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SUPPLEMENTARY RESTRAINT SYSTEM (SRS)
8
7. COMPONENTS
7.1. RESTRAINT WITHOUT AIRBAGS
Restraints system without airbags consists of
following main components:
Seat Belt.
Emergency Locking Retractor (ELR).
Micro-switch (inside seat belt buckle).
A. SEAT BELT
With these seat belts occupants have to buckle
the seat belts before starting to drive the vehicle.
B. EMERGENCY LOCKING RETRACTOR (ELR)
It is a locking mechanism which is activated in
following conditions:
When a sudden deceleration is sensed
When the seat belt webbing pull-out speed
exceeds a threshold value
When one side of the vehicle is more inclined
than the other side.
E.g. If one of the vehicle tyre goes off-road during
driving.
C. MICRO-SWITCH / SEAT BELT REMINDER
WARNING LAMP
Micro switch is a device which indicates the
whether the seat belt is worn or not. This switch
activates the warning light
(which is in the
instrument cluster
) If the seat belts are not
buckled properly or not worn.
7.2. RESTRAINT WITH AIRBAGS
i.
ECU
The SRS ECU gets power supply from vehicle
battery and is designed to perform the following
functions in the air bag system:
FUNCTIONS
CRASH DETECTION
SRS ECU monitors vehicle deceleration levels to
detect crashes which are severe enough to
warrant deployment.
AIR BAG DEPLOYMENT
When sensors detect a frontal crash of sufficient
severity, and send signals to the SRS ECU which
in turn take deployment decision and causes
enough current to flow to the air bag (inflator)
modules to deploy them.
Once Crash is detected, Airbag ECU publishes
Crash Out Signal on CAN bus to BCM and EMS.
BCM then enables door unlock and EMS performs
fuel Cut-Off.
AIRBAG WARNING LAMP CONTROL AFTER
FIRST CRASH:
“AIR BAG” warning lamp is turned and kept ON.
Once Airbag firing signal is given, ECU cannot be
reset using diagnostic tester.
Once Airbag ECU fires the restraint components,
ECU is locked and should be replaced.
Refer post-accident procedures for details
ENERGY RESERVE
SRS ECU maintains a Reserve energy supply to
provide deployment energy after ignition voltage is