WO2017134747A1

WO2017134747A1 - Method and device for controlling in-cylinder direct-injection internal combustion engine

Info

Publication number: WO2017134747A1
Application number: PCT/JP2016/053097
Authority: WO
Inventors: 亮内田; 田中　大輔; 祐子志方
Original assignee: 日産自動車株式会社; ルノーエス．ア．エス．
Priority date: 2016-02-02
Filing date: 2016-02-02
Publication date: 2017-08-10

Abstract

This method for controlling an in-cylinder direct-injection internal combustion engine forms a gas flow in a cylinder, performs fuel injection for injecting fuel to be combusted around a spark plug in or after a compression stroke, and spark ignites an air-fuel mixture formed by the fuel injected by the fuel injection. In this control method, pre-compression injection that varies gas flow in a direction that stabilizes combustion is carried out during the compression stroke and prior to fuel injection.

Description

In-cylinder direct injection internal combustion engine control method and control apparatus

The present invention relates to control of a direct injection type internal combustion engine.

Control of an internal combustion engine that directly injects fuel into the cylinder, in which fuel is injected during the compression stroke, and the mixture is unevenly distributed around the spark plug by using the tumble flow as the in-cylinder gas flow. It has been known. By performing such stratified combustion, the entire cylinder can be made leaner than the stoichiometric air-fuel ratio, so that fuel efficiency can be improved. JP3963088B describes control for retarding ignition timing significantly (for example, after compression top dead center) when performing the above stratified combustion for the purpose of promoting warm-up of the exhaust purification catalyst. Yes.

However, in the configuration in which the air-fuel mixture is transported to around the spark plug using the in-cylinder gas flow, the air-fuel mixture transported around the spark plug is likely to flow by the in-cylinder gas flow. In particular, when the ignition timing is retarded as in the control described in the above document, it is difficult to cause the air-fuel mixture to stagnate around the ignition plug until the ignition timing. That is, it is difficult to perform stratified combustion by the control described in the above document, and the combustion stability is lowered.

Therefore, an object of the present invention is to enable stable combustion even when the ignition timing is greatly retarded.

According to an aspect of the present invention, a fuel injection that forms a gas flow in the cylinder and injects fuel to be burned around the spark plug is performed after the compression stroke, and the mixture formed by the fuel injected by the fuel injection is formed. A control method for spark ignition is provided. In this control method, pre-compression injection that changes the gas flow in a direction in which combustion is stabilized is performed during the compression stroke and before the fuel injection.

FIG. 1 is a schematic configuration diagram in the vicinity of a combustion chamber of a direct injection type internal combustion engine. FIG. 2 is a diagram showing the relationship between the fuel injection timing and the tumble flow strength. FIG. 3 is a diagram illustrating an example of the relationship between fuel spray and tumble flow. FIG. 4 is a diagram illustrating another example of the relationship between fuel spray and tumble flow. FIG. 5 is a timing chart of tumble flow strength. FIG. 6 is a schematic view of the combustion chamber ceiling surface. FIG. 7 is a diagram for explaining the spray beam. FIG. 8 is a schematic configuration diagram in the vicinity of a combustion chamber of a direct injection type internal combustion engine. FIG. 9 is a timing chart when the first-compression injection of the first embodiment is executed. FIG. 10 is a schematic configuration diagram in the vicinity of a combustion chamber of a direct injection type internal combustion engine. FIG. 11 is a timing chart in the case where the compressed pre-injection in the second embodiment is executed. FIG. 12 is a map showing the momentum of fuel spray. FIG. 13 is a diagram for explaining the spray beam.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram around a combustion chamber of a direct injection type internal combustion engine (hereinafter also referred to as “engine”) 1 to which the present embodiment is applied. Although FIG. 1 shows only one cylinder, this embodiment can also be applied to a multi-cylinder engine.

The cylinder block 1B of the engine 1 includes a cylinder 2. A piston 3 is accommodated in the cylinder 2 so as to be able to reciprocate. The piston 3 is connected to a crankshaft (not shown) via a connecting rod 12 and reciprocates as the crankshaft rotates. The piston 3 includes a cavity 10 described later on a crown surface 3A (hereinafter also referred to as a piston crown surface 3A).

The cylinder head 1A of the engine 1 includes a concave combustion chamber 11, and an intake passage 4 and an exhaust passage 5 that communicate the combustion chamber 11 with the outside of the engine. The combustion chamber 11 is configured as a so-called pent roof type, and a pair of intake valves 6 are disposed at the opening of the intake passage 4, and a pair of exhaust valves 7 are disposed at the opening of the exhaust passage 5. An ignition plug 8 is disposed along the axis of the cylinder 2 at a substantially central position of the combustion chamber 11 surrounded by the pair of intake valves 6 and the pair of exhaust valves 7.

In the intake passage 4, a tumble control valve 13 as a gas flow generation device is arranged. Note that the shape of the flow path of the intake passage 4 may be configured such that the intake air flowing into the combustion chamber 11 forms a tumble flow without providing the tumble control valve 13. In this case, the intake passage 4 is a gas flow generation device.

Further, a fuel injection valve 9 is arranged at a position between the pair of intake valves 6 in the cylinder head 1A so as to face the combustion chamber 11. The directivity of fuel spray injected from the fuel injection valve 9 will be described later.

The intake valve 6 and the exhaust valve 7 are driven to open and close by camshafts (not shown). Note that a variable valve mechanism may be arranged on at least one of the intake side or the exhaust side so that the valve opening timing and the valve closing timing can be variably controlled. The valve opening timing is the timing for starting the valve opening operation, and the valve closing timing is the timing for ending the valve closing operation. As the variable valve mechanism, a known mechanism such as a mechanism that changes the rotational phase of the camshaft relative to the crankshaft or a mechanism that can change not only the rotational phase but also the operating angle of each valve can be used.

An exhaust purification catalyst for purifying the exhaust gas of the engine 1 is interposed on the exhaust flow downstream side of the exhaust passage 5. The exhaust purification catalyst is, for example, a three-way catalyst.

The piston 3 includes the cavity 10 in the piston crown surface 3A as described above. The cavity 10 is provided at a position biased toward the intake side on the piston crown surface 3A. The fuel injection valve 9 is arranged so that the fuel spray is directed to the cavity 10 when fuel is injected when the piston 3 is in the vicinity of the compression top dead center. The cavity 10 has such a shape that the fuel spray (B in the figure) bounced off after colliding is directed toward the spark plug 8.

It should be noted that the cavity 10 may be located at the center of the piston crown surface 3A or other position as long as the condition that the fuel spray collides is satisfied.

The fuel injection amount, fuel injection timing, ignition timing, and the like of the engine 1 are controlled by the controller 100 according to the operating state of the engine 1. The controller 100 includes a microcomputer that includes a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface). It is also possible to configure the controller 100 with a plurality of microcomputers.

Also, the fuel injection timing here is the timing at which fuel injection is started. In order to execute these controls, the engine 1 includes various detection devices such as a crankshaft angle sensor, a cooling water temperature sensor, and an air flow meter that detects an intake air amount.

In addition, although this embodiment demonstrates the structure which forms the stratified air-fuel mixture around the spark plug 8 using the cavity 10, it is not necessarily restricted to this. For example, even if the fuel injection valve 9 is disposed adjacent to the spark plug 8 and the fuel injected from the fuel injection valve 9 with a short drive pulse stays around the spark plug 8 to form a stratified mixture. Good.

Next, control of the engine 1 having the above configuration will be described.

First, the conventionally known control at the cold start will be described.

As a control at the time of cold start, super retarded stratified combustion for promoting the activation of the exhaust purification catalyst is known (for example, JP 2008-25535 A). At this time, at the time of cold start, since combustion is performed under severe conditions from the viewpoint of combustion stability at a low temperature, control that can ensure combustion stability is desired.

In super retarded stratified combustion, the controller 100 sets the ignition timing to the first half of the expansion stroke, for example, 10-30 deg after compression top dead center. Further, the controller 100 performs so-called multi-stage injection in which the amount of fuel required per cycle is injected in a plurality of times. In the case of the two-stage injection, the controller 100 sets the first fuel injection timing in the first half of the intake stroke, and sets the second fuel injection timing in the second half of the compression stroke until the fuel spray reaches the ignition timing. It is set to the timing when it can reach the periphery of.

Here, the first fuel injection amount and the second fuel injection amount (stratified injection amount) in the case of two-stage injection will be described.

The air-fuel ratio of the exhaust gas discharged by the above-mentioned super retarded stratified combustion is stoichiometric (theoretical air-fuel ratio). The controller calculates the amount of fuel that can be completely combusted with the amount of intake air per cycle (hereinafter also referred to as the total fuel amount), as in the general fuel injection amount setting method. A part of the total fuel amount, for example, 20 to 90% by weight is set as the first injection amount, and the rest is set as the second injection amount.

In super retarded stratified combustion, the air-fuel ratio of the exhaust gas may be leaner than stoichiometric.

When the fuel injection amount is set as described above, the fuel spray injected in the first fuel injection diffuses into the cylinder 2 without colliding with the cavity 10, mixes with air, and is stoichiometric throughout the combustion chamber 11. A leaner homogeneous mixture (A in the figure) is formed. The fuel spray (B in the figure) injected in the second fuel injection (stratified injection) collides with the cavity 10 and is wound up to reach the vicinity of the spark plug 8 and around the spark plug 8. Concentrates the richer mixture than stoiki. Thereby, the air-fuel mixture in the combustion chamber 11 is in a stratified state. If a spark is ignited by the spark plug 8 in this state, combustion that is resistant to disturbance with misfire suppressed is performed. By the way, although the combustion mentioned above is stratified combustion, in order to distinguish from the general stratified combustion whose ignition timing is before compression top dead, it is called super retarded stratified combustion.

The first fuel injection described above is divided into two, and the fuel amount required per cycle is divided into a total of three injections, two for the intake stroke and one for the compression stroke. Also good. In this case, the third injection is stratified injection.

Here, the fuel injection timing in the super retarded stratified combustion will be described with reference to FIG. FIG. 2 is a timing chart in which the horizontal axis is the crank angle. In the figure, IT1 indicates the first fuel injection timing, IT2 indicates the stratified injection fuel injection timing, solid line A indicates the strength of the tumble flow, and solid line B indicates the fuel adhesion characteristics to the piston 3. In the figure, TDC means top dead center and BDC means bottom dead center.

It is known that tumble flow is effective in improving fuel efficiency and reducing exhaust emissions. Since the tumble flow is formed by the intake air flowing into the combustion chamber 11 after the intake valve 6 is opened, the strength of the tumble flow gradually increases during the intake stroke. However, when the volume of the combustion chamber 11 increases as the piston 3 moves down, the flow rate of the tumble flow decreases. For this reason, the intensity of the tumble flow reaches the first peak (1st peak) during the intake stroke and starts to decrease.

When entering the compression stroke, the volume of the combustion chamber 11 is reduced as the piston 3 is raised, so that the flow velocity of the tumble flow starts to rise, and the strength of the tumble flow also rises accordingly, and the second peak ( 2nd peak). Thereafter, when the piston 3 further rises, the tumble flow is crushed, so that the strength of the tumble flow gradually decreases and eventually the tumble flow disappears.

The fuel adhesion characteristic to the piston 3 indicates how much fuel adheres to the crown surface 3A of the piston 3 when the injected fuel collides with the piston 3. As shown in the figure, the fuel adhesion amount increases as the piston 3 approaches the top dead center. This is because the distance between the piston 3 and the fuel injection valve 9 decreases as the piston 3 approaches the top dead center, and more fuel collides with the piston 3.

When the fuel adhering to the piston 3 is repeatedly carried over to the next cycle without being vaporized or combusted during the cycle, the liquefied fuel is accumulated in the piston 3. In this state, when the exhaust purification catalyst is switched to the normal combustion mode in response to the warm-up completion or acceleration request, the accumulated fuel is burned by the combustion flame that has propagated to the piston 3 and the PM emission amount increases. End up. The normal combustion mode referred to here is a combustion mode in which fuel is injected during the intake stroke or compression stroke, and spark ignition is performed at an ignition timing close to MBT (optimum ignition timing).

From the viewpoint of suppressing the PM emission amount, the crank angle range in which the fuel injection timing can be set is limited based on the fuel adhesion amount to the piston 3. The NG range in FIG. 2 is an example of a crank angle range in which setting of the fuel injection timing is prohibited. Note that the amount of fuel admissible on the intake top dead center side is larger than that on the compression top dead center side. This is because the time to the ignition timing is longer when adhering to the piston 3 on the intake top dead center side than when adhering on the compression top dead center side, and the amount of evaporation / vaporization from the adhering to ignition Because there are many.

As described above, the fuel injection timing of the stratified injection is a range in which the fuel spray collides with the cavity 10 and there is a time allowance for the collided fuel spray to form a stratified mixture around the spark plug 8 by the ignition timing. Is set in consideration of the amount of fuel adhering to the piston 3.

By the way, as shown in FIG. 2, if the tumble flow is still strong at the fuel injection timing of the stratified injection, the fuel spray injected by the stratified injection is flowed by the tumble flow and stratified around the spark plug 8. It becomes difficult to form an air-fuel mixture. Therefore, as the tumble flow is enhanced to improve the fuel efficiency and reduce the exhaust gas, it becomes more difficult to form a stratified mixture, and the combustion stability in the super retarded stratified combustion decreases.

As described above, since the strength of the tumble flow decreases as the compression top dead center is approached, the stratified mixture becomes easier to form as the fuel injection timing of the stratified injection is delayed. However, the amount of fuel adhering to the piston 3 increases as the fuel injection timing is delayed. For this reason, in the conventional fuel injection control conventionally known, the fuel injection timing of the stratified injection takes into account the balance between the ease of forming the stratified mixture and the amount of fuel adhering to the piston 3. It was.

In contrast, in this embodiment, the fuel injection control described below is executed to ensure the combustion stability of super retarded stratified combustion even when the tumble flow is enhanced to improve fuel efficiency and reduce exhaust emissions. To do. Further, according to the fuel injection control of the present embodiment, the amount of fuel adhering to the piston 3 does not increase in order to ensure the combustion stability.

3 and 4 are diagrams for explaining the outline of the fuel injection control according to the present embodiment.

When fuel is injected during the compression stroke, as shown in FIG. 3, the vortex center of the main flow of the tumble flow (hereinafter also simply referred to as “the vortex center of the tumble flow” or “vortex center”) is positioned lower than the fuel spray. In some cases, as shown in FIG. 4, the tumble flow vortex center may be higher than the fuel spray. FIG. 4 shows a state where the piston 3 is raised from the state shown in FIG. Since the tumble flow vortex is crushed as the piston 3 moves up, the tumble flow vortex center is higher in FIG. 4 than in FIG. 3.

In the case of FIG. 3, the tumble flow strength is increased by combining the fuel spray traveling direction vector and the tumble flow vortex rotation direction vector at the collision position between the fuel spray and the tumble flow vortex.

On the other hand, in the case of FIG. 4, the fuel spray traveling direction vector and the tumble flow vortex rotational direction vector face each other at the collision position between the fuel spray and the tumble flow vortex, so the tumble flow strength decreases. To do.

FIG. 5 is an enlarged view from the vicinity of the 2nd peak in FIG. 2 until the tumble flow disappears. The broken line in the figure shows the tumble flow strength of FIG. 2, and the solid line shows the tumble flow strength when fuel is injected at the fuel injection timing of FIG. As shown in the figure, when fuel is injected at the fuel injection timing of FIG. 4, the height of the 2nd peak is suppressed, and the timing at which the tumble flow strength decreases is also advanced.

Therefore, in the present embodiment, before stratified injection, fuel injection is performed to weaken the strength of the tumble flow to such an extent that a stratified mixture can be formed around the spark plug 8. That is, in the state shown in FIG. 4, stratified injection is performed after fuel injection (hereinafter also referred to as “compressed pre-injection”) for changing the tumble flow in a direction in which combustion by spark ignition is stabilized. .

Note that the total fuel amount is not changed even when the first-compression injection is performed. For example, the injection amount of the first fuel injection that is performed during the intake stroke is reduced by the amount that is injected by the first-compression injection. The fuel spray injected by the compression first injection is diffused and mixed by colliding with the tumble flow, so that the amount of fuel adhering to the piston 3 does not increase by performing the compression first injection. It should be noted that the injection amount of the stratified injection may be reduced and the injection may be performed by the first-compression injection. Further, if the discharge performance is within the allowable range, the total fuel amount may be increased by the amount corresponding to the first-compression injection without changing the injection amounts of the first fuel injection and the stratified injection.

Here, the fuel injection timing of the first compression injection will be described.

FIG. 6 is a view of the ceiling surface of the combustion chamber 11 as seen from the piston side. In the following description, the tip of the fuel injection valve 9 (hereinafter also referred to as “injection valve tip”) is the base point, the axis passing through the base point and the bore center is the X axis, and the axis orthogonal to the X axis in FIG. The Y axis is assumed. Note that an axis orthogonal to the X axis and the Y axis, that is, an axis extending from the base point along the bore axis is defined as a Z axis.

FIG. 7 is a view showing fuel spray injected from the fuel injection valve 9. The fuel injection valve 9 is a so-called multi-hole type injection valve having a plurality of injection holes. In this embodiment, the fuel injection valve 9 has six injection holes, and six spray beams B1-B6 injected from each injection hole spread in an umbrella shape. The center of the circle including the tip of each spray beam is defined as the spray beam centroid C, and a straight line passing through the injection valve tip B and the spray beam centroid C is defined as the spray beam centroid line.

Based on the above, an example of the injection timing of the first compression injection will be described.

(First embodiment)
FIG. 8 is a schematic configuration diagram in the vicinity of the combustion chamber of the engine 1. In FIG. 8, the ignition plug 8, the fuel injection valve 9, the tumble control valve 13, and the like are omitted.

The point D in the figure is the vortex center of the tumble flow at the piston position in FIG. Geometrically, the vortex center is defined as a position on the bore center line and higher than the crown surface 3A of the piston 3 by (combustion chamber height Hch + stroke amount S) / 2. The combustion chamber height is a distance from the piston crown surface position when the piston 3 is at the top dead center to the highest position on the combustion chamber ceiling surface. The stroke amount is the distance from the piston crown surface position when the piston 3 is at top dead center to the piston crown surface position at a predetermined timing.

The point B in the figure is the above-mentioned injection valve tip. Point C in the figure is the above-mentioned spray beam gravity center. The broken line arrow in the figure is the spray beam barycentric line described above.

In the first embodiment, the pre-compression injection is executed when the vortex center D of the tumble flow is on the piston top dead center side with respect to the spray beam barycentric line on the XZ plane. That is, from when the vortex center D rises as the piston 3 rises and is located on the piston top dead center side with respect to the intersection of the bore center line and the spray beam barycentric line, stratified injection is started. The pre-compression injection is performed at any timing in the period.

Tumble flow is counterclockwise on the XZ plane on the piston bottom dead center side from the vortex center D. Therefore, during the above period, the spray beam acts to prevent the tumble flow from progressing and reduce the tumble flow strength at the position where the spray beam collides with the tumble flow. The action of reducing the strength of the tumble flow is an action of changing the tumble flow in a direction in which stratified combustion around the spark plug is stabilized.

FIG. 9 is a timing chart in the case where the first-compression injection is executed at the fuel injection timing of the first embodiment.

9 is the fuel injection timing of the first compression injection. FIG. 9 shows the case of the advance side limit ((a) in the figure) and the case of the retard side limit ((b) in the figure).

In the tumble flow strength chart, the solid line indicates that the pre-compression injection is not executed, the broken line indicates that the fuel injection timing of the compression pre-injection is the advance limit, and the alternate long and short dash line indicates that the fuel injection timing of the compression pre-injection is the retard limit Shows the case.

This chart shows a case where stratified injection is executed at the timing of the retard side limit. The retard side limit of the stratified injection is determined based on the ignition timing in consideration of the period required for the fuel injected in the stratified injection to form a stratified mixture.

Timing t1 is the timing at which the vortex center D is located on the spray beam barycentric line. This is the advance side limit of the fuel injection timing of the pre-compression injection in the first embodiment. In FIG. 9, the timing t1 is the timing for starting the first-compression injection, but may be the timing for ending.

Timing t2 is the latest timing among the fuel injection timings in which the pre-compression injection can be completed before the stratified fuel injection timing. That is, the timing t2 is a retard side limit of the fuel injection timing of the first compression injection. In FIG. 9, the timing t <b> 2 is the start timing of the previous compression injection, but may be the end timing.

If the pre-compression injection is executed at the timing t1, the 2nd peak of the tumble flow decreases as shown in the figure, and the strength of the tumble flow at the start of the stratified injection decreases, so that the combustion stability of the stratified combustion increases. Further, even when the pre-compression injection is executed at the timing t2 after the 2nd peak, the rate of decrease in the strength of the tumble flow is increased as shown in the figure, so that the combustion stability of the stratified combustion similarly increases.

Therefore, if the fuel injection timing of the first compression injection is set as in the first embodiment, the combustion stability of the stratified combustion can be increased.

(Second embodiment)
In the second embodiment, the range in which the fuel injection timing of the pre-compression injection can be set is made narrower than in the first embodiment.

FIG. 10 is a schematic configuration diagram showing the vicinity of the combustion chamber of the engine 1 as in FIG. In FIG. 10, the position of the piston 3 is closer to the top dead center than in FIG. Point E in the figure is the intersection of the spray beam barycentric line and the piston crown surface 3A. The “collision position between the spray beam barycentric line and the piston crown surface” represents the distance in the X direction from the point B at the position where the spray beam barycentric line and the piston crown surface 3A intersect on the XZ plane.

FIG. 11 is a timing chart in the case where the first-compression injection is executed at the fuel injection timing of the second embodiment. Similarly to FIG. 9, the injection timing chart shows the case of the advance side limit ((a) in the figure) and the case of the retard side limit ((b) in the figure).

The collision position chart indicates the position on the X axis of the collision position between the spray beam barycentric line and the piston crown surface 3A.

On the XZ plane, the inside of the cylinder of the engine 1 is long in the bore center line direction when the piston 3 is at the bottom dead center position, and geometrically as the piston position approaches the top dead center from the bottom dead center. After approaching the isotropic direction and becoming isotropic, the piston 3 rises and becomes longer in the bore radial direction. Here, “geometrically isotropic” means that the sum of the stroke amount S and the combustion chamber height Hch is equal to the bore diameter (L2 × 2).

In accordance with this, the tumble flow vortex is gradually shaped from an elliptical shape whose major axis is the bore center line direction into a circular shape, and when the piston 3 rises, it is compressed by the piston 3 so that it collapses. In this process, the angular velocity of the vortex increases as the vortex approaches a circle. That is, when the inside of the cylinder is geometrically isotropic, the tumble flow strength has a 2nd peak.

If the pre-compression injection is performed when the tumble flow strength reaches the 2nd peak, it is considered that the energy of the fuel spray injected in the pre-compression injection can be efficiently used to reduce the tumble flow strength. On the other hand, if the fuel injection timing of the pre-compression injection is much earlier than the 2nd peak, the tumble flow strength decreases due to the injection, but the angular velocity increases as the vortex approaches a circular shape thereafter, so the energy of the fuel spray of the pre-compression injection is increased. Cannot be used efficiently.

Therefore, in the second embodiment, as shown in FIG. 11, the advance side limit t1 of the fuel injection timing of the first compression injection is set to (stroke amount S + combustion chamber height Hch) :( bore diameter L2 × 2) = 1: 1. The timing is as follows. In FIG. 11, the timing t <b> 1 is the end timing of the compression early injection, but may be the start timing.

As shown in FIG. 11, the retard side limit t2 of the fuel injection timing of the pre-compression injection is a timing at which the collision position between the spray beam barycentric line and the piston crown surface 3A is on the bore center line. Since the spray beam is formed in an umbrella shape, when the collision position is on the intake side with respect to the bore center line, the kinetic energy of the spray beam on the lower side in the Z-axis direction with respect to the spray beam center of gravity is It is lost by collision with the surface 3A and cannot be used to reduce the tumble flow strength. Therefore, the pre-compression injection is performed before the collision position is on the intake side of the bore center line.

When the pre-compression injection is performed at the above-mentioned advance side limit or retard side limit, the tumble flow strength can be reduced until stratified injection as shown in the figure.

It should be noted that the advance side limit and the retard side limit of the compressed pre-injection in the first and second embodiments are merely examples. Based on the technical idea described above, the fuel injection timing of the first compression injection that provides the effect of reducing the tumble flow strength may be a timing at which the vortex center D is at the piston top dead center side with respect to the spray beam barycentric line. I understand that. It can also be seen that the advance side limit of the fuel injection timing of the pre-compression injection is the timing when the piston 3 is raised to a position where the rotational direction of the vortex of the gas flow and the traveling direction of the spray beam face each other. Further, it can also be seen that the retard side limit of the fuel injection timing of the pre-compression injection is the timing at which the piston 3 rises to a position where the spray beam barycentric line does not collide with the main flow of the tumble flow vortex.

Next, the fuel injection amount and injection pressure of the first compression injection in this embodiment will be described.

The combustion stability of stratified combustion increases as the tumble flow strength during stratified injection decreases. Therefore, in the present embodiment, the controller 100 controls the pre-compression injection so that the tumble flow strength is greatly decreased as the tumble flow strength is higher.

The reason why the tumble flow strength is reduced by the pre-compression injection is that the tumble flow vortex collides with the fuel spray injected by the pre-compression injection, thereby reducing the angular momentum of the tumble flow vortex. Therefore, the controller 100 increases the momentum of the fuel spray that is injected in the first-compression injection as the tumble flow strength is higher.

FIG. 12 is a map showing the relationship between the momentum of fuel spray, the fuel injection amount, and the fuel injection pressure. As shown in the drawing, the higher the fuel injection pressure and the larger the fuel injection amount, the greater the momentum of the fuel spray. That is, as a method for increasing the momentum of fuel spray, for example, the fuel injection amount may be increased or the fuel injection pressure may be increased. Of course, the fuel injection amount may be increased and the fuel injection pressure may be increased.

Incidentally, the tumble flow strength increases as the intake air amount increases, that is, as the throttle valve opening increases.

Therefore, in this embodiment, the controller 100 increases at least one of the fuel injection pressure or the fuel injection amount as the throttle valve opening increases.

Also, when the throttle valve opening is constant, the tumble flow strength increases as the engine speed increases. Therefore, the controller 100 may increase at least one of the fuel injection pressure or the fuel injection amount as the engine speed increases.

As described above, according to the present embodiment, stratified injection for forming gas flow in the cylinder and injecting stratified combustion around the spark plug is performed after the compression stroke, and fuel injected by stratified injection is formed. A control method for spark ignition of an air-fuel mixture is provided. In this control method, before the stratified injection is performed during the compression stroke, the tumble flow (gas flow) is changed in a direction in which the stratified combustion is stabilized, that is, the tumble flow strength is reduced. As a result, the fuel injected by the stratified injection can form a stratified mixture around the spark plug. As a result, the combustion stability is improved. In the present embodiment, the case where stratified combustion is performed around the dotted plug has been described. However, if the fuel injected at the end of the multistage injection burns around the dotted plug, the stratified combustion may not be required.

In the present embodiment, the timing of the first compression injection is the timing at which the vortex center D of the tumble flow rises as the piston 3 rises and the spray beam injected by the injection hole of the fuel injection valve 9 and the first compression injection. This is any timing during a period that is on the piston top dead center side with respect to the spray beam center of gravity line connecting the center of gravity. At this timing, the tumble flow strength can be reduced by the pre-compression injection.

In the present embodiment, the advance side limit of the timing of performing the previous compression injection is such that the piston 3 is raised to a position where the rotational direction of the tumble flow vortex and the traveling direction of the spray beam injected by the previous compression injection are opposed. It is timing. By setting such an advance side limit, it can be used to reduce the tumble flow strength without wasting the fuel injected in the first compression injection.

In the present embodiment, the retard side limit of the timing of performing the pre-compression injection is the timing at which the piston 3 is raised to a position where the spray beam barycentric line does not collide with the main flow of the tumble flow vortex. By setting such a retard side limit, the tumble flow strength can be reduced by the timing of starting the stratified injection, and the tumble flow strength can be increased without wasting fuel injected in the first compression injection. Available to lower.

In this embodiment, as the throttle valve opening is larger, at least one of the fuel injection pressure or the fuel injection amount of the first compression injection is increased. As the throttle valve opening increases, the intake air amount increases and the tumble flow strength increases. That is, in this embodiment, either the fuel injection pressure or the fuel injection amount is increased as the tumble flow strength increases. As a result, the tumble flow strength can be reliably reduced and combustion stability can be ensured.

In this embodiment, as the engine speed increases, at least one of the fuel injection pressure or the fuel injection amount of the first compression injection is increased. The higher the engine speed, the higher the intake air flow rate and the higher the tumble flow strength. That is, in this embodiment, either the fuel injection pressure or the fuel injection amount is increased as the tumble flow strength increases. As a result, the tumble flow strength can be reliably reduced and combustion stability can be ensured.

In the present embodiment, as shown in FIG. 7, the fuel injection valve 9 in which the fuel amount injected from each nozzle hole is equal and a plurality of spray beams are formed at equal intervals has been described. However, it is not limited to this. For example, you may use the fuel injection valve 9 as shown in FIG. 13 from which the injection quantity from each nozzle hole differs. The spray barycenter beam C and the spray beam barycenter line in this case are as follows.

FIG. 13 is a diagram in which three spray beams having different flow rates are projected on the XZ plane described above. The flow rate of the spray beam is spray beam 1> spray beam 2> spray beam 3.

The vector in the direction along the central axis of the spray beam is the spray beam vector (vector 1-3 in the figure). The magnitude of the spray beam vector is proportional to the flow rate of the spray beam.

In this case, as shown in the figure, the combined vector of vectors 1-3 is the spray beam barycenter vector. Thereby, the spray beam gravity center C and the spray beam gravity line are determined.

Thus, if the spray beam centroid C and the spray beam centroid line are defined using the spray beam vector, it is possible to deal with a wide range of cases where the number of nozzle holes and the flow rate of each nozzle hole are different.

In addition, the definition of the spray beam center of gravity C is not limited to the two types described above. As long as the effects of the above-described embodiment can be achieved, the definitions may be different from the two definitions described above.

The embodiment of the present invention has been described above. However, the above embodiment only shows a part of application examples of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. Absent.

Claims

Forming a gas flow in the cylinder,
Fuel injection for injecting fuel to be burned around the spark plug is performed after the compression stroke,
Spark-igniting an air-fuel mixture formed by the fuel injected in the fuel injection,
In a control method for a direct injection type internal combustion engine,
A control method for an in-cylinder direct injection internal combustion engine, characterized in that, during the compression stroke and before the fuel injection, pre-compression injection for changing the gas flow in a direction in which combustion is stabilized is executed.
In the control method of the direct injection type internal combustion engine according to claim 1,
The control method for a direct injection type internal combustion engine, wherein the timing of performing the first compression injection is a timing at which the fuel spray injected in the first compression injection collides with the gas flow so as to weaken the gas flow.
In the control method of the direct injection type internal combustion engine according to claim 1 or 2,
The timing of performing the pre-compression injection is a spray beam that connects the vortex center of the gas flow as the piston rises, and connects the nozzle hole of the fuel injection valve and the center of gravity of the spray beam injected by the pre-compression injection. A control method for an in-cylinder direct injection internal combustion engine at any timing during a period on the piston top dead center side with respect to the center of gravity line.
In the control method of a direct injection type internal combustion engine according to claim 2 or 3,
An in-cylinder direct injection internal combustion engine in which the advance side limit of the timing of performing the first-compression injection is a timing at which the piston is raised to a position where the rotation direction of the vortex of the gas flow and the traveling direction of the spray beam are opposed to each other Control method.
In the control method of a direct injection type internal combustion engine according to claim 2 or 3,
Control of the cylinder direct injection internal combustion engine in which the retard side limit of the timing of performing the pre-compression injection is the timing at which the piston rises to a position where the spray beam barycentric line does not collide with the main flow of the gas flow vortex Method.
An intake passage arranged so that a tumble flow is formed in the cylinder;
A fuel injection valve for injecting fuel into the cylinder;
An ignition device that sparks and ignites an air-fuel mixture formed by fuel injected from the fuel injection valve;
A control unit that performs fuel injection for injecting fuel to be burned around the spark plug after the compression stroke;
In a cylinder direct injection internal combustion engine control device comprising:
A control device for a direct injection type internal combustion engine, wherein the control unit performs a pre-compression injection that changes the gas flow in a direction in which combustion is stable during the compression stroke and before the fuel injection. .
In the control apparatus for a direct injection type internal combustion engine according to claim 6,
The in-cylinder direct-injection internal combustion engine control device performs the first-compression injection after the vortex center of the tumble flow moves to the piston top dead center side from the injection beam center of gravity of the fuel injection valve as the piston rises.