US3661132A

US3661132A - Ignition circuit with automatic spark advance

Info

Publication number: US3661132A
Application number: US882355A
Authority: US
Inventors: James B Farr
Original assignee: Tecumseh Products Co
Current assignee: Tecumseh Products Co
Priority date: 1969-12-15
Filing date: 1969-12-15
Publication date: 1972-05-09
Anticipated expiration: 1989-05-09

Abstract

A solid state capacitor discharge ignition system for use in a single-cylinder engine having a magneto for an electrical energy source wherein the capacitor is discharged through a silicon controlled rectifier in response to trigger signals generated by a trigger assembly mounted on the rotor and stator of the magneto. The trigger assembly generates at least two discrete spaced pulses at running and cranking speeds, and the spacing between the two pulses corresponds to a desired shift in the engine timing between cranking and running speeds. The trigger assembly, the silicon controlled rectifier and the circuit connection therebetween are such that both pulses are applied to the controlled rectifier at all engine speeds; but the retarded ignition pulse is effective at cranking speeds and the advance pulse is effective at running speeds.

Description

United States Patent Farr [54] IGNITION CIRCUIT WITH AUTOMATIC SPARK ADVANCE [72] Inventor: James B. Farr, Ann Arbor, Mich.

[73] Assignee: Tecumseh Products Company, Tecumseh,

Mich.

[22] Filed: Dec. 15, 1969 [21] Appl.No.: 882,355

Related U.S. Application Data [63] Continuation of Ser. No. 684,052, Nov. 17, 1967,

[ 51 May 9, 1972 Primary ExaminerLaurence M. Goodridge Attorney-Barnes, Kisselle, Raisch & Choate [5 7] ABSTRACT A solid state capacitor discharge ignition system for use in a single-cylinder engine having a magneto for an electrical energy source wherein the capacitor is discharged through a silicon controlled rectifier in response to trigger signals generated by a trigger assembly mounted on the rotor and stator of the magneto. The trigger assembly generates at least two discrete spaced pulses at running and cranking speeds, and the spacing between the two pulses corresponds to a desired shift in the engine timing between cranking and running speeds. The trigger assembly, the silicon controlled rectifier and the circuit connection therebetween are such that both pulses are applied to the controlled rectifier at all engine speeds; but the retarded ignition pulse is effective at cranking speeds and the advance pulse is effective at running speeds.

15 Claims, 15 Drawing Figures PATENTEDMAY 9:912

sum 1 [IF 3 ATTORNEYS PATENTEDMAY 9 I972 3.661 132 sum 2 OF 3 INVENTOR JAMES B. FARR ATTORNEYS PATENTEDMAY 9 1972 sum 3 OF 3 INVENTOR JAMES B. FARR ATTORNEYS IGNITION CIRCUIT WITH AUTOMATIC SPARK ADVANCE This application is a continuation of my copending application (now abandoned) Ser. No. 684,052, filed Nov. 17, 1967, and entitled IGNITION CIRCUIT WITH AUTOMATIC SPARK ADVANCE.

It is well known that the combustible charge in an internal combustion engine is normally ignited at or near top dead center during the compression stroke of the piston. Engine performance can be improved if the ignition timing varies with engine speed. Ignition may be timed at substantially top dead center during starting with the timing being advanced as the speed of the engine increases. With breaker point ignition systems, ignition timing may be advanced using mechanical means that are responsive to engine speed. Such ignition systems have numerous disadvantages associated primarily with wear of the breaker points and other parts that in time cause unwanted variation in the ignition advance.

Relatively high manufacturing costs as well as service and maintenance problems have generally precluded the use of such ignition systems having automatic timing advance on single-cylinder engines that are mass produced at the lowest possible cost. It is essential that the cost of an ignition system for single-cylinder engines be held to a minimum due to vigorous competition in the small engine field. Hence it is common practice in the small engine field to select a fixed ignition timing representing a compromise between the optimum timing at starting and at running speeds. Easy starting has been a problem with small engines, particularly with engines having manual starting. However, as long as engine timing is fixed at a compromise for starting and for running, there is a limit to which the ease in starting may be improved. Hence, it is highly desirable to provide a timing advance between starting and running speeds at a low cost. Automatic timing advance at a low cost would be particularly desirable when incorporated in solid state ignitions such as disclosed in my copending application entitled Ignition System, Ser. No. 654,860, filed July 20, 1967, now US. Pat. No. 3,490,426.

The objects of the present invention are to provide ignition systems having automatic timing advance that are compatible with solid state ignition circuits; that eliminate moving parts and hence eliminate well-known disadvantages from wear in prior ignition systems having automatic timing advance; that are simple in construction, relatively low in cost and reliable by comparison with prior ignition systems having automatic timing advance; that provide an effective shift in engine timing from an optimum timing for starting to an effective timing at running speeds; and that are particularly suited to ignition systems for single-cylinder engines that are mass produced at the lowest possible cost.

