Control apparatus for internal combustion

A contol apparatus for an internal combustion engine computing basic fuel injection period with an intake pressure and engine speed, computing a correction value from the change rate of the basic fuel injection period, and correcting the basic fuel injection period with the correction value, whereby the fuel injection rate is controlled. In order to prevent an excessive correction with the correction value at the time of rapid acceleration and rapid deceleration, the correction value is computed with the change rate restricted so as not to enlarge or the correction value is computed by multiplying a correction coefficient which is reduced in inverse proportion to the change rate and by the change rate. As a result, an excessive correction can be prevented so that over-rich and over-lean at the time of rapid acceleration and rapid deceleration can be prevented.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a control apparatus for an internal 
combustion engine, and, more particularly, to a control apparatus for an 
internal combustion engine capable of controlling fuel injection rate and 
ignition timing on the basis of detected intake pressure. 
2. Description of the Related Art 
Conventional, internal combustion engines equipped with a control apparatus 
have been known. The control apparatus computes periodically a basic fuel 
injection period on the basis of the detected intake pressure and the 
detected engine speed, obtains a fuel injection period by correcting the 
basic fuel injection period with intake air temperature and engine cooling 
water temperature, and opens the fuel injection valves to inject fuel for 
a period of time equal to the thus-obtained fuel injection period and 
injects the fuel. In this internal combustion engine, an acceleration fuel 
increment system is employed in order to improve engine response at the 
time of acceleration by detecting a change rate in the detected intake 
pressure and correcting the basic fuel injection period by an amount which 
is in proportion to the thus-detected change rate. 
In the above-described type of internal combustion engine which computes 
the basic fuel injection period on the basis of the intake pressure, a 
pressure sensor for sensing the intake pressure (absolute pressure) is 
attached to an intake pipe, and the basic fuel injection period is 
computed on the basis of the thus-sensed intake pressure. However, the 
detected values can be changed due to pulsations of the engine. These 
changes cause the basic fuel injection period to be changed, and correct 
control of, fuel inject:,on rate becomes impossible to be performed. 
In view of the foregoing, as disclosed in Japanese Patent Application 
Laid-Open No. 59-201938, the acceleration increment is performed by using 
two filters which have an individual time constant for weighting the 
output of the pressure sensor and completely erasing the pulsation 
component from the output of the pressure sensor, and an overshoot 
characteristic is given by subtracting the filter output having a 
relatively large time constant from the filter output having a small time 
constant. Then the acceleration increment is performed in accordance with 
the thus-obtained difference between the filter outputs. However, in this 
known method in which the two filters are used, since the amount of 
weighting of the output from the pressure sensor is enlarged by using the 
filter which has a relatively large time constant for the purpose of 
erasing the pulsation component, the response and resulting capability of 
the change of output from the filter with respect to the change in the 
actual change of the intake pressure can deteriorate. As a result, a delay 
in the acceleration increment attributable to the above will cause a 
deficiency in the fuel injection at the transient period of the 
acceleration and generation of a lean spike. Furthermore, in the case of 
the final stage of the acceleration, a rich spike can be generated due to 
the overshoot characteristic. 
To this end, in order to obtain a detected intake pressure of better 
response and following characteristics than in using the two filter, it 
has been recently proposed to process the output from the pressure sensor 
by using a CR filter which comprises a resistor and a condenser and which 
has a relatively reduced time constant but is capable of erasing the 
pulsation component, and to periodically convert the thus-obtained output 
from the CR filter into a digital value. In this case, since the pulsation 
component cannot be erased completely by the CR filter, two weighted 
means, each having individual relaxation or weighting amounts, are 
computed by using the thus-obtained digital value, that is, a digital 
filtering is performed, and the second weighted means having a relatively 
large weighting amount, is subtracted from the first weighted mean having 
a relatively small weighting amount so that the acceleration increment 
amount is determined on the basis of the thus-obtained difference. 
However, since the weighted means having the large weighting amount is used 
to obtain the acceleration increment amount in all of the above-described 
known methods, the response and following characteristics deteriorate. 
Therefore, there arises a phase delay of the acceleration increment 
generated in a drive pattern in which acceleration and deceleration are 
repeated, causing a case that the fuel injection rate does not meet a 
demand from the engine to increase the fuel. Consequently, a problem 
arises that the emission and driveability can deteriorate. It might, 
therefore, be considered feasible to obtain only a small weighting value 
but capable of erasing the engine pulsation component from the pressure 
sensor output, and to compute the fuel injection rate including the 
acceleration increment on the basis of the thus-obtained weighting value. 
In this method, a certain period of time needs to be taken for the time 
from computing the fuel injection period to the time at which the injected 
fuel reaches the combustion chamber this time being attributable to the 
affect of computing time and the time taken for the fuel to pass through 
the route. What is worse, a difference is generated between the intake 
pressure or weighted value used at the time of computing the fuel 
injection period and an intake pressure corresponding to the actual intake 
amount. As a result, it is impossible to conduct control with the air-fuel 
ratio demanded by the engine secured. 
This phenomenon will be described in detail with reference to FIG. 4. FIG. 
4 is a view which illustrates change in the computed basic fuel injection 
period TP and intake pressure PM at the time of acceleration of a 
4-cylinder 4-cycle internal combustion engine which has a capacity for 
fuel injection in the suction cycle once in one rotation of the engine by 
a quantity which is a half of the required quantity. In this case, since 
the fuel is arranged to be injected once in one rotation of the engine, 
that is twice in one cycle (referring to this figure, point c and point 
b), the quantity of fuel contributed to one combustion is, as can be 
clearly seen from this figure, a quantity corresponding to TPc+TPb. 
