FIRST, lets get the facts straight.
The recent announcement is no great surprise - it was announced by getrag over 6 months ago:
And here is the transmission in question - the 6DCT250
The dry clutches in the DQ200 (VW 7-speed dry DCT) are made by LUK, not BW. I don't recall who is making the Getrag (dry) clutches.
The reason for the switch to dry DCT's is purely for economy. The DQ250 is simply not a very efficient transmission - sure it's better than a conventional slush box, but it is still way off a manual. The dry DCT's are as described - likely to be just as efficient as a manual, potentially more if the ratios are optimised, potentially slightly less if the churning losses of that many more gears / shafts is truly included...
Why are wet DCT's good? Simply put, a whole lot of energy can be absorbed through a wet clutch. Note that the dry DCT's have very short 1st gear ratios compared to wet DCT's. This is so they can get the thing moving (putting little energy into the clutch in the process), then quickly shift to second - and one reason why the VW has got 7-speeds, to get more ratio coverage.
Wet DCT's - contrary to what many say / believe - are not cooled by the oil 'dipping' but by cooling oil being fed into the centre of the clutch, where it is flung outwards by centrifugal force out through the plates (which have grooves in them), cooling the plates in the process. There are grooves in the outer diameters of the clutch baskets to let the oil out. This oil also acts as a lubricant - meaning it is always switched on, the flow is merely modulated depending on demand (i.e. the more energy the clutch is absorbing, the greater the flow).
Co-incidentally, the DQ250 oil fill level is actually just over the outer clutch basket - it is dipping by less than 1" however. This though, is one of the reasons for the low efficiency as the clutch is always churning.
Other reasons for the low efficiency, are the fixed displacement pump, meaning the same pump has to provide both low through high flow for cooling (at low pressure), and low through high pressure (at low flow) for clutch clamping & gear engagement. In short - you can't tune / size the pump to deliver both high pressure and high flow, and expect it to be truly optimal at cruise.
Another efficiency issue is the slip-ring seals that deliver oil to the clutches. The seals in the DQ250 are not the most efficient.
The DQ250 clutch cooling is also fixed - i.e. you can't just cool one clutch, you have to cool both as they are a concentric design, which means you need to provide a little more cooling flow than would be really needed as well.
As you can see - there are two clear options - either provide a more efficient clutch and hydraulic system, or switch to a dry clutch, and lose the performance capability.
By choosing the 6DCT250, Ford has clearly indicated it iss targeting small cars with what could politely be termed 'average' engines. Nothing over 200lb ft, and potentially slightly poorer performance than a modern 6speed auto. But, they will be dammed efficient, and a good match for the sub 2.0 litre eco-boost engines we keep hearing about.
Finally - The DQ200 was initially developed - I understand - at a similar date to the DQ250 - like approaching a decade ago... It was quickly realised that getting the launch quality of a dry-plate system right was very difficult, to the extent they left it alone, and concentrated on the wet-clutch DCT. A few years later, processors had improved, experience had been gained, but it was (is) still HUGELY more difficult to configure a dry-clutch launch than a wet - two reasons being that the dry clutch locks up completely (the wet never does, hence you always have controlled 'microslip to monitor so you know the characteristics at all times), and secondly, the dry clutch friction co-efficiency changes with temperature - something that is not monitored, unlike a wet system which has temp sensors monitoring the fluid leaving the clutch.
So don't be afraid of dry DCT's taking over, but do accept that the DQ250 will be dropped at some point in the future, replaced by much more efficient wet DCT's, which will do everything the DQ250 does, but a lot better as well.
Modified by Gandalf at 11:16 AM 1-30-2009