|The R18 e-tron quattro hybrids at work. Click to enlarge.|
Marking the first victory of a hybrid vehicle at Le Mans, the Audi R18 e-tron quattro (earlier post), equipped with Williams Hybrid Power’s (WHP) electromechanical hybrid flywheel system, took the top two spots at the 80th running of the endurance race over the weeken. The win was Audi’s 11th Le Mans victory. The four Audi R18 cars (two hybrid, two diesel) from Audi Sport Team Joest occupied positions one, two, three and five.
Operating at the rear of all four Audi R18 cars was the latest evolution of the compact V6 TDI engine with VTG mono turbocharger that was used at Le Mans for the first time in 2011. The new ultra-light transmission with a carbon fiber housing held up to the Le Mans endurance test covering a distance of 5,151 kilometers in all four vehicles with no problems, the company said.
The engine is a 3.7-liter turbocharged (boost pressure limited to 2.8 bar absolute) 120° V6, 4 valves per cylinder, DOHC diesel direct injection TDI using a fully stressed aluminum cylinder block and equipped with a diesel particle filter. The engine delivers power of more than 375 kW (510 hp) and torque of more than 850 N·m (627 lb-ft).
WHP designed an entirely new, ultra-lightweight electric flywheel and associated power electronics for the Audi R18 e-tron quattro, working closely with Audi engineers to fully integrate the system into the car. The system provides 150 kW of power and has a top rotor speed of 45,000 rpm. The key features and benefits of the WHP system are highly suited to endurance racing and this made the WHP flywheel the prime candidate for Audi’s project when compared to other technologies such as batteries, ultra-capacitors or mechanical flywheels, WHP said.
One vehicle axle (rear) of the R18 e-tron is powered conventionally, the second (front) by two water-cooled 75 kW motors with integrated power electronics. The system integrated into the front axle includes two drive shafts, the Motor Generator Unit (MGU) supplied by Bosch, planetary gearset, the WHP KERS system, an insulation monitoring unit for high voltage safety, and the control system.
On the Audi R18 e-tron quattro, kinetic energy is recovered on the front axle during the braking phase. In the process, the wheels drive the MGU. The braking zones permitted are defined by the controller. Power from the Motor Generator Unit accelerates the carbon-fiber flywheel, which runs in a high vacuum.
After the corner is taken and the driver accelerates again, the system delivers the energy to the front axle. The regulations allow 500 kJ of energy to be transferred to the front wheels between two braking phases. The planetary gears adapt the transmission ratio during acceleration and braking. The two independently powered axles on the e-tron quattro are synchronized exclusively via electronic control strategies.
This control occurs automatically without driver intervention. The entire charging process (recuperation) is controlled by two parameters: the deceleration of the car—i.e., the braking process—and subject to the accumulator’s state of charge. The energy emission process (boost) is defined by the minimum speed of 120 km/h stipulated by the regulations, the race strategy selected, the throttle pedal movement and acceleration of the car.
With the e-tron quattro in combination with ultra lightweight design, we put a completely new technology on the grid and immediately won with it—this cannot be taken for granted by any means, particularly here at Le Mans. This weekend again showed the type of things that can happen in this race and how important perfect preparation is.—Rupert Stadler, Chairman of the Board of Management of AUDI AG
Accidents took both Toyota hybrid vehicles out the race this year.
Porsche is also using a WHP flywheel energy recovery system (KERS) in its 911 GT3 R Hybrid. The GT3 features an electrical front axle drive with two electric motors developing 60 kW each supplementing the 480-bhp (358 kW) four-liter flat-six at the rear of the 911 GT3 R Hybrid. (Earlier post.)