libro virtual

ITED Teacher:estela matter:inglish

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Edy Rolando Vasquez Puluc 5th mechanical Evening

introduction at work we may learn about different systems of the car and that through these systems, the carfinciona one hundred percent. in these systems is very elements know all the types ofcomponents contained in the function as such as the clutch system has the function to transmitthe rotation of the motor acia Broadcasts also this system is very basic in the car and through thethe car comes into office and so we may release many systems sidewalk carroo holds, we can also give aconocer about the characteristics of the engines inside the cars

Clutch

Clutch for a drive shaft: The clutch disc (center) spins with the flywheel (left). To disengage, the lever is pulled (black arrow), causing a white pressure plate (right) to disengage the green clutch disc from turning the drive shaft, which turns within the thrustbearing ring of the lever. Never will all 3 rings connect, with no gaps.

Rear side of a Ford V6 engine, looking at the clutch housing on the flywheel

Single, dry, clutch friction disc. The splined hub is attached to the disc with springs to damp chatter.

A clutch is a mechanism for transmitting rotation, which can be engaged and disengaged. Clutches are useful in devices that have two rotating shafts. In these devices, one shaft is typically driven by a motor or pulley, and the other shaft drives another device. In a drill, for instance, one shaft is driven by a motor, and the other drives a drill chuck. The clutch connects the two shafts so that they can either be locked together and spin at the same speed (engaged), or be decoupled and spin at different speeds (disengaged).

Multiple plate friction clutch This type of clutch has several driving members interleaved with several driven members. It is used in motorcycles and in some diesel locomotives with mechanical transmission. It is also used in some electronically-controlled all-wheel drive systems. This is the most common type of clutch on modern types of vehicles.

Vehicular There are many different vehicle clutch designs but most are based on one or more friction discs, pressed tightly together or against a flywheel using springs. The friction material varies in composition depending on whether the clutch is dry or wet, and on other considerations. Friction discs once contained asbestos, but this has been largely eliminated. Clutches found in heavy duty applications such as trucks and competition cars use ceramic clutches that have a greatly increased friction coefficient; however, these have a "grabby" action and are unsuitable for road cars. The spring pressure is released when the clutch pedal is depressed thus either pushing or pulling the diaphragm of the pressure plate, depending

on type, and the friction plate is released and allowed to rotate freely.

When engaging the clutch, the engine speed may need to be increased from idle, using the manual throttle, so that the engine does not stall (although in some cars, especially diesels, there is enough torque at idling speed that the car can move; this requires fine control of the clutch). However, raising the engine speed too high while engaging the clutch will cause excessive clutch plate wear. Engaging the clutch abruptly when the engine is turning at high speed causes a harsh, jerky start. This kind of start is necessary and desirable in drag racing and other competitions where speed is more of an issue than comfort.

Wet and dry A 'wet clutch' is immersed in a cooling lubricating fluid, which also keeps the surfaces clean and gives smoother performance and longer life. Wet clutches, however, tend to lose some energy to the liquid. A 'dry clutch', as the name implies, is not bathed in fluid.

Since the surfaces of a wet clutch can be slippery (as with a motorcycle clutch bathed in transmission oil), stacking multiple clutch disks can compensate for the lower coefficient of friction and so eliminate slippage when fully engaged.

Operation in automobiles

This plastic pilot shaft guide tool is used to align the clutch disk as the spring-loaded pressure plate is installed. The transmission's drive splines and pilot shaft have an identical shape. A number of such devices fit various makes and models of drivetrains In a car the clutch is operated by the left-most pedal using a hydraulic or cable connection from the pedal to the clutch mechanism. Even though the clutch may physically be located very close to the pedal, such remote means of actuation (or a multijointed linkage) are necessary to eliminate the effect of slight engine movement, engine mountings being flexible by design. With a rigid mechanical linkage, smooth engagement would be near-impossible,

because engine movement inevitably occurs as the drive is "taken up." No pressure on the pedal means that the clutch plates are engaged (driving), while pressing the pedal disengages the clutch plates, allowing the driver to shift gears or coast.

A manual transmission contains cogs for selecting gears. These cogs have matching teeth, called dog teeth, which means that the rotation speeds of the two parts have a synchronizer, a device that uses frictional contact to bring the two parts to the same speed, and a locking mechanism called a blocker ring to prevent engagement of the teeth (full movement of the shift lever into gear) until the speeds are synchronized.

Clutch Stages A Stage 1 clutch is designed to match an automobile's stock clutch in performance and driveability. These are intended for stock vehicles with little or no performance upgrades or increased torque.

Stage 2 and 2+ clutches provide greater clamping and torque capability with mildly decreased driveability respectively. These are intended for automobiles with mild to moderate engine tuning or performance upgrades resulting in increased horse power and torque beyond that of the stock engine.

Stage 3 and 3+ clutches are designed to provide higher levels of clamping and torque handling. These are typically intended only for racing purposes where extreme heat conditions are generated. Note that some Stage 3 and 3+ clutches require significant warming before performing optimally.

Non-powertrain in automobiles There are other clutches found in a car. For example, a belt-driven engine cooling fan may have a clutch that is heat-activated. The driving and driven elements are separated by a silicone-based fluid and a valve controlled by a bimetallic spring. When the temperature is low, the spring winds and closes the valve, which allows the fan to spin at about 20% to 30% of the shaft speed. As the temperature of the spring rises, it unwinds and opens the valve, allowing fluid past the valve which allows the fan to spin at about 60% to 90% of shaft speed depending on whether it's a regular or heavy-duty clutch.

There are also electronically engaged clutches (such as for an air

conditioning compressor) that use magnetic force to lock the drive and driven shafts together.

Centrifugal Some cars and mopeds have a centrifugal clutch, using centrifugal effects to engage the clutch above certain rpm, see Saxomat.

How Dual-clutch Transmissions Work Most people know that cars come with two basic transmission types: manuals, which require that the driver change gears by depressing a clutch pedal and using a stick shift, and automatics, which do all of the shifting work for drivers using clutches, a torque converter and sets of planetary gears. But there's also something in between that offers the best of both worlds -- the dual-clutch transmission, also called the semi-automatic transmission, the "clutchless" manual transmission and the automated manual transmission.

In the world of racecars, semi-automatic transmissions, such as the sequential manual gearbox (or SMG), have been a staple for years.

But in the world of production vehicles, it's a relatively new technology -- one that is being defined by a very specific design known as the dual-clutch, or direct-shift, gearbox.

Hands-On or Hands-Off A dual-clutch transmission offers the function of two manual gearboxes in one. To understand what this means, it's helpful to review how a conventional manual gearbox works. When a driver wants to change from one gear to another in a standard stick-shift car, he first presses down the clutch pedal. This operates a single clutch, which disconnects the engine from the gearbox and interrupts power flow to the transmission. Then the driver uses the stick shift to select a new gear, a process that involves moving a toothed collar from one gear wheel to another gear wheel of a different size. Devices called synchronizers match the gears before they are engaged to prevent grinding. Once the new gear is engaged, the driver releases the clutch pedal, which re-connects the engine to the gearbox and transmits power to the wheels.

So, in a conventional manual transmission, there is not a continuous flow of power from the engine to the wheels. Instead, power delivery changes from on to off to on during gearshift, causing a phenomenon known as "shift shock" or "torque interrupt." For an unskilled driver, this can result in passengers being thrown forward and back again as gears are changed.

A dual-clutch gearbox, by contrast, uses two clutches, but has no clutch pedal. Sophisticated electronics and hydraulics control the clutches, just as they do in a standard automatic transmission. In a DCT, however, the clutches operate independently. One clutch controls the odd gears (first, third, fifth and reverse), while the other controls the even gears (second, fourth and sixth). Using this arrangement, gears can be changed without interrupting the power flow from the engine to the transmission. Sequentially, it works like this: Dual-clutch Transmission Shafts

A two-part transmission shaft is at the heart of a DCT. Unlike a conventional manual gearbox, which houses all of its gears on a single input shaft, the DCT splits up odd and even gears on two input shafts. How is this possible? The outer shaft is hollowed out, making room for an inner shaft, which is nested inside. The outer hollow shaft feeds second and fourth gears, while the inner shaft feeds first, third and fifth.

The diagram below shows this arrangement for a typical five-speed DCT. Notice that one clutch controls second and fourth gears, while another, independent clutch controls first, third and fifth gears.

That's the trick that allows lightning-fast gear changes and keeps power delivery constant. A standard manual transmission can't do this because it must use one clutch for all odd and even gears.

Multi-plate Clutches Because a dual-clutch transmission is similar to an automatic, you might think that it requires a torque converter, which is how an automatic transfers engine torque from the engine to the transmission. DCTs, however, don't require torque converters.

Instead, DCTs currently on the market use wet multi-plate clutches.

A "wet" clutch is one that bathes the clutch components in lubricating fluid to reduce friction and limit the production of heat.

Several manufacturers are developing DCTs that use dry clutches, like those usually associated with manual transmissions, but all production vehicles equipped with DCTs today use the wet version.

Many motorcycles have single multi-plate clutches.

Like torque converters, wet multi-plate clutches use hydraulic pressure to drive the gears. The fluid does its work inside the clutch piston, seen in the diagram above. When the clutch is engaged, hydraulic pressure inside the piston forces a set of coil springs part, which pushes a series of stacked clutch plates and friction discs against a fixed pressure plate. The friction discs have internal teeth that are sized and shaped to mesh with splines on the clutch drum.

In turn, the drum is connected to the gearset that will receive the transfer force. Audi's dual-clutch transmission has both a small coil spring and a large diaphragm spring in its wet multi-plate clutches.

To disengage the clutch, fluid pressure inside the piston is reduced.

This allows the piston springs to relax, which eases pressure on the clutch pack and pressure plate.

We'll look at the pros and cons of dual-clutch transmissions next.

Pros and Cons of Dual-clutch Transmissions Hopefully it's becoming clear why the DCT is classified as an automated manual transmission. In principle, the DCT behaves just like a standard manual transmission: It's got input and auxiliary shafts to house gears, synchronizers and a clutch. What it doesn't have is a clutch pedal, because computers, solenoids and hydraulics do the actual shifting. Even without a clutch pedal, the driver can still "tell" the computer when to take action through paddles, buttons or a gearshift.

Driver experience, then, is just one of the many advantages of a DCT. With upshifts taking a mere 8 milliseconds, many feel that the DCT offers the most dynamic acceleration of any vehicle on the market. It certainly offers smooth acceleration by eliminating the shift shock that accompanies gearshifts in manual transmissions and even some automatics. Best of all, it affords drivers the luxury of choosing whether they prefer to control the shifting or let the computer do all of the work.

Perhaps the most compelling advantage of a DCT is improved fuel economy. Because power flow from the engine to the transmission is not interrupted, fuel efficiency increases dramatically. Some experts say that a six-speed DCT can deliver up to a 10 percent increase in relative fuel efficiency when compared to a conventional five-speed automatic.

Many car manufacturers are interested in DCT technology.

However, some automakers are wary of the additional costs associated with modifying production lines to accommodate a new type of transmission. This could initially drive up the costs of cars outfitted with DCTs, which might discourage cost-conscious consumers.

In addition, manufacturers are already investing heavily in alternate transmission technologies. One of the most notable is the continuously variable transmission, or CVT. A CVT is a type of automatic transmission that uses a moving pulley system and a belt or chain to infinitely adjust the gear ratio across a wide range. CVTs also reduce shift shock and increase fuel efficiency significantly. But CVTs can't handle the high torque demands of performance cars.

DCTs don't have such issues and are ideal for high-performance vehicles. In Europe, where manual transmissions are preferred because of their performance and fuel efficiency, some predict that DCTs will capture 25 percent of the market. Just one percent of cars produced in Western Europe will be fitted with a CVT by 2012.

Manual transmission A manual transmission (also known as a 'manual' or 'stick shift') is a type of transmission used in automotive applications. It generally utilizes a driver-operated clutch operated by a pedal or lever, for regulating torque transfer from the engine to the transmission, and a

gear-shift either operated by hand (as in a car) or by foot (as on a motorcycle). Other types of transmission in mainstream automotive use are the automatic transmission, semi-automatic transmission, and the continuously variable transmission(CVT).

Overview Manual transmissions often feature a driver-operated clutch and a movable gear selector. Most automobile manual transmissions allow the driver to select any forward gear at any time, but some, such as those commonly mounted on motorcycles and some types of racing cars, only allow the driver to select the next-higher or next-lower gear ratio. This second type of transmission is sometimes called a sequential manual transmission. Sequential transmissions are commonly used in auto racing for their ability to make quick shifts.

Manual transmissions are characterized by gear ratios that are selectable by locking selected gear pairs to the output shaft inside the transmission. Conversely, most automatic transmissions feature epicyclic (planetary) gearing controlled by brake bands and/or clutch packs to select gear ratio. Automatic transmissions that allow the driver to manually select the current gear are called semi-automatic transmissions.

Contemporary automotive manual transmissions are generally available with four to six forward gears and one reverse gear, although manual transmissions have been built with as few as two and as many as eight gears. Tractor units have at least 9 gears and as many as 24. Some manuals are referred to by the number of forward gears they offer (e.g., 5-speed) as a way of distinguishing between automatic or other available manual transmissions.

Similarly, a 5-speed automatic transmission is referred to as a 5speed automatic.

Unsynchronized transmission The earliest form of a manual transmission is thought to have been invented by Louis-RenÊ Panhard and Emile Levassor in the late 19th century. This type of transmission offered multiple gear ratios and, in most cases, reverse. The gears were engaged by sliding them (or dog clutches) on their shafts—hence the term "shifting gears," which required a lot of careful timing and throttle manipulation when shifting, so that the gears would be spinning at roughly the same speed when engaged; otherwise, the teeth would refuse to mesh.

When upshifting, the speed of the gear driven by the engine had to drop to match the speed of the next gear; as this happened naturally when the clutch was depressed or disengaged, it was just a matter of skill and experience to hear and feel when the gears managed to mesh. However, when downshifting, the gear driven by the engine had to be sped up to mesh with the output gear, requiring letting the clutch up (engagement) for the engine to speed up the gears.

Double-clutching, that is, shifting once to neutral to speed up the gears and again to the lower gear, is sometimes needed. In fact, such transmissions are often easier to shift without using the clutch at all. When using this method, the driver has to time the shift with relative precision to avoid grinding the gears. The clutch, in these cases, is only used for starting from a standstill. This procedure is common in racing vehicles and most production motorcycles.

Even though automotive transmissions are now almost universally synchronised, heavy trucks and machinery as well as dedicated racing transmissions are usually not; such transmissions are colloquially referred to as "crashboxes." Non-synchronized designs are used for several reasons. The friction material, such as brass, in synchronizers is more prone to wear and breakage than gears, which are forged steel, and the simplicity of the mechanism improves reliability and reduces cost. In addition, the process of shifting a synchromesh transmission is slower than that of shifting a non-synchromesh transmission. For racing of production-based transmissions, sometimes half the teeth (or "dogs") on the synchros are removed to speed the shifting process, at the expense of greater wear.

Heavy duty trucks utilize unsynchronized transmissions in the interest of saving weight. Military edition trucks, which do not have to obey weight laws, usually have a synchronized transmission.

Highway use heavy-duty trucks in the United States are limited to 80,000 pounds GVWR, and the lighter the curb weight for the truck, the more cargo can be carried, and with a synchronizer adding weight to a truck that could otherwise be used to carry cargo, most drivers are simply taught how to double clutch, initially, and then most eventually gravitate to shifting without the clutch.

Similarly, most modern motorcycles still utilize unsynchronized transmissions as synchronizers are generally not necessary or desirable. Their low gear inertias and higher strengths mean that forcing the gears to alter speed is not damaging, and the selector

method on modern motorcycles (pedal operated) is not conducive to having the long shift time of a synchronized gearbox. Because of this, it is still necessary to synchronize gear speeds by blipping the throttle when shifting into a lower gear on a motorcycle.

Synchronized transmission

Top and side view of a typical manual transmission, in this case a Ford "Toploader", used in cars with external floor shifters.

Modern gearboxes are constant mesh, i.e., all input and drive gears are always in mesh. Only one of these meshed pairs of gears is locked to the shaft on which it is mounted at any one time, while the others are allowed to rotate freely. This greatly reduces the skill required to shift gears.

Most modern cars are fitted with a synchronized gear box, although it is entirely possible to construct a constant mesh gearbox without a synchromesh, as found in a motorcycle, for example. In a constant mesh gearbox, the transmission gears are always in mesh and rotating, but the gears are not rigidly connected to the shafts on which they rotate. Instead, the gears can freely rotate or be locked to the shaft on which they are carried. The locking mechanism for any individual gear consists of a collar (or "dog collar") on the shaft which is able to slide sideways so that teeth (or "dogs") on its inner surface bridge two circular rings with teeth on their outer circumference: one attached to the gear, one to the shaft (one collar

typically serves for two gears; sliding in one direction selects one transmission speed, in the other direction selects the other). When the rings are bridged by the collar, that particular gear is rotationally locked to the shaft and determines the output speed of the transmission.

In a synchromesh gearbox, to correctly match the speed of the gear to that of the shaft as the gear is engaged, the collar initially applies a force to a cone-shaped brass clutch attached to the gear, which brings the speeds to match prior to the collar locking into place. The collar is prevented from bridging the locking rings when the speeds are mismatched by synchro rings (also called blocker rings or balk rings, the latter being spelled "baulk" in the UK). The gearshift lever manipulates the collars using a set of linkages, so arranged so that one collar may be permitted to lock only one gear at any one time; when "shifting gears," the locking collar from one gear is disengaged and that of another engaged. In a modern gearbox, the action of all of these components is so smooth and fast it is hardly noticed.

The modern cone system was developed by Porsche and introduced in the 1952 Porsche 356; cone synchronizers were called "Porsche-type" for many years after this. In the early 1950s only the second-third shift was synchromesh in most cars, requiring only a single synchro and a simple linkage; drivers' manuals in cars suggested that if the driver needed to shift from second to first, it was best to come to a complete stop then shift into first and start up again. With continuing sophistication of mechanical development, however, fully synchromesh transmissions with three speeds, then four speeds, and then five speeds, became universal by the 1980s.

Many modern manual transmission cars, especially sports cars, now offer six speeds.

Reverse gear, however, is usually not synchromesh, as there is only one reverse gear in the normal automotive transmission and changing gears while moving into reverse is not required.

Internals Shafts Like other transmissions, a manual transmission has several shafts with various gears and other components attached to them.

Typically, a rear-wheel-drive transmission has three shafts: an input

shaft, a countershaft and an output shaft. The countershaft is sometimes called a layshaft.

In a rear-wheel-drive transmission, the input and output shaft lie along the same line, and may in fact be combined into a single shaft within the transmission. This single shaft is called a mainshaft. The input and output ends of this combined shaft rotate independently, at different speeds, which is possible because one piece slides into a hollow bore in the other piece, where it is supported by a bearing.

Sometimes the term mainshaft refers to just the input shaft or just the output shaft, rather than the entire assembly.

In some transmissions, it's possible for the input and output components of the mainshaft to be locked together to create a 1:1 gear ratio, causing the power flow to bypass the countershaft. The mainshaft then behaves like a single, solid shaft, a situation referred to as direct drive.

Even in transmissions that do not feature direct drive, it's an advantage for the input and output to lie along the same line, because this reduces the amount of torsion that the transmission case has to bear.

Under one possible design, the transmission's input shaft has just one pinion gear, which drives the countershaft. Along the countershaft are mounted gears of various sizes, which rotate when the input shaft rotates. These gears correspond to the forward speeds and reverse. Each of the forward gears on the countershaft is permanently meshed with a corresponding gear on the output shaft. However, these driven gears are not rigidly attached to the output shaft: although the shaft runs through them, they spin independently of it, which is made possible by bearings in their hubs. Reverse is typically implemented differently, see the section on Reverse.

Most front-wheel-drive transmissions for transverse engine mounting are designed differently. For one thing, they have an integral final drive and differential. For another, they usually have only two shafts; input and countershaft, sometimes called input and output. The input shaft runs the whole length of the gearbox, and there is no separate input pinion. At the end of the second (counter/output) shaft is a pinion gear that mates with the ring gear on the differential.

Front-wheel and rear-wheel-drive transmissions operate similarly.

When the transmission is in neutral, and the clutch is disengaged, the input shaft, clutch disk and countershaft can continue to rotate under their own inertia. In this state, the engine, the input shaft and clutch, and the output shaft all rotate independently.

Dog clutch The gear selector does not engage or disengage the actual gear teeth which are permanently meshed. Rather, the action of the gear selector is to lock one of the freely spinning gears to the shaft that runs through its hub. The shaft then spins together with that gear.

The output shaft's speed relative to the countershaft is determined by the ratio of the two gears: the one permanently attached to the countershaft, and that gear's mate which is now locked to the output shaft.

Locking the output shaft with a gear is achieved by means of a dog clutch selector. The dog clutch is a sliding selector mechanism which is splined to the output shaft, meaning that its hub has teeth that fit into slots (splines) on the shaft, forcing it to rotate with that shaft. However, the splines allow the selector to move back and forth on the shaft, which happens when it is pushed by a selector fork that is linked to the gear lever. The fork does not rotate, so it is attached to a collar bearing on the selector. The selector is typically symmetric: it slides between two gears and has a synchromesh and teeth on each side in order to lock either gear to the shaft.

Synchromesh If the teeth, the so-called dog teeth, make contact with the gear, but the two parts are spinning at different speeds, the teeth will fail to engage and a loud grinding sound will be heard as they clatter together. For this reason, a modern dog clutch in an automobile has a synchronizer mechanism or synchromesh, which consists of a cone clutch and blocking ring. Before the teeth can engage, the cone clutch engages first which brings the selector and gear to the same speed using friction. Moreover, until synchronization occurs, the teeth are prevented from making contact, because further motion of the selector is prevented by a blocker (or "baulk") ring.

When synchronization occurs, friction on the blocker ring is relieved and it twists slightly, bringing into alignment certain grooves and notches that allow further passage of the selector which brings the

teeth together. Of course, the exact design of the synchronizer varies from manufacturer to manufacturer.

The synchronizer[2] has to change the momentum of the entire input shaft and clutch disk. Additionally, it can be abused by exposure to the momentum and power of the engine itself, which is what happens when attempts are made to select a gear without fully disengaging the clutch. This causes extra wear on the rings and sleeves, reducing their service life. When an experimenting driver tries to "match the revs" on a synchronized transmission and force it into gear without using the clutch, the synchronizer will make up for any discrepancy in RPM. The success in engaging the gear without clutching can deceive the driver into thinking that the RPM of the layshaft and transmission were actually exactly matched.

Nevertheless, approximate "rev-matching" with clutching can decrease the general delta between layshaft and transmission and decrease synchro wear.

Reverse The previous discussion normally applies only to the forward gears.

The implementation of the reverse gear is usually different, implemented in the following way to reduce the cost of the transmission. Reverse is also a pair of gears: one gear on the countershaft and one on the output shaft. However, whereas all the forward gears are always meshed together, there is a gap between the reverse gears. Moreover, they are both attached to their shafts: neither one rotates freely about the shaft. What happens when reverse is selected is that a small gear, called an idler gear or reverse idler, is slid between them. The idler has teeth which mesh with both gears, and thus it couples these gears together and reverses the direction of rotation without changing the gear ratio.

Thus, in other words, when reverse gear is selected, in fact it is actual gear teeth that are being meshed, with no aid from a synchronization mechanism. For this reason, the output shaft must not be rotating when reverse is selected: the car must be stopped. In order that reverse can be selected without grinding even if the input shaft is spinning inertially, there may be a mechanism to stop the input shaft from spinning. The driver brings the vehicle to a stop, and selects reverse. As that selection is made, some mechanism in the transmission stops the input shaft. Both gears are stopped and the idler can be inserted between them.

Whenever the clutch pedal is depressed to shift into reverse, the mainshaft continues to rotate because of its inertia. The resulting speed difference between mainshaft and reverse idler gear produces gear noise [grinding]. The reverse gear noise reduction system employs a cam plate which was added to the reverse shift holder. When shifting into reverse, the 5th/reverse shift piece, connected to the shift lever, rotates the cam plate. This causes the 5th synchro set to stop the rotating mainshaft.

A reverse gear implemented this way makes a loud whining sound, which is not normally heard in the forward gears. The teeth on the forward gears of most consumer automobiles are helically cut. When helical gears rotate, their teeth slide together, which results in quiet operation. In spite of all forward gears being always meshed, they do not make a sound that can be easily heard above the engine noise. By contrast, most reverse gears are spur gears, meaning that they have straight teeth, in order to allow for the sliding engagement of the idler, which is difficult with helical gears. The teeth of spur gears clatter together when the gears spin, generating a characteristic whine.

It is clear that the spur gear design of reverse gear represents some compromises—less robust, unsynchronized engagement and loud noise—which are acceptable due to the relatively small amount of driving that takes place in reverse. The gearbox of the classic SAAB 900 is a notable example of a gearbox with a helical reverse gear engaged in the same unsynchronized manner as the spur gears described above. Its strange design allows reverse to share cogs with first gear, and is exceptionally quiet, but results in difficult engagement and unreliable operation. However, many modern transmissions now include a reverse gear synchronizer and helical gearing Design variations Gear variety Manual transmissions in passenger vehicles are often equipped with 4, 5, or more recently 6 forward gears in conventional manual transmissions with a gear stick, and up to 7 forward gears in semiautomatic transmissions. Nearly all have one reverse gear. In three or four speed transmissions, in most cases, the topmost gear is "direct", i.e., a 1:1 ratio. For five speed or higher transmissions, the highest gear is usually an overdrive gear, with a ratio of less than

1:1. Older cars were generally equipped with 3-speed transmissions, or 4-speed transmissions for high performance models and 5speeds for the most sophisticated of automobiles; in the 1970s, 5speed transmissions began to appear in low priced mass market automobiles and even compact pickup trucks, pioneered by Toyota (who advertised the fact by giving each model the suffix SR5 as it acquired the fifth speed). Today, mass market automotive manual transmissions are essentially all 5-speeds, with 6-speed transmissions beginning to emerge in high performance vehicles in the early 1990s, and recently beginning to be offered on some highefficiency and conventional passenger cars. A very small number of 7-speed 'manual-derived' transmissions are offered on high-end performance cars, such as the Bugatti Veyron 16.4, or the BMW M5.

Both of these cars feature a paddle shifter.

External overdrive On earlier models with three or four forward speeds, the lack of an overdrive ratio for relaxed and fuel-efficient highway cruising was often filled by incorporating a separate overdrive unit in the rear housing of the transmission. This unit was separately actuated by a knob or button, often incorporated into the gearshift knob.

Shaft and gear configuration On a "conventional" rear-drive transmission, there are three basic shafts; the intput, the output, and the countershaft. The input and output together are called the "mainshaft", since they are joined inside the tranmission so they appear to be a single shaft, although they rotate totally independently of each other. The input length of this shaft is much shorter than the output shaft. Parallel to the mainshaft is the countershaft. There are a number of gears fixed along the countershaft, and matching gears along the output shaft, although these are not fixed, and rotate independently of the output shaft. There is sliding "dog collars" or "dog clutches" between the gears on the output shaft, and to engage a gear to the shaft, the collar slides into the space between the shaft and the inside space of the gear, thus rotating the shaft as well. One collar is usually mounted between two gears, and slides both ways to engage one or the other gears, so on a four speed there would be two collars. A front-drive tranmission is basically the same, but simplified. There are only two shafts, the input and the output. Rather that input shaft

driving the countershaft with a pinion gear, the input shaft takes over the countershafts job, and the output shaft runs parallel to it. The gears are positioned and engaged just as they are on the countershaft-output shaft on a rear-drive. This merely eliminates one major component, the pinion gear. Part of the reason that the input and output are in-line on a rear drive unit is to relieve torsion stress on the transmission and mountings, but this isn't an issue in a frontdrive as the gearbox is integrated into the transaxle.

The basic process is not universal. The fixed and free gears can be mounted on either the input or output shaft, or both.

Automatic transmission

An 8 gear automatic transmission An automatic transmission (commonly "AT" or "Auto") is an automobile gearbox that can change gear ratios automatically as the vehicle moves, freeing the driver from having to shift gears manually. Similar but larger devices are also used for heavy-duty commercial and industrial vehicles and equipment.

Most automatic transmissions have a set selection of possible gear ranges, often with a parking pawl feature that will lock the output shaft of the transmission. Continuously variable transmissions (CVTs) can change the ratios over a range rather than between set gear ratios. CVTs have been used for decades in two-wheeled scooters but have seen limited use in a few automobile models.

Recently, however, CVT technology has gained greater acceptance among manufacturers and customers, especially in Nissan automobiles and gas-electric Hybrid vehicles.

Some machines with limited speed ranges or fixed engine speeds, such as some forklift trucks and lawn mowers, only use a torque converter to provide a variable gearing of the engine to the wheels.

Comparison with manual transmission In most Asian markets except the Indian subcontinent, automatic transmissions have become very popular since the 1990s. Most cars sold in the United States since the 1950s have been equipped with an automatic transmission, though it remains common practice to advertise the cheaper priced model with a manual transmission and treat the automatic as an upgrade. However, like in India, Europe sees higher popularity of manual transmissions. Automatic transmissions are easier to drive and consequently, in some jurisdictions, drivers passing their driving test in an automatictransmission vehicle will not be licensed to drive a manualtransmission vehicle.

Automatic transmission modes Conventionally, in order to select the mode, the driver would have to move a gear shift lever located on the steering column or on the floor next to him/her. In order to select gears/modes the driver must push a button in (called the shift lock button) or pull the handle (only on column mounted shifters) out. Some vehicles (like the Aston Martin DB9) position selector buttons for each mode on the cockpit instead, freeing up space on the central console. Vehicles conforming to US Government standards must have the modes ordered P-R-N-D-L (left to right, top to bottom, or clockwise). Prior to this, quadrant-selected automatic transmissions often utilized a P-ND-L-R layout, or similar. Such a pattern led to a number of deaths and injuries owing to unintentional gear mis-selection, as well the danger of having a selector (when worn) jump into Reverse from Low gear during engine braking maneuvers.

Automatic Transmissions have various modes depending on the model and make of the transmission. Some of the common modes are: Park (P) – This selection mechanically locks the transmission, restricting the car from moving in any direction. A parking pawl prevents the transmission—and therefore the vehicle—from moving, although the vehicle's non-drive wheels may still spin freely. For this reason, it is recommended to use the hand brake (or parking brake) because this actually locks (in most cases) the rear wheels and prevents them from moving. This also increases the life of the transmission and the park pin mechanism, because parking on an incline with the transmission in park without the parking brake

engaged will cause undue stress on the parking pin. An efficientlyadjusted hand brake should also prevent the car from moving if a worn selector accidentally drops into reverse gear during early morning fast-idle engine warmups.

A car should be allowed to come to a complete stop before setting the transmission into park to prevent damage. Usually, PARK is one of only two selections in which the car's engine can be started. In many modern cars and trucks (notably those sold in the US and Canada), the driver must have the footbrake applied before the transmission can be taken out of park. The Park position is omitted on buses/coaches with automatic transmission (on which a parking pawl is not practical), which must be placed in neutral with the parking brakes set.

Reverse (R) – This puts the car into the reverse gear, giving the ability for the car to drive backwards. In order for the driver to select reverse they must come to a complete stop, push the shift lock button in (or pull the shift lever forward in the case of a column shifter) and select reverse. Not coming to a complete stop can cause severe damage to the transmission. Many modern automatic gearboxes have a safety mechanism in place, which does to some extent prevent (but doesn't completely avoid) inadvertently putting the car in reverse when the vehicle is moving. This mechanism usually consists of a solenoid-controlled physical barrier on either side of the Reverse position, which is electronically engaged by a switch on the brake pedal. Therefore, the brake pedal needs to be depressed in order to allow the selection of reverse. Some electronic transmissions prevent or delay engagement of reverse gear altogether while the car is moving.

Some shifters with a shift button allows the driver to freely move the shifter from R to N or D, or simply moving the shifter to N or D without actually depressing the button. However, the driver cannot put back the shifter to R without depressing the shift button to prevent accidental shiftings, especially at high speeds, which could damage the transmission.

Neutral/No gear (N)– This disconnects the transmission from the wheels so the car can move freely under its own weight. This is the only other selection in which the car can be started.

Drive (D)– This allows the car to move forward and accelerate through its range of gears. The number of gears a transmission has

depends on the model, but they can commonly range from 3 (predominant before the 1990s).

OverDrive ([D], OD, or a boxed D) - This mode is used in some transmissions to allow early Computer Controlled Transmissions to engage the Automatic Overdrive. In these transmissions, Drive (D) locks the Automatic Overdrive off, but is identical otherwise. OD (Overdrive) in these cars is engaged under steady speeds or low acceleration at approximately 35-45 mph (approx. 72 km/h). Under hard acceleration or below 35-45 mph, the transmission will automatically downshift. Vehicles with this option should be driven in this mode unless circumstances require a lower gear.

Second (2 or S) – This mode limits the transmission to the first two gears, or more commonly locks the transmission in second gear.

This can be used to drive in adverse conditions such as snow and ice, as well as climbing or going down hills in the winter time. Some vehicles will automatically upshift out of second gear in this mode if a certain rpm range is reached in order to prevent engine damage.

First (1 or L) – This mode locks the transmission in first gear only. It will not accelerate through any gear range. This, like second, can be used during the winter season, or for towing.

How Differentials Work If you've read How Car Engines Work, Engine Image Gallery you understand how a car's power is generated; and if you've read How Manual Transmissions Work, you understand where the power goes next. This article will explain differentials -- where the power, in most cars, makes its last stop before spinning the wheels.

The differential has three jobs:  

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To aim the engine power at the wheels To act as the final gear reduction in the vehicle, slowing the rotational speed of the transmission one final time before it hits the wheels To transmit the power to the wheels while allowing them to rotate at different speeds (This is the one that earned the differential its name.)

In this article, you'll learn why your car needs a differential, how it works and what its shortcomings are. We'll also look at several types of positraction, also known as limited slip differentials.

Why You Need a Differential Car wheels spin at different speeds, especially when turning. You can see from the animation below that each wheel travels a different distance through the turn, and that the inside wheels travel a shorter distance than the outside wheels. Since speed is equal to the distance traveled divided by the time it takes to go that distance, the wheels that travel a shorter distance travel at a lower speed. Also note that the front wheels travel a different distance than the rear wheels.

For the non-driven wheels on your car -- the front wheels on a rearwheel drive car, the back wheels on a front-wheel drive car -- this is not an issue. There is no connection between them, so they spin independently. But the driven wheels are linked together so that a single engine and transmission can turn both wheels. If your car did not have a differential, the wheels would have to be locked together, forced to spin at the same speed. This would make turning difficult and hard on your car: For the car to be able to turn, one tire would have to slip. With modern tires and concrete roads, a great deal of force is required to make a tire slip. That force would have to be transmitted through the axle from one wheel to another, putting a heavy strain on the axle components.

What is a Differential?

The differential is a device that splits the engine torque two ways, allowing each output to spin at a different speed.

The differential is found on all modern cars and trucks, and also in many all-wheel-drive (full-time four-wheel-drive) vehicles. These allwheel-drive vehicles need a differential between each set of drive wheels, and they need one between the front and the back wheels as well, because the front wheels travel a different distance through a turn than the rear wheels.

Part-time four-wheel-drive systems don't have a differential between the front and rear wheels; instead, they are locked together so that the front and rear wheels have to turn at the same average speed.

This is why these vehicles are hard to turn on concrete when the four-wheel-drive system is engaged.

Open Differentials We will start with the simplest type of differential, called an open differential. First we'll need to explore some terminology: The image below labels the components of an open differential.

When a car is driving straight down the road, both drive wheels are spinning at the same speed. The input pinion is turning the ring gear and cage, and none of the pinions within the cage are rotating -both side gears are effectively locked to the cage.

Note that the input pinion is a smaller gear than the ring gear; this is the last gear reduction in the car. You may have heard terms like rear axle ratio or final drive ratio. These refer to the gear ratio in the differential. If the final drive ratio is 4.10, then the ring gear has 4.10 times as many teeth as the input pinion gear. See How Gears Work for more information on gear ratios.

When a car makes a turn, the wheels must spin at different speeds.

Differentials and Traction The open differential always applies the same amount of torque to each wheel. There are two factors that determine how much torque can be applied to the wheels: equipment and traction. In dry conditions, when there is plenty of traction, the amount of torque applied to the wheels is limited by the engine and gearing; in a low traction situation, such as when driving on ice, the amount of torque is limited to the greatest amount that will not cause a wheel to slip under those conditions. So, even though a car may be able to produce more torque, there needs to be enough traction to transmit that torque to the ground. If you give the car more gas after the wheels start to slip, the wheels will just spin faster.

Clutch-type Limited Slip Differential The clutch-type LSD is probably the most common version of the limited slip differential.

Image courtesy Eaton Automotive Group's Torque Control Products Division This type of LSD has all of the same components as an open differential, but it adds a spring pack and a set of clutches. Some of these have a cone clutch that is just like the synchronizers in a manual transmission.

The spring pack pushes the side gears against the clutches, which are attached to the cage. Both side gears spin with the cage when both wheels are moving at the same speed, and the clutches aren't really needed -- the only time the clutches step in is when something happens to make one wheel spin faster than the other, as in a turn.

The clutches fight this behavior, wanting both wheels to go the same speed. If one wheel wants to spin faster than the other, it must first overpower the clutch. The stiffness of the springs combined with the friction of the clutch determine how much torque it takes to overpower it.

Getting back to the situation in which one drive wheel is on the ice and the other one has good traction: With this limited slip differential,

even though the wheel on the ice is not able to transmit much torque to the ground, the other wheel will still get the torque it needs to move. The torque supplied to the wheel not on the ice is equal to the amount of torque it takes to overpower the clutches. The result is that you can move forward, although still not with the full power of your car.

Differential (mechanical device)

Differential gear in a car (cut model)

Input torque is applied to the ring gear (blue), which turns the entire carrier (blue), providing torque to both side gears (red and yellow), which in turn may drive the left and right wheels. If the resistance at both wheels is equal, the planet gear (green) does not rotate, and both wheels turn at the same rate.

If the left side gear (red) encounters resistance, the planet gear (green) rotates about the left side gear, in turn applying extra rotation to the right side gear (yellow).

A differential is a device, usually but not necessarily employing gears, capable of transmitting torque and rotation through three shafts, almost always used in one of two ways. In one way, it receives one input and provides two outputs; this is found in most automobiles. In the other way, it combines two inputs to create an output that is the sum, difference, or average, of the inputs.

In automobiles and other wheeled vehicles, the differential allows each of the driving wheels to rotate at different speeds, while for most vehicles supplying equal torque to each of them. In automotive applications, the differential and its housing are sometimes collectively called a "pumpkin" (because the housing resembles a pumpkin).

Purpose A vehicle's wheels rotate at different speeds, especially when turning corners. The differential is designed to drive a pair of wheels with equal force, while allowing them to rotate at different speeds. In vehicles without a differential, such as karts, both driving wheels are forced to rotate at the same speed, usually on a common axle driven by a simple chain-drive mechanism. When cornering, the inner wheel travels a shorter distance than the outer wheel, so with no differential the result is the inner wheel spinning and/or the outer wheel dragging, and this results in difficult and unpredictable handling, damage to tires and roads, and strain on (or possible failure of) the entire drive train.

Functional description

The differential on the rear axle of a car The following description of a differential applies to a "traditional" rear-wheel-drive car or truck: Power is supplied from the engine, via the transmission , to a drive shaft (British term: propeller shaft, more commonly abbreviated to "prop-shaft"), which runs to the differential. A spiral bevel pinion gear at the end of the propeller shaft is encased within the differential itself, and it meshes with the large spiral bevel ring gear (British term: crown wheel). (The ring and pinion may mesh in hypoid orientation, not shown.) The ring gear is attached to a carrier, which holds what is sometimes called a spider, a cluster of four bevel gears in a rectangle, so each bevel gear meshes with two neighbors and rotates counter to the third, that it faces and does not mesh with. Two of these spider gears are aligned on the same axis as the ring gear and drive the half shafts connected to the vehicle's driven wheels. These are called the side gears. The other two spider gears are aligned on a perpendicular axis which changes orientation with the ring gear's rotation. These two gears are just called pinion gears, not to be confused with the main pinion gear. In the two figures shown above, only one pinion gear (green) is illustrated. (Other spider designs employ different numbers of pinion gears depending on durability requirements.) As the carrier rotates, the changing axis orientation of the pinion gears imparts the motion of the ring gear to the motion of the side gears by pushing on them rather than turning against them (that is, the same teeth stay in contact), but because the spider gears are not restricted from turning against each other, within that motion the side gears can counter-rotate relative to the ring gear and to each other under the same force (in which case the same teeth do not stay in contact).

Thus, for example, if the car is making a turn to the right, the main ring gear may make 10 full rotations. During that time, the left wheel will make more rotations because it has further to travel, and the right wheel will make fewer rotations as it has less distance to travel.

The side gears will rotate in opposite directions relative to the ring gear by, say, 2 full turns each (4 full turns relative to each other),

resulting in the left wheel making 12 rotations, and the right wheel making 8 rotations.

The rotation of the ring gear is always the average of the rotations of the side gears. This is why if the wheels are lifted off the ground with the engine off, and the drive shaft is held (preventing the ring gear from turning inside the differential), manually rotating one wheel causes the other to rotate in the opposite direction by the same amount.

When the vehicle is traveling in a straight line, there will be no differential movement of the planetary system of gears other than the minute movements necessary to compensate for slight differences in wheel diameter, undulations in the road (which make for a longer or shorter wheel path), etc.

Loss of traction One undesirable side effect of a differential is that it can reduce overall torque - the rotational force which propels the vehicle. The amount of torque required to propel the vehicle at any given moment depends on the load at that instant - how heavy the vehicle is, how much drag and friction there is, the gradient of the road, the vehicle's momentum and so on. For the purpose of this article, we will refer to this amount of torque as the "threshold torque".

The torque on each wheel is a result of the engine and transmission applying a twisting force against the resistance of the traction at that wheel. Unless the load is exceptionally high, the engine and transmission can usually supply as much torque as necessary, so the limiting factor is usually the traction under each wheel. It is therefore convenient to define traction as the amount of torque that can be generated between the tire and the ground before the wheel starts to slip. If the total traction under all the driven wheels exceeds the threshold torque, the vehicle will be driven forward; if not, then one or more wheels will simply spin.

To illustrate how a differential can limit overall torque, imagine a simple rear-wheel-drive vehicle, with one rear wheel on asphalt with good grip, and the other on a patch of slippery ice. With the load, gradient, etc., the vehicle requires, say, 2000 N路m of torque to move forward (i.e. the threshold torque). Let us further assume that the non-spinning traction on the ice equates to 400 N路m, and the asphalt to 3000 N路m.

If the two wheels were driven without a differential, each wheel would push against the ground as hard as possible. The wheel on ice would quickly reach the limit of traction (400 N·m), but would be unable to spin because the other wheel has good traction. The traction of the asphalt plus the small extra traction from the ice exceeds the threshold requirement, so the vehicle will be propelled forward.

With a differential, however, as soon as the "ice wheel" reaches 400 N·m, it will start to spin, and then develop less traction ~300 N·m.

The planetary gears inside the differential carrier will start to rotate because the "asphalt wheel" encounters greater resistance. Instead of driving the asphalt wheel with more force, the differential will allow the ice wheel to spin faster, and the asphalt wheel to remain stationary, compensating for the stopped wheel by extra speed of the spinning ice wheel. The torque on both wheels will be the same limited to the lesser traction of 300 N·m each. Since 600 N·m is less than the required threshold torque of 2000 N·m, the vehicle will not be able to move.

An observer will simply see one stationary wheel and one spinning wheel. It will not be obvious that both wheels are generating the same torque (i.e. both wheels are in fact pushing equally, despite the difference in rotational speed). This has led to a widely held misconception that a vehicle with a differential is really only "onewheel-drive". In fact, a normal differential always provides equal torque to both driven wheels (unless it is a locking, torque-biasing, or limited slip type).

Traction-adding devices

ARB, Air Locking Differential

There are various devices for getting more usable traction from vehicles with differentials. 

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A simple solution for a standard "open" differential is to partially apply the vehicle's handbrake when one wheel is spinning, as this often provides sufficient resistance to increase the overall torque and allow the other driven wheel to move the vehicle. This only works where the handbrake acts on the driven wheels, as in the traditional rear-drive layout.

Naturally, the handbrake should be released as soon as the vehicle is moving again.

Another solution is the limited slip differential (LSD), the most well-known of which is the clutch-type LSD. With this differential, the side gears are coupled to the carrier via a stack of clutch plates which allows extra torque to be sent to the wheel with high resistance than available at the other wheel.

A locking differential, when locked, allows no difference in speed between the two wheels on the axle. It employs a mechanism for allowing the planetary gears to be locked relative to each other, causing both wheels to turn at the same speed regardless of which has more traction; this is equivalent to removing the differential entirely.

A high-friction differential (such as the torsen differential where the friction is between the gear teeth rather than at added clutches) which sends more torque to the wheel with high resistance than available at the other wheel.

Electronic traction control systems usually use the ABS system to detect a spinning wheel and apply the brake to that wheel. This progressively raises the reaction torque at that wheel, and the differential compensates by transmitting more torque through the other wheel - the one with better traction.

A viscous coupling unit can replace a center differential entirely or be used to limit slip in a normal differential. It works on the principle of allowing the two output shafts to counterrotate relative to each other by way of a system of slotted plates that operate within a viscous fluid, often silicone. The fluid allows slow relative movements of the shafts, such as those caused by cornering, but will strongly resist high-speed movements, such as those caused by a single wheel spinning.

This system is similar to a limited slip differential.

A four-wheel-drive vehicle will have at least two differentials (one for each pair of wheels) and possibly a center differential to apportion power between the front and rear axles. In many cases (eg. Lancia Delta Integrale, Porsche 964 Carrera 4 of 1989 [2]) the center differential is an epicyclic differential (see below) to divide the torque asymmetrically between the front and rear axle. Vehicles without a center differential should not be driven on dry, paved roads in four wheel drive mode, as small differences in rotational speed between the front and rear wheels cause a torque to be applied across the transmission. This phenomenon is known as "wind-up" and can cause damage to the transmission or drive train. On loose surfaces these differences are absorbed by the tire slippage on the road surface.

A transfer case may also incorporate a center differential, allowing the drive shafts to spin at different speeds. This permits the fourwheel-drive vehicle to drive on paved surfaces without experiencing "wind-up".

Electricity and matter ELECTRICITY is a physical phenomena involving positive and negative charge. All matter is made up of atoms, and atoms are made up of smaller particles. The three main particles making up an atom are the proton, the neutron and the electron. Electrons spin around the center, or nucleus, of atoms, in the same way the moon spins around the earth. The nucleus is made up of neutrons and protons. Electrons contain a negative charge, protons a positive charge. Neutrons are neutral -- they have neither a positive nor a negative charge.

There are many different kinds of atoms, one for each type of element. An atom is a single part that makes up an element. There are 118 different known elements that make up every thing. Each atom has a specific number of electrons, protons and neutrons. But no matter how many particles an atom has, the number of electrons usually needs to be the same as the number of protons. If the numbers are the same, the atom is called balanced, and it is very stable. So, if an atom had six protons, it should also have six electrons. The element with six protons and six electrons is called carbon. Carbon is found in abundance in the sun, stars, comets, atmospheres of most planets, and the food we eat. Coal is made of carbon; so are diamonds Some kinds of atoms have loosely attached electrons. An atom that loses electrons has more protons than electrons and is positively

charged. An atom that gains electrons has more negative particles and is negatively charge. A charged atom is called an ion. Electrons can be made to move from one atom to another. When those electrons move between the atoms, a current of electricity is created. The electrons move from one atom to another in a flow.

One electron is attached and another electron is lost.

This chain is similar to the fire fighter's bucket brigades in olden times. But instead of passing one bucket from the start of the line of people to the other end, each person would have a bucket of water to pour from one bucket to another. The result was a lot of spilled water and not enough water to douse the fire. It is a situation that's very similar to electricity passing along a wire and a circuit. The charge is passed from Atom to atom when electricity is passed.

Since all atoms want to be balanced, the atom that has been unbalanced will look for a free electron to fill the place of the missing one. We say that this unbalanced atom has a positive charge" (+) because it has too many protons. Since it got kicked off, the free electron moves around waiting for an unbalanced atom to give it a home. The free electron charge is negative, and has no proton to balance it out, so we say that it has a negative charge (-).

So what do positive and negative charges have to do with electricity?

Scientists and engineers have found several ways to create large numbers of positive atoms and free negative electrons. Since positive atoms want negative electrons so they can be balanced, they have a strong attraction for the electrons. The electrons also want to be part of a balanced atom, so they have a strong attraction to the positive atoms. So, the positive attracts the negative to balance out.

The more positive atoms or negative electrons you have, the stronger the attraction for the other. Since we have both positive and negative charged groups attracted to each other, we call the total attraction charge. When electrons move among the atoms of matter, a current of electricity is created. This is what happens in a piece of wire. The electrons are passed from atom to atom, creating an electrical current from one end to other, just like in the picture.

Electricity is conducted through some things better than others do.

Its resistance measures how well something conducts electricity.

Some things hold their electrons very tightly. Electrons do not move through them very well. These things are called insulators. Rubber, plastic, cloth, glass and dry air agood insulators and have very high resistance. Other materials have some loosely held electrons, which

move through them very easily. These are called conductors. Most metals -- like copper, aluminum or steel -- are good conductors.

Electrical conductor In science and engineering, an electrical conductor is a material which contains movable electric charges. In metallic conductors, such as copper or aluminum, the movable charged particles are electrons (see electrical conduction). Positive charges may also be mobile in the form of atoms in a lattice that are missing electrons (known as holes), or in the form of ions, such as in the electrolyte of a battery.

All conductors contain electric charges which will move when an electric potential difference (measured in volts) is applied across separate points on the material. This flow of charge (measured in amperes) is what is meant by electric current. In most materials, the direct current is proportional to the voltage (as determined by Ohm's law), provided the temperature remains constant and the material remains in the same shape and state.

Most familiar conductors are metallic. Copper is the most common material used for electrical wiring. Silver is the best conductor, but is expensive. Gold is used for high-quality surface-to-surface contacts.

However, there are also many non-metallic conductors, including graphite, solutions of salts, and all plasmas. See electrical conduction for more information on the physical mechanism for charge flow in materials.

Non-conducting materials lack mobile charges, and so resist the flow of electric current, generating heat. In fact, all nonsuperconducting materials offer some resistance and warm up when a current flows. Thus, proper design of an electrical conductor takes into account the temperature that the conductor needs to be able to endure without damage, as well as the quantity of electrical current.

The motion of charges also creates an electromagnetic field around the conductor that exerts a mechanical radial squeezing force on the conductor. A conductor of a given material and volume (length Ă— cross-sectional area) has no real limit to the current it can carry without being destroyed as long as the heat generated by the resistive loss is removed and the conductor can withstand the radial forces. This effect is especially critical in printed circuits, where conductors are relatively small and close together, and inside an

enclosure: the heat produced, if not properly removed, can cause fusing (melting) of the tracks.

Since all non-superconducting conductors have some resistance, and all insulators will carry some current, there is no theoretical dividing line between conductors and insulators. However, there is a large gap between the conductance of materials that will carry a useful current at working voltages and those that will carry a negligible current for the purpose in hand, so the categories of insulator and conductor do have practical utility.

Thermal and electrical conductivity often go together (for instance, most metals are both electrical and thermal conductors). However, some materials are practical electrical conductors without being a good thermal conductor.

Conductor size In many countries, conductors are measured by their cross section in square millimeters. However, in the United States, conductors are measured by American wire gauge for smaller ones, and circular mils for larger ones.

Conductor materials Please note: Anodized Aluminum is a Non-Conductor of an electric current.

Of the metals commonly used for conductors, copper has a high conductivity. Silver is more conductive, but due to cost it is not practical in most cases. However, it is used in specialized equipment, such as satellites, and as a thin plating to mitigate skin effect losses at high frequencies. Because of its ease of connection by soldering or clamping, copper is still the most common choice for most light-gauge wires. Aluminum has been used as a conductor in housing applications for cost reasons. It is actually more conductive than copper when compared by unit weight, but it has technical problems related to heat and its coefficient of thermal expansion, which tends to loosen connections over time.

Conductor voltage The voltage on a conductor is determined by the connected circuitry and has nothing to do with the conductor itself. Conductors are usually surrounded by and/or supported by insulators and the insulation determines the maximum voltage that can be applied to any given conductor.

Voltage of a conductor "V" is given by V = IR where I is the current, measured in amperes V is the potential difference measured in volts R is the resistance measured in ohms Conductor ampacity The ampacity of a conductor, that is, the amount of current it can carry, is related to its electrical resistance: a lower-resistance conductor can carry more current. The resistance, in turn, is determined by the material the conductor is made from (as described above) and the conductor's size. For a given material, conductors with a larger cross-sectional area have less resistance than conductors with a smaller cross-sectional area.

For bare conductors, the ultimate limit is the point at which power lost to resistance causes the conductor to melt. Aside from fuses, most conductors in the real world are operated far below this limit, however. For example, household wiring is usually insulated with PVC insulation that is only rated to operate to about 60 째C, therefore, the current flowing in such wires must be limited so that it never heats the copper conductor above 60 째C, causing a risk of fire. Other, more expensive insulations such as Teflon or fiberglass may allow operation at much higher temperatures.

The American wire gauge article contains a table showing allowable ampacities for a variety of copper wire sizes.

Isotropy

If an electric field is applied to a material, and the resulting induced electric current is in the same direction, the material is said to be an isotropic electrical conductor. If the resulting electric current is in a different direction from the applied electric field, the material is said to be an anisotropic electrical conductor.

Insulator (electrical)

Conducting copper wire insulated by an outer layer of polyethylene An insulator, also called a dielectric, is a material that resists the flow of electric current. An insulating material has atoms with tightly bonded valence electrons. These materials are used in parts of electrical equipment, also called insulators or insulation, intended to support or separate electrical conductors without passing current through themselves. The term is also used more specifically to refer to insulating supports that attach electric power transmission wires to utility poles or pylons.

Some materials such as glass or Teflon are very good electrical insulators. A much larger class of materials, for example rubber-like polymers and most plastics are still "good enough" to insulate electrical wiring and cables even though they may have lower bulk resistivity. These materials can serve as practical and safe insulators for low to moderate voltages (hundreds, or even thousands, of volts).

Physics of conduction in solids Electrical insulation is the absence of electrical conduction.

Electronic band theory (a branch of physics) predicts that a charge will flow whenever there are states available into which the electrons in a material can be excited. This allows them to gain energy and thereby move through the conductor (usually a metal). If no such states are available, the material is an insulator.

Most (though not all, see Mott insulator) insulators are characterized by having a large band gap. This occurs because the "valence" band containing the highest energy electrons is full, and a large energy gap separates this band from the next band above it. There is always some voltage (called the breakdown voltage) that will give

the electrons enough energy to be excited into this band. Once this voltage is exceeded, the material ceases being an insulator, and charge will begin to pass through it. However, it is usually accompanied by physical or chemical changes that permanently degrade the material's insulating properties.

Materials that lack electron conduction are insulators if they lack other mobile charges as well. For example, if a liquid or gas contains ions, then the ions can be made to flow as an electric current, and the material is a conductor. Electrolytes and plasmas contain ions and will act as conductors whether or not electron flow is involved.

Uses Insulators are commonly used as a flexible coating on electric wire and cable. Since air is a insulator, no other substance is needed to "keep the electricity within the wires." However, wires which touch each other will produce cross connections, short circuits, and fire hazards. In coaxial cable the center conductor must be supported exactly in the middle of the hollow shield in order to prevent EM wave reflections. And any wires which present voltages higher than 60V can cause human shock and electrocution hazards. Insulating coatings prevent all of these problems.

In electronic systems, printed circuit boards are made from epoxy plastic and fiberglass. The nonconductive boards support layers of copper foil conductors. In electronic devices, the tiny and delicate active components are embedded within nonconductive epoxy or phenolic plastics, or within baked glass or ceramic coatings.

In high voltage systems containing transformers and capacitors, liquid insulator oil is the typical method used for preventing sparks.

The oil replaces the air in any spaces which must support significant voltage without electrical breakdown. Other methods of insulating high voltage systems are ceramic or glass wire holders and simply placing the wires with a large separation, using the air as insulation.

Semiconductor Semiconductor is a material that has a resistivity value between that of a conductor and an insulator. The conductivity of a semiconductor material can be varied under an external electrical field. Devices made from semiconductor materials are the foundation of modern electronics, including radio, computers, telephones, and many other

devices. Semiconductor devices include the transistor, many kinds of diodes including the light-emitting diode, the silicon controlled rectifier, and digital and analog integrated circuits. Solar photovoltaic panels are large semiconductor devices that directly convert light energy into electrical energy. In a metallic conductor, current is carried by the flow of electrons. In semiconductors, current can be carried either by the flow of electrons or by the flow of positivelycharged "holes" in the electron structure of the material.

Silicon is used to create most semiconductors commercially. Dozens of other materials are used, including germanium, gallium arsenide, and silicon carbide. A pure semiconductor is often called an ―intrinsic‖ semiconductor. The conductivity, or ability to conduct, of semiconductor material can be drastically changed by adding other elements, called ―impurities‖ to the melted intrinsic material and then allowing the melt to solidify into a new and different crystal. This process is called "doping".

Doping The property of semiconductors that makes them most useful for constructing electronic devices is that their conductivity may easily be modified by introducing impurities into their crystal lattice. The process of adding controlled impurities to a semiconductor is known as doping. The amount of impurity, or dopant, added to an intrinsic (pure) semiconductor varies its level of conductivity. Doped semiconductors are often referred to as extrinsic. By adding impurity to pure semiconductors, the electrical conductivity may be varied not only by the number of impurity atoms but also, by the type of impurity atom and the changes may be thousand folds and million folds.

Dopants The materials chosen as suitable dopants depend on the atomic properties of both the dopant and the material to be doped. In general, dopants that produce the desired controlled changes are classified as either electron acceptors or donors. A donor atom that activates (that is, becomes incorporated into the crystal lattice) donates weakly-bound valence electrons to the material, creating excess negative charge carriers. These weakly-bound electrons can move about in the crystal lattice relatively freely and can facilitate conduction in the presence of an electric field. (The donor atoms introduce some states under, but very close to the conduction band

edge. Electrons at these states can be easily excited to the conduction band, becoming free electrons, at room temperature.)

Conversely, an activated acceptor produces a hole. Semiconductors doped with donor impurities are called n-type, while those doped with acceptor impurities are known as p-type. The n and p type designations indicate which charge carrier acts as the material's majority carrier. The opposite carrier is called the minority carrier, which exists due to thermal excitation at a much lower concentration compared to the majority carrier.

The Distribution System

The distribution system is the set of elements that regulate the opening and closing valves at the right time and in turn the entry of the mixture (fresh gas) and the output of waste gases from the cylinders at the appropriate time after the explosion occurred.

Now where in the opening and closing the intake and exhaust valves, so it will be the proper functioning of the motor (forward or delay the opening and closing the corresponding valves).

Different types of compression chambers The compression chambers are classified by their geometric shape.

The shape of the compression chambers is fundamental to the performance and power.

The way the camera is imposed by the layout and size, both spark plugs and valves.

Some types of compression chamber used.

Cylindrical chamber it is widely used for its simplicity in design, and proper functioning caused by the proximity of the spark to the point of maximum utilization are economic.

Chamber of bath and wedge usually manufactured valves in the cylinder head and spark plug is located laterally. They have the advantage that the path of the spark is very short and reduces excessive turbulence of the gas.

Elements of the distribution system

The main elements of the distribution are: camshaft, gear knob, and the valves to their docks.

Are classified according to their function: • Interior Elements Air inlet valve or or exhaust valves • External Elements or camshaft.

And Command Element.

Or Taqua.

Or beam • Interior Elements These elements are the intake valves and exhaust valves.

Valves Are responsible for opening or closing of inlets or outlet gas mixture burned in the cylinders.

In each valve, there are two parts: head and tail. The head, which is shaped like a mushroom, is the valve that acts as a true, as the opening or closing the intake and exhaust openings. Tail or rod, (extension of the head) is that slides within a guide, you will receive at its end opposite to head the drive to open the valve.

The valves are cooled by the guides, mostly, and the head.

The valves that are damaged are the exhaust due to the high temperatures that have to withstand 1000 ° C. Springs The valves are kept closed on its seat by the action of a spring.

The docks should have sufficient strength and elasticity to prevent rebounds and maintain contact with the controls.

Or ensure the mission of the valve and keep it flat on the seat.

Or the number of springs can be simple or double.

Valve Guides Due to the high speeds, the distribution system is operated many times in short periods of time. To avoid premature wear of Openings in the cylinder head where to move the valves and stems are used as light alloys in the manufacture of cylinder head, these holes will provide some guidance G bushes, called guides valve, wear and ride, usually under pressure in the cylinder head.

The guides allow the valve is focused and driven.

External Elements Are all mechanisms that provide control between the crankshaft and the valves. These elements include: camshaft, control elements, and push or seesaws taqua. According to the system, the engines sometimes lack some of these elements.

Camshaft Is an axis that controls the opening of the valves and allows closure. It has spread over a number of the cam, in number equal to the number of valves that have the motor.

Control elements The control system consists of a crankshaft pinion, placed on the end opposite the engine flywheel and the other pinion bearing the camshaft on one end that rotates in solidarity with him.

In diesel engines the gear is used to control movement, usually with the pump nozzles.

Transmission gears When the crankshaft and camshaft are far apart, so it is not possible to connect them directly, you can use a mechanism consisting of a series of gears in between it takes to pass the motion.

Transmission chain As in the previous case, this method is used when the crankshaft and camshaft are well spaced. Here the two are linked by a gear chain.

Is the most used today, although the life of the toothed belt is much lower than that of other systems. If it breaks, the engine will suffer great consequences.

Taqua These are elements which are interposed between the cam and the element that these actions. Its mission is to increase the contact surface between these elements and the cam. The taqua have to be very tough to withstand the pull of the cam and overcome the resistance of the springs of the valves.

Taqua hydraulic The hydraulic taqua operate in an oil bath and are supplied with lubricant circuit of the engine lubrication system.

Pushers or taqua be automatically adjusted to accommodate variations in the length of the valve stem at different temperatures.

Rod pusher There is no bearing on the engine camshaft in the head.

The rods are placed between the rocker and taqua.

They have the task of transmitting the beam motion caused by the cams.

The pusher rods: Or solid or hollow steel or light alloy.

Or dimensions are reduced to a minimum to have a low inertia, while a good resistance to deformation.

Or the side of spherical shape has taqua.

Or the side of the seesaw has a concave shape that allows you to receive the screw adjustment.

Rocker They are levers oscillate around an axis beam axis, which is placed between the valves and the rocker rods or between the valves and cams, in the case of a camshaft in the head.

Rocker swing The engines used in camshaft head. The axis of rotation passes through one end of the seesaw. Is also known as the "semibalancĂ­n. Get direct the movement of camshaft and transmits it to the valve stem through its free end.

Rocker rocker The engines used camshaft side.

The valves are on the head. The axis of rotation passes through the center of the seesaw. One end is the movement of the pusher rod and transmits it to the valve stem on the other end.

Camshaft in the cylinder head (OHC) Is the most used. The operation of the valves is either directly or through an organ. This makes use engines that reach a high number of revolutions, but the command is more delicate.

The drive can be: or direct.

Or indirect.

OHC system of direct drive It is a system that takes a few elements. Used motor revolution.

The transmission between the crankshaft and camshaft is usually done through toothed belt neoprene. Use compression chamber hemispheric type, often used three or four valves per cylinder.

These systems present the problem that is difficult to design cylinder head.

You can carry one or two trees in the butt cam, DOHC call system, if two camshafts.

OHC system of indirect actions This system is almost like the previous one, with the only difference being that the cam shaft actuates a semibalancĂ­n positioned between the cam and the valve spool.

The operation is very similar to the direct drive system.

By turning the cam, push the semibalancĂ­n, which comes into contact with the tail of the valve, causing it to open.

Lubrication Systems Internal combustions engines require lubrication in operation that moving parts slide smoothly over each other. Insufficient lubrication subjects the parts of the engine to metal-to-metal contact, friction, heat build-up, rapid wear often culminating in parts becoming friction welded together eg pistons in their cylinders. Big end bearings seizing up will sometimes lead to a connecting rod breaking and poking out through the crankcase.

Several different types of lubrication systems are used. Simple twostroke engines are lubricated by oil mixed into the fuel or injected into the induction stream as a spray. Early slow-speed stationary and marine engines were lubricated by gravity from small chambers similar to those used on steam engines at the time—with an engine tender refilling these as needed. As engines were adapted for automotive and aircraft use, the need for a high power-to-weight ratio led to increased speeds, higher temperatures, and greater pressure on bearings which in turn required pressure-lubrication for crank bearings and connecting-rod journals. This was provided either by a direct lubrication from a pump, or indirectly by a jet of oil directed at pickup cups on the connecting rod ends which had the advantage of providing higher pressures as the engine speed increased.

Lubrication System: The lubrication system of an automobile is mostly used for collecting, cleaning, cooling and re circulating oil in the engine of vehicle. The main function an automobile lubrication system is to circulate and deliver oil to all the moving parts of an engine in order to lessen friction between surfaces that comes in contact with each other. The lubrication system of an automobile acts to reduce engine wear caused by the friction of its metal parts, as well as to carry off heat

Oil Filters: Oil Filters refer to devices or tools which are used for filtering impurities and dirty residue mixed in the oil that lubricates and greases an internal combustion engine of the vehicle.

Oil Pumps: Oil Pumps are the mechanical devices used for distributing oil to the other moving parts of the engine of an automobile. More specifically, oil pump is a pivotal part of an automobile lubrication system, which is used for dispensing pressurized oil through suction or by applying pressure. In other words, these devices are especially created to raise, compress or transfer fluids to the other important parts of an engine. There are innumerable types of oil pumps like automotive fuel pumps, electric fuel pumps available in the market to suit your desired specifications.

Oil Strainers: Oil Strainers refer to a coarse-mesh metal screen, which are used for trapping foreign and impure particulate matter present in oil. This device makes sure that the foreign matter like lost washers, nuts and bolts does not enter into the oil pump. Oil strainers are generally located between the oil reservoir space and oil pump. These strainers are mostly made of stainless steel, aluminum, cast bronze, brass, chrome, copper, nickel, platinum, plastic, wrought iron, polyvinyl chloride and other materials.

Specific Usage Oils: Specific Usage Oils and Lubricants are of many types which used in various applications that are explained in greater details below:

Air Filter Cleaner: Air Filter Cleaneris specially treated high quality detergent that provides quick, efficient and comfortable cleaning of air filters.

Air Filter Oil: Air Filter Oil is a chemical or a fuel used for tuning and moistening the foam filter element of an air filter.

Compressor Oil: This type of oil is specifically used for lubricating the working parts such as bearings, pistons, rings, cylinders and valves along with the pressurized spaces in a compressor.

Engine Oil: This type of liquid oil acts as a protective lubricating barrier that carries the excessive heat away from moving engine parts. Engine oil is used for cleaning, lubricating as well as cooling of an internal combustion engine.

Gear Oil: Gear Oil also called as motor oil, this type of oil is produced exclusively for lubricating transmissions, transfer cases, and differentials in automobiles. These oils have strong sulfur smell and can be used for enhancing the shifting performance of gearboxes.

Oil Additives: Oil additives are the liquids that are supposedly used for reducing engine wear and enhancing fuel efficiency.

Oil Stabilizer: Oil Stabilizer are the additional components added to the oil in order to enlarge and extend its life and reduces oil

temperature in any type of engine be it gasoline or diesel. Moreover, oil stabilizers also discard noise, leaks as well as overheating in worn gearboxes.

Lubricators and Lubrication Systems Lubricators and lubrication systems are used to apply controlled or metered amounts of lubricant. Applications include compressed air lines, dies, chains, cables, bearings, gears, pumps, spindles and other rotating or moving machine components. Important parameters to consider when specifying lubricators and lubrication systems include capacity, lubrication flow rate, operating pressure, and maximum operating temperature. Capacity refers to the volume of lubricant that the reservoir can hold. The flow rate is the rate at which the lubrication is dispensed. Operating pressure refers to the maximum allowable pressure that the lubricator can be operated.

This specification only applies to pneumatically or hydraulicallyoperated lubricators. Gravity-fed lubricators operate at atmospheric pressure. Maximum operating temperature is the full-required range of ambient operating temperature.

Media choices for lubricators and lubrication systems include dry lubricant, grease, oil, and air and oil. Operation or actuation mechanisms include electric, electrochemical, gravity, hydraulic, manual, mechanical, and pneumatic. Delivery methods for lubricators and lubrication systems include constant level, full flow, metered quantity, mist or fog or micro-fog, and spray. Constant level lubrication systems are designed to keep a constant level of lubrication fluid in a bearing housing or gearbox. They are also referred to as fixed level. Full flow lubricators dispense un-metered liquid lubricant. A metered quantity lubricator dispenses a measured or metered amount of lubrication with each application. These lubricators often require metering valves that dictate the amount of lubrication applied. Features common to lubricators and lubrication systems include adjustable volume, low level safety switches, pressure switches, temperature switches, pressure gauges, temperature gauges, integral filters, and heat exchangers.

The job of the lubrication system is to distribute oil to the moving parts to reduce friction between surfaces which rub against each other.

The lubrication system used by the Wright brothers is quite simple.

An oil pump is located on the bottom of the engine, at the left of the figure. The pump is driven by a worm gear off the main exhaust valve cam shaft. The oil is pumped to the top of the engine, at the right, inside a feed line. Small holes in the feed line allow the oil to drip inside the crankcase. In the figure, we have removed the fuel system and peeled back the covering of the crankcase to see inside.

The oil drips onto the pistons as they move in the cylinders, lubricating the surface between the piston and cylinder. The oil then runs down inside the crankcase to the main bearings holding the crankshaft. Oil is picked up and splashed onto the bearings to lubricate these surfaces. Along the outside of the bottom of the crankcase is a collection tube which gathers up the used oil and returns it to the oil pump to be circulated again. Notice that the brothers did not lubricate the valves and rocker assembly for the combustion chambers.

How Car Cooling Systems Work

Although gasoline engines have improved a lot, they are still not very efficient at turning chemical energy into mechanical power.

Most of the energy in the gasoline (perhaps 70%) is converted into heat, and it is the job of the cooling system to take care of that heat.

In fact, the cooling system on a car driving down the freeway dissipates enough heat to heat two average-sized houses! The primary job of the cooling system is to keep the engine from overheating by transferring this heat to the air, but the cooling system also has several other important jobs.

The engine in your car runs best at a fairly high temperature. When the engine is cold, components wear out faster, and the engine is less efficient and emits more pollution. So another important job of the cooling system is to allow the engine to heat up as quickly as possible, and then to keep the engine at a constant temperature.

Diagram of a cooling system: how the plumbing is connected

Radiator A radiator is a type of heat exchanger. It is designed to transfer heat from the hot coolant that flows through it to the air blown through it by the fan.

Most modern cars use aluminum radiators. These radiators are made by brazing thin aluminum fins to flattened aluminum tubes.

The coolant flows from the inlet to the outlet through many tubes mounted in a parallel arrangement. The fins conduct the heat from the tubes and transfer it to the air flowing through the radiator.

The tubes sometimes have a type of fin inserted into them called a turbulator, which increases the turbulence of the fluid flowing through the tubes. If the fluid flowed very smoothly through the tubes, only the fluid actually touching the tubes would be cooled directly. The amount of heat transferred to the tubes from the fluid running through them depends on the difference in temperature between the tube and the fluid touching it. So if the fluid that is in contact with the tube cools down quickly, less heat will be transferred. By creating turbulence inside the tube, all of the fluid mixes together, keeping the temperature of the fluid touching the

tubes up so that more heat can be extracted, and all of the fluid inside the tube is used effectively.

Picture of radiator showing side tank with cooler Pressure Cap The radiator cap actually increases the boiling point of your coolant by about 45 F (25 C). How does this simple cap do this? The same way a pressure cooker increases the boiling temperature of water.

The cap is actually a pressure release valve, and on cars it is usually set to 15 psi. The boiling point of water increases when the water is placed under pressure.

When the fluid in the cooling system heats up, it expands, causing the pressure to build up. The cap is the only place where this pressure can escape, so the setting of the spring on the cap determines the maximum pressure in the cooling system. When the pressure reaches 15 psi, the pressure pushes the valve open, allowing coolant to escape from the cooling system. This coolant flows through the overflow tube into the bottom of the overflow tank.

This arrangement keeps air out of the system. When the radiator cools back down, a vacuum is created in the cooling system that pulls open another spring loaded valve, sucking water back in from the bottom of the overflow tank to replace the water that was expelled

Thermostat

The thermostat's main job is to allow the engine to heat up quickly, and then to keep the engine at a constant temperature. It does this by regulating the amount of water that goes through the radiator. At low temperatures, the outlet to the radiator is completely blocked -all of the coolant is recirculated back through the engine.

Once the temperature of the coolant rises to between 180 and 195 F (82 - 91 C), the thermostat starts to open, allowing fluid to flow through the radiator. By the time the coolant reaches 200 to 218 F (93 - 103 C), the thermostat is open all the way.

If you ever have the chance to test one, a thermostat is an amazing thing to watch because what it does seems impossible. You can put one in a pot of boiling water on the stove. As it heats up, its valve opens about an inch, apparently by magic! If you'd like to try this yourself, go to a car parts store and buy one for a couple of bucks.

The secret of the thermostat lies in the small cylinder located on the engine-side of the device. This cylinder is filled with a wax that begins to melt at around 180 F (different thermostats open at different temperatures, but 180 F is a common one). A rod connected to the valve presses into this wax. When the wax melts, it expands significantly, pushing the rod out of the cylinder and opening the valve. If you have read How Thermometers Work and done the experiment with the bottle and the straw, you have seen this process in action -- the wax just expands a good bit more because it is changing from a solid to a liquid in addition to expanding from the heat.

This same technique is used in automatic openers for greenhouse vents and skylights. In these devices, the wax melts at a lower temperature.

Fan Like the thermostat, the cooling fan has to be controlled so that it allows the engine to maintain a constant temperature.

Front-wheel drive cars have electric fans because the engine is usually mounted transversely, meaning the output of the

engine points toward the side of the car. The fans are controlled either with a thermostatic switch or by the engine computer, and they turn on when the temperature of the coolant goes above a set point. They turn back off when the temperature drops below that point.

Rear-wheel drive cars with longitudinal engines usually have enginedriven cooling fans. These fans have a thermostatically controlled viscous clutch. This clutch is positioned at the hub of the fan, in the airflow coming through the radiator. This special viscous clutch is much like the viscous coupling sometimes found in all-wheel drive cars.

Water Pump

The water pump is a simple centrifugal pump driven by a belt connected to the crankshaft of the engine. The pump circulates fluid whenever the engine is running.

The water pump uses centrifugal force to send fluid to the outside while it spins, causing fluid to be drawn from the center continuously. The inlet to the pump is located near the center so that fluid returning from the radiator hits the pump vanes. The pump vanes fling the fluid to the outside of the pump, where it can enter the engine.

The fluid leaving the pump flows first through the engine block and cylinder head, then into the radiator and finally back to the pump.

DISTRIBUTION SYSTEM

It is formed by a group of pieces and the auxiliary organizational elements of the motor that act perfectly coordinated to allow realizing the complete cycle of the motor.

And its purpose is open and to close the valves at the suitable moment and following a diagram that will vary according to the type of motor.

ELEMENTS OF THE SYSTEM

Valves, seats, guides and elements of fixation.

Camshaft and elements of control.

Pushers and balance beams.

LUBRICATION SYSTEM To reduce to the minimum the movable wear of a gun of the motor, that takes place by its friction and to avoid its smelting by the excess of heat.

By the interposition of a fine film of lubricant between the metallic pieces or surfaces that could get to make contact with enemy, or he is under pressure or by sliding, avoiding in this way the wearing down of pieces of the motor.

To cool the movable parts and those to which the circuit of refrigeration does not have access. To reduce the coefficient of dynamic friction. Under pressure to cushion and to absorb shocks between the submissive elements. To carry out a cleaning of the impurities.

Cooling System

Combustion temperature 2000 ° C to 2500 º C. Cooling temperature 82 º C to 86 º C. Iron melts at 1370 º C. Disintegrates steel 815 º C. A 50% solution of ethylene glycol and 50% water: Boiling point: 129 º C. Frostbite: -36.5 ° C.

Its purpose is to remove sufficient heat to keep the working temperature range of the engine, which makes the engine work efficiently.

its aim is to prevent the iron and steel melts disintegrates due to the high temperatures reached.

Prevent the oil film is too thin and lose their properties.

Compensate the temperature of the elements that absorb the heat of combustion.

CONCLUSION

All car bullets using the same systems as the function of the vehicle is transporting people from one place to another car also contains accessory uses any car with the only difference is the make and model in addition to that, too modern cars now have are more electrical systems and sensors.

It also functions as the transmission clutch brake system lubrication system and other systems have the same function in the car

Bibliography e-silk

Injection Book book of mechanical and wikipedia 1