GB2196153A - Fuel system for a multi-cylinder engine - Google Patents

Abstract

A fuel system for a multi-cylinder engine comprises an engine driven pump means having a plurality of outlets connected to the injection nozzles of the engine and electromagnetically operated valve means for controlling the fuel flow through each outlet. The valve means is controlled by a power module 21 which receives fuel quantity signals from a fuel circuit 23 supplied to the power module at an appropriate time by a distributor 22. Any speed variation of the engine due to differences in the quantities of fuel injected are detected by a comparison circuit 32 which through a compensator 29 adjusts the fuel quantity signals generated by the distributor 22. The comparison circuit 32 compares the engine speed over one working stroke of the engine with the engine speed over the preceding working stroke. <IMAGE>

Description

SPECIFICATION Fuel system for multi-cylinder engine This invention relates to a fuel system for a multi cylinder engine of the kind comprising engine driven pump means having a plurality of outlets for connection to the injection nozzles respectively of the associated engine, electromagnetically operable valve means operable to control the amount of fuel which is delivered through each outlet and a control circuit for controlling the valve means in accordance with desired and actual engine operating parameters.

In one form of such a fuel system the pump means comprises a fixed stroke plunger which delivers fuel from a pump chamber by way of a distributor member to the outlets in turn and the valve means comprises a spill valve which can spill fuel from the pump chamber to controt the amount of fuel supplied through the outlets. In such a system even though the valve may be operated for the same period the amount of fuel which is delivered through the injection nozzles of the engine may vary due to the nozzles and the associated connecting pipes not being identical. Moreover, even though the cylinders of an engine may receive the same quantity of fuel the combustion characteristics may differ.

Another form of fuel system of the aforesaid kind is described in British Specification 2041577A in which the pump means comprises a plurality of individual engine actuated pumps and the valve means comprises individual electromagnetically operable spill valves associated with the pumps respectively. The valves are controlled by the control system so that in theory the same amount of fuel is delivered through each outlet. The actual power developed at each working stroke of the engine can vary as described above but this system has the added disadvantage that it is impossible to build the pumps and valves in an identical manner so that exactly the same amount of fuel is delivered through each outlet.

In a further form of such a system the pump is a rotary distributor pump in which the quantity of fuel which is delivered through the outlets of the pump is varied by using the electromagnetically operable valve means to control the amount of fuel which is admitted to the pumping chamber of the pump during the filling periods thereof. The valve means may take the form of an adjustable throttle.

In a still further form of system the pump is again of the rotary distributor type but in this case the extent of movement of the pumping plunger or plungers during the filling of the pumping chamber is controlled to enable the quantity of fuel delivered through the outlets to be varied. This is achieved by altering the axial setting of the distributor member in which the plunger or plungers is/are mounted and this has the effect of varying the relative position of co-operating stop surfaces which determine the allowed movements of the plunger or plungers. The axial setting of the distributor member is determined by varying, using an electromagnetically operable valve means which may comprise a valve or valves, the hydraulic pressure which is applied to the distributor member.

Again with the further systems described it is often the case that even though the valve means is set to ensure that the same quantity of fuel is admitted to the pumping chamber, the amount of fuel which flows through the injection nozzles which are connected to the outlets respectively varies and also the combustion characteristics of the cylinders of the engine can vary. The effect is that during the firing stroke of one or more cylinders more or less power is developed than during the firing strokes of the remaining cylinders. This results in irregular operation of the engine in particular at low engine speeds and this irregular opration can be accompanied by excessive engine noise and the excessive emission of noxious substances in the engine exhaust.

The object of the invention is to provide a fuel system of the kind specified in a simple and convenient form.

According to the invention a fuel system of the kind specified comprises transducer means for providing a pulse signal at each working stroke of the engine, speed measuring means for measuring the time period between successive signals, means for comparing the time period between one pulse and the preceding pulse with the time period between the one pulse and the following pulse to produce a series of difference signals, and means responsive to said difference signals for adjusting said valve means to reduce said difference signals, Examples of fuel systems in accordance with the invention will now be described with reference to the accompanying drawings in which:: Figure 1 is a diagrammatic representation of one example of a fuel system, Figure 2 is a block diagram showing the electronic components which control the operation of a valve shown in Figure 1, Figures 3 and 4 show further examples of fuel system, and Figure 5 is a diagram similar to Figure 2 to control the operation of the valve means of the system of Figure 3.

Referring to Figure 1 of the drawings the system comprises a reciprocating plunger pump which is generally indicated at 10 and which comprises a cylinder 11 in which is mounted a reciprocable plunger 12. The plunger 12 is conveniently loaded in the outward direction by means of a spring not shown, into contact with a cam 13 which is mounted upon a cam shaft driven in timed relationship with the engine. The cylinder 11 has an outlet 14 which communicates with a fuel injection nozzle 15 by way of a spring loaded delivery valve indicated at 16.

Formed in the wall of the cylinder 11 is a filling port 17 which is uncovered by the plunger 12 when the latter moves outwardly. The port 17 communicates with a source of fuel 18. Also communicating with the cylinder 11 is a spill valve 19 which is controlled by an electromagnetic device the winding of which is indicated at 20. The valve is so arranged that the winding 20 must be energised to close the valve.

In use, during inward movement of the plunger 12 as soon as the port 17 is covered by the plunger, the fuel contained in the cylinder 11 is pressurised and if the valve 19 is closed, the fuel will be delivered through the outlet 14 to the injection nozzle 15 by way of the delivery valve 16. If during the inward movement of the plunger, the valve 19 is opened the pressure in the cylinder will fall below that required to maintain the delivery valve and the valve member in the nozzle in the open position and the fuel displaced by the plunger 12 will flow to a drain by way of the spill valve 19. During outward movement of the plunger fuel will flow into the cylinder 11 as soon as the port 17 is uncovered.

However, filling of the cylinder can be arranged to take place by way of the valve 19 as soon as the plunger starts to move outwardly in which case the valve 19 is connected to the source 18 of fuel under pressure.

The portion of the system described with reference to Figure 1 represents what is necessary to supply fuel to one injection nozzle of the engine and for a multi-cylinder engine there are as many components as shown in Figure 1, as there are engine cylinders although it will be appreciated that only a single source of fuel is required.

Referring now to Figure 2 of the drawings, the windings 20 of the valves 19 are connected to the outputs respectively of a socalled power module 21. The module 21 contains solid state power circuits which can be operated to cause flow of electric current in the windings 20 in response to signals provided by a so-called distributor 22. The distributor is provided with two main input signals one of which is provided by a so-called fuel circuit 23 and the other of which is provided by a sequence circuit 24. The input to the sequence circuit is obtained from a sensor 26 which is positioned to provide a pulse signal each time a mark 27 provided on a wheel 28, passes the sensor. The wheel 28 is driven at half the engine speed and there are as many marks 27 as there are engine cylinders.

The signals supplied by the sequence circuit 24 to the distributor 22 are such that the winding 20 of the appropriate spill valve 19 is energised at the desired time. The signal supplied by the fuel circuit 23 determines the time period in terms of degrees of engine rotation for which a particular winding is energised. The fuel circuit receives the signal from the sequence circuit so that the signal indicative of fuel quantity and which is supplied to the distributor is of a pulsed nature. The fuel circuit 23 determines the duration of fuel delivery on the basis of a control signal provided by a control or governor circuit 25. This receives a demand signal from a transducer associated with the throttle pedal of the vehicle powered by the engine and it receives an engine speed signal from a speed circuit 30 which receives as its input signal, the output signal of the sensor 26.On the basis of the speed signal and the demand signal, the circuit 25 generates a desired fuel signal which is processed in the fuel circuit 23 so that the pulses of the pulse signal fed to the distributor are of the appropriate duration. The governor circuit may also receive further signals indicative of other engine operating parameters.

As mentioned earlier in the specification the construction of the various components shown in Figure 1 is such that even though the power module supplies electric current to the windings 20 for the same time during the respective working cycles, the amount of fuel delivered to the injection nozzles 15 will vary.

If for example, one nozzle delivers appreciably more fuel than the other nozzles, the speed of the engine will momentarily increase during the working cycle of the cylinder associated with that nozzle since more power will be produced. Similarly if a nozzle supplies less fuel the engine will slow down.

The distributor 22 has further inputs from a so-called compensator circuit 29 which also receives the signals from the sequence circuit.

A further input to the compensator circuit 29 is from a comparison circuit 32 which at one input is supplied with the existing speed signal from the speed circuit 30 and at another input is provided with the preceding speed signal generated by the speed circuit this being supplied by a delay circuit 31 which is reset by the signal from the sensor. In effect therefore the output of the comparison circuit is the difference between the time period between one pulse and the preceding pulse generated by the sensor and the time period between the one pulse and the following pulse.

The difference signals will have a sign depending on whether the following period is longer or shorter than the preceding period.

The difference signals are stored in the compensator circuit 29 and at the correct time a correction signal is applied to the distributor 22 so that an injection nozzle which is delivering more fuel to its combustion chamber thereby causing a shortening of the respective time period, delivers less fuel and vice versa.

The extent of compensation may be limited so that full compensation is only achieved after a number of complete engine cycles.

The wheel 28 has been described as having as many marks 27 as there are engine cylinders. It may however be provided with a greater number of marks for example twice the number. In this case the assessment of the speed difference will involve a number of pulses corresponding to a period of not greater than one working cycle of the engine.

As an alternative the wheel 28 may be the flywheel of the engine in which case half the number of marks are required.

In Figure 3 of the drawings there is shown another form of fuel system which is described in greater detail in the specification of British patent 2037365. The pump comprises a drive shaft 32 which is integrally formed with an annular member 33 of enlarged diameter and within which is located the end portion of a rotary distributor member 34 which is housed within a body part 35. The distributor member is axially movable and is adapted to be driven from the annular member 33 by drive members which engage within radial slots formed in the member 33. The aforesaid slots also accommodate cam followers comprising shoes 36 which at their outer ends carry rollers 37 for engagement with the internal peripheral surface of a surrounding annular cam ring not shown.The shoes are axially fixed relative to the distributor member and are slidable in a radial direction in the aforesaid slots formed in the annular member 33. At their inner ends the shoes engage plungers 38 respectively housed within a diametrically disposed bore formed in the distributor member. The internal surface of the annular member 33 is tapered to form stop surfaces, and the shoes 36 are provided with complementary stop surfaces so that the axial position of the cam followers relative to the annular member will determine the maximum outward movement of the plungers 38.

The central portion of the bore defined between the plungers communicates by way of a passage 39, with a longitudinally extending groove-40 formed on the periphery of the distributor member and the groove can register in turn with a plurality of inlet ports 41 formed in the body part. The inlet ports 41 communicate with the outlet of a low pressure supply pump 42 the pressure of which is conveniently controlled so that it varies in accordance with the speed of operation of the apparatus, by means of relief valve 43. Alternately arranged with the ports 41 are a plurality of outlet ports 44 only one of which is shown and which are connected in use to the injection nozzles respectively of the associated engine.

The distributor member is biased away from the drive shaft by means of a coiled compression spring 45 which conveniently is located within a recess formed in the drive shaft. As the distributor member is moved by the action of the spring, the plunger 38 can move further outwardly while fuel is being supplied tQ the bore through a port 41 and the groove 40, thereby increasing the amount of fuel which is supplied to an outlet during the next inward movement of the pumping plungers.

The movement of the distributor member 34 against the action of the spring is effected by supplying fuel under pressure to a chamber 46 into which the end of the distributor member remote from the drive shaft projects. the end surface of the distributor member is subject to the pressure of fuel in the chamber 46 and thereby a force is developed which urges the distributor member against the action of the spring 45.

The control of the fuel pressure in the chamber 46 is effected by valve means 47 which includes a landed valve member 48 the central recess of which communicates with the chamber 46. In the central position of the valve member as shown, a passage 49 leading to a drain is covered by one land and a passage 50 communicating with the outlet of the low pressure pump, is covered by the other land. The valve member can be moved in either direction by the action of an actuator 51 and the arrangement is such that if the valve member is moved downwardly the chamber 46 is brought into communication with the drain by way of the passage 49. On the other hand if the valve member is moved upwardly the chamber 46 is brought into communication with the passage 50.In the former case fuel can escape from the chamber 46 and the distributor member will move towards the right to increase the amount of fuel supplied to the associated engine and in the latter case fuel will flow into the chamber 46 to move the distributor member towards the left against the action of the spring 45 thereby causing a reduction in the amount of fuel supplied. The valve member 48 is returned to its intermediate position before engagement of the stop surfaces so that the distributor member is hydraulically locked before contact of the shoes and the stop surfaces take place.

In the modification which is shown in Figure 4, the chamber 46 is permanently in communication with the drain by way of the passage 52 which contains a restrictor. In addition, an electromagnetically operable valve 53 is provided which affords permanent communication between the chamber and the outlet of the low pressure pump and the magnitude of the current flowing in the solenoid winding of the valve 53 determines the degree of restriction imposed by the valve. The pressure in the chamber 46 can therefore be altered by altering the current flowing in the winding of the valve and therefore the axial position of the distributor member can be controlled. A suitable valve for this purpose is described in British patent specification 2064720B.

Referring now to Figure 5 which shows a control circuit suitable for use with the pump shown in Figure 3. In the pump shown in Figure 3 the valve member 48 of the valve 49 can move in opposite directions from its control position and therefore the actuator 51 is provided with a pair of windings 54, 55. The flow of current in the windings is effected by a control circuit 56 and this receives a feedback signal indicative of the position of the distributor member 34 from a sensor 57.

The control circuit receives a control signal from a so-called distributor circuit 58, and the control signal represents a desired distributor member position signal. The control signal can undergo a general change in level as the amount of fuel required to be supplied to the engine varies as a result of governor action or by a change in operator demand but it can also undergo- instantaneous changes in level to take into account the discrepancies in fuel delivery noted above.

The distributor circuit 58 is provided with two main input signals one of which is provided by a so-called fuel circuit 59 and the other of which is provided by a sequence circuit 60. The input to the sequence circuit is obtained from a sensor 61 which is positioned to provide pulse signals each time a mark 62 on a wheel 63, passes the sensor. The wheel is driven at half the engine speed and there are as many marks 62 as there are engine cylinders. As with the previous example the wheel can be driven at engine speed with half the number of marks. The signals supplied by the sequence circuit 60 are such that the windings 54 or 55 are only energised for a short period to allow adjustment of the position of the distributor member before the shoes 36 engage the stop surfaces.The signal provided by the fuel circuit 59 represents the desired position of the distributor member and this signal is determined by the fuel circuit on the basis of an input signal provided by a control or governor circuit 64. This receives a demand signal from a transducer (not shown) associated with the throttle pedal of the vehicle powered by the engine and it also receives an engine speed signal from a speed circuit 65 which receives at its input signal, the output signal of the sensor 61. On the basis of the speed signal and the demand signal, the circuit 64 generates a desired fuel signal which is processed in the fuel circuit 59 to provide the desired distributor member position signal.

In order to compensate for the discrepancies in fuel delivery and engine combustion chamber characteristics the distributor circuit 58 has further inputs from a so-called compensator circuit 66 which also receives the signals from the sequence circuit 60. A further input to the compensator circuit 66 is from comparator 67 which at one input is supplied with the existing speed signal from the circuit 65 and at another input with the preceding signal generated by the speed circuit this being supplied by a delay circuit 68 which is reset by the signal from the sensor. In effect therefore the output of the comparator 67 is the difference between the time period between one pulse and the preceding pulse generated by the sensor and the time period between the one pulse and the following pulse.

The difference signals will have a sign depending on whether the following period is longer or shorter than the preceding period.

The difference signals are stored in the compensator circuit 66 and at the correct time a correction signal is supplied to the distributor circuit 58 so that an instantaneous change occurs in the control signal applied to the control circuit 56. The distributor member 34 is therefore moved to a new setting to alter the quantity of fuel supplied at the next delivery of fuel after which it reverts to its original setting. The extent of compensation may be limited so that full compensation is only achieved after a number of complete engine cycles.

As described the circuit of Figure 5 is for use with the pump shown in Figure 3. For the pump shown in Figure 4, the valve 53 must be open all the time to maintain the pressure in the chamber 46. The winding of the valve 56 may be supplied from the power circuit but in this case there must be a continuous flow of current in the valve winding which is varied at the appropriate time to alter the position of the distributor member to provide the change of fuel delivery by the pump to effect correction of the aforesaid discrepancies.

The form of pump which incorporates a valve which acts as an adjustable throttle to control the quantity of fuel supplied to the pump during the filling strokes thereof can be controlled by the circuit of Figure 5 as modified for the pump shown in Figure 4. In this case the sensor 57 is responsive to the setting of the valve member of the valve.

Claims (3)

1. A fuel system for a multi-cylinder engine comprising engine driven pump means having a plurality of outlets for connection to injection nozzles respectively of the associated engine, electromagnetically operable valve means operable to control the amount of fuel which is delivered through each outlet, a control circuit for controlling the valve means in accordance with desired and actual engine operating parameters, transducer means for providing a pulse signal at each working stroke of the engine, speed measuring means for measuring the time period between successive signals, means for comparing the time period between one pulse and the preceding pulse with the time period between the one pulse and the following pulse to produce a series of difference signals and means responsive to said difference signals for adjusting said valve means to reduce said difference signals.

2. A fuel system according to Claim 1 in which the means for comparing the time periods comprises a comparator having a pair of inputs one of which is connected directly to the output of said speed measuring means and the other of which is connected to to the output of said speed measuring means by way of a delay circuit, said delay circuit having a reset input connected to said sensor.

3. A fuel system for a multi-cylinder engine substantially as hereinbefore described with reference to the accompanying drawings.