Consumption Calculation Question

[Fibb222]

Am I correct in assuming that if I drove a warmed up Prius steadily for 2.5 minutes consuming 5.0 L/100km the whole time and then stopped for 2.5 minutes where the ICE was off, that the 5 minute average bar would read out 5.0 L/100km for that period. i.e. in its calculation, the MFD computer only uses the time when the engine is running, in this case, the first 2.5 minutes.

In a similar scenario where everything else is the same but the ICE idled for the last minute would the 5 min average be somewhere higher than 5.0 L/100km. i.e. the computer would take into account the gas consumed at idle as well.

Thanks

[qbee42]

The computer doesn't ignore the time when the ICE is not running, but no fuel is being consumed because the ICE is not running. The calculation is just fuel burned vs miles driven over the last 5 minutes, whether the Prius is running the ICE, coasting, gliding, or getting towed by a pack of wild dogs.

Tom

[eagle33199]

like the previous poster said, it's simply the amount of gas consumed divided by the distance traveled within that 5 minute window (opposite for us MPG users).

Time really doesn't mean anything, except as a convenient way to separate the readings and make a cool looking graph.

[Tideland Prius]

No, it'll probably show closer to 2.5L/100km or something like that. It's based purely on time (so highway driving would benefit the most or any time you're constant moving and not in a traffic jam).

[vincent1449p]

<div class='quotetop'>QUOTE(Tideland Prius @ Oct 31 2006, 09:34 AM) [snapback]341039[/snapback]</div>

No, it'll probably show closer to 2.5L/100km or something like that. It's based purely on time (so highway driving would benefit the most or any time you're constant moving and not in a traffic jam).
[/b]

Sorry, I 've to disagree with you. Your 2.5L/100km will be true if the OP did not stop for 2.5 mins but continued in ICE-off mode covering about the same distance as the 1st 2.5 mins.

Let's assume the OP travelled at 60kmh.
Distance covered in 2.5 mins = 60/60*2.5 = 2.5km
Fuel consumed at 5.0L/100km = 5/100*2.5 = 0.125 litres

If the OP stopped for the next 2.5 mins,
Distance covered in 5 mins = 2.5+0 = 2.5km
Fuel consumed for 5 mins = 0.125+0 = 0.125 litres
Final FC = 0.125/2.5*100 = 5L/100km

Howerver, if the OP continued at the same speed,
Distance covered in 5 mins = 2.5+2.5 = 5km
Fuel consumed for 5 mins = 0.125+0 = 0.125 litres
Final FC = 0.125/5*100 = 2.5L/100km

[Tideland Prius]

<div class='quotetop'>QUOTE(vincent1449p @ Oct 30 2006, 06:35 PM) [snapback]341071[/snapback]</div>

Sorry, I 've to disagree with you. Your 2.5L/100km will be true if the OP did not stop for 2.5 mins but continued in ICE-off mode covering about the same distance as the 1st 2.5 mins.

Let's assume the OP travelled at 60kmh.
Distance covered in 2.5 mins = 60/60*2.5 = 2.5km
Fuel consumed at 5.0L/100km = 5/100*2.5 = 0.125 litres

If the OP stopped for the next 2.5 mins,
Distance covered in 5 mins = 2.5+0 = 2.5km
Fuel consumed for 5 mins = 0.125+0 = 0.125 litres
Final FC = 0.125/2.5*100 = 5L/100km

Howerver, if the OP continued at the same speed,
Distance covered in 5 mins = 2.5+2.5 = 5km
Fuel consumed for 5 mins = 0.125+0 = 0.125 litres
Final FC = 0.125/5*100 = 2.5L/100km
[/b]

Yeah but the Consumption Screen is based on 5 mins. It wouldn't matter if it travelled that 2.5 mins in 5 kms or 0 kms cause they both took 2.5 mins according to the screen (and both with engine off).

[Fibb222]

<div class='quotetop'>QUOTE(eagle33199 @ Oct 30 2006, 01:11 PM) [snapback]340852[/snapback]</div>

like the previous poster said, it's simply the amount of gas consumed divided by the distance traveled within that 5 minute window (opposite for us MPG users).

Time really doesn't mean anything, except as a convenient way to separate the readings and make a cool looking graph.
[/b]

That's what I thought but efusco wrote this in another thread.