Other objects, features and advantages of the present invention will be apparent in connection with the following description. the appended claims and the accompanying drawings in which:

FIG. 1 is a view diagrammatically illustrating a magneto having a main charging coil and a pair of trigger coils having different turns;

FIG. 2 is a circuit diagram of a solid state, capacitordischarge ignition circuit used with the magneto shown in FIG.

FIG. 3 is a diagram illustrating waveforms of voltages generated in the trigger coils of FIGS. 1 and 2;

FIG. 4 is a fragmentary view of a magneto showing another embodiment of the present invention wherein two trigger coils are arranged with different air gaps;

FIG. 5 is a circuit diagram illustrating the modification in the circuit of FIG. 2 for the dual coil arrangement of FIG. 4;

FIG. 6 illustrates a still further modification for the circuits of FIGS. 2 and 5 to isolate the trigger coils from each other;

FIG. 7 is a fragmentary view of a magneto showing yet another embodiment wherein a single trigger coil is arranged on a narrow U-shaped core to develop consecutive triggering pulses;

FIG. 8 is a circuit diagram illustrating modification of the circuit of FIG. 2 for the single trigger coil and U-shaped core of FIG. 7;

FIG. 9 is a diagram illustrating waveforms for voltages generated in the modification of FIGS. 7 and 8;

FIG. 10 is a fragmentary view of a magneto showing a still further embodiment wherein a single trigger coil is arranged on a wide U-shaped core;

FIG. 11 is a diagram illustrating waveforms of voltages generated in the single coil modification of FIG. 10;

FIG. 12 illustrates a still further modification of the present invention;

FIG. 13 illustrates a modification of the present invention wherein two coils are wound on the same core and connected in pushpull;

FIG. 14 is a diagram illustrating the waveforms of the voltages generated in modification of FIG. 13', and

FIG. I5 is a circuit diagram illustrating one temperature compensation circuit.

Referring more particularly to FIGS. 1-3, there is illustrated a magneto designated generally at 10 and comprising a stator 12 and a rotor 14 which is drivingly connected to the crankshaft of a single-cylinder engine (not shown) so as to rotate in a clockwise direction as viewed in FIG. 1 in synchronism with the engine. A permanent magnet 18 embedded in rotor 14 has a north pole face 20 and a south pole face 22 that extend circumferentially along the inner periphery of rotor 14.

Faces

20, 22 have a magnetic gap 23 therebetween. The stator 12 is fastened on the engine by suitable means and is stationary relative to rotor 14. Mounted on stator 12 is a main charging coil assembly 26 which includes a charging coil 28 wound on the center leg 32 of an E-shaped core 34. This arrangement provides a rapid flux reversal through the center leg 32 generating a relatively high voltage in the coil 28. Two

trigger coil assemblies

40, 41 are also mounted on stator 12 in spaced relation to each other and to the main coil assembly 26.

The trigger coil assembly 40 generally comprises a coil 42 wound on a core 44 which is mounted at its radially inner end on a plate 46 adjustably fastened on the stator 12. Core 44 projects radially outwardly of stator 12 with the radially'outer end spaced from rotor 14 to form an air gap 48 with magnet 18. Trigger coil assembly 41 comprises a trigger coil 43 wound on a core 45 which is mounted at its inner end on a plate 47 also adjustably fastened on stator 12. Core 45 has an air gap 50 with magnet 18. As illustrated in FIGS. 1 and 2, coil 42 has fewer turns than coil 43 and the

air gaps

48, 50 are substantially equal. The angular displacement between axis 50 of the charging coil 28 and the axis 52 of the trigger coil 42 is designated 0 1 whereas the corresponding angular displacement of the axis 53 of the coil 43 is designated 0 2 and the an gular displacement between the axes S2, 53 is designated 6 6 l and 6 2 may also be considered as representing crankshaft angles and also time. In general the crankshaft angle, 0 of the trigger coil assembly 40 is selected to provide an advanced ignition timing when the engine is running. The crankshaft angle, 6 of the trigger coil assembly 41 is selected to provide a retarded ignition timing when the engine is cranked during starting.

Referring more particularly to the circuit in FIG. 2, a Zener diode 58 is connected directly across the charging coil 28 to regulate the maximum positive voltage generated in coil 28 when the upper terminal as viewed in FIG. 2 is positive. Also connected across the charging coil 28 is a series circuit comprising a silicon diode 60, a capacitor 62 and the primary winding 64 of an ignition transformer 66. The secondary winding 68 of transformer 66 is directly connected across a spark plug 72. Connected directly across the serially connected capacitor 62 and winding 64 is a silicon controlled rectifier 74 having an anode 76, a cathode 78 and a gate 80. The trigger coils 42, 43 are connected in parallel with each other and across the gate 80 and cathode 78 to provide triggering signals to the gate to initiate conduction of rectifier 74 as the coils 42,

43 are swept by a magnet 18. The

coils

42, 43 are wound on the

cores

44, 45, respectively, and are connected to the gate 80 so as to have the same relative polarity as indicated by the dots in FIG. 2.

