Doctor Glyndwr wrote:
By a hybrid, no less. The car is bonkers. The 2l V4 petrol engine puts out 720 bhp. The electric motor is another 440 bhp.
I've been
reading about how it works and oh my God, it's amazing.
Quote:
With the 919 Hybrid, Porsche has developed a new field of technology at racing speed. For the “Mission E”, a fully electric road-going concept sports car unveiled in 2015, the designers adopted the 800-Volt technology from the prototype racer. Porsche has exhausted all possibilities in designing the two-time Le Mans winner – especially in terms of the drive concept. It consists of the two-litre, V4 turbocharged petrol engine, the most efficient combustion motor that Porsche has built up to now, and two different energy recovery systems.
One turbine converts surplus energy into electrical energy
During braking, a generator at the front axle converts the car’s kinetic energy into electrical energy. In the split exhaust system, one turbine drives the turbocharger while another converts surplus energy into electrical energy. The braking energy contributes 60 per cent, with the remaining 40 per cent coming from exhaust gas. The recuperated electrical energy is stored temporarily in a lithium-ion battery and feeds an electric motor on demand. “On demand” means: the driver wants to accelerate and calls up the energy at the press of a button. In accordance with the latest regulation changes, the power from the combustion engine is just under 368 kW (500 HP), and the output from the electric motor is well over 294 kW (400 HP).
The use and interplay of these two energy sources require a sophisticated strategy. In every braking phase, energy is won – that is, recuperated. On the Nürburgring’s 5.148-kilometre Grand Prix circuit this happens 17 times per lap, before every corner. The amount of recovered energy depends on the severity of the braking manoeuvre, or in other words, the speed at which the driver arrives at the corner and how tight it is. Braking and recuperation last until the apex of every corner, the driver then accelerates again. In this moment, the aim is to utilise as much energy as possible. Hence, the driver steps on the throttle pedal using fuel energy, and also “boosts” electrical energy from the battery.
The hybrid powertrain of the Porsche 919 Hybrid
While the combustion engine drives the rear axle, the electric motor takes care of the front axle. The 919 catapults out of the corner without any loss of traction using all-wheel drive – and in the process recuperates energy again because on the straights the extra turbine in the exhaust tract is hard at work. At constantly high engine speeds, the pressure in the exhaust system increases rapidly and drives the second turbine connected directly to an electric generator. Both energy sources, however, are limited by the regulations: a driver may not use more than 1.8-litres of fuel per lap and no more than 1.3 kilowatt hours (4.68 megajoules) of electricity. He must calculate this carefully so that at the end of the lap he has used exactly this amount – no more, no less. He who uses more is penalised. He who uses less, loses performance. He must stop “boosting” and lift his foot off the throttle at exactly the right moment.
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Arguably Porsche’s bravest decision for the hybrid system of the 919 was opting for 800 Volts. Establishing the voltage level is a fundamental decision in electric drive systems. It influences all else – the battery design, electronics design, e-motor design and charging technology. Porsche pushed this as far as possible.
It was difficult to find components for this high voltage, particularly a suitable storage medium. Flywheel generator, supercapacitors or battery? Porsche chose a liquid-cooled lithium-ion battery, with hundreds of individual cells, each enclosed in its own cylindrical metal capsule – seven centimetres high and 1.8 centimetres in diameter.
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An everyday comparison: If an empty lithium-ion battery in a smartphone had the same power density as the 919, it would be completely recharged within a lot less than a single second. The downside: A brief chat and it would be empty again.
It's not totally clear but it sounds like the driver is essentially individually managing two throttles (the petrol and the electric) at all times. I wasn't sure if it worked out for itself when the turn the electric motor on and off or not.