Idling speed control system of an internal combustion engine

The present invention is adapted for providing an idling speed control system of an internal combustion engine, which exhibits a good response for changes in an engine load, comprising: a throttle valve which controls the amount of intake air for the engine; an actuator which includes an electric motor for variably controlling the opening of the throttle valve; a rotation speed detector for detecting the rotation speed of the engine; an idling condition detector for detecting the idling condition of the engine; and a control, responsive to the detected output of the idling condition detector means, for generating feedback control pulses to intermittently drive said electric motor so that the detected rotation speed of the engine under the idling condition may converge into a target idling rotation speed while, responsive to the output of a detector that detects the operation condition of the engine load operated under the idling condition of the engine, or to the detected output of said rotation speed detector indicating that the detected rotation speed has dropped to an abnormally low rotation speed of the engine, for generating drive control pulses at a time independent of said feedback control pulses to drive said electric motor in a predetermined direction.

TECHNICAL FIELD 
The present invention relates to a system for controlling idling rotation 
speed of an internal combustion engine employed in an automobile or the 
like. 
BACKGROUND ART 
Some automobiles are equipped with an apparatus for controlling the idling 
rotation speed, by comparing the engine rotation speed under idling 
condition with a target idling rotation speed, changing the opening of a 
throttle valve depending upon the deviation therebetween so that the 
engine speed is controlled at a target rotation speed, thereby reducing 
the consumption of fuel under the idling condition. 
Conventional apparatuses for controlling the idling speed use a cheaply 
constructed DC motor that works as an actuator to change the opening of 
the throttle valve, the DC motor being controlled in a rotating direction 
which corresponds to a speed deviation polarity between a target rotation 
speed and a practical rotation speed. To improve the control precision, 
furthermore, the DC motor is intermittently driven by intermittent 
feedback control pulses of a predetermined period, and the pulse width 
thereof is controlled depending upon the amount of the speed deviation. In 
this conventional apparatus, the pulse period is set so that the pulse 
pause interval hereinafter referred to as hold time becomes relatively 
long, by taking into consideration a snaking time of the DC motor and the 
delay time between the time when the opening of the throttle valve is 
changed and the time when the change of the engine speed is reflected 
thereby. Therefore, when it is expected that the engine rotation speed 
changes or drops abnormally due to the operation of loads such as an 
air-conditioning apparatus or a power steering appratus during a 
predetermined hold time, it is necessary to wait for the next pulse even 
when an estimated correction according to a pulse width correction is to 
be effected by detecting the operation of such loads. Accordingly, 
response for the change in the engine load is delayed possibly causing the 
engine to stall. 
DISCLOSURE OF THE INVENTION 
The present invention has been made in order to solve the above-mentioned 
problem, and its object is to provide an idling rotation speed control 
system of an internal combustion engine that exhibits a good response for 
changes in an engine load. 
For this purpose, according to the present invention, provision is made of 
detection means to detect the operation condition of the engine load as 
operated under the idling condition or an abnormally low engine speed and 
a feedback control means to generate feedback control pulses of 
predetermined periods and holding time. The invention provides control 
means to generate control pulses responsive to abnormal changes in the 
operation condition or engine speed to change the opening of a throttle 
valve at a time independent of the generation of an ordinary feedback 
control pulse, and holding time.

BEST MODES FOR PRACTICING THE INVENTION 
FIG. 1 is a structural diagram illustrating one embodiment of the present 
invention. In this figure, the structure of the engine will be described 
first. Reference numeral (1) denotes a piston, (2) denotes a cylinder, (3) 
denotes an intake valve, (4) denotes an exhaust valve, (5) denotes an 
exhaust pipe, (6) denotes a catalytic converter rhodium, (7) denotes an 
intake pipe, and (8) denotes a throttle valve. On the upstream side of the 
throttle valve (8), there are provided a venturi (9) and an air cleaner 
(10). The fuel in a float chamber (11) is sucked in and atomized via a 
main fuel path (12) as the air sucked in via the air cleaner (10) passes 
through the venturi (9) so that the mixture gas of the fuel and the intake 
air is introduced into the cylinder (2) through the throttle valve (8) and 
the intake pipe (7). 
Here, a main air bleed (13) is provided in the main fuel path (12), and the 
fuel in the float chamber (11) is preliminarily divided into fine droplets 
by the air sucked in through a main air bleed path (14) formed on the 
upstream side of the venturi (9) and them atomized. 
An idle port (15) is formed on the downstream side of the throttle valve 
(8), and further, a slow air bleed path (16) is provided on the upstream 
side of the venturi (9). The fuel in the main fuel path (12) is divided 
into fine droplets in the slow air bleed (17) by the air sucked in through 
the slow air bleed path (16), and is blown out of the idle port (15). This 
ensures the supply of the fuel maintained under the idling condition where 
the throttle valve (8) is almost closed. In this case, the amount of the 
fuel blown from the idle port (15) is adjusted by a slow adjust screw 
(18). 
The throttle valve (8) is coupled to an accelerator pedal (not shown). When 
the automobile is running, the throttle valve is opened to a degree that 
corresponds to the amount by which the accelerator pedal is depressed 
while under the idling condition where the accelerator pedal is liberated, 
the throttle valve is opened to a degree (almost fully closed) that is 
necessary to maintain the idling operation condition. The throttle valve 
(8) is equipped with a level (19), on the rotary axis thereof, which is 
driven by an actuator (20) which will be hereinafter described, thereby 
varying the opening of the throttle valve under the idling condition. 
Described herebelow is the structure of a system for controlling the idling 
speed. Reference numeral (20) denotes an actuator which consists of a DC 
motor (21) and a gear mechanism (22). The rotary motion of the DC motor 
(21) is converted by the gear mechanism (22) into the linear motion of a 
plunger (23) which actuates the lever (19) to change the opening of the 
throttle valve (8). The DC motor (21) is supplied with a forward rotation 
control pulse U of a predetermined pulse width and with a reverse rotation 
control pulse D sent from a control circuit (30). The actuator (20) is 
provided with an idling condition detector switch (24) which turns on 
(closes) when the tip of the plunger (23) hits on the lever (19), i.e., 
under the idling condition where the accelerator pedal is liberated. 
Reference numeral (25) denotes a rotation speed detector for detecting the 
engine rotation speed in which rotation pulse signals of a period 
corresponding to the engine rotation speed N are taken out of a connection 
point between an ignition coil (26) and an interrupter (27). Reference 
numeral (28) denotes an operation start switch (hereinafter abbreviated as 
A/C.S) of an air-conditioning apparatus which is one of the engine loads, 
(29) denotes a transmission switch which detects that the transmission 
(not shown) is at the neutral position or that the clutch (not shown) is 
engaged (trod in), namely that the engine is disconnected from the wheels, 
and (30) denotes a control circuit which controls the opening of the 
throttle valve under the idling condition relying upon signals produced by 
the idling switch (24) which detects the idling condition, produced by the 
speed detector 25, produced by the A/C.SW (28), and produced by the 
transmission switch (29), such that the engine rotation speed converges 
into a target rotation speed N.sub.O. 
The control circuit (30) consists, as shown in FIG. 2, of an operation 
processing unit (hereinafter abbreviated as CPU) (300), a read-only memory 
(hereinafter abbreviated as ROM) (301) which stores a program for 
controlling the idling speed and stores constants etc., a random access 
memory (hereinafter abbreviated as RAM) (302) which stores an interim 
result of arithmetic operation etc., and an interface circuit (hereinafter 
abbreviated as IFC) (303) for transmitting and receiving signals between 
the above-mentioned various switches and the actuator (20). 
The operation of the above-mentioned structure will now be described with 
reference to flow charts shown in FIGS. 3 and 4. 
