JP2005155395A - Cylinder direct injection type internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform stratified combustion operation excellent in fuel economy and exhaust emission in wider operation range. <P>SOLUTION: A fuel injection valve and an ignition plug are arranged at a center position on an upper surface of a combustion chamber, a cavity is formed at a center position of a piston crown surface. This engine includes two stratified combustion modes of a first stratified operation mode (mode 1) in which fuel before impinging on a piston during fuel injection or right before fuel injection completion is ignited and a second stratified operation mode (mode 2) in which fuel via the piston is ignited after fuel injection completion. Operation of the mode 2 is performed at low engine speed and in a high engine load zone and operation of the mode 1 is performed at high engine speed and in a low engine load zone. A swirl generation means such as a swirl control valve is included, stronger swirl is given in the mode 1 than the mode 2 under same operation conditions. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an improvement in a direct injection type internal combustion engine that realizes stratified combustion by injecting fuel into a cylinder.

Patent Document 1 discloses an example of a direct injection type internal combustion engine. In the internal combustion engine of Patent Document 1, a cavity, that is, a piston bowl is provided in the piston crown surface, a fuel injection valve is disposed in the vicinity of the piston bowl, and fuel spray is caused to collide with the peripheral wall surface of the piston bowl. By forming a spray circulation flow toward the center, an appropriate stratified mixture is formed in the cylinder, thereby reducing fuel consumption.
JP-A-11-82028

  However, in the above-described configuration, the size of the stratified mixture formed via the piston (in other words, colliding with the piston) is generally determined by the shape of the piston cavity, that is, the cavity volume.

  In this case, if stable combustion is performed under a certain stratified operation condition and an attempt is made to realize good fuel consumption and exhaust emission, good combustion is established under other stratified operation conditions with different engine speeds and loads. There is a concern that a so-called rebound will occur.

  For example, when the engine speed is high, the crank angle advances (piston rise) relative to the mixture formation time is relatively faster than when the engine speed is low, and it is assumed that the fuel injection timing and fuel injection period are the same. (This is proportional to the engine load), and a predetermined ignition timing is reached before the combustible mixture reaches the vicinity of the spark plug. Although it is conceivable to avoid the above problem by setting the injection timing to the advance side as the engine rotational speed increases, in early injection, it becomes difficult to catch the fuel spray by the piston cavity. In particular, it is necessary to use fuel spray injected at a spray angle (bevel angle) of a certain degree or more in consideration of performing combustion with a uniform mixture by intake stroke injection in the entire load region. It is not possible to set the correct injection timing.

  In addition, if the cavity is made large so that it is easy to catch the spray, the depth of the cavity will be restricted from the viewpoint of the compression ratio. It becomes difficult.

  In other words, with the configuration in which the fuel that always passes through the piston cavity is always ignited during stratified combustion as in the conventional case, it is difficult to perform stable and good fuel consumption and exhaust operation with respect to the engine speed. .

  On the other hand, when considering the engine load level, the stratified mixture in the vicinity of the spark plug tends to become lean in the stratified operation at a low load in the same mixture formation process, and the combustion stability is deteriorated and the fuel consumption is deteriorated. It becomes a trend. In a stratified operation at a high load, the stratified mixture in the vicinity of the spark plug becomes excessively concentrated, and there is a concern that smoke and HC increase.

  In order to solve the above-described problems, the present invention switches between two types of combustion systems according to the engine rotational speed and the engine load in the stratified operation conditions. The gas flow in the cylinder suitable for the combustion method is provided.

  That is, the direct injection type internal combustion engine of the present invention has an ignition plug and a fuel injection valve in the upper part of the combustion chamber, and has a cavity near the approximate center of the piston crown surface. Then, as an operation mode for performing stratified combustion, a first stratified operation mode for igniting fuel before colliding with a piston during fuel injection or immediately after the end of fuel injection, and igniting fuel via the piston after the end of fuel injection A second stratification operation mode.

