Title:
ARRANGEMENT FOR PREVENTING CURRENT FLOW IN THE IGNITION COIL OF AN INTERNAL COMBUSTION ENGINE DURING STANDSTILL CONDITIONS
United States Patent 3745985
Abstract:
The transistor which, when blocked, interrupts the primary current in the ignition coil thereby causing a spark is also blocked by an additional control system when the interval between ignition pulses becomes long enough to indicate engine standstill.


Inventors:
HOHNE G
Application Number:
05/183502
Publication Date:
07/17/1973
Filing Date:
09/24/1971
Assignee:
Robert Bosch, GmbH (Stuttgart, DT)
Primary Class:
Other Classes:
123/630
International Classes:
F02P3/04; F02P3/055; F02P15/12; (IPC1-7): F02P3/02
Field of Search:
123/148E,148S,146.5D,148 315
View Patent Images:
US Patent References:
3581720ELECTRONIC ENGINE R.P.M. LIMITING DEVICE1971-06-01Hemphill
3534719SPEED LIMITING IGNITION SYSTEM1970-10-20Minks
3264521Voltage suppression network for ignition systems1966-08-02Huntzinger
3262438Ignition system for internal combustion engines1966-07-26Holford
3087001Breakerless ignition system1963-04-23Short et al.
2943131Transistor ignition system1960-06-28Kerr
Primary Examiner:
Goodridge, Laurence M.
Assistant Examiner:
Flint, Cort
Claims:
What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims

1. In an internal combustion engine having a crank shaft and an ignition circuit, an arrangement for preventing current flow in said ignition circuit during standstill conditions, comprising, in combination, first switch means connected to said ignition circuit for interrupting the current through said ignition circuit in response to a control signal, thereby creating a spark; control signal furnishing means for furnishing said control signal in synchronism with the rotation of said crank shaft; energy storage means furnishing a storage signal indicative of the energy stored therein; means continually supplying energy to said energy storage means; first control means comprising semi-conductor switching means connected to said energy storage means for discharging energy from said energy storage means in response to each of said control signals; and second control means interconnected between said energy storage means and said first switch means for furnishing an additional control signal to said first switch means in response to a storage signal indicative of energy storage exceeding a predetermined energy storage.

2. An arrangement as set forth in claim 1, wherein said ignition circuit means comprise an ignition coil having a primary winding and a secondary winding; a source of D.C. voltage; and wherein said first switch means connect said primary winding of said ignition coil to said source of D.C. voltage, and disconnect said primary winding from said source of D.C. voltage in response to said control signals.

3. An arrangement as set forth in claim 2, wherein said energy storage means comprise a storage capacitor; and wherein said storage signal is the voltage across said capacitor.

4. An arrangement as set forth in claim 3, wherein said second control means comprise threshold circuit means furnishing said additional control signal when said voltage across said storage capacitor exceeds a predetermined voltage.

5. An arrangement as set forth in claim 2, wherein said first switch means comprise a switching transistor having a collector, emitter, and base.

6. An arrangement as set forth in claim 5, further comprising a first transistor having a collector-emitter circuit and a base; and means connecting said collector-emitter circuit to said base of said switching transistor.

7. An arrangement as set forth in clain 3, further comprising voltage stabilizing means interconnected between said source of D.C. voltage and said storage capacitor.

8. An arrangement as set forth in claim 4, wherein said threshold circuit means comprise a threshold circuit transistor having an emitter-collector circuit and a base; and Zener diode means connecting said base of said threshold circuit transistor to said storage capacitor.

9. An arrangement as set forth in claim 3, wherein said semi-conductive switching means comprise a switching transistor having an emitter-collector circuit connected in parallel with said storage capacitor, and resistance means connected in series with said emitter-collector circuit of said switching transistor.

10. An arrangement as set forth in claim 9, wherein said switching transistor has a base; and wherein said first control means further comprise RC circuit means interconnecting said control signal furnishing means and said base of said switching transistor.

11. An arrangement as set forth in claim 10, wherein said control signal furnishing means comprise a mechanical switch; further comprising cam means operated in synchronism with the rotation of said crank shaft for oeprating said mechanical switch means.

12. An arrangement as set forth in claim 10, wherein said control signal furnishing means comprise magnetic means, said magnetic means having rotor means driven in synchronism with the rotation of said crank shaft, and winding means in operative proximity of said rotor means for furnishing said control signals.

13. In an internal combustion engine having a crank shaft, an ignition system, comprising, in combination, ignition spark furnishing means furnishing a spark upon activation; first switch means connected to said ignition spark furnishing means for activating said ignition spark furnishing means in response to a control signal; control signal furnishing means for furnishing said control signal in synchronism with the rotation of said crank shaft; energy storage means comprising storage capacitor means, for furnishing a storage signal indicative of the energy stored therein; first control means connected between said energy storage means and said control signal furnishing means for controlling the energy stored in said energy storage means as a function of the control interval between successive ones of said control signals; and second control means interconnected between said energy storage means and said first switch means for furnishing an additional control signal to said first switch means in response to a storage signal indicative of energy storage resulting from a control interval exceeding a predetermined control interval, said second control means comprising a threshold circuit transistor having an emitter-collector circuit and a base; and Zener diode means connecting said base of said threshold circuit transistor to said storage capacitor.

Description:
BACKGROUND OF THE INVENTION

This invention relates to an ignition system for internal combustion engines. More specifically, it relates to such an ignition system which comprises a source of D.C. voltage and an ignition coil having a primary winding connected to said source of ignition voltage by means of a switching arrangement which is opened for initiation of a spark. In combustion engines having a battery for furnishing the D.C. voltage and having an ignition coil which stores the energy and transfers the so-stored energy to a spark plug at the proper ignition time, a quiescent current flows in the primary circuit as long as the ignition is not shut off. This so-called quiescent current may be as high as several amperes and is very undesirable since it loads both the ignition coil and the battery unnecessarily.

In a known arrangement for preventing the flow of such quiescent current, a thermostat is heated through the quiescent current and, when a particular temperature is reached, a switch is activated which interrupts the primary current flow. However, such arrangements are complicated and unreliable, since the effective value of the current in the primary winding of the coil for low engine speeds is only somewhat smaller than the quiescent current under standstill conditions. Further, the additional contact in this type of automatic switching arrangements also decreases the reliability of the ignition circuit under normal operation.

It has further been proposed for systems using mechanical interrupter switches in the primary circuit of the ignition coil, that the angle of rotation throughout which such mechanical switches be closed be kept relatively small, thus minimizing the risk that the interrupter switch is closed when the ignition is still opened and the engine has stopped. Such a solution cannot be used for high speed internal combustion engines, since the angle of closure for such machines must be particularly large in order that a sufficiently big magnetic field may be created in the ignition coil. This is also true for transistorized ignition circuits in which the mechanical interrupter switch has been replaced by a transistor.

SUMMARY OF THE INVENTION

It is an object of the present invention to furnish an ignition arrangement wherein the quiescent current through the primary winding of the ignition coil is interrrupted upon engine standstill and while the ignition switch is still connected. This invention comprises an ignition arrangement for internal combustion engines having a crank shaft. It comprises spark furnishing means furnishing an ignition spark upon activation and first switch means which activate said spark furnishing means in response to control signals. It further comprises means for furnishing said control signal in synchronism with the rotation of said crank shaft of said engine. Further, energy storage means are furnished which furnish a storage signal indicative of the energy stored therein. First control means control the energy stored in said energy storage means as a function of the interval between successive ones of said control signals. Further, second control means are interconnected between said energy storage means and said first switch means and furnish an additional control signal to said first switch means when said storage signal indicates that the time interval between successive ones of said control signals exceeds a predetermined time interval.

