Control System For Blocking Fuel Injection In An Internal Combustion Engine

Abstract

Opening pulses for fuel injectors are furnished by a multivibrator. The pulses are applied to a resistance-capacitance network which furnishes a negative pulse having an amplitude which varies with the speed and the temperature of the engine. This signal is applied to the base of a switching transistor whose bias is controlled by the accelerator pedal. The collector of the switching transistor is connected to the base of an auxiliary transistor, whose collector is connected by means of a feedback resistance to the base of the switching resistor. The opening pulse is also applied to the base of the auxiliary transistor by means of a series resistance-capacitance circuit. Blocking of the auxiliary transistor causes transmission of the opening pulse to the injector. The auxiliary transistor blocks only upon simultaneous conduction of the multivibrator furnishing the opening pulse and the switching transistor. The circuit is arranged to block the transmission of the opening pulses in case of speeds exceeding the idling speed while the accelerometer pedal is not depressed.

Description

BACKGROUND OF THE INVENTION

This invention relates to a control system for activating electromagnetic injection means in an internal combustion engine. In this type of control system a monostable multivibrator may be used to determine the length of time that the injection means are open as a function of an operating parameter of the engine, as, for example, the pressure in the intake manifold. More particularly, it relates to a control system wherein it is desired to terminate the fuel injection if the accelerator valve is closed and if, in addition, the speed of the engine exceeds the highest permissible idling speed by a predetermined amount. The type of control system using a monostable multivibrator is very effective in practice since the amount of fuel delivered to the engine can be readily varied to conform to the particular operating conditions. However, it has been found desirable to shut off the fuel supply at the above-mentioned conditions, namely excessive speed in the presence of a closed accelerator valve. This prevents unburnt fuel from reaching the exhaust and thus prevents contamination of the atmosphere as well as preventing excessive fuel consumption. The type of condition under which the engine may be operating at excessive speeds with closed accelerator valve may for example occur when the vehicle goes downhill and the engine is used effectively as a brake.

In order to assure that the engine will continue to operate in the idling phase, the blocking of the injection mentioned above must be suspended when the speed of the engine is below a predetermined amount, which predetermined value is above the idling speed with a sufficient margin of safety. A known solution for this problem is taught in German Pat. No. 1,220,179. This comprises a bistable multivibrator and at least one network connected to the input of said bistable multivibrator. This network is connected alternately to each of two supply lines having different potentials by means of a switch. The network is an RC network with rectifiers. The output of the network varies with engine speed and is applied to the bistable multivibrator whose state determines whether or not the opening pulses furnished by another multivibrator are transmitted to a selected injector.

Further, injection systems are known in which two such networks are used, each tuned to a different limiting speed. Thus it can be accomplished that the injection process is stopped at a higher speed when the speed of the engine is increasing, and is restarted at a lower speed when the speed of the engine is decreasing.

SUMMARY OF THE INVENTION

The object of this invention is to furnish a control system which is substantially simpler than the above-discussed control system.

It is a further object of this invention to provide such a control system wherein both the upper speed at which the blocking of the fuel supply takes place and the lower limiting speed wherein said fuel injection is resumed depend also upon the operating temperature of the internal combustion engine.

This invention thus is a control system in an internal combustion engine having a crank shaft and at least one injection means adapted to inject fuel into the engine in response to an opening signal. The combustion engine further has means for furnishing said opening signals in synchronism with the rotation of the crank shaft. The control system for such an engine, and for preventing the activation of said injection means at predetermined speeds exceeding the idling speed in the presence of a substantially closed accelerator valve, comprises switching circuit means having a switching control element and adapted to have a first or second stable state in response to the total signal at said switching control element. It further comprises network means interconnecting said means for furnishing said operating signals and said switching control element. The network means are adapted to furnish an operating signal at said switching control element which varies at least in part with the speed of said internal combustion engine. Further applied to said switching control element is a biasing signal. This biasing signal changes from a first to a second biasing value when the accelerator valve closes. The invention also comprises auxiliary circuit means having an auxiliary control element and an auxiliary output circuit. The auxiliary circuit means are also adapted to assume either a first or a second stable state. Further comprised in the invention are first interconnecting means interconnecting said auxiliary output circuit and said switching control element, second interconnecting means interconnecting said auxiliary control element and the output of said switching circuit means; third interconnecting means interconnecting the means for furnishing the opening signals and the auxiliary control element; and fourth interconnecting means interconnecting the auxiliary output circuit and the injection means in such a manner that the opening signal is applied to said injection means when said auxiliary circuit means is in the first stable state, and that the opening signal is not applied to the injection means when the auxiliary output circuit is in the second stable state.

