How Autonomous Emergency Braking (AEB) Works

An autonomous emergency braking system is an extension of the emergency braking assistant. An emergency braking assistant is a predictive driver assistance system for motor vehicles that warns the driver in case of danger, supports emergency braking (brake assistant) or brakes automatically. This is to avoid collision with an obstacle or reduce the collision speed. Some emergency braking assistants may take additional safety measures. Collision avoidance system (CAS) or a pre-crash system, forward-collision warning system, collision mitigation system, autonomous emergency braking falls among automobile safety system designed to prevent or reduce the severity of a collision.

Function

Vehicles with emergency braking assistants usually have sensors to determine distances, acceleration, steering angle, steering wheel angle and pedal positions. From the measured values of these sensors, the on-board computer calculates whether there are indications of a hazardous situation and/or a critical driving condition. The data of some sensors are also used for other purposes. For example, ABS and driving dynamics control (also called ESP or ESC) use the data of the sensors on the wheels. Many emergency braking assistants, for example, warn the driver, not enough distance from the vehicle in front before automatically reducing and braking the fuel supply. These systems are designated differently depending on the vehicle manufacturer or automotive supplier and bear a proprietary name.

Emergency Brake Assist

In the emergency braking assistant, sensors monitor the environment and first warn the driver of critical situations to allow them to react. If the system detects that a collision is imminent, it calculates how hard the vehicle needs to be braked to avoid the collision. When the driver brakes, the system increases the braking pressure by the required level.

At low speeds, e.g. in urban traffic, emergency braking assistants detect vehicles in front or standing and automatically prepare the braking system for emergency braking. If the driver does not react to the situation, the emergency brake assistant can trigger an emergency brake so that there is no collision in the first place. If a collision is unavoidable, the emergency braking assistant at least reduces the strength of the impact and thus the risk of injury to the occupants of the vehicles involved.

Many newer systems respond not only to other vehicles but also to other road users such as pedestrians or cyclists. This prevents or mitigates head-on collisions and significantly increases safety for pedestrians and cyclists. Often a better camera is combined with sensors for the pedal positions. The assistant is thus able to better assess the driver’s behaviour according to the situation and to assist the driver in coping with difficult situations. If, for example, the emergency braking assistant detects a critical situation for emergency braking due to a rapidly released accelerator pedal and powerfully operated brake pedal, the full braking pressure, which is necessary for maximum deceleration, is immediately set up. Besides, further measures for the protection of occupants can be taken, depending on the system.

Autonomous emergency braking

Here, there are additional and more accurate sensors are usually available compared to the emergency braking assistant. For example, for safe detection of the distance to the frontman and its speed, a radar sensor is often installed, which is not required for the simpler systems. The validity of the forecasts allows the initiative to be reversed: it is not the driver who actively triggers the system as it does with the emergency braking assistant, but the driver can oversteer the system. If the driver does not take any action, the system becomes active on its own and brakes the vehicle.

When detecting a critical situation, the driver is visually and acoustically warned in the first stage. If the driver does not react to this, the system first initiates a significant speed reduction (partial braking). If the calculated distance becomes too small and the driver has still not reacted, full braking is triggered to avoid the collision with an obstacle or at least to minimize the force of the impact. If the system detects the obstacle or vehicle in front of it late, the system can also immediately initiate partial braking, if necessary full braking, without warning the driver. These measures are usually accompanied by further measures for the protection of occupants.

Multi-collision brake

If an accident is detected by the airbag control unit and the vehicle then drives even further, the multi-collision brake triggers braking of the vehicle to avoid further collisions or at least reduce the kinetic energy of the vehicle as much as possible. In addition to the airbag control unit, depending on the system, other sensors of the vehicle, such as body sound sensors or pressure sensors in the doors, can be taken into account for the decision on the activation of the multi-collision brake.

An occupant protection system detects potentially dangerous situations such as slingshots, heavy oversteering or understeering, or too little distance. It reacts by reversibly tensioning the mechanical belt tensioners before the possible emergency, placing seats in an upright optimal position and closing the window and sliding roof. Depending on the equipment of the vehicle, foldable headrests can also be installed or massage systems can be used in seats for better grip.