Audi A7 Sportback h-tron quattro

Audi: A7 Sportback H-Tron Quattro Wouldn’t Be Sporty Enough Without Plug-in Hybrid Drivetrain

At last month’s LA Auto Show, Volkswagen’s luxury arm Audi unveiled a world-first: a performance plug-in hybrid with a hydrogen fuel cell rather than an internal combustion engine providing range-extending capabilities.

The Audi A7 H-Tron Quattro Concept combined hydrogen fuel cell technology with a plug-in hybrid.

The Audi A7 H-Tron Quattro combines hydrogen fuel cell technology with a plug-in hybrid.

At the time, we said Audi’s A7 Sportback H-Tron Quattro was the most logical implementation of hydrogen fuel cell technology we’ve seen to date, combining the low running costs and zero-emissions capabilities of a plug-in vehicle with range-extending capabilities of hydrogen. Solving the problem of limited and costly hydrogen refuelling infrastructure while simultaneously solving the limited-range problem of traditional plug-in vehicles, the A7 Sportback H-Tron Quattro seemed to offer it all without any compromise. In short, it seemed a well engineered, expert solution.

But as Automotive News (subscription required) found out over the weekend, the real reason for Audi unveiling a plug-in hydrogen hybrid vehicle at the LA Auto Show while parent company Volkswagen stuck to a hydrogen-only vehicle doesn’t paint current hydrogen fuel cell technology in a positive light.

In the words of Dr. Prof. Ulrich Hackenberg, Audi’s research and development chief, the marriage of plug-in hybrid and hydrogen technologies was needed to “make it a proper Audi.”

Audi's A7 H-Tron Quattro simply wasn't powerful enough as a hydrogen-only vehicle.

Audi’s A7 H-Tron Quattro simply wasn’t powerful enough as a hydrogen-only vehicle.

Or to put it another way, the hydrogen fuel cell stack Audi had access to simply wasn’t powerful enough to give the Audi A7 Sportback H-Tron Quattro the kind of performance required of any vehicle wishing to wear the famous Quattro name plate.

On its own, the hydrogen fuel cell technology in the A7 Sportback H-Tron Quattro is capable of outputting just over 100 kilowatts of power — or 137 brake horsepower. Worse still, in its stock configuration as a hydrogen-only vehicle, only two wheels would have been driven, meaning Audi couldn’t have used the Quattro name.

Instead, Hackenberg explained, Audi engineers used the plug-in drivetrain found in Audi’s recently-launched A3 e-Tron Sportback, adding a second motor to drive the other axle and providing a combined power output of 170 kilowatts.

Producing more than 398 foot-pounds of torque, the two drivetrains work together to accelerate the A7 Sportback H-Tron Quattro from 0-62 mph in a much more respectable 7.9 seconds. For those taking notes, that’s hardly as quick as some Audi models — and in fact a similar speed to the BMW i3 REx — but considering its 4,299 pound kerb weight, that’s far better than it could have been.

Audi’s decision to use a plug-in hybrid hydrogen drivetrain not only casts doubt on the performance of other hydrogen fuel cell vehicles, but confirms what we’ve seen so far from any automaker dabbling in hydrogen fuel cell technology.

While hydrogen fuel cell stacks might make it possible to power a zero emission vehicle on compressed hydrogen and oxygen from the air we breathe, fuel cell stack development needs a major improvement in energy density before we see sporty, performance-oriented hydrogen fuel cell vehicles wooing the crowds at major auto shows.


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  • Greg

    That’s really good news. I hope to see most cars evolve to a 50 mile Electric via battery, with the extended range supplied by some option. Slow charge while parked at work or train station, and possibly at home. nnnIt would be good to move the competition to finding the best “extender”, while accepting that the battery should be the basis of all. Model S, Volt (2016), i3, Leaf… would all fit this future. nnnBack to Audi though – why a 100kW fuel cell? Surely 60kW would be ample. A Model S needs about 30 kW to maintain 70 mph indefinitely – so is the extra kW unnecessary, or because the Audi will frequently go at 100mph, or tow a caravan… or just less efficient (higher drag)?nnnI assume that the battery can supply the full 170kW to the motor (rather than 70kW added to the fuel cell 100kW)?

    • jeffhre

      Acceleration and hills?

      • Greg

        As an example only, a Tesla doesn’t need a generator at all to have brilliant acceleration and hills. 30kW fuel cell could keep a Tesla battery at 25% charge no problem. nnI’ve come to the conclusion that car manufacturers have incredible problems making good battery packs, and they’re instead comfortable with less capable batteries which combine with higher power fuel cells (or generators in the Volt). once better (Tesla level) batteries are common the fuel cells will be able to be made smaller and cheaper.

        • jeffhre

          Good point and likely all true. My conclusion is a bit different though. I get the feeling that once car makers are comfortable with better batteries, then batteries will have improved to the point that the smart ones, four to five years from now, will begin to figure out that range extenders aren’t needed. Not even smaller and cheaper ones.nnnLooking at the landscape today. A complicated, range extended car would have to be prototyped now to make that window. You mentioned the Volt, a concept GM pioneered in late 2007, though GM now appears to be ready to put the Bolt in production for the 2017 MY.nnnI can’t forget that using a FC range extender means that the range would be extended by a refueling system that does not exist yet, with fuel that is three times more expensive than using electricity directly.nnnIt’s a concept that currently requires the “range extender” to acquire it’s own range extender, much more regularly the the battery which ironically depends on it for extended range. As a last resort a BEV can plug into any outlet to slowly gain more range. And ideally plug into a power plant on the owners roof – with no emissions.

  • CDspeed

    So in other words hydrogen cars at this point have poor performance, and will need to be developed further to gain higher levels of driving performance. Whereas electric cars are sporty by nature, I know which one I want. Well………..already have.

  • David Peilow

    I’m no hydrogen fan (unless it’s powering a rocket) but this article is plain wrong.nnAFAIK all hydrogen cars have a buffer battery that is used for acceleration and hill climbing. In all other scenarios the continuous power usage is a few tens of horsepower (80 mph = ~30 bhp). So as long as the fuel cell – or other range extender – is able to supply the continuous power requirement and top up the buffer, the car will have good performance.nnFurthermore, in the case of hydrogen infrastructure, having a range extender makes it less (not more) likely to be economical. That is because if you only need to fill up with hydrogen for 10% of your miles, that is 10% of the income to pay for what is already an expensive, green field roll out.

    • Espen Hugaas Andersen

      The Mirai has a battery capable of 22 kW. It doesn’t make a whole lot of difference.nnFor a performance model, you either need a really huge fuel cell, or you can put in enough batteries to get the desired performance. But if you’re adding a 5-10 kWh / 100-200 kW battery, why not stick a plug on there as well?

      • David Peilow

        Simply not true. You need a fuel cell capable of supplying average demand and a battery with sufficient power density. Ultracapacitors would work well here, or the types of rapid discharge/charge batteries we often read about in the EV news. You do not need a large battery for the job, just a powerful one.nnA large fuel cell is needed for high – I.e. illegal in most countries – top speeds but not acceleration. It has nothing to do with whether the car can be made Quattro or not. That it is claimed otherwise shows this is just a marketing exercise.

        • Espen Hugaas Andersen

          Say you need 100 kW in addition to the fuel cell. The best li-po cells at an acceptable cost and acceptable life span can handle around 20C, so you’d need 5 kWh. You might be able to do something similar with supercaps, but at what cost?

          • David Peilow

            You wouldn’t use LiPo for this application. Li Titanate or other chemistry with high power density/ cycle life.nnAs for power needed at high speed

          • Espen Hugaas Andersen

            If you look at Toshiba SCiB, for instance, it can handle an 8C discharge. So you’d need 12.5 kWh for 100 kW, or 140 kg in battery cells alone. Lipo is the right batteries for the job, they excel at discharge rate. (Well, lipo, *or* NiMH, which is what you have in the Mirai.)

          • David Peilow

            I’m taking about the Altairnano Li Titanate cells that can handle 100C discharge at 6W/gram power density.nnThat would mean a 17 kg battery with just over 1 kWh of storage is possible.

      • jeffhre

        Did you mean 2.2KW?

        • Roger Pham

          22 kw out of a 1.3-kwh battery pack is correct.

  • jeffhre

    Why would I opt to extend the range of my plug-in with a fuel that does not have any stations, for the sake of the higher performance of an Audi – which has no convenient refueling points available. Seems like the range extender , needs a range extender, considering there are hundreds of millions of 220 V outlets, ten of thousands of EV charging spots, and a handful of H2 stations.

    • Roger Pham

      Have patience, grasshopper, H2 stations will be built along roadways, so-called hydrogen highways!

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