Piston ring

Abstract

To provide a piston ring formed by laminating two ring members in an axial direction, which has excellent sealability, and also has excellent productivity and assemblability.SOLUTION: A piston ring 1 is formed by laminating two ring members in an axial direction in an annular groove provided on an outer periphery of a piston that reciprocates in a cylinder. The two ring members are made of the same shape and the same material. The ring member 1A has: an abutment 6 that is formed by a pair of opposing end surfaces, and is V-shaped when viewed from an outer diameter side of the ring; and a mountain-shaped convex part 7 fitted into the abutment 6 on a ring side surface 4 at a position circumferentially spaced from the abutment 6. The two ring members are laminated one another, with the convex part of one ring member fitting into the abutment of the other ring member.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a piston ring for a reciprocating compressor.

Background Art

[0002] Generally, a reciprocating compressor has a structure including a piston and a cylinder, and is used to compress a fluid by the reciprocating movement of the piston with respect to the cylinder. In such a reciprocating compressor, a piston ring is used for the purpose of sealing the fluid in the gap between the piston and the cylinder. The piston ring is mounted in an annular groove provided in the piston. When the piston reciprocates in the cylinder, the outer peripheral surface of the piston ring makes sliding contact with the inner peripheral surface of the cylinder, thereby maintaining internal airtightness.

[0003] In order to ensure the sealing performance in the piston ring, conventionally, a technique of using a plurality of ring members in combination has been proposed. For example, Patent Document 1 and Patent Document 2 disclose a piston ring having a structure in which two ring members are stacked in the axial direction with the positions of the joints shifted. It is thereby said that even if a gap is generated at the joint of one ring member, the other ring member can prevent the leakage of the fluid. Note that the joint is a structure generally provided in the piston ring and refers to the cut portion of the piston ring.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In Patent Document 1 mentioned above, in order to prevent the relative position of the joint of the overlapping ring members from shifting, a step is formed in the circumferential direction of the ring as an anti-rotation shape, and the steps of the two ring members are engaged to be positioned. Further, in Patent Document 2, in order to ensure the sealing performance, a low-pressure groove is formed in the ring member arranged on the low-pressure side for the purpose of enhancing the adhesion between the two ring members. When the gas on the low-pressure side enters the low-pressure groove, the ring pressed from the high-pressure side adheres more strongly due to the pressure difference.

[0006] In order to exhibit the functions of these piston rings, two ring members with different shapes must be separately manufactured and then assembled in the correct order. Therefore, there is a tendency for productivity and assembly workability to be inferior.

[0007] The present invention has been made in view of such circumstances, and an object thereof is to provide a piston ring that is excellent in sealing performance and also excellent in productivity and assembly workability in a piston ring configured by stacking two ring members in the axial direction.

Means for Solving the Problems

[0008] The piston ring of the present invention is a piston ring configured by stacking two ring members in the axial direction in an annular groove provided on the outer circumference of a piston that reciprocates in a cylinder. The two ring members are made of the same shape and the same material. The ring member has a joint that forms a V shape when viewed from the outer diameter side of the ring and is composed of a pair of opposing end faces, and a mountain-shaped convex portion that fits into the joint on the ring side surface at a position circumferentially separated from the joint. The piston ring is characterized in that the convex portion of one ring member fits into the joint of the other ring member and they are overlapped with each other.

[0009] The ring member is characterized in that the convex portion is provided at a position 180° circumferentially away from the joint.

[0010] It is characterized in that the height t from the ring side surface of the convex-shaped portion and the axial length T of the ring member satisfy the relationship of 0.75 < (t / T) < 1.0.

[0011] At the joint, the angle θ1 formed between the pair of end faces is characterized in that 15° < θ1 < 150°. Further, it is characterized in that the angle θ1 and the peak angle θ2 of the mountain shape of the convex-shaped portion satisfy the relationship of |θ1 - θ2| ≤ 2°.

[0012] When the maximum width of the joint in the ring member is W1 and the width at the base of the convex-shaped portion is W2, it is characterized in that the relationship of W1 ≤ W2 is satisfied.

[0013] The height t from the ring side surface of the convex-shaped portion and the axial length T of the ring member satisfy the relationship of 0.75 < (t / T) < 1.0. At the joint, the angle θ1 formed between the pair of end faces is 15° < θ1 < 150°. When the maximum width of the joint in the ring member is W1 and the width at the base of the convex-shaped portion is W2, it is characterized in that the relationship of W1 ≤ W2 is satisfied.