In a preferred embodiment of the present invention, the switch means are activated in synchronism with the rotation of the engine crank shaft to open the primary winding of the ignition coil, thereby inducing a spark. Further, the energy storage means may be a capacitor which is charged continually and periodically discharged, also in synchronism with the rotation of the engine. When the engine stands still, this capacitor is no longer discharged. The voltage across it thus reaches a particular voltage value which exceeds a predetermined voltage. This in turn causes the opening of the switch means interrupting the current in the primary winding of the coil. This arrangement thus does not introduce additional contact into the circuit. It is thus a more reliable arrangement than the known arrangements.

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 is a block diagram showing an ignition system in accordance with the present invention;

FIG. 2 is a circuit diagram of an ignition arrangement using a mechanical interrupter switch; and

FIG. 3 is a circuit diagram of a transistorized ignition system using a magnetic source of control signals.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiment of the invention will now be described with reference to the drawing.

FIG. 1 shows a block diagram wherein an ignition system is energized from a source of D.C. voltage 11 via an ignition switch 10. Switch means 12 are connected via a line 13 with the primary winding 14a of an ignition coil 14. The secondary winding 14b of the ignition coil 14 has one terminal connected to the primary winding and a second terminal connected via an ignition cable 15 to spark plug 16. The common point of the primary and second windings is connected to ground. One terminal of the ignition switch 10 is directly connected to the positive side of the battery 11, while the other terminal is connected to a series circuit comprising a variable resistance 18 and a capacitor 17 whose other terminal is connected to ground. Capacitor 17 constitutes energy storage means. The common point of resistance 18 and capacitor 19 is connected to one side of a first control arrangement 19 whose second side is connected to ground potential. The common point of resistance 18 and capacitor 17 is further connected to a second control means 23 whose output in turn activates switch means 12 via line 22. A line 21 between first control means 19 (indicated in FIG. 1 as a switching arrangement) and switch means 12 which constitutes first switch means, indicates the synchronous operation of element 12 and 19 during the rotation of the crank shaft of the engine.

This Figure operates as follows.

When switch 10 is closed and the engine is running, current flows through primary winding 14a when switch 12 is closed, thereby causing a magnetic field to build up. During the running of the engine, switch 12 is opened in synchronism with the rotating of the crank or cam shaft, thereby causing the magnetic field to collapse, which in turn induces a pulse in the secondary winding causing a spark to appear. Further, capacitor 17 is charged from the D.C. voltage source 11 via resistance 18. However, each time switch 12 is opened, the first control means 19 are activated via line 21 so that the capacitor is short-circuited briefly. Thus the capacitor is periodically discharged while the engine is turning.

When, however, the engine has stopped while the ignition switch 10 is still closed, the voltage on capacitor 17 exceeds a predetermined voltage. Second control means 23 then furnish an additional control signal to first switch means 12 which opens the switch means. Thus the primary circuit of ignition coil 14 is opened, and no quiescent current can flow. The value of adjustable resistor 18 is such that capacitor 17 reaches the predetermined voltage which causes the operation of second control means 23 during a time interval of approximately one second. This insures that switch means 12 are only opened after a time interval wherein it is certain that no ignition pulse will be required, that is that the engine is standing still. As mentioned above, while the engine is running, capacitor 17 is discharged by first control means 19 each time a spark is created in response to a first control signal.

FIG. 2 shows a circuit diagram of an ignition arrangement in which the first switch means 12 comprise a pnp power transistor 30. The ignition arrangement is connected to a source of D.C. voltage of 12 volts via a positive line 29 and a ground line. A capacitor 31 and a Zener diode 32 are connected in parallel with the emitter-collector circuit of transistor 30. The collector of transistor 30 is connected with the primary winding or ignition coil 34 via a resistance 33 of approximately 1 ohm. The secondary winding of ignition coil 34 is connected via an ignition cable 35 to a spark plug 36. The first control signal furnishing means which control the operation of transistor 30 when the engine is running comprise a rotating cam 37a which operates an interrupter switch 37. The switch 37 is connected via a series circuit comprising a resistance 38 of 1,000 ohms, and a diode 39 to the positive line 29. The common point of resistor 38 and diode 39 is connected via a line 41 to the base of a transistor 42 which is an npn control transistor. The collector connection 43 of transistor 42 is connected to line 29 via a resistance 44, while its emitter is directly connected to ground. The value of resistance 44 is 1,000 ohms. The collector terminal 43 is further connected to the base of a further npn control transitor 45 which acts as an amplifier and has a collector connection 46 which is connected to line 29 via the series combination of a resistor 47 and a resistor 48, each of which is 15 ohms. At the common point of resistors 47 and 48 is connected the base of pnp power transistor 30.

The ignition arrangement further comprises a monitoring arrangement 49 which causes transistor 30 to block when the engine is standing still, and switch 37 is closed. The monitoring arrangement comprises voltage stabilizing means which comprise a Zener diode 50 connected in parallel with a capacitor 51 of 2 micro-farads. The parallel combination of the Zener diode 50 and capacitor 51 has one terminal connected to the ground line and a second terminal connected via a resistance 53 of 220 ohms to the positve line 29. A stabilized voltage therefore appears on line 52 which connects one terminal of resistor 53 to the above-mentioned parallel circuit of Zener diode 50 and capacitor 51. Further connected to line 52 is a resistance 54 of approximately 100 kilo ohms and a capacitor 54 of 20 micro-farads connected in series with said resistance. The line 56 connecting resistance 54 and capacitor 55 is further connected via a resistance 57 of 10 ohms with the collector of an npn control transistor 58 and further with the base of a transistor 60 via a Zener diode 59. The emitter of transistor 60 is connected to ground while its collector is connected to line 52 via a resistance 69 and is further connected to the collector of transistor 42 via a line 68. The emitter of transistor 60 as well as that of transistor 42, is connected to ground. Transistor 58 also has an emitter connected to ground while its base is connected to a resistance 61 of 1.5 kilo ohms of a capacitor 62 of 5 nano-farads, as well as a resistance 63 of 1 1/2 kilo ohms whose other terminal is connected to ground. The other terminal of capacitor 62 is connected via a line 64 with a further resistance 65 of 1 kilo ohm. The other terminal of resistor 65 is connected to line 52. The voltage at line 52 is a stabilized voltage, as mentioned above, of approximately 6.8 volts. Capacitor 62 is further connected via a line 64 to a diode 66 whose cathode is connected to one terminal of interrupter switch 37. A further diode 67 is connected from the base of transistor 58 to ground. Transistor 58 and the circuitry connected therewith constitute first control means, while transistor 60 and its associated circuitry constitute second control means.

When the engine is running, interrupter switch 37 is operated and closed in synchronism with the rotation of the engine by cam 37a. Thus, a rectangular voltage pulse appears across its contacts. These pulses are applied via line 41 to the base of transistor 42, thereby creating positive pulses at the collector 43 of transistor 42. Since collector 43 is connected to the base of transistor 45, negative pulses appear at the collector 46 of transistor 45. The pulses appearing at the common point of resistors 48 and 47 therefore correspond to the rectangular pulses on line 41. Transistor 30 thus is conductive and non-conductive in accordance with, respectively, the closing and opening of interrupter switch 37 by cam 37a. When transistor 30 is conductive, the primary circuit of ignition coil 34 is closed and current flows through transistor 30, protective resistance 33, and the primary winding of the ignition coil 34. A magnetic field is thus built up in the ignition coil. If transistor 30 is now blocked at the required ignition time, the primary current is interrupted, inducing a high voltage in the secondary winding of the ignition coil and thereby creating a spark at spark plug 36. In order to protect it from voltages induced in the primary circuit when a spark is created in the secondary circuit, the emitter-collector circuit of transistor 30 is shunted by capacitor 31 and Zener diode 32.

When the engine is standing still and the ignition switch is opened, capacitor 62 is charged via resistors 53, 65 and 63 and is discharged when switch 37 is closed. Further, capacitor 55 is charged via resistors 54 and 53. Capacitor 55 is discharged via transistor 58. Since the base of transistor 58 is connected to capacitor 62 via resistance 61, a positive voltage pulse appears at the base of this transistor for each charging of capacitor 62. This positive pulse switches transistor 58 to the conductive state each time interrupter switch 37 is opened and capacitor 55 is discharged via resistance 57 and the emitter-collector circuit of transistor 58. Since the base of transistor 60 is also connected with line 56, which is connected to capacitor 55 via Zener diode 59, the value of resistor 54 must be so chosen that capacitor 55 is discharged before the voltage across the capacitor exceeds the breakdown voltage of Zener diode 59.

When the engine is standing still and interrupter switch 37 is closed, transistor 58 is blocked so that capacitor 55 can no longer be discharged. As soon as the voltage across capacitor 55 reaches the breakdown voltage of Zener diode 59, a positive pulse appears at the base of transistor 60 causing this transistor to become conductive. Zener diode 59 and transistor 60 thus constitute a threshold circuit. The collector of transistor 60, as well as the base of transistor 45, are switched substantially to ground potential, causing transistor 45 to block. When transistor 45 is blocked, the emitter-base voltage of transistor 30 is sustantially equal to zero so that transistor 30 blocks thereby interrupting the primary circuit of ignition coil 34.

When the engine is first started up, opening of interrupter switch 37 causes capacitor 62 to charge and base of transistor 58 to become positive for a short while, causing transistor 58 to become conductive and capacitor 55 to be discharged. When interrupter switch 37 is closed, transistor 30 is switched to the conductive condition via transistors 42 and 45. The ignition arrangement operates in the manner described above.

FIG. 3 shows the transistorized ignition arrangement wherein the first control signals are supplied magnetically rather than by a mechanical interrupter, as shown in FIG. 2. It should be stated that the first control signals, as defined herein, are furnished in synchronism with the rotation of the engine during the running of the engine, either by the magnetic means shown in FIG. 3, or by interrupter switch 37 of FIG. 2. The additional control signals are furnished by the monitoring arrangement and interrupt the primary circuit of the ignition coil when the engine is standing still. To return to FIG. 3, rotor 71 rotates in the direction of the arrow 70 inducing alternating positive and negative pulses in a winding 72. One terminal of winding 72 is connected to ground potential, while the other terminal is connected to the cathode of a diode 73 whose anode is connected to the base of an npn control transistor 74. The base of transistor 74 is connected via a resistance 75 of 18 kilo ohms to a stabilized voltage line 76. The stabilized voltage line 76 is connected to a resistance 77 to positive line 80 which is connected to the positive side of a source of D.C. voltage. Line 76 is further connected to ground potential via a Zener diode 78. A capacitor 79 is connected in parallel with Zener diode 78. The source of D.C. voltage may again be a 12 volt battery. A capacitor 81 and a diode 82 are connected in parallel to the base-emitter circuit of transistor 74. The emitter of transistor 74 is connected to ground via a resistance 83. Its collector is connected to line 76 via a resistance 84 and is further connected to the base of a further npn control transistor 85. The emitter of transistor 85 is connected to its base via a capacitor 86 and is also connected to ground via resistance 83. The collector of transistor 85 is connected to line 76 via a resistance 87 of 1.5 kilo ohms and is further connected via an RC circuit comprising a capacitor 88 connected in series with resistance 89 of 1 1/2 kilo ohms to the input of a monostable multivibrator. The monostable multivibrator comprises two npn transistors 90 and 91 whose emitters are connected in parallel via a line 92 and via a resistance 93 of 22 ohms to ground. A diode 94 is connected in parallel to the base-emitter circuit of transistor 90. The collector of transistor 90 is connected to line 76 via a resistance 95 of 1.5 kilo ohms, and is further connected with the base of transistor 91 via a capacitor 96. The base of transistor 91 is connected to line 76 via a resistance 97 of 15 kilo ohms, while its collector is connected via resistance 98 of 15 kilo ohms with the base of transistor 90. The output of the monostable multivibrator, namely the collector of transistor 91, is further connected to line 80 via two series resistances 90 and 100 of 1 1/2 kilo ohms and 820 ohms, respectively. The resistors 99 and 100 serve as voltage dividers and have a common point connected to the base of a pnp transistor 101 whose emitter is connected to line 80 and whose collector is connected to the base of a transistor 103 via a resistance 102 of 330 ohms. Npn transistor 103 has an emitter connected to ground and a collector connected to line 80 via a voltage divider comprising series connected resistors 104 and 105 of 15 and 10 ohms, respectively. The base of pnp power transistor 106 (first switching means) is connected to the common point of resistors 105 and 104. The emitter of transistor 106 is connected to line 80, while its collector is connected via a resistance 107 with one end of primary winding of an ignition coil 108. The other end of the primary winding of ignition coil 108 is connected to ground. The secondary winding of ignition coil 108 is connected through an ignition cable 109 with spark plug 110. The emitter-collector circuit of power transistor 106, in parallel to which are connected capacitor 111 and Zener diode 112, thus lies in the primary circuit of ignition coil 108.

This ignition arrangement also has a monitoring arrangement 113. Monitoring arrangement 113 comprises a capacitor 114, one of whose terminals is connected to ground and the other of whose terminals is connected via a resistance 115 of approximately 100 kilo ohms and a line 116 to line 76. The collector-emitter circuit of an npn transistor 118 is connected in series with a resistance 117 of 10 ohms, in parallel to capacitor 114. The base of transistor 118 is connected via an RC differentiating circuit comprising a capacitor 120 of 5 nano-farads and a resistance 119 of 1.5 kilo ohms with a line 121 to the collector of transistor 85. A diode 122 is connected in parallel to the emitter-base circuit of transistor 118. The base of an npn transistor 124 is connected via a Zener diode 123 to the common point of resistance 117 and capacitor 114. The emitter of transistor 124 is connected to ground via line 125, while its collector 126 is directly connected to the base of transistor 91. The output of transistor 124 taken at its collector, constitutes the additional control signal.

While the engine is running, rotor 71 rotates, inducing a sequence of alternatingly positive and negative pulses in coil 72. The positive pulses are blocked by diodes 73, while the negative pulses required for control of the first switching means, namely transistor 106, are applied to the base of transistor 74. Transistor 74 is conductive since it is connected to the stabilized voltage at line 76. However, upon appearance of a negative pulse from winding 72, transistor 74 blocks. This causes the potential at the collector of transistor 74 to rise for a short time so that the signal at transistor 74 is a rectangular pulse. Of course transistor 74 remains conductive only for the duration of the negative pulse at its base, thereby making the rectangular pulse at its collector a narrow one. The signal at the collector of transistor 74 appears in inverted form at the collector of transistor 85. Through differentiation of the leading and trailing edge, a positive and a negative impulse therefore are generated at capacitor 88. The negative impulse is shunted by diode 94, while the positive impulse reaches the base of transistor 90, causing this transistor to become conductive. This causes the potential at the collector of transistor 90 to drop sharply. Since capacitor 96 operates as a differentiator, a negative impulse appears at the base of transistor 91. Transistor 91 was previously maintained in a conductive condition by its connection to line 76 via resistance 97. The negative impulse causes it to block for short time, whereby the potential at the collector of transistor 91 instantaneously rises to the potential of line 80. This potential is applied to the base of transistor 90 via resistance 98 maintaining the latter transistor in a conductive state. Only when the negative impulse at capacitor 96 has died down, can transistor 91 again assume the conductive state. This causes the emitter-base potential of transistor 90 to become substantially equal to zero, causing 90 to block. Transistors 90 and 91 thus work as a monostable multivibrator, furnishing rectangular positive pulses at the output of said monostable multivibrator (resistor 99). These pulses are applied to the base of transistor 101 causing this transistor to block, so that resistance 102 is temporarily disconnected from line 80. Transistor 103, whose base is connected to resistance 102, thus is blocked for the duration of the pulse. A positive rectangular pulse is created at the base of transistor 106 due to the blocking of transistor 103. The voltage at the base of transistor 106 becomes substantially equal to the voltage on line 80. This causes transistor 106 to block, thereby interrupting the primary current through the ignition coil 108. This blockage of current causes a high voltage to be induced in the secondary of ignition coil 108 causing a spark to appear at spark plug 110. When the control pulse at the base of transistor 106 is removed, the primary circuit of the ignition coil is again closed through transistor 106, allowing the creation of a magnetic field in the ignition coil.

While the engine is running, the monitoring arrangement 113 operates as follows. Capacitor 114 is charged continually via resistance 115 from line 76. For each halfwave emanating from the rotor 70, transistor 74 blocks shortly. Since transistor 85 is conductive for the same time that transistor 74 is blocked, a rectangular pulse appears at the collector of transistor 85. This rectangular pulse is differentiated by capacitor 120, so that a positive and negative impulse appear at the common terminal of resistance 119 and the base of transistor 118. The negative pulse is shunted to ground via diode 122, leaving only the positive pulse to become effective. This causes the transistor to switch shortly to a conductive state, so that capacitor 114 can discharge over resistance 117 and transistor 118.

The values of resistance 115 are such that the voltage on capacitor 114 can only reach the breakdown voltage of Zener diode 123 when no first control pulses appear, that is, when the motor is standing still and no pulses are being generated in coil 72. When the breakdown voltage of Zener diode 123 has been reached, the base of transistor 124 becomes postive, switching transistor 124 into the conductive condition. Since the collector of transistor 124 is connected via line 126 with the base of transistor 91, the base of this transistor (91) is connected to ground through transistor 124, causing transistor 91 to block. This causes the base of transistor 101 to assume the potential of line 80, so that transistor 101 blocks. Since the base of transistor 103 is connected to the collector of transistor 101 via resistance 102, blocking of transistor 101 results in clocking of transistor 103. As a result thereof, the base of transistor 106 assumes the potential of line 80, causing transistor 106 to block, thereby interrupting the primary circuit of the ignition coil.

The invention is not to be limited to the embodiments shown. For example, an npn switching transistor can be substituted for pnp power transistor 106. Further, the npn control transistors can be replaced by pnp transistors with only minor changes in the circuit. Further of course, other values for the capacitor-resistors and other electronic building components may be used. Obviously when a multi-cylinder internal combustion engine is used, the secondary winding of the ignition coil is connected to a distributor which furnishes the high voltage pulses for the individual spark plugs. Further, the invention is to include all types of ignition circuits wherein the current through the primary circuit of the coil is interrupted by a switching element during normal circuit operation in order to create the spark and is further interrupted by a monitoring arrangement when the engine is standing still. The particular manner of obtaining the additional control signal disclosed herein, namely if a charge across a capacitor exceeds a predetermined charge, due to lack of shunting of said capacitor when the engine is standing still, can of course readily be replaced by an arrangement wherein a capacitor is normally charged and only drops below a certain charge value when no first control signals are being received. Other forms of storage elements can also of course be used in substitution for the capacitor.

While the invention has been illustrated and described as embodied in specific transistorized ignition circuitry and monitoring arrangement, it is not intended to be limited to the details shown, since various modifications, structural and circuit 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 he 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.