64 % of Prius Power gets to wheels during max acceleration?

Before you say something like that, you should be aware that there are other people that have actually driven a Prius here.

 

Depends on whether you are counting the lbs of shredded rubber and rubber turned to smoke as useful work or not.

 

Well I'm curious so I've ordered a replacement for the OBD scanner 'I loaned' (i.e., apparently gave away). In the meanwhile, I can get some preliminary data with our NHW11.

What I'll do is a series of ICE rpm limited acceleration tests:

• get vehicle weight with driver, fully inflate tires
• warm-up, 30 minutes
• start recording GPS
• start recording OBD scanner (ICE rpm, MG1 torque, velocity, MAF)
• Repeat test
  • hold ICE at constant RPMs (3900, 3200, 2400, 1800, 1200)
  • 0-62 mph (100 km/h) - level road
  • shift to "N" - until braking required
  • repeat each rpm range at least 3 times, each direction, 5 times if problem
• Save GPS and OBD data
• Take home to analyze

With this set of data, we'll have:

1. ICE power
2. KE change during each run
3. fuel consumption during each run

We should be able to plot a series of curves for each ICE rpm setting showing transmission efficiency as a function of speed and ICE rpm:

​

(ICE_joule - KE) / ICE_joule :: ICE power versus vehicle change in kinetic energy (KE)​

(fuel_joule - ICE_joule) / fuel_joule :: ICE efficiency​

(fuel_joule - KE) / fuel_joule :: tank-to-wheel efficiency​

distance covered to reach 62 mph​

Sad to say, I won't be able to measure the ZVW30 fuel burn during the tests due to limits of the OBD scanner. However, Frank might be able to do it. I'll do all of my calculations in standard units with a table of SAE conversion factors.

Bob Wilson

 

i understand traditional auto's pretty well ... but i am still trying to wrap my head around the Prius with so many automotive paradigms different. i got my moms a prius a week ago and i am amazed with some new discovery everyday ... i am an mech engineer and like understanding things. I have taken IC engines as a master level course so i understand engines very well and just looked up the power split device a couple of days ago.

in his example i know he is using some ball park numbers .... typically when people dyno hp they say 15% drive train loss over manufacturer tested brake horsepower ... but its really just ball park number for the 'avg car' ... i looked at how RX-7 dyno'd low compared to high torque engines... i had rx-7 and rx-8's and they have low torque/high horsepower engines because they rev so high ... with horsepower and proper gearing torque doesn't matter at mid/high speeds but at low speed u can only gear so low till the losses accelerating those gears causes inertia high losses... ... its a somewhat laborious calculation but each time u slow down the drive shaft with gearing the inertial loss becomes less pronounced. any way i did some calculations with the rx-7 sized gear train vs a much higher torque gear train and came up with huge inertial losses in 1st and 2nd gear for the low torque rotary (because its geared lower with due its 8500 rpm max hp). Also any sort of F=ma calculation with accel integrated is wrong when different class vehicles are compared unless u include Torque = J * Omega calculations thru out the drive train i found ... that's what those fudge transmission losses are, the inertia of the drive train ... rotational friction of shafts and gears is small, 2% friction i think, maybe 1%. Granted lots of bearings adds up but its not 20%. i all so did some top speed calculations, with published Cd and typical friction losses and those where very accurate. that convince me more how critical accelerating the rotary inertia is.

one note the prius has a very thermally efficient engine, its a pseudo Atkins cycle. Like other said thermal cycles in general are VERY inefficient, so in thermal term 38% is very good. Also the gas engine can be more efficient if u keep it its best Specific fuel consumption at full load (part throttle & idle is very inefficient/hp produced).. the problem is if u make it small enough to drive full throttle all the time, its just too slow a car.

i hate to ask a question in someones else s thread but i don't understand either electric motors or battery's that much .... before i all ways thought electric motors where about 90% efficient if used in the design envelope... but now i read it really depends on load and drops a lot if as u move away from design points .. i also googled discharge/charge efficiency of a Nimh battery and its seems to be as high as 66% if 50 discharged and approach 33% if either 25% or 75% discharged ... that made me wonder if the Prius battery gauge is show the true charge or the allowable charge ... when its at max charge about 3/4 bars is there really 3/4 charge or more like 2/3 charge sp charge discharge efficiency is higher. Also my layman's understanding of brakes on the prius is i'm not using friction brakes if i don't fill the meter and i am some amount above 7 mph.

 

OK?

 

0-60 acceleration times are meaningless in the real world. How a car feels performance wise is related to speed to speed acceleration times. I don't know if it is true but if you are rolling along in traffic at say 30km/hr and then give the throttle a quick stab, like if you are merging into a faster flowing traffic stream, the Prius responds remarkably well. Maybe it is just that you get used to only using the acceleration you need, (i.e. not much) and when it does go it takes you a little by surprise. I wonder if in response to a quick prod on the accelerator the Prius actually runs the electric side at over 100% output. It feels like it. That is the good thing about electric motors, they can be overloaded and most are most efficient in the 100-110% band.