EP0115447A1 - Carburettor with enrichment device controlled by an electromagnetic valve - Google Patents

Abstract

1. Carburetor for an internal combustion engine comprising a main fuel delivery circuit which opens at the throat of a venturi (17) which is located in the induction passage of the carburetor, a circuit for idling and low load running which opens into the induction passage downstream of a driver controlled throttle (12) and an enrichment device for delivering additional fuel to the induction passage during certain phases of operation of an engine fed by the carburetor, the device being provided with an adjustment electrically controlled valve (40) which is energized by an electronic circuit which is responsive to at least one operating parameter of the engine and which is adapted to deliver control pulses having a variable duty ratio, characterized in that it comprises an acceleration pump (23) provided with an inlet conduit having a non-return check valve (25a) and a delivery channel (26) which feeds the induction passage and the idling circuit with fuel, on which channel said electrically controlled valve (40) is located, the pump being arranged for the vacuum which prevails in the induction passage to be able to draw fuel through the pump and the electrically controlled valve when the latter is open, in that the electronic circuit (41) is responsive to at least one operating parameter among speed, engine temperature and degree of opening of the throttle, and in that the delivery channel (26) of the pump opens into the induction passage, at a location close to the throat of the venturi, through two coaxial passages (28, 42) which are separated by a chamber which communicates with the idling circuit (18) of the carburetor, which possibly has no other fuel supply than the acceleration pump.

Description

The present invention relates to carburetors for internal combustion engines of the type which include a main fuel spouting circuit opening at the neck of a venturi placed in the intake duct, an idling and low-load running circuit opening in the intake duct downstream of a throttle unit controlled by the driver and an enrichment device for supplying the intake duct with additional fuel during certain operating phases of an engine powered by the carburetor , device provided with an adjustment solenoid valve supplied by an electronic circuit sensitive to at least one operating parameter of the engine and capable of supplying pulses of variable duty cycle control.

Among the carburetors of this type, mention may be made in particular of that described in patent application FR-A-2 419 403. The enrichment device, designed to deliver fuel both in the venturi and in an air channel of the idling circuit, is controlled by an electronic circuit intended to bring the air / petrol mixture supplied to the engine to the stoichiometric composition. This solves the problems of engine operation in steady state, both at high load and at low load. But it is not possible to make a motor work properly by supplying it, at all speeds, with a stoichiometric mixture of air and gasoline. Certain operating phases, such as acceleration, cold running or full load, make it necessary or at least desirable to supply the engine with a rich mixture. To achieve this result, provision has generally been made hitherto for independent circuits to fulfill various functions. However, it is difficult to control in a simple manner the flow rate of fuel supplied by the various circuits so that the composition and the quantity of mixture supplied to the engine at all speeds are satisfactory.

The present invention aims to provide a carburetor which meets the requirements of practice better than those previously known, in particular in that it makes it possible to satisfactorily adjust the richness of the mixture supplied to the engine, at all speeds, using only simple means.

To this end, the invention proposes in particular a carburetor of the kind defined above, characterized in particular in that it comprises a recovery pump provided with an intake duct equipped with a non-return valve and with a delivery pipe supplying the intake pipe and the fuel idling circuit, on which said solenoid valve is interposed, the pump being provided so that the vacuum which prevails in the intake pipe is capable of sucking fuel through the pump.

In an advantageous embodiment of the invention, the discharge pipe of the pump opens into the intake pipe, near the neck of the venturi, by means of two coaxial passages separated by a chamber communicating with the circuit of carburetor idle, which has no fuel supply other than the acceleration pump.

So that a failure of the electronic circuit results in degraded, but still acceptable, functioning of the carburetor and not by an almost impossibility of starting the engine and making it run cold, the solenoid valve is advantageously of the open type at rest. To avoid a risk of self-ignition when the engine stops, it is advisable to provide the electronic circuit with a time delay which keeps the solenoid valve closed for a determined period of time after switching off the ignition. This same circuit can be provided to cut off the supply of fuel to the engine during deceleration operation, that is to say when the engine rotates beyond a predetermined speed while the throttle valve is in the open position. minimal.

