Reduced compression height dual gallery piston, piston assembly therewith and methods of construction thereof
A piston assembly, piston therefor and methods of construction are provided. The assembly includes a piston head and connecting rod operably coupled thereto via a wrist pin. The piston head has an upper crown with a combustion bowl and an undercrown surface. The lower crown includes axially aligned pin bores receiving the wrist pin. An upper wall of the lower crown has an oil inlet, an oil outlet and a concave, saddle bearing surface that bears against the wrist pin. A toroid-shaped outer cooling gallery is formed between wall portions of the upper and lower crowns, wherein the outer cooling gallery surrounds an inner cooling gallery. The connecting rod is fixed to the wrist pin for conjoint oscillation. The connecting rod has an oil passage in fluid communication with a through hole in the wrist pin to allow oil to flow therethrough into the inner cooling gallery via the oil inlet.
1. A method of constructing a piston assembly for an internal combustion engine, comprising:
forming a piston head having upper and lower crowns;
forming the upper crown having an upper combustion surface having a combustion bowl depending therein with an undercrown surface opposite the combustion bowl;
forming an annular upper outer wall portion and an annular upper inner wall portion depending from the undercrown surface;
forming a pair of laterally spaced pin bosses depending from an upper wall of the lower crown and having axially aligned pin bores for receipt of a wrist pin;
forming a pair of diametrically opposite skirt portions extending between the pin bosses;
forming a concave, saddle bearing surface extending between the pin bosses in the upper wall of the lower crown;
forming at least one oil inlet through the saddle bearing surface;
forming at least one oil outlet in the upper wall of the lower crown;
forming the lower crown having an annular lower outer wall portion and an annular lower inner wall portion extending upwardly from the upper wall;
fixing the upper and lower outer annular wall portions to one another and fixing the upper and lower inner annular wall portions to one another and forming a toroid-shaped outer cooling gallery surrounding an inner cooling gallery;
fixing an end of a connecting rod to the wrist pin for conjoint oscillation therewith and bringing an oil passage in the connecting rod into fluid communication with a through hole in the wrist pin; and
configuring the through hole in the wrist pin for fluid communication with the at least one oil inlet in the upper wall during reciprocation of the wrist pin against the saddle bearing surface.
2. The method of claim 1 further including configuring the through hole in the wrist pin for intermittent fluid communication with the at least one oil inlet in the upper wall during reciprocation of the wrist pin against the saddle hearing surface.
3. The method of claim 1 further including orienting the at least one oil outlet to direct oil directly onto an outer surface of the wrist pin.
4. The method of claim 3 further including aligning the at least one oil outlet in substantially tangent relation to an outer surface of the wrist pin.
5. The method of claim 1 further including forming the at least one oil outlet as a pair of oil outlets on opposite sides of the pin bore axis from one another.
6. The method of claim 1 further including forming the at least one oil inlet along a central longitudinal axis along which the piston reciprocates.
7. The method of claim 1 further including forming a plurality of radially extending reinforcement ribs along the undercrown surface within the outer cooling gallery.
8. The method of claim 7 further including forming reinforcement ribs along the undercrown surface within the inner cooling gallery.
9. The method of claim 1 further including joining the upper crown and the lower crown to one another via friction welding or induction welding.
10. The method of claim 1 further including forming the upper crown and the lower crown as a monolithic piece of material in a casting process.