US 3630177 A
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United States Patent 3,l5l,450 10/1964 Blackaby lnventor Gerhard Engel Stuttgart-Zuffenhnnsen, Germany Appl. No. 863,439 Filed Oct. 3, 1969 Patented Dec. 28, 1971 Assignee Robert Bosch Gmbl-I Stuttgart, Germany Priority Oct. 12, 1968 Germany P 18 02 859.6
SPEED CONTROL FOR INTERNAL COMBUSTION ENGINE 14 Claims, 5 Drawing Figs.
US. Cl 123/32 EA Int. Cl F02!) 3/00 Field of Search 123/32 E,
32 EL,140.3,140 FG References Cited UNITED STATES PATENTS 8/1948 Mock 123/130 2,918,911 12/1959 061mm. 123/32 2,936,744 5 1960 Paule. 123/32 3,032,025 5/1962 Lang. 123/32 3,036,564 5 1962 061m 123/32 3,407,193 10/1968 Lang 123/32 FOREIGN PATENTS 360,498 3/1938 Italy 123/140 Primary Examiner-Mark M. Newman Assistant Examiner-Ronald B. Cox 7 Attorney-Michael S. Striker ABSTRACT: The position of a regulator rod controls the amount of fuel during each operating cycle by an injection pump. The position of the rod depends on hydraulic pressure which in turn is controlled by means of an electric valve, The electric valve responds to a control signal which is furnished by a multistage closed loop control circuit in dependence on the difference between a first feedback signal signifying the position of the regulator rod and a desired fuel injection signal varying in dependence both on the motor speed and the position of the accelerator pedal.
PATENTEU DEC-28 I97! SHEET 3 UF 3 SPEED CONTROL FOR INTERNAL COMBUSTION ENGINE BACKGROUND OF THE INVENTION This invention relates to an arrangement for adjusting the speed of an internal combustion engine. In particular, it relates to the adjustment of the speed of a diesel motor, within a family of load-speed characteristic curves of such a diesel motor. Such diesel motors comprise a regulator member for adjusting the quantity of fuel injected during each operating cycle.
'This invention particularly relates to an arrangement for controlling the motion of such a regulator member, thus controlling the amount of fuel injected during each operating cycle.
Diesel motors are often incorporated in vehicles in which a constant operating speed is desired. Such vehicles include, for example, street cleaning vehicles or various agricultural vehicles as for example, tractors. In order to achieve constant operating speed, the motors are equipped with a control arrangement which causes the diesel motor to have a constant speed, unless a signal for a change in speed is furnished by the accelerator pedal.
Many such control arrangements, which are also called variable speed governors, are known. These are built on the basis of hydraulic, pneumatic or mechanical principles which have achieved a high degree of reliability in the present state of the art. Such arrangements have to meet a number of requirements dictated by the characteristics of diesel motors. These include a limitation of the maximum amount of fuel furnished, regardless of load; a controlled variable dependence of speed on load; and a decrease or shut-off of the fuel injected if a predetermined maximum speed is exceeded.
All these factors, which will be discussed in detail below, must be adjusted individually in the control arrangement for the particular diesel motor type being used and its characteristic curves. This is generally achieved in the factory by building in particular springs, cam discs, insertion of shims or washers, adjustment of various detents, etc. It is particularly desirable that such a regulating arrangement should allow full utilization of the power of the motor with which it is associated. Thus it must be possible for the control arrangement to achieve a sharp regulation of the amount of fuel injected at the maximum speed, so that the diesel motor may be driven to its highest speed at the maximum fuel injection rate.
For these reasons, the conventional control arrangements of various speed governors are designed in general from the beginning to fit a particular type of diesel motor. Thus, it is the practice in general to build a particular control arrangement for each type of motor. This, of course, prevents large production runs and makes the procurement of spare parts more difficult. Attempts carried out to date to furnish a single control arrangement suitable for all types of motors, have failed so far, since the requirements differ too greatly from one type to the other.
SUMMARY OF THE INVENTION It is the object of this invention to furnish a variable speed governor which does not have the drawbacks of the known mechanical types of governors.
In particular, the arrangement in accordance with the present invention consists at least in part of electronic components whose different parameters may be readily adjusted, even at the motor. They may thus be used readily for different types of motors. Further, it is an object of the present invention to furnish a speed adjustment system in which the complete power of the diesel motor may be fully utilized.
This invention thus comprises an arrangement for adjusting the speed of an internal combustion engine within a family of load-speed characteristic curves, at least in part under operator control. It comprises injection means for injecting a regulatable quantity of fuel during each operating cycle. Regulator means for regulating said quantity of fuel during each of said operating cycles are provided, these regulator means functioning in response to a control signal. Further provided are first feedback signal furnishing means, for furnishing a first feedback signal having a characteristic varying as a function of the quantity of fuel actually injected during each operating cycle. Furnished as well are second feedback signal furnishing means which supply a second feedback signal having an electrical characteristic which varies in dependence upon the speed of the internal combustion engine. Adjustment means for varying said electrical characteristic of said second feedback signal under operator control are provided. These adjustment means furnish the desired fuel injection signal. Closed loop control circuit means having at least an input stage and an output stage receive said first feedback signal and said desired fuel in.- jection signal at a first and second input, respectively, of said input stage. The output of said input stage is a difference signal which is amplified in said output stage and, following said amplification, constitutes the control signal controlling said regulator means.
In particular, the regulator means comprise an electrically controlled hydraulic valve system which controls the pressure determining the position of the regulator member, or rod, which in turn determines the quantity of fuel injected during each cycle.
The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING FIG. I is a block diagram of an arrangement in accordance with the present invention,
FIG. 2 is a more detailed diagram of the arrangement shown in FIG. 1;
' FIG. 3 shows the characteristic curves of a diesel motor, in
particular, the quantity of fuel injected as a function of speed;
FIG. 4 is a detailed diagram showing the regulating means in accordance with this invention; and
FIG. 5 is a circuit diagram showing the amplifier means and safety arrangement in accordance with this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiment of this invention will now be described with reference to the Figures. The same or corresponding parts shown in different Figures are labeled with the same reference number.
FIG. I shows, schematically, an internal combustion engine 11, called a motor hereinafter, which is mechanically coupled to a tachometer 12 which furnishes a voltage varying as a function of the motor speed. The tachometer output is connected to the first input of adjustment means, whose second input is connected to the accelerometer pedal, 14. The adjustment means serves to furnish a adjusted second feedback signal which is supplied to amplifier means 15, at a second input of said amplifier means. The first input of the amplifier means receive a first feedback signal which has an amplitude depending upon the quantity of fuel injected during each cycle. The output of the amplifier means I5 is used to control the injection pump 16 as a function of the difference between the signals received at its first and second inputs. The injection pump 16 is connected to the motor both mechanically and, of course, over fuel supply pipes. A safety arrangement 20 is connected between the electrical output of the tachometer l2 and a third input to the amplifier means 15.
More details are shown in FIG. 2. The motor 11 drives both the tachometer I2 and the injection pump 16 either over separate shafts or a common shaft with the motor speed rr,,,,,,. Fuel lines 17 lead from the injection pump 16 to the individual cylinders of the motor 11. The exhaust gases are collected in an exhaust manifold 18 and ejected therefrom. The injection pump 16 supplies fuel to the motor 11 independence on the position of a control member, or control rod 19, which is controlled by the amplifier means 15 via a cylinder arrangement 21. The control rod 19 is connected to the piston 22 of the cylinder arrangement 21 by means of a linkage 23 which has a collar 24. Pressure is exerted against one side of the collar 24 by means of a spring 26 whose other end is connected to a fixed member 25. The pressure of the spring tends to push control rod 19 in the direction of the arrow to a position which corresponds to a zero quantity of injected fuel. Linkage 23 is further mechanically coupled to the movable arm of a potentiometer 27, one embodiment of first feedback signal furnishing means. The potentiometer 27 has one terminal connected to a positive supply line 28 and the other terminal connected to the negative or ground of the supply source, namely a battery 31.
In addition to the rod-piston arrangement set forth above, the regulator means of the present invention comprise a pump 81 which pumps a pressure medium as for example oil, into the cylinder 21. The supply of the pressure medium to cylinder 1 is controlled by means of a pressure regulating valve 82, while the flow from cylinder 21 is controlled by means of a magnetic valve 83. The magnetic valve is connected with the output terminal of the amplifier means 15. Since the pump 81 pumps a substantially constant amount of the pressure medium per unit time, a safety device, namely an overflow valve 84 is furnished to guard against excessive pressure in the fluid conducting system. The fluid conducting means, or pipes 85 are arranged between the cylinder 21, the throttle 82 and the magnetic valve 83.
FIG. 3 will be used for explanation of the functioning of the speed adjusting arrangement of this invention. Embodiments of this type of arrangement are disclosed, for example, in US. Pats. 3,425,401 and 3,407,793. The operation is as follows. FIG. 3 shows a family of characteristic curves of a diesel motor. When the motor 11 of FIG. 2 is started, the amplifying means 15, in conjunction with the throttle 82 and the magnetic valve 83, cause a strong movement of the piston 22, causing the control rod 19 of injection pump 16 to be moved to a position corresponding to fuel excess for starting. It remains in this position until the motor has reached the speed n denoted as its starting speed. This process takes place along the dashed lines labeled 33 in FIG. 3. After the speed n has been reached, the amplifying means 15, controlled by tachometer 12 via the adjustment means 13, cause an adjustment of the magnetic valve 83 and thus a movement of the piston 22. Spring 26 pushes rod 19 back by an amount sufficient to keep the speed above the starting speed n The amount of fuel injected varies depending upon whether the motor is operating under load, or whether it is free wheeling. For free wheeling, the portion of the curve labeled 34, generally known as a no load decrease" characteristic applies.
The speed of the motor, n,,,,,,, may be increased under operator control by means of activation of the pedal 14. If a medium load is assumed and a medium speed n,,, as desired, then the pedal 14 must be depressed sufficiently that the control arrangement 13, 15 furnishes a sufficient quantity of fuel 0,, by means of the cylinder and piston arrangement 21, 22, the control rod 19 and the injection pump 16. In FIG. 3, this corresponds to point 35. In order to keep the speed substantially constant, more fuel is injected for increasing loads. During such increasing loads, a slight decrease of the speed may be permitted. This is shown in FIG. 2 along curve 36. For reasons of stability, the system is so arranged that the decrease in speed due to increasing load is not compensated for completely. so that a small dependence of speed upon load may be found. This dependence of speed upon load is called the governing coefficient and is represented by the slope of line 36.
In general, the governing coefficient depends upon the speed. If a higher speed is desired for an unchanging load, the
pedal must be depressed further. In accordance with the movement of the pedal, if this movement is slow, the point 35 moves along the line 37 representing a constant quantity of injected fuel, for example up to a point 38. If the pedal is moved suddenly, the point 35 may move along a loop, since in that case,'the amount of fuel injected per operating cycle also undergoes a sudden change. Under a varying load, the motor then operates from point 38 along the line 39 having a governing coefficient since, for purposes of clarity, this coefficient has been pictured as constant in FIG. 3.
If, for a particular position of the pedal 14, indicated in FIG. 3 by lines 36, the load is completely removed from the motor, or the motor is operating in a freewheeling manner, themeans l3 and 15 will still provide a minimum quantity of fuel Or. as shown in line 41 of FIG. 3. On the other hand, the stroke of the control rod 19, and thereby the maximum fuel to be injected is limited to a fixed quantity 0, so that even under the highest loads of motor 11, only a limited quantity of fuel may be injected. This is called a negative full load adjustment, and corresponds to line 42 in FIG. 3. This full load adjustment prevents more fuel being furnished to the motor than it can burn. It thus prevents the appearance of smoke in the exhaust. It is thus seen that, if a motor is first operated at an average speed n,,, for an average load, and the motor is then unloaded, the amount of fuel injected is not decreased further when the motor has reached the speed n,,; however, on the other hand, the amount of fuel is also not increased further, if the speed has decreased to a value n, due to increasing load. If the load is removed suddenly, the amount of fuel injected is throttled until the motor speed has reached line 37. Thereafter the control rod 19 is again controlled until the point 35 is reached. The line from point 38 to point 35 is thus also a loop. If the motor 11 should be overloaded, the speed, for constant maximum injected fuel quantity, decreases along line 43 to zero.
If the motor operates at a higher speed, smoke may be formed in the exhaust even for quantities of fuel which are less than the maximum Q,,. Thus, starting with a predetermined speed, the arrangement limits the amount of fuel injected more closely, as shown in FIG. 3 by line 44. This line has a slope '11. Lines 42 and 44 may be called smoke limit lines. The limitation of the fuel to a predetermined maximum under different conditions not only prevents the excess formation of smoke, but also unnecessary fuel consumption.
If the motor approaches the maximum permissible speed n the magnetic valve 83 is closed completely, so that the spring 16 pushes the regulator rod 19 until the limit of its movement in the direction of the arrow, thus causing the fuel supply to be shut off completely. Then further depression of the pedal 14 cannot achieve an increase in speed. This process may be called speed limiting" and is shown in FIG. 3 by speed limiting line 45.
Some details of the regulator means are shown in FIG. 4. The spring 26 is, at one terminal, applied to a fixed member 25. The other end of the spring pushes against the collar 24, which is integrally mounted with the linkage 23. The piston 22 is mounted on linkage 23. The cylinder 21 is connected to fluid conducting means or pipe which furnishes the pressure medium, for example oil. The pump 81, which is not shown in the Figure, pushes the oil through throttle 82 into the pipe 85. The amount of fluid flowing from the cylinder is regulated by magnetic valve 83. The amplifier means, which are not shown in FIG. 4, control the winding 47 of the magnetic valve 83.
FIG. 5 is a circuit diagram of the amplifier means 15 and the safety arrangement 20. The amplifier means comprise a differential amplifier which has a first transistor 48. To the emitter of this first transistor, is connected a first emitter resistance 49. The second transistor of the differential amplifier has a second emitter, to which is connected a second emitter resistance 51. The other terminals of the resistors 52 and 49 are connected together and are further connected to the second power supply line, the negative side, by means of a resistance 53. The collector of the first transistor 48 is directly connected to the first power supply line, the positive side, labeled 28 in FIG. 5. The collector of the transistor 50 is connected to line 28 by means of a collector resistance 54. The base of the first transistor 48 is connected with the movable arm of potentiometer 27, which is not shown in FIG. 5, while the base of the second transistor 50 is connected to the output of the adjustment means 13. Both transistors 48 and 50 constituting the differential amplifier are NPN-transistors.
The collector of the second transistor 50 is connected to the base of an NPN-transistor 56 whose emitter is directly connected to line 28. This transistor and its associated circuitry form a first output stage. The collector of transistor 56 is connected to line 29 by means of a parallel circuit consisting of collector resistance 57 and a filter capacitor 58. Between the collector of transistor 56 and the base of power output transistor 59, is a limiting resistance 60. The emitter of NPN- transistor 59 is connected via an emitter resistance 61 to line 29, while the collector is connected to line 28 by means of the activating coil 47, or electrical input element, of the magnetic valve 83. The limiting resistance 62 in series with the coil 47 of the magnetically controlled hydraulic valve, herein called magnetic valve for simplicity, may be dispensed with in some applications. A feedback resistance 54 is connected between the collector and the base of transistor 59. A parallel circuit consisting of a resistance 65 and a capacitor 66 is connected between the collector of transistor 59 and the base of transistor 56.
