Description & Operation: Notes
The main components of Supplementary Restraint System (SRS) include an inflatable air bag/gas generator module, electronic SRS control unit, 2 crash sensors, contact ring, energy capacitor/voltage transformer (integrated into SRS control unit), SRS warning light, driver knee bolster mounted under steering column, and an Emergency Tensioning Retractor (ETR) passenger seat belt assembly. See Fig 1 and Fig 2. If vehicle is equipped with passenger-side air bag, air bag module is installed inside dash, above glove box. For SRS to operate properly, 3-point seat belts must be worn.
SRS is activated by crash sensors when vehicle's deceleration rate is equal to a head-on collision impact greater than 11 MPH. When SRS control unit receives signal from crash sensors, it transmits voltage signal to the gas generator pellets in air bag modules and to the pellet in ETR passenger seat belt assembly. Voltage signal ignites gas generator pellets to produce a quantity of non-toxic nitrogen gas.
In the air bag modules, the nitrogen gas passes through a tiny filter to fill and deploy the air bags in about 30 milliseconds. After the air bags inflate to maximum expansion, the nitrogen gas is released away from driver through 2 ventilation holes in rear of air bag. The entire sequence of air bag inflation and collapse takes about 30-35 milliseconds.
In the Emergency Tensioning Retractor (ETR) passenger seat belt assembly, the ignited nitrogen gas forces a piston to be driven downward in tube attached to seat belt assembly. Piston has a cable attached to it. Cable pulls on seat belt reel, increasing seat belt tension and holding front seat passenger tightly against seat backrest.