However, the intake pressure representing the actual amount of intake air 
at the time of combustion is the intake pressure illustrated by symbol a 
when the suction cycle is completed (at the lower dead center in the 
suction cycle). As described above, the existence of a time delay tD 
between the intake pressure at the time of computing the fuel injection 
period and the intake pressure representing the actual amount of intake 
air at the time of combustion causes is to be impossible for fuel to be 
injected in accordance with the actual amount of intake air. As a result, 
it becomes impossible to conduct control with the air-fuel ratio demanded 
by the engine secured. On the other hand, it might, therefore, be 
considered feasible to reduce the time delay tD to the extent which can be 
neglected by reducing the computing time or the like (if the lower dead 
center in the suction cycle and the point b coincide with each other). 
However, in the internal combustion engines which injects fuel once during 
one engine rotation, fuel is supplied only by a quantity, corresponding to 
TPc+TPb although the amount of fuel corresponding to 2TPb needs to be 
supplied during one cycle. As a result, the fuel quantity becomes lessened 
by an amount obtained by TPb-TPc (=.DELTA.TP) at the time of acceleration. 
To this end, the applicant of the present invention has proposed a known 
method capable of correcting the amount of fuel shortage .DELTA.TP (see 
Japanese Patent Application No. 61-277019 (Japanese Patent Application 
Laid-Open No. 63-131840) and Japanese Patent Application No. 61-277020 
(Japanese Patent Application Laid Open No. 63-131841). 
The principle of these known arts will be described referring to a 
4-cylinder 4-cycle internal combustion engine which injects fuel once 
during one engine rotation. 
As described with reference to FIG. 4, neglecting the time delay tD after 
computing the fuel injection period, the basic, fuel injection period TP 
corresponding to the actual amount of intake air can be expressed by the 
following formula (1). 
EQU TP=TPb+.DELTA.TP (1) 
On the other hand, it is assumed that the acceleration is performed at a 
constant speed as shown in FIG. 5. Since difference .DELTA.TP in the basic 
fuel injection period between that at the point b and that at the point C 
and the difference .DELTA.TP' in the basic fuel injection period at the 
point b and point b' are equal to each other, the basic fuel injection 
period TPb' at point b' can be expressed by the following formula (2) by 
using the basic fuel injection period TPb at the point b and the 
above-described .DELTA.TP (=TP'). 
EQU TPb'=TPb+.DELTA.TP (2) 
Assuming that the basic fuel injection period is performed every 
360.degree. CA, a basic fuel injection period advanced by 360.degree. CA 
from the point b is, as will be understood from the formula (2), 
estimated. 
Accordingly, assuming that the calculation of the basic fuel injection 
period is performed every CY [.degree.CA], and converting the time delay 
tD between the point a and point b shown in FIG. 4 into a crank angle CAD, 
the amount of correction corresponding to this crank angle CAD can be 
derived as follows. 
##EQU1## 
As a result, the basic fuel injection period advanced by the predetermined 
crank angle CAD from the point b can be estimated. Therefore, considering 
the correction at the change from the point c to point b, basic fuel 
injection period TP corresponding to the actual amount of intake air when 
used at the time of computing the basic fuel injection period every CY 
[.degree.CA] can be expressed by the following formula (4) using the basic 
fuel injection period TP.sub.0 computed immediately before the lower dead 
center in the suction cycle. 
EQU TP=TP.sub.0 +k.multidot..DELTA.TP (4) 
where k represents 
##EQU2## 
and .DELTA.TP represents the difference obtained by subtracting the basic 
fuel injection period computed CY [.degree.CA] previously from the present 
basic fuel injection period TP.sub.0. The thus obtained difference becomes 
a positive value in the case of acceleration, while the same becomes a 
negative value in the case of deceleration. 
In the case where the CR filter is used, the CR filter output can be 
considered to substantially represent the actual intake pressure 
attributable to the excellent response of the same with respect to the 
change in the actual change in the intake pressure. However, weighted mean 
(corresponding to the weighted value) for computing the basic fuel 
injection period is delayed, as shown in FIG. 6, behind the actual intake 
pressure. This delay (control delay tD') can be generated due to the delay 
in detection by the pressure sensor, the delay in transmitting a signal 
through the input circuit, the delay in computing timing due to any of the 
above-described types of delay, the delay in the computing period, and 
delay caused from weighting the CR filter outputs. Therefore, it is 
necessary to estimate the fuel injection period by estimating the actual 
intake pressure PMb taking into consideration the control delay tD' 
(corresponding to crank angle CAD') from the PMb' for computing the fuel 
injection rate at Point "b" shown in FIG. 6, computing the basic fuel 
injection period on the basis of the thus-obtained estimated value and 
consideration of the above-described time delay tD. 
Therefore, including the correction of the control delay tD' (=CAD') in the 
above-described formula (4), the fuel injection period TP can be expressed 
as follows. 
EQU TP=TP.sub.0 +K.sub.1 .multidot..DELTA.TP (5) 
##EQU3## 
In a case where the basic fuel injection period TP is calculated from the 
intake pressure PM and engine speed NE, the formula (5) can be expressed 
by the following formula (6) by using the difference in the weighting 
value of the intake pressure (value obtained by subtracting the weighting 
value for computing the basic fuel injection period by CY.degree.CA 
earlier from the present weighting value for computing the basic fuel 
injection period), that is, by using the change rate .DELTA.PM in the 
weighting value, since TP.varies.PM 
EQU TP=TP.sub.0 +K.sub.1 .multidot..DELTA.PM.multidot.C (6) 
where C represents a proportional constant for converting the intake 
pressure into the fuel injection period. 
