US3898969A

US3898969A - Fuel supply systems for engines

Info

Publication number: US3898969A
Application number: US429373A
Authority: US
Inventors: Malcolm Williams; Christopher Robin Jones; Richard William Crookes
Original assignee: CAV Ltd
Current assignee: CAV Ltd
Priority date: 1973-01-06
Filing date: 1973-12-28
Publication date: 1975-08-12
Anticipated expiration: 1992-08-12
Also published as: FR2213417A1; DE2400412A1; GB1460013A; JPS4997126A; IT1002598B; FR2213417B1

Abstract

A fuel system for an engine has control means determining the rate of supply of fuel to the engine. This control means is responsive to system parameters, one of which is obtained from a demand transducer. The minimum speed of the engine is limited in accordance with the rate of supply of fuel to be produce an idling curve having a predetermined slope, and this slope is increased if the engine speed is below a predetermined value.

Description

United States Patent Williams et al.

[ 1 Aug. 12, 1975 FUEL SUPPLY SYSTEMS FOR ENGINES Inventors: Malcolm Williams, Solihull;

Christopher Robin Jones, Alcester; Richard William Crookes, Solihull, all of England C.A.V. Limited, Birmingham, England Filed: Dec. 28, 1973 Appl. No.: 429,373

Assignee:

Foreign Application Priority Data Jan. 6, 1973 United Kingdom 890/73 US. Cl. 123/139 E; 123/140 R; 290/40 A; 60/3928 Int. Cl. F02!) 3/00; F02m 39/00 Field of Search 123/102, 139 E, 32 EA, 123/140 R; 290/40 A; 60/3928 References Cited UNITED STATES PATENTS 10/1968 Lang 123/139 E 3,425,401 Z/l969 Lang 123/139 E 3,693,603 9/1972 Lemawczyk.. 123/139 E 3 699,935 10/1972 Adler 123/139 E Primary Examiner-Charles J. Myhre Assistant Examiner-Ronald B. Cox Attorney, Agent, or FirmHolman & Stern 3 Claims, 5 Drawing Figures PUMP 3 OUTPUT Q SPEED PATENTEU 3,898,969

SHEET 1 ACTUATOR PUMP ENGINE DRIVE 23 44 H SPEED CIRCUIT 5 /TRANSDUCER I PEDAL POSITION I TRANSDUCER MAXIMUM $258355? 27 A5 @555? /---#SOURCE 29 25 2b 24 {8\ CURRENT SOURCE Z2\ Ho 21 u u 53 55 g 52 SOURCE-\\ PATENTED 3,898,969

SHEET 2 W PEDAL osmow SPEED PUMP OUTPUT- FIG. 2. FIG. 3). F154.

PUMP OUTPUT FUEL SUPPLY SYSTEMS FOR ENGINES This invention relates to fuel systems for engines, particularly, but not exclusively, compression-ignition engines.

A system according to the invention includes control means determining the rate of supply of fuel to the system, a demand transducer providing an input to the control means to influence the output thereof, means for limiting the minimum speed of the engine in accordance with the rate of supply of fuel to produce an idling curve having a predetermined slope, and means for increasing the slope of the idling curve when the engine speed is below a predetermined value.

Preferably, the means for increasing the slope supplements the input to the control means from the demand transducer, so as to simulate an increased demand.

The accompanying drawings illustrate one example of the invention as applied to a fuel injection system for a diesel engine driving a road vehicle. In the drawings,

FIG. 1 is a circuit diagram, partly in block form, of the system FIGS. 2 to 4 respectively illustrate the outputs of three transducers used in the system, and

FIG. 5 represents a fuelspeed characteristic for an engine to be controlled by the arrangement of FIGS. 1 to 4.

Referring first to FIG. 1, a pump 11 provides fuel to an engine 12, the rate of supply of fuel being determined by a control rod 13 forming part of the pump 11, and the position of which is determined by a actuator 14. The control rod 13 is loaded by a spring to a position in which the pump 11 produces a Zero output, and the actuator 14 moves the control rod 13 against the action of the spring to increase the output of the pump 1 1.

