US3884207A

US3884207A - Magneto-generator ignition system

Info

Publication number: US3884207A
Application number: US394636A
Authority: US
Inventors: Iii Andrew Kuehn
Original assignee: SYSTEMATICS Inc
Current assignee: SYSTEMATICS Inc
Priority date: 1973-09-06
Filing date: 1973-09-06
Publication date: 1975-05-20
Anticipated expiration: 1992-05-20

Abstract

An energy storage and discharge control circuit for use with the ignition system of an internal combustion engine. During the time interval when the breaker points are opening, a capacitor is charged with a voltage through a polarity determining diode network. When the voltage has increased to a certain level, a semiconductor switch is turned on, allowing the charge on the capacitor to be directed through the primary winding of the ignition coil to increase the voltage induced in the secondary of the coil and to control the voltage-time characteristic of the energy impulse which is applied to the engine''s spark plug.

Description

United States Patent [191 Kuehn, III

[4 1 May 20, 1975 1 1 MAGNETO-GENERATOR IGNITION SYSTEM [75] Inventor: Andrew Kuehn, 111, St. Paul, Minn.

[73] Assignee: Systematics, Inc., St Paul, Minn.

[22] Filed: Sept. 6, 1973 [21] Appl. No.: 394,636

[52] US. Cl.... 123/148 R; 123/149 R; 315/209 CD Primary ExaminerCharles .1. Myhre Assistant ExaminerRonald B. Cox

[57] ABSTRACT An energy storage and discharge control circuit for use with the ignition system of an internal combustion engine. During the time interval when the breaker points are opening, a capacitor is charged with a voltage through a polarity determining diode network. When the voltage has increased to a certain level, a semiconductor switch is turned on, allowing the charge on the capacitor to be directed through the primary winding of the ignition coil to increase the voltage induced in the secondary of the coil and to control the voltage-time characteristic of the energy impulse which is applied to the engines spark plug.

2 Claims, 4 Drawing Figures MAGNETO-GENERATOR IGNITION SYSTEM BACKGROUND OF THE INVENTION This invention relates generally to an improvement in the ignition system of internal combustion engines, particularly multi-cylinder engines, such as are commonly employed in snowmobiles and other vehicles, and more specifically to a novel ignition energy storage and discharge network for producing an energy pulse of predetermined characteristics which improves the performance of such an engine.

A well-known form of ignition circuit for a multiple cylinder, two-cycle internal combustion engine is the combination of a magneto-generator and ignition coil for developing a high tension voltage across the gap of a spark plug. The magneto-generator generally comprises a coil or combination of coils cooperating with one or more magnets mounted on a revolving flywheel. The movement of the magnets with respect to the coils induces a current therein. At a point in time of the compression phase of the operational cycle, which point is determined by the opening ofa set of cam operated breaker points, this current flow is suddenly diverted into the primary winding of the ignition coil, causing a high voltage to be induced in the secondary winding thereof and ultimately across the gap in the spark plug. The voltage is sufficiently high to break down the air/fuel mixture in the gap and produce a hot spark for ignition of the mixture present in the cylinder. In this conventionalsystem, a capacitor is connected in parallel with the breaker points to prevent sparking and attendant pitting of the points as well as to electrically tune the magneto-generator circuit to maximize the energy transfer to the spark plug.

The present ignition circuits suffer from several deficiencies. First, the time rate of increase of the high tension voltage is normally slower than desired for firing a spark plug, especially when the plug is partially fouled or shorted. In that condition, the somewhat slow voltage rise rate causes the plug to fire with less stored energy than desired in the secondary winding of the ignition coil, thus reducing the size of the initial capacitive discharge across the plug gap. Secondly, the presently available systems tend to allow a prolonged current flow through the plug gap following the initial breakdown which does not add appreciably to the ignition of the air/gas mixture. Further, because of the inductive nature of the ignition coil, the initial rise of voltage across the breaker points may be extremely rapid, limited only by the presence of the capacitor connected in parallel therewith, thus causing arcing or sparking at the points and attendant wear and pitting.

SUMMARY OF THE INVENTION The present invention obviates these deficiencies. In accordance with the essential features of the present invention, means are provided to temporarily store the energy which is being transferred from the magnetogenerator, and at a precise point in time determined by a solid-state switch, this stored energy is released into the primary winding of the ignition coil in the form of an energy pulse which has predetermined rise and fall time characteristics.

More specifically, the circuit of the present invention includes a capacitor connected in series between the coils of the magneto-generator and the primary winding of the ignition coil. A diode network is connected in circuit with the capacitor and the magneto-generator coil so that the capacitor will be charged with a predetermined polarity without the need for current to flow through the primary winding of the ignition coil. Then,

a solid-state discharge control circuit is provided which, when triggered on, permits a controlled current pulse to flow through the ignition coil for the purpose of inducing a high tension voltage across the gap of the spark plug.

It is accordingly an object of the present invention to provide an inexpensive circuit for improving and controllably modifying the operational characteristics of a conventional magneto-generator ignition system for an internal combustion engine, particularly with multiple cylinders.

Another object of the invention is to provide a circuit modification for improving the performance characteristics of such internal combustion engines.

Still another object of the present invention is to provide a simple, inexpensive electronic circuit which is easily installed and which improves the operating characteristics of such engines.

These and other objects of the invention will become apparent to those skilled in the art upon a study of the following detailed description of the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a block diagram representation of the preferred embodiment of the present invention;

FIG. 2 is an electrical schematic showing one arrangement for implementing the block diagram of FIG.

FIG. 3 is a diagram showing the waveform of the generated voltage and the affect of point closure thereon; and

FIG. 4 illustrates a suppression circuit suitable for use in the circuit of FIG. 2 for removing negative-going spikes which might cause off-cycle firing.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the block diagram of FIG. 1, there is shown a conventional ignition system for a twocylinder, two-cycle internal combustion engine incorporating the present invention. Specifically, there is shown enclosed by the dashed line box 10, the solidstate energy storage and discharge circuit which has been devised to improve the performance characteristics of such an ignition system.

The overall system includes a flywheel 12 which is secured to the drive shaft 14 and which is provided with a permanent magnet 16 integrally mounted therein, as is conventional. In close proximity to the periphery of the flywheel 12 there is positioned a pair of magnetogenerator coils I8 and 20, with one such coil being provided for each cylinder in the engine. When the permanent magnet 16 moves past these coils, an electrical current will be induced in the coils. Each of the coils l8 and 20 has one of its terminals connected in common to a grounded bus 22. In the circuit shown in FIG. 1, the circuit components positioned above this grounded bus 22 are associated with a first cylinder of a two cylinder engine (hereinafter referred to as cylinder A) and the circuit components located below the grounded bus 22 are associated with the second cylinder (hereinafter referred to as cylinder B).

Connected in parallel with the magneto-generator coil 18 between ground bus 22 and a conductor 24 is a set of breaker points 26 for cylinder A. Similarly, connected in parallel with the magneto-generator coil between the ground bus 22 and a conductor 28 is a second set of breaker points 30 associated with cylinder B of the engine. In each instance, breaker points or

contacts

26 and 30 are operated by a revolving cam (not shown) secured to the drive shaft as is conventional.

Points

26 and 30 operate in complementary fashion. In other words, when the breaker points 26 are open, points 30 will be closed, and vice-versa. In order to reduce arcing across the breaker points 26 upon opening, a capacitor 32 is connected between ground conductor 22 and the outer conductor 24. A second capacitor 34 is connected between ground bus 22 and conductor 28 for a similar purpose.

In prior art magneto-generator type ignition systems, the primary winding of the ignition coil (autotransformer) is connected directly in parallel with the breaker points between the grounded bus 22 and the

outer conductors

24 and 28. As long as the breaker points remain closed, the ,coils l8 and 20 are shorted and a relatively high circulating current flows in these coils. When the breaker points open, this circulating current will be diverted through the primary winding of the induction coil and will cause a relatively high voltage to be developed across the secondary winding thereof and applied across the gap of the spark plugs.

In FIG. 1, the ignition coil for cylinder A is identified by numeral 36 and that for cylinder B is identified by numeral 38. In implementing the present invention in a conventional ignition system, the

leads

24 and 28 normally connected to the

outer terminals

40 and 42 of the'

ignition coils

36 and 38 respectively are severed, as is the ground bus 22 which is connected to the common terminal 44 of the primary windings of

coils

36 and 38. Inserted in series between the conductor 24 and the terminal 40 is an energy storage device, here shown as capacitor 46. Similarly, a capacitor 48 is connected in series between the conductor 28 and the terminal 42 on transformer 38. A discharge control circuit 50, which is described more fully hereinbelow, is connected between the

conductors

24 and 28 at

junctions

52 and 54 respectively. Connected in parallel with the primary winding of ignition coil 36 is a polarity directing circuit 56. A similar circuit 58 is connected in parallel with the primary winding of the ignition coil 38.

The spark plug for cylinder A is connected across the secondary winding of ignition coil 36 and is shown in FIG. 1 at 60. Likewise, the spark plug associated with cylinder B is connected across the secondary winding of ignition coil 38 and is shown at 62.

OPERATION FIGURE 1 In order to understand the operation of the circuit of FIG. 1, let it be assumed that the breaker points 26 are just beginning to open and that the breaker points 30 are closed. Immediately prior to the opening of the breaker points 26, the current induced in the magnetogenerator coil 18 had been circulating through the points 26 and no current was being delivered to the other portions of the circuit associated with cylinder A. Upon opening of the breaker points 26, this circulating current in coil 18 is diverted through conductor 24, capacitor 46 and the polarity directing device 56 and through ground conductor 22 back to the grounded terminal of the coil of magneto-generator 18. The affect of this current is to cause the capacitor 46 to become charged with a voltage having the polarity as indicated by the markings adjacent thereto. As the capacitor 46 is initially charging, the discharge control circuit 50 acts as an open circuit whereas the polarity directing device 56 acts as a short circuit, preventing any current from flowing into the primary winding of the ignition coil 36.

The discharge control circuit has a characteristic such that when the voltage or charge developed on the capacitor 46 reaches a predetermined level, the discharge control circuit will be rendered conductive. Once the discharge control circuit 50 is conducting, a current will flow from the positively marked terminal of capacitor 46, through the discharge control circuit 50, through conductor 28, through the closed points 30 associated with cylinder B, through the ground conductor 22 to the junction 44 and thence through the primary winding of induction coil 36 and the junction 40 back to the negatively marked terminal of the capacitor 46, thus discharging the capacitor. The current flowing through the primary winding of the ignition 36 induces a very high voltage across its secondary winding caus' ing the air/gas mixture existing between the gap in the spark plug 60 to break down capacitively and ignite the fuel mixture within the cylinder. It is to be noted that during the time that the capacitor 46 is discharging, the polarity directing device 56 will be in a blocking condition such that all of the discharge current will be available to the primary winding of the transformer 36.

In a similar fashion, if it is now assumed that breaker points 30 are commencing to open and that the points 26 are closed, it will be seen that the circulating current from the magneto-generator coil 20 will be diverted through conductor 28, the capacitor 48, the polarity determining network 58, and the grounded bus 22 so as to cause the capacitor 48 to charge up in a direction indicated by the polarity markings thereon. When the charge on capacitor 48 exceeds a predetermined threshold determined by the characteristics of the discharge control circuit 50, the discharge control circuit 50 will be rendered conductive and the capacitor 48 will begin to discharge through circuit 50, conductor 24, points 26, ground bus 22, the primary winding of ignition coil 38 back to the negative terminal of the capacitor 48. The effect of this discharge current is to cause a substantial voltage to be developed across the secondary winding of the coil 38 so as to break down the air/fuel mixture in the gap of spark plug 62 associated with cylinder B and ignite the mixture within the cylinder.

Thus, it can be seen that by connecting the discharge control circuit 50 in circuit with the breaker points 26 and 30, only one such discharge control circuit is needed to implement the improved ignition system for a two-cylinder internal combustion engine.

Illustrated in FIG. 2, is one arrangement for implementing the system diagram of FIG. 1 with commercially available electronic components. In FIG. 2, the various circuit components described functionally in FIG. 1 have been given the same identifying numerals as utilized in FIG. 1. As is illustrated, the discharge control circuit 50 comprises a resistive voltage

divider including resistors

64 and 66 connected in series across the

conductors

24 and 28. Connected in parallel with the resistor 66 is a capacitor 68. The discharge control circuit also includes a semi-conductor switching device, here shown as a Triac 68. The control or gate electrode of the Triac 68 is connected to a junction 70 between the

resistors

64 and 66. The input and output electrodes of the Triac 68 are connected in series with an inductor 72 between the

conductors

24 and 28. A pair of oppositely poled diodes 74 and Y76 are connected together across the inductor 72 and the common terminal thereof is connected to the center tap on the inductor 72.

The

polarity directing circuits

56 and 58 each include a series combination of a resistor and a diode. More particularly, the anode of a diode 78 is connected by a conductor to the junction point 40, while the cathode thereof is connected through a resistor 80 to the ground bus 22. Similarly, the polarity directing network 58 includes a diode 82 having its anode connected by a conductor to the junction 42 and its cathode connected through a resistor 84 to a junction on the ground bus 22.

OPERATION FIGURE 2 The operation of the circuit of FIG. 2 will be considered with the situation assumption made that the Triac 68 is nonconducting and that the breaker points 26 have just opened whereas the breaker points 30 are closed. As was explained in connection with FIG. 1, upon opening of the points 26, the circulating existing in the magneto-generator coil 18 will be diverted through conductor 24, through capacitor 46, through the diode 78 and resistor 80 and through the ground bus 22 back to the ground terminal of the coil 18. With the breaker points 30 closed, the conductor 28 will be at ground potential and a voltage proportional to the voltage developing on capacitor 46 will appear at the junction point 70 of the voltage divider comprised of

resistors

64 and 66. Thus, the capacitor 68 connected in parallel with the resistor 66 will maintain this voltage and when the potential appearing at junction 70 exceeds the threshold value for initiating conduction in Triac 68, it will do so, causing a discharge current to flow from the capacitor 46 through the inductor 72, through the Triac 68, through conductor 28 and the closed breaker points 30 and thence through the grounded bus 22 to the junction 40 back to the negative terminal of the capacitor 46. Because of the manner in which the polarity directing diode 78 is poled, it blocks any current that might otherwise flow therethrough so that the capacitive discharge current will all flow through the primary winding of the ignition coil 36.

The purpose of the inductor 72 and the by-

pass diodes

74 and 76 is to limit the current surge that might otherwise flow through the Triac 68, thus protecting it from being damaged. In the case where cylinder A is being fired, only one-half of the inductance 72 is in circuit with the Triac 68, the other half being by-passed by the diode 76. When it is cylinder B that is being fired, again only one-half of the inductance 72 will be in circuit with the Triac 68 since diode 74 will serve as a by-pass for the other one-half of the inductance. The

diodes

74 and 76 when conducting permit current circulation through one-half of the inductor 72 to thereby allow any residual charge on capacitor 46 to be dissipated.

The voltage dividing networds 64 and 66 along with the capacitor 68 have an interesting affect on the discharge characteristics of the

energy storage capacitors

46 and 48. Because the charge on the capacitor 68 is related to the time constant C X (R ee/R R,,,,), the charging of the capacitor 68 lags behind that of the

capacitor

46 or 48, whichever one is being charged. When the engine is being cranked for starting or is running at a very low RPM, the release of energy from the coils of the magnetogenerator is lower than normal. Thus, the discharge of energy from the

capacitors

46 or 48 will take place at a lower-"voltage level since the time constant is less of a factor on following the charge rate. Thus, the discharge of energy from the

capacitors

46 or 48 will take place at a lower voltage level since the time constant is less of a factor on following the charge rate. Thus, the presence of a sufficient voltage to cause triggering is insured and provides a degree of timing retard, aiding in the ignition process at cranking. Once the engine RPM is at normal running or cruising speed, the charge rate of the

capacitors

46 and 48 stabilize, causing both a stabilization of timing advance and a higher stored voltage level prior to the triggering of the discharge control circuit.

Referring again to the

polarity determining circuits

56 and 58, depending upon which cylinder is being fired, one or the other will act as a low impedance circuit for the primary winding of the ignition coil being energized, thus allowing the discharge current to continue to flow in a unidirectional manner until the energy is completely transferred to the secondary winding of the ignition coil, thus completing the discharge period at the plug gap. The

resistors

80 and 84 can be chosen to restrict the period of discharge to any desired value.

Due to the continuing current flow from the coils l8 and 20 of the magneto-generator (depending upon which coil has its associated breaker points open), the Triac 68 remains in conduction to prevent a further transfer of energy to the ignition coil until the charge on the

capacitor

46 or 48 has been dissipated.

Various modifications may be made to the circuit of FIG. 2 depending upon the type of magneto-generator employed. More specifically, the embodiments of FIGS. 1 and 2 were described in connection with a magneto-generator arrangement which produced a positive voltage on the

outer conductors

24 and 28. If the magneto-generator employed was of the type producing a positive voltage on conductor 24 and a negative voltage on conductor 28, it would not be necessary to use a bidirectional current switching device such as a Triac but instead a unidirectional device such as a SCR could be used. Further, in this latter arrangement, it would be necessary to reverse the direction of the diode 82. If the magneto-generator employed was of the type to produce a negative voltage on both

conductors

24 and 28, again a bidirectional semiconductor switching device such as a Triac would be necessary, but in this instance each of the

diodes

78 and 82 shown in FIG. 2 would be reversed in polarity.

Still another modification permits the use of the present invention witha single cylinder internal combustion engine. In this arrangement, the voltage divider comprised of

resistors

64 and 66 would be connected between the conductor 24 and the ground bus 22 as would the input electrode of the Triac 68. The polarity directing diode would be poled such that its cathode would be connected to the conductor 40.

When a special type of spark plug is employed in the system of FIG. 1, it is sometimes undesirable to fire the plug off-cycle, i.e., due to the reverse generation of the magneto-generator when the cylinder is not in a charged condition, but when the points are still open. The solidline waveform illustrated in FIG. 3 shows the normal opencircuit voltage output of a given one of the magneto-

generator coils

18 or 20. The dotted-line shows the effect on the generated waveform when the points close. Normal firing will take place somewhere in zone F during the positive cycle of the generated waveform. A negative going spike (shown by the shaded portion of FIG. 3) may be produced just before the points close at C. Further positive and negative going excursions are shorted out by the closed points. To suppress the negative going excursion just prior to the time of point closure, the circuit of FIG. 4 may be included. This circuit operates in a conventional fashion to clamp the negative going excursion at ground.

While the triac devices are, to a certain extent, devices with built-in triggering features, it is sometimes desirable to utilize a discrete triggering device in the signal input to the triac. For this purpose, either a diac or Zener diode may be utilized to obtain a repeatable threshold point in the circuit.

Although the present invention has been described to a certain degree of particularity, it should be understood that the present disclosure has been made only by way of example and that numerous changes in the details of circuitry and the combination and arrangement of parts and elements (some of which have been suggested) may be resorted to without departing from the scope and spirit of the present invention.

1 claim:

1. In an ignition system for a two-cylinder internal combustion engine of the type having for each cylinder an ignition coil cooperating with a magneto-generator for producing a current in said coils, a set of cam operated breaker points for periodically coupling the current flow from said magneto-generator to said ignition coils and thereby producing a high voltage pulse for delivery to the spark plugs, the improvement comprising;

a. first and second energy storage devices having two terminals connected in series between said magneto-generators and said ignition coils;

b. first and second unidirectional current conducting devices connected in series with said first and second energy storage devices and said magnetogenerators for causing said first and second energy storage devices to be charged with a predetermined polarity;

c. a discharge control circuit adapted to be alternately connected between said first energy storage device and one of said ignition coils and the second energy storage device and the other of said ignition coils by means of said breaker points, for alternately controlling the discharge of said first and second energy storage devices through its associated ignition coil; and

d. said discharge control circuit comprising:

1. a voltage divider connected in parallel with the magneto-generators associated with said two cylinders;

2. a semiconductor switching device having an input electrode, and output electrode and a control electrode;

3. means connecting said input and output electrodes to one terminal of said first and second energy storage devices respectively; and

4. means connecting said control electrode to said voltage divider such that when the voltage applied to said control electrode exceeds a predetermined threshold, one of said energy storage devices is discharged through a path including said semiconductor switching device, one of said ignition coils and the breaker points associated with the other of said ignition coils.

2. An ignition system for a two-cylinder internal combustion engine comprising in combination:

a. a first terminal, a second terminal and a grounded terminal;

b. a first magneto-generator coil connected between said first terminal and said ground terminal;

0. a second magneto-generator coil connected between said second terminal and said grounded ter minal;

d. first and second sets of cam actuated breaker points connected in parallel with said first and second mangeto-generator coils;

e. capacitor means connected in parallel with said first and second sets of breaker-points;

f. a first energy storage device and a first unidirectional current conducting device connected in series between said first terminal and said grounded terminal;

g. a second energy storage device and a second unidirectional current conducting device connected in series between said second terminal and said grounded terminal;

h. a first autotransformer type ignition coil connected in parallel with said first unidirectional current conducting device and a second autotransformer type ignition coil connected in parallel with said second unidirectional current conducting device; and

i. a discharge control circuit connected between said first and second terminals;

j. said discharge circuit comprising:

1. a semiconductor current control means having an input electrode connected to said first terminal, and an output electrode connected to said second terminal and a control electrode;

2. a voltage dividing network connected between said first and second terminals; and

3. means connecting said control electrode to said voltage dividing network.

UNITED STATES PATENT OFFICE CERTIFICATE OF CGRRECHQN PATENT NO. i 3,884,207

DATED 3 May 20, 1975 'NVENTOWS) Andrew Kuehn III it is certified that error appears in the ab0veidentified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 28, after "circulating" insert current Column 8, line 30, in Claim 2, sub-paragraph d, the word "mangeto" should read magneto fiigned and gealed this fif D3) 0% August1975 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN M K 11 1 Commissioner ufluu'ms and Trademarks

Claims

1. In an ignition system for a two-cylinder internal combustion engine of the type having for each cylinder an ignition coil cooperating with a magneto-generator for producing a current in said coils, a set of cam operated breaker points for periodically coupling the current flow from said magneto-generator to said ignition coils and thereby producing a high voltage pulse for delivery to the spark plugs, the improvement comprising; a. first and second energy storage devices having two terminaLs connected in series between said magneto-generators and said ignition coils; b. first and second unidirectional current conducting devices connected in series with said first and second energy storage devices and said magneto-generators for causing said first and second energy storage devices to be charged with a predetermined polarity; c. a discharge control circuit adapted to be alternately connected between said first energy storage device and one of said ignition coils and the second energy storage device and the other of said ignition coils by means of said breaker points, for alternately controlling the discharge of said first and second energy storage devices through its associated ignition coil; and d. said discharge control circuit comprising: 1. a voltage divider connected in parallel with the magnetogenerators associated with said two cylinders; 2. a semiconductor switching device having an input electrode, and output electrode and a control electrode; 3. means connecting said input and output electrodes to one terminal of said first and second energy storage devices respectively; and 4. means connecting said control electrode to said voltage divider such that when the voltage applied to said control electrode exceeds a predetermined threshold, one of said energy storage devices is discharged through a path including said semiconductor switching device, one of said ignition coils and the breaker points associated with the other of said ignition coils.

2. An ignition system for a two-cylinder internal combustion engine comprising in combination: a. a first terminal, a second terminal and a grounded terminal; b. a first magneto-generator coil connected between said first terminal and said ground terminal; c. a second magneto-generator coil connected between said second terminal and said grounded terminal; d. first and second sets of cam actuated breaker points connected in parallel with said first and second mangeto-generator coils; e. capacitor means connected in parallel with said first and second sets of breaker points; f. a first energy storage device and a first unidirectional current conducting device connected in series between said first terminal and said grounded terminal; g. a second energy storage device and a second unidirectional current conducting device connected in series between said second terminal and said grounded terminal; h. a first autotransformer type ignition coil connected in parallel with said first unidirectional current conducting device and a second autotransformer type ignition coil connected in parallel with said second unidirectional current conducting device; and i. a discharge control circuit connected between said first and second terminals; j. said discharge circuit comprising:

3. means connecting said control electrode to said voltage dividing network.