HEXA

Anti-lock Braking System(ABS)

2. Pressure Reduction Phase :

If the ECU detects that the % 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 the

controlled wheel speed returns to the vehicle

reference speed.

Solenoid

valve

Electricity

status

Valve

open-

close

Open-close

channel

INLET

Master cylinder

-Wheel

cylinder

OUTLET

OPEN

Wheel

cylinder -

reservoir

3. Pressure increase Phase :

As the ECU detects that the speed of the

controlled wheel has increased to the vehicle

reference speed and hence the % slip reduced. It

will sequentially deactivate the outlet and inlet

valves switching them to their normal positions.

With the outlet valve closed further pressure

reduction is prevented and the inlet valve can be

opened to allow brake fluid from the TMC to enter

the wheel brake increasing the brake pressure

once again. If the driver releases the brake at any

time during ABS control the inlet valves will be

deactivated and fluid can return to the TMC via

the inlet valve and the one way valve.