Compression ring, compression ring combination, and ring body

Abstract

This compression ring has: a ring body for being fitted into a ring groove formed in a piston, the ring body having formed in the inner circumferential surface thereof an inner circumferential groove that is recessed toward the radially outer circumferential side; and a coil expander that is disposed to the radially inner circumferential side of the ring body in the ring groove, and abuts the inner circumferential groove of the ring body, and spring-urges the ring body toward the radially outer circumferential side. The ring body is made of steel. Additionally, a value (d1 / a1) obtained by dividing the nominal diameter (d1) of the compression ring by the radial thickness (a1) of the ring body is 57.0 or less.

Description

Compression rings, compression ring combinations, and ring bodies

[0001] The present disclosure relates to a compression ring attached to a piston of an internal combustion engine.

[0002] Internal combustion engines typically used in automobiles feature a piston ring combination consisting of a compression ring and an oil ring. The compression ring is located on the combustion chamber side of the piston, while the oil ring is located on the crankcase side. These rings slide along the cylinder wall. The oil ring functions as an oil seal, scraping excess engine oil (lubricant) off the cylinder wall toward the crankcase, thereby preventing oil leakage into the combustion chamber (oil leak). The oil ring also prevents piston seizure during engine operation by adjusting the amount of oil to maintain an appropriate lubricant film on the cylinder wall. The compression ring also functions as a gas seal, preventing combustion gas from leaking from the combustion chamber to the crankcase (blow-by) by maintaining an airtight seal, and as an oil seal, scraping off excess oil that the oil ring cannot completely remove, thereby preventing oil leak.

[0003] Furthermore, Patent Document 1 discloses a piston ring as a compression ring for a high-power diesel engine, which includes an outer ring and an expander. The expander is made of a Ni-based alloy and has a coil shape. The expander is disposed so as to abut against the inner peripheral side of the outer ring and applies tension to the outer ring.

[0004] Japanese Patent Application Publication No. 2004-124999 Japanese Patent Application Publication No. 2015-108417 Japanese Patent No. 6475416

[0005] In internal combustion engines with compression rings having a relatively large nominal diameter (e.g., 100-240 mm), the piston stroke is longer than in internal combustion engines with compression rings having a relatively small nominal diameter. Therefore, compression rings attached to pistons in internal combustion engines with a relatively large nominal diameter are required to improve their ability to conform to the inner wall surface of the cylinder. One possible way to improve the conformity of the compression ring is to increase the ring tension of the compression ring. However, increasing the ring tension of the compression ring may result in an excessive increase in friction when the compression ring slides along the inner wall surface of the cylinder.

[0006] Furthermore, in order to improve the tracking ability of the compression ring, it is also conceivable to adopt a structure in which an expander is disposed on the inner peripheral side of the ring main body (outer ring), as disclosed in, for example, Patent Document 1. However, when this structure is adopted for a compression ring that is attached to a piston of an internal combustion engine having a relatively large nominal diameter, there is room for improvement in terms of suppressing an increase in blow-by gas.

[0007] The present invention has been made in view of the above-mentioned problems, and its object is to provide a technology for a compression ring attached to a piston of an internal combustion engine having a relatively large nominal diameter, which is capable of improving tracking while suppressing an increase in ring tension and suppressing an increase in blow-by gas.

[0008] A compression ring according to a first aspect of the present invention is a compression ring that is attached to a piston of an internal combustion engine having a nominal diameter (d1) of 100 mm to 240 mm. The compression ring includes: a ring body that is attached to a ring groove formed in the piston, the ring body having an inner circumferential groove formed on its inner surface that is recessed radially outward; and a coil expander that is positioned radially inward in the ring groove from the ring body, abuts against the inner circumferential groove of the ring body, and urges the ring body radially outward, wherein the ring body is made of steel, and the value (d1 / a1) obtained by dividing the nominal diameter (d1) of the compression ring by the radial thickness (a1) of the ring body is 57.0 or less.

[0009] In the compression ring according to the first aspect of the present invention, when the coil expander abuts against the inner circumferential groove of the ring body, the radial distance from the outermost portion of the outer surface of the ring body to the innermost portion of the coil expander may be 1 / 25 or less of the nominal diameter of the compression ring.

[0010] In the compression ring according to the first aspect of the present invention, the inner circumferential groove on the inner circumferential surface of the ring body may have a depth of 0.15 mm or more.

