Audi Quattro boss details Ultra system

WITH the launch of Audi’s second-generation Q5 mid-sized SUV, its adaptive Quattro Ultra transmission system that debuted under the more niche A4 Allroad is now in its first mass model application and will continue to roll out under more vehicles.

Unlike all previous Quattro systems which offered permanent four-wheel drive, the Ultra technology allows the rear wheels to be disconnected when not required, reducing transmission losses and boosting fuel economy.

Other manufacturers offer similar systems but the Audi solution has two points of disconnection to minimise energy-robbing rotating mass and is a more efficient system than its competitors, according to the car-maker.

At the rear of the seven-speed dual-clutch gearbox, a multi-plate pack with electro-mechanical actuator disconnects the propshaft, while a second dog-clutch disconnects one half-shaft from the rear differential.

Not only does the Ultra technology remove drive to the rear wheels, but the second point of disconnection prevents further unnecessary energy loss through friction generated by turning the differential gears.

But how effective is the system at reducing losses and improving fuel economy? At the Audi Q5 international launch in Mexico last week, we rode shotgun with Audi AG head of four-wheel-drive development Dieter Weidemann and the all-paw expert explained the Ultra difference.

During winter testing in Sweden, Mr Weidemann said the team devised an experiment to measure the effort required to turn the differential and highlight how much energy is spared by disconnecting it.

An initial test drive in minus 20-degree conditions was conducted with the differential disconnected and after one hour the differential oil temperature was measured at minus 10 degrees. The same test drive was conducted again but with the differential connected but after another hour the oil temperature had risen to 30 degrees.

Mr Weidemann explained that the energy required to heat the differential mechanicals, casing and oil by 50 degrees from atmospheric would have a significant effect on fuel economy and would certainly be noticed at the pump, but the Ultra system limited temperature increase to just 10 degrees.

Rather than employ a second actuator to disconnect the diff clutch, the Ultra system uses an innovative approach that imperceptibly winds off the dog clutch using wheel rotation and a threaded half shaft.

When it is necessary to reinstate four-wheel drive, a solenoid releases the spring-loaded clutch allowing the castelations to re-engage drive, but Mr Weidemann said developing a system that released the solenoid at precisely the right time was a significant challenge.

The solution required a complex map that predicted half-shaft and differential speed matching in advance of synchronisation as well as a management program that would allow for different solenoid response times according to temperature.

Convincing Audi management of the value of the Ultra system was another challenge, according to Mr Weidemann but the engineer eventually gained unanimous support by demonstrating the advantages of the transmission through an ingenious application.

During GoAuto’s drive of the new Q5, Mr Weidemann talked us through the clever software which has now evolved into a slick iPad application and can show a huge variety of critical transmission information.

The system of sensors and actuators are so sensitive it can detect a specific friction coefficient of each tyre, driving style and micro slip, which is where hard acceleration, tread shuffle or low friction causes the tyre to slip without breaking full traction.

The process of sharing drive between the front and rear wheels is so smooth that the driver is unaware of any Ultra activity but the clever application reveals the constant and rapid activity of the latest Quattro technology.

You might think that a four-wheel-drive system would have little or no benefit on a 76km road trip in perfect conditions and largely on freeways, but at the conclusion of our journey the application revealed a total of 27 activations for a variety of reasons.

In some instances it was to boost grip when accelerating while turning out of a junction to prevent wheel spin, other times it was to maintain a driving line or simply to improve steering feel.

Audi was considering releasing the application to customers but the car-maker is confident driving the Q5 is enough to understand the value of Quattro Ultra and, until the second-gen Q5 arrives in the third quarter of 2017, you will just have to take our word that the system is simply brilliant.