SUPPLEMENTARY RESTRAINT SYSTEM (SRS) 11 24.7 COMPONENTS A RESTRAINT WITHOUT AIRBAGS Restraints system without airbags consists of following main components: Seat Belt. Emergency Locking Retractor (ELR). Micro-switch. I. SEAT BELT With these seat belts occupants have to buckle the seat belts before starting to drive the vehicle. II. 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. III. MICRO-SWITCH / SEAT BELT REMINDER WARNING LAMP Micro switch is a device which indicates the whether the seat belt is engaged or not. This switch activates the warning light (which is in the instrument cluster) if the seat belts are not worn or not buckled properly. B 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 ENERGY RESERVE SRS ECU maintains a Reserve energy supply to provide deployment energy after ignition voltage is lost during crash. However, the energy reserve is for a limited duration, therefore battery terminals and its connection to airbag ECU needs to be checked. 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 crash of sufficient severity, it sends signal to the SRS ECU which in turn sends signal to the air bag (inflator) modules for deployment. LAMP CONTROL AFTER FIRST CRASH: “AIR BAG” warning lamp is turned and kept ON. SRS ECU needs replacement if it has sensed a crash.
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