XWD, Cross-Wheel Drive or Haldex Generation 4 are names for the all-wheel drive system that was first introduced in 2008 in the Saab Turbo X. The system was developed jointly by Saab Automobile AB and the Swedish Haldex Group. It ensures optimal torque distribution between the front and rear axles based on driving style and vehicle operating conditions. It prevents wheel slip and improves fuel efficiency. Until 2011 this system was used for the Saab 9-3, Saab 9-5 and Opel Insignia.
How XWD works
The system is controlled by the electronic unit, which communicates with the control units of the engine, gearbox and ABS and ESP. Wheel speed, brake force and yaw rate data is sent to the system's control unit and used to control the PTO unit. Torque is transmitted from the engine via a cardan shaft to an electronically controlled limited-slip differential. The latter ensures that the torque is distributed to the rear wheels.
Torque transmission
- Up to 100% when slipping one of the two axles
- 50% on both axles for optimal acceleration, improved traction and a more stable position of the car
- 90% on the front wheels when driving on the highway for economical fuel consumption
- Approx. 60% on the front axle when driving on wet or slippery surfaces
- Up to 85% on one of the rear wheels when maximum traction is desired while driving.
The disadvantages of XWD
- The seals wear out faster.
- The gear oil deteriorates quickly.
- The system requires frequent maintenance.