Porsche all wheel drive explained

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Porsche

911 Carrera 4 - From 1989 - (system type?) three differential system using computer-controlled hydraulic clutches to help distribute power to the four wheels.

From 1994 - (system type?) mechanical limited slip at rear, viscous coupling in the center.

From 1999 - Automatic all wheel drive. Viscous coupling just behind front differential, transferring from 5 to 40 % up front.

Figure: Porsche 911 Carrera 4 (unknown model year, probably 1994-1999) center differential with a multi-plate differential locking clutch. Appears to be a full-time all wheel drive (?) system with torque distribution 31/69% front to rear.

Figure: Porsche 911 Carrera 4 front differential

959 - permanently locked multi-plate hydraulic clutch in the center. Unlocked only if turning at low speed, for example while parking. Torque distribution in this vehicle is adjusted even before wheelspin occurs. Gathering information from numerous sensors (i.e. g force sensor, accelerator pedal position, speed, and even turbo pressure) while accelerating, computer changes normal 40front/60back torque split, sending up yo 80% to the rear wheels, even if all four wheels are rotating with the same speed.

Last updated: 2010-07-28 16:11

There is 1 comment

George

January 11, 2010 - 01:34

Subject:

I wonder how asymmetric the torque split of the planetary center differential would had to have been, to avoid offending Porsche loyalists?
www.autozine.org
It seems 31/69 was not enough, maybe 20/80 would have kept the oversteer on demand, reduced understeer at the limit, and kept the 'pure' steering feel of rear drive.

The Bugatti EB110, if I recall correctly, was 27/73, and wasn't as rear heavy as a 911.