EP0051529B1 - Control device for the regulation of the optimal conducting time of an ignition coil for an internal-combustion engine - Google Patents

Description

The present invention relates to an ignition coil control device with optimal conduction time regulation for an internal combustion engine.

The spark which causes the ignition of the compressed explosive mixture inside a cylinder of an internal combustion engine is produced by the breakdown of the electric current flowing in the primary of a coil and thereby causing an overvoltage. in high school connected to candles. The primary electrical circuit of the coil must therefore remain closed for a sufficient time, greater than or at least equal to the time required to fill the current necessary to obtain the nominal energy in said coil.

On so-called transistorized ignitions, where the classic mechanical switch is replaced by a position sensor which controls a power transistor, the opening time of the primary circuit is constant and equal to the minimum time necessary for producing the spark. This solution, like the mechanical solution, offers a major drawback relative to the current consumption at low speeds, compared to the current strictly necessary for filling the coil with sufficient energy.

Another solution consists in controlling the coil during a constant conduction time whatever the rotation speed of the motor. If this time is strictly equal to the filling time necessary for the coil, we are led to the minimum current consumption by the ignition circuit. A solution of this kind, applied to an all-electronic ignition where the transistor power unit is controlled by a computer which determines the advance angle at ignition at all times, was the subject of FR- A-2 358 564 filed on July 15, 1976 in the name of the Régie nationale des plants RENAULT for "ignition coil control device for combustion engine with constant conduction time •. This solution has the advantage of the parameterized adjustment of the constant conduction time thanks to the use of a programmable logic network (PLA). However, it does not make it possible to overcome all the parameters such as the battery voltage, the temperature or others which influence the intensity of the current in the coil and, consequently, on the time necessary for obtaining of nominal energy across the coil.

US-A-4,018,202 attempts to solve this problem using an ignition coil control device with optimal conduction time regulation comprising means for strictly measuring the time of each ignition cycle. necessary for obtaining the nominal energy at the terminals of the coil and means for calculating from said measured time and the angular location signal an optimal conduction time to control the conduction of the coil at the next ignition cycle.

These means include a position counter which, at each ignition cycle, is incremented by the angular tracking signal and a preloaded speed counter which is decremented at each period by a clock signal by this same angular tracking signal .

When the contents of the two counters have become equal, a comparator causes the coil to go into conduction by means of a rocker which is brought back to zero at the instant of ignition. The conduction time strictly necessary to obtain the nominal energy across the coil is detected by a current limiting amplifier and this time is used to adjust the period of the clock signal during which the speedometer is counted down.

Such a device implies that the toothed crown integral in rotation with the crankshaft and used to generate the angular tracking signal has a high number of teeth, otherwise the resolution of the angular tracking signal would be insufficient to measure the speed during each period of the signal. clock and to ensure ignition with the required precision, which is generally of the order of a degree. However, experience shows that it is practically impossible to produce crowns with hundreds of teeth industrially at an acceptable cost.

• - t_e engendré est le temps de conduction de la bobine,
• - N est un nombre de fractions angulaires ou périodes du signal de repérage angulaire de période TSD, et
• - s est une quantité faible liée à la différence de résolution entre l'angle d'avance à l'allumage et l'angle de conduction de la-bobine.

This is the reason why it is known in many electronic ignition computers to use crowns having only a few tens of teeth while performing electronic interpolation of the angular reference signal to obtain the desired angular precision for the ignition. In calculators of this type, the ignition advance angle is expressed as the sum of an integer number of teeth or periods of the angular tracking signal and a fraction of tooth or period represented by a number of periods of the interpolation signal. For its part, the conduction angle of the coil, the accuracy of which is less critical, is expressed in number of periods of the angular location signal, so that such a computer has a transfer function of the form ^t e generated - N TSD + ₆ WHERE:

• - t _e generated is the conduction time of the coil,
• N is a number of angular fractions or periods of the angular location signal of period TSD, and
• - s is a small quantity linked to the difference in resolution between the ignition advance angle and the conduction angle of the coil.

