JP3030226B2 - Car lean burn engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lean burn engine for an automobile which reduces fuel consumption by performing a lean burn in a specific operation region.

[0002]

2. Description of the Related Art In recent years, various lean burn engines have been developed which perform lean burn (lean combustion) by setting the air-fuel ratio to lean in an operating range such as low speed and low load of the engine. When the air-fuel ratio is made leaner, the pumping loss (particularly, the loss due to negative pressure resistance in the intake stroke) is reduced by increasing the amount of air with respect to the fuel, and the combustion gas temperature is reduced, resulting in heat loss (around the combustion chamber). Heat energy deprived of the cooling system) and exhaust gas loss are reduced, and by reducing these pumping loss and heat loss, thermal efficiency is increased and fuel consumption is reduced.

In making such an air-fuel ratio lean,
Improvement of air-fuel ratio control accuracy, promotion of leanness by improvement of flammability, improvement of emission, and the like have been conventionally considered.

For example, Japanese Patent Application Laid-Open No. Sho 59-208141 uses a lean sensor that generates an output signal that is substantially proportional to the oxygen concentration in exhaust gas, and uses the lean sensor with an air-fuel ratio leaner than the stoichiometric air-fuel ratio. A lean control method that improves the control accuracy by performing feedback control of the air-fuel ratio according to the output and setting and correcting the control target value of the output of the lean sensor according to the target air-fuel ratio has been proposed. It is shown.

[0005] The development of a new generation lean-burn engine in 92048 of "Academic Lecture Preprints 924 Volume 2" issued by the Society of Automotive Engineers of Japan includes a method of improving the lean limit of the air-fuel ratio by strengthening the swirl. Describes a lean burn engine in which the air-fuel ratio is set to a lean value so that the amount of NOx emitted from the combustion chamber becomes sufficiently low within a range not to reach.

[0006]

In this type of lean burn engine, there is a point to be improved in reducing NOx.

More specifically, as described in the above-mentioned preprint of the academic lecture, the NOx ratio in the exhaust gas from the engine is highest when the air-fuel ratio is around 16, and is lower on the lean side. Although NOx tends to decrease gradually as the vehicle leans, conventionally, in order to sufficiently reduce NOx, the air-fuel ratio must be made extremely large and lean.
Therefore, it is necessary to increase the lean limit, and there is a problem in that the torque obtained in such a high lean state has a limit, and the operating range in which lean burn is possible is limited. Therefore, it is required not only to make the air-fuel ratio lean as described above, but also to reduce the amount of NOx generated in the lean burn operation region further by other methods.

Conventionally, for example, Japanese Patent Application Laid-Open No.
As shown in Japanese Patent Application Publication No. 1 (1993) -1997, an injector for injecting fuel is provided for each cylinder, and an air assist mechanism for supplying mixing air to the injector is provided. There is known a technique in which a mechanism is operated to promote atomization of fuel to improve combustibility. However, the means for promoting the combustion by the air assist mechanism is such that the combustion is promoted and the H
Since it is used to reduce C and CO, and it is generally considered that NOx increases when combustion is promoted, it has never been considered to use an air assist mechanism to reduce NOx. Had not been.

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to reduce the amount of NOx generated in a lean burn engine for an automobile while improving the combustibility in a lean burn state. In particular, as will be described in detail later, it was found that NOx was reduced in spite of improvement in combustibility by promoting atomization of fuel using an air assist mechanism in a state where the air-fuel ratio was set to lean. It is intended to provide a lean burn engine capable of effectively reducing NOx in a lean operation region based on the above.

According to the present invention, an injector for injecting fuel is provided for each cylinder in a lean burn engine for an automobile having a lean operation region in which combustion is performed at a leaner air-fuel ratio than the stoichiometric air-fuel ratio. An air assist mechanism for supplying air for atomizing the injected fuel to the cylinders, control means for performing fuel injection from each of the injectors in the intake stroke of each cylinder , and each cylinder
One of the two intake ports provided for each
An on-off valve disposed in the combustion chamber, air is supplied to each of the injectors at least in the lean operation region by an air assist mechanism, and an oblique swirl is introduced into the combustion chamber.
Closing the on-off valve so as to generate
In the lean operation region, the air-fuel ratio of the entire air-fuel mixture in the combustion chamber is set to an air-fuel ratio near the lean combustion limit, and the air supply and the generation of the diagonal swirl near the ignition plug are performed. The fuel injection timing from each of the injectors is set such that a stratified state in which the local air-fuel ratio is about 10% richer than the air-fuel ratio of the entire air-fuel mixture is obtained.

[0011]

[0012]

[0013]

According to the engine of the present invention, when the engine is in the lean operation region, air is supplied to each injector by the air assist mechanism to atomize the fuel. When the fuel is atomized in the lean burn state in this manner, the combustibility is enhanced, and moreover, since the lean burn is performed uniformly, the portion having a high combustion temperature is reduced, and the NOx generation amount is reduced.

Further, by performing stratification in the lean operation region, the lean burn limit is increased, and the NOx reduction effect is enhanced by the increase in leanness and the effect of promoting atomization by air assist. In particular, when the on-off valve is closed and oblique swirl is generated in the combustion chamber and the air is supplied by the air assist mechanism, the local air-fuel ratio near the ignition plug increases the overall air-fuel ratio. By obtaining a stratified state that is about 10% rich with respect to the air-fuel ratio, NOx can be improved by improving the lean burn limit by appropriate stratification and promoting the atomization by air assist.
The reduction effect is sufficiently enhanced.

[0015]

An embodiment of the present invention will be described with reference to the drawings.
First, an outline of a lean burn engine according to an embodiment of the present invention will be described with reference to FIG. In this figure, reference numeral 1 denotes an engine body, and a combustion chamber 2 is formed in each cylinder, and the combustion chamber 2 has first and second combustion chambers, which will be described in detail later.
Intake ports 3 and 4 and first and second exhaust ports 5 and 6
The ports 3 to 6 are provided with intake valves 7, 8 and exhaust valves 9, 10, respectively.

The intake system 20 of the engine includes an intake manifold 21 and a common intake passage 30 upstream of the intake manifold 21. An air cleaner 31, a thermal air flow sensor 32, and a throttle valve 33
Are arranged. Further, an intake bypass passage 34 that bypasses the throttle valve 33 is formed. The intake bypass passage 34 includes an ISC passage 35 for adjusting the amount of intake air when idling and the like and an air passage 36 for increasing the amount of intake air when cold. The above ISC
The passage 35 is provided with an ISC valve 37 that controls the air flow rate of the ISC passage 35 under duty control, and the air passage 36 is provided with a temperature-sensitive valve 38 that opens when cold.

An injector 4 for injecting fuel for each cylinder is provided near an intake port on the downstream side of the intake system 20.
0 is provided, and an on-off valve 41 for opening and closing the second intake port 4 is provided. The opening / closing valve 41 is operated by a negative pressure responsive actuator 42, and a driving system corresponding thereto is provided with a vacuum tank 43 for storing a negative pressure introduced from a surge tank of the intake manifold 21, and between the tank 43 and the actuator 42. Solenoid valve 4 arranged to supply and discharge negative pressure to and from the actuator 42
4 and the like are provided.

The injector 40 is a so-called AMI (air mixture type injector) in which fuel is atomized by supplying mixing air near the injection port. A fuel supply system including a fuel supply passage 48 for supplying fuel from a fuel tank 45 via a fuel pump 46 and a filter 47, a return passage 50 provided with a pressure regulator 49, and the like is provided for the injector 40. A mixing air supply system (air assist means) and an evaporative fuel supply system, which will be described in detail later, are provided.

On the other hand, an oxygen concentration sensor 6 for detecting the oxygen concentration in the exhaust gas corresponding to the air-fuel ratio of the air-fuel mixture is provided in the exhaust system.
0 and a catalyst device 61 are provided. The oxygen concentration sensor 60 is configured to obtain an output substantially proportional to the oxygen concentration in the exhaust gas so that the lean air-fuel ratio can be detected. Further, the catalyst device 61 has a function of reducing NOx even at an air-fuel ratio leaner than the stoichiometric air-fuel ratio. Specifically, the catalyst device 61 is disclosed in Japanese Patent Application No. 5-126552 previously filed by the present applicant. The catalyst device described is used. That is, the catalyst in the catalyst device 61 is one in which a noble metal is supported as an active species on an active species supporting base material. Preferably, zeolite is used as an active species-supporting matrix, and Ir and Pt are supported as active species, or Ir, Pt, and Rt are supported as active species.

As various detection elements for air-fuel ratio control and the like, in addition to the air flow sensor 32 and the oxygen concentration sensor 60, a throttle opening sensor 62 for detecting an opening of a throttle valve, and a throttle fully closed state are detected. An idle switch 63, an intake air temperature sensor 64 for detecting an intake air temperature, a water temperature sensor 65 for detecting an engine water temperature, a knock sensor 66 for detecting an engine knock, and the like. And a cylinder discrimination sensor 69 that outputs a cylinder discrimination signal.

The signals from these detection elements are input to a control unit (ECU) 70 for controlling the engine. The control unit 70 controls the fuel injection amount and the injection timing from the injector 40, and further controls the ISC valve 37, the solenoid valve 44 in the drive system of the on-off valve 41, and the mixing air supply system for the injector 40. The control unit 70 also controls an air control valve 51 provided, a purge solenoid valve 58 provided in the evaporative fuel supply system, and the like.

Next, the specific structure of each part of the lean burn engine will be described.

2 to 4 show a specific structure of the engine body. As shown in these figures, the engine body 1
In each of the cylinders described above, basically, when the first and second intake valves 7 and 8 are opened, the air-fuel mixture is sucked into the combustion chamber 2 from the first and second intake ports 3 and 4. After the air-fuel mixture is compressed by the piston 11, it is ignited by the spark plug 12,
The fuel is burned, and the combustion gas is discharged from the first and second exhaust ports 5 and 6 when the first and second exhaust valves 9 and 10 are opened. An injector 40 is provided in the first intake port (hereinafter, referred to as P port) 3, while opening and closing control is performed in the second intake port (hereinafter, referred to as S port) 4 or a passage upstream thereof in accordance with an operation state. An opening / closing valve 41 is provided.

In this embodiment, when the open / close valve (hereinafter, referred to as a TSC valve) 41 as a tumble swirl control valve is closed, a tumble (vertical vortex) and a swirl (lateral vortex) are combined. The port arrangement, the port shape, and the like are set so that an oblique spiral swirl is generated in the combustion chamber 2.

More specifically, the P port 3 and the S port 4 are composed of straight portions 3a and 4a which extend substantially linearly in the upstream portion in the flow direction of the intake air.
In the vicinity of the downstream ends of the valves a and 4a, there are formed curved portions 3b and 4b which curve downward and reach the respective valve seats 13 and 14 (see FIGS. 3 and 4). And, each straight portion 3 in the P port 3 and the S port 4
The extension of the port center lines Lp1 and Ls1 of the ports a and 4a corresponds to the valve end 7a located on the center side of the combustion chamber 2 when the valve seats 13 and 14 and the first and second intake valves 7 and 8 are at maximum lift. ,
8a. This allows
The flow resistance of the intake air supplied from the P and S ports 3 and 4 to the combustion chamber 2 is reduced. The port center lines Lp1, Lp
The extension of s1 is the valve seats 13, 14 and the valve ends 7a, 8a.
It is best to set it so that it passes through the center.

The combustion chamber 2 is a pent roof lens type combustion chamber. The valve clamping angle θ between the intake valves 7 and 8 and the exhaust valves 9 and 10 is narrowed to about 30 °, and is a DOHC direct drive type. It is designed to be driven by a valve operating mechanism (not shown). The angle (throat offset angle α1) between the valve center line L1 of the first intake valve 7 and the throat center line Lp1 of the P port 3 is relatively large, and the second
Angle formed between the valve center line L2 of the intake valve 8 and the throat center line Ls1 of the S port 4 (throat offset angle α2)
Is set relatively small, for example, α1 = 30 °,
α2 = 12 °. In this manner, when the intake is performed only from the P port 3, the vortex S having an inclination angle (the angle formed with the cylinder center line) γ of 35 ° to 55 ° is generated. The S port 4 generates a tumble T in the combustion chamber 2.

