Method of making and using a piston ring assembly
Reference Number: N 01-02
Inventors: Rao, V. Durga N.; Kabat, Daniel M.
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.