Control system for the quantity of air to be inducted into engine

This invention relates to a control system for the quantity of air to be inducted, which is suitable for use in controlling the idling speed of an engine, for example, for an automotive vehicle or the like. It is an object of the present invention to permit a change of the same degree to the quantity of air to be inducted for the compensation of a load without being affected by the temperature of the engine and also to precisely obtain inducted air in a quantity required inherently. The control system is constructed of STM valve (12) interposed in a bypass passage (11) of a throttle valve (8), ROM (36) for storing opening data for the setting of the position of the STM valve (12), the opening data corresponding to engine operation states, a limiter (13) interposed in the bypass passage (11) in series with the STM valve (12), the opening of the limiter being variable depending on the engine temperature, target opening setting device (45,46) for correcting a target opening on the basis of the engine temperature upon setting the target opening on the basis of the opening data obtained from the ROM (36) in accordance with an engine operation state, and an ISC driver (44) for controlling the opening of the STM valve (12) to the target opening from the target opening setting device (45,46).

TECHNICAL FIELD 
This invention relates to a control system for the quantity of air to be 
inducted into an engine, which is suitable for use in controlling the idle 
speed (idling speed) of an engine, for example, for an automotive vehicle 
or the like. 
BACKGROUND ART 
Techniques have already been proposed to accurately control the idling 
speed of an engine in correspondence with the speed and temperature of the 
engine and the operation states of accessories installed in association 
with the engine, such as an air conditioner and a power steering, by 
arranging an idling speed control valve [hereinafter called an "ISC (idle 
speed control) valve"] in a throttle bypass passage and controlling the 
opening of the ISC valve on the basis of signals indicative of the 
respective operation states. 
According to such a technique, target openings (or target engine speeds) 
corresponding to respective engine temperatures are set in advance. The 
ISC valve is first controlled to a target opening (or at an opening which 
makes it possible to control the engine speed to a target engine speed). 
When a change occurs in the load of the air conditioner or the like, the 
opening of the ISC valve is controlled further by a degree corresponding 
to the kind of the change in the load so that any change in the engine 
speed due to the change in the load can be compensated. 
In this technique, the ISC valve is designed to permit setting the quantity 
of inducted air in a wide range from the setting of a large quantity of 
inducted air required at the time of a cold engine state to the setting of 
a small quantity of inducted area needed at the time of a hot engine state 
because there is a large difference between the quantity of air to be 
inducted through a throttle bypass passage required at the time of the 
cold engine state and the quantity of air to be inducted through the 
throttle bypass passage needed at the time of the hot engine state. The 
above technique therefore involves the problem that the idling speed 
becomes higher at the time of a hot state than it is needed if any trouble 
occurs on the ISC valve or its drive circuit or the like and the ISC valve 
is hence fixed at the setting for the large quantity of inducted air for 
the time of the cold state. 
As is disclosed in Japanese Patent Application Laid-Open (Kokai) No. SHO 
64-87843 or the like, a technique has been proposed accordingly to arrange 
a valve element (limiter), which operates responsive to the temperature of 
the engine, in the bypass passage in series with the ISC valve so that at 
the time of a hot state, especially, the maximum quantity of air inducted 
and flowing through the bypass passage at the time of the hot state is 
limited to prevent any unnecessary increase in the idling speed. 
The arrangement of such a limiter in the bypass passage is however 
accompanied by the problem that the flow rate so controlled is affected by 
the opening of the limiter, for example, as shown in FIG. 11 especially 
when the opening of the ISC valve is relatively large. 
Described specifically, consider, for example, the state that the engine 
temperature is relatively low (in this case, the maximum bypass flow rate 
by the limiter is relatively high) and most of accessories to the engine 
are not operated (State A) and the state that the engine temperature is 
relatively high (in this case, the maximum bypass flow rate by the limiter 
is relatively low) and most of the accessories other than a specific 
accessory are operated (State B). Assume that in each of the states, the 
opening of the ISC valve is substantially the same in a relatively high 
opening range. 
Also assume that operation of the specific accessory was started from this 
state and the opening of the ISC valve has been increased by a degree 
preset corresponding to the accessory in both the states. Although the 
opening has been increased by the same degree in both State A and State B, 
the influence of the limiter is smaller in State A so that the quantity of 
air to be inducted is increased by a greater degree whereas the influence 
of the limiter is relatively greater in State B so that the quantity of 
air to be inducted is increased by a smaller degree. Consequently, despite 
the occurrence of the same load by the same accessory in both the states, 
the increase in the quantity of air to be inducted for the compensation of 
the load is affected by the engine temperature and is hence not performed 
by the same degree. 
Further, consider the above situation under the same temperature condition. 
The influence by the limiter is small when the opening of the ISC valve is 
relatively small but, when the above opening becomes relatively large, the 
degree of influence of the limitation to the flow rate by the limiter 
increases. Here again, there is the problem that air to be inducted cannot 
be obtained precisely in a quantity inherently required in accordance with 
the degree of influence by the limier on the basis of the opening of the 
ISC valve if the change in the opening of the ISC valve is simply set at a 
fixed value in correspondence to a change in a specific operation state 
typified by a change in the operation of the accessory. 
The present invention has been completed with such problems in view, and 
has as an object the provision of a control system for the quantity of air 
to be inducted into an engine so that, where an ISC valve and a limiter 
are arranged in series with each other in a bypass passage, the opening of 
the ISC valve is controlled while applying a correction in accordance with 
the state of temperature of the engine, thereby making it possible to 
independently make a change to the quantity of air inducted for the 
compensation of a load without being affected by the engine temperature 
and also to accurately obtain inducted air in a quantity inherently 
required in accordance with the degree of influence of the limiter which 
varies based on the opening of the ISC valve. 
DISCLOSURE OF THE INVENTION 
Accordingly, a control system according to the present invention for the 
quantity of air to be inducted into an engine comprises: a first control 
valve interposed in a bypass passage which bypasses a throttle valve 
disposed in an intake passage of the engine; means for storing opening 
date for setting the position of the first control valve, the opening data 
having been preset corresponding to operation states of the engine; a 
second control valve interposed in the bypass passage so that the second 
control valve is located in series with the first control valve, the 
opening of the second control valve being variable depending on the 
temperature state of the engine; means for setting a target opening of the 
first control valve by detecting an operation state of the engine and 
obtaining the opening data corresponding to the operation state from the 
storage means and also for performing, upon setting the target opening on 
the basis of the opening data so obtained, correction of the target 
opening on the basis of at least one of information on a temperature state 
of the engine and information on an opening of the first control valve; 
and valve opening setting means for controlling the opening of the first 
control valve to the target opening set by the target opening setting 
means. 
The storage means may store first opening data for a hot state of the 
engine and second opening data corresponding to operation states of an 
accessory of the engine, and the target opening setting means may 
comprises first setting means for setting a tentative target opening by 
using both the first opening data and the second opening data, and second 
setting means for making correction to the tentative opening, which has 
been set by the first setting means, on the basis of at least one of the 
information on the temperature state of the engine and the information on 
the opening of the first control valve and hence setting the target 
opening. 
The storage means may store the opening data corresponding to a difference 
between an engine speed and a target engine speed; and the target opening 
setting means may comprise first setting means for setting a tentative 
target opening by using both another tentative target opening, which has 
been set immediately before, and the opening data, and a second setting 
means for making correction to the tentative target opening, which has 
been set by the first setting means, on the basis of at least one of the 
information on the temperature state of the engine and the information on 
the opening of the first control valve and hence setting the target 
opening. 
The target opening setting means may make the correction to the target 
opening on the basis of both the information on the temperature state of 
the engine and the information on the opening of the first control valve. 
The storage means may store target opening correcting correction 
coefficients corresponding to at least one of information on temperature 
states of the engine and information on openings of the first control 
valve; and the target opening setting means may obtain from the storage 
means the correction coefficient corresponding to at least one of 
information on a temperature state of the engine and information on an 
opening of the first control valve and may multiply the target opening by 
the correction coefficient so obtained, whereby the correction of the 
target opening is performed. Here, the correction coefficients may be set 
so that the correction coefficients become smaller as the temperature of 
the engine decreases or the opening of the first control valve increases. 
The storage means may store target opening correcting correction 
coefficients as a map corresponding to the information on the temperature 
state of the engine and the information on the opening of the first 
control valve; and the target opening setting means may obtain from the 
map in the storage means the correction coefficient corresponding to the 
information on the temperature state of the engine and the information on 
the opening of the first control valve and may multiply the target opening 
by the correction coefficient so obtained, whereby the correction of the 
target opening is performed. The correction coefficients may be set so 
that the correction coefficients become smaller as the temperature of the 
engine decreases or the opening of the first control valve increases. 
According to the control system of this invention for the quantity of air 
to be inducted into the engine, opening data corresponding to an operation 
state of the engine is read from the storage means by the target opening 
setting means. Upon setting the opening data as a target opening for the 
first control valve, correction is made to the opening data (the target 
opening for the first control valve) on the basis of at least one of 
information on a temperature state of the engine and information on an 
opening of the first control valve. The opening of the first control valve 
is then controlled by the valve opening setting means to the target 
opening set by the target opening setting means. 
Further, the storage of the first opening data for the hot state of the 
engine and the second opening data corresponding to operation states of an 
accessory of the engine in the storage means makes it possible, upon 
setting a target opening for the first control valve by the target opening 
setting means, to set a tentative target opening by the first setting 
means on the basis of both the first opening data and the second opening 
data and then to make correction to the tentative opening by the second 
setting means on the basis of at least one of the information on the 
temperature state of the engine and the information on the opening of the 
first control valve and hence to set the target opening. 
The storage of the opening data corresponding to a difference between an 
engine speed and a target engine speed in the storage means makes it 
possible--upon setting a target opening for the first control valve by the 
target opening setting means--to set a tentative target opening by the 
first setting means on the basis of both another tentative target opening, 
which has been set immediately before, and the opening data and then to 
make correction to the tentative target opening by the second setting 
means on the basis of at least one of the information on the temperature 
state of the engine and the information on the opening of the first 
control valve and hence to set the target opening. 
At the target opening setting means, the correction to the target opening 
can be made on the basis of both the information on the temperature state 
of the engine and the information on the opening of the first control 
valve. 
The storage of the target opening correcting correction coefficients in the 
storage means, said coefficients corresponding to at least one of 
information on temperature states of the engine and information on 
openings of the first control valve (and optionally becoming smaller as 
the temperature of the engine decreases or the opening of the first 
control valve increases), makes it possible--upon making correction to the 
target opening for the first control valve by the target opening setting 
means--to obtain from the storage means the correction coefficient 
corresponding to at least one of information on a temperature state of the 
engine and information on an opening of the first control valve and then 
to multiply the target opening by the correction coefficient so obtained, 
whereby the correction of the target opening can be performed. 
The storage of the target opening correcting correction coefficients as a 
map in the storage means, said coefficients corresponding to the 
information on the temperature state of the engine and the information on 
the opening of the first control valve (and optionally becoming smaller as 
the temperature of the engine decreases or the opening of the first 
control valve increases), makes it possible--upon making correction to the 
target opening for the first control valve by the target opening setting 
means--to obtain from the map in the storage means the correction 
coefficient corresponding to the information on the temperature state of 
the engine and the information on the opening of the first control valve 
and then to multiply the target opening by the correction coefficient so 
obtained, whereby the correction of the target opening can be performed. 
According to the control system of this invention for the quantity of air 
to be inducted into the engine, the system is provided with the means for 
storing the opening data for the first control valve, said opening data 
having been set in advance corresponding to an operation state of the 
engine (the temperature state of the engine, the engine speed or the state 
of operation of an accessory). By the target opening setting means, the 
operation state of the engine is detected, the opening data corresponding 
to the operation state is obtained from the storage means, and the 
tentative target opening for the first control valve is then set. The 
tentative target opening is thereafter corrected based on at least one of 
the information on the temperature state of the engine and the information 
on the opening of the first control valve. The control system therefore 
has the advantages that a change to the quantity of air to be inducted for 
the compensation of a load can be effected independently without being 
affected by the temperature of the engine and inducted air can be obtained 
precisely in an inherently-needed quantity on the basis of the opening of 
the first control valve and in accordance with the degree of influence by 
the second control valve.

BEST MODE FOR CARRYING OUT THE INVENTION 
With reference to the drawings, a description will hereinafter be made of a 
control system according to the one embodiment of the present invention 
for the quantity of air to be inducted to an engine. 
An engine system for an automotive vehicle, to which the system according 
to the present invention is applied, can be illustrated as shown in FIG. 
3. In FIG. 3, the (internal combustion) engine which is designated at 
numeral 1 has an intake passage 3 and an exhaust passage 4, both of which 
are communicated to a combustion chamber 2. The communication between the 
intake passage 3 and the combustion chamber 2 is controlled by an intake 
valve 5, while the communication between the exhaust passage 4 and the 
combustion chamber 2 is controlled by an exhaust valve 6. 
The intake passage 3 is provided with an air cleaner 7, a throttle valve 8 
and an electromagnetic fuel injection valve (injector) 9, which are 
arranged successively from an upstream side of the intake passage 3. The 
exhaust passage 4, on the other hand, is provided with an 
exhaust-gas-cleaning catalytic converter (three-way catalyst) 10 and an 
unillustrated muffler (noise eliminator) successively from an upstream 
side of the exhaust passage 4. Further, the exhaust passage 3 is provided 
with a surge tank 3a. In addition, the throttle valve 8 is connected to an 
accelerator pedal (not shown) via a wire cable so that the position of the 
throttle valve 8 is regulated according to the stroke of the accelerator 
pedal. 
Incidentally, the intake passage 3 is provided, as depicted in FIG. 3 and 
FIG. 4, with a bypass passage 11 which extends bypassing the throttle 
valve 8. Inserted in this bypass passage 11 is a stepper motor valve 
(hereinafter called the "STM valve"; the first control valve) 12 which 
functions as an ISC valve. 
The STEM valve 12 is, as shown in FIG. 4, constructed of a valve element. 
12a which can be brought into contact with a valve seat portion 11a formed 
on an upstream side in the bypass passage 11, a stepper motor 12b for 
controlling the position of the valve element 12a, and a spring 12c 
biasing the valve element 12a in the direction that the valve element is 
pressed against the valve seat 11a (i.e., in the direction that the bypass 
passage 11 is closed). 
By adjusting the position of the valve element 12a stepwise (according to 
the number of steps) relative to the valve seat portion 11a (i.e. the 
position relative to the horizontal direction in the drawing) by the 
stepper motor 12b, the opening between the valve seat portion 11a and the 
valve element 12a, that is, the opening of the STM valve 12 can be 
controlled. 
By controlling the opening of the STM valve 12 by ECU which will be 
described subsequently herein, intake air can be fed to the engine 1 
through the bypass passage 11 during idling irrespective of operation of 
the accelerator pedal by the driver. By changing its opening, the quantity 
of air to be inducted through the throttle bypass passage can be 
controlled. 
Further, a limiter (the second control valve) 13 is interposed in the 
bypass passage 11 so that the limiter is located in series with the STM 
valve 12. This limiter 13 is changed in opening in correspondence to the 
temperature state of the engine 1 and, as is illustrated in FIG. 4, is 
constructed of a valve element 13a, which can be brought into contact with 
a valve seat portion 11b formed on a downstream side in the bypass passage 
11, and a drive unit 13b for adjusting the position of the valve element 
13a. 
The drive unit 13b of the limiter 13 is made, for example, of a wax or a 
bimetal. Its volume or shape is caused to vary in correspondence to the 
temperature state of the engine 1, so that the position of the valve 
element 13a relative to the valve seat portion 11b (i.e., the 
position-relative to the horizontal direction in the drawing) can be 
adjusted in a stepless manner to control the opening between the valve 
seat portion 11b and the valve element 13b, that is, the opening of the 
limiter 13. 
Around an outer peripheral portion of the drive unit 13b of the limiter 13, 
a coolant 14 for the engine 14 is introduced very close to the outer 
peripheral portion so that the drive unit 13b is operated under the 
influence of the temperature of the coolant 14 as the temperature state of 
the engine 1. As the limiter 13, a butterfly valve of the bimetal type can 
be used as a specific example. 
The opening of the limiter 13, that is, the position of the valve element 
13a is controlled by the drive unit 13b so that the valve element is fully 
opened (i.e., is brought to a most opened position), for example, at 
-30.degree. C. when the temperature state of the engine (i.e., the 
temperature of the coolant 14) is low but is fully closed (i.e., is 
brought to a most closed position at which the valve element is not fully 
closed and some intake air is still allowed to pass through the bypass 
passage 11), for example, at +40.degree. C. when the temperature state of 
the engine 1 is high. This control of the opening of the limiter 13 is 
performed by the drive unit 13b in a manner fully independent from the 
below-described control of the opening of the STM valve 12 by ECU. 
By the limiter 13 as described above, the maximum quantity of intake air 
which is allowed to pass through the bypass passage 11 at the time of a 
hot state is limited, thereby making it possible to avoid any 
unnecessarily high increase in the idling speed at the time of the hot 
state. 
In FIG. 3, numeral 15 indicates a fuel pressure regulator. This fuel 
pressure regulator 15 is actuated responsive to a negative pressure in the 
intake passage 3 to control the quantity of fuel to be returned from an 
unillustrated fuel pump to an unillustrated fuel tank, so that the 
pressure of fuel to be injected from the injector 9 can be controlled. 
Owing to the construction as described above, air--which has been inducted 
through the air cleaner 7 in accordance with the opening of the throttle 
valve 8 and also the openings of the STM valve 12 and the limiter 13--is 
mixed with fuel from the injector 9 at the place of an intake mainfold to 
achieve an appropiate air/fuel ratio. By actuating the spark plug 16 at an 
adequate timing within the combustion chamber 2, the resulting air-fuel 
mixture is caused to burn so that an engine torque is produced. The 
air-fuel mixture is then exhausted at exhaust gas into the exhaust passage 
4 and, subsequent to purification of the three toxic components CO, HC and 
NOx in the exhaust gas through the catalytic converter 10, is deadened in 
noise and then released to a side of the surrounding atmosphere. 
To control the operation state of the engine 1, various sensors are 
arranged. First, as is shown in FIG. 3, a portion where intake air flowed 
past the air cleaner 7 flows into the intake passage 3 is provided with an 
air flow sensor (inducted air quantity sensor) 17 for detecting the 
quantity of the inducted air from Karman vortex information, an intake air 
temperature sensor 18 for detecting the temperature of the intake air, and 
an atmospheric pressure sensor 19 for detecting the atmospheric pressure. 
At the position of arrangement of the throttle valve 8 in the intake 
passage 3, there are arranged a throttle position sensor 20 in the form of 
a potentiometer for detecting the position of the throttle valve 8 as well 
as an idling switch 21 for mechanically detecting a fully-closed state of 
the throttle valve 8 (i.e., an idling state) from the position of the 
throttle valve 8. 
On the side of the exhaust passage 4, on the other hand, an oxygen 
concentration sensor (hereinafter referred to simply as the "O.sub.2 
sensor") 22 for detecting the concentration of oxygen (O.sub.2 
concentration) in the exhaust gas is disposed on an upstream side of the 
catalytic converter 10. Other sensors include a coolant temperature sensor 
23 for detecting the temperature of the coolant 14 for the engine 1, a 
crank angle sensor 24 for detecting a crank angle (which can also function 
as a speed sensor for detecting an engine speed Ne), etc. 
Detection signals from these sensors and switch are inputted to an 
electronic control unit (ECU) 25 as shown in FIG. 2. 
The hardware construction of ECU 25 can be illustrated as shown in FIG. 2. 
ECU 25 is provided as a principal component thereof with CPU (processor) 
26. To CPU 26, detection signals from the intake air temperature sensor 
18, the atmospheric pressure sensor 19, the throttle position sensor 20, 
the O.sub.2 sensor 22 and the coolant temperature sensor 23 are inputted 
via an input interface 28 and an analog/digital converter 29. 
Directly inputted through an input interface 35 to CPU 26 are detection 
signals from the air flow sensor 17, the idling switch 21, the crank angle 
sensor 24, the vehicle speed sensor 30 and the like; and on/off signals 
from an air conditioner switch 31, a power steering switch 32, current 
consumer switches (switches of fog lamps, head lamps and the like) 33, an 
ignition switch (key switch) 34 and the like. 
Through a bus line, CPU 26 also exchanges data with ROM (memory means) 36, 
in which various data to be described subsequently with reference to FIG. 
6 through FIG. 10 are stored along with program data and fixed value data, 
and also with RAM 37 which is updated, that is, successively rewritten and 
also with battery backed-up RAM 38 whose stored contents are held as long 
as it is connected to a battery. 
Incidentally, the data in RAM 37 are cleared and reset when the ignition 
switch 34 is turned off. 
As a result of computation by CPU 26, ECU 25 outputs signals for 
controlling the state of operation of the engine 1 and the states of 
various accessories and the like, for example, various control signals 
such as a fuel injection control signal, an idling speed control signal, 
an air conditioner control signal, a fuel pump control signal, an ignition 
timing control signal, an engine check lamp lighting signal, and an alarm 
lamp lighting signal. 
Of these control signals, the fuel injection control (air/fuel ratio 
control) signal is outputted from CPU 26 to an injector solenoid 9a 
(precisely, a transistor for the injector solenoid 9a), which is arranged 
to drive the injector 9, via an injector solenoid driver 39. Further, the 
ignition timing control signal is outputted from CPU 26 to a power 
transistor 39 via an ignition coil driver 40, so that the individual spark 
plugs 16 are successively caused to produce sparks through the power 
transistor 41, an ignition coil 42 and a distributor 43. Further, the ISC 
control signal is outputted from CPU 26 to the stepper motor 12b for the 
STM valve 12 via an ISC driver (which functions in FIG. 1 as the valve 
opening setting means to be described subsequently herein) 44. 
Now paying attention to the idling speed control during idling, ECU 25 is 
provided, as shown in FIG. 1, with target opening setting means for 
revolution number feedback (NFB) control and also with target opening 
setting means 46 for position feedback (PFB) control. 
Further, ROM 36 employed in the present embodiment stores opening setting 
opening data for the STM valve 12, said opening setting opening data 
having been set in advance corresponding to operation states of the engine 
1, and also correction data (correction coefficients k) to be used upon 
correction of target openings at the target opening setting means 45,46, 
and stores, for example, the below-described data (1) to (4) or the like 
in the form of functions or a map or table. 
In the present embodiment, each opening data for the STM valve 12 is set in 
terms of a corresponding number of drive steps by the stepper motors 12b. 
(1) Data for use upon NFB control, for example, opening data (corrected 
positions) .DELTA.P corresponding to speed differences .DELTA.Ne between 
engine speeds Ne (as detected by the crank angle sensor 24) and target 
engine speeds Ne.sub.OBJ, as illustrated in FIG. 6. 
(2) Date for use upon PFB control, for example, first opening data (basal 
opening data upon PFB control) P.sub.BASE corresponding to temperature 
states of the engine 1 (i.e., coolant temperatures as detected by the 
coolant temperature sensor 23), as illustrated in FIG. 7. 
(3) Date for use upon PFB control, for example, second opening data 
corresponding to operation states of various accessories to the engine 1 
(in the present embodiment, corrected opening data P.sub.AC corresponding 
to operations of the air conditioner, corrected opening data P.sub.PS 
corresponding to operations of the power steering, and corrected opening 
data P.sub.EL corresponding to operations of current consumers). 
(4) Correction data (correction coefficients k which multiply tentative 
target openings to be described subsequently herein) for use upon 
correction of target openings at the target opening setting means 45,46, 
for example, correction coefficients k corresponding to information on 
temperature states of the engine (i.e., coolant temperatures as detected 
by the coolant temperature sensor 23) as illustrated in FIG. 8 i.e., those 
set at 0.5 when the coolant temperature is -30.degree. C., linearly 
increasing up to +40.degree. C., and set at 1.0 at +40.degree. C. and 
higher), or correction coefficients k corresponding to information on 
temperature states of the engine and information on openings of STM valve 
12 (i.e., tentative target openings P.sub.OBJ(t) or P.sub.OBJ to be 
described subsequently herein) as illustrated in FIG. 9 [i.e., those set 
smaller as the coolant temperature decreases or the actual opening (number 
of steps) of the STM valve 12 increases; 0.5 at the minimum and 1.0 at the 
maximum]. 
Incidentally, the above-described opening data (1)-(3) are set 
corresponding to a time at which the temperature of the coolant 14 is high 
(for example, +40.degree. C.) and the limiter 13 is most closed. 
On the other hand, RAM 37 employed in the present embodiment stores, for 
example, a target engine speed Ne.sub.OBJ needed upon reading the 
above-described opening data (1) and information on an opening of the STM 
valve 12 (i.e., P.sub.OBJ(t-1) set immediately before by a first setting 
means 45) required upon calculation of a tentative target opening 
P.sub.OBJ(1) at the first setting means 45A of the NFB opening setting 
means 45 as will be described subsequently herein. The target engine speed 
Ne.sub.OBJ can be stored in ROM 36. 
The NFB target opening setting means 45 and the PFB target opening setting 
means 46 are operated when the engine 1 is in an idling state (i.e., when 
the idling switch 21 is ON). They receive from ROM 36 opening data 
corresponding to the state of operation of the engine 1 (i.e., information 
obtained from the switches 31-33 and the sensors 20,23,24) and set a 
tentative target opening P.sub.OBJ for the STM valve 12. They also obtain 
a correction coefficient k from ROM 36 on the basis of at least one of 
information on the state of temperature of the engine 1 from the coolant 
sensor 23 and information on an opening of the STM valve 12, correct the 
tentative target opening P.sub.OBJ by the correction coefficient k and 
hence set an actual target opening P.sub.ACT. 
Here, the NFB target opening setting means 45 operates during idling in 
stoppage and performs feedback control of the opening of the STM valve 12 
so that the speed Ne of the engine 1 can be controlled to the target 
engine speed Ne.sub.OBJ stored in RAM 37. The NFB target opening setting 
means is constructed of the first setting means 45A an second setting 
means 45B. 
The first setting means 45A reads from RAM 37 the tentative target opening 
P.sub.OBJ(t-1) set immediately before and also reads from ROM 36 the 
opening data .DELTA.P corresponding to the difference .DELTA.Ne in engine 
speed between the engine speed Ne detected by the crank angle sensor 24 
and the target engine speed Ne.sub.OBJ stored in RAM 37. Based on both the 
tentative target opening P.sub.OBJ(t-1) and the opening data .DELTA.P, the 
first setting means sets the tentative opening P.sub.OBJ(t) 
(=P.sub.OBJ(t-1) +.DELTA.P). 
Further, the second setting means 45B reads from ROM 36 the correction 
coefficient k corresponding to at least one of the information on the 
state of the temperature of the engine 1 from the coolant temperature 
sensor 23 and the information on the opening of the STM 12 from RAM 37, 
multiplies the tentative target opening P.sub.OBJ(t), which has been set 
by the first setting means 45A, by the correction coefficient k to correct 
the tentative target opening P.sub.OBJ(t) and sets the thus-corrected 
value as the actual target opening P.sub.ACT (=k.multidot.P.sub.OBJ(t)). 
The PFB target opening setting means 46, on the other hand, operates at the 
time of idling in running and also at the time of operation of one or more 
of the accessories during idling. To obtain high responsibility, the PFB 
target opening setting means performs direct control (actually, open-loop 
control) with respect to the opening (position, the number of steps) of 
the STM valve 12. The PFB target opening setting means is constructed of 
first setting means 46A and second setting means 46B. 
The first setting means 46A reads from ROM 36 the first opening data 
P.sub.BASE corresponding to the state of temperature of the engine 1 from 
the coolant sensor 23 an also reads the second opening data P.sub.AC, 
P.sub.PS, P.sub.EL corresponding to the states of operations of the 
various accessories to the engine 1, said second opening data being 
obtained as on/off signals of the switches 31-33, and by using (adding) 
these data together, sets the tentative target opening P.sub.OBJ. 
On the other hand, the second setting means 46B, like the second setting 
means 45B described above, reads from ROM 36 the correction coefficient k 
corresponding to at least one of the information on the state of 
temperature of the engine 1 from the coolant temperature sensor 23 and the 
information on the opening of the STM valve 12 from RAM 37, multiplies the 
tentative target opening P.sub.OBJ, which has been set by the first 
setting means 46A, by the correction coefficient k to correct the 
tentative target opening P.sub.OBJ and sets the thus-corrected value as 
the actual target opening P.sub.ACT (=k.multidot.P.sub.OBJ). 
In the present embodiment, the ISC driver 44 is designed to function as 
valve opening setting means for controlling the opening of the STM valve 
12 to the actual target opening P.sub.ACT which has been set by the target 
opening setting means 45 or 46. 
The tentative target opening P.sub.OBJ(t) set by the first setting means 
45A in the NFB target opening setting means 45 is stored in RAM 37, so 
that it can be used as the tentative target opening P.sub.OBJ(t-1) set 
immediately before and needed upon setting the next tentative target 
opening P.sub.OBJ(t). 
Next, idling speed control by the system of this embodiment constructed as 
described above will be described using the flow chart of FIG. 5. 
The idling speed control which is performed in accordance with the 
procedures shown in FIG. 5 is started upon detection of an ON state of the 
idling speed switch 21 and also an idling state of the engine 1. First 
read in CPU 26 of ECU 25 are information on the state of operation of the 
engine 1, for example, an engine speed Ne from the crank angle sensor 24, 
a coolant temperature from the coolant temperature sensor 23 (information 
on the state of temperature of the engine 1), vehicle speed information 
from the vehicle speed sensor 30, and on/off signals from the switches 
31-33 for various accessories as well as an A/N ratio from the air flow 
sensor 16, an intake air temperature from the intake air temperature 
sensor 18, an atmospheric pressure from the atmospheric pressure sensor 
19, and the like (step S1). 
Based on the vehicle speed information from the vehicle speed sensor 30 and 
the on/off signals from the switches 31-33 for the various accessories, it 
is then determined whether the engine is in an idling state in stoppage or 
in an idling or accessory-operated state in running. When the engine is in 
the idling state in stoppage, the revolution number feed back control 
(NFB) is selected to have the NFB target opening setting means 45 
operated. When the engine is in the idling or accessory-operated state in 
running, the position feed back (PFB) control is selected to have the PFB 
target opening setting means 46 operated (step S2). 
When the NFB control has been selected in step S2, a timer is started to 
determine if a control period (for example, 1 second) has elapsed (step 
S3), so that the processing and control can be performed in every control 
period. If the control period is over, processings in the below-described 
steps S4 to S8 are performed by the NFB target opening setting means 45 on 
the basis of data read at that time point. 
Namely, the engine speed difference .DELTA.Ne between the engine speed Ne 
detected by the crank angle sensor 24 and the target engine speed 
Ne.sub.OBJ stored in RAM 37 is calculated at the first setting means 45A 
of the NFB target opening setting means 45 (step S4), and the opening data 
.DELTA.P corresponding to the engine speed difference .DELTA.Ne is read or 
calculated in accordance with data stored in ROM 36, for example, those 
shown in FIG. 6 (step S5). The opening data .DELTA.P can be stored in 
advance in ROM 36 as data corresponding to the engine speed difference 
.DELTA.Ne, or can be calculated by storing in advance a function on engine 
speed differences .DELTA.Ne, said function being capable of affording such 
data as shown in FIG. 6, in ROM 36, reading the function from ROM 36 and 
then introducing the engine speed difference .DELTA.Ne into the function. 
With respect to the opening data .DELTA.P, a dead zone is set so that, as 
is illustrated in FIG. 6, .DELTA.P becomes 0 when the absolute value of an 
engine speed difference .DELTA.Ne is not greater than a predetermined 
value N.sub.1 (&gt;0). When the engine speed difference .DELTA.Ne is greater 
than +N.sub.1, .DELTA.P is set at a value which is proportional to 
(.DELTA.N.sub.1 -N.sub.1). When the engine speed difference .DELTA.Ne is 
smaller than -N.sub.1, .DELTA.P is set at a value which is proportional to 
(.DELTA.Ne+N.sub.1). A change .DELTA.P to the opening of the STM valve 12, 
said change being required to reduce the engine speed difference .DELTA.Ne 
to 0, is calculated. 
At the first setting means 45A of the NFB target opening setting means 45, 
the tentative target opening P.sub.OBJ(t-1) set immediately before (i.e., 
at the time of the preceding control period) is read from RAM 37 and the 
opening data .DELTA.P obtained as described above is added to the 
tentative target opening P.sub.OBJ(t-1), whereby the present tentative 
target opening P.sub.OBJ(t) =(P.sub.OBJ(t-1) +.DELTA.P) is calculated and 
set. (step S6). 
To the present tentative target opening P.sub.OBJ(t) obtained by the first 
setting means 45A, correction based solely on the coolant temperature from 
the coolant temperature sensor 23 (i.e., the information on the state of 
temperature of the engine 1) or correction based on the coolant 
temperature and the present tentative target opening P.sub.OBJ(t) is 
applied by the second setting means 45B, so that the actual target opening 
P.sub.ACT is calculated (step S7). 
Here, to perform the correction based solely on the coolant temperature 
from the coolant temperature sensor 23 (i.e., the information on the state 
of temperature of the engine 1), a correction coefficient k in a range of 
0.5 to 1.0, said correction coefficient corresponding to the coolant 
temperature from the coolant temperature sensor 23, is read from ROM 36 on 
the basis of such a graph as shown in FIG. 8, the present tentative target 
opening P.sub.OBJ(t) is multiplied by the correction coefficient k to 
correct the present tentative target opening P.sub.OBJ(t), and the value 
so corrected is set as the actual target opening P.sub.ACT. 
The correction coefficient k can be stored in advance as data corresponding 
to the coolant temperature from the coolant temperature sensor 23, Ne, or 
can be calculated by storing in advance a function on coolant 
temperatures, said function being capable of affording such data as shown 
in FIG. 8, in ROM 36, reading the function from ROM 36 and then 
introducing the coolant temperature into the function. 
The correction coefficients k shown in FIG. 8 has been set as described 
above so that it is at 0.5 when the coolant temperature is -30.degree. C., 
linearly increases up to +40.degree. C., and is at 1.0 at +40.degree. C. 
and higher. Further, the present tentative target opening P.sub.OBJ(t) 
calculated in step S6 is set as described above so that it is set 
corresponding to the state that the coolant temperature is +40.degree. C. 
and the limiter 13 is most closed. 
Accordingly, the correction coefficient k becomes 1.0 when the coolant 
temperature is +40.degree. C. or higher so that the present tentative 
target opening P.sub.OBJ(t) is set as is. In the coolant temperature range 
from +40.degree. C. to -30.degree. C. at which the limiter 13 is brought 
into the most opened state, the correction coefficient k ranges from 1.0 
to 0.5 so that the present tentative target opening P.sub.OBJ(t) is 
corrected by a smaller degree (to a half at the minimum) as the coolant 
temperature becomes lower and k.multidot.P.sub.OBJ(t) is set as the actual 
target opening P.sub.ACT. 
With respect to both the state that the coolant temperature (engine 
temperature) is relatively low and the maximum bypass flow rate as set by 
the limiter 13 is relatively high and the state that the coolant 
temperature is relatively high and the maximum bypass flow rate as set by 
the limiter 14 is relatively low, there is the conventional tendency that, 
even if correction of the same degree (the same number of steps) is made 
to the opening of the STM valve 12 in a range of relatively large openings 
of the STM valve (ISC valve) 12, the influence of the limiter 13 is 
smaller and the change to the quantity of air to be inducted tends to 
become greater in the former state but the influence of the limiter 13 is 
greater and the change to the quantity of air to be inducted tends to 
become smaller in the latter state. Accordingly, the change to the 
quantity of air to be inducted by the STM valve 12 is affected by the 
engine temperature and is not made to the same extent. 
By conducting the correction in step S7 as described above, it is however 
possible for the below-described reasons to perform the same change by the 
STM valve 12 to the quantity of air to be inducted without being affected 
by the engine temperature. As the temperature of the coolant becomes 
lower, the tentative target opening P.sub.OBJ(t) is corrected by a smaller 
degree to k.multidot.P.sub.OBJ(t), which is then set as the actual target 
opening P.sub.ACT. In FIG. 10, the correction coefficient k becomes 
greater at high temperatures, for example, with respect to such an 
increase .DELTA.P in the opening as indicated by arrow 1. Although the 
increase in the actual target opening P.sub.ACT is substantially the same 
as .DELTA.P as indicated by arrow 3, the correction coefficient k becomes 
smaller at low temperatures so that the increase in the actual target 
opening P.sub.ACT can be made smaller as indicated by arrow 2. It is hence 
possible to perform the change by the STM valve 12 to the quantity of air, 
which is to be inducted, to the same extent without being affected by the 
engine temperature. 
It has been described in the above about the control in which in step S7, 
the correction coefficient k is determined based solely on the coolant 
temperature from the coolant temperature sensor 23 while using such a 
graph as shown in FIG. 8 and the correction of the present tentative 
target opening P.sub.OBJ(t) is then performed. To perform correction on 
the basis of the coolant temperature from the coolant temperature sensor 
23 and the present tentative target opening P.sub.OBJ(t), a correction 
coefficient k in the range of 0.5 to 1.0, said correction coefficient 
corresponding to the coolant temperature from the coolant temperature 
sensor 23 and the present tentative target opening P.sub.OBJ(t), is read 
from ROM 36, for example, on the basis of such a table as shown in FIG. 9, 
the present tentative target opening P.sub.OBJ(t) is multiplied by the 
correction coefficient k to correct the present tentative target opening 
P.sub.OBJ(t), the value so corrected is then set as an actual target 
opening P.sub.ACT. Here, correction coefficients k shown in FIG. 9 are 
set, as described above, smaller as the coolant temperature decreases and 
the actual opening (the number of steps) of the STM valve 12 increases 
(0.5 at the minimum and 1.0 at the maximum). 
As a consequence, it is possible to perform a change by the STM valve 12 to 
the quantity of air, which is to be inducted, without being affected by 
the engine temperature as in the correction performed based solely on the 
coolant temperature from the coolant temperature sensor 23. 
Conventionally, under the same temperature conditions, the degree of 
influence of a limitation by the limiter 13 to the flow rate increases 
when the opening of the STM valve (ISC valve) 12 becomes relatively large. 
As shown in FIG. 9, the present tentative target opening P.sub.OBJ(t) is 
however considered even under the same temperature conditions so that the 
correction coefficient k is made smaller to give a smaller actual target 
opening P.sub.ACT as the value of the present tentative target opening 
P.sub.OBJ(t) increases (the opening becomes greater). The above control 
can therefore accurately obtain inducted air in a quantity inherently 
required depending on the degree of influence of the limiter 13 which 
varies based on the opening of the STM valve 12. 
The actual target opening P.sub.ACT obtained in step S7 as described above 
is stored (step S8) and the opening of the STM valve 12 is controlled by 
the ISC driver 44 to the stored actual target opening P.sub.ACT from the 
NFB target opening setting means 45, so that during idling in stoppage, 
the opening of the STM valve 12 is feedback controlled to maintain the 
speed Ne of the engine 1 at the target engine speed Ne.sub.OBJ stored in 
RAM 37. 
When the PFB control is selected in step S2, on the other hand, the timer 
is started as in step S3 to determine if a control period (for example, 1 
second) has elapsed (step S9), so that the processing and control can be 
performed in every control period. If the control period is over, 
processings in the below-described steps S10-S19,S8 are performed by the 
PFB target opening setting means 46 on the basis of data read at that time 
point. 
Namely, at the first setting means 46A of the PFB target opening setting 
means 46, the first opening data P.sub.BASE (the basal opening data for 
the time of the PFB control) corresponding to the coolant temperature (the 
state of temperature of the engine 1) from the coolant temperature sensor 
23 is read in accordance with data stored in ROM 36, for example, those 
shown in FIG. 10 (step S10). 
Incidentally, the first opening data P.sub.BASE can be stored in advance in 
ROM 36 as data corresponding to the coolant temperature or can be 
calculated by storing in advance a function on coolant temperatures, said 
function being capable of affording such data as shown in FIG. 10, in ROM 
36, reading the function from ROM 36 and then introducing the coolant 
temperature into the function. 
As is illustrated in FIG. 10, the first opening data P.sub.BASE is set, for 
example, as a function which is in inverse proportion to the coolant 
temperature so that the first opening data decreases as the coolant 
temperature becomes higher but increases as the coolant temperature 
becomes lower. 
At the first setting means 46A of the PFB target opening setting means 46, 
the tentative target opening P.sub.OBJ (=P.sub.BASE +.DELTA.P) is 
calculated and set by detecting the states of operations of the various 
accessories to the engine 1 [the air conditioner, the power steering, the 
current consumers (fog lamps, head lamps, etc.)] on the basis of on/off 
signals from the air conditioner switch 31, the power steering switch 32 
and the current consumer switches 33, and when the individual switches 
31-33 are ON, reading from ROM 36 the second opening data 
P.sub.AC,P.sub.PS,P.sub.EL corresponding to quantities of air to be 
increased in correspondence to the operations of the accessories and then 
adding these opening data P.sub.AC, P.sub.PS,P.sub.EL to the first opening 
data P.sub.BASE obtained in step S10 (steps S11-S18). 
Namely, as is illustrated in FIG. 5, it is first determined in step S11 
whether the air conditioner switch 31 is ON. If it is ON, the opening data 
P.sub.AC for the time of operation of the air conditioner is read and set 
as an increase .DELTA.P in the opening data from ROM 36 (step S12). If it 
is OFF, 0 is set as an increase .DELTA.P in the opening data (step S13). 
It is next determined whether the power steering switch 32 is ON (step 
S14). If it is ON, the opening data P.sub.PS for the time of operation of 
the power steering is read from ROM 36 and is added to the increase 
.DELTA.P in the opening data (step S15). Further, it is also determined 
whether the current consumer switches 33 are ON (step S16). If they are 
ON, the opening data P.sub.EL for the time of operation of the current 
consumers is read from ROM 36 and is added to the increase .DELTA.P in the 
opening data (step S17). 
The finally-obtained increase .DELTA.P in the opening also determined 
whether the current consumer switches 33 are ON (step S16). If they are 
ON, the opening data P.sub.EL for the time of operation of the current 
consumers is read from ROM 36 and is added to the increase .DELTA.P in the 
opening data (step S17). 
The finally-obtained increase .DELTA.P in the opening data is then added to 
the first opening data P.sub.BASE obtained in step S10, whereby the 
tentative target opening P.sub.OBJ is calculated and set (step S18). 
To the tentative target opening P.sub.OBJ obtained by the first setting 
means 46A, correction based solely on the coolant temperature from the 
coolant temperature sensor 23 (i.e., the information on the state of 
temperature of the engine 1) or correction based on the coolant 
temperature and the present tentative target opening P.sub.OBJ is applied 
by the second setting means 46B in exactly the same manner as explained in 
step S7, so that the actual target opening P.sub.ACT is calculated (step 
S19). 
The actual target opening P.sub.ACT obtained in step S19 as described above 
is stored (step S8) and the opening of the STM valve 12 is controlled by 
the ISC driver 44 to the stored actual target opening P.sub.ACT from the 
PFB target opening setting means 46, so that during idling in running or 
responsive to operations of the accessories during idling, the opening 
(the position or the number of steps) of the STM valve 12 is directly 
controlled with high responsibility. 
As a result, where the STM valve 12 and the limiter 13 are arranged in 
series with each other in the bypass passage 11, the opening of the STM 
valve 12 is controlled while applying correction in accordance with the 
temperature state of the engine 1 (i.e., the coolant temperature) so that 
a change to the quantity of air, which is to be inducted for the 
compensation of a load, can be performed to the same extent without being 
affected by the engine temperature. Further, the use of such data as shown 
in FIG. 9 makes it possible to precisely obtain intake air in a quantity 
inherently required depending on the degree of influence of the limiter 13 
which varies based on the opening of the STM valve 12. 
In the embodiment described above, the description was made of the case 
where the system according to the present invention was applied to the 
engine (internal combustion engine) for the automotive vehicle. The system 
of the present invention is however not limited to the above embodiment. 
It can be applied likewise to engines employed as various power sources 
and the like and can bring about similar advantageous effects. 
INDUSTRIAL APPLICABILITY 
As has been described above, the control system according to the present 
invention for the quantity of air to be inducted into an engine is useful 
in controlling the idling speed not only in an engine for an automotive 
vehicle (an internal combustion engine) but also in engines employed as 
various power sources and the like, and is suited especially in 
controlling the idling speed of an engine in which an ISC valve and a 
limiter arranged in series with each other in a throttle valve bypass 
passage.