US3060346A - Electronic ignition control system for internal combustion engines - Google Patents

Description

2 Sheets-Sheet 1 G. SOHNER ELECTRONIC IGNITION CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINES Oct. 23, 1962 Filed June 21. 1960 "WE/woe 1962 G. SOHNER 3,060,346

ELECTRONIC IGNITION CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINES Filed June 21. 1960 2 Sheets-Sheet 2 F/Ci. 5

az/z/mxw 55/111/6/1 A rim/v5 Y United rates Fatent U l 3,060,346 ELECTRONIC IGNITION CQNTRQL SYSTEM FOR INTERNAL COMBUSTIDN ENGlNES Gerhard Siihner, Endersbach, Kreis Waiblingen, Germany, 'assignor to Robert Bosch G.rn.b.H., tuttgart, Germany Filed June 21, 1960, Ser. No. 37,672 Claims priority, application Germany July 11, 1959 8 Claims. (Cl. 315-171) The present invention relates to electronic ignition con" trol systems for internal combustion engines of the type comprising an ignition coil or transformer having a pri mary winding and a secondary winding, the latter being connected to the spark plugs through a distributor synchronized with the engine and said primary winding being connected to a source of operating current, such as a storage battery, through an electronic relay or trigger circuit which serves to generate ignition voltage pulses in said secondary winding, such as by a temporary change from a normal stable condition to an unstable condition of said circuit, by a periodic input voltage applied thereto from an auxiliary A.C. generator also coupled or otherwise synchronized with the operation of said engine.

In electronic ignition systems of this type, the control generator and electronic trigger circuit or relay take the place of the conventional mechanical make-and-break device or interrupter switch operated by a cam controlled by the engine crankshaft and synchronized with the spark plug distributor.

In the operation of ignition systems of the above general type in connection with piston-type or reciprocating and the like internal combustion engines, it is necessary to advance the point or instant of ignition of the combustible mixture during the compression operating stroke of the engine in relation to the angular position of the crankshaft or spark plug distributor, as the speed of rotation of the engine increases, in such a manner as to substantially compensate for the ignition delay or reduction of the combustion period during the higher operating speeds. For this purpose, the conventional mechanical ignition advance control devices comprise, in addition to the cam-operated make-and-break contact in the primary circuit of the ignition coil, a mechanical advance mechanism which functions to displace said cam relative to said contact as the speed of rotation of the engine increases, in such a manner as to advance the ignition point relative to the compression or upper dead center position of the piston, in a manner well known in the art. Aside from the fact that the known mechanical ignition advance devices, which may be controlled by centrifugal force and/ or by the partial vacuum within the intake manifold, are subject to serious difiiculties and defects, foremost among which are the problem of sparking and arcing of the make-and-break contacts, they are not suitable ordinarily for effecting a more desirable displacement of the ignition point in successive steps or ranges by the aid of simple mechanical means or control devices. Furthermore, the known mechanical ignition advance control devices are costly both in manufacture and assembly by requiring a series of accurately adjusted levers and the like mechanical transmission elements.

Accordingly, an important object of the present invention is the provision of an improved ignition control system for internal combustion engines including automatic ignition advance control means, which operates purely electronically or without the use of mechanical parts or control devices.

Another object of the invention is the provision of an electronic ignition advance control system for internal combustion engines, whereby the advance of the ignition point with increasing engine speed is effected in prede- Bfihhfiib Patented Get. 23, 1962 termined successive steps or ranges, to suit any practical design conditions and operating requirements.

Yet another object of the invention is the provision of a purely electronic ignition control system for internal combustion engines embodying automatic ignition advance control means, which is both simple in design as well as efficient and reliable in operation, and which is substantially free from the above-mentioned and related disadvantages and defects inherent in the ignition control systems and methods according to the prior art.

The invention, both as to the above and ancillary objects, as well as the novel aspects thereof, will be better understood from the following detailed description of a preferred practical embodiment, taken in reference to the accompanying drawings forming part of this specification and in which:

FIG. 1 is a schematic circuit diagram of a complete electronic ignition control system including automatic ignition advance control means and being constructed in accordance with the principles of the invention;

FIG. 2 is a partial diagram illustrating one form of frequency-dependent impedance mean forming a basic element of the invention;

FIG. 3 is a cross-sectional view of a preferred construction of the ignition control A.C. generator also forming part of the invention and being schematically shown in FIG. 1;

FIG. 4 shows a series of theoretical curves explanatory of the function and operation of the invention; and,

FIG. 5 shows a stepped ignition advance angle characteristic or diagram obtainable by the use of a control system constructed in accordance with the invention.

Like reference characters denote like parts in the different views of the drawings.

With the foregoing objects in view, the present invention, according to one aspect of carrying the same into effect, involves generally the utilization of a known one-shot or mono-stable multi-vibrator or an equivalent electronic trigger circuit, preferably a circuit using solid state or semiconductor devices such as transistors as control elements, 'which upon being operated by the ignition control AC. voltage or pulses from a normally stable condition to an unstable condition is automatically returned to said first condition after lapse of a predetermined time period depending upon or being otherwise controlled by the constants or parameters of the circuit, in such a manner as to result in a series of interrupting ignition current pulses in the primary winding of the ignition coil or transformer. The ignition control voltage pulses or half cycles in the form of a suitably shaped non-sinusoidal AC. voltage, being produced by a control generator or alternator in synchronism with the rotation of the engine shaft, are advanced as to their time phase position as the frequency or engine speed increases by the provision of a suitable frequency-dependent impedance means or network in the input of the trigger circuit, substantially without the aid of any mechanically moving parts. In other words, the frequency-dependent network is interposed between the A.C. control generator and the input of the multivibrator or equivalent trigger circuit. Preferably, the AC. control voltage or pulses, by a suitable design of said generator, has a shape as to contain a substantial number of harmonic components, such as a trapezoidal or the like non-sinusoidal shape, whereby to result in both an advance of the ignition angle, as Well as in an increase of the steepness or rise time angle of the ascending branch of the AC. half cycles or control pulses. By the proper design of the frequency-dependent network such as to selectively vary the amplitude of predetermined harmonics of said voltage or control pulses, as the frequency or engine speed is varied, it is possible to obtain a desired step-like control of the ignition phase or angle within the power stroke or cycle of the engine as a function of the engine speed, to suit any operating and design conditions and requirements. In its simplest form, the advance of the ignition point may be controlled or effected by the provision of a four-pole circuit or network interposed between the control generator and the trigger circuit and comprising at least a series capacitor and a parallel inductor designed to resonate at predetermined harmonic frequencies of the AC. control voltage within the engine speed operating range, in such a manner as to result in a desired step-like control of the ignition advance angle as a function of the engine speed, as will become further apparent from the following description of the preferred practical embodiment of the invention shown by the drawings.

Referring more particularly to FIG. 1 of the drawings, there is shown, by way of example, an ignition control system for a four-cylinder internal combustion engine comprising an ignition coil or transformer 12 having a secondary winding connected to a rotary distributor schematically shown at 13 and a primary winding connected in series with the emitter-collector path E-C of a power transistor 11, an electric mono-stable trigger circuit or multivibrator 2t and an AC. control generator 21 connected to the input of said trigger circuit through a frequency-dependent four-pole circuit or network 22 designed to effect or control the ignition point advance, in the manner described in greater detail hereafter.

