One of the most important control system of an automobile is BRAKE SYSTEM .They are required to stop the vehicle within the smallest possible distance and is done by converting kinetic energy of the vehicle into heat energy which is dissipated into atmosphere.

The main requirements of brakes are given below :- 

1. The brakes must be strong enough to stop the vehicle within the minimum possible distance in an emergency. But this should also be consistent with safety. The driver must have a proper control over the vehicle during emergency braking and the vehicle must not skid.
2. The brakes must have good antifade characteristics and their effectiveness should not decrease with constant prolonged application.

The actual stopping distance of vehicle while braking depends on the following factors:-

1. Vehicle speed
2. Condition of the road surface
3. Condition of tyre tread
4. Coefficient of friction between the tyre tread and the road surface
5. Coefficient of friction between the brake drum/disc and brake lining/friction pad
6. Braking force applied by the driver.
   

DISC BRAKES :- As shown in fig a disc brake consists of a cast iron disc bolted to the wheel hub and a stationary housing called caliper. The caliper is connected to some stationary part of the vehicle, like the axle casing or the stub axle and is cast in two parts, each part containing a piston. In between each piston and disc there is a friction pad held in position by retaining pins, spring plates etc., passages are drilled in the caliper for the fluid to enter or leave each housing. These passages are also connected to another one for bleeding. 

When the brakes are applied hydraulically actuated pistons move the friction pads into contact with the disc, applying equal and opposite forces the later. On releasing the brakes the rubber sealing rings act as return springs and retract the pistons and the friction pads away from the disc.