BACKGROUND OF THE INVENTION
This invention relates generally to an ignition system and more particularly to a solid state capacitor discharge ignition system for operation with a flywheel magneto of either single or multiple cylinder engines.
Heretofore, magneto type ignition systems found relative widespread use with small gasoline engines, such as one, two, three or four cylinder, two or four cycle engines, because this type of ignition system is relatively simple in circuit arrangement and component requirements and is inexpensive to produce while being easy to operate. Some of the magneto ignition systems of this type may include a flywheel mounted on the engine shaft and a permanent magnet, formed on or secured to the periphery of the flywheel. The permanent magnet is positioned at a particular location on the circumference of the flywheel with respect to the piston firing position of the engine. A paramagnetic core is mounted to a support on the engine so as to be firmly held in place and spaced in close proximity with the flywheel such that each time the magnet on the circumference of the flywheel passes the paramagnetic core, a magnetic field is induced into the core. This magnetic field is thus utilized to induce a voltage into a winding on the paramagnetic core in a well-known manner. The voltage induced into the winding, as a result of rotational movement of the magnet past the paramagnetic core, is applied through a diode and stored in a capacitor for a brief interval before this energy is then applied to the primary winding of an ignition coil by the closing of a breaker point assembly. That is, after the energy developed by the magnet and coil is stored in the capacitor, breaker points close abruptly to discharge the capacitor into the primary winding of a high voltage step-up ignition coil to induce spark voltage at its secondary winding. Although these types of magneto ignition systems have proven relatively reliable and inexpensive for the general purpose intended, i.e., providing ignition sparks for small engines, they still have several problems which cause starting and running difficulty. Another, more conventional type of magneto ignition, is one where the breaker points are connected in shunt with coil winding and are closed during buildup of the magnet flux. The points are then opened when maximum energy is stored in the winding to produce the necessary spark discharge.
Among several of the problems of concern in such magneto ignition systems, one is the unreliability of components such as the breaker points. For example, at fast engine speed, even for small engines having a few number of cylinders, there may be bounce of the breaker points thus causing erratic ignition characteristics and poor engine operation. In some cases the bounce will tend to discharge the capacitor of the ignition system prematurely so that when a subsequent operation of the breaker points occur, this now being at the proper ignition timing point, the reduced charge on the capacitor may be insufficient to effect a proper ignition spark. Also, the rubbing block of the breaker points, which is of insulative material, tends to wear down with use, which is a common and unavoidable problem, and because of this, the breaker points need adjustment from time to time, and eventually replacement of the complete breaker point assembly is necessary. Pitting of the metal contacts of the breaker point assembly is also of concern in that the spacing of the gap between the contacts changes as a result of such pitting and the ignition timing may be changed as a result sufficient to cause hard starting or rough running. Also, this pitting, in many cases, will cause an increase in resistance between the metal contacts to reduce the current flow therethrough and reduce the spark energy. Still another difficulty with regard to the breaker points, this being particularly true with respect to small engines of the outdoor industrial or recreational type, is that oil, gasoline, and dirt can get on the breaker points to cause a malfunction because of the high resistance when the points are closed, and in some cases, the breaker points will not make contact at all.
Another of the problems of such magneto ignition systems is the inability to produce a sufficiently high spark voltage over the complete operating range of the engine, starting from low cranking speeds and all the way up to the higher operating speeds. To insure sufficient high voltage at the low cranking speed, a large number of turns are provided on a pickup coil positioned to receive magnetic flux from the magnet on the flywheel, the amount of voltage being proportional to the number of turns of the coil. High voltage can also be obtained by maximum magnetic coupling between the magnet on the flywheel and the pickup coil, this being obtained by a close spacing, on the order of thousand of an inch between the pickup coil and the flywheel. However, at high engine speeds each of the above approaches to produce high voltage at low speed becomes a problem at the higher speeds because too much voltage is obtained and may cause voltage breakdown and deterioration of the various components in the ignition system. Of particular concern is the increased rate of deterioration of the spark plug electrodes at the higher voltages particularly since this higher voltage is, in many cases, well in excess of that necessary to ensure proper ignition and combustion of the fuel within the engine.