We see that the invention makes it possible to reduce the number to 1 of solenoid valves required to fulfill several functions of a very different nature, which constitutes a very significant simplification compared to the solutions previously proposed.

Furthermore, the invention makes it possible to use an acceleration pump controlled by vacuum, that is to say much simpler than a pump controlled by a mechanical linkage from the main throttling member. We know that the acceleration pumps controlled by vacuum - have been abandoned practically at present due to their serious drawback: when the engine stops, the acceleration pump injects its contents into the admission. This drawback is eliminated, in a particular embodiment of the invention, by providing a narrow orifice for communication between the discharge chamber of the acceleration pump and the constant level tank which supplies it. The solenoid valve remaining closed for a determined time interval after switching off the ignition, the discharge compartment of the accelerator pump is emptied into the tank at constant level.

The invention is capable of being applied to very different carburetors, and in particular to so-called constant vacuum carburetors, although it seems particularly advantageous in the case of so-called variable vacuum and fixed nozzle carburetors.

The invention will be better understood on reading the following description of a variable vacuum carburetor which constitutes a particular embodiment given by way of non-limiting example. The description refers to the single figure which accompanies it and shows those of the constituents of the carburetor which are concerned by the invention, in schematic form, partially in elevation and partially in vertical section through the axis of the intake duct.

The inverted carburetor shown in the Figure comprises a body (10) in several assembled parts in which is formed an intake duct 11. The lower part of the duct 11 contains a main throttling member formed by a butterfly 12 carried by a rotary axis 13 and controlled by the driver by means of a linkage not shown. The upper part of the duct 11 constitutes an air inlet 14 generally provided with an air filter, not shown, and containing an air flap 21 belonging to a starting system which will be described later.

The fuel supply circuits to the engine are supplied by a tank 15 at constant level N. This tank supplies a main fuel spouting circuit which will not be described in detail since it may be of conventional constitution. It will generally comprise an emulsion well 47 supplied from the constant level tank 15 and connected to a passage 16 opening at the neck of a venturi 17. A slow-motion and idling circuit at low load comprises a channel 18 which opens into downstream in the intake duct, on the one hand, by an idle orifice 19 situated downstream of the end of the butterfly valve whatever the position of the latter and, on the other hand, by progression holes 20, also called "bypass holes", located so as to pass from upstream to downstream of the end of the butterfly 12 when the latter is ajar from its minimum open position to bring it to the position shown in 12a.

The air flap 21 belonging to the starting device is carried by an eccentric pin 22. It is controlled either manually from a pull tab located on the dashboard, or automatically as a function of the engine temperature, for example by a bimetallic strip. This air flap 21 causes, when it is closed while the engine is running, a high vacuum at the outlet of the main spouting circuit.

The carburetor further comprises an acceleration pump 23. The pump shown in the Figure, of the vacuum-controlled type, comprises a variable volume chamber 24 connected to the tank 15 by a suction channel 25 provided with a valve d 25a. This chamber 24 is also connected to the intake duct by a discharge channel 26. The chamber 24 is delimited by a movable pumping member, constituted by a flexible membrane 29 which separates it from a chamber 30 connected by a channel 31 to the part of the intake duct 11 situated downstream of the butterfly valve. A spring 32 contained in the chamber 30 tends to push the membrane in a direction tending to decrease the volume of the chamber 24. A stop (not shown) can be provided to limit this movement.

The operation of such a pump is well known. When the driver opens the throttle valve 12 while the engine is running, the vacuum decreases in the chamber 30 and the spring 32 pushes the diaphragm 29 and discharges fuel from the chamber 24 towards the intake duct 11. The pump 23 also fills a role of enricher under load, the vacuum which then prevails at the neck of the venturi 17 being sufficient to suck fuel from the chamber 24 towards the conduit.

In the illustrated embodiment of the invention, a solenoid valve 40 intended to be controlled by pulses of variable duty cycle is interposed on the discharge conduit 26. This solenoid valve is controlled by an electronic circuit 41 capable of supplying current slots variable duty cycle between 0 and 1, ratio determined by the value of the input signals it receives from various sensors sensitive to engine operating parameters.

The discharge channel of the pump is designed to be able to supply the intake duct either directly, near the neck of the venturi, or via channel 18 of the idling circuit. For this, the calibrated orifice 28 through which the fuel from the channel 26 escapes opens into the channel 18 of the idling circuit. The passage 42 for supplying air to the channel 18 is placed in the extension of the injection orifice 28. In order for the injection into the intake duct to take place properly, the passage 42 is of larger section than that of the orifice 28: this is not a particular subjection, an air inlet orifice always having a diameter greater than the associated fuel inlet orifice.

In order to avoid the drawback of the usual vacuum acceleration pumps, an orifice 43 of small section connects the variable-volume chamber 24 of the pump 23 to the tank 15.

The electronic circuit 41 constitutes a calculation unit making it possible to develop the duty cycle of the pulses supplied to the solenoid valve 40 from various input signals. The frequency of the pulses may be constant and fixed by an oscillator incorporated in circuit 41. More frequently, it will be fixed by the speed of the engine: it suffices for this to place, for example on the ignition distributor, a sensor providing a pulse per turn.

The input signals received by the sensor must make it possible to calculate the duty cycle to be given to the control pulses of the solenoid valve at idle and at full load. One can choose, as corresponding information, the speed of rotation of the motor V supplied by a sensor 45 and the opening angle a of the throttle valve 12, supplied by a sensor 44. Other parameters can be used, in particular the vacuum which reigns downstream of the butterfly 12.

In addition, to calculate the duty cycle required during cold operation, a signal representative of the engine temperature must be supplied to the circuit 41. This signal can be obtained using a sensor 46 subjected to the temperature of l engine cooling water.

In general, it will be advantageous to use a circuit 41 comprising a memory of the so-called "cartographic" type, providing a value of the duty cycle for each pair of values V, a. To the value provided by the memory is applied a correction coefficient, additive or multiplicative, function of the temperature e. Finally, the circuit 41 will include timing means, making it possible to supply a duty cycle signal 1 during a deter mined (usually a few seconds) after switching off the ignition.

• Lorsque le moteur est au ralenti, c'est-à-dire que le papillon 12 est dans sa position d'ouverture minimale et que la vitesse est faible, la forte dépression qui règne dans le conduit d'admission 11 en aval du papillon aspire du combustible orovenant de la chambre 24 à travers un clapet anti-retour éventuel, le canal 26 et l'orifice calibré 28 qui joue le rôle de gicleur de ralenti. En même temps, la dépression aspire de l'air d'émulsion par le passage calibré 42. Le rapport cyclique des signaux fournis à l'électrovanne 40 est déterminé par le circuit 41 en fonction de la température 8 du moteur, ou d'un autre paramètre : cet effet se combine à celui du volet d'air 21 qui assure un enrichissement énergique au cours de la phase de lancement et au cours des premières secondes de fonctionnement.

The operation of such a carburetor is then as follows, during the phases where circuit 41 intervenes. Idling of the engine and progression:

• When the engine is idling, that is to say that the throttle valve 12 is in its minimum open position and that the speed is low, the strong vacuum which prevails in the intake duct 11 downstream of the throttle valve fuel coming from the chamber 24 through a non-return valve, the channel 26 and the calibrated orifice 28 which acts as an idle jet. At the same time, the vacuum draws in emulsion air through the calibrated passage 42. The duty cycle of the signals supplied to the solenoid valve 40 is determined by the circuit 41 as a function of the temperature 8 of the engine, or of a another parameter: this effect is combined with that of the air flap 21 which provides energetic enrichment during the launch phase and during the first seconds of operation.

