Piston ring

Abstract

The invention relates to a piston ring. A piston ring (100) for a piston of a reciprocating internal combustion engine comprises a ring section (1) and a lock section (2). The lock segment (2) comprises a circumferential parting line (7) at a first axial parting line distance (PaT) from the top surface (T) of the piston ring (100) and at a second axial parting line distance (PaB) from the bottom surface (B) of the piston ring (100). Furthermore, the piston ring (100) comprises an arcuate profile (10) having a circumferential pivot line (8) at a first axial pivot line distance (PiT) from the top surface (T) and at a second axial pivot line distance (PiB) from the bottom surface. The axial distance (9) between the circumferential parting line and the pivot line is less than 20% of the axial width of the piston ring. The arcuate profile (10) may include a most protruding, axially extending flat section (14). The flat section (14) comprises a circumferential parting line (7).

Description

TECHNICAL FIELD

[0001] The present invention relates to a piston ring for a piston of a reciprocating internal combustion engine, to a piston having such a piston ring, to a reciprocating internal combustion engine having such a piston, and to a method for manufacturing a piston ring. BACKGROUND

[0002] The invention preferably relates to an internal combustion engine, such as a large marine or ship engine or a stationary engine, the cylinder of which has an inner diameter of at least 200 mm. The engine is preferably a two-stroke engine or a two-stroke crosshead engine. The engine can be a diesel or gas engine, a dual-fuel or a multi-fuel engine. The combustion of liquid and / or gaseous fuel in such an engine as well as compression ignition or forced ignition is possible.

[0003] The internal combustion engine can be a longitudinal scavenging two-stroke engine.

[0004] The term "internal combustion engine" also refers to large engines which can not only be operated in Diesel mode (Diesel mode is characterized by compression ignition of the fuel), but also in Otto mode (Otto mode is characterized by forced ignition of the fuel) or in a mixture of both modes. Furthermore, the term "internal combustion engine" includes, inter alia, dual-fuel engines and large engines in which compression ignition of the fuel is used for forced ignition of another fuel. Forced ignition can be achieved, for example, by using a pre-chamber, a spark plug and / or a pilot fuel. The engine speed is preferably below 800 rpm (in particular for four-stroke engines), more preferably below 200 rpm (in particular for two-stroke engines), which is a hallmark of low-speed engines.

[0005] The fuel can be diesel, marine diesel, heavy fuel oil, emulsions, suspensions, methanol or ethanol, but also other fluids such as liquefied natural gas (LNG), liquefied petroleum gas (LPG), natural gas (NG), petroleum gas (PG) and the like.

[0006] Other possible fuels that can be added on demand are: liquefied biogas (LBG), biofuels (e.g. oil made from algae or seaweed), ammonia, hydrogen, synthetic fuels from CO2(e.g. made by e-gas or e-liquid).

[0007] Large ships, in particular vessels for the transport of goods, are usually powered by internal combustion engines, in particular diesel and / or gas engines, mainly two-stroke crosshead engines.

[0008] The piston of a reciprocating piston internal combustion engine, in particular of a dual-fuel or Otto cycle type, is provided with a piston ring which is seated in a groove in the piston and serves to seal the combustion chamber against the outside.

[0009] Piston rings used in reciprocating piston internal combustion engines and especially in two-stroke large two-fuel or Otto cycle designs of reciprocating piston internal combustion engines usually have a substantially rectangular cross-section. Due to the special shape of the working surface of the piston ring, slight deviations from the rectangular shape can occur in the area of the working surface. The outwardly facing side of the piston ring can be arc-shaped.

[0010] The height of a conventional piston ring measured in axial direction is usually smaller than the cross-sectional dimension in radial direction, i.e. the difference between the outer diameter and the inner diameter. Typical values for the axial width as a function of the nominal diameter of the piston ring are listed in DIN 34110, for example.

[0011] Such a piston ring is known, for example, from DE 197 20 779 C1.

[0012] In the present application, the term "axial" refers to the direction perpendicular to the ring plane of the piston ring, which usually corresponds to the axial direction of the piston and the cylinder when the piston ring is mounted to the piston. Similarly, the term "radial" relates to the radial direction of the piston ring geometry and the term "circumferential" relates to the circumferential direction of the piston ring geometry.

[0013] The piston ring can comprise a piston ring lock, for example as shown in CH 229 278, EP 1 655 522 B1 or EP 3 889 471 B1, wherein the piston ring lock is formed by two locking ends of the piston ring. A tongue can be formed at the male locking end of the piston ring and a recess is formed at the female locking end. The recess can open towards the radial outside and towards one axial side and can extend over a portion of the radial width and a portion of the axial width of the piston ring.

[0014] The tongue and the recess are designed and arranged such that they can slide over each other in the circumferential direction of the piston ring. Due to the tongue, the parting line in the area of the tongue is interrupted in both axial and radial direction. This design is therefore also referred to as "airtight" lock.

