Piston
A ferrous piston for gasoline powered engines having dimensions which achieve reduced mass and improved performance is provided. The piston crown has a thickness of less than 4 mm and includes valve pockets with an axial clearance between the valve pockets and an uppermost ring groove of less than 1.5 mm. The pin bosses have an axial thickness of less than 3.7% of a bore diameter, which is the largest outer diameter of the piston, measured between a pin bore and the crown at 1 mm from an inner face forming the pin bore. Each pin boss has a radial thickness of less than 3% of the bore diameter measured between the pin bore and a lower end of the pin boss. An undercrown surface presents a projected area of less than 45% of a total piston bore area, wherein the total piston bore area is πBD 2 /4, BD being the bore diameter.
1. A piston, comprising:
a piston body and piston crown formed of a ferrous material;
said piston crown including a crown wall presenting an undercrown surface for being exposed to cooling oil during operation;
said piston body presenting a bore diameter being the largest outer diameter of said piston body;
said piston body including a pair of pin bosses extending from said piston crown, each of said pin bosses including an inner face forming a pin bore surrounding a pin bore axis;
each of said pin bosses having an axial thickness of less than 3.7% of said bore diameter measured between said pin bore and said piston crown at 1 mm from said inner face forming said pin bore;
each of said pin bosses having a radial thickness of less than 3% of said bore diameter measured between said pin bore and a lower end of said pin boss;
said piston crown including at least one valve pocket formed in said crown wall;
said piston crown including a ring belt extending from said upper surface, said ring belt including a plurality of ring grooves, wherein an axial clearance between said valve pocket and an uppermost one of said ring grooves is less than 1.5 mm;
wherein said piston does not include a closed oil cooling gallery along said undercrown surface; and
where said piston includes a window above the pin bore of each pin boss defining a passage for oil flow.
2. The piston of claim 1 , wherein said pin bores each have an upper half surface extending upwardly from said pin bore axis, said upper half surface presents a projected pin bore area being less than 10% of a total piston bore area, said total piston bore area being πBD 2 /4, wherein BD is said bore diameter.
3. The piston of claim 2 , wherein said inner faces forming said pin bores have a straight profile.
4. The piston of claim 1 , wherein said crown wall presents an upper surface for being exposed to combustion.
5. The piston of claim 4 , wherein said hollowed regions extend to within 2 mm of said undercrown surface.
6. The piston of claim 1 , wherein each of said hollowed regions is bridged by a pair of pin boss piers, and each of said pin boss piers has a thickness of less than 9.5% of said bore diameter.
7. The piston of claim 1 , wherein said crown wall presents an upper surface for being exposed to combustion, and said piston has a compression height measured from said pin bore axis to said upper surface of less than 30% of said bore diameter.
8. The piston of claim 1 , including a pair of skirts depending from said piston crown and spaced from one another by said pin bosses, each of said skirts having an outer surface providing a projected skirt area, a combined projected skirt area of said skirts is less than 40% of a total piston bore area, said total piston bore area being πBD 2 /4, wherein BD is said bore diameter.
9. The piston of claim 8 , wherein said combined projected skirt area is 27% to 34% of said total piston bore area.
10. The, piston of claim 8 , wherein each of said skirts includes a chord width of 30% to 60% of said bore diameter, said skirts increase in width from said chord width to said piston crown, and said skirts increase in width from said cord width to a lower end of said skirts.
11. The piston of claim 8 , wherein said skirts include panels being inwardly or outwardly curved from a plane by at least 0.7 mm and skirt wings projecting beyond said panels by more than 1 mm.
12. The piston of claim 8 , including at least one stiffening rib disposed along an undercrown surface of said piston crown, and/or one of said skirts.
13. The piston of claim 1 , wherein said crown wall presents an upper surface for being exposed to combustion, said crown wall having a crown wall thickness extending from said upper surface to said undercrown surface, said crown wall thickness being less than 4 mm;
said piston crown including a least one valve pocket formed in said crown wall; and
said piston crown including a ring belt extending from said upper surface, said ring belt including a plurality of ring grooves, wherein an axial clearance between said valve pocket and an uppermost one of said ring grooves is less than 1.5 mm.
14. The piston of claim 13 , wherein said undercrown surface presents a projected undercrown area of less than 45% of a total piston bore area, said total piston bore area is πBD 2 /4, BD being said bore diameter;
said pin bores each have an upper half surface extending upwardly from said pin bore axis, said upper half surface presents a projected pin bore area equal to less than 10% of said total piston bore area;
said inner faces forming said pin bores of said pin bosses have a straight profile;
said piston has a compression height measured from said pin bore axis to said upper surface of said piston crown of less than 30% of said bore diameter; and
further including a pair of skirts extending from said piston crown and spaced from one another by said pin bosses, and each of said skirts having an outer surface providing a projected skirt area, and a combined projected skirt area of said skirts is less than 40% of said total piston bore area.
15. The piston of claim 14 , wherein said ring grooves are spaced from one another by lands, said lands include a top land depending from said upper surface and having an axial thickness of less than 3% of said bore diameter, and a second land spaced from said top land by one of said ring grooves and having an axial thickness of less than 3.5% of said bore diameter;
said hollowed regions extend to within 2 mm of said undercrown surface;
each of said hollowed regions is bridged by a pair of pin boss piers, each of said pin boss piers having a thickness of less than 9.5% of said bore diameter;
said projected skirt area is 27% to 34% of said total piston bore area;
each of said skirts includes a chord width of 30% to 60% of said bore diameter, said skirts increase in width from said chord width to said piston crown, and said skirts increase in width from said cord width to a lower end of said skirts;
said skirts include panels inwardly or outwardly curved from a plane by at least 0.7 mm and skirt wings projecting beyond said panels by more than 1 mm; and
further including at least one stiffening rib disposed along an undercrown surface of said piston crown, and/or one of said skirts; and
a coating formed of manganese phosphate disposed on said inner faces of said pin bosses forming said pin bores.