LA MOTOR SHOW: Audi A7 Sportback h-tron quattro
Audi's alternative power options receive a hydrogen boostIt took Audi a long time to join the hybrid race. Now it's leapfrogging pure electric cars directly into fuel cell cars and it's starting with one of its biggest and most expensive models.
The German premium brand has not just shown a fuel-cell concept, though, because it's allowing selected journalists to test its A7 Sportback h-tron quattro on the streets of Los Angeles this week.
Claiming a 500km range from its zero-emission fuel-cell A7, Audi insists the all-wheel drive h-tron will hit 100km/h in 7.8 seconds and on to a 180km/h top speed, all without any luxury or feature handicaps inside the cabin.
Though officially dubbed a working prototype, the A7 h-tron quattro is a rolling 170kW/540Nm power station run, in the main, on its hydrogen fuel cell.
Its fuel cell replaces the conventional petrol or diesel engines under the bonnet and the exhaust system, which only has to deal with water vapour, is made from light weight plastic.
The 300-cell fuel-cell stack forces the hydrogen onto an anode, where each atom is broken into protons and electrons, with the protons migrating through the polymer cell membranes to reach the cathode. There they react with oxygen, forced as air into the stack by an electric turbocharger, to create water vapour.
The electrons, meanwhile, supply the car's electricity, delivering between 0.6 and 0.8 Volts per cell for a system voltage of between 230 and 360 Volts.
But the A7 h-tron quattro has another trick up its sleeve. It's also a plug-in hybrid. It marries the A3 e-tron's 8.8kW/h battery pack to the system, and it can be regenerated under braking or via a cable and socket, giving the car an extra 50km of range and acting like a reserve fuel tank.
The A7 h-tron is driven by two electric motors, one for each axle. The two motors have no mechanical linkages and Audi uses them to deliver computer controlled all-wheel drive, all the time.
"The A7 Sportback h-tron quattro is a genuine Audi – at once sporty and efficient," Audi's board member in charge of development, Dr Ulrich Hackenberg, said.
"Conceived as an e-quattro, its two electric motors drive all four wheels and the h-tron concept car shows that we have mastered fuel-cell technology.
"We are in a position to launch the production process as soon as the market and the infrastructure are ready," he insisted.
The two power sources are connected via a DC/AC converter, because they operate at different voltages, converting the fuel cell's direct current output into the alternating current demanded by the electric motors to drive the car.
The permanently excited synchronous electric motors each pump out 85W of power, but can be "overboosted" to 114kW for short bursts. They also deliver 270Nm of torque each, from zero rpm onwards, and are cooled by the same cooling circuit that takes care of the DC/AC converter. The housings for the motors also include a single-speed 7.6:1 transmission in a planetary gear set.
Surprisingly, it only weighs 1970kg and its four hydrogen tanks can be refueled in just three minutes, while the electric battery pack takes between two and four hours to recharge.
The aluminium and protective carbon-fibre hydrogen tanks can store 5kg of H2 beneath the boot floor, ahead of the rear axle and along the central tunnel, storing the gas at 700 bar of pressure.
Audi claims it will use a kilogram of hydrogen per 100km, which converts under the NEDC combined cycle to 3.7 litres/100km of petrol.
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