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 piston assembly for an internal combustion engine, comprising:
a piston head having an upper crown and a lower crown joined together by an annular outer wall and an annular inner wall, said upper crown having an upper combustion surface and a combustion bowl depending therein with an undercrown surface provided opposite said combustion bowl, said lower crown having an upper wall and a pair of laterally spaced pin bosses depending from said upper wall, said pin bosses having pin bores aligned axially with one another along a pin bore axis, a concave bearing surface formed in said upper wall and extending between said pin bosses to form a continuous bearing surface with said pin bores, a toroid-shaped outer cooling gallery bounded between said annular outer wall and said annular inner wall and an inner cooling gallery bounded by said annular inner wall, said upper wall having at least one oil inlet and at least one oil outlet extending into said inner cooling gallery;
a wrist pin having a through hole; and
a connecting rod having an end fixed to said wrist pin for conjoint oscillation therewith, said connecting rod having an oil passage aligned for fluid communication with said through hole in said wrist pin and with said oil inlet to allow oil to flow through the connecting rod, through the wrist pin, and through the oil inlet into said inner cooling gallery and outwardly from said inner cooling gallery through said at least one oil outlet.
2. The piston assembly of claim 1 wherein said oil passage is configured for constant fluid communication with said through hole and for intermittent fluid communication with said at least one oil inlet.
3. The piston assembly of claim 1 wherein said at least one oil outlet is aligned to direct oil directly onto an outer surface of said wrist pin.
4. The piston assembly of claim 3 wherein said at least one oil outlet is aligned substantially tangent to an outer surface of said wrist pin.
5. The piston assembly of claim 4 wherein said at least one oil outlet includes a pair of oil outlets formed on opposite sides of said pin bore axis from one another.
6. The piston assembly of claim 1 wherein said one oil inlet is aligned along a central longitudinal axis along which said piston reciprocates.
7. The piston assembly of claim 1 further including a plurality of reinforcement ribs extending radially along said undercrown surface within said outer cooling gallery.
8. The piston assembly of claim 1 wherein said upper crown and said lower crown are joined to one another by a weld joint.
9. The piston assembly of claim 1 wherein said upper crown and said lower crown are formed as a monolithic piece of material in a casting process.
10. The piston assembly of claim 1 wherein said upper wall forms a substantially flat floor in said inner cooling gallery.
11. The piston assembly of claim 10 wherein said upper wall forms a substantially flat floor in said outer cooling gallery.
12. The piston assembly of claim 1 wherein said through hole extends along a first longitudinal axis and said through passage extends along a second longitudinal axis, said first longitudinal axis being inclined relative to said second longitudinal axis.
13. A piston for an internal combustion engine, comprising:
a piston head having upper and lower crowns, said upper crown including an upper combustion surface having a combustion bowl depending therein with an undercrown surface opposite said combustion bowl, said upper crown further including an annular upper outer wall portion and an annular upper inner wall portion depending from said undercrown surface, said upper inner wall portion being spaced radially inwardly from said upper outer wall portion; and
said lower crown depending from said upper crown and including a pair of laterally spaced pin bosses having axially aligned pin bores for receipt of a wrist pin and a pair of diametrically opposite skirt portions extending between said pin bosses, said lower crown including an upper wall having a concave, saddle bearing surface extending between said pin bosses to provide a continuous bearing surface, in combination with said pin bores, said lower crown including an annular lower outer wall portion and an annular lower inner wall portion, said lower annular outer and inner wall portions extending upwardly from said upper wall, said upper and lower annular outer wall portions being fixed to one another and said upper and lower annular inner wall portions being fixed to one another and forming a outer cooling gallery surrounding an inner cooling gallery; and including at least one oil inlet extending through said saddle bearing surface into said inner cooling gallery, and wherein said outer oil gallery includes at least one oil inlet and at least one oil outlet both of which are spaced laterally from and out of communication with said saddle bearing surface and in open communication with an interior space inboard of said skirt portions.
14. The piston of claim 13 further including at least one oil outlet extending through said upper wall in generally tangential relation with said saddle bearing surface to allow oil to flow outwardly from said inner cooling gallery onto the wrist pin.
15. The piston of claim 14 wherein said at least one oil outlet includes a pair of oil outlets formed on opposite sides of said pin bore axis from one another.
16. The piston of claim 14 wherein said at least one oil inlet is aligned along a central longitudinal axis along which the piston reciprocates.
17. The piston of claim 13 further including a plurality of reinforcement ribs extending radially along said undercrown surface within said outer cooling gallery.
18. The piston of claim 13 wherein said upper crown and said lower crown are joined to one another by a weld joint.
19. The piston of claim 13 wherein said upper crown and said lower crown are formed as a monolithic piece of material in a casting process.
20. The piston of claim 13 wherein said upper wall forms a substantially flat floor in said inner cooling gallery.
21. The piston of claim 20 wherein said upper wall forms a substantially flat floor in said outer cooling gallery.
22. The piston of claim 13 wherein said inner cooling gallery is sealed.