US3889648A

US3889648A - Fuel systems for engines

Info

Publication number: US3889648A
Application number: US347729A
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: 1975-06-17
Anticipated expiration: 1992-06-17
Also published as: IT982933B; FR2179080A1; CA991725A; ES413339A1; GB1429771A; DE2316817A1; FR2179080B1; AR207103A1; JPS4914819A; IN140470B

Abstract

A fuel system for an engine has an electronic governor controlling a pump, the governor receiving a number of signals including one signal from a transducer meansuring engine speed. This transducer includes a pump circuit, and is characterised in that the capacitor of the pump circuit is connected across the input and output of an operational amplifier.

Description

United States Patent Williams et a1.

FUEL SYSTEMS FOR ENGINES Inventors: Malcolm Williams, Solihull;

Geoffrey Albert Kenyon Brunt, Glastonbury; Christopher Robin Jones, Alcester, all of England C.A.V. Limited, London, England Assignee:

Filed: Apr. 4, 1973 Appl. No.: 347,729

Foreign Application Priority Data Field of Search 123/139 E, 32 EA, 32 AE, 123/102; 60/3928; 73/398; 307/247, 266, 268; 328/165, 158

[56] References Cited UNITED STATES PATENTS 3,478,512 11/1969 Brahm 123/32 EA 3,695,242 10/1972 Tada 1 23/32 EA 3,699,935 10/1972 Adler 123/102 3,717,174 12/1973 Butscher 123/32 EA 3,724,430 4/1973 Adler 123/32 EA 3,724,433 4/1973 Voss 123/32 EA Primary ExamIneP-CharIes J. Myhre Assistant ExaminerRonald B. Cox Attorney, Agent, or Firm1-1o1man & Stern [57] ABSTRACT A fuel system for an engine has an electronic governor controlling a pump, the governor receiving a number of signals including one signal from a transducer meansuring engine speed. This transducer includes a pump circuit, and is characterised in that the capacitor of the pump circuit is connected across the inpu and output of an operational amplifier.

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PATENTEIJJUN 17 I975 3,888,848

sum 2 l A AZ l r #50. as I 1 wlsb I 17 29a 25 A Sin 4 Z2 3 |6b PUMP OUTPUT PATENTEDJunNms 8888.848

SHEET 3 FIG. H.

46a Sla 82a 9 la 1 FUEL SYSTEMS FOR ENGINES This invention relates to fuel systems for engines, particularly, but not exlcusively, compression-ignition engines. The invention further resides in electronic pump circuits for use in such systems and for other purposes.

In one aspect, the invention resides in a fuel system for an engine, comprising in combination a pump sup plying fuel to the engine, an actuator controlling the pump, and an electronic governor for controlling the actuator, said governor receiving electrical signals representing engine speed and at least one further engine parameter, the speed signal being obtained using a transducer producing an 21.0. output at a frequency proportional to engine speed, an a pump circuit for converting said signal to a do signal, said pump circuit including a capacitor across which is developed a voltage proportional to the frequency of the ac. output, said capacitor being connected across the input and output terminals of an operational amplifier.

In another aspect, the invention resides in an electronic pump circuit in which a voltage dependent on the frequency of an ac. input is developed across a capacitor, characterised in that the capacitor is connected across the input and output terminals of an operational amplifier.

In the accompanying drawings,

FIG. 1 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 pulse shaping circuit used in FIG. 1 or FIG. 6,

FIG. 9 is a circuit diagram illustrating a modification of the arrangement shown in FIG. 8,

FIG. 10 is a circuit diagram illustrating one form of pump circuit,

FIG. 11 is a circuit diagram illustrating another form of pump circuit,

FIG. 12 is a circuit diagram of a third form of pump circuit, and

FIGS. 13 to are wave forms illustrating the operation of FIG. 12.

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 electro-mechanical actuator 13 to determine the pump output.