The operation of the ignition described hereinabove can best be understood in connection with the waveforms illustrated in FIG. 3 wherein crankshaft angles, are plotted along the abscissa axis and voltage is plotted along the ordinate axis. The abscissa axis can also be considered as generally representing time at different scales for different engine speeds. It will be understood that the waveforms in FIG. 3 are for purposes of explanation and are not necessarily intended to be to scale. When the engine is turned at a relatively low cranking speed during starting, as magnet 18 sweeps past the charging coil 28, the alternating voltage generated in coil 28 is rectified by diode 60 to charge capacitor 62 to the polarity indicated in FIG. 2. As magnet 18 continues rotation in a clockwise direction past trigger coil assembly 40, an alternating triggering signal 84 (FIG. 3) is generated in coil 42 and ap plied to gate 80. The signal 84 comprises three

pulses

87, 87', 87" of alternating polarity. Coil 42 is connected to gate 80 so that the first pulse 87 is negative, the second pulse 87 is positive and the third pulse 87" is negative. In the preferred embodiment, only the positive pulse 87' is used. Pulse 87' is generated when gap 23 passes core 44. Rectifier 74 has a critical gate voltage designated at the voltage level 86 in FIG. 3. The number of turns in coil 42 is selected so that at cranking speeds pulse 87' has an amplitude substantially below level 86 and hence does not fire rectifier 74. As magnet 18 continues to rotate past the trigger coil assembly 41, an alternating voltage 88 is generated in the second trigger coil 43. The signal 88 also includes a first negative pulse 89, a second positive pulse 89 and a third negative pulse 89". The number of turns in coil 43 is selected so that at cranking speeds, pulse 89" exceeds level 86 to initiate discharge of capacitor 62 through rectifier 74. The duration of pulse 89 is sufficient to allow capacitor 62 to completely discharge in a damped oscillatory manner through rectifier 74 on one discharge half-cycle and through

diodes

58, 60 on the opposite discharge half-cycle.

By way of example, coil 43 may have times the number of turns in coil 42 to assure sufficient amplitude difference between pulses 87', 89' at cranking speeds so that the pulse 87' will not fire rectifier 74 but pulse 89' will. A ratio of at least greater than five to one between the peak amplitudes of the pulses 89', 87 is preferred to obtain sufficient amplitude separation. The location, 0 of trigger coil 43 is correlated to the engine cycle so that the retarded ignition pulse 89' fires rectifier 74 at the desired crankshaft angle to facilitate easy starting, for example, at or near top dead center in the compression stroke.

As soon as the engine starts the voltage generated in coil 42 increases substantially. Hence at running speeds the first positive pulse 91' in the gate voltage from coil 42, corresponding to pulse 87', exceeds the threshold level 86 at the crankshaft angle 0 1 to fire rectifier 74 and initiate discharge of capacitor 62. The location, 9 of coil 43 is selected so that the advanced ignition timing pulse 91 exceeds level 86 at the desired crankshaft angle for running speeds, for example, an angle of 22 before top dead center. Although the amplitude of the retarded pulse corresponding to pulse 89 is also increased substantially at running speeds, the retarded pulse is ineffective since capacitor 62 is substantially fully discharged in response to pulse 91. By way of example, on engines in the 2.5-7 horsepower range a typical cranking speed is in the range of 300-400 RPM with minimum cranking speeds of 100-150 RPM and a typical idle speed is above 1,500 RPM. The circuit is designated to provide a timing shift in a speed range of 800I,000 RPM. The timing shift provides easy starting and acceptable engine performance.

Although pulses 87' and 89' are used in the preferred embodiment, it will be apparent that other pulse pairs may also be used. For example, by reversing the coil leads the first pulses corresponding to

pulses

87, 89 will be positive and have the desired time separation for a timing shift of about 20. Referring to the embodiment of FIGS. 4 and 5, the

trigger coil assemblies

40, 41 are replaced by corresponding trigger coil assemblies 100, 101. Except for the triggering circuit for rectifier 74, enclosed in dashed lines in FIGS. 2 and 5, the ignition circuit for the dual coil arrangement illustrated in FIGS. 4 and 5 is the same as that shown in FIG. 2. The trigger coil assembly includes a trigger coil 102 wound on a core 104 which is mounted at its inner end on a plate 106 adjustably fastened on stator 12. Core 104 has an air gap 108 with magnet 18 (FIG. 1). The trigger coil assembly 10] comprises a trigger coil 103 wound on a core which is mounted at its radially inner end on a plate 107 adjustably fastened on stator 12. Core 105 has an air gap 111 with magnet 18. Coils I02, I03 have the same number of turns but the air gap 108 is substantially greater than the air gap 111. With the difference in air gaps at any given speed of rotor 14, the signal generated in coil 103 will have a substantially higher amplitude than the signal generated in coil 102.

