventional fashion by the throttle. The pivoting of thi valve between the closed position shown in the drawings an an open position controls the amount of air which can be sucked into the engine and this in turn entrains with it f from the carburettor to adjust the working output of the engine.

A fuel/air passageway 16 is positioned in parall with the induction air passage 12 and has an air inlet orifice 18 at its upstream end, an inlet fuel jet 20 from fuel reservoir 21, various progression ports 22 and 24 upstream of the valve 14 and an idling port 26 downstream the valve 14. During idling conditions, the valve 14 is i the closed position shown and a small amount of air and fu mixture passes along the passageway 16 and out through the idling port 26 into the air passage 12 downstream of the v 14. The richness of this mixture during idling conditions adjusted by an idle mixture adjusting screw device 27 whic be moved in or out relative the wall of the carburettor si it has an external screw thread 28 which mates with a threaded bore 30 in the wall of the carburettor (see Figur 2 and 3) . As the valve 14 progressively opens, more and mo air can be sucked through the passage 12 and progressively more and more fuel is entrained through the progression po 24 and then the ports 24 and 22. As thus far described, the carburettor 10 is conventiona1.

Referring now to Figures 2 and 3, the idle mixtu adjusting screw device 27 comprises an outer sleeve 32 whi has the external screw thread 28 in its outer surface mati with the threaded bore 30. Within the outer sleeve 32 is central plunger 34 and between the plunger and sleeve is a compression coil spring 36.

The plunger has a tapered nose or tip 38 and the longitudinal axis of the plunger is aligned with the axis the port 26.

The tip 38 is formed of a finely tapered portion 38a_ and a coarsely tapered portion 38b. The advantage of this is that the finer portion 38a_ which initially project into the port 26 can be used to give a very fine adjustmen of the idling mixture. However, when the tip 38 is to blo the port 26, the coarser portion 38b then abuts around the edge of the idling port 26 and sits on a corresponding sha seating 26a_ around the edge of the port so giving sudden closure of the port when required. In addition, this has advantage that the coarser tapered portion is more unlikel to jam in the port than the finer tapered portion 38a_. Th

OMPI plunger also has a solid cylindrical core 40 of smaller diameter than the internal diameter of the sleeve 32 and around which is positioned the spring 36. The core is a sliding/sealing fit within the left-hand end 42 of the sl which has a tapered, outer region which matches the taper region on the tip of the plunger and a bore 44 which εlida carries the core 40. The end 42 of the sleeve also has a seating 46 against which the tip of the plunger abuts when the position shown in Figure 2. The spring bears against a cup-shaped washer 48 fixed to the end of the core 40 and urges the plunger to t open position of the device 27 shown in Figure 2.

Under normal operating conditions of the engine, the plunger 34 is in this open position and the device 27 operates in an entirely equivalent way to the idle mixture adjusting screw of a conventional carburettor. Thus, the 38 can be moved so as to progressively close or open the p 26 by rotating the sleeve 32 so moving the overall device and its tip more to the left or more to the right to adjus the richness of the fuel/air mixture during idling conditions.

Extending longitudinally from the tip 38 of the plunger is a bore 50. This communicates with a radial bor 52 which in turn communicates with the region between the sleeve 32 and plunger 34 in the region containing the spri 36. Fixed to the end of the core of the plunger is a diaphragm 56 which is in turn sealed to a flared end 58 of the sleeve. The diameter and flaring of this end of the sleeve and the diameter of the diaphragm are chosen so as give sufficient force to overcome the effect of the compression spring 36 when the pressure between the sleeve and piston reduces to a preselected figure below atmospher pressure.

During the existence of a high "vacuum" in the passage 12, e.g. a vacuum of the order of 20 to 26 inches to 66 cm) of mercury caused by engine deceleration or engi braking, air from the region between the sleeve 32 and plunger 34 is exhausted through the bores 50 and 52. When this pressure is sufficiently reduced, the diaphragm 56 wi push the plunger to the left to the closed position of the device 27 shown in Figure 3 because of the excess atmosphe pressure on the diaphragm. As a result, the tip of the plunger closes the port 26 and stops all flow of fuel/air mixture through the port 26. Therefore, the possibility o incorrect combustion and potentially illegal pollution through the exhaust is prevented and in addition there is saving in fuel.

Once the engine ceases to decelerate, pressure i the passage 12 rapidly increases and as a result the press within the region between the sleeve and plunger increases with air entering through the ports 50 and 52 and once the

-$jRE

OMFI pressure has increased sufficiently, the spring 36 overco the excess atmospheric pressure applied to the other side the diaphragm and moves the plunger back to the right tow the normal open position shown in Figure 2. Such a condi exists during engine idling or during normal driving conditions of the engine.

As will be appreciated, the device 27 according the invention is relatively simple and cheap to construct has the advantage that no significant change in the actual carburettor body itself or operation of the carburettor is necessary. Therefore, an existing carburettor can readily adapted to conform to the invention by replacing the conventional idle mixture adjustment screw with a- device 2 according to the invention. Instead of providing a bore through the plunger the pressure in the manifold can be sensed through a separ conduit from a tap on the manifold.

