US Patent 7219908 Steer wheel control system with stationary piston and reciprocating cylinder

A steering system control apparatus having a centering unit for resisting off-center movement of the steer wheels of a vehicle and returning them to a selected center position after each such movement. A centering shaft is connected to the steering shaft of a vehicle steering gear for rotational reciprocation therewith and an intermediate rotational position thereof defines a neutral position that is remotely adjustable by a trimming unit to vary the selected center position of the steering system during vehicle operation. A holding force and a return force are applied to the centering shaft by a pressurized cylinder arranged for reciprocal movement relative to a stationary piston.