Piston ring arrangement and piston for hydrogen engine

Abstract

The invention relates to a piston ring device for a hydrogen engine, which comprises a sealing system piston ring and a compression ring which are respectively arranged on an oil control ring and an oil scraping ring. Wherein the piston ring device is used for controlling the pressure rise caused by blow-by between a sealing system piston ring and a compression ring, so that the pressure between the sealing system piston ring and the compression ring is higher than the pressure in a combustion chamber of a cylinder, especially in a second part of a working stroke, namely between 60 degrees and 450 degrees after an ignition top dead center; preferably, the ignition top dead center is between 50 degrees and 540 degrees, preferably, the ignition top dead center is between 20 degrees and 540 degrees, and even more preferably, the ignition top dead center is between 0 degree and 540 degrees. These pressure conditions are achieved in an engine speed between 60 and 5000 revolutions per minute, preferably between 1500 and 4500 revolutions per minute, more preferably between 2000 and 4000 revolutions per minute, most preferably between 2500 and 3500 revolutions per minute.

Description

Technical Field

[0001] This invention relates to a piston ring assembly and piston for hydrogen engines, particularly hydrogen internal combustion engines. Background Technology

[0002] Hydrogen engines suffer from lubricating oil pre-ignition at high power levels. This can cause lubricating oil droplets that enter the combustion chamber from between the upper compression ring and cylinder wall during the compression stroke. Different combustion boundary conditions can be achieved based on the injection principles of direct injection (DI) or port injection (PFI).

[0003] As with conventional diesel engines, the compression stroke applies near-adiabatic compression to the cylinder filler, causing the gases in the combustion chamber to heat up. The hydrogen-air mixture has a high auto-ignition temperature of 585°C, which cannot be reached with conventional or higher compression ratios (at least without preheating the intake air).

[0004] Because the hydrogen-air mixture burns relatively quickly, pressure overlap occurs as the crankshaft continues to rotate after ignition, delivering individual oil droplets to the combustion chamber. These droplets are also transported by gas volumetric flow rate. Another drawback is that the oil consumption of a hydrogen engine is expected to be similar to that of a conventional internal combustion engine. For an engine consuming approximately 5 liters of fuel per 100 kilometers, it is estimated that 100 milliliters of oil will be consumed every 2,500 kilometers, or 4 milliliters of oil per 100 kilometers.

[0005] Therefore, although hydrogen engines produce almost no carbon monoxide and carbon dioxide, they are not completely zero-emission.

[0006] Therefore, it is essential to further reduce the already very low oil consumption of internal combustion engines. Summary of the Invention

[0007] According to a first aspect of the invention, a piston ring assembly for a hydrogen engine is provided, comprising a piston ring assembly consisting of three piston rings and an additional sealing system extending above the first piston ring of the piston ring assembly, characterized in that the piston ring assembly is used to control the pressure rise below the additional sealing system caused by blow-by, such that the pressure curves above the first piston ring and below the additional sealing system, particularly in the second part of the working stroke, i.e., between 60° and 450° after top dead center of ignition, are at least 80% higher than the combustion chamber pressure curve.

[0008] In another embodiment of the piston ring assembly for a hydrogen engine, the additional sealing system includes one or more sealing system piston rings.

[0009] In another embodiment of the piston ring assembly for a hydrogen engine, the piston ring assembly moves axially toward the crankcase to make room for an additional sealing system.

[0010] In another additional embodiment of the piston ring assembly for a hydrogen engine, an additional sealing system is located above the original position of the first piston ring of the piston ring assembly.

[0011] In another additional embodiment of the piston ring assembly for a hydrogen engine, the pressure curves above the first piston ring and below the additional sealing system are always higher than the pressure curve below the first piston ring of the piston ring assembly.

[0012] In another embodiment of the piston ring assembly for a hydrogen engine, the blow-by volume of the first element of the sealing assembly is increased by specifically designed leakage compared to conventional piston rings with low blow-by volume. This can be achieved, for example, by adjusting the end gap to between 0.1 and 5 mm, targeted side leakage, or by employing other design features, very large sealing gaps, or special under-dimensions.

[0013] In one exemplary additional embodiment of the piston ring assembly for a hydrogen engine, the volume is increased by an expansion groove. This groove can be arbitrarily positioned on the piston ring, thereby increasing the final volume between the piston and the cylinder wall.

[0014] In another exemplary embodiment of the piston ring arrangement for a hydrogen engine, the blow-by volume of the sealing system piston ring is increased by leakage compared to conventional sealing system piston rings with low blow-by volume. This can be achieved, for example, by adjusting the end gap to between 0.1 and 5 mm, targeted side leakage, or by employing other design features.

[0015] In another additional embodiment of the piston ring assembly for a hydrogen engine according to any of the preceding claims, pressure is maintained by adjusting the end gap. The end gap is adjusted here by an end gap adjusting device (e.g., a file).

[0016] In another additional embodiment of the piston ring assembly for a hydrogen engine, the height of the first piston ring of the piston ring assembly is reduced axially with an additional sealing system to reduce the inertial force of the first piston ring.

[0017] In another embodiment of the piston ring assembly for a hydrogen engine, at least one piston ring of the ring assembly is designed as a rectangular ring with an annular groove on its running surface below the pivot point. This piston ring may be an E-line™® ring from Tenneco™®.

[0018] The present invention provides a piston ring assembly for a hydrogen engine and an assembly of the assembly with a piston, the assembly including a sealing system piston ring and a piston ring assembly with a compression ring, an oil control ring and an oil scraper ring.

[0019] This piston ring assembly controls the pressure rise caused by blow-by between the sealing system piston rings and the compression piston rings, ensuring that the pressure between the piston rings remains higher than the pressure inside the cylinder or combustion chamber from the middle of the working stroke until at least the end of the stroke. The sealing system piston rings and compression rings act as valves, trapping blow-by gases between the sealing system piston rings and the first piston ring of the piston ring assembly shortly after ignition of the air-fuel mixture. This results in a constant overpressure relative to the first piston ring, at least in the lower half of the working stroke. This overpressure forces oil adhering to the cylinder wall downwards towards the crankcase by the oil pressure above the first piston ring. In this configuration, the pressure between the sealing system piston rings and the first piston ring is higher than the pressure inside the cylinder combustion chamber, particularly in the second part of the working stroke, specifically between 60° and 450° after ignition top dead center (TDC), preferably between 50° and 540°, more preferably between 20° and 540°, and even more preferably between 0° and 540° after TDC. Due to the pressure conditions in these angular regions, only a small amount of oil can flow through the second compression piston ring to the sealing system piston ring. Now, the oil film for the sealing system piston ring to slide on becomes so thin that the sealing system piston ring cannot tear off oil droplets from the oil film that would affect the combustion process of the hydrogen engine. These pressure conditions are achieved at engine speeds between 60 and 5000 rpm, preferably between 1500 and 4500 rpm, even more preferably between 2000 and 4000 rpm, and most preferably between 2500 and 3500 rpm.

[0020] In this document and the following text, the terms "piston ring of the sealing system," "upper piston ring of the piston ring assembly," "upper compression piston ring of the piston ring assembly," "first compression ring of the piston ring assembly," and "first piston ring of the piston ring assembly" may be used as synonyms. Furthermore, the terms "compression ring of the ring assembly," "first compression piston ring of the ring assembly," "first piston ring of the ring assembly," "first piston ring," and "first compression ring" may also be used as synonyms.

[0021] The term "above" is synonymous with "combustion chamber side" or "towards the combustion chamber." The term "below" is synonymous with "crankcase side" or "towards the crankcase."

[0022] It is necessary to define the speed range here because the pressure loss caused by the annular gap is greater in low-speed internal combustion engines than in high-speed internal combustion engines. This effect is particularly evident in Wankel engines, which exhibit better combustion chamber sealing, lower fuel consumption, and fewer exhaust emissions at high speeds than at low speeds. Specifying the speed range provides experts with piston speed and time ranges so that overpressure in the gap between the sealing system piston rings and compression rings can be taken into account when designing the sealing system piston rings and compression rings.

[0023] In this document and hereinafter, "compression ring" and "sealing system piston ring" are used in the singular; however, it should be noted that a piston ring assembly may also use two or more sealing system piston rings and two or more compression rings. Such embodiments are also included within the scope of the claims, as they also comprise at least one sealing system piston ring and at least one compression ring, respectively.

[0024] This design is based on the following concept: Prioritizing an additional sealing system, preferably in the form of a sealing system piston ring and facing the combustion chamber, before the traditional top ring of the ring assembly, brings the previous top ring (i.e., the previous first compression ring) into the operating range familiar to conventional gasoline and diesel engines. Similarly, controlled blow-by of the sealing system piston ring between the compression piston rings generates overpressure exceeding 90°, starting at least from 45° after top dead center, i.e., the latter half of the working stroke, above the combustion chamber pressure. This is due to the pressure drop within the cylinder caused by the piston's downward movement during the working stroke. Blow-by of the first compression ring is minimized. Furthermore, the sealing system piston ring is optimized for minimized "reverse blow-by," thereby capturing the initial blow-by during the first 90° after top dead center of the working stroke between the sealing system piston ring and the compression piston ring. Thus, towards the end of the working stroke, the pressure between the sealing system piston ring and the compression piston ring is higher than the pressure inside the combustion chamber. Therefore, the overpressure above the first compression ring can be maintained for a longer period, helping to push oil droplets towards the crankcase.

[0025] A preferred embodiment of the piston ring assembly includes the features of the above embodiments. Here, the pressure retention capability of the piston ring structure at a specific operating speed is also defined.

[0026] In another embodiment of the piston ring assembly, the clamping force of the sealing system piston ring is less than that of the first compression piston ring for most of the four-stroke cycle, wherein the sealing system piston ring may have the same average diameter as the compression piston ring in the relaxed state, and / or the clamping force of the sealing system piston ring may be less than or greater than that of the compression piston ring, and / or wherein the product of a specific clamping force of the sealing system piston ring and the running surface height is less than the product of a specific clamping force of the compression piston ring and the running surface height.

[0027] Here, the sealing strength of the sealing system piston ring is lower than that of the compression piston ring to achieve a relatively rapid pressure rise in the area between the sealing system piston ring and the first compression piston ring. The primary function of the first compression piston ring is to counteract the pressure rise within the crankcase. Compared to conventional internal combustion engines, the design dimensions of this compression piston ring are more precise because the prolonged high pressure between the first and second compression piston rings exacerbates blow-by. Indeed, the higher pressure caused by blow-by is present not only during the working stroke but ideally should continue until the end of the next intake stroke. Therefore, blow-by occurs at the compression ring not only for about a quarter of the four-stroke cycle (albeit to a lesser extent) but also for almost three-quarters of the four-stroke cycle, leading to increased pressure within the crankcase. This prolonged blow-by time at the compression piston ring results in increased pressure within the crankcase, which can be balanced by using a larger crankcase ventilation system with an oil separator.

[0028] In another embodiment of the piston ring assembly, the axial dimension of the cross-section of the sealing system piston ring is larger than that of the first compression ring. The function of the piston rings is quite clear: the upper ring should act as a valve, while the first piston ring should act as a pressure barrier from top to bottom. This requires the compression piston ring to have a different inertial force compared to the sealing system piston ring, which essentially only seals the crankcase to prevent any overpressure.

[0029] In another exemplary piston ring assembly, the sealing system piston rings also have a DLC (diamond-like carbon) coating on at least the running surface region, wherein the first compression ring of the ring assembly also preferably has a DLC coating on at least one running surface. DLC, or diamond-like carbon, is a partially amorphous carbon variant containing a large number of carbon atoms bonded together by covalent bonds arranged in a tetrahedral pattern. These bonds are partially at 109°25' angles; however, over a large spacing range, the entire coating does not form a long-range diamond lattice structure. This DLC coating exhibits particularly high wear resistance and has a particularly positive effect on the ultra-thin lubricating film of the sealing system piston rings.

[0030] According to another aspect of the invention, a piston for a hydrogen internal combustion engine is provided, the piston comprising four or at least four piston ring grooves, wherein at least one upper piston ring groove is provided for receiving a sealing system piston ring in a piston assembly as described above, and at least another piston ring groove is provided for receiving a piston ring assembly having at least one first compression piston ring.

[0031] According to an exemplary embodiment of the piston, the piston further includes at least one groove located between the two upper piston ring grooves to increase the volume between the two upper compression piston rings. These grooves may also be provided between the ring assemblies to achieve volume matching.

[0032] The objective of this invention is to maintain an overpressure between the piston rings and the first compression ring of the sealing system for as long as possible, which is higher than the crankcase pressure and preferably also higher than the current cylinder pressure. The larger volume between the two upper compression rings helps to maintain this overpressure for a longer period while maintaining the same leakage rate, as the inter-piston ring region is filled during the starting working stroke.

[0033] In another exemplary embodiment of the piston, multiple grooves are arranged in a grid pattern along the circumferential and axial directions. The grid of grooves or recesses forms a two-dimensional lattice seal, restricting gas flow in both the axial and circumferential directions in the region between the piston ring grooves and the first compression ring groove. This may have a positive effect in other embodiments. The two-dimensional lattice seal also creates a space that can maintain overpressure relative to the combustion chamber and the region below the first compression ring for a longer period of time, at the same gas loss rate. The lattice helps to reduce blow-by in the circumferential direction of the ring gap. Alternatively, linear or hexagonal arrays can also be used.

[0034] According to another aspect of the invention, an embodiment of the piston ring device described above is combined with an embodiment of a piston conforming to the invention described above for use in a hydrogen engine, wherein the piston is further equipped with at least one oil scraper ring and at least one oil control ring.

[0035] According to another aspect of the invention, an internal combustion engine having the above-described piston ring and piston combination is provided.

[0036] In another additional embodiment of the internal combustion engine, it includes at least one cylinder, wherein each cylinder has a DLC coating in at least one area that can contact the compression piston ring of at least one piston, and / or wherein the internal combustion engine includes a crankcase ventilation system with an oil separator. Because blow-by from the first compression ring of the piston ring assembly towards the crankcase increases over time, an oil separator is required to prevent engine oil from entering the combustion chamber through the crankcase ventilation system and the intake manifold, thereby avoiding pre-ignition. Attached Figure Description

[0037] The present invention will be illustrated below with schematic diagrams and non-scale diagrams of exemplary embodiments.

[0038] Figure 1 This is a schematic partial cross-sectional view used to illustrate the installed piston ring assembly.

[0039] Figure 2 This is a pressure curve achieved by the present invention, the exemplary piston ring assembly, and the exemplary piston.

[0040] Figures 3 to 5 This mainly relates to different embodiments of pistons used with piston ring assemblies conforming to the present invention. Detailed Implementation

[0041] In the description and illustrations, the same or similar terms, names and symbols are used to refer to the same or similar components and elements.

[0042] Figure 1 A partial cross-sectional view of a piston ring assembly conforming to the present invention in a hydrogen internal combustion engine in a rest position or in a stationary state is shown. In the figure, the piston is arranged within a cylinder, with the cylinder or cylinder inner surface indicated by a line on the left. The axis of rotational symmetry is parallel to this line, while the straight line representing the cylinder inner surface on the right is outside the view. (Although this strictly applies only to practically rotationally symmetric components, it is not strictly applicable to all features of an internal combustion engine due to the influence of ring clearance, piston pins, and other components and features). Figure 1 In subsequent figures, the combustion chamber is located at the top, and the cylinder head is not shown. The crankcase is located at the bottom of the figure. The piston has four piston ring grooves: a first upper compression piston ring groove, showing the first upper compression piston ring; a second lower compression piston ring groove, showing the second compression piston ring; and an oil control piston ring groove, which contains an oil control piston ring (designed as an eLine ring) and an oil scraper groove, which has an oil passage leading towards the crankcase or piston interior. A piston skirt (not shown) is connected below the oil control piston ring groove. Valve recesses or grooves, piston pins, or other conventional features are not shown.

[0043] The radially outer region above the first upper compression piston ring groove is referred to as the fire bank or "first bank" or "bank 1," even though this region may have other non-"bank" surface structures, such as grooves. The inter-ring region between the first and second compression piston ring grooves, i.e., the inter-ring region of the compression piston ring, is hereinafter also referred to as the "second bank" or "bank 2," even though this region may have other non-"bank" surface structures, such as grooves. In this case, the piston has a contraction in the bank 2 region to slightly increase the volume of the inter-ring region. The object of the invention is to maintain the pressure in the inter-ring region above the crankcase pressure for as long as possible, which can be improved with a larger gas volume at the same leakage rate, but it should be noted that this gas volume must be kept small or low enough so that blow-by gas from the upper compression ring can achieve a sufficient pressure rise in the inter-ring region.

