WO1993012339A1

WO1993012339A1 - Electronic ignition system for gas and petrol engines

Info

Publication number: WO1993012339A1
Application number: PCT/IT1992/000162
Authority: WO
Inventors: Antonella Marcotullio
Original assignee: Marigam S.A.S. Di Marcotullio Antonella & C.
Priority date: 1991-12-19
Filing date: 1992-12-15
Publication date: 1993-06-24
Also published as: AU3265993A; IT1250967B; ITRM910954A0; ITRM910954A1

Abstract

Electronic ignition device with double spark for gas and petrol engines, using an inductive spark and a capacitive spark, which employs a low impedance and high efficiency coil (84), and electromagnetic inductors or breaker points distributors to fix the ignition time; involved time constants allow to determinate the time between the two sparks.

Description

Description Electronic ignition system for gas and petrol engines

Technical Field

This invention relates to an electronic ignition system for gas and petrol engines in which an inductive spark and a capacitive spark are provided at the ignition time, respectively, slightly delayed one from the other, so that a total ignition time is provided longer than the one which is provided by commercial ignition systems.

Background Art

At the present time electronic ignition systems have almost completely replaced traditional ignition devices because they offer, usually, several advantages as a reduced fuel consumption, a better accelleration and an improved engine efficiency.

Anyway some cars are still delivered by the manufacturers provided by a traditional ignition (breaker points and low efficiency spark coil). It is to point out that electronic ignitions usually furnished as standard kit, provide just one spark

(inductive spark) , the energy of which results moreover to be limited. This system has no chance to be modified neither to provide a double spark nor to increase the energy of the discharge because the same system is based on the use of an integrated module. The limits of aforesaid ignition systems have been the presupposition for projects of systems founded on the emission (at the ignition time) of a couple of sparks instead of the single spark. In this sense, projects of ignition systems with double spark, such as the one concerning kit LX786 presented in number 113 of february 1987 "Nuova Elettronica" , have been issued by magazines specialised in electronics. The device in question provides at the ignition time two sparks, the first one provided by inductive discharge, the other one provided by capacitive discharge. The use of this device shows a modest, but tangible fuel saving and a light general improvement of the performances of the car where it is installed but on condition that the engine is not required for maximum performances. The aforesaid device presents several limits: 1) the energy provided by the circuit of capacitive discharge is modest: this is due in part to the dimensioning devices and to the charge voltage of the discharge capacitor (limited to a value of 150 volt) and in part to the project choice of keeping the up- σonverter blocked for a longer time than the time it is really necessary_? moreover the efficiency of the up- converter is low because an evident dissimetry in biasing push-pull output stage appears; with consequent heat over-production by just one of the two output devices (this heat over-production does not depend on the energy really provided) ; 2) it is not possible to use high efficiency ignition coils which being characterized by a very low impedance, would not be hardly stressed, suffering therefore a tolerable thermic stress, and not imposing, at the same time, a too hard thermic stress on the driving device;

3) the energy of the inductive discharge diminishes considerably (until an inadeguate level for the best ignition) while the engine revolutions increase ;

4) while the revolutions increase the already modest energy of the capacitive discharge diminishes moreover until a so low level to cause the stop of the engine;

5) there is no possibility to use, as driving pulses, the ones provided by the electromagnetic inductor, integrated in electronic ignition systems, usually furnished on the equipments of the most recent cars;

6) energy absorption in condition of switched off engine appears with consequent and unjustified thermic stress of the ignition coil and unjustified reduction of the capacity of the aboard battery. Other documentations concerning electronic systems have been issued about providing the inductive discharge spark (among these it is to mention the one which appeared in October 1989 "Progetto" ) , which try to improve ignition process; however they also show problems and limits such as the too high heating of the output device which provides to charge inductive coil ignition; the low energy available to charge the aforesaid coil; a non-linear absorption curve with increasing revolutions; a not instantaneous ignition.

Disclosure of the Invention

It is an object of the present invention providing a reliable and cheap electronic ignition system, with a double spark, which is able to make a high energy for the capacitive discharge. It is a further object of the present invention to be able to use high efficiency and low i pedence coil, so as, also to avoid that the coil is crossed by a current when the engine is stopped and it is switched off. Moreover it is wished to provide for the inductive discharge, a high and constant discharge energy, i.e. independent of the revolutions of the engine. Einally it is a further object of the present invention to drive sparks with pulses produced by the electromagnetic inductor already present in the cars equipped with electronic ignition, keeping anyway the compatibility with the breaker points of the contact breaker, and of improving the performances of the ignition system so that to assure the best operation for any revolution speed of the engine, by providing the necessary and best time constants in the inductive discharge circuits and in the capacitive discharge circuits. The aforesaid objects have been obtained providing an electronic ignition system which produces a double spark (a capacitive one and an inductive one), at the ignition time, with so much power to minimise the unburnt fuel. The two sparks are delayed one from the other by means of the effect of a time constant provided subsequently the common elements to the two circuits, disposed to provide the single sparks. The capacitive discharge is obtained by a circuit including an up-converter, a discharge capacitor and a SCR diode. As up-converter is used a device usually employed for PWM (pulse width modulation) converter which anyway for what is necessary for the present invention, is embodied to work with a constant (and maximum) pulse width, with a feedback which blocks completely its operation when a predeterminate voltage (about 270 volt) for the capacitors recharge is obtained, then to trigger it again at the minimum increase of the aforesaid value. This embodiment brings a good power efficiency, both for the very steep front of the square wave signal by which power output devices are biased and for the good biasing simmetry of the push-pull connected output devices. Above all this last aspect allows to find a remedy for the unbalances of the other embodiments which use two devices to obtain biasing signal for the output stage (for example an oscillator and a phase shifter devider) ; as previously said, unbalances cause an overproduction of heat in only one of the push-pull connected output devices and the total efficiency of the converters is significantly damaged.

The aforesaid described up-converter is blocked, besides by the feedback, also at the time of the occurrance of the capacitive discharge: this block is necessary both not to overload the up-converter during the conducting condition of the SCR diode and to assure the cut off of the SCR when the discharge has occurred. This block time depends on a particular time constant calculated so that it is so short to let immmediate converter restarting, but it is enough to cover the time during which the capacitive discharge occurs. Hence the block time of the converter is independent of the duty cycle of the device which produces biasing pulses (breaker points or electromagnetic inductor), which, anyway maintains the syncronising function.

The up-converter previously described assures the energetic recharge of the discharge capacitors in an almost constant pattern and therefore independent of the revolution speed of the engine.

To provide the inductive discharge, the circuit concerning the invention presents solutions to maintain almost constant (while the engine revolutions vary) the saturation time of the ignition coil so that it is possible to use high efficiency coils which are characterised by a low inductance and which let the storage of a very high energy with a very short charge time; on the contrary, these coils don't allow very long saturation times which would produce a very high thermic stress on the device.

The sizes of the time constants concerning this last circuit are such as to shorten saturation time of the coil in comparison with how long it would be required by a possible distributor points pulse generator (about 60% duty cycle) ; furthermore, time constants provide to make the pulse longer (it being very short) ; this pulse comes from a possible electromagnetic inductor, which, if not processed, would require a very short saturation time for the coil with a consequent low energetic production. The processing of this pulse, which is led to the input of the ignition system, is such as that the pulse coming from the process available for the coil inductive charge, shows the cutoff front (discharge point) in perfect synchronism with the cutoff front of the input pulse while the ascent front (charge starting point) is temporally shifted, related to the ascent front of the input pulse, in leading or in delay, according to the fact that the input pulse is too large or too fast, respectively.

The values of some time constants provide the use of means with precisely fixed values and sometimes out of the standard (they are obtained by a parallel of more than one means) with regard to the electronic components which usually are possible to be found on the market, in order to obtain from the ignition system an exact operation and avoiding unwished interactions between the means of the system; in particular it has been considered fundamental employing a capacitor of about 170 nanoF in the portion of the circuit which gives rise to the starting front of the inductive charge pulse. The value of this capacitor establishes a fundamental element to be able to define a long conduction time and therefore to be able to store a very high energy in the coil.

As a consequence of the optimization of the energy amount stored in the coil, a linearisation of the current absorption curve is obtained which shows an almost linear graph with the revolution speed of the engine. Furthermore, as regards the best choice of the time constants working in the circuit, it is to be mentioned the presence of a resistance approximately comprised between. 50 and 100 KOhm in parallel with a capacitor of about 40 nanoF, which being provided on the input of the starting signal differentiator, decide the minimum timing of the pulse which brings to saturation the ignition coil; the choicing of these values lets both the improvement of the inductive discharge production and the improvement of the capacitive discharge production; as a matter of fact this last has to occur necessarly during the cutoff time of the output device relative to the inductive discharge; if it would not be so, all the energy of the capacitance discharge would result null, because it would be shortcircuited to ground. Furthermore the circuit embodying the invention is provided of an interface which allows both to connect on the traditional breaker points distributor and to connect on the most recent electromagnetic inductor distributor; in order to be able to use these last devices an on-off biased monotransistor is employed which provides to amplify the synchronism signal coming from the said inductor. Furthermore the present ignition system is provided by proper circuital means which avoids the energy absorption in the case the ignition switch is off and the engine is blocked; in fact in this case a timer provides for breaking in half a second the supply to the ignition coil, avoiding the superheating of it and preventing that a portion of the battery board energy is uselessly wasted; in the same operation the same timer provides for blocking the up-converter.

