Steel piston with cooling gallery and method of construction thereof

1. A piston for an internal combustion engine, comprising:

a top part having an uppermost surface with annular inner and outer upper joining surfaces depending from said uppermost surface;

a bottom part having a pair of pin bosses providing a pair of laterally spaced pin bores aligned with one another along a pin bore axis and having a pair of upwardly extending annular inner and outer lower joining surfaces joined by separate respective inner and outer weld joints to said inner and outer upper joining surfaces with an annular cooling gallery formed radially between said upper joining surfaces and radially between said lower joining surfaces, said bottom part having a combustion bowl wall recessed below said uppermost surface, said combustion bowl wall having a thickness extending between an upper apex and a lower apex underlying said upper apex with an annular valley surrounding said upper apex and said lower apex;

at least one of said top and bottom parts including a ring belt with a plurality of ring grooves for receiving piston rings, said ring belt including an uppermost groove, a pair of lower grooves below said uppermost groove, and a bottom groove below said pair of lower grooves and above a pair of skirt panels for additional weight reduction;

wherein said top part is made from a different material than said bottom part and is friction welded to said bottom part through a friction welded joining surface extending transversely across said piston below said uppermost groove of said plurality of ring grooves and above said pair of lower grooves of said plurality of ring grooves;

wherein an upper-most portion of each of said pin bores is above a lower-most portion of said bottom groove, and

wherein said upper apex of said combustion bowl is located between an uppermost portion of said uppermost groove and a lower most portion of said uppermost groove;

wherein said skirt panels are joined to said pin bosses by strut portions, and at least one of said strut portions having an opening.

2. The piston of claim 1 wherein said uppermost surface has an outer diameter and wherein said skirt panels are on opposite sides of said pin bore axis and wherein each of said skirt panels has a radially extending thickness ranging from about 2.0% to 3.0% of said outer diameter.

3. The piston of claim 2 wherein said combustion bowl wall thickness is about 2.5% to 4.0% of said outer diameter.

4. The piston of claim 1 wherein a compression height extends between said pin bore axis and said uppermost surface and said uppermost surface has an outer diameter, said compression height having a ratio to said outer diameter between about 38% to 45%.

5. The piston of claim 1 wherein said top part and said bottom part extend along a longitudinal central axis and said cooling gallery is non-concentric with said longitudinal central axis.

6. The piston of claim 5 wherein said combustion bowl wall has a uniform thickness.

7. The piston of claim 5 wherein said cooling gallery is asymmetrical about said longitudinal central axis.

8. The piston of claim 5 wherein said cooling gallery has an oil inlet with an oil deflector cast as one piece with said bottom part, said oil deflector extending radially across said oil inlet to substantially bifurcate said oil inlet.

9. The piston of claim 1 wherein said top part and said bottom part extend along a longitudinal central axis and said cooling gallery undulates relative to said longitudinal central axis.

10. The piston of claim 9 wherein said cooling gallery has a floor, said floor rising in smooth undulating fashion over said pin bores.

11. The piston of claim 1 wherein said pair of skirt panels are diametrically opposite one another, each of said skirt panels having opposite sides extending generally parallel to a central longitudinal axis and being operably joined to said pin bosses, each of said skirt panels having a continuously varying wall thickness extending between said opposite sides.

12. The piston of claim 11 wherein each of said skirt panels have central regions between said opposite sides, said central regions having a thickness about 5% less than a thickness of said skirt panels at said opposite sides.

13. The piston of claim 1 wherein said recessed groove walls extend uninterruptedly along entire circumferentially extending widths of said skirt panels.

