JP2011225407A - Porous heat insulating member and internal combustion engine with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous heat insulating member and an internal combustion engine with the same, which can prevent the occurrence of damage.SOLUTION: There is provided the porous heat insulating member 10 in which the tensile strength of an outer periphery 38 is larger than that of a central part 40, for example, porous particles 42 are connected by binders 44 and an amount of the binders 44 in the outer periphery 38 is larger than the amount of the binders 44 in the central part 40. According to the invention, the porous heat insulating member 10 can prevent the occurrence of damage.

Description

  The present invention relates to a porous heat insulating member and an internal combustion engine including the same.

  There has been proposed a technique for reducing a cooling loss at a low load by providing a heat insulating member on a wall surface of a combustion chamber of an internal combustion engine. On the other hand, when a heat insulating member is provided on the wall surface of the combustion chamber of the internal combustion engine to insulate the combustion chamber, the wall temperature of the combustion chamber becomes high at a high load, and knocking or abnormal combustion may occur. In order to suppress the occurrence of knocking or the like, for example, Patent Document 1 describes that a porous heat insulating member is provided only on a part of the top surface of the piston.

JP-A-11-193721

  The porous heat insulating member has, for example, heat insulating properties with low thermal conductivity and low heat capacity. When the porous heat insulating member having such heat insulating properties is provided on the wall surface of the combustion chamber, the temperature of the porous heat insulating member changes following the temperature of the combustion gas generated in the combustion chamber. Due to this temperature change, damage may occur in the outer peripheral portion of the porous heat insulating member. This breakage may progress to the entire porous heat insulating member over time.

  The present invention has been made in view of the above problems, and an object thereof is to provide a porous heat insulating member capable of suppressing the occurrence of breakage and an internal combustion engine including the same.

  The above object can be achieved by a porous heat insulating member characterized in that the tensile strength of the outer peripheral portion is larger than the tensile strength of the central portion. According to this, generation | occurrence | production of the damage of a porous heat insulation member can be suppressed.

  The said structure WHEREIN: It has a structure where the porous particle was connected with the binder, and it can be set as the structure where the quantity of the said binder in the said outer peripheral part is large compared with the quantity of the said binder in the said center part. According to this structure, generation | occurrence | production of the failure | damage of a porous heat insulation member can be suppressed, suppressing the increase in the heat conductivity and heat capacity of a porous heat insulation member.

  In the above configuration, when the thermal conductivity is 0.05 to 0.5 W / mk, the amount of the binder in the region of the outer peripheral portion and the depth from the surface is between 50 μm and 200 μm is the center. The configuration can be larger than the amount of the binder in the section. According to this configuration, it is possible to further suppress an increase in the thermal conductivity and heat capacity of the porous heat insulating member while suppressing damage to the porous heat insulating member.

  The above object can be achieved by an internal combustion engine comprising the porous heat insulating member according to any one of claims 1 to 3 on a wall surface of a combustion chamber.

  According to the present invention, the occurrence of breakage of the porous heat insulating member can be suppressed.

FIG. 1 is an example of a schematic cross-sectional view of a porous heat insulating member according to a comparative example. FIG. 2 is an example of a schematic diagram showing changes in the surface temperature of the porous heat insulating member. FIG. 3A to FIG. 3D are examples of schematic views showing the temperature in the depth direction of the porous heat insulating member. FIG. 4 is an example of a schematic diagram illustrating a configuration of the internal combustion engine including the porous heat insulating member according to the first embodiment. Fig.5 (a) is an example of the cross-sectional schematic diagram of the piston in FIG. 4, FIG.5 (b) is an example of an upper surface schematic diagram. FIG. 6 is an example of a schematic diagram illustrating the porous heat insulating member according to the first embodiment. FIG. 7 is an example of a schematic diagram illustrating the porous heat insulating member according to the second embodiment.