More particularly the

air gaps

108, 111 are selected so that the triggering signal generated in coil 102 has the same relationship to the triggering signal generated in coil 103 as signal 84 (FIG. 3) generated in the coil 42 (FIGS. 1 and 2) has to the signal 88 generated in coil 43. Coils I02, 103 are connected in parallel with each other and directly across the gate 80 and the cathode 78.

Coils

102, 103 have the same relative polarity as indicated by the dots in FIG. 5 and are connected to gate 80 so that the second pulse in each coil generated when gap 23 passes the respective cores will be positive as with pulses 87', 89' for coils 42, 43 (FIGS. 1-3). Hence the operation of the modification of FIGS. 4 and 5 will be apparent from the description in connection with FIGS. l-3.

Referring to FIG. 6, a modification for the circuit of FIG. 2 is illustrated wherein a silicon diode 114 is connected in series with coil 42 across coil 43. Diode 1 I4 is poled in the direction shown to decouple coil 42 from coil 43 during the positive pulse 89'. To simplify the description, the various pulses are illustrated in FIG. 3 as relatively sharp pulses occuring at different times. However the pulses may be of longer duration with some of the pulses coincident with, or at least overlapping, other of the pulses depending on the configuration of magnet 18 together with the parameters and the separation of

coil assemblies

40, 41. For example, if the negative pulse 87" overlaps the positive pulse 89 the gate voltage may be reduced to such an extent that the retard pulse 89 may not fire rectifier 74 at low cranking speeds. Additionally, with coil 42 connected directly across coil 43, coil 42 will load coil 43 impairing the effect of the retard pulse 89, particularly where, as in FIGS. 1 and 2, coil 42 has fewer turns than coil 43. However diode I14 minimizes these problems where required.

FIGS. 7-9 illustrate still a further modification for providing consecutive timing pulses whose phase and amplitude relationship at low cranking speed and at higher running speed provide automatic timing advance. The coils 40, 41 (FIG. 1-3) are replaced with a single trigger coil assembly which comprises a U-shaped core 122 mounted at its radially inner end on stator 12. Core 122 has legs 124, 126 spaced closely together. A single coil 128 is wound on leg 124 which is considered as a leading leg in that it is the first of the legs 124, 126 encountered by the leading edge 131 of the north pole face 20 during rotation of rotor 14. The angular separation between the core legs 124, 126 and the circumferential length of the leading pole face 20, that is, the angular separation between the leading and trailing edges of the pole face 20 are correlated to the engine timing cycle to obtain the required timing shift. More particularly, the leading edge 131 of the pole face 20 and the center line 130 of the gap 23 (in effeet, the trailing edge of face 20) have an angular displacement 6' equal to the desired timing shift, corresponding to the angle 0 3 (FIGS. I and 3). Coil 124 is connected directly across gate 80 and cathode 78 of rectifier 74 as illustrated in FIG. 8. The ignition circuit for the narrow U-shaped core arrangement of FIG. 7 is identical to that disclosed and described in connection with the circuit of FIG. 2, except for the trigger circuit enclosed in dotted lines (FIGS. 2 and 8), i.e., the connection of the trigger coil 128 to the rectifier 74.

The manner in which the advance and retard pulses are developed using the U-shaped core illustrated in FIGS. 7 and 8 will be more apparent in connection with the waveforms illustrated in FIG. 9. FIG. 9a is the plot of fiux, 5, versus crankshaft angle, 0, or the equivalent time, t, and similarly FIG. 9b is a plot of the voltage, V, versus crankshaft angles, 6, or the corresponding time, I. As magnet 18 approaches the trigger coil assembly 120 the first flux change is in a direction which is assumed to be negative going as illustrated by the waveform portion 113 (FIG. 9a). When the leading edge 131 of pole 20 reaches the trailing core leg 126, some of the flux from leg 124 is shunted to the leg I26 causing a flux reversal and providing a positive going flux at coil 124 designated at 135 in FIG. 9a. As magnet 18 sweeps past the trigger coil assembly 120, the flux in leg 124 remains substantially constant until the gap 123 reaches the trigger coil assembly 120 causing a rapid flux change in a positive going direction designated at 137 (FIG. 9b). The remaining portion of the flux waveform is not utilized in the embodiment being described. Referring to the voltage waveform illustrated in FIG. 9b, the first positive going flux change 135 generates a low amplitude positive timing pulse 136 in coil 124 and the more rapid positive going flux change 137 generates a larger amplitude positive timing pulse 138 in the coil 124. The magnitude of the advanced timing pulse 136 generated at low cranking speeds is substantially below the critical threshold level 86 (FIGS. 3 and 9b). The gating pulse 138 is substantially greater than the critical level 86 and passes through level 86 at the desired crankshaft angle 6' to facilitate easy starting, that is at or just about top dead center. When the engine starts the rate of change of the first positive going flux reversal, corresponding to the flux reversal designated at 135, increases substantially generating an advanced timing pulse 140 which exceeds the threshold level 86 at the desired advanced timing position 0" in FIG. 9b. Thus discharge of capacitor 62 is initiated at the desired crankshaft angle, 0' in response to pulse 140 when the engine is operating at running speeds.

