Air Bag Systems: Description and Operation

Airbag - Supplemental restraint system

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

In case of the frontal crash, the G-sensor gets the collision deceleration. The collision deceleration information is converted into digital data and transmitted to CPU(Central Processing Unit). The CPU calculates the digital data and compares them with designed data to decide whether it has to send a signal to deploy the airbag module (including pretensioner) or not. If the calculation result by the CPU is correspond to the designed data, it decides to send a deployment signal.

At the same moment, the safing sensor, which is linked linearly on deployment circuit, checks whether the deceleration is caused by actual physical collision, or by other electronic waves and mal effect. So, only when both the signal of deployment from the CPU and closing of safing sensor switch come together, the airbag can be deployed.

Driver is protected by a steering wheel mounted airbag. Air Bag-Supplemental Restraint System consists of Airbag Module pretensioner, Airbag Diagnostic Unit, and wire harness & clock-spring assembly.

Driver Airbag (DAB) module consists of bag cover, airbag, retainer ring, retainer housing, and inflator. Passenger Airbag (PAB) module consists of deployment door, bag assembly, inflator, and retainer housing. Because of size difference, PAB module incorporates a larger, tubular shaped inflator.

The driver airbag cover is made of TPE (Thermos Plastic Elastomer), and it is spilt along tear seam on it in case of a collision. Airbag is made of Nylon 66, and its surface is coated with silicone. A vent hole is provided at back side of airbag to deflate airbag after its inflation not to block driver's sight. Inflator produces nitrogen gas by igniting solid propellant pellets inside inflator. Igniters is triggered by electrical current and igniters ignition intensifier, which ignites propellant pellets. Heat sink and filter cools and filters nitrogen gas as it enters airbag.

Airbag diagnostic unit (ADU) contains CPU, memory, auxiliary power supply and acceleration sensor and safing sensor.

Auxiliary power supply is installed to guarantee deployment of airbag even when battery cables are cut off in a collision.

CPU not only triggers airbag deployment but also performs diagnostics. CPU initiates a test sequence every time ignition key is turned "ON" and meanwhile, Airbag Indicator is illuminated for 4 - 6 seconds. When sequence is completed and no fault is found, lamp goes out. If any failure is discovered, warning lamp will stay "ON" or flicker to warn driver. Even while driving, CPU continually monitors circuits and components of airbag system. If a failure occurs within system while driving, warning lamp is immediately illuminated. Contents of those detected failures are stored in memory and can be read with an external diagnostic module like Hi-Scan Pro Tool.

Clock spring assembly is incorporated into 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.