Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - EPA roll-down coef vs HP at 100 mph

bwilson4web · 06-16-2013, 01:29 AM

Hi

Recently we were discussing the HP-to-road power in a thread over at PriusChat. So I posted a recent chart showing the power required for a Volt vs Prius Plug-In (PiP):

One of the posters correctly pointed out that my chart projects ~27 hp at 100 mph. Obviously something is wrong as this is off by a factor of four. Perhaps you' all can spot my error?

I'm using the following:

Test Car List Data Files | Cars and Light Trucks | US EPA - source of roll down coefficients
drag HP = (A + B*v + C*(v*v)) / 7.5 :: "v-velocity mph", A, B, C from tables

Now in the past, I've used an OBD scanner to record ICE rpm and MG1 torque to calculate shaft HP. This has been in fine agreement with the specs for our NHW11 (2003 Prius.) So I need to repeat this analysis using the EPA roll down coefficients and compare. But I'm really scratching my head on this one.

Any thoughts?

The reason this is important is the title of the thread,"64% of Prius Power gets to wheels during max acceleration?" The original poster is using some raw acceleration numbers and the vehicle weight to calculate the HP-to-road metric and found only 64% is getting there. This suggests an exceptional transmission efficiency loss.

Understand, I'm OK with this as it may provide more insights about Prius transmission efficiency . . . if we can find independent confirmation. Unfortunately, I did a bad thing . . . loaned out my 2010 Prius OBD scanner. This one can read out ICE rpm and MG1 torque providing the raw HP data at the input to the transmission.

Thanks,
Bob Wilson

06-16-2013, 01:29 AM	#1 (permalink)
bwilson4web Engineering first Join Date: Mar 2009 Location: Huntsville, AL Posts: 843 17 i3-REx - '14 BMW i3-REx Last 3: 45.67 mpg (US) Blue Bob's - '19 Tesla Std Rng Plus Thanks: 94 Thanked 248 Times in 157 Posts	EPA roll-down coef vs HP at 100 mph Hi Recently we were discussing the HP-to-road power in a thread over at PriusChat. So I posted a recent chart showing the power required for a Volt vs Prius Plug-In (PiP): One of the posters correctly pointed out that my chart projects ~27 hp at 100 mph. Obviously something is wrong as this is off by a factor of four. Perhaps you' all can spot my error? I'm using the following: Test Car List Data Files \| Cars and Light Trucks \| US EPA - source of roll down coefficients drag HP = (A + Bv + C(vv)) / 7.5 :: "v-velocity mph", A, B, C from tables Now in the past, I've used an OBD scanner to record ICE rpm and MG1 torque to calculate shaft HP. This has been in fine agreement with the specs for our NHW11 (2003 Prius.) So I need to repeat this analysis using the EPA roll down coefficients and compare. But I'm really scratching my head on this one. Any thoughts? The reason this is important is the title of the thread,"64% of Prius Power gets to wheels during max acceleration?" The original poster is using some raw acceleration numbers and the vehicle weight to calculate the HP-to-road metric and found only 64% is getting there. This suggests an exceptional transmission efficiency loss. Understand, I'm OK with this as it may provide more insights about Prius transmission efficiency . . . if we can find independent confirmation. Unfortunately, I did a bad thing . . . loaned out my 2010 Prius OBD scanner. This one can read out ICE rpm and MG1 torque providing the raw HP data at the input to the transmission. Thanks, Bob Wilson __________________ 2019 Tesla Model 3 Std. Range Plus* - 215 mi EV 2017 BMW i3-REx - 106 mi EV, 88 mi mid-grade Retired engineer, Huntsville, AL