Engine control strategy

Details Engine control strategy Engine control strategy

1998-01-09

2001-07-10

Argenbright, Tony M. (Department: 3747)

Internal-combustion engines

Combustion chamber means having fuel injection only

Having a particular relationship between injection and...

C123S0730CA, C123S295000, C123S305000, C123S478000, C123S486000, C123S531000, C123S533000

Reexamination Certificate

active

06257200

ABSTRACT:

The present invention relates to an engine control strategy and, in particular, to a method for controlling the occurrence of certain events in the operation of an engine.
The applicant's U.S. Pat. No. 4,693,224 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 U.S. Pat. No. 4,934,329, 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 into 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 generally 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 means or injector ceases delivery of the fuel entrained in the gas into the combustion chamber of the engine and generally relates to the closing time of the delivery 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 U.S. Pat. No. 4,800,862, 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. Such an injection system is disclosed in published 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 ignition is equally of significant importance in such systems.
In previous practice, the SOA position has typically been identified with reference to a particular angle of rotation of the crankshaft whilst the 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 open 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 one 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 ms 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 rpm, 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

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