Crankcase of an engine

1. A crankcase of an engine having a crankshaft therein, comprising:

a skirt part formed in a circumferential direction of the crankshaft; and

plural stiffening ribs provided on a wall surface of the skirt part as inclined at a predetermined degree angle to the axis of the crankshaft, said predetermined degree angle having a non-zero vertical component perpendicular to said crankshaft and a non-zero horizontal component parallel to said crankshaft,

wherein a stiffening rib in said plural stiffening ribs extends from a first side of the skirt part to a second side of the skirt part.

2. The crankcase of an engine according to claim 1 , wherein the stiffening ribs are provided on the wall surface of the skirt part in different directions than each other, and are arranged in a lattice.

3. The crankcase of an engine according to claim 1 , wherein said stiffening ribs are inclined at an elevation angle of approximately 45 degrees to an axis of said crankshaft.

4. The crankcase of an engine according to claim 1 , wherein said stiffening ribs are inclined at a depression angle of approximately 45 degrees to an axis of said crankshaft.

5. The crankcase of an engine according to claim 1 , wherein said stiffening ribs extend from said first side of said skirt part to said second side of said skirt part at equal intervals.

6. The crankcase of an engine according to claim 1 , wherein said stiffening ribs are disposed on an outer surface of said skirt part.

7. A crankcase of an engine having a crankshaft therein, comprising:

a skirt part formed in a circumferential direction of the crankshaft;

plural stiffening ribs provided on a wall surface of the skirt part as inclined at a predetermined degree angle to the axis of the crankshaft, said predetermined degree angle having a non-zero vertical component perpendicular to said crankshaft and a non-zero horizontal component parallel to said crankshaft; and

a joint part provided on one side of the skirt part for connecting the skirt part with a bearing cover supporting the crankshaft, wherein an end of the stiffening rib is set at a same position as the joint part.

8. A crankcase of an engine having a crankshaft therein, comprising:

a skirt part formed in a circumferential direction of the cranksbaft;

plural stiffening ribs provided on a wall surface of the skirt part as inclined at a predetermined degree angle to the axis of the crankshaft, said predetermined degree angle having a non-zero vertical component perpendicular to said crankshaft and a non-zero horizontal component parallel to said crankshaft; and

a joint part provided on one side of the skirt part for connecting the skirt part with a bearing cover supporting the crankshaft, wherein an end of the stiffening rib is set at a same position as the joint part.

9. The crankcase of an engine according to claim 8 , wherein an intersection point of the end of the stiffening ribs arranged in the lattice is set at the same position as the joint part.

10. A crankcase of an engine having a crankshaft therein, comprising:

a skirt part formed in a circumferential direction of the crankshaft; and

plural stiffening ribs provided on a wall surface of the skirt part as inclined at a predetermined degree angle to the axis of the crankshaft, said predetermined degree angle having a non-zero vertical component perpendicular to said crankshaft and a non-zero horizontal component parallel to said crankshaft,

wherein the crankcase comprises a circularly abutting surface, said circularly abutting surface comprising fastener holes.

11. The crankcase of an engine according to claim 10 , further comprising a bearing cover abutted on said abutting surface.

12. A crankcase of an engine having a crankshaft therein, comprising:

a skirt part formed in a circumferential direction of the crankshaft; and

plural stiffening ribs provided on a wall surface of the skirt part as inclined at a predetermined degree angle to the axis of the crankshaft, said predetermined degree angle having a non-zero vertical component perpendicular to said crankshaft and a non-zero horizontal component parallel to said crankshaft,

wherein said stiffening ribs are disposed on an inner surface of said skirt part.

13. A crankcase of an engine having a crankshaft therein, comprising:

a skirt part formed in a circumferential direction of the crankshaft;

a first set of stiffening ribs; and

a second set of stiffening ribs,

wherein said first set of stiffening ribs and said second set of stiffening ribs are provided on a wall surface of the skirt part inclined at a predetermined degree angle to an axis of the crankshaft,

wherein said predetermined degree angle has a non-zero vertical component perpendicular to said crankshaft and a non-zero horizontal component parallel to said crankshaft, and

wherein a stiffening rib in said first set of stiffening ribs and said second set of stiffening ribs extends from a first side of the skirt part to a second side of the skirt part at equal intervals.

14. The crankcase of an engine according to claim 13 , wherein said first set of stiffening ribs are perpendicular to said second set of stiffening ribs.

15. The crankcase of an engine according to claim 13 , wherein said first set of stiffening ribs are inclined at an elevation angle of approximately 45 degrees to the axial of said crankshaft.

16. The crankcase of an engine according to claim 13 , wherein said second set of stiffening ribs are inclined at a depression angle of approximately 45 degrees to the axial of said crankshaft.

17. The crankcase of an engine according to claim 13 , wherein said first set of stiffening ribs are provided on the wall surface of the skirt part in a different direction than said second set of stiffening ribs.

18. The crankcase of an engine according to claim 13 , wherein said first set of stiffening ribs and said second set of stiffening ribs form a lattice.

19. An engine comprising:

a crankshaft,

wherein said crankcase comprises:

a skirt part formed in a circumferential direction of the crankshaft;

a first set of stiffening ribs; and

a second set of stiffening ribs,

wherein said first set of stiffening ribs and said second set of stiffening ribs are provided on a wall surface of the skirt part inclined at a predetermined degree angle to an axis of the crankshaft,

wherein said predetermined degree angle has a non-zero vertical component perpendicular to said crankshaft and a non-zero horizontal component parallel to said crankshaft, and

wherein a stiffening rib in said first set of stiffening ribs and said second set of stiffening ribs extends from a first side of the skirt part to a second side of the skirt part at equal intervals.