JPH0689659B2 - Stratified combustion engine - Google Patents

Description

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

(Prior Art) Conventionally, in the engine, fuel consumption and NOx reduction are realized by the synergistic effect of the pumping loss reduction effect by eliminating the throttle valve and the direct injection method that directly injects fuel into the combustion chamber. 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 so that the inside of the combustion chamber is closed. An engine has been proposed in which a rich air-fuel mixture layer is formed in the upper part to realize stratified combustion.

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 rich mixture layer is attenuated or destroyed due to the turbulence 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 low fuel consumption and low NOx can be realized by eliminating the throttle valve and adopting the direct injection method as described above, if a specific successful example is found. The current situation is that there are none.

Further, in stratified combustion, an air layer that directly contributes to combustion and an excess air layer that does not contribute to combustion exist in contact with each other,
When the excess air ratio is particularly large or when the air flow is strong, the heat loss becomes large and the combustion stability is impaired due to the decrease in the combustion temperature. Therefore, it is necessary to maintain the combustion temperature appropriately. This is especially required during low load operation that requires stratified charge combustion.

(Object of the Invention) The present invention is intended to solve the problems pointed out in the above-mentioned prior art, and introduces air into the combustion chamber without throttling, and further forms a plurality of air layers in the combustion chamber. In such a 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 and appropriately maintaining the combustion temperature.

(Means for Achieving the Purpose) As a means for achieving the above object, the stratified combustion engine of the present invention has 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 passage for supplying air to the center of the combustion chamber so as to generate an air flow having a flow direction different from that of the swirl flow,
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 supplying EGR gas into the main intake passage. Done E
The GR gas supply control means and the fuel supply means adapted to supply fuel toward the second air layer are provided.

(Operation) According to the present invention, by the above means, (1) since the first air layer and the second air layer formed in the combustion chamber in the intake stroke have different flow characteristics, the stratified state can be maintained. (2) The temperature of the second air layer is raised by supplying EGR gas to the first air layer that surrounds the second air layer that directly contributes to the combustion, and as described above, Since the fuel is supplied into the second air layer in which the favorable stratified state is maintained and the stratified temperature is increased, the combustion temperature in the combustion chamber is high and the stratified combustion is effectively and stably achieved. become.

(Embodiment) A preferred embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

(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 an exhaust passage 15 that 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 intake manifolds 5 described later, respectively.

The intake manifold 5 has a merging passage portion 30 extending in the cylinder array direction as shown in FIGS. 1 to 3. The merging passage portion 30 is divided into two upper and lower passages, that is, a first passage portion 33 located at the lower portion and a second passage portion 34 located at the upper portion by a partition wall formed in the interior thereof and extending in the longitudinal direction. ing. Further, the first passage portion 33 and the second passage portion
Of the 34, in the first passage portion 33, main intake branch passages 31, 31, ... connected to the main intake passages 11 of the cylinders of the engine,
.. connected to the auxiliary intake passages 12 of the respective cylinders are integrally formed in the second passage portion 34. Therefore, the air introduced from the upstream end portion 5a (see FIG. 3) of the intake manifold 5 into the merging passage portion 30 is divided into two parts, and a part of the air is introduced from the first passage portion 33 into each main intake passage portion 31. , 31 …… through the main intake passages 11, 11 …… of each cylinder of the engine, and a part of the other from the second passage portion 34 through the auxiliary intake passages 32, 32 ……. Are sucked into the main intake passages 11, 11 ... of each cylinder of the engine.

Furthermore, the main intake passages 31, 31, ... and the auxiliary intake passages 3
2,32 ... are the main intake control valve 21 and the auxiliary intake control valve, respectively.
22 are provided. 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. still,
Specific control methods of the main intake control valve 21 and the auxiliary intake control valve 22 will be described in detail later.

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 22 is open, the air is below the piston 4. It is freely introduced into the combustion chamber 3 due to the suction load accompanying the movement.

On the other hand, between the first passage portion 33 of the confluence passage portion 30 of the intake manifold 5 and the exhaust pipe 17 of the engine, the present invention is applied and is connected by an EGR passage 18 provided with an EGR valve 19 in the middle thereof. By controlling the opening / closing of the EGR valve 19, the intake manifold 5 is connected to the first passage portion 33 side as needed.
EGR gas G can be supplied. In addition, this EGR
Similar to the main intake control valve 21 and the auxiliary intake control valve 22, the valve 19 has its operation controlled by a control device 27 described later, and its specific operation method will be described later.

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 21.
And the operation of controlling the opening / closing operation of the auxiliary intake control valve 22 and the EGR valve 19 or controlling the fuel (setting the injection amount and injection timing). In this embodiment, the operation of the main intake control valve 21, the auxiliary intake control valve 22 and the EGR valve 19 are 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. 4, 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 kept fully open up to the operating region on the higher rotation side, which is obtained by adding the region II to the operating region shown by, and is fully closed in the other operating regions.

(Control of EGR valve 19) The purpose of supplying EGR gas to the main intake passage 11 side is to control the temperature of the air layer (first air layer 51 in this embodiment) that does not contribute to combustion when stratified charge combustion is performed. It is intended to raise the temperature by mixing the high temperature EGR gas, and thereby to raise the combustion temperature of the combustion performed in the second air layer portion existing inside thereof.

For this reason, the EGR valve 19 is controlled in the same control mode as the auxiliary intake control valve 22. That is, the valve is opened in the operation region indicated by the region I in FIG. 4 during the normal operation other than the start and when the engine temperature is sensed, and is closed in the other operation regions. Further, when the engine is cold, the valve is opened in both the operating region shown by region I and the operating region shown by region II in FIG. 4, and closed in the other operating regions. Since the stratified charge combustion is not performed at the time of starting, the EGR valve 19 is held closed.

Furthermore, the opening of the EGR valve 19, that is, the control of the EGR gas amount, is a request that the temperature of the EGR gas itself is high when the load of the engine is high, so that a substantially uniform amount of heat is constantly given to the air layer. Therefore, as shown in FIG. 5, the EGR gas amount is controlled to decrease as the engine load increases.

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 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) At engine start, as described above, the main intake control valve 21 and the EGR
The valve 19 is held fully closed. Further, since this operating state is included in the region I, the auxiliary intake control valve 22 is held fully open. Therefore, the intake air is introduced in this case only from the side of the auxiliary intake passage 12, neither the air nor the EGR gas is introduced from the side of the main intake passage 11, and the swirl flow is not 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 kept fully open, but the auxiliary intake control valve 22 and the EGR valve 19 are respectively set to three values of engine speed, engine load, and engine temperature. Opening / closing is controlled based on the control element. 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 where the combustibility needs to be improved by stratified combustion) Since the auxiliary intake control valve 22 and the EGR valve 19 are both opened and maintained, the air-EGR gas mixture from the main intake passage 11 and the auxiliary intake passage 11 (downward movement of the piston 4) are also retained. Only air is introduced into the combustion chamber 3 from the intake passage 12. Therefore, the _first mixture formed in the outer peripheral portion of the combustion chamber 3 by the mixture of air and EGR gas introduced while generating the swirl flow (arrow A ₁ ) from the main intake passage 11 in the combustion chamber 3. Air layer (strictly speaking, mixture layer) 51
(The portion outside the boundary line L) and the air introduced from the auxiliary air intake passage 12 while generating the air flow (arrow A ₂ ) in the piston axial direction, the central portion of the combustion chamber 3 (the first air layer 51). There are two air layers inside and outside of the second air layer 52 (inside the boundary line L) formed on the inside) and having different flow characteristics (in other words, the inside second air layer). 52 is surrounded by the outer first air layer 51). Two air layers 51,52 separated inside and outside
Since the flow characteristics are different, it is unlikely that the stratified state will be attenuated or destroyed by merging with each other, and the separated state (stratified state) is the turbulence of the air in the cylinder accompanying the upward movement of the piston 4. Despite the action, it is maintained near the compression top dead center. Therefore, when the fuel is injected from the injector 8 toward the second air layer 52 side in the vicinity of the compression top dead center, the injected fuel is efficiently mixed with the air in the second air layer 52 and the combustion is performed. A mixture layer having a concentration close to the stoichiometric air-fuel ratio is surely formed locally in the chamber 3 (promotion and maintenance of the stratification ratio).

Further, in this case, the temperature of the first air layer 51 is higher than that in the case where only the air is sucked by the EGR gas G mixed therein. Therefore, naturally, the second air layer 52 existing in a state of being wrapped inside by the first air layer 51 is also
The temperature of the first air layer 51 is increased due to the influence of heat of the first air layer 51.

A high level of stratified combustion is realized by the synergistic effect of promoting and maintaining the stratification and increasing the combustion temperature.

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. For this reason, in this operating region, both the auxiliary intake control valve 22 and the EGR valve 19 are held fully closed, intake air is introduced only from the main intake passage 11 side, and the high output operation of the engine is performed by the high level swirl effect. Will be realized.

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.

Further, in the above embodiment, the EGR gas G is introduced into the confluent passage portion 3
Although it is supplied from the upstream side of 0, the present invention is not limited to this. For example, as shown by the chain line (reference numeral 18 ') in FIG. You can also

Further, in the above embodiment, the EGR gas is supplied to the main intake passage 11
To supply air to the first air layer 51 (fresh air)
However, the present invention is not limited to this, and the introduction of fresh air to the main intake passage 11 side is stopped,
It is also possible to form the first air layer 51 using only EGR gas.

(Effects of the Invention) In the stratified combustion engine of the present invention, the main intake passage that supplies 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 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. Intake control means, EGR gas supply control means for supplying EGR gas into the main intake passage, and fuel supply means for supplying fuel toward the second air layer It is characterized by that.

Therefore, according to the stratified combustion engine of the present invention, (1) since the flow characteristics of the first air layer and the second air layer formed in the combustion chamber in the intake stroke are different, It is easy to maintain, and (2) the temperature of the second air layer is raised by supplying the EGR gas to the first air layer that surrounds the second air layer that directly contributes to combustion, and as described above. Since the fuel is supplied toward the second air layer in which the relatively good stratified state is maintained and the stratified temperature is increased, the combustion temperature in the combustion chamber is high, and the stratified combustion is effectively and stably achieved. The effect is obtained.

[Brief description of drawings]

FIG. 1 is a horizontal cross-sectional view of a main part of a stratified charge combustion engine according to an embodiment of the present invention, FIG. 2 is a horizontal cross-sectional view of II-II of FIG. 1, and FIG. 3 is a vertical cross-sectional view of III-III of FIG. FIG. 4 is an operating characteristic diagram of the main intake passage and the auxiliary intake passage, and FIG. 5 is an operating characteristic diagram of the EGR valve shown in FIG. 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 18 ...... EGR passage 19 ...... EGR valve 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 EGR gas supply control means for supplying EGR gas into the main intake passage, and fuel supply means for supplying fuel toward the second air layer.