US3408536A

US3408536A - Breakerless oscillator ignition system

Info

Publication number: US3408536A
Application number: US580795A
Authority: US
Inventors: Oscar F Tibbs
Original assignee: Individual
Current assignee: Individual
Priority date: 1966-09-20
Filing date: 1966-09-20
Publication date: 1968-10-29
Anticipated expiration: 1985-10-29

Description

o. F. TIBBS 3,408,536

BREAKERLESS OSCILLATOR IGNITION SYSTEM Oct. 29, 1968 Filed Sept. 20, 1966 I I 1 OSCAR'F. mass syo ase Q ATTORNEYS United States Patent 3,408,536 a BREAKERLESS OSCILLATOR IGNITION SYSTEM Oscar F. Tibbs, Ripley, Tenn., assignor of one-half to John W. Buzick, Monette, Ark.

Filed Sept. 20, 1966, Ser. No. 580,795

Claims. (Cl. 315-212 This invention relates to an ignition system for automobiles and the like, and more particularly, it relates to an improved solid state ignition system in which mechanical timing means and mechanical voltage .varying means areeliminated.

Conventional ignition systems employ mechanical breaker points to time the fiow of current through the ignition system to the distributor. However, these mechanical devices suffer from several disadvantages, the most important of which is that the voltage of the current delivered to the spark plugs cannot be varied to adapt to changing load requirements. If the voltage is set too low the spark plugs will not fire effectively at high engine speeds; and if the voltage is set too high, the plugs and other elements of the ignition system will burn out during periods when a low voltage drop is required in the system.

An early attempt to overcome this problem was the development of a magneto which varied the voltage in accordance with engine speed. However, the fact that the magneto depended for eflicient operation on the precision of moving mechanical parts has caused many problems. Consequently, the magneto has not been accepted as a satisfactory means for overcoming the inherentdisadvantages of the conventional breaker point timing mechanisms. 7

With the devlopment of transistors, attempts were made to design solid state ignition systems which would overcome the disadvantages of mechanical timing means. At first, transistors were employed to supplement the ignition coil in developing a high voltage, low current oscillating current, thereby reducing the load on the breaker points. However, this merely eliminated some of the problems associated with breaker points,-but it did not eliminate the need for breaker points and thus,'it was still not possible to vary the voltage to adapt to changing load requirements. 1

Thus, it is a purpose of thepresent invention to'pro- Vide a radically different solid state ignition system having many of the advantages of previous ignition systems while eliminating the disadvantages. The present system not only eliminates mechanical timing means, but also allows variation of the voltage, without mechanical moving parts, to adapt to changing load requirements.

In the ignition system of the present invention the concept of periodic timing of electricity through the circuit is completely disregarded. Rather, in the present system pulsating DC current is developed continuously within the system. The system is designed to counteract difiiculties which would normally be encountered during the periods when pulses are being generated by the system but not delivered to the distributor and to the spark plugs. By employing this entirely dilferent approach, all mechanical timing means and voltage varying ineans have been eliminated. In this respect, the present invention has the advantages (but not the disadvantages) of a magneto. Consequently, the present system may be referred to, for convenience, as a solid state magneto or an electronic magneto. The periods when current is being delivered through the distributorto the spark plugs will be referred to as the load condition, and

the periods when current is not being delivered through the distributor to the spark plugs will be referred to as the no load condition. In the previous conventional ignition system difliculties such as damaging high voltage surges were not created'since the breaker points caused the current to be cut off during these "01? periods. With the present system,'however, means are provided for absorbing these high voltage surges in such a manner that (1) these surges cause no 'harm-to the elements of the ignition system, (2) the surges will not cause the pulsating DC current of the ignition system to be cut off, and (3) spurious AC current surges transmitted to the ignition system from the generator of alternator will not cause the pulsating current to cut off.

