US3587550A - Electronic ignition control system - Google Patents

Abstract

THE ELECTRONIC IGNITION CONTROL SYSTEM INCLUDES A MAGNETIC TIMING PULSE SOURCE DRIVEN IN CORRELATION TO THE CRANKSHAFT OF AN ENGINE WHICH GENERATES TIMING PULSES TO CONTROL THE INTERVAL DURING WHICH AN IGNITION TRIGGER PULSE IS APPLIED TO A ROTATING TRANSFORMER DISTRIBUTOR. THE TRANSFORMER DISTRIBUTOR IS ALSO DRIVEN IN FIXED RELATIONSHIP TO THE ENGINE CRANKSHAFT, AND OPERATES TO COUPLE THE TRIGGER PULSE TO A POWER SWITCH FOR A SELECTED ENGINE CYLINDER. THE POWER SWITCH, UPON RECEIPT OF A TRIGGER PULSE, PASSES POWER FROM A POWER CIRCUIT TO AN IGNITION COIL, WHILE A BIASING VOLTAGE IS APPLIED TO PREVENT OPERATION OF THE POWER SWITCHES FOR THE REMAINING ENGINE CYLINDERS.

Description

United States Patent [72] Inventor Richard Zechlin Belolt, Wis.

[2i 1 Appl. No. 825,275

[22] Filed May 16, 1969 [45] Patented June 28, 1971 [73] Assignee Fairbanks Morse Inc.

New York, N.Y.

[54] ELECTRONIC IGNITION CONTROL SYSTEM 3,453,512 7/1969 Polakowski ABSTRACT: The electronic ignition control system includes a magnetic timing pulse source driven in correlation to the crankshaft of an engine which generates timing pulses to control the interval during which an ignition trigger pulse is applied to a rotating transformer distributor. The transformer distributor is also driven in fixed relationship to the engine crankshaft, and operates to couple the trigger pulse to a power switch. for a selected engine cylinder. The power switch, upon receipt of a trigger pulse, passes power from a power circuit to an ignition coil, while a biasing voltage is applied to prevent operation of the power switches for the remaining engine cylinders.

1 32' 15 54 I i z 2 56 52 PATENTED JUN28 l9?! SHEET 1 [IF 2 INVENTOR Richard Zach/in BY QM (423% ATT( JRNI'IY PATENTED Juuzsasn SHEET 2 UF 2 INVENTOR Richard Zach/in ATTORNEY ELECTRONIC IGNITION CONTROL SYSTEM BACKGROUND OF THE INVENTION Conventional ignition systems for internal combustion engines employ a rotating mechanical distributor in combination with a breaker and breaker points to synchronize fuel ignition with engine operation. Mechanical breaker points are subject to rapid deterioration under the power requirements necessary to produce effective ignition pulses in an ignition coil.

With the development of solid state semiconductor technology, noncontact solid state electronic ignition circuits were proposed to replace the mechanical distributor and breaker systems. These circuits often employ the rectified output from a magneto or similar AC generator to charge a capacitor, which is then discharged by means of a solid state switching circuit into the primary of an ignition coil associated therewith.

While the known solid state ignition circuit are a significant improvement over conventional mechanical systems, they are subject to deficiencies which often prevent effective and reliable fuel ignition. For example, silicon controlled rectifiers (SCRs) are commonly employed to provide switching control functions in solid state electronic ignition circuits. These SCRs are connected in circuit with ignition coils, spark plugs, and similar high energy components which are likely to generate stray potentials sufficient to cause SCR conduction. in known electronic ignition. circuits, it is possible for misfire of an unselected engine cylinder to occur due to conduction of a normally nonconducting SCR in response to stray potentials generated during the firing of a selected cylinder.

Similarly, system malfunction can occur due to the failure of an SCR to cease conduction at the termination of a programmed time interval. Known electronic ignition systems fail to provide a source of biasing potential for control SCRs to insure termination of conduction at a desired time to maintain the timing essential to an effective ignition system.

Finally, many electronic ignition systems employ ineffective mechanical units for distributing ignition pulses to the SCR control switches for the engine cylinders and for advancing the timing of ignition pulses with respect to engine position. Ideally, these functions should be accomplished electronically.

It is a primary object of the present invention to provide a novel and improved electronic ignition control systemadapted to provide reliable and effective operation over a wide range of engine speeds.

Another object of the present invention is to provide a novel and improved electronic ignition control system which incorporates a single master source to govern the timing of ignition pulses for firing all engine cylinders so that unbalanced timing between cylinders is eliminated.

A further object of the present invention is to provide a novel and improved electronic ignition control system which includes semiconductor switching devices to provide firing power to each engine cylinder ignition coil and a rotating transformer distributor to couple a trigger pulse to an appropriate switching device.

Another object of the present invention is to provide a novel and improved electronic ignition control system which includes semiconductor switching devices to provide firing power to each engine cylinder ignition coil and means to positively preclude conduction of the remaining semiconductor switches when a selected switch conducts to fire an associated engine cylinder.

A further object of the present invention is to provide a novel and improved electronic ignition control system including semiconductor control switches conductive during timed intervals and means for biasing said switches to provide positive shutoff at the end of a timed interval.

Another object of the present inventionis to provide a novel and improved electronic ignition control system adapted to facilitate a controlled spark timing with respect to engine speed.

A still further object of the present invention is to provide a novel and improved electronic ignition control system operative to provide timing pulses in response to engine operation and to automatically vary the timing of such pulses in response to engine speed.

These and other objects of the present invention will become apparent upon consideration of the following specification with reference to the accompanying drawings in which:

FIG. 1 is a circuit diagram of the electronic ignition control system of the present invention; and

FIG. 2 is a sectional view of the transformer distributor for the electronic ignition control system of the present invention.

Basically, the electronic ignition control system of the present invention employs a novel timing pulse control circuit having a single, master timing pulse source to govern spark application to all engine cylinders, thereby eliminating unbalanced timing between cylinders. This timing pulse source includes a magnet driven in correlation to engine crankshaft position which operates in conjunction with a single pickup coil to develop timing pulses. These timing pulses, which increase both in amplitude and frequency with an increase in engine speed, operate to control the application of ignition trigger pulses to a firing control circuit. A resistor-capacitor in series with the reactance of the pickup coil facilitates controlled spark timing with respect to engine speed.

The timing pulses from the timing pulse control circuit determine the time interval during which an ignition trigger pulse is provided to a rotating transformer distributor which operates to couple the trigger pulse to an appropriate power switch for a selected engine cylinder. Operation of a selected power switch permits a power circuit to apply voltage to an ignition coil to fire the associated cylinder, while the power switches for the remaining engine cylinders are controlled to prevent cylinder misfiring. At the termination of the cylinder firing cycle, a switch control signal insures the deactivation of the previously operable power switch.

Referring now to the drawings, the electronic ignition control system indicated generally at 10 receives power for ignition energy from a magneto or similar AC generator (not shown) across input terminals 12. The source power from the input terminals is rectified by a full wave rectifier bridge 14, the output of which is connected through a resistor 16 to provide a charging path for a capacitor 18. A Zener diode 20 is connected across the output terminals of the rectifier bridge between the bridge output and the resistor 16. The resistor serves as a current charge limiting resistor, and when the sum of the capacitor volts plus charging current times the resistance of the resistor equals the Zener voltage of the Zener diode, the system becomes limited by the Zener voltage. This protects system components against operation beyond component inherent potential capabilities.

The application of power to the input terminals 12 causes the capacitor 18 to charge, and at the same time current flow occurs through a resistor 24 to charge a capacitor 26. In parallel with capacitor 26 is a Zener diode 22 and a series circuit consisting of a center coil 28 for a transformer distributor 30, to be hereinafter described, and the anode to cathode circuit of asilicon controlled rectifier (SCR) 32. ln the absence of a gating signal to the gate of the SCR 32, the SCR is nonconducting and no current can flow between the anode and cathode thereof. Thus the capacitor 26 will charge to the Zener voltage value of the Zener diode 22 and will remain at that level.

Once thecapacitors l8 and 26 are charged, the electronic ignition control system 10 is ready for operation. The operation of the system occurs in response to timing pulses provided by a pulser unit 34 which includes a pulser magnet 36 having four evenly spaced magnetic poles 38. These magnetic poles are formed by radially extending pole arms which constitute alternately occurring north and south magnetic poles.

The pulser magnet 36 is preferrably a permanent magnet, but may also be formed by suitable electromagnets. The pulser magnet is driven by a rotatable shaft 40 which is correlated to the crankshaft position of an internal combustion engine associated with the electronic ignition control system 10. This correlation between the shaft 40 and the crankshaft may be achieved by conventional coupling means, such as gears, geared belts, etc.

The pulser unit 34 also includes two spaced pole shoes 42 which are arranged so that individual adjacent but opposite poles 38 of the pulser magnet 36 simultaneously pass past each pole shoe during rotation of the pulser magnet. The pole shoes are joined by a connecting pin 44 which operates as a core for a pulser pickup coil 46. Thus rotation of the pulser magnet past the pole shoes causes flux changes to occur in the connecting pin'for the pulser pick up coil. These flux changes produce voltages across output terminals 48 and 50 for the pulser pickup coil, and for each revolution of the pulser magnet, two cycles of output voltage appear across the output terminals of the pulser pickup coil.

For purposes of illustration, assume that upon rotation of the pulser magnet 36, a small positive voltage is initially produced at the output terminals 48 to 50 of the pulser pickup coil. Voltage at terminal 48 causes current to flow through a resistor 52 connected in parallel to a capacitor 54 to the gate of the SCR 32. A parallel resistor 56-diode 58 combination provides a parallel impedance for the gate of SCR 32.

duction occurs in the SCR 32, and the previously charged capacitor 26 is permitted to discharge in a path provided through the center coil 28 of the transformer distributor 30, the anode to cathode of the SCR 32 and back to the capacitor 26.

The transformer distributor 30 includes a center arm 60 which is mounted upon a rotating shaft 62. The shaft 62 also mounts the center coil 28 and provides a flux path therefrom to the center arm. The shaft is driven in fixed relationship to engine crankshaft position by suitable coupling drive means, not shown, as was the magnet shaft 40 for the pulser magnet I input line 78.

A flux path is provided from the pole pieces 76 through a backing plate 80 and the center arm shaft 62 back to the center coil 28. Thus, with current flowing in the center coil and the transformer distributor center arm 60 aligned magnetically with a secondary winding, flux flows from the center coil through a magnetic path formed by the shaft 62, the

center arm, a pole piece 76, the backing plate 80 and the shaft 62 back to the center coil. This changing flux induces a voltage in the corresponding secondary winding.

As most large engines are four cycle engines, step-up speeds would be employed from the engine crankshaft to the magnet shaft 40 of the pulser unit 34. Therefore the transformer distributor center arm 60 will be rotated at a speed substantially lower than that of the engine crankshaft. In the common six cylinder engine, the magnet shaft and pulser magnet 36 might travel at 1.5 times the engine crankshaft speed, which in turn requires that the transformer center-arm 60 travel at one-third of the rotational speed of the pulser magnet. The end result is:

TA rpm/engine rpm= engme rpm X which equals l/2 a 3 where TA=transformer center arm 60. Therefore, the transformer center arm makes one revolution for two engine revolutions which is required in a four cycle engine to fire all cylinders.

Upon receiving ating si nal, the anode 'r'acsrsoae Gan The induced voltage in a secondary winding of the transformer distributor 30 causes a control signal to be provided to a power switching circuit for a specific engine cylinder. The electronic ignition control system 10 includes one power switching circuit for each engine cylinder, such power switching circuits being indicated at 82-92. These power switching circuits are identical in construction, each being electrically connected to one of the secondary windings 64- 74. Therefore, for purposes of illustration, the construction and operation of the power switching circuit 86 connected to the transformer secondary winding 70 will be described, it being understood that the remaining power switching circuits are constructed for operation in an identical manner when the transformer center arm 60 moves opposite the transformer secondary winding associated therewith.

The changing flux occurring when the transformer center arm 60 moves into position opposite the transformer seconda ry winding 70, as shown in FIG. 1, induces a voltage in the secondary winding. One terminal of the secondary winding 70 is commonly connected with the remaining transformer secondary windings to the power input line 78, while the remaining terminal thereof is directly connected to the gate electrode of an SCR 94 in the power switching circuit 86. A resistor 96 is connected to provide a parallel gate resistance for the SCR 94, while a capacitor 98 shunts the anode to cathode path through the SCR.

