GB2041577A - Fuel System for internal combustion engines - Google Patents

Abstract

A fuel system for an engine includes a fuel pump 12 having an electromagnetically controlled spill valve which is energised by a drive circuit 13 when, during a pumping stroke of the pump, it is required to supply fuel. The system also includes timing control means 33 which supplies a control signal to the drive circuit 13 and itself receives timing signals from transducers 16, 17 which are mounted on the associated engine. The timing control means supplies a signal at the appropriate time to start the delivery of fuel and of a duration appropriate for the amount of fuel to be supplied. A governor means 34 generates a signal indicative of the amount of fuel to be supplied to the engine.

Description

SPECIFICATION Fuel system for an internal combustion engine This invention relates to a fuel system for supplying fuel to a combustion chamber of an internal combustion engine and of the kind comprising a fuel pump including a plunger reciprocable within a bore, an outlet from one end of said bore and which in use is connected to a fuel injection nozzle positioned on the engine to direct fuel into the combustion chamber of the engine, spill passage means through which fuel can escape from said chamber at some time during the inward movement of the plunger, valve means for controlling the flow of fuel through said passage means and control means for determining the setting of said valve means.

In a known fuel system of this type the plunger is actuated by a cam driven in timed relationship with the associated engine and the spill passage means includes a spill port formed in the wall of the bore.

The plunger itself controls the flow of fuel through the spill port and during the inward movement of the plunger the spill port is first covered by the plunger after which fuel flows through the outlet and then after further inward movement of the plunger, by virtue of a helical control edge on the wall ofthe plunger, the spill port is again uncovered and fuel once again flows through the spill port so that the delivery of fuel through the outlet ceases. The angular setting of the plunger determines the amount of fuel supplied through the outlet and the angular setting of the plunger is determined by a speed governorwhich may be of a mechanical or electrical nature.

One of the problems with the known form of system especially when the pressure of fuel is very high is leakage along the working clearance defined between the plunger and the bore and it is proposed to provide a valve means which is in no way associated with the plunger. Since the plunger in the known system provides a timing function in that it determines by closure of the spill port, the instant of the start of delivery of fuel, it is necessary when utilizing a valve means separate from the plunger to operate .he valve in timed relationship with the associated engine. Conveniently, the valve is operated by electromagnetic means which in turn is supplied with electric current at the appropriate time by a drive circuit. The operation of the drive circuit is controlled by the control means.

According to the invention in a fuel system of the kind specified said valve means comprises an electro-magnetically operable valve, a drive circuit for said valve, timing control means operable to supply a control signal to said drive circuit, means for supplying timing signals to said control means, wL ereby the timing control means supplies a control signal at the correct instant and of a length appropri e to the engine speed and the amount of fuel required to be supplied to the engine, and governor means for supplying to the timing control means a signal indicative of the amount of fuel to be supplied to the combustion chamber.

An example of a system in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 shows the layout of the system fitted to an engine, Figure 2 shows in sectional side elevation an example of a fuel pump forming part of the system, Figure 3 is a plan view of the pump shown in Figure 2 with parts broken away to show the internal construction of the pump, Figure 4 is a block diagram of the electrical portion of the system, Figure 5 is a further block diagram illustrating in detail one of the blocks seen in Figure 4.

Figure 6shows one example of the delivery/speed map of the system.

With reference to Figure 1 of the drawings a multi-cylinder compression ignition engine is indicated at 10 and has six cylinders. Fuel is supplied to ihe combustion spaces by fuel injection nozzles 11 respectively and fuel is supplied to the injection nozzles by individual fuel pumps 12. An example of a pump 12 is seen in Figures 2 and 3 and the pumps are driven by cams respectively (not shown) mounted on a cam shaft within the engine. Each pump 12 includes an electromagnetically operable valve to which power is supplied by a drive circuit 13. The drive circuit may be located in a single unit or a number of units less than the number of drive circuits.

The drive circuits are controlled by respective control signals which are supplied by an electronic circuit 14 to be described, and signals are supplied to this unit by three transducers 15,16 and 17. Transducer 15 provides a high rate pulse signal indicative of engine speed and for this purpose it senses the passage of teeth on a wheel driven by the engine.

