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BRAKES
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3. Pressure Reduction Phase:
If the ECU detects that the percentage Slip
relative to the other wheels and vehicle reference
speed is still increasing during the pressure hold
phase and the wheel is tending further towards
lock it will start the pressure reduction phase, as
the existing brake pressure in the wheel brake is
too high. It will activate the relevant outlet valve
within the hydraulic modulator, switching it from its
normally closed position to open. This will allow
fluid to pass from the wheel brake into the
accumulator chamber within the modulator. At the
same time, the ECU will activate the return pump
integrated into the modulator to draw fluid from
the accumulator and wheel brake and return it to
the TMC. This fluid being returned to the TMC is
what is felt as the pulsations at the pedal, and the
amplitude of the pulsations is relative to the
amount of fluid that needs to be reduced.
Pressure reduction will continue until controlled
wheel returns to the vehicle reference speed.
Solenoid
valve
Electricity
status
Valve
open
Open- close
channel
close
INLET
ON
CLOSE
Master
cylinder
Wheel
cylinder
OUTLET
ON
OPEN
Wheel
cylinder
Reservoir
D. FAIL-SAFE FUNCTION:
If the ABS system detects any fault that may
adversely affect its performance it will switch to a
fail-safe shut down mode. When this happens the
electricity supply to the solenoid valves is
deactivated, stopping control signal output, this
causes the valves to switch to their default state.
(Open for inlet valves / Closed for Outlet valves)
The System will light the relevant warning lamp at
the same time to inform the driver the vehicle has
either an ABS or an ABS and EBD failure.
In this condition, the conventional hydraulic brake
circuit will still function, allowing brake pressure to
reach all wheels. It should be noted that with an
ABS fault, it will be possible to lock the wheels
and in the Case of an EBD failure the brake force
proportioning between front and rear will no
longer function and hence rear wheel lock is
possible before front.