What is ABS? How it works? What is its use?
ABS is a system which prevents wheels from locking up and help maintain the grip with the road. ABS stands for Anti-lock braking system. The system is originally developed for air-crafts in 1930 for icy and wet conditions. It was later adopted for use in cars by Ford in 1970. Almost all the modern day cars are equipped with ABS and it the foundation of electronic stability control systems.
ABS was originally developed to prevent wheels from locking up during hard braking. Modern ABS also try to maximize the braking forces generated by the tires by preventing the slip ratio between the tires and the brakes exceeding the optimum value.
“ The basic objective of the ABS either holds or release the braking pressure on the wheels if there is a danger of the wheel locking .”
How does it work?
All brake system depends upon the force of friction for their operation. Brakes operate most efficiently when they are applied so that the wheels do not quite lock but continue to turn without slipping on the road. This is because more energy can be absorbed when the wheels are turning than when the brakes lock the wheels so that the tires slide on the road. A speeding vehicle is likely to skid when brakes are suddenly applied. The driver then loses control of the vehicle and becomes a passenger in his own vehicle.
What ABS does that when it detects the wheel lock it temporarily releases the brake, allowing the wheel to turn again. It then continuously and repeatedly applies the brake pressure allowing the driver to remain in control of the vehicle and reducing the risk of skidding.
Thus, the basic objective of the ABS either holds or release the braking pressure on the wheels if there is a danger of the wheel locking. At the same time, ABS need to again permit the application of the brakes when the danger of the locking has been avoided. The ABS system could also hold or release the braking pressure to keep the slip ratio at the optimum value.
In a Car, the ABS can be single channel, two channel, three channel or four channel while in bikes it can be single or dual channel. If a vehicle has two channel ABS it implies that ABS is provided in two of the vehicle wheels. Each channel controlled by the ABS has a valve in Open, Closed or released condition.
When the valve is in “Open” condition, the pressure for the master cylinder is passed right to the brake, allowing the brakes to be controlled by the driver.
When the valve is in “Closed” condition the brake pressure is isolated from the master cylinder and the driver cannot increase the brake pressure.
When the valve is in “released” condition the brakes are isolated and the braking pressure is reduced. In addition to the driver being not able to apply the brakes, the braking pressure is also continuously reduced.
The major task of the ABS is to detect when the wheel slip, and ironically no sensor can detect it. The sensors used in ABS detect the wheel rotation and an algorithm is used to predict the wheel locking and if locking has been averted. These algorithms are programmed in the electronic control unit (ECU) of the ABS and usually use the acceleration or deceleration of wheel rotation to predict the wheel locking.
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