The modified device 60 shown in Figure 4 is simi to that described above in connection with Figures 2 and 3 except that no spring 36 is provided and the end cover 62 encloses the end of the device to provide a sealed region on the outer side of the diaphragm 56. This region is evacuated to a calibrated low pressure to correspond to th "vacuum" in the manifold 12 at which the plunger is requir to move from the open to the closed position actually show in Figure 4.

^RE O PI s__v_. w- ^SNATl It is found that the device 60, shown in Figure can be made more sensitive and accurate as compared with t use of the spring 36 provided in the device 27 shown in Figures 2 and 3 to control the moment when the plunger mov between its open and closed positions.

Some carburettors have on an auxiliary idling po or the last of their progression ports positioned downstre or alongside the throttle valve in its closed position at around the point 66 shown in Figure 1. As a result that e if the device 27 or the device 60 is used to close the idl port 26, it is still possible for fuel/air mixture to be sucked through this additional port from downstream of the throttle valve. Therefore, in these circumstances, the blocking of the idling port with a device 27 or the device is not always completely effective. Instead the fuel/air mixture can be stopped from leaving the passageway 16 by a device which vents the region at the lower end of the passageway 16 to normal atmospheric pressure so reducing o avoiding any suction of fuel along the passageway 16. Suc an embodiment will now be described in connection with Fig 5. Many modern vehicles have dual diaphragm dis¬ tributors with which to retard the spark under idling conditions and open the butterfly valve 14 slightly under idling conditions. Because of this manifold pressure unde idling is often higher than normal, e.g. 12 inches (30.5 c of mercury and as the throttle is opened slightly, the manifold pressure can reduce to 18 to 20 inches (46 to 51 of mercury whilst under engine deceleration the pressure be less than otherwise. If only pneumatic sensing is use actuate the device as for example in the devices described Figures 2 to , hunting may occur. As a result in the cas of engines having these emission control techniques it is important to sense the deceleration condition of the engin electrically and/or mechanically and not actual manifold pressure. Further it is relatively simple and reliable to sense the deceleration condition of the engine electricall and so electrical sensing can be used with all devices of invention, actuation of a solenoid by use to control the operation of the device.

The device shown in Figure 5 includes an idle mi adjusting tube 100 screwed into the threaded bore 30 in th wall of the carburettor and a solenoid controlled valve 10 The tube 100 has at one end a tip 104 arranged t project into the idling port 26. As with the device 27 described above, the tube 100 can be progressively screwed into or out from the threaded bore 30 so that the tip 104 adjusts the extent of opening of the idling port 26 and so controls the idling mixture of the engine.

The tube 100 has a longitudinal bore 110 terminating in small vent holes 112. At the outer end of tube, the bore 110 is open and the open outer end of the

UEA

OMPI tube is connected by a length of flexible tubing 120 to th valve 102.

The valve 102 includes a plunger 125, movable by means of a solenoid 122 to open to the atmosphere or close port 124 which is in communication with the tubing 120. W the port 124 is opened, then the region of the passageway is vented to the atmosphere through the tubing 120, bore 1 and vent holes 112. If desired a replaceable filter can b provided over the valve 102 to filter the air before it ca enter the carburettor.

The carburettor shown in Figure 5 has an auxilia idling port 24. Therefore blocking off the idling port 26 during deceleration may not prevent some fuel from being sucked into the manifold and so the region 128 at the lowe end of the passageway 16 is vented to atmosphere by openin the valve 102 so as to avoid sucking petrol air mixture do the passageway 16.

The actuation of the solenoid 122 is controlled a combination of an electronic engine speed switch 152, e. a pulse integrating chip, and a throttle position sensing switch 154 which controls a relay 160 in turn controlling actuation of the solenoid 122. Under normal engine operation, i.e. engine speed greater than 1,000 rpm and th throttle open, the solenoid 122 is energised and plunger 1 is moved to the left in the sense shown in Figure 5 becaus the switch contacts 162 of the relay are closed. During engine deceleration when the throttle va 14 is closed the throttle position switch 154 is closed a the engine speed switch 152 is closed whilst the engine s remains above 1,000 rpm. Therefore the relay 160 is energised which in turn opens its contacts 162 and de-energises the solenoid 122. This allows plunger 125 t move to the right in the sense shown in Figure 5 which ope up the port 124 so venting the region 128 to the atmospher This therefore stops the flow of fuel through port 26. As engine speed drops below 1,000 rpm or the throttle is opened, the relay 160 is de-energised and in t the solenoid 122 is de-energised so that the plunger 125 moves to the left in the sense shown in Figure 5 thus agai allowing fuel to flow through the idling port 26 enabling engine to run at idle speed or faster.

In some cases it may be desirable both to block idle jet and vent the region near the base of the passagew 16. The device 250 shown in Figure 6 enables this to be achieved. The device 250 shown in Figure 6 comprises an ou cylindrical sleeve 252 which has a threading to enable it be screwed into the threaded bore 30 in the wall of the carburettor. Within the sleeve 252 is slidably mounted a plunger 254. This has at one end a tip 256 arranged to project into the idling port 26. The device 250 can be progressively screwed into or out from the threaded bore 3 so that the tip 256 adjusts the extent of opening of the idling port 26 and so controls the idling mixture of the engine.

The tip 256 is formed of a finely tapered portio 256a_ and a coarsely tapered portion 256b for the reasons described above in connection with Figures 2 and 3.

Formed to the outer end of the sleeve 252 is a solenoid casing 259 containing a solenoid 260. The movabl core 262 of the solenoid is joined to and supports the plunger 254 so that it is slidable relative the outer slee 252.

The plunger is urged in its normal position towa the left as viewed in Figure 6 by means of a coil spring 2 Vent holes 272 are provided in the end of the casing 259 a core 262 so that a passage 273 between the plunger 254 and sleeve 252 is in communication with the atmosphere.

The plunger 254 has an additional seating 274 against which it sits on the end of the sleeve 252. When plunger is in its open position shown in Figure 6, the seating 274 closes against the end of the sleeve.

The actuation of the solenoid 260 is controlled exactly the same way as described above in connection with Figure 5.

The operation of the device 250 as far as blocki the idling port 26 is concerned, is more or less the same for the device 27 as shown in Figures 2 and 3. Thus, duri engine deceleration the solenoid 260 is de-activated and the spring 270 moves the plunger to the left in the sense shown in Figure 6 and the portion 256b closes the idling 26. This movement also opens the seating between the sea 274 and the end of the sleeve and so atmospheric air can pass along the air passage 273 to the region 104 so reduc the suction effect at the lower end of the passageway 16 caused by the auxiliary port 24. The effect is therefore prevent the passage of fuel/air mixture down the passagewa 16 during periods of deceleration or engine braking. When the engine reaches idling speed or the throttle is depressed, the solenoid is again activated and the plunger moves back to the right to its original positi shown in Figure 6. Although the solenoid 260 is shown as actuating plunger 254 directly it could do so indirectly by means of for example a flexible bowden cable connection from a solenoid positioned remotely from the carburettor if there a difficulty in positioning the relative bulky solenoid cl to the carburettor.

One advantage of the devices shown in Figures 5 6 is that they prevent dieseling of the engine once the ignition switch of the vehicle is opened. Thus, when the ignition of the vehicle is switched off, the solenoid is d activated and automatically the region 104 is vented and/o the plunger closes the port 26 so preventing further fuel/ mixture from reaching the engine.

Claims

WHAT WE CLAIM IS:

1. A carburettor for an internal combustion engine comprising a throttle valve, an idling port through which fuel/air mixture is supplied on the downstream side of th valve when the latter is in a closed position, a channel leading to the idling port and along which the fuel/air mixture is drawn, a longitudinally adjustable idle mixture adjusting device having a tapered tip projecting into the channel and manually movable to move the tip towards and a from the port to set the idling mixture of the engine, and means operable through the idle mixture adjusting device f preventing the supply of fuel through the idling port duri engine deceleration.

2. A carburetor as claimed in Claim 1 in which mean are provided to move the said tip towards the said idling port to prevent the supply of fuel during engine deceleration.

3. A carburettor as claimed in Claim 2 in which the operating means comprise an electrically operated solenoid for moving the tip.

4. A carburettor as claimed in Claim 3 in which pressure sensing means are provided for detecting the pressure downstream and moving the tip to close the idling port when the "vacuum" downstream of the throttle valve exceeds a certain figure.

5. A carburettor as claimed in any preceding claim which the idle mixture adjusting device has a port running or near its tip to a pressure sensing device forming part the said operating means.

6. A carburettor as claimed in any preceding claim which the idle mixture adjusting device comprises an outer threaded sleeve capable of being screwed into the carburet in place of the idle mixture adjusting screw, and a plunge longitudinally movable within the sleeve, the plunger havi the tapered tip formed on an end projecting from that slee

7. A carburettor as claimed in any of claims 1 to 4 which electrical means are provided to sense engine speed the throttle position, and those means are arranged to activate the device to prevent the supply of fuel through idling port during engine braking or deceleration.

8. A carburettor as claimed in any of claims 1 to 4 which means are provided for venting to atmosphere the reg of the channel leading to the idling port near the idling port so as to prevent the supply of fuel during engine deceleration.

9. An idle mixture adjusting device for a carburett an internal combustion engine comprising a body having an outer screwthread to enable it to be screwed to the idle m adjusting screw hole of a carburettor, a pointed/ tapered projecting into the channel and manually movable to move t tip towards and away from the port to set the idling mixtu of the engine, and operating means forming part of the id mixture adjusting device for moving the tip towards the sa idling port to close it and/or venting to atmosphere the region of the tip during periods of engine deceleration.

10. A device as claimed in Claim 9 further comprisin sensing means for engine deceleration including means sens engine speed by measuring the rate of ignition pulses and electrical switch means for sensing the throttle position.