JPH0316495B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an internal combustion engine idle speed control method for automatically controlling the idle speed of the 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 is subjected to electrical loads such as headlights, air conditioners, etc., mechanical loads, etc. In such a case, the load on the engine increases and the engine speed drops abnormally, which tends to cause engine stall. For this reason, conventionally, the target idle speed is measured according to the engine cooling water temperature and engine load condition, the difference between the target idle speed and the actual engine speed is detected, and the difference is reduced so that the error becomes zero. The applicant has disclosed 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 size of the engine. Proposed.

The proposed method for controlling the idle speed of an internal combustion engine controls the amount of auxiliary air supplied to the internal combustion engine when the throttle valve is fully closed and the engine speed falls below a predetermined speed that is higher than the target idle speed. Starts auxiliary air amount control using a deceleration mode in which the control valve is controlled so that the engine speed becomes a target idle speed lower than the predetermined engine speed, and the throttle valve is fully closed and the engine speed reaches the target idle speed. When you fall below the number,
The system starts auxiliary air amount control using a feedback mode that controls the control valve according to the difference between the actual engine speed and the target idle speed so as to maintain the engine speed at the target idle speed. be. 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 valve is to prevent engine stall, and from that point of view, the valve opening duty ratio of the auxiliary air amount control valve during auxiliary air amount control in deceleration mode is It is necessary to set the amount of auxiliary air to be larger than the amount of auxiliary air required to maintain the normal idling speed, taking into account variations in temperature conditions of the engine, etc.

Therefore, for example, when driving down a gentle slope with the throttle valve fully closed without disengaging the clutch, the engine rotates at a slightly higher speed than the target idle speed, and the amount of auxiliary air is reduced by the feedback mode. There was a problem that control was slow to start.

