Pistons with oil retaining cavities

Details Pistons with oil retaining cavities Pistons with oil retaining cavities

1986-12-08

1988-08-02

Garrett, Robert E.

Expansible chamber devices

With lubricating means

Piston has lubricant retaining or conducting means

92208, 123193P, F01B 3110

Patent

active

047607718

DESCRIPTION:

BRIEF SUMMARY
The invention relates to pistons for internal combustion engines or compressors.
The movement of a piston within an associated cylinder or liner includes complex lateral movement in addition to the basic reciprocatory movement. These lateral movements arise as a result of the clearance between the piston and the associated cylinder or liner and the varying lateral loads on the piston as a result of the varying angle of an associated connecting rod and the varying loads on the crown of the piston during the compression/ignition cycle.
During reciprocatory movement, there is the need to maintain hydrodynamic lubrication between the piston and the associated cylinder or liner, so preventing the rapid increase in frictional forces which occurs when mixed or boundary lubrication is present. There is also the need to reduce or minimise the so-called "piston slap" which occurs particularly when the engine or compressor is under load and when the piston is at top or bottom dead centre. This is because such noise is generated by contact between these parts and implies the presence of undesirable wear. It has previously been thought necessary, in order to maintain hydrodynamic lubrication between the piston and the associated cylinder or liner, to have a substantially continuous skirt surface on the piston over which a lubricating film is generated. It has also been thought possible to mitigate "piston slap" by the creation of a full belt of oil between the piston skirt and the associated cylinder or liner to provide viscous damping of the transverse motion of the piston at top and bottom dead centre.
However, it has recently been discovered, as discussed in U.K. Patent Specification No. 2,104,188, that the load transmitting area of the skirt of a piston can be reduced substantially with mixed or boundary lubrication occurring by measures to ensure the provision of efficient hydrodynamic lubrication over specific bearing areas of the skirt. However, this reduction of hydrodynamically lubricated skirt area tends, in theory at least, to increase the noise generated on "piston slap", as a result of the reduced quantity of oil between the piston and the associated cylinder or liner.
According to the invention, there is provided a piston for an internal combustion engine or compressor, of the kind comprising a crown, a gudgeon pin bore and two skirt portions on opposite sides of the gudgeon pin bore, characterised in that each skirt portion has formed therein a plurality of cavities such that at least one part of said skirt portion remains for the transmission of lateral loads from the piston to an associated cylinder or liner, the cavities being arranged in rows, each row extending around the associated skirt portion, the cavities holding lubricant for passage over said at least one remaining part of the skirt portion to lubricate said skirt part hydrodynamically during reciprocation of the piston, and for damping lateral movement of the piston.
The following is a more detailed description of two embodiments of the invention, by way of example, reference being made to the accompanying drawings in which:
FIG. 1 is a side elevation of a first form of piston for an internal combustion engine showing a plurality of rows of cavities formed in a skirt portion of the piston,
FIG. 2 is a section of the skirt portion of the piston of FIG. 1 on the line II--II of FIG. 1,
FIG. 3 is a section of the skirt portion of the piston of FIG. 1 on the line III--III of FIG. 1,
FIG. 4 is a section of the skirt portion of the piston of FIG. 1 on the line IV--IV of FIG. 1,
FIG. 5 is a section of the skirt portion of the piston of FIG. 1 on the line V--V of FIG. 1,
FIG. 6 is a side elevation of a second form of piston for an internal combustion engine and formed with rows of cavities on a skirt portion of the piston, and
FIG. 7 is a part-section of a skirt portion of the piston of FIG. 6 on the line VII--VII of FIG. 6.
Referring to FIG. 1, the first piston is formed from aluminum or aluminum alloy by casting, for example squeeze casting, or by

REFERENCES:
patent: 1016561 (1912-02-01), Grabler
patent: 1760122 (1930-05-01), Drevitson
patent: 2195552 (1940-04-01), Alexandrescu
patent: 2407440 (1946-09-01), Osborne
patent: 4535682 (1985-08-01), Collyear et al.
Enkele Bijzonderheden, E. H. Hulst, 9/50.

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