JP3202243B2 - Internal combustion engine with coke scraping ring in cylinder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a piston having a coke scraping ring within a cylinder, the piston being displaceable longitudinally within the cylinder and having a piston ring provided thereon. The ring slides along the generally cylindrical inner surface of the cylinder when the piston is displaced, forming a pressure-tight partition between the volume below the piston and the working chamber, the partition of the working chamber being the piston. The uppermost piston ring, which is located above the uppermost piston ring of
A coke scraping ring, defined by the piston, the inner surface of the cylinder and the cylinder cover, protrudes from the inner surface of the cylinder and extends annularly at an axial position, the uppermost piston when the piston is at its top dead center position. The present invention relates to an internal combustion engine, wherein the ring is arranged at a position near the lower edge of the coke scraping ring.

Such an engine with a coke scraping ring is known from a four-stroke engine having both intake and exhaust valves in the cylinder cover. The purpose of this coke scraping ring is to scrape coke deposits from a cylindrical uppermost piston section located above the uppermost piston ring.

This uppermost piston ring forms a lower limit of the combustion chamber in an annular space located between the uppermost piston part above the piston ring and the inner surface of the cylinder. As a result, some of the combustion products penetrate into this annular space and accumulate on the outer surface of the uppermost piston part. Also, lubricating oil from the inner surface of the cylinder is sprayed on this outer surface. The remainder of the lubricating oil and the deposits of combustion products are:
Under the influence of the strong heat of combustion, when the engine rotates, it changes into a cohered layer of coke on the outer surface of the piston. If a coke scraping ring is not used, the thickness of the coke layer will increase until it contacts the inner surface of the cylinder.

In order to prevent damage to the cylinder and piston ring, it is important to maintain a suitable lubricant film between these mutually movable parts. When the layer of coke on the outer circumference of the piston accumulates to its maximum thickness and contacts the inner surface of the cylinder, it will interfere with the thin oil film and absorb and / or scrape some of the lubricating oil This has a detrimental effect on the lubrication state. In the worst case, the lubricating oil can be highly degraded locally, which can damage the piston ring or liner.

The coke scraping ring in a known four-stroke engine limits the thickness of the coke layer as the piston moves near its top dead center and the uppermost piston section reciprocates through the coke scraping ring. The annular upper and lower edges of the scraping ring scrape off the coke that contacts these edges. Since the scraping ring protrudes from the inner surface of the cylinder, it is prevented from growing to a thickness of the coke layer such that the coke layer comes into contact with the inner surface of the cylinder.

Known engines with a coke scraping ring include four
Because the engine is a stroke engine, and the intake and exhaust valves of the four-stroke engine are both located within the cylinder cover, its operating parameters have little effect depending on whether or not a coke scraping ring is used. I do not receive. In this four-stroke engine, scavenging of the cylinder is performed by an independent piston stroke between each working stroke, and the supply of combustion air is made from above to below through the suction valve during the subsequent lower suction stroke. Thus, the coke scraping ring has no effect on cylinder scavenging and air supply. A more important factor for achieving more favorable results, achieved by the coke scraping ring in a four-stroke engine, is the movement of the piston itself with respect to the inner surface of the cylinder. This four-stroke cycle applies a different load to the piston during every other upstroke and the type of load changes every other during the downstroke. As a result, the radial position of the piston near the top dead center position is constantly changing, so that the coke scraping ring scrapes the coke deeper than a depth equal to its own inner diameter, thereby covering the coke. A gap is automatically formed between the cut uppermost piston portion and the coke scraping ring. Uniflow scavenging type 2
In the case of a stroke crosshead engine, the situation is not so straightforward, and experiments with coke scraping rings known from four stroke engines have resulted in increased fuel consumption and, in particular, in terms of damage to the uppermost ring, It has been found that there are inconvenient driving problems. Such damage is surprising, as the coke scraping ring was expected to actually improve the lubrication of the piston ring.

It is an object of the present invention to mitigate the above-mentioned problems and to enable an advantageous use of a coke scraping ring in a two-stroke crosshead engine.

In view of this, the present invention provides a uniflow scavenging, two-stroke crosshead engine in which the engine has a scavenging port located in the lower portion of the cylinder, the coke scraping ring having a cylindrical inner surface. , Characterized in that a number of leakage grooves extending obliquely with respect to the longitudinal axis of the cylinder from the lower surface to the upper surface of the coke scraping ring are provided.

The disadvantages identified when using the known coke scraping ring in a two-stroke engine may be explained by utilizing the following mechanism. In a two-stroke crosshead engine, the piston performs a compression stroke during each ascent operation and a working stroke during each descent operation. This means that each time the piston rises and falls through the coke scraping ring, the piston is loaded in substantially the same way. For this reason, the piston performs a uniform and repetitive movement pattern near its top dead center position. This tendency to have a uniform motion pattern is enhanced by the crosshead, which guides the lower end of the piston rod to translate completely along the longitudinal axis of the cylinder. As a result, the coke deposits on the piston periphery accumulate to such an extent that they accurately conform to the coke scraping ring, and there is a gap between the coke scraping ring and the uppermost piston part. Almost disappears. As the top of the piston passes through the coke scraping ring during the compression stroke, between the protruding scraping ring and the uppermost piston ring, an annular ring between the outer surface of the piston where the coke layer has accumulated and the inner surface of the cylinder A cavity is formed in the axial direction. This upward movement of the piston causes the annular cavity to rapidly shorten in the axial direction, resulting in a strong compression of the air in that cavity, thus creating a very high load on the uppermost piston ring. Let it.

Leakage grooves formed in the cylindrical inner surface of the coke scraper ring reduce or eliminate pressure buildup in the annular cavity. The reason is that the air in the annular cavity can escape through the leak groove to a part of the working chamber (combustion chamber) located above the top of the piston. This prevents the presence of the coke scraping ring from placing a large load on the uppermost piston ring. The factor is that the effective compression ratio is 1
This is of particular importance in today's large two-stroke crosshead engines, which are very large, such as pairs 16 to 1:20, which themselves cause very high loads on the piston ring.

The oblique formation of the leak groove can ensure that the coke is scraped off even in the area opposite to the leak groove. The portion of the coke deposit opposite to the lower opening formed in the leak groove does not intersect with the lower edge of the coke scraping ring, but during the continuous upward movement of the piston, the upper edge of the leak groove is removed. And is scraped off to the desired dimensions. The coke particles scraped in these grooves travel into the space above the piston due to leaking air squirting through the grooves.

Furthermore, the leakage groove prevents an increase in fuel consumption. When there are no leak grooves, the effective area of the piston is reduced during the first stage of combustion, when the top of the piston is at or above the coke scraping ring. It prevents the coke scraping ring from transmitting the elevated pressure in the working chamber (combustion chamber) down to the uppermost piston ring (the effective area of the piston covers the entire cross-sectional area of the cylinder). Because. These leak grooves reduce or eliminate the pressure drop at the coke scraping link during both the compression and working strokes,
For this reason, the specific fuel consumption is not substantially affected by whether or not the coke scraping ring is used.

A large two-stroke engine with high cylinder output, such as 1500 to 5500 kW, in which fuel is injected into a cylinder by two, three or four fuel injectors that generate a mist of spray fuel in a specific direction In particular, the coke scraping ring provides a further advantage, which is particularly advantageous.
The burning of the fuel produces a relatively intensive heat effect, but the coke scraping ring covers the uppermost piston ring when the piston is near its top dead center position (maximum heat load), Also, since only the hot gas passes through the leakage groove to the piston ring, the thermal load is evenly distributed across the uppermost piston ring, and therefore a film of heat-sensitive lubricating oil adhering to the inner surface of the cylinder To protect.
Both factors contribute to a better working condition for the piston ring pack and improve the effectiveness of preventing coke on the piston from contacting the lubricant film.

As an alternative to the arrangement of the leakage groove formed in the cylindrical inner surface of the coke scraping ring, the internal combustion engine described in the introduction part which is designed to have the coke scraping ring in the cylinder is also within the scope of the present invention. It is possible, and its features are:
The engine is a uniflow scavenging two-stroke engine having a scavenging port formed in a lower cylinder portion thereof, and a cylindrical outer surface of an uppermost piston portion disposed at a position below the uppermost piston ring. , So that there are several leakage grooves extending upward from the top of the piston part to the region of the annular groove for the uppermost piston ring. In this case, the cylindrical inner surface of the coke scraping ring can be formed as a consistent circular cylindrical surface. During each cycle of the engine, both compressed air and combustion gases flow through the leak channel, which prevents coke from depositing in the channel.

In one embodiment, the generally cylindrical inner surface of the cylinder is formed by an upper cover portion and a lower liner portion, and a coke scraping ring is located on top of the liner portion. The coke scraping ring may be a shrink-fit ring in a recess in the inner surface of the liner or, alternatively, a protruding portion of the liner's own material, ie, an integral and integral part of the liner. In this latter case, the piston with the piston rod must be installed during its assembly, before the liner is machined into position in the engine, so that the piston extends through the liner from below to above. . In this first case, this embodiment offers the advantage of allowing the coke scraping ring to be retrofitted to an existing engine.

In one alternative embodiment, the generally cylindrical inner surface of the cylinder is formed by an upper cover portion and a lower liner portion, and the coke scraping ring is located at the bottom of the cover portion. Also, in this case, the coke scraping ring may be a separate ring inserted into the recess of the upper cover portion, or may be formed integrally with the cover portion. The lower part of this cover part is precisely turned to a smaller inside diameter than the part located above it. If these leakage grooves are to be placed in the coke scraping ring, they can then be machined in the lower part of the cover part. This alternative embodiment is particularly applicable to cylinders that are subject to high thermal loads and whose cylinder cover is made of a material that is more heat resistant than liners. By placing the coke scraper ring in its cylinder portion, when the uppermost piston ring is in the top dead center position, the partitioning surface between the liner and the cover is moved down to the area directly above that position be able to.

This leakage groove accounts for 0.25 to 50%, preferably 5 to 40%, and optimally 20 to 30% of the axial area of the coke scraping ring projecting from the substantially cylindrical inner surface of the cylinder.
Is preferably occupied. The area of the leak groove is 0.
Below 25%, the pressure drop in the coke scraping ring becomes excessive, and if the leakage area is above 50%, no further advantageous effects are obtained. Although the 5% limit still reduces the pressure, the operating conditions are significantly improved, while the 40% limit usually prevents a pressure drop in the coke scraping ring. You can be completely satisfied. An area in the range of 20 to 30% provides a reasonable compromise between desirably minimizing or zeroing the pressure drop and desirably evenly distributing the heat load.

For a uniflow scavenging engine, the scavenging port is preferably opened by the upper surface of the piston. This means that the coke scraping ring must not protrude excessively from the inner surface of the cylinder. The reason is that if the width of the annular space between the coke layer and the inner surface of the cylinder is too large, the port is opened by the uppermost piston ring passing above the port at the end of the working process. is there. Thus, for a cylinder bore in the range of 250 to 1000 mm, the coke scraper ring should be in the range of 0.5 to 5 mm from the inner surface of the cylinder (at least 0.2 m
Preferably, only m) protrudes. Projecting distance is 0.2m
A short distance of m or 0.5 mm ensures that the scavenging port is completely shut off until the top surface of the piston has passed. In the largest engines, the coke scraping ring is suitable to protrude a few mm (at least 1 mm), while for smaller engines it is 0.5 mm.
A distance of ~ 2 mm is appropriate. The distance the ring protrudes
If it is less than 0.25 mm, it will be more difficult to ensure that the coke deposits do not contact the lubricant film on the inner surface of the cylinder.

The uppermost piston portion located above the uppermost piston ring has a smaller diameter than the lower piston portion with the piston ring, and the inner diameter of the coke scraping ring is smaller than the diameter of the uppermost piston portion. Also from 2
Preferably it is 6 mm (at least 0.5 mm), optimally 1 to 4 mm larger than the diameter. With such a diameter ratio, the coke layer is 0.5 to 3 mm, optimally 0.75 to 2 mm
Which means that a suitable gap is provided for radially positioning the piston with respect to the coke scraping ring without the risk of the outer periphery of the piston contacting the scraping ring. enable.

