ONE PIECE CAST FERROUS CROWN PISTON FOR INTERNAL COMBUSTION ENGINE

Abstract

A one-piece piston having an investment or other permanent or non-permanent mold/die precision cast piston crown, rod flange and piston skirt. The piston crown has a relative constant thickness, a flange requiring minimal machining and a skirt providing for a wall with a support against the angular shifting of the piston. This improves the distribution of heat within such crown and the angular stability of the piston wall at the piston rod connection.

Claims

1. A piston designed for reciprocatable movement within a combustion chamber of an internal combustion engine, said piston comprising: a piston crown with an integrally cast piston skirt comprising two equal and opposing arcuate surfaces each of which comprises an arc of less than 180 degrees with the centerline of each arcuate section perpendicular to the axis of the connecting rod connecting pin bore; two integrally cast connecting rod connecting flanges all of which are precision cast of high-strength ferrous material net to finished dimensions on all inner and outer surfaces to provide a controlled thickness throughout to ensure mechanical and thermal consistency with only secondary finishing of an outer cylindrical surface of the crown, outer edges of the connecting rod flanges, two connecting rod bearing surfaces, and a top surface of the crown, while eliminating machining operations necessary to achieve constant and correct cross sectional dimensions of the crown and the piston skirt; and a cooling oil dam that is positioned adjacent a lower edge of the crown and attachable to the crown by an interference fit, wherein each operative part of the crown comprises a substantially constant thickness throughout as initially precision cast to net finished dimensions, wherein a portion of the piston defines at least one multi-arcuate horizontal cross-section, wherein the multi-arcuate horizontal cross-section includes arcs including different radii, wherein the crown defines a ring groove and an oil groove on an exterior surface.

2. The piston of claim 1, wherein the connecting rod flanges extend dependingly from an inner surface of the crown, each of the connecting rod flanges having a lower end, each of the rod flanges being either tapered from the inner surface of the crown to a reduced section at the lower end, or parallel to the axis of a connecting rod.

3. The piston of claim 1, wherein the crown has a circumferentially interrupted lower surface, and the piston skirts comprise two equal and directly opposing arcuate skirt sections parallel to the vertical axis of the piston, each of the sections include a controlled thickness throughout to ensure mechanical and thermal consistency, and to ensure consistent contact with the cooperating cylinder wall surfaces.

4. The piston of claim 1, wherein the multi-arcuate horizontal cross-section is defined by an exterior surface of the piston crown above the ring groove.

5. The piston of claim 1, wherein the piston further comprises a ring land between one or more of the ring grooves and the multi-arcuate horizontal cross-section is defined by an exterior surface of the ring land.

6. The piston of claim 1, wherein the piston further comprises an oil control ring groove below the ring groove and a ring land between the oil control ring groove and the ring groove, wherein the multi-arcuate horizontal cross-section is defined by the ring land between the oil control ring groove and the ring groove.

7. The piston of claim 1, wherein the multi-arcuate horizontal cross-section is defined by the piston skirt.

8. A piston designed for reciprocatable movement within a combustion chamber of an internal combustion engine comprising: a piston crown with an integrally cast piston skirt comprising two equal and opposing arcuate surfaces each of which comprises an arc of less than 180 degrees with the centerline of each arcuate section perpendicular to the axis of the connecting rod connecting pin bore; two integrally cast connecting rod connecting flanges each of which are precision cast of high-strength ferrous material net to finished dimensions on all inner and outer surfaces to provide a controlled thickness throughout to ensure mechanical and thermal consistency with only secondary finishing of an outer cylindrical surface of the crown, outer edges of the rod connecting flanges, a rod connection bearing seat, and a top surface of the crown, while eliminating machining operations necessary to achieve constant and correct cross sectional dimensions of the crown and the piston skirt; and a pair of spaced-apart, substantially planar connecting rod flanges extending between the arcuate sections, wherein each operative part of the crown comprises a substantially constant thickness throughout as initially precision cast to net finished dimensions, wherein the piston skirt is configured to ensure consistent contact with the cooperating cylinder wall surfaces.

