JP6380457B2 - Method for forming a thermal barrier layer of a piston for an internal combustion engine - Google Patents

Description

  The present invention relates to a method for forming a heat shield layer of 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. Cooling loss 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 disturbance of in-cylinder flow and reduce cooling loss in the squish area. It is an object of the present invention to provide a method for forming a heat shield layer of a piston for an internal combustion engine.

  In order to achieve the above object, in the present invention, a magnetic material is contained in the heat shielding material forming the heat shielding layer, and the heat shielding material is applied to the top surface of the piston body, and then the magnet is used to form the heat shielding material. The thickness of the heat material was adjusted.

That is, a method for forming a heat shield layer for a piston for an internal combustion engine disclosed herein includes an application step of applying a heat shield material to the top surface of a piston body, and a heat shield material by curing the heat shield material applied in the application step. A method for forming a heat shielding layer for a piston for an internal combustion engine, comprising a curing step for forming a layer, the heat shielding material comprising a heat resistant resin, a number of magnetic material particles dispersed in the heat resistant resin, and a number of The heat-resistant resin holds the magnetic material particles and the hollow particles on the top surface of the piston body, and fills the space between the magnetic material particles and / or the hollow particles. And an adjustment step of adjusting the thickness of the heat shield material by a magnetic force between the coating step and the curing step.

  According to the present invention, 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 rivet, a grindstone or the like, the heat shield material is not touched without touching the surface of the heat shield material. The thickness can be adjusted. In this way, a heat-insulating layer having a smooth surface can be formed even on the top surface of the piston body having a complicated shape. Thus, the level difference formed on the surface of the heat shield layer can be minimized, disturbance of the in-cylinder flow can be suppressed, and cooling loss can be reduced.

  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.

  Preferably, a squish area surface for forming a squish area of the combustion chamber of the internal combustion engine is formed on the outer peripheral side of the top surface of the piston body, and the heat shield layer includes at least the squish area surface of the top surface of the piston body. An outer peripheral portion formed on the outer peripheral side top surface, and an inner peripheral portion formed on the piston main body top surface and on the inner peripheral side of the outer peripheral portion, and in the adjusting step, The thickness of the outer peripheral portion of the heat shield layer gradually decreases from the radially inner peripheral side to the outer peripheral side of the piston body top surface, and the outer periphery of the inner peripheral portion of the heat shield layer. The side end surface is adjusted so as to be smoothly connected from the inner peripheral side end surface of the outer peripheral portion.

  According to this configuration, it is possible to adjust the thickness of the heat shield material at a location corresponding to the boundary between the outer peripheral portion and the inner peripheral portion of the heat shield layer without touching the surface of the heat shield material. Thus, the surface of the boundary can be smoothly connected without forming an edge or the like at the boundary.

  Further, since the thickness of the heat shielding material at the outer peripheral portion can be formed so as to continuously decrease toward the outer peripheral side without a step, the disturbance of the in-cylinder flow particularly in the squish area is suppressed, and the squish area Even if knocking occurs, crack growth can be suppressed, and damage and peeling of the heat shield layer can be suppressed.

  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 the adjustment step, after the pre-application step of applying a heat-shielding material to a portion where the thickness is not adjusted in the adjustment step, the drying step of drying the heat-shielding material applied in the pre-application step, and the drying step A post-application step of applying a heat-shielding material to the portion whose thickness is to be adjusted.

  According to this configuration, the portion of the magnetic material in which the thickness of the heat shield layer is desired to be maintained at a predetermined thickness is dried and cured in advance by the drying step, so that the heat shield material in the subsequent adjustment step. When a magnetic force is applied to, only the portion where the thickness of the heat shield layer is desired to be adjusted can be adjusted.

  Preferably, the post-coating step and the adjusting step are 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.

  Preferably, the magnetic material particles are magnetite fine particles.

  According to this configuration, since it is possible to easily respond to a subtle change in the magnetic field, the heat shielding material can be easily molded, and the thermal conductivity is low, so that the excellent heat shielding performance of the heat shielding layer 21 is maintained. be able to.

The heat shield layer further includes a number of hollow particles, and the heat resistant resin holds the magnetic material particles and the hollow particles on the top surface of the piston body, and the magnetic material particles and / or the hollow particles. A base material of the heat shielding layer is formed by filling between the particles.

  Thereby, the thermal insulation performance of a thermal insulation layer can be improved effectively.

  Preferably, the heat resistant resin 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.

  Preferably, the hollow particles are glass balloons.

  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, the surface of the heat shielding material is touched unlike the conventional method of physically adjusting the thickness of the heat shielding material by touching the surface of the heat shielding material with a hammer or a grindstone. The thickness of the heat shielding material can be adjusted without any problem. In this way, a heat-insulating layer having a smooth surface can be formed even on the top surface of the piston body having a complicated shape. Thus, the level difference formed on the surface of the heat shield layer can be minimized, the disturbance of the in-cylinder flow can be suppressed, and the cooling loss can be reduced. 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.

FIG. 1 is a cross-sectional view schematically showing an engine according to an 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 IV-IV. 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 flowchart for explaining a method for forming a heat shield layer of a piston. FIG. 9 is an enlarged cross-sectional view of the piston body after the pre-application process. FIG. 10 is a view corresponding to FIG. 9 after the post-application process. FIG. 11 is a view corresponding to FIG. 9 showing a state during the adjustment process. FIG. 12 is a plan view of the piston body showing a state during the pre-coating step. FIG. 13 is a view corresponding to FIG. 12 showing a state during the post-application process. FIG. 14 is a view corresponding to FIG. 12 showing a state during the adjustment process. FIG. 15 is a view for explaining a state in which there is a step in the heat shield layer in the conventional piston. FIG. 16 is a diagram illustrating a model for calculating the heat flux with respect to the height of the step. FIG. 17 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.

<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 is formed by the crown surface 10 of the piston 1, the cylinder bore of the cylinder block 2, the combustion chamber wall surface formed in the cylinder head 3, and the front surfaces of the umbrella portions 4A and 6A of the intake / exhaust valves 4 and 6. 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 includes a piston main body 19 that is a base material of the piston 1 and a shield provided on the top surface of the piston main body 19 from the viewpoint of reducing the cooling loss of the combustion chamber of the engine E. The thermal layer 21 is provided.

  The piston main body 19 is made of an aluminum alloy, and is subjected to heat treatment of T7 treatment or T6 treatment. The top surface of the piston main body 19 includes a cavity surface 11 ′ constituting the cavity portion 11 and a squish area surface 12 ′ constituting 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, a binder material (heat resistant resin) 32, and magnetic material particles 33.

  That is, the heat shielding layer 21 includes a binder material 32, a large number of hollow particles 31 dispersed therein, and a large number of magnetic material particles 33 from the viewpoint of improving the heat shielding performance of the heat shielding layer. The binder material 32 holds the magnetic material particles 33 and the hollow particles 31 on the top surface of the piston body 19 and fills the space between the magnetic material particles 33 and / or the hollow particles 31 to form the base material of the heat shield 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.

The hollow particles 31 contain air with low thermal conductivity in the internal space. Specifically, for example, Si-based oxide components (for example, silica balloon, glass balloon, shirasu balloon, fly ash balloon, airgel balloon, etc.) , Silica (SiO ₂ )) or an Al-based oxide component (for example, alumina (Al ₂ O ₃ )) is preferably employed, and a glass balloon is particularly preferably employed. 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, for example, a silicone resin which 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, while being able to reduce the thermal conductivity of the heat insulation layer 21, the outstanding adhesiveness of the top surface of the piston main body 19 and the heat insulation layer 21 can be obtained.

Specifically, the magnetic material particles 33 are fine particles such as magnetite Fe ₃ O ₄ and permalloy Fe—Ni. These magnetic material particles can easily respond to subtle changes in the magnetic field, so that it is easy to form a heat shielding material, and because the thermal conductivity is low, the heat shielding layer 21 has excellent heat shielding performance. In particular, fine particles of magnetite Fe ₃ O ₄ stabilized with a surfactant are preferred. The average particle diameter of the magnetic material particles is preferably 1 nm to 100 nm, more preferably 1 nm to 50 nm, and particularly preferably 1 nm to 20 nm, from the viewpoint of ensuring uniform dispersibility in the binder material.

  As shown in FIG. 2, the heat shield layer 21 according to the present embodiment includes a heat shield layer outer peripheral portion 21 b formed on the outer peripheral side top surface including at least the squish area surface 12 ′ of the top surface of the piston main body 19, and a piston. A heat shield layer inner peripheral portion 21a formed on the inner peripheral side of the top surface of the main body 19 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 no particular difference in thickness so that the thickness gradually decreases from the radially inner peripheral side of the top surface of the piston body 19 toward the outer peripheral side. It is formed so as to continuously decrease. Moreover, the heat shielding layer inner peripheral part 21a is formed so that the surface is smoothly connected from the inner peripheral side end of the heat shielding layer outer peripheral part 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.

  FIG. 15 shows a structure of a heat shield layer 21 provided on the top surface of the conventional piston main body 19. 15 includes a heat shield layer outer peripheral portion 21b provided on the outer peripheral side of the top surface of the piston body 19 including the squish area surface 12 ′, and a heat shield layer provided on the inner peripheral side of the top surface of the piston main body 19. A step 22 resulting from a difference in thickness between the inner peripheral portion 21a and the inner peripheral portion 21a is formed. Consideration will be given to the in-cylinder flow disturbance that may occur in the vicinity of the squish area due to the presence of the step 22.

  As shown in FIG. 16, when a model in which a heat shield layer 21 is provided on a flat surface 41 is created and a gas temperature is assumed to be 1000K and a wall temperature is 500K, a flow 42 having a flow velocity equivalent to a 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. 17 shows a calculation result of the heat flux generated on the upper surface 25 of the heat shield 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. 17, 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 in-cylinder flow 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.

  According to the above configuration, the surfaces of both sides of the heat shield layer 21 are smoothly connected at the boundary 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. Therefore, the disturbance of the in-cylinder flow on the surface of the heat shield layer can be suppressed, and the 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 of the piston body 19, even if knocking occurs in the squish area, the crack grows. It is possible to suppress the damage and peeling of the heat shield layer 21, and to further enhance the effect of suppressing the disturbance of the in-cylinder 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 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 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 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. 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 of the piston main body 19 is covered with the heat shielding layer inner peripheral portion 21a and the heat shielding layer outer peripheral portion 21b. Thereby, damage and peeling of the heat shield layer 21 can be effectively suppressed while obtaining excellent heat shield performance over the entire top surface of the piston body 19. In particular, the heat shield layer outer peripheral portion 21b covers all the squish area surfaces 12 'of the squish area portions 12a, 12b, 12c, and 12d. As a result, even if knocking occurs in the squish area, it is possible to suppress the growth of cracks, to suppress the damage / peeling of the heat shield layer 21, and to further suppress the effect of disturbance of in-cylinder flow on the surface of the heat shield layer 21. The cooling loss can be reduced by increasing. 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-insulating layer 21 having a uniform thickness is formed on the inner peripheral side of the top surface of the piston main body 19, 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.

  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, the in-cylinder flow may be disturbed as in the case where the step is formed. Therefore, from the viewpoint of effectively preventing disturbance of in-cylinder flow, the outer peripheral side end portion thickness of the heat shield layer outer peripheral portion 21b is preferably the inner peripheral side end portion thickness of the heat shield layer outer peripheral portion 21b. % To 60%, more preferably 25% to 55%, and particularly preferably 30% to 50%.

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

  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.

<Method for forming a heat shield layer of piston>
Next, a method for forming a heat shield layer for a piston according to the present embodiment will be described.

  First, the heat shield material 62 for forming the piston main body 19 and the heat shield layer 21 is prepared.

  About the piston main body 19, the recessed part for cavity formation is formed in the top surface, and stain | pollution | contamination, such as oil and fat adhering to the top surface of the piston main body 19, is removed by a degreasing process.

  In addition, a heat shielding material 62 is prepared by stirring and mixing a liquid silicone resin as the binder material 32, a glass balloon as the hollow particles 31, and a hexane solution of magnetite fine particles (average particle diameter of 10 nm) as the magnetic material particles 33. The content of the magnetic material particles in the heat shield material 62 is preferably 5% by mass from the viewpoint of controlling the pulling speed of the heat shield material 62 by magnetic force to form the surface of the heat shield material 62 more smoothly. It is 50 mass% or less, More preferably, it is 10 mass% or more and 45 mass% or less, Most preferably, it is 15 mass% or more and 40 mass% or less. If necessary, the viscosity of the heat shielding material 62 is adjusted by adding a thickener or a dilution solvent.

In order to increase the adhesion between the piston main body 19 and the heat shielding material 62, particularly the silicone resin, it is preferable to subject the top surface of the piston main 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 a micro unevenness | corrugation in the top surface 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, as shown in FIG. 8, the heat shielding material 62 is applied to the top surface of the piston body 19 using a spray 61, a brush, or the like (application step S1).

  Specifically, for example, the coating step S1 includes the following three steps. That is, as shown in FIGS. 9 and 12, first, only the top surface outer peripheral portion including the squish area surface 12 ′ on the top surface of the piston body 19 is masked, and the top surface inner peripheral portion including the cavity surface 11 ′ and the like is masked. The necessary number of times of overcoating is performed, and the heat shielding material 62 is applied by the spray 61 to the portion corresponding to the heat shielding layer inner peripheral portion 21a in which the thickness of the heat shielding material 62 is not adjusted in the adjustment step S4 described later (first) Application process S11). The masking can be performed using a masking tape or a resin-based masking film.

  Next, the heat shield material 62 applied in the previous application step S11 is preliminarily dried using hot air drying, an infrared heater, or the like to form the heat shield layer inner peripheral portion 21a (drying step S12). The preliminary drying is preferably 150 ° C. or higher and 200 ° C. or lower, more preferably 160 ° C. or higher and 190 ° C. or lower, and particularly preferably 175 ° C. from the viewpoint of maintaining the shape of the layer of the heat shielding material 62 in the adjusting step S4 described later. Above 185 ° C., preferably 10 minutes or more and 2 hours or less, more preferably 20 minutes or more and 1.5 hours or less, particularly preferably 30 minutes or more and 1 hour or less.

  Thereafter, masking of the squish area surface 12 'is removed, and the surface of the squish area surface 12' is degreased. And as shown in FIG.10 and FIG.13, the thermal-insulation material 62 is apply | coated to the site | part corresponded to the thermal-insulation layer outer peripheral part 21b which adjusts thickness in adjustment process S4 mentioned later (post-application process S13). At this time, the heat shielding material 62 is applied so that the thickness of the outer periphery 21b of the heat shield layer on the outer peripheral side of the top surface is thinner than the thickness of the inner periphery 21a of the heat shield layer.

  Then, as shown in FIGS. 11 and 14, the thickness of the heat shielding material 62 of the heat shielding layer outer peripheral portion 21b is adjusted by using the magnetic force of the magnet 51 to be inclined (adjustment step S4). 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 62 is pulled up by the magnetic force. Thereby, in the heat shield layer outer peripheral part 21b, the amount of the heat shield material 62 increases at a position close to the heat shield layer inner peripheral part 21a, while the amount of the heat shield material 62 attached at the outer peripheral side position. Less. 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. In addition, the magnetic field intensity 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 62 by the magnetic force to form the surface of the heat shield material 62 more smoothly.

  In addition, by moving the magnet several times from the outer peripheral side of the top surface to the inner peripheral side of the top surface, the heat shield layer outer peripheral portion 21b has no thickness difference from the radially inner peripheral side to the outer peripheral side of the piston main body top surface. It can be formed smoothly so as to decrease continuously.

  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, the heat shielding material applied to the top surface of the piston main body 19 in the application step S1 is subjected to a heat treatment for several hours to several tens of hours at a temperature of about 180 ° C., for example, and is cured to be cured. The heat shield layer 21 is formed on the top surface (curing step S5). 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.

  According to the above configuration, the thickness of the heat shield material can be adjusted without touching the surface of the heat shield material. In this way, a heat-insulating layer having a smooth surface can be formed even on the top surface of the piston body having a complicated shape.

  According to this configuration, unlike the conventional method of physically adjusting the thickness of the heat shielding material by touching the surface of the heat shielding material with a grindstone or a grindstone, the outer periphery of the heat shielding layer without touching the surface of the heat shielding 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, disturbance of in-cylinder flow can be suppressed, and cooling loss can be reduced.

  In addition, 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, disturbance of in-cylinder flow particularly in the squish area is effective. In addition, even if knocking occurs in the squish area, the growth of cracks can be suppressed, and damage and peeling of the heat shield layer can be suppressed.

  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 S4, 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 S4 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.

[Other Embodiments]
The heat shielding material applied in the pre-application process S11 and the post-application process S13 may be mixed with the same material as in the above-described embodiment in different amounts. Moreover, what mixed the different material may be used. In particular, by increasing the content of the magnetic material particles 33 in the heat shield material formed in the heat shield layer outer peripheral portion 21b as compared with the heat shield material formed in the heat shield layer inner peripheral portion 21a, the outer periphery of the heat shield layer is increased. The part 21b can be easily formed.

  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 prevents turbulence in the cylinder flow in the squish area and reduces cooling loss. Is extremely 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 (heat-resistant resin)
33 Magnetic material particles 62 Heat shield material E Engine

Claims (7)

An application process for applying a heat shielding material to the top surface of the piston body;
A method for forming a heat shielding layer of a piston for an internal combustion engine, comprising: a curing step of curing the heat shielding material applied in the coating step to form a heat shielding layer,
The heat shielding material contains a heat resistant resin, a large number of magnetic material particles dispersed in the heat resistant resin, and a large number of hollow particles .
The heat-resistant resin holds the magnetic material particles and the hollow particles on the top surface of the piston body, and forms a base material of the heat shield layer by filling between the magnetic material particles and / or the hollow particles,
A method for forming a heat shielding layer for a piston for an internal combustion engine, comprising an adjustment step of adjusting the thickness of the heat shielding material by a magnetic force between the coating step and the curing step. In claim 1,
A squish area surface for forming a squish area of the combustion chamber of the internal combustion engine is formed on the outer peripheral side of the top surface of the piston body,
The thermal barrier layer is
An outer peripheral portion formed on an outer peripheral side top surface including at least the squish area surface of the piston main body top surface;
An inner periphery formed on the top surface of the piston body and on the inner periphery of the outer periphery;
In the adjustment step, the thickness of the heat shield material is:
While the thickness of the outer peripheral portion of the heat shield layer gradually decreases from the radially inner peripheral side of the piston body top surface toward the outer peripheral side,
The formation of a heat shielding layer for a piston for an internal combustion engine, wherein the outer peripheral side end surface of the inner peripheral part of the heat insulating layer is adjusted so as to be smoothly connected from the inner peripheral side end surface of the outer peripheral part Method. In claim 1 or claim 2,
The coating process includes
A pre-application step of applying a heat shielding material to a portion where the thickness is not adjusted in the adjustment step;
A drying step of drying the heat shielding material applied in the previous application step;
A method for forming a thermal barrier layer for a piston for an internal combustion engine, comprising a post-application step of applying a thermal barrier material to a portion whose thickness is adjusted in the adjustment step after the drying step. In claim 3,
The method for forming a thermal barrier layer for a piston for an internal combustion engine, wherein the post-coating step and the adjusting step are repeated a plurality of times. In any one of Claims 1 thru | or 4,
The method for forming a heat shield layer of a piston for an internal combustion engine, wherein the magnetic material particles are magnetite fine particles. In any one of Claims 1 thru | or 5 ,
The method for forming a heat shield layer of a piston for an internal combustion engine, wherein the heat resistant resin is a silicone resin. In any one of Claims 1 thru | or 6 ,
The said hollow particle is a glass balloon, The heat insulation layer forming method of the piston for internal combustion engines characterized by the above-mentioned.

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