However, the device described in US-A-4,018,202 is not applicable to an ignition computer having a transfer function of the aforementioned type. Indeed, if the angular location signal is used to increment and decrement the two counters, the number of angular fractions read during a clock signal period will be insufficient to obtain a correct image of the engine accelerations or decelerations, whereas if the interpolation signal is used, the absence of angular position adjustment during an ignition cycle may lead to major errors under the same conditions. Another reason for the incompatibility of the device in accordance with patent US-A-4018202 with an ignition computer having the aforementioned transfer function is that the latter works on angles and must be charged before each ignition cycle with a coil conduction time translated in the form of an angular value as a function of the engine rotation speed, while the device of the above US patent directly generates a conduction time during the ignition cycle considered.

On the other hand, the solution consisting in varying the clock frequency used to sample the speed signal to take account of the variations in the time necessary for obtaining the nominal energy at the terminals of the coil measured at each cycle of ignition appears complex and costly in components.

Finally, US-A-3,908,616 and WO-A-80.02,862 describe devices for regulating the conduction time of an ignition coil which both use targets linked in rotation to the engine crankshaft and associated with sensors providing two angular location signals at each cycle, for example at each half-turn in the case of a four-cylinder engine. This low number of identified angular positions requires the use of electronic devices which do not allow the instantaneous angular position of the crankshaft to be known with sufficient precision in the event of strong acceleration or deceleration of the engine. In addition, the devices of these last two patents do not provide for regulation of the conduction time based on the measurement, at each ignition cycle, of the time strictly necessary for obtaining the nominal energy at the terminals of the coil.

The invention aims to provide an ignition coil control device based, such as that described in patent US-A-4,018,202, on the measurement at each ignition cycle of the time strictly necessary for obtaining the nominal energy at the terminals of the coil, while being compatible with a computer having a transfer function of the form t _c generated = N. TSD + ε, that is to say in which the conduction time is expressed, at the value s near, in the form of an integer number of angular divisions such as teeth of the crown linked to the crankshaft of the engine.

une seconde horloge de période TH,, un second compteur incrémenté, à chaque période TSD du signal de repérage angulaire, par la seconde horloge pendant un temps t_o = NB - TH₁ tel que NB = NA, et un troisième compteur incrémenté pendant le temps t_o par un signal d'interpolation de période TSD/n jusqu'à un nombre

de telle sorte que le temps de conduction optimal calculé par le dispositif est :

ledit nombre N étant transmis à l'étage de sortie du calculateur qui engendre un temps de conduction :

où ε est une quantité faible et connue.To this end, the subject of the invention is an ignition coil control device with optimal conduction time regulation associated with the output stage of an ignition advance computer for an internal combustion engine producing a TSD period angular location signal corresponding to an angular reference such as a tooth in the starter crown associated with the engine, comprising means for measuring the time t _c measured at each ignition cycle strictly necessary for obtaining the nominal energy at the terminals of the coil and means for calculating from said measured time t _c and the angular location signal an optimal conduction time t _c for controlling the conduction of the coil at the following ignition cycle, characterized in that that said device comprises a first clock of period TH ₂ , a first counter incremented by the first clock during the time t _c measured up to a number NA such that:

a second clock of period TH ,, a second counter incremented, at each period TSD of the angular location signal, by the second clock for a time t _o = NB - TH ₁ such that NB = NA, and a third counter incremented during the time t _o by an interpolation signal of period TSD / n up to a number

so that the optimal conduction time calculated by the device is:

said number N being transmitted to the output stage of the computer which generates a conduction time:

where ε is a small and known quantity.

et n étant le nombre fixe de signaux d'interpolation apparaissant à chaque période TSD, on constate que le rapport entre t_c calculé et t_c mesuré ne dépend que du choix du rapport TH₁/TH₂.With such a device, the optimal conduction time of the coil is recalculated at each TSD period of the angular tracking signal, and it is the last calculated value which will be taken into account by the ignition computer to control the conduction of the coil on the next ignition cycle. This calculated value being equal to

and n being the fixed number of interpolation signals appearing at each TSD period, it can be seen that the ratio between t _c calculated and t _c measured only depends on the choice of the TH ₁ / TH ₂ ratio.

According to a characteristic of the invention, the first counter is preloaded by a loading signal with a number nt, the optimal conduction time calculated by the device being:

• les figures 1 et 2 représentent un ensemble de signaux permettant de situer le problème résolu par la présente invention ;
• la figure 3 est un schéma équivalent à l'étage de sortie d'un calculateur numérique d'avance à l'allumage qu'il convient d'utiliser en association avec le dispositif de commande selon la présente invention ;
• la figure 4 représente schématiquement un exemple de réalisation d'un dispositif de commande conforme à la présente invention ;
• les figures 5 et 6 représentent divers chronogrammes de signaux présents dans le circuit de l'invention et facilitant la compréhension du fonctionnement de ce dernier.

Other characteristics will emerge from the description which follows and which is given only by way of example. For this purpose, reference is made to the accompanying drawings in which:

• Figures 1 and 2 show a set of signals for locating the problem solved by the present invention;
• FIG. 3 is a diagram equivalent to the output stage of a digital ignition advance computer which should be used in association with the control device according to the present invention;
• FIG. 4 schematically represents an exemplary embodiment of a control device according to the present invention;
• Figures 5 and 6 show various timing diagrams of signals present in the circuit of the invention and facilitating the understanding of the operation of the latter.

• à la ligne L₁ le signal de repérage angulaire de période TSD ;
• à la ligne L₂ le courant traversant la bobine ;
• à la ligne L₃ l'évolution du contenu NA d'un compteur de mesure du temps t_c strictement nécessaire pour obtenir l'énergie nominale aux bornes de la bobine ;
• à la ligne L₄ la fenêtre de mesure angulaire de durée t_o proportionnelle à la mesure du temps t_c strictement nécessaire, générée à chaque fraction du signal de repérage, grâce à l'incrémentation d'un compteur dont le contenu NB est en permanence comparé au contenu NA du compteur de temps ;
• à la ligne L_s, l'évolution du nombre N obtenu par comptage d'un signal d'interpolation de résolution n fois plus élevée que le signal de la ligne L₁ durant la fenêtre de la ligne L₄.

The timing diagram in Figure 1 shows:

• at line L ₁ the angular tracking signal of period TSD;
• at line L ₂ the current passing through the coil;
• on line L ₃ the evolution of the content NA of a time measurement counter t _c strictly necessary to obtain the nominal energy at the terminals of the coil;
• at line L ₄ the angular measurement window of duration t _o proportional to the measurement of time t _c strictly necessary, generated at each fraction of the locating signal, thanks to the incrementation of a counter whose NB content is permanently compared to the NA content of the time counter;
• at line L _s , the evolution of the number N obtained by counting an interpolation signal of resolution n times higher than the signal of line L ₁ during the window of line L ₄ .

• à la ligne L₁₁ le signal désigné par la suite TSD et qui est le signal dent ou signal de repérage angulaire issu de la couronne du démarreur et fourni par l'intermédiaire d'un capteur de proximité ;
• à la ligne L_12' deux points morts hauts (PMH) successifs ;
• à la ligne L₁₃, la forme du courant au travers du circuit primaire de la bobine d'allumage ;
• à la ligne L₁₄, l'instant de déclenchement de l'étincelle d'allumage ;
• à la ligne L_15' un signal de régulation correspondant au temps de régulation « treg à à la ligne L₁₃ et, à la ligne L_16' le signal d'allumage en sortie du calculateur sur son conducteur 110 à la figure 3.

In FIG. 2, there is shown successively:

• at line L ₁₁ the signal subsequently designated TSD and which is the tooth signal or angular location signal from the starter ring and supplied by means of a proximity sensor;
• at line L _{12 '} two successive top dead centers (TDCs);
• at line L ₁₃ , the shape of the current through the primary circuit of the ignition coil;
• at line L ₁₄ , the instant of ignition spark ignition;
• at line L _{15 ′} a regulation signal corresponding to the regulation time “treg at at line L ₁₃ and at line L _{16 ′} the ignition signal at the output of the computer on its conductor 110 in FIG. 3.

The signal illustrated in line L ₁ in FIG. 1 is the same as that illustrated in line L ₁₁ in FIG. 2. The scales are different.

• - t_c: temps de conduction strictement nécessaire à l'obtention du courant nominal au travers de la bobine,
• - treg : temps de régulation durant lequel on maintient le courant nominal au travers de la bobine jusqu'à l'apparition de l'instant d'allumage représenté à la ligne L,₄ et durant lequel le dispositif de commande de puissance doit dissiper une énergie non négligeable afin d'assurer cette régulation.

The device which is the subject of the invention is intended to minimize, in the generation of the supply signal of the primary circuit of the ignition coil, line L _{13 'in} FIG. 2, the time "treg" said to regulate the primary current of the coil . In this one, a2 represents the conduction time actually generated at each half-turn T _o of the motor and broken down as follows:

• - t _c : conduction time strictly necessary to obtain the nominal current through the coil,
• - treg: regulation time during which the nominal current is maintained through the coil until the appearance of the ignition instant shown on line L, ₄ and during which the power control device must dissipate a significant energy to ensure this regulation.

It is the measurement of the time strictly necessary during a half-turn T _o which, by means of the control device according to the present invention, must allow the following half-turn to apply to the inputs 107 of an adder 101 of the output stage of the computer illustrated in FIG. 3, the optimal value N: number of angular fractions or periods of the angular tracking signal, leading to generate a total time a2 close to t _o and less than T _o .

It is accepted that t _c , conditioned by the value of the battery voltage, the eigenvalue of the self-inductance of the ignition coil and the apparent resistance of the charging circuit, remains constant from one half-turn to the next.

The only fundamental quantity at the input of the device according to the invention is therefore the time t _c which makes it possible to continuously recalculate the number of angular fractions N to be supplied to the output stage of the computer in order to reconstruct the time t _c at best, whatever the instantaneous speed of rotation of the motor.

FIG. 3 is an equivalent diagram of the output stage of a digital ignition advance computer usable in association with the control device according to the present invention.

According to the representation of FIG. 3, the output stage of the computer comprises a counter-accumulator 100 connected by inputs 104 to the outputs of a memory which has not been represented to receive an angular digital value No representative of it advance to beget. The counter-accumulator 100 also has a loading-106 input connected to a sequencer not shown and an input of L ₁ count 105 by which it receives the signal TSD illustrated in the line. L ₁ of the Figure 1. Half of the most significant outputs 108 of the counter-accumulator 100 are connected as inputs on the adder 101 already encountered and all of the outputs 108 of the counter-accumulator 100 are connected, moreover, as inputs on a door. logic 102 with AND function whose output 111 is connected to the return to zero input of a flip-flop 103 whose activation input is connected to the output conductor 109 of the adder-comparator 101 which is of limited capacity and which, when there is overflow, emits a pulse on its conductor 109 to actuate the flip-flop 103. The flip-flop 103 directly supplies on its output conductor 110 the command signal of the coil as illustrated in line L ₁₆ of FIG. 2. The result of the addition made at 101 between the number N and the content of the angular counter 100 causes the instant of conduction N · TSD before the instant of ignition. The number N is therefore found to be directly equal to the number of angular fractions or periods of the angular locating signal illustrated in line L ₁₁ of FIG. 2 which separates the instant of conduction from the instant of ignition.

Figure 3 is the equivalent of the output stage of the ignition advance computer as described in FR-A-2 237 421 filed on October 9, 1975 by the Régie nationale des plants RENAULT for "electronic ignition control method and device for an internal combustion engine". More generally, we can say that the output stage of any ignition advance computer having a transfer function of the form: t _c = N · TSD + e in which ε is a small quantity and known, all the other quantities having been previously defined, is satisfactory for being associated with the control device according to the present invention which will now be described in conjunction with FIG. 4.

According to the representation of FIG. 4 of the output stage of the computer 2 as shown and described in connection with FIG. 3, two conductors 37 and 38 leave in the direction of a logic block 36. The conductor 37 transmits the signals successive ignition as shown in Figure 2, line L ₁₆ and in Figure 5, line L ₂ '. The conductor 38 transmits the regulation signals as shown in FIG. 2, line L ₁₅ and in FIG. 5, line L ₃ '. Line L ₁ 'Figure 5 represents two successive TDCs. The logic block 36 is connected by a first output 39 to an input of a logic gate 32 with AND function in order to transmit to it a signal illustrated on line L4 ′, FIG. 5 and which is representative of the conduction time strictly necessary for the coil, ci -after called _measured tc _' The second input 34 of logic gate 32 is attacked by a clock H ₂ of period TH ₂ corresponding to the illustration of line L5', Figure 5. The pulses present on output 33 of gate logic 32 with AND function and which are represented on line L ₇ 'of FIG. 5 penetrate inside a counter 1 by its clock input connected to the conductor 33. The logic block 36 is connected by a second output 41 to the reset input of counter 1 which receives a pulse as shown in line L ₆ ′ in FIG. 5 before the reception of the pulses from logic gate 32 with AND function. At the end of the measured time t _c (line L ₄ ', fig. 5), the counter 1 presents on its outputs 5 a number NA defined as follows:

