antilock braking systemm
TRANSCRIPT
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A
REPORT
ON
ANTI-LOCK BRAKING SYSTEM (ABS)
Submitted In Partial Fulfilment of Requirement For Award Of Degree
BACHELOR OF TECHNOLOGY
IN
MECHANICAL ENGINEERING
Submitted To: Submitted By:-
Dr. H.C. Garg Tarun (09162003)
HEAD OF DEPARTMENT (ME) (8th
Semester)
Department Of Mechanical Engineering
Guru Jambheshwar University Of Science & Technology
Hisar (125001)
March,2013
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Introduction
Wheel lockup during braking causes skidding which in turn cause a lossof traction and vehicle control.
This reduces the steering ability to change direction. So the car slips &out of control.
With ABS system, the driver can brake hard, take the evasive action andstill be in control of the vehicle in any road condition at any speed and
under any load.
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Hydraulic Brakes
A simple braking system consists of a master cylinder, and four wheelcylinders.
When the brake pedal is pressed the piston in the master cylinder forcesthe 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.
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What Is Wheel Slip?
Normal driving will not notice difference
Anti-lock Event
Unrestricted tire rotation is 0% slip Tire locked up is 100% slip When we have 100% slip, the tire loses traction and vehicle motion
changes into heat energy. (Not very effective!)
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ABS
The skidding and lack of control was caused by the locking of wheels.
The release and reapply of the brake pedal will avoid the locking of thewheels which in turn avoid the skidding.
This is exactly what an antilock braking system does.
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Pressure Module
When the brake pedal is pumped or pulsed the pressure is quickly appliedand released at the wheels. This is called pressure modulation. Pressure
modulation works to prevent the wheel locking.
ABS can modulate the pressure to the brake as often as 15 times perseconds.
ABS precisely controls the slip rate of The wheels to ensure maximumgrip force from the tyre and it there by ensures maneuverability and
stability of the vehicle.
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Slip Rate
During ABS operation, the target slip rate can be from 10 to 30%.
0% slip means the wheel is rolling freely, while 100 % means the wheelis fully locked.
A slip rate of 25 % means the velocity of a wheel is 25 % less than that ofa freely rolling wheel at the same vehicle speed.
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Main Components
Speed Sensors
Electrical Control Unit (ECU)
Hydraulic Control Unit (HCU) Accumulator
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Wheel Speed Sensor
Detects rotation of wheel
Permanent magnet type
3 Parts Permanent magnet Coil Yoke
Induces AC voltage varied frequency
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Electrical Control Unit (ECU)
Inputs and Outputs
Some ABS ECUs have dual boards
Controls HCU Full Diagnostics Controls Warning Lights Can control each wheel brake independently. (four channel) Most are
three channel
Mechanical Noises
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Hydraulic Control Unit (HCU)
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Accumulator
Stores high pressure brake fluid from Pump
Supplies high pressure fluid in ABS mode
2800 to 3400 PSI Must bleed before replacement or service
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Pump And Motor
Motor is 12V Electric
Works independently of the base brake system
Pressurizes brake fluid up to 2800 psi. Turns on when ever pressure drops below a predetermined level Some are replaceable seperately
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Advantages
It allows the driver to maintain directional stability and control oversteering during braking
Safe and effective Automatically changes the brake fluid pressure at each wheel to maintain
optimum brake performance.
ABS absorbs the unwanted turbulence shock waves and modulates thepulses thus permitting the wheel to continue turning under maximum
braking pressure.
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Disadvantages
It is very costly
Maintenance cost of a car equipped with ABS is more.
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Conclusion
Statistics show that approximately 40 % of automobile accidents are dueto skidding.
These problems commonly occur on vehicle with conventional brakesystem which can be avoided by adding devices called ABS
If there is an ABS failure, the system will revert to normal brakeoperation. Normally the ABS warning light will turn on and let the driver
know there is a fault