The first documented case of brakes in use was in ancient Rome. These simple brakes were composed of a lever that when pulled, pressed a wooden block onto the outside of a metal lined wheel. The primary force for braking with this device was friction. This method was effective due to the slow speeds at which the carts traveled; however, it was an inadequate form of slowing runaway carts. This method of braking was used for centuries with little design improvement.
Figure 1: Example of the Lever Brake
When the Michelin brothers created the rubber-covered wheel wooden blocks were replaced with drum brakes. Louis Renault invented drum brakes in 1902. Instead of applying a block to the outside of the wheel, drum brakes were mounted inside of the wheel hubs. This helped minimize debris blockage and reduce the loss in braking friction. Drum brakes are still in use in cars as handbrakes due to the large amount of force needed in order to overcome the brake force while at rest.
Figure 2: Example of a Drum Brake
With the introduction of the assembly line, cars became heavier and faster,
which created a need for a more powerful braking system. Malcolm Loughead created a four-wheeled hydraulic braking system. The hydraulic system uses lines filled with hydraulic fluid rather than cable driven braking systems. The main advantage to hydraulic braking systems is that they can apply a greater braking force than cable systems. Cable brakes fatigue faster than hydraulic brakes due to a the constant tension that the cable is under. Hydraulic brakes allowed the driver to apply less force onto the brake pedal while still stopping in a the same short distance.
Throughout braking history the issue of overheating has been a constant problem. Heat occurs when the brake pads come in contact with the braking surface. The key factor in dispersing heat is having a larger surface area for the brake to cool down. Disk brakes have a large surface area exposed to the air, which helps it to remain cooler. There are holes and grooves cut into the rotor of the braking system to allow water and debris to be moved off the braking surface and minimize interference, which causes loss of braking force.
Figure 3: Example of a Disk Brake
Disk brakes did not start becoming popular in vehicles until the 1950’s even though they were invented around 1902. Disk brakes are attached inside the rim of the vehicle and spin in unison with the wheel. When force from the driver’s foot is applied to the brake pedal the brake fluid travels through hydraulic cables and becomes amplified by the power braking system attached to the engine; this in turn pushes the brake fluid against the caliper which uses frictional force to slow the vehicle. Faster vehicles need brake pads and calipers to be made of different materials to replicate the same braking distance needed to stop slower less advanced vehicles, due to the greater amount of inertia that is trying to be stopped.
There are five main materials used in brake rotors. The five materials most commonly found in brake rotors are cast iron, steel, layered steel, aluminum, and high carbon irons. Production cars use cast iron brakes due to the amount of abuse that they can handle without cracking or failing. Steel brakes have a lighter weight and heat capacity, but lack durability in repeated uses. Heat can disperse faster with layered steel brakes because adding layers to simple steel brakes allows for a
stronger material that can withstand a more rigorous workload. Aluminum brakes have the lowest weight of all vehicle rotors. Heat is dispersed quicker, however the total capacity for heat absorption is lower than in steel brakes; this is why aluminum is most commonly used in motorcycles and other small vehicles. The final type for brake material that is used is high carbon iron. High amounts of carbon allow for increased heat diffusion, which makes this type of brake most commonly used in high performance vehicles.
Figure 4: Brake Rotors
Brake pads have been made with different materials throughout the years depending on the intended use. Asbestos was the most popular material due to its ability to absorb and disperse heat. After scientific studies, asbestos has been found to be a highly toxic material and has been banned from use in vehicles in the United States. With asbestos illegal to use, brake manufactures were forced to create safer brakes from a material that will not harm the general public. Organic brakes are made from materials that can withstand heat, for example; glass and varieties of rubber are mixed with a heat resilient resin to produce safer brakes. The advantages of using organic brake pads are that they are usually quieter and are
easier to dispose. Even so, organic brakes are not typically used because they wear easily and dust particles collect between the pad and wheel, which decreases the braking surface.
Figure 5: Brake Pads
With a lighter weight to slow down, motorcycles use organic and ceramic brake pads. Ceramic brake pads are the most effective type of brake pads but are the most costly. The most common type of brake pad is made with a mixture of several types of metals. These metallic brakes are durable while still being cost efficient. The negative factors for using metallic brakes are that they work best when warm and it may take longer to slow down at first when driving in cold weather. With advances in material science, brakes will continue to improve to match the advances in car technology.