Within the scope of the present invention, it is also possible for the coke scraping ring to protrude further from the inner surface of the cylinder by more than the above-mentioned distance, and correspondingly reduce the diameter of the uppermost piston part, It is possible to increase the thickness of the annular space around the part and the inner surface of the cylinder. Such a design allows the scavenging port to open earlier, i.e. when the uppermost piston ring passes at the end of the working process,
Also, the opening timing of the exhaust valve and other engine parameters depending on the opening timing of the scavenging port need to be changed according to the supply of scavenging gas at an early stage.

The number of leak grooves in the coke scraping ring or piston is such that the desired leak area and the thermal load acting on the uppermost piston ring are desirably uniform, and that more leak ports can be used. To this end, it relies on having a larger leakage area and more even distribution of the heat load. Suitably, the coke scraping ring or piston is provided with 4 to 30 leak grooves.

It is preferable to form 15 or more leakage grooves, since a remarkable advantage is obtained by making the thermal load in the uppermost piston ring uniform.

If the leak grooves are formed on the outer circumference of the uppermost piston portion, they may extend parallel to the axis of the cylinder, and there is a risk that debris of coke may be immediately taken into the leak groove and clog the leak groove. It is advantageous to have none. Otherwise, the number and dimensions of the leak grooves can be selected in the same way as the leak grooves of the coke scraping ring, ie in the same way as described below.

Next, embodiments of the present invention will be described in more detail below with reference to extremely schematic drawings. In the accompanying drawings, FIG. 1 is a simplified cross-sectional view of an engine with a coke scraping ring according to the present invention.

FIG. 2 is an enlarged partial sectional view showing an area around a coke scraping ring in a cylinder of the engine of FIG.

FIG. 3 is a non-extended side view of a portion of the coke scraping ring.

FIG. 4 is a plan view of a part of the coke scraping ring.

FIG. 5 is a perspective view of the uppermost piston portion provided with a leakage groove in a region above the uppermost piston ring.

FIG. 6 is a corresponding view of another embodiment of a piston having a leakage groove.

The engine illustrated in FIG. 1 is a heavy fuel fuel that combustion of the fuel forms residual products that can deposit as coke on its surface in the engine's working chamber (combustion chamber). It is a large two-stroke engine of the uniflow scavenging type using oil cooking. Depending on the size and number of cylinders, this engine can be between 2,000 and e.g. 70,000k
An output of W can be generated. Such engines have been conventionally used as main engines of ships or as stationary power generation engines. In both cases, it is important that the engine be able to operate for a very long time without checking or disassembling the components of the engine.
The engine should be able to operate continuously for more than two years without disassembly, which requires that the components of the cylinder be in the best possible operating condition.

The immovable parts of the engine include a base plate 1 on which a crankshaft 2 is supported, and an engine frame box 3 mounted on the base plate and supporting a cylinder portion 4 on an upper surface thereof.
And The cylinder liner 5 is fastened to the top plate 6 in the cylinder part by the cover stud 7 and the cylinder cover 8. The cylinder liner is
It has a thick upper part, which sits on the upper surface of the top plate via an annular intermediate member 9. The cylinder liner also has an elongated lower part that protrudes downward into the cylinder part 4. The cylinder liner has a number of scavenging ports 10 at its lower end, and when the piston is near its bottom dead center, the scavenging receiving section 11
The scavenging air and the supply air flow into the cylinder through these scavenging ports. An exhaust valve housing 12 having a hydraulically operable exhaust valve is located at the center of the cylinder cover. When the exhaust valve opens, the scavenging air from the exhaust port flows upward through the cylinder, and at the same time, the combustion gases flow out through the exhaust valve and into the exhaust receiving section 13, from which the gas is , And flows into the exhaust pipe through the supercharger. The engine is charged at a high pressure, for example, up to a charge pressure of 3.5 to 4 bar.

A connecting rod 14 connects the crankshaft 2 to a crosshead 15 which reciprocates in a translational manner at the lower end of a piston rod 17 along a longitudinal axis of the cylinder by a guide plate 16 in the engine room box. I will guide you to exercise. Piston 18 is attached to the top of the piston rod. As shown most clearly in FIG. 2, the piston has several (eg, four) piston rings.
19, 19 ', the piston ring sliding along the inner surface of the cylinder liner and the working chamber 20 and the volume located below the piston (communicating with the scavenging-filled cylinder part) To form a pressure seal partition.

The combustion chamber, that is, the working chamber 20 includes an inner surface of the cylinder cover 8, an inner surface of the cylinder liner 5, and a piston 18.
, The uppermost piston ring 19 ', and the outer periphery of the uppermost piston portion 21 extending upwardly from the uppermost piston ring. The uppermost piston portion 21 has a smaller diameter than the lower portion of the piston, and therefore, between the outer surface of the uppermost piston portion and the inner surface of the cylinder, there is an annular space 22, in which the annular space 22 is formed. , Coke accumulates on the outer surface of the piston.

An annular coke scraping ring 23 in the cylinder protrudes from the inner surface of the cylinder to scrape off the coke that has accumulated on the outer surface of the uppermost piston portion 21, so that these accumulations have a maximum equal to the inner diameter of the coke scraping ring. Never exceed the diameter of. Preferably, when the piston is in its top dead center position as shown, the upper piston ring 19 'is positioned below the coke scraping ring 23 at a spacing less than the height of a single ring. The take-up ring is positioned in the longitudinal direction of the cylinder. This ensures that the coke layer is substantially substantially scraped off to the uppermost piston ring. However,
For example, only a distance corresponding to the height of two or three rings,
Even when the coke scraping ring is further positioned somewhat higher, a significant coke scraping effect can be obtained.

3 and 4, on its inner surface, the coke scraping ring is formed with several leakage grooves 24, which interact with a part of the annular space 22 arranged below the coke scraping ring. A gas flow communication is formed between the chamber 20 and the remaining upper portion. The flow area of the leak groove is appropriately set so that the pressure drop in the coke scraping ring is negligible. Advantageously, these leakage grooves are evenly distributed along the inner circumference of the coke scraping ring, since the heat load on the uppermost piston ring 19 'is more uniform. The depth of this leak groove can be equal to the distance the coke scraping ring projects with respect to the inner surface of the cylinder. This is particularly advantageous if the scraping ring projects from the inner surface by a distance of at least 0.25 mm (eg, 0.5 to 3 mm). The annular space 22 is wide, and the scavenging port 10 is
If the piston and the scavenging ring are formed such that they open, the depth of the leak groove must be less than the thickness of the coke scraping ring projecting inward. The gas flow through the individual grooves at deeper locations increases and the thermal load acting on the uppermost piston ring becomes extremely large locally, so that the depth of these leakage grooves is 3-4 mm or more. Preferably not. By forming an appropriate number of grooves having a depth of not more than 1.5 to 2 mm and a leakage amount of 15 or more, extremely uniform heat distribution becomes possible.

The width of the leak groove is selected based on the number of leak grooves, the depth of the groove and the desired total flow area, in particular the total axial cross-sectional area of the end of the groove. To achieve a uniform heat load,
In most cases, a groove width of 5 to 30 mm is appropriate, and a groove width of 10 to 20 mm is preferable.

The leakage groove 24 extends in an oblique direction with respect to the longitudinal axis of the cylinder, so that the upper end 25 of the groove is circumferentially displaced with respect to the lower end 26 of the groove. This offers the advantage that the coke layer is scraped off along the entire circumference of the upper piston part 21. In the example shown, the longitudinal axis of the leakage groove forms an angle of 45 ° with the longitudinal axis of the cylinder. Of course, other angles, such as 15 ° to 80 °, can be employed. This angle corresponds to the width of the groove, so that the groove does not overlap axially between the upper end 25 of the groove and the lower end 26 of the groove. For manufacturing reasons, the leak groove preferably extends linearly between the upper and lower ends of the groove, but of course, such as an L-shaped or other non-linear path, may be used. Other designs that create flow communication between the upper end 25 and the lower end 26,
In fact, it can work.

5 and 6 show an embodiment in which the leakage groove is arranged on the upper surface of the piston in the uppermost piston part. For reasons of simplicity, the same reference numbers have been used above for elements of the same type.
It will be understood that the piston ring is omitted in the drawings.

