EP0059654A1 - Carburetor for an internal combustion engine - Google Patents

Abstract

This carburetor comprises a body (101) provided with a fuel spray device (103), an air flap (109) and a butterfly valve (104) rotatably mounted in the body respectively upstream and downstream of the spray, a spring (113) urging the flap (109) towards its fully closed position, a diaphragm capsule (116) sensitive to the vacuum prevailing at the engine intake manifold, a linkage (112 - 114) connecting the air shutter (109) and the device membrane (116) and a manually actuated cam (125). The cam (125) comprises a stop (130) movable between an active position and a retracted position where it allows, in cold operation, the capsule (116) and the linkage (112 - 114) to tilt the flap (109 ) between minimum and maximum opening positions, depending on the engine load.

Description

The present invention relates to a starting flap carburetor for an internal combustion engine.

In a large number of carburettors currently used, the "choke" allowing the cold start of the engine is constituted by a mechanism comprising a starting flap rotatably mounted in the body of the carburetor upstream of the fueling device. When the choke is fully pulled, the air shutter closes completely and closes the carburetor body. As soon as the engine starts, a membrane capsule connected to the intake manifold opens the air flap thanks to the vacuum then prevailing in the intake manifold due to the very low degree of opening of the throttle valve. After this start-up phase, the choke is partially pushed back for cold operation. This has the effect of placing the air shutter in an intermediate ajar position between its closed position and its fully open position.

Of course, the total or partial closing of the air shutter has the effect of enriching the air-gasoline mixture supplied to the engine, this enrichment being all the more important the more the air shutter is closed.

This therefore results for motor vehicles equipped with such carburetors overconsumption in cold operation This overconsumption is all the more important as the engine is cooler as shown in Figure 9 of the accompanying drawings in which the curve A represents, depending of the mileage covered, the consumption (liters / 100 km) of an engine after cold start at an ambient temperature of -5 ° C while curve C illustrates the consumption of the same engine after hot start.

However, statistical studies have shown that a very large number of vehicles, especially in urban areas, were used to make daily journeys of a few kilometers, that is to say in the most unfavorable area of the curve A. Substantial fuel savings could therefore be realized if we reduced , during cold operation, the overconsumption of many motor vehicles fitted with starting flap carburetors.

French Patent 2,393,161 describes a carburetor which contributes to providing a solution to this problem. This carburetor is of the type comprising at least one body provided with a fuel spraying device, an air shutter mounted to rotate in the body upstream of the spraying device, a throttle valve for controlling the load of the engine mounted to rotate in the body downstream of the spraying device, elastic means urging the air shutter towards its fully closed position, a device for actuating the vacuum-sensitive shutter prevailing at the intake manifold, a linkage link between the device sensitive to depression and the air shutter comprising at least one articulation, said actuation device sensitive to depression and said linkage being arranged to allow the tilting of said shutter between its fully closed position and a maximum open position at against the elastic means, and a manually actuated cam rotatably mounted between a first position, corresponding to the cold start, where it cooperates with said linkage p or limit the stroke at the opening of the shutter in a partially open position, at least a second position, corresponding to cold operation, where it allows tilting of the shutter between a minimum open position and said position maximum opening and a third position where it keeps the air shutter in the fully open position.

However, the arrangement of this carburetor is relatively complex and costly to produce because it comprises a large number of different parts which are movable relative to one another. The invention aims to produce a carburetor of the above type which is of a particularly simple and inexpensive construction.

To this end, the subject of the invention is a carburetor of the aforementioned type, characterized in that the cam comprises an appendage which, in the first position of the cam, is interposed in the path of movement of the joint and which, in the second position of the cam is outside the path of movement of the joint. Thus, in the second position of the cam, the vacuum-sensitive actuating device can actuate the flap between the minimum and maximum opening positions, and this by means of a minimum of modifications compared to a conventional carburetor such as this will result from the rest of the description.

