Brak...it is an electrically driven hydraulic pump which actuates the linear piston. The ram is tied to the steering quadrant through a bolted joint. Valving takes it out of the circuit when the AP is not steering and the ram merely slides freely back and forth. It is much faster than the screw type mechanisms and I believe more powerful and reliable under long term load.
curious. that was always something I wondered. I have hydraulic steering and autopilot and there it is simple - if steering does not move the ram - autopilot pump does. I had trouble simulating the separate ram behavior (I connected one side to the other - but could not get it to move freely).
Anyway, I see the point and it looks like a nice all in one setup.