Cylinder liner having three-tiered surface finish

A cylinder assembly for use in an internal combustion engine is disclosed. The cylinder assembly may include a cylinder, a piston disposed within the cylinder, a plurality of piston rings encircling the piston, and a cylinder liner fitted around the piston in a cylindrical space in which the piston reciprocates. The piston may reciprocate within the cylinder along a longitudinal direction of the cylinder. The cylinder liner may include an upper section, a middle section, and a lower section. The upper section may be composed of a first texture; the middle section may be composed of a second texture that is rougher than the first texture; and the lower section may be composed of a third texture that is smoother than the first texture and the second texture.

TECHNICAL FIELD

The present disclosure relates generally to a cylinder liner and, more particularly, to a cylinder liner having a three-tiered surface finish.

BACKGROUND

Internal combustion engines convert chemical energy in fuel into mechanical energy through a series of explosions within a combustion chamber of the engine. These explosions cause pistons of the engine to reciprocate within associated cylinders. Each piston is typically connected to a crankshaft by a connecting rod, such that movement of the piston results in rotation of the crankshaft. The cylinders can be arranged in two banks positioned at an angle to each other. Each bank usually includes a group of cylinders located on the same side of the crankshaft with their axes lying in a common plane passing through an axis of the crankshaft. Each piston is typically encircled by a plurality of piston rings, which are received by machined grooves defined in the outer surface of the piston and help to seal off the combustion chamber. A cylinder liner can be fitted in a cylindrical space in which the piston reciprocates to protect the cylinder from wear and degradation.

During engine operation, the cylinder liner forms a sliding surface for the piston and piston rings. Over time, the cylinder liner can experience wear from friction of the piston and piston rings and therefore degrade in performance. For example, the piston and/or the piston rings can scuff the liner by forming local microscopic welding to the cylinder liner. Cylinder liners fitted for uniflow two-stroke diesel engines can be particularly sensitive to wear induced by scuffing because hard particulates can be dragged along the cylinder liner after passing by intake ports in the cylinder wall. Scuffing can result in elevated friction and wear of the cylinder liner, which can reduce the durability, reliability, and efficiency of the engine.

Reducing cylinder liner wear is generally accomplished by ensuring that adequate lubrication exists between the piston and/or the piston rings and the cylinder liner. One attempt to provide lower friction and wear to cylinder liners is described in U.S. Pat. No. 7,104,240 to Vuk et al. (“Vuk”) that issued on Sep. 12, 2006. Vuk discloses a cylinder liner that includes a plurality of discrete oil retaining indentations in a predefined pattern on its surface. Vuk aims to improve lubrication by arranging the distribution density of the discrete oil retaining indentations to correspond to the greatest lubrication needs of the cylinder liner. In particular, the discrete oil retaining indentations are more densely positioned at the longitudinal ends of the cylinder liner and less densely positioned at the longitudinal middle of the cylinder liner.

Although the discrete oil retaining indentations of Vuk may help reduce cylinder liner friction and wear, it may be less than optimal. This is because the configuration disclosed in Vuk may result in excessive oil being retained on the upper section of the cylinder liner. Excessive oil left on the upper section of the cylinder liner may subsequently be carried to the combustion chamber by the piston rings. The excessive oil may be burned during the combustion process and subsequently injected into the atmosphere as undesirable particulate emissions via an exhaust manifold of the engine. The particulate emissions produced by the discrete oil retaining indentations of Vuk may not meet governmental emission standards.

SUMMARY

In one aspect, the present disclosure is related to a cylinder assembly. The cylinder assembly may include a cylinder, a piston disposed within the cylinder, a plurality of piston rings encircling the piston, and a cylinder liner fitted around the piston in a cylindrical space in which the piston reciprocates. The piston may reciprocate within the cylinder along a longitudinal direction of the cylinder. The cylinder liner may include an upper section, a middle section, and a lower section. The upper section may be composed of a first texture. The middle section may be composed of a second texture that is rougher than the first texture. The lower section may be composed of a third texture that is smoother than the first texture and the second texture.

In another aspect, the present disclosure may be related to a cylinder liner. The cylinder liner may include an upper section, a middle section, and a lower section. The upper section may be composed of a first texture. The middle section may be composed of a second texture that is rougher than the first texture. The lower section may be composed of a third texture that is smoother than the first texture and the second texture.

DETAILED DESCRIPTION

FIG. 1illustrates an exemplary embodiment of an engine10that may be, for example, a diesel engine, a gasoline engine, or a gaseous fuel-powered engine. Engine10, in this embodiment, is a two-cycle diesel engine associated with a locomotive (not shown). Engine10may include, among other things, an assembly of pistons12, connecting rods14, and a crankshaft16. Each piston12may be connected to crankshaft16by a corresponding one of connecting rods14, such that movement of piston12results in rotation of crankshaft16. These components may operate together to transform chemical energy in fuel into useful rotational motion of crankshaft16through a series of explosions within combustion chambers18of engine10. These explosions may cause pistons12and connecting rods14of engine10to reciprocate within cylinders20. In this manner, cylinders20may serve as pressure vessels in which the process of combustion takes place and as guides for pistons12sliding within them.

Cylinders20may be arranged within a cylinder block22in two banks positioned at an angle to each other. Each bank may include a group of cylinders20located on the same side of crankshaft16with their axes lying in a common plane passing through an axis of crankshaft16. Each cylinder20may be sealed at its top by a cylinder head26. Piston12, reciprocable within cylinder20, may thus define a variable-volume combustion chamber18.

Cylinder20may be sealed at its bottom by piston12and a plurality of piston rings (not shown). The piston rings may help to seal off combustion chamber18and may be received by machined grooves defined in an outer surface of piston12. For example, each piston12may have four compression rings on an upper portion to seal cylinder20from cylinder block22. This arrangement may guard against combustion gases leaking past piston12into cylinder block22and may provide a means by which surplus heat may be transmitted from piston12to the walls of cylinder20. Piston12may also have two oil control rings positioned on a lower portion to control lubrication and prevent excess oil consumption by effectively distributing the lubricating oil on the walls of cylinder20.

FIG. 2illustrates a sectional view of an exemplary cylinder liner28that may be used to protect an associated cylinder20from wear and degradation caused by piston12. Cylinder liner28may have a generally cylindrical shape and may be removably fitted within cylinder20in which piston12reciprocates. During operation of engine10, cylinder liner28may form a sliding surface for piston12and the piston rings as piston12is driven in an up-and-down reciprocating motion by connecting rod14and crankshaft16.

The inner surface of cylinder liner28may be divided into an upper section34, a middle port relief section36, and a lower section38. Upper section34may be characterized by an axial length of approximately 1.5-2.5 times the axial length of middle port relief section36. Lower section38may be characterized by an axial length of approximately 2-3.5 times the axial length of middle port relief section36. Middle port relief section36may be characterized by intake ports40arranged at a common axial location around the circumference of cylinder liner28. Intake ports40may be arranged such that the area above and below intake ports40are approximately equal. This arrangement may help ensure proper cylinder scavenging for engine10, whereby fresh air for a new cycle may be introduced into cylinder20and rotation of crankshaft16may force any remaining exhaust from the previous power stroke from cylinder20.

As piston12and/or the piston rings reciprocate within cylinder20, they may impart damage to cylinder liner28in the form of scuffing. Scuffing may occur with the formation of local microscopic welds between piston12and/or the piston rings and cylinder liner28. Scuffing may also result from the piston rings dragging debris passing through intake ports40across the inner surface of cylinder liner28. To help reduce scuffing to cylinder liner28, adequate lubrication at the sliding interface between piston12and cylinder liner28should be maintained. For this purpose, cylinder liner28may be provided with a variable surface finish such that higher degrees of roughness and porosity are applied to sections of cylinder liner28that may be subject to a greater risk of scuffing during engine operation. This roughness and porosity may facilitate oil retention at desired locations.

The surface roughness of cylinder liner28may be represented by a variety of roughness parameters, including, for example, arithmetic mean value Ra, mean roughness depth Rz, and root-mean-square average Rq. Of these, Rais more common and is therefore used to describe cylinder liner28of the present disclosure. Ramay be calculated based on an average of the peaks and valleys associated with the surface of cylinder liner28. Higher values of Ramay indicate a higher degree of roughness. Conversely, lower values of Ramay indicate a smoother finish.

The roughness characteristics of cylinder liner28may also be explained using V0, a term known in the art to describe the volume of oil retained by scratches (e.g., cross-hatched grooves or cross-hatching) imparted to the sections of cylinder liner28. V0may be a dimensionless unit. Higher values of V0may indicate higher volumes of retained oil and therefore a higher oil consumption. Accordingly, higher values of V0may correspond to higher values of Raand therefore a higher degree of roughness. Conversely, lower values of V0may indicate lower volumes of retained oil and therefore a lower oil consumption. Lower values of V0may therefore correspond to lower values of Raand consequently a smoother finish. With the parameters of Raand V0set forth above, the variable surface finish corresponding to the various lubrication needs of cylinder liner28of the present disclosure will now be described.

Lower section38of cylinder liner28may be subject to a reduced risk of scuffing relative to upper section34and middle port relief section36because the oil control rings positioned on the lower portion of piston12may not encounter as great a load as the compression rings positioned on the upper portion of piston12. As such, lower section38may not require a significant amount of oil to counter the loading experienced between the compression rings and cylinder liner28, and may therefore be provided with a smoother finish. In particular, lower section38may be provided with an Ravalue of approximately 15-25 micro-inches and a V0value of approximately 0.05-0.10. In such an arrangement, lower section38of cylinder liner28may be characterized by a reduced retention of lubricating oil. For example, as will be appreciated, lower section38, relative to upper section34and middle port relief section36, may require the least amount of lubrication of cylinder liner28.

Upper section34of cylinder liner28may be subject to a higher risk of scuffing relative to lower section38due to the harsh pressure and temperature conditions of combustion chamber18. For example, increased friction and pressure may be observed in upper section34at the interface of cylinder liner26and the piston rings. Upper section34may therefore require a higher degree of oil retention and may be provided with an Ravalue of approximately 15-35 micro-inches and a V0value of approximately 0.05-0.30. In such an arrangement, upper section34of cylinder liner28may be characterized by an intermediate degree of surface roughness and therefore an intermediate degree of oil retention relative to lower section38and middle port relief section36.

Middle port relief section36of cylinder liner28may be subject to an increased risk of scuffing relative to upper and lower sections34,38, and may therefore require the highest degree of oil retention of cylinder liner28. This increased risk may be associated with the severe pressure and temperature conditions experienced in this region of cylinder liner28. As with upper section34, increased friction and pressure may be observed between cylinder liner28and the piston rings. An increased loading on the piston rings may also occur as a result of the reduced area characterizing middle port relief section36due to the presence of intake ports40. Whereas cylinder liner28may be characterized circumferentially by a generally full circle in upper and lower sections34,38, in middle port relief section36, intake ports40may reduce the surface area available to support the same loads carried in upper and lower sections34,38. This results in a higher pressure between cylinder liner28and the piston rings in middle port relief section36.

Additionally, middle port relief section36may also experience greater wear due to a tendency of piston12to deviate slightly from a perfectly linear up and down reciprocating motion and to instead obliquely strike cylinder liner28. This may cause increased scuffing to the area above and below intake ports40. Greater wear may also result from the piston rings dragging debris entering through intake ports40across the inner surface of cylinder liner28.

Middle port relief section36may therefore be provided with an Ravalue of approximately 35-55 micro-inches and a V0value greater than approximately 0.10. In this arrangement, middle port relief section36may be characterized by the highest degree of surface roughness relative to upper and lower sections34,38of cylinder liner28. Middle port relief section36, requiring the highest amount of lubrication of cylinder liner28for proper function of engine10, may thus be provided with the greatest degree of oil retention.

In this manner, cylinder liner2$ may be provided with a three-tiered surface finish in which the degree of roughness of each tier may correspond to the lubrication needs of the different sections that are subject to different conditions of temperature and pressure within cylinder20. In this arrangement, cylinder liner28may be provided with adequate lubrication to both reduce friction and wear and to help decrease the potential for harmful particulate emissions.

FIG. 3illustrates an exemplary method that may be used to produce cylinder liner28.FIG. 3will be discussed in more detail in the following section to further illustrate the disclosed concepts.

INDUSTRIAL APPLICABILITY

The disclosed cylinder liner may provide an efficient means to help reduce friction and wear in an engine such as, for example, a two-stroke diesel engine. In particular, the disclosed cylinder liner may help reduce the risk of scuffing that may result under the harsh pressure and temperature conditions of combustion chamber18. The disclosed cylinder liner may be of particular application to uniflow two-stroke diesel engines that are especially vulnerable to scuffing because of particulates entering through intake ports40and being dragged along cylinder liner28during engine operation. In addition, the disclosed cylinder liner may help reduce harmful particulate emissions by reducing oil remaining on cylinder liner28from being burned in combustion chamber18and subsequently introduced into the atmosphere. In this regard, the disclosed cylinder liner may also beneficially help to reduce excess oil consumption generally.

FIG. 3illustrates a flowchart depicting an exemplary method that may be used to produce cylinder liner28.FIG. 3will now be discussed in detail. The exemplary method illustrated inFIG. 3may utilize honing, which may be recognized by one skilled in the art as an abrasive machining process that produces a particular finish for surfaces such as cylinder liner28. Honing involves scrubbing an abrasive against cylinder liner28along a controlled path of upper section34, middle port relief section36, and lower section38. This process may cut away irregularities and result in a more uniform finish. Such abrasives may be composed of irregularly shaped particles called grit and designated by a grit stone number. Lower grit stone numbers may produce a rougher finish. Conversely, higher grit stone numbers may produce a smoother finish. One skilled in the art will recognize that achieving a specific surface finish through honing may require the selection of a proper grade of abrasives and correctly adjusting the speed applied to such abrasives during the honing process. It should be noted that although honing may be recognized in the art, one skilled in the art will further recognize that the parameters and steps constituting the most suitable surface finish for cylinder liner28may be unique.

Before honing begins, cylinder liner28may be characterized by a surface of generally uniform texture. The subsequent honing process may produce a surface finish characterized by cross-hatching. This cross-hatching may provide the roughness needed to help cylinder liner28retain the lubricating oil necessary for proper functioning of engine10. The cross-hatching of the present cylinder liner28may be manufactured through a five-step procedure involving honing. It is contemplated that these steps may be performed in the order described, in reverse order, or simultaneously, if desired.

In step110, upper section34and middle port relief section36of cylinder liner28may be hardened. Hardness may be measured on several hardness scales, including, for example, the Brinnell scale and various levels of the Rockwell scale. Of these, the Rockwell C scale is more appropriate to describe cylinder liner28of the present disclosure because of its applicability to harder materials such as steel. The Rockwell C scale may be based on the indentation hardness associated with cylinder liner28. Hardness measured on the Rockwell C scale may be a dimensionless unit. Higher values on the Rockwell C scale may indicate a harder material. Conversely, lower values on the Rockwell C scale may indicate a softer material.

The hardening of step110may involve hardening upper section34and middle port relief section36until a phase change is realized in cylinder liner28and a particular hardness greater than approximately 50 on the Rockwell C scale is reached. This hardness may not necessarily characterize the entire composition of cylinder liner28. For example, this hardness may be of a thickness of approximately ten thousandth of an inch, extending from the inner surface of cylinder liner28. The hardening of step110may utilize any of several methods known in the art to harden a material, including, for example, laser hardening or induction hardening. Laser hardening may involve treating cylinder liner28with a gas laser, such as a carbon dioxide laser. The laser beam may be focused on upper section34and middle port relief section36until a phase change is realized in cylinder liner28. Similarly, induction hardening upper section34and middle port relief section36may involve heating and rapidly cooling upper section34and middle port relief section36using an induction heater until a particular hardness greater than approximately 50 on the Rockwell C scale is reached. Other hardening methods known in the art may also be used.

In this manner, step110may increase the porosity of upper section34and middle port relief section36by creating internal hardness. The porosity imparted to cylinder liner28may permit individual local pockets on its surface to hold more oil than, for example, lower section38. This may provide a lubricated surface for the movement of piston12and/or the piston rings against cylinder liner28. Hardening may be followed by grinding, if desired. Grinding may be applied to straighten and size cylinder liner28.

In step120, cylinder liner28may be rough honed with a 150 grit super-abrasive at a speed of approximately 250 RPM for approximately 2.5-3 minutes to provide a comparatively rough surface. In one example, the main bore of cylinder liner28may be rough-honed to approximately 9.058 inches. In step130, middle port relief section36may be port relief honed with a 400 grit super-abrasive at a speed of approximately 175 RPM for approximately 2 minutes. Step130may utilize across-hatch angle of approximately 5-17°, which may affect V0. In particular, this angle may help middle port relief section36retain more oil.

In step140, upper section34may be finish honed with a 400 grit super-abrasive at a speed of 200 RPM for approximately 2.5-3 minutes. In step150, lower section38may be finish honed with a 400 grit super-abrasive at a speed of approximately 200 RPM for approximately 2.5-3 minutes. Steps140and150may utilize a cross-hatch angle of approximately 30-40°, which may affect V0. In particular, this angle may produce cross-hatching to upper and lower sections34,38that promotes less oil retention.

The finish hone of step140may be applied in a manner such that contact is not made with middle port relief section36. This may be achieved through different means. For example, in this embodiment, middle port relief section36is twelve thousandth of an inch larger than upper and lower sections34,38. The abrasives used in the honing process may therefore be arranged to travel only along middle port relief section36and avoid contact with upper and lower sections34,38. Other methods known in the art may also be utilized, including the use of a rubber covered cylindrical shield to cover middle port relief section36and expose upper and lower sections34,38during these steps.

The disclosed method may produce a three-tiered surface finish in which upper section34, middle port relief section36, and lower section38exhibit variable surface roughness characteristics that provide for the lubrication needs of the respective sections. In particular, upper section34may be provided with an Ravalue of approximately 15-35 micro-inches and a V0value of approximately 0.05-0.30. Middle port relief section36may be characterized by an Ravalue of approximately 35-55 micro-inches and a V0value greater than approximately 0.10. Lower section38may be characterized by an Ravalue of approximately 15-25 micro-inches and a V0value of approximately 0.05-0.10. One skilled in the art will recognize that the degree of roughness, as measured by an Ravalue, will vary slightly throughout the extent of the respective portions of cylinder liner28due to mechanical deficiencies associated with the super-abrasives used for honing cylinder liner28. A similar variation may be associated with V0values.

In this manner, upper section34, middle port relief section36, and lower section38may be provided with an amount of oil correlating to their respective lubrication needs. For example, lower section38may be provided with a smoother finish because the oil control rings positioned on lower portion of piston12may not encounter as great a load as the compression rings positioned on upper portion of piston12. As such, lower section38may not require increased oil to counter the loading experienced between the compression rings and cylinder liner28. Similarly, middle port relief section36may be provided with a high degree of surface roughness to satisfy its higher lubrication needs due to an increased load on the piston rings caused by engine dynamics and the reduced area between the piston rings and cylinder liner28.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed cylinder liner without departing from the scope of the disclosure. Other embodiments of the cylinder liner will be apparent to those skilled in the art from consideration of the specification and practice of the cylinder liner disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.