CYLINDER LINING FOR AN INTERNAL COMBUSTION ENGINE

Abstract

Cylinder liner for an internal combustion engine, comprising an inner side (2) forming a running surface, wherein the cylinder liner has at least one thermal insulation (4) extending circumferentially around the cylinder liner, wherein the insulation (4) forms a cavity filled with insulating material, wherein the insulation (4) is arranged radially outwards from the running surface, wherein the cylinder liner has an outer side (6) and the insulation (4) is arranged between the running surface and the outer side (6), wherein the running surface has a length L in the axial direction and the insulation (4) begins at a distance of 15-20% of the length L and extends from there in the crankcase direction.

Description

Field of invention The present invention relates to a cylinder liner for an internal combustion engine. State of the art Friction within the piston-piston ring-cylinder system can be divided into contact friction, mixed friction, and hydrodynamic friction. Hydrodynamic friction accounts for a large portion of the total friction. This is one of the main reasons why increasingly lower viscosities are sought for engine oils, as hydrodynamic friction is directly proportional to oil viscosity. Oil viscosity, in turn, is temperature-dependent. Since the cylinder temperature is generally highest at top dead center (TDC) and lowest at bottom dead center (DDC) along the stroke, the oil viscosity is low at TDC and increases continuously towards DDC. Furthermore, hydrodynamic friction is directly proportional to piston speed. Since piston speed is highest in the middle of the piston stroke, a low oil viscosity is desirable there to achieve low hydrodynamic friction. From a friction point of view, a high oil viscosity at the dead points is ideal for reducing contact friction, and a low oil viscosity towards the center of the cylinder liner is ideal for reducing hydrodynamic friction. From DE 27 34 254 A1, a cylinder liner for a reciprocating internal combustion engine, which is installed in a machine frame, is already known. The cylinder liner is in operative communication with a heat pipe, which is essentially jacket-shaped and extends from a cooling water chamber to or into the collar, wherein the heat pipe has internal means, e.g. a capillary structure, which enable the transport of the liquid heat transfer medium along the cylinder tube even against gravity. From DE 102 25 062 B4, a cylinder liner of a reciprocating internal combustion engine is already known, to which at least one first coolant channel in the region of a top dead center of a piston movement of a piston of the reciprocating internal combustion engine and a group of second coolant channels in the middle liner region and in the region of a bottom dead center of a piston movement of a piston of the reciprocating internal combustion engine are assigned. The technical objective of the invention is to optimize the oil viscosity along the stroke position. Summary of the invention According to a first aspect, the invention relates to a cylinder liner for an internal combustion engine, comprising an inner surface that forms a running surface, wherein the cylinder liner has at least one thermal insulation extending circumferentially around the cylinder liner, wherein the insulation is arranged radially outwards from the running surface. The advantage of the cylinder liner according to the invention lies in the fact that heat dissipation via the cylinder liner is reduced by insulation within the cylinder liner, resulting in lower oil viscosity and thus reduced hydrodynamic friction in this area. The insulation of the cylinder liner can be continuous or extend only partially around the cylinder liner. In one exemplary embodiment of the cylinder liner, the insulation forms a closed ring that extends around the entire cylinder liner. Because the insulation forms a closed ring around the entire cylinder liner, optimal insulation is achieved without any heat exchange taking place in gaps. In an exemplary embodiment of the cylinder liner, the cylinder liner has an outer surface, with the insulation arranged between the running surface and the outer surface. In another exemplary embodiment of the cylinder liner, the insulation is designed as an evacuated or fluid-filled cavity. Vacuum insulation provides thermal insulation by reducing heat transfer caused by air molecules. The vacuum can prevent both convection and heat conduction. An example of preventing heat conduction is the design of a Dewar vessel. In another exemplary embodiment of the cylinder liner, the cavity is filled with insulating material. Filling the cavity of the cylinder liner with insulating material, such as glass wool, asbestos, etc., offers advantages in terms of cost, maintenance and manufacturing. In an exemplary embodiment of the cylinder liner, the running surface has a length L in the axial direction, with the insulation starting at a distance of 15-20% and extending from there in the crankcase direction. The maximum length L of the running surface is measured from the upper, combustion chamber-side edge of the cylinder liner. The insulation area is defined according to the preceding feature, as it is not practical to start earlier due to the piston ring land height, since the piston rings are not in hydrodynamic engagement there. Furthermore, the ring land area is precisely where heat should be dissipated for cooling. In another exemplary embodiment of the cylinder liner, the running surface has a piston stroke length K in the axial direction between a top dead center and a bottom dead center, wherein the insulation begins at a distance of 15-20% from the top dead center and extends from there towards the bottom dead center. The piston stroke length K refers to a piston movement of an engine for which the cylinder liner is designed. The insulation area is defined according to the preceding feature, since it is not practical to start earlier due to the piston land height, as the piston rings are not in hydrodynamic engagement there. Furthermore, the fire land area is precisely where heat is dissipated for cooling. The insulation can even extend beyond bottom dead center. In another exemplary embodiment of the cylinder liner, the radial thickness of the insulation and / or the thermal resistance of the insulation in the axial direction increases from a combustion chamber towards a crankcase and / or first increases and then decreases again. The advantage of an increasing and / or initially increasing and then decreasing radial thickness of the insulation and / or the thermal resistance of the insulation in the axial direction from a combustion chamber towards a crankcase is that the oil viscosity is optimally adapted to the operating conditions. In an exemplary embodiment of the cylinder liner, the insulation is arranged at a maximum of 85-95%, preferably 88-92%, particularly preferably 89-91% of an operating temperature in a region of the running surface where a piston's top dead center is located in conventional cylinder liners. The insulation is defined in operating temperature ranges according to the preceding feature, since cooling is necessary in higher operating temperature ranges and therefore heat dissipation must not be reduced. In another exemplary embodiment of the cylinder liner, at least one insulation in the axial direction is divided into 2-6 sections and / or at least one insulation in the circumferential direction is divided into 2-72 sections or sub-areas thereof. Insulation in both axial and circumferential directions can be optimally adapted to the operating conditions to influence the oil viscosity at the running surface in such a way as to reduce friction. The axial direction corresponds to the stroke direction. Sections in the axial direction are separated by webs or insulated to varying degrees, and sections in the circumferential direction are also separated by webs or insulated to varying degrees. The advantage of the webs is their ability to absorb the load generated by piston movement within the cylinder liner. This reduces deformation and extends the service life of the cylinder liner. In another exemplary embodiment of the cylinder liner, the insulating material is selected from or consists of the group comprising plastic, foam glass, titanium, mineral / glass wool, ceramic particles, composite materials, pearlite and / or porous or foamed metal such as cast iron, metal spray coatings or alloys. In an exemplary embodiment of the cylinder liner, the insulating material has a porosity between 20-80%, preferably 40-80%, and particularly preferably 60-80%. The insulating effect can be easily adapted to operational requirements through the porosity. In another exemplary embodiment of the cylinder liner, the cylinder liner is manufactured by 3D printing and / or the insulation is produced by spraying metal and ceramic. 3D printing allows for the on-demand creation of any desired structure with minimal material consumption. However, it is preferable to print or injection mold only the insulation. In another exemplary embodiment of the cylinder liner, the insulation material has no porosity but conducts less heat than a cylinder liner material. Lower porosity allows for unrestricted load bearing, thereby reducing deformations and extending the service life of the cylinder liner. Brief description of the drawings Exemplary embodiments of the invention are described in more detail below with reference to the figures, where Fig. 1 shows a sectional view of a cylinder liner with thermal insulation, and Fig. 2 shows a sectional view of a cylinder liner with material insert in the thermal insulation, which is not covered by the invention. Detailed description of the drawings Fig. 1 shows a sectional view of a cylinder liner according to an embodiment of the invention. The cylinder liner has an inner surface 2, which forms a running surface for a piston, an outer surface 6 and a circumferential insulation 4. At the upper end of the cylinder liner, on the outer surface 6, there is a circumferential projection that allows the cylinder liner to be inserted precisely into an engine block. Furthermore, at the upper end of the cylinder liner, on the inner surface 2, there is a circumferential rectangular recess designed for a piston ring. This piston ring prevents the formation of hard carbon deposits on the piston's land. This is achieved by the piston ring having a smaller inner diameter than the cylinder bore diameter. As the piston passes top dead center, the piston ring scrapes the unwanted carbon deposits from the piston, or prevents deposits from forming on the land in the first place. In a central region of the cylinder liner, spaced apart from the top and bottom, there is a circumferential thermal insulation cavity. This cavity has a rectangular cross-section and wall thicknesses of 2 on the inside and 6 on the outside, which are of the same constant radial thickness. Furthermore, the cylinder bore length L and piston stroke length K are shown. The cylinder bore length L extends axially over the entire cylinder liner, while the piston stroke length K only extends to the end of the cavity. This means that bottom dead center corresponds to the lower end of the thermal insulation. Fig. 2 shows a sectional view of a cylinder liner according to another embodiment, which is not covered by the invention. The cylinder liner has an inner surface 2, which forms a running surface for a piston, an outer surface 6, and a circumferential insulation 4. At the upper end of the cylinder liner on the outer side 6, there is also a circumferential projection, which allows the cylinder liner to be inserted precisely into an engine block. Furthermore, at the upper end of the cylinder liner on the inner side 2, there is also a circumferential rectangular recess, which is intended for a fire ring. In a central region of the cylinder liner, spaced apart from the top and bottom, there is a circumferential thermal insulation formed by inserting material into a cavity. The cavity has a rectangular cross-section, is located on the outer surface 6 of the cylinder liner, and has a wall thickness on the inner surface 2 that is constant radially thick. The outer diameter of the material insert is equal to the outer diameter of the cylinder liner at the respective location. Furthermore, the cylinder bore length L and piston stroke length K are shown. The cylinder bore length L extends axially over the entire cylinder liner, while the piston stroke length K only extends to the end of the cavity. This means that bottom dead center corresponds to the lower end of the thermal insulation. Reference symbol list 2 Inside 4 Thermal insulation 6 Outside K Piston stroke length L Length of running surface

Claims

Cylinder liner for an internal combustion engine, comprising an inner side (2) forming a running surface, wherein the cylinder liner has at least one thermal insulation (4) extending circumferentially around the cylinder liner, wherein the insulation (4) forms a cavity filled with insulating material, wherein the insulation (4) is arranged radially outwards from the running surface, wherein the cylinder liner has an outer side (6) and the insulation (4) is arranged between the running surface and the outer side (6), wherein the running surface has a length L in the axial direction and the insulation (4) begins at a distance of 15-20% of the length L and extends from there in the crankcase direction. Cylinder liner according to claim 1, wherein the insulation (4) forms a closed ring extending around the entire cylinder liner. Cylinder liner according to claim 1 or 2, wherein the running surface has a piston stroke length K in the axial direction between a top dead center and a bottom dead center, wherein the insulation (4) begins at a distance of 15-20% from the top dead center and extends from there towards the bottom dead center. Cylinder liner according to one of the preceding claims, wherein a radial thickness of the insulation (4) and / or a thermal resistance of the insulation (4) increases in the axial direction from a combustion chamber towards a crankcase and / or first increases and then decreases again. Cylinder liner according to one of the preceding claims 1, 3-4, wherein the at least one insulation (4) is divided into 2-6 sections in the axial direction and / or the at least one insulation (4) is divided into 2-72 sections in the circumferential direction. Cylinder liner according to one of the preceding claims, wherein the insulating material is selected from the group comprising plastic, foam glass, titanium, mineral / glass wool, ceramic particles, composite materials, perlite and / or porous or foamed metal such as cast iron, metal spray coatings or alloys. Cylinder liner according to one of the preceding claims, wherein the insulating material has a porosity between 20-80%, preferably 40-80%, particularly preferably 60-80%. Cylinder liner according to one of claims 1 or 2, wherein the cylinder liner is manufactured by 3D printing and / or the insulation (4) is manufactured by spraying metal and ceramic.

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