14. The piston of claim 1 , wherein said bottom groove is discontinuous across said pin bosses.

15. A piston for an internal combustion engine, comprising:

a top part having an uppermost surface with annular inner and outer upper joining surfaces depending from said uppermost surface;

a bottom part having a pair of pin bosses providing a pair of laterally spaced pin bores axially aligned along a pin bore axis and having a pair of upwardly extending annular inner and outer lower joining surfaces joined by separate respective inner and outer weld joints to said inner and outer upper joining surfaces with an annular cooling gallery formed radially between said upper joining surfaces and radially between said lower joining surfaces, said top part and said bottom part forming a piston head region having an outer diameter;

at least one of said top and bottom parts including a ring belt with a plurality of ring grooves for receiving piston rings, said ring grooves including an uppermost groove, a pair of lower grooves below said uppermost groove, and a bottom groove below said pair of lower grooves and above a pair of skirt panels for additional weight reduction, wherein an upper-most portion of each of said pin bores is above a lower-most portion of said bottom groove;

wherein said top part is made from a different material than said bottom part and is friction welded to said bottom part through a friction welded joining surface extending transversely across the piston below said uppermost groove of said plurality of ring grooves and above said pair of lower ring grooves of said plurality of ring grooves;

a compression height extending between said uppermost surface of said top part and said pin bore axis, said compression height ranging between about 38% to 45% of said piston head region outer diameter;

wherein at least one of said top and bottom parts includes a combustion bowl; and

wherein said upper apex of said combustion bowl is located between an upper most portion of said uppermost groove and a lower most portion of said uppermost groove.

16. The piston of claim 15 wherein said combustion bowl is in said bottom part and wherein said combustion bowl includes a combustion bowl wall which has a uniform thickness.

17. The piston of claim 15 wherein said top part and said bottom part extend along a longitudinal central axis and said cooling gallery is non-concentric with said longitudinal central axis.

18. The piston of claim 17 wherein said cooling gallery is asymmetrical about said longitudinal central axis.

19. The piston of claim 17 wherein said cooling gallery has an oil inlet with an oil deflector cast as one piece with said bottom part, said oil deflector extending radially across said oil inlet to substantially bifurcate said oil inlet.

20. The piston of claim 15 wherein said top part and said bottom part extend along a longitudinal central axis and said cooling gallery undulates relative to said longitudinal central axis.

21. The piston of claim 20 wherein said cooling gallery has a floor provided by said bottom part, said floor rising in smooth undulating fashion over said pin bores.

22. The piston of claim 15 wherein said skirt panels are configured diametrically opposite one another, each of said skirt panels having opposite sides extending generally parallel to a central longitudinal axis and being operably joined to said pin bosses, each of said skirt panels having a continuously varying wall thickness extending between said opposite sides.

23. The piston of claim 22 wherein each of said skirt panels has a central region between said opposite sides, said central regions having a thickness about 5% less than a thickness of said skirt panels at said opposite sides.

24. A piston for an internal combustion engine, comprising:

a top part having an uppermost surface with annular inner and outer upper joining surfaces depending from said uppermost surface;

a bottom part having a pair of pin bosses providing a pair of laterally spaced pin bores aligned with one another along a pin bore axis and having a pair of upwardly extending annular inner and outer lower joining surfaces joined by separate respective inner and outer weld joints to said inner and outer upper joining surfaces with an annular cooling gallery formed radially between said upper joining surfaces and radially between said lower joining surfaces, said bottom part having a combustion bowl wall recessed below said uppermost surface, said combustion bowl wall having a thickness extending between an upper apex and a lower apex underlying said upper apex with an annular valley surrounding said upper apex and said lower apex;

at least one of said top and bottom parts including a ring belt with a plurality of ring grooves for receiving piston rings, said ring grooves including an uppermost groove, a pair of lower grooves below said uppermost groove, and a bottom groove below said pair of lower grooves and above a pair of skirt panels for additional weight reduction wherein an upper-most portion of each of said pin bores is above a lower-most portion of said bottom groove;

wherein said top part is made from a different material than said bottom part and is friction welded to said bottom part through a friction welded joining surface extending transversely across the piston below said uppermost groove of said plurality of ring grooves and above said pair of lower ring grooves of said plurality of ring grooves;

wherein said bottom has a back wall presenting a convex shape; and

wherein said upper apex of said combustion bowl is located between an upper most portion of said uppermost groove and a lower most portion of said uppermost groove.