Differential (Mechanical Device)

Differential Differential (mechanical device) device)

ZF  Differential.   Differential. The drive shaft shaft enters from the front and the driven axles run left left and right.

A spur gear differential differential constructed by engaging the planet gears of two co-axial  two co-axial  epicyclic  epicyclic gear trains. The casing is the carrier for  this planetary gear train.

A  differential  is a  gear train with train  with three shafts that has the property that the angular velocity of one shaft is the average of the angular velocities of the others, or a fixed multiple of that average.

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Ove Overvi rview Car differential of a Škoda a  Škoda 422

In  In   automobiles  automobiles   and other wheeled vehicles, the differential allows the outer drive wheel to rotate faster than the inner inner drive wheel wheel during a turn. This is necessary necessary when the vehicle turns, making the wheel that is traveling around around theoutside theoutside of the the turnin turningg curv curvee roll roll farthe artherr and faster faster than the other. The average of the rotational speed of the the two two drivin drivingg whee wheels ls equal equalss theinput rotat rotatio ionalspee nalspeedd of the drive shaft. An increase in the speed of one wheel is balanced by a decrease in the speed of the other. When used in this way, a differential couples the input shaft (or prop shaft) to the pinion the  pinion,, which in turn runs on the ring the ring gear of gear of the differential. This also works as reduction gearing. On rear wheel drive vehicles the differential may may conne connect ct to half-s half-shaf hafts ts insi inside de an axle axle housi housing, ng, or drive drive Automotive differ differential: ential: The drive gear 2 is mounted on the carshafts thatconn that connect ect to the rear driving driving wheels wheels.. Front Front wheel wheel rier 5 which supports the planetary bevel gears 4 which engage shafts drive vehicles tend to have the pinion on the end of the the driven bevel gears 3 attached to the axles 1. main-shaft of the gearbox and the differential is enclosed 1

2 HISTORY 

2 in the same housing as the gearbox. There are individual drive-shafts to each wheel. A differential consists of one input, the drive shaft, and two outputs which are the two drive wheels, however the rotation of the drive wheels are coupled to each other by their connection to the roadway. Under normal conditions, with small tire slip, the ratio of the speeds of the two driving wheels is defined by the ratio of the radii of the paths around which the two wheels are rolling, which in turn is determined by the track-width of the vehicle (the distance between the driving wheels) and the radius of the turn.

Non-automotive uses of differentials include performing analog arithmetic. Two of the differential’s three shafts are made to rotate through angles that represent (are proportional to) two numbers, and the angle of the third shaft’s rotation represents the sum or difference of the South-pointing chariot  model  two input numbers. The earliest known use of a differential gear is in the Antikythera mechanism, circa 80 BCE, as a   non-magnetic, mechanized compass. Some which used a differential gear to control a small sphere such chariots may have used differential gears. representing the moon from the difference between the 658, 666 AD: two Chinese Buddhist monks and ensun and moon position pointers. The ball was painted gineers create south-pointing chariots for Emperor black and white in hemispheres, and graphically showed [1] Tenji of Japan. the phase of the moon at a particular point in time. See also the Chinese South-pointing chariot. An equation  1027, 1107 AD: Documented Chinese reproducclock that used a differential for addition was made in tions of the south-pointing chariot by Yan Su and 1720. In the 20th Century, large assemblies of many difthen Wu Deren, which described in detail the meferentials were used as analog computers, calculating, for chanical functions and gear ratios of the device example, the direction in which a gun should be aimed. much more so than earlier Chinese records. However, the development of electronic digital comput1720: Joseph Williamson uses a differential gear in ers has made these uses of differentials obsolete. Military a clock. uses may still exist. See Electromagnetic pulse. Practically all the differentials that are now made are used in   1810: Rudolph Ackermann  of Germany invents automobiles and similar vehicles. a four-wheel steering system for carriages, which some later writers mistakenly report as a differential. •

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History

There are many claims to the invention of the differential gear, but it is possible that it was known, at least in some places, in ancient times. Some historical milestones of the differential include: •

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  100 BC–70 BC: The Antikythera mechanism has been dated to this period. It was discovered in 1902 on a shipwreck by   sponge divers, and modern research suggests that it used a differential gear to determine the angle between the ecliptic positions of the Sun and Moon, and thus the phase of the Moon.[1][2]   30 BC–20 BC: Differential gear systems possibly used in China

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227–239 AD: Ma Jun from the Kingdom of Wei in China invents the first historically verifiable  southpointing chariot, which provided cardinal direction

 1827: modern automotive differential patented by watchmaker Onésiphore Pecqueur (1792–1852) of the  Conservatoire National des Arts et Métiers in France for use on a steam wagon.[3][4]   1832: Richard Roberts of England patents “gear of compensation”, a differential for road locomotives.   1874:  Aveling and Porter of Rochester, Kent list a crane locomotive in their catalogue fitted with their patent differential gear on the rear axle. [5]   1876:  James Starley of Coventry invents chain-drive differential for use on bicycles; invention later used on automobiles by Karl Benz. 1897: first use of differential on an Australian steam car by David Shearer.   1958:  Vernon Gleasman patents the  Torsen dualdrive differential, a type of  limited-slip differential that relies solely on the action of gearing, instead of a combination of clutches and gears.

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Epicyclic differential

displaced axially, such that they mesh only for the part of their length between the two spur gears, and rotate in opposite directions. The remaining length of a given pinion meshes with the nearer spur gear on its axle. Therefore, each pinion couples that spur gear to the other pinion, and in turn, the other spur gear, so that when the drive shaft rotates the carrier, its relationship to the gears for the individual wheel axles is the same as that in a bevel-gear differential.

A spur gear differential is constructed from two identical coaxial epicyclic gear trains assembled with a single carrier such that their planet gears are engaged. This forms a planetary gear train with a fixed carrier train ratio  R = 1. Epicyclicgearing is usedhereto apportion torque asymmetrically. −

The input shaft is the green hollow one, the yellow is the low torque output, and the pink is the high torque output. The force applied in the yellow and the pink gears is the same, but since the arm of the pink one is 2× to 3× as big, the torque will be 2× to 3× as high.

An epicyclic differential can use epicyclic gearing to split and apportion torque asymmetrically between the front and rear axles. An epicyclic differential is at the heart of the Toyota Prius automotive drive train, where it interconnects the engine, motor-generators, and the drive wheels (which have a second differential for splitting torque as usual). It has the advantage of being relatively compact along the length of its axis (that is, the sun gear shaft). Epicyclic gears are also called planetary gears because the axes of the planet gears revolve around the common axis of the sun and ring gears that they mesh with and roll between. In the image, the yellow shaft carries the sun gear which is almost hidden. The blue gears are called planet gears and the pink gear is the ring gear or annulus.

In this case, the fundamental formula for the planetary gear train yields, ωs

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ωa

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 ω c  ω c

=

1,

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or

ωc  =

1 (ω  +  ω ). 2 s

a

Thus, the angular velocity of the carrier of a spur gear differential is the average of the angular velocities of the sun and annular gears.[6] In discussing the spur gear differential, the use of the term annular gear   is a convenient way to distinguish the sun gears of thetwo epicyclic gear trains. Thesecond sun gear serves the same purpose as the annular gear of a simple planetary gear train, but clearly does not have the internal gear mate that is typical of an annular gear.

Ring gears are also used in starter motors.

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Non-automotive applications

Spur-gear differential

Chinese south-pointing chariots may also have been very early applications of differentials. The chariot had a This is another type of differential that was used in some pointer which constantly pointed to the south, no matearly automobiles, more recently the Oldsmobile Toron- ter how the chariot turned as it travelled. It could thereado, as well as other non-automotive applications. It con- fore be used as a type of  compass. It is widely thought sists of spur gears only. that a differential mechanism responded to any difference A spur-gear differential has two equal-sized spur gears, between the speeds of rotation of the two wheels of the one for each half-shaft, with a space between them. In- chariot, and turned the pointer appropriately. However, stead of the Bevel gear, also known as a miter gear, as- the mechanism was not precise enough, and, after a few sembly (the “spider”) at the centre of the differential, miles of travel, thedial could have very well been pointing there is a rotating carrier on the same axis as the two in the complete opposite direction. shafts. Torque from a prime mover or transmission, such The earliest definitely verified use of a differential was in as the drive shaft of a car, rotates this carrier. a clock made by Joseph Williamson in 1720. It employed Mounted in this carrier are one or more pairs of identical pinions, generally longer than their diameters, and typically smaller than the spur gears on the individual half-shafts. Each pinion pair rotates freely on pins supported by the carrier. Furthermore, the pinion pairs are

a differential to add the  equation of time to  local mean time, as determined by the clock mechanism, to produce solartime, which would have been the same as the reading of a sundial. During the 18th Century, sundials were considered to show the “correct” time, so an ordinary clock

6 APPLICATION TO VEHICLES 

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to use their readings to obtain clock time. In the first half of the twentieth century, mechanical analog computers, called differential analyzers, were constructed that used differential gear trains to perform addition and subtraction. The U.S. Navy Mk.1 gun fire control computer used about 160 differentials of the bevel-gear type. A differential gear train can be used to allow a difference between two input axles. Mills often used such gears to apply torque in the required axis. Differentials are also used in this way in watchmaking to link two separate regulating systems with the aim of averaging out errors. Greubel Forsey use a differential to link two double tourbillon systems in their Quadruple Differential Tourbillon. Differential used to control the take-up reel of a paper tape reader  made by Tally circa 1962. The bevel gears spin freely on their  shafts, unless a brake shoe stops the left gear. This causes the  planet gear to drive the output shaft at half the speed of the driven  gear on the right.

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Application to vehicles

Video explaining the purpose and the principle of a differential  (8 minutes, with subtitles).

A vehicle with two drive wheels has the problem that when it turns a corner the drive wheels must rotate at different speeds to maintain traction. The automotive differential is designed to drive a pair of wheels 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. Planetary differential used to drive a chart recorder  circa 1961. The motors drive the sun and annular gears, while the output is taken from the planet gear carrier. This gives 3 different speeds depending on which motors are on.

When cornering, the inner wheel travels a shorter distance than the outer wheel, so without a differential either the inner wheel rotates too quickly or the outer wheel rotates too slowly, which results in difficult and unpredictable handling, damage to tires and roads, and strain on (or possible failure of) the drivetrain.

would frequently have to be readjusted, even if it worked perfectly, because of seasonal variations in the equation of time. Williamson’s and other equation clocks showed sundial time without needing readjustment. Nowadays, we consider clocks to be “correct” and sundials usually incorrect, so many sundials carry instructions about how

In rear-wheel drive automobiles the central drive shaft (or prop shaft) engages the differential through a  hypoid gear(ring and pinion). The ring gear is mounted on the carrier of the planetary chain that forms the differential. This hypoid gear is a bevel gear that changes the direction of the drive rotation.

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Hypoid gear pair that connects an automotive drive shaft to a differential.

If the left sun gear (red) encounters resistance, the planet gear  (green) spins as well as revolving, allowing the left sun gear to slow down, with an equal speeding up of the right sun gear (yellow).

right wheel making 8 rotations.

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Functional description

The rotation of the ring gear is always the average of the rotations of the side sun gears. This is why if the driven roadwheels are lifted clear of the ground with the engine off, and the drive shaft is held (say, leaving the transmission in gear preventing the ring gear from turning inside the differential), manually rotating one driven roadwheel causes the opposite roadwheel 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 minutemovements necessary to compensate for slight differences in wheel diameter, undulations in the road which make for a longer or shorter wheel path, etc.

Input torque is applied to the ring gear (blue), which turns the entire carrier (blue). The carrier is connected to both sun gears (red and yellow) only through the planet gear (green). Torque is transmitted to the sun gears through the planet gear. The planet   gear revolves around the axis of the carrier, driving the sun gears. If the resistance at both wheels is equal, the planet gear revolves without spinning about its own axis, and both wheels turn at the same rate.

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Loss of traction

One undesirable side effect of an open differential is that it can limit traction under less than ideal conditions. The amount of traction 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 following description of a differential applies to a tra- the gradient of the road, the vehicle’s momentum, and so ditional rear-wheel-drive car or truck with an open or lim- on. ited slip differential combined with a reduction gearset The torque applied to each driving  wheel is the result of using bevel gears (these are not strictly necessary – see the engine, transmission, and drive axle applying a twistspur-gear differential): ing force against the resistance of the traction at that roadThus, 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 farther to travel, and the right wheel will make fewer rotations as it has less distance to travel. The sun gears (which drive the axle half-shafts) will rotate at different speeds relative to the ring gear (one faster, one slower) by, say, 2 full turns each (4 full turns relative to each other), resulting in the left wheel making 12 rotations, and the

wheel. In lower gears, and thus at lower speeds, and unless the load is exceptionally high, the drivetrain can supply as much torque as necessary, so the limiting factor becomes the traction under each wheel. It is therefore convenient to define traction as the amount of force that can be transmitted between the  tire and the road surface before the wheel starts to slip. If the torque applied to one of the drive wheels exceeds the threshold of traction, then that wheel will spin, and thus provide torque only

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9 ACTIVE DIFFERENTIALS 

at the other driven wheel equal to the sliding friction at the slipping wheel. The reduced net traction may still be enough to propel the vehicle slowly. An open (non-locking or otherwise traction-aided) differential always supplies close to equal torque to each side. To illustrate how this can limit torque applied to the driving wheels, imagine a simple  rear-wheel drive  vehicle, with one rear roadwheel on asphalt with good grip, and the other on a patch of slippery ice. It takes very little torque to spin the side on slippery ice, and because a differential splits torque equally to each side, the torque that is applied to the side that is on asphalt is limited to this amount.[7][8] Based on the load, gradient, etc, the vehicle requires a A cutaway drawing of a car’s rear axle , showing the crown wheel  and  pinion of the final drive, and the smaller differential gears certain amount of torque applied to the drive wheels to move forward. Since an open differential limits total torque applied to both drive wheels to the amount used by the lower traction wheel multiplied by 2, when one wheel is on a slippery surface, the total torque applied to the driving wheels may be lower than the minimum torque required for vehicle propulsion.[9] A proposed alternate way to distribute power to the wheels, is to use the concept of a   gearless  differential, about which a review has been reported by Provatidis, [10] but the various configurations seem to correspond either to the “sliding pins and cams” type, such as the  ZF  B70 available on early VWs, or are a variation of the  ball differential. Many newer vehicles feature traction control, which partially mitigates the poor traction characteristics of an A cutaway view of an automotive final drive unit which contains open differential by using the  anti-lock braking system the differential  to limit or stop the slippage of the low traction wheel, increasing the torque that can be applied to the opposite wheel. While not as effective as a traction-aided differen- 9 Active differentials tial, it is better than a simple mechanical open differential with no traction assistance. A relatively new technology is the electronically controlled 'active differential'. An   electronic control unit (ECU) uses inputs from multiple sensors, including yaw rate, steering input angle, and lateral acceleration—and adjusts the distribution of torque to compensate for undesirable handling behaviours like understeer. Active differentials used to play a large role in the  World Rally Championship, but in the 2006 season the  FIA has limited the use of active differentials to only those drivers who have not competed in the World Rally Championship in the last five years. Fully integrated active differentials are used on the Ferrari F430, Mitsubishi Lancer Evolution, and on the rear wheels in the  Acura RL. A version manufactured by ZF  is also being offered on the B8 chassis  Audi S4 and Audi A4.[11] The Volkswagen Golf GTI Mk7 in Performance trim also has an electronically controlled frontaxle transverse differential lock, also known as VAQ. [12] ARB, air-locking differential 

The second constraint of the differential is passive—it is actuated by the friction kinematics chain through the ground. The difference in torque on the roadwheels and

7 tires (caused by turns or bumpy ground) drives the second degree of freedom, (overcoming the torque of inner friction) to equalise the driving torque on the tires. The sensitivity of the differential depends on the inner friction through the second degree of freedom. All of the differentials (so called “active” and “passive”) use clutches and brakes for restricting the second degree of freedom, so all suffer from the same disadvantage—decreased sensitivity to a dynamically changing environment. The sensitivity of the ECU controlled differential is also limited by the time delay caused by sensors and the response time of the actuators.

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Automobiles without differentials

Although most automobiles in the developed world use differentials there are a few that do not. Several different types exist: •

by its freewheel. Thus, while turning, the vehicle had only one driving wheel. Driving in reverse is impossible as is engine braking due to the freewheels.

 Race cars and trucks in certain classes. Drag racing is done in a straight line (and often on a prepared surface), which obviates the need for a differential. A spool is used to make a solid connection between both drive wheels, which is simpler and less likely to break under very heavy acceleration. Racing on dirt or mud tracks also allows the use of spools, because the loose surface gives way while cornering. NASCAR mandates the use of spools in their cars, which does cause axle wind-up, and degrades handling in turns. Other forms of racing without differentials include tractor pulling, mud bogging, and other 4x4 motorsports where differential action is not needed.  Vehicles with a single driving wheel. Besides motorcycles, which are generally not classified as automobiles, this group includes most three-wheeled cars. These were quite common in Europe in the mid-20th Century, but have now become rare there. They are still common in some areas of the developing world, such as India. Some early four-wheeled cars also had only one driving wheel to avoid the need for a differential. However, this arrangement led to many problems. The system was unbalanced, the driving wheel would easily spin, etc.. Because of these problems, few such vehicles were made.  Vehicles using two freewheels. A freewheel, as used on a pedal bicycle for example, allows a road wheel to rotate faster than the mechanism that drives it, allowing a cyclist to stop pedalling while going downhill. Some early automobiles had the engine driving two freewheels, one for each driving road wheel. When the vehicle turned, the engine would continue to drive the wheel on the inside of the curve, but the wheel on the outside was permitted to rotate faster

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 Vehicles with two  continuously variable transmissions, such as the   DAF Daffodil. The Daffodil, and other similar vehicles which were made until the 1970s by the Dutch company  DAF, had a type of transmission that used an arrangement of belts and pulleys to provide an infinite number of gear ratios. The engine drove two separate transmissions which ran the two driving wheels. When the vehicle turned, the two wheels could rotate at different speeds, making the two transmissions shift to different gear ratios, thus functionally substituting for a differential. The slower moving wheel received more driving torque than the faster one, so the system had limited-slip characteristics. The duplication also provided redundancy. If one belt broke, the vehicle could still be driven.  Light vehicles with closely spaced rear wheels, such as the Isetta and Opperman Unicar, or very low mass vehicles.   Vehicles with separate motors for the driving wheels.   Electric cars   can have a separate motor for each driving wheel, eliminating the need for a differential, but usually with some form of gearing at each motor to get the large wheel torques necessary. A multi-motor electric vehicle such as the Dual Motor Tesla Model S  can electronically control the power distribution between the motors on a millisecond scale, in this case acting as a centre differential where open differentials are still employed left-to-right. [13]

See also

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 Ball differential

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 Equation clock

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  Hermann Aron#Electricity meters

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 Limited slip differential

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 Locking differential

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 Torque vectoring

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  Whippletree (mechanism)

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 Tests on rollers

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References

[1] Wright, M. T. (2007). “The Antikythera Mechanism reconsidered” (PDF).  Interdisciplinary science reviews . 32 (1). Retrieved 20 May 2014.

13 EXTERNAL LINKS 

8 [2] Presentation given to the NHRF in Athens, 6 March 2007 – M. T. Wright [3] Britannica Online [4]   “History of the Automobile”. General Motors Canada. Retrieved 2011-01-09. [5] Preston, J.M. (1987), Aveling & Porter, Ltd. Rochester., North Kent Books, pp. 13–14, ISBN 0-948305-03-7 includes sectional drawing. [6] J. J. Uicker, G. R. Pennock and J. E. Shigley, 2003, Theory of Machines and Mechanisms,  Oxford University Press, New York. [7] Bonnick, Allan. (2001)  “Automotive Computer Controlled Systems p. 22 [8] Bonnick, Allan. (2008). “Automotive Science and Mathematics p. 123 [9] Chocholek, S. E. (1988) “The development of a differential for the improvement of traction control” [10] Provatidis, Christopher, G. (2003). “A critical presentation of Tsiriggakis’ gearless differential”.  Mobility & Vehicles Mechanics  29 (4): 25–46; also: http://users.ntua.gr/ cprovat/index_en.htm [11]  “ZF Press release”. Zf.com. Retrieved 2011-01-09. [12]  “Golf VII GTI”. pistonheads.com. Retrieved 2013-0624. [13] Davies, Alex(2014-10-10). “The Model D Is Tesla’sMost Powerful Car Ever, Plus Autopilot”.   Wired.com. Retrieved 2014-10-11. Musk said the added efficiency is thanks to the electronic system that will shift power between the front and rear motors from one millisecond to the next, so each is always operating at its most efficient point

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External links A video of a 3D model of an open differential An article explaining differentials with illustrations and video   “Around the Corner”   (1937), a   Jam Handy film made for Chevrolet explaining very clearly how an open differential works.

 Popular Science, May 1946,  How Your Car Turns Corners , a large article with numerous illustrations on how differentials work.

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Text and image sources, contributors, and licenses

14.1 •

Text

 Differential (mechanical device)  Source:  https://en.wikipedia.org/wiki/Differential_(mechanical_device)?oldid=763136533  Contribu-

tors:  Robert Merkel, Jkominek, Josh Grosse, Heron, Michael Hardy, DopefishJustin, Kku, Wapcaplet, Iluvcapra, CesarB, Ahoerstemeier, Mac, Angela, Glenn, Silthor~enwiki, Samw, Smack, Raven in Orbit, GRAHAMUK, Emperorbma, Hawthorn, Dino, Dysprosia, Greglocock, Ed g2s, Morven, Finlay McWalter, Twang, Robbot, Kadin2048, Nurg, Praveenc, Carnildo, Geraint Bevan, Smjg, BenFrantzDale, RealGrouchy, Khalid hassani, Brockert, Rogerzilla, Sfoskett, Sonett72, Corti, ArnoldReinhold, LindsayH, Bender235, Calamarain, Mattisgoo, Cacophony, Bdoserror, Harald Hansen, Elipongo, Hooperbloob, Alansohn, The RedBurn, Cjthellama, Sobolewski, Ronark, Dennis Bratland, Postrach, A D Monroe III, Unixxx, Bobrayner, VsevolodSipakov, Dolphonia, Mitsukai, Bgwhite, YurikBot, StuffOfInterest, RussBot, Sparky132, Supasheep, Hellbus, RadioFan, Hydrargyrum, DarkPhoenix, Voidxor, Natkeeran, Bota47, 1717, Knotnic, Clayhalliwell, Chrishmt0423, Simxp, Aqn, Groyolo, Kayotic, Attilios, KnightRider~enwiki, SmackBot, Cavenba, David.Mestel, Jagged 85, Scott Paeth, UrsaFoot, Cs-wolves, Chris the speller, Colonies Chris, Pianohacker, Ianmacm, DMacks, Dmh~enwiki, Rklawton, Nafango2, Nagle, Hvn0413, Dl2000, Beefyt, Hu12, D'lin, Frank Lofaro Jr., Mikiemike, CmdrObot, Van helsing, WeggeBot, Cydebot, Karimarie, EdiOnjales, Alucard (Dr.), Pjvpjv, RB30DE, Gamebm, EdJogg, Cbrucker, Rps, Rjathar, Salgueiro~enwiki, SkoreKeep, Kadros~enwiki, Lklundin, IanOsgood, Nikevich, Choppingmall, Pgn674, Gun Powder Ma, Sigmundg, Keith D, R'n'B, CommonsDelinker, Mcwilshire, Rlsheehan, Rizan, Gem-fanat, NewEnglandYankee, Bigdumbdinosaur, Totsugeki, DorganBot, Idioma-bot, VolkovBot, Thomas.W, Philip Trueman, Af648, Rei-bot, Turm, Ferengi, DesmondW, Geometry guy, Andy Dingley, Typ932, Unknown Unknowns, PericlesofAthens, SieBot, WereSpielChequers, The verymodel of a minor general, Sound-Mind, Quest for Truth, Marquetry28, Fratrep, Svick, Smellsofbikes, Mild Bill Hiccup, Jonnogibbo, CounterVandalismBot, Fatsamsgrandslam, Jusdafax, Three-quarter-ten, MechEngr2884, ChrisHodgesUK, XLinkBot, Wikiuser100, Little M ountain 5, NellieBly, ZooFari, MystBot, Addbot, Springee, M.nelson, Ronhjones, Mephiston999, NjardarBot, Glane23, Oldmountains, AnnaFrance, Lightbot, Ralf Roletschek, Luckas-bot, Yobot, Amirobot, PMLawrence, Underthedial, AnomieBOT, Götz, Jim1138, Piano non troppo, Materialscientist, Another Stickler, Xqbot, Mario972, Douglas W. Jones, Rudimae, Ravyr, FrescoBot, Tobby72, BigMikeSpd, Teotocopulos, Craig Pemberton, Citation bot 1, Dana60Cummins, MondalorBot, White Shadows, CProvat, Begoon, Leelee456789123, Tayler1995, RjwilmsiBot, Jackehammond, Becritical, EmausBot, Dcirovic, Ὁ οἶστρος, DOwenWilliams, ClueBot NG, Smtchahal, Frietjes, Widr, Sasakubo1717, Cather B, Helpful Pixie Bot, Martin of Sheffield, BG19bot, Vagobot, Prof McCarthy, Hz.tiang, Mark Arsten, Romit1sharma, Sh4nce21, BattyBot, ChrisGualtieri, Hmainsbot1, OldTimeNESter, CsDix, Anderoo165, Eric Corbett, Esetzeko, Narky Blert, Crystallizedcarbon, Maths314, Buya619, Espr14, Bender the Bot, Alcedonia, Unknowntouncertain and Anonymous: 260