According to a particular embodiment of the carburetor, the cam has a first surface which cooperates with the articulation to fix the minimum opening position of the flap in the second position of the cam and to fix the fully open position of the flap in the third position of the cam, and a second surface formed on the appendage and which cooperates with the articulation to fix the position of the shutter ajar in the first position of the cam.

According to another characteristic, the linkage is constituted by a link connected respectively to a movable membrane of the device sensitive to depression and, by the articulation, to a lever integral in rotation with the air flap.

According to yet another characteristic of the invention, the maximum opening position is the fully open position of the shutter.

• - La figure 1 est une vue schématique du mécanisme à volet de départ à froid d'un carburateur conventionnel, représentant ledit mécanisme dans la position "repoussée" du starter ;
• - La figure 2 est une vue analogue à la figure 1 représentant le mécanisme dans la position qui précède le démarrage à froid, le starter étant tiré à fond ;
• - La figure 3 représente le mécanisme dans la même position du starter qu'à la figure 2, mais immédiatement après le démarrage du moteur
• - La figure 4 représente le mécanisme des figures 1 à 3 dans la position partiellement repoussée du starter ;
• - La figure 5 est une vue schématique d'un mécanisme à volet de départ suivant l'invention représenté dans une position équivalente à celle de la figure 1 ;
• - La figure 6 est une vue du mécanisme de la figure 5 représenté dans une position équivalente à celle de la figure 2 ;
• - La figure 7 est une vue du mécanisme des figures 5 et 6 représenté dans une position équivalente à celle de la figure 3 ;
• - La figure 8 est une vue du mécanisme des figures 5 à-7 représenté dans une position équivalente à celle de la figure 4 ;
• - La figure 9 est un graphique montrant la courbe A de consommation d'un moteur fonctionnant à froid avec un carburateur conventionnel, la courbe B de consommation du même moteur équipé d'un carburateur à mécanisme de départ à froid suivant l'invention et la courbe C du même moteur après démarrage à chaud ; et
• - La figure 10 est une vue en coupe partielle d'un système particulier de réalisation pour l'application de la dépression du collecteur d'admission à la capsule à dépression.

Other characteristics and advantages of the invention will emerge from the description which follows of an embodiment given only by way of example and illustrated by the appended drawings in which:

• - Figure 1 is a schematic view of the cold start flap mechanism of a conventional carburetor, representing said mechanism in the "pushed back" position of the choke;
• - Figure 2 is a view similar to Figure 1 showing the mechanism in the position preceding the cold start, the choke being pulled fully;
• - Figure 3 shows the mechanism in the same position of the choke as in Figure 2, but immediately after starting the engine
• - Figure 4 shows the mechanism of Figures 1 to 3 in the partially pushed back position of the choke;
• - Figure 5 is a schematic view of a starting flap mechanism according to the invention shown in a position equivalent to that of Figure 1;
• - Figure 6 is a view of the mechanism of Figure 5 shown in a position equivalent to that of Figure 2;
• - Figure 7 is a view of the mechanism of Figures 5 and 6 shown in a position equivalent to that of Figure 3;
• - Figure 8 is a view of the mechanism of Figures 5 to-7 shown in a position equivalent to that of Figure 4;
• FIG. 9 is a graph showing the consumption curve A of an engine operating cold with a conventional carburetor, the consumption curve B of the same engine equipped with a carburetor having a cold start mechanism according to the invention and the curve C of the same motor after hot start; and
• - Figure 10 is a partial sectional view of a particular embodiment for applying the vacuum from the intake manifold to the vacuum capsule.

FIG. 1 schematically illustrates the mechanism with a conventional starting flap of a carburetor of which the outline of the body 1 has been shown in fine lines, assumed to be transparent for the clarity of the drawing. The body 1 comprises a venturi 2 in which is mounted a fuel spray device 3. Downstream of the venturi 2, a throttle valve 4 is rotatably mounted around an eccentric axis 5 between a completely closed position delimited by a stop 6 and a fully open position. The rotation of the butterfly 4 is controlled by a lever 7 to which is hooked a spring 8 urging the butterfly 4 towards its closed position.

