US3884195A

US3884195A - Electronic control system for internal combustion engine

Info

Publication number: US3884195A
Application number: US235289A
Authority: US
Inventors: Fernand R C Murtin; Loic Mercier
Original assignee: ELECTRONIQUE INFORMATIQUE SOC
Current assignee: Societe Industrielle dElectronique et dInformatique; ELECTRONIQUE INFORMATIQUE SOC
Priority date: 1969-01-31
Filing date: 1972-03-16
Publication date: 1975-05-20
Anticipated expiration: 1992-05-20
Also published as: DE2004269A1; GB1304262A; NL7001419A; ES376079A1

Abstract

Fuel injectors for an internal-combustion engine are controlled by duration-modulated pulses whose width depends on a plurality of parameters, namely the rotational speed and the temperature of the engine and the air pressure at two points of the intake manifold. The width of the modulated pulses depends on the magnitude of one parameter and on binomials of the other parameters. A computer formed by cascaded operational amplifiers with fractional gain and adding circuits establishes the variable operating period of the injectors which are provided with two coils, i.e. a premagnetization coil energized by a constantduration pulse and a control coil receiving the durationmodulated pulse in staggered relationship with the former.

Description

United States Patent [1 1 Murtin et a1.

[5 1 ELECTRONIC CONTROL SYSTEM ron INTERNAL COMBUSTION ENGINE [75] Inventors: Fernand R. C. Murtin; Loic Mercier, both of Paris, France [73] Assignee: Socite' lndustrielle dElectronique et dlnformatique, Paris, France [22] Filed: Mar. 16, 1972 [21] Appl. No.: 235,289

Related U.S. Application Data [63] Continuation-impart of Ser. No. 7,78], Feb. 2, 1970,

abandoned.

[30] Foreign Application Priority Data Jan. 31. 1969 France 69.02057 Feb. 12.1969 France 69.03225 Mar. 7. 1969 France 69.06443 [52] U.S. C1...... 123/32 EA; 123/119 R; 123/32 AB [51] Int. Cl. F021) 3/00 [58] Field of Search 123/32 AB, 32 EA, 119 R [56] References Cited UNITED STATES PATENTS 3,456,628 7/1969 Bassot et a1. 123/32 EA 3,515,104 6/1970 Reichardt 123/32 EA 3,522,794 8/1970 Reichardt et al.. 123/32 EA 3.665398 5/1972 Kamazuka 123/32 EA 14 1 May 20, 1975 Du bno [57] ABSTRACT Fuel injectors for an internal-combustion engine are controlled by duration-modulated pulses whose width depends on a plurality of parameters, namely the rotational speed and the temperature of the engine and the air pressure at two points of the intake manifold. The width of the modulated pulses depends on the magnitude of one parameter and on binomials of the other parameters. A computer formed by cascaded operational amplifiers with fractional gain and adding circuits establishes the variable operating period of the injectors which are provided with two coils, i.e. a premagnetization coil energized by a constant-duration pulse and a control coil receiving the durationmodulated pulse in staggered relationship with the former.

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SHEET 5 OF 8 wmhwmw H QB r Wm ELECTRONIC CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINE This application is a continuation-in-part of our copending application Scr. No. 7,78l filed 2 February I970 and now abandoned.

The present invention relates to a fuelinjectioncontrol system for internal-combustion engines in which fuel is introduced under pressure at a point adjacent the intake ports of the piston cylinders of the engine with the aid of valves or injectors controlled by a generator of pulses of variable duration. The width of the pulses Controlling the injectors depends on sensed operating parameters or engine conditions; hence, a fuel-injection system can be considered as a computer designed for driving from these parameters the signals controlling the circuitry which determines the duration of the injectiontiming pulses.

In the prior art, a variablc-durationpulse generator is usually a relaxation oscillator, namely aa monostable 2 element (monoflop) or a bistable element (flip-flop) whose operating cycle is readily controlled by varying the resistance or capacitance of an R-C circuit or the inductance or resistance of an L-R circuit forming part thereof. U.S. Pat. No. 3.483.85Lfor example, discloses a flip-flop whose pulse period is controlled by varying the mutual inductance of a transformer whereas US. Pat. No. 3,456,628 describes a flip-flop whose pulse period is controlled by altering the value ofa variable resister.

The conventional fuelinjection systems take account of various parameters. The most suitable parameter is the rate of air mass admitted to the cylinders but. as its value is quite difficult to obtain, it is generally replaced by the pressure and temperature ofthe air in the intake manifold. Other usual parameters are the speed of the engine and the engine temperature.

According to our invention, injection is controlled by three parameters P, T, p. P is conventionally the back pressure in the intake manifold ahead of the cylinders; I its magnitude is generally proportional to load, varying inversely with the rotational engine speed for a given throttle opening. T is the engine temperature as measured in degrees Kelvin. Parameter p is a subatmospheric pressure measured at a constricted throat of the manifold in which is located the accelerator-controlled throttle valve of the engine. The magnitude ofp decreases with increasing air speed resulting from a narrowing of the gap around the throttle valve; parameter p is thus indicative of the position of the accelerator pedal.

The three parameters P, T, p are related to the optimum injection interval 1' by the following equation:

PH+ NH +B H +7( n)l (I) wherein coefficient K, a, B, '7, T are constants and N is the speed of the engine in turns per minute. Typical empirical values for these constants are:

In the above equation, p and P are expressed in bars. The right side of equation l) comprises a variable Kp which is multiplied by a product of three binomials.