Yet another of the problems of magneto ignition systems is their general inability and/or complexity to provide gradual spark advance of the ignition timing. Such magneto ignition systems, particularly for small engines, either provide no spark advance whatever or provide only a step function spark advance whatever to have one position for starting of the engine and a second position for optimum fast running speed of the engine. When no spark advance at all in incorporated, the ignition timing is generally set to afford the best possible starting characteristics while having a relatively efficient running characteristic. However, this is true only for particular environmental situations such as temperature and humidity and because of changes in either of these environmental conditions, the starting of the engine may be very difficult, if not impossible. On the other hand, the step function spark advance provides optimum conditions only for starting and maximum running speeds and, as such, does not take into consideration that the engine may at times be operated at intermediate speeds. The intermediate speeds, therefore, depending on the point the step function of spark advance occurs, either have no ignition advance or maximum ignition advance and in either case it would be an improper timing characteristic for the intermediate engine speed and load than taking place. This arrangement not only causes inefficient running of the engine, but wastes fuel and may cause substantial amounts of pollutants in the form of unburnt gasoline to be exhausted into the atmosphere.
Still another problem which arises with magneto ignition systems is where the pickup coil is a combined unit having both the charging winding and the trigger winding formed on a single paramagnetic core. This type of pickup coil has the advantage of being relatively inexpensive and small in size. However, it produces a trinary peaked waveform each time the flywheel magnet passes it. This trinary peaked waveform has the disadvantage of providing a trigger pulse following the charge pulse which does not have a gradually changing slope at the leading edge of the pulse. The slope of the trigger pulse, which follows the charge pulse, changes erratically during changes in engine speed so that any attempt to utilize this pulse to acquire a uniformly changing spark advance is futile. This subsequent pulse will, however, provide a satisfactory step function spark advance of ignition timing between slow speed, i.e., cranking speed for starting, and high speed for doing work. Heretofore, the first peak of the trinary peaked waveform has not been used as a trigger pulse because to do so would appear to discharge the ignition capacitor before it is actually charged because the charging of the capacitor takes place after the first peak, i.e., during the second peak.
SUMMARY OF THE INVENTION
Accordingly, the general objects of this invention are to provide an improved magneto type ignition system for use with internal combustion engines.
The general objects of this invention include providing a magneto ignition system which requires no breaker point maintenance or adjustment and which completely eliminates ignition failure due to breaker point malfunction.
Still among the general objects of this invention is the provision of a magneto type ignition system which produces a substantially uniform spark discharge over the entire operating range of engine speeds, from cranking speed to full running speed, so that erosion of the spark plug electrodes is maintained at a minimum.
The general objects further include providing a magneto type ignition system which can provide a gradual spark advance of ignition timing over the entire speed range of the engine from cranking speed, for easier starting, to full running speed, for maximum efficiency.
One of the features of this invention is the utilization of a single pickup coil structure which has a pair of windings formed about a common paramagnetic core member. One winding is used to induce a large voltage into a capacitor of a capacitor discharge ignition circuit and the other winding is used as a trigger pulse producing element, which eliminates the need of breaker points, to render a silicon controlled rectifier conductive and discharge the charged capacitor into the primary winding of an ignition coil. The charge delivered to the ignition coil is transformer coupled to a high voltage secondary winding which is connected to the spark plug, thus producing the spark at its electrodes.
Yet another feature of this invention is the use of a blanking circuit which eliminates the trigger peak immediately following a charge peak so that a first peak of a trinary peaked waveform can be used as the trigger pulse. The trigger winding will develop three peaks, one positive, the next negative and the last positive, again, while the charge winding will have similar peaks, but of opposite polarity. The middle peak from the charge winding is applied to the capacitor of the ignition circuit. However, because of the erratic change in rise time of the following third peak, this being due to the second peak also having some effects on the discharge of the capacitor, it is uniquely provided that the first of the three peaks be used for triggering the ignition circuit while the third of such peaks is rendered ineffective in the circuit. By utilizing the first of the three peaks, automatic and gradual spark advance of ignition timing is achieved as a result of the smooth change in slope or rise time of the first peak. In the case of a four cylinder engine, where two cylinders are fired simultaneously, the coil pickups are mounted in pairs adjacent opposite sides of the flywheel and the charge winding of one coil pickup is associated with the trigger winding of the other coil pickup and this crisscross association provides trigger pulses which are the first pulses of the trinary peaked waveform rather than the third pulses as is usually the case. Where a single coil pickup is used, the third peak of each trinary peaked waveform is eliminated by a special blanking circuit.
