GB2512920A

GB2512920A - Fuel system control

Info

Publication number: GB2512920A
Application number: GB1306650.1A
Authority: GB
Inventors: Michael Smith; Daniel Jessup
Original assignee: Perkins Engines Co Ltd
Current assignee: Perkins Engines Co Ltd
Priority date: 2013-04-12
Filing date: 2013-04-12
Publication date: 2014-10-15
Anticipated expiration: 2033-04-12
Also published as: GB2512920B; GB201306650D0

Abstract

Disclosed is a method of controlling a fuel injector for an internal combustion engine having a fuel system comprising a source of high pressure fuel such as a common rail and at least two fuel injectors fed by the source of high pressure fuel. The method comprises the steps of: measuring and recording the fuel pressure in the common rail at a set of predetermined intervals during operation of the fuel system (these interval samples may be pressure measurements taken every 6o of crank angle), measuring and recording the fuel pressure in the common rail at a set of predetermined events during the operation of the fuel system (these event samples may be a specific crank angle such as 30o before top dead centre), determining a compensation value for a first fuel injector from a last interval sample and a last event sample taken immediately before operation of a second fuel injector (this establishes the previous known pressure change between a known a reference pressure - the event pressure and the pressure just prior to injection as given by the last interval pressure measurement before the last injection event), applying the compensation value to an event sample taken before an imminent operation of the first fuel injector to provide a compensated pressure andÂ calculating a pulse width for the imminent operation of the fuel injector based on the compensated pressure. A fuel control system using the method and an engine comprising the fuel system are also disclosed.

Description

FUEL SYSTEM CONTROL

TECHNICAL FIELD

The present disclosure relates to Improvements In the control of a fuel system and more specifically to a method of controlling the delivery of fuel to fuel injectors In an engine such as a combustIon engine.

BACKGROUND

Many different fuel systems may be utilized to Introduce fuel Into the combustion chambers of an engine.

One such fuel system Is known as the common rail fuel system. A typical common rail fuel system utilIzes one or more pumping mechanIsms to pressurIze fuel and dIrect the pressurized fuel to a common manIfold. Such a manifold is generally known as a common raIl, and provides a source of pressurised fuel. A pluralIty of fuel Injectors draw pressurized fuel from the common rail and inject one or more shots of fuel per cycle Into the combustion chambers. In order to optImIze engIne operation, fuel withIn the raIl is maIntaIned wIthIn a desired pressure range through the precIse control of the pumping mechanisms.

In a typical fuel delIvery system for a combustIon engine a transfer pump may be used to pump fuel from a storage tank, and to delIver It at low pressure to a hIgh pressure fuel pump. The high pressure fuel pump pressurizes the fuel to a hIgh pressure and delivers It to the common raIl. However a particular issue may arise If the pumping events of the hIgh pressure fuel pump are out of phase wIth the fuel injectIon events. This may occur, for example, If a three lobe high pressure fuel pump is used in the fuel system for a four cylinder engine. The resultant effect of this may be a variation in the rail pressure for different injeotion events and an uneven spread of delivery of fuel across the injectors for a fixed injector nozzle opening duration. This reduces engine stability and emissions consistency.

SUMMARY

According to this disclosure there is provided a method of controlling the operation of a fuel injector in a fuel system, said fuel system comprising: a source of high pressure fuel; and at least a first fuel injector and a second fuel injector, which first and second fuel injectors are supplied with fuel by the source of high pressure fuel and are operated sequentially; said method comprising the steps of: measuring and storing pressures in the source of high pressure fuel at a plurality of predetermined intervals during operation of the fuel system (interval samples) measuring and storing pressures in the source of high pressure fuel at a plurality of predetermined events during operation of the fuel system (event samples) determining a compensation value for the first fuel injector from a last interval sample and a last event sample taken immediately before a preceding operation of the second fuel injector; applying the compensation value to an event sample taken before an imminent operation of the first fuel injector to provide a compensated pressure; and calculating a pulse width for the imminent operation of the first fuel injector based on the compensated pressure.

