Quote:
Originally Posted by NISFAN
Interesting that Honeywell Garrett, the worlds largest Turbo manufacturer came out with an electric assist patent and prototypes probably about a decade ago, yet have not gone any further with it......why do you think that is?
The other thing that makes me chuckle in your wiki link, is the whole reason for using turbo chargers in the first place is to use the efficiency of the low or unboosted state where the engine uses significantly less fuel. To add a device that artificially maintains boost, is surely defeating the object? May as well stay with a larger NA.
The biggest factor in Turbo lag is the inertia of the entire turbine unit. Hence the reason for using smaller turbo's to overcome the inertia issue. Also why some manufacturers use ceramic turbine blades instead of metallic ones, again to reduce weight of rotating mass and lower inertia....
....so someone thinks it is a good idea to add clutches and gearboxes to turbines significantly increasing inertia all to reduce lag? Doesn't take a rocket scientist to how anti productive that thinking is.
My guess is all this is more focussed on harvesting the 'wasted' energy than reducing lag.  |
Garrett Turbo's view on eBoosting:
http://www.acarplace. com/ cars/ turbochargers.html
Quote:
What is E-boosting and what are its prospects? E-boosting stands for electrical-assisted boosting; by incorporating a very high speed electrical motor in rotating assembly of a turbocharger, you can drive it up to very high speeds, before you have exhaust gases to do so. It is very powerful, specifically when there is no exhaust gas available, such as at idle, or in stop and go.
It is entirely integrated inside the turbocharger, with virtually “real-estate” penalty to speak of. The size of the electric motor is about an inch long. It makes the turbocharger an inch longer, with no impact on the timing and virtually no impact on the weight. The trick is to make electrical motors are capable of motoring more than 120,000 rpm and withstand mechanical loads in excess of 200,000 rpm – because turbos spin that fast.
The other challenge is to get enough electrical energy into their designs. The majority of cars use 12 volt or a 14-volt alternator.42 volt would be a significant help. But we believe that electric boost is feasible with 12-volt systems. The prospect is very real for electric boost. You will see it in premium diesels such as the Renault Aspach (sic) or the Peugeot A06 (in Europe). They have limited space and need lots of power density and bottom end. I also clearly see it in high-end gasoline engines, built for high performance.
I could imagine it in a (Chevrolet) Corvette or (Ford) Mustang Cobra like vehicle, having an electrical-assist turbo. If you go to 42 volt or a hybrid, e boosting would also allow very aggressive downsizing of the (IC) engine. This would allow very aggressive downsizing of the engine. Instead of applying a three-liter V6, you could apply a one-liter internal combustion engine, equipped with an electrical boost turbo plus an electric motor. You can only do extreme downsizing – 50 percent or more – with electrical assist turbocharging.
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Garrett's final report on Electric Boosting Systems:
http://www.osti.gov/bridge/servlets/...ive/841240.pdf
This report provides very interesting reading!
http://www.bmwblog.com/2011/07/09/ed...trical-assist/
You oversimplify when you state the reason to go turbo is "
to use the efficiency of the low or unboosted state where the engine uses significantly less fuel. To add a device that artificially maintains boost, is surely defeating the object? May as well stay with a larger NA."
What you are saying is that modern turbo engines don't boost before medium revs???
The fuel economy benefit of a smaller turbo engine vs a larger NA engine is more complicated than boost/no-boost:
Less cylinders means less frictional losses (significantly less). Fewer combustion cycles per rpm etc. A modern turbo engine is on boost from very low revs anyway. In a "M-mode" I wouldn't think fuel consumption was the main priority either...
It's not only inertia that is the reason for going to a smaller turbo. A large turbo will need larger amounts of exhaust gas to spool up but will be able to handle higher rpms and the resulting larger volumes of exhaust gases. A small turbo spools quicker as it's a smaller amount of exhaust gas needed to rotatet the turbine, but restricts exhaust gas flow at higher rpm's. This is also one area where the MGU would come into play. You can have a larger turbo, that can handle high rpm's, but with reduced lag from the assist of the MGU.