This arrangement, while requiring much less equipment than the previously known arrangements also permits the simple introduction of the operating temperature as a criterion for influencing the blocking of the fuel supply as stated above.

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 shows an injection system including the circuit diagram of an electric control system according to this invention;

FIG. 2 shows a variation of cutoff speeds and injection-resumption speeds as a function of temperature for the control system shown in FIG. 1;

FIG. 3 shows a second embodiment of the control system of this invention, using two speed responsive networks;

FIGS. 4a to 4c show a number of characteristic lines for the networks of FIG. 3, as a function of temperature.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment of this invention will now be discussed with reference to the FIGS.

The injection system shown in FIG. 1 is used in a four-cylinder internal combustion engine 1. The spark plugs 2 are connected to a high voltage ignition supply which is not shown. Coordinated with each individual cylinder of the internal combustion engine is an inlet valve which is not shown in FIG. 1. These inlet valves are each situated on a connecting pipe which connect the individual cylinder to the inlet pipe 3. Each of these connecting pipes is equipped with injection means, namely electromagnetically activated injection valves 4. Each of these injection valves is supplied with fuel from a fuel distributor 6 via fuel lines numbered 5 in FIG. 1. A pump 7, delivers the fuel to the fuel distributor and the fuel lines 5 under substantially constant pressure of approximately 2 atmospheres.

Each of the injection valves 4 comprises a magnetizing winding which is not shown. One terminal of each of the magnetizing windings is connected to ground, while the other terminal of each winding is connected via connecting lines 8 with one of the four resistors labeled 9 in FIG. 1. The resistors 9 are connected in pairs, each pair to one of the power transistors 10, 11. Each power transistor has an emitter, both of these emitters being connected to the cathode of a diode 12 whose anode is connected to the positive supply line. It is the function of the diode 12 to assure the blocking of the power transistors between consecutive injections.

The power transistor 10, together with a driving transistor 14, which is an NPN-type transistor and a transistor 16 which serves as an AND gate, form the first control channel, while power transistor 11, in conjunction with its driving transistor 15 and transistor 17, which also serves as an AND gate constitute the second control channel of the injection system. The channels are selected alternately by means of a common bistable multivibrator 20 which is framed in the dashed lines in FIG. 1. Each channel allows injection to take place at two of the four injection valves. This multivibrator comprises two NPN-type transistors, 21 and 22, each having an emitter directly connected to the negative supply line 19 and a collector connected to the positive supply line 13 by means of a load resistance. The load resistances are labeled 23 and 24 respectively. The collector of transistor 21 is also connected to a series circuit comprising resistors 251, 261 and diode 271 whose anode is connected to resistor 261, while its cathode is connected to the base of transistor 22. Similarly, the collector of transistor 22 is connected via a series feedback network of resistances 25, 26 and diode 27 to the base of transistor 21. The base of transistor 22 is also connected to the negative supply line by means of a resistance 281, while the base of transistor 21 is connected to the negative supply line by means of a resistance 28. One or the other of the control channels is selected by means of the switches 31 and 32. The switches are housed in the distributor for the high voltage ignition of the internal combustion engine. This distributor is not shown. Each switch has a fixed contact connected to the negative supply line 19 and a movable arm connected to the common point of resistors 25 and 26, and 251, 261, respectively. The base of AND gate transistor 16 is connected to the collector of transistor 21 by means of a resistance 34. AND gate 16 can only be blocked, thus causing its associated power transistor 10 and driving transistor 14 to become conductive, when transistor 21 is conductive. This condition exists when switch 32 is closed. After a further rotation of crankshaft 30 of the internal combustion engine the other switch is closed, causing transistor 21 to be blocked and, therefore, transistor 22 to become conductive. The base of AND gate 17 is connected to the collector of transistor 22 by means of a resistance 35. Thus transistor 17 becomes blocked. The group of injection valves which are coordinated with power transistor 10 can thus only be activated to cause an injection when transistor 21 has become conductive through the closing of the switch 32, while the second group of valves is chosen by means of switch 31.

Switches 31 and 32 not only serve the function of selecting the particular group of valves, they also signify the start of each consecutive injection process. The amount of fuel injected during each injection process is dependent upon the duration of the injection process. In order to coordinate the quantity of fuel to the particular operating conditions of the internal combustion engine, a monostable multivibrator 40 is provided. This monostable multivibrator has an input transistor 41 and an output transistor 42. The element which serves to determine the injection time is a transformer 44 which has a primary winding 43 connected in the collector circuit of transistor 42. The secondary winding 45 has a first terminal connected to the common point of a resistance 46 and 47 whose other terminals are respectively connected to the positive and negative supply lines 13 and 19. The base of input transistor 41 is connected to the negative supply line via a resistance and to the positive supply line by means of a diode 48 and a resistance 49 to the positive supply line. The diode is connected so that the transistor 41 is kept in a conductive condition in the interval between consecutive injection processes, by allowing the necessary base current to flow. The anode of diode 48 is connected to the anodes of three additional diodes 51, 50, and 52. The cathode of diode 50 is connected to the secondary winding 45 of transformer 44. The two other diodes, 51 and 52, conduct the pulses required to switch the multivibrator 40 to its unstable state, thus causing an opening pulse 53 to be generated at point C, the collector of transistor 42. The pulses which switch the multivibrator are supplied via two differentiating capacitors 54 and 55. One of these is connected to the collector of transistor 21, while the other is connected to the collector of transistor 22. The other terminals of the differentiating capacitors 54 and 55 are connected to the diodes 51 and 52, respectively. Each of these terminals is further connected to a separate voltage divider connected between the positive and negative supply lines.

As stated above, it is desired that the width of the opening pulse depends upon the various operating conditions of the internal combustion engine. Many such arrangements are known. That shown in FIG. 1 is an example only. The particular example shown in FIG. 1 shows an arrangement whereby the width of the opening pulse depends upon the pressure in the inlet means of the engine. Thus a pressure element 58 is connected behind the accelerator valve 57 in the direction of intake. A core 59 is mechanically linked to the membrane of this pressure element by means of a linkage indicated by a dash-dot line in FIG. 1. The arrangement is such that the core is pulled away from the winding as the inlet pressure in pipe 3 increases relative to the outside atmospheric pressure. Thus the less the inlet pressure, the shorter the opening pulses 53 which are furnished by the multivibrator 40. Multivibrator 40 constitutes a means for furnishing opening signals, or opening pulses.

