US3699935A

US3699935A - Fail-safe fuel injection control arrangement for internal combustion engines

Info

Publication number: US3699935A
Application number: US97271A
Authority: US
Inventors: Karl-Heinz Adler; Johannes Locher; Rudolf Lemanczyk; Edgar Schonart
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1969-12-13
Filing date: 1970-12-11
Publication date: 1972-10-24
Anticipated expiration: 1989-10-24
Also published as: GB1338096A; DE1962570A1; CH518445A; DE1962570B2; SE355639B; DE1962570C3; FR2073654A5

Abstract

An electrically controlled control element determines fuel injection per operating cycle. The control circuit determining position of control element receives signals indicating gas pedal position, engine speed, and feedback signal indicating control element position. Each of these signals varies with corresponding parameter in such a manner that interruption of the signal causes minimum fuel injection. Additional limiting circuits within control system also designed to cause minimum fuel injection during circuit failure.

Description

United States Patent Adler et al. 1 Oct. 24, 1972 s41 FAIL-SAFE FUEL INJECTION 3,425,401 2/1969 Lang ..123/ 102 CONTROL ARRANGEMENT FOR 3,517,260 6/1970 Oishi ..123/102 INTERNAL COMBUSTION ENGINES [72] Inventors: Karl-Heinz Adler, Leonberg; Johannes Locher, Stuttgart; Rudolf Lemanczyk, Stuttgart; Edgar Schonart, Stuttgart, all of Germany [73] Assignee: Robert Bosch GmbI-I, Stuttgart, Germany [22] Filed: Dec. 11, 1970 [21] Appl. No.: 97,271

[30] Foreign Application Priority Data Dec. 13, 1969 Germany ..P 19 62 570.8

[52] US. Cl ..123/102, 123/32 EA, 123/139 E [S 1] Int. Cl ..F02d 11/10 [58] Field of Search ..123/102, 140, 139 E [56] References Cited UNITED STATES PATENTS 3,407,793 10/1968 Lang ..123/102 Primary Examiner-Laurence M. Goodridge Attorney-Michael S. Striker [5 7] ABSTRACT An electrically controlled control element determines fuel injection per operating cycle. The control circuit determining position of control element receives signals indicating gas pedal position, engine speed, and feedback signal indicating control element position. Each of these signals varies with corresponding parameter in such a manner that interruption of the signal causes minimum fuel injection. Additional limiting circuits within control system also designed to cause minimum fuel injection during circuit failure.

34 Claims, 7 Drawing Figures genera/0r PATENTEDHBI 24 I9 2 3 699.935

SHEU 1 0F 3 excess speed v prevenh'on stage 6 7confrol rod acfivafor control I L 4 21 amplifier 23 rod pos/ffon sensor 5 l 3 Y m 0c 12 ggggg 22 am ml-er J1 r 1speed 2/ sensor com/er er 4characfer/sf/c curve generator conro/ ele men? csmon max \NVENTORS Karl-Heinz ADLER Johannes LOCHER Rudolf LEMANCZYK Edgar SCHONAPT By A d/ 9 71 thmr AT TOR N EY PATENTED I97? 3.699.935

sum 3 [1F 3 FIGS INVENTORS Karl-Heinz ADLER Johannes LOCHER Rudolf LEMANCZYK Edgar SCHOHA theirATTORNEY FAIL-SAFE FUEL INJECTION CONTROL ARRANGEMENT FOR INTERNAL COMBUSTION ENGINES BACKGROUND OF THE INVENTION This invention relates to a control circuit for controlling the movement of the control element determining the quantity of fuel injected during each operating cycle of an internal combustion engine, and more particularly, of a Diesel engine. The amount of fuel to be injected per operating cycle varies in dependence on operating parameters of the engine, as for example the position of the accelerator or gas pedal, the speed of the motor, and possibly other parameters. In the type of system under discussion, the position of the fuel control element relative to a null position wherein a predetermined minimum quantity of fuel is injected, varies in dependence on a fuel control signal. A preferred type of control circuit comprises a high-gain D.C. amplifier which responds to signals derived from sensors sensing the above-mentioned operating parameters.

It is known that in optimum regulation of the injection pump may be achieved by varying the amount of fuel injection during each operating cycle corresponding both to the engine speed and to the position of the gas pedal in accordance with the characteristic curves of the particular motor. The particular characteristic curves, as for examples curves of fuel injection plotted versus speed may be simulated by means of a high-gain D.C. amplifier used as an operational amplifier and furnishing the proper control voltage for controlling the movement of the control element and thereby the fuel supply. In particular, the extreme values of these curves are important since they are very different for different Diesel motors and must be matched exactly to a particular motor. For example, the maximum permissible engine speed must not be exceeded and, for each particular engine speed, a maximum permissible fuel injection must also not be exceeded. Furthermore, if the motor is not overloaded, a predetermined minimum speed must be maintained in order to prevent a stopping of the motor. It is obvious that a large number of electronic building blocks, sensors, and a control element are required which may not be sufficiently protected from extremely difficult operating conditions especially if the system is used in a commercial vehicle. Therefore, interruptions of the circuit can occur, and in particular, interruptions of the signals supplied by the sensing means. Such interruptions may lead to excessively high fuel injection in conventional systems, thereby causing damage to the motor if it is driven to excessively high speeds. Further, of course, such operating conditions constitute a safety hazard.

SUMMARY OF THE INVENTION It is an object of the present invention to devise a regulating system which, at the least, greatly decreases the above-mentioned risk in safety and in motor damage. It is desired that the system be so constructed that interruption in any of the sensed signals and possible circuit interruptions within the control system cause a minimum and not a maximum fuel injection.

The sensing means which are particularly vulnerable in the type of control system under discussion here are the sensing means which sense the position of the accelerator, that is the gas pedal in a commercial vehicle.

Therefore, in accordance with this invention, a clamping circuit is provided which furnishes a signal corresponding to a null position of the accelerator in the absence of such an accelerator signal. Further, the maximum accelerator signal is also electrically limited by the clamping circuit, thereby making an exact adjustment of the mechanical movement of the gas pedal unnecessary since the limiting values are determined electrically.

In conventional systems, the gain of the DC. amplifier, when used as an operational amplifier, is changed by changing the efiective feedback resistance, that is, by adding further resistances in parallel with said feedback resistance. Such a decrease in feedback resistance results in a smaller amplification. Thus, if this parallel switching of additional resistances is interrupted, a high amplification results. This is avoided in a preferred embodiment of the invention, wherein the gain of the amplifier stage is changed by switching resistances at the input of the DC. amplifier in order to change the gain thereof.

In conventional systems, the speed voltage indicating by its amplitude the engine speed is made to vary proportionally to said engine speed. If now this signal is interrupted, the control circuit tends to increase the speed. Since does not result in a corresponding increase in the speed signal, the fuel supply is increased further and further. Thus, in accordance with a further embodiment of the present invention, the DC. voltage indicating engine speed has an amplitude which varies inversely with engine speed. Therefore, an interruption of this signal indicates maximum engine speed to the control system causing a decrease in fuel supply.

ln order to provide a stable control circuit, conventional systems furnish a sensor which is responsive to the position of the control element regulating the fuel injection and furnishes a signal corresponding to said position and therefore to the actual amount of fuel being injected to a control amplifier. The control amplifier further has an input receiving the output of the high-gain D.C. amplifier which corresponds to the characteristic curves of the engine. This control amplifier then furnishes sufficient current, possibly via a power amplification stage, to activate the activating means moving the control element or control rod. In the conventional arrangement, the feedback signal or voltage is small when the control element is in a null position causing minimum fuel injection and increases with increasing fuel injection. if this control circuit is broken, an increase in injected fuel to the motor results. In accordance with the present invention, this effect is avoided by making the feed-back voltage inversely proportional to the position of the control element.

In order to minimize the amount of equipment required for constructing the overall system, the system is so operated that a large amplitude voltage derived from the DC. amplifier causes minimum fuel injection, while a small D.C. amplifier voltage results in maximum fuel injection.

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 accompany drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a block diagram showing a control arrangement in accordance with the present invention;

FIG. 2 shows the characteristic curves of the engine, namely position of control element versus engine speed at different gas pedal positions;

FIG. 3 shows the fuel control signal as a function of motor speed for different positions of the gas pedal;

FIG. 4 shows the sensing means producing a speed signal in dependence on motor speed;

FIGS. 5a and 5b show pulse sequences generated in the circuit of FIG. 4; and

FIG. 6 is a circuit diagram of the input, output and feedback circuits of the DC amplifier.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the present invention will now be discussed with reference to the drawing.

FIG. I shows a system of the present invention in block diagram form. Shown on the left are various sensors, and on the right the activating means which activate the control element which in turn controls the fuel injection. Thus it is seen that the speed of the motor depends on the circuit which comprises a sensor 1, which is responsive to engine speed, and whose output is converted in a stage 2 to a speed voltage U which varies inversely with motor speed. The signal U. is fed to a characteristic curve simulating circuit 4 which comprises a DC. amplifier 3. The fuel control signal U, is furnished at the output of circuit 4 and is amplified in a control amplifier 5. It is applied to the control element activating means 7 via a stage 6 which contains a circuit preventing excessively high speeds. The activating means 7 in turn activate a control rod 8. As is well known, the position of the control rod 8 causes more or less fuel to be injected via the injection pump of the motor per operating cycle of said motor, thereby causing the motor to be operated at a corresponding speed depending upon motor load.

The position of the control rod is substantially proportional to the amount of fuel injected per operating cycle. In the null position of the rod (point zero, FIG. 2), a predetermined minimum fuel quantity is fed to the motor. In the extreme position 10, an excess amount of fuel is supplied which is required during the starting operation. When a predetermined minimum speed, corresponding to point 11 of FIG. 2, has been reaChed, the control system in accordance with FIG. 1 takes over to determine the amount of fuel injected. It is seen that for any gas pedal position at) through (14, the position of the control element, and thereby the quantity of fuel injected, can be determined for each engine speed.

In the null position of gas pedal 12, even a small load will result in a low-speed characteristic as shown in line 13 of FIG. 2. Under normal operating conditions, the fuel supply for different positions of the accelerator pedal is increased for speeds below the maximum noload speed 14 in order to prevent further speed decreases, while upon reaching a relatively high speed 15, the fuel supply is drastically reduced. In the intermediate region 16, the fuel supply during increasing speeds is decreased only to such an extent that a constant position of the gas pedal and constant load, do not result in an increase in motor speed, that is, the motor speed is kept substantially constant. The maximum fuel injected is limited by line 17 which corresponds to the so-called smoke boundary of the motor, namely that point wherein unburnt fuel will be found in the exhaust of the engine. At low speeds, it is generally sufficient that the control rod not exceed a particular end position as shown at point 19 of FIG. 2, while at higher speeds it is often required to effect a further decrease in the maximum permissible fuel supply in accordance with curve 20. A second signal to be supplied to the characteristic curve generating circuit is a sensed signal corresponding to the position of the gas pedal. This is supplied by sensor 12 which does not contain movable contacts, but comprises an inductive sensor to which is supplied an alternating voltage of constant amplitude and frequency from an oscillator 21. The acceleration signal corresponding to the accelerator position is limited to extreme values for a null and maximum position independent of the mechanical movement limits of the pedal by a clamping circuit 22. For this stabilization of the main regulating circuit, shown in FIG. 1 by heavy lines, it is generally necessary to provide an auxiliary regulating circuit with feedback control. This circuit comprises a sensor for sensing the control rod position. This is labeled 23 in FIG. I and may be mechanically connected to the control rod. Sensor 23 furnishes a feedback signal or voltage which depends on control element position to an input of control amplifier 5. Sensor 23 may be constructed similarly to gas pedal sensor 12 and may also receive a stable alternating voltage from oscillator 21.

All sensors are so constructed that the inputs to circuit 4 are such that an interruption in any of the sensing circuits will cause a decrease in fuel supply rather than an increase. The characteristic curve generating circuit 4 of FIG. 1 is further so constructed that its output voltage U,,, the fuel control voltage, varies substantially inversely proportionally to control rod position relative to the null position.

The sensed voltage corresponding to the position of gas pedal 12 has a low value when the gas pedal is in the null position. This causes a high output at the output of stage 4, thereby causing the control rod to return to the null position at intermediate or high speeds. If the acceleration signal is absent because of a malfunction, a fuel control signal is generated which corresponds to a null position of gas pedal 12.

FIG. 4 shows the speed sensing means which furnish a speed voltage corresponding to engine speed. It is seen that inductive speed sensor means 24 furnish a pulse sequence whose frequency is proportional to engine speed. This pulse sequence is applied via a capacitor 25 to a Schmitt trigger 26, which furnishes trigger pulses having the required low rise times to trigger a monostable multivibrator 27. Of course the trigger pulses for monostable multivibrator 27 have the same frequency as the pulses in the pulse sequence. The multivibrator furnishes a pulse sequence at a first output terminal whose frequency also corresponds to engine speed and whose pulses have a constant pulse width and amplitude. However, for generating the speed signal, the second output of the multivibrator is utilized wherein pulses of constant amplitude and constant interpulse interval are furnished. At low speeds, as shown in H0. 5a, broad pulses result, while at higher speeds (FIG. 5b), the pulse width decreases. The filter 31 is connected to the output 29 furnishing the pulse sequence as shown in FIGS. 50 and 5b. This filter derives the average value 32 from the signals, which average value is roughly proportional to the inverse of the engine speed. This D.C. value 32 possibly further amplified via amplifier 33 yields the desired speed voltage U which varies inversely proportionally with engine speed.

FIG. 6 shows one embodiment for a stage 4 fumishing the characteristic motor curves. This circuit furnishes a fuel control signal U,, in response to the speed signal U and the acceleration signal U FIG. 6 shows a DC. amplifier 35 which is used as an operational amplifier and may comprise integrated circuits. The operational amplifier is supplied the voltage U via an input resistance 36. As is well known, the gain of the DC. amplifier varies as a function of feedback resistance 37 and input resistance 36 in accordance with the following relationship:

The voltage U is supplied at a terminal 38. Further connected to terminal 38 is one end terminal each of a

voltage divider

39 and 40, each of which comprises two resistances. The other terminal of voltage divider 40 is connected to the positive supply terminal 41, while the other end of voltage divider 39 is connected to ground. Voltage divider tap 42 of second voltage divider 39 is connected to the cathode of a diode 43 whose anode is connected to the input of DC amplifier 35 via a resistance 44 and a diode of opposite polarity, 45. The first voltage divider tap, 47, is connected to the input of DC amplifier 35 via a temperature compensating diode 48, a resistance 49, and a diode 50 whose polarity is opposite to that of diode 48.

Diodes

48 and 50 are connected with opposite polarity to the corresponding

diodes

43 and 45.

Diodes

43 and 48 are respectively connected to a

resistance

52 and 51 each of these resistances furnishing a voltage biasing these diodes in the forward direction. Thus resistance 51 is connected between the anode of diode 43 and the positive terminal 41, while resistance 52 is connected between the cathode of diode 48 and ground.

Diodes

43 and 48 respectively serve to compensate for the temperature changes in

diodes

45 and 50. The latter are switched between conductive and non-conductive states in ac cordance with the speed voltage U At low engine speeds, U assumes a high positive value, causing diode 45 to become conductive. This in turn causes two low resistance resistors, namely resistor 44 and the upper portion of voltage divider 39 to be connected in parallel with input resistor 36. This results in higher am-plification (gain) of DC. amplifier 35. The gain corresponds to the slope of to lines 54 in FIG. 3. At a predetermined engine speed n FlG. 3, the voltage U has decreased sufficiently to cause diode 45 to block, so that only input resistance 36 remains efiective at the input of the DC. amplifier. If resistance 55, the lower part of voltage divider 39, is a variable resistance, the speed n may be adjusted to correspond to the most favorable speed of the particular motor being used.

For a relatively large range of engine speed (n, through n resistance 36 only is effective. This resistance is so chosen that, for increasing speed, the quantity of fuel injected per cycle is decreased suffciently that for the same load in the same position of the gas pedal, no increase in speed results.

Starting with a very high engine speed n,, the voltage U has decreased sufficiently that diode 50 is switched to the conductive stage causing resistance 49 and resistor 56 to be inserted in parallel with input resistance 36. This again causes an increase of amplification of amplifier 35 which, for any increase in motor speed, causes a very rapid decrease of fuel injection to a predetermined minimum fuel injection, thereby preventing a further increase of engine speed. Resistor 56 should also be a variable resistor so that the speed n may be adjusted for the particular motor being used.

in addition to the speed signal U the acceleration signal U indicating the position a of the gas pedal, is also furnished to the control circuit. The voltage furnished by an inductive sensor is applied to a diode whose cathode is connected to ground via a capacitor 71. A discharge resistance 72 is connected in paral lel with capacitor 71. The voltage across capacitor 71 is small for a null position a, of gas pedal 12 and is high in the end position of the gas pedal. This voltage is applied to the base of an npn transistor 73 whose collector is connected to the positive voltage terminal 41 and whose emitter is connected to the tap of voltage divider means comprising a resistance 74 connected to terminal 41 and a resistance 75 connected to ground. The tap, or common point of

resistances

74 and 75, is connected to the base of a pnp transistor 76 whose collector is connected to ground and whose emitter is connected to terminal 41 via a resistance 77. The emitter is further connected to ground via a resistance 78,

resistances

77 and 78 therefore forming second voltage divider means whose tap is the common point of

resistances

77 and 78. The emitter of transistor 76 is further connected to an additional voltage divider 67, connected between said emitter and ground. The tap of the additional voltage divider 77 is connected to the input of DC. amplifier 35.

