US3559629A

US3559629A - Static lead correction device for the ignition of an internal combustion engine

Info

Publication number: US3559629A
Application number: US793708*A
Authority: US
Inventors: Henri Joseph Sauvignet
Original assignee: Compteurs Schlumberger SA
Current assignee: Compteurs Schlumberger SA
Priority date: 1968-01-25
Filing date: 1969-01-24
Publication date: 1971-02-02
Anticipated expiration: 1988-02-02
Also published as: GB1226502A; FR94998E; DE1901557A1

Abstract

The static correction device for advancing ignition controlled by an electromechanical or electronic detector incorporates a circuit for forming a signal received during the passage of a nonactive part of the cam and issuing a signal which partially charges a first condenser and discharges it during a time equal to the difference between the passage time of the nonactive part of the cam, and the charging time, a second charging condenser partially charging during a time inversely proportional to the speed during the passage of the nonactive part of the cam and completely discharging after that with a current proportional to the voltage at the terminals of the first condenser. The end of the discharge of the second condenser trips a temporization which is a function of the speed and interrupts the primary current of the ignition coil, by the intermediary of an amplifier circuit, so as to produce an induced current in the secondary of the ignition coil.

Description

United States Patent [54] STATIC LEAD CORRECTION DEVICE FOR THE IGNITION OF AN INTERNAL COMBUSTION ENGINE 8 Claims, 17 Drawing Figs.

[52] US. I 123/148, 315/209 [51] Int. Cl. F02p 3/02 [50] Field of Search 123/148E,

[56] References Cited UNITED STATES PATENTS 3,202,146 8/1965 Short et al. 123/ 148 3,361,123 1/1968 Kasama et al 123/148 Primary Examiner-Laurence M. Goodridge Attomey-Pierce, Scheffier and Parker ABSTRACT: The static correction device for advancing ignition controlled by an electromechanical or electronic detector incorporates a circuit for forming a signal received during the passage of a nonactive part of the cam and issuing a signal which partially charges a first condenser and discharges it during a time equal to the difference between the passage time of the nonactive part of the cam, and the charging time, a second charging condenser partially charging during a time inversely proportional to the speed during the passage of the nonactive part of the cam and completely discharging after that with a current proportional to the voltage at the terminals of the first condenser. The end of the discharge of the second condenser trips a temporization which is a function of the speed and interrupts the primary current of the ignition coil, by the intermediary of an amplifier circuit, so as to produce an induced current in the secondary of the ignition coil.

' PATENIEU FEB 2 I97! SHEET, 1 BF 4 PATENTEU FEB 2 I97! SHEET 2 [IF 4 Q0 A I S Q )T Q 1d 4/ g a w h mm k fi E E g a w r 1% Ll M G 5 5 L g dflw Q g 3 m: W h 8 F 5. @Q 3 -H lm 5 a 5 Q 1 ix mww Nov sov STATIC LEAD CORRECTION DEVICE FOR THE IGNITION OF AN INTERNAL COMBUSTION ENGINE The present invention relates to an electronic ignition device with lead controlled by a detector of an electromechanic al or electronic type. A detector of this kind is described in a copending application Ser. No. 780,046 filed Nov. 29, I968, in the name of Bernard Varaut and assigned to the same assignee as is the present application.

In accordance with the invention, the detector controls temporization members with several time constants for charging and discharging as a function of the speed of the engine. Specifically, an intercalated resistance is used in the emitter of a transistor biased by a condenser of a first temporization for supplying a collector current proportional to the voltage at the terminals of this condenser. Thus, it is possible to control the discharge current of a condenser of a second temporization. The resistance which can vary as a function of the air pressure depression (vacuum condition) in the intake piping defines the factor of proportionality.

The main object of the present invention is to effect an improved device directly usable on the voltage of the battery without amplifying the source by adjusting the discharge current of the second as a function of the speed of the engine.

