FR2540940A1 - Method and device for automatically optimising the richness of a carburetted mixture for a heat engine - Google Patents

Abstract

Method and device for automatically optimising the richness of a carburetted mixture for a heat engine. It is characterised in that it consists in predetermining a reference speed Vc for the engine 3, in measuring the actual rotational speed VR of the said engine, in comparing the said reference and actual speeds, the said comparison determining a speed difference which is measured, in controlling the flow rate of at least one of the constituents of the mixture as a function of the measured difference so that the mixture admitted to the engine produces a variation in the actual rotational speed and bringing it to a value close to the predetermined reference speed of the engine. Application particularly to governing a heat engine of a heat pump.

Description

Method and device for automatically optimizing the richness of a fuel mixture for an internal combustion engine.

 The present invention relates to a method and a device for automatically optimizing the richness of a fuel mixture for a heat engine.

 The heat engine is of the type operating by means of a mixture of a fuel and an oxidizer such as gas and air respectively. Such mixing is carried out in a mixer which, in the case of conventional heat engines, consists of a carburetor located downstream of said engine.

In a conventional carburetor, the quantity of fuel mixed with the air is a function of the speed of passage of said air through a pressure-forming member such as a venturi. In the metering carburetor
by primary component, the richness of carburetion varies according to the operating conditions of the engine, which obliges to choose an average point of carburetion sufficiently rich to not risk an incident of operation. The adjustment of the richness of carburetion, once the predetermined mean point, necessarily results in an increase in the consumption of fuel compared to that which would give an optimal adjustment.

 On the contrary, the method and the device according to the present invention are suitable for all variations in the operating conditions of an engine such as temperature, air humidity, calorific value of the fuel, etc.

 The method according to the invention is applied to a heat engine associated with means for controlling the admission of a mixture of fuel and oxidizer into said engine, and it is characterized in that it consists in predetermining a set speed for the engine, to measure the actual speed of rotation of said engine, to compare said setpoint and actual speeds, so as to determine a difference between said setpoint and actual engine speeds, and to control the means for admitting said mixture by function of said difference so that the mixture admitted into the engine brings the actual speed of rotation close to the predetermined set speed.

 According to another characteristic, a narrow band of speeds is predetermined on each side of the target speed and the means for admitting the mixture are regulated so that the difference between the target speeds and the actual rotation speed of the motor is less than one of said speed bands.

 According to another characteristic, the method also consists in measuring and memorizing the speed of rotation of the engine at a given instant, in applying a first fixed increment to the control of the means for admitting the fuel mixture, in detecting the direction of variation means of admission and the variation of the speed of rotation compared to the speed memorized for said increment and at the end of a given time, to apply to the means of admission a second increment in the same direction as the previous one when said first increment has the effect of increasing the speed of rotation, and repeating the memorization and detection phases so as to bring the engine operating point to the maximum of its efficiency curve.

Other characteristics and advantages will emerge more clearly on reading the description given below by way of indication but not limiting of an embodiment of the invention, as well as of the appended drawing in which
Figure 1 is a simplified view of the device according to the invention, the mixer being shown in section
Figure 2 is a block diagram of the mixer automation
Figure 3 is a schematic representation of means. for measuring the engine speed.

 The device according to the invention comprises a new mixer (1) in which a bore (la) is formed and which is connected by an intake manifold (2) to a heat engine (3). The fuel mixture necessary for the operation of the engine (3) is constituted for example by air, introduced into the mixer (1) through a filter (4), and by gas directly injected into the bore 1a of the mixer. The gas flow is adjusted by a valve screw (5) mounted on one side of the mixer (1) and which moves relative to a seat (6) formed by a free end of a gas intake pipe (7) made in one or more parts and on which is mounted a pressure regulator-regulator.

The valve 5 is coupled to a control servomotor 8 of gas despite through a rubber sleeve (9). In the mixer (l) is arranged a throttle valve (10) whose rotation about a vertical axis is controlled by a servomotor (11), the connection of the throttle shaft with the servomotor also being made by means of '' a rubber sleeve 12.

