JPS6325351A - Rotation speed control method for engine - Google Patents

Abstract

PURPOSE:To enable stabilization of an idle rotation speed right after the starting, by a method wherein control is effected so that, after elapse of a given time commencing in the starting of an engine, a control amount is changed in a direction in which an intake air amount or an air-fuel mixture feed amount is increased. CONSTITUTION:When a throttle valve 16 is closed and an engine 10 is in an idle running state, an air control unit 60 determines a target value of an idle rotation speed according to an engine cooling water temperature, and determines a control amount based on a result of comparing an actual idle rotation speed with a target value. By means of the control amount, an air control valve 30 is controlled, and the magnitude of an amount of auxliary air bypassing the throttle valve 16 is controlled. In which case, since, until a given time lapses after the starting of the engine 10, a target value is raised through the working of a timer circuit, a control amount right after the starting is more changed in a direction, in which an auxiliary air amount is increased, than that prevailing after some time lapses after the starting of the engine. This constitution increases an idle rotation speed, and stabilizes an idle rotation speed right after the starting.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the idle rotation speed of an engine that drives an automobile or the like.

[Conventional technology]

Conventionally, regarding the idle speed of an automobile engine,
In order to control the idle rotation speed to a designed target value in a maintenance-free manner, for example, the deviation between the actual engine idle rotation speed and the target value is determined by a computer, and the intake air amount or mixture of the engine is adjusted according to this deviation. A closed loop control method has been proposed to control the amount of air supplied.

[Problem that the invention seeks to solve]

However, in the above control method, the computer calculates the target value using only the engine cooling water temperature as a parameter, and one target value is determined for the same engine temperature condition and control is performed. If the cooling water temperature is the same, the rotational speed will be controlled to be the same even if the engine is started immediately after the engine is started, or even if the engine is started with a lower cooling water temperature and reaches that temperature after a certain period of time.

However, immediately after the engine starts and after a predetermined period of time has elapsed after starting as mentioned above, even if the cooling water temperature is the same, the resistance the engine receives is different, and the friction between various parts of the engine is greater in the former, so it is natural that the front The resistance increases. Therefore, if the target value is determined only based on the cooling water temperature as described above, if the engine starts with a relatively high cooling water temperature, the target value will be set low from the start, but as mentioned above, immediately after starting, the target value will be set low. Due to the large resistance, the engine's idle speed becomes unstable, and in some cases, there is a risk of stalling.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems, and to provide an engine rotational speed control method that can stabilize the idle rotational speed of the engine immediately after the engine is started.

[Means for solving problems]

In order to solve the above problems, in the present invention, the target value of the idle rotation speed of the engine is determined according to the engine cooling water temperature, the actual idle rotation speed of the engine is detected, and this actual idle rotation speed and the A control amount is determined based on the comparison result, and the engine intake air amount or mixture supply amount is controlled based on this control amount, and the actual idle speed is adjusted to the target value. In the engine rotational speed control method, the engine rotational speed control method detects the start of the engine, and changes the control amount in a direction in which the intake air amount or the mixture supply amount increases in a predetermined time after the engine starts. The engine rotation speed control method is characterized by controlling the engine rotation speed.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An apparatus for carrying out the control method according to the present invention will be described below with reference to embodiments shown in the drawings.

In FIG. 1, an engine 10 is a known four-cycle spark ignition engine that drives an automobile, and it takes in main air through an air cleaner IL air flow meter 12, an intake pipe 13, a surge tank, and each intake branch pipe 14, and fuels e.g. Gasoline is supplied through an electromagnetic fuel injection valve 1 installed in an intake branch pipe 14.
It is supplied by injection from 5.

The main intake air amount of the engine 10 is adjusted by a throttle valve 16 that is arbitrarily operated, while the fuel injection amount is adjusted by a fuel control unit 20 that constitutes a computer. The fuel control unit 20 is a known unit that determines the fuel injection amount using the engine rotational speed measured by an electromagnetic pickup 21 that serves as a rotational speed sensor and the intake air amount measured by the airflow meter 12 as basic parameters. A signal from a warm-up sensor 22 or the like is input to the engine, and the fuel injection amount is increased or decreased based on this signal.

