| 摘要 |
<p>A retraction system is described for allowing disengagement of retrieval latch dogs (114) of a down hole running tool (14) from a bit locking sleeve (18). The locking sleeve (18) is slidably retained within a drive sub (12) and includes a pair of slots (66) which are engaged by the retrieval latch dogs (114) when the tool (14) is used to retrieve bit segments (16) from the drive sub (12). The retraction system includes a sleeve (76) which is slidably mounted on a main body (74) of the tool (14) and spring (174) which is biased to push the sleeve (76) over the retrieval latch dogs (114). The sleeve (76) has a pair of diametrically opposed slots (235) through which the retrieval latch dogs can extend for contacting the inner surface (28) of the drive sub (12). The retraction system also includes a length (44) of the inner surface of the drive sub (12) which is made of progressively reducing diameter in the direction of retraction of the tool (14) from the drive sub (12). The upper end of each slot (235) is provided with a bevel (236) for directing the retrieval latch dogs (114) in the inward direction. To withdraw the tool (14) from the drive sub (12), the retrieval latch dogs (114) are disengaged from the bit locking sleeve (18) by the combined action of the shape of surface portion (44) which acts to push the retrieval latch dogs (114) inwardly, together with the force of spring (174) and the bevelled surfaces (236) which act to push the sleeve (74) over the retrieval latch dogs (114) thereby disengaging it from the bit locking sleeve (18).</p> |
