Mechanical World: Anti lock Braking System (ABS) - Benefits, Components and Working.,

ABS

ABS (Anti-lock Braking System) is a brake system which prevents the locking of wheels and avoids the skidding of vehicles during turns, sharp and sudden braking. It maintains better stability and handling.

Now the most advanced vehicles employ the ABS brakes for braking. It allows the driver to maintain the steering control during hard braking situations.

The ABS Module

The ABS module is located under the hood on the driver’s side. It is composed of three parts, the Electronic Brake Traction Control Module, Brake Pressure Modulator Valve and the Pump. Most of the process on the ABS system center on the Control Module. The Control Module houses the computer and electronics that make the ABS work. In fact, the Control Module does not even need any instruction from the main ECU to work. The only communication between the ECU and the Controller is to turn the ABS light on and off and to interface for Diagnostic Trouble Codes and testing functions. On cars with ESP, there is also a module under the back seat that monitors the position of the vehicle and can apply braking to any of the four wheels to control unstable handling conditions.

Major components of the anti-lock brake system consist of a

ABS Brake control module.
Solenoid valve assembly.
Speed sensors.
Wiring, and the amber ABS brake warning light.

Working Steps

The ABS Module:

The brake control module is a computer that receives information from the speed sensor and helps in activation of brakes. It is the core component of the ABS.

In cars when one wheel is approaching lock-up pressure can be vented allowing the wheel nearing lock-up to speed up.If a wheel is too fast pressure can be increased to slow down the wheel. If both wheel are approximately the same speed the brake control module can enter a pressure hold mode of operation.

ABS system can maintain extremely high static pressure and must be disabled before attempting repairs.

Normally pumping brake 20-30 times will release pressure.

Electronic Brake Control Module

Solenoid Valve Assembly:

A Solenoid Valve Assembly In ABS

A solenoid valve is an electromechanical valve for use with liquid or gas. The valve is controlled by an electric current through a solenoid.

A solenoid valve has two main parts: the solenoid and the valve. The solenoid converts electrical energy into mechanical energy which, in turn, opens or closes the valve mechanically.

Solenoid valves are the most frequently used control elements in fluidics. Their tasks are to shut off, release, dose, distribute or mix fluids. In ABS brakes these valves are used to control the brake fluid to the brakes according to the variations and feed of electrical signals from the ABS control module.

Speed Sensors:

Speed Sensor In Wheel

Speed Sensor Used In ABS Brakes

The main use of a speed sensor is to monitor the speed of the wheels in the vehicle. ABS speed sensors are located at the wheel hubs of the vehicle. These sensors constantly monitor the rotation of each wheel to evaluate whether the ABS system needs to override manual braking of the vehicle in slippery conditions. The speed sensor calculates revolutions as well as evaluates continuity between all wheels. Any detection of differences in rotation can result in ABS engaging to control braking.

Speed sensors convert the pulses created by the contact between the magnet and sensor ring through a coil attached to the sensor. This voltage is passed along to the controller. The controller counts the number of pulses to determine wheel speed and evaluates whether the ABS system should intercede to control braking.

Wiring & ABS Brake Amber, Red Warning Lights:

Wiring:

The wiring of ABS in car and bikes,

ABS System In Car

ABS System In Bike

ABS Wiring In Bike

Warning Lights:

The Red warning light indicates the failure or problems in the hydraulic system, circuit and the Amber light is used to indicate the testing of microprocessor, low brake fluid levels, brake pad wear outs and improper hydraulic lines.

Working

The ABS module controls all the braking components.

When applying brake two things happen simultaneously,

The wheel which rotates at higher speeds comes to halt suddenly.
On applying the brake the brake fluid is forced to the brake calipers to activate brake.

Based on this and calculating these two factors the ABS brakes are deployed.

The first condition: Wheel comes to halt suddenly,

The speed sensor monitors the rotation of the wheel. It sends the input signals to the ABS module regarding the speed of wheel rotation. Depending on the rotation of the wheel the signal is sent to the ABS module which activates the brakes and balances the fluid pressure for the braking to take place perfectly.

The second condition: Brake fluid is forced to the brakes,

Here three types of changes takes place,

First, During a sudden brake the brakes has to be applied hard, so the fluid pressure has to be very high for sudden brake to take place. This allows the brake fluid to be transmitted suddenly to brakes to activate the brake. The brake fluid to the brakes is controlled by a solenoid valve which is controlled by the ABS module.

This is called as the pressure increase mode, If this continues for the entire braking process the wheel gets locked and the tyre starts to skid.

Hence it is necessary to ensure the pressure of the brake fluid, when the wheel comes close to lock the speed sensor detects the change and sends the signal to ABS module. The ABS module activates the solenoid valve which immediately holds the brake fluid and reduces the pressure to prevent wheel lock. This is called as the pressure hold mode. The pressure cannot be held for the entire braking process. if so happens the brakes will fail.

When the pressure of brake fluid is self sufficient enough to rotate wheels free, the signal is again sent to solenoid valve. The vent solenoid opens allowing the fluid to flow back and increase the pressure.

All these three process happens up to 18 times per second and prevents the wheel from getting locked. Its just like pumping the brakes up to 18 times per second.

ABS brake system are classified into,

Integrated
Non integrated

An integrated system has the master cylinder and control valve assembly made together.

A non integrated has the master cylinder and control valve assembly made separate.

ABS operates using the same hydraulic principal as conventional brakes.

ABS system only operates when wheel lock-up is emanate.

A bussing noise and bakes pedal vibration is normal during ABS operation

ABS brakes are either

1 Channel

3 Channel

4 Channel

1 channel ABS system controls the rear wheel together.

A 1 channel system only has 1 speed sensor and control valve assembly.

A three (3) channel ABS system control the rear wheel together and the front independently.

Three channel ABS system have 3 speed sensor and one (1) control module

ABS Brakes Application Method:

When operating a vehicle fitted with ABS never pump the brakes, doing so the ABS system becomes ineffective, always apply a firm pressure on brakes while braking.