Briefly, the magneto ignition system of this invention includes a flywheel mounted permanent magnet, a charge-trigger coil structure mounted close to the magnet for producing both a capacitor charging voltage and a trigger voltage, an energy storage capacitor, a silicon controlled rectifier for discharging of the storage capacitor and a high voltage ignition coil. The ignition coil may be of the type associated with each spark plug as is common for small gasoline engines. As the magnet mounted on the flywheel moves past the charge-trigger coil combination, a high energy pulse is produced in the charge winding while a lower energy trigger pulse is produced in the trigger winding. Where the ignition arrangement includes two such charge-trigger coil combinations, each charge-trigger coil can be used to deliver sparks to two cylinders simultaneously of a four cylinder, two cycle, engine. In this case only one of these sparks is effective because the other cylinder is on its exhaust stroke. The charge-trigger coil units are in opposite sides of the magneto flywheel alternately to develop a trinary peaked waveform by the magnetic flux induced therein. High energy pulses are retained in the storage capacitor until the trigger pulse from the opposite charge-trigger coil unit renders the associated silicon controlled rectifier conductive. This duplex arrangement of components provides means to eliminate the effectiveness of the third peak of the pulse so that only the first peak is used as a trigger pulse.
In the case of a single cylinder engine, triggering is obtained from the same type of charge-trigger coil combination, but in this case a blanking circuit is utilized to eliminate the third peak of the waveform to disable the ignition system for a short period of time during the existence of this third peak. Therefore, during the following trinary peaked waveform, the first peak is used as the trigger pulse to effect a discharge of the capacitor ignition system to produce a spark.
Initial timing of the magneto ignition system of this invention is obtained by precisely setting the magnet flywheel relative to the keyway on the engine shaft so that this permits the charge on the capacitor to occur substantially before top dead center of piston travel and fire the spark plug at the top dead center position at cranking and/or at slow speeds. Gradual spark advance of the ignition timing is obtained from the changing slope of the first peak trigger pulse which changes automatically with increasing engine speed, thus providing a completely electronic spark advance system responsive only to engine speed. This type of spark advance provides much smoother idling and easy starting of the engine as well as maximum power efficiency and fuel consumption at the higher operating speeds. By the time the engine reaches its working speed, most of the ignition advance will have occured and the ignition advance will level off at the desired engine speed. The solid state ignition system incorporated herein can be rather easily modified and adapted to most single and multiple cylinder flywheel magneto type engines.
Along with basic design simplicity and elimination of breaker points, the magneto type ignition system of this invention also has several performance advantages over previous systems. Ignition coils can be used which provide very fast high voltage rise time and a short spark duration of approximately 75 microseconds to afford a better firing of fouled spark plugs and extend their usable life considerably without adversely affecting engine performance. The combination of the charge-trigger coil in one unit provides gradual spark advance of ignition timing, this advance occurring over a range of approximately 24°, more or less, and the maximum limit of spark advance can be set by a simple adjustment to conform to the particular type of engine involved.
A voltage dependent resistor is provided in the circuit to minimize the adverse effects of excessively high voltage sparks at high engine speed, a condition which would otherwise cause rapid deterioration of the spark plug electrodes. That is, during high engine speed the high voltage charge from the charge-trigger coil is somewhat limited by a voltage dependent resistor connected in parallel with the charge winding. Temperature compensation components are also provided in the circuit to stabilize the electronic advance characteristic and to provide for easy starting at temperature extremes. The circuit is simple and inexpensive to manufacture and is efficient and reliable in operation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of one circuit arrangement of a magneto ignition system constructed in accordance with this invention;
FIG. 2 is a schematic diagram of an alternate circuit arrangement of a magneto ignition system constructed in accordance with this invention;
FIG. 3 illustrates a trinary peaked waveform produced by the charge winding of the pickup coil used in the circuit arrangement of this invention and which waveform is illustrative of slow engine speed;
FIG. 4 illustrates a trinary peaked waveform produced by the trigger winding of the pickup coil used in this invention; and
FIG. 5 is a trinary peaked waveform similar to that of FIG. 4, but which is illustrative of fast engine speed.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, a magneto type solid state ignition system is designated generally by reference numeral 10 and includes a plurality of ignition coils corresponding in number to the number of cylinders associated with the engine, not shown, to which the ignition system may be incorporated. Here, a pair of ignition coils 12 and 14 are connected in series, one with the other, to receive the same current pulse and produce a simultaneous spark discharge at associated spark plugs 13 and 15, respectively. In this arrangement the engine will have two of its pistons in the same position with respect to top dead center, but each will be of a different stroke, i.e., one piston being in the power stroke and the other piston being in the exhaust stroke. Spark discharge at one of the spark plugs 13 or 15 during the exhaust stroke will have no effect whatever on engine performance and only the spark occurring in the cylinder having the power stroke will ignite the fuel in that particular cylinder. Similarly, a second pair of ignition coils 16 and 18 are connected in series, one with the other, and also include associated spark plugs 17 and 19, respectively. The ignition coils 16 and 18, together with their spark plugs 17 and 19, are cooperative with another pair of pistons of the engine in the same manner as mentioned above.
Energizing current for the ignition coils 12, 14, 16 and 18 is provided by discharge of a capacitor at the proper time sequence during rotation of the engine. A capacitor 20 has one end thereof connected to ground potential and its other end connected to the anode of an electronic switch device 21, preferably it being a silicon controlled rectifier as illustrated herein. The cathode of the silicon controlled rectifier 21 is connected to the positive terminal of the first ignition coil 12. Similarly, a second capacitor 22 has one end thereof connected to ground potential and the other end thereof connected to the anode of a second electronic switch device 23, it also being a silicon controlled rectifier which, in turn, has its cathode connected to the positive terminal of the ignition coil 16. Silicon controlled rectifiers 21 and 23 are alternately rendered conductive so as to deliver energizing current first to one pair of serially connected ignition coils and then to the other pair of ignition coils such that for each half cycle or half revolution of the engine a spark producing voltage is developed at the appropriate one of the spark plugs 13, 15, 17 and 19.
First and second pickup coil means 26 and 27 are positioned in close spaced relation to a magneto flywheel 28 which is rotated by the crank shaft of the engine as is well-known in the art. The magneto flywheel 28 has a permanent magnet segment 29 formed on or attached to the circumference of the flywheel and is so positioned relative to a keyway 30 so that proper timing of the engine is achieved.
The pickup coil means 26 has a paramagnetic core 31 about which is wound a pair of windings 32 and 33; the winding 32 being a capacitor charging winding and the winding 33 being a trigger circuit winding. A first circuit means is used to charge the capacitor 22 and is here shown as the winding 32 which has one end thereof connected to ground potential by a line 34 and the other end thereof connected to capacitor 22 through a diode 36. In this manner a relatively high voltage charge can be placed on the capacitor 22, and diode 36 prevents the voltage from leaking off because it is now reversed biased by the charge on the capacitor. The amount of voltage applied to capacitor 22 is substantially limited, at least at high engine rpm's, by a voltage dependent resistor 37 which is connected in shunt relation to the charging winding 32. The rate at which the magnet 29 passes the windings 32 and 33 will be one of the factors determining the voltage on capacitor 22, i.e., the faster the magnet moves, the higher the voltage. The voltage dependent resistor 37 therefore limits the amount of charge that can be placed on the capacitor 22 during high speed operation, thus reducing the tendency of erosion of the spark plug electrodes as a result of an over voltage condition.
A second circuit means, comprising lines 38 and 39, apply trigger pulses from the trigger winding 32 to the gate cathode circuit of silicon controlled rectifier 21, thus causing conduction thereof to discharge the associated capacitor 20. The gate-cathode circuit of silicon controlled rectifier 21 includes a variable resistance element 40, which is used to set the upper limit of the automatic spark advance of the ignition system, and a temperature responsive resistor 41, which is used to stabilize the circuit under a wide range of temperature conditions to ensure easy starting of the engine under all weather conditions.
The pickup coil means 27, in like manner, includes a capacitor charging winding 43 and a trigger winding 44. Here, the first circuit means includes a line 46 and a diode 47 connected in series with the capacitor 20 to apply thereto a relatively high voltage charge, the value of which is limited at high speeds by a voltage dependent resistor 48 connected in parallel with the winding 43. A second circuit means includes a pair of lines 49 and 50 connected to the gate-cathode circuit of silicon controlled rectifier 23 to render the same conductive during the appropriate point in the ignition timing cycle. Here also a variable resistance element 51 is connected in parallel with a temperature responsive resistor 52 and each function substantially in the same manner as do the variable resistance element 40 and the temperature responsive resistor 41. The crisscross or duplex interrelationship between the charging capacitors 20 and 22, relative to the trigger windings 32 and 44, respectively, provide a means for charging the capacitors during the positive peak 75b of the waveform 75, FIG. 3, produced, and the charging windings 32 and 43 of the pickup coils 26 and 27, respectively, while discharge of the capacitors occur at a point in time before it would otherwise be charged by the first peak 76a of the waveform 76 of FIG. 4. The crisscrossing or duplex relationship of the two circuits is one means of rendering the third peak 75c or 76c of the trinary peaked waveform ineffective in the circuit. Therefore, the first peak 76a of the next following trinary waveform produced at the trigger winding is the one that is effective to trigger the silicon controlled rectifier associated therewith. That is, the third peak of the trinary peaked waveform produced by each of the coil structures 26 and 27 will occur at the gate of the associated silicon controlled rectifier when no charge is on the associated capacitor in circuit therewith, and the first peak of the trinary peaked waveform will occur at the gate of the silicon controlled rectifiers when a charge exists on the capacitors and which charge is the result of the second peak of a previous trinary peaked waveform.
Referring now to FIG. 2, there is seen an alternate form of ignition system which can be used with a magneto flywheel of an engine and is designated generally by reference numeral 60. Here, an ignition coil 61 has the primary winding 62 thereof connected in parallel with a storage capacitor 63 which supplies energizing current thereto to produce a high voltage spark at a secondary winding 64. Connected in series with the primary winding 62 is an electronic switching device 66, such as a silicon controlled rectifier, which is rendered conductive to discharge capacitor 63 through the primary winding 62. A resistance element 67 and a diode 68 are connected in parallel with the primary winding 62 to prevent extraneous oscillations from occurring during rapid discharge of capacitor 63.
Pickup coil means 70 is provided with a capacitor charging winding 71 and a trigger winding 72, and may take a form similar to either of the pickup coil means 26 or 27 of FIG. 1. However, in this embodiment, windings 71 and 72 are tied together at a common third circuit line 73, which, during normal running operation, is an ungrounded common line.
The pickup coil means 70 produces trinary peaked pulse waveforms in the same manner as the pickups 26 and 27 of FIG. 1. The positive polarity portions 75b of waveform 75 is developed at the winding 71 and used to charge the capacitor 63 and positive polarity portions 76a of the waveform 76 from the winding 72 are used to trigger the silicon controlled rectifier 66. For example, the waveforms 75 and 76 of FIGS. 3 and 4, respectively, illustrate the trinary peaked portions 75a, 75b and 75c, and 76a, 76b and 76c, which is repetitive for each spark produced by the circuit 60. Also, the waveform 75 is that which is developed across the winding 71 while the waveform 76 is developed across the winding 72 is of the same wave configuration but of opposite polarity. FIGS. 3 and 4 illustrate the trinary peaked waveform as produced at slow engine speeds when the magnet on the flywheel passes the pickup coil means 70 at a relatively slow speed. By way of example, the negative peak 75a, as developed across the winding 71, has no effect on the charging circuit of capacitor 63 because of the polarity of a series connected diode 76. On the other hand, the positive second peak 75b is applied through the diode 76 to charge capacitor 63. The maximum value of this peak voltage is limited by a voltage dependent resistor 77 connected in parallel with the winding 71, this limiting action occurring most effectively at the higher engine speeds. Now that capacitor 63 is charged, a trigger pulse applied to silicon controlled rectifier 66 will discharge the capacitor and produce a spark. However, the subsequent peak 76c, which is positive from winding 72, is not sensed at the gate-cathode circuit of silicon controlled rectifier 66 because this pulse is blanked by placing a charge across a capacitor 78 during the same time the capacitor 63 is charged. The blanking charge on capacitor 78 is applied through a diode 79, a resistor 80 and a second diode 81. Resistor 80 forms part of a voltage divider network with a second resistor 82 to limit the voltage value on capacitor 78. The blanking charge on capacitor 78 will render a second silicon controlled rectifier 83 highly conductive and this second silicon controlled rectifier is connected across the gate-cathode circuit of the main silicon controlled rectifier 66. That is, capacitor 78 is connected to the gate-cathode circuit of silicon controlled rectifier 83 through a resistor 84 which holds this silicon controlled rectifier in a highly conductive state. The low resistance current path produced as a result of the high conductive state of silicon controlled rectifier 83 will nullify any signal by substantially short circuiting the gate-cathode voltage on the main silicon controlled rectifier 66 thereby causing the third peak 76c to be ineffective. Capacitor 78 will continue to discharge through resistor 84 and the gate-cathode circuit of the silicon controlled rectifier 83 for the entire duration of the peak 76c.
A transistor 86 has its emitter-collector junction connected in parallel with the capacitor 78 and is rendered conductive by the first peak 76a to ensure complete discharge of capacitor 78 or at least to a sufficient level so that the silicon controlled rectifier 83 is rendered non-conductive when the first peak 76a again occurs. It is this first peak 76a that renders silicon controlled rectifier 66 conductive to discharge capacitor 63 and produce a spark at the secondary winding 64 of the ignition coil 61. The base electrode of the transistor 86 is connected to the trigger winding 72 via a resistor 87 which applies the necessary bias to the transistor 22. The trigger winding 72 is connected to the gate electrode of silicon controlled rectifier 66 through a resistor 88 and a diode 89 connected in series therewith.
To insure proper operation of the silicon controlled rectifier 66, a fixed resistor 90 and a variable resistor 91 are connected in a gate-cathode circuit thereof together with a temperature responsive resistor 92, which is used to stabilize the circuit. However, fixed resistor 90 may be eliminated if desired. Variable resistor 91 is used to set the maximum degree of advance of the spark discharge for the particular engine involved. That is, the total number of degrees of spark advance can be adjusted for each different kind of engine using the ignition system of this invention merely by adjusting the value of the resistor 90 which changes the voltage level on the gate-cathode circuit. To prevent extraneous firing of silicon rectifier 66, a capacitor 93 is provided to shunt any transient voltages which may occur in the gate-cathode circuit thereof.
A Run-Stop switch 94 is provided and has the movable contact thereof connected to ground potential and which is switched between an open circuit condition and a closed circuit connection which will connect ground to the common line 73. When the common line 73 is grounded in this manner, a high energy pulse that may be applied to storage capacitor 63 is effectively shunted to ground, and no output spark voltage will be developed.
Referring now to FIG. 5, the trinary peaked waveform is designated generally by reference numeral 95 and has the first peak designated by reference numeral 95a, the second peak by reference numeral 95b, and the third peak by reference numeral 95c, and this waveform is representative of fast engine speed as compared to trinary peaked waveform 75 and 76, shown in the FIGS. 3 and 4, for slow engine speed. The waveform of FIG. 5 illustrates what takes effect at the higher engine speeds. Here, it can be seen that by utilizing the first peak 76a of FIG. 4, or 95a of FIG. 5, the rate of change of slope of the leading edge of this peak changes gradually and uniformly to provide an automatic and gradual spark advance of ignition timing over the entire speed range of the engine. At lower speeds, the slope of the leading edge of the peak 76a will produce a spark at point 99 which will be near top dead center of the piston while at higher speeds the rapid increase in slope of the leading edge, as shown by the peak 95a, will cause the spark to occur at point 100 which is as much as 35°, more or less, before top dead center of the piston.
The reason that peak 76c cannot be used to provide uniform gradual spark advance is that it follows the charging peak 75b and the slope between the peaks 76b and 76c does not change gradually with gradual increases of engine speed. The charging peak 75b is seen as a gradual change from a maximum positive voltage to a maximum negative voltage. However, at the higher speed this change occurs abruptly from a positive voltage to negative voltage to produce the third peaked pulse 95c with almost a vertical slope at the leading edge of the waveform 95c, as seen in FIG. 5. It is this third peak 75c or 95c which is blanked or eliminated by the blanking circuit of FIG. 2 so that the first peak 75a or 95a serves as the trigger pulse.
What has been described is a highly efficient circuit arrangement whereby a trinary peaked waveform is developed and only the first peak, one that precedes a charging peak, is used as a trigger pulse for the ignition circuit. This first peak, therefore, provides uniform gradual sparked advance of ignition timing throughout the entire range of engine speeds because of the uniform gradual change in slope of the leading edge of this peak. Accordingly, it will be understood that the variations and modifications of this invention may be effected without departing from the spirit and scope of the novel concepts disclosed and claimed herein.