The solid state ignition system according to the present invention operates in the following manner. Direct current from the automotive battery is continuously converted to pulsating DC current in a converter and then delivered to the ignition coil and hence through the distributor to the spark plugs. Although this pulsating DC current is generated continuously by the converter, the DC pulses are delivered from the ignition coil through the distributor to the spark plugs only during the load condition of the system which is when the distributor rotor is in the vicinity of a terminal leading to a spark plug. During the no load condition, when the rotor is between spark plug terminals, current is not delivered from the ignition coil to the distributor, During the no load condition high voltage surges build up. These surges are capable of damaging the elements of the system. However, in the present system, means are provided for absorbing the high voltage surges developed in the ignition coil and in the converter of the system so that no damage results to these parts. This excess voltage in the ignition coil is discharged to ground while the excess voltage developed in the converter is absorbed by a capacitor.

An important feature of the present invention is that the voltage delivered to the distributor during the load conditionwill vary automatically to match the load requirements of the engine. That is, at low speeds when the voltage requirements at the engine are relatively low, then a low voltage current will be delivered to the spark plugs. When the load requirements at the engine are increased, such as at high speeds, then the voltage delivered to the engine will automatically increase accordingly. This result is obtained since the system will allow voltage build up to high resistance, high speed, conditions in much the same manner as the voltage builds up in the no load condition. When the higher voltage level is reached, the DC pulses will be delivered through the distributor to the spark plugs at this higher voltage level;

Many additional advantages are attributable to the present ignition system. The spark plugs themselves have a long life since the high voltage spark pulses tend to clean carbon deposits olf of the plugs and improve the efiiciency thereof. Also, since the voltage will increase automatically to match the engine load conditions it is possible to operate the automobile efliciently with a variety of fuels since combustion is not dependent upon a single spark at a given voltage level as in the conventional systems but on a series of spark pulses or spikes throughout the combustion stroke at the right voltage lead. Also, with the present system the distributor capand rotor are not pitted or burned by arcing during the switching action, this result being due to 'the low current therethrough.

Thus it is an object of the present invention to provide an improved solid state ignition system which overcomes many disadvantages of previous ignition systems.

It is another object of this invention to provide an ignition system in which the voltage delivered to the spark plugs will vary in accordance with the load conditions in the engine.

It is still another object of this invention to provide an automotive ignition system in which conventional timing means are eliminated. It is still another object of this invention to provide an automotive ignition system in which a pulsing DC current is developed by a converter means for delivery to the spark plugs during the load position of the distributor and in which high voltage surges created during the no load condition are absorbed by the system without causin damage to the elements of the system.

Other objects and the attendant advantages of the present invention will become apparent in the detailed description to follow of a preferred embodiment of the invention together with the accompanying drawings wherein:

FIGURE 1 is a schematic view illustrating a preferred embodiment of the present invention.

FIGURE 2 illustrates voltage as a function of time at the ignition coil during different operating conditions.

The structure and operation of the invention will now be described with respect to a preferred embodiment of the invention as shown in the drawings. However, it should be understood that the particular values of the elements in the present embodiment are chosen for purposes of illustration and may be varied within the scope of the invention.

A 12 volt DC battery is connected through a switch 20 to a ballast resistor 21 and then to a converter 11 having a converter transformer 12. From the converter 11 pulsating DC current is delivered to the ignition coil 13 and then to the distributor 14 and the spark plugs 15. In the described embodiment the ignition coil has turn ratio of 250:1, and this will govern the number of turns of the converter transformer. However, other ignition coil turn ratios such as 100:1 and 400:1 may also be used. To employ the present invention with an ignition coil having these other turn ratios it would only be necessary to change the number of turns of the converter transformer.

