hours of electrical energy correspond to eight megajoules – and that is the highest energy class stipulated in the regulations. Porsche was the first and, in 2015 at least, the only manufacturer who dared to push the limits so far. Audi and Toyota were only able to achieve four and six megajoules respectively.
For the concept choice a very close look at the individual alternatives was taken. There was no question that Porsche would use the braking energy at the front axle masses of energy from areas already partially developed combined with massive progress. For the second system brake energy recuperation at the rear axle or through utilising exhaust gas were considered. Two aspects pointed in favour of the exhaust solution: Firstly weight, and then efficiency. With brake energy recovery, the system has to recuperate energy within a very short space of time, which means coping with a lot of energy, but at the expense of weight. The acceleration phases, however, are much longer than the braking phases, which allow a longer period of recuperation and make the system lighter. Plus with the combustion engine the 919 already has a drive system on the rear axle. Even more power at the rear would have generated more inefficient wheel spin. Moreover, this leads to tyre wear and can even badly damage the rubber.
Courageous fundamental decisions
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 cm in diameter.
In both a road and racing car, power density and energy density must be balanced. The higher the power density of a cell, the faster energy can be recharged and released. The other parameter, energy density, determines the amount of energy that can be stored. In racing, the cells – figuratively speaking – must have a huge opening. Because as soon as the driver brakes, a massive energy hit comes in, and when he boosts it must leave at exactly the same speed. 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 20 seconds. The downside: A brief chat and it’s empty again. So that the smartphone lasts for days, the energy density has priority, and that means storage capacity.
The 919 as a testing lab
In an electric car for everyday use, storage capacity translates into range. In this regard, the requirements of the racing car and a road-going electric car are different. But with the 919 Porsche has advanced into regions of hybrid management that were previously unimaginable. The permanently excited synchronous machines earmarked for the Mission E concept car are practically the civilian siblings of the Motor Generator Unit (MGU) from the Le Mans prototype. The 919 served as the testing lab for the voltage level of future hybrid systems. From this experience, the colleagues in production development gained the courage to introduce the four-door Mission E with 800-Volt technology. The concept should go into production at the end of the decade.
via : http://zumzumauto.blogspot.com/
For the concept choice a very close look at the individual alternatives was taken. There was no question that Porsche would use the braking energy at the front axle masses of energy from areas already partially developed combined with massive progress. For the second system brake energy recuperation at the rear axle or through utilising exhaust gas were considered. Two aspects pointed in favour of the exhaust solution: Firstly weight, and then efficiency. With brake energy recovery, the system has to recuperate energy within a very short space of time, which means coping with a lot of energy, but at the expense of weight. The acceleration phases, however, are much longer than the braking phases, which allow a longer period of recuperation and make the system lighter. Plus with the combustion engine the 919 already has a drive system on the rear axle. Even more power at the rear would have generated more inefficient wheel spin. Moreover, this leads to tyre wear and can even badly damage the rubber.
Courageous fundamental decisions
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 cm in diameter.
In both a road and racing car, power density and energy density must be balanced. The higher the power density of a cell, the faster energy can be recharged and released. The other parameter, energy density, determines the amount of energy that can be stored. In racing, the cells – figuratively speaking – must have a huge opening. Because as soon as the driver brakes, a massive energy hit comes in, and when he boosts it must leave at exactly the same speed. 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 20 seconds. The downside: A brief chat and it’s empty again. So that the smartphone lasts for days, the energy density has priority, and that means storage capacity.
The 919 as a testing lab
In an electric car for everyday use, storage capacity translates into range. In this regard, the requirements of the racing car and a road-going electric car are different. But with the 919 Porsche has advanced into regions of hybrid management that were previously unimaginable. The permanently excited synchronous machines earmarked for the Mission E concept car are practically the civilian siblings of the Motor Generator Unit (MGU) from the Le Mans prototype. The 919 served as the testing lab for the voltage level of future hybrid systems. From this experience, the colleagues in production development gained the courage to introduce the four-door Mission E with 800-Volt technology. The concept should go into production at the end of the decade.
via : http://zumzumauto.blogspot.com/
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