The two intake valves 7, 8 are respectively
It comprises the valve stems 7b, 8b and the umbrellas 7c, 8c.
The lower surfaces of c and 8c are arranged so as to be parallel to the ceiling surface of the combustion chamber 2. The valve angle of the first intake valve 7 (the angle between the lower surface and the upper surface of the umbrella portion) β1 is the valve angle of the second intake valve 8
It is set larger than 2. Thereby, the flow path between the first intake valve 7 and the throat portion of the P port 3 at the time of valve lift becomes narrower than the flow path between the second intake valve 8 and the throat portion of the S port 4. , P port 3 side increases the intake air flow rate, and S port 4 side secures the flow rate.

Further, a port edge 15 is formed below the outlet of the P port 3, and a squish area 16 is formed around the first intake valve 7 in the combustion chamber 2. The flow rate of air to the valve is increased.

According to such a structure of the combustion chamber and the intake port, a strong vortex in which a tumble and a swirl are combined is obtained by the intake from the P port 3, and the like.
Even in the lean burn state where the burning speed tends to slow down,
The formation of a uniform mixture and the improvement of the combustion rate are compatible, and a good combustion state is obtained.

That is, as shown in FIG.
The turbulence intensity from the intake to the first half of the compression stroke is large,
Although the effect of the air-fuel mixture homogenization is great, the turbulence intensity in the latter half of the compression stroke is small.
Then, in the case of the above-described intake port structure, advantages of both swirl and tumble are obtained, and the average turbulence intensity from the intake stroke to the compression stroke is increased. FIG. 5 shows that the swirl ratio Sr is 3.3 and 4.2.
It shows the relationship between the swirl inclination angle (the angle between the swirl center line and the cylinder center line) γ and the average turbulence intensity R,
As shown in this figure, by setting the swirl ratio Sr to about 3 or more and setting the swirl inclination angle γ in the range of 35 ° to 55 °, particularly preferably 45 °, the average turbulence intensity is greatly increased. Thus, the mixture is made uniform and the combustion speed is improved.

Here, the definition and the method of obtaining the swirl ratio will be described. The swirl ratio is generally defined as a value obtained by dividing the number of revolutions of a lateral vortex of an air-fuel mixture (intake air) in a cylinder by the number of engine revolutions.

[0032] Then, the turning speed of the horizontal vortex of the mixture, for example in the engine bore diameter is D as shown in FIG. 7, the position F ₂ the downwardly from the cylinder head lower surface F ₁ by a distance of 1.75D An impulse swirl meter 80 is arranged, a torque acting on the impulse swirl meter 80 (impulse swirl meter torque) is detected, and a calculation is performed by a well-known method based on the impulse swirl meter torque. Incidentally, in FIG. 7, F ₃ shows the top surface of the piston 11 at the bottom dead center position.

The impulse swirl meter torque is measured in the following procedure. That is, placing the impulse swirl meter 80 to the position of the F _2, by reproducing the energy of the swirl acting impulse swirl meter 80 in the piston top surface, the degree of swirl energy in the vicinity of the piston top surface at the normal time Measure if present. The impulse swirl meter 80 has many honeycombs, and the impulse swirl meter 80
When a swirl acts on each of the honeycombs, a force in the swirl flow direction acts on each of the honeycombs, and an impulse swirl meter torque G acting on the whole is calculated by integrating the forces applied to the respective honeycombs.

More specifically, assuming that the air-fuel mixture is sucked into the combustion chamber 2 during a period from the opening of the intake valve to the bottom dead center, the air-fuel mixture is supplied to the inner peripheral surface of the combustion chamber 2 during this period. , And its turning speed becomes maximum at the bottom dead center position.
Therefore, the swirl ratio is obtained by integrating the angular momentum of each crank from the start of opening of the intake valve to the bottom dead center. Based on such knowledge, in this example, the swirl ratio Sr is calculated by the following equations (1) and (2).

[0035]

Sr = ηv · {DS · ∫ (cf · Nr · dα)} / { ^nd · ² · (∫cf · dα) ² } (1) Nr = 8 · G / (M · D · V ₀ ) (2) where Sr is the swirl ratio and ηv is the volumetric efficiency (ηv =
1), D is bore diameter, S is stroke, n is the number of intake valves, d
Is the throat diameter, cf is the flow coefficient for each valve lift,
Nr is a dimensionless rig swirl value for each valve lift,
α is the crank angle, G is the impulse swirl meter torque, M is the mass of air charged into the cylinder during the intake stroke, and V ₀ is the speed head.

The above equation (2) is derived by the following procedure.

[0037]

[Number 2] G = I · ωr ...... (3 ) I = M · D 2/8 ...... (4) (4) and (3) an assignment ^{G = M · D 2 · ωr} / 8 ...... (5 ) From (5) D · ωr = 8 · G / (MD) (6) By the way, Nr = D · ωr / V ₀ (7) Substituting (6) into (7) Nr = 8 · G / (M · D · V 0) However, I is air inertia moment of the cylinder in the intake stroke end (piston bottom dead center), the ωr are Rigusuwaru value.

FIG. 8 shows a mixing air supply system and an evaporative fuel supply system for the injector 40. In this figure, an injector 40 is provided for each of the P ports 3 of a plurality of cylinders (for example, four cylinders), and an AMI air supply passage 5 having an air control valve 51 is provided in a mixing air supply system for these injectors 40.
2 are provided. This AMI air supply passage 52
The upstream side is connected to the intake bypass passage 34 (see FIG. 1), and the downstream side is branched and connected to each injector 40.

Further, a bypass passage 5 for bypassing the air control valve 51 is provided in the AMI air supply passage 52.
The bypass passage 53 is provided with an orifice 54 through which a small amount of air flows when idling.

The evaporative fuel supply system includes a canister 56.
A purge passage 57 extending from (see FIG. 1) is provided, and a purge solenoid valve 58 is provided in the purge passage 57. The purge passage 57 is connected to the AMI air supply passage 5.
Mixing chamber 55 formed upstream of branch point 2
It is connected to the. Evaporated fuel generated in the fuel tank or the like and trapped in the canister 56 is supplied to the vicinity of the injection port of each injector 40 via the purge passage 57 when the purge solenoid valve 58 is opened, and is supplied with fuel spray during the intake stroke. It is supplied to the combustion chamber 2 of each cylinder. The purge solenoid valve 58 is driven when a predetermined purge execution condition is satisfied (for example, when air-fuel ratio feedback control is performed and the engine water temperature is equal to or higher than a predetermined temperature), and the engine is operated so that a predetermined purge amount is obtained. Is controlled according to the operating state of the vehicle.

FIG. 9 and FIG.
2 shows a specific structure of. In these figures, an injector mounting hole 400 communicating with the P port 3 is formed in the cylinder head 1a of the engine, and the injector 40 is fitted in the injector mounting hole 400. The distal end portion 401 of the injector 40 is formed in a cylindrical shape so as to surround the injection port.
An annular air introduction space 402 is formed between the cylinder head 1a and the peripheral wall of the injector mounting hole 400, and an air introduction port 403 for communicating the air introduction space 402 with an external air supply passage is formed in the cylinder head 1a. ing. Further, the tip side portion 401 of the injector 40
The space in front of the nozzle and the air introduction space 4
A communication hole 404 is provided radially, and an orifice 405 is formed in the communication hole 404.

Then, fuel is injected from the injection port of the injector 40 toward the P port 3 at a predetermined timing, and is introduced into the air introduction space 402 when an intake negative pressure acts on the space in front of the injection port. The air is blown into the space in front of the nozzle through the orifice 405, and the injected fuel is mixed by the air.

The control of the air-fuel ratio, the control of the fuel injection timing from the injector 40, and the control of the mixing air supply system by the control unit 70 shown in FIG. 1 are performed as follows.

In the control of the air-fuel ratio, the air-fuel ratio is set to be leaner than the stoichiometric air-fuel ratio in a predetermined operation range. For example, as shown in FIG. 11, the stoichiometric air-fuel ratio is in an operating range from a low load range to a predetermined load except a fully closed throttle range (idle range or fully closed deceleration range) in the low and medium speed ranges of the engine. It is set to be leaner (λ> 1) than the fuel ratio. In the illustrated example, a predetermined lean air-fuel ratio near the lean burn limit is set in most of the lean operation region. In this embodiment, swirl generation, stratification, and AM are performed.
The air-fuel ratio in this region is set to about 22 because the lean burn limit is increased to about 25 by the action of promoting combustion by atomizing the fuel in I. In the lean operation region other than this region, the air-fuel ratio is within a certain range (for example, 19
２２22) is changed according to the operating state. Further, the air-fuel ratio is set to the stoichiometric air-fuel ratio (λ = 1) or richer (λ <1) in the region on the higher load side and the higher speed side than the idling region or the lean operation region. Is done.

However, the control of the air-fuel ratio is not limited to this example. For example, a constant lean air-fuel ratio may be set in the entire lean operation range.

As the control of the fuel injection timing from the injector 40, a so-called sequential timed injection for injecting fuel at a predetermined timing for each cylinder is performed. The fuel is injected at a predetermined timing of the intake stroke so that the air-fuel mixture becomes slightly richer than other parts.
Desirably, the degree of stratification is adjusted so that the air-fuel mixture around the ignition plug does not become too rich and increase NOx, and more specifically, injection is performed within a period up to ATDC of 60 °. Has become.

In the control of the mixing air supply system, the air control valve 51 is opened to supply air to the injector 40 in an operation region including the lean operation region. For example, when the air control valve 51 is idling, Closed, open at other times.

The TSC valve 41 is also controlled according to the operating state. For example, as shown in FIG.
The open / close switching line of the C valve 41 is set so as to substantially coincide with the limit line on the high-speed side of the lean operation region. The TSC valve 41 is closed on the low-speed side and the TSC valve 41 is opened on the high-speed side. .

According to the lean burn engine of the present embodiment as described above, the air-fuel ratio is set to lean in a predetermined operating region of the engine, and the lean burn is performed.
Fuel efficiency in this operating region is improved. An AMI is used for the injector 40, and the injector 40
When the mixing air is supplied to the fuel, the fuel is atomized, whereby the air-fuel mixture is homogenized and the combustibility is improved.

In particular, mixing air is supplied to the injector 40 even in the lean operation region in which the lean burn is performed, whereby the effect of reducing the amount of NOx generated in the lean burn state can be obtained.
This will be described with reference to FIGS.

FIG. 12 shows the relationship between the air-fuel ratio and the amount of NOx emission examined by the inventor. The line A shows the NOx upstream of the catalyst when the mixing air is not supplied to the injector. Emissions (engine NOx
Similarly, the line B shows the NOx emission amount downstream of the catalyst in the case where the mixing air is not supplied and a conventional general three-way catalyst is used as the catalyst device, and the line C1 shows the same as in the present embodiment. In the case where the mixing air is supplied and the conventional general three-way catalyst is used as the catalyst device, the NOx emission amount downstream of the catalyst and the line C2 indicate the mixing air supply and the catalyst device as in this embodiment. Indicates a NOx emission amount downstream of the catalyst when a catalyst having NOx purification performance is used even with a lean air-fuel ratio. FIG. 12 also shows the relationship between the air-fuel ratio, the fuel efficiency, and the torque fluctuation in the case of the engine of the embodiment.

As shown in this figure, when the mixing air is supplied even when the air-fuel ratio is lean, the N.sub.N in the lean region is smaller than when the mixing air is not supplied.
Ox emissions are greatly reduced. The reason is that, in the lean burn state, the average combustion temperature in the combustion chamber is relatively low, and in such a situation, when the fuel is atomized by the mixing air, the local combustion temperature variation becomes small, and NOx It is considered that this is because the portion where the temperature is higher than the generation temperature is reduced.

Referring to FIG. 13, a first example shows a fuel distribution state in a combustion chamber when a normal injector is provided at an intake port to perform fuel injection. Shows the fuel distribution state in the combustion chamber when the fuel is injected while supplying the mixing air using the injector 40 of the present embodiment, that is, the AMI, and the third example shows the fuel distribution state when the fuel is supplied in a gasified state. The distribution state is schematically shown, and as shown in FIG.
When the fuel is used, the fuel is greatly atomized as compared with a normal injector by the action of the mixing air. And
When the air-fuel ratio is lean, if the fuel particle size is large, NOx is likely to be generated in a portion where the combustion temperature is high due to local combustion temperature variation, as in the case where the mixture distribution is uneven. On the other hand, as the fuel particle diameter becomes smaller, the portion where the combustion temperature is high is reduced by performing the lean burn evenly, and the NOx generation amount is reduced. Therefore, FIG.
As shown in FIG. 4, when the AMI is used, the NOx emission amount is smaller in the lean region than in the normal injector 40.

If the fuel can be gasified and supplied, the NOx emission will be further reduced. However, an injector is provided in the intake port for accurate air-fuel ratio control and stratification by sequential timed injection. In this case, it is practically difficult to gasify and supply the fuel. Therefore, atomizing the fuel injected from the injector 40 with the mixing air is an effective method for reducing NOx in the lean region while satisfactorily controlling the air-fuel ratio and the like.

In this embodiment, the fuel injection from the injector 40 is performed in the intake stroke, so that the air-fuel ratio near the ignition plug becomes slightly richer than the air-fuel ratio of the entire air-fuel mixture in the combustion chamber. Since stratification is performed, and thereby ignitability in a lean state is ensured, it is possible to make the air-fuel ratio lean enough.

In particular, in the lean operation region, the air-fuel ratio of the entire air-fuel mixture in the combustion chamber is set to a value near the lean burn limit, and the local air-fuel ratio near the spark plug is set to be lower than the air-fuel ratio of the entire air-fuel mixture. If the fuel injection timing from each of the above-mentioned injectors is set so as to obtain a stratified state that is about 10% rich, as shown in FIG.
The x reduction effect is enhanced.

That is, FIG. 15 shows that the injector has AM
While using I to supply the mixing air,
By changing the fuel injection timing from the injector, the local air-fuel mixture distribution is variously changed, and the rate of change in thermal efficiency, NOx
The data in the case of examining the rate of change and the lean burn limit are shown. Note that [(local air-fuel mixture distribution) = (total air-fuel ratio)-
(Air-fuel ratio near the spark plug)]. The rate of change of thermal efficiency and the rate of change of NOx are obtained when the total air-fuel ratio is set to a constant value (approximately 22) and when the total air-fuel ratio is set to a value smaller than the lean burn limit by a certain margin α. And data.

As shown in FIG.
When the stratified state is at a certain level, the lean burn limit is greatly increased as compared with the case where stratification is not performed (when the local air-fuel mixture distribution is 0). If the stratification is too high, the lean burn limit will be lowered due to the non-uniform distribution of the air-fuel mixture and the combustion stability will be impaired. And the thermal efficiency also worsens.

Then, the stratified state where the local air-fuel mixture distribution is about 2 (that is, the air-fuel ratio near the spark plug is about 10% rich relative to the whole air-fuel ratio) and the air-fuel ratio is a value near the lean combustion limit ( When the value is set to a value smaller by a certain margin α), the air-fuel ratio is made lean by moderate stratification and the atomization of the fuel is promoted by the AMI, and the NOx is greatly reduced. Moreover, thermal efficiency is improved.

In the stratified state where the local air-fuel mixture distribution is about 2, the end of the fuel injection from the injector is set at A in the intake stroke.
It is obtained by setting TDC to about 60 °.

[0061]

As described above, according to the present invention, in a lean burn engine, an air assist mechanism for supplying air for atomizing fuel to injectors provided for each cylinder is provided, and at least a lean operation region is provided. Since the air is supplied to each of the injectors, the atomization of the fuel is promoted in the lean burn state, so that a portion having a high combustion temperature is reduced,
The amount of generated NOx can be greatly reduced.

