A brake is a mechanical device that takes motion by absorbing energy from a moving system. It is used for slowing or stopping a vehicle in motion, wheel, axle, or to prevent the motion, most often accomplished by means of friction.
Brakes may be broadly described into using of friction, pumping, or the electromagnetics. One brake might use principles like: for example, a pump may pass fluid by an orifice to create friction:
system used in cars:
FAD: Brake disc front
FPD: Brake disc rear
FPT: Rear brake drum
CF: Brake control
SF: servo brake
PF: Brake Pump
SLF: Brake Fluid Reservoir
RF: Splitter braking
FS: Parking Brake
Frictional brakes are most used and can be divided broadly into “shoe” or a “pad” brakes, using an explicit wear surface, and hydrodynamic brakes too, such as parachutes, which use friction in a working fluid and do not explicitly wear off. Typically the term “friction brake” is means pad/shoe brakes and excludes hydrodynamic brakes, even though friction id used by hydrodynamic brakes. Friction (pad/shoe) brakes are often used in rotating devices using a stationary pad and a rotating wear surface. Common configurations have shoes that contract to rub on the outside of a rotating drum, such as a band brake which is a rotating drum with shoes that expand to rub the inside of a drum, usually called a “drum brake”, although other drum configurations are also possible; and pads that pinch a rotating disc, mostly called a “disc brake”. Other brake configurations are used, but not much often. For example, PCC trolley brakes usually have a flat shoe which is attached to the rail with an electromagnet; the Murphy brake always pinches a rotating drum, and the Ausco Lambert disc brake uses a hollow disc (two parallel discs having a structural bridge) with shoes that sit in between the disc surfaces and expand in a lateral manner.
A drum brake is a vehicle brake in which the friction is made by a set of brake shoes that press against the inner surface of the rotating drum. The drum is connected to the rotating road wheel’s hub.
Drum brakes can generally be seen on older car and truck models. However, because of their low cost of production, drum brake setups are installed on the rear of some low-cost newer vehicles too. Comparing them to modern disc brakes, drum brakes wear out faster due to their tendency to overheat.
The disc brake is used for slowing or stopping the rotation of a road wheel. A brake disc (or rotor in U.S. English), which is usually made of cast iron or ceramic, is connected to the wheel or to the axle. To stop the wheel, friction material is used in the form of brake pads (mounted in a device called a brake caliper) which is forced in the following ways mechanically, hydraulically, pneumatically or electromagnetically against all sides of the disc. Friction causes the disc and attached wheel either to slow or to be stopped.
Pumping brakes are often used when a pump is already part of the machinery. For example, an internal-combustion piston motor can stop the fuel supply, and then internal pumping losses of the engine start to create some braking. Some engines use a valve override called a Jake brake to increase pumping losses to a great extent. Pumping brakes can dump energy like heat, or can become regenerative brakes that recharge a pressure reservoir known as hydraulic accumulator.
Electromagnetic brakes are used where an electric motor is already part of the machinery. For example, many hybrid gasoline/electric vehicles make use of the electric motor as a generator to charge electric batteries and also can be used as a regenerative brake. Some diesel/electric railroad locomotives make use of the electric motors to generate electricity which is then sent to a resistor bank and dumped as heat. Some vehicles, like some transit buses, don’t already have electric motor but use a secondary “retarder” brake that is effectively a generator with an internal short-circuit. Brake related to this are eddy current brakes, and electro-mechanical brakes (which actually are magnetically driven friction brakes, but nowadays are just called “electromagnetic brakes”).
Electromagnetic brakes slow down an object with the help of electromagnetic induction, which creates resistance and in turn either heat or electricity is produced. Friction brakes apply pressure on two separate objects to slow the vehicle in a controlled way.
Brakes are often described according to several characteristics like:
- Peak force – The peak force is the maximum decelerating effect that can be achieved. The peak force is often greater as compared to traction limit of the tires, in which case the brake can cause a wheel to skid.
- Continuous power dissipation – Brakes usually get hot in use, and fail when the temperature gets quite high. The greatest amount of power (energy per unit time) that can be given away through the brake without failure is the continuous power dissipation. Continuous power dissipation often depends on the temperature and speed of ambient cooling air.
- Fade – As a brake heats, it might become less effective, leading to brake fade. Some designs are inherently prone to fade, but other designs are relatively immune. Further, use considerations, such as cooling which often has a big effect on fade.
- Smoothness – A brake that is grabby, has pulses and chatter, or otherwise exerts varying brake force might lead to skids. For instance, railroad wheels have little traction, and friction brakes without an anti-skid mechanism often result in skids, which increases the maintenance costs and leads to a “thump thump” feeling for riders inside the car.
- Power – Brakes are often described as “powerful” when a small human application force leads to a braking force that is higher than the usual for other brakes in the same class. This notion of “powerful” which isn’t related to continuous power dissipation, and may be confusing in that a brake may be “powerful” and brake strongly with a gentle application, yet have lower (worse) peak force than a less “powerful” one.
- Pedal feel – Brake pedal feel encompasses subjective perception of brake power output as a function of travelling by pedal. Pedal travel is influenced by the fluid displacement of the brake and other factors are also included.
- Drag – Brakes have varied amount of drag in an off-brake condition depending upon design of the system to accommodate total system compliance and deformation that exists under braking with ability to retract friction material from the rubbing surface during off-brake condition.
- Durability – Friction brakes have wear surfaces that must be renewed during regular periods. Wear surfaces include the brake shoes or pads, and also include the brake disc or drum. There might be trade-offs, for instance, a wear surface that generates high peak force may also wear quickly.
- Weight – Brakes are often “added weight” in that they serve no function other than this. Further, brakes are often mounted on wheels, and unsprung weight can significantly hurt traction in certain circumstances. “Weight” might mean the brake itself, or may include additional support structure.
- Noise – Brakes usually create some minor noise when they are applied, but often create squeal or grinding noises that are quite loud.
It consists of the following Parts –