Audi has just unveiled prototypes of its A6 and RS5 that feature an electric turbocharger working in conjunction with standard turbocharging to improve power and efficiency by 15% to 20%. The electric turbo takes less than a quarter of a second to spool up to full speed, and provides immediate engine boost until the regular turbocharger comes up to full boost. In other words, the dreaded “turbo lag” associated with turbocharged engines is completely eliminated.
Autoblog got to talk to Audi at length about the benefits of electric turbocharging. Take for example the TDI engine Audi currently used in the A6, which produces 240 hp and 428 lb-ft of torque. The prototype TDI engine with electric supercharger puts out 326 hp and 479 lb-ft of torque, an improve of 86 horsepower 51 lb-ft of torque. Meanwhile the prototype RS5 TDI engine with twin turbos and electric turbocharger pumps out an even more impressive 385 hp and 553 lb-ft of torque. With the enhanced engine, both cars are capable to 0 – 100 KPH/ 0 to 62 MPH sprints in about 4 seconds.
Those are impressive numbers. So why haven’t electric superchargers been used before? Quite simply, the electricity they require is beyond the capacity of a typical 12 volt electrical system. Both Audi prototypes utilize a 48 volt system that is compatible with the higher voltages found in today’s hybrid and electric vehicles. Audi decided to use 48 volt systems to save weight, reduce complexity, and insure passenger safety.
Steve McKinley, Honeywell Turbo Technology’s vice president of engineering, told Autoblog:
“We’ve been in pre-development for more than ten years. It was a matter of waiting for that electric infrastructure to develop on the vehicles. You have to have a fair amount of power going into the supercharger, But when you have other parts of the vehicle being electrified, it becomes possible to use some of that power for the turbo.”
At present, the electric turbocharger and exhaust turbocharger are two separate units because electric motors do not tolerate the heat found in exhaust gasses. Eventually, the two may be combined into one unit connected to the electric motor by a shaft running through the V of the engine. Interestingly, this is precisely the solution Mercedes has adopted for its 2014 Formula One engines. A side benefit is that a generator can also be connected to the same shaft to help meet the car’s electrical needs.
As environmental concerns and government regulations have put pressure on conventional internal combustion engines, the automotive world has embraced turbochargers as a way of making engines more efficient without sacrificing power. Ford has led the way with its EcoBoost family of engines, and now Audi is showing that compound turbocharging using electric turbochargers can significantly increase performance and efficiency even more.
This new technology will likely be applied first to high performance, top of the line models. In fact, Volkswagen Group technical chief Ulrich Hackenberg tells Autocar magazine that Audi will release an SQ7 equipped with electric turbocharger technology in 2016,making it the world’s first production vehicle equipped with an electric turbo.
Industry analysts expect it will take 5 to 10 years for electric superchargers to become common in mainstream vehicles. In the meantime, Audi is leading the way into the future.