Patent Publication Number: US-2019195363-A1

Title: Piston ring

Description:
TECHNICAL FIELD 
     The present invention relates to a piston ring that is used in an internal combustion engine. 
     BACKGROUND ART 
     A piston ring that is used in an internal combustion engine of an automobile or the like is provided in, for example, a ring groove on an outer circumferential surface of a piston. An outer circumferential surface of the piston ring comes into sliding contact with an inner circumferential surface of a bore, and one side surface of the piston ring comes into contact with a side surface of the ring groove, whereby a function of preventing blow-by gas from a combustion chamber side toward a crankcase side is provided. Such a piston ring has a split ring shape with a joint section for the convenience of mounting into the ring groove, and thus there is a problem with the inhibition of blow-by gas in the joint section. 
     With respect to the above-described problem, for example, Patent Literature 1 discloses a piston ring having a special joint structure. In a joint section of this piston ring, a protrusion portion which forms a wedge shape having a cross-section that tapers inward in a radial direction and extends in a circumferential direction is provided at one joint end. In addition, a recess portion that serves as a reception portion of the protrusion portion is provided at the other joint end. In this configuration, the sealability of blow-by gas is improved by ensuring the degree of adhesion between mating surfaces of the protrusion portion and the reception portion. 
     CITATION LIST 
     Patent Literature 
     (Patent Literature 1) Japanese Unexamined Utility Model Publication No. S60-108748 
     SUMMARY OF INVENTION 
     Technical Problem 
     Meanwhile, when the piston ring is mounted into the ring groove on the outer circumferential surface of the piston, the piston ring is mounted into the ring groove by expanding the inner diameter of the ring to be equal to or larger than the outer diameter of the piston. The piston in which the piston ring has been mounted is inserted into a cylinder block in an engine assembly step. 
     When the piston is inserted into the cylinder block, the diameter of the piston ring is reduced to the inner diameter of a cylinder. At this time, compared to a piston ring having a joint structure called an ordinary straight joint, in the piston ring having the special joint structure as described in Patent Literature 1, there is a case in which the protrusion portion and the recess portion provided in the joint section collide with each other. At this time, a corner portion of the protrusion portion first collides with the other joint end, and at least one of chipping and breakage occurs in the joint section of the piston ring, and thus there is a concern that a property of sealing a fluid (sealability) cannot be sufficiently ensured. 
     An object of the present invention is to provide a piston ring capable of inhibiting the breakage of a joint section and preferably ensuring sealability. 
     Solution to Problem 
     A piston ring according to an aspect of the present invention is a piston ring including an annular body having an inner circumferential surface and an outer circumferential surface facing each other and a joint section formed in the body, in which, in the joint section, on one side surface of the body, a first protrusion portion that protrudes from one joint end toward the other joint end and a first reception portion that receives the first protrusion portion in the other joint end are provided, on the other side surface of the body, a second protrusion portion that protrudes from the other joint end toward the one joint end and a second reception portion that receives the second protrusion portion in the one joint end are provided, on an inner circumferential surface side of the body, a first male portion that protrudes from the second protrusion portion toward the second reception portion and a first female portion that receives the first male portion in the second reception portion are provided, on an outer circumferential surface side of the body, a second male portion that protrudes from the first protrusion portion toward the first reception portion and a second female portion that receives the second male portion in the first reception portion are provided, the first male portion has an inclined surface or a curved surface having a convex shape which faces the outer circumferential surface side and is inclined with respect to a mating surface with respect to the first female portion so that a front end of the first male portion tapers, and the second male portion has an inclined surface or a curved surface having a convex shape which faces the inner circumferential surface side and is inclined with respect to a mating surface with respect to the second female portion so that a front end of the second male portion tapers. 
     In the piston ring, both of the front ends of the first male portion and the second male portion taper. In addition, the inclined surface or the curved surface having a convex shape which faces the outer circumferential surface side in the first male portion and the inclined surface or the curved surface having a convex shape which faces the inner circumferential surface side in the second male portion are provided so as to face each other in the thickness direction of the piston ring. The above-described first and second male portions are provided in the joint section, whereby it is possible to cause the surface in the first male portion and the surface in the second male portion to first collide with each other when, for example, the diameter of the piston ring is reduced. In this case, the inclined surfaces, the curved surfaces, or the inclined surface and the curved surface, which are not provided with any corner portions, first collide with each other, and thus prevent the joint ends from being stuck to each other. Therefore, the concentration of a force being applied to reduce the diameter of the piston ring on the joint section is prevented, and it is possible to inhibit the breakage of the joint section. Additionally, a stepped interface is formed at a position at which the first protrusion portion and the first reception portion face each other on one side surface of the body and a position at which the second protrusion portion and the second reception portion face each other on the other side surface of the body are not in alignment. In addition, a stepped interface other than the above-described stepped interface is formed at a position at which the first male portion and the first female portion face each other on the inner circumferential surface side of the body and a position at which the second male portion and the second female portion face each other on the outer circumferential surface side of the body are not in alignment. Therefore, during the use of the piston ring, the two stepped interfaces are closed, whereby it is possible to inhibit gas passing through the joint section of the piston ring. Therefore, according to the piston ring, the joint ends being stuck to each other is prevented, the breakage of the joint section is inhibited, and it is possible to favorably ensure sealability. 
     The first male portion may have an inclined surface facing the outer circumferential surface side, and the second male portion may have an inclined surface facing the inner circumferential surface side. In this case, it is possible to bring the inclined surface in the first male portion and the inclined surface in the second male portion into surface contact with each other when both inclined surfaces collide with each other, and thus the concentration of stress does not easily occur. Therefore, it is possible to easily inhibit the breakage of the joint section. Additionally, the inclined surfaces slide along each other when the diameter of the piston ring is reduced, and it is possible to easily reduce the diameter of the piston ring. 
     The first male portion may have a curved surface having a convex shape which faces the outer circumferential surface side, and the second male portion may have a curved surface having a convex shape which faces the inner circumferential surface side. In this case, it is possible to favorably inhibit the first male portion and the second male portion from being stuck to each other. 
     The first male portion may have a front end surface which is a mating surface with respect to the first female portion and extends perpendicular to a circumferential direction, and the second male portion may have a front end surface which is a mating surface with respect to the second female portion and extends perpendicular to the circumferential direction. In this case, both of the front ends of the first male portion and the second male portion are as thick as the front end surfaces. Therefore, it is possible to ensure strength in the front ends of the first male portion and the second male portion and favorably inhibit the breakage of the joint section. 
     In a first internal corner portion formed by the first female portion and the second male portion, a first opposite surface which faces the inclined surface or the curved surface having a convex shape that faces the outer circumferential surface side of the first male portion may be provided, in a second internal corner portion framed by the second female portion and the first male portion, a second opposite surface which faces the inclined surface or the curved surface having a convex shape that faces the inner circumferential surface side of the second male portion may be provided, the first opposite surface may be a curved surface having a concave shape or a planar surface which faces the inner circumferential surface side, and the second opposite surface may be a curved surface having a concave shape or a planar surface which faces the outer circumferential surface side. In this case, it is possible to narrow a gap between the inclined surface or the curved surface of the first male portion and the first opposite surface and a gap between the inclined surface or the curved surface of the second male portion and the second opposite surface. Therefore, it is possible to inhibit the accumulation of sludge or the like in the above-described gaps. 
     The first opposite surface may be a curved surface having a concave shape which faces the inner circumferential surface side, and the second opposite surface may be a curved surface having a concave shape which faces the outer circumferential surface side. 
     The first opposite surface may be a planar surface which faces the inner circumferential surface side, and the second opposite surface may be a planar surface which faces the outer circumferential surface side. 
     A piston ring according to another aspect of the present invention is a piston ring including an annular body having an inner circumferential surface and an outer circumferential surface facing each other and a joint section formed in the body, in which, in the joint section, on one side surface of the body, a first protrusion portion that protrudes from one joint end toward the other joint end and a first reception portion that receives the first protrusion portion in the other joint end are provided, on the other side surface of the body, a second protrusion portion that protrudes from the other joint end toward the one joint end and a second reception portion that receives the second protrusion portion in the one joint end are provided, on an outer circumferential surface side of the body, a first male portion that protrudes from the second protrusion portion toward the second reception portion and a first female portion that receives the first male portion in the second reception portion are provided, on an inner circumferential surface side of the body, a second male portion that protrudes from the first protrusion portion toward the first reception portion and a second female portion that receives the second male portion in the first reception portion are provided, the first male portion has an inclined surface or a curved surface having a convex shape which faces the inner circumferential surface side and is inclined with respect to a mating surface with respect to the first female portion so that a front end of the first male portion tapers, and the second male portion has an inclined surface or a curved surface having a convex shape which faces the outer circumferential surface side and is inclined with respect to a mating surface with respect to the second female portion so that a front end of the second male portion tapers. 
     In this piston ring, both of the front ends of the first male portion and the second male portion taper. In addition, the inclined surface or the curved surface having a convex shape which faces the inner circumferential surface side in the first male portion and the inclined surface or the curved surface having a convex shape which faces the outer circumferential surface side in the second male portion are provided so as to face each other in the thickness direction of the piston ring. The above-described first and second male portions are provided in the joint section, whereby it is possible to cause the surface in the first male portion and the surface in the second male portion to first collide with each other when, for example, the diameter of the piston ring is reduced. In this case, the inclined surfaces, the curved surfaces, or the inclined surface and the curved surface, which are not provided with any corner portions, first collide with each other, and thus prevent the joint ends from being stuck to each other. Therefore, the concentration of a force being applied to reduce the diameter of the piston ring on the joint section is prevented, and it is possible to inhibit the breakage of the joint section. Additionally, a stepped interface is formed at a position at which the first protrusion portion and the first reception portion face each other on one side surface of the body and a position at which the second protrusion portion and the second reception portion face each other on the other side surface of the body are not in alignment. In addition, a stepped interface other than the above-described stepped interface is formed at a position at which the first male portion and the first female portion face each other on the outer circumferential surface side of the body and a position at which the second male portion and the second female portion face each other on the inner circumferential surface side of the body are not in alignment. Therefore, during the use of the piston ring, the two stepped interfaces are closed, whereby it is possible to inhibit gas passing through the joint section of the piston ring. Therefore, according to the piston ring, the joint ends being stuck to each other is prevented, the breakage of the joint section is inhibited, and it is possible to favorably ensure sealability. 
     The first male portion may have an inclined surface facing the inner circumferential surface side, and the second male portion may have an inclined surface facing the outer circumferential surface side. In this case, it is possible to bring the inclined surface in the first male portion and the inclined surface in the second male portion into surface contact with each other when both inclined surfaces collide with each other, and thus the concentration of stress does not easily occur. Therefore, it is possible to easily inhibit the breakage of the joint section. Additionally, the inclined surfaces slide along each other when the diameter of the piston ring is reduced, and it is possible to easily reduce the diameter of the piston ring. 
     The first male portion may have a curved surface having a convex shape which faces the inner circumferential surface side, and the second male portion may have a curved surface having a convex shape which faces the outer circumferential surface side. In this case, it is possible to favorably inhibit the first male portion and the second male portion from being stuck to each other. 
     The first male portion may have a front end surface which is a mating surface with respect to the first female portion and extends perpendicular to a circumferential direction, and the second male portion may have a front end surface which is a mating surface with respect to the second female portion and extends perpendicular to the circumferential direction. In this case, both of the front ends of the first male portion and the second male portion are as thick as the front end surfaces. Therefore, it is possible to ensure strength in the front ends of the first male portion and the second male portion and favorably inhibit the breakage of the joint section. 
     In a first internal corner portion formed by the first female portion and the second male portion, a first opposite surface which faces the inclined surface or the curved surface having a convex shape that faces the inner circumferential surface side of the first male portion may be provided, in a second internal corner portion formed by the second female portion and the first male portion, a second opposite surface which faces the inclined surface or the curved surface having a convex shape that faces the outer circumferential surface side of the second male portion may be provided, the first opposite surface may be a curved surface having a concave shape or a planar surface which faces the outer circumferential surface side, and the second opposite surface may be a curved surface having a concave shape or a planar surface which faces the inner circumferential surface side. In this case, it is possible to narrow a gap between the inclined surface or the curved surface of the first male portion and the first opposite surface and a gap between the inclined surface or the curved surface of the second male portion and the second opposite surface. Therefore, it is possible to inhibit the accumulation of sludge or the like in the above-described gaps. 
     The first opposite surface may be a curved surface having a concave shape which faces the outer circumferential surface side, and the second opposite surface may be a curved surface having a concave shape which faces the inner circumferential surface side. 
     The first opposite surface may be a planar surface which faces the outer circumferential surface side, and the second opposite surface may be a planar surface which faces the inner circumferential surface side. 
     A surface-treated film may be provided on at least one surface of the inner circumferential surface, the outer circumferential surface, the one side surface, the other side surface, the mating surface with respect to the first female portion, the inclined surface, and the curved surface having a convex shape in the first male portion, the mating surface with respect to the second female portion, the inclined surface, and the curved surface having a convex shape in the second male portion. In this case, the body can be protected by the surface-treated film. 
     The body may be formed of metal or an alloy. Therefore, it is possible to sufficiently ensure the heat resistance of the piston ring. 
     The body may be formed of a resin composition having heat resistance. Therefore, it is possible to easily form the joint section while ensuring the heat resistance of the piston ring. 
     The resin composition may include a filler for improving the heat resistance. Therefore, it is possible to ensure the heat resistance of the piston ring. 
     Advantageous Effects of Invention 
     According to the piston ring according to the aspect of the present invention, it is possible to inhibit the breakage of the joint section and favorably ensure sealability. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view illustrating a first embodiment of a piston ring according to an aspect of the present invention. 
         FIG. 2  is an enlarged perspective view of a joint section of the piston ring illustrated in  FIG. 1 . 
         FIG. 3  is an enlarged perspective view illustrating the joint section of the piston ring illustrated in  FIG. 1  from one side surface. 
         FIG. 4  is an enlarged perspective view illustrating the joint section of the piston ring illustrated in  FIG. 1  from the other side surface. 
         FIG. 5  is an enlarged view of the joint section of the piston ring illustrated in  FIG. 1  seen from the other side surface. 
         FIG. 6A  is an enlarged view illustrating a piston ring according to a comparative example having a reduced diameter, and  FIG. 6B  is an enlarged view illustrating a piston ring according to the first embodiment having a reduced diameter. 
         FIG. 7A  is an enlarged view of the joint section of the piston ring in a free state seen from an outer circumferential surface side, and  FIG. 7B  is an enlarged view of the joint section of the piston ring after being assembled into the piston seen from the outer circumferential surface side. 
         FIG. 8  is an enlarged view of a joint section of a piston ring according to a modified example of the first embodiment seen from the other side surface. 
         FIG. 9A  is an enlarged view of a joint section of a piston ring according to a second embodiment seen from the other side surface, and  FIG. 9B  is an enlarged view of a joint section of a piston ring according to a modified example of the second embodiment seen from the other side surface. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, preferred embodiments of a piston ring according to an aspect of the present invention will be described in detail with reference to drawings. 
     First Embodiment 
       FIG. 1  is a perspective view illustrating a first embodiment of the piston ring according to the aspect of the present invention. A piston ring  1  illustrated in the drawing is provided in, for example, a ring groove on an outer circumferential surface of a piston ring in an internal combustion engine in an automobile. An outer circumferential surface  2   d  of the piston ring  1  comes into sliding contact with an inner circumferential surface of a bore, and a side surface  2   b  of the piston ring  1  comes into contact with a side surface of the ring groove and serves as a sealing surface, whereby a function of preventing blow-by gas from a combustion chamber side toward a crankcase side is provided. 
     This piston ring  1  includes an annular body  2  and a joint section  3  formed in a part of the body  2 . The body  2  forms a substantially rectangular cross-sectional shape having a long side in a thickness direction and a short side in a width direction, the substantially rectangular cross-sectional shape being formed by a side surface  2   a  (one side surface) and the side surface  2   b  (the other side surface) which are gap faces in the width direction and an inner circumferential surface  2   c  and the outer circumferential surface  2   d  which are gap faces in the thickness direction. The body  2  is formed of, for example, metal or an alloy (cast iron or steel containing a plurality of metal elements) and thus has a sufficient strength, a sufficient thermal resistance, and a sufficient elasticity. 
     A surface of the body  2  is provided with, for example, a surface-treated film. The surface-treated film is, for example, a hard chromium-plated layer, a PVD-treated layer, a nitride layer of iron, chromium, or the like, or a hard film such as a diamond-like carbon (DLC) film. The abrasion resistance of the body  2  is improved by the surface-treated film. The surface of the body  2  refers to the side surfaces  2   a  and  2   b,  the inner circumferential surface  2   c,  and the outer circumferential surface  2   d.    
       FIG. 2  is an enlarged perspective view of the joint section  3  of  FIG. 1 .  FIG. 3  is an enlarged perspective view illustrating the joint section  3  of the piston ring  1  illustrated in  FIG. 1  from a side surface  2   a .  FIG. 4  is an enlarged perspective view illustrating the joint section  3  of the piston ring  1  illustrated in  FIG. 1  from a side surface  2   b.  As illustrated in  FIGS. 2 to 4 , the joint section  3  is a separation formed in a part of the body  2  and is provided for the purpose of ensuring a mounting property of the piston ring  1  being mounted into the ring groove on the outer circumferential surface of the piston. In the joint section  3 , in a state in which the piston ring  1  is yet to be mounted into the ring groove, one joint end  11  and the other joint end  12  are in a state of facing each other with a predetermined interval therebetween. 
     In the joint section  3 , as illustrated in  FIG. 2  to  FIG. 4 , a first protrusion portion  13  that protrudes from the one joint end  11  toward the other joint end  12  and a first reception portion  14  that receives the first protrusion portion  13  in the other joint end  12  are provided on the side surface  2   a  of the body  2 . In addition, a second protrusion portion  15  that protrudes from the other joint end  12  toward the one joint end  11  and a second reception portion  16  that receives the second protrusion portion  15  in the one joint end  11  are provided on the side surface  2   b  of the body  2 . 
     More specifically, in the first protrusion portion  13 , an approximately half portion on the side surface  2   a  of the body  2  is in a state of protruding from the one joint end  11  in an approximately rectangular cross-sectional shape. In addition, in the first protrusion portion  13 , a front end corner on the side surface  2   b  which faces the first reception portion  14  is notched. Therefore, a notched surface Si is formed at a front end of the first protrusion portion  13  on the side surface  2   b  which faces the first reception portion  14 . In the first reception portion  14 , an approximately half portion of the other joint end  12  on the side surface  2   a  of the body  2  is in a state of being notched in an approximately rectangular cross-sectional shape according to the shape of the first protrusion portion  13 . Each of a front end surface  13   a  that is a surface of the first protrusion portion  13  which faces the first reception portion  14  and a front end surface  14   a  that is an opposite surface of the first reception portion  14  which faces the first protrusion portion  13  has an approximately rectangular shape that extends perpendicular or approximately perpendicular to the circumferential direction. 
     Similarly, in the second protrusion portion  15 , an approximately half portion on the side surface  2   b  of the body  2  is in a state of protruding from the other joint end  12  in an approximately rectangular cross-sectional shape. In addition, in the second protrusion portion  15 , a front end corner on the side surface  2   a  which faces the second reception portion  16  is notched. Therefore, a notched surface S 2  is formed at a front end of the second protrusion portion  15  on the side surface  2   a  which faces the second reception portion  16 . In the second reception portion  16 , an approximately half portion of the one joint end  11  on the side surface  2   b  of the body  2  is in a state of being notched in an approximately rectangular cross-sectional shape according to the shape of the second protrusion portion  15 . 
     Furthermore, on the side surface  2   b  of the body  2  and on an inner circumferential surface  2   c  side of the body  2 , a first male portion  21  that protrudes from the second protrusion portion  15  toward the second reception portion  16  and a first female portion  22  that receives the first male portion  21  in the second reception portion  16  are provided. In addition, on the side surface  2   b  of the body  2  and on an outer circumferential surface  2   d  side of the body  2 , a second male portion  23  that protrudes from the second reception portion  16  toward the second protrusion portion  15  and a second female portion  24  that receives the second male portion  23  in the second protrusion portion  15  are provided. Therefore, on the side surface  2   b,  the first male portion  21 , the first female portion  22 , the second male portion  23 , and the second female portion  24  form a so-called step joint. 
     Hereinafter, the first male portion  21 , the first female portion  22 , the second male portion  23 , and the second female portion  24  will be described in detail in this order using  FIG. 5 .  FIG. 5  is an enlarged view of the joint section  3  seen from the side surface  2   b.    
     As illustrated in  FIG. 5 , the first male portion  21  is in a state in which an approximately half portion on the inner circumferential surface  2   c  side of the second protrusion portion  15  protrudes. Specifically, the first male portion  21  has a mating surface  21   a  with respect to the first female portion  22  and an inclined surface  21   b  which faces the outer circumferential surface  2   d  side and is inclined with respect to the mating surface  21   a  so that a front end of the first male portion  21  tapers. The mating surface  21   a  is a front end surface which is positioned closer to a front end side of the first male portion  21  than the inclined surface  21   b  and on the inner circumferential surface  2   c  side and extends perpendicular to the circumferential direction. One end of the mating surface  21   a  and the inner circumferential surface  2   c  form the right angle. The inclined surface  21   b  is a flat surface connected to an end of the mating surface  21   a  on the outer circumferential surface  2   d  side and is formed by, for example, notching a corner portion of the first male portion  21  on the outer circumferential surface  2   d  side. The mating surface  21   a  and the inclined surface  21   b  form an obtuse angle. The angle formed by the mating surface  21   a  and the inclined surface  21   b  is, for example, 110° or more or 120° or more, and, 170° or less, 160° or less, or 150° or less. The proportion of the inclined surface  21   b  in the first male portion  21  in the thickness direction is, for example, 0.1 times or more, 0.2 times or more, or 0.5 times or more and 100 times or less, 50 times or less, or 35 times or less the proportion of the mating surface  21   a.    
     The second male portion  23  is in a state in which an approximately half portion on the outer circumferential surface  2   d  side of the second reception portion  16  protrudes. Specifically, the second male portion  23  has a mating surface  23   a  with respect to the second female portion  24  and an inclined surface  23   b  which faces the inner circumferential surface  2   c  side and is inclined with respect to the mating surface  23   a  so that a front end of the second male portion  23  tapers. The mating surface  23   a  is a front end surface which is positioned closer to a front end side of the second male portion  23  than the inclined surface  23   b  and on the outer circumferential surface  2   d  side and extends perpendicular to the circumferential direction. One end of the mating surface  23   a  and the outer circumferential surface  2   d  form the right angle. The inclined surface  23   b  is a flat surface connected to an end of the mating surface  23   a  on the inner circumferential surface  2   c  side and is formed by, for example, notching a corner portion of the second male portion  23  on the inner circumferential surface  2   c  side. The mating surface  23   a  and the inclined surface  23   b  form an obtuse angle. The angle formed by the mating surface  23   a  and the inclined surface  23   b  is, for example, 110° or more or 120° or more, and, 170° or less, 160° or less, or 150° or less. The proportion of the inclined surface  23   b  in the second male portion  23  in the thickness direction is, for example, 0.1 times or more, 0.2 times or more, or 0.5 times or more and 100 times or less, 50 times or less, or 35 times or less the proportion of the mating surface  23   a.    
     The first female portion  22  is in a state in which an approximately half portion of the second reception portion  16  on the inner circumferential surface  2   c  side is notched so as to be not in contact with the first male portion  21 . An opposite surface  25   a  with respect to the inclined surface  21   b  (a first opposite surface) is provided in a first internal corner portion  25  formed by the first female portion  22  and the second male portion  23 . The opposite surface  25   a  forms a curved surface having a concave shape which faces the inner circumferential surface  2   c  side and smoothly connects the mating surface  23   c  of the second male portion  23  with respect to the first male portion  21  and the mating surface  22   a  of the first female portion  22  with respect to the first male portion  21 . Meanwhile, a base end side of the second male portion  23  which forms the first internal corner portion  25  is thicker than a front end side of the second male portion  23 , and thus a strength to breakage (breakage strength) on the base end side of the second male portion  23  increases. 
     The second female portion  24  is in a state in which an approximately half portion of the second protrusion portion  15  on the outer circumferential surface  2   d  side is notched so as to be not in contact with the second male portion  23 . An opposite surface  26   a  with respect to the inclined surface  23   b  (a second opposite surface) is provided in a second internal corner portion  26  formed by the second female portion  24  and the first male portion  21 . The opposite surface  26   a  forms a curved surface having a concave shape which faces the outer circumferential surface  2   d  side and smoothly connects the mating surface  21   c  of the first male portion  21  with respect to the second male portion  23  and the mating surface  24   a  of the second female portion  24  with respect to the second male portion  23 . Meanwhile, a base end side of the first male portion  21  which forms the second internal corner portion  26  is thicker than a front end side of the first male portion  21 , and thus a strength to breakage (breakage strength) on the base end side of the first male portion  21  increases. 
     The action effect of the piston ring  1  having the above-described configuration will be described using  FIG. 6 .  FIG. 6A  is an enlarged view illustrating a piston ring according to a comparative example having a reduced diameter, and  FIG. 6B  is an enlarged view illustrating the piston ring  1  according to the first embodiment having a reduced diameter. 
     In the assembly of the piston ring (the mounting into the ring groove on the outer circumferential surface of the piston), first, the inner diameter of the ring is expanded to be equal to or larger than the outer diameter of the piston, thereby mounting the piston ring into the ring groove. The piston in which the piston ring has been mounted is inserted into a cylinder block in an engine assembly step. At this time, the diameter of the piston ring is reduced to the inner diameter of a cylinder so as not to hinder the insertion of the piston into the cylinder block due to the piston ring. Meanwhile, the diameter of the piston ring is reduced using, for example, a jig such as a taper cone. 
     Here, as illustrated in  FIG. 6A , in a piston ring  100  according to the comparative example, a first male portion  121  does not have the inclined surface  21   b,  and a second male portion  123  does not have the inclined surface  23   b.  Therefore, a corner portion  121   d  is provided at a front end of the first male portion  121  on the outer circumferential surface  2   d  side, and a corner portion  123   d  is provided at a front end of the second male portion  123  on the inner circumferential surface  2   c  side. When the diameter of the above-described piston ring  100  is expanded, as illustrated in  FIG. 6A , there is a case in which the corner portion  121   d  of the first male portion  121  may collide with a front end surface  123   a  of the second male portion  123  and the corner portion  121   d  may strike the second male portion  123  (or the corner portion  123   d  of the second male portion  123  may collide with a front end surface  121   a  of the first male portion  121  and the corner portion  123   d  may strike the first male portion  121 ). In this case, a force being applied to expand the diameter of the piston ring  100  may be concentrated on the first male portion  121  and the second male portion  123 , and there is a case in which at least one of chipping and breakage occurs in joint ends  111  and  112 . 
     On the other hand, in the piston ring  1  according to the first embodiment, both the front ends of the first male portion  21  and the second male portion  23  taper. In addition, the inclined surface  21   b  of the first male portion  21  and the inclined surface  23   b  of the second male portion  23  are provided so as to face each other in the thickness direction of the piston ring  1 . The first male portion  21  and the second male portion  23  described above are provided in the joint section  3 , whereby, in a case in which the joint ends  11  and  12  collide with each other when the diameter of the piston ring  1  is reduced as illustrated in  FIG. 6B , it is possible to cause the inclined surfaces  21   b  and  23   b  to first collide with each other. In this case, the inclined surfaces  21   b  and  23   b  which are not provided with a corner portion collide with each other, and thus the first male portion  21  and the second male portion  23  are not easily stuck to each other. Additionally, the inclined surfaces  21   b  and  23   b  come into surface contact with each other during the collision, and thus the concentration of stress does not easily occur. Therefore, it is possible to easily inhibit the breakage of the joint section  3 . Furthermore, the inclined surfaces  21   b  and  23   b  slide along each other in accordance with a force being applied to reduce the diameter of the piston ring  1 , and it is possible to easily close the piston ring  1 . 
     Additionally, as illustrated in  FIG. 5 , in the piston ring  1 , a position at which the first male portion  21  and the first female portion  22  face each other on the inner circumferential surface  2   c  side of the body  2  and a position at which the second male portion  23  and the second female portion  24  face each other on the outer circumferential surface  2   d  side of the body  2  are not in alignment in the circumferential direction of the body. Therefore, in a case in which the joint section  3  is seen from the side surface  2   b,  a stepped interface C 1  is formed by the mating surface  21   a  and the inclined surface  21   b  of the first male portion  21 , the mating surface  22   a  of the first female portion  22 , the opposite surface  25   a  of the first internal corner portion  25 , the mating surface  21   c  of the first male portion  21 , the mating surface  23   c  of the second male portion  23  with respect to the first male portion  21 , the opposite surface  26   a  of the second internal corner portion  26 , the mating surface  23   a  and the inclined surface  23   b  of the second male portion  23 , and the mating surface  24   a  of the second female portion  24 . 
     In the stepped interface C 1 , the mating surface  21   c  of the first male portion  21  with respect to the second male portion  23  and the mating surface  23   c  of the second male portion  23  with respect to the first male portion  21  are not easily affected by temperature expansion during the use of the piston ring  1 . In addition, even in a case in which a load generated by the vertical motion of the piston is applied to the piston ring  1 , the load does not easily apply in an opposite direction of the mating surfaces  21   c  and  23   c,  and friction also has a little influence, and thus it is possible to maintain the interval between the mating surfaces  21   c  and  23   c  to be small. Therefore, it becomes possible to minimize the circulation area of gas in the stepped interface C 1 , and it is possible to inhibit gas which has flown in from the inner circumferential surface  2   c  side of the piston ring  1  from flowing through the stepped interface C 1  and out of the outer circumferential surface  2   d  side. 
       FIG. 7A  is an enlarged view of the joint section  3  of the piston ring  1  in a free state seen from the outer circumferential surface  2   d  side, and  FIG. 7B  is an enlarged view of the joint section  3  of the piston ring  1  after being assembled into the piston seen from the outer circumferential surface  2   d  side. As illustrated in  FIG. 7B , when the piston ring  1  is mounted into the ring groove on the outer circumferential surface of the piston, a position at which the first protrusion portion  13  and the first reception portion  14  face each other on the side surface  2   a  of the body  2  and a position at which the second protrusion portion  15  and the second reception portion  16  face each other on the side surface  2   b  of the body  2  are not in alignment in the circumferential direction of the body  2 . Therefore, in a case in which the joint section  3  is seen from the outer circumferential surface  2   d  side, a stepped interface C 2  is formed by the front end surface  13   a  of the first protrusion portion  13 , the front end surface  14   a  of the first reception portion  14 , the notched surface S  1 , the mating surface  13   b  of the first protrusion portion  13  with respect to the second protrusion portion  15 , the mating surface  15   b  of the second protrusion portion  15  with respect to the first protrusion portion  13 , the notched surface S 2 , the front end surface  15   a  of the second protrusion portion  15 , and the front end surface  16   a  of the second reception portion  16 . 
     Therefore, in a case in which the piston ring  1  is mounted into the ring groove on the outer circumferential surface of the piston and receives a load generated by the vertical motion of the piston, the mating surface  13   b  of the first protrusion portion  13  and the mating surface  15   b  of the second protrusion portion  15  match with each other in the width direction of the body  2 , and the stepped interface C 2  is closed, whereby it is possible to shield gas flowing out in the width direction of the piston ring  1 . Meanwhile, as illustrated in  FIGS. 7A and 7B , an internal corner portion  31  formed by the first protrusion portion  13  and the second reception portion  16  and an internal corner portion  32  formed by the first protrusion portion  13  and the second reception portion  16  are respectively chamfered and configure curved surfaces having a concave shape. 
     The first male portion  21  has a front end surface which is the mating surface  21   a  with respect to the first female portion  22  and extends perpendicular to the circumferential direction, and the second male portion  23  has a front end surface which is the mating surface  23   a  with respect to the second female portion  24  and extends perpendicular to the circumferential direction. Therefore, the front ends of the first male portion  21  and the second male portion  23  are respectively as thick as the mating surfaces  21   a  and  23   a.  Therefore, it is possible to ensure strength at the front ends of the first male portion  21  and the second male portion  23 , and it is possible to favorably inhibit the breakage of the joint section  3 . 
     In the first internal corner portion  25  formed by the first female portion  22  and the second male portion  23 , the opposite surface  25   a  which faces the inclined surface  21   b  of the first male portion  21  is provided, in the second internal corner portion  26  formed by the second female portion  24  and the first male portion  21 , the opposite surface  26   a  which faces the inclined surface  23   b  of the second male portion  23  is provided, the opposite surface  25   a  may be a curved surface having a concave shape which faces the inner circumferential surface  2   c  side, and the opposite surface  26   a  may be a curved surface having a concave shape which faces the outer circumferential surface  2   d  side. In this case, it is possible to narrow a gap between the inclined surface  21   b  of the first male portion  21  and the opposite surface  25   a  and a gap between the inclined surface  23   b  of the second male portion  23  and the opposite surface  26   a.  Therefore, it is possible to inhibit the accumulation of sludge or the like in the above-described gaps. 
     On at least one surface of the side surfaces  2   a  and  2   b,  the inner circumferential surface  2   c,  and the outer circumferential surface  2   d,  a surface-treated film may be provided. In this case, the body  2  can be protected by the surface-treated film. 
     The body  2  may be for lied of metal or an alloy. Therefore, it is possible to sufficiently ensure the heat resistance of the piston ring  1 . 
     In the first embodiment, the first male portion  21  has the inclined surface  21   b;  however, in a modified example, the first male portion  21  may have, for example, a curved surface  21   d  having a convex shape which is inclined with respect to the mating surface  21   a  and faces the outer circumferential surface  2   d  side as illustrated in  FIG. 8 . Similarly, in the modified example, the second male portion  23  may have a curved surface  23   d  having a convex shape which is inclined with respect to the mating surface  23   a  and faces the inner circumferential surface  2   c  side instead of the inclined surface  23   b.  When the curved surfaces  21   d  and  23   d  are provided in the joint section  3  as described above, it is possible to favorably inhibit the first male portion  21  and the second male portion  23  from being stuck to each other during the mounting of the piston ring  1  into the ring groove on the outer circumferential surface of the piston. Additionally, as illustrated in  FIG. 8 , it is possible to further narrow a gap between the curved surface  21   d  of the first male portion  21  and the opposite surface  25   a  of the first internal corner portion  25 , and it is possible to further narrow a gap between the curved surface  23   d  of the second male portion  23  and the opposite surface  26   a  of the second internal corner portion  26 , and thus it is possible to favorably inhibit the accumulation of sludge or the like in the above-described gaps. 
