GB2080425A - Air valve carburettor for internal combustion engines - Google Patents

Abstract

The pressure drop between the float chamber 6 and the fuel outlet 5 is modified by the air valve 10 which is positioned by a diaphragm actuator 13. One actuator chamber 14 communicates with the induction passage 1 between the valves 3 and 10 and the other chamber 18 contains a pressure determined by a differential-pressure valve 24. The valve member 25 is subject. In addition to the forces due to the spring 29 and the pressures acting on the diaphragm 23, to a force dependent upon engine operating conditions, e.g. engine cooling water temperature, exhaust composition or altitude <IMAGE>

Description

SPECIFICATION Carburettor for internal combustion engines The invention relates to a carburettor for internal combustion engines, with an intake channel containing a voluntarily actuated main throttle valve and, upstream of this, an auxiliary throttle valve, the flow of fuel being determined by the pressure drop between a float chamber and a location in the intake channel intermediate between the two throttle valves, the pressure drop being controlled by a pneumatic device which actuates the auxiliary throttle through a linkage.

A carburettor of this kind provides control of the pressure which determines the rate of flow of fuel, i.e. in a conventional carburettor the pressure in the venturi, so that mixture composition can be corrected, for example enriched when the engine is warming up, for starting and for acceleration.

And altitude corrections can be made. Such corrections are required for optimising exhaust gas composition, reducing fuel consumption and compensating for bad drivability.

An arrangement of this kind described in the German Offenlegungsschrift 26 55 226 has a pneumatic device in the form of a diaphragm capsule whose diaphragm is acted on, on its one side, by atmospheric pressure and, on its other side, by induction-pipe suction whose effect is modified by a pulse-energised electromagnet controlled by an electronic controller responsive to exhaust gas composition.

The arrangement makes it possible to enrich the mixture, within certain limits, during steadystate operation of the engine.

But this known arrangement has the serious disadvantage that in fluctuating operation of the engine the changes in induction-pipe suction act directly in the working chamber of the diaphragm capsule, changing the position of the auxiliary throttle valve and producing undesired changes in mixture composition.

The conventional method for influencing the auxiliary throttle valve by means of a thermostatic bimetal spring has the disadvantage that although with increasing engine load, i.e. with increasing air flow, the eccentrically mounted auxiliary throttle valve does open approximately in proportion to the air flow, nevertheless it cannot do so in true proportion to the air flow because the spring force of the bimetal spring increases with the air flow, producing a counter-force which prevents full opening of the auxiliary throttle valve. This results in pressure-drop changes across the auxiliary throttle valve which increase mixture enrichment with increasing air flow, an effect which is undesired.

The intention in the present invention is to provide a carburettor in which the mechanism for enriching the mixture by controlling fuel flow compensates, in a simple way, the influence of changing induction-pipe suction with increasing air flow.

Starting from a carburettor of the kind mentioned at the beginning, the problem is solved, according to the invention, in that one chamber of the pneumatic device, which is in the form of a diagram capsule, communicates through a channel with the intermediate location in the intake channel between the main throttle valve and the auxiliary throttle valve, the other chamber, this being the working chamber, containing a desired pressure which it receives through a channel from a differential-pressure servo valve.

What is obtained is that a desired pressure is produced at the intermediate location of the intake channel, between the two throttle valves, because the diaphragm capsule which controls the auxiliary throttle valve equalises the pressures acting on the two faces of its diaphram and consequently the auxiliary pressure at the intermediate location. When the main throttle valve is opened, the pressure at the intermediate location changes. This pressure is transmitted to a chamber of the diaphragm capsule with the result that the diaphragm shifts into a new position to equalise the pressures on its two faces, the movement of the diaphragm changing the position of the auxiliary throttle valve. When the process has been completed the pressure at the intermediate location in the intake channel is once more the desired pressure.

The servo valve has a diaphragm which is acted on, in the one direction, by atmospheric pressure in a chamber and, in the other direction, by a force which acts against the atmospheric pressure, the servo valve having another chamber which communicates through a channel with the working chamber of the diaphragm capsule, the working chamber being vented through a constricted orifice to the external atmosphere, the diaphragm actuating a valve which communicates through a channel with the intake channel at a location where induction-pipe suction prevalls, so that the induction-pipe suction provides servo energy to maintain the desired pressure.

