Piston for internal combustion engine
OwnerWalter Joseph Griffiths, Kenneth John Streetinventors
Life of this patent
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Abstract
An engine piston (10) comprising a crown (12) and a tubular body portion (30) containing gudgeon pin bosses (46) and force transmitting regions (66) has the body portion forged, preferably of steel, as two or more circumferentially incomplete segments (1001, 1002) which extend about a longitudinal piston axis (14) and are joined into the tubular form by welding or the like. The segments are forged in a direction perpendicularly to the piston axis which permits the formation of regions of differing wall thickness along the tubular body length and mass saving recesses (70) between force transmitting struts (661) and (662) that are not possible with forging a unitary tubular body from one end.
Claims40
An engine piston comprising a substantially circular crown having a periphery generated about a longitudinal piston axis, and, extending from, the crown portion surrounding said longitudinal axis, a forged body portion having a tubular side wall that forms a piston skirt open at one end remote from the crown and substantially closed at the crown end, said tubular side wall extending longitudinally of the piston axis between said open and crown ends and bisected by a thrust plane including said piston axis, a pair of gudgeon pin bosses formed integrally with the side wall, each boss extending from the side wall spaced from the open and crown ends along a substantially diametric pin axis perpendicular to the thrust plane towards the other boss and spaced apart therefrom and apertured along at least part of its length along the pin axis to provide bearing support for a gudgeon pin, and a plurality of force transmitting struts forged integrally with each boss and extending axially from the boss to the crown end, each strut extending along the boss to the side wall and to a limited extent across the boss to define at least one radially open gallery between the boss and the crown end.
A piston as claimed in any one of the preceding claims in which the body portion comprises in the tubular side wall at least one oil control ring groove and at least one drainage duct extending from said groove through the tubular wall between the thrust plane and the struts.
A piston as claimed in any one of the preceding claims in which the tubular side wall includes, between the open end and the gudgeon pin bosses, an internal thickening of the side wall defining a strengthening band extending about the periphery of the skirt portion.
A piston as claimed in any one of the preceding claims in which the tubular side wall has at least one mass saving region of reduced wall thickness centered on the thrust axis, spaced axially from the strengthening band and the closed end and circumferentially from the pin bosses.
A piston as claimed in any one of the preceding claims in which the end of the gudgeon pin aperture in each boss is recessed from the outer surface of the side wall.
A piston as claimed in any one of the preceding claims in which the proximal inboard ends of the gudgeon pin bosses are substantially parallel to each other and the thrust plane.
A piston as claimed in any one of the preceding claims in which the tubular side wall is, between said struts, of substantially uniform thickness circumferentially of the wall.
A piston as claimed in any one of the preceding claims in which there are associated with each gudgeon pin boss at least a pair of struts disposed symmetrically each side of the pin axis and substantially of the pin aperture.
A piston as claimed in any one of the preceding claims in which the body portion comprises a plurality of body segments each defined by a side wall part, curved about a longitudinal segment axis coincident with the piston axis and extending circumferentially between longitudinally extending boundary edges, and an end wall part extending about said segment axis between substantially radially extending boundary edges, said segments being joined together along the boundary edges and at least two of the segments, facing each other across the piston axis, each including a gudgeon pin boss and associated force-transmitting struts.
A piston as claimed in any one of claims 18 to 33 in which the features formed within each segment all have boundaries which extend substantially perpendicular to the thrust plane in accordance with forging in a direction perpendicular to the segment axis.
A piston as claimed in any one of the preceding claims in which the crown and body portion are each made of steel.
A method of making an engine piston having a crown defined about a piston axis, and a body portion, extending with respect to the crown along the piston axis, having a tubular side wall that forms a piston skirt extending between an open end and a substantially closed crown end defined by a body end wall,
- the method comprising
- forming at least the body portion as a plurality of body segments defined by side wall parts curved about a longitudinal segment axis and having longitudinally extending boundary edges,
- forming two segments each with a gudgeon pin boss integral with the side wall part and joining the segments along the boundary edges such that segment axes coincide and define the piston axis, and the gudgeon pin bosses oppose in substantially diametric alignment perpendicularly to the segment axis and define a gudgeon pin axis,
- the method being characterised by
- forging each of said two segments from a steel blank along a forging axis perpendicular to the segment axis and therein forging a said boss and a body end wall part to a greater thickness in the forming direction than at least one radially open gallery region between the boss and body end wall part.
Dependencies are inferred from the claim text.