The disclosure further provides a fuel system

comprising: a source of high pressure fuel; at least one pressure sensor located to measure the pressure in the source of high pressure fuel; at least a first fuel injector and a second fuel injector, which first and second fuel injectors are supplied with fuel by the source of high pressure fuel and are operated sequentially; and an electronic control module, said electronic control module being programmed to:-capture and store measurements of rail pressure taken by the at least one pressure sensor at a plurality of predetermined intervals during operation of the fuel system and at a plurality of predetermined events during operation of the fuel system; determine a compensation value for the first fuel injector from a last interval sample and a last event sample taken immediately before a preceding operation of the second fuel injector; apply the compensation value to an event sample taken before an imminent operation of the first fuel injector to provide a compensated pressure; calculate a pulse width for the imminent operation of the first fuel injector based on the compensated pressure; and open the first fuel injector for the calculated pulse width.

The disclosure further provides an engine comprising: the fuel system as claimed in claim 11 or claim 12; at least four cylinders; at least one reciprocating piston located in each cylinder; a rotatable crankshaft to which the pistcns are connected such that pairs of the pistons reciprocate together; a fuel injector arranged to inject fuel into each cylinder, operation of the fuel injectors being controlled by the electronic control module; wherein the first and second fuel injectors are the fuel injectors associated with a pair of cylinders in which a pair of pistons reciprocate together.

BRIEF DESCRIPTION OF THE DRAcINCS

Figure 1 is a schematic representation of a fuel system of a four cylinder common rail internal combustion engine; Figure 2 is a graph illustrating rail pressure compensation in the fuel system of Figure 1 based on pressure at the start of an injection event; and Figure 3 is a graph illustrating rail pressure compensation in the fuel system of Figure 1 based on average pressure during an injection event.

DETAILED DESCRIPTION

Figure 1 illustrates one exemplary embodiment of a fuel system 10 of a four cylinder common rail internal combustion engine 11, which may be controlled by the method of the present disclosure. The fuel system 10 is designed to deliver fuel (e.g. diesel, gasoline, heavy fuel, etc.) from a location where fuel is stored to the combustion chamber(s) of the engine 11 where it will be combusted. The energy released by the combustion process is captured by the engine 11 and used to generate a mechanical source of power.

Although Figure 1 shows a fuel system for a diesel engine, the fuel system 10 of the present disclosure may be the fuel system of any type of engine (e.g. other internal combustion engines, such as a gaseous fuel or petrol engines, turbines etc.). The fuel system 10 of Figure 1 may include a fuel source such as a tank 12, a transfer pump 13, a high pressure fuel pump 14, a common rail 15 (or other source of high pressure fuel), at least one pair of fuel injectors 16 and an electronic control module (ECM) 17. It may also include a pressure relief valve 18.

The tank 12 (or reservoir) is typically a storage container for storing the fuel that the fuel system 10 delivers to the engine 11. The transfer pump 13 may be fluidly connected to both the tank 12 and the high pressure fuel pump 14 and configured to pump fuel from the tank 12 and deliver it to the high pressure fuel pump 14 at a generally low pressure. The high pressure fuel pump 14 may be fluidly connected to the common rail 15 and may be controlled to pressurise the incoming fuel to a high pressure for delivery to the common rail 15. The common rail 15, which is intended to be maintained at the pressure generated by the high pressure fuel pump 14, may serve as the source of high pressure fuel for each of the fuel injectors 16.

The high pressure fuel pump 14 may be a cam driven piston pump. Cam driven pumps may comprise one or more reciprocating piston elements which are driven by a cam mounted on a camshaft which may rotate at half engine speed.

The cam of a cam driven pump may have three lobes and may be 240° out of phase to give a pumping stroke every 120°. Such a cam driven pump would therefore provide three primary pumping pulses within one engine cycle (720°) . Various configurations of high pressure fuel pump 14 may he used, for example the Denso HP4 High Pressure Fuel Pump which has a suction metering valve. Other high pressure fuel pumps 14 may be used which may have an outlet metering valve.

