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Porsche 919 Hybrid (since 2014)
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The experiences with the 911 GT3 R Hybrid and the 918 Spyder also influenced the development of the Porsche 919 Hybrid. With it, the sports car brand returned to the top class of the World Endurance Championship (WEC) in 2014, and therefore also to the 24 Hours of Le Mans. With system performance of over 900 hp (662 kW), the 919 Hybrid, which was developed from the ground up and is extremely complex, is the fastest test laboratory and the most innovative racing car that Porsche has ever built.
From the beginning, its bold technical concept followed a clear objective: Optimum energy efficiency through the greatest possible effectiveness of all the components. This applies equally to the aerodynamics of the Le Mans prototypes and to the uncompromising lightweight construction of all the elements, particularly the energy recovery and drive systems – cutting-edge technologies that are of great importance for use in series-production models. These technologies include the 800-volt technology, which also distinguishes the purely electrically driven Mission E concept vehicle. The series-production version of the four-door sports car study will be launched before the end of the decade.
In view of the WEC technical regulations, which were introduced for the first time in 2014 and offer the 919 engineers great freedom for creative solutions, Porsche chose an unusual path: The hybrid drive is based on two different energy recovery systems. The first works relatively conventionally and was derived from the 911 GT3 R hybrid: A generator on the front axle transforms kinetic energy into electrical energy in braking phases. The second is more advanced and even today is unprecedented on the starting grid of the World Sports Car Championship because it accesses the thermodynamic energy of the exhaust gas flow. To do so, an additional turbine generator unit takes on the task of the wastegate: The control valve protects turbo systems from overloads by allowing pressure peaks to dissipate. From this exhaust gas energy, which was previously lost, the unit referred to as the MGU-H (Motor Generator Unit Heat) generates electrical current. As a result, the Porsche 919 Hybrid is the only sports car in the LMP1-H top class that recovers excess energy not only during braking, but also during acceleration.
Regarding the question of the 919 storage medium, the flywheel energy storage system used in the 911 GT3 R Hybrid initially seemed to be the first choice, but Porsche once again pursued a bolder path with an innovative concept: The self-developed, liquid-cooled lithium-ion batteries, which are based on cell technology from the partner company A123 Systems, combine relatively large storage capacity with high power density. Thus they offer the best compromise between fast power consumption and power output. In acceleration phases their energy flows to the front generator, which then functions as a single electric motor and drives both front wheels via a differential. This gives the Porsche 919 Hybrid a temporary all-wheel drive, because the power of the just 2.0 litre four-cylinder V-combustion engine goes to the rear axle alone.
A noteworthy point in the LMP1-H regulations of the WEC is that the amount of electrical energy that can be recovered per lap and be re-boosted is limited. In 2015 the Porsche 919 Hybrid became the first prototype to be launched in the 8-megajoule top category. For the 13,629-kilometre long “Circuit des 24 Heures” at Le Mans, this means that the prototype may apply exactly 2.22 kilowatt hours (kWh) of current per lap, and consume the equivalent of 8 MJ (1 MJ = 0.28 kWh) and a maximum of 4.31 litres of petrol. The electrical energy that the Porsche 919 Hybrid recovered at Le Mans in each of the 24-hour races in 2015 and 2016, where it was victorious both years, would be enough to power a single-family home for three months.
