05/359137

04/01/1975

05/10/1973

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Brunswick Corporation (Skokie, IL)

123/406.570

315/209R, 123/655, 123/600

F02P5/155; F02P7/03; F02P5/145; F02P7/00; F02P5/04

123/117R,117A,148E 315/209

Antonakas, Manuel A.

Cangelosi J. A.

Andrus, Sceales, Starke & Sawall

I claim

1. Triggering apparatus for an ignition system for an internal combustion engine for operating a plurality of individual circuits each having a switching means selectively actuated for transferring of energy, comprising a generator having winding means for establishing triggering signals for each of said switching means, said generator including a cyclically moving means including a first means for establishing first polarity triggering signals in said winding means and a second means similarly coupled to said winding means for establishing second polarity signals in said same winding means, a separate winding means connected to each of said switching means with the first polarity signal actuating the corresponding switching means, and circuit means connecting the opposite end of each separate winding means to a different one of said switching means to establish actuation thereof prior to actuation from said corresponding winding means, and an electronic control switch means interconnected to said winding means to effectively disable the circuit means for said second polarity signals and selectively operable to enable said circuit means for said second polarity signals and thereby provide an automatic spark advance control.

2. The triggering apparatus of claim 1 having means included to actuate said control switch means above a selected speed of said internal combustion engine, and means associated with said electronic control switch means to maintain said electronic control switch means actuated until such time as the engine speed drops a selected level.

3. In an ignition system for a multiple cylinder internal-combustion engine having individual firing circuits for each cylinder, each firing circuit having a main switching means selectively actuated for transferring of energy to the associated firing means, the improvement in an engine driven triggering signal source and its interconnecting circuit means comprising a generator having a plurality of winding means for establishing a triggering signal for each of said switching means, said generator including a cyclically moving means including a first means for establishing a first polarity triggering signal in each one of said plurality of winding means and a second means similarly coupled to said winding means for establishing an opposite second polarity signal in each one of said same plurality of winding means, said plurality of winding means including a separate winding means connected to each of said switching means with the first polarity signal actuating the corresponding switching means, and circuit means interconnecting the opposite ends of each one of said separate winding means to a different one of said switching means to selectively transmit the opposite second polarity signal to a different one of said switching means from that associated with the first polarity signal to establish actuation thereof at a different time than from said corresponding separate winding means whereby each of said winding means is selectively operable to operate either one of the two switching means with only the first polarity signal operable in one speed range and only the second polarity signals operable in a second speed range to provide an automatic spark advance control.

4. The ignition system of claim 3 including an electronic control switch means interconnected to said winding means to effectively disable all of the circuit means for said second polarity signals and selectively operable to enable all of said circuit means for said second polarity signals.

5. The ignition system of claim 4 including speed responsive means coupled to and driven in synchronism with said internal-combustion engine and operable to actuate said control switch means above a selected speed.

6. The ignition system of claim 5 including means associated with said electronic control switch means to maintain said electronic control switch means actuated above said selected speed and to de-energize said electronic control switch means when the engine speed drops below a selected level appropriately related to said selected speed.

7. An ignition system triggering apparatus for a multiple cylinder internal combustion engine including multiple channel main firing switch means having individually triggered input means and providing an automatic advance firing of the several cylinders above a selected speed, comprising a stator having a plurality of trigger windings mounted in circumferentially spaced relation, a rotating magnetic member driven in synchronism with the engine and rotatably mounted coaxially to the stator, said magnetic member having a first magnetic discontinuity sequentially coupled to the windings and generating a family of triggering pulses of first polarity, said rotating magnetic member having a second discontinuity of an opposite magnetic flux change from said first discontinuity and sequentially coupled to said windings and generating a second family of triggering pulses of an opposite polarity, said second discontinuity being spaced from said first discontinuity in accordance with a first angle dependent on said circumferential spacing between said trigger windings and with a second preselected angle of advance firing for the engine, and circuit means connecting each of said triggering windings to the individually triggered input means of the main firing means for two of said cylinders and wherein each triggering winding initiates a retard firing of one of the cylinders at selected engine speeds and said same triggering winding initiates an advanced firing of a different cylinder at other engine speeds.

8. The ignition system triggering apparatus of claim 7 wherein said main switch means are threshold responsive switch means and wherein said circuit means includes a first polarity branch circuit means having unidirectional conducting means connected to conduct the first polarity signals from each one end of said windings and a second opposite polarity branch circuit means including an electronic switch means connected to conduct the second polarity signals from each opposite end of said windings.

9. The ignition system triggering apparatus of claim 8 wherein said electronic switch means is a triggered means, a sensing switching means connected to actuate said electronic switch means, and means generating a voltage signal sensibly proportional to the speed of the engine and connected to actuate the sensing switching means to actuate the electronic switch means above a selected speed so as to cause said electronic switch means to conduct and apply said opposite polarity pulses to the said threshold responsive switch means, whereby each said opposite polarity pulse triggers a different one of said threshold responsive switch means from the threshold responsive switching means triggered by the first polarity pulse of the corresponding winding to automatically advance the firing.

10. The ignition system triggering apparatus of claim 8 wherein said electronic switch means includes a common solid state switch and a plurality of individual isolating diode means for conducting the opposite polarity signals of each of said trigger windings.

11. In the ignition system of claim 10 wherein said common switch is a controlled rectifier means having one main terminal connected to a common return line and the other main terminal connected to the windings in series with said individual isolating diode means, a sensing switching means connected to a gate means of the controlled rectifier means, signal means for generating a signal sensibly proportional to speed, and circuit means connecting the signal means to the input of said sensing switching means, such that the common solid state switch switches above said selected speed to a conductive state opposite to that state obtained below said selected speed.

12. In the ignition system of claim 7 wherein said circuit means includes first branch circuits including unidirectional conducting means for transmitting said first polarity signals from the first ends of said plurality of trigger windings and second branch circuits including unidirectional conducting means for transmitting said second polarity signals from the opposite second ends of said windings, a common connection from each main firing means to the corresponding sides of said unidirectional conducting means in a first branch circuit of one winding for transmitting first polarity signals therefrom and in a second branch circuit of a different winding for transmitting second polarity signals therefrom, so as to selectively actuate said main switching means, said first branch circuit having its return path directly from the main firing switch means back to the winding, and said second branch circuit having its return path passing through a common controlled switch means, said common connection including an auxiliary path means required for biasing purposes joining into said return paths prior to their separation, a unidirectional conducting means being provided in said auxiliary path and having a forward threshold voltage level closely approximating the threshold triggering voltage level of said main firing switch means to effectively maintain full signal transfer through said first branch circuit for all levels up to said threshold voltage level.

13. In the ignition system of claim 12 wherein said circuit means provides for corresponding connection of each of said windings through similar first and second branch circuits, each of said first branch circuits including a first diode means connected to a first end of one of said windings, a controlled rectifier having gate and cathode means, a resistor connected in series between said diode means and the gate of said controlled rectifier means, a common bias voltage storage capacitor connected to the cathode of said controlled rectifier, and a return resistor connected from the other end of said capacitor to the opposite end of the same winding; each of said second branch circuits including a second diode means connected to the junction of said opposite end of the winding and said return resistor, a common connection between the output sides of said first diode means of one winding and said second diode means for a different second winding, a third diode means connected to the first end of said second winding, a common controlled switch means connected between said third diode means and said common bias capacitor, said control switch means being in series for currents flowing through said second diode means but not included in the path for currents flowing through said first diode means, said common controlled switch means being selectively actuated to establish an angularly advanced firing of the engine.

14. In the ignition system of claim 13 wherein said controlled switch means includes a gated unidirectional conducting switch means having an input gate means, a transistor interconnected between said gate and to a control power source, a speed responsive means providing a voltage varying sensibly with engine speed, said transistor having an input circuit connected to said speed responsive means.

15. In the ignition system of claim 14 having a bias voltage capacitive storage means charged by the output signals of said windings, and establishing a voltage output sensibly proportional to the speed of the engine, a drain transistor means connected across said capacitive means in series with a resistance means, said resistance means having at least one portion connected in common in series with said controlled switch means and connected to actuate said drain transistor to partially discharge said capacitive storage means and prevent overcharging of said capacitive storage means.

16. In the ignition system of claim 14 wherein said speed responsive means is a bias voltage capacitive means charged by the output signals of said windings, including a voltage dividing resistor network connected across said capacitive means to turn on said transistor at a selected voltage of said capacitive means.

17. In the ignition system of claim 14 wherein said speed responsive means includes an electronic tachometer circuit including a resistance-capacitance network connected in series with a unidirectional conducting means to the trigger windings to conduct said first polarity signals.

18. In the ignition system of claim 17 wherein said unidirectional conducting means includes a Zener diode means connected to said network and to each of said windings by a separate diode means.

19. In the ignition system of claim 14 wherein a separate power alternator is provided having high and low speed windings and said speed responsive means includes an electronic tachometer circuit including a resistance-capacitance network connected in series with diode means to said high speed winding of the alternator, a Zener diode connecting the output of the network to the input circuit of said transistor.

20. An ignition system for an internal combustion engine employing a threshold responsive triggered switching means including a trigger signal generator having a plurality of windings for generating timed spaced trigger signals, a firing energy source means having at least one output varying sensibly in amplitude with the speed of the engine, and having a self-biasing capacitive circuit means operatively connected in the triggering circuitry associated with the switching means and establishing a modifying signal substantially proportional to the output of the trigger signal generator to thereby effectively establish a variable threshold switching voltage essentially matched to the output voltage of the trigger signal generator, said generator establishing time spaced alternate polarity pulses in each winding, the improvement in the interconnection of said generator to said switching means comprising a first polarity branch circuit means to complete individual circuits for conducting the first polarity signal of each of said generator windings to a first one of said switching means for time spaced operation of said switching means, a second opposite polarity branch circuit means which includes an electronic switch means effectively in series with said windings to complete individual circuits for conducting the opposite polarity signal of each of said generator windings to a different second one of said switching means with said electronic switch means being common to all of said second circuit means, said second polarity branch circuit being connected to actuate the switching means at a different time than the actuation from said corresponding winding means to provide an automatic advance control, said electronic switch means having an input control means, a speed sensing means capable of producing a control voltage varying sensibly with engine speed, said speed sensing means connected to said input control means to actuate said electronic switch means when said control voltage exceeds a selected level, only one of said first and second polarity pulses being operable with the electronic switch means not operated and only the other of said polarity pulses being operable with the electronic switch means operated.

21. The ignition system of claim 20 wherein said electronic switch means is a solid state unidirectional switching means connected in the second opposite polarity branch circuit return paths to said windings, wherein said input control means is a level sensing switching means connected between the input means of the unidirectional switching means and the said speed sensing means, and where said speed sensing means generates an output signal sensibly proportional to the speed of the engine and is connected to actuate said level sensing switching means to initiate conduction of said unidirectional switching means.

22. The ignition system of claim 21 wherein said solid state unidirectional switching means includes a controlled rectifier connected as a common series element in series with a plurality of isolating diodes connected one each to each of said windings, said controlled rectifier having a gate as said input means.

23. The ignition system of claim 21 wherein said speed sensing means includes a voltage dividing network connected across said self-biasing capacitive circuit means and where the output of said voltage dividing network connects to the input of said level sensing switching means.

24. The ignition system of claim 21 wherein said speed sensing means includes a pulsed tachometer circuit connected to the windings and including unidiectional means to transmit only one of said polarity signals.

25. The ignition system of claim 24 wherein said unidirectional means only transmits the first polarity signals.

26. The ignition system of claim 21 wherein said source means includes a separate alternator as a main power source, and said speed sensing means includes a pulsed tachometer circuit connected to the alternator and including unidirectional means to transmit one polarity of the alternator output.

27. The ignition system of claim 26 wherein said alternator has a low speed winding and a high speed winding, and said tachometer circuit is connected to said high speed winding.

28. The ignition system of claim 21 wherein said speed sensing means maintains said unidirectional switching means continuously on at all speeds above said selected speed and thereby applying said opposite polarity pulses to trigger a different one of said threshold switching means from the switching means triggered by the first polarity pulse of the corresponding winding, said opposite polarity pulses also being applied to said self-biasing capacitive circuit means, and drain means responsive to the opposite polarity pulse conduction through said electronic switch means and operable to conduct current sensibly proportional to the current passing through said electronic switch means and thereby establishing a controlled discharge of said self-biasing capacitive circuit means to prevent overcharging of the self-biasing capacitive circuit means.

29. An electrical power system for firing of an internal combustion engine employing a triggered switch means and for supplying separate electrically powered load means, comprising a main alternator having a plurality of power windings having output means for driving of said load means, said main alternator also having said power windings connected to output means having control switching means connected to supply triggering power to said triggered switch means, and a separate trigger generator connected to the control switching means, said trigger generator including a separate trigger winding for each engine cylinder and a magnetic rotor establishing alternate polarity pulses in each winding, a first polarity branch circuit means connecting said windings to complete individual circuits for conducting the first polarity signal of each of said trigger windings to a first one of said control switching means, a second opposite polarity branch circuit means including an electronic switch means connecting each of said windings to complete individual circuit for conducting the opposite polarity signal of each of said generator windings to a different one of said control switching means from that associated with the first polarity signal to establish actuation thereof at a different time than said corresponding separate winding means to provide an automatic spark advance control, with said electronic switch means being common to all of said second circuit means, and means responsive to the engine speed to actuate said electronic switch means whereby said first polarity pulse signals are operable in one speed range and said second polarity pulse signals are operable in a second speed range.

30. The electrical power system of claim 29 wherein said engine includes a shaft with a flywheel secured to one end, said main alternator being a multipole alternator excited by a multipolar magnet ring secured to said flywheel, and said trigger generator includes said magnet rotor which is an annular member secured to said shaft and having said trigger windings mounted in equicircumferential spacing about said annular member.

BACKGROUND OF THE INVENTION

This invention relates to a triggered ignition system and particularly to a system employing switching means for selectively supplying power to the several ignition means with respect to a variable desired firing point.

Electronic ignition systems have recently been developed to provide improved ignition in internal combustion engines and the like. A highly satisfactory electronic system employs a capacitor which is charged to a relatively high voltage and then rapidly discharged to provide the firing energy to a selected spark plug. Such capacitor discharge ignition systems may employ a battery power supply in combination with a dc to dc converter for charging of the capacitor to the firing level or alternatively may employ an alternator coupled to and driven by the engine to produce an alternating output which is rectified and applied to charge the capacitor.

Capacitor discharge ignition systems and the like have also been developed with individual outputs for the several cylinders in order to eliminate the requirement for distributors and the like. Further, the switching is advantageously constructed with special trigger signal generating circuits to eliminate the necessity for breaker points.

A very satisfactory capacitor discharge ignition system is shown in applicant's copending application entitled IGNITION SYSTEM WITH ADVANCE STABILIZING MEANS which was filed on Nov. 23, 1971 with Ser. No. 201,457. As more fully disclosed in such application particularly as applied to an outboard motor or the like, an alternator is coupled to the flywheel of an internal-combustion engine and connected via a rectifier circuit to charge a main firing capacitor. A separate signal generator is also coupled to the flywheel and establishes properly timed individual triggering signals. The output of the main firing capacitor is connected to a discharge network including a controlled rectifier, the gate of which is connected to the output of an appropriate trigger circuit to provide for the discharge of the capacitor for proper firing of the respective cylinder of the engine. A bias network is incorporated into the trigger circuit to prevent uncontrolled and erratic advance firing signals which can result in a condition of engine speed instability and possible engine damage.

However, in snow vehicles and other applications there is a distinct need for an automatic spark advance for electronic ignition systems such as disclosed in that application, for example. Thus, in certain high speed internal-combustion engines, the ignition system is advantageously provided with automatic advance and retard generating means for varying operation of the igniting means in the respective cylinders with the engine speed. For example, U.S. pat. No. 3,464,397 discloses a plurality of individual windings for each cylinder, cooperating with a restricted number of flywheel driven magnet poles, to produce the properly timed firing pulses, with a Zener diode or the like connected in the circuit of one of the windings associated with each cylinder to provide for selective application of a pulse signal to a controlled switch to thereby produce a "retard spark" for such cylinder below a certain speed and an "advance spark" above such speed. However, the provision of a plurality of windings increases the cost of such systems, and reduces the space available for any needed auxiliary windings for the generation of battery charging and lighting power. Further, the restrictions on the maximum number and configuration of flywheel driven magnet poles, serves to limit the power that can be generated by such auxiliary windings. As an alternative, in systems where adequate alternator capacity must be provided for charging of the ignition system main capacitor and for the battery charging and lighting loads, a separate trigger pulse generator having specially shaped magnet poles can be employed. In each triggering coil of the pulse generator the shaped poles produce a first and smaller "advance" flux change followed at an appropriate angle by a second and much larger "retard" flux change in the ame direction as the first change. The second and larger flux change generates in each trigger coil a large "regard pulse," strong enough to be operative at all speeds, whereas the first and smaller flux change generates in each coil a small "advance pulse" which only becomes strong enough to be operative above a selected speed. Both pulses are of the same polarity and are directed to the same controlled switching means for an appropriate cylinder. When the advance pulse triggers the discharge of the main capacitor, the larger retard pulse arriving later finds no energy remaining for discharge. Following the retard pulse, the alternator recharges the main capacitor, and the trigger magnets restore the flux conditions existing prior to the first pulse. The flux restoration generates a third but opposite polarity signal in the trigger coil to which the switching means does not respond. In practice, the specially shaped magnet pole construction presents difficulties with respect to producing within each trigger coil a pair of suitably strong, closely spaced yet distinctly defined pulses, particularly when the triggering pulse generator is to have a small diameter such that it can fit inside the flywheel space not already used by the alternator, and where it will be subjected to the stray fields of the magnet ring of the alternator. Indeed, in snowmobiles, large outboard motors and the like, a relatively large multi-pole alternator magnet ring is normally provided as part of the flywheel. The alternator may advantageously be constructed with a pair of poles having charging windings for the capacitor discharge ignition system, and a plurality of other poles having windings suitable for charging of a battery and operating the lighting systems. Such alternators are quite large, and the separate trigger generator is limited by the remaining available space. In such construction, the generation of an adequate trigger pulse at relatively low cranking speed while providing a distinct advance pulse at an intermediate speed, where both pulses are distinct, one from the other, and where both are well above the noise voltages generated by the stray fields from the alternator magnet ring is both difficult and costly.

Thus, although electronic type automatic switching spark advance has been proposed, the prior art devices have not produced a practical automatic electronic advance system particularly for engines requiring a large main alternator utilizing most of the available space underneath the flywheel.

SUMMARY OF THE PRESENT INVENTION

The present invention is particularly directed to a reliable advance-retard on-off electronic switching automatic spark advance system for a distributor-less ignition system.

More particularly, the present invention is directed to a multiple cylinder internal-combustion engine ignition system wherein separate firing circuits are provided for the several cylinders. A trigger signal generator is provided having a separate coil means for a pair of related cylinders. The signal generator includes means for cyclically coupling of each coil means to a pair of magnetic field means to generate time spaced and opposite polarity pulses in each of the coil means. Diode and switching means connect the opposite polarity pulses to the different firing circuits for the related pair of cylinders to provide for an automatic spark advance at a selected speed. The network in particular includes an electronic switch which normally holds the circuit inoperative to one polarity of pulses. At a selected speed, the switch is actuated to introduce the corresponding polarity pulses as advance pulse signals which through suitable steering means are connected to fire the second cylinder of the related cylinder pairs. When that cylinder is actuated by the normal triggering pulse, it has already been fired. The normal triggering signal is thus merely a redundant actuation of the already discharged capacitor circuit.

Applicant has found that with suitable electronic switching, this invention provides an economical and reliable ignition system with automatic spark advance. The circuit is relatively simple because the same multiple triggering windings which generate the normal firing signals are also employed to generate the advanced firing signals. The only additional requirement is the electronic switching and steering circuitry required to control and redirect, respectively, the advance firing signals.

The circuit is advantageously constructed with a rotating magnet generator similar to that shown in the copending application of James R. Draxler entitled PULSE GENERATOR FOR IGNITION SYSTEMS which was filed on Nov. 23, 1971 with Ser. No. 201,456 and assigned to the same assignee as the present application. That system employs a rotating magnet structure having abutting north and south poles defining a peripheral magnetic change. For any given single coil, this construction inherently generates at equally spaced time intervals relatively positive and negative pulse signals at the oppositely located magnetic discontinuities. However, with any given single coil, it is merely necessary to rearrange the magnets to locate the discontinuities, not opposite to one another, but rather at appropriate points, to automatically properly generate a normal or first polarity triggering pulse for a first spark plug in a first cylinder, and an advance or second polarity triggering pulse for a second spark plug in a second cylinder which are conducted into the circuit by suitable switching and steering means connected to the opposite ends of each coil or winding in accordance with the teaching of this invention.

Further, in accordance with a particularly novel aspect of the present invention, the self-biasing network of applicant's copending application defines a tachometer type signal directly related to the operating speed of the engine. This signal can advantageously be applied to an electronic switching circuit to activate the second or opposite polarity signal circuitry and thus establish an automatic spark timing advance. In such circuit, means should be provided to prevent the opposite polarity signals from overcharging of the self-biasing network. If this is not done, a hysteresis effect is introduced into the circuit causing the system to provide an automatic advanced timing but requiring an excessive reduction in engine speed to return to the normal or retarded timing condition.

In a preferred construction of the present invention, an auxiliary controlled rectifier in series with steering diodes completes the circuit path for the opposite polarity signals. The gate of the auxiliary controlled rectifier is interconnected through a transistor to the self-biasing network, which provides power to hold the auxiliary controlled rectifier in a continuous "gated-on" condition above a selected speed. The transistor and therefore the auxiliary controlled rectifier is initially turned on from a tachometer circuit means such as the self-biasing capacitor or a separate circuit connected to the trigger pulse generator or connected to the ignition charging alternator. A drain switching circuit is connected to increase the draining rate of the charge in the capacitive self-bias means and minimize any possibility of overcharge in the self-biasing network in order to essentially eliminate hysteresis effect.

In accordance with conventional electronic design, temperature effects can be minimized by using appropriate thermistor networks or the like.

In regard to the exact speed at which the automatic electronic advance occurs, some slight variation may be expected from engine to engine; however, the variation should not be so significant as to cause any objectionably wide range of engine speeds at which the automatic advance occurs in normal production type engines.

The present invention thus provides an improved distributor-less ignition system with an automatic electronic spark advance which can be advantageously applied to snowmobiles, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings furnished herewith illustrate a preferred construction of the present invention in which the above advantages and features are clearly disclosed as well as others which will be readily understood from the description of the illustrated embodiments.

In the drawings:

FIG. 1 is a schematic illustration of a capacitor discharge ignition system employing a triggering control constructed in accordance with the present invention;

FIG. 2 is a diagrammatic illustration of the triggering generator constructed to operate the triggering control shown in FIG. 1;

FIG. 3 is a graphical illustration showing the automatic timing advance resulting from the circuit and structure shown in FIGS. 1 and 2;

FIG. 4 is a partial schematic illustration of a triggering circuit similar to that shown in FIG. 1 with an alternative speed sensing means for establishing the automatic advance signals; and

FIG. 5 is a view similar to FIG. 4 showing a still further alternative construction of developing a tachometer signal for establishing the speed at which automatic advance occurs.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

Referring to the drawings and particularly to FIGS. 1 and 2, a three-cylinder engine 1 is diagrammatically illustrated having three individual spark plugs 2, 3 and 4 for firing of the individual cylinders. Each of the spark plugs 2-4 is coupled through a separate firing circuit 5, 6 and 7, respectively, to a common capacitor 8 to provide for selective transfer of the energy in the capacitor 8 to the several spark plugs 2, 3 and 4 in proper time spaced relationship so as to achieve the correct angular relationship to the rotating crankshaft of engine 1. The capacitor 8 is charged from an alternator 9 coupled to and driven by the engine 1. The discharge of the capacitor 8 is controlled by a trigger generator 10, the output of which is selectively connected to circuits 5, 6 and 7 through diode steering and electronic switching circuits 11 and 48 and through cascaded trigger circuits 12 to provide for proper actuation thereof for operation of engine 1.

The altenrator 9 is preferably a dual winding alternator providing for selective high and low speed charging of capacitor 8 and in accordance with the teaching, for example, of U.S. Pat. No. 3,566,188. Capacitor 8 is properly charged as a result of the dual winding construction during both low and high speed operation to a selected level for triggering of the firing of the respective spark plus 2-4.

Generally, charging alternator 9 includes a low speed winding 13 which has a very large number of turns of fine wire, and a high speed winding 13a which has a much smaller number of turns of heavier wire. Low speed winding 13, because of its large number of turns, will develop voltages in excess of the insulation rating of the wire if low speed winding 3 is forced to operate without load current. Diode charging network 14 provides a load across low speed winding 13 regardless of the polarity of voltage generated in winding 13. When the voltage generated in winding 13 is of the polarity to charge capacitor 8, the load current flows through winding 13a, winding 13, diodes 14a, 14b, into capacitor 8. When the voltage generated in winding 13 is of the polarity to discharge capacitor 8, diodes 14a, 14b prevent the discharge, but diode 14c provides the path for the load current required by winding 13. Low speed winding 13 is particularly operable during cranking and low speed engine operation to directly charge the capacitor 8 through diode charging network 14 and indirectly charge the cascaded triggering circuit capacitor 15 which controls the discharge of capacitor 8 to the related spark plugs 2-4. The capacitor 15 is charged through a high resistance divider including resistors 16 and 16a connected between capacitor 8 and ground 17. The high speed winding 13a is connected by network 14 to directly charge the capacitor 8 and also to directly charge the cascaded trigger circuit capacitor 15 through a low-resistance divider, including resistors 18 and 18a, and a diode 19.

The several discharge circuits 5, 6 and 7 are similarly constructed and consequently the discharge circuit 5 is described in detail with the corresponding elements of the circuits 6 and 7 identified by corresponding primed numbers. The discharge circuit 5 includes an electronic discharge switch shown as a controlled rectifier 20 connecting the positive side of the capacitor 8 to the primary of a pulse transformer 21, the secondary of which is connected across the related spark plug 2. Thus, with the capacitor 8 charged, the firing of controlled rectifier 20 results in the capacitor 8 being rapidly discharged through the pulse transformer 21 to fire the spark plug 2.

A diode and capacitor combination 21a is shown connected across the primary of the transformer 21 to improve the operation. The diode acts to extend the duration of the spark by allowing the energy that has been discharged from the capacitor 8 into pulse transformer 21 to remain in transfer 21 in the form of a strong magnetic field sustained by the free-wheeling current flowing in the loop comprised of the primary winding of transformer 21 and the diode of the combination 21a.

The capacitor of combination 21a helps to absorb the very high frequency and amplitude voltage transient generated by the spark discharge which is coupled from secondary to primary of transformer 21 and then conductively coupled from the primary of transformer 21 up the interconnecting lead into discharge circuit 5.

The spark discharge of spark plug 2 normally occurs when the capacitor 8 still has enough energy to fire a second spark plug. By absorbing much of the transient voltage generated by the firing of spark plug 2, transient-induced firing of discharge circuitss 6 or 7, and thus spark plugs 3 or 4, is inhibited.

The controlled rectifier 20 is controlled in proper timed relation by the output of the trigger generator 10 and in particular is connected thereto in the illustrated embodiment of the invention through the cascaded trigger circuit 12 including a coupling transformer 22 having a secondary winding 23 connected across the gate to cathode circuit of the controlled rectifier 20.

The circuits 6 and 7 are similarly conttrolled by individual trigger signal coupling transformers 24 and 25 of circuit 12. The latter circuit and its connection for the circuit 5 will be described in deail with the corresponding circuits 6 and 7 described by the primed and double primed numbers.

The cascaded trigger circuit 12 includes the common capacitor 15 forming a common power source for selective discharge through the respective transformers 22, 24 and 25 for selective triggering of the corresponding discharge circuits 5, 6 and 7. The capacitor 15 is charged to a satisfactory level through a resistor and diode network having its output at node 26 and having one of its two inputs connected to receive energy from capacitor 8 and having the other of its inputs connected to receive energy from high speed alternator winding 13a. Thus, the circuit includes the pair of high resistance series connected resistors 16 and 16a connected between capacitor 8 and ground 17. The capacitor 15 is connected across the resistor 16 between ground and the resistor 16a. At low engine speeds, where the low speed winding is providing the charging current to capacitor 8, capacitor 8 charges up and in turn provides a small charging current through resistor 16a to capacitor 15 in parallel with the resistor 16. The second pair of lower resistance series connected resistors 18 and 18a are connected between the output of high speed winding 13a and ground 17. Diode 19 connects the junction of the resistors 18 and 18a to the capacitor 15 to provide a path for charging current to the capacitor from high speed winding 13a, said path becoming active at high speeds.

Thus, at low speeds, the resistors 16 and 16a charge the capacitor 15 prior to triggering. These resistors also act as a high resistance safety bleeder on the main capacitor 8 to drain the energy from the ignition system when the engine is stopped. The resistors 16 and 16a are relatively high resistance elements, however, to avoid heavy drain on the capacitor 8 particularly during cranking and low speed operation.

At high engine speeds, as hereinafter developed, there is only a relatively short period during which to charge the capacitor 15 which is insufficient to allow adequate charging through the high ohmic value resistors 16 and 16a. Resistors 18 and 18a have a much lower resistance and as a result of operating from the high speed alternator winding 13a can readily charge the capacitor 15 during the relatively short charging period which exists during high speed running conditionss with the spark advanced.

The diode 19 is employed because the output of the high speed winding 13a, which is applied across resistors 18 and 18a, is an alternating voltage. The diode 19 prevents capacitor 15 from discharging through the low valued resistor network 18 and 18a as well as rectifying the alternating voltage.

The capacitor 15 is discharged through the respective transformers 22, 24 and 25 by selective triggering of associated controlled rectifiers 27, 28 and 29, respectively, of circuit 12. The discharge circuits including rectifiers 27, 28 and 29 are similarly constructed and, consequently, the circuit for the controlled rectifier 27 and associated transformer 22 is described in detail with the corresponding elements for circuits including rectifiers 28 and 29 generally identified by corresponding primed and double primed numbers.

The transformer 22 includes a primary winding 30 connected between the capacitor 15 and controlled rectifier 27. The primary winding 30 is of course suitably coupled to the secondary winding 23 by a suitable transformer core 31 to provide an appropriate pulse to the gate of the rectifier 20 when the rectifier 27 is triggered on. The rectifier 27 is, in turn, controlled by the output of the generator 10 which is schematically shown in FIG. 1 and is diagrammatically illustrated in FIG. 2.

The present invention is particularly directed to the trigger generator 10 and circuit 11 for sequential actuation of circuits 5, 6 and 7. Consequently, the construction of the alternator and the charging of capacitor 8, as well as the main discharging circuits, are only briefly described herein. Reference may be made to the previously referred to copending applications as well as to other known systems for details of construction not more fully set forth herein.

