US3502060A - Electronic ignition system - Google Patents

Description

March 24, 1970 o. F. TIBBS ELECTRONIC IGNITION SYSTEM 2 Sheets-Sheet 1 Filed Oct. 16, 1968 INVENTOR OSCAR E TIBBS ATTORNEYS 0. F. TiBBS ELECTRONIC IGNITION SYSTEM March 24, 1970 2 Sheets-Sheet 2 Filed Oct. 16, 1968 INVENTOR OSCAR F. TIBBS ATTORNEYS United States Patent 3,502,060 ELECTRONIC IGNITION SYSTEM Oscar F. Tibbs, Ripley, Tenn., assignor to John W. Buzick, Monette, Ark. Continuation-impart of applications Ser. No. 580,795, Sept. 20, 1966, and Ser. No. 648,903, June 26, 1967. This application Oct. 16, 1968, Ser. No. 768,119

Int. Cl. F02p 1/00;H05b 37/02, 39/04 US. Cl. 123-148 2 Claims ABSTRACT OF THE DISCLOSURE A transistorized ignition system for a multi-cylinder engine which employs no breaker points and no mechanical moving parts provides a constant voltage which is harmlessly absorbed by the system when the spark plugs are not firing. The system includes a transistorized transformer control circuit which converts battery supplied D.C. into pulsating D.C., which is fed to the ignition coil.

CROSS REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of application Ser. No. 580,795, filed Sept. 20, 1966, now US. Patent No. 3,408,536, and of application Ser. No. 648,903, filed June 26, 1967.

BACKGROUND OF THE INVENTION Conventional ignition systems employ mechanical breaker points to time the flow 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 whereas if the voltage is set too high the spark plugs and/or other elements of the ignition system may burn out during periods when the system voltage requirements are low.

In an early attempt to overcome such problems a form of the so-called magneto was developed which varied the voltage in accordance with engine speed. However, the fact that the magneto depends for efficient operation on a precise mechanical interrelation between the parts has greatly limited the effectiveness thereof. Consequently, the magneto has not been accepted as a satisfactory means for overcoming the inherent disadvantages in conventional breaker point timing mechanisms.

With the development of transistors, a number of attempts were made to design solid state ignition systems which overcome the disadvantages of mechanical timing means. Transistors have been employed to supplement the operation of an ignition coil in developing a high voltage, low ampere oscillating current to thereby reduce the load on the breaker points. However this approach merely eliminates some of the problems associated with breaker points and does not eliminate the need for breaker points so that the basic problems remained, that is, to provide a voltage which is available during all the changing load requirements and which is adapted to those requirements.

SUMMARY OF THE INVENTION In accordance with the present invention a radically different solid state ignition system is provided which has many of the advantages of previous ignition systems but in which the disadvantages of these systems are eliminated. The present system not only eliminates mechanical timing but also permits control of the system voltage, without mechanical moving parts, such that the voltage supplied adapts to changing load requirements during acceleration and other conditions.

In the system of the invention a pulsating direct current is generated continuously and the system is adapted to counteract problems which would normally be encountered during the periods when pulses are being generated but not delivered to the distributor and to the spark plugs. As noted, by employing this entirely novel approach, all mechanical breaker points and voltage varying means have been eliminated and hence the present invention is similar in this respect to a magneto to the type described. Consequently, the present system may be conveniently referred to as a solid state magneto or an electronic magneto. A period when current is being delivered through the distributor to the spark plugs will be referred to hereinafter as a load period or condition and a period when current is not being delivered through the distributor to the spark plugs will be referred to as a no load period or condition. In the previous conventional ignition systems problems such as damaging high voltage surges were avoided because the breaker points employed in such systems caused the current flow to be interrupted during periods of no load. With the present system, however, means are provided for absorbing these high voltages surges in such a manner that (1) these surges cause no harm to the elements of the ignition system and (2) the surges will not cause interruption of the pulsating DC current of the ignition system. Further, it is noted that spurious A.C. current surges transmitted to the ignition system from the generator or alternator will not cause interruption of the pulsating DC. current.

