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Audi unveils h-tron quattro fuel cell SUV concept at Detroit; MLB evo platform

by Mike Millikin

In a demonstration of its ongoing development of advanced alternative powertrains, Audi unveiled the new h-tron quattro fuel cell concept vehicle at the North American International Auto Show (NAIAS). Like its production-bound sibling the e-tron quattro battery-electric vehicle, the h-tron concept is based on Audi’s second-generation modular longitudinal platform (MLB evo, earlier post).

The Audi h-tron quattro concept combines an Audi fifth-generation fuel cell stack delivering up to 110 kW with a power-optimized 1.8 kWh HEV battery that can provide a temporary boost of 100 kW for combined peak system power of 210 kW. The car can be fully refueled with hydrogen in around four minutes, and is then ready to drive for up to 600 kilometers (372.8 miles). Unlike the 3-motor e-tron quattro, the h-tron uses two electric motors, one on each axle, and so drives like a “conventional” electric vehicle, notes Audi Head of Electric Powertrain Siegfried Pint—i.e. without the potential for the type of advanced dynamics control offered by the e-tron quattro. (Earlier post.)



The decision to go with two motors was based on the power capability of the fuel stack, Pint said. However, in a demonstration of the flexibility of the MLB evo platform components, the Audi engineers took the 140 kW motor from the e-tron quattro front axle and used it for the rear axle of the h-tron; and took one of the 90 kW rear axle motors from the e-tron quattro to use for the front axle in the h-tron.

“When we planned the e-tron [quattro], we already had in mind the h-tron [quattro], to show the flexibility of the MLB evo platform.”
—Siegfried Pint

Each motor powers one set of wheels—as on the technology demonstrator Audi A7 Sportback h-tron quattro (a plug-in hybrid design with an 8.8 kWh pack), which Audi presented in November 2014. (Earlier post.) The torque can be varied continuously for both axles.

An intelligent management system controls the interplay between the two motors as appropriate for the situation, placing maximum emphasis on efficiency. At low loads only the front axle receives propulsive power, and at very low speeds the power is supplied solely by the battery.

A heat pump for the interior air conditioning and a large solar roof that generates up to 320 watts, equivalent to adding up to 1,000 kilometers (621.4 mi) to the range annually, also boost efficiency.

A Cd value of 0.27 makes a major contribution to maximizing range and efficiency. Aerodynamic elements down the flanks, on the underbody and at the rear improve the way air flows around the car at higher speeds. Cameras take the place of exterior mirrors, further enhancing aerodynamics and efficiency.

With 550 N·m (405.7 lb-ft) of system torque, the Audi h-tron quattro accelerates from 0 to 100 km/h (62.1 mph) in less than seven seconds; its top speed is governed at 200 km/h (124.3 mph). According to the New European Driving Cycle, fuel consumption of the h-tron quattro is around one kilogram (2.2 lb) of hydrogen per 100 kilometers (62.1 mi).

(As two rough comparisons, Toyota’s production Mirai fuel-cell sedan, with a 114 kW fuel cell stack and a 113 kW traction motor, has an NEDC fuel consumption—calculated from the JC08 homologated value—of 0.76 kg H2/100 km, according to Toyota. The Hyundai iX (Tucson) Fuel Cell Vehicle SUV, with a 100 kW stack and 100 kW motor, has an NEDC fuel consumption of 0.95 g H2/100 km. )

Fuel cell stack. The fifth generation of fuel cell technology from Audi and Volkswagen uses lighter materials to reduce the weight and to improve performance, responsiveness, service life and efficiency compared to the fourth generation fuel cell technology applied in the A7 Sportback h-tron. With an efficiency rating in excess of 60%, the fuel cell now surpasses any combustion engine. The stack, comprising 330 individual cells, is housed in the forward structure. Depending on the load point, the stack operates in the range of 220 to 280 volts.

The focus of development for the fifth generation stack (Ballard is Audi and Volkswagen’s development partner, earlier post) is on new materials for the diaphragms and the bipolar plates of the membrane electrode assemblies (MEAs) that guide the gases in the stack while keeping the cells separate. They help to make the entire unit lighter, smaller, stronger and also more economical, especially as the content of the precious metal platinum catalyst has been reduced. The operating life and responsiveness are improved, and hydrogen consumption is cut.

The fifth-generation fuel cell technology operates at a temperature level of up to 95 ˚C, an increase of 15 degrees compared with the previous generation. The higher thermal operating range enables a reduction in the balance of plant (BoP), Pint noted, as the cooling requirements are not as demanding. A high-efficiency heat pump absorbs the waste heat from the electrical components and a thermoelectric auxiliary heating element maintain pleasant temperatures inside the car. The car starts down to -28 ˚C.

Battery. Complementing the 110 kW fuel cell is a compact lithium-ion battery designed for optimum power output. The battery, weighing less than 60 kilograms (132.3 lb), is located beneath the passenger compartment to optimize the center of gravity. It supplies up to 100 kW of power, ample for a temporary, forceful burst when accelerating. When the car is braked it stores the recovered energy.

The driver can influence the degree of recuperation by selecting either gliding mode or coasting recuperation. The four wheel brakes only cut in if harder or emergency braking is required.

The storage battery operates over the range of 220 to 460 volts—a 3-way DC/DC converter in the engine compartment equalizes the difference compared with the fuel cell’s voltage level.

A separate low-temperature circuit keeps the driveline and high-voltage battery components sufficiently cool even when the car is driven sportily.

3-way power DC/DC converter. One of the key features of the h-tron quattro concept is the 3-way power DC/DC converter. The 3-way converter connects the battery, fuel cell and power electronics. By doing so, the h-tron can maintain the high output voltage level without power loss from voltage drop, Pint said.

Hydrogen storage. The three hydrogen tanks are located beneath the passenger compartment or luggage compartment but do not impinge on the interior. At a pressure of 700 bar, they store enough hydrogen for a range of up to 600 kilometers (372.8 mi)—i.e., about 6 kg.

Every tank is made up of several layers: the inner tank made with gas-tight polyamide is wrapped in carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP). Like a car with combustion engine, refueling takes about four minutes. at a maximum rate of 1.5 kg/minute.

The hydrogen tanks differ in size. The front one is installed longitudinally beneath the center console, and the two other tanks transversely beneath the rear seats and luggage compartment respectively. Together with the battery, they are secured to a structural frame. Neither on the fuel cell drive version nor on the Audi e-tron quattro concept do the tanks or battery impinge on the interior. This also demonstrates the versatility of the new MLB evo platform.

The three tanks communicate with the refueling system by infrared interface and equalize the pressure and temperature levels. The stainless steel hydrogen tank cap is located on the front right wing of the sporty SUV; its flap opens electrically.

zFAS and domain architecture. The h-tron quattro uses the zFAS domain controller for driving assistance systems, as does the e-tron quattro. When the latter moves into production in 2018, it will use the second-generation of the technology, shown at CES 2016. (Earlier post.)

All available sensor information is processed by the zFAS. It computes a complete model of the car’s surroundings in real time and makes this information available to the assistance systems and the piloted driving systems. They can assume driving tasks during parking or in stop‑and‑go traffic on freeways at speeds of up to 60 km/h (37.3 mph).

The movement to a domain-controlled architecture, with zFAS being an example of one of the domain controllers relieves a tremendous burden from current powertrain controllers, Pint noted. For the e-tron quattro, he said, Audi will have a torque domain controller to handle the intricate interplay between the 3-motor systems to deliver optimal performance and dynamics.

Renewable hydrogen and market prospects. While Audi is strongly committed to the commercialization of battery-electric e-tron platforms (Audi of America is targeting 25% of its sales to be e-tron by 2025, earlier post), there is less of an obvious current case for hydrogen.

On the one hand, Pint observed, hydrogen offers a long-distance solution with a fast refill—almost a diesel-like use case, in other words, compared to the shorter ranges and longer fill times for most current EVs. As battery technology improves, and as fast charging infrastructure develops for longer trips, hydrogen value proposition in that area may erode.

While Audi will not commercialize a hydrogen vehicle in this decade, Pint said, the ultimate decision as to whether or not to add the h-tron to showrooms will come down to the “two Ifs”: if there is a sufficient hydrogen infrastructure in place and if there is customer demand.

Unlike electric vehicles, for which there is already a massive slow-speed recharging infrastructure in place and for which rapid charging networks are being built (including Audi’s commitment to 150kW charging using the CCS standard connectors), the hydrogen infrastructure still needs to be built.

Furthermore, from a greenhouse gas point of view, the hydrogen ultimately needs to be derived from renewable sources if there is to be sufficient environmental benefit. The Audi e‑gas facility in Werlte, Germany is demonstrating the production of hydrogen with green power, and there are other green hydrogen approaches, but these would need to be scaled up aggressively.





With enough batteries FCEVs can do most of the local trips on electric storage, the FC is just for longer trips and quick refills.

Impressive engineering feat. Kudos, Audi.

>While Audi will not commercialize a hydrogen vehicle in this decade, Pint said, the ultimate decision as to whether or not to add the h-tron to showrooms will come down to the “two Ifs”: if there is a sufficient hydrogen infrastructure in place...

That is the dilemma. Spend a few hundred million on a 150kW fast charge network, or a few tens of billions on a hydrogen refueling network.

Decisions, decisions.

@SJC, where on that cutaway illustration do you see enough room to stuff a Chevy Volt sized 16kWh battery? How would that car handle another 600 lbs weight and still perform well?

How do you make a business case for hydrogen refueling stations that are only used 1/10 of the amount of time they would be otherwise?

What is the (near term) justification for regulators and consumers of the expense vs gasoline PHEVs if the PHEV can already achieve a 90% carbon reduction?



I am not going to argue, that is not what this site is for. It is about constructive solutions to provide "sustainable mobility".


In 1959, Allis Chalmers made the first fuel cell vehicle, a 15 KW tractor. I was 16 years old and had learned to drive an Allis Chalmers tractor so I can remember the announcement of the fuel cell tractor. It was obviously the next great step forward and just around the corner along with the turbine powered and flying commuter cars.

Fuel cells have their place but I doubt that it will be powering cars anytime soon.


eci said:

'where on that cutaway illustration do you see enough room to stuff a Chevy Volt sized 16kWh battery? How would that car handle another 600 lbs weight and still perform well?'

The thesis behind battery cars is that they are going to improve.

The 1.8 kwh battery in this car weighs 60 kg, but this sort of high cycling and power battery weighs a lot more than that in a PHEV or a BEV.

The battery for the Bolt comes out to 138 Wh/kg
So 60 kgs of that battery would have around 8.28 kwh, as much as a typical present PHEV, not Volt like AER but no point of use pollution when the fuel cell cuts in.

That battery is for a BEV, and present PHEV batteries are lower density.

But if one assumes increases in battery energy density, then it would work fine.

And if one does not assume increases in battery energy density and reductions in cost, then the case for BEVs too falls apart, whilst non plug in FCEVs would continue to work fine.


eci said:

'How do you make a business case for hydrogen refueling stations that are only used 1/10 of the amount of time they would be otherwise?'

They fit in fine at gasoline stations, and are being put in there in the UK.


eci said:

'Spend a few hundred million on a 150kW fast charge network, or a few tens of billions on a hydrogen refueling network.'

Try adding up all the costs, not just the bits that serve your case.

You need somewhere to plug BEVs in at home, and most people in most of the world do not have garages.

Not only would it be immensely challenging and inconvenient, verging on the utterly impractical, to wire up ALL of them, but FCEVs introduced at the same time would mean that there would be no need to provide for the difficult ones.

It is pure nonsense to imagine that there is some sort of existential conflict between fuel cells and batteries.

They both work far better together than apart.


I have to agree with Davemart. There is penty of room for both technologies. The 50% of us living in cold weather areas and/or without easy (low cost) access to home charging units, would do better with FCEVs with 500+ Km all weather range.

The price of clean H2 will soon be competitive with gasoline/diesel/ethanol in many places. Availability will be there if/when FCEVs are.

Early clean H2 stations could be done with large enough subsidies (from manufacturers and governments) to accelerate availability and to keep H2 retail price low.

You make some good points, Davemart. I don't see room on that diagram for even 5x the battery they depict, but you're right, when batteries are 5x present energy density, it would fit. It does beg the question of the competitiveness of fuel cells when today's typical 100 mile EV would thus have 500 mile range.

All cars save three shift taxies park somewhere while their owners sleep. If a city can install street lights and parking meters, they could as easily wire up EV chargers, especially the new wireless charging pads sold by Qualcomm, Plugless or several others. No cords to manage, any parking space could be a charger. City could raise a lot more recenue than parking meters, and the billing could be fully automated.

For the cost of one $4 million H2 station, which serves only 100 customers per day, over 400 wireless charging pads could be installed. No supply trucks needed.

I don't see any existential threat between the two technologies. I just see one being economically competitive, and the other, at least at oresent time, not being economic or ready for deployment at scale, but being rushed to market anyway.

The comments by both Hyundai Tucson FCV owners and the few hand-picked Mirai owners are not favorable. As a result of Mirai owner feedback, Toyoya has halted sales of the Mirai at most dealers intil more fueling stations are installed.

When a product is pulled off sale shortly after a big launch with a lot of promotion, its safe to conclude that it's not quite ready for showtime. I'm sure they'll get things sorted, but If I were an apartment dweller without access to off street parking, I'd probably buy a PHEV and lobby hard for workplace charging, rather than roll the dice on a 57,000 FCV I may not be able to drive anywhere if my one local H2 station goes down.

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