Developed to operate at up to 95deg C (an increase of 15deg on the fourth-generation fuel cell stack used in the Audi A7 h-tron prototype driven by Autocar in Los Angeles in 2014), the latest stack is mounted up front underneath the bonnet in the space traditionally taken up by the combustion engine on existing Audi models and has been conceived to operate in temperatures as low as -28deg C.
Described as being lighter, smaller, stronger and more economical than the unit it replaces, the new fuel cell stack is claimed to boast an efficiency rating of up to 60% – more than double that of a typical combustion engine.
One key development being touted by Audi is the reduction in the amount of platinum used in its production, making it cheaper and more environmentally friendly. A newly conceived heat pump is also claimed to absorb waste heat more efficiently, reducing the typical heat build-up within the interior associated with early fuel cell prototypes.
In combination with a relatively small 1.8kWh lithium ion battery mounted within the floor in the middle of the passenger compartment that provides an additional boost of 100kW (134bhp) for short periods, the fuel cell stack is claimed to provide the h-tron quattro with a range of up to 373 miles. All up, the battery is claimed to weigh just 60kg.
While the fuel cell operates at between 220 and 280 volts, the battery can run between 220 and 480 volts. A DC converter mounted within the engine compartment is used to equalise the difference, providing electrical energy to a pair of electric motors – one mounted within the front axle assembly with 90kW (121bhp) and another on the rear axle producing up to 140kW (188bhp). Each electric motor has its own single-speed planetary gearset, which acts as a differential.
The set-up differs from that used by the earlier all-electric e-tron quattro, which featured three electric motors – one up front and two at the rear - as well as a much larger lithium ion battery with a capacity of 95kWh.
All up, the h-tron quattro boasts a combined system output of 210kW, or 282bhp, along with what Audi describes as system torque of 406lb ft. This compares with the 370kW (496bhp) and 435lb ft of the significantly heavier but more aerodynamic e-tron quattro.
It is sufficient, according to Audi’s figures, to provide the four-seat concept with a theoretical 0-62mph time of less than seven seconds and 124mph top speed. By comparison, the e-tron quattro has respective figures of 4.6sec and 131mph.
The driver can influence the amount of energy recuperated on a trailing throttle by selecting one of two modes: gliding or coasting. Fuel consumption is put at around one kilogram per 62 miles.
Underpinning the concept is a modified version of the MLB platform from the upcoming second-generation Q5. It has been reworked with an altered floorpan and structural elements to accommodate the batteries low down for the best possible centre of gravity.
The suspension - a five-link design both front and rear - features air springs with both adaptive damping and a self-levelling function to automatically lower the body in two stages by up to 30mm for improved aerodynamic efficiency at constant motorway speeds.
Drawing on developments brought to the latest Q7, the h-tron quattro also adopts four-wheel steering with up to 5deg of movement on the rear wheels to reduce the turning circle and aid manoeuvrability at lower speeds around town while increasing agility at higher speeds.
Stretching to 4880mm in length, 1930mm in width and 1540mm in height, the e-tron quattro is 250mm longer, 30mm wider and 115mm lower than the existing first-generation Q5.
While the drag coeffiicent of 0.27 beats that of existing Audi models, it fails to match the 0.25 of the e-tron quattro due to the requirement for additional cooling for the fuel cell stack at the front end.
The interior of the h-tron quattro draws heavily on the design originally unveiled on the Prologue concept at last year’s Los Angeles motor show. It provides seating for up to four, with two individual seats front and rear.
Among the highlights is a trio of OLED displays, as planned for the fourth-generation A8 due out in 2017. Boot space is put at 500 litres – 115 litres less than the e-tron quattro due to the packaging of the hydrogen tanks.
Giving a glimpse at the sort of autonomous driving technology we can expect to see on future Audi models, the h-tron quattro comes equipped with all the various technologies the German car maker has developed as part of its so-called Piloted Driving research programme, including radar sensors, stereo cameras, ultrasonic sensors and a laser scanner.
All systems are controlled in a central driver system known as zFAS. It computes a complete model of the concept car’s surroundings in real time and makes the information available to the assistance system. They then carry out various driving tasks at speeds of up to 37mph.
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