The static lead correction device for advancing ignition controlled by an electromechanical or electronic detector incorporating, for instance, a cam driven by the crankshaft of the engine and comprising magnetic poles or conductors whose number depends on the number of engine cylinders comprises a circuit for forming the detector signal received during the passage of a nonactive part of the cam and issues a signal in phase opposition in relation to the detector signal and a fixed duration signal whose origin coincides with the appearance of the detector signal, the fixed duration signal partially charging a first condenser and discharging it during a time equal to the difference between the passage time of the nonactive part of the cam, and the charging time, the voltage at the terminals of the first condenser being an increasing function of the speed, a second charging condenser partially charging during a time inversely proportional to the speed during the passage of the nonactive part of the cam and completely discharging after the appearance of the active part of the cam with a current proportional to the voltage at the terminals of the first condenser, the discharge time of the second condenser being equal to the time passing between the appearances of the active part of the cam and the moment when the spark is started.

A voltage divider system is branched between the poles of.

the source and associated with switching means branched in parallel to various levels of the divider system for creating voltage thresholds on the emitter of at least one control transistor, so that the discharge current of the second condenser is a nonlinear function of the charge voltage of the first condenser.

In this manner, the end of the discharge of the second condenser trips a temporization which is a function of the speed and interrupts the primary current of the ignition coil, by the intermediary of an amplifier circuit, so as to produce an induced current in the secondary of the ignition coil.

According to another embodiment of the invention, the first condenser comprises a charge time constant and two discharge time constants.

According to another embodiment, the second condenser comprises a charge time constant,a charge limitation circuit and a discharge circuit for the imposed current.

According to one embodiment of the present invention, means of switching are made by transistors of the PNP type having their respective emitters branched in derivation through threshold resistances respectively connected at various levels of the voltage divider, the respective base of said transistors being in common connection to the first condenser According to another development of the invention, the switching means are formed by a set of diodes having their respective cathodes branched in derivation through threshold resistances connected to the various levels of the voltage divider, their anodes having a common connection to the emitter of the control transistor whose collector conducts the discharge current of the second condenser.

According to another development of the invention, the emitter of the control transistor has its base connected to the first condenser whose load voltage is a growing function of the speed, the collector of this transistor being connected to a second condenser wliose charging time is inversely proportional to the speed, the increase of voltage of the charge of the first condenser releasing one of the switching means considered as a function of one of the voltage thresholds.

According to still another development of the invention, at least one resistance or the ratio of the resistances inserted in the emitter of the semiconductor charged by the capacity of the first temporization is variable as a function of the depression in the intake piping, so as to supply a collector current proportional to the voltage at the terminals of the first condenser.

Other characteristics of the invention are shown by the description which follows and attached drawings, given as examples of embodiment without limitative character.

FIG. 1 is a diagrammatic perspective of an internal combustion engine comprising the device of the invention.

FIG. 2 is a circuit diagram of the device according to the invention.

FIGS. 3, 3a and 3b are curves showing the shapes of signals at high rotation speeds and thus illustrating a method of operating the device of FIG. 2.

FIGS. 30 to 3e are curves showing the rate of lead signals at high speeds of the engine.

FIGS. 4, 4a and 4b are curves showing shapes of signals at low rotation speeds, thus illustrating another method of operating the device of FIG. 1.

' FIGS. 4c to 4e are curves showing the rate of the lead signals at low speeds of the engine.

FIG. 5 shows an alternative of part of the diagram of FIG. I.

FIG. 6 shows another alternative of the diagram of FIG. 2.

FIG. 7 shows the rate of curves as operating the alternatives of the diagram according to FIGS. 5 and 6.

In FIG. I, there is a diagrammatical representation of a four-cylinder engine 1, in each cylinder of which a piston 2 slides whose connecting-rod 3 is jointed at its foot on one of the crank-pins 4 of the crankshaft 5, rigidly connected to a flywheel 6 and also a distributing device 7 which functions to direct, in a given order, current pulses produced from the device of the invention, designated as a whole by 8 to each ignition plug 9. The device 8 comprises a depression plug connected, for instance, to an intake collector of the engine.

The device 8 is also connected to a probe forming part of it and whichis intended to detect the successive passage of two members 11 and 12 carried by the flywheel 6. In this manner, two current pulses are produced by setting up two sparks by two distinct spark plugs for each revolution of the crankshaft 5 as will be the case for a four-cylinder engine operating according to a four-stroke cycle.

