JPS61277841A - Idle rotation control method for internal-combustion engine - Google Patents

Abstract

PURPOSE:To improve the fuel consumption by forcibly starting the auxiliary air flow control in feedback mode upon continuation of specific engine rotation with fully closed throttle valve for specific interval. CONSTITUTION:When the engine rotation is lower than specific level, it is decided whether the throttle valve opening thetaTH is fully closed or not in step 3. If the engine rotation Ne is lower than a level NH for starting feedback control to target idle rotation, it will move to step 14. In step 14, duty ratio DOUT for feedback mode control is operated to produce the driving signal of control valve with correspondence to the operated duty ratio DOUT in step 16 thus to perform feedback mode control. Consequently, fuel consumption can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for automatically controlling the idle speed of an internal combustion engine to a predetermined value.

(Prior art and its problems) In an internal combustion engine, when idling is performed when the engine cooling water temperature is low below a predetermined value, or during idling, the engine may suffer from electrical corrosion of headlights, air conditioners, etc., or mechanical load. In such cases, the load on the engine increases and the engine speed drops abnormally, which tends to cause engine stall. For this reason, conventionally, a target idle speed is set according to the engine coolant temperature and engine load condition, the difference between the target idle speed and the actual engine speed is detected, and the difference is adjusted so that the difference becomes zero. The present applicant has provided a method for controlling the idle speed of an internal combustion engine, which maintains the engine speed during idling at a target idle speed by controlling the amount of auxiliary air supplied to the engine according to the magnitude of the engine speed. proposed by.

The method for controlling the idle speed of an internal combustion engine according to this proposal is as follows: 7) When the throttle valve is fully closed and the engine speed is below a predetermined speed that is higher than the target idle speed, the amount of auxiliary air supplied to the internal combustion engine is as follows: auxiliary air amount control is started in a deceleration mode in which the control valve that controls the engine speed is controlled to a target idle speed lower than the predetermined engine speed, and when the throttle valve is fully closed and the engine speed is above the predetermined speed. Assistance by a feedback mode that controls the control valve according to the difference between the actual engine speed and the target idle speed to maintain the engine speed at the target idle speed when the engine speed falls below the target idle speed. This starts air volume control. That is, the conditions for starting the auxiliary air amount control in the feedback mode are when the throttle valve is fully closed and the engine speed has fallen below the target idle speed. However, the original purpose of this type of idle speed control is to prevent engine stalling, and from that perspective, the valve opening duty ratio of the auxiliary air amount control valve when controlling the auxiliary air amount in deceleration mode is Taking into account temperature conditions, engine variations, etc., it is necessary to set the amount of auxiliary air to be more than the amount of auxiliary air required to maintain the normal idling speed.

Therefore, for example, when driving down a gentle slope with the clutch not disengaged and the throttle valve fully closed, the engine rotates at a portion slightly higher than the target idle speed, and the auxiliary air amount control by feedback mode is activated. There was a problem that it did not start easily.

(Objective of the Invention) The present invention has been made in view of the above circumstances, and it is an object of the present invention to start auxiliary air amount control in feedback mode as soon as possible during idling operation with the throttle valve fully open, and to lower the engine speed as much as possible. An object of the present invention is to provide a method for controlling the idle speed of an internal combustion engine, which can improve fuel efficiency.

(Means for Solving the Problems) In order to solve the above-mentioned problems, in the present invention, when the throttle valve is fully closed and the engine speed is below a predetermined speed that is higher than the target idle speed, the internal combustion engine is Starts auxiliary air amount control using a deceleration mode that controls the control valve that controls the amount of auxiliary air supplied so that the engine speed becomes a target idle speed lower than the predetermined engine speed, and fully closes the throttle valve. When the engine speed falls below the target idle speed, the control valve is operated according to the difference between the actual engine speed and the target idle speed to maintain the engine speed at the target idle speed. In an internal combustion engine idle speed control method that starts auxiliary air amount control in a feedback mode, the engine speed is higher than the target idle speed when the throttle valve is fully closed, and the target idle speed is equal to the predetermined speed. When the rotational speed continues to be lower than the reference rotational speed for a predetermined period of time, the auxiliary air amount control using the feedback mode is forcibly started.

(Example) Hereinafter, one example of the present invention will be described based on the drawings. 1st
The figure is a schematic configuration diagram showing the entire idle speed control device for an internal combustion engine for carrying out the method of the present invention. The intake port 1a of the engine 1 is connected to the other end of an intake pipe 3 having an air cleaner 2 inserted into its opening. An exhaust pipe 4 is provided at the exhaust port 1b of the engine 1.
is connected at one end. A throttle valve 5 is interposed midway inside the intake pipe 3. One end of a ventilation pipe 6 is connected to the intake pipe 3 downstream of the throttle valve 5, and the other end of the ventilation pipe 6 is connected to a middle of a communication pipe 7. An auxiliary air amount control valve (hereinafter referred to as a control valve) 8 is provided at one end of the communication pipe 7, and a fast idle control device 9 is provided at the other end. The control valve 8
is for controlling the amount of auxiliary air supplied to the engine 1 via the communication pipe 7, the ventilation pipe 6, and the intake pipe 3. The control valve 8 is a normally closed solenoid valve, and has a valve casing 8a.
, a valve body 8b provided within the valve casing 8a, and a solenoid 8c. A connection port 8d of the valve casing 8a is connected to one end of the communication pipe 7, and a vent port 8d is connected to one end of the communication pipe 7.
e is opened to the atmosphere, and the air cleaner 1 is connected to the vent 8e.
o is attached. The vent 8e is opened and closed by the valve body 8b, one end of the solenoid 8c is electrically connected to the anode of a power source (battery) 11, and the cathode of the power source 11 is electrically grounded. . The other end of the solenoid 8c is an electronic control unit (hereinafter referred to as EC).
12 (referred to as U). The fast idle control device 9 operates when the engine coolant temperature is lower than a predetermined value (for example, 60° C.) and supplies a sufficient amount of auxiliary air to the engine 1 through the communication pipe 7, the ventilation pipe 6, and the intake pipe 3. The fast idle control device 9 includes a housing 9a, a conical valve body 9c biased in the valve closing direction by a spring 9b, Detection device 9 that expands and contracts the rod 9d in response to engine coolant temperature
e and rotates with the expansion and contraction of the rod 9d of the detection device 9e to displace the valve body 9c in the opening/closing direction and the spring 9
The lever 9g is biased in a direction to open the valve body 9c at a point f. The housing 9a has a connection port 9h
and a vent 91. These connection ports 9h and ventilation ports 91
communicate with each other via a center hole 9k of a valve seat 9j in the housing 9a, and the center hole 9k communicates with the valve body 9c.
It will be opened and closed at A connection port 9h of the housing 9a is connected to the other end of the communication pipe 7, a vent 91 is open to the atmosphere, and an air cleaner 13 is attached to the vent 91. A fuel injection valve 14 is located in the intake pipe 3 located between the engine 1 and the ventilation pipe 6, and an intake pipe absolute pressure sensor (hereinafter referred to as PBA sensor) 1 is connected via a branch pipe 15.
6 are attached to each. The fuel injection valve 14
is connected to a discharge port of a fuel injection pump (not shown) and is electrically connected to the ECU 12. The PBA sensor 16 is electrically connected to the ECU 12, and the PBA sensor 16 converts the absolute pressure within the intake pipe 3 into an electrical signal, which is sent to the ECU 12. The throttle valve 5 includes a throttle valve opening sensor (hereinafter referred to as
17 (referred to as θTH sensor) is attached, and the θ
The TH sensor 17 is electrically connected to the ECU 12,
The θTH sensor 17 converts the opening degree of the throttle valve 5 into an electrical signal and sends it to the ECU 12. The engine 1 includes an engine coolant temperature sensor (hereinafter referred to as 7).
The 7w sensor 18 is electrically connected to the IF and CU 12, and the TW sensor 18 converts the engine cooling water temperature, which represents the engine temperature, into an electrical signal, which is sent to the ECU 12. sent to. Around the camshaft or crankshaft of the engine 1 (both not shown), an engine rotation speed sensor (
19 (hereinafter referred to as Ne sensor) is installed,
The Ne sensor 19 is electrically connected to the ECU 12.