The pressure relief valve (PRy) 18 is a component or assembly which may selectively direct fuel from the common rail 15 to the tank 12 via a drain line 20 when the pressure of the fuel within common rail 15 exceeds a certain threshold. This threshold may depend on the characteristics of each particular fuel system 10.

The fuel injectors 16 may be located within the engine 11 in a position which enables the fuel injectors 16 to inject high pressure fuel into the combustion chambers of the engine 11. Alternatively they may be located so as to inject the fuel into pre-chambers or ports upstream of the combustion chamber. Fuel injectors 16 generally serve as metering devices which control when fuel is injected into the combustion chambers, how much fuel is injected, and the manner in which the fuel is injected (e.g. the angle of the injected fuel, the spray pattern, etc.). When a fuel injector 16 is energised, the injector valve opens allowing pressurised fuel to sguirt out through the injector nozzle into the combustion chamber. Each fuel injector 16 may be continuously fed with fuel by the common rail 15, such that any fuel injected by a fuel injector 16 may quickly be replaced by additional fuel from the common rail 15. Most modern engines have multi-port fuel injection systems (also known as port, multi-point or seguential fuel injection) These systems typically have a fuel injector 16 for each cylinder 21, 22, 23, 24 in the cylinder block (not illustrated), located so that they spray directly into the oomhustion chamber.

The ECM 17 is an electronic control module which may be arranged to receive multiple input signals from multiple sensors associated with various systems of engine 11 (including the fuel system 10) . The input signals may be indicative of the operating conditions of those various systems (e.g. common rail fuel pressure, fuel temperature, throttle position, engine speed, etc.). The ECM 17 may use these input signals to determine how to control the fuel system 10 which includes, inter alia, operation of the high pressure fuel pump 14 and each of the fuel injectors 16. It is desirable that the fuel system 10 ensures that fuel is constantly fed to the engine 11 in the appropriate amounts, at the right times, and in the right manner to support the required operation of the engine 11. The quantity of fuel supplied to the engine 11 is determined by the length of time that the fuel injectors 16 stay open (pulse width) . The pulse width is inversely related to the pressure difference across the injector inlet and the injector outlet. Thus the pressure of the fuel supplied to the fuel injeotors 16 affects the pulse width.

In multi-cylinder engines, pairs of pistons may reciprocate together to assist in engine balancing and may drive a rotatable crankshaft. In a four cylinder engine the cylinders are conventionally numbered in sequence. For example in a four cylinder engine they are numbered 1-2-3-4.

In the drawings cylinder 1 is designated numeral 21; cylinder 2 is designated numeral 22; cylinder 3 is designated numeral 23; and cylinder 4 is designated numeral 24. The pistons in the first and fourth cylinders 21,24 usually reciprocate together, and the pistons in the second and third cylinders 22,23 usually reciprocate together. When one piston in a pair is on the compression stroke the other piston is on the exhaust strcke. The firing order of the cylinders 21, 22,23,24(in this example the firing order is designated 1-3-4-2, i.e. in the drawings cylinders 21-23-24- 22) is achieved by the sequence of fuel injection and the ECM 17 controls the correct tiring sequence. The paired cylinders may thus have substantially the same characteristics for injection events, such as injection timing and rail pressure.

At least one rail pressure sensor 19 is provided to measure the rail pressure in the common rail 15 and to send signals relating to the measured rail pressure to the ECJ4 17. The rail pressure sensor 19 may be a piezo resistive type sensor, which provides a linear signal voltage output to the FOM 17, or another suitable type of sensor. The rail pressure sensor 19 may be screwed into the common rail 15 or affixed in another suitable manner. The rail pressure sensor 19 may alternatively be located within a fuel injector 16.

The ECM 17 is programmed to receive and store measurements of rail pressure taken by the rail pressure sensor 19 at a plurality of predetermined intervals and events. From these the ECM 17 calculates a compensation value which is applied to a further rail pressure measurement and the resulting compensated rail pressure value is used to calculate the appropriate pulse width (opening duration) for each fuel injector 16.

A first set of measurements of rail pressure, referred to herein as interval samples (P1), are taken at regular predetermined intervals. These intervals may he a function cf crank angle, which may be 6° intervals of crank angle, or another predetermined interval or crank angle. The crank angle is measured from the cylinder bore centre line at top dead centre (TDC) . The interval may alternatively he a time interval as a function of engine speed. A number of historical samples are stored by the ECM 17, for example the samples taken over the previcus 7200 crank angle.

A second set of measurements of rail pressure, referred to herein as event samples (fa) , are taken at predetermined events associated with the operation of the engine (fixed engine events) . These samples may be taken at predetermined (fixed) crank angles which relate to a fixed injection event, for example 30° before TDC with respect to each cylinder TDC.

The ECN 17 calculates a compensation value (AP) for the imminent cylinder to fire using the event and interval samples taken immediately before the preceding firing of its paired cylinder (last event sample and last interval sample) . Thus for a 1-3-4-2 firing sequence, the compensation value (AP1) for cylinder 21 may be calculated using previous samples taken for cylinder 24; the compensation value (AP2) for cylinder 22 may be calculated using previous samples taken for cylinder 23; the compensation value (AP4) for cylinder 24 may be calculated using previous samples taken for cylinder 21; and the compensation value (AP3) for cylinder 23 may be calculated using previous samples taken for cylinder 22.

The compensation value (AP) for the next cylinder to fire may be calculated by subtracting the event sample (P=8) -10 -from the interval sample (P), each of which was taken just before the start of the previous injection event for its paired cylinder. The compensation value (A?) is added to the event sample (Pfa) which has just been taken for the next cylinder to fire. The resulting compensated pressure (PJ is used to calculate the pulse width for the next cylinder to fire.

Figure 2 illustrates one (non-limiting) numerical example of how the compensation valve is calculated. The pressure at the start of injection into cylinders 22 and 23 is 99.SMpa. The pressure at the start of injection into cylinders 21 and 24 is 98Mpa. The average injection pressure during the injection event is 96.75F4pa for cylinders 22 and 23, and 95Mpa for cylinders 21 and 24. The event samples taken immediately prior to the firing of cylinders 22 and 23 are each 96lYipa. The event samples taken immediately prior to the firing of cylinders 21 and 24 are each 98.5Mpa.

AP23 = the compensation value for cylinder 23 which is the next cylinder to fire P122 = the interval sample taken immediately before the last injection event for cylinder 22 = the event sample taken immediately before the last injection event for cylinder 22 fa23 = the last event sample taken before cylinder 23 Is about to fire c2 = the compensated pressure for cylinder 23 AP2 = -= 98.4Mpa -96Mpa = +2.4 c2? = fa23 + AP2 = 96L4pa + 2.4 = 98.4Mpa -11 -AP21 = the compensation value for cylinder 24 which is the next cylinder to fire P171 = the interval sample taken immediate'y before the last injection event for cylinder 21 a21 = the event sample taken immediately before the Thst injection event for cylinder 21 = the last event sample taken before cylinder 24 is about to tire c24 = the compensated pressure for cylinder 24 io AP24 = -P21 = 98.3Mpa -98.5Mpa = -0.2 = ja24 + AP24 = 98.5Mpa -0.2 = 98.3Mpa Alternatively the compensated pressure may be based on the average pressure (P) during the injection event. The average pressure (Pay) may be determined from interpolation (linear or non linear) of the interval sample (last interval sample)taken before the start of the injection event (Ph) and the interva' sample (next interval sample)taken after the end of the injection event (Pie) Using the average pressure (P) may improve the accuracy of the compensation as account is taken of the variations in overlap anqe between the pumping and injection events. This is a function of pump flow demand, start at injection angle, injector fuel delivery, engine speed and rail pressure. Figure 3 illustrates another non-limiting example of this strategy using this method of calculating the compensation value (A?) = the compensation value for cylinder 23 which is the next cylinder to fire = the interval sample taken immediately before the Thst injection event for cylinder 22 -12 -ie22 = the interval sample taken immediately after the last injection event for cylinder 22 ;v22 = the average pressure for the injector of cylinder 22 a22 = the event sample taken immediately before the last injection event for cylinder 22 = the last event sample taken before cylinder 23 is about to tire c23 = the compensated pressure for cylinder 23 av22 = ± (±i:22 and P022) = 5(98.5Mpa and 93.9Mpa) = 96. 8Mpa = p.22 -f22 = 96.8L4pa -96Mpa = +0.8 PC23 = fa23 + AP23 = 96Mpa + 0.8 = 96.8Mpa AP24 = the compensation value for cylinder 24 which is the next cylinder to tire = the interval sample taken immediately before the last injection event for cylinder 21 ie2l = the interval sample taken immediately after the last injection event for cylinder 21 P2i = the average pressure for the injector of cylinder 21 = the event sample taken immediately before the last injection event for cylinder 21 fa24 = the last event sample taken before cylinder 23 is about to fire c21 = the compensated pressure for cylinder 24 P21 = ±(P1 and Pe2) = ±(98.5Mpa and 91.5Mpa) = 951'4pa AP21 = av21 -fa21 = 95Mpa -98.5Mpa = -3.5 = a24 + AP24 = 98.5Mpa -3.5 = 95t4pa -13 -The event sample may also correspond to the pressure at the start of injection and the interval sample may be a pressure taken at an interval before the start of injection, which may be 5ms. In this strategy the interval sample is subtracted from th event sample to give the compensation value. This compnesation value is then added to the interval sample of the injector which is about to fire.

