US3662720A

US3662720A - Fuel injection arrangement for iternal combustion engines

Info

Publication number: US3662720A
Application number: US55084A
Authority: US
Inventors: Karl-Ernst Boeters; Klaus Streit; Gerhard Conzelmann; Hermann Schmid; Hans-Joachim Fleischer
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1969-07-22
Filing date: 1970-07-15
Publication date: 1972-05-16
Anticipated expiration: 1989-05-16
Also published as: CH506709A; GB1319078A; FR2031006A5; DE1937111A1

Abstract

An AND circuit, controlled by an engine-rpm-dependent bistable multivibrator, triggers a monostable circuit that produces a pulse having a length dependent on the intake-manifold-suction pressure. This pulse partly controls a logic circuit also controlled by the output of the multivibrator. The logic circuit, in turn, controls an amplifier the output of which operates the fuel injection spray valves.

Description

United States Patent Boeters et al.

[ May 16, 1972 [54] FUEL INJECTION ARRANGEMENT FOR ITERNAL COMBUSTION ENGINES [72] inventors: Karl-Ernst Boeters, Berlin; Klaus Streit,

Tubingen; Gerhard Conzelmann, Leinfelden; Hermann Schmid, Goppingen; Hans- Joachim Fleischer, Berlin, all of Germany [73] Assignee: Robert Bosch GmbH, Stuttgart, Germany [22] Filed: July 15, 1970 [2]] Appl. No.: 55,084

[30] Foreign Application Priority Data July 22, I969 Germany ..P 19 37 111.0

[52] U.S.Cl. ..123/32 EA, 123/119, 123/179A [51] Int. Cl ..F02m 51/00 [58] Field ofSearch .l ..l23/32 AE, 32 EA, ll9

[56] References Cited UNITED STATES PATENTS 3,430,616 3/1969 Glockler et al. ..123/32 EA Primary Examiner-Laurence M. Goodridge Attorney-Michael S. Striker [57] ABSTRACT An AND circuit, controlled by an engine-rpm-dependent bistable multivibrator, triggers a monostable circuit that produces a-pulse having a length dependent on the intakemanifold-suction pressure. This pulse partly controls a logic circuit also controlled by the output of the multivibrator. The logic circuit, in turn, controls an amplifier the output of which operates the fuel injection spray valves.

21 Claims, 2 Drawing Figures PATENTEDm 16 I972 SHEET 2 OF 2 f/Ie/r .Jrronvn FUEL INJECTION ARRANGEMENT FOR ITERNAL COMBUSTION ENGINES BACKGROUND OF THE INVENTION The invention relates to a fuel injection arrangement for internal combustion engines.

Among the arrangements of the prior art are those having a monostable circuit that produces pulses of which the duration is dependent on an operating parameter of the engine, so that the operating time of the injection control means, such asthe fuel injection spray valves, is dependent on the pulse length. Consequently, the amount of fuel injected is at least partly de pendent on this operating parameter, which is usually the suction pressure prevailing in the intake manifold.

Prior-art arrangements of thisvsort are made with discrete electrical components. With these fuel injection arrangements as few electrical components as possible must be used, in order to simplify manufacture and to reduce costs.

SUMMARY OF THE INVENTION An object of the invention is to produce a circuit arrangement that lends itself particularly well to manufacture as a monolithic circuit, and in which very few capacitors and coils are used. The number of resistors and semiconductor elements, on the other hand, does not play an appreciable role in the cost of the circuit of the invention, nor does it appreciably increase the difficulty of manufacturing the circuit.

The fuel injection arrangement of the invention consists essentially of fuel injection control means, such as injection spray valves, monostable circuit means for producing pulses of which the duration is dependent on an operating parameter of the engine for at least partly determining the operating time of the fuel injection control means and thereby the amount of fuel injected, bistable multivibrator means responsive to the engine rpm to generate pulses, and differentiating-stage logical-circuit means connecting the bistable multivibrator means to the monostable circuit means and responsive to the operation of the former to trigger the latter, whereby the amount of fuel supplied by the fuel injection control means to the engine varies in accordance with the operating condition of the engine.

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 drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 schematically shows the fuel injection arrangement; and

FIG. 2 is a circuit diagram of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 the fuel injection arrangement is intended for a four cylinder internal combustion engine 10, the spark plugs 11 of which are connected to a high voltage source, not shown. An electromagnetically operated fuel injection spray valve 13 is located in the immediate neighborhood of the engine intake valve (not shown), and issupported on each of the branches of an intake manifold 12. The four valves 13 are the fuel injectors proper. A distributor 15 provides fuel at constant pressure through a line 14 to each of these valves. A pump 16 sucks the fuel from a tank 17 and pumps it into the distributor. The pump 16 can be driven electrically or by the internal combustion engine.

An rpm dependent pulse transmitter 18 is connected to the internal combustion engine 10. Operatively connected to this pulse transmitter is a circuit 19, which triggers a bistable multivibrator 20 to one or the other of its two states. Connected to this bistable multivibrator is a differentiating stage logical, or

AND, circuit 21, which is connected to a monostable circuit 22. The operation of the monostable circuit 22 is influenced by a suction pressure detector 23, which is constructed as a transmitter that comprises a variable inductor. The length of the pulse generated by the monostable circuit 22 depends upon the negative pressure prevailing in the intake manifold 12. The output pulse of the monostable circuit 22 influences the time that the fuel injection spray valve 13 are open. In order that other operating parameters ,of the internal combustion engine can also determine the opening time of these valves, and therefore determine the amount of fuel sucked in, a correcting circuit 24 is connected after, the monostable circuit. In the correcting circuit the signals of various other operating parameters can be used to influence the opening time of the valve 13. A logic circuit 25 is connected after the monostable circuit 22 and the correcting circuit 24. The logic circuit, in dependence on the output signals of the bistable multivibrator 20 and the monostable circuit 22 and/or the correcting circuit 24, distributes the fuel injection pulse to a group of two valves 15.

FIG. 2 shows the monolithic integrated portion of the fuel injection arrangement. The bistable multivibrator 20 has a first transistor 26 and a second transistor 27. The emitters of the two transistors are connected together and are connected to a common negative line 28, which is connected to ground. A voltage divider, comprised of series connected

resistors

29, 30, and 31, connects the base of the first transistor 26 to a common positive line 32. A further voltage divider, comprised of

resistors

33, 34, and 35, connects the base of the second transistor 27 to the positive line 32. A capacitor 36 is connected between ground and the junction of the resistors 29 and 30. To this same junction is connected a resistor 37, which is connected to one terminal of a switch 38, the other terminal of which is also connected to ground. The switch 38 is operated by the rpm dependent circuit 19. A capacitor 39 is connected between ground and the junction between the resistors 33 and 34. A resistor 40 is connected to this junction and also to one terminal of a switch 41, the other terminal of which latter is connected to ground. This switch is also operated by the circuit 19. The collector of the first transistor 26 is connected to the common junction between the

resistors

34 and 35, and the collector of the second transistor 27 is connected to the common junction between the

resistors

30 and 31.

' The bistable multivibrator 20 operates in the following manner. If, for example, the switch 38 is closed, a negative signal is conducted through the resistors 37 and 29 to the base of the first transistor 26, and the latter, which has been conductive, is cut off. The second transistor 27 becomes conductive, and consequently the potential at the common junction between the

resistors

30 and 31 becomes much less positive. The result is that the potential at the junction between the resistors 29 and 30 also becomes much less positive. Any possible contact chatter of the switch 30 cannot interfere with the triggered state of the bistable circuit.

When the second switch 41 is closed the second transistor 27 is immediately shutofi; but the first transistor 26 remains conductive until the capacitor 36 charges through the

resistors

30 and 31 to that voltage-the threshold voltage-at which the first transistor 26 begins to conduct. Thus, when the switch 41 is closed both transistors 26 and 27 are temporarily shutoff until the capacitor 36 has sufficiently recharged. The same is true when the switch 38 is closed. In this instance the capacitor 39 charges through the

resistors

34 and 35, and when the threshold voltage of the second transistor 27 is reached the latter turns on. During the time that it takes until the threshold voltage of the second transistor 27 is reached, both transistors 26 and 27 are shut off. The resistors 37 and 40 form with the respective capacitors 36 and 39 low pass filters that suppress high frequency interference, which, for example, can be caused by the ignition system. Moreover, the resistors 37 and 40 limit the charging current of the capacitors 36 and 39 when the switches are closed; and they dampen oscillations, which can occur in the oscillatory circuit comprised by the capacitors 36 and 39 and the wiring inductance.

