JP2012031814A - Piston of internal combustion engine, and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a piston having a skirt part, in which tensile stress to be generated in an upper part of a pin hole becomes higher and fatigue deterioration in the upper part of the pin hole is more accelerated, and additionally, in which a lower part is thicker than an upper part.SOLUTION: The piston of an internal combustion engine includes: a piston body 11; a pair of skirt parts 12A and 12B; a pair of side wall parts 13A and 13B; and pin holes 14A and 14B. The piston includes a hollow formed by a bottom wall surface of the piston body, inner peripheral wall surfaces of both the skirt parts and inner peripheral wall surfaces of both the side wall parts. A protrusion part 20 is provided in the outer wall surface of the side wall parts, extending in a direction from a region of the outer wall surface of the side wall part adjacent to the piston body and the skirt part to a region of the outer wall surface of the side wall part adjacent to a side part of the pin hole part.

Description

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

  Patent Document 1 discloses a piston for an internal combustion engine. The piston includes a cylindrical piston main body, a pair of skirts extending downward from the piston main body, a pair of sidewalls connecting the skirts to each other, and a pair of side walls provided on each side wall. And a pin hole. And the side wall part of this piston has the thickness which becomes thin toward the upper part from the lower part. Therefore, in this piston, the rigidity of the upper part of the sidewall part is low, and the rigidity of the lower part of the sidewall part is high. The rigidity of the sidewall part affects the rigidity of the skirt part, the rigidity of the skirt part close to the part of the sidewall part having low rigidity is low, and the part of the skirt part close to the part of the sidewall part having high rigidity. The rigidity is high. Therefore, in the piston disclosed in Patent Document 1, as a result, the rigidity of the upper part of the skirt part is low and the rigidity of the lower part of the skirt part is high. And the following effects are acquired by this.

  That is, when the piston is disposed in the cylinder bore of the internal combustion engine, the internal combustion engine is operated, and fuel is combusted in the combustion chamber during the expansion stroke, a high combustion pressure is applied to the top wall surface of the piston main body. Here, generally, there is a slight clearance between the outer peripheral wall surface of the piston body and the inner peripheral wall surface of the cylinder bore, and between the outer peripheral wall surface of the skirt portion and the inner peripheral wall surface of the cylinder bore. Therefore, in this case, when a high combustion pressure is applied to the top wall surface of the piston body, the piston is connected to the piston pin (that is, the pin hole formed by the pin hole) so that the piston central axis is inclined with respect to the cylinder bore central axis. Will rotate around the center axis of the piston pin. And when a piston rotates in this way, the upper part of one skirt part and the lower part of the other skirt part contact | abut strongly against a cylinder bore inner peripheral wall surface.

  On the other hand, in the exhaust stroke following the expansion stroke, the pressure applied to the top wall surface of the piston main body portion decreases because the pressure in the combustion chamber decreases. At this time, the piston rotates about the piston pin so that the piston center axis coincides with the cylinder bore center axis. When the piston rotates in this way, the upper portion of one skirt portion and the lower portion of the other skirt portion that are strongly in contact with the inner peripheral wall surface of the cylinder bore are separated from the inner peripheral wall surface of the cylinder bore.

  That is, during engine operation (that is, during operation of the internal combustion engine), the upper part of one skirt part and the lower part of the other skirt part repeatedly hit the inner peripheral wall surface of the cylinder bore repeatedly or away from it.

  Here, if the rigidity of the upper part of the skirt is high, the part is difficult to deform. For this reason, when the upper part of the skirt portion strongly hits the inner peripheral wall surface of the cylinder bore, so-called slap noise or oil film breakage occurs between the upper part of the skirt portion and the inner peripheral wall surface of the cylinder bore. Therefore, in order to suppress the occurrence of such slap noise and oil film breakage, the rigidity of the upper part of the skirt part is set so that the upper part of the skirt part easily deforms when it hits the inner peripheral wall surface of the cylinder bore. It is preferable that it is low. As described above, in the piston disclosed in Patent Document 1, since the rigidity of the upper portion of the skirt portion is low, the effect of suppressing the occurrence of slap noise and oil film breakage can be obtained.

  Further, when the rigidity of the lower part of the skirt is low, the part is easily deformed. For this reason, when the lower part of the skirt part strongly hits the inner peripheral wall surface of the cylinder bore, the lower part of the skirt part is greatly deformed, so that the inclination of the piston central axis with respect to the cylinder bore central axis becomes large. As a result, the upper part of the skirt portion more strongly hits the inner circumferential wall surface of the cylinder bore, so that a slap sound or oil film breakage is likely to occur. Of course, when the lower part of the skirt part strongly hits the inner peripheral wall surface of the cylinder bore, the lower part of the skirt part is greatly deformed. End up. Therefore, in order to suppress such fatigue deterioration, the rigidity of the lower part of the skirt part is increased so that the lower part of the skirt part is not easily deformed when the lower part of the skirt hits the cylinder bore inner wall surface. Preferably it is. As described above, in the piston disclosed in Patent Document 1, since the rigidity of the lower part of the skirt portion is high, it is difficult for slap noise or oil film breakage to occur, and the lower part of the skirt portion is in the cylinder bore. The portion that becomes the fulcrum of deformation of the lower portion when hitting the peripheral wall surface is less likely to be fatigued.

  As described above, various effects can be obtained by changing the thickness of the sidewall portion for each portion of the sidewall portion, instead of making the thickness of the sidewall portion constant over the entire sidewall portion.

Japanese Utility Model Publication No.2-132834 Japanese Utility Model Publication No. 3-92544 Japanese Utility Model Publication No. 3-89958 JP-A-4-219570

  By the way, when the piston is arranged in the cylinder bore of the internal combustion engine, the piston pin is inserted into the pin hole of the piston, one end of the connecting rod is connected to the piston pin, and the other end of the connecting rod is connected to the crankshaft. The When the internal combustion engine is operated, when fuel burns in the combustion chamber during the expansion stroke, a large load (hereinafter referred to as “combustion pressure load”) due to combustion pressure is applied to the top wall surface of the piston body. . The combustion pressure load is transmitted from the piston to the connecting rod via the piston pin, and is transmitted from the connecting rod to the crankshaft. Therefore, when the top wall surface of the piston body receives a combustion pressure load, the piston supports the combustion pressure load at the pin hole. Therefore, due to a large combustion pressure load, the inner peripheral wall surface of the upper portion of the pin hole portion (hereinafter referred to as “pin hole upper portion”) is the upper portion of the piston pin (hereinafter referred to as “piston pin upper portion”) Since the contact surface between the inner peripheral wall surface of the upper portion of the pin hole and the outer peripheral wall surface of the upper portion of the piston pin is small, the surface pressure of these wall surfaces becomes a high surface pressure. As a result, the pin hole upper portion and the piston so that the radius of curvature of the inner peripheral wall surface of the pin hole upper portion and the outer peripheral wall surface of the piston pin upper portion are larger than the original radius of the pin hole and the original radius of the piston pin, respectively. The pins are deformed together. As a result, the upper portion of the pin hole is bent, and tensile stress is generated in the inner peripheral wall surface portion of the upper portion of the pin hole. On the other hand, in the exhaust stroke and the intake stroke following the expansion stroke, the pressure in the combustion chamber becomes low, so the tensile stress generated in the inner peripheral wall surface portion of the upper portion of the pin hole disappears. During the engine operation, the expansion stroke, the exhaust stroke, and the intake stroke are repeatedly performed, so that the portion above the pin hole is likely to be fatigued.

  In the field of pistons, there is a demand for weight reduction of pistons and reduction of friction related to pistons, and the diameter of pin holes may be reduced in order to achieve this requirement. However, when the pin hole diameter is reduced, the radius of curvature of the inner peripheral wall surface of the pin hole upper portion and the outer peripheral wall surface of the piston pin upper portion is reduced. For this reason, since these wall surfaces are strongly pressed against each other by a smaller contact surface, the surface pressure of these wall surfaces becomes a higher surface pressure, and as a result, the tensile stress generated in the pin hole upper portion becomes higher, The fatigue deterioration of the pin hole upper portion is further promoted.

  Accordingly, an object of the present invention is to provide a piston capable of reducing the diameter of the pin hole while suppressing fatigue deterioration in the upper portion of the pin hole.

  By the way, when a piston having a cavity inside is manufactured by a mold, the cavity of the piston is generally formed using a core. Specifically, the cavity is formed by solidifying the piston material in a state where the piston material (that is, the material constituting the piston) is arranged around the core. And after formation of a cavity, a core is extracted from a cavity.

  On the other hand, as described above, the piston disclosed in Patent Document 1 has a specific purpose (that is, the purpose of reducing the rigidity of the upper portion of the sidewall portion and increasing the rigidity of the lower portion of the sidewall portion). The thickness of the sidewall portion is reduced from its lower part toward its upper part. Here, for example, for a certain purpose, the thickness of the skirt portion may be decreased from the lower portion toward the upper portion. And the piston which has such a skirt part is equipped with the cavity in the inside, and when this piston is manufactured with a type | mold, if a cavity is formed using the general core mentioned above, a core will be formed after formation of a cavity. When trying to extract the core from the cavity, the lower part of the skirt part gets in the way, and the core cannot be extracted from the cavity.

  Therefore, another object of the present invention is to provide a method of manufacturing a piston having a skirt portion in which the thickness of the lower portion is larger than the thickness of the upper portion.

  In order to achieve the above object, a first invention of the present application includes a columnar piston main body and a substantially extending downwardly parallel to the central axis of the piston main body from the bottom wall surface of the piston main body. A pair of partially annular skirt portions and a pair of flat sides that extend downward from the bottom wall surface of the piston body portion in parallel to the central axis of the piston body portion and connect the skirt portions to each other The piston main body having a wall portion and an annular pin hole portion provided in these side wall portions and having a central axis perpendicular to an extending plane of the side wall portion. The present invention relates to a piston of an internal combustion engine in which a cavity is formed by the bottom wall surface of the portion, the inner peripheral wall surfaces of both skirt portions, and the inner wall surfaces of both sidewall portions. In the piston of the internal combustion engine of the present invention, the outside of the sidewall portion adjacent to the side portion of the pin hole portion from the region of the outer wall surface of the sidewall portion adjacent to the piston main body portion and the skirt portion. A raised portion extending in a direction toward the wall surface region is provided in the sidewall portion.

  According to this invention, the piston which can make the diameter of a pin hole small is provided, suppressing fatigue deterioration of the upper part of a pin hole part. That is, when the piston is disposed in the cylinder bore and the internal combustion engine is operated, when the fuel burns in the combustion chamber in the expansion stroke, a large combustion pressure load (that is, a large pressure due to the combustion pressure) is applied to the top wall surface of the piston body. Load). Then, due to this large combustion pressure load, the inner peripheral wall surface of the upper portion of the pin hole (that is, the upper portion of the pin hole portion) is the outer peripheral wall surface of the upper portion of the piston pin (that is, the upper portion of the piston pin inserted into the pin hole). So that the radius of curvature of the inner peripheral wall surface of the upper pin hole portion and the outer peripheral wall surface of the upper piston pin portion is larger than the original radius of the pin hole and the original radius of the piston pin, respectively. Both the upper part and the piston pin are deformed. As a result, tensile stress is generated in the inner wall surface side portion of the pin hole upper portion. On the other hand, in the exhaust stroke and the intake stroke following the expansion stroke, the pressure in the combustion chamber becomes low, so the tensile stress generated in the inner peripheral wall surface portion of the upper portion of the pin hole disappears. During the engine operation, the expansion stroke, the exhaust stroke, and the intake stroke are repeatedly performed, so that the portion above the pin hole is likely to be fatigued. Here, in the present invention, a raised portion is provided in the sidewall portion. And this bulging part is a side wall in the direction from the area of the outer wall surface of the sidewall part adjacent to the piston body part and the skirt part to the area of the outer wall surface of the sidewall part adjacent to the side part of the pin hole part. It extends in the department. Therefore, this protruding portion transmits the bending force of the piston main body due to the combustion pressure load to the side portion of the pin hole portion. Then, due to the force transmitted to the side portion of the pin hole portion, a force is applied to the pin hole portion in the direction of suppressing the bending of the upper portion of the pin hole due to the combustion pressure load in the expansion stroke. Thereby, the bending of the upper portion of the pin hole is suppressed, and as a result, the occurrence of tensile stress in the upper portion of the pin hole portion is suppressed. For this reason, even if the diameter of the pin hole is reduced, fatigue deterioration of the upper portion of the pin hole portion is suppressed. Therefore, according to this invention, the piston which can make the diameter of a pin hole small is provided, suppressing the fatigue deterioration of the upper part of a pin hole part.

