JP6090282B2 - Method for forming a heat insulating layer on the inner peripheral surface of a cylindrical hole - Google Patents

Description

  The present invention relates to a heat insulating layer forming method for forming a heat insulating layer on an inner peripheral surface of a cylindrical hole, a heat insulating layer forming structure, and an engine including the heat insulating layer forming structure.

  In industrial equipment and consumer equipment that require energy supply, various types of heat insulating materials have been conventionally used in order to increase energy efficiency, and research and development of heat insulating materials have been conducted. For example, in an automobile, in order to reduce engine cooling loss and increase its thermal efficiency, research and development of a heat insulating layer provided on a wall surface of a combustion chamber is underway.

Therefore, as such a heat insulating layer, for example, Patent Document 1 describes a structure in which hollow particles formed by a spray coating method are dispersed in a silicone resin layer. Patent Document 2 describes a structure in which hollow particles are arranged in a ZrO ₂ layer in a finely packed state.

  By the way, in order to reduce the cooling loss of the engine, the place where the heat insulating layer is provided includes the piston top surface, the cylinder head facing the piston, the intake / exhaust valve, the cylinder bore surface, etc. Regarding the method and the heat insulating layer structure, there is no specific description in both patent documents.

  In this regard, Patent Document 3 discloses that in the cylinder liner, at least a part on the combustion chamber side of the top ring at the piston top dead center position is formed by a sprayed portion of a heat insulating material continuous from the inner periphery to the outer periphery over the entire circumference in the circumferential direction. The structure is described.

JP 2014-1718 A International Publication No. 2009/020206 Pamphlet JP 2014-80903 A

  In general, considering the heat insulating performance of the heat insulating layer, it is desirable that the thickness of the heat insulating layer be as uniform as possible. However, it is extremely difficult to form a heat insulating layer having a uniform thickness only on the inner peripheral surface of the cylindrical hole by a conventional method such as thermal spraying. Therefore, in the thing of the said patent document 3, an annular groove is formed in the outer peripheral surface of a cylinder liner, and after filling a thermal insulation material in this annular groove by thermal spraying, an inner peripheral surface is ground and the inner peripheral surface side is made. The heat insulation layer is exposed. According to this method, a uniform heat insulating layer can be formed.

  However, this method requires grinding of both the outer circumferential surface and the inner circumferential surface of the cylinder liner, which is not practical because it requires labor. In general, since the sprayed portion is porous, the occurrence of cracks due to thermal deformation of the cylinder block, the disturbance of the combustion gas flow due to the influence of surface roughness, and the like are also problems.

  Therefore, it is considered effective to absorb the thermal deformation of the cylinder block by forming a hollow particle-containing silicone-based resin heat insulating layer as in Patent Document 1 on the inner peripheral surface of the cylindrical hole. However, materials such as silicone resins have a lower hardness than thermal spray materials. For this reason, when the piston is inserted from the upper part of the cylinder block (on the cylinder head side) after the heat insulating layer is formed, there is a concern that the surface of the silicone resin heat insulating layer may be damaged by the piston ring during the insertion.

  Accordingly, the present invention provides a method for easily forming a heat insulating layer when a heat insulating layer is provided on the inner peripheral surface of a cylindrical hole, such as a cylinder bore surface of a cylinder block of an engine, a structure in which such a heat insulating layer is formed, and It is an object to provide an engine having such a structure.

  In order to solve the above-mentioned problems, in the present invention, a coating film is formed by applying a heat insulating material such as a hollow particle-containing silicone resin substantially uniformly on a metal thin plate, and the coating film side becomes the inner peripheral surface. In this way, the thin plate was rounded into a cylindrical shape together with this thin plate, and the heat-treated thin plate was placed on the inner peripheral surface of the cylindrical hole to form a heat insulating layer on the inner peripheral surface of the cylindrical hole.

That is, the heat insulating layer forming method disclosed herein is a heat insulating layer forming method in which a heat insulating layer is formed on the cylinder bore surface of a cylinder block of an engine, and the cylinder is positioned more than the position of the top ring at the top dead center of the piston on the cylinder bore surface. Forming a coating film by applying a step of expanding the diameter of the head to the head side and applying a heat insulation material with a lower thermal conductivity than the thin plate to the surface of the thin metal plate to a substantially uniform thickness. Forming a coating-coated thin plate on which the coating film is formed, and forming the cylindrical plate so that the back surface of the thin plate on which the coating film is not formed can come into contact with the enlarged portion of the cylinder bore surface A heat treatment step of heat-treating the formed thin plate with a coating film to convert the coating film into a heat-insulating layer, and a jig for inserting a piston in the diameter-expanded portion of the cylinder bore surface. The cylinder through the tool A piston inserting step of inserting the piston in A, after the piston insertion step, characterized in that a placing step of placing said heat-insulation layer provided sheet to the enlarged diameter portion.

