US3861368A

US3861368A - Capacitive discharge ignition system for an internal combustion engine

Info

Publication number: US3861368A
Application number: US365919A
Authority: US
Inventors: Peter Dogadko
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1973-06-01
Filing date: 1973-06-01
Publication date: 1975-01-21
Anticipated expiration: 1992-01-21

Abstract

A capacitive discharge ignition system for an internal combustion engine includes first and second sets of charging and trigger coils, two capacitive discharge ignition circuit arrangements each including a charging capacitor and a silicon rectifier switch for discharging the charging capacitor and two ignition coils. The two charging coils provide a split power supply which charges the capacitor of the first ignition circuit arrangement to a predetermined voltage of a first polarity and a capacitor of the second ignition circuit arrangement to approximately the same voltage at an opposite polarity. The capacitors are charged in steps rather than all at once. Delay circuits coupled to the trigger coils of the first and second sets of coils shunt the third of a series of three pulses induced in the corresponding trigger coils to prevent the operation of a corresponding silicon controlled rectifier switch thereby avoiding premature discharge of the charging capacitors as well as the operation of the engine in reverse.

Description

United States Patent [191 Dogadko Jan. 21, 1975 CAPACITIVE DISCHARGE IGNITION SYSTEM FOR AN INTERNAL COMBUSTION Primary Examiner-Charles J. Myhre Assistant Examiner.loseph Cangelosi Attorney, Agent, or Firm-Vincent J. Rauner; Donald J. Lisa [57] ABSTRACT A capacitive discharge ignition system for an internal combustion engine includes first and second sets of charging and trigger coils, two capacitive discharge ignition circuit arrangements each including a charging capacitor and a silicon rectifier switch for discharging the charging capacitor and two ignition coils. The two charging coils provide a split power supply which charges the capacitor of the first ignition circuit arrangement to a predetermined voltage of a first polarity and a capacitor of the second ignition circuit arrangement to approximately the same voltage at an opposite polarity. The capacitors are charged in steps rather than all at once. Delay circuits coupled to the trigger coils of the first and second sets of coils shunt the third of a series of three pulses induced in the corresponding trigger coils to prevent the operation of a corresponding silicon controlled rectifier switch thereby avoiding premature discharge of the charging capacitors as well as the operation of the engine in re- 8 Claims, 3 Drawing Figures Paten ted Jan. 21, 1915 3,861,368

2 Shoots-Shoot- 8 CHARGING COIL l6 TRIGGER COIL l8 CHARGING COIL 2O TRIGGER COIL 22 CHARGING CAPACITOR CHARGING CAPACITOR l4 FIRING I I CYL#2 CAPACITIVE DISCHARGE IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE BACKGROUND This invention relates generally to vehicle ignition systems and more particularly to capacitive discharge ignition systems.

With conventional capacitive discharge ignition sys tems commonly used with internal combustion engines, such as, for example, two cylinder/two cycle marine engines, there is normally provided a charging and trigger coil. A magnet member mounted on the engine flywheel is rotated past the coils in succession to produce pulses for charging the capacitor of the system and for triggering circuitry for discharge thereof. As the magnet approaches each of the coils, a first polarity pulse is produced and as the magnet moves away from each of the coils an opposite polarity pulse is produced. Conventionally, rectifying circuitry is used to half wave rectify the second polarity pulses produced by the charging coil and as such only the first polarity pulses actually are used for charging the capacitor.

In addition to the above, it is desirable with small engines of the outboard marine type, to utilize as little space as possible in the engine housing to accommodate the capacitive discharge ignition system elements. Thus, the charging coils and trigger coils are normally placed as close together as is possible adjacent the flywheel of the engine. Often, however, close placement of the coils causes a premature operation of the trigger circuitry used for discharging the ignition capacitor and can in some instances cause reverse operation of the engine. This may damage the engine. Normally, no preventative measuresare taken to prevent the above from occurring and a quick turn off of the engine is relied upon.

SUM MARY Accordingly, it is a primary object of the present invention to provide a new and improved capacitive discharge ignition system for use with an internal combustion engine which includes a charging and trigger coil arrangement and which makes use of both first and secnd polarity pulses produced for charging the ignition capacitor means of the system.

It is another object of the present invention to provide a capacitive discharge ignition system of the above described type which can be made compact and wherein placement of the charging and trigger coils can be as desired without fear of premature operation of the triggering circuit which discharges the capacitor and/0r reverse engine operation.

It is yet another object of the present invention to provide a capacitive discharge ignition system which includes delay circuitry for preventing premature operation of the discharge triggering circuitry and reverse operation of the engine.

It is still another object of the present invention to provide a capacitive discharge ignition system which is efficient and reliable in operation and relatively inexpensive to produce.

It is also another object of the present invention to provide a capacitive discharge ignition system which is especially useful with a two cylinder/two cycle engine, such as, for example, and outboard marine engine.

Briefly, a preferred embodiment of the capacitive discharge ignition system according to the invention includes first and second sets of charging and trigger coils, two capacitive discharge ignition circuit arrangements each including a charging capacitor and a silicon controlled rectifier for discharging the charged capacitor and two ignition coils. The two charging coils provide a split power supply which charges the capacitor of the first ignition circuit arrangement to a predetermined voltage of one polarity and the capacitor of the second ignition circuit arrangement to approximately the same voltage at an opposite polarity. The capacitors are charged in steps rather than all at once as is conventionally done.

Delay circuits coupled to the trigger coils of the first and second sets of coils prevents premature operation of the silicon controlled rectifiers as well as the operation of the engine in reverse.

DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a schematic diagram of a preferred embodiment of the capacitive discharge ignition system according to the invention;

FIG. 2 is an enlarged, side view of a flywheel/magneto arrangement used in conjunction with the capacitive discharge ignition system illustrated in FIG. 1; and

FIG. 3 is a diagrammatical representation of the voltage pulses, etc., provided by the capacitive discharge ignition system of FIG. 1.

DETAILED DESCRIPTION Referring now to the drawings in greater detail wherein like numerals have been employed throughout the various views to designate similar components, there is illustrated in FIG. 1 a capacitive discharge ignition system 10 according to the invention.

The system includes first and

second circuit portions

13, 15, respectively, each of which includes an

ignition capacitor

12, 14, respectively, a pair of charge and trigger coils l6, l8 and 20, 22, respectively, and a semiconductor switch for triggering the discharge of the capacitor, herein taking the form of silicon controlled rectifiers (SCRs) 24, 26, respectively. Also, two

ignition coil arrangements

28, 30 are provided, each coil arrangement being coupled to a spark plug (not shown) in an internal combustion engine, herein a two cycle, two cylinder engine, at

output points

32, 34 of the circuit portions, respectively.

In addition to the above, there is provided in each of the circuit portions of the capacitive discharge ignition system 10, a

delay circuit

36,38, respectively, for preventing premature triggering of the discharge of the

capacitors

12, 14, respectively, which may otherwise occur due to the close placement of the charging and trigger coils of the system.

Because the circuit portions l3, 15, are essentially the same, the connections of circuit portion 13 only will be described. Circuit portion 15 is connected in a similar manner.

Referring to circuit portion 13, one side of charging coil 16 thereof is connected via

leads

40, 41 and diode 42 to junction 44 at one side of ignition capacitor 12. The capacitor is connected at junction 46 via lead 48 to the opposite side of the coil 16.

Trigger coil 18 is connected at one side over lead 50 and through diode 52 to the gate electrode 54 of the SCR 24. The cathode 55 of the SCR is connected back effectively to junction 44. The anode 56 of the SCR is connected to junction 58 whereat a return lead 60 connects back to the opposite side of the coil 18. The primary 62 of the ignition coil arrangement 28 is also connected to junction 58. The opposite side of the ignition coil is connected to lead 48. The secondary 64 is also connected at one side to lead 48 and at the opposite side to output point 32.

The delay circuit 36 of circuit portion 13 includes a capacitor 66 connected in series with a diode 68 between

leads

50, 60. The base 70 of a transistor 72 is connected through a resistor 74 to a junction point 76 between the diode and capacitor 68, 66. The emitter and collector electrodes, 78, 80, respectively, of the transistor are connected to leads 50, 60, respectively.

Diodes

82, 84 interconnect the

circuit portions

13, 15 for proper operation thereof.

FIG. 2 illustrates one embodiment of a flywheel arrangement for the capacitive discharge ignition system of FIG. 1. Charging and

trigger coil pair

16, 18 is wound oppositely on the center leg 86 of an E-shaped magnetizable core structure 88.

Coils

20, 22 are wound oppositely about the center leg 90 of a similar E-shaped core 92. The coil pairs and core structures are placed at 180 with respect to each other on the flywheel arrangement.

A magnet assembly 94 is provided in the embodiment shown which includes a permanent magnet 96 and a pair of

pole pieces

98, 100 on either side thereof for providing a three pulse or trimary output waveform across the charging and

trigger coils

16, 18 and 20, 22, respectively, as the magnet moves by (See FIG. 3).

The operation of the capacitive discharge ignition system of FIG. 1 is as follows:

As the magnet assembly 94 is initially moved past

coils

16, 18, a first polarity pulse is produced across coil 18, herein a positive polarity pulse (See FIG. 3), which is applied to the gate electrode 54 of SCR 24 via diode 52. Because, initially no charge is present on capacitor 12, the conduction of the SCR has no effect.

Simultaneously with the production of a positive going pulse across coil 18, a negative going pulse of a predetermined magnitude is produced across charging coil 16 to apply a first step charging current to capacitor 14 of the polarity shown in FIG. 1. The-path for application of the charge is via lead 48, through capacitor 14 and via diode 82. It should be noted, that the capacitors l2, 14 are charged in opposite directions.

The second pulse of the trimary pulses produced across charging coil 16 by the movement of magnet assembly 94

past coils

16, 18, is of a greater magnitude than pulses one and three produced thereacross because of increased flux flow through the E-shaped core structure (See FIG. 2). The second pulse of a positive polarity and increased magnitude is produced across coil 16 simultaneously with the negative pulse of a lesser magnitude produced across coil 18. The higher voltage pulse across charging coil 16 charges capacitor 12 in the direction shown to a first level (See FIG. 3,

' capacitor 12) and the voltage across trigger coil 18 is negative bias to the base of transistor 72 to operate the pulses produced thereacross. Thus, the pulse across coil 16 provides a second step charge to capacitor 14 to charge the latter to a higher negative voltage (See graph, FIG. 3). The positive pulse produced across trigger coil 18, however, is shunted by the transistor 72 which is in a state of conduction, thereby preventing SCR 24 from operating to conduction and from prematurely discharging capacitor 12.

The magnet assembly thereafter passes about the flywheel structure and functions similarly to step charge capacitor 12 to a higher voltage level and likewise to charge capacitor 14 to a predetermined voltage level of opposite polarity as shown in FIG. 3.

As the magnet assembly revolves back to pass by coils l6, l8, SCR 24 is now operated to conduction since the charge on capacitor 66 has dissipated and transistor 72 is turned off. The SCR 24 is actuated by the first positive polarity pulse produced across trigger coil 18 (See firing curve, FIG. 3). The operation of SCR 24 discharges capacitor 12 into ignition coil arrangement 28 providing a current to the spark plug (not shown) connected at output point 32 of the secondary 64 of the coil arrangement. After firing the spark plug, the cycle repeats itself.

Movement of the magnet assembly past the

coils

20, 22, thereafter fires capacitor 14 through ignition coil arrangement 30 to provide current to a spark plug (not shown) connected at the output point 34.

The delay in firing the silicon controlled rectifiers provided by shunting the trigger pulses through transistor 72 and its counterpart in circuit portion 15 of the capacitive discharge ignition system according to the invention, prevents premature discharge of the capacitors and prevents the engine being controlled by the ignition system from operating in reverse.

If the rotation of the engine should be reversed, as is often the case with outboard marine and the like engines, the polarities produced in the charging and trigger coil pairs as the magnet assembly 94 passes thereby, is reversed also. The

capacitors

12 and 14 are charged however as above, but no triggering of the

SCRs

24, 26 takes place since a first negative pulse produced across the trigger coils activates the delay circuits by charging the capacitors included therein to operate the transistors of the circuits. Every successive pulse of positive polarity will thereafter be shunted to prevent the SCRs from firing, thus precluding the engine from operating in the reverse direction.

While a particular embodiment of the invention has been shown and described, it should be understood that the invention is not limited thereto since many modifications may be made. It is therefore contemplated to cover by the present application any and all such modifications as fall within the true spirit and scope of the appended claims.

I claim:

1. A capacitive discharge ignition system for an internal combustion engine having at least two cylinders including in combination: first and second charging capacitors, first and second means for charging said first and second charging capacitors, each said first and second charging means providing pulses of first and second polarities, said first charging means being connected electrically to said first charging capacitor and charging the latter when providing pulses of a first polarity and said second charging means being connected electrically to said second charging capacitor and charging the latter when providing pulses of a second polarity, first and second ignition coil means one for each cylinder coupled electrically to said first and second charging capacitors, respectively, first and second trigger means connected to said first and second capacitors, respectively, and to said first and second ignition coil means, respectively, for selectively discharging said first and second capacitors, respectively, into a corresponding one of said first and second ignition coil means and first means electrically interconnecting said first charging means with said second capacitor and second means electrically interconnecting said second charging means with said first capacitor, said second capacitor being charged by second polarity pulses from said first charging means and said first capacitor means being charged by first polarity pulses from said second charging means.

2. A capacitive discharge ignition system as claimed in claim 1 wherein said first and second interconnecting means include oppositely poled semiconductor diodes.

3. A capacitive discharge ignition system as claimed in claim 1 wherein said first and second charging means include first and second charging coils, respectively, wherein said first and second trigger means include first and second trigger coils, respectively, wherein said system further includes an arrangement including magnet means rotatable in accordance with the operation of said engine along a predetermined closed loop path, said first charging and trigger coils being mounted at a first location in cooperating relation with respect to said arrangement adjacent the path of said magnet and said second charging and trigger coils being mounted in cooperating relation with respect to said arrangement at a second location spaced from said first location, along said path, the movement of said magnet past said first charging and trigger coils inducing first and second polarity pulses therein, respectively, and movement of said magnet past said second charging and trigger coils inducing second and first polarity pulses therein, respectively, the first polarity pulses in said first charging coil charging said first capacitor to a predetermined voltage level of a corresponding polarity, the second polarity pulses in said second charging coil charging said second capacitor to a predetermined voltage level of a corresponding polarity, said second polarity pulses in said first charging coil charging said second capacitor to a higher voltage level of a corresponding polarity and said first polarity pulses in said second charging coil charging said first capacitor to a higher voltage level of a corresponding polarity.

4. A capacitive discharge ignition system as claimed in claim 3 further including a first magnetizable core means on which said first charging and trigger coil means are wound in opposite directions and second magnetizable core means on which said second charging and trigger coil means are wound in opposite directions, wherein said magnet means is movable about a circular path and wherein said first magnetizable core means is positioned about said path from said second magnetizable core means.

5. A capacitive discharge ignition system as claimed in claim 3 wherein each said trigger means further includes switch means coupled electrically to a corresponding one of said capacitors, each said switch means being operated to a closed state in response to a pulse at a corresponding one of said trigger coils, thereby to discharge a corresponding capacitor into a respective ignition coil means, and wherein said system further includes first and second delay circuit means, each said delay circuit means being coupled to a corresponding one of said trigger coils and switch means, each said delay circuit means being operated for a given time period in response to a predetermined pulse at a corresponding one of said trigger coil means thereby preventing the operation of a corresponding one of said switch means.

6. A capacitive discharge ignition system as claimed in claim 5 wherein the movement of said magnet means past said first charging and trigger coils and said second charging and trigger coils, respectively, induces a series of three pulses in the last-mentioned coils, respectively, the first and third pulses being of a common polarity, wherein the second of said three pulses induced in said first and second charging coils charges corresponding ones of said first and second charging capacitors, wherein the first and third pulses induced in said first and second charging coils charges the other of said first and second charging capacitors, wherein the first of said three pulses induced in said first and second trigger coils operates corresponding switch means to discharge a corresponding one of said capacitors and wherein the second of said three pulses induced in said first and second trigger coils operates a corresponding one of said delay circuit means, whereby the third of said three pulses induced in said first and second trigger coils is prevented by a corresponding one of said delay circuit means from reoperating a corresponding one of said switch means.

7. A capacitive discharge ignition system as claimed in claim 6 wherein each said delay circuit means includes capacitive means and a transistor operatively connected thereto, each said transistor being coupled electrically with respect to a corresponding one of said switch means, wherein the second of said three pulses induced in each said trigger coil charges a corresponding one of said capacitors in said respective delay circuit means thereby to bias said transistors to a state of conduction to shunt the third of said three pulses induced in said trigger coils, respectively, for preventing operation of said corresponding switch means.

8. A capacitive discharge ignition system as claimed in claim 6 wherein the second of said series of three pulses induced in said first and second charging coil means is of a magnitude considerably greater than that of said first and third pulses.

Claims

4. A capacitive discharge ignition system as claimed in claim 3 further including a first magnetizable core means on which said first charging and trigger coil means are wound in opposite directions and second magnetizable core means on which said second charging and trigger coil means are wound in opposite directions, wherein said magnet means is movable about a circular path and wherein said first magnetizable core means is positioned 180* about said path from said second magnetizable core means.