Brake

A brake is a mechanical device that inhibits motion by absorbing energy from a moving system.

[1] It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction.

Brakes are generally applied to rotating axles or wheels, but may also take other forms such as the surface of a moving fluid (flaps deployed into water or air).

The Saab B 17 dive bomber and Vought F4U Corsair fighter used the deployed undercarriage as an air brake.

However, because of their low production cost, drum brake setups are also installed on the rear of some low-cost newer vehicles.

A brake disc (or rotor in U.S. English), usually made of cast iron or ceramic, is connected to the wheel or the axle.

For example, an internal-combustion piston motor can have the fuel supply stopped, and then internal pumping losses of the engine create some braking.

Some engines use a valve override called a Jake brake to greatly increase pumping losses.

Some vehicles, such as some transit buses, do not already have an electric motor but use a secondary "retarder" brake that is effectively a generator with an internal short circuit.

Friction brakes apply pressure on two separate objects to slow the vehicle in a controlled manner.

[4] This additional force is supplied by the manifold vacuum generated by air flow being obstructed by the throttle on a running engine.

Because of low vacuum at high RPM, reports of unintended acceleration are often accompanied by complaints of failed or weakened brakes, as the high-revving engine, having an open throttle, is unable to provide enough vacuum to power the brake booster.

Heavier road vehicles, as well as trains, usually boost brake power with compressed air, supplied by one or more compressors.

This happened in the Tuscan GP, when the Mercedes car, the W11 had its front carbon disc brakes almost bursting into flames, due to low ventilation and high usage.

[7] These fires can also occur on some Mercedes Sprinter vans, when the load adjusting sensor seizes up and the rear brakes have to compensate for the fronts.

However, this retraction must accommodate all compliance in the system (under pressure) as well as thermal distortion of components like the brake disc or the brake system will drag until the contact with the disc, for example, knocks the pads and pistons back from the rubbing surface.

This brake drag can lead to significant parasitic power loss, thus impacting fuel economy and overall vehicle performance.

[9] In the 1890s, Wooden block brakes became obsolete when Michelin brothers introduced rubber tires.

[10] In 2005, ESC — which automatically applies the brakes to avoid a loss of steering control — become compulsory for carriers of dangerous goods without data recorders in the Canadian province of Quebec.