Fluid Mechanics Applications/B-12:Role of braking system in automobiles

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Introduction: In this we will study the role of braking system in automobiles. A vehicle brake is used in vehicle to slow down its speed by converting its kinetic energy into heat. Actually the brakes transfer a force to the tyres due to friction and tyres in return transfer that force to the road also in the form of friction. The hydraulic system, most commonly used usually has six main stages: the brake pedal the brake boost(vacuum servo),the master cylinder, the apportioning valves, and finally the road wheel brakes themselves. Modern cars have brakes on all four wheels, operated by a hydraulic system. The brake may be of disc type or drum type. The front wheels play a very important rile in stopping the car than the rear ones because of the fact that on braking weight of the car shift to the forward. The braking power of disc brake is much more efficient than drum brake. Disc brakes are used in high performance cars or luxurious cars and drum brakes are used in old cars or non luxurious cars.

History of braking system It is important to understand the problem associated with the braking in the past, and the advances that has been made to overcome this problem.one of the very first type of braking system was that of crude system used before the roman empire. This involve a brake lever that pressed a simple wooden block against the wheel in order to slow down the cart by friction.2000 years went by with no improvement un this technology! In the old west the lever and the block method, was still prevalent on stage coaches. Early locomotives also use the block against the wheel. This system is still in use today but in combination with disc brakes and other systems.

The 20th century-The 20th century brought many changes in braking systems. Hydraulic system were a major improvement in 1920's-1940's.in the 1960's drum brakes came in almost all cars and trucks. However much like the drum brake the design of disc brake is its limited thermal mass. Every time you apply the brake the mass increases in temperature. this can be demonstrated by modern race cars whose brakes glow red hot during races. when brakes get hot the stresses increases and performance fades.

Retarders-The inability of air cooled friction brakes to absorb energy for prolonged durations created a market for products called "retarders". There are several type of retarders which provide a retarding force especially for downhill braking to improve safety. Safety is improved due to energy absorbing capability of these non frictional devices.

The following describes the basic types of retarders:

Engine brakes: this is mostly for large tractor trailer. They absorb energy by converting the diesel engine into an air compressor by hydraulically opening the exhaust valves at the end of the compressor stroke. This produces a "popping noise" due to which it has become outlawed 8n some areas.

Exhaust brakes- they are most commonly used on diesel engine with standard transmission. They are less effective with an automatic, and not practical on gas engines. They are located after the exhaust manifold and create a back up pressure on the engine exhaust by closing a butterfly or gate valve. These products are not very effective on low speeds but they provide a reasonable performance on long downhill braking.

Hydrodynamic retarders-They are another driveline braking system. These products produce retardation by shearing fluid, usually iolite kinetic energy produced by the shearing is converted into heat which is indirectly to the engine cooling system. Some of the negatives of this type of products are high parasitic losses when it is not in use. These products are famous for markets such as transit buses and heavy duty trucks.

Brake components-The list includes-

(1)Brake Pads-Steel backing plates used in disk brakes; friction material is bound to the surface facing the rotor and is usually made of ceramic metal or other hard wearing composite material.

(2)Brake Shoes-Two pieces of sheet steel welded that carry the brake lining.

(3)Brake Drum-Rotating drum shaped component used in drum brakes.

(4)Brake Lining-Heat resistant soft but tough material with a high friction characterstics housed inside a brake shoe.

(5)Rotor-Cast iron brake disk connected to wheel and/or axle; sometime made of reinforced carbon-carbon, ceramic matrix or other composite.

(6)Piston-A moving component contained by a cylinder.

(7)Caliper-A device on which brake pads and pistons are mounted

●Floating Calipers: moves relative to rotor; uses a piston on a single side of a disk to push inner brake pad into the braking surface before pulling caliper body in to apply pressure on opposite side of disk; also known as "sliding caliper".

●Fixed Calipers: does not move relative to rotor and is sensitive to imperfections; uses one or more single pairs of opposing pistons to clamp from each side of rotor.

(8)Master Cylinder-A device that converts the non hydraulic pressure from the foot into hydraulic pressure and controls "slave cylinders" at the opposite end of the hydraulic system.

(9)Vacuum Servo/Brake Booster-A component used to enhance the master cylinder and augment pressure from a driver's foot through the use of vacuum in the engine intake; only effective while vehicles engine is running. TYPES OF BRAKES

References:(1)www.how a car works.com/basics/how-the-braking-system-works