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Subscribe to this threadPorsche Carrera 4 could switch to Haldex AWD system
(Page 1 of 1)
Dondonel @ Mar 27th 2008 2:37PM
Haldex is not viscous coupling, neither faux AWD. The initial system was a simple/cheap clutch based differential, compared to the clutch based differentials available at that time (much cheaper than Porsche PSK for instance).
For manufacturers today, Haldex-like differentials are any clutch based differentials. Haldex can be used for any axle differential, as well as for the center differential.
Clutch based differential are better than any of the alternatives, mechanical (Torsen) or viscous coupling, because they can be controlled better and in most cases are more efficient as well.
mk @ Mar 27th 2008 3:00PM
Not sure where you get your info...
But most haldex systems are viscous couplings, some of the newest ones with a computer controlled clutch associated with it.
That is not a differential at all. Viscous-bias and/or clutch-engagement elements can be used INSIDE a differential as a limited slip device, or torque-bias adjustment, but those components are not the differential themselves. A differential uses gears to multiply motion outputs but not lock those outputs together, and is constantly engaged, and can't be disengaged.
Haldex does not use a center differential at all. It uses a rear differential which is driven by a driveshaft that takes power off of the front differential, by way of a viscous coupling, and maybe a clutch, as I mentioned.
The Bugatti Veyron's Haldex system is, of course, more advanced, and with a mid-engine arrangement drives the rear wheels natively, with power taken off for front assist, which is more natural to a performance car. It probably also uses a host of computer controlled clutch packs to manage torque distribution, considering how much the car costs, and how much power it has.
Chances are, if Porsche 911 were to get haldex, it would be similar to that, rather than the simpler, less capable FWD-rear-assist Haldex systems, but a center differential is still better.
A car with a real center differential, like Audi's longitudinal-layout Quattro, and Subaru's AWD systems are much more capable, and are constantly engaged, they don't "automatically engage", they never disengage, and have a more even torque bias split, and they prevent more slip than a reactive system like haldex possibly can.