The converter transformer winding 34 and a second, or feedback primary winding 36. The converter transformer 12 also has a first secondary winding 45, a second secondary winding 40 and a third secondary winding 48. Connected in series between the first primary winding 34 and ground 29 is an alternately conducting and nonconducting transistor Q This second transistor may be employed, if desired, to augment the first transistor although the system is operative without it. The power circuit electrodes of the second transistor are connected in parallel with those of Q while the base electrode of the second transistor is connected to the base electrode of Q The first primary winding 34 may be constructed of 20 gauge wire having approximately 100 to 125 turns. It has been found that 20 gauge wire will draw a sufficient current while avoiding heat problems. The 15 turns of primary winding 34 closest to the DC battery are wound in parallel with the turns on the second primary winding 36 to maximumize the inductive coupling between these windings. Satisfactory results have been obtained if this secondary winding has approximately 14-18 turns and is formed of 18 gauge wire. One side of the winding 36 is connected to the emitter electrode 25 while the other side is connected to the base electrode 27 of the transistor Q 1 The collector electrode 26 of the transistor Q is connected to ground at 29 and a capacitor 28 is connected across the emitter 25 and the collector 26 of the tran- 12 has a first primary sistor. The capacitance of the capacitor 28 is chosen so that it can absorb the charge developed in the converter during the no load condition of the system. In the present embodiment a value of 0.5 pf. has been found to be suitable.

The three secondary windings each have the same number of turns, but each secondary winding is constructed from a different gauge wire. In the illustrated embodiment of windings 45, 40 and 48 are of 28 gauge, 26 gauge and 24 gauge wire respectively. These three windings, like the first and second primary windings, are wound together in parallel fashion in order to maximize inductive coupling between the windings. The first secondary winding 45 is relatively thin, 28 gauge wire, and it is thus highly sensitive to transient voltages generated across the transformer 12. In this manner, the DC pulses generated on the primary side of transformer 12 in winding 34 are picked up in winding 45 for delivery to the igntion coil 13. This winding 45 is connected to the emitter of the transistor through a filter capacitor 47 which may have a value of about 0.1 pf. The second secondary winding 40, being of 26 gauge wire, is not as susceptible to transient voltages as the winding 45. The purpose of winding 40 is to maintain a bias on the control electrode 27 of the transistor Q This winding, which is in series with the resistor 42, having a value of approximately ohms, provides a balance bias for the base 27 of the transistor Q. In this manner the winding 40 will provide a proper bias on the base electrode 27 under all operating conditions. Finally, the third secondary winding 48 is of a much heavier wire, 24 gauge wire, and is the output wire from the converter transformer which delivers the pulsating DC current from the converter 11 to the ignition coil 13. All three secondary windings are connected to ground at a common point 44.

A type of transistor found suitable for use in the present circuit is the RCA power transistor 2N1906 which develops a collector to base voltage of volts and a collector to emitter voltage of 60 volts. A transistor of this type may be turned on and off at a rate of 12,000 times per second.

The positive side of output secondary winding 48 is connected by conductor 49 to the positive side of the primary winding 50 of the coil 13. The opposite side of winding 50 is connected to ground. The positive side of winding 50 is also connected to one end of a secondary winding 52 which is then connected through the laminations of the transformer at 52' to the distributor 14 through the lead line 53.

The present system operates as follows: Transistor Q is continuously switching between the on and off states thereof and thus, pulsating DC current is being developed by the converter at all times. However, with the present invention the rotor 55 of the distributor 14 is conducting current to the terminals only when the rotor is in the vicinity of a terminal 56, that is, at the load condition. When rotor.55 is between terminals 56, it is insulated so that no current fiows through the rotor 55 or the lead line 53. This is the no load condition.

In previous systems it was necessary to terminate the current flowing to the ignition coil when the rotor 55 was in the no load condition. Otherwise the voltage surges developed at that point would burn out various elements of the system, such as for example the transistor, or other weak points of the system. However, the present system is designed to absorb these voltage surges in such a manner that they cause no damage to the various elements of the circuit. Because of this design it is also possible to develop any voltage within the auto coil 13 up to the coil limit, and this limit would be high enough to assure efficient operation of the engine at high speed, for example 100,000 volts.

During the load condition current from the battery 10 will pass through the primary winding 34 and through the emitter, base and collector-electrodes to ground 29 at the design frequency ofthetransistor circuit (using the RCA 2N1906 transistor this may be up to 12,000 cycles per second). Duringthis load condition the DC pulses will be delivered across the converter transformer and to the ignition coil with a wave form A as shown in FIG- URE Z. This pulsating DC current is picked up by winding 40to exert ,a bias on the base electrode 27 while a continuous DC bias on the base 27 is provided by secondary primary winding 36 as described hereinabove. This pulsating current is also picked up by output coil 48 which delivers the DC pulses to the ignition coil 13 for delivery to the distributors 14 and spark plugs 15. Duringv the load condition, at low speed the voltage delivered by coil '13 may be in the range of 20,000- 30,000vlts. f

Two situations arise in which the normal low speed voltage of the pulsating current from the ignition coil to the distributor is varied. The first situationis the no load condition referred to above. The second situation is during the load condition when the engine is operated at a high speed. Here the resistance within the spark plugs increases greatly due to lower compression of the fuel mixture in the engine cylinders.

In the first situation the pulsating current developed and delivered by the transistor Q cannot be delivered from the ignition coil 13 to the spark plugs since the end rotor 55 is insulated (not near any terminal 56). There fore, the voltage in the secondary winding 52 does not pulsate but rises gradually as shown atcurve C in FIGURE 2. In previous systems this increase in voltage would damage the system, as a result of which it was necessary to interrupt the current flow to the ignition coil by mechanical timing means.

However, in the present invention this high voltage is absorbed in two ways. First, the relatively heavy gauge secondary winding 48 and ignition winding 50 provide a discharge path to ground for surge voltages so that voltage increases within the ignition coil will not harm the elements of the converter, such as, for example, the transistor Q itself. Next, since the transistor circuit continues to oscillate during the no load" condition of the distributor a means must be provided for absorbing the current pulses on the primary side of the converter transformer since they cannot be delivered across the transistor without shorting it out. The capacitor 28 is employed for this purpose. While the distributor is in a no load condition the capacitor 28 will charge up thereby absorbing the electrical energy generated on the primary side of the converter transformer 12 during the times that the transistor circuit is oscillating but the ignition coil is not delivering current to the spark plugs. When the distributor reaches another load condition the capacitor 28 will discharge and the DC pulses will again be delivered to the ignition coil 13. The capacitance of 28 is so chosen that it will be capable of absorbing the electrical charge developed in the converter during the time that the distributor is in the no load condition.

The second situation where the normal low speed voltage of the pulsating current from the ignition coil to the distributor is varied during the load condition at high engine speeds. Initially, as engine speed increases, the voltage across the ignition coil is insufficient to cause an efficient spark because of the higher resistance at the spark plug gap. In conventional ignition systems this would result in an insufiicient spark at the plugs. In the present igition system, however, as the engine speed increases the voltage in the ignition coil buids up in much the same manner as it did during the no load" condition, until it reaches a level at which it can deliver voltage spikes continuously to the plugs. The pulsating DC current will then be delivered continuously and efficiently to the distributor, and hence to the plugs, at the new higher voltage level as shown in FIGURE 2 at wave form C to provide efficient sparking for the high engine speed.

In an auto ignition system it is also possible for spurious AC signals to enter the ignition system. These signals could cause the collapse of the pulsating DC current and cut off of the transistor. With the present invention when such AC signals are present the discharging of capacitor 47 will prevent transistor Q from being turned off. A quick voltage spike can be obtained effectively with a 0.1 t. capacitance at 47.

The specific values of elements shown in the preferred embodiment of ,the present system are provided for illustartion and not for limitation. .It might be noted, however, that -with the values in the illustrated embodiment the entire system operates efiiciently at the 12,000 c.p.s. developed by the transistor so that heat problems are eliminated and it is not necessary to equip the transistor with a heat sink. Of course the system could also be designed to operate efiiciently with other transistor designs. It should be apparent that many other variations and modifications are possible within the spirit and scope of the invention as defined in the appended claims vwherein:

Iclaim:

1. A converter device adapted for use in the ignition system of a spark ignited internal combustion engine for changing direct electrical current to pulsating DC current comprising: a converter transformer means having at least a first primary winding and at least first and second inductively coupled secondary windings, an oscillator means including at least one alternately conducting and nonconducting amplifier means having first and second power circuit electrodes and a control electrode, a capacitor means connected in parallel across the power circuit electrodes, and a control means for controlling the voltage at the control electrode, said first primary winding having one end connected to said first power circuit electrode and having its other end adapted to be connected to a source of electrical energy, the other power circuit electrode being connected to ground, said first secondary winding having one endconnected to the said first power circuit electrode through a capacitor means, and said second secondary winding being an output winding and having one end adapted to deliver pulsating DC current from said converter, said first and second secondary winding being connected at their other ends to ground.

2. A converter device as claimed in claim 1 wherein said amplifier means is a transistor, said control electrode being a base electrode, said converter transformer further including a second primary winding inductively coupled to said first primary winding and having one end connected to said first power circuit electrode and its other end connected to the base electrode.

3. A converter device as claimed in claim 2 wherein said converter transformer further includes a third secondary winding inductively coupled to said first and second secondary windings, said third secondary winding having one end connected to the base electrode and its other end connected to ground, wherein said second primary winding and said third secondary winding comprise the said control means and exert an electrical bias on the said base electrode.

4. A converter device as claimed in claim 3 wherein the first, second and third secondary windings each have the same number of turns, the first secondary winding be ing thinner and the second secondary winding being thicker than the said third secondary winding.

5. A converter device as claimed in claim 4 wherein the said secondary windings each have approximately 40-46 turns and said capacitor means across the power circuit electrode has a value of approximately 0.5 ,uf.

6. A converter device as claimed in claim 5 wherein said first primary winding has approximately -125 turns and said second primary winding has approximately 14-18 turns, and said second primary winding is coupled to those turns of the first primary winding closest to that end of the first primary winding adapted to be connected to the source of electrical energy.

7. An electrical system for supplying electrical energy to an internal combustion enginecomprising: a source of DC electrical energy, a converter means for continuously converting the electrical current from said source to pulsating DC current, an ignition coil for receiving the pulsating DC current from said converter and delivering the same to a spark plug of an internal combustion engine, wherein the voltage of the current delivered from the ignition coil varies in proportion to the-electrical re.- sistance between the ignition coil and the internal combustion engine or the electrical resistance in the internal combustion engine whichever resistance is the higher of the two, and means within the converter means for absorbing high voltage surges developed within the ignition coil and the converter means when the said electrical resistances increase above that resistance corresponding to the lowest normal operating resistance inthe internal combustion engine. a

8. An electrical system as claimed in claim 7 wherein said converter includes a continuously oscillating amplifier means having power circuit electrodes and a control electrode and a converter transformer means and said means for absorbing the high voltage surges includes a capacitor means connected across the power circuit electrodes of the amplifier means and a means for discharging the high voltage developed within the ignition coil to ground. I

9. An electrical system for supplying electrical energy to an internal combustion engine comprising, a source of DC electrical energy, a converter means for continuously converting the electrical current from said source to pulsating DC current, an ignition coil for receiving the pulsating current from said converter and delivering the same to a spark plug of an internal combustion engine, the converter transformer means having at least a first primary winding and at least first and second inductively coupled secondary windings, an oscillator means including at least one alternately conducting and nonconducting amplifier means having first and second power circuit electrodes and a control electrode, a capacitor means connected in parallel across the power circuit electrodes, and a control means for controlling the voltage at the control electrode, said first primary winding having one end connected to said first power circuit electrode and having its other end adapted to be connected to a source of electrical energy, the other power circuit electrode being connected to ground, said first secondary winding having one end connected'to the said first power circuit electrode through a capacitor means, and said second secondary winding being. an output winding and having one end adapted to deliver pulsating DC current from said converter, said first and second secondary windings being connected at their other ends to ground, whereby when the resistance to the flow of pulsating DC current is offered either between the ignition coil and the internal combustion engine or in the internal combustion engine, high voltage surges'developed in .8 the ignition coil maybe discharged to ground through the said second secondary "winding; andipiilsa'tingcurrent developed by the .converter may be absorbed bysaid capacitor means connected across the power circuit *elec- 10. An electrical system as claimed in claim '9 wherein said ignition coil has a primary winding and a' secondary winding, said primary winding having a first end connected to thesaid one end ofthe second secondary Windingbf the converter transformer,'andsaidfirst end of said-primary ignition c'oil winding'also beingconnected to the' fi'rst end of the ignition'coil sec'ondary'winding; the second end of-said ignitioncdil primary winding being connected to ground, and the second end of said ignition c'oil secondary winding adapted to be connected to the spark plug of the internal combustion engine; "11. An electrical system as claimed in claim 10 wherein said amplifier means is'a transistor, said control-electrode being abase electrode, said converter transformer further including a secondary primary 'winding inductively coupledto "said 'fir'st primary winding and'ha'ving one end connected to said first power circuit electrode and its other end connected to the base electrode.

