The current Audi A4, the German luxury brand's best-selling car in the U.S., has been with us since the 2009 model year.

When it's replaced for the 2014 model year, the model line will include not only a sedan and a wagon but also a pair of hybrids--one that plugs in--and a brand-new Quattro all-wheel drive system that uses an electric motor to power the rear wheels.

The details come courtesy of Britain's CAR magazine and its longtime German industry insider, George Kacher.

First, the A4 Hybrid will use a powertrain derived from the VW Group hybrid system using a 226-hp, 2.0-liter four-cylinder engine and a single electric motor between the engine and an adapted conventional automatic transmission.

That system has already been launched in the Audi Q5 Hybrid crossover utility vehicle, where the electric motor has a peak power out put of 40 kilowatts (54 hp).

The 2014 Audi A4 will offer the company's first Quattro all-wheel drive system to power the rear wheels electrically, rather than mechanically.

It will use a pair of 50-kilowatt (68-hp) 60-kilowatt (78-hp) electric motors to turn the rear wheels. Each motor will be individually controlled, to provide traction and stability control on turns and if wheel slip occurs, simply by delivering different amounts of electricity to inside and outside wheels.

2013 Audi A4

2013 Audi A4

With a larger lithium-ion battery pack, the plug-in hybrid system--like similar systems from many makers--is likely to offer up to 20 miles of electric range.

But with such powerful motors on the rear axle, the plug-in hybrid may use the rear motors--perhaps with the addition of the third hybrid motor up front as well--to give the A4 Plug-In Hybrid significant acceleration in all-electric mode.

The goal is to let the A4 Plug-In Hybrid use all-electric power to enter and traverse the zero-emission zones that are expected to be imposed in many European capital cities over the next decade.

The A4 Plug-In hybrid will likely be called A4 E-tron, one of several E-tron plug-in models Audi has shown as concepts and will launch into the market over the next five years.

We also know that the next Audi A4 will offer a TDI diesel powertrain in the U.S., the first for a volume Audi model. (Its current diesel offerings, the Q5 large sport-utility vehicle and the A3 compact hatchback, are both low-volume models.)


Follow GreenCarReports on Facebook and Twitter.