Technicality of hypermiling

Dominic, you are correct about gliding: it is the momentum of the car that takes you forward. And it is very similar to neutral, though there are subtle differences. For the benefit of those besides you and me and in the interest of brevity (rare for me, I know), I'll simply link to the other thread where we discussed this in depth.

As for whether gliding or green arrows is better, gliding is more efficient. Let's see if I can make this make sense. [Physicists, correct me as needed.]

This is all about using energy to move the car, all of which effectively comes from the ICE. You might say, "Well how about when it runs in EV mode and uses battery power?" Energy to charge the battery originally came from the ICE. You might say, "What about regeneration, that's not from the ICE?" Well, yes it is, indirectly. You would never have the opportunity to regenerate if the ICE hadn't gotten the car up to speed. The ICE is the only source of energy to move the car, whether directly or indirectly.

Energy of course is neither created nor destroyed; it simply is converted to other forms. With those conversions are inevitable losses, often as the original form is being converted to useless heat energy as a byproduct of the the desired conversion. When the ICE lights in a stationary vehicle, the stored energy in gasoline is converted to kinetic energy to make the car move. But there is a substantial loss from heat. If acceleration is greater than what the ICE can provide, it uses some from the battery. But with that comes losses as the stored chemical energy is converted first to electrical energy and then kinetic energy; the battery and electrical conduction system heat up along the way. If the ICE generates more power than the car needs, it directs some of the excess to the battery -- with limitations. (More on that in a minute.) But with that are more losses ... and so on.

So with the ICE as the only source of power, every time we fail to use the kinetic energy that it creates for us and we allow it to convert it back to some other form, we've introduced some inefficiencies. This is what happens with green-arrow coasting -- i.e., regeneration. On the other hand, if we have the opportunity to use energy in its existing state and eliminate the conversion losses, then it behooves us to do so. That is exactly what we're doing with gliding: We can put most of that kinetic energy to use to move the vehicle.

The problem with directing any of it to the battery is that eventually it will be used again for propulsion, and with that come these inevitable losses -- energy that you have wasted that could have been used to propel the car directly. The car likes to keep the battery at an optimal 60%. It will accept more with sustained regeneration, but the higher it gets the less it accepts it and the more it wants to use it. So as it uses it, again, we suffer conversion losses.

A single arrow from the battery to the motor indeed indicates EV mode and pure battery propulsion. But that's not what I said. I said "green arrows to the battery." With your foot off the pedal. (Nothing propels the car with your foot off the pedal except its existing kinetic energy.) That is what I call coasting.

PLEASE study the links I've provided. You're wanting a lot of detail, and you seem confused on some of these points. That's fine and I don't mind helping you. But this has all been covered in other threads and in other forums. After you've take some time to study them, then come on back here and we'll try to clarify.

 

Sorry about the confusion in terms, and thanks to JimboK for the correction. I'll bow out here, since JimboK is I think the better informed and better teacher. I'll just restate my opinion that the (correctly) identified advantage of glide vs coast with regards to less energy conversion is much less important in the grand scheme of overall mpg than avoiding low efficiency ICE use and giving more attention to minimizing brake use.

Happy hypermiling !

 

You enthusiasts are something else...has anyone thought about compiling this collective wisdom and selling it to Toyota, its sales outlets, or perhaps an auto magazine ?
I've learned more from this site after casual reading for several hours than I absorbed from many years of reading consumer publications.
Thanks to all for the time you spend "educating" us Newbys.

 

Minor point, that 0 - 'x' kilowatts breaks over around 10, not
20. 50 battery amps at nominal SOC, and that's when the ICE
lights to help out.
.
Snead, you've got it a little backwards -- it's *we* who are still
learning about what Toyota's known all along and designed into
the car originally. Maybe they didn't anticipate *all* the fine
points but they certainly built in plenty of efficiency-improving
hacks and we're just figuring out how to take advantage of them.
After all, someone had to have written the video game before
others can play it, right?
.
_H*

 

Modesty will get you nowhere...Toyota's very good car would still be giving me 38/42 mpg without this site's collective wisdom. I read the manual and even put the door jamb air pressure in my tires but...this site filled in the essential points to begin fully using the Prius efficiently. :rockon:

 

Absolutely. Hang out on cleanmpg for a lot more along
those lines. We've got people hypermiling *semis*, f'krissake..
.
_H*

 

A couple of years ago I read a fascinating account of the history of hypermiling. The author traced it to the old Soviet Union, where Mafioso types had their grande American cars and open roads, but very little fuel. So their drivers would open up the throttle to a speed of 40 mph or so, then cut the engine and coast in neutral down to a low speed before restarting the car and repeating the cycle.

Sound familiar ? The Prius just lets us do the same thing; in part automaticaly, in part by driver intent. And we don't have to grind the starter or do without power steering or power brakes :rockon: