2. Presentation Outline
What is an Anti-Lock Braking System (ABS) ?
Motivation for ABS Development
ABS Component Overview
ABS Components
How Does ABS Works ?
ABS Configuration
Advantages & Disadvantages
Summary
References
3. What is ABS ?
Anti-lock braking system (ABS) is an
automobile safety system that allows the wheels on
a motor vehicle to maintain tractive contact with
the road surface according to driver inputs while
braking, preventing the wheels from locking up
(ceasing rotation) and avoiding uncontrolled
skidding.
4. Motivation for ABS
Under hard braking, an “ideal” braking system
should:
Provide the shortest stopping distances on
all surfaces
Maintain vehicle stability and steer ability
Anti-lock braking systems were developed to
best meet these needs.
5. ABS Components Overview
• Typical ABS Components:
Wheel Speed Sensors (up to 4)
Valves
Pump
Electronic Control Unit (ECU)
6. 1) Wheel Speed Sensor (WSS)
The ABS needs some way of knowing
when a wheel is about to lock up.
The speed sensors, which are located
at each wheel provides this information.
ABS Components
7. 2) Valves
There is a valve in a brake line of each brake controlled by the
ABS . On some systems, the valve has three positions :
In position one, the valve is open, pressure from the master
cylinder is passed right through to the brake.
In position two, the valve blocks the line, isolating that brake
from the master cylinder.
In position three, the valve releases some of the pressure from
the brake.
8. 3) Pump
Since the Valve is able to release some pressure from the
brakes, there has to be some way to put that pressure back.
That is what the pump does ; when a valve reduces the
pressure in a line, the pump is there to get the pressure
back up. ABS ‘pumps’ the brakes much faster than any driver
could.
Anti-lock brake pump and valves
9. 4) Electronic Control Unit
It’s a computer in the car. The ECU receives
information from each individual wheel speed sensor
, in turn if a wheel loses traction the signal is sent to the
controller , the controller will then limit the brake force
and activate the ABS modulator which actuates the
valves on and off.
10. We will discuss how one of the simpler system works.
Sensors at each of the four wheels sense the rotation of the wheel.
Too much brake application wheel stop rotating
Sensors ECU releases brake line pressure wheel turns
again.
then ECU applies pressure again stops the rotation of the wheel
releases it again and so on
This releasing and re-application or pulsing of brake pressure happens
20 times per second or more.
This keeps the wheel just at the limit before locking up and
skidding no matter
how hard you apply the brakes.
How Does ABS works ?
11. With ABS, all you have to do
in an emergency is quickly
squeeze the brake pedal as hard
as you can and hold it there. Let
the system do the finesse work
for you.
Anti-lock brake components
14. ADVANTAGES DISADVANTAGES
Improves vehicle stability
Rapid deceleration is
efficient
Improves cornering of
wheels
Avoids skidding of
wheels, hence increases
tires life.
Insures vehicle safety
Costly as compared to
conventional braking
systems.
Braking is inefficient when
the ignition is switched off.
15. Summary
An ABS typically consists of:
Up to 4 wheel speed sensors
An ABS ECU
Pumps and Valves
The vehicle’s physical brakes
An ABS is designed to modulate braking pressure to attain the
peak coefficient of kinetic friction between tire & road, &
avoid total wheel lockup.
An ABS, under hard braking conditions, is designed to reduce
stopping distances under most conditions, while maintaining
vehicle stability and steer ability.