 The two servomotors 8 and II are rotary digital servomotors and will not be described in detail since they are well known to specialists. As an indication, they can be of the type marketed under the name TELER TS360, and are capable of rotating 90 degrees in less than half a second. The two servomotors are controlled in turn separately or together by a microprocessor 13. As a result, the gas and air + gas mixture flow rates can therefore be adjusted independently. In addition, the geometric characteristics of the mixer (1) are such that if the valve (5) and the butterfly (10) are subjected to an identical rotation, the richness of the combined mixture obtained, at the corresponding speed of rotation of the motor, remains approximately constant. As in the transient phase, the regulation step which will be described below, will apply identical rotations to the servomotors 8 and 11, the two characteristics of the flow rate of the gas and of the mixture must be present. supplying the engine 3 are correctly initialized and that they evolve in parallel so that the richness of the fuel mixture allows the engine to operate for all the possible openings of the valve 5 and of the throttle valve 10.

 The initialization consists in predetermining a position of one of the two members of the valve 5 or of the butterfly -10 relative to the other. It is a manual operation which consists in modifying the coupling position of one of the two servomotors corresponding to the prepositioned member. It is important to note that the parallelism of the characteristics does not need to be rigorous, since in stable regime, the optimization function, described below, corrects the richness of the fuel mixture.

 It goes without saying that in the following description, the technical characteristics mentioned depend to a very large extent on the operating conditions of the heat engine used: In a particular application, that of a heating system comprising a heat pump the compressor of which constitutes the main load of said thermal engine, the latter has been chosen to operate between 2000 and 3000 revolutions / minute and, more precisely, at 2500 revolutions / minute which constitutes, in what follows, the set speed V of said engine 3.

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When the engine 3 starts, means 15 for measuring the speed of rotation of the said engine indicate that it is stopped. The control orders, issued by the microprocessor 13, preposition the servomotors 8 and 11 for easy starting. As soon as the actual rotation speed VR of the motor, measured by the means 15, reaches the set value VcR, the microprocessor 13 goes on a regulation algorithm.

 In this operating mode, the rotation commands of the servomotors 8 and 11, delivered by the microprocessor 13, are identical, so that the richness of the fuel mixture is only slightly modified.

The rotation speed VR is sent by a line 16 to a comparator 17 which determines the difference AV between the reference speeds Vc and the actual rotation VR.

The AV deviation thus measured is transmitted to means 18 comprising a proportional and integral regulation algorithm which progressively reduces the AV deviation between the measurement of the rotation speed VR and the
R set speed Vc. For this, the signals, at the output of the means 18, control the rotation of the vomiting units 8 and 11 so that the gas and Qmixture flow rates are such that they cause a variation in the rotation speed VR of the engine 3. On the FIG. 2, the block 19 diagrammatically represents the 8-valve 5 servomotor couple while the block 20 represents the ll-butterfly servo couple 10, the connection between the means 18 and the blocks 19 and 20 being shown by lines 21 and 22 respectively . Line 22 leads to means 23 arranged upstream of block 20, and capable of putting or interrupting the connection between means 18 and block 20.

On either side of the set speed
Vc, a narrow band or dead band BM is determined, for example equal to 50 revolutions / minute. When the AV deviation, by the command on blocks 19 and 20 and therefore on the gas and Qmixture flow rates becomes less than the dead band BM, the microprocessor 13 switches to.

another algorithm called optimization algorithm represented diagrammatically in FIG. 2 by a block 24 which is also connected to the means 23. Under these conditions, the motor 3 therefore rotates substantially at the reference speed Vc more or less the dead band BM.

 When the optimization algorithm is put into service, the real rotation speed VR of the motor 3 is put into memory, the link between the output of the motor 3 and the means 24 being materialized by a line 25.

 A small positive or negative increment, for example 0.8%, is applied to the single servomotor 11 via the means 23 and the butterfly valve 10 of the mixture is brought into a new position.

 If the said increment corresponds to an increase in the opening of the throttle valve 10, there is a depletion of the fuel mixture admitted into the engine 3.

If said increment corresponds to a reduction in opening of the throttle valve 10, there is enrichment of the fuel mixture since, in both cases, the gas flow rate Q has not been modified. They
gas then follows a slight modification of the carburetion which causes a slight variation in the actual rotation speed of the engine 3. This variation is detected after a given time, for example 10 seconds, then the news of speed is compared. actual rotation with memorized speed VM
When the increment has the effect of increasing the actual rotational speed, it is deduced therefrom that the efficiency of the engine has increased since the flow rate of the gas Q gas has remained identical. Under these conditions, a second increment of same value and same direction and the above process is repeated until the maximum yield is obtained.

When the increment has the effect of reducing the speed of rotation of the motor 3, the efficiency decreases because the gas flow rate Qgaz has remained the same. Under these conditions, to the first increment is added another increment of opposite sign; and the process of comparing the rotation speed VR with the memorized speed is repeated
It should be noted that at each reiteration, the rotational speed is stored in order to be able to be compared, after modifications of the carburetion, to the new speed value obtained at the end of the interaction period.

 The optimization algorithm proceeds dopc by systematic and successive tests at constant time intervals, which has the effect of bringing the engine operating point to the maximum of its efficiency curve, then making it oscillate around this point maximum yield.

 It can happen that the optimization algorithm acts on the engine so that deviation AV is outside the dead band BM. Then, the microprocessor 13 abandons the optimization algorithm and switches to the regulation algorithm 18 until the deviation AV is reduced and again enters the dead band BM. It follows that the optimization algorithm is initiated once more in the manner indicated above, with an increment different from that which has been stored in a memory of the microprocessor 13, since each increment applied to the servomotor 11 is stored in such a way as to avoid applying, as far as possible, increments which cause the optimization algorithm 24 to switch too quickly to the regulation algorithm 18.

 It is easy to see that the device according to the invention allows automatic control of the carburetion and adapts to all the variations in engine operating conditions such as temperature, air humidity, calorific value of the fuel, fouling, load, etc., to ensure in each case the optimum richness allowing the minimum fuel consumption for an equivalent mechanical energy supplied.

 Indeed, if the motor 3 is for example subjected to a sudden increase in the load, the speed decreases and the microprocessor 13 simultaneously increases the openings of the butterfly 10 and of the valve 5.

Instantly, the engine does not accelerate t the flow of mixed Mixture therefore remains substantially identical but the flow of gas Qgaz increases since it depends on the opening of the valve 5. The fuel mixture introduced into the engine 3 is enriched in improving the operating conditions of the engine 3. Conversely, when the engine 3 is subjected to a sudden decrease in the load, the fuel mixture is temporarily depleted.

 In all of the foregoing, reference has been made to means 15 for measuring the actual speed of rotation of the motor. Among these means, there may be mentioned those which can be incorporated in the microprocessor 13 - which achieves the acquisition of the speed of rotation VR by counting for example the time separating two electrical ignition pulses, which calculates the flow rates Q gas and Mixture to be supplied as a function of the speed VR and of the reference speed V c which is given to it, and which finally elaborates the control signals of the servomotors 8 and 11, in the form of rings of variable length for carrying out the calculated correction .

 Sometimes and this occurs when the engine 3 is ignition by platinum screws, the electrical ignition pulses are not clear enough to be used. Therefore, an optical reading measuring device shown diagrammatically in FIG. 3 can be used. The reference 26 indicates a flywheel of the engine on which a light beam 27 is sent which, after reflection on said flywheel 26, is received on a detector 28. The signal delivered by the detector 28 is shaped in a conventional shaping circuit constituted for example by a Schmitt triffer 29 and a monostable 30, so as to have slots 31 as indicated above, the slots 31 being addressed in the appropriate processing circuit of the microprocessor 13.

Claims (22)

 1. A method of automatic regulation and optimization of the richness of a fuel mixture for a heat engine, of the type according to which the flow rate of at least one of the constituents of the mixture is regulated as a function of the actual speed of rotation of the engine, characterized in that it consists in predetermining a target speed for the motor, in measuring the actual speed of rotation of said motor, in comparing said target and actual speeds, said comparison determining a speed difference which is measured, in controlling the flow rate of at least one of the constituents of the mixture as a function of the difference measured so that the mixture admitted into the motor produces a variation in the actual speed of rotation and bring it to a value close to the set speed predetermined motor.  2. Method according to claim 1, characterized in that on each side of the set speed is delimited a speed band and in that the regulation of said flow of the constituents of the mixture is such that said measured difference is less than one of said speed bands.  3. Method according to claim 2, characterized in that the regulation consists in maintaining substantially constant the richness of the fuel mixture by simultaneously varying the flow rate of the constituents of said mixture in the same direction and of a substantially equal value.  4. Method according to claim 2, characterized in that each speed band is low compared to the value of the set speed.  5. Method according to claim 3, character-ized in that the value of each speed band is equal to about 50 revolutions / minute.  6. Method according to claim 1, characterized in that it further comprises the following steps: measuring and storing the real rotation speed at a given instant; applying a first fixed positive or negative increment to the control of said flow rate of at least one of the constituents of the fuel mixture; detecting the direction of the variation of the real speed of rotation of the motor for the fixed increment applying a second increment in the same direction as the first on said control when the first increment has the effect of increasing said real speed of rotation, and repeat the memorization and detection steps until the motor reaches its maximum efficiency.  7. Method according to claim 6, characterized in that it consists in adding another increment of sign opposite to the previous increment applied when the latter has the effect of reducing the actual speed of rotation, and in repeating the steps of memorization and of detection.  8. Method according to one of claims 5 or 6, characterized in that each increment and its sign are stored in memory at each iteration.  9. Method according to one of claims 1 to 8, characterized in that the constituent of the fuel mixture which is modified is the fuel.  10. Method according to one of claims 1 to 9, characterized in that the step of regulating the mixing flow rate is only initiated each time that the difference between the actual speed of rotation and the speed of. setpoint is greater than the largest of the speed bands delimited around the setpoint speed.  11. Device for the implementation of the method according to claims 1 to 10, of the type comprising a mixer connected to an engine, means for controlling the admission of a fuel and an oxidizer, an adjusting butterfly disposed in the mixer and the opening of which determines the flow rate of the fuel mixture admitted into said engine, characterized in that the mixer is constituted by a body in which a bore is formed, and in that the fuel intake means are constituted by a valve, at least part of which opens into said bore and capable of coming to bear on a seat constituted by one end of a fuel intake pipe.  12. Device according to claim 11, characterized in that the valve is rotary.  13. Device according to claim 12, characterized in that the rotation of the valve is controlled by a servomotor controlled by a microprocessor.  14. Device according to claim 11, characterized in that the rotation of the admission control butterfly of the fuel mixture is controlled by a servomotor controlled by a microprocessor.  15. Device according to one of claims 13 and 14, characterized in that in the connection of the valve and the butterfly to their respective servomotor is interposed a flexible sleeve.  16. Device according to claims 13 and 14, characterized in that the same microprocessor works from a measurement of the actual speed of rotation of the motor from the control orders to said servomotors.  17. Device according to claim 16, characterized in that the control orders are developed from a measured difference between the actual rotation speed and a predetermined set speed, and applied to the control servomotors so as to reduce said deviation and bring the actual speed of rotation as close as possible to the set speed.  18. Device according to one of claims 13 to 16, characterized in that the microprocessor comprises means for developing control orders for the only servomotor associated with the butterfly when the measured speed difference is less than a predetermined speed band provided on each side of the set speed, the control orders lead to an increment in the rotation of the throttle in a certain direction so as to determine the direction of variation of the actual speed of rotation of the engine.  19. Device according to claim 18, characterized in that the increment applied is of the order of 0.8%.  20. Device according to one of the preceding claims, characterized in that the measurement of the real speed of rotation of the engine is carried out by the microprocessor from a time count separating two electrical ignition pulses of said engine.  21. Device according to one of claims 11 to 19, characterized in that the measurement of the real speed of rotation of the motor is carried out by the microprocessor from an optical reading, in particular by means of a light beam directed on a flywheel of said motor, a detector of the beam reflected by said flywheel and whose signal delivered is shaped in the form of slots which are addressed to the microprocessor.  22. Device according to claim 11, characterized in that it comprises a microprocessor, two servomotors controlled by said microprocessor and associated one with the valve and the other with the butterfly, means for measuring the real speed of rotation of the motor , said microprocessor, on the basis of the speed of rotation measured and compared with a predetermined reference speed, developing on the one hand a regulation step modifying, by a simultaneous action on the two servomotors, the actual speed of rotation to bring it at a value close to the set speed and, on the other hand, then an optimization step capable of carrying out systematic and successive measurements, at constant time intervals, of the speed of rotation and of the other operating parameters, so as to maintain the engine operating point at the maximum of its efficiency curve.