In accordance with a presently preferred embodiment of the invention, direct current from a conventional source such as an automobile storage battery is continuously converted to a pulsating DC. current in a transistor oscillator circuit, this resultant pulsating current being delivered to the ignition coil and hence through the distributor to the spark plugs. Although this pulsating DC. current is generated continuously by the transistor oscillator circuit a current is induced to fiow through the ignition coil and distributor to the spark plugs only during the load condition of the system, that is, when the distributor rotor is in the vicinity of a terminal leading to a spark plug. During no load conditions, i.e., when the distributor rotor is between spark plug terminals, current is not delivered from the ignition coil through the distributor either because the rotor and corresponding spark plug terminals are not close enough to permit conduction, or, if these elements are close enough to permit conduction, the compression in the engine cylinder is insuflicient to permit the spark plug to fire and thus to permit the circuit to be completed to ground. It will be appreciated that during no load conditions high voltage surges build up which are capable of damaging the elements of the system. In accordance with an important feature of the invention, these surges are absorbed by the ignition coil and the transistor oscillator circuit so that no damage results.

In accordance with a further important feature of the present invention the resistance at the spark plugs during the load condition varies automatically with the compression in the combustion chamber. As this resistance increases the sparking is retarded and in this way the voltage may be maintained constant while the sparking across the spark plug gap is retarded until the correct. combustion conditions are present regardless of whether the engine is being operated at high or low speed.

Many additional advantages are attributable to the ignition system of the invention. The life of spark plugs themselves is sufficiently prolonged because the constant, high voltage spark pulses tend to clean carbon deposits off the spark plugs and to generally improve the efficiency thereof. Further, with the present system the distributor cap and rotor are not pitted or burned by arcing.

A further feature of the present invention which is of particular importance today in view of the many problems associated with exhaust pollutants, is that fuel combustion is substantially improved. In the present system the spark will automatically be retarded by the engine compression conditions which results in more complete fuel combustion.

Other features and advantages of the present invention will be set forth in or become apparent from the detailed description of a presently preferred embodiment of the invention found hereinbelow.

BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is a schematic circuit diagram of a presently preferred embodiment of the present invention.

FIGURE 2 is a schematic circuit diagram similar to FIGURE 1 wherein a form of the invention adapted to systems employing a positive ground is shown.

DESCRIPTION OF THE PREFERRED EMBODIMENT Although the structure and operation of the invention will be described with respect to presently preferred embodiments of the invention it will be understood that the particular values of the components given are merely illustrative and that these values may, of course, be varied without departing from the scope of the invention.

Referring to FIGURE 1, a 12 volt D.C. storage battery is connected from ground 11 through a switch to a transformer 30. Transformer 30 delivers an induced current through conductor 39 to the primary winding 51 of an ignition coil 50. A very high voltage is induced in the secondary winding 52 of coil 50 and is transmitted through the distributor cap 60 to the distributor rotor 62 and thence to terminals 63 and spark plugs 61. In the described embodiment the ignition coil 50 has a turns ratio of 250:1, this turns ratio governing the number of turns of the transformer 30. However, it is noted that other standard ignition coil turns ratios such as 100:1 and 400:1 may also be used. To utilize an ignition coil having a different turns ratio it would only be necessary to change the number of turns of the transformer 30.

The transformer 30 has a primary winding 31 and a feedback winding 32 which is primary in the sense of being connected through primary coil 31 to the input, but secondary in the sense of being wound closely in parallel with secondary windings 33, 34 and 35. Each of the five windings 31 to 35 has been provided With an S or F at either end thereof which are intended to designate start or finish. These designation are thought to be helpful as an aid in winding the transformer as well as in distinguishing the embodiment of FIGURE 2 described below. Each layer of windings is separated by a .0025 inch thick plastic insulating tape.

The primary winding 31 may be constructed of 20 gauge wire having approximately 125 turns. It has been found that 20 gauge wire will draw a sufiicient current while avoiding heat problems. The turns of winding 32 are wound in parallel with secondary windings 33, 34 and 35 to maximize the inductive coupling between these windings. Satisfactory results have been obtained if winding 32 has approximately 1418 turns and is formed of 18 gauge wire.

Windings 33, 34 and 35 each have the same number of turns but each winding is constructed from a different gauge wire. In an exemplary embodiment the windings 33, 34 and 35 are of 24 gauge, 26 gauge and 28 gauge wire, respectively. These three windings, like the primary and feedback windings, are wound together in parallel in order to maximize inductive coupling between the windings. One end of winding 34 is connected through a filter capacitor 36, which may have an exemplary value of about .047 ,uf., to the 12 volt D.C. source 10 while the other end is grounded at 47. One end of winding 35 is connected to the 12. volt source through a 500 f. capacitor 37 while the other end is connected directly into the laminated core 38 of transformer 30 as indicated.

