MPG Display question

I 'think' you answered your own question.

This screen is showing Consumption: GASOLINE consumption, not electric battery consumption. "The conditions for the 5 minute duration are going downhill where I've been charging the battery and using little or no gas."

 

That's how you gen Prius displays when you burn zero gas in a five-minute segment.

FWIW - I'd rather see 99.9 myself.

 

It's a divide by zero issue. In most parts of the world, mileage is expressed as fuel burned per standard distance. In the U.S., we use distance covered per standard fuel volume. Either way it's a fraction, and you have a problem if the denominator is zero. Anything divided by zero is undefined - in this case it would be infinite. Lacking any way to conveniently display infinity, Toyota elected to use a blank bar.

Tom

 

The fact that anything except zero divided by zero is infinity probably dosen't help the developer/programmer trying to deside what value to assign to mpg when gallons equals zero for any period of time.

 

Sorry! didn't see your post. You must have beat me to the "Submit Reply" button. :bolt:

 

Not a problem. I do that all of the time. Usually Tony beats me to the post.

Your answer was better anyway. It said the same thing in less words, with more clarity.

Tom

 

Thanks! Yours mentioned the blank bar though and I didn't know that. We're still on the wait list.

 

No, when coasting or braking it doesn't turn on. It is spinning (to keep one of the motor/generator units from over-revving), but there is no fuel flow.

 

Others can opine, but it's not a matter of opinion. Many of us with added instrumentation have documented the absence of fuel flow. What you're likely feeling is the ICE spinning up. See this for a detailed discussion.

Now, if you transition through the 41 MPH threshold while coasting or gliding on a downgrade, for some reason apparently known only to Toyota engineers the ICE does briefly light. It produces a very subtle but noticeable shudder; maybe that's what you're feeling. It lasts only a couple of seconds and then the ICE shuts down, remaining in its spin-only mode until either speed drops below 41 or the go-pedal is depressed enough to fire it up.

 

Ding ding ..... we have a winner! There is NO way to express MPG when you burn NO gas.

... Brad

 

Zero to 99.9 are vaild MPG's. Zero gallons divided into miles driven is infinity. 99.9 may look neater on the MFD than blank or whatever but would not be accurate. 99.9 MPG & infinity are not equal values.

 

Maybe we need to extend the scale to infinity. That would be some non-linear scale.

There have been other posts about this, but I'd like to see a third dimension on the chart showing miles driving during that five minute period. Being able to flip those around might be nice too.

Tom

 

This is silly. A full bar (99.9 MPG) does NOT mean 99.9 MPG. It means 99.9 ***OR MORE*** MPG. Since the limit of M/G as G aproaches 0 for all values of M and G greater than 0 is positive infinity, I clearly believe that positive infinity qualifies as 99.9 OR MORE. Now if you don't use any gas AND you don't move, then I can see a dilemma. (Though I would argue that since 0/G is 0 for all values of G other than 0, an argument can be made for 0 in that situation.)
EDIT:Yes, I know that anything divided by zero is technically undefined. However, using the limit of a function as a value approches an undefined value is appropriate in many situations.
EDIT2:Yes, I know infinity is not equal to 99.9. Guess what? Infinity is not equal to 0 either.

 

Does it always light in this condition, because I posted a few days ago about this not happening on a downhill glide. I was looking for the transition and got nothing.

 

It may be silly, but it is still a developers nightmare. I did not mean to cause confusion. I don't have my prius yet and am not fimilar with the bars. Our Avalon's trip computer maxes out at 99.9 also and never bothered me because it is not part of a database. I perhaps added my 2 cent were it did not belong. The problem depends of the design of the MFD and/or maintaining of a database. The Prius if I understsand correctly, at least with the EV Mod, can actually be moved around for short distances without using any gas at all. If it is moved 100ft, 100ft divided by zero displays 99.9mpg. If it is driven 3 miles w/o using gas it would still display 99.9 mpg for the interval. Neither sampling is actually 99.9 mpg. There needs to be a differenciation of some sort. This is the designers challenge. What to do with specific intervals were 0 gallons are used and distance is covered. How do you incorporate these samplings for intervals, where you encounter the abhorrent divide by zero, into the database, that is made up of x number of samplings, in a meaningful manner? Perhaps the display could show the ¥ symbol. I personally do not have a problem with 99.9 meaning =>99.9 unless you are trying to add it as a data point into a database.

 

I've never known it not to except in neutral.