JP2018112156A - Piston of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston of an internal combustion engine that can improve combustion efficiency and restrain knocking at the same time.SOLUTION: A piston comprises a piston body and a low heat conductive layer. The piston body comprises a piston head and a piston skirt. The low heat conductive layer is located on the piston head on the side of a combustion chamber of an internal combustion engine, and has lower heat conductivity than that of the piston body. A cooling passage extends in the piston head in a circumferential direction of an axis, and allows fluid for cooling the piston head to flow.SELECTED DRAWING: Figure 1

Description

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

  Conventionally, for example, Patent Document 1 discloses a piston for an internal combustion engine that is made of metal and in which a low heat conductive member is cast on the top of the piston.

JP 2009-257187 A

  With conventional pistons, it has been difficult to achieve both improvement in combustion efficiency of the internal combustion engine and suppression of knocking.

  The piston of the internal combustion engine according to an embodiment of the present invention preferably includes a low heat conduction layer on the combustion chamber side of the piston head and a cooling passage in the piston head.

  Therefore, both improvement in combustion efficiency and suppression of knocking can be achieved.

1 schematically shows a cross section of a part of an engine taken along a plane passing through the axis of one cylinder of the first embodiment. 1 is a perspective view of a piston according to a first embodiment. FIG. 2 is a front view of the piston of the first embodiment as viewed from the combustion chamber side in the axial direction (hereinafter referred to as an axial front view). FIG. 3 shows a cross section (sectional view taken along the line IV-IV in FIG. 3; hereinafter referred to as an axial cross section) of the piston according to the first embodiment taken along a plane passing through the axis. FIG. 6 is an axial front view of a piston according to a second embodiment. FIG. 10 is an axial front view of a piston according to a third embodiment. FIG. 6 shows an axial cross section of a piston according to a fourth embodiment. FIG. FIG. 9 shows an axial cross section of a piston according to a fifth embodiment. FIG. FIG. 10 is an axial front view of a piston according to a sixth embodiment. 10 shows an axial cross section of a piston according to a sixth embodiment. 9 shows an axial cross section of a piston according to a seventh embodiment. 9 shows an axial cross section of a piston according to an eighth embodiment. The boundary part of the inner periphery of the holding | maintenance part and the outer periphery of a low heat conductive layer in the axial direction cross section of the piston of 9th Embodiment is expanded and shown.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

[First embodiment]
First, the configuration will be described. An internal combustion engine (engine) 100 of the present embodiment shown in FIG. 1 is a 4-stroke gasoline engine and is applied to a vehicle such as an automobile. The engine 100 includes a piston 1, a cylinder block 10, a cylinder head 11, a crankshaft 12, a connecting rod (connecting rod) 13, a piston pin 14, a combustion chamber 15, an ignition device, and a valve. The valve has two intake valves 16 and two exhaust valves 17. A crankshaft 12 is rotatably installed on the cylinder block 10. The cylinder block 10 is provided with a cylindrical cylinder liner (cylinder sleeve) 101. The inner peripheral side of the cylinder liner 101 functions as an inner wall of the cylinder 9. The piston 1 is accommodated inside the cylinder 9 so as to be able to reciprocate. Inside the cylinder liner 101 is a cooling passage 102. Cooling water circulates in the cooling passage 102.

  The piston 1 has a piston body 2 and a low heat conductive layer 3. The piston 1 (piston body 2) has a bottomed cylindrical shape, and includes a piston head (crown portion) 4, a piston boss (apron portion) 5, and a piston skirt (skirt portion) 6. The piston head 4 has a crown surface portion 40 and a land portion 41. The cross section of the piston head 4 (crown surface portion 40) cut along a plane orthogonal to the moving direction of the piston body 2 inside the cylinder 9 is substantially circular. A line passing through the center point of the cross section and parallel to the moving direction of the piston body 2 is referred to as an axis line (reference axis line) 43. The direction in which the axis 43 extends (the above moving direction of the piston body 2) is referred to as the axis direction. In the axial direction, the side of the piston head 4 with respect to the piston boss 5 and the piston skirt 6 is referred to as one side, and the opposite side is referred to as the other side. The crown surface portion 40 is on one side in the axial direction of the piston head 4. There is a crown surface (top surface) 400 on one side in the axial direction of the crown surface portion 40. The crown surface 400 has a substantially circular outline when viewed from the axial direction. The land portion 41 extends from the outer peripheral side of the crown surface portion 40 to the other side in the axial direction. There are three annular grooves (ring grooves) 410 on the outer periphery of the land portion 41. A piston ring 7 is installed in the ring groove 410. Inside the land portion 41 is an annular cooling passage (cooling channel) 8.

  As shown in FIG. 2, the piston boss 5 and the piston skirt 6 extend from the piston head 4 (land portion 41) to the other side in the axial direction. The inner peripheral sides of the piston skirt 6 and the piston boss 5 are hollow. There are a pair of piston bosses 5 on both radial sides of the piston 1. Each piston boss 5 has a pin boss 50. Each pin boss 50 has a piston pin hole 51. The piston pin hole 51 extends through the pin boss 50 in the radial direction of the piston 1. There are a pair of piston skirts 6 on both radial sides of the piston 1. The piston skirt 6 is sandwiched between the piston bosses 5 and 5 in the circumferential direction of the piston 1 (around the axis 43). Both piston skirts 6 and 6 are connected by a piston boss 5. The piston skirt 6 slides against the inner wall of the cylinder 9. The end of the piston pin 14 is fitted into the piston pin hole 51. As shown in FIG. 1, the piston 1 is connected to one end side (small end portion) of the connecting rod 13 via a piston pin 14. The other end side (large end portion) of the connecting rod 13 is connected to the crankshaft 12.

  An oil jet (oil jet device) 18 is installed in the cylinder block 10. The oil jet 18 has a check valve and a nozzle 180. The oil jet 18 is supplied with oil from a passage (main gallery) inside the cylinder block 10, and this oil is directed from the nozzle 180 toward the other side in the axial direction of the piston 1 (opposite the crown surface 400 in the piston head 4). Spray in the axial direction.

  The cylinder head 11 is installed in the cylinder block 10 so as to close the opening of the cylinder 9. The cylinder head 11 is provided with valves 16 and 17, a fuel injection nozzle, and an ignition device. As shown in FIG. 1 (when the piston 1 is at top dead center), a combustion chamber 15 is defined between the crown surface 400 of the piston 1 and the cylinder head 11. The crown surface 400 is directly exposed to the combustion gas inside the combustion chamber 15. The piston boss 5 and the piston skirt 6 are on the opposite side of the combustion chamber 15 with respect to the piston head 4. The combustion chamber 15 is a pent roof type. Two intake ports 111 are opened in one of two plane portions (inclined surfaces) constituting a pent roof shape on the cylinder head 11 side, and two exhaust ports 112 are opened in the other. The intake valve 16 switches the communication state between the intake port 111 and the combustion chamber 15, and the exhaust valve 17 switches the communication state between the exhaust port 112 and the combustion chamber 15. The ignition device is, for example, an electronic control type, and each cylinder 9 includes a spark plug (ignition plug). The electrode 19 of the spark plug is located at the apex of the pent roof and overlapping the center of the crown surface 400 (axis 43) in the axial direction.

