IN A CYLINDER LINER

Technical field

The present invention relates to a cylinder liner for a piston engine, such as a large two-stroke crosshead engine. Further, the present invention relates to a method for distributing oil along an inside surface of a cylinder liner.

Background art

In order to optimize the operational conditions of marine engines and to prevent shutdowns to the largest extent possible, the operational state of the engines is checked at regular intervals. One common cause for impaired engine state or for shutdowns is that the piston rings have become worn-out or burnt and consequently need to be replaced. Experience has shown, however, that the cause may equally well be the cylinder liners which, when examined, have been found to be in a worn state or to no longer exhibit a smooth surface because of depositions of soot or of abrasive or corrosive attacks on the cylinder liner walls. Attacks of this kind might be due to sulphurous fuel used to operate the engine, which in combination with steam produces sulphuric acid that condenses at predetermined temperature and pressure levels in the engine. The effects on the cylinder from the abrasive or corrosive attacks are localized because of the uneven distribution of cylinder oil, of gas leakage via openings, such as passages between piston rings and cylinder liner, and/or variations of the cylinder wall temperature.

A crucial issue for maintaining a smooth operation of the engine is consequently that the distribution of cylinder oil is optimized. There are some known methods to improve the oil transport between the piston rings and the inner surface of the cylinder liner. WO9630159, for example, discloses a cylinder liner for a piston engine, such as a large two-stroke crosshead engine. The cylinder liner has a running surface for the piston rings on the inner surface of the liner, which running surface, at least in the area closest to the piston top dead centre position, has a partially wave-shaped pattern in which the wave troughs are separated by substantially plane areas. The wave-shaped pattern will ensure an improved oil transport between the piston rings and the inner surface of the cylinder liner by facilitating the oil transport for the piston rings while reciprocating within the cylinder liner.

There are, however, problems with the technique above and additional prior art. The wave-shaped pattern is rather quickly worn out during use. The optimization of the oil distribution is thereby lost and the smooth operation of the engine is compromised. The outer profile of the piston rings will be worn out even before the wave-cut pattern, which in turn will reduce their capability to transport oil within the cylinder liner.

Summary of the invention

It is an object of the present invention to provide an improvement of the prior art. More particularly, it is an object of the present invention to provide a cylinder liner which allows an optimized distribution of cylinder oil for an increased time interval during use in order to minimize the wear of the cylinder liner. Further, it is an object of the present invention to provide a method for distributing oil along an inside surface of a cylinder liner.

These and other objects as well as advantages that will be apparent from the following description of the present invention are achieved by a cylinder liner for a piston engine according to the independent claim.

According to a first aspect, these and other objects are achieved, in full or at least in part, by a cylinder liner for a piston engine, such as a large two- stroke crosshead engine. The cylinder liner comprises an inside surface, at least one groove formed in said inside surface, said at least one groove having an upper and a lower end portion, wherein a first angle is formed between a geometric line extending along said inside surface and a groove surface in said upper end portion, and a second angle is formed between the geometric line extending along said inside surface and the groove surface in said lower end portion. The cylinder liner is characterized in that said second angle is significantly larger than said first angle. Due to the above mentioned angle proportions, the transition between the groove surface and the inner surface in the upper end portion of the cylinder liner will be blunt, and the transition between the groove surface and the inner liner surface in the lower end portion of the cylinder liner will be sharp. Such a groove configuration will contribute to an optimized distribution of cylinder oil in the cylinder liner even after the outer profile of the piston rings has been worn out. Since the wear of the cylinder liner is reduced by means of the optimized distribution of cylinder oil, also the wear of the grooves will be reduced and their life time will accordingly be increased automatically. The piston ring will be able to transport the oil upwardly in the longitudinal direction of the cylinder liner in a normal fashion due to the blunt transition in the upper end portion of the groove. However, the sharp transition in the lower end portion of the groove will restrict the oil from following the piston back down. Since the oil is fed into the cylinder liner in the lower part of the cylinder liner, the distribution of cylinder oil within the cylinder liner will accordingly be optimized. This will in turn contribute to a reduced oil consumption and less wear using the same oil dosage.

The first angle may lie in a range between 0 ^° and 1 ^° , and the second angle may lie in a range between 5 ^° and 120 ^° , which are preferred

embodiments of the present invention.

The at least one groove may be formed as a continuous spiral along the inner surface extending from a top to a bottom of said cylinder liner, which makes the groove easy to create since it can be made in one moment.

The cylinder liner may comprise at least two grooves, and a height of a pitch of the groove in the longitudinal direction of the cylinder liner may substantially correspond to a distance between the at least two grooves in the longitudinal direction of the cylinder liner.

The at least one groove may be annular and formed as a closed circle along a circumference of the inner surface, which makes the groove easy to create.

The cylinder liner may comprise at least two grooves, and a height of each groove in the longitudinal direction of the cylinder liner may substantially correspond to a distance between the at least two grooves in the longitudinal direction of the cylinder liner.

According to a second aspect, these and other objects are achieved, in full or at least in part, by a method for distributing oil along an inside surface of a cylinder liner. The method comprises forming at least one groove in said inside surface, said at least one groove having an upper and a lower end portion, comprising forming a first angle between a geometric line extending along said inside surface and a groove surface in said upper end portion, and forming a second angle between the geometric line extending along said inside surface and the groove surface in said lower end portion. The method is characterized in that said second angle is significantly larger than said first angle.

The first angle may lie in a range between 0 ^° and 1 ^° , and the second angle may lie in a range between 5 ^° and 120 ^° .

The at least one groove may be annular and form a closed circle along a circumference of the inner surface.

The said at least one groove may form a continuous spiral along the inner surface extending from a top to a bottom of the cylinder liner.

The method may further comprise forming at least a second groove, wherein a height of each groove in the longitudinal direction of the cylinder liner substantially corresponds to a distance between said at least one groove and said at least second groove in the longitudinal direction of the cylinder liner.

Other objectives, features and advantages of the present invention will appear from the following detailed disclosure, from the attached claims, as well as from the drawings. It is noted that the invention relates to all possible combinations of features.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [element, device, component, means, step, etc.]" are to be interpreted openly as referring to at least one instance of said element, device, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

As used herein, the term "comprising" and variations of that term are not intended to exclude other additives, components, integers or steps.

When the cylinder liner is in a horizontal position, the "top part" of the cylinder liner is the end part of the cylinder liner at which the piston is in a position closer to a cylinder head of the engine than when in a position in the corresponding end part of the cylinder liner.

When the cylinder liner is in a horizontal position, the "bottom part" of the cylinder liner is the end part of the cylinder liner at which the piston is in a position further away from the cylinder head of the engine than when in the "top part" the cylinder liner as defined above.

When the cylinder liner is in a horizontal position, the "upper end portion" of the groove is the part of the groove closest to the "top part" of the cylinder as defined above.

When the cylinder liner is in a horizontal position, the "lower end portion" of the groove is the part of the groove closest to the "bottom part" of the cylinder as defined above.

The "grooves" referred to in the application are achieved by cutting a pattern into the inner surface of the cylinder liner by means of a cutting tool, and not by means of traditional honing.

Brief description of the drawings

The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein:

Fig. 1 is a cross sectional view of an inner surface of a cylinder liner according to prior art, and

Fig. 2 is a cross sectional view of the inner surface of a cylinder liner according to one exemplary embodiment of the present invention. Detailed description of preferred embodiments of the invention

Fig. 1 illustrates a cross section of an inner surface 1 of a cylinder liner 2 according to known prior art. The inner surface 1 comprises annular shaped grooves 3 extending along the circumference of the cylinder liner 2. The grooves 3 have an upper and a lower end portion 4, 5. In the upper end portion 4 a first angle a is formed between a geometric line (L) extending along said inside surface 1 and a groove surface 6 in said upper end portion 4. In the lower end portion 5, a second angle β is formed between the geometric line (L) extending along said inside surface 1 and the groove surface 6 in said lower end portion 5. The first and second angles α, β are of the same size.

In Fig. 2, a cross sectional view of the inner surface 10f a cylinder liner 2' according to one embodiment of the present invention is illustrated. The inner surface 1 ' of the cylinder liner 2' comprises annular shaped grooves 3' extending along the circumference of the cylinder liner 2'. The grooves 3' have an upper and a lower end portion 4', 5'. In the upper end portion 4' a first angle a' is formed between a geometric line (U) extending along said inside surface 1 ' and a groove surface 6' in said upper end portion 4'. In the lower end portion 5', a second angle β' is formed between the geometric line (U) extending along said inside surface 1 ' and the groove surface 6' in said lower end portion 5'. The second angle β' is significantly larger than the first angle α'. The first angle a' preferably lies in a range between 0 ^° and 1 ^° , and the second β' preferably lies in a range between 5 ^° and 120 ^° . A height (Η') of each groove 3' in the longitudinal direction of the cylinder liner 2' substantially corresponds to a distance (D') between the two grooves 3' in the longitudinal direction of the cylinder liner 2'.

In the cylinder liner 2', the distribution of cylinder oil is effected from the bottom part of the cylinder liner, i.e. in the lower end portion 5' of the cylinder liner 2'. The reason for not supplying cylinder oil to the upper end portion 4' of the cylinder liner 2' is basically that the temperature is too high in that area. Since the oil is supplied to the bottom part of the cylinder, it is important that the piston rings transport the oil in an upward direction in the cylinder liner 2'. That is to say, from the lower end portion 5' of the cylinder liner 2' towards the upper end portion 4' of the cylinder liner 2'. Due to the slightly rounded outer profile of the piston rings, which bear against the inner surface 1 ' of the cylinder liner 2', the cylinder oil is transported up and down during use of the engine. When the rounded outer profile of the piston rings is worn down, they will no longer contribute to the oil distribution within the cylinder liner 2' to the same extent. However, due to the angle proportions of the grooves 3' according to the present invention, the transition between the groove surface 6' and the inner surface 1 ' in the upper end portion 4' of the cylinder liner 2' will be blunt, and the transition between the groove surface 6' and the inner liner surface 2' in the lower end portion 5' of the cylinder liner 2' will be sharp. Such a groove configuration will contribute to an optimized distribution of cylinder oil even after the outer profile of the piston rings has been worn out. The best result in achieved when the difference between the first angle a' and the second angle β' is maximized. The piston ring will be able to transport the oil upwardly in the longitudinal direction of the cylinder liner in a normal fashion due to the blunt transition in the upper end portion 4' of the groove 3'. However, the sharp transition in the lower end portion 5' of the groove 3' will restrict the oil from following the piston back down. Since the oil is feed into the cylinder liner 2' in the lower part of the cylinder liner 2', the distribution of cylinder oil within the cylinder liner 2' will accordingly be optimized.

According to a second aspect of the invention a method for distributing oil along an inside surface of a cylinder liner is provided. The method comprises forming at least one groove in said inside surface, said at least one groove having an upper and a lower end portion, comprising forming a first angle between a geometric line extending along said inside surface and a groove surface in said upper end portion, and forming a second angle between the geometric line extending along said inside surface and the groove surface in said lower end portion. The method is characterized in that said second angle is significantly larger than said first angle.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended claims.

For instance, the inner surface 1 ' may be provided with one single groove 3' that is formed as a continuous spiral along the inner surface 1 ' extending from a top to a bottom of the cylinder liner 2'.

The distance (D') between the grooves as well as the height (Η') of the grooves may be varied.

The grooves (3') do not have to be continuous around the entire circumference of the inner surface (1 ') of the cylinder liner (2'). They can, for example, extend along half of the circumference of the inner surface (1 ') of the cylinder liner (2').