Piston manufacturing method

Abstract

To provide a piston manufacturing method capable of mass manufacturing pistons whose space parts are filled with particles and which have an aggregation restraining structure.SOLUTION: In a piston manufacturing method, first plural blocks 101-114 having a three-dimensional shape made by solidifying a mixture of water and a particulate matter and having grooves 121-123 concaved on sides are prepared. The plural blocks 101-114 are overlaid on each other, so as to prepare a core 100 having a first through hole 131, a second through hole 132 and a third through hole 133. The core 100 is arranged inside a cavity and clamped. Molten metal is injected in the cavity and the first through hole 131, the second through hole 132 and the third through hole 133 of the core 100. By solidifying the molten metal, a piston body 20 having the space part 30 is formed. At the same time, a first beam member 51, a second beam member 52 and a column member 52 are formed. Finally, water is discharged from the space part 30 of the piston body 20.SELECTED DRAWING: Figure 7

Description

Technical Field

[0005] , ,

[0001] The present invention relates to a method for manufacturing a piston that reciprocates within a cylinder of an engine.

Background Art

[0002] In an engine (reciprocating engine) provided with a piston that is reciprocally accommodated within a cylinder, from the viewpoints of improving fuel efficiency and ensuring output, it is conceivable to increase the compression ratio and reduce the inertial weight of the piston. Here, in order to reduce the inertial weight, conventionally, a space has been provided inside the piston to achieve weight reduction. However, when the maximum value of the combustion pressure is increased, both the vibration of the engine and the noise increase due to the vibration generated in the piston. Therefore, the piston, which is the source of vibration, is required to have both weight reduction and vibration suppression.

[0003] As a conventional structure that attempts to achieve both weight reduction and vibration suppression of the piston, which is the source of vibration, as described in Patent Document 1, a structure in which a particulate filler is filled in the space of the piston at a movable filling rate has been proposed. In this structure, during the reciprocating movement of the piston, the particulate filler moves inside the space, thereby converting the energy of the vibration generated in the piston into thermal energy due to the friction between the particulate fillers, and thereby making it possible to attenuate the vibration of the piston.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in a structure that uses particulate filler material to fill the space inside the piston to dampen vibrations generated in the piston, a phenomenon occurs where the particulate filler material aggregates during the reciprocating movement of the piston and moves back and forth as an almost single mass inside the space. As a result, the vibration suppression function due to friction between the particulate fillers cannot be effectively exerted.

[0006] Therefore, it is conceivable to provide a structure within the space that suppresses particle aggregation, but it is difficult to mass-produce pistons that are filled with particles within the space and also equipped with an aggregation-suppressing structure.

[0007] This invention has been made in view of the above circumstances, and aims to provide a method for manufacturing a piston that enables mass production of pistons in which particles are filled inside the space and which have an aggregation suppression structure. [Means for solving the problem]

[0008] The present invention relates to a method for manufacturing a piston for an internal combustion engine, wherein a space is formed inside the piston body and the space is filled with granular material, and comprises a block preparation step of preparing a plurality of blocks having a three-dimensional shape with a plurality of faces and edges at the boundaries of two adjacent faces, and grooves in which the edges are recessed inward into the three-dimensional shape by solidifying a mixture of a fluid base material and the granular material; and a core preparation step of preparing a core having the beam through hole by overlapping the plurality of blocks and connecting the widthwise side edges of the grooves of each of the plurality of blocks to form a beam through hole extending in a direction intersecting the reciprocating motion of the piston, and bonding the plurality of blocks to each other. The invention is characterized by comprising: a mold clamping step of placing the core inside a cavity corresponding to the external shape of the piston body and clamping the mold; a molten metal injection step of injecting molten metal made of the piston material into the beam through-holes of the cavity and the core; a molten metal solidification step of solidifying the molten metal to form the piston body inside the cavity and the space corresponding to the external shape of the core inside the piston body, and further forming a beam member inside the beam through-holes in a direction intersecting the reciprocating direction of the piston inside the space; and a base material discharge step of discharging the base material from the space of the piston body after the molten metal solidification step.

[0009] This invention provides a groundbreaking piston manufacturing method that enables mass production of pistons equipped with powder and granular material and an agglomeration-suppressing structure by giving the core used to form the piston's cavity during casting two functions: filling the cavity with powder and granular material and forming an agglomeration-suppressing structure.

[0010] In other words, in the piston manufacturing method described above, first, in the block preparation step, a mixture of a fluid base material and granular material is solidified to prepare a plurality of blocks having a three-dimensional shape with multiple faces and edges at the boundaries of two adjacent faces, and at least one edge recessed inward into the three-dimensional shape. Next, in the core preparation step, the plurality of blocks are stacked on top of each other and the widthwise side edges of the grooves of the plurality of blocks are joined to form through-holes for beams that extend in a direction intersecting the reciprocating motion of the piston, and the plurality of blocks are bonded together to prepare a core having through-holes for beams. Then, in the molten metal injection step, the molten metal flows into the through-holes for beams of the core together with the cavity, and in the molten metal solidification step, a piston body having a space is formed, and a beam member extending in a direction intersecting the reciprocating motion of the piston is formed inside the space.

[0011] Subsequently, after solidification and mold opening, the fluid base material, one of the core's constituent materials, is discharged from the space within the piston body, leaving the other core's constituent materials, the powder and granular material, to remain in the internal space of the piston. This makes it possible to mass-produce pistons with the internal space filled with powder and granular material and equipped with beam members as a coagulation-suppressing structure, using general piston casting techniques.

[0012] As described above, the beam member extends in a direction intersecting the reciprocating direction of the piston, and therefore can function as an agglomeration suppression structure. That is, even if the granular material temporarily accumulates at the end of the space in the direction of reciprocating motion during the piston's reciprocating movement, the granular material collides with the beam member as it moves in the reciprocating direction, promoting the dispersion of the granular material and changing its direction of movement. As a result, the beam member can function as an agglomeration suppression structure that suppresses the aggregation of the granular material. Furthermore, as a result, friction between the granular material is amplified, making it possible to effectively suppress the vibration of the piston.

[0013] In this invention, "block" refers to a component or segment having a three-dimensional shape with multiple faces for forming a core and edges at the boundaries of two adjacent faces. Any shape having multiple faces and edges at the boundaries of two adjacent faces is acceptable, and various shapes such as a roughly cubic shape or a roughly rectangular parallelepiped shape are included.

[0014] In the piston manufacturing method described above, it is preferable that in the core preparation step, a core having two beam through-holes that intersect each other is prepared by combining and bonding the plurality of blocks together so that two beam through-holes intersect each other, and in the molten metal solidification step, two beam members that intersect each other are formed inside the two beam through-holes that intersect each other.

[0015] In the above manufacturing method, it becomes possible to simultaneously form two beam members that intersect each other during piston casting, improving the workability of piston manufacturing. Moreover, in pistons manufactured using the above method, the two beam members are spread planarly over a wide area of ​​the space, so that the granular material can reliably collide with one of the beam members as it moves in the reciprocating direction, dispersing the granular material and thus reliably enhancing the damping effect.

[0016] In the piston manufacturing method described above, it is preferable that in the core preparation step, a core having the beam through-hole and the column through-hole is prepared by combining and bonding the plurality of blocks together so as to form the beam through-hole and the column through-hole extending in the reciprocating direction, in the molten metal injection step, the molten metal is injected into the beam through-hole and the column through-hole of the cavity and the core, and in the molten metal solidification step, the beam member is formed inside the beam through-hole and the column member is formed inside the column through-hole.

[0017] In the above manufacturing method, it becomes possible to simultaneously form a beam member extending in a direction intersecting the reciprocating direction and a column member extending in the reciprocating direction during piston casting, thereby improving the workability of piston manufacturing. Furthermore, in pistons manufactured using the above method, even if the rigidity of the space portion of the piston body is weak, the column member extending in the reciprocating direction supports the inner wall of the space portion in the reciprocating direction, thereby reinforcing the space portion of the piston body. Therefore, it becomes possible to suppress the aggregation of powder and granular material by the beam member and reinforce the piston body by the column member.

[0018] In the piston manufacturing method described above, the base material contains water, and in the block preparation step, it is preferable to prepare the plurality of blocks by freezing a mixture of the water and the powder at -40 degrees Celsius or below.

[0019] In the piston manufacturing method described above, the water contained in the base material is readily available, and by adjusting the amount of water, the amount of powder and granules to be filled can be easily adjusted when mixing the water and granules. Furthermore, by freezing the mixture of water and granules at -40 degrees Celsius or below, it is possible to improve the heat resistance of the block when it comes into contact with high-temperature molten metal. In addition, when preparing the core, it is possible to easily bond the blocks together by applying water to the opposing surfaces of two adjacent blocks.

[0020] In the piston manufacturing method described above, the filling rate of the granular material into the space is preferably 35 to 50% in terms of volume ratio to the volume of the space.

[0021] Within the above range, the piston manufactured by the above manufacturing method allows the powder or granules to move smoothly back and forth within the space, and the damping effect of the piston is reliably achieved. [Effects of the Invention]

[0022] As described above, according to the method for manufacturing a piston of the present invention, it is possible to mass-produce a piston in which particles are filled inside the space portion and which includes a beam member as an aggregation suppression structure.

Brief Description of the Drawings

[0023] [Figure 1] As an example of a piston manufactured by the method for manufacturing a piston of the present invention, it is a partially cutaway perspective view of a piston in which powder particles are accommodated inside a piston body and a dispersion frame having first to second beam members and column members is accommodated. [Figure 2] It is a view of a partially cutaway piston showing the powder particles and the dispersion frame accommodated inside the piston body of FIG. 1 as seen from the rear side. [Figure 3] It is a view of a partially cutaway piston showing the powder particles and the dispersion frame accommodated inside the piston body of FIG. 1 as seen from the right side. [Figure 4] It is a view of a partially cutaway piston showing the powder particles and the dispersion frame accommodated inside the piston body of FIG. 1 as seen from above. [Figure 5] It is an explanatory view schematically showing the positional relationship between a pair of space portions and a pair of dispersion frames of FIG. 1. [Figure 6] It is an explanatory view schematically showing that the dispersion frame of FIG. 1 has a face-centered cubic structure. [Figure 7] It is a flowchart of a method for manufacturing a piston according to an embodiment of the present invention. [Figure 8] It is a flowchart showing a specific procedure of a step of preparing the block of FIG. 7. [Figure 9] It is an explanatory view schematically showing a plurality of blocks formed by the step of preparing the block of FIG. 7. [Figure 10] It is a specific example of a plurality of blocks formed by the step of preparing the block of FIG. 7, and is an explanatory view showing a plurality of blocks before joining for forming cores corresponding to a pair of space portions of FIG. 5. [Figure 11] It is a plan view of a plurality of blocks before joining of FIG. 10. [Figure 12] Figure 10 shows the bottom views of the multiple blocks before they were combined. [Figure 13] This is a view from the right side of the multiple blocks shown in Figure 10 before they were combined. [Figure 14] Figure 10 shows the multiple blocks before they are combined, viewed from the front. [Figure 15] This is a schematic diagram illustrating the core formed by the process of preparing the core shown in Figure 7, and is an explanatory diagram illustrating the core formed using multiple blocks shown in Figure 9. [Figure 16] As a specific example of a core formed by the process of preparing the core shown in Figure 7, Figure 10 shows a core formed by combining multiple blocks, and this is a perspective view of the core corresponding to the pair of spatial parts and distributed frame shown in Figure 5. [Figure 17] This is a view of the core of Figure 16 from the right side. [Figure 18] This is a view of the core of Figure 16 from the front. [Figure 19] This is a cross-sectional view showing the state in which the core is placed inside the mold cavity during the mold clamping process. [Figure 20] This is a cross-sectional view showing the state after the molten metal has solidified, the mold has been opened, and the water, which is the base material of the core, has been vaporized and discharged. [Figure 21] This is a schematic diagram illustrating a modified example of a piston manufactured by the manufacturing method of the present invention, specifically a distributed frame with a body-centered cubic structure composed of four beam members passing through the center and diagonals of a cube. [Modes for carrying out the invention]

[0024] Hereinafter, a method for manufacturing a piston according to an embodiment of the present invention will be described in detail with reference to the drawings.

[0025] In this embodiment, in the following description of the piston 1 and core 100, "up and down direction" is synonymous with the direction of the central axis of the cylinder of the engine (not shown) (cylinder axis direction) and the reciprocating direction of the piston 1, with the combustion chamber side of the engine being "up" and the opposite side (crank chamber side) being "down". "Front and back direction" is the direction parallel to the axis direction of the engine's crankshaft, with one side being "front" and the other "rear". Furthermore, "left and right direction" is the direction perpendicular to both the "up and down direction" and the "front and back direction," with one side being "left" and the other "right". In this case, the left side is the side facing the intake side from the exhaust side of the combustion chamber, so the left side is synonymous with the intake side. Similarly, the right side is the side facing the exhaust side from the intake side, so the right side is synonymous with the exhaust side. This is why "IN" and "EX" are included in parentheses next to "left" and "right" in the diagram.

[0026] [I. Overview of Pistons Manufactured Using This Manufacturing Method] The piston manufactured by the manufacturing method of the present invention is a piston for an internal combustion engine and is a component that reciprocates vertically within the cylinder of the engine. As shown in Figures 1 to 5 below, the piston 1 has a piston body 20 in which a pair of space sections 30 are formed inside, separated in the front-rear direction, powdered material 40 filled in each of the pair of space sections 30, and a dispersion frame 50 formed inside each of the pair of space sections 30. The dispersion frame 50 is a frame-like structure for suppressing the aggregation of the powdered material 40, and has a first beam member 51 extending in the front-rear direction, a second beam member 52 extending in the left-right direction, and a column member 53 extending in the up-down direction. A detailed explanation of the configuration of the piston 1 will be given later.

[0027] [II. Method for manufacturing piston 1] An overview of the manufacturing method of the piston according to this embodiment will be explained with reference to Figure 7.

[0028] As shown in Figure 7, the method for manufacturing a piston comprises the following steps.

[0029] First, as a block preparation step S1, a plurality of blocks 101 to 114 (see Figures 10 to 14) are prepared as components for forming the core 100 (see Figures 16 to 18) that forms a pair of spaces 30 in the piston body 20. Each of the plurality of blocks 101 to 114 has grooves 121 to 123 (see Figures 10 to 14), as described later.

[0030] Next, as the core preparation step S2, the multiple blocks 101 to 114 having the grooves 121 to 123 described above are bonded together to prepare a core 100 having multiple through holes 131 to 133 (see Figures 16 to 19).

[0031] Next, as the mold clamping process S3, the core 100 is placed inside the cavity of the mold (casting mold) and the mold is clamped.

[0032] Next, as the molten metal injection process S4, molten metal made from the piston material is injected into the cavity and the multiple through holes 131 to 133 of the core 100.

[0033] Then, in the molten metal solidification step S5, the molten metal is solidified to form the piston body 20 having a space 30 and the distributed frame 50 (specifically, the first beam member 51, the second beam member 52, and the column member 53).

[0034] After the molten metal has solidified, in the base material discharge step S6, the water, which is the base material, is discharged from the space 30 of the piston body 20.

[0035] Next, we will explain each of the above steps S1 to S6 in more detail.

[0036] (Block preparation process S1) Block preparation step S1 is a step of preparing a plurality of blocks 101 to 114 having grooves 121 to 123 as shown in Figures 10 to 14, as described above. This block preparation step S1 will first be briefly explained using the simplified model shown in Figure 9. In the simplified model in Figure 9, a plurality of (four in Figure 9) blocks B1 to B4 are prepared by solidifying a mixture of base material BS and powder / granule material PW. The four blocks B1 to B4 each have a groove G on the side SD of each block B1 to B4 at the point where these four blocks B1 to B4 abut together. The groove G has a shape that is recessed inward at the side SD of the block.

[0037] In the specific block preparation process S1, multiple blocks 101 to 114 (see Figures 10 to 14) are prepared according to the procedure shown in the flowchart of Figure 8.

[0038] First, in step S21, a liquid (e.g., water) that serves as a fluid base material is mixed with powdered material 40 (granular material such as metal or ceramics).

[0039] Next, in step S22, the mixture of liquid (e.g., water) and powder granules 40 is placed in a mold corresponding to the shape of each of the multiple blocks 101 to 114 and molded into the shape of the multiple blocks 101 to 114.

[0040] Finally, by cooling the mixture to below -40 degrees Celsius and freezing (solidifying) it, several frozen blocks 101 to 114 are completed.

[0041] As shown in Figures 10 to 14, each of the multiple blocks 101 to 114 has a three-dimensional shape having multiple faces and edges at the boundaries of two adjacent faces, and grooves 121 to 123 in which at least one edge is recessed inward of the three-dimensional shape.

[0042] Each of the multiple blocks 101 to 114 is a component or segment having a three-dimensional shape with multiple faces and edges at the boundaries of two adjacent faces, and any shape having multiple faces and edges at the boundaries of two adjacent faces is acceptable. This three-dimensional shape includes various shapes, such as a roughly cubic shape or a roughly rectangular parallelepiped shape.

[0043] In this embodiment, blocks 101 to 114 each have flat surfaces facing other blocks, but the surfaces that constitute the outer surface of the core 100 (i.e., the surfaces that are exposed to the outside of the core 100) are curved, resulting in a three-dimensional shape. This makes it possible to form a core 100 with a complex external shape by combining multiple blocks 101 to 114.

[0044] Furthermore, the three-dimensional shape referred to in the present invention may be a shape in which, in some of the multiple faces constituting the three-dimensional shape, two adjacent faces and the edges of their boundary lie on the same plane. For example, two, four, or six adjacent blocks of the above-mentioned multiple blocks 101 to 114 can be combined, the planes facing other blocks can be combined to make them adjacent on the same plane, and grooves can be formed along the edges of the boundary between two adjacent faces on that same plane.

[0045] Grooves 121 to 123 are formed on the edges of each block at the point where four of the multiple blocks 101 to 114 are joined together. Grooves 121 to 123 have a cross-section that is recessed inward in an arc shape for the multiple blocks 101 to 114. Specifically, grooves 121 to 123 are formed as follows.

[0046] The groove 121 extends in the front-to-back direction to form a pair of front and rear first through holes 131 that extend in the front-to-back direction of the core 100. The groove 121 corresponding to the front first through hole 131 is formed on the side of each block at the abutting joint of the first block set consisting of four blocks 107-110 corresponding to the foremost part of the core 100, and on the side of each block at the abutting joint of the second block set consisting of four blocks 101-104 at the rear of the first block set. The groove 121 corresponding to the rear first through hole 131 is formed on the side of each block at the abutting joint of the third block set consisting of four blocks 111-114 corresponding to the rearmost part of the core 100, and on the side of each block at the abutting joint of the fourth block set consisting of four blocks 101, 102, 105, and 106 adjacent to the front of the third block set.

[0047] The grooves 122 extend in the left-right direction to form a pair of front and rear second through holes 132 that extend in the left-right direction of the core 100. The grooves 122 corresponding to the front second through hole 132 are formed on the sides of each block at the abutting joint of the fifth block set consisting of four blocks 101, 103, 107, and 109 on the front and right side, and on the sides of each block at the abutting joint of the sixth block set consisting of four blocks 102, 104, 108, and 110 on the front and left side. The grooves 122 corresponding to the rear second through hole 132 are formed on the sides of each block at the abutting joint of the seventh block set consisting of four blocks 101, 105, 111, and 113 on the rear and right side, and on the sides of each block at the abutting joint of the eighth block set consisting of four blocks 102, 106, 112, and 114 on the rear and left side.

[0048] The grooves 123 extend vertically to form a pair of front and rear third through holes 133 that extend vertically in the core 100. The grooves 123 corresponding to the front third through hole 133 are formed on the edges of each block at the abutting joint of the ninth block set, consisting of four front and upper blocks 101, 102, 107, and 108, and on the edges of each block at the abutting joint of the tenth block set, consisting of four front and lower blocks 103, 104, 109, and 110. The grooves 123 corresponding to the rear third through hole 133 are formed on the edges of each block at the abutting joint of the eleventh block set, consisting of four rear and upper blocks 101, 102, 111, and 112, and on the edges of each block at the abutting joint of the twelfth block set, consisting of four rear and lower blocks 105, 106, 113, and 114.

[0049] (core preparation process S2) In the core preparation step S2, as explained using the simplified model shown in Figure 9, multiple frozen blocks B1 to B4, each having a groove G, are stacked on top of each other, and the widthwise side edges G1 of the groove G of each of the multiple blocks B1 to B4 are joined together. This forms a through hole H, as shown in the simplified core model in Figure 15, and by bonding the opposing surfaces of the blocks B1 to B4 together, a core is formed that has a through hole H formed by the joining of the grooves G.

[0050] In the specific core preparation step S2, the frozen blocks 101 to 114 having the grooves 121 to 123 shown in Figures 10 to 14 are bonded together to prepare a frozen core 100 having the through holes 131 to 133 shown in Figures 16 to 18.

[0051] Specifically, the core 100 shown in Figures 16-18 comprises a pair of first corresponding portions 136 having an external shape corresponding to a pair of space portions 30 (see Figure 5) of the piston body 20, and a pair of second corresponding portions 37 having an external shape corresponding to a pair of narrow flow channels 31 (see Figure 5) connecting the pair of space portions 30. Note that 135 is a projection for draining moisture contained in the core 100 that has frozen after the mold has been opened. The projection 135 is located midway in the front-to-back direction and on both sides in the left-to-right direction on the lower surface of the core 100.

[0052] Each of the pair of first corresponding portions 136 has a first through hole 131 extending in the front-to-back direction, a second through hole 132 extending in the left-to-right direction, and a third through hole 133 extending in the up-to-down direction.

[0053] The first through-hole 131 is a first beam through-hole and corresponds to the first beam member 51 (see Figure 5) that extends in the front-rear direction of the distributed frame 50.

[0054] The second through-hole 132 is a second beam through-hole and corresponds to a second beam member 52 (see Figure 5) that extends in the left-right direction of the distributed frame 50. The second through-hole 132 is perpendicular to (i.e., intersects at 90 degrees with) the first through-hole 131.

[0055] The third through-hole 133 is a through-hole for a column and corresponds to a column member 53 (see Figure 5) that extends vertically in the distributed frame 50. The third through-hole 133 extends vertically through the intersection of the first through-hole 131 and the second through-hole 132.

[0056] Since water is used as the base material for each of the blocks 101 to 114, it is possible to bond the blocks together by applying water to the opposing surfaces of the blocks.

[0057] The core 100 described above is composed of a mixture of water as a base material and granular material 40. The amount of granular material 40 filling the core 100 is set so that the filling rate of the granular material 40 in the space 30 is 35-50% of the volume of the space 30.

[0058] (Mold clamping process S3) In the mold clamping process S3, the core 100 is placed inside the cavity of a mold (casting mold) that has a cavity corresponding to the outer shape of the piston body 20, and the mold is clamped.

[0059] Specifically, the core 100 prepared as described above is placed in the cavity 220a formed by the combination of segments 221 to 224 that constitute the mold 220, as shown in Figure 19, and the mold 220 is clamped. Here, among the segments 221 to 224 that constitute the mold 220, segment 222 is provided with two recesses 220b into which the two protrusions 135 of the core 100 can be inserted.

[0060] When placing the core 100 inside the cavity 220a, the position and orientation of the core 100 inside the cavity 220a can be defined by inserting the projection 135 of the core 100 into the recess 220b.

[0061] (Molten metal injection process S4) In the molten metal injection process S4, molten metal (molten metal, for example, molten aluminum alloy) made from the piston material is injected into the cavity and the multiple through holes 131 to 133 of the core 100. Specifically, in Figure 19, the molten metal is injected into the cavity 220a from a sprue (not shown) and into the first to third through holes 131 to 133 of the core 100 shown in Figures 16 to 18. At this time, the temperature of the molten metal during injection is approximately 800°C. The molten metal injected into the cavity 220a begins to solidify from the part in contact with the core 100.

[0062] Meanwhile, after the molten metal is poured into the core 100, its temperature gradually rises to around 0°C, and then remains at around 0°C for a short period. After remaining at around 0°C for a short time, the core 100's temperature rises, and the water, which is the base material of the core 100, begins to vaporize.

[0063] (Molten metal solidification process S5) In the molten metal solidification process S5, the molten metal is solidified in the cavity 220a, thereby forming a piston body 20 inside the cavity 220a and a pair of spaces 30 corresponding to the outer shape of the core 100 inside the piston body 20.

[0064] In addition, a distributed frame 50 is formed inside each of the pair of space sections 30 of the core 100, having two beam members 51, 52 and a column member 53 as shown in Figures 1 to 5. Specifically, beam members are formed inside the first through hole 131 and the second through hole 132 of the core 100, extending in a direction that intersects the reciprocating motion direction (vertical direction) of the piston within the space section 30, namely, a first beam member 51 extending in the front-to-back direction and a second beam member 52 extending in the left-to-right direction. Furthermore, a column member 53 extending in the reciprocating motion direction (vertical direction) is formed inside the third through hole 133.

[0065] (Base material discharge process S6) In the base material discharge process S6, after the molten metal solidification process described above, the water, which is the base material constituting the core 100, is discharged in a vaporized state from the space 30 of the piston body 20.

[0066] Specifically, as shown in Figure 20, after a predetermined time has elapsed since the molten metal was poured into the cavity 220a and the molten metal has solidified, the mold 220 is opened. As a result, the water, which is the base material BS that made up the core 100, is vaporized and discharged to the outside from the portion of the projection 135 that is exposed from the piston body 20 (i.e., the part where the molten metal has solidified). The granular material 40, which is the other constituent material of the core 100, remains in the space 30 inside the piston body 20. The diameter or width of the projection 135 is set to a dimension that allows the water to vaporize and be discharged, but also allows the granular material 40 to remain in the space 30.

[0067] In the manufacturing method according to this embodiment, the projection 135 is made to protrude toward the side of the piston head 21 opposite to the top surface, where the skirt portion 26 is provided. However, the projection 135, like the other parts of the core 100, is made of water and will vaporize. After the projection 135 disappears, an opening is formed on the lower surface of the piston head 21 where the projection 135 was located, but this can be sealed by welding or other means when the manufacturing of the piston body 20 is completed.

[0068] [III. Features of the piston manufacturing method of this embodiment] (1) In the manufacturing method of the piston 1 of this embodiment, first, in the block preparation step, a mixture of a fluid base material BS and granular material 40 is solidified to prepare a plurality of blocks 101 to 114 (see Figures 10 to 14) having a three-dimensional shape with multiple faces and edges at the boundaries of two adjacent faces, and grooves 121 to 123 in which at least one edge is recessed inward of the three-dimensional shape. Next, in the core preparation process, multiple blocks 101 to 114 are stacked on top of each other, and the widthwise side edges of the grooves 121 to 123 of each of the multiple blocks 101 to 114 are joined together to form a first through-hole 131 and a second through-hole 132, which are beam through-holes that extend in directions (front-to-back and left-to-right directions in this embodiment) that intersect the reciprocating motion direction of the piston (up and down direction in this embodiment). By bonding the multiple blocks 101 to 114 together, a core 100 having the first through-hole 131 and the second through-hole 132, which are beam through-holes, is prepared (see Figures 16 to 18). Then, in the molten metal injection process, the molten metal flows into the first through-hole 131 and the second through-hole 132, which are beam through-holes of the core 100, together with the cavity 220a (see Figure 19). In the molten metal solidification process, a piston body 20 having a pair of space portions 30 is formed, and a first beam member 51 and a second beam member 52 (see Figure 5) extending in the front-rear and left-right directions are formed inside the space portions 30.

[0069] Subsequently, after solidification and mold opening, the fluid base material BS (see Figure 20), which is one of the constituent materials of the core 100, is discharged from the space 30 of the piston body 20, leaving the other constituent material of the core 100, the powder granules 40, to remain in the space 30 inside the piston. This makes it possible to mass-produce pistons 1 with the powder granules 40 filling the space 30 and equipped with a first beam member 51 and a second beam member 52 as a coagulation suppression structure, using general piston casting techniques.

[0070] As described above, the first beam member 51 and the second beam member 52 extend in directions (front-back and left-right directions) that intersect with the reciprocating direction of the piston (up and down direction), and are therefore capable of functioning as an agglomeration suppression structure. That is, even if the granular material 40 temporarily gathers at the vertical ends of the space 30 during the reciprocating movement of the piston 1, the granular material 40 collides with the first beam member 51 and the second beam member 52 as it moves in the vertical direction, promoting the dispersion of the granular material 40 and changing the direction of movement of the granular material 40. As a result, the first beam member 51 and the second beam member 52 can function as an agglomeration suppression structure that suppresses the agglomeration of the granular material 40. Furthermore, as a result, friction between the granular material 40 is amplified, making it possible to effectively exert the vibration suppression function of the piston.

[0071] (2) In the manufacturing method of the piston 1 of this embodiment, in the core preparation step, a core 100 having two intersecting beam through-holes, the first through-hole 131 and the second through-hole 132, is prepared by combining and bonding a plurality of blocks 101 to 114 together so that two beam through-holes, the first through-hole 131 and the second through-hole 132, are formed so that they intersect each other. Then, in the molten metal solidification step, two intersecting first beam members 51 and second beam members 52 are formed inside the two intersecting beam through-holes, the first through-hole 131 and the second through-hole 132.

[0072] In the above manufacturing method, it becomes possible to simultaneously form two intersecting first beam members 51 and second beam members 52 during the casting of the piston 1, thereby improving the workability of piston manufacturing. Moreover, in the piston 1 manufactured by the above manufacturing method, the two first beam members 51 and second beam members 52 are spread planarly over a wide area of ​​the space 30, so that the granular material 40 can reliably collide with one of the multiple first beam members 51 and second beam members 52 as it moves in the vertical direction, thereby dispersing the granular material 40 and reliably enhancing the damping effect.

[0073] (3) In the manufacturing method of the piston 1 of this embodiment, in the core preparation step, a core 100 having the first through-hole 131 and second through-hole 132, which are beam through-holes, and the third through-hole 133, which is a column through-hole, is prepared by combining and bonding a plurality of blocks 101 to 114 together so as to form the first through-hole 131 and second through-hole 132, which are beam through-holes, and the third through-hole 133, which is a column through-hole.

[0074] In the molten metal injection process, molten metal is injected into the first through-hole 131, second through-hole 132, and third through-hole 133 of the cavity 220a and core 100. In the molten metal solidification process, the first beam member 51 and the second beam member 52 are formed inside the first through-hole 131 and the second through-hole 132, and the column member 53 extending in the vertical direction is formed inside the third through-hole 133.

[0075] In the above manufacturing method, it becomes possible to simultaneously form the first beam member 51 and the second beam member 52, which extend in the front-rear and left-right directions, along with the column member 53, which extends in the vertical direction, during the casting of the piston 1, thereby improving the workability of piston manufacturing. Furthermore, in the piston 1 manufactured by the above manufacturing method, even if the rigidity of the space 30 portion of the piston body 20 is weak, the column member 53, which extends in the vertical direction, supports the inner wall of the space 30 in the vertical direction, thereby reinforcing the space 30 portion of the piston body 20. Therefore, it becomes possible to suppress the aggregation of the powder 40 by the first beam member 51 and the second beam member 52 and to reinforce the piston body 20 by the column member 53.

[0076] (4) In the manufacturing method of the piston 1 of this embodiment, the base material BS constituting the core 100 contains water. In the block preparation step, a mixture of water and granular material 40 is frozen at -40 degrees Celsius or below to prepare a number of blocks 101 to 114.

[0077] In the manufacturing method of the piston 1 described above, the water contained in the base material BS is easily procured, and by adjusting the amount of water, the amount of powder 40 to be filled when mixing the water and powder 40 can be easily adjusted. Furthermore, by freezing the mixture of water and powder 40 at -40 degrees Celsius or below, it is possible to improve the heat resistance of blocks 101 to 114 when they come into contact with high-temperature molten metal. In addition, when preparing the core 100, it is possible to easily bond the blocks together by applying water to the opposing surfaces of two adjacent blocks among blocks 101 to 114.

[0078] (5) In the manufacturing method of the piston 1 of this embodiment, the filling rate of the powder 40 into the space 30 is 35 to 50% as a volume ratio of the volume of the space 30.

[0079] Within the above range, in a piston 1 manufactured by the above manufacturing method, the powder 40 can move smoothly back and forth inside the space 30, and the damping effect of the piston 1 is reliably achieved.

[0080] (modified version) (A) In the manufacturing method of the above embodiment, water is used as the base material, which is one of the constituent materials of the core. However, the present invention is not limited to this, and various materials can be used as the base material as long as they are fluid. Other base materials may include materials containing salt, for example, a mixture of salt and a coagulant. When a base material containing salt is used in this way, after the mold opening process, hot water can be injected into the space 30 of the piston body 20 to discharge the salt from inside the space 30.

[0081] (B) Although the piston 1 manufactured by the manufacturing method of the above embodiment includes a column member 53 in addition to the first beam member 51 and the second beam member 52, forming a column member is not essential in the present invention. The column member may be omitted, and a piston may be manufactured with a configuration consisting only of beam members extending in a direction intersecting the reciprocating direction, for example, a configuration comprising one or both of the first beam member 51 extending in the front-rear direction and the second beam member 52 extending in the left-right direction. Alternatively, a piston may be manufactured with a configuration comprising beam members extending in a direction intersecting the reciprocating direction and inclined with respect to the front-rear direction or the left-right direction. Furthermore, a piston may be manufactured with a configuration in which multiple beam members intersect at numerous intersections in a single space 30, for example, a configuration comprising multiple beam members arranged in a matrix.

[0082] (C) Although the manufacturing method of the above embodiment shows an example where the piston 1 manufactured by the manufacturing method has a reciprocating motion direction that coincides with the vertical direction, the piston's reciprocating motion direction may not coincide with the vertical direction. For example, the reciprocating motion direction may be inclined in the front-to-back or left-to-right direction relative to the vertical direction, or the reciprocating motion direction may coincide with the horizontal direction. In such cases, the effects and advantages of the above embodiment can still be achieved.

[0083] [IV. Detailed description of the configuration of piston 1] Next, the configuration of the piston 1 described above will be explained in more detail. Figures 1 to 5 show the specific structure of the piston 1 manufactured by the manufacturing method of the present invention. Figure 1 is a perspective view, Figures 2 to 4 show the granular material 40 and dispersion frame 50 housed in the space 30 inside the piston 1 after a portion of the piston 1 has been cut out, and Figure 5 is a schematic diagram showing the positional relationship between a pair of space 30 and a pair of dispersion frames 50.

[0084] As described above, the piston 1 comprises a piston body 20, powder / granular material 40 (see Figures 1 to 4), and a dispersion frame 50 (see Figures 1 to 6).

[0085] As shown in Figures 1 and 2, the piston body 20 has a piston head 21 and a pair of skirt portions 26 extending downward from the outer circumference of the piston head 21.

[0086] The piston head 21 is a relatively flat cylindrical member and comprises a crown surface 22 that forms the bottom surface of the engine's combustion chamber and an outer peripheral surface 24 that slides against the side circumferential surface of the engine's cylinder. The crown surface 22 is the surface facing the ceiling surface of the pent-roof type combustion chamber, and its main area, excluding its outer edge, is formed to protrude in a mountain shape to correspond to the said ceiling surface. A cavity 23 that is recessed downward is formed in the crown surface 22. The cavity 23 is a recess for receiving fuel injection from an injector (not shown) located on the ceiling surface of the combustion chamber, and in this embodiment, it is formed in a substantially elliptical shape in plan view.

[0087] Multiple (in this case, three) ring grooves 25 are formed on the outer circumferential surface 24 of the piston head 21, into which piston rings (not shown) are fitted. The piston rings have the function of preventing combustion gases from leaking from the combustion chamber to the crankcase of the engine, and the function of scraping off excess oil adhering to the side surface of the cylinder.

[0088] The pair of skirt portions 26 are positioned such that one is on the left side (intake side) and the other is on the right side (exhaust side). Each skirt portion 26 slides against the side surface of the cylinder, which suppresses oscillating vibrations when the piston 1 reciprocates.

[0089] A pair of front and rear vertical walls 27 are provided on the underside of the piston head 21, between the two skirt portions 26. The front vertical wall 27 is a wall portion that extends in the left-right direction to connect the front ends of the two skirt portions 26, and the rear vertical wall 27 is a wall portion that extends in the left-right direction to connect the rear ends of the two skirt portions 26.

[0090] Each pair of vertical walls 27 has a pin boss portion 28 in its left-right intermediate section. Each pin boss portion 28 is an annular wall portion that defines a pin hole 28a that penetrates in the front-rear direction. A piston pin (not shown), which extends in the front-rear direction, is fixedly inserted into the pin hole 28a to connect the piston body 20 to a connecting rod (not shown). That is, the piston pin is fixed to the piston body 20 in a state that straddles the pair of vertical walls 27 by fitting its front and rear ends into the pin holes 28a of each pin boss portion 28. Furthermore, the small end (upper end) of the connecting rod is externally fitted onto the middle section of the piston pin located between the two pin boss portions 28. In other words, the piston body 20 is connected to the small end of the connecting rod via the piston pin. The small end of the connecting rod is housed in an upwardly recessed receiving recess 29 (see Figure 3) located in the middle section of the pair of pin boss portions 28 in the front-rear direction.

[0091] Inside the piston head 21, specifically, a pair of spaces 30 are formed above each of the pair of pin bosses 28. The pair of spaces 30 are arranged in a front-to-back direction with a receiving recess 29 in between them.

[0092] Each space 30 is formed such that its cross-section along the front-to-back direction (the cross-section cut by a cross-section perpendicular to the left-to-right direction) widens towards the center, as shown in Figures 1 and 2. More specifically, each space 30 has a bottom surface that protrudes downward when viewed in the front-to-back direction, and the amount of this protrusion is largest at the center position in the left-to-right direction of the piston body 20. In other words, each space 30 is formed such that its cross-sectional area (i.e., the cross-sectional area of ​​the cross-section perpendicular to the left-to-right direction shown in Figure 3) widens as it approaches the center O of the pin hole 28a in Figures 1 and 2. Therefore, the cross-sectional area of ​​each space 30 is largest at the position corresponding to the center O of the pin hole 28a (the center in the left-to-right direction). Furthermore, each space 30 is formed such that its width in the front-to-back direction narrows towards the bottom. Also, as shown in Figure 3, the width of each space 30 in the front-to-back direction is set to be largest in the vertical direction at the height of the uppermost ring groove 25 of the three ring grooves 25. Then, the first beam member 51 and the second beam member 52 perpendicular to it are positioned at the height of each space 30.

[0093] In this embodiment, the pair of spaces 30 are connected through a pair of narrow channels 31 that extend in the front-rear direction along the outer circumference of the piston body 20, as shown in Figure 5. Therefore, one large space is formed inside the piston body 20 by the pair of spaces 30 and the pair of channels 31.

[0094] As shown in Figures 1-4, powders 40 and dispersion frames 50 are arranged in each of the spaces 30.

[0095] The granular material 40 is an aggregate of many fine particles. The granular material 40 is packed into the space 30 at a packing rate that allows it to move within the space 30 (i.e., a packing rate that does not completely block the space 30 with the granular material 40).

[0096] If the filling rate of the powder 40 is, for example, 35-50% as a volume ratio of the volume of the space 30 as described above, the powder 40 can smoothly disperse by colliding with the two beam members 51 and 52 of the dispersion frame 50 during reciprocating movement.

[0097] As described above, granular materials such as metals and ceramics are used as the powder or granules 40. More specifically, powders or granules made of inorganic materials such as ceramics or metallic materials that have sufficient heat resistance to withstand the heat generated during piston casting and engine operation are selected. The size and shape of the particles of the powder or granules 40 are appropriately selected to satisfy the conditions that allow the powder or granules 40 to move within the space 30 as the piston 1 reciprocates.

[0098] As shown in Figures 1 to 5, the dispersion frame 50 is positioned inside each space 30 and is configured to disperse the powder 40 as it reciprocates within the space 30 in conjunction with the reciprocating movement of the piston 1.

[0099] As described above, the distributed frame 50 includes a first beam member 51 and a second beam member 52 as at least one beam member extending in a direction intersecting the reciprocating direction (vertical direction) (the front-rear direction and left-right direction shown in Figures 1-6). More specifically, the distributed frame 50 of this embodiment includes a first beam member 51 extending in the front-rear direction, a second beam member 52 extending in the left-right direction, and a column member 53 extending in the reciprocating direction (vertical direction). The first beam member 51 is a cylindrical member extending in the front-rear direction, and both ends thereof are supported by a pair of side walls of the space 30 that face each other in the front-rear direction. The second beam member 52 is a cylindrical member extending in the left-right direction, and both ends thereof are supported by a pair of side walls of the space 30 that face each other in the left-right direction. The column member 53 is a cylindrical member extending in the vertical direction, and both ends thereof are supported by the top wall and bottom wall of the space 30 that face each other in the vertical direction.

[0100] In this embodiment, the first beam member 51 and the second beam member 52 are arranged as multiple beam members such that they intersect (are perpendicular to) each other in a plan view. Note that the first beam member 51 and the second beam member 52 only need to intersect, they do not need to be perpendicular to each other.

[0101] The intersection point 54 where the first beam member 51 and the second beam member 52 intersect is located in a position that coincides with the pin boss portion 28 when viewed from the reciprocating direction (vertical direction), that is, it is above the pin boss portion 28. Specifically, the intersection point 54 is located above the center O of the pin hole 28a of the pin boss portion 28.

[0102] The first beam member 51, which is one of the intersecting beam members 51 and 52, extends along each pin boss portion 28. Specifically, as shown in Figures 1 and 3, the first beam member 51 extends along the center line C (a line extending in the front-rear direction) passing through the center O of the pin hole 28a of the pin boss portion 28.

[0103] The column member 53 extends vertically through the intersection 54 where the first beam member 51 and the second beam member 52 intersect.

[0104] As described above, the distributed frame 50 of this embodiment is a face-centered cubic structure composed of two beam members 51 and 52 that extend orthogonally to each other in a plan view, namely a first beam member 51 extending in the front-to-back direction and a second beam member 52 extending in the left-to-right direction, and a column member 53 that extends vertically through the intersection 54 of the first beam member 51 and the second beam member 52, as shown in Figure 6.

[0105] In this face-centered cubic structure, the first beam member 51, the second beam member 52, and the column member 53 extend so as to connect the centers of opposing planes S11, S12, S21, S22, S31, and S32 that constitute the cube. Specifically, the first beam member 51 extends in the front-to-back direction, connecting the centers of two opposing planes S11 and S12 in the front-to-back direction. The second beam member 52 extends in the left-to-right direction, connecting the centers of two opposing planes S21 and S22 in the left-to-right direction. The column member 53 extends in the up-to-down direction, connecting the centers of two opposing planes S31 and S32 in the up-to-down direction.

[0106] In this embodiment, the first beam member 51, the second beam member 52, and the column member 53 constituting the dispersion frame 50 are cylindrical, so they are highly effective in dispersing the powder 40 when they collide with it, and the beam members are less prone to deterioration and wear. The present invention does not particularly limit the cross-sectional shape of these beam members 51, 52, and column member 53, and any cross-sectional shape (for example, a polygonal cross-sectional shape) is acceptable as long as it is possible to disperse the powder 40.

[0107] If the volume ratio occupied by the distributed frame 50 within the space 30 is 15% or less (preferably 6-6.8%), the damping effect of the piston can be fully exerted by the effective dispersion of the powder 40, even if the number and thickness of the beam members 51, 52 and column members 53 are reduced.

[0108] The first beam member 51, the second beam member 52, and the column member 53 that constitute the distributed frame 50 are integrally formed together with the piston body 20 by casting, as described above.

[0109] (Features of piston 1 above) (1) The piston 1 described above has a configuration in which particulate powder 40 is filled in the space 30 of the piston body 20, and is equipped with a dispersion frame 50 for dispersing the powder 40. The dispersion frame 50 is equipped with at least one beam member (first beam member 51 and second beam member 52) that extends in a direction intersecting the reciprocating direction of the piston 1. Therefore, during the reciprocating movement of the piston 1, even if the powder 40 temporarily accumulates at the end of the space 30 in the reciprocating direction (vertical direction), i.e., at the bottom or top of the space 30, the powder 40 collides with the beam members of the dispersion frame 50 as it moves vertically, promoting the dispersion of the powder 40 and changing the direction of movement of the powder 40. This suppresses the aggregation of the powder 40 and amplifies the friction between the powder 40, so that the vibration suppression function of the piston 1 can be effectively exercised.

[0110] Furthermore, the first beam member 51 and the second beam member 52 support the inner wall of the space 30 of the piston body 20, thereby increasing the strength of the piston body 20. In other words, the distributed frame 50, including the first beam member 51 and the second beam member 52, can be used as a reinforcing member for strengthening the piston body 20.

[0111] (2) In the piston 1 described above, as shown in Figure 4, the first beam member 51 and the second beam member 52 are arranged to intersect each other in a plan view, so that the first beam member 51 and the second beam member 52 are spread out planarly over a wide area of ​​the space 30. Therefore, as the granular material 40 moves in the reciprocating direction (up and down direction), it is possible to reliably collide with either the first beam member 51 or the second beam member 52 and disperse the granular material 40, thereby reliably increasing the damping effect.

[0112] In particular, as shown in Figure 4, even in a large open space 30 in plan view, the first beam member 51 and the second beam member 52 are spread out planarly over a wide area as described above, so the granular material 40 can reliably collide with the first beam member 51 and the second beam member 52 and be dispersed.

[0113] (3) In the piston 1 described above, as shown in Figure 4, the piston body 20 is provided with a pin boss portion 28 into which a piston pin connecting the engine's connecting rod and the piston body 20 is inserted, at a position that overlaps with the space portion 30 when viewed from the reciprocating direction (vertical direction) (i.e., at a position below the space portion 30).

[0114] The intersection point 54 where the first beam member 51 and the second beam member 52 intersect is located in a position that coincides with the pin boss portion 28 when viewed from above, that is, it is above the pin boss portion 28.

[0115] At the position above the pin boss portion 28 in the space 30, the vertical width of the space 30 is widest, and consequently the bottom surface of the space 30 is lowest, making it easy for the powder granules 40 to accumulate. Therefore, in the above configuration, since the intersection point 54 of the beam members is above the pin boss portion 28, it is possible to disperse the powder granules 40 that have accumulated at a position on the bottom surface of the space 30 that overlaps with the pin boss portion 28 when viewed from the vertical direction, by causing them to collide with the first beam member 51 and the second beam member 52, which intersect during reciprocating motion.

[0116] (4) In the piston 1 described above, as shown in Figures 3 and 4, the first beam member 51 of the intersecting first beam member 51 and second beam member 52 extends along the pin boss portion 28. Therefore, it is possible to reliably cause the granular material 40 that has accumulated at a position overlapping with the pin boss portion 28 when viewed from the reciprocating direction (vertical direction) at the bottom surface of the space portion 30 to collide with the first beam member 51 extending along the pin boss portion 28 while moving in the vertical direction, thereby dispersing the granular material 40.

[0117] (5) In the piston 1 described above, the distributed frame 50 further includes column members 53 that extend in the vertical direction, as shown in Figures 1 to 6. The rigidity of the space 30 portion of the piston body 20 is weak, but the column members 53 that extend in the vertical direction support the inner wall of the space 30 in the vertical direction, thereby reinforcing the space 30 portion of the piston body 20.

[0118] Furthermore, since the column member 53 is located above the pin boss portion 28, it is possible to effectively reinforce the portion of the piston body 20 located above the pin boss portion 28. More specifically, at the location above the pin boss portion 28 in the space portion 30, the bottom surface of the space portion 30 is the lowest, and the vertical dimension of the space portion 30 is large, so the rigidity of the piston body 20 at the location above the pin boss portion 28 is relatively weaker than other parts. Therefore, by arranging the column member 53 on the pin boss portion 28 as described above, it becomes possible to effectively reinforce the piston body 20.

[0119] (6) In the piston 1 described above, the distributed frame 50 is a face-centered cubic structure composed of a first beam member 51 and a second beam member 52 that extend orthogonally to each other in a plan view, as shown in Figure 6, and a column member 53 that extends vertically through the intersection 54 of the first beam member 51 and the second beam member 52.

[0120] With this configuration, a high dispersion effect of the powder 40 can be obtained with only three rod-shaped members, namely two beam members (i.e., the first beam member 51 and the second beam member 52) and one column member 53. Moreover, since the first beam member 51, the second beam member 52 and the column member 53 intersect at one point, the strength of the dispersion frame 50 and the piston body 20 supported by it is increased.

[0121] Furthermore, with this configuration, it is possible to obtain a high damping effect while sufficiently reducing the volume ratio occupied by the distributed frame 50 within the space 30.

[0122] (7) In the piston 1 described above, the volume ratio occupied by the dispersion frame 50 within the space 30 is 15% or less (preferably 6-6.8%). Within this range, it is possible to effectively disperse the powder granules 40 while reducing the number and thickness of the beam members of the dispersion frame 50, thereby fully exhibiting the damping effect of the piston.

[0123] (Variation of piston 1) In the above embodiment, a face-centered cubic distributed frame 50 (i.e., a configuration comprising a first beam member 51 extending in the front-rear direction, a second beam member 52 extending in the left-right direction, and a column member 53 extending in the up-down direction) was described as an example of the piston 1, but it is not limited to this. Various configurations can be adopted for the distributed frame as long as it comprises at least one beam member extending in a direction intersecting the reciprocating motion direction.

[0124] As a variation of the distributed frame, for example, as shown in Figure 21, the distributed frame 60 may be a body-centered cubic structure composed of four beam members 61, 62, 63, and 64 that intersect in the reciprocating direction (vertical direction).

[0125] The four beam members 61, 62, 63, and 64 extend along the four diagonals passing through the center BC of the cube, that is, they extend to connect two of the six corners P1 to P8 of the cube. Specifically, the 11th beam member 61 passes through the center BC and connects corners P1 and P8. The 12th beam member 62 passes through the center BC and connects corners P2 and P7. The 13th beam member 63 passes through the center BC and connects corners P3 and P6. The 14th beam member 64 passes through the center BC and connects corners P4 and P5.

[0126] In this body-centered cubic dispersion frame 60, a high dispersion effect of the powder 40 can be obtained with the four beam members 61-64. Moreover, since the four beam members 61-64 intersect at one point, the strength of the dispersion frame 60 and the piston body 20 supported by it is increased.

[0127] Furthermore, with this configuration, it is possible to obtain a high damping effect while sufficiently reducing the volume ratio occupied by the distributed frame 50 within the space 30.

[0128] Furthermore, the face-centered cubic dispersion frame 50 shown in Figure 6 is preferable to the face-centered cubic dispersion frame 50 shown in Figure 6 because it collides with and disperses the powder granules 40 using fewer beam members than the body-centered cubic dispersion frame 60 shown in Figure 21, resulting in a higher damping effect. [Explanation of symbols]

[0129] 1 piston 20 Piston body 30 Space section 40 Powder 50 distributed frames 51 First beam member 52 Second beam member 53 Column members 54 intersection 100 core Blocks 101-114 121~123 Groove 131 First through hole 132 Second through hole 133 Third through hole

Claims

1. A method for manufacturing a piston for an internal combustion engine, wherein a space is formed inside the piston body and the space is filled with powder or granular material, A block preparation step involves solidifying a mixture of a fluid base material and the granular material to prepare a plurality of blocks having a three-dimensional shape with multiple faces and edges at the boundaries of two adjacent faces, and having grooves in which the edges are recessed inward within the three-dimensional shape. A core preparation step is to prepare a core having the beam through-hole by overlapping the plurality of blocks and connecting the widthwise side edges of the grooves of each of the plurality of blocks, thereby forming a beam through-hole extending in a direction intersecting the reciprocating motion direction of the piston, and by bonding the plurality of blocks together, A mold clamping step is performed by placing the core inside a cavity corresponding to the outer shape of the piston body in a casting mold and clamping the mold, A molten metal injection step in which molten metal made of the piston material is injected into the through-hole for the beam in the cavity and the core, A molten metal solidification step in which the molten metal is solidified to form the piston body inside the cavity and the space inside the piston body corresponding to the outer shape of the core, and further, a beam member is formed inside the beam through hole in a direction intersecting the reciprocating direction of the piston inside the space, After the molten metal solidification step, a base material discharge step is performed in which the base material is discharged from the space of the piston body, including, A method for manufacturing a piston, characterized by the following:

2. In the method for manufacturing a piston according to claim 1, In the core preparation step, a core having two beam through-holes that intersect each other is prepared by combining and bonding the plurality of blocks together so that two beam through-holes are formed that intersect each other. In the molten metal solidification process, two beam members intersecting each other are formed inside two beam through-holes that intersect each other. A method for manufacturing a piston, characterized by the following:

3. In the method for manufacturing a piston according to claim 1 or 2, In the core preparation step, a core having the beam through-hole and the column through-hole is prepared by combining and bonding the plurality of blocks together so as to form a column through-hole that extends in the reciprocating direction along with the beam through-hole, In the molten metal injection step, the molten metal is injected into the through-holes for the beam and the through-holes for the column of the cavity and the core. In the molten metal solidification process, the beam member is formed inside the beam through-hole and the column member extending in the reciprocating direction is formed inside the column through-hole. A method for manufacturing a piston, characterized by the following:

4. In the method for manufacturing a piston according to claim 1 or 2, The aforementioned base material contains water, In the block preparation step, the plurality of blocks are prepared by freezing the mixture of water and the powder at -40 degrees Celsius or lower. A method for manufacturing a piston, characterized by the following:

5. In the method for manufacturing a piston according to claim 1 or 2, The filling rate of the granular material into the space is 35 to 50% as a volume ratio of the volume of the space. A method for manufacturing a piston, characterized by the following:

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