Range Rover P38
75
SUPPLEMENTARY RESTRAINT SYSTEM
NEW RANGE ROVER
6
DESCRIPTION AND OPERATION
SYSTEM COMPONENTS DESCRIPTION
SRS Diagnostic and Control Unit (DCU)
The SRS DCU controls the operation of the
supplementary restraint systems by using collision
detection sensors to determine the incidence of a
crash event. There are two basic types of system
utilised:
•
Single point sensed SRS system
•
Distributed SRS system
Both systems utilise the same basic DCU, but the
distributed system also features additional front crash
sensors mounted external to the DCU. The type of
system configuration used is dependent on the
relative market requirements.
The DCU is fitted to the centre console bracket
underneath the console storage bin and mounted to
the bracket by three Torx bolts. The unit is connected
to ground via a dedicated earth eyelet located under
the centre console next to the DCU and attached to
the mounting bracket by a Torx bolt.
A yellow 50-pin connector provides the SRS DCU
connection with the vehicle harness on models from
99MY onwards.
The DCU can sense crash events to the vehicle,
monitored via internal accelerometers. The
acceleration data is electronically processed by an
internal microprocessor controller to determine the
severity of the crash condition. The DCU is able to
use the input data to distinguish between a severe
crash situation and a minor impact or rough road
conditions and so prevent spurious deployment.
An electromechanical safing sensor is incorporated
into the DCU which is a normally open switch, but
closes at a preset deceleration limit. Electronic
switches for each of the squibs are activated if the
severity of the crash condition exceeds a
pre-determined trigger value.
CAUTION: It is important that the DCU is
correctly mounted and is fitted in the
designated location and orientation.
MAIN SENSOR
The main sensor is a deceleration detection device
which is contained in the DCU. The sensor consists of
a spring and weight system which is attached to strain
gauges in a Wheatsone bridge circuit. The ’balance’
nodes of the bridge circuit is connected to an
integrated circuit that can instantly detect a change in
the monitored resistance.
In the event of a collision, the spring and weight move
causing a corresponding change in the resistance of
the related strain gauge. If the change in strain gauge
resistance is greater than a preset value, it
corresponds to a crash condition of sufficient severity
to warrant SRS component deployment. In this case,
the processor provides a signal to initiate airbag
and/or seatbelt pre-tensioner deployment.
Deployment will only be carried out if a confirmation
signal that a crash condition is occurring is received
by the SRS DCU. Crash condition confirmation is
achieved by simultaneous actuation of the safing
sensor and/or one or more of the front crash sensors
in the case of a distributed system.
SAFING SENSOR
This sensor is also contained within the DCU and is
included in the DCU internal circuitry to prevent
unintentional detonation of SRS components. The
safing sensor is connected in series with the main
sensor and operates at comparatively lower rates of
deceleration. When the safing sensor closes in
conjunction with the main sensor exceeding the
trigger value, the electronic switches are activated,
allowing electrical current to be supplied to the driver
and passenger airbag squibs.
The side airbag modules are controlled by electronic
switching and the safing sensor acts as an arming
sensor for the seatbelt pre-tensioners.
SINGLE POINT SENSED SYSTEM
This system relies on the DCU’s internal deceleration
sensor and safing sensor to provide the control inputs
required to confirm activation conditions for SRS
component deployment.
DISTRIBUTED SRS SYSTEM
The DCU used for the distributed SRS system is
identical to the single point system, with the exception
that two external front crash sensors provide
additional inputs to the unit for determining and
confirming a crash condition in conjunction with the
DCU’s internal accelerometer.