Active Steering
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Active steering is an automotive technology utilised by BMW which varies the degree that the wheels turn in response to the steering wheel. At lower speeds, this technology reduces the amount that the steering wheel must be turned -- improving performance in situations such as parking and other urban area traffic maneuvers. At higher speeds, the performance is such that steering becomes more responsive and provides improved directional stability.
In a parking situation, the computer varies the ratio so that the steering wheel needs less than two turns to move the wheels lock to lock. As vehicle speeds increase, the steering ratio increases, so it takes more turns of the steering wheel to move the wheels and increases vehicle stability. Besides providing variable steering ratios, the computer is linked with the vehicle stability control system to aid in directional stability of the vehicle.
If the driver experiences a skid or slide because of poor road conditions, the Active Steering will react to information from the yaw rate sensors to modify the steering angle of the front wheels to stabilize the vehicle. This occurs much faster than the driver can react. If the Active Steering angle is not enough, then the Stability Control system intervenes to help as well.
Safety is one of the prime objectives of this system. Steering angle sensors on the steering column sense the direction the driver wants to go and the system only intervenes if the car is beyond stable limits. If an error or problem occurs in the electronics, the computer shuts down the operation of the electric motor, locking the ring gear of the planetary gear set and making it fixed ratio steering. Finally, if there is a problem inside the planetary gear unit (an unlikely scenario), there is a second shaft that runs all the way through from the steering wheel shaft to the steering rack so that conventional steering is available.
