| 摘要 |
<p>The present invention provides a directional drilling apparatus for use in the directional drilling of bore holes. In one embodiment the apparatus comprises a plurality of cutting elements movably mounted with respect to a rotatable body member, wherein the cutting elements are movable between first, radially retracted, positions and radially extended, positions for cutting. A rotary valve is provided for synchronising the movement of the cutting elements between their respective extended and retracted positions in accordance with the rotational position of the body member in the bore hole being drilled. Control of the directional drilling system is effected by synchronised movement of the cutting elements from an inner to an outer radial position in accordance with the angular position of the drill bit.</p> |
