|Title of Invention||
A MEHTOD FOR CONTROLLING FUEL TO A COMBUSTIONS CHAMER OF AN INTERNAL COMBUSTION ENGINE"
|Abstract||Disclosed is a method of controlling the introduction of a fuel/gas mixture to a combustion chamber (27) of an Internal combustion -engina (9) by an injection means (29) comprising a fuel metering means (30) and a delivery injector (31) wherein, under certain engine operating conditicns the end of the duration of opening of the delivery injector (31) is established by an engine control means to be at a particular crank angle.|
|Full Text||The present invention relates to an engine control strategy and, in particular, to a method for controlling the occurrence of cerain events in the operation of an engine.
The applicant's US Patent No. 4693224 discloses a method of dual fluid direct injection Into the combustion chamber of an internal combustion engine. The method typically involves delivery of a metered quantity of fuel to each combustion chamber of an engine by way of a compressed gas, generally air, which entrains the fuel and delivers it from a delivery injector nozzle.
Typically, a separate fuel metering injector, as shown for example in the applicant's US Patent No. 4934329, delivers, or begins to deliver, a metered quantity of fuel into a holding chamber within, or associated with, the delivery injector prior to the opening of the delivery injector to enable direct communication with a combustion chamber. When the delivery injector opens, the pressurised gas, or in a typical embodiment, air, flows through the holding chamber to deliver the fuel previously metered thereinto to the engine combustion chamber. The utilisation of a holding chamber enables the metering of fuel -for delivery and the actual delivery thereof to the combustion chamber to be separated Jnto two distinct events. •
In an engine operated in accordance with such a direct fuel injection strategy; a" number of controlled events occur including start of fuel (SOF), end of fuel (EOF), start of air (SOA), end of air (EOA) and ignition.
Start of fuel (SOF) is the time at which the fuel injector or a fuel metering means begins metering fuel into the holding chamber and generally relates to the opening time of the fuel metering means or fuel injector.
End of fuel (EOF) Is the time at which the fuel injector or a fuel metering means ceases metering fuel into the holding chamber and jjenerally relates to the closing time of the fuel metering means or fuel injector.
Start of air (SOA) is the time at which the delivery means or injector, referred to above, begins delivery of the fuel entrained in the gas into the combustion chamber of the engine and generally relates to the opening time of the delivery means or injector.
End of air (EOA) is the time at which the delivery neans or injector ceases delivery ot the fuel entrained in ihe gas into the combustion chamhpr of the engine and generally relates to the closing time of the delive'y means or injector.
Together, SOF and EOF define the duration for which the fuel metering injector is opened, SOA and EOA define the duration for which the delivery injector is opened and EOF and SOA define a fuel air delay (FAD) period, this being the period between the end of the fuel metering event and the commencement of the delivery of the fuel entrained in the gas
These events may occur in this sequence, although ignition may occur just prior to EOA. Other variations in the order of these events are possible depending upon certain engine operating requirements or strategies. For example, SOA may occur at various times prior to EOF in order to provide certain desired fuel fluxing conditions. An example of this is shown in the applicant's US Patent No. 4800862, the contents of which are hereby incorporated by reference.
The relationship between ignition and EOA is" typically of significant importance to. the operation of the engine and generally ignition occurs in close time proximity to EOA, especially under idle conditions. Due to the fact that, to obtain combustion within the engine combustion chambers, an ignitable fuel-air
mixture is required at or around the spark plug, a disruption to the desired relationship between the occurrence of EOA and ignition for a particular engine may result in combustion instability or stalling, especially under low or idle speed conditions. This is also true for certain single fluid injection systems wherein a desired 'relationship exists between the occurrence of the end of fuel injection and the timing of ignition.
Similar comments apply to other dual fluid injection systems which do not necessarily have a separate fuel metering injector and hence a SOF and EOF event. In particular, the applicant has developed and applied for patents for certain simplified fuel injection systems wherein a positive displacement fuel metering pump is used to meter discrete quantities of fuel for subsequent delivery directly into a combustion chamber of an engine by an air or delivery
injector in a similar manner to that described hereinbefore, ouch an injection system is disclosed in the applicant's Australian Patent Application No. 65608/94, the contents of which are hereby incorporated by reference. The relationship between the occurrence of the EOA and Igniilon is; equally of significant importance in such systems.
In previous practice, the SOA position has typically boen identified with
reference to a particular angle of rotation of the crankshaft whilst tie EOA has been calculated therefrom upon consideration of a desired duration for the delivery event. That is, SOA has typically been calculated or set in the crank domain whilst EOA has been calculated or set in the time domain. Typically, EOA is determined to occur at a particular time after SOA, as established in the crank domain, by adding time increments corresponding to the known required time delay for which the air or delivery injector is to be held cpen and the pulse width of a fuel/air delivery event. The pulse width is typically a function of engine operating conditions, notably including engine speed, and is set by an engine management system.
Thus, the above sequence of events is calculated from ono point (SOA) and assumes an average engine speed notwithstanding that engine operating conditions may, and often do, vary subsequent to a given point.
As an example, SOA may occur at a crank angle of 40° BTDC. The calculated time increment for the air or delivery injector opening time as determined by an ECU of an" engine management system of the engine may amount to say 3.32 m.s and this, time increment., is established at an engine speed of 600 rpm which is assumed to remain constant when scheduling the! EOA and ignition events. The ignition timing is established in the crank domain.
However, the engine speed may change, for example falling from say 600 rpm to 500 rpm due to, for example, the application of a load to the engine such as from a gear change occurring from idle following scheduling of the events for the next combustion event. In particular regard to this example, on engaging gear, the engine speed may drop as much as 100 rpm within 1-2 firing events. This is particularly so in marine engines which typically have a low rotational inertia and can drop around 100-200 rpm when put into gear from
idle. The inertia of such engines is generally small compared to a vehicle engine, however the instantaneous load which is applied to the engine by going into gear is relatively large. This will typically cause an error in the occurrence of the EOA in the sequence of events. For example, at 600 rpn, EOA during idle operation should occur at around 28° BTDC. A 100 rpm drop in engine speed post-scheduling may result in EOA being positioned at around 30° BTDC (a 2° advance in the timing) due to the fixed delivery duration. This error, bearing in mind that the relationship between EOA and ignition is typically most important to provide satisfactory combustion stability at idle and low load, may cause less efficient operation of the engine.
The impact of a fall in engine speed on the calculated fuel/air delay (FAD) may also be detrimental to engine operation. As SOF, in the case where the system includes a fuel metering injector, is calculated from the average engine speed and this speed may drop, the FAD becomes variable. This is likely to affect the fuel fluxing, as measured by the air/fuel ratio profile during the air/fuel delivery event. For example, it may be desired to introduce a majority of the fuel to the combustion chamber early in the delivery event and an error in the FAD may alter this. In particular, it is likely at idle that a reduced -AD will contribute to the existence of s rich mixture at EOA and the opposite for an increased FAD.
Accordingly, it is the object of the present invention to provide, fora fuel injection system, a method of controlling an engine in which-scheduling of events for an engine operating cycle maintains a desired relationship between the end of the fuel delivery event or, in the case of a dual fluid injection system, EOA, and ignition that is conducive to efficient operation of tho engine.r
With this object in view, the present invention provides a methdcTbf controlling the introduction of fuel to a combustion chamber of an internal combustion engine by an injection system comprising a delivery means wherein, at least under certain engine operating conditions, the end of the duration of opening of the delivery means and the timhg of ignition are established by an engine control means to be at a respective crank angle.
Preferably, the delivery means is a direct injection delivery injector.
• According to a different embodiment, the present invention provides a method of controlling the introduction of a fuel/gas mixture to a combustion chamber of an internal combustion engine by an injection means comprising a delivery injector wherein, under certain engine operating conditions, the end of the duration of opening of the delivery Injector is established by an engine control means to be at a particular crank angle.
Preferably, fuel is metered to said delivery injector by a fuel metering means which may take the form of a fuel metering injector. However, other fuel metering devices such as pumps, especially positive displacement pumps, may be employed instead.
Conveniently, the delivery injector may take the form of a gas injector, for example, an air injector communicating with a combustion chamber of the engine. However, air may be delivered in admixture with other gases which may enhance or promote combustion, for example hydrogen.
Preferably, the commencement of opening of the air injector, or SOA, is also to be established in terms of a particular crank angle, In this manner, any error Implicit In calculating SOA in the time domain may' be reduced or eliminated. However, SOA may, if desired, be calculated in the time domain.
In this latter regard, conveniently SOA may be established by subtraction of a required duration of opening of the air injector from EOA. That is, once EOA has been scheduled in the crank domain, time increments ccfresponding to the known required time delay for which the air injector is to be held open may be subtracted from this EOA setting hence providing a SOA setting in the time domain. Alternatively, SpAm^a^be provided by look-up maps programmed with appropriateSOA'setting's for specifrc engine operating conditions as defined, for example, by different engine speed and/or load conditions.
Conveniently, Ignition is conveniently scheduled in the crank angle domain where EOA is scheduled in that domain.
Conveniently, the commencement of opening of the delivery injector (SOA) is scheduled subsequent to or simultaneously with the scheduling of the end of the duration of opening of the delivery injector (EOA).
The EOA and ignition time settings may be changed, lor example, midway through an injection event. For example, if the detected «nglne speed has dropped, look-up map values may indicate a more appropriates set of timings or settings. Due primarily to a level of fuel hang-up in the fuel system, an increase Or a decrease in Ihe duialiun of the delivery or injection ovsnt will typically result
in a corresponding increase or decrease in the quantity of fuel delivered.
The establishment of the end of the duration of opening of the air injector, or EOA, In the crank angle domain may occur under bo-:h idle or off-idle operating conditions. However, if desired, this method of establishing the EOA may be utilised under one such set of operating conditions whilst a different method for establishing the EOA may be utilised for the othor set of operating conditions. In this regard, the relationship between EOA and ignition is of special importance under idle operating conditions where ignition is required to be closely related to EOA.
Hence, in one embodiment of the method of the invention, EOA may particularly be established in the crank angle domain undar idle conditions. Under off-idle conditions where the relationship between EOA and ignition may be less critical, the engine control means, which may be in the form of an electronic control unit (ECU), may revert to establishment of EOA in the time domain following establishment of SOA in the crank ancjle domain in the manner previously described. For example, at high engine speeds it may be preferred to schedule EOA and ignition in the time domain because crank domain scheduling may pose difficulties under such circumstances. Such difficulties may arise due to a fall in accuracy or other encoder processing limitations.
Preferably, at idle and low engine speeds, EOA, and advantageously ignition, is scheduled in the crank domain whilst at high engine speeds, EOA is scheduled in the time domain.
Preferably, at idle and low engine loads, EOA, and advantageously ignition, is scheduled in the crank domain whilst at high engine loads, EOA is scheduled in the time domain.
Equally, all or some of the remaining events SOF, EOF, SOA and ignition may occur in the crank domain at low or idle speeds while seme or all may be scheduled in the time domain at higher engine speeds.
Conveniently, SOA for just off-idle conditions is matched with SOA calculated at idle as any discontinuity between Idle and just off-idle conditions may cause engine instability and possible stalling. Accordingly, look-up maps
may be provided which smooth the transition between SOA at idle and SOA under off-idle conditions through use ot a transition loutirus advantagooucly programmed in the engine control means.
Establishment of appropriate crank angles or timings, whether for SOA, EOA, both, or ignition, may suitably be achieved by utilisation of an encoder, the use of which is well established in the art of control of engines, A multi-tooth encoder enables sampling of engine position and/or speed a! owing for average speed data to be employed as a basis for SOA/EOA calculation rather than raw speed measured, say at Intervals of 60° of crank rotation. However, either average or raw speed data may be utilised for the SOA/EOA calculation. Preferably, raw speed data is used at idle whilst average speed data is used off-idle.
In a further aspect, the invention provides an engine control system for controlling the introduction of a fuel/gas mixture to a combuslion chamber of an internal combustion engine by an injection means including a delivery injector comprising an engine control means programmed to establish, under certain engine operating conditions, the end of the duration of opening (EOA) of a delivery or air injector as a crank angle.
The engine control means may be programmed to also establish the commencement of opening of the delivery or air Injector, o: SOA, as a crank angle.
Conveniently, the commencement of opening of the air injector (SOA) is established subsequent to or simultaneously with the establishment of the end of the duration of opening of the air injector (EOA),
The establishment of EOA in the crank angle domain may occur under both idle or off-idle operating conditions and the engine control means, which
may be an electronic control unit (ECU) may be established accordingly. However, if desired, this method for establishing EOA in the crank angle domain may be utilised under one set of engine operating conditions whilst a different method for establishing EOA may be utilised for another set oi engine operating conditions as discussed above. For example, the electronic control unit may be programmed such that EOA is established in the crank angle doma'n under idle conditions and as a time related setting under off-idle conditions.
The engine control system may employ an encoder to provide speed and jjuaiiic/n data on tho bade of which pnA may hft fistablished as a crank angle or time related setting, whichever is dgsired.
Application of the method and system of the invention can help maintain stability of engine operation at low speed even under no load idle conditions. This is particularly so in regard to low inertia engines wherein the speed changes between firing events are typically more pronounced at idle. Further, whilst this speed discrepancy may not be that great between firing events on a higher inertia engine, similar advantages may be evident during driver demanded speed changes (i.e acceleration and deceleration].
It has besn found that in certain engines, use of the method and system of the invention wherein both EOA and ignition are set in the crank domain has enabled relatively low idle speeds which previously could rot be achieved to
become possible. For example, it has been found that an engine which previously had a minimum stable idle at around 600 rpm is now able to hold a stable idle at around 300 - 350 rpm. It is evident, that flow-on benefits of such low idle' speeds can ensue and would include better fuel consumption and better NVH characteristics.
The present invention may be more clearly understood from the following description of a preferred embodiment thereof made with reference to the accompanying drawings in which:
Figure 1 is a sectional view of one cylinder of a two stroke cycle engine in which the control method of the invention is applicable;
Figure 2 is an elevational view partly in section of a fuel injection system for use in the delivery of fuel to the engine shown in Figure 1; and
Figure 3 is a graph of the various events occurring in a typical engine operating cycle.
Referring now to Figure 1, the engine 9 is a two stroko cycle engine, of generally conventional construction, having a cylinder 10, cranKcase 11 and piston 12 that reciprocates in the cylinder 10. The piston 1!2 is coupled by a connecting rod 13 to the crankshaft 14. The crankcase 11 is provided with air induction ports 15, incorporating conventional reed valves 19, and transfer passages 16 (only one shown) communicate the crankcase 11 with respective transfer ports, two of which are shown at 17 and 18.
The transfer ports 17 and 18 are each formed in the v/all of the cylinder 10 with their respective upper edge located in the same diametral plane of the cylinder 10. An exhaust port 20 is formed in the wail of the cylinder 10 generally opposite the transfer port 18. The upper edge of the exhaus: port 20 is slightly above the diametral plane of the transfer port's 17, 18 uppsr edges, and will accordingly close later in the respective cylinder combustion cycle.
The detachable cylinder head 21 has a combustion cavity 22 into which a spark plug 23 and delivery Injector nozzle 24 project. The cavity 22 is such as to promote stratification as disclosed in the applicant's US Patent No. 4719880, the contents of which are hereby incorporated by reference, and details of its construction may be obtained therefrom. However, a cavity of this type is not essential and other configurations of the cylinder head 21 are comprehended by the present disclosure.
The injector nozzle 24 is an integral part of a fuel injection system 29 whereby fuel entrained in air is delivered to the combustion chamber 27 of the engine 9 by the pressure of the air supply. One embodirrient of such a fuel injection system 29 is illustrated in Figure 2 of the drawings,
The fuel injection system 29 incorporates a suitable commercially available fuel metering device 30 which may be a fuel metering injector, such as an automotive type throttle body injector coupled to a delivery or air injector 31 having a holding chamber 32 therein. Fuel is" typically drawn from a fuel reservoir by a fuel pump via a pressure regulator and del'vered through -fuel inlet port 33 to the fuel metering device 30. The metering device 30, operating
in known manner, meters an amount of fuel into the holding chamber 32 via a hollow valve stem 35 of the injector 31 in accordance witr the engine fuel demand. Excess fuel supplied to the fuel metering device 30 is returned to the fuel reservoir. It is to be noted that the particular construction of the fuel metering device 30 is not critical to the present Invention and any suitable device may be used Including positive displacement metaring devices as
In operation, the holding chamber 32 is pressurised by air supplied from an air source such as a compressor, via a pressure regulator and through an air conduit 37. Delivery valve 43 is actuated to permit the pressurised air to discharge the metered amount of fuel through injector nozzle 24 into the combustion chamber 27 of the engine 9. Delivery valve 451 is of the poppet valve construction opening inwardly to the combustion chamber 27, that is, outwardly from the holding chamber 32.
The delivery valve 43 is coupled, via the hollow valve stem 35 which passes through the holding chamber 32, to an armature 41 of a solenoid assembly 47 located within a housing 48 of the air injector 31. The valve 43 is biased to the closed position by the spring 40 and is opened by energising the solenoid assembly 47. Further details of the injection system 29 may be obtained by way of reference to the applicant's US Patent No. 4934329, the contents of which are incorporated herein by reference,
It will be recalled that the valve 43 is the delivery valve, and hence, its opening time accords with SOA and its closing time accords with EOA. Similarly, the fuel metering device 30 has an opening time which accords with SOF and a closing time which accords with EOF.
Both opening and closing of the fuel and delivery injectors 30 and 31 is dictated by the energisation of solenoids in relation to the engine cycle by a suitable electronic control means or processor. The processcr receives an input signal from a speed sensor which may take the form of an encoder. Suitable encoders are well known in the art and an example is disclosed in US Patent No. 4941445 assigned to Motorola Inc.
The encoder provides engine speed data and, through appropriate signal processing, data about the angular position of the crankshaft 14 and hence components of the engine 9. Average or raw speed data nrmy be used by the electronic processor but better performance may be gained through use of data averaged over a short period of time. In this regard, it may be preferred to employ raw speed data at Idle and average speed data off-idlo.
Determination of the average or raw speed is utilised to determine an appropriate crank angle for the closing of the delivery injector 31 (EOA). EOA is typically established by reference to a look-up map provided with various values of EOA in relation to engine speed. If desired, the look-up map may be subject to other engine operating conditions, such as engine load.
If desired, the opening time of the delivery injector 31 (SOA) and opening and closing timAs of the fuel meteringInjector 30 may be provided by the same look-up map and the value may be in terms of crank angle or time. However, the SOA value or SOF and EOF values for a particular engine operating condition or set of engine operating conditions could be provided by a different look-up map If desired. Ignition time may equally be set by the electronic processor. A diagram showing the typical operating sequence of these events in one embodiment is shown in Figure 3.
The processor provides appropriate signals to the delivery injector 31, solenoid actuator 47, fuel metering device 30 and spark plug 23 in accordance with the determinations, whether in the crank angle or tine domain, of the opening and closing times of the various injectors 30, 31 and activation time of the spark plug 23jatjhe required time for ignition. The general construction of suitable speed sensors discussed above and load or demand indicators are well known in the industry, as are processors for performing the engine control functions.