The cathode of the SCR 94 is tied through a parallel resistor 100 capacitor 102 combination to the common power line extending from the resistor 16. The relative resistive values of the resistor 16 and the resistor-capacitor combination including the resistor 100 and the capacitor 102 are such that the completion of a current path from the anode to cathode of the SCR 94 will cause the capacitor 18 to discharge. Thus, when the capacitor 26 discharges through the center coil 28, the

voltage induced in the secondary winding 70 gates the SCR 94 into conduction. The stored energy in the capacitor 18 is released, and current flows from the capacitor through the primary winding 104 of an ignition coil 106 in series with the anode of the SCR 94, the anode to cathode circuit of the SCR, the parallel circuit formed by the resistor 100 and capacitor 102, and back to the capacitor 18. The resulting rapid application of voltage to the primary winding of the ignition coil induces a hi voltage in a secondary winding 108 for the ignition coil w ich will cause a spark between the terminal thereof and ground through a spark plug or similar known spark means, not shown. This spark fires the associated engine cylinder.

The ground connection shown connected to the ignition coil 106 in FIG. 1 constitutes a common for secondary spark return and is positive with respect to the common line extending from the resistor 16 to the anode of the diode 58.

Conduction of any of the SCRs in the remaining power switching circuits 82, 84, 88, and 92 while the SCR 94 is conducting will possibly result in the misfiring of another engine cylinder at an unwanted time. To provide a positive control which precludes such misfire, the cathodes of each SCR in the power switching circuits 8292 are connected to the top of the parallel RC combination of the resistor and capacitor 102, while the gates thereof are connected through the associated gate resistors to the bottom side of the parallel RC combination. Current flow through the parallel RC combination when the capacitor 18 is discharging through the SCR 94, develops a positive voltage at the top of the RC combination, thereby rendering the bottom side thereof negative. This, with capacitor 18 discharging through SCR 94, the gates of all the remaining SCR's in the power switching units 82, 84, 88, 90 and 92 will be negative with respect to the cathodes thereof, and accidental conduction of these SCR's is prevented. The capacitor 102 will operate to maintain this bias potential for a short interval after the capacitor 18 has discharged.

Ignition coils are inherently inductive devices, and therefore the current that is caused to flow through the SCR 94 by the discharge of capacitor 18 will try to continue to flow when the capacitor reaches zero potential. This coil current can flow through capacitor 18 or through the resistor 16 andparallel path Zener diode 20 and rectifiers in the bridge 14. The resistor 16 provides a relatively high impedance path for the coil current, so that the bottom of the capacitor 18 is charged positive and the top negative. When coil current reaches zero, the capacitor now acts as a source which attempts to force current from the cathode to the anode of the SCRs in the power switching circuits 8292. As the inherent shutoff of an SCR is enhanced by a source attempting to force current from the cathode to anode thereof, positive shutoff of the previously conducting SCR 94 is accomplished. The capacitor 18 will discharge through resistor 16, the time to discharge the capacitor being longer than the maximum shutoff time for the SCR 94.

When SCR 94 ceases to conduct and the capacitor 18 has discharged through the resistor 16, the capacitor will again begin to charge from the output of the bridge rectifier 14 for a new ignition cycle. As this occurs, the engine and pulser magnet 36 continue to rotate until the pulser magnet reaches a point relative to the poles shoes 42 which will result in a trigger pulse being again provided to the gate of the SCR 32. During this interval, the transformer center arm 60 will have traveled to a position centered on the pole piece 76 for the transformer secondary winding 72 so that the power switching circuit 84 may now be activated in the manner previously described in connection with the power switching circuit 86.

During the interval between the deactivation of the power switching circuit 86 and the activation of the power switching circuit 84, the positive voltage on the gate electrode of the SCR 32 will first continue for 180 electrical degrees from the pulser magnet 36 which is actually 90 mechanical degrees of the pulser magnet due to the four pole construction thereof. Capacitor 26 cannot charge during this period even though capacitor 18 may be fully recharged, as SCR 32 is conducting. When the voltage at pulser coil output terminal 48 goes negative, the gate electrode of SCR 32 will be driven negative and the SCR will shut off. The capacitor 26 will now charge to the Zener voltage of Zener diode 22 and be ready to provide a trigger pulse through the center coil 28 of the transformer distributor 30 when the SCR 32 is rendered conductive by the pulser unit 34.

The parallel combination of the resistor 52 and capacitor 54 provides a means for electrically determining the mechanical shaft position at which ignition will take place for various speeds. Either or both the resistor 52 and capacitor 54 may be made variable, as shown in H0. ll, so that controlled spark timing with respect to speed can be achieved.

Both the induced voltage in the pulser pickup coil 46 and the frequency thereof is proportional to speed. Therefore, on the basis of speed alone, the spark should advance with speed. Conversely, however, the reactance of the pulse receiving coil increases with speed to retard the spark. The capacitor 54 presents a high impedance at low speeds, but at higher speeds, the impedance is lower and acts to provide spark advance. With these factors known, circuit equations may be used to make accurate predictions of ignition timing versus engine speed.

The use of a single pulse receiving coil eliminates unbalanced timing between engine cylinders. Systems employing multiple pulse receiving coils require, for equal timing between cylinders, highly symmetrical magnetic paths for all coils. With a single coil, an irregularity is of no consequence, as the main magneto body can be rotated a few degrees to take up differences between units. As sparks to all cylinders are governed by one source, the single pulse receiving coil and pulser magnet, all sparks will be in the same relative location to top dead center of each of the engine cylinders and will be in the same relative location to each other with a change in speed if some advance is employed with resistor 52 and capacitor 54.

It will be readily apparent to one skilled in the art that the present invention provides a novel and improved electronic ignition system which is capable of providing accurate and efficient firing of a plurality of engine cylinders. The arrangement and type of components utilized within this invention may be subject to numerous modifications well within the purview of this inventor who intends only to be limited to a liberal interpretation of the specification and appended claims.

lclaim:

1. An electronic switching control circuit for triggering a plurality of electronic switching units in timed, spaced succession comprising distributor means adapted to provide triggering pulses to said electronic switching units to activate said switching units in succession, said distributor means including a plurality of spaced secondary coil means, each said secondary coil means being connected to one of said electronic switching units and a primary means mounted for movement past said secondary coil means, said primary means being operative to induce a potential in an adjacent secondary coil means upon receipt by said primary means of a trigger signal, a source of potential, solid state switch means connected to selectively pass or block a trigger signal from said source of potential to said primary means in response to gating pulse signals, and switch control means for operating said solid state switch means in timed relation to the movement of said primary means, said switch control means operating to provide a full wave gating pulse signal to positively gate said solid state switching means on and off.

2. The electronic switching control circuit of claim 1 wherein said primary means is mounted for rotation about a central axis, said secondary coil means being arranged concentrically about said central axis and spaced from said primary means.

3. The electronic switching control circuit of claim 2 wherein said switch control means includes pulser magnet means rotatable about a central axis in timed relationship to the rotation of said primary means and a pulser coil connected to provide gating pulse signals to said solid state switch means, said pulser magnet means being magnetically coupled to said pulser coil to develop gating pulse signals across output terminals thereof.

4. The electronic switching control circuit of claim 3 wherein said switch means is a silicon controlled rectifier having an anode to cathode path connected in series circuit with said primary means and a gate electrode connected to receive gating pulse signals from the output terminals of said pulser coil.

5. The electronic switching control circuit of claim 3 wherein a gate pulse adjusting means is connected between said pulser coil and said solid state switch means to vary the timing of said gating pulse signals, said gate pulse adjusting means including an adjustable resistor-capacitor timing circuit.

6. The electronic switching control circuit of claim 4 wherein rotation of said pulser magnet means operates to sequentially reverse the polarity of the potential developed thereby across the terminals of said pulser coil to provide said full wave gating pulse signal to positively gate said silicon controlled rectifier on and off.

7. An electronic switching control circuit for controlling the ignition of an internal combustion engine by successively applying an ignition potential to the primary of an ignition coil for each engine cylinder comprising a plurality of electronic switching units, each such electronic switching unit being connected in series with the primary of an ignition coil for one of said engine cylinders, distributor means adapted to provide triggering pulses to said electronic switching units to activate said switching units in succession, said distributor means including a plurality of spaced secondary coil means, each said secondary coil means being connected to one of said electronic switching units, and a primary means mounted for movement past said secondary coil means in timed relation to the speed of said engine, said primary means being operative to induce a potential in an adjacent secondary coil means upon passage through said primary means of a trigger signal, a source of potential, a first capacitive means connected to be charged from said source of potential, trigger switch means connected to selectively control the discharge of said first capacitive means through said primary means, trigger switch control means for operating said trigger switch means in timed relation to the speed of said engine, and a second capacitive means connected to be charged from said source of potential, said second capacitive means being connected to discharge through the primary of an ignition coil upon activation of the switching unit connected therewith.

8. The electronic switching control circuit of claim 7 wherein said trigger switch control means includes pulser magnet means rotatable by said internal combustion engine about a central axis and a pulser coil connected to provide switching pulses to said trigger switch means, said pulser magnet means being magnetically coupled to said pulser coil to develop switching pulses across the output terminals thereof.

9. The electronic switching control circuit of claim 8 wherein said primary means includes a center coil connected in series with said first capacitive means and said trigger switch means, and a center arm mounting said center coil and providing a flux path therefor, said center arm being rotatable by said internal combustion engine about a central axis, and said secondary coil means being arranged concentrically about said central axis and spaced from said center arm.

10. The electronic switching control circuit of claim 7 wherein each of said electronic switching units includes a silicon controlled rectifier having an anode, cathode and gate electrode, the anode to cathode circuit of each such controlled rectifier being connected in series with the primary of an ignition coil and the gate electrode being connected to one of the secondary coil means of said distributor means.

11. The electronic switching control circuit of claim 10 wherein a biasing means is connected to the gate electrode of each said silicon controlled rectifier, said biasing means operating upon conduction of one of said controlled rectifiers to maintain the remaining controlled rectifiers nonconductive.

12. The electronic switching control circuit of claim 10 wherein the cathode electrodes of said silicon controlled rectifiers are commonly connected in a return path to said second capacitive means, said second capacitive mear'is operatingsubsequent to the conduction of one of said controlled rectifiers and the discharge of said second capacitive means through the primary of an associated ignition coil to provide a reverse bias over said return path to terminate conduction of said controlled rectifier.

13. The electronic control circuit of claim 8 wherein an adjustable electronic spark advance means is connected between said pulser coil and said trigger switch means, said adjustable electronic spark advance means being adapted to vary the timing of switching pulses from said pulser coil to set ignition timing with respect to engine speed.

14. The electronic switching control circuit of claim 9 wherein said trigger switch means is a silicon controlled rectifier having an anode to cathode circuit connected in series with the center coil of said distributor means and a gate electrode connected to receive trigger pulses from the output terminals of said pulser coil, the rotation of said pulser magnet means operating to sequentially reverse the potential across the terminals of said pulser coil to provide a full wave trigger pulse to positively gate said trigger switch means on and off.

15. The electronic switching control circuit of claim 14 wherein each of said electronic switching units includes a silicon controlled rectifier having an anode, cathode and gate electrode, the anode to cathode circuit of each such controlled rectifier being connected in series with the primary of an ignition coil, and the gate electrode being connected to one of the secondary coil means of said distributor, the cathode electrodes of the silicon controlled rectifiers of all of said electronic switching units being commonly connected in a return path to said second capacitive means, said second capacitive means operating subsequent to the conduction of one of said controlled rectifiers and the discharge of said second capacitive means through the primary of an associated ignition coil to provide a reverse bias over said return path to terminate conduction of said controlled rectifier.

16. The electronic switching control circuit of claim 15 wherein a biasing means is connected to the gate electrode of each silicon controlled rectifier in said electronic switching units, said biasing means including a parallel resistor-capacitor circuit included in the return path to said second capacitive means and operating upon conduction of one of said controlled rectifiers to maintain the remaining controlled rectifiers nonconductive.

17. The electronic switching control circuit of claim 16 wherein an adjustable electronic spark advance means is connected between said pulser coil and the gate electrode of the silicon controlled rectifier of said trigger switch means, said adjustable electronic spark advance means including an adjustable, parallel resistor-capacitor circuit adapted to vary the timing of trigger pulses from said pulser coil to set ignition timing with respect to engine speed.

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