  Further, in the second invention of the present application, in the piston of the internal combustion engine of the first invention, the wall portion of the sidewall portion opposite to the side from which the protruding portion protrudes extends along the protruding portion. Grooves are formed.

  According to this invention, since the groove is formed on the wall surface of the sidewall portion, the weight of the piston is reduced.

  In the third invention of the present application, in the piston of the internal combustion engine of the first or second invention, a plane including the center axis of the pin hole and the center axis of the piston is referred to as a pin hole vertical plane, A portion of the pin hole portion in the vicinity of the pin hole vertical plane, the portion on the piston main body side with respect to the central axis of the pin hole portion is referred to as a pin hole upper portion, and includes the central axis of the pin hole portion and A plane perpendicular to the central axis is referred to as a pin hole horizontal plane, a pin hole portion in the vicinity of the pin hole horizontal plane is referred to as a pin hole horizontal portion, and the pin hole upper portion and the pin hole horizontal portion are substantially When the pin hole portion located in the middle is referred to as an obliquely upper portion of the pin hole, the raised portion is inclined from the region of the outer wall surface of the sidewall portion adjacent to the piston body portion and the skirt portion. Adjacent to upper part That substantially straight extending towards the region of the outer wall surface of the sidewall portion.

  According to this invention, even if the diameter of the pin hole is reduced, the fatigue deterioration of the upper portion of the pin hole is more reliably suppressed. That is, when a large combustion pressure load is applied to the top wall surface of the piston body, tensile stress is generated in the upper portion of the pin hole due to this large combustion pressure load as described in relation to the first invention. In this regard, if a force is applied to the pin hole diagonally upper portion from the region of the outer wall surface of the sidewall portion adjacent to the piston body portion and the skirt portion, the bending of the pin hole upper portion is suppressed well, and as a result, the pin hole It has been found by the inventor's research that the generation of tensile stress in the upper part is well suppressed. Here, in the present invention, the raised portion is substantially straight from the region of the outer wall surface of the sidewall portion adjacent to the piston body portion and the skirt portion toward the region of the outer wall surface of the sidewall portion adjacent to the pin hole diagonally upper portion. It extends to. For this reason, the bending force of the piston main body due to the combustion pressure load is applied to the pin hole diagonally upper portion from the region of the outer wall surface of the sidewall adjacent to the piston main body and the skirt. For this reason, even if the diameter of the pin hole is reduced, the fatigue deterioration of the upper part of the pin hole is more reliably suppressed.

  In order to achieve the above object, the fourth invention of the present application is a columnar piston main body, and extends downward from the bottom wall surface of the piston main body in parallel to the central axis of the piston main body. And a pair of flat shapes extending downwardly from the bottom wall surface of the piston body portion in parallel to the central axis of the piston body portion and connecting the skirt portions to each other. A cavity is formed by the bottom wall surface of the piston main body, the inner peripheral wall surfaces of both skirt portions, and the inner wall surfaces of both sidewall portions, and a lower portion of the skirt portion. The present invention relates to a method for manufacturing, using a mold, a piston having a thickness larger than that of a portion above the skirt portion. In the method of the present invention, the inner wall surface of one side wall portion and the bottom wall surface portion of the piston main body portion adjacent to the inner wall surface, the inner walls of both skirt portions adjacent to the inner wall surface of the side wall portion. A first core that defines a peripheral wall portion, an inner wall surface of the other sidewall portion, a bottom wall portion of the piston main body adjacent to the inner wall surface, and an inner wall surface of the other sidewall portion; A second core defining inner peripheral wall portions of both adjacent skirt portions, a bottom wall surface portion of the piston body portion not defined by the first core and the second core, and the first A first core and a second core that define a portion of the inner peripheral wall surface of the one skirt portion that is not defined by the first core and the second core; A third core disposed between the first core and the first core A portion of the bottom wall surface of the piston main body not defined by the child and the second core and a portion of the inner peripheral wall surface of the other skirt portion not defined by the first core and the second core. A fourth core that is defined and disposed between the first core and the second core; the first core; and the second core A fifth core that defines a portion of the bottom wall surface of the piston main body that is not defined by the third core and the fourth core, wherein the first core and the second core The cavity is formed in the piston by the core, the third core, and the fifth core disposed between the fourth core and the fourth core.

  According to the fourth aspect of the present invention, the wall surfaces formed by the outer wall surfaces of the first core to the fifth core allow the bottom wall surface of the piston main body, the inner peripheral wall surfaces of the skirt portions, and the side wall portions to be An inner wall surface is defined, whereby a cavity is formed in the piston. Since each core occupies only a partial area in the cavity of the piston, all these cores can be extracted from the cavity of the piston.

  In the fifth invention of the present application, in the method of the fourth invention, the first core, the second core, the third core, the fourth core, and the fifth core. After the cavity is formed in the piston by the first, the fifth core is withdrawn, then the third and fourth cores are withdrawn, and then the first core And the second core is extracted.

  According to the fifth aspect, all the cores can be easily extracted from the cavity in the piston.

(A) is a side view of the piston of the first embodiment, and (B) is a bottom view of the piston. It is a side view of the piston of 1st Embodiment similar to FIG. 1 (A). It is sectional drawing of the protruding part of the piston of 1st Embodiment along line XX of FIG. It is the same figure as FIG. 1 (A), However, It is the side view which showed the piston provided with the protruding part different from the protruding part of 1st Embodiment. FIG. 2 is a view similar to FIG. 1A and showing a plurality of surfaces taking cross sections of a sidewall portion and a skirt portion of the piston of the first embodiment. FIG. 6 is a view similar to FIG. 5 for explaining the surface shown in FIG. 5. (A) is the figure which showed the cross section of the side wall part and skirt part of the piston of 1st Embodiment which followed the surface A of FIG. 5, Similarly, (B)-(G) is respectively It is the figure which showed the cross section of the side wall part and skirt part of the piston of 1st Embodiment which followed the surface BG of FIG. 5, (H) is the side wall part and skirt of the piston of 1st Embodiment. It is the figure which showed the bottom end surface with a part. FIG. 2 is a view similar to FIG. 1A and showing a plurality of surfaces taking cross sections of a sidewall portion and a skirt portion of the piston of the first embodiment. FIG. 9 is a view similar to FIG. 8 for explaining the surface shown in FIG. 8. FIG. 2 is a view similar to FIG. 1A and showing a plurality of surfaces taking cross sections of a sidewall portion and a skirt portion of the piston of the first embodiment. FIG. 11 is a view similar to FIG. 10 for explaining the surface shown in FIG. 10. FIG. 2 is a view similar to FIG. 1A and showing a plurality of surfaces taking cross sections of a sidewall portion and a skirt portion of the piston of the first embodiment. FIG. 13 is a view similar to FIG. 12 for explaining the surface shown in FIG. 12. (A) is a longitudinal sectional view around the skirt portion of the piston of the first embodiment, (B) is a longitudinal sectional view around the skirt portion of the piston different from the piston of the embodiment of the present invention, ( C) is a longitudinal sectional view around the skirt portion of the modified example of the piston of the first embodiment. (A) is a view similar to FIG. 1 (A), and is a side view of the piston of the second embodiment, and (B) is a side wall of the piston along line YY of (A). It is a longitudinal cross-sectional view of a part. FIG. 15A is a view similar to FIG. 15B, showing a state in which oil is retained in a recess of the piston when the piston of the second embodiment is disposed in the cylinder bore. (B) is the same figure as Drawing 15 (B), and is a figure showing signs that oil diffuses in the hollow of the piston when the piston is arranged in a cylinder bore. It is a figure similar to FIG.1 (B), Comprising: It is a bottom view of the piston of 3rd Embodiment. It is a figure similar to FIG.1 (B), Comprising: It is a bottom view of the piston of 4th Embodiment. (A) is a view similar to FIG. 3, and is a cross-sectional view of a raised portion provided on the first sidewall portion of the piston of the fifth embodiment, and (B) is a view similar to FIG. 3. It is sectional drawing of the protruding part provided in the 2nd side wall part of the same piston. It is the figure which looked at the piston of embodiment of this invention from the bottom end surface, Comprising: It is the figure which showed the core utilized in order to form the cavity of the piston of embodiment of this invention. It is a figure similar to FIG. 1 (A), Comprising: It is a side view of the piston of 6th Embodiment or 7th Embodiment. (A) is a cross-sectional view of the skirt portion of the piston of the sixth embodiment along line Z1-Z1 in FIG. 21, and (B) is the skirt of the piston along line Z2-Z2 in FIG. FIG. (A) is a cross-sectional view of the skirt portion of the piston of the seventh embodiment along line Z1-Z1 in FIG. 21, and (B) is the skirt of the piston along line Z2-Z2 in FIG. FIG.

  Hereinafter, embodiments of the piston of the present invention will be described with reference to the drawings. FIG. 1 shows the piston of the first embodiment. FIG. 1 (A) is a side view of the piston of the first embodiment, and FIG. 1 (B) is a bottom view of the piston. As shown in FIG. 1, the piston 10 includes one main body portion (hereinafter referred to as “piston main body portion”) 11, a pair of skirt portions 12 </ b> A and 12 </ b> B, a pair of sidewall portions 13 </ b> A and 13 </ b> B, Pin hole portions 14A and 14B.

  In the following description, the term “upward” refers to “upward” in the drawing of FIG. 1A (for example, when the piston body 11 is disposed when the pin hole portions 14A and 14B are used as a reference). The term “downward” represents “downward” (that is, the direction opposite to “upward”) on the drawing of FIG. 1A, and the term “side” The term “outward” represents the direction from the inside of the piston 10 toward the outside of the piston, and the term “inward” represents the direction of the piston 10. The direction from the outside toward the inside of the piston (that is, the direction opposite to “outward”). The “bottom end surface” is an end surface facing downward.

  The piston main body 11 is a cylindrical portion centered on the piston center axis C1. The piston main body 11 has a wall surface 111 (hereinafter referred to as “piston main body top wall surface”) 111 and a piston central axis C1 that forms a circular surface centered on the piston central axis C1 and faces upward. One wall surface (hereinafter referred to as the “piston body bottom wall surface”) 112 that forms a circular surface at the center and faces downward, and a cylindrical surface centered on the piston center axis C1 are arranged outward. 1 facing outer peripheral wall surface (hereinafter, this wall surface is referred to as “piston body outer peripheral wall surface”) 113.

  The piston body outer peripheral wall surface 113 connects the outer peripheral end of the piston main body top wall surface 111 and the outer peripheral end of the piston main body bottom wall surface 112 to each other. The piston body outer peripheral wall surface 113 is formed with a plurality of annular grooves 114 centered on the piston center axis C1. Each of these grooves 114 accommodates an annular oil ring (not shown). A cavity 115 is formed in the piston main body top wall surface 111.

