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On Sep 23th, 2019, a new world record for 0-400-0 km/h was set at Råda airfield in Sweden by the Koenigsegg Regera . During this attempt, the Regera averaged around 1.1MW of dissipation during the braking phase, the system dissipated enough energy to power the average American home for just under 2 hrs. On almost every powered wheeled vehicle the brake system produces more deceleration force than the drivetrain’s acceleration force.
ORIGINS
The first wheeled vehicle brake systems consisted simply of a block of wood and a lever mechanism. To stop a vehicle, the lever was pulled, forcing the block of wood to grind against the steel rim of the wheel. Wooden brakes were commonly used on horse-drawn carriages and would even be used on early steam-powered cars that were effectively steam powered carriages.
DRUM BRAKES
The first brake system specifically designed for cars with pneumatic tires would be developed from an idea first devised by Gottlieb Daimler. Daimler’s system worked by wrapping a cable around a drum coupled to a car’s wheel. As the cable was tightened, the wheel would be slowed down by friction. While it was far more responsive than a wooden block, the exposed friction material of the external design made it less effective when exposed to the elements.
This idea evolved into the drum brake with a fixed plate and two friction shoes. These early systems used a mechanical cam that, when rotated, would apply a force through the web to the lining table and its friction material. On drum brakes, the shoe located towards the front of the vehicle is known as the primary shoe while the rearward one is designated the secondary shoe.
MASTER CYLINDER
At the drunk brake, a hydraulic cylinder containing two pistons replaces the cam mechanism, applying a force outwards on the brake shoes as pressure builds within the system. In hydraulic brake systems, a combination of rigid hydraulic lines made from either steel or a nickel-copper alloy and flexible reinforced rubber hoses are used to transfer fluid pressure between the master cylinder and the brake cylinders. Hydraulics also increased safety, through redundancy by allowing the brake system to be split into two independent circuits using tandem master cylinders. Four wheel-hydraulic brakes would first appear on a production car with the 1921 Duesenberg Model A though Rickenbacker would be the first manufacturer to offer them on vehicles that were mid-priced and more mass-appealing, in 1922. Shortly thereafter, other manufacturers would adopt hydraulic brakes and it quickly became the industry standard.
VACUUM BOOSTER
Many of these ideas involved using compressors to pressurize either air or hydraulic fluid and in order reduce the force needed by an operator to actuate a vehicle's brakes. First introduced by the Pierce-Arrow’s motor car company in 1928, this system, originally designed for aviation, uses the vacuum generated by an engine’s air aspiration to build a vacuum within a device known as a brake vacuum servo. By the 1930s, vacuum-assisted drum brakes began to grow in popularity.
DISC BRAKES
The next leap in braking technology got its start in England in the late 1890s with the development of a disc-type braking system by the Lanchester Motor Company. This system used a cable operated clamping device called a caliper that would grab a thin copper disc that was coupled to the wheel, in order to slow its rotation. By 1955, Citroën would introduce the Citroen DS, the first true mass-production car to field disc brakes. For the vast majority of modern disc-brakes systems, the disc or rotor is made from gray cast iron.
ABS
These systems attempt to modulate brake pressure to find the optimal amount of braking force the tires can dynamically handle, just as they begin to slip. In most situations, maximum braking force occurs when there is around 10-20% slippage between the braked tire’s rotational speed and its contact surface. By the early 1950’s the first widely used anti-skid braking system, called Maxaret, would be introduced by Dunlop.
It would take the integration of electronics into braking to make the concept viable for cars. As the wheel’s rotation starts to accelerate as it transitions out of braking the controller rapidly increases hydraulic pressure to the wheel once again until it sees the deceleration again.
COMPOSITES
Around the early 2000’s a derivative material known as carbon fiber-reinforced silicon carbide would start appearing in high end sports cars. Called carbon-ceramic brakes, they carry over most of the properties of carbon-carbon brakes while being both more dense and durable and they possess the key property of being effective even at the lower temperature of road car use.
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11 сен 2022
