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Antilock Braking Systems

Page history last edited by Natila 9 years, 3 months ago


Nura, Natila, Neha


You have your license, you drive a car, you are now aware of the dangers in the road.


You’re driving along one day with your music blasted while cruising on the icy road with just about no idea what might happen next. This incident is probably going to give you second thoughts the next time you are on the road.


Concentrate, or else, the car in front of you might just brake immediately and up goes your demerit points.


Take a look:




You are now considered a careless driver.


Alternately, if you had a working Anti- lock breaking system (ABS), this situation might have not been so portentous.




ABS stands for Anti-lock braking system

The ABS makes the 'Brake Pads' on your car rapidly clap against the 'Rotors' instead of closing right on them so the wheel does not lock in a single position when braking hard.

If the wheel was to lock in one place, for example on an icy road, chances are the car will slide or skid, which is what ABS is meant to avoid.

(To compare: If there was a bicycle wheel spinning and you closed in on it with a finger on each side, slowly the wheel would slow down.

Brake pads and Rotors work the exact same way, your fingers represent the brake pads while the spinning wheel represents a 'Brake Rotor')




An Anti-lock Braking System is meant to help the driver maintain their the steering ability when braking on slippery surfaces without skidding

ABS was created to reduce skidding and maintain control of steering the car when braking.




The controller is monitoring the speed sensors at all times.

It looks for the unordinary deceleration in the wheels seconds before it locks up.

If it were to remain unchecked the wheel would stop turning before the car could. In an example the car could take about 5 or 6 seconds to stop, but the wheel would lock up in a second.

For a car to stop moving in a second is currently impossible.

The ABS reduces the  pressure on the brake until an acceleration is possible which is where pressure on the brake is increased again until another deceleration comes. This happens very quickly so the tire wheels don’t lock up and stop with the car, rather than before the car.



The ABS is consisted of four major parts:

 1.        Speed Sensors – the thing that tells the ABS the wheels are about to lock up. The speed sensors are found in every wheel.

2.         Valves – controlled by the ABS is a valve in the brake line of every brake. There are three positions:

a. Open – where pressure from the master cylinder is passed right to the brake

b. Blocked – where the valve is closed and isolates the brake from the master cylinder. It prevent pressure from rising if you press the brake harder

c. Released – where the valve frees pressure from the brake.

3.         Pump – this is what puts the pressure back into the brake once it has been freed.

 4.        Controller – basically the little computer in the car that’s there watching everything.



This photo portrays the different parts to the Anti-lock braking system:



Simple Physics:


Brake Pads are positioned in a way that they can close in on the rotors that are attached to the spinning wheel.

The car stops because of the friction between the brake pads and rotors, which slows down the wheel.

The brake pads also generate heat due to friction in the process.




Car without ABS:

There is only one source of friction which is between the tire and the ground.


Car with ABS:
Two sources of friction are present.

the first source of friction comes from the friction of the car and the pavement and the second comes from between the Brake Pads and the Rotor.


The friction between the Brake Pads and Rotor are meant to act indirectly to control the friction between the tires and the roads.


ABS locks your brakes, but slowly unlocks it while pumping so that it can re-gain traction


The ABS increases the coefficient of friction to help with the deceleration of the car to help maintain a good speed


The Brake difference is between static and kinetic friction coefficients

There is a lot of friction on a object at rest, but once you start to get it moving, it can start to slide, and at that point, there is almost no friction.


In this case, the wheel is rolling, it is not sliding. Therefore there is more friction than a object sliding.

But when you brake and skid, you are now sliding. And now you have less friction.


What the Anti-lock does at this point is that it recognizes the car is sliding and helps the car regain control in the car wheels by rolling for them to re-gain friction.


How Disk Brakes Work: http://www.youtube.com/watch?v=rgbDyJhBb4c








Video Demonstrations:


(Unfortunately, these videos are on www.youtube.com and will not be allowed on school)









Questions to test your knowledge of this brief introduction:



1. How do the four important components of the Anti-lock Braking System work?

     In a brief but detailed description describing how they work together.




2. Based on the information and diagram above name the 3 main parts of an Anti-lock Braking System




3. Based on the information and diagram above name the detailed parts of an Anti-lock Braking System







Frequently Asked Questions:


1. When would an anti-lock braking system start to work?

Anti-lock Braking System only operates either on an attempt to stop by putting full pressure on the brakes or when wheels are skidding, and ABS will help control the car


2. What does anti-lock braking system prevent when used in an emergency stopping situation?

The Anti-lock Braking system  is meant to prevent the cars brakes from entirely locking to help control your speed so one can steer in the right direction.



Braking hard on a slippery surface without ABS:


Slippery surface without ABS


Braking Hard on a slippery surface with ABS:


Slippery surface with ABS


3. What is the advantage of anti-lock braking system?


It will help with the control of your car so that you will be able to steer out of trouble without your wheels locking


4. How do I use ABS?


Apply steady and constant pressure only.

Do not pump the brake pedal.




5. Is the vibration and loud sound normal?


The noise that is created, along with the vibrations are totally normal. 

These indicate that your Anti-lock Braking System is functional and is in use.





One should allow longer stopping distance with ABS









Question #1 Answer:

There are 4 main components to the Anti-lock Braking System,

The 3 seperate components are the Speed Sensors, Valves and Pump. The 4th one is the controller which controls all the action that the Speed Sensors, Valves and Pumps are making.

The speed sensors are able to detect when the wheels of the vehicle are going to lock up.

These sensors send the information to the main ABS system.


The valves then first open so that pressure is applied directly to the brake. But to prevent pressure from rising any further, the valves are blocked so the brake is isolated from the main cylinder.


When the vehicle is out of danger, the valve releases pressure from the brake, so that the vehicle can travel in normal speed.

Lastly, it’s the pump’s job to refill the pressure into the brake after its been freed by the valve.


Question #2 Answer: 

1. Wheel Speed Sensor 

2. ABS Control Module

3. Hydraulic Pump and Valves


Question #3 Answer:

a) Rear Wheel Speed Sensor

b) Stop Lamp Switch

c) Master Cylinder

d) Hydraulic Modulator

e) Left Hand, Front Wheel Speed Sensor

f) Right Hand, Front Wheel Speed Sensor

g) ABS Control Module

h) ABS Off Warning Lamp





















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