| 摘要 |
PCT No. PCT/AU96/00526 Sec. 371 Date Feb. 27, 1998 Sec. 102(e) Date Feb. 27, 1998 PCT Filed Aug. 22, 1996 PCT Pub. No. WO97/08379 PCT Pub. Date Mar. 6, 1997A retraction system allows disengagement of retrieval latch dogs of a down hole running tool from a bit locking sleeve. The locking sleeve is slidably retained within a drive sub and includes a pair of slots which are engaged by the retrieval latch dogs when the tool is used to retrieve bit segments from the drive sub. The retraction system includes a sleeve which is slidably mounted on a main body of the tool and spring which is biased to push the sleeve over the retrieval latch dogs. The sleeve has a pair of diametrically opposed slots through which the retrieval latch dogs can extend for contacting the inner surface of the drive sub. The retraction system also includes a length of the inner surface of the drive sub which is made of progressively reducing diameter in the direction of retraction of the tool from the drive sub. The upper end of each slot is provided with a bevel for directing the retrieval latch dogs in the inward direction. To withdraw the tool from the drive sub, the retrieval latch dogs are disengaged from the bit locking sleeve by the combined action of the shape of surface portion which acts to push the retrieval latch dogs inwardly, together with the force of spring and the beveled surfaces which act to push the sleeve over the retrieval latch dogs thereby disengaging it from the bit locking sleeve.
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