Patent ID: 7717197

Claim:
An apparatus ( 10 ) for keeping a down hole drilling tool vertically aligned, comprising: a tubular cuter housing ( 12 ) having a first end ( 14 ), a second end ( 16 ), a longitudinal axis ( 18 ) and a circumferential wall ( 20 ) that defines an interior bore ( 22 ); centralizers ( 24 ) in spaced relation around the circumferential wall ( 20 ) at the second end ( 16 ) of the tubular housing ( 12 ), the centralizers ( 24 ) being pivotally mounted to the outer housing ( 12 ) for pivotal movement between an extended position and a retracted position; pistons ( 26 ) positioned in piston chambers ( 25 ) which are arranged radially in relation to the longitudinal axis ( 18 ), the pistons ( 26 ) having an extended position and a refracted position, the pistons ( 26 ) underlying each of the centralizers ( 24 ) such that, in the extended position the pistons ( 26 ) provide a force to urge the centralizers ( 24 ) to the extended position; a plurality of discrete drilling fluid chambers ( 30 ), each of the drilling fluid chambers ( 30 ) communicating with one of the piston chambers ( 28 ) of one of the pistons ( 26 ), the position of the piston ( 26 ) being controlled by a hydraulic pressure in the drilling fluid chamber ( 30 ), each of the drilling fluid chambers ( 30 ) having an inlet ( 32 ) through which drilling fluids enter and an outlet ( 34 ), the outlets for the drilling fluid chambers being arranged in an annular configuration; a tubular pendulum ( 36 ) having a circumferential wall ( 38 ), a first end ( 40 ), and a second end ( 42 ), the first end ( 40 ) being pivotally secured within the interior bore ( 22 ) of the outer housing ( 12 ) for omni-directional pivotal movement, the pendulum ( 36 ) moving from a concentric pivotal position to an angularly offset pivotal position by force of gravity as the outer housing ( 12 ) deviates from a vertical orientation, such that, as the pendulum ( 36 ) moves between the concentric pivotal position and the angularly offset pivotal position, the pendulum ( 36 ) adjusts the hydraulic pressure in at least one drilling fluid chamber ( 30 ) by physically restricting flow of fluid in one of the concentric pivotal position or the angularly offset position and allowing the flow of fluid through the corresponding outlet ( 34 ) of the at least one drilling fluid chamber ( 30 ) in another of the concentric pivotal position or the angularly offset position, such that, as the hydraulic pressure changes, the piston ( 26 ) in communication with the at least one drilling fluid chamber ( 30 ) adjusts the position of the centralizers ( 24 ) until the outer housing ( 12 ) returns to the vertical position.