What is an Anti-lock Braking System (ABS) in cars, and how does it work?

Team Ackodrive6, Jun, 2022

Brakes are the primary and important safety equipment in an automobile. Be it four-wheelers or two-wheelers; brakes are necessary to slow down the vehicle or bring it to a halt. And with cars getting more advanced and powerful, the braking system has also evolved over the past few decades. One of the highlights of that evolution is the ABS (Anti-lock Braking System). So, what is ABS in cars? Without any 'panic braking', read on to know what ABS is and how it works.

What is an Anti-lock Braking System (ABS) in cars

What is an Anti-lock Braking System (ABS)?

An Anti-lock Braking System in cars means a system that prevents the wheels from locking up during panic/hard braking. Without ABS, the wheels can quickly stop rotating and start to slide under panic braking. The role of an ABS or Anti-skid braking system is to prevent the wheels from losing traction under heavy braking by modulating the brake pressure. To understand what ABS is in a car, let’s look at an example scenario.

Example: You are driving on a highway at a speed of around 80 to 90 kmph. A pedestrian crosses the road out of nowhere without observing the oncoming traffic. To avoid hitting the pedestrian, you slam on the brakes in panic. Here the outcome of the panic braking can differ with and without ABS.

  • With ABS: As soon as you press the brake pedal, the ABS kicks in to prevent the wheel lockup. ABS modulates the brake pressure and does not allow the wheels to lose traction (lock up). Hence, your car will stop safely in a short distance, and you avoid a potential accident.

  • Without ABS: When you slam on the brakes in panic, the wheels will lose traction and start sliding. In other words, they lock up. Once that happens, you are just a passenger. You will have no control over the brake or steering, and the vehicle will continue to move forward/skid with wheels sliding on the road surface. It can lead to a severe accident.

So, now you know the difference ABS can make in dire situations. It can be a lifesaver in such panic braking scenarios. This safety feature is mandatory for all cars in India. Hence, all the new vehicles come with this crucial piece of safety equipment.

How does the ABS in cars work?

You already know what happens when you brake heavily in emergency/panic situations. The aggressive input on the brake pedal results in the sudden application of brakes, and the tyres lose traction and stop rotating. This phenomenon is called wheel lockup. The job of the ABS is to prevent it and enable you to halt the car safely.

To understand the working of an ABS, you need to know the main components of the system. Four main components make up the Anti-skid braking system. They are wheel speed sensors, pressure release valves, a hydraulic motor and a controller/ECU (Electronic Control Unit).

In simple terms, ABS works on the principle of threshold braking. Generally, threshold braking is a popular term in motor racing, where the driver modulates the brake pedal pressure to enhance the braking force. The technique involves releasing the brake pedal when the wheel begins to slip and then applying the brakes again when the wheel regains traction. However, the ABS does it automatically.

Glance through the points below to understand the Anti-lock Braking System working mechanism.

  • The wheel speed sensors monitor the speed of each wheel.

  • When your car’s wheels lock up, the sensors detect the sudden change in the wheel speed and relay the information to the controller.

  • The controller interprets the signal as a wheel lock and sends a signal to the hydraulic motor to release the brake pressure.

  • The braking pressure is reduced via pressure-release valves.

  • After the brake pressure release, the wheels gain traction and start to rotate.

  • Once that happens, the speed sensors get into the action and send another signal to the controller.

  • This time the controller sends a signal to the pump to close the pressure-release valve to stop the loss of the brake pressure and increase the braking force.

  • This cycle repeats several times until the vehicle comes to a stop without any wheel locking.

Now, you may think it can be done by humans too, and ABS is an unnecessary system that adds to the vehicle’s cost. Yes, even humans can modulate the brake pedal, but the reaction time will be too slow to stop the wheels from locking. In contrast, even an entry-level Anti-skid Braking System performs threshold braking around 15 to 17 times per second. Such a quick reflex is humanly impossible. Hence, ABS comes to your rescue!

Types of Anti-lock Braking System

The Anti-skid Braking System can be further divided into three types based on the number of wheel speed sensors and pressure-release valves. Refer to the below table for more details on different types of ABS in cars.

Type of ABS Details
Four channel-four sensor This type of ABS consists of separate sensors and valves for each wheel.
Three channel-four sensor It has separate sensors for each wheel, and the front wheels have separate valves. But the rear wheels get only one valve.
Three channel-three sensor The front wheels get separate sensors and valves. However, the rear wheels get only one valve and sensor.

What are the components of an ABS?

As mentioned earlier, ABS comprises four main components. In this section, we will briefly explain the Anti-Lock Braking System components.

1. Wheel speed sensors

Wheel speed sensors calculate the deceleration and acceleration of the wheel. It comprises a toothed wheel, a magnet/electromagnetic coil and a Hall Effect Sensor. When the wheel is in motion, it generates a magnetic field around the sensor. The fluctuation of the magnetic field creates voltage, and it sends a signal to the controller, which reads the wheel speed.

2. Pressure release valves

As the name suggests, they are the valves that help control the brake pressure. In some of the systems, the valves operate in three positions.

Position 1: The valve opens, and the pressure from the master cylinder passes on to the brake. 

Position 2: The valve closes and separates the master cylinder and the brake. It prevents any further rise in the brake pressure. The valve operates in this position when the driver slams on the brake in emergencies.

Position 3: The valve releases some of the brake pressure.

3. Hydraulic motor

The hydraulic motor restores brake pressure after the vales release the pressure. When the wheels lock up, the controller sends a signal to the valve to release the brake pressure. Post that, restoring the brake pressure is crucial to slow down/stop the vehicle. The controller modulates the motor to provide the desired amount of brake pressure.

4. Controller

The controller is nothing but an ECU that receives information from the wheel speed sensors. It also sends a signal to the hydraulic motor once it detects a wheel lockup. It is also responsible for the activation of ABS as it modulates the hydraulic motor to release or increase the brake pressure.

Why is the Anti-lock Braking System (ABS) important?

ABS is a crucial safety feature to be safe on the road. Indian roads are unpredictable, and you never know what's around the next corner. Hence, you should always be ready to take evasive action, and the Anti-lock Braking System assists in doing that. Below are some of the points that highlight the importance of ABS.

  • It prevents your car from skidding under hard braking. Hence, you can safely bring the vehicle to a stop even in dire situations.

  • ABS also shortens the braking distance. So, you can stop the car at a shorter distance, which is crucial in emergencies.

  • It is beneficial in adverse weather conditions. It assists you to brake efficiently on wet, icy and slippery roads.

  • Lastly, ABS can save your life by avoiding a potential accident. So, never ignore any issues with your car's Anti-lock Braking System. Get the ABS fixed on priority if there is a system malfunction.

Advantages of Anti-lock Braking System

Below are the advantages of ABS.

  • It prevents the wheels from locking up under hard/panic braking and eliminates the chances of skidding or losing control of your vehicle. Hence the car will be stable even under aggressive braking.

  • It also maintains the vehicle’s steerability. Since the wheels don’t lock, you can easily steer the car.

  • ABS reduces the braking distance, especially on slippery surfaces such as wet or icy roads.

  • One of the most critical advantages of ABS is that it reduces the chances of a collision when you are driving on the road.

Disadvantages of ABS

When we say cons, there are no functional disadvantages of an Anti-lock Braking System. Below are some of the disadvantages of ABS in cars.

  • ABS increases the vehicle’s cost. However, the additional safety it offers to the car owner/driver completely justifies the higher price.

  • ABS and off-roading do not go hand in hand. That’s because it does not work well on loose surfaces such as dirt or gravel. ABS increases the stopping distance on loose surfaces.

  • Lastly, ABS requires additional maintenance due to the presence of ABS-related components.

Also, read: Alloy wheels vs steel wheels: Which is better for your car? 

ABS and EBD

You may have come across the EBD while glancing through the safety features of a car. In some car brochures, you may have observed it along with ABS, like “ABS with EBD”. So, how is EBD different from ABS?

EBD stands for Electronic Brakeforce Distribution, and it is also another crucial safety feature related to the brake. When you brake, EBD calculates which wheel needs more braking power and which wheel needs less depending on various factors such as wheel traction, wheel angle, vehicle’s weight, etc. 

Typically, in a front-engine car, most of the brake force is applied to the front as it is a front-heavy vehicle. Some advanced EBD systems immediately transfer the brake force to the rear wheel just before the weight transfer to the front of the car.

Similar to ABS, EBD also prevents the wheels from locking up. However, EBD does it by regulating the brake distribution across all four wheels, whereas ABS works by modulating the brake pressure.

Cars with ABS vs cars without ABS

The below table highlights the key differences between a non-ABS and ABS-equipped car.

Parameters ABS-equipped car Non-ABS car
Traction under heavy braking The wheels do not lock up under hard braking because ABS ensures the wheels have enough traction to avoid slippage. The wheels easily lock up under panic braking. The tyres lose traction immediately when you slam on the brakes.
Braking distance Shorter braking distance. Longer braking distance than ABS-equipped cars.
Steering under heavy braking Maintains steerability even when you brake hard. It loses steerability once you brake hard as wheels lock up and slide on the road surface.
Vehicle stability The car remains stable under heavy braking. The car loses its stability and can skid if you harshly apply the brake.
Cost Higher than non-ABS cars. Lower than ABS-equipped cars.

Frequently asked questions (FAQs)

Below are some commonly asked questions and their answers related to the Anti-lock Braking system in cars.

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What do I do if my car doesn’t have ABS?

If there are no compatible ABS kits available for your car or you don’t have the budget to invest in such kits, you can improve your braking technique. Be gentle on the brakes, especially on wet or icy roads. Also, you can practise brake modulation in a safe environment so that you know what to do in an emergency.

What does it mean if the Anti-lock Braking System light stays on when I drive my car?

If the ABS light blinks or stays on when driving the car, there is some issue with the safety equipment. You should immediately drive to the nearest service centre to rectify the problem as it is one of the crucial safety features of your car.

Does ABS help me to stop the car faster?

Yes, technically, the Anti-skid Braking System reduces the braking distance. That means you can stop the car faster with ABS intervention. However, ABS can increase the braking distance under certain conditions, such as loose surfaces.

What are the symptoms of a faulty ABS sensor?

Below are some of the symptoms of a bad ABS sensor.

  • The ABS light stays on when you drive the car.

  • Traction/Stability control is disabled, or you cannot activate it.

  • Your vehicle is unstable under braking.

  • ABS is not consistent when you brake hard.

  • Increased braking distance.

Do all cars have an Anti-lock Braking System in India?

Yes, all cars do come with ABS in India. ABS is mandatory for all cars in India from April 2019. The Ministry of Road Transport and Highways (MoRTH) has made this safety feature compulsory for all vehicles.

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