EP0852667B1 - Method for determining an optimal air-fuel mixture ratio in an internal combustion engine, and device therefor - Google Patents

Abstract

A method for determining an optimal air-fuel mixture ratio in an internal combustion engine is disclosed. The engine comprises a speed controller for maintaining a constant engine speed. The method comprises feeding an initial air-fuel mixture to the engine and controlling the engine speed by adjusting the throttle valve position. Said method further comprises the steps of causing a plurality of ratio jumps in the mixture fed to the engine; measuring changes in the valve position for each ratio jump; determining whether the changes in the valve position are lower than a threshold value, in which case the mixture has the optimal mixture ratio, or higher than the threshold value, in which case the mixture ratio must be changed; and, if required, correcting the mixture ratio of the initial mixture fed to the engine depending on the magnitude of the measured changes in the valve position. Said method is particularly useful in engines for lawn mowers, power generators, etc.

Description

The present invention relates to a method for determining the optimal richness of an air / fuel mixture feeding a combustion engine internal and a corresponding device. More particularly, this device is intended to equip motors of the type used in pumps, generator sets, lawn mowers etc ...

Motors of the type mentioned above are generally used at constant speed, whatever the load. Their fuel system, must therefore supply them with air and fuel appropriately, whatever the engine load.

On the other hand, out of concern for the quality of the environment, it appeared necessary to impose pollutant emission standards for these small internal combustion engines, as is already the case, for engines fitted to motor vehicles.

To reduce pollution from an engine, it is imperative to burn at maximum fuel, during the combustion phase of the mixture. It suits therefore to determine the optimal mixture of air and fuel (i.e. the optimal richness of the mixture) allowing complete combustion. When the engine is thus fed, with a mixture with the optimal richness, one notices that the torque delivered by the engine is also optimal, as well as the speed of motor rotation. To verify that an engine is operating at optimum richness, it therefore it suffices to determine what is the air / fuel mixture, giving a speed maximum motor rotation.

Unfortunately in the case of lawn mowers, groups generators etc, the engine is equipped with a cruise control in order to present a constant speed of rotation. For such motors, with cruise control, engine speed monitoring is therefore not significant of the torque and optimum wealth. Monitoring of another motor parameter is therefore essential. On the other hand, this monitoring must require the least number of specific sensors possible, in order not to increase the cost.

The object of the invention is therefore to create a method and a device adapted to vary the richness of a mixture feeding a motor to internal combustion equipped with a speed regulator, in a simple and economical by using as few specific sensors as possible, in order to to determine what is the optimal wealth value of this engine.

• provoquer une pluralité de sauts de richesse dans le mélange alimentant le moteur,
• mesurer les variations de la position du papillon correspondantes à chacun des sauts de richesse,
• en déduire lorsque les variations de position du papillon sont inférieures à un seuil que le mélange est à la richesse optimale et lorsque les variations de position de papillon sont supérieures à ce seuil que la richesse du mélange doit être modifiée et,
• effectuer, le cas échéant, une correction de la richesse du mélange initial alimentant le moteur en tenant compte de l'amplitude des variations de position papillon mesurées.

To this end, the present invention relates to a method for determining the optimum richness of an air / fuel mixture supplying an internal combustion engine, said engine comprising in particular a speed regulator adapted to vary the opening angle of a throttle valve for admitting the mixture in order to maintain the engine at a constant speed of rotation, the method consisting in supplying the engine with an initial air / fuel mixture and in regulating the speed of rotation of the engine by acting on the position of the throttle, said process being characterized in that it also consists in:

• cause a plurality of wealth jumps in the mixture feeding the engine,
• measure the variations in the position of the butterfly corresponding to each of the wealth jumps,
• deduce therefrom when the variations in throttle position are less than a threshold that the mixture is at the optimum richness and when the variations in throttle position are greater than this threshold that the richness of the mixture must be modified and,
• if necessary, correct the richness of the initial mixture supplying the engine, taking into account the amplitude of the measured throttle position variations.

The advantage of such a process lies in the fact that the monitoring of the position of the butterfly is easy to achieve with an inexpensive sensor. Also holding account of the amplitude of the variations of the throttle position, makes it possible to determine quickly the optimum richness of the engine in question. The higher this determination is fast and the less the engine pollutes when starting.

The determination of the optimal richness is carried out at least at each startup and is then applied for the duration of engine operation. This determination can also be made after each significant change in the resistive torque of the motor.

Advantageously, as optimal wealth is sought at each start, engine wear, fuel composition, etc. are continuously taken into account.

The present invention also relates to a device according to claim 7, putting in implements the process described above.

• la figure 1 est une vue schématique représentant, un dispositif selon l'invention appliqué à un moteur présentant un carburateur,
• la figure 2 est une vue montrant les variations simultanées de la richesse et de la position du papillon, et
• la figure 3 est une vue schématique représentant un dispositif selon l'invention appliqué à un moteur muni d'un système à injection électronique.

Other objects, characteristics and advantages of the present invention will emerge on reading the description which follows, by way of nonlimiting example and with reference to the appended drawings, in which:

• FIG. 1 is a schematic view showing a device according to the invention applied to an engine having a carburetor,
• FIG. 2 is a view showing the simultaneous variations in the richness and in the position of the butterfly, and
• Figure 3 is a schematic view showing a device according to the invention applied to an engine with an electronic injection system.

According to the embodiment shown in Figure 1, the motor 10 according to the invention comprises a single cylinder 11 (as is generally the case for the small engines in question) receiving an air / fuel mixture in from a carburetor 12. This carburetor, of the conventional type, is supplied on the one hand in air via an air filter 13, and on the other hand in fuel via a fuel tank 14, fitted with a flow actuator 15 delivering the fuel inside the carburetor.

The motor according to the invention is also provided with a regulator of speed 16, of known type, compensating for variations in rotation speed of the engine by acting on the position of a throttle valve 17 for admitting the mixture.

The engine according to the invention further comprises a sensor 18 adapted to determine the position of the butterfly. This sensor is for example a simple potentiometer.

The position sensor 18, the fuel flow actuator 15 and the engine 10 are also connected to a computer 19, implementing the method for determining the optimum richness according to the present invention.

This process is described below.

The motor 10 according to the invention is firstly put into operation. For this purpose the carburetor 12 mixes, on the one hand, in a predetermined manner the fuel from the tank 14 supplied by the flow actuator 15 and other part, the air having passed through the filter 13. In a known manner once the engine in on cruise control 16 acts on the throttle position to maintain constant engine speed. Indeed by varying the opening angle of the throttle causes variations in the engine torque and therefore variations in the diet. The operation of such a motor fitted with a cruise control is known per se and will not be detailed here.

According to the invention, when the engine is running, and preferably shortly after starting, the computer 19 causes a plurality of wealth jumps S1 (Figure 2). Preferably we cause three jumps of consecutive wealth. In general we start by increasing the richness r of mixture feeding the engine. The position sensor 18 then measures the variations in the position of the butterfly caused by these jumps in wealth.

When the engine is running at constant load, if these jumps of wealth have caused the butterfly to close (case shown in Figure 2, the butterfly initially showing 45 ° opening and during the wealth jump 43 ° opening) is that the richness of the mixture has caused an increase in engine rotation speed and that the cruise control imposed a reduction of this rotation speed to maintain it at a constant speed. The computer therefore concludes that the optimal torque of the engine is not reached, and that the mixture supplying the engine is currently too lean. The calculator averages the throttle position variations during the series of wealth jumps made. Based on this value, it determines the correction to add to the richness of the mixture so that it is at the optimum torque.

This correction is made through the flow actuator 15 which will act on the quantity of fuel supplied to the carburetor.

As soon as this correction is made the engine is supposed to run to its optimum torque and therefore to its minimum of pollution.

A new series of wealth jumps is then ordered by the calculator. The variations of the position of the butterfly created by this new series wealth jumps are then very small. Indeed when the engine is at its optimum torque, variations in richness do not significantly cause diet variations. The mean of the butterfly position variations during this new series of jumps, is then below a minimum threshold of variation. In this case the engine is at its optimal torque and the richness of the mixing is also optimal.

Of course the process according to the present invention is repeated on number of times required, until optimal wealth is detected.

As soon as this optimal richness is determined, it is applied to the engine for the duration of its operation.

To facilitate the work of the calculator when determining the correction to be made to the richness of the mixture, maps are carried out from a typical engine. These maps give according to wealth initial mixing, the correction to be applied according to the average of the variations of butterfly position measured. So we memorize a first table giving for each average angle of opening of the butterfly before application of the jumps of richness and for each variation of throttle position after application of jump richness, the value of the correction to be applied to the mixture when the mixture initial is too poor, and a second table giving, similarly, the value of the correction to be applied to the mixture when the initial mixture is too rich.

When the initial mixture is too rich, the correction to be made is a decrease in the amount of fuel supplied to the carburetor, and when the initial mixture is too lean it is an increase in the amount of fuel to be injected which should be carried out.

In the example given above (Figure 2) the initial mixture was too poor since it caused the butterfly to close. Of course in the case an excessively rich initial mixture, on the contrary, an opening of the butterfly which is observed. The first series of wealth jumps made therefore aims, on the one hand, to determine the richness of the initial mixture (too rich or too poor), and on the other hand to determine the amplitude of the butterfly position variations measured, to determine the appropriate correction.

If this amplitude is greater than a determined threshold experimentally on a typical engine, a correction is to be applied. On the other hand if this amplitude is below this threshold, the engine operates at richness optimal and no correction is to be applied.

The maps carried out on a typical engine make it possible to simplify the job of the calculator who only has to look for the mean of variation measured as the correction to apply.

However, as a variant, the computer may very well carry out the calculations required, for each series of wealth jumps, to determine the correction to be applied.

It will be noted that the plurality of wealth jumps is made in injecting quantities of fuel different from the initial quantities supplying engine. Similarly, we could obtain a plurality of wealth jumps in injecting quantities of air different from the initial quantities supplying the engine.

Figure 3 shows an engine not only equipped with a regulator speed 16, but also an injection system 15 '. In this case there is no carburetor and the throttle is simply placed in the manifold engine intake. The carburetor is replaced by the intake manifold in which the mixture of air and fuel is carried out.

The process for determining the optimal richness of the mixture supplying the engine according to the invention remains identical to that explained with regard to Figure 1. In the case of this engine, however, it is the injection time of the fuel which is modified and the correction maps therefore include correction values which correspond to fuel injection times.

The rest of the above process described with reference to Figure 1 remains applicable. It should be noted that in the case of an engine equipped with a cruise control and a fuel injection system it's not necessary to add a throttle position sensor, because this engine already has one for calculating the injection time. It will thus be noted that the adaptation of such an engine to make it conform to the new standards of pollution is inexpensive.

Instead of changing the amount of fuel supplied to the engine to cause the wealth jumps, we can modify the quantity of air admitted.

Claims (10)

1. Process for determining the optimum richness of an air and fuel mixture feeding an internal combustion engine, said engine (10) comprising, in particular, a speed regulator (16) adapted to vary the opening angle of a throttle valve (17) for intake of the mixture into the engine in order to keep the engine at a constant speed of rotation, the process involving feeding the engine with an initial air and fuel mixture and regulating the speed of rotation by acting upon the position of the throttle valve, said process being characterised in that it also involves:

   causing (15, 15') a plurality of jumps in richness in the mixture feeding the engine,

   measuring (18) the variations in the position of the throttle valve corresponding to each of the jumps in richness,

   deducing (19) from them, when the variations in the position of the throttle valve are smaller than a threshold, that the mixture is at the optimum richness and when the variations in the position of the throttle valve are greater than this threshold, that the richness of the mixture must be modified and,

   if necessary, correcting the richness of the initial mixture feeding the engine while allowing for the amplitude of the variations measured in the position of the throttle valve.
2. Determination process according to claim 1, characterised in that a plurality of jumps in richness is brought about by injecting quantities of fuel different from the initial quantities feeding the engine.
3. Determination process according to claim 1, characterised in that a plurality of jumps in richness is brought about by injecting quantities of air different from the initial quantities feeding the engine.
4. Determination process according to claim 1, characterised in that three consecutive jumps in richness are effected and in that the variations in the position of the throttle valve measured during these three jumps are averaged to determine the correction in richness to be applied.
5. Determination process according to one of the preceding claims, characterised in that a first table is stored, giving, for each mean value of throttle valve opening angle and for each variation in opening angle, the correction to be applied to the initial mixture when the initial mixture is too lean and a second table giving, for each mean value of throttle valve opening angle and for each variation in opening angle, the correction to be applied to the initial mixture when the initial mixture is too rich.
6. Determination process according to claim 5, characterised in that each of these tables is stored in a mapping for each type of engine.
7. Device employing the determination process according to one of the preceding claims, characterised in that it comprises:

   a speed regulator acting on the position of a throttle valve (17) for intake of the mixture into the engine,

   means (15, 15') adapted to impose jumps in richness on the initial air and fuel mixture feeding the engine,

   a measuring means (18) for the variations in the position of the throttle valve

   a calculating means (19) adapted to determine the richness of the initial mixture feeding the engine, and

   a means for determining the correction to be applied to the richness of the mixture as a function of the initial position of the throttle valve, the amplitude of the variations measured in the position of the throttle valve and the richness of the initial mixture.
8. Device according to claim 7, characterised in that the means adapted to impose jumps in richness consist of a fuel flow rate actuator (15).
9. Device according to claim 7, characterised in that the means for determining the correction to be applied consist of two mappings giving the correction to be applied as a function of the variations in the position of the throttle valve, when the initial mixture is lean and when it is rich respectively.
10. Device according to one of claims 7 to 9, characterised in that when the engine comprises an electronic injection system (15'), the correction to be applied is a variation of the fuel injection time.

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