Patent ID: 7954561

Claim:
A direction adjustment tool for a downhole drilling apparatus, the tool comprising: a tubular housing adapted to be incorporated into a downhole drilling apparatus; a plurality of steering pushers slidably mounted to said housing, wherein each said steering pusher is moveable between a respective extended position in which said steering pusher engages a wall of a borehole formed by the drilling apparatus, and a respective retracted position, in which the steering pusher does not engage the wall of the borehole; a hollow rotary shaft adapted to be incorporated into the drilling apparatus for transmitting drive to a drill bit of the drilling apparatus, wherein the shaft defines a passage for transmitting drilling fluid to the drill bit; at least one first pressure chamber defined between said housing and said shaft and communicating with said passage, wherein at least one said steering pusher is adapted to be moved from the retracted position to the extended position thereof as a result of increase of fluid pressure in at least one respective said first pressure chamber; a pendulum member pivotably mounted relative to the housing such that a longitudinal axis of the pendulum member extends in a substantially vertical direction when said shaft is not rotating relative to the housing and when a longitudinal axis of the shaft extends in a substantially vertical direction; a control mechanism adapted to prevent movement of at least one said steering pusher to the extended position thereof as a result of the angle between the longitudinal axis of the shaft and the longitudinal axis of the pendulum member exceeding a predetermined amount, in order to cause at least one said steering pusher to adjust the direction of drilling of the drilling apparatus towards a substantially vertical direction and/or to resist movement of the direction of drilling away from a substantially vertical direction; and a plurality of second pressure chambers, wherein at least one said steering pusher is adapted to move from the retracted position to the extended position thereof as a result of increase of fluid pressure in at least one respective said second pressure chamber, and said control mechanism comprises a plurality of pistons, wherein each said piston communicates with at least one said first pressure chamber and at least one said second pressure chamber and has a first condition in which the piston does not engage the pendulum member and increase of fluid pressure in a said first pressure chamber communicating with said piston causes said piston to move relative to the housing to increase pressure in the or each second pressure chamber communicating with said piston to move the corresponding steering pusher to the extended position thereof, and a second condition in which the piston engages the pendulum member to limit movement of said piston relative to the housing to prevent movement of the corresponding steering pusher to the extended position thereof.