The connection between the amplifier and the safety arrangement is furnished by a diode 68, whose anode is connected to the base of transistor 59 and whose cathode is connected to the collector of a transistor 69 which forms part of a bistable circuit included in the safety arrangement 20. The emitter of this transistor 69 is connected with the emitter of a second transistor 70. The emitters are connected over a common emitter resistance 71 to line 29. Both transistors 69 and 70 are NPN-transistors. The collector of the transistor 70 is connected to the base of transistor 59 by a parallel circuit consisting of a resistance 72 and a capacitor 73. The base of the first transistor 69 is connected to line 29 by means of a resistance 74. The collector of the first transistor 69 is connected to the positive line 28 by means of a resistance 75, while the collector of transistor 70 is connected to this line by means of collector resistance 76. A resistance 77 is connected between the collector of the transistor 69 and the base of transistor 70. The parallel circuit consisting of resistance 72 and capacitor 73, as well as the resistance 77, are the feedback elements of the bistable circuit having transistors 69 and 70. The base of the second transistor 70 is connected to line 28 by means of a resistance 78. A diode 91 has an anode connected to the base of transistor 70 and a cathode connected to the point 92. Between the point 92 and the positive line 28 is a biasing resistance 93; between the point 92 and the output of the tachometer 12 is a coupling capacitor 94.
The operation of the arrangement of FIG. 4 is as follows:
The pressure medium pumped by pump 81 flows through the valve 82. After the valve, within the pump 85, a substantially constant pressure exists. Because of this substantially constant pressure in the chamber of the cylinder 21, the piston 22 is pushed out of the cylinder. Of course the piston 22 is connected to the control rod 19, which is not shown here. This process is opposed by the spring power of spring 26 which tends to push the piston back into the cylinder housing 21. The magnetic valve 83 controls the flow of the pressure medium out of the cylinder by opening or closing in response to the control signal furnished by amplifying means 15, which are not shown in FIG. 4. In dependence of the position of the pedal 14 and on the information delivered by tachometer l2 regarding the speed of the motor, an equilibrium is achieved between the pressure of the pressure medium and the spring power exerted by the spring 26, causing the piston 22 to remain in a stable position.
The differential amplifier shown in FIG. 5 with transistors 48 and 50 constantly compares the desired voltage furnished by the adjustment means 13 with the voltage fed back by potentiometer 27. The voltage which results at the collector of the transistor 50 serves to control the magnetic valve 83 over the following amplifier stages. The common emitter resistor 53 of the differential amplifier may be replaced by a conventional constant current source. This constant current source may, for example, comprise a transistor with a fixed baseemitter voltage. As soon as the voltage supplied by adjustment means 13 substantially exceeds the base potential of transistor 48, the collector voltage of transistor 50 decreases. This causes the transistor 56 to change from a blocked to a conductive condition. This then causes the transistor 59 associated with the power output stage to assume its conductive condition. The collector of NPN-transistor 59 is connected with the base of transistor 56 over the feedback networks 65 and 66. This causes the amplifier stage to operate as a switch. By choice of the correct components, the difference between the switching states of the power output transistor for switching in and switching out may be kept small. The limiting resistance 62 serves to linearize the collector current but may be dispensed with. The emitter resistance 61 serves to stabilize the emitter current relative to changes in temperature and also serves to generate an emitter biasing voltage which is required for the functioning of a safety arrangement described below. Thus if the voltage furnished by adjustment means 13 increases, causing transistor 59 to become conductive, the winding 47 of the magnetic valve 83 becomes activated, closing the magnetic valve. In case of a failure of the battery voltage, the winding 47 of the magnetic valve 83 cannot be activated, so that the valve 83 opens in any case, thus decreasing the pressure in pipe 85. Thus the spring 26 can push the piston 22 into the cylinder housing 21, causing an interruption of the injection of fuel into the motor and thus causing the motor to stop.
Further, precautions must be taken that the motor does not exceed a maximum permissible speed. This is achieved by means of a safety arrangement 20 shown in FIG. 5. The tachometer 12, or one winding thereof, which, in the embodiment shown in FIG. 5, has one terminal connected to the negative line 29, furnishes a sinusoidal alternating voltage. This alternating voltage is decoupled over capacitor 94 and connected to point 92. However, at this point 92, a positive potential exists, derived from line 28 by means of resistance 93, so that the voltage furnished by tachometer 12 is superimposed upon this DC potential. A positive potential also exists at the base of transistor 70 of the bistable circuit comprising transistors 69 and 70 because of the connection to the positive line by means of resistance 78. Thus the transistor 70 is in a conductive condition, while the transistor 69 is blocked. As long as the motor 11 is at standstill, the potential at the point 92 is substantially equal to the potential at line 28, or twelve volts in the embodiment shown in FIG. 5. When the motor is running, the potential at point 92 is pulled in the negative direction in synchronism with the alterations of the voltage furnished by tachometer 12. The amplitudes of the voltage furnished by tachometer 12 increase with increasing motor speed. Starting with a predetermined amplitude of the negative half of the voltage, the diode 91 begins to conduct. Thus the base potential of transistor 70 becomes more negative, transistor 70 finally becomes nonconductive, causing transistor 69 to become conductive. The cathode potential of diode 68 now decreases substantially to the emitter potential of transistor 69. This causes diode 68 to become conductive and causes the base potential of transistor 59 in amplifier means 15 to assume a low value. Thus the base current flowing in transistor 59 no longer suffices to cause a collector current in transistor 59 of sufficient magnitude to activate the winding 47 of the magnetic valve 83. Thus the magnetic valve 83 opens. The pressure in pipe decreases. The spring pushes the piston 22 and thus the control rod 19 into a position corresponding to a zero quantity ofinjected fuel. A step change in collector potential of transistor 69 is fed back to the base of transistor 70 by means of resistance 77, thus furnishing an assurance against a reswitching of the bistable circuit with the following positive half-wave of the voltage furnished by tachometer 12. Thus after the safety arrangement has been activated, the motor becomes to a complete standstill and can only be put back into operation by means of a renewed starting procedure.
The safety arrangement may be tested frequently, by causing the normal shutoff of the motor to be effected by it. If it is desired that the motor may not be restarted after the safety arrangement has operated, then a fusing arrangement can be furnished in the collector circuit of transistor 69 which fuse opens when the safety arrangement is activated. ln this case of course the testing of the safety arrangement in the normal shutting off of the motor must be dispensed with,
The present invention allows the manufacturing of a simple combined electronic-hydraulic regulating arrangement. The electronic control of the magnetic valve is achieved preferably by means of a differential amplifier which compares the voltage furnished as a function of speed and adjusted by means of the accelerator pedal with a voltage furnished by a potentiometer whose variable arm is connected with the control rod mechanically. Temperature drift of the differential amplifier and therefore the temperature drift of the whole amplifying means, is negligible for present function, since the output stage which furnishes the winding of the magnetic valve with current is operated in a switching type operation. The arrangement in accordance with this invention thus operates even under the most difficult conditions which arise in the operation of commercial vehicles very safely and with great reliability.
While the invention has been illustrated and described as embodied in electronic and mechanical arrangements, it is not intended to be limited to the details shown, since various modifications, structural and circuit changes may be made without departing in any way from the spirit of the present invention.
What is claimed as new and desired to be protected by Let ters Patent is set forth in the appended:
l. Arrangement for adjusting the speed of an internal combustion engine within a family of load-speed characteristic curves, at least in part under operator control comprising, in combination, means for furnishing a regulatable quantity of fuel during each operating cycle of said internal combustion engine; regulator means for regulating said quantity of fuel during each of said operating cycles in response to a control signal; first feedback signal furnishing means, for furnishing a first feedback signal having an amplitude varying as a function of the actual quantity of fuel injected during each operating cycle; second feedback signal furnishing means for furnishing a second feedback signal having an amplitude which varies in dependence upon the actual speed of said internal combustion engine; adjustment means for varying said amplitude of said second feedback signal under operator control, thus fumishing a desired fuel injection signal; first and second power supply lines; and closed loop control circuit means having at least an output stage and an input stage, said input stage comprising a differential amplifier, said differential amplifier comprising a first and second semiconductor element, each of said semiconductor elements having a first and second output electrode and a control electrode, said first feedback signal being applied to said control electrode of said first semiconductor element and said desired fuel injection signal being applied to said control electrode of said second semiconductor element, said differential amplifier means further comprising common resistance means connecting said first output electrodes of said first and second semiconductor elements to said second power supply line and means connecting said second output electrode of said first and second semiconductor elements with said first power supply line, whereby a difference signal varying as a function of the difference in amplitude of signals applied at said first and second control electrode appears at said first output electrodes; and wherein said output stage amplifies said difference signal and furnishes said control signal at a control circuit output in dependence thereon.
2. Arrangement for adjusting the speed of an internal combustion engine within a family of load-speed characteristic curves, at least in part under operator control, comprising, in combination, means for furnishing a regulatable quantity of fuel during each operating cycle of said internal combustion engine; regulator means for regulating said quantity of fuel during each of said operating cycles in response to a control signal; first feedback signal furnishing means, for furnishing a first feedback signal having a characteristic varying as a function of the actual quantity of fuel injected during each operating cycle; tachometer means for furnishing a second feedback signal having an electrical characteristic which varies in dependence upon the actual speed of said internal combustion engine; adjustment means for varying said electrical characteristic of said second feedback signal under operator control, thus furnishing a desired fuel injection signal; and closed loop control circuit means having at least an input stage and an output stage, said input stage having a first input receiving said first feedback signal, a second input receiving said desired fuel injection signal, and an output furnishing a difference signal varying as a function of the difference between the signals applied at said first and second inputs, said output stage amplifying said difference signal and furnishing said control signal at a control circuit output in dependence thereon; further comprising bistable circuit having an input connected to said tachometer and an output connected to said closed loop control circuit means, for causing a zero fuel injection when the speed of said engine exceeds a predetermined maximum speed.
3. A system as set forth in claim 1, wherein said regulator means comprise a regulator member adapted to move along a predetermined path in response to pressure applied at a predetermined location,-said regulator member being connected to said fuel furnishing means in such a manner that the quantity of fuel injected during each operating cycle of said combustion engine depends upon the location along said path of said regulator member; means for applying a hydraulic pressure at said predetermined location; and electrically controlled hydraulic valve means for varying said hydraulic pressure in response to said control signal.
4. A system as set forth in claim 3, wherein said first feedback signal furnishing means comprise electrical feedback means, having a movable arm mechanically intercoupled with said regulator member, and adapted to generate a first electrical feedback signal varying as a function of the location of said regulator member along said predetermined path.
5. A system as set forth in claim 1, wherein said semiconductor elements are transistors.
6. A system as set forth in claim 3, wherein said output stage comprises a first output stage; and a power output stage.
7. A system as set forth in claim 6, wherein said first output stage comprises a PNP-transistor.
8. A system as set forth in claim 6, wherein said hydraulic valve means comprise an electrical input element; wherein said power output stage comprises an output semiconductor element having an output control electrode and an output circuit; wherein said first output stage comprises a first output semiconductor element having a first output control electrode; first passive circuit means intercoupling the output of said first output stage and said output control electrode; second passive circuit means intercoupling said output'circuit and said first output control electrode; and wherein said electrical input element of said hydraulic valve means is connected in said output circuit of said power output stage.
9. A system as set forth in claim 8, wherein said output semiconductor element is an NPN-transistor.
10. A system as set forth in claim 2, wherein said bistable circuit comprises a first and second NPN-transistor.
11. A system as set forth in claim 10, wherein said second feedback signal furnishing means comprise a tachometer, having at least one tachometer winding; wherein one side of said winding is connected to said second power supply line; wherein said safety arrangement further comprises a capacitor having a first capacitor terminal connected to the second terminal of said winding, and a second capacitor terminal; wherein said safety circuit means further comprises a resistor having a first resistor terminal connected to the second capacitor terminal, and a second resistor terminal connected to said first power supply line; and wherein said safety circuit means further comprises rectifier means having an anode connected to the gate of said first NPN-transistor and a cathode connected to said first resistor terminal.
12. A system as set forth in claim 11, wherein said second NPN-transistor has a second collector, a second emitter and a second gate; further comprising second rectifier means having an anode connected to said third input of said amplifier means, and a cathode connected to said second collector.
13. A system as set forth in claim 2, wherein the varying characteristic of said first feedback signal and said desired fuel injection signal is the amplitude of said signals.
14. A system as set forth in claim 2, wherein said output stage of said closed loop control circuit means comprises an output transistor have an output control electrode; and wherein the output of said bistable circuit is connected to said output control electrode.