Audi delivered the shocks...

Audi delivered the shocks at this yearтЂ™s Detroit Motor Show with a stunning new sports car aimed at the Porsche Cayman.

The German maker wowed visitors when it threw the covers off this electric concept. WhatтЂ™s more, the model is not solely a motor show fantasy: it previews a new baby brother for the R8 supercar, set to be called the R4.

Sharing the same тЂ�e-tronтЂ™ label as its R8-derived stablemate, which was revealed at last SeptemberтЂ™s Frankfurt expo, the newcomer is 22cm shorter than the R8, but bigger than the TT. It will be offered with conventional engines and an all-electric powertrain, as shown here, when it goes on sale in 2012.

The repetition of the e-tron moniker is no coincidence, either. Audi bosses confirmed in Detroit that all the firmтЂ™s future electric cars will wear the badge тЂ“ and claimed that one day the technology will become as well known as the companyтЂ™s famous quattro 4WD system.

Based on an aluminium spaceframe chassis, the e-tron gets carbon fibre-reinforced plastic panels to keep weight to a minimum. ItтЂ™s around 250kg lighter than the first e-tron at roughly 1,350kg, and will bethe lightest Audi on sale.

Between the cabin and the rear axle is the same electric drivetrain as the Frankfurt model, albeit with two motors instead of four. These drive the rear wheels and can deliver up to 204bhp and a claimed 2,650Nm of torque. This mind-boggling figure is for at-the-wheel performance, rather than taken from the crank as usual, and so is artificially high. However, it still describes the awesome power and response on offer from the motors.

Early figures suggest the car will sprint from 0-62mph in only 5.9 seconds while, in order to preserve the batteries, the top speed is limited to 124mph. With a potential range of 155 miles per charge, company engineers promise that the batteries can be topped up in as little as two hours, although owners will need a special 400-volt electricity supply.

The R4 will also be available with normal petrol engines, set to be mounted in the rear. Likely candidates include the 268bhp 2.0-litre turbo from the TTS and the 2.5 five-cylinder turbo unit from the TT RS. Diesel TDI technology is also in the pipeline. Designed in Munich, the latest e-tron is the work of exterior boss Steve Lewis. He said: тЂњMany of the styling themes тЂ“ such as the sharper lines and more pronounced arches тЂ“ show how weтЂ™re going to take Audi design forward.тЂќ

Prices are yet to be confirmed. But given the R4тЂ™s position below the R8 and ТЈ100,000 e-tron, yet above the TT, they should start from ТЈ50,000, rising to ТЈ70,000 for the electric variant.