US3897763A

US3897763A - Fuel system for engines

Info

Publication number: US3897763A
Application number: US347730A
Authority: US
Inventors: Malcolm Williams; Geoffrey Albert Kenyon Brunt; Christopher Robin Jones
Original assignee: CAV Ltd
Current assignee: CAV Ltd
Priority date: 1972-04-04
Filing date: 1973-04-04
Publication date: 1975-08-05
Anticipated expiration: 1992-08-05
Also published as: JPS5534296B2; IN140152B; FR2179081B1; FR2179081A1; BR7302423D0; JPS4914818A; GB1429293A; CA991726A; IT982934B; ES413340A1

Abstract

A fuel system, particularly for a diesel engine, has a closed loop control system including an electronic governor powered by positive and negative supply lines and incorporating a summing amplifier the output from which controls the pump. The noninverting input of the amplifier is connected to a third supply line, which is maintained at a fixed percentage of the potential between the positive and negative supply lines. Also, the signals applied to the amplifier have magnitudes proportional to the potential between the positive and negative supply lines, so that fluctuations in the supply voltage do not affect the operation of the system.

Description

United States Patent Williams et al. 1 Aug. 5, 1975 {54] FUEL SYSTEM FOR ENGINES 3.578.871 /1971 Sakumoto l23/32 EA 3.630177 12/197] Engel .1 [23/32 EA [I'lVCntOl'SI Malcolm wllllams, SOllhUli'. 36659OU 5/ 97 l I H Geoffrey Albert Kenyon Brunt, 3.693.603 9/1972 Lemanczyk 123/32 EA Glaston ury; Chri ph r R bin 3.699.935 10/1972 Adler 123/32 EA Jones, Alccster. all of England 3.707.950 1/1973 Schlimme... l23/32 EA 3.724.433 4/1973 V055 123/32 EA {731 Assgneci Bmmgham 3.777.174 12/1973 ButSCher 123/32 EA England 22 Filed; Apr. 4 973 Primar E, :aminerCharles J. Myhre Assistant E.\'uminerRonald B. Cox I2] I Appl' Nu: 347'730 Attorney, Agent. or FirmHolman 8L Stem Foreign Application Priority Data i 1 ABSTRACT Apr 4. 1972 United Kingdom 15340/72 A fuel System, Particularly for a diesel engine. has a W73 Uniwd Kingdom 15355; closed loop control system including an electronic governor powered by positive and negative supply [52] us C| H 123/139 290740; 0 lines and incorporating a summing amplifier the out- 6059'09 put from which controls the pump. The non-inverting 1. 11 int. c1. F02m 39/00; F02b 3/00 input of the amplifier is connected to a third pp [53] Field 0 Search 33 3 5 33 EA 32 AE line, which is maintained at a fixed percentage of the 33 1 1 3935 393 2 40 potential between the positive and negative supply lines. Also. the signals applied to the amplifier have I 5 References Cited magnitudes proportional to the potential between the UNITED STATES PATENTS positive and negative supply lines, so that fluctuations in the supply voltage do not affect the operation of the 3.425.401 2/!969 Lang a a 1 123/32 EA System- 3.478.5l2 ll/l969 Brahm 123/32 EA 3.543.792 l2/l970 Palmer 123/32 EA 4 Claims, 9 Drawing Figures l3 I A 2| SHEET PATENTED AUG 5 I975 U P T U 3 0 DI l. M 0 0 l W 2 F v o 6 9 i b 2 w i 3 2 3 2r 2 a 7.. P. /3 01 D 2 8 II E l 1 6 v 2 s 2 FIG. 4

3, PATENTEUAUG 5191s 897 763 sum 2 PUMP OUTPUT SPEED FIG? SHEET PATENTED AUG 5 I975 FIG.8

FIG.9

FUEL SYSTEM FOR ENGINES This invention relates to fuel systems for engines.

A fuel system according to the invention includes a pump supplying fuel to the engine, and a closed loop control system controlling the pump, the closed loop control system including an electronic governor which is powered by positive and negative supply lines and incorporates a summing amplifier the output from which controls the pump, said amplifier having its noninverting input connected to a third supply line which is maintained at a fixed percentage of the potential between the positive and negative supply lines, and having applied to its inverting input at least two signals of opposite polarity with respect to said third supply line, said signals having magnitudes proportional to the potential between the positive and negative supply lines.

