Turbochargers are a popular technology in the automotive world as of late. It allows rather low displacement engines to have relatively high power outputs, while also managing to return fairly good fuel consumption figures (on paper).
Despite the technology being decades old, some of its drawbacks could still be improved upon. One of these issues is the well-known problem of turbo size. A smaller turbine spools up quicky but runs out of steam at higher revs while a bigger turbine offers enough power at high revs but often is too slow at lower revs which results in turbo lag.
BMW has now patented its own idea on how to address these issues, and it involves the use of an often rumored "electric turbocharger
We reported before that BMW has considered (or may still be considering) the use of an electric turbocharger as part of a potential tri-turbo 6-cylinder engine for the next generation F80 M3 (the latest rumors point towards a bi or tri-turbo inline-6 as the new M3's powerplant). While we still don't know if the next gen M3 will be powered by an engine with an electric turbocharger, we do now know how such an electric turbocharger would be implemented, courtesy of a patent application BMW submittted to the German patent office.
First, here's an explanation of the electric turbo's individual parts (as labeled in the diagrams):
1) turbo layout
2') turbine axle
3') compressor axle
4) electric motor (and alternator)
5) turbo axle
6) (turbine axle) clutch
7) (compressor axle) clutch
We've highlighted and colored the following schematic diagrams to show how the technology works:
Unlike a traditional mechanical turbo layout, (exhaust) turbine and (intake) compressor aren't fixed on the same axle. Via the clutches #6 and #7 both the turbine and the compressor can be uncoupled from the turbine axle (#5). When the engine is idling or coasting, both clutches are open and an electric motor (#4) can operate without any load. Via gearing (#8) the speed of of the e-motor and the turbo axle can be further adjusted.
If the driver steps on the pedal the clutch (#7) closes and connects the electric motor (#4) to the compressor (#3). Due to the inertia of the (running!) electric motor, the compressor spools up quickly and compresses enough air to make for a fast engine response, which results in less lag. The turbine (#2) which wouldn't be able to spool up the compressor quickly enough is decoupled due to the clutch (#6) still being open.
Once the turbine (#2) has reached a certain speed, the clutch (#6) closes and both the turbine and the electric engine are used to run the compressor (#3).
When maximum boost is reached, the electric motor switches to an alternator mode, generates power for the battery, and avoids the turbine exceeding a certain speed. This renders a wastegate needless and ensures sure no energy from the turbine is wasted. If the driver backs off the accelerator, both clutches (#6, #7) open and the electric motor can continue running without any load from the turbine or the compressor.
According to BMW's patent application, this invention makes for a great engine response, particularly during the transition from idling to load. It also renders a wastegate needless and adds efficiency. We can't tell if this technology will actually make it into the next M3, but this sounds amazing without any doubt.
Thanks to klaus kneip for his tips!
We'll keep you updated on the subject, in the meantime check out our previous coverage and spyshots of the F80 M3: http://www.bimmerpost.com/m3/f30m3/