Piston rings

Abstract

The outer peripheral surface of the piston ring has a cutting surface that forms a notch between the outer peripheral end portion and the lower surface, the cutting surface including: a first surface, provided between the outer peripheral end surface and the bottom; and a second surface, provided between the bottom and the lower surface, the second surface being inclined in a manner away from the central axis of the piston ring as it approaches the crank chamber side, the inclination angle of the second surface relative to the lower surface being greater than 50° and less than 85°, and when the axial width of the piston ring is set to h1, and the axial distance between the connecting portion of the cutting surface and the outer peripheral end surface and the connecting portion of the cutting surface and the lower surface is set to H, H / h1 is greater than 0.2 and less than 0.4.

Description

Technical Field

[0001] The invention relates to a piston ring. Background Art

[0002] The internal combustion engine installed in ordinary automobiles adopts the following structure: the piston attached to the cylinder is provided with three piston rings obtained by combining two compression rings (pressure rings) including a top ring and a second ring and an oil ring. As for these three piston rings, the top ring, the second ring, and the oil ring are attached to the ring groove formed on the outer peripheral surface of the piston in order from the upper side (combustion chamber side), and slide on the inner wall surface of the cylinder. The oil ring farthest from the combustion chamber has an oil sealing function that suppresses the oil from flowing out to the combustion chamber side (oil rising) by scraping off the excess engine oil (lubricating oil) attached to the inner wall surface of the cylinder to the crank side, and prevents the burning of the piston accompanying the operation of the internal combustion engine by adjusting the oil amount so that the lubricating oil film is appropriately maintained on the inner wall surface of the cylinder. The compression ring has an air sealing function that suppresses the combustion gas from flowing out from the combustion chamber side to the crank chamber side (blowby) by maintaining airtightness, and an oil sealing function that suppresses the oil from rising by scraping off the excess oil that is not scraped off by the oil ring. By combining such piston rings, the blowby gas and fuel consumption in the internal combustion engine are reduced. In addition, it is known that the oil scraping performance can be improved by setting the second ring as an oil scraper ring having a stepped notch (undercut) formed at the lower part of the outer circumference (for example, Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2003-113940

[0006] Patent Document 2: Japanese Patent Application Publication No. 2020-193666

[0007] Patent Document 3: International Publication No. 2016 / 121483 Summary of the invention

[0008] Problems to be solved by the invention

[0009] However, in conventional internal combustion engines equipped with piston rings having undercuts, during the downward stroke of the piston, a portion of the oil on the inner wall of the cylinder may flow on the surface of the undercut and hit the chamfered portion of the ring groove formed on the piston, and flow into between the lower surface of the piston ring and the lower wall surface of the ring groove. Such oil may flow out to the combustion chamber side, so that the fuel consumption may increase.

[0010] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a technology capable of reducing the fuel consumption of an internal combustion engine in a piston ring having an undercut shape.

[0011] Solutions for solving problems

[0012] In order to solve the above-mentioned problems, the present invention adopts the following means. That is, the present invention is a piston ring attached to the piston of an internal combustion engine, wherein the piston ring has: an outer peripheral surface, which is arranged on the outer periphery of the piston ring; an inner peripheral surface, which is arranged on the inner periphery of the piston ring; an upper surface, which is the end surface of the axial end surface of the piston ring that faces the combustion chamber side in the internal combustion engine; and a lower surface, which is the end surface of the axial end surface of the piston ring that is located on the crank chamber side in the internal combustion engine, the outer peripheral surface has: an outer peripheral end surface, which includes an outer peripheral end portion, and the outer peripheral end portion has the largest diameter in the cross section of the piston ring that is orthogonal to the circumferential direction; and a cut surface, which connects the outer peripheral end surface and the lower surface in a manner of forming a notch extending in the circumferential direction of the piston ring between the outer peripheral end surface and the lower surface, and the cut surface includes : The bottom is the innermost part of the cut surface in the radial direction of the piston ring; the first surface is arranged between the outer peripheral end surface and the bottom and faces the crank chamber side; the second surface is arranged between the bottom and the lower surface and faces the radial outer side, the second surface is inclined in a manner away from the central axis of the piston ring as it approaches the crank chamber side, and in a cross section of the piston ring orthogonal to the circumferential direction, the inclination angle of the second surface relative to the lower surface is greater than 50° and less than 85°, and when the axial width of the piston ring is set to h1, and the axial distance between the connecting portion of the cut surface and the outer peripheral end surface and the connecting portion of the cut surface and the lower surface is set to H, H / h1 is greater than 0.2 and less than 0.4.

[0013] According to the piston ring of the present invention, a part of the oil scraped off by the piston ring flows along the inclination of the second surface, thereby discharging the part of the oil toward the outer peripheral side of the piston ring and easily falling to the crank chamber side, thereby preventing the oil from flowing between the lower surface of the piston ring and the lower wall surface of the ring groove.

[0014] Furthermore, in the present invention, when a distance D between a connection portion between the cut surface and the outer peripheral end surface and a connection portion between the cut surface and the lower surface in the radial direction of the piston ring is defined as 0.2 mm ≤ D ≤ 0.6 mm.

[0015] Furthermore, in the present invention, the first surface may be inclined so as to be away from the crank chamber as it approaches the radial inner side of the piston ring, and in a cross section of the piston ring orthogonal to the circumferential direction, the inclination angle of the first surface relative to the lower surface may be less than 30°.

[0016] Furthermore, in the present invention, the cutting surface may include a third surface, the third surface includes the bottom and connects the first surface and the second surface, the third surface is concavely curved, and the radius of curvature of the third surface is greater than or equal to 0.05 mm and less than or equal to 0.2 mm.

[0017] Furthermore, in the present invention, the cut surface may further include a lower R surface connecting the second surface and the lower surface, and a curvature radius of the lower R surface may be greater than or equal to 0.01 mm and less than or equal to 0.2 mm.

[0018] Furthermore, in the present invention, in an internal combustion engine in which a plurality of compression rings are attached to a piston, the piston ring may be a second ring attached at a second position from a combustion chamber side among the plurality of compression rings.

[0019] Effects of the Invention

[0020] According to the present invention, the fuel consumption of the internal combustion engine can be further reduced in the piston ring having an undercut shape. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a cross-sectional view showing a part of an internal combustion engine provided with a second ring according to the embodiment.

[0022] Figure 2 This is a cross-sectional view for explaining the outer peripheral surface of the second ring in the embodiment.

[0023] Figure 3 This is a cross-sectional view of the vicinity of the second ring when the piston is in a descending stroke in the internal combustion engine of the embodiment.

[0024] Figure 4 This is a cross-sectional view of the vicinity of the second ring when the piston is in a descending stroke in the internal combustion engine of Comparative Example 1.

[0025] Figure 5 This is a cross-sectional view for explaining the outer peripheral surface of the second ring according to a modified example of the embodiment.

[0026] Figure 6 3 is a cross-sectional view of the second ring of Comparative Example 2.

[0027] Figure 7 3 is a cross-sectional view of the second ring of Comparative Example 3.

[0028] Figure 8 This is a graph showing the analysis results of the oil outflow rate.

[0029] Fig. 9 This is a graph showing the relationship between θ1 and the oil outflow rate.

[0030] Fig.10 This is a graph showing the relationship between H / h1 and the oil outflow rate.

[0031] Fig.11 This is a graph showing the relationship between D and the oil outflow rate.

[0032] Fig.12 This is a diagram showing the analysis results of oil flow distribution. DETAILED DESCRIPTION

[0033] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. The embodiment described below applies the present invention to a second ring as an example of a piston ring. In an internal combustion engine in which a plurality of compression rings are attached to a piston, the second ring is a compression ring attached to the second position from the combustion chamber side among the plurality of compression rings. However, the piston ring of the present invention is not limited to the second ring. The present invention can also be applied to a top ring as a compression ring attached to the position closest to the combustion chamber, and an oil ring attached to the position farthest from the combustion chamber. In addition, unless otherwise specified, the configuration described in the following embodiments is not intended to limit the technical scope of the invention to only this.

[0034] It should be noted that, in the following description, unless otherwise specified, the "circumferential direction" refers to the circumferential direction of the piston ring. Unless otherwise specified, the "radial direction" refers to the radial direction of the piston ring. The "radial inner side" refers to the inner peripheral surface side of the piston ring, and the "radial outer side" refers to the opposite side. Unless otherwise specified, the "axial direction" refers to the direction along the central axis of the piston ring. In addition, the "upper wall surface" of the ring groove of the piston refers to the inner wall on the combustion chamber side of the inner wall of the ring groove, and the "lower wall surface" refers to the inner wall on the crank chamber side.

[0035] [internal combustion engine]

[0036] Figure 1 1 is a cross-sectional view showing a portion of an internal combustion engine 100 including a second ring 40 according to an embodiment. Figure 1 , a cross section along the central axis of the piston indicated by reference numeral 20 is shown. Figure 1 As shown, the internal combustion engine 100 of the first embodiment includes a cylinder 10, a piston 20 attached (inserted) to the cylinder 10, and a plurality of piston rings 30, 40, 50 attached to the piston 20. In the internal combustion engine 100 of the embodiment, two compression rings (a top ring 30 and a second ring 40) and one oil ring 50 are attached to the piston 20. Of the two compression rings, the top ring 30 is attached to the position closest to the combustion chamber, and the second ring 40 is attached to the second position from the combustion chamber side. The oil ring 50 is attached to the position farthest from the combustion chamber.

[0037] like Figure 1 As shown, in the internal combustion engine 100, a clearance PC1 is formed by ensuring a predetermined separation distance between the outer peripheral surface 20a of the piston 20 and the inner wall surface 10a of the cylinder 10. In addition, on the outer peripheral surface 20a of the piston 20, a first annular groove 201, a second annular groove 202, and a third annular groove 203 are formed in sequence from the upper side (combustion chamber side) at predetermined intervals along the axial direction of the piston 20. The annular grooves 201 to 203 are formed on the entire circumference of the outer peripheral surface 20a as grooves extending in an annular shape around the axis of the piston 20. Figure 1As shown, each annular groove is formed to include a pair of groove walls (inner walls) arranged in an upper and lower manner. In the pair of groove walls, the groove wall on the upper side is called the upper wall surface W1, and the groove wall on the lower side is called the lower wall surface W2. In addition, the groove wall connecting the inner peripheral edge of the upper wall surface W1 and the inner peripheral edge of the lower wall surface W2 in each annular groove is called the bottom wall surface W3. Figure 1 As shown, the top ring 30 is mounted on the first ring groove 201, the second ring 40 is mounted on the second ring groove 202, and the oil ring 50 is mounted on the third ring groove 203. In addition, by forming the ring grooves 201 to 203 on the piston 20, the top land L1, the second land L2, and the third land L3 are defined in sequence on the piston 20 from the combustion chamber side. It should be noted that in this specification, the top land L1, the second land L2, and the third land L3 are sometimes referred to as the land L1 in the piston 20. Figure 1 As shown, the state in which each piston ring is attached to the piston 20 and the piston 20 is attached to the cylinder 10 is referred to as the "use state".

[0038] The top ring 30 and the second ring 40 are compression rings as a type of piston ring, which are mounted on the piston attached to the cylinder of the internal combustion engine, and slide on the inner wall surface of the cylinder as the piston reciprocates. The top ring 30 and the second ring 40 have their own tension so that they press the inner wall surface 10a of the cylinder 10 when attached to the ring groove. The oil ring 50 is a so-called three-piece oil ring as a type of piston ring, which includes: a pair of scrapers (Segments) 501, 501 sliding on the inner wall surface 10a of the cylinder 10 and a spacer expander (Spacer Expander) 502 that applies force to the pair of scrapers 501, 501 radially outward (on the inner wall surface 10a side). The second ring 40 as an example of the piston ring of the present invention is described in detail below.

[0039] [Second Ring]

[0040] like Figure 1As shown, the second ring 40 has an outer peripheral surface 1, an inner peripheral surface 2, an upper surface 3, and a lower surface 4. The outer peripheral surface 1 is a surface provided on the outer periphery of the second ring 40. The inner peripheral surface 2 is a surface provided on the inner periphery of the second ring 40. The upper surface 3 is an end surface of the axial end surface of the second ring 40 that faces the upper side (combustion chamber side) in the internal combustion engine 100. The lower surface 4 is an end surface of the axial end surface of the second ring 40 that faces the lower side (crank chamber side) in the internal combustion engine 100 (in use state). The axial width of the second ring 40 (hereinafter also referred to as the axial width) is defined by the upper surface 3 and the lower surface 4. As for the second ring 40, in the use state, the upper surface 3 is opposite to the upper wall surface W1 of the second annular groove 202, the lower surface 4 is opposite to the lower wall surface W2 of the second annular groove 202, the outer peripheral surface 1 is in sliding contact with the inner wall surface 10a of the cylinder 10, and the inner peripheral surface 2 is opposite to the bottom wall surface W3 of the second annular groove 202. The second ring 40 has a circular ring shape formed with a seam (not shown). In addition, the second ring 40 has its own tension so that the outer peripheral surface 1 presses the inner wall surface 10a of the cylinder 10 when attached to the second annular groove 202. In addition, as Figure 1 As shown, the second ring 40 has an undercut shape in which a notch portion (undercut) indicated by reference numeral 5 is formed at the lower portion of its outer circumference. The notch portion 5 extends along the circumferential direction of the second ring 40 and is formed over the entire circumference of the second ring 40. In the use state, the notch portion 5 becomes an oil accumulation portion. When the piston 20 descends, when the second ring 40 scrapes off the oil in the gap PC1, the oil will be buffered in the notch portion 5, thereby suppressing the increase in oil pressure. As a result, good oil scraping performance can be obtained. It should be noted that the notch portion 5 does not need to be formed over the entire circumference of the second ring 40. For example, the notch portion 5 may not be formed near the joint portion. That is, the notch portion 5 may be formed in the second ring 40 except for the joint end portion forming the joint portion. Thereby, the air sealing performance can be improved.

[0041] Figure 2 4 is a cross-sectional view for explaining the outer peripheral surface 1 of the second ring 40 according to the embodiment. Figure 2 , a portion of a cross section of the second ring 40 perpendicular to the circumferential direction is shown. Figure 2 As shown, the outer circumferential surface 1 of the second ring 40 has a conical surface 11 , a cutting surface 12 and a connecting surface 13 .

[0042] like Figure 2 As shown, the tapered surface 11 includes an outer peripheral end portion indicated by reference numeral 1a, which is a surface that slides on the inner wall surface 10a of the cylinder 10 in the internal combustion engine 100. The outer peripheral end portion 1a is a portion of the second ring 40 having the largest diameter in a cross section perpendicular to the circumferential direction of the second ring 40. Figure 2The outer peripheral end 1a shown is formed as an edge, but it can also be formed as a surface with rounded corners. The tapered surface 11 is inclined in a manner that approaches the central axis of the second ring 40 (that is, in a manner that reduces the diameter) with the outer peripheral end 1a as the lower edge as it approaches the upper side (combustion chamber side) from the outer peripheral end 1a. As a result, the outer peripheral shape of the second ring 40 of the embodiment is a tapered undercut shape. The tapered surface 11 is equivalent to the "outer peripheral end face" of the present invention. It should be noted that the outer peripheral end face of the present invention can also be a straight surface with the same outer diameter regardless of the axial position. In this case, the straight surface as a whole becomes the outer peripheral end face. In addition, the outer peripheral end face of the present invention can also be a barrel shape that is curved in a convex manner toward the radial outside. In this case, the apex of the barrel shape becomes the outer peripheral end, and an undercut is formed downward from the apex.

[0043] like Figure 2 As shown, the connection surface 13 connects the upper edge of the conical surface 11 and the outer peripheral edge of the upper surface 3. It should be noted that, in the present invention, the connection surface 13 is not a necessary structure.

[0044] like Figure 2 As shown, the cut surface 12 is provided to form a notch 5 between the tapered surface 11 and the lower surface 4, connecting the tapered surface 11 and the lower surface 4. The cut surface 12 includes a bottom B1, a first surface 121, a second surface 122, a third surface 123 and a lower R surface 124.

[0045] like Figure 2 As shown, the bottom B1 is the portion of the cut surface 12 located most innerward in the radial direction of the second ring 40. That is, the bottom B1 is the portion of the cut surface 12 closest to the central axis of the second ring 40 and is the deepest portion of the notch 5.

[0046] like Figure 2 As shown, the first surface 121 is a surface provided between the conical surface 11 and the bottom B1, facing (toward) the lower side (crank chamber side). At this time, the first surface 121 of this example is provided in parallel with the lower surface 4, and is orthogonal to the axial direction of the second ring 40. The first surface 121 is parallel to the lower surface 4, so it is convenient to process the notch portion 5 (cut surface 12). In addition, the outer peripheral edge of the first surface 121 is connected to the outer peripheral end portion 1a which is the lower edge of the conical surface 11. However, the present invention is not limited to this. The first surface 121 may also be inclined relative to the lower surface 4. In addition, other surfaces (such as R surfaces) may be sandwiched between the first surface 121 and the conical surface 11.

[0047] like Figure 2 As shown, the second surface 122 is a surface provided between the bottom B1 and the lower surface 4, and faces (orients) the radially outer side of the second ring 40 (the inner wall surface 10a side of the cylinder 10). The second surface 122 is inclined so as to be away from the central axis of the second ring 40 as it goes downward (the crank chamber side). Figure 2As shown, in the cross section of the second ring 40 perpendicular to the circumferential direction, the angle of the corner formed by the second surface 122 and the lower surface 4, that is, the inclination angle of the second surface 122 relative to the lower surface 4 is set to θ1. In the second ring 40 of the embodiment, θ1 is an acute angle. More specifically, θ1 is set to 50°≤θ1≤85°.

[0048] like Figure 2 As shown, the third surface 123 is a surface connecting the first surface 121 and the second surface 122. The third surface 123 includes a bottom B1. The third surface 123 is concavely curved. The third surface 123 of the embodiment is an R surface formed in an arc shape, and its curvature radius R1 is fixed in the entire area of ​​the third surface 123. That is, the third surface 123 of the embodiment is formed by a single arc whose curvature does not change. In the second ring 40 of the embodiment, R1 is set to 0.05mm≤R1≤0.2mm. However, the present invention is not limited to this. In addition, in the present invention, the shape of the third surface is not limited to an arc shape. The third surface can also be formed in a manner in which the curvature partially changes, for example.

[0049] like Figure 2 As shown, the lower R surface 124 connects the lower edge of the second surface 122 and the outer peripheral edge of the lower surface 4. The lower R surface 124 is a so-called R angle, and is formed in an arc shape so as to be convex in a cross section perpendicular to the circumferential direction of the second ring 40. Figure 2 As shown, the curvature radius of the lower R surface 124 is set to r1. It should be noted that, in the present invention, the lower R surface 124 is not an essential structure.

[0050] Here, if Figure 2 As shown, the axial width of the second ring 40 is set to h1. Figure 2 , reference numeral 12a indicates the connection portion between the cutting surface 12 and the tapered surface 11, and reference numeral 12b indicates the connection portion between the cutting surface 12 and the lower surface 4. In the second ring 40 of the embodiment, the connection portion 12a is consistent with the outer peripheral end portion 1a. At this time, the distance between the connection portion 12a and the connection portion 12b in the axial direction of the second ring 40 is set to H, and the distance between the connection portion 12a and the connection portion 12b in the radial direction of the second ring 40 is set to D. In the second ring 40 of the embodiment, h1 and H are set to 0.2≤H / h1≤0.4. It should be noted that the range of h1 is not particularly limited, but is preferably set to 0.8mm≤h1≤2.5mm, for example.

[0051] [Oil seal performance]

[0052] Next, the oil scraping performance of the second ring 40 according to the embodiment will be described. Figure 3 This is a cross-sectional view of the vicinity of the second ring 40 when the piston 20 is in a descending stroke in the internal combustion engine 100 of the embodiment. Figure 4This is a cross-sectional view of the vicinity of the second ring 60 when the piston 20 is in a descending stroke in the internal combustion engine 200 of Comparative Example 1. Figure 3 and Figure 4 , a cross section along the central axis of the piston 20 is shown. Figure 4 The internal combustion engine 200 of the comparative example 1 shown is different from the internal combustion engine 100 of the embodiment in that a conventional second ring 60 having a tapered undercut shape is attached to the second ring groove 202 of the piston 20 instead of the second ring 40 of the embodiment. Figure 3 and Figure 4 Reference symbol F1 indicates relative flow of a portion of oil present on the inner wall surface 10a of the cylinder 10 with respect to the piston 20. Reference symbol C1 indicates a chamfered portion formed between the lower wall surface W2 of the second annular groove 202 and the outer peripheral surface 20a of the piston 20.

[0053] like Figure 4 As shown, in the internal combustion engine 200 of Comparative Example 1, a part of the oil scraped off by the second ring 60 may flow on the undercut surface. In this case, the part of the oil may not fall into the gap PC1, but may hit the chamfered portion C1 of the second annular groove 202 and flow into between the lower surface 4 of the second ring 60 and the lower wall surface W2 of the second annular groove 202. Therefore, in Comparative Example 1, a part of the oil that flows into between the lower surface 4 of the second ring 60 and the lower wall surface W2 of the second annular groove 202 flows out to the combustion chamber side, so the fuel consumption may increase.

[0054] On the other hand, in the internal combustion engine 100 of the embodiment, the outer peripheral surface 1 of the second ring 40 has the second surface 122 inclined at an angle of 50° or more and 85° or less relative to the lower surface 4 as described above. Figure 3 As shown in FIG. 1 , a portion of the oil scraped off by the second ring 40 flows from the bottom B1 along the inclination of the second surface 122, thereby being discharged toward the outer peripheral side of the second ring 40. As a result, the portion of the oil falls into the gap PC1 of the third land L3 and flows toward the crank chamber side. Thus, the oil is prevented from flowing between the lower surface 4 of the second ring 40 and the lower wall surface W2 of the second annular groove 202.

[0055] [Function, Effect]

[0056] As described above, in the second ring 40 of the embodiment, the cut surface 12 forming the notch 5 includes a second surface 122 provided between the bottom B1 and the lower surface 4 and facing the outer side in the radial direction, the second surface 122 is inclined so as to be away from the central axis of the second ring 40 as it goes downward, and the inclination angle θ1 of the second surface 122 relative to the lower surface 4 is 50° or more and 85° or less. Moreover, in the second ring 40 of the embodiment, H / h1 is 0.2 or more and 0.4 or less.

[0057] If θ1 is less than 50°, the oil flowing along the second surface 122 will hit the inner wall surface 10a of the cylinder 10, and the oil may not fall smoothly into the piston gap PC1. In addition, if θ1 is greater than 85°, the oil flowing along the second surface 122 may not fall into the gap PC1, but will flow between the lower surface of the second ring 40 and the lower wall surface W2 of the second ring groove 202. The second ring 40 of the embodiment is set to 50°≤θ1≤85°, so that the oil flowing along the oblique surface 122 can be discharged to the outer peripheral side of the second ring 40 and easily fall into the gap PC1. It should be noted that θ1 is more preferably set to 50°≤θ1≤80°, and more preferably set to 60°≤θ1≤80°.

[0058] In addition, if H / h1 is less than 0.2, the volume of the notch 5 cannot be sufficiently ensured, and the oil scraping performance will be reduced. In addition, when H / h1 is greater than 0.4, the axial width of the tapered surface 11 as a surface sliding on the inner wall surface 10a of the cylinder 10 cannot be sufficiently ensured. The second ring 40 of the embodiment is set to 0.2≤H / h1≤0.4, which can suppress the reduction in the amount of oil scraping and ensure the axial width of the sliding surface. It should be noted that H / h1 is more preferably set to 0.2≤H / h1≤0.3.

