SAFARI

ANTI-LOCK BRAKES

ABS

Fig. 14

6. ELECTRONIC BRAKE DISTRIBUTION (EBD)

EBD substitutes load conscious reducing valve. Its

function is not determined by the brake pressure or

the weight transfer but by the amount of wheel slip.

EBD function is an additional program to the

conventional ABS program. It reduces the pressure

at the rear depending upon the wheel slip and

pressure reduction is carried out after certain

pressure-maintaining phase. It maintains the brake

pressure to both the rear wheels same. If any of the

rear wheels is still over braked, ABS becomes

operational. EBD warning lamp is turned on in

case of error in the EBD system. EBD failure does

not necessarily mean ABS failure.

EBD (Electronic Brake-force Distribution) Control

Necessity

During braking, whenever the rear axle wheels

lock before the front axle wheels, the vehicle

will loose its control & it may start to spin. This

is because, braking is always associated with

a certain weight transfer from rear axle onto

the front axle wheels. Due to this drift of the

vehicle weight, there will be lesser normal force

acting on the rear axle when compared to the

front axle. Due to lesser normal force, rear axle

wheels can support lesser brake pressure. In

a passenger vehicle, as a counter measure to

this problem, the brake circuit for the rear axle

will be fitted with LCRV (Load conscious

regulating valve). This LCRV avoids the locking

of rear axle wheels before the front axle wheels.

But LCRV is a mechanical vehicle component

and it cannot result in ideal brake force

distribution for the rear axle wheels. LCRV

distributes rear brake force according to vehicle

load to a certain degree.

The brake force required for optimum braking

may be different for each wheel. This is

depending on the road surface, the condition

of the friction material of brake lining/ pad &

also the condition of the tyres (old/ new). With

LCRV, when the same brake force reaches both

the rear axle wheels, ideal braking cannot be

achieved by the rear axle wheels.

When the LCRV fails in any vehicle, the driver

has no chance of knowing about this failure.

Under this condition, when braked, the vehicle

may deviate/ spin (depending on the brake force

applied by the driver) from the intended driving

direction.

In the Safari vehicle with ABS system, the ECU

incorporates a special function by name EBD

(Electronic Brake force Distribution). With this

EBD, the conventional mechanical LCRV has

Outlet Pressure

Inlet Pressure (bar)

Inlet Pressure

EBD start point

Vehicle equipped with LCRV

Vehicle equipped with EBD system

Outlet Pressure

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