The components of

voltage dividers

74,75 and 77,78 are such that transistor 73 becomes conductive only after a predetermined small acceleration signal has been exceeded, while, for a predetermined maximum acceleration signal, transistor 76 blocks. Thus, while transistor 73 is blocked for low acceleration signals, the voltage appearing at the tap of the voltage

divider having resistors

74 and 75 is used as a lower limiting value, while, for high acceleration signals, transistor 76 is blocked and the limiting value is determined by the voltage at the tap of the second voltage divider means, namely at the common point of

resistors

76 and 77. Thus, the action of a circuit is made independent of the mechanical movement of the gas pedal at its extreme values.

Although the positioning of the control rod for minimum fuel supply can be assured by furnishing an excess voltage U (line 58, FIG. 3), the lower value 59 which controls the maximum fuel injection must be determined very accurately in order to prevent unburned fuel from reaching the exhaust. This is accomplished by a voltage divider comprising resistors 60 and 61, which constitute output voltage divider means. The

7 common point of resistors 60 and 61 is connected to the output terminal 63 of the DC. amplifier 35 via a diode 62, whose cathode is connected to terminal 66 which is the common point of the output voltage divider means. Terminal 63 is further connected to the positive supply terminal 41 via a load resistance 64.

If the voltage at output 63 decreases because of increased current flow through load resistance 64, until it becomes less than the voltage appearing at terminal 66 via the output voltage divider means, then the latter voltage becomes effective since the output diode 62 blocks. The voltage at terminal 66 is the value 65 indicated in FIG. 3 under these conditions. In order that the value 65 be accurately maintained, independent of variations in supply voltage and temperature, it is desirable that the voltage at terminal 41 be supplied from a stabilized supply which is connected to line and maintains the supply voltage constant in spite of line voltage variations and temperature variations.

As shown in FIG. 2, the upper limit of fuel injection must be further decreased at high speeds so that the limit 59 must be decreased for optimum operation. This shaping of the maximum fuel injection line at higher speeds, is accomplished by switching a further variable resistance 80 in parallel to the adjustable resistance 60 of the output voltage divider means. This resistance 80 has one terminal connected to terminal 41 and is connected to terminal 66 via the anodecathode circuit of a diode 81. The anode of diode 81 is further connected via a diode 82 to the collector of a transistor 83. The anode of diode 82 is connected to the anode of diode 81. The emitter of transistor 83 is connected to ground via a resistance 84. The base of transistor 83 is connected to the voltage divider tap of a voltage divider 86 which is connected between terminal 38, where the speed voltage is furnished, and ground. Connected between the base of transistor 83 and the tap of voltage divider 86 is a diode 85 which serves as temperature compensation for the transistor characteristics and whose anode is connected to the base of transistor 83. An adjustable feedback resistance 87 is connected between the collector and base of transistor 83, while collector of transistor 83 is further connected to terminal 41 via a load resistance 88.

For high speed voltages U that is for low engine speeds, transistor 83 is conductive and the voltage drop across load resistance 88 sufficiently large to block diode 81. Therefore, the divider ratio of output voltage divider is unaffected. However, if voltage U decreases for higher speeds, a smaller current flows through transistor 83 and diode 81 becomes conductive, causing resistance 80 to be connected in parallel to resistance 60. Resistance 80 is adjusted to yield the desired limiting value 89, while the value of feedback resistance 87 determines the slope of section 90. It should be noted that malfunction in this stage also results in a decrease of the injected fuel. As shown in FIG. 1, fuel control signal U is applied, via control amplifier 5, to an excess speed prevention stage 6. The latter stage, for sufiiciently high values of speed voltage U (that is for speeds urider a predetermined maximum n furnishes a control current to the control element thereby counteracting, for example, the force of a spring. This causes control rod 8 to be moved to a position, which in turn is monitored by sensor 23. Sen

sor 23 delivers a high-feedback voltage when the control rod is in a null position (zero fuel injection), while for a maximum fuel injection a low feedback voltage is furnished. If this circuit is broken causing a zero voltage to be fed back to control amplifier 5, this simulates a control element in a position furnishing maximum fuel injection, thereby causing a movement of the control element towards the null position.

During the starting of the motor, the voltage U derived from stage 4 may be temporarily short-circuited until such time as the minimum predetermined starting speed 1 1 has been reached.

Malfunction in activating means 7 or control rod 8, as for example the breaking of the spring or sticking of control rod 8, allows the possibility that no movement to the null position results and that the motor exceeds the maximum permissible speed. ln order to prevent this, an additional speed control arrangement, separate from activating means 7 and control rod 8, may be provided to block the supply of fuel as soon as a maximum permissible speed has been exceeded. This additional arrangement can have a further additional control stage, or may be controlled by the excess speed prevention stage 6 shown in H6. l.*( *The circuit furnishing the voltage UGP which means the electrical signal for the position a of the gas pedal; the excessive speed prevention stage 6 of F 16. l; the activating means controlelement connections both mecanical and electrical; and the sensor 23 which furnishes a signal corresponding to the control rod position are fully described in the U.S. Pat. No. 3,407,793.)

While the invention has been illustrated and described as embodied in particular clamping and input circuit arrangements, 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 stand-point of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

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

1. ln an internal combustion engine, a fail-safe fuel injection control arrangement, for furnishing a predetermined minimum fuel injection upon failure of system components, comprising, in combination, injection means having an electrically activated control element controlling by its position along a predetennined path the quantity of fuel injected per operating cycle of said engine, said control element having a null position causing said predetermined minimum fuel injection; activating means moving said control element along said predetermined path in correspondence to fuel control signals, said activating means moving said Control element to said null position in response to a predetermined fuel control signal; a plurality of sensing means, each furnishing a sensed signal corresponding to a predetermined operating parameter of said engine; voltage supply means furnishing a supply voltage, and

electrical control circuit means energized by said voltage supply means, having inputs connected to said sensing means, and a control output connected to said activating means for furnishing said fuel control signals in response to said sensed signals, said electrical control circuit means and said sensing means cooperating in such a manner that failure in one of said sensing means resulting in absence of one of said sensed signals causes the furnishing of said predetermined fuel control signal at said control output, thereby causing minimum fuel injection.

2. An arrangement as set forth in claim 1, wherein said electrical control circuit means further furnish said predetermined fuel control signal in the absence of said supply voltage.

3. An arrangement as set forth in claim 2, wherein said electrical control circuit means comprises first circuit means having inputs connected to said sensing means and furnishing an output signal at a first circuit output as a function of said sensed signals and in accordance with the characteristic curves of said engine; control amplifier means having a reference input connected to said first circuit output and a control output connected to said activating means.

4. An arrangement as set forth in claim 3, further comprising control element position sensing means furnishing a feedback signal corresponding to said position of said control element; and wherein said control amplifier means further comprises a feedback input connected to said control element position sensing means, whereby said control amplifier furnishes said fuel control signal as a function of the difference between said feedback signal and said reference input.

5. An arrangement as set forth in claim 4, wherein said first circuit means comprise high-gain D.C. amplifier means.

6. An arrangement as set forth in claim 5, wherein said feedback signal has an amplitude varying inversely with the position of said control element away from said null position.

7. An arrangement as set forth in claim 6, wherein said feedback signal is a feedback voltage having a predetermined maximum amplitude when said fuel control element is in said null position and a predetermined minimum amplitude when said fuel control element is in the position causing maximum injection.

8. An arrangement as set forth in claim 2, wherein said sensing means comprise speed sensing means furnishing a speed voltage varying inversely with the speed of said engine.

9. An arrangement as set forth in claim 8, wherein said speed sensing means comprise inductive speed sensor means furnishing a predetermined number of pulses per engine rotation; and speed converter means connected to said inductive speed sensor means and furnishing a D.C. speed voltage having an amplitude inversely proportional to the frequency of said pulses.

10. An arrangement as set forth in claim 9, wherein said speed converter means comprise pulse forming means connected to said speed sensor means; and monostable multivibrator means connected to said pulse forming means and furnishing, at a multivibrator output, an inverted multivibrator output pulse sequence, said multivibrator output pulse sequence having a pulse repetition frequency corresponding to engine speed, and pulses of substantially equal width and amplitude; and filter means connected to said multivibrator output and furnishing, at a filter output, said D.C. speed voltage.

11. An arrangement as set forth in claim 10, further comprising an excess speed control switching stage having an input connected to said speed sensing means and an output connected to said activating means, said speed control switching stage furnishing said predetermined fuel control signal upon receipt of a speed signal corresponding to an engine speed exceeding a predetermined maximum speed.

12. An arrangement as set forth in claim 8, wherein said engine comprises an accelerator; wherein said sensing means comprise acceleration sensing means furnishing an acceleration signal varying as a function of the position of said accelerator relative to an accelerator null position and having a predetermined minimum acceleration signal amplitude at said ac celerator null position; wherein said electrical control circuit means comprises a high-gain D.C. inverting amplifier, said high-gain D.C. inverting amplifier furnishing said predetermined fuel control signal in response to said predetermined minimum acceleration signal in the presence of a speed signal corresponding to an engine speed exceeding a predetermined minimum speed.

13. An arrangement as set forth in claim 12, wherein said acceleration sensing means comprise inductive sensor means; and clamping circuit means connected to said inductive sensor means and furnishing said predetermined minimum acceleration signal in the presence of acceleration signals less than said predetermined acceleration signal.

14. An arrangement as set forth in claim 13, wherein said clamping circuit means comprise first voltage divider means having a voltage divider tap furnishing said predetermined minimum acceleration signal; first transistor means having a control circuit and an output circuit; means connecting said output circuit to said voltage divider tap and said control circuit to said inductive sensor means; and wherein said first transistor means is blocked for acceleration signals less than said predetermined minimum acceleration signal.

15. An arrangement as set forth in claim 14, further comprising second voltage divider means having a second voltage divider tap furnishing a predetermined maximum acceleration signal; second transistor means having a second transistor output circuit and a second transistor control circuit; means connecting said second transistor output circuit to said tap of said second voltage divider means and said second transistor control circuit to said tap of said first voltage divider means.

16. An arrangement as set forth in claim 12, where in said high-grain D.C. amplifier means comprise feedback circuit means having a feedback circuit impedance and input circuit means having an input circuit impedance, whereby the gain of said high-gain D.C. amplifier means varies in dependence upon the relationship between said feedback circuit impedance means and said input circuit impedance means; further comprising speed network means interconnected between said speed sensing means and said input circuit, for changing said input circuit impedance as a function of engine speed.

17. An arrangement as set forth in claim 16, wherein said feedback circuit, said input circuit, and said speed network each comprise resistances; and wherein the re sistance of said speed network means varies as a function of engine speed.

18. An arrangement as set forth in claim 16, wherein said input circuit is a first resistance; and wherein said speed network means comprise a second resistance and second switching means connected to said second resistance and connecting said second resistance in parallel with said first resistance when said speed signal corresponds to an engine speed less than a predetermined minimum engine speed.

19. An arrangement as set forth in claim 18, wherein said speed network further comprises a third resistance, and third switching means connected to said third resistance and connecting said third resistance in parallel with said first resistance when said speed signal corresponds to an engine speed exceeding a predetermined maximum engine speed.

20. An arrangement as set forth in claim 19, wherein said second and third switching means respectively comprise second and third diode, respectively connected in series with said second and third resistance.

21. An arrangement as set forth in claim 20, wherein said voltage supply means comprise a first and second voltage supply terminal; wherein said speed network means comprise first voltage divider means connected between said first voltage supply terminal and a first terminal of said first resistance, and having a first voltage divider tap; and wherein said third diode has a cathode connected to the input of said high-gain D.C. amplifier means; further comprising means connecting said third resistance to said first voltage divider tap.

22. An arrangement as set forth in claim 21, wherein said means connecting said third resistance to said first voltage divider tap comprise a temperature compensatin g diode.

23. An arrangement as set forth in claim 22, wherein said speed network means comprise second voltage divider means connected from said first terminal of said first resistance to said second voltage divider terminal, and having a second voltage divider tap; further comprising means connecting said second voltage divider tap with one terminal of said second resistance in series with said second diode.

24. An arrangement as set forth in claim 23, wherein said means connecting said second voltage divider tap to a terminal of said second resistance connected in series with said second diode comprise an additional temperature compensating diode.

25. An arrangement as set forth in claim 24, wherein said first and second voltage divider means respectively comprise a first and second adjustable resistor.

26. An arrangement asset forth in claim 16, further comprising output connecting means connecting the output of said D.C. amplifier means to said activating means in such a manner that a minimum D.C. amplifier output signal causes maximum fuel injection; further comprising output clamping means connected to the output of said D.C. amplifier means for clamping said D.C. amplifier output signal to a predetermined minimum output signal in the presence of DC. amplifier output signals less than said predetermined set forth in claim 26, wherein said D.C. amplifier means comprise a final stage having a load resistance; wherein said voltage supply means comprise a first and second voltage supply terminal; and wherein said output clamping means comprise output voltage divider means connected from said first to said second voltage supply terminal and having a voltage divider output tap; further comprising an output diode having an anode connected to said load re sistance and a cathode connected to said output voltage divider tap, the voltage at said output voltage divider tap constituting said fuel control signal.

28. An arrangement as set forth in claim 27, wherein said output voltage divider means comprise a variable resistor.

29. An arrangement as set forth in claim 28, wherein said feedback resistance is connected from said output voltage divider tap to the input of said high-gain D.C. amplifier means.

30. An arrangement as set forth in claim 29, further comprising additional fuel limiting circuit means connected to said output voltage divider tap for decreasing the maximum permissible fuel injection at high engine speeds.

31. An arrangement as set forth in claim 30, wherein said additional fuel limiting circuit means comprise a fuel limiting resistance; and switching means connected to said fuel limiting resistance and said voltage divider tap of said output voltage divider means in such a manner that said additional fuel limiting resistance is connected in parallel with a predetermined portion of said output voltage divider means when said switching means is in a conductive condition; and further circuit means switching said switching means to said conductive condition when said engine speed exceeds a second predetermined engine speed.

32. An arrangement as set forth in claim 31, wherein said switching means comprise a diode having a cathode connected to said output voltage divider tap and an anode connected to said fuel limiting resistance; and wherein said further circuit means comprise transistor means having an output circuit connected to said fuel limiting resistance and a base circuit connected to said speed sensing means in such a manner that said diode is blocked when said transistor means is conductive and is conductive when said transistor means is blocked.

33. An arrangement as set forth in claim 32, further comprising a feedback resistor connected from the collector of said transistor means to the base of said transistor means.

34. An arrangement as set forth in claim 33, wherein said feedback resistor and fuel limiting resistor are variable resistors.

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Claims

1. In an internal combustion engiNe, a fail-safe fuel injection control arrangement, for furnishing a predetermined minimum fuel injection upon failure of system components, comprising, in combination, injection means having an electrically activated control element controlling by its position along a predetermined path the quantity of fuel injected per operating cycle of said engine, said control element having a null position causing said predetermined minimum fuel injection; activating means moving said control element along said predetermined path in correspondence to fuel control signals, said activating means moving said control element to said null position in response to a predetermined fuel control signal; a plurality of sensing means, each furnishing a sensed signal corresponding to a predetermined operating parameter of said engine; voltage supply means furnishing a supply voltage, and electrical control circuit means energized by said voltage supply means, having inputs connected to said sensing means, and a control output connected to said activating means for furnishing said fuel control signals in response to said sensed signals, said electrical control circuit means and said sensing means cooperating in such a manner that failure in one of said sensing means resulting in absence of one of said sensed signals causes the furnishing of said predetermined fuel control signal at said control output, thereby causing minimum fuel injection.

12. An arrangement as set forth in claim 8, wherein said engine comprises an accelerator; wherein said sensing means comprise acceleration sensing means furnishing an acceleration signal varying as a function of the position of said accelerator relative to an accelerator null position and having a predetermined minimum acceleration signal amplitude at said accelerator null position; wherein said electrical control circuit means comprises a high-gain D.C. inverting amplifier, said high-gain D.C. inverting amplifier furnishing said predetermined fuel control signal in response to said predetermined minimum acceleration signal in the presence of a speed signal corresponding to an engine speed exceeding a predetermined minimum speed.

17. An arrangement as set forth in claim 16, wherein said feedback circuit, said input circuit, and said speed network each comprise resistances; and wherein the resistance of said speed network means varies as a function of engine speed.

22. An arrangement as set forth in claim 21, wherein said means connecting said third resistance to said first voltage divider tap comprise a temperature compensating diode.

26. An arrangement asset forth in claim 16, further comprising output connecting means connecting the output of said D.C. amplifier means to said activating means in such a manner that a minimum D.C. amplifier output signal causes maximum fuel injection; further comprising output clamping means connected to the output of said D.C. amplifier means for clamping said D.C. amplifier output signal to a predetermined minimum output signal in the presence of D.C. amplifier output signals less than said predetermined minimum output signal.

27. An arrangement as set forth in claim 26, wherein said D.C. amplifier means comprise a final stage having a load resistance; wherein said voltage supply means comprise a first and second voltage supply terminal; and wherein said output clamping means comprise output voltage divider means connected from said first to said second voltage supply terminal and having a voltage divider output tap; further comprising an output diode having an anode connected to said load resistance and a cathode connected to said output voltage divider tap, the voltage at said output voltage divider tap constituting said fuel control signal.