ABS prevents wheels from locking up during braking to maintain traction. It consists of wheel speed sensors, a controller, hydraulic modulator, and braking system. The sensors monitor wheel speed and acceleration. The controller receives sensor signals to calculate wheel speed and slippage. It commands the hydraulic modulator to release or apply brake pressure as needed to each wheel. This allows ABS to maximize braking force for shorter stops while maintaining steering control on slippery surfaces.

1. ADVANCED EMBEDDED SYSTEMS
Presentation by
SIDDHARTHA E
M Tech (VLSI Design And
Embedded Systems)
DEPARTMENT OF ELECTRONICS AND COMMUNICATION
ANTI LOCK BRAKING SYSTEM”

2. WHAT IS ABS?
An anti-lock braking system is a safety anti-skid braking system used on aircraft
and on land vehicles, such as cars, motorcycles, trucks, and buses. ABS operates
by preventing the wheels from locking up during braking, thereby maintaining
tractive contact with the road surface.

3. INTRODUCTION
 During severe braking or on slippery surfaces, wheels approach lockup which
causes loss of traction and vehicle control.
 It also reduces steering ability to change the direction.
 ABS modulates the brake line pressure independent of the pedal force, to bring the
wheel speed back to the slip level range that is necessary for optimal braking
performance.

4. COMPONENTS OF ABS
ABS consists of –
•Wheel speed sensors
•Controller unit
•Hydraulic modulator Unit
•Braking system

5. Wheel Speed Sensors
The purpose of the wheel speed sensor is to monitor speed of each wheel and
then to determine the acceleration and de-acceleration of the wheels.
Electro-magnetic or Hall-effect pulse pickups with toothed wheels mounted
directly on the rotating components of the drivetrain or wheel hubs.
As the wheel turns the toothed wheel (pulse ring) generates an AC voltage at the
wheel-speed sensor.
The voltage frequency is directly proportional
to the wheel's rotational speed.

6. Electronic Controller Unit
The ECU gets the information from all the wheels and then control or limit the
brake force to the each wheel.
The electronic control unit receives, amplifies and filters the sensor signals for
calculating the wheel rotational speed and acceleration.
ABS is usually implemented in ECU.
ECU assists the vehicle operator to prevent wheel lockup by regulating the wheel
slip.

7. Hydraulic Unit
The hydraulic pressure modulator is an electro-hydraulic device for reducing,
holding, and restoring the pressure of the wheel brakes by manipulating the
solenoid valves in the hydraulic brake system.
Hydraulic unit actuates the brakes by increasing the hydraulic pressure or
bypassing the pedal force to reduce the braking power.
Depending on the design, this device may include a pump, motor assembly,
accumulator and reservoir

8. Braking system
 Brake System Components consists of a master cylinder, and four wheel
cylinders.
 When the brake pedal is pressed the piston in the master cylinder forces the
liquid out of the cylinder.
 This liquid presses the two pistons in the wheel cylinders outwards. These
two pistons push the brake shoes out words.
 When the pedal is pressed the primary
piston moves to the left .
 When it crosses the bypass port the liquid
is forced along the pipe lines to the wheel cylinders.
 When the pedal is released the primary piston is
moved back wards it is the spring, which pushes the piston back wards.

9. How ABS works
When a wheel lockup is detected or eminent, ECU commands HCU to release
the brake pressure to allow the wheel velocity to increase and the wheel slip to
decrease.
Once the wheel velocity spins up, ECU re-applies the brake pressure to confine
the wheel slip to a predetermined value or interval.
HCU Controls hydraulic brake pressure to each disc brake caliper or wheel
cylinder based on input from the system sensors, thereby controlling wheel
speed.

11. Objectives of ABS
1. To reduce stopping distances
The distance to stop is a function of the mass of the vehicle, the initial velocity,
and the braking force.
By maximizing the braking force the stopping distance will be minimized if all
other factors remain constant.
2. Stability
Although decelerating and stopping vehicles constitutes a fundamental purpose of
braking systems, maximum friction force may not be desirable in all cases
For example not if the vehicle is on a so-called p-split surface (asphalt and ice, for
example), such that significantly more braking force is obtainable on one side of
the vehicle than on the other side.

12. 3.Steerability
Good peak frictional force control is necessary in order to achieve satisfactory
lateral forces and, therefore, satisfactory steerability.
Steerability while braking is important not only for minor course corrections but
also for the possibility of steering around an obstacle.

13. TYPES OF ABS
Anti-lock braking system or ABS has different types of brakes based on number of
channels used.
1. Four channel four sensor ABS
• There is speed sensor on all four wheels and a separate valve for all the four
wheels.
2.Three channel , three sensor ABS
• This scheme is commonly found on pick up trucks with four
wheels ABS, has a speed sensor and a valve for each of the front wheels, with one
valve and one sensor for both rear wheels.
3.One channel , one sensor ABS
• It has one valve ,which controls both rear wheels, and one speed sensor, located in
the rear axle.

14. 4.Two-channel, four sensor ABS
• It uses a speed sensor at each wheel, with one control valve each for the front and
rear wheels as a pair.
• If the speed sensor detects lock up at any individual wheel, the control module pulses
the valve for both wheels on that end of the car.
5.Three-channel, four-sensor ABS
• There is a speed sensor on all four wheels and a separate valve for each of the front
wheels, but only one valve for both of the rear wheels.
• Older vehicles with four-wheel ABS usually use this type.

15. Advantages of ABS
 It allows the driver to maintain directional stability and control over steering
during braking.
 Safe and effective.
 ABS helps in shortening the stopping distance.
 Automatically changes the brake fluid
pressure at each wheel to maintain optimum
brake performance.
 ABS absorbs the unwanted turbulence shock waves and modulates the pulses
thus permitting the wheel to continue turning under maximum braking pressure.

16. Disadvantages of ABS
 Increased cost it adds to the overall cost of a vehicle.
 Also maintenance costs go up as the sensors on each wheel are expensive and get
heavy on the pocket if they run out of calibration.
 The job of anti-lock brakes is to provide sure footed braking. But this also has a
side effect that is the inconsistent stopping distances on various surfaces under
variable conditions.
 These electronic systems are quiet delicate and easy to harm which increases the
possibilities of system damages.

17. Conclusion
Statistics show that approximately 40 % of automobile accidents are due to
skidding.
These problems commonly occur on vehicle with conventional brake system
which can be avoided by adding devices called ABS
If there is an ABS failure, the system will revert to normal brake operation.
Normally the ABS warning light will turn on and let the driver know there is a
fault.

18. REFERENCES
Anti Lock Braking System: How Does The ABS Technology ..
“https://www.scienceabc.com”
Antilock braking system - Bosch Mobility Solutions “https://www.bosch-
mobility-solutions.com › driving-safety-systems › antil”...
Anti-lock braking system – Wikipedia “https://en.wikipedia.org › wiki › Anti-
lock_braking_system”
How Anti-Lock Brakes Work | HowStuffWorks
“https://auto.howstuffworks.com › ... › Brakes › Brake Types”
What do they mean by ABS -|CarDekho.com “https://www.cardekho.com ›
show-answers › Performance-and-Handling”