US3857043A

US3857043A - Interlock circuit for blocking operation of starter motor of a combustion engine

Info

Publication number: US3857043A
Application number: US00323719A
Authority: US
Inventors: A Habasch
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1972-02-21
Filing date: 1973-01-15
Publication date: 1974-12-24
Anticipated expiration: 1991-12-24
Also published as: JPS4896929A; FR2173581A5; IT973279B; DE2208045A1

Abstract

A voltage produced by the rotation of the armature of the starter motor of a combustion engine is used to control the operation of a threshold switch for cutting off or blocking the operation of the starter motor. A voltage produced by the generator driven by the engine is used only to block operation of the starter motor when the engine is running and the starter motor already stopped. The signal from the generator is provided directly to a cut-off relay through a diode as well as indirectly through an OR-gate at the input of the threshold switch to which the voltage signal from the starter motor itself is also furnished. A storage capacitor is used to prevent premature reactivation of the starter.

Description

United States Patent 1191 Habasch [111 3,857,043 [451 Dec. 24, 1974 INTERLOCK CIRCUIT FOR BLOCKING OPERATION OF STARTER MOTOR OF A COMBUSTION ENGINE [75] Inventor: Ahmed I-Iabasch, Schwieberdingen,

Germany [73] Assignee: Robert Bosch GmbH, Stuttgart,

Germany [22] Filed: Jan. 15, 1973 [21] Appl. No.: 323,719

[30] Foreign Application Priority Data Cummins 290/37 Primary ExaminerG. R. Simmons Attorney, Agent, or Fir'mFlynn & Frishauf 57 ABSTRACT A voltage produced by the rotation of the armature of the starter motor of a combustion engine is used to control the operation of a threshold switch for cutting off or blocking the operation of the starter motor. A voltage produced by the generator driven by the engine is used only to block operation of the starter motor when the engine is running and the starter motor already stopped. The signal from the generator is provided directly to a cut-off relay through a diode as well as indirectly through an OR-gate at the input of the threshold switch to which the voltage signal from the starter motor itself is also furnished. A storage capacitor is used to prevent premature reactivation of the starter.

15 Claims, 4 Drawing Figures Patentd Dec. 24, WW!

3 Sheets-Sheet l m Q50 \22 Bud Patented Dec. 24,

3 Sheets-Sweet 5 This invention relates to an interlock system for switching off the starter motor of a combustion engine after a successful start and for preventing untimely activation of the starter motor. The system is designed for combustion engines coupled to a generator connected to charge a battery, which supplies electricity over an ignition switch to the engine and, also, over a further switch to the starter motor.

Interlock systems of this general class are known in which a starter blocking relay is provided to prevent the starter motor from being energized while the engine is running or shortly after an unsuccessful attempt to start, and also to prevent the motor from being energized too long after the engine has started. Such switching arrangements involve a considerablee number of relays which are activated in dependence upon the output voltage of the generator. Since the output voltage of the generator of a motor vehicle is to a large extent dependent upon temperature and whereas motor vehicle components are subject to very large temperature variations, and, finally, relays also exhibit temperature dependence in their operation, the known switching systems do not provide with sufficient reliability for the deenergization of the starter motor at the desired operating conditions of the engine. In addition the known switching arrangements for this purpose are cumbersome and expensive on account of the large number of relays and othercomponents used in their construction. I

It is a principal object of this invention to provide a switching arrangement, which because of its purpose may be called an interlock system, that provides a reliable shutting off of the starter motor when the engine speed is reached at which the engine can keep running by itself and likewise reliably prevents an untimely turning on of the starter motor.

A further object of the invention is to provide an interlock system for this purpose that is inexpensive to produce and is adapted to work safely and reliably under rough operating conditions to which a motor vehicle may be subject.

Subject matter of the present invention: Briefly, a switch in the current supply of the starter motor for blocking energization of the starter motor is arranged to be dependent for its activation mainly upon a voltage produced by 'the rotation of the armature of the starter motor when that motor is running, but is controllable by the generator voltage when the starter motor is stopped or almost stopped while the engine is running.

