Lightweight nodular iron crankshaft for heavy duty engine

A casting, comprising:

• an automobile vehicle crankshaft casting of a nodular iron including:
• multiple main journals coaxially aligned on a common crankshaft axis;
• multiple crankpin journals fixedly connected to the main journals by individual webs;
• and
• multiple counterweights fixedly connected to the casting;
• multiple lightening holes, wherein the multiple main journals each include one of the multiple lightening holes integrally formed therein during casting and individual ones of the multiple crankpin journals each include one of the multiple lightening holes integrally formed therein during casting;
• the multiple lightening holes of the multiple crankpin journals having a V-shaped geometry and having a bottom V-section disposed between a first opening end and a second opening end;
• and
• a bubble space that forms an indent in selected ones of the multiple lightening holes, wherein the bubble space is located proximate to a mid-portion of selected ones of the multiple lightening holes of the multiple crankpin journals, the bubble space outwardly directed with respect to the common crankshaft casting axis and oppositely positioned away from the bottom V-section, the bubble space including a top surface and a bottom surface, the bottom surface positioned closer to the common crankshaft casting axis than the top surface, the top surface having a first concave-shaped transition surface located proximate to and facing toward the first opening end, wherein the first concave-shaped transition surface transitions into a first convex-shaped surface which further transitions into a straight segment opposite to the bottom V-section, wherein the straight segment transitions into a second convex-shaped surface which further transitions into a second concave-shaped transition surface located proximate to and facing toward the second opening end, the bottom surface having a third concave-shaped transition surface located proximate to and facing toward the first opening end, wherein the third concave-shaped transition surface transitions into a bottom straight segment proximate-to the bottom V-section, wherein the bottom straight segment transitions into a fourth concave-shaped transition surface located proximate to and facing toward the second opening end, the bubble space locally increasing a passage size of the selected ones of the multiple lightening holes and reducing a mass of the individual ones of the multiple crankpin journals, wherein a skin surface of the bubble space is approximately 0.5 mm deep and reduces at least one material property of the crankshaft casting.

A method to produce an automobile vehicle crankshaft, comprising:

• creating a casting of a nodular iron including:
• coaxially aligning multiple main journals on a common crankshaft axis;
• and
• fixedly connecting multiple crankpin journals between successive ones of the multiple main journals by individual webs;
• forming multiple lightening holes, wherein individual ones of the multiple lightening holes are formed within individual ones of the multiple crankpin journals during casting, wherein each of the multiple lightening holes is V-shaped having a bottom V-section disposed between a first opening end and a second opening end;
• and
• locating a bubble space that forms an indent in selected ones of the multiple lightening holes proximate to a mid-portion of selected ones of the multiple lightening holes, the bubble space outwardly directed with respect to the common crankshaft casting axis and oppositely positioned away from the bottom V-section, the bubble space including a top surface and a bottom surface, the bottom surface positioned closer to the common crankshaft casting axis than the top surface, the top surface having a first concave-shaped transition surface located proximate to and facing toward the first opening end, wherein the first concave-shaped transition surface transitions into a first convex-shaped surface which further transitions into a straight segment opposite to the bottom V-section, wherein the straight segment transitions into a second convex-shaped surface which further transitions into a second concave-shaped transition surface located proximate to and facing toward the second opening end, the bottom surface having a third concave-shaped transition surface located proximate to and facing toward the first opening end, wherein the third concave-shaped transition surface transitions into a bottom straight segment proximate-to the bottom V-section, wherein the bottom straight segment transitions into a fourth concave-shaped transition surface located proximate to and facing toward the second opening end, the bubble space locally increasing a passage size of the selected ones of the multiple lightening holes and thereby reducing a mass of the individual ones of the multiple crankpin journals, wherein a skin surface of the bubble space is approximately 0.5 mm deep and reduces at least one of a Young's modulus, a tensile strength and a fatigue strength at the skin surface.