Advantages of the Invention

[0014] The piston ring of the present invention is a piston ring formed by stacking two ring members axially. Since the two ring members have the same shape and the same material, they can be manufactured collectively without distinction between the high-pressure side and the low-pressure side, and the productivity is excellent. Further, each of the ring members has a mating opening formed by a pair of opposing end faces and having a V-shape when viewed from the outer diameter side of the ring, and a mountain-shaped convex portion that fits into the mating opening on the ring side surface at a position circumferentially spaced from the mating opening. The convex portion of one ring member fits into the mating opening of the other ring member and they are stacked, that is, the two ring members are positioned and fitted at positions where the mating openings do not overlap, so that relative rotation of the two ring members is prevented, and the mating openings of the two ring members can be prevented from overlapping in the axial direction, so that leakage of fluid can be suppressed. Also, even during assembly, since it is only necessary to assemble common ring members to each other, the assembly workability is excellent.

[0015] Since the ring member has a convex portion at a position 180° circumferentially away from the mating opening, when the two ring members are overlapped, the distance between the mating openings of the two ring members becomes longer, so that the sealing performance can be further improved.

[0016] Since the height t of the convex portion from the ring side surface and the axial length T of the ring member satisfy the relationship of 0.75 < (t / T) < 1.0, the sealing performance can be further improved by ensuring the contact area with the end face of the mating opening. Also, it is possible to surely prevent the convex portion from protruding from the side surface on the opposite side of the mating ring member.

[0017] Since the angle θ1 formed between the pair of end faces at the mating opening is 15° < θ1 < 150°, the strength at the convex portion and the mating opening can be ensured, which leads to maintaining the sealing performance. Further, since the angle θ1 and the tip angle θ2 of the mountain shape of the convex portion satisfy the relationship of |θ1 - θ2| ≤ 2°, it is easy to suppress the occurrence of a fluid leakage path, and the sealing performance can be further improved.

[0018] When the piston ring is in use, the pressure of the fluid acts on the ring member on the high-pressure side, and the ring member on the low-pressure side is pressed against the side surface of the annular groove, so that the two ring members are pressed against each other. In the ring member, since the width (circumferential distance) W2 at the base of the convex-shaped portion is equal to or greater than the maximum width of the joint (circumferential maximum distance between a pair of end faces) W1, when the two ring members are pressed against each other, the convex-shaped portion fitted in the joint spreads the end face of the joint in the circumferential direction like a wedge. As a result, the end face of the joint and the convex-shaped portion are in close contact, the gap between them is less likely to occur, and the two ring members receive a force in the direction of expanding in the radial direction, increasing the force pressing against the inner peripheral surface of the cylinder, so that higher sealing performance can be exhibited.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0020] FIG. 1 is a schematic view of an example of a reciprocating compressor using the piston ring of the present invention. The reciprocating compressor 11 includes a cylinder 12 and a piston 13, and the piston 13 is connected to a piston rod 14. An annular groove (not shown) for mounting the piston ring 1 is formed on the outer peripheral surface of the piston 13, and the piston ring 1 is incorporated in the annular groove. A fluid such as gas is introduced into the compression chamber 15, compressed by the reciprocating movement of the piston 13 with respect to the cylinder 12, and then discharged to the outside. In FIG. 1, one piston ring 1 is mounted on the piston 13, but the number of piston rings 1 mounted on the piston 13 is not particularly limited.

[0021] As shown in FIG. 1, the piston ring 1 is configured by axially overlapping two ring members 1A and 1B. By shifting the positions of the joints (see FIG. 2) of the ring members 1A and 1B and overlapping them, even if fluid leaks from the joint of one ring member 1A, the other ring member 1B can seal it.

[0022] In the present invention, the two ring members 1A and 1B are made of the same shape and the same material. Therefore, the ring members can be produced collectively without distinguishing between the high-pressure side and the low-pressure side, and the productivity is excellent. Also, when assembling to the piston 13, it is only necessary to assemble two of the same type of ring members together and assemble them into the annular groove of the piston 13. Since there is no distinction in the arrangement between the compression chamber 15 side (high-pressure side) and the proximal end side of the piston 13 (low-pressure side), the assembly workability is excellent.

