GB2102063A - Optional full load mixture enrichment for internal combustion engines - Google Patents

Abstract

Under full load (i.e., with throttle valve 2 wide open) a switch 45 is closed which will, if a manually operable switch 48 is also closed, cause closure of a solenoid valve 44 thereby increasing the pressure drop across throttle 43 and causing more fuel to be injected to enrich the air fuel mixture supplied to the engine. If the switch 48 is open, this full load enrichment will not occur, thus allowing more economical engine operation. <IMAGE>

Description

SPECIFICATION Spark ignition engines for vehicles The invention relates to a spark ignition engine for a vehicle having a device for full load enrichment of the fuel air mixture fed to the engine from a mixture forming system (whether it be a carburettor, mechanical or electrical fuel injection system).

Such mixture forming systems deliver a fuel-air mixture with a stoichiometric mixture ratio during normal running, but an operating device is provided to produce a richer fuel-air mixture for certain running conditions. Thus, under full load, enrichment of the fuel-air is effected, because maximum power is reached with an air count of 0.9. Fuel enrichment however produces increased fuel consumption.

For purposes of fuel economy, there has been an increasing tendency to make the top gear of the gear box very high or to provide an auxiliary top "economy" gear, in order to lower the speed of the engine and also the fuel consumption when maximum power is not required, as for example, on a motorway journey at 2/3 of maximum speed.

To achieve noticeable fuel economy, this top gear of the gear box may be designed with such a high ratio (for example, 0.9 :1), that the driving speed is reduced already when driving up a slight and optically hardly noticeable gradient with the position of the accelerator pedal maintained unaltered at half-throttle, for example. As the driver normally wishes to maintain his driving speed, he presses the accelerator pedal down more violently, with the results that driving in top gear frequently takes place at full throttle, as a consequence of which the fuel economy which is the main objective of the high top gear is reduced because of full load enrichment.

The problem underlying the invention is to avoid this drawback of known mixture forming systems, and broadly stated the invention provides a spark ignition vehicle engine including a fuel richening device for full load enrichment of the fuel-air mixture fed to the engine from a mixture forming system, and including means for putting the enrichment into or out of operation as desired.

As a result of the invention, the driver himself is able to determine whether he wishes to drive economically at low power, or at full power and correspondingly higher fuel consumption.

In order to implement the invention, only relatively simple modifications are needed to existing mixture forming systems. For mixture enrichment in carburettors for example there is normally provided a small duct leading from the float chamber and opening into the intake manifold upstream of the venturi. A valve which can be actuated as desired by the driver can be inserted into this small duct. In the case of fuel injection systems which inject continuously into the induction pipe (see for instance DE 25 20 322) full load enrichment occurs by varying a control pressure, which is regulated by a valve which is controlled by the pressure conditions in the induction pipe downstream of the throttle valve.In such systems the invention can be achieved by means of a blocking member, which can be actuated as desired by the driver, located in the low pressure pipe from the induction pipe to the aforementioned valve. In one particular electronic injection system (see for instance DE 27 07 411) the control pressure is controlled by an electromagnetic valve, full load enrichment once again being effected by the actuation of this valve in dependence upon the low pressure in the induction pipe or on the position of the throttle valve. Here, the invention can be achieved by means of a switch in the electric circuit to the electromagnetic valve.

In one particular mechanical fuel injection system (see for instance DE 28 05 563) the variation of the fuel-air ratio occurs by variation of a differential pressure via a fuel proportioning valve by means of a differential pressure control valve, which has two chambers separated from each other by a diaphragm. Full load mixture enrichment here can be achieved by the two chambers of this valve being connected together by a by-pass with a variable cross-section, where the variation of the cross-section occurs by means of a valve which is actuated in dependence upon the position of the throttle valve or on the low pressure in the induction pipe.In a fuel injection system of this type, the invention may be achieved by means of an interrupter which can be actuated as desired by the driver positioned in the control system of this valve, which, depending upon the design of the valve, may be a low pressure pipe connected to the induction pipe, an electrical circuit or a mechanical link.

The apparatus for putting into or out of operation the device for full load mixture enrichment conveniently has a switch or other operating element located within reach of the driver. It is also advantageous to provide an optical indicator device from which the driver can recognize whether the full load enrichment system has been switched on or off.

In order to reduce fuel consumption even further during the full load running, it is advantageous to provide some correction of the ignition timing angle with the switching-off of the full load enrichment system in such a way that the ignition timing is advanced relative to the timing when running with full load enrichment. If the ignition timing angle reaches 250 for example, during full load enrichment, i.e. when running with an air count of roughly 0.9, the ignition timing angle should be advanced to 300 before top dead centre, when full load enrichment is switched off, i.e. when running with an air count of 1.0, for example.

