JP2017203437A - Piston for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit damage or detachment of a heat shielding layer due to knocking while forming the heat shielding layer at a squish area surface, and prevent generation of a turbulence in a squish area to reduce cooling loss.SOLUTION: A heat shielding layer outer peripheral part 21b provided on an outer peripheral side including a squish area surface 12' of a top face of a piston body 19 and a heat shielding layer inner peripheral part 21a provided on an inner peripheral side thereof are smoothly connected at the boundary therebetween without any step part.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a piston for an internal combustion engine.

  Conventionally, in metal products exposed to high temperature gas such as engine parts, in order to suppress heat transfer from the high temperature gas, that is, cooling loss, a heat shielding layer is formed on the surface of the metal base material. ing. As an example, it is known to form a heat shield layer made of an organic material containing inorganic oxides such as zirconia and hollow particles on the top surface of a piston main body that defines a combustion chamber of an engine.

  By the way, a squish area may be formed in the gap between the top surface of the piston body that defines the combustion chamber and the lower surface of the cylinder head. When the heat shield layer is provided on the surface (squish area surface) that forms the squish area of the top surface of the piston body, the temperature of the heat shield layer becomes high, and the squish area surface itself Becomes hot. For this reason, in the combustion process, when high-temperature and high-pressure end gas (unburned gas mixture far from the spark plug) flows into the squish area, heat is dissipated from the end gas to the squish area by the high-temperature squish area. Blocked and knocking can occur. And a crack arises in the thermal insulation layer formed in the squish area surface, damage and peeling of a thermal insulation layer are caused, and thermal insulation performance is lost.

  Thus, an internal combustion engine is described in which a heat shield layer is not formed on the squish area surface of the top surface of the piston body, and a heat shield layer is formed only in other portions (for example, see Patent Document 1). ).

  According to the internal combustion engine of Patent Document 1, since a heat shield layer is not formed on the squish area surface, heat radiation from the end gas to the squish area surface is promoted, and the occurrence of knocking is suppressed.

JP 2011-169232 A

  However, with the configuration of Patent Document 1, it is not possible to reduce the cooling loss in the region where the heat shield layer is not formed. In addition, a step due to the thickness of the heat shield layer occurs at the boundary between the part where the heat shield layer is formed and the part where the heat shield layer is not formed. May increase.

  Therefore, in the present invention, while forming a heat shield layer on the squish area surface, it is possible to suppress damage and separation of the heat shield layer due to knocking, and to prevent generation of turbulent flow in the squish area and reduce cooling loss. The object is to provide a piston for an internal combustion engine.

  In order to achieve the above object, in the present invention, a step is formed between the boundary between the heat shield layer provided on the outer peripheral side including the squish area surface of the top surface of the piston body and the heat shield layer provided on the inner peripheral side thereof. The connection was made smoothly.

  That is, a piston for an internal combustion engine disclosed herein includes a piston body having a squish area surface that forms a squish area of an internal combustion engine combustion chamber on the outer peripheral side of the top surface, and a heat shield layer formed on the top surface of the piston body. The heat shield layer is formed on the outer peripheral side including at least the squish area surface of the top surface of the piston main body, and the radially inner peripheral side of the piston main body top surface An outer peripheral portion whose thickness gradually decreases from the outer peripheral side toward the outer peripheral side, and an inner peripheral side of the outer peripheral portion at the top surface of the piston body, and an outer peripheral end surface is an inner peripheral side of the outer peripheral portion And an inner periphery formed so as to be smoothly connected from the end surface.

  According to the present invention, since the surface is smoothly connected at the boundary between the outer peripheral end of the inner peripheral portion and the inner peripheral end of the outer peripheral portion of the heat shield layer, the turbulent flow on the surface of the heat shield layer Generation | occurrence | production can be suppressed and a cooling loss can be reduced. In addition, the outer peripheral part is formed so as to cover the entire squish area surface, and since the film thickness is gradually reduced toward the outer peripheral side of the top surface of the piston body, cracks are generated even if knocking occurs in the squish area. It is possible to suppress the growth of the heat shield layer and to prevent damage and peeling of the heat shield layer.

  In a preferred aspect, the outer peripheral portion of the heat shield layer is formed such that the thickness continuously decreases without a step from the radially inner peripheral side to the outer peripheral side of the piston main body top surface. Thereby, since the outer peripheral part surface is also formed smoothly without a level | step difference, the suppression effect of turbulent flow generation | occurrence | production on the surface of a thermal-insulation layer can be heightened more.

  In the present specification, “no step” means that the difference in height between the outer peripheral surface of the heat shield layer and the boundary between the outer peripheral portion and the inner peripheral portion of the heat shield layer is 10 μm or more. It means that there is no inclination within an inclination angle of 20 ° with respect to the axis.

  In a preferred embodiment, the entire top surface of the piston body is covered with the inner and outer peripheral portions of the heat shield layer. Accordingly, it is possible to effectively suppress damage and peeling of the heat shield layer while obtaining excellent heat shield performance over the entire top surface of the piston body.

  In a preferred aspect, the outer peripheral side end thickness of the outer peripheral portion of the heat shielding layer is 20% or more and 60% or less of the inner peripheral side end thickness of the outer peripheral portion.

  If the gradient of the radial cross section at the outer peripheral portion is too large, turbulence may occur as in the state where the step is formed. With this configuration, it is possible to effectively prevent the occurrence of turbulence.

  In a preferred embodiment, the radial width of the outer peripheral portion of the heat shield layer is not less than 5% and not more than 30% of the outer diameter of the piston body top surface.

  If the outer peripheral area is too large, the proportion of the thin region in the entire heat shield layer increases, which may reduce the heat shield performance. According to this configuration, it is possible to achieve both the durability of the heat shield layer and the heat shield performance.

  In a preferred aspect, the thickness of the inner peripheral portion of the heat shield layer is constant.

  Thereby, since the heat-insulating layer having a uniform thickness is formed on the inner peripheral side of the top surface of the piston body, an excellent heat-insulating performance can be obtained.

  In the present specification, the constant thickness of the predetermined region of the heat shield layer means that the thickness of the heat shield layer in the predetermined region is set to a thickness within a range of about 10% from the average thickness. It means being.

  In a preferred embodiment, the heat shield layer includes a large number of hollow particles, and a binder that holds the hollow particles on the top surface of the piston body and fills the space between the hollow particles to form a base material of the heat shield layer. ,including. Thereby, the thermal insulation performance of a thermal insulation layer can be improved effectively.

  In a preferred embodiment, the binder is a silicone resin. Thereby, while being able to reduce the thermal conductivity of a thermal insulation layer, the outstanding adhesiveness of the top surface of a piston main body and a thermal insulation layer can be acquired.

  In a preferred embodiment, the hollow particle is a glass balloon. Thereby, while being able to make the thermal conductivity of a thermal insulation layer low, the intensity | strength can also be improved.

  As described above, according to the present invention, since the surface is smoothly connected at the boundary between the outer peripheral side end of the inner peripheral portion and the inner peripheral end of the outer peripheral portion in the heat shield layer, Generation of turbulent flow on the surface of the layer can be suppressed, and cooling loss can be reduced. In addition, the outer peripheral part is formed so as to cover the entire squish area surface, and since the film thickness is gradually reduced toward the outer peripheral side of the top surface of the piston body, cracks are generated even if knocking occurs in the squish area. It is possible to suppress the growth of the heat shield layer and to prevent damage and peeling of the heat shield layer.

FIG. 1 is a cross-sectional view schematically showing an engine according to a first embodiment of the present invention. FIG. 2 is a plan view showing a crown surface of the piston according to the embodiment of FIG. 1. FIG. 3 is a plan view showing the top surface of the piston body of the piston of FIG. 4 is a cross-sectional view of the piston of FIG. 2 taken along the line III-III. FIG. 5 is an enlarged cross-sectional view of the heat shield layer of FIG. FIG. 6 is an enlarged cross-sectional view of the heat shield layer of FIG. FIG. 7 is a graph plotting the heat shielding rate and the rate of increase of the remaining film against the ratio of the slope length s to the piston diameter d of the heat shielding layer. FIG. 8 is a view for explaining a state in which there is a step in the heat shield layer in the conventional piston. FIG. 9 is a diagram illustrating a model for calculating the heat flux with respect to the height of the step. FIG. 10 is a graph showing the heat flux (plane ratio) with respect to the height of the step calculated by the model of FIG.

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

[First Embodiment]
<Engine configuration>
A direct injection engine (internal combustion engine) E shown in FIG. 1 has a piston (internal combustion engine piston) 1, a cylinder block 2, a cylinder head 3, and a combustion chamber side opening end of an intake port 5 formed inside the cylinder head 3. An intake valve 4 configured to open and close, an exhaust valve 6 configured to open and close a combustion chamber side opening end of an exhaust port 7 formed inside the cylinder head 3, an injector 8, and a spark plug 9 are provided. The piston 1 reciprocates in the cylinder bore of the cylinder block 2.

  The combustion chamber of the engine (combustion chamber of the internal combustion engine) includes a crown surface 10 of the piston 1, a cylinder bore of the cylinder block 2, a combustion chamber wall formed in the cylinder head 3, and front surfaces of the umbrella portions 41 and 61 of the intake and exhaust valves 4 and 6. Formed with. As shown in FIG. 1 and FIG. 2, a concave cavity portion 11 that forms a cavity of the combustion chamber is provided at a substantially central portion of the crown surface 10 of the piston 1. Further, a squish area, which is a step portion for directing the flow direction of the air-fuel mixture in the combustion chamber to the center portion of the combustion chamber during the compression stroke, is provided on the outer edge portion of the crown surface 10 on the outer edge side away from the cavity of the combustion chamber. There is a squish area 12 for forming. In the crown surface 10 of the piston 1 according to this embodiment, the squish area portion 12 includes squish area portions 12a, 12b, 12c, and 12d.

<Heat shield layer>
As shown in FIGS. 2 and 4, the piston 1 is provided on the top surface 10 ′ of the piston main body 19 from the viewpoint of reducing the cooling loss of the piston main body 19 which is the base material of the piston 1 and the combustion chamber of the engine E. And a heat shield layer 21.

  The piston main body 19 is made of an aluminum alloy, and is subjected to heat treatment of T7 treatment or T6 treatment. As shown in FIG. 3, the top surface 10 ′ of the piston main body 19 includes a cavity surface 11 ′ that constitutes the cavity portion 11 and a squish area surface 12 ′ that constitutes the squish area portion 12. Note that the squish area surface 12 ′ in the present embodiment includes squish area surfaces 12 a ′, 12 b ′, 12 c ′, and 12 d ′ shown as hatched regions in FIG. 3. In FIG. 4, the squish area surfaces 12 a ′ and 12 c ′ are on the outer peripheral side of the top surface 10 ′ of the piston main body 19 from the position indicated by the broken line. That is, the squish area portions 12a, 12b, 12c, and 12d shown in FIGS. 2 and 4 have squish area surfaces 12a ′, 12b ′, 12c ′, and 12d ′ on the top surface 10 ′ of the piston body 19 shown in FIG. The squish area surfaces 12a ′, 12b ′, 12c ′, and 12d ′ are formed of the heat shield layer 21.

  As shown in FIG. 5, the heat shield layer 21 is a layer including hollow particles 31 and a binder material (binder) 32.

  That is, the heat shield layer 21 includes a binder material 32 and a large number of hollow particles 31 dispersed therein from the viewpoint of improving the heat shield performance of the heat shield layer. The binder material 32 holds the hollow particles 31 on the top surface 10 ′ of the piston body 19 and fills the space between the hollow particles 31 to form the base material of the heat shielding layer 21. The binder material 32 is a low thermal conductivity material such as a silicone-based resin, for example, and the hollow particles 31 contain air with low thermal conductivity in the internal space. Thus, by dispersing the hollow particles in the binder material 32, the heat shielding layer 21 is made a layer having a lower thermal conductivity.

As the hollow particles 31, a Si-based oxide component (for example, silica (SiO ₂ )) or an Al-based oxide component (for example, alumina (Al ₂ )) such as a silica balloon, a glass balloon, a shirasu balloon, a fly ash balloon, and an airgel balloon. It is preferable to employ ceramic hollow particles containing O ₃ )), and it is particularly preferable to employ glass balloons. Thereby, while being able to make the thermal conductivity of the thermal-insulation layer 21 lower, the intensity | strength can also be ensured.

  The hollow particles 31 are preferably spherical. The average particle diameter of the hollow particles 31 is preferably 5 μm or more and 50 μm or less, more preferably 10 μm or more and 45 μm or less, and particularly preferably 15 μm or more and 40 μm or less from the viewpoint of improving the heat shielding property of the heat shielding layer 21. The content of the hollow particles 31 in the heat shielding layer 21 is preferably 5% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 45% by mass or less, particularly from the viewpoint of improving the heat shielding property of the heat shielding layer 21. Preferably they are 15 to 40 mass%.

  As the binder material 32, a heat-resistant resin can be used, and for example, a silicone resin that is a low thermal conductivity material can be used. Specifically, for example, a silicone resin composed of a three-dimensional polymer having a high degree of branching, represented by a methyl silicone resin and a methylphenyl silicone resin, can be preferably used as the silicone resin. Specific examples of the silicone resin further include, for example, polyalkylphenylsiloxane. Thereby, the thermal conductivity of the heat shield layer 21 can be lowered, and excellent adhesion between the top surface 10 ′ of the piston body 19 and the heat shield layer 21 can be obtained.

  Here, as shown in FIG. 2, the heat shielding layer 21 includes a heat shielding layer outer peripheral portion 21 b formed on the outer peripheral side including at least the squish area surface 12 ′ of the piston main body 19 top surface 10 ′, and the piston main body 19 top. A heat shield layer inner peripheral portion 21a formed on the inner peripheral side of the surface 10 'and on the inner peripheral side of the heat shield layer outer peripheral portion 21b.

