Fuel Control System For Fuel Injection Type Internal Combustion Engine

Abstract

A fuel control system for fuel injection type internal combustion engines is provided. The fuel control system comprises an actuator chamber including a movable wall connected to the fuel injection characteristic controlling element of a fuel injection pump for a fuel injection type internal combustion engine, a forward controlling electromagnetic valve disposed in a passage interconnecting said actuator chamber and a source of high pressure fluid, a reverse controlling electromagnetic valve disposed in a passage connecting said actuator chamber to a low pressure exhaust, an operating condition detector for detecting an operating condition of the engine in the form of electrical operating condition signals, a control voltage generator for receiving said operating condition signals to produce a control voltage corresponding to a predetermined fuel injection characteristic of the engine, a position voltage generator for generating a position voltage corresponding to the position of said controlling element, a comparator for comparing said control voltage with said position voltage to produce an output voltage corresponding to the difference therebetween, and a forward controlling electromagnetic valve driving circuit and a reverse controlling electromagnetic valve driving circuit selectively responsive to the output voltage of said comparator to generate an electrical output for driving said forward controlling electromagnetic valve and said reverse controlling electromagnetic valve selectively.

Description

FIELD OF THE INVENTION

The present invention relates to a fuel control system for fuel injection type internal combustion engines, wherein the quantity of fluid in an actuator chamber including a movable wall is varied by means of electromagnetic valves operated by an electrical control circuit, whereby a fuel injection characteristic controlling element of a fuel injection pump is controlled in association with the displacement of the movable wall.

Fuel control systems conventionally employed with fuel injection pumps for fuel injection type internal combustion engines have been mostly of mechanical type, in which a controlling element of a fuel injection pump which affects a fuel injection characteristic of the engine is operated by a centrifugal force produced by a weight disposed to rotate with the driving shaft of the fuel injection pump.

Howver, in order to ensure an improved engine performance or to effect noise and exhaust emission controls, it is necessary that a so-called predetermined fuel injection characteristic, such as an injected fuel quantity control characteristic or a fuel injection timing control characteristic predetermined for an engine, highly accurately meets the fuel requirement of the engine which is determined according to the operating conditions of the engine, such as the rotational speed of the engine and the accelerator position, and moreover there is a tendency that the engine operating conditions which determine such a predetermined fuel injection characteristic involve more factors than hitherto been employed, as for example, the discrimination between acceleration and deceleration of the engine.

Therefore, there is a problem that in many cases it is difficult to meet these requirements only with a conventional mechanical fuel control system of the type described above.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the foregoing difficulty. The present invention therefore comprises a fuel control system of the type in which the quantity of fuel contained in an actuator chamber 12 including a movable wall 13 is controlled by a pair of electromagnetic valves 7 and 8, so that the fuel injection characteristic controlling element of a fuel injection pump 10 is operated in response to the displacement of the movable wall 13. The fuel control system comprises an operating condition detector 1 for electrically detecting the operating conditions of an engine which are necessary to determine its predetermined fuel injection characteristic, a control voltage generator 2 for receiving the operating condition signal from the operating condition detector 1 to generate a control voltage corresponding to the fuel injection characteristic of the engine, an electrical position detector 4 for detecting the position of the fuel injection characteristic controlling element of the fuel injection pump 10 to generate a position voltage, and a comparator 3 for comparing said control voltage with said position voltage to generate an output voltage corresponding to the difference therebetween, whereby the output voltage of the comparator 3 is applied as an input signal to an electromagnetic valve driving circuit 5 or 6 so that the electromagnetic valves 7 and 8 are selectively operated with the valve actuating signals from the driving circuits 5 and 6 to effect a negative feedback in such a manner that the set point for the position of the fuel injection characteristic controlling element of the fuel injection pump 10 is selected to be one which satisfies the predetermined fuel injection characteristic.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram showing the general construction of an embodiment of a fuel control system according to the present invention.

FIG. 2 is a longitudinal sectional view of a hydraulic servo motor used with the fuel control system of the present invention.

