Vehicle motion is generated when engine output is sent through the drivetrain. The wheels, tires, suspension and steering system make sure this motion hits the ground and stays there. In addition to acceleration and steering, the braking system of a vehicle represents the third form of vehicle control, allowing drivers to slow down, stop and rotate a car through turns.
Braking is yet another variable in cars that is set based on the vehicle’s purpose and individual requirements. Some brakes are small and light for efficiency and low cost, while others are heavy duty to bring heavy cars and trucks to a halt. Selecting the right components is crucial when matching a brake system to various conditions and setups.
As with other automotive systems, brake setups have changed and improved over the years; new materials and engineering methods have contributed to the evolution of brake technologies, making them more advanced and efficient.
Friction is the primary concept of braking. A rotating part, attached to the hubs and axles of a car, is slowed by clamping it with a mechanism attached to a static part of the car, such as the spindle or suspension (a part that does not rotate while in motion). The clamping mechanism has a friction material that rides on the rotating component - with more pressure there is more resistance to rotate, ultimately bringing the car to a stop. This friction generates massive amounts of heat, which gradually wears down the individual components, making brakes one of the most commonly replaced parts on a vehicle.
A hydraulic system provides the substantial amount of force required to operate the brakes. When the brake pedal is pressed, hydraulic fluid in the system is pressurized, actuating cylinder(s) which apply pressure to increase friction. In case the main braking system fails, a secondary system, usually cable-driven, is utilized in emergencies. This system is actuated from a lever inside the cabin and locks the brakes, preventing the car from moving while parked.
Drum brakes and their variations are the oldest type of brakes and are commonly found on older economy cars and industrial trucks; their design is simple and effective for most day-to-day applications. This design has been around since early 1900s, but is gradually being phased out due to the demand for better braking performance in modern vehicles.
All components are housed within the drum and mounted to a back plate; the drum itself is made of heavy, thick steel and is attached to the rotating axle. The inside of the drum is made of a friction surface, while the compression mechanism and brake shoes are mounted to the back plate.
A wheel cylinder is actuated by the brake pedal and expands, pressing the brake shoes against the inside of the drum. This friction slows down the car. The mechanically-operated emergency brake is incorporated into this assembly and can also actuate the brake shoes.
Although drum brakes are simple and reliable, their weakness lies in being unable to stand up to repeated, heavy braking. In order to increase braking capacity - that is, to increase the friction surface, the whole assembly grows in size exponentially. Furthermore, heat dissipation becomes an issue due to the components being encased inside the drum. Heat drastically reduces the effectiveness of the friction materials and can render the brakes useless.
The vast majority of modern vehicles employ a disc brake setup, at least on the front wheels. The rotating component is called a brake disc or brake rotor and is attached to the rotating wheel hub. The brake caliper is a clamping mechanism that is fitted around the brake disc and houses hydraulically-actuated pistons and holds the brake pads. When the brake pedal is applied, the pistons squeeze the brake pads against each side of the rotor to generate the friction necessary to slow the car down.
Unlike drum brakes, this system is open and can be ventilated, which aids in dissipating heat; the friction surface is also much greater with disc brakes, which increases the efficiency of the whole system.
Vehicles with a complete disc brake system (front and rear) typically rely on an additional, smaller caliper mounted to the rear discs for the mechanical emergency brake system, which is engaged when the level in the cabin is pulled.
New materials have made disc brakes even more efficient. Racing configurations use special, high-friction pad materials and carbon-ceramic rotors, which generate less heat and reduce weight significantly. These systems are cost-prohibitive and completely overkill for the average consumer vehicle; they are usually found only on exotics and motorsports applications. As new brake technologies become available and more widespread, they will eventually trickle down to mass-produced vehicles.
Electronics have also contributed to better, more efficient braking systems. Anti-lock brake systems (ABS) use sensors to monitor wheel rotation and automatically pump the brakes if a loss of traction is detected. This technology is now standard on almost all vehicles and is one of the most important safety features for slippery or extreme braking conditions. Even the best drivers cannot pump the brakes quickly enough to match the lightning-fast pulses of an ABS system.
Modern stability control systems are even more sophisticated and use the brakes to control a car while maneuvering through corners and turns. A computer tracks individual wheel speeds and automatically applies a specific amount of braking force to each wheel, helping to stabilize and control the vehicle.
Up Next - The Brains
We have now gone over the basic mechanical aspects of a vehicle, from how it moves to how it stops to how it sticks to the road. Modern vehicles rely heavily on computers and are wired with sensors throughout the drivetrain and chassis to monitor and control every aspect of a vehicle. This ensures optimal engine operation, suspension tuning and the best possible traction, including how the car reacts in emergency situations. In the next article, we will delve into the impressive technology behind automotive electronic systems.
Previous Building Blocks - The Basics - Articles
Putting the Power Down: Wheels, Tires, Suspension & Steering
Power into Propulsion: How the Transmission & Driveline work
RPM To MPH: How Car Engines Work