WO2020196098A1

WO2020196098A1 - Diesel engine

Info

Publication number: WO2020196098A1
Application number: PCT/JP2020/011731
Authority: WO
Inventors: 和之甲田; 真幹栗林
Original assignee: ヤンマー株式会社
Priority date: 2019-03-25
Filing date: 2020-03-17
Publication date: 2020-10-01
Also published as: JP2020159222A

Abstract

Provided is a diesel engine (1) comprising a piston (5) and a fuel injection valve (6), wherein the piston (5) has, formed in the piston top surface (50), a cavity (51) which opens towards the lower surface side of a cylinder head (3) and which contains a bottom surface (51b) and an inside surface (51c), the fuel injection valve (6) injects fuel to part of the inside surface (51c) of the cavity (51), and the piston top surface (50) has dimples (52) formed on only the area (50a) corresponding to the fuel injection direction (60) of the fuel injection valve (6) in plan view.

Description

diesel engine

The present invention relates to a diesel engine mounted on construction machinery, agricultural machinery, ships, etc.

The following Patent Document 1 describes a combustion chamber structure of an internal combustion engine including a fuel injection valve for injecting fuel toward the combustion chamber, and dimples in a region where the fuel spray from the fuel injection valve does not directly hit the wall surface of the combustion chamber. The combustion chamber structure in which the is formed is disclosed. According to this configuration, air stays in the dimples to form a heat insulating layer, so that the heat insulating property can be improved and the heat loss to the piston can be reduced.

Japanese Unexamined Patent Publication No. 2011-94496

However, as a result of research, the heat loss on the top surface of the piston is larger than that on the wall surface of the combustion chamber, and in the configuration of Patent Document 1, dimples are formed on the wall surface of the combustion chamber where the heat loss is relatively small. The reduction effect of is small.

Therefore, in view of the above problems, an object of the present invention is to provide a diesel engine capable of effectively reducing heat loss.

The diesel engine of the present invention has a cylinder liner and
A cylinder head arranged so as to face the top surface of the cylinder liner,
A piston slidably fitted inside the cylinder liner,
In a diesel engine with a fuel injection device
A cavity is formed on the top surface of the piston so as to open toward the side of the cylinder head facing the cylinder liner and include a bottom surface and an inner surface surface.
The fuel injection device injects fuel toward a part of the inner surface of the cavity.
A recess is formed on the top surface of the piston only in a region corresponding to the fuel injection direction of the fuel injection device in a plan view.

According to the present invention, by forming the recess only in the region corresponding to the fuel injection direction on the top surface of the piston, the air in the recess forms a heat insulating layer, so that the piston in the fuel injection direction having the largest heat loss The heat loss to the top surface of the piston can be effectively reduced.

It is sectional drawing which shows the diesel engine which concerns on 1st Embodiment. It is a top view of a piston. It is sectional drawing of the piston which concerns on another embodiment. It is sectional drawing of the piston which concerns on another embodiment. It is sectional drawing of the piston top surface which concerns on 2nd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First Embodiment)
The diesel engine 1 includes a cylinder block 2, a cylinder head 3 arranged above the cylinder block 2, and a piston 5 slidably fitted to a cylinder liner 4 arranged inside the cylinder block 2. I have.

A cavity 51 is formed on the piston top surface 50 of the piston 5. The cavity 51 includes an opening 51a that opens toward the lower surface side of the cylinder head 3. The opening 51a is substantially circular. Further, the cavity 51 includes a bottom surface 51b and an inner side surface 51c. The bottom surface 51b is substantially circular in plan view, and the inner side surface 51c is a region between the bottom surface 51b and the opening 51a.

When the piston 5 descends, the combustion chamber is a space composed of a cylinder head 3, a cylinder liner 4, a piston top surface 50, and a cavity 51. In the combustion chamber, heat is transferred from the high temperature gas (combustion gas) to the cooling water and the lubricating oil through the cylinder head 3, the cylinder liner 4, and the piston 5, and heat loss (cooling loss) occurs. As a result of diligent research, the present inventor has the largest ratio of heat loss to the piston top surface 50 in the heat loss in the combustion chamber, and improves thermal efficiency by reducing the heat loss to the piston top surface 50. I found that it could be improved.

A fuel injection valve 6 as a fuel injection device is provided on the lower surface of the cylinder head 3. The fuel injection valve 6 of the present embodiment is arranged so that the injection port is located substantially at the center of the opening 51a of the cavity 51 in a plan view, but is not limited to this, and is arranged at a position off the center. You may. The fuel injection valve 6 injects fuel pressurized by a fuel injection pump (not shown) or high-pressure fuel stored in a common rail (not shown) into the combustion chamber. More specifically, the fuel injection valve 6 injects fuel toward a part of the inner surface 51c of the cavity 51 when the piston 5 is located near the top dead center.

The fuel injection direction 60 by the fuel injection valve 6 extends radially around the fuel injection valve 6 as shown in FIG. 2 in a plan view. The fuel injection direction 60 is the central axis direction of the injection port provided in the fuel injection valve 6. In the present embodiment, the fuel injection valve 6 is provided with four injection ports at equal intervals in the circumferential direction, and the four

fuel injection directions

60a, 60b, 60c, and 60d are at equal intervals in the circumferential direction. The jet flow from the injection port is formed in a region of ± α ° in the

fuel injection directions

60a, 60b, 60c, 60d. In the present embodiment, the fuel injection valve 6 is provided with four injection ports, but the present invention is not limited to this, and three or less or five or more injection ports may be provided.

A plurality of dimples 52 (an example of recesses) are formed on the piston top surface 50 of the piston 5. The plurality of dimples 52 are formed only in the region 50a of the piston top surface 50 corresponding to the fuel injection direction 60 of the fuel injection valve 6 in a plan view. The region 50a corresponding to the fuel injection direction 60 of the fuel injection valve 6 is a region of ± β ° of the fuel injection direction 60. Preferably, β is 22.5 or less. Also, β> α.

By forming a plurality of dimples 52 only in the region 50a of the piston top surface 50 corresponding to the fuel injection direction 60, the air in the dimples 52 forms a heat insulating layer, so that the fuel injection direction 60 having the largest heat loss The heat loss to the piston top surface 50 can be effectively reduced. When the dimples 52 are formed on the entire surface of the piston top surface 50, the wall surface temperature of the combustion chamber rises too much and intake air heating occurs, or the volumetric efficiency decreases, resulting in deterioration of combustion efficiency. By forming the dimples 52 only in the region 50a corresponding to the fuel injection direction 60, intake air heating and volumetric efficiency reduction can be suppressed.

The plurality of dimples 52 are formed by dimple processing. Dimple processing includes a method using a laser beam, a method using shot blasting, and the like. The dimple 52 of the present embodiment is formed in a hemispherical shape. The radius of the hemispherical dimple 52 is 0.5 to 100 μm, preferably 1 to 20 μm. Although the dimple 52 of the present embodiment is hemispherical, it may have another shape. Further, the shapes of the plurality of dimples 52 may be the same or different.

As described above, the diesel engine 1 of the present embodiment is the diesel engine 1 having the piston 5 and the fuel injection valve 6, and the piston 5 opens to the piston top surface 50 toward the lower surface side of the cylinder head 3. A cavity 51 including a bottom surface 51b and an inner surface 51c is formed, the fuel injection valve 6 injects fuel toward a part of the inner surface 51c of the cavity 51, and the piston top surface 50 is viewed in plan view. The dimple 52 is formed only in the region 50a corresponding to the fuel injection direction 60 of the fuel injection valve 6.

According to this configuration, by forming the dimples 52 only in the region 50a corresponding to the fuel injection direction 60 of the piston top surface 50, the air in the dimples 52 forms a heat insulating layer, so that the fuel having the largest heat loss. The heat loss to the piston top surface 50 in the injection direction 60 can be effectively reduced.

Further, in the present embodiment, as shown in FIG. 3, it is preferable that the volume of the dimple 52 increases as the distance from the cavity 51 increases. The volume of the dimple 52 is determined by the opening area and depth of the dimple 52. In the dimple 52 of the present embodiment, the radius is increased as the distance from the cavity 51 increases.

Since the size of the turbulent vortex becomes large in the latter half of the jet, it is difficult for the combustion gas to flow in even if the dimple 52 is made large, and the air in the dimple 52 can stay and maintain the heat insulating layer. Therefore, by increasing the volume of the dimples 52 and increasing the heat insulating layer of air, heat insulation can be performed more efficiently.

Further, in the present embodiment, as shown in FIG. 4, it is preferable that the region 50a in which at least the dimple 52 is formed in the piston top surface 50 is inclined so as to be lowered toward the cavity 51.

By inclining the region 50a, the reverse squish flow from the cavity 51 to the cylinder liner 4 can be relaxed. As a result, the turbulent vortex due to the reverse squish flow is not reduced, and the fuel gas can be suppressed from flowing into the dimple 52. As a result, the air in the dimples 52 stays and the heat insulating layer can be held, so that heat insulation can be effectively performed.

(Second Embodiment)
In the above-described embodiment, the recess is formed by dimple processing, but the recess may be formed by oil repellent processing. For oil repellent treatment, a method of coating the piston top surface 50 with a fluororesin such as PTFE (polytetrafluoroethylene), or a method of applying hot water treatment to the aluminum alloy piston 5 to form bemite on the piston top surface 50. There are methods and so on. The method of coating with a fluororesin makes it easy to process recesses. The method of applying hot water treatment is excellent in the durability of the recesses. When the oil repellent treatment is performed, as shown in FIG. 5, a needle-shaped structure is formed on the piston top surface 50, and a recess is formed between the adjacent needle-shaped portions 53. That is, the concave portion in the present invention is consequently formed between the convex portions (needle-shaped portion 53 in this example) formed so as to project from the reference surface with the piston top surface 50 formed in advance as the reference surface. It is a concept that includes recesses. Since the needle-shaped portion 53 forms a recess on the top surface 50 of the piston, the same effect as that of the dimple 52 described above can be obtained. Further, by performing the oil repellent treatment, it is possible to prevent the lubricating oil in the diesel engine 1 from adhering to the region 50a of the piston top surface 50 in addition to the fuel.

[Other Embodiments]
In the case of the diesel engine 1 in which swirl is generated, the fuel injected from the fuel injection valve 6 reaches the inner surface 51c of the cavity 51 while moving in the circumferential direction under the influence of the swirl. Therefore, the region 50a forming the recess is appropriately set according to the flow velocity of the swirl and the like.

The engine of the present invention is not limited to the series type in which the piston reciprocates in the vertical direction as in the above-described embodiment, but may be a horizontally opposed type in which the piston reciprocates in the horizontal direction, a V type, or the like.

Although the embodiments of the present invention have been described above based on the drawings, it should be considered that the specific configuration is not limited to these embodiments. The scope of the present invention is shown not only by the description of the above-described embodiment but also by the scope of claims, and further includes all modifications within the meaning and scope equivalent to the scope of claims.

This application claims priority based on Japanese Patent Application No. 2019-0566884 filed in Japan on March 25, 2019. Its contents are incorporated into this application by reference to this. In addition, all of the documents cited in the present specification are specifically incorporated by reference to them.

1 Diesel engine 3 Cylinder head 5 Piston 50 Piston top surface 51 Cavity 51c Inner surface 52 Dimple 53 Needle-shaped part 6 Fuel injection valve 60 Fuel injection direction

Claims

With a cylinder liner
A cylinder head arranged so as to face the top surface of the cylinder liner,
A piston slidably fitted inside the cylinder liner,
In a diesel engine with a fuel injection device
A cavity is formed on the top surface of the piston so as to open toward the side of the cylinder head facing the cylinder liner and include a bottom surface and an inner surface surface.
The fuel injection device injects fuel toward a part of the inner surface of the cavity.
A diesel engine in which a recess is formed on the top surface of the piston only in a region corresponding to the fuel injection direction of the fuel injection device in a plan view.
The diesel engine according to claim 1, wherein the recess is formed by dimple processing on the top surface.
The diesel engine according to claim 1, wherein the recess is formed by oil-repellent processing on the top surface.
The diesel engine according to any one of claims 1 to 3, wherein at least a region of the top surface of the piston in which the recess is formed is inclined so as to descend toward the cavity.
The diesel engine according to claim 2, wherein the volume of the recess increases as the distance from the cavity increases.