JP7312792B2 - oil ring - Google Patents

Description

The present invention relates to an oil ring with a pair of segments.

2. Description of the Related Art An internal combustion engine mounted on a general automobile employs a configuration in which a combination of a piston ring (an example of a ring-shaped member) including a compression ring (pressure ring) and an oil ring is mounted in a ring groove of a piston. The compression ring has a gas seal function that suppresses the outflow (blow-by) of combustion gas from the combustion chamber side to the crank chamber side by maintaining airtightness, and an oil seal function that suppresses oil rise by scraping off excess oil that was not scraped off by the oil ring. The oil ring scrapes excess engine oil (lubricating oil) adhering to the inner wall surface of the cylinder to the crank side to prevent oil from flowing out (oil rise) to the combustion chamber side, and the lubricating oil film has a function to prevent seizure of the compression ring and piston due to the operation of the internal combustion engine by adjusting the amount of oil so that it is appropriately retained on the inner wall surface of the cylinder.

Here, as the oil ring, a three-piece combination oil ring is widely used, which is a combination of a pair of segments (also called side rails) arranged independently of each other in the axial direction of the oil ring and sliding on the inner wall surface of the cylinder, and a spacer expander provided between the pair of segments and biasing the pair of segments against the inner wall surface of the cylinder. In this regard, Patent Literature 1 discloses an oil ring that reduces oil consumption and friction by differentiating the outer peripheral surface shape between the upper segment provided on the combustion chamber side and the lower segment provided on the crank chamber side in a pair of segments.

WO2019/008780 JP 2019-124288 A

In the case of an oil ring comprising a pair of upper and lower segments, the upper segment located on the combustion chamber side slides under more severe conditions than the lower segment located on the crank chamber side, so the upper segment tends to wear more easily than the lower segment. When the upper surface of the upper segment wears significantly due to long-term use, the gap (side clearance) between the upper groove wall of the ring groove and the upper segment expands, which may deteriorate the oil sealing function of the oil ring.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to provide a technique capable of preventing deterioration of the oil seal function in an oil ring provided with a pair of segments.

In order to solve the above problems, the present invention employs the following configurations. That is, the present invention provides an oil ring to be assembled to a piston in an internal combustion engine, comprising: a pair of segments formed along the circumferential direction of the oil ring using an annular wire rod as a base material and arranged independently of each other in the axial direction of the oil ring; It is an oil ring with higher wear resistance.

According to the present invention, by making the wear resistance of the base material of the upper segment arranged on the combustion chamber side higher than the wear resistance of the base material of the lower segment arranged on the crank chamber side, it is possible to reduce the wear of the upper segment that slides under more severe conditions than the lower segment. As a result, deterioration of the oil seal function can be prevented.

Further, in the present invention, the base material of the upper segment may have higher hardness than the base material of the lower segment.

Further, in the present invention, the base material of the upper segment may have a hardness higher than that of the base material of the lower segment by 30 Hv or more.

Further, in the present invention, the base material of the upper segment may have a higher carbide occupied area ratio on the surface than the base material of the lower segment.

Further, in the present invention, the material of the base material of the upper segment and the material of the base material of the lower segment may be different.

ADVANTAGE OF THE INVENTION According to this invention, in the oil ring provided with a pair of segment, the deterioration of an oil-sealing function can be prevented.

1 is a partial cross-sectional view of an internal combustion engine provided with an oil ring according to an embodiment; FIG. It is a schematic diagram which shows the structure of a reciprocating friction tester. It is a graph which shows a wear amount ratio. It is a graph which shows a wear amount ratio.

Preferred embodiments of the present invention will be described below with reference to the drawings. It should be noted that the configurations described in the following embodiments are not meant to limit the technical scope of the invention only to them unless otherwise specified.

[overall structure]
FIG. 1 is a partial cross-sectional view of an internal combustion engine 100 having an oil ring 40 according to an embodiment. FIG. 1 shows a cross section perpendicular to the circumferential direction of the oil ring 40 . As shown in FIG. 1, in the internal combustion engine 100, a predetermined separation distance is secured between the inner wall surface 10a of the cylinder 10 and the outer peripheral surface 20a of the piston 20 attached to the cylinder 10, thereby forming a piston clearance PC1. A ring groove 30 having a substantially rectangular cross section is formed in the outer peripheral surface 20 a of the piston 20 . The ring groove 30 has an upper wall 301 formed on the combustion chamber side, a lower wall 302 formed on the crank chamber side and facing the upper wall 301, and a connection wall 303 connecting inner peripheral edges of the upper wall 301 and the lower wall 302. An oil ring 40 according to this embodiment is mounted in the ring groove 30 .

The oil ring 40 is a sliding member that is attached to the piston 20 by being fitted in the ring groove 30 and that slides on the inner wall surface 10a of the cylinder 10 as the piston 20 reciprocates. The oil ring 40 is a so-called three-piece combination oil ring, and includes a pair of segments 1 and 2 and a spacer expander 3 as shown in FIG.

Hereinafter, as shown in FIG. 1, the direction (axial direction) along the central axis of the oil ring 40 is defined as the "vertical direction". Further, in the axial direction of the oil ring 40, the combustion chamber side (upper side in FIG. 1) in the internal combustion engine 100 is defined as "upper side", and the opposite side, that is, the crank chamber side (lower side in FIG. 1) is defined as "lower side". In the following description of the oil ring 40, unless otherwise specified, the term "peripheral direction" refers to the circumferential direction of the oil ring 40, the term "radial direction" refers to the radial direction of the oil ring 40, and the term "axial direction" refers to the axial direction of the oil ring 40. Further, in this specification, the state in which the oil ring is attached to the piston attached to the cylinder of the internal combustion engine as shown in FIG. 1 is referred to as the "used state". In this specification, the term “barrel shape” refers to a surface shape that is curved radially outwardly, including the apex, which is the maximum diameter of the piston ring, and includes a “symmetrical barrel shape” in which the apex is located in the center of the axial width of the ring, and an “eccentric barrel shape” in which the apex is located closer to the crank chamber than the center of the axial width of the ring. Further, in this specification, the term “tapered shape” refers to a surface shape that is inclined so as to increase in diameter toward the crank chamber.

The pair of segments 1 and 2 are annularly formed along the circumferential direction of the oil ring 40 and are provided independently from each other in the axial direction. As shown in FIG. 1, the upper segment 1, which is one of the pair of segments 1 and 2, is provided on the upper side (combustion chamber side) of the internal combustion engine 100, and the other, the lower segment 2, is provided on the lower side (crank chamber side) of the internal combustion engine 100.

As shown in FIG. 1, the upper segment 1 includes a base material 1a formed in an annular shape from a segment wire and an outer coating 1b formed on the outer peripheral surface of the base material 1a. The upper segment 1 has an outer peripheral surface 11 , an inner peripheral surface 12 , an upper surface 13 and a lower surface 14 . An outer coating 1b is formed on the outer peripheral surface 11 . The upper surface 13 and the lower surface 14 define the axial width of the upper segment 1 . The upper segment 1 is provided so that the upper surface 13 faces the upper wall 301 of the ring groove 30 in use, and slides on the inner wall surface 10a of the cylinder 10 using the outer peripheral surface 11 as a sliding surface.

As shown in FIG. 1, the lower segment 2 includes a base material 2a formed in an annular shape from a segment wire and an outer coating 2b formed on the outer peripheral surface of the base material 2a. The lower segment 2 has an outer peripheral surface 21 , an inner peripheral surface 22 , an upper surface 23 and a lower surface 24 . An outer coating 2 b is formed on the outer peripheral surface 21 . The upper surface 23 and the lower surface 24 define the width of the lower segment 2 in the axial direction. The lower segment 2 is provided so that the lower surface 24 faces the lower wall 302 of the ring groove 30 in use, and slides on the inner wall surface 10a of the cylinder 10 using the outer peripheral surface 21 as a sliding surface.

