Coasting in neutral

Besides all this, how can coasting create better mileage? Most cars will produce enough power for acceleration and to overcome air resistance. Once you have achieved your speed, coasting only "spends" the energy you have built in reserve. A moving car is stored energy. Coasting will slow your speed, making necessary to burn more fuel to bring your speed back up.

Most trips involve an equal amount of upward and downward slopes. Even if you take a trip to a lower elevation, the great mileage you got going down will be cancelled by the greater amount of fuel being burned to get back. Coasting to save fuel seems like a self-deluding game to me. I see nothing to be gained, particularly in a Prius.

 

I'll have to test a couple of versions of your question about shifting into N while stopped and pushing the defrost button that would normally start the engine while in P or D. I suspect pushing the the HVAC defrost button while stopped in N would start the engine.
Likewise, I'll also have to test your question about charge mode while in N stopped. Again, I don't see any reason why the Prime wouldn't start the engine when switching to charge mode while in N and stopped.

I don't remember ever seeing any message on the MID or ( MFD not that this type of message would normally be displayed there ) show up when in N, stopped, gliding or rolling backwards.
The one message I've seen on the MID about N is when the car doesn't like what the driver had done with the shifter it throws the message to " shift to N than to D " I haven't seen it recently and I've forgotten what shifter action(s) / error by the driver triggers that message, but it's the only one I've ever seen concerning N.
I'll see if I can get it to show up and get a better understanding of at least one of the shifter moves the Prime wouldn't accept. But I have seen it both while stopped and while moving.

And for the record I'm not saying there couldn't be a scenario where the Prime is unhappy about a drivers choice(s) in all situations and throw the message you're referring to up on the MID. I'm too well aware of how many different sets of conditions the car can be exposed to environmentally, driver behavior and sensor combinations detected, that might trigger engine on when not expected by the driver or a message in the MID I've never seen before.

Gen3 plugin had it's own set of sensor thresholds for engine on conditions. Gen4 Prime has it's own set of threshold conditions for engine on that are dialed in much more tightly, but there are so many more variations it's hard to even extrapolate how the system could possibly behave differently than expected, given a set of conditions other than the ones an owner typically experiences while driving daily.
I'm pretty confident in my belief that the Gen5 Prime is as much a new game when comparing it to the Gen4 Prime as I know how much the game changed in the Gen4 when compared to the Gen3 Plugin.

 

That wasn't any of my questions, but I won't mind if you want to test that also.

Right, whether it will use the engine to charge while in neutral, that was my question.

I mistakenly wrote this earlier:

I was mistaken about that being all the 2024 Prime owners' manual says on the subject. Somehow my search didn't find this, on page 256:



That is very much like what was in the earlier models' owners' manuals on the same topic. So that would make it especially interesting if the behavior turns out to have changed.

 

Yeah, I've never noticed regen charge while in N , in EV mode, stopped or moving
Gen3 Plugin or Gen4 Prime. But I'm usually looking at available EV miles and miles to destination instead of charge or lack there of.
I rarely shift to N Gen4 Prime, as posted on previous pg #50, Gen3 Plugin was a different story, I did shift to N and glide to extract more EV range or to keep the engine from switching on if I could glide to my destination.

 

I can't personally test these scenarios in a 2024 Prius Prime. But I can in the closely related 2024 RAV4 Prime, so just now went out and tried them:

Beginning at READY with EV and N, with the HVAC defrost button activated, my RAV4 Prime does not start the ICE. Then shift from N to P, and it promptly does start the ICE.

Beginning with EV and N, switching my RAV4 Prime from EV to CHG does not start the ICE. Then shift from N to D, and it promptly does start the ICE.

Why wouldn't it start? As explained in this and many previous threads about 2001-2023 Prii, both plug-ins and non-plug-ins, N de-energizes the MG1-MG2 field windings so that they cannot function as either motors or generators. They just mechanically free-wheel with essentially no resistance at whatever speeds are driven upon them by the wheels and ICE, easily determined from the mentioned nomograph.

With their electric motor functions disabled, they simply cannot start the ICE. And these scenarios are not the exceptional circumstances identified in the Toyota technical manuals that Chap reads where the control system will momentarily 'bend the rules' to energize MG1's field windings in order to start the ICE.

My traction battery's SOC is not anywhere near low enough right now to reasonably go test the scenarios that Chap asks for.

 

Read up elsewhere about Pulse & Glide (P&G) , a fuel-saving measure discovered before modern hybrids were invented. In a non-hybrid, or a hybrid when the ICE is spinning, a substantial amount of energy is consumed just to spin the ICE. In circumstances where you can spend part time and distance gliding with the ICE halted, you can save that ICE-spinning energy for that time, saving fuel for the overall trip and increasing mpg. After slowing down in ICE-off gliding, the energy needed to get back up to full speed can be less than having had the ICE spinning the whole time.

Doing this successfully can be tricky. It can even be done with the ICE in idle instead of completely halted, though with less savings and is even trickier, with plenty of opportunity to make mpg worse instead of better.

Current generation Prii can halt the ICE at full highway speed in the right circumstances and harvest this savings automatically, without driver action. Old generation Prii can't halt the ICE at highway speed, but can drop it to idle RPM with no fuel burn, thus harvesting some of this savings. At lower street speeds, those older models can fully halt the ICE and get all the savings.

Knowing how all this works, a Prius driver can figure out how to make somewhat more of it, or at least to not unintentionally defeat the car's efforts to do it automatically.

Old non-hybrids had non-optimized engine and transmission designs that wasted quite a lot of energy, so a well executed P&G could quite significantly boost MPG. Newer generation non-hybrids are much better designed and optimized, automatically reclaiming some of those old P&G benefits. Old hybrids automatically harvested additional savings, and newer models collect even more of it. So the modern benefits of P&G keep shrinking, as newer cars leave ever less wastage for drivers to attempt to harvest themselves.

 

I think you're right. The world record for mileage was set by a vehicle doing pulse and glide, but I think the Prius is a different matter. Since there is no disconnect between the wheels and the drive motors, it's not really neutral, and besides, coasting in neutral is illegal.

 

Old generation Prii benefited too, just not as much as in non-hybrids because Toyota's HSD system had already reclaimed so much of the non-hybrid wastage. Newer generation Prii reclaim even more, leaving less room for drivers to improve upon.

Because propulsive power is killed -- neither the ICE nor the electric system can apply torque to the wheels -- it effectively is Neutral.

That varies, some places make it illegal only on downgrades, not on level ground. With passenger cars, the demise of manual transmissions, and the transition away from drum brakes, the prohibition is rather outdated. If an observing officer can even tell that you are in neutral, then you are doing it wrong. The prohibition is much more meaningful for heavy trucks that can get into a condition where it is impossible to re-engage drive gears on run-away downhills, especially where the brakes can fade and burn.

 

Check your mirror.

The other person's descriptions pretty much match those of past experts in this forum. Except that he has dug much further into Toyota's technical literature than anyone else still participating here, reporting to us more of the finer details, exceptions, and corner cases than did past experts. And pointing us to where we can read those too.

 

Not very relevant to the rest of the discussion, but as a lot is about the Gen 5, for the record the Gen 5 no longer has that. It just relies on a beefier MG2.

 

Huh. And the sprag clutch seemed like such a clever way to get use of an operating region that wasn't formerly available.

Could it have been enough extra complexity or part count to put them off?

 

You seem to be ignoring the fact that both drive motors are connected to the drive wheels at all times. There is no clutch or any other way to disengage them.

 

So tell me, does any Prius have a clutch or even a torque converter? (I've done the research)

 

You seem to be ignoring the fact that in Neutral (outside the corner case exceptions Chap has mentioned), both those motors simply can't function as motors or generators, but only as inert flywheels. Take away any rotating electric motor's or generator's field excitation, and it can't provide any meaningful torque, beyond inertial resistance to speed change and a bit of bearing and windage friction.

In Neutral, the car's computers and electronics and electrics do not actively drive the motors to the directions and RPMs you are seeing. The wheels and ICE (if spinning) simply mechanically and passively drag the motors to those indicated RPMs. They are just small flywheels dragged along for the ride.

... unless something very significant has changed for the new 2024 model. If so, we'd like to learn more about this big new change.

Why are you asking me, not the person you have been throwing insults at? And how is a sprag clutch or torque damper (which some people call a clutch) on the ICE shaft, relevant to this thread about Neutral?

 

Just not necessary any more, I imagine - not getting use of a useful operating region.

I'm going to guess that in G5, with a beefier MG2, the battery output is the limiting factor again - all the drivetrain is higher-power. The clutch is only needed if MG2 on its own can't output as much power as the battery can supply.

 

But then again, "D" can be effectively neutral too. It can kill propulsive power and decouple the engine in "D" just as much as it can in "N". The decoupling of the engine happens all the time, automatically, and killing the power is just a matter of finding the right throttle position. "N" just forces it.

So from the point of view of trying to gain efficiency, selecting "N" doesn't do anything that you can't do in "D" with care, so shouldn't be necessary. But maybe it could make it easier.

Might possibly make things worse if it doesn't stop the engine while in "N", which I recall being a feature in older versions along with not starting it.

 

There are a couple different themes getting explored in this thread.

When the thread was started back in 2017, it was about "can I improve my MPG by using N"?

When it got reawakened three days ago midway down page two, that post brought in the claim that "The powertrain of Priuses has no neutral, only a simulated neutral, which it does by running both motors in reverse rotation to each other" and a lot of the ensuing discussion has been about that.

That kind of question about what makes neutral neutral in a Prius does recur here on PriusChat every so often as people are learning how the car works—though I don't think I've seen anyone before be quite so hung up on the idea that the car has to "run" both motors in order for them to turn. They turn pretty freely when the car just doesn't "run" them at all, and that's what happens in neutral.

That captures the idea, but I would steer away from saying "field excitation" in this context. You usually hear about that in things like universal motors and alternators, where the rotor and stator are both wound, and one set of coils makes the magnetic field for the other coils to act on.

The Prius MGs only have wound stators. The rotors are built with permanent magnets, so the magnetic field is always there, and the stator windings act on it. (Or don't act on it, when they are left open-circuited in neutral.)

 

Good illustration of the magnet's power:

 

Hmm, I guess one way to see if power is being provided to turn the motors in Neutral is to compare the power usage using Hybrid Assistant when the car parked and when it's coasting in neutral. If no power is being provided to the motors, I should have the same power output, right? I'll have the lights on (since it will use daylight running lights while in Drive but not in Park I believe) and the climate Off so it doesn't interfere with the output. My wife has the car so it will have to wait until she come back.

 

So I got to try it. The power usage while in Park with lights On and Climate Off fluctuated between 300 to 400 wh. It was the same while coasting in Neutral at 45 km/h. Then I thought of switching the display to show motors' RPM, they weren't spinning at all, at least, not reported spinning.


One thing I tried was to turn On Defrost while stopped but in Neutral with my foot on the brake. The fan started, the Defrost light turned On but the engine stayed OFF. The light remained On even when I shutdown Climate or put it back in Auto. Even when I put the car in Park, the light stayed On and the engine didn't start. I started driving and the engine stayed Off and the Defrost light stayed On. I had to shutdown the car for the light to finally turn Off. Looks like Toyota wasn't expecting someone to turn On the Defrost with the transmission in Neutral and the engine Off lol.

Edit: Thinking about the screenshot. The motors RPM is obviously wrong when in Neutral because no matter what, if the wheels are turning, so must be MG2. So that screenshot is useless