Output control apparatus for an internal combustion engine

In an output control apparatus for an internal combustion engine according to this invention, a target torque of a driving shaft of an automobile is determined in accordance with the pedaling stroke of an accelerator pedal, and a deviation between the target torque and an actual torque of the driving shaft is obtained. On the assumption that the whole system of the automobile, including the internal combustion engine, is in a steady-state operation mode, on the other hand, a steady-state output torque of the internal combustion engine, required for applying the target torque to the driving shaft, is obtained. In the output control apparatus, moreover, a steady-state suction air amount of the internal combustion engine is obtained such that the steady-state output torque is obtained in the internal combustion engine, and this steady-state suction air amount is corrected in accordance with a feedback amount based on the aforesaid deviation, so that a target suction air amount of the internal combustion engine is determined, and the opening of a throttle valve is controlled so that the target suction air amount can be obtained.

TECHNICAL FIELD 
This invention relates to an apparatus for controlling the output of an 
internal combustion engine by, for example, adjusting the opening of a 
throttle valve in the internal combustion engine. 
BACKGROUND ART 
In an internal combustion engine mounted on an automobile, for example, a 
throttle valve of this engine is mechanically connected to an accelerator 
pedal so that the valve is driven in accordance with the depth of pedaling 
of the accelerator pedal, that is, the pedaling stroke thereof. With the 
engine of this type, therefore, an operator can control the engine output, 
that is, the torque to be transmitted to a driving shaft of the 
automobile, by adjusting the opening of the throttle valve by means of the 
accelerator pedal. 
In recently offered engines for automobiles, the accelerator pedal and the 
throttle valve are electrically connected without being mechanically 
connected to each other, in contrast with the conventional case, whereby 
the opening of the throttle valve is adjusted and then the engine output 
is controlled. According to this attempt, when the accelerator pedal is 
first worked, its pedaling stroke is detected by means of a sensor, and 
the target output of the engine, that is, the target torque of the driving 
shaft of the automobile, is determined in accordance with a signal from 
the sensor. Meanwhile, an electric motor is connected to the valve shaft 
of the throttle valve, and this electric motor drives the throttle valve 
so that the opening of the throttle valve corresponds to the aforesaid 
target torque. 
When electrically controlling the engine output, as described above, the 
target torque of the driving shaft is unconditionally determined in 
accordance with the pedaling stroke of the accelerator pedal. Therefore, 
the actual torque of the driving shaft should preferably be changed 
following up the target torque without delay. After the pedaling stroke of 
the accelerator pedal is actually changed, that is, after the target 
torque of the driving shaft is changed, however, a delay, until the actual 
torque of the driving shaft reaches to the target torque depending on this 
change, is inevitably caused. As for this delay, it includes a delay 
corresponding to a time interval which elapses from the instant that air 
passes through the throttle valve until a suction stroke in which the air 
is sucked into a cylinder chamber of the engine through a surge tank and 
compression and explosion strokes for a fuel-air mixture in the cylinder 
chamber are undergone. If the automobile is furnished with an automatic 
transmission, moreover, there is a delay in transmission of power 
attributable to the torque ratio of a torque converter in a power 
transmission path which extends from the output shaft of the engine to the 
driving shaft. 
After the opening of the throttle valve is changed, as mentioned before, if 
a delay is caused until this change appears as a change of the actual 
torque of the driving shaft after undergoing the processes of production 
and transmission of the aforesaid power, the drive of the automobile 
cannot be satisfactorily controlled in accordance with the pedaling stroke 
of the accelerator pedal, that is, the opening of the throttle valve. 
This invention has been contrived in consideration of these circumstances, 
and its object is to provide an output control apparatus for an internal 
combustion engine, capable of shortening the response time which elapses 
from the instant that a target torque of a driving shaft of an automobile 
is determined until an actual torque of the driving shaft attains to the 
target torque, thereby ensuring a satisfactory drive of the automobile. 
DISCLOSURE OF THE INVENTION 
An output control apparatus for an internal combustion engine according to 
this invention comprises: adjusting means for varying the output of the 
engine in accordance with an adjusting variable; means for determining a 
target torque of a driving shaft of an automobile; means for detecting an 
actual torque of the driving shaft; means for obtaining a deviation 
between the target torque and the actual torque obtained from these means; 
means for obtaining a steady-state output torque of the engine, required 
for applying the target torque to the driving shaft, on the assumption 
that the whole system of the automobile, including the engine, is in a 
steady-state operation mode; means for obtaining a reference adjusting 
variable of the adjusting means so that the steady-state output torque is 
produced in the engine; means for obtaining a target adjusting variable of 
the adjusting means by correcting the reference adjusting variable in 
accordance with a feedback amount based on the deviation; and means for 
regulating an actual adjusting variable of the adjusting means so that the 
actual adjusting variable becomes equal to the target adjusting variable. 
According to the output control apparatus for an internal combustion engine 
described above, the steady-state output torque of the engine is obtained 
in accordance with the target torque of the driving shaft, and the 
reference adjusting variable of the adjusting means, required for the 
engine to produce the steady-state output torque, is obtained. This 
reference adjusting variable is corrected by means of the feedback amount 
based on the deviation between the target torque and the actual torque, 
whereby the target adjusting variable of the adjusting means is obtained. 
When the target adjusting variable of the adjusting means is thus 
determined in accordance with the steady-state output torque of the engine 
and the aforesaid deviation, a delay in the processes of production and 
transmission of power can be eliminated, and also, the actual torque of 
the driving shaft can be adjusted to the target torque thereof with high 
accuracy.

BEST MODE OF CARRYING OUT THE INVENTION 
Referring to FIG. 1, there is shown a block diagram of an output control 
apparatus for an internal combustion engine applied to an automobile. 
Before explaining this output control apparatus, the internal combustion 
engine and a power transmission path from this internal combustion engine 
to the driving shaft of the automobile will be described in brief. 
The internal combustion engine, that is, gasoline engine 1, is indicated by 
a chain-line block in FIG. 1. A combustion chamber 2 of this engine 1 is 
connected to suction passage 3 through a suction valve (not shown). An air 
cleaner 4 is located at that end portion of the suction passage 3 which is 
remote from the engine 1, and this air cleaner 4 comprises a filter 
element 5 and airflow sensor 6 of a Karman-vortex type. The airflow sensor 
6 detects the amount of air sucked in through the filter element 5, that 
is, the amount of suction air, and delivers a signal corresponding to the 
suction air amount. The signal from the airflow sensor 6 is supplied to an 
electronic control unit 17 for controlling the operation of a fuel 
injection device (not shown), and the electronic control unit 17 
calculates an actual suction air amount A/Nr for each cycle when the 
engine 1 executes one cycle including a suction stroke, a compression 
stroke, an explosion stroke, and an exhaust stroke, obtains the amount of 
fuel to be supplied to the engine 1 on the basis of the actual suction air 
amount A/Nr. Then, the fuel injection device injects the fuel of the 
amount determined in the electronic control unit 17 into the combustion 
chamber 2 of the engine 1 with a predetermined timing. 
That part of the suction passage 3 which is situated close to the engine 1 
is formed as a surge tank 7, and a throttle valve 8 is located in that 
portion of the suction passage 3 between the surge tank 7 and the air 
cleaner 4. The throttle valve 8 can smoothly rock from a fully-closed 
position, where the suction passage 3 is nearly closed, to a fully-open 
position, in order to adjust the amount of air flowing through the suction 
passage 3. 
The valve shaft of the throttle valve 8 projects to the outside of the 
suction passage 3, and its projecting end is connected to the output shaft 
of a DC motor 9. Thus, the rocking motion of the throttle valve 8, that 
is, the opening of the throttle valve 8, can be controlled by means of the 
DC motor 9. 
Further, a throttle opening sensor 10 is attached to the projecting end of 
the valve shaft of the throttle valve 8. The throttle opening sensor 10, 
which is formed of a potentiometer, outputs an actual opening .theta.r of 
the throttle valve 8 as a voltage signal. 
Meanwhile, a pump of a torque converter 12 is connected to a crankshaft or 
an output shaft 11 of the engine 1, which is connected to the piston of 
the engine 1 by means of a connecting rod, and a turbine of the torque 
converter 12 is connected to a transmission 14 by means of a connecting 
shaft 13. The transmission 14 is connected to a driving shaft 15, and a 
driving wheel 16 is connected to the driving shaft 15. Here the aforesaid 
torque converter 12, connecting shaft 13, and transmission 14 constitute 
an automatic transmission. 
The following is a description of an output control apparatus applied to 
the aforesaid engine 1. 
As shown in FIG. 1, the output control apparatus comprises an accelerator 
position sensor 22 which detects the depth of pedaling or pedaling stroke 
of an accelerator pedal 21 of an automobile. The accelerator position 
sensor 22 supplies a signal Ap corresponding to the pedaling stroke of the 
accelerator pedal 21 to a target torque determination section 22. The 
determination section 22 is also supplied with a vehicle speed signal v 
detected by means of a vehicle speed sensor 18. The vehicle speed sensor 
18 (not shown in detail) calculates a vehicle speed V in accordance with 
the rotating speed of the driving shaft 15. 
Based on the aforesaid signal Ap and the vehicle speed signal v or vehicle 
speed V, the section 22 determines a target torque Twt of the driving 
shaft 15 with reference to the graph of FIG. 2. The percentages for 
various characteristic curves in FIG. 2 indicate the ratios of pedaling 
strokes to the overall stroke of the accelerator pedal 20. Thus, when the 
vehicle speed V is within a low-speed region, the target torque Twt is 
determined depending only on the value of the signal Ap, without regard to 
the vehicle speed V. This indicates that the target torque Twt of the 
driving shaft 15 is set only in accordance with the depth of pedaling of 
the accelerator pedal 20 so that a feeling of acceleration of the 
automobile can be obtained when the accelerator pedal 20 is further worked 
in the state that the vehicle speed V is within the low-speed region at 
the time of starting the automobile, etc. If the vehicle speed V is not 
lower than a predetermined value, on the other hand, the target torque Twt 
takes a value which decreases as the vehicle speed V increases, even 
though the depth of pedaling of the accelerator pedal 20 is fixed. This 
indicates that the target torque Twt of the driving shaft 15 is determined 
so that the vehicle speed V can be maintained even when the accelerator 
pedal 20 is further worked, if the vehicle speed V is not lower than the 
predetermined value. 
The target torque Twt of the driving shaft 15 determined in the section 22 
is supplied to a subtraction point 23, and is also supplied to a 
calculation section 30 for calculating a target suction air amount. 
Meanwhile, an actual torque Twm of the driving shaft 15 calculated in an 
actual torque calculation section 24 is supplied to the aforesaid 
subtraction point 23. In the case of this embodiment, the actual torque 
Twm is calculated in the following manner. In the calculation section 24, 
which is supplied with a rotating speed Ne of the engine 1 detected by 
means of a rotating speed sensor 19, the actual torque Twm of the driving 
shaft 15 is calculated in accordance with the following equation, based on 
the rotating speed Ne, and a torque capacity factor C and a torque ratio 
.tau. of the torque converter 12. 
EQU Twm=.tau.(e).times.C(e).times.Ne.sup.2, 
where e is the ratio in rotating speed between the output shaft 11 of the 
engine 1 and the turbine of the torque converter 12. Based on the value of 
this ratio e, the aforesaid factor C and torque ratio .tau. can be 
obtained with reference to FIG. 3. As a result, the actual torque Twm can 
be calculated according to the above equation. 
The actual torque Twm of the driving shaft 15 need not always be obtained 
by calculation, and a torque meter may be attached to the driving shaft 15 
so that the actual torque Twm of the driving shaft 15 can be obtained by 
being directly detected by means of the torque meter. 
The actual torque Twm calculated in the actual torque calculation section 
24 is supplied to the subtraction point 23, as mentioned before. At this 
subtraction point 23, the actual torque Twm is subtracted from the target 
torque Twt, whereby a deviation .DELTA.Tw between these torques Twt and 
Twm is obtained. 
The aforementioned calculation section 30 for a target suction air amount 
will be described further in detail. The calculation section 30 can be 
further divided into three sections 31, 32 and 33. First, in the 
calculation section 31, for a steady-state output torque the target torque 
Twt of the driving shaft 15 obtained in the determination section 22 is 
received, and a steady-state output torque Teo of the engine 1 relative to 
the target torque Twt on the assumption that the engine 1 is in a 
steady-state operation mode, is calculated according to the following 
equation. 
EQU Teo=Twt/(.rho..times..tau.), 
where .rho. is the gear ratio of the transmission 14. 
The steady-state output torque Teo, thus calculated in the calculation 
section 31, is then supplied to the calculation section 32, for a 
steady-state suction air amount and a steady-state suction air amount A/No 
corresponding to the steady-state output torque Teo is obtained in this 
calculation section 32. Here the output torque Te of the engine 1 relative 
to a suction air amount A/N when the engine 1 is in the steady-state 
operation mode is previously obtained as shown in FIG. 4. When the 
steady-state output torque Teo is obtained in the calculation section 31, 
therefore, the steady-state suction air amount A/No corresponding to the 
steady-state output torque Teo can be obtained from FIG. 4 in the next 
calculation section 32. If the relationship between the suction air amount 
A/N and the output torque T of the engine 1 shown in FIG. 4 is previously 
obtained as a function, the steady-state suction air amount A/No can be 
calculated also according to this function. 
In the adjustment section 33, moreover, the deviation .DELTA.Tw obtained at 
the subtraction point 23 is received, and a adjusting variable .DELTA.A/N 
for feedback control is obtained in accordance with this deviation 
.DELTA.Tw. In obtaining the adjusting variable .DELTA.A/N in the 
adjustment section 33, any of PID, PI, and PD operations may be utilized. 
The steady-state suction air amount A/No and the adjusting variable 
.DELTA.A/N obtained in the calculation section 32 and the adjustment 
section 33 are individually supplied to an addition point 34 to be added 
therein, whereupon a target suction air amount A/Nt is calculated. As is 
evident from the above description, the target suction air amount A/Nt is 
obtained from the steady-state suction air amount a/No determined in 
accordance with the target torque Twt in consideration of a correction 
based on the deviation .DELTA.Tw between the target torque Twt and the 
actual torque Twm, that is, the adjusting variable .DELTA.A/N. 
The target suction air amount A/Nt obtained in this manner is then supplied 
to a control section 40 for a suction air amount, that is, a calculation 
section 41 for a target throttle opening in the control section 40, as 
shown in detail in FIG. 5. Also, the calculation section 41 is supplied 
with the aforesaid engine rotating speed Ne from the rotating speed sensor 
19 for the engine 1. In the calculation section 41, a throttle opening 
.theta.t is obtained from FIG. 6 in accordance with the engine rotating 
speed Ne and the target suction air amount A/Nt. The characteristic curves 
of FIG. 6, which represent the relationships between the target suction 
air amount A/Nt and the engine rotating speed Ne, shift in the direction 
of the arrow of FIG. 6 as the engine rotating speed Ne increases. 
Meanwhile, the target suction air amount A/Nt is supplied to a subtraction 
point 42 as well as to the calculation section 41, and the substraction 
point 42 is supplied with the actual suction air amount A/Nr obtained in 
the aforesaid electronic control unit 17. At the subtraction point 42, a 
deviation obtained by subtracting the actual suction air amount A/Nr from 
the target suction air amount A/Nt, that is, the deviation between the 
target suction air amount A/Nt and the actual suction air amount A/Nr, is 
obtained, and this deviation becomes a adjusting variable .DELTA..theta. 
for the feedback control as it passes through the adjustment section 43 
based on the PI operation. This adjusting variable .DELTA..theta. and the 
throttle opening .theta.t obtained in the calculation section 41 are added 
at an addition point 44, whereupon a final target throttle opening 
.theta.1 is calculated. The target throttle opening .theta.1 thus 
calculated is then supplied to a drive section 25 for the DC motor 9, 
while the drive section 25 is also supplied with the aforesaid actual 
opening .theta.r from the throttle opening sensor 10. In the drive section 
25, the target throttle opening .theta.1 and the actual opening .theta.r 
are compared, and the operation of the DC motor 9 is controlled so that 
the difference between the two openings is zero. 
Referring now to the flow chart of FIG. 7, the operation of the output 
control apparatus according to the aforementioned first embodiment will be 
described in order. 
When the accelerator pedal 20 is worked, the pedaling stroke of this 
accelerator pedal 20 is detected by the accelerator position sensor 21. In 
Step S1, the target torque Twt of the driving shaft 15 is determined in 
accordance with the signal from the accelerator position sensor 21 and the 
vehicle speed V in accordance with FIG. 2. 
In the next Step S2, the steady-state output torque Teo is calculated from 
the target torque Twt, and in Step S3, the steady-state suction air amount 
A/No is obtained from the map of FIG. 4 in accordance with the 
steady-state output torque Teo. 
The moment the aforesaid Step S1 is executed, on the other hand, Step S4 is 
also executed. In Step S4, the engine rotating speed Ne, the actual 
suction air amount A/Nr, and the vehicle speed V are detected 
individually, and in Step S5, the actual torque Twm of the driving shaft 
15 is calculated on the basis of these detected data. 
In the next Step S6, the deviation .DELTA.Tw between the target torque Twt 
previously obtained in Step S1 and the actual torque Twm is obtained, and 
in Step S7, the adjusting variable .DELTA.A/N for the feedback control of 
the target suction air amount A/Nt is calculated in accordance with the 
deviation .DELTA.Tw. Thus, in Step S8 next to Steps S3 and S7, the target 
suction air amount A/Nt is obtained by correcting the steady-state suction 
air amount A/No, that is, the target suction air amount A/Nt is calculated 
by adding the adjusting variable .DELTA.A/N to the steady-state suction 
air amount A/No. 
In the final Step S9, the opening of the throttle valve 8 is controlled so 
that the actual suction air amount A/Nr is equal to the target suction air 
amount A/No. Actually, however, the operation of the DC motor 9 is 
controlled so that the actual opening .theta.r of the throttle valve 8 is 
equal to the target throttle opening .theta.1 corresponding to the target 
suction air amount A/Nt, as mentioned before. 
According to the output control apparatus of the first embodiment described 
above, the steady-state suction air amount A/No corresponding to the 
target torque Twt of the driving shaft 15 is first obtained, and this 
steady-state suction air amount A/No is corrected by means of the 
correction based on the deviation .DELTA.Tw between the target torque Twt 
and the actual torque Twm, that is, by means of the adjusting variable 
.DELTA.A/N for the feedback control, whereby the target suction air amount 
A/No is calculated. Thus, the aforementioned delay in response in the 
processes of production and transmission of power can be eliminated. 
Thus, according to this invention, when the target torque Twt is 
determined, the steady-state output torque Teo or the steady-state suction 
air amount A/No is calculated from this target torque Twt, in 
consideration of the gear ratio .rho. of the transmission 14 and the 
torque ratio .tau. of the torque converter 12. Immediately when the actual 
suction air amount A/Nr is controlled on the basis of the steady-state 
suction air amount A/No, therefore, the output torque of the engine 1 
itself takes a value in the vicinity of the target torque Twt of the 
driving shaft 15. As a result, in view of the processes of production and 
transmission of the power, the time interval which elapses from the 
instant that the target torque Twt is determined by the working on the 
accelerator pedal 20 until the actual torque Twm of the driving shaft 15 
reaches to the target torque Twt can be shortened by a large margin, so 
that the responsiveness of the output torque of the engine 1 can be 
improved. 
Meanwhile, the target suction air amount A/Nt is obtained by adding the 
adjusting variable .DELTA.A/N, determined according to the deviation 
.DELTA.Tw between the target torque Twt and the actual torque Twm, to the 
aforesaid steady-state suction air amount A/No. In obtaining this target 
suction air amount A/Nt, moreover, the aforesaid actual torque Twm is 
calculated in consideration of the torque capacity factor C and the torque 
ratio .tau. of the torque converter 12. Thus, the power transmission delay 
in the path from the engine 1 to the driving shaft 15 can be eliminated by 
controlling the actual suction air amount A/Nr in accordance with the 
aforesaid target suction air amount A/Nt, so that the actual torque Twm of 
the driving shaft 15 can be highly accurately adjusted to the target 
torque Twt. 
Referring now to FIG. 8, there are shown the results of measurement of the 
actual torque To of the driving shaft 15 obtained by actually driving the 
automobile. As seen from FIG. 8, when the target torque Twt is determined, 
the actual torque To quickly attains to the target torque Twt while both 
the output torque Te of the engine 1 and the engine rotating speed Ne are 
changing, and is kept at the level of the target torque Twt. 
Referring now to FIG. 9, there is shown for reference the case of an 
automobile in which the accelerator pedal 20 and the throttle valve 8 are 
mechanically connected to each other. In the case of FIG. 9, the pedaling 
stroke of the accelerator pedal 20 is kept constant, so that the engine 
rotating speed Ne and the output torque Te of the engine 1 are both 
stable. The actual torque To of the driving shaft 15, however, is reduced 
with the lapse of time. This is attributable to the fact that the torque 
ratio of the torque converter 12 and the like change in a nonlinear manner 
in the power transmission path from the engine 1 to the driving shaft 15. 
In the case of the output control apparatus of this invention, therefore, 
it can be believed that in keeping the actual torque To of the driving 
shaft 15 at the level of the target torque Twt, the engine rotating speed 
Ne and the output torque Te of the engine 1 are changed so as to cancel 
the bad influences of the nonlinear elements in the power transmission 
path. In FIGS. 8 and 9, symbol F designates the vehicle body speed. 
This invention is not limited to the first embodiment described above, and 
the following is a description of a second embodiment. Since an output 
control apparatus of the second embodiment has the same basic arrangement 
as the output control apparatus of the first embodiment, the second 
embodiment will be described also with reference to FIG. 1. 
In the case of the second embodiment, as seen from FIG. 1, a parameter 
calculation section 50 and a gain calculation section 60 are added. 
The calculation sections 50 and 60 will now be described in brief. The 
calculation section 50 is stored with a mathematical model which linearly 
represents the operation mode of the engine 1, considering that the engine 
1 is in an operation mode deviated from the steady-state operation mode, 
in the processes of production and transmission of the power of the 
automobile. In the calculation section 50, therefore, various parameters 
in this mathematical model are obtained by inverse calculation based on 
the actual suction air amount A/Nr, engine rotating speed Ne, and vehicle 
speed V supplied to the calculation section 50. The parameters of the 
mathematical model obtained in the calculation section 50 are supplied to 
the gain calculation section 60. If the whole mechanism of the automobile, 
including a feedback control circuit composed mainly of the adjustment 
section 33, is regarded as one system, this calculation section 60 
calculates gains for the feedback control or gains for the PID operation 
in the case of this embodiment, i.e., proportional gain, differential 
gain, and integral gain, in accordance with the aforesaid parameters so 
that the characteristics obtained before the torque is actually 
transmitted to the driving shaft 15 after air is sucked into the engine 1 
in this system closely resemble the transfer characteristics of a 
normative response system. In the case of this second embodiment, 
therefore, the adjustment section 33 calculates the adjusting variable 
.DELTA.A/N for the feedback control from the deviation .DELTA.Tw between 
the target torque Twt and the actual torque Twm in accordance with the PID 
operation expressed as follows: 
EQU .DELTA.A/N=c0.times..intg.(.DELTA.Tw)+c1.times.(.DELTA.Tw)+c2.times.d(.DELT 
A.Tw)/dt, 
where c0, c1 and c2 are the integral, proportional, and differential gains, 
respectively. 
Alternatively, the individual gains may be obtained from a map on the basis 
of the values of the individual parameters of the mathematical model, 
supplied from the calculation section 50, the map being previously 
prepared by calculating the values of the individual gains from the 
parameter values and then stored in the calculation section 60. 
Referring to FIG. 10, there is shown the mathematical model stored in the 
calculation section 50. This mathematical model indicates the way the air 
sucked in through the throttle valve 8 is linearly reflected in the 
behavior of the automobile, that is, the torque of the driving shaft 15. 
In FIG. 10, reference symbol Ar designates the amount of air for the 
explosion stroke which is corresponds to the output torque of the engine 
1, while a21, a22, a23, a32 and a33 designate the parameters of the 
mathematical model. 
The amount of air passed through the throttle valve 8, that is, actual 
suction air amount Ai (A/Nr), is converted into the air amount Ar by means 
of a suction delay element [1/(1+Ta.times.S)]. Also, the air amount Ar is 
converted into the output torque Te of the engine 1 by means of the 
parameter a21, and this output torque Te is converted into the engine 
rotating speed Ne by means of an inertia element [1/(Ie.times.S)] of the 
engine 1. 
The engine rotating speed Ne is returned to the input side of the inertia 
element [1/(Ie.times.S)] via the parameter a22, and is converted into the 
vehicle speed V by means of the parameter a32, a gear ratio element 
[1/.rho.], and a inertia element [1/(It.times.S)] of the vehicle body. 
Then, the vehicle speed V is converted into a rotational angular speed 
.omega.t of the turbine of the torque converter 12 by means of the gear 
ratio [.rho.]. The rotational angular speed .omega.t, like the engine 
rotating speed Ne, is returned to the input side of the inertia element 
[1/(Ie.times.S)] via the parameter a23, and is also returned to the input 
side of the element [1/.rho.] via the parameter a33. 
In the above description, Ta, S, Ie, It and .rho. represent, respectively, 
the following values: 
Ta: Time constant determined by the capacity of the suction passage 3 and 
the cylinder capacity of the engine 1, 
S: Transfer function, 
Ie: Moment of inertia of the engine 1, 
It: Moment of inertia of the vehicle body, 
.rho.: Gear ratio of the transmission 12. 
When the engine rotating speed Ne is converted into the vehicle speed V, as 
shown in FIG. 10, this conversion is made in consideration of the load 
relative to the road surface. 
The aforesaid parameter a21 represents a conversion factor obtained from 
the relationship between the suction air amount A/N and the output torque 
Te of the engine 1 shown in FIG. 4, while the parameters a22, a23, a32 and 
a33 correspond to the characteristics of the torque converter 12 of FIG. 3 
used in calculating the actual torque Twm. 
Thus, it is possible to calculate the air amount Ar from the air amount Ai 
and to obtain the individual parameters by inverse calculation from the 
engine rotating speed Ne and the vehicle speed V measured actually. 
The following is a description of processes before the preparation of the 
aforementioned mathematical model. 
First, a change of mass per unit time of air in the suction air capacity at 
the region of the suction passage 3 on the lower-course side of the 
throttle valve 8 is expressed by the difference between the amount of air 
introduced from the throttle valve 8 and the amount of discharge into a 
cylinder chamber of the engine 1. 
EQU Gm=Gin-Gex, (1) 
where Gm is the mass of air in the suction air capacity, Gin is the amount 
of air passing through the throttle valve 8 per unit time, and Gex is the 
amount of air introduced into the cylinder chamber per unit time. For a 
better understanding of Gm, Gin and Gex, these values are illustrated on 
the suction passage 3 of FIG. 1. 
Since Gex is proportional to Gm and the engine rotating speed Ne, it can be 
given by the following equation. 
EQU Gex=Gm.times.Ne/To, (2) 
EQU To=(V1+V2).times.120/(V1.times..eta.), 
where V1 is the suction air capacity, V2 is the capacity of the cylinder 
chamber, .eta. is the volumetric efficiency, and To is the time constant 
per revolution of the engine 1. 
Substituting equation (2) into equation (1), we obtain equation (3) as 
follows: 
EQU Gm=Gin-(Gm.times.Ne)/To. (3) 
Equation (3) indicates that the air amount has a transfer characteristic of 
primary delay. 
Rewriting equation (3) by utilizing the relationship between Gex and Gm in 
equation (2), we obtain equation (4). 
EQU Gex=(Ne/To)(Gin-Gex). (4) 
Dividing both sides of equation (4) by the rotating speed per unit time of 
the engine 1, we obtain equation (5) related to the suction air amount 
from equation (4). 
EQU Ao=(Ne/To)(-Ao+Ai), (5) 
where Ao is the amount of air sucked into the cylinder chamber per unit 
time, and Ai is the amount of air passed through the throttle valve 8 per 
unit time. 
The air amount Ai is reflected in the output torque of the engine 1 only 
after air of the amount Ai is sucked into the cylinder chamber and the 
compression and explosion strokes are performed. The time required for the 
execution of the processes from the suction stroke to the explosion stroke 
is represented as a dead time in the feedback control, and this dead time 
is equivalent to 1.5 revolutions of the engine 1 as reckoned from the 
start of the suction stroke. Thus, if the dead time is (Lo/Ne), this dead 
time (Lo/Ne) is given by equation (6). 
EQU (Lo/Ne)=(60.times.1.5)/Ne=90/Ne. (6) 
Based equation (6), equation (7) represents the relationship between the 
air amounts Ao and Ar as a function of time t. 
EQU Ar=Ao.times.(t-(Lo/Ne)). (7) 
Meanwhile, it is assumed that the air amount Ar, the rotational angular 
speed .omega.e of the engine 1, and the rotational angular speed .omega.t 
of the turbine change by very small amounts .DELTA.Ar, .DELTA..omega.e and 
.DELTA..omega.t, respectively, from the values for the steady-state 
operation mode, in response to a change .DELTA.Ai of the air amount Ai, 
when the engine 1 and the vehicle body are in the steady-state operation 
mode. With respect to the air amount, in this case, the following relation 
holds true. 
EQU Ar+.DELTA.Ar=((.omega.e+.DELTA..omega.e)/TL).times.(-Ar-.DELTA.Ar)+Ai+.DELT 
A.Ai. (8) 
In obtaining equation (8), the time constant of the transfer characteristic 
before the air amount Ai is converted into the air amount Ar is 
approximated as a primary delay of (.omega.e/TL). 
If the engine 1 is in the steady-state operation mode, we have Ar=Ai, so 
that equation (8) can be expressed as equation (9). 
EQU .DELTA.Ar=(.omega.e/TL).times.(-.DELTA.Ar+.DELTA.Ai). (9) 
With respect to the rotational angular speed .omega.e of the engine 1, 
moreover, the following equation holds true. 
EQU I(.omega.e+.DELTA..omega.e)=Te(.omega.e+.DELTA..omega.e, 
Ar+.DELTA.Ar)-Tp(.omega.e+.DELTA..omega.e, .omega.e+.DELTA..omega.t),(10) 
where Tp is the absorption torque of the torque converter 12. 
If the output torque Te of the engine 1 and the absorption torque Tp change 
by .DELTA.Te and .DELTA.Tp, respectively, when the air amount Ar changes 
by .DELTA.Ar, we obtain 
EQU Te(.omega.e+.DELTA..omega.e, Ar+.DELTA.Ar)=Te(.omega.e, Ar)+.DELTA.Te,(11) 
EQU Te(.omega.e+.DELTA..omega.e, .omega.t+.DELTA..omega.t)=Te(.omega.e, 
.omega.t)+.DELTA.Tp. (12) 
Since the engine 1 is in the steady-state operation mode, the following 
equation is obtained with respect to the angular speeds .omega.e and 
.omega.t and the air amount Ar. 
EQU .omega.e=0, (13) 
EQU Te(.omega.e, Ar)=Tp(.omega.e, .omega.t). (14) 
An equation for the very small change of the rotational angular speed 
.omega.e of the engine 1 is given as follows: 
EQU Ie..DELTA..omega.e=.DELTA.Te-.DELTA.Tp. (15) 
Using .DELTA..omega.e, .DELTA..omega.t, and .DELTA.Ar, .DELTA.Te and 
.DELTA.Tp are given by the following linear differential equation. 
EQU .DELTA.Te=(.differential.Te/.differential..omega.e).times..DELTA..omega.e+( 
.differential.Te/.differential.Ar).times..DELTA.Ar, (16) 
EQU .DELTA.Tp=(.differential.Tp/.differential..omega.e).times..DELTA..omega.e+( 
.differential.Tp/.differential.Ar).times..DELTA..omega.t. (17) 
Likewise, the following linear differential equation is obtained with 
respect to the turbine of the torque converter 12. 
EQU .DELTA.Ar=-Ta.times..DELTA.Ar+Ta.times..DELTA.Ai, (18) 
##EQU1## 
Here, in equation (19), (.differential.Te/.differential.Ar), 
((.differential.Te/.differential..omega.e)-(.differential.Tp/.differential 
..omega.e)), and (.differential.Tp/.differential..omega.t).times.(1/Ie) 
constitute the parameters a21, a22 and a23, respectively. 
In equation (20), moreover, (.differential.Tt/.differential..omega.e) and 
((.differential.Tt/.differential..omega.t)-(.differential.T1/.differential 
..omega.t)) constitute the parameters a32 and a33, respectively. 
Tt is the output torque of the torque converter 12, and T1 is the torque 
equivalent to the load of the road surface, as mentioned before. 
Accordingly, the aforesaid system is given by the following state space 
representation formats. 
EQU .omega.=A.omega.-Bu, (21) 
EQU y=C.times..omega., (22) 
where 
.omega.=state vector of [.DELTA.Ar, .DELTA..omega.e, 
.DELTA..omega.t].sup.t, 
A=coefficient of .DELTA.Ar, .DELTA..omega.e and .DELTA..omega.t in the 
system matrixes (18), (19) and (20) of [aij], 
B=input factor vector of [Ta, 0, 0].sup.t, 
C=output factor vector (e.g., [0, 0, 1] for the turbine rotating speed), 
u=input, 
y=output. 
The above description is a description of the processes before the 
preparation of the mathematical model. 
The following is a description of transfer functions as references for the 
calculation of the individual gains in the gain calculation section 60. 
A transfer factor G(s) between the input u and the output y in equations 
(21) and (22) can be expressed by the following equation based on the 
definition of transfer functions. 
EQU G(s)=C.times.[sI-A].sup.-1 .times.B, (23) 
where s and I are an element for a differential effect and a unit matrix, 
respectively. 
Based on equation (23), a transfer function Ge(s) between the suction air 
and the rotational angular speed .omega.e of the engine 1 and a transfer 
function Gt(s) between the suction air and the rotational angular speed 
.omega.t of the turbine of the torque converter 12 are given, 
respectively, by the following equations. 
EQU Ge(s)=(b1.times.a21.times.(s-a33))/H(s), (24) 
EQU Gt(s)=(b1.times.a21.times.a32)/H(s), (25) 
where 
EQU H(s)=(s-a11).times.(s-a22).times.(s-a33)-(s-a11).times.a23.times.a32,(26) 
and further, b1=Ta and a11=-Ta. 
In obtaining a transfer function between the suction air and the torque of 
the driving shaft 15 by rearranging it into a transfer function between 
the suction air and the turbine torque of the torque converter 12, a 
linear differential equation related to .DELTA.Tt is given by the 
following equation. 
EQU .DELTA.Tt=(.differential.Tt/.differential..omega.e).times..DELTA..omega.e+( 
.differential.Tt/.differential..omega.t).times..DELTA..omega.t,(27) 
where 
EQU (.differential.Tt/.differential..omega.e)=a32.times.It, (28) 
EQU (.differential.Tt/.differential..omega.t)=(a33+k).times.It.(29) 
Substituting equations (24) and (25) into the above equations, we obtain a 
transfer function Gf(s) between the suction air and the turbine torque 
given by the following equation. 
EQU Gf(s)=(It.times.b1.times.a21.times.a32.times.(s+k))/H(s), (30) 
where k is a coefficient based on the load and calculated as follows: 
EQU k=.differential.T1/(.differential..omega.t.times.It). (31) 
Since the value of k is substantially zero, however, the transfer function 
Gf(s) is given by 
EQU Gf(s)=(It.times.b1.times.a21.times.a32.times.s)/H(s). (32) 
Here T1 is the torque equivalent to the load of the road surface. 
Dividing the numerator and denominator of equation (32) by 
(It.times.b1.times.a21.times.a32) so that the numerator of equation (32) 
is s only, we obtain 
EQU Gf(s)=s/h(s). (33) 
Here 
##EQU2## 
Thus, equation (33) represents the transfer function of the automobile as 
an object of control. 
The following is a description of processes for obtaining the individual 
gains for the PID operation. 
As shown in FIG. 11, a feedback control system and the automobile as the 
object of control are regarded as one system, and the transfer 
characteristics between the input and output of this system are caused to 
correspond to the transfer characteristics of the normative response 
system as a target. For example, a step response waveform is used as this 
normative response system, as shown in FIG. 12. 
The transfer function of the feedback control system can be expressed as 
follows: 
EQU c(s)/s=(c0+c1.times.s+c2.times.s.sup.2 + . . . )/s. (35) 
Meanwhile, the denominator of the transfer function of the normative 
response system can be expressed as follows: 
EQU r(s)=1+r0+r1.times.qs+r2.times.q.sup.2 .times.s.sup.2 + (36) 
where q is an element for normalizing the response time. 
1+r0, r1, r2, . . . are parameters for determining the response waveform, 
and these values can be selected as required. 
An open-loop transfer function of the system, including the feedback 
control system and the automobile, is given by 
EQU Go(s)=c(s)/h(s), (37) 
and this is shown in FIG. 13. 
On the other hand, a closed-loop transfer function of the system can be 
expressed as follows: 
EQU Gc(s)=1/((h(s)/c(s))+1). (38) 
This is shown in FIG. 14. 
If the closed-loop transfer function Gc(c) is equal to a transfer function 
1/r(s) of the normative response system, the following equation holds 
true. 
EQU c(s)=h(s)/(r(s)-1). (39) 
If the right side of equation (39) is developed into a denominator-based 
polynomial expression and if the respective coefficients of the individual 
terms are c0, c1 and c2, in order of degree in an ascending scale, these 
values c0, c1 and c2 can be expressed as follows: 
EQU c0=h0/r0, (40) 
EQU c1=(h0/r0).times.((h1/h0)-q.times.(r1/r0), (41) 
##EQU3## 
With respect to the aforementioned PID operation, c(s) can be given by the 
following quadratic equations. 
EQU c(s)=c0+c1s+c2s.sup.2. (44) 
Accordingly, equation (43) is solved with c3=0. 
Supposing the minimum positive value out of the solutions of equation (43) 
to be q and substituting q into equations (41) and (42), we can obtain c0, 
c1 and c2. As mentioned before, these values c0, c1 and c2 represent the 
integral, proportional, and differential gains, respectively, for the PID 
operation. 
Referring now to the flow chart of FIG. 15, the operation of the output 
control apparatus of the second embodiment will be described. 
Steps S1 to S6 and Steps S8 and S9, in FIG. 15, are executed in the same 
manner as in the case of the first embodiment shown in FIG. 7, so that a 
description of these steps is omitted. In the case of the second 
embodiment, the adjusting variable .DELTA.A/N for the feedback control is 
obtained in Steps S10 to S12. More specifically, the parameters a21, a22, 
a23, a32 and a33 of the mathematical model shown in FIG. 7 are obtained in 
Step S10, and in the next Step S11, the integral, proportional, and 
differential gains for the feedback control are obtained individually in 
accordance with these parameters and the transfer function of the 
normative response system. In Step S12, moreover, the adjusting variable 
.DELTA.A/N is calculated on the basis of the individual gains obtained in 
Step S11, and thereafter, the aforesaid Steps S8 and S9 are executed in 
succession to control the opening of the throttle valve 8. 
In the case of the second embodiment described above, the values of the 
individual parameters of the linear mathematical model change as the 
behavior of the automobile changes, that is, as the air amount Ar for the 
explosion stroke, engine rotating speed Ne, and vehicle speed V change. In 
individually calculating the integral, proportional, and differential 
gains in accordance with these parameters, the integral, proportional, and 
differential gains are calculated so that the characteristic observed 
before the torque is actually transmitted to the driving shaft 15 after 
the suction in the supposed system including the automobile and the 
feedback control system closely resembles the transfer characteristic of 
the normative response system. Accordingly, by calculating the adjusting 
variable .DELTA.A/N in accordance with these gains and controlling the 
opening of the throttle valve 8 in consideration of this adjusting 
variable .DELTA.A/N, the actual torque of the driving shaft 15 can be 
controlled in an optimum state. Thus, in the case of this second 
embodiment, the torque of the driving shaft 15 can be controlled so that 
the characteristics for the processes of production and transmission of 
the power of the automobile are always linearly grasped without regard to 
the change of the behaviour of the automobile, and the transfer 
characteristic of the aforesaid system closely resembles the transfer 
characteristic of the normative response system. Accordingly, the 
responsiveness obtained before the torque is transmitted to the driving 
shaft 15 after the suction can be greatly improved, and the actual torque 
of the driving shaft 15 can be quickly adjusted to the target torque with 
high accuracy. In consequence, with use of the output control apparatus of 
this invention, an auto-cruise control system and a traction control 
system of the automobile can be unified as one control system. 
In the case of this second embodiment, moreover, the individual gains for 
the PID operation are obtained from the parameters of the mathematical 
model, so that the automobile need not undergo a drive test to obtain 
these gains. 
If the calculation section 50 is previously stored with the mathematical 
model, furthermore, troubleshooting for the automobile can be also 
effected by using this mathematical model. 
In the first and second embodiments, any of the P, PI, PD, and PID 
operations is performed in the adjustment section 33, as described before. 
Besides these operations, however, state feedback control may be effected. 
In this case, the adjusting variable .DELTA.A/N can be calculated on the 
basis of the following equation. 
EQU .DELTA.A/N=k1A/Nr+k2Ne+k3V, 
where k1, k2 and k3 are gains. 
In the calculation section 60, the parameters of the mathematical model 
obtained in the calculation section 50 are used, and the gains k1, k2 and 
k3 are calculated so that a change of the torque given by the following 
equation is minimized. 
##EQU4## 
Although the throttle valve 8 is driven by means of the DC motor 9 in the 
foregoing embodiments, a stepping motor may be used in place of this DC 
motor 9. In this case, the stepping motor is supplied with pulses 
corresponding to the target throttle opening. Further, the drive source 
for the throttle valve 8 is not limited to an electric motor, and a 
hydraulic motor or a pneumatic motor may be used for this purpose. 
In each embodiment of this invention, furthermore, the engine is a gasoline 
engine, and the output of this engine is controlled by means of the 
suction air amount. In the case of a diesel engine, however, a fuel 
injection quantity is controlled in place of the suction air amount. 
INDUSTRIAL AVAILABILITY 
An output control apparatus for an internal combustion engine of this 
invention is intended to control the output of the internal combustion 
engine. Therefore, in the output control apparatus, a target torque of a 
driving shaft of an automobile is determined in accordance with a pedaling 
stroke when an accelerator pedal of the automobile is worked, and then an 
actual torque of the driving shaft is quickly adjusted to the target 
torque with high accuracy. Thus, the output control apparatus of this 
invention can be applied to an auto-cruise control system or traction 
control system of the automobile, or a control system uniting these 
systems.