What is ABS?
ABS is
the short form for Anti lock Braking System which is a safety device installed
in vehicles.
Why is ABS used?
ABS is
used to prevent wheel locking while applying brakes to the wheels. In certain
scenarios owing to the surrounding conditions (such as wet roads, dry surface,
snowy surface, loose gravel, etc.), wheels might skid when brakes are applied
suddenly.
In
other words, wheels might get locked which increases the stopping distance of
the vehicle and also defies the driver the control on the
steering, leading to fatal injuries and in certain cases can lead to
death. ABS helps in maintaining the traction between the wheels and the
surface, thereby preventing the wheels from locking. It also allows the driver
to steer the vehicle and avoid obstacles.
When was ABS introduced?
ABS was
developed in the year 1929 by Gabriel Voisin, a French national who designed it
only for aircraft. It was in the year 1958 that ABS was experimented on a Royal
Enfield Super Meteor Motorcycle and it greatly reduced the stopping distance of
the motorcycle. The system was however not used for commercial purpose.
Later
in the year 1970, Ford added an electronic ABS system called 'sure-track' on
the rear wheels of the Lincoln Continental model as optional for the customers.
A year later, Ford made it standard in Lincoln models. Chrysler, along with the
Bendix corporation, developed a computerized three channel, four sensor all
wheels ABS called 'Sure Brake' for its Imperial model launched in 1971.
In the year 1978, Mercedes Benz introduced the second generation ABS
with the help of Bosch. Mercedes Benz was the first company to introduce
commercial cars with ABS and also ensured large scale production of ABS. This
was all possible due to the revolution in electronics. Integrated circuits and
computers could be built which with the help of computer codes could detect the
speed of the wheels and actuating the valves in no time and made the process
simpler and accurate.
ABS Components:
ABS has
4 main components:
1.Speed sensors: ABS has to know when the
wheel is about to lock up. So sensors are located over the wheels to
provide this information.
2. Valves: Valves are located in the
brake line of each brake which can be controlled by the ABS. Valve has 3
positions in some systems:
- In position one,
the valve is open and the pressure from the master cylinder is passed
right through it to the brake.
- In position two,
the valve is closed, thereby blocking the pressure from the master
cylinder to the brake.
- In position three,
the valve releases some amount of pressure from the brake. The
controller signals the valve to release the pressure once the sensor
senses the wheel is about to slip.
3. Pump: Pump is used to restore
the pressure that was released from the brakes. The controller will control the
pump and makes it pump the required amount of pressure to the brake.
4. Controller: Controller
is the brain of the ABS, also called the Electronic Control Unit (ECU) which
receives the signals from the wheel speed sensors and modulates the ABS system
by controlling the braking valves. If the vehicle is about to slip, controller
will release the pressure from the brakes through the valve.
ABS Working:
The controller (ECU) continuously monitors the speed of each
wheel with the help of speed sensors. If the ECU detects that one wheel is
rotating slower (for a 4 wheeled vehicle) than the other wheels, then it
actuates the valve to reduce the braking pressure on that particular wheel so
that it can start rotating faster and match the speed of the other wheels.
Conversely,
for a wheel rotating faster than the other wheels, the controller actuates the
valve to increase the braking pressure on that particular wheel to slow it down
and match other wheels' speed.
The
driver can feel the ABS working through his or her foot through the brake
pedals which will be pulsating. In some cases, ABS can release or apply the
brake pressure 15 times per second.
Types of ABS:
ABS can
be classified into various types based on the number of speed sensors and
valves:
1.
Three channel, three
sensor ABS: This system has a speed sensor and a valve for each of the front
wheels, and a common speed sensor and a valve for both the rear wheels. For
rear wheels, it is located on the rear axle. This system provides maximum
efficiency for the front wheels. In the case of rear wheels, both the wheels
have to lock up for the ABS to function. There is always a possibility of one
of the rear wheels to lock up, reducing the effectiveness of ABS.
2.
One channel, one sensor
ABS: This system is commonly used only for rear wheels which will
have a common valve and a speed sensor. Both the rear wheels have to lock up so
that the ABS can work. This is a rather ineffective system.
3.
Three Channel, four
sensor ABS: This system employs separate speed sensors for each wheel and
separate valves for each of the front wheels. A common valve is used for the
rear wheels. If the controller detects lock up of one of the rear wheels, then
brake pressure will be applied on both the rear wheels.
4.
Four channel, four sensor
ABS: Separate speed sensors and valves are used for each wheel. This
system provides the maximum brake effectiveness.
5.
Two channel, two sensor
ABS: Separate speed sensors are used on each wheel and separate
valves are used for both front and rear axle. If there is a wheel lock up on
any wheel (say front left wheel), then braking pressure will be applied to both
the front wheels.
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