The air conduit 18.19 is provided to bypass the throttle valve 16, and an air control valve 30 is provided between the two conduits 18.19. Further, one end of the conduit 18 is connected to an air inlet provided between the throttle valve 16 and the air flow meter 12, and one end of the conduit 19 is connected to an air outlet provided downstream of the throttle valve 16. ing.

The air control valve 30 is basically a two-diaphragm control valve, which transmits the displacement of a diaphragm 33 whose outer periphery is wound tightly between housings 31 and 32 to a valve body 35 via a shaft 34, 36 is of the type that opens and closes. The diaphragm 33 is displaced by the pressure difference between the chambers 37 and 38, and is also displaced by the compression coil spring 4 via the spring catcher.
0, and the valve closing force of the valve body 35 is applied.

A holding plate 41 is secured together with a diaphragm 33 by tightening between the housings 31 and 32, and the shaft 34 is guided in an airtight manner by a sleeve provided on the holding plate 41.

Further, a small hole is formed in the holding plate 41, and the atmosphere is introduced into the chamber 37 through this small hole.

The valve body 35 is a needle valve, and the area of the flow path formed between the valve body 35 and the valve seat 36 is continuously changed with respect to the amount of displacement of the shaft 34.

Furthermore, the air control valve 30 includes an electromagnetic mechanism 50 that indirectly changes the opening degree of the valve body 35.

This electromagnetic mechanism 50 is wound around a synthetic resin bobbin,
An electromagnetic coil 51 fixed to the housing 31, a fixed iron core 52' disposed at the center of the TM coil 51, a plate spring 53 formed of a magnetic material and fixed to the housing 31 with a pin, and a plate spring 53 fixed to the housing 31 with a pin. It is composed of pipes 55 and 56 provided to face the valve body 54 at the tip. and,
When the electromagnetic coil 51 is not energized, the leaf spring 53
The tube 56 is closed by its own spring force, and when the electromagnetic coil 51 is energized, the tube 55 is closed by the electromagnetic force. Here, the pipe 55 is opened to the atmosphere via the air->ilter to introduce atmospheric pressure to the chamber 38, while the pipe 56 is connected to the surge tank via a pipe 57 to introduce negative intake pressure to the chamber 38. It is connected.

Accordingly, the pressure within the chamber 38 changes depending on the duty ratio of the pulse signal applied to the electromagnetic coil 51 of the electromagnetic mechanism 50, and the opening degree of the valve body 35 changes.

Excitation of the electromagnetic mechanism 50 is controlled by an air control unit 60 that constitutes a computer. This air control unit 60 includes an electromagnetic pickup 21, a warm-up sensor 22,
It is connected to an air conditioning switch 23 and a starter switch 24, from which various signals are input.

Here, the electromagnetic pickup 21 is provided facing a ring gear 25 that rotates in synchronization with the crankshaft of the engine 10, and outputs a pulse signal with a frequency proportional to the engine rotation speed. The warm-up sensor 22 is composed of a temperature sensing element such as a thermistor, and detects the temperature of the cooling water, which is representative of engine salt.

Further, when the air conditioning switch 23 is turned on, the electromagnetic clutch 27 is connected, and the air conditioner compressor 28 is connected as a load of the engine 1o.

Further, the starter switch 24 is connected to the starting electric motor 26 of the engine 10, and is turned on when the key switch of the automobile is placed in the start position.

Next, according to FIG. 2, the air control unit 60 of the computer
will be explained in detail. Digital/Analog (D/
A) The conversion circuit 100 receives a pulse signal of a frequency corresponding to the engine rotation speed from the electromagnetic pickup 21, and this signal is applied to the resistors IO1 to IO104 and the capacitor 106.
, a waveform shaping section consisting of a transistor 10B as shown in FIG.
) is output from terminal A after being shaped into a waveform as shown in FIG. Then, this signal is transferred to the capacitor 107, l1
1. Convert a voltage proportional to the actual engine rotation speed and a sawtooth wave voltage synchronized to the engine rotation into the voltage shown in FIG. Output from terminal B.

The function voltage generation circuit 200 receives the output signal of the warm-up sensor 22, the on/off signal of the air conditioning switch 23, and the on/off signal of the starter switch 24. Among these, the output of the warm-up sensor 22 is amplified by a known amplification circuit 201 to become a voltage signal corresponding to the engine cooling water temperature.The output voltage signal is transmitted via a resistor 202, a diode 203, and an on/off signal from the air conditioning switch 23. The off signal is a resistor 204,
It is output to the comparator circuit 300 via the diode 205,
Provides comparison level VD of comparison circuit 3oo.

Diode 207, capacitor 209, resistor 208.2
10.211 and the operational amplifier 206 constitute a timer circuit, the signal of the starter switch 24 is input to this timer circuit, and the output of the timer circuit is applied to the comparator circuit 300 via a resistor 212 and a diode 213. Change the comparison level VD.

In other words, this function voltage generation circuit 200 is for changing the comparison level VD representing the target value of the idle speed, and its output characteristics are as shown in FIG. 5, and as the engine coolant temperature T increases, When the air conditioning switch 23 is off, the comparison level VD is changed to a low level as shown by the solid line, and when the air conditioning switch 23 is on, the comparison level VD is changed to a high level as shown by the broken line. change.

Furthermore, when the starter switch 24 is turned on for a certain period of time, the terminal becomes a level for that period, and when the switch 24 is turned off, it becomes 0 level, resulting in a waveform as shown in FIG. 4 (1). As a result, the voltage waveform at the terminal becomes the discharge waveform shown in Figure 4 (2), and the voltage at the terminal ■ increases to the voltage vO determined by the resistors 210 and 211 as shown in Figure 4 (3). As the voltage decreases, the voltage gradually decreases. Therefore, the comparison level VD is as shown in Figure 4 (4) for the elapsed time.
The time t changes from L1 immediately after engine startup to time t.
It is maintained at a high level for a period of 0, and then reaches a level determined by the output of the warm-up sensor 22, etc.

The comparison circuit 300 includes resistors 301 to 303 and a comparator 30
4, the output voltage of the D/A conversion circuit 100 representing the actual idle rotation speed is compared with the comparison level VD determined by the output voltage of the function voltage generation circuit 200 representing the target value, and the actual idle rotation speed is determined. Speed N and target value N r e
Calculate the deviation ΔN (=N-N, .f) from f and calculate the deviation ΔN
Outputs a signal according to the

Then, the comparison circuit 300 operates as shown in FIG.
A signal C having a 0 level as shown in is output.

The integrating circuit 400 charges or discharges the capacitor 401 at a constant current according to the output signal C of the comparing circuit 300, and calculates the integrated voltage E as a control amount from the deviation ΔN.
Output. This integrating circuit 400 has resistors 402 to 4 as a constant current charging circuit in which the signal C operates at O level.
04, a transistor 409, resistors 405 to 407, a diode 408, and a transistor 410 as a constant current discharge circuit in which the signal C operates at the level.

As shown by the broken line in FIG. 3 (4), this integrating circuit 400 has a capacitor 401 charged with a constant current while the output signal C of the comparator circuit 300 is at O level, so the output voltage E increases, and the output signal C When the voltage is at the level, the capacitor 401 is discharged at a constant current, and the output voltage E is lowered.

The pulse modulation circuit 600 includes a resistor 601, a comparator 602, and an oscillator 603, and outputs a pulse signal with a duty ratio corresponding to a voltage E representing a control amount. Among these, the oscillator 603 is a known one that outputs a triangular wave voltage F with a constant period as shown by the solid line in FIG. 3(4).

The comparator 602 receives the output voltage E of the integrating circuit 400 and the triangular wave voltage F of the oscillator 601, compares both voltages, and finds that the output voltage E of the integrating circuit 400 is larger as shown in FIG. 3 (5). A pulse signal G that becomes a level only for a period is output.

The amplifier circuit 700 receives the signal G of this pulse modulation circuit 600.
This is an amplification circuit using a power transistor 701 that inverts and amplifies the output, and the output after amplification is sent to the electromagnetic coil 51 of the electromagnetic mechanism 50.
supplied to

The voltage control circuit 800 is composed of resistors 801 to 805 and diodes 806 and 807, and controls the output voltage of the terminal E of the integrating circuit 400 between the upper limit voltage of the terminal H and the terminal J.
Lower limit voltage ■Limit within the control range between 1.7.

