JPH112128A - Direct injection engine - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To reduce the emission of unburned gas when the engine is cold. A groove portion (5) is formed on a head surface (3a) of a cylinder head (3) to extend from the vicinity of an injection nozzle (4) toward the fuel injection direction. This can suppress the fuel spray injected from the injection nozzle 4 from coming into contact with the head surface 3a, so that the fuel can be prevented from adhering to the head surface 3a, and the unburned gas when the engine is cold can be prevented. Emissions can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection engine for directly injecting fuel into a cylinder (combustion chamber), and is effective when applied to a diesel engine.

[0002]

2. Description of the Related Art The combustion chamber of a direct injection type diesel engine (hereinafter abbreviated as engine) is disclosed in, for example,
As described in JP-A-269352 and JP-A-62-291425, a head of a cylinder head in which a dent is formed in a piston head to generate squish and a fuel injection nozzle (injection hole) faces the piston head. It is arranged near the surface to improve combustion efficiency.

[0003]

By disposing the injection nozzle in the vicinity of the head surface, the air sucked into the cylinder can be effectively used for combustion (explosion). However, when the engine (cylinder head, piston, etc.) is cold, a large amount of incompletely burned fuel (unburned gas) such as hydrocarbons (HC) and white smoke is discharged into the atmosphere for the reasons described below. Probability is high.

That is, when the injection nozzle is arranged near the head surface, a part of the injected fuel (spray) comes into contact with the head surface and the piston head. Therefore, when the engine is cold, the fuel that has come into contact with the head surface and the piston head does not evaporate and adheres to the head surface and the piston head in a liquid state, and the attached fuel is unburned gas. It is released into the atmosphere as.

Since the heat capacity of the piston is sufficiently smaller than the heat capacity of the cylinder head, the temperature of the piston quickly rises to a temperature sufficient to vaporize the fuel as compared with the temperature of the cylinder head. It has been confirmed by tests and examinations by the inventors that the problem of unburned gas to be emitted is mainly fuel adhering to the head surface.

In view of the above, it is an object of the present invention to reduce the emission of unburned gas when the engine is cold (when the engine is cold).

[0007]

The present invention uses the following technical means to achieve the above object. Claim 1
According to the invention described in 3, the head surface (3a) of the cylinder head (3) extends from the vicinity of the injection nozzle (4) toward the fuel injection direction, and the direction from the piston (2) toward the head surface (3a). A groove (5) is formed to be depressed in the groove.

[0008] This prevents the fuel spray injected from the injection nozzle (4) from coming into contact with the head surface (3a), thereby preventing the fuel from adhering to the head surface (3a). As a result, the emission of unburned gas when the engine is cold can be reduced. In addition, in this specification, "the vicinity of the injection nozzle (4)" is a concept that includes not only a part close to the injection nozzle (4) but also a part where the injection nozzle (4) is provided.

If the groove (5) is made unnecessarily large in order to prevent the fuel from adhering to the head surface (3a), the volume of the combustion chamber increases and the compression ratio decreases.
The temperature in the combustion chamber (the temperature of the head surface (3a)) decreases,
Rather, the amount of emission of white smoke, unburned gas, and the like increases. Therefore, the invention according to claim 2 is characterized in that the groove shape of the groove portion (5) is formed so as to conform to the shape of the fuel spray (4a) injected from the injection nozzle (4).

Thus, it is possible to prevent fuel from adhering to the head surface (3a) without making the groove (5) unnecessarily large, so that the amount of unburned gas discharged can be reliably reduced. Can be. In the invention according to claim 3,
The groove portion (5) is characterized in that the groove portion (5) is formed so as to turn toward the downstream side of the vortex (S) of the air in the cylinder (4) as it goes farther from the injection nozzle (4) in the injection direction.

Thus, the shape of the groove (5) is more conformed to the shape of the spray (4a) in the cylinder (1), so that the fuel is more securely prevented from adhering to the head surface (3a). can do. In addition, the code | symbol in the parenthesis of each said means shows the correspondence with the concrete means of embodiment mentioned later.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) In this embodiment, a direct injection type engine according to the present invention is replaced with a direct injection type diesel engine (hereinafter, referred to as a "first embodiment").
Abbreviated as engine. FIG. 1 is a schematic view of a combustion chamber of an engine according to the first embodiment.

In FIG. 1, reference numeral 1 denotes a cylinder, and 2 denotes an aluminum piston reciprocating in the cylinder 1. Reference numeral 3 denotes a cylinder head provided with an injection nozzle 4 for directly injecting fuel (light oil) into the cylinder 1 (combustion chamber). An injection hole (not shown) of the injection nozzle 4 Of these, it is located at a position slightly displaced from the head surface 3a facing the piston 2 (piston head) toward the piston 2 (piston head).

The injection nozzle 4 is a hole type nozzle having five injection holes (see FIG. 1B). Also,
The concave portion (piston cavity) 2a formed in the piston 2 (piston head) is a well-known device that generates squish to increase the combustion speed and improve fuel consumption efficiency. In addition, an ejection nozzle 4 (ejection hole) is provided on the head surface 3a.
Five grooves 5 are formed extending from the vicinity to the fuel injection side (in the present embodiment, outward from the center of the head surface 3a), and depressed in the direction from the piston 2 (piston head) toward the head surface 3a. Have been.

The groove shape of the groove 5 viewed from the piston 2 (piston head) side is as shown in FIG.
Spray 4a of fuel injected from injection nozzle 4 (injection hole)
(See FIG. 1 (b).)
The groove width W is formed so that the groove width W increases from the vicinity of the (injection hole) toward the fuel injection direction. The groove 5 has a constant groove depth D and a semicircular cross section.

Incidentally, in FIG. 1A, reference numeral 6 denotes an intake valve, and reference numeral 7 denotes an exhaust valve. Next, features of the present embodiment will be described. According to the present embodiment, the head surface 3a includes:
Groove 5 extending from the vicinity of the injection nozzle 4 toward the fuel injection direction
Is formed, it is possible to suppress the fuel spray 4a injected from the injection nozzle 4 from contacting the head surface 3a. Therefore, the fuel can be prevented from adhering to the head surface 3a, so that the emission of unburned gas can be reduced when the engine is cold.

In the groove shape of the groove 5, the piston 2
The groove shape of the groove 5 viewed from the (piston head) side is
Since it is formed in a drop shape along the shape a, the fuel can be more reliably prevented from adhering to the head surface 3a without making the groove 5 unnecessarily large. Therefore, it is possible to prevent the fuel from adhering to the head surface 3a without excessively lowering the compression ratio (without lowering the temperature in the combustion chamber (the temperature of the head surface (3a))). Emission of combustion gas can be further prevented.

By the way, according to the present invention, since the emission of white smoke and unburned gas is reduced by preventing the spray 4a from coming into contact with the head surface 3a, as shown in the graph of FIG. The nozzle 4 (injection hole) may be moved from the head surface 3a to the piston 2 (piston head) side to increase the distance between the injection nozzle 4 (injection hole) and the head surface 3a. FIG. 2 is a test result showing the relationship between the distance L between the injection nozzle 4 (injection hole) and the head surface 3a and the discharge amount of hydrocarbons (HC).

However, when the distance L increases, the head surface 3a and the spray 4a can be prevented from coming into contact with each other, but the air and fuel existing between the injection nozzle 4 (injection hole) and the head surface 3a can be prevented. Is difficult to mix, so that air existing between the injection nozzle 4 (injection hole) and the head surface 3a does not effectively contribute to combustion (explosion). For this reason, when the distance L is increased, the output of the engine is reduced, and the amount of air that contributes to the combustion of the injected fuel is small, so that a new problem occurs in that graphite is discharged into the atmosphere.

On the other hand, in the present embodiment, as described above, it is possible to prevent the spray 4a from coming into contact with the head surface 3a while keeping the compression ratio high while reducing the distance L. While preventing smoke and graphite emissions,
A decrease in engine output can be prevented. (Second Embodiment) In this embodiment, the present invention is applied to an engine having a swirl generating means (not shown) for generating a swirl (vortex) in intake air such as a helical port.

That is, as shown in FIG. 3A, the groove 5 is turned toward the air downstream side of the swirl S as the distance from the injection nozzle 4 to the injection direction increases.
Are formed in an arc shape. Accordingly, the shape of the groove 5 is more closely conformed to the shape of the spray 4a in the combustion chamber (cylinder 1), so that it is possible to more reliably prevent the fuel from adhering to the head surface 3a.

By the way, in the above embodiment, the groove depth D
Is set to be constant in order to facilitate the processing (milling) for forming the groove 5. Therefore, the groove portion 5 according to the present invention is not limited to a groove having a constant groove depth D, and the groove depth D is set to be deeper toward the injection direction so as to follow the shape of the spray 4a. It may be a drop shape.

In the above-described embodiment, the shape of the groove 5 is not limited to a drop shape, but may be a conical shape or a cylindrical shape. The cross-sectional shape of the groove 5 is not limited to a semicircle, but may be other shapes such as a rectangular shape or a triangular shape. Further, the application of the present invention is not limited to a diesel engine, but can be applied to a gasoline engine that directly injects gasoline into the cylinder 1.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an engine according to a first embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a distance L and an amount of discharged hydrocarbons.

FIG. 3 is a schematic diagram of an engine according to a second embodiment of the present invention.

[Explanation of symbols]

1 ... cylinder, 2 ... piston, 3 ... cylinder head, 4
... injection nozzle, 5 ... groove.

Continued on the front page (72) Inventor Toshiro Itatsu 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation

Claims (3)

[Claims] A piston (2) reciprocating in a cylinder (1); a cylinder head (3) provided with an injection nozzle (4) for directly injecting fuel into the cylinder (1); The cylinder head (3) is formed on a head surface (3a) of the cylinder head (3) facing the piston (2), extends from the vicinity of the injection nozzle (4) toward the fuel injection direction, and extends from the piston (2) to the head surface. A direct-injection engine having a groove (5) that is depressed in a direction toward (3a). 2. The groove according to claim 1, wherein the groove of the groove is formed so as to follow a shape of a fuel spray injected from an injection nozzle. Direct injection engine. 3. The groove (5) is formed so as to turn toward the downstream side of the vortex (S) of air in the cylinder (4) as the distance from the injection nozzle (4) to the injection direction increases. The direct injection engine according to claim 1 or 2, wherein: