Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2000-11-01
2003-03-18
Mancene, Gene (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C361S154000
Reexamination Certificate
active
06532940
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a fuel injection control system for a cylinder injection type internal combustion engine. More particularly, the present invention is concerned with a control scheme for preventing or suppressing degradation in accuracy of valve opening operation as well as fuel injection, which degradation may be brought about by external disturbances which will take place particularly when the fuel injection valve is driven with an overexcitation current at a battery voltage.
2. Description of Related Art
In recent years, the so-called cylinder injection type (or direct fuel injection type) internal combustion engine which is equipped with a fuel injection valve for injecting the fuel directly into the engine cylinder has been developed and employed increasingly in practical applications. In such cylinder injection type internal combustion engine, since the fuel is directly injected into the engine cylinder, the period during which the fuel can be injected into the cylinder is ordinarily limited at least to within a time period which extends from a suction stroke to a compression stroke of the engine. For this reason, the flow rate gain of the fuel injection valve (i.e., flow rate of the injected fuel relative to the width or duration of a driving pulse for driving the fuel injection valve) has to be increased when compared with the multi-point injection (MPI) type engine equipped with the fuel injection valves mounted in an intake pipe. In this conjunction, it is however noted that an attempt simply for increasing the flow rate gain of the fuel injection valve will incur increasing of the minimum fuel injection quantity, giving rise to a problem.
In this conjunction, it is known as an approach for improving the fuel cost performance of the engine to reduce the pumping loss of the internal combustion engine by realizing a lean stratified combustion (i.e., combustion of a lean fuel mixture in stratified state) by increasing the mass mixture ratio of the air to the fuel (i.e., air-fuel ratio) within the engine cylinder. In that case, it is necessary to decease the minimum fuel injection quantity when compared with the MPI-type internal combustion engine.
Under the circumstances, a driving system for the fuel injection valve has been proposed, as disclosed, for example, in Japanese Patent Publication No. 23100/1992. For having better understanding of the teachings of the present invention, description will first be made in some detail of the conventional fuel injection valve driving system known heretofore by reference to the drawings.
FIG. 15
is a block diagram showing only schematically a configuration of a conventional fuel injection valve driving system for a cylinder injection type internal combustion engine. Referring to the figure, a fuel injection valve control means
4
is so designed as to actuate an overexcitation drive means
2
to thereby open a fuel injection valve
1
with a first driving current (referred to as the overexcitation current) supplied from a battery power source at a battery voltage. Subsequently, the fuel injection valve control means
4
actuates a holding drive means
3
to change over the driving current, i.e., the overexcitation current, to a second driving current (referred to as the holding current) which is smaller than the first driving current or the overexcitation current, the second driving current or the holding current being fed to the fuel injection valve
1
in order to hold the same in the opened state.
By adopting the driving current changeover scheme described above in the driving system for driving the fuel injection valve
1
, the response performance or behavior of the fuel injection valve
1
can certainly be improved with the linearity of the fuel injection characteristic being maintained even in a low pulse-frequency region to an advantage, as is well.
Next, description will turn to the fuel injection control operation of the conventional injection valve driving system by reference to the timing chart shown in FIG.
16
. In this timing chart, the individual signal waveforms depicted with solid lines represent the operation of the conventional fuel injection valve driving system in the state where the battery voltage is at V
0
(see the top row (a)). The duration or width Pw
0
of the driving pulse for the fuel injection valve
1
(see the row (b)) is determined as a sum of an effective pulse width or duration Te
0
(equivalent to the effective driving time duration for the actual fuel injection) and a dead time Td
0
(see the row (e)). Parenthetically, the dead time is defined as a time period which lapses until the lift operation of the fuel injection valve
1
is actually started from a time point when the driving pulse of the width Pw
0
was applied.
In general, the dead time Td exhibits such a characteristic as a function of the battery voltage, as illustrated in FIG.
3
. From this figure, the battery voltage-versus-dead time characteristic will be self-explanately. The battery voltage-versus-dead time characteristic is previously stored in a control unit (not shown) as table or map data with the battery voltage being selected as an index parameter. Accordingly, by referencing the map data, the dead time Td can be determined on the basis of the battery voltage.
The overexcitation drive means
2
starts the driving of the fuel injection valve
1
by supplying the overexcitation current thereto in synchronism with the leading edge of the driving pulse having the pulse width Pw
0
, to thereby allow the overexcitation current to flow through a plunger coil of the fuel injection valve
1
for a predetermined proper valve open time Tk
0
(see the row (c) in FIG.
16
). Upon termination of the overexcitation driving of the fuel injection valve by the overexcitation drive means
2
, the holding drive means (also termed simply the holding means)
3
then supplies a holding current to the fuel injection valve
1
in continuation to the overexcitation driving current. The supply of the holding current by the holding drive means
3
is terminated in synchronism with the trailing edge of the driving pulse having the pulse width Pw
0
. This driving pulse itself will also be designated by Pw
0
for convenience of the description.
As another fuel injection valve driving scheme, such system is also adopted in which the battery voltage is boosted by resorting to the use of a high-voltage power supply circuit for thereby feeding an overexcitation current to the fuel injection valve
1
in an attempt for realizing the valve opening operation with enhanced response performance so that the linearity of the fuel injection characteristic can be ensured even in a lower pulse frequency region, as is disclosed in Japanese Patent Application Laid-Open Publication No. 47140/1998 (JP-A-10-47140).
However, in the conventional driving system for driving the fuel injection valve by feeding thereto the overexcitation current at the battery voltage, as in the case of the electromagnetic fuel injector driving system disclosed in Japanese Patent Publication No. 23100/1992, no consideration is paid to the changes of the fuel flow characteristics brought about by disturbances such as influences of the change in the battery voltage applied to the fuel injection valve, change in the resistance of the plunger coil constituting a part of the electromagnetic fuel injector (hereinafter this resistance of the plunger coil will also be referred to as the coil resistance), change of the fuel pressure fed to the fuel injection valve and others. Consequently, the conventional fuel injection valve driving system actually adopted in the internal combustion engine suffers a serious problem that the fuel injection quantity can not be controlled to a desired value when the disturbances such as mentioned above make appearance.
By way of example, operations of the electromagnetic fuel injection valve driving system at the battery voltage lowered to a level V
1
(<V
0
) are illustrated in
FI
Fukutomi Norihisa
Ohuchi Hirofumi
Ono Takahiko
Castro Arnold
Mancene Gene
Sughrue & Mion, PLLC
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