The current breed of hybrid LMP1 cars are the most technically advanced racecars built to date. The Porsche 919 incorporates a wide variety of technologies to improve both power and efficiency. The 919's small displacement V4 engine and high-discharge batteries are among the most sophisticated of their type, and give the 919 a whopping 900 horsepower combined. Endurance racing is Porsche's test of durability and the viability of new technology for production. What then do these endurance racers mean to the future of Porsche road cars?
The 919 isn't Porsche's first hybrid racer, that honor goes to the Porsche 911 GT3 R Hybrid of nearly a decade ago. The GT3 R Hybrid used a 31-pound flywheel to store kinetic energy which could be converted into electric energy. By contrast 919's hybrid system operates much more like a familiar hybrid road car. The system funnels energy captured by the brake and exhaust systems into large, high-discharge batteries. The 400 horsepower electrical system drives the front axle, while the 500 horsepower V4 drives the rear wheels.
How it Works: The 919's Drivetrain
While the components in the 919's hybrid system are conceptually familiar, each piece has been optimized for motorsport rather than commuting. The battery pack is the basis of the entire system, and is the system's primary difference to a road car. The liquid cooled Lithium-Ion batteries used in the 919 have a very high energy density to supply the 800-volt drivetrain. In Porsche's words a battery's energy density can be understood this way:
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. So that the smartphone lasts for days, the energy density has priority, and that means storage capacity.
The 919's system is designed to take on and discharge energy rapidly. By contrast, the hybrid system in a roadgoing car is designed to discharge slowly to improve efficiency. Over the course of a single lap of La Sarthe the 919 will discharge eight megajoules of energy, but the rapid discharge rate of the high energy density batteries mean the 919 also has to create that power each lap.
The 919's batteries cannot carry the show on their own. The more powerful of the car's two powerplants is the 2.0l, 500 horsepower V4. Porsche claims this is the most efficient combustion motor they've yet built, and it supports not one, but two energy recovery systems. The primary system recovers energy from the car's braking system, but the V4 is topped by an innovative exhaust gas recovery system. This system allows the car to recover energy on straights and under engine load, rather than merely under braking.
Into the future
In December we announced that the Mission E electric prototype had been greenlit for production. The 919 program, along with the related 918 Spyder hypercar, have contributed technology to this new program. Through the crucible of motorsport, Porsche developed efficient and reliable ways of cooling both the batteries and electric motors. The Mission E will even rely on the same 800-Volt powertrain technology used in the racer.