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Car Disc Brakes
See also: Engine Brake & Anti-lock Braking System

Brakes are mechanical components used to reduce the speed of a vehicle.

Contents

[edit] History

[edit] Trains, Trucks and Air Brakes

The need for brakes coincided with the development of high-speed transportation. The first brakes were used for trains in the late 1700’s. The earliest designs featured a manual brake lever on each train car. The train’s conductor would signal to his brakemen, who would jump from car-to-car, pulling brake levers as they went.[1] The end result was an unresponsive braking system with a very gradual stop.[2]

The next braking development was a system which used pressurized air to apply pressure to the train’s wheels. Trains had pressurized air reservoirs which would distribute air through a hose assembly to the train cars. The problem with this system was it was very susceptible to failure. If air pressure became reduced due to a loose hose fitting or puncture, then the entire system failed, and the train would be without braking power.[3]

A major breakthrough occurred in 1869, when George Westinghouse invented the triple valve air-brake. This brake system was a drastic improvement over the air brakes previously employed, because if it failed, the brakes would automatically engage. Westinghouse’s design prevented accidents stemming from run-away vehicles. It became the basis for which modern brakes are designed for trains, heavy-duty trucks, and other heavy machinery.[4] Air brakes have never been adopted for automobiles because they require large pressurized air tanks, which are too cumbersome to be placed in smaller vehicles.[5]

[edit] Early Cars and Drum Brakes

In the early days of automobiles, the most popular method of braking was to pull a lever which applied pressure directly to a tire. This method worked well to slow the vehicle; but did considerable damage to the tire’s rubber and required a considerably strong operator.[6]

In 1902, Ransom E. Olds (of Oldsmobile fame) invented the drum brake. Olds’ system was able to slow vehicles much quicker and overcame the problem of tire damage. By 1903, the majority of automobile manufacturers had adopted Olds’ design. By 1904, virtually all manufactures had done so.[7]

One issue with early brakes was that they emitted a high pitch squeal due to metal grinding on metal. This problem was solved with an invention in 1907 by Herbert Frood. Frood conceived that lining brake pads with the mineral asbestos would prevent the squeal. Asbestos was easy to work with and maintained its high friction properties at very high temperatures, making it very suitable for braking applications.[8]

The first four-wheel hydraulic brake system was invented by Malcolm Lougheed in 1918. This system had considerable advantages over previous methods, which required the operator to push the pedal extremely hard to slow the vehicle. Drivers could now gain mechanical advantage using hydraulics to thrust brake pads against brake drums; slowing the vehicle quicker, with less effort. By 1929, most luxury vehicles had four-wheel hydraulic brakes. Within a few years, it became standard on low-end vehicles also.[9][10]

[edit] Disc Brakes

Disc brakes were invented in 1898 by Elmer Ambrose Sperry, an American. However, the first disc brakes in production vehicles were produced by European automobile manufactures in the 1950’s. In fact, it wasn’t until 1973 when American manufacturers started using disc brakes.[11] The main reason for the slow adoption was that vehicles at the time were only capable of modest maximum speeds; so there was no need for improved braking power.[12]

[edit] How It Works

The fundamental goal of brakes is to convert mechanical energy into heat energy. This is accomplished by applying pressure to a moving part, which causes friction, which gives off heat, reduces the amount of mechanical energy, and slows the vehicle. Every brake operates on this principle one way or another.[13]

[edit] Drum brakes

Early drum brakes were not encased like modern drum brakes, they had exposed components. They operated by tightening a metal band around a circular rotating drum, with the drum firmly attached to one of the vehicles wheels. The metal band rubbing against the drum would create friction, which slowed the rotation of the drum, slowing the rotation of the wheel the drum was attached to, and thus the vehicle also.[14]

These exposed drum brakes were phased out by interior drum brakes. By encasing the brake’s components they were protected from the elements, so they could be used for much longer than before. The interior drum brake operates much like an exterior one; pressure is applied to a drum, which slows the wheel, and in turn slows the vehicle. They differ in how pressure is applied to the drum. Where early drum brakes used a metal band to constrict the drum, newer drum brakes thrust a brake pad against the interior wall of the drum to slow it down.[15][16]

[edit] Disc brakes

Disc brakes operate in a similar fashion to a drum brakes. Instead of a drum, disc brakes have a rotating disc attached to the wheel. Pressure is applied to the side of the disc with a brake pad, which slows the disc, which in turn slows the wheel, and thus the vehicle also.[17]

[edit] Air brakes

Air brakes work by maintaining enough air pressure in the brake assembly to force the brakes to stay open. When the brake pedal is applied, pressure is released from within the brake assembly, which forces the brake to engage.[18]

[edit] Types

Air Brakes: Air pressure is used to force the brakes open. If pressure is reduced, the brakes engage. Air brakes are used in heavy trucks and trains.

Hydraulic Brakes: Hydraulic pressure is used to gain a mechanical advantage, increasing stopping power. This system is common in smaller vehicles.

Mechanical Brakes: The operator’s own force is applied to the brake pads. Mechanical brakes can be found on most bicycles.

[edit] Common Manufactures

  • ABS Friction
  • Akebono
  • BrakePro
  • Capital Tool & Design
  • Fritec
  • Haldex
  • Halla
  • MGM Brakes
  • NAPA United
  • Nisshinbo
  • Nucap
  • OE Quality Friction Inc.
  • Raybestos
  • Sloan
  • TMD Friction
  • Wellman Products Group

[edit] References

  1. Train Air Brake Description and History. SDRM.com [September 16, 2009].
  2. How Air Brakes Work. HowStuffWorks.com [September 16, 2009].
  3. How Air Brakes Work. HowStuffWorks.com [September 16, 2009].
  4. George Westinghouse. About.com [September 16, 2009].
  5. How Air Brakes Work. HowStuffWorks.com [September 16, 2009].
  6. Automobile Brakes History. MotorEra.com [September 16, 2009].
  7. Automobile Brakes History. MotorEra.com [September 16, 2009].
  8. Automobile Brakes History. MotorEra.com [September 16, 2009].
  9. Automobile Brakes History. MotorEra.com [September 16, 2009].
  10. Brakes. Bryant University Community Webs [September 16, 2009].
  11. Automobile Brakes History. MotorEra.com [September 16, 2009].
  12. Brakes. Bryant University Community Webs [September 16, 2009].
  13. Brakes. Bryant University Community Webs [September 16, 2009].
  14. Brakes. Bryant University Community Webs [September 16, 2009].
  15. Drum brake history. MadAbout-KitCars.com [September 16, 2009].
  16. Brakes. Bryant University Community Webs [September 16, 2009].
  17. Brakes. Bryant University Community Webs [September 16, 2009].
  18. How Air Brakes Work. HowStuffWorks.com [September 16, 2009].