| 摘要 |
PCT No. PCT/SE97/01398 Sec. 371 Date Mar. 15, 1999 Sec. 102(e) Date Mar. 15, 1999 PCT Filed Aug. 25, 1997 PCT Pub. No. WO98/12410 PCT Pub. Date Mar. 26, 1998A coupling piece for use in drilling has a first connection (2) for connecting to an upper rotary percussion device (3), and a second connection (4) for connecting to a drill tube string (5) provided with an annular drill bit (23). The coupling piece has a first chamber (11) and a second chamber (12) separated by a piston. The pressure in the first chamber (11) is used to supply a lower percussion device (8) connected to a third connection (6) associated with the coupling piece with driving medium and for displacing the lower percussion device (8) towards the ground (15). The pressure in the second chamber (12) is used to decrease the force between the lower percussion device (8) and the ground (15) when further drill string elements are added to a drill string (7) of which the lower percussion device (8) forms a part. |
