US3431901A - Electronic ignition circuit - Google Patents

Description

March 11, 1969 w. P. ROGERS ELECTRONIC IGNITION CIRCUIT Filed Sept. 28, 1966 INVENTOR.

WILLIAM PAUL ROGERS BY ATTORNEYS United States Patent 3,431,901 ELECTRONIC IGNITION CIRCUIT William Paul Rogers, 200 W. Merchant Sh, Audubon, NJ. 08106 Filed Sept. 28, 1966, Ser. No. 582,572 U.S. Cl. 123-148 Int. Cl. F02p 1/00; H05b 41/36 4 Claims ABSTRACT OF THE DISCLOSURE Background of the invention This invention relates to electronic ignition systems, and particularly to electronic circuits for adaptation to ignition systems for internal combustion engines for the purpose of improving their performance or reliability.

Various apparatuses have been proposed for effecting the production of an electric spark to ignite the fuel-air mixture in internal combustion engines. Among the various systems, the systems involving the use of an induction coil to produce a high volt-age spark are the most prevalent.

The Kettering system is the most common of the systems using induction coils. In it, a pair of contacts or points are connected between a source of current and the primary Winding of an induction coil. These points are opened and closed mechanically by a cam. When closed, they permit current to build up in the primary of the coil, and when they are opened, the energy stored in the primary causes a high voltage to be induced in the secondary winding of the coil to produce a spark.

In the Kettering system, the amount of energy which can be stored in the coil is limited because heavy currents cause severe damage to the points. Typical currents which can be handled by the points without causing rapid deterioration are of the order of four to six amperes. For better performance of the engine, however, it may be desired to operate the primary at considerably heavier current values.

Even at low current values, in the Kettering system, deterioration of the points is rapid, and they must be replaced quite often. For this reason, many modifications have been proposed for solving the problem of point damage. In the majority of these proposals, an electronic switching means, for example, a transistor, is inserted in the circuit delivering current to the primary of the coil, and is controlled by the opening and closing action of the cam-operated points. Since little current is needed to control the operation of the electronic switching device, the points need only carry a comparatively small current, and their life is greatly extended.

The points in most automobile engines are opened and closed under the operation of a cam having multiple lobes. This cam is ordinarily part of the distributor drive shaft or is splined or otherwise suitably fixed to the distributor shaft. The shape of the cam is ordinarily very symmetrical. In an eight-cylinder engine, for example, a cross-section of the cam taken on a plane perpendicular to its axis of rotation is usually in the form of a regular octagon with its corners slightly rounded. The points are opened by the lobes of the cam, and are permitted to be closed by the depressions of the cam. Because of the configuration of the cam, only a limited amount of time is available for the building up of current in the primary of the coil. Current is only delivered to the primary during approximately one-half the time interval between sparks. Ideally, the points should be closed during almost the entire interval between sparks, and opened only momentarily. Such an operation would permit significantly more energy to be stored in the primary, and hence, a more intense spark would be produced. The limitation to the amount of energy which is able to be stored in the primary becomes most apparent when an engine is operated at high speeds since the time between successive sparks is quite short, and, the inductance of the primary limiting the rate of current buildup, the current flowing through the primary may be considerably smaller than maximum at the time of current interruption.

While the problem of point deterioration is effectively solved by the inclusion of electrical switching means in the Kettering system, the limitation to the stored energy in the primary is a problem common to the basic Kettering system, and to the Kettering system including the various electronic modifications. The effective dwell time can be increased by eliminating the points and cam and substituting more complex devices, for example, photoelectric or magnetic pick-ups to sense the proper time at which the spark is to occur. These systems require extensive modifications to the ignition system for their installation, and are, for the most part, prohibited by their high cost and unreliability. Even in these systems, however, since timing is controlled by the engine shaft, whatever switching is involved requires appreciable angular movement and therefore an appreciable portion of the interval between sparks.

Summary of the invention The present invention, is applicable to the present ignition systems without extensive modifications, and can be installed in place of a Kettering ignition system easily. It can be used in conjunction with ignition systems involving photoelectrically or magnetically operated timing means to improve their performance. The system of the present invention overcomes both of the limitations previously mentioned as inherent in the Kettering ignition system. In fact, various already existing switching means can be modified in accordance with this invention to produce the desired results. In short, in this invention the opening of the points to produce a spark is sensed, and a switching means is made to short-circuit the points almost immediately following their opening so that, in effect, the circuit controlled by the points is opened only momentarily. As a result, current is delivered to the primary of the coil during nearly the entirety of the interval between sparks. In this invention, the points only carry a small current, and, as a result, their life is greatly extended.

An object of this invention, therefore, is to provide an electronic ignition circuit for internal combustion engines which produces an intense spark even at high engine speeds, and which is extremely simple in construction, and which may be adapted without extensive modifications to already existing ignition systems.

Brief description 0 the drawings FIGURE 1 is a schematic diagram showing a first embodiment of the invention;

FIGURE 2 is a schematic diagram of a second embodiment of the invention; and

FIGURE 3 is a schematic diagram of a third embodiment of the invention.

Description of the preferred embodiments Referring to FIGURE 1, a battery 2 is shown, which may be an automobile storage battery included in the usual charging system which need not be shown. Battery 2 is connected to charge capacitor 4 through a resistor 6. The negative side of battery 2 is connected to ground. The positive side of capacitor 4 is connected to the base of transistor 8 through resistor 10, and is connected to the emitter of transistor 8 through diode 12. A pair of conventional points 14 are shown connected at one side to ground, and at the other side to the base of transistor 8 through resistor 16. The collector of transistor 8 is connected through the primary 18 of induction coil 28 to ground, and a capacitor 22 is connected across primary 18. The Zener diode 24 and capacitor 26 are connected in parallel between the emitter and collector of transistor 8, and a resistor 28 is connected between the emitter of transistor 8 and ground.

One side of the secondary winding 30 of induction coil 20 is connected to ground, and the other side is connected to distributor rotor 32. Distributor contacts 34 (which normally form part of the distributor cap) are each connected to a spark plug 36. Element 38 of the spark plug is connected internally to line 40 which leads to the distributor contacts, and element 42 of the spark plug is grounded through the engine block (not shown). A spark plug is provided for each distributor contact.

A silicon controlled rectifier 44 is connected across points 14 with its cathode connected to the ground side. A silicon controlled rectifier will be referred to hereafter in this specification as an SCR. The cathode of diode 46 is connected to the gate of SCR 44, and its anode is connected to ground. Diode 48 has its cathode connected to the gate of SCR 44, and its anode connected through Zener diode 50 to the ungrounded side of primary winding 18.

The operation of the circuit of FIGURE 1 will first be described as it might be with elements 44, 46, 48 and 50 eliminated and their connections open-circuited, under which conditions the circuit would be conventional. When points 14 are closed, there is sufficient base current in resistor 16 to cause transistor 8 to be saturated. Capacitor 4 prevents destruction of components which would otherwise be caused by transient voltages occurring in the supply circuitry. It is charged by battery 2 through resistor 6 when the points are open, and discharges through diode 12, and through transistor 8, and through primary 18 to the potential across these elements, aiding the building of primary current. The current in primary 18 continues to build up until points 14 open. At this time, transistor 8 is cut off. Diode 12 aids the points in causing transistor 8 to cut off suddenly since it provides a bias between the base and emitter of transistor 8 due to its forward voltage drop. The current in primary 18 of induction coil 20 is suddenly interrupted, and, as a result, the magnetic field collapses so that a high voltage pulse is produced in secondary 30. This pulse is conducted through the distributor rotor 32, and through a distributor contact 34 to produce a spark at the gap formed between elements 38 and 42 in a spark plug. When points 14 are again closed under the action of their associated cam, transistor 8 is again saturated, and the cycle is repeated. In the operation just described, the period between the occurrence of a spark and the closure of the points is a large part of the operating cycle of the circuit. As stated this has been a normal type of operation of one form of transistorized ignition system.

The circuit operates similarly when elements 44, 46, 48 and 50 are included, in accordance with the present invention, except for the following:

When the points open, a transient condition occurs in which, due to the self-inductance of the primary, capacitor 22 acquires a charge with its lower terminal positive and its upper terminal negative. At the same time the capacitor 26 charges with its upper terminal positive and its lower terminal negative, and the charge is limited by the breakdown voltage of Zener 24 so that the transistor is protected against an excessive voltage. Concurrently with this transient and continuing thereafter, the operation of consequence occurs. When the spark occurs, the voltage in primary 18 increases toward positive, and after the spark extinguishes, the ringing voltage causes capacitor 22 to become charged positively, the energy charging capacitors 22 being the residual energy remaining in the induction coil after completion of the spark. The charge on capacitor 22 builds up until the voltage drop across Zener diode 50 reaches its breakdown potential at which time a positive pulse is delivered through Zener diode 50 and diode 48 to the gate of SCR 44. As a result, SCR 44 conducts and causes transistor 8 again to become saturated (the base becoming connected to ground through resistor 16 and the SCR), and to conduct current to primary 18. SCR 44 by-passes points 14 while they are still opened, and, as a result, current in primary 18 begins building up before points 14 close, and can therefore build up to a higher level to produce a higher voltage in the secondary 30 of induction coil 20 when the next interruption oocursrWhen points 14 again close, SCR 44 becomes unlatched, and when the points open, the SCR is non-conductive until its gate again receives a positive pulse as described. In the circuit shown in FIGURE 1, the positive pulse is received at the gate of SCR 44 just after completion of the spark. Diode 46 reestablishes normal SCR condition, while isolating positive gating pulses from ground. Zener diode 50 prevents the positive voltage which exists at the collector of transistor 8, while it is conducting, from triggering the SCR.

Referring to FIGURE 2, the construction is the same as that of FIGURE 1 except that SCR 52, which is connected across points 14 has its gate connected through diode 54 and through diode 56 to ground. A capacitor 58 is connected between the junction of diodes 54 and 56 and the ungrounded side of primary 18.

