Porsche 918 RSR hybrid concept car (2011)
Premiere: January 10, 2011 NAIAS North American International Auto Show in Detroit
Powerplant: 3.4V8 with 414kW @10.300rpm + 2 electric motors 75 kW each (peak power 564 kW)
Gearbox: 6-speed racing gearbox
Very beautiful, but confusing - the 918 RSR concept car is a mix between a racing car and a street car. It is not a full race car and it definitely isn’t a street car.
KERS
There are different Kinetic Energy Recovery Systems engineered. In the F1 cars the electric motor/generator is connected to the engine and therefore the rear wheels and the energy is stored in the supercapacitor (they are able to store energy 100 times faster than regular batteries). The system Porsche used in the 918 RSR, is somewhat different.
KERS/hybrid system in 918 RSR concept car
The 918 RSR concept car looks like the 918 Spyder, but the hybrid concept is from the 911 997 GT3 R Hybrid racing car and not from the 918 Spyder. The internal combustion engine and gearbox in the 918 RSR are developments based on the units from RS Spyder racing car. There are two electric motors/generators installed on the front axle and the energy is stored in the flywheel capacitor, which is basically also an electric motor. The flywheel runs on ceramic bearings and operates in vacuum, so it doesn’t wind down so quickly. When driver presses the brake pedal, the electric link between the motors/generators and the flywheel capacitor is established. Now, the electric motors also help to brake the car, meaning they help to reduce the brake disc temperatures and wear. If you would have the electric motors connected to the capacitor all the time, it would decrease the power of the car, so it is connected only during braking and acceleration. In order to spin the flywheel to its maximum of 36.000 rpms, it takes many pre-corner brakings. At the push of a button, the pilot is able to call up the energy stored in the charged flywheel accumulator and use it during acceleration or overtaking manoeuvres. The flywheel is braked electromagnetically to supply up to 150 kW from its kinetic energy to the electric motors on the front axle. This additional power is available for around 8 seconds when the flywheel is spinning at its maximum speed. The front electric motors also offer a torque vectoring function by means of variable torque distribution between left and right front wheels. This improves traction and steering response while exiting corners.
Article © James Herne / Stuttcars.com
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