ZF: New seatbelt pretensioner actively positions occupants correctly in dangerous situations

An old saying in accident research goes: Proper occupant protection is provided by a correct seating position and a properly fitted seatbelt. Especially in the crucial milliseconds before an unavoidable collision, the new, connected seatbelt from ZF can fully exert its effectiveness by actively positioning the occupants correctly and securing them optimally. The seatbelt system obtains its information from the vehicle's sensors. When a hazardous situation is detected, the seatbelt pulls the occupant into the seat. Only then does the pyrotechnic and thus irreversible tightening occur. The heart of the system is the electromechanical seatbelt pretensioner ACR8, which can do even more – for example, it can retract seatbelt slack, provide less tension and thus more comfort, or alert the driver through vibration on the seatbelt, potentially gaining up to a second in reaction time.

Additional advantage: The ACR8 requires even less installation space!

The core of the protection system is the further developed active seatbelt pretensioner ACR8 (Active Control Retractor), which links the information available in the vehicle and can electromotively retract the seatbelt to build up targeted seatbelt force. In addition to the already described functions, the ACR8 offers further advantages for car manufacturers: No separate NCAP self-certification is required for the use of the new system. The ACR8 is also available as a seat-integrated variant, which requires only 60 millimeters of installation depth instead of 82. This allows it to be integrated into all types of car seats without limiting the design. When asked whether it could become even more compact in the future, this had to be denied, as the seatbelt itself has a certain thickness, which determines the diameter of the seatbelt reel when wound. Moreover, the mechanics requires space to operate effectively.

We were allowed to try the system ourselves – it works!

We were able to experience everything – except for the irreversible tightening – live in Friedrichshafen and must say: we were impressed. Because when the seatbelt tugs at you because you overlooked something, you actually react faster than when some diodes are blinking! And then, the seatbelt really pulls you sustainably into a proper seating position!

The two restraint systems, seatbelt and airbag, work together as protection systems almost "hand in hand": Initially, the seatbelt holds back the torso but releases it gradually towards the airbag in the milliseconds following the crash, until the air cushion catches the occupant. If the seatbelt lacks these reserves, for example, because the torso was already too far forward during the crash, the likelihood of injury can increase. This is where the idea of repositioning comes into play.

Repositioning: Utilizing the crucial seconds before the crash

Even during buckling up, the seatbelt actively engages and reduces the so-called seatbelt slack, pulling the seatbelt (previously only typically in more expensive vehicles) once in a defined manner, so that it fits snugly against the occupant.

If the vehicle sensors detect a dangerous driving situation that could lead to hard braking or possibly a collision, the seatbelt system can use this time to enhance occupant protection. To achieve this, it is networked not only with the sensors but also with the automatic emergency braking assistant, and pulls the occupant with precisely dosed force into the correct position and holds them there during the braking maneuver. In the event of a subsequent crash, the ensuing pyrotechnic tightening and the entire restraint system can achieve optimal effectiveness, thus minimizing the consequences of the accident.

The belt shakes you awake: Up to 36 meters safety buffer at 130 km/h

Additionally, the belt system with the ACR8 can be used as a haptic signal transmitter, for example, for warnings or information dissemination. It can "wake up" drivers when they are drowsy or alert them when switching from automated to manual driving by high-frequency pulsation of the belt, indicating that the driver needs to take control again. Thus, the belt system can be integrated into the user interface of automated vehicles to capture the driver's attention. In tests, ZF has measured a reduction in reaction time by up to one second compared to optical or acoustic signals. At highway speeds, this corresponds to a distance of 36 meters.