The invention may be performed in various ways, and one preferred embodiment with some possible modifications will now be described by way of example with reference to the accompanying drawings, in which Figure 1 is a diagram indicating fuel consumption in dependence upon mean pressure, and Figure 2 is a diagrammatic illustration partly in cross-section of a fuel injection system according to the invention.

The fuel consumption curve of a particular engine related to mean pressure at a speed of n = 30001/min is illustrated in Figure 1. The mixture forming system of the engine normally delivers a fuel-air mixture with a stoichiometric mixture ratio, that is with an air count of 1.0. The part of the curve shown in chain lines is produced with this mixture ratio.As the maximum power of an engine is reached not with an air count of 1.0, but with an air count of approximately 0.9, every mixture forming system (whether it be a carburettor, mechanical or electrical fuel injection system) contains an automatically operating device for full load enrichment, which automatically comes into effect and produces the desired full load enrichment when the throttle is in a predetermined position, i.e. when the accelerator pedal is pressed down a considerable distance or pressed down to its fullest extent. In the diagram, full load enrichment starts at Point A at a mean pressure of approximately 7 bars, and it produces an increase in the mean pressure of up to approximately 8.7 bars, corresponding to Point B. As can be seen, the fuel consumption also increases as a result of the full load enrichment.If the full load enrichment is now switched off by the driver, Point C will be reached if the optimal ignition angle of, for example, 250 before top dead centre is maintained for the air count of 0.9, which exists with full load enrichment. As can be seen, a mean pressure of approximately 8.3 will be obtained with a simultaneous noticeable reduction in fuel consumption without full load enrichment.

If the ignition angle for running without full load enrichment, i.e. with the air count of 1.0, is now made optimal, corresponding to an advance of the ignition timing to approximately 300 before top dead centre, Point D will be reached at full load, which in relation to running without full load enrichment but with a non-optimal ignition angle, causes an increase in the mean pressure, and at the same time, a perceptible reduction in fuel consumption.

The diagram shows that the power loss a, which occurs as a result of running without full load enrichment but with an optimal ignition angle (Point D) is not particularly great in relation to running with full load enrichment (Point B), but causes a reduction b of fuel consumption by approximately 7%. As a result of the invention, whereby the full load enrichment can be brought into or out of operation as desired, the driver is thus given the ability to produce the increase in power caused by full load enrichment only when maximum power is actually required, such as for example, when he is overtaking or travelling up gradients, whilst during normal running he can relinquish full load enrichment in order to obtain a not inconsiderable fuel economy.

In Figure 2 is illustrated a fuel injection system with full load enrichment which can be switched on as desired. 1 indicates an induction pipe of a mixture-compressing spark-ignition engine, which pipe contains a controllable throttle valve 2 and an air metering member 3, which moves according to the quantity of air flowing through in the direction of the arrow. The metering member 3 is in the form of an obturator plate and is located in a conical section 4 of the induction pipe 1. The plate 3 is pivotally mounted at a remote pivot 5 and acts on the movable valve piston 6 of a fuel proportioning valve 7. The valve piston 6 is located in a cylindrical bore 8, in the wall of which a number of control slots 10 are provided, corresponding to the number of injection nozzles 9 as indicated by arrows.To each control slot 10 is connected a diaphragm valve 11 , which has two chambers 13 and 14, which are separated from each other by a diaphragm 12. In order to regulate the pressure difference via the control slots, there is provided a differential pressure control valve 20, which has two chambers 22 and 23 separated from each other by a diaphragm 21. The chamber 22 is charged with fuel under system pressure by an electrically driven fuel pump 24, via a pipe 39, the system pressure being determined by a system pressure relief valve 25. The chamber 22 is also in communication via a pipe 26 and a passage 27, with an annular groove 28 in the valve piston 6 of the fuel proportioning valve 7.

The second chamber 23 is connected to the first chamber 22 via a by-pass pipe 42, which branches off from the pipe 26 and has a throttle, and is also connected to the second chambers 14 of all the diaphragm valves 11 by a pipe 29, which branches off between the throttle 43 and the chamber 23.

The differential pressure control valve 20 contains a valve body 30, which is pressed by a spring 31 against the diaphragm 21. The valve body 30 has a bore 32 which is in communication with the chamber 23 and comes into communication to a greater or lesser extent with an annular groove 33 in the wall of the bore 34 which receives the valve body 30. The annular groove 33 is in communication via a passage 35 and a return pipe 36, with the fuel tank 37. The prestress of the spring 31 can be adjusted and hence the level of the differential pressure at the proportioning valve 7 regulated, by means of a screw 38. Fuel delivered by the fuel pump 24 passes through the pipe 39 into the first chamber 22 of the differential pressure control valve 20, and from there by the pipe 26 and the passage 27 into the annular groove 28 of the valve piston 6, whilst part of the fuel flow runs through the bypass pipe 42 and the throttle 43 to the chamber 23, and also passes through the pipe 29 into the chamber 14 of each diaphragm valve 11. The piston valve 6 is shifted in an upward direction out of the rest position illustrated by the obturator plate 3, depending upon how it is deflected by the quantity of air flowing through the induction pipe 1, against a readjusting force which, in this example, is created by a spring 40, as a result of which its control edge 41 uncovers the control slots 10 to a greater or lesser extent, in proportion to the deflection of the plate 3.The fuel then passes through the passages 1 5 into the first chambers 13 of the diaphragm valves 1 from where it flows through the valve apertures 1 6 to the appropriate injection nozzles 9.