[0044] Figure 2The pressure curves of an engine conforming to this invention are shown, where different curves represent the pressure inside the combustion chamber, the pressure between the ring grooves, and the pressure inside the crankcase. The horizontal axis (x-axis) represents the crankshaft angle in degrees, with a total angle of 720° (two revolutions) for the four strokes. The 0° angle value corresponds to the top dead center of the working stroke. The bottom dead center of the intake stroke (-180°) represents the start of the four-stroke cycle and is also the starting point of this graph. The bottom constant pressure curve corresponds to the pressure inside the crankcase. The curve running above it corresponds to the pressure of "shore 4," that is, the pressure in the area between the control ring and the scraper ring. The curve located above the "shore 4" pressure curve (slightly higher than and ahead of it) corresponds to the pressure of "shore 3," that is, the pressure between the second compression piston ring and the control ring. These pressure lines do not intersect each other and are entirely within the range of 0 to 4 bar. The relatively smooth curve above the three lower pressure lines corresponds to the pressure between the piston rings and the first compression ring in the sealing system, i.e., the pressure in the "land 2" region, which is the area between the upper and lower compression rings. The highest pressure value is visible at the lowest point of this pressure variation curve. The pressure inside the combustion chamber, i.e., the pressure in the "land 1" region, has the largest amplitude and greatest fluctuation, reaching its maximum value at or near top dead center. The combustion chamber pressure curve shows a second peak at 360°, at which point the exhaust valve is closed and the intake valve is not yet open. The graph clearly shows that, in most areas, the pressure between the two compression piston rings constitutes the highest pressure in the system. This generates constant blow-by along the crankcase direction at the second compression ring, pushing excess oil towards the oil control ring along the crankcase direction through overpressure, helping to maintain the thinnest possible oil film on the cylinder wall.

[0045] Figure 3 A separate groove is shown in the region between the piston ring and the first compression piston ring of the pressure reservoir sealing system. This groove could also be a conventional piston ring groove, in which case the piston ring would not be inserted into the groove.

[0046] Figure 4 One embodiment is shown in which the region between the sealing system piston ring and the first compression piston ring, i.e., "shore 2," is reduced in diameter relative to the fire shore, "shore 1," "shore 3," "shore 4," "shore 5," and the piston skirt, thereby forming a pressure storage chamber. Even a mere fraction of a millimeter's retraction of "shore 2" significantly increases the gas storage volume. From Figure 4 It can also be seen that the compression piston rings used to control the effects of inertial forces can have different cross-sections, and therefore different axial heights or materials. Preferably, the second piston ring is lighter in mass than the additional sealing element.

[0047] Figure 5Another embodiment is shown, in which two sealing system piston rings and two compression rings are used. This embodiment does not make any modifications to the piston that could create a gas storage volume. The illustrated embodiment has a total of six piston rings and six piston ring grooves, with the top two being sealing system piston rings, the middle two being compression rings, the second to last being a 0815 minute ring, and the bottom one being an oil scraper ring.

[0048] In addition, a piston ring assembly for a hydrogen engine is provided, comprising a sealing system piston ring and a first compression ring of a sealing assembly, wherein the sealing system piston ring has an inclined upper edge between its upper ring side and its running surface, the edge increasing the amount of blow-by gas into the crankcase, wherein the sealing system piston ring is configured for negative torsion, and wherein the first compression ring has a chamfer at the radially inner edge of its upper ring side, thereby causing the first compression ring to be positively torsion.

[0049] In the piston ring device conforming to any of the foregoing embodiments, the sealing system piston ring has a smaller clamping force than the first compression piston ring, the average diameter of the sealing system piston ring in the relaxed state is smaller than that of the first compression piston ring, and / or the clamping force of the sealing system piston ring is smaller than that of the first compression piston ring, and / or the product of a specific clamping force of the sealing system piston ring and the running surface height is smaller than the product of a specific clamping force of the first compression piston ring and the running surface height.

[0050] In another piston ring assembly, the radial dimension of the cross-section of the sealing system piston ring is smaller than that of the first compression ring.

[0051] In another type of piston ring assembly, the axial dimension of the cross-section of the piston ring in the sealing system is smaller than that of the first compression ring of the sealing assembly.

[0052] In another piston ring assembly, the first compression ring has a groove between the lower ring side and the running surface, the groove extending circumferentially and preferably terminating before the corresponding end.

[0053] In another piston ring assembly, the sealing system piston rings are provided with a DLC coating at least in the running surface region, wherein preferably the first compression ring is also provided with a DLC coating at least in one running surface.

[0054] In another embodiment of the piston ring assembly, there are multiple sealing system piston rings and / or piston ring groups having multiple compression piston rings.

Claims

1. A piston ring assembly for a hydrogen engine, comprising a piston ring assembly consisting of three piston rings and an additional sealing system disposed above the first piston ring of the piston ring assembly, characterized in that, The piston ring assembly is used to control the pressure rise below the auxiliary sealing system caused by blow-by, such that the pressure curves above the first piston ring and below the auxiliary sealing system, especially in the second part of the working stroke between 60° and 540° after ignition top dead center, exceed the combustion chamber pressure curve and are above the combustion chamber pressure curve for at least 80% of the defined range.

2. The piston ring assembly for a hydrogen engine according to claim 1, wherein the additional sealing system comprises one or more sealing system piston rings.

3. The piston ring assembly for a hydrogen engine according to claim 1 or 2, wherein the piston ring assembly is axially movable toward the crankcase to make room for the additional sealing system.

4. The piston ring assembly for a hydrogen engine according to claim 1, 2 or 3, wherein the additional sealing system is arranged above the original position of the first piston ring of the piston ring assembly.

5. The piston ring assembly for a hydrogen engine according to claim 1, 2, 3 or 4, characterized in that, The pressure curves above the first piston ring and below the additional sealing system are always located above the pressure curve below the first piston ring of the ring assembly.

6. The piston ring assembly for a hydrogen engine according to any one of claims 1 to 5, wherein, Compared to conventional piston rings with low blow-by volume, the blow-by volume of the first piston ring of the sealing assembly is increased by leakage, for example, by adjusting the end gap to between 0.1 and 5 mm, targeted side leakage, or by adopting other design features.

7. The piston ring assembly for a hydrogen engine according to any of the preceding claims, wherein the volume is increased by an expansion groove.

8. The piston ring device for a hydrogen engine according to any one of claims 1 to 7, wherein, The blow-by volume of piston rings in a sealing system is increased by leakage (compared to conventional piston rings with low blow-by volume), for example, by adjusting the end gap to between 0.1 and 5 mm, targeted side leakage, or by employing other design features.

9. The piston ring assembly for a hydrogen engine according to any of the preceding claims, wherein, Pressure is maintained by adjusting the end gap.

10. The piston ring assembly for a hydrogen engine according to any of the preceding claims, wherein, The height of the first piston ring in the piston ring assembly decreases axially under the additional sealing system to reduce the inertial force of the first piston ring.

11. The piston ring assembly for a hydrogen engine according to any of the preceding claims, wherein, At least one piston ring of the ring assembly is a rectangular ring with an annular groove on its running surface below the pivot point.

12. A piston ring assembly for a hydrogen engine according to any of the preceding claims, comprising a sealing system piston ring and a first piston ring of a piston ring assembly, the first piston ring being configured as a first compression ring and disposed on an oil control ring and an oil scraper ring, wherein, The piston ring assembly is used to control the pressure increase caused by blow-by between the piston rings of the sealing system and the first compression ring, so that the pressure between the piston rings of the sealing system and the compression ring is higher than the pressure inside the cylinder combustion chamber, especially in the second part of the working stroke, i.e., between 60° and 450° after ignition top dead center, preferably between 50° and 540° after ignition top dead center, even more preferably between 20° and 540° after ignition top dead center, and even more preferably between 0° and 540° after ignition top dead center (relative to the top dead center of the working stroke). These pressure conditions are achieved when the engine speed is between 60 and 5000 rpm, preferably between 1500 and 4500 rpm, even more preferably between 2000 and 4000 rpm, and most preferably between 2500 and 3500 rpm.

13. A piston for a hydrogen internal combustion engine, comprising at least four piston ring grooves and configured to receive a piston ring assembly for a hydrogen engine according to any of the preceding claims; wherein at least one upper piston ring groove is configured to receive a sealing system piston ring, and wherein at least one piston ring groove located below at least one upper piston ring groove is configured to receive at least one first piston ring of the piston ring assembly.

14. The piston according to claim 13, further comprising at least one groove disposed between the two upper piston ring grooves, thereby increasing the volume between the two upper compression piston rings, wherein, The groove is preferably designed as at least one expansion groove.

15. The piston according to claim 13 and / or 14, wherein, The at least one groove is configured as a plurality of annular grooves extending circumferentially to form a groove seal, and / or wherein the plurality of grooves form a grid along the circumferential and axial directions, wherein the grooves or recessed grid thereby form a two-dimensional lattice seal that restricts the flow of gas in the region between the upper two compression annular grooves along the axial and circumferential directions.

16. A combination of a piston ring assembly according to any one of claims 1 to 12 and a piston according to any one of claims 13 to 15 for a hydrogen engine, wherein the combination further comprises at least one oil scraper ring and an oil control ring.

17. An internal combustion engine having at least one piston according to claims 13 to 15.

18. The internal combustion engine of claim 17, comprising at least one cylinder having a DLC coating at least in the area in contact with the compression piston rings of the at least one piston, and / or wherein the internal combustion engine includes a crankcase ventilation system with an oil separator.

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