A differentiating-stage logical circuit is connected to the bistable multivibrator. This logical circuit, which is an AND circuit, comprises a transistor 42 having first, second, and third emitter diodes 43, 44, and 45. The collector of the transistor 42 is connected to its base, which is connector through a resistor 46 to the common positive line 32. The first emitter diode 43 is connected to the collector of the first transistor 26, and the second emitter diode 44 is connected to the collector of the second transistor 27. The third emitter diode 45 is connected to the base of a first switching transistor 47 and also to a base resistor 55, the other terminal of which latter is connected to ground. The transistor 47 comprises a switching path between its emitter and collector. The collector of the first switching transistor 47 is connected through a collector resistor 48 to the common positive line 32, and the emitter of the first switching transistor 47 is connected through an emitter resistor 49 to a common negative line 28 as well as through the base of a second switching transistor 50. The switching path of the first switching transistor 47 is connected in parallel with the switching path of a fifth switching transistor 51, the base of which latter is connected to a capacitor 52 which is also connected to ground. The base of transistor 51 is also connected through a resistor 53 to the collector of a fourth switching transistor 54. The emitter of this fourth switching transistor 54 is connected to the common negative line 28, and the collector of this transistor is connected through

selector resistors

56 and 57 to the common positive line 32. To the junction between the

resistors

56 and 57 is connected a collector the third switching transistor 58, the emitter of which is connected to the base of the fourth switching transistor 54 and the base of which is connected to the anode of a diode 59. The anode of the diode 59 is also connected through resistors 60 and 61 to the collector of the second switching transistor 50. The emitter of the second switching transistor 50 is connected to the common negative line 28, and the collector is connected to the base of a transistor 62, of which latter a collector is connected to the common positive line 32 and the emitter through a resistor 63 to the base of an output transistor 64. The emitter of this latter transistor is connected to the common negative line 28 and the collector is connected through

collector resistors

65 and 66 to the common positive line 33. The coupling capacitor 67 is connected to the junction between the

resistors

66 and 65. One terminal of the primary winding 68 of the suction pressure detector 23 is connected through the collector of the second switching transistor, and the other terminal is connected through a resistor 69 to the common positive line 32. The first terminal of the secondary winding 70 of the suction pressure detector is connected to the cathode of the diode 59, and the second terminal of the secondary is connected to the junction between two resistors 71 and 72 forming a voltage divider, and also to the junction between a resistor 75 and a diode 73. The series arrangement of the resistor 75, diode 73 and a further resistor 74 forms a voltage divider.

The operation of the AND circuit, which acts as a differentiating stage, and of the monostable circuit 22 will now be described. When both transistors 26 and 27 of the bistable multivibrator 20 are temporarily non-conductive, the emitter diodes 43 and 44 of the transistor 42 are shut off; and a positive signal is conducted through the resistor 46 and the emitter diode 45 through the base of the first switching transistor 47, thereby turning on the switching path of this latter transistor. As a result, there is conducted to the base of the second switching transistor 500 positive signal. This second switching transistor also becomes conductive, and a current begins to flow in the primary winding 68 of the suction pressure detector 23. Therefore, there is induced in the secondary winding 70 of the detector a negative voltage, which shuts off the switching transistors 58 and 54. These latter transistors are normally kept conductive by the resistor 60. The potential on the collector of the transistor 54 becomes more positive, and

therefore the fifth switching transistor 51 becomes conductive and keeps the second switching transistor 50 conductive, even after one of the transistors 26 and 27 has again been triggered to the conductive state. The voltage in the windings 68 and 70 of the suction pressure detector 23 dies away in accordance with an 2 function, the time constant of which is essentially determined by the inductance of the primary winding 68 and the value of the resistor 69. As a result of the voltage dying away, the voltage at the base of the third switching resistor 58 reaches the threshold value, which value is determined by the emitter diode of the transistors 54 and 58. The switching transistors 54 and 58 are consequently once again made conductive, and the transistor 51 and the second switching transistor 50 are again shut off.

