Red side: Turbine for exhaust gases. Blue side: Compressor that feeds air into the engine.
How a Turbocharger Works: For Dummies Imagine, if you will, two pinwheels, connected by a shaft. If you blow on one pinwheel, the other turns. This is essentially how a turbocharger works. The first pinwheel, called the turbine, runs on pressure from the engine’s hot exhaust gasses. It, in turn, rotates the shaft that is connected to the compressor at the other end. That compressor is able to force more air into the engine at a faster rate than normal. Extra air means extra fuel can be burned.That’s how a tiny turbocharged four-cylinder engine can make more power than V-8 engines from less than a decade ago. The great news is that the turbo is only active when you need it, that is, at full throttle. If you're just cruising along it doesn't do much of anything, so fuel economy is much better, despite the extra power. Of course, the opposite is true, too: If you're a leadfoot, you'll wind up burning just as much fuel as you would with a bigger engine. At low engine speeds, the exhaust turbine doesn’t receive much pressure to move it, which also means that the compressor cannot force more air into the engine to create more power. If you suddenly put the gas pedal to the floor, it takes time for that exhaust pressure to build up and get everything started. This is one of the factors behind turbo lag at low engine operation speeds. It’s also why many makers of sports cars have moved to more expensive turbochargers made of ceramic materials. They’re lighter and start spinning earlier, allowing the engine to make more power faster. What BMW’s Turbocharger Does Differently Where the shaft in the middle connects the turbine and compressor in a traditional turbocharger, the proposed BMW unit has a tiny clutch sandwiched in between the two, decoupling two sides so they don't always have to spin at the same speed. When coasting on the highway, disconnecting both can leave the electric motor from having to spin either the turbine or compressor, allowing the engine to work as efficiently as a non-turbo engine without any extra load. When more power is needed, the electric motor turns on instantly, spinning the power-making compressor. When the exhaust gas pressure builds up high enough, the clutch reconnects the turbine and the electric motor to link all of the units again, as in a traditional turbocharger. Under really heavy use, such as when the engine is running at full-speed and the turbocharger is at its power-producing limit, the electric motor turns into a generator, using the spinning turbo to generate electricity to help charge the car’s battery. The cycle begins again as the turbocharger is used and disused. BMW and other manufacturers have already minimized lag in recent years with advancements such as lightweight components, moving the turbine as close as possible to the exhaust, and other tricks, and its recent advancements can be seen in its turbocharged four-, six-, eight-, and twelve-cylinder engines. If this system of miniaturizing a gas-electric hybrid motor within a turbocharger makes it to a production car, it could change the way automakers think about forced-induction engines. Source: BimmerPost