An air flap 9 for the cold start is also rotatably mounted around an eccentric axis 10 in the body 1, upstream of the venturi 2. This flap can switch between a completely closed position delimited by a stop 11 and a total open position which is that shown in Figure 1. The axis 10 is integral with one end of a lever 12 which controls the movements of the air flap 9 between its open and closed positions. A spring 13 attached to the lever 12 biases the flap 9 towards its closed position.

The other end of the lever 12 is connected by a linkage 14 to the membrane 15 of a capsule 16 whose internal volume is placed in communication by a pipe 17 with that of the intake manifold (not shown) of the engine (also not shown) on which the carburetor is mounted. When a vacuum prevails at the intake manifold, the membrane 15 is drawn towards the inside of the capsule against a spring 18.

The linkage 14 comprises a first link 19 articulated at one end on the lever 12 and the other end of which 20 is slidably received in a buttonhole 21 of a second link 22 integral in translation with the membrane 15.

The articulation axis 23 of the lever 12 with the connecting rod 19 is guided in a light 24 of a cam 25 articulated around an axis 26 parallel to the axes 5, 10 and 22. The rotational movements of the cam 25 around of its axis 26 are controlled by a lever 27 integral with the axis 26 and a rod 28 with manual actuation. A part of the external contour of the cam 25 constitutes a first cam surface D with which the free end of the lever 7 cooperates, while the opposite edges of the light 29 define two other cam surfaces E and F with which the end of lever 12.

In the following description of the operation of the device described above, it will be assumed that it equips a motor vehicle engine, it being understood that the invention is not limited to such an application. Before the cold start of the engine, the vehicle stopped, the choke is normally pushed back fully, which corresponds to the position shown in Figure 1: the throttle valve 4 is then completely closed and the starting flap 9 completely open.

Before starting, the choke is pulled out fully, thus moving the rod 28 from the position in FIG. 1 to that of FIG. 2. This results in a rotation of the lever 27 in the direction of the arrow F and a consecutive rotation of the same angle of the cam 25 which comes into the position of FIG. 2. During this rotation, the end 23 of the lever 12 follows the cam surface E under the effect of the traction exerted by the spring 13, until that the flap 9 arrives in the closed position delimited by the stop 11. The bearing of the flap 9 against the stop 11 can occur before the cam has completed its rotational movement so that, as shown in the figure 2, the end 23 of the lever 12 may be slightly detached from the cam surface E. The lengths of the links 19 and 22 and of the buttonhole 21 are such that, in this position, the membrane 15 being completely pushed back by the spring 18, the end 20 of the link is in support against the bottom of the buttonhole 21, on the side of the free end of the link 22. Simultaneously, during the rotation of the cam 25, the cam surface D gradually pushes the lever 7 to half open the throttle valve 4 as far as in the position of figure 2.

Once the engine has started, a vacuum is created in the intake manifold, downstream of the throttle valve 4, because it is only slightly ajar. This vacuum is also applied to the capsule 16 by the pipe 17 and attracts the membrane 15 against the spring 180 The displacement of the membrane 15 causes that of the articulation 23 of the rod 19 with the lever 12, until this articulation abuts against the surface of cam F of the lumen 26, as shown in Figure 3. This defines a half-open position of the choke 9, which ensures a slight loss of fuel / air mixture from the start of m _'tor and avoids its choking immediate. Of course, in this position which corresponds to the accelerated idle, the position of the cam 25 has not varied, the choke being always fully pulled.

As soon as the engine has turned sufficiently after starting, a first "pushing" of the choke is carried out which brings the cam 25 into the position shown in FIG. 4. During the rotation of the cam 25, the cam surface E pushes back the articulation 23 and rotates the lever 12 and the air shutter 9 to the partial open position of FIG. 4. The air / petrol mixture supplied by the carburetor is therefore leaner than in the case of accelerated idling of Figure 3, while still being substantially richer than in the fully open position of the air flap. The rotation of the cam 25 also has the effect of allowing the butterfly valve 4 to close thanks to the adapted profile of the cam surface D.