[0015] The dimensions of the tongue and the recess are usually made such that the tongue and the recess have a clearance of between 0.05 mm and 0.1 mm, which can be in the same order of magnitude as the arc or even greater.

[0016] The pivot line of the arc-shaped piston ring can be defined by the maximum extension line of the arc. Before wear of the ring, the pivot line corresponds to the contact line of the piston ring with the cylinder liner. However, during use, a wear trace can form in an axial area around the pivot line, which contacts the cylinder liner.

[0017] For known piston ring locks, in which the recess opens towards the outside, the pivot line can be arranged parallel to the circumferential parting line and axially spaced apart therefrom and arranged on the tongue.

[0018] When pressure is generated from the inside of the piston ring, the inner portion of the piston ring lock, e.g. the locking end with the groove, presses against the outer portion of the piston ring lock, e.g. the locking end with the tongue.

[0019] When there is pressure in the combustion chamber and the piston ring is pressed axially against the piston groove, pressure from the inside typically occurs.

[0020] Due to the pressure from the inside of the piston ring, the locking end can open slightly and allow hot gases to escape to the outside, which can lead to damage of the piston ring in the area of the piston ring lock.

[0021] In this case, sharp edges can occur, which can damage the cylinder wall.

[0022] The roughness of the outside of the piston ring can be reduced by polishing or grinding. For example, EP3802905B1 discloses coating a piston ring and then grinding it to remove peaks without penetrating the coating, so that valleys and plateaus remain in the coated surface. EP2969384A1 teaches a step of grinding the piston ring to a final longitudinal thickness. SUMMARY

[0023] It is the task of the present invention to provide a piston ring, a piston having such a piston ring, a reciprocating internal combustion engine having such a piston, and a method for manufacturing a piston ring of the above-mentioned type, which at least partially avoids the disadvantages of the prior art solutions and / or which provides a sufficient sealing and a longer durability of the piston ring and the cylinder liner.

[0024] This object is achieved by a piston ring for a piston of a reciprocating internal combustion engine of the present invention.

[0025] According to a first aspect of the present invention, a piston ring for a piston of a reciprocating internal combustion engine comprises a ring segment and a lock segment.

[0026] The ring segment has an axial width in the axial direction, a maximum thickness in the radial direction, an inner diameter and an outer diameter. The ring segment can have a substantially rectangular cross-section, wherein the axial width is smaller than the maximum thickness. The lock segment can have the same radial extension and axial extension.

[0027] Typically, the axial width can be in the range of 5mm to 50mm, the outer diameter in the range of 200mm to 2000mm, and the maximum thickness in the radial direction in the range of 6mm to 60mm.

[0028] The lock segment comprises a male locking end and a female locking end. The male locking end comprises a tongue and the female locking end comprises a recess, so that the tongue can be inserted into the recess. The recess is open towards the radial outside and the bottom side of the piston ring.

[0029] Preferably, the cross-section of the recess corresponds to the cross-section of the tongue, such that when the piston ring is mounted, there is only a small gap between the recess and the tongue in axial and radial direction, the gap preferably being less than 0.1 mm.

[0030] In the present application, the top side corresponds to the first axial side and the top surface corresponds to the surface on the first axial side of the piston ring. Similarly, the bottom side corresponds to the second axial side and the bottom surface corresponds to the surface on the second axial side of the piston ring. When the piston ring is mounted, the top surface is typically closer to the cylinder head and the bottom surface is closer to the crankcase.

[0031] The locking segment comprises a circumferential split line, which is at a first axial split line distance from the top surface of the piston ring and at a second axial split line distance from the bottom surface of the piston ring, the first and second axial split line distances preferably being constant along the circumferential extension of the circumferential split line, such that the circumferential split line is parallel to the top and bottom surfaces of the piston ring.

[0032] Preferably, the first and / or second axial split line distance is at least 10% of the axial extension of the piston ring.

[0033] The circumferential split line is the ideal line between the recess and the tongue. In use, there can be a small axial gap between the recess and the tongue. However, the width of this gap is typically two orders of magnitude smaller than the axial extension of the piston ring. Hence, the position of the split line can be specified with the accuracy of the gap width.

[0034] The piston ring comprises an arc-shaped profile on a radially outward facing surface of the piston ring.

[0035] The arc-shaped profile comprises a circumferential pivot line, which is at a first axial pivot line distance from the top surface of the piston ring and at a second axial pivot line distance from the bottom surface of the piston ring.

[0036] The first axial pivot line distance between the pivot line and the top surface and the second axial pivot line distance between the pivot line and the bottom surface of the piston ring are preferably constant around the circumference, such that the pivot line is parallel to the top and bottom surfaces of the piston ring.

[0037] Preferably, the first axial pivot line distance between the pivot line and the top surface is equal to or larger than the second axial pivot line distance between the pivot line and the bottom surface of the piston ring. When mounted, the pivot line can be arranged in the lower half of the piston ring. This is to reduce the outwardly directed force generated from the piston ring onto the cylinder liner. This is due to the increased counter pressure acting on the outside of the piston ring above the pivot line (due to the increased surface area above the pivot line).

[0038] The axial distance between the circumferential split line and the pivot line is less than 20%, preferably less than 10%, of the axial width of the piston ring.

[0039] Preferably, the first axial pivot line distance between the pivot line and the top surface is less than the first axial split line distance between the circumferential split line and the top surface. Thus, when installed, the pivot line can be above the circumferential split line. Alternatively, the opposite is also possible, i.e. the first axial pivot line distance between the pivot line and the top surface can also be greater than the first axial split line distance between the circumferential split line and the top surface. Then, when installed, the pivot line can be below the circumferential split line.

[0040] Alternatively or in addition to the apparent circumferential pivot line, the arcuate profile can comprise a most protruding, axially extending flat segment. The flat segment protrudes radially furthest.

[0041] The flat segment comprises the circumferential split line.

[0042] In the present application, a "flat segment" means that in cross-section the outer profile of the segment has a curvature with a radius in the radial direction that is at least five times, preferably ten times, larger than the radius of the rest of the profile in the radial direction, in particular the flat segment has a radius of curvature in the radial direction that is larger than 10 m. Even more preferably, the radius is close to infinity.

[0043] The flat segment extends over the circumferential split line and, when present, over the pivot axis. The pivot line can be arranged in the flat segment centrally or non-centrally with respect to the axial direction.

[0044] Preferably, the distance between the flat segment and the top surface of the piston ring and / or the distance between the flat segment and the bottom surface of the piston ring is at least 5% of the axial width of the piston ring.

[0045] Thus, preferably, the flat segment is arranged non-adjacent to the top surface and / or the bottom surface of the piston ring, such that a distance is maintained between the top surface and / or the bottom surface and the edge of the flat segment.

[0046] The flat segment can be arranged closer to the bottom surface than to the top surface. Then, the distance between the flat segment and the top surface is larger than the distance between the flat segment and the bottom surface.

[0047] The arrangement of the circumferential split line close to the radially most protruding part of the piston ring, i.e. the pivot line or the flat segment, provides a pressure during use sufficient to press oil from the cylinder liner to the split line. The potential space between the top surface of the tongue, which tends to the recess in the axial direction, and the bottom surface of the recess, which tends to the tongue in the axial direction, can be filled with oil. Thus, the circumferential split line remains airtight.

[0048] The arrangement of the circumferential parting line relative to the outer shape of the arcuate profile of the piston ring provides the appearance of a wear track in the axial section comprising the circumferential parting line. However, the wear track is still the most prominent area and provides the pressure for guiding oil to the circumferential parting line. Thus, this leads to a wear on the piston ring even after use, i.e. after the engine has been in use for a while, considering this amount of wear on the piston ring, the potential space between the top surface of the tongue and the bottom surface of the recess can be filled with oil and the circumferential parting line remains airtight.

[0049] Preferably, at least a portion of the circumferential pivot line and / or the flat section can be arranged in the lower axial half of the piston ring when installed. This is advantageous because during use, generally more pressure is generated from the top surface, which generally faces the combustion chamber. This leads to a reduction of the outwardly directed pressure of the piston ring against the cylinder liner, which is explained above.

[0050] However, it should be noted that the opposite case is also possible, i.e. the arrangement of at least a portion of the circumferential pivot line and / or the flat section in the upper axial half of the piston ring.

[0051] The pivot line can coincide with the parting line. However, when the edge portions are located on the mostly protruding pivot line, there is a risk that, in particular when the piston ring is brittle, e.g. due to a brittle coating material, the edge portions of the lock section can be forced outwardly during use and can be damaged.

[0052] Alternatively, the axial distance between the circumferential parting line and the pivot line is at least 2% of the axial width of the piston ring. This enhances the durability.

[0053] The axial length of the flat section is at least 5% of the axial width of the piston ring.

[0054] The axial extension of the flat section can be 5% to 50% of the axial width of the piston ring.

[0055] Thus, after a while of use, the parting line is in a wear track but not the most prominent. The edge portions are protected because they do not touch the cylinder liner.

[0056] The arcuate profile can have a curvature with a radius that is larger than the outer diameter of the piston ring. In case the piston ring has a flat section, the curvature has an even larger radius in this section.

[0057] The arcuate profile can have a section of circular shape, e.g. in both sides of the flat section.

[0058] The arc-shaped profile can have a height of 0.01 mm to 1 mm. In the present context, "height" refers to the difference between the maximum and minimum radial width of the radially outward facing surface of the piston ring. The height of the profile corresponds to the degree of protrusion of the pivot line or the most protruding flat section.

[0059] Although the height can be of the same order of magnitude as the gap between the male part and the female part of the lock section, the arc is sufficient to provide an axially limited contact surface between the piston ring and the cylinder liner, which can be seen in the wear track. Typically, the wear track extends axially over only a part of the axial extension of the outer surface of the piston ring.

