Crankshaft for reciprocating engine

1. A crankshaft for a reciprocating engine, the crankshaft comprising:

journals that define a central axis of rotation;

crank pins that are eccentric with respect to the journals;

crank arms connecting the journals to the crank pins; and

counterweights integrated with the crank arms,

wherein the journals, the crank pins, the crank arms, and the counterweights are integrated into a seamless body,

wherein the crankshaft is to be mounted in a reciprocating engine; and

wherein each of the crank arms has a first recess and a second recess in a surface adjacent to the crank pin, the first recess and the second recess spaced apart from each other and disposed inward of peripheral regions in both sides along an edge of the surface, the peripheral regions are thicker than the first and second recesses, the first recess and the second recess disposed along the peripheral regions, thereby making a central region inward of the first recess and the second recess thick.

2. The crankshaft for a reciprocating engine according to claim 1 , wherein the first recess and the second recess are symmetric with respect to a line connecting an axis of the journal to an axis of the crank pin.

3. A crankshaft for a reciprocating engine, the crankshaft comprising:

journals that define a central axis of rotation;

crank pins that are eccentric with respect to the journals;

crank arms connecting the journals to the crank pins; and

counterweights integrated with the crank arms,

wherein the crankshaft is to be mounted in a reciprocating engine; and

wherein each of the crank arms has a first recessed portion and a second recessed portion in a surface adjacent to the crank pin, the first recessed portion and the second recessed portion disposed inward of peripheral regions in both sides along an edge of the surface, each of the first and second recessed portions including a free end portion, which is disposed outward of an edge of the journal and between an axis of the crank pin and the central axis of rotation when viewed from a direction along the central axis of rotation, the peripheral regions are thicker than the first and second recessed portions, the first recessed portion and the second recessed portion disposed along the peripheral regions, thereby making a central region inward of the first recessed portion and the second recessed portion thick, wherein the first recessed portion and the second recessed portion are connected together at a center of rotation of the crankshaft so as to form a u-shaped recess.

4. The crankshaft for a reciprocating engine according to claim 3 , wherein the first recessed portion and the second recessed portion are symmetric with respect to a line connecting an axis of the journal to the axis of the crank pin.

5. A crankshaft for a reciprocating engine, the crankshaft comprising:

journals that define a central axis of rotation;

crank pins that are eccentric with respect to the journals;

crank arms connecting the journals to the crank pins; and

counterweights integrated with the crank arms,

wherein the crankshaft is to be mounted in a reciprocating engine; and

wherein each of the crank arms has a first recessed portion and a second recessed portion in a surface adjacent to the crank pin, the first recessed portion and the second recessed portion disposed inward of peripheral regions in both sides along an edge of the surface, each of the first and second recessed portions including a free end portion, which is disposed outward of an edge of the journal and between an axis of the crank pin and the central axis of rotation when viewed from a direction along the central axis of rotation, the peripheral regions are thicker than the first and second recessed portions, the first recessed portion and the second recessed portion disposed along the peripheral regions, thereby making a central region inward of the first recessed portion and the second recessed portion thick, wherein the first recessed portion and the second recessed portion are connected together at a position shifted toward the crank pin from a center of rotation of the crankshaft so as to form a u-shaped recess.

6. The crankshaft for a reciprocating engine according to claim 5 , wherein the first recessed portion and the second recessed portion are symmetric with respect to a line connecting an axis of the journal to the axis of the crank pin.

7. A crankshaft for a reciprocating engine, the crankshaft comprising:

journals that define a central axis of rotation;

crank pins that are eccentric with respect to the journals;

crank arms connecting the journals to the crank pins; and

counterweights integrated with the crank arms,

wherein the crankshaft is to be mounted in a reciprocating engine; and

wherein each of the crank arms has a first recessed portion and a second recessed portion in a surface adjacent to the crank pin, the first recessed portion and the second recessed portion disposed inward of peripheral regions in both sides along an edge of the surface, each of the first and second recessed portions including a free end portion, which is disposed outward of an edge of the journal and between an axis of the crank pin and the central axis of rotation when viewed from a direction along the central axis of rotation, the peripheral regions are thicker than the first and second recessed portions, the first recessed portion and the second recessed portion disposed along the peripheral regions, thereby making a central region inward of the first recessed portion and the second recessed portion thick, wherein the first recessed portion and the second recessed portion are extended along the edge of the journal and are connected together at a position shifted toward the counterweight from a center of rotation of the crankshaft so as to form a u-shaped recess.

8. The crankshaft for a reciprocating engine according to claim 7 , wherein the first recessed portion and the second recessed portion are symmetric with respect to a line connecting an axis of the journal to the axis of the crank pin.