Interruption of the idling circuit during deceleration:

When the sensor 44 indicates that the throttle valve is closed and that the sensor 45 indicates that the speed exceeds a threshold corresponding to deceleration operation, the circuit 41 excites the solenoid valve 40 in direct current, which cuts off the supply of fuel to the engine. The element of the circuit 41 necessary for this function can be very simple and be limited to a door indicating the presence of the two conditions. Optionally, a third condition (very high depression in the intake manifold, gear ratio engaged, etc.) can be provided. It requires the presence of an additional sensor.

Choking when switching off the engine ignition:

On certain engines, it is necessary to stop the supply of fuel through the idling circuit when the engine ignition switch is cut off, to prevent the engine from continuing to operate in self-ignition.

To achieve this result, it is sufficient for the circuit 41 to be provided to supply, for a predetermined period of time after switching off the ignition, a continuous signal for closing the solenoid valve 40.

This time delay also makes it possible to prevent the acceleration pump 23, if it is pneumatically controlled, from sending the fuel contained in the chamber 24 to the intake duct 11. For this, it suffices that the time delay (duration of closing of the solenoid valve 40 after switching off the ignition) is sufficient for the fuel contained in the chamber 24 to be returned to the tank at constant level by the calibrated orifice 43 before reopening.

Acceleration

When the butterfly valve 12 opens, the reduction in vacuum in the chamber 30 causes the membrane 29 to move by the spring 32 (to the right in the Figure). Fuel is discharged to the intake duct 11 via the discharge channel 26, the calibrated orifice 28 and the passage 42. The orifice 43 returning to the tank is obviously of significantly smaller cross section than the orifice 28. The passage 42, of larger section than the calibrated orifice 28, advantageously has a frustoconical shape flared upwards.

The circuit 41 can be provided to modulate the quantity of fuel sent by the pump 23 as a function of the engine temperature (or other parameters, for example the brutality of the acceleration). For this, the circuit 41 adjusts the opening duty cycle of the solenoid valve 40 as a function of the representative temperature signal supplied by the sensor 46 or of any other signal representative of an acceleration parameter. It should be noted that one can obtain, from the opening signal supplied by the sensor 44, an opening speed signal, by bypass.

Modulation of the richness at full engine load:

When the engine is running at full load, i.e. the throttle valve 12 is wide open, the vacuum which prevails at the neck of the venturi 17 sucks fuel from the chamber 24 via the passage 42, the orifice 28 and the discharge channel 26. This operating regime can be detected from the signals provided by the sensors 44 and 45. The circuit 41 can be provided to then supply the solenoid valve 40 with a control signal the duty cycle of which is determined by pre-programmed values as a function of one or more parameters, for example the speed of the engine. These values are contained in a memory associated with circuit 41.

Engine running cold:

The carburetor shown in Figure has a starting flap 21 which when in the closed position where it is shown, provides the high enrichment necessary for starting the engine. The butterfly is then held in a slightly open position (position 12a indicated in dashes in the Figure) so that the vacuum generated by the engine is transmitted to the outlet of the main spouting system 16. The control of the air shutter 21 and that of the butterfly can be ensured by conventional means, which therefore need not be described here. The starting flap 21 is intended to open quickly after starting the engine. The richness necessary for the proper functioning of the engine is subsequently ensured, during heating, by the circuit which sends the solenoid valve 40 a signal the duty cycle of which is essentially a function of the temperature signal supplied by the probe 46.