The circuitry for supplying these opening pulses to the power transistors 10 or 11 will now be described. Auxiliary circuit means, here illustrated by a transistor 60 are connected to the output of monostable multivibrator 40 in such a way that the base of transistor 60 is connected to the collector of transistor 42; specifically, the base of transistor 60 is connected to the common point of a resistor 61 and 62 which form part of a voltage divider which also comprises a resistor 63 and is connected from the negative to the positive supply line. The collector of transistor 42 is directly connected to the common point of resistors 62 and 63. The collector of transistor 60 is connected to the positive supply line by means of resistor 65. The collector of transistor 60 is further connected to fourth connecting means which interconnect the auxiliary transistor 60 and the injection means in such a way that the opening pulse is transmitted to the injection means when the transistor 60 is in the first stable state and is blocked from the injection means when the transistor 60 is in the second stable state. The fourth connecting means comprise a transistor 67 which has a base connected to the collector of transistor 60 by means of a resistance 66. The transistor 67 is a preamplifier and is an NPN transistor. The collector of this transistor is connected to the base of AND gate transistor 17 by means of a resistance 68. It is further connected to AND transistor 16 by means of a resistance 69. When an opening pulse 53 is generated, auxiliary transistor 60 is blocked and the preamplifier transistor 67 becomes conductive. This causes the particular AND gate to become blocked whose associated transistor 21 or 22 becomes conductive. The injection process is ended as soon as the transistor 67 returns to its original blocked condition.

It is an object of this invention to conserve fuel and to cause as little unburnt fuel as possible to appear in the exhaust gases of the internal combustion engine. Thus if the internal combustion engine is driven at speeds greatly exceeding the idling speed when the accelerator valve is closed, whereby the engine serves as a brake during the compression stroke, it is desired to prevent the injection of fuel. This is accomplished by the combination of network means denoted by 71 in FIG. 1, and switching circuit means, comprising transistor 70 in FIG. 1. The network means specifically comprise a resistance 72 connected to the collector of transistor 42, and a capacitor 73 connected in series with said resistance 72. Further, a diode 74 is connected to the common point of resistor 72 and capacitor 73, as is a resistance 75 in parallel with said diode. Resistance 75 is a variable resistor. A capacitor 76 is connected in series with the parallel combination of diode 74 and resistance 75. The other terminal of capacitor 76 is connected to the negative supply line by means of a resistance 77. The other terminal of capacitor 73 is connected to the common point P of two resistors 78 and 79, whose other terminals are respectively connected to the positive and negative supply lines. Further connected to point P is the cathode of a diode 80 whose anode is connected to the base of switching transistor 70. The above-described network generates a voltage at point P during the opening pulse which serves as a criterion for the speed of the internal combustion engine.

During the operation of the circuit, which will be described in more detail below, the capacitors 73 and 76 are discharged as long as transistor 42 is in the conductive condition and generating an opening pulse 53. The discharge time is independent of the speed of the engine. Capacitor 73 and 76 are charged as long as transistor 42 is blocked. Charging of capacitor 73 takes place through resistance 72 and is a short time constant charging process. The resultant voltage on capacitor 73 is positive on the terminal connected to resistance 72, since point C is effectively at the positive potential when transistor 42 is blocked. In contrast, the charging of capacitor 76 is effected with a large time constant. Thus the voltage developed across this capacitor will depend upon the speed of the engine. The polarity is such that the terminal connected with resistance 77, and marked Q in FIG. 1, is negative. When diode 74 is conducting, as is the case during the opening pulse, the maximum negative voltage developed at point P depends upon the algebraic sum of the voltages across capacitances 73 and 76, and will be more negative the higher the speed.

As was explained above, it is desired to block the fuel transmission if the speed is excessively high when the accelerator valve is closed, or in idling position. Thus, the position of the accelerator valve is the second criterion required for the shutoff of the fuel supply. This criterion is supplied as follows. A switch S is mechanically coupled to the gas pedal 56. The movable arm of the switch S is connected to ground, while a fixed terminal 81 is connected to a terminal 82 which in turn is connected to the common point of resistors 83 and 84 which are in the base circuit of transistor 70. Resistor 83 has a second terminal connected to the positive supply line, while resistor 84 has a second terminal connected to the base of transistor 70 by means of a diode 85 whose cathode is connected to said base. The base of transistor 70 is further connected to the collector of transistor 60 by means of a feedback resistance 86 which is herein referred to as first interconnecting means. The collector of transistor 70 is connected to the base of transistor 60 by means of second interconnecting means, namely a resistance 87. The collector of transistor 70 is further connected to the positive supply line by means of a load resistance 88.

