Piston and cylinder of an internal combustion engine and internal combustion engine

A piston of a cylinder of an internal combustion engine includes: an upper piston crown; a radially outer surface; a plurality grooves arranged on the radially outer surface; and a plurality of piston rings each positioned in a respective one of the grooves. The radially outer surface forms a top land arranged between the upper piston crown and an uppermost one of the grooves of the piston, and the top land has an axial length and a non-abrasion-proof coating.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a piston of a cylinder of an internal combustion engine, to a cylinder of an internal combustion engine and to an internal combustion engine.

2. Description of the Related Art

From DE 10 2013 009 415 A1 a piston of a cylinder of an internal combustion engine is known, which is moveably guided, up and down, in a cylinder liner. In a recess of the cylinder liner, a flame ring is positioned. Into a radially outer surface of the piston, grooves are introduced which accommodate the piston rings. Between a front or upper piston crown of the piston and the uppermost or front-most groove of the piston, the radial outer surface of the piston forms a so-called top land, wherein the flame ring of the cylinder liner serves, among other things, for scraping off deposits from the radially outer surface of the piston, in particular in the region of the top land.

Between the radially outer surface of the piston, namely the top land, and the flame ring a clearance is necessary in order to make possible undisturbed moving of the piston in the cylinder liner. In this clearance between piston and flame ring, a so-called waste volume forms, in which a fuel mixture can collect, which participates in the combustion only ineffectively. For reducing the waste volume and thus for increasing the engine efficiency, the clearance between the piston and the flame ring is selected, according to the prior art, as small as possible. This requires high manufacturing tolerances.

From DE 10 2013 009 415 A1 it is known, for reducing the waste volume, to pull the piston crown, at the radially outer edge, axially to the back.

SUMMARY OF THE INVENTION

Starting out from this, it is an object of the present invention to create a new type of piston of a cylinder of an internal combustion engine, a cylinder of an internal combustion engine and an internal combustion engine.

This object may be achieved by a piston having a top land. The piston, in the region of the top land, comprises or carries a soft, non-abrasion-proof coating. During a local contact of the top land of the piston with the flame ring developing during the operation, the coating can be locally removed to exactly set the clearance necessary for operation between piston and flame ring, namely without demanding high manufacturing tolerances. By way of the non-abrasion-proof coating, the waste volume between piston and flame ring can be minimized and the engine efficiency increased.

Preferentially, the non-abrasion-proof coating consists of resin-bonded graphite. Such a coating is particularly preferred in order to set, during the engine operation, the clearance necessary for the operation between piston and flame ring by local abrasion of the coating.

According to a further development of the invention, the non-abrasion-proof coating has a thickness between 0.02 mm and 0.2 mm, preferentially between 0.05 mm and 0.15 mm. This thickness of the non-abrasion-proof coating is particularly preferred in order to set during the engine operation, the clearance between piston and flame ring necessary for the operation.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1shows an extract of a cylinder10of an internal combustion engine according to the invention as per a first exemplary embodiment of the invention in the region of a cylinder liner11, and of a piston12that is moveably guided, up and down, in the cylinder liner11. The piston12has a radially outer surface13and a front or upper piston crown14. In the piston crown14, a trough15can be centrally introduced. On its radially outer surface13, the piston12comprises grooves16a,16band16c. Piston rings17a,17b,17care inserted into these grooves16a,16band16c, respectively of the piston12. The two upper piston rings17a,17bare referred to as compression rings and the lower piston ring17cas an oil scraper ring.

A top land18of the piston12extends between the piston crown14and the uppermost or front-most groove16aof the piston12. The distance between the uppermost or front-most groove16aof the piston12and the piston crown14cis referred to as top land height18hof the top land18.

The cylinder liner11accommodates a flame ring19. The flame ring19is inserted into a recess20of the cylinder liner11. During operation, the piston12can be cleaned in the region of its top land18with the help of the flame ring19. In particular, the flame ring19serves for scraping off deposits, such as, for example, coke, from the radially outer surface13of the piston12in the region of the top land18and thus in the region of the top land height18h.

In the exemplary embodiment shown inFIG. 1, an outer diameter of the radially outer surface13conically decreases in the region of the top land18, seen from the front-most or uppermost groove16a, in the direction of the piston crown14, at least in regions. Between the top land18and the flame ring19, a free space21is formed, which determines the clearance between the flame ring19and the top land18of the piston12. In this free space21, fuel can collect during engine operation, which is only inefficiently combusted. For this reason, this free space21is also referred to as a waste volume.

In order to keep the waste volume21as low as possible even with low manufacturing tolerances and an increase the efficiency of an internal combustion engine, the top land18carries a non-abrasion-proof coating22radially outside.

This relatively soft, non-abrasion-proof coating22can be removed during a local contact between the top land18and the flame ring19, to thereby set the clearance necessary for operation between the top land18of the piston12and the flame ring19to a minimum during the engine operation. This increases the efficiency of the engine.

The non-abrasion-proof coating22is preferentially a coating of resin-bonded graphite.

The piston12is preferentially a piston assembled from a piston lower part that is not shown and a piston upper part, wherein piston lower part and piston upper part can both consist of steel or cast iron, in particular spheroidal graphite cast iron. Light metal can also be utilized.

The non-abrasion-proof coating22consists of a softer material than the material of the piston lower part and of the piston upper part. Furthermore, the non-abrasion-proof coating22consists of a softer material than the flame ring19and the cylinder liner11.

Further properties of the non-abrasion-proof coating22are a temperature resistance up to 250° C., a resistance to attacks by fuel and lubricating oil, and a good adhesion/bonding. The hardness of the coating22preferably is in a hardness range from 10-50 HB (Brinell). Soft materials such as, for example, resin-bonded graphite or heat-resistant plastics satisfy these properties.

The non-abrasion-proof coating22of preferentially resin-bonded graphite preferentially has a thickness between 0.02 mm and 0.2 mm, preferably between 0.05 mm and 0.15 mm.

In the exemplary embodiment ofFIG. 1, the non-abrasion-proof coating22is applied to that region of the top land18, which, emanating from the uppermost or front-most groove16a, conically tapers in the direction of the piston crown14. Here, the coating22is applied to this region over its entire axial extent or over its entire axial length. Accordingly, the coating22inFIG. 1ends in the region of the piston crown14.

Compared with this,FIG. 2shows a modification of the invention in which the non-abrasion-proof coating22is configured shorter and ends at a distance from the piston crown14.

Preferentially, the piston12according to the invention is an oil-cooled piston.

The invention does not only relate to the piston12as such but rather also to a cylinder10with a cylinder liner11and a piston12according to the invention, as well as an internal combustion engine having at least one, preferentially multiple, such cylinder/s10.

With the invention it is possible to improve the engine efficiency namely by reducing the waste volume21between flame ring19and top land18.

The invention can be employed both with diesel internal combustion engines and also with spark-ignition gas engines as well as dual-fuel engines, namely both with two-stroke and also with four-stroke internal combustion engines. The invention is employed in particular with pistons of large engines such as diesel engines or gas engines or diesel-gas engines on ships, the outer diameter of which is in particular in the range between 100 mm and 600 mm.

LIST OF REFERENCE NUMBERS

18hTop land height