2017 Audi A4 allroad: Less quattro is More

With the redesigned A4 allroad, Audi is introducing a new version of its all-wheel drivetrain that will soon be used the brand’s other models like the A4, the A5 and possibly the Q5.

Known as quattro ultra, it has the distinction of uncoupling the rear axle with an eye towards reducing fuel consumption by 0.3 L/100 km, according to Audi, compared to a conventional full-time all-wheel drive. What’s more, it helps reduce CO2 emissions by approximately seven grams per kilometre, putting it on par with a two-wheel-drive vehicle of equivalent size.

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This new mechanism is very advanced from a technical perspective. It’s different from current systems developed by rival manufacturers that simply open a clutch to avoid sending torque to the rear wheels, but whose main mechanical components continue to turn, leading to continued high fuel consumption.

Disconnection and immobilization

The best thing about quattro ultra is that it not only disconnects the rear axle when all-wheel drive isn’t needed, but it goes the extra mile by immobilizing the drive shaft as well as the drive gear and pinion linked to the rear axle. With these components now immobile, there’s no more friction and the loss of fuel efficiency that comes with it. The car then runs as though it were a simple front-wheel drive vehicle.

Reactivity in two tenths of a second

When the system detects that all-wheel drive is warranted, it reacts in a mere two tenths of a second by closing the clutch, making the central driveshaft spin and engaging the rear axle half-shaft to send torque on the rear axle.
The system relies on an array of sensors that measure grip in real time and take into account a series of parameters like accelerator compression, steering and lateral acceleration, among others. Remarkably, the system can “anticipate” the need to engage AWD even before it becomes necessary by demonstrating great reactivity.

Forty kilometres, 96% efficiency and 11 connections

To put the system to the test, Audi asked us to drive on a 40-odd kilometre loop with one of their engineers on board. The engineer was equipped with an iPad linked to the all-wheel drive system, allowing us to see, in real time, when the car was driving only its front wheels and when it was driving on all four.

The car begins in all-wheel drive mode by default, but if it’s going in a straight line and the driver is taking it easy on the accelerator, it will start to run as a front-wheel drive. The moment the driver accelerates suddenly or the car enters a turn at a higher speed, the system reacts in two-tenths of a second and the all-wheel drive is engaged.

Never once over the entire trip did I feel the decoupling of the rear axle and the handling remained constant. I even went with the flow and adjusted my driving to engage the all-wheel drive as little as possible. I ended up doing 96% of the course in front-wheel drive, with the all-wheel drive engaging just eleven times, a record according to our engineer riding shotgun.

For Audi, it’s clear that this new all-wheel drive is a step in the right direction to reduce fuel consumption and you can expect it to spread throughout the brand. As for communication with the public, however, this mechanism poses a problem.

After years spent convincing buyers that full-time AWD was an important factor in safety and performance, the brand now has to explain to these same people that having four powered wheels isn’t essential 100% of the time. It’s true, but getting the word out is going to take some effort