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Images

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 File:Around_the_Corner_(1937)_24fps_selection.webm   Source:    https://upload.wikimedia.org/wikipedia/commons/3/3e/Around_

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ZF_Differentialgetriebe.jpg License:  CC BY-SA 3.0  Contributors:   Own work Original artist:   Aconcagua (talk) •

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tributors:  Own work  Original artist:  Douglas W. Jones   File:Commons-logo.svg  Source:   https://upload.wikimedia.org/wikipedia/en/4/4a/Commons-logo.svg License:  PD  Contributors:  ?  Original artist:  ?  File:Differential_(Manual_of_Driving_and_Maintenance).jpg   Source:    https://upload.wikimedia.org/wikipedia/commons/3/3b/ Differential_%28Manual_of_Driving_and_Maintenance%29.jpg License:    Public domain   Contributors:   Scan from (1937)  Manual of  Driving and Maintenance for Mechanical Vehicles (Wheeled), HMSO Original artist:   Andy Dingley (scanner)   File:Differential_free.png  Source:  https://upload.wikimedia.org/wikipedia/commons/6/61/Differential_free.png License:  CC-BY-SA3.0 Contributors:   en:Image:Differential_free.png. This image was originally uploaded on en.wikipedia.org by user:  Wapcaplet.  Original  artist:   Wapcaplet   File:Differential_locked-2.png   Source:    https://upload.wikimedia.org/wikipedia/commons/5/5a/Differential_locked-2.png   License:  CC-BY-SA-3.0 Contributors:    Differential_locked.png  Original artist:   Differential_locked.png: Wapcaplet   File:Differentialgetriebe2.jpg   Source:  https://upload.wikimedia.org/wikipedia/commons/f/fe/Differentialgetriebe2.jpg  License:  CCBY-SA-3.0 Contributors:  Own work Original artist:  DrJunge   File:Epicyclic_gear_ratios.png Source:  https://upload.wikimedia.org/wikipedia/commons/d/d5/Epicyclic_gear_ratios.png License:  CCBY-SA-3.0 Contributors:  ?  Original artist:  ?   File:Folder_Hexagonal_Icon.svg Source:  https://upload.wikimedia.org/wikipedia/en/4/48/Folder_Hexagonal_Icon.svg License:   Cc-bysa-3.0 Contributors:  ?  Original artist:  ?   File:Portal-puzzle.svg Source:   https://upload.wikimedia.org/wikipedia/en/f/fd/Portal-puzzle.svg License:  Public domain  Contributors:  ? Original artist:  ?

14 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES 

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  File:Question_book-new.svg   Source:   https://upload.wikimedia.org/wikipedia/en/9/99/Question_book-new.svg  License:   Cc-by-sa-3.0

Contributors:  Created from scratch in Adobe Illustrator. Based on Image:Question book.png created by User:Equazcion  Original artist:  Tkgd2007 •

  File:South-pointing_chariot_(Science_Museum_model).jpg   Source: 

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  File:Sprocket35b.jpg Source:   https://upload.wikimedia.org/wikipedia/commons/d/d1/Sprocket35b.jpg License:  Public domain  Contrib-

  https://upload.wikimedia.org/wikipedia/commons/c/ce/ South-pointing_chariot_%28Science_Museum_model%29.jpg License:  CC BY 3.0 Contributors:  Own work Original artist:   Andy Dingley

utors:  Own work Original artist:   Hapesoft •

 File:Spur_gear_differential_(Manual_of_Driving_and_Maintenance).jpg   Source: 

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  File:Transmission_diagram.JPG  Source:  https://upload.wikimedia.org/wikipedia/commons/2/27/Transmission_diagram.JPG License: 

  https://upload.wikimedia.org/wikipedia/ commons/7/75/Spur_gear_differential_%28Manual_of_Driving_and_Maintenance%29.jpg License:  Public domain Contributors:   Scan from (1937) Manual of Driving and Maintenance for Mechanical Vehicles (Wheeled), HMSO Original artist:   Andy Dingley (scanner) CC-BY-SA-3.0 Contributors:  No machine-readable source provided. Own work assumed (based on copyright claims). Original artist:  No machine-readable author provided. 17177 assumed (based on copyright claims).

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