TIAGO

BRAKES

C. BRAKING WITH ABS INTO OPERATION:

In the case of braking where the ABS ECU

detects a significant difference in the wheel speed

information from the individual wheels. The

electronic control unit instructs the hydraulic

modulator to modulate the brake pressure being

applied at the affected wheel(s). There are three

stages to this control.

1. 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.

Solenoid

valve

Electricity

status

Valve

open

Open- close

channel

close

INLET

OFF

OPEN

Master

cylinder

Wheel

cylinder

OUTLET

OFF

Wheel

cylinder

Reservoir

2. Pressure Maintaining (Hold) Phase:

When the braking forces being applied are higher

than can be transmitted to the road surface for a

specific wheel the ECU will detects that wheel as

tending towards lock (Slip relative to other wheels

and a calculated vehicle reference speed). It will

activate the relevant Inlet

valve within the

hydraulic modulator, switching it from its normally

open position to closed, hence preventing further

pressure being transmitted from the TMC to the

affected wheel brake. As the outlet valve is also

closed in this phase the pressure at the wheel is

maintained.

If the driver reduces the brake pedal effort during

ABS control brake fluid can return to the TMC

through the one way valve located within the

modulator in parallel to the Inlet valve.