[0023] FIG. 2 is a perspective view showing an example of the ring member 1A. Since the ring member 1B has the same shape, the description thereof is omitted. As shown in FIG. 2, the ring member 1A is an annular body having a substantially rectangular cross section. In the ring member 1A, chamfers may be provided at the corners between the ring inner peripheral surface 2 and the both side surfaces 4 of the ring, either linearly or curvilinearly. When the ring member 1A is manufactured by injection molding, a stepped portion that becomes a protruding portion from the mold may be provided at this portion.

[0024] As shown in FIG. 2, the ring member 1A is a cut-type ring having a joint 6 at one location in the circumferential direction of the ring, and is expanded in diameter by elastic deformation and mounted in the above-described annular groove. The joint 6 is composed of a pair of opposing end faces 5 and 5', and forms a V shape when viewed from the outer diameter side of the ring. Further, it is preferable that the pair of end faces 5 and 5' inclined with respect to the side face 4 are isosceles triangles. Specifically, it will be described later with reference to FIG. 4(a).

[0025] Further, the ring member 1A integrally has a mountain-shaped convex portion 7 that can be fitted into the joint 6 at a position circumferentially separated from the joint 6 and on the ring side face 4 where the distance between the end faces 5 and 5' of the joint 6 is longer. In FIG. 2, the convex portion 7 is formed from the outer peripheral surface 3 of the ring to the inner peripheral surface 2 of the ring. The outer peripheral surface of the convex portion 7 forms a continuous surface with the outer peripheral surface 3 of the ring, and the inner peripheral surface of the convex portion 7 forms a continuous surface with the inner peripheral surface 2 of the ring. The convex portion 7 has a pair of inclined surfaces 7a and 7a' rising from the ring side face 4, and the interval between the inclined surfaces 7a and 7a' is formed to become smaller as it moves away from the ring side face 4. Further, it is preferable that the pair of inclined surfaces 7a and 7a' inclined with respect to the side face 4 are isosceles triangles.

[0026] The piston rings of the present invention are overlapped with each other such that the convex portion of one ring member is fitted into the joint of the other ring member. Specifically, the convex portion of the other ring member (also referred to as the mating ring member) is fitted into the joint 6 of the ring member 1A, and the joint of the other ring member is fitted into the convex portion 7 of the ring member 1A. In this case, in the ring member 1A, if the circumferential distance between the joint 6 and the convex portion 7 is short, as a result, the positions of the joints of the two ring members approach each other in the circumferential direction, so that the seal distance (the distance between the ring side faces that contact each other between the joints) becomes short, and there is a possibility that fluid is likely to leak.

[0027] Therefore, it is preferable that the joint 6 and the convex portion 7 in the ring member 1A are separated in the circumferential direction. Specifically, when the central angle of the middle portion of the joint 6 with respect to the circumferential center point O of the ring member 1A is set to 0°, the circumferential positions of the joint 6 and the convex portion 7 are preferably 90° or more. Further, from the viewpoint of maximizing the distance between the joints of the two ring members (maximizing the seal distance), when the central angle of the middle portion of the joint 6 with respect to the circumferential center point O of the ring member 1A is set to 0°, the circumferential positions of the joint 6 and the convex portion 7 are more preferably 180°.

[0028] The ring member 1A in Fig. 2 has a convex portion 7 at a position 180° away from the joint 6 in the circumferential direction, and the ring member 1A' in Fig. 3 has a convex portion 7 at a position 90° away from the joint 6 in the circumferential direction.

[0029] Next, with reference to Fig. 4, the specific configurations of the joint and the convex portion will be described. The ring member 1A shown in Fig. 4 represents the ring member in the free state before being mounted on the piston. Fig. 4(a) shows a partially enlarged view of the periphery of the joint as viewed from the ring outer diameter side, and Fig. 4(b) shows a partially enlarged view of the periphery of the convex portion as viewed from the ring outer diameter side.

[0030] As shown in Fig. 4(a), the joint 6 is composed of a pair of end faces 5 and 5' that face each other in the circumferential direction, and forms a V shape when viewed from the ring outer diameter side. In other words, the joint 6 is in the form of a V-groove formed by penetrating along the radial direction from the ring outer peripheral surface to the ring inner peripheral surface. In Fig. 4(a), the end faces 5 and 5' are each formed by inclined planes inclined with respect to the axial direction and are spaced apart from each other. The width of the joint 6 is formed so as to continuously narrow (or widen) from one end side in the axial direction to the other end side. W1 in Fig. 4(a) represents the maximum width of the joint 6.

[0031] The ring member 1A only needs to be capable of expanding its diameter. For example, in a free state, the pair of end faces 5 and 5' may be in contact with each other at a part (for example, the axial end portions 5a and 5a'). Further, in order to prevent the ends from being bent or chipped, chamfers with a linear or curved shape may be provided.