The following operating conditions result from the above-described circuitry, which includes the speed-responsive part of network 71:

1. When accelerator valve 57 is open, switch S is also open. Thus only one of the two above-named criteria for shutting off the fuel injection exists and the fuel injection should thus not be blocked.

1a. If the output transistor 42 of multivibrator 40 is blocked, and thus no opening pulse is being generated, the auxiliary transistor 60 is in the conductive condition. Switching transistor 70 is held in the conductive condition via resistances 83 and 84 and diode 85. It cannot be blocked through any negative pulse which might appear at point P.

1b. If transistor 42 becomes conductive and generates an opening pulse 53, transistor 70 remains conductive, since the negative pulse appearing at point P is not sufficient to block it. When transistors 42 and 70 are conductive simultaneously, the auxiliary transistor 60 is blocked and thus the opening pulse 53 can be transmitted to one of the power transistors 10 or 11. Thus an injection process takes place for the duration of the opening pulse 53 at the injection means selected by means of bistable multivibrator 20.

2. If however the accelerator valve 57 is in the idling position, and therefore the switch S is closed, the possibility exists that the fuel supply will be blocked if the speed of the engine increases excessively.

2a. In the interval between two opening pulses 63 output transistor 42 is in the blocked condition, transistor 60 is conductive, and transistor 70 is blocked since terminal 82 is now at ground potential. A negative pulse appearing at point P would thus be ineffective, since transistor 70 is already blocked.

2b. If, at very low speeds, the transistor 42 becomes conductive, thus generating an opening pulse 53, transistor 70 is initially blocked, as it is in the interval between two opening pulses, so that transistor 60 would normally remain conductive over resistances 87 and 88. However, the resistance 62 which is in the base circuit of transistor 60, is shunted by means of a series combination of a capacitor 90 and a resistance 91. The capacitor 90 may, for example, be approximately 1 .mu.f. The capacitor 90, resistance 91 and the line 64 furnish the third interconnecting means, interconnecting the base of transistor 60 to the output of transistor 42. In the intervals between opening pulses, the capacitor 90 is charged by the base current of transistor 60 to the voltage existing across resistance 62. The charge stored on the capacitor causes the transistor 60 to receive a blocking pulse at the beginning of an opening pulse. The transistor 60 is thus blocked causing switching transistor 70 to become conductive via the feedback resistance 86. Since the auxiliary transistor 60 remains blocked for the total duration of the opening pulse 53, an injection process takes place at the injection valve.

2c. If, however, the speed of the engine is very high, namely high enough so that the potential at point P, caused by the charge on capacitance 73, is very negative, then the transistor 70 can become conductive only during the discharge time of capacitance 90, which discharge time is in the order of 10 .mu.sec. Thus the transistor 70 will be blocked again immediately even during the duration of the opening pulse 53, thus causing the transistor 60 to resume its conductive condition. The injection valve cannot respond to an opening pulse which only exists for approximately 10 msec. and thus remain closed. The fuel supply is thus blocked until such time as, either, the accelerator valve is opened, or the speed is decreased to a lower value, which, however, still exceeds the idling speed as will further be described below. In particular, the speed at which the fuel resumption occurs is hereinafter denoted as n.sub.1. Beneath the speed n.sub.1, the opening pulses are transmitted to the injection means as described in paragraph (2b) above even if the accelerator valve is still closed.

As implied above, the speed at which the fuel supply is blocked, which will be denoted by n.sub.o, is not necessarily identical to the speed n.sub.1 at which the fuel supply is resumed. This will be discussed further below.

However, first, it should be noted that the values n.sub.1 and n.sub.o mentioned above are, for the system described above, independent of the operating temperature of the engine. However, it is desirable to increase the idling speed greatly during the winter in order to assure a trouble-free operation of the engine.

Thus it will be noted that in FIG. 1, one terminal of capacitance 73 is connected not only to the common point of resistors 78 and 79 which form a voltage divider arrangement, but also to a common point of negative temperature coefficient resistance 93 and a fixed resistance 94 which are also connected in a voltage divider arrangement between the positive and negative supply line. The common point of the voltage divider including the negative temperature coefficient resistance may be connected to the common point P of the voltage divider arrangement with resistances 78 and 79 by means of a resistance 95. The NTC resistance 93 is in a heat-conductive connection with the internal combustion engine 1 and increases in resistance the lower the operating temperature of the engine. As the operating temperature of the engine decreases, the potential at point P thus increases for lower temperatures. Capacitor 73 charges, in the interval between opening pulses 53, to a potential which corresponds to the difference between the potential at point P and the positive potential at positive supply line 13. Thus the charge on capacitor 73 is less at lower temperatures. Thus when transistor 42 becomes conductive at the beginning of the next opening pulse 53, a less negative pulse is generated at point P, which becomes ineffective at an earlier point in time. For the reasons set forth in paragraph (2c) above, the fuel cutoff speed n.sub.o is then correspondingly higher.

As described above, the charge on capacitance 76 depends upon the speed, and now the charge on capacitance 73 becomes temperature dependent. Since the cutoff of tube 70 is determined by the algebraic sum of the voltages on capacitances 76 and 73 as explained above, and the voltage on capacitor 73 becomes smaller with decreasing temperatures, obviously the cutoff point for transistor 70 will be reached for lower voltages on capacitance 76. This condition exists at higher speeds. Thus the NTC resistance 93 causes the fuel cutoff speed n.sub.o, as well as the fuel resumption speed n.sub.1 to assume higher values with decreasing operating temperatures.

In order to achieve sufficient stability and circuit conditions in the vicinity of the two speeds n.sub.o and n.sub.1, the circuit is arranged in such a manner that the cutoff speed n.sub.o is substantially higher than the resumption speed n.sub.1. For this purpose an interconnecting resistance 98, is connected between the point Q on the one hand and the collector of transistor 70 on the other hand. In this way, the potential at point Q is kept at substantially the value of the negative supply line 19 while the transistor 70 is conducting, but is at a substantially higher potential, fixed by the dividing ratio of resistances 88, 98 and 77 when transistor 70 is blocked. Thus if a sufficiently high negative pulse is generated at point P to block transistor 70, the capacitor 76 receives a charge during the opening pulse which is opposed to the charge it acquires in the interval between opening pulses. This charge thus tends to make terminal Q positive with respect to the other terminal of capacitor 76. This effectively increases the charging time of capacitance 76. In order that the transistor 70, may, as described under paragraph (2b) above, furnish the next opening pulse 53 to the transistors 10 and 11 when the accelerator valve is closed by blocking transistor 60 for the duration of this pulse, the negative pulses appearing at point P at the beginning of these opening pulses may not extend for a longer time period than the discharge time of capacitor 90. In this way the cutoff speed n.sub.o at which the injection process is blocked at increasing speeds, is substantially higher at a given operating temperature than the resumption speed n.sub.1 at which the fuel injection is resumed for decreasing speeds.

FIG. 2 shows the variation of the cutoff speeds n.sub.o and the resumption speeds n.sub.1 in dependence on the operating temperature. In particular, the solid lines correspond to the condition wherein resistances 78 and 79 are relatively high while resistances 93, 94 and 95 are comparatively low, so that NTC resistance 93 has a great influence. The dashed lines show that n.sub.o is maintained a constant amount above n.sub.1, if instead of the NTC resistance a fixed resistance is used, thus eliminating the temperature dependence.

For a second preferred embodiment of the present invention, two speed-responsive networks arranged in parallel with each other may be used as is shown in FIG. 3. The first network may be subject to a high temperature dependence, and is constructed similarly to the network 71 shown in FIG. 1. Its components are thus labeled with the same reference numbers as in FIG. 1. The second network 171 is similar but not identical. Its components have reference numbers which are increased by 100 relative to the corresponding components of the network 71. The second network 171 is not influenced by temperature, since it has no NTC resistance. Furthermore, its capacitor 173 is connected to the base of transistor 70 by means of a diode 180 and is further connected to resistance 196 whose other terminal, together with diode 174 and resistance 175, is connected to a second capacitor 176.

As shown in FIGS. 4a through 4c, the cutoff speeds n.sub.o2 of the second network as well as the resumption speeds n.sub.12 of the network are straight lines parallel to the temperature axis. Because of the intercoupling resistance 198 which connects the collector of transistor 70 to point Q', the cutoff speed n.sub.o2 exceeds the resumption speed n.sub.12 by approximately 400 r.p.m. In the particular example, the resumption speed n.sub.12 is assumed to be approximately 800 r.p.m. Because of NTC resistance 93 the first network is greatly influenced by the temperature. The cutoff speed n.sub.o1, as well as the resumption speed n.sub.11 are shown in dashed lines.

In general, it is desirable that the cutoff speed is not increased further by decreasing temperatures if the temperature is below a specified amount, for example -10.degree. C. However, even for these low temperatures, it is desirable to maintain a difference between the cutoff and the resumption speeds. For instance if networks 71 and 171 are connected in parallel, but mutually decoupled, to the base of transistor 70, the cutoff speed, for increasing engine speeds, is determined by the network which is tuned to the lower cutoff speed. For the case illustrated in FIG. 4a, the resulting cutoff speed n.sub.o shown in the solid curve follows the constant cutoff speed n.sub.o2 of the second network 171 for temperatures less than -10.degree. C., and corresponds to the cutoff speed n.sub.o1 of the first network at higher temperatures. Under the conditions shown in FIG. 4a, the networks are adjusted so that the temperature dependent values of the resumption speed n.sub.11 of the first network are always beneath the constant resumption speeds n.sub.12 of the second network 171. Thus n.sub.11 determines the resumption of the fuel injection process throughout.

The same is true when the networks are adjusted to yield the characteristic curves shown in FIG. 4b. The difference between FIGS. 4b and 4a results from the fact that a much more substantial difference exists between the speeds n.sub.11 and n.sub.o1 throughout the whole range. Since the cutoff frequency n.sub.o1 is at all temperatures higher than the temperature-independent cutoff speed n.sub.o2, the resulting cutoff speed n.sub.o will be constant regardless of temperature.

In FIG. 4c, the networks are adjusted so that the cutoff speed n.sub.o varies with temperature approximately as it did in FIG. 4 a. However, n.sub.11 is greater than n.sub.12 at very low temperatures, thus causing n.sub.12 to determine the fuel injection resumption speed n.sub.1 at low temperatures. At higher temperatures the resumption speed n.sub.11 of the first network becomes lower than the fixed resumption speed n.sub.12 of the second network and therefore controls the actual resumption of fuel injection in the engine.

While the invention has been illustrated and described as embodied in a control system using a particular type of speed-responsive network, it is not intended to be limited to the details shown, since various modifications and circuit and structural changes may be made without departing in any way from the spirit of the present invention.

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

Claims

I claim:

