Note: Descriptions are shown in the official language in which they were submitted.
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FUEL METERING SYSTEM FOR ~N INTERNAL COMBUSTION ENGINE
_ . . . _ . .
This invention relates to a uel meterinq syste~
having improved ability to handle transient fuel meter~ng
modes of operation. ~ore particularly, it relates to a fuel
5 metering system for an internal combustion engine wherein the
fuel control system of the engine is better enabled, as
compared to the prior art, to handle the transient conditions
that occur during engine accelerations, decelerations
(negative acceleration) and other conditions that cause
fluctuations to occur on a temporary basis in the flow of fuel
from the engine's primary fuel metering apparatus to its
combustion chamber or chambers.
In internal combustion engines, the rate at which
fuel is metered to the engine varies during engine operation.
15 Changes in engine load cause the engine's fuel metering
apparatus to increase or to decrease the rate at which fuel is
metered to the engine. As a result, the engine must change
from a first state, where engine operation and fuel flow rate
is quite stable, to a second state, where these conditions
20 again become stable. T~e-conditions in between the st~ble
states are of a transient character in that the rate of fuel
flow varies continuously and can produce undesirable air/fuel
ratios. For example, with carburetion or other central
location of the fuel metering apparatus, there is an intake
25 manifold passage that the vaporized or atmoized fuel must
traverse in order to reach the engine's combustion chamber or
chambers. At a given engine load, prior art fuel control
systems under transient engine operation are unable to
maintain precise air/fuel ratios until the conditions in the
30 engine's intake passages have sta~ilized. Sudden
accelerations cause an increase in the rate at which liquid
fuel is deposited on the walls-of the intake passages (wall
wetting), and sudden decelerations produce a lessened rate of
deposition. The reason for this has to do with the changing
35 vapor pressures. The higher the vapor pressure, the more the
fuel tends to accumulate on the walls of the intake passages.
Vapor pressure is a partial pressure, and the major
contributor to pressure in the intake passage is air. The air
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pressure in the intake passages in general is below
atmospheric, unless the usual throttle valve is fully open,
during engine operation.
While the wall-wetting changes, the amount of fuel
metered by the fuel metering apparatus on the engine is not
the amount of fuel that actually reaches the engine's
combustion chambers within the charge transport time (air/fuel
delivery time) applicable to the particular engine speed and
load conditions at the time. The engine speed and load under
10 stable engine operating conditions are the factors primarily '
determinative of the transport time of the air/fuel mixture
from the fuel metering apparatus to the engine's respective
combustion chambers. This applies to both central point fuel
metering and multipoint fuel metering systems. Central point
fuel systems include both the conventional carburetion system
and the recently developed central point fuel injection system
that has two electromagnetic fueI injectors positioned in a
throttle body (air valve) to inject fuel into the incoming
airstream. The multipoint system is exem~lified by electronic
fuel injection syste~s- ~ t~ provide an electromagnetic fuel
inj'ector for each of the engine's combustion chambers, with
each injector injectin~- fuel into the intake passage -
immediately upstream of the intake v,alve for the associated
combustion chamber. -
A search of the prior art has not revealed any
patents of particular relevance with respect to the subject
matter hereof. However, the following patents are of general
background interest.
U.S. Patent No. 3,794,003 to ReddY teaches an
electronic deceleration control system which is responsive to
engine RPM and intake manifold absolute pressure. The system
compu,tes the first derivative of the manifold pressure to
provide an immediate indication of the deceleration demand
independent of throttle position or minimum manifold pressure.
The system curtails or terminates fuel delivery to the engine
when manifold pressure is above a predetermined value. Fuel
delivery is restored after the manifold pressure has returned
above a second predetermined value. Engine RPM also is a
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`.- ` - 3
~actor employed in this fuel control system.