The invention will be described by way of example with reference to the accompanying drawings, wherein:

, FIG. 1 is a basic circuit diagram of an interlock system switching off the starter motor and preventing untimely activation of the starter motor;

FIG. 2 is a block diagram of the electronic portion of the interlock system shownin FIG. 1; and

FIG. 3 is a circuit diagram of the electronic portion of the interlock system shown in FIG. 1, and

FIG. 4 is a circuit diagram of a modification of part of the circuit of FIG. 1.

A starter motor 10 is shown in FIG. 1 in a schematic representation. It has an armature 11, a main stator winding 12 and an auxiliary stator winding 13. The main winding 12 and the auxiliary'winding 13 can be connected to a battery 16 over a switch 14 constituted by the contact of a starter relay 15. For normal activation of the starter relay 15 it is necessary to close both the ignition switch 17 and the starter switch 18. Operation of the latter energizes a winding 19 of a relay 20 which then closes its contacts to energize the starter relay 15 and the holding winding of the stator gear magnet 22, the actuation winding 26 of which is controlled by a contact of starter relay15 through which current is supplied when starter relay 15 operates. Operation of starter relay 15 results in applying the conducting bridge 23 against contacts 24 and 25 and thus connects the battery 16 with the auxiliary winding 13. Energization of auxiliary winding 13 of the starter motor 10 turns the armature 11 of the motor slowly and since at the same time the actuation winding 26 of the starter gear magnet is energized in series with the armature 11 the pinion 2 7 of the starter can with relative case be engaged with the ring gear shown at 28, which is connected with the combustion engine not further I shown in the drawing. As the pinion thus engages the ring gear, as shown by broken lines at 29, switching contacts 30 are moved over to their second position. In this position the contacts 30 connect the auxiliary winding 13 of starter-motorltl directly to ground (instead of only to ground through the armature 11). Furthermore, in this position the activation winding 26 of the starter gear magnet 22 is deenergized, so that the pinion is held engaged with the ring gear henceforth only as the result of current through the holding winding 21 of the starter gear magnet. In the circuit as shown in dashed lines in FIG. 1, the activation winding 26 of the starter gear magnet 22 is energized in series with the armature 11, first in parallel with the winding 13, at which time most of the voltage appears across the windings 13 and 26, and then, after the relay oper-' ates, in parallel with the winding 12, at which time a great deal more of the voltage appears across the armature 11, so that the current through the winding 26 drops considerably. In the circuit shown in dotted lines inFIG. 1, the current in the winding 26 is fully cut off at the contacts 30A by operation of the relay 22. Concurrently with the switching of contacts 30 a mechanical blocking of the further pulling in of the conducting bridge 23 of the contacts 14 of the starter relay 15 is released by mechanical connection indicated by the broken lines 31, so that the conducting bridge 23 of the starter relay may now connect contact 24 with contact 32. In this position of the contacts 14 current from the battery 16 may flow over contact 24, conducting bridge 23 and contact 32 to'the main stator winding 12 of the criminator switch 34. The operation of the threshold switch 34 can also be accomplished by a voltage change produced in the main stator winding 12 as the result of the rotation of the armature 11 or by a voltage induced in an auxiliary winding provided in the stator of the Starter motor. Such an auxiliary winding can be separately provided on the stator, or can be the auxiliary winding 13.

In the circuit shown in the drawings, after the mechanical linkage 31 has unblocked the starter relay 15 so that the contact 23 energizes the main stator winding 12 of the starter motor, the lefthand input of the OR- gate 33 shown in FIG. 1 is in effect connected to the tap of a voltage divider formed by the stator winding 12 and the armature winding 11. As the rotation of the armature 11 speeds up, the voltage across the armature rises until the voltage is sufficient to operate the OR- gate. Obtaining this voltage from the stator winding as above suggested, for the case of a shunt wound starter motor, for example, or an auxiliary stator winding is shown in FIG. 4, where the stator winding 12' is supplied from the battery through a resistor 12" as well as through a contact of the relay 15, which may for example be the contact 32.

The operation of the threshold switch 34 causes current to flow through the winding 35 of a relay 36 to open the contacts 37 located in the curved supply circuit for the relay 19. As a result of this function, the relay 36 or its contact 37 may be referred to as a circuit breaker. The opening of the contacts 37 deenergizes relay 19, causing the contacts 20 to open. In consequence the winding of starter relay 15 is likewise deenergized and the conducting bridge 23 returns to the position shown in the drawing, so that both the auxiliary winding 13 and the main winding 12 of the starter motor are disconnected from the current supply. At the same time the holding winding 21 of the starter gear magnet 22 is deenergized, so that the pinion is pulled out of engagement with the ring gear 28, for example by spring pressure, and the starter motor 10 then gradually runs down and stops.

Since no armature voltage is provided by the armature 11 when the starter motor 10 is stopped, it could happen that while the combustion engine is running the driver of the motor vehicle inadvertently tries to start the engine by closing the starter switch 18. In order to prevent the activation of the starter motor in this case, a connection is provided from a generator 38 driven by the engine of the vehicle, through the OR-gate 33, to the threshold switch 34. So long as the engine is running, the generator 38 supplies a voltage which is sufficient to keep the threshold switch 34 operated and thereby to interrupt by means of relay 35 the current supply of relay 19. In consequence the contacts 20 are also opened, so that starter relay and the holding winding 21 of the starter gear magnet 22 cannot be activated.

FIG. 2 shows a block diagram of the electronic portion of the interlock circuit of FIG. 1. This electronic portion includes an input stage 33, which contains the OR-gate 33. The threshold switch 34 is connected with the input stage 33' and is also connected with a cut-off signal stage 39 that contains a timed inhibiting circuit. An electrical connection is provided from the cut-off signal stage 39 to the control and switching elements 40 to which the starter relay is connected. Also connected to the starter relay 15 is a cut-off transient detector, which recognizes the end of a false start of the engine.

' This cut-off transient detector 41 is connected back to the cut-off stage 39. The manner of operation of the circuit will be described with referenceto the diagram shown in greater detail in FIG. 3.

As shown in FIG. 3, the OR-gate 33 is constituted by the two diodes 42 and 43, in series with which

input resistors

44 and 45 are respectively connected. On its input side resistor 44 is connected with the armature ll of the starter motor 10 and resistor 45 is connected to the output of the generator 38. The cathodes of diodes 42 and 43 are connected together and their common connection is further connected through a resistor 46 to the base of a transistor 47, which is one of two transistors arranged in a differential amplifier circuit. The collector of transistor'47 is connected over a load resistor 48 with the positive voltage bus 49, while its emitter is connected in common with the emitter of a second transistor 50 to a resistor 51 the other end of which is connected to the negative voltage bus 52. The collector of transistor 50 is likewise connected over a load resistor 53 to the positive voltage bus 49. A feedback resistor 54 is connected between the collector of transistor 50 and the base of transistor 47, thus causing the differential amplifier to operate in the manner of a threshold switch. The output connection of the OR-gate 33, that is to say the cathodes of the diodes 42 and 43, is also connected to a capacitor 55 and to a resistor 56 the other terminals of which are both connected with the negative voltage bus. The base of a first transistor 58 is connected to the output of the threshold switch, that is, to the collector of transistor 47, over a base series resistor 57. The emitter of transistor 58 is connected over a resistor 59 with the positive voltage bus 49, while the collector of the same transistor is connected over a resistor 60 with the negative voltage bus 52. In addition, the anode of a diode 61 is connected to the collector of transistor 58, while the cathode of the diode 61 is connected to a capacitor 62 the other terminal of which is connected to the negative voltage bus 52. The cathode of diode 61 is also connected to the base series resistor 63 of a second transistor 64. The emitter of this second transistor 64 is directly connected to the nega tive voltage bus 52, while the collector of that transistor is connected not only over a resistor 65 with the positive voltage bus 49 but also over base series resistor 66 to the base of a third transistor 67, the emitter of which is directly connected to the positive voltage bus 49 and the collector of which has a connection over a diode 68 with the control winding 35 of a relay 36. The same terminal of the control winding 35 of relay 36 is also connected over another diode 69 directly to the output of generator 38. The other end of the control winding 35 of relay 36 is connected to the negative voltage bus 52 and at this point a Zener diode 70 is connected between the negative voltage bus 52 and the positive voltage bus 49 to regulate the voltage difference.

The contacts 37 of relay 36 lie, as already shown in FIG. I, in the current supply circuit of relay 19, so that it is not necessary in FIG. 3 to show the connection of contacts 37 to the starter switch 18 not shown in this figure. In parallel to the control winding of relay 19 a diode 71 is connected, which has the function of suppressing voltage peaks occurring when the relay operates or releases. The contacts 20 of relay 19 are connected on one side to the positive voltage bus 49 and on the other side to a conductor leading to the starter relay 15. The starter relay 15 at this same connection is also connected over a resistor 72 to the cathode of a diode 73, the anode of which is connected to the emitter of a transistor 74. The base of transistor 74 is directly connected to the negative voltage bus 52, while the collector of that transistor is connected over a resistor 75 to the cathode of one of two series connected

diodes

76 and 77. The anode of diode 77 is connected to the emitter of a transistor 78 the collector of which is connected back to the junction of the collector of transistor 47 and the base series resistance 57. The base of transistor 78 is connected to a timing circuit consisting of a capacitor 79 and a resistor 80, with the other terminals of that capacitor and that resistor being connected to the negative voltage bus 52. The base of transistor 78 is also connected to the cathode of a diode 81, the anode of which is connected over a resistor 82 with the starter relay 15.

In parallel to the control winding 35 of relay 36 is connected a diode 83 and a capacitor 84.

The manner of operation of the circuit just described is as follows. In quiescent condition, that is, when neither the starter motor nor the generator 38 is running, the transistor 50 of the threshold switch 34 is in its conducting condition and its mate transistor 47 is non-conducting. If now the starter switch 18 is actuated (assuming ignition switch 17 has been closed) the starter motor 10 begins to turn todrive the engine by means of pinion 27 and ring gear 28. The armature voltage of armature ll of starter motor 10 then rises with increasing rate of rotation and finally when a speed is reached sufficient for self-sustaining operation of the engine, an armature voltage is produced sufficient to switch transistor 47 into its conducting condition. Transistor 50 is thereby turned off. While transistor 47 conducts, the potential at its collector is sufficiently negative to switch transistor 58 into its conducting condition. When transistor 58 conducts, a positive signal is provided over diode 61 and resistor 63 to the base of transistor 64 and switches the latter to its conducting condition. When transistor 64 conducts, a negative signal will be produced on the base of transistor 67, which will also be put into conducting condition, since it is of the type complementary to the transistor 64, where upon approximately the entire supply voltage will be applied to. the control winding 35 of relay 36. I

Energization of relay 36 opens its contacts 37, thus interrupting the current supply for relay 19, which causes the circuit element of that relay to open the contacts 20 by taking the position shown in the drawing, which. is to say that the current supply for the starter relay is interrupted, which in turn deenergizes the starter motor 10 and withdraws the pinion 27 of the starter from the ring gear 28 of the engine, so that the starter motor coasts to a stop.

In order to prevent a reactivation of the starter motor 10 after it has come to a stop and while the engine is still running, a signal provided by the generator 38 is connected over a resistor 45 and the diode 43 to the base of transistor 47. This signal keeps transistor 47 in its conducting condition, so that relay 36 remains activated and the current supply for relay 19 remains interrupted.

.To protect the electronic components and to increase the safety and reliability of the circuit a further connection between the generator 38 over diode 69 to the control winding 35 of relay 36 is provided, so that so long as the generator 38 is operating it is assured over the relatively direct path through diode 69 that the starter motor 10 cannot be activated. In order to prevent reaction of the signal from generator 38 which is provided over diode 69 to the winding 35 of relay 36 from affecting the rest of the circuit, the diode 68 is interposed between the collector of transistor 67 and the connection between diode 69 and the control winding 35 of relay 36.

In order to prevent engagement of the pinion 27 with the ring gear 28 while the starting motor 18 is still running after an unsuccessful attempt to start the engine, the capacitor 62 is provided and so connected that it will be charged by conduction through transistor 58 andhold transistor 64 in its non-conducting condition after the disappearance of an input signal at the

resistors

44 and 45. In consequence the control winding 35 of relay 36 continues to be energized and contacts 37 will be held open as the result of the discharge currentv of capacitor 36 for a definite time determined by the magnitude of capacitor 62, since as already explained capacitor 62 provides a positive signal to the base of transistor 64 so that transistor 64 and transistor 67 both remain in their conducting condition, so that for the period determined by capacitor 62 a voltage somewhat approaching the full supply voltage is applied to the control winding 35 of relay 36. Thus, as already described, the current supply'circuit of the winding of relay 19 is held open at the contacts 37 the current supply of starter relay 15 is blocked at the contacts 20.

A further precaution against untimely activation of starter relay 15 is provided by utilizing the negative voltage peaks produced by starter relay 15 when its current supply is cut off. When the current supply of starter relay 15 is interrupted by the opening of contacts 20 of relay 19, a negative voltage peak is produced which proceeds over resistance 72 and diode 73 to the emitter of transistor 74. Since the base of transistor 74 is permanently connected with the negative voltage bus 52, transistor 74 is switched into its conducting condition by the negative voltage pulse on its emitter and then provides a signal over resistor 75 and

diodes

76 and 77 to the emitter of transistor 78, where this sig-' nal then also appears at the base, of transistor 78 if a positive signal is present at that point. A' positive signal is indeed present at the base of transistor 78 when relay 19 was energized a sufficiently long time beforehand to have closed contacts 28, so that through the conditions described the charging of capacitor 79 can take place over resistor 82 and diode 81. By a suitable choice of the size of capacitor 79 the result can be otained that voltage peaks produced by bouncing of the switching contacts 28 are insufficient to charge capacitor 79 to such an extent that a positive signal will be applied to the base of transistor 78 that is of sufficient magnitude to switch transistor 78 into its conducting condition. If therefore capacitor 79 is charged enough so that after interruption of the current supply circuit of relay 15 by contacts 20 the voltage on capacitor 79 is sufficient to put transistor 78 into its conducting condition, then a signal initiated by a negative transient pulse of the starter relay will reach the base of transistor 58 and hold it in its conducting condition. In consequence, the operation of

transistor

64 and 67 will assure that substantially the full supply voltage will be applied to the control winding 35 of relay 36 and that, in addition, the conduction of transistor 58 will allow capacitor 62 to charge. After the pulse at the starter relay 15 drops off, the reoperation of starter relay will then also be prevented by the condition of capacitor 62 for a definite period of time, as previously described.

As a further stabilizing and protective measure against disturbing voltages, the Zener diode 70 and a resistor 85-are provided for voltage stabilization of the supply voltage for the entire circuit. In addition, the provision of diode 83 and

capacitors

55 and 84 suppress the effects of disturbing voltages present in the current supply network of the motor vehicle.

It is not necessary for the purpose of the invention to use mechanical switching operated by electro-magnetic relay means as shown at 14, l5, l9 and 36, for example, and it is feasible to use semi-conductor type control switches in their place.

Referring again to FIG. 2, the block 39 which was referred to as a cut-off signal stage including a timed inhibiting circuit may also be referred to as an interconnecting circuit including delay means for prolonging the blocking signal provided by the threshold switch means designated by the block 34'of FIG. 2. Likewise, the block '40, which was referred to as designating switching elements may be referred to as a circuit breaker means breaking the operating circuit of the relay coil 15 and the block 41, previously designated as the cut-off transient detector may be referred to as part of the delay means for prolonging the block or cut-off signal (it refers to the

circuit including the'transistors

74 and 78 and the capacitor 79).

I claim:

1. An interlock system for cutting off or blocking the operation of the starter motor of a combustion engine, comprising:

a battery;

a generator (38) for charging said battery coupled to said engine so as to be driven thereby;

an engine ignition switch connected to one pole of said battery;

a starter motor having an armature windingand at least one stator winding;

a manual starter switch connectable to said battery through said engine ignition switch and connected in circuit with said starter motor;

an electrically controlled starter switch means (l4,

15) in circuit with said starter motor and said starter switch, and

means for blocking operation of said electrically controlled starter switch means in response to voltage generated in a winding of said starter motor (10) by the revolution of said armature of said starter motor (10) when said starter motor is running and to the voltage generated by the revolution of the rotor of said generator (38) when said starter motor is quiescent, said blocking means including OR-gate means having one input responsive to said voltage generated by revolution of said armature of said starter motor while said starter motor is energized, threshold switch means responsive to said OR-gate means, circuit breaker means for breaking the operating circuit of said electrically controlled starter switch means and circuit means interconnecting said threshold switch means and said circuit breaker means and having delay means for prolonging operation of said circuit breaker means for a predetermined interval after return of said threshold switch means to its quiescent condition.

