SCOPE OF THE INVENTION

[0001] The present invention relates to a cylinder liner for internal- combustion engines. In particular, the invention relates to a cylinder liner including an outer surface with projections and cavities of different shapes and structures.

DESCRIPTION OF THE PRIOR ART

[0002] In combustion engines that have an engine block made from an aluminum alloy, cylinder liners are usually inserted in the cylin der borehole of the engine block. The cylinders are made up of cylin drical tube sections and the inner surfaces thereof form the combustion space of the combustion chamber of the engine. The outer surfaces are often treated to provide the outer surface with a rough texture. This rough texture ensures adhesion of the cylinder liner to the engine block when the coating is cast in the engine block.

[0003] In addition to this, it is common for combustion engines to have cylinders made of a metal that is different from the engine block so as to improve the performance thereof, since the material used for the cylinder usually has better tribological properties (friction, wear and lubrication during contact between solid surfaces) in relative motion and mechanical properties than the material used for the engine block.

[0004] The adherence between these two materials is one of the most important factors affecting the performance of the engine, since the projections on the rough outer surface provide a mechanical bond between the coating and the engine block.

[0005] The coatings described in patents US 10215128 and US7383805B2 guarantee greater adherence, forming a rough outer surface that provides a surface area with more outward projections to create a mechanical bond between the coating and the engine block. Thus, these patents guarantee good adherence by controlling the size and dispersion of the projections.

[0006] However, over the years, technological advances have helped to improve both the cast cylinder liner and the production meth od thereof.

[0007] This is because, in view of the various advantages provided by internal-combustion engines, internal-combustion engines need to be continuously improved to guarantee increasingly high levels of safe ty, durability and efficiency in these engines.

[0008] Thus, although the current cast cylinder liners for combus tion engines satisfy the requirements for which the liners are designed, there are some areas in which the liners can be improved, specifically in terms of greater dimensional control and less distortion of the cylin der.

[0009] Specifically, it has been observed that the average density of the projections in the existing cast cylinder liners can be readily ad justed as a function of the requirements of the casting process and ap plication to the intended engine, while the layout and maximum height of the projections and cavities of the existing liners vary randomly over the surface, making the casting process difficult to control.

[0010] More specifically, it has been observed that the random var iations in said features is directly related to adherence of the cylinder to the engine block.

OBJECTIVES OF THE INVENTION

[0011] One objective of the present invention is to provide a cast cylinder liner and a method for producing a cast cylinder liner in which the density, size and shape of the projections and cavities are consid ered, in particular the layout and maximum §height of the cavities.

[0012] Another objective of the present invention is to provide a cast cylinder liner and a method for producing a cast cylinder liner in which the rough surface of the liner has enhanced dimensional preci sion and adherence, as well as better distribution of local distortion re sistance.

[0013] Furthermore, one objective of the present invention is to provide a cast cylinder liner and a method for producing a cast cylinder liner that result in a higher joining strength and lower distortion.

SHORT DESCRIPTION OF THE INVENTION

[0014] The objectives of the present invention are achieved by a cast cylinder liner for an internal-combustion engine including an outer surface provided with a plurality of projections and cavities, in which the height of the outer surface is between 0.1 mm and 0.6 mm and there are between 4 and 15 cavities per 0.5 mm ² . [0015] In addition to this, the objectives of the present invention are achieved by means of a method for producing a cast cylinder liner for an internal-combustion engine comprising the steps of coating a cen trifugal mold with a refractory to form an outer surface provided with a plurality of projections and cavities, pouring casting material into the mold to form the cylinder, and rolling the coated outer surface of the cylinder to form a rolled outer surface once the casting material has hardened.

SHORT DESCRIPTION OF THE FIGURES

[0016] Other objectives and features of the present invention are set out in the detailed description below, with reference to the attached drawings. In any case, the drawings should be understood to be pro vided for illustrative purposes and not to define the limits of the inven tion.

[0017] In the drawings, in which similar reference signs denote similar elements in all of the views:

Figure 1 shows a view of the cylinder liner according to the invention,

Figure 2 shows a magnified lateral cross section view of the object shown in figure 1 ,

Figure 3 shows a magnified lateral cross section view of an embodiment of the object shown in figure 1 ,

Figure 4 shows a magnified lateral cross section view of an embodiment of the object shown in figure 1 , and

Figure 5 shows a magnified lateral cross section view of the embodiments shown in figures 3 and 4. DETAILED DESCRIPTION OF THE INVENTION

[0018] As shown in the figures, the present invention relates to a cast cylinder liner 1 for internal-combustion engines including an outer surface 2 that has particularly enhanced adherence properties.

[0019] The surface is covered with projections 3 and cavities 4 of variable shapes and sizes that are created by spraying a coating onto a mold, before casting the cylinder liner 1 in the mold.

[0020] The projections 3 are usually conical or needle-shaped, with bases that are wider than the tips thereof. The cavities 4 are then formed about each of the projections.

[0021] The present invention also relates to a method for producing the cast cylinder liner 1 in which the coating can be formed by spraying a mold during a centrifugal casting process. Firstly, the mold is sprayed with the coating while rotating so that the surface of the mold is coated uniformly. A casting material is then poured into the mold and left to harden. The mold is in rotation during the coating, casting and solidifi cation processes.

[0022] The coating material can be any type of refractory material applicable to the invention.

[0023] Thus, the present invention relates to a centrifugal casting method and a cast cylinder liner 1 , in which the outside of the coating is impressed onto the cylinder by projections and cavities of specific size, shape and density. [0024] With regard to the density of the projections and cavities, the projections and cavities can be adjusted using various processing steps of the coating and as a function of how the coating is applied to the mold. The density of the projections and cavities can be adjusted to suit the processing and molding technique of the engine block to guar antee proper seating and interconnection between the coating and the engine block. For example, if the engine block is molded using the high-pressure die casting technique, the coating can have a higher density of projections.

[0025] Other engine-block molding techniques, such as gravity and precision sand casting or low-pressure sand casting of the shape of the projections and cavities of the coating, can include projections with lower densities, thereby enabling the opening or spacing between the projections to be increased to facilitate the flow of material from the en gine block into the structures of the projections before the material set tles about the cylinder liners.

[0026] With regard to the features relating to the size and shape of the projections and cavities, the present invention makes use of pro cesses related to metal rolling.

[0027] Specifically, the present invention provides a cast cylinder liner 1 for an internal-combustion engine including an outer surface 2, 5 provided with a plurality of projections 3 and cavities 4, in which the outer surface 2, 5 has a height of between 0.1 mm and 0.6 mm and there are between 4 and 15 cavities 4 per 0.5 mm ² .

[0028] In a preferred but non-limiting embodiment the outer surface 2, 5 of the cast cylinder liner 1 includes a rough region that varies along the axial length of the cylinder 1 , such that the plurality of projections 3 and cavities 4 have a height of between 0.1 mm and 0.6 mm and are arranged in the first 30 mm from the top of the cylinder.

[0029] More specifically, the present invention provides a method for producing a cast cylinder liner 1 for an internal-combustion engine that comprises the following steps: (i) coating a centrifugal mold with a refractory to form an outer surface 2 provided with a plurality of projec tions 3 and cavities 4, and (ii) pouring a casting material into the mold to form the cylinder 1 , in which (iii) the outer surface 2 of the cylinder 1 is rolled to form a rolled outer surface 5, once the casting material has hardened.

[0030] In a preferred but non-limiting embodiment, the plurality of projections 3 and cavities 4 on the outer surface 2 have a height of be tween 0.1 mm and 1.1 mm and a density of between 110 and 300 pro jections/cm ² .

[0031] Furthermore, the rolling step according to the present inven tion provides a rate of reduction of 30% to 65% to form a rolled outer surface 5, such that the tallest projections are leveled and new projec tions and cavities are formed. In a preferred but non-limiting embodi ment, in the layout there are between 4 and 9 cavities per 0.5 mm.

[0032] Table 1 shows the layout and number of cavities per mm of the cylinder. Table 1

[0033] The measurements in table 1 are summarized for reference purposes. Software analysis is used to determine the different geome tries of the projections and cavities. One of these determinations is a base to classify the circularity of the projections and cavities. The soft ware can determine circularity using a base graph or various meas urements, such as the short and long dimensions of each projection and cavity.

[0034] Thus, advantageously, the present invention guarantees properties in the end product that are more uniform by flatten ing/leveling the tallest projections and creating new cavities, thereby providing greater control over the dimensions of the cylinder and uni formly enhanced adherence, as well as a higher joining force.

[0035] The reduction of some projections is compensated by the creation of new projections and cavities.

[0036] In addition to this, advantageously, a more uniform adher ence helps to reduce cylinder distortion, and consequently fewer harm ful particulate gases produced during combustion, as well as lower consumption of engine lubricating oil.

[0037] Although preferred embodiments have been described, it should be noted that the scope of the present invention covers other possible variations and is only limited by the content of the attached claims, including possible equivalents therein.