WO2020059371A1 - Method for manufacturing piston for internal combustion engine - Google Patents

Abstract

This method for manufacturing a piston has a core arrangement step, a molten metal pouring step, a mold release step, and a lubricating liquid return hole forming step. The core arrangement step involves installing a core, which has a first recessed part, in a predetermined position with respect to a body part-forming casting mold of a casting mold. The lubricating liquid return hole forming step involves forming an oil return hole by drilling in a position that overlaps a first protruding part in the circumferential direction of a first axis line, and is offset from the first protruding part in the first axis line direction.

Description

Method for manufacturing piston of internal combustion engine

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

Conventionally, a piston having a cooling channel for cooling in a piston head is known (Patent Document 1). Further, a piston having a lubricating liquid return hole communicating a ring groove and the inside of the piston in a piston head portion is known (Patent Document 2).

JP 2018-71546 A Patent No.6251850

(4) In a piston having a cooling channel and a lubricating liquid return hole, if the axial dimension is reduced due to a demand for weight reduction, the cooling channel may interfere with the lubricating liquid return hole.

An object of the present invention is to provide a method of manufacturing a piston of an internal combustion engine that can suppress interference between a cooling channel and a lubricant return hole.
A method for manufacturing a piston of an internal combustion engine according to one embodiment of the present invention includes a core disposing step, a pouring step, a releasing step, and a lubricating liquid return hole forming step. In the core disposing step, the core having the first core-concave portion is placed at a predetermined position with respect to the casting mold for forming the main body of the casting mold. In the oil return hole forming step, a drill is formed at a position overlapping with the first cooling channel-projection in the circumferential direction of the first axis and offset from the first cooling channel-projection in the direction of the first axis. A lubrication liquid return hole is formed by processing.

Therefore, in the embodiment of the present invention, interference between the cooling channel and the lubricating liquid return hole can be suppressed.

FIG. 2 is a perspective view of a piston 1 of the engine according to the first embodiment. FIG. 2 is a plan view of the piston 1 according to the first embodiment. FIG. 2 is a bottom view of the piston 1 according to the first embodiment. FIG. 3 is a sectional view taken along line S4-S4 of FIG. 2 in the first embodiment. FIG. 5 is a cross-sectional view taken along line S5-S5 of FIG. 4 in the first embodiment. FIG. 6 is an end view taken along line S6-S6 of FIG. 5 in the first embodiment. FIG. 6 is an end view taken along line S7-S7 of FIG. 5 in the first embodiment. FIG. 2 is a cross-sectional view of the first protrusion 10 according to the first embodiment as viewed from a radial outside of a first axis L1. FIG. 4 is a perspective view of a core 17 after a concave portion forming step in the first embodiment. FIG. 2 is a schematic view of a casting mold 14 according to the first embodiment. FIG. 6 is an end view taken along line S6-S6 of FIG. 5 in a second embodiment.

[Embodiment 1]
First, the configuration of the piston 1 according to the first embodiment will be described.
1 is a perspective view of a piston 1 of an engine (internal combustion engine) according to Embodiment 1, FIG. 2 is a plan view of the piston 1, FIG. 3 is a bottom view of the piston 1, and FIG. 4 is a cross-sectional view taken along line S4-S4 of FIG. FIG. The engine is, for example, a 4-stroke gasoline engine, and is applied to vehicles such as automobiles. The piston 1 is connected to one end of a connecting rod via a piston pin. The other end of the connecting rod is connected to the crankshaft.
The piston 1 is made of an aluminum alloy (for example, Al-Si-based AC8A). The piston 1 has a piston head portion 2, a first skirt portion 3, a second skirt portion 4, a first pin boss portion 5, a second pin boss portion 6, a first pin boss portion 5, and a second pin boss portion 6. The first pin boss 5 has a first piston pin hole 5a, and the second pin boss 6 has a second piston pin hole 6a.

The piston head 2 has a cylindrical portion 7 and a crown plate 8. The cylindrical portion 7 has a cylindrical shape. The cylindrical portion 7 has three ring grooves (a first ring groove 7a, a second ring groove 7b, and a third ring groove 7c) on the outer peripheral side. A piston ring is mounted in each of the ring grooves 7a, 7b, 7c. Here, on a plane passing through the entire circumference of the first ring groove 7a, an axis passing through the center of the first ring groove 7a and perpendicular to the plane is defined as a first axis L1. An axis parallel to the longitudinal direction of the piston pins inserted into the first piston pin hole 5a and the second piston pin hole 6a and orthogonal to the first axis L1 is defined as a second axis L2. Further, an axis orthogonal to both the first axis L1 and the second axis L2 is defined as a third axis L3. The crown plate-shaped portion 8 is provided on one side (combustion chamber side) of the tubular portion 7 in the direction of the first axis L1. The crown plate-shaped portion 8 has four valve recesses (crown-recess) 8a on one of the first axes L1. The valve recess 8a is a recess provided along the shape of the corresponding valve in order to avoid interference between the piston 1 and the intake or exhaust valve, that is, a relief groove for the valve.

