CN111801488A - Internal combustion engine valve - Google Patents

Abstract

A valve for an internal combustion engine is provided that minimizes the possibility of peeling off the outer periphery of a heat insulation layer fixed to the bottom surface of the valve. The bottom surface (5) of the valve faces the combustion chamber (S), and a heat insulation layer (11) is fixed to the bottom surface (5). A peripheral wall portion (16) is integrally provided on the bottom surface (5) to surround the heat insulation layer (11). The inner peripheral surface (16i) of the peripheral wall portion (16) abuts against the entire peripheral surface (11p) of the heat insulation layer (11) over the entire thickness range from the bottom surface (5) of the valve to the surface of the heat insulation layer (11).

Description

Internal combustion engine valve

technical field

The present invention relates to a valve for an internal combustion engine used as an intake valve and an exhaust valve in an internal combustion engine (engine) of an automobile or the like.

Background technique

In an internal combustion engine (engine) of an automobile or the like, an intake port and an exhaust port open to a combustion chamber are provided with internal combustion engine valves as intake valve and exhaust valve, respectively. This internal combustion engine valve includes a shaft portion and a head (Head) integrated with one end of the shaft portion in an enlarged diameter state. On the other hand, the diameter is reduced as it approaches the shaft portion from the valve bottom surface, and a seat surface (Seat) is provided on the back side of the valve bottom surface in the outer peripheral portion of the head portion. The internal combustion engine valve is arranged in the combustion chamber so that the back surface of the head faces the openings of the intake port and the exhaust port, respectively. The internal combustion engine valve is operated by a valve mechanism. (Seat) The valve seat inserts provided on the opening peripheral portions of the intake port and the exhaust port are separated and seated, respectively, thereby opening and closing the intake port and the exhaust port, respectively.

In addition, in the above-mentioned internal combustion engine, as shown in Patent Document 1, an internal combustion engine in which a heat insulating layer is provided on a wall surface defining a combustion chamber for the purpose of improving thermal efficiency has been proposed. In this case, since the valve bottom surface of the internal combustion engine valve (intake valve, exhaust valve) also divides the combustion chamber, the valve bottom surface also becomes a wall surface that divides the combustion chamber. Improve thermal efficiency.

prior art literature

Patent Literature

Patent Document 1: Japanese Patent No. 5629463

SUMMARY OF THE INVENTION

The problem to be solved by the invention

However, the present inventors discovered that when the above-mentioned valve (head) for an internal combustion engine is used in the combustion chamber, the heat insulating layer peels off from the outer peripheral portion of the valve bottom surface, and from the outer peripheral portion to the radially inner portion (from the peeling point as a starting point) The radial center portion) tends to peel off. It is assumed that when such a valve for an internal combustion engine is used, the thermal efficiency of the internal combustion engine cannot be sufficiently improved.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to suppress, as much as possible, the possibility of peeling off the outer peripheral portion of the heat insulating layer from the valve bottom surface in a valve for an internal combustion engine in which a heat insulating layer is fixed to the valve bottom surface.

means of solving problems

In order to achieve the above-mentioned object, the following structures (1) to (19) are employed.

(1) In a valve for an internal combustion engine in which a heat insulating layer is fixed to the valve bottom surface facing the combustion chamber,

A peripheral wall is integrally provided on the valve bottom surface in a state of surrounding the heat insulating layer,

The inner peripheral surface of the peripheral wall is in contact with the entire peripheral surface of the thermal insulating layer over the entire thickness range from the valve bottom surface to the surface of the thermal insulating layer.

According to this configuration, the peripheral wall covers the entire peripheral surface of the heat insulating layer in the entire thickness range from the valve bottom surface to the surface of the heat insulating layer, so that the valve bottom surface (joint surface) and the heat insulating layer (joint surface) form a The boundary (line) is not exposed to the outside due to the peripheral wall, and it is possible to prevent the combustion gas (pressure, temperature, etc.) from acting on the boundary between the valve bottom surface and the heat insulating layer, thereby preventing the outer peripheral portion of the heat insulating layer from peeling off (rolling up) with respect to the valve bottom surface. Even if a force to peel off from the valve bottom surface acts on the outer peripheral portion of the heat insulating layer, and actions such as peeling and warping of the outer peripheral portion of the heat insulating layer occur, the outer peripheral portion of the heat insulating layer and the inner peripheral surface of the peripheral wall will be affected. A frictional force is generated therebetween, and the action of the outer peripheral portion of the heat insulating layer trying to peel off can also be suppressed by this frictional force. Therefore, the possibility of peeling off the outer peripheral part of the heat insulating layer from the valve bottom surface can be suppressed as much as possible.

(2) Under the configuration of (1), the configuration is as follows:

The heat insulating layer is arranged on the valve bottom surface in a diameter-reduced state retracted radially inward from the outer peripheral edge of the valve bottom surface.

According to this configuration, it is of course possible to obtain the same effects as those of (1) above (the use of the peripheral wall to suppress the combustion gas from externally acting on the boundary (line) between the valve bottom surface and the heat insulating layer, and the internal peripheral surface and the heat insulating layer based on the peripheral wall). The contact relationship of the entire peripheral surface of the layer, the action of the outer peripheral portion of the heat insulating layer trying to peel off from the valve bottom surface is suppressed by friction), even if the thermal expansion coefficient of the heat insulating layer is different from the thermal expansion coefficient of the valve bottom surface, it is based on the use of The fact that the diameter of the heat insulating layer is shorter than the diameter of the valve bottom surface can suppress the shrinkage amount of the radial inner side of the heat insulating layer and the radial direction of the valve bottom surface during thermal shrinkage, compared with the case where the heat insulating layer is fixed to the entire valve bottom surface. The difference in the shrinkage of the inner side, or the difference in the amount of expansion of the radially outer side of the heat insulating layer during thermal expansion and the radially outer side of the valve bottom surface, can suppress the force in the direction of peeling from the valve bottom surface acting on the heat insulating layer. peripheral part.

(3) Under the configuration of (2), the configuration is as follows:

The thermal expansion coefficient of the thermal insulation layer is smaller than the thermal expansion coefficient of the bottom surface of the valve,

The inner peripheral surface of the peripheral wall is connected to the entire peripheral surface of the heat insulating layer, and one end surface of the peripheral wall is connected to the valve bottom surface on the outer peripheral side of the heat insulating layer.

According to this configuration, since the peripheral wall is combined with the valve bottom surface and the entire peripheral surface of the heat insulating layer, the peripheral wall stretches the entire peripheral surface of the heat insulating layer radially outward with the thermal expansion of the valve bottom surface. When the heat shrinks, the peripheral wall presses (tightens) the entire peripheral surface of the thermal insulation layer radially inward. Therefore, at the time of thermal expansion and thermal contraction, the peripheral wall acts on the thermal insulation layer with a force in the direction of reducing the difference in expansion and contraction between the thermal insulation layer and the valve bottom surface, thereby further suppressing the possibility of peeling of the thermal insulation layer from the valve bottom surface. .

(4) Under the configuration of (3), the configuration is as follows:

The outer edge of the heat insulating layer is set closer to the outer edge of the valve bottom surface than the radial center of the valve bottom surface.

According to this structure, even if it adopts the structure which suppresses the peeling by thermal expansion and thermal contraction which act on the outer peripheral part of a heat insulating layer, a heat insulating function can be basically ensured by a heat insulating layer.

(5) Under the configuration of (3), the configuration is as follows:

The peripheral wall is formed of a coating material that covers not only the entire peripheral surface of the thermal insulating layer but also the entire thermal insulating layer including the surface of the thermal insulating layer.

According to this configuration, the covering material covers the surface of the heat insulating layer while being coupled to the valve bottom surface, and presses the surface side of the heat insulating layer toward the valve bottom surface. Compared with the case of the entire peripheral surface, the action of the outer peripheral portion of the heat insulating layer trying to peel off from the valve bottom surface can be effectively suppressed.

(6) Under the configuration of (5), the configuration is as follows:

The covering material is set to cover the entire portion of the outer peripheral side of the heat insulating layer in the valve bottom surface,

A heat insulating component is contained in the coating material.

According to this configuration, even when the diameter of the heat insulating layer is made shorter than the diameter of the valve bottom surface in order to suppress peeling of the heat insulating layer due to thermal expansion and thermal contraction, the difference is that the coating material does not cover the heat insulating layer on the valve bottom surface. Compared with the case of the whole part on the outer peripheral side, the heat insulating property of the valve bottom surface can also be improved.

(7) Under the configuration of (3), the configuration is as follows:

The thermal expansion coefficient of the peripheral wall is set to be larger than the thermal expansion coefficient of the heat insulating layer.

According to this structure, during thermal expansion and thermal contraction, the followability of the peripheral wall with respect to the valve bottom surface can be improved higher than that of the heat insulating layer, and the diameter of the peripheral wall (the inner peripheral surface) can be adjusted according to the thermal expansion and thermal contraction of the valve bottom surface. The radial force acts on the entire peripheral surface of the thermal insulation layer, and through the thermal expansion and thermal contraction of the peripheral wall itself, radial force can also act on the thermal insulation layer, further reducing the expansion difference between the thermal insulation layer and the bottom surface of the valve or Poor shrinkage. Therefore, the possibility of peeling off the heat insulating layer from the valve bottom surface can be further suppressed.

(8) Under the configuration of (5), the configuration is as follows:

An extension portion is provided on the covering material, and the extension portion extends to an edge portion from the valve bottom surface to the valve seat surface,

An engaging portion is provided on the edge portion,

The extension part of the covering material is mechanically engaged with the engaging part.

According to this configuration, the mechanical engagement between the extension portion of the covering material and the edge portion can improve the bonding strength between the covering material and the valve bottom surface, and improve the resistance of the covering material against actions such as peeling and warping of the outer peripheral portion of the heat insulating layer. ability.

(9) Under the configuration of (1), the configuration is as follows:

A recess is formed on the bottom surface of the valve, which expands radially outward from the center in the radial direction of the bottom surface of the valve.

The heat insulating layer is fixed to the bottom wall of the recess, and the entire peripheral surface of the heat insulating layer is covered by the inner peripheral wall of the recess serving as the peripheral wall.

According to this configuration, the inner peripheral wall of the recess on the bottom surface of the valve is used to cover the entire peripheral surface of the heat insulating layer with the inner peripheral wall of the recess, and the same effect as the above (1) can be achieved.

(10) Under the configuration of (9), the configuration is as follows:

The entire peripheral surface of the heat insulating layer is also fixed to the inner peripheral wall of the recess.

According to this configuration, with the expansion and contraction of the valve bottom surface, the inner peripheral wall of the recess also expands and contracts with the same thermal expansion coefficient as that of the valve bottom surface, and the thermal expansion and contraction of the inner peripheral wall of the recess (displacement in the radial direction) movement), radial force can also act on the entire peripheral surface of the heat insulating layer, significantly reducing the difference in expansion or shrinkage between the heat insulating layer and the bottom surface of the valve. Therefore, the possibility of peeling of the heat insulating layer from the valve bottom surface can be extremely effectively suppressed.

(11) Under the configuration of (9), the configuration is as follows:

The coating material is bonded to the surface of the heat insulating layer and the valve bottom surface in the recess so as to cover the entire surface of the heat insulating layer and the valve bottom surface.

According to this configuration, not only the relationship between the heat insulating layer and the inner peripheral wall of the recess, but also the covering material bonded to the surface of the heat insulating layer and the valve bottom surface resists peeling, warping, etc. of the outer peripheral portion of the heat insulating layer. The possibility of peeling off the outer peripheral portion of the heat insulating layer from the valve bottom surface is suppressed. Of course, in this case, in the radial direction of the valve bottom surface, the actual length of the valve bottom surface in contact with the covering material is limited by the presence of the recess, so the influence of thermal expansion and thermal contraction can be reduced, and the coating can be sufficiently ensured The bond strength of the material to the bottom of the valve.

(12) Under the configuration of (1), the configuration is as follows:

The heat insulating layer is formed by integrating a plurality of respective structural layers in a stacked state.

According to this structure, the heat insulating layer has a laminated structure composed of a plurality of structural layers, and even if there is a boundary between adjacent structural layers, the same effect as the above (1) can be obtained.

(13) Under the configuration of (1), the configuration is as follows:

The thermal expansion coefficient of the thermal insulation layer is different from the thermal expansion coefficient of the bottom surface of the valve,

The thickness of the outer peripheral part of the said heat insulating layer is thinner than the thickness of the part radially inner side rather than the outer peripheral part of this heat insulating layer.

According to this structure, it can suppress that a bending stress acts on the outer peripheral part of a heat insulating layer at the time of thermal expansion or thermal contraction, and a crack arises based on this bending stress.

That is, due to the difference in thermal expansion coefficient between the heat insulating layer and the valve bottom surface, the heat insulating layer and the valve bottom surface (valve bottom surface portion) are integrally flexed during thermal expansion and thermal contraction, and bending stress acts on them. Among them, the maximum bending stress with respect to the heat insulating layer is generated as edge stress on the outer surface of the heat insulating layer in the thickness direction, and the value of the maximum bending stress increases as the distance from the neutral plane to the outer surface in the wall thickness direction is longer. . Therefore, the longer the distance from the midplane to the outer surface in the wall thickness direction, the higher the possibility of cracks occurring in the outer peripheral portion of the heat insulating layer. The deeper the depth. In addition, when the heat insulating layer and the valve bottom surface (valve bottom surface portion) are integrally flexed, the radius of curvature of the heat insulating layer becomes smaller in the outer peripheral portion having the heat insulating layer than in the radially inner portion of the outer peripheral portion. In this case, the small curvature radius will further increase the above-mentioned bending stress and further increase the possibility of crack generation. Therefore, in this claim 13, by making the thickness of the outer peripheral portion of the thermal insulating layer thinner than the thickness of the radially inner portion of the thermal insulating layer, the outer surface in the thickness direction from the neutral plane in the thermal insulating layer is reduced. distance to reduce the maximum bending stress during thermal expansion and thermal contraction. As a result, as described above, the occurrence of cracks due to the bending stress acting on the outer peripheral portion of the heat insulating layer can be suppressed, and the outer peripheral portion of the heat insulating layer can be suppressed from peeling off from the valve bottom surface due to cracks.

(14) In the configuration of (13), the configuration is as follows:

The thickness of the outer peripheral part of the said heat insulating layer is set so that it may become thin toward the radial direction outer side of this heat insulating layer.

According to this configuration, among the thicknesses of the outer peripheral portion of the heat insulating layer, the thickness of the radially outer portion where the possibility of occurrence of cracks is high becomes thinner, the occurrence of cracks can be reliably suppressed, and accordingly, the occurrence of cracks can be reliably suppressed. The outer peripheral portion of the heat layer was peeled off from the valve bottom surface due to cracks. On the other hand, in this case, only the thickness of the outer peripheral portion of the heat insulating layer is thinner than the thickness of the radially inner portion of the heat insulating layer, and since the thickness becomes thinner toward the radially outer side, the heat insulating layer The thickness of the outer peripheral portion of the valve is not thinned as much as possible, and the thermal insulation degradation of the thermal insulation layer on the bottom surface of the valve can be suppressed as much as possible. Therefore, it is possible to reliably suppress peeling of the outer peripheral portion of the heat insulating layer due to cracks while suppressing a decrease in the heat insulating properties of the heat insulating layer on the valve bottom surface as much as possible.

(15) Under the configuration of (14), the configuration is as follows:

A recess is formed on the bottom surface of the valve, which expands radially outward from the center in the radial direction of the bottom surface of the valve.

The inner peripheral wall of the recess is inclined toward the radially outer side of the recess as it goes toward the opening side of the recess,

The insulating layer is fixed on the bottom wall of the recess,

The entire peripheral surface of the heat insulating layer is inclined so as to expand radially outward of the heat insulating layer toward the surface side in the thickness direction of the heat insulating layer. abutment, and the surface of the heat insulating layer is set to be flush with the portion of the bottom surface of the valve other than the recess.

According to this configuration, the outer peripheral portion of the heat insulating layer can be made thinner toward the radially outer side while the entire peripheral surface of the heat insulating layer is in contact with the inner peripheral wall of the recess. Therefore, while suppressing the fall of the heat insulating function of the heat insulating layer as much as possible, it is possible to suppress peeling of the heat insulating layer with respect to the valve bottom surface due to the action of the combustion gas and the generation of cracks.

Furthermore, in this case, since the surface of the heat insulating layer is set to be flush with the portion of the valve bottom surface other than the recess, the entire valve bottom surface can be flattened, and a general valve with a flat valve bottom surface can be secured. The basic structure and basic performance it has.

(16) Under the configuration of (15), the configuration is as follows:

The coating material is combined with the surface of the heat insulating layer and the bottom surface of the valve in the recess so as to cover the entire surface of the heat insulating layer and the bottom surface of the valve.

According to this configuration, not only the effect due to the contact between the inner peripheral wall of the recess and the entire peripheral surface of the heat insulating layer is obtained, but also the coating material bonded to the surface of the heat insulating layer and the valve bottom surface resists peeling of the outer peripheral portion of the heat insulating layer, Operation such as warping can further suppress the possibility that the outer peripheral portion of the heat insulating layer is peeled off from the valve bottom surface. Of course, in this case, in the radial direction of the valve bottom surface, the actual length of the valve bottom surface in contact with the covering material is limited by the presence of the recess, so the influence of thermal expansion and thermal contraction can be reduced, and the covering material can be sufficiently secured. Bond strength relative to the bottom of the valve.

(17) Under the configuration of (14), the configuration is as follows:

A recess is formed on the bottom surface of the valve, which expands radially outward from the center in the radial direction of the bottom surface of the valve.

The inner peripheral wall of the recess is inclined toward the radially outer side of the recess as it goes toward the opening side of the recess,

The insulating layer is fixed on the bottom wall of the recess,

The entire peripheral surface of the heat insulating layer is inclined so as to expand radially outward of the heat insulating layer toward the surface side in the thickness direction of the heat insulating layer. Abut,

The surface of the said heat insulating layer is formed in the state which raised the outer side rather than the said recessed opening.

According to this configuration, the outer peripheral portion of the heat insulating layer can be made thinner toward the radially outer side while the entire peripheral surface of the heat insulating layer is in contact with the inner peripheral wall of the recess, and the heat insulating layer can be prevented from leaking from the valve. At the same time as the amount of bulge of the bottom surface, the thickness of the portion of the heat insulating layer radially inward from the outer peripheral portion is increased. Therefore, the heat insulating property of the valve bottom surface can be improved while improving the peeling-inhibiting effect of the heat insulating layer and the flattening of the entire valve bottom surface as much as possible.

(18) Under the configuration of (13), the configuration is as follows:

The peripheral wall is formed of a coating material that covers not only the entire peripheral surface of the thermal insulating layer but also the entire thermal insulating layer including the surface of the thermal insulating layer.

According to this configuration, the covering material covers the surface of the heat insulating layer while being coupled to the valve bottom surface, and presses the surface side of the heat insulating layer toward the valve bottom surface, so that the covering material covers only the entire heat insulating layer. Compared with the case of the peripheral surface, it is possible to effectively suppress the action of the outer peripheral portion of the heat insulating layer peeling off from the valve bottom surface (including the occurrence of cracks in the outer peripheral portion of the heat insulating layer).

(19) Under the structure of (13), the structure is as follows:

The thermal expansion coefficient of the heat insulating layer is smaller than the thermal expansion coefficient of the valve bottom surface.

According to this configuration, even when the thermal expansion coefficient difference based on the thermal insulation layer is smaller than the thermal expansion coefficient of the valve bottom surface, the same effects as those of claim 13 described above can be obtained.

Invention effect

As can be seen from the above description, according to the present invention, in the internal combustion engine valve in which the heat insulating layer is fixed to the valve bottom surface, the possibility of peeling off the outer peripheral portion of the heat insulating layer from the valve bottom surface can be suppressed as much as possible. As a result, the peeling of the heat insulating layer can be suppressed from spreading to the entire valve bottom surface starting from the peeling point of the outer peripheral portion of the heat insulating layer with respect to the valve bottom surface.

Description of drawings

FIG. 1 is an explanatory diagram showing an intake valve or an exhaust valve of an internal combustion engine valve used as a first embodiment of the internal combustion engine.

FIG. 2 is an explanatory diagram illustrating the head portion of the valve according to the first embodiment.

FIG. 3 is an explanatory diagram simply showing the vertical cross-sectional structure of FIG. 2 .

FIG. 4 is a plan view of FIG. 3 viewed from above.

FIG. 5 is an explanatory diagram explaining thermal expansion that occurs between the valve bottom surface (head) and the heat insulating layer.

FIG. 6 is an explanatory diagram explaining thermal shrinkage that occurs between the valve bottom surface (head) and the heat insulating layer.

FIG. 7 is an explanatory diagram simply showing the action of the combustion gas with respect to the valve of the first embodiment.

FIG. 8 is an explanatory diagram simply showing the action of the combustion gas with respect to a general valve provided with a heat insulating layer.

9 is a diagram showing the structures of the laminates of Experimental Examples 1 to 3 and the peeling rate of the peripheral portion of the laminates as the results of each experiment.

FIG. 10 is an explanatory diagram illustrating a state in which an experiment of an experimental example is performed using a durability testing machine.

11 is a photographic view showing the peeling state of the peripheral portion of the laminate before and after the experiment in Experimental Example 1 (magnification: 5 times the whole view, each part is magnified 50 times).

FIG. 12 is a photographic view showing the peeling state of the peripheral part of the laminate before and after the experiment in Experimental Example 2 (magnification: 5 times the whole view, each part is enlarged 50 times).

13 is a photographic view showing the peeling state of the peripheral portion of the laminate before and after the experiment in Experimental Example 3 (magnification: 5 times the whole view, each part is enlarged 50 times).

14 is an explanatory diagram conceptually explaining a state in which the peripheral wall portion stretches the entire peripheral surface of the heat insulating layer radially outward at the time of thermal expansion as a function of the peripheral wall portion of the valve of the first embodiment.

15 is an explanatory diagram conceptually explaining a state in which the peripheral wall portion tightens the entire peripheral surface of the heat insulating layer radially inward at the time of thermal contraction as a function of the peripheral wall portion of the valve of the first embodiment.

FIG. 16 is a graph showing the structure of Experimental Example 4 and the peeling rate of the heat insulating layer as an experimental result thereof.

17 is a photographic view showing the peeling state of the peripheral portion of the laminate before and after the experiment in Experimental Example 4 (magnification: 5 times the whole view, each part is enlarged 50 times).

FIG. 18 is an explanatory diagram illustrating the head portion of the valve according to the second embodiment.

19 is a vertical cross-sectional view showing a head portion of a valve according to a third embodiment.

FIG. 20 is a plan view of FIG. 19 viewed from above.

FIG. 21 is an enlarged view in which FIG. 19 is enlarged.

22 is a vertical cross-sectional view showing a head portion of a valve according to a fourth embodiment.

FIG. 23 is an explanatory diagram illustrating a state in which the head portion of the valve is changed to a deflected state due to thermal contraction.

FIG. 24 is an enlarged explanatory diagram illustrating generation of bending stress by enlarging the portion W in FIG. 23 .

25 is a vertical cross-sectional view showing a head portion of a valve according to a fifth embodiment.

26 is a vertical cross-sectional view showing a head portion of a valve according to a sixth embodiment.

Detailed ways

Hereinafter, embodiments of the present invention will be described based on the drawings.

In FIG. 1 , reference numeral 1 denotes an intake valve or an exhaust valve (hereinafter, referred to as a valve) as a valve for an internal combustion engine attached to the cylinder head 2 .

A part of the wall surface of the cylinder head 2 defines the combustion chamber S. An intake port and an exhaust port (hereinafter referred to as a port) P are formed in the cylinder head 2 so as to open to the combustion chamber S, and a valve seat insert 9 is provided on the opening periphery of the port P.

The valve 1 includes, as a valve main body 1A, a shaft portion (Stem) 3 and a head portion (Head) 4 integrated with one end of the shaft portion 3 in an enlarged diameter state. The head 4 has a structure in which the front end face of the head 4 is a valve bottom face (Face) 5 that has a width and is circular in front view, and on the other hand, shrinks as it approaches the shaft portion 3 from the valve bottom face 5 . In this head 4, a seat surface (Seat) 7 is formed via a margin part (Margin) 6 on the back side of the valve bottom surface 5 in the outer peripheral part. The valve 1 is arranged in the combustion chamber S so that the back surface of the head 4 faces the opening of the port P, and the valve 1 is operated by the valve actuator 10, and the seat surface (Seat) of the head 4 in the valve 1 is operated. 7 is separated and seated with respect to the valve seat insert 9 of the peripheral edge portion of the port P opening. Thereby, the valve 1 (head 4 ) opens and closes the port P with the valve bottom surface 5 of the valve body 1A facing the combustion chamber S side.

In the present embodiment, SUH11 is used as the material of the valve body 1A. Therefore, the thermal conductivity of the valve body (SUH11) is about 20.5 W/m·K (at room temperature), and the thermal expansion coefficient is about 11.0×10 ⁻⁶ /°C (at room temperature).

In the valve 1 described above, the heat insulating layer 11 is fixed (bonded) to the valve bottom surface 5 of the valve body 1A, as shown in FIGS. 2 and 3 . In the present embodiment, the heat insulating layer 11 includes a first heat insulating layer 12 and a second heat insulating layer having the same diameter as the first heat insulating layer 12 stacked in this order in the direction away from the valve bottom surface 5 (the upper direction in FIG. 3 ). 13. The valve bottom surface 5 and the first heat insulating layer 12 and the first heat insulating layer 12 and the second heat insulating layer 13 are respectively bonded (sintered) by firing. Therefore, the thermal insulation layer 11 forms the boundary B1 between the valve bottom surface 5 and the first thermal insulation layer 12 , and forms the boundary B2 between the first thermal insulation layer 12 and the second thermal insulation layer 13 . In addition, in FIGS. 2 and 3 , the thickness of the heat insulating layer 11 (the first heat insulating layer 12 and the second heat insulating layer 13 ) is shown exaggeratedly (the thicknesses of the heat insulating layer 12 and the second heat insulating layer 13 ) are not easy to be shown in the actual illustration (the thicknesses of the heat insulating layers 11 and 4 below). the same in the figure).

The above-mentioned first heat insulating layer 12 and second heat insulating layer 13 exhibit a heat insulating function by forming a fine porous structure. Therefore, in the present embodiment, the first heat insulating layer 12 and the second heat insulating layer 13 contain, as components, hollow ceramic beads or hollow glass beads as inorganic pigments, and a binder having excellent heat resistance . More specifically, the first heat insulating layer 12 contains hollow ceramic beads or hollow glass beads: about 40 to 80 wt %, a binder (for example, a silicon-based binder or a zirconia-based binder) with respect to the whole. mixture): about 20 to 60 wt %, the second heat insulating layer 13 contains hollow ceramic beads or hollow glass beads: about 50 to 90 wt %, a binder (for example, a silicon-based binder) with respect to the whole or zirconia-based binder): about 10 to 50 wt%.

In this case, regarding the content of the hollow ceramic beads or the hollow glass beads, the second heat insulating layer 13 is larger than the first heat insulating layer 12 as described above. This is to make the thermal conductivity of the second heat insulating layer 13 lower than the thermal conductivity of the first heat insulating layer 12 based on the adjustment of the existence amount of fine hollows (the hollows of ceramic beads or glass beads), thereby effectively improving the heat insulating property, and Based on the adjustment of the amount of hollow ceramic beads or hollow glass beads, the thermal expansion coefficient of the first thermal insulation layer 12 is adjusted to be an intermediate value between the thermal expansion coefficient of the second thermal insulation layer 13 and the thermal expansion coefficient of the valve bottom surface 5, and the relative thermal expansion coefficient is reduced. The influence (peeling etc.) based on the difference of thermal expansion and the difference of thermal contraction in the 1st heat insulation layer 12 and the 2nd heat insulation layer 13. Of course, in this case, the thermal expansion coefficients of the first thermal insulation layer 12 and the second thermal insulation layer 13 are both smaller than the thermal expansion coefficient of the valve bottom surface 5 .

More specifically, the first heat insulating layer 12 has a thermal conductivity of 0.4 to 1.2 W/m·K (at room temperature) at a layer thickness of about 20 to 100 μm on the valve bottom surface 5 , and the second heat insulating layer 13 is On the first heat insulating layer 12 , the thermal conductivity is 0.2 to 1.0 W/m·K (at room temperature) at a layer thickness of about 20 to 250 μm.

In addition, regarding the thermal expansion coefficient of the heat insulating layer 11 (the first heat insulating layer 12 and the second heat insulating layer 13 ), the thermal expansion coefficient of the heat insulating layer 11 is smaller than the thermal expansion coefficient of the valve bottom surface 5 , and the second heat insulating layer 13 Under the basic structure in which the coefficient of thermal expansion is smaller than the coefficient of thermal expansion of the first heat insulating layer 12, the difference between the coefficients of thermal expansion of the first heat insulating layer 12 and the second heat insulating layer 13 is smaller than that of the valve body 1A and the first heat insulating layer 12. . This is for making the thermal influence (peeling etc.) between the first heat insulating layer 12 and the second heat insulating layer 13 lower than that between the valve bottom surface 5 and the first heat insulating layer 12 .

As shown in FIGS. 3 and 4 , the heat insulating layer 11 (the first heat insulating layer 12 and the second heat insulating layer 13 ) has a diameter smaller than that of the outer edge of the valve bottom surface 5 . Specifically, the outer edge of the heat insulating layer 11 is set closer to the outer edge of the valve bottom surface 5 than the radial center portion O of the valve bottom surface 5 . This is to reduce the length of the valve body 1A (valve bottom surface 5 ) and the heat insulating layer by reducing the length that is the subject of thermal expansion and thermal contraction while basically ensuring the heat insulating function with respect to the valve bottom surface 5 by the heat insulating layer 11 . The thermal expansion difference and the thermal shrinkage difference of the thermal expansion coefficient difference of 11 suppress the peeling of the heat insulating layer 11 from the valve bottom surface 5 .

With regard to the peeling of the heat insulating layer 11 from the valve bottom surface 5 and the diameter reduction of the heat insulating layer 11 as a measure for suppressing the peeling, the heat insulating layer 11 and the entire valve bottom surface 5 are sintered (bonded) as an example, based on FIG. 5 , FIG. 6 will be described in detail.

In the valve 1, the valve bottom surface 5 (valve main body 1A) and the heat insulating layer 11 are actually sintered and integrated, but if the valve bottom surface 5 and the heat insulating layer 11 are thermally expanded and contracted independently, the valve bottom surface 5 The coefficient of thermal expansion is larger than the coefficient of thermal expansion of the heat insulating layer 11 , therefore, during thermal expansion, the reference state shown in FIG. 5( a ) is as shown in FIG. In the state of diameter expansion, the difference in expansion amount ΔLe based on the difference in thermal expansion coefficient occurs. This expansion amount difference ΔLe is obtained by the following formula.

ΔLe=ΔLe1-ΔLe2=(α1-α2)×D×ΔTe

In this case, ΔLe1: the expansion amount of the valve bottom surface 5, ΔLe2: the expansion amount of the heat insulating layer, α1: the thermal expansion coefficient of the valve bottom surface 5, α2: the thermal expansion coefficient of the heat insulating layer, D: the heat insulating layer 11 before thermal expansion and the diameter (object length) of the valve bottom surface 5, ΔTe: temperature change during thermal expansion.

On the other hand, at the time of thermal contraction, as shown in FIG. 6( a ) in the reference state shown in FIG. 6( b ), the diameter of the valve bottom surface 5 becomes a state in which the diameter of the valve bottom surface 5 is smaller than the diameter of the heat insulating layer 11 , resulting in a thermal expansion coefficient based on Poor shrinkage difference ΔLc. This shrinkage difference ΔLc is obtained by the following formula.

ΔLc=ΔLc1-ΔLc2=(α1-α2)×D×ΔTc

In this case, ΔLc1: the shrinkage amount of the valve bottom surface 5, ΔLc2: the shrinkage amount of the heat insulating layer, α1: the thermal expansion coefficient of the valve bottom surface 5, α2: the thermal expansion coefficient of the heat insulating layer, D: the heat insulating layer before thermal shrinkage 11 and the diameter of the valve bottom surface 5 (object length), ΔTc: temperature change during thermal shrinkage.

Actually, as described above, in the valve 1 described above, the difference in expansion amount ΔLe and difference in contraction amount ΔLc based on the difference in thermal expansion coefficients are intended to occur in the state where the valve bottom surface 5 and the heat insulating layer 11 are sintered and integrated. Therefore, it is presumed that the phenomenon at this time changes from the reference state shown in FIG. 5( a ) to FIG. 5( c ) at the time of thermal expansion, the valve bottom surface 5 expands in diameter, and on the other hand, the outer peripheral edge portion of the heat insulating layer 11 Among them, the portion closer to the joint surface with the valve bottom surface 5 at this time is pulled radially outward. Therefore, it is considered that the larger the above-mentioned difference in expansion amount ΔLe at this time, the easier it is for the heat insulating layer 11 to peel off with respect to the valve bottom surface 5 .

On the other hand, it is estimated that the phenomenon during thermal shrinkage changes from the reference state shown in FIG. 6( a ) (the same state as the reference state shown in FIG. 5( a ) to FIG. On the other hand, when the diameter is reduced, the portion of the outer peripheral edge portion of the heat insulating layer 11 that is closer to the joint surface with the valve bottom surface 5 at this time is pulled radially inward. Therefore, it is considered that the larger the aforementioned shrinkage amount difference ΔLe at this time, the easier it is for the heat insulating layer 11 to peel off from the valve bottom surface 5 .

Therefore, the present inventors have noticed that the difference in expansion ΔLe and the difference in shrinkage ΔLc become smaller when the target length D that affects thermal expansion and thermal contraction is shortened in the equations for obtaining the above-mentioned difference in expansion amount ΔLe and difference in shrinkage amount ΔLc In this regard, the target length D to be affected by thermal expansion and thermal contraction is determined as the length of the portion where the heat insulating layer 11 and the valve bottom surface 5 are sintered (bonded), and the diameter of the heat insulating layer 11 is larger than the diameter of the valve bottom surface 5 It is combined with the valve bottom surface 5 in a reduced diameter state.

As shown in FIGS. 2 to 4 , the valve bottom surface 5 and the heat insulating layer 11 on the valve bottom surface 5 are covered with a coating material 15 . The covering material 15 is formed into a bottomed substantially cylindrical shape in a state where the bottom side is disposed away from the valve bottom surface 5, and the covering material 15 is provided with a peripheral wall portion 16 serving as a peripheral wall and integrally provided with the peripheral wall portion 16. Bottom wall portion 17 of the bottom. The clad material 15 (the peripheral wall portion 16 and the bottom wall portion 17 ) contains ceramics such as zirconia, alumina, silica, and silicate as main components, and a hollow material that is a component of the above-mentioned heat insulating layer 11 Ceramic beads and hollow glass beads are not included in the coating material 15 . As a result, the coating material 15 has a thermal conductivity that is as close as possible to that of the thermal insulation layer 11 by the main component, even if it is not the same as the thermal insulation layer 11 (thermal conductivity of the valve bottom surface 5 (valve main body 1A) > the coating The thermal conductivity of the coating material 15 > the thermal conductivity of the heat insulating layer 11 ), on the other hand, the thermal expansion coefficient of the coating material 15 is as close as possible to the thermal expansion coefficient of the valve bottom surface 5 (thermal expansion coefficient of the valve bottom surface 5 > The thermal expansion coefficient of the coating material 15 Thermal expansion coefficient>thermal expansion coefficient of the heat insulating layer 11). In the present embodiment, as the coating material 15 , a material having a thermal conductivity of 0.2 to 4 W/m·K (at room temperature) and a thermal expansion coefficient equal to or less than that of the valve body 1A is used. In addition, in FIGS. 2 to 4 , the thickness of the covering material 15 (the peripheral wall portion 16 and the bottom wall portion 17 ) is exaggerated because it is not easy to actually show it (the same is true for the drawings after FIG. 5 ). .

As shown in FIG. 3 , one end surface (lower end surface in FIG. 3 ) of the peripheral wall portion 16 is bonded (sintered) to the valve bottom surface 5 on the outer peripheral side of the heat insulating layer 11 . The inner peripheral surface 16i of the peripheral wall portion 16 covers (surrounds) the entire thickness range from the valve bottom surface 5 to the surface 13s of the second thermal insulating layer 13 in a state of contacting the entire peripheral surface 11p of the thermal insulating layer 11. The entire peripheral surface 11p of the heat layer 11, the boundary B1 between the valve bottom surface 5 and the first heat insulation layer 12, and the boundary B2 between the first heat insulation layer 12 and the second heat insulation layer 13 are not exposed to the outside. In the present embodiment, the inner peripheral surface 16i of the peripheral wall portion 16 is bonded (sintered) to the entire peripheral surface of the heat insulating layer 11 .

In addition, in the present embodiment, the outer peripheral surface of the peripheral wall portion 16 expands to the outer peripheral edge of the valve bottom surface 5 in the radial direction of the valve bottom surface 5 . As a result, the entire portion of the valve bottom surface 5 on the outer peripheral side of the heat insulating layer 11 is covered by one end surface (thick wall surface) of the peripheral wall portion 16 , and the peripheral wall portion 16 is different from the heat insulating layer 11 due to its material (component). However, the thermal insulation properties at the portion of the valve bottom surface 5 where the thermal insulation layer 11 does not exist is ensured. In this case, the thickness of the peripheral wall portion 16 is determined depending on how large the diameter of the heat insulating layer 11 is, but it is possible to suppress peeling of the outer peripheral portion of the heat insulating layer 11 while emphasizing the heat insulating property with respect to the valve bottom surface 5 . In this case, the diameter of the heat insulating layer 11 tends to increase, while the thickness of the peripheral wall portion 16 is reduced, so as to ensure the heat insulating property of the valve bottom surface 5 while emphasizing the suppression of peeling of the outer peripheral portion of the heat insulating layer 11 . In this case, the diameter of the heat insulating layer 11 tends to decrease, while the thickness of the peripheral wall portion 16 is increased. In the present embodiment, the thickness of the peripheral wall portion 16 is 1 μm to 30 μm, and the heat insulating layer 11 is present on the radially inner side of the inner peripheral surface 16 i of the peripheral wall portion 16 .

As shown in FIGS. 3 and 4 , the bottom wall portion 17 is in contact with the surface 11s ( 13s ) of the heat insulating layer 11 (second heat insulating layer 13 ) and covers the surface 11 s ( 13 s ). The bottom wall portion 17 is integrally provided on the other end face of the peripheral wall portion 16 so as to close the other end opening. The bottom wall portion 17 is due to the fact that the peripheral wall portion 16 is combined with the valve bottom face 5 , since the second heat insulating layer 13 When a force in a direction away from the other end of the peripheral wall portion 16 (upward direction in FIG. 3 ) acts on the bottom wall portion 17 , the force is resisted. In the present embodiment, the bottom wall portion 17 is also bonded (sintered) to the surface 13s of the second heat insulating layer 13, and the thickness of the bottom wall portion 17 is 1 μm to 30 μm.

Therefore, such a valve 1 has the following functions.

(1) In the valve 1 , while ensuring the thermal insulation of the valve bottom surface 5 as much as possible, peeling of the outer peripheral portion of the thermal insulation layer 11 due to the action of the combustion gas is suppressed.

Even if the head 4 of the valve 1 is used in a state of being disposed in the combustion chamber S, since one end surface of the peripheral wall portion 16 in the coating material 15 is coupled to the valve bottom surface 5, and the inner surface of the peripheral wall portion 16 in the coating material 15 is bonded to the valve bottom surface 5 Since the peripheral surface 16i is combined with the entire peripheral surface 11p of the heat insulating layer 11 (the first heat insulating layer 12 and the second heat insulating layer 13) over the entire thickness range, the combustion gas does not act on the valve as shown in FIG. 7 . The boundary B1 between the bottom surface 5 and the first heat insulation layer 12 , and the boundary B2 between the first heat insulation layer 12 and the second heat insulation layer 13 . Therefore, peeling of the outer peripheral portion of the first heat insulating layer 12 with respect to the valve bottom surface 5 or peeling of the second heat insulating layer 13 with respect to the first heat insulating layer 12 is suppressed.

Furthermore, in the present embodiment, the covering material 15 is provided with a bottom wall portion 17 at the other end of the peripheral wall portion 16 , and the bottom wall portion 17 covers the second heat insulating layer 13 in a state of being bonded to the surface 13s. For the surface 13s of the second heat insulating layer 13 , the peripheral wall portion 16 and the bottom wall portion 17 enclose the entire heat insulating layer 11 . Combustion gas does not act (enter) into the boundary between the surfaces 16i (see FIG. 7 ), and the outer peripheral portion of the heat insulating layer 11 is prevented from peeling off due to the action of the combustion gas with high reliability.

On the other hand, not only the basic thermal insulation with respect to the valve bottom surface 5 is ensured by the thermal insulation layer 11 , but also the portion of the valve bottom surface 5 where the thermal insulation layer 11 is not arranged has thermal conductivity as close as possible to the thermal insulation layer 11 . Since the peripheral wall part 16 of the coating material 15 of the coefficient covers this part, the heat insulation property with respect to this part can also be ensured.

Therefore, the thermal insulation layer 11 and the peripheral wall portion 16 of the covering material 15 can ensure the thermal insulation performance with respect to the valve bottom surface 5 as much as possible, and the effect by the combustion gas can be suppressed with high reliability, and the first thermal insulation layer 12, The outer peripheral portion of the second heat insulating layer 13 is peeled off.

In this case, regarding thermal expansion and thermal contraction, the thickness of the peripheral wall portion 16 in the covering material 15 is remarkably smaller than the radius of the valve bottom surface 5 (the target length that affects thermal expansion and thermal contraction is small), and the The thermal expansion coefficient of the peripheral wall portion 16 (the covering material 15 ) is close to the thermal expansion coefficient of the valve bottom surface 5 (valve body 1A) to improve the followability. Therefore, the peripheral wall portion 16 is prevented from peeling off with respect to the valve bottom surface 5 due to thermal expansion or thermal contraction. .

On the other hand, as shown in FIG. 8 , when the peripheral wall portion 16 of the covering material 15 does not cover the entire peripheral surface 11p of the heat insulating layer 11 (the first heat insulating layer 12 and the second heat insulating layer 13 ), combustion The gas directly acts on the boundary B1 and the boundary B2 , and the outer peripheral portion 11 a of the heat insulating layer 11 tends to be easily peeled off with respect to the valve bottom surface 5 .

(2) In the valve 1, peeling of the outer peripheral portion 11a of the heat insulating layer 11 due to the difference in thermal expansion or the difference in thermal contraction is suppressed.

The inventors have found that the outer peripheral portion 11a of the heat insulating layer tends to peel off from the valve bottom surface 5. However, in the present embodiment, the heat insulating layer based on the difference in thermal expansion or the difference in thermal contraction is suppressed from two different viewpoints. Peeling of the outer peripheral portion 11a.

(2-1) First, as described above, the heat insulating layer 11 is bonded to the valve bottom surface 5 in a state where the diameter is reduced from the diameter of the valve bottom surface 5 . This specifically means that when the target length D that affects thermal expansion and thermal contraction is shortened in the equations for obtaining the difference in expansion amount ΔLe and the difference in contraction amount ΔLc based on the above-mentioned difference in thermal expansion coefficient, the difference in expansion amount ΔLe and the difference in contraction amount ΔLc The target length D affecting the expansion difference ΔLe and the shrinkage difference ΔLc is determined to be the length of the joint portion of the heat insulating layer 11 and the valve bottom surface 5 .

Thereby, as already described, peeling of the heat insulating layer outer peripheral portion 11 a with respect to the valve bottom surface 5 is suppressed as the diameter of the heat insulating layer 11 decreases with respect to the diameter of the valve bottom surface 5 .

FIG. 9 shows the experimental methods of Experiment Examples 1 to 3 which prove the above-mentioned content, and the evaluation of each experimental result. In Experimental Examples 1 to 3, a durability test was performed on the valve of the structure unique to each experimental example as an experimental method under common experimental conditions, and the respective experimental results were evaluated by a common evaluation method.

(a) Common experimental conditions

test subject

The heat insulating layer 11 (the first heat insulating layer 12 and the second heat insulating layer 13 ) and the covering layer 17 (corresponding to the bottom wall portion 17 of the covering material 15 ) are laminated on the valve bottom surface 5 . 17 Poppet valve of the same reference numeral 17)

Heat insulating layer 11: The first heat insulating layer 12 and the second heat insulating layer 13 shown in the first embodiment are laminated

Coating layer 17: constituted only by the bottom wall portion 17 of the coating material 15 shown in the first embodiment

Overall layer thickness of the heat insulating layer and the coating layer (hereinafter, referred to as the laminate 26 ): 120 μm

Bonding of the valve bottom surface 5 and the first heat insulating layer 12, bonding of the first heat insulating layer 12 and the second heat insulating layer 13, bonding of the second heat insulating layer 13 and the covering layer 17: sintering

Valve: Diameter of valve bottom surface 5: 32mm Material: SUH11

Experimental content

The valve 1E of each of Experimental Examples 1 to 3 was subjected to a durability test using the durability tester 20 (valve-valve seat wear tester). As shown in FIG. 10 , in the durability test, after the valve 1E of each experimental example is placed on the durability tester 20, the valve 1E is moved up and down by the rocker arm 22 while the rotor 25 rotates around the axis of the valve 1E. A state in which the flame from the gas burner 21 is applied to the valve bottom surface 5 . In FIG. 10 which shows the content of the experiment, 23 is a thermometer for measuring the temperature of the valve bottom surface 5, and 24 is a water jacket for cooling the durability tester.

Durability test conditions

Up and down speed of valve 1E: 3000rpm (equivalent to 6000rpm in engine speed)

Rotation speed of valve 1E (rotation speed): 20rpm

Temperature of valve 1E (valve bottom surface temperature): 400°C

Gas used for gas burner: LPG

Durability test time: 50hr

Intermediate check time of experimental results: 10, 20, 30, 40, 50hr

(b) Experimental method peculiar to each experimental example (structure of peculiar laminated body 26 (heat-insulating layer 11 and coating layer 17 ))

Experimental Example 1: A system in which the entire valve bottom surface 5 (diameter 32 mm) is covered with the laminated body 26 (diameter 32 mm) (refer to the structural diagram of Experimental Example 1 in FIG. 9 )

Experimental Example 2: A method in which the valve bottom surface 5 (diameter 32 mm) is covered with a laminated body 26 (diameter 29 mm) smaller in diameter than the valve bottom surface 5 (refer to the structural diagram of Experimental Example 2 in FIG. 9 )

Experimental Example 3: A method in which the diameter of the laminated body 26 is further reduced in diameter (26 mm in diameter) compared to the case of Experimental Example 2 (refer to the structural diagram of Experimental Example 3 in FIG. 9 )

(c) Common evaluation methods

After the experiment of each experimental example, image information of the state of the laminated body 26 on the valve bottom surface 5 (the state viewed from the axial direction of the shaft portion 3 in the valve 1E) was obtained, and the peeling area of the laminated body 26 was derived from the image information. , the peeling rate was obtained by dividing the peeling area by the area of the laminate 26 covering the valve bottom surface 5 (hereinafter, referred to as the total area). Then, a larger value of the peeling ratio is evaluated as a larger degree of peeling of the laminated body (the heat insulating layer 11 and the covering layer 17 ) 26 with respect to the valve bottom surface 5 .

(d) Results and evaluation of each experiment

Regarding Experimental Example 1, peeling of the laminate 26 started to occur at the outer peripheral portion of the valve bottom surface 5 10 hours after the start of the experiment, and the state shown in FIG. 11 was reached 20 hours after the start of the experiment, and 50 hours after the start of the experiment. The peeling rate at the time point was 11.8%.

In Experimental Example 2, the state shown in FIG. 12 was obtained after 50 hours from the start of the experiment, and the peeling rate at this time point was 4.5%.

In Experimental Example 3, the state shown in FIG. 13 was obtained 50 hours after the start of the experiment, and the peeling ratio at this time point was 2.8%.

As can be understood from the above, the more the diameter of the laminated body 26 is reduced, the more it is possible to suppress the peeling of the laminated body 26 on the valve bottom surface 5 .

(2-2) Second, the inner peripheral surface 16i of the peripheral wall portion 16 in the covering material 15 is in the entire thickness range from the valve bottom surface 5 to the surface 11s of the heat insulating layer 11, and the heat insulating layer in the reduced diameter state The entire peripheral surface of 11 is joined, and one end face of the peripheral wall portion 16 is joined at a portion of the valve bottom surface 5 where the heat insulating layer 11 does not exist, and the thermal expansion coefficient of the coating material 15 is as close as possible to the valve bottom surface 5 (head). The thermal expansion coefficient of part 4) is larger than the thermal expansion coefficient of the heat insulating layer 11 .

As a result, during thermal expansion, as shown in FIG. 14 , the thermal expansion (diameter expansion) of the peripheral wall portion 16 itself, and further the thermal expansion (diameter expansion) of the peripheral wall portion 16 and the valve bottom surface 5 cooperate with each other, and the entire peripheral surface 11p of the heat insulating layer 11 cooperates. When it is stretched radially outward (refer to the arrow in FIG. 14 ), the portion of the heat insulating layer 11 that is farther from the valve bottom surface 5 receives a larger tensile force. Therefore, the above-mentioned difference in thermal expansion amount ΔLe based on the difference in thermal expansion coefficient between the valve bottom surface 5 and the thermal insulation layer 11 is reduced, and peeling of the thermal insulation layer 11 due to thermal expansion is suppressed.

Also in this case, in the present embodiment, the bottom wall portion 17 of the covering material 15 is intended to thermally expand (diametrically expand) outward in the radial direction. Therefore, as in the case of the valve bottom surface 5, the thermal expansion force is assumed to be The force for expanding the diameter of the peripheral wall portion 16 acts to increase the tensile force for pulling the entire peripheral surface 11p of the heat insulating layer 11 radially outward. In addition, the fact that the thickness of the peripheral wall portion 16 is relatively large and the strength thereof is improved also contributes to reliably imparting the above-described tensile force to the entire peripheral surface 11p of the heat insulating layer 11 . In addition, at this time, even if the outer peripheral portion of the heat insulating layer 11 tries to warp, frictional force is generated between the outer peripheral portion of the heat insulating layer 11 and the inner peripheral surface 16i of the peripheral wall portion 16 at this time, and even if this distance The warpage or the like of the outer peripheral portion of the heat layer 11 generates a force (force toward the bottom wall portion 17 ), and the bottom wall portion 17 also resists the force. Therefore, in the present embodiment, the peeling-suppressing effect of the heat insulating layer 11 is also enhanced according to these circumstances.

On the other hand, at the time of thermal shrinkage, as shown in FIG. 15 , the thermal shrinkage (diameter reduction) of the peripheral wall portion 16 itself and the thermal shrinkage (diameter reduction) of the valve bottom surface 5 cooperate with the thermal contraction (diameter reduction) of the valve bottom surface 5 to shrink the entire circumference of the heat insulating layer 11 . When it is pressed (tightened) inward in the radial direction thereof (refer to the arrow in FIG. 15 ), the portion farther away from the valve bottom surface 5 in the heat insulating layer 11 receives a greater pressing force. Therefore, the above-mentioned difference in shrinkage amount ΔLc based on the difference in thermal expansion coefficient between the valve bottom surface 5 and the heat insulating layer 11 is reduced, and peeling of the heat insulating layer 11 due to heat shrinkage is suppressed.

At this time, the bottom wall portion 17 of the covering material 15 is also intended to be thermally shrunk (reduced in diameter) radially outward. Therefore, as in the case of the valve bottom face 5 , the thermal shrinkage force is used as the force required to reduce the diameter of the peripheral wall portion 16 . The force acts so that it increases the pressing force for pressing the entire peripheral surface of the heat insulating layer 11 radially inward. Therefore, even in the case of thermal contraction, the peeling-suppressing effect of the heat insulating layer 11 is enhanced similarly to the case of thermal expansion.

FIG. 16 shows an experimental method peculiar to Experimental Example 4 which proves the above-mentioned content, and the evaluation of each experimental result. Experimental Example 4 is an example in which the valve 1E of the unique structure was subjected to a durability test under the above-mentioned common experimental conditions, and the test results were evaluated by the same common evaluation method as described above.

Unique experimental method of experimental example 4

In Experimental Example 4, the valve bottom surface 5 (diameter 32 mm) was covered with a heat insulating layer 11 (diameter 29 mm) smaller in diameter than the valve bottom surface, and the heat insulating layer 11 and the valve bottom surface 5 were covered with a covering material 15 The mode of the part where the heat insulating layer 11 does not exist (refer to the structure diagram of the experimental example 4 in FIG. 16 ).

Experimental results of experimental example 4

In Experimental Example 4, the state shown in FIG. 17 was obtained 50 hours after the start of the experiment, and the peeling rate at this time point was 0%. From this fact and the experimental results of Experimental Example 2 described above, it can be understood that the coating material 15 , especially the peripheral wall portion 16 contributes to suppressing peeling of the thermal insulation layer 11 due to the difference in thermal expansion coefficient.

FIG. 18 shows the second embodiment, FIGS. 19 to 21 show the third embodiment, FIGS. 22 to 24 show the fourth embodiment, FIG. 25 shows the fifth embodiment, and FIG. 26 shows the sixth embodiment. In each of the embodiments, the same components as those of the first embodiment described above are denoted by the same reference numerals, and descriptions thereof will be omitted.

The second embodiment shown in FIG. 18 shows a modification of the first embodiment.

In this second embodiment, the edge portion 6 of the outer peripheral portion of the head portion 4 is formed with the protrusion 28 as an engaging portion over the entire circumference of the head portion 4 .

On the other hand, the peripheral wall portion 16 in the covering material 15 is integrally provided with an extension portion 29 that extends to the edge portion 6 , and the extension portion 29 is bonded (sintered) with the edge portion 6 to the protrusion 28 . Mechanically snapped.

Thereby, the bonding strength between the covering material 15 and the valve bottom surface 5 can be improved, and the ability of the bottom wall portion 17 of the covering material 15 to resist peeling and warping of the outer peripheral portion 11a of the heat insulating layer can be improved.

The third embodiment shown in FIGS. 19 to 21 shows a modification of the first embodiment.

In the third embodiment, the valve bottom surface 5 is formed with a recess 31 that expands radially outward from the center in the radial direction of the valve bottom surface 5 . The heat insulating layer 11 (the first heat insulating layer 12 and the second heat insulating layer 13 laminated and integrated with the first heat insulating layer 12 ), the heat insulating layer 11 (the first heat insulating layer 12 ) are accommodated in the recess 31 . The bottom surface of the recess 31 is bonded (eg, sintered) to the bottom wall 31b of the recess 31, and the entire peripheral surface 11p of the heat insulating layer 11 is bonded (eg, sintered) to the inner peripheral wall 31wi of the recess 31 as the peripheral wall in abutting state.

In addition, the entire surface 11s ( 13s ) of the heat insulating layer 11 (second heat insulating layer 13 ) and the valve bottom surface 5 (except the portion of the recess 31 ) in the recess 31 are covered by the covering material 15 , and the covering The material 15 is bonded (eg, sintered) to the surface 11s of the heat insulating layer 11 and the valve bottom surface 5 in these recesses 31 .

As a result, the entire peripheral surface 11p of the heat insulating layer 11 is covered by the recessed inner peripheral wall 31wi of the valve bottom surface 5, and the combustion gas does not directly act on the valve bottom surface 5 and the first heat insulating layer 12. The boundary B1 between the two, and the boundary B2 between the first thermal insulation layer 12 and the second thermal insulation layer 13 . On the other hand, in the third embodiment, not only can the basic heat insulating property with respect to the valve bottom surface 5 be ensured by the heat insulating layer 11 , but also the portion of the valve bottom surface 5 where the heat insulating layer 11 is not disposed is provided with Since the coating material 15 having the thermal conductivity as close to the thermal conductivity of the heat insulating layer 11 as possible covers this portion, it is possible to secure the heat insulating property with respect to this portion.

In addition, during thermal expansion, the inner peripheral wall 31wi of the recess expands in diameter to stretch the entire peripheral surface 11p of the heat insulating layer 11 radially outward, and the portion of the heat insulating layer 11 that is farther from the bottom wall 31b of the recess 31, the greater the tensile force. On the other hand, at the time of thermal shrinkage, the inner peripheral wall 31wi of the recess shrinks in diameter to press (tighten) the entire peripheral surface 11p of the heat insulating layer 11 radially inward. The portion of the bottom wall 31b is subjected to a larger pressing force. Therefore, at the time of thermal expansion, the difference in the thermal expansion amount based on the difference in thermal expansion coefficient between the recess bottom wall 31b and the first thermal insulation layer 12 and the thermal expansion coefficient difference between the first thermal insulation layer 12 and the second thermal insulation layer 13 is reduced. At the time of shrinkage, the difference in the amount of shrinkage based on the difference in thermal expansion coefficient between the bottom wall 31b of the recess and the first thermal insulation layer 12 and the thermal expansion coefficient difference between the first thermal insulation layer 12 and the second thermal insulation layer 13 decreases. The peeling of the outer peripheral portion of the thermal insulation layer 11 having a difference in thermal expansion coefficient due to shrinkage is suppressed.

In this case, since the recessed inner peripheral wall 31wi is used as the peripheral wall, and a peripheral wall with sufficient strength is used, the tensile force during thermal expansion or the pressing force during thermal contraction can be reliably applied to the peripheral surface of the heat insulating layer 11, The reliability of the peeling suppression of the heat insulating layer 11 due to the difference in thermal expansion coefficient caused by thermal expansion or thermal contraction can be made high.

Furthermore, even if the outer peripheral portion of the heat insulating layer 11 tries to warp, frictional force is generated between the outer peripheral portion of the heat insulating layer 11 and the recess inner peripheral wall 31wi at this time, and even if the outer peripheral portion of the heat insulating layer 11 The warpage of 11a or the like generates a force (force toward the covering material 15), and the covering material 15 also resists the force. Of course, at this time, in the radial direction of the valve bottom surface 5, the actual length of the valve bottom surface 5 in contact with the covering material 15 is limited by the presence of the recess 31. Therefore, the influence of thermal expansion and thermal contraction is reduced, and the covering material is sufficiently ensured. The bonding strength of the covering material 15 with respect to the valve bottom surface 5 .

The fourth embodiment shown in FIGS. 22 to 24 shows a modification of the first embodiment.

This fourth embodiment shows that cracks are prevented from occurring in the heat insulating layer 11 due to the bending stress due to the difference in thermal expansion coefficient caused by thermal expansion or thermal contraction. Therefore, the heat insulating layer 11 due to the cracks is intended to be suppressed from the valve bottom surface. 5 of the peeling. Therefore, in the fourth embodiment, the thickness of the outer peripheral portion 11 a (length in the vertical direction in FIG. 22 ) of the heat insulating layer 11 fixed to the valve bottom surface 5 which is a flat surface as a whole is thinner than that of the outer periphery of the heat insulating layer 11 . The thickness of the radially inner portion 11b of the portion 11a.

Specifically, a case of thermal contraction of the valve 1 will be described as an example. When the thermal expansion coefficient of the heat insulating layer 11 is smaller than the thermal expansion coefficient of the valve bottom surface 5, as shown in FIG. Then, the heat insulating layer 11 and the valve bottom surface 5 (valve bottom surface portion) are integrally flexed, and bending stress acts on them. FIG. 24 is an enlarged view showing the W portion (outer peripheral portion) shown in FIG. 23 . As can be seen from this FIG. 24 , when the heat insulating layer 11 on the valve bottom surface 5 is bent due to thermal contraction, the bending stress is given by

σ=(y/ρ)E

To represent. Here, ρ: the curvature radius of the neutral plane N in the outer peripheral portion 11a, y: the distance from the neutral plane N, y/ρ: strain, E: longitudinal elastic modulus.

Therefore, when the bending stress σ with respect to the heat insulating layer 11 reaches the maximum value at the distance y from the neutral plane N, that is, when the distance ymax from the neutral plane N to the outer surface in the thickness direction of the heat insulating layer 11 (edge stress When ) reaches the maximum value, the larger the distance ymax from the neutral plane N to the outer surface in the wall thickness direction, the larger the maximum value (maximum bending stress) σmax. As a result, as the thickness of the heat insulating layer 11 increases, the maximum bending stress σmax increases. In such a case, the possibility of cracks occurring in the heat insulating layer 11 increases. The thicker the thickness, the deeper the crack is. In particular, the outer peripheral portion 11a of the heat insulating layer 11 has the effect of the above-mentioned combustion gas and the effect of the difference in thermal expansion coefficient between the heat insulating layer 11 and the valve bottom surface 5. The curvature radius ρ tends to be smaller than the curvature radius ρ' of the portion 11b radially inward of the outer peripheral portion 11a (the curvature tends to be larger), and the possibility of cracks occurring in the outer peripheral portion 11a is obtained from the above It can be seen from the expression of the bending stress that it is larger than that of the portion 11b radially inward of the outer peripheral portion 11a.

Thus, as shown in FIG. 22 , by making the thickness of the outer peripheral portion 11a of the thermal insulation layer 11 thinner than the thickness of the portion 11b radially inward of the outer peripheral portion 11a, the thickness of the thermal insulation layer 11 from the neutral plane N to the wall is reduced. As the distance y from the outer surface in the thickness direction decreases, the maximum bending stress σmax during thermal expansion and thermal contraction decreases.

Specifically, the thickness of the portion 11b radially inward of the outer peripheral portion 11a of the heat insulating layer 11 is maintained at a constant thickness, while the thickness of the outer peripheral portion 11a is set to increase as the thickness of the outer peripheral portion 11a increases toward the heat insulating layer 11 . The outer peripheral edge 11aa of the heat insulating layer 11 reaches the vicinity of the outer peripheral edge of the valve bottom surface 5 with the peripheral surface of the heat insulating layer 11 having a slight thickness formed on the outer peripheral edge 11aa.

Thereby, generation|occurrence|production of a crack can be suppressed reliably in the heat insulating layer outer peripheral part 11a, and it can suppress that the heat insulating layer outer peripheral part 11a peels off from the valve bottom surface 5 by a crack. On the other hand, in this case, only the thickness of the outer peripheral portion 11a of the heat insulating layer 11 is thinner than the thickness of the radially inner portion 11b of the heat insulating layer 11, and the thickness becomes thinner as it goes radially outward, so Therefore, the thickness of the outer peripheral portion 11 a of the heat insulating layer 11 is not reduced as much as possible, and the heat insulating property of the heat insulating layer 11 on the valve bottom surface 5 can be suppressed as much as possible.

In addition, in the present embodiment, the coating material 15 not only covers the peripheral surface of the heat insulating layer outer peripheral edge 11aa with a small thickness, but also covers the surface 11s of the heat insulating layer 11, and is bonded to the heat insulating layer 11 and the valve bottom surface 5 . Therefore, regarding the covering material 15, the same functions as those of the above-described first embodiment and the like are ensured.

In addition, in the present embodiment, the peripheral surface 11p of the heat insulating layer 11 is used as the minute thickness portion of the outer peripheral edge 11aa of the heat insulating layer 11, and the other exposed portions are used as the surface 11s, but the heat insulating layer 11 may be included. The part of the outer peripheral part 11a of the heat insulating layer 11 serves as the peripheral surface 11p.

The fifth embodiment shown in FIG. 25 shows a modification of the above-described third and fourth embodiments. In this fifth embodiment, except for the first embodiment, the same components as those in the third and fourth embodiments are denoted by the same reference numerals, and descriptions thereof are omitted.

This fifth embodiment shows that the thickness of the outer peripheral portion 11a of the heat insulating layer 11 is reduced in a state where the inner peripheral wall 31wi of the recess 31 is used as the peripheral wall.

In the fifth embodiment, as in the fourth embodiment, the valve bottom surface 5 is formed with a recess 31 that expands radially outward with the center portion in the radial direction of the valve bottom surface 5 as the center. It is inclined so as to be directed toward the radially outer side of the recess 31 toward the opening 31 o side of the recess 31 . The heat insulating layer 11 is fixed (sintered) to the bottom wall 31 b of the recess 31 , the surface 11 s of the heat insulating layer 11 is formed as a flat surface, and the peripheral surface 11 p of the heat insulating layer 11 is formed toward the surface side in the thickness direction of the heat insulating layer 11 . Expand its diameter radially outward. The entire peripheral surface 11p of the heat insulating layer 11 is bonded (sintered) to the recess inner peripheral wall 31wi in a state of abutment, and the surface of the heat insulating layer 11 is set to be opposed to the portion of the valve bottom surface 5 other than the recess 31 flush.

Then, the coating material 15 is bonded to the surface 11s of the heat insulating layer 11 and the valve bottom surface 5 in the recess 31 so as to cover the entire surface 11s of the heat insulating layer 11 and the valve bottom surface 5 . The surface formed on the valve bottom surface 5 is formed as a flat surface.

Therefore, in the fifth embodiment, the entire peripheral surface 11p of the heat insulating layer 11 can be brought into contact with the recess inner peripheral wall 31wi, and the outer peripheral portion 11a of the heat insulating layer 11 can be made thinner toward the radially outer side. While reducing the thermal insulation function of the thermal insulation layer 11 as much as possible, it is possible to inhibit the thermal insulation layer 11 from peeling off from the valve bottom surface 5 due to the action of the combustion gas and the occurrence of cracks. Of course, in the present embodiment, since the heat insulating layer 11 is joined to the valve bottom surface 5 in a state of being smaller in diameter than the valve bottom surface 5 , the peeling suppression effect by the diameter reduction of the heat insulating layer 11 can be obtained.

In addition, the surface 11s of the heat insulating layer 11 is set so as to be flush with the portion of the valve bottom surface 5 other than the recess 31, and the surface of the coating material 15 formed on the valve bottom surface 5 becomes a flat surface accordingly. Therefore, even when the heat insulating layer 11 is provided on the valve bottom surface 5, the entire valve bottom surface side can be flattened (planarized), and the basic structure and basic performance of a general valve with a flat valve bottom surface can be secured.

Furthermore, the coating material 15 bonded to the surface of the heat insulating layer 11 and the valve bottom surface 5 resists peeling, warping, etc. of the outer peripheral portion of the heat insulating layer 11 , thereby further suppressing the possibility that the outer peripheral portion 11 a of the heat insulating layer is peeled off from the valve bottom surface 5 . sex. Of course, in this case, in the radial direction of the valve bottom surface 5, the actual length of the valve bottom surface 5 in contact with the covering material 15 is limited by the presence of the recess 31. Therefore, the influence of thermal expansion and thermal contraction can be reduced sufficiently. The bonding strength of the cladding material 15 with respect to the valve bottom surface 5 is securely ensured.

The sixth embodiment shown in FIG. 26 shows a modification of the above-described fourth and fifth embodiments. In the sixth embodiment, except for the first embodiment, the same components as those in the fourth and fifth embodiments are denoted by the same reference numerals, and the description thereof will be omitted.

This sixth embodiment shows an embodiment in which peeling suppression of the outer peripheral portion 11 a of the heat insulating layer and flattening of the entire valve bottom surface 5 side are achieved as much as possible, and the heat insulating property of the heat insulating layer 11 is improved compared with the fifth embodiment. Way.

In the sixth embodiment, not only the structure in which the heat insulating layer 11 is filled in the cavity 31 is combined with the inner peripheral wall 31wi and the bottom wall 31b of the cavity 31 (the structure in the fifth embodiment) Moreover, the surface 11s of the heat insulating layer 11 is formed in the state which raised slightly on the outer side rather than the opening 31o of the recessed part 31. Specifically, the surface 11s of the radially inner portion 11b of the heat insulating layer 11 is parallel to the valve bottom surface 5 (the recess bottom wall 31b ) at a position slightly outside of the opening 31o of the recess 31, while the heat insulating layer 11 The surface 11s of the outer peripheral portion 11a of the outer peripheral portion 11a is formed so as to expand radially outward toward the inner side in the thickness direction of the heat insulating layer 11 (downward in FIG. 26 ), and the outer edge of the surface 11s is separated from the spacer at the position of the recess opening edge 31oo. The peripheral surface 11p of the heat layer 11 is connected. Therefore, the entire thickness of the heat insulating layer 11 is thicker than that of the fifth embodiment while making the heat insulating layer surface 11s as flat as possible.

Furthermore, in this embodiment, the coating material 15 is bonded to the surface 11s of the heat insulating layer 11 and the valve bottom surface 5 so as to cover the entire surface 11s of the heat insulating layer 11 and the valve bottom surface 5 .

Therefore, in the sixth embodiment, the peeling suppression effect of the outer peripheral portion 11 a of the heat insulating layer and the flattening of the entire valve bottom surface 5 side can be achieved as much as possible, and the heat insulating layer 11 can be improved compared with the fifth embodiment. Thermal insulation.

In addition, in the present embodiment, the recess inner peripheral wall 31wi is used as the peripheral wall, and the surface in contact with the recess inner peripheral wall 31wi in the heat insulating layer 11 is used as the peripheral surface 11p, but not only the heat insulating layer 11 may be used. The surface in contact with the recessed inner peripheral wall 31wi also includes the surface in contact with the outer peripheral portion of the coating material 15 as the peripheral surface 11p. In this case, the recessed inner peripheral wall 31wi and the outer periphery of the coating material 15 The part forms the peripheral wall.

As mentioned above, although embodiment was demonstrated, the following aspects are included in this invention.

(1) In each embodiment, as the peripheral wall, the bottom wall portion 17 is omitted and the peripheral wall composed of only the peripheral wall portion 16 is used.

(2) The thickness of the peripheral wall portion 16 is set so as not to cover the entire portion of the valve bottom surface 5 where the heat insulating layer 11 does not exist.

(3) As the engaging portion of the edge portion 6, various engaging portions such as concave portions are used.

(4) As the material of the valve body 1A, SUH35 (thermal conductivity: about 12.6 W/m·K (at room temperature), thermal expansion coefficient: about 1.5×10 ^-6 /°C (at room temperature)) or the like is used.

(5) As the heat insulating layer 11, a heat insulating layer composed of a single layer and a heat insulating layer composed of three or more layers are used.

(6) In the third embodiment (see FIG. 21 ), the recess inner peripheral wall 31wi is inclined radially inward or radially outward of the recess 31 toward the opening of the recess 31 .

Description of reference numerals

1 valve

5 valve bottom

6 edge

11 Insulation layer

11a Outer periphery of heat insulating layer

11b Radial inner portion of thermal insulation

11p Perimeter of Insulation Layer

11s surface of thermal insulation

12 First Insulation Layer

13 Second insulation layer

13s The surface of the second thermal insulation layer 13

15 Covering material

16 Peripheral wall (peripheral wall)

16i Inner peripheral surface of peripheral wall portion 16 (inner peripheral surface of peripheral wall)

17 Bottom wall

29 Extension

31 recess

31b Bottom wall of recess

31wi Inner peripheral wall of recess (peripheral wall, inner peripheral surface of peripheral wall)

31o recessed opening

O Radial center portion of valve bottom surface 5

S Combustion chamber.

Claims (19)

1. A valve for an internal combustion engine, in which a heat insulating layer is fixed to a valve bottom surface facing a combustion chamber,

a peripheral wall integrally provided on the valve bottom surface so as to surround the heat insulating layer,

the inner peripheral surface of the peripheral wall abuts against the entire peripheral surface of the heat insulating layer over the entire thickness range from the valve bottom surface to the surface of the heat insulating layer.

2. The valve for an internal combustion engine according to claim 1,

the heat insulating layer is disposed on the valve bottom surface in a reduced diameter state that is radially inwardly retracted from an outer peripheral edge of the valve bottom surface.

3. The valve for an internal combustion engine according to claim 2,

the thermal insulation layer has a coefficient of thermal expansion less than the coefficient of thermal expansion of the valve bottom surface,

the inner peripheral surface of the peripheral wall is joined to the entire peripheral surface of the heat insulating layer, and one end surface of the peripheral wall is joined to the valve bottom surface on the outer peripheral side of the heat insulating layer.

4. A valve for an internal combustion engine according to claim 3,

the outer edge of the heat insulating layer is set closer to the outer edge of the valve bottom surface than the radially central portion of the valve bottom surface.

5. A valve for an internal combustion engine according to claim 3,

the peripheral wall is formed of a covering material that covers the entire heat insulating layer including not only the entire peripheral surface of the heat insulating layer but also the surface of the heat insulating layer.

6. A valve for an internal combustion engine according to claim 5,

the covering material is set to cover the entire portion of the outer peripheral side of the heat insulating layer in the valve bottom surface,

the coating material contains a heat insulating component.

7. A valve for an internal combustion engine according to claim 3,

the thermal expansion coefficient of the peripheral wall is set to be larger than that of the heat insulating layer.

8. A valve for an internal combustion engine according to claim 5,

an extension portion is provided in the cover member, the extension portion extending to an edge portion from the valve bottom surface to a valve seat surface,

the edge portion is provided with an engaging portion,

the extension portion of the covering material is mechanically engaged with the engagement portion.

9. The valve for an internal combustion engine according to claim 1,

a recess extending radially outward from a radially central portion of the valve bottom surface,

the heat insulating layer is fixed to the bottom wall of the recess, and the entire peripheral surface of the heat insulating layer is covered by the inner peripheral wall of the recess as the peripheral wall.

10. The valve for an internal combustion engine according to claim 9,

the entire peripheral surface of the heat insulating layer is also fixed to the inner peripheral wall of the recess.

11. The valve for an internal combustion engine according to claim 9,

a coating material is bonded to the surface of the heat insulating layer in the recess and the valve bottom surface so as to coat the entire surface of the heat insulating layer and the valve bottom surface.

12. The valve for an internal combustion engine according to claim 1,

the heat insulating layer is formed by integrating a plurality of respective structural layers in a laminated state.

13. The valve for an internal combustion engine according to claim 1,

the thermal insulation layer has a coefficient of thermal expansion different from that of the valve bottom surface,

the thickness of the outer peripheral portion of the heat insulating layer is thinner than the thickness of a portion radially inward of the outer peripheral portion of the heat insulating layer.

14. The valve for an internal combustion engine according to claim 13,

the thickness of the outer peripheral portion of the heat insulating layer is set to be thinner toward the radially outer side of the heat insulating layer.

15. The valve for an internal combustion engine according to claim 14,

a recess extending radially outward from a radially central portion of the valve bottom surface,

the inner circumferential wall of the recess is inclined toward a radially outer side of the recess as facing the opening side of the recess,

the heat insulation layer is fixed on the bottom wall of the concave part,

the entire peripheral surface of the heat insulating layer is inclined so as to expand radially outward of the heat insulating layer as it goes toward the thickness direction surface side of the heat insulating layer, and the surface of the heat insulating layer is set flush with the portion of the valve bottom surface other than the recess.

16. The valve for an internal combustion engine according to claim 15,

a coating material is bonded to the surface of the heat insulating layer in the recess and the valve bottom surface so as to coat the entire surface of the heat insulating layer and the valve bottom surface.

17. The valve for an internal combustion engine according to claim 14,

a recess extending radially outward from a radially central portion of the valve bottom surface,

the inner circumferential wall of the recess is inclined toward a radially outer side of the recess as facing the opening side of the recess,

the heat insulation layer is fixed on the bottom wall of the concave part,

the entire peripheral surface of the heat insulating layer is in contact with the inner peripheral wall of the recess in a state of being inclined so as to expand radially outward of the heat insulating layer as facing the thickness direction surface side of the heat insulating layer,

the surface of the heat insulating layer is formed in a state of bulging outside of the recess opening.

18. The valve for an internal combustion engine according to claim 13,

the peripheral wall is formed of a covering material that covers the entire heat insulating layer including not only the entire peripheral surface of the heat insulating layer but also the surface of the heat insulating layer.

19. The valve for an internal combustion engine according to claim 13,

the thermal expansion coefficient of the thermal insulation layer is smaller than that of the valve bottom surface.

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