View Single Post
Old 03-08-2009, 11:28 PM   #41 (permalink)
bwilson4web
Engineering first
 
bwilson4web's Avatar
 
Join Date: Mar 2009
Location: Huntsville, AL
Posts: 788

14 i3-REx - '14 BMW i3-REx
Last 3: 45.67 mpg (US)

17 Prime Plus - '17 Toyota Prius Prime Plus
90 day: 58.25 mpg (US)
Thanks: 75
Thanked 194 Times in 125 Posts
Actually it works quite nicely for the Toyota and Ford hybrids. The Atkinson cycle and hybrid transmissions provide a relatively flat ICE efficiency. When I put in my NHW11 Prius numbers there was good agreement on:
  • 100 mph mileage - 22 MPG measured and calculated
  • 18 mph maximum range - the model shows ~92 MPG and mine show ~84 MPG
  • 5 mph MPG - the model shows 65 MPG and mine 55 MPG
This is close enough without going nuts but you are right that Otto cycle vehicles need an 'efficiency' curve or table, not a single number.

One of the less well know aspects of hybrids is their ability to keep the engine in an extended, peak BSFC range. There are a two inflection points, the maximum EV speed, 42 mph for Prius, and maximum MG1 rpm that at higher speeds requires the engine to turn faster than idle. But these are subtle effects not well understood outside of the hybrid community. Think of them as shift points and that is close enough.

Bob Wilson

__________________
2019 Std. Range Plus Model 3 - 134 MPG3 || 2014 BMW i3-REx - 117 MPGe, 39 MPG
JuiceBox 40 Pro (240 VAC, 40 A), KHONS portable (120-240 VAC, 12-32 A)
Retired engineer, Huntsville, AL (five times AutoPilot saved.)

Last edited by bwilson4web; 03-08-2009 at 11:36 PM..
  Reply With Quote