The new 2017 Audi A4 Allroad and both feature a new variation on the the automaker's famous Quattro all-wheel-drive power train. Dubbed "Quattro with ultra technology," the new system adds the ability to seamlessly decouple the front wheels to increase fuel economy. We've tested the system on both vehicles and found its operation so seamless that we couldn't tell what it was actually doing behind the scenes.
So I grabbed a Q5, cornered an Audi engineer and asked way too many questions. Here's what I learned.
A tale of two clutches
Like most tech, Audi's Quattro with Ultra consists of two parts: hardware and software. On the hardware side Ultra features an electronically controlled multiplate clutch where the prop shaft -- which sends power to the rear wheels -- meets the transmission and a dogleg clutch inside of the rear differential.
The multiplate clutch is used for fine control, shifting the torque distribution between the front and rear wheels. When the software, which we'll get to in a moment, detects that grip is sufficient that all wheels don't need to be driven, the multiplate clutch can send 100 percent of available torque to the front wheels and disconnect.
This is the first point where Audi says that its system is different from other on-demand all-wheel drive systems. Most on-demand systems can disconnect at a center differential, but still leave the rear differential and prop shaft spinning with the rear wheels. Ultra features a decoupling dogleg clutch in the rear axle differential that stops the shaft and diff from spinning, reducing friction while cruising and saving a bit more fuel.
When the system needs to re-engage the rear wheels, it first begins re-engagement with the multiplate, which brings the prop shaft and rear differential back up to operating speed and then, bang, the dogleg clutch in the rear diff instantly engages the rear wheels. Only, there's no bang or jerk, because the transition should be seamless like a perfectly rev-matched shift from a dual-clutch transmission. The entire re-engagement process takes just 200 milliseconds, about half the time it takes you to blink.
Proactive, not reactive
Like any good all-wheel drive system, Audi's Quattro with Ultra system is loaded up with all sorts of sensors monitoring wheel speed versus vehicle speed, incline, inertia, throttle and steering position and more. All stated, over 100 parameters are monitored and fed into Quattro's electronic brain.
However, instead of just monitoring and reacting to grip, Quattro with Ultra monitors, models and simulates into the future to make predictions. It basically builds a constantly updating profile of driving conditions and driver behavior.
So, if I'm driving on a dry road, it will learn that there's a high level of available grip and know exactly how it can react to my steering and throttle inputs. If I then drive onto a sandy beach, the computer's estimates of available grip will shrink significantly and it will use more generous all-wheel drive when responding to my throttle input. Ideally, by knowing how much grip is available before I step on the gas, it can be proactive and already have Quattro engaged before any wheel can spin.
Likewise, if I carry a lot of speed into corners or make big throttle inputs, the system will begin to profile me as a "dynamic" driver and engage Quattro accordingly. If I then slow down and keep more constant speed, it will begin to adjust its reactions to my driving through "comfort" and "economical" profiles and spend more time in front-wheel drive.
Quattro with Ultra's performance can also be affected by the Drive Select mode chosen by the driver. Vehicles with an off-road setting can lock the system into all-wheel operation and dynamic modes may cause the system to more aggressively engage the rear wheels.
On the road
According to Audi, Quattro with Ultra can predict driving conditions up to 500 milliseconds into the future based on these grip and driver profiles, giving its 200-ms clutches plenty of time to react. In the car, Audi's engineer presented a tablet running a diagnostics app to demonstrate how that works on the road.
Quattro with Ultra always initially defaults to all-wheel drive to give the best grip from a stop and to allow the computer a few moments to evaluate grip and build its model. On the screen, a red indicator let me know that Quattro was operating in all-wheel mode. In the dry conditions of my testing, that indicator changed to white at around 20-30 mph to indicate front-wheel drive.
In the app was a circular graph that indicated how much grip was available versus how much was being used. If I drove in sand or dirt, that circle shrank to indicate Quattro's best estimate of the reduction of grip. Back on asphalt, the circle would grow. As I approached the limits by steering or accelerating, the Quattro indicator would light up.
I also noticed that sometimes Quattro would engage during straight-line acceleration even when I was nowhere near to the limits of the grip. Audi's engineer explained this was designed to reduce torque steer that you typically get from strong front-drive acceleration by sending more power to the rear, non-steering wheels. Nice.
As a novelty, Audi showed me charts measuring how much of my time was spent front-wheel driving. It turns out that Quattro with Ultra only engaged all-wheel for 12 to 15 percent of my driving time. It would fire up for a pass, a corner or an off-road passage and then instantly disengage again for highway driving. On one hand, the system wasn't active for a large percentage of the operation time but on the other it had activated dozens of times during just one day's drive in very dry conditions (I imagine those charts would look different where it was raining or snowing) without penalizing the fuel economy much when it didn't need to.
Without the diagnostics indicator -- which you won't find in a production Q5 -- the system's operation was completely seamless. I had no way of telling whether the system was operating in front- or all-wheel drive mode. This is good, because it means there was no noticeable wheel slip or jerkiness in the operation. It just worked.