In the accompanying drawings,

FIG. 1 is a circuit diagram, partly in block form, illustrating one example of the invention.

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 example of the invention.

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

FIG. 8 is a circuit diagram showing one form of power supply circuit, and

FIG. 9 is a circuit diagram illustrating one form of check circuit for the power supply circuit.

All the examples described relate to a fuel injection system 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, a fuel pump 11 supplies fuel to the cylinders of an engine 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 a control rod 14 the axial position of which determines the rate of supply of fuel to the engine 12 by the pump 11. The axial position of the control rod 14 is controlled by an electromechanical actuator 13 to determine the pump output.

The system further includes three

transducers

15, 16 and 17. The transducer produces an output in the form of a voltage shown in FIG. 2, the magnitude of the voltage being dependent on the rotational speed of the engine. The transducer 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 the transducer 16 conveniently senses the axial position of the control rod 14 as indicated by the dotted line. The transducer 17 produces a voltage representing demand. Typically, the transducer 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 the transducer 17 is a voltage representing demanded engine 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

15, 16.

The outputs from the

transducers

15, 16 and 17 are all applied, by way of resistors 15a, 16a, 17a, converting the signals to current signals, to the inverting terminal of an operational amplifier 18 connected as a summing amplifier, whilst the output from the transducer 16 is also connected through a resistor 16b to the inverting terminal of an operational amplifier 19 connected as a summing amplifier. The

amplifiers

18 and 19 are powered by positive and

negative supply lines

21, 22 derived from the vehicle battery and have their non-inverting terminals connected to a line 23 which is kept at a reference potential mid-way between the potentials of the

lines

21, 22. The origin in FIGS. 2 to 4 is the potential of the line 23. All the transducers are powered from the supply lines, which are of course intended to remain at constant potentials. However, the transducer outputs are proportional to the potential between the

lines

21, 22 and so if this potential varies, so will the transducer outputs.

The output from the amplifier 18 is fed through a diode 24 to a drive circuit 25 which incorporates a power amplifier and which serves to control the electro-mechanical actuator 13. Similarly, the output terminal of the amplifier 19 is connected to the drive circuit 25 through a diode 26. The

diodes

24 and 26 together constitute a discriminator, which ensures that only the

amplifier

18, 19 producing the more positive output is coupled to the drive circuit 25 at any given instant. Thus, if the amplifier 18 is producing the more positive output, then the diode 26 is reverse biased, and if the amplifier 19 is producing the more positive output, the diode 24 is reverse biased. FIG. 1 also shows the

feedback resistors

27, 28 associated with the

amplifiers

18, 19 respectively, and it will be noted that the feedback circuit for each amplifier is taken from the input terminal of the drive circuit 25. By virtue of this arrangement, the effective forward voltage drop across the

diodes

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. The amplifier 18 receives current inputs representing demanded speed, actual speed, and pump output. These inputs are compared, and the amplifier 18 produces an output which is fed to the drive circuit 25, and modifies the pump output until the input signals to the amplifier 18 are balanced, at which point the output from the amplifier 18 becomes such that the drive circuit 25 produces just sufficient current to keep the control rod 14 in the position it has assumed.

There is an inversion stage between the amplifiers l8, l9 and the pump, so that the smaller the output from the amplifier 18, the greater the demanded pump output. The amplifier 19 receives a signal by way of the resistor 16b representing pump output and also receives a reference current from a reference source 20. If the demanded pump output exceeds a predetermined value, then the amplifier 19 produces a positive output which is more positive than the output of the amplifier 18, so that the diode 24 ceases to conduct as previously explained and the amplifier 19 produces an output to the drive circuit 25 to limit the pump output. When the amplifier 19 is producing an output, the system operates in the same way as when the amplifier 18 is producing an output to reduce the output of the amplifier 19 to a value such that the output from the drive circuit 25 keeps the control rod 14 in the position it has assumed. The system will stay in this condition until the amplifier I8 demands less fuel than the maximum set by the amplifier 19. When the amplifier l8 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. The line 40 is set by the amplifier 18 by virtue of the way in which the comparison of actual and demanded speeds is modified in accordance with the input from the transducer 16. The line 40 in the drawings represents 50 percent demand, and is one of a family of curves stretching from demand to l00 percent demand. The extremes of this family, that is to say no demand and full demand, are indicated at 38 and 43. The line 38 is set by a current source 31 providing an input to the inverting terminal of the amplifier 18, to ensure that the engine speed varies with pump output in the manner indicated by the line 38 even when the demand is zero. The maximum speed is set by a control 29 shown in FIG. 1 and which acts by limiting the maximum demand from the transducer 17. The line 35 is the maximum fuel line which is set by the amplifier 19 as previously explained.

