piston

Abstract

To provide a piston that can control the location of crack occurrence in the heat shielding film provided on the top surface. [Solution] The piston 20 is installed inside the cylinder of an internal combustion engine. A heat shield film 30 is formed on the top surface 22 of the piston 20. The heat shield film 30 is composed of a first portion 31 and a second portion 32 which is thinner than the first portion 31.

Description

Technical Field

[0001] The present invention relates to a piston provided in an internal combustion engine.

Background Art

[0002] As disclosed in Patent Document 1, a piston is provided in a cylinder of an internal combustion engine, and a combustion chamber is partitioned by the piston. That is, the top surface of the piston faces the combustion chamber. In order to suppress heat transfer from the combustion chamber to the piston, a heat insulating film is formed on the top surface of the piston.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The linear thermal expansion coefficient is different between the constituent members of the piston and the material of the heat insulating film. Therefore, stress caused by differences in the amount of thermal expansion and contraction between the piston and the heat insulating film is applied to the heat insulating film. In addition, a load caused by the cylinder pressure, which is the pressure inside the cylinder where the piston is provided, is applied to the heat insulating film. The cylinder pressure fluctuates greatly during the operation of the internal combustion engine. Therefore, the greater the stress amplitude, which is the amplitude of the load fluctuation, the greater the load acting on the heat insulating film. Therefore, if the internal combustion engine is used over a long period of time, cracks may occur in the heat insulating film. Depending on the crack generation position, the heat transfer suppression effect from the combustion chamber to the piston may be significantly reduced.

Means for Solving the Problems

[0005] A piston designed to solve the above problems is provided inside the cylinder of an internal combustion engine. The piston is equipped with a heat shield on its top surface. The heat shield is composed of a first portion and a second portion that is thinner than the first portion. [Effects of the Invention]

[0006] The piston described above has the effect of being able to control the location of crack formation in the heat shield film provided on its top surface. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic diagram showing an internal combustion engine equipped with a piston according to an embodiment. [Figure 2] Figure 2 is a top view of the piston shown in Figure 1. [Figure 3] Figure 3 is a cross-sectional view taken along the line 3-3 in Figure 2. [Figure 4] Figure 4 is a diagram illustrating the process of cracks occurring in the heat-shielding film. [Modes for carrying out the invention]

[0008] An embodiment of the piston will be described below with reference to Figures 1 to 4. <Configuration of an internal combustion engine> Figure 1 shows an internal combustion engine 10 equipped with a piston 20 of this embodiment. The internal combustion engine 10 further comprises a plurality of cylinders 11, an intake passage 12, and an exhaust passage 13. Only one of the plurality of cylinders 11 is shown in Figure 1. Within the plurality of cylinders 11, a combustion chamber 14 is partitioned by the piston 20. A fuel injection valve 15 and a spark plug 16 are also provided for each of the plurality of cylinders 11.

[0009] Air is introduced into the combustion chamber 14 via the intake passage 12. Fuel is supplied to the combustion chamber 14 from the fuel injection valve 15. Then, in the combustion chamber 14, the mixture of air and fuel is burned by the spark discharge of the spark plug 16. The exhaust gas generated in the combustion chamber 14 by the combustion of the mixture is discharged into the exhaust passage 13.

[0010] <Piston configuration> As shown in Figure 1, the piston 20 comprises a piston body 21 made of a metal material and a heat shield film 30. The piston body 21 has a top surface 22 that faces the combustion chamber 14.

[0011] As shown in Figures 2 and 3, a projection 23 is provided on the top surface 22. The projection 23 is ring-shaped and surrounds the center of the top surface 22. The heat shield film 30 is a thin film provided on the top surface 22. The heat shield film 30 is a film that suppresses the transfer of heat from the combustion chamber 14 to the piston 20. As shown in Figure 3, the protruding portion 23 is covered by the heat shield film 30.

[0012] The heat-shielding film 30 is composed of a first portion 31 and a second portion 32 which is thinner than the first portion 31. The second portion 32 is provided on the protruding portion 23. Therefore, the second portion 32 is provided so as to surround the center of the top surface 22. Furthermore, the portion of the heat-shielding film 30 that is inside the second portion 32 and the portion that is outside the second portion 32 are each the first portion 31.

[0013] <Operation of this embodiment> The operation of this embodiment will be explained with reference to Figure 4. During the combustion stroke of the internal combustion engine 10, the heat shield film 30 is exposed to high temperatures. On the other hand, the heat insulating effect of the heat shield film 30 relatively suppresses the temperature rise of the piston body 21. Furthermore, the linear thermal expansion coefficients of the constituent materials of the piston body 21 and the heat shield film 30 are different. Therefore, compressive stress acting on the heat shield film 30 is caused by the difference in the amount of thermal expansion between the piston body 21 and the heat shield film 30.

[0014] Since the heat-insulating film 30 is a thin film, the heat capacity of the piston 20 is larger than that of the heat-insulating film 30. Therefore, in the intake stroke of the internal combustion engine 10, the piston 20 becomes hotter than the heat-insulating film 30. As a result, tensile stress acts on the heat-insulating film 30.

[0015] That is, during the operation of the internal combustion engine 10, the period in which compressive stress acts on the heat-insulating film 30 and the period in which tensile stress acts on the heat-insulating film 30 are alternately repeated. Therefore, cracks 100 are likely to occur in the heat-insulating film 30.

[0016] In addition, a load caused by the in-cylinder pressure, which is the pressure in the cylinder 11, is applied to the heat-insulating film 30. The load applied to the heat-insulating film 30 fluctuates. The greater the stress amplitude, which is the amplitude of such load fluctuations, the more likely the heat-insulating film 30 is to be damaged.

[0017] In the heat-insulating film, cracks are likely to occur in vulnerable parts as described above. The thinner part is more vulnerable than the thicker part. Therefore, cracks are more likely to occur in the thinner part than in the thicker part.

[0018] In this regard, the heat-insulating film 30 of the piston 20 includes not only the first part 31 but also the second part 32 that is thinner than the first part 31. That is, as shown in FIG. 4, in the heat-insulating film 30, cracks 100 are more likely to occur in the second part 32 than in the first part 31. Therefore, in the piston 20 of the present embodiment, the occurrence of cracks 100 in the first part 31 is suppressed.

[0019] <Effects of the present embodiment> (1) When cracks 100 occur in the piston 20 of the present embodiment, cracks 100 are more likely to occur in the second part 32 than in the first part 31. Therefore, in the piston 20, the location where cracks 100 occur can be controlled.

[0020] (2) In the piston 20, the central portion becomes the hottest. Heat moves from the high-temperature portion to the low-temperature portion. Therefore, if a crack 100 occurs in the central portion of the piston 20, the heat insulation characteristics by the heat insulation film 30 will be significantly reduced.

[0021] In this regard, in the present embodiment, as shown in FIG. 2, the second portion �2 is provided so as to surround the center of the top surface 22. Therefore, it is difficult for a crack 100 to occur in the heat insulation film 30 at the central portion of the piston 20. Thus, in the piston 20, even if a crack 100 occurs in the heat insulation film 30, it is possible to suppress a significant reduction in the heat insulation characteristics by the heat insulation film 30.

[0022] <Modified Example> The above embodiment can be implemented with the following modifications. The above embodiment and the following modified examples can be implemented in combination with each other within a technically non-contradictory range.

[0023] · If it is possible to form the heat insulation film 30 including the first portion 31 and the second portion 32 on the top surface 22, the protrusion 23 may not be provided on the top surface 22. · If the second portion 32 forms an annular shape, it does not have to be a circular ring shape.

[0024] · If the second portion 32 surrounds the center of the piston 20, it does not have to form an annular shape.

Explanation of Reference Numerals

[0025] 10…Internal combustion engine, 11…Cylinder, 20…Piston, 21…Piston body, 22…Top surface, 23…Protrusion, 30…Heat insulation film, 31…First portion, 32…Second portion.

Claims

1. A piston located inside the cylinder of an internal combustion engine, Equipped with a heat-shielding film on the top surface, The heat-shielding film is composed of a first portion and a second portion that is thinner than the first portion. piston.

2. The second portion is provided so as to surround the center of the top surface, Of the heat-shielding film, the portion inside the second portion and the portion outside the second portion are each the first portion. The piston according to claim 1.

3. The aforementioned second part is ring-shaped. The piston according to claim 2.

4. The top surface is provided with a protrusion, and the second portion is provided on the protrusion. A piston according to any one of claims 1 to 3.

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