  As shown in FIG. 4, the heat shield layer outer peripheral portion 21 b has a thickness that particularly decreases so that the thickness gradually decreases from the radially inner peripheral side of the top surface 10 ′ of the piston body 19 toward the outer peripheral side. It is formed so as to continuously decrease without a step. The heat shield layer inner peripheral portion 21a is characterized in that the surface is formed so as to be smoothly connected from the inner peripheral side end of the heat shield layer outer peripheral portion 21b. In other words, the boundary between the outer peripheral side end surface of the heat shield layer inner peripheral portion 21a and the inner peripheral side end surface of the heat shield layer outer peripheral portion 21b is smoothly connected. The operational effects of this configuration will be described below.

  FIG. 8 shows the structure of the heat shield layer 21 provided on the top surface 10 'of the conventional piston body 19. As shown in FIG. 8 is provided on the outer peripheral side of the heat shield layer outer peripheral portion 21b including the squish area surface 12 ′ on the outer peripheral side of the piston main body 19 top surface 10 ′, and on the inner peripheral side of the piston main body 19 top surface 10 ′. A step 22 resulting from the difference in thickness between the two inner peripheral portions 21a of the heat shield layer is formed due to the difference in thickness between the two. Consider the turbulent flow that can occur near the squish area due to the presence of the step 22.

  As shown in FIG. 9, when a model in which the heat shield layer 21 is provided on the flat surface 41 is created and the gas temperature is assumed to be 1000K and the wall temperature is 500K, a flow 42 having a flow velocity equivalent to squish flow of 7.9 m / s is obtained. The amount of heat generated on the upper surface 25 of the heat shield layer 21 relative to the thickness of the heat shield layer 21, that is, the height h of the step 22, that is, the heat flux was calculated. FIG. 10 shows a calculation result of the heat flux generated on the upper surface 25 of the heat shielding layer 21 with respect to the height h as a ratio to the heat flux when the height h of the step 22 is 0, that is, only the flat surface 41. .

  As shown in FIG. 10, when the height h of the step is in the range of 25 to 100 μm, for example, it can be seen that the heat flux increases by 3% to 10% compared to the case where the step h is 0. That is, it can be seen that the flow rate in the cylinder is disturbed by the step 22 and is increased from the flat heat flow rate.

  Thus, the presence of the step 22 can disturb the squish flow generated in the squish area and stay in the vicinity of the squish area. If it does so, the heat | fever of a squish flow will escape to the cylinder bore wall surface etc. of the cylinder block 2, and will lead to the increase in a cooling loss.

  In the present embodiment, by adopting the above-described configuration, in the boundary portion between the outer peripheral side end portion of the heat shield layer inner peripheral portion 21a and the inner peripheral side end portion of the heat shield layer outer peripheral portion 21b in the heat shield layer 21, both Since the surfaces are smoothly connected, generation of turbulent flow on the surface of the heat shield layer can be suppressed, and cooling loss can be reduced. Further, since the outer peripheral portion 21b of the heat shield layer is set so that the thickness gradually decreases without a step toward the outer peripheral side of the top surface 10 'of the piston body 19, even if knocking occurs in the squish area, the crack is generated. In addition, it is possible to suppress the damage and separation of the heat shield layer 21 and to further increase the effect of suppressing the generation of turbulent flow on the surface of the heat shield layer 21, thereby reducing the cooling loss.

  In addition, you may form the boundary part of the outer peripheral side edge part of the heat shielding layer inner peripheral part 21a, and the inner peripheral side end part of the heat shielding layer outer peripheral part 21b in the rounded shape. As shown in FIG. 4, the top surface 10 ′ of the piston body 19 according to the present embodiment has different inclination angles between the squish area surface 12 ′ and other surfaces. 2, the squish area surface 12 ′ forming the squish area portion 12a is parallel to a plane perpendicular to the axis of the cylindrical piston main body 19, as shown in FIG. On the other hand, the top surface 10 ′ of the piston body 19 from the squish area surface 12 ′ toward the cavity surface 11 ′ is formed so as to be inclined with respect to a plane perpendicular to the axis of the piston body 19. Therefore, on the top surface 10 'of the piston main body 19 according to the present embodiment, the thickness of the heat shielding layer outer peripheral portion 21b continuously decreases without a step from the inner peripheral side of the piston main body 19 in the radial direction to the outer peripheral side. However, the apparent inclination of the heat shield layer outer peripheral portion 21b and the heat shield layer inner peripheral portion 21a with respect to the plane perpendicular to the axis of the piston body 19 is substantially the same, and the inner peripheral side end of the heat shield layer outer peripheral portion 21b. The boundary portion between the outer peripheral side end portion of the heat shield layer inner peripheral portion 21a is smoothly connected with almost no change in the inclination angle.

  Further, the apparent inclination angle of the heat shielding layer outer peripheral portion 21b and the heat shielding layer inner peripheral portion 21a with respect to the plane perpendicular to the axis of the piston main body 19 is the boundary even when the inclination angle of any part is large. The part surfaces are formed so as to be connected smoothly. As shown in FIG. 4, the apparent inclination angle of the top surface 10 ′ of the piston body 19 extending from the squish area surface 12 ′ forming the squish area portion 12 c to the cavity surface 11 ′ is the apparent inclination angle of the heat shield layer outer peripheral portion 21 b. Therefore, the apparent inclination angle of the heat shielding layer inner peripheral portion 21a with respect to the plane perpendicular to the axis of the piston main body 19 is larger than the apparent inclination angle of the heat shielding layer outer peripheral portion 21b. Even in this case, the boundary portion between the inner peripheral side end portion of the heat shield layer outer peripheral portion 21b and the outer peripheral side end portion of the heat shield layer inner peripheral portion 21a is smoothly connected.

  As shown in FIG. 2, it is preferable that the entire top surface 10 'of the piston body 19 is covered with the heat shielding layer inner peripheral portion 21a and the heat shielding layer outer peripheral portion 21b. Accordingly, it is possible to effectively suppress damage and peeling of the heat shield layer 21 while obtaining excellent heat shield performance on the entire top surface 10 ′ of the piston body 19. In particular, the outer peripheral portion 21b of the heat shield layer covers all the squish area surfaces 12a ', 12b', 12c ', 12d' of the squish area portions 12a, 12b, 12c, 12d. As a result, even if knocking occurs in the squish area, the growth of cracks can be suppressed, and damage / peeling of the heat shield layer 21 can be suppressed. Cooling loss can be reduced. Further, as shown in FIG. 2, the heat shield layer inner peripheral portion 21a is formed in a circular shape in plan view, but the heat shield layer outer peripheral portion 21b is formed so as to cover the entire squish area surface 12 ′. In this case, the heat shield layer inner peripheral portion 21a may be formed in any shape such as a circle or an ellipse.

  The thickness of the heat shielding layer inner peripheral portion 21a is preferably 40 μm or more and 150 μm or less, more preferably 50 μm or more and 120 μm or less, and particularly preferably 60 μm or more and 100 μm or less from the viewpoint of obtaining excellent heat shielding performance. And it is preferable that the thickness of the heat shielding layer inner peripheral part 21a is constant. Thereby, since the heat shield layer 21 having a uniform thickness is formed on the inner peripheral side of the top surface 10 ′ of the piston main body 19, excellent heat shield performance can be obtained.

  Further, the thickness of the heat shielding layer outer peripheral portion 21b is preferably 8 μm or more and 90 μm or less, more preferably 12.5 μm from the viewpoint of preventing breakage / peeling of the heat shielding layer outer peripheral portion 21b while maintaining high heat shielding performance. It is 66 μm or less, particularly preferably 18 μm or more and 50 μm or less.

  In other words, if the gradient of the radial cross section of the heat shield layer outer peripheral portion 21b is too large, turbulence may occur as in the state where the step is formed. Therefore, from the viewpoint of effectively preventing the occurrence of turbulent flow, the outer peripheral side end portion thickness of the heat shield layer outer peripheral portion 21b is preferably 20% of the inner peripheral side end portion thickness of the heat shield layer outer peripheral portion 21b. It can be made 60% or less, more preferably 25% or more and 55% or less, and particularly preferably 30% or more and 50% or less.

  Further, the radial width of the outer peripheral portion 21b of the heat shield layer is preferably 5% or more and 40% or less, more preferably 5% or more and 30% or less, particularly preferably 5%, of the outer diameter of the top surface 10 'of the piston body 19. It is within 25%.

  As shown in FIG. 6, when the diameter of the piston main body 19 is d and the slope length of the heat shield outer peripheral portion 21b is s, the ratio (%) of the slope length s to the diameter d of the piston main body 19 is occupied. FIG. 7 shows a plot of the heat shield rate (%) of the heat shield layer 21 and the increase rate (%) of the remaining film. The heat shielding rate (%) of the heat shielding layer 21 can be calculated based on the simulation result. Further, the increase rate (%) of the remaining film can be calculated based on the actual machine verification result.

  If the radial width of the heat shield layer outer peripheral portion 21b is larger than 40%, the proportion of the thin region in the entire heat shield layer is increased, which may reduce the heat shield performance. In addition, if the radial width of the heat shield layer outer peripheral portion 21b is smaller than 5%, the heat shield performance is high, but the heat shield layer may be easily damaged or peeled off. According to this configuration, it is possible to achieve both the durability of the heat shield layer and the heat shield performance.

<Manufacturing method of piston>
Next, the manufacturing method of the piston which concerns on this embodiment is demonstrated.

  First, a heat shield material for forming the piston body 19 and the heat shield layer 21 is prepared.

  The piston body 19 is formed with a cavity-forming recess on the top surface 10 ', and dirt such as oil and fingerprints adhering to the top surface 10' of the piston body 19 is removed by a degreasing process.

  In addition, a heat shielding material is prepared by stirring and mixing a liquid silicone resin as the binder material 32 and a glass balloon as the hollow particles 31. If necessary, the viscosity of the heat shielding material is adjusted by adding a thickener or a diluting solvent.

In order to increase the adhesion between the piston body 19 and the heat shielding material, particularly silicone resin, it is preferable to subject the top surface 10 'of the piston body 19 to a roughening treatment. As the roughening treatment, for example, blasting such as sand blasting is preferably performed. For example, the blasting process can be performed using an air blasting apparatus, using alumina having a particle size of # 30 as an abrasive, and processing conditions of a pressure of 0.39 MPa, a time of 45 seconds, and a distance of 100 mm. In addition, not only this but when the piston main body 19 consists of Al alloy, you may make it form micro unevenness | corrugation in top surface 10 'of the piston main body 19 by an alumite process. For example, the alumite treatment can be performed using an oxalic acid bath under a treatment condition of a bath temperature of 20 ° C., a current density of 2 A / dm ² , and a time of 20 minutes.

  Thereafter, a heat shielding material is placed on the top surface 10 'of the piston body 19, and the heat shielding material is pressed against the piston body top surface 10' by a mold having a molding surface that follows the shape of the top surface 10 'of the piston body 19. It extends over the entire top surface 10 '.

  In the present embodiment, the molding surface of the mold is such that the thickness of the outer peripheral portion 21b of the heat shielding layer of the squish area surface 12 ′ gradually decreases from the inner peripheral side in the radial direction of the top surface of the piston body 19 toward the outer peripheral side. Form. And the molding surface of a shaping | molding die is formed so that the outer peripheral side end part surface of the heat shielding layer inner peripheral part 21a may be smoothly connected from the inner peripheral side end part surface of the said heat shielding layer outer peripheral part 21b. In addition, the connection part of the outer peripheral side end part surface of the thermal-insulation layer inner peripheral part 21a and the inner peripheral side end part surface of the said heat-shielding layer outer peripheral part 21b is good also as a rounded shape.

  Next, the heat shielding material applied to the top surface 10 ′ of the piston main body 19 is subjected to a heat treatment for several hours to several tens of hours at a temperature of about 180 ° C., for example. As a result, the silicone resin (binder) is cured, a large number of hollow particles 31 are densely filled, and the thermal barrier layer 21 in which the space between the particles is filled with the binder material 32 is obtained.

  In addition, according to this method, it is good also as a structure which bakes the thermal insulation layer 21 simultaneously by heating a shaping | molding die during shaping | molding. Thereby, the manufacturing process of the heat insulation layer 21 can be simplified. Moreover, when baking the thermal insulation layer 21 simultaneously, it can be set as the structure which cools the piston main body 19 by methods, such as water cooling or air cooling from the inner side of a piston skirt, for example. Thereby, the adhesiveness of the heat-insulating layer 21 and the top surface 10 ′ of the piston main body 19 can be improved.

[Second Embodiment]
Hereinafter, other embodiments according to the present invention will be described in detail. In the description of these embodiments, the same parts as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

<Heat shield layer>
The heat shielding layer 21 according to the present embodiment further includes magnetic particles in addition to the configuration of the first embodiment.

Specifically, the magnetic particles are fine particles such as magnetite Fe ₃ O ₄ and permalloy Fe—Ni. Since these magnetic particles can easily respond to subtle changes in the magnetic field, the heat shielding material can be easily molded, and the thermal conductivity is low, so that the heat shielding performance of the heat shielding layer 21 is maintained. In particular, fine particles of magnetite Fe ₃ O ₄ stabilized with a surfactant are preferred. The average particle diameter of the magnetic particles is preferably 1 nm or more and 100 nm or less, more preferably 1 nm or more and 50 nm or less, and particularly preferably 1 nm or more and 20 nm or less from the viewpoint of ensuring uniform dispersibility in the binder material.

<Manufacturing method of piston>
In addition to the liquid silicone resin as the binder material 32 and the glass balloon as the hollow particles 31, a heat shielding material is prepared by stirring and mixing a hexane solution (average particle diameter of 10 nm) of magnetite fine particles as magnetic particles. If necessary, the viscosity of the heat shielding material is adjusted by adding a thickener or a diluting solvent.

  The content of the magnetic particles in the heat shielding material is preferably 5% by mass to 50% by mass, more preferably 10% by mass to 45% by mass, and particularly preferably 15% by mass to 40% by mass. It is.

  Thereafter, the heat shielding material is applied to the top surface 10 'of the piston body 19 by using a spray or a brush (application step S1).

  Specifically, for example, the coating step S1 includes the following three steps. That is, first, only the outer peripheral portion of the top surface 10 ′ including the squish area surface 12 ′ of the top surface 10 ′ of the piston body 19 is masked, and the required number of times is applied to the inner peripheral portion of the top surface 10 ′ including the cavity surface 11 ′ and the like. The thermal barrier material is applied to a portion corresponding to the inner peripheral portion 21a of the thermal barrier layer where the thickness of the thermal barrier material is not adjusted in the adjustment step S2 described later (pre-application step S11). The masking can be performed using a masking tape or a resin-based masking film.

  Next, the heat shielding material applied in the previous application step S11 is preliminarily dried using hot air drying, an infrared heater or the like to form the heat shielding layer inner peripheral portion 21a (drying step S12). The preliminary drying is preferably performed at 150 ° C. or higher and 200 ° C. or lower, more preferably 160 ° C. or higher and 190 ° C. or lower, particularly preferably 175 ° C. or higher and 185 ° C., from the viewpoint of maintaining the shape of the heat shielding material layer in the adjusting step S2 described later. It is carried out at a temperature of not higher than 10 ° C., preferably 10 minutes to 2 hours, more preferably 20 minutes to 1.5 hours, and particularly preferably 30 minutes to 1 hour.

  Thereafter, masking of the squish area surface 12 'is removed, and the surface of the squish area surface 12' is degreased. And a heat-shielding material is apply | coated to the site | part corresponded to the heat-shielding layer outer peripheral part 21b which adjusts thickness in adjustment process S2 mentioned later (post-application process S13). At this time, the heat shielding material is applied so that the thickness of the heat shielding layer outer peripheral portion 21b on the outer peripheral side of the top surface 10 'becomes thinner than the thickness of the heat shielding layer inner peripheral portion 21a.

  Then, using the magnetic force of the magnet 51, the thickness of the heat shield material of the heat shield layer outer peripheral portion 21b is adjusted, and is inclined (adjustment step S2). Specifically, for example, the magnet is moved from the outer peripheral side of the top surface toward the inner peripheral side of the top surface, and the heat shielding material is pulled up by the magnetic force. Thereby, in the heat shield layer outer peripheral portion 21b, the amount of the heat shield material increases at a position close to the heat shield layer inner peripheral portion 21a, while the amount of the heat shield material decreases at a position on the outer peripheral side. . Thus, the heat shielding layer outer peripheral portion 21b configured to gradually decrease in thickness from the inner peripheral side to the outer peripheral side in the top surface radial direction of the piston main body 19 is obtained. The magnetic field strength of the magnet 51 can be set to, for example, 200 to 250 kA / m from the viewpoint of controlling the pulling speed of the heat shield material by the magnetic force to form the surface of the heat shield material more smoothly.

  In addition, by moving the magnet a plurality of times from the top surface outer peripheral side to the top surface inner peripheral side, the thickness of the heat shield layer outer peripheral portion 21b increases from the radially inner peripheral side to the outer peripheral side of the piston main body top surface 10 ′. It can be formed smoothly so as to continuously decrease without a step.

  Further, the magnet is reciprocated a plurality of times from the intestinal outer peripheral side to the top inner peripheral side at the boundary between the inner peripheral side end portion of the heat shielding layer outer peripheral portion 21b and the outer peripheral side end portion of the heat insulating layer inner peripheral portion 21a. Thus, it is possible to obtain the heat shield layer 21 in which the surfaces of both end portions are smoothly connected.

  Finally, a baking process is performed in the same manner as in the first embodiment, and the heat shielding material applied in the application step S <b> 1 is cured to form the heat shielding layer 21 on the top surface 10 ′ of the piston body 19.

  According to the present invention, the thickness of the heat shield material can be adjusted without touching the surface of the heat shield material. As a result, a heat shielding layer having a smooth surface can be formed on the top surface 10 ′ of the piston body 19 having a complicated shape.

  According to this configuration, unlike the conventional method of physically adjusting the thickness of the heat shield material by touching the surface of the heat shield material with a spatula or a brush, the outer periphery of the heat shield layer without touching the surface of the heat shield material. It is possible to adjust the thickness of the heat shielding material at a location corresponding to the boundary portion between the portion and the inner peripheral portion. Thus, the surface of the boundary can be smoothly connected without forming an edge or the like at the boundary. As a result, the level difference formed on the surface of the heat shield layer can be minimized, the disturbance of the in-cylinder flow in the combustion chamber can be suppressed, and the cooling loss can be reduced.

  Further, since the thickness of the heat shielding material of the heat shielding layer outer peripheral portion 21b can be formed so as to continuously decrease toward the outer peripheral side without a step, it is possible to effectively generate turbulence particularly in the squish area. In addition to the suppression, even if knocking occurs in the squish area, it is possible to suppress the growth of cracks and suppress the damage and peeling of the heat shield layer.

  In addition, since the thickness of the heat shield layer can be freely changed by controlling the magnetic force, it is possible to form the heat shield layer without greatly changing the equipment even for pistons with different diameters, for example. it can.

  In addition, as described above, the magnetic material of the portion where it is desired to keep the thickness of the heat shield layer at a predetermined thickness is applied in the first application step S11 and then dried and cured in advance in the drying step S12. Thus, when a magnetic force is applied to the heat shield material in the subsequent adjustment step S2, only the portion where the thickness of the heat shield layer is desired to be adjusted can be adjusted.

  The post-coating step S13 and the adjusting step S2 may be repeated a plurality of times.

  According to this configuration, by applying the heat shielding material of the portion where the thickness of the heat shielding layer is desired to be divided into a plurality of times and adjusting the thickness, the fine thickness can be adjusted, The surface of the heat shield layer can be formed more smoothly. In addition, a heat shield layer having a smooth surface can be effectively formed even in a piston having a large diameter.

  The present invention suppresses damage and separation of the heat shield layer due to knocking while forming a heat shield layer on the surface of the squish area, and also prevents turbulent flow in the squish area and reduces cooling loss. Very useful.

DESCRIPTION OF SYMBOLS 1 Piston 10 Crown surface 10 '(Piston main body) Top surface 11 Cavity part 11' Cavity surface 12, 12a, 12b, 12c, 12d Squish area part 12 ', 12a', 12b ', 12c', 12d 'Squish area surface 19 Piston body 21 Heat shield layer 21a Heat shield layer inner periphery (inner periphery)
21b Heat shield layer outer periphery (outer periphery)
31 Hollow particles 32 Binder material (binder)
E engine

Claims (9)

A piston body having a squish area surface that forms a squish area of the combustion chamber of the internal combustion engine on the outer peripheral side of the top surface;
A heat insulating layer formed on the top surface of the piston body;
A piston for an internal combustion engine comprising:
The thermal barrier layer is
An outer peripheral portion that is formed on the outer peripheral side including at least the squish area surface of the top surface of the piston main body, and whose thickness gradually decreases from the radially inner peripheral side to the outer peripheral side of the piston main body top surface;
An inner peripheral part formed on the inner peripheral side of the outer peripheral part on the top surface of the piston main body, the outer peripheral side end part surface being smoothly connected from the inner peripheral side end part surface of the outer peripheral part; A piston for an internal combustion engine, comprising: In claim 1,
The outer peripheral portion of the heat shield layer is formed so that the thickness continuously decreases without a step from the radially inner peripheral side to the outer peripheral side of the top surface of the piston body. piston. In claim 1 or claim 2,
A piston for an internal combustion engine, characterized in that the entire top surface of the piston body is covered with an inner peripheral portion and an outer peripheral portion of the heat shield layer. In any one of Claim 1 thru | or 3,
A piston for an internal combustion engine, wherein an outer peripheral end thickness of an outer peripheral portion of the heat shield layer is 20% or more and 60% or less of an inner peripheral end portion thickness of the outer peripheral portion. In any one of Claims 1 thru | or 4,
A piston for an internal combustion engine, wherein a radial width of an outer peripheral portion of the heat shield layer is 5% or more and 30% or less of an outer diameter of a top surface of the piston body. In any one of Claims 1 thru | or 5,
A piston for an internal combustion engine, wherein a thickness of an inner peripheral portion of the heat shield layer is constant. In any one of Claims 1 thru | or 6,
The thermal barrier layer is
Many hollow particles,
A piston for an internal combustion engine, comprising: a binder that holds the hollow particles on a top surface of the piston body and fills a space between the hollow particles to form a base material of the heat shield layer. In claim 7,
The piston for an internal combustion engine, wherein the binder is a silicone resin. In claim 7 or claim 8,
The internal combustion engine piston, wherein the hollow particles are glass balloons.

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