Air Bag Systems: Description and Operation
The Supplemental Air Bag Restraint System (SRS) is designed to provide increased accident protection IN ADDITION TO that provided by the three-point safety belt system. Safety belt use is necessary to obtain the best occupant protection and to receive the full advantages of the supplemental air bag. FORD RECOMMENDS THE USE OF SAFETY BELT SYSTEMS FOR ALL VEHICLE OCCUPANTS.
The supplemental air bag restraint electrical system consists of:
- Driver side air bag module
- Passenger side air bag module
- Air bag sliding contact
- LH fender primary crash sensor and bracket
- RH fender primary crash sensor and bracket
- Center radiator primary crash sensor and bracket
- Rear center cowl safing sensor and bracket
- Air bag diagnostic monitor
- Air bag indicator
- Tone generator (internal to the air bag diagnostic monitor)
Steps 1-3 take place in a fraction of a second. The following steps describe how the air bag system works:
1. The sensors in the vehicle detect a severe frontal impact. When at least one front or center air bag sensor and the center cowl safing rear air bag sensor and bracket close at the same time, electric current flows to the inflator and ignites the chemicals.
2. The chemicals then rapidly burn in the metal container. The rapid burning produces nitrogen gas and small amounts of dust. The nitrogen gas and dust are cooled and filtered during inflation of the air bag.
3. The inflating air bag splits open the trim cover. The air bag then rapidly unfolds and inflates.
4. After inflation, the gas empties through holes in the air bag. The air bag deflates at once.
Electrical System
The Supplemental Air Bag Restraint System (SRS) is powered directly from the battery. The air bag system can function with the ignition switch in any position, including OFF and LOCK. The air bag system can also function when the driver and passenger seats are unoccupied. The electrical system performs three main functions:
- Detects impacts
- Supplies electrical power to the igniter
- Monitors the system to determine system readiness
The electrical system components include:
- Air bag indicator
- Wiring harness and air bag sliding contact
- Sensors
- Air bag diagnostic monitor
- Igniter within driver side air bag module and passenger side air bag module.
Sensors
WARNING: VEHICLE SENSOR ORIENTATION IS CRITICAL FOR PROPER SYSTEM OPERATION. IF A VEHICLE EQUIPPED WITH AN AIR BAG SYSTEM HAS BEEN INVOLVED IN A CRASH WHERE THE FENDERS OR GRILLE AREA HAVE BEEN DAMAGED, INSPECT THE SENSOR MOUNTING BRACKETS FOR DEFORMATION. IF DAMAGED, THE SENSOR SHOULD BE REPLACED WHETHER OR NOT THE AIR BAG IS DEPLOYED. IN ADDITION, ENSURE THAT THE BODY STRUCTURE IN THE AREA OF THE SENSOR MOUNTING IS RESTORED TO ITS ORIGINAL CONDITION.
The three air bag sensors are located at the front of the vehicle along the body chassis. The RH and LH fender primary crash front air bag sensor and brackets are located beneath the front fenders on the right and left front bumper cover supports. The radiator primary crash center air bag sensor and bracket is located on the radiator support.
The air bag sensors each consist of:
- A sensing mass
- A bias magnet
- A cylindrical tube
- Two electrical contacts
During normal operation, the bias magnet holds the sensing mass in place. The two electrical contacts remain open during normal operation. Upon impact, the sensing mass pulls away from the bias magnet and rolls down the cylinder toward the electrical contacts. When the sensing mass hits the electrical contacts, it completes the air bag deployment circuit.
The air bag deployment circuit is engaged when the safing sensor completes the power circuit while the LH or RH fender primary crash front air bag sensor and bracket or the radiator primary crash center air bag sensor and bracket complete the ground circuit to the igniter to deploy the air bags.
Unless the air bag sensor is damaged during impact, the sensing mass returns to its original position after making contact.
The center cowl safing rear air bag sensor and bracket is located beneath the center console against the bulkhead. It detects the vehicle deceleration rate in the event of a collision.
The center cowl safing rear air bag sensor and bracket consists of:
- A sensing mass
- A bias magnet
- A cylindrical tube
- Two electrical contacts
The design and operation of the center cowl safing rear air bag sensor and bracket is much like that of the LH or RH fender primary crash front air bag sensor and bracket and radiator primary crash center air bag sensor and bracket. The primary difference is the calibration; a center cowl safing rear air bag sensor and bracket magnet is weaker than the LH or RH fender primary crash front air bag sensor and bracket or radiator primary crash center air bag sensor and bracket magnets. The center cowl safing rear air bag sensor and bracket will trigger when the vehicle crashes into a rigid barrier at approximately one or two mph.
The center cowl safing rear air bag sensor and bracket makes sure that, in the event of an electrical short circuit in one of the LH or RH fender primary crash front air bag sensor and bracket or radiator primary crash center air bag sensor and bracket or wiring, the air bags will not deploy when not required.