• Oct 14, 2007

The F-16 is inherently unstable and cannot fly without computerized nannies to keep it aloft. As AWD systems in cars get more complex and can do more things more quickly, one wonders if there will come a time when we'll be absolutely unable to drive without gizmos to make sure rubber stays on road. Torque vectoring is the next step in AWD, its contribution being that it can get power to any wheel nearly instantly without having to use the brakes or cut power.

Most current AWD control wheelspin by braking a spinning wheel or cutting the power from the engine. Torque vectoring is achieved by using redesigned differentials that can distribute power to the wheel or wheels that have traction. That means that wheels don't need to be stopped, and even better, you won't suffer from a sudden loss of power as you're negotiating an unexpected loss in traction. The systems in use now or being developed work on FWD, RWD, and AWD cars, and can get power to any wheel or combination of wheels. Ricardo's system can do so in a tenth of a second.

We drove Acuras with SH-AWD (Super Handling All Wheel Drive) earlier this year on an ice track in Montreal, and the difference is remarkable. Where other SUV's stopped in the middle of an icy corner either due to braking or power loss, the Acuras maintained their lines almost at speed. Mitsubishi has used the technology for almost a decade now on its Lancer Evolutions, and Audi and BMW will be joining the party later this year with new systems from Ricardo and ZF.

[Source: Popular Mechanics]



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  • 22 Comments
      • 7 Years Ago
      wait, im confused. i thought the torsen system in audis already did this. its a purely mechanical system that shifts the torque to the wheels that arent spinning freely.
      the traction control that brakes loose wheels is an entirely different, yet complimentary, system
        • 7 Years Ago
        Audi does not do this. They have a clever mechanical setup that assures that all 4 wheels are being driven symmetrically. Subaru does this too, but with viscous type limited slip differentials. Pretty much everyone else, BMW including, uses something licensed from or based on the Haldex system, which is poohpoohed by AWD fanatics as not being "true" AWD, because of the forementioned loss of power that happens when the vehicle enters a slippery bit.

        The drawback to the Audi/Subaru strategy is that it really *is* true 4x4 and that sort of thing eats up a *lot* of fuel.
      • 7 Years Ago
      Everyone here seems to be talking about basic All Wheel Drive and Limited Slip Differentials. This article is about Torque Vectoring. There are major differences, but instead of researching and learning, it seems most people are just running their mouths.
      • 7 Years Ago
      EVO AYC FTW!
      • 7 Years Ago
      Bah. MIEV (via Ferdinand Porsche) for the win.
      • 7 Years Ago
      Actually, SH-AWD is a FULL-time AWD system. In regular driving, 90% of the power is sent to the front while 10% is sent to the back. Whenever one accelerates, power is automatically/instantly reverted to the rear wheels for optimal traction and best acceleration numbers. 90% is the maximum amount of power sent to the rear wheels, hence 10% of the power will ALWAYS be on either set of wheels. Though only up to 90% can be at the rear, 100% of that 90% can go to one singular wheel. So thing no other AWD system can do yet.

      The SH-AWD system beats all other AWD systems w/ torque vectoring because it also has an over drive gear the actually makes the outside rear wheel spin faster than the other 3 wheels thus "rotating" the car around a corner. I believe the MDX and RDX has a 1.7% overdrive while the RL's more complex system overdrives it 3.7%.

      All three of Acura's cars that have SH-AWD currently are FWD-based but the new Acura NSX is supposed to be RWD-based making it perform AND feel like a RWD car.
      • 7 Years Ago
      Hard to add to the technical knowledge that has already been brought to bear here.

      Although I disagree with the statement that FWD with snows is better than AWD with all-seasons. a dumb rolling axle is no help in the snow, and tends to slide and move around.

      There is no way that a snow tire has twice the traction of an all-season tire for the same size contact patch. With AWD you are applying torque with twice the contact patch area, something that is more than just the difference between all-seasons and snows.

      And 4 snows on subaru AWD, FAN-TASTIC. I know. I have it, and unfortunately can't call in stranded from work in the winter, unless there are 4-foot drifts across the roads that any sort of a car simply can't punch through without damage.

      But I agree. SH-AWD is overly complex, and the effect is barely better than the overly complex haldex coupling AWD setups.

      Audi Torsen Quattro is good, but they seem to have gone away from torsen diffs at the axles, and rely on electronic brake force distribution to channel power away from the slipping wheel, which seems like a bit of a cop out to me.

      Subaru AWD, however, is one of the best on the market. Anything more than a 4-speed automatic (90% front bias) has better AWD than most other cars, and SUVs, and even better than the straight transfer case in my old pickup truck.

      5-speed manuals get 50% to front and rear, and turbo legacys get a viscous LSD in the rear axle. The 5-speed automatics get variable torque bias, on demand, with traction and stability control.

      The STI does one better, with a driver-controlled center differential, with automatic and manual settings for front-to-rear torque bias, from 65% rear, to ~100% rear bias, IIRC, again with limited rear slip.

      The japanese S204 limited edition STIs upgrade that with torsen front and rear axle torque-biasing limited slip, in addition to the DCCD. It doesn't get much better than that. I wish that were available in the US market.

      But it is mostly mechanical, and robust, and doesn't try to second-guess and cover-up deficiencies in the drivetrain and chassis.

      It seems like a better idea to allow electronic controls, like DCCD, to improve on a solid system, rather than to mask an inferior one.
        • 7 Years Ago
        I have driven RWD with "snows" on all 4, FWD with same and AWD with snows on all 4 as well (all sedans).

        Personally, I like the opportunity to throttle steer in the snow and believe that I have better control of the car in a slippery situation if I can do that.

        My order of preference for snow driving with 4 snows...:
        1. Rear-biased AWD
        2. Front Biased AWD
        3. RWD
        4. FWD
      • 7 Years Ago
      The F-16 is not "inherently unstable". The F-16's claim to fame is that it is the first fighter to employ fly-by-wire which is computer-controlled electrical actuation of the flight-control systems. Fly-by-wire is a requirement of unstable designs, but having fly-by-wire does not mean that an aircraft is inherently unstable. Fly-by-wire provides many benefits such as weight savings, faster control response and reduced maintenance over conventional hydraulic control systems.

      The first unstable design to fly successfully was the X-29 forward-swept-wing experimental aircraft. It came after the F-16 entered service.
      • 7 Years Ago
      So, how exactly is this better than Torsen?
      • 7 Years Ago
      Saab already has this XWD.
        • 7 Years Ago
        No it does not.
        Saab XWD (cross wheel drive) is nothing but the latest Haldex coupled rear axle system (generation 4) plus an 'eLSD' which is just a computer controlling a lock up clutch pack on the rear differential. There isn't any shuffling, only adjustable yaw damping by locking/unlocking the rear differential. That is all.
        There isn't any reason all the haldex implementations can't have this (other than maybe some contractual stipulation) The new Golf R36 comes to mind, or the Volvo S80 T6.
      • 7 Years Ago
      help me out here...
      what are the main differences between this AH-AWD and say Saab's XWD?

      AH-AWD is mechanical and XWD is Electrical; which will be better than cars go hybird or electric.

      Which is better for winter conditions?
      • 7 Years Ago
      Almost everyone (including the original article, to a large extent) seems to have missed the point of torque vectoring. It's not about traction: any system which can reduce the speed difference between wheels (either through a viscous coupling or Gerodisk approach, or just by locking them together) will get you pretty much all the traction there is going.

      What TV can do is influence the vehicle's response to steering inputs. Centre TV can correct power-on under- or oversteer by transferring torque away from the axle which is losing grip; the Skyline GTR's system (and also Porsche 959 I think) can vector torque towards the front to partially achieve this. I'm not sure whether the front is overdriven: if it is, this could allow 100% of the torque to be vectored to the front; if not, the best that can be achieved is a locked centre, leaving the tyres to decide exactly how much goes to each end.

      Axle TV (normally rear) is even more effective, as it can inject a yaw moment to help the car turn in. This is the biggest difference over any normal LSD, which can only provide a stabilising moment (at least until you're on the edge of power-on oversteer). This is what's used on the Evo 8 MR and onwards to give it such responsive, tail-happy but controllable handling.
      • 7 Years Ago
      My Subaru does very well with viscous limited-slip center and rear diffs- great in the wet, incredibly capable in snow. Just a reminder that complex electronic tomfoolery isn't always necessary and that simpler systems that split torque effectively in different situations have been around for some time.

      Although I have to admit, EVO X S-AWC seems pretty awesome.
        • 7 Years Ago
        Well, AWD at all isn't necessary in the snow, let alone electronic tomfoolery to make each wheel's power output independent.
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