E60 Active Front Steering
E60 Active Front SteeringModel: E60
Production: Start of Production MY 2004
Active Front Steering
System Desciption Topics
^ Understand basic AFS operation
^ Locate and Identify AFS components
^ Perform AFS Initialization/Start-up procedure
^ Perform Wheel Alignments on AFS equipped vehicles
Active Front Steering
Conventional rack and pinion power steering is used in the E60. Two items of options (SA) are also available:
^ Servotronic
^ The active front steering system (AFS)
The active front steering option is only available in conjunction with the Servotronic option.
The design and operating principle of the Servotronic option have remained the same as in previous models.
The active front steering system is introduced on BMW vehicles for the first time on the E60.
The electronic controlled steering system assists the driver beyond the usual assist of the power steering with a variable steering ratio. The core element of the steering system is the so called superimposing gear. The superimposing gear is a ring gear which is part of a simple planetary gear set integrated into the steering rack between the steering spindle and the pinion gear. An electric motor engages the ring gear via a worm gear drive as a function of the vehicle speed. In this way, the steering system can modify the front wheel angle by changing the output ratio of the steering rack. The electric motor can be run in forward or reverse depending on the needs of the AFS system. When the motor is run in the forward direction, the steering is more direct. When the motor is run in reverse, the steering is less direct.
In critical situations, the steering system can specifically modify the wheel angle engaged by the driver and thereby stabilize the vehicle more quickly than the driver. The active front steering system is integrated in the vehicle electrical system via the Powertrain CAN (PTCAN) and the new Chassis CAN (FCAN).
The active front steering system is very closely linked to the Dynamic Stability Control (DSC) drive control system. Sensors and signals used by DSC are also used by the active front steering control unit.