Part 1 Of 2
Air Bag And Safety Belt Pretensioner Supplemental Restraint System (SRS)
COMPONENT LOCATIONS - SHEET 1 OF 2
COMPONENT LOCATIONS - SHEET 2 OF 2
OVERVIEW
WARNING: All pyrotechnic devices are dangerous. Before performing any procedures on any pyrotechnic device, read all information contained within the Standard Workshop Practices.
The SRS (supplemental restraint system) activates pretensioners and/or air bags if the vehicle suffers an impact above preset limits. When it activates the pretensioners/air bags the SRS (supplemental restraint system) also disconnects the starter lead from the battery. The SRS (supplemental restraint system) consists of:
^ An RCM (restraints control module)
^ Four side impact sensors
^ An occupancy sensor(NAS (north American specification) only)
^ An occupancy sensor module (NAS (north American specification) only)
^ Safety belt switches
^ Safety belt pretensioners
^ A driver air bag
^ A passenger air bag
^ Side air bags
^ Front head air bags
^ Rear head air bags
^ A battery disconnect unit
^ A clockspring
^ A warning lamp
^ A driver knee bolster airbag
^ A belt minder sensor
^ A passenger airbag deactivation switch (Not NAS and Australia)
^ A passenger airbag deactivation indicator (not Australia).
The SRS (supplemental restraint system) features selective activation of the air bags and pretensioners, and two stage driver and passenger air bags. The driver and passenger air bags each have two gas generators which are fired sequentially, with a variable time delay between firings to adjust the speed of air bag inflation to the severity of the crash impact.
RCM (restraints control module)
The RCM (restraints control module) is installed on the top of the transmission tunnel, beneath the transmission gear selector lever assembly, and controls the operation of the SRS (supplemental restraint system). The main functions of the RCM (restraints control module) include:
^ Crash detection and recording.
^ Air bag and pretensioner firing.
^ Self test and system monitoring, with status indication via the warning lamp and non-volatile storage of fault information.
WARNING: The electrical connectors must not be connected to the restraints control module unless it is properly secured to the vehicle. Movement of the restraints control module while connected to the vehicle wiring could cause air bag deployment.
A safing function is provided by accelerometers in the RCM (restraints control module) to concur impacts. Various firing strategies are employed by the restraints control module to ensure the air bags/pretensioners that are fired are appropriate to the severity and direction of the impact. The firing strategy used also depends on the inputs from the safety belt buckle switches, seat position sensor, passenger air bag deactivation switch, and the occupant classification sensor, dependant on market.
An energy reserve in the RCM (restraints control module) ensures there is always a minimum of 150 milliseconds of stored energy available if the power supply from the ignition switch is disrupted during a crash. The stored energy is sufficient to produce firing signals for the driver air bag, the passenger air bag and the safety belt pretensioners.
When the ignition is switched on the RCM (restraints control module) performs a self test and then performs cyclical monitoring of the system. If a fault is detected the RCM (restraints control module) stores a related fault code and sends the signal to illuminate the air bag warning indicator. The faults can be retrieved by the Land Rover approved diagnostic system via the high speed CAN (controller area network) bus connection (J1962). If a fault that could cause a false fire signal is detected, the RCM (restraints control module) disables the respective firing circuit, and keeps it disabled during a crash event.
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 the headlamp surround panel below the headlamps.
There are four side impact sensors located in the passenger compartment, as follows:
^ One attached to the base of each B/C pillar
^ One attached to the base of each D pillar.
Each impact sensor incorporates an accelerometer and a microchip powered by a feed from the RCM (restraints control module). The power feed also provides the interface connection through which the side impact sensor communicates with the RCM (restraints control module) using serial data messages. Acceleration is evaluated by the microchip and transmitted to the 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 'digital acceleration' messages to the restraints control module. If a fault is detected the relevant impact sensor sends a fault message, instead of the digital acceleration message, to the restraints control module. The RCM (restraints control module) then stores a related fault code and illuminates the air bag warning indicator. Faults can be retrieved by the Land Rover approved diagnostic system from the RCM (restraints control module) via the high speed CAN (controller area network) bus connection (J1962).
PASSENGER AIR BAG DEACTIVATION SWITCH (ALL EXCEPT NAS AND AUSTRALIA)
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.
PASSENGER AIR BAG DEACTIVATION INDICATOR (ALL EXCEPT AUSTRALIA)
The passenger air bag deactivation indicator is installed in the overhead console (on the header rail). 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) that warrants disablement
^ The passenger air bag is deactivated with the passenger air bag deactivation switch (where fitted)
^ The occupant classification sensor sends a passenger air bag disable state.
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. While the ignition is on, the RCM (restraints control module) supplies the sensor with power, and monitors the return current.
When the seat frame moves forwards, the sensor moves over the edge of the seat track, which changes the reluctance of the sensor. The change of current 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 seat track.
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, the RCM (restraints control module) uses the normal time delay between firing the two stages.
OCCUPANT MONITORING
There are two types of occupant monitoring:
^ In all markets except NAS & Australia, vehicles have an occupant detection sensor
^ In NAS markets, vehicles have an occupant classification system
For markets which have an occupant detection sensor, this has no interface with the restraints system and only provides the belt reminder function.
For markets that have an occupant classification system, this provides the RCM (restraints control module) with the occupancy status of the front passenger seat. The restraints control module uses this and the seat buckle status in the evaluation of the firing strategy for the passenger front air bag, side air bag, and pretensioner.
SAFETY BELT SWITCHES
A safety belt switch is installed in the buckle of each front safety belt to provide the RCM (restraints control module) with a status signal of the related safety belt(s). When the safety belt is unfastened the switch outputs a low current to the RCM (restraints control module). When the safety belt is fastened the switch outputs a high current to the RCM (restraints control module).
OCCUPANCY SENSOR
The occupancy sensor is installed in the cushion of the front passenger seat between the foam padding and the cover.
The sensor consists of a foil contact circuit, embedded in a plastic sheet. Weight on the sensor reduces the resistance of the circuit. The occupancy sensor is directly connected to the instrument cluster and has no input into the SRS (supplemental restraint system).
OCCUPANT CLASSIFICATION SYSTEM
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 sensor is located in the lower safety belt anchor point.
Safety Belt Tension Sensor
The occupant classification module supplies a reference voltage to the pressure sensor and the safety belt tension sensor and, from the returned 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 4 possible states which are detailed in the following table.
OCCUPANCY SENSOR MODULE
The occupancy sensor module is installed on the underside of the front passenger seat. The module supplies a power feed to the occupancy sensor and monitors the return voltage to determine if the seat is occupied or not. The result is transmitted to the RCM (restraints control module) on the High speed CAN (controller area network) bus. The occupancy sensor module also monitors for short and open circuits in the occupancy sensor. If it detects a fault, the occupancy sensor module transmits a fault message in place of the status message.
PRETENSIONER
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 and attached to a bracket on the inboard side of the seat.
Each pretensioner has a tube containing propellant and a piston. The piston is attached to a steel cable, the opposite end of which is attached to the safety belt buckle. A squib in the base of the tube provides an ignition source when triggered by a fire signal from the RCM (restraints control module).
On receipt of a fire signal from the RCM (restraints control module), the squib ignites the propellant. The propellant produces nitrogen gas that rapidly expands to drive the piston along the tube, pulling the cable and drawing the buckle downwards.
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.
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 driver air bag deploys. The inflated volume of the air bag is 57 liters (2.01 ft3).