The rotational speed of the engine 12 is sensed by a transducer 15 which produces an output voltage of the form indicated in FIG. 2, this output voltage being at a maximum when the engine speed is low. The transducer 15 provides a current input by way of a resistor 16 to the inverting terminal of an operational amplifier 17 which receives its power from a pair of

terminals

18, 19 and has its non-inverting terminal connected to a terminal 21. The terminal 18 is positive with respect to the terminal 19, and the terminal 21 is at a potential mid-way between the potentials of the

terminals

18, 19. The origin in FIGS. 2 to 4 represents the potential of the terminal 21. The output from the amplifier 17 is fed through a diode 22 to the input terminal ofa drive circuit 23 operating the actuator 14. The amplifier 17 also receives input from a current source 24 which sets the minimum speed of the engine and by way of a pair of

resistors

25, 26 respectively from a pair of

transducers

27, 28. The transducer 27 senses the pump output by detecting the position of the control rod 13, and produces an output voltage of the form shown in FIG. 3. The transducer 28 is operable by the pedal of the road vehicle. and produces an output voltage representing demand, this voltage being of the form shown in FIG. 4. The operational amplifier 17 is connected as a summing amplifier, and for this purpose has a feedback resistor 29 which is connected between the input of the drive circuit 23 and the inverting terminal of the amplifier 17.

There is further provided an operational amplifier 31 the inverting terminal of which receives a signal by way of a resistor 32 from the transducer 27, and also receives a signal from a current source 33 used to set the maximum pump output. The output from the amplifier 31 is fed through a diode 33 to the drive circuit 23, and feedback to the inverting terminal of the amplifier 31 is taken by way of a resistor 34 from the input of the drive circuit 23.

Ignoring for the moment the components shown in the lower half of FIG. 1, the operation of the system is best explained with reference to FIG. 5. The line 41 in FIG. 5 is one of a family of curves representing engine demand, and for the sake of convenience can be said to represent 50 percent maximum speed. If the pedal is set to the 50 percent position, then it provides an input to the amplifier l7, and this input is compared with the actual speed signal by way of the resistor 16. If there were no input from the transducer 27, then the amplifier 17 would simply compare the demanded speed with the actual speed, and operate the drive circuit 23 to cause the actuator 14 to move the control rod 13 to vary the pump output until the actual and desired speeds were equal. However, by virtue of the signal through the resistor 25 representing pump output, the slope shown on the curve 41 in FIG. 5 is obtained. In other words, for a 50 percent demand, the position of the engine on the curve 41 will depend on the pump output, so that there is a range of speeds for a 50% demand, dependent upon the load on the engine.

It will be seen that whenever the amplifier 17 is producing a positive output which is greater than the output of the amplifier 31, the diode 33 is reverse biased so that the amplifier 31 plays no part in the operation. The purpose of the amplifier 31 is to limit the maximum pump output, as indicated by the curve 42 in FIG.

- 5. If at any time the maximum pump output reaches the curve 42, then by virtue of the current source 33 and the connection through resistor 32, the amplifier 31 produces an output which is a greater positive output than the output produced by the amplifier 17, so that the diode 22 is now reverse biased, and the amplifier 31 provides an input to the drive circuit 23. Although the output from the amplifier 31 is a larger positive output than the output from the amplifier 17, this actually represents a demand for less fuel, and so the fuel is regulated in such a way that the pump output does not exceed the quantity indicated by the curve 42.

As previously explained, the curve 41 is one of a family of curves representing different demands. The zero demand curve is shown, partly dotted, at 43, and is set by the current source 24 so that, ignoring the lower part of FIG. 1, the minimum speed follows the curve 43. The maximum speed of the engine is indicated by the curve 44, and is set by a source 45 which acts by limiting the maximum demand of the demand transducer 28.

The dotted curve 46 shown in FIG. 5 is a function of the engine, not the control system, and represents the no-load idling speed of the engine. As will be seen, the no-load zero demand operating point is the point 47 in FIG. 5.

With the arrangement thus far described, the engine will operate at the point 47 during no-load idling. However, if a load is imposed on the engine in these circum stances, the engine speed falls substantially as shown by the dotted portion of the curve 43. This substantial possible change in speed at zero demand can result in an undesirable jerk, and in some cases stalling of the engine. The problem occurs particularly on vehicles with automatic transmission, where engagement of the transmission with the vehicle at rest and no demand imposed by the pedal will result in an increase in load.

In order to overcome this difficulty the slope of the curve 43 is increased below a predetermined speed, as shown by the solid line 43a. As a result, the change in speed with load is substantially reduced. The predetermined speed will depend on the engine, and need not be the point 47. The change in slope is achieved by effectively applying to the inverting terminal of the amplifier 17 a further current simulating a predetermined demand, this signal being applied to the amplifier 17 only when the engine speed falls below the predetermined speed. For this purpose, the transducer provides an input to the base of an n-p-n transistor 51, the collector of which is connected through a resistor 52 and a diode 53 in series to the terminal 18, and the emitter of which is connected to the terminal 19 through

resistors

54, 55 in series. A second n-p-n transistor 56 has its collector connected through a resistor 57 to the terminal 18, and its emitter connected to the terminal 19 through a resistor 58 and the resistor 55 in series. The base of the transistor 56 is connected through a resistor 59 to the terminal 18, and through a resistor 61 to the terminal 19. The collector of the transistor 51 is connected to the base of a p-n-p transistor 64 having its emitter connected through a resistor 65 to the collector of the transistor 56 and its collector connected to the inverting terminal of the amplifier 17. As previously explained with reference to FIG. 2, the transducer 15 produces its greatest output when the engine speed is at a minimum value. At high speeds, the output voltage of the transducer 15 is insufficient to turn on the transistor 51, and the

transistors

56, 64 are off. With decreasing speed, the long tailed

pair

51, 56 share the current flow in the resistor 55, until at the predetermined speed the

transistors

51, 56 are conducting equally and the transistor 64 is off but about to conduct. Any further decrease in speed causes the transistor 56 to conduct more than the transistor 51, so that the transistor 64 conducts to supplement the current flowing to the inverting terminal of the amplifier 17, so producing the line 43a in FIG. 6. The resistor 64 is used to set the slope of the line 43a, and the resistor 61 to set the predetermined speed. The arrangement used minimises drift with, for example, temperature in the predetermined speed, and in particular the diode 53 balances the base-emitter diode of the transistor 64.

The arrangement shown is an all speed governor, but

the invention can be applied to other forms of governor. For example, the invention could be applied to a two-speed governor in which the amplifier 17 com pares the pump output with a demand signal derived from the pedal, and representing the desired pump output. In this case, the input through the resistor 16 to the amplifier 17 is not required. The transducer 15 now provides a current input to the amplifier 31, which serves in this case to limit the maximum speed. The signal from the transducer 27 is still fed to the amplifier 31 so that the maximum speed is dependent upon pump output as indicated by the slope of the curve 44 in FIG. 5. The source 45 in this example is provided with a signal from the transducer 15 and is used to set the maximum pump output, and the source 24 would require an input from the transducer 15 so that its output is speeddependent to give the required slope of the curve 43. The output from the transistor 64 is still applied to the amplifier 17 in this arrangement, and has basically the same effect.

We claim:

1. A fuel supply system for an engine, including control means for determining the rate of fuel supply by the system, a demand transducer for providing a signal to the control means representing a demanded engine operating parameter thereby defining engine operating curves having a first predetermined slope, means for limiting the minimum speed of the engine in accordance with the rate of supply of fuel to produce an engine idling curve of a second predetermined slope less steep than said first predetermined slope, and means operable when the engine speed falls below a predetermined value for supplementing the input applied to the control means by the demand transducer so as to simulate an increased demand and produce an engine idling curve having a third predetermined slope steeper than said first predetermined slope.

2. A fuel supply system as defined in claim 1, wherein said third predetermined slope is substantially vertical thereby effecting a substantially maximum rate of fuel supply to the engine when said engine speed falls below said predetermined value.

3. A system as claimed in claim 2 in which the control means comprises a pump supplying fuel to the engine, an actuator controlling the output of the pump, and an electronic governor controlling the actuator, the governor receiving an input from the demand transducer and from at least one further transducer responsive to a sys-

Claims

2. A fueld supply system as defined in claim 1, wherein said third predetermined slope is substantially vertical thereby effecting a substantially maximum rate of fuel supply to the engine when said engine speed falls below said predetermined value.

3. A system as claimed in claim 2 in which the control means comprises a pump supplying fuel to the engine, an actuator controlling the output of the pump, and an electronic governor controlling the actuator, the governor receiving an input from the demand transducer and from at least one further transducer responsive to a system parameter.