# A Review of Seatbelt Technologies and Their Role in Vehicle Safety
## 3 Results
### The Pretension System  
Seatbelt pretensioners are mechanisms that are activated during an impact or collision. Their purpose is to minimize the gap between the belt and the occupant's body, ensuring a tighter fit and thus reducing the passenger's movement, reducing the risk of injury in frontal collisions. The development of seatbelt pretension systems has undergone significant advancements, evolving from passive restraint mechanisms to sophisticated, dynamically responsive safety components. Initially, conventional seatbelt systems functioned solely as reactive restraints, allowing a degree of slack before engaging in the event of a collision. However, with advancements in automotive safety engineering, pretensioning mechanisms have been introduced to mitigate this slack, thereby enhancing occupant protection by ensuring a more secure restraint prior to impact. \begin{table}
\begin{tabular}{c c} \hline \hline
**Type of Locking Mechanisms** & **Characteristics** \\ \hline \multirow{7}{*}{Vehicle movement-activated sensor (CS)} & This type of mechanism locks the retractor in two situations: \\  & It must not lock if the locking device is tilted by up to 12\({}^{\circ}\) from its normal \\  & installation position. It must lock if the \\  & locking device is tilted by at least 27\({}^{\circ}\) (for \\  & Type 4 retractors) from its normal \\  & installation position. \\  & The second situation is related to vehicle \\  & deceleration. According to ECE-R16, the \\  & retractor locks at a deceleration of 0.45 g \\  & but remains unlocked for decelerations up \\  & to 0.3 g. \\ \hline \multirow{7}{*}{Seatbelt movement-activated sensor (WS)} & This mechanism locks the seatbelt \\  & retractor if the webbing deceleration, \\  & according to ECE-R16, exceeds 2.0 g, \\ \cline{1-1}  & allowing approximately 50 mm of \\ \cline{1-1}  & additional webbing to be pulled from the \\ \cline{1-1}  & spool before locking. \\ \cline{1-1}  & For decelerations below 0.8 g, the retractor \\ \cline{1-1}  & does not lock. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Type of locking mechanisms in a retractor. One notable innovation in pretensioner technology involves a dual-stage activation system that sequentially engages two pretensioners at different time intervals. This approach ensures the elimination of lap-belt slack, thereby optimizing occupant restraint and reducing forward displacement during a collision [16]. Additionally, the integration of retractable seatbelt systems equipped with pretensioners has further improved retraction efficiency and occupant stabilization during rapid deceleration [17]. Advancements in miniaturization have also contributed to the refinement of pretensioner technology. The development of compact gas generators with integrated electrical connectors has enhanced the efficiency and integration of seatbelt pretensioners with airbag deployment systems, ensuring a coordinated safety response in the event of a crash [18]. Beyond pyrotechnic and retraction-based systems, motorized seatbelt tensioners represent a significant innovation in active restraint technology. These systems utilize an electric drive motor and a gear mechanism to dynamically adjust seatbelt tension in hazardous driving conditions. To prevent mechanical failure under excessive torque, an overload clutch mechanism is employed to disengage the gear system, thereby preserving the structural integrity of the pretensioner [19]. Furthermore, contemporary advancements in seatbelt pretension systems incorporate intelligent control mechanisms that regulate tension throughout various phases of an impact event. These adaptive systems modulate restraint force in real time, balancing occupant protection with comfort by preventing excessive pressure while maintaining optimal retention [20]. These systems usually use a pyrotechnic device to pull the belt rearward. The command to trigger the pretensioner in the event of an impact is carried out by mechanisms activated by sensors that detect an imminent or ongoing collision.