Variable steering-gear ratio

The variable steering-gear ratio function adapts the steering-gear ratio to the vehicle's road speed.

Steering is direct when the vehicle is moving at low speed. The planetary gearbox with override function contributes significantly to handling when the vehicle is moving at low speeds and when it is being maneuvered into tight parking spaces.

It is not longer necessary for the driver to feed the steering wheel through his or her hands in order to maneuver. When the vehicle is at a standstill, less than 2 complete turns of the steering wheel is all that is needed to move the wheels from lock to lock.

At high speeds the steering-gear ratio increases. The steering becomes less direct, further improving the intrinsically high standard of steering systems featured to date in BMW vehicles.

The safety function: 

The electric servomotor of the planetary gearbox is limited by an electric servomotor lock that blocks the worm gear of the planetary gearbox.

The electric servomotor lock is spring-loaded, with the force of the spring countered by the power supply.

Any interruption of the power supply consequently locks the worm gear.

When the planetary gearbox is locked in this way, it ensures that the steering column enables the driver to steer the vehicle. Under these circumstances, the steering reacts like a conventional, direct, steering gear system.

The purely mechanical steering linkage between the steering wheel and the front wheels is sustained even if the Active Steering fails.