When the vehicle is involved in an accident at a certain angle with respect to the frontal impact, the gas generator is ignited by an electrical signal from the SRSCM.
The gas escaping from the gas generator will cause the piston to move in the pretensioner gear cylinder.
The gear train rotates the piston gear and the planetary gear rotates the planetary gears.
As a result, the belt is tensioned due to the rotation of the drum. Therefore, a pretensioner belt reduces the severity of injury to the driver and front passenger by pretensioning the belt. This prevents the driver and front passenger from moving forward and avoids hitting the steering wheel or instrument panel.