According to this structure, since the coating film of a heat insulating material is formed on a flat metal thin plate, a coating film with a good film quality having a substantially uniform thickness can be easily formed. Then, processed into cylindrical thin plates with a coating film in accordance with the cylinder bore surface of the cylinder bore, by firing a coating film to form a heat insulating layer, so installing a thin plate with the heat insulating layer into the cylinder bore, conveniently into the cylinder bore It is possible to form a heat insulating layer with a good film quality having a substantially uniform thickness. And a heat insulation layer can be fixed more reliably by forming a diameter expansion part and installing the said thin plate with a heat insulation layer in this diameter expansion part. Moreover, a heat insulation layer can be formed in a desired position by forming an enlarged diameter part in a desired position. In addition, since an oil jet device or the like is disposed at the lower part of the cylinder block, and the main journal interval of the connecting rod is narrower than the diameter of the cylinder bore, there is no method other than inserting the piston from the cylinder head side of the cylinder block. However, as described above, if the heat insulating layer is formed on the inner peripheral surface of the cylinder bore and then the piston is inserted, the heat insulating layer having a lower hardness than the sprayed layer may be damaged by the piston ring. Therefore, with the above-described configuration, the piston can be inserted before the heat insulating layer is formed, and the piston can be inserted without the piston ring damaging the heat insulating layer. In addition, since the thin plate with a heat insulating layer is installed closer to the cylinder head than the top ring position of the top dead center of the piston, the piston ring does not contact the surface of the heat insulating layer even when the piston slides. Deterioration can be prevented.

  Here, as a method for forming the coating film, for example, a doctor blade method, a spray coating method, a brush coating method, or the like can be used, and a doctor blade method can be used particularly preferably. Thereby, the coating film of substantially uniform thickness can be formed effectively. In the present invention, the “substantially uniform thickness” means that the surface roughness of the heat insulating layer after baking the coating film is Ra 10 μm or less.

  Moreover, it is preferable that the coating film of a heat insulating material includes a large number of hollow particles and a binder that fills the space between the hollow particles and holds the hollow particles on the thin plate.

  As the hollow particles, for example, ceramic hollow particles such as alumina bubbles, fly ash balloons, shirasu balloons, silica balloons, and airgel balloons can be employed.

  As the binder, for example, a silicone resin made of a three-dimensional polymer having a high degree of branching, represented by methyl silicone resin and methylphenyl silicone resin, can be used. Specific examples of the silicone resin include polyalkylphenylsiloxane.

  By including hollow particles in the silicone resin having a low thermal conductivity, a large amount of air having a low thermal conductivity is included, and the coating film has a lower thermal conductivity.

  Moreover, in the forming process of the thin plate with a coating film, both ends of the thin plate can be joined by welding, brazing, adhesive, or the like.

The present invention can be added to the cylinder bores in the cylinder block of the engine, for example a cylinder liner, the intake pipe to be joined to the cylinder bore, the exhaust pipe, is applied to the inner circumferential surface of the cylindrical bore of the entrance tube or the like of the turbocharger .

For example, the structure in which the heat insulating layer is formed is a heat insulating layer forming structure in which a heat insulating layer is formed on the cylinder bore surface of the cylinder block of the engine, and the cylinder head is positioned more than the position of the top ring at the piston top dead center of the cylinder bore surface. A diameter-enlarged portion having a stepped diameter is formed on the side portion, and the heat insulating layer is formed by applying a heat insulating material having a lower thermal conductivity than the thin plate on the surface of the metal thin plate to a substantially uniform thickness. The thin plate with a heat insulating layer formed of the coating film and formed with the heat insulating layer is formed into a cylindrical shape so that the back surface of the thin plate is in contact with the inner peripheral surface of the enlarged diameter portion formed on the cylinder bore surface. The heat insulating layer is formed by fitting the formed thin plate with the heat insulating layer into the diameter-expanded portion, so that the cylinder head is positioned more than the top ring position at the top dead center of the piston on the cylinder bore surface via the thin plate. And the end face on the cylinder head side of the cylinder block side of the cylinder block is the end face on the cylinder head side of the cylinder block. The surface of the heat insulation layer of the thin plate with a heat insulation layer is flush with a cylinder bore surface other than the enlarged diameter portion of the cylinder bore surface, and the thin plate with a heat insulation layer is the cylinder block. may have a structure that is pressed and fixed with a gasket interposed between said cylinder head.

In such a structure, the heat insulating layer is formed on a flat metal thin plate, and a thin plate with a heat insulating layer processed into a cylindrical shape in accordance with the cylinder bore surface of the cylinder bore is simply installed in the cylinder bore. A cylinder bore surface on which a heat insulating layer having a good film quality having a thickness is formed can be easily obtained. In addition, since the heat insulating layer is formed on the cylinder head side from the top ring position at the top dead center of the piston, it is possible to suppress heat loss from the cylinder block that constitutes the combustion chamber, that is, to reduce cooling loss and to reduce the inside of the cylinder bore. Even if the piston reciprocates, the piston ring does not slide on the heat insulating layer, and the heat insulating layer is not damaged, so that deterioration of the heat insulating layer can be prevented. Furthermore, the said heat insulation layer is formed in the said enlarged diameter part by installing the said thin plate with a heat insulation layer in the said enlarged diameter part. Thus, the heat insulating layer can be more securely fixed on the inner peripheral surface of the cylinder bore. And since the said thin plate with a heat insulation layer is press-fixed by the gasket interposed between the said cylinder block and a cylinder head, a heat insulation layer can be more reliably fixed on a cylinder bore internal peripheral surface.

For example, an engine having a heat insulation layer having high heat insulation performance and durability on the inner peripheral surface of the cylinder bore can be provided.

As described above, according to the present invention, since installing a cylindrically shaped thermal insulation layer provided sheet into the cylinder bore, forms an insulating layer of good film quality with a substantially uniform thickness in conveniently within the cylinder bore can do.

FIG. 1 is a front view showing the structure of the engine according to the first embodiment. FIG. 2 is a diagram showing a heat insulating layer forming structure according to the first embodiment. FIG. 3 is a view for explaining the heat insulating layer forming method according to the first embodiment. FIG. 4 is a view for explaining a coating film forming method by a doctor blade method in the heat insulating layer forming method according to the first embodiment. FIG. 5 is a plan view of a thin plate with a coating film formed in the heat insulating layer forming method according to the first embodiment. FIG. 6 is a view for explaining a method of inserting a piston into a cylinder bore in the heat insulating layer forming method according to the first embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or its application.

[First Embodiment]
<About the engine>
FIG. 1 shows the structure of an engine employing a heat insulating layer forming structure according to the present invention.

  In the engine E shown in FIG. 1, 1 is a piston, 2 is a cylinder block, 3 is a cylinder head, 4 is an intake valve for opening and closing an intake port 5 of the cylinder head 3, 6 is an exhaust valve for opening and closing an exhaust port 7, and 8 is It is a fuel injection valve.

  The combustion chamber of the engine E is formed by the top surface of the piston 1, the inner peripheral surface of the cylinder block 2, the lower surface of the cylinder head 3, and the lower surface of the umbrella portion of the intake / exhaust valves 4 and 6 (surface facing the combustion chamber). .

  A cavity 9 is formed on the top surface of the piston 1, and a top ring 10 is installed on the outer peripheral surface of the upper end of the piston 1, and the piston 1 reciprocates in the cylinder bore 11 of the cylinder block 2. Note that the illustration of the spark plug is omitted.

<About heat insulation layer formation structure>
In the heat insulating layer forming structure according to the present embodiment, the heat insulating layer 13 is located on the inner peripheral surface of the cylinder block 2, that is, on the bore surface (cylinder bore surface) of the cylinder bore 11, rather than the position of the top ring 10 at the top dead center of the piston 1. This is a structure formed on the cylinder head 3 side.

  That is, as shown in FIG. 2, the stepped diameter-expanded portion 14 is formed in a portion closer to the cylinder head 3 than the position of the top ring 10 at the top dead center of the piston 1 on the cylinder bore surface. The heat insulating layer 13 is formed in the enlarged diameter portion 14 by installing the thin plate 12 on which the insulating layer 13 is formed in the enlarged diameter portion 14.

  The thin plate 12 is made of metal, and for example, aluminum, cast iron alloy, or the like can be used. The thickness of the thin plate 12 is 0.30 mm to 5.0 mm, more preferably 0.50 mm to 3.0 mm, and particularly preferably 0.70 mm to 1.5 mm. Further, the width of the thin plate 12 preferably corresponds to the axial diameter expansion amount of the cylinder bore 11 in the expanded diameter portion 14, and specifically, for example, 1.0 cm to 3 mm from the end of the cylinder bore 11. It is 5 cm, preferably 1.5 cm to 3.0 cm, particularly preferably 2.0 cm to 2.5 cm.

  The heat insulating layer 13 is made of a heat insulating material having lower thermal conductivity than the thin plate 12, and forms a matrix (matrix) of the heat insulating layer 13 by filling a large number of hollow particles made of inorganic oxide and the space between the hollow particles. And a silicone resin binder that holds the hollow particles on the thin plate 12.

  As the hollow particles, for example, ceramic hollow particles such as alumina bubbles, fly ash balloons, shirasu balloons, silica balloons, and airgel balloons can be employed.

  As the binder, for example, a silicone resin made of a three-dimensional polymer having a high degree of branching, represented by methyl silicone resin and methylphenyl silicone resin, can be used. Specific examples of the silicone resin include polyalkylphenylsiloxane.

  The thin plate 12 on which the heat insulating layer 13 is formed is pressed and fixed by a gasket 15 interposed between the cylinder block 2 and the cylinder head 3.

<About heat insulation layer formation method>
The heat insulation layer formation structure concerning this embodiment can be formed by the method shown in FIG.

(Formation of thin plate with heat insulation layer)
First, a heat insulating material 13a having a lower thermal conductivity than the thin plate 12 is applied on the surface of the thin plate 12 to a substantially uniform thickness to form a coating film 13b (A1).

The thin plate 12 and the heat insulating material 13a are prepared. By degreasing, dirt such as oil and fingerprints adhering to the thin plate 12 is removed. Moreover, the heat insulating material 13a which stirred and mixed the hollow particle and the binder is prepared. If necessary, a thickener or a dilution solvent is added to adjust the viscosity of the heat insulating material 13a. In order to increase the adhesion between the thin plate 12 and the heat insulating material 13a, particularly the binder, it is preferable to subject the thin plate 12 to a surface roughening treatment. As the roughening treatment, for example, blasting such as sand blasting is preferably performed. For example, the blasting process can be performed using an air blasting apparatus, using alumina having a particle size of # 30 as an abrasive, and processing conditions of a pressure of 0.39 MPa, a time of 45 seconds, and a distance of 100 mm. In addition, not only this but when the thin plate 12 consists of aluminum alloys, you may make it form a micro unevenness | corrugation in the top surface of the piston 1 by an alumite process. For example, the alumite treatment can be performed using an oxalic acid bath under a treatment condition of a bath temperature of 20 ° C., a current density of 2 A / dm ² , and a time of 20 minutes.

  In the coating film forming step A1, as a method for forming a coating film, for example, a doctor blade method, spray coating, brush coating, or the like can be used. In this embodiment, a doctor blade method is used.

  As shown in FIG. 4, according to the doctor blade method, the thin plate 12 is disposed on the conveyor T, and the heat insulating material 13 a is placed on the thin plate 12. And the conveyor T is moved to the arrow direction in FIG. At this time, the heat insulating material 13a is stretched by the blade B arranged above the thin plate 12 by a predetermined distance from the surface of the thin plate 12, and a coating film 13b having a thickness corresponding to the predetermined distance is formed on the surface of the thin plate 12. It is formed. If necessary, application by the doctor blade method can be repeated (overcoated) to obtain a desired thickness. Thereby, the coating film 13b can be formed on the thin plate 12 with a substantially uniform thickness.

  Subsequently, the coating film 13b is preliminarily dried by hot air drying, an infrared heater or the like. In addition, the thickness of the coating film 13b is set to be 40 μm or more and 200 μm or less, for example.

  Next, the coated thin plate 12 on which the coating film 13b is formed is formed into a cylindrical shape (A2).

  At this time, as shown in FIG. 5, the coated thin plate 12 is formed in a cylindrical shape so that the back surface of the coated thin plate 12 can contact the inner peripheral surface of the enlarged diameter portion 14 formed on the cylinder bore surface. Is done. In other words, the outer diameter of the formed thin plate with a coating film 12 coincides with the inner diameter of the enlarged diameter portion 14.

  Further, as shown in FIG. 5, the formed coated thin plate 12 has a joint W. That is, both ends of the coated thin plate 12 are joined by, for example, welding, brazing, adhesive, or the like to form the joint W.

  And the thin film 12 with a coating film shape | molded is heat-processed, the coating film 13b is baked, and the heat insulation layer 13 is obtained (A3).

  As the heat treatment, the formed thin plate 12 with a coating film is subjected to a baking treatment at a temperature of, for example, about 180 ° C. for several hours to several tens of hours. Thereby, a binder hardens | cures, many hollow particles are closely filled, and the heat insulation layer 13 with which these particle | grains were filled with the binder is obtained. In addition, it is preferable that the surface roughness of the heat insulation layer 13 after baking a coating film is Ra10micrometer or less.

  Through the above steps A1 to A3, the heat insulating layer 13 is formed, and the thin plate 12 with the heat insulating layer having the outer diameter that matches the inner diameter of the enlarged diameter portion 14 can be formed. According to this method, since the heat insulating coating film 13b is formed on the flat thin plate 12, it is possible to easily form the heat insulating layer 13 of good film quality having a substantially uniform thickness.

(Cylinder bore surface diameter expansion processing)
First, as shown in FIG. 2, a diameter-expanded portion 14 having a stepped diameter is formed on the cylinder bore surface at the end on the cylinder head 3 side of the top ring 10 position at the top dead center of the piston 1 (see FIG. 2). 3, B1).

  The enlarged diameter portion 14 is formed by boring the cylinder bore surface. After forming the enlarged diameter portion 14 by boring, finishing honing is performed.

  The diameter expansion processing amount in the radial direction of the bore surface preferably corresponds to the thickness of the thin plate 12 with a heat insulating layer, and specifically, for example, 0.34 mm to 5.1 mm, more preferably 0.54 mm to The thickness is 3.1 mm, particularly preferably 0.74 mm to 1.6 mm. Particularly preferably, the amount of diameter expansion processing is set so that the surface of the heat insulation layer 13 is flush with the inner peripheral surface other than the diameter expansion portion 14 when the thin plate 12 with the heat insulation layer is installed.

  Further, the diameter expansion processing amount in the axial direction of the bore surface is 1.0 cm to 3 from the end of the cylinder bore 11 because the diameter expansion portion 14 is formed only on the cylinder head side of the top ring 10 at the top dead center of the piston 1. 0.5 cm, preferably 1.5 cm to 3.0 cm, particularly preferably 2.0 cm to 2.5 cm.

  Next, as shown in FIG. 6, the piston 16 insertion jig 16 is installed in the cylinder bore 11 from the cylinder head 3 side, and the piston 1 is inserted into the cylinder bore 11 through the jig 16 (FIG. 3, B2). . In the present embodiment, the jig 16 is formed so as to fit into the enlarged diameter portion 14.

  Thus, by inserting the piston 1 into the cylinder bore 11 before inserting the thin plate 12 with the heat insulating layer into the enlarged diameter portion, the piston 1 can be inserted without the piston ring damaging the heat insulating layer.

(Insertion into the expanded part of the thin plate with heat insulation layer)
As shown in FIG. 2, the thin plate 12 with a heat insulating layer is inserted into the enlarged diameter portion 14 provided on the cylinder head 3 side with respect to the cylinder block 2 in which the enlarged diameter portion 14 is formed and the piston 1 is inserted. (FIG. 3, S1).

  Since the expanded diameter portion 14 is formed in a step shape, the thin plate 12 with the heat insulating layer is fitted into the expanded diameter portion 14 and is not installed in the cylinder bore 11 than the expanded diameter portion 14. It can be fixed more securely on the cylinder bore surface.

  Then, as shown in FIG. 2, the thin plate 12 with a heat insulating layer is pressed and fixed by a gasket interposed between the cylinder block 2 and the cylinder head 3 (FIG. 3, S2). Thereby, a heat insulation layer can be more reliably fixed on a cylinder bore surface.

  As described above, according to the heat insulating layer forming method according to the present embodiment, the coated thin plate 12 is processed into a cylindrical shape according to the cylinder bore surface, and the heat insulating layer 13 is formed by firing the coating film 13b. Since the thin plate 12 with the heat insulating layer is installed in the enlarged diameter portion 14 formed in the cylinder bore 11, the heat insulating layer 13 having a good film quality having a substantially uniform thickness can be easily formed in the cylinder bore 11. Further, since the heat insulating layer 13 is formed after the piston 1 is inserted into the cylinder bore 11, it is not damaged when the piston 1 is inserted. Further, since the heat insulating layer 13 is formed closer to the cylinder head 3 than the position of the top ring at the top dead center of the piston, the piston ring does not contact the surface of the heat insulating layer even when the piston 1 slides. Deterioration of the layer can be prevented.

  Moreover, the engine provided with such a heat insulation layer formation structure shall have the heat insulation layer which has high heat insulation performance and durability in the cylinder bore surface upper part.

[Second Embodiment]
The second embodiment according to the present invention will be described below. The same parts as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the first embodiment, the heat insulating layer 13 is formed directly on the cylinder bore surface of the cylinder block 2, but a cylinder liner is installed on the cylinder bore 11, and the heat insulating layer 13 is formed on the inner peripheral surface of the cylinder liner. It can also be configured.

  In this case, in B1 of FIG. 3, the inner peripheral surface of the cylinder liner is subjected to a diameter expansion process to form the expanded diameter portion 14, and then the cylinder liner is joined to the cylinder bore 11, and then to B2 of FIG. The piston 1 shown is inserted.

  The present invention is extremely useful because a heat insulating layer having a good film quality having a substantially uniform thickness can be easily formed in a cylindrical hole.

1 Piston 2 Cylinder block 3 Cylinder head 10 Top ring 11 Cylinder bore (cylindrical hole)
12 Thin Plate 13 Heat Insulating Layer 13a Heat Insulating Material 13b Paint Film 14 Expanded Diameter Part 15 Gasket

Claims (7)

A heat insulating layer forming method for forming a heat insulating layer on a cylinder bore surface of a cylinder block of an engine,
A diameter expansion step of forming a diameter-expanded portion having a diameter increased stepwise on the cylinder head side from the position of the top ring at the top dead center of the piston on the cylinder bore surface;
A coating film forming step of forming a coating film on the surface of the metal thin plate by applying a heat insulating material having a lower thermal conductivity than the thin plate to a substantially uniform thickness;
A forming step of forming a thin plate with a coating film on which the coating film has been formed, into a cylindrical shape so that a back surface of the thin plate on which the coating film is not formed can come into contact with the enlarged diameter portion of the cylinder bore surface;
A heat treatment step of heat-treating the molded thin plate with a coating to convert the coating into a heat insulating layer;
A piston insertion step of disposing a piston insertion jig in the enlarged diameter portion of the cylinder bore surface, and inserting the piston into the cylinder bore through the jig;
A heat insulation layer forming method comprising: an installation step of installing the heat-treated thin plate with a heat insulation layer in the enlarged diameter portion after the piston insertion step. In claim 1,
The jig is formed so as to be fitted to the enlarged diameter portion of the cylinder bore surface,
When the jig is fitted to the enlarged diameter portion, the inner peripheral surface of the jig and the inner peripheral surface of the cylinder bore surface other than the enlarged diameter portion are flush with each other. Forming method. In claim 1 or claim 2,
The diameter expansion step is a step of forming the diameter expansion portion by performing a finishing honing process after performing a boring process on the cylinder bore surface. In any one of Claim 1 thru | or 3,
In the diameter expansion step, the heat expansion layer forming method is characterized in that an axial diameter expansion amount in the diameter expansion portion is gradually increased toward a diameter expansion direction of the cylinder bore. In any one of Claims 1 thru | or 4,
A heat insulation comprising a pressing and fixing step of pressing and fixing the thin plate with a heat insulating layer installed in the enlarged diameter portion with a gasket interposed between the cylinder block and the cylinder head after the installation step. Layer formation method. In any one of Claims 1 thru | or 5,
In the coating film forming step, the coating film is formed by a doctor blade method. In any one of Claims 1 thru | or 6,
The said coating film is equipped with many hollow particles and the binder which hold | maintains the said hollow particle on the said thin plate while filling between these hollow particles, The heat insulation layer forming method characterized by the above-mentioned.

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