     Second Embodiment 
     Hereinafter, piston rings according to a second embodiment and a modified example thereof will be described using  FIGS. 9A and 9B . In the second embodiment, common description between the first embodiment and the second embodiment will not be repeated. 
       FIG. 9A  is an enlarged view of a joint section of a piston ring according to the second embodiment seen from the other side surface. A piston ring  1 A illustrated in  FIG. 9A  is different from the piston ring  1  of the first embodiment in terms of the positions of the first male portion  21 , the first female portion  22 , the second male portion  23 , and the second female portion  24 . Specifically, on the side surface  2   b  of the body  2  and on the outer circumferential surface  2   d  side of the body  2 , the first male portion  21  that protrudes from the second protrusion portion  15  toward the second reception portion  16  and the first female portion  22  that receives the first male portion  21  in the second reception portion  16  are provided. In addition, on the side surface  2   b  of the body  2  and on the inner circumferential surface  2   c  side of the body  2 , the second male portion  23  that protrudes from the second reception portion  16  toward the second protrusion portion  15  and the second female portion  24  that receives the second male portion  23  in the second protrusion portion  15  are provided. 
     The first male portion  21  in the piston ring  1 A has the inclined surface  21   b  which faces the inner circumferential surface  2   c  side and is inclined with respect to the mating surface  22   a  with respect to the first female portion  22  so that the front end tapers. Similarly, the second male portion  23  has the inclined surface  23   b  which faces the outer circumferential surface  2   d  side and is inclined with respect to the mating surface  24   a  with respect to the second female portion  24  so that the front end tapers. Additionally, the opposite surface  25   a  provided in the first internal corner portion  25  foamed by the first female portion  22  and the second male portion  23  forms a curved surface having a concave shape which faces the outer circumferential surface  2   d  side, and the opposite surface  26   a  provided in the second internal corner portion  26  formed by the second female portion  24  and the first male portion  21  forms a curved surface having a concave shape which faces the inner circumferential surface  2   c  side. 
     In the piston ring  1 A according to the second embodiment as well, in a case in which the joint ends  11  and  12  collide with each other when the diameter of the piston ring  1 A is reduced, it is possible to cause the inclined surfaces  21   b  and  23   b  to first collide with each other. Therefore, in the second embodiment as well, the same action effect as in the first embodiment is provided. 
       FIG. 9B  is an enlarged view of a joint section of a piston ring according to a modified example of the second embodiment seen from the other side surface. The first male portion  21  in the modified example illustrated in  FIG. 9B  may have the curved surface  21   d  having a convex shape which is inclined with respect to the mating surface  21   a  and faces the inner circumferential surface  2   c  side. Similarly, in the modified example, the second male portion  23  may have the curved surface  23   d  having a convex shape which is inclined with respect to the mating surface  23   a  and faces the outer circumferential surface  2   d  side instead of the inclined surface  23   b.  When the curved surfaces  21   d  and  23   d  are provided in the joint section  3  as described above, the same action effect as in the modified example of the first embodiment is provided. 
     The present invention is not limited to the first embodiment and the second embodiment. For example, in the first embodiment and the second embodiment, the body  2  being formed of metal or an alloy has been exemplified; however, in a case in which greater importance is put on ease of assembly, the body  2  of the piston ring  1  may be formed of a resin composition such as a synthetic resin. In this case, the piston ring  1  may be formed of a resin composition having heat resistance. Therefore, it is possible to easily form the joint section  3  while ensuring the heat resistance of the piston ring  1 . Meanwhile, the resin composition having heat resistance is, for example, a resin composition including at least one of polyimide (PI), polyamide-imide (PAT), polytetrafluoroethylene (PTFE), polybenzimidazole (PBI), polyetherketoneketone (PEKK), polyether ketone (PEK), polyether ketone ether ketone ketone (PEKEKK), and liquid crystal polymer (LCP). Additionally, the resin composition may include a filler for improving the heat resistance of the resin composition. In such a case, it is possible to sufficiently ensure the heat resistance of the piston ring  1 . 
     In the first embodiment, the opposite surface  25   a  of the first internal corner portion  25  is a curved surface having a concave shape which faces the inner circumferential surface  2   c  side, but is not limited thereto. For example, the opposite surface  25   a  may be a planar surface facing the inner circumferential surface  2   c  side. In this case, the opposite surface  25   a  is an inclined surface that is inclined with respect to the mating surface  22   a  of the first female portion  22  with respect to the first male portion  21  and connects the mating surface  22   a  and the mating surface  23   e  of the second male portion  23  with respect to the first male portion  21 . Similarly, the opposite surface  26   a  of the second internal corner portion  26  may be a planar surface facing the outer circumferential surface  2   d  side. In this case, the opposite surface  26   a  is an inclined surface that is inclined with respect to the mating surface  24   a  of the second female portion  24  with respect to the second male portion  23  and connects the mating surface  24   a  and the mating surface  21   c  of the first male portion  21  with respect to the second male portion  23 . Furthermore, in the second embodiment, the opposite surface  25   a  may be a planar surface facing the outer circumferential surface  2   d  side, and the opposite surface  26   a  may be a planar surface facing the inner circumferential surface  2   c  side. 
     In the first and second embodiments, the first male portion  21  has the inclined surface  21   b,  and the second male portion  23  has the inclined surface  23   b,  but the configuration is not limited thereto. For example, the second male portion  23  may have the curved surface  23   d  having a convex shape while the first male portion  21  has the inclined surface  21   b.  Similarly, the second male portion  23  may have the inclined surface  23   b  while the first male portion  21  has the curved surface  21   d  having a convex shape. 
     In the first embodiment, the opposite surface  25   a  of the first internal corner portion  25  is a curved surface having a concave shape which faces the inner circumferential surface  2   e  side, and the opposite surface  26   a  of the second internal corner portion  26  is a curved surface having a concave shape which faces the outer circumferential surface  2   d  side, but the opposite surfaces are not limited thereto. For example, the opposite surface  26   a  of the second internal corner portion  26  may be a planar surface facing the outer circumferential surface  2   d  side while the opposite surface  25   a  of the first internal corner portion  25  is a curved surface having a concave shape which faces the inner circumferential surface  2   c  side. Similarly, the opposite surface  26   a  of the second internal corner portion  26  may be a curved surface having a concave shape which faces the outer circumferential surface  2   d  side while the opposite surface  25   a  of the first internal corner portion  25  is a planar surface facing the inner circumferential surface  2   c  side. Furthermore, in the second embodiment, the opposite surface  26   a  may be a planar surface facing the inner circumferential surface  2   c  side while the opposite surface  25   a  is a curved surface having a concave shape which faces the outer circumferential surface  2   d  side, and the opposite surface  26   a  may be a curved surface having a concave shape which faces the inner circumferential surface  2   c  side while the opposite surface  25   a  is a planar surface facing the outer circumferential surface  2   d  side. 
     In the first and second embodiments, the mating surface  21   a  is a front end surface that extends perpendicular to the circumferential direction, but is not limited thereto. For example, the mating surface  21   a  may be an inclined surface forming a sharp angle with the inclined surface  21   b  or may be a part of the curved surface  21   d.  Similarly, the mating surface  23   a  may be an inclined surface forming a sharp angle with the inclined surface  23   b  or may be a part of the curved surface  23   d.    
     In the first and second embodiments, the surfaces of the body  2  are the side surfaces  2   a  and  2   b,  the inner circumferential surface  2   c,  and the outer circumferential surface  2   d,  but are not limited thereto. For example, the surfaces of the body  2  may include the respective surfaces configuring the joint section  3 . The respective surfaces configuring the joint section  3  include, for example, the front end surfaces  13   a,    14   a,    15   a,  and  16   a,  the mating surfaces  13   b,    15   b,    21   a,    21   c ,  22   a,    23   a,    23   c,  and  24   a,  the inclined surfaces  21   b  and  23   b,  the curved surfaces  21   d  and  23   d,  the opposite surfaces  25   a  and  26   a,  and the notched surfaces S 1  and S 2 . Meanwhile, the surface-treated film may be provided not only on the side surfaces  2   a  and  2   b  of the body  2 , the inner circumferential surface  2   c,  and the outer circumferential surface  2   d  but also on at least one surface of the respective surfaces configuring the joint section  3 . In this case, it is possible to favorably inhibit the breakage of the body  2  configuring the joint section  3 . 
     In the first and second embodiments, when the piston ring  1  is mounted into the ring groove on the outer circumferential surface of the piston, the side surface  2   a  may be disposed on a combustion chamber side of the piston, and the side surface  2   b  may be disposed on the crankcase side of the piston. In this case, the mating surface  21   c  of the first male portion  21  with respect to the second male portion  23  and the mating surface  23   c  of the second male portion  23  with respect to the first male portion  21  are not easily affected by temperature expansion, and the influence of friction during the use of the piston ring  1  also decreases. Therefore, it is possible to maintain the interval between the first male portion  21  and the second male portion  23  in the thickness direction to be small. 
     In the first and second embodiments, when the piston ring  1  is mounted into the ring groove on the outer circumferential surface of the piston, the side surface  2   a  may be disposed on the crankcase side of the piston, and the side surface  2   b  may be disposed on the combustion chamber side of the piston. In this case, it is possible to favorably inhibit oil loss via the piston ring  1 , and thus the oil consumption amount can be reduced. 
     In the first and second embodiments, the piston ring  1  has a substantially rectangular cross-sectional shape, but the cross-sectional shape is not limited thereto. For example, the cross-sectional shape of the piston ring  1  may be a keystone shape, may be a tapering shape, or may be a barrel face shape. 
       1 ,  1 A . . . PISTON RING,  2  . . . BODY,  2   a  . . . SIDE SURFACE (ONE SIDE SURFACE),  2   b  . . . SIDE SURFACE (THE OTHER SIDE SURFACE),  2   c  . . . INNER CIRCUMFERENTIAL SURFACE,  2   d  . . . OUTER CIRCUMFERENTIAL SURFACE,  3  . . . JOINT SECTION,  11  . . . ONE JOINT END,  12  . . . THE OTHER JOINT END,  13  . . . FIRST PROTRUSION PORTION,  13   a  . . . FRONT END SURFACE,  13   b  . . . MATING SURFACE,  14  . . . FIRST RECEPTION PORTION,  14   a  . . . FRONT END SURFACE,  15  . . . SECOND PROTRUSION PORTION,  15   a  . . . FRONT END SURFACE,  15   b  . . . MATING SURFACE,  16  . . . SECOND RECEPTION PORTION,  16   a  . . . FRONT END END SURFACE,  21  . . . FIRST MALE PORTION,  21   a  . . . MATING SURFACE (FRONT END SURFACE),  21   b  . . . INCLINED SURFACE,  21   d  . . . CURVED SURFACE HAVING CONVEX SHAPE,  22  . . . FIRST FEMALE PORTION,  23  . . . SECOND MALE PORTION,  23   a  . . . MATING SURFACE (FRONT END SURFACE),  23   b  . . . INCLINED SURFACE,  23   d  . . . CURVED SURFACE HAVING CONVEX SHAPE,  24  . . . SECOND FEMALE PORTION,  25  . . . FIRST INTERNAL CORNER PORTION,  25   a  . . . OPPOSITE SURFACE (FIRST OPPOSITE SURFACE),  26  . . . SECOND INTERNAL CORNER PORTION,  26   a  . . . OPPOSITE SURFACE (SECOND OPPOSITE SURFACE), C 1 , C 2  . . . STEPEED INTERFACE, S 1 , S 2  . . . NOTCHED SURFACE