PISTON WITH MULTI-ARCUATE CROSS-SECTION AND LUBRICANT EXHAUST APERTURE

Abstract

A piston and methods for constructing a piston for use in an internal combustion engine are presented wherein the piston includes a cylindrical body extending from the crown. The cylindrical body defines a ring groove, and a portion of the cylindrical body defines a non-circular cross-section below the ring groove. The ring groove is configured to correspond with an associated sealing ring. The non-circular cross-section creates a gap between the cylindrical body and an associated cylinder wall enabling a quantity of oil to pass from an annular region between the cylindrical body and the associated cylinder wall.

Claims

1-16. (canceled)

17. A piston for use in an internal combustion engine, said piston comprising: an upper member, wherein said upper member includes: a crown located at a top surface of said upper member; a combustion surface extending radially inward from said crown; a first upper connecting surface integrally formed on a bottom side of said upper member, said first upper connecting surface is downwardly directed; a second upper connecting surface integrally formed on said bottom side of said upper member, said second upper connecting surface is downwardly directed, a lower member, wherein said lower member includes: a pair of opposing skirts, each skirt defines a bore formed therethrough, said bore having a bore centerline; a first lower connecting surface integrally formed on a top side of said lower member, said first lower connecting surface is upwardly directed; and a second lower connecting surface integrally formed on a top side of said lower member, said second lower connecting surface is upwardly directed, wherein said first and second lower connecting surfaces are concentrically oriented; wherein said lower member is integrally connected to said upper member by friction welding such that said first upper connecting surface and said first lower connecting surface form a first welded joint therebetween and said second upper connecting surface and said second lower connecting surface form a second welded joint therebetween.

18. The piston of claim 17, wherein one or both of said upper and lower members comprise a forging.

19. The piston of claim 17, wherein one or both of said upper and lower members comprise a precision casting to net final dimensions.

20. The piston of claim 17, further comprising at least one multi arcuate circumferential groove formed into an outer surface of said upper member and at least one multi arcuate circumferential groove formed into an outer surface of said lower member.

21. The piston of claim 17, wherein said first upper connecting surface, said second upper connecting surface, said first lower connecting surface, and said second lower connecting surface are precision cast to net final dimensions.

22. The piston of claim 17, further comprising at least one integral cooling oil reservoir formed adjacent to said combustion surface when said upper and lower members are friction welded together.

23. A piston for use in an internal combustion engine, said piston comprising: a forged or cast upper member, said upper member including: a combustion surface located at a lower elevation than a top surface of said upper member; a pair of bores formed through said lower member for receiving a connecting rod pin; and at least two concentrically positioned upper and lower connecting surfaces, wherein said lower member is attached to said upper member by way of friction welding such that each of said at least two upper connecting surfaces of said upper member forms a welded joint with one of said at least two lower connecting surfaces, wherein at least one multi arcuate circumferential groove formed into an outer surface of said upper member and at least one multi-arcuate circumferential groove formed into an outer surface of said lower member, wherein at least one outer surface of said upper member and said lower member defines a multi-arcuate horizontal cross section, wherein at least one such multi-arcuate horizontal cross-section is located below said oil control ring groove, wherein at least one such multi arcuate horizontal cross-section is located at said ring land, wherein a plurality of said multi-arcuate horizontal cross-sections located on the outer surface of the piston, wherein at least one of said plurality of said multi-arcuate horizontal cross-sections is oriented at a radial offset from another of said plurality of said multi-arcuate horizontal cross-sections, wherein at least one of said multi-arcuate horizontal cross-section is generally non-circular in shape, wherein at least one of said multi-arcuate horizontal cross-section is defined by a series of intersecting arcs, wherein at least one of said multi-arcuate horizontal cross-section comprises a portions selected from the group consisting of elliptical portions, hyperbolic portions, and parabolic portions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] These and other features of the present disclosure, and their advantages, are illustrated specifically in embodiments of the disclosure now to be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:

[0020] FIG. 1 is a top perspective of an embodiment of a friction-welded piston of the present disclosure;

[0021] FIG. 2 is a bottom perspective of the piston shown in FIG. 1;

[0022] FIG. 3 is an oblique perspective view of an embodiment of upper and lower pieces of a two-piece friction-welded piston prior to joining by friction welding;

[0023] FIG. 4 is a bottom view of an embodiment of the upper piece of a two-piece friction-welded piston;

[0024] FIG. 5 is an oblique perspective view of the lower piece of the piston shown in FIG. 1;

[0025] FIG. 6 is a side view of the piston shown in FIG. 1 oriented at 90 relative to the view shown in FIG. 5;

[0026] FIG. 7 is a side view of the piston shown in FIG. 1, oriented at 90 relative to the view shown in FIG. 6;

[0027] FIG. 8 is an oblique vertical cross-sectional view of the completed piston as shown in FIG. 1, taken along the line 8-8 in FIG. 1;

[0028] FIG. 9 is a vertical cross-sectional view of the bottom piece of a two-piece friction-welded piston;

[0029] FIG. 10 is a vertical cross-sectional view of the piston shown in FIG. 1, taken along the line 10-10 in FIG. 1;

[0030] FIG. 11 is a horizontal cross-sectional view of the piston shown in FIG. 6, taken along the line 11-11 in FIG. 6;

[0031] FIG. 12 is an oblique vertical cross section of an embodiment of a completed two-piece friction-welded piston according to at least one embodiment of the present disclosure;

[0032] FIG. 13 is an oblique view of the piston shown in FIG. 12; and

[0033] FIG. 14 is a horizontal cross section of an embodiment of the piston demonstrating one of a multiple known embodiments of a multi arcuate vertical cross section which may be incorporated in the piston.

[0034] It should be noted that all the drawings are diagrammatic and not drawn to scale. Relative dimensions and proportions of parts of these figures may have been shown exaggerated or reduced in size for the sake of clarity and convenience in the drawings. The same reference numbers are generally used to refer to corresponding or similar features in the different embodiments. Accordingly, the drawing(s) and description are to be regarded as illustrative in nature and not as restrictive.

DETAILED DESCRIPTION

[0035] Example embodiments that incorporate one or more aspects of the present disclosure are described and illustrated in the drawings. These illustrated examples are not intended to be a limitation on the present disclosure. For example, one or more aspects of the present disclosure can be utilized in other embodiments and even other types of devices. Moreover, certain terminology is used herein for convenience only and is not to be taken as a limitation on the present disclosure.

[0036] 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.

[0037] Turning to FIG. 1, an embodiment of a piston 20 is shown, wherein a portion of the piston 20 includes a multi-arcuate cross-section 24 which will be described in greater detail below. The piston 20 is a generally cylindrical member wherein an upper portion 26 of the piston 20 forms the lower boundary of a combustion chamber formed within each combustion cylinder of an internal combustion engine (not shown). The upper portion 26 includes a substantially flat crown 28 having a central recess 30, or combustion surface, extending radially inward from the crown 28. In one example, the upper portion 26 includes at least one recess 34 formed into the crown 28 to prevent contact between the crown 28 and the combustion air intake and exhaust valves (not shown) during operation. In the illustrated embodiment shown in FIG. 1, the crown 28 includes four (4) recesses 34 formed therein, but it should be understood by one of ordinary skill in the art that any number of recesses 34 can be formed into the crown 28 to prevent contact between the crown 28 and any selected number of exhaust or air intake valves.

[0038] The piston 20 further includes a cylindrical body 36 depending from the crown 28. The cylindrical body 36 defines at least one groove formed about the outer circumferential surface of the cylindrical body 36. In the illustrated embodiment, the piston 20 includes two (2) compression ring grooves 38 and one oil control ring groove 39 formed into the outer circumferential surface (best seen in FIGS. 7-9). The compression ring grooves 38 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 41 (best seen in FIG. 10). However, it should be understood by one of ordinary skill in the art that other numbers of compression ring grooves 38 and oil control ring grooves 39 in various arrangements can be formed into the outer circumferential surface of the piston 20. Each of the ridges 42 between the grooves 38, 39 can be termed a ring land or a piston land.

[0039] In the shown example, the top two compression ring grooves 38 cooperate with the piston sealing rings to form a seal between the combustion chamber and the crankcase of the engine. The goal is to prevent combustion gases from passing into the crankcase and prevent oil from passing into the combustion chamber. During the compression and power strokes, at least one of the piston sealing rings seals the combustion gases and reduces and/or prevents blow-by.

[0040] Additionally, the oil control ring groove 39 cooperates with the oil control ring 41 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 41 scrapes the cylinder walls to return the scraped oil back toward the crankcase. One goal of the oil control ring 41 is to reduce and/or prevent oil passage between the face of the oil control ring 41 and the cylinder through the ring gap or pass behind the oil control ring 41. While not shown, the oil control ring 41 can include any number of structures, including multiple-piece rings used with an expander/spacer.

[0041] In one example, the piston 20 includes a truncated outer surface that forms a pair of opposing surfaces 44. The surfaces 44 are formed as substantially flat portions of the outer circumferential surface of the piston 20, and the surfaces 44 are substantially aligned in a parallel manner and can be equidistant from the central axis. Each surface 44 defines a bore 46 formed through the surface 44. The bore 46 includes an axis that is perpendicular to the central axis of the piston 20. The bore 46 is configured to cooperate with a connecting rod pin (not shown) for allowing the piston 20 to be operatively connected to a connecting rod (not shown) that translates the piston 20 within the combustion cylinder of an engine. The portions 48 of the piston 20 cylindrically extending between each of the opposing surfaces 44 form the outer boundary of an integral cooling reservoir 50 (best seen in FIG. 8).

[0042] As shown in FIGS. 10 and 11, a portion of the cylindrical body 36 defines one or more multi-arcuate, horizontal cross-section 24 below the oil control ring groove 39. As described above, one purpose of an oil control ring 41 is to wipe or remove a quantity of excess oil from an associated internal cylinder wall 56 as the piston 20 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 24 creates a passage 54 between the cylindrical body 36 and the associated cylinder wall 56 of an engine, thereby enabling a quantity of oil to more easily pass from an annular region 58 between the cylindrical body 36 and the associated cylinder wall 56 to an area adjacent one of the pair of opposing surfaces 44. This enables the oil control ring 41 to more efficiently accomplish its task and move and/or remove a greater quantity of oil from the cylinder wall 56 and the annular region 58.

[0043] In one example, as shown in FIG. 11, the multi-arcuate horizontal cross-section 24 includes a radius 59 of the cylindrical portions 48 that is less than the radius 60 corresponding to the passage 54 portion of the multi-arcuate horizontal cross-section 24. In this way, the multi-arcuate horizontal cross-section 24 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 61, 62, 63. As shown, the radius 60 defines the multi-arcuate cross-section at the top and bottom of FIG. 11, while radius 59 defines the multi-arcuate cross-section to the right and left. Radius 60 is greater than radius 59, and the resulting arcs have different center points 61, 62, 63.

[0044] 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 24 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 24 can be defined by a series of intersecting arcs. In yet another example, the multi-arcuate horizontal cross section 24 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 54 between the cylindrical body 36 and the associated cylinder wall 56 of the engine as shown in FIG. 10.

[0045] As shown in FIGS. 3-5, the piston 20 can include two distinct sections, such as an upper member 64 and a lower member 66 which are formed separately and joined together to form a single piston 20. The upper member 64 of the piston 20 is a generally cylindrical member that forms the upper portion of the piston 20 including the previously described crown 28 and the central recess 30. In the illustrated embodiment, the upper member 64 includes two (2) compression ring grooves 38 (also known as oil ring grooves) and a portion of one oil control ring groove 39 formed into the outer circumferential surface thereof. However, it should be understood by one of ordinary skill in the art that any number of compression ring grooves 38 and/or oil control ring grooves can be formed into the outer circumferential surface of the upper member 64 at any appropriate location on the central axis of the piston 20 above the bore 46.

[0046] As shown in FIGS. 3-4, the upper member 64 includes a first upper connecting surface 70 and a second upper connecting surface 74 formed on the downwardly-directed portion thereof. The first and second upper connecting surfaces 70, 74 are substantially concentrically disposed, wherein the first upper connecting surface 70 is positioned radially inward relative to the second upper connecting surface 74 of the piston 20. Although the illustrated embodiment of the piston 20 will be explained below as having two connecting surfaces on the upper member that mate with and correspond to two connecting surfaces on the lower member by which the upper and lower members 64, 66 are joined together via friction welding, it should be understood by one of ordinary skill in the art that the upper and lower members 64, 66 can be configured to include any number of corresponding connecting surfaces for connecting the upper member 64 to the lower member 66. In an embodiment, the first and second upper connecting surfaces 70, 74 are oriented substantially parallel and are coplanar. In another embodiment, at least one of the first or second upper connecting surfaces 70, 74 are parallel with respect to the crown 28 of the upper member 64 but are non-coplanar; and either of which may be located in a single or multiple planes with respect to one another such that each of which correspond with the concentrically disposed surfaces located in the opposite member.

[0047] As shown in FIGS. 1-3 and 5, the lower member 66 extends downwardly from the upper member 64 and includes a generally cylindrical shape along with the previously described pair of opposing surfaces 44. Each surface 44 includes a bore 46 formed therethrough, and the surface bores 46 are configured to receive a connecting rod pin (not shown) for operatively connecting the connecting rod to the piston 20. The portions of the lower member 66 cylindrically extending between each of the opposing surfaces 44 form the outer boundary of the integral cooling reservoir 50.

[0048] The lower member 66 can include one or more compression ring grooves 38 formed into the circumferential outer surface thereof, as shown in FIGS. 1-3 and 5. In the illustrated exemplary embodiment, the lower member 66 includes a portion of one oil control ring groove 39 formed therein. In an embodiment, the lower member 66 includes a first lower connecting surface 76 and a second lower connecting surface 78 formed on the upwardly-directed portion thereof, as shown in FIGS. 3 and 5. The first and second lower connecting surfaces 76, 78 are substantially concentrically disposed, wherein the first lower connecting surface 76 is positioned radially inward relative to the second lower connecting surface 78 of the lower member 66. In an embodiment, the first and second lower connecting surfaces 76, 78 are oriented substantially parallel relative to each other as well as vertically aligned (co-planar) relative to the axial centerline of the piston 20. In another example, at least one of the first lower connecting surface 76 is higher than the second lower connecting surface 78. In yet another example, the first lower connecting surface 76 is lower than the second lower connecting surface 78.

[0049] In a first exemplary embodiment, as shown in FIGS. 6-9, the upper and lower members 64, 66 of the piston 20 are configured such that the first and second upper connecting surfaces 70, 74 are coplanar and the first and second lower connecting surfaces 76, 78 are similarly coplanar. As such, when the upper member 64 is connected to the lower member 66, the resulting joints between the upper and lower member 64, 66 are likewise substantially coplanar. In another exemplary embodiment, as shown in FIG. 10, the first upper connecting surface 70 is positioned a greater vertical distance away from the crown 28 than the second upper connecting surface 74 such that the first and second upper connecting surfaces 70, 74 are non-coplanar. In a like manner, the first lower connecting surface 76 is non-coplanar relative to the second lower connecting surface 78. This non-coplanar position can be referred to as a vertical offset. This vertical offset between the lower connecting surfaces 76, 78 is the same vertical offset between the first and second upper connecting surfaces 70, 74.

[0050] Although the embodiment illustrated in FIG. 10 shows that the first upper connecting surface 70 is spaced apart vertically from the crown 28 a greater distance than the second upper connecting surface 74, it should be understood by one of ordinary skill in the art that the first upper connecting surface 70 can also be vertically spaced apart from the crown 28 a smaller distance than the second upper connecting surface 74. The same relative spacing and vertical offsets apply equally to the first and second lower connecting surfaces 76, 78 in a corresponding manner to ensure coincident contact between the upper and lower connecting surfaces during a friction-welding process. It is also to be appreciated that the lower connecting surfaces 76, 78 can be vertically located anywhere along the central axis of the piston 20, and can be located on a ring land, in a compression ring groove 38, or in the oil control ring groove 39. It is also to be noted that the first upper connecting surface 70, and thus the first lower connecting surface 76, are located vertically below a horizontal line tangent to the bottom of the interior wall of the central recess 30, or combustion bowl.

[0051] The upper and lower members 64, 66 are formed separately and later joined together to form the complete piston 20. In an embodiment, the upper and lower members 64, 66 are formed using steel, other ferrous material or other high temperature/high strength metals such as titanium, Monel, Inconel, or similar. The material used for the upper and lower members should be of adequate strength and have sufficient heat resistance to impart the needed strength for use in a diesel or other internal combustion engine. The upper and lower members 64, 66 are both precision cast to net final dimensions. Precision cast to net final dimensions specifically means in the embodiments described herein, that both of the final as-cast pieces does not require additional machining to any of the upper connecting surfaces 70, 74 or lower connecting surfaces 76, 78 prior to joining the upper and lower members 64, 66 in a friction or inertial welding process.

[0052] 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 64, 66 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 64, 66 means that the first and second upper connecting surfaces 70, 74 and the first and second lower connecting surfaces 76, 78 have a surface finish roughness of less than about 125 Ra. Although limited post-casting machining may be performed on other surfaces of the upper and lower members 64, 66 for other reasons, the precision cast to net final dimensions of the first and second upper connecting surfaces 70, 74 and the first and second lower connecting surfaces 76, 78 require no post-casting machining whatsoever in order to friction weld the upper and lower members 64, 66 together.

[0053] Assembly of the piston 20 includes joining the precision cast to net final dimension upper member 64 to the precision cast to net final dimension lower member 66 by way of friction welding or inertial welding in which the first and second upper connecting surfaces 70, 74 and the first and second lower connecting surfaces 76, 78 are as cast and not in any manner machined prior to the friction welding process. In one example, both the upper and lower members 64, 66 are either rotated such that they continuously rotate in opposing directions about the axial centerline of the piston 20, or one is fixed and the other continuously rotated with respect thereto until the welding process is completed. As one or more of the upper and lower members 64, 66 are continuously rotated, the members are pressed along the longitudinal axis of the piston assembly together such that the first upper connecting surface 70 of the upper member 64 and the first lower connecting surface 76 of the lower member 66 as well as the second upper connecting surface 74 of the upper member 64 and the second lower connecting surface 78 of the lower member 66 contact each other, and additional axial pressure applied to the respective upper and lower members 64, 66 together causes a localized friction weld that integrally and permanently joins the upper member 64 to the lower member 66 without other and/or further manufacturing steps needed to accomplish said joinder

[0054] For the purposes of this disclosure, the sole source as well as the entirety of the heat necessarily required for the friction welding process is created solely and exclusively by the friction between the two pieces generated by the above axial pressing during the continuous relative rotation between the upper member 64 and the lower member 66.

[0055] Upon completion of the friction-welding process, the first upper connecting surface 70 and the first lower connecting surface 76 form a first welded joint 80, and the second upper connecting surface 74 and the second lower connecting surface 78 form a second welded joint 84. As explained above with respect to FIGS. 6-9, in an embodiment, the first welded joint 80 between the first upper and lower connecting surfaces 70, 76 and the second welded joint 84 between the second upper and lower connecting surfaces 74, 78 are substantially coplanar. Also, as explained above with respect to FIG. 10, in another embodiment, the first welded joint 80 between the first upper and lower connecting surfaces 70, 76 and the second welded joint 84 between the second upper and lower connecting surfaces 74, 78 are vertically offset and non-coplanar.

[0056] With reference to FIGS. 12 through 14, an embodiment of a two-piece friction-welded piston 20 is shown, wherein the piston includes an upper member 24 and a lower member 23. The upper member 24 of the piston 20 is a nominally cylindrical member that forms the upper portion of the piston 20. The piston 20 is positioned such that the upper member 24 forms the lower boundary of a combustion chamber within each combustion chamber of each cylinder of an engine (not shown). The upper member 24 includes a substantially flat crown 28 having a central recess 30, or combustion surface, extending radially inward therefrom. The upper member 24 further includes at least one circumferential groove 1, 2, and 3 formed about the outer circumferential surface 24 hereof, wherein each of the grooves 1, 2, and 3 is configured to receive a piston to cylinder bore sealing ring (not shown). In the illustrated embodiment, the upper member 24 includes at least two (2) grooves 1, 2, and 3 formed into the outer circumferential surface. However, it should be understood by one of ordinary skill in the art that any number of grooves 1, 2 and 3 can be formed into the outer circumferential surface of the upper member 24.

[0057] Along the outer perimeter of the piston 20 are nominally multi arcuate surfaces 1, 2, 3, 4, 5, 6, 7, and 8; which act as the body of the piston, grooves for sealing rings, and as diametrically opposing skirts.

[0058] The upper and lower members 23, 24 are formed separately and later joined together to form the complete piston 20. In an embodiment, the upper and lower members 23, 24 are formed using steel, other ferrous material or other high temperature/high strength metals such as titanium, Monel, Inconel, or similar. The material used for the upper and lower members 23, 24 should be of adequate strength and have sufficient heat resistance to impart the needed strength for use in a diesel or other internal combustion engines.

[0059] Any combination of the upper and lower members 23, 24 can be precision cast to net final dimensions. Precision cast to net final dimensions generally means that the final cast piece does not require additional machining of multiple surfaces of the piston. Also, by precision casting to net final dimensions, additional machining to form the surfaces of the integral cooling oil reservoir is eliminated. In an embodiment, precision casting to net final dimensions of the one or more surfaces of the piston means that the precision cast to net final dimension 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 22, 24 means that the subject surfaces have a surface finish roughness of less than about 125 Ra. Although post-casting machining may be performed on other surfaces of the upper and lower members 24, 26 for other reasons, the precision cast to net final dimensions of the referenced surfaces may not require additional post-casting machining. However, in each such embodiment, the surfaces 1, 2, 3, 4, 5, 6, 7, and 8 may have a multi arcuate vertical cross-section 11 and can be also constructed of forgings or machined from solid pieces of material.

[0060] In another example, the multi-arcuate, horizontal cross-section 11 can be generally non-circular (e.g., ovoid) in shape. In other words, the perimeter of the multi-arcuate, horizontal cross-section 11 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 transition thereof continuous. Any point on the non-circular perimeter belongs to an arc with a constant radius (shorter or longer). In another example, multi-arcuate, horizontal cross-section 11 can be defined by a series of intersecting arcs. In yet another example, the multi-arcuate horizontal cross-section 11 can include elliptical portions, hyperbolic portions, parabolic portions, or even some straight lines.

[0061] In one example, as shown in FIG. 14, the multi-arcuate horizontal cross-section 11 includes a radius 12 of the cylindrical portions 13 that is less than the radius 14. In this example, the multi-arcuate horizontal cross-section 11 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 15, 16, and 17. As shown, the radius 12 defines the multi-arcuate cross-section at the top and bottom of FIG. 12 while radius 13 defines the multi-arcuate cross-section to the right and left. Radius 15 is greater than radius 14, and the resulting arcs have different center points 15, 16, and 17.

[0062] Additionally, it is to be appreciated that the piston members 22, 24 can be constructed prior to friction welding using any suitable material and by any suitable process. For example, the piston members 23, 24 can be precision cast to near net dimension from steel. Other examples can include piston members 23, 24 made by forgings, or any other suitable method of construction. Other examples can include an upper member 23 and a lower member 24 comprising dissimilar metals.

[0063] Typical friction welded pistons which are made from two pieces consist of a steel cast or forged crown and a separate skirt, usually cast or forged of the same or a compatible steel alloy which guides the piston assembly in the combustion cylinder of an engine. Alternatively, as-cast conventional steel castings may be used which, prior to friction welding the crown and skirt components, the crown typically undergoes extensive and costly machining operations, which includes incorporating one or more circumferentially disposed recesses that are configured to accept sealing rings and machining of the interior of the piston for dimensional consistency.

[0064] 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.