Since the above-described control time delay tD' can be assumed to be 
substantially constant as to the time periodical phenomenon, it is 
enlarged in proportion to the engine speed. The crank angle CAD' can be 
obtained by calculation, and the value K.sub.1 at each of the engine 
speeds can be obtained regardless of the error at the time of 
manufacturing the engines to be tested. Although the case is described in 
which the basic fuel injection period is computed at every predetermined 
crank angle (CY.degree. CA) in the above-described description, the method 
can be embodied in a case where the basic fuel injection period is 
computed periodically. In this case, although the correction of CAD' with 
the engine speed becomes needless, the delay is affected by the engine 
speed. Therefore, the overall amount of K.sub.1 needs to be subjected to 
correction with the engine speed. In the above description, the case where 
fuel is injected once during one rotation of the engine is described 
above. However, in the case of an individual injection system in which 
each of the cylinders individually injects fuel, the above described time 
delay tD' causes it to become impossible for fuel to be injected in 
accordance with the actual amount of intake air. Therefore, it is 
preferable to estimate the intake pressure (pressure in the vicinity of 
the lower dead center in the suction cycle) representing the actual amount 
of intake air at the time of computing the fuel injection period which is 
advanced by one cycle from computing the present basic fuel injection 
period. As a result, the method can be embodied in individual injection 
engines. 
However, in the known method in which the basic fuel injection period TP is 
computed with the formulas (5) and (6), the change rate .DELTA.PM becomes 
too large a value at a time of rapid acceleration. This leads to the 
generation of an overshoot of the fuel injection period TAU as shown in 
FIG. 12 (1), causing the air-fuel ratio to become too rich. As a result CO 
and HC emissions are increased and driveability is worsened. Furthermore, 
in the internal combustion engines described above, since the basic 
ignition advance is obtained from the weighted value of the intake 
pressure and the engine speed, and the thus obtained basic ignition 
advance at the time of acceleration is corrected by the change rate 
.DELTA.PM, the correction of the basic ignition advance with the change 
rate .DELTA.PM becomes incorrect at a time of rapid acceleration. 
Furthermore, since the correction with the change rate .DELTA.PM becomes 
incorrect at the time of rapid deceleration, the fuel injection rate and 
ignition timing cannot meet the demand of the engine, causing worsened 
driveability and emission. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a control apparatus for 
an internal combustion engine capable of bringing the control factor to a 
suitable level by correctly performing a correction at the time of rapid 
acceleration or rapid deceleration when the internal combustion engine is 
controlled by computing the control factor, such as basic fuel injection 
period, basic ignition advance and so on, from a weighted value of the 
intake pressure. 
It is another object of the present invention to provide a control 
apparatus for an internal combustion engine capable of making a control 
factor a suitable value by properly performing correction over the entire 
region covering rapid acceleration and rapid deceleration when the 
internal combustion engine is controlled as described above. 
In order to achieve the above-described objects, the first aspect of the 
present invention lies in a control apparatus, an embodiment of which is 
shown in FIGS. 2 and 3, comprising: a pressure sensor A for detecting 
intake pressure; a weighting means B for obtaining a weighting value which 
weights the change in a signal transmitted from the pressure sensor A; a 
control factor computing means C for computing a control factor for 
controlling the engine on the basis of the weighting value; a change rate 
computing means D for computing a change rate of the weighting value or 
the control factor; a correction means H for correcting the control factor 
on the basis of a correction value by performing control to prevent an 
increase in the correction value which is computed on the basis of the 
change rate; and a control means G for controlling the engine on the basis 
of the control factor which has been corrected by the correction means H. 
The weighting means B according to the present invention obtains the 
weighting value by weighting the signal transmitted from the pressure 
sensor that detects the intake pressure. The weighting value can be 
obtained from the weighted mean which has been computed previously with 
the weight of the weighted mean weighted and a present weighted means 
computed with the present level of the signal transmitted from the 
pressure sensor A. That is, the weighted means PMNi derived from the 
following formula (7) can be used as the weighting value. 
##EQU4## 
where PMNi-1 represents a weighted mean which has been previously 
computed, PMAD represents the present level of the signal transmitted from 
the pressure sensor and N is a coefficient related to the weighting. The 
same can employ a value obtained by directly converting the output 
transmitted from the pressure sensor into a digital value or a value 
obtained by converting the output from the pressure sensor which has been 
processed by the CR filter into a digital value. Such a weighted mean can 
be obtained through a digital filtering treatment. 
The control factor computing means C computes the control factor for 
controlling the engine on the basis of the weighting value. The control 
factor can be exemplified through a basic fuel injection period and a 
basic ignition advance. This control factor computing means C controls at 
least one of the basic fuel injection periods and the basic ignition 
advance. The change rate computing means D computes the change rate of the 
weighting value or the change rate of the control factor. The correction 
means H corrects the control factor by restricting the correction value 
determined on the basis of the change rate. The control means G controls 
the engine on the basis of the thus-corrected control factor. Since the 
correction is, as described above, so performed the correction value is 
not enlarged and the control factor can be prevented from being 
excessively enlarged. 
As described above, since the control is performed so that the control 
factor cannot be enlarged excessively, the excessive correction 
attributable to the change rate at the time of rapid acceleration and 
rapid deceleration can be prevented. As a result, emission and 
driveability can be improved. 
The second aspect of the present invention lies in, as shown in FIG. 2, a 
control apparatus comprising: a restriction means E for restricting the 
correction means H in such a manner that the change rate does not exceed a 
predetermined level; and a control factor correction means F for 
correcting the control factor on the basis of the change rate which has 
been restricted by the restriction means E. The restriction means E 
restricts the change rate which has been computed by the change rate 
computing means D in such a manner that the same does not exceed the 
predetermined level. The control factor correction means F corrects the 
control factor which has been computed by the control factor computing 
means C on the basis of the change rate restricted as described above. The 
control means G controls the engine on the basis of the thus-corrected 
control factor. Since the restriction is performed so that the change rate 
does not exceed the predetermined level, and thereby the correction value 
is restricted from being enlarged, an excessive correction can be 
prevented and thus the correction can be performed correctly. 
With the restriction means, excessive correction at the time of rapid 
acceleration can be prevented attributable to the control being performed 
in such a manner that the change rate does not exceed a predetermined 
positive level at the time of rapid acceleration. Another type of 
excessive correction at the time of rapid deceleration can be prevented 
attributable to the control being performed in such a manner that the 
change rate does not exceed a predetermined negative level (does not 
become below the predetermined negative level). In addition, an excessive 
correction at the time of rapid deceleration can be prevented by 
performing a restriction in such a manner that the absolute value of the 
change rate does not exceed a predetermined level. 
As described above and according to the present invention, since the change 
rate of the weighting value and the change rate of the control factor are 
restricted not the exceed the corresponding predetermined levels, 
excessive correction at the time of rapid acceleration and rapid 
deceleration can be prevented. As a result, an effect can be obtained 
where emission and driveability can be improved. 
The third aspect of the present invention lies in a control apparatus 
comprising: a coefficient setting means I for setting a correction 
coefficient which is inverse to the absolute value of the change rate; and 
a control factor correction means J for correcting the control factor on 
the basis of a produce of the change rate and the correction coefficient. 
The coefficient setting means I determines the correction coefficient which 
is inverse to the absolute value of the change rate. The correction means 
J corrects the control factor which has been computed by the control 
factor computing means C on the basis of the product of the change rate 
and the correction coefficient. The control means G controls the engine on 
the basis of the thus-corrected control factor. Since the correction 
coefficient is, as described above, arranged to be reduced inverse to the 
absolute value of the change rate, the correction value can be reduced as 
much as possible at the time of rapid acceleration or deceleration in 
which the absolute value of the change rate is enlarged. Therefore, the 
response of excessive correction can be sufficiently maintained in the 
region in which the absolute value of the change rate is reduced at the 
transient period of acceleration or deceleration. In addition, the 
correction value can be continuously reduced from the intermediate period 
of the acceleration of deceleration to the final period of the same 
through which the absolute value of the change rate is enlarged so that 
overshoot can be significantly reduced. In addition overshoot in the 
acceleration and the deceleration regions in which the absolute value of 
the change rate is relatively small can be significantly reduced since the 
correction coefficient become small in inverse proportion to the absolute 
value of the change rate from the transient period of acceleration and 
deceleration to the intermediate period of the same. 
As described above, according to the present invention, since the control 
factor is corrected by using the correction coefficient which can be 
reduced in inverse proportion to the absolute value of the change rate, 
overshooting can be reduced over a region from rapid acceleration and 
deceleration to moderate acceleration and deceleration with the transient 
response to excessive correction secured. As a result, the effects of 
improvement in emission and driveability can be obtained.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of the present invention will be described in detail with 
reference to the drawings. In the description given hereinafter, a case in 
which a fuel injection period is used as a control factor will be 
described in principle. FIG. 7 illustrates schematically an internal 
combustion engine provided with a fuel injection rate control apparatus in 
which the present invention can be embodied. 
This engine is arranged to be controlled by an electronic control circuit 
such as a microcomputer. Down stream from an air cleaner (omitted from 
illustration), a throttle value 8 is disposed. A linear throttle sensor 10 
which transmits a voltage corresponding to the throttle opening degree, is 
attached to this throttle valve 8, and a surge tank 12 is provided down 
stream from the throttle valve 8. A semiconductor type pressure sensor 6 
is attached to the surge tank 12. The pressure sensor 6 is connected to a 
filter 7 (see FIG. 8) comprising a CR filter having a small time constant 
(for example 3 to 5 msec) and exhibiting an excellent response for erasing 
a pulsation component from intake pressure. The filter may be included 
within the pressure sensor. Furthermore, a bypass 14 is disposed in such a 
manner that it bypasses the throttle valve 8 and communicates up stream 
from the throttle valve 8 and the surge tank 12 which is disposed down 
stream from the throttle valve 8. An ISC (Idle Speed Control) valve 16B is 
disposed within this bypass 14. The degree of opening of this ISC valve 
16B is adjusted by a pulse motor 16A which includes a 4-pole stator. The 
surge tank 12 is connected to a combustion chamber of an engine 20 via an 
intake manifold 18 and an intake port 22. A fuel injection valve 24 is 
respectively attached to the cylinders in such a manner that these 
injections valves 24 project into a space within the intake manifold 18. 
The combustion chamber of the engine 20 is connected to a catalyser device 
(omitted from illustration) filled with a catalytic converter rhodium via 
an exhaust port 26 and an exhaust manifold 28. An O.sub.2 sensor for 
transmitting a signal which is inverted at a theoretical air fuel ratio is 
attached to this exhaust manifold 28. A cooling water temperature sensor 
34 is attached to an engine block 32 in such a manner that the cooling 
water temperature sensor 34 penetrates the engine block 32 and projects 
into a space within a water jacket. This cooling water temperature sensor 
34 transmits a water temperature signal by detecting the temperature of 
the engine cooling water which represents the engine temperature. The 
engine temperature may be represented by the detected engine oil 
temperature. 
An ignition plug 38 is respectively attached to the cylinders in such a 
manner that the ignition plug 38 penetrates a cylinder head 36 and 
projects into the combustion chamber. These ignition plugs 38 are 
connected to an electronic control circuit comprising a microcomputer via 
a distributor 40 and an igniter 42. A cylinder determining sensor 46 and a 
rotation angle sensor 48, each of which is composed of a signal rotor 
secured to a distributor shaft and a pickup secured to a distributor 
housing, are attached within the distributor 40. The cylinder determining 
sensor 46 transmits a cylinder determination signal, for example, every 
720.degree. CA, while the rotation angle sensor 48 transmits an engine 
speed signal, for example, every 30.degree. CA. 
As shown in FIG. 8, the electronic control circuit 44 comprises: a 
microprocessing unit (MPU) 60, a read only memory (ROM) 62, a random 
access memory (RAM) 64, a backup RAM (BU-RAM) 66, an input/output port 68, 
an input port 70, output ports 72, 74, and 76, and a data bus and control 
bus 75 connecting the above described components. An analog to digital 
(A/D) converter 78 and a multiplexer 80 are connected to the input/output 
port 68 in the sequential order of this description. The pressure sensor 6 
is connected to the multiplexer 80 via the CR filter 7 composed of a 
resistor R, a condenser C, and a buffer 82, and the cooling water 
temperature sensor 34 is also connected to the same via a buffer 84. The 
linear throttle sensor 10 is connected to the multiplexer 84. The MPU 60 
controls the multiplexer 80 and the A/D converter 78, and successively 
converts the output from the pressure sensor 6, the output from the linear 
throttle sensor 10 and that from the cooling water temperature sensor 34 
inputted through the CR filter 7 into digital signals, and has the 
thus-obtained digital signals stored in the RAM 64. Therefore, the 
multiplexer 80, the A/D converter 78 and the MPU 60 serve as sampling 
means for periodically sampling the output from the pressure sensor. The 
O.sub.2 sensor 30 is, via a comparator 88 and a buffer 86, connected to 
the input port 70. The cylinder determining sensor 46 and the rotational 
angle sensor 48 are also connected to the input port 70 via the wave 
shaping circuit 90. The output port 72 is connected to the igniter 42 via 
a drive circuit 92. The output port 74 is connected to the fuel injection 
valve 24 via a drive circuit 94 provided with a down-counter. The output 
port 76 is connected to the pulse motor 16A of the ISC valve via a drive 
circuit 96. Reference numeral 98 represents a clock, and 99 represents a 
timer. The above-described ROM 62 previously stores a program for a 
control routine which will be described hereinafter. 
A control routine according to the present invention will be described in 
the case where the present invention is embodied in the above-described 
engine and a weighting value is detected with a weighted mean obtained by 
calculation. Although the values which do not obstruct the thesis of the 
present invention are used in the description given hereinafter, the 
present invention is not limited to these values. 
FIG. 9 illustrates an A/D converting routine executed every 4 msec. In step 
100, a signal transmitted from the pressure sensor 6 is supplied to the 
A/D converter 78 via the CR filter 7, buffer 82 and the multiplexer 80. 
The intake pressure PM which has been digitally converted by the A/D 
converter 78 is taken in as digital value PMAD. In the next step 102, a 
weighted means PMNi of the present intake pressure is computed in 
accordance with the formula (7) by using the digital value PMAD of the 
intake pressure and the weighted mean PMNi-.sub.1 of the intake pressure 
computed previously by 4 msec, arranging the weight coefficient N (for 
example 4) of the formula (7) to be n. In step 104, in order to compute 
the next weighted mean of the intake pressure, the weighted mean PMNi of 
the present intake pressure is stored in the 4 ms register as the weighted 
mean PMNi-.sub.1 of the previous intake pressure. 
FIG. 1 illustrates a routine for computing a fuel injection period which is 
carried out at every fuel injection period computing timing (in a 
4-cylinder 4-cycle engine it is every 360.degree. CA). In step 110, 
coefficient K.sub.1 is computed and also coefficient C is taken in. This 
coefficient K.sub.1 is obtained as shown in FIG. 10 by taking engine speed 
NE in step 106 and computing the coefficient K.sub.1 corresponding to the 
present engine speed NE from the map shown in FIG. 11 in step 108. The 
coefficient K.sub.1 is stored in the ROM in the form of a map obtained by 
a calculation. This coefficient K.sub.1 is expressed by an increasing 
function, increasing from 1.0 in accordance with a rise in the engine 
speed NE as shown in FIG. 11. In this case, the coefficient C may be 
either a constant or a variable. 
In the next step 112, the weighted mean of the present intake pressure is 
taken in as PMN. Since the weighted mean PMNi of the present intake 
pressure is stored in the register as PMNi-.sub.1 in step 104 shown in 
FIG. 9, the weighted mean of the present intake pressure can be taken in 
as PMN by reading the value of this register. In the next step 114, the 
present basic fuel injection period TP.sub.0 is computed conventionally by 
using the weighted mean PMN of the present intake pressure which has been 
taken in step 112 and the engine speed NE. In the next step 116, the 
change rate .DELTA.PM of the weighted mean of the intake pressure is 
computed by subtracting the weighted mean PMNO of the previous intake 
pressure used for computing the previous basic fuel injection period CA 
360.degree. CA from the weighted means PMN of the present intake pressure. 
In the next step 118, it is determined whether the change rate .DELTA.PM 
exceeds a predetermined negative value -.alpha. (for example -50 
mmHg/rotation) or not. If .DELTA.PM &lt;-.alpha., it is determined that the 
present state is in a rapid deceleration state and, in step 120, the value 
of the .DELTA.PM is made -.alpha. for the purpose of preventing the change 
rate .DELTA.PM from becoming less than -.alpha.. On the other hand, in 
step 122, with .DELTA.PM.gtoreq.-.alpha., it is determined whether the 
change rate .DELTA.PM is below a positive predetermined value .beta. (for 
example 50 mmHg, one rotation) or not. If .DELTA.PM&gt;.rarw..beta., it is 
determined that the state is in a rapid acceleration state, and in step 
124, the change rate .DELTA.PM is made .beta. in order to prevent 
.DELTA.PM from exceeding .beta.. 
Next, in step 126, the coefficient K.sub.1 is computed in step 108, the 
change rate .DELTA.PM of the weighted means of the intake pressure 
computed in step 116, and the coefficient C for converting the intake 
pressure into the fuel injection period are multiplied so as to compute 
the increment TC {which corresponds to the second term on right side of 
the formula (6)}. In step 128, by adding the increment TC to the 
present basic fuel injection period TP.sub.0, the present basic fuel 
injection period TP.sub.0 is corrected. Then, in step 130, the weighted 
mean PMN of the present intake pressure is stored in the register in place 
of the weighted mean PMNO of the intake pressure which was the pressure 
360.degree. CA previously. In step 132, the basic fuel injection period TP 
is corrected by intake air temperature and engine cooling water 
temperature so as to compute the fuel injection period TAU. As a result, 
fuel is injected once during a rotation of the engine in a fuel injection 
rate controlling routine (omitted from illustration). 
In the above-described step 132, the basic fuel injection period TP used 
for computing the fuel injection period TAU is corrected in accordance 
with the formula (6) described in step 128 and delay attributable to the 
control delay can be prevented. As a result, since the corrected value 
corresponding to the actual air intake amount can be obtained, a change in 
the air-fuel ratio at the time of mode change is prevented. Since the 
change rate of the weighted mean of the intake pressure is restricted in 
step 120 or step 124, the excessive correction at the time of rapid 
acceleration and deceleration can be prevented. The change in the fuel 
injection time TAU becomes as illustrated in FIG. 12 (2) and the overshoot 
corresponding to hatching is prevented. Alternatively to .DELTA.PM, 
.DELTA.TP may be employed to compute the fuel injection period TAU on the 
basis of the formula (5). 
Next, a second embodiment of the present invention will be described. 
Similar to the first embodiment, if control is performed with .DELTA.TP or 
.DELTA.PM.multidot.C in order to make the correction amount K.sub.1 
.multidot..DELTA.TP (or K.sub.1 .multidot..DELTA.PM.multidot.C) a suitable 
value in a rapid change state, the overshoot can be rapidly reduced in the 
regions in which these values exceed the upper or lower limits .beta. and 
-.alpha.. However, the above-described overshoot can be generated in the 
regions which do not reach the upper limit, causing driveability and 
emission to deteriorate. 
To this end, the second embodiment is arranged to be capable of performing 
a proper correction over the entire region of rapid acceleration and rapid 
deceleration. 
A control routine according to the second embodiment in the case where the 
present invention is embodied in the above-described engine and the 
weighted value is detected by the weighted mean obtained by a calculation, 
will be described with reference to FIG. 13. 
The components shown in FIG. 13 and corresponding to those in FIG. 1 are 
given the same reference numerals and the description is omitted. 
Since a routine for computing the weighted mean PMNi is the same as that 
shown in FIG. 9 and a routine for computing the coefficient K.sub.1 is the 
same as that shown in FIG. 10, the descriptions are omitted. 
In step 116, the change rate .DELTA.PM of the weighted mean of the intake 
pressure is computed, then, in step 140, correction coefficient K.sub.0 
corresponding to the present change rate .DELTA.PM is computed from the 
map for the correction coefficient K.sub.0 represented by the function of 
the change rate .DELTA.PM shown in FIG. 14. This correction coefficient 
K.sub.0 is arranged to become smaller in the region .DELTA.PM.gtoreq.0 in 
inverse proportion to the .DELTA.PM, while becoming smaller in the region 
.DELTA.PM&lt;0 in proportion to .DELTA.PM, it being, as a whole, arranged to 
be reduced in inverse proportion to .vertline.{PM.vertline.. The curve 
which indicates the correction coefficient K.sub.0 is asymmetric with 
respect to the axis of the ordinate, and the change ratio of the 
correction coefficient K.sub.0 in the region .DELTA.PM&lt;0 is arranged to be 
larger than that in the region .DELTA.PM.gtoreq.0. The reason for this 
lies in that an engine pumping action shown generally at the time of 
deceleration causes a relatively larger change in the intake pressure than 
for the intake pressure at the time acceleration. Therefore, the change in 
the correction coefficient K.sub.0 is larger in the region .DELTA.PM&lt;0 
than in the region .DELTA.PM.gtoreq.0. The correction coefficient is 
determined properly in accordance with the types of the engines, and it 
may be determined as to become symmetrical with respect to the axis of 
ordinate. The dashed line in FIG. 14 represents the change in the 
correction coefficient K.sub.0 equal to the case where the limitation 
.DELTA.PM=.beta. is realized when .DELTA.PM&gt;0 (for example, 50 
mmHg/rotation). As can be clearly seen from this figure, the correction 
coefficient can be smoothly reduced according to this embodiment and the 
overshooting can be suitably reduced in any acceleration and deceleration 
cases. In addition, since the correction coefficient is retained in the 
form of the map, an enlarged freedom upon the application can be obtained. 
In the next step 146, the coefficient K.sub.1 computed in step 108, 
correction coefficient K.sub.0 computed in step 140, change rate .DELTA.PM 
of the weighted mean of the intake pressure computed in step 116, and 
coefficient C for converting the intake pressure into the basic fuel 
injection period are multiplied so as to compute the increment TC. As a 
result, as described in the first embodiment, fuel is injected once during 
a rotation of the engine in accordance with the fuel injection rate 
control routine (omitted from the illustration). 
In step 132, since the basic fuel injection period Tp used for computing 
the fuel injection period TAU is corrected on the basis of the 
above-described formula (6) with the excessive correction prevented with 
the correction coefficient K.sub.0, the delay due to the control delay can 
be prevented. As a result, the correction value corresponding to the 
actual amount of intake air can be obtained. Therefore, the change in the 
air-fuel ratio at the time of rapid change can be prevented. The change in 
the fuel injection period TAU at this time becomes as shown in FIG. 15 (B) 
so that the transient response at the rapid change can be sufficiently 
maintained and the overshooting can be reduced. FIG. 15 (A) illustrates 
the change in the fuel injection period according to the first embodiment. 
