Saab XWD
XWD, an acronym for Cross-Wheel Drive, is an advanced all-wheel drive system designed by Haldex in partnership with Saab[1]. Also known as Haldex Generation 4, it is an intelligent permanent all-wheel drive system that can pre-emptively and continuously change torque distribution before wheel slip occurs.
To achieve optimum take-off performance, Saab XWD is capable of completely locking the front and rear axles, but can also adapt as little as 4% of torque to the rear wheels during highway cruising, thus maximizing fuel economy. To ensure immediate traction, torque distribution can be transferred to the wheel with the most grip in fractions of a second, and using the two couplings the XWD system can send 85% of available torque to a single rear wheel.
An ECU continuously collects various data from the car's onboard systems, and in conjunction with the ESP, ABS and TCS calculates the most optimal toque distribution in the driveline.
The XWD system debuted on the 2008 Saab Turbo X, equipped with an electronically controlled limited slip differential (eLSD), and is also available as an option on 2008.5 Saab 9-3 Aeros (in sedan and combi body styles), without the eLSD. It will be available through the rest of the 9-3 line-up by 2009, and will be the standard drivetrain for the new generation Saab 9-5, expected as a 2010 model year vehicle. XWD will also underpin Saab's upcoming cross-over utility vehicle, the 2009 Saab 9-4X.
While the Haldex Genertion 4 system will be made available to other automobile manufacturers starting 2009, the XWD moniker is a trademark owned by Saab Automobile AB, and thus cannot be used by any other make.[2]