TIAGO

BRAKES

A. BRAKING WITHOUT ABS IN OPERATION:

In case of normal braking operation when no

wheel speed differences are detected and neither

ABS nor EBD are active, when the driver presses

the brake pedal, brake pressure developed in

tandem master cylinder (TMC) reaches to each

wheel through hydraulic control unit (HCU).

During this phase, both inlet & outlet solenoid

valves are switched OFF (or not excited) by the

ECU. Hence the inlet valve is open and outlet

valve remains closed allowing the brake fluid to

flow freely through the inlet valve and to the

relevant wheel.

When the driver releases brake pedal, the brake

fluid flows back from the wheel, through the

respective one way valve towards TMC.

Solenoid

valve

Electricity

status

Valve

open

Open- close

channel

close

INLET

OFF

OPE

Master

cylinder

Wheel

cylinder

OUTLET OFF

CLOS

Wheel

cylinder

Reservoir

BRAKING

WITH

EBD

INTO

OPERATION:

In case of a braking where the ABS ECU detects

a slip difference between the front and rear

wheels, EBD comes into operation. If the

difference in wheel slip between the front and rear

wheels exceeds a predetermined threshold the

ABS activates the pressure inlet valves for the

rear wheels, closing the valves and preventing

further pressure build up at that rear axle.

If during the braking event, this slip ratio between

the front and rear axle reduces below the

threshold level the inlet valves will be de-activated

and switch back to their normally open state

allowing further pressure increase at the rear axle.

In this way the rear axle can follow more closely

to the Ideal braking force distribution curve for the

rear axle.

If the driver releases the brake, the inlet valves

will be deactivated and fluid can return to the TMC

via the inlet valve and the one way valve.

EBD control only acts upon the rear axle and can

only limit pressure being applied to a rear wheel, it

cannot perform pressure reductions.

Solenoid

valve

Electricity

status

Valve

open

Open- close

channel

close

INLET

Master

cylinder

Wheel

cylinder

OUTLET

OFF

Wheel

cylinder

Reservoir

Fig: Pressure increase on rear axle following

ideal brake force distribution curve.