[0062] Particularly, in the lean operation area, the
One of the two intake ports provided for each cylinder
The on- off valve located at the air port is closed and the tilt
In the state where the swirl is generated and the air is supplied by the air assist mechanism, the air-fuel ratio of the entire air-fuel mixture in the combustion chamber is set to an air-fuel ratio near the lean burn limit, and Since a stratified state in which the local air-fuel ratio is about 10% richer than the air-fuel ratio of the entire air-fuel mixture is obtained, an appropriate stratified state in which the air-fuel mixture distribution in the combustion chamber does not become significantly uneven Is obtained, and the air-fuel ratio is made lean and the atomization is promoted by the air assist, whereby the NOx reduction effect can be further enhanced.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one embodiment of a lean burn engine of the present invention.

FIG. 2 is a schematic plan view showing a combustion chamber structure.

FIG. 3 is a schematic sectional view on a first intake port side.

FIG. 4 is a schematic sectional view on the side of a second intake port.

FIG. 5 is a characteristic diagram of average turbulence intensity.

FIG. 6 is a diagram showing a comparison between swirl and tumble.

FIG. 7 is an explanatory view showing a measuring means and a measuring method for swirl.

FIG. 8 is a diagram showing an air supply system and an evaporative fuel supply system for the injector.

FIG. 9 is a cross-sectional view showing a specific structure of the air mixture type injector.

FIG. 10 is a partially cutaway perspective view of the injector.

FIG. 11 is a diagram showing an air-fuel ratio control region in correspondence with an engine speed and a throttle opening.

FIG. 12 is a diagram showing a relationship between an air-fuel ratio and fuel efficiency, torque fluctuation, and NOx emission.

FIG. 13 is a diagram showing various examples of a fuel distribution state in a combustion chamber.

FIG. 14 is a diagram showing a relationship between various examples shown in FIG. 12 and NOx emission amounts.

FIG. 15 shows the local mixture distribution in the combustion chamber and the lean burn limit,
It is a figure which shows the relationship between a NOx change rate and a thermal efficiency change rate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 2 Combustion chamber 40 Injector 41 On-off valve 51 Air control valve 52 Air supply passage 70 Control unit

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁷ Identification code FI F02D 45/00 301 F02D 45/00 301G F02M 69/00 310 F02M 69/00 310E 360 360C 69/04 69/04 G (72) Inventor Yasuyoshi Hori 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture, inside Mazda Corporation (72) Inventor Futa Nishioka 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Inside Mazda Corporation (72) Inventor, Tetsushi Hosokai No.3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Inventor Noriko Oka No.3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Pref. 3-1 Fuchu-cho Shinchi, Mazda Co., Ltd. (72) Inventor Tsutomu Fujimoto 3-1 Fuchu-cho Shinchi, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) Inventor, Masaki Harada No.3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (56) References JP-A-59-51138 (JP, A) JP-A-6-66176 (JP, A) JP-A-6-10807 ( JP, A) JP-A-61-16224 (JP, A) JP-A-58-204959 (JP, A) JP-A-3-114551 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , (DB name) F20D 41/00, 41/40

Claims (1)

(57) [Claims] In a lean burn engine for an automobile having a lean operation range in which combustion is performed at a leaner air-fuel ratio than a stoichiometric air-fuel ratio, an injector for injecting fuel is provided for each cylinder, and an injector is injected to each injector. An air assist mechanism for supplying air for atomizing fuel, a control means for performing fuel injection from each of the injectors in the intake stroke of each cylinder, and a control unit provided for each cylinder
Assigned to one of the two intake ports
And an on-off valve provided to supply air to each of the injectors by the air assist mechanism at least in the above-described lean operation region, and to generate an oblique swirl in the combustion chamber.
The on-off valve is closed so that the air-fuel ratio of the entire air-fuel mixture in the combustion chamber is set to an air-fuel ratio near the lean burn limit in the lean operation region, and the supply of the air and the generation of the oblique swirl are performed. The fuel injection timing from each of the above injectors is set so that a stratified state in which the local air-fuel ratio near the spark plug is about 10% richer than the air-fuel ratio of the entire air-fuel mixture while the fuel injection is performed is obtained. An automotive lean burn engine characterized by the following.