Oil ring

Abstract

A shoulder space, which is a groove-shaped space surrounded by a pair of shoulder parts and a connecting part, is formed in the outer peripheral part of a main body ring of the oil ring, and the outer peripheral surface of the main body ring includes a pair of first groove wall surfaces provided on both sides of the bottom surface of the shoulder space in the axial direction, and a pair of second groove wall surfaces provided on both sides of the bottom surface of the shoulder space in the axial direction. The main body ring has a pair of first groove wall surfaces which are connected to the bottom surface and are formed so as to expand in diameter with increasing distance in the axial direction from the bottom surface, and in a cross-section including the window hole and orthogonal to the circumferential direction, when the angle formed between the upper first groove wall surface of the pair of first groove wall surfaces, which is provided on the combustion chamber side of the internal combustion engine, and the radial direction of the main body ring is theta1, theta1 < = 60 degrees.

Description

Technical Field

[0001] This invention relates to an oil ring composed of a main ring and a spiral expander. Background Technology

[0002] Internal combustion engines used in conventional automobiles employ a piston configuration consisting of a combination of piston rings, including compression rings and oil rings, mounted on the piston. Axially, the compression ring is located on the combustion chamber side, and the oil ring on the crankcase side; they function by sliding against the cylinder wall. The oil ring has a sealing function, preventing oil from flowing out of the combustion chamber (oil rise) by scraping excess engine oil (lubricating oil) adhering to the cylinder wall to the crankcase side; and a function of preventing piston seizure associated with engine operation by adjusting the oil quantity to properly maintain a lubricating oil film on the cylinder wall. The compression ring has a sealing function, preventing combustion gases from flowing out of the combustion chamber side to the crankcase side (blow-by) by maintaining an airtight seal; and a sealing function, preventing oil rise by scraping off excess oil that the oil ring has not completely scraped off.

[0003] Here, a two-piece combined oil ring, consisting of a main body ring and a spiral expander, is widely used as the oil ring. In the main body ring, a pair of shoulders sliding on the cylinder wall are connected by a connecting portion. The spiral expander, formed of spirally wound wire, applies force to the main body ring against the cylinder wall. In this combined oil ring, a window is formed at the connecting portion to discharge oil that has been scraped off by the shoulders and trapped between them to the inner circumferential surface of the main body ring. By discharging oil through this window, the oil pressure between the shoulders generated during sliding on the cylinder wall decreases, preventing the shoulders from floating on the oil film. As a result, the oil scraping ability of the shoulders is maintained.

[0004] Regarding two-piece combined oil rings, the following technology is disclosed: to improve the flowability of oil by tilting at least one of the opposing sidewalls of the through oil hole for oil supply relative to the direction of oil flow (e.g., Patent Document 1).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2006-194272

[0008] Patent Document 2: Japanese Patent Application Publication No. 2011-220519

[0009] Patent Document 3: Japanese Patent No. 7148667 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] To reduce oil consumption through the oil ring, the surface pressure between the sliding surface of the shoulder and the cylinder wall is typically increased to further scrape oil off the cylinder wall. However, the increased ring tension used to increase surface pressure contributes to increased friction, while the reduced sliding area of ​​the shoulder contributes to decreased wear resistance. Therefore, optimization of the orifice shape, orifice position, and the shape of the inner surfaces (opposite faces) of the pair of shoulders is required to facilitate the discharge of oil trapped between the shoulders to the inner circumferential surface of the oil ring. However, even with these measures, during prolonged operation, insoluble substances such as carbon sludge can sometimes accumulate as deposits between the shoulders due to oil deterioration; the reasons for this are not yet fully understood.

[0012] In addition, compared with petroleum-based engine oils, plant-based engine oils produce more carbon sludge and the like, and this carbon sludge adheres firmly, so there is a concern that this carbon sludge will accumulate as deposits between the shoulders and block the openings.

[0013] Furthermore, for example, when vegetable oil is used as a substitute for diesel fuel, carbon deposits will increase after prolonged operation compared to when light oil is used, thus increasing the likelihood of piston rings, including oil rings, getting stuck.

[0014] Therefore, as a major cause of deposit accumulation, the inventors have focused not only on oil retention during internal combustion engine operation but also on oil retention when the engine is stopped. The object of this invention is to provide an oil ring that can suppress oil retention between the shoulders of the oil ring when the internal combustion engine is stopped.

[0015] Solution for solving the problem

[0016] To solve the above problems, the present invention employs the following configuration. Specifically, the present invention is an oil ring fitted to a piston of an internal combustion engine. The oil ring comprises: a main ring, formed in an annular shape, having a pair of shoulders arranged axially and a connecting portion connecting the pair of shoulders; and a helical expander disposed on the inner circumference of the main ring, applying force to the main ring radially outward. A shoulder space is formed on the outer circumference of the main ring, extending along the circumferential direction of the main ring. The shoulder space is a groove-shaped space surrounded by the pair of shoulders and the connecting portion. A groove is formed on the bottom surface of the shoulder space. A window hole extends radially through the main body ring. The outer circumferential surface of the main body ring includes a pair of first groove walls, wherein the pair of first groove walls are axially located on both sides of the bottom surface of the shoulder space. The pair of first groove walls are connected to the bottom surface and are formed to expand in diameter as they move away from the bottom surface in the axial direction. In a cross section containing the window hole and orthogonal to the circumferential direction, when the angle between the upper first groove wall of the pair of first groove walls located on the combustion chamber side of the internal combustion engine and the radial direction of the main body ring is defined as θ1, θ1 ≤ 60°.

