US3366098A - Current transfer electrical ignition system - Google Patents

Description

Jan. 30, 1968 w. F. PALMER CURRENT TRANSFER ELECTRICAL IGNITION SYSTEM Filed Oct. 22, 1965 //V l/E/V 7'01? WILL/AM F. PALMER ATTOR/VEY United States Patent 3,366,098 CURRENT TRANSFER ELECTRICAL IGNITION SYSTEM William F. Palmer, Lowell Road, Carlisle, Mass. 01741 Filed Oct. 22, 1965, Ser. No. 501,436 6 Claims. (Cl. 123-148) ABSTRACT OF THE DISCLOSURE An electrical switching circuit utilizing transistorized components to control current flow. in high voltage discharge means. A parallel inductance provides for storage of energy pulses is incorporated directly with the transistor amplifier circuit. Conventional low turns ratio ignition coils may now be utilized in any automotive ignition system employing transistors.

The present invention relates generally to transistorized electrical circuits and more particularly to a novel current transfer electrical ignition system for use in many applications such as internal combustion engines.

The well known ignition circuit in conventional battery operated combustion engines utilizes a transformer coil, a condenser and mechanical circuit breaker contacts coupled to some mechanical moving means to conductively connect the inductive load to the direct current power source. Upon interruption of the current flow a large inductive voltage is generated in the secondary windings which in turn fires the spark plugs. The contacts therefore effectively function as a make-and-break switch in the primary circuit of the ignition coil. It is required that they carry currents in the order of five to ten amperes when closed and withstand several hundred volts of coil kickback voltage when they open and thereby break the circuit. The high current density and substantial voltages across the breaker contacts result in oxidation, erosion, burning, and pitting which requires frequent maintenance and replacement to continue efficient performance of the ignition circuit. Due to the higher speed of the modern day multi-cylinder engines the time period when the contacts are closed is relatively short and the current build up does not reach full value before the points open again. The output voltage begins to achieve only a fraction of its full capability.

In recent years considerable interest has been shown in electrical circuits utilizing transistor amplifiers to carry the high current and isolate the kickback voltage from the breaker contacts which now handle only a small signal current to bias the transistor in the conductive state and a relatively low voltage in their non-conductive state. Such transistor systems commonly incorporate the transformer primary in the emitter or collector circuit and the circuit breaker contacts are conductively connected to the base electrode. The transistor therefore entirely controls the current flow from the voltage source to the transformer primary and the contacts merely switch the transistor on and off. The use of the transistor has led to faster current build up with little peak current fall-off at higher engine speeds. Additionally the contacts have been proven to be relatively free of the disadvantages arising in conventional electrical ignition circuits.

One of the necessary requirements, however in prior art transistorized ignition systems has been the need for a specially designed low primary inductance coil to cope with the voltage rating of commercially available transis- 3,366,098 Patented Jan. 30, 1968 ICC tor amplifiers. Conventional ratio ignition coils having a value of between 70 and 90:1 must therefore be replaced by one having a ratio of approximately 250 to 400:1 in order that the transistor voltage ratings are not exceeded. In practice then special high ratio transistor coils will be more expensive than the conventional standard ratio coil. Difficulties in education of qualified service personnel and occasional transistor failures have also hindered wider acceptance of transistorized circuits in ignition systems.

Several suggested protective circuits have therefore evolved in the art in an attempt to incorporate the advantages of transistorized operation together with standard conventional ratio coil transformers. One such teaching incorporates the use of the so-called series stacking technique employing lower voltage transistor amplifiers or expensive high voltage transistors in order to withstand the 200 volts or more of primary kickback. Other such systems employ inversion or rectification to obtain DC voltage across an energy storage condenser which in turn is discharged into the transformer primary to result in a capacitive discharge circuit for the production of the high-voltage secondary energizing pulse. Such circuits can further complicate matters in that complexities are introduced as well as additional expense which fails to meet the first test or requirement for a simplified circuit means for the conversion of present ignition system circuits to the full utilization of transistor operation. In addition, such complex circuitry often fails to provide the appropriate high speed response or eliminate the high speed roll off of the output voltage.

The primary object of the present invention is the provision of a novel electrical ignition circuit.

A further object of the present invention is the provision of a novel transistorized ignition system for automotive applications.

A still further object of the invention is the provision of a current transfer means utilizing a conventional ratio ignition transformer or coil to generate the high voltage pulse.

. An additional object of the present invention is the provision of a novel transistorized ignition system adapted for use in internal combustion engines to provide for improved circuit breaker contact life without extensive or costly modifications of existing electrical circuit components now utilized in such systems.