The first skirt portion 3 and the second skirt portion 4 are provided on the other side of the cylindrical portion 7 in the direction of the first axis L1, and are separated from each other across the first axis L1 in the direction of the third axis L3. It is arranged.
Each of the first pin boss portion 5 and the second pin boss portion 6 is provided on the other of the crown plate-shaped portion 8 in the direction of the first axis L1, and the first axis L1 in the direction of the second axis L2. Are spaced apart from each other. The inner peripheral surfaces 5b and 6b of the first pin boss portion 5 and the second pin boss portion 6 are used for positioning the piston 1 by abutting a jig (clamp) when drilling an oil return hole 12 described later. Function as a positioning part; The first piston pin hole 5a and the second piston pin hole 6a are circular through holes whose centers are on the second axis L2.

ピ ス ト ン As shown in FIG. 4, the piston head 2 has a cooling channel 9 therein. The cooling channel 9 is a substantially annular space whose center is on the first axis L1 and extends in the circumferential direction of the first axis L1. The cooling channel 9 is located between the first ring groove 7a and the third ring groove 7c in the direction of the first axis L1. The piston head 2 has an inlet (lubricating liquid introduction passage) 9a and an outlet 9b. The inlet 9a and the outlet 9b are passages extending along the direction of the first axis L1, one end of which is connected to the cooling channel 9, and the other end of which is open to the other surface of the crown plate 8. When viewed from the direction of the first axis L1, the inlet 9a and the outlet 9b are arranged at symmetrical points (points on the first axis L1). The inlet 9a faces the injection port of the oil jet nozzle in the direction of the first axis L1. The oil jet is installed in the cylinder block. The oil jet injects oil supplied from the main gallery of the cylinder block toward one of the first axis L1.

FIG. 5 is a sectional view taken along line S5-S5 of FIG.
The piston head portion 2 has two first convex portions (first cooling channel-convex portion) 10 and two second convex portions (second cooling channel-convex portion) 11. The first convex portion 10 and the second convex portion 11 have a convex shape protruding toward the cooling channel 9 (toward one of the first axis L1). The cooling channel 9 has substantially the same cross-sectional area along the cross section passing through the first axis L1 in a region other than the portion where the first cooling channel convex portion 10 and the second convex portion 11 are formed.
The first protrusion 10 and the second protrusion 11 are provided at positions offset from each other in the circumferential direction of the first axis L1. Further, the inlet 9a and the outlet 9b are formed at positions offset from the first protrusion 10 and the second protrusion 11 in the circumferential direction of the first axis L1.

The offset amount Δd1 between the first protrusion 10 and the entrance 9a in the circumferential direction of the first axis L1 is formed to be larger than the diameter of the first protrusion 10. The same applies to the offset amount Δd2 between the first protrusion 10 and the outlet 9b in the circumferential direction of the first axis L1, and Δd2 is formed to be larger than the diameter of the first protrusion 10. Note that Δd1 and Δd2 may be the same.
The two first protrusions 10, 10 are provided at positions symmetrical with respect to each other on a plane perpendicular to the first axis L1, with the point P1 on the first axis L1 being the center of symmetry. That is, the two first convex portions 10, 10 are in a two-fold symmetric relationship. The same applies to the two second convex portions 11, 11, which are in a two-fold symmetry relationship.

6 is an end view taken along line S6-S6 of FIG. 5, and FIG. 7 is an end view taken along line S7-S7 of FIG.
The first convex portion 10 is a cross section passing through the first axis L1 and passing through a point bisecting the first convex portion 10 in the circumferential direction of the first axis L1, that is, a cross section of the piston 1 shown in FIG. In, the boundary between the cooling channel 9 and the cooling channel 9 is inclined with respect to the first axis L1.
The piston head 2 has an oil return hole (lubricating liquid return hole) 12 and an oil introduction hole (lubricating liquid introduction hole) 13. The oil return hole 12 overlaps with the first convex portion 10 in the circumferential direction of the first axis L1, and is offset from the first convex portion 10 in the direction of the first axis L1 (the first convex portion). This is a through-hole formed on the other side than 10). The oil return hole 12 has its longitudinal direction inclined in the same direction as the inclination direction of the first convex portion 10.

The oil introduction hole 13 overlaps with the second convex portion 11 in the circumferential direction of the first axis L1, and is offset from the second convex portion 11 in the direction of the first axis L1 (the second convex portion). It is a hole with a bottom formed on the other side of (11).
The oil return hole 12 and the oil introduction hole 13 overlap the first skirt portion 3 and the second skirt portion 4 in the circumferential direction of the first axis L1.
FIG. 8 is a cross-sectional view of the first protrusion 10 as viewed from the radial outside of the first axis L1. As shown in FIG. 8, the first convex portion 10 is orthogonal to the radial axis of the first axis L1, and overlaps the first convex portion 10 and the oil return hole 12 in the radial direction of the first axis L1. The section has an arc shape with the first center point P2 as the center of the radius of curvature. The oil return hole 12 has a circular shape centered on the first center point P2.

Next, a method for manufacturing the piston 1 will be described.
The manufacturing method includes a core forming step, a core disposing step, a pouring step, a release step, a heat treatment step, and a machining step.
The core forming step is a step of forming a core, and includes a core body portion forming step and a concave part (first core-recess) forming step. The core body forming step includes forming a doughnut-shaped core body (first state of the core body) by molding a powder (eg, sodium chloride, sand, or the like) and extending in the circumferential direction of the first axis L1. ) Is formed.

In the recess forming step, the first recess (first core-recess) 17c, the second recess (second core-recess) 17d, This is a step of forming a pair of engagement holes (core-positioning portions) 17b.
In the first embodiment, a drill is used when forming the first concave portion 17c, the second concave portion 17d, and the pair of engagement holes 17b. Etc. may be used.
FIG. 9 is a perspective view of the core 17 after the recess forming step. The core body 17a has an annular shape extending in the circumferential direction of the first axis L1. The pair of engagement holes 17b are engaged with a pair of support pins 16 to be described later, so that the core 17 with respect to the main body forming mold 15 in the direction of the first axis L1 and the circumferential direction of the first axis L1. Can be installed at a predetermined position. The first concave portion 17c and the second concave portion 17d are provided two by two at predetermined positions in the circumferential direction of the first axis L1 in the core main body portion 17a, and the concave portions opening toward the outside of the core main body portion 17a. It has a shape.

FIG. 10 is a schematic diagram of the casting mold 14.
The casting mold 14 has a casting mold 15 for forming a main body and a pair of support pins (casting mold-positioning portion) 16. The casting die 15 for forming the main body portion has a cavity (internal space) capable of forming the piston head portion 2, the first skirt portion 3, the second skirt portion 4, the first pin boss portion 5, and the second pin boss portion 6 in the pouring step. Has 15a. The molten metal poured from the gate 15b is guided to the cavity 15a through the runner 15c. The pair of support pins 16 are provided inside the cavity 15a, and hold the core 17.
The core disposing step is a step of disposing the core 17 in the casting mold 14, and by engaging a pair of support pins 16 with a pair of engagement holes 17b formed in the core 17, At a predetermined position in the cavity 15a.

The pouring step is a step of pouring the molten metal from the gate 15b into the cavity 15a.
The release step is a step in which the casting die 14 is opened and the piston in the first state is taken out after the molten metal is solidified to form the piston in the first state. The piston in the first state has a cooling channel 9, a first convex portion 10, a second convex portion 11, and a piston-positioning portion (the inner peripheral surfaces 5b, 6b of the first pin boss portion 5 and the second pin boss portion 6). . The cooling channel 9 is an annular space formed by the core body 17a. The first convex portion 10 and the second convex portion 11 have a convex shape formed by the first concave portion 17c and the second concave portion 17d.

The heat treatment step is a step of performing a heat treatment on the piston in the first state after the mold release, and improves the properties of the cast first state piston to adjust it to appropriate strength and hardness.
In the machining step, the piston in the first state after the heat treatment step is machined, and the crown plate-shaped portion 8, the valve recess 8a, the first piston pin hole 5a, the second piston pin hole 6a, each ring groove 7a, 7b, This is a step of forming the outer shape of the piston 1 such as 7c. Further, the inner wall of the hole formed by removing the pair of support pins 16 is processed to form the inlet 9a and the outlet 9b of the cooling channel 9.
The machining step includes an oil return hole forming step. The oil return hole forming step is a step of forming an oil return hole 12 and an oil introduction hole 13 in the cylindrical portion 7 by drilling.

Next, the operation and effect of the first embodiment will be described.
In recent years, with the demand for downsizing turbo engines, pistons having a cooling channel in a cylindrical portion have been increasingly used. By flowing oil through the cooling channel, the rise in piston temperature can be suppressed, and knocking can be suppressed. On the other hand, in order to comply with stricter exhaust regulations year by year and to improve user satisfaction, an oil return hole for reducing oil consumption is indispensable as a specification of a piston. The oil scraped off from the inner wall of the cylinder by the piston ring is returned to the oil pan from the oil return hole, so that the amount of oil entering the combustion chamber can be reduced.

Here, when making the cooling channel and the oil return hole compatible, it is necessary to avoid interference (communication) between them. This is because, when both are communicated, the oil supplied to the cooling channel flows backward through the oil return hole and enters the combustion chamber, so that the consumption of oil increases. Conventionally, in order to solve this problem, the axial size of the cooling channel is shortened and the oil return hole is inclined. However, when the dimension of the cooling channel in the axial direction is shortened, the surface area of the cooling channel is reduced, so that the cooling effect is reduced. In order to reduce the weight of the piston in the future, it is essential to shorten the axial dimension of the piston, and it is expected that the layout will be more severe. Further, when the oil return hole is inclined, the penetration position of the oil return hole inside the piston becomes a portion where the stress is relatively high in the skirt portion.

On the other hand, the method of manufacturing the piston 1 according to the first embodiment includes a core disposing step, a pouring step, a mold releasing step, and an oil return hole forming step. In the core disposing step, the core 17 having the first concave portion 17c is placed at a predetermined position with respect to the casting mold 15 for forming the main body of the casting mold 14. In the piston in the first state obtained after the mold releasing step through the pouring step, the first convex part 10 formed by the first concave part 17c protrudes toward the cooling channel 9. In the oil return hole forming step, oil is returned by drilling to a position that overlaps with the first protrusion 10 in the circumferential direction of the first axis L1 and is offset from the first protrusion 10 in the direction of the first axis L1. A hole 12 is formed. At this time, since the cooling channel 9 has a shape that escapes the oil return hole 12, the cooling channel 9 and the oil return hole 12 are moved in the direction of the first axis L1 while preventing interference between the cooling channel 9 and the oil return hole 12. Can be approached by As a result, the axial dimension of the piston 1 can be shortened, so that fuel efficiency can be improved by weight reduction. A sufficient surface area of the cooling channel 9 can be secured. Furthermore, since it is not necessary to incline the oil return hole 12 greatly, the penetrating position of the oil return hole 12 inside the piston can be laid out at a portion with relatively low stress, and a decrease in strength and productivity can be suppressed.

The method for manufacturing the piston 1 according to the first embodiment includes a core forming step. In the core forming step, a core main body forming step of compacting the powder to form a core main body in a first state (doughnut type), and cutting the core main body in the first state with a drill. Accordingly, a concave portion forming step of forming the first concave portion 17c is provided. Here, if the first recess is formed by molding, a difference in the powder compression ratio between the core body and the first recess occurs due to a difference in thickness between the core body and the first recess. Occurs. This difference in compression ratio causes the core to crack. On the other hand, by cutting the first concave portion 17c with a drill, it is not necessary to form the first concave portion 17c in the core body 17a in the first state. Generation can be suppressed.
The oil return hole 12 has its longitudinal direction inclined in the same direction as the inclination direction of the first convex portion 10. Thereby, a change in the thickness between the two can be suppressed. As a result, the distance between the two can be further reduced, and the size of the piston 1 can be reduced.

The inner peripheral surfaces 5b and 6b of the first pin boss portion 5 and the second pin boss portion 6 function as a piston-positioning portion for positioning the piston 1 by abutting a jig when drilling the oil return hole 12. I do. This eliminates the need to separately provide a portion for positioning the piston 1 on the piston 1, thereby reducing manufacturing costs.
In a section orthogonal to the radial axis of the first axis L1 and overlapping the first convex portion 10 and the oil return hole 12 in the radial direction of the first axis L1, the first convex portion 10 has a first center point. The oil return hole 12 has an arc shape with P2 as the center of the radius of curvature, and the oil return hole 12 has a circular shape with the first center point P2 as the center. That is, by making the center of the radius of curvature of the arc shape of the first convex portion 10 coincide with the center of the circular shape of the oil return hole 12, a change in the thickness between the two can be suppressed.

The cooling channel 9 has substantially the same cross-sectional area in a cross section passing through the first axis L1 in a region other than the portion where the first convex portion 10 is formed. Thereby, in a portion other than the first convex portion 10, a sufficient oil flow path cross-sectional area can be secured, so that the cooling performance of the piston 1 can be improved.
The piston 1 has a second convex portion 11, and the second convex portion 11 has a point P1 on the plane of the first axis L1 as a center of symmetry on a plane perpendicular to the first axis L1, and a first convex portion. It is provided at a position symmetrical to 10, and has a convex shape protruding toward the cooling channel 9. In other words, by providing the biconvex portions 10 and 11 at point-symmetric positions, a structure can be provided regardless of the installation direction of the core 17 for forming the biconvex portions 10 and 11. As a result, the operation of installing the core 17 on the casting die 15 for forming the main body in the core disposing step can be facilitated.

Piston 1 has second convex portion 11 and oil introduction hole 13. The second convex portion 11 is provided at a position offset from the first convex portion 10 in the circumferential direction of the first axis L1, and has a convex shape protruding toward the cooling channel 9. The oil introduction hole 13 is a bottomed hole formed at a position overlapping with the second protrusion 11 in the circumferential direction of the first axis L1 and offset from the second protrusion 11 in the direction of the first axis L1. It is. Thus, by introducing the oil into the oil introduction hole 13 and further introducing the oil into the first skirt portion 3 and the second skirt portion 4, the lubrication performance of both skirt portions 3, 4 can be improved. Thus, not only the penetrated oil return hole 12 but also the bottomed oil introduction hole 13 can be combined with the second convex portion 11 to reduce the size and weight of the piston 1.

The inlet 9a and outlet 9b of the cooling channel 9 and the oil return hole 12 are offset in the circumferential direction of the first axis L1. Here, if the inlet portion 9a and the outlet portion 9b and the oil return hole 12 overlap in the circumferential direction of the first axis L1, the inlet portion 9a or the outlet portion 9b and the oil return hole 12 intersect, The oil injected from the oil jet nozzle may flow backward through the oil return hole 12 to the outer peripheral surface side of the piston 1. Therefore, the above problem can be prevented by offsetting both in the circumferential direction of the first axis L1.
The offset amount Δd1 between the first protrusion 10 and the entrance 9a in the circumferential direction of the first axis L1 is formed to be larger than the diameter of the first protrusion 10. Further, the offset amount Δd2 between the first protrusion 10 and the outlet 9b in the circumferential direction of the first axis L1 is formed to be larger than the diameter of the first protrusion 10. That is, by sufficiently maintaining the distance between the oil return hole 12 and the inlet portion 9a that overlap the first convex portion 10 in the circumferential direction and the distance between the oil return hole 12 and the outlet portion 9b. The thickness between the two can be ensured, and the strength of the piston 1 can be maintained.
The oil return hole 12 overlaps the first skirt 3 and the second skirt 4 in the circumferential direction of the first axis L1. That is, since the first skirt portion 3 and the second skirt portion 4 are thicker in the radial direction than the first pin boss portion 5 and the second pin boss portion 6, the piston in the case where the oil return hole 12 is provided is provided. (1) The influence on the overall strength can be suppressed.

[Embodiment 2]
Since the basic configuration of the second embodiment is the same as that of the first embodiment, only the portions different from the first embodiment will be described.
FIG. 11 is an end view taken along line S6-S6 of FIG. 5 in the second embodiment.
In the second embodiment, the valve recess 8a overlaps with the second convex portion 11 in the circumferential direction of the first axis L1, and is offset from the second convex portion 11 in the direction of the first axis L1 (the second convex portion). The second embodiment is different from the first embodiment in that it is formed on one side (11 side of FIG. 11). Thus, by combining the valve recess 8a with the second convex portion 11, the size and weight of the piston 1 can be reduced.

[Other embodiments]
As described above, the embodiment for carrying out the present invention has been described. However, the specific configuration of the present invention is not limited to the configuration of the embodiment, and there are design changes and the like within a range not departing from the gist of the invention. Are also included in the present invention.
The core body is not limited to an annular shape, and may have at least an arc-shaped portion.
The cooling channel may be a C-shaped space.
In the case where the cooling channel-convex portion is provided in addition to the first cooling channel-convex portion, as long as the cross-sectional area of the cooling channel-excluding the region of the plurality of cooling channel-convex portions is substantially the same. Good.

The technical ideas that can be grasped from the embodiment described above will be described below.
In one aspect of the method for manufacturing a piston of an internal combustion engine, the piston is provided on a piston head, a first skirt, a second skirt, a first pin boss, a second pin boss, and the first pin boss. A first piston pin hole provided, and a second piston pin hole provided in the second pin boss portion, wherein the piston head portion includes a cylindrical portion and a crown plate portion, and the cylindrical portion includes: A first ring groove is provided on the outer peripheral side and has a cylindrical shape, and an axis passing through the center of the first ring groove and perpendicular to the plane is defined as a first line on a plane passing through the entire circumference of the first ring groove. An axis parallel to the longitudinal direction of the piston pin inserted into the first piston pin hole and the second piston pin hole and orthogonal to the first axis is a second axis, and the first axis and the second axis are Axis perpendicular to both axes Is the third axis, the crown plate-shaped portion is provided on one of the cylindrical portions in the direction of the first axis, and each of the first skirt portion and the second skirt portion is The first pin boss portion and the second pin boss portion are provided on the other of the cylindrical portions in the direction of the first axis, and are spaced apart from each other across the first axis in the direction of the third axis. Each of the pin boss portions is provided on the other of the crown plate-shaped portions in the direction of the first axis, and is spaced apart from each other across the first axis in the direction of the second axis. In the manufacturing method, in a core disposing step of disposing a core in a casting die, the casting die includes a casting die for forming a main body portion, and a casting die-positioning portion. Piston head section, the Forming a skirt portion, the second skirt portion, the first pin boss portion, and the second pin boss portion, wherein the casting mold-positioning portion is provided inside the casting mold for forming the main body portion; The core can hold a core, the core includes a core body, a core-positioning part, and a first core-recess, and the core body is arranged in a circumferential direction about the first axis. The core-positioning portion abuts the casting mold-positioning portion so that the core-positioning portion is formed in the direction of the first axis and in the circumferential direction with respect to the first axis. The core can be installed at a predetermined position with respect to a casting mold, and the first core-recess is provided at a predetermined position in a circumferential direction with respect to the first axis of the core body, Concave opening toward the outside of the core body Having a shape, the core disposing step, a pouring step, which is performed after the core disposing step, injects the molten metal into the casting mold, the pouring step, and a demolding step. Then, after the molten metal is solidified to form a piston in a first state, the casting mold is released from the piston in the first state. Forming a lubricating liquid return hole in the piston in the first state by drilling, and forming a piston in a second state, wherein the piston in the first state is provided with a cooling channel and a first channel. A cooling channel-convex portion and a piston-positioning portion, wherein the cooling channel is an arc-shaped space formed by the core body, and the first cooling channel-convex portion is 1 core-by recess The piston-positioning portion is capable of specifying a position for forming the lubricating liquid return hole by abutting on a jig during the drilling, and The lubricating fluid return hole overlaps with the first cooling channel-projection in a circumferential direction about the first axis, and the first cooling channel-projection in the direction of the first axis. Forming the lubricating liquid return hole, which is a through hole formed at the offset position.

In a more preferred aspect, in the above aspect, the method includes a core forming step, wherein the core forming step includes a core body portion forming step in a first state and a first core-recess forming step. In the first core-recess forming step, the first core-recess is formed by cutting the core main body with the drill in the first state.
In another preferred aspect, in any one of the above aspects, the first cooling channel-projection is defined by the first cooling channel-projection passing through the first axis and in a circumferential direction about the first axis. In a cross section passing through the bisecting point, a boundary between the cooling channel and the cooling channel is inclined with respect to the first axis, and the lubricating liquid return hole is formed such that a longitudinal direction of the lubricating liquid return hole is The cooling channel 1 is inclined in the same direction as the inclination direction of the projection.
In still another preferred embodiment, in any one of the above-described embodiments, the piston-positioning portion may be a surface of the first pin boss portion facing the second pin boss portion in the direction of the second axis, or the second pin boss portion. The pin boss is provided on a surface facing the first pin boss.

In still another preferred aspect, in any one of the above aspects, the first cooling channel tunnel-projection and the lubricating fluid are orthogonal to a radial axis with respect to the first axis and radially with respect to the first axis. In a cross section overlapping with the return hole, the first cooling channel-convex portion has an arc shape having a first center point as a center of a radius of curvature, and the lubricating liquid return hole has the first cooling channel-convex portion. It has a circular shape centered on the center point.
In still another preferred aspect, in any one of the above aspects, the cooling channel has a cross-sectional area of a cross section passing through the first axis in a region other than a portion where the first cooling channel-convex portion is formed. It is almost the same.
In yet another preferred aspect, in any of the above aspects, the piston has a second cooling channel-projection, wherein the second cooling channel-projection is a plane perpendicular to the first axis. , A point on the line of the first axis is a center of symmetry, the first cooling channel is provided at a position symmetrical with respect to the convex portion, and has a convex shape protruding toward the cooling channel.

In still another preferred aspect, in any of the above aspects, the piston has a second cooling channel-projection and a lubricating liquid introduction hole, and the second cooling channel-projection includes the first cooling channel-projection. In the circumferential direction about the axis, the first cooling channel is provided at a position offset from the convex portion, has a convex shape protruding toward the cooling channel, and the lubricating liquid introduction hole is provided in the circumferential direction about the first axis. A bottomed hole that overlaps with the second cooling channel-projection in the direction and is formed at a position offset from the second cooling channel-projection in the direction of the first axis.
In yet another preferred aspect, in any of the above aspects, the piston has a second cooling channel-projection and a crown-recess, and the second cooling channel-projection comprises the first cooling channel-projection. In a circumferential direction about the axis, the first cooling channel is provided at a position offset from the convex portion, and has a convex shape protruding toward the cooling channel, and the crown-recess is formed on the crown plate-shaped portion. A second cooling channel in the circumferential direction about the first axis, the second cooling channel in the circumferential direction about the first axis, and the second cooling channel in the direction of the first axis. It is formed at a position offset from the part.

In still another preferred aspect, in any of the above aspects, the piston includes a lubricating liquid introducing passage provided in the piston head portion, and the lubricating liquid introducing passage extends along a direction of the first axis. A passage having one end connected to the cooling channel and the other end being a surface of the piston head portion facing the combustion chamber of the internal combustion engine in the crown plate-shaped portion in the direction of the first axis; The lubricating liquid introduction passage is open toward the opposite side of the crown surface, and is formed at a position offset from the first cooling channel-convex portion in a circumferential direction about the first axis.
In still another preferred aspect, in any of the above aspects, an offset amount between the first cooling channel-convex portion and the lubricating liquid introduction passage in a circumferential direction with respect to the first axis is equal to the first cooling channel-convex portion. Larger than the diameter of.
In still another preferred aspect, in any of the above aspects, the lubricating liquid return hole overlaps the first skirt portion in a circumferential direction about the first axis.

Note that the present invention is not limited to the above-described embodiment, and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described above. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of one embodiment can be added to the configuration of another embodiment. Further, for a part of the configuration of each embodiment, it is possible to add, delete, or replace another configuration.

This application claims the priority based on Japanese Patent Application No. 2018-176822 filed on Sep. 21, 2018. The entire disclosure of Japanese Patent Application No. 2018-176822 filed on September 21, 2018, including the specification, claims, drawings, and abstract, is incorporated herein by reference in its entirety.

1 Piston 2 Piston head 3 First skirt 4 Second skirt 5 First pin boss 5a First piston pin hole 5b Inner peripheral surface (piston-positioning portion) 6 Second pin boss 6a Second piston pin hole 6b Peripheral surface (piston-positioning part) 7 cylindrical part 7a first ring groove 8 crown plate-shaped part 8a valve recess (crown-recess) 9 cooling channel 9a inlet part (lubricating liquid introduction passage) 10 first convex part (first Cooling channel-convex portion) 11 Second convex portion (second cooling channel-convex portion) 12 Oil return hole (lubricant return hole) 13 Oil introduction hole (lubricant introduction hole) 14 Casting die 15 For body formation Casting die 16 Support pin (Casting die-positioning part) 17 Core 17 a 部 Core body part 17 b Engagement hole (core-positioning part) 17 c First recess (first core-recess) L1 first axis L2 2 axis L3 3rd axis

Claims (12)

A method for manufacturing a piston of an internal combustion engine,
The piston includes a piston head, a first skirt, a second skirt, a first pin boss, a second pin boss, a first piston pin hole provided in the first pin boss, and the second pin boss. A second piston pin hole provided,
The piston head portion includes a cylindrical portion and a crown plate portion,
The tubular portion has a tubular shape and includes a first ring groove on an outer peripheral side,
In a plane passing through the entire circumference of the first ring groove, an axis passing through the center of the first ring groove and perpendicular to the plane is defined as a first axis, the first piston pin hole and the second piston pin hole. When an axis parallel to the longitudinal direction of the piston pin inserted into the first axis and orthogonal to the first axis is defined as a second axis, and an axis orthogonal to both the first axis and the second axis is defined as a third axis. , The crown plate-shaped portion is provided on one of the cylindrical portions in the direction of the first axis,
Each of the first skirt portion and the second skirt portion is provided on the other of the cylindrical portions in the direction of the first axis, and is separated from each other across the first axis in the direction of the third axis. It is provided,
Each of the first pin boss portion and the second pin boss portion is provided on the other of the crown plate-shaped portions in the direction of the first axis, and is separated from each other across the first axis in the direction of the second axis. It is provided as
The manufacturing method of the piston includes a core disposing step, a pouring step, a mold releasing step, and a lubricating liquid return hole forming step,
In the core disposing step, a core is disposed in a casting mold,
The casting mold includes a casting mold for forming a body portion, a casting mold-positioning portion,
The casting die for forming the main body portion forms the piston head portion, the first skirt portion, the second skirt portion, the first pin boss portion, and the second pin boss portion,
The casting mold-positioning part is provided inside the body part forming casting mold, and can hold the core,
The core includes a core body, a core-positioning portion, and a first core-recess.
The core body has an arc shape extending in a circumferential direction about the first axis,
The core-positioning portion abuts on the casting mold-positioning portion, so that the core is positioned relative to the main body portion forming casting die in the direction of the first axis and in the circumferential direction with respect to the first axis. Can be installed in place
The first core-recess is provided at a predetermined position in a circumferential direction with respect to the first axis of the core body, and has a concave shape that opens toward the outside of the core body. And
The pouring step is performed after the core disposing step, and is a step of injecting a molten metal into the casting mold.
In the releasing step, after the molten metal solidifies and becomes a piston in a first state, the casting mold is released from the piston in the first state,
The lubricating liquid return hole forming step includes forming a lubricating liquid return hole in the piston in the first state by drilling, and forming a piston in a second state.
The piston in the first state has a cooling channel, a first cooling channel-convex portion, and a piston-positioning portion,
The cooling channel is an arc-shaped space formed by the core body,
The first cooling channel-convex portion has a convex shape formed by the first core-concave portion,
The piston-positioning portion is capable of specifying a position where the lubricating liquid return hole is formed by contacting a jig during the drilling,
The lubricating fluid return hole overlaps with the first cooling channel-projection in a circumferential direction about the first axis, and the first cooling channel-projection in the direction of the first axis. It is a through hole formed at the offset position,
A method for manufacturing a piston of an internal combustion engine. A method for manufacturing a piston of an internal combustion engine according to claim 1,
Including a core forming step,
The core forming step includes a core main body part forming step in a first state and a first core-recess forming step.
The first core-recess forming step is a method for manufacturing a piston of an internal combustion engine in which the first core-recess is formed by cutting a core body portion with a drill in the first state. The method for manufacturing a piston of an internal combustion engine according to claim 2,
The first cooling channel-projection is a cross section passing through the first axis and passing through a point bisecting the first cooling channel-projection in a circumferential direction about the first axis. Is inclined with respect to the first axis,
The method of manufacturing a piston of an internal combustion engine, wherein the lubricating liquid return hole has a longitudinal direction of the lubricating liquid return hole inclined in the same direction as the inclination direction of the first cooling channel-convex portion. The method for manufacturing a piston of an internal combustion engine according to claim 2,
The piston-positioning portion is disposed on a surface of the first pin boss portion facing the second pin boss portion or a surface of the second pin boss portion facing the first pin boss portion in the direction of the second axis. A method for manufacturing a piston of an internal combustion engine provided. The method for manufacturing a piston of an internal combustion engine according to claim 1,
A first cooling channel in a cross section orthogonal to a radial axis with respect to the first axis and overlapping with the first cooling channel tunnel-projection and the lubricating liquid return hole in a radial direction with respect to the first axis; The channel-convex portion has an arc shape having a first center point as a center of a radius of curvature, and the lubricating liquid return hole has a circular shape centered at the first center point. Manufacturing method. The method for manufacturing a piston of an internal combustion engine according to claim 1,
A method of manufacturing a piston of an internal combustion engine, wherein a cross-sectional area of a cross section of the cooling channel passing through the first axis is substantially the same in a region other than a portion where the first cooling channel-convex portion is formed. The method for manufacturing a piston of an internal combustion engine according to claim 1,
The piston has a second cooling channel-convex;
The second cooling channel-convex portion is located on a plane perpendicular to the first axis, with a point on the line of the first axis as the center of symmetry, and symmetrically positioned with respect to the first cooling channel-convex portion. And a method of manufacturing a piston of an internal combustion engine having a convex shape protruding toward the cooling channel. The method for manufacturing a piston of an internal combustion engine according to claim 1,
The piston has a second cooling channel-convex portion, and a lubricating liquid introduction hole,
The second cooling channel-convex portion is provided at a position offset from the first cooling channel-convex portion in a circumferential direction about the first axis, and has a convex shape protruding toward the cooling channel. ,
The lubricating liquid introduction hole overlaps the second cooling channel-projection in the circumferential direction about the first axis, and the second cooling channel-projection in the direction of the first axis. A method of manufacturing a piston of an internal combustion engine, which is a bottomed hole formed at an offset position. The method for manufacturing a piston of an internal combustion engine according to claim 1,
The piston has a second cooling channel-convex and a crown-recess;
The second cooling channel-convex portion is provided at a position offset from the first cooling channel-convex portion in a circumferential direction about the first axis, and has a convex shape protruding toward the cooling channel. ,
The crown-recess is provided in the crown-plate portion, has a concave shape, overlaps with the second cooling channel-projection in a circumferential direction about the first axis, and A method for manufacturing a piston of an internal combustion engine, wherein the piston is formed at a position offset from the second cooling channel-convex portion in a direction of one axis. The method for manufacturing a piston of an internal combustion engine according to claim 1,
The piston includes a lubricating liquid introduction passage provided in the piston head portion,
The lubricating fluid introduction passage is a passage extending along the direction of the first axis, one end of which is connected to the cooling channel, and the other end of the piston head portion in the direction of the first axis of the piston head. The face plate-shaped portion is open toward the opposite side of the crown surface, which is a surface facing the combustion chamber of the internal combustion engine, and the lubricating liquid introduction passage extends in the circumferential direction about the first axis. 1 Cooling channel-A method of manufacturing a piston of an internal combustion engine formed at a position offset from a projection. The method for manufacturing a piston of an internal combustion engine according to claim 10,
A method for manufacturing a piston of an internal combustion engine, wherein an offset amount between the first cooling channel-projection and the lubricating liquid introduction passage in a circumferential direction about the first axis is larger than a diameter of the first cooling channel-projection. The method for manufacturing a piston of an internal combustion engine according to claim 1,
The method of manufacturing a piston of an internal combustion engine, wherein the lubricating liquid return hole overlaps the first skirt portion in a circumferential direction about the first axis.

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