Extended PRE-SAFE® protection: Prevention is better than cure

May 15, 2013
Ten years ago, Mercedes-Benz unveiled a groundbreaking safety concept in the form of the PRE-SAFE® anticipatory occupant protection system, which has been undergoing continuous refinement ever since. Now, the safety pioneer is increasing protection levels once again.
The new PRE-SAFE® functions can help to prevent collisions with pedestrians and vehicles in front in city traffic, defuse dangerous situations caused by traffic behind and enhance the protection offered by the seat belts.
  • The PRE-SAFE® Brake now also can detect pedestrians and initiate autonomous braking to avoid a collision at speeds up to 50 km/h.
  • PRE-SAFE® PLUS can recognise an imminent rear-end collision and warn the following traffic by activating the rear hazard warning lights at a high frequency. If the danger of a collision persists, the system can also firmly apply the stationary vehicle's brakes and thus minimise the risk of whiplash injuries by reducing the forward jolt caused by the impact. This additionally can reduce the risk of secondary accidents. Immediately before impact, the PRE-SAFE® anticipatory occupant protection measures, especially the reversible belt tensioners, are deployed.
  • With PRE-SAFE® Impulse, the driver and front passenger are pulled away from the direction of impact by their seat belts at an early phase of the crash before the resulting occupant deceleration sets in. This can substantially reduce the risk and severity of injuries in a frontal collision.
Including pedestrian detection and City Brake function: BAS PLUS with Cross-Traffic Assist and PRE-SAFE® Brake
Pedestrian detection has been added to the BAS PLUS with Cross-Traffic Assist and PRE-SAFE® Brake functions, while autonomous braking for vehicles in front has undergone a major enhancement too.
Thanks to the combination of stereo camera and radar sensors, it is now possible to detect pedestrians in front of the vehicle. Visual and acoustic warnings are triggered when a hazard is spotted. If the driver then reacts by braking, the braking power will be boosted by BAS PLUS with Cross-Traffic Assist as the situation requires, right up to a full brake application. Should the driver fail to react, the PRE-SAFE® Brake triggers autonomous vehicle braking. The PRE‑SAFE® Brake with pedestrian detection is active up to approx. 72 km/h, and is able to prevent collisions with pedestrians autonomously up to an initial speed of 50 km/h.
Evaluations of GIDAS accident data by Mercedes-Benz indicate that this new technology could avoid six percent of pedestrian accidents and reduce the severity of a further 41 percent. The operating range of the autonomous braking function for stationary vehicles has been optimised so that rear-end collisions can likewise be avoided at speeds of up to 50 km/h.
BAS PLUS with Cross-Traffic Assist and the PRE-SAFE® Brake with pedestrian detection rely on the same sensors employed for the adaptive cruise control DISTRONIC PLUS with Steering Assist: the new stereo camera plus the multistage radar sensor system.
Safety measures in response to an imminent rear impact: PRE-SAFE® PLUS
PRE-SAFE® PLUS offers an extension of the familiar occupant protection measures in situations where traffic behind poses a danger. A radar sensor in the rear bumper monitors the traffic behind the vehicle. If the risk of an impact from the rear is detected, the rear hazard warning lights are activated with a high frequency (5 Hz) to alert the driver of the vehicle behind (not on vehicles with USA/Canada coding). If the vehicle is stationary and the driver wishes it to remain so (e.g. by applying the brakes, activating the HOLD function or engaging "P" using the selector lever), if the danger of a collision persists PRE-SAFE® PLUS comes to the driver's aid by increasing the brake pressure in order to keep the vehicle firmly braked. In addition, immediately before impact the PRE-SAFE® anticipatory occupant protection measures, especially the reversible belt tensioners, are deployed.
Keeping the vehicle firmly braked when another vehicle hits it from behind greatly reduces the strain placed on the occupants, such as the risk of whiplash injuries. At the same time, it serves to protect other road users too by restricting uncontrolled vehicle movements after the initial impact that could lead to secondary collisions, such as running into a vehicle in front or colliding with pedestrians or other road users at junctions.
Intelligent countermovement: PRE-SAFE® Impulse
Mercedes-Benz is extending the front seat belt's protective function with the introduction of PRE-SAFE® Impulse: at an early phase of the crash, before the resulting deceleration sets in, the front occupants are pulled away from the direction of impact and deeper into their seats by their seat belts. By the time the accident enters the phase when loads peak, the extra distance they are retracted by can be used while dissipating energy in a controlled fashion thanks to additional force limiting in the belt buckle. Pre-acceleration and force limitation allow the occupants to be temporarily isolated from the effects of the crash, significantly reducing the risk and severity of injuries in a frontal collision.
With PRE-SAFE® Impulse, the seat belt strap can be retracted by pyrotechnic means at all three belt anchorage points, both in the pelvis and chest area, and released again with controlled force at the buckle and in the shoulder area. The fundamental difference compared to conventional belt tensioners is that the force for retracting the belt strap is maintained more consistently for a much longer time. The deployment logic fires the seat belt system's belt tensioners progressively depending on the seriousness of the accident. In this way, the tensioning force can be adapted as required. The PRE-SAFE® Impulse system is integrated in the seat's structure and supplements the pyrotechnic reel tensioner with a pyrotechnic buckle and anchor fitting tensioner including central gas generator.