Eaton Bullish On The "Downspeeded" Supercharged Future
TTAC’s man-about-the-junkyard Murilee Martin has made the bold claim that we live in the golden age of cheap superchargers, but when it comes to new cars, we may be entering another “golden age” for superchargers as well. Eaton’s Ken Davis tells Automotive News [sub] that his firm is looking at doubling its supercharger sales as the technology comes into its own as a fuel-saving measure. Though turbochargers have received the lions share of attention as the industry moves towards downsized, forced-induction engines, Davis argues that supercharger have their own role to play in the effort, specifically when it comes to “downspeeding” engines to produce better power at lower RPM. He adds
Audi is our largest supercharger customer, and we are on a couple of platforms with Nissan… Nissan will bring their supercharged vehicles here. We’ll be on Audi and Volkswagen platforms, too. We are starting to get some attention.
I don't get this. A supercharger requires a more powerful engine to begin with, to drive the supercharger's rotor. That can require a lot of horsepower, especially on big engines. I do remember reading about clutch-controlled superchargers that only engaged when they were needed, but that was more about improving fuel economy in overpowered cars, rather than improving the performance of small engines.
Oh, how I love superchargers. I've got two cars, each equipped with Eaton devices. Buick Park Avenue Ultra with a supercharged 3.8L V-6 (Eaton M90) - sucks gas under acceleration, but returns 28-32 mpg on the highway. The charger whine is not very pronounced, but is usually noticeable above 5,000 rpm. This is an older design, but is still quite capable of keeping up with more modern technology. Jaguar S-Type R with a supercharged 4.2L V-8 (Eaton M112) - this car is phenomenal; still sucks gas under acceleration, but can easily obtain 25-28 mpg on the highway. That, to me at least, is incredible. A 4,000lb 400hp car getting that kind of mileage. The charger whine above 4,000 rpm is absolutely glorious. The new Eaton TVS in the XFR is also quite the device, and sounds as good as it performs: http://www.youtube.com/watch?v=fa5ivpJwmIQ
Todays top fuel dragster uses over 400 hp to turn the blower. Interesting fact.
The key is in the use of the words "low rpm". The interaction of the supercharger 'drag' on the engine (power needed to run the compressor) and the valvetrain/fueling results in efficiency within a relatively narrow RPM band. Above that range, it consumes a huge amount of engine power without a proportional benefit from the boost it provides. Turbos have similar issues with respect to boost, but because they're driven by exhaust they don't waste engine power in the process. I suspect the systems Eaton has in mind all involve clutching/unclutching the supercharger to avoid those problems, but at the end of the day the supercharger still has to be driven from the crankshaft, and doesn't recover any power from the exhaust. It cannot possibly be as efficient as a turbocharger.