Multitasking is the norm for many high-level engineers, a situation compounded by the necessity for OEMs to find successful multiple solutions to meet global environmental challenges. The salient aspect of this work involves alternative powertrains, with hybrid and pure EV issues towering above all else.
Until recently, it could be argued that hybrids (mainly gasoline but also diesels) were just a stepping stone toward the all-electric vehicle, but with the convincing advance of plug-in systems, which offer a flexible solution in terms of performance, economy, cost, and particularly range, there are indications that the EV star, with its downside of battery cost and limited range, may be waning for some.
“A hybrid vehicle is of great interest to some markets such as the U.S. and China," said Michael Dick, Audi’s technology development boss. "This is why a [hybrid] electric vehicle based on an A6 is being developed within the scope of a partnership between Audi and the prestigious Tongji University in China. As far as introducing a pure electric vehicle is concerned, however, we consider only urban small-car concepts such as the A1 e-tron and a pure-electric sports car concept based on the R8 e-tron to be viable.”
A major reason for this is the cost of batteries, but particularly the lack of range they provide, notably in inclement conditions. The note of caution from Dick echoes a reference in a speech by current Audi CEO Rupert Stadler some four years ago in which he referred to the need for caution in the context of “sustainability.”
It is significant that parent company Volkwagen’s highly futuristic XL1 concept uses a plug-in hybrid solution powered by half a 1.6-L TDI engine with a light-alloy cylinder block producing 35 kW (48 hp) and a 20-kW motor with a 5-kW·h lithium-ion battery. Volkswagen is planning both a pure electric and a hybrid version of the Golf.
Some companies, the Renault-Nissan Alliance among them, are investing very heavily in pure EVs, demonstrating the continuing dichotomy of views on what route will be taken by alternative powertrain solutions. Renault has four EVs in development, and its specialist teams are working toward models achieving 400 km (249 mi) between recharging by 2020.
The Audi A1 e-tron concept is not pure electric in the fullest sense because it uses a small Wankel range-extender engine. Because it runs at constant speed, the technology does not exhibit the disadvantages of such an engine: relatively poor fuel consumption and emissions. The (probably limited) production A1 e-tron is slated for production, although Audi has not confirmed the time frame.
With its emphasis on hybrids across the broader model range, Audi will introduce the Q5 quattro hybrid this summer and at the recent European launch of the new conventional A6, took along the hybrid version of that model too. Its appearance was significant and emphasized the importance of hybrid technology to Audi, which is also to be extended to the A8 in 2012.
All three hybrids will share similar technology—a 2.0-L gasoline direct injection turbocharged TFSI power unit allied to a 33-kW synchronous electric motor with a combined system output of 180 kW (241 hp) and 480 N·m (354 lb·ft). Fitted to the Q5, the combined-cycle NEDC fuel consumption figure is less than 7.0 L/100 km.
Such is the efficiency of Audi’s diesel TDI engine range, however, that the A6 hybrid will not quite match the fuel consumption or CO2 levels of the 155-kW (208-hp) diesel 2.0-L, said David Ingram, Audi U.K.’s Product and Technology Manager. “As a pure electric vehicle, the A6 hybrid will cover 3-4 km and speeds up to 100km/h in that mode. With our expanding hybrid range, we are responding to market needs. As for fuel-cell technology, we do not at present see it providing a full, everyday cost-effective solution for an only car – which hybrid technology does. We continue to see pure EVs as having limitations that are too severe and that would in general compromise a car’s functions—the exceptions being A1 e-tron, our city/small car and the first e-tron sports car that we showed at Frankfurt in 2009, which will go into limited production in 2012.”
Audi has put its diesel hybrid technology on hold until markets that do not have diesel fuel acceptability (notably the U.S.) change direction. “At present we feel our TDI powertrains provide the best economical solution,” said Ingram.
Bernd Huber, Technical Project Manager for the Q5, said the hybrid version of the car would have an eight-speed (with widely spaced ratios) Tiptronic transmission without a torque converter. “Its place is taken by the disk-shaped electric motor, combined with a multiplate clutch operating in an oil bath; it couples and decouples the electric motor and TFSI. The fast-shifting hybrid gear unit contributes significantly to efficiency of the vehicle.”
A pulse-controlled inverter is fitted in the plenum chamber of the engine compartment. A separate low-temperature water-filled circuit cools the power electronics. A dc/dc converter couples the electric consumers in the 12-V electrical system with the high-voltage network.
Each Audi hybrid uses a lithium-ion battery system weighing 38 kg (84 lb) and positioned in a crash-safe area beneath the loading floor. The battery reduces luggage space in the A6’s trunk by around 20%. Cooling is via a fan drawing temperate air from the vehicle interior or at high temperatures, a refrigerant circuit.
In place of an engine rev counter, hybrids get a power meter (marked 0-100%) that also incorporates multicolored segments showing how the vehicle is being powered. The instrument display also includes charge level of the battery. An MMI (multimedia interface) screen also shows operating states and power flows.
David Ingram said quiet hybrid technology is proving very effective in the A8, due to be launched in 2012, particularly for city chauffeur work. The 3.0-L diesel has a combined CO2 emissions figure of 159 g/km, but the hybrid beats that to return 144 g/km.
“We are researching all powertrain options,” said Ingram. “Application of battery-only technology depends on space and capacity—both need to improve significantly before there is a great uptake of EVs, and that improvement is proving slow.”