CYLINDER LINER FOR INSERTION INTO AN ENGINE BLOCK, AND ENGINE BLOCK

Abstract

A cylinder liner for insertion into an aluminum internal-combustion engine block may include a cylindrical body of cast iron having a circumferential external surface. The cylinder liner may also have a coating deposited on and surrounding the external surface. The external surface may have a specific roughness, and the coating may include at least 98% by volume of pure nickel, and a remainder composed of impurities.

Claims

1. A cylinder liner for insertion into an aluminum internal-combustion engine block , the cylinder liner comprising: a cylindrical body of cast iron having a circumferential external surface; and a coating deposited on and surrounding the external surface; wherein the external surface has a specific roughness, and the coating includes at least 98% by volume of pure nickel, and a remainder composed of impurities.

2. The cylinder liner as claimed in claim 1, wherein the specific roughness is greater than 0.60 μm.

3. The cylinder liner as claimed in claim 1, wherein the coating is applied by electrodeposition.

4. The cylinder liner as claimed in claim 1, wherein the coating has a thickness ranging between 3 μm and 20 μm.

5. The cylinder liner as claimed in claim 1, wherein the cylinder liner is insertable into an engine block by one of high-pressure die-casting (HPDC), low-pressure die-casting (LPDC), or gravity die-casting.

6. A cylinder liner for insertion into an aluminum internal-combustion engine block, the cylinder liner comprising: a cylindrical body of cast iron having a circumferential external surface; and a coating deposited on and surrounding the external surface; wherein the coating has a melting point ranging between 1500° C. and 1700° C. and the engine block has a melting point ranging between 500° C. and 700° C.

7. An internal-combustion engine comprising at least one cylinder liner including: a cylindrical body of cast iron having a circumferential external surface; and a coating deposited on and surrounding the external surface; wherein the external surface has a specific roughness, and the coating includes at least 98% by volume of pure nickel, and a remainder composed of impurities.

8. The internal-combustion engine as claimed in claim 7, wherein the impurities include at least one of oxygen, carbon, manganese, and copper.

9. The internal-combustion engine as claimed in claim 7, wherein the specific roughness is greater than 0.60 μm.

10. The internal-combustion engine as claimed in claim 9, wherein the specific roughness is 0.70 μm.

11. The internal-combustion engine as claimed in claim 9, wherein the specific roughness is 0.90 μm.

12. The internal-combustion engine as claimed in claim 7, wherein the coating is applied by electrodeposition.

13. The internal-combustion engine as claimed in claim 7, wherein the coating has a thickness ranging between 3 μm and 20 μm.

14. The internal-combustion engine as claimed in claim 13, wherein the thickness ranges between 3 μm and 10 μm.

15. The internal-combustion engine as claimed in claim 7, further comprising an engine block, wherein the cylinder liner is insertable into the engine block by one of high-pressure die-casting (HPDC), low-pressure die-casting (LPDC), or gravity die-casting.

16. The internal-combustion engine as claimed in claim 7, further comprising an engine block, wherein the coating has a melting point ranging between 1500° C. and 1700° C., and the engine block has a melting point ranging between 500° C. and 700° C.

17. The cylinder liner as claimed in claim 1, wherein the impurities include at least one of oxygen, carbon, manganese, and copper.

18. The cylinder liner as claimed in claim 2, wherein the specific roughness is 0.70 μm.

19. The cylinder liner as claimed in claim 2, wherein the specific roughness is 0.90 μm.

20. The cylinder liner as claimed in claim 4, wherein the coating ranges between 3 μm and 10 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The cylinder liner for insertion into an engine block may be better understood by means of the following detailed description based on the figures listed below:

[0026] FIG. 1—perspective view of a cylinder liner;

[0027] FIG. 2—perspective view of an engine block provided with cylinder liners;

[0028] FIG. 3—photograph of the metallographic structure of a cross section of a prior-art cylinder liner;

[0029] FIG. 4—photograph of the metallographic structure of a cross section of a cylinder liner of the present invention;

[0030] FIG. 5—photograph of the metallographic structure of a cross section of a cylinder liner, showing the diffusion layer;

[0031] FIG. 6—photograph of the metallographic structure of a cross section of a cylinder liner of the present invention;

[0032] FIG. 7—photograph of a cylinder liner provided with an external surface with an undulation profile;

[0033] FIG. 8—photograph of a cylinder liner provided with a rough external surface;

[0034] FIG. 9—photograph of a cylinder liner provided with an external surface with thread profile;

[0035] FIG. 10—representation of a graph defining the bonding force for cylinder liners with different roughnesses;

[0036] FIG. 11—representation of a graph defining heat transfer in the case of different types of coating applied to a cylinder liners;

[0037] FIG. 12—top view of an engine block with inserted cylinder liners;

[0038] FIG. 13—top view of a detail of the engine block, showing the distance between the inserted cylinder liners.

DETAILED DESCRIPTION

[0039] The field of the present invention relates to internal-combustion engines, more particularly the interaction between the cylinder liners 10 and the respective engine block 8. An engine block 8 with inserted liners 10 is achieved by pouring/injecting molten metal around the cylinder liners 10 that have previously been placed in the respective mold. Typically, the metal of the engine block 8 is a light metal, such as aluminum or an aluminum alloy.

[0040] The cylinder liner 10 requires its bonding to the engine block 8 to be assured and also the guarantee that, after cooling of the molten metal poured into the mold, regions 15 empty of metal (casting defects) do not arise. As explained in the prior art, guaranteeing such a combination is somewhat complex.

[0041] In order correctly to understand the present invention, it is necessary to clarify certain concepts and paradigms. As defined above, there are two types of casting for fitting cylinder liners into aluminum-alloy engine blocks 8. High-pressure die-casting, denoted as HPDC, and low-pressure die-casting, denoted as LPDC. HPDC is commonly used and offsets the lower temperature of the aluminum by pressurized injection thereof. In such cases, the coatings 5 tend to be consumed less, since the aluminum cools more rapidly. In the case of LPDC, the coatings, for one and the same thickness, tend to suffer greater wear, giving rise to the defects that are known as voids 15 (see FIG. 3). The technology used for casting the block, in accordance with current concepts, interacts directly with the thickness of the coating 5 and, in turn, with the quality of the heat transfer.

[0042] In addition, it is necessary to achieve good bonding between the liner 10 and the engine block 8, which results directly from the chemical parity between the coating 5 and the aluminum alloy of the engine block 8.

[0043] Lastly, consideration has to be given to the size of the engine block 8. As is known, the principal producers place pressure on engine designers to minimize engine size, which amounts to saying that they reduce the interbore spacing 12 (see FIGS. 12 and 13). Thus, any reduction in the thickness of the coating 5 leads to a reduction in the interbore spacing 12. Taking account of the fact that, in LPDC, prior-art coatings have to be thicker in order for voids 15 not to be generated, the existence of a coating 5 that successfully reduces the interbore spacing 12 and at the same time is thinner and furthermore thus allows insertion of the liner 10 using either of the two die-casting technologies (HPDC and LPDC) is a doubly advantageous solution.

[0044] As shown in FIG. 1, a cylinder liner 10 is provided with a hollow cylindrical body or tube 1, generally constituted from a ferrous alloy, such as cast iron or grey cast iron. This cylindrical body 1 provides two surfaces, in particular the internal surface 3 where a piston will move axially and the circumferential external surface 2. It is this external region that will be surrounded by the molten metal of the engine block 8, but only after its external surface 2 has been subjected to the coating 5, thereby configuring the present invention.

[0045] The coating 5 of the present invention is applied directly to the external surface 2, the latter being constituted from pure nickel (Ni99) with the remainder comprising impurities. In other words, the nickel applied is that known commercially as Ni99, i.e. the most pure nickel capable of being applied as a coating, the fact remaining, that, despite the purity thereof being fairly high, there will always be a small percentage of impurities. However, these impurities do not affect the creation of the layer that alloys with the engine block 8 (see FIG. 4). As a preferred embodiment, the coating 5 is composed of at least 98% by volume of pure nickel, the remainder being composed of impurities such as oxygen and/or carbon and/or manganese and/or copper.

[0046] This coating 5 is applied by means of an electrodeposition process. It should be noted that the use of the electrodeposition application process for the coating 5 is one of the principal guarantees of the results of the present invention. In the prior art, use is normally made of thermal spray-coating processes, which result in coating thicknesses in excess of 200 μm With electrodeposition, however, it is possible to provide coatings with thicknesses that range, preferably, between 3 μm and 20 μm or, preferably, 3 μm to 10 μm, i.e. a value 10% below that achieved by the prior art. By itself, this characteristic already very significantly guarantees the reduction in the interbore spacing 12 and, by reducing the thickness of the coating 5, also reduces the cost involved in this step.

[0047] The coating 5 of the present invention will be applied to a cylinder liner 10 with a specific roughness, as shown in FIGS. 6, 7, and 8, it being possible for this external surface 2 to comprise a surface with undulations (see FIG. 7), a rough surface (see FIG. 8) or a surface with a thread profile (see FIG. 9). These surfaces 2, with specific roughness, help to increase the bonding strength and transfer of heat between the liner 10 and the engine block 8, as shown in prior-art document US2011/0154988, from the current applicant.

[0048] The application of a coating 5 of pure nickel is already known in the prior art in the case of smooth liners 10. However, this application results in the formation of a diffusion layer 6 (see FIG. 5) between the aluminum of the engine block 8 and the cast iron of the liner 10, forming a fragile intermetallic compound (iron-nickel-aluminum), which may suffer fracture during operation of the engine.

[0049] The present invention uses a liner 10 provided with an external surface 2 with a specific roughness, which results in a greater area of contact between the aluminum of the engine block 8 and the cast-iron liner 10, and a turbulent material flow is introduced during casting, thereby reducing the time of contact between the aluminum and the external surface 2, which thus prevents the formation of a diffusion layer 6, resulting only in filling of the casting gaps and consequently bonding of the liner 10 to the block 8.

[0050] The absence of a diffusion layer 6 and the coating 5 of pure nickel guarantee exponential gains in terms of bonding for the liner 10. As may be seen in FIG. 10, the liner 10 with a specific roughness on the external surface 2 bonds twice as strongly when a roughness of 0.70 μm is used as compared to a roughness of under 0.60 μm. Furthermore, when a roughness of 0.90 μm is used, the liner 10 offers 30 times as much bonding strength as compared to the liner 10 with a roughness of less than 0.60 μm.

[0051] Moreover, FIG. 10 shows the exponential increase in the bonding of the liner 10 when the application of the coating 5 of nickel is combined with the roughness of the liner 10. The liner 10 with the coating of nickel has its bonding strength increased three-fold when a roughness of less than 0.60 μm is increased to 0.70 μm and, furthermore, when a roughness of below 0.60 μm is increased to 0.90 μm bonding of the liner 10 is 55 times as strong, i.e. bonding is obtained that is 25 times as strong as compared to the liner 10 with roughness only and without the application of the coating 5 of nickel.

[0052] As may be seen in FIG. 5, the diffusion layer 6 is formed upon application of the coating 5 of nickel to a liner 10 with an external surface 2 provided with a roughness of less than 0.60 μm. The formation of this diffusion layer 6 results in poorer bonding of the liner 10 to the block 8 and moreover allows the possibility of fractures occurring during the period of operation of the engine.

[0053] Meanwhile, FIG. 6 shows a liner 10 provided with an external surface 2 with a roughness greater than 0.60 μm, preferably a roughness of 0.70 μm, and more preferably a roughness of 0.90 μm. In this case, there is no diffusion layer 6, which thus increases bonding of the liner 10 to the block 8 and further eliminates the occurrence of fractures.

[0054] In connection with the efficiency of heat transfer, FIG. 11 clearly shows that this efficiency increases by 20% when the liner 10 comprises the coating 5 of Ni99 as compared to other liners 10 that do not include any type of coating.

[0055] FIG. 11 shows that the present invention offers a clear advantage in terms of heat transfer as compared to the prior art, and in turn promotes better control of distortion of the bore of the cylinder liner 10 and also improved clearance between piston and liner 10. This results in a reduction in the consumption of lubricating oil and in the consumption of fuel (considering the lower loads tangential to the ring in order to reduce attrition) and, consequently, lower CO.sub.2 emissions.

[0056] The advantage of a coating of pure nickel (Ni99) over all existing prior-art coatings is connected to the roughness of the surface and the difference between the melting point of the pure nickel of the coating 5 of the liner 10, which ranges between 1500° C. and 1700° C., and the melting point of the aluminum alloy of the engine block 8, which ranges between 500° C. and 700° C. This difference in temperatures, allied with roughness, guarantees greater bonding strength when the liner 10 is inserted into the engine block 8.

[0057] It should be noted, further, that the present invention successfully promotes the insertion of liners 10 without voids 15, as may be seen from FIG. 4.

[0058] The concept of the present invention is thus an alternative for modern engines in which the engine block 8 uses an aluminum alloy. As the thickness of the coating 5 is fairly thin, for example 10 μm or 12 μm (see FIG. 4), satisfactory bonding of the liner 10 combined with the low external diameter tolerances of the liner 10 allow the design of compact engine blocks 8, i.e. with a shorter interbore spacing 12.

[0059] In comparison to the thermal spray-coating process used in the prior art, which requires coatings with thicknesses of close on 200 μm owing to the specific characteristics of the process, the present invention uses, for example, a coating of 10 μm, and this difference results in a reduction in the interbore spacing of the cylinders (see FIG. 13).

[0060] This reduction gives rise to a considerable reduction in the weight of the engine block 8, which is the major objective of principal producers on account of the advantages mentioned above.

[0061] Preferred illustrative embodiments having been described, it should be understood that the scope of the present invention encompasses other possible variations, and is limited only by the content of the appended claims that include possible equivalents.