2. An interlock system as defined in claim 1 in which the armature (11) of said starter motor (10) is connected for energization only in sseries with a stator winding of said motor and in which one input of said OR-gate means is responsive to the armature voltage of said starter motor (10).

3. An interlock system as defined in claim 1 in which said one input of said OR-gate means is responsive to a change of voltage in a stator winding of said starter motor (10) which is'caused by the revolution of said armature of said starter motor.

4. An interlock system as defined in claim 1 in which said threshold switch means (34) comprises a differential amplifier to one input of which a portion of the output voltage of said battery is provided as a reference voltage and to the other input to which the output of said OR-gate means is provided.

5. An interlock system as defined in claim 4 in which when the threshold voltage of said threshold switch (34) is reached, said circuit breaker means (35, 36, 37) is actuated in response to the output voltage of one of the transistors (47, 50) included in said differential amplifier and the actuation of said circuit breaker means interrupts the control circuit of a control switch (19, 20) in the current supply circuit of said electrically controlled starter switch means. I

6. An interlock system as defined in claim 5 in which said delay means includes a storage element (62) arranged to be charged after the operation of said threshold switch means (34) and thereby to hold said circuit breaker means (35, 36,37) operated and said control circuit open for a predetermined period after the return of said threshold switch means (34) to its unoperated condition.

7. An interlock system as defined in claim 6 in which said storage element (62) is also arranged to be charged in response to a signal produced by the opening of said control switch (19, 20) in the current supply circuit of said electrically controlled starter switch means (l4, 15) so that said storage device (62) may hold said circuit breaker means (35, 36, 37) operated for a predetermined period and thereby block for said period the control circuit of said control switch (19, 20) provided in said current supply circuit of said electrically controlled starter switch means (14, 15).

8. An interlock system as defined in claim 1 in which said interconnecting circuit means includes:

a first transistor (58) arranged to be responsive to the operation of said differential amplifier having output electrode connected to a capacitor (62) included in said delay means;

a second transistor (64) having its control electrode connected to said capacitor (62);

a third transistor (67) adapted to be activated by said second transistor and adapted to activate the operating circuit (35) of said circuit breaker means (35,36, 37).

9. An interlock system as defined in claim 8 in which said first transistor (58) has a control electrode connected by circuit means to the control circuit of said electrically controlled starting switch means and responsive to reverse voltage peaks thereof.

10. An interlock system as defined in claim 9 in which said control electrode of said first transistor (58) is connected over the switching path of a fourth transistor (78), over diodes (76, 77, 73) and resistors (75, 72)

and over the switching path of a fifth transistor (74) to the said control circuit of said electrically controlled starting switch means (l4, 15).

11. A interlock system as defined in claim in which said fourth transistor (78) has a base electrode connectedwith'a capacitor (79) which is connected to the voltage of said battery when said control circuit of said electrically controlled starting switch means (l4, is energized, whereby as said capacitor approaches its charged condition a switching of said fourth transistor into its conducting condition is produced.

12. An interlock system as defined in claim 1 in which a direct electrical connection is provided through a diode between the output of said generator (38) and the operating circuit (35) of said circuit breaker means (35, 36, 37).

13. An interlock system as defined in claim 1 in which a starter gear magnet for engaging said starter motor with said engine is provided with an activating winding and a holding winding and in which said holding winding is energized in parallel with the control circuit of said electrically controlled starter switch means and said activating winding is activated through a switching path of said electrically controlled starter switch means.

14. An interlock system as defined in claim 13 in which said electrically controlled starter switch means and said starter gear magnet are mechanically interlocked to provide a second operated position of said electrically controlled starter switch means after said starter gear magnet is activated such that with cooperation of contacts operated by said starter gear magnet, said starter motor is supplied reduced power in the first position of said electrically controlled switch means and full power in said second position and such that said activating winding is deenergized when said switch means is in its second position.

15. An interlock system as defined in claim 1, in which said starter motor has a stator winding arranged to be energized in series with its armature when full power is applied to said starter motor, the armature having a winding one end of which is connected in series with said stator winding as aforesaid and the other end of which is grounded to the motor structure, and in which system the connection of said armature winding to said stator winding is also connected to one input of said OR-gate means to provide thereto a voltage induced in said armature winding as the result of the revolution of said armature (11).

Claims

1. An interlock system for cutting off or blocking the operation of the starter motor of a combustion engine, comprising: a battery; a generator (38) for charging said battery coupled to said engine so as to be driven thereby; an engine ignition switch connected to one pole of said battery; a starter motor having an armature winding and at least one stator winding; a manual starter switch connectable to said battery through said engine ignition switch and connected in circuit with said starter motor; an electrically controlled starter switch means (14, 15) in circuit with said starter motor and said starter switch, and means for blocking operation of said electrically controlled starter switch means in response to voltage generated in a winding of said starter motor (10) by the revolution of said armature of said starter motor (10) when said starter motor is running and to the voltage generated by the revolution of the rotor of said generator (38) when said starter motor is quiescent, said blocking means including OR-gate means having one input responsive to said voltage generated by revolution of said armature of said starter motor while said starter motor is energized, threshold switch means responsive to said OR-gate means, circuit breaker means for breaking the operating circuit of said electrically controlled starter switch means and circuit means interconnecting said threshold switch means and said circuit breaker means and having delay means for prolonging operation of said circuit breaker means for a predetermined interval after return of said threshold switch means to its quiescent condition.

3. An interlock system as defined in claim 1 in which said one input of said OR-gate means is responsive to a change of voltage in a stator winding of said starter motor (10) which is caused by the revolution of said armature of said starter motor.

5. An interlock system as defined in claim 4 in which when the threshold voltage of said threshold switch (34) is reached, said circuit breaker means (35, 36, 37) is actuated in response to the output voltage of one of the transistors (47, 50) included in said differential amplifier and the actuation of said circuit breaker means interrupts the control circuit of a control switch (19, 20) in the current supply circuit of said electrically controlled starter switch means.

6. An interlock system as defined in claim 5 in which said delay means includes a storage element (62) arranged to be charged after the operation of said threshold switch means (34) and thereby to hold said circuit breaker means (35, 36, 37) operated and said control circuit open for a predetermined period after the return of said threshold switch means (34) to its unoperated condition.

7. An interlock system as defined in claim 6 in which said storage element (62) is also arranged to be charged in response to a signal produced by the opening of said control switch (19, 20) in the current supply circuit of said electrically controlled starter switch means (14, 15) so that said storage device (62) may hold said circuit breaker means (35, 36, 37) operated for a predetermined period and thereby block for said period the control circuit of said control switch (19, 20) provided in said current supply circuit of said electrically controlled starter switch means (14, 15).

8. An interlock system as defined in claim 1 in which said interconnecting circuit means includes: a first transistor (58) arranged to be responsive to the operation of said differential amplifier having output electrode connected to a capacitor (62) included in said delay means; a second transistor (64) having its control electrode connected to said capacitor (62); a third transistor (67) adapted to be activated by said second transistor and adapted to activate the operating circuit (35) of said circuit breaker means (35,36, 37).

10. An interlock system as defined in claim 9 in which said control electrode of said first transistor (58) is connected over the switching path of a fourth transistor (78), over diodes (76, 77, 73) and resistors (75, 72) and over the switching path of a fifth transistor (74) to the said control circuit of said electrically controlled starting switch means (14, 15).

11. A interlock system as defined in claim 10 in which said fourth transistor (78) has a base electrode connected with a capacitor (79) which is connected to the voltage of said battery when said control circuit of said electrically controlled starting switch means (14, 15) is energized, whereby as said capacitor approaches its charged condition a switching of said fourth transistor into its conducting condition is produced.