JP2018071474A - Internal combustion engine and piston - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine that suppresses generation of a pollution substance and improves durability of a piston.SOLUTION: An engine 1 includes: a piston 20 reciprocating inside a cylinder 10; and an injection nozzle 52 for injecting fuel into a combustion chamber 21 formed by the piston 20. The piston 20 has: a cavity 22 forming the combustion chamber 21; and inner peripheral surfaces 231a to 231h and recess parts 232a to 232h formed along a circumferential direction so as to promote movement of fuel in the circumferential direction, in a lip part 221 of the cavity 22 positioned in a fuel injection direction.SELECTED DRAWING: Figure 4

Description

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

2. Description of the Related Art A vehicle such as a truck is provided with an internal combustion engine in which fuel is directly injected into a combustion chamber and mixed with air to burn the mixture.
For example, an internal combustion engine described in Patent Document 1 below includes a piston that reciprocates in a cylinder and an injection nozzle that injects fuel into a combustion chamber formed by the piston. The injection nozzle is located on the center side of the combustion chamber, and injects fuel in the radial direction and mixes it with air.

JP 2006-121573 A

  By the way, in order to reduce the pollutants discharged by the internal combustion engine, it is desirable to increase the combustion efficiency of the air-fuel mixture in the combustion chamber. However, in the internal combustion engine of Patent Document 1, the fuel injected in the radial direction collides with the inner peripheral wall surface of the piston, and the subsequent mixing with air is not promoted, so the combustion efficiency cannot be increased.

  There is also a demand for further improvement in the durability of the piston. For example, in a piston, compressive stress is generated by thermal expansion accompanying combustion, but it is desirable to relax the compressive stress in order to improve durability.

  Accordingly, the present invention has been made in view of these points, and an object thereof is to provide a piston having high combustion efficiency and durability.

According to a first aspect of the present invention, there is provided an internal combustion engine comprising a piston that reciprocates in a cylinder and an injection nozzle that injects fuel into a combustion chamber formed by the piston. A plurality of irregularities formed along the circumferential direction in order to promote the movement of the fuel in the circumferential direction on the cavity formed and the inner circumferential wall surface of the cavity located in the fuel injection direction And an internal combustion engine.
According to such an internal combustion engine, the fuel injected from the injection nozzle to the inner peripheral wall surface of the cavity flows while maintaining the flow velocity along the circumferential direction by the uneven portions smoothly connected to each other. In this way, the fuel flows in a state where the flow velocity is not reduced, so that the mixing of the fuel and air in the combustion chamber (particularly, the concave portion of the uneven portion) is promoted. As a result, the combustion efficiency is improved and the generation of pollutants in the internal combustion engine can be suppressed. In addition, since the concave portion serves as a refuge for compressive stress generated due to thermal expansion due to combustion in the combustion chamber, the compressive stress can be relaxed. As a result, the durability of the piston can be improved.

  Further, the injection nozzle has a plurality of injection holes for injecting the fuel in different directions, and a convex portion of the concave and convex portions is formed at a portion where the fuel injected by each of the plurality of injection holes hits. Each may be located.

  Further, the concave portion of the concave and convex portion may be a groove portion that is formed so as to be curved with a predetermined curvature.

  Further, the top surface of the convex portion of the concave and convex portion may be formed so as to be located on a virtual circle having the center of the cavity as a center point.

In a second aspect of the present invention, a piston of an internal combustion engine into which fuel is directly injected, and a cavity forming a combustion chamber, and an inner peripheral wall surface of the cavity located in the fuel injection direction, In order to promote the movement of the fuel in the circumferential direction, a piston is provided that includes a plurality of concave and convex portions formed along the circumferential direction.
According to such a piston, the fuel injected to the inner peripheral wall surface is divided in the circumferential direction by the concavo-convex portions smoothly connected to each other, and flows while maintaining the flow velocity along the circumferential direction. In this way, the fuel flows in a state where the flow velocity is not reduced, so that the mixing of the fuel and air in the combustion chamber (particularly, the concave portion of the uneven portion) is promoted. As a result, the combustion efficiency is improved and pollutants in the exhaust gas can be suppressed. In addition, since the concave portion serves as a refuge for compressive stress generated due to thermal expansion due to combustion in the combustion chamber, the compressive stress can be relaxed. As a result, the durability of the piston can be improved.

  ADVANTAGE OF THE INVENTION According to this invention, while producing | generating the pollutant in an internal combustion engine, there exists an effect that durability of a piston can be improved.

It is a schematic diagram which shows a part of internal structure of the engine 1 which concerns on one Embodiment of this invention. 3 is a top view of the piston 20. FIG. 2 is a cross-sectional perspective view of a cavity 22 and a peripheral portion of a piston 20. FIG. It is a schematic diagram for demonstrating the positional relationship of the injection holes 53a-53h of the injection nozzle 52, inner peripheral surface 231a-231h, and recessed part 232a-232x. It is a schematic diagram for demonstrating the flow of the fuel in the internal peripheral surface 231a and recessed part 232a, 232h.

<Configuration of internal combustion engine>
An internal configuration of an engine 1 that is an internal combustion engine according to an embodiment of the present invention will be described with reference to FIG.

  FIG. 1 is a schematic diagram showing a part of an internal configuration of an engine 1 according to an embodiment. The engine 1 is mounted on a truck as an example, and is a direct injection diesel engine that directly injects fuel into a cylinder. The engine 1 generates power by burning and expanding a mixture of fuel and air (intake air) in a cylinder. Further, the engine 1 discharges the exhaust gas after combustion. For this reason, the engine 1 repeats a cycle including an intake stroke, a compression stroke, a combustion / expansion stroke, and an exhaust stroke. As shown in FIG. 1, the engine 1 includes a cylinder 10, a piston 20, an intake valve 30, an exhaust valve 40, and an injector 50.

  The cylinder 10 is a cylinder in which the piston 20 reciprocates. Air is sucked into the cylinder 10. The engine 1 is a multi-cylinder engine having a plurality of cylinders 10.

  The piston 20 reciprocates up and down in the cylinder 10. The piston 20 is connected via a connecting rod 25 to a crankshaft (not shown) that converts the reciprocating motion of the piston 20 into rotational motion. A cavity 22 forming a combustion chamber 21 is provided at the center of the top surface of the piston 20. The detailed configuration of the cavity 22 will be described later.

  The intake valve 30 and the exhaust valve 40 are valves that can be opened and closed, respectively. The intake valve 30 introduces air from the intake pipe 32 into the cylinder 10 when opened. The exhaust valve 40 discharges the exhaust gas after combustion in the cylinder 10 to the exhaust pipe 42 when opened. In addition, although pollutants may be contained in the exhaust gas, the generation of pollutants in the internal combustion engine can be suppressed by increasing the combustion efficiency of the air-fuel mixture in the engine 1.

  The injector 50 injects fuel into the combustion chamber 21 by a predetermined injection amount at a predetermined injection timing. The fuel is directly injected into the compressed air in the combustion chamber 21, so that combustion / expansion occurs and pushes down the piston 20. The injector 50 has an injection nozzle 52 that injects fuel provided at the tip. The injector 50 injects fuel toward the inner side wall of the cavity 22 when the piston 20 reaches near the compression top dead center. That is, the injector 50 injects the fuel obliquely downward.

  The intake valve 30, the exhaust valve 40, and the injector 50 are controlled by a control device 100 that controls the operation of the engine 1. For example, the control device 100 controls the fuel injection timing and the injection amount by the injector 50.

<Detailed configuration of piston cavity>
A detailed configuration of the cavity 22 of the piston 20 will be described with reference to FIGS. 2 and 3.

FIG. 2 is a top view of the piston 20. FIG. 3 is a cross-sectional perspective view of the cavity 22 and the peripheral portion of the piston 20.
The cavity 22 forms a combustion chamber 21 (FIG. 1) in which the sucked air and the fuel injected from the injector 50 are mixed and burned. The cavity 22 is recessed in a cylindrical shape. Specifically, as shown in FIG. 3, the cavity 22 has a lip portion (mouth portion) 221, a hollow portion 222, and a central raised portion 223.

  The lip portion 221 is an inner peripheral wall surface that is connected to the top surface 20a of the piston 20 as shown in FIG. 3 and has a curvature in the vertical direction. The injector 50 injects fuel so that the fuel collides in the vicinity of the lip portion 221. As will be described in detail later, the lip portion 221 has inner peripheral surfaces 231a to 231h and concave portions 232a to 232h as shown in FIG. 2 in order to promote the movement of the fuel in the circumferential direction along the lip portion 221. Is formed. In the present embodiment, the inner peripheral surfaces 231a to 231h and the concave portions 232a to 232h correspond to the concavo-convex portions formed along the circumferential direction.

  The hollow portion 222 is connected to the lip portion 221 and is provided below the lip portion 221. The recess 222 is formed to be curved using a predetermined curvature, a shape in which different curvatures are connected, or a relaxation curve.

  The central raised portion 223 is connected to the recessed portion 222 and is provided so as to protrude to the center of the cavity 22. The central raised portion 223 has a truncated cone shape or a certain curvature. The lip portion 221, the recessed portion 222, and the central raised portion 223 are continuously formed, so that the flow of air and fuel in the cavity 22 is made smooth.

Next, the inner peripheral surfaces 231a to 231h and the recesses 232a to 232h provided on the lip portion 221 will be described.
The inner peripheral surfaces 231a to 231h and the recesses 232a to 232h are alternately formed in the circumferential direction of the lip portion 221 as shown in FIG. Further, the inner peripheral surfaces 231a to 231h and the recesses 232a to 232h are continuously formed in a wave shape. For example, the inner peripheral surface 231a is continuous with the recess 232a and the recess 232h. As a result, the lip portion 221 is a smoothly continuous inner wall surface.

  Each of the inner peripheral surfaces 231a to 231h is formed so as to be positioned on a circle (specifically, a broken-line circle shown in FIG. 4) having the center of the cavity 22 as a center point. For this reason, the inner peripheral surfaces 231a to 231h are curved surfaces.

  The recesses 232a to 232h are provided alternately with the inner peripheral surfaces 231a to 231h in the circumferential direction. That is, in FIG. 2, the inner peripheral surface 231a, the concave portion 232a, the inner peripheral surface 231b, the concave portion 232b,..., The inner peripheral surface 231h, and the concave portion 232h are provided in this order. The concave portions 232a to 232h are groove portions formed so as to be curved with a predetermined curvature, respectively. Specifically, the recesses 232a to 232h are formed in a crescent shape.

  In the present embodiment, the positions of the inner peripheral surfaces 231 a to 231 h and the recesses 232 a to 232 h are provided so as to correspond to the fuel injection direction from the injection nozzle 52 of the injector 50. Specifically, inner peripheral surfaces 231a to 231h are provided at positions where fuel injected from the injection nozzle 52 collides.

  FIG. 4 is a schematic diagram for explaining the positional relationship between the injection holes 53a to 53h of the injection nozzle 52, the inner peripheral surfaces 231a to 231h, and the recesses 232a to 232h. As shown in FIG. 4, the injection nozzle 52 is located on the center of the cavity 22 (specifically, the central raised portion 223). And the injection nozzle 52 has the eight injection holes 53a-53h. The injection holes 53a to 53h are arranged on the outer peripheral surface of the injection nozzle 52 so as to be separated at a predetermined interval in the circumferential direction. The injection holes 53a to 53h each inject fuel in the radial direction (the direction of the arrow shown in FIG. 4). In the following, it is assumed that the fuel injection direction is the radial direction.

  Of the inner peripheral surfaces 231a to 231h and the recesses 232a to 232h, inner peripheral surfaces 231a to 231h are positioned on the extension of the fuel injection direction by the injection holes 53a to 53h. For example, an inner peripheral surface 231a is provided at a collision point of fuel injected from the injection port 53a. Thereby, the fuel injected from the injection holes 53a to 53h collides with the inner peripheral surfaces 231a to 231h. In this embodiment, since the recesses 232a to 232h are provided so as to be smoothly connected to the inner peripheral surfaces 231a to 231h, the fuel that has collided with the inner peripheral surfaces 231a to 231h is directed to the adjacent recesses 232a to 232h. Flow without reducing the flow velocity and mix with air.

  As an example, the fuel flow in the vicinity of the inner peripheral surface 231a will be described with reference to FIG. The fuel flow in the vicinity of the inner peripheral surfaces 231b to 231h is the same as the fuel flow in the vicinity of the inner peripheral surface 231a, and thus the description thereof is omitted.

FIG. 5 is a schematic diagram for explaining the flow of fuel in the inner peripheral surface 231a and the recesses 232a and 232h. In FIG. 5, the flow of the fuel injected from the injection hole 53a is indicated by a one-dot chain line arrow.
As shown in FIG. 5, the fuel injected from the injection holes 53a flows in the radial direction toward the inner peripheral surface 231a. The fuel, for example, collides with the inner peripheral surface 231a to branch in the circumferential direction, and flows to the concave portion 232a and the concave portion 232h located on both sides of the inner peripheral surface 231a. At this time, since the recesses 232a and 232h are smoothly connected to the inner peripheral surface 231a, the branched fuel flows like a slide on the recesses 232a and 232h, so the flow rate of the fuel toward the recesses 232a and 232h decreases. Can be suppressed. By maintaining the flow rate of the fuel in this manner, the fuel is easily mixed with air in the recesses 232a and 232h, and the mixing of the fuel and air is promoted. As a result, the combustion efficiency of the air-fuel mixture in which fuel and air are mixed can be improved, and the generation of pollutants in the internal combustion engine can be suppressed.

Further, when the recesses 232a to 232h are provided in the lip portion 221, the compressive stress (specifically, in the piston 20 generated due to thermal expansion due to combustion in the combustion chamber 21 is compared with the case where the recesses 232a to 232h are not provided. Specifically, the compressive stress in the lip portion 221 can be reduced. This is because the recesses 232a to 232h serve as a refuge for the compressive stress even if compressive stress occurs. Thus, the durability of the piston 20 can be improved by reducing the compressive stress.
In order to relieve the compressive stress, a method of forming the recesses 232a to 232h deeply may be considered, but from the viewpoint of achieving both the promotion of mixing of fuel and air and the improvement of the durability of the piston 20, It is desirable that the inner peripheral surfaces 231a to 231h and the recesses 232a to 232h are wavy without increasing the depth of the recesses 232a to 232h.

  In the above description, the recesses 232a to 232h have a crescent shape, but are not limited thereto. If the fuel flows smoothly from the inner peripheral surfaces 231a to 231h to the recesses 232a to 232h, the recesses 232a to 232h may have other shapes.

<Effect in this embodiment>
According to the above-described embodiment, the lip portion 221 of the cavity 22 into which fuel is injected from the injection nozzle 52 is arranged along the circumferential direction in order to promote the movement of the fuel in the circumferential direction along the lip portion 221. Inner peripheral surfaces 231a to 231h and recesses 232a to 232h, which are uneven portions formed in this manner, are provided.
In such a case, the fuel injected from the injection nozzle 52 to the lip portion 221 flows while maintaining the flow velocity along the circumferential direction by the inner peripheral surfaces 231a to 231h and the recesses 232a to 232h that are smoothly connected to each other. . As described above, the fuel flows in a state where the flow velocity does not decrease, so that mixing of fuel and air in the combustion chamber 21 (particularly, the recesses 232a to 232h) is promoted. As a result, the combustion efficiency is improved and the generation of pollutants in the internal combustion engine can be suppressed.
Further, since the recesses 232a to 232h serve as escape points for the compressive stress generated due to the thermal expansion caused by the combustion in the combustion chamber 21, the compressive stress can be relaxed. As a result, the durability of the piston 20 can be improved.

  In the above description, the lip portion 221 is provided with the eight inner peripheral surfaces 231a to 231h and the concave portions 232a to 232h, respectively, but is not limited thereto. For example, when the number of injection holes of the injection nozzle 52 is six, the inner peripheral surface of the lip portion 221 and the number of concave portions may be six.

  In the above description, the recesses 232a to 232h are formed to be curved with a predetermined curvature, but the present invention is not limited to this. For example, the recesses 232a to 232h may not be curved with a predetermined curvature.

  In the above description, the engine 1 is mounted on the truck. However, the present invention is not limited to this. For example, the engine 1 may be mounted on a bus or a ship.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Engine 10 Cylinder 20 Piston 21 Combustion chamber 22 Cavity 52 Injection nozzle 53a-53h Injection hole 221 Lip part 231a-231h Inner peripheral surface 232a-232h Concave part

Claims (5)

A piston that reciprocates in a cylinder;
An injection nozzle for injecting fuel into a combustion chamber formed by the piston;
An internal combustion engine comprising:
The piston is
A cavity forming a combustion chamber;
A plurality of concavo-convex portions formed along the circumferential direction on the inner circumferential wall surface of the cavity located in the fuel injection direction, in order to promote the movement of the fuel in the circumferential direction;
An internal combustion engine. The injection nozzle has a plurality of injection holes for injecting the fuel in different directions,
The convex portions of the concave and convex portions are respectively located in portions where the fuel injected by each of the plurality of injection holes hits.
The internal combustion engine according to claim 1. The concave portion of the concavo-convex portion is a groove portion formed so as to be curved with a predetermined curvature.
The internal combustion engine according to claim 1 or 2. The top surface of the convex portion of the concavo-convex portion is formed so as to be located on a virtual circle with the center of the cavity as a center point.
The internal combustion engine according to any one of claims 1 to 3. A piston of an internal combustion engine into which fuel is directly injected,
A cavity forming a combustion chamber;
A plurality of concavo-convex portions formed along the circumferential direction on the inner circumferential wall surface of the cavity located in the fuel injection direction, in order to promote the movement of the fuel in the circumferential direction;
A piston.

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