Hydrostatic steering
A hydrostatic steering system (also called full-hydraulic steering) is a special design of the steering , in which the actual steering forces not by the vehicle operator, but by a from the engine of the vehicle driven hydraulic pump to be applied. It differs from hydraulic steering assistance ( power steering ) in that there is no mechanical connection between the steering wheel and the wheels to be steered, which means that the vehicle is much more flexible when it comes to making the connection, since only pipes or hoses are required to make the connection .
construction
A hydrostatic steering essentially consists of a so-called steering unit , which sits on the steering column and directs a certain amount of hydraulic fluid into the steering cylinder (s) according to the steering angle and steering direction, hydraulic lines and one or more hydraulic cylinders on the wheels to be steered. A hydraulic pump is required for the required pressure ; a so-called priority valve is also required to supply other hydraulic systems .
use
Such steering systems are mainly used in heavy commercial vehicles (e.g. combine harvesters , forklifts ). On the one hand, this extremely reduces the force to be applied by the driver , and on the other hand, it is also much easier to implement in vehicles with rear-wheel steering, as long shafts, linkages and deflection gears are not required.
disadvantage
Since the function of the steering depends on the pressure in the hydraulic circuit, a failure of the hydraulic pump could lead to serious accidents. For this reason, modern steering units are designed in such a way that if there is a pressure drop, the integrated metering pump works as a hand pump and thus the vehicle remains controllable. To avoid the problem of large steering forces, there are steering units with several sets of gears as metering pumps, one (or more) of which are switched off in an emergency in order to change the transmission ratio between the steering wheel and the wheels by reducing the delivery volume.