In the bypass pipe 42, there is located in parallel with the throttle 43, which serves to produce a constant differential pressure, a normally open solenoid valve 44 which, in order to produce full load enrichment when the throttle valve 2 is fully open, is actuated in the closing direction by means of a switch 45 in the current supply line 46. The switch is closed by a cam 47 fixed to the throttle valve shaft 2a when the throttle valve 2 is fully open. The control valve 20 keeps the differential pressure constant during normal running. In order to produce full load enrichment and to feed a correspondingly larger quantity of fuel to the injection nozzles 9, the valve 44 is closed by closing the switch 45 and the differential pressure is thereby increased. The result of this is that a larger quantity of fuel is injected. In order to be able to switch off this full load concentration as desired, a manually operable make-and-break switch 48 is located in the line 46, by which the current supply to the solenoid valve 44 can be broken. The switch 48 may have a second pair of contacts 49, located in a control circuit 50 of a device for ignition timing adjustment (not shown) in order to produce a shift of the ignition angle when the full load enrichment is switched off, as has been described heretofore in conjunction with the diagram of Figure 1.

Claims (6)

1. A spark ignition engine for a vehicle, including a fuel enrichment device for full load enrichment of the fuel-air mixture fed to the engine from a mixture forming system and including means for putting the enrichment into or out of operation as desired,

2. A vehicle engine as claimed in Claim 1, including means for advancing the ignition timing when the full load enrichment is out of operation, in relation to the ignition timing when running under full load enrichment.

3. A vehicle engine as claimed in Claim 1 or Claim 2, in which the mixture forming system is a carburettor with a float chamber and a venturi and a small duct is provided for full load enrichment, leading from the float chamber and opening into the air intake upstream of the venturi, and including a selectively operable valve located in the said duct.

4. A vehicle engine as claimed in Claim 1 or Claim 2, in which the mixture forming system is a continuously operating fuel injection system including a metering member which is located in the air induction pipe and which is moved against a readjusting force according to the quantity of air flowing through, and arranged to adjust a fuel metering valve for metering a quantity of fuel which is proportional to the quantity of air, and in which the readjusting force is created in a control pressure pipe by pressurised fluid with a constant but optionally variable pressure, and this pressure, for purposes of full load enrichment, can be reduced by a valve which connects the control pressure pipe to a reservoir and reacts to the low pressure in the induction pipe upstream of the metering member, and including a selectively operable closure device in the low pressure pipe between the induction pipe and the valve.

5. A vehicle engine as claimed in Claim 1 or Claim 2, in which the mixture forming system is an injection system providing continuous injection into the induction pipe, and including a metering member which moves according to the quantity of air flowing through the induction pipe and which actuates a fuel proportioning valve for metering a quantity of fuel which is proportional to the quantity of air, wherein proportioning occurs at a pressure difference which is constant but can be varied by a differential pressure control valve in dependence upon operating parameters, which control valve has two chambers separated from each other by a diaphragm, of which the first chamber is subjected to the pressure upstream of the proportioning valve, whilst the second chamber is in communication with a return pipe via a valve which is controlled by the diaphragm, and the two chambers of the differential pressure control valve can be connected together by a bypass for purposes of full load enrichment, the cross-section of which can be varied in dependence upon the position of the throttle valve by a valve which can be selectively opened or closed by the driver.

6. A vehicle engine as claimed in Claim 1 or Claim 2, in which the mixture forming system is an electronic fuel injection system which injects fuel continuously into the air induction pipe, in which there is located a throttle valve and a metering member which is movable against a readjusting force, depending upon the quantity of air flowing through the pipe, and which adjusts a fuel proportioning valve for metering a quantity of fuel which is proportional to the quantity of air, and the readjusting force is created by pressurised fluid, whose pressure can be lowered by an electromagnetic valve in a control pressure pipe for purposes of full load enrichment, which valve brings the control pressure pipe in communication with a reservoir when the pressure pipe in communication with a reservoir when the pressure in the induction pipe rises, whilst in the induction pipe there is provided a pressure switch which reacts when there is a rise in pressure and is so connected to the circuit elements controlling the valve for the control pressure, that the control pressure valve is regulated so as to produce an enrichment of the fuel-air mixture, and including a selectively operable switch located in the control pipe of the control pressure valve.