Patent ID: 7118118

Claim:
An apparatus for positioning at least one steerable member connected to a steering shaft for movement to either side of a selected center position in response to rotational reciprocation of a steering shaft, said apparatus comprising resistance means for providing a holding force resisting steering forces tending to move said steerable member to either side of said center position, said resistance means comprising: a centering shaft and means for connecting said centering shaft to the steering shaft for rotational reciprocation around a shaft axis, a rotational position of said centering shaft defining a centering position corresponding to said selected center position; a first centering piston cooperating with a first centering cylinder to define a first centering chamber; a second centering piston cooperating with a second centering cylinder to define a second centering chamber, each of said first and second centering pistons being arranged to reciprocate independently of the other between a rest position and an active position for compressing a fluid within its corresponding chamber; actuator means comprising first push means for causing compressive movement of said first centering piston, second push means for causing compressive movement of said second centering piston, and arcuate means driven by said centering shaft for arcuate movement around an actuating axis to either side of a neutral position corresponding to said centering position in response to rotational reciprocation of said centering shaft, said arcuate means being arranged to engage each of said first and second push means independently of the other so that rotation of said centering shaft away from said centering position to one side causes compressive movement of said first centering piston without moving said second centering piston and rotation of said centering shaft away from said centering position to the other side causes compressive movement of said second centering piston without moving said first centering piston; and, centering fluid means for providing a pressurized fluid in each of said first and second centering chambers so that fluid pressure against said centering pistons provides said holding force by opposing movement of said steerable member toward either side of said selected center position and provides a return force continuously biasing said steerable member toward said selected center position during movement of said steerable member to either side of said selected center position, the rest position of each of said centering pistons corresponding to the neutral position of said arcuate means, and said fluid pressure causing each of said centering pistons to bias said arcuate means toward said neutral position during said compressive movement.