Stumbled on this thread and want to follow up:

Coasting and Neutral
From what I've read Neutral is a not a Hypermiler's friend; it appears shifting into Neutral can actually start the gas engine. Use the Glide mode accessed by lightly pressing the gas - it's more fluid than constant shifting anyway, and in most cases will cut the gas out, leaving you with infinite miles per gallon.

Best way to get max regen
The very best way is to let go of all pedals and let the automatic regen-only brakes (no friction brakes) stop you. This will take a very long time, however. Use it if you like but not to come to a full stop if anyone's behind you... it truly is grandma driving.

The second best way is to decelerate using the brakes as slowly as possible. Search brakes and regen here or on PriusChat and you'll find a very complicated graph which basically states that the harder you press the brakes, the more the friction brakes are used and the less regen you get. So, lightly applying the brakes early rather than braking sharply late will max your regen.

As a concrete example, every time I get off the highway on my way home, my battery maxes out. It didn't used to because I decelerated more rapidly. I'm typically travelling between 60 and 70mph and begin by letting go of both pedals so the regen-only slows me to about 50mph. I let go gradually so the car doesn't lurch as it moves to regen mode. At that point I get to the ramp and begin braking moderately. The ramp goes downhill for about 1/8th of a mile. At the stop light at the bottom my battery is always full. If I drive 70 to that ramp, shoot down it a bit then stop the way everyone else on that ramp tends to, my battery shows no noticable gain on the display, though I'm sure I get a little bit of energy from it.

 

ken1784, schwa,

If I have the choice to use regenerative braking or lightly pressing on the brake pedal; is one method more efficent than the other?

In other words, will more energy be stored in the battery if I come to a complete stop from 30 mph using regenerative braking until say 7 mph where the friction brakes engage or if I use less distance and stop from 30 mph with light braking all the way to the stop?

Thanks,

Chris

 

THanks for this. I am still trying to get some real MECHANICAL reason not to use neutral to coast. Does anyone here have a response to this. AS to the illegality, well, arguably, modern Automatics dont really hold the road as to manuals, so the illegality is a historic artifact of licensing laws. All arguments pertaining to automatics not being in neutral are not relevant (to the best of my knowledge) to the Prius drive system which uses a planetary gear. I also wonder why Toyota would have "allowed" the option if it was somehow detrimental to the transmission.

 

Maybe the neutral discussion should be continued here? There's some reference to the questions you're asking there.
https://www.greenhybrid.com/discuss/...l?page=1&pp=10

The topic is also touched on here - in particular, that gas is used by Neutral:
https://www.greenhybrid.com/discuss/...50.html?page=1

Warning: That second thread is a lot of reading.

 

Attila's experiment shows the pedal value 17 is the most efficient.
http://vassfamily.net/ToyotaPrius/CAN/brindex.html

Ken@Japan

 

Ken1784,

Thank you for your reply.

I was in really bad traffic for our area and was getting upset by the repetitive accelerating and braking that I was forced to do (watching my FE tank). I noticed that I had a really high SOC after a few lights and it got me thinking that I hadn't run the engine "all that long" or regened enough to get the SOC that high.

I will have to learn the feel for braking (roughly 22 seconds from 45 to 5 mph) and see if that makes a difference in my FE when I am forced to come to a stop using the brake pedal rather than gliding (no arrows).

If the data is correct; I should see more SOC to use at my discretion. A higher SOC seems to help keep my impg higher during pulses and could be used to EV in appropriate zones before I know that I have to run at higher speeds anyway.

Thanks,

Chris

 

One question that has not been answered. If the battery is fully charged and when you are going down a long downhill stretch of road, where does the re-generated energy go? Unlike diesel electric freight trains, there are no resistive stacks in the Prius to dissipate the heat from the excess engergy. I contend that no re-generation occurs in this situation, and you are forced to use the brakes or the 'B' mode to maintain your desired speed.

I still contend that re-generation occurs when you lift your foot off the accellerator pedal and not when you press the brake pedal. The brake pedal is connected to the computer system so it can make better decisions. Re-generation current is dependant on the state of charge of the battery, and the speed of the generator. Once the battery is fully charged, the current drops to zero, and re-gereration stops, no matter what the other conditions are.

Towing in neutral not recommend - usually because the engine/systems is not running and there is no lubrication pumps moving oil around to keep the gears properly lubricated. While not specifically mentioned in the manual, coasting in Neutral with the systems ON probably is not detrimental, but as mentioned eslewhere it is usually illegal to do so, not to mention unsafe.

just my nickle's worth.

 

Regen braking without brake pedal:
Yup, a small amount occurs when you release Accel above 7mph. For none you must Glide.

Regen braking at full charge:
This is easy to accomplish in the Honda Civic Hybrid and the mechanics of the car do change. Braking feels much less responsive as you must press hard to get the friction brakes to engage. I've driven a lot of Priuses and never gotten this to happen, probably because of how aggressively the Prius CPU keeps the State of Charge at 70%. So either it can't happen, or creating the conditions for it to happen is nearly impossible. Plug-In mods may change that however.

Towing in Neutral:
A normal car disengages the wheels from the engine via the clutch in Neutral. The Prius has no clutch so is still engaged, and in addition to no oil pressure, the electric engine may now be forcibly spinning over 42mph/10000rpm. If the gas engine were to spin as well you could go higher, but the electric engine will have no resistance while the gas engine will... so over 42mph is probably dangerous.