L322 Range Rover System Description and Operation
RESTRAINT SYSTEMS
75-20
DESCRIPTION AND OPERATION
Operation
SRS
In a collision the sudden deceleration or acceleration is measured by the side impact sensors and the crash sensors
in the DCU. The DCU evaluates the readings to determine the impact point on the vehicle and whether the
deceleration/acceleration readings exceed the limits for firing the airbags, the pretensioners and the battery
disconnect unit. The DCU incorporates the following limits to cater for impacts of varying severity and at different
points on the vehicle:
l
Pretensioner
l
Driver and passenger airbag 1
l
Driver and passenger airbag 2
l
Driver and passenger airbag 3
l
Driver and passenger airbag 4
l
Rear impact
l
Battery disconnect unit
l
LH side and head airbags
l
RH side and head airbags.
Firing Strategies
The seat belt pretensioners are fired when either the pretensioner or the rear impact limit is exceeded. In a frontal
impact, the DCU only fires the pretensioners if the safing sensor has closed, and also evaluates the inputs from the
seat belt switches (where fitted) and the seat occupancy module before it comes to a firing decision.
The driver and passenger airbags are fired in a frontal impact. The time delay between firing the two gas generators
in each airbag decreases with the increasing severity of the impact, until, at the most severe impact limit (driver and
passenger airbag 4), the gas generators are fired simultaneously. In a frontal impact, the DCU only fires the driver
and passenger airbags if the safing sensor has closed, and also evaluates the inputs from the seat belt switches (NAS
only) and the seat occupancy module before it comes to a firing decision.
If there is a fault with a seat belt switch input (NAS only), the DCU assumes the seat belt is fastened for the
pretensioner firing strategy and unfastened for the airbag firing strategy. If there is a fault with the occupancy detection
sensor, the DCU assumes the front passenger seat is occupied.
Front and Rear Impact Firing Strategy (All Except NAS)
Passenger Seat
Status
Strategy
Applicable Pretensioner
Driver Airbag
Passenger Airbag
–
Fired at pretensioner or
rear impact limit
Fired at limit 2 or above
–
Occupied
Fired at pretensioner or
rear impact limit
–
Fired at limit 2 or above
Unoccupied
Fired at pretensioner or
rear impact limit
–
Not fired