What is brake? Definition / Function / Types and application

What is Brake?

The brake is a mechanical device that stops motion by absorbing energy from the moving system. It is used to slow down or stop a moving vehicle, wheel, axle, or to stop its movement, most often accomplished through friction.

Backgrounds

Most brakes typically use friction between two pressed surfaces together to convert the kinetic energy of the moving object into heat, although other methods of energy conversion may be employed. For example, regenerative braking converts too much electrical energy, which can be stored for later use. Other methods convert kinetic energy into potential energy in such stored forms as kinetic air or pressurized oil. The eddy current brake uses magnetic fields to convert kinetic energy into a brake disc, fin, or rail into an electric current, which is converted into heat. Still, other braking methods convert kinetic energy into different forms, for example by transferring energy to a rotating wheel.

Brakes are usually applied to rotating axles or wheels, but can also take other forms such as the surface of a fluid (flaps positioned in water or air). Some vehicles use a combination of braking mechanisms, such as drag racing cars with both wheel brakes and parachutes, or airplanes with both wheel brakes and air-drawn flaps during landing.

Since the kinetic energy increases quadratically with momentum ({\ display style K = mv ^ {2} / 2} K = mv ^ {2} / 2), an object moving to 10 m / s has 100 times the energy. , Which is one of the same mass is increasing at 1 m / s, and the resulting theoretical braking distance, when braking at the traction limit, is up to 100 times longer. In practice, fast vehicles usually have significant air drag, and the energy lost in air drag increases rapidly with speed.

Almost all wheeled vehicles have some type of brake. Even luggage carts and shopping carts may have them for use on a moving ramp. Most fixed-wing aircraft have brakes applied to the chassis. Some aircraft also feature air brakes that are designed to reduce their speed in flight. Notable examples include gliders and some World War II aircraft, mainly some fighter jet aircraft and many dive bombers of the era. These allow the aircraft to maintain a safe speed in a steady descent. The Saab B 17 dive bomber and the Vought F4U Corsair fighter used undercarriage positioned as air brakes.

Friction brakes on automobiles store braking heat in drum brakes or disc brakes and allow it to slowly flow into the air when braking. Some vehicles may use their engines to apply brakes while traveling downhill.

When the brake pedal of a modern vehicle with a hydraulic brake is pushed against the master cylinder, a piston eventually pushes the brake pad against the brake disc which slows the wheel. The same happens on the brake drum as the cylinder pushes the brake shoe against the drum which slows the wheel.

Types of brake

Brakes can be broadly described as friction, pumping, or the use of electromagnetics. A brake can use several principles: for example, a pump can pass fluid through an orifice to create friction:

Friction

Friction brakes are the most common and can be broadly divided into "shoe" or "pad" brakes, using a clear wear surface, and hydrodynamic brakes, such as parachutes, in a working fluid. Use friction and do not wear it clearly. The term "friction brake" is commonly used for pad/shoe brakes and excludes hydrodynamic brakes, even though hydrodynamic brakes use friction. Friction (pad/shoe) brakes are often static pads and rotating devices with a rotating surface. Common configurations include shoes that contract to rub the outside of a rotating drum, such as a band brake; A rotating drum with shoes that extend to the rubbing inside the drum, commonly referred to as "drum brakes", although other drum configurations are possible; And pads that pinch a rotating disc, commonly referred to as a "disc brake". Other brake configurations are used, but less frequently. For example, PCC trolley brakes include a flat shoe that is attached to a rail with an electromagnet; The Murphy brake pinches a rotating drum, and uses a hollow disc (two parallel discs with a structural bridge) with the Ausco Lambert disc brake shoes that sit between the disc surfaces and subsequently expand.

A drum brake is a vehicle brake in which friction is caused by a set of brake shoes that press against the inner surface of the rotating drum and the drum is connected to the rotating roadwheels hub.

Drum brakes can usually be found on older car and truck models. However, due to their low production costs, drum brake setups are also fitted behind some low-cost new vehicles. Compared to modern disc brakes, drum brakes tend to deteriorate faster due to their tendency to overheat.

Disc brakes are a device for slowing or stopping the rotation of a road wheel. A brake disc (or rotor in American), usually made of cast iron or ceramic, is attached to the wheel or axle. To stop the wheel, friction material (mounted in a device called a brake caliper) is forced mechanically, hydraulically, pneumatically, or electromagnetically on both sides of the disc in the form of a brake pad. Friction causes the disc and attached wheel to slow down or stop.

Pumping

The pumping brakes are often used where a pump is already part of the machinery or mechanism. For example, an internal-combustion piston motor may have its fuel supply shut off, and then the engine's internal pumping losses create some braking. Some engines use a valve override called the Jake brake to increase pumping losses. Pumping brakes can dump energy as heat, or regenerative brakes that recharge a pressure reservoir called a hydraulic accumulator.

Electromagnetic

Electromagnetic brakes are likewise often used where an electric motor is already part of the machinery. For example, many hybrid types of gasoline / electric vehicles use electric batteries as a generator to charge electric batteries and also as a regenerative brake. Some diesel / electric rail locomotives use electric motors to generate electricity, which is then sent to a resistor bank and dumped as heat. Some vehicles, such as some transit buses, do not already have an electric motor but use a secondary "retard" brake that is effectively a generator with an internal short circuit. Related types of such brakes are heel current brakes, and electro-mechanical brakes (which are actually magnetically driven friction brakes but nowadays are often also called "electromagnetic brakes").

Electromagnetic brakes slow down an object through electromagnetic induction, which creates resistance and in turn produces heat or electricity. Friction brakes apply pressure on two different objects to slow down the vehicle in a controlled manner.

Features

Brakes are often described according to several characteristics:

Peak force - The peak force is the maximum decelerating effect that can be achieved. The peak force often exceeds the traction limit of the tires, in which case the brake may cause a wheel skid.

Continuous power dissipation - The brakes are usually hot in use and fail when the temperature is too high. The largest amount of power (energy per unit time) that can be decomposed through the brakes without fail is constant power dissipation. Continuous power dissipation often depends on attrition, ambient cooling air temperature, and speed.

Fade - As brake heat, it may be less effective, called brake fed. Some designs fade naturally, while other designs are relatively immune. In addition, the use of the idea, such as cooling, often has a major effect on the fade.

Smoothing - A brake that is grabby, pulsating in the pulses, or otherwise skid may be caused by excess separating the brake force. For an example, rail wheels have little traction, and the frictionless brakes without an anti-skid mechanism often lead to the skids, which anincrease maintenance costs and lead to a feeling of "thump thump" for the rider.

Power - Brakes are often described as "powerful" when a small human application force leads to a braking force that is more than typical for other brakes in the same orbit. This notion of "powerful" is not related to sustained power dissipation, and there can be confusion as to whether a brake can be "powerful" and brake strongly with a gentle brake application, yet less "powerful". There is less (worse) peak force than. Brake.

Pedal Feeling - Brake pedal feel incorporates the subjective perception of brake power output as a function of pedal travel. Pedal travel is affected by the fluid displacement of the brake and other factors.

Drag - Brakes have a variety of drag in the off-brake position depending on the design of the system to accommodate the total design and deformation of the system, which is the ability to withdraw friction material from the off-brake position to the brake-brake position Exists with.

Durability 

Friction brakes have to wear surfaces that must be periodically renewed. Wear surfaces include brake shoes or pads, and also brake discs or drums. For example, there may be tradeoffs, a wear surface that produces a high peak force can also wear out quickly.

Weight - Brakes are often "extra weight" in that they perform no other function. In addition, the brakes are often applied to the wheels, and ungrounded weight can cause considerable damage to traction under certain circumstances. "Weight" may mean the brake itself or may include an additional support structure.

Noise - Brakes typically produce some minor noise when applied, but often produce squeal or grinding noises that are quite loud.

Foundation Components

Foundation components are brake-assembly components on the wheels of a vehicle, designated to form the basis of the rest of the brake system. These mechanical parts present around the wheels are controlled by the air brake system.

There are three types of foundation brake systems are "S" cam brakes, disc brakes, and wedge brakes.

Brake boost

Most modern passenger vehicles, and light vans, use a vacuum-assisted brake system, greatly increasing the force applied by its operator to the bra of the vehicle. This additional force is supplied by a manifold vacuum generated by the airflow interrupted by the throttle on a flowing engine. This force is greatly reduced when the engine is running at fully open throttle, as the difference between ambient air pressure and manifold (absolute) air pressure decreases, and therefore the available vacuum decreases. However, brakes are rarely applied at full throttle; The driver lifts the right foot off the gas pedal and moves to the brake pedal - unless left-foot braking is used.

Due to low vacuum at high rpm, reports of unintentional acceleration are often accompanied by complaints of unsuccessful or weak brakes, since the high-revving engine, being an open throttle, provides enough vacuum to power the brake booster. Is unable to This problem is overcome in vehicles equipped with automatic transmissions because the vehicle will automatically downshift upon application of the brakes, increasing the torque given to the driven wheels in contact with the road surface.

Heavy vehicles, as well as trains, typically boost brake power with compressed air, supplied by one or more compressors.

Noise

Although ideally, a brake would convert all kinetic energy into heat, in practice a significant amount could be converted to acoustic energy rather than contributing to noise pollution.

For road vehicles, the noise produced varies considerably with tire construction, road surface, and magnitude of deceleration. Different things can cause noise. These are indications that brake wear issues may occur over time.

The fire

A railway brake malfunction can cause a spark and a forest fire. In some very extreme cases, disc brakes may become red hot and ignite. This happened at the Tuscan GP, ​​when the Mercedes car, the W11's front carbon disc brake, almost burst into flames due to low ventilation and high usage. These fires can also occur on some Mercedes Sprinter vans when the load-adjusting sensor is seized and the rear brakes have to compensate for the fronts.

Incapacity

A significant amount of energy is always lost when braking, even with regenerative braking that is not fully efficient. Therefore, a good metric of efficient energy use while driving is to keep in mind how much braking to do. If much of the deceleration is caused by unavoidable friction rather than braking, then most of the service is ejected from a vehicle. Minimizing brake use means maximizing fuel economy behavior.

While energy is always lost during the occurrence of a brake, a secondary factor affecting efficiency is "off-brake drag", or drag that occurs when the brake is not intentionally acted upon. After the braking event, the hydraulic pressure in the system drops, allowing the brake caliper piston to retract. However, this return must accommodate all pressures (under pressure) in the system, as well as thermal deformation such as brake discs or brake systems, unless contact with the disc, for example, pads and pistons knockback is. Rub surface. During this time, significant brake drag may occur. This brake drag can cause significant parasitic power loss, thus affecting fuel economy and overall vehicle performance.