September 18, 2002

BMW’s new ActiveSteering incorporates mechanical and drive-by-wire technologies

Whitby, Ontario… BMW has announced a new system in steering: ActiveSteering. BMW ActiveSteering takes the responsivness of BMW’s traditional steering one step further by introducing a technology that allows the front wheels to be positioned more accurately according to the drivers input.

BMW ActiveSteering includes a planetary gearbox incorporated into a split steering column. Acting through a self-inhibiting gear wheel, an electric motor assists as required in this planetary gearbox, either increasing or decreasing the steering angle of the front wheels.

BMW ActiveSteering is based on the principle of overlapping steering angles. This is done through an electromechanical adjuster that adjusts the steering angle determined by the driver. The split steering column is made up of two input and one output shaft. One incoming shaft is connected with the steering wheel, the second is driven by an electric motor via a self-inhibiting gear wheel transmission that reduces the transmission ratio. The overall steering angle is created from a combination of the drivers input on the steering wheel and the angle determined by the electric motor. The electric motor determines its angle input through a combination of sensors that determine driving condition. Finally ActiveSteering communicates with the DSC control unit through the car’s on board communication network.

The greatest advantage of ActiveSteering over steer-by-wire systems is that there is a mechanical aspect to the feedback. ActiveSteering allows for a mechanical link to the road tires while incorporating the benefits of steer-by-wire. Thereby allowing the driver to have realistic feedback on the road conditions and what the tires are doing.

The safety benefits of such a system are clear. Whenever driving stability is limited, for example on wet or slippery roads or in crosswinds, ActiveSteering quickly assists and improves driving stability. Even in parking lots ActiveSteering will demonstrate its benefits by allowing the steering wheel to be turned less. The direct steering transmission ratio of ActiveSteering enables the driver to achieve the same turning radius in two rotations of the steering wheel, where the driver may have traditionally made three rotations.

ActiveSteering is particularly evident at low and medium speeds, where it can change the steering angle of the wheels faster than the driver would be able. The driving benefits of ActiveSteering become most obvious on twisty roads where ActiveSteering chooses a more direct steering transmission than a conventional steering system, thereby increasing the vehicle’s agility and nimble responsiveness.

The requirements of a vehicle’s steering system are extremely varied. At slower speeds the front wheels should respond as directly as possible to the drivers inputs, while at higher speeds the steering should become less direct. However, it is equally important that the steering does not become numb and continues to provide feedback to the driver. BMW ActiveSteering accomplishes this balance.

BMW ActiveSteering will be introduced on one of the next BMW model Series as an optional extra.

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