1651 / 1906
SUPPLEMENTARY RESTRAINT SYSTEM (SRS)
3
24.2 WORKING OF RESTRAINTS
A. RESTRAINTS WITHOUT AIRBAGS
This restraint system falls under the category of Pri-
mary restraint systems.
PRIMARY RESTRAINT SYSTEM
Seat belts are known as primary restraints systems
as they provide the basic safety to occupants during
driving or accidents.
WORKING
The basic purpose of seat belts is to control occu-
pant movement inside the vehicle during driving
conditions, abrupt braking or accidents. They help in
avoiding or reducing the contact severity of occu-
pants with vehicle interiors.
It is necessary to wear the seat belts by the occu-
pants before starting to drive the vehicle. The seat
belts have a retractor mechanism which ensures
only the required seat belt webbing length is availa-
ble for occupant usage. This reduces the risk of any
loose webbing over the body of occupants. The seat
belts have a locking mechanism which gets activated
in relevant conditions thereby preventing any loose
belt webbing to come out of retractor.
This phenomenon helps in controlling occupant
movement inside the vehicle.
COMPONENTS
1. Seat belt
2. Micro switch
3. Indicator lamp in cluster
B. RESTRAINTS WITH AIRBAGS
This restraint system falls under the category of
Supplementary restraint system.
SUPPLEMENTARY RESTRAINT SYSTEM
(SRS)
Air bags are the secondary restraint system as no
action is required by the vehicle occupant for the
activation of air bags.
WARNING
Seat belts shall be worn by every occupant whenev-
er they ride a vehicle. This is applicable whether a
vehicle is equipped with supplementary restraints
systems (SRS) or not.
24.3 WORKING OF SRS
Whenever there is an accident the sensor mounted
remotely sends crash signal to the ECU. The type of
accident and its severity, determines the time-to-fire
different airbags in the system. The basic function of
an airbag is to provide cushioning effect to occu-
pants.
There are remote sensors mounted for sensing dif-
ferent frontal and side accidents. These sensors are
connected to the electronic control unit (ECU) of the
system. When an accident event input signal crosses
a pre-defined threshold level in ECU, the ECU trig-
gers the relevant restraints components in the sys-
tem. This helps in providing necessary protection to
occupants. The airbags and seat belt pretensioners
get triggered through ECU signal. The load limiter in
the seat belts is a mechanical device which gets ac-
tivated when the forces on the occupant upper body
region crosses a defined force threshold limit.
WARNING
RPLL seat belts for Driver and Passenger should be
fitted only in the vehicle fitted with both frontal air-
bags.
COMPONENTS
1. ECU
2. Remote Sensors
Front remote sensor / Front Impact Sensor
Side remote sensor / Side Impact Sensor
3. Air bags
Driver air bag
Passenger air bag
Side air bag
Curtain air bag
4. RPLL
5. Clock spring
6. Airbag warning lamp
7. PAB deactivation switch
8. PAB indicator
9. Airbag warning labels