[0011] In a compression ring according to a first aspect of the present invention, the inner circumferential groove is formed on the inner surface of the ring body at approximately the center of the width dimension of the ring body, and the width of one side of the portion other than the inner circumferential groove formed on both sides of the inner circumferential groove in the axial direction of the ring body on the inner surface of the ring body may be 0.4 mm or more and 1 / 4 or less of the width of the ring body.

[0012] In the compression ring according to the first aspect of the present invention, the positional deviation of the groove center of the inner circumferential groove in the axial direction of the ring body over the entire circumference of the inner circumferential surface of the ring body may be 0.1 mm or less.

[0013] In the compression ring according to the first aspect of the present invention, the cross-sectional shape perpendicular to the circumferential direction of the inner circumferential groove formed on the inner surface of the ring body may be either an arch shape, a trapezoid shape, or a shape with tapered sides and an R-shaped bottom surface.

[0014] A compression ring combination according to a second aspect of the present invention is a combination of a plurality of compression rings to be fitted into a plurality of ring grooves in a piston of an internal combustion engine having a nominal diameter of 100 mm to 240 mm, and at least one of the plurality of compression rings is the compression ring according to the first aspect of the present invention.

[0015] A third aspect of the present invention provides a compression ring body for mounting on a piston of an internal combustion engine having a nominal diameter (d1) of 100 mm to 240 mm, the compression ring body having an inner circumferential groove formed on its inner surface that is recessed radially outward, a coil expander that is disposed radially inward in the ring groove of the piston and biases the ring body radially outward abuts against the inner circumferential groove, the compression ring body is made of steel, and the value (d1 / a1) obtained by dividing the nominal diameter (d1) of the compression ring by the radial thickness (a1) of the ring body is 57.0 or less.

[0016] According to the present invention, for a compression ring that is attached to a piston of an internal combustion engine having a relatively large nominal diameter, it is possible to improve tracking while suppressing an increase in ring tension and to suppress an increase in blow-by gas.

[0017] Fig. 1 is a diagram illustrating a configuration of a portion of an internal combustion engine according to an embodiment. Fig. 2 is a cross-sectional view illustrating the configuration of a compression ring according to an embodiment. Fig. 3 is a diagram illustrating the results of a simulation that determines the influence on the amount of blow-by gas when a value d1 / a1 obtained by dividing the nominal diameter of the compression ring by the radial thickness of the ring body is changed. Fig. 4 is a diagram illustrating an evaluation of the simulation results. Fig. 5 is a diagram illustrating an example of the shape of an inner circumferential groove formed on the inner circumferential surface of the ring body according to a modified embodiment of the embodiment.

[0018] Specific embodiments of the present disclosure will be described below with reference to the drawings. The dimensions, materials, shapes, and relative positions of the components described in the present embodiments are not intended to limit the technical scope of the present disclosure unless otherwise specified.

[0019] <Embodiment> [Overall Configuration] FIG. 1 is a diagram showing the configuration of a portion of an internal combustion engine according to an embodiment. FIG. 1 shows the configuration of a piston 20 in one cylinder 10 of an internal combustion engine 100. The nominal diameter d1 of the compression ring 1 of the internal combustion engine 100 according to this embodiment is 100 mm to 240 mm. Examples of the material for the piston 20 include steel, cast iron, and aluminum. In FIG. 1 , reference numeral 30 denotes the combustion chamber side of the internal combustion engine 100, and reference numeral 40 denotes the crank chamber side of the internal combustion engine 100. In the following description, the combustion chamber side 30 of the internal combustion engine 100 is referred to as the upper side of the piston 20 in the axial direction, and the crank chamber side 40 of the internal combustion engine 100 is referred to as the lower side of the piston 20 in the axial direction.

[0020] As shown in FIG. 1 , four piston rings 1 to 4 are assembled to the piston 20. More specifically, three compression rings 1 to 3 (top ring 1, second ring 2, and third ring 3) are assembled to the upper side of the piston 20, and one oil ring 4 is assembled to the lower side of the piston 20. Four ring grooves are formed in the outer peripheral surface 20a of the piston 20 at predetermined intervals in the axial direction of the piston 20. Each ring groove extends annularly around the axis of the piston 20 and is formed around the entire circumference of the outer peripheral surface 20a. In the piston 20, one of the compression rings 1 to 3 or the oil ring 4 is installed in each ring groove in order from the top. The compression rings 1 to 3 and the oil ring 4 are all sliding members that slide on the inner wall surface 10a of the cylinder 10 as the piston 20 reciprocates within the cylinder 10. The compression rings 1 to 3 slide on the inner wall surface 10a of the cylinder 10, thereby suppressing the outflow of combustion gas (blow-by) from the combustion chamber side to the crank chamber side.