A control circuit including a transistor Q is connected in series between primary winding 31 and ground 29. Transistor Q Which may for example be an RCA power transistor 2N3731, includes an emitter electrode 41, which is connected to the finish end of winding 32, a collector electrode 42 connected to ground at 29 and a control or base electrode 43 which is connected through a resistor 45 to the start end of winding 32. The electrodes of transistor Q are identified by the same numerals with the letter a attached thereto and are connected as shown. Similarly, resistor 45a and ground 29a correspond to resistor 45 and ground 29, respectively. A capacitor 44 is connected from a point on the connection between emitters 41 and 41a to a ground denoted 46, the capacitance of capacitor 44 being chosen such that the charge developed in the circuit during the no load condition of the system will be absorbed by capacitor 44. A capacitance value of 0.5 ,uf. has been found to be suitable for this purpose. It is noted that by varying the capacitance value of capacitor 44 the on and off times of transistors Q and Q can be correspondingly varied. A second transistor Q is shown in FIGURE 1 but is not required for operation of the circuit. Transistor Q2 is used only as a reserve such that if one of the transistors Q or Q fails, the inoperative transistor can be simply removed so that the ignition system will again operate. The power electrodes of transistor Q are connected in parallel with those of transistor Q while the base electrode of transistor Q is connected to the base electrode of transistor Q It is believed to be essential that the core 38 of transformer 30 not be grounded. To this end the entire transformer 30, including the windings, is enclosed within conventional paper insulation. In addition, it is preferred that the paper-insulated transformer 30 be enclosed within a metal shield of the same material as the core laminations in that such shielding isolates the transformer 30 from external frequency effects and, more importantly, provides control of the field of the transformer 30 such that the system will operate continuously rather than sporadically as has been found to be the case when a shield is not used.

The ungrounded end of winding 33 is connected through conductor 30 to one end of each of the inductively coupled ignition coil Windings 51 and 52. The other end of primary winding 51 is connected to ground at 54 while the other end of secondary winding 52 is connected to the distributor cap 60 through conductor 53. Windings 51 and 52 connected in opposition and winding 52 is tapped to the core of the ignition coil as is indicated at 52a. The spark plugs which are of standard construction are indicated schematically at 61 and are grounded at 64. It is noted that no structural modification in the cylinders is necessary in order to permit mounting of the spark plugs and that any conventional means of installing the spark plugs is satisfactory.

Although the operation of the system of the invention is perhaps not completely understood the system is believed to operate as set forth hereinafter. Transistors Q and Q are continuously being switched between the active and inactive states thereof, thus causing a pulsating DC. current to be generated in the primary winding 31 and in primary-secondary winding 32. A corresponding pulsating DC. current is induced in winding 33 which is conducted through the distributor cap 60 and thence to rotor 62, to terminals 63 and finally to spark plugs 61. However, current will pass to spark plugs 61 only when the rotor 62 is in the vicinity of a terminal 63, that is, under load conditions. When distributor rotor 62 is positioned between terminals 63 the rotor 62 is in sulated from the terminal 63 such that the current path therebetween is broken. In prior art systems it is necessary to terminate the current flowing to the ignition coil when the distributor rotor is in a position corresponding to no load because the voltage surges developed during this time may otherwise destroy various elements of the system. Similarly, in the system of the invention, under no load conditions, the voltage developed in the circuit cannot be delivered from the ignition coil 50 to the spark plugs 61 because the end of rotor 62 is insulated as explained hereinabove. However, whereas in previous systerns the voltage can gradually rise to a point at which damage to the system can occur (and as a result it is necessary to interrupt the current flow to the ignition coil by mechanical timing means in such systems), such voltage rises or surges are harmlessly absorbed in the present system. Surge currents in the present system are discharged through the secondary winding 33 and through primary coil winding 51 to ground with any reflected surges also being harmlessly absorbed. Therefore, the voltage within the ignition coil 50 does not increase and sensitive elements in the system such as the transistors Q and Q are not damaged. Further, capacitor 28 by charging up during no load conditions will absorb the voltage generated on the primary side of the transformer 30. Thus the present system maintains a constant voltage which is utilized for spark ignition of the combustible air-fuel mixture under load conditions but which is harmlessly absorbed by the system under no load conditions.