The resistor 804 of the limiting circuit 800 is connected to the functional voltage generating circuit 20.
Since it is connected to the output of the amplifier circuit 201 that outputs a voltage signal according to the engine cooling water temperature of 0, the upper limit voltage V
, and the lower limit voltage ■□7 can have characteristics dependent on the engine cooling water temperature T as shown in FIG. 6 by appropriately selecting the values of the respective resistors 801, 802, and 803.

Further, the resistor 805 is connected to the I terminal of the timer circuit of the functional voltage generating circuit 200, and the upper limit voltage (2) is maintained by the terminal summer voltage shown in FIG. 5(3) until time t0 has elapsed after the engine is started. , and the lower limit voltage V a 5n are raised by a certain level and change to a higher level, and then the upper and lower limit voltages □8 and V m i n change to normal levels.

With this configuration, when the potential of the capacitor 401 of the integrating circuit 400 rises and exceeds the upper@voltage V□8, the diode 806 becomes conductive, and eventually the capacitor 401
The potential cannot rise above the upper limit voltage V + *ax, and conversely, even if the potential decreases, it cannot be lowered below the lower limit voltage V , i. Therefore, the voltage amplitude of the capacitor 401 is limited. Can be done.

Next, the operation of the above configuration will be explained. When the throttle valve 16 is closed and the engine 10 is in idle operation, the idle rotation speed is determined by the air control unit 6.
When the output voltage is lower than the target value (set circuit speed) corresponding to the comparison level VD determined by the zero function voltage generation circuit 200, the output of the D/A conversion circuit 100 also decreases with respect to the comparison level VD.

Therefore, the output of the D/A conversion circuit 100 is always lower than the comparison level VD, or even if it becomes higher, it is only for a short time. Therefore, the output signal of the comparison circuit 300 indicating the rotational speed deviation ΔN depends on the deviation ΔN. The pulse signal is always at 0 level or a pulse signal with a small duty ratio. As a result, the output voltage E of the integrating circuit 400, which indicates the control amount, increases.

Therefore, in the pulse modulation circuit 600, the period t during which the integral voltage E is larger than the triangular wave voltage F of the oscillator 603 (the period during which the comparator 602 is at the level) increases, the duty ratio increases, and the electromagnetic coil 51 of the electromagnetic mechanism 50 increases. The proportion of time in which the air is energized increases, the opening degree of the air control valve 30 increases, the amount of auxiliary air that bypasses the throttle valve 16 increases, and the idle speed of the engine 10 increases.

On the other hand, when the idle rotation speed is higher than the target value (set rotation speed), the output of the D/A conversion circuit 100 is always higher than the comparison level VD that provides the target value, but it is low (for a short time, if at all). The output signal of the comparator circuit 300 is always a pulse signal with a large duty ratio.The output voltage E of the integrated integration circuit 400 is decreasing (.

Therefore, in the pulse modulation circuit 600, the period L during which the integral voltage E is larger than the triangular wave voltage F of the oscillator 603 (that is, the period during which the comparator 602 is at the level) decreases, and the electromagnetic coil 51 of the electromagnetic mechanism 50 of the air control valve 30 When energized, the citrus rate decreases, that is, the opening degree of the air control valve 30 decreases, the amount of auxiliary air bypassing the throttle valve 16 decreases, and the idle speed of the engine 10 decreases.

In this way, the engine rotational speed is set to the comparison level V at which the output of the function voltage generation circuit 200 is determined by the air control unit 60 at idle when the throttle valve 16 is closed.
It is controlled to a target value (set rotational speed) corresponding to D.

However, the comparison level VD that determines this target value increases as the engine cooling water temperature decreases, as shown by the dark line in Figure 5, depending on the output of the warm-up sensor 22. Since the rotational speed can be increased, stable idling operation can be maintained.

In addition, after the engine starts, the comparison level VD representing the target value is raised by the timer circuit until a time L0 of several seconds to several minutes has elapsed, so the comparison level VD is raised by the amount that the comparison level VD is raised immediately after the engine is started. Since the output voltage E indicating the control amount changes in the direction of increasing the amount of auxiliary air compared to when a while has elapsed, the idle rotation speed is increased and the idle rotation speed immediately after the engine starts is stabilized.