The adjustable pulse generators of the prior art are not adapted to produce pulses whose duration depends on the product of three binomials, each a function of a particular parameter; the duraction of their output pulses is substantially determined by two parameters only. In a monotlop, for instance, the duration of the pulse depends on a product LC, of a resistance R times a capacitance C and the pulse period depends on a sum (R C, +R C R, and R being two resistances and C and C two capacitances. Let us assume that a resistance R is allowed to vary proportionally to a binomial of a first parameter N according to R rt l (1N) and that a capacitance C is allowed to vary proportionally to a binomial of a second parameter P according C C( 1 BP then the pulse duration will vary according to RC=rc(l +aN) (l =BP) and the pulse period will vary according to R C +connected R C my (I a N l B P 2 2 2 2)( +B2 2) which, by neglecting the second-order terms. can be transformed into R C R C r c l+a,N,+,B,P,)+r c l+a N +B P l Therefore the pulse duration varies proportionally to a product of two binomials. each depending on a single parameter, and the pulse period varies proportionally to a sum of two binomials, each depending on two pa rameters. For obtaining a pulse duration depending on three binomials, it would be necessary to let this pulse duration be substantially determined by a combination of three variable impedance elements. In fact, we are aware only of teachings of pulse durations depending on two parameters and on the logarithm of a third parameter (see Reference Data for Radio Engineers," fourth edition, International Telephone and Telegraph Corporation, formulae on page 472). Obtaining a three-parameter-binomial dependence would require inclusion of an exponential function of the parameter which appears in the formula by its logarithm.

The injection system according to our invention includes a computer having circuit means for converting the critical parameter values into analog voltages; operational amplifiers are provided with suitably dimensioned feedback resistors to multiply these voltages with the corresponding fractional constants a, B, 7, their outputs being then added to the original analog voltages with the aid of summing circuits in order to form the desired binomials of the respective parameters.

Pursuant to a preferred feature of our invention, use is made of high-speed electromagnetic injectors each provided with a pair of solenoid coils, i.e. a premagnetization or biasing coil and an injection-control or working coil. Two pulses are respectively applied to these coils, i.e. a priming pulse of constant duration and a control pulse whose width depends on the measured parameters. The primary pulse begins before the control pulse and terminates after the latter has come into existence.

The above and other features of our invention will be described hereinafter in detail with reference to the accompanying drawing in which:

FIG. 1 represents in the form of a block diagram an injection-control system for a vehicular internalcombustion engine according to our invention;

FIG. 2 is a perspective view of the engine with the injectors and associated circuitry;

FIG. 3 is a somewhat diagrammatic view of a part of a gasoline engine provided with the injection-control system of FIG. 1;

FIG. 4 is a cross-sectional view of a pressure sensor included in the system;

FIG. 5 is a cross-sectional view of a fuel injector also included in the system;

FIG. 6 is a circuit diagram of a sensor-controlled voltage generator shown in H6. 1;

FIG. 7 is a circuit diagram of a pulse-duration modulator also shown in FIG. 1;

FIG. 8 is a set of graphs showing the signal waveforms at different points of the circuit of FIG. 7; and

FIG. 9 schematically represents a monitor circuit included in the system.

In FIGS. 1 and 2 we have diagrammatically illustrated an automotive gasoline engine 1, a temperature sensor 2 and two pressure sensors or gauges 3 and 3'. The engine (FIG. 2) comprises a driven shaft 11, an intake manifold l2-and four cylinders 13a, 13b, 13c, 13d. Shaft ll, like the cam shaft of conventional four-stroke engines, rotates at half the speed of the engine crankshaft (not shown) acted upon by the cylinder pistons. Four electromagnetic pick up coils 14a, 14b, 14c, 14d are equispaced about the shaft 11 for periodic excitation by a permanent trigger magnet 15 revolving on the shaft. Synchronizing pulses, marking the beginning of respective injection cycles for the several cylinders, are produced in the coils when the magnet passes in front thereof and are fed, through

respective leads

10a, 10b, 10c, 10d, on the one hand to a pulse-duration modulator 6 and on the other hand to the setting or l inputs of respective injector-control flip-

flops

7a, 7b, 7c, 7 d.

Four output terminals of modulator 6 are connected, through leads 60a 60d, to resetting or 0" inputs of the flip-flops 7a 7d.

The output terminals of temperature and pressure sensors 2, 3 and 3' are connected via respective leads 20, 30, 30' to a jointly controlled analog-voltage generator 5.

Flip-flops or bistables are electronic switches well known in the electronics art and are described, for example in a textbook by Jacob Millman and Herbert Taub, McGraw-Hill Book Company, Inc., NY. l956, chapter 5, pages 140 ff and FIG. 5.2. A flip-flop is essentially a two-transistor regenerative circuit that can exist indefinitely in either of two stable states (which may be designated 0 and l and can be caused to make an abrupt transition from one state to the other. It is used for the generation of rectangular waves from short pulses and for storing single or multiple bits in binary registers or pulse counters. The trigger pulse employed to induce a transition from one state to the other may be introduced in such a manner as to produce either symmetrical or unsymmetrical triggering. ln unsymmetrical triggering, a trigger pulse applied to one input is effective in inducing a transition in only one direction (generally termed setting"). A second trigger pulse from a separate source must be applied to a different input to achieve the reverse transition (resetting). [n symmetrical triggering, successive trigger pulses a plied to a common input switch the flip-flop to its alternate state from whichever state it happens to be in. The two outputs ofa flip-flop energized in the l and 0 states will be called hereinafter the set and reset outputs, respectively.

As distinct from flip-flops, monoflops have a normal or 0 state from which they may be switched to an offnormal or 1 state for a predetermined period, as determined by a built-in time-constant network. They may, therefore, be used as timing means to measure relatively short intervals.

The set outputs of flip-

flops

7a, 7b, 7c, 7d actuate, by way of respective leads a, 70b, 70c, 70d and AND

gates

9a, 9b, 9c, 9d, associated solenoid valves 18a, 18b, 18c, 18d located at the fuel inlets of cylinders 13a, 13b, 13c, 13d near the upper-dead-center positions of their pistons.

AND gates are disclosed on pages 397-400 of the textbook above referred to. An AND gate has two or more inputs to each of which is applied a pulse of common polarity. The gate has a single output at which a pulse appears if and only if pulses are applied simultaneously to all inputs. If the input pulses are not of the same duration, the output pulse will be present only as long as the input pulses overlap.

The other inputs of AND gates 90 9d are normally energized through conductors 400C and 40bd by a monitor circuit 4 responsive to the position of an accelera tor pedal 41 aboard the vehicle and to the engine speed as defined by the frequency of the pulses on lead 100.

The reset outputs of flip-flops 70, 7c, on the one hand, and 7b, 7d, on the other hand, are connected to the inputs of AND gates Sac and Sbd whose outputs are returned to modulator 6 through leads 8011c and bd, respectively.

Under conditions of small or negative loads, e.g. during downhill driving, monitor circuit 4 responds to the combination of retracted pedal and relatively high velocity to de-energize the conductors 4000 and 40bd, thereby closing AND gates 9a 9d and inhibiting the operation of the injection actuators 18a l8d regardless of the states of the associated flip-flops 7a 7d. This inhibition of combustion allows the engine to operate as a more effective brake and further reduces the pollution of the atmosphere. Circuitry suitable for use in component 4 will be described below with reference to FIG. 9.

Temperature sensor 2 (H6. 3) is a temperaturedependent resistor located in cylinder 13a. Such resistors, giving an output signal proportional (with a proportionality factor 7) to the difference between an actual temperature T and a reference temperature T are known in the heat-control art. For example, resistors with 'y 5.10 and T 333K are available on the market under the commercial name TUS 23".

Pressure sensor 3 (also representative of sensor 3') has been illustrated in H0. 4. This sensor comprises a metallic housing consisting of two

parts

301, 302 which are bolted or otherwise secured to each other by means not shown and between which a resilient, preferably metallic, diaphragm 303 is clamped. The interior of housing'30l, 302 is divided by this diaphragm into two compartments 304, 305, compartment 304 communicating via a bore 306 in a threaded nipple 307 with the air space (specifically the manifold 101 of H6. 3 described hereinafter) whose pressure is to be measured; an orifice 308 connects the compartment 305 with a source of substantially constant fluid pressure, advanta geously the outer atmosphere. Diaphragm 303 supports a metallic boss 309 from which a conducting rod 310 slidably projects through a dielectric sleeve 31] in housing portion 302; rod 310 is surrounded with sliding fit by a metallic bushing 312 connected to its outgoing terminal lead 30. A spur 314 on rod 310 contacts a coil of resistance wire 315 wound around an insulating core 316; wire 315 is grounded at one end of housing portion 302 and connected at its other end to a positive bus bar 61. Thus,

elements

314 and 315 constitute a potentiometer delivering on conductor 30 a voltage which, through a suitable design of resistance coil 315, may be caused to vary substantially linearly with the pressure differential acting upon the diaphragm 303.

FIG. 5 shows a preferred construction of an injector 18 representative of any of the fuel injectors 18a 180' shown in F10. 2. A cylindrical housing 1,801 of nonmagnetic material threadedly engages a nozzle 1,802 whose outlet 1,803 is normally closed by a beveled tip 1804 of a tubular armature 1805 of magnetically permeable material which is slidably guided in a similarly permeable ring 1807. Another tubular member 1808 of permeable material, confronting the armature 1805 across an air gap 1809, is fixedly clamped within housing 1801 through the intermediary of ring 1807, a tubular'winding support 1810 enclosing the

members

1805 and 1808, a ferromagnetic shell 1811 embracing the ring 1807 and the support 1810, and an internally threaded insert 1812 projecting from the housing end opposite nozzle 1802. A nipple 1813 is screwed into insert 1812 and forms an abutment for a compression spring 1814 received within

members

1805 and 1808, this spring tending to urge the tip 1804 against its seat 1803. A fluid path for fuel entering the bore of nipple 1813 extends through the spring chamber within

members

1805 and 1808 and through a pair of lateral orifices 1815 in tip 1804 to a space 1816 surrounding that tip, this space being open toward the outside upon a withdrawal of tip 1804 from nozzle mouth 1803.

A magnetic circuit, interrupted by the air gap 1809, will thus be seen to include the

permeable elements

1805, 1807, 1808 and 1811, this circuit being formed around a pair of annular clearances which receive two

electromagnetic coils

1817, 1818 carried on support 1810. As described hereinafter with reference to FIG. 1,

windings

1817 and 1818 are sequentially energized in staggered relationship and are aidingly intercon nected so that their joint excitation opens the injection valve represented by armature tip 1804 and nozzle mouth 1803. The preliminary energization of biasing winding 1817, insufficient in itself to displace the armature 1805 against the force of spring 1814, generates enough flux to shift the operating point of the electromagnetic circuit to the linear portion of its hysteresis curve whereby the valve opens promptly upon the subsequent energization of the working winding 1818. To-

ward the end of the injection interval, biasing winding 1817 is de-energized (preferably after having been energized for a fixed period) but the remanence of the ferromagnetic elements, together with the continuing current flow in winding 1818, holds the armature 1805 retracted while again established an operating point on the linear portion of the hysteresis curve. Upon the deenergization of winding 1818, after a variable period depending upon the controlling parameters, spring 1814 quickly returns the armature to its closure position.

We shall now refer to FIG. 3 wherein elements already shown in FIGS. 1 and 2 include the monitor circuit 4, the pedal 41, the control shaft 11 with its magnet 15 and the electromagnetic pick-up coil 14a excitable thereby, together with the output lead of that coil extending to pulse-duration modulator 6. The tempe rature and pressure sensors 2, 3 and 3' are connected to analog-voltage generator 5 via

respective conductors

20, 30 and 30'. Pressure sensors 3 and 3' are mounted in the wall 102 of an intake manifold 101 communicating with the atmosphere through a port 103 from which it is separated by a constriction 104. A butterfly-type throttle valve or damper 105, rotatable about a gudgeon 106, is mechanically linked with the pedal 41 for clockwise rotation when the pedal is depressed against the force of a restoring spring 107. Pedal 41 is electri cally grounded through its contact with the metallic manifold housing 102 which has a further constriction 108 separating the manifold 10] from a neck 109 leading to a combustion cylinder partly shown in 13a. This cylinder has an inlet port 111 closable by a poppet valve 112 which is conventionally biased into a closure position by a spring 113 and is periodically opened by a cam shaft which may form an extension of shaft 11. Temperature sensor 2 is disposed in a cooling channel 114 within the wall of cylinder 130 through which water cooled by the radiator of the engine is circulated. in the case of an air-cooled engine, this temperature sensor 2 may be mounted in direct contact with the cylinder wall. It will be understood that the remaining cylinders have similar inlets branched off the manifold 101 via other constrictions such as that shown at 108.

Fuel injector 18a is conncted via a supply conduit 115 to the high-pressure side of an electrical gear pump 116 which delivers the fuel at constant pressure, independent of the engine speed. The low-pressure side of the pump communicates with a fuel reservoir 117. injector 18a is controlled from flip-flop 7a through AND gate 9a via a lead 90a (see also FIG. 1).

With the throttle valve in a position of near closure, corresponding to idling of the engine under noload conditions, pedal 41 comes to rest against an adjustable backstop in the form of a screw 118 seated in an insulating bushing 119 on housing 102. A conductor 400, leading from screw 118 to monitor 4, is therefore grounded whenever pedal 41 is in its retracted position.

Pressure sensor 3 communicates with a bore 121 which opens into the manifold 101 at the narrowest point of its constricted throat 104 to detect the subatmospheric pressure p existing at this point whenever combustion air streams inwardly past the damper 105 toward the cylinders, the absolute magnitude of this pressure varying inversely with air speed. Pressure sensor 3 communicates with a similar bore 122, opening directly into the manifold downstream of bore 121 between

constrictions

104 and 108, to measure a back pressure P proportional to the load as explained above.

FIG. 6 shows the details of the sensor-controlled analog-voltage generator 5 of FIGS. 1 and 2.

The arm of the potentiometer 315 of pressure sensor 3 is connected to the direct or noninverting input 30 of an operational amplifier 501 having a voltage divider 502-503 connected between its output and ground. The junction of

resistors

502 and 503 is connected to the inverting input of amplifier 501. The gain of the amplifier is (Rm RsosllR (see IEEE Spectrum," Apr. 1971, Linear Circuit Applications of Operational Amplifiers" by Larry L. Schick, P16. 298, page 48) which is made equal to constant K of equation 1 The output signal of amplifier 501 is thus the analog of the product Kp.

The signal Kp issuing from operational amplifier 501 is applied to the potentiometer of sensor 3'. The arm of this potentiometer is connected to the direct or noninverting input 30' of an operational amplifier S04 having a voltage divider 505-506 connected between its output and ground. The junction of

resistors

505 and 506 is connected to the inverting input of an amplifier 504 whose gain is (R R )/R which is made equal to constant B. The output signal of amplifier 504 is thus the analog of Kp X BP. The output signals of

amplifiers

501 and 504 are applied to a network of identi cal summing resistors 507, 508, S09 forming an adding network (see Reference Data for Radio Engineers," fourth edition, International Telephone and Telegraph Corporation, page 458). Resistor 509 has an extremity grounded and its other extremity connected to the direct or noninverting input of an operational amplifier 510. The signal voltage vsng at this input can be expressed by Operational amplifier 510 is connected as a voltage to-current converter (see IEEE Spectrum already cited, FIG. 26, page 47). The arrangement comprises an input series resistor 511, a feedback resistor 512 connected to the inverting output, a voltage divider 513-514 connected between the amplifier output and ground, and the temperature-dependent resistor element 2 of thermal coefficient 31 connected between the direct input and ground in parallel with resistor 514. The resistance R of this temperature sensor has a value 'y(TT,,). The junction of resistors 513 and 514 is also connected to the direct input. It is known (eg. from the cited reference) that if ats/ 514 am 511 the current i: through resistor 2 is proportional to the input signal Kp( l-l-BP) in accordance with the relation ship Therefore, the signal voltage V; across resistor 2 is given by The signal voltages V and V; are added in a summing network formed by

identical resistors

517, 518, 5l9, similar to the summing resistors 507, 508, 509. The signal voltage V across resistor 519 is therefore expressed as follows:

The ungrounded terminal of resistor 519 is connected to two parallel paths, the first comprising a re sistor 520 and the second being formed from three

series resistors

521, 522, 523, these two paths being grounded through a parallel resistor 524.

The train of pulses from coil 14a (FIG. 3), whose repetition frequency or cadence is proportional to engine speed N, is applied through lead a to the gate of a field-effect transistor 516. The source of transistor 516 is grounded and its drain is connected to an integrating R-C circuit formed of a series resistor 522 and a shunt capacitor 525. Resistor 521 is a decoupling resistor and

resistors

520, 523, 524 are identical elements of a summing network. The signal voltage developed across resistor 520 is the voltage V of equation (3); the com- 8 posite signal voltage V appearing across resistor 523 is given by 523 IINKM l+B )l o)l wherein a is determined by the relative magnitude of

impedances

521, 522, 525. The final analog voltage V appearing across shunt resistor 524 is proportional pt 1+ 1N l+/ )l i+-/( .)1 and consequently to the desired injection interval 1- as per equation (1).

Anolog voltage V is normally applied to a buffer operational amplifier 526 whose output signal controls the pulse-duration modulator 6 through a lead 56.

In FIG. 7 we have shown modulator 6 as including a power supply such as the battery of the vehicle driven by the engine. Battery 60 has its positive terminal connected to the aforementioned bus bar 61 maintained at, say, +6 volts, its negative terminal being connected to a bus bar 62 carrying, say 6 volts whereas an intermediate point is connected to a grounded bus bar 63. The bus bars 61, 62, 63 serve to feed and bias an analog-voltage repeater 64, a sawtooth-voltage generator 65, a comparator 66 comparing the voltages respectively produced by circuits 64 and 65, and a starting circuit 67.

The analog-voltage repeater 64 is a Wheatstone bridge having four corners I, ll, III, IV and four arms. The first arm l-ll is formed by the analog-voltage generator S of FIG. 6. The second arm ll-lll nd the third arm lll-lV are formed by

respective resistors

641 and 642, the latter being in parallel with a capacitor 643. The fourth arm lV-l is formed by two resistors 644 and 645, a transistor 640 bridging the

resistors

642 and 644. Transistor 640 has its emitter grounded through bus bar 63 and its collector connected to positive bus bar 61 through a resistor 645. The base of transistor 640 is biased through a variable resistor 646 and connected to the starting circuit 67.

The corners l and ll] of the supply diagonal of the Wheatstone bridge are respectively connected to

bus bars

61 and 63 whereas the corners ll and IV of the reading diagonal of the bridge are respectively connected to the direct and inverting input terminals of an operational amplifier 647. The output 647' of operational amplifier 647 is connected to an input 667' of comparator 66. Operating current is supplied to amplifier 647 by means of leads 649 and 649', respectively connected to

bus bars

61 and 62.

A pair of oppositely poled Zener diodes 648 and 648' are connected across the reading diagonal ll-lV of the bridge in order to limit the magnitude of input signal of either polarity fed to amplifier 647.

The function of transistor 640 and capacitor 643 will be explained with the operation of the pulse-duration modulator 6.

i The sawtooth-voltage generator 65 comprises a PNP transistor 650 having a capacitor 651 in its collector circuit and a resistor 652 in its emitter circuit. The base of transistor 650 is biased by a voltage divider formed from two resistors 653 and 654, resistor 654 being shunted by a capacitor 655. Capacitor 651 is bridged by an NPN transistor 656 serving for its discharge as described hereinafter. lt is well known (see the textbook above referred to, page 236) that the signal developed across the capacitor 651 has a sawtooth waveform. The signal available at output terminal 657 of sawtooth-voltage generator 65 is applied to the other input terminal 667 of comparator 66.

Signal comparator 66 comprises two

mirrorsymmetrical NPN transistors

660 and 660 having a common emitter circuit in which an injector transistor 66] and a resistor 662 are serially connected to negative bus bar 62; the paired transistors 660 and 660' are provided with respective collector resistors 663 and 663.

Transistors

660, 660' and 661 form a differential amplifier; transistor 66] acts as a source of current which divides between transistors 660 and 660' according to the base bias thereof.

The collector of NPN transistor 660 is further connected to the base of a PNP transistor 664 having an emitter directly tied to bus bar 61 and a collector connected to ground on bus bar 63 through two series resistors 664' and 664". The junction of resistors 664' and 664" is connected to the base of an NPN transistor 665 having its collector connected to bus bar 61 through a resistor 665' and its emitter directly connected to grounded bus bar 63. Resistors 661' and 661" form a voltage divider between ground and negative battery for biasing the base of current-injecting transistor 66].

The collector of transistor 665 is connected to the output terminal 668 of comparator 66 through a circuit formed by a series capacitor 669' and a shunt resistor 669". Output terminal 668 is tied to the resetting inputs of flip-flops 7a and 7c.

The starting circuit 67 comprises two

PNP transistors

670 and 670 having emitter resistors 671, 671 and collector resistors 672, 672'. The collectors of transis'

tors

670 and 670 are respectively connected to the bases of transistors 656 and 640, their bases being jointly connected to the output of NAND gate Sac.

Generally, the pulse-duration modulator shown in FIG. 7 operates as follows (see also FIG. 8):

Flip-flops 7a and 7c are alternately operated in phase opposition by trigger pulses 910a, 9100 on leads 10a, 10c respectively. Leads 700, 70c apply durationmodulated pulses 970a, 970C of width 7 to the fuelinjection valves 180, 186 (FIG. 2) unless this action is inhibited as later described. The injection interval is terminated whenever the charge of capacitor 651 of sawtooth-voltage generator 65 reaches the level of the voltage generated by the analog-voltage repeater 64.

When the rising amplitude of the voltage on input 667 matches that of the signal on input 667', transistor 660 conducts whereby the base of transistor 664 is driven negative to turn the latter transistor on. Thereupon the transistor 665 becomes conductive and develops a negative spike 9600c across resistor 665', this spike being applied through a coupling capacitor 669' to the resetting inputs of flip-flops 7a and 7c to reverse whichever these flip-flops had previously been set by a pulse 9100 or 9101 on lead 100 or 10c, respectively.

NAND gate Sac is connected to the reset outputs of flip-flops 7a and 7c and gives rise to pulses 980m which persist as long as flip-flops 7a and 7c are simultaneously reset. Pulses 980m are applied through lead 80ac to the joined bases of two mirror-symmetrical PNP transistors 670 and 670' which thus become conductive. The resulting pulses developed across their

collector resistances

672 and 672 respectively turn on the transistor 656 ofsawtooth-voltage generator 65 and the transistor 640 of voltage repeater 64. Capacitor 651 is thereby discharged through transistor 656; upon the termination of each pulse 980ac, capacitor 651 begins to charge along a line V (representing the voltage on terminal 667) to the level of variable voltage V on terminal 667'.

Resistor 642 and capacitor 643 form an integrating circuit for biasing the transistor 640. The effect of pulses 980ac as amplified by transistor 670' is to build up a bias voltage across capacitor 643, thereby reducing the effective magnitude of the analog voltage V applied via lead 56 to the noninverting input of operational amplifier 647 whereby the output voltage V of this amplifier depends upon the balance between the voltage V and the reference voltage V applied to its inverting input.

The higher the positive output signal V of operational amplifier 647, the longer will be the time required for condenser 651 to charge up to the level of that signal. This lengthens the injection interval 7 (line 700, FIG. 8) and correspondingly shortens the complementary period 1" for the discharge of condenser 651. As a result, reference voltage V goes more positive whereby the effective input signal of amplifier 647 in creases more slowly. as does the base potential oftransistor 660', with consequent limitation of the lengthening of the injection interval. Thus, the feedback from the flip-flops 7a, 7c via conductor 8011c to the input of amplifier 647 stabilizes the injection interval 'r.

Such a lengthening of the injection interval, due to a more positive driving voltage V from sensing circuit 5, indicates a change in operating conditions of a nature calling for additional fuel. ln the opposite case, of course, the voltage at the direct input of 647 will de crease to foreshorten the injection time.

FlG. 9 represents in detail the monitor circuit 4 of FIG. 1. It comprises an integrating R-C network formed of a resistor 401 and a capacitor 402, resistor 401 being connected to lead 100. Network 401-402 is similar to the integrating network 522-525 of FIG. 6 in that the charge voltage across its capacitor 402 depends on the frequency of pulses 910a, i.e. on the speed of the engine. The voltage of capacitor 402 is compared in an operational amplifier 403 with a predetermined reference voltage obtained from a voltage divider 404-405. The output voltage of amplifier 403 is positive when the capacitor potential exceeds the reference voltage and is zero when the capacitor potential is lower than the reference voltage.

The output lead 406 of amplifier 403 is connected to an inverting input of an AND gate 407 and in parallel therewith to a noninverting input of a NAND gate 412. Lead 400 groundable by pedal 41 (cf. FIG. 3) is connected in parallel to the other, inverting inputs of AND gate 407 and NAND gate 412; this lead is connected to positive potential on bus bar 61 through a resistor 414. The output of AND gate 407 is connected to an electromagnetic relay 408 (FIG. 6) through a lead 409 whereby the output of NAND gate 412 is connected to lead 4000 (FIG. 1). With relay 408 unoperated, its armature 4081 connects the resistance network 520-523 to the operational amplifier 526 feeding the output lead 56.

If the pedal 41 is retracted to its idling position and, at the same time, the engine speed is relatively low, there is ground potential on line 400 and zero voltage on line 406. Under these conditions, AND gate 407 opens and energizes relay 408 (FIG. 6) whose armature 4081 thereupon disconnects the analog voltage of generator from the input of amplifier S26 and connects thereto in its stead a constant reference potential obtained from a voltage divider 410-411. NAND gate 412 conducts and energizes its output lead 40ac so that coincidence gates 9a and 9c (FIG. 1) are enabled to pass the timing pulses 970a and 9706' on leads 70a and 70c, respectively, whose duration at this point is fixed at a minimum consistent with the power requirements at low load.

If, with the pedal 41 still retracted, the engine 1 accelerates beyond the speed threshold established by

voltage divider

404, 405, gate 407 is blocked so that relay 408 releases and restores the connection between voltage generator 5 and pulse-width modulator 6. NAND gate 412 is now cut off and

gates

90, 9c are blocked, thereby preventing injection to avoid waste of fuel, reduce atmospheric pollution and help slow down the engine.

When pedal 41 is depressed to indicate a demand for power, lead 400 goes positive so that AND gate 407 remains inhibited whereas NAND gate 412 energizes its output lead 40ac irrespectively of the state of conductivity of amplifier 403. This situation, occurring during normal driving, brings into play the multiple-parameter injection control described above.

Whenever AND gates 9a 9d are enabled by the energization of their input leads 4000 and 40bd from men itor 4, the injection control pulses 970a 970d (FIG. 8) respectively passing therethrough from conductors 70a 70d appear on their output leads 90a 90d (generally indicated at 90 in FIG. 5) as actuating pulses which energize the second-stage solenoid coils or working windings 1818 of the corresponding injectors 18a 18d. The associated first-stage solenoid coils or biasing windings 1817 thereof are energized, in staggered relationship with windings 1818, by pulses 1,490a 1,490d of constant width (illustrated in dot-dash lines in FIG. 5) by corresponding monoflops 413a 413d; these monoflops are tripped by the synchronizing pulses 910a 910d from coils 14a 14d transmitted to the monoflops via leads a 10d. Delay networks 91a 91d in leads 90a 90d serve to offset the leading edges of control pulses 970a 970d from those of priming pulses 1490a l490d with which they are seen to coincide in FIG. 8, thereby making the injection interval r definitely coincident with the respective control pulse. The delay introduced by networks 910 91d should be sufficient to let the trailing edges of the shortest control pulses 970a 970d lag behind those of the associated priming pulses 1490a 149041.

The pulses 97012 and 970d, shown in FIG. 8, are generated by flip-flops 717, 7d or FIG. 1 under the control of setting pulses from

leads

10b, 10d and resetting pulses from leads 60!), 6011, the latter being periodically energized by a section of pulse-width modulator 6 (not illustrated in detail) identical with the one shown in FIG. 7 for feeding the resetting leads 60a, 60c of flipflops 70, 7c.

Modulator 6 may be regarded, in part, as an analog/- digital converter which derives from the parametercontrolled analog output of computer 5 a set of binary signals adapted to be used in the logic circuitry 70 7d etc. of FIG. 1.

We claim:

1. A fuel-injection-control system for an internalcombustion engine having a plurality of piston cylinders provided with intakes for combustion air, respective fuel injectors feeding said cylinders, and a shaft driven by the thrust of an exploding air-fuel mixture ignited in each cylinder, comprising:

electric actuating means for each of said fuel injectors;

a generator of synchronizing pulses having a cadence proportional to engine speed;

electric sensing means in said engine responsive to different combustion-determining parameters, said sensing means including a first pressure gauge positioned at a constriction of a common intake manifold for said cylinders, a second pressure gauge positioned at a location in said manifold downstream of said constriction, and a temperature-responsive resistor in close proximity to at least one of said cylinders;

voltage-generating means connected to said generator and to said sensing means for synthesizing from their outputs an analog voltage as a function of said parameters and said engine speed; and

timing means controlled by said voltage-generating means for energizing said actuating means for a recurrent period proportional to said analog voltage, said timing means including an analog/digital converter and electronic switch means responsive to binary output signals from said converter, said switch means being connected to said generator for establishing recurrent operating cycles for said injectors under the control of said synchronizing pulses;

said voltage-generating means comprising a first operational amplifier having an input circuit including said first pressure gauge, a second operational amplifier in cascade with said first amplifier having an input circuit including said second pressure gauge, and a third operational amplifier in cascade with said second amplifier having an input circuit including said temperature-responsive resistor.

2. A system as defined in claim 1, further comprising first summing means in the input circuit of said third amplifier for adding the output of said first amplifier to that of said second amplifier, second summing means for adding the outputs of said first, second and third amplifiers to generate a composite signal voltage, and integrating means connected to said second summing means and to said generator for multiplying said signal voltage by a speed factor dependent upon the cadence of said synchronizing pulses.

3. A system as defined in claim 1 wherein said composite signal voltage is proportional to the product of a first parameter times a binomial of a second parameter multiplied by a binomial of the third parameter, further comprising third summing means connected to said second summing means and said integrating means for introducing a binomial of engine speed into said analog voltage as said speed factor.

4. A system as defined in claim 2 wherein at least said second and third amplifiers have fractional gains.

5. A system as defined in claim 4 wherein said analog voltage is proportional to an injection period 1' Kp(l+aN) (1+3?) [l+*y(T'-Tu)l. N being the engine speed, 11 being the air pressure at said constriction, P being the air pressure at said downstream location, K being a constant, B being the gain of said second amplifier, being the thermal coefficient of said temperature-responsive resistor, 01 being a function of impedance values of said integrating means.

6. A fuel-injection-control system for an internalcombustion engine having a plurality of piston cylinders provided with intakes for combustion air, respective fuel injectors feeding said cylinders, and a shaft driven by the thrust of an exploding air-fuel mixture ignited in each cylinder, comprising:

electric actuating means for each of said fuel injectors;

a generator of synchronizing pulses having a cadence proportional to engine speed.

a first, a second and a third sensor in said engine responsive to different combustion-determining parameters;

said voltage-generating means comprising a first operational amplifier having an input circuit including said first sensor, a second operational amplifier in cascade with said first amplifier having an input circuit including said second sensor, and a third operational amplifier in cascade with said second amplifier having an input circuit including said third sensor.

7. A system as defined in claim 6, further comprising first summing means in the input circuit of said third amplifier for adding the output of said first amplifier to that of said second amplifier, second summing means for adding the outputs of said first, second and third amplifiers to generate a composite signal voltage, and integrating means connected to said second summing means and to said generator for multiplying said signal voltage by a speed factor dependent upon the cadence of said synchronizing pulses.

8. A system as defined in claim 6 wherein the admission of combustion air to said cylinders is controlled by an accelerator pedal adapted to be depressed from a retracted position to indicate a demand for increased engine power, further comprising monitoring means connected to said switch means and responsive to the position of said pedal for inhibiting the energization of said actuating means under the control of said analog voltage in a state of reduced engine load.

9. A system as defined in claim 8 wherein said monitoring means is connected to said generator and is ef fective in said retracted position of the pedal to establish a predetermined energization period for said actuating means at relatively low engine speeds and permanently de-energizing said actuating means at relatively high engine speeds.

10. A system as defined in claim 9 wherein said timing means includes a source of constant voltage connectable by said monitoring means to said converter, in lieu of said analog voltage, at said relatively low engine speeds in said retracted pedal position.

1]. A system as defined in claim 6 wherein said actuating means comprises for each injector a pair of aidingly connected solenoid coils including a biasing coil and a working coil, said switch means being responsive to said synchronizing pulses for supplying a priming pulse or fixed duration to said biasing coil at the beginning of an operating cycle and for subsequently supplying a timing pulse of variable width, proportional to said analog voltage, to said working coil in staggered relationship with said priming pulse, said timing pulse being effective only in the presence of said priming pulse to actuate the injector and maintaining same actuated past the termination of said priming pulse.

1!: k i l

Claims

1. A fuel-injection-control system for an internal-combustion engine having a plurality of piston cylinders provided with intakes for combustion air, respective fuel injectors feeding said cylinders, and a shaft driven by the thrust of an exploding air-fuel mixture ignited in each cylinder, comprising: electric actuating means for each of said fuel injectors; a generator of synchronizing pulses having a cadence proportional to engine speed; electric sensing means in said engine responsive to different combustion-determining parameters, said sensing means including a first pressure gauge positioned at a constriction of a common intake manifold for said cylinders, a second pressure gauge positioned at a location in said manifold downstream of said constriction, and a temperature-responsive resistor in close proximity to at least one of said cylinders; voltage-generating means connected to said generator and to said sensing means for synthesizing from their outputs an analog voltage as a function of said parameters and said engine speed; and timing means controlled by said voltage-generating means for energizing said actuating means for a recurrent period proportional to said analog voltage, said timing means including an analog/digital converter and electronic switch means responsive to binary output signals from said converter, said switch means being connected to said generator for establishing recurrent operating cycles for said injectors under the control of said synchronizing pulses; said voltage-generating means comprising a first operational amplifier having an input circuit including said first pressure gauge, a second operational amplifier in cascade with said first amplifier having an input circuit including said second pressure gauge, and a third operational amplifier in cascade with said second amplifier having an input circuit including said temperature-responsive resistor.

5. A system as defined in claim 4 wherein said analog voltage is proportional to an injection period Tau Kp(1+ Alpha N) (1+ Beta P) (1+ gamma (T-To)), N being the engine speed, p being the air pressure at said constriction, P being the air pressure at said downstream location, K being a constant, Beta being the gain of said second amplifier, gamma being the thermal coefficient of said temperature-responsive resistor, Alpha being a function of impedance values of said integrating means.

6. A fuel-injection-control system for an internal-combustion engine having a plurality of piston cylinders provided with intakes for combustion air, respective fuel injectors feeding said cylinders, and a shaft driven by the thrust of an exploding air-fuel mixture ignited in each cylinder, comprising: electric actuating means for each of said fuel injectors; a generator of synchronizing pulses having a cadence proportional to engine speed; a first, a second and a third sensor in said engine responsive to different combustion-determining parameters; voltage-generating means connected to said generator and to said sensing means for synthesizing from their outputs an analog voltage as a function of said parameters and said engine speed; and timing means controlled by said voltage-generating means for energizing said actuating means for a recurrent period proportional to said analog voltage, said timing means including an analog/digital converter and electronic switch means responsive to binary output signals from said converter, said switch means being connected to said generator for establishing recurrent operating cycles for said injectors under the control of said synchronizing pulses; said voltage-generating means comprising a first operational amplifier having an input circuit including said first sensor, a second operational amplifier in cascade with said first amplifier having an input circuit including said second sensor, and a third operational amplifier in cascade with said second amplifier having an input circuit including said third sensor.

9. A system as defined in claim 8 wherein said monitoring means is connected to said generator and is effective in said retracted position of the pedal to establish a predetermined energization period for said actuating means at relativeLy low engine speeds and permanently de-energizing said actuating means at relatively high engine speeds.

11. A system as defined in claim 6 wherein said actuating means comprises for each injector a pair of aidingly connected solenoid coils including a biasing coil and a working coil, said switch means being responsive to said synchronizing pulses for supplying a priming pulse or fixed duration to said biasing coil at the beginning of an operating cycle and for subsequently supplying a timing pulse of variable width, proportional to said analog voltage, to said working coil in staggered relationship with said priming pulse, said timing pulse being effective only in the presence of said priming pulse to actuate the injector and maintaining same actuated past the termination of said priming pulse.