阅读说明：本技术 内燃机的活塞和内燃机的活塞冷却控制方法 (Piston for internal combustion engine and piston cooling control method for internal combustion engine ) 是由 助川义宽 高桥智一 于 2018-04-12 设计创作，主要内容包括：本发明提供能够提高热效率、减少排出气体有害成分,并且抑制爆震和提前点火等异常燃烧的发生的新的内燃机的活塞。在活塞内形成有冷却通路(200),并且在活塞顶面的表面设置有：第1隔热层(101),其由热导率和体积比热比活塞基材小的材料形成；和第2隔热层(102),其由热导率和体积比热比该第1隔热层(101)小的材料形成,连接第1隔热层(101)和冷却通路(200)的第1距离设定成小于连接第2隔热层(102)和冷却通路(200)的第2距离。能够利用第2隔热层减少冷却损失,并且利用第1隔热层促进附着于活塞的燃料的气化,减少排出气体有害成分。此外,由于第1距离小于第2距离,第1隔热层的温度不会过度上升,能够抑制爆震和提前点火的发生。(The invention provides a new piston for an internal combustion engine, which can improve the thermal efficiency, reduce harmful components in exhaust gas, and suppress the occurrence of abnormal combustion such as knocking and pre-ignition. A cooling passage (200) is formed in the piston, and a surface of the piston top surface is provided with: a 1 st heat insulating layer (101) formed of a material having a thermal conductivity and a volume specific heat smaller than that of the piston base material; and a 2 nd thermal insulation layer (102) formed of a material having a thermal conductivity and a volume specific heat smaller than that of the 1 st thermal insulation layer (101), wherein a 1 st distance connecting the 1 st thermal insulation layer (101) and the cooling passage (200) is set smaller than a 2 nd distance connecting the 2 nd thermal insulation layer (102) and the cooling passage (200). The 2 nd heat insulating layer can reduce cooling loss, and the 1 st heat insulating layer can promote vaporization of fuel adhering to the piston, thereby reducing harmful components in the exhaust gas. Further, since the 1 st distance is smaller than the 2 nd distance, the temperature of the 1 st heat insulating layer does not rise excessively, and occurrence of knocking and preignition can be suppressed.)

1. A piston for an internal combustion engine, which has a piston main body formed with a cooling passage, and in which a 1 st heat insulating layer and a 2 nd heat insulating layer that become a part of a combustion chamber are formed on a top surface of the piston main body, characterized in that:

the 1 st insulating layer is formed of a material having a smaller thermal conductivity and a volume specific heat equal to or smaller than that of a piston base material forming the piston body,

The 2 nd thermal insulation layer is formed of a material having a thermal conductivity and a volumetric specific heat that is less than the thermal conductivity and volumetric specific heat of the 1 st thermal insulation layer,

the distance separating the 1 st insulating layer from the cooling passage is set smaller than the distance separating the 2 nd insulating layer from the cooling passage.

2. The piston of an internal combustion engine as set forth in claim 1, wherein:

The 1 st insulating layer is formed at a position overlapping with at least a part of the cooling passage when viewed from the combustion chamber side in a sliding direction of the piston main body.

3. The piston of an internal combustion engine as set forth in claim 2, wherein:

The ratio of the projected area of the 1 st heat insulating layer overlapping the cooling passage to the projected area of the 1 st heat insulating layer is set to be larger than the ratio of the projected area of the 2 nd heat insulating layer overlapping the cooling passage to the projected area of the 2 nd heat insulating layer when viewed from the combustion chamber side in the sliding direction of the piston main body.

4. The piston of an internal combustion engine as set forth in claim 1, wherein:

When the moving direction of the piston body moving to the lower dead point is set to be lower, at least a part of the lower surface of the 1 st heat insulation layer is positioned lower than the lower surface of the 2 nd heat insulation layer.

5. A piston for an internal combustion engine according to any one of claims 1 to 3, wherein:

The 1 st heat insulating layer is disposed on a region side of the combustion chamber having a larger radius than the 2 nd heat insulating layer.

6. A piston for an internal combustion engine according to any one of claims 1 to 3, wherein:

The 1 st insulating layer and the cooling passage are formed in a circular or circular arc shape and are disposed in the piston main body.

7. a piston for an internal combustion engine according to any one of claims 1 to 3, wherein:

The cooling passage is formed closer to the exhaust side than the vicinity of the center of the combustion chamber.

8. a piston for an internal combustion engine according to any one of claims 1 to 3, wherein:

A cavity is formed on the top surface of the piston main body, and at least the bottom surface of the cavity is provided with the 1 st heat insulation layer.

9. The piston for an internal combustion engine of claim 8, wherein:

the cavity overlaps at least a part of the cooling passage when viewed from the combustion chamber side in a sliding direction of the piston main body, and a width of the cooling passage on the cavity side is larger than a width of the cooling passage on a side opposite to the cavity.

10. The piston for an internal combustion engine of claim 8, wherein:

An inlet of the cooling oil of the cooling passage is formed at the cavity side, and an outlet of the cooling oil of the cooling passage is formed at the opposite side of the cavity.

11. A piston for an internal combustion engine according to any one of claims 1 to 10, wherein:

The piston main body is used for an in-cylinder direct injection internal combustion engine including a fuel injection valve that directly injects fuel into the combustion chamber.

12. The piston for an internal combustion engine according to claim 11, wherein:

The 1 st heat insulating layer is formed at a position intersecting at least 1 of axes of the spray injected from the fuel injection valve when the piston main body is located near a middle position between a top dead center and a bottom dead center.

13. A piston for an internal combustion engine, which has a piston main body formed with a cooling passage, and in which a 1 st heat insulating layer and a 2 nd heat insulating layer that become a part of a combustion chamber are formed on a top surface of the piston main body, characterized in that:

The 1 st insulating layer is formed of a material having a smaller thermal conductivity and a volume specific heat equal to or smaller than that of a piston base material forming the piston body,

The 2 nd thermal insulation layer is formed of a material having a thermal conductivity and a volumetric specific heat that is less than the thermal conductivity and volumetric specific heat of the 1 st thermal insulation layer,

the 1 st heat insulating layer is disposed on the intake side and the exhaust side of the combustion chamber from the vicinity of the center thereof, and the distance between the 1 st heat insulating layer disposed on the exhaust side and the cooling passage is set to be smaller than the distance between the 2 nd heat insulating layer and the cooling passage.

14. A piston for an internal combustion engine according to any one of claims 1 to 13, wherein:

The 1 st insulating layer and the 2 nd insulating layer are formed of a porous medium, and the porosity of the 1 st insulating layer is set to be smaller than the porosity of the 2 nd insulating layer.

15. A piston for an internal combustion engine according to any one of claims 1 to 13, wherein:

The thickness of the 1 st insulating layer is set to be larger than the thickness of the 2 nd insulating layer.

16. A piston for an internal combustion engine according to any one of claims 1 to 15, wherein:

The total area of the 1 st insulating layer forming the combustion chamber is set smaller than the total area of the 2 nd insulating layer forming the combustion chamber.

17. A piston cooling control method of an internal combustion engine, characterized in that:

A piston comprising the internal combustion engine of any one of claims 1 to 16; a cooling medium supply mechanism that supplies a cooling medium into the cooling passage; and a cooling medium variable mechanism that changes a flow rate of the cooling medium,

The coolant variable mechanism adjusts the amount of coolant supplied from the coolant supply mechanism to the cooling passage based on the temperature of the coolant or the temperature of the lubricant.

18. The piston cooling control method of an internal combustion engine according to claim 17, characterized in that:

When the cooling water temperature or the lubricating oil temperature is high, the amount of the cooling medium supplied to the cooling passage is increased as compared to when the cooling water temperature or the lubricating oil temperature is low.

19. The piston cooling control method of an internal combustion engine according to claim 17, characterized in that:

when the cooling water temperature or the lubrication oil temperature is lower than a predetermined temperature, the supply of the cooling medium to the cooling passage is stopped, and when the cooling water temperature or the lubrication oil temperature is higher than the predetermined temperature, the cooling medium is supplied to the cooling passage.

20. A piston cooling control method of an internal combustion engine, characterized in that:

a piston comprising the internal combustion engine of any one of claims 1 to 16; a cooling medium supply mechanism that supplies a cooling medium into the cooling passage; and a cooling medium variable mechanism that changes a flow rate of the cooling medium,

During an idling stop of the internal combustion engine, a cooling medium is supplied from the cooling medium supply mechanism to the cooling passage.

Technical Field

The present invention relates to a piston forming a combustion chamber of an internal combustion engine, and more particularly, to a piston of an internal combustion engine having a heat insulating layer formed on a combustion chamber side surface of a top surface of a piston main body, and a cooling control method of the piston.

Background

In an internal combustion engine such as a gasoline engine, a part of heat generated by combustion is discharged from a combustion chamber to the outside through a piston, a cylinder wall surface, and the like, and becomes a cooling loss. In order to improve the thermal efficiency of the internal combustion engine, it is necessary to reduce the cooling loss. Then, the following methods are known: a so-called temperature-varying heat insulation method is a method in which a layer having low thermal conductivity and low heat capacity is formed on the combustion chamber side surface of the top surface of the piston main body, which occupies a large area in the combustion chamber wall surface, so that the surface temperature of the top surface of the piston main body follows the in-cylinder combustion gas temperature with little time delay to reduce the heat flux on the piston surface.

in the following description, a surface forming a combustion chamber including a top surface formed in a piston main body is referred to as a top surface internally. Accordingly, the top surface of the piston main body refers to a combustion chamber side surface of the piston main body.

On the other hand, when fuel droplets adhere to the top surface of the piston main body having a reduced heat capacity, the piston temperature at the adhering portion decreases, the fuel vaporization performance deteriorates, and the heat efficiency decreases. Further, this leads to an increase in harmful components in exhaust gas such as PM (carbon particles), HC (unburned hydrocarbon), and the like, particularly at the time of cold start.

In order to improve the thermal efficiency and reduce harmful components in the exhaust gas, japanese patent application laid-open No. 2013-67823 (patent document 1) discloses a technique in which an anodized layer having low thermal conductivity and low heat capacity is formed on the top surface of the piston main body, and a metal coating layer having relatively high heat capacity as compared with the anodized layer is disposed on the surface of the fuel injection region in the anodized layer.

Disclosure of Invention

Technical problem to be solved by the invention

however, as described in patent document 1, when an anodized layer having low thermal conductivity and low heat capacity is formed on the top surface of the piston main body and a metal coating layer having relatively high heat capacity as compared with the anodized layer is disposed on the surface of the fuel injection region in the anodized layer, the temperature of the metal coating layer having high heat capacity is excessively increased during combustion of the air-fuel mixture, and abnormal combustion such as knocking and preignition is induced. Therefore, development of a piston for suppressing abnormal combustion such as knocking and pre-ignition and a cooling control method for cooling the piston are required.

The object of the present invention is to provide a novel piston for an internal combustion engine and a cooling control method for the piston, which can reduce harmful components in exhaust gas while improving thermal efficiency and suppress occurrence of abnormal combustion such as knocking and pre-ignition.

Means for solving the problems

The 1 st feature of the present invention is that a cooling passage is formed in a piston main body, and a 1 st heat insulating layer and a 2 nd heat insulating layer are provided on a top face of the piston main body, the 1 st heat insulating layer being formed of a material having a smaller thermal conductivity and a smaller volumetric specific heat than a piston base material, the 2 nd heat insulating layer being formed of a material having a smaller thermal conductivity and a smaller volumetric specific heat than the 1 st heat insulating layer, a 1 st spaced distance connecting the 1 st heat insulating layer and the cooling passage being set smaller than a 2 nd spaced distance connecting the 2 nd heat insulating layer and the cooling passage.

A second feature of the present invention is that the variable cooling medium supply mechanism is provided, which supplies the cooling medium into the cooling passage of the piston main body, and which changes the supply amount of the cooling medium supplied to the cooling passage by the variable cooling medium supply mechanism based on the temperature of the cooling water or the temperature of the lubricating oil of the internal combustion engine by changing the flow rate of the cooling medium.

Effects of the invention

According to the present invention, the 2 nd heat insulating layer can reduce cooling loss, and the 1 st heat insulating layer can promote vaporization of fuel adhering to the top face of the piston main body, thereby reducing harmful components in the exhaust gas. Further, since the 1 st distance between the 1 st heat insulating layer and the cooling passage is smaller than the 2 nd distance between the 2 nd heat insulating layer and the cooling passage, the 1 st heat insulating layer is efficiently cooled by the cooling passage, so that the temperature of the 1 st heat insulating layer does not excessively rise, and occurrence of abnormal combustion such as knocking and preignition can be suppressed.

Drawings

Fig. 1 is a sectional view showing a section of an internal combustion engine having a piston according to embodiment 1 of the present invention.

Fig. 2 is an explanatory diagram showing a correlation between thermal conductivity and volumetric specific heat of the base material and the heat insulating layer constituting the piston shown in fig. 1.

Fig. 3 is a plan view of the piston shown in fig. 1 viewed from the cylinder head side.

Fig. 4 is an enlarged sectional view showing a section of a portion near the top surface of the piston shown in fig. 1.

Fig. 5 is an explanatory diagram for explaining an example of the method of controlling the opening degree of the coolant flow rate adjustment valve.

fig. 6 is an explanatory diagram for explaining another example of the opening degree control method of the cooling oil flow rate adjustment valve.

Fig. 7 is an explanatory diagram for explaining still another example of the opening degree control method of the cooling oil flow rate adjustment valve.

Fig. 8 is an explanatory diagram for explaining a change in temperature of the surface of the piston in 1 combustion cycle (cycle).

fig. 9 is an explanatory diagram for explaining a temperature change of the 1 st insulating layer of the piston shown in fig. 4.

Fig. 10 is a plan view illustrating an area ratio of the 1 st adiabatic layer to the 2 nd adiabatic layer of the piston shown in fig. 3.

fig. 11 is a sectional view showing a section of an internal combustion engine having a piston according to embodiment 2 of the present invention.

Fig. 12 is a plan view of the piston shown in fig. 11 viewed from the cylinder head side.

Fig. 13 is a sectional view showing a section of an internal combustion engine having a piston according to embodiment 2 of the present invention.

Fig. 14 is an explanatory diagram for explaining the positional relationship between the upper surface of the piston and the fuel injection valve shown in fig. 13, and is an explanatory diagram for showing a case where the number of the 1 st heat insulating layer is single.

Fig. 15A is an explanatory diagram illustrating a positional relationship between the upper surface of the piston and the fuel injection valve shown in fig. 13, and is an explanatory diagram illustrating a case where there are a plurality of the 1 st heat insulating layers.

Fig. 15B is a plan view of the piston for explaining the positional relationship between the fuel injection point and the 1 st insulating layer in fig. 15A.

Fig. 16 is a plan view in the case where the piston shown in fig. 13 is provided with a plurality of 1 st heat insulating layers.

fig. 17 is a sectional view schematically showing the structure of the surface layer of the piston.

Fig. 18 is an enlarged view schematically showing the structure of metal particles constituting the metal layer of fig. 17.

Detailed Description

hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the embodiments below, and various modifications and application examples of the technical concept of the present invention are included in the scope of the present invention.