EP2700801A1 - Cylinder liner for a reciprocating combustion engine, method for producing a support ring for a cylinder liner and support ring - Google Patents

Abstract

The cylinder liner has support ring (3) that is placed on outer support surface (4) of the cylinder liner main portion around a cylinder axis (A) of the cylinder liner main portion. The support ring is supported on the support surface through a contact surface (31). The supporting ring is designed such that induced radial enlargement of the cylinder liner main portion is limited to preset value by the support ring with respect to the cylinder axis. An independent claim is included for method for manufacturing supporting ring of cylinder liner.

Description

The invention relates to a cylinder liner with a support ring for a reciprocating internal combustion engine, in particular for a longitudinally purged two-stroke large diesel engine, a method for producing a support ring for a cylinder liner, and a support ring according to the preamble of the independent claim of the respective category.

Large diesel engines are often used as drive units for ships or in stationary operation, eg for driving large generators for generating electrical energy. The engines usually run for long periods in continuous operation, which places high demands on the reliability and availability. Therefore, for the operator in particular long maintenance intervals, low wear and an economical handling of fuels and supplies are central criteria for the operation of the machines. Among other things, the piston running behavior in the cylinder liner of such large-bore, slow-running diesel engines is a determining factor for the length of the maintenance intervals, the availability and the lubricant consumption also directly for the operating costs and thus for the economy. Thus, the complex problem of the piston running behavior of large diesel engines is becoming more and more important.

As is well known, the stresses to which the cylinder liner is exposed in the operating state, in the upper region of the cylinder liner, ie where the piston passes in the vicinity of the cylinder cover in the operating state top dead center is particularly large. In the vicinity of the top dead center position of the piston, so when the volume of the combustion chamber enclosed by cylinder liner, cylinder cover and piston is approximately minimal, the air fuel mixture is ignited. It thus act high temperatures and pressures in the cylinder liner, which also not least due to the movement of the piston and thus constantly changing dynamic volume of the combustion chamber, also subject to strong dynamic changes.

Therefore, it has long been known at the upper end of the cylinder liner in the vicinity of the cylinder cover, for example, to provide cooling rings, which are preferably equipped with a water cooling, so that at least a portion of the resulting heat loads on the cooling ring from the cylinder liner are wegführbar. Sometimes simple cooling rings are provided, such as already in the US 937,200 shown.

Another, so far little noticed problem relates to the dynamic strains of the cylinder liner, in particular the radial dynamic expansions of the cylinder liner near the upper end of the cylinder liner, ie in the vicinity of the cylinder cover, where in the top dead center position of the piston, the combustion chamber volume is minimal and, As described above, the thermal stresses due to the combustion process are particularly large. The combustion of the fuel in the combustion chamber of the cylinder liner leads not only to high temperatures or temperature fluctuations in the cylinder liner, but how already mentioned, also to enormous combustion pressures and associated dynamic pressure fluctuations in the combustion chamber, which of course do not remain without effects on the cylinder liner.

Due to the enormous combustion pressure in the combustion chamber and the enormous pressure fluctuations in the combustion chamber associated with the combustion or the movement of the piston, the cylinder liner experiences very strong, periodic, not only, but especially at its upper end, where the combustion starts in the combustion chamber during operation alternating radial expansions and radial reductions in its diameter. That The diameter of the cylinder liner changes periodically in the operating state, ie it is alternately periodically smaller and larger. It should also be considered that, especially in the case of a large diesel engine, the cylinder liner is additionally under an enormous axial bias by extending in the longitudinal direction of the cylinder liner tie rod.

The combination of axial static mechanical prestressing by the tie rods with a static thermal strain load due to increased temperature, already leads in the absence of the aforementioned dynamic expansion phenomenon that extending in the longitudinal and circumferential direction of the cylinder neutral zone in the radial central region in the cylinder wall the cylinder liner is formed, which is exposed to substantially no or only very small radial stresses. At the same time, tensile stresses extending radially outside the neutral zone in the circumferential direction form in the cylinder wall of the cylinder liner and compressive stresses which extend in the circumferential direction radially within the neutral zone form.

In the operating state, in addition to the previously described, essentially static phenomena, the dynamic temperature and pressure fluctuations on the cylinder liner now also change, of course the tensile and compressive stress conditions in the cylinder wall of the cylinder liner accordingly.

If, in addition to the static strains, the cylinder liner is still dynamically stretched in the radial direction, for example due to the combustion pressure suddenly rising in the combustion chamber during operation, the neutral zone moves radially inwards. As a result, the tensile forces in the wall of the cylinder liner grow radially outside the neutral zone massively, while the tensile forces radially inside the neutral zone are getting smaller and may even substantially disappear.

That is, the cylinder liner is exposed, at least in the radial direction by the dynamic radial strains enormous periodically fluctuating forces and mechanical stresses that expose the cylinder liner in addition to the thermal loads and enormous mechanical loads, which ultimately leads to premature fatigue and thus, the life of the cylinder liner is reduced and maintenance intervals are shortened. In addition, of course, the piston running behavior is adversely affected because the piston is no longer optimally adapted to the inner diameter of the cylinder liner due to the diameter variations of the cylinder liner, since the inner diameter is constantly changing, which ultimately adversely affect the combustion process and thus the entire operation of the engine can. In the final consequence, of course, this leads to higher operating costs and, in the worst case, can also increase the operational safety and, for example, even the safety of a system operated by the engine, e.g. negatively affect the safety of a ship, which of course must be prevented at all costs.

The object of the invention is therefore an improved cylinder liner for a reciprocating internal combustion engine, in particular for a longitudinally flushed To provide slow running two-stroke large diesel engine available, in which the known from the prior art problems are avoided, which can compensate better especially the occurring in the operating state enormous thermal and mechanical loads, in particular the static and dynamic thermal strains occurring so that a higher reliability of the internal combustion engine is ensured, maintenance intervals can be extended, the life of the cylinder liner is significantly increased, and thus ultimately the cost of operating the engine can be significantly reduced.

The objects of the invention that solve these objects in terms of apparatus and method are characterized by the features of the independent claims of the respective category.

The dependent claims relate to particularly advantageous embodiments of the invention.

The invention thus relates to a cylinder liner for a reciprocating internal combustion engine, in particular two-stroke large diesel engine, wherein a support ring is provided on an outer support surface of the cylinder liner concentric about a cylinder axis of the cylinder liner that the support ring is supported via a contact surface of the support ring on the support surface. According to the invention, the support ring is designed such that a radial enlargement of the cylinder liner induced in relation to the cylinder axis can be limited to a predefinable value by the support ring.

It is essential that the induced radial enlargement of the cylinder liner can be limited to a predefinable value by the inventive support ring. This is for example with the cooling ring of the aforementioned US 937,200 not possible, as it expands under thermal stress substantially as much as the Cylinder liner, since the cylinder liner and the cooling ring are made of materials with the same or very similar radial coefficients of thermal expansion, so that the cooling ring can not act as a support ring in the context of the present invention, since he is unable to the radial magnification of the cylinder liner limit.

A cylinder liner of the present invention therefore has a backing ring that preferably has an effective radial coefficient of thermal expansion that is less than an effective radial thermal expansion coefficient of the cylinder liner. That is, if the support ring and the cylinder liner are subjected to substantially equal thermal stress, the resulting thermal expansion of the support ring in the radial direction will be less than the corresponding radial thermal expansion that the cylinder liner would have if there were no support ring on the cylinder liner. As a result, the radial thermal expansion of the cylinder liner is limited by a corresponding design of the support ring to a predeterminable extent under thermal load, because the support ring prevents radial expansion beyond the predetermined amount.

In addition to its function as a radial expansion limiting means, a support ring of the present invention may also serve as a mating surface for a seal of a per se known cooling water space arranged in the cylinder liner.

A support ring with the properties according to the invention can be realized, for example, by selecting a material for the support ring which has a smaller coefficient of thermal expansion in the circumferential direction of the support ring than the material is produced from the cylinder liner.

Depending on the choice of material for the support ring, the effective radial thermal expansion coefficient of the support ring may also be zero or even less than zero. This can be achieved, for example, by selecting a material for the support ring which has a spatially anisotropic coefficient of thermal expansion. That is, the material may e.g. in a longitudinal direction formed in the circumferential direction of the support ring, have a smaller expansion coefficient than in a direction perpendicular thereto. In particular, such a material in the longitudinal direction may also have a thermal expansion coefficient equal to or less than zero, which means that e.g. under temperature increase the material and thus the support ring made therefrom in the longitudinal direction in the length not changed, or even shortened in the longitudinal direction, which corresponds to a negative coefficient of thermal expansion in the longitudinal direction.

This can e.g. be achieved in that the support ring is made at least of a carbon material and a fixing resin, in particular of wound carbon fiber bundles or carbon mats.

The aforementioned spatial anisotropic effect in the thermal expansion coefficient is often based on the orientation of the strongest atomic bonds in the longitudinal direction of the material. For crystalline materials, these can be crystal planes and, for polymers, e.g. be the molecular chains.

For example, graphite is composed of individual layers. The high strength and the high modulus of elasticity of the C fibers are based on the strong bonding of the graphite crystals in one layer plane. High strength values can not only be achieved with static load. Carbon fibers also have excellent fatigue resistance. Due to the orientation of the strong covalent bonds of the Graphite crystal in the fiber longitudinal direction behaves the C-fiber - in contrast to the glass fiber - significantly anisotropic. It is often of particular interest that the moduli of elasticity in fiber longitudinal and transverse directions can often differ by one or more orders of magnitude.

In addition to the mechanical properties of modulus of elasticity and strength, the anisotropy also affects the thermal expansion coefficient. This is e.g. transverse to the fiber direction, but smaller in the fiber direction than transverse to the fiber direction, or zero or even negative. This effect can be more pronounced the higher the graphite crystals are aligned, i. the higher the fiber-parallel elastic modulus. These properties of polymer or carbon materials are known per se.

In a particularly preferred embodiment, the contact surface of the support ring with respect to the cylinder axis of the cylinder liner is inclined at a contact angle, preferably but not necessarily, the support surface is inclined with respect to the cylinder axis at a support angle. Particularly preferably, the contact angle corresponds to the support angle, wherein the contact angle is in particular equal to the support angle. In practice, the contact surface in practice is advantageous in the direction towards the upper end of the cylinder liner, ie in the installed state in the direction of the cylinder cover, inclined in the direction of the cylinder axis, so that the support ring has a conical inner structure which widens from the upper end of the cylinder liner that the support ring can be particularly easily mounted on the support surface of the cylinder liner.

The assembly or replacement of the support ring can also be facilitated by the fact that the support ring on a cylinder cover in the installed state facing the end of the cylinder liner in a Stützringnute, is preferably arranged in a direction open towards the cylinder cover Stützringnute.

In addition, it goes without saying that a support ring according to the invention can also be provided at any point with respect to the axial direction on the cylinder liner, so for example in the middle or at the bottom of the cylinder liner or at any other point.

The invention further relates to a method for producing a support ring for a cylinder liner of the present invention, wherein a carbon material is molded with the aid of a molded part as a carbon ring, with a fixing resin is applied, and the carbon material is cured with the fixing resin at a predetermined fixing temperature as a support ring ,

Preferably, the support ring is made of wound carbon fiber bundles or carbon mats, wherein the cylinder liner itself can be used as a molded part, for example by the carbon material is wound as a carbon ring on the cylinder liner, is applied to the fixing resin, and the carbon material with the fixing resin at a predetermined fixing temperature is cured on the cylinder liner to the support ring.

It goes without saying that, of course, as a molded part, a separate, suitably designed fixing can be used, in particular in a method according to the invention, a curing at room temperature fixing resin can be used.

In practice, concrete methods for producing a carbon fiber supporting ring are possible with in part different advantages. Basically, it is in the application as a reinforcement of Cylinder around a loaded on train support ring. The support ring is thereby more or less expanded by the thermal expansion of the cylinder and the gas pressure during combustion. The carbon fibers used in the support ring can even have a negative coefficient of thermal expansion, so that the ring counteracts the expansion of the cylinder. In order to achieve the highest possible rigidity of the ring in the tangential direction with a constant cross section, it is advisable to wind the carbon fibers (fiber bundles, also called rovings). Alternatively, unidirectional bands (also known as pre-pregs) may be used. Fiber mats can also be used in principle, however, the achievable modulus of elasticity in the longitudinal direction by the mehrdirektionalen structure is significantly lower and the larger modulus in the transverse direction offers less advantages, since the ring is not loaded in the transverse direction so high, except in transverse contraction under load , The stiffness of the support ring at a given cross section can therefore be adjusted individually for each support ring by the choice and the orientation of the fibers.

The production of the support ring itself can also be done in different ways. Either the fiber is, as already mentioned, wound directly onto the cylinder liner, for example into a groove provided for this purpose or closed in the axial direction or else onto a separate mold. If the carbon fiber is wound directly onto the cylinder, this offers the advantage that the ring automatically rests without play. Due to the high operating temperature of, for example, about 175 ° C, the resin must be cured at elevated temperature to use it at such high temperatures can. During hardening / tempering, the cylinder also heats up and this experiences a thermally induced strain in the radial direction. This has the consequence that the support ring is pre-expanded during curing and in the "final state" no longer rests without clearance on the cylinder at room temperature. As a result, the support ring partially its supportive effect to lose. Therefore, it is recommended to work with a resin that cures at room temperature.

Another way around the aforementioned problem is that the support ring can be made using a separate mold. When manufacturing or specifying the manufacturing tolerances, the thermal expansion of the mold during the annealing process can be taken into account. Thus, the support ring is pre-stretched to the desired extent during curing. In addition, it is recommended that the inner surface of the support ring and the outer surface of the cylinder be made conical in order to compensate for any manufacturing tolerances can. However, the conical angle should be kept so small that there is self-locking between ring and cylinder. The support ring is then pushed with force during assembly.

As already mentioned above, a contact surface can be formed on the support ring particularly preferably under a conical contact angle.

Furthermore, it is understood that in practice, a radial thermal expansion coefficient of the support ring can be set particularly advantageous equal to zero or even less than zero.

Finally, the invention also relates to a support ring for a cylinder liner, which is preferably produced by a method according to the invention.

Fig. 1

einen erfindungsgemässen Zylinderliner mit einem Stützring aus Karbonmaterial;

The invention will be explained in more detail below with reference to the schematic drawing. Show it:

Fig. 1

an inventive cylinder liner with a support ring of carbon material;

In Fig. 1 schematically a section of an inventive cylinder liner 1 is shown with a support ring 3 made of a carbon material, which was prepared according to a particularly preferred embodiment of an inventive method.

It can be seen clearly how the support ring 3 is arranged on an outer support surface 4 of the cylinder liner 1 concentrically about a cylinder axis of the cylinder liner 1 and supported on the support surface 4. According to the present invention, the support ring 3 is designed such that a radial enlargement of the cylinder liner 1 induced with respect to the cylinder axis A can be limited to a predefinable value by the support ring 3.

The support ring 3 of Fig. 1 is made of a wound carbon fiber bundle and a fixing resin, wherein the cylinder liner 1 was used as a molding by the carbon material wound as a carbon ring on the cylinder liner 1, was applied to the fixing resin, and the carbon material with the fixing resin at a predetermined fixing temperature, preferably at Room temperature was cured on the cylinder liner 1 to the support ring 3. The support ring 3 gem. Fig. 1 has an effective radial thermal expansion coefficient which is less than zero.

In the particularly preferred embodiment of the Fig. 1 is the contact surface 31 with respect to the cylinder axis A at a contact angle α in the direction of the cylinder cover 5 and inclined in the direction of the cylinder axis A. Accordingly, the support surface 4 is inversely inclined relative to the cylinder axis A at a support angle β such that the contact angle α corresponds to the support angle β, the contact angle α in the specific embodiment of Fig. 1 is equal to the support angle β. The support ring 3 is on a cylinder cover. 5 facing end of the cylinder liner 1 in a cylinder cover 5 open Stützringnute 6 arranged.

The skilled person understands immediately that the invention is not limited to the exemplary embodiments explained, but that also simple developments and in particular all technically meaningful combinations of the embodiments are covered by the invention. Moreover, it goes without saying that the application of the invention is not limited to two-stroke large diesel engines, but in principle with any other type of engine, e.g. can also be used in gas engines, four-stroke engines or other engines.

Claims (15)

Cylinder liner for a reciprocating internal combustion engine (2), in particular two-stroke large diesel engine, wherein a support ring (3) on an outer support surface (4) of the cylinder liner is provided concentrically about a cylinder axis (A) of the cylinder liner that the support ring (3) via a contact surface (31) of the support ring (3) on the support surface (4) is supported, characterized in that the support ring (3) is formed such that by the support ring (3) with respect to the cylinder axis (A) induced radial magnification of Cylinder liner can be limited to a predetermined value. Cylinder liner according to claim 1, wherein the contact surface (31) is inclined with respect to the cylinder axis (A) at a contact angle (α). Cylinder liner according to one of claims 1 or 2, wherein the support surface (4) is inclined with respect to the cylinder axis (A) at a support angle (β). Cylinder liner according to one of the preceding claims, wherein the contact angle (α) with the support angle (β) corresponds, wherein the contact angle (α) in particular equal to the support angle (β). Cylinder liner according to one of the preceding claims, wherein the support ring (3) on a cylinder cover (5) facing in the installed state end of the cylinder liner in a Stützringnute (6), preferably in a direction towards the cylinder cover (5) open Stützringnute (6) is arranged , Cylinder liner according to one of the preceding claims, wherein the support ring (3) has an effective radial thermal expansion coefficient which is smaller than an effective radial thermal expansion coefficient of the cylinder liner. Cylinder liner according to one of the preceding claims, wherein the effective radial thermal expansion coefficient of the support ring (3) is equal to zero or less than zero. Cylinder liner according to one of the preceding claims, wherein the support ring (3) is made at least of a carbon material and a fixing resin, in particular of wound carbon fiber bundles or carbon mats. A method for producing a support ring (3) for a cylinder liner (1) according to any one of the preceding claims, wherein a carbon material is formed with the aid of a molded part as a carbon ring, is applied with a fixing resin, and the carbon material with the fixing resin at a predetermined fixing temperature as a support ring (3) is cured. A method according to claim 9, wherein the support ring (3) is made of wound carbon fiber bundles or carbon mats. A method according to claim 9 or 10, wherein the cylinder liner (1) is used as a molding by winding the carbon material as a carbon ring on the cylinder liner (1) to which fixing resin is applied, and the carbon material with the fixing resin at a predetermined fixing temperature on the resin Cylinder liner (1) to the support ring (3) is cured. A method according to claim 9 or 10, wherein a fixing mold is used as the molded part. Method according to one of claims 9 to 12, wherein on the support ring (3) a contact surface (31), preferably at a conical contact angle (α) is formed, and / or wherein a radial thermal expansion coefficient of the support ring (3) equal to zero or less than zero is set. A method according to any one of claims 9 to 13, wherein a room temperature curing fixing resin is used. Support ring for a cylinder liner (1) according to one of claims 1 to 8, and / or produced by a method according to one of claims 9 to 14.

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