A cylinder realizing reduced reciprocation friction between a piston ring and a bore surface of the cylinder in a region where the piston ring slides. The cylinder in which a piston slides on a bore surface of the cylinder. A plurality of recesses is formed in a stroke center region in the bore surface of the cylinder. The stroke center region is a region between an under face position of a ring groove for a bottom piston ring at a top dead center of the piston and a top face position of a ring groove for a top piston ring at a bottom dead center of the piston. The total of areas of all of the recesses is in the range of 1% to 80% when an area of the stroke center region is 100%, and the recesses are not formed in a region other than the stroke center region of the bore surface of the cylinder.
1. A cylinder in which a piston slides on a bore surface of the cylinder, wherein a plurality of recesses is formed in a stroke center region in the bore surface of the cylinder, the stroke center region is a region between an under face position of a ring groove for a bottom piston ring at a top dead center of the piston and a top face position of a ring groove for a top piston ring at a bottom dead center of the piston,
total of areas of all of the recesses is in the range of 1% to 80% when an area of the stroke center region is 100%, and
the recesses are not formed in a region other than the stroke center region of the bore surface of the cylinder.
2. The cylinder according to claim 1 , wherein a cylinder liner is fixed on an inside of the cylinder, and the plurality of recesses is formed in the bore surface of the cylinder liner.
3. The cylinder according to claim 1 , wherein at least one of the plurality of recesses is formed in each of cross-sections of a cylinder circumferential direction, in the stroke center region.
4. The cylinder according to claim 2 , wherein at least one of the plurality of recesses is formed in each of cross-sections of a cylinder circumferential direction, in the stroke center region.
5. The cylinder according to claim 1 , wherein a ten-point-height of roughness profile Rz, specified by JIS B0601-1994, in the region where the recesses are not formed, in the stroke center region is 4 μm or less.
6. The cylinder according to claim 2 , wherein a ten-point-height of roughness profile Rz, specified by JIS B0601-1994, in the region where the recesses are not formed, in the stroke center region is 4 μm or less.
7. The cylinder according to claim 4 , wherein a ten-point-height of roughness profile Rz, specified by JIS B0601-1994, in the region where the recesses are not formed, in the stroke center region is 4 μm or less.
8. The cylinder according to claim 1 , wherein an average length in cylinder axial directions of the recesses is equal to or less than a length in a cylinder axial direction of the top piston ring among piston rings used.
9. The cylinder according to claim 2 , wherein an average length in cylinder axial directions of the recesses is equal to or less than a length in a cylinder axial direction of the top piston ring among piston rings used.
10. The cylinder according to claim 4 , wherein an average length in cylinder axial directions of the recesses is equal to or less than a length in a cylinder axial direction of the top piston ring among piston rings used.
11. The cylinder according to claim 7 , wherein an average length in cylinder axial directions of the recesses is equal to or less than a length in a cylinder axial direction of the top piston ring among piston rings used.
12. The cylinder according to claim 1 , wherein an average length in cylinder radial directions of the recesses is in the range of 2 μm to 1,000 μm.
13. The cylinder according to claim 2 , wherein an average length in cylinder radial directions of the recesses is in the range of 2 μm to 1,000 μm.
14. The cylinder according to claim 4 , wherein an average length in cylinder radial directions of the recesses is in the range of 2 μm to 1,000 μm.
15. The cylinder according to claim 7 , wherein an average length in cylinder radial directions of the recesses is in the range of 2 μm to 1,000 μm.
16. The cylinder according to claim 11 , wherein an average length in cylinder radial directions of the recesses is in the range of 2 μm to 1,000 μm.
17. The cylinder according to claim 1 , wherein the cylinder is used for an internal combustion engine.
18. The cylinder according to claim 2 , wherein the cylinder is used for an internal combustion engine.
19. The cylinder according to claim 4 , wherein the cylinder is used for an internal combustion engine.
20. The cylinder according to claim 7 , wherein the cylinder is used for an internal combustion engine.
21. The cylinder according to claim 11 , wherein the cylinder is used for an internal combustion engine.
22. The cylinder according to claim 16 , wherein the cylinder is used for an internal combustion engine.