Expansible chamber devices – Piston with rigid axially extending hollow stem – Hollow stem forms axially extending fluid passage
Patent
1988-08-29
1990-07-03
Garrett, Robert E.
Expansible chamber devices
Piston with rigid axially extending hollow stem
Hollow stem forms axially extending fluid passage
92157, 92159, 92187, 92DIG1, 92DIG2, 384206, 384300, 384908, F01B 3100
Patent
active
049381210
DESCRIPTION:
BRIEF SUMMARY
The invention relates to pistons for sliding in cylinders of reciprocating internal or external combustion engines and compressors, i.e., machines in which a working gas contained in the or each cylinder by a transverse surface of the piston is at both high pressure and high temperature, and it preferably, but not exclusively, concerns pistons for two-stroke or four-stroke reciprocating internal combustion engines. The invention more particularly relates to those of these pistons which have, within an externally cylindrical skirt, a partly spherical bearing surface for receiving in the manner of a ball joint the partly spherical head of a connecting rod. For reasons which will be explained hereinafter, the bearing surface of the piston and/or the head of the rod may have by construction a shape which is partly not strictly spherical but, for simplifying the description, the expression "spherical" will be used in this context for designating a shape which is exactly or approximately spherical.
Such pistons are for example disclosed in French patents No. 965,449 and No. 1,547,151 and the British patent No. 293,506. In these known pistons, the two partly spherical elements of the piston and rod, which are composed of metal, move in contact with each other, at least if one ignores the thin film of lubricating oil maintained therebetween by introduction of oil under pressure which comes for example from a passageway extending longitudinally within the rod see in this respect French patent No. 965,449 and the British patent No. 293,506).
An object of the invention is to enable the articulation between the piston and the rod to resist large forces applied to the piston by the maximum pressures cyclically established in the variable-volume chamber defined by the piston inside the cylinder.
Hereinafter, when expressions such as "upper", "lower", "above" or "below" are used, it will be assumed that the piston is so oriented that its axis is vertical and the rod is positioned below the piston. This hypothesis is merely intended to simplify the description and therefore does not imply that the piston is in fact oriented in this way when it is mounted in an internal combustion engine or compressor.
According to a first aspect of the invention, the piston of the type defined hereinbefore is essentially characterized in that it possesses an inner cavity open at the end opposed to said transverse surface and laterally defined at least partly by a cylindrical bearing surface of revolution; the space defined within this cavity of the piston by the partly spherical head of the rod is filled with a viscous, pasty or plastically-deformable fluid which is practically incompressible at the operating pressures and temperatures of the piston; the diameter of said cylindrical bearing surface is very slightly larger than the diameter of the partly spherical head of the rod so that the operational clearance between said cylindrical bearing surface and partly spherical head is small enough to prevent any migration of said fluid out of said space at the operating temperatures and pressures of the piston.
Preferably, the generatrices of said cylindrical bearing surface are parallel to those of the cylindrical skirt of the piston, this cylindrical bearing surface being generally coaxial with this skirt.
In order to avoid any eventual loss of said fluid, a thin fluid-tight metal shell is advantageously interposed between the partly spherical head of the rod and said fluid and is locally maintained in position by an interference fit with said cylindrical bearing surface, the assembly being such that the part of the shell creating the interference with the cylindrical bearing surface is movable in a direction parallel to the axis of this cylindrical bearing surface under the effect of forces exceeding a given limit.
According to a second aspect of the invention, a piston provided for sliding in the cylinders of reciprocating internal or external combustion engines and compressors, i.e., machines in which a working gas contained in the or ea
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Denion Thomas
Garrett Robert E.
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