We’ve had 40 years of Audi quattro

Quattro is a ubiquitous tech today for four-ringed vehicles. When you see an Audi, you assume it has all-wheel-drive. And over the course of the last 40 years, this concept has only grown stronger by the decade. Driving technology that’s refined and exceptional today wasn’t forged on road, of course. The Audi quattro all-wheel-drive system was baptized by Group B fire.

But the idea of bringing all-wheel-drive to Audi started even before motorsport ambitions. It has to do with military tech borrowed from the Volkswagen side of the family. Engineers at Audi saw the improved off-road and bad-weather capability of the VW Type 183. Also called the Iltis, this was a Jeep-type vehicle for Germany and its four-wheel-drive system saw it scrambling in and out of tough situations using parts taken off an Audi 100.

What’s the diff?

The first version of quattro utilized a trio of differentials. These were all mechanical diffs, with one in the nose, a center diff, and one on the rear axle. The driver of the car could lock the center differential and the front and rears would work together. Audi used this setup until the late 80s.

Soon the all-wheel-drive system received a Torsen differential in the middle. This update helped better distribute torque between the front and rear axles. Unlike the earlier quattro-equipped models, the Torsen diff worked automatically instead of being manually selected. How did it work? Here’s how Audi explains it:

The Torsen center differential housed a pair of helical planetary gears. The gears were held in tight-fitting pockets inside the housing and splined together through spur gears at their ends. These spur gears did not allow the planetary gears to rotate in the same direction. However, when an axle would lose traction, the spur gears would help channel torque to the wheels with traction. This could allow up to two-thirds of the vehicle’s torque to be sent to either the front or rear axle.

A move to Haldex

The Torsen setup works great for Audi vehicles with an engine laid out longitudinally. Smaller Audi vehicles, however, started appearing with transverse engines. Namely, the 2000 Audi TT and its beautiful Bauhaus body. To keep quattro available, Audi employed a Haldex coupling for proper power routing.

As the driveshaft comes off the back of the gearbox, it runs into the Haldex coupling. This sits ahead of the rear differential and it uses hydraulic pressure to engage all-wheel-drive when necessary. It’s about sensing the differing speeds between its input and output shafts, which in turn drives a hydraulic system that actuates a clutch. When the conditions are right, the rear differential gets to work.

Efficiency and Complexity

Audi quattro has evolved dramatically over the last 40 years. You have different setups for the different platform architectures, with each serving torque-varying relevance as needed by vehicle case. The standard quattro system works much in the same way as the original, actually. But it’s mechanical bits are aided by a suite of electronics, sensors, meters, and more.

This allows all three differentials to provide a near-constant stream of adjustments based on the exact driving conditions you face.

Even more amazing is that Audi now has a fully electric quattro system as well. It’s offered on the E-Tron and it’s the fastest reacting system in the stable. The E-Tron quattro setup is comprised of a pair of electric motors and a pair of single-speed transmissions for each motor. These motors and the controlling computers can react immediately to changing power needs at each wheel.

In fact, Audi is taking this a step further with the development of an E-Tron wearing two motors at the back (instead of just one front and one rear). This would allow for even greater control of power delivery. Not to mention… more power available.

This technology follows a familiar flow. What was originally intended for military use was adopted for motorsport and then perfected out on the road. And now 40 years later, Audi quattro remains one of the premier all-wheel-drive systems on the market. This means you can pretend to have a little bit of Group B adventure, even if you’re daily commute isn’t flocked with stages of insane fans. Take the curvy road and enjoy the ride.

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12 Comments

  1. There’s the Quattro (or, Ur-Quattro), and then there’s just “quattro”. The former, I think of the badass S1 racer like the one in your lead image. The latter, I think of the humdrum Q5 (my wife’s “driving appliance”) sitting in our garage.

    Speaking of Audis, though, an R8 accelerated (hard) past me when I was out on the bike this week, and I was surprised that it sounded like a giant motorcycle. I don’t think I’ve ever really heard one wind up before. I just assumed they would sound similar to a Viper, but they definitely don’t.

    1. No they’re somewhere between Lamborghini and Viper. Closer to the Italian though, for sure.

      1. Dunno… all are at a price tag well beyond my ear’s calibration range. Regardless, it was impressive.

  2. Getting all this done mechanically eternally impresses my not-too-mechanically-adept-brain. I mean, it’s great work getting this done with sensors and digital controls, too, but gears, levers and oils as the only input? Pretty cool. And I still don’t understand how a Haldex clutch works and why half the all wheel drive community intuitively spits on the floor whenever they hear “Haldex”…

    1. The Haldex coupling is basically a clutch, and I think does away with the need for a centre differential which would be what upsets purists. Especially when they apply the Quattro name that was supposed to signify a particular (revered) technology to something entirely different. The clutch allows the front and rear axles to turn at different rates by slipping.

      A haldex system is fundamentally the same as a lot of fwd systems which can be 2wd until the computer decides otherwise, and I dare say early versions would have had room for improvement.

      1. Does that make a Haldex a fancier version of the viscous coupling used on the Vanagon Syncro among others. Those use the magic of thixotropic liquids to adjust torque. Also credit where credit is due the Jensen FF appears to be the first design with a center differential, followed by the Range Rover and the Jeep Quadra Trac system

        1. More flexible/controllable I suppose, but I don’t think Haldex works mechanically only, ie without an electronic controller

    2. The early Haldex system is hydraulically engaged. When the input shaft spins relative to the output shaft that causes a piston pump to move pumping fluid into the servo that applies pressure to a wet clutch. Supposedly it only takes 1/4 of rotation to build enough pressure to cause some clutch engagement. There is an electronic valve that controls the release of pressure. This allows it to dump the pressure so that the clutch won’t engage when the ABS is engaged or during tight parking maneuvers. The problem with this kind of system is that it goes in and out. That valve always lets some pressure bleed off and the pump doesn’t work once the clutch is engaged. So wheel slips, clutch engages, slip stops, clutch disengages, slip occurs, clutch engages and on it goes.

      Honda’s Real Time system works on a similar principle. In it there is a vane pump attached to the input and output. If they turn at the same speed the fluid just pumps between the two, but if one spins faster pressure builds between them which pressurizes the servo that engages the wet clutch. Again once the they are turning the same speed pressure is not being made and since those vane pumps aren’t positive displacement the pressure slowly bleeds off and the system disengages, it also takes a good amount of slip to build enough pressure to engage it.

      The “best” Quattro system is the one with the Torsen center diff. That diff mechanically senses the torque on each output, hence the TORque, SENsening name. So it and other Torsen center diff systems truly does send more of the power to the axle with more grip.

  3. Iltises are still lingering around here relatively cheaply (thanks to Bombardier, the Canadian Armed Forces drove them for years). I’m now a little compelled to find out how one with extra power (and a cage, as they have like zero crash protection) would drive.

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