[0021] The following describes the configuration of the top ring 1 of the compression rings 1 to 3 according to this embodiment. However, the configuration of the compression ring according to this embodiment can also be applied to the second ring 2 or the third ring 3. Furthermore, the configuration of the compression ring according to this embodiment may be applied to any two or all three of the top ring 1, second ring 2, and third ring 3.

[0022] [Configuration of Compression Ring] Figure 2 is a cross-sectional view illustrating the configuration of the compression ring according to this embodiment. Figure 2 shows a cross section perpendicular to the circumferential direction of the compression ring 1. As shown in Figure 2, the compression ring 1 according to this embodiment includes a ring body (outer link) 11 and a coil expander 12.

[0023] In the following description, as shown in Figure 2, the direction along the central axis of the compression ring 1 (axial direction) is defined as the "up-down direction." Furthermore, in the axial direction of the compression ring 1, the combustion chamber side of the internal combustion engine 100 (upper side in Figure 1) is defined as the "upper side," and the opposite side, i.e., the crank chamber side (lower side in Figure 1), is defined as the "lower side." Furthermore, in the following description of the compression ring 1, unless otherwise specified, the "circumferential direction" refers to the circumferential direction of the compression ring 1, and the "radial direction" refers to the radial direction of the compression ring 1. The circumferential direction, radial direction, and axial direction of the compression ring 1 respectively coincide with the circumferential direction, radial direction, and axial direction of the ring body 11 and the coil expander 12.

[0024] The compression ring 1 is fitted into a ring groove 50 formed in the outer peripheral surface 20a of the piston 20. The ring groove 50 has an upper wall 51 formed on the combustion chamber side, a lower wall 52 formed on the crank chamber side facing the upper wall 51, and a connecting wall 53 connecting the inner peripheral edges of the upper wall 51 and the lower wall 52. The ring body 11 of the compression ring 1 is made of steel and is a single ring formed in an annular shape, and is fitted into the ring groove 50 of the piston 20. On the other hand, the coil expander 12 of the compression ring 1 is formed in an annular shape by spirally wound wire, and is arranged radially inner than the ring body 11 in the ring groove 50, and urges the ring body 11 radially outward.

[0025] The surfaces of the ring body 11 include an outer peripheral surface S1, an inner peripheral surface S2, an upper surface S3, and a lower surface S4. The upper surface S3 and the lower surface S4 are axial end surfaces of the ring body 11. The upper surface S3 and the lower surface S4 define the width (axial dimension) h1 of the ring body 11. The outer peripheral surface S1 is a surface that connects the outer peripheral edges of the upper surface S3 and the lower surface S4. The inner peripheral surface S2 is a surface that connects the inner peripheral edges of the upper surface S3 and the lower surface S4. When the piston 20 equipped with the compression ring 1 is inserted into the cylinder 10 as shown in FIG. 2 (hereinafter, sometimes referred to as the "used state"), the outer peripheral surface S1 of the ring body 11 slides against the inner wall surface 10a of the cylinder 10. In use, the inner peripheral surface S2 of the ring body 11 faces the connecting wall 53 of the ring groove 50, the upper surface S3 faces the upper wall 51, and the lower surface S4 faces the lower wall 52. The upper surface S3 and the lower surface S4 of the ring body 11 may each have a tapered shape (keystone shape) that is inclined so that the width (axial dimension) of the ring body 11 decreases toward the inner peripheral side.

[0026] The shape of the outer peripheral surface S1 of the ring body 11 shown in Figure 2 is a straight shape in which the entire outer peripheral surface S1 is in sliding contact with the inner wall surface 10a of the cylinder 10. However, the shape of the outer peripheral surface S1 of the ring body 11 is not limited to a straight shape. For example, the shape of the outer peripheral surface S1 of the ring body 11 may be a barrel shape that is curved so as to be convex outward in the radial direction. The shape of the outer peripheral surface S1 of the ring body 11 may also be a tapered shape that is inclined so that the thickness (circumferential dimension) of the ring body 11 increases toward the bottom.

[0027] As shown in FIG. 2 , an inner circumferential groove H1 recessed radially outward is formed in a portion of the inner circumferential surface S2 of the ring body 11. In FIG. 2 , a two-dot chain line CL1 represents a centerline passing through the center of the width of the ring body 11. The inner circumferential groove H1 is formed in the approximate center of the width of the inner circumferential surface S2 of the ring body 11. The portion S22 of the inner circumferential surface S2 of the ring body 11 that forms the inner circumferential groove H1 (hereinafter, also referred to as the "groove forming surface S22") has an arc shape, so that the cross section of the inner circumferential groove H1 perpendicular to the circumferential direction has a bow shape. The groove center CP1 (i.e., the deepest portion of the inner circumferential groove H1), which is the center of the width of the groove forming surface S22, is located on the centerline CL1. In addition, the portion S21 other than the groove forming surface S22 formed on both sides of the inner circumferential groove H1 in the axial direction on the inner circumferential surface S2 of the ring body 11 may be referred to as the "remaining surface S21" below.

[0028] In use, as shown in FIG. 2 , the coil expander 12 abuts against the inner circumferential groove H1 formed on the inner circumferential surface S2 of the ring body 11 (i.e., the coil expander 12 abuts against the groove-forming surface S22). This causes a portion of the coil expander 12 to be housed in the inner circumferential groove H1. The coil expander 12 is an annular coil spring made of a spirally wound wire material such as steel. The outer diameter m1 of the coil expander 12 may be, for example, equal to or greater than half the width h1 of the ring body 11. In use, the coil expander 12 is mounted radially inward of the ring body 11 in the ring groove 50 so as to generate an expanding force toward the outer circumferential side in the radial direction. The expanding force of the coil expander 12 abutting against the inner circumferential groove H1 biases (presses) the ring body 11 toward the outer circumferential side in the radial direction. In use, that is, when the coil expander 12 abuts against the inner circumferential groove H1 of the ring body 11, the innermost portion IP1 of the coil expander 12 (i.e., the portion closest to the connecting wall 53 of the ring groove 50) is located on the center line CL1.

[0029] The thickness (radial dimension) a1 of the ring body 11 is determined by the outer peripheral surface S1 and the inner peripheral surface S2. More specifically, the thickness a1 of the ring body 11 is determined as the radial distance from the outermost portion OP1 of the outer peripheral surface S1 to the remaining surface S21 of the inner peripheral surface S2. As shown in FIG. 2 , if the outer peripheral surface S1 has a straight shape, the radial position of the outer peripheral surface S1 is determined as the position of the outermost portion OP1. On the other hand, if the outer peripheral surface S1 has a barrel shape, a straight shape, or other shape in which only a portion of the outer peripheral surface S1 is in sliding contact with the inner wall surface 10a of the cylinder 10, the portion of the outer peripheral surface S1 that is in sliding contact with the inner wall surface 10a of the cylinder 10 is determined as the outermost portion OP1. The depth c1 of the inner circumferential groove H1 on the inner peripheral surface S2 of the ring body 11 is determined as the radial distance from the remaining surface S21 to the groove center CP1 (i.e., the deepest portion of the inner circumferential groove H1), which is the center of the groove forming surface 22 in the width direction.

[0030] [Dimensions of the Compression Ring] Next, the dimensions of the compression ring 1 according to this embodiment will be described. (i) The value d1 / a1 obtained by dividing the nominal diameter d1 of the compression ring 1 by the radial thickness a1 of the ring body 11 is 57.0 or less. (ii) When the coil expander 12 abuts against the inner circumferential groove H1 of the ring body 11, the radial distance A1 from the outermost portion OP1 on the outer circumferential surface S1 of the ring body 11 to the innermost portion IP1 of the coil expander 12 is 1 / 25 or less of the nominal diameter d1 of the compression ring 1. (iii) The depth c1 of the inner circumferential groove H1 on the inner circumferential surface S2 of the ring body 11 is 0.15 mm or more. (iv) On the inner peripheral surface S2 of the ring body 11, the width b1 of one side of the remaining surfaces S21 formed on both sides in the axial direction across the inner circumferential groove H1 is 0.4 mm or more and ¼ or less of the width h1 of the ring body 11. (v) On the inner peripheral surface S2 of the ring body 11, the positional deviation of the groove center CP1 of the inner circumferential groove H1 in the axial direction over the entire circumference is 0.1 mm or less.

[0031] [Actions and Effects] In the compression ring 1 according to this embodiment, the coil expander 12 biases the ring body 11 radially outward, thereby improving the followability of the compression ring 1 while suppressing an increase in ring tension. Furthermore, in the compression ring 1 according to this embodiment, the coil expander 12 is disposed so as to abut against the inner circumferential groove H1 formed in the inner circumferential surface S2 of the ring body 11. This allows a portion of the coil expander 12 to be housed in the inner circumferential groove H1, thereby suppressing localized twisting of the coil expander 12 when the compression ring 1 slides. As a result, the coil expander 12 can bias the ring body 11 approximately uniformly in the circumferential direction.

[0032] Furthermore, in the compression ring 1 according to this embodiment, the ring body 11 is made of steel. This allows the radial thickness a1 of the ring body 11 to be reduced while maintaining strength, compared to when the ring body 11 is made of cast metal. By reducing the radial thickness a1 of the ring body 11, the followability of the compression ring 1 can be improved. Furthermore, by making the ring body 11 out of steel, it becomes easier to apply surface treatments to the ring body 11 to improve wear resistance, such as nitriding, PVD coating, or DLC treatment.

[0033] <<Action and Effect of (i) Above>> Furthermore, in the compression ring 1 according to this embodiment, as described in (i) above, the value d1 / a1, obtained by dividing the nominal diameter d1 of the compression ring 1 by the radial thickness a1 of the ring body 11, is set to 57.0 or less. Here, the smaller the radial thickness a1 of the ring body 11, the more the followability of the compression ring 1 can be improved. However, it has been newly discovered that when a compression ring 1 having a structure including the ring body 11 and the coil expander 12 is applied to a piston of an internal combustion engine having a nominal diameter of 100 mm to 240 mm, reducing the radial thickness of the ring body 11 significantly increases the amount of blow-by gas. Therefore, in this embodiment, the radial thickness a1 of the ring body 11 is limited to a range such that d1 / a1 is 57.0 or less.

[0034] 3 and 4, a description will be given of the results of a simulation that determines the effect on the amount of blow-by gas when d1 / a1 is changed in a plurality of internal combustion engines with different nominal diameters of the compression ring 1, and the evaluation of the results. In the simulation, the amount of blow-by gas was determined when a compression ring having a ring body and a coil expander, such as the compression ring 1 according to this embodiment, was applied to the top ring of a piston. In addition, the reference value (base) for the evaluation of the amount of blow-by gas was set to the amount of blow-by gas when a compression ring without a coil expander was applied to the top ring of a piston.

[0035] FIG. 3 shows the results of a simulation in which the amount of blow-by gas generated in one cylinder during one cycle was determined for each crank angle when an internal combustion engine A (nominal diameter: 240 mm) was operated at rated output. In FIG. 3, the horizontal axis represents crank angle, and the vertical axis represents the amount of blow-by gas (flow rate). Furthermore, lines L1 to L5 in FIG. 3 show the transition of the amount of blow-by gas when different configurations of the radial thickness a1 of the ring body 11 (different d1 / a1) were applied to the compression ring 1 of the TOP ring. Similar simulations were also performed on internal combustion engine B (nominal diameter: 170 mm) and internal combustion engine C (nominal diameter: 100 mm).

[0036] FIG. 4 shows an evaluation of the simulation results performed as described above for each of internal combustion engines A to C. In the evaluation, the average value of the amount of blow-by gas during one cycle when each configuration of the compression ring 1 of the TOP ring, in which the radial thickness a1 of the ring body 11 differed, was calculated based on the simulation results. Furthermore, the value of 1 when the compression ring 1 without the coil expander 12 was applied to each of internal combustion engines A to C, which served as the reference value for evaluation, was set to 1. The increase rate of the average amount of blow-by gas during one cycle (blow-by increase ratio) was calculated as an evaluation value for each configuration in which the radial thickness a1 of the ring body 11 differed. In the evaluation, a blow-by increase ratio of 1.6 was set as the upper limit of the allowable range.

[0037] 4, in all of the internal combustion engines A to C, the radial thickness a1 of the ring body is the largest (d1 / a1 is the smallest) in the compression ring 1 that does not have the coil expander 12. In a configuration in which the compression ring 1 having the ring body 11 and the coil expander 12 is applied to the TOP ring of a piston, the larger d1 / a1 is (the smaller the radial thickness a1 of the ring body is), the larger the blow-by increase ratio becomes. However, in all of the internal combustion engines A to C, if d1 / a1 is 57.0 or less, the blow-by increase ratio is equal to or less than the upper limit of the allowable range of 1.6.

[0038] Therefore, in the compression ring 1 according to this embodiment, the upper limit of d1 / a1 is set to 57.0. As a result, even when the compression ring 1 having a structure including the ring body 11 and the coil expander 12 is applied to a piston of an internal combustion engine having a nominal diameter d1 of the compression ring 1 of 100 mm to 240 mm, it is possible to suppress an increase in blow-by gas within an allowable range.

[0039] <<Action and Effect of (ii) Above>> Furthermore, in the compression ring 1 according to this embodiment, the coil expander 12 is disposed in the ring groove 50 more inward than the ring body 11. Therefore, the innermost periphery IP1 of the coil expander 12 is positioned closest to the connecting wall 53 of the ring groove 50. In this case, if the innermost periphery IP1 of the coil expander 12 is too close to the connecting wall 53 of the ring groove 50, there is a risk that the coil expander 12 will interfere with the connecting wall 53 of the ring groove 50. Therefore, in the compression ring 1 according to this embodiment, as described in (ii) above, when the coil expander 12 abuts against the inner circumferential groove H1 of the ring body 11, the radial distance A1 from the outermost periphery OP1 on the outer circumferential surface S1 of the ring body 11 to the innermost periphery IP1 of the coil expander 12 is set to 1 / 25 or less of the nominal diameter d1 of the compression ring 1. This makes it possible to ensure a sufficient circumferential distance between the innermost periphery IP1 of the coil expander 12 and the connection wall 53 of the ring groove 50. Therefore, it is possible to suppress interference of the coil expander 12 with the connection wall 53 of the ring groove 50.

[0040] <<Action and Effect of (iii) Above>> Generally, in internal combustion engines with a compression ring nominal diameter of 100 mm to 240 mm, the cylinder liner (or bore) is often not replaced until the radial wear on the inner wall surface of the cylinder exceeds an increase of 0.30 mm in nominal diameter (0.15 mm in cross section). Therefore, the compression ring 1 according to this embodiment must ensure conformability to the inner wall surface 10 a of the cylinder 10 at least until the radial wear on the inner wall surface 10 a of the cylinder 10 reaches an increase of 0.30 mm in nominal diameter. Furthermore, even if the compression ring 1 conforms to the inner wall surface 10 a of the cylinder 10 until the radial wear on the inner wall surface 10 a of the cylinder 10 reaches an increase of 0.30 mm in nominal diameter, it is necessary to maintain the coil expander 12 from coming off the inner circumferential groove H1 of the ring body 11. Therefore, in the compression ring 1 according to this embodiment, as described in (iii) above, the depth c1 of the inner circumferential groove H1 on the inner circumferential surface S2 of the ring body 11 is set to 0.15 mm or more. This allows the ring body 11 to expand in diameter as the inner wall surface 10 a of the cylinder 10 wears, causing the position of the inner circumferential surface S2 of the ring body 11 to move radially outward. Even if the coil expander becomes stuck at the nominal diameter position due to carbon sludge and is no longer able to expand in diameter, a portion of the coil expander 12 can remain housed in the inner circumferential groove H1 of the ring body 11 until the amount of radial wear on the inner wall surface 10 a of the cylinder 10 reaches an increase in the nominal diameter of at least 0.30 mm. Therefore, even if the compression ring 1 follows the inner wall surface 10a of the cylinder 10 until the amount of radial wear on the inner wall surface 10a reaches an increase of 0.30 mm in nominal diameter, the coil expander 12 can be kept from coming off the inner circumferential groove H1 of the ring body 11.

[0041] <<Action and Effect of (iv) Above>> Furthermore, if the width b1 of the remaining surface S21 on the inner circumferential surface S2 of the ring body 11 is excessively small, chipping is likely to occur in the portion of the ring body 11 that forms the remaining surface S21. On the other hand, it is necessary to form an inner circumferential groove H1 on the inner circumferential surface S2 of the ring body 11 that is large enough to accommodate the coil expander 12, which has an outer diameter m1 large enough to exert the necessary biasing force, without dislodging it. Therefore, in the compression ring 1 according to this embodiment, as described in (iv) above, the width b1 of one side of the remaining surface S21 formed on both axial sides of the inner circumferential groove H1 on the inner circumferential surface S2 of the ring body 11 is set to 0.4 mm or more and ¼ or less of the width h1 of the ring body 11. By setting the width b1 of one side of the remaining surface S21 to 0.4 mm or more, chipping can be suppressed in the portion that forms the remaining surface S21. Furthermore, by making the width b1 of one side of the remaining surface S21 equal to or less than 1 / 4 of the width h1 of the ring body 11, it is possible to ensure a groove forming surface S22 on the inner surface S2 for forming an inner groove H1 large enough to accommodate the coil expander 12 having a sufficiently large outer diameter m1 without it coming off.

[0042] <<Action and Effect of (v) Above>> The ring body 11 also has a gap (not shown). Here, if the axial positional deviation of the groove center CP1 of the inner circumferential groove H1 in the circumferential direction on the inner circumferential surface S2 of the ring body 11 is large, the axial positional deviation between the cross sections of the ring body 11 facing each other across the gap also becomes large. If the axial positional deviation between the cross sections of the ring body 11 facing each other across the gap also becomes large, localized wear is likely to occur on the upper surface S3 and lower surface S4 of the gap between the ring bodies 11. Therefore, in the compression ring 1 according to this embodiment, as described in (v) above, the axial positional deviation of the groove center CP1 of the inner circumferential groove H1 over the entire circumference on the inner circumferential surface S2 of the ring body 11 is set to 0.1 mm or less. This makes it possible to prevent the axial positional deviation between the cross sections of the ring body 11 facing each other across the gap from becoming large.

[0043] [Modifications] Next, modifications of this embodiment will be described. In the above-described embodiment, the cross-sectional shape perpendicular to the circumferential direction of the inner circumferential groove H1 formed on the inner circumferential surface S2 of the ring body 11 is arch-shaped. However, the shape of the inner circumferential groove formed on the inner circumferential surface S2 of the ring body 11 is not limited to this. FIGS. 5A and 5B are diagrams illustrating examples of the shape of the inner circumferential groove formed on the inner circumferential surface of the ring body. Both FIGS. 5A and 5B illustrate cross sections perpendicular to the circumferential direction of the ring body 11. In both the cross-sectional shapes of FIGS. 5A and 5B, the inner circumferential surface S2 of the ring body 11 includes a groove-forming surface S22 and a remaining surface S21. Furthermore, in both FIGS. 5A and 5B, the groove center CP1, which is the center of the groove-forming surface 22 in the width direction, is located on the center line CL1.

[0044] In the example shown in FIG. 5A , the inner circumferential groove H2 formed on the inner circumferential surface S2 of the ring body 11 has a trapezoidal cross-sectional shape perpendicular to the circumferential direction. More specifically, the groove-forming surface S22 forming the inner circumferential groove H2 includes both side surfaces S221, S222 and a bottom surface S223 of the inner circumferential groove H2. The wall surfaces located in the vertical direction of the inner circumferential groove H2 are the side surfaces S221, S222, and the wall surface located on the radially outer side of the inner circumferential groove H2 is the bottom surface S223. The both side surfaces S221, S222 of the inner circumferential groove H2 have a tapered shape that slopes toward the center line CL1 as it moves from the inner circumferential side to the outer circumferential side. The bottom surface S223 of the inner circumferential groove H2 is a plane that is approximately perpendicular to the center line CL1 and connects the outer edges of the both side surfaces S221, S222. By forming the two side surfaces S221, S222 and the bottom surface S223 of the inner circumferential groove H2 in this manner, the cross section of the inner circumferential groove H2 perpendicular to the circumferential direction becomes trapezoidal.

[0045] In the example shown in Fig. 5(B), the cross-sectional shape perpendicular to the circumferential direction of the inner circumferential groove H3 formed on the inner circumferential surface S2 of the ring body 11 has tapered side surfaces and an R-shaped bottom surface. More specifically, similar to the example shown in Fig. 5(A), the groove forming surface S22 forming the inner circumferential groove H3 includes both side surfaces S221, S222 and a bottom surface S223 of the inner circumferential groove H3. Furthermore, for the inner circumferential groove H3, the wall surfaces positioned in the vertical direction of the inner circumferential groove H3 are the side surfaces S221, S222, and the wall surface positioned on the radially outer side of the inner circumferential groove H3 is the bottom surface S223. Similar to the example shown in Fig. 5(A), both side surfaces S221, S222 of the inner circumferential groove H3 have a tapered shape that slopes toward the center line CL1 as it moves from the inner circumferential side to the outer circumferential side in the radial direction. On the other hand, the bottom surface S223 of the inner circumferential groove H3 is rounded and protrudes radially outward, forming an apex at the position where it intersects with the center line CL1. The bottom surface S223 of the inner circumferential groove H3 also connects the outer edges of both side surfaces S221 and S222.

[0046] Even if the inner circumferential groove formed on the inner circumferential surface S2 of the ring body 11 of the compression ring 1 has the shape shown in Figures 5(A) and 5(B), the coil expander 12 can be brought into contact with the inner circumferential groove. Therefore, a portion of the coil expander 12 can be accommodated in the inner circumferential groove.

[0047] REFERENCE SIGNS LIST 1... Compression ring 10... Cylinder 11... Ring body 12... Coil expander 20... Piston 50... Ring groove 100... Internal combustion engine S1... Outer peripheral surface S2... Inner peripheral surface H1... Inner peripheral groove

Claims

1. A compression ring to be fitted to a piston of an internal combustion engine having a nominal diameter (d1) of 100 mm to 240 mm, comprising: a ring body to be fitted to a ring groove formed in the piston, the ring body having an inner circumferential groove formed on its inner surface that is recessed radially outward; and a coil expander that is positioned radially inward of the ring body in the ring groove, abuts against the inner circumferential groove of the ring body, and urges the ring body radially outward, wherein the ring body is made of steel, and the value (d1 / a1) obtained by dividing the nominal diameter (d1) of the compression ring by the radial thickness (a1) of the ring body is 57.0 or less.

2. A compression ring as set forth in claim 1, wherein, when the coil expander is in contact with the inner circumferential groove of the ring body, the radial distance from the outermost part of the outer surface of the ring body to the innermost part of the coil expander is 1 / 25 or less of the nominal diameter of the compression ring.

3. A compression ring as set forth in claim 1, wherein the depth of the inner circumferential groove on the inner circumferential surface of the ring body is 0.15 mm or more.

4. The compression ring according to claim 1, wherein the inner circumferential groove is formed on the inner circumferential surface of the ring body at approximately the center of the width dimension of the ring body, and the width of one side of the portions of the inner circumferential surface of the ring body other than the inner circumferential groove formed on both sides of the inner circumferential groove in the axial direction of the ring body is 0.4 mm or more and 1 / 4 or less of the width of the ring body.

5. A compression ring according to claim 1, wherein the positional deviation of the center of the inner circumferential groove in the axial direction of the ring body is 0.1 mm or less over the entire circumference of the inner circumferential surface of the ring body.

6. A compression ring as set forth in claim 1, wherein the cross-sectional shape of the inner circumferential groove formed on the inner circumferential surface of the ring body, taken perpendicular to the circumferential direction, is either an arch shape, a trapezoid shape, or a shape with tapered sides and an R-shaped bottom.

7. A combination of multiple compression rings to be fitted into multiple ring grooves in a piston of an internal combustion engine having a nominal diameter of 100 mm to 240 mm, wherein at least one of the multiple compression rings is a compression ring as defined in any one of claims 1 to 6.

8. A ring body of a compression ring to be attached to a piston of an internal combustion engine having a nominal diameter (d1) of 100 mm to 240 mm, wherein an inner circumferential groove is formed on the inner circumferential surface, recessed radially outward, and when attached to the ring groove formed in the piston, a coil expander, which is positioned radially inward from the ring body in the ring groove and urges the ring body radially outward, abuts against the inner circumferential groove, and is made of steel, and the value (d1 / a1) obtained by dividing the nominal diameter (d1) of the compression ring by the radial thickness (a1) of the ring body is 57.0 or less.

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