Schaeffler Group has developed a high-precision ball screw drive, the performance density of which exactly matches the high demands of electromechanical automotive steering systems. The new sub-assembly is currently being used on Volkswagen’s latest Tiguan model.
Schaeffler supplies the ball screw drive to Volkswagen, as well as a toothed rack, which is partly designed as a spindle on which the drive is located. Ball screw drives are used to transform rotary motion into linear motion through a direct coupling between the drive element and the output element. In the Tiguan, the ball nut is driven by a servomotor, which is linked to the ball screw drive via a belt.
Unlike hydraulic steering systems, where a pump constantly supplies pressure to provide steering motion, the electric motor becomes active only at the moment when steering motion is initiated. Pump and feeds are therefore no longer required, which reduces the space required for operating the steering system.
The demands placed on this ball screw drive are high. It is able to support high dynamic loads, thanks to appropriate spindle dimensions and high material strengths and, as it has low internal friction, the driver can directly feel the low frequency changes on the wheel when driving. This is particularly important for driver handling.
For applications on other vehicle models, Schaeffler can modify the ball screw drive in such a way that the steering characteristics and driver handling vary depending on the customer’s wishes.