Expansible chamber devices – Piston – Open-ended hollow skirt type
Patent
1986-04-30
1987-10-27
Ostrager, Allen M.
Expansible chamber devices
Piston
Open-ended hollow skirt type
92239, F16J 104
Patent
active
047021519
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a piston for an internal combustion engine comprising a crown, a piston axis, a ring band extending around the crown, gudgeon pin bosses supporting the crown and defining a gudgeon pin bore having an axis, and a skirt.
The purpose of the skirt is to transmit lateral thrust forces from the piston to an associated cylinder or liner. In many pistons, the skirt is formed by a generally cylindrical surface extending around the piston and depending from the ring band for lubricated contact with the associated cylinder or liner. Such a skirt has the disadvantage that the oil film between the skirt and the associated cylinder or liner is of substantial area and so the frictional forces generated by such film are also substantial. In addition, such a skirt is comparatively rigid and this requires the skirt to be a comparatively loose fit in the associated cylinder or liner in order to accommodate changes in piston and cylinder shape due to temperature changes, since the rigidity of the skirt does not allow the skirt to flex to accommodate such changes. Such a loose fit increases the incidence of piston slap so increasing noise.
There have been various proposals for reducing the load transmitting skirt area, to reduce the frictional forces, but some of these proposals have not provided adequate lubrication of these reduced area. In addition, others of these proposals have not dealt with the problem of the rigidity of these skirt areas.
According to a first aspect of the invention, there is provided a piston for an internal combustion engine comprising a crown, a piston axis, a ring band extending around the crown, gudgeon pin bosses supporting the crown and defining a gudgeon pin bore having an axis and a skirt characterised in that the skirt is formed by two pairs of arcuate skirt portions on opposite sides of the gudgeon pin bore, the arcuate skirt portions of each pair being connected to the gudgeon pin bosses and including at least one upper arcuate skirt portion adjacent to but spaced from the ring band by a gap, and at least one lower arcuate skirt portion spaced from said at least one upper arcuate skirt portion by an axially and circumferentially extending gap, each arcuate skirt portion being disposed about a plane including the piston axis and normal to the gudgeon pin bore axis and extending only partially around 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 section through a first form of piston for an internal combustion engine,
FIG. 2 is a section on line II--II of FIG. 1,
FIG. 3 is a section of a second form of piston for an internal combustion engine, and
FIG. 4 is a section on the line IV--IV of FIG. 3.
Both the piston of FIGS. 1 and 2 and the piston of FIGS. 3 and 4 are made by a casting process using either an iron or a steel material, aluminium or an aluminium alloy. They are pistons for Diesel engines.
Referring now to the piston of FIGS. 1 and 2, this piston comprises a crown 10 surrounded by a ring band 11 and having two gudgeon pin bosses 12a, 12b. The crown 10 is provided with a depression 13 which receives a precision cast steel combustion bowl 14 having on its undersurface projections 15 which space the bowl 14 from the depression 13 and so form an insulating air gap 16 therebetween. The combustion bowl 14 is a shrink-fit in the depression. The crown 10 also has an annular outer surface which is spray-coated with a suitable ceramic 17 to a depth of 2 mm in order to provide a heat-resistant coating on the crown 10.
The ring band 1 depends from the crown 10 and is formed with a plurality of piston ring grooves 18. Webs 19 are provided between the crown 10 and the ring band 11 in order to provide a ring band with the required rigidity.
A support 20 extends upwardly from each gudgeon pin boss 12a, 12b and is connected to the undersurface of the depression 13 in order to support the crown 10 and the ring band 11 on the gudgeon pin bo
REFERENCES:
patent: 2032849 (1936-03-01), Nelson
patent: 2066613 (1937-01-01), Day
patent: 3307456 (1967-03-01), Etienne
patent: 3987709 (1976-10-01), Day
patent: 4161165 (1979-07-01), Belush et al.
Munro Robert
Speaight David C.
AE PLC
Ostrager Allen M.
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