' In FIG. 2, the probe 100 is shown in one of its possible execution modes and comprises facing the flywheel 6 or a cam driven by this flywheel or another turning member of the engine, a coil L connected in parallel with a condenser C to form an oscillating circuit whose resonance frequency has for C is a connecting condenser which forms a counterreacting loop with a counterreaction resistance R branched, on the one hand, on the point A of the coil L and on the other, on the emitter of a transistor T. A diode D rectifies, at point B the alternating voltage coming from the oscillating circuit LC A condenser C filters the output current of the transistor T. A

value resistance R and a diode D form a biasing circuit of the base of the transistor T.

As shown in FIG. 2, this probe 100 is connected by the

terminals

104, 105 to a circuit 101 enabling the shaping to be obtained of signals coming from this probe. The probe 100 supplied supplies a signal, all or nothing, according as to whether the members 11 or 12 forming the active parts of the flywheel 6 are passing, or not passing, in front of it.

The shaping circuit 101 comprises

transistors

106 and 107. The base of the transistor 106 is branched on to the junction point 108 of the common ends of two resistances in

series

109, 112. The voltage divider formed by the

resistances

109, 112 is branched, on the one hand, to a negative potential line, 110, and on the other, to the terminal 105 of the probe 100. The negative voltage line is grounded.

The emitter of the transistor 106 is connected to the negative line 110 and its collector to a resistance 114 connected to the positive line 111. The collector of the transistor 106 also comprises two derivations at two

points

113 and 115, the one effecting the junction with a complex circuit 102, the other connected to a condenser 116 whose output at point 117 is common to a resistance 1 18 and the base of the transistor 107.

The emitter of the transistor 107 is connected to the line 110, whereas its collector is branched at 119 to the resistance 120 connected to the conductor 111. The collector of the transistor 107 is also connected to the circuit 102 described hereafter by means of a resistance 130.

The circuit 102 functions for drawing up the definition of a time basis z= in which is the angle corresponding to each active part 11 of 12 of the flywheel or cam 6, a the angle of ignition advance and w the speed. This time basis is obtained from variable temporization members specifically comprising the

capacities

121 and 122. The capacity 121 has a time charge constant and two time discharge constants; the capacity 122 ha a charge time constant and a discharge time constant.

To this end, the derivation at point 113 is connected to point 123 of a voltage divider comprising resistances in

series

124, 125, the latter resistance being connected to the line 1 10. The middle point 126 is connected to the base of a transistor 127 whose emitter is connected to the line 110. The collector of the transistor 127 is connected to a point 128 and a resistance 129 whose other end ends at the line 1 1 1.

Moreover, the collector 119 of the transistor 109 is connected by a resistance 130 to a point 131 common to a resistance 132 connected to the line 110, and the base of a transistor 133 whose emitter is connected to the negative line 110.

The collector of the transistor 133 is connected, on the one hand, to a resistance 134 branched in series to the

common points

135, 136 with the condenser 121 anda resistance 137 connected in parallel with the condenser 121 on the line 110, and on the other hand, to the resistance 138 in series with a diode 139 connected to point 128.

A circuit for charging the condenser 122 comprises, from the line 111: the resistance 140 and the base of a transistor 141 forming part of a following circuit 103. A voltage reducer branched between the

lines

110, 111 comprises

resistances

142, 143 with an intermediate point 144 connected by a diode 145 to

points

146, 147 common to the link with the resistance 140 and the condenser 122; the charge of said condenser is limited by the voltage through the reducer described and the diode 145.

A diode 148 prevents the charge of the condenser 122 through the resistance 129 and the circuit passing through

points

146 and 147.

A transistor 149 has its emitter fed from the line 111 through aresistance 151 and its collector connected to a point 150 on the liaison circuit between the condenser 122 and the base of the transistor 141. The base of the transistor 149 is connected to

common points

135, 136. The value of the resistance 151 may vary, for instance, as a function of the depression in air pressure in the intake piping of the engine due to the action of the device 8a of FIG. 1.

The circuit 103 is a voltage threshold device controlled by a signal coming from the condenser 122, so as to obtain an output signal causing each spark of the spark plug 9.

The circuit 103 comprises the transistor 141 mentioned above whose collector is connected at an intermediate point 152 of a voltage divider placed between the

lines

110, 111 and formed by

resistances

153, 154. The intermediate point 152 is connected by means of a condenser 155 to the base of a transistor 156, which base is subjected as well as the collector, to the voltage of the line 111 by means of resistances, respectively 157 and 160. The condenser 155 and the resistance 157 form a time basis for the transistor 156.

The emitter of the transistor 156 is connected to a power

amplifier comprising transistors

158 and 159 mounted in cascade. The transistor 158 has its collector fed by the line 111 through the resistance 161 and its emitter comprises a ground connection at the point 163 by a resistance 162. The transistor 159 has its collector fed by the line 111 through the primary winding 164 of the ignition coil 165 in series with a diode 166 and its emitter branched on to ground.

The diode 166 avoids the oscillating discharge effect that might occur through the primary winding 164 owing to an inverted voltage and entails destruction of the transistor 159.

The operation of the circuits 100 to 103 described above is explained by FIGS. 3, 3a to 3e as well as FIGS. 4, 4a to 4e, respectively for high and low rotation speeds of the engine.

FIGS. 3 and 4 represent signals corresponding to the passage of the active part of the flywheel 6 in front of the detector 100 (FIG. 1). Square waves of duration 1,, t and t, t, show the oscillating state of the electronic detector for the inactive parts of the flywheel 6; the space I 1' between the squares shows the ,blocked state of the detector during the passage of the active part of the flywheel.

In FIGS. 3a and 4a, the squares at the moments t and It show the variations of the charge voltage V,, in the emittercollector circuit of the transistor 107, squares whoseduration is a function of the first time base formed by the condenser 116 and the resistance 118. The signal V,, is taken at the point 119 in the circuit 101.

FIGS. 3b and 4b show the variations of the charge voltage- U,. of the condenser 121.

FIGS. 3c and 40 show the variations of the charge voltage V, of the condenser 122 at

common points

146, 147 and FIGS. 3d, and 4d show those of the output voltage V, towards the transistor 141.

The regulating of the angle [3 or advance ignition angle is comprised between a moment id and the moment t, which corresponds to the passage of the piston through dead center.

In FIGS. 3e and 4e, the tripping of the spark at the moment 1,; and its duration until the moment I, are defined by the level of the voltage U, from the moment corresponding to the origin of the advance angle.

At high speeds, the tripping of the spark at the moment 1,, (FIG. 30) is situated before the moments t,, or t' which mark the end of the passage of the active part of the flywheel (dead center). On the other hand, at low speeds, the tripping of the spark at the moment I (FIG. 4e) corresponds to the moment t or t',,, i.e., when the angle a is slight or zero.

For facilitating the description, the working is described from the moment 1,, which follows the passage of the piston 2 at dead center. In this case, the oscillations of the detector 100 saturate the transistor 106 which becomes passing whereas the

transistors

107 and 127 are blocked, which has the effect of discharging the coridenser 116 through the resistance 118 and the transistor 106. Simultaneously, the transistor 107 is blocked and the transistor 133 can pass.

Up to that moment t,,, the condenser 121 partially charges from the voltage of the source (line 1 11) through the resistance 134 and the transistor 133 which is saturated, which represents the time constant referred to in the foregoing.

Between the moments the condenser 121 partially discharges in a first circuit passing through the resistance .137 in parallel and in a second circuit formed by the resistance 129, the diode 139, the resistances 138 and 124, the

transistors

127 and 133 being bIocked.This partiaI discharge corresponds to the first time constant of discharge of said condenser !21. r

The transistor 127 being blocked, the condenser- 122 charges from the voltage of the source through the resistance 140 and-by the base of the transistor 141 which issatiirated,

owing to this. The charge is limited to the level of the voltage defined by the

resistance reducer

142, 143 and the diode 145.

The discharge of the condenser 121 occurs during the moments r, t, of the cycle following through the resistance 137. There are thus two discharge time constants for the condenser 121.

The moment 1,. corresponds to the beginning of the active part 1 1 or 12 of the flywheel from which 100 is blocked.

It should be noticed that at all times the transistor 149 supplies a collector current proportional to the voltage at the terminals of the condenser 121 and that the proportionality factor is defined by the resistance 151 whose value is a function of the depression in the intake piping.

At the moment t the voltage at the condenser terminals 121 is so much the higher as the of the engine is greater.

At low speeds, the charge voltage of the condenser 122 reaches the voltage V, at point 144, which is fixed by the

resistances

142 and 143, and for higher speeds the charge voltage decreases owing to the time constant defined by the resistance 140.

It is advisable that the transistor 149 deliver to the condenser 122 when the potential V, at point 150 is negative in relation the negative pole (line 110) of the source. In these conditions, the voltage available for the amplification system (resistance 151 and transistor 149) is always at least equal to the voltage of the source.

The time which elapses between the moment 2,. and r corresponds to the discharge of the condenser 122 owing to the current of the collector of the transistor 149 passing through the

common points

146, 147, the diode 148 and the transistor 127, the transistor 141 being blocked. During this time interval, there is the complete charge of the condenser 155 through the resistance 153 and the

transistors

156, 158, 159 made passing.

Atthe moment t, which corresponds to the end of the discharge of the condenser 122, the transistor 141 becomes saturated which enables the discharge of the condenser 155 through the resistance 157 and the transistor 141 and which blocks the

transistors

156, 158, 159, cutting out the primary current of the coil.

By the effect of the extra breaking current, the spark appears at the secondary winding at the moment t,,. The duration of the spark between the moments r corresponds to the dischargingtime of the condenser 155 and may decrease with and 149, the

condensers

121 and 122, the

resistances

134, 137

and 151, the

common points

135, 136 and 150 have the same references as in said FIG. 2.

One thus finds the emitter of the transistor 149 connected by a resistance 151 to the positive line 111, the collector connected to point 150, on the one hand, to the condenser 122, and on the other, to the transistor 141.

According to this arrangement, transistors 149a, 149b, 1490 have their emitters connected by resistances respectively 151a, 151b, 1510 to voltage dividers each comprising resistances such as 251, 252, 251a, 1520, 251b and 252b. For drawing up the formulas given in that which follows, the resistances 151, 1510, 151b and 1510 correspond respectively to r,,, r,, r and r Without changing anything in the character of the invention it is quite understood that the number of transistors can be different to that taken as an example in FIG. 5.

The bases of transistors 149 to 1490 are connected together and to

points

135, 136 common with the 137 and the condenser 121. The collectors of these transistors are connected together as well as the condenser 122 by the point 150, on the one hand, and the base of transistor 14] on the other. This latter connection conveys the discharge current of the second condenser 122.

The working of the circuit 202 (FIG. 5) is explained as follows in relation to FIG; 7.

When the voltage U0 at the terminals of condenser 121 is less than 14, which is the voltage at the terminals of the resistances 251, the transistor 149 only is passing, and the other transistors 149a to 1490 are blocked. The discharge current of the second condenser 122 is expressed by:

r being the resistance 151a.

If the voltage U0 is comprised between u and u a being the voltage at the terminals of the resistance 251b, the main current becomes:

r being the resistance 151b.

Thus, progressively as U0 exceeds the reference thresholds u,, a :4 defined by the voltage dividers through the resistances 151 to 1510, the transistors such as 149, 149a, 149b.....are successively released, which enables a nonlinear variation curve to be obtained of the discharge current I (FIG. 7).

On this curve, one sees the variations 1 1 I of the discharge current as a function of the various levels of voltage u to u., which corresponds to the increase of voltage of U0,.

FIG. 6 shows an alternative 302 of the circuit 202 of FIG. 5 and the members having the same function retain the same reference numerals.

In the circuit 302, the emitter of transistor 149 is connected to the line 1 11 by a resistance 253 and a set of diodes replaces the resistances 151 to 1510 of FIG. 5.

The set comprises diodes 254a, 2541: and 2540 whose cathodes are respectively fed by

threshold resistances

255, 256, 257, which are individually connected in this order to points 258, 259 and 260 of a voltage divider branched between the lines and 111. The divider comprises

resistances

261, 262, 263 and 264. The

points

258, 259, 260 respectively determine the voltage levels u u u It is quite obvious that a different number of diodes could be used without changing the character of the invention.

The working of the circitit 302 of FIG. 6 is similar to that 202 of FIG. 5.

Progressively, as the voltage U0 exceeds the reference thresholds u u u; defined by the

various points

258, 259, 260 of the voltage divider, as well as by the

threshold resistances

255, 256, 257, the diodes 254a, 254b, 254:: are successively released, enabling the same nonlinear variation curve to be found of the discharge circuit (FIG. 6) as a function of the voltage Uc,.

For the two examples of circuits 202 (FIG. and 302 (HO. 6), when the voltage Uc, decreases, the discharge current backs gradually as a function of the threshold of the voltage u u,, u which corresponds to the successive locking of the transistors such as 149 or diodes such as 254.

Without going outside the scope of the invention, we can vary, either emitter resistances such as 151 or 253, or the ratio of resistances such as 251, 252 or 261 to 264 as a function of the depression in air pressure in the intake piping by means of the device 80.

lclaim:

1. Static device for the ignition of internal combustion engines of the two-stroke or four-stroke type, in which the ignition moment depends at least on the rotation speed of the engine crankshaft, said device comprising a spark plug per cylinder of the engine, a distributor mechanism for directing current pulses respectively to each spark plug of each cylinder, a revolving member or cam driven by said crankshaft and comprising at least one active zone and one inactive zone, said cam being placed facing an electronic probe, said electronic probe comprising a bistable oscillator with a fixed frequency disposed facing said cam so that it produces pulses during the passage of the inactive part thereof and is blocked during the passage of the active part, said oscillator having a rectifying and filtering circuit so that it produces rectangular signals corresponding to the inactive parts of the cam and to both the duration and frequency of which image the rotation speed of the crankshaft, a pulse generating circuit having a fixed time constant smaller than the duration of the rectangular signals and being connected to the rectifying and filtering circuit of said electronic probe, so that rectangular pulses are produced by said pulse generating circuit with the same origin as said rectangular signals and a fixed duration, a first capacitor connected to said pulse generating circuit, so that said first capacitor is charged during a fixed duration corresponding to each one of said pulses, a resistive discharge circuit having at least two discharge resistors connected to said first capacitor so that said capacitor has two discharge time constants, a second capacitor connected to the first capacitor by one of said resistors of the discharge circuit thereof, a first electronic gate also connected to said second capacitor and to said rectifying and filtering circuit of said bistable oscillator, so that said first capacitor is progressively discharged through the two resistors of each discharge circuit from the end of each pulse of a fixed duration according to a first time constant and that the rectangular signals from said rectifying and filtering circuit keep closed said first electronic gate which is open as soon as said signals are interrupted whereby said first capacitor is brought to be discharged according to a second time constant in one only of the two resistances of its discharge circuit and said second capacitor also discharged in dependency of said second time constant of said first capacitor, a second electronic gate placed at the input of a voltage threshold circuit and connected to said second capacitor whereby said gate is closed during the duration of the discharge of said second capacitor function of said second time constant of said first capacitor, and open at the end of said discharge, said voltage threshold circuit comprising a capacitor connected to said second electronic gate and to an ignition circuit connected to said distributor mechanism so that the opening of said second electronic gate puts into action said ignition circuit at the end of discharge of said second capacitor to produce an ignition spark at a moment which is a function both of the duration of the discharge of the second capacitor and of the end of each rectangular signal. 7 I

2. Device according to claim 1, wherein said second capacitor is connected to said rectifying and filtering circuit by said first electronic gate so that the rectangular signals are applied to said second capacitor, thereby receiving a charge which is inversely proportional to the rotation spee "of the crankshaft,

said second capacitor being discharged at the end of each rectangular signal causing the closing of said first electronic gate. a l

3. Device according to claim 1, wherein further the discharge circuit of said first capacitor comprises a variable resistor the magnitude of which is a function of the vacuum in the engine so that the second time constant of said first capacitor is a function of said vacuum.

4. Device according to claim 1, wherein the first capacitor is connected to at least a source of constant voltage so that the charge voltage which is applied to it is at the most equal to said constant voltage and that the discharge voltage of said first capacitor controls thedischarge voltage of the second capacitor and the control moment of said threshold circuit.

5. Device according to claim 4, comprising further voltage dividers parallely placed with a source of constant voltage, switching means connected to each voltage divider and respectively to sets of resistors constituting one of the resistors of the discharge circuit of said first capacitor, so that the discharge voltage of said capacitor is successively a function of said resistors and causes the discharge of said second capacitor in dependency thereof.

6. Device according to claim 5, in which the switching means are made by transistors PNP having their respective emitters branched in derivation through threshold resistances respectively connected to each voltage divider, their bases being connected in common to the first capacitor, their collectors being connected in common to the second capacitor, one of the transistors having the control function for a given voltage threshold. I

7. Device according to claim 5, in which the switching means are formed by a scale of diodes having their respective cathodes branched in derivation through threshold resistances connected to the various levels of the voltage divider, their anodes being made in common with a transmitter of the semiconductor of control whose collector conveys the discharge current of the second capacitor.

8. Device according to claim 7, in which the control semiconductor has its base connected to the first capacitor whose charge voltage is an increasing function of the speed, the collector of this semiconductor being connected to a second capacitor whose charge time is inversely proportional to the speed, the increase of voltage of the charge of the first capacitor releasing one of the switching means considered as a function of the one of the voltage thresholds.

Claims

1. Static device for the ignition of internal combustion engines of the two-stroke or four-stroke type, in which the ignition moment depends at least on the rotation speed of the engine crankshaft, said device comprising a spark plug per cylinder of the engine, a distributor mechanism for directing current pulses respectively to each spark plug of each cylinder, a revolving member or cam driven by said crankshaft and comprising at least one active zone and one inactive zone, said cam being placed facing an electronic probe, said electronic probe comprising a bistable oscillator with a fixed frequency disposed facing said cam so that it produces pulses during the passage of the inactive parT thereof and is blocked during the passage of the active part, said oscillator having a rectifying and filtering circuit so that it produces rectangular signals corresponding to the inactive parts of the cam and to both the duration and frequency of which image the rotation speed of the crankshaft, a pulse generating circuit having a fixed time constant smaller than the duration of the rectangular signals and being connected to the rectifying and filtering circuit of said electronic probe, so that rectangular pulses are produced by said pulse generating circuit with the same origin as said rectangular signals and a fixed duration, a first capacitor connected to said pulse generating circuit, so that said first capacitor is charged during a fixed duration corresponding to each one of said pulses, a resistive discharge circuit having at least two discharge resistors connected to said first capacitor so that said capacitor has two discharge time constants, a second capacitor connected to the first capacitor by one of said resistors of the discharge circuit thereof, a first electronic gate also connected to said second capacitor and to said rectifying and filtering circuit of said bistable oscillator, so that said first capacitor is progressively discharged through the two resistors of each discharge circuit from the end of each pulse of a fixed duration according to a first time constant and that the rectangular signals from said rectifying and filtering circuit keep closed said first electronic gate which is open as soon as said signals are interrupted whereby said first capacitor is brought to be discharged according to a second time constant in one only of the two resistances of its discharge circuit and said second capacitor also discharged in dependency of said second time constant of said first capacitor, a second electronic gate placed at the input of a voltage threshold circuit and connected to said second capacitor whereby said gate is closed during the duration of the discharge of said second capacitor function of said second time constant of said first capacitor, and open at the end of said discharge, said voltage threshold circuit comprising a capacitor connected to said second electronic gate and to an ignition circuit connected to said distributor mechanism so that the opening of said second electronic gate puts into action said ignition circuit at the end of discharge of said second capacitor to produce an ignition spark at a moment which is a function both of the duration of the discharge of the second capacitor and of the end of each rectangular signal.

2. Device according to claim 1, wherein said second capacitor is connected to said rectifying and filtering circuit by said first electronic gate so that the rectangular signals are applied to said second capacitor, thereby receiving a charge which is inversely proportional to the rotation speed of the crankshaft, said second capacitor being discharged at the end of each rectangular signal causing the closing of said first electronic gate.

4. Device according to claim 1, wherein the first capacitor is connected to at least a source of constant voltage so that the charge voltage which is applied to it is at the most equal to said constant voltage and that the discharge voltage of said first capacitor controls the discharge voltage of the second capacitor and the control moment of said threshold circuit.

6. Device according to claim 5, in which the switching means are made by transistors PNP having their respective emitters branched in derivation through threshold resistances respectively connected to each voltage divider, their bases being connected in common to the first capacitor, their collectors being connected in common to the second capacitor, one of the transistors having the control function for a given voltage threshold.