Seat Belt Tensioner: Description and Operation

GENERAL DESCRIPTION

CAUTION:
- Driver and front passenger air bags and seat belt pre-tensioner deploy and operate in all head-on collisions that exceed the threshold to activate the SRS system.
- The specific value is the equivalent impact when a vehicle collides against a concrete (fixed) wall at approximately 25 kph (16 mph) or more.
- The SRS and pre-tensioner may not work under the following conditions:
- A head-on collision is less than the specific value.
- A vehicle collides on its rear end.
- A vehicle rolls over or is in a similar position.

Apart from driver's and front passenger's air bags and seat belts with pre-tensioner fitted as standard, some models can be equipped with optional side air bags on both driver's and front passenger's sides, increasing the passive safety level.

SEAT BELT WITH PRE-TENSIONER
The seat belts with pre-tensioner work simultaneously with the SRS. The pre-tensioner takes up seat slack immediately when a collision takes place by that restraining the front passengers sooner than the SRS. This prevents the passengers from moving forwards.




SEAT BELT WITH PRE-TENSIONER

CAUTION: Never disassemble the seat belt with pre-tensioner.

The driver's and front passenger's seat belt pretensioners take up seat belt slack immediately when a collision takes place, thus restraining the passengers on the seats simultaneously with the SRS air bags. This improves the passive safety. When the G sensor in the SRS-ECU detects impact above a certain level during a collision, the pretensioner operates as follows:
1. The igniting heater heats up according to the signal from the SRS-ECU.
2. This ignites the gas generant and explosive gas will be generated.
3. The strip is pushed outwards by the gas pressure. As the strip wound around the clutch sleeve is pulled out, the clutch sleeve rotates at high speed.
4. The clutch sleeve rotates to wind the webbing.