Haldex XWD

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:

Haldex XWD

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:

Haldex TTD 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.

—–

Haldex eLSD 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!

—–

Haldex ECU 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.

16 thoughts on “Haldex XWD

  1. I wonder how similar this is to the Mitsubishi S-AWC system which seems to be getting better coverage in the press. Haldex provides a more understandable explanation of their system, but it sounds like the Mitsu system is similar However, the Mitsu press release doesn’t give good details. I hope the Haldex system is a cut above the Mitsu system, e.g., locking front and rear at takeoff, quicker response, more compact, lighter, etc. If someone understands the differences, please explain.
    http://autobeat.blogspot.com/2007/07/mitsubishi-motors-develops-s-awc.html

  2. This system looks great, but being new to all things AWD, how does this system differ from “run-of-the-mill” AWD? I mean, what’s so special about this system? How about that “SH-AWD” (Super Handling AWD) Acura (Honda) has?

    Another thought comes to mind: with 20 sensors and an ECU controlling the XWD system what if one fails? How would the driver know? How would your mechanic know (assuming you’re out of warranty and don’t take it to the assumedly-well-trained dealer mechanic)? As you know the more complexity in a machine the more likely it is to fail. Am I just being a worry-wart?

    Does the added weight of this system adversely affect fuel economy? When looking for a new car for my mom we went by the AUDI dealer and they kept showing her A4s equipped with Quattro. I asked why anyone in Southern California would need AWD and the sales guy admitted that there’s very little use for it and that it hurts fuel economy and that some people just demand all the “bells and whistles” whether they need it or not. I can maybe understand if it were an S4 and required the transfer of power to the pavement, but these were base level A4s with Quattro…

  3. Gripen,

    My understanding regarding XWD vs. standard AWD is the following:

    First, in the standard AWD system, there must first be slippage of the wheels before torque can be transferred elsewhere. This new system allows the torque to be sent back to the rear axle without any wheel slippage.

    Second, the XWD system allows you to transfer up to 40% of the torque between the rear wheels individually. I don’t think most AWD systems can do that.

    Don’t quote me on it, but I swear I heard them mention this system is lighter than most AWD systems (40 or 60 kilos??). Anyone have info or a quote on that?

    And third, it seems I read up on something that both left and right wheels on an axle lose power if only one wheel slips with AWD; that is, unless you have a Torsen differential (found in Hummers and some higher end Audis I think?). But like I said, I may be wrong- this is all off memory and I’m no engineer!

    I totally agree with you- so many people either have no idea what they’re talking about, or they want some feature for the sake of its bling and frills when they really don’t need it. I’d say Quattro really isn’t going to do you much good in places like Arizona or Las Vegas or SoCal, unless you got some serious torque to put to the ground. But it’s a bragging feature for many Audi owners around, that’s for sure!

  4. See the transparent vehicle in the XWD EXPLORE page of the technical tab….What is it. 9-4 maybe??

  5. the haldex XWD system looks pretty nice with some innovations that should generate a lot of press for saab . i wonder if there will be any user selectable modes such as launch or sport available?
    i would be very interested in the impact on fuel economy. a 300 HP XWD sport combi that gets 30 mpg would be a big seller for Saab. on the downside i echo concerns regarding potential malfunction and repair issues . anyone know the track record of Haldex in audi TT and volvo?

    /btw liking the new site Swade good job!

  6. I was just reading up on the new XC90 ovloV and it is using the Haldex AWD also.
    “The Haldex all-wheel-drive system sends 95 percent of engine torque to the front wheels in normal driving. If the front tires lose traction, up to 65 percent of engine power can be transferred to the rear wheels”. edmunds just did a drive in it. They liked the car but did not like the engine.

  7. ehall1: ovloV may use a Haldex AWD system, but not the innovative new XWD system that SAAB has debuted.

    Note that it says “If the front tires lose traction, up to 65 percent of engine power can be transferred to the rear wheels”. The XWD system in the SAABs is predictive and doesn’t require the tire to lose traction before transferring power. Also, the XWD system can split the power between the rear wheels if necessary, whereas I believe a typical AWD system sends equal power to both rear wheels, even if one has lost traction.

    I haven’t seen anyone else point out something I found interesting: Haldex is a Swedish firm.

  8. Oops, make that “95 percent” in my attempt at quoting in my comment above… :-(

  9. I wish, on that video, that I could have seen the actual speed. As it is, it is obvious that Mr. Backlund is an incredibly well-practiced, finely trained driver in an equally finely tuned car.

    I love the concept of XWD, especially since it doesn’t require slippage before power transfer, but will predictively transfer power to the rear on takeoff, then towards the front as you drive. BEAUTIFUL!

  10. Can you imagine how advantageous the XWD system would be in a WRC car? I would love to see SAAB jump back into rally racing with an XWD-equipped 9-1.

    The only thing I fear is that though SAAB have the exclusive on this fourth-gen Haldex system, surely that’s not forever. How long before other manufacturers are allowed to buy the system? By the time the 9-1 comes out SAAB will likely no longer be the only auto manufacturer with the rights to the XWD system, meaning that their potential advantage in rally racing would be lost.

  11. 1985 Gripen,

    Yes Haldex is Swedish, another point of note is that the XWD plant is in Mexico.

    The whole concept of 95% RWD LSD is great news for Saab in any environment or weather. Try turning ESP/TCS off on a FWD 9-3 and planting the foot, RHS front tyre goes up in smoke.

  12. Was it not that Saab owned the “XWD” trademark? Why is Haldex using it for their fourth generation AWD system now?

  13. Well if XWD is Saab’s trademark it makes some sense. If Haldex or anybody else want to use it Saab gets some sort of royalties. Or maybe Haldex gets to use it as some payout therefore reducing Saab’s development outlay. In any case IP is good business.

  14. But once Haldex starts putting this system into other manufacturers’ vehicles they can’t use the XWD name (assuming SAAB owns the trademark). They’ll have to name it something else.

  15. Yes but the “other” manufacturers can pay Saab for use of the trademark. Betcha they won’t though.

Comments are closed.