Electronic Regulator With Fuel Injection Control For Diesel Engines

Abstract

Arrangement for controlling fuel injection. Transducers generate first and second signals indicative of first and second engine operating conditions. Fuel-quantity selector generates electrical quantity signal indicative of the quantity of fuel to be injected per combustion cycle as a predetermined function of said first and second signals. Timer generates electrical timing signal indicative of time of commencement of fuel injection with respect to the combustion cycle as a predetermined function of said first and second electrical signals. Fuel-injection means commences fuel injection at a time with respect to the combustion cycle indicated by said timing signal, and at such time injects an amount of fuel indicated by said quantity signal.

Description

BACKGROUND OF THE INVENTION

The invention relates to a fuel injection regulator for diesel engines, the regulator having an electronic generator for producing an electrical signal indicative of the quantity of fuel to be injected. The fuel injection regulator further has a fuel injection unit timing.

As a rule with diesel engines, the fuel is injected by a high pressure fuel injection pump into the combustion chamber in time with the engine stroke. Since the fuel injection pump is connected to the combustion chamber by lines and spray nozzles, the beginning of the fuel injection does not coincide with the beginning of the compression stroke of the pump, the beginning of the compression stroke being that moment at which a piston of the pump begins to expel fuel. The pressure created by the piston propagates in the form of a pressure wave through the lines to the nozzles, so that there is a delay between the opening of a spray nozzle and the beginning of the compression stroke. This delay, called fuel injection lag, depends, among other factors, on the length of the lines, on the opening pressure to which the nozzles are adjusted, and on the engine rpm.

In practical operation, the influence of the engine rpm is particularly of concern. For example, if within the range of operating rpms, the injection lag is too great, this can interfere with make satisfactory engine operation. In these cases, it is necessary to install a special unit to control, during operation, the moment at which the fuel is injected. With the diesel engines commonly used up to the present time, satisfactory operation can be obtained, as a general rule, if the injection is made rpm dependent. However, with high speed and high output diesel engines, far better operation can be had if the moment at which the injection begins is dependent not only on rpm, but also on the engine load.

SUMMARY OF THE INVENTION

An object of the invention is to provide for diesel engines a fuel injection regulator that precisely adjusts the beginning of the injection in dependence on both the rpm and the load.

A further object of the invention is the regulator of the preceding object, which regulator enables the injection to be made dependent on any desired operating and control parameters, including non-linear parameters, of the engine.

Briefly, the invention consists of transducer means for generating at least first and second electrical signals indicative of respective first and second variable engine operating conditions. Fuel-quantity selecting means generates an electrical quantity signal indicative of the quantity of fuel to be injected per combustion cycle as a predetermined function of said first and second electrical signals. Timing means generates an electrical timing signal indicative of the time of commencement of fuel injection with respect to the combustion cycle as a predetermined function of said first and second electrical signals. Fuel-injection means commences fuel injection at a time with respect to the combustion cycle indicated by said timing signal, and at such time injects an amount of fuel indicated by said quantity signal.

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 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 DRAWINGS

FIG. 1 is a block diagram of the arrangement of the invention;

FIG. 2 graphically shows the relationship of the timing signal to the speed and accelerator signals;

FIG. 3 is a circuit diagram of the timing means;

FIG. 4 schematically shows details of the servo systems shown in FIG. 1; and

FIG. 5 is a circuit diagram of a pulse-width modulator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram of an arrangement according to the invention.

A first transducer 11 generates a first electrical signal Un indicative of engine speed. A second transducer 10 generates a second electrical signal U.alpha. indicative of the position of the (non-illustrated) accelerator pedal.

The first (speed) signal and second (accelerator) signal are applied to the two inputs of fuel-quantity selecting means 12 which generates an electrical quantity signal Uk indicative of the amount of fuel to be injected into a cylinder during the combustion cycle. Selecting means 12 generates the quantity signal Uk as a predetermined, and typically very non-linear function of the first and second signals Un, U.alpha.. A fuel-quantity selecting means of the general type in question is described, for example, in German patent 1,267,905.

The speed signal Un is also applied to one input of timing means 17. The quantity signal Uk is applied to the other input of timing means 17. Timing means 17 generates, as a predetermined function of signals Un and Uk, a timing signal U.sub.NW indicative of the time of commencement of fuel injection with respect to the cylinder combustion cycle. The functional relationship between signals Un, Uk and U.sub.NW will be discussed with respect to FIG. 2.