The trigger circuit, in the example shown, comprises a pair of PNP transistors 30 and 31 forming a mono-stable or one-shot multivibrator, the first or input transistor 30 having its emitter E connected to the plus potential line 33 of a battery or the like current source 35 through a biasing or stabilizing resistor 32 of about 25 ohms, said battery having its minus pole grounded or connected to the metal mass of the engine, in a manner well known to those skilled in the art. The emitter E of the transistor 30 is further connected through a resistor 29 of 200 ohms to the minus potential line 34 also being grounded or connected to the metal mass of the engine. Connected in the lead from the collector C of the transistor 30 to the minus line 34 is a resistor 36 of 200 ohms and a further resistor 37 of 600 ohms connected in series with the former. Connected between the junction point of the resistors 36 and 37 and the base B of the second or output transistor 31 is a resistor 33 of 10K ohms which is shunted by a capacitor 39 of 2 mmfd. Connected in the lead of the emitter E of the transistor 31 is a biasing or stabilizing resistor 41 of about 60 ohms, while the collector C of the transistor 31 is connected to the minus line 34 through a further resistor 42 of about 300 ohms. The base B of the transistor 39 is further connected to the collector C of the transistor 31 through a feedback resistor 43.

The emitter E of the transistor 31 is further connected to the base B of the power or output transistor 11 which has its emitter-collector path EC connected in series with the primary winding of the ignition coil 12, the secondary winding of the latter being connected to the rotary distributor contact 17 of the distributor 13 which is driven by the camshaft of the internal combustion engine, as indicated by the dot-dash line 16 in the drawing. The distributor contact 17 cooperates, in the example shown, with four stationary contacts 18 each of which is connected to one of the spark plugs 25 of the internal combustion engine through an ignition cable 19, in the manner well known and understood.

Further coupled with the camshaft 16 is the rotating armature 50 of the control generator or alternator 21 schematically shown in FIG. 1. In its preferred construction, as shown in FIG. 3, the generator is mounted within the casing 51 of the distributor 13. In the embodiment shown, the armature 50 of the generator, which advantageously may consist of compressed high-coercive force powdered magnetic material, is directly mounted upon the drive shaft 52 of the distributor, said shaft carrying a coupling or driven member 54 at its lower end projecting from the neck 53 of the casing 51, said driven member being adapted to engage a suitable driving member (not shown) becoming coupled with the camshaft 16 upon inserting the neck 53 into a suitable bore or mounting opening in the motor casing.

The single ring-shaped generator winding 55 is arranged within the annular space provided by a pair of cupshaped magnetic yoke members 56 and 57 of soft iron or the like high permeability material, said members being arranged with their cylindrical portions in edge-to-edge relation and having bottom portions provided with central openings, to accommodate the armature 50, as shown in the drawing. The yoke members 56 and 57 are further provided with spaced integral lugs 58 and 59 projecting from the inner ends or edges of said openings in directions parallel to the axis of and in spaced relation to the armature 50, to provide multiple pole pieces cooperating with said armature, in the manner described presently. For this purpose, the armature is provided with consecutive pairs of circumferential permanent magnetic north and south pole faces produced by means of a suitable magnetization process, in a manner well known to those skilled in the art.

More particularly, in the example shown of a fourcylinder engine, each yoke member 56 and 57 is provided with four equally spaced lugs or pole pieces 58 and 59, respectively, with the lugs of one member projecting into the intervening spaces between the lugs of the other member, while the armature is provided with four pairs of consecutive north and south pole faces. As a consequence, there are established in this manner a plurality of closed magnetic flux paths extending from one pole, say north, of the armature 50 to the adjacent pole piece or lug 58, by way of the air gap between the armature and said pole piece, through members 56 and 57 and back to the adjoining south pole face upon the armature through the adjacent lug 59 and air gap, respectively. The winding is thus linked with all said flux paths or magnetic circuits, whereby to cause the resultant total flux variations during the rotation of the armature to induce an AC. voltage in the winding 55, said voltage having a shape depending upon the design and spacing of the lugs 58 and 59, as well as of the shape and configuration of the pole faces of the armature 50.

