What is Anti-Lock Braking System (ABS); Its Working Principle & Various Components (With PDF & FAQs)

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.

Antilock Braking System
Antilock Braking System

So, with ABS, the driver can easily slow down the vehicle with ABS and even change the direction of the vehicle if a large rock suddenly appears in front of the vehicle. Simply put, ABS prevents your vehicle’s wheels from locking up all the time and helps bring your vehicle to a stop without the wheels skidding.

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 system 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 understand this better, consider an incident. When you are driving a car on a highway and suddenly an obstacle appears in front of you and you suddenly apply the brakes. This locks the wheels of the car and causes the car to start skidding on the road. Also, when skidding, you cannot hold the steering wheel and move the car in the desired direction. Eventually, you will come across this obstacle and face an accident.

Consider another situation. You are currently driving a car with an antilock braking system. When you hit an obstacle on the road and apply the brakes abruptly. But this time, the car’s ABS system prevents the wheels from locking and skidding. At this point, you can control the steering to prevent the car from hitting obstacles. In this way, the ABS system prevents the vehicle from skidding and provides more control over the vehicle to prevent accidents.

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

Antilock Braking System
Antilock Braking System

Source: Encyclopedia Britannica, Inc

Electric Control unit

The controller used in the ABS system 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

Used to calculate wheel acceleration and deceleration. It consists of a gear and an electromagnetic coil or a magnet and a Hall effect sensor to generate a signal. As the vehicle’s wheels or differential rotate, a magnetic field is induced around the sensor. This magnetic field fluctuation produces a voltage across the sensor. This generated voltage sends a signal to the controller. Using voltage, the controller reads the acceleration and deceleration of the wheel.

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: –

i) Pump
ii) Accumulator
iii) Solenoid Valves

Pump: 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 with the intention to offer a preferred quantity of strain and decrease the slipping of the wheel.

Accumulator: 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.

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 system has four channels, one for each wheel, and the hydraulic control unit has two solenoid valves for each wheel.

Normal braking is assisted by the vacuum power braking system. Another variation has three channels, one for the front wheels and one for the rear wheels.

The system has two solenoid valves on each channel. Greater steering control is available with these systems.

The pressure regulation makes on all four wheels allows the brakes to operate very safely and bring the car to a stop in the shortest possible distance.

The control module closes the intake solenoid when it detects that deceleration may cause the wheels to lock. This prevents any further liquid from entering the circuit.

If the wheel is still decelerating and there is a possibility of locking, the ECU will open the exhaust solenoid valve. After the brake is released, the control module returns the intake and exhaust solenoid valves to their original positions.

The control module also calculates the slip ratio for each wheel via wheel speed sensors. If the slip ratio is high, it sends a control signal to the modulator.

Integral Anti-lock Braking System

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

Four Wheel System:

When the brakes are applied, the deceleration of each wheel is monitored by the control module. A signal is sent to the hydraulic unit if the deceleration is too high and the wheels are likely to lock.

The hydraulic unit should initially keep the fluid pressure in the wheel constant and not increase. If the deceleration is still large, lower the fluid pressure.

This is achieved by the control module sending a signal to a solenoid valve that activates the hydraulic unit. This prevents the wheels from locking when braking.

On the other hand, if there is insufficient braking force, the control module sends a signal to the hydraulic unit to increase hydraulic pressure and increase braking force.

This control cycle is repeated many times depending on the braking demand.

As soon as the brake pedal is released, the piston in the brake master cylinder returns, and the fluid from the booster chamber returns to the reservoir. When braking under normal conditions, the pushrod operates the lever. This moves the spool valve, closing the opening between the intensifier chamber and reservoir. It also partially opens the accumulator port. Fluid moves under high pressure from the accumulator to the booster chamber.

The fluid pushes the piston forward, increasing the thrust on the pushrod. When the control unit detects a wheel lock, the valve opens. The valves supply fluid to the chambers between the pistons of the master cylinder and between the retract sleeve and the pistons of the first master cylinder.

High-pressure fluid in the retraction sleeve pushes back the push rod and brake pedal. In fact, the high-pressure fluid is supplied by the accumulator, not by the actuation of the brake pedal.

Control valves also open and close solenoid valves to control wheel braking. When the solenoid valve opens, the piston in the master cylinder delivers fluid to the front wheels and the booster chamber delivers fluid to the rear wheels.

Closing these shuts off the master cylinder and booster chamber. Fluid returns from the wheel to the reservoir.

Braking is done in curves and the anti-lock braking system must work differently in this situation.

Working of Anti-lock Braking System (ABS)

The controller (ECU-Electronic Control Unit) reads the signal from the speed sensor of each wheel.

If the driver brakes hard, the wheels will decelerate faster and the wheels may lock up.

When the ECU reads a signal indicating a sudden decrease in wheel speed, it sends a signal to the valve to close it and reduce brake pad pressure to prevent the wheels from locking.

The wheel will start accelerating again and send the signal to the controller again. Now open the valve and increase the pressure on the brake pads to apply the brakes. This causes the wheel to slow down again and try to come to a stop.

When a driver brakes hard, this braking and releasing process occurs 15 times per second. This prevents the wheels from locking and the vehicle from skidding. Braking with the ABS system allows the driver to steer the vehicle and reduces the risk of a vehicle collision.

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

When the ABS is in operation, it can be felt by the driver through pulsation in the brake pedal; this happens because of the rapid opening and closing of the valves. The pulsing action of the pedal tells the driver that the ABS system is in operation. Any fault in the ABS system is indicated on the instrument panel of the vehicle and it will work when the fault is completely removed.

What are the 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%.

What are the Disadvantages of Anti-lock Braking System?

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

FAQs: Frequently Asked Questions

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.

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Atul Singla

Hi ! I 'm Atul. I am PMP certified Mechanical (Piping) Engineer with more than 17 Years of experience. Worked in the field of Plant design for various industries such as refinery, petrochemical & chemical, Fertilizer, gas Processing industries. Developed passion about Piping while working with national & international engineering consultants on diverse projects involving international clients. Developed courses on Piping Engineering to share the knowledge gained after working with many industry experts, through out these years.

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