LA Auto Show: Hydrogen fuel cell drive is back
Hydrogen fuel cells turn hydrogen into electricity which then is stored in a battery and used to drive one or more electric traction motors. Though fuel cell vehicles are basically electric cars, this concept enables significantly higher driving ranges compared to today’s battery electric cars (BAVs) – Toyota claims a range of 480 km (300 miles) whereas the battery capacity of most standard electric vehicles (save Tesla) is only enough for some 120 to 160 km. What’s more, refilling the hydrogen tank at a filling station takes only some three minutes and thus is much shorter than recharging the battery of a BAV which takes at least 20 minutes even with quick charging technology.
Fig. 1: Toyota’s Mirai is ready for series production
Toyota undoubtedly has the most advanced technology for fuel cell cars. The Japanese company will make its Mirai available to the public in Japan as early as mid-December (2014, of course). The Mirai offers a system power of 113 kW (154 hp). Toyota’s fuel cell, located beneath the floor of the passenger compartment, offers a specific power of 3.1 kW per litre of volume, a value that makes it the most efficient fuel cell worldwide. The system of fuel cell stacks, up-converters and high-presure hydrogen tank is the result of some 20 years of research.
Toyota’s fuel cell stacks for the first time utilise finely-woven 3D channels that ensure even current generation at the cell surface and this guarantee maximum efficiency at compact dimensions. For instance, the power density of the new Mirai is 2.2 times as high as it was the case with Toyota’s FCHV-adv research vehicle. The up-converter offers an output voltage of up to 650 V, which enabled the vehicle designers to shrink the size of the electric motor as well as the number of the fuel cells.
The hydrogen is stored at a pressure of 700 bar in a tank made of three layers of carbon-reinforced plastic material. Though its size has been reduced against the FCHV-adv predecessor, it offers 20 litres higher volume. For the case that hydrogen leaks out, sensors send a warning to the cockpit and switch off immediately the supply.
Fig. 2: Fuel cell stack beneath the floor, hydrogen tanks (in yellow) in the rear part at the Mirai
The AC synchronous motor generates a torque of 335 Nm which is comparable to most midsize vehicles, but like any electric drive, this torque is developed already at zero rpm, translating in a healthy acceleration – within 9.6 seconds the Mirai has reached the speed of 100 kmph (about 60 mph).
German manufacturers Audi and Volkswagen also jump onto the fuel cell band wagon at the LA Auto show. Though both companies also have conducted research for quite some years, they however cannot provide series vehicles. Nevertheless, their concept cars also are quite interesting. The Audi A7 Sportback h-tron Quattro combines the fuel cell with a rather strong traction battery that enables it to drive up to 50 km without activating the fuel cell. In contrast to the Toyota, the Audi has a second electric motor at the rear axle, providing four-wheel drive without a mechanical connection between front and rear axle.
Fig. 3: Audi combines fuel cell with battery electric concept in its A7 h-tron
As to the driving range, Audi is a little bit ahead of the Toyota with a range of 500 km. In contrast to Toyota, Audi furnished particulars as to the fuel efficiency: The vehicle – a relatively large sedan – consumes 1 kilogram of hydrogen on 100 km distance which is comparable to a fuel efficiency of 3.7 litres of gasoline at the same distance. Offering a system performance of 170 kW, the lithium-ion battery that can be charged separately contributes 8.8 kW. Audi’s fuel cell stack contains more than 300 cells generating a voltage of 0.6 to 0.8 V each. This adds up to a system voltage of 230 to 360 V, significantly lower than Toyota’s. Audi specifies the fuel cell’s overall efficiency at 60 %, almost twice as high as a conventional combustion engine.
Audi’s parent company Volkswagen did not want to remain in the background and also presents a vehicle with a fuel cell drive. Unlike Audi however who says its A7 Sportback h-tron Quattro can enter series production as soon as market and infrastructure justify it, Volkswagen’s Golf HyMotion is characterised as a "progressive research vehicle", which probably means that its status us somewhere between feasibility study and series maturity.
Fig. 4: Fuel cells and hydrogen tanks in the rear at Volkswagen’s Golf Hymotion
With the Audi it shares its driving range of 500 km, but its system performance of 100 kW is somewhat lower. The motor is the same as in the e-Golf, the electric version of VWs popular compact car. Volkswagen highlighted its strategy to implement alternative drives in high-volume vehicles which means that once the fuel cell version is ready for production it will be implemented in a production model that has everyday practicality. Volkswagen was the only company of this fuel cell trio to address the major roadblock for the acceptance of this alternative drive concept: The lack of a filling network. "Before the market launch, a hydrogen infrastructure first must be created," the company said in a statement. Indeed, this could effectively hinder a widespread acceptance.
Related articles:
Artificial photosynthesis breakthrough promises low cost hydrogen automobiles
UKH2Mobility project maps out future of hydrogen fuel cell cars in the UK
Toyota rolls fuel cell vehicle to series production
Fuel cell cars on the long march to the market
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