Broadly stated, the invention envisages the incorporation in an electrical ignition system of a transistor current amplifier and a shunt inductance in parallel with the primary winding of the conventional ratio power transformer or coil with the base of transistor controlled by the pulse generation means such as the circuit breaker contacts. Any suitable inductance such as a choke coil or transformer may be utilized in the practice of the invention. Upon closure of the contacts the inductor is energized by the direct current voltage source since the transistor is in the conductive state. Opening of the contacts results in interruption of current flow in the transistor and transfer of stored energy to the primary winding of the conventional step-up power transformer or coil. This reversing or bucking current flows immediately into the primary winding of the step-up transformer and leads to an induced voltage in the secondary winding in much the same manner as the conventional interruption of current induces high voltage pulses. The main feature of the invention therefore is the direct control of the transistor amplifier by the pulse generation means together with the energizing of the parallel inductance for the storage of what may be referred to as an arresting current which becomes the energy source to the primary winding of a step-up power transformer upon the opening of said means. A departure from prior art transistorized electronic ignition systems is noted wherein the transistor was tied only to the primary winding during conduction with the contacts closed. In some instances elaborate circuits have been designed involving plural transistor amplifiers with one transistor in the conductive state while the pulse generation means are closed and another transistor is sequentially energized after the first transistor is non-conductive. The present invention seeks to eliminate all superfluous circuitry and provide for a speedy and less expensive retrofit package to incorporate the advantages of transistor operation in present day ignition system with operation under both systems still permissible should transistor failure arise during operation.

The flow of current during the period of energy storage in the parallel inductance means may be effectively isolated from the conventional step-up power transformer by unidirectional current biasing means to prevent the flow of current into the primary winding of the conventional ratio transformer. Such isolation means include diode rectifiers, 4-layer diodes or silicon controlled rectifiers with suitable gating circuits. Numerous embodiments of a parallel inductance circuit arrangement will be described for various electrical ignition systems.

Other objects, features and advantages will be evident after consideration of the following detailed specification and reference to the accompanying drawings in which:

FIG. 1 is a schematic circuit diagram of an exemplary embodiment of the invention;

FIG. 2 is a schematic circuit diagram of a modified embodiment of the invention;

FIG. 3 is a schematic circuit diagram of an alternative embodiment of the invention utilizing an auto-transformer as the parallel inductance; and

FIG. 4 is a schematic circuit diagram of another alternative embodiment utilizing an isolation transformer and other modifications of the circuits shown in FIGS. 1, 2 and 3.

Referring to the drawing there is shown in FIG. 1 an exemplary circuit of the invention. A direct current source 10, which may have a value of six or twelve volts in present day automotive equipment, powers the circuit. The negative terminal 12 is grounded and the positive terminal 14 is connected to one pole of ignition switch 16. While a negatively grounded system has been illustrated, it is understood that with appropriate modifications, for example the use of an NPN transistor amplifier instead of the PNP type or a phase inverter stage, the invention may be equally applicable to positively grounded systems. In non-automotive applications, the grounding may be immaterial.

The other pole of switch 16 is conductively connected through a current limiting resistor 18 to the primary winding 20 of step-up power transformer or ignition coil 22. The secondary winding 24 provides for the induced high voltage for application to the conventional spark plug load through the distributor by means of lead 26. For the purposes of this specification details of the high voltage distribution system have been omitted as unnecessary to an understanding of the invention and the symbol H.V. collectively refers to any high voltage load.

The transformer 20 will have the conventional high primary inductance and low turns ratio in the range of approximately 70 to 90:1 since this invention is to be practiced in present ignition systems in a retrofit manner without any transformer modifications necessary. In the present state of the art applicable to transistorized ignition systems the much lower primary inductance and high turns ratio in the range of 250 to 400:1 is required to reduce the kickback voltage across the transistor amplifier.

In the conventional ignition system, pulse generation means 28 of the circuit breaker type are employed having contacts 30 and 32 grounded on one side to complete the primary ignition circuit along with a condenser (not shown) across the contacts to assist in reducing arcing. The operation of the conventional system is as follows: With switch 16 closed the contacts assume a make-andbreak function. Upon closure of contacts 30 and 32 the primary ignition circuit loop is completed and current flows from the direct current source 10 through the primary winding until the Ohms law value is achieved. Upon contact opening the circuit is sharply interrupted and the abrupt reduction in current flow induces a high voltage for ignition in the secondary of the transformer in accordance with the well known principles of induction. The abrupt change which has developed is from current out of primary 20 to zero and at high engine speeds when contact closure time is of short duration the ignition spark may cut out as much as 30% of the time in the 3,000-5,000 r.p.m. region.