FIG. 3 is a diagram showing the basic predetermined fuel injection quantity control characteristics of a Diesel engine.

FIG. 4 is an electrical wiring diagram of the electrical control circuit.

FIG. 5 is a characteristic diagram of a control voltage pattern generated by the control voltage generator.

FIG. 6 shows the principal part of another embodiment of the hydraulic servo motor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will be described in detail with reference to the accompanying drawings. Referring now to FIG. 1 which shows the construction of a fuel control system of the invention, numeral 1 designates an engine operating condition detector for detecting the operating conditions of an engine, such as, the rotational speed of the engine and the accelerator position necessary for determining a predetermined fuel injection characteristic of the engine and for generating an electrical operating condition signal, such as a speed voltage corresponding to the rotational speed of the engine or an accelerator voltage corresponding to the accelerator position. Numeral 2 designates a control voltage generator for receiving as its input signal the operating condition signal from the operating condition detector 1 to generate a control voltage corresponding to a predetermined fuel injection characteristic of the engine. This control voltage generator has the same function as an analog function generator with the predetermined fuel injection characteristic as a function pattern.

Numeral 3 designates a comparator which compares said control voltage and a position voltage received from a position voltage generator 4 which voltage corresponds to the position of a fuel injection characteristic controlling element of a fuel injection pump 10 to thereby generate an output voltage corresponding to the difference between said two voltages. Numerals 5 and 6 designate respectively a forward controlling electromagnetic valve driving circuit and a reverse controlling electromagnetic valve driving circuit, so that depending on whether the output voltage of the comparator 3 is above or below a reference value, either the forward controlling electromagnetic valve driving circuit 5 or the reverse controlling electromagnetic valve driving circuit 6 generates a valve actuating signal to operate the electromagnetic valve. Numerals 7 and 8 designate a forward controlling electromagnetic valve and a reverse controlling electromagnetic valve, respectively, which are opened upon receipt of the valve actuating signal from the valve driving circuits 5 and 6, respectively.

Numeral 9 designates a hydraulic actuator in which the quantity of fluid in its actuator chamber is varied in accordance with the opening and closing of the forward controlling electromagnetic valve 7 and the reverse controlling electromagnetic valve 8, whereby the position of its movable wall is determined according to this variation and thus the fuel injection characteristic controlling element of the fuel injection pump 10 is operated in response to the displacement of the movable wall.

The forward controlling electromagnetic valve 7, reverse controlling electromagnetic valve 8 and hydraulic actuator 9 constitute a fluid servo motor 11 an embodiment of which is shown in FIG. 2.

In FIG. 2, numerals 7 and 8 designate the above-described forward and reverse controlling electromagnetic valves, respectively and numeral 9 designates the above-mentioned hydraulic actuator. The construction and operation of the electromagnetic valves 7 and 8 will be explained with reference to the forward controlling electromagnetic valve 7, in which numeral 17 designates an energizing coil, 18 a movable iron core connected to a valve 19, 20 a spring adapted to urge the valve 19 to its valve seat and thus place the electromagnetic valve 7 in its closed position when no energizing current flows in the energizing coil 17. When there is a current flow in the energizing coil 17, a magnetic attractive force is produced so that the movable iron core 18 is moved and thus the valve 19 is moved away from the valve seat thereby opening the passage through the electromagnetic valve 9. The construction and operation just described are identical with those of the reverse controlling electromagnetic valve 8.

The hydraulic actuator 9 includes the movable wall 13 disposed in the actuator chamber 12 so that the hydraulic pressure in the actuator chamber 12 exerts a force on the movable wall 13, while a counteracting spring 14 also exerts a force on the movable wall 13 in a direction that counteracts the force due to the hydraulic force. The fluid volume in the actuator chamber 12 is determined by the forward controlling electromagnetic valve 7 which opens and closes a passage 15 communicating with the high hydraulic pressure source and the reverse controlling electromagnetic valve 8 which opens and closes a passage 16 leading to the low pressure exhaust. When no energizing current is supplied to both of the forward and reverse controlling electromagnetic valves 7 and 8, the two valves are maintained in the closed position. Thus, neglecting the fluid leakages at the seals of the two valves, no fluid is admitted into and out of the actuator chamber 12 so that the fluid volume in the actuator chamber 12 remains at a fixed value and the movable wall 13 also assumes a fixed position with the result that the hydraulic pressure in the actuator chamber 12 remains in a state of equilibrium dependent upon the force of the counteracting spring 14. Numeral 13a designates a connecting rod connecting the movable wall 13 to the fuel injection characteristic controlling element of the fuel injection pump 10. When an electromagnetic valve actuating signal is produced from the forward controlling electromagnetic valve driving circuit 5, an energizing current flows into the energizing coil 17 of the forward controlling electromagnetic valve 7. This opens the electromagnetic valve 7 so that the passage 15 leading to the high hydraulic pressure source is opened, admitting the fluid from the high hydraulic pressure source into the actuator chamber 12 and thus moving the movable wall 13 in the direction of the arrow, i.e. the forward direction. On the other hand, when the reverse controlling electromagnetic valve driving circuit 6 produces a valve actuating voltage, the reverse controlling electromagnetic valve 8 is opened so that the passage 16 communicating the actuator chamber 12 to the low pressure exhaust is opened. When this occurs, the fluid in the actuator chamber 12 is forced through the passage 16 by the force of the counteracting spring 14, thereby moving the position of the movable wall 13 in the direction opposite to the direction of the arrow, i.e. the reverse direction. The movement of the movable wall 13 is transmitted through the connecting rod 13a to the fuel injection characteristic controlling element of the fuel injection pump 10 so that this controlling element is operated to regulate the amount of the fuel injected. The connecting rod 13a is connected to a movable contact 63' of a potentiometer 63. Consequently, in response to the movement of the connecting rod 13a, a voltage corresponding to the position of the movable wall 13 is generated at a point S.

Next, the present invention as embodied in a control system for controlling the amount of fuel injected to a Diesel engine will be explained. FIG. 3 illustrates a diagram showing the most fundamental predetermined characteristics of the amount of fuel injected to a Diesel engine. In the figure, the ordinate represents the predetermined fuel injection quantity Q per cycle per cylinder for the engine and the abscissa represents the rotational speed N of the engine. The parameter is the accelerator position .theta. with .theta. = 0 representing the minimum accelerator position, .theta. = .theta.M representing the maximum accelerator position, and 0 < .theta. < .theta.M. Of the predetermined fuel injection quantity characteristics shown in the figure, the curve connecting the points A, B, E and C represents the starting enrichment and idling fuel injection characteristic with the value of Q.sub.S representing the quantity of fuel to be injected for starting the engine and N.sub.S and N.sub.A representing the number of revolutions dependent upon the starting enrichment speed and the idling speed, respectively. The predetermined quantity of fuel injected when the engine is idling will be determined along the curve BCG. The curve drawn through points E, F and G represents the full-load fuel injection quantity characteristic which is a predetermined fuel injection quantity characteristic of the engine at its full load operation. In this case, Q.sub.F represents the full-load injection quantity and N.sub.SP and N.sub.M represent the maximum output revolution and the maximum normal revolution of the engine, respectively. The curve connecting points H, I and G represents a predetermined fuel injection quantity characteristic of the engine under its part load condition when the accelerator position .theta. = .theta..sub.1.

Referring now to FIG. 4, there is shown an electrical wiring diagram of an embodiment of the fuel control system of the present invention for obtaining the predetermined fuel injection quantity characteristics shown in FIG. 3. In the figure, numeral 1 designates the operating condition detector consisting of a speed detector 22 for generating a speed voltage (V.sub.X) proportional to the rotational speed of the engine and an accelerator detector 23 for generating a voltage corresponding to the position of the accelerator, i.e. an accelerator voltage (V.sub.A). The speed detector 22 comprises a toothed wheel 24 of magnetizable material which is related to the engine r.p.m. and an electromagnetic pickup 25 composed of a pickup coil wound around a permanent magnet and located opposite to the toothed wheel 24. The electromagnetic pickup 25 generates a pulse voltage having a frequency proportional to the rotational speed of the engine and the waveform of this pulse voltage is then reshaped by a transistor 26. The reshaped pulse voltage is thereafter applied to a DC converter circuit consisting of diodes 27 and 28, capacitors 29 and 30 and a resistor 31, thus generating a speed voltage across an emitter resistor 33 of a transistor 32 constituting an emitter follower. The accelerator detector 23 generates a DC voltage corresponding to the position of the accelerator by means of a potentiometer 34 operatively associated with the accelerator pedal.

Numeral 2 designates the control voltage generator for generating a control voltage corresponding to the basic predetermined fuel injection quantity characteristic of the Diesel engine shown in FIG. 3. The control voltage generator 2 comprises a start-idling control voltage generator 36, a full load-part load control voltage generator 37 and an upper limit selection circuit 38. In the starting-idling control voltage generator 36, the speed voltage V.sub.S is applied as its inversion input, while the resistance values of resistors 40, 41, 42, 43 and 44 for determining the gain of the operational amplifier 39 and a bias voltage applied to its non-inversion input in accordance with the speed voltage V.sub.SS corresponding to the starting enrichment revolution N.sub.S and the speed voltage V.sub.SA corresponding to the idling revolution N.sub.A shown in FIG. 5 are selected and adjustment is effected by a potentiometer 48 connected to an amplifier output terminal 47 to obtain an output voltage V.sub.CS corresponding to the starting enrichment fuel injection quantity Q.sub.S.

Accordingly, a control voltage V.sub.C1 generated at a point p changes with variations in the speed voltage V.sub.S substantially as shown by the curve connecting points A', B', C' and G' in FIG. 5 (the voltage reference is assumed to be at the point of a ground connection). The full load-part load control voltage generator 37 receives the speed voltage V.sub.S and the accelerator voltage V.sub.A as an inversion input and a non-inversion input to a differential operational amplifier 49. If the accelerator position .theta. is .theta. = .theta..sub.M, .theta. = .theta..sub.1 and .theta. = .theta..sub.0, respectively, then the accelerator voltage V.sub.A is V.sub.A = V.sub.M, V.sub.A = V.sub.1 and V.sub.A = V.sub.0, respectively, while the resistance values of resistors 50, 51, 52, 34' and 34" are selected according to the speed voltages V.sub.SP and V.sub.SM corresponding to the maximum power revolution M.sub.SP and the maximum normal revolution N.sub.M, respectively, and adjustment is effected by a potentiometer 53 connected to the output terminal of the operational amplifier 49 to provide an output voltage V.sub.F corresponding to the full load fuel injection quantity Q.sub.F.

Accordingly, if the accelerator voltage is V.sub.A = V.sub.M, then a control voltage V.sub.C2 generated at a point g changes with variations in the speed voltage V.sub.S substantially as shown by the curve JF'G' shown in FIG. 5. On the other hand, when V.sub.A = V.sub.1 and V.sub.A = V.sub.0, respectively, the control voltage V.sub.C2 changes substantially as shown by the curves JH'I'G' and JE'C"G', respectively.

The upper limit selection circuit 38 comprises diodes 54 and 55 and a resistor 56 and current amplification is effected in an emitter follower transistor 57 thus generating the control voltage V.sub.C across terminals r and e of an emitter resistor 58. In accordance with the characteristic of the upper limit selection circuit 38, the control voltage V.sub.C assumes a value equal to the value of either the control voltage V.sub.C1 generated at the point p or the control voltage V.sub.C2 generated at the point g, which is greater than the other. Accordingly, the pattern of the control voltage V.sub.C becomes as shown with solid lines in FIG. 5 and it corresponds with the pattern of the predetermined fuel injection quantity characteristic shown in FIG. 3.

Numeral 3 designates the comparator to which the control voltage V.sub.C generated by the upper limit selection circuit 38 is applied through a resistor 61 as an inversion input to a differential operational amplifier 60, while a voltage V.sub.P obtained by dividing the power supply voltage by a potentiometer 63 is applied through a resistor 62 as a non-inversion input to the operational amplifier 60. The voltage dividing ratio of the potentiometer 63 varies in response to the movement of the fuel injection quantity controlling element of the fuel injection pump (e.g., the fuel control rack in a line type fuel injection pump) and thus the voltage V.sub.P at the point S provides a voltage corresponding to the position of the fuel injection quantity controlling element of the fuel injection pump, i.e. a position voltage, with the result that the fuel quantity Q pumped from the fuel injection pump is proportional to the position voltage V.sub.P. Thus, if Q = Q.sub.S, then V.sub.P = V.sub.CS and if Q = Q.sub.F, then V.sub.P = V.sub.F. The comparator 3 compares the control voltage V.sub.C with the position signal V.sub.P and produces the output voltage V.sub.O corresponding to the difference between the two voltages. Assuming now that V.sub.b represents the output voltage of the comparator 3 when V.sub.P = V.sub.C and that .DELTA.V and .delta. respectively represent the dead zones of the forward and reverse controlling electromagnetic valve driving circuits 5 and 6 in terms of the input and output voltages of the comparator 3 (where .DELTA.V > 0, .delta.>0), if .vertline.V.sub.P - V.sub.C .vertline..ltoreq..DELTA.V, then the output voltage V.sub.0 of the comparator 3 is given as V.sub.b - .delta..ltoreq.V.sub.0 .ltoreq.V.sub.b + .delta., if V.sub.P - V.sub.C > .DELTA.V, then V.sub.0 .ltoreq. V.sub.b + .delta., and if V.sub.P - V.sub.C < - .DELTA.V, then V.sub.0 < V.sub.P - .delta..

The output voltage of the comparator 3 is applied to the forward controlling electromagnetic valve driving circuit 5 and the reverse controlling electromagnetic valve driving circuit 6. In the forward controlling electromagnetic valve driving circuit 5, the level of the output voltage of the comparator 3 is adjusted by a potentiometer 67 and a Zener diode 68 to provide an electromagnetic valve actuating output, so that when V.sub.0 < V.sub.b - .delta., a transistor 69 is rendered non-conductive causing a transistor 70 to become conductive and thus applying an actuating output voltage to the energizing coil 17 of the forward controlling electromagnetic valve 7 to open it and thus move the movable wall 13 of the hydraulic servo motor in the forward direction. On the other hand, when V.sub.0 .gtoreq. V.sub.b + .delta., the transistor 69 is rendered conductive and the transistor 70 is thus rendered non-conductive producing no valve actuating output voltage, so that the forward controlling electromagnetic valve 7 remains closed and thus the movable wall 13 of the hydraulic servo motor is not moved.

Next, in the reverse controlling electromagnetic valve driving circuit 6, the output voltage level of the comparator 3 is also preset by a potentiometer 72 and a Zener diode 73 so as to generate an electromagnetic valve actuating output voltage. Thus, when V.sub.0 .gtoreq. V.sub.b + .delta., a transistor 74 conducts rendering a transistor 75 non-conductive and a transistor 76 conductive, so that a valve actuating output voltage is applied to a energizing coil 77 of the reverse controlling electromagnetic valve 8, thereby moving the movable wall 13 of the hydraulic servo motor in the reverse direction.

With the construction and operation described above, if, under a given operating condition of the engine, the position of the fuel injection characteristic controlling element of the fuel injection pump 10 goes beyond the position which satisifes the predetermined fuel injection quantity characteristic shown in FIG. 3 in excess of a preset value, then there holds a relation V.sub.P > V.sub.C + .DELTA.V between the position voltage V.sub.P and the control voltage V.sub.C. When this occurs, the output voltage of the comparator 3 becomes V.sub.0 > V.sub.b + .delta., causing the reverse controlling electromagnetic valve driving circuit 6 to apply a valve actuating output voltage to the reverse controlling electromagnetic valve 8 and thus cause the hydraulic servo motor to move the fuel injection characteristic controlling element in the reverse direction, i.e. the direction to decrease the quantity of fuel injected. On the contrary, when the position of the fuel injection characteristic controlling element falls short of the position which satisfies the predetermined fuel injection quantity characteristic in excess of a preset value, then there holds a relation V.sub.P < V.sub.C - .DELTA.V and the output voltage of the comparator 3 becomes V.sub.0 < V.sub.b - .delta.. Consequently, the forward controlling electromagnetic valve driving circuit 5 applies a valve actuating output voltage to the forward controlling electromagnetic valve 7, causing the hydraulic servo motor to move the fuel injection characteristic controlling element in the forward direction, i.e. the direction to increase the quantity of fuel injected. On the other hand, when the deviation of the position of the fuel injection characteristic controlling element from the position which satisfies the predetermined fuel injection quantity characteristic remains within a predetermined range of limits, then there holds a relation .vertline.V.sub.P - V.sub.c .vertline..ltoreq. .DELTA.V and hence .vertline.V.sub.0 - V.sub.b .vertline..ltoreq. .delta., so that both of the forward controlling electromagnetic valve driving circuit 5 and the reverse controlling electromagnetic valve driving circuit 6 produce no valve actuating output voltage and thus the hydraulic servo motor does not cause the fuel injection characteristic controlling element to change its existing position. In this manner, the position of the fuel injection characteristic controlling element of the fuel injection pump 10 is automatically controlled employing the position which satisfies a predetermined characteristic of fuel quantity injected to an engine as a desired value.

The hydraulic servo motor used in the illustrated embodiment may also be constructed as shown in FIG. 6. In the figure, numerals 7 and 7' designate forward controlling electromagnetic valves; 8 and 8' reverse controlling electromagnetic valves. All of these electromagnetic valves are of the identical construction as the electromagnetic valve 7 shown in FIG. 2. A hydraulic actuator 9' is provided with two actuator chambers 12' and 12" and two movable walls 13' and 13" fixedly spaced away from each other with a preset distance by a connecting rod 13'a.

Numeral 15 designates a passage leading to a source of high hydraulic pressure, 16 a passage leading to a low pressure exhaust. The connecting rod 13'a is also connected to the fuel injection characteristic controlling element. Thus, when a valve actuating output voltage is applied to the forward controlling electromagnetic valves 7 and 7', the connecting rod 13'a is moved in the direction of the arrow, while the application of a valve actuating output voltage to the reverse controlling electromagnetic valves 8 and 8' causes the connecting rod 13'a to move in the direction opposite to the direction of the arrow. Thus, if the forward controlling electromagnetic valve driving circuit 5 and the reverse controlling electromagnetic valve driving circuit 6 of the electrical control circuit shown in FIG. 4 are used to actuate the forward controlling electromagnetic valves 7 and 7' and the reverse controlling electromagnetic valves 8 and 8', respectively, a fuel control means equivalent to the hydraulic servo motor shown in FIG. 2 may be constructed. In this case, however, the hydraulic servo motor of FIG. 6 is advantageous because of its ease of manufacture and maintenance due to the reduced pressure of the high hydraulic pressure source.

While the fuel control system of the present invention has been described as used in controlling the quantity of fuel injected, the present invention may also be applied to the control of fuel injection timing. In this case, the operating condition detector electrically detects such operating conditions of an engine as the engine rotational speed and the acceleration of the engine speed which are necessary to determine the time of injecting the fuel to the engine, and the control voltage generator generates a control voltage corresponding to a predetermined fuel injection time control characteristic of the engine, whereby the control voltage thus obtained and the position voltage corresponding to the detected position of the fuel injection time controlling element of the fuel injection pump 10 are applied to the comparator to produce a comparator output voltage corresponding to the difference between the two voltages and thus actuate the corresponding electromagnetic valve of the hydraulic servo motor through its electromagnetic valve driving circuit. Therefore, the construction of such a fuel injection time control system is identical with that shown in FIG. 2.

In addition to various kinds of oils, fluids such as compressed air may be used as the actuating fluid with the present invention.

It will thus be seen that the present invention provides a fuel control system of the type employing an electromagnetic valve-operated fluid servo motor to operate a fuel injection characteristic controlling element of a fuel injection pump, wherein operating conditions of an engine are electrically detected and utilized as input information to provide a control voltage corresponding to a predetermined fuel injection characteristic of the engine, and the position of the fuel injection characteristic controlling element of the fuel injection pump is detected as a position voltage, whereby the control voltage and the position voltage are compared in a comparator to produce a comparator output voltage corresponding to the difference between the two voltages, the comparator output voltage being used to selectively actuate the electromagnetic valves of the fluid servo motor to control the position of the fuel injection characteristic controlling element of the fuel injection pump, thereby automatically controlling the position of the fuel injection characteristic controlling element, with that position which satisfies the predetermined fuel injection characteristic of the engine as its desired value. Thus, there is a great advantage over the conventional fuel control systems for fuel injection type internal combustion engines in that a greater variety of engine operating conditions than heretofore possible can be detected to thereby highly accurately control the quantity of fuel injected to suit a predetermined fuel injection characteristic designed to improve various efficiencies of an engine.

Claims

We claim:

1. A fuel control system for a fuel injection type internal combustion engine comprising a fluid servo motor including an actuator chamber having a movable wall connected to a fuel injection quantity controlling element of a fuel injection pump for the engine, a forward controlling electromagnetic valve provided in a passage connecting said actuator chamber to a high pressure fluid source, and a reverse controlling electromagnetic valve provided in a passage connecting said actuator chamber to a low pressure exhaust; an operating condition detector for detecting operating conditions of the engine to generate electrical operating condition signals; a control voltage generator for receiving said operating condition signals to generate a control voltage corresponding to a predetermined quantity of fuel injected to the engine; a position voltage generator for generating a position voltage corresponding to the position of said fuel injection quantity controlling element; a comparator for comparing said control voltage with said position voltage to generate an output voltage corresponding to the difference between said voltages; and a forward controlling electromagnetic valve driving circuit and a reverse controlling electromagnetic valve driving circuit selectively responsive to said output voltage of said comparator to generate an electrical output for selectively opening said forward controlling electromagnetic valve and said reverse controlling electromagnetic valve of said fluid servo motor, wherein said operating condition detector comprises speed detecting means for generating a voltage proportional to the rotational speed of the engine and acceleration detecting means for generating a voltage corresponding to the position of the accelerator; and said control voltage generator comprises start-idling control voltage generating means connected to said speed detecting means and having an operational amplifier for generating an output voltage corresponding to the starting enrichment fuel injection quantity, full load-part load voltage generating means connected to said acceleration detecting means and said speed detecting means having an operational amplifier for generating an output voltage corresponding to the full load fuel injection quantity, and upperlimit selection circuit means connected to said start-idling control voltage generating means and said full load-part load voltage generating means for generating a voltage equal to the value of either of said output voltages whichever is greater than the other.

2. A fuel control system for a fuel injection type internal combustion engine according to claim 1, wherein said fluid servo motor comprises a pair of movable walls reciprocatingly mounted in said actuator chamber and fixedly supported and spaced away from each other by a connecting rod connectable to said fuel injection quantity controlling element, a first fluid chamber defined between one of said pair of movable walls and one of the inner wall ends of said actuator chamber, a second fluid chamber defined between the other of said pair of movable walls and the other of said inner wall ends of said actuator chamber, a first forward controlling electromagnetic valve provided in a passage connecting said first fluid chamber to said high pressure fluid source and a second reverse controlling electromagnetic valve provided in a passage connecting said first fluid chamber to a low pressure exhaust, and a first reverse controlling electromagnetic valve provided in a passage connecting said second fluid chamber to said high pressure fluid source and a second forward controlling electromagnetic valve provided in a passage connecting said second fluid chamber to said low pressure exhaust, whereby when only said first and second forward controlling electromagnetic valves are opened, said pair of movable walls are moved in the direction which causes said fuel injection quantity controlling element to effect a forward control, whereas when only said first and second reverse controlling electromagnetic valves are opened, said pair of movable walls are moved in the direction opposite to said forward controlling direction.