As shown in FIG. 1, a spacer expander 3 is provided between a pair of segments 1, 2 and is self-tensioning so that it expands in use. Therefore, the upper segment 1 and the lower segment 2 are urged radially outward by the spacer expander 3 , and the outer peripheral surface 11 of the upper segment 1 and the outer peripheral surface 21 of the lower segment 2 press the inner wall surface 10 a of the cylinder 10 . As a result, an oil sealing function is obtained, and an oil film is formed so that the engine oil present on the inner wall surface 10a of the cylinder 10 has an appropriate thickness. The shape of the spacer expander according to the present invention is not particularly limited.

As shown in FIG. 1, in the oil ring 40 according to this embodiment, the outer peripheral surfaces 11, 21 of the pair of segments 1, 2 are formed into a symmetrical barrel shape with low friction. However, in the present invention, the shape of the pair of segments is not limited to that shown in FIG. For example, the outer peripheral surface of the upper segment located on the upper side of the pair of segments may have an eccentric barrel shape with excellent oil scraping performance, and the outer peripheral surface of the lower segment located on the lower side may have a symmetrical barrel shape with low friction, or both the outer peripheral surfaces may have an eccentric barrel shape. As a result, it is possible to reduce the oil consumption of the internal combustion engine 100 while suppressing an increase in friction. Alternatively, the outer peripheral surface of the upper segment may have a symmetrical barrel shape, and the outer peripheral surface of the lower segment may have an eccentric barrel shape. In addition, the outer peripheral surface 11 of the upper segment 1 may be tapered for excellent oil scraping performance, or both outer peripheral surfaces may be tapered. Alternatively, the outer peripheral surface of the upper segment may be tapered, and the outer peripheral surface of the lower segment may be symmetrical barrel-shaped.

In the oil ring 40 according to this embodiment, the base material 1a of the upper segment 1 and the base material 2a of the lower segment 2 are different. More specifically, the material of the base material 1a and the material of the base material 2a are different from each other. The base material 1a of the upper segment 1 is made of SWRH72A and has a hardness of 450 Hv or more and 550 Hv or less. On the other hand, the base material 2a of the lower segment 2 is made of SUS440B and has a hardness of 300 Hv or more and 420 Hv or less. The hardness of the base material 1a is higher than that of the base material 2a, and the difference therebetween is 30 Hv or more and 150 Hv or less. However, the material of the base material of the segment is not limited to the above. SUS, SWRH and the like are exemplified as the material of the base material of the segment. Also, martensitic stainless steel, silicon chromium steel, aluminum alloy, or the like may be used as the base material. In that case, the difference in hardness between the substrate 1a and the substrate 2a may be 270 Hv or less, 200 Hv or less, or 180 Hv or less.

The outer coating 1b and the outer coating 2b according to this example are formed as DLC coatings with high abrasion resistance. In addition, the outer coating is not limited to the DLC coating, but the nitriding coating, Ni-P
It may be formed as a hard coating including at least one layer of a plating coating, a chromium plating coating, a PVD coating, and a DLC coating. The outer coating 1b of the upper segment 1 and the outer coating 2b of the lower segment 2 may have different configurations. In addition, the outer coating is not an essential configuration in the present invention, and either or both of the upper segment and the lower segment may not have the outer coating. A surface treatment coating containing at least one of a coating film, a resin coating, a chemical conversion coating, an oxidation coating, a nitriding coating, a Ni—P plating coating, a chromium plating coating, a PVD coating, and a DLC coating may be formed on the axial end faces (upper surface 13 and lower surface 14) of the upper segment 1 and the axial end faces (upper surface 23 and lower surface 24) of the lower segment 2. The term "coating film" refers to a film formed by applying paint. A "resin coating" refers to a coating formed of a resin material. Examples of the "coating film" and "resin coating" include a resin coating film made of water-based or oil-based resin paint. "Chemical conversion coating" refers to a coating formed by chemical conversion treatment. Examples of chemical conversion treatments include triiron tetraoxide treatment (blackening), phosphate treatment, and chromate treatment. Examples of phosphate treatment include manganese phosphate treatment, zinc phosphate treatment, and iron phosphate treatment. A "nitriding coating" refers to a coating formed by infiltrating nitrogen into a metal surface by nitriding. “Oxidation treatment film” refers to a film formed by oxidizing a metal surface by oxidation treatment. Examples of oxidation treatment include alumite treatment. “Ni—P plating film” refers to a film formed by electroless Ni—P plating. In addition, the term "chromium-plated film" refers to a film formed by chromium plating. Chrome plating is also called industrial chrome plating. A "PVD (physical vapor deposition) treated film" refers to a film formed by the PVD method. A "DLC (Diamond Like Carbon) treated coating" refers to an amorphous hard carbon coating mainly composed of hydrocarbons and allotropes of carbon.

[About wear resistance]
In general, in the case of an oil ring comprising a pair of upper and lower segments, the upper segment located on the combustion chamber side slides under more severe conditions than the lower segment located on the crank chamber side, so the upper segment tends to wear more easily than the lower segment. Therefore, if the upper surface of the upper segment (the surface on the side of the combustion chamber) wears significantly due to long-term use, the gap (side clearance) between the upper groove wall of the ring groove and the upper segment expands, which reduces the oil seal function of the oil ring, and there is a concern that oil consumption will increase in the high speed range of the internal combustion engine.

On the other hand, in the oil ring 40 according to the present embodiment, the base material 1a and the base material 2a are made of different materials so that the wear resistance of the base material 1a of the upper segment 1 arranged on the combustion chamber side is higher than the wear resistance of the base material 2a of the lower segment 2 arranged on the crank chamber side. Specifically, the material of the base material 1a is SWRH72A, and the material of the base material 2a of the lower segment 2 is SUS440B, so that the hardness of the base material 1a is higher than that of the base material 2a. As a result, wear of the upper segment 1 can be reduced, and deterioration of the oil seal function can be prevented.

The abrasion resistance of the segment base material was evaluated by a reciprocating friction test using a reciprocating friction tester. FIG. 2 is a schematic diagram showing the configuration of the reciprocating friction tester. A reciprocating friction test using a reciprocating friction tester is performed using a pin-on plate type reciprocating friction tester whose outline is shown in FIG. The upper test piece used in the reciprocating motion friction test is a pin which is assumed to be the base material of the segment, and the material of the pin is the same as the wire material for the segment. The pin used for the upper test piece has a diameter of 8 mm, and the tip (sliding surface) of the pin is mirror-finished so as to have a radius of curvature of 18 mm. A plate (equivalent to AC8A material) that resembles a piston is used as the lower test piece.

In the reciprocating friction test, the lower test piece was slid against the upper test piece by stroking the lower test piece with a movable block. Lubricating oil was supplied to the sliding interface between the upper test piece and the lower test piece using a tubing pump or an air dispenser. The test conditions at this time are shown below. <Test conditions>
・Stroke: 50mm
・Load: 50N
・Speed: 200 cycles/min
・Lubricating oil: 0W-20
A pin representing the substrate 1a of the upper segment 1 was used as an upper test piece A, and a pin representing the substrate 2a of the lower segment 2 was used as an upper test piece B. A reciprocating friction test was performed on each pin to compare the amount of wear. The same SWRH72A as the base material 1a was used as the material of the upper test piece A, and the same SUS440B as the base material 2a was used as the material of the upper test piece B. FIG. 3 is a graph showing the results of the reciprocating friction test, showing the wear amount ratio. As a result of the measurement, the wear amount ratio between the upper test piece A and the upper test piece B was, as shown in FIG. 3, upper test piece A:upper test piece B=0.2:1.0. From this, it was found that the base material 1a of the upper segment 1 has higher wear resistance than the base material 2a of the lower segment 2. FIG.

[Action/Effect]
As described above, in the oil ring 40 according to the present embodiment, the materials of the base materials of the pair of segments 1 and 2 are different from each other so that the wear resistance of the base material 1a of the upper segment 1 is higher than the wear resistance of the base material 2a of the lower segment 2. Specifically, the material of the base material 1a is a SWRH material having higher hardness than the SUS material that is the material of the base material 2a. By making the wear resistance of the base material 1a higher than the wear resistance of the base material 2a, the wear of the upper segment 1 can be reduced, and the deterioration of the oil seal function can be prevented. Due to such characteristics, the oil ring 40 according to the embodiment can be suitably used for gasoline engines and engines using low-viscosity oil in which there are many chances of direct contact between the segments and the inner wall of the ring groove. However, the internal combustion engine to which the oil ring according to the present invention is applied is not limited to these. Here, in the oil ring 40 according to the present embodiment, the material of the base material 1a of the upper segment 1 and the material of the base material 2a of the lower segment 2 are different to make the hardness of the base material 1a higher than that of the base material 2a, thereby making the wear resistance of the base material 1a higher than the wear resistance of the base material 2a. The hardness difference between the base material 1a and the base material 2a is not particularly limited, but like the oil ring 40 according to the present embodiment, the hardness of the base material 1a of the upper segment 1 is preferably higher than that of the base material 2a of the lower segment 2 by 30 Hv or more. In addition, in the oil ring 40 according to the present embodiment, the pair of segments 1 and 2 are made different in surface color by making the base materials of the pair of segments 1 and 2 different. Thereby, the identifiability of the pair of segments 1 and 2 can be improved.

[Modification]
Modifications of the embodiment will be described below. In the following description, differences from the above-described oil ring will be mainly described, and detailed descriptions of similar configurations will be omitted.

[Modification 1]
In the oil ring 40 of Modification 1, the material of the base material 1a of the upper segment 1 and the material of the base material 2a of the lower segment 2 are the same. In the case of Modification 1, for example, the hardness can be varied by varying the manner of heat treatment. According to Modification 1 as well, by making the hardness of the base material 1a of the upper segment 1 higher than the hardness of the base material 2a of the lower segment 2, the wear resistance of the upper segment 1 is increased, and deterioration of the oil seal function can be prevented. The difference in hardness between the base material 1a and the base material 2a is not particularly limited, but the hardness of the base material 1a of the upper segment 1 is preferably higher than that of the base material 2a of the lower segment 2 by 30 Hv or more.

[Modification 2]
In the oil ring 40 of Modification 2, the carbide occupied area ratios (carbide deposition rates) on the surfaces of the base materials of the pair of segments 1 and 2 are different from each other so that the wear resistance of the base material 1a of the upper segment 1 is higher than the wear resistance of the base material 2a of the lower segment 2. The carbide occupied area ratio refers to the ratio of the area of carbide occupying the surface of the segment. The carbide occupied area ratio can be obtained, for example, by acquiring an image of the base material surface with a metallurgical microscope after etching treatment with a marble reagent, binarizing the acquired image, and calculating the area ratio of the white portion. However, the method for calculating the carbide occupied area ratio is not limited to this.

In Modified Example 2, the base material 1a of the upper segment 1 and the base material 2a of the lower segment 2 are made of stainless steel with different carbon and chromium contents. More specifically, the base material 1a of the upper segment 1 is made of 17chromium SUS material, which is martensitic stainless steel containing a large amount of chromium, and the base material 2a of the lower segment 2 is made of 13chromium SUS material, which is stainless steel with a slightly low chromium content. However, the material of the segment according to the present invention is not limited to this. In modification 2, the carbide occupied area ratio of the base material 1a of the upper segment 1 is 7.2% to 15.3% by the above calculation method, and the carbide occupied area ratio of the base material 2a of the lower segment 2 is 0.2% to 2.0%. That is, in Modification 2, the substrate 1a of the upper segment 1 has a higher carbide occupied area ratio than the substrate 2a of the lower segment 2, and the difference is 5.2% or more.

In addition, in Modification 2, the material of the base material 1a of the upper segment 1 and the material of the base material 2a of the lower segment 2 may be the same. When the base material 1a and the base material 2a are made of the same material, the size of the carbides can be changed by, for example, different heat treatment methods, and the carbide occupation area ratios can be varied. In addition, the upper segment 1 and the lower segment 2 may be made of different base material materials to make the carbide occupied area ratios different from each other.

As described above, in Modification 2, the base materials of the pair of segments 1 and 2 are different from each other such that the carbide occupied area ratio of the base material 1a of the upper segment 1 is higher than the carbide occupied area ratio of the base material 2a of the lower segment 2. By making the carbide occupied area ratio of the base material 1a of the upper segment 1 higher than the carbide occupied area ratio of the base material 2a of the lower segment 2, the wear resistance of the upper segment 1 is improved, and deterioration of the oil seal function can be prevented. In addition, the difference in the carbide occupied area ratio between the base material 1a and the base material 2a is not particularly limited. In Modification 2, the surface colors of the pair of segments 1 and 2 are made different from each other by making the carbide occupied area ratios of the base material surfaces of the pair of segments 1 and 2 different. Thereby, the identifiability of the pair of segments 1 and 2 can be improved.

The wear resistance of the base material of the segment according to Modification 2 was evaluated by the reciprocating friction test described above. A reciprocating friction test was performed on each of the pins representing the base material 1a of the upper segment 1 as an upper test piece C and the pin representing the base material 2a of the lower segment 2 as an upper test piece D to compare the amount of wear. The material of the upper test piece C was the same 17 chromium SUS material as the base material 1a, and the material of the upper test piece D was the same 13 chromium SUS material as the base material 2a. In addition, the carbide occupied area ratio of the upper test piece C was set to 7.2% to 15.3% by the above calculation method, and the carbide occupied area ratio of the upper test piece D was set to 0.2% to 2.0%, so that the difference in the carbide occupied area ratio was 5.2% or more. FIG. 4 is a graph showing the results of the reciprocating friction test, showing the wear amount ratio. As shown in FIG. 4, the upper test piece C of the upper segment 1 having a larger carbide occupied area ratio had higher wear resistance than the upper test piece D of the lower segment 2 .

<Others>
Although the preferred embodiments of the present invention have been described above, the various forms described above can be combined as much as possible.

100: Internal combustion engine 10: Cylinder 20: Piston 30: Ring groove 40: Oil ring 1: Upper segment 2: Lower segment 3: Spacer expander 1a, 2a: Base material

Claims (4)

An oil ring assembled to a piston in an internal combustion engine,
A pair of segments formed along the circumferential direction of the oil ring using an annular wire as a base material and arranged independently of each other in the axial direction of the oil ring; and a spacer expander arranged between the pair of segments.
In order to reduce wear of the upper segment of the pair of segments located on the combustion chamber side in the internal combustion engine, the material of the base material of the upper segment and the material of the base material of the lower segment are different so that the base material of the upper segment has higher wear resistance than the base material of the lower segment of the pair of segments located on the crank chamber side in the internal combustion engine, and the surface colors of the pair of segments are different from each other.
oil ring. the base material of the upper segment is harder than the base material of the lower segment;
The oil ring according to claim 1. The base material of the upper segment has a hardness higher than that of the base material of the lower segment by 30 Hv or more,
The oil ring according to claim 1 or 2. The base material of the upper segment has a higher carbide occupied area ratio on the surface than the base material of the lower segment.
The oil ring according to claim 1.

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