In the current internal combustion engines with electri¬ cal ignition the fuel is sucked in through a spray nozzle of the carburettor by the vacuum generated in the supply duct connected to an air suction opening when opening an intake valve or port, and then the fuel is finally distributed through the air flow taken in.

This vaporisation is, then, not only adapted to a given kind of fuel, but is, moreover, only optimal under definite operational conditions, so that, mostly, several vaporising nozzles ^• 10 are to be used in order to obtain, at different engine speeds, a possibly good fuel supply, and, moreover, if a sudden acceleration is desired, an auxiliary pump coupled to the throttle valve in the air supply duct is to be used in order to satisfy the suddenly in¬ creased fuel demand, since the vaporisation by suction operates '15 too slowly. Conversely, when suddenly throttling .the air passage, the.suddenly reduced demand will not immediately be followed, so that fuel will be lost then. In such an engine it is not possible to obtain an optimal air/fuel ratio under all circumstances.

A certain improvement can be obtained by means of so 20 called -fuel injection, in which the fuel is no longer vaporised by the vacuum in the supply duct, but also then it is not possible to obtain an optimal air/fuel ratio under all circumstances.

As the petrol prices rise, also the need, on the one hand, for a possibly economical use of this fuel, and, on the 2.5 other hand, for the use of other fuels increases. This should not require changes in the engine itself, such as, for instance, an adaptation of the compression ratio to the combustion qualities of a different fuel, as long as such other fuels are not available to such an extent that an adaptation of new engines would become 30 sensible, as, for instance, in the case of Diesel engines. More¬ over it is desirable to be able to use a different fuel also in existing petrol engines without requiring expensive provisions, and the use of petrol should remain possible if the other fuel cannot be replenished in time. This is already usual when usin ^^grjjt f O

liquefied distillation gas (LPG) which is not available everywhere, and replenishing cannot take place in an arbitrary point. The use of such a gas requires, however, special auxiliary parts for allowing the liquefied gas to vaporise and to depressurise to a 5 suitable pressure, and an additional difficulty is that the com¬ position of such a gaβ (i.e. the propane/butane ratio) is not the same everywhere, so that an optimal adjustment cannot be reached under all circumstances.

Furthermore the use of alcohol as an additive for petrol 0 or even as a fuel may increase in the near future, which will require still other adjustments of the air/fuel ratio, this again - dependent on the mixing ratio used.

All these difficulties prevent, for the time being, a wider use of other fuels for internal combustion engines for 5 vehicles, and, moreover, the already mentioned need for a more economical use of the available fuels still exists.

It is an object of the invention to provide a system which is adapted to maintain, at any moment and under all circum¬ stances, an optimal air/fuel ratio at the inlet side of an inter- 0 nal combustion engine, and this, in particular, irrespective of - the character of the used fuel, so that also when switching over to a fuel of a different kind or different composition a possibly favourable consumption can be ensured.

To that end the system of the invention is characterised 5 by an air flow meter included in the supply duct, by a fuel in¬ jection nozzle opening in said duct near the engine inlet, by a fuel metering pump connected to this nozzle, and adapted to press liquid fuel co ing from a fuel reservoir under pressure towards ^' " said nozzle, and by an electronic control circuit adapted to control 0 the fuel pump, on the basis of the air flow intensity as determined by the air flow meter, in such a manner that the quantity of fuel supplied to the nozzle is equal to the quantity of fuel required for an optimal combustion of the measured air flow -intensity.

In order to simplify the control of the metering pump, 5 fuel flow meter is preferably included in the ^' fuel supply duct which is connected to the control circuit as well, which circuit is designed in such a manner that it tries to maintain the desired

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ratio between the signals αoming from both flow meters by an adapte control of the pump.

Preferably the liquid flow meter is arranged behind the liquid pump, since, there, as a consequence of the compression, no gas bubbles which might disturb the measurement will be present in the liquid anymore.

Since the operation of the engine when accelerating or decelerating or adapting to changing load conditions is controlled by means of the throttle valve, which will lead to a corresponding variation of the air flow through the supply duct to which the amount of fuel is to be adapted for ensuring an optimal combustion, measuring the air flow is a suitable magnitude for adapting the control thereto. Since the characteristics of the various kinds of internal combustion engines are known, and also electronic pro- cessing and control circuits can be adapted to following such characteristics, the problem in question is solved in principle, ;ind the direct injection of the liquid fuel under pressure into the air flow enables an unambiguous metering, the the fuel, which, more¬ over, can immediately follow very quickly changing demands. It is, moreover, advisable to perform the air flow measure ment as a mass flow measurement, since the mass of air is decisive for the amount of liquid to be supplied. Thus the influence of fluctuations in the quality of the air can be eliminated. Preferably the air flow meter is arranged before the throttle valve, since, there, only the air sucked in by the engine will be measured.

If the engine should be suitable for different fuels, the control circuit can be provided with an adjustment part which is .. adapted to adjust the control circuit to the control characteristics required for the different fuels, and to that end a selector switch can be used which is coupled to a selector valve for the various fuels, so that, when switching to an other fuel, the control circuit is automatically adapted thereto.

If, furthermore, the composition of the fuel within the class itself can vary, and an adapted control of the air/fuel ratio is desired, the adjustment part of the control circuit can be adapted to be able to take such differences into account, and said adjust¬ ment part can, in particular, be coupled with a sensor included in

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the fuel duct which is aa-isitive for such, dif erence...

The injection nozzle is, in particular, provided with a closure valve which will be opened only on reaching a given pressure difference between the outlet and inlet sides of the metering pump, so that an unambiguous metering independent of the pressure of the fuel in the fuel reservoir in question will be ensured, and, more¬ over, leaking away of fuel at a standstill of the pump is prevented. The nozzle possesses a very narrow aperture, so that a considerable pressure difference cai be maintained at this nozzle. All this allows to conduct liquefied -gas in the liquid condition towards the nozzle without a preceding decompression, so that also an un¬ ambiguous metering thereof becomes possible.

Furthermore it can be favourable to connect the control ■circuit to an element for determining the rotational speed of the engine and/or to a sensor for the temperature of the engine, in order to obtain an additional adaptation of the fuel metering to the naeds, for example for maintaining a given minimal speed at zero load, or for controlling the fuel supply when braking on the engine. Thereto the throttle valve in the air supply duct can be shunted by means of a shunt provided with a control element, the latter being designed for being actuated depending on the measure¬ ment of the temperature and/or rotational speed of the engine, in particular in order to readjust the air flow as needed and indepen- dent of the throttle valve, e.g. for controlling the rotational speed of the engine.

The control circuit can, furthermore, be designed for determining the fuel consumption, for adjusting the ignition, and -^ so on, and, moreover, by means of an exhaust sensor the exhaust gas composition of the engine can be determined, and the fuel metering can be readjusted if the quality of the exhaust gas would indicate •_n incorrect ratio between quantities of air and fuel.

In order to simplify the inclusion of the air flow meter and the injection nozzle, both can be provided with flanges of the current dimensions, by means of which a connection with the air supply duct, a possibly present throttle valve, and the inlet side of the motor can be effected in a simple manner.

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The invention will be elucidated below by reference to a drawing in which the system according to the invention is shown as a block diagram.

In the drawing a normal internal combustion engine is shown at 1, which, by means of a supply duct 2, is connected to a throttle valve 3 and an air filter . These elements, shown above an interrupted line 5. are of the current type, and need not to be replaced or changed. Only the elements below said line 5 belong to the system of the invention. In the duct 2 a flow meter 6 is included which is adapted to measure the flow-through rate of the air sucked in. Preferably this meter is a mass flow meter. Since the mass of air is decisive for the combustion affect, its measurement is a correct basis for metering the quantity of fuel which will provide an optimal co - bustion. The measurement is independent of the temperature and pressure of the air sucked in so that this measurement will be de¬ pendable under all circumstances. Moisture present in the air will contribute to the mass measurement, but this will not lead to an incorrect result since, moisture,'.like air, will contribute to the combustion. The reading of a mass flow meter is, therefore, more dependable than that of a volume flow meter.

The flow meter 6 is, preferably, arranged before the throttle valve 3 as shown, so as to avoid that, at a substantially closed. throttle valve 3 _. fuel possibly present in the duct 2 would disturb the measurement.

The flow meter is connected to a control input 7 of a electronic control circuit 8 which is designed in such a manner that it will be capable of determining, in function of the characte¬ ristic of the engine, the optimal quantity of fuel corresponding to the measured quantity of air.

This control circuit comprises an adjustment part 9 designed to adapt the operation of the control circuit to the kind of fuel if the engine 1 should operate on different kinds of fuel, for example, apart from petrol, also onliquefied distillation gas (LPG) and/or alcohol mixtures or the like. To that end an adjustment input 10 thereof is, for example, coupled to a selector valve 11 adapted to connect at will a fuel supply duct 12 to different fuel reservoirs 13 ..C,

The duct 12 is provided with a metering pur_p h which,

if necessary by the intermediary of a servo amplifier 15, is con¬ nected to an output 16 of the control circuit 8. Although it is possible to design the circuit 8 so that the output signal de¬ termines the metering operation of the pump k. it is better to perform the control by means of a flow meter 17 included in the flow duct 12 and connected to an additional control input 18 of the circuit 8, the pump Λ being controlled in such a manner that the desired ratio between the signals at the inputs 7 and 18 is maintained. In this manner the fuel metering becomes independent of the kind and yield, of the pump, so that also in the case of wear of the pump a correct metering is maintained. Preferably the flow meter 17 is arranged behind the pump k so that, then, •there is no longer any risk that vapour bubbles possibly present in the fuel would disturb the measurement, since these vapour bubbles disappear again in the pump by compression.

The pump 1 is, by means of a duct 19 _. connected to an injection nozzle 20 opening into the supply duct 2 near the engine. This nozzle has a very narrow bore so that a rather large pressure drop will occur thereat, and liquid can be injected into the duct 2 by means of this nozzle, and the liquid flow can be very accurately and quickly adapted to the fluctuating conditions.

The inlet side of the engine is hot,so that immediately vaporisation of the liquid will take place there. This leads to a certain heat removal from the engine which is now effectively used and needs not to be removed by means of the cooling liquid, and, moreover, cooling of the air will lead to a better filling of the cylinders.

The nozzle 20 is, furthermore, provided with a valve, not shown, which remains closed until, the difference between the pressure in the duct 19 and that in the duct 12 (i.e. the pressure in the reservoir 13 in question) exceeds a given value. The latter pressure is led towards the valve 20 by means of a measuring duct 21. In the nozzle a membrane is present which is connected to a valve, e.g. a needle valve, and at one side thereof the pressure in the duct 19, and at the other side the pressure in the duct 21 is present, and a spring provides the required presetting. If desired the valve can be made adjustable, e.g. dependent on the kind of fuel, and, if necessary, an additional connection to the circuit 8 can be provided.

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In this manner the operation of the metering pump 1^ is completely independent of the pressure of the fuel itself. Thereby it becomes possible to lead liquefied gas in the liquid condition through the pump 1 , so as to obtain an accurate metering thereof. The liquefied gas will, then, vaporise only after leaving the nozzle 20. The above-mentioned pressure control prevents that de- pressurisation will take place in the duct 12 and/or 1 . and also at a standstill of the pump 1 no gas can escape through this nozzle 20. Of course additional safety means can be used in order to interrupt the supply of liquefied gas, e.g. at a standstill of the engine, switching off the ignition, etc.

If the quality of a given fuel can vary, e.g. in the case of different kinds of petrol, different mixing ratios of pro¬ pane and butane in liquefied gas, different mixing ratios of al- cohol and petrol e.a., it can be desirable to readjust the control circuit accordingly. To that end the adjustment part 9 can be pro¬ vided with an additional input 22 connected to a manual adjustment means 23 _* It is also possible to include in the fuel duct a sensor 2k connected to the input 22 and sensitive for differences in the - quality of the fuel, and, for instance-, ^' a sensor sensitive for differences in the dielectric constant, the heat conductivity, the optical characteristics etc. at different fuel compositions can be used to that end. Such a sensor can, moreover, determine differences in the- kind of fuel, so that the coupling between the selector 11 and the output 10 will, then, be superfluous.

Furthermore it can be important to tune the fuel supply to the rotational speed of the engine 1, and a sensor 25 included in the engine is used therefor, said sensor being connected to an v additional control input 26 of the circuit 8. By means thereof, for instance, a minimum rotational speed can be maintained at zero load, and, if braking on the engine is required, during which the throttle valve 3 is completely closed, the fuel supply can be con¬ trolled accordingly. Moreover sometimes a better adaptation to the characteristics of the engine can be obtained thereby. The rotati- onal speed sensor can, for instance, co-operate with the fly-wheel or the ignition. The presence of a rotational speed meter enables, furthermore, to construct the circuit 8 so that also the ignition and particularly the ignition moment can be controlled thereby. Furthermore a heat sensor 27 can be provided in the engine which is

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connected to an input 28 of the circuit 8. Thereby, for instance, an adaptation of the fuel supply when starting can be obtained, if, in a cold engine, a larger quantity of fuel at a given quanti¬ ty of air is required. In the drawing a shunt duct 29 shunting the throttle valve and being provided with a control element 30 is shown, the latter being connected to an additional output 3 of the circuit 8. Thereby it becomes possible to control additionally the quanti¬ ty of air sucked in. by the engine 1 independent of the positionofthe throttle valve 3 _. e.g. dependent on the indications of the sensors 25 and/or 27 for the rotational speed and the temperature resp. of the engine. This can, for instance, be important when braking on the motor for a long time during a descent with a closed throttle valve, and then the engine may become too cold, so that, then, by letting through some air and an according dose of fuel the tempe¬ rature of the engine can be kept at a suitable level. Moreover, when the engine is running at zero load, the air supply can be re¬ adjusted in this manner, e.g. under control of the flow meter 6.

In the exhaust 32 of the engine 1 a sensor 33 can, more- over, be included, which is sensitive for the composition of the exhaust gas, e.g. for the oxygen and/or carbon dioxide content thereof. An oxygen surplus indicates an air excess, and a carbon dioxide surplus an air deficiency. This sensor 33 is connected to an additional input 3^ of the circuit 8 in order to readjust the fuel supply accordingly, e.g. in such a manner that a low oxygen content is maintained in the exhaust gases. This additional control can only be switched on as soon as the sensor 27 has indicated that the engine has reached a suitable temperature.

On the basis of the various collected data the circuit 8 can, for example, calculate the fuel consumption which can be in¬ dicated by a meter 35 connected to an output _> k. The circuit 8 can be extended still further in order to process data supplied there¬ to in still other manners.

For connecting such a system to an existing engine, use can be made of the available throttle valve, and then only the carburettor part is to be made inoperative and the elements 6 and 20 are to be included in the duct 2. These elements can, for in¬ stance, be made in the form of rather thin discs having dimensions corresponding to those of the duct 2, which discs are -crovided with

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flanges corresponding to the current flanges of air supply ducts 2, carburettors and engine manifolds, thus allowing a simple __.oum.ii_g.

In new engines it will be generally prefered to use a composite unit comprising the elements 6 and 20 as well as an inter- mediate throttle valve >.

It will be clear that many modifications are possible within the scope of the invention.

-BUREA

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