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Haldex isn't 'fake-AWD' by any stretch of the imagination, if that is what you are trying to imply (Not Sure). This new system uses a multi-plate clutch center differential developed by a Swedish company, Haldex, and computer software from the Austria 4WD specialist Steyr-Daimler-Puch. The Haldex center differential is similar to Porsche 959's PSK (Porsche-Steuer Kupplung) system, but it is only smaller, simpler, and cheaper thus making mass production feasible. The center differential is mounted near the rear axle and just in front of the rear differential.
The clutch pack consists of 6 discs, and they are immersed in oil to reduce friction. Actuation is made by hydraulic pressure. Normally the input and output shafts rotate with a speed difference (could be implemented by different final drive ratio), therefore the discs are rotating relative to each other. When no pressure is applied, the clutch is not engaged thus torque will not be transferred to the rear axle. Increase the pressure on the multiplate clutch, the latter will be partially engaged, thus sending torque to the rear axle. The more the clutch engages, the more torque transfers to the rear axle.
The beauty of the Haldex system is that the computer determines how much torque is to be sent to the rear wheels. Normally it is 50:50, but in tight corners when wheels on one of the axles is slipping, the driver can easily feel the torque being transferred from one to the other axle. In non-slip conditions Haldex can be adjusted in a variety of torque split formats such as 50/50, 95/5, 65/35, and so on depending on the vehicle and driving environment encountered.
The other great thing about Haldex that is not possible with primitive mechanical AWD systems such as Quattro is that the computer can interact with engine management and active suspension components. Torque split can be changed based on suspension geometry changes and engine speed/torque characteristics at any given moment.
There is nothing fake about the Porsche 959's PSK (Porsche-Steuer Kupplung), Steyr-Daimler-Puch AWD software programming, or Haldex AWD. Also, considering the fact the Ferrari and Maserati's parent company Fiat, just got a license from Haldex AB of Sweden to use their AWD system on future cars. The Nissan Skyline GT-R with ATTESA E-TS PRO AWD also uses a multi-plate clutch pack. This car is known to have the best current 'desirable-handling' production AWD systems in the world because it combines RWD's power oversteering with AWD's maximum cornering limit.
posted by 144.167.12...
, Sat, 1 Dec 2001 02:53:27
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