In the operation of the circuit of FIGURE 2, as soon as points 14 are opened, transistor 8 is cut off, and the ungrounded side of primary 18 becomes negative. Capacitor 58 is charged through diode 56 at this time so that its side connected to the junction of diodes 56 and 54 is positive with respect to its side connected directly to the ungrounded side of primary 18. At the initiation of the spark, as the voltage at the ungrounded side of the primary becomes less negative, the junction of diodes 54 and 56 is forced positive with respect to ground, and a positive pulse is passed through diode 54 by the discharge of capacitor 58 to trigger the SCR. As in the circuit of FIGURE 1, transistor 8 immediately becomes conductive, and current begins to build up in primary 18 almost immediately after points 14 open. In the circuit of FIGURE 2, the positive gating pulse is produced just after initiation of the spark.

In the circuit of FIGURE 3, points 14 are by-passed by SCR 60, the gate of which is connected through diode 62 to one side of a secondary winding 64 of induction coil 66. The opposite side of winding 64 is grounded. Induction coil 66 is of a special construction in that it has a primary winding 68 and two secondary windings, 64 and 70 respectively. Primary winding 68 is connected between the collector of transistor 8 and ground, and secondary winding 70 has its ungrounded side connected to deliver a high voltage pulse to rotor 32 of the distributor.

In operation, the circuit of FIGURE 3 is similar to the circuits of FIGURES 1 and 2 except that the gating pulse for SCR 60 is derived from a separate winding of the induction coil 66. When breaker points 14 open, transistor 8 immediately becomes cut off, and current in primary winding 68 tends to charge capacitor 22 to a. negative potential. At this time, a spark is produced at the gap of a spark plug 36. Capacitor 22, being charged negatively, subsequently produces a current in the opposite direction in primary winding 68. Secondary Winding 64 is wound in such a direction that, at this time, a positive pulse is delivered from it through diode 62 to the gate of SCR 60 to cause SCR 60 to conduct. When SCR 60 begins to conduct, transistor 8 immediately be comes saturated and current is restored to primary winding68.

In each of the circuits described, the breaker points need only carry a very small current, and consequently, they may be used over long periods of time with great reliability. While the use of a transistor or other electronic switching device to carry current to the primary from the source is desirable for the purpose of preventing excessive deterioration of the breaker point, the breaker points or other equivalent switching means may be used to carry full primary current, and an SCR may be connected across the points and controlled to shunt the points while they are open immediately following the occurrence of a spark.

The primary advantage achieved by this invention is that an engine provided with an ignition circuit constructed in accordance with the invention will operate more efiiciently at high rotational speeds since an intense spark is produced over a wide range of speeds. Each of the circuits described may be installed in an engine originally provided with a standard Kettering ignition system with a minimum of difliculty. In the case of the circuit of FIGURE 3, it would be ordinarily necessary to replace the original induction coil with a coil having a separate secondary winding.

It will be apparent that various modifications can be made to the construction of the invention without departing from its scope as defined in the following claims.

What is claimed is:

1. An ignition system for an internal combustion engine comprising an induction coil having a primary winding having a shunt capacitance and a secondary winding, means providing a spark gap connected across said secondary winding, a source of current, switching means controlled by said engine to assume alternately opened and closed conditions, means delivering current to said primary winding when said switching means is in a closed condition and interrupting delivery of current to said primary Winding when said switching means is in an opened condition to produce a spark in said spark gap, a gate-triggered semiconductor avalanche device connected in shunt with said switching means, and triggering means for said device energized by current in said primary winding sensed in response to discharge of the secondary to cause said device thereafter to become conductive upon attainment of a predetermined condition in said primary winding following the initiation of the discharge at the gap and independent of the opening of the switching means.

2. An ignition system according to claim 1 in which said triggering means includes means connected between said primary winding and the gate of said avalanche device for triggering said avalanche device into conduction when the primary voltage reaches a predetermined value following the extinguishing of sparking current in said secondary Winding.

3. An ignition system according to claim 1 in which said triggering means includes a capacitor connected at one end to said primary winding, means maintaining a charge on said capacitor, and means delivering the charge on said capacitor to the gate of said avalanche device to trigger said avalanche device when the voltage across said primary winding reaches a predetermined value following the initiation of sparking current in said secondary Winding.

4. An ignition system according to claim 1 in which said triggering means includes an additional secondary winding on said induction coil and diode means connecting said additional winding to the gate of said avalanche device, said additional winding being wound, and said diode means being arranged in directions such that a gating impulse is delivered by said diode means to the gate of said avalanche device following the extinguishing of sparking current in said secondary winding.

References Cited UNITED STATES PATENTS 3,363,615 1/1968 Meyerle l23148 3,087,001 4/1963 Short et al. 123148 3,213,320 10/1965 Worrell 3l5209 3,273,014 9/1966 Gershen 3l5212 3,320,939 5/1967 Huntzinger et al. 123148 3,331,362 7/1967 Mitchell 123-l48 LAURENCE M. GOODRIDGE, Primary Examiner.

US. Cl. X.R.

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