A disc brake is a braking mechanism that uses a disc as the surface to create friction. A disc brake is commonly used in the front wheels but in some vehicles, they are used in all the four wheels.
How different is it from the hydraulic system?
The hydraulic system in the brake works the same as the drum brake, but the application of the friction is different. The friction is applied in the rotor disc and not to a drum. It is very similar to a cycle’s braking system where the friction is applied from both the sides to the wheel. But in a disc brake, friction is applied to the disc and instead of brake wires, hydraulic lines are used.
The rotor disc:
The rotor disc is a metal disc made out of a special type of iron. Due to friction, they generate a lot of heat and this heat has to be dissipated to reduce wear and tear of the disc. Discs can sometimes be ‘ventilated’, that is it may contain slots within the disc to allow free-flowing of air, to allow heat dissipation. In addition to this, discs may also be cross-drilled to reduce heat. But this has a disadvantage because; discs which are cross-drilled are prone to metal fatigue, a reason why it is avoided in high-performing race cars. To avoid warping of the disc, the disc may be mounted a little loose to the hub with coarse splines. This enables the disc to expand symmetrically and also avoid thermal stress.
Like the drum braking system, there is a component that receives input and applies pressure to the disc. In the disc brake, this is called a caliper. The caliper contains a piston which is much larger in size than a drum brake piston. Unlike the drum brake, in the floating variety if disc brakes, there is just one piston, but the brake shoes are two in number. One of the brake pad is in contact with the piston and moves along with it. The other piston is simply attached to the caliper. This mechanism adjusts the brake pads and always keeps them in position and so they don’t have to be manually or automatically readjusted.
In four-wheel disc brake vehicles, a drum is included in the rear wheels for emergency braking. It does not use hydraulics but is activated using a cable. Some vehicles also have a lever that turns a screw or activates a cam and pressure is directly applied to the disc.