Brake system assingment


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Brake system assingment

  2. 2. Introduction THE BRAKEBrake (device), device used to slow and stop a rotating wheel and thus a movingvehicle. Brakes such as those on automobiles, trucks, trains, and bicycles usefriction between a wheel and another object to slow the motion of the vehicle.The friction created by the rubbing together of two objects generates a largeamount of heat. A brake system must be capable of dissipating the heat asrotating wheels slowly, because excess heat can cause the brakes to lose theirgrip and fail.Automobile braking devicePassenger cars and light trucks use a hydraulic brake system to stop motionSuch a system uses a chemical-based liquid known as brake fluid to transmitpressure from a brake pedal to the brakes on each wheel. Aviator and inventorMalcolm Longhead, one of the founders of the Lockheed Martin Corporation,invented hydraulic brakes in 1918. Four-wheel hydraulic brakes were introducedon the 1921 Duesenberg and the 1924 Chrysler automobile models.To apply the brakes, the driver steps on a brake pedal. The pedal pushes apiston inside an assembly called the master cylinder, which is filled with brakefluid. The master cylinder is connected to the wheel brakes by hollow steel tubescalled brake lines, which are also filled with brake fluid. Pushing the pistonsqueezes the fluid inside the master cylinder, creating hydraulic pressure. Sinceliquid cannot be compressed, the pressure is transmitted through the brake linesto additional pistons inside each brake. These pistons push brake linings againstdrums and discs attached to the wheels in order to slow the vehicle down. Forsafety purposes, the brake system for the four wheels of a car or truck is dividedinto two separate circuits (each with its own piston inside the master cylinder). Ifa fluid leak in either circuit causes a loss of pressure, the two brakes in the othercircuit will still be operational to stop the vehicle. Cars and trucks use two typesof brakes, called drum brakes and disc brakes, to stop motion.Prior to 1965, all cars and trucks had drum brakes on the front and rear wheels.Drum brakes consist of curved brake shoes that rest within a rotating ironcylinder, or drum, connected to the axle and the wheel. When drum brakes areapplied, hydraulic pressure from the master cylinder pushes a pair of pistons inthe drum against the brake shoes. The shoes then press against the wall of thedrum, slowing the wheel. When the brakes are released, springs pull the shoesback away from the drum. Various types of self-adjusting mechanisms withindrum brakes help maintain the correct amount of distance between the shoesand drum.
  3. 3. In 1965 disc brakes were introduced on automobiles. Disc brakes have greaterstopping power than drum brakes and are usually installed on the front wheels toimprove braking during sudden stops. Disc brakes consist of a metal disc, orrotor, that is connected to the wheel. A device called a caliper rests on the edgeof the rotor and holds two friction pads on either side of the rotor. Applying thebrakes causes fluid to push a piston within the caliper, which pinches the brakepads against the rotor and slows the wheel. Disc brakes do not have returnsprings, like those in drum brakes, to disengage the brakes. Instead, a sealaround the piston bends slightly when the brakes are applied and then retracts topull the piston back away from the rotor when the brake pedal is released. Also,disc brakes rely on a very small amount of wobble, called run out,that is normallypresent in the rotor. When the brakes are released, the runout of the rotor simplypushes the pads away from the rotor.Disc brakes are considered superior to drum brakes, because disc brakes canhandle higher braking temperatures and dissipate heat more quickly. Also, discbrakes do not trap water as drum brakes can. When drum brakes become wet,they suffer a decrease in braking, called brake fade, which can happen whendriving through deep puddles. Most cars and trucks use disc brakes on the frontwheels and drum brakes on the rear wheels, although some cars now featuredisc brakes on all wheels.Disc brakes generally require added pedal pressure, so most vehicles equippedwith these brakes have power-braking systems to reduce a driver’s pedal effort.Most power-braking systems use a vacuum to increase braking power. Anengine’s pistons create a vacuum as they draw air into the engine. This vacuumis connected by a tube to both sides of a special spring-loaded diaphragmlocated near the master cylinder. When the brake pedal is pressed, ordinary air isallowed to enter on one side of the vacuum diaphragm. The vacuum on the otherside then pulls the diaphragm to one direction with added force. This added forceis sent to the master cylinder, increasing braking power.Both drum and disc brakes contain several features to dissipate the large amountof heat produced by friction. If the heat is not dissipated, the brakes maymalfunction. To dissipate heat more quickly, many rotors are vented and havecooling fins sandwiched between the faces of the rotor. Most disc brakes usesemi metallic brake pads that contain chopped steel-wool fiber to aid heatdissipation. The brake linings on drum brakes are made of heat-resistantmaterial. Prior to the introduction of disc brakes, most vehicles had brake liningsthat contained asbestos fiber. Asbestos brake linings were mostly discontinued inthe late 1980s because of the health risks posed by asbestos. Even so, somereplacement brake linings made by parts manufacturers still contain asbestos.
  4. 4. Disc and Drum BrakesDisc and drum brakes create friction to slow the wheels of a motor vehicle. Whena driver presses on the brake pedal of a vehicle, brake lines filled with fluidtransmit the force to the brakes. In a disc brake, the fluid pushes the brake padsin the caliper against the rotor, slowing the wheel. In a drum brake, the fluidpushes small pistons in the brake cylinder against the hinged brake shoes. Theshoes pivot outward and press against a drum attached to the wheel to slow thewheel. Anti-lock braking system (A.B.S)In 1985 the first antilock brake system (ABS) was introduced for motor vehicles inthe United States as a safety feature to give drivers more control when braking.ABS uses a microprocessor and individual wheel-speed sensors to monitor thebrakes. Hydraulic control valves for each brake circuit prevent skidding duringpanic stops or when braking hard on wet or slippery surfaces. By 1990 ABS wasavailable on about 25 percent of all new cars and trucks. ABS is now available onover 90 percent of all new vehicles.Wheel-speed sensors monitor the rotation of each wheel. When the brakes areapplied, the ABS microprocessor compares wheel speeds. If one or more wheelsare rotating more slowly than the others are (a situation that causes wheel lockupand loss of driver control), the system energizes control valves to isolate theaffected brake circuit. Brake pressure is held momentarily and is then releasedbefore it is reapplied. This cycle allows the wheel to regain traction and preventsskidding. The hold-release-reapply cycle is repeated rapidly for as long as
  5. 5. needed or until the vehicle comes to a stop. The cycling of the ABS controlvalves and pulsating hydraulic pressure can usually be heard and felt through thebrake pedal. These indicators are designed intentionally to alert the driver thatthe ABS is assisting braking. The driver should maintain firm pedal pressurewhile the ABS is active, as pumping the pedal can defeat the action of the ABSand increase the stopping distance. The ABS does not operate during normalbraking and does not engage unless one or more wheels start to lose traction.Improvements in ABS technology now allow some systems to prevent wheel spinwhen accelerating on wet or slippery surfaces. This capability is known astraction control. When the wheel-speed sensors detect that a drive wheel isstarting to spin, the ABS applies the brake on the affected wheel to slow it down.Some of these newer systems also provide additional control when cornering orchanging lanes.The ABS is a four-wheel system that prevents wheel lock-up by automaticallymodulating the brake pressure during an emergency stop. By preventing thewheels from locking, it enables the driver to maintain steering control and to stopin the shortest possible distance under most conditions. During normal braking,the ABS and non-ABS brake pedal feel will be the same. During ABS operation,a pulsation can be felt in the brake pedal, accompanied by a fall and then rise inbrake pedal height and a clicking sound.Vehicles with ABS are equipped with a pedal-actuated, dual-brake system. Thebasic hydraulic braking system consists of the following: ABS hydraulic control valves and electronic control unit Brake master cylinder Necessary brake tubes and hoses Hydraulic Control Unit (HCU). Anti-lock brake control module. Front anti-lock brake sensors / rear anti-lock brake sensors. HOW A.B.S WORKSWhen the driver hits the brakes this pressurizes a hydraulic system which causesthe brake pads to squeeze against the discs which causes the car to slow down.If the ABS system detects that one wheel is slowing down more rapidly than therest (a symptom of wheel-lock) it automatically reduces the brake pressure onthis wheel by opening a pressure release valve in the hydraulic system. ABS alsohas the ability to build the pressure back up via the hydraulic motor. The systemreacts remarkably quickly, and compared wheel speeds many times a second.
  6. 6. ABS systems can act on just the front wheels (which do most of the brakingwork), or all four depending on what car youre driving.An ABS system consists of the following components: Some wheel speed sensors Brake calipers A hydraulic motor Some pressure release valves A quick thinking computer (or control module) which coordinates the whole process Anti-lock Brake Systems (ABS) operates as follows: 1. When the brakes are applied, fluid is forced from the brake master cylinder outlet ports to the HCU inlet ports. This pressure is transmitted through four normally open solenoid valves contained inside the HCU, then through the outlet ports of the HCU to each wheel. 2. The primary (rear) circuit of the brake master cylinder feeds the front brakes. 3. The secondary (front) circuit of the brake master cylinder feeds the rear brakes.
  7. 7. 4. If the anti-lock brake control module senses a wheel is about to lock, based on anti-lock brake sensor data, it closes the normally open solenoid valve for that circuit. This prevents any more fluid from entering that circuit. 5. The anti-lock brake control module then looks at the anti-lock brake sensor signal from the affected wheel again. 6. If that wheel is still decelerating, it opens the solenoid valve for that circuit. 7. Once the affected wheel comes back up to speed, the anti-lock brake control module returns the solenoid valves to their normal condition allowing fluid flow to the affected brake. 8. The anti-lock brake control module monitors the electromechanical components of the system. 9. Malfunction of the anti-lock brake system will cause the anti-lock brake control module to shut off or inhibit the system. However, normal power- assisted braking remains. 10. Loss of hydraulic fluid in the brake master cylinder will disable the anti-lock system. [li[The 4-wheel anti-lock brake system is self-monitoring. When the ignition switch is turned to the RUN position, the anti-lock brake control module will perform a preliminary self-check on the anti-lock electrical system indicated by a three second illumination of the yellow ABS wanting indicator. 11. During vehicle operation, including normal and anti-lock braking, the anti- lock brake control module monitors all electrical anti-lock functions and some hydraulic operations. 12. Each time the vehicle is driven, as soon as vehicle speed reaches approximately 20 km/h (12 mph), the anti-lock brake control module turns on the pump motor for approximately one-half second. At this time, a mechanical noise may be heard. This is a normal function of the self- check by the anti-lock brake control module. 13. When the vehicle speed goes below 20 km/h (12 mph), the ABS turns off. 14. Most malfunctions of the anti-lock brake system and traction control system, if equipped, will cause the yellow ABS warning indicator to be illuminated. Actuation Methods / MechanismActuators are used on machinery, appliances, vehicles and medical devices tocause motion of one part relative to another. Examples include automaticopeners on supermarket doors, solenoid operated power door locks, and fillvalves on washing machines. Actuators are available for every range of linearand rotational movement and type of motive force that drives them. Actuatorsmay have total movements from hundredths of an inch to many feet.Considerations for implementing actuator applications include range of motion,driving force, mounting options, materials and motive power methodologyrequired.
  8. 8. Actuation Method Types Actuation methods include mechanical, electro-magnetic, pneumatic, vacuum, hydraulic and thermal sealed systems. All usually use one form of energy to cause the release or movement of another form of energy. Mechanical Actuatorso Mechanical actuators are many times driven by human power, such as lever hood or trunk openers on automobiles where the lever inside the car is connected to a cable which then pulls a spring loaded latch, releasing the hood for opening. Electrical Actuatorso Electrical actuators include solenoids which create a magnetic field in the cylindrical opening inside a coil, drawing in an actuation plunger to create linear motion. Electrical solenoids are used on industrial machines, appliances, vending machines and in many areas of transportation including automotive starters, choking mechanisms, fuel injection systems and safety interlocks. Pneumatic and Vacuum Actuatorso Air driven actuators include pneumatic cylinders, bellows and vane motors. Large diaphragm motors open and close pneumatically actuated control valves or adjust their proportional position for throttling control. When combined with return springs, pneumatic actuators can be used to position dampers or to lift doors. Air brakes on large trucks use rugged diaphragm actuation motors. Automotive air conditioning and heating systems use manifold vacuum to energize small diaphragm actuators on air dampers and water valves. Hydraulic Cylinders Hydraulic actuators are used in all forms of transportation braking. One of the advantages of hydraulic braking is that brake fluid is incompressible and its force can be multiplied to thousands of pounds. Automotive disc brake calipers and brake cylinders are examples of hydraulic actuators. Actuators used in jacking, lifting and pressing all use hydraulic cylinders.
  9. 9. o Actuator Mechanism Causes of brake failure Several factors can interfere with this friction and lead to brake failure: Grease or oil on brakes causes brake failure, because it interferes with friction. If oil leaks, it may indicate that an oil seal has failed. When the brakes overheat to a great degree, the metal in the brake rotors or drums develops hard spots. These are known as hot spots. The hot spots resist the friction from the brake shoes and pads. Because the shoes or pads have nothing they can grasp, theres no friction. Consequently, braking power is lost. Brakes that squeal indicate that the brake pads are wearing thin. By the time the brakes begin making a grinding sound, theyve worn down past the pads to the rotors, which will cost more than pads to replace
  10. 10. Fault Causes Remedies Noisy brake Weak shock absorber Change Axle supports insecure Retighten Broken springs change Erratic brake Weak road springs Change Bad steering geometry Alignment Brake unbalanced Oil or brake fluid  Remove, wash on linings and refit back Distorted brake  Straiten or change drum  Inflate the tyres tyre evenly inflated  Re-tight the back back plate loose plate on the axle  Re-change the worn steering steering connection connection bolts connecting  Re-tight back axle suspension spring loose lining of different  Put correct grades type or grade and same type Brake spongy  Low fluid level in Top up with fluid reservoir  Defective hose(if Remove and blow blocked) and
  11. 11. leaking out, change hose  Master cylinder main cap worn  Leak past master Remove and cylinder secondary replace new one cap Remove and  Air in the system change Bleeding to eradicate air from the system Brake grab Lining not bedded Repaired in Wrong type of Fit in the correct lining type Oil or brake fluid Wash with petrol, lining clean with sand Loose back plate paper or en-cloth on anchor pins and refit Brake pedal Lining not bedded Repaired in Brake drum Change grabbed or worn out Master cylinder You tight back to it loosed on mount sitting Brake pedal hard Seized piston in Change wheel cylinder Scrub with sand Oil or brake fluid paper Wash with on lining fuel, clean and Binding brake refit back pedal Clean rust area and wash with fluid and refit Far brake pedal Air in system Bleed to eradicate travel air from the Cracked braked system drum Remove and change totally Change part that Leak in system cause leakage(pipe, hose) Low fluid level in Top up the level reservoir with brake fluid
  12. 12. Excessive clearance between Adjust lining and drum Excessive pushrod Adjust the push clearance rod Brake drag Pull off spring Change broken or wear Master cylinder by Remove and clean pass port chocked Seized piston in Change wheel cylinder Shoe seized Change piston on anchor pin Change Hand brake mechanism seized Change Pedal return spring Change or clean Binding pedal rust area and refit Hand brake cable back over adjusted pedal to pushrod Re-adjust the adjustment too hand brake small Brake inefficient Lining not bedded Change Lining greasy Wash and sand Incorrect type of paper before fit lining Remove and change to correct type of lining
  13. 13. References A project on braking system 1995