XWD - transverse drive

The Saab XWD system allows 100% of the engine torque to be transferred fully automatically to the front or rear wheels only, depending on the driving needs: on the one hand, traction is improved even in poor road conditions, on the other, the ESP response threshold is increased.

The system uses two "hearts": one at the front of the transmission called the PTU (power take-off unit), the other located at the rear called the "RDM" (rear drive module), connected through a shaft. Both of these modules use fourth-generation Haldex multi-plate clutches as torque dividers, and upon request, you can install a limited-slip differential at the rear. Unlike conventional viscous clutch systems (in which torque is transmitted to the rear axle after a slip phase, which raises the temperature of the oil contained in the clutch, which increases its viscosity), the XWD transfer case clutch discs hold the front torques against each other by hydraulic pressure and immediately activate reverse gear. According to Saab technicians, this results in an immediate increase in traction and acceleration from standstill. When the gear is engaged, the engine torque is continuously distributed between the axles by a valve in the transfer case, which increases or decreases the pressure on the clutch discs.

It is useful to emphasize that in order to reduce fuel consumption on motorway sections with constant speed, only 5-10% of the engine torque is transferred to the rear axle.