In the embodiment illustrated in FIG. 10, the trigger coil assembly 144 generally comprises a U-shaped core 146 mounted on stator 12. The core 146 has radially disposed legs I48, 150 whose circumferential displacement to each other is wide by comparison to the spacing between legs 124, 126 in FIG. 7. A single coil 152 is wound on the trailing core leg 150. The angular displacement between

legs

148, 150 is selected relative to the circumferential length of the pole shoes 20, 22 to obtain the flux waveform 160 (FIG. 11a) which generates consecutive timing pulses having the required phase and amplitude relationships at cranking speed and at running speed. The connection (not shown) of the trigger coil 152 to the gate 80 is the same as that shown in FIG. 8 for the coil 124.

More particularly, the angular displacement between

legs

148, 150 is equal to or less than the angular separation between the leading edge 154 of pole face 20 and the trailing edge 156 of pole face 22 but greater than the length of pole face 20. For the clockwise rotation of magnet 18 illustrated in FIG. 10, as magnet 18 approaches the leg 148 and moves to the position relative to core 146 illustrated in FIG. 10, the flux linking coil 152 increases in a negative direction as illustrated by the first negative going portion 162 of waveform 160. As magnet 18 continues past the position illustrated in FIG. and the trailing edge 156 of the south pole 22 breaks from leg 148, the flux in coil 152 reverses to a positive going flux at 166. As the north pole sweeps past the leg 150 the flux in coil 152 remains relatively constant at 168 until the air gap 23 reaches the leg 150 at which point there is a rapid flux change 170 in a positive going direction. The flux then remains substantially constant and finally drops off to zero as the south pole 20 clears leg 150.

The corresponding voltages generated in coil 152 are shown in FIG. 11b. At cranking speeds the first positive going fiux change at 166 is relatively slow and generates a corresponding advance ignition pulse 176 whose amplitude is substantially below the critical threshold'level 86. However at cranking speeds the relatively rapid flux change generates a retarded ignition timing pulse 180 whose amplitude exceeds the critical threshold value 86 at the desired crankshaft angle, 0 to facilitate easy starting. After the engine starts the rate of change of flux in coil 152 when the leg 148 clears the trailing edge 156 of the south pole 122 increases substantially. This causes a corresponding large increase in the amplitude of the advanced ignition timing pulse as illustrated by the pulse 182 (FIG. 11). Pulse 182 exceeds the level 86 at the crankshaft angle t9 to provide the desired ignition timing advance at running speeds. Hence during cranking the retarded ignition timing pulse 180 is effective to generate a spark in plug 72. When the engine is running the advanced ignition timing pulse 182 is effective to generate the spark at plug 72.

FIG. 12 illustrates another modification in a triggering coil circuit wherein each of the

coils

186, 188 are connected in series with respective isolating

diode

190, 192 across the gatecathode of rectifier 74.

Coils

186, 188 have a different number of turns as illustrated in FIG. 12. Diode isolation would also be useful with trigger coils having different air gaps as described hereinabove in connection with the embodiment of FIGS. 4 and 5. Diode 190 corresponds to diode 114 (FIG. 6) whereas diode 192 isolates coil 186 from negative pulses generated in coil 188 and from loading by coil 188. The operation of the circuit illustrated in FIG. 12 is similar to the operation of the circuit illustrated in FIG. 6. For example, referring to FIGS. 3 and 12 diode 192 would block the first negative pulse 89 in coil 188 so that pulse 89 does not interfere with the advanced timing pulse 87 generated in coil 186. The isolation provided by the

diodes

190, 192 may be required to provide effective separation between the triggering pulses generated in the two

coils

186, 188 depending on the particular configura tion of magnet 18 and the design of

coils

102, 103.

FIG. 13 illustrates still another embodiment for generating two spaced triggering pulses having the desired phase and amplitude relationships at cranking speed and at running speed. Two trigger coils 204, 206 are wound on a common core 208 which is mounted on the stator 12 so as to be swept by magnet 18 during each revolution of rotor 14. Coil 204 has fewer turns than coil 206.

Coils

204, 206 are each connected in series with a respective isolating

diode

210, 212 across gate 80 and cathode 78 through a common connection 214. A single coil having a tap at the connection 214 is also contemplated. As indicated by the dots in FIG. 13, coils 204, 206 are oppositely poled in push-pull to gate 80.