Operation in stabilized operation at normal operating temperature:

The circuit 41 can be provided to then supply the solenoid valve 40 with a continuous current of permanent closure. But the circuit can also be provided to intervene then, by using the fact that the vacuum, coming from the neck of the venturi and from the idle channel 18, applied to the outlet of the orifice. 28, makes it possible to draw fuel through chamber 24. This flow rate can be adjusted by modulating the duty cycle of the control signals of the solenoid valve 40 as a function of operating parameters of the engine. In particular, it is then possible to perform closed loop operation by supplying the circuit 41 with a signal representative of the composition of the engine exhaust gases. This signal can be provided by a lambda probe 48 (in dashes in the Figure) plunging into the exhaust manifold 49.

However, this complication will generally not be desirable, unless it is necessary to meet the requirements of binding pollution legislation.

We will not describe here the constitution of the 4-1 _' circuit, because many different arrangements can be used. However, it should be noted that this circuit will generally include a digital computing device, for example a microprocessor associated with a working RAM and with read only memories for storing preprogrammed values, as well as at least one analog-digital converter for converting the analog parameters supplied by the sensors in digital data usable by the computing unit.

The invention is susceptible of numerous variant embodiments and, in particular, it is adaptable to a constant vacuum carburetor, in which an auxiliary throttle member movable as a function of the flow rate which traverses the intake duct gives a section of passage of fuel towards the intake duct a value depending on its position, itself representative of the air flow.

Claims (10)

1. Carburetor for internal combustion engine comprising a main fuel spouting circuit opening at the neck of a venturi (17) placed in the intake duct of the carburetor, a low-load idling and running circuit opening in the duct intake system downstream of a throttle unit (12) controlled by the driver and an enrichment device for supplying the intake pipe with additional fuel during certain operating phases of an engine powered by the carburetor , device provided with an adjustment solenoid valve (40) supplied by an electronic circuit sensitive to at least one operating parameter of the engine and capable of supplying control pulses of variable duty cycle, characterized in that it comprises a pump recovery or acceleration (23) provided with an intake duct fitted with a non-return valve and a discharge channel (26) supplying the intake duct and the idling circuit in fuel, channel on which said solenoid valve is interposed, the pump being provided so that the vacuum which prevails in the intake duct is capable of sucking fuel through the pump. 2. Carburetor according to claim 1, characterized in that the discharge channel (26) of the pump opens into the intake duct, near the neck of the venturi, by means of two coaxial passages (28, 42) separated by a chamber communicating with the idle circuit (18) of the carburetor, which may have no other fuel supply than the acceleration pump. 3. Carburetor according to claim 2, characterized in that the passage (42) for communication between the chamber and the intake duct is of greater section than the passage (28) for communication of the discharge channel (26) with the circuit of idle (18). 4. Carburetor according to claim 1, 2 or 3, characterized in that the solenoid valve (40) is of the open type at rest and in that the electronic circuit (41) includes a time delay for keeping the solenoid valve closed for a predetermined time after switching off the ignition of the engine. 5. Carburetor according to any one of the preceding claims, characterized in that the acceleration pump is of the vacuum-controlled type and comprises an orifice (43) for communication between the variable volume chamber and the constant level tank (15 ) who feeds it. 6. Carburetor according to any one of the preceding claims, characterized in that the electronic circuit comprises a calculating member associated with a map memory supplying a value of the duty cycle of the signals applied to the solenoid valve for each pair of speed values of rotation of the motor and of the opening angle of the throttle member. 7. Carburetor according to claim 6, characterized in that the electronic circuit is provided with an engine temperature sensor and in that it is provided for applying a correction coefficient, additive or multiplicative, to the duty cycle as a function of said temperature. 8. Carburetor according to any one of the preceding claims, characterized in that said circuit comprises storage means making correspond a value of the duty cycle of the signals applied to the solenoid valve to each temperature value during the cold idling operation. 9. Carburetor according to any one of the preceding claims, characterized in that it comprises an air flap (21) with rapid opening after launching the engine. 10. Carburetor according to any one of the preceding claims, characterized in that the electronic circuit is designed to maintain the solenoid valve in the closed position when the engine operating parameters indicate an operation in deceleration.

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