9. The piston of claim 8, wherein the multi-arcuate horizontal cross-section is defined by an exterior surface of the piston crown above the ring groove.

10. The piston of claim 8, wherein the piston further comprises a ring land between one or more of the ring grooves and the multi-arcuate horizontal cross-section is defined by an exterior surface of the ring land.

11. The piston of claim 8, wherein the piston further comprises an oil control ring groove below the ring groove and a ring land between the oil control ring groove and the ring groove, wherein the multi-arcuate horizontal cross-section is defined by the ring land between the oil control ring groove and the ring groove.

12. The piston of claim 8, wherein the multi-arcuate horizontal cross-section is defined by the piston skirt.

13. A piston designed for reciprocatable movement within a combustion chamber of an internal combustion engine comprising: a piston crown with an integrally cast piston skirt and two rod connecting flanges precision cast of high-strength ferrous material net to finished dimensions on all inner and outer surfaces to provide a controlled thickness throughout to ensure mechanical and thermal consistency with only secondary finishing of an outer cylindrical surface of the crown, outer edges of the rod connecting flanges, a rod connection bearing seat, and a top surface of the crown, while eliminating machining operations necessary to achieve constant and correct cross sectional dimensions of the crown and the piston skirt, and wherein each of the rod connecting flanges includes a center opening formed therethrough to provide a contact surface that is generally cylindrical, wherein the surface area of an upper half of the contact surface that is closer to the crown is greater than the surface area of a lower half of the contact surface that is farther from the crown, wherein each operative part of the crown comprises a substantially constant thickness throughout as initially precision cast to net finished dimensions.

14. The piston of claim 13, wherein the multi-arcuate horizontal cross-section is defined by an exterior surface of the piston crown above the ring groove.

15. The piston of claim 13, wherein the piston further comprises a ring land between one or more of the ring grooves and the multi-arcuate horizontal cross-section is defined by an exterior surface of the ring land.

16. The piston of claim 13, wherein the piston further comprises an oil control ring groove below the ring groove and a ring land between the oil control ring groove and the ring groove, wherein the multi-arcuate horizontal cross-section is defined by the ring land between the oil control ring groove and the ring groove.

17. The piston of claim 13, wherein the multi-arcuate horizontal cross-section is defined by the piston skirt.

18. The piston of claim 1, wherein at least one tribological coating is applied to a surface of the piston.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The above mentioned and other features of this disclosure will become more apparent and the disclosure itself will be better understood by reference to the following description of embodiments of the disclosure taken in conjunction with the accompanying drawings, wherein:

[0038] FIG. 1 is a view of a piston incorporating the present disclosure taken substantially along lines 1-1 in FIG. 2;

[0039] FIG. 2 is a side view of the piston of FIG. 1 taken generally along lines 2-2 of FIG. 1;

[0040] FIG. 3 is a top view of piston crown of FIG. 1;

[0041] FIG. 4 is a side view of the piston of FIG. 1;

[0042] FIG. 5 is a perspective view of the piston of FIG. 1;

[0043] FIG. 6 is a cross-section view taken along lines 6-6 in FIG. 1;

[0044] FIG. 7 is a cross-section view taken along lines 7-7 in FIG. 1;

[0045] FIG. 8 is a cross-section view taken along lines 8-8 in FIG. 1;

[0046] FIG. 9 is a cross-section view taken along lines 9-9 in FIG. 1;

[0047] FIG. 10 is a cross-section view taken along lines 10-10 in FIG. 4; and

[0048] FIG. 11 is a cross-section view taken along lines 11-11 in FIG. 2.

[0049] Corresponding reference characters indicate corresponding parts throughout the views of the drawings.

DETAILED DESCRIPTION

[0050] The disclosure will now be described in the following detailed description with reference to the drawings, wherein embodiments are described in detail to enable practice of the disclosure. Although the disclosure is described with reference to these specific embodiments, it will be understood that the disclosure is not limited to these embodiments. But to the contrary, the disclosure includes numerous alternatives, modifications and equivalents as will become apparent from consideration of the following detailed description.

[0051] For example, the terms “higher,” “up,” “lower,” “down,” and “below” refer to directions relative to the central axis of a piston. The terms higher and up are intended to indicate a position on the piston closer to a crown of the piston. The terms lower, down, and below are intended to indicate a position closer to the opposite end of the piston from the crown. Additionally, the term “vertical cross section” indicates a cross section of the piston along a plane that is parallel or co-planar with the central axis of the piston. “Horizontal cross section” indicates a cross section of the piston along a plane that is transverse to the central axis of the piston. Still further, in the drawings, the same reference numerals are employed for designating the same elements.

[0052] Referring now to FIG. 1, the disclosure relates to a piston 20 for use in an internal combustion engine together with an investment cast method of manufacturing the piston. An example would be to utilize the piston 20 in an original manufacture of an after-market repair or remanufacture of a Detroit Diesel, Cummins, or Caterpillar diesel. The piston 20 itself in the shown embodiment is a one piece piston having a crown 25 and a piston skirt 51. The crown 25 is the main combustion chamber interactive part of the piston 20. This crown 25 is investment or other permanent or non-permanent mold/die precision cast. This provides for the creation of both internal and external surfaces of a complex part with dimensional stability in a single initial manufacturing step. The crown 25 is thus of substantially lighter weight than a typical forged or sand cast ferrous piston and amenable to a more complex design. This reduces the complexity and cost of the final secondary finish manufacturing. Further, the surface finish of the piston crown is relatively smooth and free of surface defects. The crown 25 can thus be investment or other permanent or non-permanent mold/die precision cast with minimal finish manufacturing tolerances (i.e., the crown is cast to zero net size finished or only minimally oversized - only that necessary to allow secondary finishing within a commercially acceptable range). This enables one to materially and substantially reduce the complexity of manufacturing of the piston 20 for internal combustion engines by casting them to dimensionally net shape and size and by therefore eliminating machining operations necessary to achieve constant and correct cross sectional dimensions of the crown and attendant skirt.

[0053] It is desirable to increase the service life of the piston 20 by manufacturing it from wear resistant ferrous materials that further remain dimensionally stable under conditions of high heat and pressure. In addition to the known and proven ferrous materials, and while the crown 25 shown is of steel alloy, it is possible to make the piston out of other metals that are subject to or adaptable to net dimensional casting methods which presently include investment casting, lost wax casting, lost foam casting, metallic and non-metallic permanent mold casting, and precision non-permanent mold casting.

[0054] This piston combining the use of net dimensional casting processes increases the adaptability of the piston to numerous applications with minimal additional tooling and/or material considerations. It is also noted that the weight reduction of the precision net dimensional cast piston is particularly important wherein the reduction of reciprocating mass increases both the efficiency and the service life longevity between repair and rebuilding operations thereof.

[0055] A rod connection flange 35 is investment or other permanent or non-permanent mold/died precision cast integrally with the crown 25 and a later described piston skirt 51 in the same casting operation. The rod connection flange 35 of the piston 20 locates the piston skirt 51 relative to the crown 25. The rod connection flange 35 thus cooperates with the later described piston skirt 51 to provide angular stability to the crown 25 with respect to the cylinder 100. This angular stability with a limited area about the circumference of the piston 20 aids in evening out any differential wear about the circumference of the piston 20. This evening out is especially true for forces perpendicular to the longitudinal axis 76 of a wrist pin 71.

[0056] This piston combining the use of net dimensional casting processes increases the adaptability of the piston 20 to numerous applications with minimal additional tooling and/or material considerations. It is also noted that the weight reduction of the precision net dimensional cast piston 20 is particularly important wherein the reduction of reciprocating mass increases both. The efficiency and the service life longevity between repair and rebuilding operations.

[0057] In addition, the balance or weight differential as manufactured between multiple pistons is reliable and predictable for economy in maintenance of inventory, replacement purposes, and the process of dynamically and statically balancing the reciprocating and rotating masses of an engine.

[0058] This secondary operation in the embodiment disclosed includes finishing the outer surface 30 of the crown 25 (in consideration of the diameter of the cylinder in the engine), the outer edge 31 of the rod connection flange 35 (in consideration of the inner dimension of the piston skirt 51), the bearing seat 32 (to match the outer diameter of the sleeve bearing 70), and the dimension of the top surface of the crown 25 (to match the bearing seat 32 to the head of the engine to provide the desired combustion ratio at top dead center piston location). This further reduces the cost of the piston 20 significantly over alternative processes such as forging or conventional casting and subsequent machining.

[0059] Due to the use of a precision net to dimension casting, the crown 25 can be produced of a ferrous material with a thinner cross section, a more intricate shape, and with a higher initial tolerance than otherwise possible. Further, features as set forth are otherwise difficult or costly to machine can be included but are not limited to a cast in place dam of planar section at or near the inner diameter of the crown 25 for cooling oil retention, a separate metal plate so forming an oil retention dam fixed in similar place by (i) a circular spring ring, (ii) friction welding, (iii) interference fit, (iv) resistance or fill welding, (v) rotational locking, and (vi) adhesives and/or similar means.

[0060] The outer surface 30 of the crown 25 has ring grooves 40 is designed to cooperate with the piston rings (as shown in representational form in FIG. 12) and the inner wall of the cylinder liner 100 to define the lower extent of the combustion chamber. An oil groove 41 located below the rings on the upper surface 20 of the crown 25 reduces friction by providing for a lubricant flow at the critical location in the engine.

[0061] Due to the use of a net to dimension cast piston, the process finishing the outer surface 30 is significantly reduced from alternative manufacturing processes (such as the previously described forging). Typically, only a minor secondary operation is necessary in order to provide the finish dimensions for the outer surface 30 of the crown 25 due to the accuracy of the casting process, and then primarily to provide dimensional stability for the outer surface 30, the outer edge 31 of the bearing seat 32 and the top surface 20 of the crown 25. This equalizes any given piston to another so as to provide a more efficient and balanced engine and one where the uppermost ring groove is immediately adjacent to the top of the crown 25.

[0062] Further, the use of a net dimensional ferrous casting, the thickness of the crown 25 between the outer surface 30 and the lower confines of the swirl chamber 43 on top of the crown 25 and the inner surfaces 36 on the underside 45 of the crown 25 is of a predictable and substantially constant thickness throughout as initially cast (see dashed lines 44 in FIG. 1). This constant and predictable thickness allows for the efficient transfer of heat and reduction of heat distribution differences within the crown 25. This is in addition to the reduction of weight and reliability of balance due to the accuracy of initial casting of the piston 20.

[0063] Further, the auxiliary cooling oil, which is typically sprayed upward from a fixed location beneath the low travel extent of the piston 20, can penetrate further and more evenly within the crown 25 to provide for a more efficient and even heat removal from the piston rings 40 and the swirl chamber 43 at the top of the piston 20 by such cooling oil.

[0064] The outer edge 31 of the rod connection flange 35 of the crown 25 locates the piston skirt 51 relative to the crown 25. The outer edge 31 itself cooperates with the later described piston skirt 51 to provide angular stability to the crown 25 in respects to the cylinder 100. This in turn evens out the wear about the circumference of the crown 25, thus to reduce any differential wear about the circumference of the piston 20.

[0065] This even distribution of wear by this edge 31 is especially true for forces perpendicular to the longitudinal axis of the wrist pin 71.

[0066] The seat 32 of the crown 25 is designed to retain the piston rod pin in a location relative to the piston (via sleeve bearing 70 in the embodiment shown). This serves as the main mechanical interconnection between the piston rod 80 and the piston 20. The seat 32 also cooperates with the wrist pin 71, the piston skirt 51 through the wrist pin 71 to provide angular stability of the crown 25 with respect to the cylinder 100. This evens out any differential wear about the circumference of the piston 20. This evening out is especially true for cocking forces about the longitudinal axis of the wrist pin 71 in both those applications where pin thrust offset is used as in other form engines and otherwise.

[0067] As this seat is a circular hole extending straight through the rod connection flanges 35 of the crown 25, it is amenable to a simple finishing operation due to the accuracy of the initial casting process.

[0068] A sleeve bearing 70 is inserted through the rod connection flange 35 in the crown 25 to the wrist pin 71 and thus the connecting rod 80. The use of an independent sleeve bearing 70 allows for the optimization of materials. This also allows the sleeve bearing 70 to be of a non-ferrous metal alloy or other material suitable to a moving, high force rotary interconnection while also allowing the crown 25 to be of a different material (a ferrous or ferrous alloy disclosed).

[0069] The use of a separate sleeve bearing 70 also allows for the repair of this high stress area by the replacement of a relatively simple part instead of the entire piston, thus increasing the service life of the remainder of the piston 20.

[0070] The constant surface between the piston rod 80 and the piston 20 is designed such that this surface area between these two is greater in the direction of significant power transfer than the direction of return movement. For this reason, the sleeve bearing 70 has a contact surface area 72 on the crown 25 side of the piston 20 significantly greater than the return surface area 75. As a result of this relationship, the crown 25 has sufficient contact area to develop the power inherent in the engine incorporating same. If desired, for example to increase the tear off resistance, the contact surface area 75 can be enlarged.

[0071] In this example, the sleeve bearing 70 allows the flow of pressurized oil between a passage 81 in the piston rod 80 to the oil groove 41 thus to lubricate this critical location, a plate or dam 42 closing the bottom of the galley 45 of the crown 25 provides a reservoir for this cooling oil in the various forms noted above and herein.

[0072] The cooling oil dam or retention plate 42 is held in place proximally at the lower edge of the crown 25 by the application of a snap ring or circle ring set in a groove or by the application of the mechanical bending or folding of a segmented or non-segmented extension of the crown 25 material generally parallel to the axis of the piston rod in either the cold or warm state. In one embodiment, the cooling oil dam or retention plate 42 is held in place proximally at the lower edge of the crown 25 by the application of an interference fit between the inner and outer dimensions of said plate dam and the piston body. In another embodiment, the cooling oil dam or retention plate 42 is held in place proximally at the lower edge of the crown 25 by fixing the same in the precision casting process by casting in place. In another embodiment, the cooling oil dam or retention plate 42 is held in place proximally at the lower edge of the crown 25 by the incorporation of extending tabs on the plate that are inserted in generally segmented apertures in the lower surface of the crown 25 and rotated into a locking mode.

[0073] The piston skirt 51 completes the piston 20. Due to the dimensional stability and complexity of its associated crown 25, this skirt 51 can be of relatively simple construction. The particular piston skirt disclosed has a vertical outside surface, a center opening 52, and a lock ring access 55. The outside surface of the piston skirt 51 cooperates with the inner wall of the cylinder 100 of the engine to support the crown 25 against any tipping or angular displacement in respect to the longitudinal axis of the cylinder 100. As previously discussed, this support is provided through the outer edge 31 and the seat 32 of the crown 25.

[0074] To efficiently provide the support for the crown 25, the center opening 52 of the piston skirt 51 has two opposed flat support surfaces 53 and pin seat 54. These together cooperate with the connecting rod flange 35 as previously set forth to support the crown 25 against angular movement in a side wards direction (angular cocking re: the longitudinal axis 76 of the wrist pin 71).

[0075] Insofar as there are no known forces acting axially or laterally on the piston perpendicular to the axis of the piston pin below the part of the crown 25 that supports the sealing rings, all those parts of the piston usually comprising the skirt thereof regardless of material or one or two piece construction have been eliminated except for the two arcuate sections of the skirt 51.

[0076] The lock ring access 55 allows for physical access to the lock rings 77 which retain the wrist pin 71 in its designed position in respect to the piston 20. This lock ring access 55 generally is a straight cut across the inner surface 36 of the piston skirt 51. This allows for efficient access to the lock ring 77. In addition, a lock ring access 55 can allow for a use of original wrist pins 71 should that be desired (if necessary by varying the location of the lock ring groove). The straight flat surfaces 53 are amenable to being formed in a single manufacturing step.

[0077] The piston further includes a cylindrical body depending from the crown. The cylindrical body defines at least one groove formed about the outer circumferential surface of the cylindrical body. In the illustrated embodiment, the piston includes two (2) compression ring grooves and one oil control ring groove formed into the outer circumferential surface. The compression ring grooves are configured for use with piston sealing rings (not shown), and the oil control ring groove is configured for use with an oil control ring (best seen in FIG. 11). However, it should be understood by one of ordinary skill in the art that other numbers of compression ring grooves and oil control ring grooves in various arrangements can be formed into the outer circumferential surface of the piston. Each of the ridges between the grooves can be termed a “ring land” or a “piston land.”

[0078] Additionally, the oil control ring groove cooperates with the oil control ring to control the oil that is introduced onto the cylinder walls by lubricating oil circulating in the engine and cooling oil injected into the piston crown and subsequently exiting into the engine crankcase. The oil control ring scrapes the cylinder walls to return the scraped oil back toward the crankcase. One goal of the oil control ring is to reduce and/or prevent oil passage between the face of the oil control ring and the cylinder through the ring gap or pass behind the oil control ring. While not shown, the oil control ring can include any number of structures, including multiple-piece rings used with an expander/spacer.

[0079] In one example, the piston includes a truncated outer surface that forms a pair of opposing surfaces. The surfaces are formed as substantially flat portions of the outer circumferential surface of the piston, and the surfaces are substantially aligned in a parallel manner and can be equidistant from the central axis. Each surface defines a bore formed through the surface. The bore includes an axis that is perpendicular to the central axis of the piston. The bore is configured to cooperate with a connecting rod pin (not shown) for allowing the piston to be operatively connected to a connecting rod (not shown) that translates the piston within the combustion cylinder of an engine. The portions of the piston cylindrically extending between each of the opposing surfaces form the outer boundary of an integral cooling reservoir (best seen in FIG.).

[0080] As shown in FIG. 11, a portion of the cylindrical body defines one or more multi-arcuate, horizontal cross-section below the oil control ring groove. As described above, one purpose of an oil control ring is to “wipe” or remove a quantity of excess oil from an associated internal cylinder wall as the piston moves through a downward stroke. The oil is then returned to the other portions of the engine, which may include a crankcase and/ or oil sump. The multi-arcuate, horizontal cross-section creates a passage between the cylindrical body and the associated cylinder wall of an engine, thereby enabling a quantity of oil to more easily pass from an annular region between the cylindrical body and the associated cylinder wall to an area adjacent one of the pair of opposing surfaces. This enables the oil control ring to more efficiently accomplish its task and move and/or remove a greater quantity of oil from the cylinder wall and the annular region. The same is true for the multi-arcuate horizontal cross section at each of the other locations on the piston, namely, the crown outside diameter, the ring lands, the skirt, etc.

[0081] In one example, as shown in FIG., the multi-arcuate horizontal cross-section includes a radius of the cylindrical portions that is less than the radius corresponding to the passage portion of the multi-arcuate horizontal cross-section. In this way, the multi-arcuate horizontal cross-section is defined by four arcs of constant radius, where one pair of arcs have equal radii that are different from the equal radii of the other pair of arcs. By definition, the two pairs of circular arcs have different center points. As shown, the radius defines the multi-arcuate cross-section at the top and bottom of FIG., while radius defines the multi-arcuate cross-section to the right and left. Radius is greater than radius, and the resulting arcs have different center points.

[0082] In another example, the multi-arcuate, horizontal cross-section is generally ovoid in shape. In other words, the perimeter of the multi-arcuate, horizontal cross-section can be a figure constructed from two pairs of arcs, with two different radii. The arcs are joined at a point, in which lines tangential to both joining arcs lie on the same line, thus making the joint smooth. Any point on the ovoid perimeter belongs to an arc with a constant radius (shorter or longer). In another example, multi-arcuate, horizontal cross-section can be defined by a series of intersecting arcs. In yet another example, the multi-arcuate horizontal cross section can include elliptical portions, hyperbolic portions, parabolic portions, or even some straight lines. It is to be understood that other cross-section shapes and/or other similar shapes are also contemplated, so long as the horizontal cross-sectional shape creates the described passage between the cylindrical body and the associated cylinder wall of the engine as shown in FIG. 11.

[0083] Also, by precision casting to net final dimensions, additional machining to form the any of the surfaces of the integral cooling oil reservoir is eliminated. In an embodiment, precision casting to net final dimensions of the upper and lower members means that the precision as-cast dimensional tolerance is between about +/− 0.010 inches to about +/−0.020 inches. In another embodiment, precision casting to net final dimensions of the upper and lower members means that certain surfaces include a surface finish roughness of less than about 125 Ra.

[0084] In one example, the at least one tribological coating is applied to at least one the exterior and /or interior of the surfaces of the piston. The coating can be any suitable tribological coating or coatings including, but not limited to, manganese phosphates, manganese iron phosphates, zinc phosphates, tin compounds, ceramics, etc. In one example, the at least one tribological coating has a thickness of less than about 6 μm. In another example, the at least one tribological coating has a thickness of greater than about 18 μm. In one example, the at least one tribological coating can have a grain size of less than about 10 μm. In another example, the at least one tribological coating has a grain size of greater than about 50 μm.

[0085] Alternatively, or additionally, a tribological coating 126 can be applied to an exterior surface of the pin. The at least one tribological coating can have the same thickness and grain size parameters as the at least one tribological coating applied to the cylindrical surface.

[0086] Applying the at least one tribological coating to the pin and/or the cylindrical surface of the bore can have several benefits. First, a tribological coating such as manganese phosphate can improve the wear resistance of the wear surfaces of the piston components. This often enables piston and engine parts to have a longer expected service life, and help reduce decreasing performance characteristics over time, thereby maintaining required operational and long-term durable performance. The at least one tribological coating can also retain oil and lubricants, thereby improving a scuffing resistance of the piston. Furthermore, tribological coatings can offer improved corrosion resistance, again helping to improve piston and engine service life.

[0087] Turning to FIG. 6, a cross-section view of the piston is shown. The multi-arcuate horizontal cross-section is shown at the crown of the piston, below the top surface and above a ring groove. Turning to FIG. 7, another cross-section view of the piston is shown, this view taken between two of the ring grooves on the ring land of the piston. Turning to FIG. 8, a cross-section view of the piston shows the multi-arcuate horizontal cross-section between a lower ring groove and the oil control ring groove. Turning to FIG. 9, a cross-section view of the piston shows the multi-arcuate horizontal cross-section below the oil control ring groove. FIG. 10 shows the multi-arcuate horizontal cross-section at the skirt.

[0088] While this disclosure has been written in conjunction with the specific embodiments described above, it is evident that many alternatives, combinations, modifications and variations are apparent to those skilled in the art. Accordingly, the described embodiments of this disclosure, as set forth above are intended to be illustrative only, and not in a limiting sense. Various changes can be made without departing from the spirit and scope of this disclosure. Combinations of the above embodiments and other embodiments will be apparent to those of skill in the art upon studying the above description and are intended to be embraced therein. Therefore, the scope of the present disclosure is defined by the appended claims, and all devices, processes, and methods that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein. Furthermore, to the extent that the term “includes” is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term “comprising” as “comprising” is interpreted when employed as a transitional word in a claim.

[0089] What is claimed is: