All about Anti-Locking Brakes in an Automobile

Anti-lock braking system is a powerful braking system used in modern automobiles. An anti-lock braking system prevents the wheel locking or skidding. An electrical control unit, hydraulic actuator and individual wheel speed sensors that work together to prevent brakes from locking. We’ll discuss in this article the components of an anti-locking brake system and its working.

The primary components of an anti-locking brakes are electronic control unit (ECU), hydraulic control unit/modulator, wheel sensor unit, power booster and master cylinder assembly.

Components of an anti locking braking system
Electronic control unit (ECU)
The main purpose of an electronic control unit (ECU) is to receive signals from different sources. A sensing device is located at the brake pedal that provides a brake-operating signal and another device is located in the ignition system to signals the engine operation. Another input signal is from the wheel speed sensors. These signals are used to control the hydraulic control unit/Modulator and wheel lock. When a wheel starts to lock, ECU operates a solenoid valve to reduce hydraulic pressure.

Hydraulic control unit/modulator
ECU sends electrical signals to the hydraulic control unit/modulator. It executes the command signals using three solenoid valves connected in series. These solenoid valves are connected with master cylinder and the braking circuits, one valve is connected to the front wheel hydraulic circuit, and one for both of the rear wheels.

When signals from the wheel speed sensor show no tendency for wheel to lock, the ECU won’t send any control current to the solenoid coil. The solenoid valve will be idle state, and the hydraulic pressure from the master cylinder is supplied to the brake unit at the wheel. When the control unit detects any lock-up, it sends a command current signals to the solenoid coil. This causes the armature and valve to move upward, and isolate the brake circuit from the master cylinder.

Master cylinder assembly
The master cylinder is connected to the brake pedal through a push rod. Master cylinder is divided in to two parts. It consists of a primary piston, and a secondary piston. During normal braking, as the speed of the wheel falls,electric current won’t flow from the ECU to the hydraulic unit. The solenoid valve is not energized. The brake master cylinder hydraulic pressure is applied to the brake unit.

Speed sensors
ABS needs some sensing units to know when a wheel is about to lock up. For this, speed sensors are used. These are located near each wheel, in some cases they are located on the differential, provide this information to the control unit. This system provide maximum braking power.

When the ABS system is in operation you will feel a pulsing in the brake pedal due to rapid opening and closing of the valves.

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