Range Rover P38
70
BRAKES
NEW RANGE ROVER
10
DESCRIPTION AND OPERATION
Hydraulic components
Numbers refer to location of components illustrations
Brake booster/ABS modulator unit
Mounted in the same position as a conventional brake
master cylinder/servo unit, the brake booster/ABS
modulator contains the following components: fluid
reservoir, power valve, master cylinder, isolating
valve, ABS control valves and servo cylinders. It also
contains the ETC solenoid control valves
NOTE: The brake booster/ABS modulator
unit is not a serviceable item, if internal
failure occurs a new unit must be fitted.
The fluid reservoir and its seals may be changed
in the event of damage.
WARNING: Extreme care must be taken
when changing reservoir seals to avoid
ingress of debris.
Fluid reservoir - 1.
Mounted on top of the unit, the plastic reservoir is
subdivided internally to provide separate capacity for
brake fluid used in the hydrostatic and power circuits.
A central tube incorporates a filter. A built in fluid level
warning switch and a finer filter for the power circuit
fluid are also incorporated. The fluid level warning
switch is closed when there is sufficient fluid in
reservoir.
On manual vehicles, the reservoir also supplies fluid
to the clutch system.
Master cylinder - 2.
Operation the of master cylinder displaces a volume
of brake fluid into the servo cylinders and increases
fluid pressure. Piston movement inside the master
cylinder will also activate the power valve.
Power valve - 3.
The power valve is an extension of the master
cylinder, it controls fluid pressure in the power circuit
in direct proportion to pressure in the master cylinder.
The power valve is of spool valve design.
Isolating valve - 4.
The isolating valve consists of two solenoid valves
controlling fluid inlet and outlet. Their function is to
disconnect the master cylinder from the servo
cylinders and to connect the servo cylinders to the
reservoir return during ABS function.
ABS solenoid control valves, 8 off - 5.
Each pair, comprising inlet and outlet solenoid valves,
control ABS braking to each wheel. In response to
signals from the ECU, the valves decrease, hold or
increase brake pressure according to the need to
retain wheel rotation and obtain optimum braking. The
solenoid valves are designed to respond rapidly to
ECU signals.
Servo cylinders, 2 off - 6.
Servo cylinders have five functions:
1. To provide combined energy from both
hydrostatic and power circuit to brake calipers.
2. To provide ’brake feel’ at the brake pedal.
3. To provide hydrostatic (master cylinder) braking
through the servo cylinders to calipers in the
event of no power circuit pressure to servo
cylinders.
4. To provide braking from the power circuit and
from hydrostatic fluid remaining in servo cylinder,
in event of no hydrostatic circuit pressure from
master cylinder.
5. To provide ABS control to the front calipers in
response to pressure modulations in the power
circuit.