Range Rover P38
70
BRAKES
NEW RANGE ROVER
6
DESCRIPTION AND OPERATION
ANTI-LOCK BRAKE SYSTEM - DESCRIPTION
Anti-lock Braking System (ABS)
NOTE: On vehicles up to 99MY, the
Anti-lock Brake System (ABS) is a
standard feature, with Electronic Traction
Control (ETC) optional. On vehicles from 99MY the
ABS and ETC is standard on all models.
The brake system is hydraulically power assisted with
an integrated, electronically controlled four channel
ABS system.
The use of a power assisted brake system means
that, during brake application, additional hydraulic
energy is provided by the hydraulic power unit.
This hydraulic power unit consists of an electrically
driven pump and an accumulator which stores
hydraulic energy in readiness for brake application. A
pressure switch controls hydraulic pump operation to
maintain fluid pressure in the accumulator.
Fluid pressure is distributed from the brake
booster/ABS modulator unit to each of the four brake
calipers. Foot pedal pressure is assisted by pressure
created in the master cylinder and direct pressure
from the power valve. The combination of the master
cylinder and the power valve allows the driver to vary
braking force by varying force applied to the brake
pedal.
The hydraulic system comprises two completely
independent circuits, with a vertical i.e. front/rear split.
The combined POWER and HYDROSTATIC
CIRCUIT supplies the front calipers. The POWER
CIRCUIT supplies the rear calipers.
The purpose of ABS is to prevent the vehicle wheels
locking during brake application, maintaining vehicle
steerability and stability. This allows the vehicle to be
steered while the brakes are applied, even under
emergency conditions, and to avoid obstacles where
there is sufficient space to redirect the vehicle.
The ABS system on vehicles up to 99MY uses a ’C’
series ABS ECU which includes an optional two wheel
electronic traction control feature. The ECU has a
single connector and is located on the bulkhead
behind the glovebox.
On vehicles from 99MY a ’D’ series ABS ECU is used.
The ’D’ series ECU features four wheel electronic
traction control which is a standard feature on all
models. The ECU has three connectors and is located
in the same position as the ’C’ series ECU.
The ABS ECU receives wheel speed information from
four wheel speed sensors. The ECU monitors the
deceleration of each wheel during braking and, in the
event of one or more wheels being outside the
expected values, controls via the hydraulic system the
braking force available to that wheel.
When the wheel speed has returned to within the
expected limits, the ECU restores the hydraulic
pressure to the wheel. The ABS system allows
optimal stopping distances to be achieved and
prevents the wheels from locking.
The system is active after the ignition is switched to
position II and has completed a bulb check. ABS and
ETC warning lamps in the instrument pack warn of
system operation and failure. Normal (non-ABS)
braking remains available in the event of an ABS
system failure.
When the ABS system operates, the driver will
experience an audible noise from the ABS modulator
and vibration transmitted through the brake pedal.
WARNING: ABS IS AN AID TO RETAINING
STEERING CONTROL AND STABILITY
WHILE BRAKING.
•
ABS CANNOT DEFY THE NATURAL LAWS
OF PHYSICS ACTING ON THE VEHICLE.
•
ABS WILL NOT PREVENT ACCIDENTS
RESULTING FROM EXCESSIVE CORNERING
SPEEDS, FOLLOWING ANOTHER VEHICLE
TOO CLOSELY OR AQUAPLANING, I.E.
WHERE A LAYER OF WATER PREVENTS
ADEQUATE CONTACT BETWEEN TYRE AND
ROAD SURFACE.
•
THE ADDITIONAL CONTROL PROVIDED BY
ABS MUST NEVER BE EXPLOITED IN A
DANGEROUS OR RECKLESS MANNER
WHICH COULD JEOPARDISE THE SAFETY
OF DRIVER OR OTHER ROAD USERS.