"There's an active thread about interpretting the Consumption screen...it's problematic to try to read much into it in any kind of non-steady speed conditions as it incorporates a time factor into mpg.

For instance....Let's say you got 50mpg for the first minute of driving in a 5 minute period. Then you stopped to get a Taco at "The Bell" during the next 4 minutes. Even though distance over gallons you should show 50mpg the Consumption screen will divide that 50mpg by 5 (for the 5 minutes) and show an average mpg for that 5 minute block of 10mpg. A little odd."

[efusco]

<div class='quotetop'>QUOTE(eagle33199 @ Oct 30 2006, 03:11 PM) [snapback]340852[/snapback]</div>

like the previous poster said, it's simply the amount of gas consumed divided by the distance traveled within that 5 minute window (opposite for us MPG users).

Time really doesn't mean anything, except as a convenient way to separate the readings and make a cool looking graph. [/b]

Sorry, but that's not correct. the formula is (distance/fuel consumed) / 5min = avererage mpg

[eagle33199]

<div class='quotetop'>QUOTE(efusco @ Oct 31 2006, 08:49 AM) [snapback]341176[/snapback]</div>

Sorry, but that's not correct. the formula is (distance/fuel consumed) / 5min = avererage mpg
[/b]

Here's a simple algorithm for what happens, to make things clear:

reset all totals
after 5 minutes:
- total fuel consumption since reset
- total miles driven since reset
- output to MFD total distance/total consumption --> this is a 5 minute bar


The confusion in the graph comes from the fact that not all bars are equivalent. You could spend 5 minutes in line at McDonalds, inching up on electric, and get a 5 min bar that says no fuel was consumed (100mpg), then get on the highway and travel 5 miles in the next 5 minutes, averaging over those 5 minutes 40mpg - Looking at the display, you would think you averaged 70mpg over the past 10 minutes, but we know that the distance traveled for each bar isn't the same, so the average is actually 40mpg (since there was essentially no distance in the first bar)

If you doubt this, there's one real easy way to test it: go out to the car, drive around a bit to get it warmed up (say in circles in a parking lot) get to the start of a 5 minute bar and do your best to get great mileage, then stop halfway through the bar - you'll see that the time aspect just gives you the "window" over which that average was calculated - it doesn't effect the average itself.

The formula you presented evan does not give you MPG as the final result - it gives you miles/gallon/minute, which doesn't make any sense. Also, if this was true, then in order for the Prius to get 50mpg over a tank, every 5 minute bar (on average) should show 10, not 50 (since 50MPG/5 min = 10), which it clearly doesn't...

[efusco]

<div class='quotetop'>QUOTE(eagle33199 @ Oct 31 2006, 08:28 AM) [snapback]341206[/snapback]</div>

If you doubt this, there's one real easy way to test it: go out to the car, drive around a bit to get it warmed up (say in circles in a parking lot) get to the start of a 5 minute bar and do your best to get great mileage, then stop halfway through the bar - you'll see that the time aspect just gives you the "window" over which that average was calculated - it doesn't effect the average itself.

The formula you presented evan does not give you MPG as the final result - it gives you miles/gallon/minute, which doesn't make any sense. Also, if this was true, then in order for the Prius to get 50mpg over a tank, every 5 minute bar (on average) should show 10, not 50 (since 50MPG/5 min = 10), which it clearly doesn't... [/b]

Again, I assure you, you are mistaken.

If I drive for 2.5min at 60mpg then stop the car without shutting off the mpg of the 5 min bar will show an mpg of 30mpg, not 60mpg. It averages your mpg for the 5 min period. If you get 60mpg at a steady speed for 5 min your average is 60mpg. If you go 60mpg for 1 min out of that 5 min the average will be 12mpg. That is why the information is of so little value unless you're traveling a steady speed or unless you're using each 5 minute segment on a particular route to compare one trip to the next.



IOW, if I drive the same 30 min trip to work each day and the 3rd 5 minute segment is a complex section of hills and turns that I'm trying to become more efficient at I can compare the mpg for that segment from day to day to see if I'm getting better in that section...but if my speed within that section varies the mpg on the display is not necessarily an accurate representation.



That's why Norm built in a mpg/mile graph into CAN-View...much more helpful and intuitive IMO.