U.S. Patent No. 3,969,614 to Moyer et al discloses an
engine control system employing a digital computer that
calculates on a real-time basis the proper setting for one
controlled variable while taking into account the effect of a
setting of another controlled variable to provide stable
engine operation at all times. The computer is programmed to
repetitively calculate values for the controlled variables
from an algebraic function or functions describing a
predetermined desired relationship between a first controlled
output variable and a second controlled output variable.
UOS. Patent Wo. 3,964,443 to Hartford teaches a
digital engine control system that may be used to control a
fuel injection system in which engine i~take manifold
pressure, engine RPM and engine temperature are utilized as
inputs to a computer.
U.S. Patent ~,086,884 to Moon et al teaches a fuel
control system for a spark ignition internal combustion engine
wherein the fuel is delivered with central point fuel
injection. The fueI i ~iection pulse width determines the
quantity of fuel delivered to the engine and this is
calculated by the speed-~ensity approach for determining the
mass air flow.
In accordance with the invention, an improved fuel
metering system is provided that is particularly suitable for
use with a spark ignition internal combustion engine. The
principles of the improvement may, however, be extended to
othex engine designs, such as Diesel, external combustion and
turbine. Each of these other engine types requires an
30 air/fuel mixture and may need the transient control provided
by the invention. A Diesel engine involves the direct
injection of fuel into the engine's combustion chamber or
prechamber (indirect injection Diesel), but the quantity of
fuel that remains on the walls of the combustion chamber or
35 prechamber and the variation of such quantity may be of
considerable importance in the adequate control of Diesel
engine exhaust emissions and fuel economy. Continuous
combustion engines, on the other hand, do not require the
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degree of fuel control required by internal combustion engines
because combustion is continuous and an excess of air is
always available~ It is not inconceivable, however, that such
engines may one day r~quire compensation for transient
deposits of fuel in the intake passage to the "external"
combustion chamber of such an engine. Such compensation would
be of particular importance where the response of the engine
to changes in rate of fuel flow ~s significant.
The improved fuel control system of the invention is
designed to take into account the variations that occur in the
quantity of fuel that is deposite~ in the liquid state in the
intake passage ar passages of an engine. The air/fuel ratio
of the mixture in the intake passages varies depending upon
the initial metering of fuel in proportion to the incoming air
and also as a function of the net transfer of fuel from the
surfaces o the intake passages to the inducted air/fuel
mixture or vice versa. The incoming air, after being ,~ixed
with fuel at some point or points in the intake passage, flows
into the engine's combustion chambers. Liquid fuel on the
walls of the combustion ~c~ambers may be included in the net
transfer.
In accordance with the present invention, there
is provided a fuel metering system for an internal combustion
engine, the engine having a passage through which a mixture
of air and fuel is inducted into the combustion chamber
or chambers of the engine, the fuel metering system compris-
ing: (a) a fuel system having electrically settable
means for controlling the rate at which fuel is metered
into the engine's intake passage; and (b) means for modify~
ing the rate at which fuel is metered into the engine's
intake passage to take into account the rate at which
fuel is transferred from the surfaces of the intake passage
to the inducted air/fuel mixture or from the airlfuel
mixture to the surfaces of the intake passages, the means
for modifying the rate at which fuel is metered being
a digital computer programmed to calculate repetitively
a value representing a current transfer rate of the intake
surface fuel and wherein the calculated value is used
to modify the rate at which fuel otherwise would be metered
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into the engine's intake passage.
The invention is described further, by way of
illustration, with reference to the accompanying drawings,
in which:
Figure 1 is a schematic block diagram of a basic fuel
control system and a transient compensation system that is
used to modify as necessary the computer-calculated fuel
quantity determined by the basic system; and
Figure 2 is a graph of the intake manifold absolute
pressure o an internal combustion engine versus the quantity
of liquid fuel residing on its intake manifold under
equilibrium conditions of engine operation.
