阅读说明：本技术 用于具有十字头的大型二冲程涡轮增压单流扫气式内燃发动机的活塞中的环组件中的活塞环 (Piston ring for use in a ring assembly in a piston of a large two-stroke turbocharged uniflow-scavenged internal combustion engine with crosshead ) 是由 耶斯佩尔·韦斯·福格 于 2021-06-11 设计创作，主要内容包括：一种在活塞环组件中使用的活塞环。活塞环包括：环本体,该环本体具有轴向距离为环高的第一侧面和第二侧面、在整个环高上轴向地延伸的外周向面、内周向面、以及位于环形分隔件处的第一端部部分和第二端部部分。第一过渡部,该第一过渡部位于外周向面与第一侧面之间；第二过渡部,该第二过渡部位于外周向面与第二侧面之间。外周向面的轴向范围的中间部分,该中间部分具有第一硬度。外周向面的轴向范围的第一外周部分,该第一外周部分从中间部分延伸至第一过渡部,该第一外周部分具有第二硬度。外周向面的轴向范围的第二外周部分,该第二外周部分从中间部分延伸至第二过渡部,该第二外周部分具有第二硬度,并且第一硬度大于第二硬度。(A piston ring for use in a piston ring assembly. The piston ring includes: a ring body having first and second sides axially spaced by a ring height, an outer circumferential face extending axially over the ring height, an inner circumferential face, and first and second end portions at an annular divider. A first transition portion between the outer circumferential surface and the first side surface; a second transition portion located between the outer circumferential surface and the second side surface. A mid-portion of the axial extent of the outer circumferential surface, the mid-portion having a first hardness. A first outer peripheral portion of the axial extent of the outer peripheral face, the first outer peripheral portion extending from the intermediate portion to the first transition, the first outer peripheral portion having a second hardness. A second outer peripheral portion of the axial extent of the outer peripheral surface, the second outer peripheral portion extending from the intermediate portion to a second transition, the second outer peripheral portion having a second hardness, and the first hardness being greater than the second hardness.)

1. A piston ring (34, 36) for use in a piston ring assembly located in an annular ring groove (33) on a side wall of a piston (10) of a large two-stroke turbocharged uniflow scavenged internal combustion engine with crosshead for sealing against pressure in a combustion chamber (32), the piston ring (34, 36) comprising:

a ring body (50) having:

a first side (46) and a second side (47), the first side being axially spaced from the second side by a ring height (Hr),

an outer circumferential surface (41) extending axially over the entire ring height (Hr),

an inner circumferential surface (42) extending axially over the entire ring height (Hr), and

a first end portion (38) and a second end portion (39) at an annular partition allowing expansion and contraction of the piston ring (34, 36),

a first transition between the outer circumferential face (41) and the first side face (46), and which is rounded,

a second transition between the outer circumferential face (41) and the second lateral face (47), and which is rounded,

a middle portion of an axial extent of the outer circumferential surface (41), the middle portion having a first hardness,

a first outer peripheral portion of the axial extent of the outer peripheral face (41), the first outer peripheral portion extending from the intermediate portion to the first transition, the first outer peripheral portion having a second hardness,

a second outer peripheral portion of the axial extent of the outer peripheral surface (41) extending from the intermediate portion to the second transition, the second outer peripheral portion having the second hardness,

the first hardness is greater than the second hardness,

wherein the first peripheral portion extends axially over the entire first height (H1) and is formed by the material of the ring body (50), and the second peripheral portion extends axially over the entire second height (H2) and is formed by the material of the ring body (50).

2. The piston ring (34, 36) of claim 1 wherein the first hardness is a vickers hardness between 350HV and 550 HV.

3. The piston ring (34, 36) according to claim 1 or 2, wherein the second hardness is a brinell hardness of 200HB to 300 HB.

4. The piston ring (34, 36) as set forth in any one of claims 1-3 wherein said outer circumferential surface (41) is radially convex.

5. The piston ring (34, 36) according to claim 4, wherein the outer circumferential surface (41) projects radially with a first radius (R1) that is 0.5 to 1.5 times a diameter of the piston ring (34, 36).

6. The piston ring (34, 36) according to any one of claims 1-5, wherein the intermediate portion extends over an entire hard height (Hc), and wherein the hard height (Hc) is between 50% and 75% of the ring height (Hr).

7. The piston ring (34, 36) according to any one of claims 1-6, wherein the intermediate portion is formed by a hard coating (52).

8. The piston ring (34, 36) according to claim 7, wherein the hard coating (52) is applied to the ring body (50) by spraying.

9. The piston ring (34, 36) according to claim 7 or 8, wherein a maximum radial thickness (CT) of the hard coating is between 1.5% and 4% of the ring height (Hr) of the piston ring (34, 36).

10. The piston ring (34, 36) according to any one of claims 1-9, wherein the first side surface (46) and/or the second side surface (47) is at least partially chromium plated.

11. The piston ring (34, 36) according to any one of claims 1 to 10, wherein the piston ring (34, 36) has an outer diameter in a range between 400mm and 1000 mm.

12. The piston ring (34, 36) according to any one of claims 1-11, wherein the ring height (Hr) is between 1.4 and 2.5 times the ring outer diameter.

13. The piston ring (34, 36) according to any one of claims 1-12, wherein the first hardness is at least 50 times the second hardness when measured by the vickers hardness test.

Technical Field

The present disclosure relates to piston rings for use in ring assemblies in ring grooves in pistons of large two-stroke turbocharged uniflow scavenged internal combustion engines with crossheads, in particular piston rings provided with a hard coating on the outer circumferential surface.

Background

Large two-stroke turbocharged uniflow scavenging engines with crossheads are commonly used in the propulsion system of ships or as the main power in power plants. Typically, these engines operate using heavy fuel oil or marine diesel, or using gaseous fuels such as natural gas or petroleum gas.

The engine piston is provided with a ring assembly that seals against combustion pressure to prevent combustion gases from penetrating into the scavenge air space. In addition, the piston ring ensures even distribution of cylinder oil to form a lubricating film on the inside of the cylinder liner. The piston rings in the ring assembly seal the piston reciprocating at a speed of about 10m/sec for compressed air and combustion gases at a pressure of about 250bar and a temperature of about 400 ℃, and the piston rings use only a few drops of cylinder oil as lubrication per engine revolution, and the expected service life of all piston rings is thousands of hours. Therefore, the main requirements for piston rings are higher wear and corrosion resistance and less drop in elasticity at high temperatures.

Due to the erosive nature of the combustion gases produced when working with heavy fuel oil, the inner wall of the cylinder liner is lubricated with a special cylinder lubricating oil, which protects the inner wall of the cylinder liner from the erosive components of the combustion gases. The provision of cylinder lubrication and the size of the components involved, for example a piston with a diameter between 25cm and 108cm, is why the ring assemblies of large two-stroke turbocharged uniflow scavenged engines differ from those of small four-stroke internal combustion engines. One major difference is the fact that: the ring assemblies of large uniflow scavenged internal combustion engines require distribution of cylinder oil supplied through the cylinder liner, while the ring assemblies of small four-stroke internal combustion engines need to ensure that the lubricating oil is scraped off the cylinder liner during the piston stroke towards Bottom Dead Center (BDC) to avoid the final entry of lubricating oil into the combustion chamber, resulting in excessive lubricating oil consumption and undesirable combustion products from the lubricating oil in the combustion chamber. Thus, the piston ring for a four-stroke internal combustion engine has sharp edges/transitions between the outer circumferential surface and the side facing the crankshaft to ensure a scraping effect. In contrast, the transition between the outer circumferential surface of the piston ring and the side facing the crankshaft for large two-stroke turbocharged uniflow scavenged internal combustion engines needs to be a rounded edge/transition to avoid scraping cylinder oil from the inner surface of the cylinder liner during the piston stroke towards bottom dead center. Also for the same reason of distributing the cylinder oil over the cylinder liner, the transition between the outer circumferential surfaces in the side facing the combustion chamber also needs to be rounded, thereby protecting the cylinder liner. In both cases, the rounded transition has a funnel effect of the cylinder oil, i.e. opposite to the scraping effect.

The ring assembly of a large two-stroke turbocharged uniflow scavenged internal combustion engine with crosshead typically comprises three or four piston rings. In particular, the top piston ring may be a controlled pressure relief ring (CPR ring), i.e. the associated piston ring or a groove in the associated piston is provided with a pressure relief groove which allows a well-defined and controlled flow of hot gas from the combustion chamber to the underside of the top piston ring, thereby reducing the pressure drop over the top ring and distributing the load over the rings in the ring assembly. Typically, the lowermost piston ring is not a CPR ring, i.e. is airtight. Furthermore, in some large two-stroke turbocharged uniflow scavenged internal combustion engines, all piston rings including the top ring are airtight, leaving the lower piston ring more or less in a passive state.

The outer peripheral side of the piston ring is coated with a hard coating which may extend the life of the piston ring and is intended to reduce galling of the cylinder liner. However, the ever increasing pressure in the combustion chamber and the new types of fuel, such as gaseous fuel, e.g. natural gas, put higher demands on the ability to resist scuffing.

Disclosure of Invention

It is an object of the present disclosure to provide a piston ring which overcomes or at least reduces the above mentioned problems.

The foregoing and other objects are achieved by the features of the independent claims. Further embodiments are evident from the dependent claims, the description and the drawings.

According to a first aspect, there is provided a piston ring for use in a piston ring assembly located in an annular ring groove on a side wall of a piston of a large two-stroke turbocharged uniflow scavenged internal combustion engine having a crosshead for sealing against pressure in a combustion chamber, the piston ring comprising:

a ring body having:

a first side and a second side, the first side being at an axial distance of the ring height from the second side,

an outer circumferential surface extending axially over the entire ring height,

an inner circumferential surface extending axially over the entire ring height, an

A first end portion and a second end portion, the first end portion and the second end portion being located at an annular partition that allows for expansion and contraction of a piston ring,

a first transition between the outer circumferential surface and the first side surface, and the first transition being rounded,

a second transition between the outer circumferential face and the second side face, the second transition being rounded,

a middle portion of an axial extent of the outer circumferential surface, the middle portion having a first hardness,

a first outer peripheral portion of the axial extent of the outer peripheral face, the first outer peripheral portion extending from the intermediate portion to a first transition, the first outer peripheral portion having a second hardness,

a second outer peripheral portion of the axial extent of the outer peripheral surface, the second outer peripheral portion extending from the intermediate portion to a second transition portion, the second transition portion having a second hardness,

the first hardness is greater than the second hardness,

wherein the first outer peripheral portion extends axially over the entire first height and is formed by the material of the ring body, and the second outer peripheral portion extends axially over the entire second height and is formed by the material of the ring body.

The inventors have realized that different degrees of ring distortion caused by different pressures during the load cycle and by different engine load levels (mean effective pressure) are a major factor in the risk of galling. The inventors have come to the insight that a hard coating over the entire height of the ring (the entire outer circumferential surface) has the disadvantage that the desired barrel shape of the outer circumferential surface cannot be maintained nor achieved by wear of the outer circumferential surface. The transition between the outer circumferential surface and the flank is thus sharp due to wear and, at higher degrees of torsion, for example due to high engine load and correspondingly high pressure in the combustion chamber, will cause the piston ring to scrape the cylinder oil film from the inner surface of the cylinder liner. Such scraping and subsequent removal of the cylinder oil film from the inner surface of the cylinder liner may increase the risk of scuffing.

The inventor also finds that: it is advantageous to ensure that the surface area of the outer circumferential outer surface close to the transition towards the side is lower in hardness than the middle area of the outer circumferential outer surface, so that this lower hardness material will be removed by faster (frictional) wear than the part of the middle surface area of the outer circumferential outer surface, and the resulting receding transition forms together with the inner surface of the cylinder liner a wedge-shaped recess as a funnel for the cylinder oil film on the inside of the cylinder liner. The intermediate surface areas between the soft areas are hard-coated to ensure the durability of the piston ring and to facilitate the formation of the wedge-shaped grooves described above by hard-coated areas that are not as easily worn as less hard surface areas of the outer circumferential surface close to the transition towards the side surface. The term "intermediate" in this context is "intermediate" as seen in the axial direction of the piston ring.

In a possible embodiment of the first aspect, the material forming the surface close to the sideward transition is the same material as the material of the main ring body.

In a possible embodiment of the first aspect, the material forming the surface close to the sideward transition is different from the material of the main ring body.

According to a possible embodiment of the first aspect, the first hardness is a vickers hardness between 350HV and 550 HV.

According to a possible embodiment of the first aspect, the second hardness is a brinell hardness of 200HB to 300 HB.

According to a possible embodiment of the first aspect, the outer circumferential surface is radially convex.

According to a possible embodiment of the first aspect, the outer circumferential surface projects radially with a first radius which is 0.5 to 1.5 times the diameter of the piston ring.

According to a possible embodiment of the first aspect, the intermediate portion extends over the entire hard height, and wherein the hard height is between 50% and 75% of the ring height.

According to a possible embodiment of the first aspect, the intermediate part is formed by a hard coating.

According to a possible embodiment of the first aspect, the hard coating is applied to the ring body by spraying.

According to a possible embodiment of the first aspect, the maximum radial thickness of the hard coating is between 1.5% and 4% of the ring height.

According to a possible embodiment of the first aspect, the hardness of the first and second outer peripheral portions relative to the hardness of the intermediate portion is selected such that the surfaces of the first and second outer peripheral portions become receded relative to the surface of the intermediate portion due to wear during use.

According to a possible embodiment of the first aspect, during use, the first and second peripheral portions become retracted with respect to the imaginary arc-shaped extension of the radially convex surface of the intermediate portion, the first and second peripheral portions preferably being retracted with respect to the imaginary arc-shaped extension by a distance equal to 0.045% to 2% of the ring height.

According to a possible embodiment of the first aspect, the surfaces of the retracted first and second outer circumferential portions form together with the inner wall of the cylinder liner an oil wedge guiding the cylinder oil towards the intermediate portion.

According to a possible embodiment of the first aspect, the first side and/or the second side is at least partially chromium-plated.

According to a possible embodiment of the first aspect, the piston ring has an outer diameter in the range between 300mm and 1000 mm.

According to a possible embodiment of the first aspect, the ring height is between 1.4% and 2.5% of the ring outer diameter.

According to a possible embodiment of the first aspect, the first hardness is at least 1.4 times greater than the second hardness, when measured by the vickers/brinell hardness test.

According to a possible embodiment of the first aspect, the intermediate portion forms a complete outer circumferential surface together with the first and second outer circumferential portions.

According to a possible embodiment of the first aspect, the first hardness is substantially greater than the second hardness, preferably as measured by the vickers hardness test.

According to a possible embodiment of the first aspect, the ring body is made of vermicular cast iron.

These and other aspects will be apparent from the embodiments described below.

Drawings

In the following detailed part of the disclosure, aspects, embodiments and implementations will be explained in more detail with reference to example embodiments shown in the accompanying drawings, in which:

figure 1 is a perspective elevation view of a large two-stroke internal combustion engine according to an example embodiment,

figure 2 is a perspective side view of the large two-stroke internal combustion engine of figure 1,

figure 3 is a schematic view of a large two-stroke internal combustion engine according to figure 1,

fig. 4 is a section through a section of a piston fitted in a cylinder liner, showing a ring assembly with four piston rings,

fig. 5 is a cross-section of a piston fitted in a cylinder liner on a larger scale, showing a ring assembly with four piston rings,

figure 6 is a plan view of the top piston ring in a loaded condition,

figure 7 is a side view of the top piston ring of figure 6,

figures 8 and 9 show a side view and a top view respectively of a section of the top piston ring of figure 6 in the area around the pressure relief groove,

figure 10 is a plan view of a piston ring (not the top ring) in a loaded condition,

figure 11 is a side view of the piston ring of figure 10,

figure 12 is a cross-sectional view of an unused piston ring (top or conventional) made in accordance with an embodiment,

FIG. 13 is a cross-sectional view (before wearing) of an unused piston ring made in accordance with an embodiment, an

Figure 14 is a cross-sectional view of the piston ring used in figure 13 (worn).

Detailed Description

In the following detailed description, the internal combustion engine will be described with reference to a large two-stroke, low-speed turbocharged internal combustion engine with a crosshead in an example embodiment.

Fig. 1 and 2 are perspective elevation views of a large, low-speed turbocharged two-stroke internal combustion engine with a crankshaft 8 and a crosshead 9. The engine may be operated with a diesel cycle (compression ignition) or an otto cycle (timed ignition).

Fig. 3 shows a schematic view of the large slow turbocharged two-stroke internal combustion engine of fig. 1 and 2 and its intake and exhaust system. In this example embodiment, the engine has six cylinders arranged in a row. Large low speed turbocharged two-stroke diesel engines typically have between four and fourteen cylinders in a row carried by a cylinder frame 23 carried by the engine frame 11. The engine may for example be used as a main engine in a ship or as a stationary engine for operating a generator in a power plant. For example, the total output of the engine may range from 1000kW to 110000 kW.

In this example embodiment the engine is a two-stroke, single-flow, compression ignition engine with a scavenging port 18 at the lower region of the cylinder liner 1 and a central exhaust valve 4 at the top of the cylinder liner 1. The scavenging is transferred from the scavenging receiver 2 to the scavenging port 18 of the individual cylinder 1. The piston 10 in the cylinder liner 1 compresses the scavenging gas and fuel is injected into the combustion chamber 32 through the fuel injection valve 24 in the cylinder cover 22, with consequent combustion and exhaust gas generation.

When the exhaust valve 4 is open, the exhaust gases flow through the exhaust duct associated with the cylinder 1 into the exhaust gas receiver 3 and onwards through the first exhaust duct 19 to the turbine 6 of the turbocharger 5, from which they flow through the second exhaust duct via the economizer 20 to the outlet 21 and into the atmosphere. The turbine 6 drives a compressor 7 by means of a shaft, which is supplied with fresh air via an air inlet 12. The compressor 7 delivers pressurized scavenging air to a scavenging conduit 13 leading to the scavenging air receiver 2. The scavenging air in the conduit 13 is passed through an intercooler 14 for cooling the scavenging air.

When the compressor 7 of the turbocharger 5 is not able to deliver sufficient pressure for the scavenging air receiver 2, i.e. at low load or part load conditions of the engine, the cooled scavenging air is passed through an auxiliary blower 16 driven by an electric motor 17, which pressurizes the scavenging air flow. At higher engine loads, the compressor 7 of the turbocharger delivers sufficient compressed scavenging air, and then the auxiliary blower 16 is bypassed via the check valve 15.

The engine operates on a given fuel, such as: marine diesel, heavy fuel oil, (liquefied) natural gas, biogas, methanol, ethanol, ethane, landfill gas, methane, ethylene or (liquefied) petroleum gas (non-exhaustive list), the given fuel being supplied by a fuel supply system.

Fig. 4 and 5 show a piston 10 whose cylindrical side wall is provided with a plurality of ring grooves 33, of which a top groove 33 receives a top piston ring 34 and a lower piston ring 36 has been inserted into the lower groove 33. The top piston ring 34 and the lower piston ring 36 of a single piston 10 together form a so-called ring assembly of cooperating piston rings 34, 36. The piston 10 is of a large two-stroke turbocharged uniflow scavenged engine with crosshead and the piston 10 together with the cylinder liner 1 and the cylinder cover 22 define a combustion chamber 32 (it is noted that fig. 5 does not show an exhaust valve in the cylinder cover 22, but it will be understood that an exhaust valve will be present in the cylinder cover 22).

The piston rings 34, 36 prevent the gas pressure in the combustion chamber 32 from penetrating into the space below the piston 1.

Fig. 6 and 7 show an exemplary embodiment of a top piston ring 34 having an annular divider that substantially prevents gas flow through the divider. The top piston ring 34 has a split ring body 50 that makes it possible to partially enlarge the ring diameter at the mounting in the ring groove 33, to partially allow the two joint end portions 38, 39 of the top piston ring 34 to pull away from each other during use as the top piston ring 34 becomes worn.

The ring body 50 has first and second side faces 46, 47 axially spaced by a ring height Hr, an outer circumferential face 41 axially extending over the entire ring height Hr, and an inner circumferential face 42 axially extending over the entire ring height Hr. The first side surface 46 is intended to be facing towards the combustion chamber 32 and the second side surface 47 is intended to be facing away from the combustion chamber 32.

As shown in fig. 8 and 9, the outer circumferential face 41 of the top piston ring 34 has in an embodiment a relief groove 45 extending obliquely at an angle to the plane of the top piston ring 34. The pressure relief grooves 45 ensure that the controlled gas flows from the top side to the underside of the piston top ring 34 and thus a uniform and well-defined gas flows through the individual grooves 45.

The outer edge of the ring groove 33 is indicated by a dashed line 40. The outer circumferential surface 41 of the top piston ring 34 is in contact with the inner surface of the cylinder liner 1.

In another embodiment, the top piston ring 34 is not provided with a pressure relief groove, and the pressure relief function is provided by a groove on the piston, for example (not shown). It is also possible to operate the top piston ring 34 without controlled leakage, i.e. a gas tight top piston ring 34 which handles substantially the entire pressure difference over the piston 10.

Fig. 10 and 11 show an example embodiment of a lower piston ring 36 having an annular partition formed by joined end portions 38, 39. The lower piston ring 36 is substantially identical to the top piston ring 34, except for the presence of relief grooves in the internal combustion engine 34 and sometimes a different choice of material for the ring body 50, as will be explained in further detail below.

Fig. 12 shows a cross-sectional detail of a (top or lower) piston ring 34, 36 of an unused (new factory) piston ring 34, 36. Fig. 13 shows a similar cross section of the piston rings 34, 36, wherein the convexity of the outer circumferential surface 41 is substantially exaggerated for illustrative purposes.

The outer circumferential surface 41 preferably has a symmetrical convexly extending surface profile (when not in use). In an embodiment, the curve radius R1 describing the convexity of the outer peripheral surface 41 of the unused piston ring 34, 36 is 0.5 to 1.5 times the outer diameter of the piston ring. Thus, the outer circumferential surface 41 projects radially, having a first radius R1. For practical reasons of fitting the arrows into the available area, the arrows in fig. 12 showing radius R1 are shown in a zigzag pattern to indicate that the actual length of the arrows is greater than that shown in fig. 12.

In an embodiment, a middle portion of the outer circumferential surface 41 is provided with a hard coating 52. Thus, the surface of the hard coating 52 is convex from the factory, having a radius R1. The thickness of the hard coating is indicated by arrow CT. The range of the height of the hard coating is indicated by arrow Hc.

From the factory, the transitions between the first side surface 46 and the outer circumferential surface 41 and between the second side surface 47 and the outer circumferential surface 41 are rounded, the transitions having a diameter R2, and R2 preferably corresponds to about 0.01 to 0.1 times the ring height Hr.

A middle portion of the axial extent of the outer circumferential surface 41 has a first hardness (as measured, for example, by vickers hardness test).

A first outer peripheral portion of the axial extent of the outer peripheral surface 41, extending from the intermediate portion to the first transition portion, has a second hardness (measured, for example, by the vickers hardness test). The first peripheral portion extends over the entire height H1.

A second peripheral portion of the axial extent of the peripheral surface 41, extending from the intermediate portion to the second transition portion, has a second hardness (measured, for example, by the vickers hardness test). The second peripheral portion extends over the entire height H2. The lengths of the first height H1 and the second height H2 do not have to be the same. The surfaces of the first and second outer peripheral portions preferably have the same hardness, but this is not necessarily the case as long as the hardness of both the first and second outer peripheries is lower than the hardness of the surface of the intermediate portion.

In an embodiment, an intermediate portion of the outer circumferential surface 41 is formed by a hard coating 52, such as a thermal spray coating, a plating coating, or other suitable hard coating. In another embodiment, the intermediate portion of the outer circumferential surface is provided with a desired hardness by a surface treatment.

The first hardness is greater than the second hardness such that the intermediate portion wears slower than the outer peripheral portion. Thus, it is ensured that the outer circumferential surface 41 assumes a shape as shown in fig. 14 after wear (fig. 14 will be described in further detail below).

In an embodiment, the first hardness is between 350HV and 550 HV. In an embodiment, the second hardness is a brinell hardness of 200HB to 300 HB.

The middle portion extends over the entire hard height Hc. In an embodiment, the hard height Hc is between 50% and 75% of the ring height Hr.

In an embodiment, the maximum radial thickness CT of the hard coating 52 is between 1.5% and 4% of the ring height Hr.

In an embodiment, the first outer peripheral portion extends axially over height H1 and is formed from the material of ring body 50, and the second outer peripheral portion extends axially over height H2 and is formed from the material of ring body 50.

In an embodiment, the hardness of the first and second outer peripheral portions relative to the hardness of the intermediate portion is selected such that the surfaces of the first and second outer peripheral portions become receded relative to the surface of the intermediate portion due to wear during use.

In an embodiment, the surfaces of the retracted first and second outer circumferential portions and the inner wall of the cylinder liner together form an oil wedge guiding the cylinder oil towards the intermediate portion.

In an embodiment, first side 46 and/or second side 47 are at least partially chrome plated.

In an embodiment, the outer diameter of the piston rings 34, 36 is in a range between 300mm and 1000 mm.

In an embodiment, the ring height Hr is between 1.4% and 2.5% of the ring outer diameter.

In an embodiment, the first hardness is at least 1.4 times the second hardness when passing the vickers/brinell hardness test.

In an embodiment, the outer circumferential surface 41 has an asymmetric convex extending surface profile.

Fig. 14 shows the piston rings 34, 36 after a period of use. During use, the first and second outer peripheral portions become retracted with respect to an imaginary arc-shaped extension (indicated by the dashed line in fig. 14) of the radially convex surface of the intermediate portion, the first and second outer peripheral portions preferably being retracted with respect to the imaginary arc-shaped extension by a distance OR (oil groove), in an embodiment equal to 0.045% to 2% of the ring height Hr.

At the transition between the intermediate portion and the first and second peripheral portions, the intermediate portion has an edge covering the height OW (oil wedge) which is arranged at an angle to the rest of the intermediate portion, thereby forming a relatively sharp transition from the intermediate portion to the first and second peripheral portions. The edges of the first and second portions and the intermediate portion, which are set back, together form an ideal profile for guiding the cylinder oil towards the main section of the intermediate portion, thereby ensuring that the cylinder oil does not scrape or otherwise distort the ring.

Thus, the surfaces of the first and second outer circumferential portions are softer than the surface of the intermediate portion, resulting in the piston rings 34, 36 reaching a desired shape to reduce the risk of scraping and thereby the risk of scuffing of the cylinder liner 1.

In an embodiment, the material hardness of the surface of the ring body 50 at the peripheral portion is 10> HVB/HVA >1.4

In an embodiment, the material hardness of the surface of the intermediate portion is 500> HVB > 5000.

In an embodiment, the worn dimensions associated with Hr are:

2％>OW>7％

0.045％>OR>2％

1.5％>CT>4％

50％>Hc>80％

typically, all of the piston rings 34, 36 in the ring assembly are manufactured to be slightly non-circular. This non-circular form is required so that the piston ring, when inserted into the circular cylinder liner 1, exerts a precisely defined pressure in the circumferential direction of the entire ring. This pressure can in principle be distributed uniformly in the circumferential direction; however, for the top piston 34 used in the piston 10 of a large two-stroke turbocharged uniflow-scavenged internal combustion engine, it is generally intended to use a negative oval (negative oval) form. This means that the pressure in the region of the partition is lower than in the remaining circumferential direction, which avoids an increase in pressure on the partition during operation of the engine.

In an embodiment, the body of the top piston ring 34 is a temper hardened casting including vermicular graphite (Vermicular graphite) for use in the first groove, while in the lower groove the body of the piston ring is an alloyed gray cast iron, e.g., vermicular cast iron. In another embodiment, the bodies of all piston rings of the ring assembly are of vermicular cast iron.

In an embodiment, a ring assembly comprises:

-a top ring: the asymmetric barrel-shaped, double-coated, high-profile portion of the side is coated with chromium,

-a second ring: asymmetric barrel-shaped, running-in coated, side coated chromium,

-a third ring: asymmetric barrel-shaped, break-in coated, and

-a fourth ring: asymmetric barrel-shaped, double coated.

In another embodiment, a ring assembly comprises:

-a top ring: the side surface of the asymmetric barrel-shaped ceramic is coated with chromium ceramics,

-a lower ring: an asymmetric barrel-shaped, chromium-coated ceramic.

Various aspects and embodiments have been described in connection with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed subject matter, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the article "a" or "an" does not exclude a plurality.

Reference signs used in the claims shall not be construed as limiting the scope. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and should be considered a portion of the entire written description of this disclosure.