Its still a VAQ clutch pack unit just there is one per side of the rear bevel box. & yes the central shaft in the VAQ unit is different as the drive is now straight through instead of having to do straight through & turn back on itself to go back to the open diff. You still have the same clutch pack mechanical design & way it opens & closes via the electronically controlled hydraulics.
Fair enough.
There are NO sensors in the VAQ/Haldex units..it has no way of knowing if the wheel is slipping or if there is torque loss. The clutch pack is told to open & close by the electronics. Regardless of this maybe I misdirected as I was referring back to the GTI-PP VAQ unit situation where it feeds back into the open diff, which is not applicable in the MK8 R rear case.
Everything I wrote was from a effective, or end result, standpoint. It doesn't matter where the sensors or controller are located, or what the unit itself "knows" or "doesn't know." The effect is the same. Certain conditions, which are derived from multiple sensor's input, result in the VAQ being told to apply a certain amount of clamping force on the clutch discs. This makes it a somewhat reactive system, because sometimes the sensors input isn't enough information to preemptively close the clutch prior to slip. What I said wasn't inaccurate from an effective standpoint.
I consider torque vectoring as was claimed for electric cars, mainly on those with two or more motors. One car a UK built prototype had an electric motor in each wheel hub, providing 100% torque vectoring as each motor could be independently controlled & provide from 0% to 100% of its power to said wheel. There are cars with a motor for each axle (two motor electric cars), this still providing torque vectoring as each axle can be controlled independently, & then having either an LSD or Haldex VAQ unit on each axle gives control over the left/right torque split on that axle.
This MK8 system does NOT have independent control over each axle, nor does it have independent control over the left/right split on one axle (front) , & the rear axle cannot rotate at a faster speed or with more torque than the front axle....The front brakes will be used like mad to provide a small amount of rear bias by slowing the front axle down..
I see. I would consider that a constrained definition of Torque Vectoring. Mechanical torque vectoring has existed before such EV systems since the early to mid 2000s with Mitsubishi's AYC and Honda/Acura's SH-AWD which both used torque vectoring rear differentials. Those differentials we're more sophisticated than the Golf R, but still existed to vary torque side-to-side regardless of traction.
That's mostly how I understand mk8 Golf R too, but I don't really understand why you keep saying the front brakes need to be used to cause rear bias. The rear wheels can have more torque going to them if the fronts have less traction than the rears, assuming the clutches have enough clamping force applied. Again... Theoretically. There may be a software limitation here, but I'm about to cover that in the next section.
The front axle is driven with 50% torque all the time. The cardan shaft from the front to the bevel box is also driven at 50% torque all the time. This due the simple open diff & transfer case set up.
If one wheel at the front is on ice & the other is in the air, then the existing open diff on the front axle will just spin the wheels & the car relies on the ABS based systems to balance the wheel speeds so they match.....& the front axle will appear to be "locked"...& you have smoking brakes...
In this situation no more than 50% torque is given to the rear axle, & the clutches will be told to activate & those the rear wheels will rotate & the ECU will open/close the rear VAQ clutchs & brake the front wheels until ALL the wheels (front/rear left/right) rotational speeds match
Either I am misunderstanding how the transfer case works, or this is inaccurate. As I understand it, the transfer case is driven directly from the ring gear of the front differential. This means there isn't another differential, or a center diff, in the transfer case; it is direct drive. Therefore, if the front wheels are up in the air, with zero traction, the rear wheels will receive 100% of the torque, assuming the clutches are engaged with enough clamping force to transfer all the torque. This is true whether we're talking about the single clutch haldex or the new twin clutch system.
The system doesn't need to apply the front brakes to transfer torque rearward. There isn't an open center diff. Now, because this is all tied in with the ESC/ABS system, the front brakes may be applied as a safety measure and because safety systems take priority, but it isn't required for torque transfer in a no traction scenario on the front.
Let's think about locked differentials. With a locked diff, a single wheel cannot spin unless both are spinning, because, even if one wheel has less traction, that torque is automatically balanced between the two wheels until the limit of both wheel's traction is found. The same thing applies to the AWD system between axles.
The rear clutches cannot receive more than 50% of the engine torque due to the front transfer box, one clutch can still receive all of this 50%...there is no "slippage" for the factory power rating..& even if there was the ABS sensor which sensors wheel speed imbalance will deactivate the clutch or it might brake that wheel..whichever it decides is better...
The clutch is slipping, the wheel isn't. I assume the ABS/ECS system is smart enough to take into account steering angle and know that the wheel speed difference between the inside and outside wheels is not due to slipping, but turning. Either way, if the system disengaged the inside clutch that would mean all the rearward torque is going to the outside wheel. As I talked about earlier, that creates yaw or rotation, even if it's only 50% of the torque.
You really have no idea about the electronic controls behind the VAQ/Haldex units.
I strongly suggest you read my post on the VAQ units as this is the basis for these clutch packs...especially part 4 which is on the electronics..
I have read it; several times in fact.
. Certainly some solutions are better/more capable, but aren't they all torque vectoring?