Two main-units comprise the hydraulic part of the steering. These are the piston / cylinder, and the Control Valves with rotating union.
Piston / cylinder unit :
|Valves with Rotating Union :
|No movement of the steering wheel :
The fork is at rest and the pressure-control slide-valves are also in equilibrium, closing the inlet ports in the valve block.
|Movement of the Steering Wheel :
When the wheel is turned, this leads to a movement of the slide-valves in relation to their sleeves in the valve block. One slide-valve moves down, the other rises.
The valve which moves down connects high-pressure to one side of the piston.
The second slide-valve which rises, allows the fluid on the other side of the piston to return to the reservoir.
|Stopping of the Steering Wheel :
When the rack moves it turns the pinion, which moves the sleeves, in which the control slide-valves are situated, in the direction which would tend to make the valves return to the cut off position.
As long as the driver turns the steering wheel he holds the slide-valves in the open position, but when he ceases to turn, the sleeves return to their cut off position in relation to the slide-valves and the rack stops moving.
|Residual Pressure :
A residual pressure is maintained on either side of the piston when the steering is at rest. This pressure is maintained by the pressure-distributor valve assembly and its value is a function of the position of the pressure-control slide-valves in their sleeves. (The Crossover pressures).
NOTE : A dash-pot is situated under each slide-valve.
Mechanical Linkage :