This system basically consists of a rack-and-pinion power steering system, a planetary gear, an electric motor, some sensors and a control unit. The additional degree of freedom allows continuous and situation-dependent variation of the steering ratio. Depending on the driving situation, the effective steering angle at the wheels is therefore greater or smaller than the driver sets at the steering wheel.


Code: 80874


The active steering provides increased comfort and more active safety. It makes a steering intervention on the front axle independent of the driver possible without having to separate the mechanical coupling between the steering wheel and the front axle.

The system essentially comprises:

  1. a rack-and-pinion power steering
  2. a planetary transmission
  3. an electric motor
  4. some sensors and control unit.

The additional degree of freedom makes continuous, situation-independent variation of the steering step-up possible.


  1. The drive pinion (2) can be turned on the star handle (1, steering wheel). The gear rack (3) with plunger (4) moves to the left or the right.
  2. The stepped planetary wheels (5) turn in the worm gear (6). The worm gear is locked via the worm (7) and the electromagnetic lock (8).
  3. If you pull the armature of the lock upwards with a screwdriver, the lock is released and you can turn the knurled handle (10) on the electric motor (9). You now see how the worm gear is turned (clockwise or counter-clockwise) and how the step-up changes.
  4. When the star handle is turned, you also see how the rotary disk in the rotary disk valve moves and thus takes over the control of the hydraulic plungers (the torsion bar has not been pinned on the model in order to show this movement).

The following can also be seen on the model:

  • Hydraulic line connections (11, 12, 13)
  • Spring-loaded pressure plunger, which pushes the gear rack onto the pinion (14)
  • Electro-hydraulic converter (15)


  • Turning the steering wheel (star grip), function of the rotary slide valve, the gear rack moves, the piston moves. Thereby the step planetary wheels and the sun wheel rotate in the housing, because the worm wheel is locked by the electromechanical lock via the worm
  • When the electromechanical lock is unlocked (by an electromagnet, here by lifting the armature), the handle of the electric motor can be turned. Now the worm wheel rotates and the drive pinion moves the rack. The planetary gear adds or subtracts an adjustable motor angle to the driver angle. The sum of these two angles then acts on the drive pinion, which generates the wheel angle
  • Function of the solenoid valve on the Servotronic 2-rotary spool valve
  • Connection of the oil lines, function of the rack and pinion piston.