(Purpose of the Invention) The present invention has been made in view of the above circumstances, and it starts auxiliary air amount control using feedback mode as soon as possible during idling operation with the throttle valve fully closed, thereby controlling the engine speed to a minimum. An object of the present invention is to provide a method for controlling the idle rotation speed of an internal combustion engine, which can reduce the idle rotation speed as much as possible to 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 falls below a predetermined speed that is higher than the target idle speed, the internal combustion engine 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 also 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 so as 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 using 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. FIG. 1 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, and in the figure, 1 indicates, for example, a 4-cylinder internal combustion engine (hereinafter referred to as engine). The intake port 1a of the engine 1 is connected to the other end of a suction 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 located downstream of the throttle valve 5, and the other end of the ventilation pipe 6 is connected to the 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 first idle control device 9 is provided at the other end. The control valve 8 controls the amount of auxiliary air supplied to the engine 1 via the communication pipe 7, the communication pipe 6, and the intake pipe 3. The control valve 8 is a normally closed solenoid valve,
It 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, a vent port 8e is open to the atmosphere, and an air cleaner 10 is attached to the vent port 8e. The vent 8e is connected to the valve body 8b.
The solenoid 8 is opened and closed by the solenoid 8.
One end of c is electrically connected to the anode of a power source (battery) 11, and the cathode of the battery 11 is electrically grounded. The other end of the solenoid 8c is electrically connected to an electronic control unit (hereinafter referred to as ECU) 12. The first idle control device 9 controls the engine cooling water temperature to a predetermined value (for example,
Reitong pipe 7 and ventilation pipe 6 operate when the temperature is lower than 60℃).
By supplying a sufficient amount of auxiliary air to the engine 1 through the intake pipe 3, the engine speed is maintained higher than the normal idle speed. The first idle control device 9 includes a housing 9a, a conical valve body 9c biased in the valve closing direction by a spring 9b, and a detection device 9e that expands and contracts the rod 9d in response to engine cooling water temperature. , 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 ventilation port 9i. The connection port 9h and the vent 9i communicate with each other through a center hole 9k of a valve seat 9j in the housing 9a, and the center hole 9k is opened and closed by the valve body 9c. A connection port 9h of the housing 9a is connected to the other end of the communication port 7, a vent 9i is open to the atmosphere, and an air cleaner 13 is attached to the vent 9i. 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
16 (referred to as P _BA sensors) are attached to each. The fuel injection valve 14 is connected to a discharge port of a fuel injection pump (not shown), and
It is electrically connected to ECU12. The _PBA sensor 16 is electrically connected to the ECU 12,
The _PBA sensor 16 converts the absolute pressure inside the intake pipe 3 into an electrical signal and sends it to the ECU 12. A throttle valve opening sensor (hereinafter _referred to as θ _TH sensor) 17 is attached to the throttle valve 5 , and the θ _TH sensor 17 is electrically connected to the ECU 12 . The valve opening degree of 5 is converted into an electrical signal and sent to the ECU 12. An engine coolant temperature sensor (hereinafter referred to as T _W sensor) 18 is attached to _the engine 1, and the T _W sensor 18 is electrically connected to the ECU 12, and the T W sensor 18 is electrically connected to the ECU 12.
The sensor 18 converts the engine coolant temperature, which represents the engine temperature, into an electrical signal and sends it to the ECU.
Sent to 12th. An engine rotation speed sensor (hereinafter referred to as Ne sensor) is installed around the camshaft or crankshaft of the engine 1 (both not shown).
19 is attached, and the Ne sensor 19 is electrically connected to the ECU 12. Ne
The sensor 19 detects a crank angle position signal (hereinafter referred to as a crank angle position signal) at a predetermined angle before the top dead center (TDC) at the start of the intake stroke of each cylinder of the engine 1.
There is a device that outputs a TDC signal (referred to as TDC signal).
The signal is sent to the ECU 12. Other engine parameter sensors such as an atmospheric pressure sensor (hereinafter referred to as P _A sensor) 20 and a switch 21 of an electrical device such as a headlight are electrically connected to the ECU 12, respectively. The atmospheric pressure is converted into an electrical signal by the P _A sensor 20, and the
The switch 21 sends an on/off state signal of an electrical device, that is, an electrical load state signal applied to the engine 1 to the ECU 12.
Sent to 2. The ECU 12 has an input circuit 12a 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.
Central processing circuit (hereinafter referred to as CRU) 12b,
It is comprised of a storage means 12c for storing various calculation programs and calculation results executed by the CPU 12b, an output circuit 12d for supplying drive signals to the control valve 8 and the fuel injection valve 14, and the like.

(Function) Next, the function of the idle rotation speed control device configured as described above will be explained. When starting cold, etc.
When the engine coolant temperature is lower than a predetermined value (for example, 60°C), the detection device 9e of the fast idle control device 9 is sensitive to the engine coolant temperature, and the rod 9d is in a contracted state, and the lever 9g is moved by the spring 9f.
Rotates counterclockwise in Fig. 1 due to the biasing force of
The center hole 9k is opened by displacing the valve body 9c in the valve opening direction (rightward in FIG. 1) against the biasing force of the spring 9b. When the central node 9k is open, the air cleaner 13, the vent 9i, the central hole 9k, and the connection port 9
h. Sufficient auxiliary air is supplied to the engine 1 through the communication hole 7, the ventilation pipe 6, and the intake pipe 3, so the engine speed can be maintained higher than the normal idle speed, so idling operation in cold weather can be improved. Stable idling operation is ensured without worrying about the engine stalling. Therefore, in addition to the auxiliary air supplied to the engine 1 via the first idle control device 9, it is not necessary to supply the engine 1 with auxiliary air from the control valve 8, which will be described later.
The control valve 8 is maintained in an inoperative state until the engine coolant temperature reaches a predetermined value or higher, except for a predetermined period of time immediately after engine startup, which will be described later.

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 rod 9d rotates the lever 9g clockwise in FIG. 1 against the biasing force of the spring 9f. As a result, the valve body 9c is displaced in the valve closing direction (to the left in FIG. 1) by the biasing force of the spring 9b, and when the engine coolant temperature reaches a predetermined value or higher, the valve body 9c moves toward the valve seat 9j. , the center hole 9k is closed, and the supply of auxiliary air to the engine 1 via the fast idle control device 9 is stopped.

Note that the above-mentioned first idle control device 9
is the engine 1 engine speed so that the engine speed during idling operation can be maintained at a speed higher than the normal idling speed when the engine coolant temperature is below a predetermined value.
If it increases the amount of intake air supplied to
It is not limited to the configuration of the above-mentioned embodiment,
For example, a configuration in which the throttle valve is forcibly opened by a certain opening degree or other configurations may be used.

On the other hand, for example, headlights, brake lights,
The amount of auxiliary air supplied to the engine 1 is adjusted to accommodate the electrical load of electrical equipment such as a radiator cooling fan, which is a relatively small load on the engine 1, and to keep the engine speed at the target idle speed. A control valve 8 is used to control the supply amount of auxiliary air, which is increased or decreased with high precision. That is, ECU12
is P _BA sensor 1 every time the TDC signal of engine 1 occurs.
6. Based on the values of the respective engine parameter signals supplied from the θ _TH sensor 17, T _W sensor 18, Ne sensor 19 and P _A sensor 20, and the electrical load status signal from the switch 21 of the electrical device,
As will be described in detail later, the engine operating state and engine load state are determined, and the amount of fuel supplied to the engine 1, that is, the opening time of the fuel injection valve 14, is controlled by the control valve 8 according to the determined state. The amount of auxiliary air to be supplied, that is, the opening time of the control valve 8, is calculated, and the fuel injection valve 14 is adjusted according to each calculated value.
and a drive signal for operating the control valve 8, respectively. The solenoid 8c of the control valve 8 is energized by the valve opening duty ratio according to the calculated value to open the valve body 8b and open the vent 8e, so that a predetermined amount of air according to the valve opening duty ratio is supplied to the air cleaner. 10, the air is supplied to the engine 1 through the vent 8e, the connection port 8d, the communication pipe 7, the vent 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 intake air to maintain a desired air-fuel ratio at all times. (For example, a stoichiometric air-fuel ratio) air-fuel mixture 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 D _OUT of the control valve 8 shown in FIG.

When the engine 1 is in a deceleration state with the throttle valve fully closed and the engine speed Ne falls below the predetermined speed N _A which is higher than the target idle speed (Figure 2a)
The valve opening duty ratio D _OUT of the control valve 8 is controlled by the feedback mode (after _the time t ₃ when the engine speed Ne has decelerated along the solid line in Fig. 2, or during the solid line). As the initial value at the start (control executed after time t _{3 ′} when decelerating along the chain from The sum of the value D _E set by DX+D _E is set (see FIG. 2b). Therefore, the engine speed
Starting value N that starts feedback control to the target idle rotation speed set according to the engine coolant temperature T _W from the time when the rotation speed _Ne falls below the predetermined rotation speed N A (time t ₁ in Figure 2 a). The engine rotational speed is of course up to the point in time when it reaches the reference rotational speed _NDX that is a predetermined rotational speed higher than _H and is set according to the engine coolant temperature T _W (time t ₂ in Figure 2 a).
From the point when Ne reaches the reference rotation speed N _DX , the rotation speed is maintained for a predetermined period without falling below the starting value N _H at which feedback control to the target idle rotation speed is started.
Until the time T _HLD has elapsed (time t ₃ in Figure 2 a), control is performed in deceleration mode, that is, the initial value _D
The control valve 8 is controlled by the valve opening duty ratio set to + _DE , and auxiliary air is supplied to the engine 1.

The engine rotation speed Ne is the reference rotation speed _NDX
If the state continues for a predetermined period (T _HLD ) lower than the starting value N _H at which feedback control to the target idle speed is started, the feedback mode is forced at that point, that is, at t ₃ in Figure 2 a. control is started, and the valve opening duty ratio D _OUT of the control valve 8 is feedback controlled according to the difference between the target idle speed and the actual engine speed so that the engine speed Ne is maintained at the target idle speed. be done.

Note that when the engine speed Ne falls below the starting value N _H at which feedback control to the target idle speed starts without elapse of a predetermined period T _HLD from the time when the engine speed Ne reaches the reference speed N _DX (Fig. 2 a). At the middle point _t3 '), control based on the feedback mode is started in place of the control based on the deceleration mode. That is, the feature of the method of the present invention is that a starting value is set at which the feedback control to the target engine speed is started without a predetermined period of time _THLD elapsed from the time when the engine speed _Ne reaches the reference speed NDX.
When the engine speed falls below T _N , feedback mode control starts when the engine speed falls below the starting value N _H , and the target idle speed starts when the engine speed Ne reaches the reference speed N _DX . Even if the starting value N _{H that starts} feedback _mode control for This is so that control using the feedback mode is forcibly started when the By doing this, according to the conventional method, even if the engine speed Ne passes the point _t3 in FIG. 2, the engine speed Ne decreases along the deceleration line shown by the broken line and starts feedback control to the target idle speed. When the value falls below the starting value N _H (in Figure 2 a)
Whereas control in feedback mode does not start until time t ₅ ), according to the method of the present invention, control in feedback mode starts earlier than in the conventional method at time t ₃ in Figure 2a. gain, second
The engine speed Ne can be maintained at the target idle speed immediately after time _t4 in Figure 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 this control valve 8 is the first one.
In the ECU 12 shown in the figure, after the ignition switch (not shown) is turned on to initialize the ECU 12, the process is executed every time a TDC signal is generated. The TDC signal from the Ne sensor 19 in Figure 1 is
When input to the ECU 12, it is first determined whether or not the engine coolant temperature T _W is higher than a predetermined value T _WAI c0 (for example, 40°C) (step 1), and if the determination result is negative (No), , that is, the engine cooling water level T _W
When T _WAI c0 is lower than the predetermined value T WAI c0, the fast idle control device 9 shown in FIG. The ECT 12 stops supplying the drive signal to the control valve 8 and sets the valve opening duty ratio Do _UT to zero to fully close the control valve 8 ( Step 9, this is called sleep mode operation).

If the determination result in step 1 is affirmative (Yes), the value Me proportional to the reciprocal of the engine speed Ne is set to the target idle speed N _IC in the next step 2.
It is determined whether or not it is larger than a value M _A that is proportional to the reciprocal of a higher predetermined rotation speed N _A (for example, 1500 rpm).
In BCU12, the values Me and M _A are used instead of the rotational speeds Ne and N _A for convenience of calculation processing, and this value Me is the time interval between TDC signal pulses generated corresponding to the engine rotational speed. The higher the value, the shorter the time interval Me.

If the determination result in step 2 is negative (No) (Me<M _A ), that is, if the engine rotation speed Ne is higher than the predetermined rotation speed N _A (before time t ₁ in Figure 2 a)
Since there is no need to supply auxiliary air to the engine 1 because there is no risk of engine stall or engine vibration that is likely to occur when the engine speed is lower than the predetermined rotation speed N _A , the process moves to step 10 via step 9, which will be described later. , the valve opening duty ratio Do _UT of the control valve 8 is set to zero, and the control valve 8 is fully closed.