  The piston body 2 is formed of an aluminum alloy (for example, Al-Si AC8A) as a material (raw material) for weight reduction and the like. As shown in FIGS. 2 and 3, the side facing the combustion chamber 15 (one side in the axial direction) of the crown surface portion 40 of the piston head 4, that is, the crown surface 400 includes a recess 401, a holding portion 402, and valve recesses 403 and 404. The recess 401 has a bottomed cylindrical shape (a shallow dish shape with a flat bottom surface). The axis of the recess 401 coincides with the axis 43. The holding portion 402 is a second recess that is at the bottom of the recess 401 and is shallower than the recess 401. The holding part 402 is circular when viewed from the axial direction, and its center coincides with the axial line 43. The radius of the holding portion 402 centering on the axis 43 is smaller than the radius of the recess 401 centering on the axis 43, and the holding portion 402 is inside the recess 401. The valve recesses 403 and 404 are recesses (relief grooves of the valves 16 and 17) provided along the shape of the valves 16 and 17 in order to avoid interference between the piston 1 and the valves 16 and 17. A recess 403 for the intake valve 16 is on the intake port 111 side with respect to the axis 43. The recess 404 for the exhaust valve 17 is on the exhaust port 112 side with respect to the axis 43. The recesses 403 and 404 are outside the holding portion 402 in the radial direction of the piston 1 with the axis 43 as the center.

  As shown in FIGS. 3 and 4, the holding portion 402 accommodates the low thermal conductive layer 3. Layer 3 extends along the crown surface 400. The surface on one side in the axial direction of the layer 3 extends in the radial direction of the piston 1 continuously to the crown surface 400 (the bottom surface of the recess 401). The other surface in the axial direction of the layer 3 is in contact with the bottom surface of the holding portion 402. The outer periphery of the layer 3 is in contact with the inner periphery (inner wall) of the holding portion 402. The thickness of the layer 3 (the depth of the holding portion 402) is arbitrary. Layer 3 includes a metallic binder and zirconia (zirconium dioxide). The binder includes aluminum. The aluminum may be pure aluminum, may be the same aluminum alloy as the piston body 2, or may include both pure aluminum and aluminum alloy. Further, the binder may contain an additive in addition to aluminum.

  The cooling passage 8 includes a main body portion 80, an inlet portion 81, and an outlet portion 82. The main body portion 80 extends in the direction around the axis 43 along the outer periphery of the land portion 41. The main body 80 is annular when viewed from the axial direction, and surrounds the holding portion 402. The main body 80 overlaps at least a part of the region where the ring groove 410 is formed in the axial direction. When the main body 80 is viewed as one donut-shaped ring, the rotation axis 83 of the ring is parallel to the axis 43 (in the present embodiment, coincides with the axis 43). Further, the shape and the cross-sectional area of the main body 80 cut by a plane passing through the rotation axis 83 are constant in the direction around the rotation axis 83 (axis line 43). In the main body portion 80, the end portion 801 on the side of the crown surface 400 in the axial direction (one side in the axial direction) and the end portion 802 on the side opposite to the crown surface 400 (on the other side in the axial direction) are respectively It is on a single plane orthogonal to the axis 43.

  The inlet portion 81 and the outlet portion 82 are a pair of openings that open to the end 42 on the other axial side of the piston head 4. The inlet portion 81 and the outlet portion 82 extend in the axial direction, connect to the main body portion 80, and overlap the main body portion 80 when viewed from the axial direction. One inlet 81 is on the exhaust port 112 (valve recess 404) side with respect to the axis 43, and one outlet 82 is on the intake port 111 (valve recess 403) side with respect to the axis 43. The inlet portion 81 and the outlet portion 82 are on the opposite sides with respect to the axis 43. When viewed from the axial direction, the inlet portion 81 and the outlet portion 82 are on the same straight line passing through the axis 43. In the circumferential direction of the piston 1, the inlet portion 81 is adjacent to one piston boss 5, and the outlet portion 82 is adjacent to the other piston boss 5. The inlet 81 faces the injection port of the oil jet 18 (nozzle 180) in the axial direction.

  The radius of the holding portion 402 and the low heat conductive layer 3 centering on the axis 43 is smaller than the radius of the inner periphery centering on the rotation axis 83 of the cooling passage 8 (main body portion 80). The holding portion 402 and the layer 3 are inside the cooling passage 8 (main body portion 80) in the radial direction of the piston 1 with the axis 43 as the center. In other words, when viewed from the axial direction, the outer periphery of the layer 3 is located on the inner side in the radial direction (side closer to the axial line 43) than the inner peripheral surface of the cooling passage 8 (main body part 80). In position, the layer 3 does not overlap the cooling passage 8.

  Hereinafter, a method for manufacturing the piston 1 of the present embodiment will be described. The manufacturing method includes a casting process, a heat treatment process, a low thermal conductive layer forming process, and a machining process. In the casting process, the prototype (intermediate workpiece) of the piston body 2 is cast. Specifically, a core for forming the cooling passage 8 is installed in a mold. The core is formed in the same annular shape as the main body 80 by pressing and solidifying the powdered salt. The core is installed in the mold at a high temperature, and is supported by pins at positions corresponding to the inlet portion 81 and the outlet portion 82. When the axis 43 of the piston body 2 in the mold extends in the vertical direction, a pin that protrudes upward in the vertical direction is provided at the corresponding position on one side of the core in the rotation axis direction (lower side in the vertical direction). The core is supported by these pins so that the core is leveled. At this time, the rotation axis of the core coincides with the axis 43 of the piston body 2 (type). The upper and lower ends of the core (the plane on which the end in the rotational axis direction is located) are horizontal and orthogonal to the axis 43. In this state, the molten aluminum alloy is poured into the mold and solidified. An inner periphery of the piston main body 2 (piston skirt 6 and the like) and a main body portion 80 of the cooling passage 8 are formed, and a prototype of the concave portion 401 and the holding portion 402 is formed. Note that the prototypes of the recess 401 and the holding portion 402 may be formed by machining.

  In the heat treatment step, heat treatment is performed. As a result, the properties of the cast prototype are improved and adjusted to appropriate strength and hardness. In the low thermal conductive layer forming step, the low thermal conductive layer 3 is formed on the prototype (on the combustion chamber 15 side). Layer 3 is formed as early as after the heat treatment step. (The heat treatment step is performed before the low thermal conductive layer forming step.) In this embodiment, the layer 3 is formed after the heat treatment step and before the machining step. In the machining process, the prototype on which the layer 3 is formed is machined by a lathe or the like. The side of the piston head 4 facing the combustion chamber 15 is cut to form the crown surface 400. In addition, the inner wall of the hole formed by removing the pin that supports the core is processed to form the inlet portion 81 and the outlet portion 82 of the cooling passage 8. The salt core is melted and removed with hot water (hot water). Further, the piston pin hole 51 and the ring groove 410 are processed, and the outer diameter of the piston body 2 such as the outer periphery of the piston head 4 and the piston skirt 6 is finished. Thereby, the piston 1 is formed.

  The low thermal conductive layer formation step includes a material preparation step, a material installation step, and a sintering step. In the material preparation step, a material for forming the low thermal conductive layer 3 (hereinafter referred to as a forming material) is prepared. The forming material includes a binder powder and a zirconia powder. The binder powder is aluminum powder. Aluminum powder and zirconia powder are mixed in a predetermined (weight or volume) ratio to prepare a forming material as a mixed material that is a powder. In this mixed material, the zirconia powder is dispersed in the aluminum powder. In the material installation step, the forming material is filled into the prototype of the holding unit 402 (heat treated). Note that the position of the forming material into the original shape of the holding portion 402 is arbitrary. In the sintering step, the filled forming material (specifically, mainly aluminum powder among them) is sintered. In this embodiment, the discharge plasma sintering method is used, and sintering is performed by mechanical pressurization and pulse current heating. A carbon electrode is brought into contact with both sides of the original shape of the piston 1 in the axial direction. A pulse voltage (current) is applied from a power source in a state where the forming material is pressurized in the axial direction. The forming material is sintered by heat generation of each aluminum powder by energization, discharge plasma energy generated between the particles, and the like. A sintered body (whose volume is reduced compared to the original) is formed inside the holding portion 402. The sintered body is a sintered layer that spreads in a direction perpendicular to the crown surface 400. As a result, a prototype of the piston head 4 including the holding portion 402 that accommodates the sintered body is formed. In a machining process performed thereafter, a part of the sintered body is cut together with a part of the piston head 4 to finish the crown surface 400 including the sintered body on the surface. This sintered body becomes the layer 3.

  Next, the function and effect will be described. When the piston 1 descends in the cylinder 9 during the intake stroke, intake from the intake port 111 to the cylinder 9 is performed. In the compression stroke, when the piston 1 moves up with all the ports 111 and 112 closed, the air-fuel mixture (including fuel) is compressed. When the spark plug ignites the air-fuel mixture, the air-fuel mixture explodes (combusts) to become combustion gas. In this embodiment, the spark plug (electrode 19), which is a fire source, is located near the top center of the combustion chamber 15 (between the valves 16, 17). Further, since the shape of the combustion chamber 15 is a pent roof type, the inner wall on the outer peripheral side of the combustion chamber 15 is close to the crown surface 400 of the piston 1 (the piston head 4 at the top dead center). Therefore, when the piston 1 rises in the compression stroke, the air-fuel mixture on the outer peripheral side of the combustion chamber 15 is pushed out to the center side. Since the air-fuel mixture collects toward the electrode 19, the air-fuel mixture easily burns (combustion efficiency is improved). Combustion proceeds as the flame propagates sequentially through the mixture. The flame propagates from the electrode 19 to the other axial side (the crown surface 400 side) and the outer peripheral side.

  The low heat conductive layer 3 is on one side in the axial direction of the piston head 4 (combustion chamber 15 side). The layer 3 is a structure for reducing the thermal conductivity from the combustion chamber 15 to the piston main body 2, and functions between the combustion chamber 15 and the piston main body 2 as a heat insulating layer. The layer 3 reduces heat transfer from the gas in the combustion chamber 15 to the piston head 4 (piston body 2), and suppresses the heat of the air-fuel mixture from being taken away by the piston body 2. Therefore, a decrease in combustion efficiency (cooling loss) of engine 100 can be suppressed, and the thermal efficiency of engine 100 can be improved.

  When engine 100 is an in-cylinder direct injection type, low heat conduction layer 3 is provided on crown surface 400 at a location corresponding to at least the fuel injection region (the location where the fuel collides / explodes and the temperature and pressure are highest). It is preferably formed in the vicinity thereof. By having the layer 3 at this location, heat transfer from the gas in the combustion chamber 15 to the piston head 4 (piston body 2) can be more effectively reduced. Further, since heat absorption to the piston main body 2 is suppressed by the layer 3, the portion where the fuel adheres on the crown surface 400 quickly becomes high temperature and maintains a high temperature state. Therefore, the attached fuel is quickly vaporized and burned, so that the combustion efficiency is improved and the deterioration of the exhaust gas characteristics can be suppressed. If the layer 3 is not formed on the crown surface 400 other than the above portion, it is possible to suppress the occurrence of knocking due to an unnecessarily high temperature at a portion other than the above portion.

  Zirconia in the layer 3 is a low thermal conductivity material and has a lower thermal conductivity than the aluminum alloy that is the material (base metal) of the piston body 2. Thus, the layer 3 as a whole (on average) has a lower thermal conductivity than the piston body 2. The low thermal conductivity material is not limited to zirconia, and for example, graphite (graphite) or the like may be used. Further, the layer 3 only needs to have an average thermal conductivity lower than that of the piston body 2, and for example, the layer 3 does not need to actively contain a low thermal conductivity material. For example, the portion facing the combustion chamber 15 in the piston head 4 may function as a layer having a lower thermal conductivity than the piston body 2 by including a large amount of voids. In this embodiment, since the layer 3 actively contains a low thermal conductivity material, it is relatively easy to form a layer having a desired thermal conductivity lower than that of the piston body 2.

  The aluminum powder in the forming material adheres to each other or the piston body 2 to function as a binder, and holds the zirconia in the layer 3. The binder is not limited to aluminum, and may include other metals (magnesium or the like). Moreover, you may use not only a metal but engineering plastics, such as a polyamide imide, as a binder. In this embodiment, since the binder contains aluminum which is a material common to the piston body 2, the bonding force between the layer 3 and the piston body 2 can be easily improved. Note that the layer 3 containing the low thermal conductivity material may be formed without sintering the binder. In the present embodiment, the sintered body of the binder (aluminum powder) in the layer 3 contains more minute voids (pores) than the piston body 2 formed by casting. The voids have a lower thermal conductivity than solid solids. Accordingly, the layer 3 as a whole has a lower thermal conductivity than the piston body 2. Sintering may be performed using the principle of friction stir welding (joining). For example, the forming material is sintered by pressing a rotationally driven tool against the forming material. In this embodiment, since the discharge plasma sintering method is used, it is advantageous in that the deformation of the piston head 4 is relatively small.

