Part 1
Air Bag and Safety Belt Pretensioner Supplemental Restraint System (SRS)
General
The SRS (supplemental restraint system) provides additional protection for occupants in certain vehicle accident conditions. The SRS (supplemental restraint system) consists of:
^ A driver air bag. A passenger air bag.
^ A side air bag on each front seat.
^ Side air curtains for first and second row seats.
^ A pretensioner for each front safety belt.
^ A buckle sensor for each front safety belt.
^ Front and side impact sensors.
^ A passenger air bag deactivation indicator.
^ A passenger air bag deactivation switch (all except NAS).
^ An occupant monitoring system for the front passenger seat.
^ A position sensor for the driver seat.
^ An air bag warning indicator.
^ A clockspring.
^ A RCM (restraints control module).
The SRS (supplemental restraint system) features selective activation of the air bags and pretensioners, and two stage driver and passenger air bags. The RCM (restraints control module) monitors internal and external sensors and activates the required safety belt pretensioners and air bags if the sensors detect an impact or roll-over above preset limits.
Driver air bag
The driver air bag forms the center pad of the steering wheel. Four pins and two latches locate and secure the driver air bag to the steering wheel. The latches consist of wire springs on each side of the driver air bag which engage with hooks in the steering wheel. The driver air bag is released from the steering wheel by pulling on the wire springs with a special tool inserted through a slot on each side of the steering wheel hub. Springs on the locating pins then push the driver air bag away from the steering wheel.
A Lucar connector attaches a ground to the driver air bag.
The driver air bag has a two stage inflator, with separate electrical connectors for each stage. The inflator contains a nonazide propellant as the gas generator.
Lines molded into the inner surface of the driver air bag cover provide weak points that split open in a controlled manner when the air bag deploys. The inflated volume of the air bag is 57 liters (2.01 cu.ft).
Passenger air bag
The passenger air bag is located in the instrument panel, behind the upper glove compartment. The bottom of the passenger air bag is attached to a mounting bracket on the in-vehicle crossbeam. The top of the passenger air bag is attached to a chute, which, in turn, is attached to a reinforcement lid in the top of the instrument panel. When the air bag deploys, the chute guides the air bag to the underside of the reinforcement lid. The reinforcement lid incorporates two deployment doors that are forced open, splitting the instrument panel covering, when the air bag deploys.
A Lucar connector attaches a ground to the passenger air bag.
The passenger air bag has a two stage inflator, with separate electrical connectors for each stage. The inflator contains a non-azide propellant as the gas generator. The inflator uses a high pressure mix of air and hydrogen gas as the inflation medium. The inflated volume of the air bag is 130 liters (4.59 cu.ft).
Side air bags
Non NAS Side Air Bag
NAS Side Air Bag
A side air bag is attached to the outside of each front seat backrest frame, under the backrest cover. In all markets except NAS, the side air bags each consist of a single section, which deploys to protect the thorax region. In NAS markets, the side air bags each consist of two sections, inflated using a common inflator, which deploy to protect both the thorax and the pelvic regions.
The side air bags are handed, and each consist of a molded plastic case which contains the folded air bag and the inflator. In all markets except NAS the side air bags incorporate a cable that connects the igniter of the inflator to a connector in the main seat harness connector block located under the front edge of the seat cushion. In NAS markets the seat harness is connected to an electrical connector in the base of the inflator.
When a side air bag deploys it forces the front edge of the molded plastic case apart and splits open the backrest cover.
The side air bags use compressed argon as the inflation medium. In all markets except NAS the inflated volume of each side air bag is approximately 12 liters (0.42 cu.ft). In NAS markets the inflated volume of each side air bag is approximately 10 liters (0.35 cu.ft) for the thorax section and 3 liters (0.11 cu.ft) for the pelvic section.
Side air curtains
The side air curtains are designed to protect the head and upper body of first and second row occupants in side impact and roll-over situations. The side air curtains use compressed argon as the inflation medium.
