Porsche’s four-wheel drive sys­tem has be­come in­creas­ingly clever with its torque dis­tri­bu­tion. This is down to Porsche Trac­tion Man­age­ment…

Total 911 - - Avantgarde Classics -

Tyres aren’t the only thing that de­ter­mine trac­tion. For 30 years, Porsche has been util­is­ing four-wheel drive in the 911, with the Porsche Trac­tion Man­age­ment sys­tem in­creas­ing in com­plex­ity in re­cent years to op­ti­mise power trans­fer. The sys­tem op­er­ates us­ing two dif­fer­en­tials (one for each axle). With the trans­mis­sion mounted in front of the en­gine, the front dif­fer­en­tial is pow­ered by a per­fectly straight prop­shaft from the rear dif­fer­en­tial. This en­sures that power is dis­trib­uted evenly.

Trac­tion on the rear wheels is man­aged by PTV (Porsche Torque Vec­tor­ing). PTV is the rea­son Porsche no longer talks of lim­ited-slip dif­fer­en­tials. Torque vec­tor­ing not only trans­fers power from side-to-side, it also in­de­pen­dently brakes the in­side wheel to en­able greater turn-in. PTV is me­chan­i­cally op­er­ated un­less the ‘Plus’ op­tion is spec­i­fied, in which case an in­fin­itely vari­able elec­tron­i­cally lock­ing ver­sion is utilised.

With the rear wheels taken care of, the level of power dis­trib­uted to the front axle is de­ter­mined by a se­ries of sen­sors mea­sur­ing a range of pa­ram­e­ters, from steer­ing an­gle and throt­tle ap­pli­ca­tion to lat­eral and lon­gi­tu­di­nal ac­cel­er­a­tion.

This in­for­ma­tion is then used to op­er­ate the elec­tron­i­cally con­trolled dou­ble­clutch sys­tem, lo­cated just be­hind the front dif­fer­en­tial. If the rear axle is strug­gling to ap­ply all the power to the road, the elec­tron­i­cally ac­ti­vated clutch is en­gaged more pos­i­tively (tak­ing a max­i­mum of 100 mil­lisec­onds), trans­fer­ring a greater amount of the en­gine’s power to the front axle. De­pend­ing on throt­tle ap­pli­ca­tion, this sys­tem can preload, mean­ing that trac­tion is al­ways avail­able, even be­fore the driver needs it.

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