Brake

From Wikipedia, the free encyclopedia

(Redirected from Brakes)

This article is about the vehicle component. For other uses, see Brake (disambiguation).

A brake is a device for applying a force against the friction of the road, slowing or stopping the motion of a machine or vehicle, or alternatively a device to restrain it from starting to move again. The kinetic energy lost by the moving part is usually translated to heat by friction. Alternatively, in regenerative braking, much of the energy is recovered and stored for later use.

Note that kinetic energy increases with the square of the velocity (E = 1/2·m·v² relationship). This means that if the speed of a vehicle doubles, it has four times as much energy. The brakes must therefore dissipate four times as much energy to stop it and consequently the braking distance is four times as long.

Brakes of some description are fitted to most wheeled vehicles, including automobiles of all kinds, trucks, trains, motorcycles, and bicycles. Baggage carts and shopping carts may have them for use on a moving ramp.

Most aeroplanes are fitted with wheel brakes on the undercarriage. Some aircraft also feature air brakes designed to reduce their speed in flight. Notable examples include gliders and some WWII-era aircraft, primarily some fighters and many dive bombers of the era. These allow the aircraft to maintain a safe speed in a steep descent. The Saab B 17 dive bomber used the deployed undercarriage as an air brake.

Deceleration and avoiding acceleration when going downhill can also be achieved by using a low gear; see engine braking.

Friction brakes on cars store the heat in the rotating part (drum brake or disc brake) during the brake application and release it to the air gradually.

[edit] Effects on noise pollution

Brake lever on a horse-drawn hearse

Main article: Roadway noise

The action of braking for motor vehicles produces recognizable sound level emissions, varying with the specific tire types and with the roadway surface type produces considerable effect upon sound levels or noise pollution emanating from moving vehicles.^[1] There is a considerable range in acoustical intensities produced depending upon the specific tire tread design and the rapidity of deceleration required to slow the vehicle. When the brake is pushed the caliper containing piston pushes the pad towards the brake disc which slows the wheel down. On the brake drum it is similar as the cylinder pushes the brake shoes towards the drum which also slows the wheel down.

[edit] Hypermiling

Because braking (except regenerative braking) converts kinetic energy into heat energy, it wastes energy that was used earlier to gather speed. Additionally, regenerative braking is not 100% efficient at recovering energy. Because of this, an easy way to see how well you are conserving your fuel is to note how much and how often you are braking. If the majority of your slowing is from unavoidable mechanical friction or drag, this means you are more or less squeezing out most of the potential from your vehicle. Some drivers use various techniques to minimize braking to save fuel (see hypermiling).