To protect the second switching transistor 50 there is provided a bypass diode, which is formed by the base collector diode of the transistor 62.

Since the threshold voltage at the base of the third switching transistor 58 determines the period during which the monostable circuit 22 remains switched, this threshold voltage is temperature compensated by the diodes 59 and 73 and by the resistors 72 and 74.

when the second switching transistor 50 is conductive and the transistors 62 and 64 are non-conductive a positive output pulse generated by the monostable circuit 22 is conducted by the capacitor 67 to the input of the correcting circuit 24. This correcting circuit, or stage, 24 receives signals of other operating parameters of the engine 10, which parameters also influence the injection period of the valve 13. A low pass filter, comprised of the

resistors

57, 56, and 53 and the capacitor 52, is provided to suppress short negative interference pulses that can be conducted through the base of the third switching transistor 58 and that can temporarily trigger the monostable circuit 22. The values of the capacitors 36 and 39 are so determined relative to the capacitor 52 that the delay time for triggering the monostable circuit is always shorter than the length of the differentiated pulse, which latter is as long as the period of time that both transistors 26 and 27 are simultaneously nonconductive.

Positive interference pulses, which can prematurely trigger the monostable circuit 22 back to its original state when the threshold voltage at the base of the third switching transistor 58 has not yet been reached, are suppressed by means of the resistor 53 and the capacitor 52. The output pulse of the monostable circuit, appearing on the output electrode of the second switching transistor 50, is conducted by a circuit 105 to a resistor 76 connected to resistors 77 and 78. Signals of still further engine operating parameters can be conducted to these latter two resistors.

A logical circuit 25 and an amplifier are provided for receiving these signals and for controlling the injection valves 13. The logical circuit comprises two transistors 79 and 80 of which a switching path are connected in series, the emitter of a transistor 79 being connected to the negative line 28 and the collector of transistor 80 being connected through resistors 81 and 82 to the positive line 32. To the common conjunction between the resistors 81 and 82 is connected the base of an amplifier transistor 83, the emitter of which is connected to the positive line 82 and the collector of which is connected to the base of a further amplifier transistor 84. The collector of this latter transistor is connected to the positive line 32, and the emitter is connected to two series connected resistors 85 and 86. One terminal of the resistor 86 is connected to the minus line 28. An output transistor 87 is connected through a resistor 106 to the emitter of the amplifier transistor 84. The output electrode of this output transistor is connected to two fuel injection spray valves 13. There is also provided another output transistor 88, of which the base is connected to the junction between the resistors 85 and 86. The emitter of this output transistor 88 is connected to the minus line 28 and the collector is connector through a resistor 89 to the minus line. To the collector of the transistor 88 is connected the resistor 90, which is connected to the lead of a test clip 91.

Similarly constructed logic stage and amplifier stage are provided for the other two valves 13 of the four cylinder internal combustion engine 10. The switching paths of two transistors 92 and 93 are connected in series. The emitter of transistor 92 is connected to the minus line 28, and the collector of this transistor is connected through two

resistors

94 and 95 with the positive line 32. To the junction between the

resistors

94 and 95 is connected the base of an amplifier transistor 96, of which the emitter is connected through the positive line 32 and the collector to the base of a second amplifier transistor 97. A resistor 107 connects a power transistor 98 to the emitter of the second amplifier transistor 97. The output electrode of the output transistor 93 is connected to the other two valves 13 of the four cylinder engine. Two series connected resistors 99 and 100 are connected to the emitter of the second amplifier transistor, one terminal of the resistor 100 being connected to the negative line 28. To the junction between the resistors 99 and 100 is connected the base of an output transistor 101, of which the emitter is connected to the negative line 28 and the collector is connected to the resistor 90. The other terminal of the resistor 90 is connected to the test clip 91. The respective bases of the transistors 79 and 92 are connected to the common junction of the resistors 76, 77, and 78; and the bases of the transistors 80, and 93 are connected through an inverting stage, comprised of the transistors 102 and 103, with the respective output of the bistable multivibrator 20.

The logic stage 25 and the amplifier stage operate in the following manner. Depending on the state of the bistable multivibrator 20, one of the transistors 102 and 103 renders conductive one of the transistors 80 and 93. One of the transistors 79 and 92 conducts for a determined time in dependence on the voltage at the junction of the resistor, 76, 77, and 78; and, consequently, one of the transistors 83 and 96 also conducts and one of the power transistors 87 and 98 is turned on through the corresponding second amplifier transistor 84 or 97. Each power transistor 87 and 98 is connected to the operating winding of a pair of valves 13. When a power transistor is turned on the corresponding pair of valves is opened. In order to permit measurement of the valve opening time when adjusting the fuel injection arrangement, there are provided the output transistors 88 and 101, the outputs of which are connected through a resistor 90 to the test clip 91. The resistor 90 prevents shortcircuiting.

To protect against wrong polarity a current limiting device, such as a diode 104, is provided in at least one line 28 or 32 connected to the operating voltage source.

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

While the invention has been illustrated and described as embodied in a fuel injection arrangement, 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.

We claim:

1. In a fuel injection arrangement for an internal combustion engine, in combination, fuel injection control means; monostable circuit means with output connected to said injection control means and producing pulses of which the duration is dependent on an operating parameter of the engine for at least partly determining the operating time of said fuel injection control means and thereby the amount of fuel injected; bistable multivibrator means coupled to said engine and responsive to the engine rpm to generate pulses having a repetition frequency dependent on the speed of said engine; and pulse differentiating means connecting the output of said bistable multivibrator means to the input of said monostable circuit means and being responsive to the operation of the former to trigger the latter, said pulse differentiating means differentiating the output pulses of said bistable multivibrator means and forming thereby a trigger pulse for triggering said monostable circuit means, whereby the amount of fuel supplied by said fuel injection control means to the engine by the pulse duration of said monostable circuit means varies in accordance with the operating condition of the engine, said bistable multivibrator means comprising first and second transistors connected to be triggered between conductive and non-conductive states, respective switch means connected to each of said first and second transistors for triggering said respective transistor between its two states, and respective capacitor means connected to each of said switch means for delaying the triggering of the respective transistor when the respective said switch means are operated, said bistable multivibrator means having two outputs and said pulse differentiating means comprising an AND circuit connected to said two outputs to trigger said monostable circuit means when both of said first and second transistors are in the same conductive state.

2. In a fuel injection arrangement for an internal combustion engine, in combination, fuel injection control means; monostable circuit means with output connected to said fuel injection control means and producing pulses of which the duration is dependent on an operating parameter of the engine for at least partly determining the operating time of said fuel injection control means and thereby the amount of fuel injected; bistable multivibrator means coupled to said engine and responsive to the engine rpm to generate pulses having a repetition frequency dependent on the speed of said engine; and pulse differentiating means connecting the output of said bistable multivibrator means to the input of said monostable circuit means and being responsive to the operation of the former to trigger the latter, said pulse differentiating means differentiating the output pulses of said bistable multivibrator means and forming thereby a trigger pulse for triggering said monostable circuit means, whereby the amount of fuel supplied by said fuel injection control means to the engine by the pulse duration of said monostable circuit means varies in accordance with the operating condition of the engine, said bistable multivibrator means comprising first and second transistors connected to be triggered between conductive and non-conductive states, respective switch means connected to each of said first and second transistors for triggering said respective transistor between its two states, and respective capacitor means connected to each of said switch means for delaying the triggering of the respective transistor when the respective said switch means are operated, said bistable multivibrator means having two outputs and said pulse differentiating means comprising an AND circuit connected to said two outputs to trigger said monostable circuit means when both of said first and second transistors are in the same conductive state, said AND circuit being monolithic integrated circuit including a gating transistor with first, second and third emitter diodes.

3. A combination as defined in claim 1, including a respective voltage divider having first and second series connected resistance means connected to the base of each of said first and second transistors and defining a common junction; respective third resistance means connected between a respective said common junction and a respective one of said switch means; and wherein each of said capacitor means are connected to a respective said common junction.

4. A combination as defined in claim 2, wherein said first and second emitter diodes are turned off,v and said third emitter diode is turned on to conduct a positive going pulse,

when both of said first and second transistors are in the same conductive state; and said monostable circuit means comprise a first switching transistor, said switching transistor defining a first switch path that is turned on by said positive going pulse.