  Each skirt portion 12A, 12B is a substantially partial annular portion centered on the piston center axis C1. Each of the skirt portions 12A and 12B has one outer peripheral wall surface (hereinafter referred to as “skirt outer peripheral wall surface”) 121 that forms a substantially partial cylindrical surface centered on the piston center axis C1 and faces outward. And an inner peripheral wall surface 122 (hereinafter also referred to as a wall surface “skirt inner peripheral wall surface”) 122 facing inward and forming a substantially partial cylindrical surface centered on the piston center axis C1. Further, the skirt portions 12A and 12B are disposed on opposite sides symmetrically with respect to the piston center axis C1. In other words, the skirt portions 12A and 12B extend downward in parallel to the piston center axis C1 from the partial annular outer peripheral region of the piston body bottom wall surface 112 located on the opposite side to the piston center axis C1. Exist. Each skirt outer peripheral wall surface 121 is substantially flush with the piston main body outer peripheral wall surface 113.

  Each of the sidewall portions 13A and 13B is a flat portion. Each of the sidewall portions 13A and 13B has a flat outer surface (hereinafter referred to as a “side wall outer wall surface”) 131 and a flat inner surface. One inner wall surface (hereinafter, this wall surface is also referred to as “side wall inner wall surface”) 132. Further, the sidewall portions 13A and 13B are disposed on opposite sides symmetrically with respect to the piston center axis C1. In other words, the sidewall portions 13A and 13B extend downward in parallel to the piston center axis C1 from the rectangular region of the piston main body bottom wall surface 112 located on the opposite side to the piston center axis C1. ing. Further, the side ends of the sidewall portions 13A and 13B are connected to the corresponding side ends of the skirt portion 12. Therefore, each side wall part 13A, 13B is arrange | positioned between the two skirt parts 12A, 12B, and has connected these two skirt parts 12A, 12B mutually.

  Each pin hole part 14A, 14B is an annular part. Therefore, through holes (hereinafter referred to as “pin holes”) 141 are formed in the pin hole portions 14A and 14B. In these pin holes 141, one common piston pin (not shown) for connecting the piston 10 to a connecting rod (not shown) is inserted. Each pin hole portion 14A, 14B has a central axis line (that is, a central axis line of the pin hole 141, hereinafter referred to as "pin hole central axis line") C2 extending from the sidewall portions 13A, 13B. It is provided so as to be perpendicular to the plane and penetrate substantially the middle part of the sidewall portions 13A and 13B. Accordingly, one end of each of the pin hole portions 14A and 14B in a direction parallel to the pin hole center axis C2 protrudes outward from the sidewall outer wall surface 131 and is parallel to the pin hole center axis C2. The other end of each of the pin hole portions 14A and 14B in the right direction protrudes inward from the sidewall inner wall surface 132.

  In addition, each pin hole part 14A, 14B is arrange | positioned so that the center axis C2 of one pin hole 141 may correspond with the center axis C2 of the other pin hole 141. FIG. Further, since the respective pin hole portions 14A and 14B are provided in the sidewall portions 13A and 13B, and the respective sidewall portions 13A and 13B are connected to the piston main body bottom wall surface 112, the respective sidewall portions 13A and 13B. Can be said to be a connecting portion that connects the piston body 11 and the pin hole portions 14A and 14B to each other.

  Further, in the following description, the upper portions of the pin hole portions 14A and 14B indicated by the reference numeral 143 in FIG. 1A are referred to as “pin hole upper portions”, and the reference numeral 142 in FIG. The side portions of the pin hole portions 14A and 14B shown are referred to as “pin hole side portions”.

  Ribs 30 are provided on the sidewall outer wall surfaces 131 between the pin hole portions 14 </ b> A and 14 </ b> B and the piston main body portion 11. The rib 30 extends in parallel to the piston center axis C <b> 1 and connects the pin hole upper portion 143 and the piston body bottom wall surface 112.

  A cavity (hereinafter referred to as “piston cavity”) 101 is formed inside the piston 10. The piston cavity 101 is generally defined by a piston main body bottom wall surface 112, a skirt inner peripheral wall surface 122, and a sidewall inner wall surface 132.

  An oil passage (not shown) is formed inside the piston main body 11 for passing oil for cooling the piston main body 11.

  As shown in FIG. 1B, one pin hole portion (hereinafter, this pin hole portion is referred to as “first pin hole portion”) 14A and one skirt portion (hereinafter, this skirt portion is referred to as “first pin portion”). An oil introduction passage defining wall 103 is provided on the inner wall surface 132 of one side wall portion (hereinafter referred to as “first side wall portion”) 13 </ b> A between the two side walls 12 </ b> A ”(referred to as“ one skirt portion ”). ing. The oil introduction passage defining wall 103 extends from the region near the bottom end face of the first sidewall portion 13A substantially upward to the piston main body bottom wall surface 113 through the region near the first pin hole portion 14A. The oil introduction passage defining wall 103 defines an oil introduction passage 102 for introducing oil into the oil passage formed inside the piston main body 11. The oil introduction passage 102 is connected to the oil passage at the piston main body bottom wall surface 113.

  In addition, the other pin hole portion (hereinafter, this pin hole portion is referred to as “second pin hole portion”) 14B and the other skirt portion (hereinafter, this skirt portion is referred to as “second skirt portion”) 12B. An oil discharge passage defining wall 105 is provided on an inner wall surface 132 of a sidewall portion (hereinafter, this sidewall portion is referred to as a “second sidewall portion”) 13B. The oil discharge passage defining wall 105 extends from the region near the bottom end surface of the second sidewall portion 13B to the piston body bottom wall surface 113 through the region near the second pin hole portion 14B substantially upward. The oil discharge passage defining wall 105 defines an oil discharge passage 104 for discharging the oil in the oil passage formed inside the piston main body 11. The oil discharge passage 104 is connected to the oil passage at the piston main body bottom wall surface 113.

  Accordingly, the defining walls 103 and 105 are provided on the sidewall inner wall surfaces 132 corresponding to each other symmetrically with respect to the piston center axis C1.

  In the following description, the side end of the first sidewall portion 13A closer to the oil introduction passage defining wall 103 is referred to as “first side end”, and the side farther from the oil introduction passage defining wall 103 is referred to as “first side end”. The side end of the first sidewall portion 13A is referred to as “second side end”, and the side end of the second sidewall portion 13B closer to the oil discharge passage defining wall 105 is referred to as “first side end”. The side end of the second sidewall portion 13B far from the oil discharge passage defining wall 105 is referred to as a “second side end”. In the following description, the side end of the first skirt portion 12A connected to the first side end of the first sidewall portion 13A is referred to as a “first side end”, and the second sidewall portion 13B. The side end of the first skirt portion 12A connected to the second side end of the first side is referred to as a “second side end”, and the second side end connected to the first side end of the second sidewall portion 13B. The side end of the skirt portion 12B is referred to as “first side end”, and the side end of the second skirt portion 12B connected to the second side end of the first sidewall portion 13A is referred to as “second side end”. Called “end”.

  Two raised portions 20 are provided on the first sidewall portion 13A, and two raised portions 20 are also provided on the second sidewall portion 13B. These raised portions 20 are portions of the sidewall portions 13A and 13B, and are portions that protrude outward from the other portions of the sidewall portions 13A and 13B. Therefore, the sidewall outer wall surface 131 in the region corresponding to the raised portion 20 protrudes outward as compared to the sidewall outer wall surface 131 in the region other than the region.

  Next, the raised portions 20 will be described in detail.

  In the following description, the region indicated by the reference symbol AR1 in FIG. 2 is referred to as an “upper corner region”. This region is a region of the sidewall outer wall surface 131 in the vicinity of the upper end of the connection portion between the sidewall portions 13A and 13B and the skirt portions 12A and 12B (that is, in the vicinity of the connection portion between the skirt portions 12A and 12B and the piston main body portion 11). Of the outer wall surface 131 of the sidewall. Further, the region indicated by the reference symbol AR2 in FIG. 2 is referred to as a “lower corner region”. This region is a region of the sidewall outer wall surface 131 in the vicinity of the lower end of the connection portion between the sidewall portions 13A and 13B and the skirt portions 12A and 12B. Further, the region indicated by the reference symbol AR3 in FIG. 2 is referred to as “pin hole side region”. This region is a region of the sidewall outer wall surface 131 in the vicinity of the pin hole side portion 142.

  Each sidewall outer wall surface 131 has two upper corner regions AR1, two lower corner regions AR2, and two pin hole side regions AR3. Each raised portion 20 is provided on each of the sidewall portions 13A and 13B so as to extend from the upper corner area AR1 to the pin hole side area AR3 closer to the upper corner area AR1. More specifically, each raised portion 20 has a left and right pin hole portion with respect to the pin hole center axis as viewed in FIG. 2 as well as the pin hole portion 14B above the pin hole center axis as viewed in FIG. 14B extends substantially straight from the upper corner area AR1 to the pin hole side area AR3 toward a substantially central part (hereinafter referred to as “an obliquely upper part of the pin hole”). In other words, a plane including the pin hole center axis and the piston center axis is referred to as a pin hole vertical plane, and a plane including the pin hole center axis and perpendicular to the piston center axis is referred to as a pin hole lateral plane. When the portion of the pin hole portion 14B in the vicinity of the pin hole lateral plane is referred to as a pin hole lateral portion, the pin hole upper portion 143 is a portion of the pin hole portion in the vicinity of the pin hole longitudinal plane and is a piston with respect to the pin hole central axis. It is a part on the main body part 11 side, the pin hole obliquely upper part is a part of the pin hole part 14B located substantially in the middle of the pin hole upper part 143 and the pin hole lateral part, and the raised part 20 is from the upper corner area AR1. It extends substantially straight to the pin hole side area AR3 adjacent to the pin hole diagonally upper part. Further, as shown in FIG. 3, the outer wall surface of each raised portion 20 protrudes so as to form a substantially partial cylindrical surface having a line along the extending direction of the raised portion 20 as a generating line.

  Further, as shown in FIG. 3, the inner wall surface of each raised portion 20 (that is, the sidewall inner wall surface 132 corresponding to the raised portion 20) has a line along the extending direction of the raised portion 20 as a bus. It is recessed so as to form a substantially partial cylindrical surface. That is, the sidewall inner wall surface 132 is recessed along the raised portion 20 in a region corresponding to the raised portion 20. Therefore, the sidewall inner wall surface 132 is formed with a groove 21 extending from the upper corner area AR1 to the pin hole side area AR3 closer to the upper corner area AR1.

  By providing the raised portions 20 on the sidewall portions 13A and 13B, the following effects can be obtained.

  That is, when the piston 10 is disposed in the cylinder bore of the internal combustion engine, the combustion chamber (not shown) is formed by the piston body top wall surface 111, the cylinder bore inner wall surface (not shown), and the cylinder head bottom wall surface (not shown). Is formed. A piston pin (not shown) is inserted into the pin hole 141, and the piston 10 is connected to a connecting rod (not shown) via the piston pin.

  Here, when the internal combustion engine is operated and a mixture of fuel and air is combusted in the combustion chamber in the expansion stroke, a large combustion pressure load (that is, a load due to the combustion pressure) is applied to the piston main body top wall surface 111. Then, due to this large combustion pressure load, the inner peripheral wall surface of the pin hole upper portion 143 is pressed against the outer peripheral wall surface of the piston pin upper portion (that is, the upper portion of the piston pin), and as a result, the inner peripheral wall surface of the pin hole upper portion 143 And the pin hole upper part 143 and the piston pin are both deformed so that the curvature radius of the outer peripheral wall surface of the piston pin upper part is larger than the original radius of the pin hole 141 and the original radius of the piston pin, respectively. As a result, tensile stress is generated in the inner peripheral wall surface portion of the pin hole upper portion 143. On the other hand, in the exhaust stroke and the intake stroke following the expansion stroke, the pressure in the combustion chamber decreases, so the tensile stress generated in the inner peripheral wall surface portion of the pin hole upper portion 143 disappears.

  Since the expansion stroke, the exhaust stroke, and the intake stroke are repeatedly performed during engine operation (that is, during operation of the internal combustion engine), the pin hole upper portion 143 is likely to be deteriorated due to fatigue (hereinafter referred to as deterioration due to this fatigue). Is called "fatigue degradation").

  Here, in the piston of the first embodiment, the raised portions 20 are provided on the sidewall portions 13A and 13B. These raised portions 20 extend substantially straight from the upper corner region AR1 to the pin hole side region AR3 toward the diagonally upper portion of the pin hole in the sidewall portions 13A and 13B. Therefore, these raised portions 20 transmit the bending force of the piston main body 11 due to the combustion pressure load to the pin hole side portion 142. Then, due to the force transmitted to the pin hole side portion 142, a force is applied to the pin hole portion 14B in a direction to suppress the bending of the pin hole upper portion 143 due to the combustion pressure load in the expansion stroke. Thereby, the bending of the pin hole upper portion 143 is suppressed, and as a result, the occurrence of tensile stress in the pin hole upper portion 143 is suppressed. For this reason, even if the diameter of the pin hole is reduced, fatigue deterioration of the pin hole upper portion 143 is suppressed. Therefore, according to the first embodiment, the diameter of the pin hole can be reduced while suppressing fatigue deterioration of the pin hole upper portion 143.

  By the way, the raised part 20 of 1st Embodiment is an example of the raised part of this invention. That is, the raised portion of the present invention includes any raised portion extending in the direction from the upper corner area AR1 toward the pin hole side area AR3. In other words, in the raised portion of the present invention, the compressive force applied to the sidewall portions 13A and 13B by the displacement of the piston body outer peripheral portion 116 due to the deflection of the piston body portion 11 is applied to the sidewall portion 13A. , 13B along any path extending from the upper corner area AR1 to the pin hole side area AR3. In other words, the protruding portion of the present invention has a protruding portion on the pin hole side from the upper corner region AR1 so as to suppress the deflection of the piston body 11 when the piston body top wall surface 111 receives a combustion pressure load. Any raised portion extending in the direction toward the region AR3 is included.

  Accordingly, the raised portion of the present invention also includes a raised portion 20 of the shape shown in FIG. That is, each raised portion 20 shown in FIG. 4 extends in a substantially arc shape with a central portion protruding toward the lower corner area AR2 in the extending direction. In other words, each raised portion 20 extends from the upper corner area AR1 substantially downward to the central portion thereof, and the extending direction of the raised portion 20 is pin hole side portion 142 in the central portion. The direction gradually changes in the direction toward, and extends toward the pin hole side portion 142 when the center portion is exceeded.

  Moreover, in 1st Embodiment, it replaces with providing the protruding part 20 extended from upper corner area | region AR1 to pin hole side area | region AR3 in side wall part 13A, 13B, and replaces from upper corner area | region AR1 to pin hole side area | region. You may make it provide the protruding part extended in a part of area | region to AR3 in side wall part 13A, 13B.

  Moreover, in 1st Embodiment, it replaces with providing the protruding part 20 extended continuously in sidewall part 13A, 13B, and the protruding part divided | segmented into several parts and extended is sidewall part 13A, 13B. You may make it provide in.

  Further, in the first embodiment, instead of providing the protruding portion 20 protruding outward in the sidewall portions 13A and 13B, the protruding portion protruding inward may be provided in the sidewall portions 13A and 13B. Good. In this case, in the first embodiment, instead of forming the groove 21 extending along the raised portion 20 on the sidewall inner wall surface 132, the groove extending along the raised portion is formed on the sidewall outer wall surface 131. It is formed.

  By the way, as described above, the groove 21 is formed along the raised portion 20 in the sidewall inner wall surface 132 corresponding to the raised portion 20. When the groove 21 is formed in this way, the effect that the piston 10 is reduced in weight can be obtained. Of course, when this effect is not required or when it is preferable that the groove 21 is not provided on the sidewall inner wall surface 132, the groove 21 may not be formed on the sidewall inner wall surface 132.

  Next, a connection form between the sidewall portions 13A and 13B and the skirt portions 12A and 12B will be described.

  In the following description, the side wall portions 13A, 13B and the skirt portions 12A, 12B are collectively referred to as “piston lower wall”, and the cross section of the piston lower wall cut by a specific surface is referred to as “piston lower wall cross section”. The bottom end surface of the piston lower wall is referred to as the “piston lower wall bottom end surface”, and the connecting portion between the side wall portion and the skirt portion of the piston lower wall cross section or the piston lower wall bottom end surface is referred to as the “piston lower wall connecting portion”. The side wall portion in the vicinity of the piston lower wall connection portion is referred to as “side wall connection portion”, the skirt portion in the vicinity of the piston lower wall connection portion is referred to as “skirt connection portion”, and the piston lower wall cross section Or, the direction in which the side wall connecting portion extends toward the piston lower wall connecting portion on the bottom end surface of the piston lower wall is The direction in which the skirt connecting portion extends toward the piston lower wall connecting portion on the piston lower wall cross section or the bottom surface of the piston lower wall is called the “skirt extending direction”. The angle at which the direction and the skirt extending direction intersect is referred to as “piston lower wall intersection angle”.

  As shown in FIG. 5, a plurality of surfaces A to G for taking a piston lower wall cross section are set. Here, as shown in FIG. 6, a plane P1 perpendicular to the piston center axis C1 is referred to as a “horizontal plane”, and a distance D1 between the horizontal plane P1 and the pin hole center axis C2 is defined as a “horizontal plane distance”. The planes A to G shown in FIG. 5 are horizontal planes P1 having different horizontal plane distances D1.

  In the example shown in FIG. 5, the horizontal plane distance D1 of the surface D is zero. With respect to the surface D, the surface A and the surface G are symmetric, the surface B and the surface F are symmetric, and the surface C and the surface E are symmetric. Further, the horizontal plane distance D1 between the surfaces A and G is the largest, the horizontal plane distance D1 between the surfaces B and F is the next largest, and the horizontal plane distance D1 between the surfaces C and E is set the next largest.

  7A to 7G show cross sections of the piston lower wall when viewed from below by cutting the piston lower wall along these surfaces A to G, respectively, and the piston lower wall bottom end surface is shown in FIG. 7 (H).

  As can be seen from FIG. 7, in the piston 10, the piston lower wall crossing angle (the angle indicated by the reference sign AN in FIG. 7) gradually increases from the lower side to the upper side in the piston lower wall. .

  Therefore, the piston lower wall crossing angle in the upper part of the skirt portions 12A and 12B is relatively large. According to this, the following effects can be obtained.

  That is, when the piston 10 is disposed in the cylinder bore and the internal combustion engine is operated, the skirt portions 12A and 12B receive a so-called thrust force from the inner peripheral wall surface of the cylinder bore. During engine operation, the temperature of the upper part of the skirt parts 12A and 12B (hereinafter, this part is also referred to as “skirt upper part”) is the center part of the skirt part (hereinafter referred to as “skirt central part”) and the skirt part. It becomes higher than the temperature of the lower part (hereinafter, this part is referred to as “skirt lower part”). For this reason, the degree of thermal expansion of the upper part of the skirt is greater than the degree of thermal expansion of the central part of the skirt and the lower part of the skirt. Therefore, when the thrust resistance of the upper part of the skirt (that is, resistance to deformation due to the thrust force) is high, there is a high possibility that a so-called interference fit is generated in which the upper part of the skirt is relatively strongly pressed against the inner peripheral wall surface of the cylinder bore. On the other hand, when the thrust resistance of the upper part of the skirt is low, when the upper part of the skirt is thermally expanded, the upper part of the skirt can be deformed inward in the radial direction with respect to the piston center axis C1. Low. Therefore, in order to suppress the interference fit, it is preferable to reduce the thrust resistance of the upper part of the skirt.

  Here, the greater the piston lower wall crossing angle, the lower the thrust resistance of the skirt portions 12A, 12B. In the piston 10, since the piston lower wall crossing angle gradually increases from the lower side to the upper side in the piston lower wall, the piston lower wall crossing angle of the upper part of the skirt is relatively large. Accordingly, since the thrust resistance of the upper part of the skirt is low, the interference fit of the upper part of the skirt is suppressed.

  Moreover, in the piston 10, the piston lower wall crossing angle of the lower part of the skirt is relatively small. According to this, the following effects can be obtained.

  That is, when the piston 10 is disposed in the cylinder bore and the internal combustion engine is operated, a force is applied to the piston 10 to displace the piston 10 so that the piston center axis C1 is inclined with respect to the cylinder bore center axis. The lower part of the skirt is pressed against the inner peripheral wall surface of the cylinder bore. At this time, if the rigidity of the lower part of the skirt is low, the lower part of the skirt can be easily deformed inward. Therefore, when the lower part of the skirt is pressed against the inner peripheral wall surface of the cylinder bore, the lower part of the skirt is deformed inward. On the other hand, if the rigidity of the lower part of the skirt is high, even if the lower part of the skirt is pressed against the inner peripheral wall surface of the cylinder bore, the lower part of the skirt does not deform inward. Therefore, in order to prevent the skirt lower part from being deformed inward, it is preferable to increase the rigidity of the skirt lower part.

  Here, the smaller the piston lower wall crossing angle, the higher the rigidity of the skirt portions 12A and 12B. In the piston 10, since the piston lower wall crossing angle gradually increases from the lower side to the upper side in the piston lower wall, the piston lower wall crossing angle of the lower part of the skirt is relatively small. Therefore, since the rigidity of the lower part of the skirt is high, the inward deformation of the lower part of the skirt is suppressed.

  Thus, in the piston 10, the piston lower wall crossing angle gradually increases from the lower side to the upper side in the piston lower wall, thereby suppressing the interference fit of the upper part of the skirt and inward of the lower part of the skirt. Suppression of deformation is achieved at the same time.

  By the way, in the piston 10, a plurality of piston lower wall cross sections are obtained as follows, and when the piston lower wall cross section and the piston lower wall cross angle at the piston lower wall bottom end face are compared with each other, the piston lower wall cross angle is also compared. Is gradually increased from below to above in the piston lower wall.

  That is, as shown in FIG. 8, a plurality of surfaces A to G for taking a piston lower wall cross section are set. Here, as shown in FIG. 9, a plane P2 including the pin hole center axis C2 and the piston center axis C1 is referred to as a “reference plane”, and a plane P3 extending to one side of the reference plane P2. And the plane P4 extending to the other side of the reference plane P2 is a pair of planes P3 and P4 that are symmetrical with respect to the reference plane P2 and intersect with each other. When a pair of planes coinciding with the axis C2 are referred to as “pair planes” and an angle AN1 between the pair planes P3 and P4 is referred to as “interplane angle”, planes A to G shown in FIG. The plane-to-plane angles AN1 are different planes P3 and P4, respectively.

  In the example shown in FIG. 8, the inter-plane angle AN1 is set to be larger in the order of the opposite planes A to G.

  When the piston lower wall crossing angle in the piston lower wall cross section when the piston lower wall is cut along these opposite planes A to G and the piston lower wall crossing angle in the piston lower wall bottom end surface are compared with each other, the piston lower wall The crossing angle gradually increases from the bottom to the top in the piston lower wall.

  Further, in the piston 10, a plurality of piston lower wall cross sections are obtained as follows, and the piston lower wall cross angle is also compared when the piston lower wall cross section and the piston lower wall cross angle at the piston lower wall bottom end surface are compared with each other. Is gradually increased from below to above in the piston lower wall.

  That is, as shown in FIG. 10, a plurality of surfaces A to G for taking a piston lower wall cross section are set. Here, as shown in FIG. 11, a plane P2 including the pin hole center axis C2 and the piston center axis C1 is referred to as a “reference plane”, and a plane P5 extending to one side of the reference plane P2. A pair of planes P5 and P6 constituted by a plane P6 extending to the other side of the reference plane P2 and symmetric with respect to the reference plane P2 are referred to as “pair planes”. When the angle AN2 between the planes P5 and P6 is referred to as an “interplanar angle”, and the distance D2 between the line intersecting the planes P5 and P6 and the pin hole central axis C2 is referred to as a “plane distance”, FIG. The planes A to G shown in FIG. 2 are opposite planes P5 and P6 with different plane-to-plane angles AN2 and cross-sectional plane distances D2.

  In the example shown in FIG. 10, the angle between the planes of the plane D is 180 °. And with respect to the opposing plane D, the opposing planes A to C are arranged on the upper side, and the opposing planes E to G are arranged on the lower side. Further, with respect to the pair plane D, the pair plane A and the pair plane G are symmetric, the pair plane B and the pair plane F are symmetric, and the pair plane C and the pair plane E are symmetric. The plane distance D2 between the planes A and G is the largest, the plane distance D2 between the planes B and F is the next largest, and the plane distance D2 between the planes C and E is the next largest. Further, the inter-plane angle AN2 is set to be larger in the order of the planes A to C and E to G.

  When the piston lower wall crossing angle in the piston lower wall cross section when the piston lower wall is cut along these opposite planes A to G and the piston lower wall crossing angle in the piston lower wall bottom end surface are compared with each other, the piston lower wall The crossing angle gradually increases from the bottom to the top in the piston lower wall.

  Further, in the piston 10, a plurality of piston lower wall cross sections are obtained as follows, and the piston lower wall cross angle is also compared when the piston lower wall cross section and the piston lower wall cross angle at the piston lower wall bottom end surface are compared with each other. Is gradually increased from below to above in the piston lower wall.

  That is, as shown in FIG. 12, a plurality of surfaces A to G for taking a piston lower wall cross section are set. Here, as shown in FIG. 13, a plane P2 including the pin hole center axis C2 and the piston center axis C1 is referred to as a “reference plane”, and a cylindrical surface having the center axis on the reference plane P2 as the center. When P7 is simply referred to as “cylindrical surface” and the distance D3 between the line intersecting the cylindrical surface P7 and the reference plane P2 and the pin hole central axis C2 is referred to as “cylindrical surface distance”, it is shown in FIG. The surfaces A to C and E to G are cylindrical surfaces P7 having different radii of curvature and cross-sectional plane distances D3, and the surface D shown in FIG. 12 is perpendicular to the reference plane P2. It is a surface including the pin hole central axis C2.

  In the example shown in FIG. 12, with respect to the surface D, the cylindrical surfaces A to C are arranged on the upper side, and the cylindrical surfaces E to G are arranged on the lower side. Regarding the surface D, the cylindrical surface A and the cylindrical surface G are symmetric, the cylindrical surface B and the cylindrical surface F are symmetric, and the cylindrical surface C and the cylindrical surface E are symmetric. The sectional plane distance D3 between the cylindrical surfaces A and G is the largest, the sectional plane distance D3 between the cylindrical surfaces B and F is the next largest, and the sectional plane distance D3 between the cylindrical surfaces C and E is set the next largest. Yes. Further, the radius of curvature of the cylindrical surfaces A and G is the smallest, the radius of curvature of the cylindrical surfaces B and F is set to the next smallest, and the radius of curvature of the cylindrical surfaces C and E is set to the next smallest.

  And when the piston lower wall is cut along these cylindrical surfaces A to C and E to G and the surface DD, the piston lower wall crossing angle in the piston lower wall cross section and the piston lower wall crossing angle in the piston lower wall bottom end surface Are compared with each other, the piston lower wall crossing angle gradually increases from the lower side to the upper side on the piston lower wall.

  As described above, if the characteristics related to the piston lower wall crossing angle described with reference to FIGS. 5 to 13 are comprehensively expressed, in the piston 10, at least the piston lower wall crossing angles (at the two piston lower wall cross sections that do not cross each other) Or, the piston lower wall crossing angle in the piston lower wall cross-section located higher is lower than the piston lower wall crossing angle in one piston lower wall cross-section and the piston lower wall bottom end face). It can be said that it is larger than the piston lower wall crossing angle in the piston lower wall cross section (or the piston lower wall bottom end face).

  Incidentally, as can be seen from FIG. 7, in the piston 10, the side wall connecting portion (that is, the portion of the side wall portions 13 </ b> A and 13 </ b> B near the piston lower wall connecting portion) is at least curved. The curvature radius of the side wall connecting portion (hereinafter, this curvature radius is referred to as “side wall curvature radius”) gradually decreases from the lower side to the upper side in the side wall portion.

  In the piston 10, the side wall connecting portion at the bottom end surface of the piston lower wall may extend linearly, or the lower side section of the lower piston wall and the side wall connecting portion at the bottom end surface of the piston lower wall are linear. It may extend to.

  As described above, in the piston 10, the side wall curvature radius gradually decreases from the lower side to the upper side in the side wall portions 13A and 13B. Therefore, the sidewall curvature radius in the upper portion of the sidewall is relatively small. According to this, the following effects can be obtained.

  That is, as described above, in order to suppress the interference fit, it is preferable to reduce the thrust resistance of the upper part of the skirt. Here, the smaller the sidewall curvature radius, the lower the thrust resistance of the skirt. Therefore, in the piston 10, the sidewall curvature radius gradually decreases from the lower side to the upper side in the side wall portions 13A and 13B, so that the thrust resistance of the upper part of the skirt is low, and the interference fit of the upper part of the skirt is suppressed. Is done.

  Further, as described above, in the piston 10, the sidewall curvature radius gradually decreases from the lower side to the upper side in the side wall portions 13A and 13B. Therefore, the sidewall curvature radius in the lower portion of the sidewall is relatively large. According to this, the following effects can be obtained.

  That is, as described above, in order to suppress the inward deformation of the skirt lower part, it is preferable to increase the rigidity of the skirt lower part. Here, the larger the sidewall curvature radius, the higher the rigidity of the skirt portion. Therefore, in the piston 10, the sidewall curvature radius gradually decreases from the lower side to the upper side in the side wall portions 13A and 13B. Therefore, the rigidity of the lower part of the skirt is high, and the deformation of the lower part of the skirt is inward. Is suppressed.

  As described above, in the piston 10, the side wall curvature radius gradually decreases from the lower side to the upper side in the side wall portions 13A and 13B, thereby suppressing the interference fit of the upper part of the skirt and the inner side of the lower part of the skirt. Suppression of deformation to the same has been achieved at the same time.

  Next, the thickness of the skirt portions 12A and 12B when measured in a direction perpendicular to the piston center axis C1 will be described.

  In the piston 10, the skirt portions 12A and 12B have a thickness that gradually increases from the top to the bottom in the skirt portion as shown in FIG. The thickness is also called “skirt thickness”). According to this, the following effects can be obtained.

  That is, the skirt portions 12A and 12B are connected to the piston main body 11 having high rigidity at their upper ends (hereinafter, the upper ends are referred to as “skirt upper ends”). Accordingly, if the skirt portions 12A and 12B have a constant thickness throughout, the thrust resistance of the skirt portion (that is, the ability to withstand deformation due to the thrust force) is the lower end of the skirt portion (hereinafter referred to as this lower portion). The end tends to become higher from the “skirt lower end” toward the upper end of the skirt.

  Therefore, for example, as shown in FIG. 14B, when the skirt portions 12A and 12B have a thickness that gradually decreases from the upper end of the skirt toward the lower end of the skirt, the central region of the skirt portion The thickness of this part (hereinafter this part is also referred to as “skirt central part”) and the part of the lower region of the skirt part (hereinafter this part is also referred to as “skirt lower part”) are relatively thin. The thrust resistance of these parts is significantly reduced. In this case, when the thrust force is applied to the skirt portions 12A and 12B, at least the central portion of the skirt is recessed. In this case, an acute corner portion is formed at the boundary portion between the concave portion of the skirt central portion and the non-dented portion of the skirt portion. When such a corner portion is formed in the skirt portions 12A and 12B, friction between the skirt portion and the inner peripheral wall surface of the cylinder bore increases at the corner portion.

  However, when the skirt portions 12A and 12B have a thickness that gradually increases from the upper end of the skirt toward the lower end of the skirt as in the piston 10, the thickness of the skirt central portion and the thickness of the skirt lower portion are relatively Since it is thick, the thrust resistance of these parts is relatively high. Of course, the thickness of the upper region of the skirt portions 12A and 12B (hereinafter, this portion is referred to as the “skirt upper portion”) is relatively thin, but since this portion is a portion close to the piston body 11, The thrust resistance of this part is relatively high.

  Thus, in the piston 10, since the thrust resistance of the skirt portions 12A and 12B as a whole is high, the central portion of the skirt is not recessed by the thrust force (or even if the skirt central portion is deformed so as to be recessed). The deformation amount is very small and the area of the recessed portion is very small). Therefore, an increase in friction between the skirt portions 12A and 12B and the cylinder bore inner peripheral wall surface is suppressed.

  By the way, as described above, when the thrust resistance of the upper part of the skirt is high, there is a high possibility that the interference of the upper part of the skirt will occur. It is preferable to reduce the resistance.

  Here, in the piston 10, as described above, the skirt portions 12A and 12B have a thickness that gradually increases from the lower end of the skirt toward the upper end of the skirt, and the thickness of the upper portion of the skirt becomes relatively thin. Yes. Accordingly, since the thrust resistance of the upper part of the skirt is low, the interference fit of the upper part of the skirt is suppressed.

  By the way, as shown in FIG. 14A, the skirt outer peripheral wall surface 121 is a partial cylindrical surface with the piston center axis C1 as the center, but a portion having a large diameter with respect to the piston center axis C1 (hereinafter, this portion is referred to as “ When the large-diameter portion is on the skirt outer peripheral wall surface 121, a large thrust force is applied to the large-diameter portion. Therefore, it can be said that this large-diameter portion is easily dented by the thrust force. And as above-mentioned, in order to suppress that the friction between skirt part 12A, 12B and a cylinder bore inner peripheral wall surface becomes large, it is preferable to suppress that the skirt outer peripheral wall surface 121 dents. Therefore, when the diameter of each part of the skirt outer peripheral wall surface 121 with respect to the piston center axis C1 is different, the thickness of each part may be increased in proportion to the diameter of the part. According to this, even when the skirt outer peripheral wall surface 121 has a large-diameter portion, the friction between the skirt portions 12A, 12B and the cylinder bore inner peripheral wall surface is suppressed.

  As described above, when the thickness of each part of the skirt parts 12A and 12B is increased in proportion to the diameter of the part, when the large diameter part is in the central region of the skirt outer peripheral wall surface 121, as a result, The thickness of the upper part of the skirt is thin. For this reason, since the thrust resistance of the upper part of the skirt is low, the interference fit of the upper part of the skirt is suppressed.

  By the way, when the large diameter portion is in the central region of the skirt outer peripheral wall surface 121, the skirt outer peripheral wall surface 121 is prevented from being recessed radially inward with respect to the piston center axis C1, and the interference fit of the upper portion of the skirt is suppressed. For this, at least the thickness of the central part of the skirt should be relatively thick and the thickness of the upper part of the skirt should be relatively thin. Therefore, in this case, the thickness of the lower part of the skirt may be relatively thin. Therefore, when the large-diameter portion is in the central region of the skirt outer peripheral wall surface 121, as shown in FIG. 14C, the thickness of the skirt central portion is made relatively thick, and the skirt upper portion and the skirt lower portion The thickness may be made relatively thin.

  In this case, since the thickness of the lower part of the skirt is relatively thin, an effect of reducing the weight of the piston 10 can be obtained.

  By the way, as mentioned above, when the piston main body part 11 bends, the side wall parts 13A and 13B are also bent using the pin hole upper part 143 as a fulcrum. Thus, the pin hole upper portion 143 serves as a fulcrum for bending the sidewall portions 13A and 13B. For this reason, the temperature of the pin hole upper portion 143 and the vicinity thereof tends to be higher than the temperatures of the other portions. Therefore, in order to suppress fatigue deterioration of the pin hole upper portion 143 and the vicinity thereof, it is desired to cool these portions efficiently.

  Therefore, in the piston 10, the pin hole upper portion 143 and the vicinity thereof may be configured as shown in FIG. That is, in the embodiment shown in FIG. 15 (hereinafter, this embodiment is referred to as “second embodiment”), the ribs 30 are recessed in the sidewall outer wall surface 131 near the pin hole upper portion 143 on both sides of the rib 30 (FIG. 15). (A), a shaded portion denoted by reference numeral 31 is provided. The wall surface that defines each recess 31 is at least approximately inwardly extending from the region adjacent to the pin hole upper portion 143 toward the inside of the sidewall portions 13A and 13B and obliquely upward. And a wall surface 33 extending substantially perpendicularly to the piston center axis C1 from the inner end of the recess slope 32 to the outside.

  The following effects are acquired by providing the depression 31 in the sidewall outer wall surface 131 in the vicinity of the pin hole upper portion 143 as in the second embodiment.

  That is, when the piston 10 of the second embodiment is disposed in the cylinder bore and the internal combustion engine is operated, oil for cooling / lubricating is provided from below into the space between the sidewall outer wall surface 131 and the cylinder bore inner wall surface. Blown up. The blown oil arrives at the pin hole upper portion 143 and the vicinity thereof through a space between the sidewall outer wall surface 131 and the cylinder bore inner wall surface.

  Here, when the concave slope 32 is not provided in the vicinity of the pin hole upper portion 143, the oil arriving at this portion flows out from this portion relatively early. That is, the time for the oil to stay around the portion near the pin hole upper portion 143 is short.

  On the other hand, when the depression slope 32 is provided in the vicinity of the pin hole upper portion 143 as in the second embodiment, the time that the oil stays in the vicinity of the portion near the pin hole upper portion is increased for the following reason. . That is, as shown in FIG. 16A, when the piston 10 is disposed in the cylinder bore 50, the piston center axis C1 is substantially parallel to the vertical direction. Therefore, when the piston is disposed in the cylinder bore, the concave slope 32 is disposed obliquely with respect to the vertical direction. For this reason, the oil that has arrived in the vicinity of the upper portion of the pin hole stays on the concave slope 32 as shown in FIG. For this reason, when the concave slope 32 is provided in the vicinity of the pin hole upper portion, the time for the oil to stay around the portion near the pin hole upper portion becomes longer.

  According to the second embodiment, the oil stays in the vicinity of the portion near the pin hole upper portion 143, so that the portion of the piston around the portion near the pin hole upper portion (that is, the pin hole upper portion 143 and The portion in the vicinity thereof is efficiently cooled.

  Furthermore, when the concave slope 32 is provided in the vicinity of the pin hole upper portion 143 as in the second embodiment, the time that the oil stays in the vicinity of the portion near the pin hole upper portion is further increased for the following reason. become longer. That is, as shown in FIG. 16B, when the piston 10 is disposed in the cylinder bore 50, the recessed inclined surface 32 is disposed obliquely with respect to the vertical direction. For this reason, the hollow slope 32 is inclined with respect to the diffusion direction of the oil arriving there. Therefore, as indicated by an arrow A in FIG. 16B, the depression slope 32 can rebound the oil that has arrived there upward. For this reason, the oil arriving at the depression slope 32 is scattered in the depression 31. That is, the oil that has arrived in the vicinity of the pin hole upper portion 143 stays around the portion in the vicinity of the pin hole upper portion. For this reason, when the concave slope 32 is provided in the vicinity of the pin hole upper portion 143 as in the second embodiment, the time for the oil to stay around the portion in the vicinity of the pin hole upper portion is further increased.

  According to the second embodiment, the oil stays in the vicinity of the portion near the pin hole upper portion 143, so that the portion of the piston around the portion near the pin hole upper portion (that is, the pin hole upper portion 143). And the vicinity thereof) are further efficiently cooled.

  By the way, the hollow 31 of 2nd Embodiment is an example of the hollow of this invention. That is, the depression of the present invention includes any depression that can retain oil in a portion near the upper portion of the pin hole.

  Therefore, in the piston of the second embodiment, instead of providing the depressions 31 on the sidewall outer wall surfaces 131 on both sides of the rib 30, the depressions are provided only on the sidewall outer wall surface 131 on one side of the rib 30. Also good.

  Further, the rib 30 has an effect of increasing the rigidity of the sidewall portions 13A and 13B between the pin hole upper portion 143 and the piston main body portion 11. However, if priority is given to the effect of retaining a larger amount of oil in the region in the vicinity of the pin hole upper portion 143 than such an effect, the sidewall outer wall surfaces on both sides of the rib 30 in the piston of the second embodiment. In addition to providing the recess 31 in 131, a recess similar to the recess 31 of the piston 10 of the second embodiment may be provided on the outer wall surface of the rib 30 near the pin hole upper portion 143.

  Of course, in the piston of the second embodiment, instead of providing the depression 31 on the sidewall outer wall surface 131 on both sides of the rib 30, the piston of the second embodiment is formed on the outer wall surface of the rib 30 near the pin hole upper portion 143. You may make it provide the hollow similar to the hollow 31 of ten.

  Moreover, the hollow slope 32 of 2nd Embodiment is an example of the hollow slope of this invention. That is, the concave slope of the present invention includes any wall surface that can retain oil arriving at a portion near the upper portion of the pin hole when the piston is disposed in the cylinder bore. In addition, the hollow surface of the present invention includes any wall surface that can rebound upwardly the oil arriving at a portion near the pin hole upper portion when the piston is disposed in the cylinder bore.

  Therefore, as in the second embodiment, instead of providing the depression slope 31 extending obliquely upward from the sidewall outer wall surface 131 in the vertical direction on the sidewall outer wall surface 131 in the vicinity of the pin hole upper portion 143, A wall surface extending obliquely downward from the region near the pin hole upper portion 143 toward the inside of the sidewall portions 13A and 13B with respect to the piston center axis C1 is provided on the sidewall outer wall surface 131 near the pin hole upper portion 143. Alternatively, the wall surface extending in the direction perpendicular to the piston center axis C1 from the region near the pin hole upper portion 143 toward the inside of the side wall portions 13A and 13B is the side near the pin hole upper portion 143. You may make it provide in the wall outer wall surface 131. FIG.

  Incidentally, as shown in FIG. 15A, in the second embodiment, the sidewall outer wall surface 131 is provided with a raised portion 20 similar to the raised portion 20 of the first embodiment. For this reason, the portion near the pin hole upper portion 143 is more efficiently cooled by the oil for the following reason.

  That is, the raised portion 20 of the second embodiment is provided on the sidewall portions 13A and 13B so as to extend from the pin hole side region AR3 to the upper corner region A1 in the same manner as the raised portion 20 of the first embodiment. ing. In other words, the raised portion 20 is in the direction away from the pin hole from the region of the sidewall outer wall surface 131 in the vicinity of the depression 31 (that is, in the vicinity of the depression slope 32) and in the vicinity of the pin holes 14A and 14B. In this case, the sidewall outer wall surface 131 extends obliquely upward. In other words, the raised portion 20 is in the vicinity of the depression 31 (that is, in the vicinity of the depression slope 32) and away from the pin hole portion from the region of the sidewall outer wall surface 131 in the vicinity of the pin hole portions 14A and 14B. It extends in the direction and obliquely upward to the region of the sidewall outer wall surface 131 adjacent to the piston body 11.

  Therefore, when the piston 10 is disposed in the cylinder bore so that the piston center axis C1 is parallel to the vertical direction, the upper region of the raised portion 20 (that is, the outer wall surface of the raised portion 20 extends along the extending direction thereof. The outer wall surface of a region located on the upper side when divided into two regions by a surface perpendicular to the sidewall outer wall surface 131 is inclined at least with respect to the vertical direction. For this reason, this outer wall surface can capture and retain the oil flowing out from the recess 31, and can also capture and retain the oil arriving at the sidewall outer wall surface 131 above the raised portion 20. Can do. In other words, the raised portion 20 can keep the oil in the vicinity of the pin hole upper portion 143 and the vicinity thereof. Then, the pinned oil cools the portion near the pin hole upper portion 143 and the surrounding portion. For this reason, in the second embodiment, the portion in the vicinity of the pin hole upper portion 143 and the surrounding portion are further efficiently cooled by the oil.

  In addition, the recess 31 of the above-described embodiment can retain oil not a little regardless of the viscosity of the oil. However, the higher the viscosity of the oil, the more the recess 31 can hold the oil more reliably. In addition, the raised portion 20 of the above-described embodiment can retain oil not a little regardless of the viscosity of the oil. However, the higher the oil viscosity, the more reliably the raised portion 20 can retain the oil.

  As shown in FIG. 1B, in the above-described embodiment, the oil introduction passage defining wall 103 is provided on the inner wall surface of the first sidewall portion 13A, and the inner wall of the second sidewall portion 13B is provided. An oil discharge passage defining wall 105 is provided on the wall surface. Next, the defining walls 103 and 105 will be described in detail.

  When the oil introduction passage defining wall 103 is provided as shown in FIG. 1B, the oil introduction passage defining wall 103 is a portion near the first side end of the first sidewall portion 13A. As a result, the rigidity of the portion in the vicinity of the first side end of the first skirt portion 12A connected to the first side end of the first sidewall portion 13A is also increased. However, the second side wall portion 13B is not provided with a wall such as the oil introduction passage defining wall 103 that increases the rigidity of the second side wall portion 13B in the vicinity of the second side end. The rigidity of the portion in the vicinity of the second side end of the first skirt portion 12A connected to the second side end of 13B is not increased. Therefore, the rigidity of the portion near the first side end of the first skirt portion 12A is higher than the rigidity of the portion near the second side end of the first skirt portion 12A.

  By the way, when the piston is disposed in the cylinder bore and the internal combustion engine is operated, the skirt portions 12A and 12B receive a thrust force from the inner peripheral wall surface of the cylinder bore. This thrust force increases or decreases. Here, when the thrust force increases, at least a part of the skirt portions 12A and 12B is deformed by the thrust force. After that, when the thrust force is reduced, the shape of the deformed skirt portions 12A and 12B returns to the original shape.

  Here, the rigidity of the portion in the vicinity of the first side end of the first skirt portion 12A is higher than the rigidity of the portion in the vicinity of the second side end of the first skirt portion 12A by the oil introduction passage defining wall 103. In this case, the degree of deformation of the first side end portion of the first skirt portion 12A due to the thrust force is smaller than the degree of deformation of the second side end portion of the first skirt portion 12A due to the thrust force. That is, in the first skirt portion 12A, the degree of deformation of the first side end portion due to the thrust force is different from the degree of deformation of the second side end portion due to the thrust force. When the deformation degrees are different from each other as described above, a large stress is generated in a part of the first skirt portion 12A when the first skirt portion 12A is deformed by receiving a thrust force. After that, when the thrust force received by the first skirt portion 12A is reduced, the shape of the deformed portion of the first skirt portion 12A returns to the original shape, and the large amount generated in a part of the first skirt portion 12A. The stress disappears. As described above, when a large stress is generated in the first skirt portion 12A or the large stress disappears, the first skirt portion 12A is deteriorated due to fatigue.

  Therefore, in order to suppress such fatigue deterioration of the first skirt portion 12A, as shown in FIG. 17, the first side end of the first skirt portion 12A is not provided without providing the oil introduction passage defining wall 103. An oil introduction port 104 for introducing oil into the oil passage inside the piston main body 11 is formed in a portion of the piston main body bottom wall surface 112 near the upper end of the connection portion between the first side wall 13A and the first side wall 13A. You may make it provide.

  In the embodiment shown in FIG. 17 (hereinafter, this embodiment is referred to as “third embodiment”), the rigidity of the first skirt portion 12A is uniform over the entire area. Generation of a large stress in a part is suppressed. For this reason, fatigue deterioration of the first skirt portion 12A is suppressed.

  Similarly, the rigidity of the portion near the first side end of the second skirt portion 12B is higher than the rigidity of the portion near the second side end of the second skirt portion 12B by the oil discharge passage defining wall 105. In this case, the degree of deformation of the portion on the first side end side of the second skirt portion 12B due to the thrust force is smaller than the degree of deformation of the portion on the second side end side of the second skirt portion 12B due to the thrust force. That is, in the second skirt portion 12B, the degree of deformation of the first side end portion due to the thrust force and the degree of deformation of the second side end portion due to the thrust force are different from each other. When the deformation degrees are different from each other as described above, a large stress is generated in a part of the second skirt portion 12B when the second skirt portion 12B is deformed by receiving a thrust force. Then, when the thrust force received by the second skirt portion 12B is reduced, the shape of the deformed portion of the second skirt portion 12B returns to the original shape, and the large amount generated in a part of the second skirt portion 12B. The stress disappears. As described above, when a large stress is generated in the second skirt portion 12B or the large stress disappears, the second skirt portion 12B is deteriorated due to fatigue.

  Therefore, in order to suppress the fatigue deterioration of the second skirt portion 12B, as shown in FIG. 17, the first side end of the second skirt portion 12B is not provided without providing the oil discharge passage defining wall 105. An oil discharge port 105 for discharging oil from the oil passage inside the piston body 11 to the piston body bottom wall surface 112 in the vicinity of the upper end of the connection portion between the first sidewall and the first side wall 13B. May be provided.

  In the third embodiment shown in FIG. 17, since the rigidity of the second skirt portion 12B is uniform throughout, it is possible to suppress a large stress from being generated in a part of the second skirt portion 12B. . For this reason, fatigue deterioration of the 2nd skirt part 12B is suppressed.

  By the way, in the above-described embodiment, when the piston is disposed in the cylinder bore, oil is blown to the oil inlet 104 from below the bottom end surface of the sidewall, and this blown oil is applied to the oil inlet 104. Inflow. Therefore, when the oil introduction port 104 is provided in the piston main body bottom wall surface 112 like 3rd Embodiment, oil will not flow into the oil introduction port 104 efficiently.

  Therefore, the second skirt portion 12B is provided on the thrust side in order to efficiently flow oil into the oil inlet 104 while suppressing fatigue deterioration of the skirt portions due to the uneven rigidity of the skirt portions 12A and 12B. 18, the inner wall surface of the first sidewall portion 13A between the first pin hole portion 14A and the first lateral end of the first skirt portion 12A as shown in FIG. An oil introduction passage defining wall 103 extending from the bottom end surface of the first side wall portion 13A to the piston body bottom wall surface 112 is provided at 132, and the oil introduction passage defined by the oil introduction passage defining wall 103 is defined as a piston. 10 is connected to the oil passage in the interior of the piston 10 in the vicinity of the upper end of the connecting portion between the first side end of the second skirt portion 12B and the first side end of the second sidewall portion 13B. The oil discharge port 105 may be provided in the bottom wall surface 112 (that is, the second sidewall portion 13B between the second pin hole portion 14B and the first side end of the second skirt portion 12B). The oil discharge passage defining wall 105 is not provided on the inner wall surface).

  In the embodiment shown in FIG. 18 (hereinafter, this embodiment is referred to as “fourth embodiment”), since the second skirt portion 12B is disposed on the thrust side, the first skirt portion is operated during engine operation. The thrust force received by 12A is smaller than the thrust force received by second skirt portion 12B. Accordingly, the oil introduction passage defining wall 103 is provided on the inner wall surface 132 of the first sidewall portion 13A between the first pin hole portion 14A and the first lateral end of the first skirt portion 12A. Even if the rigidity of the first side end portion of the first skirt portion 12A and the rigidity of the second side end portion of the first skirt portion 12A are different from each other, the thrust force received by the first skirt portion 12A Is relatively small, a large stress is not generated in a part of the first skirt portion 12A. Therefore, fatigue deterioration of the first skirt portion 12A is suppressed.

  In the fourth embodiment, the oil introduction passage defining wall 103 extends from the bottom end surface of the first sidewall portion 13A to the piston main body bottom wall surface 112, so that the oil introduction port 104 is connected to the first sidewall portion 13A. It is formed near the bottom end face. Therefore, the oil efficiently flows into the oil inlet 104.

  On the other hand, in the fourth embodiment, the oil discharge passage defining wall 105 is provided on the inner wall surface 132 of the second sidewall portion 13B between the second pin hole portion 14B and the first lateral end of the second skirt portion 12B. Since this is not done, the rigidity of the second skirt portion 12B is uniform throughout. Therefore, even if the second skirt portion 12B is disposed on the thrust side and the thrust force received by the second skirt portion 12B is relatively large, a large stress is not generated in a part of the second skirt portion 12B. Therefore, fatigue deterioration of the second skirt portion 12B is suppressed.

  By the way, in the above-described embodiment, the combustion chamber formed by the piston top wall surface 111 and the cylinder bore inner peripheral wall surface generally discharges exhaust gas from the intake port and the combustion chamber for introducing air into the combustion chamber. The exhaust port is connected. Here, the temperature of the exhaust gas discharged from the combustion chamber is higher than the temperature of the air introduced into the combustion chamber. Therefore, the temperature in the region in the combustion chamber near the exhaust port is higher than the temperature in the region in the combustion chamber near the intake port. Therefore, the temperature of the cylinder bore inner peripheral wall surface close to the exhaust port is higher than the temperature of the cylinder bore inner peripheral wall surface close to the intake port. Therefore, when the piston of the above-described embodiment is disposed in the cylinder bore and the internal combustion engine is operated, the temperature of the piston portion close to the exhaust port becomes higher than the temperature of the piston portion close to the intake port.

  On the other hand, in the above-described embodiment, the cooling effect by the oil in the piston portion near the oil introduction port 104 is higher than the cooling effect by the oil in the piston portion far from the oil introduction port 104.

  Therefore, from the viewpoint of efficiently cooling the entire piston with oil, the skirt portion closer to the oil inlet 104 (that is, the first skirt portion 12A in the above-described embodiment) is disposed near the exhaust port and The piston of the above-described embodiment is disposed in the cylinder bore so that the skirt portion far from the oil inlet 104 (that is, the second skirt portion 12B in the above-described embodiment) is disposed near the intake port. Is preferred.

  Incidentally, in the first embodiment, the oil introduction passage defining wall 103 and the oil discharge passage defining wall 105 are provided on the sidewall inner wall surface 132 in order to form the oil introduction passage 102 and the oil discharge passage 104. When the defining walls 103 and 105 are provided on the sidewall inner wall surface 132 as described above, the weight of the piston is larger than when the defining walls 103 and 103 are not provided on the sidewall inner wall surface 132. Becomes heavier. On the other hand, in the field of pistons, there is a demand for weight reduction of pistons. Therefore, even when the oil introduction passage 102 and the oil discharge passage 104 are formed, it may be desired to reduce the weight of the piston as much as possible.

  Therefore, in the first embodiment, even if the oil introduction passage 102 and the oil discharge passage 104 are formed, these passages 102 and 104 are formed as shown in FIG. 19 in order to reduce the weight of the piston as much as possible. May be.

  That is, in the embodiment shown in FIG. 19 (hereinafter, this embodiment is referred to as “fifth embodiment”), as shown in FIG. 19A, the first pin hole portion 14A and the first skirt Oil is obtained by closing the groove 21 formed along the raised portion 20 on the inner wall surface of the raised portion 20 provided in the first sidewall portion 13A between the first side end of the portion 12A with the wall 22. An introduction passage 102 is formed. That is, the raised portion 20 is used as a part of the oil introduction passage defining wall 103.

  As described above, when the raised portion 20 is used as a part of the oil introduction passage defining wall 103, the weight of the piston is reduced as compared with the case where the raised portion 20 is not used as a part of the oil introduction passage defining wall 103. The

  In the fifth embodiment, as shown in FIG. 19B, the second sidewall portion 13B between the second pin hole portion 14B and the first lateral end of the second skirt portion 12B is provided. An oil discharge passage is formed by closing a groove 21 formed along the raised portion 20 on the inner wall surface of the provided raised portion 20 with a wall 23. That is, the raised portion 20 is used as a part of the oil discharge passage defining wall 105.

  Thus, when the raised portion 20 is used as a part of the oil discharge passage defining wall 105, the weight of the piston is reduced compared to the case where the raised portion 20 is not used as a part of the oil discharge passage defining wall 105. The

  The concept of the fifth embodiment in which the raised portion 20 is used as a part of the oil introduction passage defining wall 103 is that the oil discharge passage defining wall 105 is not provided and only the oil introduction passage defining wall 103 is provided. It is also applicable to the fourth embodiment.

  By the way, the piston of the first embodiment includes a piston cavity 101 defined by the sidewall inner wall surface 132, the skirt inner circumferential wall surface 122, and the piston main body bottom wall surface 112. Here, when manufacturing such a piston using a mold, the piston cavity 101 is formed using a core corresponding to the shape of the piston cavity 101. Specifically, the piston cavity 101 is formed by solidifying the piston material in a state where a material constituting the piston (hereinafter referred to as “piston material”) is disposed around the core.

  By the way, when the piston cavity 101 is formed by solidifying the piston material in a state where the piston material is arranged around the core, the core needs to be extracted from the piston cavity 101 after the piston cavity 101 is formed. Here, unlike the piston of the embodiment described above, when the inner peripheral wall surface of the skirt is a partially cylindrical surface centered on the piston central axis, or the upper peripheral edge of the skirt with respect to the piston central axis line In the case of a partially conical surface extending from the bottom of the skirt toward the lower end of the skirt (for example, as shown in FIG. 14B), the core can be easily removed from the piston cavity after the piston cavity is formed. Can be extracted.

  However, as described with reference to FIGS. 14A and 14C, as a result of making the thickness of a part of the skirt portions 12A and 12B thicker than the thickness of the other parts, a part of the skirt inner peripheral wall surface 122 is obtained. Is protruding inward, it is extremely difficult to extract the core from the piston cavity 101 after the piston cavity 101 is formed.

  Therefore, when the piston of the first embodiment is manufactured using a mold, the piston cavity 101 is formed as follows, and the core is extracted from the piston cavity after the piston cavity is formed.

  That is, in the embodiment of the present invention, the core shown in FIG. 20 is used to form the piston cavity 101 in the piston.

  Specifically, (1) “the entire inner wall surface of the first sidewall portion 13A”, “the portion of the inner peripheral wall surface of the first skirt portion 12A in the vicinity of the first side end of the first skirt portion 12A” and “the first wall surface”. “The portion of the inner peripheral wall surface of the second skirt portion 12B near the second side end of the second skirt portion 12B” and “the portion of the piston main body bottom wall surface 112 near the upper end of the first sidewall portion 13A” are defined. The first core 41; (2) “the entire inner wall surface of the second sidewall portion 13B” and “the portion of the inner circumferential wall surface of the first skirt portion 12A in the vicinity of the second side end of the first skirt portion 12A”. And “the portion of the inner peripheral wall surface of the second skirt portion 12B near the first side end of the second skirt portion 12B” and “the portion of the piston body bottom wall surface 112 near the upper end of the second sidewall portion 13B”. A second core 42 to be defined; and (3) “first skirt portion 12. The third inner core 43 defining “the remaining inner peripheral wall portion” and “the portion of the piston main body bottom wall surface 112 in the vicinity of the intermediate portion of the upper end of the first skirt portion 12A”, and (4) “second skirt” A fourth core 44 defining a portion of the remaining inner peripheral wall surface of the portion 12B and a portion of the piston main body bottom wall surface 112 in the vicinity of the intermediate portion at the upper end of the second skirt portion 12B, and (5) “piston A core comprising a fifth core 45 that defines the “remaining portion of the main body bottom wall surface 112” is used.

  When the piston cavity 101 is formed, the third core 43 and the fourth core 44 are interposed between the first core 41 and the second core 42, respectively, and the first core 41 and the second core 42, respectively. The fifth core 45 is disposed between the first core 41 and the second core 42 and between the third core 43 and the fourth core 44. It arrange | positions so that the 1 core 41-the 4th core 44 may be contacted. The outer shape of the first core 41 to the fifth core 45 is such that the outer shape formed by these cores 41 to 45 defines the piston cavity 101 when arranged as described above. The shape matches the shape of the wall surface.

  Then, after the piston cavity 101 is formed by the first core 41 to the fifth core 45, the fifth core 45, the fourth core 44, the third core 43, the second core 42, the first If the core 41 is extracted from the piston cavity 101 in the order, the cores 41 to 45 are easily extracted from the piston cavity 101.

  By the way, in the case where the piston of the first embodiment is manufactured by a mold, the above-described idea of forming the piston cavity 101 is broadly lower than the lower part of the inner peripheral wall surface of the skirt and the upper part of the inner peripheral wall surface of the skirt. The present invention can also be applied to the case where the piston cavity is formed in the case where the piston having the protruding portion protruding toward the piston cavity is manufactured by a mold.

  By the way, when manufacturing the piston of 1st Embodiment using a type | mold, the cross-sectional shape of the skirt parts 12A and 12B is shown in FIG. (Hereinafter, the embodiment shown in FIG. 22 is referred to as “sixth embodiment”) or the shape shown in FIG. 23 (hereinafter, the embodiment shown in FIG. 23 is referred to as “seventh embodiment”). ).

  22A is a cross-sectional view of the second skirt portion 12B of the piston of the sixth embodiment along the line Z1-Z1 in FIG. 21, and FIG. 22B is a line Z2 in FIG. FIG. 22 is a transverse cross-sectional view of the second skirt portion 12B of the piston of the sixth embodiment along -Z2, and in the piston 10 of the sixth embodiment, as shown in FIG. The upper portion of 12B has a shape in which the inner peripheral wall surface 12CN of the central region is recessed from the inner peripheral wall surface 12LT of the side region in the peripheral direction in the circumferential direction of the second skirt portion 12B. Accordingly, a belt-like groove 123 extending in a direction parallel to the piston center axis C1 is formed in the central region in the circumferential direction of the second skirt portion 12B on the inner peripheral wall surface 122 of the upper portion of the second skirt portion 12B. Yes. And between the center area | region of the upper part of the 2nd skirt part 12B in which this strip | belt-shaped groove | channel 123 is formed, and the side area | region of the said upper part, it is piston center rather than the inner peripheral wall surface 12LT of the side area | region. A protruding portion 124 protruding toward the axis C1 is formed.

  On the other hand, in the piston 10 of the sixth embodiment, as shown in FIG. 22B, the lower portion of the second skirt portion 12B has a constant thickness in the circumferential direction of the second skirt portion 12B. That is, the strip-shaped groove 123 and the protruding portion 124 formed on the inner peripheral wall surface 122 of the upper portion of the second skirt portion 12B are not formed in the lower portion of the second skirt portion 12B.

  In the piston 10 of the sixth embodiment, although not shown, the first skirt portion 12A also has the same shape as the second skirt portion 12B.

  FIG. 23A is a transverse sectional view of the second skirt portion 12B of the piston of the seventh embodiment along the line Z1-Z1 in FIG. 21, and FIG. 23B is a line Z2 in FIG. It is a cross-sectional view of the second skirt portion 12B of the piston of the seventh embodiment along -Z2, and in the piston 10 of the seventh embodiment, as shown in FIG. The upper portion of 12B has a shape in which the inner peripheral wall surface 12CN of the central region is recessed from the inner peripheral wall surface 12LT of the side region in the peripheral direction in the circumferential direction of the second skirt portion 12B. Accordingly, a belt-like groove 123 extending in a direction parallel to the piston center axis C1 is formed in the central region in the circumferential direction of the second skirt portion 12B on the inner peripheral wall surface 122 of the upper portion of the second skirt portion 12B. Yes. However, between the central region of the upper part of the second skirt portion 12B in which the belt-like groove 123 is formed and the side region of the upper part, the piston center is located more than the inner peripheral wall surface 12LT of the side region. A protruding portion protruding toward the axis C1 is not formed.

  On the other hand, in the piston 10 of the seventh embodiment, as shown in FIG. 23B, the lower portion of the second skirt portion 12B has a constant thickness in the circumferential direction of the second skirt portion 12B. That is, the strip-like groove 123 formed on the inner peripheral wall surface 122 of the upper part of the second skirt part 12B is not formed in the lower part of the second skirt part 12B.

  In the piston 10 of the seventh embodiment, although not shown, the first skirt portion 12A has the same shape as the second skirt portion 12B.

  By the way, the piston of embodiment mentioned above has a pair of pin hole part. However, the piston of the above-described embodiment may have one substantially annular pin hole. In this case, the pin hole portion is provided so as to penetrate both the sidewall portions 13A and 13B. Of course, the central axis of this pin hole is perpendicular to the extending plane of both sidewalls 13A, 13B.

  DESCRIPTION OF SYMBOLS 10 ... Piston, 11 ... Piston main-body part, 12A, 12B ... Skirt part, 13A, 13B ... Side wall part, 14A, 14B ... Pin hole part, 20 ... Raised part, 21 ... Groove, 31 ... Depression, 32 ... Depression slope , 41 ... 1st core, 42 ... 2nd core, 43 ... 3rd core, 44 ... 4th core, 45 ... 5th core, 101 ... Cavity of piston, 112 ... Bottom wall surface of piston main-body part 121 ... Outer peripheral wall surface of the skirt portion, 122 ... Inner peripheral wall surface of the skirt portion, 131 ... Outer wall surface of the sidewall portion, 132 ... Inner wall surface of the sidewall portion, 142 ... Side portion of the pin hole portion, 143 ... Pin hole AR1 ... Upper corner region, AR2 ... Down corner region, AR3 ... Pin hole side region, C1 ... Piston center axis

Claims (5)

  A columnar piston main body, a pair of substantially partial annular skirts extending downward from the bottom wall surface of the piston main body parallel to the central axis of the piston main body, and the bottom of the piston main body A pair of flat sidewall portions extending downward from the wall surface in parallel to the central axis of the piston body portion and connecting the skirt portions to each other, and an annular pin provided on the sidewall portions A pin hole portion having a central axis perpendicular to the extending plane of the sidewall portion, the bottom wall surface of the piston body portion, the inner peripheral wall surfaces of both skirt portions, and both sidewalls In the piston of the internal combustion engine in which a cavity is formed by the inner wall surface of the portion, the pin hole extends from the region of the outer wall surface of the sidewall portion adjacent to the piston main body portion and the skirt portion. The piston of the internal combustion engine side wall portion outer wall surface area raised portion extending in a direction toward the of the is provided in the side wall portion adjacent to the side portion of the.   2. The piston of the internal combustion engine according to claim 1, wherein a groove extending along the raised portion is formed in an inner wall surface portion of the sidewall portion corresponding to the raised portion.   A plane including the center axis of the pin hole and the center axis of the piston is referred to as a pin hole vertical plane, which is a portion of the pin hole near the pin hole vertical plane and is related to the center axis of the pin hole. A portion on the main body side is referred to as a pin hole upper portion, and a plane that includes the central axis of the pin hole and is perpendicular to the central axis of the piston is referred to as a pin hole horizontal plane. When the portion of the hole portion is referred to as a pin hole lateral portion, and the portion of the pin hole portion located approximately in the middle between the pin hole upper portion and the pin hole lateral portion is referred to as a pin hole obliquely upper portion, the raised portion is Claims extending substantially straight from an outer wall surface area of the sidewall portion adjacent to the piston main body portion and the skirt portion toward an outer wall surface region of the sidewall portion adjacent to the pin hole diagonally upper portion. Item 1 or 2 Piston of an internal combustion engine as set forth.   A columnar piston main body, a pair of substantially partial annular skirts extending downward from the bottom wall surface of the piston main body parallel to the central axis of the piston main body, and the bottom of the piston main body A pair of flat sidewalls extending downward from the wall surface in parallel to the central axis of the piston body and connecting the skirts to each other, and the bottom wall of the piston body and both A cavity is formed by the inner peripheral wall surface of the skirt portion and the inner wall surfaces of both sidewall portions, and the thickness of the lower portion of the skirt portion is thicker than the thickness of the upper portion of the skirt portion. In the method of manufacturing a piston using a mold, the inner wall surface of one sidewall portion and the inner wall surface of the sidewall portion on the same side as the bottom wall surface portion of the piston main body portion adjacent to the inner wall surface A first core that defines a portion of an inner peripheral wall surface of both adjacent skirt portions, an inner wall surface of the other sidewall portion, and a bottom wall surface portion of the piston main body portion adjacent to the inner wall surface; A second core that defines a portion of the inner peripheral wall surface of both skirt portions adjacent to the inner wall surface of the sidewall portion, and the piston main body portion that is not defined by the first core and the second core. A first core that defines a bottom wall surface portion and an inner peripheral wall surface portion of the one skirt portion that is not defined by the first core and the second core; A third core disposed between the first core and the second core; a portion of the bottom wall surface of the piston main body not defined by the first core and the second core; and the first core The other core not defined by the second core and the second core A fourth core that defines a portion of the inner peripheral wall surface of the cart portion, the fourth core disposed between the first core and the second core; A fifth core defining a bottom wall surface portion of the piston main body not defined by the core, the second core, the third core, and the fourth core, The cavity is formed in the piston by the first core, the second core, the third core, and the fifth core disposed between the fourth core and the fourth core. Method.   After the cavity is formed in the piston by the first core, the second core, the third core, the fourth core, and the fifth core, The method of claim 4, wherein the core is extracted, then the third core and the fourth core are extracted, and then the first core and the second core are extracted.

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