First, as the engine is started, the CPU (300) executes such a processing 
as shown in FIG. 3 in accorddance with the program stored in the ROM 
(301). That is, the CPU (300) receives output signals of the speed 
detector (25) and measures the period of said signals to detect the 
present engine rotation speed N (step 100), and then calculates the target 
rotation speed N.sub.O under the idling condition (step 101). The target 
rotation speed N.sub.O under the idling condition varies depending upon 
whether or not the air-conditioning apparatus is in operation, and has 
been determined as shown, for example, in Table 1. 
TABLE 1 
______________________________________ 
Air-conditioning 
Target idling rotation 
apparatus speed 
______________________________________ 
ON (operation) 900 RPM 
OFF (non-operation) 
700 RPM 
______________________________________ 
This target idling rotation speed N.sub.O has been stored beforehand as a 
constant in the ROM (301). Therefore, the calculation of the target idling 
rotation speed N.sub.O is effected by reading the above constant out of 
the ROM (301). 
Next, the CPU (300) discriminates in steps (102) and (103) whether or not 
the engine speed N lies in a controlled range of 400 RPM to 1500 RPM. When 
the engine speed does not lie within the controlled range, in step (114) 
the drive mode of the actuator (20) is set to the hold mode so that no 
control is executed for the actuator (20). When the engine speed N lies 
within the controlled range of from 400 RPM to 1500 RPM, however, step 
(104) discriminates whether or not the transmission switch (29) is on 
i.e., whether or not the transmission is at the neutral position, or 
whether or not the clutch is engaged, based on the output signal of the 
transmission switch (29), and thereafter, the next step (105) 
discriminates whether or not the idling detector switch (24) is on. As a 
result, when the transmission switch (29) is found to be off, it is 
assumed that the automobile is running so that in step (114) the drive 
mode is set to the hold mode. When the idling detector switch (24) is made 
off even under the condition where the transmission switch is on, it is 
assumed that the driver is operating the accelerator pedal so that in step 
(114) the drive mode is set to the hold mode. In either case, no control 
is executed for the actuator (20). 
However, when the transmission switch (29) is on (neutral condition or the 
clutch being engaged) and when the idling detector switch (24) is on, it 
is assumed that a main fuel is supplied to the engine through the idle 
port (15) or that the engine is under the idling condition so that the 
next step (106) is to discriminate whether or not the A/C.SW (28) has 
changed from on to off or from off to on. As a result, if there is no 
change in the state of the A/C.SW (28), in the next step (107) whether or 
not the engine speed N has dropped from a value of 500 RPM or more to an 
abnormally small value of 500 RPM or less is discriminated. As a result, 
if the engine rotation speed has not dropped to the abnormally small 
value, in the next step (108) a deviation (absolute value) between the 
target rotation speed N.sub.O and the present engine rotation speed N is 
determined, and further whether or not the deviation is greater than a 
predetermined value .DELTA.N.sub.D is detected. When the deviation is 
smaller than .DELTA.N.sub.D, in step (114) the drive mode of the actuator 
(20) is set to the hold mode. However, when the deviation is greater than 
the predetermined value .DELTA.N.sub.D, the processing is executed in the 
subsequent steps (109) to (113) to converge the engine speed N into the 
target rotation speed N.sub.O. 
Namely, in step (109), the present engine rotation speed N is compared with 
the target rotation speed N.sub.O. If N.sub.O &gt;N, the opening of the 
throttle valve (8) is required to be controlled so as to open. Therefore, 
the drive mode of the actuator (20) is set to an opening mode. Conversely, 
if N.sub.O &lt;N, the opening of the throttle valve (8) is required to be 
controlled so as to close. Accordingly, the drive mode of the actuator 
(20) is set to a closing mode. Then, in step (112), a drive time data 
P.sub.W of the actuator (20) corresponding to the deviation (N.sub.O -N) 
between N.sub.O and N is read out of the ROM (301). The relationship 
between the drive time data P.sub.W and the deviation (N.sub.O -N) has 
been so determined that the drive time data P.sub.W increases nearly in 
proportion to the increase in the deviation (N.sub.O -N) or (N-N.sub.O) as 
shown in FIG. 5. 
Thus, as there is obtained the drive time data P.sub.W of actuator (20) 
corresponding to the deviation between the idling target rotation speed 
N.sub.O and the present engine rotation speed N, in step (113) the CPU 
(300) causes the IFC (303) to generate the forward rotation control pulse 
U or the reverse rotation control pulse D to drive the actuator (20) only 
for a period of the drive time data P.sub.W in the direction corresponding 
to the drive mode. In this case, the forward rotation control pulse U is 
generated when the drive mode indicates the opening direction while the 
reverse rotation control pulse D is generated when the drive mode 
indicates the closing direction. 
Therefore, the throttle valve (8) is controlled and set in a direction 
corresponding to the target idling rotation speed N.sub.O, and the engine 
rotation speed N converges into the target rotation speed N.sub.O. 
Thereafter, the CPU (300) repeates the processing starting with step (100) 
and causes a control pulse corresponding to the change in the rotation 
speed at that moment after a fixed hold time T.sub.H has lapsed. 
Thus, the engine rotation speed N is maintained at the target rotation 
speed N.sub.O by such opening and opening controls of the throttle valve 
(8), that is feedback control, corresponding to the deviation between the 
target rotation speed N.sub.O and the engine rotation speed N. 
However, when the A/C.SW (28) has changed from on to off or from off to on, 
the CPU (300) detects this change in step (106). In step (115), a further 
detection is made to determine whether or not this change is from on to 
off or vice versa. If this change is toward the on-state, the drive mode 
of the actuator (20) is set to the opening drive mode (step 116). On the 
other hand, if this change is toward the off-state, the drive mode is set 
to the closing drive mode (step 117). Then, in the next step (118) a 
rotation speed change caused by the increase or decrease of the engine 
loads due to the start operation or the stop operation of the 
air-conditioning apparatus is estimated to read out of the ROM (301) the 
drive time data P.sub.WAC of actuator (20) that corresponds to the 
estimated change in the loads. Then, in step (113) the IFC (303) is caused 
to generate the forward rotation control pulse U or the reverse rotation 
control pulse D to drive the actuator (20) only for a period of the drive 
time data P.sub.WAC in the direction corresponding to the drive mode. 
Therefore, at a moment when the air-conditioning apparatus starts its 
operation, the opening of the throttle valve (8) is opened by a degree 
which corresponds to the drive time data P.sub.WAC whereas at a moment 
when the air-conditioning apparatus stops its operation, the opening of 
the throttle valve (8) is closed by a degree corresponding to the data 
P.sub.WAC. 
After having effected such an estimated control, the CPU (300) works to 
converge the idling speed into the target rotation speed N.sub.O by means 
of the feedback control through steps (100) to (112). 
In this case, the processing steps of the pulse drive control in step (113) 
are arranged as shown in the flow chart of FIG. 4, in which, at a time 
when the operation of the air-conditioning apparatus is started or 
stopped, the actuator (20) is immediately driven to effect the estimated 
control without waiting for the lapse of the predetermined hold time 
T.sub.H. 
Namely, in FIG. 4, when an ordinary feedback control without any change in 
the A/C.SW (28) is being carried out, the process of the CPU (300) passes 
through the judgement of step (200) and detects in step (201) whether or 
not the predetermined hold time T.sub.H has lapsed. When the hold time has 
not lapsed, the processes of the steps (100) to (113) are repetitively 
executed. When it is detected that the predetermined hold time T.sub.H has 
lapsed, in step (202) the drive mode of the actuator (20) is set to the 
opening mode or the closing mode. Then, in step (203) the drive time data 
P.sub.W determined by step (112) of FIG. 3 is set in a register for timer 
in the RAM (302), so that the forward rotation control pulse U or the 
reverse rotation control pulse D corresponding to the drive mode begins to 
be generated from the IFC (303). Then, the next step (204) is to determine 
whether or not the time for generating the control pulse U or D has 
lapsed, i.e., whether or not the drive time of the actuator (20) has 
reached P.sub.W. When the drive time has reached that, the generation of 
the control pulse U or D is stopped. Then, in step (205), the 
predetermined hold time T.sub.H is set in the register for timer, and in 
the next step (206), the drive mode is set to the hold mode, so that the 
process proceeds to step (100) of FIG. 3. This causes, under the ordinary 
feedback control, the actuator (20) to be intermittently driven by control 
pulses with the pause interval of the predetermined hold time T.sub.H 
whereby the engine rotation speed N is converged into the target rotation 
speed N.sub.O. 
However, when the A/C.SW (28) had changed into on or off, the process of 
the CPU (300) passes through the judgement of step (200) and in step (207) 
the drive mode of actuator (20) is set to the mode determined by step 
(116) or (117) of FIG. 3, and then in the next step (208) the drive time 
data T.sub.WAC determined by step (118) of FIG. 3 is set in the register 
for timer to cause the IFC (303) to start to generate the forward rotation 
control pulse U or the reverse rotation control pulse D corresponding to 
the drive mode. After it is detected in the next step (209) that the drive 
time has lapsed, the drive mode is set to the hold mode, and the process 
proceeds to step (100) of FIG. 3. This causes, when the A/C.SW (28) 
changes its state, the actuator (20) to be immediately driven without 
waiting for the lapse of the predetermined hold time T.sub.H. 
Therefore, when the A/C.SW (28) has changed, for example, from off to on, 
the forward revolution control pulse U is generated in the middle of the 
hold time T.sub.H as shown in FIG. 6. 
On the other hand, the same estimated control is carried out even when the 
engine rotation speed N has abnormally dropped to 500 RPM or less, the CPU 
(300) sets in step (116) the drive mode of the actuator (20) to the 
opening drive mode where the throttle valve (8) is opened, and then, in 
step (118), reads the drive time data P.sub.WAC out of the ROM (301). 
Then, passing through the judgement of step (200) of FIG. 4, the processes 
of steps (207) to (209) are executed. The throttle valve (8) is thereby 
opened by an opening that corresponds to the drive time data P.sub.WAC. 
Consequently, the engine rotation speed N is immediately restored in its 
increasing direction. 
According to this embodiment as described above, the engine rotation speed 
can be converged into a target rotation speed in quick response to 
variations in the engine loads or changes into an abnormally dropped 
speed, making it possible to prevent the engine rotation speed from 
quickly changing or from going into halt. Further, since use is made of a 
cheaply constructed DC motor as an actuator to control the opening of the 
throttle valve, the engine rotation speed can be converged into the target 
rotation speed at a low cost and with a good precision owing to an 
intermittent control. 
FIG. 7 is a flow chart illustrating a second embodiment of the present 
invention, showing a portion of the pulse control step (113) that 
corresponds to FIG. 4 of the first embodiment. 
Also in the case of the second embodiment, operations relates to FIG. 3 are 
the same as the aforementioned operations and so the descriptions thereof 
are omitted. What makes the embodiment of FIG. 7 different from the 
embodiment of FIG. 4 is that when the A/C.SW (28) changes into on or off 
or when the engine rotation speed drops to 500 RPM or less, the control 
pulse P.sub.WAC is generated independently of the feedback control pulse 
while the time for generating the feedback control pulse that is generated 
next to the independent control pulse P.sub.WAC is retarded behind the 
above pulse P.sub.WAC by a predetermined period of time, so that the 
feedback control pulse P.sub.W and the control pulse P.sub.WAC will not be 
concurrently generated. 
Herebelow is described in detail the operation when the A/C.SW (28) changes 
into on or off, or when the engine rotation speed drops to 500 RPM or 
less. The operation under the ordinary feedback control is the same as 
that of FIG. 4, and so the descriptions thereof are omitted. 
When the A/C.SW (28) changes into on or off, the process of the CPU (300) 
passes through step (200) and proceeds to step (202) irrespective of 
whether or not the hold time T.sub.H has lapsed. In step (202), the drive 
mode of actuator (20) is set to the mode determined by step (116) or (117) 
of FIG. 3, and then in the next step (203) the drive time data T.sub.WAC 
determined by step (118) of FIG. 3 is set in the register for timer, 
thereby causing the IFC (303) to initiate the generation of the forward 
rotation control pulse U or the reverse rotation control pulse D 
corresponding to the drive mode. Then, in the next step (204), the lapse 
of the drive time is detected, then in step (205), the predetermined hold 
time T.sub.H is set in a register for timer, and then in the next step 
(206), the drive mode is set to the hold mode. The process then proceeds 
to step (100) of FIG. 3. 
Therefore, when the A/C.SW (28) changes, for example, from off to on, the 
forward revolution control pulse U is generated in the middle of the hold 
time T.sub.H as shown in FIG. 6. 
Also when the engine rotation speed N becomes an abnormally dropped speed 
of 500 RPM or less, the estimated control is effected in the same manner. 
That is, as the CPU (300) detects in step (107) of FIG. 3 that the engine 
rotation speed N has dropped to 500 RPM or less, it sets, in step (116), 
the drive mode of actuator (20) to the opening mode where the throttle 
valve (8) is to be opened and then in step (118), reads the drive time 
data P.sub.WAC out of the ROM (301). Then, passing through the judgement 
of step (200) of FIG. 4, the processing of steps (202) to (206) is 
executed. The throttle valve (8) is thereby opened by an opening that 
corresponds to the drive time data P.sub.WAC. Consequently, the engine 
rotation speed N is immediately restored in its increasing direction. 
In this case, the CPU (300) under program control provides control means 
responsive to the output of the detector 25 that detects an abnormally low 
speed of the engine for generating a control pulse which is transmitted to 
the actuator 20 and, after such an estimated control has been executed, 
the predetermined hold time T.sub.H is set again in step (205). Therefore, 
the forward rotation control pulse U or the reverse rotation control pulse 
D by means of the feedback control (control through steps (109) to (112) 
of FIG. 3) after the estimated control, is inhibited from being generated 
until the hold time T.sub.H as set again has lapsed as shown in the time 
chart of FIG. 8. Namely, under a transient response condition of the 
engine due to the estimated control, the feedback control is inhibited for 
the predetermined period of time T.sub.H, and is started after the 
predetermined period of time has passed. This makes it possible to avoid 
the overlapping of the estimated control and the feedback control so that 
a contrary effect such as a rapid change due to the overlapping of both 
controls can be prevented. Moreover, the controlled variable by the 
estimated control can be set independently of the feedback control. 
According to this embodiment as described above, the engine rotation speed 
can be converged into a target rotation speed in quick response to changes 
in the engine loads or changes into an abnormally low rotation speed so 
that the engine rotation speed can be prevented from quickly changing or 
from going into halt. Further, since a DC motor is used as an actuator to 
control the opening of the throttle valve, the engine rotation speed can 
be converged into a target rotation speed at a low cost and with a good 
precision owing to an intermittent control. Further, it is possible to 
avoid the overlapping of the estimated control and the feedback control. 
Therefore, a contrary effect such as a rapid change of the engine rotation 
speed due to the overlapping of both controls can be prevented, and the 
engine rotation speed can be converged into a target rotation speed 
precisely and quickly. 
Although the foregoing description has dealt with the case where an 
air-conditioning apparatus is exemplified as an engine load, the invention 
can be similarly put into practice even in the case of a power steering 
apparatus or the like. 
INDUSTRIAL APPLICABILITY 
The present invention can be adapted not only for the control of the 
internal combustion engine of an automobile but also for the control of 
the internal combustion engines of other industrial machineries.