The samples used may alternatively be those taken at the start of current, i.e. when the current is initiated to energize the fuel injector 16, rather than the start of the actual injection.

INDUSTRIAL APPLICABILITY

During operation of the fuel system 10, the transfer pump 13 draws fuel from the tank 12 and provides the fuel to the high pressure fuel pump 14. The high pressure fuel pump 14 pressurizes the fuel to a high pressure and directs the high pressure fuel to the common rail 15. The fuel is then directed from the common rail 15 to each of the fuel injectors 16.

Where the pressurisation events of the high pressure fuel pump 14 are out of phase with the injection events the method of the present disclosure provides a compensation strategy to alleviate the afcrementioned issues.

One method of determining an appropriate compensation to apply may be to directly measure the injection pressure as close to the start of the injection as possible and the adjust the injector opening duration accordingly. However the design of some FOMs 17 may be such that this may not be possible. The compensation strategy of the method of the -14 -present disclosure eliminates the need for such direct measurement. This strategy looks at historical pressure differences to determine a predicted pressure immediately before injection. After the compensation is applied, the spread in fuel deliveries across the cylinders 21,22,23,24 may be reduced. This may improve fuel delivery accuracy, engine stability and emissions consistency.

In a non-compensated rail pressure sampling system where there is a 3:2 pumping event to injection event ratio the injectors associated with cylinders 21 and 24 may have the same rail pressure characteristics as injection events on an engine 11 with a 1:1 pumping event to injection event ratio with a pumping event followed by an injection event.

The injectors associated with cylinders 22 and 23 have the pumping event overlapping with the injection event. The sampled rail pressure is lower for these injectors compared to injectors associated with cylinders 21 and 24 so the calculated opening time for the injector to deliver the same volume of fuel is longer. The start of injection pressure and the average pressure associated with cylinders 22 and 23 are higher so there will be a higher fuel flow rate from the injectors associated with thcse cylinders compared to the injectors associated with cylinders 21 and 24.

In the injector delivery compensation strategy of the present disclosure the delivery of fuel to the injectors is evened out. Compared to the non-compensated fuel delivery, the injectors associated with cylinders 22 and 23 deliver less fuel than the injectors associated with cylinders 1 and 4, whilst there is little effect on the injectors associated with cylinders 21 and 24.

-15 -As described above, the EON 17 calculates a compensation value which is applied to a further rail pressure measurement and the resulting compensated rail pressure value is used to caloulate the appropriate pulse width (opening duration) for the next fuel injector 16 to operate.

The method of the present disclosure may be used for a wide range of engines having one or more pairs of cylinders each with an associated injector, which injectors are operated sequentially. For example the engine 11 may have 4, 6, 8 or 12 cylinders.

Claims

-16 -CLAIMS: 1. A method of controlling the operation of a fuel injector in a fuel system, said fuel system comprising: a source of high pressure fuel; and at least a first fuel injector and a second fuel injector, which first and second fuel injectors are supplied with fuel by the source of high pressure fuel and are operated sequentially; said method comprising the steps of: measuring and storing pressures in the source of high pressure fuel at a plurality of predetermined intervals during operation of the fuel system (interval samples) measuring and storing pressures in the source of high pressure fuel at a plurality of predetermined events during operation of the fuel system (event samples) determining a compensation value for the first fuel injector from a last interval sample and a last event sample taken immediately before a preceding operation of the second fuel injector; applying the compensation value to an event sample taken before an imminent operation of the first fuel injector to provide a compensated pressure; and calculating a pulse width for the imminent operation of the first fuel injector based on the compensated pressure.
2. The method as claimed in claim 1 in which the compensation value is calculated by subtracting the last event sample taken immediately before the preceding operation of the second fuel injector from the last interval sample taken immediately before the preceding operation of the second fuel injector.

-17 -
3. The method as claimed in claim 1 in which the compensation value is determined using an average pressure during the preceding operation of the second fuel injector.
4. The method as claimed in claim 3 in which the average pressure is determined from the last interval sample taken immediately before the preceding operation of the second fuel injector and a next interval sample taken immediately after the preceding operation of the second fuel injector.
5. The method as claimed in claim 3 or claim 4 in which the compensation value is calculated by subtracting the last event sample taken immediately before the preceding operation of the second fuel injector from the average pressure.
6. The method as claimed in claim 1 in which the compensation value is determined by subtracting the interval sample from the event sample.
7. The method as claimed in any one of the preceding claims in which the compensated pressure is calculated by adding the compensation value to the event sample taken before the imminent operation of the first fuel injector.
8. A method as claimed in any one of the preceding claims in which the fuel system is the fuel system of an engine, and the interval samples are measured as a function of crank angle.
9. A method as claimed in claim 8 in which the interval samples are measured at 6° intervals of crank angle.-18 -
10. A method as claimed in any one of the preceding claims in which the fuel system is the fuel system of an engine having a cylinder associated with each fuel injector and the event samples are measured at crank angles which relate to fixed engine events.
ii. A method as claimed in claim 10 in which the fixed engine events are top dead centre for each cylinder.
12. A fuel system comprising: a source of high pressure fuel; at least one pressure sensor located to measure the pressure in the source of high pressure fuel; at least a first fuel injector and a second fuel injector, which first and second fuel injectors are supplied with fuel by the source of high pressure fuel and are operated sequentially; and an electronic control mcdule, said electronic control module being programmed to:-capture and store measurements of rail pressure taken by the at least one pressure sensor at a plurality of predetermined intervals during operation of the fuel system and at a plurality of predetermined events during operation of the fuel system; determine a compensation value for the first fuel injector from a last interval sample and a last event sample taken immediately before a preceding operation of the second fuel injector; apply the compensation value to an event sample taken before an imminent operation of the first fuel injector to provide a ccmpensated pressure; -19 -calculate a pulse width for the imminent operation of the first fuel injector based on the compensated pressure; and open the first fuel injector for the calculated pulse width.
13. A fuel system as claimed in claim 12 further comprising a high pressure fuel pump for supplying pressurised fuel to the source of high pressure fuel.
14. An engine comprising: the fuel system as claimed in claim 12 or claim 13; at least four cylinders; at least one reciprocating piston located in each cylinder; a rotatable crankshaft to which the pistons are connected such that pairs of the pistons reciprocate together; a fuel injector arranged to inject fuel into each cylinder, operation of the fuel injectors being controlled by the electronic control module; wherein the first and second fuel injectors are the fuel injectors associated with a pair of cylinders in which a pair of pistons reciprocate together.
15. An engine as claimed in any one of claims 12 to 14 in which the source of high pressure fuel is a common rail.
16. An engine as claimed in any one of claims 12 to 15 in which the high pressure fuel pump is a cam driven piston pump comprising a cam having three lobes.