Method and system to control fuel injection

Abstract

 A method of operating/controlling fuel injectors in an engine comprising n cylinders, where said fuel injectors are operated by a plurality of banks, m, and where the number of banks, m, is less than the number of fuel injectors, n, comprising, assigning of each of said banks to a particular cylinder, and assigning at least two banks to the remaining (n-m) cylinders. The engine may comprise 3 cylinders, and use a first and a second bank, the first bank being assigned to the first cylinder, the second bank being assigned to the second cylinder, and both of said banks being assigned to the third cylinder. A first injection pulse from a first bank may be applied to one or more fuel injectors of a cylinder during a first period and applying at least a second injection pulse in said second period to the one or more fuel injectors of said same cylinder. A long pulse may thus be split and shared.

Description

Technical Field

[0001] Aspects of the invention relate to a method and system applicable to fuel injected internal combustion engines, and in particular concerns a system and method of controlling fuel injected into the cylinders of such engines.

Background of the Invention

[0002] Typically fuel injectors for both petrol and diesel engines are electrically or electronically operated under the control of, e.g., an Engine Control Unit. The fuel injectors themselves are actuated electrically using solenoid or piezoelectric means. In known systems, for example, the actuation is provided by electrical/electronic circuitry, some of this circuitry may be common, i.e. shared by more than one injector, and thus certain circuitry may be utilised for more than one cylinder.

[0003] Specifically, fuel injectors for gasoline direct injection are driven usually by a high-side circuit (which includes two FETs), this circuit connects one pin of its coil to a positive voltage (either battery or a boost voltage) and a low-side circuit (including one FET) which connects the other pin of the coil to ground, allowing current to flow.

[0004] Whereas it is usual for each fuel injector to have its own dedicated low-side circuit, the high side circuitry is usually shared by two fuel injectors in respect of two cylinders, the two cylinders being opposing cylinders. The reason for this shall be explained hereinafter. The high side circuitry is often referred to as a high-side "bank". The term "bank" referred to hereinafter should be interpreted generally as any circuitry (which may include coils/drivers etc.) which is used by the fuel injectors, and which is common to (i.e. shared by ) more than one fuel injector.

[0005] In four-cylinder, 4-stroke engines, for each 720° rotation of the crankshaft, each cylinder goes through a complete cycle of intake, compression, combustion and exhaust; in a typical operating mode therefor, fuel is injected into each cylinder in this period. Therefore, the injection/ignition times with respect to two opposing cylinders are separated by a crankshaft rotation of 360°. This is a sufficient enough period for shared circuitry to operate both injectors of the two such opposing cylinders. By using such shared circuitry such as the high-side circuit with respect to two cylinders/injectors, allows the component count, and thus costs to be reduced.

[0006] The 360° window is required, because in circumstances or systems where a very long injection is required, the injection may span more than 240° in order to deliver either a large quantity of fuel (e.g. cold start with alcohol or when the fuel pressure is below normal ,e.g.pump failure) or several injections into the same cylinder over a wide crank angle range.

[0007] In such a way, for four cylinder engines, only two banks are required, i.e. only two high side circuits. It is to be noted that sometimes there will be a main injection to the intake stroke (about 300° before top dead centre (TDC)) and under some operating modes, there is additionally a late injection close to ignition (25° after TDC).

[0008] With 3-cylinder engines, a problem exists in terms of implementing such shared systems as there are no opposing cylinders; such a scheme is thus impossible to apply. For 3-cylinder 4-stroke engines, again for each sparking/injection event in respect of the same cylinder, there is a 720° crankshaft rotation; however such events are separated with respect to other cylinders by crankshaft rotation of 240° (720°/3). If two banks are used in total, and if two cylinders share one bank, there will thus be an injection window of 240° crank-angle, whilst the 3^rd injector having its own bank will have an injection window of 720°. Thus a third bank is required in such applications, because, as mentioned there are circumstances where the fuel injection in a cylinder takes place over more than 240°. Furthermore using such an arrangement prevents using the same ECU for both 3 and 4 cylinder applications. In addition, most direct injection driver application specific integrated circuits (ASICs) only support two banks, thus they require special adaptation or duplication of parts.

[0009] In modem injection strategies is desirable to have a 360° window for each bank, which means for a 3-cylinder engine, using one high-sided driver (bank) per injector, actually requiring more components (3 x 2FETs, plus pre-drivers) than a 4-cylinder engine (2 x 2FETs plus pre-drivers)! This inevitably increases the number of components and thus the cost.

[0010] It is an object of the invention to provide a system and method for controlling a plurality of injectors in a combustion engine which provides an efficient use of components whilst not compromising performance.

Summary of the Invention

[0011] In a first aspect is provided a method of operating or controlling fuel injectors in an engine, wherein power to fuel injectors for the cylinders are provided by a plurality of banks, and with respect to a (single) injection phase for fuel injector of a particular cylinder, power therefor is provided by at least two t banks.

[0012] In a second aspect is provided a method of operating/controlling fuel injectors in an engine comprising n cylinders, where said fuel injectors are operated by a plurality of banks, m, and where the number of banks, m, is less than the number of fuel injectors, n, comprising, assigning of each of said banks to a particular cylinder, and assigning at least two banks to the remaining (n-m) cylinders.

[0013] The engine may comprise 3 cylinders, and using a first and a second bank, the first bank being assigned to the first cylinder, the second bank being assigned to the second cylinder, and both of said banks being assigned to the third cylinder.

[0014] The assignment may be controlled/effected by an Engine Management Unit A first bank may be assigned to a cylinder over a first period and a second bank may be assigned to said same cylinder over second period.

[0015] Said periods may be substantially contiguous, adjacent and/or sequential in terms of time and/or engine crankshaft angle.

[0016] The engine may be a 3-cylinder engine and said first and/or second periods may be in the order of 480° crankshaft angle. With respect to successive injection phases in all cylinders, said banks may be assigned alternately.

[0017] The method may be as claimed in any preceding claim comprising providing or applying a first injection pulse from a first bank to one or more fuel injectors of said cylinder during said first period and providing or applying at least a second injection pulse in said second period to the one or more fuel injectors of said same cylinder. The pulses may be are provided by splitting a predetermined pulse.

[0018] In a third aspect of the invention is provided a system of operating or controlling fuel injectors in an engine, having means to provide power to fuel injectors of the cylinders by a plurality of banks, and with respect to a (single) injection phase for fuel injector of a particular cylinder, means to provide said power therefor by at least two banks.

[0019] In a fourth aspect of the invention is provided a system to operate or control fuel injectors in an engine comprising n cylinders, where said fuel injectors are operated by a plurality of banks, m, and where the number of banks, m, is less than the number of fuel injectors, n, comprising means to assign of each of said banks to a particular cylinder, and means to assign at least two banks to the remaining (n-m) cylinders.

Brief Description of the Drawings

[0020] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figures 1a and 1 b shows a schematic representation illustrating the sharing of banks (high-sided) according to examples of the invention for 3- and 5- cylinder engines respectively.

Figure 2 shows the circuitry that can be used in an example, in the case of a 3-cylinder engine.

Figures 3a to 3e show a single chart showing a timeline illustrating an example of the invention applicable to a 3-cylinder engine.

Figures 4a to 4c show a single chart showing a timeline for three scenarios illustrating how an example of the invention can be applied.

Description of the Preferred Embodiments

[0021] The inventors have determined that even though the total injection window required for each cylinder may be around 360°, this window does not necessarily have to be continuous (in terms of injection pulse).

[0022] In an example applicable to 3 cylinder engines, two (e.g. high sided) banks are used (referred to as banks A and B). Bank A can be assigned with respect to injection (e.g. the injector) for a first cylinder, bank B assigned with respect to injection (the injector) for a second cylinder, and both banks can be assigned with respect to injection in a third cylinder; in other words injection duties (that is to say the providing the requisite electrical/electronic operation/pulses to the fuel injector) for the third cylinder are shared by both banks. Such an arrangement provides the fuel injector(s) for cylinders, with two separate but contiguous windows, where the injector is assigned a first bank (e.g. bank A) to provide a sub-pulse and then (e.g. immediately or shortly as possible thereafter) assigned a second bank top provide a second sub-pulse. A single long pulse is thus split into two sub-pulses.

[0023] This is shown in figure 1, where the banks are controlled by an ECU, and operate the injectors for three cylinders:, Cyl 1, Cyl 2, Cyl 3.

[0024] Appropriate control software (e.g. in the ECU) assures that the injection pulses are placed in the correct bank according to injection (crankshaft) angle and that they do not span the window separation used to switch banks. (The term "separation window" will be explained further hereinafter). There may be a small switching delay and consequentially the usable range is reduced by a few degrees and thus the windows are not strictly speaking contiguous. In refined examples, this is preferably taken into account by the software controlling the injection. In any case it has very little effect in practice.

[0025] Aspects of the invention are thus also applicable to where there may be two injections (pulses) in a combustion phase; the very long injection pulses are sometimes split into two separate pulses for cold starts at low fuel pressure.

[0026] Figure 2 shows a more detailed figure of the circuitry that can be used in an example of the invention in the case of a 3-cylinder engine. It shows the high side 21, comprising two high-side banks 24a and 24b, and low side, comprising low side banks 25. The banks the high-side and low-side are connected via, and supply current to, coils 23 which are used to actuate fuel injectors with respect to 3 cylinders. The high side banks comprise two FETs. Switching means comprising two switches 26a and 26b is also provided, and allows current to be provided to the centre coil from either the first or second high side banks 24a or 24b. The banks and/or the switching means may be controlled by a vehicle ECU. Although on the low-side, there is usually one bank (comprising a FET) per cylinder, an additional bank (FET) may be provided so that the arrangement can be used in 4-cylinder applications.

[0027] Figures 3a to 2e, shows a chart showing a single timeline to illustrate an embodiment of the invention; it is separated into 5 sections which should be regarded as joining on from each other. It illustrates how two banks A and B can be used with respect to injection in a three cylinder 4 stroke engine. The chart shows the timeline with respect to the three cylinders (Cyl 1, Cyl 2 and Cyl 3) in respect to crankshaft angle along the x-axis. The top three rows show the cycles (intake, compression, power and exhaust) for each cylinder. The lower three rows illustrates the assignment/availability of the two banks to the fuel injectors of the 3 cylinders along the same timeline. The lightning symbol in the first three rows represents the ignition, i.e. sparking to ignite the fuel/air mixture in the cylinder. Generally speaking the injection event for that cylinder occurs in a window (time frame) around this point.

[0028] In the example, cylinder 1 uses (is assigned) only bank A, cylinder 2 only bank B, and cylinder 3 uses both banks A and B.

[0029] If we look at figure 2a, from the point of 150° crankshaft angle, the first sparking event is in respect of cylinder 2. For this, bank B is assigned to cylinder 2 for a period 1, ranging from 150 to 390). The period 1 thus shows the total period available/assigned to bank B for cylinder 2, thus this can be considered as a "bank B available window". Within this is a further shorter period 2 during which fuel may be injected into the cylinder period and can be considered as a required or desired period for bank B for cylinder 2. It is to be noted that during this time there may be more than one injection event. During period 1, bank A is assigned to cylinder 3 and cylinder 1 does not have an assigned bank.

[0030] Looking at figure 2b, the next sparking event is at 480° which occurs in cylinder 3, and injection take places over a time period 4. During the period 3 (from 390° to 630°), bank B is assigned to (the injector for) cylinder 3; thus period 4 shows the total period bank B is available/assigned to cylinder 3. During this period 4, bank A which was previously assigned to cylinder 3 is switched such that it is made available/assigned to cylinder 1 in preparation for the next phase. During this period cylinder 2 does not have any banks assigned to it. Within period 4 there is a further shorter period 3 during which fuel may be injected into the cylinder (and can be considered as a required or desired period for bank B for cylinder 3).

[0031] Referring to figure 2c, in the next phase, the next sparking event occurs in cylinder 1. Bank A has already been switched in preparation to be assigned to cylinder 1. Bank A is used to provide fuel injection in cylinder 1 over the time period 6, which lies within time period 5, spanning from crankshaft angle 630° to 150°. During period 5 bank A is assigned to cylinder 1 and bank B to cylinder 2. Cylinder 3 does not have any bank to be assigned to it during this period.

[0032] Referring to figure 2d, the next sparking/injection event occurs in cylinder 2. Bank B is assigned to cylinder 2 over period 7 which ranges from crankshaft angles 150° to 390°, and bank A is assigned to cylinder 3 during this period, cylinder 1 does not have any bank assigned to it in this period. Injection of fuel occurs over time period/window 8 which lies within period 7. Period 7 can thus be considered an available window for bank B to be used by cylinder 2.

[0033] Referring to figures 2d and 2e, the next sparking event occurs in cylinder 3. Bank B is assigned for fuel injection with respect to this cylinder over the whole of time period 9, thus providing a possible window for bank B to be used by cylinder 3. During the same time period bank A is assigned to cylinder 1. Injection occurs in time window 10.

[0034] If we now look at the figure, it is to be noted that the (maximum) window where there are no banks assigned to a particular cylinder in all cases is 240°, and therefore there will always be at least 480° available window. In some cases a cylinder is assigned the two different banks over two time contiguous periods spanning 480°. For example, in time periods 2 and 4 which span 150° to 630°, cylinder 3 is assigned bank A and then bank B.

[0035] In summary therefore, there will always be a 480° period in which either bank A or bank B will be available to the (fuel injector) of each the cylinder. According to aspects of the invention, this is made use of when for example controlling arranging a fuel injection over a long period, e.g. which spans more than 240° in order to deliver either a large quantity of fuel. In examples of the invention, fuel injection in a particular cylinder is consequential to the injector receiving two pulses, each from a different but available bank, rather than one long one from a single bank. In other words, a long pulse which would otherwise be used to if there was a 360° window available (i.e. provided) by a single bank, is split into two smaller (sub) pulses; the sub-pulses being provided by different banks..

[0036] In a basic example to illustrate this, at the bottom of figures 3d and 3e, is shown how a required long injection pulse 31, has been divided into two smaller pulses 32 and 33. (Sub) pulse 32 is provided by bank A and (sub) pulse 33 provided by bank A. Of course the provision of the two pulses has to be controlled such that they do not span the boundary 34. The 240° windows can be shifted in the crank angle domain the limitation being that a pulse may not cross the (e.g. 240°) boundary.

[0037] There may be a minimum delay of about 100µs between the switching the bank on cylinder 3. The advantage is that that if the pulses are split to avoid boundary crossing a window.

[0038] The term "injection phase" (for a particular cylinder) with respect to the claims should be interpreted as a phase which occurs once in a cylinder cycle, e.g. one in 720° crankshaft angle rotation in a 4-stroke engine, and this is the phase where fuel is injected into the cylinder prior/during a combustion phase. Actual injection may occur 2 or more times in such an injection phase.

[0039] Figures 4a to 4c show a single chart showing a timeline over crankshaft angle for three scenarios illustrating how an example of the invention can be applied. The figure is separated into sections (a,b,c) which should be regarded as joining-on from each other.

[0040] The first scenario, at the top of the figure, illustrates normal operation of an engine and the timeline for invents with respect to a cylinder, showing exhaust, intake, compression and power phases. During the intake phase there is shown a small window (pulse) during which fuel is injected. The crankshaft angle between the start of this and the TDC is in the order of 220-320°. An available window of 240° provided by one of the banks is sufficient for this.

[0041] The second scenario illustrates a stratified start. This may comprise of an optional injection pulse during the intake stroke followed by a further injection pulse in the compression stroke. The required injection timespan/window can be provided by a first window from one bank, and a second window from another bank.

[0042] In the third scenario the scenario is a "catalyst light-off" mode with at least 2 spaced injections. There is a first injection (pulse) which takes place during the intake, a possible second injection which takes place over a period which spans the intake and compression phases. There is also a further injection which takes place in a short pulse (duration 5) after sparking.

[0043] The first two injections can be provided by a first available window form a first bank and the small post-injection pulse can be provided by a second bank. The banks in the last two scenarios provide the requisite functionality (e.g. provide pulses) for fuel injection for the same fuel injector/cylinder during an injection phase. Thus the two banks in successive, adjacent or contiguous periods in terms of time/crankshaft angles, act together in sequence to provide the requisite pulses for an injection phase for the same fuel injector. Terms and phraseology in the description and claims such as referring to "assigning of each of said banks to a particular cylinder" should be interpreted generally, and include the banks providing requisite functionality in terms of providing the requisite fuel injection (pulses) to injector(s) for the individual ones of cylinders. The assigning may manifest itself in the control of pulses/signals from (e.g. the ECU) to the banks, and or the banks providing fuel injectors with required voltages, currents, pulses, etc. For example, assigning two banks (in sequential/contiguous/adjacent order) to fuel injectors in the same cylinder during an injection phase can be construed to include provision in a first period of a pulse to injectors(s) of a particular cylinder by a first bank and the provision in a second (e.g. adjacent) period of a further pulse to the injector(s) of the same cylinder.

[0044] The invention thus reduces the number and therefore cost of components in 3 cylinder engines. Furthermore, the same ECU hardware can be utilised for both 3 and 4 cylinder applications (engines) with little extra hardware or cost.

[0045] A further advantage of the arrangement and method is that if one high-side driver/banks fails, two cylinders will be able to run on the remaining bank assuring a usable, "limp-home" mode.

[0046] It is to be noted that the invention is applicable to engines where they may be more than one injector per cylinder. The implementation of such examples would be clear to the skilled person.

[0047] The above description is considered that of the preferred embodiments only. Modifications of the invention will occur to those skilled in the art and to those who make or use the invention. Therefore, it is understood that the embodiments shown in the drawings and described above are merely for illustrative purposes and not intended to limit the scope of the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the doctrine of equivalents.

Claims

1. A method of operating or controlling fuel injectors in an engine, wherein power to fuel injectors for the cylinders are provided by a plurality of banks, and with respect to an injection phase for a fuel injector of particular cylinder, power therefor is provided by at least two banks.

2. A method as claimed in claim 1 wherein said engine comprises n cylinders, said fuel injectors are operated by a plurality of banks, m, and where the number of banks, m, is less than the number of fuel injectors, n, comprising, assigning of each of said banks to a particular cylinder, and assigning at least two banks to the remaining (n-m) cylinders.

3. A method as claimed in claim 2 wherein n is an odd number.

4. A method as claimed in claims 1 to 3 wherein said engine comprises 3 cylinders, and using a first and a second bank, the first bank being assigned to the first cylinder, the second bank being assigned to the second cylinder, and both of said banks being assigned to the third cylinder.

5. A method as claimed in claims 1 to 4 where said assignment is controlled/effected by an Engine Management Unit.

6. A method as claimed in claim 1 to 5 wherein a first bank is assigned to a cylinder over a first period and a second bank is assigned to said same cylinder over second period.

7. A method as claimed in claim 6 said periods being substantially contiguous, adjacent and/or sequential in terms of time and/or engine crankshaft angle.

8. A method as claimed in claim 6 or 7 wherein, said engine is a 3-cylinder engine and said first and/or second periods are in the order of 480° crankshaft angle.

9. A method as claimed in claim 1 to 8 wherein, with respect to successive injection phases in all cylinders, said banks are assigned alternately.

10. A method as claimed in any preceding claim comprising providing or applying a first injection pulse from a first bank to one or more fuel injectors of said cylinder during said first period and providing or applying at least a second injection pulse in said second period to the one or more fuel injectors of said same cylinder.

11. A method as claimed in claim 10 wherein said pulses are provided by splitting a predetermined pulse.

12. A system of operating or controlling fuel injectors in an engine, having means to provide power to fuel injectors of the cylinders by a plurality of banks, and with respect to an injection phase for a particular cylinder, means to provide said power therefor by at least two banks.

13. A system as claimed in claim 12 where the engine comprises n cylinders, where said fuel injectors are operated by a plurality of banks, m, and where the number of banks, m, is less than the number of fuel injectors, n, comprising means to assign of each of said banks to a particular cylinder, and means to assign at least two banks to the remaining (n-m) cylinders.

14. A system as claimed in claim 12 wherein n is an odd number.

15. A system as claimed in claims 12 or 13 wherein said engine comprises 3 cylinders, and using a first and a second bank, the first bank being assigned to the first cylinder, the second bank being assigned to the second cylinder, and both of said banks being assigned to the third cylinder.

16. A system as claimed in claims 12 to 15 comprising an Engine Management Unit

17. A system as claimed in claim 12 to 16 having means to assign a first bank to a cylinder over a first period and means to assign a second bank to said same cylinder over a second period.

18. A system as claimed in claim 17 wherein said time periods being a substantially contiguous, sequential or adjacent in terms of time and/or engine crankshaft angle.

19. A system as claimed in claims 12 to 18, said engine is a 3-cylinder engine and said first and/or second periods are in the order of 480° crankshaft angle.

20. A system as claimed in claim 12 to 19 wherein, with respect to successive injection phases in all cylinders, means to assign said banks are alternately.

21. A system as claimed in claim 12 to 20 comprising mean to provide or apply a first injection pulse from a first bank to one or more fuel injectors of said cylinder during said first time period and means to provide or apply at least a second injection pulse in said second period to the one or more fuel injectors of said same cylinder.

22. A system as claimed in claim 21 having means to provide said pulses by mean to split a predetermined pulse.

Drawing