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Ok, After getting burned by Yahoo, I AM taking this discussion here!
You others follow please
Playing with Graham's constant-speed spreadsheet model is
quite enlightening. Enter the engine speeds of 2136, 2349,
2563, 2776, and 2990 for 50, 55, 60, 65, and 70 mph produces:
75.72, 70.67, 65.29, 59.79, and 54.42 for estimated MPG. Those
speeds essentially stop MG1. The resulting MPG values are
approximately 4 mpg higher then the as-delivered spreadsheet.
Interestingly, using the excel solver to maximize MPG by varying
the engine RPM produces essentially identical MPG values, although
it doesn't quite stop MG1.
The idea of "clutching the sun gear" is essentially one and the same
thing. I did not ever intended to describe HOW one puts a brake
to MG1, just that it be mechanically stopped (via an electric control).
There should be no concern of MG2 free-wheeling - one need not
allow a path for any current to flow due to its back-emf, although
it is good to generate whatever power is necessary to run the car
accessories and add/subtract power to handle the small terrain/wind
variations too.
Try as I might, I can't get any better acceleration by stopping MG1 -
it always hurts on that score.
I'm supposing that Graham put actual measured ICE rpms at cruising
speed in his spreadsheet. I wonder if the model is off a bit or whether
Toytota sacrificed efficiency for reduced engine wear and a quieter
cabin.
[%sig%]
You others follow please
Playing with Graham's constant-speed spreadsheet model is
quite enlightening. Enter the engine speeds of 2136, 2349,
2563, 2776, and 2990 for 50, 55, 60, 65, and 70 mph produces:
75.72, 70.67, 65.29, 59.79, and 54.42 for estimated MPG. Those
speeds essentially stop MG1. The resulting MPG values are
approximately 4 mpg higher then the as-delivered spreadsheet.
Interestingly, using the excel solver to maximize MPG by varying
the engine RPM produces essentially identical MPG values, although
it doesn't quite stop MG1.
The idea of "clutching the sun gear" is essentially one and the same
thing. I did not ever intended to describe HOW one puts a brake
to MG1, just that it be mechanically stopped (via an electric control).
There should be no concern of MG2 free-wheeling - one need not
allow a path for any current to flow due to its back-emf, although
it is good to generate whatever power is necessary to run the car
accessories and add/subtract power to handle the small terrain/wind
variations too.
Try as I might, I can't get any better acceleration by stopping MG1 -
it always hurts on that score.
I'm supposing that Graham put actual measured ICE rpms at cruising
speed in his spreadsheet. I wonder if the model is off a bit or whether
Toytota sacrificed efficiency for reduced engine wear and a quieter
cabin.
[%sig%]