A comparator 6 is attacked, on the one hand, by the outputs 5 of the first counter 1, on the other hand, by the outputs 12 of a second counter 9 whose clock input 10 is connected to the output of a door logic 13 with AND function. This logic gate 13 is attacked on its input 15 by a signal for the start of synchronous counting of the angular location signal as shown in line L ₁ "of FIG. 6 and on its second input 4 by a clock H ₁ of period TH _1. These are the pulses present on the output 10 of the logic gate 13 which increment the counter 9 by its clock input itself having been reset to zero by its input 11 thanks to a synchronous pulse of the angular tracking signal and preceding the arrival of the first pulse present on input 15.

The clock input 19 of a D type flip-flop 17 receives the counting start signal at the same time as the input 15 of the logic gate 13 and thus switches its output Q20 to the high state as shown in the line L ₂ "in FIG. 6. When the content of counter 9 reaches a value: NB = NA, after a time, t _o = NB - TH, the output 7 of comparator 6 is activated and sets the flip-flop to zero 17. The resulting signal illustrated in line L2 "of FIG. 6 of duration t _o = NB - TH, is applied to the input 20 of a logic gate 21 with AND function. The second input 22 of the logic gate 21 is activated by pulses of period TSD / n illustrated in line L ₃ ", FIG. 6. Multiple frequency n of the angular location signal TSD, this interpolation signal can be generated in accordance with the teaching of FR-A-2 446 467 filed on January 9, 1979 in the name of the Régie Nationale des Usines Renault for “process and apparatus for locating the angular position of a part with a rotating movement •.

The pulses exiting from the logic gate 21 with AND function, the number of which is equal to N = t _o / (TSD / n) penetrate by its clock input 24 inside a counter 25 previously reset by its input 26 by the same signal as that applied to counter 9 by its input 11. The counting result N appears on the outputs 28 of counter 25 and is loaded into a memory 29 which is activated on its loading input 30 by a synchronous signal signal of angular tracking preceding the reset pulse of the counters 9 and 25. It is this same number N present on the outputs 31 of the memory 29 which is applied to the inputs 107 of the output stage of the electronic computer 2 such that it has been explained using Figure 3.

The line L ₄ "in FIG. 6 illustrates the number of pulses of period TDS / n passed through the measurement window illustrated in line L ₂ "in figure 6.

or:

d'où

et

The calculated conduction time is therefore equal to.

gold:

from where

and

The technician can give the ratio n - (TH ₁ / TH ₂ ) any value he deems useful and in particular the value one which leads to the permanent obtaining of the equation:

• Préchargement d'une valeur nt dans le compteur 1 par son entrée 41.
• Préchargement d'une valeur nd dans le compteur 25 par son entrée 26. On obtient en sortie :
  

The device described authorizes the installation of two preloading numbers or offsets in the counters 1 and 25 of FIG. 4 which are explained as follows:

• Preloading of a value nt in counter 1 by its input 41.
• Preloading of a value nd in the counter 25 by its input 26. We obtain at output:
  

Note that if the input 41 of the counter 1 and the input 26 of the counter 25 correspond to their reset inputs, the output function is described by equation (1) above.

The control device which is the subject of the present invention makes it possible, during the initialization phase of starting the vehicle, to program, for the first ignition which is generated, a constant conduction time equal to the maximum conduction time encountered in extreme conditions. Operating.

The initialization signal emitted by the computer 2 of FIG. 4 arrives, by a conductor 43, at a first input of a logic gate 42 with OR function which activates by its output 45 the loading input of the counter 1.

n max = t _e max / TH ₂ conduct if we set δ _i = 1 and δ _i = 0 during the initialization phase to be generated at the output of the computer 2.

It is possible to integrate within the device according to the invention a security function; in the event that the information relating to the regulation level shown in line L ₁₅ of FIG. 2 is missing. The input 38 of the logic block 36 not having detected the presence of this last signal, said logic block 36 generates on a third output 44 a loading pulse which is transmitted to the counter 1 via the same logic gate 42 with OR function previously encountered.

If we set δ _P = 1 and δ _P = 0 when the regulation information on conductor 38 is lost, the output of computer 2 can be written:

Claims (11)

1. Ignition coil control device with optimum conduction time regulation associated with the output stage (2) of an ignition advance computer for an internal combustion engine, producing an angular reference signal having a period TSD corresponding to an angular reference marking such as a tooth on the starter motor ring which is associated with the engine, comprising means (32, 45) for measuring in each ignition cycle the time t_c measured which is strictly necessary for producting the nominal energy at the terminals of the coil and means (1, 6, 9, 17, 25) for computing from said time t_c measured and the angular reference signal an optimum conduction time t_{c calcuted} for controlling conduction of the coil in the following ignition cycle, characterised in that said device comprises a first clock (H₂) having a period TH₂, a first counter (1) which is incremented by the first clock (H₂) during the time t_{c measured} to a number NA such that:

a second clock (H₁) having a period TH_1' a second counter (9) which is incremented in each period TSD of the angular reference signal by the second clock (H_i) for a time to = NB · TH₁ such that NB = NA, and a third counter (25) which is incremented during the time to by an interpolation signal having a period TSD/n to a number

such that the optimum conduction time calculated by the device is :

said number N being transmitted to the output stage of the computer (2) which generates a conduction time:

wherein e is a small known quantity.

2. A device according to claim 1, characterised in that the first counter (1) is preloaded by a loading signal with a number nt, the optimum conduction time calculated by the device being :

3. A device according to claim 2 characterised in that the measuring means (32-45) comprise a logic block (36) connected by two of its inputs (37-38) to two outputs of the output stage of the computer (2) for respectively receiving therefrom the coil conduction signal (37) and a regulation signal (38) which is active, when the nominal energy is attained at the terminals of the coil, the logic block (36) supplying at a first output (39) to a logic AND-gate (32) a counting authorisation signal which is equal in duration to said time t_c measured necessary for producting the nominal energy at the terminals of the coil and, at a second output (41), to the first counter (1), the loading signal preceding the counting authorisation signal, the logic AND-gate (32) being connected by a second input (34) to the first clock (A₂) and by its output to the clock input (33) of the first counter (1).

4. A device according to claim 3, characterised in that the logic block (36) is connected by a third output (44) to a first input of a logic OR-gate (42) for supplying a loading pulse to an input (45) of the first counter (1) in the absence of the regulation signal, a second input (43) of the logic OR-gate (42) being connected to an output of the computer (2) to receive therefrom an initialisation signal in the initialisation phase corresponding to the first igintion cycle.

5. A device according to claim 4, characterised in that, in the first ignition produced, the first counter (1) is preloaded by the computer (2) by way of the logic OR-gate (42) with a number n max. such that the optimum calculated conduction time is :

wherein δ_i = 1 and δ _⊥ = 0 during said initialisation phase.

6. A device according to claim 5 characterised in that, in the absence of the coil regulating signal, said loading pulse supplied to the first counter (1) by the logic block (36) is such that the calculated optimum conduction time is :

wherein 8p = 1 and δ _P = 0 at the time at which the coil regulating information is lost.

7. A device according to any one of claims 1 to 6 characterised in that the third counter (25) is preloadedby an input (26) with a value nd such that said number N transmitted to the output stage of the computer (2) is increased by the value nd and that the calculated condution time t_c calculated is increased by the value nd - TSD.

8. A device according to any one of claims 1 to 7 characterised in that it comprises a logic comparator (6) connected on the one hand to the outputs (5) of the first counter (1) and on the other hand to the outputs (12) of the second counter (9) and whose output (7) is connected to the zero resetting input of a D-type flip-flop (17) whose clock input (19) receives a signal which is synchronous with each rising edge of the angular reference signal and whose output is reset to zero by the comparator (6) at the end of the time to = NB - TH₁ such that NB = NA, a second AND-gate (21) connected by way of one of its inputs to the output of the D-type flip-flop (17) and receiving at its other input (22) the interpolation signal of period TSD/n the output of the second AND-gate (21) being connected to the third counter (25), and a memory (29) connected between the third counter (25) and the output stage of the computer (2) and in which the calculated number N is stored.

9. A device according to any one of the preceding claims characterised in that the clock inputs (33, 10 and 24 for authorising counting of the periods TH₂, TH₁ and TSD/n by the first, second and third counters (1, 9, 25) respectively determine the value of the ratio :

10. A device according to claims 3, 4 and 7 characterised in that the loading inputs (41, 45 and 26) of the first and third counters (1, 25) determine the value of the numbers nt, n max. and nd, which may be between zero and the maximum capacity of the counters (1, 26) used.

Images