2.3 differentials

8/10/2019 2.3 Differentials

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Analysis of Open and Torsen

DifferentialGroup Members:

Scott Anderson

Michael Bullard

Jason Yount



Differential Overview

• When turning, the

inner and outer wheels

have arcs of differentturning radii

• Consequently, the

inner wheels travel

less distance than theouter wheels



Differential Overview

• Because the turning paths

of the inner and outer

wheels are different, the

wheels on both axles need

to be able to spin

independently of each

other

• A differential is used toallow the wheels to spin at

different speeds



Different Types of Differentials

• Open Differential

• Limited Slip

Differential (LSD) – Clutch LSD

– Viscous Coupling LSD

– Locking LSD

– Torsen LSD



Schematic of an Open Differential

• The “Sun” gear and

“Ring” gear are

identical and supply power to the drive

axles.

• The planetary gears, or

spider gears allow theaxles to rotate at

different speeds.



• The open Differential is a planetary gear

set. Therefore the following equation

applies

Open Differential

gear sunof velocityangular

gear ring of velocityangular

carrier planet of velocityangular

gear ring onteethof number N

gear sunonteethof number N

N

N

s

r

c

r

s

c s

cr

r

s



Open Differential

• The number of teethon the ring gear andsun gear are equal andthe planetary gearformula is simplified

• The angular velocityof the differential isequal to the averageangular velocity of theaxles

2,1 sr

cr

s

c s

cr

r

s

therefore N

N

N

N



Open Differential Problems

• As a result, if one

wheel has little

friction there is noresistance to its

rotation and slipping

occurs

• The slipping wheelwill spin twice as fast

as the differential Left rear tire

slipping on sandy

surface



The Torsen Differential

• The Torsen

Differential is capable

of perfectdifferentiation

• The Torsen

Differential transfers

power to the wheelswith traction

Torque transferred to

wheel with traction



How the Torsen Differential Works

• Power is transferred fromthe engine to thedifferential housingcausing the housing to

turn• Power flows from the

housing to the wormwheels attached to thehousing

• The worm wheels aremeshed with the wormgears attached to the axleswhich turns the axle with

the differential housing



Differential Function

• When turning, the outer wheelturns at a high RPM withrespect to the differentialhousing

• Therefore, the outer wheel axleturns its worm gear and itsmating worm wheel

• The mating worm wheels aremeshed together by spur gears – Perfect Differentiation: as one

wheel increases speed theother wheel decreases speed proportionally

– Torque is maintained at bothwheels while cornering



Traction Loss By One Wheel

• Spinning wheel turnsits worm gear whichturns its mating worm

wheel• Mating worm wheel

wants to turn oppositeworm wheel

• Opposite worm wheeltransfers power toopposite worm gear



Traction Loss By One Wheel

• Opposite worm gear is

attached to the axle of

the wheel with traction – The slipping wheel

does not spin

– Torque is transferred to

the wheel with traction



Torque Transfer

• The torque bias ratio

determines the amount

of torque transferred andis dependant on the gear

design

– 5:1 ratio transfers 5 times

the torque to the wheel

with traction

– If one wheel loses all

traction no torque is

transferred to the wheel

with traction Torque transferred to

wheel with traction



Application of Torsen Differentials

• Torsen differentials

are used in off-road

and high performanceall-wheel drive

vehicles.

• Torsens can also be

handy on icy or dirtroads



Automobile Companies Using the

Torsen Differential

– AM General

– Audi – BMW

– Ford

– GM

– More specific details athttp://www.torsen.com

/oem.htm

– Honda

– Lexus – Land Rover

– Mazda

– Toyota

– Volkswagen



Companies Using Torsen

Differential• General Motors

– Camaro SS 1998

• AM General

– Hummer

• Audi

– A4 Quattro

• BMW

– Z3

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