Steel piston with cooling gallery and method of construction thereof

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.

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.