| 摘要 |
A downhole drilling tool comprises a drillstring and a drilling head. A freewheel (88) for transferring drive from the drillstring to the drilling head is positioned between the drillstring and the drilling head. The freewheel (88), comprises a first race (90), a second race (92), a guide ring (94) located between the first race and the second race, and at least one locking element (102) retained partly in a recess (100) of the first race and partly in a recess (98) of the guide ring. In use, the locking element moves between a locked position in which the locking element is forced into engagement with the second race and a release position in which the locking element is released from the second race. The locking element may be a ball bearing or a roller. |
