JP4363386B2 - 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 mainly injected in an intake stroke are set to be switchable. Yes. Of these, the compression stroke injection mode (compression lean injection mode) is a mode in which fuel is injected when the piston rises or ends, and when the piston is near the top dead center of the compression stroke, the fuel is injected toward the spark plug. The injection mode (spray guide injection mode) in which the fuel is injected and fuel is supplied to the spark plug by the fuel injection force (penetration force) and the fuel is directly ignited, and before the top dead center of the compression stroke, There is known a mode (wall guide injection mode) in which fuel is injected toward the concave portion, and fuel is collected in the vicinity of the spark plug by the rise of the piston and ignited.

  Also, in the intake stroke injection mode, the fuel is premixed and the air-fuel ratio of the entire combustion chamber is made uniform, and stable ignition and reliable flame propagation are realized to obtain a sufficiently high output. Can do. In the intake stroke injection mode, the stoichiometric mode in which a large output is obtained with the air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio (stoichio), and the air-fuel ratio is made leaner (for example, A / F 15 to 20) than the stoichiometric. There are provided a lean mode for improving the fuel consumption, an enrich mode for temporarily enriching the air-fuel ratio more than that of stoichiometric during sudden acceleration or the like.

In such an in-cylinder injection engine, the compression stroke injection mode (compression lean mode), the intake stroke injection stoichiometric mode (stoichio mode), the intake stroke injection lean mode (intake) based on the engine speed and the engine load. Each operation mode such as a lean mode and an intake stroke injection rich mode (enrich mode) is switched.
Further, in Patent Document 1 below, as a compression stroke injection mode, a first operation mode in which fuel is ignited before colliding with a piston during fuel injection or immediately after fuel injection, and fuel that has passed through the piston after fuel injection is completed. And a second operation mode for igniting the engine, and a technique for switching these operation modes in accordance with the engine operation state is disclosed.
JP 2004-353594 A

By the way, in the spray guide injection mode described above, combustion can be performed with a leaner air-fuel ratio than in the wall guide injection mode, and thus there is an advantage that fuel consumption is good. Therefore, there is a desire to operate in the spray guide injection mode as much as possible during the operation of the engine.
However, the spray guide injection mode has a problem that the combustion stability tends to fluctuate with respect to a change in fuel pressure (hereinafter referred to as fuel pressure), and it is difficult to always operate the engine stably. Hereinafter, the combustion stability in the spray guide injection mode will be briefly described with reference to the drawings. FIG. 11 is a diagram illustrating the combustion stability characteristics in the spray guide injection mode in the idle operation (no-load operation). In the figure, the vertical axis represents the ignition timing, and the horizontal axis represents the injection timing.

In the figure, the region surrounded by the closed curve is a region where stable combustion can be realized (stable combustion region), and this region changes when the fuel pressure varies. In particular, in the idle operation in the spray guide injection mode, the stable combustion region becomes narrower as the fuel pressure becomes higher, and the stable combustion region becomes wider as the fuel pressure becomes lower.
Therefore, a low fuel pressure is required to realize stable combustion in the spray guide injection mode during idle operation. However, in the operation region other than the idle operation, a relatively high fuel pressure (corresponding to the high fuel pressure in FIG. 11) is required to establish the spray guide injection mode. It is necessary to reduce the fuel pressure when shifting from idling to idling.

  However, even when the fuel pressure is decreased during idle operation from other than idle operation, the fuel pressure cannot be decreased quickly due to a control delay or the like. There is a case where the mode is shifted to the injection mode. In such a case, since the combustion stable region is narrow as described above, there is a risk of misfire in some cases.

  The present invention has been devised in view of such problems, and is directed to an in-cylinder injection internal combustion engine that prevents misfire during idle operation and ensures the operational reliability of the engine (internal combustion engine). An object is to provide a fuel injection control device.

  A fuel injection control device for a cylinder injection type internal combustion engine according to the present invention is a fuel injection control device for a cylinder injection type internal combustion engine in which fuel is directly injected into a cylinder and ignited by a spark plug. A first fuel injection mode (spray guide) in which fuel is injected toward the spark plug in the vicinity of the top dead center of the stroke, and fuel is supplied to the spark plug by the injection force of the fuel and ignited; A second fuel injection mode in which fuel is injected at a timing earlier than the fuel injection timing of the first fuel injection mode, and the fuel is collected in the vicinity of the spark plug and ignited by raising the piston along the top surface of the piston ( And a fuel pressure detecting means for detecting or estimating the pressure of the injected fuel, the switching means comprising the internal combustion engine. Switching the fuel injection mode between the first fuel injection mode and the second fuel injection mode in accordance with the fuel pressure detected or estimated by the fuel pressure detecting means in the low load operation region. It is characterized (claim 1).

Further, it is preferable to prohibit the first fuel mode when the fuel pressure is equal to or higher than a predetermined pressure.
And an idle operation detecting means for detecting or determining an idle operation of the internal combustion engine, wherein the switching means changes the operation state of the internal combustion engine from an idle operation to an idle operation based on information from the idle operation detection means. When the change is detected or determined, if the fuel pressure detected or estimated by the fuel pressure detecting means is equal to or higher than a predetermined pressure, the first fuel injection mode is prohibited and the fuel injection mode is changed to the first fuel injection mode. The fuel injection mode may be switched to the second fuel injection mode (claim 3).

  The vehicle further includes vehicle speed detecting means for detecting the speed of the vehicle on which the internal combustion engine is mounted, idle operation detecting means for detecting or determining the idle operation, and fuel pressure adjusting means for adjusting the fuel pressure. When it is determined that the operation state of the internal combustion engine has been changed from idle operation to idle operation based on information from the driving detection means, and when stop of the vehicle is detected or determined based on information from the vehicle speed detection means, the The fuel pressure adjusting means lowers the fuel pressure so that the fuel pressure becomes less than the predetermined pressure, and the switching means prohibits the first fuel injection mode until the fuel pressure becomes less than the predetermined pressure, and changes the fuel injection mode to the fuel pressure. The second fuel injection mode may be set (claim 4).

According to the fuel injection control device for a direct injection internal combustion engine of the present invention, the first fuel injection mode and the second fuel injection mode are switched according to the fuel pressure in the low load operation region of the internal combustion engine. , The combustion is stable and misfire can be avoided. Therefore, there exists an advantage which can improve the driving | operation reliability of an engine (Claims 1-3).
Further, there is an advantage that fuel consumption can be improved while reliably avoiding an engine stall during traveling of the vehicle (claim 4).

Hereinafter, embodiments of the present invention will be described.
First, a fuel injection control apparatus for a direct injection internal combustion engine according to a first 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, FIG. FIG. 3 is a schematic diagram showing the configuration of the main part of the internal combustion engine. FIG. 2 is a diagram for explaining the spray guide injection mode, FIG. 3 is a diagram for explaining the wall guide injection mode, and FIG. FIG. 5 is a flowchart for explaining the operation thereof, FIG. 6 is a diagram for explaining the combustion stability in each fuel injection mode, and FIG. 7 is a map for setting the fuel injection mode. .

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.

  A fuel supply path 9 is provided between the injector 4 and a fuel tank (not shown), and a low pressure fuel pump, a variable fuel pressure pump (high pressure fuel pump) 10 and the like (not shown) are interposed on the fuel supply path 9. ing. A delivery pipe 9a for supplying fuel to each cylinder is provided downstream of the variable fuel pressure pump 10, and the delivery pipe 9a is connected to a branch passage 9b branched for each cylinder. Each branch passage is connected to the injector 4 of each cylinder.

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 displaced 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 electronically controlling the overall operation. Further, on the input side of the controller 11, an engine speed sensor 15 for detecting the engine speed, an air flow sensor (AFS) 16 for detecting the intake flow rate, a fuel pressure sensor (fuel pressure detecting means) 30 for detecting the fuel pressure, and an accelerator. An accelerator opening sensor 31 for detecting the opening is connected. Here, since the controller 11 can detect the idling operation based on the accelerator opening obtained by the accelerator opening sensor 31, the accelerator opening sensor 31 can be referred to as an idling operation detecting means. Further, the engine load is detected based on the accelerator opening, and the accelerator opening sensor 31 can also be referred to as load detecting means. An idle switch that detects whether the accelerator is fully closed may be provided as the idle operation detection means. Further, the engine load may be obtained based on the intake air flow rate obtained by the air flow sensor (AFS) 16, and in this case, the air flow sensor 16 functions as a load detection means.

The controller 11 is provided with fuel injection mode switching means 12 for switching the fuel injection mode. Based on the information obtained from the sensors 15, 16, 30, 31, the fuel injection mode is switched. The fuel injection mode is set by the 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 (see FIG. 7) using the engine speed Ne and the load Pe as parameters, and basically the fuel injection mode corresponding to these parameters is determined from the map. It is read out and 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 conditions are that the throttle opening is below a predetermined opening (low load), the engine speed is below a predetermined speed (low rotation), the water temperature is warm (for example, 80 ° C. or higher), and the fuel pressure is More than a predetermined value.

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 mixture as a whole in the combustion chamber.
Here, in the compression stroke injection mode (compression lean injection mode), when the piston 2 is in the vicinity of the compression stroke top dead center, fuel is injected toward the spark plug 5 and the fuel is directly ignited. Spray guide injection mode (refer to FIG. 2) as the fuel injection mode 1 and fuel is injected toward the concave portion 6 of the piston 2 before the top dead center of the compression stroke. A wall guide injection mode (see FIG. 3) is provided as a second fuel injection mode that is collected in the vicinity and ignited.

  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, as shown in FIG. It is possible to operate at a super lean air / fuel ratio (for example, A / F 25 to 40) as compared with the wall guide injection mode in which fuel is injected toward the recess 6 of the piston 2 before the top dead center of the compression stroke. Therefore, this spray guide injection mode has an advantage that fuel efficiency is very good.

In the wall guide injection mode, fuel with a good ignitability is collected in the vicinity of the spark plug to form a layered mixture in the cylinder, and as a whole, the air / fuel ratio is extremely lean (for example, A / F 20 to 25). ).
On the other hand, when the intake stroke injection mode is selected, a control signal for the injector 4 is output from the intake stroke injector control means 13 to control the operation of the injector 4. In this case, fuel injection is performed during the intake stroke, and an air-fuel ratio air-fuel mixture corresponding to the operating state of the engine 1 is formed in the combustion chamber and combustion is performed.

  In the intake stroke injection mode, it is possible to achieve stable ignition and reliable flame propagation to achieve a sufficiently high output while making the air-fuel ratio of the entire combustion chamber uniform by premixing the fuel. , Stoichiometric mode in which the air-fuel ratio is close to the stoichiometric air-fuel ratio (stoichio) and a large output can be obtained, and an enrichment mode in which the air-fuel ratio is temporarily made richer than stoichio during sudden acceleration, etc. Is provided. In the intake stroke injection mode, either the stoichiometric mode or the enriched mode is selected from the map shown in FIG. 7 according to the engine speed Ne and the load Pe.

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 described above, in the spray guide injection mode, combustion is possible at an ultra-lean air-fuel ratio, and thus there is an advantage that fuel consumption is good. For this reason, there is a desire to operate in the spray guide injection mode as much as possible during the operation of the engine 1, but in the spray guide injection mode, a relatively high fuel pressure is required except for the idle operation, and a low fuel pressure is required during the idle operation. For this reason, it is necessary to lower the fuel pressure when shifting from idle operation to idle operation in the spray guide injection mode.

  Here, S / G shown in FIG. 6 indicates the combustion stability characteristic of the spray guide injection mode during idle operation, and the combustion stable region at high fuel pressure (required fuel pressure during non-idle operation) is It is found that it is narrower than the combustion stable region at low fuel pressure (required fuel pressure during idle operation), and it is difficult to obtain stable combustion when the spray guide injection mode is executed at high fuel pressure during idle operation.

  For this reason, it is necessary to quickly reduce the fuel pressure when shifting from the non-idle operation to the idle operation, but the fuel pressure does not decrease quickly due to a delay in the control of the variable fuel pressure pump 10, and the fuel pressure is thereby sufficiently increased. There is a case where the mode is shifted to the spray guide injection mode of the idle operation without being lowered. In such a case, if the fuel pressure is not reduced to the required pressure as described above, combustion may become unstable and misfire may occur.

  On the other hand, as shown in FIG. 6, in the wall guide injection mode (see W / G in the figure), a stable combustion region is wide even at high fuel pressure during idle operation, and relatively stable operation is possible. Become. Therefore, it is necessary to properly use the spray guide injection mode and the wall guide injection mode depending on the fuel pressure during idle operation. Therefore, in the fuel injection control device according to the present embodiment, when it is determined that the spray guide injection mode has shifted from the idle operation to the idle operation, the fuel pressure (fuel pressure) is focused as an index indicating the combustion stability. If the fuel pressure is equal to or higher than a predetermined pressure value, the spray guide injection mode is temporarily prohibited, and the wall guide injection mode with high combustion stability is switched instead. Further, when it is determined that the fuel pressure has decreased to a predetermined pressure value, the spray guide injection mode is restored.

  Hereinafter, in detail, the controller 11 determines that the engine 1 has become idle operation (low-load operation) when accelerator-off is detected based on information from the accelerator opening sensor 31 during execution of the spray guide injection mode. To do. At this time, the pressure of the fuel supplied from the high-pressure pump 10 decreases to establish the spray guide injection mode in the idle operation, but this fuel pressure does not decrease rapidly, so that the spray guide injection is still performed at the time of idling determination. It does not drop to a pressure sufficient to establish the mode.

  Therefore, the controller 11 determines whether or not the fuel pressure has decreased to a predetermined pressure (or a predetermined value) P1 at which the spray guide injection mode is reliably established, based on information from the fuel pressure sensor 30, and the fuel pressure is predetermined. If the pressure value is equal to or greater than the pressure value P1, the spray guide injection mode (first fuel injection mode) is prohibited and the wall guide injection mode (second fuel injection mode) is set even when the engine 1 is idling. It is like that.

When the fuel pressure becomes less than the predetermined pressure value P1, the wall guide injection mode is switched to the spray guide injection mode again.
Contrary to the above, the second predetermined pressure value P2 (≧ P1) at which the spray guide injection mode is reliably established other than the idle operation also when the operation is shifted from the idle operation to the non-idle operation in the spray guide injection mode. Until this is the case, the spray guide injection mode is prohibited and the engine is operated in the wall guide injection mode. The fuel pressure is increased when shifting from idle operation to non-idle operation, but due to the characteristics of the high-pressure pump 10, the fuel pressure changes more quickly when the normal fuel pressure is increased than when the fuel pressure is decreased. Therefore, when shifting from idle operation to other than idle operation, it is not necessary to execute the prohibition of the spray guide injection mode as described above.

Since the fuel injection control apparatus for a direct injection internal combustion engine according to the first embodiment of the present invention is configured as described above, its operation will be described with reference to the flowchart of FIG.
First, the engine speed Ne and the load information Pe are captured (steps S1 and S2), and then it is determined whether or not the compression stroke injection mode permission water temperature (lean permission water temperature) is equal to or higher (step S3). Here, if it is less than the compression stroke injection mode permission water temperature, the compression stroke injection mode (compression lean mode) is prohibited, and the fuel injection mode is set to the stoichiometric mode or the enrich mode (step S4).

  On the other hand, if it is equal to or higher than the compression stroke injection mode permission water temperature, it is next determined whether or not it is in a lean operation possible range (step S5). That is, the current rotational speed Ne and load Pe are applied to a map (see FIG. 7) stored in the controller 11, and it is determined whether or not the engine is in the lean operation region (operation region in the compression stroke injection mode). And if it is out of a lean driving | operation area | region, it will progress to step S4 mentioned above, and will drive | operate in stoichiometric mode or rich mode.

  On the other hand, if the engine is in the lean operation range, it is determined whether or not the engine speed Ne is smaller than the predetermined speed and the load Pe is smaller than the predetermined load (step S6). Here, when the engine speed Ne is smaller than the predetermined speed and the load Pe is smaller than the predetermined load, the engine operating state is within the operating range of the compression stroke injection mode in FIG. Accordingly, it is determined that the fuel injection mode can be changed within the operation range, that is, the idle operation region.

In this case, it is determined whether the fuel pressure is lower than the predetermined pressure or higher than the predetermined pressure (step S7). If the fuel pressure is lower than the predetermined pressure, the spray guide (S / G) injection mode is set (step S8). If the pressure is equal to or higher than the predetermined pressure, the wall guide (W / G) injection mode is set (step S9) and the process returns.
In step S6, if the engine speed Ne is equal to or higher than the predetermined speed or the load Pe is equal to or higher than the predetermined load, the process proceeds to step S8 without passing through step S7, and the spray guide (S / G) Set to injection mode and return. That is, in this case, since the fuel pressure is set high and the stable combustion can be achieved even in the spray guide injection mode, the fuel pressure is fixed to the spray guide injection mode.

This will be specifically described with reference to the time chart shown in FIG. 4. When the driver starts to return the accelerator (throttle) as shown in FIG. 4D while the engine 1 is operating in the spray guide injection mode ( In response to this, the volumetric efficiency Ev of the intake air decreases and the fuel pressure gradually decreases (see FIGS. 4B and 4C).
Thereafter, when the volume efficiency Ev becomes such that combustion stability cannot be maintained in the spray guide injection mode in the low load range, or when it is determined as the idle operation range (t = t2), the fuel pressure at this time is equal to or higher than the predetermined pressure P1. The spray guide injection mode is prohibited, and the wall guide injection mode is executed instead of the spray guide injection mode. When the fuel pressure becomes less than P1, the fuel injection mode is switched from the wall guide mode to the spray guide injection mode again (t = t3).

  As described above in detail, according to the fuel injection control device for a direct injection internal combustion engine according to the first embodiment, when the spray guide injection mode shifts from the non-idle operation to the idle operation, the stable combustion state The spray guide injection mode is prohibited and the wall guide injection mode is switched to the wall guide injection mode until the fuel pressure is reduced to the predetermined fuel pressure that can ensure the fuel pressure, so that the combustion is stable when shifting from idle operation to idle operation and avoids misfire. can do. Therefore, the operation reliability of the engine can be improved. Further, when the fuel pressure becomes equal to or lower than the predetermined fuel pressure P1, the operation is switched to the spray guide injection mode again, so that an operation with good fuel efficiency can be realized while realizing stable combustion.

  Further, when the spray guide injection mode is shifted from the idle operation to the non-idle operation, the spray guide injection mode is used until the spray guide injection mode is reliably established in the non-idle operation until the second predetermined pressure value P2 is reached. Is prohibited and the engine is operated in the wall guide mode, the combustion during the transition from idle operation to non-idle operation can be stabilized and misfire can be avoided. Driving reliability can be improved.

  Next, a second embodiment of the present invention will be described. FIG. 8 is a schematic block diagram showing the functional configuration of the main part. Now, in this 2nd Embodiment, the switching conditions to wall guide injection mode differ from 1st Embodiment, and other than this is the same. Therefore, below, a different part from 1st Embodiment is mainly demonstrated, the code | symbol same as 1st Embodiment is quoted in the part comprised similarly, and the overlapping description is abbreviate | omitted as much as possible.

  In the internal combustion engine fuel injection control apparatus according to the second embodiment, as in the first embodiment, the fuel injection mode of the engine 1 is set to the compression stroke injection mode when a predetermined operating condition is satisfied. Yes. In the compression stroke injection mode, fuel injection is basically performed in the spray guide injection mode, and the mode is switched to the wall guide injection mode according to the operating state of the engine 1.

That is, as in the first embodiment, a controller (control means) 11 is attached to the engine 1 as shown in FIG. 8, and information from the engine speed sensor 15, the airflow sensor 16, and the like is provided in the controller 11. Based on this, the fuel injection mode is switched.
In addition to the sensors described in the first embodiment, a vehicle speed sensor (vehicle speed detection means) 32 that detects the speed of the vehicle is connected to the input side of the controller 11 as shown in FIG. Vehicle speed information is input to the controller 11 from this vehicle speed sensor.

  And in this 2nd Embodiment, at the time of execution of spray guide injection mode, based on the information from the accelerator opening sensor 31, the accelerator-off is detected and the engine 1 is determined to be in idle operation (low load operation). Then, the fuel pressure is switched to a low fuel pressure by the variable fuel pressure pump 10 on the condition that the vehicle speed = 0 (vehicle stop) (fuel pressure adjusting means). The fuel pressure adjusting means may be a regulator provided in a return passage for returning the fuel supplied to the delivery pipe 9a to the fuel tank. Then, the pressure of the fuel is detected, and if the fuel pressure is equal to or higher than the predetermined pressure P1, the spray guide injection mode is prohibited and the wall guide injection mode is executed. When the fuel pressure becomes less than the predetermined pressure value P1, The wall guide spray mode is switched to the spray guide spray mode again.

  That is, even when the vehicle is shifted to the idle operation region due to the accelerator being off, the fuel injection is executed in the wall guide injection mode (second fuel injection mode) having a wide stable combustion region without lowering the fuel pressure when the vehicle is traveling. When the vehicle stops traveling, the fuel pressure is switched to a low fuel pressure. Thereafter, the wall guide injection mode or the spray guide injection mode is selected based on the fuel pressure.

As described above, in the second embodiment, the conditions relating to the vehicle speed are further added to the first embodiment described above, and when idling (accelerator is off), the spray guide injection is performed if the vehicle is running. The mode is prohibited and the spray guide injection mode can be executed only when the stop of the vehicle is detected.
This is to avoid the spray guide injection mode in idle operation as much as possible during vehicle travel. That is, the spray guide injection mode has better fuel efficiency than the wall guide injection mode, but the wall guide injection mode is more reliable in terms of combustion stability during idle operation. On the other hand, it is necessary to reliably avoid engine stall while the vehicle is running.

  Therefore, in the second embodiment, even when the engine operating state shifts to idle operation, switching to a low fuel pressure is prohibited if the vehicle is traveling, and spray guide injection is performed during idle operation while the vehicle is traveling. The mode is avoided. Also, if the vehicle is stopped, even if an engine stall occurs, the safety of the vehicle will not be impaired. In this case, switch to a low fuel pressure so that the spray guide injection mode is established immediately. The operation is performed in the spray guide injection mode as much as possible.

Since the fuel injection control device for a direct injection internal combustion engine according to the second embodiment of the present invention is configured as described above, its operation will be described with reference to the flowchart of FIG.
First, the engine speed Ne, the accelerator opening, the vehicle speed, and the fuel pressure are sequentially taken from each sensor (steps S11 to S14). Next, it is determined whether or not the compression stroke injection mode permission water temperature is equal to or higher (step S15). If the compression stroke injection mode permission water temperature is lower than the compression stroke injection mode permission water temperature, normal control excluding the compression stroke injection mode (compression lean mode) is executed. (Step S16). That is, in this case, the compression stroke injection mode is prohibited and either the stoichiometric mode or the rich mode is selected.

  On the other hand, if the compression stroke injection mode permission water temperature or higher, it is next determined whether the accelerator is fully closed (idle operation) (step S17). If the accelerator is not fully closed, normal control including the compression stroke injection mode is performed. (Step S18). That is, in this case, the current rotation speed Ne and the load Pe are applied to a map (see FIG. 7) stored in the controller 11, and the fuel injection mode corresponding to the operation state is set. If it is determined in step S17 that the accelerator is fully closed, it is then determined whether the vehicle is stopped based on the vehicle speed (step S19).

  When it is determined that the vehicle is stopped, the fuel pressure is switched to a low fuel pressure to establish spray guide injection (step S20). Next, the current fuel pressure is compared with a predetermined fuel pressure P1 at which the spray guide injection mode is established (step S21). If the fuel pressure is equal to or greater than the predetermined value P1, the spray guide injection mode is prohibited and the wall guide injection mode is set. On the other hand, if it is determined that the fuel pressure has become less than the predetermined fuel pressure P1, the fuel injection mode is switched to the spray guide injection mode (step S23).

  If it is determined in step S19 that the vehicle is traveling, the fuel pressure is set to a high fuel pressure for normal control (step S24). Next, it is determined whether or not a predetermined fuel cut permission condition is satisfied (step S25). If the fuel cut permission condition is satisfied, the fuel cut mode is executed (step S26). If the fuel cut permission condition is not satisfied, it is determined whether or not the current engine speed Ne is less than a predetermined speed (step S27), and if it is less than the predetermined speed, the wall guide injection mode is set. (Step S22) If the engine speed Ne is equal to or higher than the predetermined speed, the spray guide injection mode is set (Step S28). In other words, if the accelerator is fully closed (idle operation), the vehicle is running, and the fuel cut prohibition condition is satisfied, the spray guide injection mode up to that point can be used as long as it is in a relatively high rotation range. Is maintained. This is because the wall guide injection mode is not established in the low rotation range, or stable combustion cannot be obtained in the low rotation range. On the other hand, since the wall guide injection mode is established if the rotation is relatively low, the wall guide injection mode is set if the rotation is less than the predetermined rotation.

  This will be specifically described with reference to the time chart shown in FIG. 9. First, when the vehicle is traveling in the spray guide injection mode, the accelerator is returned and the throttle is fully closed as shown in FIG. 9 (e) (t = t1) At this time, as shown in FIG. 9 (f), since the vehicle is running (vehicle speed ≠ 0), the fuel pressure is maintained at a high fuel pressure (see FIG. 9 (a)). At this time, if the fuel cut condition is satisfied, the fuel injection mode is entered and the fuel injection is stopped (see FIG. 9C). Therefore, as shown in FIG. 9B, the air-fuel ratio (A / F) is maximized.

After that, as shown in FIG. 9D, when the engine speed Ne decreases and the fuel cut condition is not satisfied (t = t2), the fuel injection is resumed. At this time, since the vehicle is still running, the fuel pressure is maintained at a high fuel pressure, whereby the wall guide injection mode is set as the fuel injection mode.
When the vehicle speed becomes 0, the fuel pressure is switched to a low fuel pressure (t = t3). After that, when the fuel pressure reaches a predetermined low fuel pressure P1, it is switched again to the spray guide injection mode with good fuel efficiency (t = t4).

  In other words, the spray guide injection mode provides stable fuel at high fuel pressure when the engine speed is relatively high, but if the engine speed decreases, combustion stability decreases at high fuel pressure and low fuel pressure is required. Two points: low fuel pressure spray-guided injection mode is better than wall-guided injection mode at high fuel pressure at low revolutions, but wall-guided injection mode is superior in combustion stability Therefore, the wall guide injection mode and the spray guide injection mode are switched in the operation region of the compression stroke injection mode.

  Specifically, when the vehicle enters the operating range of the compression stroke injection mode, the vehicle is operated in the spray guide injection mode, which stably burns at high fuel pressure and has good fuel efficiency, and the engine speed decreases to idle operation. When the vehicle is running, the high fuel pressure is maintained for the purpose of reliably avoiding the engine stall while the vehicle is running and the wall guide injection mode with high combustion stability is set. At the same time, the fuel injection is executed in the spray guide injection mode.

Therefore, according to the fuel injection control device for a direct injection internal combustion engine according to the second embodiment of the present invention, in addition to the same advantages as those of the first embodiment, it is possible to reliably avoid an engine stall during traveling of the vehicle, and to reliably There is an advantage that a highly reliable fuel injection control device can be provided.
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 second embodiment, the vehicle stop is not necessarily limited to the vehicle speed = 0, and may be determined to be a vehicle stop if the vehicle speed is equal to or lower than a predetermined vehicle speed (for example, 2 km / h).

It is a typical block diagram which shows the function structure of the principal part of the fuel-injection control apparatus of the direct injection internal combustion engine which concerns on 1st Embodiment of this invention. It is a mimetic diagram showing the important section composition of the direct injection internal combustion engine to which the 1st embodiment of the present invention is applied, and is a figure for explaining spray guide injection mode. FIG. 2 is a schematic diagram illustrating a configuration of a main part of a direct injection internal combustion engine to which the first embodiment of the present invention is applied, and is a view for explaining a wall guide injection mode. It is a time chart for demonstrating an effect | action of the fuel-injection control apparatus of the direct injection internal combustion engine which concerns on 1st Embodiment of this invention. It is a flowchart for demonstrating the fuel-injection control apparatus of the direct injection internal combustion engine which concerns on 1st Embodiment of this invention. It is a figure explaining the effect | action of the fuel-injection control apparatus of the direct injection internal combustion engine which concerns on 1st Embodiment of this invention, Comprising: It is a figure explaining the combustion stability in each fuel-injection mode. It is a figure explaining the effect | action of the fuel-injection control apparatus of the direct injection internal combustion engine which concerns on 1st Embodiment of this invention, Comprising: It is a map for setting a fuel-injection mode. 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 which concerns on 2nd Embodiment of this invention. It is a time chart for demonstrating an effect | action of the fuel-injection control apparatus of the direct injection internal combustion engine which concerns on 2nd 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 which concerns on 2nd Embodiment of this invention. It is a figure for demonstrating the combustion stability in the compression stroke injection in an idle driving | operation.

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 15 engine speed sensor (engine speed detection means)
16 Air flow sensor (intake air amount detection means)
30 Fuel pressure sensor (Fuel pressure detection means)
31 Accelerator opening sensor (idle operation detection means)
32 Vehicle speed sensor (vehicle speed detection means)

Claims (4)

A fuel injection control device for an in-cylinder injection internal combustion engine in which fuel is directly injected into a cylinder and ignited by an ignition plug,
A first fuel injection mode in which fuel is injected toward the spark plug near the top dead center of the compression stroke of the internal combustion engine, and fuel is supplied to the spark plug by the fuel injection force to ignite, and during the compression stroke Second fuel injection mode in which fuel is injected at a timing earlier than the fuel injection timing in the first fuel injection mode, and the fuel is collected in the vicinity of the spark plug and ignited by raising the piston along the top surface of the piston. Switching means capable of switching between, and
Fuel pressure detecting means for detecting or estimating the pressure of the injected fuel,
The switching means has the first fuel injection mode and the second fuel injection mode according to the fuel pressure detected or estimated by the fuel pressure detecting means when the operating range of the internal combustion engine is a low load operating range. And a fuel injection control device for a direct injection internal combustion engine. 2. The fuel injection control device for a direct injection type internal combustion engine according to claim 1, wherein when the fuel pressure detected or estimated by the fuel pressure detecting means is equal to or higher than a predetermined pressure, the first fuel mode is prohibited. Comprising idle operation detecting means for detecting or judging the idle operation of the internal combustion engine,
The switching means is
Based on information from the idle operation detection means, it is detected or determined that the operating state of the internal combustion engine has been changed from idle operation to idle operation, and the fuel pressure detected or estimated by the fuel pressure detection means is 3. The in-cylinder injection type according to claim 2, wherein when the pressure is determined to be equal to or higher than a predetermined pressure, the first fuel injection mode is prohibited and the fuel injection mode is switched to the second fuel injection mode. A fuel injection control device for an internal combustion engine. Vehicle speed detecting means for detecting the speed of a vehicle on which the internal combustion engine is mounted;
Idle operation detecting means for detecting or determining the idle operation;
Fuel pressure adjusting means for adjusting the pressure of the fuel;
With
When it is determined that the operation state of the internal combustion engine has been changed from idle operation to idle operation based on information from the idle operation detection means, and when the stop of the vehicle is detected or determined based on information from the vehicle speed detection means,
The fuel pressure adjusting means reduces the fuel pressure so that the fuel pressure is less than a predetermined pressure,
The switching means prohibits the first fuel injection mode until the fuel pressure becomes less than a predetermined pressure, and sets the fuel injection mode to the second fuel injection mode. 3. A fuel injection control device for a direct injection internal combustion engine according to 2.

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