CYLINDER LINER

FIELD OF THE INVENTION

[0001] The subject matter as described herein, relates to a cylinder block of an internal combustion engine and more particularly, but not exclusively, to a cylinder liner in the cylinder block of such engine.

BACKGROUND OF THE INVENTION

[0002] A cylinder liner (also known as cylinder sleeve) is generally made of cast iron and forms a lining around the inner surface of a cylinder bore, which is accomodated in a cylinder block made of aluminium alloy in an internal combustion engine. The inner radial surface of the cylinder liner is in contact with the piston rings. The liner improves the wear resistance of the inner surface of the cylinder bore as the piston rings reciprocate against the cast iron surface of the cylinder liner rather than the aluminium alloy surface of the cylinder bore of the cylinder block.

[0003] The cylinder block is a bimetallic structure and its production involves insertion of such cylinder liner inside a pressure diecast tool and subsequent injection of an aluminium alloy to produce the cylinder block. The cast iron cylinder liner shows poor bonding with the inner radial surface of the cylinder bore made of aluminium alloy and there is absence of any significant metallurgical bonding between the two. Further, the interface of the cylinder liner and the cylinder bore is not continuous which leads to poor heat dissipation, higher bore distortion and higher oil consumption. The present invention intends to solve all or any of the above problems and obviate any lacunae in the prior art.

SUMMARY OF THE INVENTION

[0004] It is therefore an object of the present invention to improve the bonding between the outer radial surface of the cylinder liner and inner surface of the cylinder bore which results in better heat dissipation. It is another object of the present invention to provide a process for coating the outer radial surface of the cylinder liner which removes the aforementioned problems. To this end, a homogenous coating is introduced around the outer radial surface of the cylinder liner through twin wire arc spray process which is made of an alloy of aluminium with less than or equal to 12 weight % of silicon. The cylinder liner is then used as an insert during die casting of the cylinder block and the coating forms an interface with the cylinder liner and the inner surface of the cylinder bore.

[0005] The foregoing objectives and summary provide only a brief introduction to the present subject matter. To fully appreciate these and other objects of the present subject matter as well as the subject matter itself, all of which will become apparent to those skilled in the art, the ensuing detailed description of the subject matter and the claims should be read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The above and other features, aspects, and advantages of the subject matter will be better understood with regard to the following description, appended claims and accompanying drawings where:

FIG. 1 shows a twin wire arc spray process to obtain a coating on a cylinder liner.

FIG. 2 shows a microscopic view of the coating between the cylinder liner and the cylinder bore.

FIG. 3 depicts a detailed microscopic section view of the cylinder liner with coating showing the presence of pin holes.

FIG. 4 shows an ED AX analysis graph showing metallurgical bonding of cylinder liner and inner surface of the cylinder bore of the cylinder block.

FIG. 5 shows the temperature mapping of a cylinder bore with coated cylinder liner and the uncoated cylinder liner.

DETAILED DESCRIPTION OF THE INVENTION

[0007] The present invention is now explained with the help of rendered FIGs. 1-5. Various'other features and embodiments of the cylinder liner according to the present invention here will be discernible from the following further description thereof, set out hereunder. The brief description is to be understood as an exemplary embodiment and reading of the invention is not intended to be taken restrictively.

[0008] The present invention discloses a homogenous coating around the outer radial surface of the cylinder liner formed specifically through a twin wire arc spray process to achieve better heat dissipation by reducing undesirable voids. The said coating is made of aluminium-silicon alloy. According to an aspect of the present subject matter, such aluminium alloy comprises with 0 to 12 weight % of Silicon. The thickness of the coating may be between 0.05 to 0.15 mm.

[0009] As depicted in FIG. 1, a twin wire arc spray process is used to obtain the coating on the cylinder liner. As the electrically conductive wires are fed towards each other, a short circuit is established between the wires creating an arc with a temperature of around 5000 degree Celsius. This heat causes the wire tips to melt and compressed gas air is used to atomize the molten tips and propel the droplets towards the substrates at velocities exceeding lOOm/sec.

[00010] The complete process involves the steps of solvent cleaning and abrasive blasting along with predefined process parameters. During solvent cleaning step, a hydrocarbon dry cleaning solvent is used. As per ASTM D 235, Type I regular solvent with flash point of 38 degree Celsius may be used. During abrasive blasting (open nozzle type), abrasive and the air. flow is adjusted to produce a bluish-coloured air stream at the nozzle which signals optimum mix. The abrasive media is angular steel grit with 58-60 HRC and blast profile is within 50 to 100 microns. According to a feature of the present subject matter, the spray pattern is oval shaped and the stand off distance (nozzle to surface distance) is at least 15 cm. the spray width is within 2 to 4 cm and the spray angle is within 85 to 90 degrees.

[00011] During the pressure die casting of the cylinder block, the cylinder liner with the coating obtained through aforementioned process is used as an insert. Thus the coating is present between the outer radial surface of the cast iron cylinder liner and the inner surface of the aluminium cylinder bore of the cylinder block shown in FIG.2. From the EDAX analysis as shown in FIG. 4, it is clear there is transfer of elements from the cylinder liner surface to the inner surface of the cylinder bore and vice versa at the interface in the blocks with coated cylinder liner. The aluminium alloy present on the outer surface of the cylinder liner forms a metallurgical bonding with that of the pressure die cast alloy of the cylinder bore. However in case of the blocks with uncoated cylinder liners, there is an absence of such a bonding.

[00012] The combination of high temperature and particle velocities give arc sprayed coatings superior bond strengths, low porosity levels at high spray rates and low oxide content. Further, the twin arc spray process is a cold process as the substrate temperature can be kept low during spraying thus avoiding metallurgical changes and distortion within the cylinder liner insert. This process also gives control over thickness of coating. Furthermore, the coating provides structural strength to the cylinder liner which would otherwise crack due to absence of a mechanical bonding between the cylinder liner and cylinder block.

[00013] Cylinder blocks with coated cylinder liners and those with uncoated liners were tested to determine the difference in heat dissipation properties. The cylinder blocks were machined to map the temperature by inserting thermocouples very close to the cylinder bore at eight different locations. In cylinder blocks with coated cylinder liners, the temperature rise in the cylinder bore is quickly removed away through the fins, due to better heat dissipation through the coating unlike the ones without the coating. Thus, as shown in FIG. 5, the cylinder bore temperature will be always lower in cylinder blocks with coated cylinder liners, thus reducing the bore distortion compared to the uncoated ones. In the figure. SI refers to the block with a coated liner and S2 refers to the block with an uncoated liner. Results of temperature mapping in cylinder blocks also reveal that the uncoated blocks near the cylinder bore reveal higher temperature compared to the uncoated ones enabling better heat dissipation in the blocks with coated cylinder liners.

[00014] Further as shown in FIG. 3, with the process described herein, the interface between the cylinder liner and the inner surface of the cylinder bore is without voids, and also reduces pin holes.

[00015] The present subject matter is thus described. The description is not intended to be exhaustive nor is it intended to limit the invention to the precise form disclosed. It will be apparent to those skilled in the art that the disclosed embodiments may be modified in light of the above description. The embodiments described are chosen to provide an illustration of principles of the invention and its practical application to enable thereby one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore the forgoing description is to be considered exemplary, rather than limiting, and the true scope of the invention is that described in the appended claims.

We claim:

1. A method for processing an outer radial surface of a cylinder liner comprising: providing a homogenous coating around the outer radial surface of the cylinder liner through twin wire arc spray process wherein the spray pattern is oval shaped, the stand-off distance is at least 15 cm, the spray width is within 2 to 4 cm and the spray angle is within 85 to 90 degrees and, wherein the coating comprises of an alloy of aluminium with less than or equal to 12 weight % of silicon.

2. The method as claimed in claim 1, wherein the coating has a thickness in the range of 0.05mm and 0.15mm.

3. A cylinder block comprising the cylinder liner as claimed in any of the preceding claims as an insert.

4. A cylinder block comprising: a cylinder bore, a cylinder liner, a homogenous coating around an outer radial surface of the cylinder liner and interfacing an inner surface of a cylinder bore fabricated through twin wire arc spray process, the coating made of an alloy of aluminium with less than or equal to 12 weight % of silicon, wherein the spray pattern is oval shaped, the stand-off distance is at least 15 cm, the spray width is within 2 to 4 cm and the spray angle is within 85 to 90 degrees and wherein further, the coating has a thickness in the range of 0.05mm and 0.15mm.