Method and apparatus for controlling the idling rotational speed of an internal combustion engine

The actual rotational speed of an internal combustion engine is detected, and the detected rotational speed is compared with upper and lower limit speed values to generate a control signal indicative of the change in the idle air flow to the engine to maintain the actual rotational speed within a desired range. The idle air flow to the engine is adjusted in response to the generated control signal. The above detection of the actual rotational speed or the adjusting is started after a predetermined period of time is passed from the moment when the engine falls into a predetermined idling condition.

BACKGROUND OF THE INVENTION 
The present invention relates to a method of and apparatus for controlling 
the idling speed of an internal combustion engine. 
A known method of controlling the idling speed consists of adjusting the 
position of a throttle valve or a flow-control valve in a throttle valve 
by-pass intake passage, by using a valve-control motor, such as a step 
motor or a servo motor, in feedback response to the running speed when the 
engine is idling. 
According to the conventional control method of this type, the feedback 
control is immediately started when the operating condition of the engine 
becomes a predetermined idling condition. The predetermined idling 
condition exists when the throttle valve is at the idling position and the 
running speed of a vehicle is nearly zero. However, the rotational speed 
of the engine is not immediately stabilized just after the predetermined 
idling condition is established; the engine usually runs at a relatively 
high speed for a while due to the moment of inertia and then runs at a 
gradually decreasing speed. Therefore, if the feedback control is 
initiated immediately after the predetermined idling condition is 
established, as has been done in the conventional art, a so-called 
undershoot phenomenon takes place in which rotational speed abruptly 
decreases. In the worst case, the engine stalls. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide a method of 
and apparatus for controlling the idling rotational speed, which is 
capable of effectively preventing the rotational speed of the engine from 
being erroneously controlled when feedback control of the idling 
rotational speed is initiated. According to the present invention, the 
operating condition of the engine is monitored and an idling state signal 
is generated when the engine is in a predetermined idling condition. A 
rotational speed signal is also generated which indicates the actual 
rotational speed of the engine. After a predetermined period of time is 
passed from the moment when the idle state signal is generated, the 
rotational speed signal is compared with upper and lower limit speed 
signals to generate a control signal which indicates the change in the 
idle air flow to the engine necessary to maintain the actual rotational 
speed of the engine within a desired range. The idle air flow to the 
engine is adjusted in response to the control signal. 
The above and other related objects and features of the present invention 
will be apparent from the description of the present invention set forth 
below, with reference to the accompanying drawings, as well as from the 
appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 schematically illustrates a system for controlling the idling speed, 
which is applied to an electronically controlled fuel injection-type 
internal combustion engine according to an embodiment of the present 
invention. In FIG. 1, reference numeral 10 denotes an engine body, and 12 
denotes an intake passage having a throttle valve 14. A control valve 18 
is provided in a by-pass intake passage 16 which communicates the intake 
passage on the upstream side of the throttle valve 14 with the intake 
passage on the downstream side of the throttle valve 14, by-passing the 
throttle valve 14; the control valve 18 works to control the 
cross-sectional area of the passage 16. Further, the opening and closing 
of the control valve 18 is controlled by a valve control motor 20, such as 
a step motor or a d-c servo motor. The motor 20 is energized by an 
electric current which is supplied from a drive circuit 22 via lines 24. 
The drive circuit 22 is controlled by drive signals from a control circuit 
26. 
A throttle position switch 28 is mounted on the shaft of the throttle valve 
14 to detect whether the throttle valve 14 is located at the idling 
position. The detection signal is sent to the control circuit 26 via a 
line 30. 
A distributor of the engine is provided with a crank-angle sensor 34 which 
produces a crank angle pulse or a primary ignition pulse at every rotation 
of a predetermined crank angle. The crank angle pulses are sent to the 
control circuit 26 via a line 36. 
A drive-shaft angle sensor 38 produces an angle pulse at every 
predetermined-angle rotation, of a rotary shaft such as a drive shaft or a 
shaft for driving the speedmeter which rotates a predetermined angle is 
proportion to the turn of a wheel of the vehicle on which the engine is 
mounted. The angle pulses from the sensor 38 are fed to the control 
circuit 26 via a line 40. 
As is well known, in electronic control fuel injection-type internal 
combustion engines, the flow rate of the intake air sucked into the engine 
is detected by an air-flow sensor 42 disposed in the intake passage 12, 
and fuel is supplied in an amount in accordance with the detected flow 
rate of the intake air into a combustion chamber 48 of the engine from a 
fuel injection valve 46 mounted in an intake manifold portion 44. 
Therefore, the rotational speed of the engine can be controlled by 
controlling the flow rate of intake air by the throttle valve 14 or the 
control valve 18. 
FIG. 2 is a block diagram illustrating an example of the control circuit 26 
of FIG. 1. In this case, a digital computer of the stored program type is 
used in the control circuit 26. The digital computer consists of a central 
processing unit (CPU) 50 which executes a variety of calculations, a 
random access memory (RAM) 52 which is capable of temporarily storing 
data, a read-only memory (ROM) 54 which stores the control programs, 
calculation constants and various tables used for the calculations, an 
input interface 56, and an output interface 58. All of these elements are 
interconnected via a bus 60. 
The input interface 56 receives binary vehicle-speed signals that represent 
the running speed of the vehicle fed from a vehicle-speed signal generator 
circuit 62 which is made up of a conventional circuit for measuring, 
relying upon a counter or the like, the time interval between the angle 
pulses from the, drive-shaft angle sensor 38. The input interface further 
receives binary rotational speed signals which represent the rotational 
speed of the engine fed from a rotational speed signal generator circuit 
64 which is made up of a conventional circuit for measuring, relying upon 
a counter or the like, the time interval of the crank-angle pulses from 
the crank-angle sensor 34. The input interface 56 further receives a 
throttle switch signal of the level "1" or "0" which represents whether 
the throttle valve 14 is at the idling position or not, and which is 
produced by the throttle position switch 28. According to the embodiment 
of FIG. 2, the drive circuit 22 for driving the valve-control motor 20 
which consists of a step motor is connected to the output interface 58. An 
electric current for exciting the step motor is produced by the drive 
circuit 22 responsive to a drive signal of four bits fed from the CPU 50 
via the bus 60 and the output interface 58. 
The operation of the embodiment will be illustrated below with reference to 
a flow chart shown in FIG. 3 which schematically represents the flow of an 
interrupt processing program for controlling the idling speed that is 
stored in the ROM 54. 
The CPU 50 executes the interrupt processing routine of FIG. 3 in response 
to an interrupt request which is produced at every 100 milliseconds. At a 
point 70 the CPU 50 discriminates whether the throttle switch signal from 
the throttle position switch 28 is "1" or "0". When the throttle switch 
signal is "1 ", i.e., when the throttle valve is not at the idling 
position, the program proceeds to points 71 and 72 where the timer flag, 
that will be used in subsequent processing, is set to "1", and T, which 
will be used in a subsequent time-measuring processing, is reset to zero. 
The interrupt processing routine of this time is thus finished, and the 
program returns to the main routine. 
When it is so discriminated at the point 70 that the throttle switch signal 
is "0", i.e., when the throttle valve 14 is at the idling position, the 
program proceeds to a point 73 where it is discriminated, relying upon the 
vehicle-speed signal, whether the present vehicle speed is smaller than 1 
km per hour or not. When the vehicle speed is equal to or greater than 1 
km per hour, the program proceeds to the points 71 and 72. When it is so 
discriminated that the vehicle speed is smaller than 1 km per hour, the 
program proceeds a point 74 presuming that the engine is under the 
predetermined idling condition. According to this embodiment as mentioned 
above, the predetermined idling condition is established when the throttle 
valve is at the idling position and when the vehicle speed is smaller than 
1 km per hour. In the above-mentioned embodiment, the digital signal 
having a value corresponding to the present vehicle speed is formed by the 
vehicle-speed signal generator circuit 62, and whether the signal 
represents the vehicle speed of smaller than 1 km per hour is 
discriminated by the CPU 50. However, the above discrimination may be 
effected in the vehicle-speed signal generator circuit 62, and a signal 
"1" or "0" which is the result of discrimination may be fed the CPU 50 via 
the input interface 56. 
At the point 74, the CPU 50 discriminates whether the timer flag is "1" or 
not. When the engine falls under the predetermined idling condition and 
thus the program reaches the point 74 for the first time, the timer flag 
remains at "1". Therefore, the program proceeds to a point 75 where T is 
increased by one. This T should be set to zero and the timer flag should 
be set to "1" in the initial processing routine when the engine is 
started. Then, at a point 76, the CPU 50 discriminates whether T is equal 
to ten. If T is not equal to ten, the interrupt processing routine is 
finished and the program returns to the main routine. At the point 76, if 
it is discriminated that T is equal to ten, the program proceeds to points 
77 and 78 where T is reset to zero, the timer flag is set to "0", and the 
processing routine after the point 79 is executed, i.e., processing 
routine is executed to control the idling speed by feedback. 
According to this embodiment as mentioned above, when the engine operating 
condition reaches the predetermined idling condition, the idling speed is 
not immediately controlled by feedback according to points 80 through 83, 
but is controlled after the interrupt processing of FIG. 3 is performed 
ten times. Namely, since the interrupt processing routine is effected at a 
period of 100 milliseconds, the feedback control is initiated when the 
time period of one second is passed from the moment at which the engine 
falls into the predetermined idling condition. Once the above-mentioned 
delay is carried out while the feedback control is being initiated, the 
timer flag is set to "0" at the point 78. In the subsequent interrupt 
operation cycles, therefore, the program directly proceeds from the point 
74 to the point 79, and the feedback control is immediately executed 
without delay. 
Below is mentioned the feedback control processing in the points 79 through 
83. 
As the program reaches the point 79, the CPU 50 introduces a rotational 
speed signal which represents the actual rotational speed of the engine, 
from the rotational speed signal generator circuit 64, and at the point 
80, the CPU 50 discriminates whether the rotational speed is greater than 
a predetermined upper-limit value of idling speed or not. When the 
rotational speed of the engine is greater than the upper-limit value, the 
program proceeds to the point 81 where a drive signal is produced to the 
output interface 58 so that the control valve 18 is driven toward the 
closing direction. In the embodiment of FIG. 2, if the valve control motor 
20 is a step motor of the four-pole two-phase excitation type, the drive 
signal will take the form of any one of "1100", "0110", "0011" or "1001". 
If it is presumed that a drive signal corresponding to the present 
position of the step motor 20 takes the form "0110", the drive signal of, 
for example, "1100" should be produced to the output interface 58 at the 
point 81. The drive circuit 22 then generates an exciting current to the 
phase which corresponds to "1" of the drive signal. Therefore, the step 
motor 20 is turned by one step in a given direction, and the control valve 
18 is actuated by a predetermined amount toward the direction to close the 
valve. Therefore, the flow rate of the intake air is reduced 
correspondingly, causing the rotational speed to decrease. 
If it is so discriminated in the point 80 that the actual rotational speed 
is slower than the upper-limit value, the program proceeds to the point 82 
where it is discriminated whether the actual rotational speed is slower 
than the predetermined lower-limit value of the idling speed or not. When 
the actual rotational speed is smaller than the lower-limit value, the 
program proceeds to the point 83 where a drive signal is fed to the output 
interface 58 so that the control valve 18 is driven toward the opening 
direction. This means that a drive signal is produced in order to rotate 
the valve control motor 20 in the opposite direction. Therefore, the flow 
rate of the intake air sucked into the engine is increased causing the 
rotational speed to increase. 
When it is so discriminated in the point 82 that the actual rotational 
speed equal to or greater than the lower-limit value, i.e., when the 
rotational speed lies within a range of upper-limit value and lower-limit 
value of idling speed, the interrupt processing routine is finished 
without changing the position of the valve control motor 20. 
FIG. 4 is a diagram illustrating the functions and effects of the 
above-mentioned embodiment. In FIG. 4, (A) denotes the rotational speed of 
the engine, (B) denotes a throttle switch signal, and (C) denotes the 
vehicle-speed characteristics, relative to the lapse of time. When the 
throttle valve 14 is returned to the idling position at a moment t.sub.1, 
the throttle switch signal is inverted from "1" to "0" as shown in FIG. 4 
(B). As the vehicle speed becomes smaller than 1 km per hour at a moment 
t.sub.2 as indicated in (C), the predetermined idling condition is 
established. According to the conventional art, the feedback control was 
immediately initiated at the moment t.sub.2. As represented in FIG. 4 (A), 
therefore, the rotational speed N of the engine of that moment was often 
higher than the upper-limit idling speed Nmax due to the moment of inertia 
and, consequently, the control valve 18 was driven toward the closing 
direction causing the rotational speed to be drastically decreased, as 
indicated by a broken line. In the worst cases, therefore, the engine 
often stalled. According to the embodiment of the present invention, 
however, when the feedback control is initiated, it is lagged by a time 
t.sub.d (for example, one second) behind the moment t.sub.2 at which the 
predetermined idling condition is established. Therefore, the rotational 
speed is stabilized through the time t.sub.d and lies between the 
upper-limit value Nmax and the lower-limit value Nmin as indicated by a 
solid line in FIG. 4 (A). According to the present invention, therefore, 
the above-mentioned undesirable phenomenon inherent in the conventional 
art does not take place. 
The above embodiment of FIG. 2 has employed a step motor to drive the 
control valve 18. However, it is, of course, allowable to control the 
valve 18 by using a d-c servo motor instead of the valve control motor. 
According to the above-mentioned embodiment, furthermore, the opening 
degree of the flow-control valve in the by-pass intake passage is adjusted 
to control the flow rate of the intake air when the engine is in the 
idling condition. The method of the present invention, however, can also 
be applied to an engine which does not have the by-pass intake passage and 
in which the closing position of the throttle valve is controlled to 
control the flow rate of the intake air when the engine is in the idling 
condition. 
FIG. 5 illustrates a setup for mechanically coupling the valve control 
motor 90 to the throttle valve 92 when the present invention is applied to 
engines of this type. Referring to FIG. 5, the tip of an arm 94, attached 
to the rotary shaft of the throttle valve 92, pushes the end surface of a 
linear actuator member 96. The end surface of the linear actuator member 
96 serves as a stopper. As the motor 90 rotates, the linear actuator 
member 96 moves in the directions of the arrow 98. Therefore, the closing 
position of the throttle valve 92 or, in other words, the opening degree 
of the throttle valve when the engine is in the idling condition, is 
controlled responsive to the rotating amount of the motor 90. The rotating 
amount of the motor 90 can be easily converted into the movement of the 
linear actuator member 96 in the axial direction by, for example, forming 
a worm screw on the rotary shaft of the motor 90, and inserting the 
portion of worm screw into a threaded hole formed in the linear actuator 
member 96. This mechanism can also be adapted to the coupling between the 
control valve 18 and the motor 20 in the embodiment of FIG. 1. The setup, 
operation, functions and effects of a control unit for the motor 90 of the 
embodiment of FIG. 5 are quite the same as those of the above-mentioned 
embodiment. 
FIG. 6 is a block diagram illustrating a further embodiment of the present 
invention in which the control circuit portion is made up of an analog 
control circuit 26'. In FIG. 6, the valve control motor 20, the drive 
circuit 22 for driving the step motor, the throttle position switch 28, 
the drive-shaft angle sensor 38, and the crank angle sensor 34 are 
constructed quite in the same manner as those of the above-mentioned 
embodiment. 
A throttle switch signal of the level "0" from the throttle position switch 
28, i.e., a signal which indicates that the throttle valve 14 is at the 
idling position, is inverted by an inverter 100 to the level "1", and is 
fed to an AND circuit 102. An angle signal from the drive-shaft angle 
sensor 38 is fed to a vehicle-speed discrimination circuit 104 which 
produces a signal of the level "1" when the vehicle speed is decreased to 
below 1 km per hour. Therefore, as the throttle valve 14 comes to the 
idling position, and the vehicle speed decreases below 1 km per hour, the 
AND circuit 102 produces the output of the level "1", and a timer circuit 
106 commences the operation for measuring the time. 
On the other hand, the crank angle signal from the crank angle sensor 34 is 
fed to the rotational speed signal generator circuit 108 consisting, for 
example, of a frequency-voltage converter or the like. Therefore, a 
voltage proportional to the rotational speed of the engine is produced by 
the generator circuit 108. The output voltage is applied to one input 
terminal of each of the comparators 110 and 112. The other input terminals 
of each of the comparators 110 and 112 are, respectively, served with 
reference voltages that are fed from reference voltage circuits 114 and 
116 and correspond to the upper-limit value and lower-limit value of the 
idling speed. Therefore, when the rotational speed of the engine becomes 
greater than the upper-limit value, the comparator 110 produces a signal 
of the level "1". Further, when the rotational speed becomes smaller than 
the lower-limit value, the comparator 112 produces a signal of the level 
"1". 
The output of the timer circuit 106 assumes the level "1" after a 
predetermined period of time has passed from the moment at which the 
output of the AND circuit 102 assumed the level "1", i.e., after a 
predetermined period of time has passed from the moment at which the 
predetermined idling condition was established. Consequently, and AND 
circuits 118 and 120 are opened, the outputs from the comparators 110 
and/or 112 are applied to the drive signal generator circuit 122, and the 
idling speed is controlled by feedback. 
Upon receipt of a signal of the level "1" from the comparator 110 via the 
AND circuit 118, the drive signal generator circuit 122 produces a drive 
signal which drives the valve control motor 20 so that the control valve 
18 moves toward the closing direction. Upon receipt of a signal of the 
level "1" from the comparator 112 via the AND circuit 120, on the other 
hand, the drive signal generator circuit 122 produces a drive signal which 
drives the valve control motor 20 so that the control valve 18 moves in 
the opposite direction. 
Other operations and effects of this embodiment are quite the same as those 
of the aforementioned embodiment. 
According to the method of the present invention as illustrated in detail 
in the foregoing, the idling speed is controlled by feedback after a 
predetermined period of time has passed from the moment at which the 
predetermined idling condition was established. Even when the feedback 
control is initiated, therefore, the rotational speed is not erroneously 
controlled, there does not take place the undershooting phenomenon with 
regard to the rotational speed, and the engine does not stall. 
As many widely different embodiments of the present invention may be 
constructed without departing from the spirit and scope of the present 
invention, it should be understood that the present invention is not 
limited to the specific embodiments described in this specification, 
except as defined in the appended claims.