coasting with prius in neutral - Gas Savers

95_corolla · 10-02-2007, 08:34 PM

Hello everyone I have a question about coasting the prius in neutral. These are the circumstances:

the car will be ON but shifted into neutral I believe I engine will shut off because I will not be accelerating. I don't think this will cause any damage since the engine shuts off automatically and may turn on if it needs to charge batteries. have any prius owners tried this. My parents just got a prius and I have been hypermileing in my corolla but can't wait to try the prius.

Thanks for your replies.

rh77 · 10-03-2007, 04:04 PM

Quote:

Originally Posted by 95_corolla

Hello everyone I have a question about coasting the prius in neutral. These are the circumstances:

the car will be ON but shifted into neutral I believe I engine will shut off because I will not be accelerating. I don't think this will cause any damage since the engine shuts off automatically and may turn on if it needs to charge batteries. have any prius owners tried this. My parents just got a prius and I have been hypermileing in my corolla but can't wait to try the prius.

Thanks for your replies.

I rented a Prius for about 300 miles last week and tried this very technique. From a discussion afterward with some expert Prius hypermilers (one of which is DiamondLarry), they recommend keeping it in D unless you're going down a mountain grade (as I had), then shift to B for additional engine braking. The ScanGauge was providing some misleading info, which led me to engine-off coast instead -- which was unnecessary.

The engine should cut fuel delivery while decelerating. If I understand correctly, if you're concerned about too much engine-braking or regen-braking, there should be a sweet-spot in the throttle that allows a "free-wheeling" coast without shifting to N (no arrows on the display or yellow-only EV input.

LSS, IIRC, N will keep the engine running during coast. For sure above 41 mph.

Prius owners can probably chime-in and offer more advice.

I'd say get comfortable with the car first (for me that took a little while) -- then get to know what it wants. After that, get into some advanced technique and you're all set. Best FE to ya...

RH77

diamondlarry · 10-03-2007, 07:00 PM

If you are on a flat road, I think there is a slight benefit to coasting/gliding in neutral. This is because there is a relay that is disengaged when shifting to neutral.

Quote:

I don't think this will cause any damage since the engine shuts off automatically and may turn on if it needs to charge batteries.

This not entirely correct. In a Prius, when you put it into neutral, the engine stays in the state it was in when the car was put in neutral ie, if it was running it will stay running and if the engine is off, it will stay off, even if the battery runs low. This is why I get a big warning screen when I stop somewhere and put the emergency brake on and open the door before I put the car in park. I hope this helps.

1993CivicVX · 10-03-2007, 07:07 PM

My mom's Prius does not behave like that. When you put it in neutral the engine shuts off, no matter the speed. I don't think the engine has ever come on while the car was in neutral. Would be interesting to see what happens if you put the A/C on while the car is in neutral to see if that would turn the engine on.

MetroMPG · 10-03-2007, 08:28 PM

The owner's manual of my sister's Camry hybrid specifically warns about leaving the car in N for extended periods with the power on. I'd be very surprised if the engineers hadn't designed in some logic to protect the high v pack from getting dangerously low, but that seems to be their concern.

Edit: that said, going to N is the only way to effectively P&G in the Camry hybrid, because the glide band is ridiculously narrow and nearly impossible to maintain using just the accelerator. But glides aren't usually long enough for using N to be a concern (in terms of draining the pack).

95_corolla · 10-04-2007, 02:10 AM

1993civicvx what year is your moms prius

1993CivicVX · 10-04-2007, 06:21 AM

2007

Ryland · 10-04-2007, 07:23 AM

as I understand it, if you let up on the gas pedal twice, just a little, but rather sharply, because the car is a drive by wire set up, it tells the cars computer to turn the engine off and run off electric for a while, not sure how it desides to turn the engine back on, but if you are coasting it makes sense to do.

diamondlarry · 10-04-2007, 05:20 PM

Hmm, mine is a 2007 as well. If my engine is running when I put it in N, it stays running. If it's not running when I go to N, it stays off. I have an EV switch that I can use to turn off the engine anytime up to 34 mph. Once the engine dies, I throw it in N and use the switch to enable the engine again but it doesn't come back on until I put it back in D.

1993CivicVX · 10-04-2007, 06:00 PM

Diamondlarry how are you knowing if the engine has turned off or not? Are you going by auditory or are you looking at the computer screen? I am going by auditory and the screen. Often the engine will be running when the cmoputer screen says nothing is running, particularly when the car is warming up.

Ryland, yes you are right. Unless you have the AC on or the heat on, when you lift your foot off the gas (just once - just have to remove your foot form the throttle and the engine will shut off. There are some exceptions to this which I have no idea why. Like, sometimes the engine won't shut off when you take your foot off the accelerator. Or sometiems it will come back on while coasting to my driveway. never understood it. I think in cooler weather it happens more frequently than in warmer weather. (40s, 50s or 60s as compared to 70s, 80s, 90s)

my mom's doesn't have the EV switch.

diamondlarry · 10-04-2007, 06:13 PM

I verify that the engine is off mainly from the Scanguage showing 0 rpm's and also by sound/feel. When I first got the car I used only the computer screen but started using the Scanguage to verify engine-off when I felt the engine running when the screen showed it as off.

The EV switch is not offered on the Prius in America but I got one from Coastal Technologies.

Hockey4mnhs · 10-04-2007, 11:17 PM

These cars are so awesome i want to try driving one but i don't know anyone with one.

FireEngineer · 10-05-2007, 07:41 AM

You cannot use the MFD or sound/feel to be absolute the engine is not running. In neutral the engine is very smooth and you will not be aware unless you have a scangauge.

Having said that the best thing to beginning hypermile in the Prius is to learn to glide. Once you learn to glide and pulse and glide then you can experiment with neutral.

Neutral typically works best when you have down slopes that will carry your glide over 40MPH. On the flat the difference is minimal. Neutral just disconnects the inverter and hybrid electronics from the MG's, especially MG2. You will still have the drag from the silent chain, reduction gears and power split device. An advantage to gliding over neutral is in glide there is a small 5 amp draw to MG2 that counters the friction of the above gear train. In neutral you'll still draw about 1-1.5 amp from the hybrid system for the DC-DC converter and more for the AC if its running. Neutral will not allow the engine to start and recharge the hybrid battery, nor will you get any regenerative braking energy back.

Above all else experiment, Larry has found somethings that work for him and he does very well. On my routes I never use neutral and my summer average, excluding my road trips, is in the mid 70's with a tank at 80.1 MPG. Best to go to cleanmpg.com and read Wayne Gerdes P&G article and go to PriusChat and look around. Oh, an engine block heater would help too.

Wayne

1993CivicVX · 10-05-2007, 08:15 AM

Quote:

Originally Posted by Hockey4mnhs

These cars are so awesome i want to try driving one but i don't know anyone with one.

I'd prefer my manny VX over a Prius any day.

Now if Toyota would be a nice company they'd make a Prius with a manual transmission for some happy fun FE. Does the Prius come in manual in any other countries?

rh77 · 10-05-2007, 08:36 AM

Quote:

Originally Posted by 1993CivicVX

I'd prefer my manny VX over a Prius any day.

Now if Toyota would be a nice company they'd make a Prius with a manual transmission for some happy fun FE. Does the Prius come in manual in any other countries?

Not to my knowledge. The whole propulsion system is based on the Hybrid Synergy Drive system, which is a complex CVT-based transmission. The best bet for a manual-hybrid is an older Honda (Civic or Insight).

I have the same feelings -- too bad you can't run through the gears...

How cool would a Manual CNG-Hybrid Civic be?

RH77