Интересно писание за актив. диф. 4wd на порш 959
Porsche 959's PSK system - the most sophisticated
Until today, Porsche 959's PSK (Porsche-Steuer Kupplung) system is still the only one which make use of variable torque split for maximum traction under normal conditions. In most of the time, torque split between front and rear is 40:60, that is, the same as the car's weight distribution. In hard acceleration, weight transfer to the rear axle increases traction in the rear tyres while reduces traction in the front. Then PSK will transfer up to 80% torque to the rear axle in order to make better use of traction. On slippery road (even tyre slip is yet to occur), 50:50 torque slit is used. In any time, computer determines the torque split ratio by analysing parameters such as throttle position, steering angle, g-force and even turbo boost. Therefore PSK system provides optimum traction under all conditions, unlike other 4WD systems which can only varies torque split whenever tyre slip occurs.
Mechanism
Porsche PSK uses a multi-plate clutch instead of center differential. You may call it a "differential clutch" as well. The multi-plate clutch has 6 pairs of frictional plate, each pair is independently controlled by computer and actuated by hydraulic pressure. This simply equals to 6 independent clutches.
To make this system work, the front and rear driveshafts must run at different speed in normal condition. (so 959 adopted a pair of front tyres with 1% larger diameter than the rear's) Because of the speed difference between front and rear driveshafts, the 2 frictional plates of each independent clutch are rotating relatively to each other. When apply hydraulic pressure to the first clutch, a small amount of torque will transfer to the front axle. But note that the two driveshafts cannot be fully locked up unless all 6 clutches are locked simultaneously.
Now, you may see how it works: lock up 2 clutches, 3 clutches ... and the torque to front wheels will be increased, subsequently, torque split could be 50:50 if all the clutches are fully engaged. Of course, all these action is controlled by computer.
This is only for "normal" condition. Like other 4WD systems, when tyre slip occurs, most of the torque could be
sent to either axle.
What about energy loss and wear due to the slipping clutches? As the speed difference is very small, Porsche claimed energy loss is no greater than 0.4% of the power developed by the engine. As for wear, the clutch is dimensioned that it was negligible and caused no problem during the whole life span.
Advantage: Variable torque split even in normal condition. Best use of traction.
Since computer monitors and controls everything, theoretically it can cope with any normal or abnormal condition without being limited by the design of mechanical parts. The result is fast response and adaptive.
Disadvantage: Heavy and expensive
Who use it ? Porsche 959 only
естествено имам предвид че те са в основите му не че са взели частите 1:1 и са глобили .... края на 70 те години 924 измъква фирмата от сериозната финансова криза и спомага за развитието на 911 като цяло..... и скоро ще пуснат наследника на 928 4 врати седан ... както и да е 924, 944 , 928 са огромен маркентингов успех
и тъй като 928 е чист GT клас автомобил и панамерата се доближава до този клас като изключение правят двете врати повече .... мотор отзаде, при това боксров няма нищо общо с GT културата ...затова се приема, че панамерата е наследник а 928 
.но съм го казал:
както и да е гаража си е нейн 
