JP2007198228A - Piston for internal combustion engine and device for manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce manufacturing cost and increase degree of freedom in a shape of a recessed part in a piston for an internal combustion engine casted and formed with having the recessed part opening on a crown surface on a crown part. <P>SOLUTION: The recessed part 13 is formed by molds 22, 25 with inclining at least part of a circumference wall 13a of the recessed part 13 to form an under cut shape. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a piston for an internal combustion engine which is cast-molded with a concave portion opened in a crown surface in the crown portion, and an improvement of a manufacturing apparatus for manufacturing the piston.

Patent Document 1 discloses a technique in which a machining process is performed after casting when forming a recess in which at least a part of a side wall has an undercut shape in a crown portion of a piston used in a direct injection internal combustion engine. It has been.
Japanese Patent Laid-Open No. 10-61487

  However, as disclosed in the above-mentioned Patent Document 1, the machining process not only increases the manufacturing cost but also reduces the degree of freedom of the shape of the recess.

  The present invention has been made in view of such circumstances, and is intended for internal combustion engine pistons that can reduce the manufacturing cost and increase the degree of freedom of the shape of the recesses, and the internal combustion engine piston that can appropriately manufacture the piston for the internal combustion engine. It aims at providing the manufacturing apparatus of a piston.

  In order to achieve the above object, an invention according to claim 1 is the piston for an internal combustion engine which is cast-molded with a concave portion opened in the crown surface in the crown portion, and at least a part of the peripheral wall of the concave portion is undercut. The concave portion is formed by a mold so as to be inclined so as to have a shape.

  A second aspect of the invention is an internal combustion engine piston manufacturing apparatus for manufacturing the internal combustion engine piston according to the first aspect, comprising a plurality of molds for forming the recesses, and these molds. Among them, a mold for forming the peripheral wall of the recess is provided with a crown surface forming portion for forming the crown surface.

  According to a third aspect of the present invention, in addition to the configuration of the second aspect of the invention, a peripheral wall forming portion that forms a part of the peripheral wall of the concave portion, a bottom surface forming portion that forms a part of the bottom surface of the concave portion, and A plurality of side molds each having the crown surface forming portion at the lower end portion and divided in the circumferential direction of the concave portion, and the bottom surface forming portion of the side molds cooperate to form the entire bottom surface. A center mold that has a bottom center forming portion at the lower end to form the center of the bottom surface and is disposed at a position surrounded by the side molds and is movable up and down. The side molds can be positioned according to the vertical movement of the mold and can be released from the positioning state of the side molds.

  According to a fourth aspect of the invention, in addition to the configuration of the third aspect of the invention, the inner side surface of each side mold has a positioning contact end wall at the lower end and a slide engagement end wall at the upper end. The center mold is provided with a plurality of protrusions that are movably inserted into the guide recesses of the side molds. Each side mold is positioned and each guide recess is positioned in accordance with the contact of the projection with the positioning contact end wall of each guide recess on a guide ring that is fixedly disposed surrounding the mold. A guide that guides the side molds to slide upward while moving in the diameter-reducing direction as the center mold rises by bringing the protrusions into contact with the sliding engagement end walls. The surface of the peripheral wall of the recess Without even and which are located to be inclined so as to approach the center mold toward the upper and having an inclination angle of the steeper than some of the inclination angle.

  In addition to the configuration of the invention described in claim 4, the invention according to claim 5 is characterized in that the center around the center mold is orthogonal to the axis of the center mold and on the first straight line passing through the axis. The first and second side molds disposed on both sides of the mold and the first and second side molds disposed on both sides of the center mold on a second straight line passing through the axis and orthogonal to the first straight line. The third and fourth side molds that are formed larger than the two side molds are disposed, and the recess forming protrusions that form the valve recesses disposed on the crown surface of the piston are the third and fourth. It protrudes in the said crown surface formation part of the side metal mold | die of this invention, It is characterized by the above-mentioned.

  According to the first aspect of the present invention, since the concave portion in which at least a part of the peripheral wall is inclined so as to have an undercut shape is formed by the mold, the degree of freedom of shape of the concave portion can be increased and the piston can be It is possible to reduce the manufacturing cost by reducing the number of machining steps to be performed. Moreover, the durability of the piston can be improved by forming a surface chill layer formed on the surface of the concave portion when the molten metal touches the cold mold.

  Further, according to the invention of claim 2, by providing the crown surface forming portion on the mold that forms the peripheral wall of the recess among the plurality of molds that form the recess, the number of mold divisions is reduced as much as possible. It is possible to reduce the shape error between the molds and form the concave portion with high accuracy, thereby contributing to improvement in engine performance.

  According to invention of Claim 3, while forming a recessed part with a some side metal mold | die and the center metal mold | die enclosed by those side metal molds, each side metal mold is positioned by the vertical movement of a center metal mold | die. In addition, the mold structure can be simplified by allowing the mold release operation.

  According to the fourth aspect of the present invention, each side mold is positioned by the center mold being lowered and the plurality of protrusions contacting the positioning contact end walls at the lower ends of the guide recesses of the plurality of side molds. The center mold is raised, and the protrusions are brought into contact with the sliding engagement end walls at the upper ends of the guide recesses of the side molds and further raised, so that the side molds move in the diameter reducing direction. Each side mold will be released smoothly and quickly according to the upward movement of the center mold, maintaining the surface accuracy of the recess even if the center mold moving speed is increased. Therefore, it is possible to improve product quality and reduce manufacturing costs.

  Further, according to the fifth aspect of the present invention, the shape accuracy of the valve recess is improved by preventing the valve recess from straddling between adjacent molds even if the valve recess becomes larger corresponding to the increase in the size of the valve of the internal combustion engine. As a result, the engine performance can be improved.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on one embodiment of the present invention shown in the accompanying drawings.

  1 to 6 show an embodiment of the present invention. FIG. 1 is a longitudinal sectional view of a piston for an internal combustion engine, which is a sectional view taken along line 1-1 of FIG. 2, and FIG. 2 is a plan view of the manufacturing apparatus, FIG. 3 is a longitudinal sectional view of the manufacturing apparatus, which is a sectional view taken along line 3-3 in FIG. 4, FIG. 4 is a sectional view taken along line 4-4 in FIG. FIG. 6 is a cross-sectional view corresponding to FIG. 3 for sequentially showing the manufacturing process.

  First, in FIG. 1 and FIG. 2, this piston 11 is cast-molded so as to be used in a direct injection type internal combustion engine, and a recess opening in the crown surface 12 is formed at a substantially central portion of the crown portion 11a. 13, and at least a part of the peripheral wall 13 a of the concave portion 13, in this embodiment, all of the peripheral wall 13 a is inclined so as to have an undercut shape, and the bottom surface 13 b of the concave portion 13 is directed toward the center portion thereof. The recess 13 is formed to have a shallow depth.

  Around the recess 13, the crown portion 11 a is provided with valve recesses 14 and 14 for intake valves slightly recessed from the crown surface 12 and valve recesses 15 and 15 for exhaust valves slightly recessed from the crown surface 12. Each is provided with a pair.

  3 to 5, the manufacturing apparatus for casting the piston 11 forms a lower mold 16 having a protrusion 16 a that forms the inner surface side of the piston 11 and an outer surface of the side wall of the piston 11. The side wall forming hole 18 into which the protrusion 16 is inserted is formed at the lower portion, and an annular step 20 is formed between the upper end of the side wall forming hole 18 so as to have a larger diameter than the side wall forming hole 18. An upper mold 17 having a support hole 19 in the upper portion and disposed on the lower mold 16, and a guide ring inserted and fixed in the support hole 19 with the lower end abutting against the stepped portion 20. 21, surrounded by first to fourth side molds 22, 23, 24, and 25 that are divided into a plurality of, for example, four pieces in the circumferential direction and disposed in the guide ring 21, and the side molds 22 to 25. And a center mold 26 Positioning and said each side mold 22 to 25 in response to vertical movement of the serial center mold 26 configured as a possible release operation from the positioning state of the side molds 22 to 25. Thus, a cavity 27 for casting the piston 11 is formed by the lower mold 16, the upper mold 17, the guide ring 21, the first to fourth side molds 22 to 25, and the center mold 26. The

  The center mold 26 extends vertically and is movable up and down. The center mold 26 is arranged around the center mold 26 on a first straight line L1 passing through the axis C perpendicular to the axis C of the center mold 26. On both sides of the center mold 26 on the first and second side molds 22 and 23 disposed on both sides of the mold 26 and on a second straight line L2 passing through the axis C and orthogonal to the first straight line LI. Third and fourth side molds 24 and 25 that are arranged and formed larger than the first and second side molds 22 and 23 are arranged, and the first and second side molds 22 and 22 are arranged. 23 is formed symmetrically with respect to the axis C of the center mold 26, and the third and fourth side molds 24, 25 are formed symmetrically with respect to the axis C of the center mold 26.

  First and second fitting grooves 28 and 29 for slidably fitting the first and second side molds 22 and 23 to the guide ring 21, and the third and fourth side molds 24. , 25 are slidably fitted, and third and fourth fitting grooves 30, 31 orthogonal to the first and second fitting grooves 28, 29 are opened at both upper and lower ends of the guide ring 21. Thus, it is formed to extend vertically.

  The first and second side molds 22 and 23 include a peripheral wall forming portion 34 that forms a part of the peripheral wall 13a of the concave portion 13, a bottom surface forming portion 36 that forms a part of the bottom surface 13b of the concave portion 13, and Each of the third and fourth side molds 24, 25 has a peripheral wall forming a part of the peripheral wall 13 a of the recess 13. The piston 35 includes a forming portion 35, a bottom surface forming portion 37 for forming a part of the bottom surface 13 b of the concave portion 13, and a crown surface forming portion 39 for forming a part of the crown surface 13 at the lower end portion. 11 is formed in cooperation with the crown surface forming portions 38, 39,... Of the side molds 22 to 25 and a part of the lower surface of the guide ring 21, and the peripheral wall 13a of the recess 13 is The circumference of the first and second side molds 22, 23 Forming portions 34 ..., and it is formed by the third and peripheral wall forming portion 35 ... de cooperation of fourth side mold 24 and 25.

  Moreover, recess-forming projections 41 and 41 that form valve recesses 14 for intake valves arranged on the crown surface 12 of the piston 11 are projected from the crown-surface forming portion 39 of the third side mold 24, and Recess forming projections 42, 42 that form valve recesses 15 for the exhaust valve are projected from the crown surface forming portion 39 of the fourth side mold 25.

  At the lower end of the center mold 26, the entire bottom surface 13b of the recess 13 can be formed in cooperation with the bottom surface forming portions of the first to fourth side molds 22-25. A bottom surface center forming portion 40 that forms the center portion is provided.

  At least the lower part of the center mold 26 has four inclined surfaces 43, 44, 45, 46 individually corresponding to the first to fourth side molds 22 to 25, and is formed in a quadrangular prism shape, The inclined surfaces 43 to 46 are formed so as to move away from the axis of the center mold 26 as they go upward, and at least the lower part of the center mold 26 becomes narrower as it goes downward. The inner side surfaces of the first to fourth side molds 22 to 25 are also formed to be inclined so as to correspond to the inclined surfaces 43 to 46 of the center mold 26.

  On the inner side surfaces of the first and second side molds 22 and 23, guide recesses having a contact end wall 47 for positioning at the lower end and an engaging end wall 49 for sliding at the upper end and extending vertically. 51 are provided, and the inner side surfaces of the third and fourth side molds 24 and 25 have positioning contact end walls 48 at the lower end and slide engagement end walls 50 at the upper end. Thus, guide recesses 52 extending vertically are provided. On the other hand, on the inclined surfaces 43 to 46 of the center mold 26, protrusions 53 are movably inserted into the guide recesses 51, 52, of the first to fourth side molds 22-25. .., But projecting with the same position along the axis of the center mold 26.

  The first guide recesses 51 are horizontally connected to the upper and lower guide groove portions 51a, which are positioned at the upper and lower ends of the positioning end walls 47 and the sliding engagement end walls 49, and the upper ends of the guide groove portions 51a. The second guide recesses 52 are formed with guide groove portions 52a extending in the vertical direction with their upper and lower end positions defined by the positioning end walls 48 and the sliding engagement end walls 50. And guide hole portions 52b extending horizontally through the upper ends of the guide groove portions 52a.

  The guide groove portions 51a, 52a are provided on the inner side surfaces of the first to fourth side molds 22-25 so that the protrusions 53 can be slid up and down, and the guide hole portions 51b, 52b are provided in the first to fourth side molds 22 to 25 so that the protrusions 53 that are in contact with the sliding engagement end walls 49, 50 can be slidably fitted. . Thus, the protrusions 53 are slidably fitted into the guide holes 51b, 52b in a state where the protrusions 53 are in contact with the sliding end walls 49, 50,. The first to fourth slide molds 22 to 25 can be moved to the side close to the axis C of the center mold 26.

  In addition, the first to fourth side molds 22 to 25 are positioned in the lower limit position in contact with the step portion 20 of the upper mold 17 for positioning the first to fourth side molds 22 to 25. The abutting end walls 47, 48, ... are in the same position in the direction along the axis of the center mold 26, whereas the sliding engagement end walls 49, ... of the first and second side molds 22, 23 are The third and fourth side molds 24 and 25 are located below the sliding engagement end walls 50. That is, the guide recesses 52 of the third and fourth side molds 24 and 25 are formed longer than the guide recesses 51 of the first and second side molds 22 and 23.

  Further, in the first and second fitting grooves 28 and 29 in the guide ring 21, the portions facing the outer surfaces of the first and second side molds 22 and 23 are formed with recesses 13 in the crown portion 11 a of the piston 11. The guide surfaces 54 are provided so as to be closer to the center mold 26 toward the upper side while being inclined at a steeper angle than the inclination angle of the peripheral wall 13a, respectively, and the third and fourth fitting grooves 30, 31 are provided. In the portion opposed to the outer surface of the third and fourth side molds 24 and 25, as it goes upward while being inclined at a steeper angle than the inclination angle of the peripheral wall 13 a of the recess 13 in the crown portion 11 a of the piston 11. The guide surfaces 55 are inclined so as to be close to the center mold 26, and the outer surfaces of the side molds 22 to 25 are also in sliding contact with the guide surfaces 54, 55, respectively. Is formed inclined so that.

  In such a manufacturing apparatus, the center mold 26 is moved down so that the protrusions 53 are positioned at the contact end walls 47 for positioning the guide recesses 51... 52 in the first to fourth side molds 22 to 23. , 48..., 48... Are brought into contact with the inclined surfaces 43 to 46 of the center mold 26 and the outer surfaces thereof are guided surfaces 54. As shown in FIG. 3, the lower mold 16, the upper mold 17, the guide ring 21, the first to fourth side molds 22 to 25, and the center mold 26 are positioned. Thus, the cavity 27 is formed, and the piston 11 is cast-molded by pouring molten metal into the cavity 27. At this time, the concave portion 13 of the piston 11 is formed by the peripheral wall forming portions 34, 35, and the bottom surface forming portions 36, 37,..., And the bottom surface center forming portion 40 of the center die 26. Will be.

  After the casting of the piston 11, as shown in FIG. 6 (a), the center mold 26 is first raised, and the protrusions 53 corresponding to the first and second side molds 22, 23 are formed in the first portion. And it is made to contact | abut to the sliding engagement end wall 49 ... of the guide recessed part 51 ... in the 2nd side metal mold | die 22,23, and also raises as shown in FIG.6 (b). Then, an upward force is applied to the first and second side molds 22 and 23, but the guide surfaces 54 are in sliding contact with the outer surfaces of the first and second side molds 22 and 23. Since it inclines so that it may approach the center metal mold | die 26 side as it goes to, the 1st and 2nd side metal mold | dies 22 and 23 are the upper sides, moving the lower end part to the diameter reduction direction, ie, the direction which mutually adjoins. , And the guide surface 54 has a steeper inclination angle than the inclination angle of the peripheral wall 13a of the recess 13, so that the lower end portions of the first and second side molds 22, 23 Moves away from the peripheral wall 13a of the recess 13 of the piston 11 formed in the cavity 27, and moves to the space side generated as the center mold 26 ascends.

  Next, when the center mold 26 is further raised, as shown in FIG. 6C, the protrusions 53 corresponding to the third and fourth side molds 24, 25 become the third and fourth side molds. 24, 25 abuts against the sliding engagement end walls 50 of the guide recesses 52, and an upward force acts on the third and fourth side molds 24, 25 as the center mold 26 rises. To do. Moreover, since the guide surfaces 55 that are in sliding contact with the outer surfaces of the third and fourth side molds 24 and 25 are inclined so as to approach the center mold 26 side as they go upward, the third and fourth The four side molds 24, 25 slide upward while moving their lower end portions in the direction of reduction in diameter, that is, in the direction in which they are close to each other, and the guide surfaces 55 are more inclined than the inclination angle of the peripheral wall 13a of the recess 13. Also, the lower end portions of the third and fourth side molds 24 and 25 are formed from the peripheral wall 13a of the concave portion 13 of the piston 11 formed in the cavity 27. 35... Are moved away from the space generated as the center mold 26 ascends.

  Next, the operation of this embodiment will be described. The crown portion 11a of the piston 11 is provided with a concave portion 13 opened to the crown surface 12, and this concave portion 13 is formed on the peripheral wall 13a when the piston 11 is cast. Is formed by the first to fourth side molds 22 to 25 and the center mold 26 so that at least a part (the front part in this embodiment) is inclined so as to have an undercut shape. The degree of freedom in shape can be increased, and the number of machining steps to be applied to the piston 11 can be reduced to reduce the manufacturing cost. Moreover, the durability of the piston 11 can be improved by forming a surface chill layer on the surface of the recess 13 which is generated when the molten metal touches a cold mold.

  The manufacturing apparatus for manufacturing the piston 11 includes first to fourth side molds 22 to 25 and a center mold 26 that form the recess 13, and the recess 13 of the molds 22 to 26 is included. The first to fourth side molds 22 to 25 that form the peripheral wall 13a are provided with crown surface forming portions 38 to 39 that form the crown surface 12 of the piston 11, so that the number of mold divisions is reduced as much as possible. In addition, it is possible to reduce the shape error between the divided dies and form the concave portion 13 with high accuracy, thereby contributing to improvement in engine performance.

  In addition, the manufacturing apparatus includes peripheral wall forming portions 34, 35,... Forming a part of the peripheral wall 13a of the recess 13, bottom surface forming portions 36, 37,. First to fourth side molds 22 to 25 each having a crown surface forming portion 38... 39 forming a part of the crown surface 12 at the lower end portion and divided in the circumferential direction of the concave portion 13; It is possible to form the entire bottom surface 13b in cooperation with the bottom surface forming portions 38, 39, etc. of the side molds 22 to 25, and to lower the bottom surface center forming portion 40 that forms the central portion of the bottom surface 13b. Each of the side molds according to the vertical movement of the center mold 26. The center mold 26 includes a center mold 26 that is disposed at a position surrounded by the side molds 22 to 25 and is movable up and down. 22-25 positioning and Serial because it is configured as a possible release operation from the positioning state of the side molds 22 to 25, it is possible to simplify the mold structure.

  Further, the inner side surfaces of the side molds 22 to 25 have positioning contact end walls 47..., 48... At the lower end and slide engagement end walls 49. Guide recesses 51, 52, ... are provided, respectively, and a plurality of protrusions 53, which are movably inserted into the guide recesses 51, 52, ... of the side molds 22-25 in the center mold 26, are provided. Are projected on the guide ring 21 that is fixedly disposed surrounding the side molds 22 to 25, and the positioning contact end walls 47, 48, of the guide recesses 51, 52, ... The side molds 22 to 25 are positioned in response to the contact of the protrusions 53, and the protrusions are formed on the sliding engagement end walls 49, 50, of the guide recesses 51, 52,. 53 ... are brought into contact with the center mold 2 Guide surfaces 54... 55 that guide the side molds 22 to 25 so as to slide upward while moving in the direction of diameter reduction in accordance with the rise of at least a part of the peripheral wall 13 a of the recess 13. The inclination angle is steeper than the inclination angle and is inclined so as to be closer to the center mold 26 as it goes upward. The center mold 26 is lowered to form a plurality of protrusions 53. The side molds 22 to 25 are positioned by abutting against the positioning contact end walls 47..., 48... At the lower ends of the guide recesses 51. Is raised and the projections 53 are brought into contact with the slide engagement end walls 49, 50 at the upper ends of the guide recesses 51, 52,. Side gold Since the side molds 22 to 25 are slid upward while moving in the diameter reducing direction, and the side molds 22 to 25 are smoothly and quickly released according to the upward movement of the center mold 26, the center mold Even if the moving speed of the mold 26 is increased, the surface accuracy of the recess 13 can be maintained, so that the quality of the product can be improved and the manufacturing cost can be reduced.

  In addition, the first and second side molds disposed on both sides of the center mold 26 around the center mold 26 on a first straight line L1 passing through the axis perpendicular to the axis C of the center mold 26. From the first and second side molds 22 and 23, the molds 22 and 23 are disposed on both sides of the center mold 26 on the second straight line L2 passing through the axis C and orthogonal to the first straight line L1. The third and fourth side molds 24, 25 that are formed to be larger are arranged, and the recess forming protrusions 41, 42 that form the valve recesses 14, 15, which are arranged on the crown surface 12 of the piston 11. Are projecting from the crown surface forming portions 39 of the third and fourth side molds 24, 25, so that the valve recess 14 corresponds to the increase in the size of the intake and exhaust valves of the internal combustion engine. ..., 15 ... are big Valve recesses 14 ... between adjacent die even, 15 ... is the valve recesses 14 ... not way want extend over, 15 ... increases the shape accuracy of, can contribute to the thus engine performance improvement.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the present invention described in the claims. It is.

  For example, in the said Example, guide recessed part 51 ..., 52 ... provided in the inner surface of the 1st-4th side metal molds 22-25 is made into guide groove part 51a ..., 52a ..., and the upper end of guide groove part 51a, 52a ... The guide holes 51b, 52b, ... are formed to extend horizontally through the first through fourth, but the first to fourth in a state where the projections 53 are in contact with the slide engagement end walls 49, 50, .... As long as the side molds 22 to 25 can be slid to the side close to the axis of the center mold 26, the guide recess may be formed as a groove having no guide hole.

It is a longitudinal cross-sectional view of the piston for internal combustion engines, and is a cross-sectional view taken along line 1-1 of FIG. It is a 2 arrow top view of FIG. It is a longitudinal cross-sectional view of a manufacturing apparatus, Comprising: It is sectional drawing which follows the 3-3 line of FIG. FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. It is a perspective view which shows a part of manufacturing apparatus in the middle of a manufacturing process. It is sectional drawing corresponding to FIG. 3 for showing a manufacturing process one by one.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Piston 11a ... Crown part 12 ... Crown surface 13 ... Recess 13a ... Perimeter wall 13b ... Bottom surface 14, 15 ... Valve recess 22 ... 1st side metal mold 23 ... Second side mold 24 ... Third side mold 25 ... Fourth side mold 26 ... Center molds 34, 35 ... Peripheral wall forming portions 36, 37 ... .. bottom surface forming portions 38, 39... Crown surface forming portion 40... Bottom surface center forming portions 41, 42... Recess forming projections 47, 48.・ Sliding engagement end walls 51 and 52... Guide recess 53... Projections 54 and 55... Guide surface C .. axis L1 of the center mold. 2 straight lines

Claims (5)

  In a piston for an internal combustion engine that has a recess (13) opened in the crown surface (12) in the crown (11a) and is cast, at least a part of the peripheral wall (13a) of the recess (13) is undercut. The piston for an internal combustion engine, wherein the concave portion (13) is formed by a mold (22, 23, 24, 25, 26).   An internal combustion engine piston manufacturing apparatus for manufacturing an internal combustion engine piston according to claim 1, comprising a plurality of molds (22-26) for forming the recesses (13). 22 to 26), the crown surface forming portions (38, 39) for forming the crown surface (12) are provided in the molds (22 to 25) for forming the peripheral wall (13a) of the recess (13). An internal combustion engine piston manufacturing apparatus.   A peripheral wall forming portion (34, 35) for forming a part of the peripheral wall (13a) of the concave portion (13), and a bottom surface forming portion (36, 37) for forming a part of the bottom surface (13b) of the concave portion (13). ) And the crown surface forming portions (38, 39) at the lower end portions, respectively, and a plurality of side molds (22-25) divided in the circumferential direction of the recess (13), and the side molds ( 22 to 25) cooperate with the bottom surface forming portions (36, 37) to form the entire bottom surface (13b) and form a central portion of the bottom surface (13b). And a center mold (26) that is disposed at a position surrounded by the side molds (22 to 25) and that can move up and down, and for moving the center mold (26) up and down. Positioning of each side mold (22-25) according to Wherein each of the side mold Rabbi (22-25) releasing claim 2 production apparatus for an internal combustion engine piston, wherein a is configured operate as enable from positioning of.   The inner side surfaces of the side molds (22 to 25) have positioning contact end walls (47, 48) at the lower end and sliding engagement end walls (49, 50) at the upper end. Guide recesses (51, 52) are provided respectively, and are inserted into the center mold (26) in a movable manner in the guide recesses (51, 52) of the side molds (22-25). A plurality of protrusions (53) are provided to project the guide recesses (51, 52) to a guide ring (21) fixedly arranged surrounding the side molds (22-25). The side molds (22 to 25) are positioned and the slides of the guide recesses (51, 52) according to the contact of the protrusions (53) with the contact end walls (47, 48). The protrusion (53) on the engagement end wall (49, 50) Guide surfaces (54, 55) for guiding the side molds (22 to 25) to slide upward while moving in the diameter-reducing direction as the center mold (26) rises due to contact. ) Is provided so as to have an inclination angle steeper than at least a part of the inclination angle of the peripheral wall (13a) of the recess (13) and to be closer to the center mold (26) toward the upper side. An apparatus for manufacturing a piston for an internal combustion engine according to claim 3.   Around the center mold (26), on both sides of the center mold (26) on a first straight line (L1) passing through the axis perpendicular to the axis (C) of the center mold (26) The first and second side molds (22, 23) and the center mold (26) on the second straight line (L2) passing through the axis (C) and orthogonal to the first straight line (L1). The third and fourth side molds (24, 25) are arranged on both sides of the first and second side molds (22, 23) and are larger than the first and second side molds (22, 23). ) Of the third and fourth side molds (24, 25) are provided on the crown surface (12) of the third and fourth side molds (24, 25). The internal combustion engine according to claim 4, wherein the internal combustion engine projects from the forming portion (39). The piston of the manufacturing apparatus.

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