Steering system with the hydraulic steering booster was designed to make control of the vehicle more comfortable and precise in different operating modes. In addition, it contributes to the safety of driving. There are 2 main types of the steering systems which are used in modern cars, namely the rack-and-pinion and worm-type.

Both can be equipped with a hydraulic booster.

The advantages of the power steering system over the steering without hydraulic booster are best felt when you are parking or driving at a low speed.

There can be distinguished 2 types of the power steering systems. The first has a constant coefficient of power assistance and the second, where the coefficient depends on the speed (SERVOTRONIC).


  1. Electronic speedometer (only systems with SERVOTRONIC).
  2. Electronic control unit (only systems with SERVOTRONIC).
  3. Electro-hydraulic converter (only systems with SERVOTRONIC).
  4. Steering unit, equipped with a hydraulic cylinder.
  5. Hydraulic pump.
  6. Hydraulic fluid reservoir.
  7. High pressure oil line.
  8. Low pressure oil line.


So how does it work? Let’s take the rack-and-pinion steering system for example.

Hydraulic fluid flows from its reservoir (6) to the hydraulic steering pump (5) where it is compressed. The liquid travels under pressure through the high pressure oil line (8) (hose or pipe) and enters the steering unit (4) under the pressure of 70-180 bar depending on the car model.

The steering unit is equipped with a distribution unit (the spool valve), which mainly functions in two modes:

System reaction

The spool valve unit combines the high pressure oil line and drain line. The fluid passively travels from the high pressure oil line to the oil reservoir (6).

System reaction

You turn the steering wheel and the oil lines in the spool valve switch correspondingly. The valve allows the fluid to the working cylinder, which creates power assistance (Hydraulic press principle). At this moment the piston’s back cavity joins with the low-pressure oil line, through which the fluid travels back to the reservoir. As soon as no effort is applied to the steering wheel the system returns to its neutral state (see point 1).


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