With reference now to the drawings, there is shown in
Figure 1, a basic fuel metering system 10 and a transient
compensation fuel metering system 12. The basic fuel metering
system has an engine 16 that produces certain operational
conditions that are sensed via an engine sensor system 14, as
is indicated by the arrow 1~. With the sensor system
connected by electrical leads 32, which may be in the form of
a data bus for transmi~trng digital information, the engine
operating conditions may be used in the computer calculation
of the rate at which it ls desired that fuel be mete.ed to the
engine 16 at a particular instan~ in time. This rate is
calculated by the basic fuel metering system 10. Fuel is
supplied to the engine with the use of a fuel system 18 that
delivers fuel to th:e engine, as indicated by arrow 17, in
response to a suitable signal appearing on the electrical or
mechanical path represented by the arrow 19.
The basic fuel metering system 10 prefe~ably includes
a di~ital computer of the type employed in the fuel metering
system described in commonly assigned U.S. Patent 3,969,614 to
- Moyer et al and preferably is capable of calculating a fuel
injection pulse width to provide a desired air/fuel ratio.
The pulse width may be determined by the use of a computer
calculation that determines the quantity of fuel to be
delivered to the engine per injection in response to the mass
air flow into the engine's intake passages at the time of
injection. A mass air Elow meter or other device may be used
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to determine directly the mass air flow. Alternatively,
- a speed-density type of indirect determination of mass
air flow into the engine may be made, as is done with
the improved fuel metering system described in U.S. Patent
4,086~884 to Moon et al. The system of the Moon et al
patent now has been further improved in the manner described
in Canadian patent application Serial No. 357,122 filed
July 24, 1980, in the name of Ford Motor Company of Canada,
Limited, entitled "A Method for Improving Fuel Control
in an Internal Combustion Engine".
The transient fuel metering compensation system 12 is
intended to modify the basic rate of fuel metering calculated
by the digital computer. The compensation takes into account
the rate at which fuel is removed from~ or added to the liquid
residing on the surfaces of the engine's intake passages.
This transfer rate, if necessary, may include variations in
the quantity of liquid fuel that remains within the combustion
chamber of the engine as a deposit on its walls. When the
fuel metering rate (a fuel injector pulse width multiplied by
the number of injec~io~-per unit time and the fuel delivery
rate duriAy injection) is calcuiated y the basic fuel
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metering system 10, the rate of mass air flow into the engine
must first be dete~lnined as inclicated at 30 in Figure 1. At
33, a desired air/fuel ratio is detiermined based upon t'ne
engine operating conditions prevailing as of the time the rate
of mass air flow is determined. Via the electrical or
computer paths 34 and 35, the digital computer determines a
desired rate of mass fuel flow into the engine by dividing the
rate of mass air flow by the desired air/fuel ratio. The
result, on electrical or computer path 37, then is used in the
computation of a fuel flow demand, that is, a fuel flow rate
that takes into account the transfer of fuel onto and from the
quantity of liquid fuel residing on the surfaces of the
engine's intake passages. This fuel flow demand appears on
electrical or mechanical path 19 and controls the metering of
fuel by the ~uel system 18.
The fuel system 18 may be a conventional carburetor
or a set of electromagnetic fuel injectors. In the preferred
form of the invention, the fuel syste~n is a throttle body
mounted on the enginels intake manifold. The throttle body
has two electromagnetic fuel injectors positioned to inject
liquid fuel into the airstream entering the intake manifold
through the throttIe body. The injectors may be pointed
downwardly at a location just above the throttle plate or
plates mounted within the throttle body to control the rate of
mass air flow into the engine.
The fuel flow demand is determined at point 20 in the
system depicted in Figure 1. This signal is a ¢ombination of
the desired fuel mass flow rate with a second rate term,
identified (TRISFn) (constant). The second term accounts for
30 variation in the quantity of liquid fuel residing on the
surfaces of tne engine's intake passages. The constant in
this term is a scaling factor. The factor TRISFn is the
transfer rate of the fuel on the surfaces of the engine's
intake passages. This factor, along with other quantities
35 used in the description below, is defined as follows:
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l~S41
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TRISF = d(AISF) = Transfer Rate of the Intake Surface Fuel
dt
AISF - Actual Intake Surface Fuel
EISF - Equilibrium Intake Surface Fuel
ISTC = Intake Surface Time Constant
The transfer rate is expressed in units of mass per unit time.
Actual and equilibrium intake surface fuel is expressed in
mass units, and the intake surface time constant is in units
of time. The intake surface time constant is a measure of the
actual time required for fuel leaving the liquid state on the
intake surfaces to become a gas or vapor in the intake mixture
moving toward the engine's combustion chamber or chambers and
vice versa.
The product of the transfer rate of the intake
surface fuel and the time constant is equal to the difference
between the equilibrium intake surface fuel and the actual
lntake surface fuel, or, stated mathematically: ;
,
(TRISF) (ISTC)~ = ISTC d(AIS_ = EISF -- AISF
dt
:
This is a differential equation. Under steady state
conditions, d(AISF)/dt is equal -to zero and the actual intake
surface fuel AISF i;s the equilibrium intake surface fuel.
However, under transient conditions of engine operation, where
the equilibrium intake surface fuel EISF is changing between
two diferent values corresponding to two different states of
substantially stable engine operatlon, the differential
e~uation above may be solved for the purpose of allowing t'ne
engine's fuel metering system to take into account the
quantity of fuel entering and leaving the induction stream due
to changing EISF states~. The fuel flow demand is a fuel flow
rate equal to the desired fuel flow rate less the net transfer
-~ 30 rate from the intake surfaces to the inducted mixture.
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The desired fuel flow rate is calculated as
previously described, but the TRISF compensation of the basic
fuel metering system computation is accomplished separately by
the digital computer preferably used to handle both the basic
fuel metering and TRISF computations. In the transient
compensation system, the EISFn is calculated or is found in
computer tabular memory and is available as a number
applicable to the particular engine operating conditions
prevailing at the time the fuel metering computation is being
made. The subscript "n" denotes the current EISF, AISF and
TRISF values and the subscript "(n-l)" denotes the values
thereof at a prior time, such as the immediately preceding
computer computation cycle.
In the solution of the differential equation defining
TRISF, several computer or electronic techniques could be
employed. There are several mathematical methods of
approximating the solution using a trial and error technique.
The solution also may be obtained by employing tables that
contain TRISF values for various engine operating conditions.
The preferred form of the invention uses a combination of
these techniques and approximates the solution to the equation
based upon results obtained from a prior solution. The prior
solution, as well as the solution in progress at a given time,
is calculated from values obtained in the prior solution of
the differential equation as well as with the use of a table
of values for the equilibrium intake surface fuel (~ISF).
Thé EISF may be expressed as a function of one or
more engine operating parameters, such as engine speed and
engine load. In Figure 2, EI5F is related to intake maniEbld
absolute pressure, a quantity that is closely related to the
load on the engine. Other parameters indicative of intake air
or mixture flow rate or indicative of engine torque also may
be used. A family of curves is shown to indicate that EISF
also is a function of engine speeds indicated by RPM numbers
that appear at the right-hand side of each curve. The
variables could be interchanged Lf a different family of
curves were to be used. Points 93 and 97 on the 1000 RPM
'.',`'4 curve designate two different engine power output requirements
at the same engine speed. In a vehicle application of an
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engine, this might correspond to a change from operation of
the vehicle on level ground to operation on an upward incline
with increased throttle opening to maintain engine speed. In
such situation, the engine speed would remain substantially
5 constant if the throttle valve (conventionally used on the
engine to control airflow and powex output) were to be opened
to increase the engine's power output. Opening of the
throttle causes the intake manifold absolute pressure (MAP) to
increase and thus, engine operation shifts from point 97 to
10 point 93. Pressures corresponding to these ~oints are
indicated by lines 99 and 95 respectively. The EISF values at
these points are respectively indicated by lines 96 and 94O
Line 98 in Figure 2 designates an actual intake
surface fuel (AISF) that necessarily occurs at some time
15 betweeen equilibrium engine operation at points 97 and 93.
The AISF value or values occurring between equilibrium points
are used in determining the transfer rate of the intake
surface fuel and determination therefrom of the fuel flow
demand as indicated in block 20. In this way, transient
20 compensation of the fuel metering rate calculated by the basic
system 10 may be achieved to take into account the liquid fuel
transferred from the enginels intake passages to its induction
mixture and vice versa.
The intake surface fuel at equilibrium engine
25 operation is not changing and can be ignored. During changes
or transients occurring in engine operation, however, accurate
fuel metering requires that allowance be made for the
contribution of the inducted air/fuel mixture to the quantity
of liquid fuel residing on the intake passage surfaces or the
30 contribution of fuel to the air/fuel mixture from the intake
surface deposits. The fuel leaving the intake surfaces
; becomes an aerosol or vapor or gas and mixes with the air and
fuel moving along the intake passage; This intake surface
fuel is added to the metered quantity of fuel as determined by
35 the current fuel setting. On the other hand, gaseous fuel
that is deposited on the intake passage surfaces undergoes a
change in state and subtracts from the quantity of fuel that
actually reaches the engine's combustion chamber.
:, '' , ' ., '~ ~ ,
When fuel is added to the air/fuel mixture, it must
be subtracted from the desired quantity that is obtained from
the step indicated in block 36 of Figure 1. Thus, fuel that
is removed from the walls of the intake passages and added to
5 the inducted mixture is given an opposite mathematical sign as
compared to the desired fuel flow so that, when combined in an
additive process, the result is a value that represents the
actual fuel flow demand, that is, the quantity of fuel that
must be metered to provide the desired air/fuel ratio, taking
into account the transient fuel addition provided by the fuel
removed from the intake passage surfaces and inducted into the
engine's combustion chambers. Of course, fuel removed from
the air/fuel mixture moving toward the combustion chambers is
given the same mathematical sign as the desired fuel flow so
that, when combined in additive fashion therewith, the fuel
~flow demand will include an extra allowance for that fuel
which is removed from the inducted mixture and deposited on
the intake passage surfacesO
When the fuel flow demand is the same as the desired
fuel flow determined as indicated by block 36, the fuel supply
system is not providing any transient compensation. The
air/fuel ratio of the air/fuel mixture inducted into the
; engine under transient conditions is a combination of the
metered fuel and the quantity of fuel obtained from or added
to that deposited previously on the intake passage surfaces.
; This latter quantity is obtained as a result of changes in the
pressure within the intake manifold under the various
conditions of engine operation. If the pressure increases as
a result of increased throttle opening or reduced load on the
engine, then the partial pressure of oxygen and noncombustible
gases~in the intake mixture increases correspondingly and the
partial pressure of the fuel vapor decreases. Fuel removed
from the mixture of gases deposits as a liquid on the surfaces
of the intake passages. Conversely, if the fuel partial
pressure lncreases as a result of other partial pressures that
are reduced, the amount of liquid ~uel deposited on the intake
passage surfaces decreases and the fuel removed from that
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-- 12 --
residing on the surfaces is inducted into the engLne's
combustion chambers. In addii:ion to pressures, there are
other factors that influence the quantity of liquid fuel on
the surfaces of the enginels intake passages.
When the air supplied to the engine is cold, the
amount of liquid fuel deposited on the intake passage surfaces
is greater than it is as the engine warms up. Thls is because
the partial pressure of the engine's intake air is greater at
lower temperatures than it is at higher temperatures, and also
10 because the fuel condenses more easily at the lower
temperatures. Also, at lower intake air or fuel temperatures,
the fuel metering;devi~e or system 18 employed may not be as
effective in thoroughly mixing the air and fuel inducted into
the engine. For these reasons, it conventionally has been
15 necessary to employ fuel enrichment devices and techniques
(the general equivalent of the choke function conventionally
employed on spark ignition engines) in order to compensate for
operation at lower temperatures. Un~ortunately, the fuel
enrichment that occùrs results in increased hydrocarbon engine
20 exhaust emissions and this has necessitated the use of
elaborate choke control devices and systems to reduce the
hydrocarbon emissions as much and as rapidly as possible.
Such reduction of the hydrocarbon emissions has impeded or
reduced the performance of the~ associated engines during the
warm-up period.
The temperature of the intake system or its
constituents is of significance with respect to the quantity
of liquid fuel that can be deposited on the intake surfaces of
the engine, The engine's intake passages may contain air, air
and fuel in nlixtUre, or air, fuel and exhaust gas in mixture.
The temperature of any of these, or of the engine and its
ntake conduit, may be used in the determination of the rate
at ~hich fuel is transferred to and from the intake mixture
from and to the intake passage surfaces. The physical
properties of the fuel.itself also are of importance and vary
both geographically and seasonally.
When it is desired to compensate the rate at which
- fuel is metered to the combustion chamber or chambers of an
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- 13 -
engine for variations in the quantity or rate of transfer of
liquid fuel residing on the intake passages surfaces in the
engine, this may be accomplished in the ~anner depicted in the
transient fuel metering system 12 of Figure 1.
In t~e Figure 1 transient fuel Inetering compensation
system 12, the value of the current transfer rate of intake
surface fuel TRISFn appears on path 46 leading to block 20 in
the basic fuel metering system lO. The TRISFn value is a
number that is repeatedly calculated and updated based upon
changes in various engine operating parameters. As indicated
in block 44, the current transfer rate of the engine's intake
surface fuel is a function f4 of variables that may be related
to one another as follows:
TRISFn = EISFn ~ AISFn ( 1)
- ISTCn
The TRISFn value cannot be calculated in the block 44
computer step until the EISFn, AISFn and ISTCn values are
known on a real-time basis, that is, while the engine is
operating and being controlled b~ the basic and transient
compensation fuel metering systems 10 and 12. EISFn can be
determined from the engine operating parameters illustrated in
Figure 2, but in reality is a functlon fl of engine intake
manifold absolute pressure, engine speed, engine intake air or
mixture temperature, engine intake system temperature (here
partially represented by the engine coolant temperature TCn),
time and air/fuel ratio (A/Fn). Fuel physical properties also
may be considered. The AjFn is, of course, the ratio of air
to fuel within the gaseous mixture adjacent the surfaces of
the intake passage and varies with position within the intake
passage. The EISFn also may be obtained from a computer
memory which has stored within it constants that define the
slope and EISF axis intercepts of a family of curves that can
represent one or more of the curves illustrated in Figure l.
If this is the case, engine speed RPMn may be used to select
the proper set of constants and a single value of the intake
manifold absolute pressure (MAP) may be used to obtain a value
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for the current equilibrium intake surface fuel EISFn. Of
course, the variables may be interchanged if desired. In any
event, the current EISFn is determined from values of one or
more engine operating parameters.
The TRISFn value of equation (1) cannot be determined
until the AISFn and ISTCn values have been obtained; the
former is subtracted from t~he EISFn value obtained as
described in the preceding paragraph and the difference
between the EISFn and AISFn values is divided by ISTCn, the
current intake surface time constant.
AISFn is approximately equal to the previous actual
intake surface fuel AISF(n_l) modified to account for changes
that may have occurred during the time elapsed since AISF(n-l)
was determined. If AISFn is regarded as a function f3 of the
elapsed time ~t just mentioned, of AISF(n-l) and of
TRISF(n-l), the following equation results;
AISFn = AISF(n-l) + [TRISF(n-l)] [ ~e]- (2)
From equation (2) above, it is clear that AISFn can be
determined, at least to a good approximation, from previous
values of TRISF~and AISF used to effect compensation of the
basic fuel meterlng system 10~ for variations in the quantity
of liquid fuel on~ehe engine'~s intake passage surfaces.
The ISTCn~ is a time constant that represents the
current or instantaneous rate at which fuel is being
25~ transferred from tne li~uid state on the intake surfaces to
; ~ the vapor or gaseous state in the inducted mixture or vice
versa~ In view of this, the ISTCn may be described as a
function of one or more engine operating parameters that
influence this rate of transfer. Thus, as is indicated in
~block~ 42 of Figure 1, ISTCn is a function~ f2 f intake
manifold absolute pressure, engine speedj engine air or intake
mixture temperature, engine intake system temperature, time,
A/Fn, and the physical properties of the fuel. The intake
surface time constant is not a constant in the sense that it
does not change, but rather is variable under some engine
operating conditions.
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The ISTC is a measure of the time required for a
fraction of the fuel that will be transferred, in response to
a difference between the equilibrium intake surface fuel EISFn
and the actual intake surface fuel AISFn existing during the
5 transient engine operation, to be transferred. Variation in
the ISTC results primarily from variations in the engine
intake system temperature and the temperature TIn of the
intake air or gaseous mixture; there may be other engine
operating parameters, such as the intake manifold absolute
10 pressure, engine speed, or time in the engine cycle, that
affect the ISTC. The ISTC variation is analogous to the
variation o~ an RC time constant in an electrical circuit as a
result of temperature or other variations that cause the
resistance and capacitance values to change. At normal engine
15 operating temperatures, the ISTC may be regarded as a
constant, but for more accurate fuel metéring capability, it
is desirable to use a plurality of values for the ISTC. The
values may be selected for a particular temperature range in
which the engine is operating or some other parameter of
20 engine operation may be selected for the determination of
which value for ISTC will be used.
If the ISTC value is selected from a table or if it
is calculated from an equation programmed into the digital
computer, then the ISTC becomes a variable that takes into
25 account variations in the physical properties of the engine's
intake manifold and its contents. This is analogous,
mathematically, to the variations in an RC time constant of an
electrical circuit which variations would be due to changes in
the resistance R and capacitance C values that determine the
30 time constant. The ISTC changes that result from variation of
engine intake system physical properties are primarily due to
engine operating and intake air temperature variations. These
variations are quite minor after engine warm-up.
After the ISTC has been selected, the digital
computer is allowed to calculate the current transfer rate of
the intake surface fuel TRISFn from equations (1) and ~2)
above. The TRISFn is applied via path 46 to the
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-- 16 --
determination of the fuel flow de~and in the basic system 10,
as s`nown in block 20.
AfteL the TRISFn value is determined, the value is
provided via path 47 to a memory update of the previous value.
5 Otherwise stated, the latest or most current value TRISFn
replaces the previous value TRISF(n-l), as indicated by block
50 in Figure 1, and the updated value is applied to a memory
52 over path 51. The memory uses the updated value as the
value for TRISF(n_l) in equation (2) above for the calculation
10 of wnat is to become the next TRISFn, which a~ain causes t'ne
~emory 52 to be updated.
Similarly, the value for AISFn, determined with the
use of equation (2) above, is calculated repeatedly. A clock
or pulse generator, conventionally required by a digital
15 computer engine control system to update the fuel-metering
control setting, is used in the computer determination of tne
time elapsed since tne last update of the ~ISFn calculation.
The current AISFn value is via line 63 to the calculation of
the TRISFn value and also is made available, as indicated in
20 block 65, for the update via path 66 of a memory 67 containing
the AISF(n-l) value used in the calcula~tion of a new AISFn
from equation (2). This process preferably is repeated at the
same rate at which the TRISFn calculations are made.
.
:: : : : : :
.
.
. ~ . . :
