JP2000220505A - Control device for direct injection internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of engine stall or instability of an engine caused by output shortage even when external load is applied to the engine by appropriately controlling auxiliary air amount and air-fual ratio to be applied to the engine during idling operation. SOLUTION: A target air-fuel ratio factor KOBJ is set according to a current value IDET supplied to an electrically driven device mounted on a car during idling operation of an engine (S32 to S34, S36 to S39). A control rate ICMD of an auxiliary air amount control valve is calculated by using an external load correction item ILOAD which is set according to the external load. The control amount is corrected by using a target air-fuel ratio correction factor KIAFDI which is set according to the target air-fuel ratio factor KOBJ.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a direct injection internal combustion engine which supplies fuel directly into a combustion chamber, and more particularly to a control device for controlling an intake air amount and an air-fuel ratio of the engine.

[0002]

2. Description of the Related Art An intake passage for bypassing a throttle valve is provided in an intake system of an internal combustion engine, and the amount of air (auxiliary air amount) sucked into the engine through the bypass intake passage is controlled. Techniques for controlling the engine speed (rotation speed) in the operating state have been known. For example, in Japanese Patent Publication No. 2-35867, in an idle operation state of the engine, the auxiliary air amount is feedback-controlled so that the detected engine speed becomes the target engine speed, and according to the load of the electric device applied to the engine. A control method of correcting the auxiliary air amount by calculating a correction amount of the auxiliary air amount and adding or subtracting the correction amount according to ON / OFF of the electric device is shown.

Further, a direct injection internal combustion engine that directly supplies fuel into the combustion chamber can perform combustion even when the air-fuel ratio of the air-fuel mixture is considerably leaner than the stoichiometric air-fuel ratio. A lean operation for controlling the air-fuel ratio to about 20 to 50 is performed.

[0004]

However, the control method disclosed in Japanese Patent Publication No. 2-35867 is based on the premise that the air-fuel ratio is set near the stoichiometric air-fuel ratio. There are the following problems when applied to control.

That is, when the air-fuel ratio is increased to a considerable extent as in the lean operation of a direct injection internal combustion engine, the engine torque decreases as compared with the operation at the stoichiometric air-fuel ratio.
If a large amount of auxiliary air is required and the amount of auxiliary air is controlled in the same manner as in operation at the stoichiometric air-fuel ratio, the amount of auxiliary air will be insufficient and the engine output will be insufficient when an external load such as an electric device is applied to the engine. And there is a problem that the rotation fluctuation during idling increases.

SUMMARY OF THE INVENTION The present invention has been made to solve this problem, and appropriately controls the amount of auxiliary air supplied to the engine and the air-fuel ratio to perform lean operation even in an idle state to improve fuel efficiency. It is an object of the present invention to provide a control device for a direct injection internal combustion engine that can prevent engine stoppage due to insufficient output and unstable engine rotation even when an external load is applied to the engine.

[0007]

According to the first aspect of the present invention, there is provided a control apparatus for a direct injection internal combustion engine for directly supplying fuel into a combustion chamber, wherein an external load acting on the engine is detected. External load detecting means, target air-fuel ratio setting means for setting a target air-fuel ratio of the air-fuel mixture generated in the combustion chamber according to the detected external load, and an air-fuel ratio of the air-fuel mixture with the target air-fuel ratio. Air-fuel ratio control means for controlling the air-fuel ratio to coincide with each other; intake air amount control means for controlling the amount of air taken into the combustion chamber provided in the intake system of the engine; Control amount calculation means for calculating a control amount of the intake air amount control means,
Correction means for correcting the control amount of the intake air amount control means according to the target air-fuel ratio.

Here, the "external load" is, for example, an electric device such as a compressor of an air conditioner, a power steering, a headlight or a radio.

According to this configuration, the air-fuel ratio of the air-fuel mixture generated in the combustion chamber is controlled so as to coincide with the target air-fuel ratio set according to the external load, and the control of the intake air amount control means is performed. Since the amount is controlled according to the external load, and this control amount is corrected according to the target air-fuel ratio,
Even in the idle state, lean operation is performed to improve fuel efficiency, and even when an external load is applied to the engine, it is possible to prevent the engine from stopping or the engine rotation from becoming unstable due to insufficient output. The target air-fuel ratio setting means sets the target air-fuel ratio stepwise according to the external load, for example, an air-fuel ratio of 4.
It is desirable to set such as 0, 30, 25.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of an internal combustion engine (hereinafter referred to as “engine”) and a control device thereof according to an embodiment of the present invention. For example, a throttle valve 3 is provided in the middle of an intake pipe 2 of a four-cylinder engine 1. Is arranged. The throttle valve 3 has a throttle valve opening (θTH) sensor 4
And outputs an electric signal corresponding to the degree of opening of the throttle valve 3 and supplies it to an electronic control unit (hereinafter referred to as “ECU”) 5.

An auxiliary air passage 17 that bypasses the throttle valve 3 is connected to the intake pipe 2.
7, an auxiliary air control valve 18 for controlling the amount of auxiliary air.
Is provided. The auxiliary air control valve 18 is connected to the ECU 5, and the ECU 5 controls the valve opening amount.

A fuel injection valve 6 is provided for each cylinder so as to directly inject fuel into the combustion chamber of each cylinder. Each injection valve is connected to a fuel pump (not shown) and is provided with an EC.
It is electrically connected to U5, and the valve opening timing and valve opening time of the fuel injection valve 6 are controlled by a signal from the ECU 5.

On the other hand, an intake pipe absolute pressure (PBA) sensor 7 is provided immediately downstream of the throttle valve 3, and the absolute pressure signal converted into an electric signal by the absolute pressure sensor 7 is supplied to the ECU 5. Further, an intake air temperature (TA) sensor 8 is mounted downstream thereof, detects the intake air temperature TA, outputs a corresponding electric signal, and supplies the electric signal to the ECU 5. Engine water temperature (T
W) The sensor 9 includes a thermistor or the like, detects an engine coolant temperature (cooling coolant temperature) TW, outputs a corresponding temperature signal, and supplies the temperature signal to the ECU 5.

The ECU 5 is connected to a crank angle position sensor 10 for detecting a rotation angle of a crankshaft (not shown) of the engine 1, and supplies a signal corresponding to the rotation angle of the crankshaft to the ECU 5. The crank angle position sensor 10 outputs a signal pulse (hereinafter referred to as a “CYL signal pulse”) at a predetermined crank angle position of a specific cylinder of the engine 1, and a top dead center (TDC) at the start of an intake stroke of each cylinder. ) At a crank angle position before a predetermined crank angle (for a four-cylinder engine, the crank angle is 180 °).
A TDC sensor that outputs a TDC signal pulse and a CRK sensor that generates one pulse (hereinafter referred to as a “CRK signal pulse”) at a constant crank angle cycle (for example, a 30-degree cycle) shorter than the TDC signal pulse, and a CYL signal. Pulse, TDC signal pulse and CRK signal pulse
5 is supplied. These signal pulses are used for various timing controls such as fuel injection timing, ignition timing, and the like, and detection of the engine speed NE.

The three-way catalyst 16 is disposed in the exhaust pipe 12 of the engine 1 and purifies components such as HC, CO, and NOx in the exhaust gas. An oxygen concentration sensor 14 (hereinafter, referred to as an “O2 sensor 14”) as an air-fuel ratio sensor is mounted on the exhaust pipe 12 on the upstream side of the three-way catalyst 16.
The second sensor 14 detects the oxygen concentration in the exhaust gas, outputs an electric signal according to the detected value, and supplies the electric signal to the ECU 5.

The ECU 5 further includes a current value IDET supplied to an electric device mounted on a vehicle driven by the engine 1, that is, a current for detecting an output current value of an alternator (not shown) driven by the engine 1. A sensor 20, an atmospheric pressure sensor 21 for detecting an atmospheric pressure PA, and a shift position for detecting a shift position of the automatic transmission of the vehicle (whether the shift lever is in a neutral position, a parking position, a drive position, or a reverse position). Sensor 2
Various sensors such as 2 are connected, and detection signals of these sensors are supplied to the ECU 5. Although not shown, the vehicle is equipped with an air conditioner (air conditioner) and a power steering, and a signal indicating an operation state of the vehicle is supplied to the ECU 5.

The ECU 5 shapes input signal waveforms from various sensors, corrects a voltage level to a predetermined level, and converts an analog signal value into a digital signal value. The CPU 5b includes a storage unit 5c for storing various calculation programs executed by the CPU 5b, calculation results, and the like, an output circuit 5d for supplying a drive signal to the fuel injection valve 6, and the like.

The CPU 5b determines various engine operating states based on the various engine parameter signals described above, and according to the determined engine operating states,
Based on the following equation (1), a fuel injection time TOUT by the fuel injection valve 6 that operates to open in synchronization with the TDC signal pulse is calculated. TOUT = TI × KOBJ × KO2 × K1 + K2 (1) Here, TI is the basic fuel injection time of the fuel injection valve 6, and a TI map set according to the engine speed NE and the intake pipe absolute pressure PBA is searched. Is determined. TI
The map is set such that the air-fuel ratio of the air-fuel mixture generated in the combustion chamber is substantially equal to the stoichiometric air-fuel ratio in an operating state corresponding to the engine speed NE and the intake pipe absolute pressure PBA on the map.

KOBJ is a target air-fuel ratio coefficient, which is set according to engine operating parameters such as the engine speed NE, the throttle valve opening θTH, and the engine coolant temperature TW.
The target air-fuel ratio coefficient KOBJ is proportional to the reciprocal of the air-fuel ratio A / F, that is, the fuel-air ratio F / A.
Therefore, it is also called a target equivalent ratio. More specifically, in an operating state other than the idle state of the engine, according to the engine speed NE and the throttle valve opening θTH,
The stoichiometric control region, the first lean control region, and the second lean control region as shown in FIG.
In the engine operating state in which E and the throttle valve opening θTH are in the stoichiometric control range, the target air-fuel ratio coefficient KOBJ is set to approximately “1.0”, and the limit in a high-load operating state where the throttle valve is fully opened is set. It is set to a value greater than 1.0 in the operating state set. Further, in the engine operating state where the engine speed NE and the throttle valve opening θTH are in the first lean control region, the target air-fuel ratio coefficient KO
BJ is, for example, 0.67 to 0.8 (air-fuel ratio 18 to 22).
In the engine operating state in the second lean control region, for example, about 0.3 to 0.5 (a value corresponding to an air-fuel ratio of 30 to 50) is set. In the idle state of the engine, the current I
0.37 to 1.0 (air-fuel ratio 14.7, depending on DET)
To a value equivalent to 40).

KO2 is an air-fuel ratio correction calculated by proportional integral control so that the air-fuel ratio becomes the stoichiometric air-fuel ratio in accordance with the value detected by the O2 sensor 14 when the execution condition of the feedback control is satisfied in the stoichiometric control region. It is a coefficient. The air-fuel ratio correction coefficient KO2 is set to a predetermined value or a learned value when the execution condition of the feedback control is not satisfied or in the first and second lean control regions. K1 and K2 are other correction coefficients and correction variables calculated according to various engine parameter signals, respectively, and are predetermined values that can optimize various characteristics such as a fuel consumption characteristic and an engine acceleration characteristic according to an engine operating state. Is determined.

The CPU 5b further determines the valve opening timing (fuel injection timing) of the fuel injection valve 6 according to the engine operating state. More specifically, in an operating state other than the engine idling state, in the stoichiometric control region and the first lean control region of FIG. 2, the fuel is injected during the intake stroke of each cylinder in accordance with the engine speed NE and the throttle valve opening θTH. Then, in the second lean control region, it is determined that the fuel is injected in the compression stroke of each cylinder. When the engine is idle,
When the target air-fuel ratio is set from 25 to 40, injection is performed in the compression stroke, and when the target air-fuel ratio is set to the stoichiometric air-fuel ratio (14.7), injection is performed in the intake stroke. C
PU5b is the fuel injection time TOU determined as described above.
A signal for driving the fuel injection valve 6 is supplied to the fuel injection valve 6 based on T and the fuel injection timing.

The CPU 5b further calculates a valve opening control amount ICMD for controlling the valve opening amount of the auxiliary air control valve 18 according to the engine operating state by the following equation (2), and according to the valve opening control amount ICMD. The drive signal is supplied to the auxiliary air control valve 18. The auxiliary air control valve 18 is provided with a valve opening control amount ICMD.
Is controlled so as to be proportional to the valve opening amount. ICMD = (IFB + ILOAD × KIAFDI) × KIPA + IPA (2) where IFB is the target engine speed NOBJ when the detected engine speed NE is the target engine speed NOBJ in the idling state of the engine.
Is a feedback correction term calculated by the PID control so as to coincide with.

ILOAD is an external load correction term set according to the external load acting on the engine 1. KIA
FDI is a target air-fuel ratio correction coefficient set according to the target air-fuel ratio coefficient KOBJ. KIPA and IPA are an atmospheric pressure correction coefficient and an atmospheric pressure correction term both set according to the atmospheric pressure PA.

FIG. 3 is a flowchart of a process for calculating the external load correction term ILOAD. This process is performed in synchronism with the generation of the TDC signal pulse or at predetermined time intervals.
5b. In step S11, it is determined whether the automatic transmission is in the in-gear state, that is, whether or not the shift position is in a position other than parking or neutral. If the automatic transmission is in the in-gear state, the AT in-gear correction amount IAT is set to a predetermined value IATIN ( Step S13) On the other hand, when the vehicle is not in the in-gear state, the AT in-gear correction amount IAT is set to “0” (step S12). Subsequent step S
At 14, it is determined whether or not the air conditioner is operating, and when it is operating, the air conditioner correction amount IHAC is set to a predetermined value IHA.
On the other hand, if the air conditioner is not operated, the air conditioner correction amount IHAC is set to "0" (step S15).

In the following step S17, IA shown in FIG. 4 is set according to the electric load, that is, the detected current value IDET.
The CG table is searched to calculate the electric load correction amount IACG. Next, it is determined whether the steering operation has been performed, that is, whether the steering operation has been performed (step S18). If the steering operation has been performed, the power steering correction amount IPS is set to a predetermined value IPSON (step S18).
20) On the other hand, when the steering operation is not performed, the power steering correction amount IPS is set to “0” (step S19), and the process proceeds to step S21. The predetermined values IATIN, IHACON, and IPSON are experimentally determined in advance in accordance with the amount of auxiliary air to be increased during in-gear, air-conditioner on, and power steering operation, respectively.

In step S21, the AT in-gear correction amount IAT and the air-conditioner correction amount IH calculated in each of the above steps are set.
The external load correction term ILOAD is obtained by adding the AC, the electric load correction amount IACG, and the power steering correction amount IPS.
(= IAT + IHAC + IACG + IPS), and
This processing ends.

FIG. 5 is a flowchart of a process for determining the target air-fuel ratio coefficient KOBJ and determining the injection stroke. This process is performed in synchronization with the generation of the TDC signal pulse.
Alternatively, it is executed by the CPU 5b every predetermined time. In a step S31, it is determined whether or not the engine 1 is in an idle state. This determination is made because the throttle valve is almost fully closed (for example, the throttle valve opening θTH is 2 degrees or less) and the engine speed NE is equal to the predetermined speed NEL (for example, 10 degrees).
00 rpm) or less. When the engine is in an operation state other than the idle state, as shown in FIG. 2, the engine speed NE and the throttle valve opening θTH
Then, the target air-fuel ratio coefficient KOBJ and the injection stroke are determined according to (step S35).

When the engine 1 is in the idle state,
The detected current value IDET is equal to the first predetermined current value IDETH.
(Step S32), and if IDET ≦ IDETH, it is further determined whether it is larger than a second predetermined current value IDETM (eg, 40A) (Step S33), and IDET is determined. ≤ IDE
If it is TM, the third predetermined current value IDETL
(For example, 30A) is determined (step S34). Here, IDETL <IDETM <IDE
TH.

When IDET> IDETH and the electric load is large, the target air-fuel ratio coefficient KOBJ is set to 1.
0, that is, a value equivalent to the stoichiometric air-fuel ratio (step S
36), if IDETM <IDET ≦ IDETH, the target air-fuel ratio coefficient KOBJ is set to a first lean predetermined value KOBJL1 corresponding to an air-fuel ratio of 25 (step S37),
If IDETL <IDET ≦ IDETM, the target air-fuel ratio coefficient KOBJ is set to a second lean predetermined value KOBJL2 corresponding to an air-fuel ratio of 30 (step S38), and IDET is set.
If ≦ IDETL, the target air-fuel ratio coefficient KOBJ is set to a third lean predetermined value KOBJL3 corresponding to an air-fuel ratio of 40 (step S39). Further, when performing the stoichiometric operation with KOBJ = 1.0, the intake stroke injection is performed (step S36), and when performing the lean operation, the compression stroke injection is performed (steps S37, S38, S3).
9). By the processing in FIG. 5, the target air-fuel ratio coefficient KOBJ and the injection stroke are determined according to the current value IDET supplied to the on-vehicle electric device.

FIG. 6 is a flowchart of a process for calculating the target air-fuel ratio correction coefficient KIAFDI.
In synchronism with the generation of a signal pulse or at predetermined intervals, C
This is executed by the PU 5b. In this processing, the target air-fuel ratio coefficient K
The KIAFDI table shown in FIG. 7 is searched according to the OBJ, and the target air-fuel ratio correction coefficient KIAFDI is calculated. KI
The AFDI table indicates that the correction coefficient KI increases as the target air-fuel ratio coefficient KOBJ decreases, that is, as the air-fuel ratio becomes leaner.
AFDI is set to be large. In the table of FIG. 7, the coefficient value KIAFDI1 is set to 3, for example.

As described above, when the engine 1 is in the idling operation state and executes the lean operation, the valve opening control amount ICMD is corrected by the external load correction term ILOAD corresponding to the external load applied to the engine 1, and A target air-fuel ratio coefficient KOBJ is set according to an electric load (detected current value IDET) which is one of the loads, and a correction coefficient KIAFDI set according to the target air-fuel ratio coefficient KOBJ.
The valve opening control amount ICMD is corrected by
Appropriate air-fuel ratio setting and auxiliary air amount control according to the external load applied to the engine 1 can be performed. Even in an idle operation state, the lean operation is performed to improve the fuel efficiency, and the engine is stopped due to insufficient output and the engine is stopped. Rotational instability can be prevented.

FIG. 8 shows the external load and the absolute pressure PBA in the intake pipe.
FIG. 6 is a diagram showing a relationship between a target air-fuel ratio coefficient and a target air-fuel ratio coefficient KOBJ;
When the external load increases, the external load correction term IOAD and the feedback correction coefficient IFB increase, and the intake air amount increases, so that the intake pipe absolute pressure PBA gradually increases.
When the external load exceeds LEX1 in the figure, the target air-fuel ratio coefficient K
OBJ is changed from the third lean predetermined value KOBJL3 to the second lean predetermined value KOBJL2. Accordingly, the target air-fuel ratio correction coefficient KIAFDI is changed in the decreasing direction, so that the intake air amount decreases stepwise, and the intake pipe absolute pressure PBA also decreases. As the external load further increases, L
When EX2 is exceeded, the target air-fuel ratio coefficient KOBJ is changed from the second lean predetermined value KOBJL2 to the first lean predetermined value KOBJL.
It is changed to 1. Accordingly, the target air-fuel ratio correction coefficient K
IAFDI is changed in the decreasing direction and the absolute pressure PB in the intake pipe is changed.
A decreases.

In this embodiment, the current sensor 20, the shift position sensor 22, the air conditioner on / off switch (not shown), and the power steering operation detecting device correspond to external load detecting means, and the auxiliary air control valve 18 controls the intake air amount. The ECU 5 corresponds to control amount calculation means, target air-fuel ratio setting means, air-fuel ratio control means, and correction means.
More specifically, the CPU 5b calculates the valve opening control amount ICMD using the processing of FIG. 3 and equation (2).
The processing of FIG. 5 corresponding to the control amount calculating means and setting the target air-fuel ratio coefficient KOBJ corresponds to the target air-fuel ratio setting means, and the processing of calculating the fuel injection time TOUT using the equation (1) is the air-fuel ratio controlling means. And the target air-fuel ratio correction coefficient KIAF
The processing of FIG. 6 for calculating DI and the arithmetic processing of equation (2) correspond to the correction means.

The present invention is not limited to the embodiment described above, and various modifications are possible. For example, in the above-described embodiment, the target air-fuel ratio coefficient KOBJ is set according to the current detection value IDET indicating the electric load.
When the external load increases as shown in FIG. 8, the intake pipe absolute pressure PBA indicating the overall load applied to the engine increases. Therefore, according to the intake pipe absolute pressure PBA, that is, the engine load, the target similarly to the processing shown in FIG. The air-fuel ratio coefficient KOBJ may be set.

In the above-described embodiment, the target air-fuel ratio coefficient KOBJ is directly applied to the equation (1) to control the air-fuel ratio to the target air-fuel ratio.
As shown in Japanese Patent No. 84707, during lean operation,
Target air-fuel ratio coefficient KOBJ according to engine rotation fluctuation
May be corrected to calculate a lean operation correction coefficient, and the lean operation correction coefficient may be applied to equation (1).

In place of the O2 sensor 14, a wide-range air-fuel ratio sensor capable of linearly detecting the air-fuel ratio over a wide range is provided, and the fuel injection time TOUT is feedback-controlled so that the air-fuel ratio detected by this sensor matches the target air-fuel ratio. The air-fuel ratio control means may be configured as described above. Further, the intake air amount control means may be constituted by a throttle valve 4 and an actuator for driving the throttle valve 4 instead of the auxiliary air amount control valve 18, and the actuator may be controlled by the ECU 5.

[0037]

As described above, according to the first aspect of the present invention, the air-fuel ratio of the air-fuel mixture generated in the combustion chamber is:
Control is performed so as to match the target air-fuel ratio set according to the external load, and the control amount of the intake air amount control means is controlled according to the external load, and this control amount is controlled according to the target air-fuel ratio. Since the correction is made, it is possible to improve the fuel efficiency by executing the lean operation even in the idling state, and to prevent the engine from stopping or the engine rotation from becoming unstable due to insufficient output even when an external load is applied to the engine.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an internal combustion engine and a control device thereof according to an embodiment of the present invention.

FIG. 2 is a diagram showing a control region of an air-fuel ratio.

FIG. 3 is an external load correction term (ILOA) of the auxiliary air supply amount.
It is a flowchart of a process of calculating D).

FIG. 4 is a diagram showing a table used in the processing of FIG. 3;

FIG. 5 shows a target air-fuel ratio coefficient (KOBJ) according to an external load.
It is a flowchart of a process of calculating.

FIG. 6 is a flowchart of a process for calculating a target air-fuel ratio correction coefficient (KIAFDI).

FIG. 7 is a diagram showing a table used in the processing of FIG. 6;

FIG. 8 is a diagram showing a relationship between an external load, an intake pipe absolute pressure (PBA), and a target air-fuel ratio coefficient (KOBJ).

[Explanation of symbols]

Reference Signs List 1 internal combustion engine 2 intake pipe 5 electronic control unit (control amount calculation means, target air-fuel ratio setting means, air-fuel ratio control means, correction means) 6 fuel injection valve 7 intake pipe absolute pressure sensor (external load detection means) 17 auxiliary air Passage 18 Auxiliary air control valve (intake air amount control means) 20 Current sensor (external load detection means) 22 Shift position sensor (external load detection means)

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Katsuhiro Kumagai, Inventor 1-4-1 Chuo, Wako-shi, Saitama Prefecture Inside Honda R & D Co., Ltd. (72) Inventor Noriyuki Irie 1-4-1, Chuo, Wako-shi, Saitama Inside Honda R & D Co., Ltd. (72) Inventor Hideyuki Oki 1-4-1 Chuo, Wako-shi, Saitama Prefecture Inside Honda R & D Co., Ltd. (72) Takashi Kiyomiya 1-4-1 Chuo, Wako-shi, Saitama Pref. F-term in Honda R & D Co., Ltd. (reference) 3G301 HA04 HA15 JA02 JA04 JA31 KA07 KA10 LA04 LB04 MA01 MA13 ND01 PA07Z PA09Z PA10Z PA11Z PD03A PD03Z PE01A PE01Z PE03Z PE05Z PE08Z PF08Z PF11Z

Claims (1)

[Claims] 1. A control device for a direct injection internal combustion engine that directly supplies fuel into a combustion chamber, comprising: an external load detection unit configured to detect an external load acting on the engine; Target air-fuel ratio setting means for setting a target air-fuel ratio of the air-fuel mixture to be generated; air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture to be equal to the target air-fuel ratio; provided in an intake system of the engine. An intake air amount control means for controlling an amount of air taken into the combustion chamber; a control amount calculation means for calculating a control amount of the intake air amount control means according to at least the detected external load; A control unit for correcting the control amount of the intake air amount control unit according to an air-fuel ratio.