Brake Assignment free essay sample

Historical development of vehicle brakes: The development of braking systems was synonymous with the invention of the wheel. It is assumed that some primitive methods of slowing and stoping the first vehicles and carts was to deploy a log attached by rope off the vehicle and allow it to drag along behind. Another assumed method may have been to deploy an anchor of wedge that could be stuck into the ground. As the development of brakes was becoming more of an important issue, the dragged systems adapted into onboard more efficient devices such as a wedge to jam against one wheel causing a skid.Although this method was easier and more efficient, it was also quite dangerous as the vehicle would often turn and in some cases cause it to overturn. The first effective braking system was introduced in 1838, the spoon brake. This system consisted of a wooden block that pressed against the iron wheel of the vehicle when a lever of foot pedal was mechanically applied by the operator. We will write a custom essay sample on Brake Assignment or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page On heavier vehicles another adaptation of this brake was used where the friction block of the spoon brake was applied to one of the pullies in the transmission. The next developed braking system invented was the external contracting band brake. This system was largely more effective than the spoon brake. The band brake consisted of a drum attached to the axle of the rear wheels or the drive shaft under the vehicle, that was accompanied by a band with a friction lining that wrapped around the drum and was applied by a hand lever that acted on a number of solid rods that pulled and in turn contracted the band around the drum. This system became popular and widely used by manufactures by 1904.In 1898 the early disc brake was developed, these brakes made a large amount of noise and were highly inefficient, and as a result soon forgotten. In there replacement was the invention of the drum brake or the internally expanding shoe brake. This development was considered to be the most effective method of braking at the time. In 1907 disc brakes were brought back out on the market with the discovery of asbestos lined brake pads. This eliminated the nose factor of the previous make and also increased the margin enormously for service intervals.The mechanically operated drum and disc brakes were the two most competitive braking systems of this time, until in 1918 the development of the hydraulically operated braking systems was introduced. This system not only allowed a more even and smooth brake distribution to be applied but also increased the strength and the flexibility of the fluid and tubes allowed the brake lines to be weaved around components or the undercarriage and reach all four wheels without disturbance or overcrowding. The Modern Hydraulic Drum Brake: This brake system was developed after the external strap brake.It is a modification based on the strap brake, which has many areas that have been improved. The drum brake is a servo-assistant system which aids the performance and braking force d ramatically. Like the disc brake the modern drum brake is operated by a series of compression cylinders and a number of flexible and corrosive resistant tubing. From the master cylinder the brake fluid (high temperature liquid) is equally distributed into four metal tubes which direct the fluid into the four slave cylinders located nearby the braking system at each of the wheels.As the operator compresses the brake pedal the brake fluid is forced into the slave cylinder from the master cylinder and squeezes the piston inside the drum to push the brake shoes apart to contact the inside of the drum and activate the friction linings. The shoes when in contact with the drum wedge and further compress against the pan as a natural self actuating function of these brakes. Because of this, when the brake pedal is released and the slave cylinders pistons retract, the shoes remain in contact, this is why a series of springs are attached to the shoes to restore the original resting position of the shoes, e liminating drag.NB: the natural self actuating system works well in forward and reverse motions when the drum contains two brake shoes, however in cars with rear disc brakes, the parking brake (a drum brake fitted to the outside of the disc) only contains one brake shoe and therefore in reverse motion when the parking brake is engaged the shoe will attempt to repel the contact with the drum and require more force to stop the vehicle.All vehicles weather they are four wheel disc, four wheel drum (older cars) or a split system contain a set of drum brakes at the rear that can be mechanically activated by the use of the parking or (e- brake), this is a safety requirement for the possibility of a malfunction in the hydraulic system so that the vehicle still may be brought to a stop. Although this brake is fitted to every car as a precaution, the cars with four wheel disc brakes use only the discs in regular braking procedure and the manually activated drum parking brake only gets activated when the car is at rest, and the e-brake is tensioned.This becomes a problem in some cases if it is not activated or adjusted for long periods of time. In manual transmission cars this is less of an issue because the parking brake is often used while the car is parked. In automatic transmission cars, often people do not use the parking brake because of the â€Å"park† mode on the gear lever which holds the vehicle when it is motionless. This means in the chance of the hydraulic brake systems failure the park brake may be too loose for the shoe to reach the drum, not retarding the vehicle in any way.To manually adjust the parking brake in these cars is quite simple and can be done at home. Simply jack the rear of the vehicle and remove the rear wheels one at a time. Locate the dust plug on the outside of the drum and remove it with a screwdriver. Rotate the drum until the hole where the dust plug was, is in the six o’clock position as this is where the adjusting mechanism is. Use a flat head screwdriver to lift the fixture flap off the notch of the star pin and rotate the star pin 2-5 notches only! Dependant on how loose the park brake is.Release the fixture flap so it engages with one of the teeth of the star pin and plug the dust plug back in before re-attaching the wheel. In cars with rear hydraulic drum brakes the parking brake is not usually an issue because most of these cars have a mechanism to automatically adjust the shoe distance when the car is in reverse. But the brakes can still be manually adjusted the same way as directed above. In the cars with the rear hydraulic drum, the cars foot brake and e-brake can be run off the same unit whilst still only having the parking brake as manually operated for safety. The Modern Hydraulic Disc Brake: The hydraulic disc brake is the latest development used in modern motor cars, as a braking system. The disc brake hydraulics is almost identical to that of the hydraulic system used for the drum brakes. This has become quite useful in the cost effective production of some utilities, smaller hatchbacks and sedans. Because these cars have less weight on the rear tyres and standard braking distribution 60/40 front to rear respectively, the rear braking system doesn’t require a large force to lock up these wheels at any speed.Maximum braking efficiency occurs the moment before the tyres lock up, as this is when traction is lost, having a split braking system (discs on the front, drums on the rear) has proven to be a cost efficient yet still effective braking system for these vehicles. On the other hand heavier vehicles and/or vehicles designed for performance usually require and have a four wheel disc system. In a disc braking system the braking fl uid from the brake fluid reservoir is compressed or â€Å"pumped up† into the master cylinder. Each time the operator compresses the brake pedal, brake fluid is compressed only with the manual application force of the driver and equally divided into two solid tubes, dividing the front and rear fluid as it enters the engine vacuum compression amplifier that is run off a pump connected to the auxiliary belt. This system amplifies the drivers manual compression by a factor needed to retard the vehicle, to a desired level. Once the fluid is compressed in the vacuum pump it is directed through non reactive and corrosive resistant material to each of the four discs.At each wheel there is a secondary cylinder called the slave cylinder which controls the pressure of the brake fluid and activates the calliper piston or pistons. When the piston is pushed by the compressive of the brake fluid the leading brake pad (inside pad furthest from wheel) comes into contact with the disc and as more pressure is applied and the calliper piston is pressured out further, the calliper housing the two brake pads is pulled across as it is attached to the piston, which in turn engages the follower brake pad.The inside brake pad in contact with the piston will always wear more than the follower because it is under more pressure and undergoes greater friction. This is why the inside or leading pad has he wear guide. (vibrates on the disc to create an irritating screech when the pad is wearing down). As both of these pads engage and squeeze the disc (which happens in hundreds of second after engaging the foot pedal) the car is slowed and/or brought to a stop.Dependant on the kerb weight, towing capacities and performance requirements of the vehicle, larger disc sizes and callipers with more pistons can be fitted to provide a greater surface area of the disc to undergo friction for improved stopping capability. When the surface area of the disc undergoing friction is increased and the stopping ability is improved more heat is generated as a bi-product (as energy cannot be created, nor destroyed but only changed).Too much heat can melt or react with the braking system to lessen the efficiency or even result in brake failure. To prevent this from happening ventilated and/or slotted rotors can be fitted to aid cooling. Most modern cars with four wheel disc brakes often have the front discs at least ventilated as the 60/40% brake distribution creates a substantial amount of heat on the front discs whereas the rear discs remain solid, as they do not attract as much heat. In the case of a more performance designed vehicle, the front brakes may be slotted and ventilated and the rears just ventilated, or both front and rear slotted and ventilated. Solid discs simply look like a thick solid â€Å"CD†. Ventilated discs are even thicker to accommodate bored holes through the centre from end to end to allow air flow and still adequate strength to withstand the compressive force of the pads.

Hippocratic Method and the Four Humors in Medicine

Hippocratic Method and the Four Humors in Medicine When todays doctors prescribe an antibiotic to fight infection, they are trying to put the patients body back in balance. While the drugs and medical explanation may be new, this art of equilibrium has been practiced since  Hippocrates day.   I do anatomize and cut up these poor beasts, he said to Hippocrates, to see the cause of these distempers, vanities, and follies, which are the burden of all creatures.- Democritus - The History of Melancholy Humors Corresponding With  the Seasons and Elements In the Hippocratic corpus (believed not to be the work of a single man of that name) disease was thought to be caused by isonomia, the preponderance of one of the four bodily humors: Yellow BileBlack BilePhlegmBlood Four humors matched the four seasons: Autumn: black bileSpring: bloodWinter: phlegmSummer: yellow bile Each of the humors was  associated with one of the four equal and universal elements: EarthAirFireWater Posited by Empedocles: Aristotle, who used the image of wine to expose the nature of black bile. Black bile, just like the juice of grapes, contains pneuma, which provokes hypochondriac diseases like melancholia. Black bile like wine is prone to ferment and produce an alternation of depression and anger...-From Linets The History of Melancholy Earth corresponds with  black bile.  Too much earth made one  melancholic.Air corresponds with blood. Too much air,  sanguine.Fire  corresponds with  yellow bile.  Too much fire,  choleric.Water  corresponds with  phlegm.  Too much water,  phlegmatic. Finally, each element/humor/season was associated with certain qualities. Thus yellow bile was thought of as hot and dry. Its opposite, phlegm (the mucus of colds), was cold and moist. Black Bile was cold and dry, while its opposite, blood was hot and moist. Black Bile: Cold and DryBlood: Hot and MoistPhlegm: Cold and MoistYellow Bile: Hot and Dry As a first step, the prudent Hippocratic physician would prescribe a regimen of diet, activity, and exercise, designed to void the body of the imbalanced humor. According to Gary Lindquesters History of Human Disease,  if it was a fevera hot, dry diseasethe culprit was yellow bile. So, the doctor would try to increase its opposite, phlegm, by prescribing cold baths. If the opposite situation prevailed (as in a cold), where there were obvious symptoms of excess phlegm production, the regimen would be to bundle up in bed and drink wine. Resorting to Drugs If the regimen didnt work the next course would be with drugs, often hellebore, a potent poison that would cause vomiting and diarrhea, signs the imbalanced humor was eliminated. Observation of Anatomy We might assume such Hippocratic ideas sprang from speculation rather than experimentation, but observation played a key role. Furthermore, it would be simplistic to say ancient Greco-Roman doctors never practiced human dissection. If nothing else, doctors had anatomical experience dealing with war wounds. But especially during the Hellenistic period, there was extensive contact with the Egyptians whose embalming techniques involved removing bodily organs. In the third century, B.C. vivisection was permitted in Alexandria where living criminals may have been put to the knife. Still, we believe Hippocrates, Aristotle, and Galen, among others, only dissected animal bodies, not human. So mans internal structure was known primarily through analogy with animals, inferences from the externally visible structures, from natural philosophy, and from function. Evaluating the Humoral Theory Such ideas might seem far-fetched today, but Hippocratic medicine was a great advance over the supernatural model that had preceded it. Even if individuals had understood enough about contagion to realize rodents were involved somehow, it was still the Homeric Apollo, the mouse god, who caused it. The Hippocratic etiology based on nature permitted diagnosis and treatment of symptoms with something other than prayer and sacrifice. Besides, we rely on similar analogies today, in Jungian personality types and ayurvedic medicine, to name two. These men demonstrated that when the nutriment becomes altered in the veins by the innate heat, blood is produced when it is in moderation, and the other humours when it is not in proper proportion.-Galen, On the Natural Faculties Bk II Black Bile Cold and Dry Too much earth Melancholic Autumn Blood Hot and Moist Too much air Sanguine Sping Phlegm Cold and Moist Too much water Phlegmatic Winter Yellow Bile Hot and Dry Too much fire Choleric Summer S​ources   www.umich.edu/~iinet/journal/vol2no2/v2n2_The_History_of_Melancholy.html  Ã‚  www.astro.virginia.edu/~eww6n/bios/HippocratesofCos.html]www.med.virginia.edu/hs-library/historical/antiqua/textn.htm accessedviator.ucs.indiana.edu/~ancmed/foundations.htm]  www.med.virginia.edu/hs-library/historical/antiqua/stexta.htmwww.med.virginia.edu/hs-library/historical/antiqua/stexta.htm