JP2010196615A - Piston for direct injection type engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piston for a direct injection type engine inhibiting fuel from becoming liquid film in a cavity. <P>SOLUTION: This piston 30 for the direct injection engine 100 includes a center cavity 41 disposed on a piston crown surface 31 and biasing fuel injected from a fuel injection valve 21 to a spark plug 22 side, and side cavities 42, 43 disposed on the piston crown surface 31 adjacently to the center cavity 41, formed in such a manner that depth of a cavity is deeper than the center cavity 41, and biasing fuel injected from the fuel injection valve 21 to a combustion chamber 12 upper part. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a piston of a direct injection engine that injects fuel directly into a combustion chamber.

  2. Description of the Related Art Conventionally, there is known a piston in which a cavity is provided in the piston crown surface and the combustibility of the air-fuel mixture is improved by the cavity.

  Patent Document 1 discloses a piston of a direct-injection engine provided with a convex portion in a cavity that promotes diffusion of injected fuel into a combustion chamber.

Japanese Patent Laid-Open No. 10-331711

  However, in the cavity of the piston described in Patent Document 1, the time for the injected fuel to reach the bottom of the cavity is shortened at a position near the injection port of the fuel injection valve. There is a problem that a part of the film becomes a liquid film and remains at the bottom. Since a part of the fuel that has been liquefied in this way is discharged to the outside as unburned HC, the exhaust performance of the direct injection engine deteriorates.

  Accordingly, the present invention has been made paying attention to such a problem, and an object thereof is to provide a piston of a direct injection engine that can suppress the formation of a fuel film in the cavity.

  The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected, it is not limited to this.

  In the piston (30) of the direct injection engine (100), the present invention is a central cavity that is provided on the piston crown (31) and deflects the fuel injected from the fuel injection valve (21) toward the spark plug (22). (41) and the piston crown surface (31) so as to be adjacent to the central cavity (41) and the cavity depth is deeper than that of the central cavity (41), from the fuel injection valve (21) And a side cavity (42, 43) for deflecting the injected fuel upward in the combustion chamber (12).

  According to the present invention, since the cavity depth of the side cavity is formed deeper than the cavity depth of the central cavity, the time until the fuel injected from the fuel injection valve reaches the bottom of the side cavity is increased, and the fuel vaporization is performed. Therefore, it is possible to suppress the fuel film formation in the side cavity.

It is a schematic block diagram of a direct injection engine provided with the piston of 1st Embodiment. It is a figure which shows the cavity formed in a piston. It is a figure which shows the cavity of the piston of 2nd Embodiment.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIG. 1 (A), FIG. 1 (B), and FIG.

  FIG. 1A is a schematic configuration diagram of a direct injection engine for a vehicle. FIG. 1B is a diagram showing a state of fuel injection of the fuel injection valve.

  Referring to FIG. 1 (A), a direct injection engine 100 includes a cylinder block 10 and a cylinder head 20.

  A cylinder 11 is formed in the cylinder block 10. A piston 30 is slidably fitted into the cylinder 11.

  The piston 30 forms a cavity 40 in the piston crown surface 31. The combustion chamber 12 is formed by the piston crown surface 31 of the piston 30, the wall surface of the cylinder 11, and the lower surface of the cylinder head 20. When the air-fuel mixture burns in the combustion chamber 12, the piston 30 receives the combustion pressure due to combustion and reciprocates the cylinder 11.

  A fuel injection valve 21 and a spark plug 22 are installed on the cylinder head 20 disposed in the upper part of the cylinder block 10.

  The fuel injection valve 21 is installed below the intake port 50 and on the side of the cylinder head 20. The fuel injection valve 21 directly injects fuel into the combustion chamber 12 to form an air-fuel mixture. The fuel injection valve 21 is a multi-hole type fuel injection valve having seven injection ports for injecting fuel, and injects fuel from each injection port as shown in FIG.

  The fuel injection timing of the fuel injection valve 21 is controlled according to the engine operating state. The fuel injection valve 21 injects fuel in the compression stroke in order to perform stratified combustion when the engine speed is low and the engine load is low. During the compression stroke injection, the fuel injection valve 21 injects fuel toward the cavity 40 of the piston 30. In contrast, at the time of high engine speed or high engine load, the fuel injection valve 21 injects fuel in the intake stroke in order to perform homogeneous combustion.

  At the time of first idling, the fuel injection valve 21 injects fuel in the intake stroke and then injects fuel again in the compression stroke.

  Referring to FIG. 1A again, the spark plug 22 is installed on the cylinder head 20 on the piston central axis. The spark plug 22 is arranged so that the ignition part faces the combustion chamber 12. The spark plug 22 ignites the air-fuel mixture formed in the combustion chamber 12.

  An intake port 50 and an exhaust port 60 are formed in the cylinder head 20 so as to communicate with the combustion chamber 12. In the direct injection engine 100, two intake ports 50 and two exhaust ports 60 are provided for each cylinder.

  The intake port 50 is provided with an intake valve 51 that is driven according to the vertical movement of the piston 30. The intake valve 51 is driven by a cam provided on the camshaft to open and close the intake port 50.

  The exhaust port 60 is provided with an exhaust valve 61 that is driven according to the vertical movement of the piston 30. The exhaust valve 61 is driven by a cam formed on the cam shaft, and opens and closes the exhaust port 60.

  Next, the cavity 40 formed in the piston 30 will be described with reference to FIGS. 2 (A) to 2 (D).

  FIG. 2A is a perspective view of the piston 30. FIG. 2B is a plan view of the piston 30, and a hatched area in FIG. 2B indicates an injection area of fuel injected during the compression stroke injection. FIG. 2C is a partial cross-sectional view of the piston 30 at the CC position in FIG. FIG. 2D is a partial cross-sectional view of the piston 30 at the DD position in FIG.

  As shown in FIGS. 2 (A) and 2 (B), the cavity 40 is formed on the piston crown surface 31 at a position shifted toward the intake port side with respect to the piston center CL. The cavity 40 includes a central cavity 41, a first side cavity 42, and a second side cavity 43.

  The central cavity 41 is provided so that a part thereof faces the ignition plug 22 and includes a central bottom portion 41A and a central wall portion 41B.

  The center bottom 41A is formed in a substantially fan shape so as to spread in the engine front-rear direction from the intake port side to the exhaust port side in plan view. The center bottom 41A is a flat surface and is formed such that the cavity depth from the piston crown surface 31 is D1.

  The central wall portion 41B is formed between the circular arc portion around the central bottom portion 41A and the piston crown surface 31. The central wall portion 41B is formed to be curved from the central bottom portion 41A toward the ignition portion of the ignition plug 22.

  The first side cavity 42 is formed adjacent to the central cavity 41 on the front side of the engine, and includes a first side bottom 42A and a first side wall 42B.

  42 A of 1st side bottom parts are formed in the semi-ellipse shape in which the engine front-back direction becomes a long axis in planar view. The first side bottom 42A is a flat surface, and the cavity depth of the first side bottom 42A is set to D2 deeper than the cavity depth D1 of the center bottom 41A.

  The first side wall portion 42 </ b> B is formed between the arc portion around the first side bottom portion 42 </ b> A and the piston crown surface 31. The first side wall portion 42B is formed to be curved from the first side bottom portion 42A toward the upper portion of the combustion chamber.

  The second side cavity 43 is formed adjacent to the central cavity 41 on the rear side of the engine, and includes a second side bottom 43A and a second side wall 43B.

  The second side bottom 43A is formed in a semi-elliptical shape with the longitudinal direction of the engine in the plan view as a major axis. The second side bottom 43A is a flat surface, and the cavity depth of the second side bottom 43A is set to D2 similarly to the cavity depth of the first side cavity 42.

  The second side wall portion 43 </ b> B is formed between the arc portion around the second side bottom portion 43 </ b> A and the piston crown surface 31. The second side wall 43B is formed to be curved from the second side bottom 43A toward the upper portion of the combustion chamber.

  The first side cavity 42 and the second side cavity 43 are formed so as to sandwich the central cavity 41 from the front-rear direction of the engine, and on the intake port side, the first side bottom 42A, the second side bottom 43A, and the first side wall 42B It is comprised so that the 2nd side wall part 43B may continue.

  With reference to FIG.2 (C) and FIG.2 (D), the spraying flow of the fuel injected toward the cavity 40 from the fuel injection valve 21 at the time of a compression stroke is demonstrated.

  Of the fuel injected during the compression stroke, the fuel injected into the central cavity 41 is directed toward the central wall 41B along the central bottom 41A as shown in FIG. 2C, and the spark plug 22 is driven by the central wall 41B. Deflected to the side. As a result, a layered mixture as an ignition source is formed around the spark plug 22.

  On the other hand, the fuel injected into the first side cavity 42 out of the fuel injected during the compression stroke is, as shown in FIG. 2D, the first side wall portion 42B along the first side bottom portion 42A. And is diffused above the combustion chamber 12 by the first side wall portion 42B. The fuel diffused from the first side cavity 42 into the combustion chamber 12 becomes an air-fuel mixture that quickly propagates the flame after ignition.

  Since the operation of the second side cavity 43 is the same as that of the first side cavity 42 described above, the description thereof is omitted.

  By the way, in the conventional method, when the distance between the injection port of the fuel injection valve and the cavity becomes short, the time taken for the injected fuel to reach the bottom of the cavity is short, so the fuel vaporization time is not limited, and the fuel is injected. Part of the fuel aggregates at the bottom to form a liquid film.

  In the piston 30 of the present embodiment, the first side bottom portion 42A and the second side bottom portion 43A have a cavity depth deeper than that of the central bottom portion 41A. The time required to reach the first side bottom portion 42A and the second side bottom portion 43A can be lengthened, and fuel vaporization can be promoted.

  As described above, in the piston 30 of the direct injection engine 100 of the first embodiment, the following effects can be obtained.

  In the piston 30, the cavity depths of the first side cavity 42 and the second side cavity 43 are formed deeper than the cavity depth of the central cavity 41, and the injected fuel reaches the first side bottom part 42A and the second side bottom part 43A. Since the time until this is increased and the vaporization of the fuel is promoted, the fuel film formation in the cavity 40 can be suppressed. Further, since the fuel injected into the first side cavity 42 and the second side cavity 43 is difficult to flow into the central cavity 41 side, the fuel in the first side cavity 42 and the second side cavity 43 and the fuel in the central cavity 41 And the formation of a fuel film due to the interference of the injected fuel is suppressed.

  Although the time until the fuel injected into the central cavity 41 reaches the central bottom 41A is slightly shortened, it reaches the central wall 41B from the central bottom 41A and reaches the spark plug 22 before the fuel injection force weakens. Since the air is deflected, a stratified air-fuel mixture can be reliably formed around the spark plug 22.

  Further, the cavity 40 of the piston 30 is formed on the intake port side. When fuel is injected in the intake stroke and the compression stroke at the time of the first idling, the air-fuel mixture is unevenly distributed on the exhaust port side by the intake stroke injection and compressed. Since the fuel-air mixture injected in the stroke is stratified around the spark plug 22 while being unevenly distributed on the intake port side, it is possible to suppress a decrease in the combustion performance of the fuel-air mixture even during engine cold start.

(Second Embodiment)
FIG. 3 is a view showing the first side cavity 42 of the piston 30 of the second embodiment, which replaces FIG. 2D of the first embodiment.

  The piston 30 of the second embodiment has substantially the same configuration as that of the first embodiment, but differs in the configuration of the first side cavity 42 and the second side cavity 43. Hereinafter, the difference will be mainly described. Since the configuration of the second side cavity 43 is the same as that of the first side cavity 42, only the first side cavity 42 will be described here.

  As shown in FIG. 3, in the first side cavity 42, the first side bottom 42A is formed as a tapered surface. 42 A of 1st side bottom parts are formed so that a cavity depth may become deep, so that it leaves | separates from the injection port of the fuel injection valve 21. As shown in FIG. The cavity depth of the first side bottom 42A at the position closest to the injection port of the fuel injection valve 21 is set to be D2.

  When the first side bottom portion 42A is configured as described above, the incident angle θ of the fuel injected toward the first side cavity 42 with respect to the first side bottom portion 42A is made larger than that when the first side bottom portion 42A is formed as a flat surface. Can also be reduced. Thus, when the incident angle θ is small, the collision force when the fuel collides with the first side bottom portion 42A is weakened, so that the aggregation of the fuel at the time of the collision is suppressed.

  As described above, in the piston 30 of the direct injection engine 100 of the second embodiment, the following effects can be obtained.

  In the piston 30, the first side bottom portion 42 </ b> A and the second side bottom portion 43 </ b> A are formed as tapered surfaces whose cavity depth increases as the distance from the injection port of the fuel injection valve 21 increases. The collision force when colliding with the side bottom 43A can be weakened. As a result, fuel agglomeration is suppressed, so that the formation of a fuel film in the first side cavity 42 and the second side cavity 43 can be suppressed more than in the first embodiment.

  Note that the present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

100 Direct Injection Engine 12 Combustion Chamber 20 Cylinder Head 21 Fuel Injection Valve 22 Spark Plug 30 Piston 31 Piston Crown 40 Cavity 41 Central Cavity 41A Central Bottom 41B Central Wall 42 First Side Cavity 42A First Side Bottom 42B First Side Wall Part 43 second side cavity 43A second side bottom part 43B second side wall part 50 intake port 60 exhaust port

Claims (6)

In the piston of a direct injection engine,
A central cavity that is provided on the piston crown and deflects the fuel injected from the fuel injection valve toward the spark plug;
A side cavity provided on the piston crown surface adjacent to the central cavity and formed so that the cavity depth is deeper than the central cavity, and deflects the fuel injected from the fuel injection valve upward in the combustion chamber;
A piston comprising: The central cavity and the side cavity are provided on the intake port side where the fuel injection valve is disposed in a plan view.
The piston according to claim 1. The side cavity comprises a cavity bottom as a flat surface,
The piston according to claim 1 or 2, characterized by the above. The side cavity includes a cavity bottom as a tapered surface such that the cavity depth increases as the distance from the injection port of the fuel injection valve increases.
The piston according to claim 1 or 2, characterized by the above. The side cavity includes a first side cavity provided on the front side of the engine and a second side cavity provided on the rear side of the engine in plan view.
The piston according to any one of claims 1 to 4, characterized in that: The first side cavity and the second side cavity are formed to be continuous with each other on the intake port side in a plan view.
The piston according to claim 5.

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