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Closer look at the brakes

.Automotive brakes depend on friction to stop; converting kinetic energy into heat energy during the process. An older style conventional automobile has the friction action take place from the wheels hub by two shoes pushing outwards on either side of the inner surface of the rotating brake drum, which is mounted to the inside of each wheel. Newer style disc brakes are more efficient and have a double sided caliper that squeezes a disc mounted to the inner side of each wheel. The drum brake tends to suffer brake fade and can fail when heavy braking causes too much heat buildup inside the drum, while the vice like grip of the caliper on the rotor with disc brakes provide superior stopping power and also allow the rotor to readily disperse heat into the atmosphere.  Drums are made from cast iron while a rotor disc can also be made of a heat resistant ceramic, titanium, or any other material with the desired properties.

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© Philipimage | Dreamstime.com – Drum Brake Removed Photo

Both pads and shoes for braking are made to be easily replaced  and had traditionally been made with asbestos, from 1903 until around the late 1980’s, but because of health concerns asbestos for any purpose has been banned. The materials used for pad and shoe linings have changed, but the criteria remains the same. The material must be heat resistant, soft, but durable with a high coefficient of both dynamic and static friction. The shoes or pads can be rebuilt with new linings which can be either riveted in place or bonded to the solid metal backing plate with a high heat adhesive. The dynamic friction coefficient is measured in Newtons and represented by the Greek letter “µ”. Standard brake linings will have a coefficient of from 0.35 µ to 0.42 µ; meaning that a force of 1000 Newton exerted on the lining results in a braking force of 400 Newton. For high speed applications in racing special pads, with superlative high heat behavior, can be used and have a rating of 0.55 to 0.62 µ. These racing pads have high iron content and perform very well with an iron rotor, but the downside is they wear out very quickly and also have a high price tag. Most disc brake designs will integrate “squealers”- a band of metal with a tang extending down the edge of the pad which will emit a high pitched noise when the brake is applied, announcing the pads have neared the end of their life span.

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© Iopeners | Dreamstime.com – Wheel Change Photo

 How does a heavy automobile decrease its forward momentum when the operator applies so little pressure to the brake pedal? Two principles are put into practice when the brakes are applied. Hydraulic Force Multiplication plus Mechanical Advantage by leverage act together giving brakes the efficiency needed to slow or stop a car quickly and safely. Modern brakes have changed and been made more responsive, but all consist of the same basic components:

  • A lever or brake pedal
  • An actuating rod or push-rod
  • Master cylinder with a piston to activate a slave cylinder at each brake. This is a sealed high pressure system connected by reinforced hydraulic lines.
  • Brake Fluid with a reservoir (master cylinder) is filled with,most commonly, a glycol-ether base, but other fluids could be used as well.
  • Brake assembly containing the slave cylinders, each with a piston to trigger the pads or shoes to apply pressure and slow the rotating drum or rotor.

Fred Duesenberg is credited for being the first to use hydraulics for braking on his 1914 race car; later using the same system in the Duesenberg automobile available from showrooms in 1921. Malcolm Lougheed capitalized on the hydraulic principle in 1918 by developing his own version, although he used the name Malcolm Lockheed on his patent application through his namesake, The Lockheed Aircraft Manufacturing Company. Most passenger vehicles manufactured since then have use Hydraulics to activate both drum and disc brakes.

Related:

www.youtube.com/watch?v=VxLTDtaRCZk

www.youtube.com/watch?v=WC5-um7PXOE

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