So a benefit of the haldex over the torsen 4x4 would be that it would put more power through the wheels as it only sends power through the front when accelerating in gear,
Erm, I think you may be slightly confused over your front vs rear and acceleration needs.
However, it is sort of identical to Torsen, in that Torsen sends torque (not "power", as power is merely a rate of work, whereas "torque" is a "turning" force) to those wheels which can use it. The simple fact, though, is that all four wheels
can utilise the traction, and that is what the Torsen utilises beautifully (proactively), and the Haldex is noticeably more "agricultural" in that it works "reactively", ie, AFTER traction is lost.
To clarify, you state that Haldex only sends torque to those wheels which needs it - but I say, so does the Torsen!
or in high grip conditions when the rear doesnt need to kick in.
Very subjective. Whilst the rear may not
need any drive, for optimum vehicle dynamics, it is considerably better for all four wheels to be permanently driven, which is where Torsen has an undisputed example. It is just like saying that because the front brakes may deal with up to 75% of the stopping power, why not ditch the rear brakes? Again, the simple fact is that even when the front anchors may provide that 75% of stopping power, the rear brakes provide a major factor in vehicle stability.
Therefore not sapping as much power as a permanent 4x4 setup.
Ahhhhh. That must be
the classic misconception of an Haldex "advantage"!
Firstly, Haldex systems require some kind of transmission "transfer box"-type of system to distribute torque to more than one axle. So does the Torsen system. = a score draw.
Haldex systems require a prop shaft to send drive to the remote (rear) axle. So does the Torsen. Another score draw.
Haldex systems require an additional remote axle cross differential. Guess what, so does Torsen. Nobody seems to have scored that winning goal yet!
Haldex systems require additional remote axle wheel drive shafts. You know what the answer is, same as Torsen!
Now, on to the specifics of "power" requirements. On a Haldex system, the underfloor prop shaft is ALWAYS driven, even if zero drive is going to the rear wheels. The Torsen only spins its propshaft whilst the rear axle is driven (the fact that the rear axle is always driven is indicitive of the Torsen prop being permanently driven). Now, this is a clear advantage to the Torsen system, because whilst the Haldex may not be driving its rear wheels, the Haldex is still suffering driveline losses in the bevel gears which drive the prop - a wasteful efficiency loss. If the Haldex was mounted within the transaxle, or before the prop, this wouldn't be so bad, but then this scenario would noticieably alter the front to rear weight distribution. Not good.
Furthermore, even when zero drive is being sent to the rear wheels, the rear axle hypoid final drive (part of the rear diff) will still sap the kinetic energy (and therefore motive power of the engine) (it is a design fact of hypoid drives, and explains why they need thick smelly heavy duty lubes). The CV joints in the rear driveshafts will also sap kinetic energy (unless the drive shaft is exactly in line, which is highly doubtful, considering dynamic movements from the independent rear suspension).
