Anti-Lock Braking Systems (ABS) How They Work & FAQ [PDF]

In this article, we shall learn about the components and working principles of the Anti-Lock Braking System. We have also provided a PDF download link of the same at the very end.

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An anti-lock braking system is a system used to prevent the wheels from skidding during hard braking. In general, vehicles without ABS lock the wheels as soon as the driver applies the brakes and depresses the brake pedal. Therefore, the wheels will slip on the road. Thus, in such a case, when a large rock suddenly comes in front of the vehicle, when the driver depresses the brake pedal, the wheels skid, and the driver loses control of the vehicle.

Anti-Lock Braking System

So, with ABS, the driver can easily slow down the vehicle and even change the direction of the vehicle if a large rock suddenly appears in front of the vehicle

Working principle of Anti-lock Braking System

It works on the principles of cadence braking and threshold braking. Cadence braking and threshold braking are techniques in which the driver applies and releases the brakes before locking the wheels, or applying and releasing the brakes before locking. This process of braking and releasing the wheels is pulsing to prevent locking and the vehicle from skidding. Drivers practice this technique to have better control of the vehicle when braking quickly and to prevent the vehicle from skidding. The ABS automatically performs this cadence of braking to prevent the wheels from locking or the vehicle from skidding when braking.

Why is Anti-lock Braking System important?

To gain a better understanding, let us consider an example scenario: while driving on a highway, a sudden obstacle appears and the driver applies the brakes, causing the wheels to lock and the car to skid uncontrollably. In this situation, steering becomes impossible, and the driver is at risk of colliding with the obstacle, resulting in an accident.

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Now, let’s examine another scenario: the same situation occurs, but this time the car is equipped with an anti-lock braking system. When the driver applies the brakes suddenly, the ABS system kicks in and prevents the wheels from locking up, thereby avoiding skidding. As a result, the driver can maintain steering control and avoid colliding with the obstacle. This demonstrates how the ABS system helps to prevent skidding and provides greater control over the vehicle, ultimately reducing the risk of accidents

What are the components used in an anti-lock braking system?

Anti-Lock Braking System
Photo By Innovation Discoveries

Electric Control unit

  • The controller used in the ABS is ECU type. Its main function is to obtain information from individual wheel speed sensors.
  • When the wheel loses traction, a signal is sent to the controller, which limits the braking force (EBD) and activates the ABS modulator.
  • An activated ABS modulator controls the on and off of the brake and the valve and varies the pressure on the brakes.

Speed Sensors

  • The wheel speed sensor is a component utilized to measure the acceleration and deceleration of vehicle wheels.
  • It is typically comprised of a gear, as well as an electromagnetic coil or magnet paired with a Hall effect sensor, which generates a signal.
  • As the wheels or differential rotate, the sensor induces a magnetic field, causing voltage fluctuations across the sensor.
  • The voltage generated is then transmitted to the controller, which interprets the acceleration and deceleration data.

Hydraulic Control Unit

  • A control unit that operates by receiving signals from an electronic control unit (ECU).
  • The Hydraulic Control Unit (HCU) sends brake fluid to the input line, stops the flow, or withdraws the brake fluid from the return line to apply or release the brake, depending on the ECU signals preventing wheels from locking up all the time.

HCU consists of the following components

  • Pump
  • Accumulator
  • Solenoid Valves
  • Master Cylinder
ABS brake System ECU module
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The pump is used to repair the strain on the hydraulic brakes after the valve releases the strain. When the controller detects wheel slip, it sends alerts to launch the valve. After the valve releases the strain furnished by the driver, it repairs a preferred quantity of strain to the braking system. The controller modulates (adjusts) the popularity of the pump to offer a preferred quantity of strain and decrease the slipping of the wheel.


It is a garage device, that is used to shop the pressurized brake fluid. The outlet of the accumulator is attached to the solenoid valves.

Solenoid Valves

Solenoid valves work with the sign acquired from the ECU to – Supply pressurized brake fluid to use the brake, To prevent the delivery of brake fluid, To take the return flow of brake fluid to launch brake pressure at the wheel.

Master Cylinder

A device for pumping brake fluid, consisting of a piston, brake fluid, and a return spring. The piston rod is connected to the brake pedal, so when the driver depresses the brake pedal, the piston forces brake fluid into the master cylinder. The oil reservoir is connected to the master cylinder which maintains the amount of oil in the system. The output of the master cylinder is connected to the hydraulic control unit.

Types of Anti-lock Braking System.

Non-Integral Anti-Lock Brake Systems

Non-integrated systems include a vacuum assist booster and master cylinder. The control unit is also separate. There are independent hydraulic units and pumps, motors, and accumulators. A solenoid valve can be provided to control the hydraulic pressure on the wheels.

Two Wheel System

These systems only have rear-wheel pressure regulation. When braking, pressure is transmitted through the valve. The control unit monitors the speed sensor signal. When it detects that the deceleration that has occurred is so great that the wheels may lock up, it activates the shut-off valve. This prevents pressure on the rear wheel and further deceleration. If this does not prevent deceleration, the control module activates the dump valve. This continues until the wheel and vehicle decelerations are equal.

Two Wheeler ABS

When the brake pedal is released, the control module disables the isolation valve. This allows fluid to flow back into the master cylinder. The control module also controls the solenoid valves. The control module also detects system errors. Wheel speed sensors continuously provide wheel speed to the control module.

Four Wheel System

The hydraulic control unit of the system has either four channels or three channels, with two solenoid valves for each wheel or two valves on each channel, respectively. Normal braking is aided by the vacuum power braking system. The four-channel system provides greater safety and shorter stopping distances as the pressure regulation operates on all four wheels.

Integral Anti-lock Braking System

The control module shuts the intake solenoid valve to prevent further liquid from entering the circuit when it detects the possibility of wheel lock-up during deceleration. If the wheel continues to decelerate and may still lock, the ECU opens the exhaust solenoid valve. After releasing the brake, the control module returns the intake and exhaust solenoid valves to their original positions. The control module also uses wheel speed sensors to calculate the slip ratio for each wheel and sends a control signal to the modulator if the ratio is high.

Integral Anti-lock Braking System

The integrated system combines the master brake cylinder, hydraulic booster, and their circuits into one unit.

Four Wheel System

The control module monitors the deceleration of each wheel when the brakes are applied. If the deceleration is too high and the wheels are at risk of locking, a signal is sent to the hydraulic unit. The hydraulic unit maintains constant fluid pressure in the wheel initially and decreases it if the deceleration is still high. This is achieved through a solenoid valve activated by a signal from the control module.

Four Wheelers ABS

Conversely, if there is insufficient braking force, the control module sends a signal to the hydraulic unit to increase hydraulic pressure and boost the braking force. This cycle is repeated as per braking demand. When the brake pedal is released, the piston in the brake master cylinder returns, and the fluid from the booster chamber returns to the reservoir.

In normal braking conditions, fluid under high pressure moves from the accumulator to the booster chamber, pushing the piston forward and increasing thrust on the pushrod. In the event of wheel lock, the control unit detects it and opens the valve. The solenoid valves are opened and closed by the control valves to regulate wheel braking. In curves, the anti-lock braking system functions differently and is designed to prevent skidding and loss of vehicle control.

Working of Anti-lock Braking System (ABS)

The Electronic Control Unit (ECU), which serves as the controller in the ABS system, receives input signals from the speed sensors on each wheel. If the driver applies sudden and forceful braking, the wheels may decelerate too rapidly and become locked, leading to skidding. To avoid this, the ECU monitors the wheel speed and signals the valve to reduce brake pad pressure when a sudden decrease in wheel speed is detected.

Working of ABS
Photo By Allergo MicroSystems

This allows the wheel to regain traction, and the ECU will then signal the valve to release and increase brake pressure once again, causing the wheel to slow down and eventually come to a stop. This process of braking and releasing occurs approximately 15 times per second during hard braking, preventing the wheels from locking and reducing the risk of skidding and collisions. By utilizing ABS, the driver can maintain steering control during emergency braking situations.

How Would you Know that the Anti-lock Braking System is in Operation?

During ABS activation, the driver may experience a pulsating sensation in the brake pedal, caused by the rapid opening and closing of valves within the system. This pulsation serves as a feedback mechanism to inform the driver that the ABS is engaged. Any malfunction in the ABS is conveyed to the driver via an indicator on the vehicle’s instrument panel, and the system will only resume normal function once the fault has been fully rectified.

Types of ABS
Photo By AliBaba

Advantages of an Anti-lock Braking System

  • Prevent wheels from locking and eliminates the possibility of skidding.
  • Vehicle skidding is completely eliminated for excellent brake control.
  • The ABS system provides better steering control.
  • It reduces the chance of a collision by 30%.

Disadvantages of Anti-lock Braking System

  • Vehicles equipped with ABS (anti-lock braking system) are more expensive than vehicles without ABS.


What is an anti-lock braking system (ABS)?

An anti-lock braking system is a vehicle safety feature that uses speed sensors to prevent the wheels from locking when the vehicle brakes. It is an essential element to prevent the car from skidding on slippery roads, which can be difficult to control.

How do Anti-lock Braking systems work on a motorcycle?

In motorcycles, antilock braking systems prevent the wheels of a driven two-wheeler from locking up under braking conditions. Based on information from wheel speed sensors, the ABS unit adjusts brake fluid pressure to maintain traction during deceleration and avoid accidents.

When was the first Anti-lock Braking System invented?

The first fully electronic anti-lock braking system was developed in the late 1960s for Concorde aircraft. The modern ABS system was invented by Mario Palazzetti (known as “Mr. ABS”) at the Fiat Research Center and is now standard on all cars.

What is the function of the brake pump in the Anti-lock Braking System?

The ABS pump is used to return pressure to the hydraulic brakes after the valve has opened. The controller changes the state of the pump to produce the desired pressure and reduce slip. In a hydraulic brake fluid system, brake fluid is the primary application of the brakes.

ABS vs EBD vs BA | How ARE These Brakes Different Than Others?

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In conclusion, Anti-Lock Braking Systems (ABS) play a critical role in modern vehicles by improving vehicle stability and reducing the risk of accidents caused by skidding. The ABS operates by monitoring wheel speed and adjusting brake pressure to prevent wheel lock-up. This allows drivers to maintain steering control during hard braking and avoid obstacles in emergency situations. The ABS has evolved over time, with newer systems offering more precise control and faster response times. With their proven track record of improving vehicle safety, ABS systems are likely to continue to be an essential feature of modern vehicles for years to come.


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