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Disc Brakes – How do they work?

Snapshot: We take brakes for granted even though they are the most sophisticated and critical component of any car. Perhaps even more critical than the engine, because they help the car stop. The articles lets you know, how do they work and answers other related questions.

Just before buying a car almost everyone considers things like – How big is the engine? How much power it’s got and what mileage does it give etc.? Not many people ask how well do the brake perform and if the car has discs or drums. Yes, it is important, but it’s something that most of us don’t consider while buying. This articles let’s you know how do the disc brakes work and answers other related questions.  

What is Brake Fade?

While it may appear that the brakes stop the car with the force of friction, and it is true. But the force of friction can be generated only if there’s difference in temperature between the rotor and brake pads. So in effect the brakes actually work by transforming the kinetic energy of the car into heat that’s generated with friction.

If the brake rotors do not cool efficiently, the relative difference that’s required for the force of friction to work would vanish. So, the energy transformation into heat would stop and in effect the brakes would stop working when there’s no difference in temperature between brake discs and brake pads. This is known as brake fade and is a dangerous phenomenon that very often develops while going down hills in hot weather.

The only way to prevent brake fade is to make frequent stops while going downhill, this would let the brakes cool, and other than that using engine braking along with main brakes would also help and would let brakes cool.

Brake fade can also occur due to old brake fluid. The brake fluid can absorb moisture over time and this moisture unlike the fluid may form steam (which unlike fluid is compressible) when heated. This can make the brakes spongy and cause them to lose effectiveness. 

What are the different components that make up the braking system?

Brakes of modern car rely of hydraulics for operation. Brake fluid that runs in the brake lining is pushed through to exert pressure and apply brakes. In working, the brake pads which are stationary are pushed against the rotors to generate friction and stop the car.

So brake linings, calliper, rotor discs, brake pads, brake fluid reservoir, master cylinder and booster are the most basic components of the braking system. The brake linings carry the incompressible brake fluid. The callipers carry brake pads, sliders, pistons etc. that together as an arrangement is mounted on the bracket. The rotor rotates along with the wheels and is the primary component on which the friction force acts while braking.

The master cylinder is device that converts non-hydraulic pressure from the brake booster into hydraulic pressure. The brake booster uses the pressure relief in the intake manifold of an internal combustion engine to reduce the pressure on the brake pedal and is an enhanced master cylinder setup that is used to reduce the amount of pedal pressure which is needed for braking. 

How does it work?

The hydraulically operated disc use Pascal’s Law for operation. According to which pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure variations remain the same. A device based on this principle can be used to multiply forces and that’s what braking system does.

While force exerted by brake pedal is not sufficient on its own to stop all four wheels, but when the brake pedal is pressed, the hydraulics system multiplies force and transmits it to brake pads. A narrow pipe feeds much wider cylinders and since the cylinders near the brakes are much wider than the one near the brake pedal, the force that you originally apply is multiplied that makes the brakes work hard against the wheels.

So brakes rely in effect on the friction force to stop the car. When the brake pedal is pressed, the force is multiplied with the use of booster and sent to the pistons present in the callipers with the use of brake fluid. The pistons push the brake pads against the rotor discs and create force of friction to stop the rotors and in effect the car. The kinetic energy of the car is thereby converted into heat.

How are ventilated disc brakes different and better?

All cars nowadays have ventilated discs, so it’s hard to find solid discs in use. The ventilated discs generally have holes drilled through them or will have radial grooves that aid cooling.

To prevent brake fade, car manufacturers use ventilated discs. Solid discs have less surface area in comparison to the solid discs so practically ventilated disc brakes cool much more efficiently than the same side solid discs. This is what makes ventilated brakes more efficient and less prone to fade.

Click here to know how a turbocharger works and why is there a lag?

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