Piston rings

Abstract

This invention provides a piston ring that suppresses gas leakage from the gap between the rings while also offering improved ease of installation on the piston. [Solution] The piston ring comprises a first ring and a second ring, both annular in shape and extending in the circumferential direction. The first ring has a first end face and a second end face opposite to the first end face in the axial direction. An engagement groove extending in the circumferential direction and recessed toward the first end face is formed on the second end face along the entire circumference of the first ring. The first ring and the second ring each have at least one first cut and at least one second cut in the circumferential direction. The second ring is engaged with the engagement groove so as to be rotatable in the circumferential direction relative to the first ring, such that the first and second cuts do not overlap each other.

Description

Technical Field

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

Background Art

[0002] For example, Japanese Patent No. 5727643 (Patent Document 1) describes a piston ring. The piston ring described in Patent Document 1 has a first ring and a second ring arranged axially one above the other. The first ring is arranged on the high-pressure side of the second ring in the cylinder. The first ring has a first surface in the axial direction, and the second ring has a second surface facing the first surface in the axial direction.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the piston ring described in Patent Document 1, a low-pressure groove extending in the circumferential direction is formed on the first surface, and a ridge extending in the circumferential direction and arranged in the low-pressure groove is formed on the second surface. However, in the piston ring described in Patent Document 1, the second ring cannot rotate circumferentially with respect to the first ring while the ridge is engaged with the low-pressure groove. Therefore, there is room for improvement in the attachment property of the piston ring described in Patent Document 1 to the piston. The present disclosure has been made in view of the problems of the prior art as described above. More specifically, the present disclosure provides a piston ring with improved attachment property to a piston while suppressing gas leakage from the joint gap.

Means for Solving the Problems

[0005] The piston rings of this disclosure comprise a first ring and a second ring, both annular in shape and extending circumferentially. The first ring has a first end face and a second end face opposite the first end face in the axial direction. An engagement groove extending circumferentially and recessed toward the first end face is formed on the second end face along the entire circumference of the first ring. The first ring and the second ring each have at least one first cut and at least one second cut in the circumferential direction. The second ring is engaged with the engagement groove so as to be circumferentially rotatable relative to the first ring such that the first and second cuts do not overlap each other. [Effects of the Invention]

[0006] The piston rings of this disclosure can improve the ease of mounting to the piston while suppressing gas leakage from the gap between the rings. [Brief explanation of the drawing]

[0007] [Figure 1] This is a plan view of piston ring 100. [Figure 2] This is a cross-sectional view taken along line II-II in Figure 1. [Figure 3] This is a bottom view of the first ring 10. [Figure 4] This is a divided plan view of the first ring 10. [Figure 5] This is a divided plan view of the second ring 20. [Figure 6] This is a cross-sectional view showing an example of piston ring 100 in use. [Figure 7] This is a plan view of the piston ring 100 according to modified example 1. [Figure 8] This is a plan view of the piston ring 100 according to modified example 2. [Figure 9A] This is a cross-sectional view of the piston ring 100 according to modified example 3. [Figure 9B] This is a cross-sectional view of the piston ring 100 according to modified example 4. [Modes for carrying out the invention]

[0008] The details of embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions will not be repeated. The piston ring according to the embodiment will be referred to as piston ring 100.

[0009] (Piston ring configuration 100) As shown in Figure 1, the central axis of the piston ring 100 is defined as the central axis A1. The direction of the central axis A1 is defined as the axial direction. The direction passing through the central axis A1 and perpendicular to the central axis A1 is defined as the radial direction. When viewing the piston ring 100 along the axial direction, the direction along the circumference of the circle centered on the central axis A1 is defined as the circumferential direction.

[0010] As shown in Figures 1, 2, 3, and 4, the piston ring 100 has a first ring 10 and a second ring 20. The first ring 10 and the second ring 20 are annular in shape and extend in the circumferential direction. The first ring 10 and the second ring 20 are formed of a resin material containing a filler, for example. This filler is a reinforcing fiber such as carbon fiber or glass fiber. This resin material is a hard resin such as PTFE (polytetrafluoroethylene) or PEEK (polyetheretherketone). However, the materials used for the first ring 10 and the second ring 20 are not limited to these.

[0011] The first ring 10 has an end face 10a and an end face 10b opposite to end face 10a in the axial direction. End face 10a forms one end face of the piston ring 100 in the axial direction. The first ring 10 has an inner circumferential surface 10c and an outer circumferential surface 10d extending in the circumferential direction. The inner circumferential surface 10c forms the inner circumferential surface of the piston ring 100. The outer circumferential surface 10d is the opposite surface of the inner circumferential surface 10c in the radial direction.

[0012] An engagement groove 10e is formed on the end face 10b, recessed toward the end face 10a. The engagement groove 10e extends in the circumferential direction. The engagement groove 10e is formed around the entire circumference of the first ring 10. The engagement groove 10e has a bottom surface 10ea, a side surface 10eb, and a side surface 10ec. In a cross-sectional view perpendicular to the circumferential direction, the bottom surface 10ea extends in the radial direction. In a cross-sectional view perpendicular to the circumferential direction, the side surfaces 10eb and 10ec are connected to the inner and outer radial sides of the bottom surface 10ea, respectively. The side surface 10ec is connected to the outer peripheral surface 10d on the opposite side from the bottom surface 10ea.

[0013] In a cross-sectional view perpendicular to the circumferential direction, the side surface 10eb extends, for example, in the axial direction. In a cross-sectional view perpendicular to the circumferential direction, the side surface 10ec has, for example, a side portion 10ec1 and a side portion 10ec2 that is radially adjacent to the outside of the side portion 10ec1. In a cross-sectional view perpendicular to the circumferential direction, the side portion 10ec1 is inclined with respect to the axial direction such that the upper end of the side portion 10ec1 is located radially outward from the lower end of the side portion 10ec1. In a cross-sectional view perpendicular to the circumferential direction, the side portion 10ec2 is inclined with respect to the axial direction such that the upper end of the side portion 10ec2 is located radially outward from the lower end of the side portion 10ec2. The inclination angle of the side portion 10ec1 with respect to the axial direction is called the first inclination angle, and the inclination angle of the side portion 10ec2 with respect to the axial direction is called the second inclination angle. The second inclination angle is greater than the first inclination angle.

[0014] A balance groove 10f recessed toward the inner peripheral surface 10c may be formed on the outer peripheral surface 10d. The balance groove 10f extends in the circumferential direction. The balance groove 10f may be formed over the entire circumference of, for example, the first ring 10. The balance groove 10f may be formed on a part of the first ring 10. The balance groove 10f is, for example, rectangular in a cross-sectional view perpendicular to the circumferential direction. A connection groove 10g recessed toward the inner peripheral surface 10c is formed on the outer peripheral surface 10d. The connection groove 10g extends in the axial direction. One end and the other end of the connection groove 10g in the axial direction are respectively continuous with the end face 10a and the balance groove 10f. Note that the balance groove 10f may not be formed on the outer peripheral surface 10d.

[0015] The second ring 20 has an end face 20a and an end face 20b which is the opposite face of the end face 20a in the axial direction. The second ring 20 has an inner peripheral surface 20c and an outer peripheral surface 20d that extend in the circumferential direction. The outer peripheral surface 20d is the opposite face of the inner peripheral surface 10c in the radial direction.

[0016] The second ring 20 is engaged with the engagement groove 10e. More specifically, for the second ring 20, the end face 20b contacts the bottom face 10ea and the side face 10ec, and the inner peripheral surface 20c contacts the side face 10eb. Note that in a state where the second ring 20 is engaged with the engagement groove 10e, the outer peripheral surface 10d and the outer peripheral surface 20d are continuous with each other to form the outer peripheral surface of the piston ring 100, and the end face 10b and the end face 20a are continuous with each other to form the other end face of the piston ring 100 in the axial direction.

[0017] The first ring 10 has a plurality of cut portions 13 in the circumferential direction. In the illustrated example, the number of cut portions 13 is two. The first ring 10 is cut at each of the plurality of cut portions 13. That is, the cut portion 13 is composed of cut surfaces that face each other in the circumferential direction. This cut surface is perpendicular to the circumferential direction. That is, the first ring 10 is straight-cut at the cut portion 13. Since the first ring 10 has a plurality of cut portions 13, it is divided into a plurality of divided pieces. In the illustrated example, since the first ring 10 has two cut portions 13, the first ring 10 is divided into a divided piece 11 and a divided piece 12. The divided piece 11 and the divided piece 12 are partial annular shapes extending in the circumferential direction.

[0018] The second ring 20 has a plurality of cut portions 23 in the circumferential direction. In the illustrated example, the number of cut portions 23 is two. The second ring 20 is cut at each of the plurality of cut portions 23. That is, the cut portion 23 is composed of cut surfaces that face each other in the circumferential direction. This cut surface is perpendicular to the circumferential direction. That is, the second ring 20 is straight-cut at the cut portion 23. Since the second ring 20 has a plurality of cut portions 23, it is divided into a plurality of divided pieces. In the illustrated example, since the second ring 20 has two cut portions 23, the second ring 20 is divided into a divided piece 21 and a divided piece 22. The divided piece 21 and the divided piece 22 are partial annular shapes extending in the circumferential direction.

[0019] As described above, since the engagement groove 10e extends in the circumferential direction and is formed over the entire circumference of the first ring 10, the second ring 20 is rotatable in the circumferential direction while being engaged with the engagement groove 10e. The second ring 20 is rotated in the circumferential direction so that each of the plurality of cut portions 23 does not overlap with any of the plurality of cut portions 13 while being engaged with the engagement groove 10e.

[0020] (Usage example of the piston ring 100) As shown in Figure 6, the piston 30 is a cylindrical member extending in the direction of the central axis A2. The piston ring 100 is attached to a groove 31 formed on the outer circumferential surface of the piston 30. More specifically, in a cross-sectional view perpendicular to the circumferential direction, the inner circumferential surface of the piston ring 100 faces the bottom surface 31a of the groove 31, one end face (end face 10a) of the piston ring 100 in the axial direction faces the side surface 31b of the groove 31, and the other end face (end face 20a, end face 10b) of the piston ring 100 in the axial direction faces the side surface 31c of the groove 31.

[0021] The piston 30, to which the piston ring 100 is attached, is inserted into the cylinder 40 of the compressor. When inserted into the cylinder 40, the piston ring 100 divides the internal space of the cylinder 40 into a high-pressure side space 41 and a low-pressure side space 42. One end face of the piston ring 100 faces the high-pressure side space 41, and the other end face of the piston ring 100 faces the low-pressure side space 42. When the pressure in the high-pressure side space 41 is applied to the piston ring 100, the other end face of the piston ring 100 in the axial direction comes into contact with the side surface 31c.

[0022] There are gaps between the side surface 31b and one end face of the piston ring 100 in the axial direction, and between the bottom surface 31a and the inner circumferential surface of the piston ring 100. Through these gaps, the pressure from the high-pressure side space 41 is applied radially outward from the inner circumferential surface of the piston ring 100, causing the piston ring 100 to expand in diameter. As a result, the inner wall surface of the cylinder 40 and the outer circumferential surface of the piston ring 100 come into contact. The balance groove 10f is connected to the high-pressure side space 41 via the connecting groove 10g. Therefore, the pressure from the high-pressure side space 41 is applied radially inward from the outer circumferential surface of the piston ring 100 through the connecting groove 10g, which reduces the contact pressure between the outer circumferential surface of the piston ring 100 and the inner wall surface of the cylinder 40.

[0023] (How to install piston ring 100) When attaching the piston ring 100 to the piston 30, firstly, the first ring 10 (divided pieces 11 and 12) is attached to the piston 30. Secondly, the second ring 20 (divided pieces 21 and 22) is engaged with the engagement groove 10e to attach the second ring 20 to the first ring 10. Thirdly, the second ring 20 is engaged with the first ring 10, that is, the end face 20b and the inner circumferential surface 20c come into contact with the engagement groove 10e. Fourthly, the second ring 20 is rotated relative to the first ring 10 so that each of the multiple cut portions 23 does not overlap with any of the multiple cut portions 13. In this way, the piston ring 100 is attached to the piston 30.

[0024] (Effect of piston ring 100) The piston ring has a gap at the joint for attachment to the piston 30. Gas leaks from the high-pressure side space 41 to the low-pressure side space 42 through this gap. Therefore, when a piston 30 with such piston rings is inserted into a cylinder 40 and used, the efficiency of the compressor may decrease.

[0025] When viewed in isolation, the first ring 10 has a gap at the joint (cut portion 13). Similarly, when viewed in isolation, the second ring 20 also has a gap at the joint (cut portion 23). However, the second ring 20 is attached to the first ring 10 by engaging with the engagement groove 10e, and each of the multiple cut portions 23 is rotated circumferentially so as not to overlap with any of the multiple cut portions 13. Therefore, when viewed as a whole piston ring 100, there is no gap at the joint, which suppresses gas leakage from the gap and, consequently, improves the efficiency of the compressor.

[0026] Furthermore, in the piston ring 100, since the second ring 20 is engaged with the first ring 10 so as to be circumferentially rotatable, the second ring 20 can be rotated relative to the first ring 10 after the first ring 10 and the second ring 20 have been mounted on the piston 30, making mounting to the piston 30 easy.

[0027] When piston rings are made of a hard (low elongation) material or when they are attached to a small-diameter piston 30, it is necessary to divide the piston ring into multiple parts in the circumferential direction. In this case, the pressure of the high-pressure space 41 acting on the inner circumferential surface of the piston ring cannot expand the diameter of the piston ring and bring it into contact with the inner wall surface of the cylinder 40, so a separate part such as a tension ring is required. In addition, in this case, after the piston ring is assembled to the piston 30, it may come off the piston 30 due to external forces such as gravity.

[0028] In contrast, with the piston ring 100, when pressure is applied radially outward from the high-pressure side space 41 to the inner circumferential surface (inner circumferential surface 10c) of the piston ring 100, the second ring 20 is rotated circumferentially relative to the first ring 10 so that each of the multiple cut portions 23 does not overlap with any of the multiple cut portions 13. As a result, the first ring 10 and the second ring 20 deform together and expand in diameter, causing the outer circumferential surface of the piston ring 100 to contact the inner wall surface of the cylinder 40. Therefore, no other parts such as tension rings are required. Furthermore, after the piston ring 100 is assembled to the piston 30, the second ring 20 is rotated circumferentially relative to the first ring 10 so that each of the multiple cut portions 23 does not overlap with any of the multiple cut portions 13. Therefore, it is difficult for the piston ring 100 to come off the piston 30 due to external forces, etc.

[0029] In the piston ring 100, the side surface 10ec has side portions 10ec1 and 10ec2, and the second inclination angle is greater than the first inclination angle, so the contact area between the end face 20b and the engagement groove 10e increases, making it difficult for gas to leak from the high-pressure side space 41 to the low-pressure side space 42 through the space between the side surface 10ec and the end face 20b. On the other hand, in the piston ring 100, the side surface 10eb extends axially in a cross-sectional view perpendicular to the circumferential direction and is not inclined with respect to the axial direction, so gas is more likely to leak from the high-pressure side space 41 to the low-pressure side space 42 through the space between the side surface 10eb and the inner circumferential surface 20c. When multiple piston rings 100 are attached to the piston 30, if the sealing performance of the piston rings 100 is too high, the load may concentrate on a particular piston ring 100 among the multiple piston rings 100. The piston ring 100 has the above-described structure of side 10eb and side 10eb, which allows for moderate gas leakage from the high-pressure side space 41 to the low-pressure side space 42, thereby suppressing the concentration of load on a specific piston ring 100.

[0030] (Variation 1) As shown in Figure 7, the direction in which the pair of cut surfaces forming the cut portion 13 face each other may be inclined with respect to the circumferential direction. Similarly, the direction in which the pair of cut surfaces forming the cut portion 23 face each other may also be inclined with respect to the circumferential direction. That is, the first ring 10 may be angle-cut at the cut portion 13, and the second ring 20 may be angle-cut at the cut portion 23.

[0031] (Modification 2) As shown in Figure 8, the first ring 10 may have only one cut portion 13, and the second ring 20 may have only one cut portion 23. In other words, the piston ring 100 only needs to have at least one cut portion 13 on the first ring 10 and at least one cut portion 23 on the second ring 20. In this case as well, since the second ring 20 is rotated circumferentially so that one cut portion 23 does not overlap with one cut portion 13, gas leakage from the gap at the joint of the piston ring 100 can be suppressed, similar to the examples shown in Figures 1 to 5.

[0032] (Modification 3 and Modification 4) As shown in Figures 9A and 9B, the balance groove 10f does not have to be rectangular in a cross-sectional view perpendicular to the circumferential direction. Let W be the width of the balance groove 10f in the axial direction. The width W may increase as it moves away from the bottom of the balance groove 10f. The width W may increase linearly with respect to the distance from the bottom of the balance groove 10f. For example, the balance groove 10f may be semicircular in a cross-sectional view in the circumferential direction (see Figure 9A). Also, the balance groove 10f may be V-shaped (see Figure 9B) or L-shaped in a cross-sectional view in the circumferential direction.

[0033] The outer surface of the piston ring 100 slides against the inner wall surface of the cylinder 40. As a result, wear progresses on the outer surface of the piston ring 100 as it is used, and the outer diameter of the piston ring 100 decreases. Consequently, the contact pressure between the outer surface of the piston ring 100 and the inner wall surface of the cylinder 40 also decreases, raising concerns that the sealing performance of the piston ring 100 will deteriorate. However, in the examples shown in Figures 9A and 9B, as the width W of the piston ring 100 decreases with wear, the pressure in the high-pressure space 41 applied radially inward from the outer surface of the piston ring 100 also decreases. Therefore, even if wear progresses on the outer surface of the piston ring 100 and the outer diameter of the piston ring 100 decreases, the decrease in contact pressure between the outer surface of the piston ring 100 and the inner wall surface of the cylinder 40 is suppressed.

[0034] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the embodiments described above, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0035] 10 First ring, 10a end face, 10b end face, 10c inner circumferential surface, 10d outer circumferential surface, 10e engagement groove, 10ea bottom surface, 10eb side surface, 10ec side surface, 10ec1 side section, 10ec2 side section, 10f balance groove, 10g connecting groove, 11 divided piece, 12 divided piece, 13 cut section, 20 Second ring, 20a, 20b end faces, 20c inner circumferential surface, 20d outer circumferential surface, 21 divided piece, 22 divided piece, 23 cut section, 30 Piston, 31a bottom surface, 31b, 31c side surfaces, 31 groove, 40 Cylinder, 41 high pressure side space, 42 low pressure side space, 100 Piston ring, A1, A2 central axis, W width.

Claims

1. It comprises a first ring and a second ring that extend in the circumferential direction, The first ring has a first end face and a second end face which is the opposite side of the first end face in the axial direction. The second end face has an engagement groove that extends in the circumferential direction and is recessed toward the first end face, formed around the entire circumference of the first ring. The first ring and the second ring each have at least one first cut portion and at least one second cut portion in the circumferential direction, The second ring is engaged with the engagement groove so as to be rotatable in the circumferential direction relative to the first ring, such that the first cut portion and the second cut portion do not overlap each other. The first ring is divided into a plurality of first segments in the circumferential direction, The piston ring is a piston ring in which the second ring is divided into a plurality of second segments in the circumferential direction.

2. The first ring has, in the radial direction, an inner circumferential surface extending in the circumferential direction and an outer circumferential surface that is opposite to the inner circumferential surface and also extends in the circumferential direction. The piston ring according to claim 1, wherein a balance groove extending in the circumferential direction and recessed toward the inner circumferential surface is formed on the outer circumferential surface of the first ring, either over the entire circumference of the first ring or on a part of the first ring.

3. The piston ring according to claim 2, wherein the width of the balance groove in the axial direction increases in proportion to the distance from the bottom of the balance groove in the radial direction.

4. The piston ring according to claim 3, wherein the width is proportional to the distance.

5. comprising a first ring and a second ring extending in the circumferential direction, The first ring has a first end face and a second end face which is the opposite side of the first end face in the axial direction. The second end face has an engagement groove that extends in the circumferential direction and is recessed toward the first end face, formed around the entire circumference of the first ring. The first ring and the second ring each have at least one first cut portion and at least one second cut portion in the circumferential direction, The second ring is engaged with the engagement groove so as to be rotatable in the circumferential direction relative to the first ring, such that the first cut portion and the second cut portion do not overlap each other. The engagement groove, in a cross-sectional view perpendicular to the circumferential direction, has a bottom surface extending in the radial direction, a first side surface connected to the inner side of the bottom surface in the radial direction, and a second side surface connected to the outer side of the bottom surface in the radial direction. In the cross-sectional view, the second side surface has a first side surface portion and a second side surface portion that is connected to the radially outer side of the first side surface portion. In the cross-sectional view, the first side portion is inclined with respect to the axial direction such that the upper end of the first side portion is located radially outward from the lower end of the first side portion. In the cross-sectional view, the second side portion is inclined at a larger angle with respect to the axial direction than the first side portion, such that the upper end of the second side portion is located radially outward from the lower end of the second side portion.

6. The piston ring according to claim 5, wherein, in the cross-sectional view, the first side portion extends in the axial direction.

7. The first ring and the second ring are formed from a resin material containing a filler, The piston ring according to any one of claims 1 to 6, wherein the resin material is PTFE or PEEK.

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