Based on the Audi 100 Avant (C3), Audi developed the first generation of the Audi duo in cooperation with Kulmbach-based Pöhlmann KG in the fall of 1989, which was presented for the first time at the Geneva Motor Show in March 1990.
An Audi 100 Avant quattro with a five-cylinder injection engine and an output of 100 kW / 136 hp was fitted with a 12.6 hp DC electric motor on the rear axle, demonstrating the feasibility of hybrid vehicles that could travel short distances with zero emissions.
The electric drive covered its energy requirements from a 64.8 volt nickel-cadmium battery pack weighing 181 kg with a capacity of 8.4 kWh, which could be fully recharged within ten hours using standard household 220 volt power.
Automobil Revue wrote on the occasion of the press launch in December 1989:
"With the 2.3-liter five-cylinder petrol engine with 100 kW (136 hp), the 100 Avant duo is also suitably motorized for long stages with a large payload. The electric drive is considerably more leisurely, although the performance can still be described as just about adequate for inner-city and residential areas: the DC motor takes the 1740 kg vehicle to a maximum of 50 km/h, and acceleration from 0 to 30 km/h is 8 s; the range is given as 30 km, with provision for recharging the battery while driving with a gasoline engine. As nickel-cadmium batteries can withstand high charging currents, the charging time with a correspondingly powerful charger is only around 45 minutes. Incidentally, Audi specifies a battery service life of 10 years.
The Audi duo is not equipped with a fully automatic control system for switching on the correct drive unit as required. Similarly, no use has been made of the option of running both engines synchronized together for extreme situations, thus providing an original all-wheel drive for low speed ranges. Will such an extension of the concept (which is of course not free) be realized at a later date?
The ignition key is used to either start the combustion engine or - after the gearshift has been moved to neutral - the electric drive is activated by pressing the "E" button. With electric drive, the car drives like an automatic; because there is no gearshift, the driver only has to press the accelerator pedal. A display provides constant information about the battery charge level. When driving with electric drive, an additional small electric motor supplies the hydraulics so that the power steering, brake servo and ABS function as usual.
Another benefit of the duo system that should not be underestimated is the improved operational safety of the vehicle: if one motor fails, the vehicle can be operated with the second, completely independent drive system. "
At the time, a sales price of CHF 65,000 to 70,000 (around DM 72,500 to 78,000 at the time) was expected for the "amazingly simple Audi hybrid system".
In 1990, the measured values for the Audi duo were determined by Automobil Revue and reached 100 km/h in 16.7 seconds (petrol engine) and 50 km/h in 23.2 seconds (electric). 11.8 liters per 100 km were stated as the total test consumption at the time.
The conclusion after the test drive was:
"Audi is understandably not taking the decision as to whether the "two-in-one" car should go into production lightly, especially as there are no precise price estimates as yet (whether the approximately 20,000 francs extra cost mentioned in the earlier article about the duo comes close to reality is completely open). A quick "yes" to the duo would undoubtedly be a considerable economic risk at the present time; on the other hand, there is already a considerable potential of possible buyers in the form of large fleet owners such as local authorities, municipal companies, cab firms, etc.. In any case, our driver trials have shown that improvements would have to be made to the acceleration capacity of the electric motor before any series production could begin. Apart from that, however, the concept already seems surprisingly mature - provided the car is used as intended."
Incidentally, this was not Audi's last hybrid prototype; others were built in the 1990s.