More particularly, in the example shown, with the generator being driven by the camshaft 16, a single revolution of the engine causes the generation of four positive and four ne ative half-cycles of the control voltage at the generator terminals 69, FIG. 2. In general, the frequency of the generated voltage should be proportional to the product of one half of the number of cylinders and the speed of rotation in revolutions per second of the engine, as will be understood.

In place of the generator construction shown by the drawing for illustration, any other suitable type of AC. generator or alternator known in the art may be utilized for the purposes of the invention, to produce a nonsinusoidal control voltage suitable for the operation of the trigger circuit 20, in the manner described in further detail hereafter.

In order to afford a better understanding of the operation of the invention, there is shown in FIG. 4 the shape of a positive half-wave U of the non-sinusoidal A.C. voltage induced in the winding 55 of the generator 21 as a function of the instantaneous rotational angle a of the armature 50. This voltage contains a substantial amount of harmonics utilized for the ignition advance control in accordance with the basic principle of the invention. The frequency-dependent four-pole network or circuit 22, FIG. 2, connected for this purpose between the output terminals 60 of the generator and the base or input of the transistor 30 may comprise a parallel inductor of 0.5 henry and a resistor 66 of about 800 ohms connected in series with said inductor, The series circuit comprised by the inductor 65 and resistor 66 is connected at one end to one of the output terminals 60 of the generator 21 which is further connected to the plus potential line 33, while the opposite end of the circuit 65, 66 is connected directly to the base B of the transistor 30, on the one hand, and to the cooperating terminal 60 of the generator 21 through a resistor 63, on the other hand, the latter being shunted by a series capacitor 69. In a practical case, the resistor 68 may have a value of 7K ohms and the capacitor 69 may have a capacitance of about 0.2 mmfd. In other words, the circuit or network 22 has the general form of a high-pas filter or impedance device.

In the following there will be first described the operation of the trigger circuit 20, followed by a description of the function of the frequency-dependent four-pole circuit 22.

With the internal combustion engine being at rest or at standstill, a steady current flows from the plus line 33 to the minus line 34 through the resistors 29 and 32 forming a voltage divider and resulting in a voltage drop across the resistor 32 providing an emitter bias voltage U, for the transistor 30. Whereas the output transistor in this condition of the system is conducting and consequently causes a current to pass through the power transistor 11 and, in turn, through the primary winding 15 of the ignition coil 12, the input transistor 30 is maintained in the blocked or non-conducting state by the action of the resistors 42, 43, 66 forming a further voltage divider connected between the plus line 33 and the minus line 34 and resulting in a bias voltage U at the base B of the transistor 30 being less than the emitter bias Voltage U whereby to result in a blocking of the collector circuit, in a manner well understood by those skilled in the art.

After the internal combustion engine has been started to result in the rotation of the camshift 16 and, in turn, of the armature of the AC. generator 21, an AC. voltage U will appear at the terminals 60 of the generator which, even with relatively low engine speeds will result in a partial voltage U being superimposed upon the direct current bias voltage U not shown in FIG. 4 in view of its negligibly small value. In FIG. 4, this portion of the induced AC. voltage U being effective at the base-emitter junction BE of the transistor 30 is shown by the curve U which may correspond, for instance, to a speed of rotation of the internal combustion engine of about 1200 rpm. (revolutions per minute). As soon as the AC. voltage U exceeds the emitter bias voltage U at the instant t FIG. 4, the transistor 30 starts to conduct and to operate the output transistor 31 from its previous conducting to the blocking or nonconducting state, by reason of the fact that the capacitor 39 during the blocked condition of the input transistor 30 has been charged to a voltage being only slightly below the voltage of the battery 35 and since, furthermore, during the transition of the transistor 30 from the nonconducting to the conducting state the collector current produces a relatively large voltage drop across the resistor 37. As a consequence, the potential of the base B of the output transistor 31 will be raised to a point above the potential of the plus line 33, whereby the transistor 31 is no longer enabled to conduct current subsequent to the instant t This action is accelerated by the negative feedback between the output of the transistor 31 and the input of the transistor 30 through the feedback transistor 43, whereby to effect a practically instantaneous transfer of conduction from the transistor 31 to the transistor 30 at the instant t Simultaneously with the blocking of the output transistor 31, the power transistor 11 is operated from the conducting to a non-conducting state, whereby to cause a sudden interruption of the magnetizing current I through the primary winding of the ignition coil 12. This, in turn, causes a collapse of the magnetic field in the iron core of the coil 12 and, in turn, the generation of a high-voltage surge or ignition pulse in the sec ondary winding of the coil being applied to one of the spark plugs 25 by way of the rotary contact 17 and resulting in the production of an ignition spark in the engine cylinder. The system then returns to the original condition of blockage of the transistor 30 and conduction of the transistors 31 and 11 and, in turn, re-establishment of the current flow through the winding 15, after completion of the discharge of the capacitor 39 through the resistor 38.

As will be understood, the camshaft 16, in the case of a four-cycle engine, is driven by the crankshaft of the internal combustion engine through a conventional 2:1 reduction gearing. Furthermore, in order to release an ignition spark once every cycle of the AC. voltage U, or every second operating stroke of the engine, it is neces sary that the time constant of the capacitor 39 and resistor 38 be small compared with a full period of the AC. voltage.

As the speed of rotation of the internal combustion engine increases, both the amplitude and frequency of the AC. voltage U are increased proportionately. As a consequence, the partial voltage or voltage drop applied by the inductor 65 and resistor 66 of the network 22 to the input of the trigger circuit 20 not only is advanced in phase as a whole as a result of the effect of the capacitor 69 of the circuit 22, but, additionally, both the phase as well as the amplitudes of the harmonics of said voltage will be subjected to considerable variation. In other words, the shape of the AC. voltage being effective at the input of the trigger circuit 20 is distorted to an extent such as to exhibit, especially in the vicinity of its transition through zero, an increased steepness or rise time angle, as shown by the curve U in the drawing repre senting a half wave of the control voltage corresponding to an increased speed of the internal combustion engine of say about 3200 rpm. compared with the curve U corresponding to a speed of 1200 rpm.

The AC. voltage U supplied by the generator 21 has a fixed phase relative to the instantaneous rotational positions of the crankshaft of the internal combustion engine by reason of the fact that the rotating armature 50 is rigidly mounted upon the camshaft 16 of the engine which is, in turn, coupled with the engine crankshaft. As a result, the control voltage U or U respectively, derived from the inductor 65 and resistor 66 and being effective at the input of the trigger circuit 20 leads the voltage U produced by the generator by a displacement or advance angle proportional to the speed of rotation of the internal combustion engine or the frequency of the control voltage, respectively. As shown in FIG. 4, the control voltage U contains only relatively weak humps, as a result of the higher harmonics, which however due to the action of the capacitor 69 and inductor 65 of the four-pole circuit 22 are accentuated and have their phase position varied relative to the fundamental wave the more the higher the speed of rotation of the generator 21. As a consequence, while the control voltage U exceeds the emitter bias voltage U of the transistor 30 at the instant t the voltage U at the higher rotational speed reaches the value of the emitter bias voltage U at an instant substantially earlier, that is, at a time t being advanced relative to the time t by the differential At, as indicated in the drawing. In other words, at an engine speed of 3200 rpm. the transistor 30 is operated from the nonconducting to the conducting state at a time being advanced by the differential At as compared with the time t corresponding to a speed of rotation of 1200 rpm. This, in turn, causes a corresponding advance of the ignition voltage pulses applied to the spark plugs of the internal combustion engine by an angle g0 leading the instantaneous rotational angle of the crankshaft at the compression dead center position within an engine operating cycle.

In FIG. 5, the ignition advance angle p is plotted as a function of the speed n of the internal combustion engine, as shown by the solid curve a. From this view it is seen that the advance angle increases rapidly to about 15 during a speed range below 1000 r.p.m. It then remains constant until about 2400 rpm. and then again increases approximately linearly to 24 until reaching 3100 r.p.m. to again remain constant at this value. The regions of constant advance angle g are due to the frequency of the harmonics passing through the resonating frequency of the network 22 within the respective speed ranges of the engine, depending upon the design of the capacitor 69 and the inductor 65. In the example shown, the resonance frequencies for the harmonics correspond to the speeds of the internal combustion engine of about 2000 and 4000 r.p.m. repectively.

An important advantage of the system of automatic ignition advance control according to the invention consists, therefore, in the complete absence of any mechanically moving parts or elements, that is, by the timing or advance control of the ignition voltage pulses purely electronically and by means of an invariant network or circuit. This results both in high operating safety and in the ease of readily adapting the system to existing types of internal combustion engines and operating requirements by a suitable design of the four-pole circuit or advance angle control netWork.

The use of the stepped ignition advance angle characteristic a according to FIG. is of special advantage in the case of internal combustion engines designed to produce a relatively high power output per unit of stroke volume swept by the pistons. In general, with engines having a relatively large stroke volume, it is desirable to advance the ignition angle in direct proportion to the increasing engine speed. However, the higher the specific power output, or power output per unit of displacement, the more it becomes necessary to effect already a relatively large ignition advance during the lower operating speeds of the engine. In other words, such an operating characteristic would have a shape as indicated by the broken line b in FIG. 5. On the other hand, engines designed for high specific power output have the disadvantage of being subject to considerable knocking within the lower speed range, say from 1200 r.p.m. to 2500 r.p.m., if operated at maximum output and by a fuel of low octane content.

The foregoing difliculty is substantially overcome by the use of a stepped advance angle characteristic of the type shown at a, FIG. 5, that is, by reducing the angle cp by about 5, in the example shown, within the range from 1200 r.p.m. to 2500 rpm, in such a manner as to result in the stepped curve shown at a. This ensures high accelerating power, on the one hand, and a suppression of knocking during the lower speed range, on the other hand. As the speed is further increased, the angle g0 may again be allowed to increase further to its final value, corresponding to maximum power output of the engine, since within this range the tendency to knocking by the engine is relatively slight only.

From the foregoing will be understood the advantage of the present invention in producing a stepped ignition advance angle characteristic by the simple expedient of a non-sinusoidal A.C. control voltage containing a considerable amount of higher harmonics at low frequencies or engine speeds, respectively, and by the utilization of a suitably designed frequency-dependent network or circuit.

Furthermore, while a mono-stable multivibrator has been shown as a trigger circuit in the drawing, it will be understood that any other electronic equivalent device may be provided for the purpose of the invention, that is, to suddenly interrupt the magnetizing current I through the collector circuit of the power transistor 11 upon increase of the frequency-dependent control voltage supplied by the network 22 above the predetermined input bias voltage (U of the trigger circuit. Thus, according to a simple modification, the circuit shown in FIG. 1 may be designed to operate the transistor 30 from its normally non-conducting state to its conducting state upon the ascending branch of the voltage U exceeding the bias voltage U in the manner described, and to return said transistor to the non-conducting state by the descending branch of U reaching a value below the bias voltage U, respectively. In other words, the circuit may operate in the manner of a bi-stable or Schmidt trigger well known in the art.

In the foregoing, the invention has been described with reference to a specific illustrative device or system. It will be evident, however, that modifications and variations, as well as the substitution of equivalent elements and circuits for those shown herein for illustration, may be made without departing from the broader scope and spirit of the invention as set forth in the appended claims. The specification and drawings are accordingly to be re garded in an illustrative rather than in a restrictive sense.

I claim:

1. The combination with an internal combustion engine including a plurality of spark plugs and a distributor connected thereto and synchronized with said engine, of an ignition control system comprising an ignition coil having a primary winding and a secondary winding connected to said distributor, a source of current, an electronic trigger circuit having an input circuit with means to bias the same by a predetermined bias potential and having an output circuit connecting said source to said primary winding, to normally pass a current through said primary winding and to interrupt said current upon triggering of said circuit by the application of an input control voltage in excess of said bias potential, to induce a high voltage ignition pulse in said secondary winding, a generator synchronized with said engine to produce a non-sinusoidal alternating current control voltage of a frequency proportional to the speed of rotation of said engine, and a phase-shifting network comprising at least a series input capacitor and a parallel output inductor and connecting said generator with said input circuit, said network designed to resonate at a frequency equal to a harmonic of said control voltage during passage through predetermined partial speed ranges by said engine, whereby to effect a step-like advance of the ignition point during an engine operating cycle as a function of increasing engine speed within a given speed operating range of said engine.

2. In an ignition control system as claimed in claim 1, said alternating current control voltage having a substantially trapezoidal shape.

3. In an ignition control system as claimed in claim 1 including a first resistor in parallel to said capacitor and a second resistor in series with said inductor.

4. In an ignition control system as claimed in claim 1, said network being designed to resonate at a frequency to cause a substantially constant ignition point advance during partial speed ranges of said engine in the neighborhood of about 2000 and 4000 revolutions per minute.

5. The combination with an internal combustion engine having a plurality of spark plugs and a distributor connected thereto and synchronized with said engine, of an ignition control system comprising an ignition coil having a primary winding and a secondary winding connected to said distributor, a source of current, a power transistor having an emitter, a base and a collector, the emitter-collector path of said transistor being connected in series with said primary winding and said source, a monostable transistor multivibrator having an input circuit with means to bias the same by a predetermined bias potential and having an output circuit coupled to the base of said power transistor, to normally pass output current through said primary winding in the stable condition of said multivibrator and to interrupt said current in the unstable condition of said multivibrator upon application of control voltage to said input circuit in excess of said bias potential, to induce a high voltage ignition pulse in said secondary winding, a generator synchronized with said engine to produce a substantially trapezoidal alternating current control voltage of a frequency proportional to the speed of rotation of said engine, and a phase-shifting network comprising at least a series input capacitor and a parallel output inductor and connecting said generator with said input circuit, said network designed to resonate at a frequency equal to a harmonic of said control voltage during passage through predetermined partial speed ranges by said engine, whereby to elfect a step-like advance of the ignition point during an engine operating cycle as a function of increasing engine speed Within :a given speed operating range of said engine.

6. In an ignition control system as claimed in claim 5, including a first resistor shunting said capacitor and a second resistor connected in series with said inductor.

7. An ignition system for an internal combustion engine, comprising a source producing a substantially non-sinusoidal alternating control voltage having a frequency synchronized with the rotation of said engine, an electronic trigger circuit having an input circuit including means to bias the same by a predetermined bias potential and triggered by said control voltage, a phase-shifting network comprising at least a series input capacitor and a parallel output inductor and connected between said source and said input circuit, said network designed to resonate at a frequency equal to a harmonic of said control voltage during passage through at least one predetermined partial speed range by said engine, whereby to efiect a step-like advance of the ignition point during an engine operating cycle as a function of increasing engine speed Within a given speed operating range of said engine.

8. In an ignition control system as claimed in claim 7, said control voltage having a substantially trapezoidal shape.

References Cited in the file of this patent UNITED STATES PATENTS 2,395,629 Kongsted Feb. 26, 1946 2,490,960 Hanchett Dec. 13, 1949 2,579,318 Hershberger Dec. 18, 1951 2,698,396 Stokman Dec. 28, 1954 2,953,719 Guiot Sept. 20, 1960 FOREIGN PATENTS 1,137,949 France Jan. 21, 1957

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