1. In an internal combustion engine having a crankshaft, at least one injection means adapted to inject fuel in response to an opening signal, and means for furnishing said opening signals in synchronism with the rotation of said crankshaft, a control system for preventing the activation of said injection means at predetermined excessive speeds in the presence of a substantially closed accelerator valve, comprising in combination, switching circuit means having a switching control element, said switching circuit means being adapted to be in a first or second stable state in dependence upon the total signal amplitude at said switching control element; network means interconnecting said means for furnishing opening signals and said switching control element, for furnishing an operating signal varying at least in part with the speed of said internal combustion engine at said switching control element; biasing signal furnishing means for changing the bias signal applied to said switching control element from a first to a second biasing value upon substantial closing of the accelerator valve of said internal combustion engine; auxiliary circuit means having an auxiliary control element and an auxiliary output circuit, said auxiliary output circuit being adapted to be in a first or second stable state in dependence upon the signal at said auxiliary control element; first interconnecting means interconnecting said auxiliary output circuit and said switching control element; second interconnecting means interconnecting said switching circuit means and said auxiliary control element; and third interconnecting means interconnecting said means for furnishing said opening signals and said auxiliary control element; and fourth interconnecting means interconnecting said auxiliary output circuit and said injection means in such a manner that said opening signal is applied to said injection means when said auxiliary output circuit is in said first stable state, and is locked from said injection means when said auxiliary output circuit is in said second stable state.

2. A control system as set forth in claim 1, wherein said first interconnecting means comprise a first resistance.

3. A control system as set forth in claim 2, wherein said second interconnecting means comprise a second resistance.

4. A control system as set forth in claim 3, wherein said means for furnishing opening signals comprise a multivibrator; and wherein said fourth interconnecting means comprise a resistance-capacitance network.

5. A control system as set forth in claim 4, wherein power to said control system is supplied by means of a first and second supply line; further comprising first voltage divider means connected between said first and second supply line and having a first and second voltage divider tap; wherein said auxiliary control element is connected to said first voltage divider tap; wherein said resistance-capacitance network is a series resistance-capacitance circuit connected from said first to said second voltage divider tap.

6. A control system as set forth in claim 5 wherein said switching control element is connected to said second supply line by means of a first and second bias resistor connected in series; and wherein said biasing signal furnishing means comprise a switch mechanically intercoupled with said accelerator valve in such a manner that said switch and said accelerator valve close substantially simultaneously, said switch having a first terminal connected to the common point of said bias resistors and a second terminal connected to a predetermined potential.

7. A control system as set forth in claim 6 wherein said predetermined potential is ground potential.

8. A control system as set forth in claim 7, further comprising a first diode interconnecting said series bias resistors and said switching control element.

9. A control system as set forth in claim 8 further comprising a second diode interconnecting said switching control element and said network means.

10. A control system as set forth in claim 9, wherein said switching circuit means and said auxiliary circuit means comprise a first and second transistor respectively.

11. A control system as set forth in claim 1 wherein said network means comprise temperature dependent circuit means in thermal contact with said internal combustion engine, and having an electrical characteristic which varies in dependence on the temperature of said internal combustion engine, whereby said operating signal varies both as a function of engine speed and engine temperature.

12. A control system as set forth in claim 11 wherein said output signal is furnished at an output point; wherein the power for said control system is supplied by a first and second supply line; and wherein said temperature dependent circuit means comprise second voltage divider means, said second voltage divider means comprising a negative temperature coefficient resistance in thermal contact with said internal combustion engine, connected in series to a fixed resistance; and means interconnecting said output point and the common point of said negative temperature coefficient resistance and said fixed resistance.

13. A control system as set forth in claim 1 wherein said network means comprise a first and second passive network; and wherein at least one of said passive networks further comprises a temperature dependent element, thereby causing said operating signal to vary both in dependence upon engine speed and engine temperature.

14. A control system as set forth in claim 1 wherein said opening signal is an opening pulse; wherein said means for furnishing said opening signal comprise means for furnishing said opening pulses at an opening pulse furnishing terminal; wherein power for said control circuit is supplied by a first and second supply line; and wherein said network means comprise a first charging resistance and a first network capacitance interconnected in series, said series connection having a first terminal connected to said opening pulse furnishing terminal, a common point, and a second terminal connected to said switching control element; a second charging resistance, a second network capacitance, and a third charging resistance series connected between said common point and said first supply line; a diode connected in shunt with said first charging resistance and having its cathode connected to said common point; and an interconnecting resistor connected between the common point of said second network capacitance and said third charging resistance at one terminal, and the output of said switching circuit means at the second terminal.