Active steering system AFS

AFS (Active Front Steering) is an active steering system, which is in essence an improved classic steering system. The main purpose of AFS is the correct distribution of power between all components of the steering system, and the main goal is to improve the efficiency of driving at different speeds. The driver, in the presence of active steering in the car, receives increased comfort and confidence in driving. Consider the principle of operation, the AFS device, and its differences from the classic steering system.

Principle of operation

Active steering is activated when the engine is started. The AFS modes of operation depend on the current vehicle speed, steering angle and the type of road surface. Thus, the system manages to optimally change the gear ratio (steering effort) in the steering gear, depending on the driving mode of the vehicle.

When the vehicle starts moving, the electric motor is turned on. It starts working after a signal from the steering angle sensor. The electric motor, by means of a worm pair, begins to rotate the outer gear of the planetary gear. The main function of the external gear is to change the gear ratio. At the maximum speed of rotation of the gear, it reaches the lowest value (1:10). All this contributes to a decrease in the number of turns of the steering wheel and increased comfort when maneuvering at low speeds.

An increase in vehicle speed is accompanied by a slowdown in the rotation speed of the electric motor. Because of this, the gear ratio increases gradually (in proportion to the increase in driving speed). The electric motor stops rotating at a speed of 180-200 km / h, while the force from the steering wheel begins to be transmitted directly to the steering mechanism, and the gear ratio becomes equal to 1:18.

If the vehicle speed continues to increase, the electric motor will restart, but in this case it will start to rotate in the other direction. In this case, the value of the gear ratio can reach 1:20. The steering wheel becomes the least sharp, its revolutions increase to the extreme positions, which ensures safe maneuvers at high speed.

AFS also helps to stabilize the vehicle when the rear axle loses traction and when braking on slippery road surfaces. Vehicle directional stability is maintained using the Dynamic Stability Control (DSC) system. It is after signals from its sensors that AFS corrects the steering angle of the front wheels.

Another feature of Active Steering is that it cannot be disabled. This system operates continuously.

Device and main components

The main components of AFS:

• Steering rack with planetary gear and electric motor. The planetary gear changes the speed of the steering shaft. This mechanism consists of a crown (epicyclic) and a sun gear, as well as a block of satellites and a carrier. The planetary gearbox is located on the steering shaft. The electric motor rotates the ring gear through a worm gear. When this gear wheel rotates, the gear ratio of the mechanism changes.
• Input sensors. Needed to measure various parameters. During AFS operation, the following are used: steering wheel angle sensor, electric motor position sensors, dynamic stability sensors, cumulative steering angle sensors. The last sensor may be missing, and the angle is calculated based on the signals from the remaining sensors.
• Electronic control unit (ECU). It receives signals from all sensors. The block processes the signal, and then sends commands to the executive devices. The ECU also actively interacts with the following systems: Servotronic electro-hydraulic power steering, engine management system, DSC, vehicle access system.
• Tie rods and tips.
• Steering wheel.

Advantages and disadvantages

The AFS system has undeniable benefits for the driver: it increases safety and comfort while driving. AFS is an electronic system that is preferred over hydraulics due to the following advantages:

• accurate transmission of the driver's actions;
• increased reliability due to fewer parts;
• high performance;
• light weight.

There were no significant shortcomings in AFS (apart from its cost). Active steering rarely malfunctions. If you still manage to damage the electronic filling, then you will not be able to configure the system yourself - you need to take the car with AFS to the service.

Application

Active Front Steering is a proprietary development of the German automaker BMW. At the moment, AFS is installed as an option on most cars of this brand. Active steering was first installed on BMW vehicles in 2003.

Choosing a car with active steering, the car enthusiast receives comfort and safety while driving, as well as ease of control. The increased reliability of the Active Front Steering system ensures long, trouble-free operation. AFS is an option that should not be neglected when buying a new car.