What is a brake?
A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction.
Most brakes commonly use friction between two surfaces being compressed to convert the kinetic energy of the moving object into heat, although other methods of converting energy can be used. For example, regenerative braking converts much of the energy into electrical energy that can be stored for later use.
Other methods convert the kinetic energy in stored forms such as compressed air or pressurized oil into potential energy. Eddy current brakes use magnetic fields to convert kinetic energy into electrical current in the brakes disc, fin, or rail, which is converted into heat.
Still, other braking methods even convert kinetic energy into various forms, for example by transferring the energy to a rotating flywheel.
Brakes are generally applied to rotating axles or wheels, but they can take other forms such as the surface of a moving liquid (valves used in water or air).
Some vehicles use a combination of braking mechanisms, e.g. Drag racing cars with both wheel brakes and a parachute or aircraft with both wheel brakes and drag flaps that are lifted into the air during landing.
How Brakes Work on A Car?
To stop a car, the brakes have to get rid of that kinetic energy. They do so by using the force of friction to convert that kinetic energy into heat. This hydraulic system multiplies the force of your foot on the brake pedal into enough force to apply the brakes and make the car stop.
Brakes work by converting kinetic energy (forward motion) into thermal energy (heat). The friction between the stationary brake pad and rotating disk or drum as it slides past the pad converts the motion of the wheel and tire into heat, much the way rubbing your hands together on a cold day will warm them up.
Bringing your car to a stop generates enough heat at each wheel to boil a liter of water in about 7 seconds. Brake temperatures can reach around 500°F during normal everyday use and can reach up to 1000°F under heavy or repetitive braking.
The brake disk or drum is designed to work as a heat sink and absorbs as much as 80% of the heat generated during stopping. Fortunately, it also makes a good radiator, cooling as it spins through the air on the way to the next stop.
The front brakes do most of the work as the vehicle’s weight pushes forward while stopping. Therefore, many vehicles are equipped with disc brakes on the front axle and drum brakes on the rear. A disc brake’s superior performance is largely due to its ability to generate friction as the brake calipers force the pads to clamp against the rotors.
The brake rotors are cleaned and dried by the brake pads dragging across them and the entire brake system is exposed to the air for efficient cooling. The advantages of rear drum brakes are lower cost and the ability to easily integrate a mechanical emergency/parking brake system.
Related: What is Disc Brake?
What is Brake system?
The brake system takes the kinetic energy of your moving vehicle and converts it to thermal energy through friction. Usually used for the back wheels (although some vehicles had four-wheel drum brakes years ago), drum brakes feature a hollow cylinder (the drum) attached to the axle that spins with the wheel.
Related: What is Drum Brake?
Parts of Brake system
Following are parts of the brake system:
- Brake Pedal
- Master Cylinder
- Brake Pads
- ABS Control Module
- Brake Booster
- Disc Brakes
- Drum Brakes
- Emergency Brake
- Brake Pedal
- Wheel Speed Sensors
1. Brake Pedal
The pedal is what you push with your foot to activate the brakes. It causes brake fluid to flow through the system to put pressure on the brake pads.
Driver steps on the brake pedal to activate the brakes. A piston in the master cylinder moves when the pedal is pressed.
2. Master Cylinder
The master cylinder is basically a plunger that is activated by the brake pedal. It is what holds the brake fluid and forces it through the brake lines when activated.
Converts non-hydraulic pressure into hydraulic pressure that the wheel cylinders use to press the brake pads against the rotors to bring the vehicle to a stop.
3. Brake Lines
Generally made of steel, brake lines are what carry the brake fluid from the master cylinder reservoir to the wheels where pressure is applied to stop the car.
4. Wheel Cylinders
The brake pads are connected to the wheel cylinders which either squeeze (disc brakes) or push apart (drum brakes) the brake pads when fluid flows into them.
5. Brake Pads
The brake pads are what actually rub against the drums or rotors. They are made of composite materials and designed to last for many, many thousands of miles. However, if you ever hear a grinding or howling noise when you try to stop your car it likely means it is time for new brake pads.
Related: What are the Types of Brake Pads?
6. ABS Control Module
Found on vehicles with ABS brakes, the module performs diagnostic checks of the ABS braking system and determines when to send the correct pressure to each wheel to prevent the wheels from locking up.
7. Brake Booster
Reduces the amount of pressure needed for braking to allow any driver to operate the brakes. Uses engine vacuum and pressure to increase the force the brake pedal puts on the master cylinder.
8. Disc Brakes
Usually found on the front wheels, disc brakes feature brake pads that press against a disc (rotor) when the brake pedal is applied to stop the vehicle. The pads are attached to a brake caliper assembly that frames the rotor.
9. Drum Brakes
Located on the rear of the vehicle, drum brakes feature wheel cylinders, brake shoes, and a brake drum. When the brake pedal is pressed, the brake shoes are forced into the brake drum by the wheel cylinders, bringing the vehicle to a stop.
10. Emergency Brake
Operates independently of the main brake system to keep the vehicle from rolling away. Also known as a parking brake, hand brake, and e-brake, the emergency brake is mainly used to keep the vehicle in place when parked.
11. Wheel Speed Sensors
As part of the ABS brake system, speed sensors monitor the speed of each tire and send the info to the ABS control module.
Types of Brake Systems
Following are the types of braking systems:
- Hydraulic braking system
- Electromagnetic braking system
- Servo braking system
- Mechanical braking system
1. Hydraulic braking system
This system is operated with brake fluid, cylinders, and friction. By creating pressure inside, glycol ether or diethylene glycol force the brake pads to stop the wheels from moving.
- The force generated in the hydraulic braking system is higher compared to the mechanical braking system.
- The hydraulic braking system is one of the most important braking systems for modern vehicles.
- With a hydraulic brake system, the likelihood of brake failure is very low. The direct connection between the actuator and the brake disc or drum greatly reduces the likelihood of brake failure.
2. Electromagnetic braking system
Electromagnetic braking systems are found in many modern and hybrid vehicles. The electromagnetic braking system uses the principle of electromagnetism to achieve smooth braking. This serves to increase the service life and reliability of brakes.
Also, conventional braking systems tend to slip, while this is supported by fast magnetic brakes. If there is no friction or need for lubrication, this technology is preferred for hybrids. Besides, it is quite modest compared to traditional braking systems. It is mainly used in trams and trains.
For electromagnetic brakes to work, a magnetic flux, when conducted in a direction perpendicular to the direction of rotation of the wheel, a rapid current flows in a direction opposite to the direction of rotation of the wheel. This creates a force opposite to the rotation of the wheel and slows the wheel down.
Advantages of Electromagnetic braking system:
- Electromagnetic braking is quick and cheap.
- With electromagnetic braking, there are no maintenance costs such as regularly replacing the brake shoes.
- Electromagnetic braking can improve the capacity of the system (such as higher speeds, heavy loads).
- Some of the energy is delivered to the utility, which reduces running costs.
- Electromagnetic braking generates a negligible amount of heat, while mechanical braking generates enormous heat on the brake shoes, which leads to brake failure.
3. Servo braking system
Also known as vacuum or vacuum-assisted braking. This system increases the pressure exerted on the pedal by the driver.
They use the vacuum that is produced in petrol engines by the air intake system in the intake pipe of the engine or by a vacuum pump in diesel engines.
A brake that uses power assistance to reduce human effort. An engine vacuum is often used in an automobile to flex a large diaphragm and operate the control cylinder.
- Servo braking system boosters are used with the hydraulic braking system. The size of the cylinder and the wheels are practically used. Vacuum boosters increase the braking force.
- Pressing the brake pedal releases the vacuum on the side of the booster. The difference in the air pressure pushes the diaphragm for braking the wheel.
4. Mechanical braking system
The mechanical braking system drives the handbrake or the emergency brake. This is the type of braking system where the braking force applied to the brake pedal is transmitted through the various mechanical connections such as cylindrical rods, fulcrums, springs, etc. to the final brake drum or disc rotor to stop the vehicle.
Mechanical brakes were used in several automobile motor vehicles, but are archaic these days due to their less effectiveness.
Types of Car Brakes
Following are the different types of brakes:
- Disc Brakes
- Drum Brakes
- Emergency Brakes
- Anti-Lock Brakes
1. Disc Brakes
Disc brakes consist of a brake rotor that is attached directly to the wheel. Hydraulic pressure from the master cylinder causes a caliper (which holds the brake pads just outside the rotor) to squeeze the brake pads on either side of the rotor. The friction between the pads and the rotor causes the vehicle to slow and stop.
Related: What is Disc Brakes?
2. Drum Brakes
Drum brakes consist of a brake drum attached to the inside of the wheel. When the brake pedal contracts, hydraulic pressure presses two brake shoes against the brake drum. This creates friction and causes the vehicle to slow and stop.
Related: What is Drum Brakes?
3. Emergency Brakes
Emergency brakes, also known as parking brakes, are secondary braking systems that work independently of the service brakes.
While there are many different kinds of emergency brakes (a stick lever between the driver and passenger, a third pedal, a push-button or handle near the steering column, etc.), almost all emergency brakes are powered by cables that mechanically apply pressure to the wheels.
They are generally used to keep a vehicle stationary while parked, but can also be used in emergencies if the stationary brakes fail.
4. Anti-Lock Brakes
Anti-lock braking systems (ABS) are found on most newer vehicles. If the stationary brakes are applied suddenly, ABS prevents the wheels from locking up in order to keep the tires from skidding. This feature is especially useful when driving on wet and slippery roads.
How your car brake system works and How to maintain it?
Cars have brakes on all four wheels that are operated by a hydraulic system. The brakes are either a disc type or drum type. Many cars have four-wheel disc brakes although some have discs for the front wheels and drums for the rear.
The car brake system works in a few ways:
- Your foot pushes on the brake pedal and the force generated by your leg is amplified several times by mechanical leverage. It is then amplified further by the action of the brake booster.
- A piston moves into the cylinder AND it squeezes the hydraulic fluid out of the end.
- Hydraulic brake fluid is forced around the entire braking system within a network of brake lines and hoses.
- The pressure is transmitted equally to all four brakes.
- The force creates friction between brake pads and disc brake rotors which is what stops your vehicle.
How to maintain your car brake system?
Car maintenance can help you save money rather than bringing your car to the shop only when something goes wrong. Care should be taken before facing an accident. When your vehicle undergoes the annual state inspection, your brakes are reviewed for roadworthiness.
Here are some steps to maintain your car braking system to help you out.
- Monitor brake fluid levels and carry out a check every three months. Brake fluid should be replaced every two years or every 30,000 to 40,000 miles.
- Brake discs should be changed when needed depending on your driving style and environmental conditions. Change your brake discs at similar intervals for a normal car. Sports car brakes should be changed after 20,000 miles. If you are having your brakes changed at Fred’s, we add new fluid into your master cylinder. Be sure to query about our BG Fluids Lifetime Plan to extend the protection of your braking system.
- Bleed your brake lines to get any air out of your system. This means that your brakes will be pumped while someone watches the bleeder valve and closes the valve when brake fluid begins to flow through.
- Have your brake pads and rotors inspected to ensure that they are in excellent working condition. If the brake is worn-down badly, it’s time to replace the brake pad.
Braking-fundamentals: friction and how it applies to automobiles
- A brake system is designed to slow and halt the motion of the vehicle. To do this, various components within the brake system must convert the vehicle’s moving energy into heat. This is done by using friction.
- Friction is the resistance to movement exerted by two objects on each other. Two forms of friction play a part in controlling a vehicle: Kinetic or moving, and static or stationary. The amount of friction or resistance to movement depends upon the type of material in contact, the smoothness of their rubbing surfaces, and the pressure holding them together.
- Thus, in a nutshell, a car brake works by applying a static surface to a moving surface of a vehicle, thus causing friction and converting kinetic energy into heat energy. The high-level mechanics are as follows.
- As the brakes on a moving automobile are put into motion, rough-textures brake pads or brake shoes are pressed against the rotating parts of the vehicle, be it disc or drum. The kinetic energy or momentum of the vehicle is then converted into heat energy by kinetic friction of the rubbing surfaces and the car or truck slows down.
- When a vehicle comes to stop, it is held in place by static friction. The friction between surfaces of brakes as well as the friction between tires and roads resist any movement. To overcome the static friction that holds the car motionless, brakes are released. The heat energy of the combustion of in-engine is converted into kinetic energy by transmission and drive train, and the vehicle moves.
Characteristics of Brakes
Brakes are often described according to several characteristics including:
- Peak force: The peak force is the maximum decelerating effect that can be obtained. The peak force is often greater than the traction limit of the tires, in which case the brake can cause a wheel skid.
- Continuous power dissipation: Brakes typically get hot in use, and fail when the temperature gets too high. The greatest amount of power (energy per unit time) that can be dissipated through the brake without failure is continuous power dissipation. Continuous power dissipation often depends on e.g., the temperature and speed of ambient cooling air.
- Fade: As a brake heats, it may become less effective, called brake fade. Some designs are inherently prone to fade, while other designs are relatively immune. Further, use considerations, such as cooling, often have a big effect on the fade.
- Smoothness: A brake that is grabby, pulses, has chatter, or otherwise exerts varying brake force may lead to skids. For example, railroad wheels have little traction, and friction brakes without an anti-skid mechanism often lead to skids, which increases maintenance costs and leads to a “thump thump” feeling for riders inside.
- Power: Brakes are often described as “powerful” when a small human application force leads to a braking force that is higher than typical for other brakes in the same class. This notion of “powerful” does not relate to continuous power dissipation, and maybe confusing in that a brake may be “powerful” and brake strongly with a gentle brake application, yet have lower (worse) peak force than a less “powerful” brake.
- Pedal feel: Brake pedal feel encompasses subjective perception of brake power output as a function of pedal travel. Pedal travel is influenced by the fluid displacement of the brake and other factors.
- Drag: Brakes have varied amounts of drag in the off-brake condition depending on the design of the system to accommodate total system compliance and deformation that exists under braking with the ability to retract friction material from the rubbing surface in the off-brake condition.
- Durability: Friction brakes have to wear surfaces that must be renewed periodically. Wear surfaces include the brake shoes or pads, and also the brake disc or drum. There may be tradeoffs, for example, a wear surface that generates high peak force may also wear quickly.
- Weight: Brakes are often “added weight” in that they serve no other function. Further, brakes are often mounted on wheels, and unsprung weight can significantly hurt traction in some circumstances. “Weight” may mean the brake itself or may include additional support structure.
- Noise: Brakes usually create some minor noise when applied, but often create squeal or grinding noises that are quite loud.
What is Brake Fluid?
Brake fluid is a type of hydraulic fluid used in hydraulic brake and hydraulic clutch applications in automobiles, motorcycles, light trucks, and some bicycles. It is used to transfer force into pressure, and to amplify braking force. It works because liquids are not appreciably compressible.
Most brake fluids used today are glycol-ether-based, but mineral oil (Citroën/Rolls-Royce liquide hydraulique minéral (LHM)) and silicone-based (DOT 5) fluids are also available.
The three main types of brake fluid now available are DOT3, DOT4, and DOT5. DOT3 and DOT4 are glycol-based fluids, and DOT5 is silicon-based. The main difference is that DOT3 and DOT4 absorb water, while DOT5 doesn’t.
The main requirements for brake fluids are high operation temperatures, good low-temperature and viscosity-temperature properties, physical and chemical stability, protection of metals from corrosion, inactivity concerning mechanical rubber articles, and lubricating effect.
Brake bleeding
Fluids cannot be compressed; however, gases are compressible. If there is any air in a fluid brake hydraulic system, this will be compressed as pressure increases. This action reduces the amount of force that can be transmitted by the fluid.
This is why it is important to keep all bubbles out of the hydraulic system. To do this, air must be released from the brakes. This procedure is called bleeding of the brake system.
The simple procedure involves forcing fluid through brake lines and out through a bleeder valve or bleeder screw. The fluid eliminates any air that may be in the system. Bleeder screws and valves are fastened to the wheel cylinder or caliper.
The bleeder must be cleaned. A drain hose is then connected from the bleeder to the glass jar where the fluid coming out from the bleeder valve is collected. Bleeding involves the repetition of procedures at each wheel to ensure complete bleeding.
Meanwhile, one person should also be assigned to top up the fluid level in a container over the master cylinder to compensate for the fluid taken out through valves. If top-up is not continued, then there are chances of air bubbles being developed in the system which further delays the process.