The Ne sensor 19 outputs a crank angle position signal (hereinafter referred to as TDC signal) at a crank angle position a predetermined angle before the top dead center (TDC) at the start of the intake stroke of each cylinder of the engine 1. Yes, the TDC signal is
Sent to CU12. Other engine parameter sensors such as an atmospheric pressure sensor (hereinafter referred to as a PA sensor) 2° and a switch 21 for an electrical device such as a headlight are electrically connected to the ECU 12, respectively.

The PA sensor 20 converts atmospheric pressure into an electrical signal and sends it to the ECU 12, and the switch 21 sends an on/off state signal of the electrical device, that is, an electrical load state signal applied to the engine 1 to the ECU 12. It will be done. The ECU 12 includes an input circuit 12a and a central processing circuit (hereinafter referred to as "central processing circuit") having functions such as shaping input signal waveforms from the various sensors, correcting voltage levels to predetermined levels, and converting analog signal values into digital signal values. 12b (referred to as a CPU), a storage means 12C for storing various calculation programs and calculation results executed by the CPU 12b, and an output circuit 12d for supplying drive signals to the control valve 8 and the fuel injection valve 14.

(Function) Next, the function of the idle speed control device configured as described above will be explained. When the engine coolant temperature is lower than a predetermined value (for example, 60°C) such as during a cold start, the detection device 9e of the fast idle control device 9 responds to the engine coolant temperature and the rod 9d is in a retracted state, and the lever 9g is The valve body 9c is rotated counterclockwise in FIG. 1 by the biasing force of the spring 9f, displacing the valve body 9c in the valve opening direction (rightward in FIG. 1) against the biasing force of the spring 9b, and opening the center hole 9k. to open. When the central term 9k is open, the air cleaner 13
Since sufficient auxiliary air is supplied to the engine 1 through the connection port 9h, the communication pipe 7, the ventilation pipe 6, and the intake pipe 3 to the ventilation port 91 and the center hole 9, the engine speed is lower than the normal idle speed. Since it can be held at a high temperature, there is no need to worry about engine stalling during idle operation in cold weather (stable idle operation is ensured. Therefore, in addition to the auxiliary air supplied to the engine 1 via the fast idle control device 9) Since it is not necessary to supply auxiliary air to the engine 1 from the control valve 8, which will be described later, the control valve 8 will not operate until the engine coolant temperature reaches a predetermined value or higher, except for a predetermined time period immediately after engine startup, which will be described later. Remains inactive.

When the rod 9d of the detection device 9e expands due to thermal expansion as the engine coolant temperature rises due to warm-up, the lever 9g is rotated clockwise in FIG. 1 by the rod 9d against the biasing force of the spring 9f. Accordingly, the valve body 9C is displaced in the valve closing direction (to the left in FIG. 1) by the biasing force of the spring 91>, and when the engine coolant temperature reaches a predetermined value or higher, the valve body 9C closes. It comes into contact with the seat 9j and closes the center hole 9k, stopping the supply of auxiliary air to the engine 1 via the fast idle control device 9.

Note that the above-mentioned fast idle control device 9 controls the amount of intake air supplied to the engine 1 so that the engine speed during idling operation can be maintained at a speed higher than the normal idle speed when the engine coolant temperature is below a predetermined value. The present invention is not limited to the configuration of the above-described embodiments, and may be, for example, a configuration in which the throttle valve opening is forcibly opened by a certain opening, or other configurations, as long as the opening of the throttle valve is increased.

