By: Koushik Paul Roll No.- 6O Mech. Engg.[3 rd Year] Bengal College Of Engineering & Technology
It is one of the most important device.
Used to retard or stop the vehicle.
Kinetic energy translated to heat energy.
Kinetic energy increases with the square of the velocity.
Wheel lockup during braking causes skidding which in turn cause a loss of traction and vehicle control
This reduces the steering ability to change direction. So the car slides out of control.
With ABS system, the driver can brake hard, take the evasive action and still be in control of the vehicle in any road condition at any speed and under any load .
ABS was first developed for AirCraft in 1929 b y French Automobile & Aircraft Pioneer Gabriel Voisin .
The German Companies BOSCH & Mercedes-Benz pioneered the first electronic version for use on Mercedes-Benz Cars in 1936 .
In 1960 A fully mechanical system used in the Ferguson P99 racing car, the Jensen FF and the Ford Zodiac , but saw no further use; the system proved expensive and, in automobile use, somewhat unreliable.
In 1975 Ford also introduced ABS on the Lincoln Continental Mark III and the Ford LTD station wagon, called “ Sure Trak ”.
In 1978 Bosch And Mercedes-Benz Introduced the first completely Electronic 4-Wheel Multi-Channel ABS system in trucks and the Mercedes-Benz S-Class .
In 1988 BMW became the world's first motorcycle manufacturer to introduce an electronic/hydraulic ABS system, this on their BMW K100 .
In 1992 Honda launched its first ABS system this on the ST1100 Pan European.
A -Wheel Speed Sensor
B -ABS control Module
C -pressure Release Valves
D -Brake caliper
A nti lock braking system is made up of a central (ECU) Electronic Control Unit and four wheel speed sensors connected to each wheel of vehicle and two hydraulic valves located in the brake hydraulics. The electronic control unit monitors record the rotating speed of four wheels on a constant basis and when this system finds a vehicle wheel rotating speed slower than the other three, where a situation arises such as an impending wheel lock.
There is a valve in the 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. This prevents the pressure from rising further should the driver push the the brake pedal harder.
III. In position three, the valve releases some of the pressure from the brake.
The ABS system causes the valves to constantly reduce hydraulic pressure to brakes of the significantly lowered speed wheel thereby causing reduction of braking force on the affected wheel.
By this process, the lower speed wheel starts turning faster than other three wheels and when the electronic control unit finds that the wheel is turning faster than the other three, automatically brake hydraulic pressure to the affected wheel is increased by the ABS system so that braking force is reapplied and the wheel slows down.
This complete process performed by the ABS system is repeated continuously throughout the drive on mostly uneven roads and can be easily detected by the driver of the car with the help of brake pedal pulsation.
Now let's put the parts together to see how anti-lock brakes work as a whole. This diagram provides both a closeup view & an example of where the brakes are located.
There are mainly three types of ABS used in the car.
Four-channel, four-sensor ABS: This is the best scheme. 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.
Three-channel, three-sensor ABS: This scheme, commonly found on pickup trucks with four-wheel ABS, has a speed sensor and a valve for each of the front wheels, with one valve and one sensor for both rear wheels. The speed sensor for the rear wheels is located in the rear axle.
One-channel, one-sensor ABS: This system is commonly found on pickup trucks with rear-wheel ABS. It has one valve, which controls both rear wheels, and one speed sensor, located in the rear axle.
Now lets see how ABS works in a car with an animation.