In other words, even if the engine cooling water temperature is the same, immediately after the engine starts, the control 4'B changes to increase the amount of auxiliary air, compared to when the engine starts at a lower temperature and reaches that temperature after a certain period of time. Since the idle rotation speed is increased by the output voltage level, which indicates the amount of power, the idle rotation speed can be stabilized by sufficiently overcoming the large resistance that the engine receives immediately after starting. By adjusting the idle speed, the warm-up time can be shortened, and this shortened warm-up time can also reduce fuel consumption and improve drivability.

Further, when the compressor 28 for the automobile cooler or air conditioner is connected to the engine 10 and driven, the ON signal of the air conditioning switch 23 is transmitted to the function voltage generating circuit 20.
0 and this circuit 200 raises the comparison level VD as shown by the broken line in FIG. Since the idle rotation speed is increased, the problem of impairing the cooling capacity of the vehicle or causing engine stall is eliminated.

Further, for example, in a case where the engine cooling water temperature has increased and warm-up has been completed, the load such as viscous resistance of the engine oil is reduced, so the amount of auxiliary air may be small. When such warm-up has been completed, the throttle valve 16 is closed and the air control unit 60 is closed when the vehicle is moved by releasing the accelerator pedal and depressing the brake pedal to decelerate and stop the vehicle.
provides closed-loop control of rotational speed. Therefore, if the brake is operated until the rotational speed becomes lower than the target value determined by the voltage generating circuit 200, the output of the integrating circuit 400 will continue to rise, which means that the opening degree of the air control valve 3° will increase, and the amount of auxiliary air will increase. Because it increases all at once, the engine speed may become abnormally high, albeit temporarily.

However, the output voltage E indicating the control amount of the integrating circuit 400 is
The voltage control circuit 800 limits the auxiliary air amount to the upper limit voltage V max, and the amount of auxiliary air does not increase beyond the amount determined by the upper limit voltage (1), thereby preventing an abnormal increase in the engine speed.

In addition, since the voltage control circuit 800 limits the output voltage E of the integrating circuit 400 to within the upper and lower limits,
Even if a problem occurs in the rotational speed signal from the rotational speed sensor, at least the rotational speed during idling can be controlled within the control range corresponding to the voltage between the upper limit and the lower limit depending on the engine cooling water temperature.

In the above embodiment, a wired logic type analog computer is used as the computer, but a stored program type microcomputer may be used for control.

In this case, the computer 60 is composed of an input interface 61, a microcomputer 62, an output interface 63, and drive circuits 64, 65 as shown in FIG.
For example, let the CPU interrupt the time every 20m5ec, and
An interrupt routine as shown in the figure may be executed.

In FIG. 9, the interrupt routine includes step 70.
When the start is started, the output signals of each sensor and switches 21 to 24 are inputted in step 71, and it is determined in step 72 whether the starter switch 24 is on, and if it is on, the target value N7°r (rpm) is set in step 73. Calculate. This target value N0° is determined by a function f(T) of the cooling water temperature T, as shown in FIG. 8, and this f(T) is stored in the memory as f(T)st in step 74.

If the starter switch 24 is off in step 72,
In step 75, it is determined whether the cooling water temperature T is 60° C. or higher. If not, in step 76, the microcomputer 62
The starter switch 24 is activated by a built-in timer.
Determine whether it has been within 5 minutes since the switch was turned off. and,
If it is within 5 minutes, in step 77 the target value N rat is set to f (T) s t stored in the memory.

If the water temperature T is 60°C or more in step 75, or if 5 minutes have passed since the starter switch 24 was turned off in step 76, the previously calculated target value N'r*f is changed to the function value f in step 78. (T), and if so, in step 79 the target value N r e
Set f to (N' rat -2(rpm)).

If in step 78 N 11° is smaller than the function value f (T), in step 80 the target value N, ... is set as the function value f
(T).

When the target value N1° is set as described above, in step 81, a deviation ΔN is calculated from the actual idle rotation speed and the target value ΔN based on the following equation.

ΔN=N−N,.

Next, in step 82, a value representing the duty ratio of the output of the electromagnetic mechanism 50 to the tm coil 51 based on the deviation ΔN is read from a map stored in advance in the ROM (read only memory) in the microcomputer 62.
Let it be the control amount. Then, the control amount is set to be within the control range between the upper limit value and the lower limit value, and the control amount is set in step 83.
output to the output interface 63.

Then, in step 84, the process returns to the main routine. The control amount indicating the duty ratio calculated by the microcomputer 62 in this way is output to the output interface 63, where it is converted into a pulse signal having the duty ratio, and output to the electromagnetic coil 51 via the drive circuit 65. be done.

However, according to this embodiment, even if the coolant temperature becomes high due to engine operation within 5 minutes after starting and the coolant temperature reaches a predetermined value of less than 60°C, step 75.76
The process proceeds to step 77 based on the target value N r
Since e f is maintained at the target value Nrmt -f (T) S L, which is set based on the cooling water temperature at startup, the engine starts at a lower temperature and reaches the predetermined value after 5 minutes or more. This is a higher target value. Therefore, the control amount changes in the direction of increasing the amount of auxiliary air, and therefore, even if the cooling water temperature is the same (less than 60°C), the idle rotation speed will change immediately after starting, and when a predetermined time (5 minutes) has passed after starting. is enhanced.

In other words, even when this stored program type microcomputer is used for control, the same effect as when the above-mentioned wired logic type computer is used for control can be obtained.

In the above embodiment, the amount of auxiliary air that bypasses the throttle valve 16 is controlled by the air control valve 30, but for example, the shaft 3 of the air control valve 30
It is also possible to control the amount of air or air-fuel mixture during idling operation by controlling the opening degree of the throttle valve 16 instead of the valve body 35 with a displacement of 4.

Further, in the above embodiment, an air control valve of the type in which the diaphragm valve is actuated by the electromagnetic mechanism 50 is used, but a magnetic type air control valve in which the valve body is directly actuated by the electromagnetic force of the electromagnetic mechanism 50 may also be used. .

Further, although the warm-up state of the engine and the connection state of the compressor are used as elements of the function voltage, the function voltage may be generated depending on other engine operating states.

Further, in the above embodiment, during normal operation other than idling operation in which the throttle valve 16 is opened, it is possible to additionally provide a circuit that maintains the output voltage of the integrating circuit 400 at a predetermined value depending on the engine temperature. This makes it possible to supply a predetermined amount of auxiliary air depending on the engine temperature during normal operation.

〔Effect of the invention〕

As described above, according to the present invention, the start of the engine is detected, and the control amount is controlled so that the amount of intake air or the amount of mixture supplied increases in a predetermined period of time after the start of the engine. Therefore, even if the cooling water temperature is the same, immediately after starting the engine,
Compared to when the engine starts at a lower temperature and reaches that temperature after a certain period of time, the idle rotation speed is increased by the above-mentioned changed control amount, so it can sufficiently overcome the large resistance that the engine receives immediately after starting, and the idle speed will be increased. This has the excellent effect of stabilizing the rotational speed, and the increased idle rotational speed immediately after startup shortens the warm-up time. As the time is shortened, fuel consumption can also be reduced, and drivability can also be improved, which are excellent effects.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of a system to which the method of the present invention is applied, Fig. 2 is an electric circuit diagram showing the air control unit shown in Fig. 1, and Figs. 3 and 4 are the respective parts of Fig. 2. The signal waveform diagram of FIG. 5 and FIG. 6 are graphs used to explain the operation.
FIG. 7 is a block diagram showing another embodiment of the computer;
FIG. 8 is a graph for explaining the operation, and FIG. 9 is a flowchart for explaining the operation of the embodiment shown in FIG. 10...engine, 16...throttle 4.21.
...Electromagnetic pickup, 22...Warm-up sensor, 24.
・・Starter switch, 30・・Air control valve, 50・
...Electromagnetic structure, 62...Microcomputer, 10
0...A-reconversion circuit, 200...Function voltage generation circuit, 300...Comparison circuit, 400...Integrator circuit, 6
00...Pulse modulation circuit.

Claims (1)

[Claims] The target value of the engine's idle rotation speed is determined according to the engine cooling water temperature, the actual idle rotation speed of the engine is detected, this actual idle rotation speed is compared with the target value, and the control is performed according to the result of this comparison. In the engine rotational speed control method, the engine rotational speed is controlled by determining the control amount and controlling the intake air amount or mixture supply amount to the engine based on the control amount so that the actual idle rotational speed matches the target value. 1. An engine rotation speed control method, comprising: detecting the start of the engine, and controlling the control amount so that the intake air amount or the mixture supply amount increases in a predetermined period of time after the engine starts.