12. An electrical system as claimed in claim 11 wherein said converter transformer'further includes a third secondary winding inductively coupled to said first and second secondary windings, said third secondary winding having'one end connected to the base electrode and its other end connected to ground, wherein said secondary primary winding and said third secondary winding comprise the said'control means and exert an electrical bias on'the said base electrode.

' 13. An electrical system as claimed in claim 12 wherein the first, second and third secondary windings each have the same number of turns, the first secondary winding being thinner and the second secondary winding being thicker than the said third secondary winding.

14. An electrical system as claimed in claim 13 wherein the said secondary windings each have approximately 40-46 turns and said capacitor means across the power circuit electrode has a value of approximately 0.5 f. 15. An electrical systemas claimed in claim 14 where; in said first primary winding has approximately -125 turns and said second primary winding has approximately 14-18 turns, and said second primary winding is coupled to those turns of the first primary winding closest to that end of the first primary winding adapted to be connected to the source of electrical energy.

References Cited UNITED STATES PATENTS 1,968,930 8/1934 Cotter et a1. 3-1s-213x 2,981,865 4/1961 Fernbach "315-214 2,984,766

5/1961 Moore 3l5-=2l4 JAMES w. LAWRENCE, Primary Examiner. C. CAMPBELL, 1a., Assistant Examiner.

Claims

1. A CONVERTER DEVICE ADAPTED FOR USE IN THE IGNITION SYSTEM FOR A SPARK IGNITED INTERNAL COMBUSTION ENGINE FOR CHANGING DIRECT ELECTRICAL CURRENT TO PULSATING DC CURRENT COMPRISING: A CONVERTER TRANSFORMER MEANS HAVING AT LEAST A FIRST PRIMARY WINDING AND AT LEAST FIRST AND SECOND INDUCTIVELY COUPLED SECONDARY WINDINGS, AN OSCILLATOR MEANS INCLUDING AT LEAST ONE ALTERNATELY CONDUCTING AND NONCONDUCTING AMPLIFIER MEANS HAVING FIRST AND SECOND POWER CIRCUIT ELECTRODES AND A CONTROL ELECTRODE, A CAPACITOR MEANS CONNECTED IN PARALLEL ACROSS THE POWER CIRCUIT ELECTRODES, AND A CONTROL MEANS FOR CONTROLLING THE VOLTAGE AT THE CONTROL ELECTRODE, SAID FIRST PRIMARY WINDING HAVING ONE END CONNECTED TO SAID FIRST POWER CIRCUIT ELECTRODE AND HAVING ITS OTHER END ADAPTED TO BE CONNECTED TO A SOURCE OF ELECTRICAL ENERGY, THE OTHER POWER CIRCUIT ELECTRODE BEING CONNECTED TO GROUND, SAID FIRST SECONDARY WINDING HAVING ONE END CONNECTED TO THE SAID FIRST POWER CIRCUIT ELECTRODE THROUGH A CAPACITOR MEANS, AND SAID SECOND SECONDARY WINDING BEING AN OUTPUT WINDING AND HAVING ONE END ADAPTED TO DELIVER PULSATING DC CURRENT FROM SAID CONVERTER, SAID FIRST AND SECOND SECONDARY WINDING BEING CONNECTED AT THEIR OTHER ENDS TO GROUND.