During load conditions sparking is controlled by the compression in the combustion chamber. The engine is timed so that as rotor 62 approaches a terminal 63 the piston is approaching what is known as top dead center. At this position compression in the cylinder will approach a maximum, which is of course the most advantageous condition for producing a good spark. Thus at top dead center the sparking across the spark plug gap will greatly increase. Just after the piston passes top dead center the explosion in the cylinder will be sufiiciently complete to propel the piston away from the cylinder head. As is, of course, well understood in the art this process will occur in each cylinder of the engine in a desired firing order. Thus, the operation of the system of the invention apart from the use of a continuous pulsating voltage as described hereinabove is otherwise similar to that of conventional ignition systems.

The embodiment of FIGURE 1 described hereinabove may be incorporated in most makes of automobiles found in the United States. However, where the system of the invention is to be incorporated into automotive vehicles such as, for example, tractors or other motorized farm vehicles, the system must be slightly modified. Farm vehicles generally provide a so-called positive ground as contrasted with the negative ground provided by the storage battery used in most automobiles. Because of the differences in polarity between the two systems, the polarities of the elements in the embodiment of FIG- URE 1 must be reversed. Thus, FIGURE 2 is an embodi- 6 ment of the invention similar to FIGURE 1 wherein the system of the invention has been adapted for use with a positive ground.

The ignition system of the embodiment of FIGURE 2 is formed by elements similar to those found in the embodiment of FIGURE 1 and these elements have been given the same reference numerals with primes attached. In FIGURE 2, the positive plate of battery 10 is connected to ground and hence the direction of current flow is reversed from that in FIGURE 1. Thus, current may be thought of as flowing from the positive ground indicated at 47 through primary winding 34'. Although the differences between the embodiments of FIGURES 1 and 2 are believed to be readily apparent from a comparison of the two figures, it should be noted that for the FIG- URE 2 embodiment the collectors of transistors Q and are insulated from the ground. It is further noted that the polarities of the ignition coil 50' of FIGURE 2 are the same as those of coil 50 of FIGURE 1.

Although the invention has been described in some detail with reference to presently preferred embodiments thereof it will be understood that modifications other than those specifically enumerated may be elfected without departing from the scope and spirit of the invention. Thus, the scope of the invention is to be determined not from the illustrative embodiment described herein before but rather from the subjoined claims.

Having described my invention in accordance with the requirements of the patent statutes, I claim:

1. An automotive ignition system comprising a source of continuous direct current electrical energy comprising a direct current battery having the positive plate thereof connected to ground; means for converting the direct current electrical energy produced by said source into pulsating direct current electrical energy, said means including at least one transistor and transformer means comprising a core, a primary winding wound on said core, one side of said primary winding being connected to ground and the other side of said primary winding being connected to a first power electrode of said at least one transistor, first, second and third secondary windings wound on said core, a feedback secondary winding connected between the base electrode of said at least one transistor and said other side of said primary winding to control biasing of said at least one transistor, said feedback secondary winding being wound on said core closely in parallel with said first, second and third secondary windings, one side of said first secondary winding being connected to the negative plate of said direct current battery and the other side of said first secondary winding forming the output of said transformer means, one side of said second secondary winding being connected to said one side of said first secondary winding and to the other power electrode of said at least one transistor and the other side of said second secondary winding being connected through a capacitance to the negative plate of said direct current battery, and one side of said third secondary winding being connected to said transformer core and the other side of said third secondary winding being connected through a further capacitance to the negative plate of said direct current battery; distributor means including an input rotor and a plurality of output terminals arranged sequentially with respect to said rotor; a plurality of spark plugs connected to said distributor output terminals; and coil means connected to the output of said transformer means and to said rotor for continuously applying said pulsating direct current electrical energy to said rotor for positions of said rotor with respect to said distributor terminals wherein current is conducted to a spark plug and for absorbing voltage surges occuring for positions of said rotor with respect to said distributor terminals wherein current is not conducted to a spark plug.

2. A system as claimed in claim 1 wherein said at least one transistor comprises a p-n-p transistor, said first power 7 8 electrode comprises the emitter electrode of said transis- 2,981,865 4/1961 Fernbach 315206 tor and said other power electrode comprising the collec- 3,018,413 l/ 1962 Neapolitakis. tor electrode of said transistor said system further com- 3,175,123 3/1965 Dilger 315-209 prising a capacitance connected between ground and the 3,408,536 10/1968 Tibbs 315212 connection between said other end of said primary winding and said emitter electrode.

References Cited UNITED STATES PATENTS 315 2()9 2,968,296 1/1961 Kaehni 123117 10 5 LAURENCE M. GOODRIDGE, Primary Examiner US. Cl. X.R.

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