I linked earlier to the website for the new Haldex XWD system as used on the new 2008 Saab 9-3. If you haven’t clicked on over yet, it really is worth a look. There’s a number of animated slideshows there to give you a good idea as to how things work with this system. Try this on for size:
As you can see, this very clever system is fully capable of delivering ample power to the wheels that need it. As little as 4% to the rear wheels when cruising and as much as 85% to a single rear wheel when needed. The system is designed to make the most of whatever torque is available, placing it where it’s required according to all the electronic gizmos controlling the system in the Haldex ECU.
Here’s the heart of the system:
The TTD coupling distributes the available torque between the front and rear axles as directed by the ECU. You can have heaps of rear drive for take-offs or up to 96% front drive for traction in snowy conditions, for example. The car is essentially able to have the best of both rear- or front-wheel-drive and of course, a combination of the two.
The electronic limited slip diff is the second coupling in the system and distributes the available torque between the left and right rear wheels as directed, once again, by the ECU. As shown in the still-shot above, the sensors in the ECU detect relative traction and can compensate by directing torque where it’s needed. This helps out with quick lateral movements, allowing for greater safety in tricky situations, and better performance when you mean to be in a tricky situation!
This is the technology that controls it all – the ECU. It uses 20 different sensors around 100 times per second to detect changes in vehicle dynamics and thereby distributes torque – front to back and in the rear, from side to side. All this works in conjunction with the Traction Control System and ABS, of course.
There’s some interesting tidbits of info on there was well, such as the Haldex timeline showing which models have used their systems over the years. I never knew the Bugatti Veyron used a Haldex system, for example. Saab’s got some pretty good company!
As I mentioned in the earlier post on the subject, there’s also a technical guide on the site, which is available as a PDF download. This gets right into the nitty-gritties of how the system works, stuff like yaw control (which brings on yawn control for me) and lots of charts and graphs. If you’re an engineering type, get on over and check it out at the ‘downloads section’.
All of this would just be talk if it weren’t being made available for the first time in the world on the new 2008 Saab 9-3. If you haven’t seen it yet, here’s Kenneth Backlund from the Saab Performance Team putting it all to good use in a Saab 9-3 SportCombi on the special test track used for the recent media events in Sweden.
If you have seen it before, then enjoy it again.