XWD (Cross Wheel Drive)

All-wheel-drive system Saab XWD (Cross Wheel Drive) has been designed in collaboration with the renowned Swedish company Haldex. This modern all-wheel drive system combines two innovative solutions: preventative actuator rear wheels based on operational measurements and active rear differential with increased slip, which ensures variable distribution of torque between the individual rear wheels.

Saab XWD

All-wheel-drive system XWD control separate control unit that works with controllers engine, transmission and control units of electromechanical systems, ABS and ESP . The system also includes a unit PTU (Power Take-off Unit) which is placed in front of the vehicle and transmits engine torque through the driveshaft to the rear axle, respectively. the drive to the rear axle bearing RDM (Rest Drive Module). This unit contains equipment for torque transmission TTD (Torque Transfer Device) and electronically controlled slip differential with increased ELSD (Electronic Limited Slip Differential). This is actually the Haldex multi-plate clutches in an oil bath.

arrangement of all-wheel drive system XWD

Traction leads to activation of the TTD module combination clutch plates hydraulic pressure. This leads also to connect the drive rear axle RDM. This smart feature is a major enhancement of existing technologies that have not yet used to connect the rear axle to drive the front wheels slip. The driver with the new all-wheel drive system can be far more sensitive to lead your car with confidence the ideal all-wheel traction and accelerate without having to worry about the fact that he can get his car into an uncontrollable skid.

RDM (Rest Drive Module)

In normal driving the torque is constant and without significant changes distributed between front and rear axles via proportional valve in the outlet module TTD. This change in pressure valve closes and opens the clutch plates. All wheels are permanently powered, so the behavior is much more agile car and balanced. Controller XWD system uses data from sensors systems, ABS and ESP , such as wheel speed and steering angle. The acquired data is then compared with that in carefully designed data maps, on which the system decides to connect the rear wheels. When driving on the highway traction is not usually a major problem, and to the rear wheels is transmitted from 5 to 10% torque. This contributes to improved stability and handling car while consuming less fuel.

XWD system components

An important part of the whole system, Saab XWD is an electronic slip differential with increased ELSD. Electronic differential ELSD is located next to the module RDM and operates on the principle of pressure-controlled clutch plates like a much larger module for transmission of torque (TTD). If the car goes down the road with varying or low adhesion, the control unit evaluates the speed of rotation of rear wheels and can transfer up to 40% torque to the wheel that runs over the surface with better grip.

This system thus contributes to improved handling during fast cornering and abrupt evasive maneuvers. In a sharp change of direction electronic differential sends torque to the rear wheel to the rear of the car better monitor and track front-wheel vehicle overall was "obedient". Car equipped with this system are significantly less inclined, the ride is calmer and more balanced. The car was better controlled without the intervention of the electronic stabilization program .

Text: John Sajdl
Photo: http://media.saab.com
Keywords: all-wheel drive, 4 × 4, XWD, SAAB