In the case where the coefficient K.sub.1 is changed in accordance with the 
engine speed as described above, it is necessary for the fuel to be 
increased more in the case where the engine is at a low temperature. That 
is, the engine cooling water temperature is at a low temperature than in 
the case where the engine cooling water temperature is at a high 
temperature since the amount of fuel adhered to the inner wall of the 
intake manifold becomes larger. Therefore, it may be arranged in such a 
manner that the coefficient K.sub.1 is expressed by a function of the 
engine speed and the engine cooling water temperature, and the coefficient 
K.sub.1 is enlarged in proportion to the rise in the engine speed, and the 
coefficient K.sub.1 is reduced in accordance with the rise in the engine 
cooling water temperature. In addition, the coefficient K.sub.1 is 
determined as function f (PMW) of the weighted mean PMN, and also the same 
may be determined as function f (NE, THW, PMW) of the engine speed NE, 
engine cooling water temperature THW and the weighted mean PMN. 
In the first embodiment, although the increment TC is computed in 
accordance with the second term of the formula (6) from the change rate 
.DELTA.PM of the weighted mean of the intake pressure so as to restrict 
the change rate .DELTA.PM, the increment may be computed from the change 
rate .DELTA.TP of the basic fuel injection period in accordance with the 
second term of the formula (5). In this case, the change rate .DELTA.TP of 
the basic fuel injection period may be restricted. 
In the second embodiment, although the increment TC is computed by 
multiplying the correction coefficient K.sub.0 and the second term of the 
formula (6) from the change rate .DELTA.PM of the weighted mean of the 
intake pressure and the correction coefficient K.sub.0, it may be computed 
by multiplying the correction K.sub.0 and the second term of the formula 
(5). Therefore, the increment TC may be computed from the change rate 
.DELTA.PM of the basic fuel injection period and the correction 
coefficient K.sub.0. In addition, although the correction coefficient 
K.sub.0 is arranged to be reduced in inverse proportion to the absolute 
value of the change rate .DELTA.PM of the weighted mean of the intake 
pressure, it may be arranged to be reduced in inverse proportion to the 
absolute value of the change rate .DELTA.PM of the basic fuel injection 
period. 
Furthermore, an arrangement may be employed in which the basic fuel 
injection period is arranged to be corrected by the following term (8). 
EQU K.sub.2 .multidot.DLPMIi.multidot.C (8) 
where K2 represents a second coefficient and can be, as shown in FIGS. 16 
and 17, changed in accordance with any of the engine speed, engine cooling 
water temperature and the intake pressure. The DLPMIi is an estimation of 
a damped value being the difference between the present weighted value 
expressed by the following formula (9) and the weighted value detected one 
period previously. It can be considered that if the engine speed NE is 
raised, the intake air velocity is also raised, and amount of fuel adhered 
to the inner wall of the intake manifold becomes reduced so that a major 
portion of the fuel can be supplied to the combustion chamber. To this 
end, the coefficient K.sub.2 is arranged to be reduced in accordance with 
the rise in the engine speed. When the engine cooling water temperature is 
raised, the amount of evaporation of fuel adhered to the inner wall of the 
intake manifold becomes reduced. Therefore, the coefficient K.sub.2 is 
arranged to be reduced in accordance with the rise in the engine cooling 
water temperature. In addition, when the intake pressure is raised, the 
amount of fuel evaporation becomes reduced and the amount of fuel adhered 
to the inner wall of the intake manifold becomes larger. Therefore, the 
coefficient K.sub.2 can be determined as to be enlarged in proportion to 
the weighted mean of the intake pressure in the following formula (9), 
EQU DLPMIi=.DELTA.PM+K.sub.3 .multidot.DLPMIi-.sub.1 (9) 
K.sub.3 represents a positive damping coefficient and DLPMIi-.sub.1 
represents an estimation computed in the previous cycle. This dampling 
coefficient K.sub.3 may employ a constant, and alternatively, may be 
determined, similarly to the coefficient K.sub.2, on the basis of the 
engine speed NE, weighted mean PMN of the intake pressure, and the engine 
cooling water temperature THW. In the case where the coefficient K.sub.3 
is changed, the damping speed is lowered by enlarging the coefficient 
K.sub.3 in the change state of the operation in which the amount of fuel 
adhered to the inner wall of the intake manifold increases, while the 
damping speed is raised by reducing the coefficient K3 in the change state 
of the operation in which the amount of fuel adhered to the inner wall of 
the intake manifold is decreased. 
Assuming that the initial value of the estimation is 0, the difference 
.DELTA.PM is changed as .DELTA.PM.sub.1, .DELTA.PM.sub.2, . . . , 
.DELTA.PMi during one calculation in the formula (9), and the i-th DLPMIi 
can be expressed by the following formula (10). 
##EQU5## 
Therefore, the estimation value is gradually enlarged from start of the 
,acceleration, and it is arranged to be a certain value from after 
completion of the acceleration to the time the same comes close to 0 by 
the damping coefficient K.sub.3. 
Simultaneously carrying out the correction for estimating the basic fuel 
injection period corresponding to the actual amount of intake air and the 
correction shown in the term (8), the basic fuel injection period TP 
becomes as expressed by the following formula (11) or formula (12). 
EQU TP=TP.sub.0 +K.sub.1 .multidot..DELTA.PM.multidot.C+K.sub.2 
.multidot.DLPMIi.multidot.C (11) 
EQU TP=TP.sub.0 +K.sub.1 .multidot..DELTA.TP+K.sub.2 .multidot.DLTPIi(12) 
Furthermore, simultaneously carrying out the correction for estimating the 
basic fuel injection period corresponding to the actual amount of intake 
air, the correction expressed by the term (8), and the correction with the 
correction coefficient K.sub.0, the basic fuel injection time TP becomes 
as shown in the following formula (13) or formula (14). 