The force acting on the diaphragm is controlled through a spring by engine operating parameters.

Consequently the metering pressure drop which determines the flow of fuel depends exclusively on the pull applied by the tension spring to the diaphragm of the servo valve and this can, for example, be determined by a control device such as a heat-sensitive expansion element or a step motor.

In another version of the invention the force applied to the diaphragm of the servo valve can be produced by a solenoid in dependence on engine operating parameters. This also changes the pull applied to the diaphragm and consequently changes the fuel-metering pressure drop. In this case the engine operating parameters can if desired, be processed by a micro-processor of the known kind, whose output signal is applied to the solenoid.

In further development of the invention the communicating channel between the intermediate location in the intake channel and the chamber of the diaphragm capsule contains a constricted orifice. This makes it possible, for example, assuming that the pull of the tension spring of the servo valve is produced only by a simple thermal expansion device, to obtain mixture enrichment not only during warming up of the engine but also during acceleration. When the main throttle valve is opened the resulting decrease in pressure at the intermediate location is transmitted only after a delay to the chamber of the diaphragm capsule.

Consequently the auxiliary throttle valve shifts in position only after a delay and for a brief period the metering pressure drop is increased, producing a temporary enrichment of the mixture for acceleration.

The invention will now be described in greater detail with the help of the example represented in the drawing.

The intake channel 1 of the carburettor 2 contains a voluntarily operated main throttle valve 3. Upstream of this is a venturi 4 in whose narrowest cross section is situated an outlet 5 for fuel derived through a constricted orifice 7 (the "main jet" of the carburettor) from a float chamber 6 whose vapour space communicates through a channel 8 with the intake channel at a point just downstream of an air filter 9, where the pressure is practically atmospheric pressure.

Upstream of the venturi 4 the intake channel contains an auxiliary throttle valve 10 connected through a linkage 11 to the diaphragm 12 of a pneumatic device in the form of a diaphragm capsule 13, one 14 of whose chambers communicates through a channel 1 5, containing a constricted orifice 16, with the intake channel 1 at a location 17 intermediate between the two throttle valves 3 and 10. The working chamber 18 of the diaphragm capsule 13 contains a spring 19 whose spring force is so weak that it serves merely to stabilise the diaphragm 12 and, apart from this, has practically no influence on the diaphragm.The working chamber 18 communicates through a constricted orifice 20 and through a channel 21 with the intake channel 1 at a location just downstream of the air filter 9, and also communicates through a channel 221 with a chamber 22 of a differential-pressure servo valve 24 containing a diaphragm 23 to which is attached a valve head 25 which cooperates with a valve seat 26 which, in turn, communicates through a channel 27 with the intake passage 1 downstream of the main throttle valve 3. The second chamber 28 of the servo valve 24 contains a spring 29 whose spring force is so weak that it serves merely to stabilise the diaphragm 23 and, apart from this, applies only a negligible force to the diaphragm.The second chamber 28 communicates through the channel 21 with the intake channel 1 at a point just downstream of the air filter 9, where the pressure is practically atmospheric pressure. Acting on the diaphragm 23 is a force in the direction of the arrow 30;; In the example shown this force is represented by a tension spring 31. Nevertheless this force is variable in dependence on engine operating parameters such as temperature and the like. For this purpose there can be attached to the tension spring 31 an expansion device of the known kind, sensitive to temperature, or a bimetal element.If this is adjusted so that when the engine is dperating normally the diaphragm 23 is pulled In the direction of the arrow 30 it becomes possible, for example, with the help of a device (not shown) for applying altitude correction, to weaken the mixture. A solenoid (not shown) responsive to exhaust gas composition can apply forces to the diaphragm to give a richer or leaner mixture.

Assuming that a thermo-sensitive expansion device is used, immersed in the cooling water and acting in the direction of the arrow 30, the carburettor functions during cold starting of the engine as follows: Before the engine is started, the expansion device, acting through the spring 31, is pulling strongly on the diaphragm 23 in the direction of the arrow 30. With gradual warming up of the engine this pull is gradually relaxed, the expansion device expanding in the direction opposite to the arrow 30, relaxing the spring 31. As long as the engine is not running, the auxiliary throttle valve 10 is fully open, irrespective of temperature, because the force of the spring 19; although little, is nevertheless sufficient, acting through the diaphragm 12 and the linkage 11, to open the auxiliary throttle 10.Under these circumstances, i.e. with the engine cold and the auxiliary throttle open, when the starter is energised suction builds up in the intake channel downstream of the main throttle valve, the suction being transmitted through the channel 27, the chamber 22 and the channel 221, to the working chamber 18 of the pneumatic device 13. After a few revolutions of the engine the pressure in the working chamber 18 has fallen far enough for the diaphragm 12, acting through the linkage 11, to pull the auxiliary throttle valve 10 towards its closed position. The pressure at the intermediate location 17 In the intake channel 1 falls, enriching the mixture by a choke effect In the known way. During idling of the cold engine the metering pressure drop between the float chamber and the venturi Is determined by the desired pressure in the working chamber 18, as established by the servo valve 24.The induction-pipe suction in the intake channel downstream of the main throttle valve 3, acting through the channel 27, provides servo energy for producing this desired pressure in response to the amount of pull, in the direction of the arrow 30, applied by the expansion device. The constricted orifice 20 allows air to leak constantly Inwards into the working chamber 18 and from there through the channel 221 and through the valve 25, 26 into the intake channei'downstream of the main throttle valve 3. But this small leakage of air is not enough to influence mixture composition appreciably. In the chamber 14 of the diaphragm capsule 13 the pressure also becomes approximately the same desired pressure, because this chamber communicates through the channel 15 and the constricted orifice 16 with the intermediate location 17 in the intake channel 1, the diaphragm 12 equalising the pressures on its two faces. The diaphragm 12, acting through the linkage 11, changes the position of the auxiliary throttle 10 so that the pressure at the intermediate location 17 is automatically adjusted. Suppose that now, either with the engine cold or with it warm, the main throttle valve is abruptly opened, a brief enrichment of the mixture is obtained in that the auxiliary throttle at first retains its position, until the pressure drop at the intermediate location 17 has been transmitted through the constricted orifice 1 6 to the chamber 14. After that, the auxiliary throttle 10 shifts in position so that, even though the air flow has changed, the pressure at the intermediate location 1 7 is once more the desired pressure as established by the servo valve 24.

Consequently in this carburettor the metering pressure drop which determines the flow of fuel depends exclusively on the value of the force acting on the diaphragm of the servo valve in the direction of the arrow 30.

Claims (6)

1. Carburettor for internal combustion engines, with an intake channel containing a voluntarily actuated main throttle valve and, upstream of this, an auxiliary throttle valve, the flow of fuel being determined by the pressure drop between a float chamber and a location in the intake channel intermediate between the two throttle valves, the pressure drop being controlled by a pneumatic device which actuates the auxiliary throttle through a linkage, characterised in that one chamber (14) of the pneumatic device, which is in the form of a diaphragm capsule (13), communicates through a channel (15) with the intermediate location in the intake channel (1) between the main throttle valve (10), the other chamber (18), this being the working chamber, containing a desired pressure which it receives through a channel (221) from a differentialpressure servo valve (24).

2. Carburettor as claimed in Claim 1, characterised in that the servo valve (24) has a diaphragm (23) which is acted on, in the one direction, by atmospheric pressure in a chamber (29) and, in the other direction, by a force (30) which acts against the atmospheric pressure; the servo valve (24) having another chamber (22) which communicates through a channel (221) with the working chamber (18) of the diaphragm capsule (13), the working chamber (18) being vented through a constricted orifice (20) to the external atmosphere; the diaphragm (23) actuating a valve (25, 26) which communicates through a channel (27) with the intake channel (1) at a location where induction-pipe suction prevails, so that the induction-pipe suction provides servo energy to maintain the desired pressure.

3. Carburettor as claimed in Claim 2, characterised in that the force (30) acting on the diaphragm (23) is controlled through a spring (32) by engine operating parameters.

4. Carburettor as claimed in Claim 2, characterised in that the force (30) acting on the diaphragm (31) is produced by a magnet system in dependence on engine operating parameters.

5. Carburettor as claimed in Claim 2, characterised in that the channel (15) contains a constricted orifice (16).

6. Carburettor according to claim 1 and substantially as described with reference to the accompanying drawing.