WO2017150321A1

WO2017150321A1 - Piston of internal combustion engine and method for manufacturing same

Info

Publication number: WO2017150321A1
Application number: PCT/JP2017/006732
Authority: WO
Inventors: 新二忍田; 森　誠治; 守門星野; 良重岩▲崎▼; 恭和栗山
Original assignee: 本田技研工業株式会社
Priority date: 2016-03-02
Filing date: 2017-02-23
Publication date: 2017-09-08

Abstract

This piston (1) of an internal combustion engine is characterized by being provided with: a cooling channel (2) that is formed inside a piston head (6) so as to be annular along the outer periphery of the piston head (6); and a fin (3) that is formed on the inner wall surface of the cooling channel (2) so as to extend in the extending direction of the cooling channel (2), wherein the fin (3) is formed at a position avoiding a part where concentration of stress occurs on the piston head (6) around the cooling channel (2).

Description

Piston for internal combustion engine and method for manufacturing the same

The present invention relates to a piston for an internal combustion engine and a method for manufacturing the same.

2. Description of the Related Art Conventionally, a piston for an automobile engine provided with an annular oil flow passage so as to go around the top is known (for example, see Patent Document 1). This piston is cooled by the oil flowing through the oil flow passage when the engine is driven. Moreover, the oil flow passage of the piston of patent document 1 is exhibiting the substantially rectangular shape by the cross sectional view orthogonal to the rotation direction. Fins are erected on the ceiling surface of the oil flow passage so as to extend along the circumferential direction.
Such a piston is improved in cooling efficiency by increasing the contact area with the cooling oil flowing through the oil flow passage by the fins.

JP 58-101250 A

However, stress is generated in the piston that slides in the cylinder bore when the engine is driven. In particular, the stress generated around the oil flow passage tends to concentrate on the fin formation site. Therefore, the formation site of the fin is more likely to be a starting point for fatigue failure or brittle failure than the site without the fin. Therefore, such a piston is desired to have excellent cooling efficiency at the top and high reliability.

Therefore, an object of the present invention is to provide a piston of an internal combustion engine that has excellent cooling efficiency and high reliability, and a method for manufacturing the same.

The piston of the internal combustion engine of the present invention that solves the above problems includes a cooling channel formed in an annular shape in the piston head along the outer periphery of the piston head, and the cooling channel extending in the extending direction of the cooling channel. And a fin formed on an inner wall surface, wherein the fin is formed at a position avoiding a stress concentration portion of the piston head around the cooling channel.
Further, in the method of manufacturing the piston of the internal combustion engine, the core including at least a portion imitating the shape of the cooling channel is disposed at a predetermined position in a mold having a cavity imitating the shape of the piston, and It has the process of inject | pouring a molten metal in a type | mold.

According to the present invention, it is possible to provide a piston for an internal combustion engine that has excellent cooling efficiency and high reliability, and a method for manufacturing the same.

It is a perspective view of the piston which concerns on embodiment of this invention. FIG. 2 is a longitudinal sectional view of a piston taken along line II-II in FIG. FIG. 3 is a partial perspective view of a piston showing a III-III cross section of FIG. 2. CAE showing a stress distribution on the inner wall surface of the cooling channel of the piston is a (C omputer A ided E ngineering) analysis diagram. It is composition explanatory drawing for demonstrating the one aspect | mode of the piston in which the fin is twisted so that a stress concentration site | part may be avoided. It is composition explanatory drawing of the metal mold | die used for manufacture of a piston. It is process explanatory drawing of the manufacturing method of the piston which uses a composite core, (a) is a partial side view including the cross section of a composite core, (b) is a composite core at the time of injecting a molten metal into a metal mold | die. (C) is a partial side view including a cross section showing a state of a cast-in composite core. It is a graph which shows the modification 1 to the modification 4 of the fin formed in the inner wall face of a cooling channel.

Next, the piston of the internal combustion engine in the embodiment of the present invention will be described.
The main feature of the piston of this embodiment is that fins are formed on the inner wall surface of the cooling channel so as to avoid the stress concentration portion of the piston head around the cooling channel.

The piston in this embodiment is assumed to be used for an automobile engine, and is disposed so as to be capable of reciprocating in a cylinder bore formed by a cylindrical space formed in a cylinder block. Incidentally, the cylinder block in which the piston is disposed includes a cylinder head in which an intake port and an exhaust port are disposed on the upper side, and a crankcase that rotatably supports the crankshaft on the lower side. The piston is attached to the crankshaft via a connecting rod (connecting rod). Oil is supplied to a cooling channel of the piston, which will be described in detail later, from an oil pan disposed below the crankcase via a predetermined path. The piston flowing when the engine is driven is cooled by the oil flowing through the cooling channel. Below, after explaining the whole structure of a piston, it demonstrates in more detail about a cooling channel and the fin formed in this cooling channel.

<Piston overall configuration>
FIG. 1 is a perspective view of the piston 1 of the present embodiment. FIG. 2 is a longitudinal sectional view of the piston 1 taken along the line II-II in FIG. In FIG. 1, the cooling channel 2 and the inlet passage 4 and the outlet passage 5 communicating with the cooling channel 2 are indicated by hidden lines (dotted lines). Further, the vertical direction in the following description is based on the vertical arrow direction shown in FIG. 1 with the cylinder head side of the piston disposed in the cylinder bore as the upward direction and the crankcase side as the downward direction.