The system further includes three

transducers

15a, 16 and 17. The transducer 15a produces an output having a frequency proportional to engine speed, this output being fed by way of a pulse shaping network 15b to a pump circuit 15c which 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 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

15d, 16a, 17a converting the signals to current signals, to the inverting termin: l 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 amplifier l8 and 19 are powered by positive and

negative supply lines

21, 22 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 of FIGS. 2 to 4 is the potential of the line 23, and the supply for the power lines is derived from the vehicle battery.

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 termnal 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 contol by the other amplifier.

The basic operation is as follows. The amplifier 18 compares the input currents it receives and modifies the pump output until the sum of the input currents is zero.

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 set by the amplifier 18 exceeds a value set by the source 20, then the amplifier 19 produces an 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. It should be noted that an increasing output from an amplifier 18 or 19 is in fact a demand for a decrease in fuel, that is to say there is an inverting stage between the amplifiers 18, 19 and the pump. 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 18 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 19, 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% demand, and is one of a family of lines stretching from demand to 100% 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 curve 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%, 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

35 and 40. The slope of the line 40 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 permitted. 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.

If the demand is changed, then assuming for the sake of argument that it changes from 50% demand to 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%, 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 engme.

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 fed to the amplifier 18 by way of the resistor 15d. The characteristics of the system are shown in FIG. 7. The line 40a is one of a family of horizontally extending lines which are set by the governor, and can be taken to represent the 50% demand line. When the pedal sets a demand of 50%, the amplifier 18 sets the required fuel level. The operating point on the line 40a will of course then depend on the load on the engine.

The amplifier l9 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 15d representing speed, and also a reference current from a source 20a 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 31a, which is similar to the current source 31 except that because the current source 31a acts on the amplifier 18, which does not receive a speed term, the current source 31a must receive a speed term as indicated by its connection to the pump circuit 150.

FIG. 8 shows one form of the pulse shaping circuit 15b. Referring to FIG. 8, the circuit is powered by the

supply lines

21, 22, 23. The input to the circuit is taken from the transducer 15a and is fed between an input terminal 45 and the line 23, and the output from the circuit is taken between a terminal 46 and the line 23.

The terminal 45 is connected to the line 23 through a resistor 47 and a capacitor 48 in series, the junction of the resistor 47 and capacitor 48 being connected to the line 23 through a resistor 49 and a capacitor 51 in series, and the junction of the resistor 49 and capacitor 51 being connected to the base of an n-p-n transistor 52. The transistor 52 has its collector connected to the line 21, and its emitter connected to the emitter of a further n-p-n transistor 53, and to the collector of an n-p-n transistor 54. The emitter of the transistor 54 is connected through a resistor 55 to the line 22, and the collector of the transistor 53 is connected through a resistor 56 to the line 21. The base of the transistor 53 is connected to the line 23 through a resistor 57. The

lines

23 and 22 are further interconnected through a resistor 58 and a pair of diodes 59, 61 in series, and the junction of the resistor 58 and diode 59 is connected to the base of the transistor 54.

The collector of the transistor 53 is connected to the base of a p-n-p transistor 62 having its emitter connected to the line 21 and its collector connected to the output terminal 46, to the collector of the transistor 53 through a capacitor 63, and through a pair of resistors 64 and 65 in series to the line 22. The junction of the resistors 64 and 65 is connected to the base of the transistor 53. Moreover, the terminal 46 is connected to the collector of an n-p-n transistor 66, the emitter of which is connected through a resistor 67 to the line 22 and the base of which is connected through a diode 68 to the line 23.

As will be seen from FIG. 1, the output between the terminal 46 and the line 22 is applied to the pump circuit c, which can take a number of forms, but usually includes a pair of diodes. The purpose of the transistor 66, the resistor 67 and the diode 68 is merely to provide two diodes which in operation will compensate for the voltage drop across the diodes in the pump circuit, so that the circuit is not affected by changes in temperature.

The ac. signal from the transducer 15a is fed between the terminal 45 and the line 23, and is filtered by the resistor-

capacitor network

47, 48, 49, 51. The

transistors

52, 53, 54 and 62 with their associated components then produce a square wave between the terminal 46 and line 22 in the following manner.

For ease of explanation, assume that the circuit is in one of its stable states with the

transistors

53, 54 and 62 conducting, the terminal 46 approximately at the potential of the line 21. The potential at the base of the transistor 53 at this stage is determined by the resistors 57, 64 and 65. This is the state the circuit assumes with the voltage at the terminal 45 relatively low. As the voltage at the terminal 45 increases, the transistor 52 starts to conduct, and since the transistor 54 acts as a constant current source, current flow through the transistor 53 is reduced. Since the base current for the transistor 62 flows through the transistor 53, conduction of the transistor 62 is alos reduced, so that the base potential of the transistor 53 is varied, and the

transistors

53 and 62 switch off rapidly by regenerative action. It will be appreciated that the rate at which the transistor 53 switches off is extremely rapid, and is not dependent on the rate at which the voltage is rising at the terminal 45 once the transistor 52 has started to conduct. Once the transistor 62 is off, then the potential at the terminal 46 is equal to the potential of the line 23, less the voltage drop across two diodes, namely the diode 68 and the base-emitter diode of the transistor 66, these diodes compensating for the diodes in the pump circuit as previously explained.

The resistors 64, 65 and 57 are selected so that the base potential of the transistor 53 when the transistor 62 is conducting is at a predetermined voltage above the line 23, and is at the same predetermined voltage below the voltage of the line 23 when the transistor 62 is off. As the input to the terminal 45 now falls, a stage is reached at which the transistor 52 conducts less, and the transistor 53 starts to turn on. As soon as the transistor 53 starts to turn on, it provides base current to the transistor 62, and by regenerative action the circuit again switches rapidly, independently of the rate of fall of voltage at the terminal 45, to the opposite state in which the

transistors

53 and 62 are on and the terminal 46 is at the potential of the line 21. Thus, the circuit produces a square wave output which in this example has a mark-space ratio of approximately unity. The use of the transistor 54 as a constant current source permits operation over a wide range of supply voltage between the

lines

21, 22. The minimum amplitude of the square wave is set by the resistors 57, 64, 65.

Turning now to FIG. 9, there is shown a modification in which both halves of each cycles of the input at terminal 45 are used. In FIG. 9, the circuit connections are not shown in detail, but are exactly the same as in FIG. 8, except for some additional components associated with the transistor 52. Thus, the transistor 52 now has its collector connected to the line 21 by way of a resistor 81, and its collector also connected to the base of a p-n-p transistor 83 with its emitter connected to the line 21 through a resistor 84 and its collector connected to a terminal 46a and further connected to the collector of an n-p-n transistor 85, the base of which is connected through a diode 86 to the line 23 and the emitter of which is connected through a resistor 87 to the line 23. It will be seen that the transistors 83 and and their associated components are equivalent to the

transistors

62 and 66 and their associated components in FIg. 8, and that the switching of these transistors is effected in accordance with the voltage across the resistor 81, in the same way as the switching of the

transistors

62 and 66 is effected by the voltage across the resistor 56 in FIG. 8. The effect is that the wave form at the terminal 46a is complementary to the wave form at the terminal 46. Obviously by taking an output from the

terminals

46 and 46a the circuit can be made to have a more rapid response, or alternatively can have the same response rate for a lower frequency input at terminal 45.

In some examples, it is preferred that the diode 68 in FIG. 8, and its equivalent diode 86 in FIG. 9, should have it anode connected to the junction of a pair of resistors connected between the

lines

23, 22.

FIG. 10 illustrates one form of pump circuit which is intended for use with the arrangement of FIG. 8. Referring to FIG. 10, the terminal 46 seen in FIG. 8 is connected to the line 23 through a series circuit including a resistor 91, a capacitor 92 and the cathode-anode part of a diode 93. The junction of the capacitor 92 and diode 93 is connected through the anode-cathode path of a diode 94 to the inverting input terminal of an operational amplifier 95 having its non-inverting input terminal connected to the line 23. The output terminal of the amplifier 95 is connected to the resistor 15d, which provides the required input to the circuit as described with reference to FIG. 1 or FIG. 6. The feedback between the output terminal of the amplifier 95 and its inverting input terminal includes a resistor 97 and a capacitor 96 in parallel and moreover the inverting input terminal of the amplifier 95 is connected to the line 22 through a resistor 98.

If the capacitor 96 and its associated conventional discharge resistor 97 were to be connected in parallel between the inverting input terminal of the amplifier 95 and the line 23, then the arrangement would constitute a conventional diode pump circuit followed by an amplifier. With such an arrangement, the capacitor 96 would acquire a charge dependent upon the frequency of the signal at the terminal 46, but the charge would not necessarily be directly proportional to the frequency at the terminal 46. However, by using the capacitor 96 in the position shown, the voltage developed across the capacitor 96 is proportional to the frequency of the input signal at the terminal 46.

Without the resistor 98, the arrangement of FIG. 10 would produce an output which for zero frequency would be at the potential of the line 23, and then would decrease towards the potential of the line 22 as the frequency increased. As will be seen with reference to FIG. 2, this is not the characteristic required, and the addition of a bias by way of the resistor 98 lifts the curve to the correct position, as shown in FIG. 2.

The arrangement of FIG. 11 is similar to that shown in FIG. 10, but is designed for use with the circuit of FIG. 9. The

components

91, 92, 93 and 94 are duplicated in FIG. 11, and are indicated with the same reference numerals and the suffix A. The operation is indentical to that of FIG. 10, except tht the input frequency to the amplifier 95 is doubled.

It is to be understood that the particular pulse shaping circuit described has advantages even when used with a conventional diode pump circuit. Moreover, the particular pump circuit described has advantages with or without the particular form of pulse shaping circuit. Additionally, the pump circuit described can be used in applications other than fuel systems.

It is a matter of some importance that the engine speed should not exceed its maximum value, becuase if it does serious damage could result. It will be noted that in the event of a failure in the pump circuit of FIG. 10 or FIG. 11 resulting in a low output voltage at the resistor 15d, then this fault will be interpreted as a high engine speed, so that the circuit will reduce the engine speed, and no damage will result. However, a fault resulting in a high output voltage at the resistor 15d will be interpreted as a low engine speed, and this is a potentially dangerous situation. This difficulty can be overcome by monitoring the output of the amplifier 95, so that if the amplifier fails action is taken to prevent damage. However, one particular convenient way of achieving the desired effect is shown in FIG. 12. The arrangement of FIG. 12 is shown for convenience as applied to a pump circuit for use with the arrangement of FIG. 8.

Referring to FIG. 12, the arrangement is similar to that shown in FIG. 10 with the omission of the resistor 98. In addition, however, the junction of the resistor 91 and capacitor 92 is connected to the line 23 through a capacitor 101 and the anode-cathode part of a diode 102 in series. The junction of the capacitor 101 and diode 102 is connected to the line 23 through the cathode-anode part of a diode 103 and a capacitor 104 in series, and the junction of the diode 103 and capacitor 104 is connected through a resistor 105 to the inverting input terminal of the amplifier 95.

The operation of the arrangement shown in FIG. 12 is best explained with reference to the wave forms in FIGS. 13, 14 and 15. Without the input from the resistor 105, the amplifier would have an output of the form shown in FIG. 13 (remembering that the resistor 98 is not present). The

capacitors

101, 104 and their

diodes

102, 103 form a conventional diode pump circuit producing an input to the amplifier 95 which is out of phase with the input through the diode 94. The form of the resultant output of the amplifier 95 is shown in FIG. 14, and it will be seen that it rises exponentially to a maximum value. The actual output of the amplifier 95 is the sum of the outputs shown in FIGS. 13 and 14, and is shown in FIG. 15. The output rises to a maximum voltage at the point 105 and falls to zero at the point 106. The portion of the curve between the

points

105, 106 is substantially linear, and the curve shown in FIG. 15 replaces the curve shown in FIG. 2. The

points

106 and 105 are then close to the maximum and minimum engine speeds respectively, and in normal operation the output from the amplifier 95 will be between the

points

105, 106. It willbe seen that the form of the curve produced ensures that both possible fault conditions of the amplifier 95 and the preceding circuits result in a low voltage output, so that the circuit fails safe. It will of course be understood that the arrangement of FIG. 12 can be used anywhere where it is desirable for a maximum output to be obtained at a particular frequency, this frequency being represented by the point 105 in FIG. 15.

It is not necessary for the resistor 105 to provide an input to the amplifier 95. Where the circuit is being used with the arrangement of FIG. 1, then if the

diodes

102, 103 are appropriately connected the resistor 105 can instead provide an input to the inverting input terminal of the amplifier 18. Similarly, where the arrangement is used with FIG. 6, the resistor 105 can be used to provide an input to the inverting input terminal of the amplifier 19. Because the amplifier 95 and the amplifier 18 (or the amplifier 19 in FIG. 6) successively sum their input signals, it will be appreciated that the overall effect of providing the input from the second pump circuit in FIG. 12 to one of the amplifiers 18 or 19 does not alter the operation of the circuit.

We claim:

1. A fuel system for an engine, comprising in combination a pump supply fuel to the engine, an actuator controlling the pump, and an electronic governor for controlling the actuator, said governor receiving electrical signals representing engine speed and at least one further engine parameter, the speed signal being obtained using a transducer producing an ac. output at a frequency proportional to engine speed, a pump circuit for converting said signal to a dc. signal, first, second and third supply lines, an operational amplifier having an inverting input terminal and a non-inverting input terminal, said amplifier being powered by the first and second supply lines and having its non-inverting input terminal connected to the third supply line, and said pump circuit including a capacitor across which is developed a voltage proportional to the frequency of the ac. output, said capacitor being connected across the inverting input and output terminals of said operational amplifier, a resistor across the capacitor, a second capacitor and a diode in series between an input terminal and the inverting input terminal, and a second diode coupling the junction of the second capacitor and first diode to the third supply line.

2. A circuit as claimed in claim 1 including a resistor coupling the inverting input terminal of the amplifier to the second line.

3. A system as claimed in claim 1 including in addition a further pump circuit providing an input to the operational amplifier or directly to the governor whereby said do. signal increases from zero to a maximum level at a minimum engine speed and then decreases substantially linearly to zero at a maximum engine speed.

4. A system as claimed in claim 1 in which the operational amplifier is biased so that it produces a maximum output at low engine speeds, falling to zero near a maximum engine speed.

5. A system as claimed in any one of claim 1 including a shaping circuit between the transducer and the first mentioned pump circuit, the shaping circuit converting the output from the transducer to substantially square wave form.

6. A system as claimed in claim 5, including a pair of supply lines providing power to the governor, said shaping circuit producing a square wave output having an amplitude proportional to the voltage between said supply lines.

7. A system as claimed in claim 6 including means modifying said amplitude to compensate for temperature dependance of components in the pump circuit.

8. A system as claimed in any one of claim 6 in which the shaping circuit includes first and second transistors connected as a long tailed pair with a constant current source in the tail, the first transistor having its base connected to the transducer, and the second transistor having a collector-base cross coupling with a third transistor providing the output from the pulse shaping circuit.

9. A system as claimed in any one of claim in which the shaping circuit includes switching components producing a second square wave output out of phase with the first output, and the capacitor across the operational amplifier is common to two pump circuits driven by the two outputs from the shaping circuit.

10. An electronic pump circuit in which a voltage dependent on the frequency of an ac. input is developed across a capacitor connected across the input and output terminals of an operational amplifier, including first, second and third supply lines, the amplifier being powered by the first and second lines and having its non-inverting input terminal connected to the third line, and the pump circuit including, in addition to the capacitor between the output terminal and the inverting input terminal of the amplifier, a resistor across the capacitor, a second capacitor and a diode in series between an input terminal and the inverting input terminal, and a second diode coupling the junction of the second capacitor and first diode to the third line.

11. A circuit as claimed in claim 10 including a resistor coupling the inverting input terminal of the amplifier to the second line.

12. A circuit as claimed in claim 10 in combination with a conventional pump circuit providing a further input to the amplifier, whereby with increasing frequency the output of the amplifier rises from zero to a maximum value and then decreases with further increase in frequency towards zero.

13. A fuel system for a compression-ignition engine, comprising in combination a pump for supplying fuel to the engine, an electro-mechanical actuator controlling the pump, and an electronic governor for controlling the actuator, said governor receiving electrical signals from three transducers representing demand, pump output and engine speed, the governor including three power supply lines, the third line being kept at a specified proportion of the potential between the first and second lines, the speed signal being obtained using a transducer producing an ac output at a frequency proportional to engine speed, a signal-shaping circuit to which said a.c. output is applied, said signal-shaping circuit producing a square wave output whose amplitude is substantially proportional to the potential between the first two supply lines, and a pump circuit for converting said square wave output to a dc. signal which at least over the working speed range decreases in magnitude relative to the third supply line with increasing speed, said d.c. signal being applied to the governor, said pump circuit including a capacitor across which is developed a voltage proportional to the frequency of the said a.c. output, said capacitor being connected across the input and output terminals of an operational amplifier.

Claims

1. A fuel system for an engine, comprising in combination a pump supply fuel to the engine, an actuator controlling the pump, and an electronic governor for controlling the actuator, said governor receiving electrical signals representing engine speed and at least one further engine parameter, the speed signal being obtained using a transducer producing an a.c. output at a frequency proportional to engine speed, a pump circuit for converting said signal to a d.c. signal, first, second and third supply lines, an operational amplifier having an inverting input terminal and a non-inverting input terminal, said amplifier being powered by the first and second supply lines and having its noninverting input terminal connected to the third supply line, and said pump circuit including a capacitor across which is developed a voltage proportional to the frequency of the a.c. output, said capacitor being connected across the inverting input and output terminals of said operational amplifier, a resistor across the capacitor, a second capacitor and a diode in series between an input terminal and the inverting input terminal, and a second diode coupling the junction of the second capacitor and first diode to the third supply line.

3. A system as claimed in claim 1 including in addition a further pump circuit providing an input to the operational amplifier or directly to the governor whereby said d.c. signal increases from zero to a maximum level at a minimum engine speed and then decreases substantially linearly to zero at a maximum engine speed.

9. A system as claimed in any one of claim 5 in which the shaping circuit includes switching components producing a second square wave output out of phase with the first output, and the capacitor across the operational amplifier is common to two pump circuits driven by the two outputs from the shaping circuit.

10. An electronic pump circuit in which a voltage dependent on the frequency of an a.c. input is developed across a capacitor connected across the input and output terminals of an operational amplifier, including first, second and third supply lines, the amplifier being powered by the first and second lines and having its non-inverting input terminal connected to the third line, and the pump circuit Including, in addition to the capacitor between the output terminal and the inverting input terminal of the amplifier, a resistor across the capacitor, a second capacitor and a diode in series between an input terminal and the inverting input terminal, and a second diode coupling the junction of the second capacitor and first diode to the third line.

13. A fuel system for a compression-ignition engine, comprising in combination a pump for supplying fuel to the engine, an electro-mechanical actuator controlling the pump, and an electronic governor for controlling the actuator, said governor receiving electrical signals from three transducers representing demand, pump output and engine speed, the governor including three power supply lines, the third line being kept at a specified proportion of the potential between the first and second lines, the speed signal being obtained using a transducer producing an a.c. output at a frequency proportional to engine speed, a signal-shaping circuit to which said a.c. output is applied, said signal-shaping circuit producing a square wave output whose amplitude is substantially proportional to the potential between the first two supply lines, and a pump circuit for converting said square wave output to a d.c. signal which at least over the working speed range decreases in magnitude relative to the third supply line with increasing speed, said d.c. signal being applied to the governor, said pump circuit including a capacitor across which is developed a voltage proportional to the frequency of the said a.c. output, said capacitor being connected across the input and output terminals of an operational amplifier.