Most efficient speed for best MPG?

[tomdeimos]

Originally posted by jdjeep98@Jan 27 2006, 07:10 AM
  Is it me, or does it seem odd to you, too, that you would get any reading below max (99.9) when you are using "battery only"... 

[snapback]198541[/snapback]

As I already said above. I igore the 99. I go by my total trip mpg.

The 99 combined with the mpg when the engine is running is generally up near 80 mpg.
When my trip gets less than that it is due to the number of stop signs and lights on my route, or traffic.

Battery will alway get you more mpg total average than running the engine. That is why the car does it. It would even improve mpg at higher speeds too if it weren't for the rpm limits.

Wayne's chart is the steady state mpg with engine going.

[jdjeep98]

Originally posted by kDB@Jan 27 2006, 07:17 AM
this happens when the ICE is running but is not helping move the car.  usually when the ICE is warming up.

[snapback]198542[/snapback]

Oooohhhh!!

OK, I get it now... It just read kind of odd to me...

[windstrings]

Originally posted by jdjeep98@Jan 27 2006, 05:23 AM
Oooohhhh!!

OK, I get it now... It just read kind of odd to me... 

[snapback]198546[/snapback]

The pulse and glide would be an excellent procedure to do if you were in a bind on gas and had to really milk it to get to a station.... just put your emerg flashers on!

[windstrings]

Originally posted by tomdeimos@Jan 27 2006, 05:23 AM

Battery will alway get you more mpg total average than running the engine.   

[snapback]198545[/snapback]

Yea and no..... the conversion losses using the battery exist and are only worth it if the alternative is to waste the energy anyway like a conventional car would...

Seems the best use is to use of energy is to let the ICE keep the car above 30mph and take it easy as to not charge the battery and bring it up to 40 and then coast or dead band with no energy going anywhere....until you coast back down to 30 again.

So basically the ICE runs or not at all.
they actually try to not use the battery, because any energy used had to be created with gas!

Its better to let the engine take it easy as long as your at optimal rpms and get it up to 40mph, and then let it turn off as you coast back down to 30mph

At least this is how the guys did it that got 110 mph.


Now when in real use, you need the Ice to get up to serious mph or serious torque to get moving on the freeway, in which case the ICE will take assistance from the battery when needed and then put it back in.
This protocol they chose because it seemed to be the most efficient with all things considered since we need freeway speeds. If the speed limit was 40, then they could reprogram the computer to chance its protocol.

In other words... there are cool things you can do for special uses and trick the computer or sneak around its regular programming by use of an EV button or learning to feather the pedal in those deadband zones etc, but the computer is programmed for everyday use.

But when you have the chance, if you want to play and no traffic is around, you can pulse and glide to save gas big time!

[DaveinOlyWA]

according to stats i made, assuming being legal and not lagging. best street speed is about 35 mph (30 mph actually gets a bit worse nearly 50% of the time). on the freeway, 50 mph is probably better, but 60 mph seems to do the best because of the more constant speed. we do have 50 mph highways around here with minimal traffic control, but even one stop every several miles is enough to kill the high numbers.

besides, check out the hypermiler thread. i believe they stuck it at around 35 mph also.

[tomdeimos]

The battery is your friend and with it you can get over 70 mpg every day if you wish to, where you can keep moving steady, and not drive other drivers crazy with pulse and glide speed variations.

With pulse and glide and no battery you may on some roads get maybe 90 mpg but I doubt you could get more. Don't forget the marathoners modified their car in ways normal drivers would not with the tire pressures and thin engine oil. Battery losses are not that major and are negligible compared to using the engine at low HP. This is very simple to confirm with the mpg readouts. The average mpg not the bar graphs!

Most people here seem to be trying to not use their battery and then complain their mpg is only 45 or something. This is why in a lot of cases. Only other reason is they could just be driving fast on highways, where max mpg is not possible anyways, or be in places like I am where you have to stop about two times per mile.

Whatever your conditions, you can do relatively way better than 80% of Prius drivers using max battery. If you are getting 70 mpg daily and want more and can put up with pulse and glide go ahead. I can't be bothered, and I don't see many reports from people doing it and getting 100 mpg!

[kk6yb]

I made a graph of Speed vs MPG using Wayne's Prius simulator and the best steady speed is in the 30's. The graph peaks at 32 mph. Avoid > 41 mph, mileage drops suddenly at 42 mpg due to spinning the ICE, and steadily above that due to drag.



This simulation is for 68F, sea level, 40% RH, 29.92", 225 payload, no AC, no wind. Click on the graph to download the excel spreadsheet.

[bwilson4web]

<div class='quotetop'>QUOTE(kk6yb @ Feb 15 2006, 04:22 PM) [snapback]210092[/snapback]</div>

I made a graph of Speed vs MPG using Wayne's Prius simulator and the best steady speed is in the 30's. The graph peaks at 32 mph. Avoid > 41 mph, mileage drops suddenly at 42 mpg due to spinning the ICE, and steadily above that due to drag.

This simulation is for 68F, sea level, 40% RH, 29.92", 225 payload, no AC, no wind. Click on the graph to download the excel spreadsheet.
[/b]

I disagree with this graph:

1) It does not reflect the lower power requirements at speeds below 41 mph.

As the vehicle rolls slower and slower, the aerodynamic componet goes to zero. This means the energy required to keep the vehicle rolling has gone down. Yet this graph shows not only a flattening but worse, an increase in power required. I do not know if the simulation is wrong but the graph is wrong.

A more accurate graph, for the NHW11 03 Prius is:




The simple act of benchmarking the various speeds has confirmed the above chart is accurate:
http://hiwaay.net/~bzwilson/prius/pri_test.html

Bob Wilson

[ken1784]

<div class='quotetop'>QUOTE(bwilson4web @ Mar 11 2007, 01:07 PM) [snapback]403612[/snapback]</div>

A more accurate graph, for the NHW11 03 Prius is:
[/b]

Hi Bob,

I don't think we can perform 120 mpg at 5 mph.
We need 24 hours to drive 120 miles by 5 mph.
Prius requires about 300W to maintain itself, "basal metabolism". About 7.2 kWh for that 24 hours is a lot of energy compare to just against driving resistance.
I would like to support Wayne's simulator.

Ken@Japan

[bwilson4web]

<div class='quotetop'>QUOTE(ken1784 @ Mar 11 2007, 12:49 AM) [snapback]403689[/snapback]</div>

Hi Bob,

I don't think we can perform 120 mpg at 5 mph.
We need 24 hours to drive 120 miles by 5 mph.
Prius requires about 300W to maintain itself, "basal metabolism". About 7.2 kWh for that 24 hours is a lot of energy compare to just against driving resistance.
I would like to support Wayne's simulator.
[/b]

We can repeat 15 mph / 24 kph in a single hour in an empty parking lot. I've already performed a 40 minute test and 'pegged' the MFD:

DISTANCE: 10.3 miles
MODIFICATION: thermistor hack (critical in cool weather!)
METHODOLOGY:
(1) fully warm up car and charge battery (~20 minutes above 42 mph)
(2) do one full lap in a flat, empty parking lot at 15 mph (*)
(3) reset MFD display
(4) hold 15 mph until all bars bars have updated, ~40 minutes
(5) take photo and have a happy

* - the goal is to normalize the battery SOC. It may make sense to modify the procedure to have "n", 5 minute display updates before resetting and taking a measurement. Regardless of how long #2 is, the key is to start the test with a normalized, battery SOC.

I would note that the simulator graph does not exceed 87 MPG. Also, the North American temperature problem that causes the ICE to run at coolant temperatures below 60C could easily explain the poor, low-speed performance in the simulator graph.

My energy based model does not reach 87 MPG until a speed of 30 mph / 48 kph. I did not include my measured NHW11 overhead ~511 W. because it is not a significant load until the lowest speeds. But between 0 and 30 mph, 15 mph is an excellent mid-point to determine what is going on. Even 20 mph should give an important data point.

Bob Wilson