Does it make sense to shift to neutral during driving?

Remember that N in the Prius does not disconnect anything, unlike a normal car. All of the pieces and parts are always engaged, and there isn't any way around it. What N does do is keep the control system from doing regeneration, powering the vehicle, or changing the state of the ICE. It could help, but it's better to feather the accelerator pedal.

Tom

 

no.

it's pointless in the prius. Besides you don't get regen gains in N

just keep it in D

on regular cars with an auto it can help FE, but it's illegal in most states

if you want to shift gears, get a car with a stick

 

1) Evan might have a different answer, but I "goose" the go-pedal just enough to get the ICE to light, then back off enough to allow modest acceleration. I want to minimize battery use as much as possible. By "modest" acceleration, I suggest keeping the instantaneous MPG at least half the vehicle speed. This keeps the ICE within efficient operating ranges.

2) Actually, at steady speeds the car operates more efficiently at speeds below 41 MPH (most efficiently at 20, in fact) where the ICE will shut down completely when not needed for propulsion. But assuming driving conditions mandate 41+, I avoid CC except on level terrain. Because of its goal of holding a precise speed, it pushes the ICE into inefficiently high ranges on uphills. See this for more.

3) Hyperstealth is another name for "warp stealth," which is reviewed here in great detail.

I disagree. First, in states where it is illegal, it generally is illegal only on downgrades. No state outlaws it on level terrain or upgrades that I know of.

Second, as Evan suggests, it is an alternative technique for gliding and, IMHO, a good one. (For the OP and others unfamiliar with gliding, do a good search on "pulse and glide.") True, there is no regeneration, but gliding is not done to regenerate. In fact, it deliberately avoids regeneration and enables better fuel economy by maximizing use of available kinetic energy. Using neutral is easier, draws less off the battery, and provides at least the same fuel economy as (and possibly better than) feathering the pedal. See this (rather long and somewhat technical) link for more.

To Dominicsavio, I wouldn't normally bombard a newbie with links so detailed, but you seem more interested in driving technique than many. Take your time, study these and the many good threads on P&G, practice, and have patience. I still am fine-tuning my technique after three years with the car. The results pay off: MPG in the low to mid-60s as of now, and often 80+ (with occasional trips above 90) in warmer weather.

 

This is a tricky question as no one answer is applicable in all cases.
Evan gives a good summary of the many little considerations:

and other folks have added more tangential considerations.

[Edit: And JimboK's post has some real meat in it to be slowly digested.]

In my experience, in general the answer is no, the energy savings are very
small.

That said, in some very specific case it might be worth considering. And that
case is probably imbedded in a larger situation that you've been able to
analyze over many repetitions.

Let's look more closely at Evan's point #3 above:

"3) Yes, it makes sense if you're in a glide below 41mph. It's the lowest
energy use/waste state you can be in ASSUMING the ICE is not spinning
when you go into neutral."

Gliding in neutral uses about 1/3 the energy from the HV battery that a "no
arrows glide" does. So if you're in a situation where maintaining high SOC is
really important, and the distance to be covered is longish, an ICE-OFF N
glide could be helpful.

I've got just this kind of situation in my daily, 28.8 mi round trip commute.
I have learned that how I handle a 1/2 mi. section at the end of the in-bound
morning run will make a 5 MPG difference at the end of the day. And getting
that 5 MPG involves a long ICE-OFF N glide at 25-30 MPH to keep the SOC as
high as possible. (I have a ScanGauge, EV switch, and grill blocking.)

You see, if when I leave the parking garage heading home I have a high 6
bar, or better yet 7 bar SOC, I can EV through a 1/4 mile run of stop signs,
traffic lights, and low speed right angle turns and have the SOC at 4 bars.

[Edit: And air temps are above 32 deg F, as EV mode is unavailable to me
at lower temps. Yes, there are many things that can nix this whole approach.]

I know that once the ICE kicks on anywhere in the run, it will continue to run
when stopped at least until the colant temps are above 130 deg F.

I will admit that in the morning it is a very delicate dance indeed, sometimes
letting the ICE run when I could "no arrows glide." But as best as I can
arrange it, that ICE-ON time keeps the temps up, saves or slightly add to
SOC, keeps me moving with traffic, and reduces MPGs by only ~0.2.

But this intentional ICE use plus the SOC saving ICE-OFF N glide sets me up
for the 5.0 MPG gain later on.

In my daily driving, this is the only time where I've found an ICE-OFF glide is
helpful.

You'll have to look carefully at your daily driving conditions to discover if
there is some different situation that might work for you.

Hope this helps.

 

These are good answers, and no one answer to this question will work for every driver. The different answers basically come down to three different viewpoints:

1) Legal - As pointed out, there are some legal issues related to N, almost all of which are carryovers from the days of manual transmissions, where a driver could lose control of a vehicle not in gear.

2) Efficiency - Pulse and glide is an efficient way to move a Prius for hypermiling. With N you can P&G with less fuss.

3) Need - There isn't any need to pulse and glide, or shift to N, or use any other hypermiling technique for ordinary driving. If you are just driving your Prius for simple transportation, then you don't need to worry about fancy techniques. Just drive it and it will do pretty well on mileage.

Tom

 

Why would you shift into neutral and risk all kinds of problems when if you back off the pedal to the sweet spot you'll find the power mode go into its own 'neutral' evidenced on the MFD as no power from the ICE nor the battery (everything grey).

 

I present my "why" in the link in my previous post. As it shows, there actually is more battery power consumed during a pedal-feathered glide.

What are these "all kinds of problems?" There are only two easily-managed risks that have been raised: the illegality of it on downgrades and the (theoretical) risk of over-revving MG1 that Evan mentions. The latter would occur in conditions that most drivers will never see, even if they routinely use neutral. It has to be invoked deliberately and then (and only then) it will happen in very limited circumstances.

 

I have done this for years with my other cars. But, with the Prius it does not help. I tried this extensively on two half tanks and I actually got worse mileage! As the other posters have said apparently the ICE keeps spinning. However any mode that you are in which does not use the engine is a good mode, whether your running from the regen feedback, the battery or in glide (stealth) The magic normal speeds are 30-40MPH. Generally difficult to maintain under normal driving conditions.:cheer2:

 

No, in a Prius everything in the drivetrain is connected all of the time. There is no clutch or shiftable gears. Look up HSD if you want the details.

Coasting in N is illegal and considered dangerous because it was and is potentially hard to get back in gear with a manual transmission. In the days before synchromesh gears and good brakes, you could find yourself coasting faster than intended, with no way to slow down. Most of this doesn't apply anymore, and none of it applies to the Prius.

Tom

 

A key point to using neutral effectively in a glide and, therefore, as a fuel-saving technique, is for the ICE to be off when the shift to neutral is made. As Tom has suggested, the ICE remains in whatever operating mode it is in when the shift is made. So if the shift is made with the ICE on, it remains on in neutral and, of course, is running inefficiently. Andyprius, maybe that explains why your fuel economy worsened.

Then it is important to know that the ICE won't spontaneously shut off until the car has progressed through its warmup stages. But once the warmup process is complete and the shift is made at <40 MPH, the ICE will not be spinning.

There is no risk in over-revving the ICE. If it's on during the shift, it simply runs at idle speed afterwards. The theoretical danger is in over-revving MG1. But that will happen only if the shift is made in an ICE-off condition at <40 MPH before a long or steep downhill that then allows coasting up to ~62 MPH. If the shift is made at 40+, then the ICE is running at the shift (before full warmup) or, as protection for MG1, spinning without fuel flow (after warmup).

Dominic, there are many that share your wish for a tachometer. Some have a ScanGauge to monitor RPM and various other operating parameters.

 

I never have liked putting automatic transmission cars in Neutral when driving, much less do I like it in the Prius with the CVT. In either case, it seems that when the car is at speed and shifted from Neutral back into Drive again the RPM's rev up like the computer is trying to find out what ratio or gear it's supposed to be in and adjusts it from there. With the engine revving up in the Prius when shifting back to Drive again I would think that it would probably defeat most if not all of any benefit you may have gained by going into Neutral. I personally think you'd be better off (and safer) by just feathering the accelerator to where the MFD shows no power being consumed or regenerated.

I don't completely understand how the Neutral in the Prius works mechanically, but in the case of a regular automatic transmission I would think it causes excessive and unnecessary wear & tear on the tranny. This may or may not be the case with the Prius, but still I've only done it at moderately low speeds just to see how it would react and I didn't like it and will not do it at any higher speeds (~40+). I'm also curious, anyone ever tried Reverse or Park at any speed to see how the car behaves? I'm pretty sure I've tried Reverse before and it just beeps at you, and I don't dare to try park. Just wondering how smart it really is.

 

How does N work in the Prius mechanically? It doesn't. Neutral in the Prius, as well as all other gears, are mechanically the same. Nothing changes. All of the same gears remain engaged. The only thing that changes is how the control system runs MG1 and MG2.

Tom

 

1) Sorry, we sometimes forget that newbies don't know the vocabulary. :blush: MG1 and MG2 are the two motor/generator units. See this thread, including the many good links within it, to learn more about the HSD (Hybrid Synergy Drive) system and power flow.

2) 41 MPH is the quoted threshold, simply, because that's the way the car is designed, for reasons known to few other than Toyota engineers.

3) What you're hearing on startup is indeed the ICE's initial firing, in the first of its warmup stages. It takes several minutes to reach its most efficient operating temperature (157F+), so it's not operating at its most efficient until then. See the link I provided previously in post #14 for a full description of the warmup process.

Do NOT let the car sit and run during warmup if you're interested in efficiency. It's burning fuel needlessly. Better to get in and start driving.