Ford Falcon. Manual — part 80

206-09-9

Anti Lock Control

206-09-9

DESCRIPTION AND OPERATION (Continued)

TCS operation - No ABS or Trac control assistance

Maintaining Pressure

When the ABS ECU detects excessive wheel

deceleration (based on the wheel speed sensor

signals), it commands the build valve to maintain

brake circuit pressure. It does this by supplying a

current to the solenoid coil. This causes the armature

and the valve to move downwards isolating the brake

circuit from the master cylinder.
NOTE: With the brake circuit isolated, brake circuit

pressure between the build solenoid and the caliper

remains constant despite increased master cylinder

hydraulic pressure.

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206-09-10

Anti Lock Control

206-09-10

DESCRIPTION AND OPERATION (Continued)

Maintaining Pressure (ABS operation)

fluid from the brake circuit back to the master cylinder

Reducing Pressure

against brake pedal pressure. The return pump

If isolation of a brake circuit between the modulator

continues to operate during the rest of the anti-lock

and the brake caliper does not reduce the excessive

cycle.

wheel deceleration, the ABS ECU commands the

decay valve to reduce hydraulic brake pressure in the Accumulators

brake circuit. During this phase, the ABS ECU

During the “pressure reduction” phase of ABS

supplies a current to the decay solenoid coil, opening

modulation, the accumulator temporarily stores fluid

the valve. This opens a passage from the brake circuit

from the brake circuits. Some road conditions require

to the accumulator and return pump inlet.

the relief of a large volume of fluid from the brake

NOTE: At this time, the brake circuit is isolated from

calipers. In such conditions, the accumulator

the master cylinder by the return pump valving, and

guarantees pressure reduction. As soon as the

the return pump is energised. This action sends brake

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206-09-11

Anti Lock Control

206-09-11

DESCRIPTION AND OPERATION (Continued)

solenoid valves move to the “pressure reduction”

position, brake fluid from the brake circuit flows into

the accumulator. Thus before the return pump starts,

the accumulator allows an immediate pressure

reduction in the brake circuit.

Reducing Pressure (ABS operation)

cycle begins again. There are approximately up to 10

Increasing (building-up) Pressure

cycles per second, depending on the state of the road

The wheel accelerates again as a result of the

surface.

reduced braking pressure. Upon reaching a specific

NOTE: Circuit pressure cannot increase above master

limit, the ECU registers the fact that the wheel is now

cylinder pressure.

not being braked sufficiently. The ECU then

de-energises the build and decay valves (0 amps) and

the formerly reduced pressure is then increased so

that the wheel is again decelerated. The ABS control

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206-09-12

Anti Lock Control

206-09-12

DESCRIPTION AND OPERATION (Continued)

Increasing (Building-Up) Pressure (ABS operation)

to 10 times a second and can function on either of the

TCS in operation (brake intervention only)

driven wheels, or both.

In this schematic, the right hand wheel speed sensor

Status

has detected that the wheel is about to enter into a

Inlet Valve

Outlet Valve

Prim-

Swit-

Motor

situation where slippage can occur from excess

ing

ching

engine torque for the road conditions.

Valve Valve

The priming valve is open allowing fluid to be drawn

Left Right

Left

Right

Open Closed

On

from the master cylinder by the pump assembly. The

switching valve is closed ensuring the fluid is directed

Open Open Closed Closed

to the wheels and not back to the master cylinder.
With the right wheel tending to slip, the inlet valve on

the left side closes allowing only the brakes to be

applied to the right wheel. This will transfer the engine

torque to left wheel. This operation can be applied up

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