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Originally Posted by dcb
Please cram the suggestion that I treat this link special with walnuts. That has to be the weirdest request I have heard yet, where is your head at? Standard forum etiquette is to provide a link plus some verbiage for context, which is precisely what I had done.
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What happened is the paper does not include a title nor author in the body. So it took a little digging to find out this is Polish professor Raf Catthoor's lecture materials. So then the common EU 'opinions' made sense as well as the simplistic analysis.
Quote:
Originally Posted by dcb
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I think you just did. My point was that there are losses when you use an engine to drive a generator to drive a motor to drive the wheels, and the prius has to do this very thing at higher speeds. Boost converters lose efficiency when they have to increase the output ratio also. . . .
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I held off on discussing how the Prius transaxle works since my critique was about the good professor's work. He didn't have measurements to backup his claims yet. The papers and metrics I provided filled in what he is missing and sad to say, reality is at odds from his claims. A cautious person might seek copies of my cited papers to gain understanding.
Quote:
Originally Posted by dcb
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You made the claim "unmatched efficiency" when, as was apparently missed in your attempt to sell more priuses, but is still supported by " * 55.5% - lowest found
* 92.7% - highest" and if 92.7% is zero electrical then 70% sounds like a reasonable swag to me.
There are plenty of operating conditions where direct drive, plus right sized atkinson will beat a priuses pants off for efficiency, especially in the high speed arena. I appreciate your love for data, but that does not mean you are completely unbiased when it comes to the prius or when choosing your words to describe it.
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I'm biased by my direct observations and the papers previously referenced that have full attribution.
Quote:
Originally Posted by dcb
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I'm afraid you have not supported . . .
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That is OK. There is no requirement for understanding what the Prius is doing. Experimentation is good and I hope folks are giving these alternates a good try. But it would be helpful to review some basic principles of operation that professor Raf Catthoor didn't cover very well.
Professor Raf Catthoor correctly identified that there are two power paths from the power split device:
He was also correct that the relative torque is fixed, 28% going the electrical path and 72% the mechanical. But both torque paths are taken at the same angular rotation speed from the ICE and the power split is proportional. This has a profound impact on efficiency calculations:
- 28% electrical * electrical_efficiency (55-97%) = electrical power path
- 72% mechanical * 92.7% (measured) = mechanical power path
In normal mode, electrical power from MG1 is routed directly to MG2 where it joins back with the mechanical power:
Counter torque is needed from the generator to get any mechanical torque. This is done by generating power that simply recombines in MG2.
There is another mode often called "heretical" where the roles are reversed. The car is traveling fast enough that MG2 can generate the power needed to drive MG1 to force mechanical path torque:
The electrical path direction is reversed. But conservation of energy leads to an interesting observation:
MG2_power = MG1_power + traction_battery_power
We see this in the data:
It has the effect of overdrive by letting the ICE spin slower.
What I'm trying to suggest is what came out of the Toyota paper:
The whole system needs to be tweaked and tuned. There is no single fix that will provide Prius efficiency.
Bob Wilson