[0032] At the joint 6, the angle θ1 formed between the pair of end faces 5 and 5' is not particularly limited, but it is preferably 15° < θ1 < 150°. If θ1 is 15° or less, the convex-shaped portion that fits into the joint 6 becomes thin, and as a result, the strength may be insufficient and it may break. On the other hand, if θ1 is 150° or more, the pair of tip portions of the joint 6 become thin, and as a result, the strength may be insufficient and it may break. If the convex-shaped portion or the like breaks, there is a concern that the sealing performance may decrease or the device may be contaminated by the fragments. From the viewpoint of making the convex-shaped portion into a wedge to easily expand the joint 6, it is more preferably 15° < θ1 < 120°, and it may be 20° < θ1 < 90°.

[0033] As shown in FIG. 4(b), the convex-shaped portion 7 forms a mountain shape that fits into the V-shaped joint 6. In FIG. 4(b), the convex-shaped portion 7 has a pair of inclined surfaces 7a and 7a' and a top portion 7b. The top portion 7b is a surface that connects the ends of the inclined surfaces 7a and 7a', and is formed by a plane parallel to the ring side surface 4. The configuration of the top portion 7b is not particularly limited. For example, it may be formed by a curved surface (a curved surface convex upward in FIG. 4(b)), or may be formed by a pair of inclined surfaces forming a mountain shape at an angle larger than the angle θ2, or may be formed by a combination thereof.

[0034] The height t protruding from the ring side surface 4 of the convex-shaped portion 7 and the axial length (ring thickness) T of the ring member 1A preferably satisfy the relationship of 0.75 < (t / T) < 1.0. In FIG. 4(b), the height t is the axial distance between the top portion 7b and the ring side surface 4. However, when the height of the top portion changes, it refers to the axial distance from the most protruding portion of the convex-shaped portion 7 to the ring side surface 4. When t / T is greater than 1.0 (that is, when T < t), the convex-shaped portion 7 protrudes beyond the ring thickness of the mating ring member from the opposite ring side surface and may abut against the side surface 13a (see FIG. 5) of the annular groove of the piston, causing the ring member to float. As a result, a gap may occur at the mating surface of the two ring members, which may become a fluid leakage path. On the other hand, when t / T is less than 0.75, the contact area between the convex-shaped portion 7 and the pair of end surfaces forming the mating portion of the mating ring member becomes small, raising concerns that fluid may easily leak. Note that the above height t and the axial length (ring thickness) T may satisfy the relationship of 0.75 < (t / T) < 0.9.

[0035] In the convex-shaped portion 7, the peak angle θ2 (the angle formed by the pair of inclined surfaces 7a, 7a') of the mountain shape is not particularly limited. However, in relation to the above angle θ1 of the mating portion, it is preferable to satisfy |θ1 - θ2| ≤ 2°. If the peak angle θ2 becomes too small compared to the angle θ1 (θ1 - θ2 > 2°), the gap between the convex-shaped portion 7 that has penetrated into the mating portion of the mating ring member and the mating portion, specifically, between the pair of inclined surfaces 7a, 7a' of the convex-shaped portion 7 and the pair of end surfaces 5, 5' of the mating portion becomes large, which may become a fluid leakage path.

[0036] On the other hand, if the peak angle θ2 of the convex-shaped portion 7 becomes too large compared to the angle θ1 of the mating portion (θ2 - θ1 > 2°), the contact state between the convex-shaped portion 7 and the pair of end surfaces of the mating portion becomes a line contact only near the root of the convex-shaped portion 7, raising concerns that fluid may easily leak. Also, there is a concern that the convex-shaped portion 7 may not enter the mating portion sufficiently, causing the two ring members to float, resulting in a fluid leakage path. Therefore, it is preferable to satisfy the relationship of |θ1 - θ2| ≤ 2°.

[0037] Incidentally, regarding the relationship between the tip angle θ2 of the convex-shaped portion 7 and the angle θ1 of the joint, in order to improve the assemblability when fitting the convex-shaped portion 7 of one ring member into the joint 6 of the other ring member, θ2 < θ1 may be satisfied.

[0038] Specifically, the tip angle θ2 of the convex-shaped portion 7 is preferably 15° < θ2 < 150°, more preferably 15° < θ2 < 120°, and may also be 20° < θ2 < 90°.

[0039] Incidentally, the rising base of the convex-shaped portion 7, that is, the boundary between the pair of inclined surfaces 7a, 7a' and the ring side surface 4 may be formed as a smooth curved surface. In that case, in order to avoid interference with the mating ring, it is necessary to provide reliefs at the corners 5b, 5b' of the joint 6. Note that the reliefs at this time may be linear or curved chamfers.

[0040] FIG. 5(a) shows an overview when two ring members are stacked and assembled. The convex-shaped portion 7 of the ring member 1A is fitted into the joint 6 of the ring member 1B, and the convex-shaped portion of the ring member 1B is fitted into the joint of the ring member 1A. Thereby, the two ring members 1A and 1B are positioned and stacked respectively. By fitting into each other, relative rotation of the ring members is suppressed.

[0041] FIG. 5(b) shows the usage state of the piston ring. During the use of the piston ring 1, the two ring members 1A and 1B receive forces in directions pressing against each other under the pressure of the sealing fluid. At this time, the opposing ring side surfaces of the ring members 1A and 1B are in close contact with each other, and the convex-shaped portion 7 fitted into the joint 6 presses the pair of end faces 5, 5' of the joint 6 like a wedge, thereby pressing the joint 6 in the circumferential direction and expanding it. As a result, the ring members 1A and 1B receive forces in the direction of expanding in the radial direction, increasing the force pressing against the inner peripheral surface of the cylinder, and thus a higher sealing performance can be exhibited. Also, the close contact between the pair of inclined surfaces of the convex-shaped portion 7 and the pair of end faces 5, 5' of the joint 6 leads to an improvement in the sealing performance.

[0042] From the viewpoint of more effectively exerting such an effect, when the maximum width of the joint 6 (circumferential distance at the portion where the pair of end faces 5 and 5' are farthest apart) is W1 and the width at the base of the convex portion 7 (circumferential distance) is W2, it is preferable that W1 and W2 (before fitting and overlapping the two ring members 1A and 1B) when assembled in the cylinder satisfy the relationship W1 < W2. Thereby, it becomes easier to more strongly exert the force for expanding the diameter of the mating ring member and pressing it against the inner peripheral surface of the cylinder.

[0043] In FIGS. 4 and 5, the convex portion 7 has a configuration with a top portion 7b, but it is not limited thereto. For example, the convex portion 7 may have no top portion, and a configuration in which a pair of inclined surfaces 7a and 7a' are directly connected. In such a case, the tip of the convex portion becomes sharp, and there is a concern of breakage or chipping, and the fragments generated thereby can be a factor in contaminating the device. Therefore, in order to prevent this, the tip may be cut into a straight line shape or a curved surface shape, or a configuration having a top portion as described above may be adopted.

[0044] The piston ring of the present invention can be suitably used in a compressor used under high pressure. For example, it is used at a high pressure of 10 MPa to 120 MPa, preferably 65 MPa to 110 MPa, and more preferably 80 MPa to 100 MPa. It may be used within such a pressure range and under non-lubricated conditions.

[0045] In the present invention, the fluid compressed by the reciprocating compressor is not necessarily limited, but it may be a gas because of its excellent sealing property. Further, the "gas" in this specification is a concept meaning a general gas, and includes gaseous fuels and the like. For example, it may be a gas such as hydrogen, natural gas, methane, or ammonia.

[0046] The material of the ring member described above is not particularly limited, but it is preferably a molded body of a resin composition. In addition, the "molded body" in this specification refers to a molded body molded by a well-known method such as injection molding, compression molding, or extrusion molding, or a product obtained by machining these molded bodies.

[0047] The resin composition of the ring member will be described below.

[0048] The base resin used in the resin composition is preferably an injection-moldable resin. Specifically, an aromatic polyether ketone-based resin, a thermoplastic polyimide resin, a polyamideimide resin, etc. can be used. The aromatic polyether ketone-based resin is a general term for resins in which benzene rings are bonded by ether groups and ketone groups, and is also called a polyaryl ether ketone resin. Examples of the aromatic polyether ketone-based resin include a polyether ether ketone resin, a polyether ketone resin, a polyether ketone ketone resin, a polyether ketone ether ketone ketone resin, etc.

[0049] In the above resin composition, the base resin is preferably contained in an amount of 50% to 95% by volume, more preferably 60% to 90% by volume, and even more preferably 70% to 90% by volume based on the total resin composition.

[0050] The above resin composition is preferably blended with a carbon material for the purpose of improving strength, elastic modulus, friction and wear characteristics, etc. Examples of the carbon material include carbon fiber, graphite, coke powder, etc. One type of carbon material may be blended alone, or a plurality of types may be combined and blended.

[0051] The above resin composition preferably contains 5% to 35% by volume of the carbon material based on the total resin composition, and more preferably 5% to 25% by volume. Further, it is preferable to contain carbon fiber as the carbon material.

[0052] The above resin composition preferably further contains 5% to 25% by volume of polytetrafluoroethylene (PTFE) resin based on the total resin composition. If the blending amount of the PTFE resin is less than 5% by volume, it is difficult to obtain the effect of improving the friction and wear characteristics under non-lubricated conditions, and if it exceeds 25% by volume, the tensile elongation characteristics of the resin composition may deteriorate. The blending amount of the PTFE resin is more preferably 10% to 20% by volume.

[0053] In addition to the above carbon material and the above PTFE resin, the resin composition may be blended with well-known resin additives to such an extent that the effects of the present invention are not inhibited. Examples of the additives include aramid fibers, inorganic substances (such as mica, talc, calcium carbonate, boron nitride, etc.), whiskers (such as calcium carbonate, potassium titanate, etc.), colorants (such as iron oxide, titanium oxide, carbon black, etc.), and other resin components.

[0054] Each material constituting the resin composition can be mixed, if necessary, using a Henschel mixer, an axial mixer, a ball mixer, a ribbon blender, etc., and then melt-kneaded using a melt extruder such as a twin-screw kneading extruder to obtain molding pellets. In addition, when melt-kneading with a twin-screw extruder or the like, side feeding may be employed for the input of the carbon material, PTFE resin, and the above-mentioned resin additives. Using these molding pellets, a ring member can be molded, for example, by injection molding. For example, additional processing or full processing may be performed using the injection molding material to finish it into the shape of a predetermined ring member.

Industrial Applicability

[0055] The piston ring of the present invention is a piston ring composed of two ring members stacked in the axial direction. It has excellent sealing performance and is also excellent in productivity and assembly workability. Therefore, it can be widely used as a piston ring and is suitable for piston rings of reciprocating compressors that compress gas.

Explanation of Reference Numerals

[0056] 1 Piston ring 1A, 1A’, 1B Ring members 2 Ring inner peripheral surface 3 Ring outer peripheral surface 4 Ring side surface 5, 5’ End faces 6 Joint 7 Convex-shaped portion 7a, 7a’ Inclined surfaces 7b Top 11 Compressor 12 cylinders 13 pistons 14 piston rods 15 compression chambers

Claims

1. A piston ring formed by stacking two ring members axially in an annular groove provided on the outer periphery of a piston that reciprocates within a cylinder, wherein the two ring members are made of the same shape and the same material, and the ring member has a joint formed by a pair of opposing end faces and having a V-shape when viewed from the ring outer diameter side, and a mountain-shaped convex portion that fits into the joint on the ring side surface at a position circumferentially spaced from the joint, and the convex portion of one ring member fits into the joint of the other ring member and they are stacked on each other. The piston ring is characterized by this.

2. The piston ring according to claim 1, wherein the ring member has the convex portion at a position 180° circumferentially away from the joint.

3. The piston ring according to claim 1 or claim 2, wherein the height t of the convex portion from the ring side surface and the axial length T of the ring member satisfy the relationship 0.75 < (t / T) < 1.

0.

4. An angle θ between the pair of end faces at the joint １ However, 15°<θ １ 3. The piston ring according to claim 1, wherein the angle is set to 150°.

5. the angle θ １ and the peak angle θ of the mountain shape of the convex portion ２ satisfy the relationship of |θ １ − θ ２ | ≤ 2°, and the piston ring according to claim 4 is characterized in that

6. In the ring member, let the maximum width of the joint be W １ , and let the width at the base of the convex portion be W ２ . When this is the case, the piston ring according to claim 1 or claim 2 is characterized by satisfying the relationship of W １ ≤ W ２ .

7. The height t of the convex portion from the ring side surface and the axial length T of the ring member satisfy the relationship 0.75 < (t / T) < 1.0, The angle θ formed between the pair of end faces at the joint １ is such that 15° < θ １ < 150°, In the ring member, let the maximum width of the joint be W １ , and let the width at the base of the convex portion be W ２ . When this is the case, W １ ≦ W ２ The piston ring according to claim 1 or claim 2, characterized by satisfying the relationship of.

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