Audi is rolling out a new version of its Quattro all-wheel-drive system that promises an efficiency improvement of at least 5 percent?more on the highway. Available exclusively on the VW Group’s modular-longitudinal platform, the new system, which Audi calls Quattro Ultra, decouples the rear axle when it’s not needed. Fewer moving parts equals less friction.
 

This is a particularly big deal for Audi, since a whopping 43 percent of all Audis globally are all-wheel drive. Audi’s new Quattro Ultra will launch first on the new A4-based Allroad, slated to go on sale in the summer of 2016.

This is how the system works: When the software decides that front-wheel drive is sufficient, it electromechanically disengages a multiplate clutch positioned right behind the transmission. A clutch in the rear differential also decouples to stop the prop shaft from rotating in order to reduce friction and losses. The reverse process, engaging the rear axle, takes a maximum of 250 milliseconds. But as quickly as it works, Audi doesn’t want the system to merely react to road conditions; in fact, reactive engagement is only the last resort and seldom happens. One instance would be when the car is traveling on a dry road and suddenly hits a slippery spot. In most circumstances, all-wheel drive already will be pre-engaged because of the proactive and predictive decisions. For example, the car will know when to expect adhesion loss at a given cornering speed about 0....