Brief Description of Drawing

Figure 1 refers to a preferred embodiment of the invention. With the only object to better explain the operation of an ignition system according to the invention and therefore without restricting the generality and the range of possible application.

Best Mode of Carrying out the Invention 1) Processing of the signal provided by the device generating pulses (electromagnetic inductor or breaker points distributor).

If the car ignition system has the electromagnetic inductor contained in standard equipment electronic distributor to produce the biasing pulses, the signal provided by the same inductor is applied between ground 83 and the base 82 of transistor 3, from whose collector it is transferred to the common point between resistances 1 and 2.

If the car ignition system has a breaker point distributor, this will be connected between the ground 83 and the aforesaid common point, where the resistance 1 has a value of about 100 ohm, having this resistance the task to cancel the effect of the capacitance usually connected with the distributor points. From this last point the signal, suitably amplitude limited and cleaned from possible spurious noises by resistance 2, by diode 4 and by capacitor 5 reaches, through the differentiator formed by the capacitor 8, and the resistances 6 and 9, the nand gate 13 and the inverter buffer 14; this last charges the capacitors 26 and 21 by means of transistor 16 and diodes 18 and 19. When the motor is stopped the capacitor 21 discharges through resistance 20 because no more pulses arrive from diode 19; consequently the inverter 22 output switches to logic level "1" blocking the transistor 99 and blocking, therefore, the output stage 60 concerning the inductive discharge; in this way no current passes through the coil.

The capacitor 26 is discharged, by the constant current absorber comprising transistor 17 and resistances 11, 12 and 27, with a saw tooth pattern; with the same pattern also the capacitor 29 is discharged by buffer 25 and diode 28, this capacitor is then richarged by the resistance 30. When, the voltage on the inverting input of the comparator 24 becomes less than the one on the non inverting input (this difference is commanded by the diode 28) , its output switches to logic level "1", le. ing the current to pass through the coil on condition that also the other input of the nand gate 23 is biased at logic level "1".

This condition results true for a long time but as soon as the inputs of the nand gate 13 are biased by logic level "1" (for example open breaker points) , the output of the aforesaid nand gate 13 switches to a logic level "0" (for the time of the constant relative to the capacitor 8 and the resistances 6 and 9) cutting off the transistor 99 (and therefore the output stage) by the nand gate 23, in synchronism with the driving pulse. At this point the pulse which will give rise to the couple of sparks, is produced. In substance, the couple of operational devices 24, 25, the inverter 14 the transistors 16, 17 and connected components, decide the moment when the starting front of the pulse by which the ignition coil 84 reaches saturation, must happen; the nand gate 13 blocks the output stage in synchronism with the biasing signal deciding the ending front of the aforesaid pulse. In this way the width of the same pulse becomes independent of the duty-cycle of the device generating pulses. These operations are completed by the nand gate 23.

The transistors 94, 96, 99 transfer the previously processed signal to the following stages. 2) Up-converter and inductive and capacitive discharge production.

The necessary voltage to charge the discharge capacitors 56 is produced by an up-converter provided by an integrated circuit (48) usually employed in PWM (pulse width modulation) converters, such as an UC 3846, which in this application is used as constant width pulse oscillator with blanking possibility.

The oscillation frequency, decided by the capacitor 34 and the resistance 35 is set at a value of about 20 Khz. Two square wave signals in opposition, one to the other, are provided by integrated circuit 48; these signals are sent to the mosfets 49, 50 which will be working in push pull, driving the transformer 53. The voltage, which is used for recharging the discharge capacitors 56 after having been full wave rectified by diodes 51 and 52, is drawed from the secondary winding of the transformer 53.

Further by means of zener diodes sequence 75 the feedback voltage is drawed from the cathodes of diodes 51, 52, this voltage, when applied (through the inverter 71 and the nand 69) to the specific pin (used as reset) in the integrated circuit 48 blocks its oscillation at the point when the same voltage overcomes the zener value of the sequence; the voltage of the transformer secondary is the same of the sequence of zener diodes, in this case 270 volt. The biasing signal from transistor 99 is set to the inverter 78 which drives the inductive discharge output stage ( osfet 60) , which therefore with the transistor 99 on cutoff front, produces i mediatly the first spark. Furthermore, the signal from transistor 99 reachs the inverter 82 with a time constant deriving from the capacitor 85 and the resistance 86, which introduces a delay in switching the logic state of the inverter in question.