It can be seen that, in this position in FIG. 4, the membrane is fully drawn into the capsule 16 under the effect of the depression due to the closing of the throttle valve. However, the movement of the membrane then no longer has any influence on that of the articulation 23 and of the flap 9 because it is the buttonhole 21 which moves relative to the end 20 of the rod 19. In d In other words, from this moment, the carburetor provides the engine with a mixture of relatively high richness, whatever the engine speed (idle, acceleration, deceleration or stabilized speed). This richness can only be reduced by manually pushing the choke as the engine warms up. When the engine has reached a normal operating temperature, the choke should in principle be pushed back fully and the flap 9 will be wide open, as shown in Figure 1.

Reference will now be made to FIGS. 5 to 8 which represent the starting flap mechanism according to the invention in different positions corresponding respectively to those of FIGS. 1 to 4 and on which the same reference numbers increased by the number 100 have been used to designate analogous elements.

This mechanism differs from the conventional mechanism described above essentially by the shape of the cam and the production of the linkage-capsule assembly. More specifically, the cam 125 has an external contour, a first part of which constitutes a cam surface D 'cooperating with the end of the lever 107 and playing the same role as the cam surface D, namely ajar the butterfly valve 104 when the choke is fully fired. On the other hand, unlike the cam 25, the cam 125 does not include a light but an appendage 130 in the form of a hook, the inner contour of which constitutes a cam surface F 'extending another cam surface E'. This cam surface E ′ plays the same role as the cam surface E and is defined by a second part of the external contour of the cam 125. On the other hand, the linkage 114 is a simple link articulated on the lever at 123 and on the membrane 115 of the capsule 116. As will emerge from the following description, the length of the link and the stroke of the membrane 115 are adapted to allow tilting of the flap 109 between its fully closed position and its position d total opening.

Figure 5 shows the mechanism in the position where the choke is fully pushed. In this position, the mechanism according to the invention plays exactly the same role as that of FIG. 1, the cam surface E 'holding the flap 109 in the fully open position.

When the choke is fully pulled, before starting the engine, the mechanism takes the position of FIG. 6. The shutter 109 is then completely closed by the traction exerted by the spring 113 while the butterfly 104 is ajar by the interaction between the cam surface D 'and the lever 107.

As soon as the engine starts, the vacuum of the intake manifold is applied to the capsule 116 and the membrane 115 applies the joint 123 against the cam surface F '. The flap 109 then takes a half-open position as shown in FIG. 7. Up to this stage, the operation of the mechanism according to the invention is therefore identical to that of the conventional mechanism.

At the first "push" of the choke, the appendix 130, which acts as a stop, is retracted by the rotation of the cam 125, as shown in FIG. 8: in fact, in this position of the cam 125, the lever 112 is free to switch between the fully open position of the shutter of FIG. 8 and a minimum open position delimited by the abutment of the joint 123 against the cam surface E '•

Consequently, the position of the starting flap 109, and therefore the enrichment of the mixture, no longer depend solely on the position of the choke, but also on the operating conditions of the engine. Thus, at idle, during deceleration or at steady speed, the vacuum in the intake manifold is high because the opening of the throttle valve is small. As shown in FIG. 8, the membrane 115 then has maximum clearance and completely opens the air flap 109. The engine, although cold, operates with an unenriched mixture identical to that which is supplied to it hot. On the other hand, as soon as, during acceleration or uphill, the throttle valve is wide open, the vacuum at the intake manifold decreases rapidly and the springs 113 and 118, suitably sized, immediately remind of the flap 109 in its position opening imposed by the ramp E 'which corresponds substantially to that of Figure 4. We then find the enrichment conditions of a conventional carburetor allowing the engine still cold to respond to a heavy load.