The generator 10 generally includes three separate windings 32, 33 and 34 mounted on a stator 35, about a rotor 36 which is coupled directly to the engine drive shaft 37. The windings 32, 33 and 34 are spaced 1/3 revolution (120°) apart.

The illustrated rotor 36 includes a pair of magnetic poless shown as a North pole 38 and a South pole 39 which defines a first polarity flux reversal at an abutting junction 40, and a second or opposite polarity flux reversal at an abutting junction 41, which is not diametrically opposite 40.

In accordance with the present invention, the three windings 32, 33 and 34, respectively, together with rotating magnetic junction 40 generate three first polarity normal retard timing pulses for triggering controlled rectifiers 27, 28 and 29, respectively; and windings 33, 34 and 32, respectively, together with rotating magnetic junction 41 generate the three second or opposite polarity advanced timing pulses for triggering the same three controlled rectifiers 27, 28 and 29, respectively. The advance and retard pulses are graphically illustrated in FIG. 2 to show the relative polarities and time relationships.

In accordance with the illustrated embodiment of the present invention, the three first polarity normal retard pulses 42, 43 and 44 are active at all engine speeds; the 3 second polarity advance pulses 45, 46 and 47 are blocked by an electronic switch 48 until a sufficient engine speed has been reached. When the engine has reached a speed requiring the advanced ignition timing, the electronic switch 48 closes and allows the three second polarity advance pulses 45-47 to become active. The three first polarity normal retard pulses 42-44 continue to be active, but now since each one as shown in FIG. 2 is shortly preceded by an advance pulse which has already triggered the capacitive discharge, as presently described, each such retard pulse finds no energy remaining to be discharged. From the standpoint of the spark plugs 2-4 the net effect is the same as if the advance pulses were fully turned on and the retard pulses were fully turned off.

At the higher engine speeds, the presence of both the advance trigger pulses and the retard trigger pulses in the gate circuits of controlled rectifiers 27, 28 and 29 merely causes each one of these rectifiers to be in a conductive state for a longer period of time than would be the case if only the retard trigger pulses were active.

Specifically, the first polarity normal retard timing pulse 42 for triggering rectifier 27 is generated when magnetic junction 40 rotates past coil 32 in the proper direction of rotation, at which time the dotted end of coil 32 is positive relative to the undotted end. The second or opposite polarity advanced timing pulse 45 for triggering the same rectifier 27 is generated when magnetic junction 41 rotates past coil 33, in the same direction of rotation of course, at which time the dotted end of coil 33 is negative relative to the undotted end. Therefore spark plug 2 of engine 1 operates with spark retarded when magnetic junction 40 and coil 32 are solely in control of the triggering of rectifier 27. Conversely, spark plug 2 operates with spark advanced when magnetic junction 41 and coil 33 are allowed to initiate the triggering of rectifier 27.

In like manner, the normal retard pulse 43 for rectifier 28 is generated when magnetic junction 40 rotates past coil 33, whereas the advance pulse 46 for rectifier 28 is generated by coil 34 when magnetic junction 41 rotates past coil 34.

Finally, the normal retard pulse 44 for rectifier 29 is generated by magnetic junction 40 acting on coil 34, whereas the advance pulse 47 for rectifier 29 is generated in response to the passage of magnetic junction 41 past coil 32.

The control over the flow of advance pulse currents is achieved by a single electronic switching means 48, which is located in a circuit leg common to all three advance pulse branch circuits. Since the normal retard pulse currents do not flow through this circuit leg, the electronic switch means 48 has no control over the retard pulse currents. The electronic switching circuit is controlled by a signal which varies with engine speed; at low engine speeds the signal is low and the electronic switch is in the open condition; at high engine speeds the signal is high enough to drive the switch into the closed or conductive condition.

More particularly, the three first polarity or normal retard timing pulses 42-44 are connected through three first polarity branch circuits, which are shown identical, one to the other. Referring to FIG. 1, the first polarity branch circuit which supplies retard timing signals to rectifier 27 includes windings 32, diode 49, gate input resistor 50, the gate-to-cathode junction of controlled rectifier 27, ground line 17, bias capacitor 51, bias line 52, and resistor 53. The gate-to-cathode junction of rectifier 27 acts much like a diode; current can flow into the gate and out of the cathode with a voltage drop very much like that of a forward-biased diode; current flow in the reverse direction encounters a very high impedance very much like that of a reverse-biased diode.

When the first polarity retard timing signal generated by the winding 32 is large enough to overcome the bias voltage on capacitor 51, as well as supply the diode drop of diode 49 and the diode-like drop of the gate-to-cathode junction of rectifier 27, then gate trigger current can flow in the first polarity branch circuit. If capacitor 15 is charged, rectifier 27 will trigger a discharge as soon as the very low gate triggering threshold current of rectifier 27 has been attained. The subsequent gate current pulse that passes through the gate-to-cathode junction acts to charge up the bias capacitor 51 and develop the self-bias voltage on line 52.

Capacitor 51 is charged by the total of the gate current pulses of rectifier 27, 28 and 29. Below the speed of automatic electronic advance, a pair of resistors 54 and 55 which are connected in series across capacitor 51 comprise the only bleeder able to drain charge from capacitor 51.

A resistor 56 in series with a diode 57 serves to transmit the negative bias voltage from line 52 into the gate circuit of rectifier 27, which keeps rectifier 27 non-conducting until either a retard pulse via diode 49 or an advance pulse via diode 58, as subsequently described, reaches node 59 to the gate circuit and subsequently attains a sufficient amplitude to supply the positive gate triggering voltage and gate triggering current of rectifier 27.

Resistor 56 constitutes a minor added shunt load on the pulse signals appearing at node 59, thereby attenuating the pulse signals somewhat. This tends to raise the minimum RPM for cranking the engine, which is undesirable. At the very low cranking speeds, however, the bias voltage in capacitor 51 is very nearly zero. The addition of diode 57 therefore effectively prevents resistor 56 from acting as an appreciable load until the pulse signal at node 59 reaches a voltage sufficient to supply the forward voltage drop of diode 57. Since this forward voltage drop is inherently very close to the gate triggering voltage of rectifier 27, even without care in selection of components, the net effect is to allow the weak pulse signal developed while cranking to reach the gate of rectifier 27 with very little attenuation, until the gate triggering voltage of rectifier 27 has been attained. Such an arrangement gives the most sensitive triggering possible at cranking speeds, thereby making the engine easier to start by hand.

A capacitor 60 is shown paralleling the gate-to-cathode junction of controlled rectifier 27 for the purpose of suppression of unwanted transient signals. Its effect upon the pulse triggering currents is so slight as to be negligible. When the engine is running, but during those intervals when controlled rectifier 27 is to be non-conducting, the negative bias voltage on line 52, reduced by the forward voltage threshold of diode 57, charges capacitor 60 to a negative voltage via resistors 56 and 50 in series. With this negative voltage standing on the gate of rectifier 27 and being sustained by capacitor 60 during the short lifetimes of any transient signals, controlled rectifier 27 has become highly immune to undesired triggering from transients, particularly those transients generated by the firing of spark plugs 3 or 4.

In the first polarity branch circuit of winding 32 just described for the control of rectifier 27, at engine speeds below that requiring the spark advance, as magnetic junction 40 approaches coil 32 the normal retard timing pulse 42 for spark plug 2 is beginning to develop. At this time, the gate of rectifier 27 and capacitor 60 are still charged negatively by the negative bias from capacitor 51. Capacitors 8 and 15 are charged from alternator 9, as previously discussed.

As magnetic junction 40 continues to approach coil 32, the pulse continues to develop its voltage. Soon a small current begins to flow in the loop comprised of winding 32, diode 49, resistor 56, diode 57, and resistor 53, which, as previously noted, weakens the pulse somewhat.

As the pulse continues to develop toward its peak value, a point is reached where an additional triggering current can start to flow in the loop comprised of winding 32, diode 49, resistor 50, gate-to-cathode junction of rectifier 27, capacitor 51, and resistor 53. Because of the sensitivity of rectifier 27, triggering occurs almost immediately after the triggering current starts to flow. Rectifier 27 discharges capacitor 15 through the transformer 22 to turn on controlled rectifier 20. As a result, capacitor 8 quickly discharges through the circuit 5 and particularly through pulse transformer 21 to fire spark plug 2.

After capacitor 8 is discharged, controlled rectifier 20 automatically returns to the blocking state, because the gate turn-on pulse to rectifier 20 is not sustained.

However, even after capacitor 15 is discharged through transformer 22, controlled rectifier 27 remains on or in the non-blocking state, because the trigger pulse from coil 32 is still present and building and is supplying gate current to rectifier 27. Gate current continues to flow, charging capacitor 51, until magnetic junction 40 rotates sufficiently beyond coil 32 to pass the peak and then reduce the voltage being generated therein.

Rectifier 27 automatically returns to the blocking state as soon as the current ceasess to flow in its gate lead, since the discharged capacitor 15 is unable to supply any holding current to rectifier 27 at this time.

Coil 32 continues to send current around the loop containing elements 32, 49, 56, 57 and 53, until magnetic junction 40 has moved well beyond coil 32 and the voltage generated therein becomes less than the two diode drops in the loop.

As magnetic junction 40 moves through the dead space between coils 32 and 33, alternator 9 recharges capacitors 8 and 15, the latter through resistor network 16 and 16a. Capacitors 8 and 15 are now charged and ready for the firing of spark plug 3.

Also while magnetic junction 40 has been moving through the dead space between coils 32 and 33, series connected bleeder resistors 54 and 55 have been draining some charge from capacitor 51 to assure that the voltage on capacitor 51 is always less than the peak triggering signals from coils 32, 33 or 34. If this were not done, capacitor 51 would charge to the peak voltage of the strongest one of the trigger signals, and the two weaker trigger signals would then be unable to trigger their associated controlled rectifiers.

As the engine speed is increased, a point is reached where it is desirable to fire spark plug 2 from the advance timing pulse 45 generated when magnetic junction 41 rotates past coil 33. Here again, the capacitive discharge will be triggered when the advanced timing current of trigger pulse 45 starts to flow into the gate of controlled rectifier 27, which occurs before the peak of this pulse current.

Because of the relationship of the negative bias voltage on capacitor 51 with engine speed, the simple means for sensing engine speed shown in FIG. 1 may be used to develop a transfer signal to actuate the switch means 48. Alternate arrangements are shown in FIG. 4 and FIG. 5.

In FIG. 1, when the engine speed has reached the desired level, the voltage across resistor 54 of series resistor network 54 and 55 reaches the threshold voltage of the base-to-emitter junction of transistor 61 which is connected to control controlled rectifier 62 via a coupling resistor 63. Above this speed, high gain transistor 61 may be considered to be essentially a short circuit from collector-to-emitter, since any collector current demanded of transistor 61 is limited to a very small value by the high resistance of resistor 63. With transistor 61 conductive, a small current flows from the positive grounded side of capacitor 51 through transistor 61 and resistor 63 into the gate circuit of controlled rectifier 62, with some going into the gate and out the cathode lead, and the rest going through a parallel resistor 64. The two currents rejoin and immediately divide and flow through separate diodes 65, 66 and 67, to and through the separate coils 32, 33 and 34, and finally return through the resistors 53, 53' and 53" to the common line 52 back to the negative ungrounded side of capacitor 51. Thus it has been shown how auxiliary controlled rectifier 62 is maintained in a non-blocking state by the small current passing into its gate lead supplied by transistor 61. However, the anode of rectifier 62 passes no current during the intervals between advance pulses, since at such times there is no net driving voltage for the loop comprised of rectifier 62, the several diodes 65, 66 and 67, the several coils 32, 33, 34, the several resistors 53, 53' and 53", and a resistor 65 ^a connected between line 52 and the anode. This means that if transistor 61 were turned off, rectifier 62 would shortly respond by recovering to its blocking state during the dead interval between advance pulses. This condition would be maintained until transistor 61 turned on again.

In FIG. 1, the operation of the opposite polarity advanced timing branch circuit for controlled rectifier 27 commences with the following initial conditions:

The engine speed is high enough such that the negative bias voltage on capacitor 51 is holding transistor 61 turned on via resistors 54 and 55. Transistor 61 is supplying a small turn-on gate drive to auxiliary rectifier 62, but rectifier 62 is not carrying current in its anode lead. Capacitor 51 is being drained by current flowing through resistor 54 feeding resistor 55; by current flowing into the emitter of transistor 61 and out the base to node 68 and also feeding resistor 55; and by current flowing into the emitter of transistor 61 and out the collector, through resistor 63, through resistor 64 and the gate-to-cathode junction of rectifier 62 in parallel, through the several diodes 65, 66 and 67, through the several coils 32, 33 and 34, and through the several resistors 53, 53' and 53".

As magnetic junction 41 approaches coil 33, a positive voltage pulse 45 is generated at the undotted end of coil 33 relative to the dotted end. At this generated pulse gathers strength as shown in FIG. 2, the three small currents that had been flowing through resistors 53, 53' and 53" all crowd into resistor 53'. As the pulse continues to develop, rectifier 62 begins passing anode-to-cathode current, increasing the voltage drop across resistor 53', and causing a voltage to appear across resistor 65 ^a .

When the voltage across resistor 53' has attained a value equivalent to two diode drops, the current path through diode 58, resistor 56 and diode 57 begins to conduct.

At this point, however, the advance pulse has not yet risen to the level necessary to fire controlled rectifier 27, as hereinafter developed.

In the advanced timing mode of operation, it has been found advantageous to employ a strong set of advance timing pulse currents driving the gates of the controlled rectifiers 27, 28 and 29, relative to a weaker set of normal retarded timing pulse currents. This strong/weak relationship gives the advance pulse currents good control over the negative bias voltage developed, and stabilizes and balances the firing of the three spark plugs while in the advanced timing mode.

As a consequence of this strong/weak relationship, the negative bias voltage on capacitor 51 however tends to increase very suddenly when the system first enters the advanced timing mode of operation, and also tends to become too high for the gate-cathode junctions of rectifiers 27, 28 and 29 to block, particularly at very high engine speeds. To overcome these difficulties, it has been found advantageous to divert a large portion of each advance timing current pulse 45-47 away from capacitor 51.

To accomplish this diversion, resistor 65 ^a is connected to control a transistor 69 through a resistor 70 to establish a diversion path 71 for that large portion of the advance pulse current that is to be diverted away from capacitor 51. Thus, resistor 65 ^a senses that one portion of the advance pulse current that is flowing and charging capacitor 51. Resistor 70 and the high gain transistor 69 assure that an essentially proportional current to that sensed by resistor 65 ^a will be diverted through the path 71.

Resistors 63 and 64 of the circuit to rectifier 62 are so high in resistance that their contribution to the total advance pulse current may be neglected.

As a result of the diversion arrangement, the large sudden increase in negative bias voltage as well as the excessive negative bias voltage developed across capacitor 51 at high speeds are effectively eliminated. The voltage across capacitor 51 tends to increase smoothly with speed, except for a small sudden increase as the system goes into the advanced timing mode, which is deemed desirable, inasmuch as it tends to insure that the advanced timing mode will be sustained until the speed drops a small amount.

Thus, when the voltage drop across resistor 65 ^a exceeds the base-to-emitter threshold of transistor 69, emitter current, and hence collector current, begins to flow in transistor 69. At this point capacitor 51 is now being heavily drained by the collector current in line 71, but as yet there is no advance pulse charging current reaching capacitor 51. The effect of the previous retard pulse charging of capacitor 51 is being dissipated, however.

As the pulse 45 in coil 33 continues to grow toward its peak value, a point is reached at which the voltage developed across resistor 53' is enough to overcome the negative bias voltage from capacitor 51, thus causing conductor 72 to be raised above ground potential. As the pulse continues to develop, conductor 72 continues to increase in positive voltage, until there is enough voltage to supply the diode drop of diode 58 plus the gate threshold triggering voltage and current of controlled rectifier 27. At this point controlled rectifier 27 triggers and initiates an action similar to the previously described capacitive discharges of trigger capacitor 15 and main capacitor 8, which results in the firing of spark plug 2.

Thus far, it has been shown how the approach of magnetic junction 41 to coil 33 at high engine speeds has resulted in the advanced triggering of rectifier 27, and the resulting advanced firing of spark plug 2. Previously, it had been shown how the approach of magnetic junction 40 to coil 32 at low engine speeds had resulted in the normal retarded firing of the same rectifier 27, and the resulting normal retarded firing of spark plug 2. The angular difference, as measured on the engine crankshaft, between these two modes of firing, is the amount of automatic electronic spark advance available to spark plug 2. Results will be very nearly identical for spark plugs 3 and 4. Control over the amount of advance is achieved by appropriate physical placement of junction 41 relative to junction 40, taking into account the relative placement of coil 33 to coil 32.

Following the advance pulse triggering of rectifier 27, the pulse continues to increase. A strong gating current now flows through resistor 50, into the gate of rectifier 27, which increases to a peak as magnetic junction 41 passes under coil 33. Emerging from the cathode of rectifier 27, a fraction of this current flows into capacitor 51, thereby increasing its charge. An even larger fraction is diverted away from capacitor 51 via line 71 and transistor 69. A small fraction flows into resistor 54 and another small fraction into the emitter of transistor 61.

Meanwhile, magnetic junction 40 has been approaching coil 32, causing the normal retard timing pulse 42 for rectifier 27 to be generated. The dotted end of coil 32 is the more positive.

As magnetic junction 40 approaches coil 32, magnetic junction 41 begins to move away from coil 33. The normal retard pulse in coil 32 increases, while the advance pulse in coil 33 decreases. The gate current supplied to rectifier 27 decreases at first, in response to the decreasing advance pulse.

A crossover point is reached where coil 32 takes over the functions of supplying gate current to rectifier 27, and supplying current to resistor 56 and diode 57.

After the crossover point, coil 32 is now charging capacitor 51. Coil 33 supplies only resistor 53' , but some of this current is a discharge current taken from capacitor 51 via diversion line 71. Current flow from coil 33 through resistor 65 ^a tend to keep diversion transistor 69 conductive.

Thus, here again the effect of the normal retard current pulse upon the negative bias voltage developed across capacitor 51 is somewhat dissipated. The overall effect is such that the advance pulses have gained effective control over the values of negative bias developed at the higher engine speeds.

Resistors 53, 54' and 53" play a role in strengthening the advance current pulses while also functioning to weaken the retard current pulses because they are connected into the opposite polarity advance pulse branch circuits as shunt loads; whereas they are connected into the first polarity normal retard branch circuits as series loads. Increasing the ohmic value of these resistors therefore favors the advance current pulses charging capacitor 51, and weakens the retard current pulses charging capacitor 51.

Previously it was shown how the retard pulse from coil 32 takes over and supplies the gate current of rectifier 27, that was formerly supplied by the advance pulse from coil 33.

Even if there were to be a short interruption of this gate current before coil 32 could take over, and rectifier 27 were to recover to its blocking state, there would be no charging of capacitors 15 or 8 before gate current from coil 32 began to flow. Consequently, there could be no normal retard firing of spark plug 2.

When magnetic junction 41 moves sufficiently away from coil 33, all advance pulse current flow ceases, and the rest of the operation is similar to that previously described in connection with normal retard firing of spark plug 2, except that there is no capacitor discharge.

In reference to the circuits of FIGS. 1, 4 and 5, a satisfactory angle of advance is approximately 25°, and such construction is shown in FIG. 2. Thus, if the relative retard firing angles, assumed as a reference, are 0°, 120° and 240°, respectively, the advanced firing angles are at 335° , 95° and 215°, respectively, where crankshaft angle in degrees increases linearly and cyclically from 0° to 360°. Thus, the illustrated junction 41 is advanced 25° beyond the normal 120° position with respect to the junction 40 and establishes a leading pulse signal in winding 33, 25° prior to the alignment of the junction 40 with the winding 32. Winding 33 thus produces the opposite polarity signal 45 which is applied via the lead 72 and diode 58 to fire the control rectifier 27, which is otherwise fired from the winding 32. This then fires the associated control rectifier 20 of circuit 5 to discharge the capacitor 8 through the transformer 21 and fire the associated spark plug 2. 25° later the junction 40 is aligned with the winding 32 and it produces the positive pulse 42 which is applied via the diode 49 to fire the same controlled rectifier 27. It will, however, find this rectifier already in a conductive state and will, consequently, merely extend its conductive period somewhat.

Each of the other windings 34 and 32 similarly create a negative or opposite polarity signal which, at speeds above the selected level, is permitted to conduct through the associated resistors 53" and 53, respectively, to line 52 returning to the opposite side of the respective windings 34 and 32 through the controlled rectifier 62 and associated steering diodes 67 and 65. The signals are transmitted through similar circuits from the corresponding sides of the windings 34 and 32, through the coupling diodes 58' and 58" , to resistors 56' and 56" and common diode 57. The coupling line 72' connects winding 34 to fire the controlled rectifier 28 and line 72" connects the winding 32 to fire the controlled rectifier 29 and thereby produce the automatic corresponding spark advance on spark plugs 3 and 4 as was produced for spark plug 2.

This condition is maintained until such time as the speed of the engine is reduced to reduce the voltage on the capacitor 51 below the level necessary to bias transistor 61 to conduct and hold the controlled rectifier 62 on. Each pulse signal not only serves to develop a voltage signal applied to trigger the appropriate one of the three controlled rectifiers 27, 28 or 29, but also serves to sustain the charge on capacitor 51. This will maintain the circuit in the advance firing state. In fact, with the circuit but without transistor 69 and resistor 70, and with resistor 65 ^a replaced by a conductor, an overcharge condition would occur with a hysteresis switching characteristic requiring excessive slowdown of the engine 1 to cut off transistor 61 and the controlled rectifier 62. l

The hysteresis effect of the switch circuit 48 is minimized by reducing the charge reaching the capacitor 51 during each of the negative pulse cycles, by establishing a proportional discharge current from the capacitor 51 to prevent excessive or overcharging, as previously described.

Referring particularly to FIG. 3, a characteristic obtained with a three-cylinder ignition system is illustrated with the revolutions per minute or speed indicated on a horizontal or X-axis and an arbitrarily reference timing angle shown on the vertical or Y-axis. To measure the ignition firing angles, the test setup employed a rotating protractor scale affixed to the flywheel, a fixed pointer adjacent to the rotating protractor scale, and an ignition timing light of the stroboscopic flash type to illuminate the pointer and scale at the instant of firing of a selected spark plug. Increasing angular readings on the test protractor indicated advance. The test stand provided a simulated engine speed range of approximately 500 rpm to 7,000 rpm.

In the low operating speed range the firing characteristic is a relatively straight line 73 which produced firing of the second cylinder at an arbitrarily referenced angle of 167.0°. The first and third cylinders should fire 120° at either side therefrom and in actual tests fired at 287.3° and 47.1°, respectively. This firing characteristic with increasing speed advanced slightly at about 1,100 rpm and switched rapidly at approximately 1,500 rpm as shown by the rapid advance line 74 which is essentially a vertical line which moved from 168° to slightly above 190°. Above that speed the engine fired essentially at an angle of 190.8° for the second cylinder as shown by firing line 75 or slightly under 25° advance. The first and third cylinders fired at 310.5° and 71.0°, respectively, or once again slightly under 25° advance.

The engine continued to fire in the advanced mode while operating above the switching speed and continued with a decreasing speed until the speed dropped very slightly below the advance triggering point, as shown by the rapid retard line 76. At the slightly lower speed the timing rapidly switched back to the line 73 as a result of the the turn-off of the controlled rectifier 62. Thus, at the slightly lower speed, the charge on the capacitor 51 dropped below the holding level for maintaining transistor 61 on and thereby removed the control signal from the controlled rectifier 62. Consequently, when the advanced timing pulse signal disappears, as it does in the interval between pulses, the anode current drops to zero, and the controlled rectifier 62 switches off and ramains off.

The circuit thus provides a simple and reliable system for producing an electronic spark advance in a distributorless ignition system employing branch circuits for different cylinders.

The speed at which the advance occurs may vary with temperature if conventional resistor elements are employed within the biasing network of a sensing transistor or switching transistor. Such effects can be significantly reduced by employing an appropriate thermistor network for the sensing resistor network. In addition, there may be some variation from engine to engine in connection with the normal construction of the triggering circuitry, trigger magnets, air gaps, etc. It is expected that all of these variations will generally be acceptable for the conventional internal-combustion engine application such as snowmobiles.

The circuit can employ other suitable sensing means responsive to the engine speed to actuate the switch means 48.

For example, in the circuit of FIG. 4 the output of the normal retard timing trigger pulses are employed to actuate a separate tachometer circuit for controlling the sensing transistor 61 at a parituclar speed. Only that portion of the trigger circuit including rectifiers 27, 28 and 29 is shown in FIG. 4 as the balance of the circuit may be as in FIG. 1. Further, the other elements in FIG. 4 corresponding to those of FIG. 1 are correspondingly numbered for simplicity of description and explanation.

In FIG. 4, the voltage dividing network connected across the capacitor 51 is replaced with a single bleeder resistor 77. The transistor 61 in the embodiment of FIG. 4 is controlled by a transistor 78 which is connected to the output of the normal timing trigger pulses to turn on at a selected speed as follows.

The emitter to collector circuit of the transistor l78 is connected in series with a current-limiting coupling resistor 79 between the common line 52 and the base of the transistor 61. The base of the transistor 78 is coupled by a resistor 80 to a branch line energized from the output of the individual windings 32, 33 and 34. A voltage dividing network includes a resistor 81 and a resistor 82 connected in series between the line 52 and the output of the windings in series with a Zener diode 83. Individual isolating diodes 84, 85 and 86, respectively, conduct the retard signal pulses of the windings 32, 33 and 34 to the one side of the Zener diode 83 such that each of the positive pulse signals are applied thereto. When the voltage exceeds the voltage of the Zener diode, a signal is conducted through the voltage dividing network of resistors 82 and 81 with the junction voltage applied via the resistor 80 to the base of the transistor 78. An averaging or smoothing capacitor 87 is connected in parallel with the resistor 81. Thus, the pulse signals serve to charge the capacitor 87 to an average level proportional to the amplitude of pulse generation. This, in essence, establishes a tachometer signal across the resistor 81 which is applied across the base to emitter junction of the transistor 78 in series with the current limiting resistor 80. At a selected engine speed the voltage drop across the resistor 81 is sufficient to turn the transistor 78 on. This then turns on the transistor 61 which is driven to conduct as a result of the voltage applied between the emitter and the common line 52 by the self-biasing capacitor 51. As a result, the controlled rectifier 62 is gated on and conducts the opposite or advance signals as in FIG. 1. It is locked in the on condition by the continued pulsing of the tachometer circuit, which keeps capacitor 87 charged.

The circuit of FIG. 4 thus functions in essentially the same manner as that of FIG. 1, but with the normal retard timing trigger pulses providing the charging of a separate tachometer network to control the initial turn-on and the holding-on of the electronic switch means 48.

A further alternative construction is shown in FIG. 5 wherein the negative half-cycles from the high speed winding 13a of the main alternator 9 are connected into a tachometer type network to generate a tachometer signal which is coupled to control the switching transistor 61. In the circuit of FIG. 5 a coupling line 88 is connected to the output of the high speed charging winding 13a, as illustrated in FIG. 1. A blocking diode 89 blocks the positive half-cycles while transmitting the negative half-cycles. The circuit includes a coupling resistor 90 in series with a parallelled resistor 91 and capacitor 92 connected between the resistor 90 and the common ground line 17. A tachometer or speed related voltage signal is thereby generated at the junction of the resistors 90 and 91 which is coupled via a Zener diode 93 in series with a base resistor 94 to the base of the transistor 61. A base to emitter resistor 95 is connected between the resistor 94 and the common ground connecting line. When the tachometer signal reaches a selected level, the Zener diode 93 conducts, a voltage signal develops across the resistor 95 to turn on the transistor 61 with a resulting turning-on of the control rectifier 62 as in FIGS. 1 and 4. This establishes the spark advance. As in the prior embodiments, the control rectifier 62 is locked on until such time as the speed drops slightly below the set switching speed.

The circuit of FIG. 5 once again functions essentially in the same manner as that of the previous embodiments with the triggering signal this time developed as a result of the negative half-cycle output of the main alternator 9 which, of course, is related to the speed of the engine.

Any other desired tachometer signal can, of course, be employed which will produce a reliable and repeatable operation of the circuit.

The circuit might also employ an advance/retard switching system which relies solely, for example, on the negative or opposite polarity signals of the windings 32-34. For example, it is possible to connect a Zener diode directly between the gate of the controlled rectifier 62 and the common return line 52 such that each advance pulse associated with a particular minimum speed may build up to a sufficient level to overcome the Zener voltage and trigger the controlled rectifier 62. However, such a system in essence removes the initial portion of each advance pulse from the branch circuits to rectifiers 27, 28 or 29 because rectifier 62 is not on until each signal rises to the Zener level. This is a very significant part of the signal and a degenerate circuit operation results compared to the lock-on circuitry previously shown and described.

Previously it was shown how the advance timing pulse for spark plug 2 was generated by the rotation of magnetic junction 41 past coil 33, whereas the normal retarded timing pulse for the same spark plug 2 was generated by the rotation of magnetic junction 40 past coil 32.

Alternate magnetic construction and circuit connection may be employed. Thus, magnetic junction 41 rotating past coil 34 may be chosen by appropriate magnet construction and circuit connection to provide the source of the advanced timing pulse for spark plug 2, with the magnetic junction 40 rotating past coil 32 providing the source of the normal retarded timing pulse for spark plug 2. The other spark plugs would be controlled similarly, of course, such that the desired balance is maintained.

Further, the circuit can also be otherwide varied to employ other suitable switching means and circuits to obtain the functions and results of the illustrated embodiments.

As previously noted, the present invention is particularly compatible with the alternator power source or system for snowmobiles or the like which require a significant amount of power for lighting and battery charging. In such systems, the alternators typically have 12 poles and are mounted inside the flywheel and the remaining space available for the trigger structure is limited. The present invention provides a trigger unit which can be mounted as a small, compact assembly within a main alternator and which will provide reliable retarded and advanced triggering of the ignition system.

The present invention thus provides a highly improved trigger system for mechanically distributorless ignition systems for multiple cylinder engines. The invention describes a novel trigger pulse generator for two-cylinder ignition applications in which three trigger coils and two rotating magnetic transitions combine to generate a total of six trigger pulses. The magnetic transitions are of opposite magnetic sense, allowing the 6 pulses to be separated by polarity into two groups of 3 pulses each. The pulses of one polarity are treated as normal retarded timing pulses, and the pulses of the opposite polarity are treated as advanced timing pulses. The advanced pulse and the retarded pulse for any given spark plug are generated in two different trigger coils, and are directed by a diode steering network to accomplish the firing of said given spark plug. Automatic electronic spark advance is accomplished by requiring the advance pulses to pass through an electronic switch, which is made conductive to effect the spark advance, and non-conductive to effect the normal spark retard. The trigger system provides electronic spark distribution in the proper sequence to the various cylinders, and inherently prevents the engine from running backwards.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims, particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.