  The low heat conductive layer 3 is held on the piston head 4 (crown surface portion 40) by the holding portion 402. Therefore, damage and falling off of the layer 3 are suppressed, and the durability of the piston 1 can be improved. Note that a preformed layer (preform) 3 may be installed in the holding portion 402 and bonded to the piston body 2. Further, the holding portion 402 may not be a (second) concave portion. In this embodiment, since the (second) concave portion functions as the holding portion 402, the layer 3 can be held more firmly. Here, the holding portion 402 is not limited to a single concave portion, and may have, for example, a plurality of concave and convex portions. Further, the layer 3 may be grown by anodizing the crown surface portion 40. In this case, the portion surrounding the anodized film on the crown surface portion 40 functions as the holding portion 402. In other words, the holding portion 402 may not be mechanically formed on the crown surface portion 40. The layer 3 may be on the side of the combustion chamber 15 in the crown surface portion 40 and may not be exposed to the combustion chamber 15. In the present embodiment, the layer 3 is exposed to the combustion chamber 15 and constitutes a part of the crown surface 400 facing the combustion chamber 15 (a part of the wall of the combustion chamber 15). Therefore, the thermal conductivity from the combustion chamber 15 to the piston body 2 can be reduced more effectively.

  On the other hand, if the temperature of the piston head 4 becomes too high, it may cause knocking. The unburned air-fuel mixture (end gas) in front of which the flame propagates is compressed by the combustion gas and becomes high temperature and high pressure. When this end gas self-ignites, knocking occurs. If the temperature of the piston head 4 becomes too high, the end gas tends to self-ignite. Specifically, since the flame propagates from the center side (spark plug electrode 19) of the combustion chamber 15 toward the outer peripheral side, knocking is likely to occur on the outer peripheral side. Further, since the exhaust port 112 is hotter than the intake port 111, knocking is more likely to occur on the exhaust port 112 side than the intake port 111 side with respect to the axis 43.

  The heat transferred from the combustion chamber 15 to the piston head 4 is released through the piston ring 7 and transferred to the cylinder liner 101 and the cooling water therein (cooling passage 102). The heat is also released when oil adheres to and flows out from the back surface of the piston 1 (opposite the combustion chamber 15 in the piston head 4) or when oil flows through the cooling passage 8. Oil functions as a coolant. This adhesion and distribution of oil is performed, for example, by injection of oil from an oil jet 18. Specifically, the inlet 81 of the cooling passage 8 serves as an inlet for oil injected from the oil jet 18. The oil introduced from the inlet 81 flows through the inside of the main body 80 to the one side and the other side around the axis 43. In the process of flowing, the oil gradually increases in temperature while taking the heat of the piston head 4 inside the piston body 2. The outlet portion 82 serves as an oil outlet. The oil that has reached the outlet portion 82 is discharged from the outlet portion 82. The discharged oil falls due to its own weight, for example, and returns to the oil pan below the engine 100. Thus, since the piston 1 is provided with the cooling passage 8, the piston head 4 is efficiently cooled, so that the occurrence of knocking can be suppressed. It is possible to achieve both reduction in cooling loss during combustion (due to layer 3) and suppression of knocking.

  The low heat conductive layer 3 is inside the cooling passage 8 in the radial direction of the piston 1 with the axis 43 as the center. The cooling loss during combustion can be effectively reduced by having the low thermal conductive layer 3 on the center side of the crown surface 400 where combustion starts when viewed from the axial direction. In addition, as seen from the axial direction, there is a projected portion of the cooling passage 8 on the outer peripheral side of the crown surface 400 (broken line in FIG. 3), so that the outer peripheral side where knocking is likely to occur is cooled, effectively suppressing knocking. can do. Since the low heat conductive layer 3 does not overlap the projected portion of the cooling passage 8 when viewed from the axial direction, the outer peripheral side of the crown surface 400 is efficiently cooled by the cooling passage 8. Therefore, it is possible to achieve both a reduction in cooling loss during combustion and suppression of knocking at a high level.

  The cooling passage 8 only needs to extend in the direction around the axis 43, and the shape seen from the axis direction may be a polygonal shape or the like. In the present embodiment, since the shape is annular, the outer peripheral side of the piston head 4 can be efficiently cooled. Further, the cooling passage 8 may be discontinuous rather than continuous in the direction around the axis 43. For example, it may be arcuate. In the present embodiment, the cooling passage 8 has a continuous annular shape around the axis 43, so that the entire circumference of the piston head 4 can be efficiently cooled. Further, in the cooling passage 8, not only the inlet portion 81 and the outlet portion 82 are opened on the opposite side (end portion 42) of the piston head 4 to the combustion chamber 15, but an arbitrary portion in the direction around the axis 43, for example, all May be open. In other words, the cooling passage 8 is not limited to a cylindrical shape, and may be a semi-cylindrical shape. In the present embodiment, the cooling passage 8 has a cylindrical shape, and the oil flows on the bottom of the main body 80 (the end 802 on the other side in the axial direction). Therefore, oil is held in the passage 8 and the piston head 4 can be efficiently cooled.

  The cooling passage 8 (main body portion 80) has an end portion 802 opposite to the combustion chamber 15 in the axial direction (on the other side in the axial direction) on a single plane orthogonal to the axial line 43 in the direction around the axial line 43. is there. Therefore, in the casting process of the piston 1, when the piston body 2 mold is installed so that the axis 43 extends on the vertical line, the end 802 on the lower side in the vertical direction of the cooling passage 8 is horizontal in the piston body 2 to be cast. become. The core for forming the cooling passage 8 is installed such that the lower end in the vertical direction is horizontal. Since the core can be easily installed and supported, the casting process of the piston 1 can be facilitated and the productivity can be improved.

  The shape of the cooling passage 8 (main body portion 80) cut by a plane passing through the axis 43 is constant in the direction around the axis 43. Therefore, when the cooling passage 8 is formed using a core, the shape of the core cut by a plane passing through the axis 43 is also constant in the direction around the axis 43. In other words, the cross-sectional shape of the core cut along a plane passing through the rotation axis of the core is constant in the direction around the rotation axis. For this reason, when forming and installing a core, the crack (damage | damage) of a core accompanying the core in a high temperature state cooling and contracting is suppressed. Therefore, the productivity of the piston 1 can be improved. The core material is not limited to salt but may be sand or the like. When the core is formed of salt as in this embodiment, it is advantageous in terms of securing the strength of the core and ease of removal of the core.

  The temperature of the oil inside the cooling passage 8 is low on the inlet portion 81 side and high on the outlet portion 82 side (the amount of heat taken from the piston head 4). Accordingly, the temperature difference between the piston head 4 and the oil can be increased on the inlet portion 81 side than on the outlet portion 82 side, so that the cooling efficiency of the piston head 4 (crown surface 400) is high. In the present embodiment, the inlet 81 is on the exhaust port 112 side with respect to the axis 43, and the outlet 82 is on the intake port 111 side with respect to the axis 43. Therefore, the cooling efficiency is higher on the exhaust port 112 side (inlet portion 81 side) than on the intake port 111 side (outlet portion 82 side). By increasing the cooling efficiency on the exhaust port 112 side where knocking is likely to occur, the occurrence of knocking can be more effectively suppressed. Here, in the piston head 4, when viewed from the axial direction, the side of the exhaust port 112 with respect to the axis 43 is when the piston head 4 is bisected by a single straight line that extends in the radial direction of the piston 1 through the axis 43. The side where the exhaust port 112 (the center of the opening in the cylinder head 11) or the exhaust valve 17 (the axial center thereof) is located. For example, a straight line parallel to the axis of the piston pin hole 51 can be selected as the straight line. The side of the intake port 111 with respect to the axis 43 is similarly defined. Whether it is the side where the exhaust port 112 (exhaust valve 17) is located or the side where the intake port 111 (intake valve 16) is located can be specified by various methods. For example, the exhaust valve 17 has a smaller valve diameter estimated from the arcs of the valve recesses 403 and 404, and the intake valve 16 has a larger diameter. As described above, the position on the side can be specified from the shapes of the valve recesses 403 and 404. It can also be specified by whether the piston pin hole 51 (the axis thereof) is closer to the thrust side or the opposite thrust side with respect to the axis 43.

  The oil jet 18 is not limited to the type installed in the cylinder block 10 and may be a type in which oil supplied from the crankshaft 12 is injected from a hole inside the connecting rod 13. In the present embodiment, since the oil jet 18 is installed in the cylinder block 10, oil can be accurately injected to any position (for example, the inlet portion 81) in the piston 1 regardless of the movement state of the connecting rod 13. Therefore, oil effectively flows into the cooling passage 8 and the piston head 4 can be efficiently cooled.

[Second Embodiment]
First, the configuration will be described. Hereinafter, members and structures common to the first embodiment are denoted by the same reference numerals as in the first embodiment, and description thereof is omitted. As shown in FIG. 5, the holding portion 402 is elliptical when viewed from the axial direction, and its center is closer to the intake port 111 (valve recess 403) side than the axial line 43. The holding part 402 is inside the recess 401. The holding portion 402 and the low thermal conductive layer 3 overlap with the axis 43 (the central portion of the crown surface 400) when viewed from the axial direction, are inside the cooling passage 8, and do not overlap with the cooling passage 8. The area of the low thermal conductive layer 3 in the direction orthogonal to the axis 43 is larger on the intake port 111 (valve recess 403) side than on the exhaust port 112 (valve recess 404) side with respect to the axis 43. Other configurations are the same as those of the first embodiment.

  Next, the function and effect will be described. The area of the low thermal conductive layer 3 in the direction orthogonal to the axis 43 (viewed from the axis direction) is larger on the intake port 111 side than on the exhaust port 112 side with respect to the axis 43. In other words, the area is smaller on the exhaust port 112 side than on the intake port 111 side. Therefore, the range of the crown surface 400 in which the cooling passage 8 can be efficiently cooled (because the layer 3 is not covered) is larger on the exhaust port 112 side than on the intake port 111 side with respect to the axis 43. That is, the cooling efficiency of the crown surface 400 by the cooling passage 8 is higher on the exhaust port 112 side than on the intake port 111 side. On the other hand, since the area of the layer 3 is large on the intake port 111 side, the cooling loss during combustion can be effectively reduced. Therefore, the reduction of the cooling loss and the suppression of knocking can be achieved at a high level. Other functions and effects are the same as those of the first embodiment.

[Third embodiment]
First, the configuration will be described. Hereinafter, members and structures common to the first embodiment are denoted by the same reference numerals as in the first embodiment, and description thereof is omitted. As shown in FIG. 6, the holding portion 402 is on the intake port 111 side with respect to the axis 43. Most of the holding portion 402 is inside the recess 401. A part of the holding portion 402 includes a recess 403 for the intake valve 16 on the outer peripheral side of the recess 401 in the radial direction of the piston 1. When viewed from the axial direction, the holding portion 402 and the low thermal conductive layer 3 do not overlap the axial line 43 (the central part of the crown surface 400), and the cooling passage 8 (broken line) on the intake port 111 (valve recess 403) side with respect to the axial line 43. ) And does not overlap the cooling passage 8 on the exhaust port 112 (valve recess 404) side. The area of the layer 3 in the direction orthogonal to the axis 43 is larger on the intake port 111 side than on the exhaust port 112 side with respect to the axis 43. Other configurations are the same as those of the first embodiment.

  Next, the function and effect will be described. The area of the low thermal conductive layer 3 in the direction orthogonal to the axis 43 (viewed from the axis direction) is larger on the intake port 111 side than on the exhaust port 112 side with respect to the axis 43. In other words, the area is smaller on the exhaust port 112 side than on the intake port 111 side. Therefore, when viewed from the axial direction, it is easy to make the area where the projected portion (broken line) of the cooling passage 8 overlaps the layer 3 smaller on the exhaust port 112 side than on the intake port 111 side with respect to the axial line 43. It is. In this case, the cooling efficiency of the crown surface 400 by the cooling passage 8 is higher on the exhaust port 112 side than on the intake port 111 side. On the other hand, as viewed from the axial direction, it is easy to increase the area where the layer 3 covers the projected portion of the cooling passage 8 on the intake port 111 side with respect to the axial line 43 rather than on the exhaust port 112 side. In this case, the cooling loss at the time of combustion can be reduced more effectively. Therefore, the reduction of the cooling loss and the suppression of knocking can be made compatible at a higher level. In the present embodiment, the projected portion of the cooling passage 8 does not overlap the layer 3 (the overlapping area is zero) when viewed from the axial direction on the exhaust port 112 side. Therefore, the cooling efficiency can be increased more effectively. On the intake port 111 side, most of the projected portion of the cooling passage 8 is covered with the layer 3 when viewed from the axial direction. Therefore, the cooling loss can be more effectively reduced. Other functions and effects are the same as those of the second embodiment.

[Fourth embodiment]
First, the configuration will be described. Hereinafter, members and structures common to the first embodiment are denoted by the same reference numerals as in the first embodiment, and description thereof is omitted. As shown in FIG. 7, the axial depth of the holding portion 402 relative to the bottom surface of the recess 401 is substantially zero at the end portion 405 on the intake port 111 side and the end portion 406 on the exhaust port 112 side. The depth gradually increases from the end portion 405 toward the axis 43 side, increases at the portion 407 between the end portion 405 and the axis line 43, and gradually decreases from the portion 407 toward the end portion 406. Become. The surface on one side in the axial direction of the low thermal conductive layer 3 is a flat surface extending in the radial direction of the piston 1 continuously from the bottom surface of the recess 401. Therefore, the thickness of the layer 3 in the axial direction also gradually increases from the end 405 toward the region 407, increases most at the region 407, and gradually decreases from the region 407 toward the end 406. The thickness of the layer 3 in the axial direction is, on the average, larger on the intake port 111 side than on the exhaust port 112 side with respect to the axial line 43. Other configurations are the same as those of the first embodiment.

  Next, the function and effect will be described. The thickness of the low thermal conductive layer 3 in the axial direction is, on the average, larger on the intake port 111 side than on the exhaust port 112 side with respect to the axial line 43. In other words, the thickness of the layer 3 is smaller on the average on the exhaust port 112 side than on the intake port 111 side with respect to the axis 43. For this reason, on the exhaust port 112 side, even if the layer 3 has the same area as the intake port 111 side when viewed from the axial direction, the effect of reducing the thermal conductivity by the layer 3 is small. Therefore, the cooling efficiency of the crown surface 400 by the cooling passage 8 is higher on the exhaust port 112 side than on the intake port 111 side. On the other hand, the above-mentioned thickness of the layer 3 on the intake port 111 side is large on average, so that even if the layer 3 has the same area as the exhaust port side when viewed from the axial direction, the thermal conductivity is reduced by the layer 3 Is big. Therefore, it is possible to achieve both a reduction in cooling loss during combustion and suppression of knocking at a high level. The thickness of the layer 3 may be gradually decreased from the end portion 405 (having a certain depth) on the intake port 111 side toward the end portion 406 on the exhaust port 112 side. The bottom surface of the holding portion 402 (the surface on the other side in the axial direction of the layer 3) is not limited to a planar shape but may be a curved surface. Other functions and effects are the same as those of the first embodiment.

[Fifth Embodiment]
First, the configuration will be described. Hereinafter, members and structures common to the first embodiment are denoted by the same reference numerals as in the first embodiment, and description thereof is omitted. As shown in FIG. 8, the bottom surface of the holding portion 402 has a planar shape that extends in the radial direction of the piston 1. The axial depth of the holding portion 402 relative to the bottom surface of the recess 401 is greater in the range from the end 406 on the exhaust port 112 side to the axis 43 than in the range from the end 405 on the intake port 111 side to the axis 43. ,small. The surface on one side in the axial direction of the low thermal conductive layer 3 is a flat surface extending in the radial direction of the piston 1 continuously from the bottom surface of the recess 401. Therefore, the thickness of the layer 3 in the axial direction is also smaller in the range from the end 406 to the axis 43 than in the range from the end 405 to the axis 43. That is, the thickness of the layer 3 in the axial direction is larger on the intake port 111 side than on the exhaust port 112 side with respect to the axial line 43. Other configurations are the same as those of the first embodiment.

  The operational effects are the same as in the fourth embodiment. Note that the thickness of the low thermal conductive layer 3 only needs to be larger on the intake port 111 side on the average than the exhaust port 112 side with respect to the axis 43, for example, a step portion where the thickness of the layer 3 changes. 408 may be located not between the position of the axis 43 but between the end 405 on the intake port 111 side and the axis 43, or the like. Further, when viewed from the axial direction, the stepped portion 408 may be curved instead of linear.

[Sixth embodiment]
First, the configuration will be described. Hereinafter, members and structures common to the first embodiment are denoted by the same reference numerals as in the first embodiment, and description thereof is omitted. As shown in FIGS. 9 and 10, the dimension (width) of the main body 80 in the radial direction around the rotation axis 83 of the main body 80 of the cooling passage 8 is the end on the intake port 111 (valve recess 403) side. It is the smallest at 803 and the largest at the end 804 on the side of the discharge port 112 (valve recess 404). The dimensions of the main body 80 gradually increase from the end 803 toward the end 804 in the direction around the rotation axis 83. The area (projected area) of the projected portion (broken line) of the cooling passage 8 in the axial direction is larger on the exhaust port 112 side than on the intake port 111 side with respect to the axis 43. The cross-sectional area of the main body 80 cut by a plane passing through the rotation axis 83 is minimum at the end 803 and maximum at the end 804. The cross-sectional area gradually increases from the end 803 toward the end 804 in the direction around the rotation axis 83. The cross-sectional area of the cooling passage 8 (main body portion 80) cut along a plane passing through the axis 43 is, on average, larger on the exhaust port 112 side than on the intake port 111 side with respect to the axis 43. Other configurations are the same as those of the first embodiment.

  Next, the function and effect will be described. The projected area in the axial direction of the cooling passage 8 is larger on the exhaust port 112 side than on the intake port 111 side with respect to the axial line 43. For this reason, the heat receiving surface of the cooling passage 8 when viewed from the crown surface 400 side, in other words, the range of the crown surface 400 in which the cooling passage 8 can be efficiently cooled is larger than the intake port 111 side with respect to the axis 43. It becomes larger on the exhaust port 112 side. Therefore, the cooling efficiency of the crown surface 400 by the cooling passage 8 is higher on the exhaust port 112 side than on the intake port 111 side. On the other hand, since the projected area (the heat receiving surface of the cooling passage 8) is small on the intake port 111 side, the cooling loss during combustion can be effectively reduced. Therefore, the reduction of the cooling loss and the suppression of knocking can be achieved at a high level.

  The cross-sectional area of the cooling passage 8 cut by a plane passing through the axis 43 is on average larger on the exhaust port 112 side than on the intake port 111 side with respect to the axis 43. Therefore, the area where the oil can adhere to the inner wall of the cooling passage 8, in other words, the internal surface area of the piston head 4 that can cool the cooling passage 8, is greater than the intake port 111 side of the exhaust port 112 with respect to the axis 43. Bigger on the side. Therefore, the cooling efficiency of the crown surface 400 by the cooling passage 8 is higher on the exhaust port 112 side than on the intake port 111 side. On the other hand, since the cross-sectional area on the intake port 111 side is smaller on the average than that on the exhaust port 112 side, cooling loss during combustion can be effectively reduced. Other functions and effects are the same as those of the first embodiment.

[Seventh embodiment]
First, the configuration will be described. Hereinafter, members and structures common to the first embodiment are denoted by the same reference numerals as in the first embodiment, and description thereof is omitted. As shown in FIG. 11, an end 802 opposite to the crown surface 400 in the axial direction in the main body portion 80 of the cooling passage 8 (the other side in the axial direction) is a single unit orthogonal to the axial line 43 in the direction around the axis 43. On one plane. An end 801 on the crown surface 400 side in the axial direction (one axial direction side) in the main body 80 is a partial region on the exhaust port 112 side with respect to the axial line 43 (a region overlapping the valve recess 404 in the direction around the axial line 43) ) 805, the distance from the end portion 802 is large and the distance from the crown surface 400 is small compared to other regions. The axial distance between the crown surface 400 and the cooling passage 8 (end 801) is smaller on the average on the exhaust port 112 side than on the intake port 111 side with respect to the axis 43. The cross-sectional area of the cooling passage 8 (main body portion 80) cut by a plane passing through the axis 43 is larger in the partial area 805 than in other areas. The sectional area is larger on the average on the exhaust port 112 side than on the intake port 111 side with respect to the axis 43. Other configurations are the same as those of the first embodiment.

  Next, the function and effect will be described. The axial distance between the crown surface 400 and the cooling passage 8 in the piston head 4 is smaller on the average on the exhaust port 112 side than on the intake port 111 side with respect to the axis line 43. For this reason, the cooling efficiency of the crown surface 400 by the cooling passage 8 is higher on the exhaust port 112 side than on the intake port 111 side. On the other hand, since the distance is large on the intake port 111 side, cooling loss during combustion can be effectively reduced. Therefore, the reduction of the cooling loss and the suppression of knocking can be achieved at a high level. Other functions and effects are the same as in the sixth embodiment.

[Eighth embodiment]
First, the configuration will be described. Hereinafter, members and structures common to the first embodiment are denoted by the same reference numerals as in the first embodiment, and description thereof is omitted. As shown in FIG. 12, the rotation axis 83 of the main body 80 of the cooling passage 8 is not parallel to the axis 43 and has an angle larger than zero. In the main body 80, an end 801 on the side of the crown surface 400 (on the one side in the axial direction) in the axial direction and an end 802 on the side opposite to the crown surface 400 (on the other side in the axial direction) are respectively in the direction around the rotation axis 83 In addition to being on a single plane orthogonal to the rotation axis 83, it is inclined with respect to the plane orthogonal to the axis 43. Due to this inclination, the end 801 is closer to the crown surface 400 on the exhaust port 112 side than the intake port 111 side with respect to the axis 43. The end 801 gradually approaches the crown surface 400 as it goes from the end 803 on the intake port 111 side to the end 804 on the exhaust port 112 side with respect to the axis 43. The distance between the crown surface 400 and the cooling passage 8 (end 801) is smaller on the average on the exhaust port 112 side than on the intake port 111 side with respect to the axis 43. The shape and the cross-sectional area of the cooling passage 8 (main body portion 80) cut along a plane passing through the axis 43 are constant in the direction around the axis 43. Such an arrangement of the cooling passage 8 is realized by, for example, installing the core in the mold so that the rotation axis of the core is inclined with respect to the axis 43 of the piston body 2 (mold) in the casting process. Is possible. Other configurations are the same as those of the first embodiment.

  Next, the function and effect will be described. The shape of the cooling passage 8 (main body portion 80) cut by a plane passing through the axis 43 is constant in the direction around the axis 43. Therefore, similarly to the first embodiment, the cracking of the core can be suppressed. As with the cooling passage 8, the other axial side of the piston head 4 (the side opposite to the combustion chamber 15) may be inclined. That is, the axial distance (thickness) between the end 42 on the other axial side of the piston head 4 and the cooling passage 8 (main body 80) is such that the intake port 111 is closer to the exhaust port 112 than the axial line 43. The shape of the end 42 may be formed so as to be the same as the side. In this case, by reducing the thickness as much as possible and reducing the mass of the piston head 4, the piston 1 can be reduced in weight and material. Similarly to the cooling passage 8, one axial direction side (combustion chamber 15 side) of the piston head 4 may be inclined. In other words, the piston head 4 has an axial distance (thickness) between the crown surface 400 and the cooling passage 8 that is the same as that of the intake port 111 on the exhaust port 112 side with respect to the axis 43. The shape of the end portion (crown surface 400) on one axial direction side of 4 may be formed. In the present embodiment, since the crown surface 400 is orthogonal to the axis line 43, the axial distance between the crown surface 400 and the cooling passage 8 is greater than the intake port 111 side of the exhaust port 112 with respect to the axis line 43. The side is smaller on average. Therefore, the same effect as the seventh embodiment can be obtained. Other functions and effects are the same as those of the first embodiment.

[Ninth Embodiment]
First, the configuration will be described. Hereinafter, members and structures common to the first embodiment are denoted by the same reference numerals as in the first embodiment, and description thereof is omitted. As shown in FIG. 13, there is a gap 409 between the inner wall of the holding portion 402 and the outer periphery of the low thermal conductive layer 3 in the radial direction of the piston 1. This gap 409 is in the entire range of the layer 3 in the direction around the axis 43. Other configurations are the same as those of the first embodiment.

  Next, the function and effect will be described. Heat can also be conducted from the low thermal conductive layer 3 to the piston body 2 (holding portion 402). In the present embodiment, there is a gap 409 between the holding portion 402 and the layer 3 in the radial direction of the piston 1. The gap 409 becomes an air layer having a low thermal conductivity, interrupts the heat conduction path from the layer 3 to the holding portion 402 (piston body 2), and suppresses heat transfer. For this reason, the efficiency with which the cooling passage 8 cools the crown surface 400 on the outer peripheral side of the layer 3 (the radially outer side of the piston 1 than the layer 3) is improved. Therefore, the knocking suppression effect can be improved. A thin layer is formed on the surface of the crown surface 400 where the flame is cooled by the piston 1 and disappears. If the size of the gap 409 is set to be equal to or smaller than the thickness of the thin layer, it is possible to suppress the entry of flame into the gap, so that the effect of suppressing the heat transfer can be obtained more reliably. The gap 409 may be in a partial range of the layer 3 in the direction around the axis 43. For example, there may be many (wide) gaps 409 in the direction around the axis 43 closer to the exhaust port 112 than to the intake port 111 with respect to the axis 43. In this case, the cooling efficiency of the crown surface 400 by the cooling passage 8 is higher on the exhaust port 112 side than on the intake port 111 side. Therefore, the reduction of the cooling loss by the layer 3 and the suppression of knocking can be achieved at a high level. Other functions and effects are the same as those of the first embodiment.

[Other Embodiments]
As mentioned above, although the form for implementing this invention was demonstrated based on drawing, the specific structure of this invention is not limited to embodiment, The design change etc. of the range which does not deviate from the summary of invention are included. Even if it exists, it is included in this invention. For example, the present invention is applicable not only to vehicles but also to engines mounted on ships and the like. The engine may be a spark ignition engine (gasoline engine), and its form is arbitrary. For example, the engine may be a two-stroke engine or may be provided with a supercharging system such as turbocharging. The fuel supply method may be an in-cylinder direct injection type that directly injects into the cylinder (combustion chamber), or a port injection type that injects into the intake port. The shape of the piston (piston body) is arbitrary. For example, the presence / absence of the concave portion on the crown surface and the shape / position thereof are not limited to the above and are arbitrary. The fluid flowing through the cooling passage is not limited to oil as long as it can cool the piston head.

[Technical ideas that can be grasped from the embodiment]
The technical idea (or technical solution, the same applies hereinafter) that can be understood from the embodiment described above will be described below.
(1) In one aspect of the piston of the internal combustion engine of the present technical idea,
A piston body comprising a metal and having a piston head and a piston skirt;
A holding portion on the combustion chamber side of the internal combustion engine in the piston head;
A low thermal conductive layer in the holding portion, having a lower thermal conductivity than the piston body;
When the axis passing through the center point of the cross section of the piston head cut by a plane orthogonal to the moving direction of the piston main body in the cylinder of the internal combustion engine and parallel to the moving direction of the piston main body is the axis, A cooling passage extending in a direction around the axis in the head and allowing fluid for cooling the piston head to flow;
Is provided.
(2) In a more preferred embodiment, in the above embodiment,
The cooling efficiency by the cooling passage of the crown surface on the combustion chamber side in the piston head is higher on the exhaust port side of the cylinder head of the internal combustion engine than on the intake port side with respect to the axis.
(3) In another preferred embodiment, in any of the above embodiments,
The low thermal conductive layer is inside the cooling passage in the radial direction of the piston centering on the axis.
(4) In still another preferred embodiment, in any of the above embodiments,
The area of the low heat conductive layer in the direction orthogonal to the axis is larger on the intake port side than on the exhaust port side with respect to the axis.
(5) In still another preferred embodiment, in any of the above embodiments,
The thickness of the low thermal conductive layer in the axial direction is, on average, larger on the intake port side than on the exhaust port side with respect to the axial line.
(6) In still another preferred embodiment, in any of the above embodiments,
The cross-sectional area of the cooling passage cut along a plane passing through the axis is, on average, larger on the exhaust port side than on the intake port side with respect to the axis.
(7) In still another preferred embodiment, in any of the above embodiments,
The axial distance between the crown surface on the combustion chamber side of the piston head and the cooling passage is, on average, smaller on the exhaust port side than on the intake port side with respect to the axis.
(8) In still another preferred embodiment, in any of the above embodiments,
The shape of the cooling passage cut by a plane passing through the axis is constant in the direction around the axis;
The cooling passage has a plane perpendicular to the axis so that an end on the crown surface side in the axial direction is closer to the crown surface on the exhaust port side than the intake port side with respect to the axis. It is slanted.
(9) In still another preferred embodiment, in any of the above embodiments,
The fluid is a coolant supplied from a cylinder block of an internal combustion engine and injected from a jet device,
The cooling passage includes a pair of an inlet portion and an outlet portion that open to the opposite side of the combustion chamber in the piston head,
The inlet portion is on the exhaust port side with respect to the axis, and serves as an inlet for the coolant.
The outlet portion is on the intake port side with respect to the axis, and serves as an outlet for the coolant.
(10) In still another preferred embodiment, in any of the above embodiments,
The projected area of the cooling passage in the axial direction is larger on the exhaust port side than on the intake port side with respect to the axial line.
(11) In still another preferred embodiment, in any of the above embodiments,
The cooling passage has an end opposite to the combustion chamber in the axial direction on a single plane perpendicular to the axial line in the direction around the axial line.
(12) In still another preferred embodiment, in any of the above embodiments,
There is a gap in the radial direction of the piston between the holding portion and the low thermal conductive layer.

DESCRIPTION OF SYMBOLS 1 Piston 2 Piston main body 3 Low heat conductive layer 4 Piston head 400 Crown surface 402 Holding part 43 Axis 6 Piston skirt 8 Cooling passage 9 Cylinder 100 Engine (internal combustion engine)
11 Cylinder head 111 Intake port 112 Exhaust port 15 Combustion chamber

Claims (12)

A piston of an internal combustion engine,
A piston body comprising a metal and having a piston head and a piston skirt;
A holding portion on the combustion chamber side of the internal combustion engine in the piston head;
A low thermal conductive layer in the holding portion, having a lower thermal conductivity than the piston body;
When the axis passing through the center point of the cross section of the piston head cut by a plane orthogonal to the moving direction of the piston main body in the cylinder of the internal combustion engine and parallel to the moving direction of the piston main body is the axis, A cooling passage extending in a direction around the axis in the head and allowing fluid for cooling the piston head to flow;
A piston for an internal combustion engine comprising: The piston of the internal combustion engine according to claim 1,
The piston of the internal combustion engine, wherein the cooling efficiency of the crown passage on the combustion chamber side in the piston head is higher on the exhaust port side of the cylinder head of the internal combustion engine than on the intake port side with respect to the axis. . The piston of the internal combustion engine according to claim 2,
The piston of an internal combustion engine, wherein the low heat conductive layer is located inside the cooling passage in a radial direction of the piston with the axis as a center. The piston of the internal combustion engine according to claim 2,
The piston of an internal combustion engine, wherein an area of the low heat conductive layer in a direction orthogonal to the axis is larger on the intake port side than on the exhaust port side with respect to the axis. The piston of the internal combustion engine according to claim 2,
The piston of the internal combustion engine, wherein the thickness of the low thermal conductive layer in the axial direction is, on average, larger on the intake port side than on the exhaust port side with respect to the axial line. The piston of the internal combustion engine according to claim 1,
The piston of an internal combustion engine, wherein a cross-sectional area of the cooling passage cut along a plane passing through the axis is on average larger on the exhaust port side than on the intake port side with respect to the axis. The piston of the internal combustion engine according to claim 1,
An internal combustion engine characterized in that an axial distance between a crown surface on the combustion chamber side of the piston head and the cooling passage is smaller on average on the exhaust port side than on the intake port side with respect to the axis. Engine piston. The piston of the internal combustion engine according to claim 7,
The shape of the cooling passage cut by a plane passing through the axis is constant in the direction around the axis;
The cooling passage has a plane perpendicular to the axis so that an end on the crown surface side in the axial direction is closer to the crown surface on the exhaust port side than the intake port side with respect to the axis. An internal combustion engine piston characterized by being inclined with respect to the internal combustion engine. The piston of the internal combustion engine according to claim 1,
The fluid is a coolant supplied from a cylinder block of an internal combustion engine and injected from a jet device,
The cooling passage includes a pair of an inlet portion and an outlet portion that open to the opposite side of the combustion chamber in the piston head,
The inlet portion is on the exhaust port side with respect to the axis, and serves as an inlet for the coolant.
The piston of the internal combustion engine, wherein the outlet portion is on the intake port side with respect to the axis and serves as an outlet for the coolant. The piston of the internal combustion engine according to claim 1,
The piston of an internal combustion engine, wherein a projected area of the cooling passage in the axial direction is larger on the exhaust port side than on the intake port side with respect to the axial line. The piston of the internal combustion engine according to claim 1,
The piston of the internal combustion engine, wherein the cooling passage has an end portion on the opposite side to the combustion chamber in the axial direction on a single plane perpendicular to the axial line in a direction around the axial line. The piston of the internal combustion engine according to claim 1,
A piston for an internal combustion engine, wherein there is a gap in the radial direction of the piston between the holding portion and the low thermal conductive layer.

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