| 摘要 |
Locking system (196) is provided for selectively locking an external sleeve (76) to a main body (74) of a downhole tool (14). Locking system (196) comprises a pair of opposed holes (198) formed in the main body (74). The holes (198) capture respective locking balls (200). A channel (210) extends from each hole (198) longitudinally about the outer surface of the main body (74). A spring (206) held within the main body (74) acts to push the balls (200) out of holes (198). Openings (212) are also formed in the sleeve (76) and disposed so that the balls (200) can protrude therethrough and contact the inner circumferential surface (28) of a drive sub (12) by virtue of the bias of spring (206). When the internal diameter of the drive sub (12) is relatively small, the balls (200) are pushed inwardly against the spring (206) and reside, at least partially, within holes (198). This prevents the balls from moving longitudinally about channels (210) thereby locking the sleeve (76) to the main body (74). However, when the internal diameter of the drive sub increases, the balls (200) are pushed radially outwardly by the spring (206) to the extent that they can then escape holes (198) and roll along channels (210). This allows the sleeve (76) to slide relative to the body (74).
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