JPH0676772B2 - Stratified combustion engine - Google Patents

Description

TECHNICAL FIELD The present invention relates to an engine and an intermediate stratified combustion engine.

In (prior art) engines conventionally, by the synergistic effect with the adoption of the direct噴方type that directly injects fuel into the reducing effect with the combustion chamber of the pumping loss due to the abolition of the throttle valve, realizing low fuel consumption ratio and low NO _X reduction Attempts are being made.

However, when the throttle valve is abolished in this way, a large amount of air is always introduced into the combustion chamber regardless of the load condition of the engine, so especially in the low load operation region of the engine with a small fuel injection amount. If the excess air ratio is large and the injected fuel is mixed with all the air in the cylinder, the air-fuel ratio of the air-fuel mixture becomes over lean, which causes problems such as ignition failure. Therefore, in the low load operation region, the injected fuel is mixed with a part of the air introduced into the combustion chamber to locally form a mixture layer having a concentration close to the stoichiometric air-fuel ratio in the combustion chamber, and the mixture is formed. The so-called stratified combustion in which the air layer portion is ignited and burned becomes an indispensable condition.

From such a background, as disclosed in Japanese Patent Laid-Open No. 58-85319, an injector is provided in the intake passage, and fuel is injected from the injector toward the combustion chamber immediately before the intake valve is closed to inject the fuel into the combustion chamber. Form a rich mixture layer on top,
An engine that has attempted to realize stratified combustion has been proposed.

However, in this method, two layers having different air-fuel mixture concentrations are formed by injecting fuel into a part of an air layer having substantially uniform flow characteristics in the entire combustion chamber, and the fuel injection is performed by the intake valve. Since it is performed immediately before closing, even if the rich mixture layer is formed in a good state in the upper part of the combustion chamber at the beginning of the compression stroke,
Near the end of the compression stroke, the above-mentioned rich air-fuel mixture layer is shelved due to the incongruity of the air in the combustion chamber due to the upward movement of the piston. It is assumed that it will not happen.

Therefore, although it has been theoretically explained that the fuel consumption and the NO _X can be reduced by eliminating the throttle valve and adopting the direct injection method as described above, a concrete example of the success is obtained. The current situation is that I cannot find it.

(Object of the Invention) The present invention is intended to solve the problems pointed out in the above-mentioned prior art, and to introduce a plurality of air layers into the combustion chamber by introducing the air into the combustion chamber without throttling. In this stratified combustion engine, the purpose is to realize a high level of stratified combustion by more reliably stratifying the air layer in the combustion chamber.

(Means for Achieving the Purpose) As a means for achieving the above object, the stratified combustion engine of the present invention includes a main intake passage for supplying air so as to generate a swirl flow in the outer peripheral portion of the combustion chamber, A sub-intake path for supplying air so that an air flow having a flow direction different from that of the swirl flow can be generated in the central portion of the combustion chamber,
Further, at least in the low load operation region of the engine, intake air is introduced from both the main intake passage and the auxiliary intake passage, and the first air layer is formed by the air introduced into the outer peripheral portion of the combustion chamber through the main intake passage. And an intake control means capable of forming a second air layer by the air introduced through the auxiliary intake passage in the center of the combustion chamber, and the second air near the compression top dead center of the piston. And a fuel supply means adapted to supply fuel toward the layers.

(Operation) According to the present invention, the first and second air layers formed in the combustion chamber in the intake stroke have different flow characteristics due to the above-mentioned means. The stratified state of the two air layers is maintained almost to the compression top dead center without being attenuated or destroyed, and the fuel is supplied to the second air layer located in the center of the combustion chamber near the compression top dead center. Thus, the stratified state of the air-fuel mixture layer portion which directly contributes to combustion until the time of ignition and the air layer portion located around it is maintained, and the stratified combustion in the combustion chamber is effectively achieved.

(Embodiment) A preferred embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

(I: Structure) FIGS. 1 and 2 show a multi-cylinder stratified combustion engine for an automobile according to an embodiment of the present invention. In each drawing, reference numeral 1 is a cylinder block, 2 is a cylinder head, and 3 is a cylinder head. Is a combustion chamber, and 4 is a piston.

The cylinder head 2 is opened and closed by an intake valve 6 2
One intake passage, that is, a main intake passage 11 and an auxiliary intake passage 12 which will be described later and which form the subject of the present invention, and an exhaust passage 15 which is opened and closed by the exhaust valve 7 are formed.

The main intake passage 11 is of a helical port type intended to generate a swirl flow, and a portion of the main intake passage 11 near the main intake port 13 opening to the combustion chamber 3 is formed in a substantially spiral shape. Therefore, the air introduced into the combustion chamber 3 from the main intake passage 11 through the main intake port 13 is the same as in FIGS.
In the figure, a swirl flow is formed along the outer peripheral portion of the combustion chamber 3 as indicated by an arrow A ₁ . Incidentally, the passage area of the main intake passage 11 is set to a size such that the main intake passage 11 alone can cover the required air amount during high-load operation of the engine.

The sub intake passage 12 has a passage area smaller than that of the main intake passage 11, and the sub intake port opening to the combustion chamber 3 thereof.
Reference numeral 14 denotes a position in the main intake passage 11 near the main intake port 13 and through the main intake port 13 to the combustion chamber 3
The opening is formed so that the central part of the can be seen. Therefore, the air introduced into the combustion chamber 3 from the auxiliary intake passage 12 through the auxiliary intake port 14 is the air flow substantially along the axial direction of the piston 4 as indicated by an arrow A ₂ in FIGS. 1 and 2. To appear.

On the other hand, the outer ends of the main intake passage 11 and the sub intake passage 12 are connected to the intake manifold 5, respectively. The intake manifold 5 has a merging passage portion 30 extending in the cylinder row direction.
And a main intake branch passage 31 connected to the main intake passage 11 of the cylinder head 2 and a sub intake branch passage 32 connected to the sub intake passage 12 by branching from the confluent passage portion 30 for each cylinder. Have Of the main intake branch passage 31 and the sub intake branch passage 32, the main intake branch passage 31 is provided with a main intake control valve 21, and the sub intake branch passage 32 is provided with a sub intake control valve 22. The main intake control valve 21 and the auxiliary intake control valve 22 are opened / closed by step motors 23, 24 which operate by receiving control signals from a control device 27, respectively.

Further, the intake system including the intake manifold 5 is not provided with a throttle valve. Therefore, when the main intake control valve 21 or the sub intake control valve 23 is open, the air is below the piston 4. It is freely introduced into the combustion chamber 3 by the suction negative pressure accompanying the movement.

In FIGS. 1 and 2, reference numeral 8 is an injector, which is inclined so that fuel can be injected toward the center of the combustion chamber 3. Further, reference numeral 9 is a spark plug, and this spark plug 9 is the injector 8 described above.
On the other hand, it is arranged so as to be located on the downstream side of the swirl flow (arrow A ₁ ).

The control device 27 receives the engine speed, the load, the atmospheric temperature (intake air temperature), the water temperature and the intake pressure, and receives the main intake control valve 2
1. It operates to open / close the auxiliary intake control valve 22 or control the fuel (setting the injection amount and injection timing). In this embodiment, the operation of the main intake control valve 21 and the auxiliary intake control valve 22 is controlled as follows.

(A: Control of Main Intake Control Valve 21) The main intake control valve 21 is controlled according to whether swirl flow is required in the combustion chamber 3 of the engine,
Specifically, when the engine is started, that is, in the operating state where swirl generation is not necessary from the viewpoint of improving ignitability, it is kept fully closed, and in other operating regions, that is, swirl flow is required to improve combustibility. It is held fully open in a certain area.

(B: Control of the sub-intake control valve 22) The sub-intake control valve 22 is held fully open particularly in an operating region where realization of stratified charge combustion is required because the ignition / combustibility of the air-fuel mixture deteriorates. Contribute to realization,
In other operating regions, it is held fully closed. Specifically, as shown in FIG. 3, it is controlled on the basis of three factors of engine speed, engine load and engine temperature. In this embodiment, when the engine is warm, as shown in FIG. As shown in the region I, the auxiliary intake control valve 22 is kept fully open in the low load region including the idle operating region, and is fully closed in the other operating regions.

On the other hand, when the engine is cold, the ignitability of the air-fuel mixture becomes worse than when it is warm.
The auxiliary intake control valve 22 is held fully open up to the operating region on the higher rotation side where region II is added to the operating region indicated by, and is fully closed in the other operating regions.

The operating timing of the injector 8 is the piston 4
Is set in advance so that fuel injection is performed near the compression top dead center.

(II: Operation and Its Action) Next, the operation of this engine and its action will be briefly described.

(A: At engine start-up) At engine start-up, the main intake control valve 21 is held fully closed as described above. Further, since this operating state is included in the region I, the auxiliary intake control valve 22 is held fully open. It Therefore, the intake air is introduced only from the side of the auxiliary intake passage 12 and not from the side of the main intake passage 11 in this case, and no swirl flow is generated in the combustion chamber 3. Therefore, the blowout phenomenon of the flame kernel due to the swirl flow does not occur, and good ignition performance, that is, startability is secured.

(B: Normal operation of engine) In this case, the main intake control valve 21 is always held fully open, but the auxiliary intake control valve 22 is based on three control elements of engine speed, engine load, and engine temperature. It is controlled to open and close. That is, for example, when the engine operating condition is in the low load operating region including the idle operating region corresponding to the region I or the region II (in other words, the operating region in which the combustibility needs to be improved by stratified combustion) Since the sub intake control valve 22 is held fully open, the air flows in the main intake passage 11 and the sub intake passage 12 as the intake stroke progresses (downward movement of the piston 4).
Are simultaneously introduced into the combustion chamber 3. Therefore, in the combustion chamber 3, swirl flow (arrow A ₁ ) from the main intake passage 11
The first air layer 51 (the portion outside the boundary line L) formed on the outer peripheral portion of the combustion chamber 3 by the air introduced while generating the air and the air flow in the piston axial direction from the auxiliary intake passage 12 (arrow A ₂ ) The combustion chamber 3 is generated by the air introduced while generating
There are two air layers inside and outside of the second air layer 52 (inside the boundary line L) formed in the central portion (inside the first air layer 51) and having different flow characteristics ( In other words, the inner second air layer 52 is surrounded by the outer first air layer 51). The two air layers 51, 52 separated into both the inside and the outside rarely merge with each other and their stratified state is attenuated or destroyed due to their different flow characteristics. ) Is maintained up to near the compression top dead center despite the turbulent action of the air in the cylinder accompanying the upward movement of the piston 4. Therefore,
When the fuel is injected from the injector 8 toward the second air layer 52 side near the compression top dead center, the injected fuel is efficiently mixed with the air in the second air layer 52, and the combustion chamber 3
A mixture layer having a concentration close to the stoichiometric air-fuel ratio is reliably formed locally inside the fuel cell, and high-level stratified combustion is realized.

On the other hand, the operating condition of the engine is the above area I or area II.
In the operating regions other than, since the fuel injection amount is large, even if this fuel is uniformly mixed with the entire amount of the air introduced into the combustion chamber 3, the mixture concentration does not become over lean, Therefore, it is not necessary to realize the stratified combustion as described above. Therefore, in this operating region, the auxiliary intake control valve 22 is held fully closed, intake air is introduced only from the main intake passage 11 side, and high output operation of the engine is realized by the high level swirl effect. Become.

In the above embodiment, the first swirl flow separated by the air introduced from the side of the main intake passage 11 and the air flow introduced from the side of the auxiliary intake passage 12 and having a flow in the piston axial direction are separated from each other. Although the air layer 51 and the second air layer 52 are formed, the present invention is not limited to this, and, for example, air introduced from the main intake passage 11 side can be provided to the outer peripheral portion of the combustion chamber. A first air layer having a swirl flow in the opposite direction is formed, while a second air layer having a swirl flow in the opposite direction is formed by the air introduced from the auxiliary intake passage 12 side, and the swirl directions differ from each other. The two air layers may be separated from each other in the combustion chamber.

(Effects of the Invention) In the stratified combustion engine of the present invention, the main intake passage for supplying air so as to generate a swirl flow in the outer peripheral portion of the combustion chamber, and the swirl flow in the central portion of the combustion chamber in the flow direction. And an auxiliary air intake passage for supplying air so as to generate different air flows, and further, at least in a low load operation region of the engine, intake air is introduced from both the main air intake passage and the auxiliary air intake passage so that the combustion chamber It is possible to form a first air layer by the air introduced through the main intake passage in the outer peripheral portion and a second air layer by the air introduced through the auxiliary intake passage in the central portion of the combustion chamber. It is characterized by including such intake control means and fuel supply means for supplying fuel toward the second air layer in the vicinity of the compression top dead center of the piston.

Therefore, according to the stratified combustion engine of the present invention, the flow characteristics of the first air layer and the second air layer formed in the combustion chamber during the intake stroke are different, so that even during the compression stroke. The stratified state of these two air layers is maintained almost to the compression top dead center without being attenuated or destroyed, and the fuel is supplied to the second air layer located in the center of the combustion chamber near the compression top dead center. Therefore, the stratified state of the air-fuel mixture layer portion that directly contributes to combustion until the time of ignition and the air layer portion located around it can be maintained well, and an effect that higher level stratified combustion can be achieved can be obtained. .

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a main part of a stratified combustion engine according to an embodiment of the present invention, FIG. 2 is a lateral sectional view taken along line II-II of FIG. 1, and FIG. 3 is a control characteristic diagram of the engine shown in FIG. Is. 1 ... Cylinder block 2 ... Cylinder head 3 ... Combustion chamber 4 ... Piston 5 ... Intake manifold 6 ... Intake valve 7 ... Exhaust valve 8 ... Injector 9 ... Spark plug 11 ... Main intake passage 12 ...... Sub intake passage 13 ...... Main intake port 14 ...... Sub intake port 15 ...... Exhaust passage 51 ...... First air layer 52 ...... Second air layer

Claims (1)

[Claims] 1. A main intake passage for supplying air so as to generate a swirl flow in an outer peripheral portion of a combustion chamber, and an air flow having a flow direction different from that of the swirl flow in a central portion of the combustion chamber. An auxiliary air intake passage for supplying air, and at least in a low load operation region of the engine, intake air is introduced from both the main intake air passage and the auxiliary intake air passage to the outer peripheral portion of the combustion chamber through the main intake air passage. Intake air control means capable of forming a first air layer by the air introduced through the auxiliary air intake passage in the central portion of the combustion chamber, and a second air layer by the air introduced through the sub-intake passage.
A stratified combustion engine comprising: a fuel supply unit configured to supply fuel toward the second air layer near the compression top dead center of the piston.