[Wutputt]

Sorry to dig up an older thread, but what a thread it is. I loved reading all your post st-anger, including the discussion with lakatu.

But there's always been a question I had about the four-wheel drive PTM system.

Originally Posted by st-anger These include permanent four-wheel Porsche Traction Management (PTM) featured as standard conveying 62 per cent of the engine's power to the rear and 38 per cent to the front wheels in its basic mode. Depending on driving requirements, up to 100 per cent of engine power may be fed to the front or to the rear for optimum stability and performance.

I just can't understand how the system can transfer up to 100% of torque to only one axle (rear or front) to cope with extreme driving situations.

Maybe my problem is just the fact I misunderstand the PTM system. The way I understand the system is explained in the following sketch. On the right is the reduction gearing, in the middle the planetary central differential and on the left the electronically controlled multiplate clutch, which can lock up front and rear axle.



Ta is the torque going to the rear wheels and Tv is the one going to the front wheels. It's only a sketch so the scale of the gears doesn't really match the reality.

The way I understand the system is as follows. The incoming torque from the transmission can either be directly fed to the ring gear of the central differential or can be diverted via the reduction gear. The PTM control unit (commanded by the driver) can engage the reduction gearing (low gearing) by a sleeve (the two arrow thingy on the sketch).
The planet gear carrier is connected to the rear driving shaft and the sun gear to the front driving shaft. And the electronically controlled multiplate clutch connects front and rear driving shaft.

In normal driving conditions the multiplate clutch is fully opened so the torque split is 38/62. When the multiplate clutch is fully locked the torque split is 50/50. In between those two extreme conditions the torque split can vary but in a controlled way. But with this system it still is impossible to transfer 100% of torque for example to the rear wheels when the front ones haven't any grip, isn’t it? Because the multiplate clutch can only lock up so at most 50% of the torque is transferred to the rear wheels.

Or has this "up to 100% of torque may be fed to the front or to the rear" feature something to do with the ABD function of PTM? So in the above extreme situation when front wheels don't have any grip, the ABD just brakes the front wheels so torque is automatically transferred to the rear wheels?

Can you clarify the situation for me?
Many thanks in advance


Oh, and one other question. I thought the only difference between Porsche's PTM and VW's 4XMotion are the gear ratio's of the central differential so PTM has a standard 38/62 split and 4XMotion a 50/50 split. Is this correct?