At cranking speed magnet 18 will generate in coil 204 the waveform illustrated in FIG. 14a. The first positive pulse 220 generated when the leading pole 20 reaches coil 204 has a peak amplitude substantially below the critical voltage level 86. The second pulse 221 which is negative is generated by the rapid flux reversal as gap 23 sweeps coil 204. However, pulse 221 is blocked from gate 80 by diode 210. The second positive pulse 222 is generated as the trailing edge of the trailing pole 22 breaks from coil 204. Pulse 222 is not used in the embodiment being described. However since coil 206 is oppositely phased relative to coil 204, magnet 18 generates in coil 206 a voltage having a waveform shown in FIG. 14b wherein the first pulse 223 and the last pulse 224 are negative. The second pulse 225 is positive and has an amplitude that exceeds the voltage level 86 at the crankshaft angle 6"}. Hence at cranking speeds the advanced ignition timing pulse 225 fires rectifier 74 at the desired crankshaft angle that facilitates easy starting. After the engine starts the magnitude of the voltages generated in coil 204 increases substantially so that at running speeds the first positive pulse 226 (FIG. 14a) generated in coil 204 exceeds the level 86 at the desired crankshaft angle 0,. As with the embodiments described in connection with FIGS. 7 and 10, the amount of the timing shift 6" is determined in part by the configuration of magnet 18. More particularly for the embodiment of FIG. 13, the shift depends on the length of the leading pole 20. It will also be apparent that although the desired amplitude relationship between pulse 220 and pulse 225 is obtained by having fewer turns in coil 204 than in coil 206, the amplitude difference is in part due to the configuration of magnet 18 and the gap 23.

It has been found particularly desirable to provide temperature compensation in ignition circuits having automatic advance of the type described hereinabove to assure that the ignition timing occurs at the proper crankshaft angle regardless of temperature. FIG. 6 illustrates one circuit that is useful with the various trigger coil arrangements to compensate for variations in the critical threshold level 86 with temperature. In the circuit of FIG. 15 the trigger coils are illustrated in block form at 240, i.e., either coils having a different number of turns (FlGS. l-3), coils having different air gaps (FIGS. 4 and 5), a single coil on a narrow U-shaped core (FIGS. 7-9), a single coil on a wide U-shaped core (FIGS. 10 and 11), or push-pull coils on a single core (FIGS. 13 and 14). A silicon diode 242 is connected in series with cathode 78 to the common return lead 244. Connected across the trigger circuit 240 is a voltage divider comprising a resistor 246 and a thermistor 248. Thermistor 248 has a negative temperature coefficient so that its resistance decreases with increasing temperature. Gate 80 is connected to the divider between resistor 246 and thermistor 248. With increasing temperatures anode-cathode leakage current through rectifier 74 develops a small voltage drop across diode 242 so that the gate cathode junction becomes reversed biased. With increasing temperature, the gate voltage developed across the thermistor drops off. Temperature compensation using either thermistor 248 or diode 242, alone, is also contemplated. The circuit also minimizes spurious triggering by ripple voltages generated by stray flux, particularly at high running speeds and at high temperatures.

it will be understood that the ignition system having automatic ignition timing advance has been described hereinabove for purposes of illustration and is not intended to indicate limits of the present invention, the scope ofwhich is defined in the following claims.

I claim:

1. An ignition system for igniting a combustible charge in an internal combustion engine having at least one cylinder, a piston operable in said cylinder, a crankshaft rotated by said piston, a spark device for said cylinder and a source of electrical energy, said ignition system comprising circuit means adapted to transfer energy from said source to said spark device at substantially a first crankshaft angle in a timing cycle of said engine when said engine is running at a predetermined running speed and at substantially a second predetermined crankshaft angle when said engine is cranked at a lower speed during starting, said energy transferring circuit means comprising electronic switch means responsive to an electrical triggering signal having a predetermined value to switch from a first state to a second state and thereby cause electrical energy to be transferred to said spark device, and trigger means for providing triggering signals to actuate said control device, said triggering means comprising coil means coupled to said switch means, permanent magnet means movable relative to said coil means and having first and second poles displaced along the direction of travel relative to said coil means so that said first pole leads said second pole relative to said coil means, said poles having a magnetic gap therebetween, core means having two core legs of magnetic material displaced from each other along the direction of magnet travel, said coil means being mounted on one of said legs, and wherein said poles of said magnet means and said displacement between said core legs are correlated to each other so that during relative motion therebetween the magnetic flux in said one leg undergoes at least two changes in the same predetermined direction but at different rates with the first occuring flux change generating a first pulsation in said coil means that occurs substantially at said first crankshaft angle and has a value below said predetermined value at said low engine speed and above said predetermined value at said running speed and the second occurring flux change generating a second pulsation in said coil means that occurs at said second crankshaft angle and has a value above said predetermined value at both said low engine speed and said running speed.

2. The ignition system set forth in claim 1 wherein said core means comprises a generally U-shaped core of magnetic material so that said core legs are magnetically coupled together.