In accordance with the teachings of the invention the only components necessary to improve over all ignition efliciency at a minimal cost are shown within the area outlined by dotted line 34. A transistor power amplifier device 36 having a high voltage rating is serially connected to the circuit breaker contacts and primary winding loop with base 38 connected to the contacts and collector 40 grounded by conductor 41. While the grounded collector circuit configuration has been illustrated, the grounded emitter circuit may also be employed. Emitter 42 in the present case therefore will be connected by conductor 43 to one end of primary winding 20. Control of the transistor amplifier conductivity will be direct through the pulse generation means 28.

A shunt circuit loop comprising inductance 44 and resistor 45 is connected by conductors 46 and 48 between the emitter 42 and switch 16. Inductance 44 will be in parallel with the primary inductance winding 20 of power transformer 21. and may comprise a simple energy storage choke coil or transformer. In the illustrative embodiment a matching ratio of approximately 121 between the parallel inductance 44 and primary inductance 20 is under consideration and to assist in a rapid charging time at modern day high engine speeds it is preferred that the choke coil or transformer have a slightly lower inductance value rating than the 6 millihenries, which is approximately the standard power transformer primary inductance rating.

In the new circuit arrangement, upon closure of the circuit breaker contacts the emitter electrode is heavily positively biased with respect to the negatively biased base. With the collector 40 at ground potential the transister 36 is now conductive and current I builds up rapidly in the circuit loop 44, 45, 46 and 48 to the Ohms law value. Simultaneously with the build up of current I in the shunt inductance circuit loop, direct current I also flows in the primary inductance circuit 18 and 20 of a value substantially equal to that of the current in the first-named circuit loop. Hence, under normal conditions a current of 4 to 5 amperes flows in each parallel circuit loop. The total power source drain would therefore be the sum of I and I or approximately 8 to 10 amperes. This value seems tolerable in modern automotive equipment. It may be preferred in some instances for the current 1 to exceed I and establish a small opposite or reverse polarity flow for use when the main spark is generated.

Immediately upon contact opening transistor 36 becomes nonconductive and tends to cut off current flow in both inductance 44 and primary inductance winding 20. If both currents had been equal prior to transistor cut off, they will (ignoring transient effects) both be arrested by their induced voltage across the transistor. If one of the currents were greater then the other it not only is arrested but a reverse current is established in the loop having the smaller current.

Referring to FIG. 2 a modification of the embodiment shown in FIG. 1 is disclosed. In this View as in the following views and specification similar components have been assigned the same reference numeral as in FIG. 1. Unidirectional current rectifier means 50 may be provided in series to isolate the primary inductance winding so that no current flows from the energy storage inductance 44 until the desired time for the transfer of current to generate the high voltage pulse. A diode rectifier has been illustrated however other components may include silicon controlled rectifiers with a gating circuit or a four layer diode. In this circuit as in FIG. 1 when the circuit breaker contacts close the transistor amplifier 36 is conductive. The unidirectional means 50 connected in concluctor 43 is reverse or off biased when current flows in the parallel inductance 44, 45, 46 and 48 and as a result no current is permitted to flow in the primary inductance winding 20. Upon opening of the contacts the transistor 36 is abruptly cut-off and this current induces a positive going potential at its lower end of winding 20 which in turn renders the diode conductive causing the stored energy to flow between inductance 44 and primary of transformer 22. This pulse of current in the primary induction and the reflection of the secondary will be opposed by the voltage induced by the changing current. This voltage is multiplied by the power transformer turns ratio at the high voltage output terminals and if we assume a current of 4 to 5 amperes flowing initially in the parallel inductance loop the result will be the same as if a primary 26) had a 4 to 5 ampere current interrupted to thereby induce a high secondary voltage pulse. With this modification the total power source drain may be effectively reduced and at the same time gaining the improved frequency or speed response capable in transistor ignition systems while employing the conventional ignition power transformer or coil.

In the preceding circuit configurations a matching ratio of 1:1 is disclosed which requires the use of transistor amplifiers having higher voltage ratings. An interesting modification will now be discussed which permits the use of transistors having lower voltage ratings and corresponding lower cost. In FIG. 3 a transformer 52 is shown which may for example have a ratio of 1:3. A tap 58 :1 winding 54 of transformer 52 is conductively connected to emitter 42 allowing section 53 to function as the primary. Base 38 is shunted by means of conductor 60 and resistor 56 to the tap 58. With the unidirectional biasing means 50 provided in conductor 57 the tap on the transformer primary is connected to ground through the transistor to thereby apply most of the power source voltage across the winding 53 of transformer 52 when the transistor is conductive and a voltage correspondingly higher by a factor of three in this example appears across the secondary 54 by induction when the pulse generation means 28 are closed andthe transistor is conductive. With this arrangement it is possible to attain 200 volts across the primary winding 20 of power transformer 22 using transistor devices having ratings of between 60 to 80 volts.

