Engine cylinder mid-stop

According to one embodiment, an internal combustion engine includes a cylinder and liner. The cylinder includes a mid-stop formed in a side wall of the cylinder. The mid-stop includes a first contact surface and an undercut between the first contact surface and the side wall. The liner is positioned within the cylinder and includes a seat having a second contact surface. The second contact surface is supported on the first contact surface.

FIELD

This disclosure relates to internal combustion engines, and more particularly to cylinder mid-stops for supporting a cylinder liner.

BACKGROUND

The incorporation of replaceable cylinder liners in the design of an internal combustion engine provides numerous advantages to the manufacturer and user of such an engine. For example, replaceable liners can be easily removed and replaced during overhaul of the engine. Additionally, cylinder liners eliminate the necessity to scrap an entire engine block during manufacture should the inside surface of one cylinder be improperly machined. To assist in maintaining the liners in place within the cylinders during use, some conventional liner and cylinder configurations employ a stop (e.g., top-stop, mid-stop, bottom-stop) on which rests a seat formed in the liner.

Despite the above and other advantages, numerous problems attend the use of replaceable cylinder liners, as is exemplified by a large variety of cylinder and liner designs previously used by engine manufacturers. While each of the previously known liner designs may have demonstrable advantages, no single design appears to be optimal or void of problems and shortcomings.

For example, conventional engine systems with cylinder mid-stop and liner seat configurations suffer from several shortcomings. For example, significant cylinder and liner distortion can be experienced at the cylinder mid-stop and liner seat interface during operation of the engine.

The distortion of the cylinder and liner can induce relative motion between the cylinder and liner at the interface between the mid-stop and seat, which causes excess wear on the mid-stop and seat. The excess wear may negatively impact the performance of the engine, and in some instances, require replacement of the entire engine block. Some conventional engine systems position an annular shim between a top-stop and liner seat to reduce wear between the top-stop and seat. However, conventional engine systems with a mid-stop configuration have not employed an annular shim. Additionally, for those engine systems that do utilize shims between the liner and cylinder, the shims can be difficult to install and align with the liner during assembly. Such shims often are installed after original assembly of the engine, such as during a repair or reconditioning of the engine. For this reason, most shims are not well suited for installation during the original assembly of the engine.

Additionally, the distortion of the cylinder and liner may cause the liner to protrude into the cylinder cavity. Protrusion of the liner into the cylinder may cause the liner to impact the piston causing wear and deformation of the piston.

SUMMARY

The subject matter of the present application has been developed in response to the present state of the art, and in particular, in response to the problems and needs of conventional engine cylinders and liners that have not yet been fully solved by currently available engine configurations. For example, conventional engine systems may attempt to mask relative motion between the cylinder and liner seat by simply addressing the symptoms of such relative motion (e.g., wear) using shims that are difficult to install or shims positioned at a top-stop interface between the cylinder and liner seat. Moreover, none of the conventional engine systems attempt to address the root cause of the relative motion. In other words, some conventional engine systems are not configured to reduce wear between mid-stop and liner seat by preventing the relative motion therebetween. Essentially, some prior art engine systems accept relative motion between mid-stop and liner seat as inevitable, but fail to provide adequate measures to account for such relative motion. Most attempts at preventing the symptoms of relative motion (e.g., incorporating shims) add to the manufacturing complexity and cost of the engine system. Other prior art engine systems focus solely on preventing the symptoms of relative motion, rather than preventing the relative motion itself.

Accordingly, the subject matter of the present application has been developed to provide an engine cylinder that overcomes many of the shortcomings of the prior art. Generally, in some embodiments, a shim is positioned between the mid-stop and seat interface to reduce wear. In certain embodiments, the shim is desired to reduce manufacturing complexity and ensure proper alignment during assembly. According to other embodiments, the cylinder mid-stop is specifically designed to limit the relative motion between the mid-stop and liner seat. Accordingly, contrary to some prior art cylinder and liner assemblies, the subject matter of the present disclosure reduces wear between the mid-stop and liner seat by utilizing various shim design and placements, and addressing the root cause of relative motion. In this manner, relative wear and motion between the mid-stop and liner seat are reduced without unnecessarily increasing the manufacturing complexity and cost of the engine.

According to one embodiment, According to one embodiment, an internal combustion engine includes a cylinder and liner. The cylinder includes a mid-stop formed in a side wall of the cylinder. The mid-stop includes a first contact surface and an undercut between the first contact surface and the side wall. The liner is positioned within the cylinder and includes a seat having a second contact surface. The second contact surface is supported on the first contact surface.

In some implementations of the engine, the cylinder defines a central axis and the first contact surface is substantially perpendicular to the central axis. The undercut can extend downwardly away from the first contact surface. In certain implementations, the mid-stop includes a mid-stop region that defines the first contact surface and the undercut defines a space between the mid-stop region and the side wall. The mid-stop region can be deformable in a radially outward direction toward the side wall when subjected to operational loads.

According to certain implementations of the engine, the undercut includes an annular groove. The undercut can be positioned radially inward from the side wall. When subjected to operational loads, the first contact surface and the second contact surface can move in a radially outward direction toward the sidewall. The undercut can facilitate co-motion of the first and second contact surface when subjected to operational loads.

In another embodiment, a cylinder for an internal combustion engine includes a channel that extends from a top end to a bottom end. The channel is defined by a sidewall. The cylinder also includes an annular mid-stop region that extends about a circumference of the channel. Further, the cylinder includes an annular undercut that extends about the circumference of the channel between the annular mid-stop region and the sidewall.

According to some implementations of the cylinder, the annular mid-stop region defines a contact surface that extends substantially perpendicularly relative to a central axis of the channel. The annular undercut can define a space between the mid-stop region and the sidewall. The annular mid-stop region may be configured to deform and move in a radially outward direction toward the sidewall into the space under operation loads.

In certain implementations of the cylinder, the annular undercut includes an annular groove that vertically penetrates the mid-stop region. The annular undercut can include a concave surface. In some implementations, a ratio of a first width of the annular mid-stop region and a second width of the annular undercut is between about 0.20 and about 0.5. A depth of the annular undercut can be more than about 2% of a height of the channel above the annular undercut. In some implementations, the annular undercut has a substantially semi-circular shaped surface.

In yet another embodiment, a method for reducing wear in an internal combustion engine that has a cylinder and a cylinder liner supported within the cylinder is disclosed. The method includes providing a mid-stop within the cylinder where the mid-stop includes a mid-stop region and an undercut positioned between the mid-stop region and a sidewall of the cylinder. Also, the method includes providing a seat on the cylinder liner and positioning the seat on the mid-stop region. The method further includes moving both the mid-stop region and seat in a radially outward direction toward the sidewall of the cylinder.

According to some implementations, the method also includes applying compressive and lateral loads to the mid-stop region and seat. Moving both the mid-stop region and seat in a radially outward direction toward the sidewall of the cylinder can occur during the application of the compressive and lateral loads. Additionally, the method can include releasing the compressive and lateral loads from the mid-stop region and seat. Further, the method may include moving both the mid-stop region and seat in a radially inward direction away from the sidewall of the cylinder during the release of the compressive and lateral loads.

DETAILED DESCRIPTION

Referring toFIG. 1, according to one embodiment, an engine10includes an engine block12with a cylinder13. The cylinder13is formed into the engine block12and includes a radially inner wall or surface that defines a liner receiving space. As defined herein, the radial direction or radially directed is associated with a direction that is perpendicular to a central axis95of the cylinder13, which is coaxial with the piston21. Further, the cylinder13includes a mid-stop or shelf42formed in the inner wall. The mid-stop42extends circumferentially about the cylinder13and separates the cylinder into an upper section above the mid-stop and a lower section below the mid-stop. The mid-stop42also separates the inner wall into an upper inner wall14A and lower inner wall14B. The upper section has a diameter greater than the lower section. Additionally, the mid-stop42is defined as a mid-stop because it is positioned within the cylinder13away from a top15(e.g., upper opening) of the cylinder13. The mid-stop42forms part of a mid-stop and liner interface40, which is defined as the physical interface between the mid-stop42and a seat44of a cylinder liner26.

