Automotive Engineer

How do you decide on the configuration of a range-extended electric vehicle?

“You start with the car’s role – it’s for urban driving. So that’s why we picked a 50km electric range for the A1 e-tron. We know that most people have a short commute to work so we know they’ll have a certain demand on battery capacity. It’s an emergency case if the range extender cuts in. 

Can a range extender be scaled-up to suit heavier applications, or would this be inefficient?

“The best driving profile for a range extender is an urban one, with a small car. If you take a big car built for longrange driving then the mechanical driveshaft between the combustion engine and the wheels is a better solution. If you drive at a higher power demand the energy conversion between the generator and the converter and then the electric motor is not good enough.

Would a two-speed transmission improve efficiency?

“It’s a trade-off against losses. If you’re going up to 200km/h you can do it with one gear ratio. If you go faster it could be more efficient to have two ratios.

How important are range extenders’ tailpipe CO2 emissions – if the combustion engine is only for emergencies, is fuel efficiency a priority?

“That’s exactly the point. The priority is not the fuel efficiency of the internal combustion engine. We believe that vehicles will be mostly plugged-in to the electricity grid to be recharged and the range extender will not run that often. But there is a test cycle – ECE R101 – which is like an artificial fuel consumption test cycle, and we achieved 1.9 litres/100km on that.

Getting CO2 emissions below 100g/km is a development target for conventional vehicles – presumably there isn’t an equivalent for range extenders?

“For sure, we try to make the vehicles as efficient as possible but the engine is only a fallback solution. We chose the Wankel engine with respect to acoustics and packaging.

When I drove the A1 e-tron I didn’t notice the engine firing up: do you think this is an important attribute?

“Electric vehicles are very smooth and very quiet. Our opinion is that the customer shouldn’t recognise when the range extender kicks in. So from our point of view it should feel like a fully electric car.

What are the pros and cons of having the engine at the back instead of the complete powertrain under the hood?

“If the combustion engine is at the rear the noise has to travel further to reach the driver’s ear. But if you have everything at the front you have an engine bay which is usually damped pretty well. There are packaging advantages with the exhaust because you don’t have to pipe it along the whole car. The other advantage is that weight distribution is better – having everything on the front axle would not be the best solution.

Audi is developing smart navigation technology to optimise range – how mature is it?

“The theory and the algorithms work and we have prototypes. But we need a certain database for it, including very detailed navigation data with not only road classes but gradients and traffic lights. This is not available in the quality we need. We want to encourage navigation system suppliers to refine their data – this would be useful for every electric vehicle. A second step – and a very useful one – would be a car-to-car and car-to-infrastructure network to share information.

Chocolate has a higher energy density than a lithium-ion battery: do you expect better technology any time soon?

“As we see it lithium-ion will be the solution for the next 5-10 years. The increase in energy density is quite slow. There will be a certain evolution but I don’t see a revolution.

You have a lot of responsibility at Audi – what do you spend most of your time working on? 

“Carbon dioxide. It doesn’t stop – it’s not hype, and CO2 reduction is a longterm trend. That’s why I’m so busy. 

How do you manage the CO2 issue?

“We have a CO2 steering committee. This team tries to decide the directions we should go in and which measures to introduce – decisions are then taken by the board.