Restraints and Safety Systems: Description and Operation

AIRBAG-SUPPLEMENTAL RESTRAINT SYSTEM

The Airbag-Supplemental Restraint System (SRS) is designed to supplement driver seat belts during front-end collisions,reducing the risk of serious injury or death. Two collision-sensitive sensors are located in the Airbag Control Unit (ACU). These two sensors (Safing sensor and G-sensor) are electrically connected to the airbag and the battery.

In case of a frontal crash, the G-sensor receives collision deceleration information. The collision deceleration information is converted into digital data and transmitted to the ACU (Airbag Control Unit). The ACU calculates the digital data and compares them with preprogrammed data to determine whether it has to send a signal to deploy the airbag module or not.If the calculation of the ACU corresponds to the preprogrammed data, a deployment signal is sent. At the same moment, the safing sensor, which is linked linearly on the deployment circuit, checks whether the deceleration has occurred due to an actual collision, or by other electronic waves and anomolies. So, the airbags will only deploy with a deployment signal from the ACU and closing of safing sensor switch.

The Driver is protected by a steering wheel mounted airbag The Airbag-Supplemental Restraint System consists of an Airbag Module, Airbag Control Unit, and wire harness & clock-spring assembly.

The driver airbag module consists of a bag cover, airbag, retainer ring, retainer housing and inflator.

The passenger airbag module consists of a deployment door, airbag assembly, inflator and retainer housing. Because of size difference, the passenger airbag module incorporates a larger, tubular shaped inflator.

The driver airbag cover is made of TPE (Thermos Plastic Elastomer), and it splits along a tear seam in the event of a collision. The airbag itself is made of Nylon 66, and the face contact surface is coated with silicone. A vent hole is provided at back side of airbag to deflate airbag immediately after inflation so that it does not interfere with the drivers vision The inflator produces nitrogen gas by igniting solid propellant pellets inside inflator. The ignitor is triggered by an electrical current and the ignitors ignition intensifier, which in turn ignites propellant pellets causing the airbag to deploy. A heat sink and filter within the unit cools and filters nitrogen gas as it enters airbag.

Airbag Control unit (ACU) consists of a ACU, memory, auxiliary power supply and G-sensor and safing sensor. An auxiliary power supply is installed to ensure airbag deployment if battery power is lost in a collision.

The ACU not only initiates airbag deployment but also performs the SRS self-test. ACU initiates a test sequence every time ignition key is turned "ON" and the Airbag Indicator is illuminated for 4 - 6 seconds. When the self test sequence is completed and no fault is found, lamp goes out. If any failure is detected, the warning lamp will stay "ON" or flash to warn driver. Even while driving, the ACU continually monitors circuits and components of airbag system. If a failure occurs within system while driving, the warning lamp is immediately illuminated. Details of those detected failures are stored in memory and can be retrieved with Scan Tool.

The clock spring assembly is incorporated into the combination switch to provide a positive connection between vehicle wire harness and driver airbag module while allowing sufficient rotation for vehicle steering. This assembly is also replaced as a complete assembly only.

The Airbag electrical connector has a shorting bar which will short across Airbag assembly circuits when the Airbag connector is disconnected The Airbag circuit is automatically shorted by the shorting bar in this way to help prevent unwanted deployment of the Airbag when servicing the instrument panel, Airbags or other SRS components.