[0017] Furthermore, in this invention, when the angle between the lower first groove wall of the pair of first groove walls located on the crankcase side of the internal combustion engine and the radial direction of the main body ring is set as θ2, θ2 ≤ 60°.

[0018] In addition, in this invention, it is also possible that 40°≤θ1≤60° and 40°≤θ2≤60°.

[0019] Furthermore, in this invention, the outer peripheral surface of the main ring may also have: an upper second groove wall surface, located axially at a position closer to the combustion chamber side than the upper first groove wall surface, the upper second groove wall surface being connected to the upper first groove wall surface and formed to expand in diameter as it approaches the combustion chamber side; and a lower second groove wall surface, located axially at a position closer to the crankcase side than the lower first groove wall surface, the lower second groove wall surface being connected to the lower first groove wall surface and formed to expand in diameter as it approaches the crankcase side. In a cross-section including the window and orthogonal to the circumferential direction, when the angle between the upper second groove wall surface and the radial direction is set as θ3 and the angle between the lower second groove wall surface and the radial direction is set as θ4, θ3≤θ1 and θ4≤θ2.

[0020] Furthermore, in this invention, in a cross-section containing the window opening and orthogonal to the perimeter direction, the bottom surface is connected to each of the pair of first groove walls via one or more curves, multiple consecutive straight lines, or a combination of one or more curves and one or more straight lines.

[0021] Invention Effects

[0022] According to the present invention, it is possible to prevent oil from accumulating between the shoulders of the oil ring when the internal combustion engine is stopped. Attached Figure Description

[0023] Figure 1 This is a partial cross-sectional view of an internal combustion engine with a combined oil ring having an implementation method.

[0024] Figure 2 This is a partially enlarged view showing the state of the combined oil ring of the embodiment when visually identified from the radially outer side.

[0025] Figure 3 This is a top view of the main ring.

[0026] Figure 4 It is a three-dimensional diagram representing a part of the main ring.

[0027] Figure 5 yes Figure 2 A-A sectional view.

[0028] Figure 6 This is a diagram showing a deformation example of the outer circumferential surface of the main ring.

[0029] Figure 7 This is a diagram showing the analytical results of the oil flow distribution in the shoulder space of an internal combustion engine when the piston is stopped at bottom dead center. Detailed Implementation

[0030] Hereinafter, preferred embodiments of the combined oil ring of the present invention will be described with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the configurations described in the following embodiments are not intended to limit the technical scope of the invention to this.

[0031] Figure 1 This is a partial cross-sectional view of an internal combustion engine 100 having a combined oil ring 40 (hereinafter referred to as oil ring 40) according to an embodiment. Figure 2 This is a partially enlarged view showing the state of the oil ring 40 of the embodiment when viewed from a radially outward perspective. Figure 1 The figure shows a cross-section of the main ring, indicated by reference numeral 1, orthogonal to the circumferential direction. Furthermore, in... Figure 1 The image shows an oil ring in the internal combustion engine 100, mounted on the piston 20 and inserted into the cylinder 10 (hereinafter referred to as the operating state).

[0032] like Figure 1As shown, in the internal combustion engine 100, a predetermined separation distance is ensured between the inner wall surface 10a of the cylinder 10 and the outer peripheral surface 20a of the piston 20 mounted on the cylinder 10, thereby forming a piston clearance PC1. Furthermore, an annular groove 30 with a generally rectangular cross-section is formed on the outer peripheral surface 20a of the piston 20. The annular groove 30 has: an upper wall 301 formed on the combustion chamber side; a lower wall 302 formed on the crankcase side, opposite to the upper wall 301; and a connecting wall 303 connecting the inner peripheral edges of the upper wall 301 and the lower wall 302 to each other. A drain hole 304 is formed in the connecting wall 303 for discharging oil flowing into the annular groove 30 to an oil pan (not shown). It should be noted that the drain hole 304 may not be formed in the connecting wall 303. In this embodiment, a combined oil ring 40 (hereinafter, oil ring 40) is mounted on this annular groove 30.

[0033] The oil ring 40 is a sliding component that slides on the inner wall surface 10a of the cylinder 10 as the piston 20 reciprocates. For example... Figure 1 and Figure 2 As shown, the oil ring 40 is a so-called two-piece oil ring. Specifically, the oil ring 40 includes: a main body ring 1, which is formed into a ring shape; and a spiral expander 2, which is formed into a ring shape from a spirally wound wire, and is disposed (attached) on the inner circumference of the main body ring 1, applying force to the main body ring 1 radially outward.

[0034] The following, such as Figure 1 As shown, the direction (axial direction) along the central axis of the main body ring 1 is defined as the "vertical direction". Furthermore, in the axial direction of the main body ring 1, the combustion chamber side of the internal combustion engine 100 ( Figure 1 The upper side of the crankcase is defined as the "upper side", and its opposite side, namely the crankcase side, is defined as the "upper side". Figure 1 The lower side of the oil ring 40 is defined as "lower side". Furthermore, in the following description of the oil ring 40, unless otherwise specified, "circumferential direction" refers to the circumferential direction of the main body ring 1, "radial" refers to the radial direction of the main body ring 1, and "axial" refers to the direction along the central axis of the main body ring 1. In the internal combustion engine 100, the oil ring 40 is mounted in the ring groove 30 with the axial directions of the main body ring 1 and the spiral expander 2 aligned with the axial direction of the piston 20.

[0035] like Figure 1As shown, the main body ring 1 has a pair of shoulders 3, 3 arranged in a ring shape in the vertical direction, and a connecting portion 4 disposed between the pair of shoulders 3, 3 and connecting the pair of shoulders 3, 3 to each other. The main body ring 1 is formed into a ring with an approximately I-shaped cross-section. Hereinafter, when explaining the pair of shoulders 3, 3 separately, the upper shoulder 3 will be referred to as the upper shoulder 3U, and the lower shoulder 3 will be referred to as the lower shoulder 3L. The main body ring 1 is made of steel, cast iron, resin, or the like. The surface of the main body ring 1 includes 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 the axial end faces of the main body ring 1 and are parallel to each other. It should be noted that the upper surface S3 and the lower surface S4 may not necessarily be parallel. The width (axial dimension) of the main body ring 1 is defined by the upper surface S3 and the lower surface S4. The outer peripheral surface S1 is the surface that connects the outer periphery of the upper surface S3 and the outer periphery of the lower surface S4. The inner peripheral surface S2 is the surface that connects the inner periphery of the upper surface S3 and the inner periphery of the lower surface S4. In use, the outer peripheral surface S1 is in sliding contact with the inner wall surface 10a of the cylinder 10, the inner peripheral surface S2 is opposite to the connecting wall 303 of the annular groove 30, the upper surface S3 is opposite to the upper wall 301, and the lower surface S4 is opposite to the lower wall 302.

[0036] like Figure 1 As shown, on the outer periphery of the main body ring 1, a pair of guide rail portions 11, 11 are arranged axially, protruding radially outward from the connecting portion 4, via a portion of a pair of shoulders 3, 3. The pair of guide rail portions 11, 11 are formed by the outer peripheral surface S1 bulging radially outward. Hereinafter, when explaining the pair of guide rail portions 11, 11 separately, the upper guide rail portion 11 will be referred to as the upper guide rail portion 11U, and the lower guide rail portion 11 will be referred to as the lower guide rail portion 11L. The upper guide rail portion 11U is formed from the outer periphery of the upper shoulder 3U, and the lower guide rail portion 11L is formed from the outer periphery of the lower shoulder 3L. Thus, the pair of guide rail portions 11, 11 are formed in a ring shape around the axis of the main body ring 1. The outer peripheral end face S11U of the upper guide rail portion 11U and the outer peripheral end face S11L of the lower guide rail portion 11L constitute the outermost radial portion of the outer peripheral surface S1, and slide in contact with the inner wall surface 10a of the cylinder 10. In this example, the outer peripheral end faces S11U and S11L are formed as flat surfaces extending in the vertical direction. However, the present invention is not limited to this, and the outer peripheral end faces S11U and S11L may also be formed as curved surfaces.

[0037] Furthermore, a shoulder space 12 (outer peripheral groove) is formed between a pair of guide rail portions 11, 11, wherein the shoulder space 12 is a groove that is recessed radially inward. The shoulder space 12 is formed as a groove-shaped space surrounded by a pair of shoulder portions 3U, 3L and a connecting portion 4, and extends along the circumferential direction of the main body ring 1. Figure 1The bottom surface indicated by reference numeral S12 in the attached drawing is the portion of the outer peripheral surface S1 that constitutes the bottom surface of the shoulder space 12. In this example, the bottom surface S12 is formed by the outer peripheral surface of the connecting portion 4. In this example, the bottom surface S12 is formed as a flat surface extending in the vertical direction. However, the present invention is not limited to this, and the bottom surface S12 may also be a curved surface. Here, the mutually opposing surfaces of the pair of guide rail portions 11U, 11L are designated as a pair of groove wall surfaces S13U, S13L. The upper groove wall surface S13U of the pair of groove wall surfaces S13U, S13L is the surface located on the outer peripheral side of the upper shoulder portion 3U (upper guide rail portion 11U) and connects the bottom surface S12, which serves as the outer peripheral surface of the connecting portion 4, to the outer peripheral end surface S11U of the upper guide rail portion 11U. Furthermore, the lower groove wall surface S13L, one of the pair of groove wall surfaces S13U and S13L, is located on the outer periphery of the lower shoulder portion 3L (lower guide rail portion 11L) and connects the bottom surface S12 to the outer periphery end surface S11L of the lower guide rail portion 11L. This pair of groove wall surfaces S13U and S13L constitutes the side surface of the shoulder space 12. The shoulder space 12 is defined by the pair of groove wall surfaces S13U and S13L and the bottom surface S12.

[0038] like Figure 1 As shown, a window V1 is formed in the main ring 1, extending radially from the outer peripheral surface S1 to the inner peripheral surface S2. More specifically, the window V1 extends radially through the upper and lower center positions of the connecting portion 4, forming on the bottom surface S12 of the shoulder space 12. Here, Figure 3 This is a top view of the main ring 1. (Example) Figure 3 As shown, the main ring 1 has an opening G1. Furthermore, Figure 4 It is a three-dimensional view representing a part of the main ring 1. Figure 4 In the attached drawing, reference numeral S5 indicates the end face of opening G1. For example... Figure 4 As shown, multiple windows V1 are arranged at equal intervals along the circumference of the main ring 1. Figure 2 As shown, the window opening V1 is formed as a roughly rectangular through hole. The inner wall surface forming the window opening V1 includes an upper wall W1 and a lower wall W2, which are orthogonal to the axial direction and opposite to each other. In this example, the upper wall W1 and the lower wall W2 are parallel to each other, and the upper wall W1 is located above the lower wall W2. It should be noted that the upper wall W1 and the lower wall W2 may not necessarily be parallel. Figure 1 As shown, the opening on the outer peripheral surface S1 side of window hole V1 is designated as outer peripheral opening V11, and the opening on the inner peripheral surface S2 side of window hole V1 is designated as inner peripheral opening V12. Figure 1 As shown, an outer peripheral opening V11 is formed on the bottom surface S12. Thus, the window opening V1 is connected to the space formed between a pair of guide rails 11, 11, namely the shoulder space 12.

[0039] like Figure 1As shown, a portion of the inner circumferential surface S2 of the main ring 1 is curved in a radially outward arc shape, thereby forming a retaining portion H1 for holding the spiral expander 2. A radially outward recessed groove is formed through the retaining portion H1, in which the spiral expander 2 is accommodated.

[0040] The spiral expander 2 is a component formed by further shaping a spiral spring made of steel or other wire wound in a spiral shape into a ring. Wire with a circular or rectangular cross-sectional shape is used for forming the spiral expander 2, but there are no particular limitations. In use, the spiral expander 2 is fitted into the annular groove 30 in a manner that generates an expanding force radially outward. Through the expanding force of the spiral expander 2, the main body ring 1 is forced (pressed) radially outward. As a result, the outer peripheral end faces S11U and S11L of the pair of guide rail portions 11U and 11L of the main body ring 1 are pressed against the inner wall surface 10a of the cylinder 10, performing an oil scraping function.

[0041] Figure 5 yes Figure 2 A-A sectional view. In Figure 5 The image shows a cross-section of the main ring 1, orthogonal to the circumferential direction and containing the window opening V1. More specifically... Figure 5 It is obtained by cutting at the part with the largest opening width of the window hole V1 in the vertical (axial) direction (hereinafter also referred to as the maximum opening part). Figure 2 Section A-A. In this example, the central portion of the window opening V1 in the circumferential direction is the maximum opening of the window opening V1. Here, the center line of the upper and lower widths of the main body ring 1 in the section orthogonal to the circumferential direction is set as the main body center line CL1. Figure 5 As shown, the main body ring 1 has a symmetrical shape, and a pair of guide rails 11, 11 are respectively positioned on opposite sides of each other along the axial direction of the main body ring 1, separated by the central line CL1. It should be noted that in this example, the pair of groove wall surfaces S13U, S13L are symmetrical in shape, but the present invention is not limited to this. The shapes of the pair of groove wall surfaces S13U, S13L can also be asymmetrical. Furthermore, in this example, the window V1 is located at the upper and lower center positions of the connecting part 4, but the present invention is not limited to this; the window V1 can also be located above or below the upper and lower center positions.

[0042] like Figure 5 As shown, the outer peripheral surface S1 of the main ring 1 is configured to include a pair of first groove wall surfaces S14U, S14L and a pair of second groove wall surfaces S15U, S15L as part of a pair of groove wall surfaces S13U, S13L. Specifically, the upper groove wall surface S13U includes the upper first groove wall surface S14U and the upper second groove wall surface S15U, and the lower groove wall surface S13L includes the lower first groove wall surface S14L and the lower second groove wall surface S15L.

[0043] A pair of first groove walls S14U and S14L are provided on both sides of the bottom surface S12 of the shoulder space 12 in the vertical direction. More specifically, the upper first groove wall S14U is provided on the upper side of the bottom surface S12 and connected to the upper end of the bottom surface S12. On the other hand, the lower first groove wall S14L is provided on the lower side of the bottom surface S12 and connected to the lower end of the bottom surface S12. This pair of first groove walls S14U and S14L are formed to be inclined in a manner that expands in diameter as it moves away from the bottom surface S12 in the vertical direction. That is, the upper first groove wall S14U expands in diameter as it tends to move upward (displaces radially outward), and the lower first groove wall S14L expands in diameter as it tends to move downward. In other words, the pair of first groove walls S14U and S14L are inclined relative to the bottom surface S12. In this example, the pair of first groove walls S14U and S14L are inclined in a straight line.

[0044] The upper second groove wall surface S15U is located above the upper first groove wall surface S14U and is connected to the upper end of the upper first groove wall surface S14U. The upper second groove wall surface S15U is inclined in a manner that increases in diameter towards the upper side. The upper second groove wall surface S15U connects the upper end of the upper first groove wall surface S14U to the lower end of the outer peripheral end face S11U. Furthermore, the lower second groove wall surface S15L is located below the lower first groove wall surface S14L and is connected to the lower end of the lower first groove wall surface S14L. The lower second groove wall surface S15L is inclined in a manner that increases in diameter towards the lower side. The lower second groove wall surface S15L connects the lower end of the lower first groove wall surface S14L to the upper end of the outer peripheral end face S11L. The opening of the shoulder space 12 is formed by the upper second groove wall surface S15U and the lower second groove wall surface S15L. In this example, the pair of second groove wall surfaces S15U and S15L are inclined in a straight line. It should be noted that in this invention, the upper second groove wall surface S15U and the lower second groove wall surface S15L are not essential components. For example, the upper end of the bottom surface S12 and the lower end of the outer peripheral end surface S11U can be connected through the upper first groove wall surface S14U, or the lower end of the bottom surface S12 and the upper end of the outer peripheral end surface S11L can be connected through the lower first groove wall surface S14L.

[0045] Here, as Figure 5As shown, in a cross-section including the window opening V1 and orthogonal to the circumferential direction, the angle formed by the upper first groove wall surface S14U relative to the radial direction of the main body ring 1 is defined as θ1. That is, θ1 is the inclination angle of the upper first groove wall surface S14U relative to an imaginary straight line extending radially. Furthermore, in the above cross-section, the angle formed by the lower first groove wall surface S14L relative to the radial direction of the main body ring 1 is defined as θ2. That is, θ2 is the inclination angle of the lower first groove wall surface S14L relative to an imaginary straight line extending radially. At this time, the pair of first groove wall surfaces S14U and S14L of the oil ring 40 in this embodiment are formed such that θ1≤60° and θ2≤60°. As a result, as will be described later, oil retention in the stopped state of the internal combustion engine 100 can be appropriately suppressed.

[0046] Here, as Figure 5 As shown, in the cross-section including the window opening V1 and orthogonal to the circumferential direction, the angle formed by the upper second groove wall surface S15U with respect to the radial direction of the main body ring 1 is set as θ3. That is, θ3 is the inclination angle of the upper second groove wall surface S15U with respect to an imaginary straight line extending radially. Furthermore, in the above cross-section, the angle formed by the lower second groove wall surface S15L with respect to the radial direction of the main body ring 1 is set as θ4. That is, θ4 is the inclination angle of the lower second groove wall surface S15L with respect to an imaginary straight line extending radially. At this time, the pair of second groove wall surfaces S15U and S15L of the oil ring 40 in this embodiment are formed such that θ3 < θ1 and θ4 < θ2. As a result, as will be described later, the axial length (axial width) of the main body ring 1 can be prevented from becoming too large.

[0047] The determination of angles θ1, θ2, θ3, and θ4 can be performed, for example, as follows. With the main ring 1 closed to its nominal diameter, the angles are determined by the central axis A1 of the oil ring 40 and the radially extending normal (e.g., ...). Figure 3 The main ring 1 is cut along the plane of the line indicated by reference numeral F1 in the attached figure. The main ring 1 is filled with resin, and after grinding, the cut plane is observed with an optical microscope, thereby obtaining angles θ1, θ2, θ3, and θ4.

[0048] In internal combustion engine 100, such as Figure 1With the oil ring 40 attached to the ring groove 30, when the piston 20 reciprocates within the cylinder 10, a pair of guide rails 11U and 11L slide on the inner wall surface 10a of the cylinder 10 at their outer peripheral end faces S11U and S11L. This causes excess oil adhering to the inner wall surface 10a to be scraped off into the oil pan (not shown) on the crankcase side. Consequently, oil outflow (oil rise) to the combustion chamber side is suppressed, and the oil quantity is adjusted to maintain a suitable lubricating oil film on the inner wall surface 10a of the cylinder 10, preventing the piston 20 from sintering during the operation of the internal combustion engine 100. At this time, the oil scraped off by the upper guide rail 11U and lower guide rail 11L falls into the oil pan through the piston clearance PC1. On the other hand, the oil that is not completely scraped off by the upper guide rail 11U and the lower guide rail 11L flows into the shoulder space 12, is discharged to the inner circumference of the main body ring 1 through the window hole V1, and falls into the oil pan through the drain hole 304.

[0049] Here, when engine oil stagnates in the shoulder space for an extended period, it deteriorates, and insoluble substances such as carbon sludge sometimes accumulate as deposits in the shoulder space of the oil ring. When these deposits accumulate in large quantities, the orifices become blocked, hindering oil drainage and becoming a major cause of the decline in the oil ring's drainage performance (the reduction in oil pressure between the guide sections achieved by the orifices). Therefore, to suppress the decline in oil ring performance, it is necessary to prevent oil from stagnating in the shoulder space (outer peripheral groove) for extended periods. Improving the fluidity of the oil in the shoulder space during engine operation is important, but the fluidity of the oil in the shoulder space when the engine is stopped is also a crucial factor. When there are areas on the inner wall of the shoulder space where oil tends to stagnate (stagnant areas), the engine oil remaining in the stagnant areas when the engine stops will adhere to these areas due to its viscosity, thus tending to remain in the shoulder space. Even if the internal combustion engine restarts, the oil adhering to the inner wall of the shoulder space will continue to adhere to the stagnation area. Therefore, the oil in the shoulder space will not be replaced, its viscosity will increase, and it will accumulate as deposits. These deposits will increase with repeated engine operation and shutdown, reducing the oil ring's drainage performance. Therefore, it is necessary to improve the oil flowability in the shoulder space when the internal combustion engine is stopped to inhibit oil stagnation.

[0050] In this embodiment, the oil ring 40 has a pair of first groove walls S14U and S14L on both sides of the bottom surface S12 of the shoulder space 12 inclined radially. These first groove walls S14U and S14L are configured to narrow as they approach the radially inward direction (that is, as they approach the window opening V1). This allows for appropriate guidance of oil towards the window opening V1 during the operation of the internal combustion engine 100, and also increases the flow rate of the oil towards the window opening V1. Consequently, the fluidity of the oil in the shoulder space 12 during the operation of the internal combustion engine 100 is improved, oil stagnation is suppressed, and fuel consumption is reduced. Furthermore, in this embodiment, the oil ring 40 is configured such that the inclination angle θ1 of the upper first groove wall S14U is θ1≤60°. By setting θ1≤60°, stagnation in the shoulder space 12 can be suppressed. When θ1 is greater than 60°, after the internal combustion engine 100 stops, oil tends to accumulate on the upper groove wall surface S13U due to its viscosity, and this upper groove wall surface S13U becomes a retention area. In this embodiment, by setting θ1 ≤ 60°, the oil flowability at the upper groove wall surface S13U can be improved, and the formation of a retention area on the upper side of the window opening V1 can be suppressed. Even when the internal combustion engine 100 is stopped, oil retention caused by viscosity can be suppressed. Therefore, even if the internal combustion engine 100 is repeatedly started and stopped, the accumulation of deposits in the shoulder space 12 will be suppressed, and the flow of oil to the window opening will not be obstructed. Therefore, according to this embodiment, the decrease in the oil discharge performance of the oil ring 40 can be suppressed. That is, the oil pressure reduction effect between the guide sections achieved by the window opening V1 can be maintained, and the durability deterioration of the oil scraping function of the oil ring can be suppressed. As a result, the increase in oil consumption can be suppressed. Furthermore, in this embodiment, the oil ring 40 is configured such that the inclination angle θ1 of the upper first groove wall surface S14U is ≤60°, and the inclination angle θ2 of the lower first groove wall surface S14L is ≤60°. This improves the flowability of oil at the pair of groove wall surfaces S13U and S13L, and suppresses the formation of stagnation portions on the upper and lower sides of the window opening V1. As a result, oil stagnation in the stationary state of the internal combustion engine 100 can be more appropriately suppressed. It should be noted that in this example, θ1 = θ2, but the present invention is not limited to this, and θ1 and θ2 may be different. Furthermore, in the present invention, θ2 ≤60° is not necessary. It should be noted that when θ1 and θ2 are equal, in order to distinguish the vertical direction of the oil ring 40 in the use state, identification marks such as engravings or paint markings may be made on the main body ring 1.

[0051] Furthermore, by making the pair of first groove walls S14U and S14L into a straight inclined shape instead of an arc, the backflow of oil near the pair of first groove walls S14U and S14L can be suppressed, and the oil can be properly discharged from the window hole V1.

[0052] Furthermore, it is preferable that θ1 and θ2 satisfy 40°≤θ1≤60° and 40°≤θ2≤60°. When θ1 and θ2 are less than 40°, the distance between the pair of first groove walls S14U and S14L becomes narrower, and the volume of the shoulder space 12 becomes smaller. Therefore, when a large amount of oil flows into the shoulder space 12, the oil pressure may rise, affecting the following performance of the oil ring 40 toward the inner wall surface 10a of the cylinder 10. By making θ1 and θ2 greater than or equal to 40°, the volume of the shoulder space 12 can be ensured, and the decrease in the following performance of the oil ring 40 toward the inner wall surface 10a of the cylinder can be suppressed. This is particularly preferable for oil rings with a large axial width. For example, in a diesel engine using a wide oil ring with an axial width h1 greater than or equal to 3 mm, it is necessary to ensure a large volume of the shoulder space 12 of the oil ring. Therefore, it is preferable that θ1 and θ2 are greater than or equal to 40°.

[0053] Furthermore, in this embodiment, the oil ring 40 has a pair of second groove walls S15U and S15L on the upper and lower sides of a pair of first groove walls S14U and S14L. The oil ring 40 is configured such that the inclination angle θ3 of the upper second groove wall S15U is θ3 < θ1, and the inclination angle θ4 of the lower second groove wall S15L is θ4 < θ2. By making the inclination angles θ2 and θ4 of the pair of second groove walls S15U and S15L relative to the radial direction smaller than the inclination angles θ1 and θ2 of the pair of first groove walls S14U and S14L relative to the radial direction, the distance between the pair of shoulders 3U and 3L at the opening of the shoulder space 12 (that is, the distance between the upper and lower guide rails 11U and 11L) can be prevented from increasing. As a result, the axial width of the main ring 1 can be prevented from becoming excessively large. It should be noted that in this example, θ3 = θ4, but the present invention is not limited to this, and θ3 and θ4 can also be different. Furthermore, when θ3 and θ4 are equal, the aforementioned identification mark can be marked on the main body ring 1 in order to distinguish the up and down direction of the oil ring 40 in the use state.

[0054] Here, Figure 5h1 represents the axial width of the main ring 1, h2 represents the opening width of the shoulder space 12, h3 represents the axial width of the window V1, and a4 represents the depth of the shoulder space 12. In this case, for example, when 2.5mm ≤ h1 ≤ 6.0mm, the preferred ranges for θ1, θ2, θ3, θ4, and h3 are as follows: When θ1 is greater than or equal to 70°, the oil residue in the shoulder space 12 will increase; therefore, it is preferred to set θ1 ≤ 60°. When θ1 and θ2 are less than 20°, with the same connecting surface length (axial length of the bottom surface S12), the volume of the shoulder space 12 will decrease, and the oil flow will deteriorate. With the same h2, the oil retention will increase; therefore, it is preferred to set 20° < θ1 and θ2. When θ3 exceeds 20°, the oil scraping performance of the oil ring 40 will decrease; therefore, it is preferred to set θ3 ≤ 20°. When θ3 and θ4 are less than 10°, the surface treatment of the edges of the outer peripheral surface of the guide rail 11 may be damaged. Therefore, it is preferable to set 10°≤θ3, θ4. When h3 is less than or equal to 0.3mm, the time until the window V1 is blocked by deteriorated oil will be shorter, and the durability will deteriorate. When h3 is greater than or equal to 2.0mm, the lateral rigidity (axial rigidity) of the main body ring 1 will decrease, and the sealing performance of the sides (upper and lower surfaces) will decrease. Therefore, it is preferable to set 0.3mm<h3<2.0mm. In addition, when 2.5mm≤h1≤6.0mm, from the viewpoint of ensuring the volume of the shoulder space 12, it is preferable to set 0.8mm≤h2≤5.0mm and 0.5mm≤a4≤1.6mm.

[0055] Figure 6 This is a magnified view showing a deformed example of the outer peripheral surface S1. Figure 6 The figure shows a portion of the outer peripheral surface S1 in a cross-section containing the window opening V1 and orthogonal to the circumferential direction. For example... Figure 6 As shown, in a modified example, the bottom surface S12 is connected to the upper first groove wall surface S14U via a connecting surface S16, and the upper first groove wall surface S14U is connected to the upper second groove wall surface S15U via a connecting surface S17. Connecting surfaces S16 and S17 are formed as curved surfaces. In this invention, as in the modified example, in a cross-section orthogonal to the circumferential direction, the bottom surface can also be connected to each of the pair of first groove walls via a curve. The connection between the bottom surface and the pair of first groove walls can also be achieved through one or more curves, multiple continuous straight lines, or a combination of one or more curves and one or more straight lines. This improves the flowability of oil between the bottom surface and the pair of first groove walls, and suppresses oil retention.

[0056] <Evaluation of Oil Discharge Performance>

[0057] The oil discharge performance of the oil ring in a stationary state of an internal combustion engine was evaluated using analytical software. The evaluation assumed that the piston stopped at the bottom dead center (BDC) of the piston stroke after its descent. More specifically, in the presence of oil, the piston was lowered from a crank angle of 0° (top dead center) to 180° (bottom dead center) using the crank angle. Based on the flow distribution in the shoulder space at the time point of 180° crank angle, the volume of oil remaining in the shoulder space (residual oil quantity) was calculated, and the ratio of the residual oil quantity to the volume of the shoulder space (shoulder space volume) (residual oil quantity ratio) was calculated. The residual oil quantity was determined based on the volume of the region in the shoulder space representing an oil volume fraction greater than or equal to 50%. When the residual oil quantity was set as X1, the shoulder space volume as X2, and the residual oil quantity ratio as X3, the residual oil quantity ratio X3 was obtained by dividing X1 by X2.

[0058] [Comparative Evaluation]

[0059] Examples 1 to 4, existing examples, and comparative examples 1 and 2 were compared below. However, the present invention is not limited to the embodiments described below.

[0060] As examples 1 to 4, the following calculations were performed. Figure 1 The residual oil amount of the oil ring 40 in the illustrated embodiment. In Example 1, θ1 = θ2 = 55°; in Example 2, θ1 = θ2 = 55°; in Example 3, θ1 = θ2 = 60°; and in Example 4, θ1 = θ2 = 40°. The existing examples and Comparative Examples 1 and 2 differ from Examples 1 to 4 in that θ1 and θ2 are greater than 60°. In the existing examples, θ1 = θ2 = 90°; in Comparative Example 1, θ1 = θ2 = 70°; and in Comparative Example 2, θ1 = θ2 = 80°. Furthermore, in Examples 1 to 4, the existing examples, and Comparative Examples 1 and 2, θ3 = θ4 = 15°.

[0061] In the comparative evaluation, Examples 1 to 4, Comparative Example 1, and Comparative Example 2 were evaluated by comparing the reduction rate of the residual oil content ratio relative to existing examples representing the current level. For Examples 1 to 4, Comparative Example 1, and Comparative Example 2, the reduction rate of the residual oil content ratio relative to existing examples was calculated. When the residual oil content ratio of existing examples is set as p, the residual oil content ratio of Examples 1 to 4, Comparative Example 1, and Comparative Example 2 is set as q, and the reduction rate is set as r, the reduction rate r is calculated using (p - q) / p × 100 [%).

[0062] If the reduction rate relative to existing examples is greater than or equal to 15%, it is classified as "A"; if the reduction rate relative to existing examples is greater than or equal to 10% but less than 15%, it is classified as "B"; if the reduction rate relative to existing examples is greater than or equal to 5% but less than 10%, it is classified as "C"; and if the reduction rate relative to existing examples is less than 5%, it is classified as "D". The classification results are shown in Table 1.

[0063] [Table 1]

[0064] θ1, θ2 [°] determination Example 1 55 A Example 2 50 B Example 3 60 A Example 4 40 B Existing examples 90 D Comparative Example 1 70 C Comparative Example 2 80 C

[0065] As shown in Table 1, in Examples 1 to 4 where θ1 and θ2 are less than or equal to 60°, the result is classified as "A" or "B", indicating a reduction rate of more than or equal to 10% in the residual oil content ratio. On the other hand, in Comparative Examples 1 and 2 where θ1 and θ2 are greater than 60°, the result is classified as "C", indicating a reduction rate of less than 10% in the residual oil content ratio. Based on the determination results in Table 1, it can be seen that compared with Comparative Examples 1 and 2, the oil discharge performance of the shoulder space of the internal combustion engine in the stationary state of Examples 1 to 4 is higher.

[0066] <Oil Distribution>

[0067] An example of the flow distribution analysis of the shoulder space used for the above-mentioned oil displacement performance evaluation is shown below. Figure 7 . Figure 7 This is a diagram showing the analytical results of the oil flow distribution in the shoulder space of an internal combustion engine when the piston is stopped at bottom dead center. Figure 7 (A) represents Example 1 (θ1 = θ2 = 55°), Figure 7 (B) represents the existing example (θ1 = θ2 = 90°). Figure 7 In this text, the gradient scale for "Volume Fraction of Oil" indicates the volume fraction of oil dispensed. For example... Figure 7 (A) and Figure 7 As shown in (B), it can be seen that the oil is retained near the inner wall surface of the shoulder space. Compared with the existing examples, the amount of oil retained in Example 1 is less.

[0068] The preferred embodiments of the present invention have been described above, but the various methods described above can be combined as much as possible.

[0069] Explanation of reference numerals in the attached figures

[0070] 1: Main ring;

[0071] 2: Spiral expander;

[0072] 3: Shoulder area;

[0073] 4: Connecting parts;

[0074] 10: Cylinder;

[0075] 20: Piston;

[0076] 30: Annular groove;

[0077] 40: Combined oil ring;

[0078] 100: Internal combustion engine;

[0079] V1: Window opening.

Claims

1. An oil ring, mounted on a piston of an internal combustion engine, said oil ring comprising: The main body ring is formed in a ring shape and has a pair of shoulders arranged axially and a connecting portion connecting the pair of shoulders; and A spiral expander, disposed on the inner circumferential side of the main ring, applies force to the main ring radially outward. A shoulder space is formed on the outer periphery of the main body ring, extending along the circumferential direction of the main body ring. The shoulder space is a groove-shaped space surrounded by the pair of shoulder portions and the connecting portion. A window opening is formed on the bottom surface of the shoulder space, extending radially through the main body ring. The outer peripheral surface of the main ring includes a pair of first groove walls, wherein the pair of first groove walls are axially disposed on both sides of the bottom surface of the shoulder space, the pair of first groove walls are connected to the bottom surface and are formed to expand in diameter as they move away from the bottom surface in the axial direction. In a cross-section including the window opening and orthogonal to the circumferential direction, when the angle between the upper first groove wall of the pair of first groove walls located on the combustion chamber side of the internal combustion engine and the radial direction of the main body ring is defined as θ1, θ1≤60°.

2. The oil ring according to claim 1, wherein, When the angle between the lower first groove wall of the pair of first groove walls located on the crankcase side of the internal combustion engine and the radial direction of the main body ring is defined as θ2, θ2≤60°.

3. The oil ring according to claim 2, wherein, 40°≤θ1≤60° and 40°≤θ2≤60°.

4. The oil ring according to claim 2 or 3, wherein, The outer peripheral surface of the main ring has: an upper second groove wall surface, axially positioned closer to the combustion chamber side than the upper first groove wall surface, the upper second groove wall surface being connected to the upper first groove wall surface and configured to expand in diameter towards the combustion chamber side; and a lower second groove wall surface, axially positioned closer to the crankcase side than the lower first groove wall surface, the lower second groove wall surface being connected to the lower first groove wall surface and configured to expand in diameter towards the crankcase side. In a cross-section including the window opening and orthogonal to the circumferential direction, when the angle between the upper second groove wall and the radial direction is set as θ3, and the angle between the lower second groove wall and the radial direction is set as θ4, θ3 < θ1 and θ4 < θ2.

5. The oil ring according to claim 1 or 2, wherein, In a cross section containing the window opening and orthogonal to the perimeter direction, the bottom surface is connected to each of the pair of first groove walls via one or more curves, multiple consecutive straight lines, or a combination of one or more curves and one or more straight lines.

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