ABS uses wheel speed sensors and hydraulic valves to prevent wheel lockup during braking. It monitors each wheel and selectively applies and releases hydraulic pressure to maintain traction. On motorcycles, ABS also uses a combined braking system to distribute brake force to the non-braked wheel. ABS systems vary in the number of channels and sensors but all aim to keep wheels rotating to allow steering during heavy braking.

2. INTRODUCTION:

3. INTRODUCTION:
• 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.
• ABS generally offers improved vehicle control and decreases
stopping distances on dry and slippery surfaces for many drivers;
however, on loose surfaces like gravel or snow-covered pavement,
ABS can significantly increase braking distance, although still
improving vehicle control.

4. INTRODUCTION:
Recent
versions not
only prevent
wheel lock
under braking,
but also
electronically
control the
front-to-rear
brake bias.

5. OPERATION:
• Typically ABS includes a central electronic control unit (ECU), four wheel
speed sensors, and at least two hydraulic valves within the
brake hydraulics.
• The ECU constantly monitors the rotational speed of each wheel; if it
detects a wheel rotating significantly slower than the others, a condition
indicative of impending wheel lock, it actuates the valves to reduce
hydraulic pressure to the brake at the affected wheel, thus reducing the
braking force on that wheel; the wheel then turns faster.

6. OPERATION:
• If the ECU detects a wheel turning significantly faster than the others,
brake hydraulic pressure to the wheel is increased so the braking force is
reapplied, slowing down the wheel.
• Some anti-lock systems can apply or release braking pressure 15 times
per second .Because of this, the wheels of cars equipped with ABS are
practically impossible to lock even during panic braking in extreme
conditions.

7. OPERATION:
• ABS applies individual brake pressure to all four wheels through a control
system of hub-mounted sensors and a dedicated micro-controller.
• A minimum of two additional sensors are added to help the system
work: these are a steering wheel angle sensor, and a gyroscopic sensor.
• When the gyroscopic sensor detects that the direction taken by the car
does not coincide with what the steering wheel sensor reports, the
controller will brake the necessary individual wheel(s) so that the vehicle
goes the way the driver intends.

8. OPERATION:

9. OPERATION:

10. ABS IN MOTORCYCLES:
• Different from cars, planes or trains, at a motorcycle rear and front wheel
are controlled separately.
• If the rider only brakes with the front or rear wheel, the braked wheel
tends to lock up faster as if both brakes would have been applied.
• Motorcycle ABS system uses Combined Braking System.
• CBS helps to reduce the danger of wheel locks and fall downs.

11. ABS IN MOTORCYCLES:
• A Combined Braking System distributes the brake force also to the non-
braked wheel to lower the possibility of a lock up, increase deceleration
and reduce suspension pitch.
• At a single CBS the brake pressure applied on the rear brake (pedal) is
simultaneously distributed to the front wheel.
• A delay valve cuts the hydraulic pressure to assure that only when strong
braking is applied, pressure is also created at the front wheel.

12. COMPONENTS:
Speed sensors:
• A speed sensor is used to determine the acceleration or deceleration of
the wheel .
• These sensors use a magnet and a coil of wire to generate a signal.
• The rotation of the wheel or differential induces a magnetic field around
the sensor.
• The fluctuations of this magnetic field generate a voltage in the sensor.

13. COMPONENTS:
• Since the voltage induced in the sensor is a result of the
rotating wheel, this sensor can become inaccurate at slow speeds.
• The slower rotation of the wheel can cause inaccurate fluctuations in
the magnetic field and thus cause inaccurate readings to the controller.

14. COMPONENTS:
Pump:
• The pump in the ABS is used to restore the pressure to the hydraulic
brakes after the valves have released it.
• A signal from the controller will release the valve at the detection of
wheel slip.
• After a valve release the pressure supplied from the user, the pump is
used to restore a desired amount of pressure to the braking system.

15. COMPONENTS:
• The controller will modulate the pumps status in order to provide the
desired amount of pressure and reduce slipping.
Controller:
• The controller is an ECU type unit in the car which 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 (EBD) and activate the ABS modulator which actuates the braking
valves on and off.

16. BRAKE TYPES:
They can be differentiated by the number of channels: that is, how many
valves that are individually controlled and the number of speed sensors.
Four-channel, four-sensor ABS:
• There is a speed sensor on all four wheels and a separate valve for all
four wheels.
• With this setup, the controller monitors each wheel individually to
make sure it is achieving maximum braking force.

17. TYPES:
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.
• Channel indicates valves in the controller system.

18. TYPES:
• Three-channel, three-sensor ABS:
• There is a speed sensor and a valve for each of the front wheels, with one
valve and one sensor for both rear wheels.
• This system provides individual control of the front wheels, so they can
both achieve maximum braking force.
• The rear wheels, however, are monitored together; they both have to
start to lock up before the ABS will activate on the rear.
• Commonly found on pickup trucks with four-wheel ABS.

19. TYPES:
Two-channel, four sensor ABS:
• 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 detect lock up at any individual wheel, the control
module pulses the valve for both wheels on that end of the car.
• Commonly found on old passenger cars.

20. TYPES:
One-channel, one-sensor ABS:
• It has one valve, which controls both rear wheels, and one speed sensor,
located in the rear axle.
• The rear wheels are monitored together and they both have to start to
lock up before the ABS kicks in.
• Commonly found on pickup trucks with rear-wheel ABS.