GB2041088A

GB2041088A - Improvements in carburettors for internal combustion engines

Info

Publication number: GB2041088A
Application number: GB8002053A
Authority: GB
Original assignee: Societe Industrielle de Brevets et dEtudes SIBE
Current assignee: Societe Industrielle de Brevets et dEtudes SIBE
Priority date: 1979-02-09
Filing date: 1980-01-22
Publication date: 1980-09-03
Also published as: IT1127344B; FR2448638A1; DE2945576C2; FR2448638B1; GB2041088B; IT8047844A0; DE2945576A1; BR8000865A

Abstract

Fuel flow from the main and slow-running systems is controlled in response to the signal from the exhaust gas oxygen probe 39 by a solenoid valve 37, 38 which when open connects the air bleed chamber 32 to atmosphere or alternatively to atmosphere or a vacuum chamber connected to the venturi throat or the intake passage 1 downstream of the throttle valve 2. <IMAGE>

Description

SPECIFICATION Improvements in carburetors for internal combustion engines The invention relates to a carburetor for an internal combustion engine of the kind which comprises a main fuel circuit opening into the intake duct of the carburetor upstream of an operator controlled throttle and an idling and progression circuit for supplying to the engine a flow of air-fuel mixture for correct operation of the engine at low speed and low load, said carburetor comprising means for metering emulsion air delivered to said circuits in response to an operating parameter of the engine, typically the composition of the exhaust gases, so as to form a regulation loop which maintains the air/fuel ratio of the mixture supplied to the engine at a predetermined value.

Carburetors are known in which the flow of emulsion air or primary air admitted into each of the fuel circuits is regulated by means of electromagnetic or solenoid valves which are alternately opened and closed. Two electromagnetic valves are then placed respectively in the main and idling circuits of the carburetor; the electromagnetic valve placed in the air intake to one circuit closes when an oxygen probe, in contact with the exhaust gases, indicates too low a mixture, and conversely.

This arrangement presents disadvantages: during the closing and the opening of each electromagnetic valve in response to the information supplied by the oxygen probe, the air/fuel ratio of the mixture supplied to the engine changes abruptly, which may cause uneven operation of the engine. Each of the circuits comprises an electromagnetic valve; several electromagnetic valves are therefore necessary to regulate the air/fuel ratio of the main fuel circuit. of the idling circuit of the engine, and possibly of other fuel circuits required for some carburetors; the cost is consequently increased.

It is an object of the invention to provide a carburetor of the above-mentioned kind which achieves progressivity of the air/fuel ratio correction, while simple in construction.

For that purpose, there is provided a carburetor of the above-defined kind, in which said metering means comprise a chamber connected to said circuits through calibrated restrictors and to an air source by an electromagnetic valve associated with a control circuit arranged to bring the electromagnetic valve into a maximum opening position and into a minimum opening position depending on the signal supplied to the circuit by a probe sensitive to said operating parameter of the engine associated with the carburetor.

In general, the electromagnetic valve will have a fully open condition and a closed condition. However, the electromagnetic valve may be of the three-way type for either connecting the chamber to the atmosphere, or connecting it to another air source, for example a vacuum compartment connected to a portion of the intake duct of the carburetor, such as the venturi throat or the part of the intake duct situated downstream of the throttle member, or closing it. This arrangement has the advantage that the compartment may be subjected to a vacuum which is directly related to the operating conditions of the engine.

The emulsion air inlet to each circuit may comprise, immediately downstream of its restrictor, a ventilation chamber and the chambers may be in communication by restricted openings. The restrictors may be of fixed section or some at least of them may be adjustable, for instance by a screw.

The invention will be better understood from the following description as a downdraught carburetor which constitutes a particular embodiment of the invention, given by way of example. The description refers to the accompanyying drawing, in which: Figure 1 is a schematical cross-section of the carburetor, the electromagnetic valve supplying the ventilation chambers of the fuel circuit being in open condition; Figures 2 and 3 show respectively, with respect to time, the opening and closing alternations of the electromagnetic valve and the variations which result therefrom of the fuel/ air ratio of the mixture delivered to the engine.

Referring to Fig. 1, there is shown a downdraught carburetor having an intake duct 1 provided with a throttle member 2 formed by a butterfly valve controlled by the operator by means of a linkage (not shown). The upper part of duct 1 forms an air inlet 3, generally provided with an air filter (not shown). The carburetor is provided with a starting device, not shown because it has no direct connection with the invention.

The main fuel circuit of the carburetor is supplied with fuel from a chamber 4 in which the fuel is maintained at a constant level N by a float 5, by means of a main jet 6.

Air and fuel are mixed in a well 8 in which dips a conventional emulsion tube 9, provided at its upper end with an emulsion air intake restrictor 7 and formed with orifices 10 dis posed below fuel level N. The primary mixture which is formed inside tube 9 flows thrau h a passage 11 and emerges at the throat of venturi 12, upstream of the throttle member 2.

The idling and progression circuit opens into the intake duct 1 through holes 13, 14 and 14a. Hole 1 3 is permanently downstream of the edge of throttle member 2, whereas holes 1 4 and 1 4a pass successively from upstream to downstream of the edge when member 2 opens from its minimum opening position, determined by a stop member (not shown). Holes 13, 14 and 1 4a are supplied with air-fuel mixture by a duct 1 5.

The fuel supply to the second circuit comprises a passage 1 6 which opens upstream into well 8 and which communicates with duct 1 5 through an idling jet 17, having a calibrated cross-sectional area. The air required for the air-fuel mixture delivered into the intake duct 1 through holes 13, 14 and 1 4a is fed through a restrictor 1 8. An adjusting screw 1 9 allows the amount of air-fuel mixture supplied by the idling circuit, downstream of throttle member 2, through hole 1 3 to be adjusted.

The venting restrictors 7n of the main circuit and 1 8 of the idling circuit are respectively supplied by chambers 30 and 31.

Chambers 30 and 31 are connected to a common chamber 32 by respective calibrated orifices 33 and 34. Calibrated orifices 33 and 34 have a cross-sectional area greater, typically by about 20%, than that of restrictors 7 and 18. Chamber 32 is connected to an air source, the atmosphere in the case of Fig. 1, through a duct 35. A passage 36 in duct 35 is controlled by the movable part 37 of an electromagnetic valve 38. In the embodiment illustrated, the movable part of the electromagnetic valve assumes one or the other of two end positions, according as to whether the electromagnetic valve is fed by an electronic circuit 41 or not. In one of the positions, the electromagnetic valve is wide open.

In the other, the movable part 37 closes completely or partially passage 36. In the latter case, the electromagnetic valve may be of the type described in European patent application published under No. 0006770.

The electronic circuit 41 is connected to a probe 39 mounted on the exhaust manifold of the engine. Probe 39 is for example an oxygen probe, supplying a signal which varies rapidly when the air/fuel ratio of the mixture supplied to the engine passes from a substoechiometic value to an over-stoechiometric value. The circuit 41 may be a threshold circuit, which opens the electromagnetic valve 38 when the fuel/air ratio of the mixture supplied to the engine exceeds a definite threshold, slightly greater than unity, and closes it when the ratio becomes less than another threshold, slightly less than unity.

The device operates as follows: When the mixture supplied to the engine, either by the main fuel circuit (when the engine operates on load), or by the idling and progression circuit (when the engine is idling or is operating with a very small load) is too lean, that means that the fuel circuits receive too much air. The cross-sectional area 36, calibrated orifices 33 and 34 and particularly restrictors 7 and 18, are so dimensioned that too much air is received when valve 38 is permanently open.

Probe 39 then delivers to the electronic control circuit 41 an information which causes the electromagnetic valve 38 to come into totally or partially closed position. As a general rule, an electromagnetic valve will be used which is in the open position when not energized From the time when electromagnetic valve 38 is closed, air is drawn by either of the fuel supply circuits from chambers 30 and 32 (or 31 and 32); the pressure drops in the chambers and the air flow rate which is drawn from the chamber decreases. Consequently, the fuel/air ratio of the primary mixture formed in the main circuit or the idling circuit increases progressively, as well as the fuel/air ratio of the mixture supplied to the engine.

As soon as probe 39 indicates an excessive fuel/air ratio, circuit 41 opens the electromagnetic valve.

It will be appreciated that electromagnetic valve 38 comes alternately into the open and closed position, shown schematically by a and b in Fig. 2. The correlative variations of the fuel/air ratio appear in Fig. 3. They are damped down due to the chambers which ensure a progressivity which avoids defective operation of the engine,and, furthermore, allows the electromagnetic valve 38 to operate at a reduced rate, so with slower wear.

The cross-sectional flow areas of the calibrated orifices 33 and 34 will be selected in each case taking into account the volume of chambers 32, 30 and 31. A calibrated passage 45 communicating chambers 30 and 31 may be provided, as shown in Fig. 1, for avoiding an abrupt change in the fuel/air ratio when going over from operation on one fuel circuit to operation on the other.

Numerous modified embodiments are possible. In particular chambers may be provided in addition to chambers 30 and 31 for supplying emulsion air to other fuel circuits. Chamber 32 may comprise a permanent calibrated ventilation hole by-passing passage 36 and permanently open. Circuit 41 may, in some cases, comprise a single theshold value, the inertia of the system being sufficient to avoid operation of the elect magnetic valve 38 at too high a frequency. A single electro-magnetic valve simultaneously controls several circuits, which constitutes a considerable factor of economy.

Claims

1. Carburetor for internal combustion engine which comprises, a main fuel circuit opening into the intake duct of the carburetor upstream of an operator controlled throttle member and an idling and progression circuit intended to supply to the engine an air-fuel mixture for correct operation of the engine at low speed and low load, comprising means for metering the supply of emulsion air to said circuits in response to an operating parameter of the engine, typically the composition of the exhaust gases so as to form a regulation loop which maintains the air fuel ratio of the mixture supplied to the engine at a predetermined value, characterized in that said metering means comprise a chamber connected to said circuits through calibrated restrictors and to an air source by an electromagnetic valve associated with a control circuit arranged to bring the electromagnetic valve into a maximum opening position and into a minimum opening position depending on the signal supplied to the circuit by a probe sensitive to said operating parameter of the engine associated with the carburetor.

2. Carburetor according to claim 1, characterized in that the electromagnetic valve has a fully open end position and a partially or totally closed end position.

3. Carburetor according to claim 1, characterized in that the electromagnetic valve is of the three-way type and is connected either to communicate the chamber to the atmosphere or to communicate it to another air source, for example a vacuum compartment connected to the intake duct of the carburetor or to separate the chamber from air sources.

4. Carburetor according to claim 3, characterized in that said vacuum compartment is connected to the thrust of a venturi or the part of the intake duct situated downstream of the throttle member.

5. Carburetor according to any one of the preceding claims, characterized in that the emulsion air intake to each circuit comprises, downstream of said chamber and upstream of the restriction of said circuit, an additional air supply circuit connected to the first one by a calibrated orifice.

6. Carburetor according to claim 4, characterized in that the additional chambers are communicated by a restricted orifice.

7. Carburetor according to claim 1, constructed and arranged substantially as described with reference to the accompanying drawing.