Air Bag Systems: Description and Operation

Air Bag-Supplemental Restraint System

Air bag-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 Air bag Diagnostic Unit (ADU). These two sensors (Safing sensor and G-sensor) are electrically connected in series with air bag 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 air bag module 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 happened 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 air bag can be deployed.
Driver is protected by a steering wheel mounted air bag. Air bag-Supplemental Restraint System consists of Air Bag Module, Air Bag Diagnostic Unit, and wire harness & clock-spring assembly.

Driver Air Bag module consists of bag cover, air bag, retainer ring, retainer housing, and inflator. Passenger Air Bag module consists of deployment door, bag assembly, inflator, and retainer housing. Because of size difference, passenger air bag module incorporates a larger, tubular shaped inflator.

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

Air Bag Diagnostic Unit (ADU) contains CPU, memory, auxiliary power supply and G-sensor and safing sensor. Auxiliary power supply is installed to guarantee deployment of air bag even when battery voltage is cut off in a collision.

CPU not only triggers air bag deployment but also performs procedures. CPU initiates a test sequence every time ignition key is turned "ON" and meanwhile, Air Bag 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 air bag 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 Kia Data Pro-II Tool.

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