  First, problems to be solved by the present invention will be described in detail. FIG. 1 is an example of a schematic cross-sectional view showing a porous heat insulating member according to a comparative example. As shown in FIG. 1, a porous heat insulating member 62 having a low thermal conductivity and a low heat capacity is provided on a wall surface 60 of a combustion chamber of an internal combustion engine. The porous heat insulating member 62 is, for example, porous silica. In an internal combustion engine, for example, an intake stroke, a compression stroke, a combustion / expansion stroke, and an exhaust stroke are performed according to the crank angle. In the intake stroke, the piston is lowered, and the mixed gas flows into the cylinder. The compression stroke raises the piston and compresses the mixed gas in the cylinder. In the combustion / expansion stroke, the mixed gas is ignited, combustion gas is generated, and the piston is pushed down. In the exhaust stroke, the piston is raised and the combustion gas in the cylinder is discharged. By performing such four strokes, the gas temperature in the combustion chamber changes. Since the porous heat insulating member 62 has a low heat capacity, the temperature changes following the change in the gas temperature in the combustion chamber.

  FIG. 2 is an example of a schematic diagram showing changes in the surface temperature of the porous heat insulating member 62, where the horizontal axis is the crank angle [° CA] and the vertical axis is the surface temperature [K] of the porous heat insulating member 62. In addition, the surface of the porous heat insulating member 62 refers to the surface exposed to the combustion chamber. As shown in FIG. 2, since the four strokes of the intake stroke, the compression stroke, the combustion / expansion stroke, and the exhaust stroke change according to the crank angle, the surface temperature of the porous heat insulating member 62 changes according to the crank angle. For example, when the crank angle is between 0 [° CA] and 180 [° CA], the intake stroke is performed and the mixed gas flows into the cylinder. Therefore, the surface temperature of the porous heat insulating member 62 follows the temperature of the mixed gas. Then drop. When the crank angle is between 180 [° CA] and 360 [° CA], the compression stroke is performed. Since the porous heat insulating member 62 is also exposed to the mixed gas during this time, the surface temperature decreases. When the crank angle is between 360 [° CA] and 540 [° CA], the combustion / expansion stroke is performed. Combustion gas is generated by igniting the mixed gas in the cylinder, and the surface temperature of the porous heat insulating member 62 rapidly increases. In the subsequent expansion stroke, the surface temperature of the porous heat insulating member 62 gradually decreases. A crank angle of 540 [° CA] to 720 [° CA] is an exhaust stroke. Also during the exhaust stroke, the surface temperature of the porous heat insulating member 62 gradually decreases.

  FIG. 3A to FIG. 3D are examples of schematic views showing the temperature in the depth direction of the porous heat insulating member 62, and the horizontal axis is the depth (μm) of the porous heat insulating member 62. The vertical axis represents the temperature (K) of the porous heat insulating member 62. 3A is a diagram at a crank angle 200 [° CA] (region 70 in FIG. 2) in FIG. 2, and FIG. 3B is a diagram at a crank angle 354 [° CA] (region 72 in FIG. 2). 3 (c) shows a porous heat insulating member 62 at a crank angle 405 [° CA] (region 74 in FIG. 2), and FIG. 3 (d) shows a crank angle 500 [° CA] (region 76 in FIG. 2). The temperature in the depth direction is shown.

  As shown in FIGS. 3A to 3D, the temperature inside the porous heat insulating member 62 does not change much, whereas the surface temperature of the porous heat insulating member 62 changes greatly. In the center portion 64 of the surface of the porous heat insulating member 62 in FIG. 1, for example, the porous particles constituting the porous heat insulating member 62 are constrained by the porous particles positioned around the porous heat insulating member 62. And tensile stress are generated. As shown in FIGS. 3B and 3C, the compressive stress is larger than the tensile stress, but the porous heat insulating member 62 is made of a porous ceramic material such as porous silica. In this case, since the porous ceramic material has a higher compressive strength than a tensile strength, it can sufficiently withstand the above compressive stress.

