Seat Belt Pretensioner


Ever increasing road fatalities has magnified the need for safety measures on vehicles. Safety devices, once perceived as luxurious accessories, increasingly, are becoming part of the vehicle as standard equipment. Evolved car buying customers are ready to pay a premium for safety features that can prevent fatality.

Seat belt is one of the oldest active safety mechanism adopted by the car manufacturers from a long time. Though it seems very simple, it is amazingly effective in shielding one from any eventuality and minimise overall damage to the passenger.

Recent statistical data released by highway safety authority in USA says that seatbelts save around 13,000 lives in US every year.


Whilst seat belts on their own are quite effective in minimizing injuries, however, seatbelts with pretensioner helps in improving seatbelts efficacy.

Pretensioner starts working as soon it senses hard braking. It works by tightening the seat belt around the passenger so that the person is held firmly in his place. The whole process starts and completes within milliseconds. Thus improving seat belt utility many fold.


Depending upon the mechanism of working, pretensioners can be classified into two categories:

: Seatbelt with mechanical pretensioner consists of a spring and tube mechanism attached to the seatbelt buckle assembly, a latching mechanism is used to compress the spring. On impact, this latching mechanism releases the spring which in turn pulls on the buckle assembly. This pulling is directly proportional to the tightening that the passenger will experience which helps in cushioning the passenger more effectively than what normal seat belt assembly would do.

ELECTRONIC PRETENSIONER: Electronic pretensioner involves use of sophisticated sensors to operate the mechanism, which many a times work in tandem with the air bags that are fitted in the vehicle.

The main parts of electronic pretensioner can be classified as:

Operating Sensor.

Explosive Charge.

ECU Tuning.

Electronic pretensioner works in tandem with airbags sensor and is tuned with the ECU of the vehicle. An explosive charge generates the gas which exerts pressure on the mechanical linkages causing the seat belt to tighten up. These type of seatbelts are usually fitted in the B-Pillar of the vehicle.

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