The boundary line 39 is a function of the engine, not the governor, and represents the no'load fuel requirements of the engine under different demands, so that the

points

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 the line 40 shown in FIG. 5. The exact position on the line 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 the lines and 40. The slope of the line is, as previously explained, a result of the input to the amplifier 18 from the transducer 16. Assuming that the engine is operating at a particular point on the line 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 the line 40, so that the speed is reduced. If the load becomes sufficiently great, the line 35 will be reached, and no further increase in pump output will be permit ted. At this point, the speed falls rapidly. If the load decreases, then the operating point moves down the line 40 with the corresponding increase in speed. If the load decreases to zero, the line 39 is reached.

[f the demand is changed, then assuming for the sake of argument that it changes from percent demand to 100 percent demand, the pump output will increase as rapidly as the pump and governor will allow until the line 35 is reached, and the engine will then move along the line 35 onto the maximum demand line 43, and will assume a position on the line 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 downward until the fuel supply is zero. The speed then decreases until the line 38 is reached, after which the operating point moves up the line 38, finishing at a point on the line 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, the amplifier 18 receives a signal from the transducer 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 the amplifier 18, but it will be noted that there is no speed term set to the amplifier 18 from the transducer 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, the amplifier 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 19 overrides the amplifier 18 in FIG. 6 in a similar manner to the arrangement in FIG. 1, except that the amplifier 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. The amplifier 19 sets the maximum speed of the engine, which is indicated by the line 43 in FIG. 7. It will be noted that the line 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 signal being fed by way of the resistor 16b.

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

It is extremely important that the line 23 is maintained at a potential which is a fixed percentage of the potential between the

lines

21, 22. As described above, this percentage is 50 percent. Because the amplifiers l8 and 19 have their non-inverting inputs connected to the line 23, the transducers have outputs which are proportional to the potential between the

lines

21, 22 and the overall system is a closed loop control system, then the fact that the line 23 is maintained at a constant percentage of the potential between the

lines

21, 22 ensures that variations in the supply voltage do not alter the operation of the system. This of course is of considerable importance where the system is employed on a vehicle, and the basic power source is the battery of the vehicle, the voltage of which can vary.

In order to understand the effect of a variation in battery voltage, assume for example that the

lines

21, 22

and 23 are at 20 volts, 0 volts and I0 volts respectively. If the resistors a, 16a, 17a are equal, then in steady state conditions, the

transducers

15, 16, 17 may produce output voltages of 13, 13 and 4 respectively. It will be seen that the 4 volts, which is 6 volts below the reference, balances the two l3 volt outputs, each of which is 3 volts above the reference. Suppose now, taking an extreme case by way of illustration, that the line 21 falls to 10 volts. For fixed values of the parameters, the transducer output voltages become 6.5, 6.5 and 2 respectively. However, the reference potential now becomes 5 volts, so that the system is still in balance.

It should be noted that the various references employed are also derived from the supply lines, and so are proportional to the potential between the

lines

21, 23.

Similar considerations of course apply to the amplifier 19, and to the

amplifiers

18 and 19 in FIG. 6.

One arrangement for maintaining the line 23 at a fixed percentage of the potential between the

lines

21, 22 is shown in FIG. 8. The arrangement is powered by the battery 52 of a road vehicle, the battery 52 having its negative terminal connected to the line 22, and its positive terminal connected to the collector of an n-p-n transistor 56, the emitter of which is connected to the line 21. The collector and base of the transistor 56 are connected respectively to the collector and emitter of a further n-p-n transistor 57, the base of which is connected to the positive battery terminal through a resistor 59, and to the terminal 22 through a Zener diode 58.

There is further provided a potentiometer

chain comprising resistors

60 and 61 connected in series between the

lines

21, 22. A point intermediate the resistor 60, 6| is connected to the base of an n-p-n transistor 62 the collector of which is connected to the line 21 and the emitter of which is connected to the line 22 by way of a resistor 63. In addition, a further n-p-n transistor 64 is provided having its emitter connected to the emitter of the transistor 62 and its collector connected to the terminal 21 by way of a resistor 65. The base of the transistor 64 is connected to the line 23.

Connected between the

lines

21, 23 is a resistor 66 and in parallel with the resistor 66 is a series combination of a resistor 67 and the collector-emitter path of an n-p-n transistor 68. The base of the transistor 68 is connected to the emitter ofa further n-p-n transistor 69 and the base of the transistor 69 is connected to the collector of the transistor 64. The collector of the transistor 69 is connected to the terminal 21, and the emitter of the transistor 69 is connected by way of a resistor 70 to the line 23.

In operation, the

transistors

56 and 57 together with the Zener diode 58 form a voltage stabilizing network so that a substantially constant voltage is obtained between the

lines

21, 22. Also shown in FIG. 8 are two

loads

53, 54 which indicate current consuming portions of the governors. In the particular example, the load 54 consumes more current than the load 53 and the resistor 66 supplies the majority of the surplus current for the load 54. In order to maintain the voltage at the line 23 at substantially the desired value the conduction of the transistor 68 is varied, and the transistor 68 together with the resistor 67 acts as a variable resistor in parallel with the resistor 66. The

resistors

60 and 61 are of equal value, so that the base voltage of the transistor 62 is maintained at the desired value of the voltage at the line 23 and the

transistors

62 and 64 act as a differential amplifier to control the base current of the

transistors

69, 68 in accordance with the difference between the desired value and the actual value of the voltage at the line 23. With this arrangement should the value of the voltage at the line 23 tend to vary in either direction then the current flowing through the transistor 68 is varied accordingly to maintain the voltage substantially constant as a known fraction of the voltage between the

lines

21, 22. This ratio will be maintained as the supply voltage varies, even if the supply voltage should fall below the breakdown voltage of the Zener diode 18, for example when cranking the engine.

FIG. 9 shows an arrangement for checking the potentials of the

lines

21, 22, 23, and effecting a control when necessary. For this purpose, a first check circuit is provided which comprises an n-p-n transistor 83 the base of which is connected to a potential divider chain constituted by

resistors

84 and 85 connected in series between the

lines

21, 22. The emitter of the transistor 83 is connected to the line 23. The collector of the transistor is connected to a first safety circuit 86 which is associated with the power amplifier 25. The safety circuit 86 serves when operated to disable the power amplifier 25 so that no current is supplied to the actuator 13. The arrangement is such that in the event that the voltage at the line 23 should fall below 50 percent of the voltage at the line 21, then the transistor 83 will conduct to cause operation of the circuit 86. In the event that the voltage at the line 23 reverts to its correct value then the safety circuit 86 will cease to operate and the amplifier 25 operates again. Thus, the circuit checks that the voltage at the line 23 relative has not fallen below a predetermined percentage of the voltage between the

lines

21, 22.

It is also necessary to sense when the voltage at the line 23 rises above a predetermined value. This is achieved by sensing the voltage at the line 23 relative to the line 21 and comparing it with a standard voltage. It will be understood of course that the first check circuit only checks for a low voltage at the line 23 relative to the desired proportion of the voltage between the

lines

21, 22. The second check circuit comprises a p-n-p transistor 87 the emitter of which is connected by way of a diode 88 to the line 22. The base of the transistor 87 is connected through a resistor 89 to a point intermediate a resistor 90 and a Zener diode 91 connected in series between the

lines

21, 22. Thus the voltage on the base of the transistor 87 will be determined by the breakdown voltage of the Zener diode 91. The collector of the transistor 87 is connected to a second safety circuit 92 associated with the power amplifier 25. The safety circuit 92 in this example serves to prevent the supply of current by the power amplifier 25 to the actuator 13. In operation, in the event that the voltage at the line 23 rises above the predetermined value set by the Zener diode, the circuit 92 will be operated to prevent the amplifier 25 supplying current to the actuator 13.

It will be noted that in the event that the voltage at the line 21 rises then the voltage at the line 23 will also rise. Hence the second check circuit indirectly but effectively, checks that the voltage at the line 21 has not risen above a desired value.

We claim:

1. A fuel system for an engine, comprising in combination, a pump for supplying fuel to the engine, an actuator for controlling the amount of fuel supplied to the engine, a power amplifier for supplying power to the actuator, a control circuit for controlling the amount of power supplied to the actuator by the power amplifier, means for supplying to the control circuit signals indicative of the actual speed of the engine, the pump output and a manually determined demand signal, a power supply circuit for connection to a source of supply, said power supply circuit having three output lines and incorporating means maintaining the voltage of one of the lines relative to one of the other lines at a predetermined percentage of the voltage between the other lines, said power supply circuit providing power for the control circuit, a first check circuit for checking the voltage on said one line relative to the voltages on said other lines, and a second check circuit for checking the actual voltage on said one line relative to one of the other lines, said check circuits when operated serving to prevent operation of the power amplifier thereby cutting off the supply of power to the actuator.

2. A fuel system for an engine including a pump supplying fuel to the engine, and a closed loop control system controlling the pump, the closed loop control system including an electronic governor which is powered by positive and negative supply lines and incorporates a summing amplifier the output from which controls the pump, said amplifier having its non-inverting input connected to a third supply line and having applied to its inverting input at least two signals of opposite polarity with respect to said third supply line, said signals having magnitudes proportional to the potential between said positive and negative supply lines, a battery providing power for the system, a voltage regulator coupling the battery to the positive and negative supply lines, variable resistance means coupling the third supply line to one of said supply lines, and comparator means continuously monitoring the potential on the third supply line and varying said resistance means to maintain the potential on said third supply line at a fixed percentage of the potential between said positive and negative supply lines.

3. A fuel system for an engine including a pump supplying fuel to the engine, and a closed loop control system controlling the pump, the closed loop control system including an electronic governor which is powered by positive and negative supply lines and incorporates a summing amplifier the output from which controls the pump, said amplifier having its non-inverting input connected to a third supply line and having applied to its inverting input at least two signals of opposite polar ity with respect to said third supply line, said signals having magnitudes proportional to the potential between said positive and negative supply lines, means monitoring the potentials of the positive and negative supply lines and maintaining said third supply line at a fixed percentage of the potential between the positive and negative supply lines, a check circuit for effecting a control to prevent supply of fuel to the engine if the potential of the third supply rail falls below said fixed percentage, the check circuit including a transistor with emitter and base terminals, one of said terminals being connected to the third supply line and the other of said terminals being connected to a potential divider connected across the positive and negative supply lines, the transistor turning on to effect the required control.

4. A fuel system for an engine including a pump for supplying fuel to the engine, and a closed loop control system controlling the pump, the closed loop control system including an electronic governor which is powered by positive and negative supply lines and incorporates a summing amplifier the output from which controls the pump, said amplifier having its non-inverting input connected to a third supply line and having applied to its inverting input at least two signals of opposite polarity with respect to said third supply line, said signals having magnitudes proportional to the potential between said positive and negative supply lines, means monitoring the potentials of the positive and negative supply lines and maintaining said third supply line at a fixed percentage of the potential between the positive and negative supply lines, a check circuit for effecting a control to prevent supply of fuel to the engine if the potential on the third supply line rises to a predetermined value, the check circuit including a transistor with emitter and base terminals, one of said terminals being maintained at a fixed potential by means of a zener diode and the other terminal being connected to the third supply line, the transistor turning on to effect the required control.

l t i

Claims

3. A fuel system for an engine including a pump supplying fuel to the engine, and a closed loop control system controlling the pump, the closed loop control system including an electronic governor which is powered by positive and negative supply lines and incorporates a summing amplifier the output from which controls the pump, said amplifier having its non-inverting input connected to a third supply line and having applied to its inverting input at least two signals of opposite polarity with respect to said third supply line, said signals having magnitudes proportional to the potential between said positive and negative supply lines, means monitoring the potentials of the positive and negative supply lines and maintaining said third supply line at a fixed percentage of the potential between the positive and negative supply lines, a check circuit for effecting a control to prevent supply of fuel to the engine if the potential of the third supply rail falls below said fixed percentage, the check circuit including a transistor with emitter and base terminals, one of said terminals being connected to the third supply line and the other of said terminals being connected to a potential divider connected across the positive and negative supply lines, the transistor turning on to effect the required control.