Chassis Systems Control
Safe braking with the
Antilock Braking System ABS
2 | Safe braking with the Antilock Braking System ABS from Bosch
Safe braking
with ABS
An everyday situation: you are relaxed at the wheel and have a good view of the road. But
what if you are taken by surprise by an obstacle in front of you or by standing traffic around
the bend? You have to slam on the brakes to save your day.
Every driver sooner or later finds himself in a
ABS is an active safety system that helps to avoid
situation where an emergency braking is neces-
accidents and supports the driver to reach his
sary. How he or she brakes is decisive. Emergency
destination safely. Bosch was the first company to
braking or even braking on a wet or slippery
introduce ABS to the market in 1978. Bosch con-
surface can cause the wheels of the vehicle to lock.
tinues to optimize ABS right up to the present day.
Locking wheels reduce the adhesion between tires
and the road surface and make the vehicle unsteerable. The vehicle no longer reacts to the steering
intention of the driver and skids towards the
obstacle.
ABS, the Antilock Braking System from Bosch
prevents the wheels from locking. If any of the
wheels begin to lock, ABS intervenes and ensures
the vehicle remains steerable and stable. The
obstacle can thus be avoided.
Safe braking thanks to stability and steerability –
with the Antilock Braking System ABS from Bosch
3 | Safe braking with the Antilock Braking System ABS from Bosch
How ABS works
In an emergency braking situation the braking force created by the driver may be greater
than the tire can handle: the wheel locks. The tire can now no longer transfer any lateral
traction forces. The vehicle becomes unstable and unsteerable. The stopping distance
increases.
In a vehicle equipped with an Antilock Braking System, the ABS control unit constantly
evaluates the speed of all wheels. If the ABS wheel-speed sensors placed at each wheel
detect a lock-up, ABS intervenes within milliseconds by modulating the braking pressure
at each individual wheel. In this way ABS prevents the wheels from locking during braking,
thus ensuring steerability and stability combined with the shortest possible braking
distance.
ABS also prevents tire damage. Locked wheels on dry asphalt can create flat spots. The
tires can then no longer ensure optimal braking.
ABS components in the vehicle
2
2
2
1
2
1
Hydraulic unit with
attached control unit
2
Wheel-speed sensors
4 | Safe braking with the Antilock Braking System ABS from Bosch
Safe braking with ABS –
be it an emergency braking...
...an emergency braking with
additional evasive action...
Emergency braking
Emergency braking and steering
An emergency braking is often the only way of
If an obstacle appears without warning, emergency
avoiding an accident. Typical situations: standing
braking may not suffice to prevent a collision: the
traffic hidden by a bend, an obstacle appearing
driver must brake and take evasive action.
suddenly or the car in front braking abruptly. The
oncoming traffic impedes evasive action. The
Because the wheels have locked, the car without
driver has to slam on the brakes.
ABS no longer responds to the driver’s steering intention and crashes into the obstacle. The car
The car without ABS needs a considerably longer
with ABS remains steerable even during emergen-
braking distance, as its wheels lock. The car with
cy braking, and the driver can safely avoid the
ABS is brought safely to a stop within a shorter
obstacle.
braking distance. This may avoid the collision.
With ABS, the vehicle can still be steered when
With ABS the vehicle stays stable during braking
braking.
and the braking distance is considerably shorter.
With ABS
With ABS
Emergency braking at 100 km/h
Emergency braking and steering
Without
ABS
Without
ABS
Safe braking with the Antilock Braking System ABS from Bosch | 5
...or an emergency braking on uneven
road surfaces
Emergency braking on varying road surfaces
In this situation the car without ABS becomes
Road surfaces which are partly wet, dirty, icy or
unstable and the driver loses control. The Antilock
covered with wet leaves, are especially dangerous.
Braking System compensates for this situation by
When braking on such uneven road surfaces the
applying different braking pressure to individual
braking powers vary considerably, particularly on
wheels. The vehicle remains in control.
the front wheels. This can cause the vehicle to spin
out of control.
With ABS, the driver brakes safely: the vehicle
remains stable and optimal stopping distances
are ensured.
With ABS
Safe braking with ABS:
u
ABS keeps the vehicle steerable during
Braking on a road surface of varying adhesion
emergency braking
uABS ensures stability during a braking
maneuver
uABS reduces the braking distance
uABS improves steerability when the brakes
are applied on road surfaces with differing
adhesion
uABS prevents tire damage in emergency
braking
Without
ABS
Important questions and answers
Why do I need ABS?
Can I have ABS retrofitted?
ABS ensures that you can brake safely: it keeps
It is not possible to have ABS retrofitted. So you
your vehicle steerable and stable in situations
should always give preference to vehicles equipped
where you have to brake hard, shortens your
with ABS when buying either a new or a used car.
braking distance and avoids tire damage.
What is the safest way to brake with ABS?
Where can I get ABS?
In an emergency, press the brake pedal quickly and
ABS is available in an increasing number of new
hard all the way down. The pulsation of the pedal
vehicles – as an option or as standard equipment.
tells you that ABS is working. You might also feel a
Next time you buy a car, ask for one equipped with
stronger brake pedal resistance. Hold the brake
ABS.
pedal until your vehicle comes to a stop. If you have
to avoid an obstacle steer while braking.
Will it pay off if I buy a vehicle with ABS?
ABS offers effective protection for your vehicle, for
Does ABS shorten the braking distance?
yourself and for other road users. If ABS helps you
In most cases the braking distance is shorter with
to avoid one single accident, your investment will
ABS than without ABS. One exception is in the
already have paid off. This is why around 80% of
case of roads with a loose surface such as sand or
people all over the world already decide to buy
gravel. Here, without ABS, wheels which lock
vehicles equipped with ABS.
create a wedge of material under them. This wedge
can lead to a reduction in the braking distance. But
beware: in this situation, the vehicle without ABS
can no longer be steered!
Robert Bosch GmbH
Chassis Systems Control
Postfach 13 55
74003 Heilbronn
GERMANY
www.bosch-abs.com
Printed in Germany
292000P00V-C/SMC2-200805-En