[0060] The outer surface of the piston ring in the region of the pivot line and / or in the region of the flat section can be ground.

[0061] In particular, the outer surface around the pivot line and / or around the flat section can be ground.

[0062] The outer surface of the piston ring in the region of the axial and circumferential extension comprising the circumferential parting line can be ground.

[0063] The ground region can comprise an axial extension which is greater than the axial distance between the circumferential parting line and the pivot line, preferably more than twice the axial distance between the circumferential parting line and the pivot line.

[0064] In the ground region, the surface can have a small roughness.

[0065] In a preferred embodiment, the arithmetic mean roughness Ra in the ground section can be less than 1 pm.

[0066] The grinding process can result in the creation of a flat portion. The ground section and the flat section can coincide.

[0067] At least a portion of the piston ring can be coated.

[0068] The piston ring can have a tread coating, i.e. a coating of the radially outer surface facing the cylinder liner.

[0069] The radially outer surface of the piston ring can comprise an upper side and / or a lower side. The piston ring can be coated only on the sides.

[0070] Any combination of all surfaces or partial surfaces except the tread can be coated, in particular with an anticorrosion coating.

[0071] At least a portion of the piston ring can be chemically or physically coated. A metal coating, for example chromium, can be electrolytically deposited on at least a portion of the piston ring. The coating can provide a hard and / or durable surface.

[0072] Most physically applied running surface coatings on piston rings for large engines (typically by flame spray or similar process) contain chromium, nickel, molybdenum and iron carbides in various compositions or mix ratios. These coatings are inherently corrosion inhibiting, but the main task is to produce a hard and / or durable surface that is at the same time low friction (smooth) against the cast iron of the cylinder liner. To prevent corrosion, other surfaces of the piston ring (upper and lower side, inside of the ring) are sometimes phosphatized, rarely chromized, especially the lower side, which prolongs the service life of the piston ring, since chromizing leads to slower side wear.

[0073] The radial extension of the tongue of the male locking end can be equal to the axial extension of the tongue of the male locking end. Preferably, in the present context, "equal" means that the difference between the axial extension and the radial extension of the tongue of the male locking end is less than 35% of the axial extension or the radial extension of the tongue.

[0074] Alternatively, the axial extension of the tongue can be greater than the radial extension.

[0075] However, if the radial extension of the tongue is greater than the axial extension of the tongue of the male locking end, the tongue is stiffer in terms of radial bending. With a stiffer tongue, the risk of bending outwards under pressure and scraping along the cylinder liner during use is lower.

[0076] According to a second aspect of the present application, the object of the present application is also achieved by a piston ring for a piston of a reciprocating internal combustion engine, in particular a piston ring as described above, wherein the piston ring comprises a phosphate base layer, preferably on top of a chromium base material coating at least a portion of the piston ring.

[0077] The phosphate base layer can be a top layer and a phosphate base surface coating.

[0078] The phosphate base layer can comprise a phosphate of iron, zinc, manganese, calcium, nickel, cobalt, magnesium, strontium, copper, aluminum, chromium, tin, titanium, zirconium, and combinations thereof. In particular, the phosphate base layer can comprise zinc phosphate, manganese phosphate, iron phosphate, iron zinc phosphate, iron manganese phosphate, calcium zinc phosphate, and / or iron calcium zinc phosphate.

[0079] The chromium base material or chromium composite coating is typically dense, hard and wear resistant, while the phosphate base layer, although not as wear resistant as the chromium base material, can provide better scratch resistance.

[0080] The phosphate base top layer can provide better protection against scuffing damage than a hard surface layer, such as a chromium base material.

[0081] Scuffing damage includes scuffing events, delamination of the surface coating, scoring on damaged cylinder liners, and even piston ring breakage.

[0082] Therefore, scuffing damage can result in significant downtime and costs.

[0083] Break-in damage can occur whenever a new piston ring is installed, for example during high load operation in initial shop tests, but also when a piston ring or liner is replaced during regular operation.

[0084] A more wear resistant phosphate-based layer or piston ring surface can provide a smooth piston ring surface which is formed during break-in. It can take several hours for the phosphate-based top layer to have its final outer profile.

[0085] After break-in, the phosphate-based layer can eventually wear off, leaving a rather conformal contact between the cylinder liner and the outer surface of the piston ring. Thus, the risk of scuffing or other forms of severe wear damage can be reduced.

[0086] The phosphate-based layer can also be applied on a ground chromium-based material.

[0087] Preferably, the phosphate-based layer has an initial thickness of 0.1 to 100 pm, more preferably a few micrometers to a few tens of micrometers, for example 2 to 50 pm.

[0088] According to a third aspect of the present application, the object of the present application is also achieved by a piston of a reciprocating internal combustion engine, the piston comprising at least one piston ring as described above in relation to the first aspect of the present application.

[0089] The piston can comprise a plurality of piston rings according to the present application as described above. Alternatively or additionally, the piston can comprise at least one gas-sealing piston ring according to the present application as described above in relation to the first aspect of the present application and one or more further piston rings, for example according to prior art solutions.

[0090] Typically, the piston can comprise a groove for retaining the piston ring.

[0091] The lower support surface of the groove can have a perpendicularity of less than or equal to 0.05 mm, preferably less than or equal to 0.03 mm.

[0092] Alternatively or additionally, the lower support surface of the groove can have a flatness of less than or equal to 0.04 mm, preferably less than or equal to 0.02 mm.

[0093] The perpendicularity is a specific geometric tolerance which controls the perpendicularity between two surfaces that are at a 90° angle, in this case the lower support surface of the groove and the tangential surface of the substantially cylindrical piston. The perpendicularity is controlled by two parallel planes as its tolerance band.

[0094] The flatness is a specific geometric tolerance which controls the flatness of a surface. A flatness of 0.04 mm means that the lower support surface which has this condition must lie within two parallel planes at a distance of 0.04 mm.

[0095] If the lower support surface of the recess does not meet the conditions of perpendicularity and / or flatness, there is a risk that the piston ring is at least slightly tilted during operation. Tilting of the piston ring can result in wear occurring in undesired areas of the outer radial surface of the piston ring.

[0096] According to a fourth aspect, the object of the present application is also achieved by a reciprocating internal combustion engine comprising a piston of this kind, the piston having a piston ring as described above with respect to the first and second aspects of the present application, respectively.

[0097] The reciprocating internal combustion engine is in particular a large marine engine, such as a low-speed two-stroke marine propulsion engine, having at least one cylinder with an inner diameter of at least 200 mm. The reciprocating internal combustion engine is preferably a two-stroke engine and / or a two-stroke crosshead engine.

[0098] According to a fifth aspect, the object of the present application is also achieved by a method for manufacturing a piston ring, preferably a piston ring as described above with respect to the first or second aspect of the present application.

[0099] The method comprises the step of providing a blank, which is preferably formed as a closed ring having a substantially rectangular cross-section.

[0100] The blank can be manufactured by casting or forging, e.g. from grey cast iron or steel.

[0101] Subsequently, the ring can be produced with the main dimensions of the final product by turning and / or milling and / or grinding the blank.

[0102] Subsequently, a locking segment is produced in the blank. Thereby a ring segment, a male locking end and a female locking end are formed. The circumferential length of the male locking end and the female locking end is adjusted so that the ring has the correct total circumference.

[0103] The locking segment can be produced by milling and / or cutting the blank. A chamfer can be produced by milling or grinding at the appropriate location of the male locking end and the female locking end to improve the tread coating and to avoid friction with the cylinder. Sharp edges can be removed by grinding and / or brushing to avoid friction with the cylinder.

[0104] The male locking end comprises a tongue and the female locking end comprises a recess, such that the tongue can be inserted into the recess. The recess is open towards the radially outer side and the bottom side of the piston ring.

[0105] The locking segment comprises a circumferential parting line, which is at a first axial parting line distance from the top side of the piston ring and at a second axial parting line distance from the bottom side of the piston ring.

[0106] The piston ring comprises an arc-shaped profile on the radially outwardly facing surface of the piston ring.

[0107] The arc-shaped profile comprises a circumferential pivot line which is at a first axial pivot line distance from the top side of the piston ring and at a second axial pivot line distance from the bottom side of the piston ring. The axial distance between the circumferential parting line and the pivot line is less than 20%, preferably less than 10%, of the axial width of the piston ring.

[0108] Alternatively or in addition to the prominent circumferential pivot line, the arc-shaped profile comprises a most prominent, axially extending flat section, wherein the flat section comprises the circumferential parting line.

[0109] During manufacturing of the piston ring, the arc-shaped profile with the pivot line can first be formed, e.g. by turning, milling and / or grinding. Subsequently, the flat section can be formed, e.g. by turning, milling, grinding, lapping and / or polishing.

[0110] Alternatively, the arc-shaped profile comprising the flat section can be formed from the blank in one step, in particular by turning, milling and / or grinding. Subsequently, the tread can be smoothed by lapping and / or polishing.

[0111] In particular, the outer surface of the piston ring in a region around the pivot line, in an axially and circumferentially extending region whose axial extension is greater than the axial distance between the circumferential parting line and the pivot line, can be lapped, such that the axially and circumferentially extending region comprises the circumferential parting line.

[0112] The lapping produces a smooth surface and can provide the flat section.

[0113] At least a portion of the blank can be coated with a coating material, in particular the outer facing surface of the blank.

[0114] Preferably, the coating step is carried out after forming the arc-shaped profile but before the smoothing step.

[0115] According to a sixth aspect, the object of the present application is also achieved by a method for manufacturing a piston ring, preferably a piston ring as described above with respect to the first and second aspects of the present application, preferably a method as described above with respect to the fifth aspect of the present application.

[0116] The method comprises the step of providing a blank, which is preferably formed as a closed ring having a substantially rectangular cross section. Subsequently, a lock section is produced in the blank. Thereby, a ring section, a male locking end and a female locking end are formed.

[0117] Preferably, at least a portion of the blank is coated with a chromium-based material, preferably by electroplating.

[0118] Preferably, the phosphate-based layer is applied on at least a portion of the blank after the step of coating at least a portion of the blank with a chromium-based material, preferably the phosphate-based layer has a thickness of 0.1 to 100 pm, more preferably the phosphate-based layer has a thickness of 2 to 50 pm. Thus, a wear-resistant phosphate-based layer can be applied on top of the rather hard chromium-based material, which helps to break-in.

[0119] The phosphate-based layer can be applied only to portions of the piston ring, for example the radially outer side. The locking end can be omitted or, in particular, the locking end can be coated, as they are areas of higher tribological requirements. The portions of the piston ring blank that are not coated can be masked.

[0120] Alternatively, portions of the surface layer can be removed after the coating process.

[0121] If necessary, the piston ring can be baked or heated after the phosphate treatment to mitigate hydrogen embrittlement.

[0122] Subsequently, the piston ring can be subjected to a finishing process to smooth the surface and to precisely set the geometry and / or thickness of the phosphate-based layer. The finishing process can include grinding, milling and / or polishing.

[0123] The application of the phosphate-based layer can comprise the following steps:

[0124] First, an iron-based layer can be applied on at least a portion of the blank or the chromium-based material, in particular by electroplating.

[0125] Subsequently, at least a portion of the iron-based layer is converted into a phosphate-based layer, preferably zinc phosphate, manganese phosphate, iron phosphate, iron zinc phosphate, iron manganese phosphate, calcium zinc phosphate and / or iron calcium zinc phosphate, preferably in a chemical bath or by electrolytic phosphating.

[0126] Alternatively, the phosphate-based layer can be deposited by electrolytic phosphating, also known as electro-phosphating.

[0127] Compared to conventional phosphating, electrolytic phosphating allows for a better control of the structure and composition of the phosphate-based layer. In particular, electro-phosphating can allow for the formation of a coating with better wear resistance properties compared to conventional phosphating methods. BRIEF DESCRIPTION OF DRAWINGS

[0128] Further advantageous aspects of the present application are explained below by means of exemplary embodiments and the accompanying drawings. Functionally identical elements are provided with the same reference signs. In the drawings:

[0129] Figure 1 A perspective view of a first example of a piston ring is shown in a schematic manner;

[0130] Figure 2 A perspective view of a locking segment of a second example of a piston ring is shown in a schematic manner;

[0131] Figure 3 A cross-sectional view of the profile of a third example of a piston ring is shown in a schematic way;

[0132] Figure 4 A cross-sectional view of the profile of a fourth example of a piston ring is shown in a schematic way;

[0133] Figure 5 A cross-sectional view of a detail of a piston is shown in a schematic way. DETAILED DESCRIPTION

[0134] Figure 1 A perspective view of a first example of a piston ring 100 is shown.

[0135] The piston ring 100 comprises a ring segment 1 and a lock segment 2.

[0136] The ring segment 1 has an axial width 11 in the axial direction 201, a radial width 12 in the radial direction 202 and an outer diameter 13.

[0137] The lock segment 2 has substantially the same extension and comprises a male locking end 3 and a female locking end 4.

[0138] Figure 2 A perspective view of the lock segment 2 of a second example of a piston ring comprising a male locking end 3 and a female locking end 4 is shown.

[0139] The male locking end 3 comprises a tongue 5 and the female locking end 4 comprises a recess 6. The tongue and the recess are dimensioned such that the tongue 5 can be inserted into the recess 6, while the bottom surfaces B of the male locking end 3 and the female locking end 4 are mostly in the same axial plane. The recess 6 opens towards the radial outside and towards the bottom surface B of the piston ring 100.

[0140] The lock segment 2 comprises a circumferential parting line 7, which is at a first axial parting line distance PaT from the top surface T of the piston ring 100 and at a second axial parting line distance PaB from the bottom surface B of the piston ring 100.

[0141] The piston ring 100 comprises a circumferential pivot line 8, which is at a first axial pivot line distance PiT from the top surface T of the piston ring 100 and at a second axial pivot line distance PiB from the bottom surface B of the piston ring 100.

[0142] The axial distance 9 between the circumferential parting line 7 and the pivot line 8 is less than 20% of the axial width 11 of the piston ring 100.

[0143] In this example, the pivot line 8 is above the parting line 7. During use, a wear trace (not shown in the figures) occurs around the pivot line 8, which also includes the parting line 7.

[0144] Figure 3 A cross-sectional profile of a ring segment of a third example of a piston ring 100 is shown.

[0145] The piston ring 100 has an arc profile 10 with a pivot line 8 defined by the most protruding point in the profile 10. The pivot line 8 is at a first axial pivot line distance PiT from the top surface T of the piston ring 100 and at a second axial pivot line distance PiB from the bottom surface B of the piston ring 100.

[0146] The arc profile 10 has a curvature with a radius R that is larger than the outer diameter 13 (see Figure 1 ) of the piston ring 100.

[0147] The arc profile 10 has a height 15 (not drawn to scale) of 0.01 mm to 1 mm.

[0148] In this example, the pivot line 8 is closer to the bottom surface B of the piston ring 100 than to the top surface T.

[0149] Alternatively, the pivot line 8 can be closer to the top surface T than to the bottom surface, as Figure 1 is shown.

[0150] In any case, a circumferential parting line 7, not shown in the figure, is close to the pivot line 8, i.e. the axial distance between the circumferential parting line 7 and the pivot line 8 is less than 20% of the axial width 11 of the piston ring 100.

[0151] Figure 4 A cross-sectional profile of a lock segment of a fourth example of a piston ring 100 is shown. The piston ring 100 has an arc profile 10 with a most protruding, axially extending flat segment 14. The flat segment 14 has an axial length 19 that corresponds to an axial extension 20 of an axially and circumferentially extending wear area 16.

[0152] In this example, the radial extension 17 of the tongue 5 of the male locking end 3 is larger than the axial extension 18 of the tongue 5 of the male locking end 3.

[0153] Figure 5 A cross-sectional view showing details of a piston 200 is shown. The piston 200 comprises a groove 201 for holding a piston ring 100 according to the present application, which is not shown in this figure.

[0154] The lower support surface 202 of the groove 201 has a perpendicularity of less than 0.03 mm with respect to a tangential surface 203 of the substantially cylindrical piston 200. Furthermore, the lower support surface 202 has a flatness of less than 0.02 mm. This enables a good fit and guidance of the piston ring and reduces tilting.

[0155] Note:

[0156] Any embodiment described with respect to the device should similarly relate to the method. Synergistic effects can result from different combinations of embodiments, although they can not be described in detail.

[0157] While the current preferred embodiments of the application have been shown and described, it is to be understood that the application is not limited to these, but can be variously embodied and practiced within the scope of the appended claims.

Claims

1. A piston ring (100) for a piston in a reciprocating internal combustion engine, particularly a large marine engine having at least one cylinder with an inner diameter of at least 200 mm, the reciprocating internal combustion engine preferably being a two-stroke engine and / or a two-stroke crosshead engine, the piston ring comprising: Ring segment (1); and Locking segment (2), the locking segment (2) includes a male locking end (3) and a female locking end (4), The male locking end (3) includes a tongue (5) and the female locking end (4) includes a recess (6), such that the tongue (5) can be inserted into the recess (6), and the recess is open toward the radially outer and bottom sides of the piston ring (100). The locking segment (2) includes a circumferential parting line (7), which is a first axial parting line distance (PaT) from the top surface (T) of the piston ring (100) and a second axial parting line distance (PaB) from the bottom surface (B) of the piston ring (100). The piston ring (100) includes an arc-shaped profile (10). The arc-shaped profile (10) includes a circumferential pivot line (8), which is a first axial pivot line distance (PiT) from the top surface (T) of the piston ring (100) and a second axial pivot line distance (PiB) from the bottom surface (B) of the piston ring (100). The axial distance (9) between the circumferential parting line and the circumferential pivot line is less than 20% of the axial width of the piston ring, preferably less than 10%, and / or The arc-shaped profile (10) includes a prominent, axially extending flat section (14), which includes the circumferential parting line (7).

2. The piston ring (100) according to claim 1, wherein, The first axial pivot line distance (PiT) between the circumferential pivot line (8) and the top surface (T) is equal to or greater than the second axial pivot line distance (PiB) between the circumferential pivot line (8) and the bottom surface (B).

3. The piston ring (100) according to claim 1 or 2, wherein, The axial distance between the circumferential parting line (7) and the circumferential pivot line (8) is at least 2% of the axial width (11) of the piston ring (100).

4. The piston ring (100) according to any one of the preceding claims, wherein, The axial length (19) of the flat section (14) is at least 5% of the axial width (11) of the piston ring (100).

5. The piston ring (100) according to any one of the preceding claims, wherein, The arcuate profile has a curvature with a radius (R) larger than the outer diameter (13) of the piston ring (100).

6. The piston ring (100) according to any one of the preceding claims, wherein, The arcuate profile has a height of 0.01 mm to 1 mm (15).

7. The piston ring (100) according to any one of the preceding claims, wherein, The outer surface of the piston ring (100) in the region of the pivot line (8) and / or in the region of the flat section (14) is ground, particularly the outer surface of the piston ring (100) around the pivot line (8), and the outer surface of the piston ring (100) in the axial and circumferentially extending region (16) including the circumferential parting line (7) is ground. Preferably, the axial extension (20) of the axial and circumferentially extending region (16) is greater than the axial distance (9) between the circumferential parting line (7) and the circumferential pivot line (8), preferably greater than twice the axial distance (9) between the circumferential parting line (7) and the circumferential pivot line (8).

8. The piston ring (100) according to any one of the preceding claims, wherein, At least a portion of the piston ring (100) is coated.

9. The piston ring (100) according to any one of the preceding claims, wherein, The radial extension (17) of the tongue (5) of the male locking end (3) is equal to or greater than the axial extension (18) of the tongue (5) of the male locking end (3).

10. A piston ring (100) for a piston in a reciprocating internal combustion engine, particularly a large marine engine having at least one cylinder with an inner diameter of at least 200 mm, the reciprocating internal combustion engine preferably being a two-stroke engine and / or a two-stroke crosshead engine, the piston ring (100) being particularly a piston ring according to any one of the preceding claims, wherein, The piston ring includes a phosphate base layer, which is preferably located on top of a chromium-based material used to coat at least a portion of the piston ring.

11. A piston (200) for a reciprocating internal combustion engine, said piston (200) comprising piston rings (100) according to at least one of the preceding claims.

12. The piston (200) according to claim 11, wherein, The piston (200) includes a groove (201) for retaining the piston ring (100), wherein the lower support surface (202) of the groove has a perpendicularity of less than or equal to 0.05 mm, preferably less than or equal to 0.03 mm, and / or wherein the lower support surface (202) of the groove (201) has a flatness of less than or equal to 0.04 mm, preferably less than or equal to 0.02 mm.

13. A reciprocating internal combustion engine, particularly a large marine engine having at least one cylinder with an inner diameter of at least 200 mm, the reciprocating internal combustion engine preferably being a two-stroke engine and / or a two-stroke crosshead engine, the reciprocating internal combustion engine comprising a piston according to any one of claims 11 and 12.

14. A method for manufacturing a piston ring (100), preferably a piston ring (100) according to at least one of claims 1 to 10, the method comprising the following steps: A blank is provided, which is preferably formed as a closed loop having a substantially rectangular cross-section; A locking segment (2) is manufactured in the blank, thereby forming a ring segment (1), a male locking end (3), and a female locking end (4). The male locking end (3) includes a tongue (5) and the female locking end (4) includes a recess (6) such that the tongue (5) can be inserted into the recess (6), and the recess (6) is open toward the radially outer side and bottom side (B) of the piston ring (100). The locking segment (2) includes a circumferential parting line (7) which is a first axial parting line distance (PaT) from the top side (T) of the piston ring (100) and a second axial parting line distance (PaB) from the bottom side (B) of the piston ring (100). The piston ring (100) includes an arcuate profile (10), wherein the arcuate profile (10) includes a circumferential pivot line (8), the circumferential pivot line (8) being a first axial pivot line distance (PiT) from the top side (T) of the piston ring (100) and a second axial pivot line distance (PiB) from the bottom side (B) of the piston ring (100), wherein the axial distance (9) between the circumferential parting line (7) and the circumferential pivot line (8) is less than 20% of the axial width (11) of the piston ring (110), preferably less than 10%, and / or The arc-shaped profile (10) includes a prominent, axially extending flat section (14), which includes the circumferential parting line (7).

15. The method according to claim 14, wherein the method comprises the following steps: The outer surface of the piston ring (100) in the region surrounding the circumferential pivot line (8) and in the axially and circumferentially extending region (16), the axial extension (20) of the axially and circumferentially extending region (16) being greater than the axial distance (9) between the circumferential parting line (7) and the circumferential pivot line (8), is ground such that the axially and circumferentially extending region (16) includes the circumferential parting line (7).

16. The method according to any one of claims 14 to 15, the method comprising the following steps: At least a portion of the blank, particularly the outward-facing surface of the blank, is coated with a coating material.

17. A method for manufacturing a piston ring (100), preferably a piston ring (100) according to any one of claims 1 to 10, the method preferably being the method according to any one of claims 14 to 16, the method comprising the following steps: A blank is provided, which is preferably formed as a closed loop having a substantially rectangular cross-section; A locking segment (2) is manufactured in the blank to form a ring segment (1), a male locking end (3) and a female locking end (4); Optionally, at least a portion of the blank is coated with a chromium-based material, preferably by electroplating. A phosphate base layer is applied to at least a portion of the blank, preferably after the step of coating at least a portion of the blank with the chromium-based material.

18. The method of claim 17, wherein the method comprises at least one of the following: (i) An iron substrate is applied to at least a portion of the blank, particularly to the chromium-based material, especially by electroplating, and then at least a portion of the iron in the iron substrate is converted into the phosphate substrate, preferably in a chemical bath or by electrolytic phosphating; and (ii) The phosphate substrate is deposited by electrolytic phosphating, particularly onto the chromium-based material.

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