In FIG. 5, on the left side of the piston, a longitudinal section through the innermost part of the liner 5 is shown, the cylinder cover 8 in the area around the coke scraping ring 23 ′ being the cylinder cover 8 It is formed directly on the material, that is, as an integral and integral part of the cover. On the right side of the piston, a corresponding longitudinal sectional view of an alternative design is shown, in which the coke scraping ring 23 'is formed directly on the material of the cylinder liner, i.e. on the liner. It is formed as an integral and consistent part. Comparing the right side and the left side of the drawing, in one and the same engine, when the coke scraping ring 23 ′ is arranged in the cylinder cover, the partition surface 27 between the cover and the liner extends in the longitudinal direction of the cylinder. It is immediately understood that the advantage of moving downwards can be realized. Since the inner surface of the cover does not constitute the sliding surface of the piston ring, it is not necessary to consider lubrication conditions and sliding characteristics when selecting a material for the cover. For this reason, the cover can be made of a material such as steel, which is typically more durable and more heat resistant than the liner material, which is cast iron. The effect of heat is greatest in the upper region of the cylinder, so that the cylinder can have a longer life as the cover extends further down.

In the embodiment shown, the coke scraping ring 23 ′ arranged on or in the liner 5, or on or in the cover 8, has a circular cylindrical inner surface 28, The inner surface 28 is annular and has no leakage grooves. Of course, it is possible to form a part of the leak groove in the coke scraping ring and a part in the piston ring, but for manufacturing reasons, the above design is preferable. It can be manufactured by appropriately turning the inner surface of the liner or cover.

The leakage groove 24 'is located in the uppermost part 21 of the piston and extends downwardly from the upper chamfered portion of the piston to the uppermost annular groove 29 for the uppermost piston ring 19'. The uppermost part 21 of the piston is high, so that when the piston is at its top dead center, the piston ring is located further down in the cylinder,
This allows the cylinder cover to extend downward along the cylinder in a further advantageous manner.

The leakage groove of FIG.
Form an angle of 30 °. In practice, this angle can be selected in the range of 0 ° to 60 ° or more, but the groove forms an angle of at least 15 ° along at least part of its length, Preferably, it is possible to prevent the upper end and the lower end of the groove from being vertically positioned such that one is above the other.

FIG. 6 illustrates one alternative embodiment of a piston, in which a leakage groove 24 "has an upper portion 24a extending parallel to the longitudinal axis of the cylinder and an upper portion of the cylinder. A lower portion 24b extending obliquely with respect to the longitudinal axis, the lower oblique portion 24b circumferentially displacing the lower end of the groove with respect to the upper end of the groove so that the coke is scraped along its entire circumference. The upper part 24a of the leak groove is not useful for scraping the coke,
There is no risk of clogging with the scraped coke particles. It is also possible to place the diagonal part of the leakage groove at the top of the groove, which means that the piston is driven when the upper part of the groove passes through the coke scraping ring during the scavenging. There is the advantage that the velocity of the gas through the groove is higher because the velocity is higher.

The design shown, with the diagonal groove portion at the lower end of the groove, the relatively high height of the uppermost portion 21 of the piston is provided by a separate piston top fixed to the lower piston portion with an annular groove for the piston ring. When formed
It is particularly advantageous. In this case, the two parts of the leakage groove can be manufactured in the same simple manner as the straight grooves in the respective piston parts.

In other respects, the area and number of the leak grooves can be formed to correspond to the leak grooves located in the coke scraping ring.

Continuation of the front page (56) References JP-A-52-27908 (JP, A) JP-A-4-321758 (JP, A) JP-A-7-38638 (JP, U) JP-A-4-24649 (JP, A) U.S. Patent 3476099 (US, A) U.S. Patent 4474147 (US, A) U.S. Patent 4770133 (US, A) U.S. Patent 3489130 (US, A) Swiss Patent Invention 672353 (CH, A5) (58) Field (Int.Cl. ⁷ , DB name) F02F 1/00-5/00

Claims (12)

(57) [Claims] A piston (18) having a coke scraping ring in a cylinder, displaceable longitudinally in the cylinder and provided with a piston ring (19, 19 '). When the ring displaces the piston,
Sliding along the generally cylindrical inner surface of the cylinder to form a pressure-tight partition between the volume below the piston and the combustion chamber (20), the combustion chamber being the uppermost piston ring of the piston; And the uppermost piston ring (19 '),
The coke scraping ring (23) is defined by a piston (18), an inner surface of a cylinder, and a cylinder cover (8), and protrudes from the inner surface of the cylinder and extends annularly at an axial position. An internal combustion engine, wherein the uppermost piston ring is disposed at a position near a lower edge of the coke scraping ring when the engine is at a top dead center position, wherein the engine has a scavenging port disposed in a lower portion of a cylinder; A uniflow scavenging two-stroke crosshead engine having (10), wherein the coke scraping ring (23) has a cylindrical inner surface extending from a lower surface to an upper surface of the coke scraping ring in a longitudinal direction of the cylinder. An internal combustion engine characterized in that several leakage grooves (24) extending obliquely with respect to the axis are provided. 2. A piston (18) having a coke scraping ring in a cylinder, the piston being displaceable longitudinally in the cylinder and being provided with a piston ring (19, 19 '). When the ring displaces the piston,
Sliding along the generally cylindrical inner surface of the cylinder to form a pressure-tight partition between the volume below the piston and the combustion chamber (20), the combustion chamber being the uppermost piston ring of the piston; And the uppermost piston ring (19 '),
The coke scraping ring (23 '), defined by a piston (18), an inner surface of a cylinder and a cylinder cover (8), protrudes from the inner surface of the cylinder and extends annularly at an axial position, wherein the piston When in the top dead center position, the internal combustion engine has an uppermost piston ring positioned near the lower edge of the coke scraping ring, the engine comprising a scavenging port formed in its lower cylinder portion ( 10) is a uniflow scavenging crosshead two-stroke engine having a cylindrical outer surface of an uppermost piston portion (21) located above the uppermost piston ring, from the top of said piston portion. Internal combustion engine characterized in that there are provided several leakage grooves (24 ') extending downward to the region of the annular groove for the uppermost piston ring (19'). 3. The internal combustion engine according to claim 1, wherein the substantially cylindrical inner surface of the cylinder is formed by an upper cover portion and a lower liner portion, and wherein the coke scraping rings (23, 23 '). Is disposed on top of said liner portion (5). 4. An internal combustion engine according to claim 1, wherein said substantially cylindrical inner surface of said cylinder is formed by an upper cover portion and a lower liner portion, and said coke scraping ring (23, 23 '). Is disposed at the bottom of the cover portion. 5. The internal combustion engine according to claim 3, wherein said scraping ring (23, 23 ') is an integral part of said cylinder liner or said upper cover part. An internal combustion engine, characterized in that the take-off ring is manufactured as a part projecting into the material of the cylinder liner or the cover part. 6. The internal combustion engine according to claim 1, wherein said leakage groove (24, 24 ') is protruded from a substantially cylindrical inner surface of said cylinder. 23. An internal combustion engine characterized in that it occupies 0.25 to 50% of the axial area. 7. The internal combustion engine according to claim 6, wherein said leakage groove (24, 24 ') is formed in an axial direction of a coke scraping ring (23, 23') protruding from a substantially cylindrical inner surface of said cylinder. An internal combustion engine characterized by occupying at most 30% of the area. 8. The internal combustion engine according to claim 1, wherein the bore of the cylinder is in a range of 250 to 1000 mm, and the coke scraping ring (23, 23 ') is provided. An internal combustion engine protruding from the inner surface of the cylinder by a distance of at least 0.2 mm. 9. The internal combustion engine according to claim 1, wherein said uppermost piston portion (21) arranged at a position above said uppermost piston ring (19 ') comprises: A smaller diameter than the lower piston portion having a piston ring,
The inner diameter of the coke scraping ring (23, 23 ') is
At least 0.5mm larger than the diameter of the uppermost piston part
An internal combustion engine characterized by being large. 10. The internal combustion engine according to claim 1, wherein the coke scraping ring (23, 23 ') or the uppermost piston part (21) has four to four. An internal combustion engine, wherein 30 leakage grooves are formed. 11. The internal combustion engine according to claim 1, wherein a longitudinal axis of the leakage groove (24, 24 ′) is 0 ° to an axial direction of the cylinder. An internal combustion engine characterized by forming an angle of 60 °. 12. The internal combustion engine according to claim 11, wherein a longitudinal axis of said leakage groove (24, 24 ') forms an angle of at least 15 ° with respect to an axial direction of said cylinder. An internal combustion engine, characterized in that: