CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims priority to U.S. Provisional Patent Application No. 62/264,994, filed December 9, 2015, the entirety of which is hereby incorporated by reference.

BACKGROUND

[0002] Plain bearing shells have previously been used as an interface layer between, for example, a piston and a roller or shaft disposed in the recess of a piston. Plain bearing shells can help to reduce friction between a rotating roller or shaft and the walls of the recess in the piston, as well as improve alignment of the roller or shaft within the recess. However, in some instances, the plain bearing shell begins to rotate as the roller or shaft rotates, thereby potentially causing friction and or alignment issues. Accordingly, a need exists for plain bearing shells that do not rotate when serving as an interface layer between pistons and rollers or shafts.

SUMMARY

[0003] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary, and the foregoing Background, is not intended to identify key aspects or essential aspects of the claimed subject matter. Moreover, this Summary is not intended for use as an aid in determining the scope of the claimed subject matter.

[0004] In some embodiments, a plain bearing shell with anti-rotation features is described. The plain bearing shell can have a generally semi-cylindrical geometry. In some embodiments, a recess is formed at each axial end of the plain bearing shell. The piston recess in which the plain bearing shell is disposed may include protrusions sized and shaped to mate with the recess at the axial ends of the plain bearing shell to thereby prevent rotation of the plain bearing shell when the plain bearing shell is disposed in the piston recess. In some embodiments, the plain bearing shell further includes thrust bearings at the axial ends of the plain bearing shell. The thrust bearings extend radially inwardly and provide an interface between axial ends of the roller or shaft and the axial ends of the piston recess. [0005] In some embodiments, a plain bearing shell has a generally semi- cylindrical geometry and further includes radially outwardly angled tabs formed in a portion of the circumferential ends of the plain bearing shell. The tabs provide an edge that is perpendicular to the axis of the plain bearing shell. The piston recess includes female imprints shaped and sized to receive the tabs and thereby prevent rotation of the plain bearing shell and assist with axial alignment of the plain bearing shell in the piston recess. The plain bearing shell can also include thrust bearing extending from the axial ends of the plain bearing shell to provide an interface between axial ends of the roller or shaft and the axial ends of the piston recess

[0006] These and other aspects of the plain bearing shell described herein will be apparent after consideration of the Detailed Description and Figures herein. It is to be understood, however, that the scope of the claimed subject matter shall be determined by the claims as issued and not by whether given subject matter addresses any or all issues noted in the Background or includes any features or aspects recited in this Summary.

BRIEF DESCRI PTION OF THE DRAWINGS

[0007] Non-limiting and non-exhaustive embodiments of the disclosed plain bearing shell, including the preferred embodiment, are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

[0008] Figures 1 a-1 e illustrate plain bearing shells with anti-rotation features according to various embodiments described herein;

[0009] Figures 2a-2e illustrate plain bearing shells with anti-rotation features according to various embodiments described herein;

[0010] Figures 3a and 3b illustrate plain bearing shells with anti-rotation features according to various embodiments described herein; and

[0011] Figure 4 illustrates plain bearing shells with anti-rotation features according to various embodiments described herein. DETAILED DESCRIPTION

[0012] Embodiments are described more fully below with reference to the accompanying figures, which form a part hereof and show, by way of illustration, specific exemplary embodiments. These embodiments are disclosed in sufficient detail to enable those skilled in the art to practice the invention. However, embodiments may be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. The following detailed description is, therefore, not to be taken in a limiting sense.

[0013] With reference to Figure 1 a, a plain bearing shell 100 is generally adapted to reside within a recess of a piston 2. The piston 2 may be, for example, for use with a radial piston engine. A roller or a shaft 3 (shown in phantom) may then be housed within plain bearing shell 100.

[0014] With reference to Figure 1 b, the plain bearing shell 100 has a generally semi-cylindrical geometry. The plain bearing shell 100 includes two opposing axial ends 10, 10', an external surface 1 1 that is shaped to fit the piston 2, and an internal surface 12 opposite the external surface 1 1 . All or a portion of the internal surface 12 can be covered with, for example, an antifriction overlay/liner. The internal surface 12 is adapted to support a roller or shaft 3 and allow the latter to rotate in the plain bearing shell 100 with a reduced coefficient of friction. The plain bearing shell 100 is also provided with two opposing circumferential ends 13, 13'.

[0015] As shown in Figure 1 b and as shown and referenced in Figure 1 c, the two axial ends 10, 10' of the plain bearing shell 100 can be under-cut to form an elongated semi-circular shaped recess 14. This recess 14 is configured to interact (e.g., mate) with a semi-circular concentric protrusion 16, 16' located at opposite ends of the recess formed in the piston 2, thereby preventing the rotation of the plain bearing shell 100 in either direction within the recess of piston 2 when a roller or shaft 3 is disposed in the piston 2 and rotating.

[0016] This anti-rotation function is assisted by the fact that the thickness of the plain bearing shell 100 (i.e., the distance between the internal surface 12 and the external surface 1 1 ) at point A is larger than its thickness at point B. If the plain bearing shell 100 is subjected to a rotating motion in the piston 2 via the rotation of the roller or shaft 3 in the piston 2, the axial ends 10, 10' (having an increased thickness at point A) will come into contact with the protrusions 16, 16' of the piston 2 and thereby stop any rotation of the plain bearing shell 100.

[0017] In summary, the plain bearing shell 100 is prevented from rotating in the piston 2 by virtue of axial ends 10, 10' forming two semi-cylindrical recess 14 that interact with corresponding protrusions 16, 16' of the piston 2. This configuration helps to assure axial positioning of the plain bearing shell 100 in the piston 2, and helps to prevent axial movement of the plain bearing shell 100.

[0018] In some embodiments, the plain bearing shell 100 is sized so that there is no contact between the angled ends of the roller or the shaft and the load area of the plain bearing shell 1 in order to satisfy tribological principles.

[0019] In order to meet this requirement, the usable length (L _max ) in the load area of the plain bearing shell is determined by the formula:

[0020] L _max = L _g - (2 x r _g )

[0021] wherein L _g is the total length of the roller or the shaft and r _g is the value of the radius of the curved portion of the roller or shaft that extends between the outer diameter of the roller or the shaft and its end faces (see, e.g., r _g as illustrated in Figure 2d). Lmax is also illustrated in Figure 1 d.

[0022] With reference to Figure 1 e, in some embodiments the plain bearing shell 100 further includes two plain thrust bearings 14, 14' extending from the axial ends 10, 10' in a radially inward direction. The orientation of the thrust bearings 14, 14' can also be considered perpendicular to the axis of the plain bearing shell 100. The thrust bearings 14, 14' help to ensure an axial plain bearing thrust function for the roller or the shaft. This prevents an increase of the coefficient of friction resulting from contact between the roller/shaft ends and the axial walls of the recess in the piston . An antifriction overlay/liner present on some or all of the opposing side walls 15, 15' of the thrust bearings 14, 14' enables a low coefficient of friction between the plain bearing shell 1 and the roller or the shaft 3.

[0023] The shape and the section (width x height) of the thrust bearings 14, 14' can be defined by the factor PV (MPa x m/s) arising from the contact between the roller or shaft and the thrust bearings, wherein P (MPa) is the pressure of contact between the opposing parts, and V (m/s) is the circumferential speed of the roller or shaft at the contact point.

[0024] As a reminder, the pressure of contact is the quotient of the axial load F (daN) delivered by the roller or the shaft on the thrust bearings and from the surface S (mm ² ) of each of the plain thrust bearing (P=F/S).

[0025] Thus, according to the axial load applied by the roller or the shaft and its circumferential speed, the size of the thrust bearings 14, 14' will be determined in order that the factor PV will remain acceptable for the chosen plain bearing material. The width of the aforementioned thrust bearings 14, 14' must be less than the width of side slots 17, 17' formed in the axial ends of the recess of the piston 2 in order not to interfere with the bearing assembly and not to influence the anti-rotation function of the plain bearing.

[0026] As shown in Figure 1 e, the protrusions 15, 15' may be configured to accommodate a plain bearing shell 100 having thrust bearings 14, 14'. Thus, in some embodiments, the protrusions 15, 15' will each include two separate protruding segments that engage with the recess 14 but which also permit the thrust bearings 14, 14' to be positioned between the two separate protruding segments of the protrusion 16, 16'.

[0027] With reference now to Figures 2a-2e, embodiments of an alternate plain bearing shell with anti-rotation features are shown.

[0028] With reference to Figure 2a, the plain bearing shell 200 has a generally semi-cylindrical geometry. The plain bearing shell 200 includes two opposing axial ends 20, 20', an external surface 21 shaped to fit with a piston, and an internal surface 22 opposite the external surface 21 . The internal surface 22 may be fully or partially covered with an antifriction overlay/liner. The plain bearing shell 200 is also provided with two opposing circumferential ends 23, 23'.

[0029] In some embodiments the two circumferential ends 23, 23' include two semi-cut tabs 24, 24' issued from the face 22 and protruding radially outwardly. These tabs 24, 24' are accommodated in a female imprint of the piston 2, which thereby prevents plain bearing shell 200 from rotating when the roller or the shaft turns in one or the other direction. [0030] With reference to Figure 2b, plain bearing shell 200 can be characterized by the fact that the two tabs 24, 24' form two parallel edges 25, 25' perpendicular to the axis of the roller or shaft and which fit against female imprint 20, 20' of the piston. This helps to assure that the axial positioning of the plain bearing shell 200 within the piston and prevents axial movement of the plain bearing shell 200.

[0031] With reference to Figure 2c, the plain bearing shell 200 can further include two plain thrust bearings 26, 26' issued from ends 20, 20'. The thrust bearings 26, 26' can be oriented perpendicular to the axis of the plain bearing shell 200 in order to assure an axial plain bearing thrust function for the roller or the shaft, preventing an increase of the coefficient of friction with a direct contact of roller/shaft ends to piston faces, and to allow a low coefficient of friction of the roller/shaft thanks the two plain thrust bearing faces 27, 27'.

[0032] The shape and the section (width x height) of the thrust bearings 26, 26' can be defined by the factor PV (MPa x m/s) arising from the contact between the roller or shaft and the thrust bearings, wherein P (MPa) is the pressure of contact between the opposing parts, and V (m/s) is the circumferential speed of the roller or shaft at the contact point.

[0033] As a reminder, the pressure of contact is the quotient of the axial load F (daN) delivered by the roller or the shaft on the thrust bearings and from the surface S (mm2) of each of the plain thrust bearings (P=F/S).

[0034] Thus, according to the axial load applied by the roller or the shaft and its circumferential speed, the size of the thrust bearings will be determined in order that the factor PV will remain acceptable for the chosen plain bearing material. The width of the aforementioned thrust bearings must be less than the width of the side slots of the piston 28, 28' in order not to interfere with the bearing assembly and not to influence the anti-rotation function of the plain bearing.

[0035] With reference to Figure 2d, the plain bearing shell 200 can be sized so that there is no contact between the angled ends of the roller or the shaft and the load area of the plain bearing shell 200 in order to satisfy tribological principles.

[0036] The usable length in the load area is determined by the formula:

[0037] L _max = L _g - (2 x r _g ) [0038] wherein L _g is total length of the roller or the shaft and r _g is the value of the radius of the curved portion of the roller or shaft that extends between the outer diameter of the roller or the shaft and its end faces. L _max is also illustrated in Figure 2d.

[0039] With reference to Figure 2e, in some embodiments the two plain thrust bearings 26, 26' can be linked to the ends 20, 20' of the plain bearing shell 100 by ties 28, 28'. These ties 28, 28' may be tilted at an angle, such as in a radially outward direction. In some embodiments, the ties are angled outwardly such that the plain thrust bearings 26, 26' extend beyond the circumference of the plain bearing shell 200. This can help to ensure no contact between the roller or the shaft in this area and thus satisfy the tribological principles described above.

[0040] With reference to Figures 3a and 3b, in some embodiments, a semi- cylindrical plain bearing shell 300 is secured to the piston 2 via welded spots or beads 37, 37' to thereby prevent rotation of the plain bearing shell. As shown in Figure 3a, the welded spots 37, 37' may be located between the piston 2 and the portion of external surface 32 proximate the circumferential ends 33, 33'. As shown in Figure 3b, the welded spots 37. 37' may be located in the countersunk areas of the piston recess.

[0041] The configurations shown in Figures 3a and 3b are in some respects less desirable and then other previously described embodiments, since they include anti- rotation features that will still prevent rotation even when welding spots or beads break down.

[0042] With reference to Figure 4, a plain bearing shell 400 is described wherein the plain bearing shell 400 extends more than 180 degrees in the circumferential direction. This plain bearing shell 400 may also be described as having a distance between circumferential ends 43, 43' that is less than the diameter of the roller or shaft 3 disposed therein. In such configurations, the roller or shaft is disposed in the plain bearing shell by sliding the roller of shaft in from either axial end of the plain bearing shell. The sub assembly of the plain bearing shell and the roller or shaft is then disposed in the piston recess. In some embodiments, the sub-assembly is spot welded to the piston in order to prevent rotation of the plain bearing shell. Once constructed in this manner, the full assembly provides the benefit of being made from three indissociable components. [0043] From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the scope of the invention. Accordingly, the invention is not limited except as by the appended claims.