Abstract:
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.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to a cylinder liner and, more particularly, to a cylinder liner having a three-tiered surface finish. 
       BACKGROUND  
       [0002]    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. 
         [0003]    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. 
         [0004]    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. 
         [0005]    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. 
         [0006]    The cylinder liner of the present disclosure solves one or more of the problems set forth above and/or other problems in the art. 
         [0007]    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. 
         [0008]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a cut-away perspective view illustration of an exemplary disclosed two-stroke engine; 
           [0010]      FIG. 2  is a cross-sectional view of an exemplary disclosed cylinder liner that may be used in conjunction with the engine of  FIG. 1 ; and 
           [0011]      FIG. 3  is a flowchart depicting an exemplary disclosed method that may be used to produce the cylinder liner of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIG. 1  illustrates an exemplary embodiment of an engine  10  that may be, for example, a diesel engine, a gasoline engine, or a gaseous fuel-powered engine. Engine  10 , in this embodiment, is a two-cycle diesel engine associated with a locomotive (not shown). Engine  10  may include, among other things, an assembly of pistons  12 , connecting rods  14 , and a crankshaft  16 . Each piston  12  may be connected to crankshaft  16  by a corresponding one of connecting rods  14 , such that movement of piston  12  results in rotation of crankshaft  16 . These components may operate together to transform chemical energy in fuel into useful rotational motion of crankshaft  16  through a series of explosions within combustion chambers  18  of engine  10 . These explosions may cause pistons  12  and connecting rods  14  of engine  10  to reciprocate within cylinders  20 . In this manner, cylinders  20  may serve as pressure vessels in which the process of combustion takes place and as guides for pistons  12  sliding within them. 
         [0013]    Cylinders  20  may be arranged within a cylinder block  22  in two banks positioned at an angle to each other. Each bank may include a group of cylinders  20  located on the same side of crankshaft  16  with their axes lying in a common plane passing through an axis of crankshaft  16 . Each cylinder  20  may be sealed at its top by a cylinder head  26 . Piston  12 , reciprocable within cylinder  20 , may thus define a variable-volume combustion chamber  18 . 
         [0014]    Cylinder  20  may be sealed at its bottom by piston  12  and a plurality of piston rings (not shown). The piston rings may help to seal off combustion chamber  18  and may be received by machined grooves defined in an outer surface of piston  12 . For example, each piston  12  may have four compression rings on an upper portion to seal cylinder  20  from cylinder block  22 . This arrangement may guard against combustion gases leaking past piston  12  into cylinder block  22  and may provide a means by which surplus heat may be transmitted from piston  12  to the walls of cylinder  20 . Piston  12  may 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 cylinder  20 . 
         [0015]      FIG. 2  illustrates a sectional view of an exemplary cylinder liner  28  that may be used to protect an associated cylinder  20  from wear and degradation caused by piston  12 . Cylinder liner  28  may have a generally cylindrical shape and may be removably fitted within cylinder  20  in which piston  12  reciprocates. During operation of engine  10 , cylinder liner  28  may form a sliding surface for piston  12  and the piston rings as piston  12  is driven in an up-and-down reciprocating motion by connecting rod  14  and crankshaft  16 . 
         [0016]    The inner surface of cylinder liner  28  may be divided into an upper section  34 , a middle port relief section  36 , and a lower section  38 . Upper section  34  may be characterized by an axial length of approximately 1.5-2.5 times the axial length of middle port relief section  36 . Lower section  38  may be characterized by an axial length of approximately 2-3.5 times the axial length of middle port relief section  36 . Middle port relief section  36  may be characterized by intake ports  40  arranged at a common axial location around the circumference of cylinder liner  28 . Intake ports  40  may be arranged such that the area above and below intake ports  40  are approximately equal. This arrangement may help ensure proper cylinder scavenging for engine  10 , whereby fresh air for a new cycle may be introduced into cylinder  20  and rotation of crankshaft  16  may force any remaining exhaust from the previous power stroke from cylinder  20 . 
         [0017]    As piston  12  and/or the piston rings reciprocate within cylinder  20 , they may impart damage to cylinder liner  28  in the form of scuffing. Scuffing may occur with the formation of local microscopic welds between piston  12  and/or the piston rings and cylinder liner  28 . Scuffing may also result from the piston rings dragging debris passing through intake ports  40  across the inner surface of cylinder liner  28 . To help reduce scuffing to cylinder liner  28 , adequate lubrication at the sliding interface between piston  12  and cylinder liner  28  should be maintained. For this purpose, cylinder liner  28  may be provided with a variable surface finish such that higher degrees of roughness and porosity are applied to sections of cylinder liner  28  that may be subject to a greater risk of scuffing during engine operation. This roughness and porosity may facilitate oil retention at desired locations. 
         [0018]    The surface roughness of cylinder liner  28  may be represented by a variety of roughness parameters, including, for example, arithmetic mean value R a , mean roughness depth R z , and root-mean-square average R q . Of these, R a  is more common and is therefore used to describe cylinder liner  28  of the present disclosure. R a  may be calculated based on an average of the peaks and valleys associated with the surface of cylinder liner  28 . Higher values of R a  may indicate a higher degree of roughness. Conversely, lower values of R a  may indicate a smoother finish. 
         [0019]    The roughness characteristics of cylinder liner  28  may also be explained using V 0 , 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 liner  28 . V 0  may be a dimensionless unit. Higher values of V 0  may indicate higher volumes of retained oil and therefore a higher oil consumption. Accordingly, higher values of V 0  may correspond to higher values of R a  and therefore a higher degree of roughness. Conversely, lower values of V 0  may indicate lower volumes of retained oil and therefore a lower oil consumption. Lower values of V 0  may therefore correspond to lower values of R a  and consequently a smoother finish. With the parameters of R a  and V 0  set forth above, the variable surface finish corresponding to the various lubrication needs of cylinder liner  28  of the present disclosure will now be described. 
         [0020]    Lower section  38  of cylinder liner  28  may be subject to a reduced risk of scuffing relative to upper section  34  and middle port relief section  36  because the oil control rings positioned on the lower portion of piston  12  may not encounter as great a load as the compression rings positioned on the upper portion of piston  12 . As such, lower section  38  may not require a significant amount of oil to counter the loading experienced between the compression rings and cylinder liner  28 , and may therefore be provided with a smoother finish. In particular, lower section  38  may be provided with an R a  value of approximately 15-25 micro-inches and a V 0  value of approximately 0.05-0.10. In such an arrangement, lower section  38  of cylinder liner  28  may be characterized by a reduced retention of lubricating oil. For example, as will be appreciated, lower section  38 , relative to upper section  34  and middle port relief section  36 , may require the least amount of lubrication of cylinder liner  28 . 
         [0021]    Upper section  34  of cylinder liner  28  may be subject to a higher risk of scuffing relative to lower section  38  due to the harsh pressure and temperature conditions of combustion chamber  18 . For example, increased friction and pressure may be observed in upper section  34  at the interface of cylinder liner  26  and the piston rings. Upper section  34  may therefore require a higher degree of oil retention and may be provided with an R a  value of approximately 15-35 micro-inches and a V 0  value of approximately 0.05-0.30. In such an arrangement, upper section  34  of cylinder liner  28  may be characterized by an intermediate degree of surface roughness and therefore an intermediate degree of oil retention relative to lower section  38  and middle port relief section  36 . 
         [0022]    Middle port relief section  36  of cylinder liner  28  may be subject to an increased risk of scuffing relative to upper and lower sections  34 ,  38 , and may therefore require the highest degree of oil retention of cylinder liner  28 . This increased risk may be associated with the severe pressure and temperature conditions experienced in this region of cylinder liner  28 . As with upper section  34 , increased friction and pressure may be observed between cylinder liner  28  and the piston rings. An increased loading on the piston rings may also occur as a result of the reduced area characterizing middle port relief section  36  due to the presence of intake ports  40 . Whereas cylinder liner  28  may be characterized circumferentially by a generally full circle in upper and lower sections  34 ,  38 , in middle port relief section  36 , intake ports  40  may reduce the surface area available to support the same loads carried in upper and lower sections  34 ,  38 . This results in a higher pressure between cylinder liner  28  and the piston rings in middle port relief section  36 . 
         [0023]    Additionally, middle port relief section  36  may also experience greater wear due to a tendency of piston  12  to deviate slightly from a perfectly linear up and down reciprocating motion and to instead obliquely strike cylinder liner  28 . This may cause increased scuffing to the area above and below intake ports  40 . Greater wear may also result from the piston rings dragging debris entering through intake ports  40  across the inner surface of cylinder liner  28 . 
         [0024]    Middle port relief section  36  may therefore be provided with an R a  value of approximately 35-55 micro-inches and a V 0  value greater than approximately 0.10. In this arrangement, middle port relief section  36  may be characterized by the highest degree of surface roughness relative to upper and lower sections  34 ,  38  of cylinder liner  28 . Middle port relief section  36 , requiring the highest amount of lubrication of cylinder liner  28  for proper function of engine  10 , may thus be provided with the greatest degree of oil retention. 
         [0025]    In this manner, cylinder liner  2 $ 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 cylinder  20 . In this arrangement, cylinder liner  28  may be provided with adequate lubrication to both reduce friction and wear and to help decrease the potential for harmful particulate emissions. 
         [0026]      FIG. 3  illustrates an exemplary method that may be used to produce cylinder liner  28 .  FIG. 3  will be discussed in more detail in the following section to further illustrate the disclosed concepts. 
       INDUSTRIAL APPLICABILITY 
       [0027]    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 chamber  18 . 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 ports  40  and being dragged along cylinder liner  28  during engine operation. In addition, the disclosed cylinder liner may help reduce harmful particulate emissions by reducing oil remaining on cylinder liner  28  from being burned in combustion chamber  18  and subsequently introduced into the atmosphere. In this regard, the disclosed cylinder liner may also beneficially help to reduce excess oil consumption generally. 
         [0028]      FIG. 3  illustrates a flowchart depicting an exemplary method that may be used to produce cylinder liner  28 .  FIG. 3  will now be discussed in detail. The exemplary method illustrated in  FIG. 3  may 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 liner  28 . Honing involves scrubbing an abrasive against cylinder liner  28  along a controlled path of upper section  34 , middle port relief section  36 , and lower section  38 . 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 liner  28  may be unique. 
         [0029]    Before honing begins, cylinder liner  28  may 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 liner  28  retain the lubricating oil necessary for proper functioning of engine  10 . The cross-hatching of the present cylinder liner  28  may 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. 
         [0030]    In step  110 , upper section  34  and middle port relief section  36  of cylinder liner  28  may 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 liner  28  of 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 liner  28 . 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. 
         [0031]    The hardening of step  110  may involve hardening upper section  34  and middle port relief section  36  until a phase change is realized in cylinder liner  28  and 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 liner  28 . For example, this hardness may be of a thickness of approximately ten thousandth of an inch, extending from the inner surface of cylinder liner  28 . The hardening of step  110  may 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 liner  28  with a gas laser, such as a carbon dioxide laser. The laser beam may be focused on upper section  34  and middle port relief section  36  until a phase change is realized in cylinder liner  28 . Similarly, induction hardening upper section  34  and middle port relief section  36  may involve heating and rapidly cooling upper section  34  and middle port relief section  36  using 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. 
         [0032]    In this manner, step  110  may increase the porosity of upper section  34  and middle port relief section  36  by creating internal hardness. The porosity imparted to cylinder liner  28  may permit individual local pockets on its surface to hold more oil than, for example, lower section  38 . This may provide a lubricated surface for the movement of piston  12  and/or the piston rings against cylinder liner  28 . Hardening may be followed by grinding, if desired. Grinding may be applied to straighten and size cylinder liner  28 . 
         [0033]    In step  120 , cylinder liner  28  may 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 liner  28  may be rough-honed to approximately 9.058 inches. In step  130 , middle port relief section  36  may be port relief honed with a 400 grit super-abrasive at a speed of approximately 175 RPM for approximately 2 minutes. Step  130  may utilize across-hatch angle of approximately 5-17°, which may affect V 0 . In particular, this angle may help middle port relief section  36  retain more oil. 
         [0034]    In step  140 , upper section  34  may be finish honed with a 400 grit super-abrasive at a speed of 200 RPM for approximately 2.5-3 minutes. In step  150 , lower section  38  may be finish honed with a 400 grit super-abrasive at a speed of approximately 200 RPM for approximately 2.5-3 minutes. Steps  140  and  150  may utilize a cross-hatch angle of approximately 30-40°, which may affect V 0 . In particular, this angle may produce cross-hatching to upper and lower sections  34 ,  38  that promotes less oil retention. 
         [0035]    The finish hone of step  140  may be applied in a manner such that contact is not made with middle port relief section  36 . This may be achieved through different means. For example, in this embodiment, middle port relief section  36  is twelve thousandth of an inch larger than upper and lower sections  34 ,  38 . The abrasives used in the honing process may therefore be arranged to travel only along middle port relief section  36  and avoid contact with upper and lower sections  34 ,  38 . 
         [0036]    Other methods known in the art may also be utilized, including the use of a rubber covered cylindrical shield to cover middle port relief section  36  and expose upper and lower sections  34 ,  38  during these steps. 
         [0037]    The disclosed method may produce a three-tiered surface finish in which upper section  34 , middle port relief section  36 , and lower section  38  exhibit variable surface roughness characteristics that provide for the lubrication needs of the respective sections. In particular, upper section  34  may be provided with an R a  value of approximately 15-35 micro-inches and a V 0  value of approximately 0.05-0.30. Middle port relief section  36  may be characterized by an R a  value of approximately 35-55 micro-inches and a V 0  value greater than approximately 0.10. Lower section  38  may be characterized by an R a  value of approximately 15-25 micro-inches and a V 0  value of approximately 0.05-0.10. One skilled in the art will recognize that the degree of roughness, as measured by an R a  value, will vary slightly throughout the extent of the respective portions of cylinder liner  28  due to mechanical deficiencies associated with the super-abrasives used for honing cylinder liner  28 . A similar variation may be associated with V 0  values. 
         [0038]    In this manner, upper section  34 , middle port relief section  36 , and lower section  38  may be provided with an amount of oil correlating to their respective lubrication needs. For example, lower section  38  may be provided with a smoother finish because the oil control rings positioned on lower portion of piston  12  may not encounter as great a load as the compression rings positioned on upper portion of piston  12 . As such, lower section  38  may not require increased oil to counter the loading experienced between the compression rings and cylinder liner  28 . Similarly, middle port relief section  36  may 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 liner  28 . 
         [0039]    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.