As shown in FIG. 1, the piston 1 includes a cylindrical piston head 6, and a sidewall 7 and a skirt 8 that are formed integrally with the piston head 6.
The piston head 6 has an upper surface 9 that defines a combustion space in the cylinder bore (not shown).

A combustion chamber 10 in which the upper surface 9 is partially depressed downward is formed at the center of the upper surface 9. In the following description, the upper surface 9 excluding the location where the combustion chamber 10 is formed may be referred to as the top surface 11.

The first ring groove 12a, the second ring groove 12b, and the third ring groove 12c are formed on the outer peripheral surface of the piston head 6 in order from the top so as to be arranged at a predetermined interval. A top ring (not shown) is attached to the first ring groove 12a. A second ring (not shown) is attached to the second ring groove 12b. An oil ring (not shown) is attached to the third ring groove 12c.

As shown in FIGS. 1 and 2, a pair of sidewalls 7 are arranged so as to face each other below the piston head 6, and are integrally formed with the piston head 6 as described above. Incidentally, FIG. 1 shows the outer surface of one of the opposing side walls 7a, and FIG. 2 shows the inner surface of one of the opposing side walls 7b. ing.

As shown in FIG. 1, a pin boss 14a in which a pin insertion hole 13a is formed is integrally formed in the sidewall 7a. As shown in FIG. 2, a pin boss 14b in which a pin insertion hole 13b is formed is formed integrally with the sidewall 7b. A piston pin (not shown) connected to the connecting rod is inserted through the pin insertion hole 13a (see FIG. 1) and the pin insertion hole 13b (see FIG. 2).

Referring to FIG. 2, a pair of skirts 8a and skirts 8b in this embodiment are arranged so as to face each other below the piston head 6. These

skirts

8a and 8b are disposed so as to connect the pair of

sidewalls

7a and 7b, and are formed integrally with the piston head 6 as described above.

The

skirts

8a and 8b form a slidable contact surface with respect to the inner peripheral surface of the cylinder bore, and have a circular peripheral surface in a cross-sectional view. That is, the pair of

sidewalls

7 a and 7 b and the

skirts

8 a and 8 b facing each other below the piston head 6 have a substantially oval outer shape in a cross-sectional view orthogonal to the central axis of the piston 1.

Further, the

sidewalls

7a and 7b and the

skirts

8a and 8b in the present embodiment are integrally formed, and have a hollow portion 15 on the inner side as shown in FIG.
The hollow portion 15 is opened downward, and the upper portion is closed by the piston head 6. The hollow portion 15 faces the pin insertion hole 13a (see FIG. 1) and the pin insertion hole 13b (see FIG. 2).

In the following description, the pair of

sidewalls

7a and 7b is simply referred to as a sidewall 7 when it is not necessary to distinguish between them. Similarly, in the pair of

skirts

8a and 8b, the pair of

pin insertion holes

13a and 13b, and the pair of

pin bosses

14a and 14b, if it is not necessary to distinguish the pair, the skirt 8 and the pin insertion are simply performed. They are referred to as hole 13 and pin boss 14.
In FIG. 2, reference numeral 10 is a combustion chamber, reference numeral 12a is a first ring groove, reference numeral 12b is a second ring groove, and reference numeral 12c is a third ring groove. Reference numeral 2 is a cooling channel described below, reference numeral 3 is a fin, reference numeral 4 is an inlet passage, and reference numeral 5 is an outlet passage.

<Cooling channel>
FIG. 3 is a partial perspective view of the piston 1 showing a III-III cross section of FIG. In FIG. 3, the fins 3 are indicated by imaginary lines (two-dot chain lines) for convenience of drawing.
As shown in FIG. 3, the cooling channel 2 is formed in the piston head 6. In other words, the cooling channel 2 is formed by partially hollowing the solid portion of the piston head 6.
The cooling channel 2 is formed along the outer periphery of the piston head 6 and has an annular shape inside the outer periphery.
In FIG. 3, reference numeral 4 denotes an inlet passage, and reference numeral 5 denotes an outlet passage. Reference numeral 7 is a side wall, reference numeral 8 is a skirt, reference numeral 14 is a pin boss, and reference numeral 16 is an inner wall surface of the cooling channel 2.

As shown in FIG. 2, the cooling channel 2 is preferably formed above the first ring groove 12a or formed in the vertical direction at the same height as the first ring groove 12a. The cooling channel 2 formed at such a position is more excellent in the cooling efficiency of the piston head 6.

As shown in FIG. 2, the cross-sectional shape of the cooling channel 2 in the present embodiment is substantially rectangular except for the fin 3 described in detail later. However, the cross-sectional shape of the cooling channel 2 is not limited to this, and may be, for example, a polygon other than a rectangle, a circle, or an ellipse.

One end of an inlet passage 4 and an outlet passage 5 is connected to the cooling channel 2. That is, one end side of the inlet passage 4 and the outlet passage 5 is open to the inner wall surface 16 of the cooling channel 2 as shown in FIG.
In addition, as shown in FIG. 3, the one end side of the entrance channel | path 4 and the exit channel | path 5 in this embodiment is avoiding the inner wall surface 16 part of the cooling channel 2 in which the fin 3 mentioned later is formed.
As shown in FIG. 2, each of the inlet passage 4 and the outlet passage 5 extends in the piston head 6 in the vertical direction so that the cooling channel 2 and the hollow portion 15 of the piston 1 communicate with each other.

In the present embodiment, the inlet passage 4 and the outlet passage 5 are formed by removing support pins 31 and 31 (see FIG. 6) disposed in the mold 20 (see FIG. 6) in the manufacturing method of the piston 1 described in detail later. It is formed in the piston head 6 as a mark.

Incidentally, the inlet passage 4 is adapted to receive an oil jet that is continuously or intermittently injected from an oil jet nozzle (not shown) disposed below the cylinder bore (not shown). . The oil jet nozzle is supplied with oil from the oil pan (not shown).
The oil flows through the cooling channel 2 from the inlet passage 4 to cool the piston head 6, and then is discharged to the hollow portion 15 of the piston 1 through the outlet passage 5. The oil discharged to the hollow portion 15 is returned to the oil pan while lubricating the sliding contact portions of the crankshaft (not shown), the connecting rod (not shown) and the like disposed below.

<Fin>
As shown in FIGS. 2 and 3, the piston 1 of the present embodiment has fins 3 formed on the inner wall surface 16 of the cooling channel 2.
As shown in FIG. 2, the fin 3 in the present embodiment is configured by a rib that is erected on the inner wall surface 16 of the cooling channel 2.
The fins 3 in this embodiment are assumed to extend continuously over the entire circumference of the cooling channel 2, but intermittently in the circumferential direction of the cooling channel 2 (in the circumferential direction) as will be described later. It is also acceptable to be formed.
The fin 3 is formed at a position that avoids the stress concentration portion of the piston head 6 around the cooling channel 2.

4, CAE (C omputer A ided E ngineering) analysis showing by extracting only the inner wall surface 16a of the inner wall surface 16 and the outlet passageway 5 of the cooling channel 2 in order to show the stress distribution in the inner wall surface 16 of the cooling channel 2 FIG. FIG. 4 shows the cooling channel 2 and the outlet passage 5 in the half of the piston 1 (the half located on the back side in FIG. 2) cut along the line II-II in FIG.

FIG. 4 (a) is a CAE analysis diagram showing a state in which the cooling channel 2 above the pin boss 14 is viewed obliquely upward from the hollow portion 15 side of the piston 1 shown in FIG. FIG. 4B is a CAE analysis diagram showing a state in which the cooling channel 2 above the pin boss 14 is looked up obliquely upward from below the outer peripheral side of the piston head 6 shown in FIG. FIG. 4C is a CAE analysis diagram showing a state in which the cooling channel 2 above the pin boss 14 is looked down obliquely downward from above the piston head 6 shown in FIG.

4 (a), 4 (b) and 4 (c) show the inside of the cooling channel 2 according to the stress of the piston head 6 (see FIG. 2) around the cooling channel 2 when the engine is driven under a predetermined condition. The stress distribution appearing on the wall surface 16 is expressed stepwise in shades of shade. Specifically, as shown in FIGS. 4 (a), 4 (b) and 4 (c), the area where the stress is 0 MPa or more and the detection limit or less is shown in white, and the shade density is the stress. According to the magnitude | size, it represented in three steps, low-stress area | region A3, medium-stress area | region A2, and high-stress area | region A1.

Of the inner wall surface 16 (see FIG. 2) of the circulating cooling channel 2 (see FIG. 2), in the cooling channel 2 on the pin boss 14 (see FIG. 2), as shown in FIG. A stress concentration site where the low-stress region A3 and the medium-stress region A2 are formed appears in the lower portion of the.

Further, in the cooling channel 2 on the pin boss 14, as shown in FIG. 4B, the low stress region A3 is formed on the inner wall surface 16 formed on the outer peripheral side (

ring grooves

12a, 12b, and 12c side in FIG. 2). The stress concentration part which consists of middle stress area | region A2 and high stress area | region A1 appears.

Further, in the cooling channel 2 on the pin boss 14, as shown in FIG. 4 (c), a low stress region A3, medium stress is formed on the inner wall surface 16 formed on the inner peripheral side (the central axis side of the piston head 6). A stress concentration site consisting of a region A2 and a high stress region A1 appears.
However, in such a cooling channel 2 on the pin boss 14, as shown in FIG. 4C, a conspicuous stress concentration portion does not appear in the upper portion of the inner wall surface 16.

Of the inner wall surface 16 (see FIG. 2) of the circulating cooling channel 2 (see FIG. 2), in the cooling channel 2 on the skirt 8 (see FIG. 2), as shown in FIG. In the upper part of the wall surface 16, a stress concentration site consisting of a low stress region A 3, a medium stress region A 2 and a high stress region A 1 appears.

However, in such a cooling channel 2 on the skirt 8, as shown in FIG. 4A, a conspicuous stress concentration portion appears in the lower portion of the inner wall surface 16 (the inner wall surface 16 on the skirt 8 side). Not.
4 (a), 4 (b) and 4 (c) show the stress distribution in the cooling channel 2 in the half located on the back side of the paper of FIG. 2, but the paper of FIG. Also in the half located on the front side, stress concentration sites appear in a mirror image (line symmetric) positional relationship with respect to the stress concentration sites shown in FIGS.

As described above, the fin 3 in the present embodiment is formed at a position that avoids the stress concentration portion, in other words, is formed on the inner wall surface 16 of the cooling channel 2 where no conspicuous stress concentration portion appears.
Specifically, the fin 3 includes at least an inner wall surface 16 formed on the pin boss 14 side of the cooling channel 2 extending between the top surface 11 of the piston 1 and the pin boss 14, and the top surface 11 of the piston 1 and the pin boss 14. An inner wall surface 16 formed on the outer peripheral side and inner peripheral side of the piston head 6 of the cooling channel 2 extending between them, and an inner surface on the top surface 11 side of the cooling channel 2 extending between the top surface 11 of the piston 1 and the skirt 8. It is formed at a position that avoids the wall surface 16.

And the fin 3 in this embodiment avoids the said stress concentration site | part by twisting around the cooling channel center axis | shaft X2 (refer FIG. 5) at least partially as demonstrated below. In addition, this cooling channel center axis | shaft X2 means the center axis | shaft of the cooling channel 2 prescribed | regulated in the extending direction (circumferential direction) of the cooling channel 2. FIG.

FIG. 5 is a configuration explanatory diagram for explaining an aspect of the piston 1 in which the fins 3 are twisted so as to avoid stress concentration sites. In FIG. 5, the piston 1 is drawn with a virtual line (two-dot chain line). FIG. 5 shows a state in which the fin 3 is twisted by showing a cross section of the cooling channel 2 in a predetermined phase of the cooling channel 2 that goes around the central axis X <b> 1 of the piston 1.

In FIG. 5, the S1-S1 cross section and the S5-S5 cross section indicate the cross section of the cooling channel 2 above the center in the circumferential direction of each skirt 8 (one skirt is not shown). In FIG. 5, the S3-S3 cross section and the S7-S7 cross section show the cross section of the cooling channel 2 above the center of each pin boss 14 (one pin boss is not shown). In FIG. 5, the S2-S2 cross section shows a cross section in the middle of changing from the S1-S1 cross section to the S3-S3 cross section, and shows a cross section at the center in the circumferential direction between S1-S3.

In FIG. 5, section S4-S4 shows a section in the middle of changing from section S3-S3 to section S5-S5, and shows a section at the center in the circumferential direction between S3-S5. In FIG. 5, the S6-S6 cross section shows a cross section in the middle of changing from the S5-S5 cross section to the S7-S7 cross section, and shows a cross section at the center in the circumferential direction between S5-S7. In FIG. 5, the section S8-S8 shows a section in the middle of changing from the section S7-S7 to the section S1-S1, and shows a section at the center in the circumferential direction between S7-S1.

In each of the sectional views of the four cooling channels 2 in FIG. 5, the left side of the drawing shows the outer peripheral side of the piston head 6, and the upper side of the drawing shows the top surface 11 side of the piston 1. Further, the arrows in the respective cross-sectional views of the eight cooling channels 2 indicate directions in which the fins 3 are twisted around the cooling channel central axis X2 when assuming the circulation direction of the cooling channel 2 returning from S1 to S1 through S5. Show. Symbols S1 to S8 appended to the arrow indicate the cross-sectional transition direction. For example, “S1 → S2” indicates a direction in which the fin 3 is twisted from S1 to S2.

As shown in FIG. 5, the fin 3 in the piston 1 of the present embodiment is a high stress region that appears above the inner wall surface 16 (on the top surface 11 side) in the S1-S1 cross section and the S5-S5 cross section on the skirt 8. It is formed on the lower side of the inner wall surface 16 so as to avoid A1 (see FIG. 4C). That is, the fin 3 is formed on the lower side of the inner wall surface 16 where a conspicuous stress concentration site does not appear.

Further, the fin 3 has a medium stress region A2 on the inner wall surface 16 on the pin boss 14 side (see FIG. 4A) and an inner wall surface 16 on the outer peripheral side in the S3-S3 cross section and the S7-S7 cross section on the pin boss 14. Is formed on the inner wall surface 16 on the upper side (the top surface 11 side) so as to avoid the intermediate stress region A2 (see FIG. 4B). That is, the fin 3 is formed on the upper side of the inner wall surface 16 where a conspicuous stress concentration portion does not appear.

Further, the fin 3 shown in the S1-S1 cross section is gradually twisted in the direction of the arrow attached to the S1-S1 cross section as the cooling channel 2 goes around, so that the fin 3 shown in the S2-S2 cross section becomes a position. Then, the fin 3 is gradually twisted in the direction of the arrow added to the S2-S2 cross section, thereby becoming the position of the fin 3 shown in the S3-S3 cross section.

Further, the displacement from the position of the fin 3 shown in the S3-S3 cross section to the position of the fin 3 shown in the S5-S5 cross section, and the position of the fin 3 shown in the S5-S5 cross section to the position of the fin 3 shown in the S7-S7 cross section. The displacement and the displacement from the position of the fin 3 shown in the S7-S7 cross section to the position of the fin 3 shown in the S1-S1 cross section are performed by gradually twisting the fin 3 in the direction of the arrow attached to each cross-sectional view.

Further, as shown in FIG. 5, the twist direction of the fin 3 in this embodiment is reversed at “S3 → S4” in the S3-S3 sectional view and “S7 → S8” in the S7-S7 sectional view. This is because the fin 3 more reliably avoids the stress concentration site.

However, the reversal of the twist direction is not essential, and as described above, the fin 3 is formed at least on the inner wall surface formed on the pin boss 14 side of the cooling channel 2 extending between the top surface 11 of the piston 1 and the pin boss 14. 16, the inner wall surface 16 formed on the outer peripheral side and the inner peripheral side of the piston head 6 of the cooling channel 2 extending between the top surface 11 of the piston 1 and the pin boss 14, and the top surface 11 of the piston 1 and the skirt 8 What is necessary is just to be formed in the position which avoids the inner wall surface 16 by the side of the top surface 11 of the cooling channel 2 extended between.

<Manufacturing method of piston>
Next, the manufacturing method of piston 1 (refer FIG. 1) of this embodiment is demonstrated.
FIG. 6 is a configuration explanatory view of the mold 20 used for manufacturing the piston 1.
As shown in FIG. 6, the mold 20 includes a pair of

side molds

21, 21 that can move in the horizontal direction, an upper mold 22 that is combined with the

side molds

21, 21 from above, and a

side mold

21, 21 from below. The lower mold 23 to be combined and a pair of core pins 24a and 24b disposed at positions corresponding to the

pin insertion holes

13a and 13b of the piston 1 (see FIG. 1) are mainly provided.

A cavity 25 simulating the shape of the inverted piston 1 (piston 1 obtained by reversing the top and bottom of the state shown in FIG. 1) is formed in the closed mold 20.
The

side molds

21 and 21 are formed with runners 26 through which the molten metal flows. The runner 26 communicates with the cavity 25 through a plurality of gates (not shown) formed at predetermined locations around the cavity 25.
A plurality of overflow outlets (not shown) connected to the ceiling surface of the cavity 25 are formed in the upper portions of the

side molds

21 and 21, and these overflow outlets are connected to the overflow reservoir 27. The overflow reservoir 27 is provided with a predetermined degassing device 28.

In FIG. 6, the code | symbol 29 is the salt core arrange | positioned in the position corresponding to the cooling channel 2 (refer FIG. 1).
The salt core 29 is formed to resemble the shape of the annular cooling channel 2 (see FIG. 5), and is disposed in the cavity 25 by a support member (not shown) provided on the lower mold 23.
Incidentally, the salt core 29 shown in FIG. 6 is substantially U-shaped in a cross-sectional view in which a portion corresponding to the fin 3 (see FIG. 5) is missing, but a third core that will be described in detail later as a modified example. The composite core 33 (see FIG. 7A) can be used.

The upper mold 22 is provided with a pair of support pins 31 and 31 penetrating the upper mold 22 in the vertical direction. These support pins 31, 31 are movable in the vertical direction with respect to the upper mold 22.
These support pins 31, 31 are disposed at positions where the tip ends in the cavity 25 penetrating the upper mold 22 correspond to the inlet passage 4 (see FIG. 2) and the outlet passage 5 (see FIG. 2), respectively. ing. Each of the tips of the support pins 31, 31 is in contact with the salt core 29 in the cavity 25.
In FIG. 6, reference numeral 32 denotes a piston that pressurizes the molten metal in the cavity 25.

In the manufacturing method of the piston 1 of this embodiment, first, the salt core 29 simulating the shape of the cooling channel 2 (see FIG. 5) is formed.
The salt core 29 is formed of a material containing salt as a main component.
Examples of the salt include sodium chloride, potassium chloride, calcium chloride, magnesium chloride, barium chloride and the like.
In addition, the material of the salt core 29 can include aggregates (for example, artificial sand and natural sand), hard powder (for example, ceramic powder) and the like as necessary.
Moreover, a commercial item can also be used as a material of the salt core 29 in this embodiment.

Next, in this manufacturing method, the salt core 29 is disposed at a predetermined position of the mold 20. Thereafter, molten metal is poured into the mold 20, and the salt core 29 is cast in the cavity 25.
Then, after the molten metal in the mold 20 is cooled, the mold is opened and the piston base material (not shown) in the mold 20 is taken out. At this time,

pin insertion holes

13a and 13b (see FIGS. 1 and 2) are formed in the trace where the core pins 24a and 24b are extracted from the piston base material. Further, an inlet passage 4 and an outlet passage 5 shown in FIG. 2 are formed at the trace where the support pins 31 are extracted from the piston base material.

Further, the salt core 29 remaining in the piston base material is taken out by water washing or air blow through traces of the support pins 31 and 31 (corresponding to the inlet passage 4 and the outlet passage 5 in FIG. 2). As a result, the cooling channel 2 (see FIG. 5) is formed on the piston base material as a trace of the salt core 29 being taken out. Thereafter, finishing processing is performed on the piston base material by cutting, polishing, etc., and a series of manufacturing steps of the piston 1 is completed.
In addition, although the manufacturing method in this embodiment has demonstrated what uses the said metal mold | die 20, a casting mold is not limited to the metal mold | die 20, Moreover, as mentioned later, this casting method is used. It is not limited.

Next, a method for manufacturing the piston 1 using the composite core 33 (see FIG. 7) according to the modification will be described. This manufacturing method is configured in the same manner as the manufacturing method described above except that a complex core 33 described below is used instead of the salt core 29 (see FIG. 6).
FIG. 7 is a process explanatory view of the manufacturing method of the piston 1 using the composite core 33, (a) is a partial side view including a cross section of the composite core 33, and (b) shows the molten metal 34 in the mold 20. FIG. 6 is a partial side view including a cross-section showing a state of the composite core 33 when injected into (see FIG. 6), and FIG. 6C is a partial side view including a cross-section showing a state of the cast-in composite core 33. . In addition, the partial side view of the composite core 33 of FIG. 7 is drawn on the basis of the composite core 33 arranged in the mold 20 like the salt core 29 shown in FIG.

As shown in FIG. 7A, the composite core 33 used in this manufacturing method imitates the first core 33 a simulating the shape of the fin 3 (see FIG. 5) and the cooling channel 2. It is comprised with the 2nd core 33b.
The second core 33b is formed of the same shape and material as the salt core 29 (see FIG. 6).

The first core 33a is disposed substantially inside the U shape in a cross-sectional view of the second core 33b. That is, as shown in FIG. 5, the first core 33a is formed on the peripheral surface of the annular second core 33b in the same manner as the fin 3 formed to be twisted in the annular cooling channel 2. It is formed so as to be twisted in the circumferential direction of the child 33b.
The first core 33 a is removed from the second core by the heat of the molten metal 34 injected into the mold 20.

Examples of the material (core material) of the first core 33a include a material that contacts the molten metal 34 in the mold 20 and melts or vaporizes.
As a specific material of the first core 33a, for example, the main component is wax, specifically, an ester of a higher fatty acid and a monohydric or dihydric higher alcohol (for example, myricyl cellotate, myricyl alcohol, Oleic acid, cetyl alcohol and the like), but are not limited thereto.

Next, in this manufacturing method, the composite core 33 is disposed in the mold 20, and the molten metal 34 is injected into the mold 20.
Thereby, the composite core 33 comes into contact with the molten metal 34 as shown in FIG. The first core 33 a is removed from the second core 33 b by the molten metal 34, while being replaced with the molten metal 34.
Thereby, the second core 33 b having the same shape as the salt core 29 (see FIG. 6) is cast by the molten metal 34.
When the molten metal 34 is cooled, the fins 3 (see FIG. 5) are formed inside the substantially U-shape of the second core 33b having the same shape as the salt core 29.

Thereafter, the mold is opened by cooling, and the second core 33b is removed in the same manner as the salt core 29, and the cooling channel 2 is formed. Thereafter, the piston base material is finished by cutting, polishing, etc., and the series of manufacturing steps of the piston 1 is completed.

The piston 1 of this embodiment can form the fins 3 twisted in the cooling channel 2 by a manufacturing method as described above, but is not limited to this manufacturing method. Although not shown in the drawings as another manufacturing method, the first core 33a is not lost by the molten metal 34 as described above, but the first core 33a is removed before the molten metal 34 is injected, and then the gold is removed. The molten metal 34 can also be poured into the mold 20. Further, a core formed by a 3D plotter (3D printer) can be disposed in the mold 30. It can also be manufactured by a stacking method using a 3D plotter (3D printer) using three-dimensional data based on the shape of the piston 1. According to this manufacturing method, the core can be omitted.

Next, the effect which the piston 1 of this embodiment and the manufacturing method show are demonstrated.
In the conventional piston (for example, refer to Patent Document 1), as described above, fins are provided over the entire circumference of the ceiling surface of the annular cooling channel in order to improve the cooling efficiency of the piston. However, when the fins are provided over the entire circumference of the ceiling surface of the annular cooling channel, as described above, at least a part of the fins is always formed at the stress concentration portion. Further, not only the above-described ceiling surface, but also when fins are formed over the entire circumference of the inner wall surface on the lower side of the cooling channel or over the entire circumference of the inner wall surface on the outer periphery side of the cooling channel, At least a portion is always formed at the stress concentration site. And if a fin is formed in a stress concentration part, it will be easier to form a starting point, such as fatigue fracture and brittle fracture, than a part which does not have a fin. Therefore, a thing more reliable than the conventional piston is desired.

On the other hand, the fins 3 in the piston 1 of the present embodiment are formed on the inner wall surface 16 of the cooling channel 2 so as to avoid stress concentration sites. Therefore, the piston 1 according to the present embodiment is less reliable than the conventional piston, and has a high reliability because it is difficult to form starting points such as fatigue fracture and brittle fracture.

Further, the piston 1 of the present embodiment includes an inner wall surface 16 (see FIG. 4A) formed on the pin boss 14 side which is a stress concentration portion, and an inner wall surface on the top surface 11 side on the skirt 8. 16 (see FIG. 4B), and the fin 3 is formed so as to avoid the inner wall surface 16 (see FIG. 4C) formed on the outer peripheral side of the piston head 6 on the pin boss 14. Yes.
Therefore, the piston 1 of the present embodiment is more reliable because it is harder to form a starting point such as fatigue fracture or brittle fracture more reliably.

In addition, the piston 1 of the present embodiment avoids a stress concentration site by the fin 3 being twisted around the cooling channel central axis X2 (see FIG. 5). This allows the fins 3 to extend so as to avoid stress concentration sites without disturbing the oil flow in the cooling channel 2.

Also, the fin 3 twisted in the cooling channel 2 has a longer length in the cooling channel 2 than a fin that is not twisted. That is, the piston 1 of the present embodiment having the fin 3 that is twisted further improves the cooling performance by increasing the heat transfer area of the fin 5 in the cooling channel 2 as compared with the piston having the fin that is not twisted. To do.

Also, in the piston 1 of the present embodiment, the fin 3 is twisted, so that the oil flowing along the fin 3 has a longer flow stroke than the oil flowing along the fin not twisted. Therefore, the oil flow rate in the cooling channel 2 is increased, and the oil flow easily forms a turbulent state. The heat exchange efficiency between the fins 3 and the oil is further improved.

Also, the manufacturing method of the piston 1 of the present embodiment employs a casting method using a salt core 29 having a recess (substantially U-shaped inner space) corresponding to the fin 3 to be twisted. As a result, the twisted fins 3 can be easily formed, which is extremely difficult in the manufacturing method by cutting.

Further, in the manufacturing method using the composite core 33 (third core), the first core 33a is disposed in the recess (substantially U-shaped inner space) of the second core 33b corresponding to the salt core 29. Since they are arranged, the shape retention when handling the composite core 33 (third core) becomes better.

In the manufacturing method using the composite core 33 (third core), the first core 33 a of the composite core 33 (third core) is removed from the second core 33 b by the heat of the molten metal 34. It is made of the material to be. As described above, the fin 3 is formed by the molten metal that has entered the removal trace of the first core 33a.

On the other hand, the salt core 29 is formed by a molten metal that has entered a recess (substantially U-shaped inner space) formed in the salt core 29 in advance. By the way, the salt core 29 is formed by filling the above-mentioned material in a mold (not shown) simulating the cooling channel 2 in which the fins 3 are formed. Therefore, the depression (substantially U-shaped inner space) of the salt core 29 corresponding to the fin 3 is limited to a shape that can be punched (a shape having a punching taper). Thereby, the shape of the fin 3 is also restricted.

On the other hand, in the manufacturing method using the composite core 33 (third core), since the first core 33a is removed by the heat of the molten metal 34, the shape of the fin 3 is limited to a shape that can be punched. It is never done. Therefore, the design freedom of the shape of the fin 3 is further improved, and the fin 3 having a larger surface area (heat transfer area) can be formed.

As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, It can implement with a various form. In the following other embodiments, the same components as those in the above-described embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.
In the above embodiment, as shown in FIG. 5, the fin 3 at the position shown in the S1-S1 cross-sectional view is gently twisted so as to be the position of each fin 3 from the S2-S2 cross-sectional view to the S8-S8 cross-sectional view. In addition, the piston 1 that has been twisted and returned to the position of the fin 3 shown in the S1-S1 cross-sectional view has been described. However, the piston 1 of the present invention is not limited to this as long as the fin 3 is formed at a position avoiding the stress concentration site.

FIG. 8 is a chart showing modifications 1 to 4 of the fin 3 formed on the inner wall surface of the cooling channel 2. In FIG. 8, the S1-S1 cross section, the S2-S2 cross section, and the S3-S3 cross section respectively correspond to the S1-S1 cross section, the S2-S2 cross section, and the S3-S3 cross section in FIG. That is, the S1-S1 cross section represents the cross section of the cooling channel 2 on the skirt 8. The S3-S3 cross section represents a cross section of the cooling channel 2 on the pin boss 14. The S2-S2 cross section represents a cross section of the cooling channel 2 at the S2 position which is an intermediate position between S1 and S3. In each of the drawings from Modification 1 to Modification 4 of FIG. 8, the left side of the drawing shows the outer peripheral side of the piston head 6, the right side of the drawing shows the inner diameter side of the piston head 6, and the upper side of the drawing shows the piston. 1 shows the top surface 11 side.

As shown in the S1-S1 cross section in Modification 1 to Modification 4 in FIG. 8, the fins 3 in the cooling channel 2 on the skirt 8 are on the top surface of the cooling channel 2 where stress concentration points appear (see FIG. 4B). The fins 3 are formed so as to avoid the above. That is, in the first and second modifications, the fin 3 is formed on the inner wall surface 16 on the inner peripheral side of the cooling channel 2. In the third modification and the fourth modification, the fins 3 are formed on the inner wall surface 16 on the outer peripheral side of the cooling channel 2.

As shown in the S3-S3 cross section in Modification 1 to Modification 4 in FIG. 8, the fin 3 in the cooling channel 2 on the pin boss 14 is connected to the inner wall surface 16 on the lower side of the cooling channel 2 where the stress concentration portion appears, and the cooling. The fins 3 are formed so as to avoid the outer peripheral side and inner peripheral wall surface 16 of the channel 2. That is, in Modification 1 to Modification 4, the fin 3 is formed on the inner wall surface 16 on the upper side of the cooling channel 2.

In the first modification, the fin 3 is twisted counterclockwise (counterclockwise) from the S1 position, and the fin 3 is formed on the inner wall surface 16 on the upper side of the cooling channel 2 at the S2 position. . Further, in the first modification, the fin 3 extends as it is without being twisted from the S2 position to the S3 position.

In the second modification, the fin 3 extends without being twisted from the S1 position to the S2 position. Further, from the S2 position to the S3 position, the fin 3 is twisted counterclockwise (counterclockwise) and formed on the upper inner wall surface 16.

In Modification 3, from the S1 position to the S2 position, the fin 3 is twisted clockwise (clockwise) and formed on the upper inner wall surface 16. Further, the fin 3 extends without being twisted from the S2 position to the S3 position.

In the modified example 4, the fin 3 extends without being twisted from the S1 position to the S2 position. Further, from the S2 position to the S3 position, the fin 3 is twisted clockwise (clockwise) and formed on the inner wall surface 16 on the inner diameter side.

In the above embodiment, the fins 3 are continuously formed over the entire circumference of the cooling channel 2, but the present invention allows the fins 3 to be formed intermittently. That is, the fin 3 in the piston 1 of the present invention may be either continuous or discontinuous as long as it is formed at a position that avoids the stress concentration portion over the entire circumference of the cooling channel 2.

In the embodiment, the fins 3 extending in the circumferential direction of the cooling channel 2 in one row are assumed, but a plurality of rows of fins 3 may be used.

DESCRIPTION OF SYMBOLS 1 Piston 2 Cooling channel 3 Fin 6 Piston head 7 Side wall

7a Side wall

7b Side wall 8 Skirt 8a Skirt 8b Skirt 10 Combustion chamber 11 Top surface 12a 1st ring groove 12b 2nd ring groove 12c 3rd ring groove 13 Pin insertion hole 13a Pin insertion hole 13b Pin insertion hole 14 Pin boss

14a Pin boss

14b Pin boss 16 Inner wall 20 Mold 21 Side mold 22 Upper mold 23 Lower mold 25 Cavity 26 Runner 29 Salt core 31 Support pin 33 Compound core

33a First core

33b Second core 34 Molten metal X2 Cooling channel central axis

Claims

A cooling channel formed annularly in the piston head along the outer periphery of the piston head;
Fins formed on the inner wall surface of the cooling channel so as to extend in the extending direction of the cooling channel;
With
The piston of an internal combustion engine, wherein the fin is formed at a position that avoids a stress concentration portion of the piston head around the cooling channel.
A cooling channel formed annularly in the piston head along the outer periphery of the piston head;
Fins formed on the inner wall surface of the cooling channel so as to extend in the extending direction of the cooling channel;
With
The piston of the internal combustion engine, wherein at least a part of the fin is twisted around a cooling channel central axis defined in an extending direction of the cooling channel.
The piston of the internal combustion engine according to claim 1,
The piston of an internal combustion engine, wherein the fin avoids the stress concentration portion by being twisted around a central axis of the cooling channel defined in the extending direction of the cooling channel.
The piston of the internal combustion engine according to claim 3,
Formed integrally with the piston head and having a pair of pin bosses connecting the connecting rods;
The piston of the internal combustion engine, wherein the fin is formed at a position avoiding an inner wall surface formed on the pin boss side of the cooling channel extending between a top surface of the piston and the pin boss.
The piston of the internal combustion engine according to claim 3,
Formed integrally with the piston head and having a pair of pin bosses connecting the connecting rods;
The internal combustion engine characterized in that the fin is formed at a position that avoids an inner wall surface formed on an outer peripheral side and an inner peripheral side of the piston head of the cooling channel extending between a top surface of a piston and the pin boss. Engine piston.
The piston of the internal combustion engine according to claim 3,
A pair of pin bosses for connecting the connecting rods, and a skirt extending from the piston head side and connecting the pair of pin bosses;
A piston for an internal combustion engine, wherein the piston is formed at a position avoiding an inner wall surface on a top surface side of the cooling channel extending between a top surface of the piston and the skirt.
The piston of the internal combustion engine according to claim 4,
The internal combustion engine piston according to claim 1, wherein the fin is formed on the top surface side of the inner wall surface of the cooling channel extending between the top surface of the piston and the pin boss.
The piston of the internal combustion engine according to claim 6,
The piston of an internal combustion engine, wherein the fin is formed on a side opposite to an inner wall surface of the cooling channel extending between a top surface of the piston and the skirt.
The piston of the internal combustion engine according to claim 3,
A piston for an internal combustion engine, characterized in that the direction of twisting around the central axis of the cooling channel is reversed halfway.
A method for manufacturing a piston of an internal combustion engine according to claim 1,
Disposing a core including at least a portion simulating the shape of the cooling channel at a predetermined position in a mold having a cavity simulating the shape of a piston, and injecting molten metal into the mold. A method for manufacturing a piston of an internal combustion engine, which is characterized by the following.
In the manufacturing method of the piston of the internal-combustion engine according to claim 10,
The core is formed of a first core made of a core material that mimics the shape of the fin and is removed by the heat of the molten metal, and a second core made of a salt core that mimics the shape of the cooling channel. A compound core consisting of a combination with children,
A method for manufacturing a piston of an internal combustion engine, comprising: injecting molten metal into the mold, removing the first core, and casting the second core.