398 / 948
Anti-lock Braking System(ABS)
6
E. WORKING OF ANTI-LOCK BRAKING
SYSTEM (ABS) :
WARNING:
1. ABS is an aid to retain steering control and
stability while braking.
2.
ABS will not prevent accidents resulting from
excessive cornering speeds, following another
vehicle too closely or aquaplaning, i.e. where
a layer of water prevents adequate contact
between tyre and road surface.
3.
ABS will not improve braking performance or
stopping distance beyond that which is
physically possible in relation to road
conditions and the vehicles tyres or brakes.
4.
The additional control provided by ABS must
never be exploited in a dangerous or reckless
manner which could jeopardise the safety of
driver or other road users.
The ABS ECU takes wheel speed information
from sensors, located within the hub carrier, and
monitors the relative deceleration/acceleration of
each wheel at all times. These signals are used to
calculate the rotational deceleration
(negative
acceleration
) rates for each wheel during braking
operation. In the event of a wheel slip condition
(i.e. rotational deceleration being outside of
allowable limits
) the hydraulic system will control
the brake line pressure by operating the
appropriate solenoid valves within the hydraulic
modulator and thus releasing the brake pressure
from that particular wheel.
Once the wheel deceleration has recovered to
within allowable limits the modulator then allows
pressure to be re-applied to the particular brake
caliper or wheel cylinder from which the brake
pressure was released.
When ABS intervention is necessary the warning
lamp will not illuminate but the driver will feel the
brake pedal pulsating and may experience audible
feedback from the modulator indicating that ABS
control is taking place.
For Best results when using an ABS-equipped
vehicle in an emergency situation take your foot
off the accelerator, Press your foot down fully,
continue pressing firmly and allow the ABS to
regulate Braking for you. This allows you to have
steering control along with maximum possible
braking.
The ABS and EBD warning lamps will illuminate
for a system check when the ignition is switched
on. Both lamps will then extinguish to indicate the
system is healthy.
(As the EBD lamp is shared
with the Parking brake lamp this will not extinguish
until the parking brake is released.)
If a fault
occurs with the system or any of its constituent
components the relevant warning lamp in the
instrument cluster will illuminate to inform the
driver for the respective fault.
i. 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 and 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-
close
Open-close
channel
INLET
OFF
OPEN
Master cylinder -
Wheel cylinder
OUTLET
OFF
CLOSE
Wheel cylinder -
reservoir