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Originally Posted by NISFAN
In theory, in practice to flow enough air to make a difference, it takes a very large amount of power.....I'm told a journal bearing turbo under full load uses 1000watts of power to drive just the bearings. Not the compressor load, just thrust bearing load. 1000watts from a 12v system is one large electric motor, just to overcome the bearing losses. The compressor requires a significant amount more than this to actually do the work it requires. You can work it out, but I'm guessing you would need 5000watts minimum. And what does that give you? when does it come into action? Everytime you are sitting at the lights idling? All the time you are cruising along the highway, just in case you want to give it some? 5000watts is around 370 Amps. That is cabling thicker than your thumb to handle that power, and draining the battery way faster than the alternator can charge. Not a practical solution.
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The thrust load on the bearing is proportionnal to the load of the compressor itself. The less mass flow the compressor is pumping the less thrust (axial) load there is on the bearing. When the throttles are closed (or intake valves in the case of a valvetronic engine), the compressor does not need to pump much mass flow to maintain boost. So not much power is needed to maintain the boost level and not much power is required to overcome the friction caused by the thrust loading.
Quote:
Originally Posted by NISFAN
Suggests that automotive electrical systems are not powerful enough to produce positive boost pressure.....and yes you can fit a prius motor and 3 phase electrical system to drive a compressor, but really? an extra 100kg's to reduce lag by a few tenths?
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An electric assist may not have the power to supply full boost at full load (WOT and high RPM). But it may be able to sustain boost at lower load levels (partial throttle).
The electric motor can also prevent the turbo from spooling down. Even if the electrical system adds inertia to the system, if the electrical motor is able to maintain some speed in the turbo, intertia is less of an issue. At partial loads, the turbine is still contributing work to keep the rotor spinning, albeit not enough to maintain full boost. An electric motor would simply assist the turbine to maintain the speed of the rotor. The electric motor would just supply the delta work required to maintain boost, not the entire work.
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?
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I see the biggest challenge in all of this mostly with the control systems. Maybe 10 years ago, the control technologies were not there to support the concepts. Great strides have been made in electronics and computer control technology since.