Unlike the conventional mechanism in which the membrane no longer has any effect from the first "push back _" of the choke, the membrane 115 of the mechanism according to the invention continues to adapt the richness of the mixture to the load of the engine until the choke has been pushed back completely. The mechanism according to the invention therefore makes it possible to achieve significant fuel savings by depleting the mixture in all conditions where the cold engine is operating under low load. Figure 9, which shows consumption curves in liters / 100 km as a function of the mileage covered after start-up, illustrates the savings thus achieved: indeed, curve B consumption of an engine equipped with an improved carburetor according to the invention after cold start indicates consumption considerably lower than that of the same engine operating under the same conditions, but with a conventional carburetor (A).

However, statistical studies have shown that a large number of vehicles make only one or more journeys of a few kilometers each day. Under these conditions of use, the fuel economy provided by the carburetor according to the invention compared to a conventional carburetor is evaluated at around 40% _c

Reference will now be made to FIG. 10 which shows, in partial section, a particular embodiment of the carburetor body 101 according to the invention mounted on an intake manifold 131. In this example, the pipe 117 opens out by two conduits in parallel 132 and 133 in a duct 134 which communicates with the interior volume of the intake manifold 131. The duct 132 has a calibration 135 while a unidirectional ball valve 136 is interposed between the duct 117 and the duct 133.

In operation, when the throttle valve 104 opens, the vacuum in the intake manifold 131 momentarily decreases: the vacuum which then prevails in the vacuum capsule 116 lifts the ball 136, which in turn makes it possible to decrease very quickly the depression at the level of the capsule 116. Consequently, the closing of the flap 109 is very rapid and makes it possible to ensure a shelter. immediate mixing of the mixture to meet the demand for acceleration.

On the contrary, during the increase in the vacuum in the intake manifold 131, the application of this vacuum to the capsule 116 is slowed down by the calibration 135, so that the speed of opening of the flap 109 is reduced, thus ensuring a gradual depletion of the mixture.

Claims (5)

1. Carburetor comprising at least one body (101) provided with a positive dis- ₈ of fuel spraying (103), an air damper (109) rotatably mounted in the body (101) upstream of the spraying device , a throttle valve (104) for controlling the load of the motor rotatably mounted in the body downstream of the spraying device, elastic means (113) urging the air flap towards its fully closed position, a device (116) d actuation of the vacuum-sensitive shutter reigning at the intake manifold, a linkage (112, 114, 123) connecting the vacuum-sensitive device (116) and the air shutter (109) comprising at least one articulation (123), said actuation device sensitive to vacuum (116) and said linkage being arranged to allow tilting of said flap (109) between its fully closed position and a maximum open position against the elastic means (113), and a manually actuated cam (125) rotatably mounted between a pre 1st position, corresponding to cold start, where it cooperates with said linkage to limit the stroke at the opening of the flap (109) in a semi-open position, at least a second position, corresponding to cold operation, where it allows tilting of the shutter (109) between a minimum open position and said maximum open position and a third position where it keeps the air shutter (109) in the fully open position, characterized in that the cam ( 125) comprises an appendage (130) which, in the first position of the cam (125), is interposed in the path of movement of the joint (123) and which, in the second position of the cam (125), is found outside the path of movement of the joint (123). 2. Carburetor according to claim 1, characterized in that the cam (125) has a first surface (E ') which cooperates with the articulation (123) to fix the minimum opening position of the flap (109) in the second position of the cam and fix the fully open position of the flap (109) in the third position of the cam (125), and a second surface (F ') formed on the appendage and which cooperates with the articulation (123) to fix the position of the shutter ajar in the first position of the cam (125). 3. Carburetor according to any one of claims 1 and 2, characterized in that the linkage is constituted by a link (114) connected respectively to a movable membrane (115) of the device sensitive to depression (116) and, by l articulation (123), to a lever (112) integral in rotation with the air flap (109). 4c Carburetor according to any one of claims 1 to 3, characterized in that the maximum open position is the fully open position of the flap (109). 5. Carburetor according to any one of claims 1 to 4, characterized in that the vacuum capsule (116) communicates with the interior volume of the intake manifold (131) via two parallel conduits comprising, l 'One (132) a calibration (135) and the other (133) a one-way valve (136) which cooperate to ensure a deceleration at the opening of the air flap (109).

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