What is a brake?

A brake is a mechanical device that absorbs energy from a moving system and inhibits its motion. It helps to slow or stop a moving vehicle, axle, wheel, etc. The braking system uses friction between two types of surfaces that are pressed together that convert kinetic energy into heat energy. For instance, we know that in the case of regenerative braking, the brakes convert energy into electrical energy which can be used for later use. The conversion of kinetic heat energy into potential energy is stored in the form of pressurized oil or air. In the brake disc, oil, or fin, the eddy current brakes convert kinetic energy into the electric current with the help of a magnetic field which is converted into heat.
Generally, such braking systems apply to the moving axles of wheels. They may also take other forms like moving fluids' surface. In the case of drag racing cars, both wheel brakes are used whereas in parachute or airplanes, both wheel brakes or drag flaps raised in to the air are used.

Mechanism of braking systems

Almost all wheeled vehicles have some or the other braking system. the shopping carts or the baggage carts have brake systems to use on the moving ramp. On the undercarriage, most fixed-wing aircraft have wheel brakes. The frictional brakes in automobiles while braking helps to store braking heat produced in the disc brake or drum brake and then conducts it into the air eventually. When the brake pedal of the vehicle with hydraulic brakes is pushed against the master cylinder, the piston in the brake system tries to push the brake pads against the brake disc and slows down the vehicle.

Types of braking system

The braking system is classified into common types such as frictional brakes, pumping brakes, or electromagnetic brakes types of the braking system. They use several kinds of principles, for instance, the case of a pump may pass brake fluid to create friction through the orifice.

Frictional

It is the most common type of brake system also classified as brake shoes or brake pads. The term friction shoe brakes only mean brake shoes or brake pads and are different from hydrodynamic brakes even if they use friction. Friction brakes have a rotating wear surface and a stationary pad. A drum brake is the kind of brake where a rotating drum with shoes expands to rub inside the drum. A disc brake has pads that pinch a rotating disc rotor that slows the rotation of the wheel. It is connected to the wheel made up of cast iron or ceramic. They are mounted in a brake caliper. To stop the movement of the wheel, these pads are forced against both sides of the discs mechanically, hydraulically, pneumatically, or electromagnetically. This friction causes the vehicle to slow or stop. Brake lines are the kind of hard metal lines found in almost all types of modern vehicles. Air brakes are the types of frictional brakes in which pressure is applied by compressing air pressing the piston by the brake pad or brake shoe to stop the vehicle.

Pumping

This type of braking system is used where the machine already contains a pump. For instance, the fuel supply can be stopped, and actuating pumping loss internally can create some braking in an internal combustion piston motor. Some engines use a valve override to increase the pumping losses. The type of braking system uses hydraulic brakes are that have brake fluid and create pumping losses.

Electrical

Brake-by-wire technology is used in automotive industries known as the ability to control brakes through electrical means. This technology is mostly used in all hybrid and battery electric type vehicles.

Electromagnetic

Electromagnetic brakes are the types of braking systems that are used when a piece of machinery already contains an electric motor. The electric motor as a generator is used by many hybrid-type vehicles to charge electric batteries and also a regenerative brake. The electric motors are used to generate the electricity in diesel or electric railroad locomotives which are then sent to a bank of resistors and are dumped as heat. The electromagnetic induction in such brakes helps to slow an object by creating resistance and in turn creates heat and electricity.

Parking brake

This braking system is also known as an emergency brake or handbrake. A parked vehicle is kept securely motionless with the help of this emergency brake. These emergency brakes consist of a cable connected to two-wheel brakes and a pulling mechanism. When the push-button handbrakes are used in a parked car, it stops it from moving forward.

Characteristics of braking system

The braking system has the following characteristics -

• Peak force - The maximum de-accelerating effect obtained is called peak force. This force is greater than the traction limit present in the tires where the brake can cause a wheel to skid.
• Continuous power dissipation - When the temperature gets too high the brakes get hot and typically fall. Continuous power dissipation is the power that a brake can dissipate without failure. The temperature and the speed are the factors on which continuous power dissipation depends.
• Fade - When a brake gets heated up it may become less effective and that is called brake fade. Some designs can fade while some designs are inherently immune.
• Smoothness - A brake that chatters, pulses, grabby, or exerts brake forces may lead to skids.
• Power - Brakes are called powerful when a small force leads to a force called the braking force that is higher than other brakes in the same category or class. The term "powerful" does not mean continuous power dissipation but a brake may be "powerful" and it may brake strongly but may have worse peak force than a brake which is less "powerful"
• Pedal feel - As a function of pedal travel a brake pedal feels encompasses a subjective kind of perception of the output of brake power. A brake pedal is situated on the floor of the vehicle to the left of the accelerator.
• Drag - In the off-brake condition, brakes have a varied amount of drag. This depends on the design of the system to accommodate system compliance, in total and deformation which is under braking. In the off-brake condition, this braking can retract friction material from the surface of rubbing.
• Durability – Friction brakes must be renewed periodically to maintain durability due to wear and tear. Surfaces that wear are the brake shoes or pads, the brake disc, or the drum. 
• Weight – Brakes are often mounted on wheels and hence are often "added weight" that serves no other function. In some circumstances, brakes can significantly hurt traction. 
• Noise – In the usual case, brakes create some minor noise when applied, it may create loud squeal or grinding noises

A dual-circuit braking system is a type of braking system where each circuit acts on the front wheels and in the rear end it acts on either of the wheels. Also, an anti-lock brake system is the type of brake which prevents us from locking up our brakes. Another kind of brake is the vacuum-assisted brake that works when the atmospheric pressure acts on the piston in a vacuum cylinder.

Context and Applications

This topic is significant in the professional  exam for undergraduate, graduate and postgraduate courses.

• Bachelors of Technology (Electrical Engineering)
• Masters of Technology (Electrical Engineering)

Practice Problems

1. Into which kind of energy does the kinetic energy convert when brakes are applied on a moving vehicle?

1. Mechanical energy
2. Heat energy
3. Electrical energy
4. Potential energy

Answer- b

Explanation- When we apply brakes on a moving vehicle, the brakes use friction in between two types of pressed surfaces, as a result, the kinetic energy is converted into heat energy.

2. On which of the following factors does the force required to stop a vehicle depend?

1. The weight of the vehicle
2. The de-acceleration rate
3. Both a and b
4. None of the above

Answer- c

Explanation- The force required to stop a vehicle depends on both the weight and the de-acceleration rate.

3. To which part in the disc brake, a disc is attached?

1. Wheel
2. Axle
3. Suspension system
4. None of the above

Answer- b

Explanation- In disc-brake, the disc is attached to the axle.

4. On which of the following principles does the hydraulic brake function?

1. Law of conservation of momentum
2. Law of conservation of energy
3. Pascal's law
4. None of the above

Answer- c

Explanation- The hydraulic brakes function on the principle of Pascal's law.

5. Where are handbrakes applicable?

1. Only front wheels
2. Only rear wheels
3. In both front and rear wheels
4. All of the above

Answer- b

Explanation- Hand brakes are applicable only in the rear wheels.

Related Concepts

• Air brake
• Anti-lock braking system
• Brake lining
• Counter-pressure brake