When the contacts open the current I in the parallel inductance circuit, as in the previous illustrations with a protective or isolation diode, will now establish a current flow into the primary winding 20 and induce the high voltage pulse desired. Battery drain will be reduced with this circuit as well. In those applications without the reverse biased diode an interesting phenomenon is observed which may be referred to as a boost effect.

During contact closure the current I flowing through the primary 20 of power transformer 22 will be approximately one-third that flowing in the parallel inductance or transformer 52 loop if resistance is suitably chosen. Hence, if 3 amperes is flowing in I 9 amperes are required in I to achieve a cancelling or bucking response. Upon contact opening the reversal of I results in an immediate return of transformer 22 to the battery end of resistor 45 instead of the transformer 52 and this boost effect results in a higher secondary voltage pulse in winding 24 or approximately 2025% extra output efficiency.

Whereas in FIGS. 1, 2, and 3 the circuit is grounded collector an additional modification is shown in FIG. 4 which illustrates a common emitter circuit. This configuration permits grounding of the primary inductance 63 of an isolation transformer 62 while the secondary 65 is floating. An additional advantage resides in the retention of the conventional condenser 68 across the contacts 28. As a result with the insertion of a simple three position switch either the conventional ignition system or the new transistorized system may be operated should maintenance or repair of any components be necessary. A diode 50 may be incorporated for improved isolation of transformer 62 from transformer 22 by means of conductor 59. A base current limiting resistor 66 is incorporated together with a resistor 64 between the base 38 and emitter 42.

The transformer 62 by means of grounding of the primary inductance permits the secondary to be returned to any point in the circuit at other DC voltages for highest efficiency. During the on time with the points closed the secondary voltage in transformer 62 adds to the reverse current when the transistor is non-conductive thereby increasing the current seen by the primary inductance 20 of the ignition transformer.

If the diode St) is omitted the current flowing during on time through the primary Winding 20 is added to the current fiowiu through resistor 45 in determining the total current in primary 63 of transformer 62. This provides the boost effects previously discussed for FIG. 3.

Many other modifications in conductive coupling of the parallel inductance with the ignition power transformer are within the concept of the invention to adapt to any retrofit application in electrical high voltage generation circuits or to improve systems incorporating the principles described. The specific embodiments shown and described herein are therefore intended to be illustrative only of the broadest aspect of the scope and tenor of the invention as set forth in the appended claims.

What is claimed is:

1. A current transfer electrical ignition system comprising:

a direct current voltage source having two terminals one of which is grounded;

a first circuit loop including serially connected to the ungrounded terminal lead, a resistor, power transformer and high voltage load;

a shunt circuit loop including a serially connected resistor and inductance conductively connected in parallel to the resistor and transformer primary winding in said first circuit loop;

pulse generation means;

transistor amplifier means having an input circuit connected to said pulse generation means and an output circuit serially connected to the parallel inductance in said shunt circuit loop;

unidirectional current control means serially connected between the shunt circuit parallel inductance and transformer primary winding;

said amplifier means being alternately conductive and non-conductive upon opening and closing of said pulse generation means to store energy in the shunt circuit loop when said amplifier means is conductive and transfer the stored energy to the transformer primary winding when said amplifier means is nonconductive.

2. An ignition system according to claim 1 wherein said inductance comprises a choke coil.

3. An ignition system according to claim 1 wherein said inductance is substantially equal to the inductance of the transformer primary winding in said first circuit loop.

4. An ignition system according to claim 1 wherein said inductance comprises a transformer having a primary to secondary winding ratio of 1:1.

5. An ignition system according to claim 1 wherein said inductance comprises a transformer having a floating primary winding and a primary to secondary winding ratio greater than 1:1.

6. An ignition system according to claim 1 wherein said inductance comprises a transformer having a grounded primary and floating secondary winding.

References Cited UNITED STATES PATENTS 8 Neapolitakis. Kuykendall. Loomis. Mieras. Walters 123148 McKendry. Hutson. Morrison. Raybin 315-209 LAURENCE M. GOODRIDGE, Primary Examiner.

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