Isuzu Amigo / Axiom / Trooper / Rodeo / VehiCross. Manual - part 1169

BRAKE CONTROL SYSTEM

5A–5

Normal Braking

During normal (non anti-lock) braking, the solenoid
valves has current flow. The dump valve is closed and
the isolation valve is opened due to spring force.

Brake fluid travels through the centre of the isolation
valve (normally open) around the dump valve (normally
closed) then to the brake pistons.

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(1) Brake
(2) Master Cylinder

5A–6

BRAKE CONTROL SYSTEM

Pressure Isolation (Pressure Maintain)

The electro-hydraulic control unit is activated when the
brakes are applied.
If the information from the wheel speed sensors
indicates excessive wheel deceleration (imminent
lockup), the first step in the anti-lock sequence is to
isolate the brake pressure being applied by the brake
pedal.

The microprocessor in the coil integrated module sends
a voltage to the coil to energize and close the isolation
valve. This prevents any additional fluid pressure
applied by the brake pedal from reaching the wheel.
With the isolation valves closed, unnecessary increase
in the brake pressure is prevented.

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(1) Brake
(2) Master Cylinder

BRAKE CONTROL SYSTEM

5A–7

Pressure Reduction

Once the brake pressure is isolated, it must be reduced
to allow the wheels to unlock. This is accomplished by
dumping a portion of the brake fluid pressure into a low
pressure accumulator.
The microprocessor activates the normally closed dump
valve to open, allowing fluid from the wheels to be
dumped into the accumulator. This is done with very
short activation pulses opening and closing the dump

valve passageway. Brake pressure is reduced at the
wheel and allows the wheel to begin rotating again. The
fluid from the brake piston is stored in the accumulator
against spring pressure and a portion of this fluid also
primes the pump.
The dump valves are operated independently to control
the deceleration of the wheel.

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(1) Brake
(2) Master Cylinder

5A–8

BRAKE CONTROL SYSTEM

Pressure Increase (Re-apply)

The re-apply sequence is initiated to achieve optimum
braking. The isolation valve is momentarily opened to
allow master cylinder and pump pressure to reach the
brakes. This controlled pressure rise continues until the
wheel is at optimum brake output or until the brake
pressure is brought up to the master cylinder output
pressure.
If more pressure is required, more fluid is drawn from
the master cylinder and applied to the brakes. The

driver may feel slight pedal pulsations, or pedal drop,
this is normal and expected. 
As fluid is re-applied to the brakes, the wheel speed will
reduce. If the wheels approach imminent lockup again,
the module will isolate, dump and re-apply again. This
cycle occurs in millisecond intervals, allowing several
cycles to occur each second. It is a much faster and
more controlled way of“pumping the pedal”.

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Legend

(1) Brake
(2) Master Cylinder