Sensor 16 provides a low rate pulse signal three times per revolution of the crankshaft of the engine and for this purpose it senses marks or the like on the flywheel of the engine. Transducer 17 provides a further low rate pulse signal once per two revolutions of the engine crankshaft. For this purpose the transducer senses the rotation of the cam shaft which drives the pumps 12. In addition the control circuit receives information from an operator control unit 18 which mayh be integral with the control circuit 14.

Turning nowto Figures 2 and 3 each pump 12 includes a plunger 20 reciprocable within a bore 19.

The plunger is biased outwardly by a coiled compression spring and is movable inwardly by a cam (not shown) on the aforesaid camshaft. A passage 21 extends from the inner end of the bore 19 and communicates with a cam 22 defined about an axially movable valve member 23. Extending from the chamber 22 is an outlet controlled by a conventional delivery valve 25. A further chamber 26 is defined about the valve member 23 and this communicates with an outlet 27 for spilled fuel and a valve controlled fuel inlet 28 which in use is connected to a source of fuel under pressure.

The valve member 23 has a head portion 29 for cooperation with a seating 30 defined between the two chambersand a passage extends through the valve member to ensure that the end sus races of the valve member are at the same pressure. The valve member 23 is actuated by an electromagnetic device 30a which includes a cup shaped armature 31 and a winding (not shown) to which electric current can be supplied. The head 29 of the valve member is moved into sealing engagement with the sealing 30 when electric current is supplied to the winding and in this condition and as shown in the Figures 2 and 3, as the plunger 20 is moved inwardly by the cam, fuel will be displaced from the bore 19 and will flow past the delivery valve 25 to the outlet 27 and to the respective fuel injection nozzle 11.When during inward movement of the plunger the winding is de-energised, the head 29 is lifted from the seating 30 and the fuel from the bore flows through the spill outlet 27 and no more fuel flows to the nozzle. The valve member 23 is biased to the open position by the action of a coiled compression spring 32. The time considered in terms of plunger movement or degrees of cam shaft rotation during which the valve member is in the closed position, determines the amount of fuel supplied to the engine and is substantially constant irrespective of engine speed.

In terms of real time then for a given volume of fuel the time the valve remains closed decreases with increasing engine speed. In the particular example the valve member remains in the open position during downward or outward movement of the plunger and during such movement of the plunger a fresh supply of fuel is delivered to the bore to fill same, through the fuel inlet 28.

With reference to Figure 4, the blocks or compo nentswhich have already been discussed have been alotted the same reference numerals previously used. The electronic circuit is divided into two main portions namely the timing circuit references 33 and the governor circuit 34. A portion of the timing circuit namely that lying within the chain dot lines but outside the dotted lines, is common to all the pumps and this also applies to the governor circuit.

The timing control circuit includes a timing distributor 35 which receives inputs from the transducers 16 and 17 and which has a number of outputs equal in number to the number of pumps 12. At each output there is obtained an identification signal appropriate for one of the pumps 12. This signal is applied to the respective portion of the timing control circuit and is utilised to control the operation of an integrator 36. The input for the integrator 36 is obtained from a decoding circuit 37 which for convenience is indicated as being part of the governor circuit 34. The decoding circuit provides a fuel speed signal the level of which increases with increasing engine speed. The voltage at the output of the integrator is therefore in terms of real time, a measure of the angle.

The output voltage of the integrator 36 is applied tc one input of a comparator 38 the other input of which receives a timing control signal 39 the derivati .7 of which will be described. When the integrator output voltage attains the level of the timing control signal 39, an output signal appears at the output of the comparator 38 and this through a pulse shaper 40 is applied to the drive circuit 13 which energises the winding of the electromagnetic device to effect closure of the valve member 23.

The output signal of the comparator 38 is also utilized to control a further integrator 41 which also receives at its input the speed signal from the decoding circuit 37. The output voltage from the integrator 41 is applied to one input of a comparator 42 which at its other input receives a fuel control signal 43. The output voltage of the integrator 41 is representative of the time during which the supply of fuel is taking place and the fuel control signal is indicative of the desired time for fuel supply. When therefore the output voltage of the integrator 41 attains the level of the fuel control signal 43 a signal is supplied to the pulse shaper 40 to remove the signal from the drive circuit 13. Thus the instant of delivery of fuel is determined by the integrator 36 and the duration of delivery by the integrator 41.The aforesaid instant and duration can be varied by varying the time control signal 39 and the fuel control signal 43 respectively.

