US3858563A

US3858563A - Electronic ignition system with means for limiting engine speed

Info

Publication number: US3858563A
Application number: US386378A
Authority: US
Inventors: Helmut Roth
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1972-08-17
Filing date: 1973-08-07
Publication date: 1975-01-07
Anticipated expiration: 1992-01-07
Also published as: FR2196435B3; GB1399687A; IT992991B; JPS4958238A; DE2240475A1; FR2196435A1

Abstract

The ignition system of an internal combustion engine includes electrical an igniting unit operative for igniting a fuel-air mixture in a cylinder of the engine. An ignition capacitor is operative for storing the electrical energy required by the igniting unit for effecting ignition of the mixture. An energy transfer arrangement is operative for causing the igniting unit to ignite the mixture by transferring to the igniting unit electrical energy stored in the ignition capacitor. An ignitioncapacitor-charging arrangement is connected to the ignition capacitor and is operative for charging the latter. A timing arrangement times the transfer of energy from the ignition capacitor to the igniting unit. An engine-speed-limiting arrangement includes a speed-monitoring capacitor and a speeddependent charging arrangement for charging the speed-monitoring capacitor by applying thereto substantially identical charging pulses having a pulse repetition frequency proportional to engine speed. A discharge arrangement connected to the speed-monitoring capacitor discharges the speed-monitoring capacitor at such a rate that the voltage across the speed-monitoring capacitor can build up to a predetermined value only if the engine speed reaches a predetermined speed. A voltage-responsive arrangement connected to the speed-monitoring capacitor is operative when the voltage across the speed-monitoring capacitor reaches said predetermined value for preventing the igniting unit from igniting the fuel-air mixture.

Description

no 3,858,563 Jan.7, 1975 ELECTRONIC IGNITION SYSTEM WITH MEANS FOR LIMITING ENGINE SPEED [75] Inventor: Helmut Roth, Stuttgart, Germany [73] Assignee: Robert Bosch GmbH, Stuttgart,

Germany [22] Filed: Aug. 7, 1973 [21] Appl. No. 386,378

[30] Foreign Application Priority Data Aug. 17, I972 Germany 2240475 [52] US. Cl. 123/118, 123/148 E [51] Int. Cl. F02p 3/06 (58] Field of Search 123/118, 102, 148 E [56] References Cited UNITED STATES PATENTS 3,356,082 l2/l967 Jukes l23/l l8 3,704,699 l2/1972 Howard 123/148 D Primary Examiner-Manuel A. Antonakas Assistant Examiner-James W. Cranson, Jr. Attorney, Agent, or FirmMichael S. Striker 57 ABSTRACT The ignition system of an internal combustion engine includes electrical an igniting unit operative for igniting a fuel-air mixture in a cylinder of the engine. An

ignition capacitor is operative for storing the electrical energy required by the igniting unit for effecting ignition of the mixture. An energy transfer arrangement is operative for causing the igniting unit to ignite the mixture by transferring to the igniting unit electrical energy stored in the ignition capacitor. An ignitioncapacitor-charging arrangement is connected to the ignition capacitor and is operative for charging the .lat-

ter. A timing arrangement times the transfer of energy from the ignition capacitor to the igniting unit. An engine-speed-limiting arrangement includes a speedmonitoring capacitor and a speed-dependent charging arrangement for charging the speed-monitoring capacitor by applying thereto substantially identical charging pulses having a pulse repetition frequency proportional to engine speed. A discharge arrangement con nected to the speed-monitoring capacitor discharges the speed-monitoring capacitor at such a rate that the voltage across the speed-monitoring capacitor can build up to a predetermined value only if the engine speed reaches a predetermined speed. A voltageresponsive arrangement connected to the speedmonitoring capacitor is operative when the voltage across the speed-monitoring capacitor reaches said predetermined value for preventing the igniting unit from igniting the fuel-air mixture.

22 Claims, 4 Drawing Figures rZl n l T as 20 5a 5 II v 81 37 57 59 U/ 55 i 83 7 79 31. 1. 26 2s 68 l/ 39 l 1.2 4 BL 74 52 i V I. 6 l 9 4 lse L 3 f 22 L8 51 r 92 31 J as 1: 1i ,1:

38 69 l r 99 98 p 9688 y 56 71 3 1 a it" Q Q7 e Patentgd Jan. 7, 1975 2 Sheets-Sheetl Fig Patented Jan. 7, 1975 2 Sheets-Sheet 2 ELECTRONIC IGNITION SYSTEM WITH MEANS FOR LIMITING ENGINE SPEED BACKGROUND OF THE INVENTION The invention relates to internal combustion engines provided with an arrangement for limiting engine speed and provided with an ignition arrangement that is rendered temporarily inoperative by the speed-limiting arrangement when the engine speed exceeds a predetermined value.

It is advantageous to provide an internal combustion engine with such a speed-limiting arrangement, in order to prevent the relatively expensive components of the engine from becoming damaged at excessive speeds due to excessive loading.

It is already known to provide internal combustion engines with speed-limiting arrangements. In one known construction the timing arrangement for timing the ignition operation comprises an AC. generator, with the speed-limiting arrangement cooperating with the generator. When the engine speed exceeds a predetermined value, the speed-limiting operation occurs. The speed-limiting operation involves the virtual shortcircuiting of the AC. generator output winding. This results in the flow of extremely high currents through the generator output winding, making it necessary to dimension such winding in such a manner that it is capable of carrying such large currents without being damaged.

SUMMARY OF THE INVENTION It is the general object of the invention to provide a speed-limiting arrangement for an internal combustion engine operating in a manner different from arrangements for this purpose known in the prior art and having more advantageous characteristics than prior-art arrangements.

This object, and others which will become more u nderstandable from the following description of a specific embodiment, can be met according to the invention by providing, in the ignition system of an internal combustion engine, in combination, electrical igniting means operative for igniting a fuel-air mixture in a cylinder of the engine. Ignition capacitor means is operative for storing the electrical energy required by the ignition means for effecting ignition of the fuel-air mixture. Energy-transfer means is operative for causing the ignition means to ignite the mixture by transferring to the igniting means electrical energy stored in the ignition capacitor means. Ignition-capacitor-charging means is connected to the ignition capacitor means and is operative for charging the latter. Timing means times the transfer of energy from the capacitor means to the igniting means. An enginespeed-limiting arrangement includes speed-monitoring capacitor means and speeddependent charging means for charging such speedmonitoring capacitor means by applying thereto substantially identical charging pulses having a pulse repetition frequency proportional to engine speed. Discharge means is connected to the speed-monitoring capacitor means and is operative for discharging the speed-monitoring capacitor means at such a rate that the voltage across the latter can build up to a predetermined value only if the engine speed reaches a predetermined speed. Voltage-responsive means connected to saidspeed-monitoring capacitor means is operative,

when the voltage across the latter exceeds such predetermined value, for preventing the igniting means from igniting the fuel-air mixture.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows an exemplary embodiment of an arrangement according to the invention, with parts of the illustrated circuit being shown in functional-block form;

FIG. 2 illustrates an alternative version of a portion of the circuitry illustrated in FIG. 1;

FIG. 3 is a detailed circuit diagram of the electronic ignition circuit depicted in functional-block form in FIG. 1; and

FIG. 4 is a detailed circuit diagram of the voltageresponsive arrangement depicted in functional-block form in FIG. 1. I

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 reference numeral 1 designates circuitry, outlined in dashed lines, for monitoring the speed of an internal combustion engine. Reference numeral 2 designates generally the electronic ignition circuitry for the engine.

The speedmonitoring arrangement 1 includes a speed-monitoring capacitor 3 provided with a capacitor discharge circuit 4, comprising of

resistors

13 and 14. The speed-monitoring arrangement 1 furthermore includes voltage-responsive means 5 operative for monitoring the voltage across the speed-monitoring capacitor 3. When the voltage across capacitor 3 builds up to a predetermined value, associated with maximum permissible engine speed, voltage-responsive means 5 responds by applying to the ignition circuitry 2 a speedlimiting signal. This is symbolically represented in FIG. 1 by the presence of a switch 6 in block 5 representing the voltageresponsive circuit. When the voltage across capacitor 3 exceeds the just-mentioned predetermined value, switch 6 becomes opened, resulting in the application of a speed-limiting signal to the ignition circuitry 2.

The speed-monitoring capacitor 3 is charged by substantially identical charging pulses having a pulserepetition frequency proportional to engine speed. More specifically, the charging pulses applied to speedmonitoring capacitor 3 have substantially identical peak values and are produced at a fixed rate relative to crankshaft speed. For example, one such pulse may be produced per crankshaft rotation, irrespective ofv crankshaft speed; alternatively, two such charging pulses may be produced per crankshaft rotation, irrespective of crankshaft speed, etc.

Advantageously, these crankshaft-synchronized charging pulses for capacitor 3 are derived not directly from the crankshaft itself, but indirectly from the crankshaft-synchronized pulses anyway being generated by the ignition circuitry 2. For example, the ignition timing signals generated in the ignition circuitry 2,

if they are crankshaft-position-synchronized, can be applied to the speed-monitoring capacitor 3 as charging pulses. Alternatively, every second such ignition timing signal, or every third such ignition timing signal, could be applied to the speed-monitoring capacitor 3 as a charging pulse. The derivation of the charging pulses for speed-monitoring capacitor 3 from the crankshaft-synchronized pulses anyway generated by ignition circuitry 2 elininates the need for additional crankshaft-activated mechanical switches, and the like.

In the illustrated embodiment of the ignition circuit 2, discussed in detail below, the ignition pulses are directly synchronized with crankshaft position. Accordingly, in the illustrated embodiment, as shown in FIG. 1, the charging pulses for speed-monitoring capacitor 3 are derived simply by providing a charging-pulse transmitting conductor 7 connected atone end to a suitable point (shown in FIG. 3) of the ignition circuitry 2, and connected at its other end via a resistor 9 and a charging diode 8 to one electrode of the speedmonitoring capacitor 3. In this way, the crankshaftposition-synchronized timing'pulses generated by the ignition circuitry 2 areapplied to the speed-monitoring capacitor 3 by means of the pulse-transmitting conductor 7.

In the illustrated embodiment, for purposes of simplicity, the generation of ignition sparks occurs in a crankshaft-position-synchronized manner--i.e., without ignition advancement or retardation. However, if the ignition circuitry is provided with ignitionadvancement components, it may nevertheless be the case that crankshaft-position-synchronized timing pulses are generated, applied perhaps to a variabledelay monostable multivbrator. In such case, the charging pulses applied to speed-monitoring capacitor 3 could still be crankshaft-position-synchronized pulses derived from the pulses generated by the ignition circuitry 2.

Furthermore, it should be noted that the crankshaftposition-synchronized pulses could, if necessary, be derived from the crankshaft directly, although, as ex plained above, it is considered more advantageous to derive the charging pulses for the speed-monitoring capacitor 3 from the pulses anyway being generated in the ignition circuitry 2. As a final possibility, it should be noted that the intended purpose of speedmonitoring circuitry 1 can be achieved even if the charging pulses applied to speed-monitoring capacitor 3 are not in fact synchronized with predetermined fixed crankshaft positions. Strictly speaking, it is sufficient if the pulse-repetition frequency of the charging pulses applied to capacitor 3 is proportional to crankshaft rotational speed.

It should be evident from FIG. 1 that the

discharge circuit

13, 14 connected across speed-monitoring capacitor 3 will be operative for discharging the capacitor 3 during the time intervals between the charging pulses. Such discharging of capacitor 3 via pulse-transmitting line 7, on the other hand, is not possible, due to the provision of blocking diode 8 whose polarity permits the flow of charging current only.

The resistance values of

resistors

13 and 14 are so selected relative to the capacitance value of capacitor 3 that these resistors will discharge capacitor 3 at such a rate, during the intervals between charging pulses, that the voltage across capacitor 3 can build up to a predetermined value only if the substantially identical charging pulses are being applied with a sufficiently high pulse-repetition frequency. In other words, the voltage across capacitor 3 can build up to such predetermined value only if the engine speed reaches a corresponding predetermined value.

The speed-monitoring circuit 1 of FIG. 1 is furthermore provided with a Zener diode connected between the junction of resistor 9 and blocking diode 8 and the grounded electrode of capacitor 3. If the voltage level of the charging pulses applied to speed-monitoring capacitor 3 exceeds a certain value, Zener diode I0 will break down, shunting away from capacitor 3 any further charging current of the charging pulse. In this It wiiiii seen from'FIG. 1 that discharge resistors 13,

. 14 together form a voltage divider connected across the speed-monitoring capacitor 3. Of these, voltage divider resistor 13 is adjustable, in order to make possible adjustments of the fraction of the voltage across capacitor 3 which is actually applied, via conductor 12, to the input 11 of voltage-responsive means 5. In the particular example depicted, the threshold voltage of voltage-responsive meansS is fixed, but can be effectively-varied by varying the fraction of the voltage across capacitor 3 that is actually applied to the input 11 of means 5. In this way, the upper permissible engine speed which the system maintains can be adjusted to suit the requirements of a particular vehicle, or other circumstances.

It is considered advantageous to introduce temperature compensation into the operation of the speedmonitoring arrangements 1. This can be done, notwithstanding the fixed threshold voltage of voltageresponsive means 5 in this embodiment, by replacing resistors 13 and/or 14 with suitable temperaturedependent components. FIG. 2 shows one such possibility. Instead of the resistor 14 shown in FIG. 1, FIG. 2 makes use of a parallel combination of an ohmic resistor l5 and a negativetemperature-coefficient resistor 16, this parallel combination being connected in series with a further negative-temperaturecoefficient resistor 19 and a further ohmic resistor 18. The provision of two temperature-dependent resistors in this manner greatly increases the temperature-independence of the system.

The ignition circuitry of the arrangement of FIG. 1 is depicted only symbolically, and generally designated by reference numeral 2, with several of the essential components of the circuitry being shown in the box designated with numeral 2. The specific circuit details of the ignition circuit 2 are shown in full in FIG. 3.

In FIG. 1, there is depicted a spark plug connected across the secondary 79 of an ignition transformer 77,

whose primary 76 is connected in circuit with the ignition capacitor and an electronic switch 68, operative for preventing discharge of ignition capacitor 20 through primary 76 except when switch 68 is conductive. In the illustrated embodiment, switch 68 is a thyristor having an anode 74, a cathode 75 and a gate electrode 67. The ignition capacitor 20 is charged by way of charging rectifier 23 from the output of an ignitioncapacitor-charging arrangement 21, shown in detail in FIG. 3.

Before leaving the symbolic showing of FIG. 1, it is to be noted that when the engine speed reaches a predetermined speed, which is selected by adjusting resistor 13, the voltage across speed-monitoring capacitor 3 builds up to a predetermined value such that the voltage applied to input 11 of voltage-responsive means 5 opens symbolically depicted switch 6, thereby applying to charging circuit 21 a speed-limiting signal having the effect of preventing charging of the ignition capacitor 20, and thereby making impossible the ignition of fuelair mixture in the engine cylinder.

FIG. 3 shows the details of ignition circuit 2 of FIG. 1. The charging arrangement 21 of the ignition circuit 2 is comprised essentially of a charging transformer 81 having a primary winding 82 and a secondary winding 83. An electronic switch 26 is connected in the primary winding current path. When-electronic switch 26 is rendered conductive, in a manner to be described, current flow builds-up in primary winding 82. When switch 26 is thereafter rendered non-conductive, in a manner to be described, the current flow through primary 82 terminates, resulting in the generation across secondary 83 of a high-voltage charging pulse which charges ignition capacitor 20 via charging diode 23.

In the embodiment illustrated, the build-up of current in primary 82 of charging transformer 81 occurs in a particularly manner. Switch 26 is briefly rendered conductive by a forward-bias voltage spike applied to its base electrode 84. This results in the initiation of current build-up in primary 82. Such current also flows through primary 85 of positivefeedback transformer 86, inducing in secondary winding 27 thereof a positive-feedback voltage sufficient to maintain transistor 26 conductive, despite the termination of the initial turn-on voltage spike. Moreover, this positive-feedback voltage actually increases the conductivity of transistor 25, to thereby effect further build up of the current in primary 82, and a further increase in the conductivity of transistor 25, etc., according to the principle of positive feedback. As will be explained in greater detail below, the speed-limiting circuitry of the illustrated arrangement is operative for-limiting engine speed by preventing the charging of ignition capacitor 20 when the engine speed exceeds a preselected value. In particular, charging of capacitor 20 is prevented by preventing the buildup of current in primary 82, and this is accomplished, specifically, by preventing positivefeedback action of the type just mentioned.

With respect, now, to the specifies of the circuitry, it is noted that the circuit includes a source 22 of DC current having a grounded negative terminal to which is also connected a negative power supply line 33 and a positive terminal to which is connected via a switch 34, a positive power supply line 35. Across the negative line 33 and the positive line 35 there is connected a crankshaft-operated electromechanical pulse generator 36 and, in series therewith, a resistor 37, with the pulse generator comprising a cam-controlled mechanical interruption switch 38 connected to the negative supply line 33.

Connected'to the junction 39 formed by resistor 37 and pulse generator 36 is a circuit branch comprised of the series connection of a resistor 40, a differentiating .capacitor 41 and a pair of diodes 42. Through these two diodes 42 base current can flow into the base 43 of an npn transistor 44. Also,connected in parallel with resistor 40 is a diode 45 having such a polarity as to be capable of conducting current into base 43 oftransistor 44 from DC. source 22. A resistor 47 is connected to the negative line 33 and to the junction 46 between capacitor 41 and the left-hand diode 42. Connected between the negative line 33 and the junction 48 of the base 43 of transistor 44 and the right-hand diode 42 is the parallel combination of a capacitor 50 and a resistor 49. The transistor 44 has its emitter 51 connected directly to the negative line 33 while its collector 52 is connected to the positive line 35 via two

resistors

53, 54.

Resistors

53, 54 form a voltagedivider. The tap of this

voltage divider

53, 54 is connected to the base 56 of a pnp transistor 57, with resistor 54 being shunted by a capacitor 58. v

The transistor 57 has its emitter 59 connected to the positive line 35 and has its collector 60 connected with the circuit junction 61. Connected to circuit junction 61 is the anode of a diode 62, with the cathode of the diode being connected to the negative line 33 via a resistor 63. Connected to the junction 64 between diode 62 and resistor 63 is a circuit branch comprised of a differentiating capacitor 65 and a resistor 66 connected in series therewith, with the terminal 71 of resistor 66 being connected directly to the gate electrode 67 of a controllable discharge thyristor 68. A diode 70 is connected between the negative line 33 and the junction 69 of capacitor 65 and resistor 66. The parallel combination of a capacitor 72 and a resistor 73 is connected across the negative line 33 and the junction 71 between resistor 66 and the gate 67 of thyristor 68.

The anode-cathode path 74, of discharge thyristor 68 forms part of the discharge current path for the ignition capacitor 20, for the flow of discharge current out of the positive plate of capacitor 20 and then from the anode 74 to the cathode 75 of thyristor 68, and then through the primary winding 76 of ignition transformer 77 back to the negative plate of ignition capacitor 20. Connected across the secondary winding 79 of charging transformer 77 is at least one spark plug 80.

In the charging arrangement 21 for the ignition capacitor 20, inductive coupling between the primary current path and the secondary current path is established by a charging transformer 81, having a primary winding 82 connected in the primary current path of the arrangement and a secondary winding 83 connected in the secondary current path of the arrangement 21.

The controllable electronic switch 26 in the illustrated embodiment is an npn transistor having a collector-emitter path 25-24 constituting a path for the flow of switching current and having a base-emitter path 84-24 constituting a'path for the flow of conductivitydetermining control current. The collector-emitter path 25-24 is connected in series with the primary winding 82 of the charging transformer 81 and is connected in series with the primary winding 85 of a positive-feedback transformer 86. The primary winding 82 of charging transformer 81 is connected between the collector 25 and the positive line 35, whereas the primary winding 85 of the positive-feedback transformer 86 is connected between the emitter 24 and the negative power supply line 33.

The base-emitter path 84-24 of transistor switch 26 is operatively connected with the secondary winding 27 of the positive-feedback transformer 86, which secondary is wound around the iron core 87 of the transformer 86. The'positive-feedback winding 27 has one terminal 88 connected to the emitter 24 of transistor switch 26, with this terminal 88'furthermore being connected to the base electrode 84 of transistor 26, via resistor 89. The other terminal 90 of positive-feedback winding 27 is connected to the base 84 of transistor 26 by way of diode 9.1. Diode 91 has such a polarity as to become forward-biased by the flow of current out of winding terminal 90 through diode 91 and into base 84 of transistor 26. A resistor 92 is connected in parallel to the diode 91. Furthermore, the base 84 of transistor 26 is connected to circuit junction 61 by way of a circuit branch comprised of a diode 94 and a resistor 93.

Connected across positive-feedback winding 27 is the anode-cathode path 29-30 of a'third electronic switch 28, here a thyristor 28. As will be evident, when the thyristor 28 becomed conductive it serves to shortcircuit the positive-feed-back winding 27.

.Connected across the anode-cathode path 29-30 of thyristor 28 is a

voltage divider

95, 96 comprised of

resistors

95 and 96, the tap, 97 of this voltage divider being connected to the gate electrode 31 of the thyristor 28. Advantageously, the voltage-divider resistor 96 connected across the gate-cathode path of thyristor 28 is a negative-temperature-coefficientresistor. and advantageously a capacitor 98 is connected across this resistor 96, to counteract short-lasting interference signals. A diode 98 is furthermore connected in parallel with voltage-divider resistor 96, with such a polarity as to become reverse-biased when current flows in a loop from terminal 90 of positive-feedback winding 27, through resistor 95, through resistor 96, and back to theterminal 88 of positive-feedback winding 27.

The voltage-responsive arrangement shown as a functional block in FIG. 1 is shown in detail in FIG. 4. The voltage-responsive standby current stage. Stage 5,

as can be seen from FIG. 4, is connected across power in FIG. 1. The standby current stage 5 shown in FIG.

which is normally reverse-biased by the voltages ordinarily established at its anode and cathode, i.e., by the voltages there prevailing when the engine speed is below the maximum permissible value. The standby current stage 5 includes a stabilizing resistor 103 connected in series with a second Zener diode 104, the stabilizing resistor 103 being connected to the positive line 35 and the anode of the Zener diode 104 being connected to ground. i.e.'. to the negativc-terminal'of the D.C. source 22. r

The thyristor switch 107, whose conductivity determines whether current can or cannot flow through standby current path 100, has a gate electrode designated with numeral 108. The anode 105 of thyristor 107 is preferably connected to the cathode of Zener diode 104,.via resistor 109. The cathode 106 of thyristor 107 is connected tothe anode of Zener diode 104. The thyristor 107 cooperates with an npn control transistor 110 to form a voltage-responsive circuit.

The base 11 of control transistor 110 forms the input of the voltage-responsive standby current stage 5. The emitter 111 of control transistor 110 is connected with the-anode of theZener diode 104, and its collector 112 is connected with the gate electrode 108 of thyristor 107 and also with the cathode of Zener diode 104, via resistor 113. Acapacitor 114 connected between base 11 and emitter 111 of transistor 110 reduces the effect upon this'transistor of short-lasting interference pulses. The operation of the circuit depicted in FIGS. 1, 3 and 4 will now be described. I

When supply switch 34 is closed, the ignition syste becomes enabled. During running of the (nonillustrated) internal combustion engine, the engine crankshaft repeatedly assumes a predetermined angular orientation such as to effect opening of camcontrolled interrupter switch 38, thereby effecting generation of a brief positive voltage pulse. This positive voltage pulse is applied to the base 43 of transistor 44, but through the intermediary of resistor 40, diode 45,

differentiating capacitor 41, and diodes 42. Differenti-v ating capacitor 41, cooperating with resistor 47, forms a differentiating circuit which differentiates the positive voltage pulse originating from the brief opening of interruptor switch 38. The differentiation of this positive voltage pulse results in the generation of a positivegoing voltage spike and a negative-going voltage spike. The rectifier diodes 42 pass only the positive-going voltage, spike. As a result, a very short-lasting turn-on voltage spike is applied to the base 43 of transistor 44, when interrupter switch 38 is briefly opened.

As a result of the turn-on voltage spike applied to the base 43 of transistor 44, the collector-emitter path 52-51 of transistor 44 becomes briefly conductive, causing a brief flow of current through

resistors

54 and 55, from positive line 35 to negative line 33. As a result of this brief flow of current, the voltage at voltagedivider tap 55 of

voltage divider

53, 54 briefly falls to a value low enough to forward-bias the base-

emitter junction

56, 59 of pnp transistor 57, which accordingly becomes conductive for a short time. During the short time that transistor 57 is conductive, the voltage at circuit junction 61 rises markedly; according, theturn-on voltage spike which is applied to the base 43 of transistor 44 in response to momentary opening of interruptor switch 38 results in the generation of a positive-going voltage spike at circuit junction 61.

The positive-going voltage thusly generated at junction 61 is applied via diode 62 to differentiating capacitor 65, which differentiates the positive-voltage spike to derive therefrom a positive-going voltage spike and a negative-going voltage spike. The negative-going voltage spike is shorted to ground by diode 70. The derived positive-going voltage spike, however, is applied via resistor 66 to the gate electrode 67 of thyristor discharge switch 38, thereby rendering the anodecathode path 74-75 of thyristor 68 conductive. The ignition capacitor 20 by this time has been fully charged, and now discharges rapidly through the anode-cathode path 74-75 and through the primary winding 76 of ignition transformer 77. This results in the generation of a very high voltage pulse across secondary winding 79, producing a sparkover between the electrodes of spark plug 80, with consequent ignition of the fuel-air mixture compressed in the engine cylinder by the cylinder piston.

The diode 78 effects a decay of the voltage of the ignition transformer 77. The capacitor 72 suppresses short-lasting interference pulses of a kind which could improperly trigger thyristor discharge switch 68. Diode 70 makes a possible a quick discharge of the differentiating capacitor 65. The capacitor 58 prevents interference signals from improperly affecting the base 56 of transistor 57. Likewise, capacitor 50 conducts interference pulses away from the base 43 of transistor 44, to ground. The resistor 49 serves to discharge the capacitor 50 and contributes to the determination of the voltage level appearing at the base 43 of transistor 44. The resistor 47 determines the charging and discharging time for the for the differentiating capacitor 41. The transistors 44 and 57, that is, their respective collectoremitter paths 51-52 and 59-60, are conductive only until a certain amount of charge has accumulated on differentiating capacitor 41. The discharge of differentiating capacitor 41 occurs upon closing of the interruptor switch 38 via the resistors 40 and 47. If the interruptor switch 38 chatters upon closing, a voltage pulse will not appear at the circuit junction 61, because the differentiating capacitor 41 will still be charged and will therefore be incapable of transmitting to the base 43 of transistor 44 a voltage sufficient to again render transistor 44 conductive.

The aforementioned positive-going voltage spike appearing at circuit junction 61 when interruptor switch 38 is briefly opened, besides triggering the discharge of ignition capacitor 20, additionally initiates the ignitioncapacitor charging operation requisite for the next discharging of the ignition capacitor. The positive-going voltage spike appearing at circuit junction 61 is communicated via diode 94 and resistor 93 to the base 84 of transistor switch 26, briefly rendering transistor 26 conductive. As a result, a flow of current begins to build-up in primary winding 82 of charging transformer 81. The current flowing through primary winding 82, as a result of the aforementioned turn-on voltage spike, also flows through primary winding 85 of positivefeedback transformer 86 a voltage of predetermined polarity. As a result of the positive-feedback voltage thusly generated across secondary winding 27, current begins to flow through secondary winding 27, from terminal 88 to terminal 90, and then through diode 91 and also through resistor 92 to the base terminal 84 of transistor 26, the current thereupon flowing back to terminal 88 via base-emitter biassing resistor 89, on the one hand, and through the base-emitter junction 84-24 of transistor 26, on the other hand. As a result, the baseemitter junction 84-24 of transistor 26 continues to be forward-biased as a result of the voltage drop across resistor 89 and as a result of the flow of current through the base-emitterjunction. Thus, even after the turn-on voltage spike appearing at junction point 61 has disappeared, transistor 26 is maintained conductive by positive-feedback action. and the flow of current through primary winding 82 of charging transformer 81 continues to build up.

The positive-feedback voltage generated across secondary winding 27 is also applied across the

voltage divider

95, 96, the tap 97 of which is connected to the gate electrode 31 of the thyristor switch 28. As the voltage generated across positive-feedback winding 27 rises, the voltage drop across resistor 96 likewise rises,

and therefore the gate-cathode voltage of thyristor 28 rises. Eventually, the gate-cathode voltage of thyristor 28 reaches such a value as to render thyristor 28 conductive. This effectively short-circuits the secondary winding 27 of the positive-feedback transformer 86, thus reducing to zero the positive-feedback voltage which has hitherto maintained transistor 26 forwardbiased and conductive. As a result, transistor 26 almost immediately becomes non-conductive. The abrupt termination of current flow through the primary winding 82 of charging transformer 81 results in the generation across secondary winding 83 of a high-voltage charging pulse. This charging pulse effects a rapid flow of charging current into ignition capacitor 20, via charging rectifier 23, to fully charge ignition capacitor 20, in preparation for the subsequent discharge thereof.

The diode 99 prevents the gate-cathode path 31-30 of the thyristor switch 28 from being biased in the wrong direction, and the capacitor 98 prevents interference pulses from improperly biasing the gatecathode path of the thyristor 28.

In the exemplary embodiment described herein, one charging pulse for the speed-monitoring capacitor 3 is generated per rotation of the engine output shaft. However, if the internal combustion engine provided with the inventive system has several cylinders, the number of charging pulses for capacitor 3 generated per rotation of the engine output shaft will be higher. It is hardly necessary to point out that not every pulse generated by the ignition circuitry need be applied to the speed-monitoring capacitor 3; for example, only every second such pulses might be actually applied to capacitor 3. Such modifications are comprehended within the scope of the invention.

As mentioned before, the Zener diode 10 of FIG. 1 is provided to limit the voltage level of the charging pulses applied to speed-monitoring capacitor 3. if during running of the engine the maximum permissible engine speed is exceeded, the charging pulses derived from circuit junction 61 (FIG. 3) and applied to capacitor 3 via pulse-transmitting line 7 will charge capacitor 3 at a rate so high that the

discharge resistors

13, 14, during the intervals between the charging pulses, cannot discharge the capacitor of all the charge being furnished to it. Accordingly, there is a net increase of the charge on the capacitor 3, and the capacitor voltage rises, until the threshold voltage of voltage-responsive standby current stage 5 is reached.

When this voltage is reached, the voltage applied via line 12 to base 11 of transistor 110 of standby current stage will be sufficient to forward-bias the

baseemitter junction

11, 111 of transistor 110, thereby rendering transistor 110 conductive. As a result, the collector-emitter voltage of transistor 110 falls towards zero, and so also falls the voltage at the gate electrode 108 of the thyristor switch 107 in the standby current path 100 of the standby current stage 5. Thyristor 107 does not immediately become non-conductive, however, because the voltage at its anode 105 remains sufficiently positive with respect to the voltage at its cathode 106, inasmuch as the voltage at anode 105 does not immediately change. The voltage at anode 105 changes in such a manner as to render thyristor 107 nonconductive only after the next completion of an ignition-capacitor charging operation.

The next completion of an, ignition-capacitor charging operation occurs the next time that the voltage across winding 27 reaches'a value so high that the voltage drop' across resistor 96 biases thyristor switch 28 to conduction. As a result, the positive-feedback winding 27 will be short-circuited, and the transistor switch 26 will become non-conductive, thereby inducing a charging voltage in secondary winding 83 of charging transformer 81. This much of the operation is the same as was explained before without regard to the speedlimiting operation.

Now, when the current flow through the collectoremitter path of transistor 26 is abruptly terminated, a voltage pulse will also be generated across positivefeedback winding 27, but the voltage pulse now generated will have a polarity opposite to that associated with a build-up of current flow in primary winding 82. The voltage thusly induced across secondary winding 27 will be applied across voltage-

divider resistors

95, 96, and the voltage appearing at voltage-divider tap 97 will be applied, via connecting line 101 to the cathode of diode 102 of FIG. 4. The voltage thusly applied to the cathode of diode 102 will besufficiently low to forward-bias the hitherto reverse-biased diode 102. Moreover, with diode 102 now conductive, the voltage applied to the anode 105 of thyristor switch 107 will now be negative relative to the voltage at the cathode 106 thereof. As a result, thyristor 107 becomes nonconductive; it will be recalled that the gate-cathode bias voltage of thyristor 107 had previously been removed, when control transistor 110 became conductive, as a result of the engine speed exceeding the permissible value.

Now that thyristor 107 has become non-conductive, the standby current path 100 becomes blocked, and the standby current is diverted along second current path 101 and passes to circuit junction 97 (FIG. 3) and to the gate electrode 31 of thyristor 28. The flow of this current via line 101 into the gate electrode 31 of thyristor 28 biases the gate-cathode junction for conduction; therefore, thyristor 28 will become conductive as soon as the voltage at its anode 29 becomes sufficiently positive with respect to the voltage at its cathode 30. This occurs upon the next opening of the interrupter switch 38, generating in the manner described before another positive-going voltage spike at circuit junction 61. Again, this voltage spike briefly renders transistor switch 26 conductive, inducing a positive-feedback voltage across secondary winding 27 of positive feedback transformer 86.

However, whereas previously (before the speedlirniting operation commenced) the positive-feedback voltage across winding 27 had to build up for a while until thyristor 28 could be rendered conductive, this is not the case now. Instead, the initial positive-feedback voltage generated across feedback winding 27 will amost immediately render thyristor switch 28 conductive, by rendering anode 29 sufficiently positive with respect to cathode 30. The feedback winding 27 is accordingly short-circuited almost immediately after transistor switch 26 is turned on by the positive-going turn-on voltage spike appearing at junction 61. As a result, transistor switch 26 becomes non-conductive almost immediately after becoming conductive. thereb preventing the build-up of current in primary winding 82. As a result, when transistr switch 26 is turned off, the current flowing in'primary winding 82 will be so small that its sudden termination will not induce across secondary'winding 83 a charging voltage sufficient to charge capacitor 20 to the extent necessary to effect ignition when the interrupter switch 38 is briefly opened at the start of the next cycle.

So long as the engine speed exceeds the permissible maximum, the voltage across capacitor 3 (FIG. 1) will exceed the predetermined value therefor, and the voltage applied to-input ll of voltage-responsive standby current stage 5 will exceed the value necessary to bias control transistor 110 (FIG. 4) into conduction. Therefore, so long as the engine speed exceeds the permissible maximum, the standby current normally flowing through standby current path will instead be diverted via line 101 and serve to. bias the gate-cathode junction of thyristor switch 28, thereby causing switch 28 to become conductive and short-circuit winding 27 every time that there is induced across winding 27 the positive-feedback voltage which normally maintains transistor switch 26 conductive. Because the fuel-air mixture in the engine cylinder will not be ignited, it is evident that the engine speed will decrease.

When the engine speed decreases to a value below the permissible maximum, control transistor 110 (FIG. 4) will become non-conductive, thereby biasing the gate-cathode junction of thyristor 107 (FIG. 4) for conduction. The next time that a positive-going voltage spike appears at junction 61, to briefly turn transistor switch 26 on, the positive-feedback voltage induced across winding 27 will be transmitted via connecting line 101 and render diode 102 non-conductive again, thereby again raising the voltage at thyristor anode 105 to a value more positive than the voltage at cathode 106. As a result, thyristor switch 107 again becomes conductive, and the current in standby current stage 5 again flows along the standby current path 100, instead of being diverted to the current path 101. With the standby current no longer diverted to thyristor gate 31 via current path 101, thyristor 28 will operate once more in the manner described earlier, i.e., in the manner in which it operates when the engine speed is below the permissible maximum value.

It will be understood that each of the elements described above, or two or moretogether, may also find a useful application in other types of circuits and constructions differing from the types described above.

While the invention has been illustrated and described as embodied in electronic ignition arrangements provided with means for automatically limiting the speed of the associated internal combination engine, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. In the ignition system of an internal combustion engine, in combination, electrical igniting means operative for igniting a fuel-air mixture in a cylinder of the engine; ignition capacitor means operative for storing the electrical energy required by said igniting means for effecting ignition of said mixture; energy transfer means operative for causing said ignition means to ignite said mixture by transferring to said igniting means electrical energy stored in said ignition capacitor means; ignition-capacitor-charging means connected to said ignition capacitor means and operative for charging the latter; timing means for timing the transfer of energy from said capacitor means to said igniting means; and engine-speedlimiting means including speed-monitoring capacitor means, speed-dependent charging means for charging said speed-monitoring capacitor means by applying thereto substantially identical charging pulses having a pulse repetition frequency proportional to engine speed, discharge means connected to said speed-monitoring capacitor means and operative for discharging said speed-monitoring capacitor means at such a rate that the voltage across the latter can build up to a predetermined value only if the engine speed reaches a predetermined speed, and voltage-responsive means connected to said speedmonitoring capacitor means and operative when the voltage across the latter exceeds said predetermined value for preventing said igniting means from igniting said mixture, wherein said discharge means comprises a discharge circuit branch connected across said speedmonitoring capacitor means and including resistor means for dissipating energy stored in said speedmonitoring capacitor means, wherein said voltageresponsive means has an input, and wherein said discharge circuit branch comprises a voltage divider having a voltage-divider tap connected to said input of said voltage-responsive means, wherein said voltage divider is comprised of a first portion and a second portion joined together at said voltage-divider tap, and wherein one of said portions is comprised of parallel-connected ohmic resistance means and negative-temperaturecoefficient resistance means and a further resistance means connected in series with the parallel combination of said ohmic and negative-temperaturecoefficient resistance means.

2. In the ignition system of an internal combustion engine, in combination, electrical igniting means operative for igniting a fuel-air mixture in a cylinder of the engine; ignition capacitor means operative for storing the electrical energy required by said igniting means for effecting ignition of said mixture; energy transfer means operative for causing said igniting means to ignite said mixture by transferring to said igniting means electrical energy stored in said ignition capacitor means; ignition-capacitor-charging means connected to said ignition capacitor means and operative for charging the latter timing means for timing the transfer of energy from said capacitor means to said igniting means; and engine-speed-limiting means including speed-monitoring capacitor means, speed-dependent charging means for charging said speed-monitoring capacitor means by applying thereto substantially identical charging pulses having a pulse repetition frequency proportional to engine speed, discharge means connected to said speed-monitoring capacitor means and operative for discharging said speed-monitoring capacitor means at such a rate that the voltage across the latter can build up to a predetermined value only if the engine speed reaches a predetermined speed, and voltage-responsive means connected to said speedmonitoring capacitor means and operative when the voltage across the latter exceeds said predetermined value for preventing said igniting-means from igniting said mixture, wherein said energy transfer means includes a transformer comprised of a secondary winding connected across said igniting means and a primary winding, and means connecting said primary winding in circuit with said ignition capacitor means and including a first electronic switch for preventing discharge of said ignition capacitor means through said primary winding except when said switch is conductive, and wherein said ignition-capacitor-charging means includes a charging transformer comprised of a primary winding and a secondary winding, a source of D.C. current connected across said primary winding of said charging transformer, and a second electronic switch connected in circuit with said source and said primary winding of said charging transformer for preventing flow of current through said primary winding of said charging transformer except when said second electronic switch is conductive, and wherein said timing means comprises means for applying a brief turn-on voltage pulse to said second-electronic switch to initiate the build-up of current flow through said primary winding of said charging transformer, and inductive positive-feedback means operative in response to build-up of current flow through said primary winding of said charging transformer for applying to said second electronic switch a control voltage maintaining the latter conductive accordingly effecting further build-up of current flow through said primary winding of said charging transformer, and wherein said ignition-capacitor-charging means comprises cut-off means automatically operative after the build-up of current in said primary winding of said charging transformer has proceeded to a predetermined extent for terminating the flow of such current by terminating the positive-feedback action of said positivefeedback means, to thereby induce a voltage pulse across said secondary winding of said charging transformer, and wherein said ignition-capacitor charging means further comprises means connecting said secondary winding of said charging transformer in circuit with said ignition capacitor means and including charging rectifier means operative for permitting current flow through said ignition capacitor means from said secondary winding of said charging transformer only when the voltage generated across the latter is of a predetermined polarity, and wherein said voltageresponsive means of said engine-speed-limiting means comprises ignition-prevention means operative when the voltage across said speed-monitoring capacitor means exceeds said predetermined value for preventing the build-up of current flow through said primary winding of said charging transformer by preventing positivefeedback action by said positive-feedback means.

3. A system as defined in claim 2, wherein said discharge means comprises a discharge circuit branch connected across said speed-monitoring capacitor means and including resistor means for dissipating energy stored in said speed-monitoring capacitor means.

4. A system as defined in claim 3, wherein said voltage-responsive means has an input, and wherein said discharge circuit branch comprises a voltage divider having a voltage-divider tap connected to said input of said voltage-responsive means.

5. A system as defined in claim 4, wherein said voltage divider is an adjustable voltage divider applying to said input of said voltage-responsive means an adjustable fraction of the voltage across said speedmonitoring capacitor means, whereby to permit adjustment of the engine speed above which ignition is prevented.

6. A system as defined in claim 4, wherein said voltage divider is comprised of a first portion and a second portion joined together at said voltage-divider tap, and wherein one of said portions is comprised of parallelconnected ohmic resistance means and negativetemperature-coefficient resistance means and a further resistance means connected in series with the parallel combination of said ohmic and negative-temperaturecoefficient' resistance means.

7. A system as defined in claim 6, wherein said further resistance means is comprised of the series connection' of an ohmic resistor and a negative-temperature-coefficient resistor.

8. A system as defined in claim 2, wherein said timing means comprises signal-generating means for generating timing signals for controlling said energy-transfer means and said ignition-capacitor-charging means, and wherein sid speed-dependent charging means comprises means operative for deriving said substantially identical charging pulses from timing pulses generated by said signal-generating means.

9. A system as defined in claim 8, wherein said means operative for deriving said charging pulses from said timing signals comprises a pulse-transmitting circuit branch onnected between said signal-generating and said speed-monitoring capacitor means and including half-wave rectifier means for permitting the flow of charging current into said speed-monitoring capacitor means while preventing discharge of said speedmonitoring capacitor means through said pulsetransmitting circuit branch.

10. A system as defined in claim 9, wherein said pulse-transmitting circuit branch further includes a resistor connected in series with said half-wave rectifier means.

11. A system 'as defined in claim 9, wherein said speed-dependent charging means further comprises Zener' diode means connected across said speedmonitoring capacitor means with such a polarity that a charging pulse applied to said speed-monitoring capacitor means will cause breakdown of said Zener diode means and shunt further charging current of said charging pulse away from said speed-monitoring capacitor means when the voltage level of such charging pulse exceeds a predetermined value, whereby to establish an upper limit on the voltage level of the charging pulses actually charging said speed-monitoring capacitor means.

12. A system as defined in claim-2, wherein said inductive positive-feedback means comprises inductor means so positioned as to have induced thereacross a voltage dependent upon the build-up of current flow through said primary winding of said charging transformer, said inductor means being so connected to said second electronic switch as to apply to the latter a control voltage maintaining the latter conductive and effecting further build-up of current flow through said primary winding of said charging transformer, and wherein said cut-off means comprises a third electronic switch connected across said inductor and operative when conductive for short-circuiting said inductor to prevent the latter from applying to said second electronic switch a control voltage sufficient to maintain said second switch conductive, and wherein said ignition-preventing means comprises means for biasing said third electronic switch for conduction when the voltage across said speed-monitoring capacitor means reaches said predetermined value.

13. A system as defined in claim 12, wherein said third electronic switch has two terminals between which current flows when said third switch is conductive and also a control terminal, and wherein said cutoff means comprises a voltage divider connected across said inductor means and having a voltage-divider impedance portion connected between said control terminal of said third switch and one of said two terminals of said third switch, to render said third switch conductive when the voltage across said inductor means increases to a predetermined extent.

14. A system as defined in claim 12, wherein said third electronic switch is a thyristor.

' 'l5. A system as defined in claim 12, wherein said ignition-preventing means comprises standby circuit means connected across said source of DC. current and normally operative for carrying a standby current but operative when the voltage across said speedmonitoring capacitor means exceeds said predetermined value for diverting said standby current to said third electronic switch and applying said standby current to said third electronic switch-as a biasing current.

16. A system as defined in claim 15, wherein said standby circuitmeans comprises a first current path for standby current and a second current path for conducting current to said third electronic switch, and wherein said second current path includes a diode having a polarity such as to permit current flow along said second path only in adirection which will biassaid third electronic switch for conduction.

17. A system as defined in claim 16, wherein said first current path is connected in series with a stabilizing resistor and with such stabilizing resistor connected across said source of DC. current, and a Zener diode connected across said first current path.

18. A system as defined in claim 16, wherein said first current path includes the anode-cathode current path of a thyristor.

19. A system as defined in claim 18, wherein said standby circuit means further includes a Zener'diode having a cathode connected to the anode of said thyristor and an anode connected to the cathode of said thyristor.

20. A system as defined in claim 19, wherein said standby circuit means further comprises a transistor having a base-emitter junction connected across said speed-monitoring capacitor means and having a collector-emitter path connected across the cathode-gate control path of said thyristor.

21. A system as defined in claim 2, wherein said timing means comprises crankshaft coupled means for generating crankshaft-position-synchronized pulses, and differentiating means for converting such crankshaft-position-synchronized pulses into voltage spikes, and wherein said speed-dependent charging means comprises means for charging said speed-monitoring capacitor means by applying thereto charging pulses derived from said voltage spikes.

22. In the ignition system of an internal combustion engine, in combination, electrical igniting means operative for igniting a fuel-air mixture in a cylinder of the engine; ignition capacitor means operative for storing the electrical energy required by saidigniting means for effecting ignition of said mixture; energy transfer means operative for causing said igniting means to ignite said mixture by transferring to said igniting means electrical energy stored in said ignition capacitor means; ignition-capacitor-charging means connected to said ignition capacitor means and operative for charging the latter; timing means for timing the transfer of energy from said capacitor means to said igniting means; and engine-speed-limiting means including speed-monitoring capacitor means, speed-dependent charging means for charging said speed-monitoring capacitor means by applying thereto substantially identical charging pulses having a pulse repetition frequency proportional to engine speed, discharge means connected to said speed-monitoring capacitor means and operative for dischargingsaid speed-monitoring capacitor means at such a rate that the voltage across the latter can build up to a predetermined value only if the engine speed reaches a predetermined speed, and voltage-responsive means connected to said speedmonitoring capacitor means and operative when the voltage across the latter exceeds said predetermined value for preventing said igniting means from igniting said mixture, wherein said timing means comprises crankshaft coupled means for generating crankshaftposition-synchronized pulses, and differentiating means for converting such crankshaft-positionsynchronized pulses into voltage spikes, and wherein said speed-dependent charging means comprises means for charging said speed-monitoring capacitor means by applying thereto charging pulses derived from said voltage spikes.

Claims

1. In the ignition system of an internal combustion engine, in combination, electrical igniting means operative for igniting a fuel-air mixture in a cylinder of the engine; ignition capacitor means operative for storing the electrical energy required by said igniting means for effecting ignition of said mixture; energy transfer means operative for causing said ignition means to ignite said mixture by transferring to said igniting means electrical energy stored in said ignition capacitor means; ignition-capacitor-charging means connected to said ignition capacitor means and operative for charging the latter; timing means for timing the transfer of energy from said capacitor means to said igniting means; and engine-speedlimiting means including speed-monitoring capacitor means, speed-dependent charging means for charging said speed-monitoring capacitor means by applying thereto substantially identical charging pulses having a pulse repetition frequency proportional to engine speed, discharge means connected to said speed-monitoring capacitor means and operative for discharging said speed-monitoring capacitor means at such a rate that the voltage across the latter can build up to a predetermined value only if the engine speed reaches a predetermined speed, and voltage-responsive means connected to said speed-monitoring capacitor means and operative when the voltage across the latter exceeds said predetermined value for preventing said igniting means from igniting said mixture, wherein said discharge means comprises a discharge circuit branch connected across said speed-monitoring capacitor means and including resistor means for dissipating energy stored in said speed-monitoring capacitor means, wherein said voltage-responsive means has an input, and wherein said discharge circuit branch comprises a voltage divider having a voltage-divider tap connected to said input of said voltage-responsive means, wherein said voltage divider is comprised of a first portion and a second portion joined together at said voltage-divider tap, and wherein one of said portions is comprised of parallel-connected ohmic resistance means and negative-temperature-coefficient resistance means and a further resistance means connected in series with the parallel combination of said ohmic and negative-temperature-coefficient resistance means.

2. In the ignition system of an internal combustion engine, in combination, electrical igniting means operative for igniting a fuel-air mixture in a cylinder of the engine; ignition capacitor means operative for storing the electrical energy required by said igniting means for effecting ignition of said mixture; energy transfer means operative for causing said igniting means to ignite said mixture by transferring to said igniting means electrical energy stored in said ignition capacitor means; ignition-capacitor-charging means connected to said ignition capacitor means and operative for charging the latter timing means for timing the transfer of energy from said capacitor means to said igniting means; and engine-speed-limiting means including speed-monitoring capacitor means, speed-dependent charging means for charging said speed-monitoring capacitor means by applying thereto substantially identical charging pulses having a pulse repetition frequency proportional to engine speed, discharge means connected to said speed-monitoring capacitor means and operative for discharging said speed-monitoring capacitor means at such a rate that the voltage across the latter can build up to a predetermined value only if the engine speed reaches a predetermined speed, and voltage-responsive means connected to said speed-monitoring capacitor means and operative when the voltage across the latter exceeds said predetermined value for preventIng said igniting means from igniting said mixture, wherein said energy transfer means includes a transformer comprised of a secondary winding connected across said igniting means and a primary winding, and means connecting said primary winding in circuit with said ignition capacitor means and including a first electronic switch for preventing discharge of said ignition capacitor means through said primary winding except when said switch is conductive, and wherein said ignition-capacitor-charging means includes a charging transformer comprised of a primary winding and a secondary winding, a source of D.C. current connected across said primary winding of said charging transformer, and a second electronic switch connected in circuit with said source and said primary winding of said charging transformer for preventing flow of current through said primary winding of said charging transformer except when said second electronic switch is conductive, and wherein said timing means comprises means for applying a brief turn-on voltage pulse to said second-electronic switch to initiate the build-up of current flow through said primary winding of said charging transformer, and inductive positive-feedback means operative in response to build-up of current flow through said primary winding of said charging transformer for applying to said second electronic switch a control voltage maintaining the latter conductive accordingly effecting further build-up of current flow through said primary winding of said charging transformer, and wherein said ignition-capacitor-charging means comprises cut-off means automatically operative after the build-up of current in said primary winding of said charging transformer has proceeded to a predetermined extent for terminating the flow of such current by terminating the positive-feedback action of said positive-feedback means, to thereby induce a voltage pulse across said secondary winding of said charging transformer, and wherein said ignition-capacitor-charging means further comprises means connecting said secondary winding of said charging transformer in circuit with said ignition capacitor means and including charging rectifier means operative for permitting current flow through said ignition capacitor means from said secondary winding of said charging transformer only when the voltage generated across the latter is of a predetermined polarity, and wherein said voltage-responsive means of said engine-speed-limiting means comprises ignition-prevention means operative when the voltage across said speed-monitoring capacitor means exceeds said predetermined value for preventing the build-up of current flow through said primary winding of said charging transformer by preventing positive-feedback action by said positive-feedback means.

5. A system as defined in claim 4, wherein said voltage divider is an adjustable voltage divider applying to said input of said voltage-responsive means an adjustable fraction of the voltage across said speed-monitoring capacitor means, whereby to permit adjustment of the engine speed above which ignition is prevented.

6. A system as defined in claim 4, wherein said voltage divider is comprised of a first portion and a second portion joined together at said voltage-divider tap, and wherein one of said portions is comprised of parallel-connected ohmic resistance means and negative-temperature-coefficient resistance means and a further resistance means connected in series with the parallel combination of said ohmic and negaTive-temperature-coefficient resistance means.

7. A system as defined in claim 6, wherein said further resistance means is comprised of the series connection of an ohmic resistor and a negative-temperature-coefficient resistor.

9. A system as defined in claim 8, wherein said means operative for deriving said charging pulses from said timing signals comprises a pulse-transmitting circuit branch onnected between said signal-generating and said speed-monitoring capacitor means and including half-wave rectifier means for permitting the flow of charging current into said speed-monitoring capacitor means while preventing discharge of said speed-monitoring capacitor means through said pulse-transmitting circuit branch.

11. A system as defined in claim 9, wherein said speed-dependent charging means further comprises Zener diode means connected across said speed-monitoring capacitor means with such a polarity that a charging pulse applied to said speed-monitoring capacitor means will cause breakdown of said Zener diode means and shunt further charging current of said charging pulse away from said speed-monitoring capacitor means when the voltage level of such charging pulse exceeds a predetermined value, whereby to establish an upper limit on the voltage level of the charging pulses actually charging said speed-monitoring capacitor means.

12. A system as defined in claim 2, wherein said inductive positive-feedback means comprises inductor means so positioned as to have induced thereacross a voltage dependent upon the build-up of current flow through said primary winding of said charging transformer, said inductor means being so connected to said second electronic switch as to apply to the latter a control voltage maintaining the latter conductive and effecting further build-up of current flow through said primary winding of said charging transformer, and wherein said cut-off means comprises a third electronic switch connected across said inductor and operative when conductive for short-circuiting said inductor to prevent the latter from applying to said second electronic switch a control voltage sufficient to maintain said second switch conductive, and wherein said ignition-preventing means comprises means for biasing said third electronic switch for conduction when the voltage across said speed-monitoring capacitor means reaches said predetermined value.

13. A system as defined in claim 12, wherein said third electronic switch has two terminals between which current flows when said third switch is conductive and also a control terminal, and wherein said cut-off means comprises a voltage divider connected across said inductor means and having a voltage-divider impedance portion connected between said control terminal of said third switch and one of said two terminals of said third switch, to render said third switch conductive when the voltage across said inductor means increases to a predetermined extent.

15. A system as defined in claim 12, wherein said ignition-preventing means comprises standby circuit means connected across said source of D.C. current and normally operative for carrying a standby current but operative when the voltage across said speed-monitoring capacitor means exceeds said predetermined value for diverting said standby current to said third electronic switch and applying said standby current to said third electronic switch as a biasing current.

16. A system as defined in claim 15, wherein said standby circuit means comprises a first current path for standby current and a second current path for conducting current to said third electronic switch, and wherein said second current path includes a diode having a polarity such as to permit current flow along said second path only in a direction which will bias said third electronic switch for conduction.

17. A system as defined in claim 16, wherein said first current path is connected in series with a stabilizing resistor and with such stabilizing resistor connected across said source of D.C. current, and a Zener diode connected across said first current path.

19. A system as defined in claim 18, wherein said standby circuit means further includes a Zener diode having a cathode connected to the anode of said thyristor and an anode connected to the cathode of said thyristor.

22. In the ignition system of an internal combustion engine, in combination, electrical igniting means operative for igniting a fuel-air mixture in a cylinder of the engine; ignition capacitor means operative for storing the electrical energy required by said igniting means for effecting ignition of said mixture; energy transfer means operative for causing said igniting means to ignite said mixture by transferring to said igniting means electrical energy stored in said ignition capacitor means; ignition-capacitor-charging means connected to said ignition capacitor means and operative for charging the latter; timing means for timing the transfer of energy from said capacitor means to said igniting means; and engine-speed-limiting means including speed-monitoring capacitor means, speed-dependent charging means for charging said speed-monitoring capacitor means by applying thereto substantially identical charging pulses having a pulse repetition frequency proportional to engine speed, discharge means connected to said speed-monitoring capacitor means and operative for discharging said speed-monitoring capacitor means at such a rate that the voltage across the latter can build up to a predetermined value only if the engine speed reaches a predetermined speed, and voltage-responsive means connected to said speed-monitoring capacitor means and operative when the voltage across the latter exceeds said predetermined value for preventing said igniting means from igniting said mixture, wherein said timing means comprises crankshaft coupled means for generating crankshaft-position-synchronized pulses, and differentiating means for converting such crankshaft-positionsynchronized pulses into voltage spikes, and wherein said speeddependent charging means comprises means for charging said speedmonitoring capacitor means by applying thereto charging pulses derived from said voltage spikes.