JP2005061271A - Cylinder direct injection type internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cylinder direct injection type internal combustion engine sufficiently reducing the adhesion of fuel to a wall surface while keeping the homogeneity of an air-fuel mixture when performing intake stroke injection. <P>SOLUTION: A period (1) when fuel spray is directed to a boundary between the bottom surface section of a cavity and the side surface section thereof, a period (2) when fuel spray is directed to the side surface section of the cavity, and a period (3) when fuel spray is directed to a clearance between a piston head and a cylinder inner wall, are set as an injection suspension period when fuel injection is performed during intake stroke. In the case that the injection suspension periods (1) to (3) are included in a fuel injection period calculated according to an engine speed/accelerator opening, a part of injection falling on the injection suspension period is transferred to the end of the injection period, and fuel injection is performed at a plurality of times after the injection suspension period. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an in-cylinder direct injection internal combustion engine, and more particularly to a technique for improving fuel injection control during an intake stroke.

2. Description of the Related Art Conventionally, an in-cylinder direct injection internal combustion engine that includes a fuel injection valve that directly injects fuel into a cylinder and switches between stratified combustion (compression stroke injection) and uniform combustion (intake stroke injection) according to the engine load state is known. (See Patent Document 1).
By the way, in the direct injection type internal combustion engine, generally, the fuel injected from the fuel injection valve is set to a high pressure even when the intake stroke injection is performed, so depending on the injection timing during the intake stroke. As a result, fuel adheres to the piston crown surface and cylinder wall surface, resulting in a problem that exhaust properties and combustibility deteriorate.

Therefore, in the thing of the said patent document 1, the amount of fuel adhesion is reduced by retarding fuel injection timing at the time of the cold machine to which fuel tends to adhere.
JP 2000-186597 A

However, even when the engine temperature is high, there is a portion where the fuel is likely to adhere depending on the shape of the combustion chamber.
In addition, if the fuel injection timing is retarded, the homogeneity of the air-fuel mixture decreases and the combustibility is deteriorated. There was also the problem of being restricted.

  The present invention has been made in view of the above problems, and in-cylinder direct injection internal combustion engine that can sufficiently reduce fuel adhesion to a wall surface or the like while maintaining the homogeneity of the air-fuel mixture when performing intake stroke injection The purpose is to provide.

  Therefore, the direct injection internal combustion engine according to the present invention is configured to set an injection stop period when performing fuel injection during the intake stroke, and to stop fuel injection by the fuel injection valve during the injection stop period. .

  According to the above configuration, the amount of fuel adhesion can be reduced by setting the time when the fuel spray is directed to the portion where the fuel is easily attached as the injection stop period and injecting the fuel while avoiding the injection stop period.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system configuration diagram of a direct injection type internal combustion engine in the embodiment.
In the internal combustion engine 1 shown in FIG. 1, a combustion chamber 5 is formed by a cylinder head 2, a cylinder block 3, and a piston 4.
The combustion chamber 5 communicates with an intake port 7 via an intake valve 6 and an exhaust port 9 via an exhaust valve 8.

The intake valve 6 and the exhaust valve 8 are opened and closed by an intake valve cam and an exhaust valve cam (not shown), respectively.
A fuel injection valve 10 is provided near the center of the upper surface (cylinder head) of the combustion chamber 5, and a spark plug 11 is disposed on the exhaust side of the upper portion of the combustion chamber 5.
In addition, a substantially cylindrical cavity 12 is provided in the vicinity of the center of the crown surface of the piston 4.

The fuel injection valve 10 and the spark plug 11 are controlled by a signal from an engine control unit 13 incorporating a microcomputer, and fuel injection and spark ignition are performed.
The engine control unit 13 receives detection signals from an accelerator opening sensor 21 that detects an accelerator opening, a rotation sensor 22 that detects an engine speed (rpm), and the like.

  In this embodiment, as a combustion mode, a stratified operation mode in which a rich air-fuel mixture is formed around the spark plug 11 by performing fuel injection during the compression stroke and lean combustion is performed, and fuel injection is performed during the intake stroke. A homogeneous operation mode in which a homogeneous air-fuel mixture is formed in the combustion chamber 5, and either the stratified operation mode or the homogeneous operation mode is selected according to the operation conditions.

Here, fuel injection control in the homogeneous operation mode in which fuel injection is performed during the intake stroke will be described.
In the present embodiment, an injection stop period is determined in advance during fuel injection during the intake stroke, and fuel injection is performed while avoiding the injection stop period. The injection stop period includes the following three periods: Is set.
(1) A period in which the fuel spray is directed to the boundary between the bottom surface portion 12a and the side surface portion 12b of the cavity 12 (see FIG. 2).
(2) A period during which the fuel spray is directed to the side surface portion 12b of the cavity 12 (see FIG. 3).
(3) A period during which the fuel spray is directed to the gap 16 between the piston head 4a and the cylinder inner wall 15 (see FIG. 4).

The engine control unit 13 stores a correlation between the injection stop period and the engine rotation speed in advance, and sets the three injection stop periods according to the engine rotation speed at that time.
And the engine control unit 13 controls the fuel injection which avoided the said injection stop period as shown to the flowchart of FIG.

In the flowchart of FIG. 5, in step S1, a fuel injection period (from the fuel injection start timing) corresponding to the required fuel injection amount and a predetermined injection start timing (or injection end timing) is determined from signals such as the engine speed and the accelerator opening. The period until the fuel injection end time) is calculated.
In step S2, it is determined whether or not any of the above-described injection stop periods (1) to (3) is included in the fuel injection period.

If the fuel injection period includes the injection stop periods (1) to (3), the process proceeds to step S3, the fuel injection period is changed so as to avoid the injection stop period, and the fuel injection period is injected. When the stop period is not included, the process proceeds to step S4 to output a fuel injection signal according to the fuel injection period.
When the fuel injection period is changed in step S3, the process returns to step S2 again to determine whether or not the changed fuel injection period includes an injection stop period, and the process of step S3 is repeated until the injection stop period is not included. .

In step S3, the fuel injection period is changed as follows.
For example, as shown in FIG. 6, when the fuel injection period calculated in step S1 includes the injection stop period (1) and the injection stop period (2), the injection stop periods (1) and (2) The portion overlapping with is a period for temporarily stopping the injection, and immediately after the fuel injection end timing calculated in step S1, the total period of the injection stop period (1) and the injection stop period (2) is Add as a period.

As a result, the required fuel injection period is divided into two with the injection stop periods (1) and (2) interposed therebetween.
As described above, as a result of moving the fuel injection period overlapping the injection stop periods (1) and (2) to the end of the injection period, this time, the fuel injection period includes the injection stop period (3). Then, a portion overlapping the injection stop period (3) is set as a period for temporarily stopping injection, and a period for the injection stop period (3) is added as an injection period at the end of the injection period.

Thus, the requested fuel injection period is divided into three times with the injection stop periods (1) and (2) and the injection stop period (3) in between.
According to the above configuration, in the intake stroke injection, fuel injection is performed while avoiding the injection stop period, so that deterioration of exhaust properties and combustibility due to fuel adhesion to the wall surface and the like can be suppressed.
Further, since the fuel injection is performed a plurality of times with the injection stop period in between, the necessary fuel can be injected even during a high load while avoiding the injection stop period.

Further, by setting the injection stop period to a period in which the fuel spray is directed to the boundary between the bottom surface portion 12a and the side surface portion 12b of the cavity 12, the fuel spray is at the boundary between the bottom surface portion 12a and the side surface portion 12b of the cavity 12. The collision does not occur and fuel adhesion can be reduced.
Further, by setting the injection stop period to a period in which the fuel spray is directed to the side surface portion 12b of the cavity 12 in addition to the period in which the fuel spray is directed to the boundary between the bottom surface portion 12a and the side surface portion 12b of the cavity 12. The direction of the fuel injected into the cavity 12 is unified from the inside of the cavity 12 to the outside of the cavity 12, and the amount of fuel that stagnates in the cavity 12 is reduced, so that a mixture with higher homogeneity can be formed. It becomes possible.

Further, the fuel injection is performed at least twice during the period in which the fuel spray is directed to the bottom surface of the cavity 12 and the period in which the fuel spray is directed to the piston crown surface outside the cavity 12. Since the fuel is distributed to both of them, it is possible to form an air-fuel mixture with higher homogeneity.
Furthermore, the injection stop period is set to a period in which the fuel spray is directed to the gap 16 between the piston head 4a and the cylinder inner wall 15 (a period in which the fuel spray is directed to the piston clevis). Since the amount of fuel that does not contribute to the fuel is reduced, it is possible to reduce unburned hydrocarbons in the exhaust gas.

Next, a second embodiment will be described.
In the present embodiment, in step S1 of the flowchart of FIG. 5, the fuel injection period is divided into two immediately before the injection stop period (1) and immediately after the injection stop period (2), and These are set so that the respective injection amounts are equal (see FIG. 7).
That is, half of the injection period corresponding to the required injection amount is set as an injection period with the injection end timing immediately before the injection stop period (1), and the other half is started immediately after the injection stop period (2). Let the injection period be the time.

In step S2, it is determined whether or not the fuel injection period calculated in step S1 includes the injection stop period (3). If the injection stop period (3) is included, the first embodiment is performed. Similarly, the injection is stopped at a portion overlapping the injection stop period (3), and an injection period corresponding to the injection stop period (3) is added to the end of the injection period.
Accordingly, the fuel injection can be divided into at least two times, a period in which the fuel injection is directed to the bottom surface 12 a of the piston cavity 12 and a period in which the fuel injection is directed to the piston crown surface outside the piston cavity 12.

Note that the shape of the cavity 12 is not limited to that shown in FIG. 1, and may be constituted by, for example, a piston having multistage cavities 31 as shown in FIG. 8.
When the multi-stage cavity 31 is provided as described above, a plurality of injection stop periods (1) and injection stop periods (2) may be set.

1 is a system configuration diagram of a direct injection type internal combustion engine in an embodiment. FIG. The figure which shows the state which the fuel spray which is the injection stop period (1) in embodiment points to the boundary of the bottom face part and side part of a cavity. The figure which shows the state which the fuel spray which is the injection stop period (2) in embodiment points to the side part of a cavity. The figure which shows the state which the fuel spray which is the injection stop period (3) in embodiment points to the clearance gap between a piston head and a cylinder inner wall. The flowchart which shows the fuel-injection control in embodiment. The figure for demonstrating the setting of the fuel-injection period by 1st Embodiment. The figure for demonstrating the setting of the fuel-injection period by 2nd Embodiment. The system block diagram which shows the in-cylinder direct injection type internal combustion engine comprised with the piston which has a multistage cavity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder head 3 ... Cylinder block 4 ... Piston 5 ... Combustion chamber 10 ... Fuel injection valve 11 ... Spark plug 12 ... Cavity 12a ... Bottom part 12b ... Side part 13 ... Engine control unit 15 ... Cylinder inner wall 16 ... Gap

Claims (7)

In a cylinder direct injection internal combustion engine equipped with a fuel injection valve that directly injects fuel into the cylinder,
An in-cylinder direct injection internal combustion engine, wherein an injection stop period is set when fuel injection is performed during an intake stroke, and fuel injection by the fuel injection valve is stopped during the injection stop period.   The in-cylinder direct injection internal combustion engine according to claim 1, wherein the injection stop period is set according to an engine speed.   3. The direct injection type internal combustion engine according to claim 1 or 2, wherein fuel injection is performed in a plurality of times with the injection stop period interposed therebetween. The fuel injection valve is provided at substantially the center of the upper portion of the combustion chamber, and a cavity for receiving fuel spray from the fuel injection valve is provided on the piston crown surface.
The in-cylinder direct injection type according to any one of claims 1 to 3, wherein the injection stop period is set to a period in which the fuel spray is directed to a boundary between a bottom surface portion and a side surface portion of the cavity. Internal combustion engine. The fuel injection valve is provided at substantially the center of the upper portion of the combustion chamber, and a cavity for receiving fuel spray from the fuel injection valve is provided on the piston crown surface.
The in-cylinder direct injection internal combustion engine according to any one of claims 1 to 4, wherein the injection stop period is set to a period in which the fuel spray is directed to the side surface of the cavity. The fuel injection valve is provided at substantially the center of the upper portion of the combustion chamber, and a cavity for receiving fuel spray from the fuel injection valve is provided on the piston crown surface.
6. The fuel injection is performed at least twice in a period in which the fuel spray is directed toward the bottom surface of the cavity and a period in which the fuel spray is directed toward the piston crown surface outside the cavity. The direct injection type internal combustion engine described in 1. The fuel injection valve is provided at substantially the center of the upper part of the combustion chamber,
The in-cylinder direct injection internal combustion engine according to any one of claims 1 to 6, wherein the injection stop period is set to a period in which the fuel spray is directed to a gap between the piston head and the cylinder inner wall. .

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