5. A combination as defined in claim 4, wherein said engine operating parameter is the intake manifold suction pressure, and including a second switching transistor having an output electrode and connected to said first switching transistor and turned on thereby when said first switching transistor conducts; and an intake-manifold-suction-pressure detector having a coil with a primary winding connected to said output electrode whereby there appears on said primary winding a voltage falling with an e function when said second transistor is turned on.

6. A combination as defined in claim 5, including a secondary winding for said coil; and wherein said monostable circuit means comprise third and fourth switching transistors connected to be triggered when said primary winding induces a voltage in said secondary winding.

7. A combination as defined in claim 6, including a temperature compensating diode connecting one end of said secondary winding to the base of said third switching transistor; and wherein the emitter of said third switching transistor is connected to the base of said first switching transistor, the collectors of said third and fourth switching transistors are connected together, and the emitter of said fourth switching transistor is connected to ground; and further including resistance means connecting the collector of said third switching transistor to positive.

8. A combination as defined in claim 7, including resistance means connected between the collectors of said third and fourth switching transistors.

9. A combination as defined in claim 8, wherein the voltage induced in said secondary winding turns off said third and fourth switching transistors.

10. A combination as defined in claim 9, wherein said fourth switching transistor comprises an output electrode; and including a fifth switching transistor having a control electrode, and a switching path that is in parallel with said first switching path, and wherein said fourth switching transistor output electrode is connected to said fifth switching transistor control electrode.

11. A combination as defined in claim 10, including resistance means connecting said fourth switching transistor output electrode to said fifth switching transistor control electrode.

12. A combination as defined in claim 11, wherein said monostable circuit means comprise an output; and including logical circuit means having an input connected to said monostable circuit means output, and an output; amplifier circuit means connected to said logical circuit means output; and wherein said fuel injection control means comprise at least one fuel injection spray valve operatively connected to said amplifier circuit means.

13. A combination as defined in claim 12, wherein said logical circuit means comprise at least two switching transistors defining each a switching path and having a respective control electrode; and wherein said monostable circuit means output is connected to the control electrode of each of said two switching transistors, whereby the operation of the latter said switching transistors is dependent at least on the suction pressure in the intake manifold.

14. A combination as defined in claim 13, wherein each of said first and second transistors has an output; and including a respective further switching transistor having each a control electrode and defining a switching path in series with each of said two switching transistors; and including a respective inverting stage connecting each of the control electrodes of said further switching transistors to a respective output of said first and second transistors.

15. A combination as defined in claim 14, wherein each of said further switching transistors has an output electrode; and

including a respective first amplifier transistor havin a control electrode and connected to each of the latter sar output electrodes.

16. A combination as defined in claim 15, including a plurality of said fuel injection spray valves; respective pairs of series connected resistors connecting different ones of said further switching transistor output electrodes to positive, and wherein the control electrode of each said first amplifier transistor is connected to the junction between the resistors of a respective said pair; and further including respective second amplifier transistors having each a control electrode connected to the collector of a respective said first amplifier transistor, and an output electrode connected to operate at least one of said fuel injection spray valves.

17. A combination as defined in claim 16, including a respective power transistor connecting to each said second amplifier transistor output electrode.

18. A combination as defined in claim 17, including for each said second amplifier transistor respective output transistor having an output electrode and a control electrode, said control electrode being connected to the control electrode of a respective said second amplifier transistor; and a test clip connected to the output electrodes of said output transistors.

19. A combination as defined in claim 18, including resistance means connected between said test clip and said output electrodes.

20. A combination as defined in claim 19, including current limiting means for limiting the circuit current flow in the event of wrong polarity.

21. A combination as defined in claim 20, wherein said circuit means are at least partly monolithic integrated circuits.

Claims

4. A combination as defined in claim 2, wherein said first and second emitter diodes are turned off, and said third emitter diode is turned on to conduct a positive going pulse, when both of said first and second transistors are in the same conductive state; and said monostable circuit means comprise a first switching transistor, said switching transistor defining a first switch path that is turned on by said positive going pulse.

15. A combination as defined in claim 14, wherein each of said further switching transistors has an output electrode; and including a respective first amplifier transistor having a control electrode and connected to each of the latter said output electrodes.