How Does ABS Work (Complete Notes)

An ABS System;- 

An Anti-lock braking system (ABS) is also known as Anti-skid braking system. An Anti lock braking system is a safety system in an Automobile that’s allows wheels on a motor vehicle to maintain tractive contact with the road surface according to driver input while braking, preventing the wheel from locking up and avoiding uncontrolled skidding.

Literally! ABS offers to decrease Stopping Distances and improve Vehicle control on dry and slippery surfaces and its also gives output on snow covered surfaces while the driver press the brake.

An Automotive Industry has launched Different Version of ABS. Recent Versions not Only Prevent wheel Components Lock under braking

Lock Under Braking, But also electronically Control Front-to-rear bias.The Function depending on its specific capabilities and implementation, is known as electronic brake-force distribution (EBS),Traction Control System (TCS) or Electronic stability control (ESC).

Components:

There are four main Component which are used in an ABS.

·        Wheel speed Sensor

·         Valve

·         Pump

·         Controller

Wheel Speed Sensor:-

A speed sensor is used to determine the acceleration or deceleration of the wheel. These Sensor Use a magnet and hall effect sensor, and an electromagnetic Coil to generate a signal. The rotation of the wheel  induces a magnetic field around the sensor. The fluctuations of this magnetic field generate a voltage in the sensor. Since the voltage induced in the sensor is a result of the rotating wheel, this sensor can become inaccurate at slow speeds.In other words! The slower rotation of the wheel can cause inaccurate fluctuations in the magnetic field and thus cause inaccurate readings to the controller.

         The speed sensors of ABS are sometimes used in indirect tire pressure monitoring system (TPMS), which can detect under-inflation of tires by difference in rotational speed of wheels.

Valve:

                There is a valve in the brake line of each brake controlled by the ABS. On some systems, the valve has three positions:

·                  In position one, the valve is open; pressure from the master cylinder is passed right through to the brake.

·                  In position two, the valve blocks the line, isolating that brake from the master cylinder. This prevents the pressure from rising further should the driver push the brake pedal harder.

·                  In position three, the valve releases some of the pressure from the brake. 

Pump:-

The pump in the ABS is used to restore the pressure to the hydraulic brakes after the valves have released it. A signal from the controller will release the valve at the detection of wheel slip. After a valve release the pressure supplied from the user, the pump is used to restore a desired amount of pressure to the braking system. The controller will modulate the pumps status in order to provide the desired amount of pressure and reduce slipping.

Controller:-

The controller is an Electronic Control Unit (ECU) type unit in the car which receives information from each individual wheel speed sensor, in turn if a wheel loses traction the signal is sent to the controller, the controller will then limit the Electronic brake-force Distribution (EBD) and activate the ABS modulator which actuates the braking valves on and off.