Different Brake Systems

Moving vehicles require a system to slow their speed and stop quickly and efficiently. Braking systems have evolved along with motorized technology. As vehicles have become faster and heavier, braking systems have had to become stronger and more durable. Several types of braking systems have been developed to stop a variety of motorized vehicles.

Drum Brakes

Drum brakes were the most common form of brakes on automobiles up until the 1970s when many manufacturers began to switch to disc brakes. However, drum brakes are still used today, both in standard hydraulic brake systems on cars and as part of air brake systems on big rig trucks. A drum brake is called such because the components are all housed inside a round drum that rotates along with the wheel. When hydraulic pressure is applied to the brake, the pressure forces the brake pads, or shoes, up against the drum. This pressure slows the wheel. The drawback of drum brakes comes when the brakes are used too much, such as in a descent down a steep hill, and heat begins to build up within the drum. The heat leads to loss of friction and can cause the brakes to fail.

Air Brakes

Air brakes are a specialty type of drum brake used in large and heavy vehicles such as big rigs, buses and construction vehicles. While most air brakes are still the drum variety, some are made using disc brakes. The air brake system includes the parking brakes, service brake and an engine-driven air compressor system with a compressed air storage tank. Compressed air is in the brake system to cause adequate pressure to stop the vehicle. As an added safety feature, a compressed air brake system also has an emergency component of a spring loaded mechanism held in place by compressed air. If pressure is lost due to mechanical failure, the spring will be released and the emergency brake will engage, stopping the vehicle.

Disc Brakes

Disc brakes are a common brake system on automobiles. They work using hydraulic pressure, a disc rotor, disc pads and a caliper assembly. The brakes are attached to the steering knuckle by the caliper assembly. When pressure is applied via the caliper piston, it forces the disc pad up against the disc rotor. The friction between the disc pads and the disc rotors causes the braking action. Since the surfaces of the disc brakes are constantly exposed to air, they tend to stay cool which minimizes brake fade. Compared to drum brakes, disc brakes have a larger caliper piston because a larger amount of hydraulic pressure is needed for disc brakes to obtain sufficient braking force.

Engine Brakes

Engine brakes are a type of braking system used on large buses and big rigs. They are sometimes called "jake brakes" because of one of the most familiar manufacturers is the Jacobs Engine Brakes Division. They are usually a supplemental braking system that is installed along with a standard braking system such as air brakes in a big rig. Engine brakes can help take wear and tear off of the regular braking system and tires as well as add a layer of braking protection. The engine brake works by retarding the forces within the engine to slow the vehicle with the application of a special valve. Engine brakes have a negative side effect of being very loud and for this reason their use has been controversial.

Vacuum Brakes

Vacuum brakes were used extensively in the 1870's on steam locomotive trains but today are obsolete. These early brakes used vacuum pressure instead of the hydraulic or air pressure used in today's disc and drum brake systems. In a vacuum brake system, braking equipment is on each car of the train. Each braking system is connected by a continuous brake pipe controlled by a valve in the driver's cab. By pulling the valve, the driver forces atmospheric pressure out of the brake pipes by an ejector, creating a vacuum. A vacuum brake system is composed of an exhauster, a brake pipe, a dummy coupling, coupled hoses, a brake cylinder, a vacuum reservoir, a brake block, brake rigging and a ball valve. The main drawback of vacuum brakes over air brakes is that they take longer to stop and require larger cylinders and are thus not as efficient.