The side air curtains are installed on the cant rails above the front and rear doors, behind the headliner.
Each side air curtain has an inflator, which is attached to the E pillar by a mounting bracket. The inflator is connected to the air curtain by a gas guide pipe.
The gas guide pipe and air curtain are secured along the cant rail by mounting brackets at each end of the gas guide pipe and two ramps. Tethers attached to the front and rear of the air curtain are anchored to the A pillar and the gas guide mounting bracket respectively. The front of the air curtain is secured to the A pillar by two mounting clips.
When the side air curtain deploys, it breaks out of the two ramps on the cant rail and extends downwards from behind the headliner. The deploying air curtain is tensioned between the tether anchor points on the A pillar and the gas guide mounting bracket. This retains the air curtain in position against the upper part of the doors and the B pillar.
Pretensioners
The pretensioners are used to tighten the front safety belts during a collision to ensure the occupants are securely held in their seats. A pretensioner is integrated into each front safety belt buckle.
Each pretensioner has a tube containing an inflator and a piston. The inflator is connected to the RCM (restraints control module). The piston is attached to a steel cable, the opposite end of which is attached to the safety belt buckle.
On receipt of a fire signal from the RCM (restraints control module), the inflator generates nitrogen gas that rapidly expands to drive the piston along the tube, pulling the cable and drawing the safety belt buckle downwards.
Safety belt sensors
The buckle of each front safety belt incorporates a Hall effect sensor that provides a safety belt status signal to the RCM (restraints control module). The RCM (restraints control module) broadcasts the status of the two front safety belts on the high speed CAN (controller area network) bus for use by the instrument cluster.
Impact sensors
Impact sensors are installed in the front and both sides of the vehicle. The use of multiple impact sensors provides shorter air bag trigger times, through faster detection of lateral and longitudinal acceleration, and improves detection accuracy.
There are two front impact sensors attached to brackets on the body front support frame, just above each front longitudinal.
There are six side impact sensors located in the passenger compartment: One attached to each front door.
^ One attached to the base of each B pillar.
^ One attached to the base of each C pillar.
Each impact sensor incorporates an accelerometer and a microcontroller powered by a feed from the RCM (restraints control module). The power feed also provides the interface connection through which the impact sensor communicates with the RCM (restraints control module) using serial data messages. Acceleration is evaluated by the microcontroller and transmitted to the RCM (restraints control module), which then makes the decision on whether or not to activate the air bags and pretensioners.
When the ignition is switched on the RCM (restraints control module) supplies power to the impact sensors, which perform a self test. After satisfactory self tests the impact sensors continually output 'sensor active' messages to the RCM (restraints control module). If a fault is detected the relevant impact sensor sends a fault message, instead of the sensor active message, to the RCM (restraints control module). The RCM (restraints control module) then stores a related fault code and illuminates the air bag warning indicator.
Passenger air bag deactivation indicator
The passenger air bag deactivation indicator is installed on the center switch pack of the instrument panel. When appropriate, the indicator illuminates to advise front seat occupants that the passenger air bag is disabled. Operation of the indicator is controlled by the RCM (restraints control module). The RCM (restraints control module) illuminates the indicator when:
^ There is a fault with the passenger air bag firing circuit(s).
^ The passenger air bag is deactivated with the passenger air bag deactivation switch (where fitted).
^ Required by passenger seat occupant monitoring (see below).
Passenger air bag deactivation switch (all except NAS)
The passenger air bag deactivation switch provides a method of manually disabling the passenger air bag. The switch is installed in the front passenger end of the instrument panel and operated by the ignition key.
When the passenger air bag deactivation switch is operated, it changes a ground connection between two pins in the connectors of the RCM (restraints control module). When the passenger air bag deactivation switch is selected to OFF, the RCM (restraints control module) disables the passenger air bag and, if the front passenger seat is occupied, illuminates the passenger air bag deactivation indicator.
Occupant monitoring
Occupant monitoring provides the RCM (restraints control module) with the occupancy status of the front passenger seat. On NAS vehicles, the RCM (restraints control module) uses the occupancy status for control of the passenger air bag deactivation indicator.
There are two types of occupant monitoring:
^ In all markets except NAS, vehicles have an occupant detection system.
^ In NAS markets, vehicles have an occupant classification system.
Occupant Detection System (All Except NAS)
The occupant detection system can only determine if the front passenger seat is occupied or unoccupied. The occupant detection system consists of a pressure sensor installed between the foam padding and the cover of the front passenger seat cushion.
The pressure sensor incorporates a number of load cells connected in series and embedded in a plastic film. Weight on the pressure sensor increases the resistance of the circuit.
The instrument cluster supplies a reference voltage to the pressure sensor and measures the current draw to determine the occupancy status. From the occupancy status, and the status of the front passenger safety belt (received from the RCM (restraints control module) on the high speed CAN (controller area network) bus), the instrument cluster determines the belt minder status.
Occupant Classification System (NAS Only)
The occupant classification system can determine if the front passenger seat is unoccupied, occupied by a small person, or occupied by a large person. The occupant classification system consists of:
^ A pressure pad, installed under the cushion of the front passenger seat, which is connected to a pressure sensor.
^ A safety belt tension sensor, integrated into the anchor point of the front passenger safety belt.
^ An occupant classification module, installed under the front passenger seat.
The pressure pad is a silicone filled bladder. Any load on the pressure pad is detected by the pressure sensor.
The safety belt tension sensor is a strain gauge that measures the load applied by the safety belt anchor to the anchor bolt.
The occupant classification module supplies a reference voltage to the pressure sensor and the safety belt tension sensor and, from the return signals, measures the loads acting on the pressure pad and the safety belt tension sensor. The load measurement from the safety belt tension sensor is used to produce a correction factor for the load measurement from the pressure pad. The tightness of the safety belt affects the load acting on the pressure pad, so without the correction factor the occupant classification module cannot derive an accurate occupancy status.
The occupant classification module translates the load readings into a seat occupancy status and transmits the result to the RCM (restraints control module), on a dedicated high speed CAN (controller area network) bus link. The occupant classification module incorporates two load limits for the seat cushion: When the load exceeds the lower limit, but is less than the upper limit, the occupant is classified as small; when the upper limit is exceeded, the occupant is classified as large.
The occupant classification system has four possible states:
^ Empty. Passenger air bag operation is disabled and the passenger air bag deactivation indicator remains off.
^ Occupied inhibit. The seat is occupied by a small person. Passenger air bag operation is disabled and the passenger air bag deactivation indicator is illuminated.
^ Occupied allow. The seat is occupied by a large person. Passenger air bag operation is enabled and the passenger air bag deactivation indicator remains off.
^ Error. There is a fault with the system. Only stage 1 (slowest deployment speed) passenger air bag operation is enabled and the passenger air bag deactivation indicator remains off.
Occupant Classification Module Harness Connector C0962
Occupant Classification Module Harness Connector C0962 Pin Details
Seat position sensor
The seat position sensor allows the RCM (restraints control module) to detect when the driver seat is forward of a given point on the seat track. The seat position sensor consists of a Hall effect sensor attached to the driver seat frame and a target plate on the seat base. While the ignition is on, the RCM (restraints control module) supplies the sensor with a power supply of 12V nominal, and monitors the return voltage. When the seat frame moves forwards, the sensor moves over the target plate, which changes the reluctance of the sensor. The change of voltage is detected by the RCM (restraints control module) and used as a switching point. The switching point is when the center of the sensor is 3 ± 4 mm from the leading edge of the target plate.
When the driver seat is forward of the switching point, the RCM (restraints control module) increases the time delay between firing the two stages of the inflator in the driver air bag. When the driver seat is rearward of the switching point, uses the normal time delay between firing the two stages.