3. The ignition system set forth in claim 2 wherein said leading pole has an effective length along its path of travel relative to said coil means that is greater than the displacement between said core legs, and said one core leg leads said other core leg along the path of travel of said magnet means so that said leading pole first encounters said one leg and then said other leg to shunt flux from said one leg to said other leg and cause a first flux change in said one leg at said first crankshaft angle, said second flux change occurring in said one core when said magnetic gap passes said one leg at said second crankshaft angle.

4. The ignition system set forth in claim 2 wherein said first and said second poles each have an effective length along the path of travel relative to said core means that is less than the displacement between said core legs, said other leg of said core leads said one leg along the path of travel of said magnet means so that magnetic flux first encounters said other leg and then said one leg, and wherein the effective lengths of said first and said second poles along the path of travel of said magnet means are correlated to the displacement between said legs so that the trailing edge of said second pole breaks from said other leg to cause a first flux change at said first crankshaft angle and then said magnetic gap passes said one leg to cause a second flux change at said second crankshaft angle.

5. In an ignition system for igniting a combustible charge in an internal combustion engine having at least one cylinder, a piston operable in said cylinder, a crankshaft rotated by said piston, a spark device for said cylinder and a source of electrical energy, wherein said ignition system comprises circuit means adapted to transfer energy from said source to said spark device at substantially a first crankshaft angle in a timing cycle of said engine when said engine is running at a predetermined running speed and at substantially a second predetermined crankshaft angle when said engine is cranked at a lower speed during starting, said energy transferring circuit means comprising electronic switch means responsive to an electrical triggering signal having a predetermined value to switch from a first state to a second state and thereby cause electrical energy to be transferred to said spark device, and trigger means for providing triggering signals to actuate said control device, that improvement wherein said trigger means comprises coil means coupled to said switch means, magnetic flux source means movable relative to said coil means and adapted to supply flux to said coil means during relative rotation therebetween, magnetic core means having two core legs displaced from each other along the direction of travel of said flux source means, said coil means being mounted on one of said legs, and wherein said displacement between said legs and the configuration of said flux source means are correlated to each other so that during relative motion therebetween flux in said one leg undergoes a first change at a first rate and then a second change at a higher rate, said first change occurs substantially at said first crankshaft angle at both said cranking speed and said running speed and said second change occurs substantially at said second crankshaft angle at both said cranking speed and said running speed.

6. In an ignition system for igniting a combustible charge in an internal combustion engine having at least one cylinder, a piston operable in said cylinder, a crankshaft rotated by said piston and a spark device for said cylinder wherein said ignition system comprises energy storage means adapted to store electrical energy from a source of electrical energy, electronic switch means responsive to a trigger signal of predetermined value for transferring energy from said storage means to said spark device at predetermined crankshaft angles according to the speed of the engine and means coupled to said switch means and operable in synchronism with said engine to generate said trigger signal, said trigger signal generating means comprises pulse generating means for generating first and second pulses having a predetermined timing displacement therebetween, said first pulse having an amplitude less than a predetermined value at a predetermined low cranking speed of said engine and an amplitude exceeding said predetermined value at a predetermined running speed, and said second pulse having an amplitude that exceeds said predetermined value at said cranking speed so that discharge of said energy storage means is initiated in response to said second pulse at said cranking speed and in response to said first pulse at said running speed, that improvement wherein said pulse generating means comprises a rotor member and a stator member, said rotor member being adapted to be driven in synchronism with said engine, magnet means carried on one of said members and having a leading pole face and a trailing pole face separated by a magnetic gap, a generally U-shaped core mounted on said other member and having first and second legs the outer ends of which face said pole faces on said magnet means to form respective air gaps therebetween when said magnet means travels past said legs, said outer ends of said legs having a predetermined displacement therebetween along the path of travel of said magnet means according to said predetermined crankshaft angles, and a coil mounted on one of said core legs and coupled to said switch means and wherein the lengths of said pole faces are correlated to said displacement between said leg ends to generate a flux in said one leg having at least two separate changes in the same polarity direction with a timing separation therebetween corresponding to said predetermined timing displacement.

7. The ignition system set forth in claim 6 wherein the displacement between said first and said second core leg ends is less than the dimension between leading and trailing edges of said leading pole face, said core being mounted on said other member so that said one core leg leads said other core leg and said magnet means travels past said one core leg and then said other core leg, and wherein the displacement between said core leg ends is correlated to said dimension between leading and trailing edges of said leading pole face so that during each revolution of said rotor said leading edge of said leading pole passes said one leg and then said other leg to provide said first flux change at a crankshaft angle corresponding to ignition timing for said running speed.

8. The ignition system set forth in claim 6 wherein said displacement between said first and said second core leg ends is less than the dimension between a leading edge of said leading pole and a trailing edge of said trailing pole, said core is mounted on said other member so that said other leg leads said one leg relative to said magnet so that said magnet passes said other leg and then said one leg during each revolution of said rotor and wherein said displacement between said core leg ends is correlated to the leading and trailing edges of said leading and said trailing poles so that during each revolution of said rotor said trailing edge of said trailing pole moves past said other core leg while the leading pole is passing said one core leg to thereby provide said first flux change at a crankshaft angle corresponding to ignition timing at said running speed and then said magnetic gap passes said one leg of said core at a crankshaft angle corresponding to ignition timing at said cranking speed.

9. The ignition system set forth in claim 6 wherein said pole faces and said core leg ends are so spaced and related to each other that successively during each revolution of said rotor a leading edge of said leading pole sweeps said one leg and then sweeps said other leg to generate said first pulse in said coil and then said magnetic gap overlies said one leg to generate said second pulse in said coil.

10. The ignition system set forth in claim 6 wherein said pole faces and said core leg ends are so spaced and related to each other that successively during each revolution of said rotor said leadirig pole overlies said one l eg while said trailin pole overlies sai other leg, then said tralllng edge of said trai ing pole moves past said other core leg while said leading pole overlies said one core leg to generate said first pulse in said coil, and then said magnetic gap overlies said one leg of said core to generate said second pulse in said coil.

ll. in a breakerless ignition system for a spark ignition engine, the combination comprising a part rotated in synchronism with the operation of said engine, a spark gap device, means including an electronic switching device for causing the occurrence of a spark at said spark gap device as said switching device is switched from a first state to a second state, a triggering coil located adjacent said part and coupled with said switching device and operable to switch said switching device from said first state to said second state when a triggering signal in said triggering coil reaches a predetermined level, a source of magnetic flux, and means for providing a circuit for said magnetic flux which circuit passes through said triggering coil, said flux circuit providing means including first and second angularly spaced core members, magnetic material means arranged on said part so as to travel sequentially past said core members, said core members being arranged to be brought into said flux circuit at two different angular positions of said part in response to rotation of said part so that flux in said first core member changes in one direction at one angular position of said part and changes in the opposite direction at the other position of said part with said second core member being operable to shunt flux from said first core member to thereby cause one of said flux changes and with said coil being coupled to said first core member so that said flux changes induce a first triggering signal with both positive and negative peaks one of which is adapted to reach said predetermined level and actuate said switching device.

12. The combination set forth in claim 11 wherein said flux circuit providing means includes means operable at a third angular position of said part to cause a further flux change in said one core member to thereby induce a second triggering signal in said coil, said second triggering signal having a higher magnitude than the magnitude of said first triggering signal so that at low engine speeds said switching device is switched from said first state to said second state at one time in the engine cycle in response to said second triggering signal and at higher engine speeds at a different time in the engine cycle in response to said first triggering signal.

13. The combination set forth in claim 12 wherein said mag netic material means has a surface adapted to sequentially sweep past said core members and having a circumferential length sufficient to simultaneously bridge said core members.

14. The combination set forth in claim 13 wherein said magnetic material member has a second surface adapted to sequentially sweep past said core members, said second surface being spaced from said first surface so as to generate said second triggering signal in said coil.

15. The combination set forth in claim 13 wherein said second core member is swept by said surface subsequent to said first core member being swept by said surface.

Claims

10. The ignition system set forth in claim 6 wherein said pole faces and said core leg ends are so spaced and related to each other that successively during each revolution of said rotor said leading pole overlies said one leg while said trailing pole overlies said other leg, then said trailing edge of said trailing pole moves past said other core leg while said leading pole overlies said one core leg to generate said first pulse in said coil, and then said magnetic gap overlies said one leg of said core to generate said second pulse in said coil.

11. In a breakerless ignition system for a spark ignition engine, the combination comprising a part rotated in synchronism with the operation of said engine, a spark gap device, means including an electronic switching device for causing the occurrence of a spark at said spark gap device as said switching device is switched from a first state to a second state, a triggering coil located adjacent said part and coupled with said switching device and operable to switch said switching device from said first state to said second state when a triggering signal in said triggering coil reaches a predetermined level, a source of magnetic flux, and means for providing a circuit for said magnetic flux which circuit passes through said triggering coil, said flux circuit providing means including first and second angularly spaced core members, magnetic material means arranged on said part so as to travel sequentially past said core members, said core members being arranged to be brought into said flux circuit at two different angular positions of said part in response to rotation of said part so that flux in said first core member changes in one direction at one angular position of said part and changes in the opposite direction at the other position of said part with said second core member being operable to shunt flux from said first core member to thereby cause one of said flux changes and with said coil being coupled to said first core member so that said flux changes induce a first triggering signal with both positive and negative peaks one of which is adapted to reach said predetermined level and actuate said switching device.

13. The combination set forth in claim 12 wherein said magnetic material means has a surface adapted to sequentially sweep past said core members and having a circumferential length sufficient to simultaneously bridge said core Members.