[0059] As described above, the second ring 40 of the embodiment is configured as described above, thereby improving the oil sealing performance and reducing the fuel consumption of the internal combustion engine 100 .

[0060] It should be noted that, from the viewpoint of improving the oil seal performance, the curvature radius r1 of the lower R surface 124 is preferably set to 0.01mm≤r1≤0.2mm, and more preferably to 0.05mm≤r1≤0.2mm. In addition, from the same viewpoint, it is more preferably set to 0.2mm≤D≤0.6mm, and further preferably to 0.2mm≤D≤0.5mm. In addition, from the same viewpoint, it is more preferably set to 0.2mm≤H≤0.6mm. However, the present invention is not limited to these values. In the case where r1 is less than 0.01mm, there is a possibility that a defect will be generated in the corner portion during the grinding process of the lower surface 4 of the second ring 40. In the case where r1 is greater than 0.2mm, the proportion of the second surface 122 in the entire cut surface 12 is reduced. It can be considered that the oil flowing on the lower surface of the ring and the oil rushing onto the piston chamfer will increase (due to the expansion of r1, the oil is guided to the lower surface of the ring), and the oil falling on the crank chamber side will decrease.

[0061] In addition, in the second ring 40 of the embodiment, the cut surface 12 includes a third surface 123, the third surface 123 includes a bottom B1 and connects the first surface 121 and the second surface 122, the third surface 123 is curved in a concave shape, and the radius of curvature of the third surface 123 is greater than or equal to 0.05 mm and less than or equal to 0.2 mm. As a result, a portion of the oil scraped off by the second ring 40 flows along the curve of the third surface 123, and is thus easily guided to the second surface 122. As a result, the oil is easily dropped into the gap PC1, and oil consumption can be further reduced.

[0062] [Modifications]

[0063] Figure 5 4 is a cross-sectional view for explaining the outer peripheral surface 1 of the second ring 40A according to a modified example of the embodiment. Figure 5 , a portion of a cross section of the second ring 40A perpendicular to the circumferential direction is shown. Figure 5 As shown, the second ring 40A is different from the above-mentioned second ring 40 in that the first surface 121 of the cut surface 12 is inclined relative to the lower surface 4 .

[0064] like Figure 5 As shown, in the second ring 40A of the modified example, the first surface 121 is inclined so as to be away from the crank chamber as it approaches the radial inner side of the second ring 40A. Figure 5 As shown, in the cross section of the second ring 40A perpendicular to the circumferential direction, the inclination angle of the first surface 121 relative to the lower surface 4 is set to θ2. In the second ring 40A of the modified example, θ2 is set to 0°<θ2≤30°. It should be noted that θ2 can also be set in the range of 0.5°≤θ2≤30°, for example.

[0065] According to the second ring 40A of the modified example, since the first surface 121 is inclined as described above, part of the oil scraped off by the second ring 40A flows along the inclination of the first surface 121 and is easily guided to the second surface 122. Thus, the oil easily falls into the gap PC1, and the oil consumption can be further reduced.

[0066] <Oil seal performance evaluation>

[0067] The oil sealing performance of the second ring of the embodiment was evaluated by analysis using analysis software. In the evaluation of the oil sealing performance, the outflow amount of oil in the descending stroke of the piston in the internal combustion engine was analyzed.

[0068] [Comparison in shape]

[0069] As Examples 1 to 2, Figure 2The oil sealing performance of the second ring 40 of the embodiment shown in the figure was evaluated. In Example 1, a second ring with h1=1.5mm, H=0.3mm, H / h1=0.2, D=0.4mm, θ1=80°, θ2=0° was used. In Example 2, a second ring with h1=1.5mm, H=0.3mm, H / h1=0.2, D=0.4mm, θ1=70°, θ2=0° was used. In addition, as Examples 3 and 4, the second ring with h1=1.5mm, H=0.3mm, H / h1=0.2, D=0.4mm, θ1=70°, θ2=0° was used. Figure 5 The oil seal performance of the second ring 40A of the modified example of the embodiment shown was evaluated. In Example 3, a second ring with h1=1.5mm, H=0.3mm, H / h1=0.2, D=0.4mm, θ1=83°, θ2=13.5° was used. In Example 4, a second ring with h1=1.5mm, H=0.3mm, H / h1=0.2, D=0.4mm, θ1=80°, θ2=10° was used. As Comparative Example 1, Figure 4 The oil sealing performance of the second ring 60 of the comparative example 1 shown was evaluated. As comparative example 2, the oil sealing performance of the second ring disclosed in Patent Document 3 (International Publication No. 2016 / 121483) was evaluated. Figure 6 It is a cross-sectional view of the second ring 70 of Comparative Example 2. As Comparative Example 3, the oil sealing performance of the second ring having a so-called Napier shape was evaluated. Figure 7 is a cross-sectional view of the second ring 80 of Comparative Example 3. Figure 6 and Figure 7 , a cross section perpendicular to the circumferential direction is shown.

[0070] [Comparison results]

[0071] Figure 8 This is a graph showing the analysis results of the oil outflow. Figure 8 , the oil outflow ratio relative to Comparative Example 1 is shown. Figure 8 The oil outflow ratio represented by the vertical axis is the ratio of the oil outflow between the lower surface of the second ring and the lower wall surface of the ring groove. Figure 8 As shown, the ratios of the amount of oil flowing out between the lower surface of the second ring and the lower wall surface of the annular groove in Comparative Examples 2 to 3 relative to Comparative Example 1 are 1.59 and 1.18, respectively. In addition, the ratios of Examples 1 to 4 relative to Comparative Example 1 are 0.77, 0.32, 0.68, and 0.59, respectively. Figure 8 The analysis results show that the amount of oil flowing out between the lower surface of the second ring and the lower wall surface of the ring groove is reduced in Examples 1 to 4 compared with Comparative Examples 1 to 3.

[0072] [Parameter evaluation]

[0073] In the second ring 40 of the embodiment, the oil sealing performance was evaluated when the inclination angle θ1 and H / h1 were changed. Fig. 9 is a graph showing the relationship between θ1 and oil outflow. Fig. 9 The relationship between θ1 and oil outflow in the following cases is shown: in the second ring of the embodiment, h1=1.5mm, H=0.3mm, H / h1=0.2, D=0.4mm, θ2=0°, θ1=40°, 45°, 50°, 60°, 70°, 80°, 85°, 90°. Fig. 9 In the figure, the oil outflow represented by the vertical axis is the amount of oil flowing out between the lower surface of the second ring and the lower wall surface of the ring groove. Fig. 9 As shown, it can be seen that when θ1 is around 70°, the oil outflow between the lower surface of the second ring and the lower wall of the ring groove decreases. Fig.10 This is a graph showing the relationship between H / h1 and oil outflow. Fig.10 In the figure, the relationship between H / h1 and the oil outflow rate is shown in the following cases: In the second ring of the embodiment, H / h1=0.15, 0.2, 0.3, 0.4, 0.45. Fig.10 In the figure, the oil outflow represented by the vertical axis is the amount of oil that flows out to the second land through the outer peripheral surface of the second ring and the inner wall surface of the cylinder. Fig.10 As shown, it can be seen that the oil outflow to the second land is relatively small when H / h1=0.2, 0.3, and 0.4, compared with the cases of H / h1=0.15 and 0.45. Therefore, it can be seen that the oil outflow to the second land is reduced by setting H / h1 to 0.2 or more and 0.4 or less. In addition, Fig.11 is a graph showing the relationship between D and oil outflow. Fig.11 , the relationship between D and the oil outflow amount in the following cases is shown: In the second ring of the embodiment, D=0.05 mm, 0.1 mm, 0.2 mm, 0.3 mm, and 0.5 mm. Fig.11 The oil outflow amount represented by the vertical axis is the amount of oil flowing out between the lower surface of the second ring and the lower wall surface of the ring groove. Fig.11 As shown, it can be seen that in the range of 0.2mm≤D≤0.5mm, the oil outflow between the lower surface of the second ring and the lower wall surface of the ring groove decreases. It can be seen that the oil outflow is the least especially when D is around 0.3mm. That is, in the range of D<0.3mm, the smaller D is, the more the oil outflow increases. It is believed that this is because the oil on the inner wall surface of the cylinder interferes with the oil in the bottom cut part (notch part) of the ring, thereby generating an oil vortex, so that the oil with a reduced flow rate flows along the lower surface of the ring. In addition, in the range of D>0.3mm, the larger D is, the more the oil outflow increases. It can be considered that this is because the amount of oil flowing along the lower surface of the ring increases due to the increase in the amount of oil hitting the chamfered part of the piston.

[0074] <Flow distribution evaluation>

[0075] The flow of oil when the second ring of the embodiment is used was analyzed using analysis software. Fig.12 This is a diagram showing the analysis results of the oil flow distribution near the second ring of the internal combustion engine during the downward stroke of the piston. Fig.12 In the figure, the gray scale of "Volume Fraction of Oil" indicates the volume fraction of oil. Fig.12 In the analysis results, the oil ratio of the black part is low (more air), and the oil ratio of the white part is high (more oil).

[0076] exist Fig.12 , the flow distribution of each of the above-mentioned Example 2, Comparative Example 2 and Comparative Example 3 is shown. Fig.12 As shown, it can be seen that the amount of oil flowing out between the lower surface of the second ring and the lower wall surface of the ring groove is smaller in Example 2 than in Comparative Examples 2 and 3.

[0077] The preferred embodiments of the present invention are described above, but the various embodiments described above can be combined as much as possible. It should be noted that the application object of the present invention is not particularly limited, but the piston ring of the present invention can also be preferably applied to a spark ignition engine, exemplified by a gasoline engine, in an internal combustion engine. However, it is also possible for the piston ring of the present invention to be applied to a compression ignition engine, exemplified by a diesel engine. In addition, when the piston ring of the present invention is applied to a spark ignition engine as a second ring, such as Figure 1 As shown, it is particularly preferred that the outer peripheral shape of the top ring is set to a barrel shape, and the outer peripheral shape of the scraper of the oil ring is set to a barrel shape. In this way, the increase in friction can be suppressed, and the gas sealing performance and oil sealing performance can be ensured. It should be noted that the "barrel shape" refers to the shape of the outer peripheral surface that includes the top with the largest diameter in the piston ring and is curved in a convex manner toward the radial outside, and is set to a symmetrical barrel shape with the top located in the upper and lower center, and an eccentric barrel shape with the top offset in either direction of the upper and lower center.

[0078] Description of reference numerals:

[0079] 1: outer surface;

[0080] 1a: outer peripheral end;

[0081] 11: Conical surface (an example of an outer peripheral end surface);

[0082] 12: cutting surface;

[0083] 121: Page 1;

[0084] 122: Side 2;

[0085] 123: Side 3;

[0086] 2: Inner circumference;

[0087] 3: upper surface;

[0088] 4: lower surface;

[0089] 5: Notch;

[0090] 10: Cylinder;

[0091] 20: Piston;

[0092] 40: second ring (an example of a piston ring);

[0093] 100: Internal combustion engine.

Claims

1. A piston ring, mounted on a piston of an internal combustion engine, wherein: The piston ring comprises: an outer peripheral surface, which is arranged on the outer periphery of the piston ring; and an inner peripheral surface, which is arranged on the inner periphery of the piston ring; The upper surface is an end surface of the axial end surface of the piston ring that faces the combustion chamber side in the internal combustion engine; and a lower surface, which is an end surface of the axial end surface of the piston ring located on the crank chamber side in the internal combustion engine, The outer peripheral surface has: an outer peripheral end surface including an outer peripheral end portion, wherein the outer peripheral end portion has a maximum diameter in the piston ring in a cross section perpendicular to the circumferential direction of the piston ring; and a cut surface connecting the outer peripheral end surface and the lower surface in a manner of forming a notch portion extending in the circumferential direction of the piston ring between the outer peripheral end surface and the lower surface, The cutting surface includes: a bottom portion, which is the innermost portion of the cutting surface in the radial direction of the piston ring; a first surface provided between the outer peripheral end surface and the bottom and facing the crank chamber side; and a second surface provided between the bottom and the lower surface and facing the radially outer side, The second surface is inclined so as to be away from the central axis of the piston ring as it approaches the crank chamber side. In a cross section perpendicular to the circumferential direction of the piston ring, the second surface has an inclination angle of 50° or more and 85° or less with respect to the lower surface. When the axial width of the piston ring is h1 and the axial distance between the connection between the cut surface and the outer peripheral end surface and the connection between the cut surface and the lower surface is H, H / h1 is 0.2 or more and 0.4 or less, The connection portion between the cut surface and the lower surface is located radially inward of the connection portion between the cut surface and the outer peripheral end surface. The cut surface is configured to discharge the oil flowing along the second surface toward the outer peripheral side of the piston ring.

2. The piston ring according to claim 1, wherein: When a distance D between a connection portion between the cut surface and the outer peripheral end surface and a connection portion between the cut surface and the lower surface in the radial direction of the piston ring is defined as 0.2 mm ≤ D ≤ 0.6 mm.

3. The piston ring according to claim 1 or 2, wherein: The first surface is inclined so as to be away from the crank chamber as it approaches the radial inner side of the piston ring. In a cross section of the piston ring orthogonal to the circumferential direction, an inclination angle of the first surface with respect to the lower surface is 30° or less.

4. The piston ring according to claim 1 or 2, wherein: The cutting surface includes a third surface, the third surface includes the bottom and connects the first surface and the second surface, The third surface is concavely curved, The radius of curvature of the third surface is greater than or equal to 0.05 mm and less than or equal to 0.2 mm.

5. The piston ring according to claim 1 or 2, wherein: The cutting surface also includes a lower R surface connecting the second surface and the lower surface, The curvature radius of the lower R surface is greater than or equal to 0.01 mm and less than or equal to 0.2 mm.

6. The piston ring according to claim 1 or 2, wherein: In an internal combustion engine in which a plurality of compression rings are attached to a piston, the piston ring becomes a second ring attached at a second position from a combustion chamber side among the plurality of compression rings.

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