Without wishing to be bound by any particular methodology, SOA, SOF, EOA and EOF events may be readily determined either in the crank angle or time domain. For example, once EOA is established, in the crank angle domain, SOA may be set in the time domain by the processor at a tima prior to EOA by a duration equal to the time the delivery injector 31 is required to remain open.12
The required pulse width for the fyel metering injector 30 and the desired fuel-lir delay (FAD) time may then be subtracted from SOA to obtain SOF and EOF /alues in the time domain. Such subtraction is not required to be performed in real time, indeed it may be desired to avoid this to reduce piocesslng delays. The look-up maps may therefore be preset for this purpose or adaptive in accordance with sensed engine speed and/or load.
It is not intended that time or crank angle domain valuos be assigned to all of the events in the engine operating cycle. Equally, whethsr a time or crank angle domain value is assigned to the events may itself depend upon engine operating conditions.
Generally, it may be desirable to set all values in the crank angle domain when the engine 9 is operating at low or idle speed. It is in this speed regime that the relationship between EGA and ignition is most critical and EOA and ignition, at least, may desirably be set in the crank angle domain in accordance with the present invention. The other events may have values set In either the time or crank angle domain though the latter may be preferred for reasons of accuracy. In these cases, engine stability may be maintained even at low speed.
^engine speed increases, SOA typically occurs progressively earlier in the cylinder combustion cycle and the relationship between EOA and ignition to which reference has previously been made may become of esser importance. Here, the electronic processor may revert to setting SOA in the crank angle domain and EOA may be set as a time interval therefrom in the time domain. Ignition may likewise be set in the time domain.
It is desirable to avoid instability on transition between idle and just off-idle conditions. Thus, a transition routine may be operated to smooth transition between SOA at idle and SOA under off-idle conditions. Appropriate look-up maps may be provided.
It is not intended that the invention be limited in its application to the engine configuration described above where a fuel metering injector 30 is employed. The accurate setting of EOA is equally important in other types of engine, as described for example in the applicant's co-pending Australian
Patent Application No. 65608/94. In that application, a positive displacement fuel metering pump is utilised rather than a solenoid ectuatad injector. However, operation of the pump is still required to be controlled to achieve delivery of a required metered quantity of fuel to a delivery injector.
The invention is also not limited in its scope to two stroke cycle engines and may be applied to tour stroke cycle engines. In either event, the engine
may be of single or multi-cylinder type. The invention is equally applicable to certain engines having single fluid injection systems and those engines which are spark ignited,
1. A method for controlling the fuel to a combustion chamber of an internal combustion engine (9) having a direct injection system (29) with at least one fuel delivery injector (24), a spark plug (23) which produces an ignition spark at a first engine crank-angle, and an electronic control unit which controls the closing of the fuel delivery injector characterized in that the said engine includes a closing means for the fuel delivery injector, the closing means being controlled with reference to a second engine crank-angle such that the difference in crank-angle between the first and second crank-angles is independent of sudden changes in engine speed.
2. The method as claimed in claim 1, wherein the said delivery injector is a gas injector (31) and fuel metered to the said gas injector (31) is by a fuel metering means (30), said fuel entrained in a gas is delivered by said delivery injector to a combustion chamber (27), and a variable associated with the end of the opening duration of the gas injector (EOA) is scheduled at a particular crank angle.
3. The method as claimed in claim 1, wherein the fuel metering means (30) is a fuel metering injector, the closing of which is set in the crank domain and the opening of which is set in the time domain.
4. The method as claimed in any of the preceding claims, wherein the said direct injection system is a dual fluid fuel injection system (29).
5. An internal combustion engine for carrying out the method as claimed in any of the preceding claims.
6. The method for controlling the fuel to a combustion chamber of an internal combustion engine substantially as herein described with reference to the accompanying drawings.
|Indian Patent Application Number||2109/DEL/1996|
|PG Journal Number||09/2008|
|Date of Filing||25-Sep-1996|
|Name of Patentee||ORBITAL ENGINE COMPANY(AUSTRALIA) PTY.LTD|
|Applicant Address||1 WHIPPLE STREET, BALCATTA, WESTERN AUSTRALIA 6021, AUSTRALIA.|
|PCT International Classification Number||F02D 19/00|
|PCT International Application Number||N/A|
|PCT International Filing date|