  On the other hand, at the end portion 68 (see FIG. 1) of the surface of the porous heat insulating member 62, for example, the porous particles constituting the porous heat insulating member 62 are not completely surrounded by the porous particles and are restrained. It is a state that has not been done. For this reason, as shown in FIG. 3C, when the surface temperature of the porous heat insulating member 62 rises, the end 68 of the surface expands due to thermal expansion. As indicated by the arrows in FIG. 1, the end portion 68 on the surface of the porous heat insulating member 62 extends, and the region that is on the inner side and on the outer peripheral side from the surface of the porous heat insulating member 62 due to the expansion. A tensile stress is generated at 66. Further, as shown in FIG. 3C, due to the time delay of the temperature change of the porous heat insulating member 62, the temperature temporarily decreases within about 100 μm from the surface of the porous heat insulating member 62, and tensile stress is generated. It will be. For this reason, in the area | region 66 which is an inner side from the surface of the porous heat insulation member 62 and is an outer peripheral side, a tensile stress will be applied twice and it will become easy to produce a damage. Therefore, an example of a porous heat insulating member capable of solving such problems and suppressing the occurrence of breakage will be described below.

  FIG. 4 is an example of a schematic diagram illustrating a configuration of the internal combustion engine 100 including the porous heat insulating member 10 according to the first embodiment. As shown in FIG. 4, the cylinder block 12 is provided with a cylinder 14. A piston 16 that reciprocates is provided in the cylinder 14. A cylindrical cylinder liner 18 is provided on the side wall of the cylinder 14 to form a sliding surface with the piston 16.

  A cylinder head 20 is disposed on the upper side of the cylinder block 12. A region defined by the top surface 22 of the piston 16 and the lower surface 24 of the cylinder head 20 is a combustion chamber 26. The wall surface of the combustion chamber 26 includes a top surface 22 of the piston 16, a lower surface 24 of the cylinder head 20, an umbrella portion of the intake valve 28 and the exhaust valve 30, and a lower surface 32 exposed to the combustion chamber 26. A porous heat insulating member 10 is provided on the top surface 22 of the piston 16.

  The cylinder head 20 is provided with an intake port 34 and an exhaust port 36. Communication between the combustion chamber 26 and the intake port 34 is controlled by opening and closing the intake valve 28. Communication between the combustion chamber 26 and the exhaust port 36 is controlled by the exhaust valve 30. A mixed gas necessary for combustion flows into the combustion chamber 26 through the intake port 34. Further, the combustion gas generated in the combustion chamber 26 is discharged to the outside through the exhaust port 36.

  Fig.5 (a) is an example of the cross-sectional schematic diagram which expanded the piston 16 in FIG. 4, FIG.5 (b) is an example of an upper surface schematic diagram. As shown in FIGS. 5A and 5B, the porous heat insulating member 10 is provided on the top surface 22 of the piston 16 that is the wall surface of the combustion chamber 26. The outer peripheral portion 38 of the porous heat insulating member 10 has a higher tensile strength than the central portion 40.

  Here, the porous heat insulating member 10 will be described in detail with reference to FIG. FIG. 6 is an example of a schematic view showing the porous heat insulating member 10 provided on the top surface 22 of the piston 16. As shown in FIG. 6, the porous heat insulating member 10 provided on the top surface 22 of the piston 16 is, for example, porous silica. The porous heat insulating member 10 has a structure in which, for example, porous particles 42 that are spherical mesoporous silica particles are connected by a binder 44 made of, for example, a metal oxide. The spherical mesoporous silica particles are particles having an average particle size of about 0.1 to 3.0 μm and a uniform particle size. The spherical mesoporous silica particles have innumerable pores having an average pore diameter of, for example, about 1 to 10 nm from the center to the surface. As described above, since the plurality of spherical mesoporous silica particles having a small particle diameter and uniform particle diameter are connected at the contact points by the binder, the spherical mesoporous silica particles are laminated with no gap. Moreover, since the innumerable pores are formed in the spherical mesoporous silica particles, a high porosity of 70% or more is realized as the whole porous heat insulating member 10. For this reason, the porous heat insulating member 10 has excellent heat insulating properties.

  The amount of the binder 44 that connects the porous particles 42 in the outer peripheral portion 38 of the porous heat insulating member 10 is larger than the amount of the binder 44 that connects the porous particles 42 in the central portion 40 of the porous heat insulating member 10. For example, when the porous particles 42 are 100 parts by weight, the binder 44 in the central part 40 of the porous heat insulating member 10 is 20 parts by weight or less, whereas the binder 44 in the outer peripheral part 38 is 20 to 40 parts by weight. It is.

  Here, a manufacturing method for forming the porous heat insulating member 10 on the top surface 22 of the piston 16 will be described. The manufacturing process includes a first step of adjusting the precursor of the porous heat insulating member 10, a second step of disposing a layer made of the precursor on the top surface 22 of the piston 16, and the precursor and the top surface 22 of the piston 16. And a third step of forming a layer of the porous heat insulating member 10 on the top surface 22 of the piston 16.

  The first step is a step of mixing, for example, a precursor of spherical mesoporous silica particles and a reactive binder. The first step will be described in detail. First, a precursor of spherical mesoporous silica particles is produced by mixing a raw material containing a silica raw material and a surfactant in a solvent and reacting them under a predetermined temperature condition. The spherical mesoporous silica particles have innumerable pores formed from the central portion toward the surface, and are mixed with the reactive binder in a state where the pores are filled with a masking substance. As a masking substance, for example, a surfactant used for adjusting a precursor of spherical mesoporous silica particles can be used. Since the reactive binder is mixed with the precursor of the spherical mesoporous silica particles in a liquid state or dissolved in a solution, the reactive binder is likely to be unevenly distributed between the spherical mesoporous silica particles due to surface tension. It becomes easy to connect spherical mesoporous silica particles with a contact.

  The second step is a step of arranging the precursor of the porous heat insulating member 10 adjusted through the first step on the top surface 22 of the piston 16 in a sheet shape. For example, after the precursor of the porous heat insulating member 10 is disposed on the top surface 22 of the piston 16, the precursor of the porous heat insulating member 10 is pressed from above with a certain surface pressure by a presser and molded into a sheet shape. Thereafter, the outer peripheral portion of the precursor of the porous heat insulating member 10 molded into a sheet shape so that the amount of the binder 44 in the outer peripheral portion 38 of the porous heat insulating member 10 is larger than the amount of the binder 44 in the central portion 40. Add reactive binder and drop.

  In the third step, the precursor of the porous heat insulating member 10 molded into a sheet shape and the top surface 22 of the piston 16 are integrally fired to form a layer of the porous heat insulating member 10 on the top surface 22 of the piston 16. It is a process to do. By integrally firing the precursor of the porous heat insulating member 10 and the top surface 22 of the piston 16, the reactive binder is polymerized to become a binder 44, and a reaction for connecting the spherical mesoporous silica particles at a contact point; The reaction in which the spherical mesoporous silica particles are bonded to the top surface 22 of the piston 16 directly or indirectly through the binder 44 and the reaction in which the masking substance filled in the pores is removed proceed simultaneously. Thereby, the porous heat insulating member 10 can be formed on the top surface 22 of the piston 16 as shown in FIG. In addition, the manufacturing method for forming the porous heat insulating member 10 on the top surface 22 of the piston 16 is not limited to the above-described manufacturing method. For example, instead of using a precursor of spherical mesoporous silica particles, it is burned in the form of particles. The porous heat insulating member 10 may be formed on the top surface 22 of the piston 16 using the spherical mesoporous silica particles.

  Thus, as shown in FIG. 6, the porous heat insulating member 10 has a structure in which the porous particles 42 are connected by the binder 44, and the amount of the binder 44 in the outer peripheral portion 38 of the porous heat insulating member 10 is The structure is larger than the amount of the binder 44 in the central portion 40. When the amount of the binder 44 increases, the bonding strength between the porous particles 42 increases, and thus the tensile strength increases. Therefore, as shown in FIG. 5, the outer peripheral portion 38 of the porous heat insulating member 10 has a higher tensile strength than the central portion 40.

  As described in the comparative example, the end 46 of the surface is extended (the arrow in FIG. 6) due to the increase in the surface temperature in the region on the inner side and the outer peripheral side from the surface of the porous heat insulating member 10. The resulting tensile stress and the tensile stress due to the time delay of the temperature change are applied. For this reason, as in Example 1, the tensile strength of the outer peripheral portion 38 of the porous heat insulating member 10 is made larger than the tensile strength of the central portion 40, so that the inner side from the surface of the porous heat insulating member 10 and Even if it is a case where the above-mentioned tensile stress is applied to the area | region which is an outer peripheral side, it can suppress damaging.

  Further, as in the first embodiment, the amount of the binder 44 in the outer peripheral portion 38 of the porous heat insulating member 10 is increased, and the increase in the amount of the binder 44 in the central portion 40 is suppressed, whereby the heat of the porous heat insulating member 10 is increased. An increase in conductivity and heat capacity can be suppressed. Therefore, according to Example 1, it can suppress that the porous heat insulation member 10 breaks, suppressing the increase in the heat conductivity of the porous heat insulation member 10 and a heat capacity.

  In Example 1, the case where the tensile strength of the outer peripheral portion 38 is made larger than the tensile strength of the central portion 40 by increasing the amount of the binder 44 in the outer peripheral portion 38 of the porous heat insulating member 10 is shown as an example. It is not limited. The tensile strength at the outer peripheral portion 38 of the porous heat insulating member 10 may be made larger than the tensile strength at the central portion 40 by other methods.

  In the first embodiment, the porous particles 42 are spherical mesoporous silica particles and the binder 44 is a metal oxide. However, the present invention is not limited to this. The binder 44 may be a metalloid oxide such as Si.

  In the first embodiment, the porous heat insulating member 10 is provided on the top surface 22 of the piston 16 as an example. For example, the lower surface 24 of the cylinder head 20 and the lower surfaces of the umbrella portions of the intake valve 28 and the exhaust valve 30 are shown. 32 is preferably provided on the wall surface of the combustion chamber 26. Further, the porous heat insulating member 10 may be provided outside the wall surface of the combustion chamber 26 of the internal combustion engine 100 or may be provided in the apparatus other than the internal combustion engine 100.

  FIG. 7 is an example of a schematic diagram illustrating the porous heat insulating member 50 according to the second embodiment. Similarly to the first embodiment, the porous heat insulating member 50 according to the second embodiment is also provided on the top surface 22 of the piston 16 that is the wall surface of the combustion chamber 26 of the internal combustion engine 100. This point will be described with reference to FIGS. Since it has been described, detailed description thereof is omitted here.

  As shown in FIG. 7, the porous heat insulating member 50 provided on the top surface 22 of the piston 16 is porous in a region Y having a depth from the surface of 50 μm to 200 μm at the outer peripheral portion 52 of the porous heat insulating member 50. The amount of the binder 44 that connects the porous particles 42 is larger than the amount of the binder 44 that connects the porous particles 42 in the central portion 54 of the porous heat insulating member 50. Note that the surface of the porous heat insulating member 50 is a surface opposite to the surface in contact with the top surface 22 of the piston 16 and is a surface exposed to the combustion chamber 26. The other configuration is the same as that of the first embodiment and has been described with reference to FIG. In addition, a manufacturing method for forming the porous heat insulating member 50 on the top surface 22 of the piston 16 can be the same as the manufacturing method described in the first embodiment, and thus the description thereof is omitted here.

  In Example 2, the porous heat insulating member 50 is the outer peripheral portion 52 of the porous heat insulating member 50, and the amount of the binder 44 in the region Y whose depth from the surface is between 50 μm and 200 μm is the binder in the central portion 54. The structure is larger than the amount of 44. When the thermal conductivity of the porous heat insulating member 50 is 0.05 to 0.5 W / mk, the end portion 56 of the surface is extended (the arrow in FIG. 7) due to the increase in the surface temperature of the porous heat insulating member 50. The resulting tensile stress is likely to be applied to the outer peripheral portion 52 between about 50 to 200 μm from the surface of the porous heat insulating member 50. For this reason, it becomes easy to generate | occur | produce damage in the area | region Y which is the outer peripheral part 52 of the porous heat insulation member 50, and whose depth is 50 micrometers-200 micrometers from the surface. Therefore, in order to suppress breakage in the region Y, the tensile strength is increased by increasing the amount of the binder 44 in the outer peripheral portion 52 of the porous heat insulating member 50 and having a depth from the surface of 50 μm to 200 μm. Is preferably increased.

  Moreover, in Example 2, since the area | region which increased the quantity of the binder 44 is small compared with Example 1, the increase in the heat conductivity and heat capacity of the porous heat insulation member 50 can be suppressed more. Therefore, according to the second embodiment, it is possible to further suppress the increase in the thermal conductivity and the heat capacity of the porous heat insulating member 50 while suppressing the damage of the porous heat insulating member 50.

  In Example 2, the region Y in which the amount of the binder 44 is increased is an example in which the depth from the surface of the porous heat insulating member 50 is a region between 50 μm and 200 μm. As described above, it is preferable to increase the amount of the binder 44 in the region where the tensile stress is generated due to the extension of the surface end portion 56 due to the increase in the surface temperature of the porous heat insulating member 50. Therefore, for example, when the thermal conductivity of the porous heat insulating member 50 is 0.05 W / mk or less, the tensile stress resulting from the extension of the surface end due to the increase in the surface temperature is the surface of the porous heat insulating member. To about 0 μm to 50 μm. Therefore, when the thermal conductivity of the porous heat insulating member 50 is 0.05 W / mk or less, the amount of the binder in the outer peripheral portion of the porous heat insulating member and the depth from the surface is between 0 μm and 50 μm It is preferable to increase the number.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to such specific embodiments, and various modifications can be made within the scope of the gist of the present invention described in the claims.・ Change is possible.

DESCRIPTION OF SYMBOLS 10 Porous heat insulation member 12 Cylinder block 14 Cylinder 16 Piston 18 Cylinder liner 20 Cylinder head 22 Piston top surface 26 Combustion chamber 28 Intake valve 30 Exhaust valve 34 Intake port 36 Exhaust port 38 Outer peripheral part of porous heat insulation member 40 Porous insulation Central part of member 42 Porous particles 44 Binder 50 Porous heat insulating member 52 Peripheral part of porous heat insulating member 54 Central part of porous heat insulating member 100 Internal combustion engine

Claims (4)

  A porous heat insulating member, wherein the tensile strength of the outer peripheral portion is larger than the tensile strength of the central portion.   The porous heat insulating member according to claim 1, wherein porous particles have a structure connected by a binder, and the amount of the binder in the outer peripheral portion is larger than the amount of the binder in the central portion. .   In the case where the thermal conductivity is 0.05 to 0.5 W / mk, the amount of the binder in the region of the outer peripheral portion and the depth from the surface being between 50 μm and 200 μm is the binder in the central portion. The porous heat insulating member according to claim 2, wherein the porous heat insulating member is larger than the amount of.   An internal combustion engine comprising the porous heat insulating member according to any one of claims 1 to 3 on a wall surface of a combustion chamber.

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