US3897762A - Fuel systems for engines - Google Patents

Abstract

A fuel system, particularly for a diesel engine, has an electronic governor receiving signals from transducers associated with the engine, and providing an input to a power amplifier which determines the pump output. In order to provide a safety feature, the magnitude of the input signal applied to the power amplifier is limited to a fixed level independent of the supply voltage of the system.

Description

United States Patent Jones et al. 1 Aug. 5, 1975 [54] FUEL SYSTEMS FOR ENGINES 3,630,177 12/1971 Engel 123/32 EA 3.665.900 5/1972 Schlimmem. 123/32 EA [75] Inventors: Christopher Robln Jones, Sol1hull; 3693'603 9/1972 Lemanczyk 123/32 EA Malcolm Williams, Glastonbury; 3,699,935 10/1972 Adler 123/32 EA Geoffrey Albert Keny n r n 3,707,950 1/1973 SchlimmeW, 123/32 EA Alcester, all of England 3,724,433 4/1973 Voss 123/32 EA 3,777,174 12/1973 Butscher 123/32 EA [73] Asslgnee: C. A. V. Limited, Blrmmgham,

England Primary Exammer--Charles J. Myhre [22] Flled: 41 Assistant ExaminerRonald B. Cox [21] Appl. No.: 347,699 Attorney, Agent, or FirmHolman & Stern [30] Foreign Application Priority Data [57] ABSTRACT 1972 United Kingdom 5354/72 A fuel system, particularly for a diesel engine, has an electronic governor receiving signals from transducers [52] 0.8.CI 123/139 E; 123/32 EA associated i the engine and providing an input to a {51} hr. Cl F02! 39/00; F02!) 3/00 power amplifier which deuirmines he pump output In [58]new Search 123/139 32 BA, 32 order to provide a safety feature, the magnitude of the 123/102; 60/3928 input signal applied to the power amplifier is limited to a fixed level independent of the supply voltage of [561 References Cited the system UNITED STATES PATENTS 3.407.793 10/1968 Lang 123/32 EA 2 Clams 9 Drawmg F'gures l4ll PUMP l2 1 1 ENGINE l5 AcruA'mR 1 V g TRANSDUCER I TRANSDUCER1 AMPLIFIERl6 1 I7 0 r I i5 25 l ,r'\

2 --TRANSDUCER MAXIMUM 17 Cl A A M DEMAND CONTROL 7 V V Cl \l-CURRENT SOURCE 23CURRENT SOURCE 3, 8 9 7, 7' 6 2 PAIENTED 5'975SHEET 1 I4 IH/PUMPIZ ENGINE ACTUATOR r 1 l I 5 TRANSDUCER I TRANSDUCER- AMPLIFIER/E "5 g, 29 0TRANSDUCER 28 MAXIMUM DEMAND CQNTROL CURRENT SOURCE g x f 24 '8 7 8.8 97, 762PATENTEU 19 5SHEET 2 PUMP OUTPUT B PUMP |2 ENGmE TRANSDUCERS ACTUATOR l4 AMPLIFIER \JTRANSDUCER; H

MAXIMUM DEMAND CONTROL oW 21 2J60 31 24 8 2 23 Z"|6b 251mm SOURCE I 2 23 F'\G.6

CURRENT SOURCE PUMP 1 ouwur 40G 43 SPEED 3. 8 9 7, 7 6 2 PATENTEU AUG 5W5 SHEET SAFETY NETWORK AJMPLIFIER FIGS 23 (AMPLIFIER 66SAFETY NETWORK 22 FUEL SYSTEMS FOR ENGINES This invention relates to fuel systems for engines.

A fuel system in accordance with the invention comprises in combination a pump for supplying fuel to the engine, a control member for determining the output of the pump, an actuator for varying the setting of said control member, a power amplifier for supplying current to said actuator, a control circuit which receives at least two input signals representing the actual and demanded values of an engine parameter and provides an input to the power amplifier, and means acting to limit the magnitude of said input signal applied to the power amplifier to a fixed level independent of the supply voltage of the system.

Preferably, the control circuit includes a summing amplifier to which the signals representing actual and demanded values are fed. In this case, said means preferably includes a device for controlling the feedback in said summing amplifier.

Preferably, the system includes an overriding control which, in the event that said means fails to limit the magnitude of the input signal to the power amplifier, operates to prevent operation of the power amplifier.

In the accompanying drawings,

FIG. I is a circuit diagram, partly in block form, illustrating one form of fuel system with which the invention can be used,

FIGS. 2 to 4 are graphs illustrating the outputs of three transducers used in FIG. 1,

FIG. 5 represents a fuel-speed characteristic for an engine to be controlled by the arrangement of FIG. 1,

FIG. 6 is a view similar to FIG. 1 of a second form of fuel system,

FIG. 7 is a view similar to FIG. 5 but showing the characteristic obtained by FIG. 6,

FIG. 8 is a circuit diagram illustrating one example of the invention as applied to the arrangement of FIG. I or FIG. 6, and

FIG. 9 is a circuit diagram illustrating a modification of FIG. 8.

The examples described relate to a fuel injection sys tem for a diesel engine driving a road vehicle, so that demand is set by an accelerator pedal. However, the arrangements shown can be used with other engines, and the engine employed need not drive a road vehicle, in which case the demand is of course set in some other way.

Referring first to FIG. 1, afuel pump 11 supplies fuel to the cylinders of anengine 12 in turn, the fuel pump being driven in a conventional manner, with the timing of injection controlled in the usual way. The driving of the fuel pump forms no part of the present invention and is not therefore described. Moreover, the type of pump used is not critical, but in the example shown the pump is a conventional in-line pump having acontrol rod 14 the axial position of which determines the rate of supply of fuel to theengine 12 by thepump 11. The axial position of thecontrol rod 14 is controlled by an eIectro-mechanical actuator 13 to determine the pump output.

The system further includes threetransducers 15, 16 and 17. Thetransducer 15 produces an output in the form ofa voltage shown in FIG. 2, the magnitude of the voltage being dependent on the rotational speed of the engine. Thetransducer 16 produces an output voltage shown in FIG. 3 the voltage being dependent on the rate of supply of fuel to the engine, (i.e. the pump output). For this purpose thetransducer 16 conveniently senses the axial position of thecontrol rod 14 as indi cated by the dotted line. Thetransducer 17 produces a voltage representing demand. Typically, thetransducer 17 is controlled by the accelerator pedal of the vehicle which is driven by the engine, and in the particular example being described, the engine is controlled by an all-speed governor, so that the output from thetransducer 17 is a voltage representing demanded en gine speed. The form of this voltage is shown in FIG. 4, and it should be noted that the slope of this output is opposite to the slopes of the outputs from the transducers l5, 16.

The outputs from the transducers IS, 16 and 17 are all applied, by way of resistors 15a, I60, I converting the signals to current signals, to the inverting terminal of anoperational amplifier 18 connected as a summing amplifier, whilst the output from thetransducer 16 is also connected through aresistor 16b to the inverting terminal of anoperational amplifier 19 connected as a summing amplifier. The amplifiers l8 and 19 are powered by positive and negative supply lines 2], 22 and have their non-inverting terminals connected to aline 23 which is kept at a reference potential mid-way between the potentials of thelines 21, 22. The origin in FIGS. 2 to 4 is the potential of theterminal 23, and the supply lines are all derived from the vehicle battery.

The output from theamplifier 18 is fed through adiode 24 to adrive circuit 25 which incorporates a power amplifier and which serves to control the electro-mechanical actuator I3. Similarly, the output terminal of theamplifier 19 is connected to thedrive circuit 25 through adiode 26. Thediodes 24 and 26 together constitute a discriminator, which ensures that only theamplifier 18, 19 producing the more positive output is coupled to thedrive circuit 25 at any given instant. Thus, if theamplifier 18 is producing the more positive output, then thediode 26 is reverse biased, and if theamplifier 19 is producing the more positive output, thediode 24 is reverse biased. FIG. 1 also shows thefeedback resistors 27, 28 associated with the amplifiers I8, 19 respectively, and it will be noted that the feedback circuit for each amplifier is taken from the input terminal of thedrive circuit 25. By virtue of this arrangement, the effective forward voltage drop across thediodes 24 and 26 is reduced by a factor dependent upon the amplifier open-loop gain, and so the temperature characteristics of the diodes become negligible when considering the temperature characteristics of the system. Also, there is a very sharp changeover from control by one amplifier to control by the other amplifier.

The basic operation is as follows. Theamplifier 18 receives current inputs representing demanded speed, actual speed and pump output.

These inputs, which are of the form seen in FIGS. 2 to 4, are compared, and if the sum of the inputs is not zero, then theamplifier 18 produces an output which is fed to thedrive circuit 25, and causes the pump output to change until the sum of the inputs is zero, at which point the output from theamplifier 18 becomes such that thedrive circuit 25 produces just sufficient current to keep thecontrol rod 14 in the position it has assumed.

Theamplifier 19 receives a signal by way of theresistor 16b representing pump output and also receives a reference current from areference source 20. If the pump output demanded by theamplifier 18 exceeds a predetermined value, then the output of theamplifier 19 will be more positive than the output of theamplifier 18, so that thediode 24 ceases to conduct as previously explained, and theamplifier 19 produces an out put to thedrive circuit 25. It should be noted that an increasing positive output from anamplifier 18 or 19 represents a demand for a decreasing pump output, that is to say there is an inverting stage between the amplifier and pump. When the amplifier I9 is producing an output, the system operates in the same way as when theamplifier 18 is producing an output to reduce the output of theamplifier 19 to a value such that the output from thedrive circuit 25 keeps thecontrol rod 14 in the position it has assumed. The system will stay in this condition until the amplifier l8 demands less fuel than the maximum set by theamplifier 19. When theamplifier 18 demands less fuel, it produces a greater positive output than the amplifier l9, and so takes over the operation.

Referring now to FIG. 5, the way in which the governor is designed and operates can be seen from the graph of pump output against speed. This graph also shows the effect of a number of controls not yet mentioned in relation to FIG. 1. Theline 40 is set by theamplifier 18 by virtue of the way in which the comparison of actual and demanded speeds is modified in accordance with the input from thetransducer 16. Theline 40 in the drawings represents 50 percent demand, and is one ofa family of lines stretching from percent demand to 100 percent demand. The extremes of this family, that is to say no demand and full demand, are indicated at 38 and 43. Theline 38 is set by acurrent source 31 providing an input to the inverting terminal of theamplifier 18, to ensure that the engine speed varies with pump output in the manner indicated by theline 38 even when the demand is zero. The maximum speed is set by acontrol 29 shown in FIG. 1 and which acts by limiting the maximum demand from thetransducer 17. Theline 35 is the maximum fuel line which is set by theamplifier 19 as previously explained.

Theboundary line 39 is a function of the engine, not the governor, and represents the no-load fuel require ments of the engine under different demands, so that thepoints 41 and 42 are the no-load engine speeds at zero and full demand, (i.e. with the pedal released and fully depressed respectively).

FIG. explains how the engine will behave in any circumstances. Suppose that the pedal has been set to demand 50 percent, corresponding to theline 40 shown in FIG. 5. The exact position on theline 40 at any given instant will depend upon the load on the engine, and so for this given setting of the pedal, the engine speed can vary within the limits set by thelines 35 and 40. The slope of theline 40 is, as previously explained, a result of the input to theamplifier 18 from thetransducer 16. Assuming that the engine is operating at a particular point on theline 40, then if the vehicle starts to go up an incline, the load will increase, and so for a given position of the pedal the operating point will move up theline 40, so that the speed is reduced. If the load becomes sufficiently great, theline 35 will be reached, and no further increase in pump output will be permitted. At this point, the speed falls rapidly. If the load decreases, then the operating point moves down theline 40 with the corresponding increase in speed. If the load decreases to zero, theline 39 is reached.

If the demand is changed, then assuming for the sake of argument that it changes from 50 percent demand to percent demand, the pump output will increase as rapidly as the pump and governor will allow until theline 35 is reached, and the engine will then move along theline 35 onto themaximum demand line 43, and will assume a position on theline 43 which is dependent upon the load.

If the demand is reduced, then assuming the demand is reduced from 50 to 0 percent, the operating point will move downwards until the fuel supply is zero. The speed then decreases until theline 38 is reached, after which the operating point moves up theline 38, finishing at a point on theline 38 determined by the load on the engine.

Turning now to FIG. 6, there is shown a second example in which the governor is a two-speed governor, that is to say a governor in which the demand signal is a fuel signal which is compared with the actual fuel, the pump output then being modified to provide the desired fuel output. In FIG. 6, theamplifier 18 receives a signal from thetransducer 16 by way of the resistor 16a, this signal representing actual fuel. A signal representing demanded fuel is fed by way of the resistor 17a to theamplifier 18, but it will be noted that there is no speed term fed to theamplifier 18 from thetransducer 15. The characteristics of the system are shown in FIG. 7. The line 40a is one ofa family of horizontally extending lines which are set by the governor, and can be taken to represent the 50 percent demand line. When the pedal sets a demand of 50 percent, theamplifier 18 sets the required fuel level. The operating point on the line 400 will of course then depend on the load on the engine.

The amplifier I9 overrides theamplifier 18 in FIG. 6 in a similar manner to the arrangement in FIG. 1, ex cept that theamplifier 19 now receives a signal by way of the resistor 15a representing speed, and also a reference current from a source 200 indicating the maximum engine speed. Theamplifier 19 sets the maximum speed of the engine, which is indicated by theline 43 in FIG. 7. It will be noted that theline 43 has a slope, that is to say the maximum permitted speed varies with pump output. This slope is obtained by feeding to the amplifier 19 a signal representing pump output, this sig nal being fed by way of theresistor 16b.

The maximum pump output, that is to say theline 35 in FIG. 7, is set by a control 29a which limits the maximum demand, in much the same way as thecontrol 29 limits the maximum speed in FIG. 1. The minimum engine speed, indicated by theline 38, is set by a current source 31a, which is similar to thecurrent source 31 except that because thecurrent source 310 acts on theamplifier 18, which does not receive a speed term, the current source 31a must receive a speed term as indicated by its connection to thetransducer 15.

Referring now to FIG. 8, thelines 23, 22 are interconnected through adiode 51 and aresistor 52 in series, and the junction of thediode 51 andresistor 52 is connected through a pair ofresistors 53, 54 respectively to the bases of a pair ofn-p-n transistors 55, 56. Thetransistors 55, 56 have their emitters connected throughdiodes 57, 58 respectively to the output terminals of theamplifiers 18, 19 and their collectors connected to the inverting input terminals of the amplifiers l8, 19 respectively. Moreover, the junction of thediode 51 andresistor 52 is also connected through aresistor 61 to the base of ann-p-n transistor 62 the emitter of which is connected throughdiodes 63, 64 in series to the output terminal of the amplifier l8 and through thediode 63 and a diode 65 in series to the output terminal of theamplifier 19. The collector of thetransistor 62 is connected to asafety network 66 coupled to theamplifier 25, and the cathode of thediode 26 is connected to theline 22 through aresistor 70.

The arrangement shown in FIG. 8 can be used in conjunction with the arrangement of FIG. 1 or with the arrangement of FIG. 6. The purpose of thetransistors 55 and 56 is to minimise the risk of damage to components within thepower amplifier 25 in the event that thepower amplifier 25 receives a dangerously high input signal from one of the amplifiers l8, 19. A high input signal to theamplifier 25 can arise, by way of example, whenever the demand is increased suddenly.

Considering first theamplifier 18, the base potential of thetransistor 55 is fixed and is negative with respect to theline 23. Thus, in order for thetransistor 55 to conduct, its emitter potential must be even more negative with respect to theline 23 than its base. If the demand is increased rapidly, then theamplifier 18 will produce a large negative output signal with respect to theline 23. This large negative signal at the output terminal of theamplifier 18 will permit current to flow through theresistor 53 to turn thetransistor 55 on. Thetransistor 55 now provides a low resistance feedback path between the output terminal of the amplifier l8 and its inverting input terminal, and this feedback path acts to limit the negative increase in the input signal provided to theamplifier 25. Thus, the input signal to the power amplifier is limited to a fixed level independent of the battery voltage.

Thetransistor 56 acts in exactly the same way in relation to theamplifier 19.

The purpose of thetransistor 62 and its associated components is to effect a control if the output of either amplifier l8, 19 becomes so negative with respect to the terminal 22 that thetransistors 55, 56 cannot cope with the situation. Thediode 63 is included so that as the potential at the output terminal of one of the amplifiers l8, 19 becomes increasingly negative, thetransistors 55 and 56 turn on before thetransistor 62. However, when thetransistor 62 does turn on, it provides an input signal to thesafety network 66 which operates theamplifier 25 to prevent damage to theamplifier 25. Thenetwork 66 can, for example, turn theamplifier 25 off.

Referring now to FIG. 9, the arrangement is similar to FIG. 8, and the same references have been used. An additional diode 51a is included in series with thediode 51, and thetransistors 55, 56 have theirbase resistors 53, 54 andemitter diodes 57, 58 omitted, and their emitter and collector connections to their respective amplifiers l8 and 19 reversed as compared with FIG. 8. In this example, the inputs to theamplifiers 18, 19 are sensed, but these inputs will of course be equal to the outputs, and so the operation is not altered. Thetransistor 62 operates as in FIG. 8, but thediode 63 is not needed.

We claim:

1. A fuel injection system for a compression-ignition engine, comprising in combination a pump for supplying fuel to the engine, an electro-mechanical actuator coupled to the pump to determine the pump output, a drive circuit for controlling the electro-mechanical actuator, first, second and third transducers producing respectively output voltages representing engine speed. pump output and demanded pump output, a first operational amplifier connected as a summing amplifier and having its inverting input connected through resistors to the second and third transducers, said first amplifier producing an output representing the difference between the actual and demanded pump outputs and also serving to restrict the maximum pump output to a predetermined value, a second operational amplifier connected as a summing amplifier and having its inverting input connected through resistors to the first and second transducers, a discriminator coupling the outputs of the amplifiers to the drive circuit, the arrangement being such that until a predetermined engine speed is attained, the discriminator couples the first amplifier to the drive circuit, but when said predetermined engine speed is reached, the discriminator couples the second amplifier to the drive circuit to limit the maximum engine speed, the maximum engine speed being varied with pump output by the second amplifier, a first low resistance feedback circuit connected between the output terminal and the inverting input of the first operational amplifier, a switching device in said feedback circuit, means for turning said switching device on when the output of the first amplifier reaches a predetermined level, a second low resistance feedback circuit connected between the output terminal and the inverting input of the second operational amplifier, a second switching device in said second feedback circuit, and means for turning the second switching device on when the output of the second amplifier reaches a predetermined value.

2. A fuel injection system for a compression-ignition engine, comprising in combination a pump for supplying fuel to the engine, an electro-mechanical actuator coupled to the pump to determine the pump output, a drive circuit for controlling the electro-mechanical ac tuator, first, second and third transducers producing respectively output voltages representing engine speed, pump output and demanded engine speed, a first operational amplifier connected as a summing amplifier and having its inverting input connected through resistors to the first, second and third transducers, said first amplifier producing an output representing the difference between the actual and demanded engine speed, but the difference being modified in accordance with the input received from the second transducer so as to provide the required engine characteristics, a second operational amplifier connected as a summing amplifier and having its inverting input connected through a resistor to the second transducer, a discriminator coupling the outputs of the amplifiers to the drive circuit, the arrangement being such that until a predetermined pump output is attained, the discriminator couples the first amplifier to the drive circuit, but when said predetermined rate of supply of fuel is reached, the discri'rninator couples the second amplifier to the drive circuit to limit the maximum rate of supply of fuel, a first low resistance feedback circuit connected between the output terminal and the inverting input of the first operational amplifier, a switching device in said feedback circuit, means for turning said switching device on when the output of the first amplifier reaches a predetermined level, a second low resistance feedback circuit means for turning the second switching device on when connected between the output terminal and the invertthe output of the second amplifier reaches a prcdetering input of the second operational amplifier, a second mined value.

switching device in said second feedback circuit, and

Claims (2)

1. A fuel injection system for a compression-ignition engine, comprising in combination a pump for supplying fuel to the engine, an electro-mechanical actuator coupled to the pump to determine the pump output, a drive circuit for controlling the electro-mechanical actuator, first, second and third transducers producing respectively output voltages representing engine speed, pump output and demanded pump output, a first operational amplifier connected as a summing amplifier and having its inverting input connected through resistors to the second and third transducers, said first amplifier producing an output representing the difference between the actual and demanded pump outputs and also serving to restrict the maximum pump output to a predetermined value, a second operational amplifier connected as a summing amplifier and having its inverting input connected through resistors to the first and second transducers, a discriminator coupling the outputs of the amplifiers to the drive circuit, the arrangement being such that until a predetermined engine speed is attained, the discriminator couples the first amplifier to the drive circuit, but when said predetermined engine speed is reached, the discriminator couples the second amplifier to the drive circuit to limit the maximum engine speed, the maximum engine speed being varied with pump output by the second amplifier, a first low resistance feedback circuit connected between the output terminal and the inverting input of the first operational amplifier, a switching device in said feedback circuit, meaNs for turning said switching device on when the output of the first amplifier reaches a predetermined level, a second low resistance feedback circuit connected between the output terminal and the inverting input of the second operational amplifier, a second switching device in said second feedback circuit, and means for turning the second switching device on when the output of the second amplifier reaches a predetermined value.

2. A fuel injection system for a compression-ignition engine, comprising in combination a pump for supplying fuel to the engine, an electro-mechanical actuator coupled to the pump to determine the pump output, a drive circuit for controlling the electro-mechanical actuator, first, second and third transducers producing respectively output voltages representing engine speed, pump output and demanded engine speed, a first operational amplifier connected as a summing amplifier and having its inverting input connected through resistors to the first, second and third transducers, said first amplifier producing an output representing the difference between the actual and demanded engine speed, but the difference being modified in accordance with the input received from the second transducer so as to provide the required engine characteristics, a second operational amplifier connected as a summing amplifier and having its inverting input connected through a resistor to the second transducer, a discriminator coupling the outputs of the amplifiers to the drive circuit, the arrangement being such that until a predetermined pump output is attained, the discriminator couples the first amplifier to the drive circuit, but when said predetermined rate of supply of fuel is reached, the discriminator couples the second amplifier to the drive circuit to limit the maximum rate of supply of fuel, a first low resistance feedback circuit connected between the output terminal and the inverting input of the first operational amplifier, a switching device in said feedback circuit, means for turning said switching device on when the output of the first amplifier reaches a predetermined level, a second low resistance feedback circuit connected between the output terminal and the inverting input of the second operational amplifier, a second switching device in said second feedback circuit, and means for turning the second switching device on when the output of the second amplifier reaches a predetermined value.

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