JPH05202754A - Fuel supply method and fuel supply device for engine - Google Patents

Abstract

PURPOSE:To properly control the air fuel ratio of the air-fuel mixture to effectively control the air fuel ratio of an air fuel mixture omnipresent part even in a stratified combustion state by forming air-fuel mixture in a sub-chamber apart from the intake air from an inlet port and supplying it from a fuel supply port to a combustion chamber. CONSTITUTION:Intake air is introduced from an inlet port to the outer peripheral side of the cylinder of a combustion chamber 4, and the air-fuel mixture formed in a sub-chamber 20 is also introduced near the center of the cylinder of the combustion chamber 4. The air fuel ratio of the air-fuel mixture in the ante-chamber that is the air fuel ratio of the air-fuel mixture formed in this sub-chamber 20 is controlled, and in the operation area, in particular, in which air fuel ration as the whole of the combustion chamber is set more lean than lambda=1, the air fuel ratio of the air-fuel mixture in the sub-chamber is controlled to approximately lambda=1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine fuel supply method and apparatus for mixing fuel and air in a sub-chamber for forming a mixture and then supplying the mixture to a combustion chamber.

[0002]

2. Description of the Related Art Conventionally, as disclosed in, for example, Japanese Unexamined Patent Publication No. 2-181067, a timing valve for opening a mixture gas supply port (nozzle port) in a combustion chamber in addition to an intake port and opening / closing this port. And by providing a pressurized air supply means and a fuel injection valve so as to supply the pressurized air and the injected fuel to the passage leading to this port, the fuel and the pressurized air are mixed and then the timing valve is opened. A fuel supply device is known in which a fuel-air mixture is supplied to a combustion chamber from a port for supplying a mixture.
According to this device, the atomization of the fuel is promoted by mixing the fuel and the pressurized air, and the air-fuel mixture is introduced into the combustion chamber separately from the intake air from the intake port. It becomes possible to create a stratified state in which the air-fuel mixture is unevenly distributed, and in the low load region, etc., lean burn due to stratified combustion can reduce fuel consumption.

[0003]

In the conventional device of this type, when the stratified charge combustion is performed in the operating region where the fuel consumption is reduced, the air supplied from the intake port to the combustion chamber and the port for supplying the air-fuel mixture are supplied. The fuel supply amount is only controlled to the lean set state with respect to the total intake air amount including the pressurized air given to the. In other words, the ratio of the total intake air amount to the fuel (the air-fuel ratio of the entire combustion chamber) is checked, and this is controlled to a value set to the lean side to some extent. Therefore, the air-fuel ratio in the unevenly distributed portion of the air-fuel mixture is not directly controlled. For this reason, even if the entire combustion chamber is in a lean set state, the air-fuel mixture may become locally richer than necessary, which may lead to deterioration of emissions due to an increase in unburned components and stratification. There is a possibility that the effect of reducing fuel consumption due to may not be sufficiently obtained.

In view of the above circumstances, the present invention properly manages the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber from a port different from the intake port, and controls the air-fuel ratio of the air-fuel mixture unevenly distributed portion even in the stratified combustion state. An object of the present invention is to provide an engine fuel supply method and apparatus that can be effectively controlled and can improve fuel efficiency and emission.

[0005]

In order to achieve the above object, a fuel supply method for an engine according to a first aspect of the present invention is a fuel and air separate from intake air introduced into a combustion chamber from an intake port. Is supplied to the combustion chamber at the beginning of the intake stroke or compression stroke via a timing valve, and the mixture is mixed in the sub-chamber for forming the air-fuel mixture. While introducing intake air, introduces the air-fuel mixture formed in the sub-chamber into the vicinity of the cylinder center of the combustion chamber, and examines the sub-chamber air-fuel ratio, which is the air-fuel ratio of the air-fuel mixture formed in the sub-chamber. The air-fuel ratio of the sub chamber air-fuel mixture is controlled to a target value.

In this method, in the operating region where the air-fuel ratio of the combustion chamber as a whole is set leaner than the stoichiometric air-fuel ratio, the sub-chamber mixture air-fuel ratio may be controlled to a substantially stoichiometric air-fuel ratio. ). Further, in the operating region where the air-fuel ratio of the entire combustion chamber is set to the stoichiometric air-fuel ratio, the air-fuel mixture is introduced into the combustion chamber from the sub-chamber while controlling the sub-chamber air-fuel ratio to be richer than the stoichiometric air-fuel ratio. At the same time, only air needs to be introduced from the intake port into the combustion chamber (claim 3).

Further, in an operating region in which the air-fuel ratio of the entire combustion chamber is set leaner than the stoichiometric air-fuel ratio, the air-fuel mixture is introduced into the combustion chamber within the period from the latter half of the intake stroke to the early stage of the compression stroke, and the combustion chamber as a whole. It is preferable that the air-fuel mixture is introduced into the combustion chamber in the first half of the intake stroke in the operating region in which the air-fuel ratio is set to the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio.

According to a fifth aspect of the present invention, an engine fuel supply system is provided with a sub-chamber for forming an air-fuel mixture which communicates with an air-fuel mixture supply port opened near the center of a cylinder of a combustion chamber, separately from the intake port. The mixture supply port is provided with a timing valve that opens at the beginning of an intake stroke or a compression stroke, and a pressurized air passage having a pressurized air supply means and a fuel injection valve are provided to the sub chamber to provide the pressurized air. The air passage is arranged so as to guide the pressurized air in a direction in which a swirl is generated in the sub chamber, and the fuel injection valve is arranged so as to inject fuel in a direction reverse to the swirl in the sub chamber.

In this device, the valve timing varying means for varying the opening / closing timing of the timing valve, and the operating range in which the air-fuel ratio of the entire combustion chamber is set leaner than the stoichiometric air-fuel ratio, the compression stroke from the latter half of the intake stroke. The air-fuel mixture is introduced into the combustion chamber within the initial period, and in the operating region where the air-fuel ratio of the entire combustion chamber is set to the stoichiometric air-fuel ratio or richer than this, the air-fuel mixture is introduced into the combustion chamber in the first half of the intake stroke. It is preferable to provide means for controlling the valve timing varying means.

Further, there are provided first flow rate detecting means for detecting the flow rate of the intake air introduced into the combustion chamber from the intake port, and second flow rate detecting means for detecting the flow rate of the pressurized air introduced into the sub chamber. Along with the flow rate detecting means and the detection signal from the air-fuel ratio detecting means provided in the exhaust passage, a means for obtaining a sub-chamber mixture air-fuel ratio which is the air-fuel ratio of the air-fuel mixture formed in the sub-chamber. Is preferably provided.

[0011]

According to the method of claim 1, stratified charge combustion is performed in a low load region or the like by supplying the air-fuel mixture that is sufficiently mixed in the sub-chamber to the vicinity of the center of the cylinder in the combustion chamber, and the cylinder is used. The air-fuel ratio of the air-fuel mixture supplied near the center is properly managed.

Particularly, in an operating region where the air-fuel ratio of the entire combustion chamber is set to be leaner than the stoichiometric air-fuel ratio, the sub-chamber mixture air-fuel ratio is controlled to a substantially stoichiometric air-fuel ratio so that the entire combustion chamber becomes lean. However, stratified charge combustion is performed in the vicinity of the center of the cylinder in a state where an air-fuel mixture having an air-fuel ratio suitable for combustion is applied. Further, in the operating region where the air-fuel ratio of the entire combustion chamber is set to the stoichiometric air-fuel ratio, a mixture richer than the stoichiometric air-fuel ratio is given from the sub-chamber, and the air-fuel ratio is increased by this and the air from the intake port. Adjusted.

In addition, in the lean operating region, the mixture is introduced into the combustion chamber from the latter half of the intake stroke to the beginning of the compression stroke, so that the diffusion of the mixture is suppressed and the air-fuel ratio of the entire combustion chamber becomes theoretical. In the operating region where the fuel ratio or richer than this is set, the air-fuel mixture is introduced into the combustion chamber in the first half of the intake stroke so that the air-fuel mixture is diffused throughout the combustion chamber.

According to the fifth aspect of the present invention, mixing of the pressurized air and the injected fuel in the sub chamber is promoted, and the above method is suitably implemented.

[0015]

Embodiments of the present invention will be described with reference to the drawings.
1 and 2 show an engine equipped with a fuel supply device according to an embodiment of the present invention. In these figures,
The engine is a cylinder block 1 and a cylinder head 2.
Etc., has an appropriate number of cylinders, and a combustion chamber 4 is formed above the piston 3 in each cylinder. The ceiling surface of the combustion chamber 4 in the cylinder head 2 has a substantially pent roof shape. In the combustion chamber 4, two primary and secondary intake ports 6 and 7, two exhaust ports 8 and 9, and a mixture supply port 15 are opened.

The intake ports 6 and 7 are adjacent to each other and are formed from one side surface of the cylinder head 2 to the combustion chamber 4 and have openings 6a and 7a at their downstream ends.
Is arranged in the intake side half of the ceiling surface of the combustion chamber 4. On the other hand, the exhaust ports 8 and 9 are adjacent to each other and are formed from the other side surface of the cylinder head 2 to the combustion chamber 4, and the openings 8a and 9a of the respective exhaust ports 8 and 9a are formed in the intake port opening 6.
It is disposed in the exhaust-side half of the ceiling surface of the combustion chamber 4 so as to face a and 7a. The mixture supply port 15 is opened near the center of the cylinder of the combustion chamber 4, and the spark plug 10 is arranged near the opening of the mixture supply port 15 in the combustion chamber 4.

An intake valve 11 is provided at each of the intake port openings 6a and 7a, and each of the exhaust port openings 8 is provided.
An exhaust valve 12 is provided on each of a and 9a. Also,
An opening / closing valve 13 is provided in the middle of the secondary intake port 7, and the opening / closing valve 13 is opened / closed by an actuator (not shown) according to the operating state, and is closed in a low intake air amount region and has a high intake air amount. The area is designed to open. Then, at least in the low intake air amount region where the on-off valve 13 is closed, intake air is introduced from the primary intake port 6 to the outer peripheral side of the cylinder to generate swirl in the combustion chamber 4.

The mixture gas supply port 15 is provided with a timing valve 16. This timing valve 1
The valve 6 is operated by a valve operating mechanism such as a cam 17 to open the valve in the early stage of the intake stroke or the compression stroke. In particular, in this embodiment, the variable valve timing mechanism 1
8, the valve opening timing of the timing valve 16 can be changed according to the operating state. Although the specific structure of the valve timing varying mechanism 18 is not limited, for example, like the valve timing varying mechanism known in the valve operating mechanism of intake / exhaust valves, it is a mechanism for changing the phase of the camshaft with respect to the crankshaft. Just configure it.

A sub-chamber 20 for forming a mixture is connected to the mixture supply port 15. The sub chamber 20 mixes fuel and air separately from the air introduced into the combustion chamber 4 through the intake ports 6 and 7 to form a mixture gas which is sent into the combustion chamber 4 through the mixture gas supply port 15. It is formed in the cylinder head 2 above the combustion chamber 4.
A pressurized air passage 21 and a fuel injection valve 22 are provided in the sub chamber 20. The pressurized air passage 21 guides pressurized air to the sub chamber 20, and the downstream end thereof is the sub chamber 20.
Open in a certain direction on the outer peripheral side of the sub chamber 2 with pressurized air
It is arranged to generate a swirl in 0. On the other hand, the fuel injection valve 22 has its injection port at the fuel port 2
It is arranged so as to communicate with the sub chamber 20 via 3 and to inject fuel in a direction reverse to the swirl in the sub chamber 20.

Reference numeral 25 denotes an intake passage, which is a common intake passage 26, a surge tank 27 downstream thereof, and a cylinder-specific intake passage 2 between the surge tank 27 and the intake ports 6 and 7.
8, an air cleaner 29 is provided on the upstream end side of the common intake passage 26, and a first air flow meter (first flow rate detecting means) 30 and a throttle valve 31 are provided in the middle of the common intake passage 26. There is. The common intake passage 2 is provided on the upstream side of the first air flow meter 30.
The pressurized air passage 21 is branched from 6. An air pump 32 as a pressurized air supply unit and a pressure adjusting valve 33 are provided in the pressurized air passage 21, and a second air flow meter (second flow rate detecting unit) is provided downstream of the pressure adjusting valve 33. 34 are provided. And the intake passage 2
Flow rate of the air introduced into the combustion chamber 4 from the intake ports 6 and 7 via the throttle valve 31 of No. 5 and the pressurized air passage 2
The flow rate of the pressurized air guided from 1 to the sub chamber 20 is separately detected by the first and second air flow meters 30 and 34.

Detection signals from both of the air flow meters 30 and 34 are input to a control unit (ECU) 40. Further, by detecting the engine speed sensor 35 for detecting the engine speed, the accelerator operation amount sensor 36 for detecting the accelerator operation amount, the engine torque sensor 37 for detecting the engine torque, and the O ₂ concentration in the exhaust gas. Linear O ₂ that detects the air-fuel ratio in the combustion chamber 4
Each detection signal from the sensor (air-fuel ratio detection means) 38 is also
It is input to the ECU 40. The ECU 40 controls the fuel injection valve 22, the pressure adjusting valve 35, and the valve timing changing means 18.

FIG. 3 shows a functional configuration of a control system by the ECU 40. In this figure, the ECU 40
Is for the fuel injection valve 22, a discriminating means 42 for discriminating the operating region based on the air-fuel ratio set map 41, and the auxiliary chamber 20.
The calculation unit 43 calculates the sub-chamber air-fuel ratio, which is the air-fuel ratio of the air-fuel mixture formed in 1., and the control unit 44 that controls the fuel injection amount. Air-fuel ratio set map 41
4, the correspondence between the air-fuel ratio of the entire combustion chamber and the operating state (engine speed and engine output) is predetermined, and the air-fuel ratio is set to the theoretical air-fuel ratio (λ =
1) A lean set region that is leaner, a region that is λ = 1, and a region that is richer than λ = 1 are defined, and operation in a predetermined range on the low rotation speed and low load side that requires fuel economy. The area (hatched area) is the lean set area. Then, the determination unit 42 causes the sensor 3
The operating states detected by the sensors 5, 36, 37, etc. are collated with the air-fuel ratio set map 41 to determine the operating region, and the arithmetic means 43 causes both air flow meters 30, 34 to be operated.
And the auxiliary chamber mixture air-fuel ratio is calculated based on the signals from the linear O ₂ sensor 38, and based on these determinations and calculations, the control unit 44 sets the auxiliary chamber mixture air-fuel ratio to the target value. The injection amount is controlled.

Further, the ECU 40 discriminates the pressure regulating valve 33 from the operating area based on the pressurizing set map 45, and the pressure regulating valve 33 based on this discrimination.
And a control means 47 for controlling. As shown in FIG. 5, the pressurizing set map 45 has a predetermined correspondence between the pressure of the pressurizing air and the operating state, and is set so that the pressure increases as the rotation speed increases and the load increases. There is. Further, the ECU 40 has a control means 48 for controlling the valve timing varying means 18 corresponding to the control of the air-fuel ratio. As will be described in detail later, the control means 48 controls the opening timing of the timing valve 16 depending on whether the air-fuel ratio of the entire combustion chamber is set to lean or λ = 1 or richer. Is changed to the timing shown in FIG. 6 (a) and the timing shown in FIG. 6 (b). 6A and 6B show the opening timing of the timing valve 16 and the fuel injection valve 22.
The fuel injection timing from 1 to 3 is shown together with the valve timings of the intake valve 11 and the exhaust valve 12.

The fuel supply method implemented by the above-mentioned device will be specifically described below. As for the control of the fuel injection valve 22 by the ECU 40, the discriminating means 42 checks which region in the air-fuel ratio set map the operating state is in. On the other hand, the linear O corresponding to the air-fuel ratio of the entire combustion chamber is calculated by the calculating means 43.
₂ The output of the sensor 38 is read, and the amount of air sent into the combustion chamber 4 through the respective paths is detected from the outputs of the air flow meters 30 and 34, and the ratio of the air passing through the sub chamber 34 is detected. Is checked, and the sub-chamber air-fuel mixture air-fuel ratio is calculated based on these values.

When the operating condition is in the lean set region, the control means 44 controls the sub chamber mixture air-fuel ratio to be approximately λ = 1, that is, the sub chamber mixture air fuel ratio. The target value is set to λ = 1, and the fuel injection amount is controlled so that the value calculated by the calculation means 43 becomes the target value. In this case, the valve opening timing of the timing valve 16 is adjusted as shown in FIG. 6 (a), that is, it is delayed within a range in which the mixture can be fed into the combustion chamber 4, and the latter half of the intake stroke is started. Within the initial period of the compression stroke, this prevents the mixture from diffusing in the combustion chamber 4 during the intake stroke.

In this way, the air-fuel mixture which is mixed in the sub chamber 20 and has the most favorable air-fuel ratio for combustion is fed from the fuel supply port 15 around the spark plug 10 of the combustion chamber 4, and the combustion chamber as a whole is very much improved. In a lean state, good stratified combustion is carried out without causing deterioration of emission. Particularly, in the sub-chamber 20, the swirl by the pressurized air and the fuel injected in the direction opposite thereto are sufficiently mixed, and in the sub-chamber 20, a mixture of approximately λ = 1 is uniformly formed and burned. By being fed into the chamber 4, a local overrich is certainly prevented from occurring. Further, the swirl caused by the intake air introduced into the combustion chamber 4 from the intake port enhances the turbulence of the air flow in the combustion chamber 4, thereby promoting the combustion. Note that FIG. 6 (a)
As shown therein, if the fuel injection from the fuel injection valve 22 is performed separately for the second floor before the opening of the timing valve 16 and during the opening of the timing valve 16, the fuel vaporization and fog in the sub chamber 20 will occur. Is further promoted.

The operating state is λ = 1 in the map of FIG.
In the region, the air-fuel ratio of the sub chamber air-fuel mixture is controlled to be richer than λ = 1, and the air-fuel mixture becomes the fuel supply port 1
5 is supplied into the combustion chamber 4 while the intake ports 6, 7
From the above, only the air is supplied into the combustion chamber, and the air and the air-fuel mixture are mixed in the combustion chamber 4, so that the air-fuel ratio of the entire combustion chamber is set to λ = 1. In this case, the opening timing of the timing valve 16 is shown in FIG.
That is, it is adjusted as shown in FIG. 5, that is, it is opened earlier than the valve opening timing in the lean set region and opened in the first half of the intake stroke, so that the air-fuel mixture sent into the combustion chamber 4 via the timing valve 16 is intaken. It diffuses during the stroke and mixes well with the air from the intake ports 6 and 7, and the combustion chamber 4
Good combustion is carried out with the air-fuel mixture uniformly dispersed throughout. Further, even in a region where the air-fuel ratio of the entire combustion chamber is richer than λ = 1, the valve opening timing of the timing valve 16 is advanced and uniform combustion is performed.

The operation of the timing valve 16
The means for adjusting the valve opening timing is not limited to the above embodiment,
For example, the opening timing and opening period of the timing valve are made variable, and in the lean set region, the valve is opened in the latter half of the intake stroke or the first half of the compression stroke, while the air-fuel ratio of the entire combustion chamber is set to λ = 1 or richer. In the region where the intake valve is opened, the timing valve may be opened for substantially the same period as the intake valve opening period. Besides, the specific structure of each part of the fuel supply device, the specific control method according to the operating state, and the like may be changed without departing from the scope of the present invention.

[0029]

According to the fuel supply method of the first aspect of the present invention, the intake air is introduced from the intake port to the cylinder outer peripheral side of the combustion chamber, and the air-fuel mixture formed by mixing the fuel and the air in the sub chamber is formed. Introduced near the center of the cylinder in the combustion chamber,
Moreover, since the air-fuel ratio of the sub-chamber mixture is checked and controlled to the target value, stratified charge combustion is possible by supplying the air-fuel mixture from the sub-chamber, and in the stratified state, the air-fuel mixture unevenly distributed near the center of the cylinder The air-fuel ratio can be managed properly.

In the above method, particularly in the operating region where the air-fuel ratio of the entire combustion chamber is set to be leaner than the stoichiometric air-fuel ratio, the sub-chamber mixture air-fuel ratio is set to a substantially stoichiometric air-fuel ratio. By controlling to 1, it is possible to improve leanness by stratified combustion, improve combustibility, prevent a local rich state from occurring, reduce unburned components, and improve fuel efficiency and emission.

Further, as described in claim 3, in the operating region where the air-fuel ratio of the entire combustion chamber is set to the stoichiometric air-fuel ratio, the sub-chamber mixture air-fuel ratio is controlled to be richer than the stoichiometric air-fuel ratio. Meanwhile, if the air-fuel ratio in the combustion chamber is adjusted by the air-fuel mixture from the sub chamber and the air from the intake port, the air-fuel mixture from the sub chamber can be satisfactorily combusted even in this region.

Further, as described in claim 4, the mixture supply timing from the sub chamber to the combustion chamber is set within the period from the latter half of the intake stroke to the initial stage of the compression stroke in the lean operating region.
In the operating region where the air-fuel ratio of the entire combustion chamber is set to the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio, the first half of the intake stroke is set, so that stratified charge combustion is effectively performed in the lean operating region and in other operating regions. It is possible to effectively carry out uniform combustion.

According to the fuel supply device of the fifth aspect,
The combustion chamber is provided with a sub-chamber for forming a mixture that communicates with a mixture supply port opened near the center of the cylinder, the mixture supply port is provided with a timing valve, and a pressurized air passage and fuel are provided for the sub-chamber. An injection valve is provided, the pressurized air passage causes a swirl in the sub-chamber, and the fuel injection valve is arranged so as to inject fuel in a direction opposite to the swirl. It can be preferably carried out, and mixing of fuel and pressurized air in the sub chamber can be promoted.

In this apparatus, as described in claim 6, when the timing valve is provided with a valve timing varying means and a control means for controlling the valve timing varying means, a mixture supply timing according to the method of claim 4 is provided. Can be adjusted by the valve timing varying means and the control means.

Further, as described in claim 7, first and second flow rate detecting means are provided so as to individually detect the flow rate of the intake air from the intake port and the flow rate of the pressurized air introduced into the sub chamber,
The sub-chamber mixture air-fuel ratio can be effectively controlled by obtaining the sub-chamber mixture air-fuel ratio on the basis of detection signals from these and the air-fuel ratio detecting means provided in the exhaust passage.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an engine including a fuel supply device according to an embodiment of the present invention.

FIG. 2 is an explanatory view showing the fuel supply device in plan view.

FIG. 3 is a functional block diagram of a control system.

FIG. 4 is an explanatory diagram showing an air-fuel ratio set map.

FIG. 5 is an explanatory diagram showing a pressure set map.

6A and 6B are explanatory views showing opening timing of a timing valve and fuel injection timing from a fuel injection valve, FIG. 6A shows a case where the air-fuel ratio of the entire combustion chamber is set to lean, and FIG. The case where the air-fuel ratio of the entire combustion chamber is set to λ = 1 is shown.