The cylinder liner26is sized and shaped to nestably mate with the cylinder13. Accordingly, the cylinder liner26includes a generally cylindrically shaped tube with a radially outer wall or surface29that substantially matches the radially inner walls14A,14B of the cylinder13. Additionally, the seat44of the liner26extends circumferentially about the liner. The seat44rests on and is supported by the mid-stop42. Accordingly, the mid-stop42and seat44each includes mating surfaces. For example, as shown inFIG. 2, the mid-stop42includes a first contact surface60and the seat44includes a second contact surface62. The region within which the first contact surface60is in contact with the second contact surface62can be defined as a contact region. The contact region illustrated inFIG. 2shows a gap between the contact surfaces60,62for convenience in illustrating the details of the present subject matter. In practice, the contact surfaces60,62will be in contact with each other during operation of the engine10.

Each of the first and second contact surfaces60,62is substantially flat and defines a plane that is substantially perpendicular to the central axis95of the cylinder13. Therefore, the first contact surface60extends substantially perpendicularly relative to the inner walls14A,14B of the cylinder13at least proximate the contact region. Likewise, the second contact surface62extends substantially perpendicularly relative to the inner wall27, and the outer wall29in some locations, of the liner26. The portion of the cylinder13defining the first contact surface60is defined herein as a mid-stop region81, and the portion of the liner26defining the second contact surface62is defined herein as a seat region83. The mid-stop region81includes the portion of the cylinder13directly adjacent (e.g., below) the first contact surface60in the radially outward direction, but the mid-stop region (and first contact surface) is spaced radially inwardly from the upper inner wall14A of the cylinder13by virtue of an undercut64as will be explained in more detail below. In fact, a radially outward portion of the mid-stop region81is defined by the undercut64. The seat region83includes the portion of the liner26directly adjacent the second contact surface62in the radially outward direction. As used herein, radially inward and outward is made with reference to the central axis95of the cylinder13.

With the seat44supported on the mid-stop42, a top end29of cylinder liner26extends upwardly just beyond the top15of the cylinder13. Although not shown, a head gasket and cylinder head are mounted to the engine block12atop the cylinder via a plurality of fasteners during assembly of the engine10. As the cylinder head is tightened against the engine block12, the cylinder head contacts and applies a compressive load50against the cylinder liner26. The compressive load50on the cylinder liner26is transferred to a corresponding tensile load applied to the mid-stop42via engagement between the mid-stop and seat28. Accordingly, the seat44is pre-loaded in compression against the mid-stop42, and the mid-stop42is pre-loaded in tension, via the compressive load50applied to the liner26via the cylinder head.

The radially inner wall or surface27of the cylinder liner26defines a channel16along which a piston21linearly travels during operation of the engine10. The portion of the channel16of the cylinder liner26above the piston21can be defined as the combustion chamber of the cylinder13. The channel16is cylindrical and sized to substantially match (e.g., be slightly less than an interference fit with) the exterior surface of the piston21. Fuel and air are combusted within the combustion chamber, with the combustion energy or forces52radiating outwardly against the walls defining the combustion chamber. A portion of the combustion energy52applies lateral loads or forces against the liner26. Another portion of the combustion energy52applies downwardly directed loads against the piston21, which drives downward movement of the piston21within the channel16.

As the piston21is downwardly driven, the piston rotates a crankshaft36as indicated by directional arrow56via a connecting rod32. The connecting rod32is rotatably coupled to the piston21at a first end30and rotatably coupled to a counterweight34of the crankshaft36at a second end32opposite the first end. The rotational energy or momentum of the crankshaft36facilitated by the counterweights34upwardly drives the piston21along the channel16. As the piston21transitions from travel in an upward direction back to a downward direction after reaching a top-dead-center (TDC) position (e.g., at the top of the piston stroke), the initial angling of the connecting rod22drives the piston into a thrust side of the liner26. The side loading of the piston21in this manner imparts a lateral or side force54against the inner wall27of the liner26and thus the inner walls14A,14B of the cylinder13.

Based on the foregoing, during operation of the engine10, axial (e.g., compressive or tensile) loads are being applied against the interface44of mid-stop42and seat44, as well as lateral (e.g., side or shear) loads. The varying axial and lateral loads can be defined as operation loads. Additionally, thermal loads affect the axial and lateral loads on the interface44. Each of the axial and lateral loads acting on the interface44affects the deformation and relative movement of the mid-stop42and seat44differently. For example, as shown inFIG. 3in dashed lines, because there are no radially outward constraints on the seat region83, the compressive load72acting on the liner26causes the seat region83of the liner to deform, squish, or bulge radially outwardly away from the central axis95of the cylinder. This radially outward deformation of the seat region83also results in micro-motion of the contact surface62in a radially outward direction78. The lateral load73acting on the liner26by virtue of the piston21tends to deflect the liner radially outwardly, which contributes to the radially outward deformation of the seat region83and micro-motion of the contact surface62in the radially outward direction78.

The compressive load70acting on the mid-stop42at the first contact surface60may also cause deformation and relative movement of the mid-stop region81. In addition to the load from the assembly of the cylinder head, the compressive load70may also include a compressive load induced by the outward deflection of the liner26due to the lateral load73. Because the liner26is axially constrained above by the cylinder head and below by the mid-stop42, the outward deflection induces a compressive load onto the mid-stop. Prior art cylinder configurations included a mid-stop80(seeFIG. 2) with a contact surface directly coupled to the radially inner wall of the cylinder. Because the contact surface is directly coupled to the inner wall, the inner wall of the cylinder, the wall provides a radially outward constraint preventing deformation in the radially outward direction. Accordingly, when applied onto the contact surface of the conventional mid-stop80, the compressive load70induced a tensile load74in the mid-stop proximate the inner wall of the cylinder that was directed away from the inner wall. The tensile load caused the conventional mid-stop80to deform axially downwardly away from the liner seat, and also caused micro-movement of the mid-stop radially inwardly away from the inner wall.

Accordingly, for prior art mid-stops80, the compressive loads70,72, side load73, and tensile load74resulted in relative micro-motion of the first contact surface of the mid-stop80and the second contact surface of the seat. More specifically, the applied loads onto conventional mid-stop and seat interfaces caused the mid-stop contact surface to move radially inwardly and the seat contact surface to move radially outwardly. The relative motion of the contact surfaces promoted significant wear of the cylinder mid-stop and liner seat.

Additionally, while some of the applied loads are relatively constant, such as the compressive load generated by the mounting of the cylinder head to the engine block12, other loads are dynamic with magnitudes that can vary or alternate during operation of the engine. For example, as the piston cycles through various positions within the channel16during the combustion cycles of the engine, the compressive and lateral loads on the interface44also cycle between varying magnitudes. Also, the compressive and lateral loads may fluctuate as the thermal loads within the system change during operation. For conventional systems, such alternating loads caused repetitive movement of the contact surfaces of the cylinder mid-stop and liner seat, which intensified the relative wear of the mid-stop and liner seat. As long as the contact surfaces of the mid-stop and liner seat experience relative motion, significant wear of the mid-stop and liner seat will occur.

To reduce, and in some cases prevent, relative motion between the contact surfaces60,62of the mid-stop42and seat44, respectively, and thus reduce wear of the mid-stop and seat during operation of the engine10, the mid-stop includes an undercut64. The undercut64is positioned between the contact surface60of the mid-stop42and the upper inner wall14A of the cylinder13. As shown inFIG. 2with reference to the prior mid-stop design80without an undercut, the undercut64extends axially downwardly relative to the central axis95of the cylinder13and the contact surface60. Accordingly, the undercut64extends below the contact surface60, which allows a portion of the mid-stop region81to be open to the space defined by the undercut, and to face the upper inner wall14A.

The application of compressive and lateral loads results in deformation and movement of the mid-stop42that is different than prior art mid-stops. For example, because the undercut64is open or faces the inner wall14A, the inner wall does not radially outwardly constraint the mid-stop region81in the same manner as with prior art mid-stops80. Accordingly, without the radially outward constraint of the wall, the compressive load70applied to the mid-stop42results in the mid-stop region81of the cylinder13deforming, squishing, or bulging radially outwardly away from the central axis95of the cylinder in substantially the same manner as the seat region83(see, e.g.,FIG. 3as shown in dashed lines). Further, the radially outward deformation of the mid-stop region81also results in micro-motion of the contact surface60in a radially outward direction76. The radially outward direction76of the movement of the mid-stop region81is the same as the radially outward direction78of the movement of the seat region81. In other words, the mid-stop and seat regions81,83move in the same direction under the same loads. Moreover, the configuration (e.g., size and shape) of the undercut64and mid-stop region81is selected such that the rate of movement is approximately the same. Because the direction and rate of motion of the mid-stop and seat regions81,83are substantially the same, the mid-stop and seat regions do not experience substantial relative motion. Consequently, without substantial relative motion, wear of the mid-stop region81by the seat region83, and wear of the seat region by the mid-stop region, is significantly reduced, and eliminated in some applications. Based on the foregoing, the introduction of the undercut64does not prevent micro-movement of the mid-stop region81and seat region83, but the undercut does reduce and even prevent relative movement between the mid-stop region and seat region.

The alternating loads experienced during operation of the engine10do not affect the benefit of restricting relative motion between the mid-stop and seat regions81,83through use of the undercut64. As has been described above, as certain compressive and lateral loads are applied to the mid-stop and seat regions81,83, the regions correspondingly bulge and move radially outwardly. As the compressive and lateral loads are released, the mid-stop and seat regions81,83retract from the deformed state back to a non-deformed state in approximately the same direction and at approximately the same rate. Accordingly, the mid-stop and seat regions81,83not only do not experience motion relative to each other during the application of loads, but the regions also do not experience motion relative to each other during the release of the loads. In this manner, relative motion and wear of the mid-stop and seat are reduced even during reciprocating and alternating loads.

Referring toFIG. 4, an embodiment of a cylinder113with a mid-stop142. The cylinder113is similar to the cylinder13ofFIG. 3, with like numbers referring to like elements. For example, the mid-stop142extends circumferentially about the cylinder113. The mid-stop142also includes a first contact surface160and a mid-stop region181defining the first contact surface. Like the first contact surface60, the first contact surface160is substantially flat and defines a plane that is substantially perpendicular to the central axis of the cylinder and an upper inner wall114A of the cylinder as indicated by directional arrow192. The first contact surface160is spaced radially inwardly from the upper inner wall114A of the cylinder113by the undercut164. In other words, the undercut164is positioned between the upper inner wall114A and the first contact surface160.

Like the undercut64, the undercut164extends axially downwardly relative to the central axis of the cylinder13and the first contact surface60as indicated by the directional arrow190, which is parallel to the central axis. Therefore, the surface of the undercut164is positioned below the first contact surface60, and thus does not contact or support a second contact surface of a liner seat. In this manner, the undercut164, like the undercut64, can be defined as a vertical undercut. The depth D of the undercut164, or the distance in the direction190from the first contact surface60to a lowermost point of the undercut, can vary as desired. The depth D is selected to provide a sufficient portion of the mid-stop region181to be open to the space defined by the undercut164to induce radially outward directed deformation of the mid-stop region as discussed above. In some implementations, the depth D of the undercut164is greater than about 2% of the height of the upper wall114A (e.g., the distance from a top of the cylinder113to the first contact surface160). The depth D is essentially equal to the height of the mid-stop region181.

The width W2of the undercut164, or the distance in the direction192from the inner wall114A to the first contact surface160also can vary as desired. The width W2is selected to provide a sufficient distance between the mid-stop region181and the upper inner wall114A such that the radially outward constraint of the inner wall does not constrain the radially outward movement and bulging of the mid-stop region. In some implementations, the width W2is about equal to the depth D. In certain implementations, as examples only, the width W2is more than about 20% of the width W3of the mid-stop region181, and can be between 20% and about 50% of the width W3in some implementations. According to certain implementations, as examples only, the width W2is more than about 20% of the total width W1of the mid-stop142, and can be between 20% and about 40% of the width W1in some implementations. Accordingly, the width W2of the undercut164can be more than about 20% of the total width W1of the mid-stop142in certain implementations, and can be between 20% and 40% of the total width W1in some implementations. In one specific implementation, as an example only, the W1is between about 4 and about 6 mm. In yet one specific implementation, as an example only, the W2is between about 1 and about 2 mm. According to one specific implementation, as an example only, the depth D is between about 1 and about 2 mm. As an example, the depth D can be between about 20% and about 70% of the width W3of the mid-stop region181is some specific implementations.

The undercut164defines an annular groove that extends circumferentially around the cylinder113. The groove is concentric with the annular first contact surface160of the mid-stop region181. As shown, the annular groove of the undercut164can be formed with a radiused (e.g., semi-circular shaped) surface with a radius R. The radius R can be any of various radiuses as desired. In one implementation, the radius R is between about 50% and about 100% of the depth D. Although the illustrated undercut164has a concave and relatively uniformly curved surface, in other embodiments the undercut can be linear or non-uniformly curved surfaces. Similarly, the mid-stop region181may include radiused inner and outer edges194,196adjacent the first contact surface160.

The cylinder and cylinder liner, including the mid-stop and seat, can be made of any of various materials and formed using any of various manufacturing techniques. For example, in one implementation, the cylinder and cylinder liner each is made from iron and the formed using a casting technique. In other implementations, the cylinder and liner can be made from aluminum and formed using a machining technique. In yet some implementations, the cylinder and liner are made from a combination of materials, or can be formed using a combination of manufacturing techniques, such as casting and machining.

Referring toFIG. 5, and according to one embodiment, a shim250is positioned within the interface240between the mid-stop242formed in the cylinder213of the engine block212and the seat244formed in the liner226. The mid-stop242may be similar to conventional mid-stop designs without an undercut. Alternatively, the mid-stop242may include an undercut as described above. In the illustrated embodiment, the shim250is a substantially flat annular ring with a generally rectangular cross-sectional shape. The shim250is sized to be supported on the contact surface260of the mid-stop242. An outer diameter of the shim250is smaller than the diameter of the cylinder213above the mid-stop242. Further, an inner diameter of the shim250is smaller than a diameter of the liner226adjacent the interface240. The shim250can have any of various thicknesses as desired.

With the shim250positioned within the interface240, a first side of the shim contacts the contact surface260of the mid-stop242and an opposing second side of the shim contacts the contact surface262of the seat244. As the contact surface260moves radially relative to the contact surface262during oscillation of the piston221, the contact surface260slides against the surface of the shim250instead of the contact surface262. Similarly, as the contact surface262moves radially relative to the contact surface260, the contact surface262slides against the surface of the shim250instead of the contact surface260. Generally, the shim250is made from a material that is different than the materials from which the cylinder213and liner226are made. In certain implementations, the shim250is made from a material that is softer than the cylinder and liner materials. For example, the cylinder213and liner226may be made from iron, steel, or aluminum, and the shim250is made from copper or a copper allow, such as brass. Because the material of the shim250is softer than the material of the cylinder213and liner226, relative movement of the cylinder and liner against the shim results in comparatively more wear of the shim than the cylinder and liner. In other words, frictional wear between the shim250and the cylinder213and liner226is predominantly transferred to the shim rather than the cylinder and liner. In this manner, cylinder and liner wear is reduced by virtue of increase wear of the shim250, which is more easily replaced compared to the cylinder and liner.

Referring toFIG. 6, according to another embodiment, a self-retaining shim350is shown. The shim350includes a wear ring352and a retaining ring354coupled to the wear ring. The wear ring352may be similar in size and shape as the shim250described above. In other words, the wear ring352can be a substantially flat annular ring with a generally rectangular cross-sectional shape. The self-retaining shim350may define a central axis about which each corresponding portion of the shim is an equal distance. Defined in this manner, the wear ring352includes opposing cylinder and liner contact surfaces370,372, respectively, that extend perpendicularly relative to the central axis (also seeFIG. 8). The retaining ring354includes a liner contact surface374that extends parallel relative to the central axis and perpendicularly relative to the cylinder and liner contact surfaces370,372. Accordingly, in certain implementations, as shown inFIG. 8, the shim350has a generally L-shaped cross-section. The retaining ring354includes a plurality of slots356formed in the ring that define a plurality of tabs357between adjacent slots. In the illustrated embodiment, the slots356are spaced apart from each other and extend longitudinally in a direction substantially parallel to the central axis or liner contact surface374. In some implementations, the slots356extend substantially the entire axial length of the retaining ring354.

As shown inFIG. 7, the self-retaining shim350is securely coupled to a cylinder liner326proximate a mid-stop seat344formed in the liner. The self-retaining shim350is centered on the radially outer surface329of the cylinder liner326such that the shim is coaxial with the liner. To facilitate self-retention of the shim350, in some embodiments, the cylinder liner326includes a retention groove346formed in the outer surface329. The retention groove346has an outer diameter that is just less than the outer diameter of the adjacent portion of the liner326below the groove. The outer diameter of the outer surface329of the liner326between the groove346and a bottom end330of the liner is at least slightly larger than the inner diameter of the shim350, as defined by the retaining ring354of the shim250, when in an unbiased or unflexed state as depicted inFIG. 6. Moreover, the outer diameter of the retention groove346is approximately equal to the inner diameter of the shim350when in an unbiased or unflexed state.

The self-retaining shim350is securely coupled to the cylinder liner326by inserting the bottom end330of the liner through the aperture defined by the shim. During insertion, the shim350is oriented such that the wear ring352is positioned between the retaining ring354and the mid-stop seat344. In other words, during the insertion process, the wear ring352is positioned about the cylinder liner326before the retaining ring354is positioned about the liner. Because in the unflexed state the outer surface329between the groove346and bottom end330has a diameter that is larger than the inner diameter of the shim350, the retaining ring354must deform radially outwardly into a flexed state in order to properly position and align the shim about the liner. The plurality of slots256and tabs257facilitate radially outward deformation or flexing of the retaining ring254by reducing the force necessary to flex the ring to fit around the liner326. Once on the liner326, the shim350is slid along the liner from the bottom end330toward the seat344and a top end328of the liner until the retaining ring354is positioned over the groove346. The shim350can be made from a resiliently flexible material, such as copper or a copper alloy (e.g., brass). Accordingly, as soon as the retaining ring354is moved toward the top end328to clear a lip of the groove354, which has a smaller diameter, the resiliently flexible tabs257at least partially unflex (e.g., return to the unbiased state) to effectively snap into place (e.g., move radially inwardly) in the groove.

With the retaining ring354positioned within the groove354, the lip of the groove may act as a stop to retain retaining ring, and thus the shim350, in place about the liner326. Once positioned about the liner326, the self-retaining shim350is retained in place on the liner during assembly or installation of the liner into the cylinder313without manual assistance. In other words, the liner326and shim350can be handled as a single, monolithic unit for assembly and installation purposes. In this manner, a shim does not need to be installed into the cylinder313and aligned with the stop342as a separate step before installing the liner326. Rather, the combined liner326and shim350may be installed into the cylinder313in a single step.

Although in the illustrated embodiment the liner326includes a retention groove346, in other embodiments, the liner does not include a retention groove. In such embodiments, without a retention groove346, the radially-inwardly directed force applied against the outer surface329of the liner326due to the resilient flexing of the tabs357typically is strong enough to adequately retain the shim350in place during assembly of the combine liner and shim in the cylinder313.

As shown inFIG. 8, when the combined liner326and shim350are installed in the cylinder313, the wear ring352is positioned within an interface340between the mid-stop342and the seat344in a manner similar to the shim250ofFIG. 5. A first side of the wear ring352of the shim350contacts the contact surface360of the mid-stop342and an opposing second side of the shim contacts the contact surface362of the seat344. With this arrangement, relative movement of the cylinder313and liner326against the shim350results in comparatively more wear of the shim than the cylinder and liner.