The concept of electric-motor-powered forced induction
is nothing new, and breakthroughs in this area have been “just around the corner” for several years. Despite this, no on has implemented electric forced induction
in a production vehicle.
BMW, however, has taken the first necessary steps to do just that, by filing a German patent application for its own electric turbocharger design, according to a recent report. Implementation may still be a ways off, but at least we know a major manufacturer is working on the technology.
To understand the design, first you need to know a little bit about the benefits and drawbacks of small versus large turbos
Small turbines are quick to spool up and provide boost via a compressor, and this design is good at providing low-end power. Conversely, they run out of boost at high RPMs, which limits their appeal.
Larger turbines take a while to spool up (creating turbo lag), but their larger compressors provide more power at high RPMs. Twin-turbo systems usually use both types of turbos to create the best performance across an engine’s operating range.
It’s probably easiest, then, to think of BMW’s electric turbocharger as a twin-turbo type of setup. The electrically powered compressor provides instant, off-the-line boost, while a turbine is powered by escaping exhaust gasses to provide higher-RPM power.
When the accelerator is pressed, the electrically-powered compressor instantly spools up to provide boost. When the turbine reaches a pre-determined operating speed, it’s coupled to the compressor to provide boost from the engine’s exhaust gases (like a conventional turbocharger).
BMW’s design uses a series of clutches to automatically engage and release both the compressor and turbine, so the system ensures smooth performance across the engine’s entire operating range and under all load conditions.
When maximum boost is achieved, the electric motor acts as an alternator and generates electricity to charge the battery. This design eliminates the need for a wastegate, since the drag of the electric motor limits the amount of boost that can be created.
According to F30Post
, BMW’s patent filing states that the design makes for superior engine response, especially in the transition from idling to acceleration. While a production car with this technology may still be years off, it certainly sounds promising.