By means of the constant time deriving from the capacitor 83 and the resistance 87, which limits the time of the pulse, and by means of the inverter 81, the pulse is applied to the transistor base 68 which biases in the best way the SCR 61 which by starting to conduct, provides for the discharge of the capacitors 56 on the ignition coil 84.

This second discharge (capacitive discharge) is provided with a short delay as regards the first (inductive discharge). This delay is decided just by the aforesaid time constant concerning the capacitor 85 and the resistance 86.

The inverter 82 produces also a pulse (with a time decided by the time constant concerning the capacitor 77 and the resistance 70) , which when is led to the nand gate 69, provides for blocking the oscillator relative to the converter, not to overload this converter at the moment when the SCR 61 is conducting, assuring in this way the sharp cutting off of the same SCR 61. Diode 57 provides to block the negative pulse produced by capacitive discharge, so that mosfet 60 is not damaged.

The network comprising resistance 58 and capacitor 59 linearises the behaviour of the whole system for any revolution speed, by reducing the "Q" of the ignition coil 84.

In a preferred embodiment of the circuit, according to the present invention, the components of the ignition device had the values which follow in the table. Also this components list is reported just as an illustrative example.

Industrial applicability

In the cars which employ the ignition system according to the principles of the invention, a substantial reducing of the fuel consuption has been noticed, above all in the case of fed gas cars, in which a fuel saving of almost 50% is attained. The cars equipped by this device have performed a high cleanness and dryness of the discharge tube.

The device obtained by embodying the present invention, placed in. a part of the engine exposed to the air flow, produced by the car motion, doesn't present any thermic problem, also in condition of city traffic. Mosfets characterised by a very low internal resistance in conduction conditions have been employed without any current restriction in order to minimize the possibility of overheating in the output stages relative to inductive discharge and up-converter.

Further advantages obtained by this ignition system are lower pollution; very instant ignition, also with a cold engine; substantially inproved accelleration and above all elasticity; increased maximum speed.

Claims

1) Electronic ignition device with double spark for gas and petrol engines, employing for the fuel ignition a capacitive discharge spark and an inductive discharge spark, these sparks being produced in subsequent times, characterized by the fact that production and timing of said sparks is accomplished by employing two distinct and interactive operating blocks one of which (A) produces and processes biasing pulses width and another one (B) produces the real sparks.

2) Electronic ignition device with double spark for gas and petrol engines, according to claim 1, characterized by the fact that up-converter means (48) of block (B) is founded on a generator device to operate in PWM, which for the objects of the present invention is embodied to operate with a constant pulse width, with a feedback presence which blocks its operation when the fixed in advance voltage is reached, providing an improved and symmetric biasing of the push pull power stage (49,50) of the same block (B).

3) Electronic ignition device with double spark for gas and petrol engines, according to the claims 1 and 2, characterized by the fact that at the moment when capacitive spark is produced, the converter (48) is blocked for a very short time constant (70, 77) , but which is enough to avoid the overload during the condution state of the SCR (61) and to assure the SCR (61) cutting off at the end of the discharge and by the fact that the blocking time of the converter (48) does not depend on the duty-cycle of the device generating biasing pulses, which supports the synchronism function, but it is decided by a specific time constant value (70,

77); this letting the best richarge of the discharge capacitor (56) .

4) Electronic ignition device with double spark for gas and petrol engines, according to any of the previous claims, characterized by the fact that as regards block (A), a capacitor (26) of about 170 nanoF is provided in the circuit which decides the pulse time of the inductive charge.

5) Electronic ignition device with double spark for gas and petrol engines, according to any of the previous claims, characterized by the fact that a resistance (6) comprised between 50 and 100 kohm parallel to a capacitor (8) of about 40 nanoF are provided in the input signal differentiator, in order to fix the minimum pulse time.

6) Electronic ignition device with double spark for gas and petrol engines, according to any of the previous claims, characterized by the fact that an improvement of the time charge of the ignition coil (84) on the ground of the choice of the specific time constants (6,8,9; 26,27) independently from the engine revolution speed in the block for producing and processing pulse width (A) , is obtained.

7) Electronic ignition device with double spark for gas and petrol engines, according to any of the previous claims, characterized by the fact that the charge time of ignition coil (84) is kept approximately constant, as regards engine revolutions and that in the case the key switch is closed (turned on control board) and the engine is stopped, the break of the feed coil is provided in a very short time.

8) Electronic ignition device with double spark for gas and petrol engines, according to claim 1, characterized by the fact that a monotranεistor stage (3) which operates in on-off states is provided to interface the ignition system with the electromagnetic inductor comprised in the distributor.