Active steering systems

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The term active steering systems refers to steering devices of motor vehicles in which the steering angle of the steered wheels can be adjusted by a mechatronic system . Depending on the steered axle , a distinction is made between active front axle steering, also known as Active Front Steering (AFS), and active rear axle steering. By installing active steering systems, it is possible to integrate various driver assistance systems , some of which are already in use or are in development:

Active front axle steering

Active front axle steering enables steering intervention on the front axle independent of the steering wheel angle. This intervention takes place either via the actuators of a steer-by-wire system or by means of an electronically controlled superposition of an angle to the steering wheel angle. In today's vehicles with active front-axle steering, only superimposition systems are used, as these guarantee steerability via the mechanical connection between the steering wheel and the steering gear if the electronic system fails. By Directive 70/311 / EEC is mandatory that the steerability of the vehicle are maintained must, "even if the hydraulic, pneumatic or electrical components of the transmission fail completely or in part." The revision of ECE Regulation R79 in 2006 however, it is "possible to use steering systems without a positive mechanical connection between the actuating device and the running wheels".

Superimposition steering

In the case of superimposed steering, an angle is superimposed on the steering wheel angle; the angle of rotation at the input of the steering gear then no longer corresponds to the angle of the steering wheel. On the one hand, this enables the steering ratio to be continuously adjusted: For maneuvering at low speeds, a direct ratio is set so that the driver needs fewer turns of the steering wheel when parking. On the other hand, when driving on the motorway, the driver can carefully control the vehicle through an indirect transmission. On the other hand, the superposition also allows rapid dynamic driving interventions by changing the wheel angle while driving while the steering wheel angle remains the same. This functionality is used in the context of a vehicle dynamics control.

To superimpose the steering angle, a superposition plate is required, which consists of a superposition gear, an electric motor and an electromechanical lock. In conjunction with the electric motor, the superposition gear enables an angle to be set on the output shaft (to the pinion of the steering gear) which differs from the angle of the input shaft (from the steering wheel). If the electrical system fails, the gearbox is locked by the lock that is closed when the power is off. In the locked state, the output shaft rotates directly with the input shaft.

History and Outlook

A superimposed steering system developed together with ZF Lenksysteme GmbH was first introduced by BMW in a series vehicle in 2003. The system is available in various models of the 3, 5, 6 and 7 series as well as in the X5 and X6 under the sales name Active Steering or in combination with a rear axle slip control (5 series (F10 / F11) or 5 series GT (F07), 6 series ( F12 / F13) and 7 series (F01 / F02)) are offered under the sales name integral active steering. With active or integral active steering, the angles are superimposed on the front axle via a planetary gear . To do this, an electric motor drives the planet carrier. Due to the unequal ratios of the input and output shafts of the planetary gear (through drive ratio ≠ 1), a relative movement occurs between the two shafts, which represents the angular superposition. A constant angular superposition therefore always takes place even when the electric motor is not rotating, i.e. purely mechanically. Active steering received the German Business Innovation Prize in January 2004 .

The system presented by Audi AG for the first time in 2007 in the Audi A4 under the sales name dynamic steering uses a harmonic drive transmission as a superimposed transmission . The dynamic steering was developed by ZF Lenksysteme GmbH in cooperation with AUDI AG.

Further developments combine the properties of superimposed steering (e.g. dynamic steering) with the properties of torque superposition (electromechanical steering - EPS). This enables steer-by-wire- like functions to be implemented without its disadvantages. So z. B. the front wheels can be steered without turning the steering wheel.

Individual evidence

  1. ↑ ECE regulation R79: Steering systems. Correction of January 20, 2006
  2. ↑ ATZ special issue Audi Q5, p. 68 atzonline.de ( Memento from November 28, 2009 in the Internet Archive )
  3. ↑ ATZ special issue Audi Q5, p. 70
  4. ↑ Active steering in the BMW 5 and 6 Series. ( Memento of September 27, 2011 in the Internet Archive ) ATZ online, accessed on August 25, 2010
  5. ↑ ATZ special issue Audi Q5, p. 70

literature

  • Braess / Seiffert (ed.): Vieweg Handbook Automotive Technology. 5th, revised and expanded edition. Vieweg & Sohn Verlag, Wiesbaden 2007, ISBN 978-3-8348-0222-4
  • ATZ - Automobiltechnische Zeitschrift: Dynamic steering in the Audi Q5. ATZ special issue no .: 2008-02. Springer Automotive Media, Wiesbaden 2008
  • Pfeffer, Peter; Harrer, Manfred: Steering manual , Vieweg + Teubner, 2011, ISBN 978-3-8348-0751-9