Quantity signal Uk and timing signal U.sub.NW are command signals which are applied to the fuel-injection means 13-16, 18-20. Fuel-injection means 13-16, 18-20 comprises two distinct servo systems, namely, one servo system 13, 14, 16 and another servo system 18-20. The fuel pump is designated by numeral 15.

Servo system 13, 14, 16 is responsive to fuel-quantity signal Uk. Block 14 represents a movable fuel-quantity setting means and associated hydraulic moving means for moving the setting means. The movable fuel-quantity setting means is known per se, and may for example be the conventional control rod which adjusts the stroke volume of the fuel injector. The hydraulic moving means of the servo system will be explained in more detail below. Feedback transducer 16 generates an electrical signal indicative of the actual setting of the fuel-quantity setting means. The actual setting of the fuel-quantity setting means is designated RW, and the corresponsing electrical feedback signal is designated U.sub.RW. The servo system 13, 14, 16 furthermore includes a comparing means 13 which compares the 9 quantity signal Uk and the feedback signal U.sub.RW and generates an activating signal corresponding to the difference between Uk and U.sub.RW, in accordance with usual servo operation. This activating signal is applied to the servo moving means of block 14.

The other servo system 18-20 is associated with fuel-injection timing. Block 19 represents movable injection-advancing means and means for moving such advancing means. The injection-advancing means is known per se and typically comprises a rotary member rotatable with and also rotatable relative to the camshaft. The time of fuel-injection commencement, during the combustion cycle, is represented in degrees of rotation of the setting means relative to the camshaft; .degree.NW designates the setting of the injection-advancing means, each setting of the injection-advancing means corresponding to a different time of fuel-injection commencement within the combustion cycle.

A feedback transducer 20 generates an electrical signal U.degree..sub.NW indicative of the actual setting of the injection-advancing means. A comparing means 18 compares the command signal U.sub.NW and the feedback signal U.degree..sub.NW and generates at its output an activating signal corresponding to the difference between such signals, in accordance with usual servo operation. This activating signal is applied to the servo moving means of block 19. The servo moving means, in the disclosed embodiment, is hydraulic, and is discussed more fully below.

FIGS. 2a, 2b illustrate the functional relationship between the timing signal U.sub.NW and the speed signal Un and the quantity signal Uk. In FIG. 2a different percentage values of Uk are the parameters for the family of characteristics shown. It will be noticed that the lines corresponding to values of 0 percent, 20 percent, 40 percent, 60 percent for Uk have a first spacing, whereas the curves corresponding to 60 percent, 80 percent, 100 percent have a second spacing; this variation as a function of Uk is explicitly illustrated in FIG. 2b.

FIG. 3 shows the wiring diagram for the timing means 17. Timing means 17 comprises an operational amplifier 25 having two inputs, an inverting input M and a non-inverting input P. The input stage of the operational amplifier is designed as a differential amplifier. The design of the output of the operational amplifier is indicated by a transistor T, connected grounded emitter. The non-inverting input P is connected by a resistor 26 to a grounded line 27 and by a resistor 28 to a positive line 29. The positive line 29 is connected to the positive terminal of a voltage source Ub. The inverting input M is connected by a negative feedback resistor 32 to the output of the operational amplifier and by an input resistor 30 to an input terminal 31. Two series-connected input resistors 34 and 36 connect a second input terminal 33 to the inverting input M. Connected between the junction 35 and the grounded line 27 is a first voltage divider composed of a conductively biased diode 37 and two resistors 38 and 40. Resistors 41 and 42 form a second voltage divider connected between the positive line 29 and the grounded line 27. A conductively biased diode 43 connects together the two junctions 39 and 44. A two-tap voltage divider, consisting of the resistors 44,45, and 46, is connected between the positive line 29 and the grounded line 27. The desired output signal voltage U.sub.NW is obtained at the positive-most second tap 47 of this voltage divider, the first tap 48 being connected to the output of the operational amplifier 25. In accordance with the invention, the voltage divider can have more than three resistors connected in series.

The timing means shown in FIG. 3 operates in the following manner. The voltage divider composed of the resistors 26 and 28 keeps the non-inverting input P at a constant potential. The operational amplifier 25 is controlled solely by the signal at the inverting input M. The operational amplifier is wired as a computer amplifier, the resistor 32 being a negative feedback resistor and the input resistor being the resistor 30 on the diode-resistance network connected to the input terminal 33. The input M controls the operational amplifier from ground potential up. For reasons of safety, the rpm n and the rpm dependent voltage Un are inversely proportional to each other; as the rpm rises, the voltage Un falls. This inverse proportionality makes operation safer, because if a lead should break or if the transducer 11 is faulty, the engine cannot be overdriven, since it appears to the regulator as though the engine is operating at maximum rpm.

In the following explanation, it will be assumed that the signal Uk is constant. As the rpm increases, the signal Un becomes smaller; but because of the reversal in polarity between the input M and the output of the operational amplifier 25, the signal U.sub.NW becomes more positive. The rate of the increase in U.sub.NW with respect to the engine rpm n, is determined by the ratio of the resistor 32 to the resistor 30. There will now be assumed a second engine operating situation in which the engine rpm n is constant and the signal Uk, changes. For reasons of safety, there is also an inverse proportionality between the selected fuel amount and the signal Uk. At no load, the voltage Uk has, therefore, its largest value. Consequently, the diode 37 conducts, because the voltage at the junction 35 is more positive than the voltage at the junction 39. If the selected fuel quantity increases, the voltage Uk falls. So long as the diode 37 conducts, the change in the signal Uk at the junction 35 (and therefore at the inverting input M) is less than if the diode does not conduct, since the junction 35 is connected by the conductive diode 37, resistor 38, and diode 43 to the junction 44 of the voltage divider consisting of resistors 41 and 42. If the signal Uk exceeds the value U.sub.ko --in other words, if the selected fuel quantity is greater than a value corresponding to U.sub.ko -- the diode 37 is cut off; and the change in the signal Uk is conducted by the resistors 34 and 36 in full measure to the inverting input M. When the diode 37 does not conduct, there is no additional loading of the input circuit between the terminal 33 and the input M, the amplification factor of the operational amplifier appears to be higher than when a conductive diode 37 connects a supplementary, grounded, load to the junction 35. This additional load is composed of the resistor 38 connected in series with the parallel resistors 40,41, and 42. As previously explained, the diode 43 is conductive at all times, and serves solely as a temperature compensator.

It is apparent from the diagrams of FIG. 2 that the injection control is active only beginning at a predetermined minimum engine rpm n and that it cannot exceed a maximum engine rpm. These two conditions are fulfilled by the voltage divider consisting of the resistors 44,45, and 46. For example, if the rpm is high, the signal voltage Un is small. Because of the change in polarity between the input M and the output of the operational amplifier 25, the output voltage of the amplifier is large: in other words, the transistor T is non-conductive. When the transistor T is non-conductive, the voltage U.sub.NW at the junction 47 is determined solely by the relative values of the resistors 44,45 and 46. In the other extreme case, in which the rpm is very small and the signal voltage Un is large, the output voltage of the operational amplifier is small because of the reversal in polarity. This means that the transistor T is saturated. This being true, the resistance of the emitter-collector path of the transistor is small, and the resistor 46 is short-circuited by the emitter-collector path of the transistor T. Consequently, the value of the signal voltage U.sub.NW at the junction 47 is, in this case, determined solely by the ratio between the resistors 44 and 45. In this way, electrical limits are provided for the largest and smallest values of the injection control.

FIG. 4 schematically shows the make-up of servo system 13, 14, 16 (FIG. 1) and the similar servo system 18-20 (FIG. 1). A cylinder and piston arrangement 55 is provided with hydraulic fluid through two openings 56 and 57. The unit 55 comprises a cylinder 59 and a piston 60 that is free to move lengthwise in the cylinder. The piston rod 61 on the piston 60 projects out of the cylinder 59, and is connected to the aforementioned movable means--i.e., the movable injection-advancing means 19 in the case of servo system 18-20 or the movable fuel-quantity setting means 14 in the case of servo system 13, 14, 16. The piston 60 divides the cylinder 59 into two pressure chambers 62 and 63, the chamber 62 having an opening 56 and the chamber 63 having an opening 57. The opening 56 is joined by a line 64 to a pressure tank 65; the opening 57 is joined by a line 66 to an electromagnetically operated hydraulic switch means 67-69 which, when a pulse is present on line 74 connects line 66 by way of a line 68 to a source of pressurized fluid 65 or by way of a line 69 to a fluid reservoir 70. The piston rod 61 is connected to a transducer 71 that converts the mechanical movements of the piston rod into a feedback signal which is conducted to a pulse-width modulator 72. The regulator 72 is part of either unit 13 or 18, shown in FIG. 1. Command means 73, which can be either the means 12 or 17, shown in FIG. 1, provides a command signal A lead 74, shown in dashed lines, connects the pulse-width modulator 72 to the solenoid of the electromagnetic valve 67. The transducer 71 corresponds to the transducer 16 or 20, shown in FIG. 1; in FIG. 4 it is shown as an inductive motion pickup.

The unit shown in FIG. 4 operates in the following manner. In its normal position, shown in FIG. 4, the two-way electromagnetic valve 67 connects the chamber 63 of the cylinder 59 to the reservoir 70, by way of the lines 66 and 69. Since the line 64 connects the chamber 62 at all times with the pressure tank 65, the piston 60 is moved to its right-most end position, which, for example, corresponds to the zero position of the control rod of a fuel injection pump. During operation, the electromagnetic valve 67 is switched back and forth by the pulse-width modulator 72 at a predetermined frequency. If the difference between the desired value and the actual value is zero, the modulator 72 provides a PWM pulse train of which the keying ratio is 1:1. Thus, the chamber 63 is alternately connected to the pressure source 65 and to the reservoir 70 for equal lengths of time, the piston 60 oscillating slightly about a position corresponding to the desire value. The amplitude of this oscillation about the desired value, depends upon the frequency of the control signal from the regulator 72. In order to ensure that the positioning force acting on the piston 60 is the same for either direction of piston movement, the right face of the piston must have twice the area of the left face, because the chamber 62 is continuously connected to the pressure source 65. However, the area of the left face is smaller than that of the right face by an amount equal to the cross-sectional area of the piston rod 61. If both chambers are connected to the pressure tank 65, the resulting positioning force acting on the piston is equal to the unit pressure times the cross-sectional area of the piston rod 61. If the chamber 63 is connected to the reservoir 70, only the pressure in the chamber 62 moves the piston 60; and the positioning force is the product of the pressure in the chamber 62 times the area of the left face of the piston.

FIG. 5 shows the wiring diagram of the pulse-width modulator of comparing means 13 (FIG. 1). A similar arrangement is associated with comparing means 18 of the other servo system 18-20. The pulse-width modulator comprises an operational amplifier having an inverting input M and a non-inverting input P. The output of the operational amplifier is connected by a negative feedback resistor 81 to the inverting input M and by a positive feedback resistor 82 to the non-inverting input P. A resistor 83 also connects the output to a positive line 84, which is connected to a voltage source Ub2. An input resistor 85 connects the non-inverting input P to an input terminal 86. A capacitor 87 connects the inverting input M to a grounded line 88. An input resistor 89 connects the inverting input to the emitter of an emitter follower transistor 90. The collector of this transistor is directly connected to the ground line 88, the emitter is connected by the load resistor 91 to the positive line 84, and the base is connected by a parallel-connected capacitor 93 and resistor 92 to the grounded line 88. A conductively biased diode 95 connects the base of the transistor 90 to an input terminal 94. A compensating resistor 97 connects the non-inverting input P to a second positive line 96, which is connected to a source of voltage Ub1. The output of the operational amplifier 80 is connected to a three-stage power amplifier, which, acting as a switch, operates the electromagnetic valve MV. The power amplifier has three transistors 98, 99, and 100. The base of transistor 98 is connected by a resistor 101 to the output of the operational amplifier and by a resistor 102 to the grounded line 88. The emitter of this transistor is connected directly to ground, and a resistor 103 connects the collector to the positive line 84. The collector of transistor 98 is connected to the base of transistor 99. A resistor 104 connects the collector of transistor 99 to the positive line 96, and the emitter of this transistor is directly connected to the base of transistor 100. The transistors 99 and 100 constitute a Darlington stage. The emitter of transistor 100 is directly connected to ground, and the collector is connected by a parallel-connected resistor 105 and capacitor 106 to one end of the solenoid of the electromagnetic valve MV. This valve is the same as the electromagnetic valve 67 in FIG. 4. The other end of the solenoid is connected to the positive line 96. The collector of this transistor is also connected by a series-connected resistor 107 and a non-conductively biased diode 108 to the positive line 96.

The circuit just described operates in the following manner. The signal Uk, which is the desired value, is conducted to the input terminal 86, whereas the signal U.sub.RW or U.degree..sub.NW, which is the actual value, is connected to the input terminal 94. For the moment it will be assumed that the voltages at the two inputs M and P are equal. In explaining the oscillatory action of the circuit, it will also be assumed that the output voltage of the operational amplifier 80 has suddenly changed from approximately +Ub2 to zero. The terminal of the resistor 81 connected to the output amplifier 80 consequently is approximately at ground potential, permitting the capacitor 87 to discharge through the resistor 81. As a consequence of this discharge, the voltage at the inverting input M falls. As soon as the voltage at the input M is smaller than the voltage at the input P, there is a difference in voltage between these two inputs, which difference in voltage drives the amplifier to its positive end state. Because of the positive feedback, the amplifier is very quickly switched to its other state. A part of the voltage jump appearing at the output of the amplifier 80 is coupled by the positive feedback resistor 82 to the non-inverting input P, causing the voltage at this input to undergo a small positive voltage jump. At the same time, the capacitor 87, being connected by the resistor 81 to the positive line 84, can charge. As soon as the capacitor 87 has sufficiently charged so that the voltage at the input M exceeds that of the input P, the voltage difference between the two inputs is such that the operational amplifier is switched to its other end state. The capacitor 87 is now again free to discharge through the resistor 81, and the voltage jump caused by the sudden switching from one state to the other is conducted by the positive feedback resistor 82 to the non-inverting input P, so that there appears a negative voltage jump on this input. Immediately after the amplifier has been switched back to its original state, the voltage at the input P is below the voltage at the input M; and the operational amplifier can only switch again when the capacitor 87 has sufficiently discharged through the resistor 81 that the voltage at the inverting input M falls below that at the non-inverting input P. The frequency at which the operational amplifier 80 oscillates depends both on the time constant of the RC network constituted by the capacitor 87 and the resistor 81, and on the size of the voltage jump conducted by the resistor 82 to the non-inverting input P when the amplifier switches from one state to the other. If the inputs M and P are under no external voltages, the voltage jumps at the input P are equal irrespective of whether the amplifier output is changing from ground potential to +Ub2 or from +Ub2 to ground potential. In this way, there is obtained a keying ratio of 1:1. If, for example, the desired value (Uk) is more positive, the discharge of the capacitor 87 takes longer and the charging is shortened. The electromagnetic valve MV is consequently energized for a longer time and de-energized for a shorter time, so that the piston 60 can be positioned until the voltage difference between the desired value and the actual value is again zero.

If the signal U.sub.RW should fail, the inverting input M assumes the voltage of the positive source Ub2, the electromagnetic valve MV is consequently de-energized (the transistor 100 being cut off), and the fuel pump controlling members return to their zero position.

Since the energization period of an electromagnetic valve depends not only on the shape of the pulse delivered to its solenoid, but also on the value of the voltage to which the solenoid is connected, the keying ratio will vary with a change in the battery voltage. If the voltage Ub1 is derived from a vehicle battery any change in the battery voltage will be conducted by the compensating resistor 97 to the input P. Consequently, the influence of the battery voltage on the keying ratio is compensated. The capacitor 93 influences the change with respect to time of the signal U.sub.RW at the base of the transistor 90. The dynamic characteristics of the control loop can be altered by the value of the capacitor 93.

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

While the invention has been illustrated and described as embodied in an electronic regulator with fuel injection control for diesel engines, it is not intended to be limited to the details shown, since various modifications and circuit changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

Claims

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

1. An arrangement for controlling the injection of fuel into at least one cylinder of an internal combustion engine comprising, in combination, transducer means having first and second transducer outputs and operative for generating at said outputs respective first and second electrical signals indicative of respective first and second variable engine operating conditions; fuel-quantity selecting means having first and second inputs respectively connected to said first and second transducer outputs and having a selecting means output, and operative for generating an electrical quantity signal whose magnitude depends upon said first and second signals in a predetermined manner and whose magnitude is indicative of the quantity of fuel to be injected per combustion cycle; timing means having one input connected to said first transducer output, another input connected to said selecting means output, and a timing means output, and operative for generating an electrical timing signal whose magnitude depends upon said first signal and said quantity signal in a predetermined manner and whose magnitude is indicative of the time during the combustion cycle at which the injection of fuel is to commence; and fuel-injection means having inputs respectively connected to said selecting means output and to said timing means output and being responsive to the magnitude of said electrical quantity signal and to the magnitude of said electrical timing signal and being operative for commencing fuel injection at the time indicated by the magnitude of said timing signal, and for at such time injecting the amount of fuel indicated by the magnitude of said quantity signal.

2. An arrangement for controlling fuel injection into at least one cylinder of an internal combustion engine, comprising in combination transducer means for generating at least first and second electrical signals indicative of respective first and second variable engine operating conditions; fuel-quantity selecting means for generating an electrical quantity signal indicative of the quantity of fuel to be injected per combustion cycle as a predetermined function of said first and second electrical signals; timing means for generating an electrical timing signal indicative of the timing of commencement of fuel injection with respect to the combustion cycle as a predetermined function of said first and second electrical signals; and fuel-injection means for commencing fuel injection at a time with respect to the combustion cycle indicated by said timing signal, and for at such time injecting an amount of fuel indicated by said quantity signal, wherein said first variable operating condition is engine speed, and wherein said transducer means has first and second transducer outputs at which said first and second signals are respectively generated, and wherein said fuel-quantity selecting means has a selecting means output at which said quantity signal is generated, and wherein said timing means comprises an operational amplifier circuit including an operational amplifier having an output connected to said fuel-injection means and an input connected to said first transducer output, and diode-resistor network means connected to said input to said amplifier and to said selecting means output and operative for establishing a non-linear relationship between said quantity signal and the signal at said input of said operational amplifier.

3. An arrangement for controlling the fuel injection into at least one cylinder of an internal combustion engine comprising, in combination, transducer means for generating at least first and second electrical signal indicative of respective first and second variable engine operating conditions; fuel-quantity selecting means for generating an electrical quantity signal whose magnitude depends upon said first and second signals in a predetermined manner and whose magnitude is indicative of the quantity of fuel to be injected per combustion cycle; timing means for generating an electrical timing signal whose magnitude depends upon said first and second signals in a predetermined manner and whose magnitude is indicative of the time during the combustion cycle at which the injection of fuel is to commence; and fuel-injection means connected to said fuel-quantity selecting means and to said timing means and responsive to the magnitude of said electrical quantity signal and to the magnitude of said electrical timing signal and operative for commencing fuel injection at the time indicated by the magnitude of said timing signal, and for at such time injecting the amount of fuel indicated by the magnitude of said quantity signal, wherein said fuel-injection means includes movable injection-advancing means movable to a plurality of settings corresponding to respective advanced and retarded fuel-injection commencement times, and a servo system for automatically moving said injection-advancing means to a position corresponding to an injection commencement time indicated by said timing signal, and wherein said fuel-injection means further includes movable fuel-quantity setting means movable to a plurality of settings corresponding to respective quantities of fuel, and another servo system for automatically moving said fuel-quantity selecting means to a position corresponding to a quantity of fuel indicated by said quantity signal, and wherein said quantity signal and said timing signal constitute command signals, and wherein at least one of said servo systems comprises moving means for moving the respective one of said movable means, feedback transducer means for generating an electrical feedback signal corresponding to the actual setting of said movable means, and means for pulse-width-modulating the difference between the respective one of said command signals and said feedback signal and applying the pulse-width-modulated difference signal to said moving means to cause the latter to effect movement of said movable means in one direction contemporaneously with the duration of width-modulated pulses and in the opposite direction during the time intervals between such width-modulated pulses.

4. An arrangement as defined in claim 1, wherein said fuel-injection means includes movable injection-advancing means movable to a plurality of settings corresponding to respective advanced and retarded fuel-injection commencement times, and a servo system for automatically moving said injection-advancing means to a position corresponding to an injection commencement time indicated by said timing signal.

5. An arrangement as defined in claim 4, wherein said fuel-injection means further includes movable fuel-quantity setting means movable to a plurality of settings corresponding to respective quantities of fuel, and another servo system for automatically moving said fuel-quantity setting means to a position corresponding to a quantity of fuel indicated by said quantity signal.

6. An arrangement as defined in claim 2, wherein said operational amplifier circuit further includes a pair of voltage supply lines for connection to a source of biasing voltage, an input resistor connected between said first transducer output and said operational amplifier input, and a pair of series-connected input resistors connected between said operational amplifier input and said selecting means output, a first voltage divider connected between one of said supply lines and the junction between said series-connected input resistors and including a diode and a pair of series-connected first voltage-divider resistors, a second voltage divider connected across said supply lines, and a diode connected between the tap of said second voltage divider and the junction between said first voltage-divider resistors.

7. An arrangement as defined in claim 2, wherein said operational amplifier has an output circuit comprising the output circuit of a transistor, a two-tap voltage divider connected across said supply lines and having a first tap connected to the output of said operational amplifier and another tap constituting the output of said operational amplifier circuit, and wherein said first signal varies inversely to engine speed, and wherein said quantity signal varies inversely to the quantity of fuel to be injected.

8. An arrangement as defined in claim 3, wherein said moving means comprises hydraulic moving means.

9. An arrangement as defined in claim 8, wherein said hydraulic moving means comprises a cylinder, a piston movable in said cylinder and dividing said cylinder into two chambers, a source of pressurized fluid, a fluid reservoir, a fluid conduit connecting said source of fluid to one of said chambers, and electromagnetically operated hydraulic switch means for alternatively connecting the other of said chambers to said source of fluid and to said fluid reservoir.

10. An arrangement as defined in claim 3, wherein the keying ratio of said pulse-width-modulated signal is 1:1 when said difference is null.

11. An arrangement as defined in claim 3, wherein said pulse-width-modulating means comprises a differential-input operational amplifier having a first input arranged to receive one of said command signals and a second input arranged to receive said feedback signal, a feedback resistor connecting said output to said first input, another feedback resistor connecting said output to said second input, supply lines for connection to a source of biasing voltage, and a capacitor connected between said second input and one of said supply lines.

12. An arrangement as defined in claim 11, wherein said modulating means further includes emitter-follower means for receiving said feedback signal and applying the same to said second input.

13. An arrangement as defined in claim 11, wherein said modulating means includes a magnetic relay connected across said supply lines and directly connected to one of said supply lines, and a compensating resistor connected between said first input of said operational amplifier and said one of said supply lines.

14. An arrangement as defined in claim 12, wherein said pulse-width-modulating means further includes fail-safe means for effecting movement by said servo system of said movable means to the null position of said movable means in response to loss of said feedback signal.

15. An arrangement as defined in claim 11, wherein said pulse-width-modulating means further includes time-delay means connected to said second input of said amplifier and operative for introducing a time delay in the application of said feedback signal to said second input.

16. An arrangement as defined in claim 11, wherein said time-delay means comprises an emitter-follower transistor connected to said input and operative for applying thereto said feedback signal, and a capacitor connected between the base of said emitter-follower transistor and one of said supply lines.

17. An arrangement as defined in claim 1, wherein said first variable engine operating condition is engine speed, and wherein said variable engine condition is the setting of an operator-activated control.

18. An arrangement as defined in claim 17, wherein said second engine operating condition is the setting of the engine accelerator.

19. An arrangement as defined in claim 1, wherein said fuel-injection means includes movable injection-advancing means movable to a plurality of settings corresponding to respective advanced and retarded fuel-injection commencement times, and a sero system for automatically moving said injection-advancing means to a position corresponding to an injection commencement time indicated by said timing signal.

20. An arrangement as defined in claim 19, wherein said fuel-injection means further includes movable fuel-quantity setting means movable to a plurality of settings corresponding to respective quantities of fuel, and another servo system for automatically moving said fuel-quantity setting means to a setting corresponding to a quantity of fuel indicated by said quantity signal.

21. An arrangement as defined in claim 20, wherein said first variable engine operating condition is engine speed, and wherein said second variable engine operating condition is the setting of an operator-activated control.

22. An arrangement as defined in claim 21, wherein said second engine operating condition is the setting of an operator-activated accelerator.