LIM­ITED SLIP DIF­FER­EN­TIALS

THE PUR­POSE, AS THE NAME SUG­GESTS, IS TO LIMIT THE AMOUNT OF WHEEL SLIP. HOW­EVER, THERE ARE SEV­ERAL DIF­FER­ENT VARI­A­TIONS WITH DIF­FER­ENT DE­GREES OF EF­FEC­TIVE­NESS.

4 x 4 Australia - - Gear -

CLUTCH-TYPE LSD

This type has a multi-plate clutch pack sim­i­lar to that in a mo­tor­cy­cle. One side of the clutch as­sem­bly is con­nected to the drive­shafts and the other to the dif­fer­en­tial gear car­rier. Var­i­ous meth­ods such as ramps or the nat­u­ral force of sep­a­ra­tion be­tween gear teeth are used to en­gage the clutch pack when the dif­fer­en­tial ex­pe­ri­ences one wheel turn­ing faster than the other, which then trans­fers some of the power to the slower-turn­ing wheel.

ONE-WAY, ONE AND A HALF, AND TWO-WAY

A one-way LSD will only pro­vide the lim­ited-slip ac­tion in one di­rec­tion – for ex­am­ple, un­der ac­cel­er­a­tion but not un­der brak­ing.

By con­trast, a 1.5-way LSD will pro­vide dif­fer­ing amounts of slip lim­i­ta­tion un­der ac­cel­er­a­tion and brak­ing, which can aid sta­bil­ity un­der heavy brak­ing.

A two-way LSD will pro­vide the same amount of lim­ited-slip ef­fect un­der both ac­cel­er­a­tion and brak­ing.

TORSEN

The torque-sens­ing dif­fer­en­tial is a lim­ited slip-type dif­fer­en­tial that uses the oneway ac­tion of worm drive gear­ing to limit slip. They also have the abil­ity of be­ing man­u­fac­tured with a TBR (torque bias ra­tio), where there is an abil­ity to send more torque to the rear wheel in a cen­tre dif­fer­en­tial ap­pli­ca­tion.

AUTO LOCKER

When think­ing of auto lock­ers, many think of ‘lunch­box lock­ers’ that re­place the spi­der gear mech­a­nism in the mid­dle of dif­fer­en­tial car­rier. Prob­a­bly bet­ter re­ferred to as un-lock­ers, lunch­box lock­ers are locked when driv­ing un­der power in a straight line. When they ex­pe­ri­ence dif­fer­ent torque loads, such as coast­ing around a cor­ner, they un­lock. This can make for in­ter­est­ing han­dling char­ac­ter­is­tics on the road, and if in­stalled in the front they’re much bet­ter in com­bi­na­tion with a part-time 4WD sys­tem.

SELECTABLE LOCKER

Viewed as the Holy Grail by many, selectable lock­ers come in two main flavours: air op­er­ated (TJM/ARB) and elec­tro­mag­netic (Elocker). Both pneu­matic lock­ers use a sim­ple dog clutch-type mech­a­nism that re­moves the dif­fer­en­tial ac­tion when ac­ti­vated. How­ever, the Elocker uses a pin and ramp mech­a­nism to op­er­ate a se­ries of pins that lock the dif­fer­en­tial. When tran­si­tion­ing from for­ward to re­verse, they un­lock then re­lock due to the for­ward and re­verse ac­ti­va­tion ramps used.

TRAC­TION CON­TROL

There are two main types of trac­tion con­trol: one re­duces en­gine power, the other re­duces the dif­fer­en­tial’s ‘power to the path of least re­sis­tance’ char­ac­ter­is­tic. Mod­ern sys­tems mon­i­tor in­di­vid­ual wheel speeds and if two wheels on the same axle are trav­el­ling at dif­fer­ing speed it brakes the spin­ning wheel – this re­quires more torque from the en­gine. As there is al­ways even torque on ei­ther side of a con­ven­tional diff, the slower wheel re­ceives ex­tra torque. Early sys­tems weren’t great but now trac­tion con­trol is al­most a vi­able al­ter­na­tive to lock­ers – the lat­est Land­cruis­ers and Pa­jeros are par­tic­u­larly good.

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