| 摘要 |
This invention relates to a drive system of the type which is suitable for use with a downhole used in oil well interventions. The invention provides an improved tractor whose speed is controllable remotely, such as from the well bore surface, using hydraulic media pumped to vary the speed of the tractor. The drive system comprises an expander assembly which is arranged around and attached to a rotor casing. The assembly comprises a mandrel (shaft) having first and second opposing threaded portions arranged coaxially. Each threaded portion is housed in an expander follower. In use, the mandrel rotates in a first sense and the first and second expander followers are driven apart one from another. When the mandrel rotates in the opposite sense the first and second expander followers are driven towards one another. |
