Audi A7 Sportback h-tron quattro: Fuel cell technology

It covers over 500 kilometers on one tank of fuel – and its exhaust emits nothing more than a few drops of water: The A7 Sportback h tron quattro uses a powerful, sporty electric drive with a fuel cell as its energy source, in combination with a hybrid battery and an additional electric motor in the rear.

Expertise in fuel cell technology

The overall electrical system power of 170 kW is transferred to both the front and the rear wheels. This drive configuration makes the emission-free Audi A7 Sportback a quattro through and through – a new departure in fuel cell cars.

“The A7 Sportback h tron quattro is a genuine Audi – at once sporty and efficient. Conceived as an e quattro, its two electric motors drive all four wheels,” explained Prof. Dr. Ulrich Hackenberg, Member of the Board of Management for Technical Development at Audi. “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 infrastructure are ready.”

New in the family of alternative driving principles: h-tron

The “h” in the name h tron denotes the chemical element hydrogen. In visual terms the technology demonstrators that Audi has brought along to the Los Angeles Auto Show basically resemble the production models. As the label with the h tron signet reveals, this concept car now takes its place alongside the other Audi models with alternative drive principles, the e tron and g tron. Externally, there is no other evidence of the fuel cell that converts hydrogen into electrical power on board the vehicle.

The fuel cell

The crucial differences are beneath the hood of the A7 Sportback: The fuel cell in the Audi technology demonstrator is installed at the front, mirroring the conventional A7 Sportback with combustion engine. Because the exhaust system only has to handle water vapor, it is made of weight saving plastic.The fuel cell itself comprises over 300 individual cells that together form a stack. The core of each of these individual cells is a polymer membrane. There is a platinum-based catalyst on both sides of the membrane.

This is how the fuel cell works: Hydrogen is supplied to the anode, where it is broken down into protons and electrons. The protons migrate through the membrane to the cathode, where they react with the oxygen present in air to form water vapor. Meanwhile, outside the stack the electrons supply the electrical power – depending on load point, the individual cell voltage is 0.6 to 0.8 volts.

The plug in hybrid

A special feature of the A7 Sportback h tron quattro is its plug in hybrid concept – this represents a logical evolution from the Audi A2 H2 and Q5 HFC test cars. It has a lithium ion battery on board that can be recharged from the power socket by lead; with an 8.8 kWh energy capacity, it has been adopted from the A3 Sportback e tron. It is located beneath the trunk and has a separate cooling circuit for thermal management.

This high performance battery makes the ideal partner to the fuel cell. It can store energy recovered from brake applications and supply considerable power for full load boosting. This paves the way for impressive acceleration, making the A7 Sportback h tron quattro truly live up to quattro standards. Both the front and rear axles have no mechanical connections for the transmission of power. In the event of slip, the torque for both driven axles can be controlled electronically and adjusted continuously.

Faszination e-quattro

Driving in the Audi A7 Sportback h tron quattro offers the full appeal of electric drive in conjunction with the new e quattro. The silent propulsion is fully available from the off, and the fuel cell reaches its maximum output within one second at full load – a more dynamic response than a combustion engine because the entire drive system involves only a few mechanical components.

With 540 Nm of propulsive power at its disposal the Audi A7 Sportback h tron quattro, which tips the scales at only around 1,950 kilograms, races from a standstill to 100 km/h in 7.9 seconds. Its top speed is 180 km/h – a top figure for its field of competitors. The e quattro concept requires precise coordination of the electric motors – the technology demonstrator offers a sporty, stable and high-traction drive that is comparable to a production car with mechanical quattro drive.