ZF Active Steering on New BMW 5-Series

Driving Dynamics and Safety Increased Through New System

FRIEDRICHSHAFEN, Germany, July 30 -- ZF Lenksysteme -- a division of ZF Friedrichshafen AG -- and BMW worked together to develop an active steering system for the new BMW 5-Series. Active steering has succeeded in realizing what is essentially a steer-by-wire function within a traditional power-steering system.

The system increases safety and driving pleasure by assisting drivers through a dynamic control system called ESP and adapts to changing road situations.

Until now, steering ratios had always been a compromise. A direct steering ratio made vehicles maneuverable in the city, but were not effective in high-speed situations. Active steering will provide the correct steering ratio for the respective driving situation. Winding roads feel more sporty, city roads require less effort and highway situations are safer because the control unit of the active steering system recognizes critical driving situations and can assist the driver in counter-steering maneuvers.

At the heart of the active steering system is a planetary gear with two input shafts and one output shaft. One is linked to the steering column, while the other engages with an electric motor to generate an extra steering angle, if necessary. The effective steering angle on the wheels is thus wider or smaller than the driver's steering wheel angle. Roughly 100 times per second, data is picked up by the control unit to determine whether -- and to what extent -- the steering angle has to be changed.

In case of a failure of the control unit or control motor, this path is blocked mechanically. Active steering functions like a traditional steering system with mechanical action on the wheels. The vehicle remains drivable without limitation and constant transmission.

The active steering system will debut as optional equipment on the new BMW 5-Series. Currently, BMW retains exclusive rights for the system.

ZF Lenksysteme GmbH is a joint venture of Robert-Bosch GmbH and ZF Friedrichshafen AG. Each partner holds 50 percent of the capital shares. The company develops, produces and sells steering technology for passenger cars and commercial vehicles.

ZF Friedrichshafen AG is a leading worldwide supplier of driveline and chassis technology. Headquartered in Friedrichshafen, Germany, ZF is among the 15 largest automotive suppliers in the world. The company has a total workforce of 53,300 at 119 locations in 25 countries, and combined revenues for the group totaled more than $10 billion in 2002.

With sales of more than $2 billion in 2002 ZF expects NAFTA region annual sales of more than $3 billion by 2004. ZF Group North American Operations are headquartered in Florence, Kentucky.