If the determination result in step 2 is positive (Me>M _A ), that is, if the engine speed Ne is lower than the predetermined engine speed N _A , then in the next step 3, the throttle valve 5 shown in FIG. It is determined whether or not the throttle valve opening θ _TH is larger than a predetermined value θ _IDLH close to fully closed, which is considered to be a substantially fully closed state, and if the determination result is negative (No), that is, the throttle valve 5 If the engine is fully closed, the process moves to the next step 4, where a value M _I c proportional to the reciprocal of the target idle speed N _I c is determined in accordance with the engine coolant temperature T _W . The value M _I c determined according to the engine coolant temperature T _W is set such that it increases as the engine coolant temperature T _W increases, for example, as shown in FIG. 4, that is, the target idle rotation speed N _I c is set to be small, for example, when the engine coolant temperature T _W is 66℃ or less, it is a value proportional to the reciprocal of 900rpm, and when it is 71℃.
At 76℃, the value is proportional to the reciprocal of 830rpm.
It is set to a value proportional to the reciprocal of 750 rpm, and the M _I c values for these engine coolant temperatures T _W are stored in the ECU 12 as table values.

After determining the value M _I c in step 4, the process moves to the next step 5, where the value Me is determined as a value M _I c proportional to the reciprocal of the target idle rotation speed N _I c determined in step 4.
The determination standard value obtained by subtracting the value ΔM _D proportional to the reciprocal of the specified engine rotation speed ΔN _D (for example, 150 rpm) from
That is, it is determined whether or not the value is greater than a value proportional to the reciprocal of the start value N _H for starting feedback control to the target idle rotation speed. This target idle speed
N _I c, feedback mode control start value N _H to target idle speed, predetermined engine speed ΔN _D ,
The relationship between the values Me and ΔM _D can be expressed mathematically as follows.

N _H =N _I c + ΔN _D = M _I c - ΔM _D Therefore, if the value M _I c is equivalent to an engine speed of 700 rpm, the discrimination 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, the determination reference value M _I c- corresponds to the start value N _H at which the value Me starts feedback control to the target idle rotation speed.
If it is larger than ΔM _D (if the engine speed Ne is lower than the starting value N _H that starts feedback control to the target idle speed, then t ₂ ′, t ₄ and t ₅ in Fig. 2(a)
At step 14, a duty ratio Do _UT for tongue control in feedback mode is calculated, and a drive signal for the control valve 8 is output in accordance with the calculated duty ratio Do _UT (step 16). ,
Control is performed in feedback mode. The control of the idle rotation speed using the feedback mode is performed, for example, by controlling the target idle rotation speed N _I c and Ne
This is done by detecting the difference between the sensor 19 and the actual engine speed, and increasing or decreasing the valve opening duty ratio Do _UT of the control valve 8 according to the magnitude of the difference so that this difference becomes zero. be exposed.

If the determination result in step 5 is negative (No), that is, if the engine speed Ne is higher than the start value N _H for starting feedback control to the target idle speed, the process moves to step 11 and the value Me
is the target idle speed N _I determined in step 4
A value M _I proportional to the reciprocal of c A discrimination reference value obtained by subtracting a value ΔMm _D proportional to the reciprocal of the specified engine rotation speed ΔNm _D (for example, 500 rpm) from c, that is, a value proportional to the reciprocal of the reference rotation speed N _DX Determine whether the size is larger than that. This target idle rotation speed N _I c, reference rotation speed N _DX , predetermined engine rotation speed ΔMm _D , value Me,
The relationship between ΔMm _{and D} is expressed as follows.

M _DX =N _I c + ΔMm _D = M _I c - ΔMm _D Therefore, if the value M _I c is the engine rotation speed phase of 700 rpm, the discrimination reference value in step 11 corresponds to the engine rotation speed of 1200 rpm. If the determination result in step 11 is negative (No), that is, if the value Me is smaller than the determination reference value M _I c - ΔMm _D corresponding to the reference rotation speed N _DX (the engine rotation speed Ne is the reference rotation speed
If it is higher than M _DX (between t ₁ and t ₂ in Figure 2 a), proceed to step 13 and set the starting value to start feedback control to the reference rotation speed N _DX and the target idle rotation speed.
_{N _} D _X as _UT
A value D _X +D _{E ,} which is the _sum of the value D
A drive signal is applied (step 16), and control is performed in deceleration mode.

If the determination result in step 11 is affirmative (Yes), that is, the engine rotation speed Ne is the reference rotation speed _NDX.
If it is lower (at time t ₂ in Figure 2 a), step 12.
Next, check whether the predetermined period T _HLD set in step 13 has elapsed, that is, whether the engine speed Ne is between the reference speed _NDX and the start value _NH at which feedback control to the target idle speed starts. Predetermined period
T Determine whether _HLD has been continuously located. If the determination result is negative (No), that is, if the predetermined period T _HLD has not elapsed (t ₂ and t ₃ ' in Figure 2a or
_t3 ) Steps 15 and 16 are executed to continue control in the deceleration mode.

If the determination result at stop 12 is affirmative (Yes), that is, the engine speed Ne has reached the starting value at which feedback control to the target idle speed starts.
When T _HLD continues to be located between N _H and reference rotational speed N _DX for a predetermined period of time (time t ₃ in Figure 2 a), steps 14 and 16 are executed to force feedback mode control. After that, when the engine speed falls below the starting value N _H at which feedback control to the target idle speed starts (time t ₄ in Figure 2 a), normal feedback mode is applied. Control takes place.

When the throttle valve 5 is opened while idling is being performed under control in the feedback mode, the determination result in step 3 becomes affirmative (Yes), and steps 6 and 7, which will be described later, are carried out. The program then moves to step 8, where the D _A cc value is set as the duty ratio Do _UT for control in the acceleration mode. In this step 8, the D _A cc value is the value obtained by subtracting the constant value ΔD _A cc from the previous duty value D _A c c _o-1 . These meanings are
When entering acceleration mode from feedback mode control, the current value D _A ccn of value D _A cc is the value D _A used in the previous feedback mode control.
The value obtained by subtracting the constant value ΔD _A cc from cc _o-1 , that is, D _A
cc _o = D _A cc _o-1 − ΔD _A cc, and in this way, the current duty value D _A cc _o is obtained by subtracting the constant value ΔD _A cc from the previous value D _A cc _o-1 each time. As the control is performed many times by executing step 16,
That is, the duty ratio is gradually reduced by control in the acceleration mode. Then, the previous value D _A cc _o-1 is zero,
That is, if D becomes ₀ , the previous value D _A in step 6
The result of the determination as to whether _cco-1 is greater than the value _D0 is negative (No), and the process moves to step 10 via step 9, which will be described later, to enter the sleep mode.

Note that when entering control in the acceleration mode in step 8 or the rest mode in step 10, the same predetermined period as the value set in step 13 is set in step 7 or 9.
Set T _HLD . This is because the judgment in step 11 may become affirmative (Yes) again in the next loop from the control state in acceleration mode or rest mode (in the case where the throttle valve 5 is opened for a short period of time and then returned to fully closed). Therefore, for such a case, T _HLD 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. In response, control of the amount of auxiliary air is forcibly started in a feedback mode that controls the 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 idle speed, which is the starting condition for original feedback mode control, the engine is forcibly shut down after a predetermined period of time. Since control based on the yield back mode is started, it is possible to improve 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 carrying out 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. 1... Internal combustion engine, 5... Throttle valve, 8
...control valve.

Claims (1)

[Claims] 1. When the throttle valve is fully closed and the engine speed is below a predetermined speed 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 has fallen below the target idle speed, the actual control is performed 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 using a feedback mode that controls the control valve according to the difference between the engine speed and a target idle speed,
When the throttle valve is fully closed and the engine speed continues to be higher than the target idle speed and lower than the reference speed between the target idle speed and the predetermined speed for a predetermined period, the feedback mode is activated. A method for controlling the idle speed of an internal combustion engine, comprising forcibly starting auxiliary air amount control.