GB2041086A - Improvements in carburettors for internal combustion engines - Google Patents

Abstract

An automatically controlled choke valve (3) is located upstream of a main fuel supply system and a butterfly valve (2) and a passage for delivering an additional air/fuel mixture is provided with a solenoid closure valve (107). That solenoid valve is controlled by an electronic circuit (111) arranged to deliver periodic electrical signals whose duty ratio depends on the temperature of the engine as detected by a sensor (112). <IMAGE>

Description

SPECIFICATION Improvements in carburettors for internal combustion engines The invention relates to carburettors for internal combustion engines of the kind which comprise an induction pipe, with a main fuel supply system opening thereto between an upstream automatically controlled starting valve and a downstream throttle valve, and an auxiliary mixture passage having an air inlet in the induction pipe downstream of the starting valve, a mixture outlet in the induction pipe downstream of the throttle valve and a closure valve in said passage operatively connected to an element adapted to respond to engine temperaure so as to be closed as the engine temperature increases, the arrangement being such that during and after full opening of the starting valve the volume of auxiliary mixture supplied to the induction pipe is progressively reduced to zero as the engine warms up to its normal operating temperature. Such carburettors will be referred to as being of the type set forth.

When the engine is cold, the enrichment is determined both by the control valve and by the starting valve. When the engine is warm, the enrichment is determined essentially by the closure valve. Finally, when the engine has reached its normal operating temperature, the starting device no longer increases the fuel/air ratio and the mixture flow.

For certain types of engines, it is of advantage to suppress the action of the starting valve, by opening it completely, shortly after starting up the engine; the increased fuel/air ratio of the mixture for cold running is then due to the action of the closure valve.

To this end, the starting valve may be controlled by a first temperature resonsive element which is arranged to heat up rapidly and the closure valve is controlled by a second temperature responsive element which is arranged to heat up slowly, so that the starting valve is put out of action before the closure valve during warm-up of the engine.

Such a construction is described in U.K. Specification 1,432,016. The second element described by way of example in that specification is an element comprising a material contained in a closed enclosure subjected to the temperature of the cooling water of the engine, called "wax capsule".

On certain types of engines, it is difficult to establish short fluid connections between the carburettor and the cooling circuit of the engine and such connections in the form of thick flexible piping are bulky. The water box around the wax capsule also increases the size of the carburettor.

According to the invention, the closure valve comprises a solenoid valve controlled by an electronic circuit arranged to deliver periodic electrical signals whose duty ratio is dependent on a temperature representative of the temperature of the engine fed by the carburettor.

The solenoid valve is typically closed when de-energized; the frequency of the pulses forming the signal may be constant, of from 10 to 30 Hertz for instance.

The electronic circuit advantageously comprises an input member formed by a temperature sensor subjected to the temperature of the cooling water of the engine.

The invention will be better understood from the following description of a particular embodiment of the invention. The description refers to the accompanying figure which is a schematic elevation and with parts in section, of a carburettor in accordance with the invention. The elements are shown in the position which they assume during running of the engine at its normal operating temperature.

For convenience and clarity, the parts corresponding to those described in specification 1,422,01 6, to which reference may be made, are designated by the same reference number.

The carburettor comprises an induction pipe 1 in which is arranged, upstream of a throttle member (or butterfly valve) 2 under the control of the operator, an eccentricaliy mounted starting valve 3 tending to open under the effect of the air flow in pipe 1, against the effect of a return force transmitted by a link 4 to a lever 5, fast with an axle 6 of valve 3.

In pipe 1 is arranged, downstream of valve 3, a fuel supply system 67 which opens in the region of the throat of a venturi 68. The air intake 69 of pipe 1 is connected to the part of pipe 1 situated downstream of butterfly valve 2, in addition to its direct connection, by a circuit comprising, from upstream to downstream, an air passage 70, provided with a calibrated orifice 71, which opens into a chamber 72, and a passage 73 which can connect chamber 72 to pipe 1 downstream of butterfly valve 2. Chamber 72 is fed with emulsified fuel or primary air/fuel mixture through a passage 74 which communicates with a well 75 whose lower portion is connected, through a passage 76 provided with a calibrated orifice 77, to a float chamber 78 with a constant level N. Float chamber 78 contains a float 79 to regulate the introduction of fuel.In well 75 dips a tube 80 which is formed with orifices 81 situated below level N. Tube 80 is supplied with air, from the air intake 69, through calibrated orifices-82 and 83 in series.

The flow in passage 73 is not controlled by progressively changing the cross sectional area between passage 73 and chamber 72, but by modifying the duty ratio or aperture ratio of a valve controlling communication between the passage and the chamber. For that, a solenoid valve 107 is used whose movable part 108 moves between two end positions. In a first position (as shown in the figure), it separates passage 73 from chamber 72. In the second position, it is fully opened.

The control winding 109 of the solenoid valve connected, by an electrical line 110, to an electronic control circuit 111 capable of delivering a periodic electric signal to winding 109, in the form of successive pulses whose duty ratio determines the aperture ratio of the solenoid valve 107. The latter is typically of a type which is closed when not energized by an electric pulse.

The electronic circuit 111 is connected to an input element. In the described embodiment, the element is a temperature sensor 11 2 subjected to a temperature representative of that of the engine. Sensor 11 2 may particularly be a probe subjected to the temperature of the cooling water of the engine and supplying an electrical signal which is a function of that temperature. In some cases, a probe could be used subjected to the temperature of another fluid, for example a lubricant.

The starting valve 3 is controlled by another temperature responsive element, subjected to the action of an electric heating resistor 100 in which a current circulates as soon as a contactor 101, actuated for example as soon as the oil pressure of the engine exceeds a predetermined threshold, is closed. The element shown in the figure is a bi-metallic spiral spring 102 one end 103 of which is fixed and the other end 104 of which is connected to a pin 105 which carries a lever 106 to which is connected link 4.

The starting valve may additionally be provided with a vacuum motor (not shown) responsive to the pressure which prevails in the induction pipe 1 downstream of the throttle member 2. That vacuum motor opens throttle valve 3 by a minimum predetermined opening as soon as the engine is self-operative.

The throttle member 2 may also be provided with conventional means for preventing it from closing beyond a determined position, when the engine is cold. Then, the vacuum created by the engine is communicated to the part of the induction pipe located between throttle member 2 and starting valve 3.

The carburettor operates as follows: it will be assumed that the engine is initially cold and at rest. When it is cranked by the starting motor, the main fuel supply system is subjected to a vacuum which allows the engine to breathe in the flow of very rich air/fuel mixture necessary for successful starting. An additional mixture flow is provided through pas sage 73: the electronic circuit 111 may be provided for supply a DC energizing current to valve 107 when the engine is cold; then, the solenoid valve has an aperture ratio equal to 1 and is permanently open.

As soon as the engine is started up and is sel operating, contactor 101 is closed by the oil pressure. Resistor 100 heats the bi-metallic spiral spring 102 which is progressively de- formed and opens starting valve 3 through the linkage comprising members 106, 4 and 5. As it opens, starting valve 3 reduces the vacuum which is exerted on the main fuel supply system 67. Thus, the fuel/air ratio of the mixture delintered by the main system decreases rapidly, for heating of bi-metallic spiral spring 102 and the correlative opening of the valve may occur fast.Due to the low temperature of the cooling fluid of the engine shortly after start-up, the temperature of probe 11 2 is low and the information transmitted by probe 11 2 to electronic circuit 111 produces a signal formed by pulses having a high duty ratio; this signal is transmitted to solenoid valve 107 by the electrical line 110, thereby valve 107 is open for times which are a high percentage of the period. Below a predetermined temperature of the cooling water of the engine, the electronic circuit 111 may even supply a DC current to solenoid valve 107.

Air flows in passages 70 and 73 and the vacuum transmittd to chamber 72 by calibrated orifice 1, results in emlsified fuel circulating through channel 74.

Thus the additional air/fuel mixture required for proper operation of the engine is obtained.

As the engine heats up, electronic circuit 111, which processes the information supplied by the temperature probe 112, delivers narrower and narrower current pulses, thus reducing the average opening time of the solenoid valve 107 and the additional amount of fuel/air mixture supplied to the engine.

Finally, when the engine reaches its normal operating temperature, the electronic circuit 111 no longer transmits signals to the solenoid valve 107 which, consequently, remains permanently closed.

It is apparent that the invention does not require a flow of cooling fluid inside the carburettor; consequently, the risks of leak are removed. In addition, hydraulic connections are replaced with electrical lines which are easily connected and do not take much place.

The invention is not limited to the particular embodiment given by way of example and, for instance, the electronic circuit may be provided with additional input sensors in order to introduce corrections based on additional operating parameters of the engine. It will be appreciated that the scope of the invention is defined only by the following claims.

Claims (6)

1. A carburettor for an internal combustion engine of the type set forth, wherein the closure valve is a solenoid valve controlled by an electronic circuit which is arranged to deliver periodic electrical signals signals whose duty ratio is dependent on a temperature representative of the temperature of the engine fed by the carburettor.

2. A carburettor according to claim 1, wherein the frequency of the signal is of from 10 to 30 Hz.

3. A carburettor according to claim 1 or 2, wherein the electronic circuit is connected to a probe subjected to the temperature of the cooling water of the engine and supplying an electric signal which is a function of the temperature.

4. A carburettor according to claims 1, 2 or 3, wherein the solenoid valve is of a type which is closed when de-energized.

5. A carburettor according to any one of claims 1 to 4, wherein the starting throttle valve is controlled by an element responsive to the temperature, subjected to the action of an electrical heating resistor fed by a circuit in which is placed a contactor actuated by the oil pressure in the engine fed by the carburettor when it exceeds a predetermined threshold.

6. A carburettor according to claim 1, constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.