JP4631645B2 - Fuel injection control device for in-cylinder injection type internal combustion engine - Google Patents

Description

  The present invention relates to a fuel injection control device for a direct injection internal combustion engine capable of executing fuel injection during a compression stroke.

  2. Description of the Related Art Conventionally, a cylinder injection gasoline engine has been put to practical use as a cylinder injection type internal combustion engine (engine) that directly injects fuel into the cylinder (inside the cylinder). Generally, in such a cylinder injection type gasoline engine, a compression stroke injection mode in which fuel is injected in a compression stroke and an intake stroke injection mode in which fuel is injected in an intake stroke are set to be switchable. Among these, the compression stroke injection mode (compression lean injection mode) is an injection mode in which fuel is injected toward the spark plug when the piston is in the vicinity of the compression stroke top dead center, and this fuel is directly ignited ( Spray guide injection mode) is known.

According to such a spray guide injection mode, a relatively stable operation can be performed with a very lean air-fuel ratio, and fuel consumption can be improved. In Patent Document 1 below, as a compression stroke injection mode, an operation mode in which fuel is ignited before or during collision with a piston immediately after fuel injection, and an operation in which fuel is ignited via a piston after fuel injection is completed. A technique for switching a mode by an engine rotational speed and an engine load is disclosed.
JP 2004-353594 A

Incidentally, in general, an internal combustion engine (engine) is provided with a controller (ECU: electronic control unit) that performs various controls such as ignition timing, fuel injection amount, valve opening / closing timing, and throttle opening. In this controller, the fuel injection amount (g / st) per stroke is calculated by the following equation based on detection information from various sensors.
Fuel injection amount (g / st) = (volume efficiency * air density * stroke volume * fuel density) * [(A / F coefficient * warm air correction coefficient * acceleration correction coefficient * intake air temperature correction coefficient * other coefficient) / 14. 7]
Here, the reciprocal of the portion other than (volume efficiency * air density * stroke volume * fuel density) in the above formula, that is, 14.7 / (A / F coefficient * warm air correction coefficient * acceleration correction coefficient * intake air temperature correction coefficient). The part represented by * other coefficients is called control A / F, and the fuel injection amount is calculated so as to be the control A / F. That is, the control A / F can also be referred to as a target A / F.

  Here, the combustion characteristics in the low rotation and medium load range in the spray guide injection mode are shown in FIG. The horizontal axis is the fuel injection timing, and the vertical axis is the ignition timing. As shown in the figure, in this operation mode, the smaller the A / F (air / fuel ratio) in the lean air / fuel ratio region (that is, the richer), the smaller the area indicating the combustion stable region and the lower the combustion stability. . In contrast, as the A / F is increased (lean) in the lean air-fuel ratio region, the combustion becomes stable. From this point, the spray guide injection mode is operated at an ultra-lean air-fuel ratio. It can be said that this is an operation mode suitable for.

Therefore, in an internal combustion engine that performs compression stroke injection, even if the fuel injection mode is switched only by the rotational speed and load of the internal combustion engine, combustion stability due to the air-fuel ratio is not taken into consideration, so that the combustion stability is reduced. It was not able to suppress enough.
The present invention has been devised in view of such problems, and an object thereof is to provide a fuel injection control device for a direct injection internal combustion engine that can be switched to a fuel injection mode corresponding to an air-fuel ratio.

A fuel injection control device for a direct injection internal combustion engine according to the present invention (Claim 1) executes a compression stroke injection mode for injecting the fuel during a compression stroke of the internal combustion engine when a predetermined operating condition is satisfied, The compression stroke injection mode includes a first fuel injection mode in which fuel is injected toward the spark plug near the top dead center of the compression stroke, and the fuel is directly ignited, and the first fuel injection mode in the compression stroke. An in-cylinder injection internal combustion engine configured to be able to switch between a second fuel injection mode in which fuel is injected at an earlier timing than the fuel injection timing, and the fuel is collected in the vicinity of a spark plug and ignited by a piston ascending. A fuel injection control device that switches between the first fuel injection mode and the second fuel injection mode in accordance with a target air-fuel ratio set according to operating conditions. S / G defined as a region for selecting the first fuel injection mode on a map in which the speed of the internal combustion engine and the load of the internal combustion engine are parameters. It possesses a combustion zone, a defined W / G combustion zone so as to overlap with the S / G fuel area as an area for selecting a fuel injection mode of the second on the map, the fuel injection mode switching means When the rotational speed of the internal combustion engine and the load of the internal combustion engine are located only in the S / G combustion region on the map, the first fuel injection mode is selected, and the rotational speed of the internal combustion engine and When the load of the internal combustion engine is located only in the W / G combustion region on the map, the second fuel injection mode is selected, and the rotational speed of the internal combustion engine and the load of the internal combustion engine are above When in the overlapping region of the S / G combustion zone and the W / G combustion zone you are, characterized in that on the basis of the target air-fuel ratio switching the fuel injection mode of the fuel injection mode and the second first It is said.

The second fuel injection mode is set to an air-fuel ratio on the rich side of the first fuel injection mode in the lean region, and the fuel injection mode switching means is an excess fuel ratio in the first fuel injection mode. First limit value setting means for setting a first limit value of the rich side air-fuel ratio, and a second limit value of the over-rich side air-fuel ratio in the second fuel injection mode with a value smaller than the first limit value And a second limit value setting means, and the rotational speed of the internal combustion engine and the load of the internal combustion engine are in the overlapping region of the S / G combustion region and the W / G combustion region on the map, and It is preferable to select the second fuel injection mode when the target air-fuel ratio is less than the first limit value (claim 2).
Further, the fuel injection mode switching means, under the fuel injection mode of the second, said purpose the Shimegisora ratio is smaller than the second limit value, the target while holding the該該second fuel injection mode It is preferable to clip the air-fuel ratio to the second limit value (Claim 3).

When the fuel injection mode switching means is in the second fuel injection mode , the rotational speed of the internal combustion engine and the load of the internal combustion engine are set in the S / G combustion region and the W / G combustion region on the map. Preferably, the first fuel injection mode is selected when the target air-fuel ratio is equal to or greater than the first limit value.
In addition, a rotation speed detection means for detecting the rotation speed of the internal combustion engine and a load detection means for detecting the load of the internal combustion engine are provided, and the first limit value setting means and the second limit value setting means are Preferably, the first limit value and the second limit value are set based on the rotation speed detected by the rotation speed detection means and the load detected by the load detection means, respectively .

According to the fuel injection control device for a cylinder injection type internal combustion engine of the present invention, since the fuel injection control mode is switched to an appropriate fuel injection mode in accordance with the target air-fuel ratio, deterioration of combustion stability can be avoided. Further, based on the combustion stability for each fuel injection mode, it is possible to set control that allows a richer air-fuel ratio. Further, fuel efficiency can be improved while realizing stable combustion according to the target air-fuel ratio.
Further, when the target air-fuel ratio in the first fuel injection mode becomes smaller than the first limit value, the mode is switched to the second fuel injection mode, so that the air-fuel ratio according to the driver's acceleration request is avoided while avoiding deterioration of combustion stability. There is an advantage that drivability can be improved.

Further, when the target air-fuel ratio in the second fuel injection mode becomes smaller than the second limit value, the target air-fuel ratio is clipped by the second limit value, so that the compression stroke injection mode is maintained and fuel efficiency is improved. Can do.
Further, after the switching to the second fuel injection mode, when the target air-fuel ratio becomes larger than the first limit value, the mode is switched to the first fuel injection mode, so that the fuel efficiency can be improved.

Further, since both the first limit value and the second limit value are set based on the engine speed and the load, fine control can be performed.
Further, when the engine speed and the load are in the overlapping region of the S / G combustion region and the W / G combustion region, the second fuel injection mode is selected based on the target air-fuel ratio, thereby improving fuel efficiency. be able to.

  Hereinafter, a fuel injection control device for a direct injection internal combustion engine according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic block diagram showing the functional configuration of the main part, and FIGS. FIG. 2 is a schematic diagram showing the main configuration of the internal combustion engine, FIG. 2 is a diagram for explaining the first fuel injection mode, FIG. 3 is a diagram for explaining the second fuel injection mode, and FIG. FIGS. 5A and 5B are diagrams showing operating regions in the first and second fuel injection modes, FIG. 5 is a diagram for explaining the characteristics of the first and second fuel injection modes, and FIG. 6 is a flowchart for explaining the operation thereof. .

As shown in FIGS. 2 and 3, the internal combustion engine (engine) applied to the present invention is a cylinder injection type internal combustion engine 1 in which fuel is directly injected into a cylinder and ignited. In the form, a gasoline engine is applied.
As shown in the figure, the combustion chamber 3 of the engine 1 is formed by the lower surface of the cylinder head 8, the wall surface of the cylinder 7, and the top surface of the piston 2. A fuel injection valve (hereinafter simply referred to as an injector) 4 is attached to the cylinder head 8. The injector 4 is arranged so that the tip side thereof faces the combustion chamber 3, and fuel is directly injected into the combustion chamber 3 from the injector 4.

On the other hand, the top surface of the piston 2 forming the lower surface of the combustion chamber 3 is formed with a recess (referred to as a cavity) 6 as shown in the drawing, and this recess 6 is curved downwardly in this embodiment. It is formed in a spherical shape. The shape of the recess 6 is not limited to a spherical surface, and various shapes can be applied.
A spark plug 5 is attached at a position slightly deviated from the center of the cylinder head 8. The injector 4 and the spark plug 5 have a fuel injection direction, a protruding amount of the spark plug 5 and the like so that at least the fuel supplied from the injector 4 can reach the tip of the spark plug 5 directly.

Incidentally, as shown in FIG. 1, the engine 1 is provided with an ECU (control means; controller) 11 for electrically controlling the overall operation.
Further, on the input side of the controller 11, an engine speed sensor (rotation speed detecting means) 15 for detecting the engine speed, an air flow sensor (AFS) 16 for detecting the intake air amount of the engine, and an accelerator for detecting the accelerator opening degree. An opening sensor (APS) 17 is connected. Although not shown, the controller 11 includes an engine load (an average effective effective pressure of the engine; engine) based on the engine speed Ne obtained by the engine speed sensor 15 and the accelerator opening obtained by the accelerator opening sensor. A load calculating means (load detecting means) for obtaining Pe is provided. The intake efficiency Ev may be obtained from the intake air amount obtained from the air flow sensor 16 and used as a load. Further, a throttle opening sensor or the like may be provided in place of the accelerator opening sensor 17, and the engine load may be detected based on detection information of these sensors.

Further, a fuel injection mode switching means 12 for switching the fuel injection mode is provided in the controller 11, and the engine speed Ne and the load Pe obtained by the engine speed sensor 15 and the accelerator opening sensor 17 described above. Based on this, the fuel injection mode is set by the fuel injection mode switching means 12.
Here, as shown in the figure, the fuel injection mode switching means 12 includes an intake stroke injection injector control means 13 that outputs an injector drive signal to the injector 4 at a timing suitable for intake stroke injection, and And a compression stroke injection control means 14 for outputting an injector drive signal at a timing suitable for the compression stroke injection.

  The fuel injection mode switching means 12 stores a map (not shown) with the engine speed Ne and the load Pe as parameters, and the fuel injection mode corresponding to these parameters is read from the map. The fuel injection mode is set. When a predetermined operating condition is established, the compression stroke injection mode is selected, and the intake stroke injection mode is selected otherwise. Here, the predetermined operating condition is that the throttle opening is a predetermined opening or less, the water temperature is warm (for example, 80 ° C. or more), the vehicle speed is a predetermined speed or less, the fuel pressure is a predetermined value or more, and the like.

When the compression stroke injection mode is selected, a control signal for the injector 4 is output from the compression stroke injection injector control means 14 to control the operation of the injector 4. In this case, fuel injection is performed during the compression stroke, and combustion is performed by forming a super lean air-fuel mixture as a whole in the combustion chamber.
When the intake stroke injection mode is selected, a control signal for the injector 4 is output from the intake stroke injection injector control means 13, and the operation of the injector 4 is controlled. In this case, fuel injection is performed during the intake stroke, and an air-fuel ratio mixture corresponding to the operating state of the engine 1 is formed in the combustion chamber and combustion is performed.

  The fuel injection mode is roughly classified into the compression stroke injection mode and the intake stroke injection mode as described above, and each of these modes is further provided with a plurality of different fuel injection modes. Of these, in the compression stroke injection mode (compression lean injection mode), fuel is injected toward the spark plug 5 when the piston 2 is in the vicinity of the compression stroke top dead center, and this fuel is directly ignited. 1 fuel injection mode (spray guide injection mode or S / G; see FIG. 2), and fuel is injected toward the recess 6 of the piston 2 before the top dead center of the compression stroke. A second fuel injection mode (referred to as a wall guide injection mode or W / G mode; see FIG. 3) for collecting and igniting fuel in the vicinity of the spark plug 5 is provided.

  Of these, the wall guide injection mode is an injection mode that realizes stable combustion at an ultra-lean air-fuel ratio by stratified combustion using an air flow formed in a cylinder. In this injection mode, as shown in FIG. 3, the combustion spray injected toward the recess 6 of the piston 2 is collected by the rise of the piston 2 and forms a relatively rich mixture near the tip of the spark plug 5. A substantially air-only layer is formed around the air-fuel mixture. Therefore, as a whole, good combustion can be realized while the air-fuel ratio is extremely lean (for example, A / F 20 to 25), and operation can be performed while saving fuel consumption.

Further, in the spray guide injection mode, as shown in FIG. 2, a layered lean state can be formed in the combustion chamber 3 by directly injecting fuel toward the spark plug 5. A stable combustion state can be obtained at an air / fuel ratio (for example, A / F 25 to 40) that is extremely leaner than that in the injection mode.
In the present embodiment, these two modes (spray guide injection mode and wall guide injection mode) can be switched by changing the timing of starting fuel injection.

  Incidentally, a spray guide injection mode executing means (first fuel injection mode setting means) 14a for setting a control signal for executing the spray guide injection mode for the injector 4 is provided in the compression stroke injection injector control means 14 of the controller 11. And an injection mode execution means (second fuel injection mode setting means) 14b for setting a control signal for executing the wall guide injection mode.

The controller 11 is also provided with a map for setting the fuel injection mode, for example, as shown in FIG. When fuel is injected in the compression stroke injection mode, either the spray guide injection mode or the wall guide injection mode is selected based on this map.
Here, the horizontal axis of the map shown in FIG. 4 is the engine rotational speed Ne, and the vertical axis is the load Pe. This map shows an area (S / G combustion area) that can be operated in the spray guide injection mode according to these parameters. ) And a region (W / G combustion region) that can be operated in the wall guide injection mode. Based on this map, the controller 11 sets the spray guide injection mode when the engine operating state is in the S / G combustion region, and sets the wall guide injection mode when it is in the W / G combustion region. To do. Further, when the engine operating state is in a region where the S / G combustion region and the W / G combustion region overlap in the figure, a spray guide injection mode with good fuel efficiency is basically selected. When the engine operating state is neither the S / G combustion region nor the W / G combustion region, intake stroke injection is selected.

When the fuel injection mode is thus set, the fuel injection mode switching means 12 of the controller 11 selects either the spray guide injection mode execution means 14a or the wall guide injection mode execution means 14b. When a different fuel injection mode is selected, the fuel injection mode is switched.
On the other hand, in the intake stroke injection mode, the fuel is premixed and the air-fuel ratio state of the entire combustion chamber is made uniform, and operation is performed so that stable ignition and reliable flame propagation can be realized and sufficient high output can be obtained. Stoichiometric mode in which the air-fuel ratio is close to the stoichiometric air-fuel ratio (stoichio), and a large output can be obtained; In addition, an enrichment mode or the like is provided in which the air-fuel ratio is temporarily concentrated (richer) than stoichiometric during sudden acceleration or the like.

Since the intake stroke injection mode has been widely known conventionally, the description of the intake stroke injection mode is omitted.
Next, the main part of the present invention will be described. As shown in FIG. 1, the controller 11 includes a first rich clip value setting means (first limit value setting means) 21 and a second rich clip value setting means (first 2 limit value setting means) 22.

Among these, the first rich clip value setting means 21 sets the limit value (referred to as the first limit value or the first rich clip value) A / F _LMT1 of the air-fuel ratio in the spray guide injection mode, Similarly, the second rich clip value setting means 22 sets an air / fuel ratio limit value (referred to as a second limit value or a second rich clip value) A / F _LMT2 in the wall guide injection mode. Here, the first rich clip value A / F _LMT1 is the limit air-fuel ratio on the rich side (over-rich side) of the air-fuel ratio (A / F) that can ensure stable combustion in the spray guide injection mode. The second rich clip value A / F _LMT2 is the limit air-fuel ratio on the rich side (over-rich side) of the air-fuel ratio (A / F) that can ensure stable combustion in the wall guide injection mode. For this reason, the rich clip value is also referred to as a rich limit.

In the spray guide injection mode, the rich air-fuel ratio is limited by the first rich clip value A / F _{LMT1, and further enrichment} is prohibited. Similarly, in the wall guide injection mode, the rich air-fuel ratio is limited by the second rich clip value A / F _{LMT2 and further enrichment} is prohibited.
The rich clip values A / F _LMT1 and A / F _LMT2 are set based on the engine speed sensor Ne and the load Pe, respectively.

  By the way, as already described above, the spray guide injection mode is a fuel injection mode capable of stable combustion at a leaner air-fuel ratio than the wall guide injection mode. This will be described with reference to the drawings. FIG. 5 is a diagram for explaining the characteristics of the spray guide injection mode and the wall guide injection mode. The horizontal axis indicates the fuel injection timing, and the vertical axis indicates the ignition timing. In the figure, regions where stable combustion can be obtained are shown for each air-fuel ratio (A / F).

As can be seen from FIG. 5, in the spray guide injection mode, the air-fuel ratio at which stable combustion can be obtained is about 25 to 40, and the combustion stable region becomes wider as the air-fuel ratio becomes leaner. On the other hand, in the wall guide injection mode, the air-fuel ratio at which stable combustion can be obtained is about 20 to 25, and the combustion stable region becomes wider as the air-fuel ratio becomes richer.
Therefore, here, the second rich clip value A / F _LMT2 for the wall guide injection mode is set to a smaller value (that is, the rich side) than the first rich clip value A / F _LMT1 for the spray guide injection mode. ing. That is, in the present embodiment, the wall guide injection mode is set to allow a richer air-fuel ratio than the spray guide injection mode based on the combustion stability for each fuel injection mode.

In this embodiment, when the target air-fuel ratio (control A / F) becomes rich during operation in the spray guide injection mode, the rich clip value A / F _LMT1 set by the first rich clip value setting means 11 is _reached. If a rich control is allowed and a control A / F smaller (rich) than the rich clip value A / F _LMT1 is required, the wall can be used if it is an operation region in which operation in the wall guide injection mode is possible. Switch to guide injection mode.

That is, in this case, referring to the map shown in FIG. 4, if the S / G combustion area and the W / G combustion area overlap, the operation in the wall guide injection mode is established. Switch from the guide injection mode to the wall guide injection mode.
When the requested control A / F is smaller than the second rich clip value A / F _LMT2 in the wall guide injection mode after switching to the wall guide injection mode (when rich), the control A / F is changed to the first control A / F. 2 Rich clip value A / F Limit (clip) with _LMT2 to restrict _{further enrichment} .

When the requested control A / F becomes larger than the first rich clip value A / F _LMT1 (when lean) after switching to the wall guide injection mode, the mode is again switched to the spray guide injection mode.
Further, when a control A / F smaller (rich) than the first rich clip value A / F _LMT1 is requested in the spray guide injection mode, and switching to the wall guide injection mode is not established. (That is, when the current operation state is outside the W / G combustion zone in the map of FIG. 4), the control A / F in the spray guide injection mode is limited by the first rich clip value A / F _LMT1 (clip ) And restrict further enrichment.

Since the fuel injection control device for a direct injection type internal combustion engine according to an embodiment of the present invention is configured as described above, its operation will be described with reference to the flowchart shown in FIG.
First, the engine speed Ne is taken in from the engine speed sensor 15 (step S1), and the volumetric efficiency Ev and the accelerator opening APS are taken in based on information from the airflow sensor 16 and the accelerator opening sensor 17 (step S2). Next, it is determined whether conditions (for example, water temperature, fuel pressure, etc.) other than the engine speed Ne and the load Pe when fuel is injected in the compression stroke injection mode (compression lean mode) are satisfied (step S3). ) If the condition of step S3 is not satisfied, the process returns.

On the other hand, if this condition is satisfied, it is determined whether or not the spray guide injection mode (represented as S / G) can be executed from the engine speed Ne and the load Pe (step S4). Specifically, in this step S4, it is determined from the map shown in FIG. 4 whether or not the current operation state (Ne, Pe) is within a region (S / G combustion region) operable in the spray guide injection mode. judge.
If it is determined in step S4 that the operation region is the spray guide injection mode, it is determined whether or not the flag is on (step S5). Moreover, if it determines with it not being in the driving | operation area | region in spray guide injection mode by step S4, it will progress to below-mentioned step S15.

  The flag in step S5 is a flag for switching between the spray guide injection mode and the wall guide injection mode. When the flag is turned on, the fuel injection mode is set to the wall guide injection mode. When the flag is turned off, the spray guide injection mode is set. Set to On / off of the flag is set in step S13 and step S24 described later, but the first routine is set to off. Accordingly, in the first routine, the process proceeds from step S5 to step S6, and in this step S6, the fuel injection mode is set to the spray guide injection mode.

Next, based on the engine speed Ne and the load Pe, an A / F correction coefficient (A / F coefficient) of the control A / F is obtained (step S7), and various other correction coefficients (warm-up correction coefficient, acceleration) A correction coefficient, an intake air temperature correction coefficient, and other coefficients are obtained (step S8), and a control A / F is calculated based on the following equation (step S9).
Control A / F = 14.7 / (A / F coefficient * warm air correction coefficient * acceleration correction coefficient * intake air temperature correction coefficient * other coefficients)
Next, the rich limit (first rich clip value or first limit value) A / F _LMT1 of the spray guide injection mode is obtained based on the engine speed Ne and the load Pe (step S10). The rich limit A / F _LMT1 may be obtained based on a map provided in the controller 11 or may be obtained based on a pre-stored calculation formula.

Then, the control A / F obtained in step S9 is compared with the rich limit A / F _LMT1 obtained in step S10 (step S11), and the control A / F is leaner (control than the rich limit A / F _LMT1). If A / F ≧ A / F _LMT1 ), the process returns as it is.
On the other hand, if the control A / F is richer than the rich limit A / F _LMT1 (control A / F <A / F _LMT1 ), the current engine operating state is the wall guide injection mode from the map shown in FIG. Is determined (step S12), and if it is within the wall guide injection mode region, the flag is turned on (step S13) and the process returns. If the current engine operating state is not within the wall guide injection mode region, the control A / F is set to the rich limit A / F _LMT1 (step S14).

That is, when the route of step S13 is passed, the routine is switched to the wall guide injection mode in the next and subsequent routines, and when the route of step S14 is passed, the control A / F is clipped to the rich limit A / F _LMT1. The
Next, the case where the current operation state (Ne, Pe) is outside the spray guide injection mode region (S / G combustion region) in step S4 described above and the case where it is determined that the flag is turned on in step S5 will be described. .

  First, in step SS4, if the current engine operation state is outside the spray guide injection mode region, in step S15, the engine operation state is within the wall guide injection mode region (W / G combustion region). If it is within the area of the wall guide injection mode, the process proceeds to step S16 and subsequent steps. If the area is outside the wall guide injection mode, the process returns. In this case, although not described in detail, the control enters the intake stroke injection mode control routine, and the intake stroke injection mode is executed.

  If it is determined in step S5 that the flag is on, the process proceeds to step S16. That is, when the control A / F in the spray guide injection mode becomes richer than the rich limit after step S6 described above, the process proceeds from step S5 to step S16 and subsequent steps in the next routine. In this case, since it is confirmed in step S12 of the immediately preceding routine that the wall guide injection mode can be established, the process proceeds to step S16 without passing through step S15.

Steps S16 to S21 correspond to steps S6 to S11 described above, and the same contents as steps S6 to S11 are executed and processed. That is, in steps S6 to S11, the control A / F and the rich limit (first rich clip value) A / F _LMT1 in the spray guide injection mode are obtained and the magnitudes of these values are compared. In S21, the control A / F and the rich limit (second rich clip value) A / F LMT2 in the wall guide injection mode are _obtained, and the magnitudes of these values are compared. Therefore, since description overlaps with step S16-S21 and step S6-S11 here, description of this part is abbreviate | omitted.

In step S21, if the control A / F in the wall guide injection mode is richer than the rich limit A / F _LMT2 (control A / F <A / F _LMT2 ), the control A / F is set to the rich limit. Clip to A / F _LMT2 (step S22). In this case, it is conceivable to change to intake stroke injection, but the compression stroke injection mode basically has better fuel efficiency than the intake stroke injection mode. It keeps and clips to the rich limit.

In step S21, if the control A / F in the wall guide injection mode is leaner than the rich limit A / F _LMT2 (control A / F ≧ A / F _LMT2 ), the rich in the spray guide injection mode. The limit A / F _LMT1 is compared with the control A / F, and the control A / F is leaner than the rich limit A / F _LMT1 in the spray guide injection mode (control A / F ≧ rich limit A / F _LMT1 ). If there is, the flag is turned off in step S24 and the process returns.

In other words, in this case, since the control A / F can obtain stable combustion even when the mode is switched to the spray guide injection mode, the mode is switched again to the spray guide injection mode having better fuel efficiency than the wall guide injection mode.
As described above in detail, according to the fuel injection control device for a direct injection internal combustion engine according to one embodiment of the present invention, the control A / F (target air-fuel ratio) in the spray guide injection mode is the rich limit (the first limit). 1 Limit value) A / F When it becomes richer (smaller) than _LMT1, it switches to the wall guide injection mode, so the air / fuel ratio can be set according to the driver's acceleration request while avoiding deterioration of combustion stability. There is an advantage that it is possible to improve the performance.

When the control A / F (target air-fuel ratio) in the wall guide injection mode becomes richer than the rich limit (second limit value) A / F _LMT2 , the control A / F is _clipped at the rich limit A / F _LMT2 . Therefore, the compression stroke injection mode is maintained without switching to the intake stroke injection mode, and fuel consumption can be improved.
Further, after switching to the wall guide injection mode, when the control A / F becomes leaner than the rich limit A / F _{LMT1 of} the spray guide injection mode (when it becomes larger), the control is switched to the spray guide injection mode. be able to.

Each of the rich limits (first and second rich clip values) A / F _LMT1 and A / F _LMT2 is set based on the engine speed Ne and the engine load Pe. It can be carried out.
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the case where the spray guide injection mode is applied as the first fuel injection mode and the wall guide injection mode is applied as the second fuel injection mode has been described. It is not necessary to apply the wall guide injection mode, and it is possible to apply the fuel injection modes of a plurality of different modes.

It is a typical block diagram which shows the function structure of the principal part of the fuel-injection control apparatus of the cylinder injection type internal combustion engine concerning one Embodiment of this invention. FIG. 3 is a schematic diagram showing a configuration of a main part of a direct injection internal combustion engine applied to the present invention, for explaining a first fuel injection mode. It is a schematic diagram which shows the principal part structure of the cylinder injection type internal combustion engine applied to this invention, Comprising: It is a figure for demonstrating 2nd fuel-injection mode. It is a figure which shows the operation area | region of the 1st and 2nd fuel injection mode of the fuel-injection control apparatus of the cylinder injection type internal combustion engine concerning one Embodiment of this invention. It is a figure for demonstrating the characteristic of the 1st and 2nd fuel injection mode of the fuel-injection control apparatus of the direct injection internal combustion engine concerning 1st Embodiment of this invention. It is a flowchart for demonstrating an effect | action of the fuel-injection control apparatus of the cylinder injection type internal combustion engine concerning one Embodiment of this invention. It is a figure which shows the change of the stable combustion area | region when an air fuel ratio fluctuates.

Explanation of symbols

1 engine (internal combustion engine)
2 Piston 3 Combustion chamber 4 Injector (fuel injection valve)
5 Spark plug 6 Recess 7 Cylinder 8 Cylinder head 11 Controller (control means)
Reference Signs List 12 fuel injection mode switching means 13 intake stroke injection injector control means 14 compression stroke injection injector control means 14a spray guide injection mode execution means (first fuel injection mode setting means)
14b Wall guide injection mode execution means (second fuel injection mode setting means)
DESCRIPTION OF SYMBOLS 15 Engine speed sensor 16 Airflow sensor 17 Accelerator opening sensor 21 1st rich clip value setting means (1st limit value setting means)
22 Second rich clip value setting means (second limit value setting means)

Claims (5)

When a predetermined operating condition is established, a compression stroke injection mode for injecting the fuel during the compression stroke of the internal combustion engine is executed, and as the compression stroke injection mode, fuel is directed toward the spark plug near the top dead center of the compression stroke. The fuel is injected at a timing earlier than the fuel injection timing of the first fuel injection mode during the compression stroke and the first fuel injection mode in which the fuel is directly ignited. A fuel injection control device for a direct injection internal combustion engine configured to be switchable between a second fuel injection mode that collects and ignites in the vicinity of a spark plug,
Fuel injection mode switching means for switching between the first fuel injection mode and the second fuel injection mode according to a target air-fuel ratio set according to operating conditions,
The fuel injection mode switching means includes an S / G combustion region defined as a region for selecting the first fuel injection mode on a map using the rotational speed of the internal combustion engine and the load of the internal combustion engine as parameters; It possesses a defined W / G combustion zone so as to overlap with the S / G fuel area as an area for selecting a fuel injection mode of the second on the map,
The fuel injection mode switching means
When the rotational speed of the internal combustion engine and the load of the internal combustion engine are located only in the S / G combustion region on the map, the first fuel injection mode is selected,
When the rotational speed of the internal combustion engine and the load of the internal combustion engine are located only in the W / G combustion region on the map, the second fuel injection mode is selected,
When the rotational speed of the internal combustion engine and the load of the internal combustion engine are in the overlapping region of the S / G combustion region and the W / G combustion region on the map, the first fuel is based on the target air-fuel ratio. A fuel injection control device for a direct injection internal combustion engine, wherein the injection mode and the second fuel injection mode are switched . The second fuel injection mode is set to a richer air-fuel ratio than the first fuel injection mode in the lean region,
The fuel injection mode switching means
First limit value setting means for setting a first limit value of the rich-side air-fuel ratio in the first fuel injection mode;
A second limit value setting means for setting a second limit value of the over-rich side air-fuel ratio in the second fuel injection mode with a value smaller than the first limit value;
The rotational speed of the internal combustion engine and the load of the internal combustion engine are in the overlapping region of the S / G combustion region and the W / G combustion region on the map, and the target air-fuel ratio is less than the first limit value . in some cases, wherein <br/> selecting a fuel injection mode of the second fuel injection control apparatus for a cylinder injection type internal combustion engine according to claim 1. The fuel injection mode switching means
Under the fuel injection mode of the second, the said purpose Shimegisora ratio is smaller than the second limit value, clips the target air-fuel ratio while maintaining the fuel injection mode of the second to the second limit value The fuel injection control device for a cylinder injection type internal combustion engine according to claim 2, wherein the fuel injection control device is a cylinder injection type internal combustion engine. The fuel injection mode switching means
Under the second fuel injection mode , the rotational speed of the internal combustion engine and the load of the internal combustion engine are in the overlapping region of the S / G combustion region and the W / G combustion region on the map, and the target The in-cylinder injection type according to any one of claims 1 to 3, wherein the first fuel injection mode is selected when the air-fuel ratio is equal to or higher than the first limit value. A fuel injection control device for an internal combustion engine. A rotational speed detection means for detecting the rotational speed of the internal combustion engine;
Load detecting means for detecting the load of the internal combustion engine;
The first limit value setting means and the second limit value setting means are both configured based on the rotation speed detected by the rotation speed detection means and the load detected by the load detection means. The fuel injection control device for a direct injection internal combustion engine according to claim 2 or 3, wherein the second limit value is set.

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