The timing control signal 39 is provided by a time scheduling circuit 44 which determines the desired timing of delivery of fuel in accordance with the speed of the engine and the load on the engine. For this purpose the circuit 44 is provided with the first speed signal of the decoder 37 and also a fuel signal which is obtained from the governor circuit 34. In addition the circuit 44 is arranged to compensate for the delay in the start of the delivery of fuel upon the supply of current to the winding by the drive circuit 13, this delay being due mainly to the time for the valve member 23 to operate.

The fuel control signal 43 is basically the signal obtained from the governor circuit 34. However, because of non-linearities in the pump which vary with the amount of fuel delivered by the pump, it is necessary to correct the fuel signal from the governor 34 before it is applied to the comparator 42.

This correction is achieved by a fuel function circuit 45 which is also supplied with the first speed signal from the decoding circuit 37.

Turning now to the governor circuit 34. This is supplied with a second speed signal from the decoding circuit 37. This signal has a level which is at its maximum for zero engine speed and which falls to zero as the engine speed reaches 110% of the maximum governed speed. The output ofthe circuit 34 is obtained from a "lowest wins" circuit 46 which in the particular example has four inputs. The circuit 46 is arranged so that the lowest of the voltages applied to the four inputs is supplied to ihe timing control circuit 33. The input 47 is connected to a safety circuit 48 which receives the second speed signal from the decoder 37. The safety circuit 48 includes portions which detect overspeed of the engine, underspeed of the engine e.g. when the engine speed is below slow cranking speed, incorrect supply voltage etc. Whenever one of these malfunctions is detected the level of the signal applied to the input 47 is reduced to zero and this has the effect of stopping the delivery of fuel to the engine.

The input 49 is connected to the output of a high gain amplifier 50 having a feedback loop. The non-inverting input of the amplifier is grounded and the inverting input is connected to a summing junction 51 to which are supplied a reference signal from a reference source 52, the demanded speed signal obtained from an operators control 53, the actual speed signal from the decoding circuit 37 and a droop control signal obtained from a droop control circuit 54 which is also supplied with the second speed signal.

Theinput 55 of the lowest wins circuit 46 receives the output from an inverter 56 which in turn receives the output of a high gain amplifier 57 having a feedback loop. The non-inverting input of the amplifier 57 is connected to ground and its inverting input is connected to a summing junction 59. The summing junction 59 is supplied with a reference signal from a reference source 58, a signal from a torque control circuit 60 which in turn receives the second speed signal from the decoder 37, a signal from a circuit 61 and optionally signals from circuits 62 and 63 which receives signals from sensors responsive to the engine exhaust temperature and the air inlet manifold pressure respectively.

Ignoring for the moment the other input of the lowest wins circuit 46 and referring to Figure 6 which shows a family of curves of engine speed against the fuel requirement of the engine. Considering for the moment the curves in the rectangle A B C Din particular the curve represented by the line numbered 64. If the engine is assumed to be working at point 65 then if the load on the engine is increased, such as to cause a reduction in speed of the engine the effect will be to increase the amount of fuel supplied to the engine to compensate for the increased load. A new working point 65a will be achieved. If on the other hand the load should decrease then the engine speed will increase and the effect will be to decrease the amount of fuel supplied to the engine. A new working point 65b will be established.The governing effect described assumes that the demanded speed of the engine is maintained the same. If the demanded engine speed is increased then the amount of fuel supplied to the engine will increase and the engine will accelerate to a new speed appropriate to the load on the engine.

The engine will then operate along a line substantially parallel with the line 64 for example the line 66.

The slope of the lines or the droop as it is known in the art is a measure of the sensitivity of the governor and its ability to control the engine speed as the load thereon varies. It will be noted from Figure 6 that at and above a speed no the slope of the lines is increased and there is a further increase in the slope at and above a speed n3.

The amplifier 50 determines the fuel supplied to the engine within the rectangle A B C D and the feedback of the amplifier determines the slope of the lines at and above the speed n3. The reduction in slope below speed n3 and speed n2 is brought about by the droop control circuit 54 which supplies an input to the summing junction 51 which in effect modifies the speed signal supplied to that junction.

he purpose of the reference source 52 is to ensure that when there is zero demand there will be zero fuel.

In Figure 6 the line A B represents the maximum fuel line but it should be noted that at a speed slightly greater than speed no there is a line 67 which slopes downwardly and which replaces the maximum fuel line A B. The line 67 indicates torque control and it means that with increasing speed the maximum amount of fuel which can be supplied to the engine decreases. The maximum fuel line and the torque control line are provided by the amplifier 57 in conjunction with the reference source 58 and the torque control circuit 60 respectively.

The effects of the circuits 62 and 63-are not shown in Figure 6 but the circuit 63 which is responsive to air inlet manifold pressure acts to reduce the maximum fuel which can be supplied to the engine when the air inlet manifold pressure is low. This has particular value for a turbo-supercharged engine.

The circuit 62 operates to reduce the maximum fuel throughout the range if the exhaust gas temperature rises above a pre-determined level as might occur for example during operation of the engine in extreme conditions.

The circuit 61 when operated by closure of a switch, has the practical effect of lowering the maximum fuel line A B to the level of the dotted line seen in Figure 6. In the example this represents about 15% of the maximum fuel. The circuit 61 is brought into opration when it is required to start the engine. The % of maximum fuel for starting purposes will depend on the associated engine. The line BC lies on the nominal maximum engine speed.

The portion ofthefuel/speed characteristic in Figure 6 which lies beyond the side B C of the rectangle is determined by a circuit 69 which feeds the input 68 of the lowest wins circuit 46. In Figure 4 the circuit 69 is shown as an amplifier which receives the actual and demanded speed signals together with a reference signal but it is in fact a more complex circuit known in the art as a slave datum loop. The details of the circuit are seen in Figure 5 and it includes a high gain amplifier 70 having a controllable feed back loop 71 connected between the output of the amplifier and a summing junction 72 connected to the inverting input. Also supplied to the summing junction is the actual speed signal from the decoder 37 and the desired speed signal obtained from the control 53 through a compensation network 73 as will be described.The putput of the aplifier 70 is connected to the input of an integrator 74 and the output of the integrator is fed to a summing junction 75 connected to the inverting input of a further high gain amplifier 76. This amplifier also has an adjustable feed back path 77 connected between its output and the junction 75.

Also supplied to the junction 75 is the speed signal from the decoder 37 and a signal from a reference source 78. The output of the amplifier 76 is connected to the input 68 of the lowest wine circuit. In addition an overall adjustable feedback loop 79 is provided between the output of the amplifier 76 and the summing junction 72.

The amplifier 70 provides an output signal which is representative of the difference between the actual and the desired engine speed and this is integrated by the integrator 74 and is then compared with the actual speed by the amplifier 76. The output of this amplifier is the fuel signal. The degree of feedback provided by the loop 71 determines the integral stability whilst the degree of feedback provided by the loop 77 determines the proportional stability.

The degree of feedback provided by the two loops can be varied using a stability control 81. The degree of overal feedback provided by the loop 79 determines the slope of the maximum speed lines 80 seen in Figure 6 and this slope can be adjusted by varying the feedback using a droop control 82. It is necessary when varying the slope in this manner to modify the demanded speed signal supplied to summing junction 72. This is achieved using the compensation circuit 73 which is a passive network. The effect of the compensation circuit is to ensure that the maximum speed line 80 always pass through the point be in Figure 6. If this circuit were not provided then whilst the slope of the lines 80 would be varied by altering the feedback, the lines 80 would not pass through the point B.

Saturation of the integrator 74 could occur when the amplifiers 50 or 57 are providing the lowest output since in this situation the output of the amplifier 70 will be large. A circuit 83 which is connected between the output of the amplifier 76 and the integrator 74 is provided to control the integrator and the practical effect is that the output of the amplifier 76 follows the lowest fuel signal.

If the feedback provided by the loop 79 is removed then the governing at high speed becomes isochronous that is to say as soon as the maximum speed is attained the engine will run at this speed irrespective of the load. A control 84 is provided for the purpose of preventing overall feedback.

An indication of the load on the engine is provided as shown in Figure 4, by an indicating device 80 which receives the signal at the output of the circuit 46.

The various controls mentioned above together with the operators control 53 are carried on a panel for operation by the operator of the engine during the use of the engine, it being appreciated that the associated engine is a specialist engine for example a marine engine or an engine of an electrical generating set.

Claims (13)

1. Afuel system for supplying fuel to a combustion chamber of an internal combustion engine and of the kind comprising a fuel pump including a plunger reciprocable within a bore, an outletfrom one end of said bore and which in use is connected to a fuel injection nozzle positioned on the engine to direct fuel into the combustion chamber of the engine, spill passage means through which fuel can escape from said chamber at some time during the inward movement of the plunger, valve means for controlling the flow of fuel through said passage means and control means for determining the setting of said valve means, characterised in that said valve means comprises an electromagnetically operable valve, a drive circuit for said valve, timing control means operable to supply a control signal to said drive circuit, means for supplying timing signals to said control means, whereby the timing control means supplies a control signal at the correct instant and of a length appropriate to the engine speed and the amount of fuel required to be supplied to the engine, and governor means for supplying to the timing control means a signal indicative of the amount of fuel to be supplied to the combustion chamber.

2. Afuel system according to claim 1 in which said timing control means includes a first integrator to which is supplied a signal indicative of the speed of the associated engine, means for generating a signal to control the operation of the integrator from said timing signals, a first comparator to which is supplied the output of the integrator, means for providing a timing control signal, said timing control signal being supplied to the other input of said first comparator, the output of said first comparator when the input signals supplied to it are substantially equal effecting operation of the drive circuit, said timing control means including a second integrator to which said speed signal is supplied, said second integrator being controlled by the output from said first comparator, a second comparator having one input connected to the output of said second integrator and its other input connected to the output of said governor means, the output of said second integrator when the input signals supplied thereto are substantially equal acting to prevent operation of said drive circuit.

3. A fuel system according to claim 2 including means for correcting the signal applied to said second comparator from the governor means to take into account variation in the output of the pump with speed.

4. A fuel system according to claim 2 or claim 3 in which the means for providing said timing control signal is supplied with a signal representative of the engine speed and a signal from said governor means whereby the timing of delivery of fuel to the engine varies in accordance with the speed of and the amount of fuel supplied to the engine.

5. A fuel system according to claims 2, 3, or 4 including a pulse circuit to which the output of said comparators are supplied, the output of said pulse circuit controlling the operation of said drive circuit.

6. Afuel system according to any one of the preceding claims in which said governor means includes a lowest wine circuit a first network for providing a first input signal to said lowest wins circuit, said first network being supplied with signals indicative of the demanded and actual engine speed, a second network for providing a second input signal to said lowest wins circuit, said second network being supplied with a reference signal and a signal indicative of the actual engine speed and a third network for providing a third input to said lowest wins circuit, said first and second circuits determining the fuel/speed characteristic below the nominal maximum engine speed, said third circuit comprising a slave datum loop to which is supplied signals representing the actual engine speed and the demanded engine speed, said third circuit determining the fuel/speed characteristic above said nominal maximum speed.

7. Afuel system according to claim 6 including a fourth circuit for providing a fourth input signal to said lowest wins circuit said fourth circuit acting to prevent the supply of fuel in the event of a fourth condition.

8. A fuel system according to claims 6 or 7 including means associated with said second circuit for reducing the maximum amount of fuel which can be supplied to the engine during starting of the engine.

9. A fuel system according to claims 6,7 or 8 in which said third circuit includes a pair of high gain amplifiers having summing junctions connected to the inverting inputs thereof, an integrator connected between the output of one amplifier and the summing junction of the other amplifier, the output of said other amplifier being connected to said third input, said summing junctions being supplied with signals representing the engine speed, feedback loops associated with said amplifiers respectively, the demanded speed signal being supplied to the summing junction associated with said one amplifier, and a further overall feedback loop connected between the output of said other amplifier and the summing junction associated with said one amplifier.

10. Afuel system according to claim 9 including means for controlling the degree of feedback provided by said feedback loops.

11. Afuel system according to claims 8,9 or 10 including a compensation network through which the demanded speed signal is supplied to the summing junction associated with said one amplifier, said compensation circuit also receiving a signal from a loop control circuit which in addition supplies a signal to control the feedback of the overall feedback loop.

12. Afuel system according to any one of claims 8,9, 10 or 11 including a circuit connected between the output of said other amplifier for controlling the operation of the integrator when the output of said other amplifier is high.

13. A fuel system for an internal combustion engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawings.