Dierential (mechanical device)

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

A spur gear dierential constructed by engaging the planet gears

of two co-axial epicyclic gear trains. The casing is the carrier for
this planetary gear train.

A dierential is a gear 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 xed
multiple of that average.

1 Overview
Car dierential of a koda 422

In automobiles and other wheeled vehicles, the dier-

ential allows the outer drive wheel to rotate faster than
the inner drive wheel during a turn. This is necessary
when the vehicle turns, making the wheel that is travel-
ing around the outside of the turning curve roll farther and
faster than the other. The average of the rotational speed
of the two driving wheels equals the input rotational speed
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 dierential couples the input
shaft (or prop shaft) to the pinion, which in turn runs on
the ring gear of the dierential. This also works as reduc-
tion gearing. On rear wheel drive vehicles the dierential
Automotive dierential: The drive gear 2 is mounted on the car-
may connect to half-shafts inside an axle housing, or drive
rier 5 which supports the planetary bevel gears 4 which engage shafts that connect to the rear driving wheels. Front wheel
the driven bevel gears 3 attached to the axles 1. drive vehicles tend to have the pinion on the end of the
main-shaft of the gearbox and the dierential is enclosed

1
2 2 HISTORY

in the same housing as the gearbox. There are individual

drive-shafts to each wheel.
A dierential 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 condi-
tions, with small tire slip, the ratio of the speeds of the
two driving wheels is dened 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 dierentials include performing
analog arithmetic. Two of the dierentials three shafts
are made to rotate through angles that represent (are pro-
portional to) two numbers, and the angle of the third
shafts rotation represents the sum or dierence of the South-pointing chariot model
two input numbers. The earliest known use of a dieren-
tial gear is in the Antikythera mechanism, circa 80 BCE, as a non-magnetic, mechanized compass. Some
which used a dierential gear to control a small sphere such chariots may have used dierential gears.
representing the moon from the dierence between the
sun and moon position pointers. The ball was painted 658, 666 AD: two Chinese Buddhist monks and en-
black and white in hemispheres, and graphically showed gineers create south-pointing chariots for Emperor
the phase of the moon at a particular point in time.[1] Tenji of Japan.
See also the Chinese South-pointing chariot. An equation 1027, 1107 AD: Documented Chinese reproduc-
clock that used a dierential for addition was made in tions of the south-pointing chariot by Yan Su and
1720. In the 20th Century, large assemblies of many dif- then Wu Deren, which described in detail the me-
ferentials 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 comput-
ers has made these uses of dierentials obsolete. Military 1720: Joseph Williamson uses a dierential gear in
uses may still exist. See Electromagnetic pulse. Practi- a clock.
cally all the dierentials 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 dieren-
tial.
2 History
1827: modern automotive dierential patented by
watchmaker Onsiphore Pecqueur (17921852) of
There are many claims to the invention of the dierential the Conservatoire National des Arts et Mtiers in
gear, but it is possible that it was known, at least in some France for use on a steam wagon.[3][4]
places, in ancient times. Some historical milestones of
the dierential include: 1832: Richard Roberts of England patents gear of
compensation, a dierential for road locomotives.
100 BC70 BC: The Antikythera mechanism has 1874: Aveling and Porter of Rochester, Kent list a
been dated to this period. It was discovered in 1902 crane locomotive in their catalogue tted with their
on a shipwreck by sponge divers, and modern re- patent dierential gear on the rear axle.[5]
search suggests that it used a dierential gear to
1876: James Starley of Coventry invents chain-drive
determine the angle between the ecliptic positions
dierential for use on bicycles; invention later used
of the Sun and Moon, and thus the phase of the
on automobiles by Karl Benz.
Moon.[1][2]
1897: rst use of dierential on an Australian steam
30 BC20 BC: Dierential gear systems possibly car by David Shearer.
used in China
1958: Vernon Gleasman patents the Torsen dual-
227239 AD: Ma Jun from the Kingdom of Wei in drive dierential, a type of limited-slip dierential
China invents the rst historically veriable south- that relies solely on the action of gearing, instead of
pointing chariot, which provided cardinal direction a combination of clutches and gears.
 3

3 Epicyclic dierential displaced axially, such that they mesh only for the part of
their length between the two spur gears, and rotate in op-
posite 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 in-
dividual wheel axles is the same as that in a bevel-gear
dierential.
A spur gear dierential is constructed from two identical
coaxial epicyclic gear trains assembled with a single car-
rier such that their planet gears are engaged. This forms
a planetary gear train with a xed carrier train ratio R =
Epicyclic gearing is used here to apportion torque asymmetrically. 1.
The input shaft is the green hollow one, the yellow is the low
In this case, the fundamental formula for the planetary
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
gear train yields,
arm of the pink one is 2 to 3 as big, the torque will be 2 to
3 as high.
s c
= 1,
An epicyclic dierential can use epicyclic gearing to split a c
and apportion torque asymmetrically between the front or
and rear axles. An epicyclic dierential is at the heart
of the Toyota Prius automotive drive train, where it in-
terconnects the engine, motor-generators, and the drive 1
c = (s + a ).
wheels (which have a second dierential for splitting 2
torque as usual). It has the advantage of being relatively Thus, the angular velocity of the carrier of a spur gear
compact along the length of its axis (that is, the sun gear dierential is the average of the angular velocities of the
shaft). sun and annular gears.[6]
Epicyclic gears are also called planetary gears because the In discussing the spur gear dierential, the use of the term
axes of the planet gears revolve around the common axis annular gear is a convenient way to distinguish the sun
of the sun and ring gears that they mesh with and roll gears of the two epicyclic gear trains. The second sun gear
between. In the image, the yellow shaft carries the sun serves the same purpose as the annular gear of a simple
gear which is almost hidden. The blue gears are called planetary gear train, but clearly does not have the internal
planet gears and the pink gear is the ring gear or annulus. gear mate that is typical of an annular gear.
Ring gears are also used in starter motors.

5 Non-automotive applications
4 Spur-gear dierential
Chinese south-pointing chariots may also have been very
early applications of dierentials. The chariot had a
This is another type of dierential that was used in some pointer which constantly pointed to the south, no mat-
early automobiles, more recently the Oldsmobile Toron-
ter how the chariot turned as it travelled. It could there-
ado, 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 dierential mechanism responded to any dierence
A spur-gear dierential 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 dierential, miles of travel, the dial 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 denitely veried use of a dierential 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 iden- a dierential to add the equation of time to local mean
tical pinions, generally longer than their diameters, and time, as determined by the clock mechanism, to produce
typically smaller than the spur gears on the individual solar time, which would have been the same as the reading
half-shafts. Each pinion pair rotates freely on pins sup- of a sundial. During the 18th Century, sundials were con-
ported by the carrier. Furthermore, the pinion pairs are sidered to show the correct time, so an ordinary clock
4 6 APPLICATION TO VEHICLES

to use their readings to obtain clock time.

In the rst half of the twentieth century, mechanical
analog computers, called dierential analyzers, were con-
structed that used dierential gear trains to perform
addition and subtraction. The U.S. Navy Mk.1 gun re
control computer used about 160 dierentials of the
bevel-gear type.
A dierential gear train can be used to allow a dier-
ence between two input axles. Mills often used such gears
to apply torque in the required axis. Dierentials are
also used in this way in watchmaking to link two sepa-
rate regulating systems with the aim of averaging out er-
rors. Greubel Forsey use a dierential to link two double
tourbillon systems in their Quadruple Dierential Tour-
billon.

Dierential used to control the take-up reel of a paper tape reader

made by Tally circa 1962. The bevel gears spin freely on their 6 Application to vehicles
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.

Video explaining the purpose and the principle of a dierential

(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 dif-
ferent speeds to maintain traction. The automotive dier-
ential is designed to drive a pair of wheels while allowing
them to rotate at dierent speeds. In vehicles without a
dierential, 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
Planetary dierential used to drive a chart recorder circa 1961. than the outer wheel, so without a dierential either the
The motors drive the sun and annular gears, while the output is inner wheel rotates too quickly or the outer wheel rotates
taken from the planet gear carrier. This gives 3 dierent speeds too slowly, which results in dicult and unpredictable
depending on which motors are on. handling, damage to tires and roads, and strain on (or pos-
sible failure of) the drivetrain.
would frequently have to be readjusted, even if it worked In rear-wheel drive automobiles the central drive shaft
perfectly, because of seasonal variations in the equation (or prop shaft) engages the dierential through a hypoid
of time. Williamsons and other equation clocks showed gear(ring and pinion). The ring gear is mounted on the
sundial time without needing readjustment. Nowadays, carrier of the planetary chain that forms the dierential.
we consider clocks to be correct and sundials usually This hypoid gear is a bevel gear that changes the direction
incorrect, so many sundials carry instructions about how of the drive rotation.
 5

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 (yel-
Hypoid gear pair that connects an automotive drive shaft to a low).
dierential.
right wheel making 8 rotations.
7 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
o, and the drive shaft is held (say, leaving the transmis-
sion in gear preventing the ring gear from turning inside
the dierential), 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 dierential movement of the planetary system of
gears other than the minute movements necessary to com-
pensate for slight dierences in wheel diameter, undula-
tions 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 8 Loss of traction
(red and yellow) only through the planet gear (green). Torque is
transmitted to the sun gears through the planet gear. The planet
One undesirable side eect of an open dierential is that
gear revolves around the axis of the carrier, driving the sun gears.
it can limit traction under less than ideal conditions. The
If the resistance at both wheels is equal, the planet gear revolves
amount of traction required to propel the vehicle at any
without spinning about its own axis, and both wheels turn at the
same rate. given moment depends on the load at that instanthow
heavy the vehicle is, how much drag and friction there is,
The following description of a dierential applies to a tra- the gradient of the road, the vehicles momentum, and so
ditional rear-wheel-drive car or truck with an open or lim- on.
ited slip dierential 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 twist-
spur-gear dierential): ing force against the resistance of the traction at that road-
Thus, for example, if the car is making a turn to the right, wheel. In lower gears, and thus at lower speeds, and un-
the main ring gear may make 10 full rotations. During less the load is exceptionally high, the drivetrain can sup-
that time, the left wheel will make more rotations because ply as much torque as necessary, so the limiting factor
it has farther to travel, and the right wheel will make fewer becomes the traction under each wheel. It is therefore
rotations as it has less distance to travel. The sun gears convenient to dene traction as the amount of force that
(which drive the axle half-shafts) will rotate at dierent can be transmitted between the tire and the road surface
speeds relative to the ring gear (one faster, one slower) by, before the wheel starts to slip. If the torque applied to
say, 2 full turns each (4 full turns relative to each other), one of the drive wheels exceeds the threshold of traction,
resulting in the left wheel making 12 rotations, and the then that wheel will spin, and thus provide torque only
6 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) dier-
ential always supplies close to equal torque to each side.
To illustrate how this can limit torque applied to the driv-
ing 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 dif-
ferential 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]
A cutaway drawing of a cars rear axle, showing the crown wheel
Based on the load, gradient, etc, the vehicle requires a
and pinion of the nal drive, and the smaller dierential gears
certain amount of torque applied to the drive wheels to
move forward. Since an open dierential 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 dierential,
about which a review has been reported by Provatidis,[10]
but the various congurations seem to correspond either
to the sliding pins and cams type, such as the ZF B-
70 available on early VWs, or are a variation of the ball
dierential.
Many newer vehicles feature traction control, which par-
tially mitigates the poor traction characteristics of an A cutaway view of an automotive nal drive unit which contains
open dierential by using the anti-lock braking system the dierential
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 eective as a traction-aided dieren- 9 Active dierentials
tial, it is better than a simple mechanical open dierential
with no traction assistance. A relatively new technology is the electronically con-
trolled 'active dierential'. An electronic control unit
(ECU) uses inputs from multiple sensors, including yaw
rate, steering input angle, and lateral accelerationand
adjusts the distribution of torque to compensate for un-
desirable handling behaviours like understeer. Active dif-
ferentials used to play a large role in the World Rally
Championship, but in the 2006 season the FIA has lim-
ited the use of active dierentials to only those drivers
who have not competed in the World Rally Championship
in the last ve years.
Fully integrated active dierentials 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 oered on the B8 chassis Audi S4
and Audi A4.[11] The Volkswagen Golf GTI Mk7 in Per-
formance trim also has an electronically controlled front-
axle transverse dierential lock, also known as VAQ.[12]
The second constraint of the dierential is passiveit
ARB, air-locking dierential is actuated by the friction kinematics chain through the
ground. The dierence in torque on the roadwheels and
 7

tires (caused by turns or bumpy ground) drives the sec- by its freewheel. Thus, while turning, the vehicle
ond degree of freedom, (overcoming the torque of inner had only one driving wheel. Driving in reverse is im-
friction) to equalise the driving torque on the tires. The possible as is engine braking due to the freewheels.
sensitivity of the dierential depends on the inner friction
through the second degree of freedom. All of the dier- Vehicles with two continuously variable transmis-
entials (so called active and passive) use clutches and sions, such as the DAF Daodil. The Daodil,
brakes for restricting the second degree of freedom, so all and other similar vehicles which were made until
suer from the same disadvantagedecreased sensitivity the 1970s by the Dutch company DAF, had a type
to a dynamically changing environment. The sensitivity of transmission that used an arrangement of belts
of the ECU controlled dierential is also limited by the and pulleys to provide an innite number of gear ra-
time delay caused by sensors and the response time of the tios. The engine drove two separate transmissions
actuators. which ran the two driving wheels. When the vehi-
cle turned, the two wheels could rotate at dierent
speeds, making the two transmissions shift to dif-
ferent gear ratios, thus functionally substituting for
10 Automobiles without dieren- a dierential. The slower moving wheel received
tials more driving torque than the faster one, so the sys-
tem had limited-slip characteristics. The duplica-
Although most automobiles in the developed world use tion also provided redundancy. If one belt broke,
dierentials there are a few that do not. Several dierent the vehicle could still be driven.
types exist: Light vehicles with closely spaced rear wheels, such
as the Isetta and Opperman Unicar, or very low mass
Race cars and trucks in certain classes. Drag racing vehicles.
is done in a straight line (and often on a prepared
surface), which obviates the need for a dierential. Vehicles with separate motors for the driving
A spool is used to make a solid connection between wheels. Electric cars can have a separate motor
both drive wheels, which is simpler and less likely for each driving wheel, eliminating the need for a
to break under very heavy acceleration. Racing on dierential, but usually with some form of gearing
dirt or mud tracks also allows the use of spools, be- at each motor to get the large wheel torques nec-
cause the loose surface gives way while cornering. essary. A multi-motor electric vehicle such as the
NASCAR mandates the use of spools in their cars, Dual Motor Tesla Model S can electronically con-
which does cause axle wind-up, and degrades han- trol the power distribution between the motors on a
dling in turns. Other forms of racing without dif- millisecond scale, in this case acting as a centre dif-
ferentials include tractor pulling, mud bogging, and ferential where open dierentials are still employed
other 4x4 motorsports where dierential action is left-to-right.[13]
not needed.
Vehicles with a single driving wheel. Besides mo- 11 See also
torcycles, which are generally not classied as au-
tomobiles, this group includes most three-wheeled Ball dierential
cars. These were quite common in Europe in the
mid-20th Century, but have now become rare there. Equation clock
They are still common in some areas of the develop-
Hermann Aron#Electricity meters
ing world, such as India. Some early four-wheeled
cars also had only one driving wheel to avoid the Limited slip dierential
need for a dierential. However, this arrangement
led to many problems. The system was unbalanced, Locking dierential
the driving wheel would easily spin, etc.. Because Torque vectoring
of these problems, few such vehicles were made.
Whippletree (mechanism)
Vehicles using two freewheels. A freewheel, as used
on a pedal bicycle for example, allows a road wheel Tests on rollers
to rotate faster than the mechanism that drives it, al-
lowing a cyclist to stop pedalling while going down-
hill. Some early automobiles had the engine driv- 12 References
ing two freewheels, one for each driving road wheel.
When the vehicle turned, the engine would continue [1] Wright, M. T. (2007). The Antikythera Mechanism re-
to drive the wheel on the inside of the curve, but the considered (PDF). Interdisciplinary science reviews. 32
wheel on the outside was permitted to rotate faster (1). Retrieved 20 May 2014.
8 13 EXTERNAL LINKS

[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. 1314, ISBN 0-948305-03-7 in-
cludes sectional drawing.

[6] J. J. Uicker, G. R. Pennock and J. E. Shigley, 2003, The-

ory of Machines and Mechanisms, Oxford University
Press, New York.

[7] Bonnick, Allan. (2001) Automotive Computer Con-

trolled Systems p. 22

[8] Bonnick, Allan. (2008). Automotive Science and Math-

ematics p. 123

[9] Chocholek, S. E. (1988) The development of a dieren-

tial for the improvement of traction control

[10] Provatidis, Christopher, G. (2003). A critical presenta-

tion of Tsiriggakis gearless dierential. Mobility & Ve-
hicles Mechanics 29 (4): 2546; 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 2013-06-

24.

[13] Davies, Alex (2014-10-10). The Model D Is Teslas Most

Powerful Car Ever, Plus Autopilot. Wired.com. Re-
trieved 2014-10-11. Musk said the added eciency is
thanks to the electronic system that will shift power be-
tween the front and rear motors from one millisecond to
the next, so each is always operating at its most ecient
point

13 External links
A video of a 3D model of an open dierential
An article explaining dierentials with illustrations
and video
Around the Corner (1937), a Jam Handy lm
made for Chevrolet explaining very clearly how an
open dierential works.

Popular Science, May 1946, How Your Car Turns

Corners, a large article with numerous illustrations
on how dierentials work.
 9

14 Text and image sources, contributors, and licenses

14.1 Text
Dierential (mechanical device) Source: https://en.wikipedia.org/wiki/Differential_(mechanical_device)?oldid=763136533 Contribu-
tors: Robert Merkel, Jkominek, Josh Grosse, Heron, Michael Hardy, DopeshJustin, Kku, Wapcaplet, Iluvcapra, CesarB, Ahoerstemeier,
Mac, Angela, Glenn, Silthor~enwiki, Samw, Smack, Raven in Orbit, GRAHAMUK, Emperorbma, Hawthorn, Dino, Dysprosia, Greglo-
cock, 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, Mat-
tisgoo, 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, StuOfInterest,
RussBot, Sparky132, Supasheep, Hellbus, RadioFan, Hydrargyrum, DarkPhoenix, Voidxor, Natkeeran, Bota47, 1717, Knotnic, Clay-
halliwell, 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,
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Lklundin, IanOsgood, Nikevich, Choppingmall, Pgn674, Gun Powder Ma, Sigmundg, Keith D, R'n'B, CommonsDelinker, Mcwilshire,
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Williams, ClueBot NG, Smtchahal, Frietjes, Widr, Sasakubo1717, Cather B, Helpful Pixie Bot, Martin of Sheeld, BG19bot, Vagobot,
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14.2 Images
File:13-04-05-Skoda_Museum_Mlad_Boleslav_by_RalfR-009.jpg Source: https://upload.wikimedia.org/wikipedia/commons/2/2f/
13-04-05-Skoda_Museum_Mlad%C3%A1_Boleslav_by_RalfR-009.jpg License: CC BY 3.0 Contributors: Own work Original artist:
Dieses Foto ist von Ralf Roletschek
File:20-TallyTakeupDrive.JPG Source: https://upload.wikimedia.org/wikipedia/commons/4/4f/20-TallyTakeupDrive.JPG License:
CC0 Contributors: Own work Original artist: Douglas W. Jones
File:ARB_Air_Locking_Differential_(RLH).JPG Source: https://upload.wikimedia.org/wikipedia/commons/c/c9/ARB_Air_
Locking_Differential_%28RLH%29.JPG License: CC BY-SA 3.0 Contributors: Own work Original artist: Richard Harvey
File:Around_the_Corner_(1937)_24fps_selection.webm Source: https://upload.wikimedia.org/wikipedia/commons/3/3e/Around_
the_Corner_%281937%29_24fps_selection.webm License: Public domain Contributors: http://archive.org/details/Aroundth1937 Origi-
nal artist: Handy (Jam) Organization
File:BAUMA_2004_ZF_Differentialgetriebe.jpg Source: https://upload.wikimedia.org/wikipedia/commons/a/ad/BAUMA_2004_
ZF_Differentialgetriebe.jpg License: CC BY-SA 3.0 Contributors: Own work Original artist: Aconcagua (<a href='//commons.wikimedia.
org/wiki/User_talk:Aconcagua' title='User talk:Aconcagua'>talk</a>)
File:ChartDriveDetail.JPG Source: https://upload.wikimedia.org/wikipedia/commons/b/ba/ChartDriveDetail.JPG License: CC0 Con-
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: ? Origi-
nal 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-SA-
3.0 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:
Dierential_locked.png Original artist: Dierential_locked.png: Wapcaplet
File:Differentialgetriebe2.jpg Source: https://upload.wikimedia.org/wikipedia/commons/f/fe/Differentialgetriebe2.jpg License: CC-
BY-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: CC-
BY-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-by-
sa-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: ?
10 14 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

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: 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
File:Sprocket35b.jpg Source: https://upload.wikimedia.org/wikipedia/commons/d/d1/Sprocket35b.jpg License: Public domain Contrib-
utors: Own work Original artist: Hapesoft
File:Spur_gear_differential_(Manual_of_Driving_and_Maintenance).jpg Source: 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)
File:Transmission_diagram.JPG Source: https://upload.wikimedia.org/wikipedia/commons/2/27/Transmission_diagram.JPG License:
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).

14.3 Content license

Creative Commons Attribution-Share Alike 3.0