EQU TP=TP.sub.0 +K.sub.0 .multidot.K.sub.1 
.multidot..DELTA.PM.multidot.C+K.sub.2 .multidot.DLPMIi.multidot.C(13) 
EQU TP=TP.sub.0 +K.sub.0 .multidot.K.sub.1 .DELTA.TP+K.sub.2 
.multidot.DLTPIi(14) 
where DLTPIi in the formula (14) is the estimation of the damping value of 
the difference between the present basic fuel injection period expressed 
by the following formula (15) and the basic fuel injection period one 
cycle before. 
EQU DLTPIi=.DELTA.TP+K.sub.3 .multidot.DLTPI-.sub.1 (15) 
Putting the intial value of the estimation to 0 in the formula (15) and 
assuming that the difference .DELTA.TP is changed during i times of 
calculations as .DELTA.TP.sub.1, .DELTA.TP.sub.2, . . . , .DELTA.TPi, the 
DLTPIi at the i-th time becomes the formula obtained by replacing 
.DELTA.PM in formula (10) by .DELTA.TP. 
The K1, K2, and K3 used in the formulas (11), (12), (13), and (14) may be 
determined on the basis of the engine speed, engine cooling water 
temperature or absolute intake air pressure in order to cover a wide range 
of changing states of operation. The coefficients which cannot change the 
demand of the fuel injection rate in the changing states of operation even 
if each of the parameters thereof are changed may be defined as constants. 
Experimental results of the changes in the acceleration increment and the 
air-fuel ratio when the basic fuel injection period is corrected as 
described above in the state where the engine is cooled will be described 
classifying the cases into a case where the present basic fuel injection 
period TP: is not corrected, a case where value KH corresponding to the 
engine warm period is used as the value of K.sub.1 and a case where the 
value Kc (&gt;KH) corresponding to the engine cool period is used as the 
value of K.sub.1. In order to simplify the description, it is arranged 
that K.sub.0 =1.0. As shown in FIG. 18 (A), in the acceleration operation 
in which the intake pressure is changed from PM.sub.1 to PM.sub.2 when the 
engine is in the cooled state, if the fuel is injected on the basis of the 
present fuel injection period TP.sub.0, the increment becomes 0 and the 
air-fuel ratio is changed as shown in FIG. 18 (C), causing the excessive 
lean spikes to be generated. As a result, the emission and the 
driveability can deteriorate. Although the lean spikes can be halved by 
correcting this basic fuel injection period TP.sub.0 and injecting fuel on 
the basis of TP.sub.0 +KH.multidot..DELTA.PM.multidot.C, a case where the 
change of the air-fuel ratio has not been as yet reduced can occur. The 
reason for this can be considered to lie in that the change in the amount 
of fuel adhered to the inner wall of the manifold is too large when the 
temperature of the engine has been lowered. If the value of K.sub.1 is 
further enlarged, value Kc which is suitable for the case where the engine 
is at a low temperature is used, and fuel is injected on the basis of 
TP.sub.0 +K.sub.c .multidot..DELTA.PM.multidot.C, so that the lean spike 
at the initial acceleration can be, as shown in FIG. 18 (C), substantially 
overcome. However, the lean spikes can remain in the latter stage of the 
acceleration and the final state of the acceleration. The reason for this 
can be considered to lie in that the intake pressure becomes enlarged at 
the latter stage of the acceleration and the final stage of the 
acceleration, causing the amount of fuel evaporation to be reduced, and 
thereby causing the amount, of adhesion to the inner wall of the intake 
manifold to become enlarged. 
Considering the above-described phenomenon, in the formulas (11), (12), 
(13), and (14), the present fuel injection period is corrected on the 
basis of a product of: the change rate expressed by the difference between 
the present basic fuel injection period and the basic fuel injection 
period computed one cycle before or the difference between the present 
weighted value and the weighted value detected one cycle before; and a 
first coefficient changed in accordance with the engine speed, and a 
product of the damping value of the change rate and the second 
coefficient. Since the estimation of this damping value maintains a 
certain value even after the acceleration is in the final stage or the 
acceleration has been completed, the lean spikes which can be generated in 
the final stage of the acceleration and after the acceleration has been 
completed when the basic fuel injection period is corrected by 
substituting K.sub.1 as for K.sub.c can be prevented. As a result, the 
air-fuel ratio at the time of changing states of operation, for example, 
changing acceleration, can be made substantially constant as shown by a 
continuous line in FIG. 18 (C) where only the air-fuel ratio corresponding 
to the formulas (11) and (13) are illustrated. 
Although the case where the fuel injection rate is controlled is described 
above, it can be embodied in a case where the ignition timing is 
controlled, and a case where the fuel injection rate and the ignition 
timing are simultaneously controlled. 
The present, invention is effective in all of the phase advance controls in 
which the change rate .DELTA.PM is used, that is, in cases where the 
following differential factors of higher order are used, the overshooting 
can be reduced and the excessive correction of the ignition timing 
attributable to the overshooting can be prevented by determining the 
ignition timing. 
##EQU6## 
In this case, it is preferable that the .DELTA..DELTA.PM and 
.DELTA..DELTA..DELTA.PM be restricted not to exceed a predetermined 
region. 
In addition, in a case where the following differential factors of higher 
order are used, the effect of reducing the overshooting with K.sub.0 can 
be obtained, and by determining the ignition timing, the excessive 
correction of the ignition timing or the like due to the overshooting can 
be prevented. 
##EQU7## 
In this case .DELTA..DELTA.PM and .DELTA..DELTA..DELTA.PM may be corrected 
with the correction coefficient K.sub.0.