JP2023105653A - piston and internal combustion engine - Google Patents

Abstract

To reduce thermal loss of an internal combustion engine.SOLUTION: A piston 100 includes: a coating 6 with a multilayer structure at a piston crown surface 12. The coating 6 includes: a low-thermal conductivity layer 4 having a thermal conductivity that is lower than a base material of the piston 100; and a high-thermal conductivity layer 5 having a thermal conductivity that is higher than the low-thermal conductivity layer 4. An uppermost layer of the coating 6 is the high-thermal conductivity layer 5 and the lowermost layer of the high-thermal conductivity layer 5 is the low-thermal conductivity layer 4.SELECTED DRAWING: Figure 1

Description

The present invention relates to pistons and internal combustion engines.

Patent Literature 1 discloses a conventional piston in which a heat insulating layer made of a porous material having a lower thermal conductivity than the base material of the piston is formed on a cavity of the crown surface of the piston.

JP 2015-218608 A

By forming a low thermal conductivity layer (insulating layer) on the crown surface of the piston, as in the conventional piston described above, heat transfer from the flame to the piston is suppressed, reducing heat loss from the inner wall surface of the cylinder. can be done.

However, even if a low thermal conductivity layer is formed on the crown surface of the piston, the low thermal conductivity layer has a flame contact portion that contacts the flame generated in the combustion chamber and a non-flame contact portion that does not contact (or is difficult to contact). When this occurs, it is difficult for heat to diffuse inside the low thermal conductivity layer, and therefore the heat from the flame contacting portion is difficult to transfer to the flame non-contacting portion, resulting in the low thermal conductivity layer having a high temperature portion and a low temperature portion. As a result, the heat loss from the low temperature portion increases, and the effect of reducing the heat loss by forming the low thermal conductivity layer on the crown surface of the piston decreases.

The present invention has been made with a focus on such problems. It is an object of the present invention to suppress deterioration in the effect of reducing heat loss when a portion and a non-flame contact portion occur.

In order to solve the above problems, a piston according to one aspect of the present invention has a multi-layered coating formed on the crown surface of the piston. The coating includes a low thermal conductivity layer having a lower thermal conductivity than the base material of the piston and a high thermal conductivity layer having a higher thermal conductivity than the low thermal conductivity layer, the top layer of the coating having a high thermal conductivity. layer, and the lower layer of the high thermal conductivity layer is the low thermal conductivity layer.

Further, in the internal combustion engine according to one aspect of the present invention, a multi-layer coating is formed on at least a portion of the combustion chamber wall surface. The coating comprises a low thermal conductivity layer having a lower thermal conductivity than the member to which the coating is applied and a high thermal conductivity layer having a higher thermal conductivity than the low thermal conductivity layer, the top layer of the coating being a high thermal conductivity layer. It is a conductivity layer, and the lower layer of the high thermal conductivity layer is the low thermal conductivity layer.

According to these aspects of the present invention, even if the coating formed on at least a part of the piston crown surface or the combustion chamber wall surface has a flame contact portion and a flame non-contact portion, the top layer of the coating has high heat conductivity. Since it is a high efficiency layer, the heat can be quickly diffused from the flame contact area to the flame non-contact area. Therefore, the temperature of the uppermost layer of the coating can be leveled, and the formation of high temperature portions and low temperature portions in the coating can be suppressed. Therefore, when a flame contact portion and a flame non-contact portion are generated in the coating, it is possible to suppress deterioration in the heat loss reducing effect of the coating.

1 is a front view of a piston according to one embodiment of the invention; FIG. FIG. 2A is a diagram illustrating the effects of a piston according to one embodiment of the present invention, that is, the effects of a piston having a low thermal conductivity layer formed on the crown surface of the piston and a high thermal conductivity layer formed on the surface thereof. . FIG. 2B is a diagram illustrating the effects of a piston according to one embodiment of the present invention, that is, the effects of a piston having a low thermal conductivity layer formed on the crown surface of the piston and a high thermal conductivity layer formed on the surface thereof. . Figure 3 shows the reflectance of the infrared rays (electromagnetic waves) emitted by the flame (luminous flame) in the combustion chamber. , and is a diagram showing the experimental results compared. FIG. 4 is a diagram for explaining problems with a piston according to a comparative example different from the present invention, that is, a piston having only a low thermal conductivity layer formed on the crown surface of the piston.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same reference numerals are given to the same constituent elements.

FIG. 1 is a front view of a piston 100 according to one embodiment of the invention.

Piston 100 is a component that is housed in a cylinder formed in a cylinder block of an internal combustion engine so as to reciprocate inside the cylinder, and forms a combustion chamber in the cylinder together with the cylinder head. A piston 100 according to this embodiment is an iron piston whose base material is cast iron, and includes a piston head 1 , a piston skirt 2 , and a piston boss 3 .

As shown in FIG. 1, the piston head 1 is a disk-shaped portion having a predetermined thickness in the axial direction of the cylinder (vertical direction in FIG. 1), and is exposed to high-temperature combustion gas during engine operation. part.

A plurality of piston ring grooves 11 are formed on the side surface of the piston head 1 along the entire circumferential direction. In the piston ring groove 11, a compression ring for suppressing compression leakage and gas leakage by maintaining the airtightness of the combustion chamber, transmitting the heat of the piston 100 to the cylinder block (inner wall surface of the cylinder) and releasing it, and the cylinder. An oil ring is attached to scrape off excess lubricating oil adhering to the inner wall surface of the cylinder and form an oil film having an appropriate thickness on the inner wall surface of the cylinder.

The piston skirt 2 is a portion formed so as to extend from the piston head 1 toward the crankshaft in the axial direction of the cylinder (lower side in FIG. 1). This is the part that has the function of suppressing the

The piston boss 3 is a portion for holding a piston pin for connecting the piston 100 and the connecting rod, and is a portion formed with a pin hole 31 for inserting the piston pin.

Here, in the present embodiment, as shown in FIG. 1, a multi-layer coating 6 is formed on a surface 12 of the piston head 1 (hereinafter referred to as "piston crown surface") that constitutes a part of the inner wall surface of the combustion chamber. It is The coating 6 according to the present embodiment is formed on the piston crown surface 12 and is made of a material having a lower thermal conductivity than the base material of the piston 100 (if the base material of the piston 100 is cast iron, for example, SUS material (stainless steel)). and a material having a higher thermal conductivity than the base material of the piston 100 (for example, aluminum if the base material of the piston 100 is cast iron) formed on the surface of the low thermal conductivity layer 4 and a high thermal conductivity layer 5. The reason why such a multi-layer coating 6 is formed on the piston crown surface 12 will be described below.

Among the various losses in an internal combustion engine, the proportion of heat loss from the inner wall surface of the combustion chamber is large. Therefore, in order to improve the thermal efficiency of the internal combustion engine, it is effective to reduce the heat loss from the inner wall surface of the combustion chamber. is.

Therefore, conventionally, in order to suppress heat transfer to the piston 100 and reduce heat loss from the inner wall surface of the cylinder, a low thermal conductivity layer 4 ( A thermal insulation layer) is being formed. However, as a result of intensive research by the inventors, it has been found that simply forming the low thermal conductivity layer 4 on the piston crown surface 12 causes the following problems, and the effect of reducing heat loss may not be sufficiently obtained. I found out.

4A and 4B are diagrams for explaining problems when only the low thermal conductivity layer 4 is formed on the piston crown surface 12. FIG.

As shown in FIG. 4, when only the low thermal conductivity layer 4 is formed on the piston crown surface 12, the low thermal conductivity layer 4 has a portion that comes into contact with the flame generated in the combustion chamber (hereinafter referred to as “flame contact portion”. ) 41 and a non-contact (or hard-to-contact) portion (hereinafter referred to as “flame non-contact portion”) 42 may occur. Note that FIG. 4 shows an example in which the central portion of the piston crown surface 12 is the flame contact portion 41 and the outer peripheral portion of the piston crown surface 12 is the flame non-contact portion 42 .

When the flame contact portion 41 and the flame non-contact portion 42 are generated in the low thermal conductivity layer 4 , the flame contact portion 41 is heated by the flame and the temperature rises. is difficult to diffuse, and therefore the heat of the flame contact portion 41 is difficult to be transmitted to the flame non-contact portion 42, so the temperature of the flame non-contact portion 42 is difficult to rise. That is, when the flame contact portion 41 and the flame non-contact portion 42 are generated in the low thermal conductivity layer 4, the flame contact portion 41 locally becomes hot, but the flame non-contact portion 42 remains at a low temperature and has a low thermal conductivity. A high temperature portion and a low temperature portion will be generated in the layer 4 .

As a result, for example, in an expansion stroke or an exhaust stroke, the temperature difference between the gas temperature in the combustion chamber and the non-flame contact portion 42 of the low thermal conductivity layer 4 increases, so heat loss from the non-flame contact portion 42 increases. . Further, as described above, the heat of the flame contact portion 41 is difficult to be transferred to the non-flame contact portion 42, so once the temperature of the flame contact portion 41 rises, it is difficult to decrease, and therefore, it is easy to maintain the high temperature. Therefore, the flame contact portion 41 raises the temperature of the air (fresh air) sucked into the combustion chamber during the intake stroke, and thus the temperature of the air-fuel mixture. This causes an increase in heat loss from the inner wall surface of the cylinder over time. Thus, when only the low thermal conductivity layer 4 is formed on the piston crown surface 12, the loss in each stroke increases when the flame contact portion 41 and the flame non-contact portion 42 are generated in the low thermal conductivity layer 4. As a result, the effect of improving the thermal efficiency of the internal combustion engine cannot be sufficiently obtained.

Therefore, in this embodiment, as shown in FIG. Hereinafter, with reference to FIGS. 2A and 2B, the effect of forming the multi-layered film 6 composed of the low thermal conductivity layer 4 and the high thermal conductivity layer 5 on the piston crown surface 12 will be described.

1, 2A and 2B, the thicknesses of the low thermal conductivity layer 4 and the high thermal conductivity layer 5 are exaggerated, and in the present embodiment, the thickness of the high thermal conductivity layer 5 is The thickness of the high thermal conductivity layer 5 is about several μm, which is thinner than the thickness of the low thermal conductivity layer 4, and the thickness of the low thermal conductivity layer 4 is about several hundred μm.

By forming the high thermal conductivity layer 5 on the surface of the low thermal conductivity layer 4 as shown in FIG. Heat is easily diffused inside the conductivity layer 5, and therefore the heat of the flame contacting portion 51 is easily transferred to the flame non-contacting portion 52, so that the temperature of the high thermal conductivity layer 5 is quickly leveled as shown in FIG. 2B. , the high thermal conductivity layer 5 can be prevented from having a high temperature portion and a low temperature portion. As described above, the high thermal conductivity layer 5 is required to quickly diffuse the heat of the flame contact portion 51 to the flame non-contact portion 52 as its function. Therefore, as described above, the thickness of the high thermal conductivity layer 5 is about several μm in this embodiment, but the thickness of the high thermal conductivity layer 5 is made as thin as possible within the range where the desired function can be exhibited. Alternatively, it is desirable to make the heat capacity as small as possible for the same purpose.

In addition, since the low thermal conductivity layer 4 exists in the lower layer of the high thermal conductivity layer 5, the heat transfer (heat conduction in the depth direction) from the flame contact portion 51 to the low thermal conductivity layer 4 side is suppressed. can be suppressed. Therefore, the transfer of heat (heat conduction in the planar direction) from the flame contact portion 51 to the flame non-contact portion 52 can be promoted, so that the high thermal conductivity layer 5 has a high temperature portion and a low temperature portion. can be further suppressed.

By forming the high thermal conductivity layer 5 on the surface of the low thermal conductivity layer 4 in this way, even if the high thermal conductivity layer 5 has a flame contact portion 51 and a flame non-contact portion 52, the high thermal conductivity layer 5 can be prevented from having a high-temperature portion and a low-temperature portion. Therefore, it is possible to suppress an increase in heat loss in the expansion stroke and the exhaust stroke due to the non-flame contact portion 52 . Moreover, due to the diffusion of heat from the flame contact portion 51 to the flame non-contact portion 52, the temperature of the flame contact portion 51 is lower than that of the flame contact portion 41 shown in FIG. Therefore, it is possible to suppress the increase in the temperature of the fresh air and thus the air-fuel mixture, thereby suppressing an increase in compression work caused by the flame contact portion 51 .

Furthermore, by using aluminum as the material of the high thermal conductivity layer 5, the following effects can be obtained.

FIG. 3 shows the reflectance of infrared rays (electromagnetic waves) emitted by flames (luminous flames) in the combustion chamber. 12 is a diagram showing the results of an experiment comparing a piston with a SUS material coating on the piston crown surface 12 (specifically, a piston with the piston crown surface 12 thermally sprayed with a SUS material). be.

As shown in FIG. 3, it can be seen that the piston whose crown surface 12 is coated with aluminum has higher infrared reflectance than the piston whose crown surface 12 is coated with SUS material. That is, the piston with the aluminum coating on the piston crown surface 12 can suppress the heat transfer from the flame in the combustion chamber to the piston 100 by radiation more than the piston with the SUS material coating on the piston crown surface 12. is shown.

Therefore, by forming a high thermal conductivity layer 5 using aluminum with high infrared reflectance on the top layer of the coating 6 formed on the piston crown surface 12, heat transfer by radiation from the flame in the combustion chamber to the piston is reduced. can be suppressed. Therefore, heat loss from the inner wall surface of the cylinder via the piston 100 can be reduced.

The piston 100 according to the present embodiment described above has a multi-layered coating 6 on the piston crown surface 12. The coating 6 includes a low thermal conductivity layer 4 having a lower thermal conductivity than the base material of the piston 100, a low thermal conductivity and a high thermal conductivity layer 5 having a higher thermal conductivity than the thermal conductivity layer 4 . The uppermost layer of the coating 6 is the high thermal conductivity layer 5 , and the lower layer of the high thermal conductivity layer 5 is the low thermal conductivity layer 4 .

As a result, even if a flame contact portion 51 and a flame non-contact portion 52 are generated in the high thermal conductivity layer 5, heat is easily diffused in the interior of the high thermal conductivity layer 5. Since it is easily transmitted to the non-contact portion 52 , the high thermal conductivity layer 5 can be prevented from having a high temperature portion and a low temperature portion, and the temperature of the high thermal conductivity layer 5 can be leveled. Therefore, it is possible to suppress an increase in heat loss from the inner wall surface of the cylinder through the piston 100 during the expansion stroke and the exhaust stroke, which is caused by the non-flame contact portion 52 . In addition, since the intake stroke can be suppressed while the flame contact portion 51 is maintained at a high temperature, an increase in compression work caused by the flame contact portion 51 can also be suppressed.

Further, in this embodiment, the high thermal conductivity layer 5 formed on the uppermost layer of the coating 6 is made of a material having a higher infrared reflectance than the low thermal conductivity layer 4 .

As a result, the infrared rays emitted by the flame in the combustion chamber are reflected, and the heat transfer from the flame to the piston 100 due to radiation can be suppressed. .

Although the embodiments of the present invention have been described above, the above embodiments merely show a part of application examples of the present invention, and the technical scope of the present invention is not limited to the specific configurations of the above embodiments. do not have.

For example, in the above embodiment, the film 6 having the high thermal conductivity layer 5 formed on the surface of the low thermal conductivity layer 4 was formed on the piston crown surface 12, but this is not the only option. A coating 6 having a high thermal conductivity layer 5 formed on the surface of a low thermal conductivity layer 4 is formed on part or all of the inner wall surface of the head, the inner wall surface of the cylinder, the crown surface of the piston, and the back surface of the valve head of the intake and exhaust valve. may That is, in an internal combustion engine in which a multi-layered coating 6 is formed on at least a portion of the combustion chamber wall surface, the coating 6 includes a low thermal conductivity layer 4 having a lower thermal conductivity than the member to which the coating 6 is applied, a low thermal conductivity a high thermal conductivity layer 5 having a higher thermal conductivity than the thermal conductivity layer 4, the uppermost layer of the coating 6 is the high thermal conductivity layer 5, and the lower layer of the high thermal conductivity layer 5 is the low thermal conductivity layer 4; good too.

In the above embodiment, the coating 6 may be formed on the entire surface of the piston crown surface 12 or may be formed only on a part of the piston crown surface 12 .

4 low thermal conductivity layer 5 high thermal conductivity layer 6 coating 12 piston crown surface 100 piston

Claims (5)

A piston in which a multi-layered film is formed on the crown surface of the piston,
The coating comprises a low thermal conductivity layer having a lower thermal conductivity than the base material of the piston and a high thermal conductivity layer having a higher thermal conductivity than the low thermal conductivity layer,
The uppermost layer of the coating is the high thermal conductivity layer, and the lower layer of the high thermal conductivity layer is the low thermal conductivity layer,
piston. The high thermal conductivity layer is formed of a material having a higher infrared reflectance than the low thermal conductivity layer,
A piston according to claim 1. The base material of the piston is iron,
The low thermal conductivity layer is made of SUS material,
The high thermal conductivity layer is composed of aluminum,
A piston according to claim 1 or claim 2. The low thermal conductivity layer is formed on the crown surface of the piston,
4. The piston according to any one of claims 1 to 3, wherein said high thermal conductivity layer is formed on the surface of said low thermal conductivity layer. An internal combustion engine in which a multi-layered film is formed on at least a portion of a combustion chamber wall surface,
The coating comprises a low thermal conductivity layer having a lower thermal conductivity than the member to which the coating is applied, and a high thermal conductivity layer having a higher thermal conductivity than the low thermal conductivity layer,
The uppermost layer of the coating is the high thermal conductivity layer, and the lower layer of the high thermal conductivity layer is the low thermal conductivity layer,
internal combustion engine.

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