JP2018025144A - Piston of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce oil dragging resistance generating between a skirt portion and a cylinder wall surface kept into contact with the skirt portion.SOLUTION: A skirt portion 3 of a piston 1 is formed in a state that a width along a piston circumferential direction is gradually narrowed toward an axial lower side of the piston. An apron portion 4 of the piston 1 has a pin boss 41 having a pin hole 42 for supporting an end portion of a piston pin, and has a pair of bent portions 43a, 43b positioned between the pin boss 41 and the skirt portion 3 in the circumferential direction of the piston. Thus oil dragging resistance generating between the skirt portion 3 and a cylinder wall surface can be reduced. Further load acting on the skirt portion 3 due to deformation of the bent portions 43 is absorbed, and an excessive contact pressure of the skirt portion 3 can be prevented.SELECTED DRAWING: Figure 1

Description

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

  For example, Patent Document 1 discloses a crown portion that defines a combustion chamber, a pair of arc-shaped skirt portions that are provided integrally with the crown portion and slide on the cylinder wall surface on the thrust side and the anti-thrust side, A piston of an internal combustion engine is disclosed that includes a pair of apron portions that connect both circumferential ends of the skirt portion and have pin boss portions.

  In this Patent Document 1, the crown portion is formed with a lightening portion along the outer surface of the upper end wall of the apron portion, and the outer surface of each pin boss portion and each of the upper end walls of the apron portion. Sites between both ends of the skirt portion in the circumferential direction are formed by bent portions that gradually expand from the outer surface of each pin boss portion toward the both ends of each skirt portion.

  For this reason, the piston in Patent Document 1 can reduce the weight of the whole piston by the thinned portion of the crown portion, and can reduce friction by reducing the surface pressure of each skirt portion against the cylinder wall surface by the bent portion of the apron portion. It has become.

JP2015-132248A

  However, the skirt portion of the piston in Patent Document 1 described above is formed so that the width along the circumferential direction of the piston gradually increases toward the lower side in the piston axial direction on the lower side in the piston axial direction. There is a problem that the drag resistance of oil increases between the skirt portion and the cylinder wall surface in contact with the skirt portion. That is, the piston disclosed in Patent Document 1 has room for further improvement in reducing the oil drag resistance described above.

  Therefore, the piston of the internal combustion engine according to the present invention has a pair of skirt portions and a pair of apron portions integrally provided on the back side of the crown portion, and the skirt portion has a piston width in the circumferential direction of the piston. The apron portions are formed so as to be gradually narrower toward the lower side in the axial direction, and each apron portion has a pair of bent portions located on both sides of the pin boss in the circumferential direction of the piston and connected to the pair of skirt portions, respectively. It is characterized by having.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to make the contact area with respect to the cylinder wall surface of a piston relatively small, the drag resistance of the oil produced between a skirt part and a cylinder wall surface can be suppressed. In addition, by providing the apron portion with the bent portion, it is possible to suppress the load on the skirt portion from being absorbed by the deformation of the bent portion and the surface pressure of the skirt portion from being excessive.

The front view of the piston of the internal combustion engine which concerns on this invention. The side view of the piston of the internal combustion engine which concerns on this invention. The bottom view of the piston of the internal combustion engine which concerns on this invention. The perspective view of the piston of the internal combustion engine which concerns on this invention. The perspective view of the piston of the internal combustion engine which concerns on this invention. Sectional drawing along the AA line of FIG. Sectional drawing along the BB line of FIG. Sectional drawing along the CC line of FIG. Sectional drawing along the DD line | wire of FIG. The side view in the other Example of the piston of the internal combustion engine which concerns on this invention. The side view in the other Example of the piston of the internal combustion engine which concerns on this invention.

  Hereinafter, an embodiment of a piston 1 of an internal combustion engine according to the present invention will be described in detail with reference to FIGS.

  1 is a front view of the piston 1, FIG. 2 is a side view of the piston 1, FIG. 3 is a bottom view of the piston 1, FIGS. 4 and 5 are perspective views of the piston 1, and FIG. 7 is a cross-sectional view taken along line BB in FIG. 1, FIG. 8 is a cross-sectional view taken along line CC in FIG. 1, and FIG. 9 is taken along line DD in FIG. FIG.

  The piston 1 is a cast product made of an aluminum alloy, and is formed integrally as a whole. The piston 1 is slidably accommodated in a cylinder (not shown) formed in a cylinder block (not shown).

  As shown in FIGS. 1, 2, 6, and 7, the piston 1 is provided integrally with a disc-shaped crown portion 2 formed relatively thick and a back surface side of the crown portion 2. A pair of skirt portions 3a and 3b on the thrust side and the anti-thrust side, a pair of apron portions 4a and 4b integrally provided on the back surface side of the crown portion 2, and the back surface side of the crown portion 2 And a pair of groove portions 5a and 5b along the outer wall surface 47 of each apron portion 4a and 4b.

  As shown in FIGS. 1, 2, and 4 to 7, the crown portion 2 has a piston crown surface 21 constituting a part of a combustion chamber (not shown) of the internal combustion engine on the surface side, and on the outer periphery. Three annular ring grooves 22 in which piston rings (not shown) are mounted are formed. Of the three ring grooves 22, a compression ring (not shown) is mounted in each of the first ring groove 22a and the second ring groove 22b on the piston crown surface 21 side. Of the three ring grooves 22, an oil ring (not shown) is mounted in the third ring groove 22 c on the back surface side of the crown portion 2.

  Here, the direction from the piston crown surface 21 toward the back surface of the crown portion 2 in the piston axial direction, that is, the lower side in FIGS. 1 and 2 is defined as the lower side in the piston axial direction. Moreover, the direction which goes to the piston crown surface 21 from the back surface of the crown part 2 among piston axial directions, ie, the upper side in FIG.1 and FIG.2, is defined as a piston axial direction upper side. Then, the first ring groove 22a is located on the uppermost side in the piston axial direction among the three ring grooves 22, and the third ring groove 22c is located on the lowermost side in the piston axial direction among the three ring grooves 22. It becomes.

  As shown in FIG. 1, the skirt portions 3a and 3b (thrust side skirt portion 3a and anti-thrust side skirt portion 3b) are arranged at left and right symmetrical positions around the piston center axis P1.

  The skirt portion 3 (skirt portions 3a, 3b) is a wall portion that is formed to be relatively thin in its entirety, and is entirely formed in an arc shape.

  As shown in FIGS. 2 and 5, the skirt portion 3 is formed so that the width along the circumferential direction of the piston gradually decreases toward the lower side in the piston axial direction. More specifically, the skirt portion 3 is formed such that the width of the skirt outer surface 31 that is in sliding contact with the cylinder wall surface along the circumferential direction of the piston gradually decreases toward the lower side in the piston axial direction.

  Further, as shown in FIGS. 2 and 6, the skirt portion 3 has an end position on the upper side in the piston axial direction of the portion connected to the apron portion 4 (apron portions 4a and 4b). 5b) of the end on the upper side in the piston axial direction, the outermost portion in the piston radial direction is positioned outside in the piston radial direction. In other words, the piston 1 has a distance D1 between an end position on the upper side in the piston axial direction of the portion connected to the apron part 4 of the skirt portion 3 and the piston central axis P1 at an upper side in the piston axial direction of the groove 5. It is set to be larger than the distance D2 between the innermost portion of the end portion in the piston radial direction and the piston central axis P1.

  Each apron part 4a, 4b is arranged on both sides of the skirt parts 3a, 3b in the piston circumferential direction. That is, the pair of skirt portions 3a and 3b and the pair of apron portions 4a and 4b are formed so as to be continuously connected in an annular shape along the piston circumferential direction.

  As shown in FIGS. 1, 3, 4, 5, 8, and 9, the apron portion 4 includes a pin boss 41 having a pin hole 42 that supports an end portion of a piston pin (not shown). And a pair of bent portions 43a and 43b positioned between the pin boss 41 and the skirt portion 3 in the circumferential direction of the piston.

  As shown in FIG. 1, the apron part 4 is formed so that the width along the circumferential direction of the piston gradually increases toward the lower side in the piston axial direction as a whole. Moreover, the apron part 4 is located in the inner peripheral side rather than the outer peripheral surface of the crown part 2 by the piston axial direction view, as shown in FIG.

  The bent portion 43 is a wall portion that is formed to be relatively thin as a whole, and is bent and formed in a crank shape as a whole.

  The bent portion 43 includes an intermediate bent portion 44 provided between the pin boss 41 and the skirt portion 3 in the piston circumferential direction, and a pin boss side bent portion 45 provided closer to the pin boss 41 than the intermediate bent portion 44 in the piston circumferential direction. And a skirt portion side bent portion 46 provided on the skirt portion 3 side of the intermediate bent portion 44 in the piston circumferential direction.

  As shown in FIGS. 8 and 9, the intermediate bent portion 44 has a convex shape toward the inner side in the piston radial direction on the lower side in the piston axial direction, and a convex shape toward the outer side in the piston radial direction on the upper side in the piston axial direction. It is formed to become.

  As shown in FIGS. 8 and 9, the pin boss side bent portion 45 has a convex shape toward the outside in the piston radial direction on the lower side in the piston axial direction, and protrudes toward the inside in the piston radial direction on the upper side in the piston axial direction. It is formed to have a shape.

  As shown in FIGS. 8 and 9, the skirt portion side bent portion 46 is formed to have a convex shape toward the outside in the piston radial direction on the lower side in the piston axial direction and the upper side in the piston axial direction.

  In this way, by setting the direction of the convex shape of the intermediate bent portion 44, the pin boss side bent portion 45, and the skirt portion side bent portion 46, the convex shape is formed toward the inner side in the piston radial direction on the outer peripheral side of the bent portion 43. Since the angle does not become an acute angle even at the location where the angle becomes, stress concentration in the bent portion 43 can be relaxed.

  The wall thickness dimension T1 of the skirt part side bending part 46 is formed so as to be relatively large. That is, the thickness T1 of the skirt portion side bent portion 46 is formed to be larger than the thickness dimensions T2 and T3 of the intermediate bent portion 44 and the pin boss side bent portion 45. Note that the thickness T1 of the skirt side bent portion 46 is larger than the thickness T2 of the intermediate bent portion 44 or the wall thickness T3 of the pin boss side bent portion 45 in forming the skirt portion bent portion 46 to be relatively large. You may make it form.

  As shown in FIG. 9, the intermediate bent portion 44 and the pin boss side bent portion 45 are formed so that the thickness dimensions T2 and T3 thereof are the same on the lower side in the piston axial direction. Moreover, the intermediate | middle bending part 44 and the pin boss side bending part 45 are each formed so that a thickness dimension may become fixed along a piston axial direction. Thus, if the thickness of the intermediate bent portion 44 and the pin boss side bent portion 45 is set, it is possible to improve the flow of molten metal during casting of the intermediate bent portion 44 and the pin boss side bent portion 45.

  The intermediate bent portion 44 and the pin boss side bent portion 45 can be formed to have different thicknesses.

  As shown in FIGS. 1, 4, and 6, the outer wall surface 47 of the apron portion 4 is located on the outer side in the piston radial direction toward the lower side in the piston axial direction in the region where the pin boss 41 is formed in the piston circumferential direction. Is formed. That is, the outer surface of the pin boss 41 is inclined so that the lower side in the piston axial direction is located on the outer side in the piston radial direction.

  As shown in FIGS. 1, 4, and 6, the outer wall surface 47 of the apron portion 4 is located outwardly in the piston radial direction toward the lower side in the piston axial direction in a region adjacent to both sides of the pin boss 41 in the piston circumferential direction. It is formed to be located. That is, a portion of the outer wall surface 47 of the apron portion 4 located between the pin boss 41 and the pin boss side bent portion 45 in the circumferential direction of the piston is inclined so as to be located on the outer side in the piston radial direction on the lower side in the piston axial direction. ing.

  That is, there is a portion formed on the outer wall surface 47 of the apron portion 4 on the upper side in the piston axial direction so as to be positioned on the outer side in the piston radial direction toward the lower side in the piston axial direction.

  As shown in FIG. 6, each of the grooves 5 a and 5 b is a space formed in a U-shaped cross section formed on the back surface side of the crown portion 2, and an area in which the pin boss 41 is formed in the circumferential direction of the piston and the pin boss 41 is formed on the upper side in the piston axial direction in a region adjacent to both sides of 41. That is, the groove portion 5 is formed so as to be continuous with a portion of the outer wall surface 47 of the apron portion 4 that is located on the upper side in the piston axial direction and located on the outer side in the piston radial direction toward the lower side in the piston axial direction. Has been.

  The groove 5 includes an inner wall surface 51 located on the inner side in the piston radial direction, an outer wall surface 52 located on the outer side in the piston radial direction, and a bottom wall surface that is located between the inner wall surface 51 and the outer wall surface 52 and continues to both. 53. The inner wall surface 51 is formed to be continuous with the outer wall surface 47 of the apron portion 4 without a step.

  As shown in FIG. 6, the inner wall surface 51 and the outer wall surface 52 have a cross section parallel to the plane including the piston center axis P1 and the pin hole axis P2, and are located on the outer side in the piston radial direction toward the lower side in the piston axis direction. It is tilted. Further, the inclination of the inner wall surface 51 coincides with the inclination of the outer wall surface 47 of the apron portion 4 that is continuous with the groove portion 5.

  That is, as shown in FIG. 6, the grooves 5 a and 5 b are each positioned on the outer side in the piston radial direction toward the lower side in the piston axial direction, and are entirely inclined with respect to the piston central axis P <b> 1.

  Accordingly, the mold (mold) used to form the groove portion 5 can be pulled out using the inclination of the outer wall surface 47 of the apron portion 4.

  The bottom wall surface 53 is formed so that the position along the piston axial direction is the position of the first ring groove 22 a provided on the outer periphery of the crown portion 2. That is, each groove part 5a, 5b is formed so that the edge part of the piston axial direction upper side may be located in the inner peripheral side of the 1st ring groove 22a.

  As described above, the piston 1 of the present embodiment is formed such that the width of the skirt portion 3 along the circumferential direction of the piston gradually decreases toward the lower side in the piston axial direction. More specifically, the width of the skirt outer surface 31 along the circumferential direction of the piston is formed so as to gradually narrow toward the lower side in the piston axial direction. Therefore, the piston 1 of the present invention can reduce the contact area with respect to the cylinder wall surface as compared with the skirt portion 3 having a constant width along the piston axial direction along the piston circumferential direction. The drag resistance of the oil produced between the wall surfaces can be suppressed.

  Further, by providing the apron portion 4 with the bent portion 43, when the skirt portion 3 is pressed against the cylinder wall surface and a large load is applied to the skirt portion 3, the bent portion 43 is deformed. That is, it is possible to suppress the load on the skirt portion 3 from being absorbed by the deformation of the bent portion 43 and the surface pressure of the skirt portion 3 from becoming excessive.

  By setting the wall thickness dimension of the skirt part side bent part 46 to be relatively large, the deformation in the other part (bent part 43) can be further promoted while suppressing the deformation in the skirt part 3, and the skirt An increase in the surface pressure of the portion 3 can be further suppressed.

  Since the load applied to the pin boss 41 increases toward the lower side in the piston axial direction, the apron portion 4 can relieve stress concentration on the pin boss 41 by increasing the width along the circumferential direction of the piston toward the lower side in the piston axial direction. it can.

  The crown 2 receives the pressure received from the combustion chamber in a so-called cantilever structure in the portion where the groove 5 is provided. However, the skirt portion 3 is a portion where the end position on the upper side in the piston axial direction of the portion connected to the apron portion 4 is the innermost portion in the piston radial direction among the end portions on the upper side in the piston axial direction of the groove portion 5. It is formed so as to be located outside in the piston radial direction. Therefore, in the piston 1 of the above-described embodiment, the portion where the groove portion 5 of the crown portion 2 is provided by the skirt portion 3 is supported, and the collapse of the portion toward the lower side in the piston axial direction can be suppressed. That is, the rigidity of the crown portion 2 can be ensured while reducing the weight of the piston 1.

  As shown in FIGS. 10 and 11, the skirt portion 3 is a pair of chamfered portions located on both sides in the circumferential direction of the piston connected to the apron portion 4. You may form so that it may have 61a and 61b. In this case, the chamfered portions 61a and 61b are formed such that the width along the piston circumferential direction gradually decreases toward the lower side in the piston axial direction. The example illustrated in FIG. 10 is an example in which the areas of the chamfered portions 61a and 61b are relatively larger than the example illustrated in FIG.

  Thus, by setting the chamfered portion 61 (the chamfered portions 61a and 61b) to the skirt portion 3, the contact area between the skirt portion 3 and the cylinder wall surface can be adjusted. The chamfered portion 61 can reduce the contact area between the skirt portion 3 and the cylinder wall surface on the upper side in the piston axial direction, and can suppress oil drag resistance generated between the skirt portion 3 and the cylinder wall surface.

  Further, the piston 1 of the above-described embodiment is formed so that the groove portion 5 is positioned closer to the center side (inner peripheral side) of the crown portion 2 toward the crown surface side of the crown portion 2, and therefore the groove portion is simply along the piston axial direction. Compared with the case of forming, the volume of the groove portion 5 can be set larger, and the weight of the piston 1 can be reduced. And since the groove part 5 is formed in the piston axial direction upper side of the area | region where the pin boss | hub 41 was formed in the piston circumferential direction, and the area | region adjacent to both sides of the pin boss | hub 41, the weight reduction effect of the desired piston 1 is acquired. Can do.

  As the piston of the internal combustion engine based on the above-described embodiment, for example, the following modes can be considered.

  In one aspect of the piston of the internal combustion engine, a crown portion having a piston crown surface constituting a part of the combustion chamber of the internal combustion engine on the front surface side, and a cylinder wall surface are integrally provided on the back surface side of the crown portion. A pair of arc-shaped skirt portions on the thrust side and the anti-thrust side that slide relative to each other, and a back surface side of the crown portion, which are integrally provided on both sides of the skirt portion in the piston circumferential direction, and a piston pin A pair of apron portions having pin bosses in which pin holes for supporting the end portions of the pins are formed. The skirt portion is formed so that the width along the circumferential direction of the piston gradually becomes narrower toward the lower side in the piston axial direction, which is the direction from the piston crown surface toward the back surface of the crown portion in the piston axial direction. Has been. The pair of apron parts and the pair of skirt parts are formed so as to be annularly connected along the circumferential direction of the piston. Each of the apron portions has a pair of bent portions that are positioned on both sides of the pin boss in the circumferential direction of the piston and connected to the pair of skirt portions, respectively.

  The bent portion includes an intermediate bent portion provided between the pin boss and the skirt portion in the piston circumferential direction on the lower side in the piston axial direction and having a convex shape toward the inside in the piston radial direction, and the piston circumferential direction. The pin boss side bent portion provided on the pin boss side of the intermediate bent portion and having a convex shape toward the outside in the piston radial direction, and the piston diameter provided on the skirt portion side of the intermediate bent portion in the piston circumferential direction. A skirt portion-side bent portion that protrudes outward in the direction, and the thickness of the skirt-side bent portion is larger than the thickness of the intermediate bent portion or the pin boss-side bent portion. It is formed to become.

  And the thickness dimension of the said skirt part side bending part is formed so that it may become larger than the thickness dimension of the said intermediate | middle bending part and the said pin boss side bending part.

  Further, the apron portion is formed so that the width along the circumferential direction of the piston gradually increases toward the lower side in the piston axial direction.

  The bent portion is provided between the pin boss and the skirt portion in the piston circumferential direction, has a convex shape toward the inside in the piston radial direction on the lower side in the piston axial direction, and extends in the piston radial direction on the upper side in the piston axial direction. An intermediate bent portion that is convex toward the outside, and provided on the pin boss side of the intermediate bent portion in the circumferential direction of the piston, and has a convex shape toward the outside in the piston radial direction on the lower side in the piston axial direction. A pin boss side bent portion that is convex toward the inside in the piston radial direction on the upper side in the direction, and provided on the skirt portion side with respect to the intermediate bent portion in the piston circumferential direction. And a skirt portion side bent portion that is convex toward the outside in the piston radial direction on the side.

  Further, the intermediate bent portion and the pin boss side bent portion are formed to have the same thickness on the lower side in the piston axial direction. The intermediate bent portion and the pin boss side bent portion may be formed so as to have a constant thickness along the piston axial direction.

  The outer wall surface of the apron portion is formed so as to be located on the outer side in the piston radial direction toward the lower side in the piston axial direction in the region where the pin boss is formed in the circumferential direction of the piston. The outer wall surface of the apron portion may be formed in a portion adjacent to both sides of the pin boss in the piston circumferential direction so as to be located on the outer side in the piston radial direction toward the lower side in the piston axial direction.

  The skirt portion is formed such that the width along the circumferential direction of the piston on the skirt surface that is in sliding contact with the cylinder wall surface gradually decreases toward the lower side in the piston axial direction.

  And the said skirt part has a pair of chamfering part located in the piston radial direction inner side with respect to the said skirt surface in the both-sides part of the piston circumferential direction connected to the said apron part. The chamfered portion is formed so that the width along the circumferential direction of the piston gradually becomes narrower toward the lower side in the piston axial direction.

  Also, the apron portion has a pair of grooves located on the back side of the crown portion along the outer wall surface of the apron portion, and the skirt portion is an end on the upper side in the piston axial direction of the portion connected to the apron portion. The part position is formed so as to be positioned on the outer side in the piston radial direction than the innermost part in the piston radial direction among the end portions on the upper side in the piston axial direction of the groove part.

DESCRIPTION OF SYMBOLS 1 ... Piston 2 ... Crown part 3 ... Skirt part 4 ... Apron part 21 ... Piston crown surface 22 ... Ring groove 41 ... Pin boss 42 ... Pin hole 43 ... Bending part 44 ... Middle bending part 45 ... Pin boss side bending part 46 ... Skirt part Side bend 47 ... outer wall

Claims (10)

A piston of an internal combustion engine,
A crown portion having a piston crown surface constituting a part of the combustion chamber of the internal combustion engine on the surface side;
A pair of arc-shaped skirt portions provided on the back side of the crown portion, the thrust side and the anti-thrust side sliding with respect to the cylinder wall surface;
A pair of apron portions integrally provided on the back surface side of the crown portion, disposed on both sides of the skirt portion in the circumferential direction of the piston, and having pin bosses formed with pin holes for supporting end portions of the piston pins; Have
The skirt portion is formed so that the width along the circumferential direction of the piston gradually becomes narrower toward the lower side in the piston axial direction, which is the direction from the piston crown surface toward the back surface of the crown portion in the piston axial direction. And
The pair of apron parts and the pair of skirt parts are formed so as to be annularly connected along the circumferential direction of the piston,
Each said apron part has a pair of bending part located in the piston circumferential direction at the both sides of the said pin boss, and being respectively connected to a pair of said skirt part, The piston of the internal combustion engine characterized by the above-mentioned. The bent portion is
On the lower side in the piston axial direction, an intermediate bent portion that is provided between the pin boss and the skirt portion in the circumferential direction of the piston and is convex toward the inside in the piston radial direction,
A pin boss side bent portion which is provided on the pin boss side with respect to the intermediate bent portion in the piston circumferential direction and has a convex shape toward the outside in the piston radial direction;
A skirt portion-side bent portion that is provided on the skirt portion side with respect to the intermediate bent portion in the circumferential direction of the piston and has a convex shape toward the outer side in the piston radial direction,
2. The piston of the internal combustion engine according to claim 1, wherein a thickness dimension of the skirt portion side bent portion is formed to be larger than a thickness dimension of the intermediate bent portion or the pin boss side bent portion. .   3. The piston of the internal combustion engine according to claim 2, wherein a thickness dimension of the skirt portion side bent portion is formed to be larger than a thickness dimension of the intermediate bent portion and the pin boss side bent portion. .   The piston of the internal combustion engine according to claim 1, wherein the apron portion is formed so that a width along a circumferential direction of the piston gradually increases toward a lower side in a piston axial direction. The bent portion is
Provided between the pin boss and the skirt portion in the circumferential direction of the piston, and has a convex shape toward the inner side in the piston radial direction on the lower side in the piston axial direction, and protrudes toward the outer side in the piston radial direction on the upper side in the piston axial direction. An intermediate bend that is shaped,
In the circumferential direction of the piston, it is provided on the pin boss side of the intermediate bent portion, and has a convex shape toward the outside in the piston radial direction on the lower side in the piston axial direction, and convex toward the inside in the piston radial direction on the upper side in the piston axial direction. A bent portion on the pin boss side that becomes a shape,
A skirt portion-side bent portion that is provided on the skirt portion side of the intermediate bent portion in the piston circumferential direction and has a convex shape toward the outside in the piston radial direction on the lower side in the piston axial direction and the upper side in the piston axial direction. The piston of the internal combustion engine according to claim 1, characterized by comprising:   6. The piston for an internal combustion engine according to claim 5, wherein the intermediate bent portion and the pin boss side bent portion are formed to have the same thickness on the lower side in the piston axial direction.   The outer wall surface of the apron part is formed so as to be positioned on the outer side in the piston radial direction toward the lower side in the piston axial direction in the region where the pin boss is formed in the circumferential direction of the piston. The piston of the internal combustion engine described.   The skirt portion is formed so that a width along a piston circumferential direction of a skirt surface slidingly contacting the cylinder wall surface is gradually narrowed toward a lower side in a piston axial direction. The piston of the internal combustion engine according to 1. The skirt portion has a pair of chamfered portions located on the inner side in the piston radial direction with respect to the skirt surface on both sides of the piston circumferential direction connected to the apron portion,
The piston of the internal combustion engine according to claim 8, wherein the chamfered portion is formed so that a width along a circumferential direction of the piston gradually decreases toward a lower side in a piston axial direction. Located on the back side of the crown, and having a pair of grooves along the outer wall surface of the apron,
The skirt portion is formed so that the end position on the upper side in the piston axial direction of the skirt portion is positioned on the outer side in the piston radial direction than the innermost portion in the piston radial direction of the end portion on the upper side in the piston axial direction of the groove portion. The piston of the internal combustion engine according to claim 1, wherein the piston is provided.

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