· The steering's system compatibility enables networking with additional safety and driver assistance systems

The environmentally friendly Servolectric from ZF Lenksysteme is making headway in the passenger car market. So far, a total of 10 million units of the electromechanical steering system have been installed in cars. Compared to hydraulic steering systems, this steering system saves about 0.4 liters of fuel in the NEDC (New European Driving Cycle) and up to 0.8 liters per 100 kilometers in city driving. Another advantage is the expanded system integration capacity. For the end customer, this means enhanced comfort and safety. With three different models, the electric power steering system can be used for all vehicle categories.

Better fuel economy without compromises
The Servolectric electric power steering system by ZF Lenksysteme, a 50:50 joint venture between Robert Bosch GmbH and ZF Friedrichshafen AG, requires energy only when the driver is actually steering. According to the latest measurements, compared to a hydraulic-driven power steering system, the electric power steering system saves 0.4 liters of fuel per 100 kilometers – this would mean that the steering system alone leads to six percent fuel savings for a compact class car with an average fuel consumption of 7.7 Liters. With a production figure of ten million units so far, this means annual savings of 400 million liters of fuel due only to the Servolectric steering system. This, in turn, means almost 950,000 tons less CO2 emitted (assuming an average of 10,000 km driven each year per vehicle).

Power-on-demand
The Servolectric's steering mechanism is based on the principles of a rack-and-pinion steering, which, in the case of the electric power steering, is linked to high-performance electronics. As soon as the driver performs a steering motion, the corresponding steering torque and speed are registered by sensors. From this data, the control unit computes the required steering support within milliseconds; then, via a spiral-toothed gear wheel or a recirculating ball gear, the servomotor transfers the optimum servo torque to the steering column, a second pinion, or the steering rack of the mechanical rack-and-pinion steering system. The electric power steering system introduced in 2002 has more advantages to offer: Space-saving installation thanks to the elimination of the steering pump and the hoses; this simplifies assembly and

helps to preserve the environment. After all, this is one of the reasons why Volkswagen Group is installing it in the entire Golf platform, just as it did with the predecessor of the current Servolectric generation. With three basic models, the ZF-Servolectric covers all vehicle classes from supermini cars to mid-size and full-size models as well as light commercial vehicles. Depending on the installation space, performance of the vehicle electrics, and required steering torque, the servo unit is mounted on the steering column, on a second pinion or parallel to the steering rack.

System capability enhances driving safety
The Servolectric can be networked with various external systems. Thus, all the information recorded regarding the steering wheel angle is available for other systems, such as the ESP or the adaptive chassis and suspension control system. At Volkswagen, special driving safety is assured thanks to the "Lane Assist" tracking system and the "Side Assist" blind spot detection. Depending on the situation, the corresponding system will intervene and recommend a counter-steering motion to the driver by means of optical, acoustic, or haptic feedback signals. The parking assistant no longer needs manual intervention on the steering wheel; the Servolectric is completely autonomous here in terms of steering intervention.

With approximately 11,000 employees at 17 locations in 10 countries, ZF Lenksysteme GmbH, a 50-50 joint venture of Robert Bosch GmbH and ZF Friedrichshafen AG, is a specialist and technological leader for Steering Technology. In 2007, the ZF Group achieved sales of more than €2.6 billion.

PT_IAA09_01 - September 2009