Method of making and using a piston ring assembly
Reference Number: N 01-02
Inventors: Rao, V. Durga N.; Kabat, Daniel M.
Owner: NISTAC
USPTO Link:5430938
Invention Summary
It is an object of this invention to overcome the problems recited above and to provide
an economical solution to them.
The invention in a first aspect is a method of making a piston ring assembly. The
method comprises (a) providing a metallic piston with a crown and an annular depending
side wall; (b) machining a stepped annular groove in the side wall having a total
height of at least 4 mm; (c) fabricating a pair of metallic split annular compression
rings nestable within said groove and effective to operate together as a superimposed
unit to seal against both the step and groove; (d) coating the groove and non-mating
surfaces of the rings with solid film lubricants; and (e) inserting the pair of coated
rings into the coated groove within their split ends out of superimposed alignment.
The rings are fabricated to provide a total combined height equal to the groove height
less 60 microns or less. The solid film lubricants are applied as a mixture of at
least two, selected from the group of graphite, molydisulfide and boronoritride, in
an emulsion carrier. The porous coating is attractive to oil and has an average particle
size of solid lubricants is preferably no greater than 5 microns. Coating can be carried
out by emulsion spraying of solid lubricant mixtures carried in a polyamide.
Such method facilitates the forming of the groove in the piston and coatings while
permitting the ring assembly to reduce blow-by, reduce crevice volume, reduce ring
flutter and eliminate ring failure. The solid film lubricant assists in eliminating
freezing of the rings against the groove sides, increasing ring fatigue life, enhancing
ring tension and reducing engine emissions.
The invention in another aspect is a method of reducing piston ring blow-by for a
piston ring assembly in a cylinder bore wall of an internal combustion engine, the
wall being bathed with oil drawn from a reservoir, the method comprises providing
a machined piston and split rings as above, and reciprocatingly operating the assembly
in the bore wall for carrying out engine operation whereby said rings act in unison
due to the friction at their mating surfaces and are free to radially adjust as a
unit with little or no inhibiting friction while maintaining sealing engagement with
the stepped groove, a side of the groove, and the oil film on the bore wall.