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April 16 2014

Anti-lock Braking System

You must be familiar with the term “ABS” or “Anti-lock Braking System”. Many vehicles, cars or bikes and even trucks and buses, come equipped with ABS, but some of us do not really know how it works. If you have a car fitted with ABS, you should first refer to user manual of your vehicle and understand its working and features.


We will discuss what ABS is, its functioning and types in this article.


ABS or Anti-lock Braking System is a safety feature that helps in preventing the wheels from locking up when one applies brakes. When a driver presses the brake pedal, the ABS allows the wheel to keep traction with the road surface and prevents the wheels from locking, this in turn avoids uncontrolled skidding of a vehicle that can cause an accident. ABS improves vehicle control and decreases the stopping distance to a great extent on any road surface.


ABS not only prevents the wheels from locking but also electronically controls the all four wheels. The ABS has four components:


•           Speed sensors

•           Pump

•           Valves

•           Controller


ABS is also known as anti-lock brake controller or Controller Anti-lock Brake (CAB). The controller keeps a record of speed and when the driver applies brake or lowers the speed, it activates the valves to reduce the hydraulic pressure of the brake, thus reducing the braking force. It then makes it easier to steer the wheels even if the brakes are applied. When the ABS system operates, one feels a throb in the brake pedal due to quick opening and closing of valves.


There are three types of ABS depending on the type of brakes which are used:


1.         Four-channel, four-sensor ABS: There is a speed sensor on all four wheels and a separate valve for all four wheels. In this, the controller monitors each wheel individually to make sure it is getting the required braking force.


2.         Three-channel, four-sensor ABS: It has 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. Earlier, the vehicles were fitted with this type.


3.         Three-channel, three-sensor ABS: It has a speed sensor and a valve for each of the front wheels, with one valve and one sensor for both rear wheels. It provides individual control of the front wheels to get maximum braking force. While the rear wheels are monitored together. The rear wheels have to start to lock up before the ABS will activate on the rear. In this type, it is also possible that one of the rear wheels will lock during a stop, thus, reducing brake effectiveness.


4.         Two-channel, four sensor ABS: It was commonly used in vehicles produced in 80’s. 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.         One-channel, one-sensor ABS: It has one valve, which controls both rear wheels, and one speed sensor, located in the rear axle. This system operates the same as the rear end of a three-channel system. The rear wheels are monitored together and they both have to start to lock up before the ABS starts operating. It is also possible that one of the rear wheels will lock, reducing brake effectiveness. This system is also easy to identify, as there are no individual speed sensors for any of the wheels.


Things to remember when applying brakes with ABS vehicle:


First and foremost, one should never pump brake pedal in a vehicle with ABS as this will take longer to stop a vehicle. One just needs to press the brake pedal firmly and let the ABS do its work. If you keep pumping brake pedal, it will disengage the ABS system and it will not work accordingly.


Always brake and steer your vehicle when using four-wheel ABS. press the brake pedal firmly and steer your vehicle normally until the car comes to a standstill.


ABS works great on wet or icy pavements but can take a longer stopping distance on loose gravel or during snow fall.


There is difference between four wheel and rear wheel ABS. In a four wheel ABS, it prevents the entire four wheels to lock up giving the driver and the maneuver easily. However, in rear wheel ABS, the front wheels will lock up when the brakes are applied. In this case, the driver should ease up on the brake pedal with just enough pressure to allow the front wheels to roll again so that the driver can steer.

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