[Explanation of symbols]

 4 Combustion chamber 6,7 Intake port 15 Fuel supply port 16 Timing valve 20 Subchamber 21 Pressurized air passage 22 Fuel injection valve 25 Intake passage 30 First air flow meter 32 Air pump 34 Second air flow meter 40 ECU

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuguo Hatahira 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Motor Corporation

Claims (7)

[Claims] 1. In addition to intake air introduced into a combustion chamber from an intake port, fuel and air are mixed in a sub-chamber for forming an air-fuel mixture, and the air-fuel mixture is intake stroke or compression stroke through a timing valve. A method of initially supplying into the combustion chamber, introducing intake air from the intake port to the cylinder outer peripheral side of the combustion chamber, and introducing the air-fuel mixture formed in the sub chamber near the cylinder center of the combustion chamber, and A fuel supply method for an engine, comprising: examining a sub-chamber air-fuel ratio, which is an air-fuel ratio of an air-fuel mixture formed in the sub-chamber, and controlling the sub-chamber air-fuel ratio to a target value. 2. The fuel for an engine according to claim 1, wherein in the operating region where the air-fuel ratio of the combustion chamber as a whole is set leaner than the stoichiometric air-fuel ratio, the sub-chamber mixture air-fuel ratio is controlled to a substantially stoichiometric air-fuel ratio. Supply method. 3. In an operating region in which the air-fuel ratio of the entire combustion chamber is set to the stoichiometric air-fuel ratio, the air-fuel mixture from the sub-chamber to the combustion chamber is controlled while controlling the air-fuel ratio of the sub-chamber to be richer than the stoichiometric air-fuel ratio. 3. The fuel supply method for an engine according to claim 2, wherein the air is introduced into the combustion chamber from the intake port. 4. In an operating region in which the air-fuel ratio of the combustion chamber as a whole is set leaner than the stoichiometric air-fuel ratio, the air-fuel mixture is introduced into the combustion chamber within the period from the latter half of the intake stroke to the early stage of the compression stroke so that the combustion chamber as a whole. The fuel supply method for an engine according to claim 3, wherein the air-fuel mixture is introduced into the combustion chamber in the first half of the intake stroke in an operating region where the air-fuel ratio is set to the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio. 5. A sub-chamber for forming an air-fuel mixture, which is connected to an air-fuel mixture supply port opened near the center of a cylinder of a combustion chamber, is provided separately from the intake port, and the air-fuel mixture supply port is provided with an auxiliary chamber at the beginning of an intake stroke or a compression stroke. A timing valve for opening is provided, and a pressurized air passage having a pressurized air supply means and a fuel injection valve are provided in the sub chamber, and the pressurized air passage pressurizes in a direction that causes swirl in the sub chamber. A fuel supply device for an engine, wherein the fuel injection valve is arranged so as to guide air, and the fuel injection valve is arranged so as to inject fuel in a direction reverse to a swirl in the sub chamber. 6. A valve timing varying means for varying the opening / closing timing of the timing valve, and an operating range in which the air-fuel ratio of the entire combustion chamber is set leaner than the stoichiometric air-fuel ratio, from the latter half of the intake stroke to the initial stage of the compression stroke. The air-fuel mixture is introduced into the combustion chamber within the period, and in the operating region where the air-fuel ratio of the entire combustion chamber is set to the stoichiometric air-fuel ratio or richer than this, the air-fuel mixture is introduced into the combustion chamber in the first half of the intake stroke. The fuel supply system for an engine according to claim 5, further comprising means for controlling the valve timing varying means. 7. A first flow rate detecting means for detecting a flow rate of intake air introduced into the combustion chamber from the intake port, and a second flow rate detecting means for detecting a flow rate of pressurized air introduced into the sub chamber. Along with the flow rate detecting means and the detection signal from the air-fuel ratio detecting means provided in the exhaust passage, a means for obtaining a sub-chamber mixture air-fuel ratio which is the air-fuel ratio of the air-fuel mixture formed in the sub-chamber. The fuel supply device for the engine according to claim 5, further comprising: