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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel supply control of an engine for
automobiles, and in particular, to a method of controlling fuel supply
suitable for performing the control to maintain an air-fuel ratio at a
proper value.
2. Description of the Related Art
In a prior art fuel supply control system of the feedback control type, a
fundamental fuel supply quantity Ti(n) (usually, given by a valve opening
time period of a fuel injection valve) in an an n-th stroke is determined
based on an air flow rate Q.sub.ay (n-1) at the inlet of a manifold
measured in an (n-1)th stroke (n is an integer, and one stroke corresponds
to 1/2 revolutions in a 4-cycle engine) and an engine speed N(n-1) as
expressed by the following formula
##EQU1##
where, k: a correction coefficient.
The determined quantity of fuel is supplied to each cylinder. This
fundamental fuel supply quantity Ti(n) is a value when the engine is in a
steady state. At the transient time when the throttle valve is opened or
closed as during acceleration or deceleration, a correction is made by
adding a correction quantity to the fundamental fuel supply quantity. This
correction quantity is obtained as a function of the amount of variation
.DELTA..theta..sub.th (n-1) with time in the degree of opening of the
throttle valve as expressed by the following formula
k=1+func(.DELTA..theta..sub.th (n-1)) (2),
and the fuel quantity to be supplied is determined by correcting the Ti(n)
in formula (1) by the correction quantity k.
The calculation method according the formula (1) is to be determined by the
fuel quantity to be supplied in the next n-th stroke by using the measured
values including the air flow rate and engine speed in the (n-1)th stroke.
In this method, if the intake air flow rate or engine speed is changed to
a great extent between the (n-1)th stroke and the n-th stroke, the fuel
quantity supplied in the n-th stroke will be deviated from a required fuel
quantity in the n-th stroke. Thus, the A/F ratio (air to fuel ratio) will
also be deviated from a target value. The appropriate fuel quantity to be
supplied should be a value which matches the amount of air actually
flowing into each cylinder in the n-th stroke. However, this amount of air
flowing into the cylinder cannot be measured by the technique at the
present time. Even it the amount of air flow into the cylinder can be
measured, since a delay is involved in the calculation, it results in that
the present fuel quantity is calculated based on the amount of air in the
past stroke. For this reason, at the transient time, since a significant
error is caused in the air-fuel ratio control, it is necessary to design
the exhaust gas control device (catalyst, EGR, etc.) with a sufficient
margin in the characteristic thereof more than required. Thus, there has
been a problem in the cost and the drivability.
The formula (2) is intended to compensate for a follow-up delay in the fuel
supply quantity during a transient state by using a change in the degree
of opening of the throttle valve. Practically, however, much time and
labor have been spent to experimentally obtain a function of the
correction coefficient which satisfied both the reduction and exhaust gas
components an the drivability. Although, not less than 50% of the
development period of the control logic has been devoted, there is a
problem in that the accuracy of control of the air-fuel ratio is still
low.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a logical formation for
controlling the air-fuel ratio, which is capable of controlling the
air-fuel ratio with high accuracy even in a transient state by predicting
the amount of air flowing into the cylinder in a future stroke by a method
that is adaptable for use with control systems of engines of varied types.
The above object can be achieved by introducing a calculation for
accurately and rationally predicting the amount of air flowing into the
cylinder in an n-th stroke based on measured data in an (n-1)th stroke and
its preceeding strokes. For the calculation, it is considered to employ
(1) a numerical formula model for prediction, and (2) a method for
predicting the amount of air flowing into the cylinder in the n th stroke
by introducing into a link mechanism consisting of an accelerator pedal
and a throttle valve, an element involving a time delay so small as to be
not sensed by the driver and by utilizing this time delay. In the
calculation including both items (1) and (2), there is an advantage of
making the prediction easier by introducing a physical delay element. On
the other hand, when only the numerical formula model mentioned in item
(1) is used, there is an advantage in that the control can be used without
modifying at all the hardware structure of the engine control system
existing at the present time.
In either case, it is a basic matter to predict the amount of air flowing
into the cylinder according to a numerical formula. However, various
methods for predicting the amount of air flowing into the cylinder are
considered depending on how the fundamental model for prediction is
formed, and further, how the inconsistency between the actual phenomenon
and the fundamental model is corrected.
A prediction logic of the present invention includes a state estimation
section and a prediction section. In the state estimation section, a
physical quantity in an (n-1)th stroke required in the prediction section,
or parameters which can not be measured are estimated by an object
characteristic model and a measured value. In other words, the estimate
value is obtained by calculating a measured value of an indirect point
parameter.
The concrete realization of this prediction logic is attained by
extensively applying a known Kalman filter or an observer theory. In the
prediction section, by using the measured value, and the estimate value
obtained in the state estimation section as initial values, the amount of
air flowing into the cylinder in an n-th stroke is predicted based on a
model representing a characteristic of the amount of air flowing into the
cylinder. The quantity of fuel supply in the n-th stroke can be determined
by this predicted value of the amount of air flowing into the cylinder and
a target air-fuel ratio. By adopting such a logical formation, the
measured value in the preceding stroke of the stroke in which the fuel is
to be supplied is not used as it is for determining the quantity of fuel
supply as in the prior art, but the measured value and the model of the
characteristic of the measurement object are utilized collectively. Thus,
a physical quantity (e.g., the amount of air flowing into the cylinder)
which can not be measured in an on-board control system (e.g., a control
system mounted on the actual engine) is estimated and predicted thereby to
utilized in determining the fuel quantity. As a result, it is possible to
clearly define logical formation for the control and to adapt the control
logic to engines of various types, and at the same time, the control of
the air-fuel ratio can be achieved with high accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram showing a basic arrangement of an embodiment
of the present invention;
FIG. 2 is a timing chart of measurement and control of physical quantities
related to the control of an engine;
FIG. 3 is a block diagram showing a detailed arrangement of the embodiment;
and
FIG. 4 is a flowchart showing a control procedure when the control shown in
FIG. 1 is performed by a microcomputer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The embodiments of the present invention will be described with reference
to the drawings. As shown in FIG. 1, as a means for measuring a state of
an engine, an air flow meter 1 at a manifold inlet, a crank angle meter 8,
and an exhaust gas air-fuel ratio meter 7 are provided, and in addition, a
throttle angle meter 2 and an accelerator pedal angle meter 3 are
provided. The signals from these meters are input to an engine electronic
control unit (not shown), and the calculated results are commanded to an
injector 5 and an ignition device 6 thereby to perform the control of the
engine.
Here, the symbols in the engine system in FIG. 1 are as follows:
Q.sub.ay : the amount of air flowing into a manifold.
.theta.th: a throttle angle,
.theta..sub.ac : an accelerator pedal angle,
G.sub.f : a fuel supply command value,
.theta..sub.adv : an ignition timing,
eG.sub.f : a fuel supply executed value,
A/Fy: an air-fuel ratio measured value,
N: an engine speed (rpm)
Tr: a cylinder generated torque, and
L: an engine load.
These symbols are also used in FIG. 2 to explain the cause and effect
relationships of parameters.
FIG. 2 shows the cause and effect relationships of the operation parameters
of the engine. Specifically, FIG. 2 shows a change in each operation
parameter of the engine which is the object of the control in each stroke.
Here, one stroke corresponds to 1/2 of a revolution in a 4-cycle engine
and represents a range of 180.degree. of the crank angle. The left side
items represent principal physical quantities, and it is illustrated how
each of these quantities changes in each stroke. For example, the amount
of air Q.sub.in flowing into the cylinder changes in a wave shape in each
stroke. This is the result of the ripples of air that are caused due to
reciprocating motion of a piston in the cylinder or movement of an intake
valve. Environmental parameters are dependent upon atomospheric pressure,
atomospheric temperature, quality of fuel, etc., and thus, they change
slowly for a period of several strokes shown in FIG. 2, and these
parameters may be regarded as approximately constant. The throttle angle
.theta..sub.th is shown to begin its opening operation in an (n-1)th
stroke. Furthermore, it will be seen from a characteristic showing the
injection quantity G.sub.f that the fuel is injected intermittently by the
injector. In this manner, the changes in the physical quantities
representing the dynamic characteristics of the object engine are shown.
In FIG. 2, each of thick solid lines has a starting point marked with a
black dot .cndot. and shows its destination with an arrow .fwdarw.,
thereby to indicate the cause and effect relationship for each physical
quantity. That is, the black dot .cndot. means that this black dot is a
factor of a change of the physical quantity which is indicated by the
arrow originating from the black dot. For example, it is shown that the
engine speed N in the n-th stroke is determined by these factors including
an engine speed N(n-1) in the (n-1-)th stroke, an engine load L(n) in the
n-th stroke, and a generated torque Tr in the n-th stroke. This cause and
effect relationship can be expressed by the relationship formula such as a
formula (4) described later. Similarly, it is also shown that the amount
of air (air quantity) Q in(n) flowing into the cylinder in the n-th
stroke, the generated torque Tr(n) in the n-th stroke, and the air-fuel
ratio measured value A/F(n+2) in the (n+2)th stroke respectively indicated
by the tips of arrows are changed by parameters corresponding to black
dots which are the origins of the arrows. Furthermore, the injection
quantity G.sub.f and the ignition time .theta..sub.adv are the quantities
obtained by the calculation based on the measured values, and they are
controlled by the control unit. Accordingly, the starting points of the
arrows indicating the G.sub.f and Q.sub.adv are in the control arithmetic
unit (control unit).
The control system based on the cause and effect relationships shown in
FIG. 2 can be represented by a model in the following manner (where, n is
a subscript representing a stroke). In this respect, the engine which is
to be represented by a model is a 4-cycle, 4-cylinder engine by way of an
example.
The amount of air flowing into cylinder:
Q.sub.in (n)=f({.theta..sub.th (.tau.) .vertline..tau..epsilon..theta.(n)},
N(n), N(n-1), .alpha.(n)) (3)
where,
.theta..sub.th (.tau.): the degree of opening of the throttle valve, .tau.
is a crank angle in the n-th stroke, and .theta.(n) is its a definition
range (time width), and
.alpha.(n): a parameter which changes slowly.
The engine speed:
##EQU2##
where, .DELTA.(n-1): required time for the stroke (n-1),
I: turning moment,
Tr(n): generated torque, and
L(n): engine load.
The generated torque:
##EQU3##
where, G.sub.f (n-2): fuel supply command value in the stroke (n-2),
e(n-2): fuel supply effective value in the stroke (n-2),
.theta..sub.adv (n): ignition time in the stroke n, and
.beta.(n) parameter which changes slowly.
The flow meter measured value:
##EQU4##
where, .gamma.(n-1): parameter which changes slowly.
The air-fuel ratio measured value:
A/F.sub.y (n-1)=p(Q.sub.in (n-5), e(n-5)G.sub.f (n-5)) (7)
The fuel supply command value:
G.sub.f (n)=Q.sub.in (n/n-1)/A/F*(n) (8)
where,
A/F*(n): Air-fuel ratio target value in the stroke in the stroke n, and
Q.sub.in (n/n-1): predicted value of flowing into cylinder in the stroke n
which is predicted based on measured information in the strokes up to the
stroke (n-1).
The ignition time command value:
##EQU5##
N(n/n-1): engine speed predicted value in the stroke n which is predicted
based on measured information up to the stroke (n-1), and
Tr*(n) target generated torque.
In the model formulas described above, the engine speed N can be changed
even in one stroke, however, a representative value in one stoke is used.
There is a possibility of causing a calculation error in the formula (4)
including an integration of time synchronization due to the use of the
above-mentioned representative value. However, in this case, it is only
necessary to narrow an integration width .DELTA.(n-1) sufficiently.
(Further, it is also necessary to store in a memory a table of a
characteristic pattern of a generated torque vs. ignition time).
The problem of predicting the amount of air flowing into the cylinder is to
obtain a prediction value Q.sub.in (n/n-1) of the amount of air flowing
into the cylinder in the n-th stroke rationally based on the models of the
above formulas (3)-(9), and from the throttle opening degree
{.theta..sub.th (.tau.).vertline..tau..epsilon..theta.(i-1)}, engine speed
N(i-1), required time for stroke .DELTA.(i-1), flow meter measured value
.theta..sub.a,y(i-1), air-fuel ratio measured value A/F.sub.y (i-1), fuel
supply command value G.sub.f, and ignition time command value
.theta..sub.adv (i-1) (where, i n) which have been measured up to the
(n-1)th stroke.
In the formulas (3)-(9), these parameters .alpha., .beta., .gamma., and
.epsilon. are included, and it is necessary to estimate these parameters.
Further, the engine load L can not be measured actually. However, as
compared with a physical quantity which changes for each stroke, the
above-mentioned parameters and the engine load L are dependent upon the
atmospheric pressure, atmospheric temperature, cylinder wall temperature,
dirt at the inlet of the manifold, dirt in the air flow meter, blockage of
the fuel supply device (injector), and quality of the fuel. Thus, these
parameters change only slowly and may be considered substantially at a
constant value. Accordingly, as a variation model changing with time of
the above-mentioned parameters may be grasped in the form of the following
formula
X(n)=X(n-1)+.eta..sub.x (n-1) (10)
where, .eta..sub.x is a random variable.
When the behavior in the control system is represented by a model in this
manner, an estimation theory represented by the Kalman filter can be
applied. In order to simplify the expression, such a vector is introduced
hereinafter.
The state quantity:
##EQU6##
The external input:
##EQU7##
The measured value:
y(n-1)=[N(n-1), Q.sub.ay (n-1), A/F.sub.y (n-1)].sup.T
The formulas (3)-(10) can be expressed collectively by using the vectors
mentioned above in the following formula
DC(n)=F(DC(n-1), u(n-1))+v y(n-1)=H DC(n-1) (11)
where,
V: variable terms .eta..sub.x (n-1) for the state quantity and
H: observation matrix.
(Practically, however, since the system is non-linear, the state vectors
can not be determined in such a simple manner. Here, with respect to a
higher order delay an estimated value which has been obtained heretofore
is used as an alternative value.)
The state estimation of the control system shown in FIG. 1 can be achieved
by calculating the following formula in accordance with the estimation
theory
DC(n-1.vertline.n-1)=DC(n-1.vertline.n-2)+K(y(n-1) -HDC(n-1.vertline.n-2))
(12)
DC(n-1.vertline.n-2)=F (DC(n-2.vertline.n-2), u(n-2))
where, K is a gain matrix obtained by the estimation theory. The formula
(12) has a recurrent structure with respect DC(i.vertline.i). Accordingly,
only by calculating this item DC(i.vertline.i) with the progress of the
strokes, it is possible to obtain an estimate value which utilizes to the
maximum extent the information which has been measured heretofore.
Next, each of the sections shown in FIG. 1 will be described. The state
estimation section 101 receives as inputs thereto a measured value
(measured vector) y(n-1), an estimate value y(n-1.vertline.n-1)
corresponding to a measured vector, and a manipulation vector u(n-2), and
calculates in accordance with the formula (12) to obtain the engine state
vector estimate value DC(n-1.vertline.n-1). The observation matrix 9 is an
observation matrix H in the second equation in the formula (11) or in the
first equation in the formula (12). The prediction section 102 performs
the calculation of the second equation in the formula (12) based on the
above-mentioned engine state vector estimation value DC(n-1.vertline.n-1)
and a manipulation vector U(n-1) (here, the index n-2becomes n-1), and
predictes an engine state prediction vector DC(n.vertline.n-1). In the
manipulation quantity determination section 103, a manipulation vector is
determined by using the above-mentioned engine state vector estimate value
and the engine state prediction vector so as to attain a control target
vector DC*.
In order to predict the air amount flowing into the cylinder, the formula
(3) which is a part of the formula (11), and the formula (10) (x
corresponds to .alpha.) may be used. However, since the throttle opening
degree in the n-th stroke is contained in the formulas and since this is
unknown in the (n-1)th stroke, either of the following methods is adopted.
(1) Prediction is made from a trend value.
Since the throttle opening degree changes in most cases linearly, the
linear prediction is used. In a concrete way, the prediction is attained
by the following formula
##EQU8##
where, .theta..sub.th (t.vertline.t'): a throttle opeing degree prediction
value at a time t which is predicted by using a measured value up to a
time t',
w(.theta..sub.th (t), .DELTA.tp): a weighting parameter, and
.DELTA.t: a measurement sampling period of the throttle opening degree
.DELTA.tp.
(When the prediction value exceeds upper and lower limits, upper and lower
limit values are used respectively.) This prediction value is a value on
the time axis. Hence, this value is converted to a crank angle expression.
{.theta..sub.th (.tau.).vertline..tau..epsilon..theta.(n)} by the engine
speed prediction value N(n.vertline.n-1) which is determined by the
formulas (4) and (5).
(2) Delay element is introduced between the accelerator pedal and the
throttle.
The accelerator pedal and the throttle valve are coupled mechanically. If a
delay element which is not sensed by a driver is introduced in the
coupling, and after detecting a change in the movement of the accelerator
pedal, if the throttle angle is predicted based on a coupling transmission
characteristic, then a lead time for the prediction will be learned. Thus,
as shown by the reference numeral 4 in FIG. 1, a delay element is
introduced in a coupling portion between the accelerator pedal 3 and the
throttle valve 2. If the delay element 4 is an electrical device, it will
become possible to predict a throttle angle from a displacement of the
accelerator pedal 3 without fail. When the reliability is considered to be
most important, it will be essential to use a mechanical device. In this
case, however, it is difficult to realize the complete delay element by
using a mechanical device. In order to cope with this difficulty, a delay
similar to that caused in the integration is introduced, and the
accelerator pedal angle per se may be predicted by a method like the
formula (13). Specifically, the accelerator pedal angle is predicted as in
the following formula
##EQU9##
.theta..sub.ac (t.vertline.t'): an accel pedal angle at a tube t which is
pedicted by using a measured value upto a time t',
w': a weighting parameter, and
.theta..sub.ac : an accel pedal angle meter measured value.
By substituting the above result to .theta..sub.ac in the following
formula, a prediction value of .theta..sub.th can be obtained.
.theta..sub.th =G(s).theta..sub.ac (15)
where, G(s) is an accel angle, throttle angle transmission function.
The overall arrangement of the above embodiment is shown in FIG. 3. In FIG.
3, the engine system which is the object of control is the same as in FIG.
1, and since reference numerals 1-7 designate identical parts, the
descriptions thereof are omitted. FIG. 3 shows the overall arrangement of
the control system, however, the basic structure is equivalent to that
shown in FIG. 1. In FIG. 3, a comparison element 200 is the same as 104 in
FIG. 1. A state estimate section 201 in FIG. 3 receives deviations
obtained by comparing a measured air-fuel ratio A/F.sub.y (n-1), a
measured engine speed N(n-1), and a measured amount of air flowing into
the manifold Q.sub.ay (n-1), respectively with an estimated air-fuel ratio
A/F.sub.y (n-1.vertline.n-1), an estimated engine speed
N(n-1.vertline.n-1), and an estimated amount of air flow Q.sub.ay
(n-1.vertline.n-1), and also a fuel supply quantity G.sub.f and an
ignition timing .theta..sub.adv which are the manipulation quantities are
inputted. By using these signals, the state estimate section 201 estimates
based on the formula (12) the amount of air flow into the cylinder
Q.sub.in (n-2.vertline.n-1), the effective fuel supply rate
e(n-2.vertline.n-1), the engine load L(n-1.vertline.n-1), the parameters
which change slowly .alpha.(n-1.vertline.n-1), .beta.(n-1.vertline.n-1),
the air-fuel ratio A/F.sub.y, the engine speed N, and the amount of air
flow into the manifold Q.sub.ay.
A throttle angle prediction section 203 performs a prediction based on the
prediction method of the formula (13) using the aforementioned trend
values for prediction, or based on the formulas (14) and (15) by
introducing the delay element between the accelerator pedal and the
throttle valve. A prediction section 204 of the amount of air Q.sub.in
flowing into the cylinder and the engine speed N predicts the amount of
air flowing into the cylinder Q.sub.in (n.vertline.n-1), and the engine
speed N(n.vertline.n-1) by using the throttle angle prediction value
.theta..sub.th (n.vertline.n-1), the estimate value of the amount of air
Q.sub.ac (n-1.vertline.n-1) flowing into the cylinder, the engine load
estimate value L(n-1.vertline.n-1), the engine speed estimate value
N(n-1.vertline.n-1), and the parameter estimate values .alpha., .beta.
which have been calculated in the state estimate section 201. A fuel
supply quantity and ignition time determining section 202, determines the
fuel supply command value G.sub.f and the ignition timing .theta..sub.adv
from the above-mentioned calculated information by using the formulas (8)
and (9) so that a target air-fuel ratio A/F*, and a target torque Tr* are
attained. In the embodiment described above, as will be seen from the
formulas defining the control operation, the amount of calculation is
relatively large. As a result, it is impossible in some cases to execute
the calculations by a small scale arithmetic unit. At the time of high
engine speeds, since the inertia of the generated torque is large as
compared with a change in the engine load, it is feasible, instead of
calculating the fuel supply quantity in each stroke, to calculate the fuel
supply quantity by suitably sampling the strokes and to provide as a fuel
supply command value by holding the calculated fuel supply quantity.
However, at the time of low engine speeds, since the inertia of the torque
is small, the influence of a change in the engine load which is an
external disturbance factor becomes significant. As a result, it is
necessary to accurately calculate the fuel supply quantity for each
stroke. A simplified method of the above embodiment for enabling, a small
scale arithmetic unit to execute will be described hereinafter.
(1) A simplified prediction method by the engine speed.
This method is based on a point of view that the amount of air Q.sub.in (n)
flowing into the cylinder is determined basically by a throttle angle
{.theta..sub.th (.tau.).vertline..tau..epsilon..theta.(i)} and an engine
speed N(i) (i.ltoreq.n-1). Specifically, it is intended to predict the
Q.sub.in (n) by the following functional formula
Q.sub.in (n)=f.sub.s1 ({.theta..sub.th
(.tau.).vertline..tau..epsilon..theta.(i)}, N(i); P.sub.s1
.vertline.i.ltoreq.n-1) (16)
where, P.sub.s1 is a parameter. As a concrete form, there is a formula as
shown below
##EQU10##
In the formula (16), the parameter P.sub.Sl is included. However, this
parameter is estimated in the following manner and the result is utilized
sequentially.
It is difficult to measure the amount of air flowing into the cylinder by
the on-board system. However, the measurement is possible by an
experimental device, and by this device, by using the amount of air
measured value Q.sub.ay throttle opening degree .theta..sub.th, and engine
speed N, a functional formula can be obtained as in the following formula
Q.sub.in (i)=g.sub.S1 (Q.sub.ay (i), {.theta..sub.th
(.tau.).vertline..tau..epsilon..theta.(i)}, N(i)) (18)
where, Q.sub.in is the amount of air flowing into the cylinder obtained by
a model formula.
In this formula, as an explanatory factor, the measured value in the same
stroke is used. However, the measured values in the preceding and
succeeding strokes may be added.
When the amount of air flowing into the cylinder is calculated posteriorly
as in the formula (18), this result is used to obtain the parameter
P.sub.S1 so that the J(P.sub.S1) in the following formula becomes minimum
##EQU11##
where, .rho.(j) is a weighting function.
By substituting the parameter P.sub.S1 obtained here, it is possible to
obtain the amount of air flowing into the cylinder in the n-th stroke. In
the formula (16), the throttle opening degrees up to the (n-1)th stroke
are utilized. However, the throttle opening degrees up to the n-th stroke
are included as the explanatory factor, and the prediction value obtained
by the throttle opening degree predicting method described in the
foregoing may be used. In this respect, since the calculation of the
parameter P.sub.S1 which makes the formula (19) minimum is carried out by a
recurrent functional formula, the calculation load does not become large.
Furthermore, in the formula (16), the air flow measured value Q.sub.ay (i)
may be added as the explanatory factor. This is useful to take the inertia
effect in the air within the manifold into consideration.
The output value of the exhaust gas air-fuel ratio sensor is used to
correct a coefficient multiplied to the fuel supply command value G.sub.f
(n). This is based on the view that the reason why the air-fuel ratio is
difficult to maintain the target value is due to blockage in the supply
device (injector), and the quality of the fuel. The correction coefficient
e(n) is estimated as in the following formula
e(n)=e(n-1) +Ke(A/F*(n-5) -A/F.sub.y (n-5)) (20)
where, Ke is an estimate gain, and the actual fuel supply command is
calculated by
e(n)Q.sub.in (n.vertline.n-1)/A/F*(n) (21)
(2) A simplified prediction, method by torque estimation.
This method utilizes the fact that the generated torque can be predicted
from the estimate value of the amount of air flowing into the cylinder,
the fuel injection quantity, and the ignition time in the past. From this
result, a change in the engine speed is predicted, and furthermore, it is
intended to predict the amount of air flowing into the cylinder by using a
throttle opening degree (predicted value). For this purpose, a model
relating to each physical quantity is established as follows.
The amount of air flowing into the cylinder:
Q.sub.in (n)=f.sub.S2 (}.theta..sub.th
(.tau.).vertline..tau..epsilon..theta.(n), N(n))} (22)
The engine speed:
##EQU12##
The generated torque:
##EQU13##
The air-fuel ratio measured value:
A/F.sub.y (n-1)=p(Q.sub.in (n-5), e(n-5)G.sub.f (n-5)) (25)
The relationship between the amount of air flowing into the cylinder and
the air flow measured value:
##EQU14##
The differences between the method based on the precise model formulas and
this simplified method reside in that in the latter, the formula (22) is
used only for the prediction of the amount of air flowing into the
cylinder and the formula (26) is used to establish the relation with
respect to the air flow meter measured value, the equation system is
formed in the difference type as far as possible and it makes it
unnecessary to solve the simultaneous equation, and the parameters to be
estimated are reduced to only the load L and the supply effective value e
thereby to reduce the load of calculation for prediction. The estimation
and prediction based on these equation systems can be performed in a
similar manner as in the method described in the foregoing.
The embodiments are described in the foregoing. In the control system, a
cooling water temperature T.sub.W is measured in many cases. Accordingly,
it is useful in reducing the load of calculation for prediction to set the
parameters included in the model formulas in a functional formula of the
cooling water temperature T.sub.W or in a table. In FIG. 4, there is shown
a flowchart of a processing procedure when the processing of FIG. 1 is
executed by a microprocessor or the like.
In the present invention, the logic is formed based on a dynamic logical
formation as compared with the prior art control logic in which the
control is directed to the steady state and at the time of a transient
state, the correction is made in accordance with the situation.
Therefore in the present invention, the following advantages are provided.
(1) Heretofore, not less than 50% of the period has been spent to develop
the correction method during a transient state in the engine operation in
order to apply the control logic to engines of various types. In the
present invention, since the logical formation is clear, such a period can
be reduced to a great extent.
(2) Since the logic itself is formed based on the dynamic phenomenon, the
control can be applied to all regions including the steady state and
transient state operation of the engine with high controlling performance.
Furthermore, the control logic with respect to the transient state can be
adapted to the actual apparatus which has been impossible.
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