The basic concept of a turbocharger is simple; exhaust gases are cycled through a turbine, linked via an axle to another turbine connected to the air intake system. This crams more air into the engine, allowing smaller engines to make more horsepower. And smaller engines generally equate to better fuel efficiency.
But turbochargers on small engines do have their drawbacks, namely turbo lag. This is the time between stepping on the gas pedal, and actual engine response. In effect you have to wait for the horsepower to kick in…kind of annoying if you’re a speed freak like me.
Faster And More Efficient
BMW is taking a different approach to turbochargers though. Rather than have both the exhaust and intake turbines on the same axle, a pair of clutches allows them to detach from each other. When the gas pedal is depressed, the already-spinning electric generator attaches to the intake-side of the turbine, immediately spooling it up and virtually eliminating turbo lag. Once the exhaust-side reaches a certain speed, it takes over for the electric motor.
Now here’s where things get really cool. Once the electric motor has disengaged from the turbo and it is being spun solely on exhaust gases, the turbo sends electricity back to the generator, which sends the excess electricity to the battery. BMW seems to be plotting a tri-turbo system of sorts, but I think the natural fit of this system would be a plug-in hybrid. Imagine recharging your Bimmer’s batteries by stomping the gas. Sends shivers right up my spine it does. I highly recommend checking out F30post’s more technical explanation of just what BMW is planning here (though I think I summed it up nicely.)
Of course this is all just based on a patent filing. BMW is also working on waste heat-recapturing technology to improve engine efficiency as well. Will these two technologies mesh, be mutually exclusive, or end up in the circular file like so many other great ideas?