  Here, in the second stratified operation mode, the air-fuel mixture formed via the piston after completion of fuel injection is sufficiently vaporized and mixed by passing through the cavity, and then is relatively uniform over the cavity. A mixture distribution is formed. Accordingly, there is an advantage that there is no concern about smoke and CO emission from the rich mixture, and it is difficult to be affected by cycle fluctuations in the mixture distribution.

  However, as the engine speed increases, there is a concern that time will be insufficient to sufficiently form a uniform air-fuel mixture. Further, as the engine rotational speed increases, the in-cylinder flow becomes stronger, so that the air-fuel mixture becomes excessively diffused and the vicinity of the spark plug may become excessively thin.

  Furthermore, when the engine load is low, a relatively uniform air-fuel mixture formed above the cavity becomes thinner than the combustible air-fuel ratio, and there is a risk of misfire.

  On the other hand, as the first stratified operation mode, fuel spray during flight before fuel injection or before colliding with the piston immediately after the end of fuel injection is immediately mixed with ambient air from the periphery of the spray shaft by mixing and vaporization. Form. The air-fuel mixture that does not pass through the piston is quickly formed as a compact air-fuel mixture immediately below the fuel injection valve regardless of the engine speed, so that stable stratified combustion can be performed regardless of the engine speed.

  In addition, even when the engine load is low, fuel (air mixture) can be reliably disposed in the vicinity of the spark gap, so that stable combustion can be realized.

  However, the fuel during or immediately after the injection has a large distribution, and in a high load region where the fuel injection amount is large, the concentration of the air-fuel mixture around the spark gap becomes deeper than the combustible air-fuel ratio, which deteriorates the combustion stability. In addition, CO or smoke may be discharged from the rich mixture.

  The invention according to claim 1 switches between these two stratified operation modes in accordance with the operation conditions of the internal combustion engine. That is, by switching between the two stratified operation modes according to the engine speed and load, the smoke emission due to the local rich mixture in the first stratified operation mode, the local lean in the second stratified operation mode It is possible to suppress discharge of unburned air-fuel mixture due to air-fuel mixture. And the swirl intensity | strength in the said 1st stratification operation mode is given relatively high with respect to the same operation condition by the said swirl production | generation means compared with the swirl intensity | strength in the said 2nd stratification operation mode.

  This is because the time from fuel injection to ignition changes in the first stratified operation mode and the second stratified operation mode. In the first stratified operation mode, the time from fuel injection to ignition is It is very short compared to the case of the second stratified operation mode. Therefore, the air-fuel mixture needs to be diffused by the gas flow in the cylinder. As described above, in the first stratified operation mode, by diffusing the air-fuel mixture by stronger swirl, it is possible to suppress the generation of smoke due to the local rich air-fuel mixture that becomes a problem in the first stratified operation mode.

  In a more specific invention of claim 2, when the engine speed is lower than a predetermined value, the second stratification operation mode is set, and when the engine speed is higher than a predetermined value, the first stratification operation is performed. Mode. And the swirl intensity | strength in the said 1st stratification operation mode is made higher than the swirl intensity | strength in the said 2nd stratification operation mode with respect to the same load.

  In the invention of claim 3, the first stratification operation mode is set when the engine load is lower than a predetermined value, and the second stratification operation mode is set when the engine load is higher than the predetermined value. And the swirl intensity | strength in the said 1st stratification operation mode is made higher than the swirl intensity | strength in the said 2nd stratification operation mode with respect to the same rotational speed.

  According to the present invention, the first stratification operation mode for igniting the fuel before colliding with the piston during fuel injection or immediately after the end of the fuel injection, and the second stratification for igniting the fuel via the piston after the end of the fuel injection. By switching the operation mode according to the engine operating conditions, it becomes possible to always perform stratified combustion stably regardless of the engine speed and load, and the fuel consumption and exhaust emission are excellent in a wide operating range. It can be. At the same time, by varying the strength of the swirl generated in the cylinder corresponding to each stratified operation mode, the combustion in each stratified operation mode becomes better.

  FIG. 1 shows a mechanical configuration of an embodiment of a direct injection type internal combustion engine according to the present invention. As shown in the figure, a combustion chamber 5 is formed by the cylinder head 1, the cylinder 3 of the cylinder block 2, and the piston 4. The combustion chamber 5 communicates with the intake port 7 via the intake valve 6 and communicates with the exhaust port 9 via the exhaust valve 8. The intake valve 6 is driven to open and close by an intake valve camshaft (not shown), and the exhaust valve 8 is driven to open and close by an exhaust valve camshaft (not shown).

  A fuel injection valve 11 for injecting fuel toward the piston 4 is provided at an approximately center position of the upper surface of the combustion chamber 5, that is, the ceiling surface on the cylinder head 1 side. The spray center line of the fuel injection valve 11 substantially coincides with the cylinder center line. An ignition plug 12 is disposed adjacent to the fuel injection valve 11, and the spark gap 12 a is located near the center of the combustion chamber 5. The fuel injection valve 11 and the spark plug 12 are controlled based on a signal from an engine control unit (not shown), and fuel injection and ignition are performed at a timing according to engine operating conditions.

  A substantially cylindrical cavity 13 is formed at the center position of the crown surface of the piston 4 so as to face the fuel injection valve 11. The cavity 13 is, for example, a reentrant type, and at the time of stratified combustion, a stratified mixture is formed mainly in the cavity 13 and above.

  On the other hand, in order to obtain an appropriate gas flow in the combustion chamber 5 mainly during stratified combustion, swirl generating means for generating swirl is provided in the cylinder. FIG. 4 shows an example of a swirl generating means in which a swirl control valve 15 comprising a butterfly valve is provided on one of a pair of intake ports 7. By closing the swirl control valve 15, an arrow appears in the cylinder 3. A swirl as shown by S is generated. The intensity of the swirl S generated in the cylinder 3 can be variably controlled by adjusting the opening degree of the swirl control valve 15.

  FIG. 5 shows a different embodiment of the swirl generating means, in which a narrow auxiliary intake passage 16 is opened at a position immediately before the intake valve 6 of one intake port 7 and a part of intake air introduced from the upstream side of the intake port 7 is introduced. In this configuration, jetting is performed along the tangential direction of the cylinder 3. Due to the intake air flow from the auxiliary intake passage 16, a swirl as indicated by an arrow S is generated in the cylinder 3. The flow of the intake air flow from the auxiliary intake passage 16 is controlled by a flow rate control valve (not shown) interposed in the auxiliary intake passage 16, and thereby the strength of the swirl S generated in the cylinder 3. Can be variably controlled.

  In any of the embodiments shown in FIGS. 4 and 5, the gas flow in the cylinder 3, that is, the swirl S can be changed without a large response delay at the time of transition.

  In the internal combustion engine of the present invention configured as described above, as a combustion mode, a stratified combustion mode in which lean operation is realized by performing fuel injection mainly during the compression stroke (particularly in the latter half of the compression stroke) and fuel consumption is improved. A homogeneous combustion mode in which fuel is injected during the intake stroke (particularly in the first half of the intake stroke) to realize the theoretical air-fuel ratio operation is provided, and is selected according to the operating state.

  Further, in the stratified combustion mode, the first stratified operation mode (mode 1) for igniting the fuel before colliding with the piston 4 during fuel injection or immediately after the end of fuel injection, and the piston 4 after the end of fuel injection There are two stratified combustion modes, the second stratified operation mode (mode 2) for igniting the fuel that has passed through, and the engine control is performed so as to switch between both in accordance with the engine speed and the engine load. Done.

  First, an outline of the air-fuel mixture formation process in the two stratified operation modes in the present invention will be described.

  FIG. 2 shows the air-fuel mixture formation process in the first stratification operation mode, that is, the stratification operation mode in which fuel is ignited before colliding with the piston 4 during fuel injection or immediately after the end of fuel injection. In the first stratified operation mode, the fuel injection timing is set near the compression top dead center. The spark gap 12a is installed near the tip of the fuel injection valve 11, and ignites immediately after the start of fuel injection or immediately after the end of fuel injection. This is to ignite the fuel in flight before the collision with the piston 4 among the injected fuel. Here, as shown in the order of (a), (b), and (c) of FIG. 2, the injected fuel spray forms an air-fuel mixture by mixing with ambient air from the tip and periphery of the spray shaft. By setting a relatively late injection timing close to the compression top dead center, the in-cylinder temperature at the time of fuel injection is high, and the fuel after injection is quickly vaporized and mixed. In the first stratified operation mode, the fuel around the spray shaft where the combustible mixture is formed is ignited in the process of rapid vaporization and mixing during or immediately after fuel injection. Therefore, in the formation of the air-fuel mixture in which the engine speed is high and the fuel advances from the fuel injection valve 11 at the upper part of the combustion chamber 5 to the ignition plug 12 at the upper part of the combustion chamber 5 again, the time is insufficient. If the combustible air-fuel mixture cannot be reliably transported to 12 or if the air-fuel mixture that collides with the piston 4 and spreads into the cavity 13 because the engine load is low and the fuel injection amount is small, the air-fuel mixture concentration is too thin. Even in such a case, according to the first stratified operation mode, stable combustion can be realized.

  On the other hand, when ignition is performed in the above-described vaporization and mixing process, under a condition where the fuel injection amount is large, an excessively rich air-fuel mixture exists even during flame propagation, and there is a risk of deterioration in combustion efficiency and exhaust emission.

  Here, when the engine rotational speed is high, the diffusion and mixing of the fuel proceeds relatively quickly due to the gas flow in the cylinder that increases substantially proportionally to the engine rotational speed, but the engine rotational speed is relatively low, and In a region where the engine load is high, it is desirable to provide time for the fuel spray to be sufficiently vaporized and mixed.

  Next, the air-fuel mixture formation in the second stratification operation mode, that is, the stratification operation mode in which the fuel that has passed through the piston 4 after fuel injection is ignited will be described with reference to FIG. In FIG. 3, the mixture formation process proceeds in the order of (a) → (b) → (c) → (d). Further, (d1) shows a state when the load is high in the last step (d), and (d2) shows a state when the load is low.

  In the second stratified operation mode, the fuel injection timing is set so that the fuel spray is received by the piston cavity 13, and the injected fuel spray collides with the bottom surface of the cavity 13. After that, the spray proceeds along the bottom surface of the piston cavity 13 by the penetration force of the spray as shown in FIG. Thereafter, a relatively homogeneous stratified air-fuel mixture is generated above the cavity 13 in the vicinity of the spark plug 12 while swirling around the combustion chamber 5 like a whirl and surrounding air is entrained.

  When the engine load is high, a relatively dense homogeneous air-fuel mixture is formed above the cavity 13 as shown in Fig. (D1), and as the engine load becomes lower, the air-fuel mixture formed above the cavity 13 as shown in Fig. (D2). The concentration becomes lighter.

  Here, the concentration of the air-fuel mixture formed is controlled so that it is within the range of the combustible air-fuel ratio and the exhaust emission is not deteriorated. That is, the fuel injection timing and ignition timing are controlled so that an appropriate amount of the air-fuel mixture protrudes from the cavity 13 in a high load region where the concentration of the homogeneous air-fuel mixture formed above the cavity 13 becomes so high that exhaust emission deteriorates. . In addition, when the concentration of the homogeneous mixture formed above the cavity 13 becomes lean enough to cause misfire, the mixture has a moderate air-fuel ratio distribution before the mixture reaches the entire area above the cavity 13. The fuel injection timing and the ignition timing are controlled so as to perform ignition.

  FIG. 6 shows switching of the combustion mode with respect to the engine speed and the engine load.

  Basically, in the region where the engine speed is low and the engine load is high, the operation is performed in the second stratification operation mode (mode 2). In the region where the engine speed is high and the engine load is low, the first The operation is performed in the stratified operation mode (mode 1). It should be noted that homogeneous combustion is performed by intake stroke injection in a high load range that is equal to or higher than a predetermined engine load and a high speed range that is equal to or higher than a predetermined engine speed.

  FIG. 7 is a map showing the control characteristics of the swirl intensity in the stratified operation region composed of the first stratified operation mode and the second stratified operation mode, and the hatched lines in the figure are equal swirl intensity lines. Indicates. That is, as described above, the intensity of the swirl S generated in the cylinder 3 is variably controlled by adjusting the opening of the swirl control valve 15, for example. FIG. 7 shows the swirl intensity that is the control target. ing. As shown in the figure, in the first stratified operation mode, the optimum swirl strength is set according to the engine speed and the engine load. Similarly, in the second stratified operation mode, the optimum swirl strength is set according to the engine speed and the engine load. And in the boundary of both, there exists a level | step difference in optimal swirl intensity | strength, ie, target swirl intensity | strength, and the swirl intensity in the 1st stratification operation mode is the swirl intensity in the 2nd stratification operation mode with respect to the same operation condition. Is also relatively high. This is because the time from fuel injection to ignition changes in the first stratified operation mode and the second stratified operation mode. In the first stratified operation mode, the time from fuel injection to ignition is It is very short compared to the case of the second stratified operation mode. Therefore, the air-fuel mixture needs to be diffused by the gas flow in the cylinder. As described above, in the first stratified operation mode, by diffusing the air-fuel mixture by stronger swirl, it is possible to suppress the generation of smoke due to the local rich air-fuel mixture that becomes a problem in the first stratified operation mode.

  FIG. 8 shows an embodiment in which, in order to simplify the control, the first stratified operation mode and the second stratified operation mode are switched in the stratified combustion region with a predetermined engine speed as a boundary. Similarly to FIG. 7, the control characteristic of the swirl strength in that case is shown. The second stratification operation mode is set when the engine speed is lower than the predetermined value, and the first stratification operation mode is set when the engine speed is higher than the predetermined value. As described above, in the first stratification operation mode, the optimum swirl strength is set according to the engine rotation speed and the engine load, and even in the second stratification operation mode, the engine rotation speed and the engine load are set. The optimal swirl strength is set accordingly. At the boundary between the two, there is a step in the optimum swirl strength, that is, the target swirl strength. For the same load, the swirl strength in the first stratified operation mode is greater than the swirl strength in the second stratified operation mode. Given relatively high.

  Similarly, FIG. 9 shows an implementation in which, in order to simplify the control, the first stratified operation mode and the second stratified operation mode are switched with a predetermined engine load as a boundary in the stratified combustion zone. An example is shown, and the control characteristics of swirl strength in that case are shown as in FIGS. The first stratification operation mode is set when the engine load is lower than the predetermined value, and the second stratification operation mode is set when the engine load is higher than the predetermined value. As described above, in the first stratification operation mode, the optimum swirl strength is set according to the engine rotation speed and the engine load, and even in the second stratification operation mode, the engine rotation speed and the engine load are set. The optimal swirl strength is set accordingly. At the boundary between the two, there is a step in the optimum swirl strength, that is, the target swirl strength, and for the same engine speed, the swirl strength in the first stratified operation mode is greater than that in the second stratified operation mode. Is given relatively higher than.

  In the second stratified operation mode in which the required swirl strength is relatively low, additional swirl generation by the swirl generating means such as the swirl control valve 15 and the auxiliary intake passage 16 described above may be stopped. . In this case, a stratified state of the fuel mixture is formed by the gas flow generated by the fuel spray injected from the fuel injection valve 11. Since the gas flow generated by spraying has small cycle fluctuations, stable combustion can be realized every cycle.

  In addition, particularly during idling, even in the first stratified operation mode, additional swirl generation by swirl generation means such as the swirl control valve 15 and the auxiliary intake passage 16 may be stopped. During idle operation, the amount of fuel injected is very small, so the fuel diffuses due to gas flow, and a lean air-fuel mixture field may be formed, increasing the amount of unburned fuel. On the other hand, by stopping the additional swirl generation, the stratified mixture is formed only by the gas flow with a small cycle fluctuation generated by the fuel spray injected from the fuel injection valve 11, so that stable combustion is achieved. realizable.

1 is a cross-sectional view showing an embodiment of a direct injection type internal combustion engine according to the present invention. Explanatory drawing which shows the air-fuel | gaseous mixture formation process of 1st stratification operation mode. Explanatory drawing which shows the air-fuel | gaseous mixture formation process of 2nd stratification operation mode. Explanatory drawing of the swirl production | generation means using a swirl control valve. Explanatory drawing of the swirl production | generation means using a sub intake passage. The characteristic view which shows the combustion mode with respect to an operating condition. The characteristic view which shows the control map of the swirl intensity | strength in each stratified operation mode. The characteristic view which shows the control map of the swirl intensity | strength of a different Example. Furthermore, the characteristic view which shows the control map of the swirl intensity of the different example.

Explanation of symbols

4 ... Piston 5 ... Combustion chamber 11 ... Fuel injection valve 12 ... Spark plug 13 ... Cavity 15 ... Swirl control valve 16 ... Sub-intake passage

Claims (7)

An in-cylinder direct injection internal combustion engine having an ignition plug and a fuel injection valve in the upper part of the combustion chamber, a cavity near the approximate center of the piston crown, and swirl generating means for generating swirl in the cylinder In
There is a first stratification operation mode in which fuel is ignited before the collision with the piston immediately after fuel injection or immediately after fuel injection, and a second stratification operation mode in which fuel is ignited via the piston after fuel injection is completed. And
Switching between these two stratified operation modes according to engine operating conditions,
An in-cylinder direct injection internal combustion engine characterized by giving a relatively high swirl strength in the first stratified operation mode to the same operating condition as compared with a swirl strength in the second stratified operation mode.   When the engine rotation speed is lower than a predetermined value, the second stratification operation mode is set. When the engine rotation speed is higher than a predetermined value, the first stratification operation mode is set and the first stratification operation mode is set for the same load. 2. The direct injection internal combustion engine according to claim 1, wherein a swirl intensity in the first stratified operation mode is higher than a swirl intensity in the second stratified operation mode.   When the engine load is lower than a predetermined value, the first stratification operation mode is set. When the engine load is higher than the predetermined value, the second stratification operation mode is set and the first stratification operation mode is set for the same rotational speed. The in-cylinder direct injection internal combustion engine according to claim 1, wherein the swirl intensity in the stratified operation mode is higher than the swirl intensity in the second stratified operation mode.   The in-cylinder direct injection internal combustion engine according to any one of claims 1 to 3, wherein swirl generation by the swirl generating means is not performed in the second stratified operation mode.   The direct injection internal combustion engine according to any one of claims 1 to 4, wherein swirl generation by the swirl generation means is not performed during idle operation even in the first stratified operation mode.   The in-cylinder direct injection internal combustion engine according to any one of claims 1 to 5, wherein the swirl generating means is composed of a swirl control valve provided at an intake port. The in-cylinder direct injection internal combustion engine according to any one of claims 1 to 5, wherein the swirl generating means includes a sub-intake passage for generating a swirl provided in an intake port.

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