AFS: definition, function, principle of operation and causes of failure

AFS (Active Front Steering) is an active steering control system for vehicles from Cadillac and BMW. It was introduced in 2003. This system controls the steering ratio based on vehicle speed and also adjusts the steering angle of the front wheels to avoid slipping. In addition, the handling and maneuverability of the vehicle is improved and driving safety is increased.

How AFS works

The steering shaft is equipped with a Planetary gear set equipped with an epicyclic gear. The planetary gear is connected to an electric motor controlled by the system. With the variable speed and direction of rotation of the planetary gear, the steering ratio can be changed and the steering response adjusted to the condition of the road surface.

The system analyzes the total angle of rotation of the steering axle, the vehicle's yaw rate and its lateral acceleration rate. Based on this data, the system calculates the required speed and direction of rotation of the motor shaft.

AFS works closely with the stability control system. The latter, in turn, then adjusts the steering angle of the front wheels to restore the vehicle's intended direction of travel in the event of oversteer.

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  • Cadillac STS
  • BMW 5 Series E60/E60, 6 Series E63/E64, X5 E70, and 1 Series E81, E87, BMW 3 Series E90, E91, E92, E93.

Causes of defects

  • The steering wheel angle sensor or the yaw rate sensor is defective
  • Improper repair of the steering rack
  • The steering angle sensor is not set correctly
  • The wheels are misaligned.

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