On the other hand, in addition to dealing with the electrical loads of electrical devices such as headlights, brake lights, and radiator cooling fans, which are relatively small loads on the engine 1, the engine speed is adjusted so that the engine speed reaches the target idle speed. A control valve 8 is used to control the amount of auxiliary air supplied to increase or decrease the amount of auxiliary air supplied to the air pump 1 with high accuracy. That is, E.C.
U12 outputs the values of engine parameter signals supplied from the PBA sensor 16, θTH sensor 17, Tw sensor 18, Ne sensor 19, and PA sensor 20 each time the TDC signal of the engine 1 is generated, and the switch 21 of the electrical device.
Based on the electrical load state signal from
Depending on these determined conditions, the amount of fuel supplied to the engine 1, that is, the opening time of the fuel injection valve 14, and the amount of auxiliary air supplied by the control valve 8, that is, the opening time of the control valve 8, are determined respectively. It calculates and supplies drive signals for operating the fuel injection valve 14 and the control valve 8 according to each calculated value. The solenoid 8c of the control valve 8 is energized by the valve opening duty ratio according to the calculated value, opens the valve body 8b and opens the vent 8e, and a predetermined amount of air according to the valve opening duty ratio is supplied to the air cleaner. 10, ventilation port 8e, connection port 8d,
It is supplied to the engine 1 via the communication pipe 7, the ventilation pipe 6, and the intake pipe 3.

The fuel injection valve 14 opens for a period of time corresponding to the valve opening duty ratio according to the calculated value and injects fuel into the intake pipe 3, and the injected fuel mixes with the intake air and always maintains the desired amount. A mixture having an air-fuel ratio (for example, a stoichiometric air-fuel ratio) is supplied to the engine 1.

Next, the idle speed control method according to the present invention will be explained with reference to a graph of changes over time of the engine speed Ne and the valve opening duty ratio DOUT of the control valve 8 shown in FIG.

When the engine 1 is in a deceleration state with the throttle valve fully open and the engine rotation speed Ne falls below a predetermined rotation speed NA higher than the target idle rotation speed (see Figure 2 (all middle block 1, valve opening duty of the control valve 8 The ratio DouT is controlled by feedback mode (it is executed after the time t1 when the engine speed Ne decelerates along the solid line in Fig. 2, or after the time t3'' when the engine speed Ne decelerates along the dotted chain from the middle of the solid line). As an initial value at the start of control), the sum of the value Dx required to maintain the normal idle rotation speed and the value Dε set in response to changes in the electrical load, that is, DX+Dε, is set. (See Figure 2 (b)).Then, the engine speed N
When e falls below the predetermined rotation speed NA (Fig. 2 (a)
) is set according to the engine cooling water temperature Tw and is larger than the start value NH by a predetermined rotational speed and starts feedback control to the target idle rotation speed set according to the engine cooling water temperature TW. Standard rotation speed N
Feedback control to the target idle speed is started not only until the engine speed Ne reaches the reference speed NDX (time t2 in FIG. 2(a)), but also from the time when the engine speed Ne reaches the reference speed NDX. The point in time when a predetermined period of time THLD has elapsed without falling below the value NH (Figure 2 (at time t3 in aJ)
Until then, the control is in deceleration mode, that is, the initial value D
Control valve 8 is controlled by the valve opening duty ratio set to X+Dε.
is controlled and auxiliary air is supplied to the engine 1.

The engine rotation speed Ne is lower than the reference rotation speed Nox and higher than the start value NH for starting feedback control to the target idle rotation speed for a predetermined period (THLD).
If it continues, control by the feedback mode is forcibly started at that point in time, that is, at time t3 in FIG. 2 (al), and the target idle speed and actual engine speed are The valve opening duty ratio DOUT of the control valve 8 is feedback-controlled in accordance with the difference between the number and the number.

Note that the starting value N+ is set to start the feedbank control to the target idle rotation speed without elapse of a predetermined period THLD from the time when the engine rotation speed Ne reaches the reference rotation speed N□x.
(at time t3' in FIG. 2), control by feedback mode is started instead of control by deceleration mode. In other words, the feature of the method of the present invention is that the engine speed Ne is the reference rotation speed N
If the speed falls below the start value NH that starts feedback control to the target idle speed without a predetermined period of time THLD elapsed from the time when the speed reaches Furthermore, when the engine speed pJe reaches the reference speed Nox, it is assumed that the engine speed pJe does not fall below the start value NH for starting feedback control to the target idle speed (even after a predetermined period of time THLD has elapsed). Another feature is that the feedback mode control is forcibly started when a predetermined period of time THLD has elapsed since the reference rotational speed Nox was reached. By doing this, according to the conventional method, the engine speed Ne falls past the point of the solid line in FIG. 2 and falls along the deceleration line shown by the broken line to a starting value at which feedback control to the target idle speed starts. When the temperature drops below NH (Fig. 2 (at time t5 in al)
In contrast, according to the method of the present invention, control in the feedback mode is not started unless the
Control in the feedback mode can be started earlier than the conventional method at time t3, and the engine speed Ne can be maintained at the target idle speed from time t4 onwards in FIG. 2(a).

FIG. 3 is a program flowchart showing a control procedure for the control valve 8 executed within the ECU 12 of FIG. The control program for the control valve 8 is executed in the ECU 12 of FIG. 1 every time the TDC signal is generated after the ignition switch (not shown) is turned on to initialize the ECU 12. T from the Ne sensor 19 in FIG.
When the DC signal is input to the ECU 12, it is first determined whether the engine coolant temperature TV is higher than a predetermined value TWAICO (for example, 40°C) (step 1), and if the determination result is negative (NO), the , that is, the engine cooling water temperature Tw
If TwAxcO is lower than the predetermined value TwAxcO, the fast idle control device 9 shown in FIG. The ECU 12 stops supplying the drive signal to the control valve 8 and sets the valve opening duty ratio DOLIT to zero so as to fully close the control valve 8 (step 9). is called a rest mode operation).

If the determination result in step 1 is affirmative (Yes), in the next step 2, a value Me proportional to the reciprocal of the engine rotation speed Ne is set to a predetermined rotation speed NA (for example, 1.50 Orpm) that is larger than the target idle rotation speed NIC. ) is larger than a value MA proportional to the reciprocal of ). In the ECU 12, the rotation speed Ne is set for convenience of arithmetic processing.

Values Me and MA are used in place of NA, and this value Me is the time interval between TDC signal pulses generated in accordance with the engine speed, and the higher the engine speed, the shorter the time interval Me.

If the determination result in step 2 is negative (No) (M
e<MA), that is, the engine rotation speed Ne is the predetermined rotation speed NA
If the rotation speed is higher than the specified rotation speed NA (before time t1 in FIG. 2(a)), there is no risk of engine stall or engine vibration that tends to occur when the rotation speed is lower than the predetermined rotation speed NA, and auxiliary air cannot be supplied to the engine 1. Since this is essential, the process moves to step 10 via step 9, which will be described later, and the valve opening duty ratio DOLIT of the control valve 8 is set to zero to fully close the control valve 8.

If the determination result in step 2 is affirmative (Yes) (
Me>MA), that is, the engine rotation speed Ne is the predetermined rotation speed N
If it is lower than A, in the next step 3, it is determined whether the throttle valve opening θTH of the throttle valve 5 shown in FIG. If the discrimination result is negative (,N'o),
That is, when the throttle valve 5 is fully closed, the process moves to the next step 4, and a value Mxc proportional to the reciprocal of the target idle speed NIC is determined according to the engine coolant temperature Tw.

The value M is determined according to the engine cooling water temperature Tw.
For example, as shown in FIG. 4, the engine cooling water temperature TW
In other words, the target idle rotation speed Nrc is set to become smaller as
830 rpm at 71℃, a value proportional to the reciprocal of m
When the temperature is 76°C, it is set to a value proportional to the reciprocal of 750 rpm, and the Mxc value for these engine coolant temperatures Tw is set as a table value in ECU1.
It is stored in 2.

After determining the value Mrc in step 4, the process moves to the next step 5, where the value Me is calculated from the value M x c, which is proportional to the reciprocal of the target idle rotation speed Nxc determined in step 4, to the engine predetermined rotation speed ΔNo (for example, 150 rpm). Discrimination reference value obtained by subtracting the value ΔMo proportional to the reciprocal, that is, the starting value N for starting feedback control to the target idle rotation speed
It is determined whether the value is greater than a value proportional to the reciprocal of H. This target idle rotation speed NxC1 Feedback control start value NH to the target idle rotation speed, engine predetermined rotation speed Δ
The relationship between No., the value Me, and ΔMo is expressed as follows.

NH=N1c+ΔNo=Ilrlc-6M.

Therefore, if the value MIC is equivalent to an engine speed of 700 rpm, the determination reference value in step 5 is equivalent to an engine speed of 850 rpm. If the determination result in step 5 is affirmative (Yes), that is, if the value Me is larger than the determination reference value M-C-ΔMo corresponding to the start value NH for starting feedback control to the target idle speed (engine If the rotational speed Ne is lower than the starting value N+ for starting feedback control to the target idle rotational speed, as shown in FIG.
lt2'.

t, lI, and t5), the process moves to step 14, and the duty ratio DOU for control in feedback mode is determined.
T is calculated, and a drive signal for the control valve 8 is output in accordance with the calculated duty ratio DOLIT (step 16).
, control is performed in feedback mode. The control of the idle speed in the feedback mode involves, for example, detecting the difference between the target idle speed NIC and the actual engine speed from the Ne sensor 19, and adjusting the magnitude of the difference so that the difference becomes zero. This is done by increasing/decreasing the valve opening duty ratio DOUT of the control valve 8 accordingly.

If the determination result in step 5 is negative (No),
That is, if the engine speed Ne is higher than the starting value NH for starting feedback control to the target idle speed, the process moves to step 11, where the value Me is a value proportional to the reciprocal of the target idle speed Nxc determined in step 4. Mzc to engine predetermined rotation speed ΔNmo (for example, 500 rpm
), that is, a value proportional to the reciprocal of the reference rotation speed Nox is determined. This target idle speed Nz
c.

Reference rotation speed Nox, engine predetermined rotation speed ΔN m D
The relationship between the % value Me and 6M m □ can be expressed as follows.

No.
, equivalent to 200 rpm. If the determination result in step 11 is negative (No), that is, if the value Me is smaller than the determination reference value MIC-ΔM m □ corresponding to the reference rotational speed Nox (engine rotational speed Ne is higher than the reference rotational speed Nox) In this case, in FIG. 2 (between t1 and t2 during AL), the process moves to step 13 and the engine speed Ne is kept between the reference speed Nox and the start value NH for starting feedback control to the target idle speed. After setting the predetermined period THLD (for example, 10 seconds) as a criterion for determining the time in which The set duty ratio DO
A drive signal for the control valve 8 is output in accordance with UT (step 16), and control in deceleration mode is performed.

If the determination result in step 11 is affirmative (Yes), that is, if the engine rotation speed Ne is lower than the reference rotation speed Nox (see FIG. Whether or not the period TH'LD has elapsed, that is, the engine rotation speed Ne is the reference rotation speed No.
It is determined whether or not the position has continued for a predetermined period THLD between x and a start value NH for starting feedback control to the target idle rotation speed. The determination result is negative (No)
If so, if the predetermined period THLD has not elapsed (between t2 and t3' or t3 in FIG. 2(a)), steps 15 and 16 are executed to continue the control in the deceleration mode.

If the determination result in step 12 is affirmative (Yes), that is, the engine rotation speed Ne is equal to the start value NH for starting feedback control to the target idle rotation speed and the reference rotation speed N.
When the THLD continues for a predetermined period between the
is executed to forcibly start control in feedback mode, and after that, the point in time when the engine speed falls below the starting value NH for starting feedback control to the target idle speed (Fig. 2 (time t4 in al) Control is performed in normal feedback mode.

When the throttle valve 5 is opened while idling is being performed under the feedback mode control in this way,
If the determination result in step 3 is affirmative (Yes), the process moves to step 8 via steps 6 and 7, which will be described later.
Duty ratio DOLI7 for control by acceleration mode
The DACC value is set as . Note that this step 8
, the DACC value is the previous duty value DAcc
n-.

It is the value obtained by subtracting a constant value ΔDACC from ΔDACC. The meaning of this is that when entering acceleration mode from feedback mode control, the current value DA c cn of value DACC is the value DA used in the previous feedback mode control.
The value obtained by subtracting the constant value ΔDACC from CCn-, that is, DA Cc, = DA Ccn-j - ΔDACC, and in this way, each time the previous value D ACC,
As control is performed many times by executing step 16 using the current duty value DAccn obtained by subtracting the constant value ΔDACC from −1, the duty ratio gradually decreases due to control in the acceleration mode. And the previous value D
If ACC,-, becomes zero, that is, DQ, the result of the determination in step 6 as to whether or not the previous value DACCn-1 is greater than the value DO becomes negative (NO), and the process proceeds to step 9, which will be described later. Then, the process moves to step 10 and enters the pause mode.

Note that when entering control in the acceleration mode in step 8 or in the pause mode in step 10, the same predetermined period THLD as the value set in step 13 is set in step 7 or 9. This is because the determination in step 11 is affirmative (Yes) again in the next loop from the control state in acceleration mode or rest mode.
This is because the throttle valve 5 may be opened for a short period of time and then returned to the fully closed position.For such cases, THLD is set for a predetermined period in step 7 or 9.

(Effects of the Invention) As detailed above, the method for controlling the idle speed of an internal combustion engine according to the present invention is such that when the throttle valve is fully closed, the engine speed is higher than the target idle speed, and the target idle speed is equal to the target idle speed. When the engine speed continues to be lower than the reference speed between a higher predetermined speed and a predetermined period of time, the difference between the actual engine speed and the target idle speed is maintained so that the engine speed is maintained at the target idle speed. Accordingly, auxiliary air amount control is forcibly started in a feedback mode that controls a control valve that controls the amount of auxiliary air supplied to the internal combustion engine.

Therefore, during idling operation with the throttle valve fully closed, even if the engine speed does not fall below the target idling speed, which is the starting condition for original feedback mode control, the feedback mode will be forced to control the engine after a predetermined period has elapsed. This has the effect of improving fuel efficiency.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing the entire idle speed control device for an internal combustion engine for implementing the method of the present invention, and FIG. 2 is a graph showing changes over time in the engine speed and the valve opening duty ratio of the control valve. FIG. 3 is a program flowchart showing the control procedure of the control valve, and FIG. 4 is a graph showing the relationship between the engine coolant temperature and the target idle speed set according to the coolant temperature. ■... Internal combustion engine, 5... Throttle valve, 8...
・Control valve. Applicant Honda Motor Co., Ltd. Agent Patent Attorney Satoshi Watanabe Otoma Kanji Nagato Leather 2 Diagram

Claims (1)

[Claims] 1. When the throttle valve is fully closed and the engine speed is below a predetermined speed that is higher than the target idle speed, the control valve that controls the amount of auxiliary air supplied to the internal combustion engine is set to the target idle speed. When the throttle valve is fully closed and the engine speed falls below the target idle speed, the engine speed is actually maintained at the target idle speed. In the method for controlling the idle speed of an internal combustion engine, the method starts auxiliary air amount control based on a feedback mode that controls the control valve according to the difference between the engine speed and the target idle speed. Forcibly starting the auxiliary air amount control in the feedback mode when the state continues for a predetermined period of time to be higher than the target idle rotation speed and lower than a reference rotation speed between the target idle rotation speed and the predetermined rotation speed. A method for controlling the idle speed of an internal combustion engine, characterized by: