Audi's quattro with ultra technology sounds awesome. We know quattro is good, so ultra technology quattro must be better, right? But what is it, what does it really mean, and - most importantly - how does it work? Let's explore.

Quattro arrived in 1980 in - appropriately - the Quattro. The permanent all-wheel drive system took the rally scene by surprise when it started to dominate the competition in the dirt. Since then, Audi and quattro all-wheel drive have become synonymous. Every model the automaker offers is available with some form of the system, and on most it comes standard (in North America, anyway).

So that's quattro, but what makes it ultra?

Audi offers multiple types of all-wheel drive systems, depending on the vehicle and the engine layout. There is a system for transverse-mounted engine cars like the A3, and multiple systems for cars and crossovers with longitudinally mounted engines. Sideways engine cars use a system with a Haldex center differential. They send power to the front wheels most of the time, but use a clutch to send power to the back wheels when needed.

Most Audis with the engines mounted lengthwise use a Torsen center differential. It detects torque imbalances between the front and rear and locks up to send torque to the wheels with grip. Just to be confusing, the Q7 and R8 use systems that are different again.

So what is ultra quattro? Well, the problem with making all-wheel drive your signature is the increased fuel consumption that comes with driving all four wheels, along with the extra weight of the extra differentials, axles and other components. As fuel economy and emissions standards tighten, Audi needs a way to make its trademark more efficient.

Enter ultra technology. In short, it's a fancy electronically controlled center differential. But it's more complicated than that and does more than that for the driver.

The new system is for Audi's longitudinally-mounted engine cars and SUVs. Like the A4, Q5, and A8, although it hasn't yet made it into all of those models.

It starts with a multi-plate wet clutch at the tail end of the transmission instead of a conventional center differential. The clutch pack works like a normal manual transmission clutch, except that in this case it controls drive to the rear axle and is actuated by the computer, not your foot. The clutch uses more plates so it can be smaller in diameter and take up less space. Five or seven clutch discs depending on the model.

Ultra quattro clutch pack, disengaged​

The clutch is activated by a worm gear drive. Think the adjuster on a crescent wrench, but with the drive turned by an electric motor.
Spin it and the clutches clamp together or loosen. With the clutch released, only the front wheels get power. With it engaged, the rears get power too.

With just that clutch pack, the driveshaft would still spin all the time, turned by the rear wheels. That increases the force needed to move the car and uses more gas. To solve that, the right-rear axle shaft is cut in two at the differential. It uses a dog clutch (the red teeth in the differential photo below), or claw clutch to engage and disengage the axle shaft from the differential. The dog clutch is a set of square teeth on both sides that is opened electronically and closed with springs.

With the right rear axle shaft disengaged, the differential no longer turns the driveshaft. The driveshaft, rear carrier, and pinion stop spinning. Less mass being turned by the engine or dragging the rear wheels means less fuel is needed to move the car.

To re-engage all-wheel drive mode, the front clutch pack is engaged, then an electromechanical pin is released that lets the right-rear axle shaft re-engage thanks to the spring pushing on it. Once that happens, quattro is officially fired up.

Ultra quattro rear differential, disengaged​

There are a lot of parts involved, but the net effect is simple. The driveshaft and diff are freed from the rest of the drivetrain on demand. That saves fuel to the tune of around 0.3 L per 100 km. Or 0.13 gallons for every 100 miles. Not a huge number, but it adds up when you look at Audi's fleet average fuel economy.

The new system does more than just save fuel. It gives Audi greater control over how power is doled out between the front and rear axles, which impacts handling and stability.

Ultra quattro rear differential, engaged​

The quattro electronics are networked in with the car's control units. Every 10 milliseconds, the system scans data like steering angle, lateral and longitudinal acceleration, engine torque, and more. Using that data, it can engage proactively, predictively, and reactively.

Proactive engagement occurs when you're driving normally and nearing maximum grip from a front tire. The focus of the system is on the data. The quattro controller predicts when the front tire will hit maximum grip in cornering or acceleration. It can finish the calculation nearly half a second before the car normally exceeds traction limits and engages the system before the driver experiences a loss of grip.

Predictive activation learns the driver's style and monitors the ESC setting and the drive select mode. It knows you're tossing the car hard into a corner with your foot on the gas, and in dynamic mode, so it engages the rear axle sooner. Drive it hard on a dry road, and the rear wheels will stay activated.

In reactive activation, which Audi says is rare in normal use, the system engages nearly instantly when sudden changes in friction are detected. Think hitting a sudden patch of ice in the winter.

Quattro with ultra technology, all wheels engaged​

As you would expect, Audi says that the system engages the rear axle more in the winter. But that doesn't mean it's on all of the time in the winter, just when the car thinks you need it.

Thanks to the worm drive's ability to engage the clutch pack progressively, Audi can use the computer controls to vary the power sent rearward. Loose engagement between the clutches sends a little power to the rear wheels. Clamp down harder and more power goes to the back. Up to 100 percent of the power can be sent to the front or rear axle, depending on what's needed.

The new system is still rolling out. It debuted on the 2017 Audi A4 Allroad, and then on the 2018 Q5 crossover. Expect it to move across Audi's lineup going forward.